PHILIPS VR2350 STEREO MATCH LINE CHASSIS DECK INTERNAL VIEW.

PHILIPS VR2350 STEREO MATCH LINE VIDEO2000 Reversable video cassette:

A reversible video cassette for portable video devices is described, said cassette having two housing halves (7, 8), mounted displaceably for changing the distance between the winding spools. The housing halves are connected to each other by two flat guide parts (13, 14) arranged in parallel. The two housing halves are releasably locked by two catch hooks (17, 18) associated with the guide parts.

VIDEO -WENDEKASSETTE PATENTANSPR·UCHE

1. Video-Wendekassette in Form eines im wesentlichen quaderf·ormigen K·orpers mit zwei darin drehbar gelagerten Wickelspulen f·ur das Magnetband und einer an einer schmalen L·angsfl·ache vorgesehenen ·Offnung mit teilweise zur·uckgesetzter Geh·ausewand zur freiliegenden Magnetbandf·uhrung, wobei die Kassette vorzugsweise aus zwei verriegelbaren im wesentlichen geschlossenen Halbteilen besteht, die zur Ver·anderung des Wickelspulenabstandes sowie zur Vergr·osserung der freiliegenden Magnetbandl·ange verschiebbar gelagert sind, d a d u r c h g e k e n n z e i c h n e t , dass die Verbindung der verschiebbaren Kassetten

-Halbteile (7,8) durch zwei flache F·uhrungsteile (13, 14) erfolgt, die in parallel angeordneten F·uhrungsnuten (19, 20), die sich in den beiden ·ausseren schmalen L·angsfl·achen (15, 16) der Geh·ausehalbteile befinden, eingelegt sind, und die Verriegelung der beiden Halbteile durch zwei seitenversetzt den F·uhrungsteilen zugeordnete Sperrhaken (17, 18) erfolgt.

2. Video-Wendekassette nach Anspruch 1, d a d u r c h g e k e n n z e i c h n e t , dass die F·uhrungsteile (13, 14) aus schmalen bandartigen Metallstreifen bestehen.

3. Video-Wendekassette nach den Anspr·uchen 1 und 2, d a d u r c h g e k e n n z e i c h n e t , dass die F·uhrungsteile aus antimagnetischem Federstahlband bestehen.

4. Video-Wendekassette nach Anspruch 1, d a d u r c h g e k e n n z e i c h n e t , dass der aus Kunststoff einst·uckig gefertigte Sperrhaken (17, 18) aus einem Hakenteil (22), einem Lagerauge (23) und einem Verbindungssteg (24) besteht, wobei der Verbindungssteg eine Schr·agfl·ache (27) aufweist.

5. Video-Wendekassette nach den Anspr·uchen 1 und 4, d a d u r c h g e k e n n z e i c h n e t , dass der Sperrhaken mittels einer Druckfeder (25) in einer die beiden Kassetten-Geh·ausehalbteile verriegelnden Lage gehalten wird.

6. Video-Wendekassette nach einem der Anspr·uche 1 bis 5, d a d u r c h g e k e n n z e i c h n e t dass die Verriegelung der beiden Kassetten-Halbteile durch Eintauchen wenigstens eines Stiftes (9, 10) in die Kassette aufgehoben wird, wobei der Stift auf die Schr·agfl·ache (27) des Sperrhaken-Verbindungssteges (24) trifft und den Haken aus einem Sperrzahn (26) hebt.

7. Video-Wendekassette nach Anspruch 6, d a d u r c h g e k e n n z e i c h n e t , dass f·ur jeden Sperrhaken ein Stift zur Entriegelung in die Kassette eintaucht. EMI11.1

Description:

VIDEO -WENDEKASSETTE BESCHREIBUNG Die Erfindung betrifft eine Video-Wendekassette in Form eines im wesentlichen quaderf·ormigen K·orpers mit zwei darin drehbar gelagerten Wickelspulen f·ur das Magnetband und einer an einer schmalen L·angsfl·ache vorgesehenen ·Offnung mit teilweise zur·uckgesetzter Geh·ausewand zur freiliegenden Magnetbandf·uhrung, wobei die Kassette vorzugsweise aus zwei verriegelbaren im wesentlichen geschlossenen Halbteilen besteht, die zur Ver·anderung des Wickelspulenabstandes sowie zur Vergr·osserung der freiliegenden Magnetbandl·ange verschiebbar gelagert sind.
Es sind Magnetbandkassetten bekannt, bei denen die Bandwickelspulen mit einem bestimmten Abstand nebeneinander in einem Kassettengeh·ause angeordnet und die Wickelspulen von aussen ·uber ger·ateseitig angeordnete Antriebsmittel antreibbar sind. Weiterhin sind auch Kassetten bekannt, die eine Ver·anderung des Abstandes der Band wickelspulen erm·oglichen. Derartige Kassetten finden insbesondere bei Videoger·aten Anwendung. Bei Ger·aten dieser Art werden von Seiten des Benutzers, je nach Verwendungszweck, differenzierte Anforderungen gestellt.
So wird z. B. zwischen netzabh·angigen Heimger·aten und netzunabh·angigen, also batteriebetriebenen, tragbaren Ger·aten unterschieden. Hierbei spielt insbesondere das Gewicht und die Gr·osse der unterschiedlichen Ger·ate eine erhebliche Rolle. So ist die Gr·osse des Ger·ates in erheblicher Weise von der Gr·osse der Kassette abh·angig.
Bei einem tragbaren Videoger·at, das beispielsweise die Bildaufzeichnung mit Hilfe einer Videokamera erm·oglichen soll, ist eine lange Aufnahmedauer, wie sie bei einem Heimger·at gew·unscht ist, nicht erforderlich. Dagegen spielen jedoch das Gewicht und die Gr·osse bei einem tragbaren Videoger·at eine erhebliche Rolle.
Aus den unterschiedlichen Anforderungen eines Benutzers an ein Video-Heimger·at einerseits und ein tragbares batteriebetriebenes Videoger·at andererseits ergeben sich zwangsl·aufig abweichende Kassettengr·ossen mit unterschiedlicher Spieldauer. Der naheliegende Wunsch, dass die kleinere, f·ur tragbare Videoger·ate geeignete Kassette, auch auf einem f·ur gr·ossere Kassetten eingerichtetem Heimger·at abgespielt werden soll, ist schwerlich zu realisieren.
Es ist zwar bereits eine Kassettenkonstruktion bekanntgeworden, bei der auch kleinere Kassetten in einem Video-Heimger·at f·ur gr·ossere standardisierte Kassetten abgespielt werden k·onnen, die daf·ur erforderliche Konstruktion ist jedoch recht kompliziert und damit teuer.
So werden gem·ass diesem Stand der Technik Zahnrad·ubersetzungen erforderlich, mit deren Hilfe der Bandwickelabstand ausgeglichen wird.
Ein weiteres Ausf·uhrungsbeispiel zur Anpassung einer kleineren Kassette in ein Heimger·at, das nur f·ur eine gr·ossere Kassette geeignet ist, sieht vor, dass die Wickel spulen in einer besonderen Lagereinrichtung schwenkbar gelagert sind. So k·onnen die Wickel spulen mit einem kleineren Abstand in ein kleineres Kassettengeh·ause und nach Verschwenken in ein gr·osseres Kassettengeh·ause eingesetzt werden. Eine Ausf·uhrung dieser Art ist ebenfalls aufwendig und erfordert vom Benutzer ein besonderes technisches Geschick.
Eine diese Nachteile teilweise vermeidbares Ausf·uhrungsbeispiel einer Kassette zur Ver·anderung des Wickelspulenabstandes sieht vor, die Wickel spulen in getrennten, zueinander verschiebbaren Geh·ausehalbteilen unterzubringen. Die beiden Geh·ausehalbteile werden hierbei durch einen als Hohlzylinder ausgebildeten F·uhrungsabschnitt in einer festen Bewegungsbahn gef·uhrt.
Nachteilig ist hierbei, dass die F·uhrung der beiden Geh·ausehalbteile keinerlei Anpassung der auseinander gezogenen Kassetten-Geh·ausehalbteile an die Lage des im Heimger·at ver·anderten Wickelspulenantriebs erm·oglicht.
Der Erfindung liegt die Aufgabe zugrunde, eine relativ kleine Video-Wendekassette f·ur tragbare Videoger·at zu schaffen, die mit geringem technischen Aufwand auch in einem f·ur gr·ossere standardisierte Kassetten vorgesehenem Video-Heimger·at abgespielt werden kann, wobei sich der Wickelspulenabstand in der Kassette dem Spulenantrieb im Heimger·at zwangsl·aufig anpasst.
Die L·osung dieser Aufgabe erfolgt erfindungsgem·ass durch die im kennzeichnenden Teil des Anspruchs 1 angegebenen Massnahmen.
Vorteilhafte Weiterbildungen ergeben sich aus den Unteranspr·uchen.
Die Erfindung wird nachfolgend unter Bezugnahme auf die Zeichnungsfiguren beispielsweise erl·autert. Es zeigt: Fig. 1 eine perspektivisch dargestellte Video-Wendekassette mit abgenom mener Abdeckung und verriegelten Kassetten-Halbteilen, Fig. 2 eine perspektivisch dargestellte Video-Wendekassette nach Fig. 1 mit auseinandergezogenen Kasset ten-H

albteilen, Fig. 3 eine schematische Draufsicht auf eine Video-Wendekassette mit aus einandergezogenen Kassetten-Halb teilen nach Fig.2, wobei ein Be reich der Kassetten-Halbteile mit aufgebrochener Geh·ausewand ge zeichnet ist und Fig. 4 eine vergr·osserte Darstellung eines des f·ur die Verriegelung der Kas setten-Halbteile vorgesehenen Sperr hakens.
Die Figur 1 zeigt eine perspektivisch dargestellte Video Wendekassette 1 - kurz Kassette genannt - mit einer von der Kassette abgehommenen Abdeckung 2. Die Abdeckung ist f·ur den normalen Verwendungsfall der Kassette in einem tragbaren Videoger·at stets auf der Kassette aufgesetzt und sch·utzt das sonst freiliegende Magnetband 3. Beim Einlegen der Kassette in ein tragbares Videoger·at wird die Abdeckung automatisch seitlich abgeklappt, und das Magnetband ist f·ur den Zugriff von ger·ateseitig vorhandenen Ausziehstiften (nicht gezeichnet) freiliegend. Die Kassette 1 weist die Form eines im wesentlichen quaderf·ormigen K·orpers auf mit zwei darin drehbar gelagerten Magnetband-Wickelspulen 4, 5. An einer schmalen L·angsfl·ache der Kassette ist eine ·Offnung mit teilweise zur·uckgesetzter Geh·ausewand 6 zur freiliegenden Nagnetband- f·uhrung vorgesehen.
Die Kassette selbst besteht aus zwei im wesentlichen geschlossenen Halbteilen 7, 8. Die einzelnen Kassetten-Halbteile 7, 8 bestehen wiederum aus zwei fast vollst·andig geschlossenen Halbschalen, die zusammengeschraubt oder nach einer der sonst bekannten Verbindungsformen haltbar zusammengef·ugt sind. Beide Kassettenhalbteile 7, 8 sind verriegelbar und k·onnen durch Eindringen von zwei Stiften 9, 10 (strichpunktiert gezeichnet) in an der Kassette vorgesehenen F·uhrungsbohrungen 11, 12 gel·ost werden. Die Kassettenhalbteile sind sodann auf einen vorgesehenen Abstand auseinanderzuziehen.
In der Figur 2 ist die Kassette im auseinandergezogenen Zustand gezeichnet. Die Verbindung der beiden verschiebbaren Kassetten-Halbteile 7, 8 erfolgt ·uber zwei flache F·uhrungsteile 13, 14. Die F·uhrungsteile sind parallel und in geringem Abstand zu den ·ausseren schmalen L·angsfl·achen 15, 16 der Kassetten-Halbteile angeordnet. Die Verriegelung der Kassettenhalbteile erfolgt im geschlossenen Zustand der Kassette ·uber die den F·uhrungsseiten zugeordneten Sperrhaken 17, 18. Die beiden F·uhrungsbohrungen 11, 12 zur Entriegelung der Sperrhaken 17, 18 liegen im Teilungsbereich der beiden Kassetten-Halbteile 7, 8 und bestehen somit aus den vier Bohrungsh·alften 11', 11" und 12', 12''.
Aus der Figur 3 sind weitere Einzelheiten ·uber die Ausgestaltung der Sperrhaken und der Lagerung der F·uhrungsteile 13, 14 in den Kassetten-Halbteilen 7, 8 zu erkennen. Die F·uhrungsteile 13, 14 sind in F·uhrungsnuten 19, 20, die sich im Inneren der Kassetten-Halbteile befinden, gelagert. Um sicherzustellen, dass sich die Kassetten Halbteile 7, 8 nicht nur in Haupterstreckungsrichtung (s. waagerechte Pfeilangabe) der Kassette 1 gegeneinander verschieben lassen, sondern auch in begrenzter Weise senkrecht hierzu (s. senkrechte Pfeilangabe) ausweichen k·onnen, sind die F·uhrungsteile 13, 14 aus schmalem Federbandstahl gefertigt.
Die Bandwickelspulen 4, 5 in der ausgezogenen Kassette k·onnen sich somit der Lage der im Heimger·at befindlichen und gegen·uber dem tragbaren Videoger·at unterschiedlichen Antriebselementen voll anpassen. Zur Begrenzung der Auszugsl·ange der Kassette weisen die F·uhrungsteile 13, 14 Begrenzungsnasen 21 auf.
Die Figur 4 zeigt einen vergr·ossert gezeichneten Ausschnitt des Sperrhakens aus einem Kassetten-Halbteil.
Der Sperrhaken 18 besteht aus einem Hakenteil 22, einem Lagerauge 23 und einem Verbindungssteg 24. Eine Druckfeder 25, die auf dem Verbindungssteg des Sperrhakens aufgesetzt ist und sich im Geh·ause des Kassetten-Halbteils abst·utzt, sorgt f·ur den n·otigen Verriegelungsdruck bei zusammengeschobenen Kassetten-Halbteilen. Im verriegelten Zustand beider Halbteile 7, 8 liegt das Sperr haken-Hakenteil 22 des einen Halbteils in einertrSperr- zahn 26 des anderen Halbteils. ·Uber eine Schr·agfl·ache 27, die sich am Sperrhaken-Verbindungssteg befindet, kann ·uber das Auftreffen eines in die Kassette eintauchenden Stiftes 9, 10 die Verriegelung des Sperrhakens aufgehoben werden. Das Hakenteil 22 des Sperrhakens weist in bekannter Weise eine Anlaufschr·age auf ·Uber einen Lagerstift ist der Sperrhaken 18 im Kassetten-Halbteil drehbar gelagert.

PHILIPS VR2350 STEREO MATCH LINE VIDEO 2000 Magnetic tape cassette with pivoting cover:

 A magnetic tape cassette of the "flip-over" type having side-by-side reels in a housing between two parallel main walls, an exposed run of tape along a front of the cassette housing, and a pivoting cover for the exposed run of tape. A single cassette cover covers the entire front of the housing, and has a pivoting arm at each side which is journalled to the cassette housing sidewalls such that the cover can be opened from its closed position in either direction to two different open positions, by pivoting toward the one or toward the other main wall of the housing. A movable slide may also cover openings which provide access behind the stretch of tape. 

 1. A magnetic tape cassette comprising

a housing, having first and second plane parallel main walls, two side walls connected to the main walls, a rear, and a front having an opening between said main walls,

two adjacent reel hubs rotatably arranged between said main walls;

a length of magnetic tape having respective ends connected to the reel hubs, a portion of said length being stretched along said front opening for cooperation with parts of a magnetic tape apparatus, and

cover means, connected to and pivotable relative to the housing about an axis parallel to said main walls and the cassette front, between a closed position and an open position,

wherein said cover means comprises a single cassette cover arranged to substantially cover the entire front of the housing when in the closed position, and connecting means for pivotally connecting said cover to the housing for movement from the closed position to a first open position by pivoting in a first direction toward the first main wall, and to a second, different open position by pivoting in a second direction toward the second main wall.


2. A cassette as claimed in claim 1, wherein

said cover comprises two pivoting arms having free ends, said arms extending along respective side walls of the cassette housing toward the housing rear when in the closed position, and

said connecting means includes pivotal bearing means disposed midway between said main walls near said free ends, for connecting the cover to said side walls such that the cover is pivotable about a single axis in both directions.


3. A cassette as claimed in claim 1, further comprising resilient means for loading said cassette cover relative to other parts of the cassette, for holding the cover in a stable balanced position in its first and in its second open position for any orientation of the cassette relative to the direction of the force of gravity.

4. A cassette as claimed in claim 1, wherein

said cover comprises two pivoting arms having free ends, said arms extending along respective side walls of the cassette housing toward the housing rear when in the closed position,

said connecting means includes pivotal bearing means disposed midway between said main walls near said free ends, for connecting the cover to said side walls, and

the pivotal bearing means comprises first pivotal bearing means for pivoting the cover in the first direction about a first pivotal axis, and second pivotal bearing means for pivoting the cover in the second direction about a second pivot axis, spaced from the first axis, the first pivotal bearing means and axis being disposed nearer the first main wall, and the second pivotal bearing means and axis being disposed nearer the second main wall.


5. A cassette as claimed in claim 4, wherein

said first pivotal bearing means includes respective first bearing journals disposed on the respective pivoting arms of the cassette cover, the second pivotable bearing means includes second bearing journals disposed on the respective pivoting arms, and the cassette housing includes stops for engaging the second bearing journals to limit the pivotable movement of the cover in its first pivoting direction, and stops to engage the first bearing journals to limit the pivotable movement of the cover in its second pivoting direction.


6. A cassette as claimed in claim 4, wherein

the first pivotable bearing means comprise first bearing journals and parts of the cassette which define first bearing recesses for receiving the first bearing journals, and

the second pivotable bearing means comprises second bearing journals and parts of the cassette which define second bearing recesses for receiving the second bearing journals,

each of said bearing recesses having an opening at its circumference to allow movement of the first bearing journals out of the first bearing recesses when the cover is pivoted about the second pivoting axis, and to allow movement of the second bearing journals out of the second bearing recesses when the cover is pivoted about the first pivoting axis.


7. A cassette as claimed in claim 4, wherein

the bearing journals are disposed on the pivoting arms of the cover,

the housing side walls include arcuate first guide slots, which each terminate in the respective openings in the circumference of the first bearing recesses, for guiding the first bearing journals with play when the cassette cover is pivoted in its second pivoting direction; and second guide slots, which each terminate in the respective openings in the circumference of the second bearing recesses, for guiding the second bearing journals with play when the cassette cover is pivoted in its first pivoting direction,

each of said guide slots having an end remote from the associated bearing recess terminating at a portion of the housing side wall, said side wall portion being one of said stops for limiting pivotable movement of the cover.


8. A cassette as claimed in claim 6, wherein

parts of the cassette define arcuate first guide slots, which each terminate in the respective openings in the circumference of the first bearing recesses, for guiding the first bearing journals with play when the cassette cover is pivoted in its second pivoting direction, and

parts of the cassette define arcuate second guide slots, which each terminate in the respective openings in the circumference of the second bearing recesses, for guiding the second bearing journals with play when the cassette cover is pivoted in its first pivoting direction.


9. A cassette as claimed in claim 8, wherein

the bearing recesses have an at least partly circular cross-section with a diameter equal to the maximum transverse dimension of the associated bearing journal plus the play,

the bearing journals have an elongate shape, with a width dimension which is smaller than the length dimension, and

the arcuate guide slots have a width dimension which is adapted to the width dimension of the associated bearing journal and is smaller than the diameter of the associated bearing recess so as to prevent movements of the cassette cover other than in the first or the second pivoting direction in every position of the cassette cover.


10. A cassette as claimed in claim 9, wherein

said bearing journals are disposed on the pivoting arms of the cover, and the guide slots are located in the housing side walls, and

each side wall of the housing further includes mounting slots extending in the direction of the bearing recesses and intersecting the guide slots at intersections, for mounting the bearing journals in the bearing recesses, said mounting slots each having an open entry side to allow unimpeded entry of the bearing journal into the mounting slot and having a bottom with a profile which extends between a first level at which there is play between the cassette cover and the cassette housing, and a second level at which the cassette cover has an interference fit between the respective bearing journals and the bottoms of the mounting slots.


11. A cassette as claimed in claim 1, each main wall having at least one cut-out which extends to the cassette front, to permit passage of an element of a cassette apparatus behind the stretched portion of the tape and withdrawal of the tape from the housing at the front,

wherein the cassette further comprises first and second slide plates disposed respectively near the first and second main walls, and means for mounting said slide plates to the housing for movement between a closing position nearer the front of the cassette and a retracted position nearer the rear of the cassette, in the closing position each slide plate at least partly closing the respective cut-out openings in the respective main wall, in the retracted position the slide plate being clear of said respective cut-out openings.


12. A cassette as claimed in claim 11, wherein

said two slide plates are parts of a single slide member which is bodily movable between a retracted position and a closing position, said member further including two side walls which extend along the side walls of the cassette housing and which interconnect the slide plates.


13. A cassette as claimed in claim 12, wherein

said slide member consists of a unitary plastic molding.


14. A cassette as claimed in claim 12, wherein

the slide member consists of two identical parts each having snap-connection means for interconnecting said identical parts through a snap connection, each of said identical parts being a unitary plastic molding.


15. A cassette as claimed in claim 12, wherein

said cover comprises two pivoting arms having free ends, said arms being disposed on the outside of the cassette housing, and extending along respective side walls of the cassette housing toward the housing rear when in the closed position, the slide member being arranged such that in the closed position of the cassette cover the slide member side walls cover the pivoting arms.


16. A cassette as claimed in claim 12, comprising resilient means for urging the cassette cover and the slide member toward each other, for holding the cassette cover in a stable balanced position under the influence of the resilient urging in its first and in its second open positions for any orientation of the magnetic tape cassette relative to the direction of the force of gravity.

17. A cassette as claimed in claim 12, wherein

each slide member side wall includes a portion prolonged to the rear of the cassette housing, so arranged that in the closing position of the slide member each side wall of the said member extends beyond the location of rear edges of the side plates when the slide member is in the more retracted position.


18. A cassette as claimed in claim 12, wherein

said slide member and said housing include cooperating stop means for preventing a slide member, mounted on the housing, from sliding off the housing in the absence of the cassette cover.


19. A cassette as claimed in claim 18, wherein

said cooperating stop means are arranged so that when the slide member is in its closing position a portion of said slide member abuts a portion of the cassette housing, and wherein said cassette includes resilient means which act both on the cassette housing and the slide member for urging the slide member toward the closing position, whereby in the closing position said stop means transmits the resilient load from the slide member to the cassette housing.


20. A cassette as claimed in claim 12, wherein

said slide member and said cassette cover include cooperating parts for causing the cassette cover to pivot toward the closed position from either one of the two open positions.


21. A cassette as claimed in claim 20, wherein

the slide member and the cassette cover include cooperating latching means for preventing the cassette cover from moving to a open position when the slide member is in the closing position.


22. A cassette as claimed in claim 21, wherein

each of the side walls of the slide member has an edge remote from the rear of the cassette housing arranged to be clear of the cassette cover, at least at locations disposed near the main walls of the housing, for engagement by an element of a cassette holder when the cassette is inserted into a cassette apparatus, so as to move the slide member to its more retracted position.


23. A cassette as claimed in claim 22, wherein

each of said edges of the slide member side walls includes a notch located midway between the main walls of the housing, and the cassette cover includes lateral projections for engaging the respective notch when the cassette cover is closed.


24. A cassette as claimed in claim 12 wherein,

at the location of the side walls of the slide member when this member is in its more retracted position, each of the side walls of the housing has a curved profile having a radius of curvature substantially equal to the distance between the two housing side walls, so arranged that the slide member may undergo at least limited twisting relative to the cassette housing whereby one side wall of the slide member becomes disposed nearer the rear of the cassette housing than the other slide member side wall, without jamming of the slide member on the housing.


25. A cassette as claimed in claim 12, comprising resilient means for urging the slide plates toward their closing positions, said resilient means acting both on the cassette housing and on the slide plates.

26. A cassette as claimed in claim 25, wherein

said two slide plates are parts of a single slide member which is bodily movable between a retracted position and a closing position, said member further including two side walls which extend along the side walls of the cassette housing and which interconnect the slide plates,

said slide member further including a connecting member halfway between the member side walls, behind the stretched tape portion, and

said resilient means for loading the slide member toward the closing position comprises a pressure spring bearing against the connecting member and the cassette housing.


27. A cassette as claimed in claim 26, wherein said slide member and the connecting member together consist of a unitary plastic molding.

28. A cassette as claimed in claim 26, wherein

the slide member consists of two identical parts each have snap-connection means for interconnecting said identical parts through a snap connection, each of said identical parts being a unitary plastic molding, and

said connecting member is formed by identical parts of said two identical parts.


Description:

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a magnetic tape cassette which is adapted to cooperate, in a first position and in a reversed second position, with parts of a cassette recording and/or playback apparatus (hereinafter referred to as a cassette apparatus); and more particularly to a cassette having first and second adjacently disposed reel hubs, which are rotatable about parallel spaced first and second axes of rotation in a cassette housing; a length of magnetic tape having a first end connected to the first reel hub and having a second end connected to the second reel hub, so as to enable it to be wound from the first reel hub to a reel on the second reel hub and back from the second reel hub to a reel on a first reel hub, and having a stretched tape portion along a front opening of the cassette housing for cooperation with parts of a cassette apparatus; and cover means connected to the cassette housing and pivotable relative thereto about a pivoting axis which is parallel to the main walls between a closed position and an open position. In the closed position, the cover extends along the front of the cassette housing, to at least partly cover the stretched portion of the magnetic tape and thus protect the magnetic tape against inadvertent damaging when the magnetic tape cassette is not placed on a cassette apparatus. The open position, when the magnetic tape cassette is placed on a cassette apparatus, allows parts of the cassette apparatus to cooperate with the stretched portion of the magnetic tape.

Magnetic tape cassettes in a variety of versions have gained a high degree of popularity in various fields of application. This may be attributed to the high vulnerability of the magnetic tape medium when not accommodated in a cassette. The magnetic tapes commonly used in magnetic tape equipment for the consumer market and also for many semiprofessional and professional uses have a thickness dimension which is very small in comparison with the width dimension. The thickness dimensions generally range between 15 and 40 um, while the width for the more customary magnetic tapes varies roughly between 12 and 25 mm. The magnetic tapes consist of a plastic foil which on one side is provided with a finely dispersed magnetizable material, and has an extremely high degree of flexibility. The magnetic tape cassette affords protection against damaging of the delicate and vulnerable magnetic tape, so that the ease of handling the magnetic tape medium is substantially improved.

For many simple applications it suffices if the front of the cassette is at least partly closed and is provided with openings for the passage into the cassette of parts of a cassette apparatus, such as a recording/playback head, an erase head and a pressure roller. Such a cassette is for example the so-called Compact Cassette, also referred to as the Philips cassette, which is generally used for audio purposes. With this cassette the magnetic tape need never be removed from the housing, so that the front may be partly closed and thus affords adequate protection of the magnetic tape against inadvertent touching. While dust can reach the magnetic tape through the openings, this seldom presents a problem in that tape application.

Still other known cassettes are intended for use with a cassette apparatus which includes a device for partly withdrawing the magnetic tape from the cassette housing and bringing the portion of the magnetic tape thus removed from the cassette housing into contact with the magnetic heads. For audio applications this enables a better guidance of the magnetic tape during its transport from the one reel to the other along the magnetic heads to be obtained, so that higher quality standards in respect of signal recording and reproduction can be achieved than with the previously mentioned Compact Cassette, in which the lace-up is determined by components of the cassette housing.

In known magnetic video tape equipment for home-entertainment use, which to date are always equipped with rotary magnetic heads which write obliquely oriented closely spaced tracks on the magnetic tape, the magnetic tape should also be withdrawn from the cassette housing. The front of the cassette housing must then be free of wall portions which could interfere with the withdrawal of the magnetic tape from the cassette housing. As a result of the absence of wall portions at the front the likelihood of the magnetic tape being touched inadvertently increases. This likelihood is further increased because the cassette apparatus customarily includes a device for withdrawing the magnetic tape from the cassette housing. Such a device enters the cassette housing through the main walls behind the magnetic tape and should engage the back side of the magnetic tape during withdrawal. Therefore, cut-outs which extend to the front are necessary in the main walls of the cassette. These cut-outs expose the edges of the magnetic tape, which exposure greatly increases the likelihood of the magnetic tape being damaged.

Another aspect of cassette design is that, when magnetic tape cassettes are used on equipment which enables higher quality audio recording and reproduction or which enables video signals to be recorded and reproduced, dust should be prevented from reaching the magnetic tape as far as possible, because dust may affect the high quality of recording and reproduction.

Therefore many magnetic tape cassettes are provided with movable cover means in order to protect the stretched portion of the magnetic tape which extends along the front of the magnetic tape cassette when the magnetic tape cassette is not located on a cassette apparatus.

2. Description of the Prior Art

Magnetic tape cassettes which are suitable for use on a cassette apparatus in a first position only and which are consequently not suitable for cooperating with the apparatus in a reversed or "flipped over" second position, so-called non-reversible cassettes, present fewer problems in respect of the protection of the magnetic tape, because only one of the two main walls need be provided with cut-outs for withdrawal of the magnetic tape from the cassette. Such a cassette is for example known from U.S. Pat. No. 3,900,172. A cassette cover closes the front of the cassette housing if the cassette is removed from a cassette apparatus. On its side which faces the rear of the cassette the cassette cover has an additional ridge which covers the back side of the magnetic tape when the cassette cover is closed. Although one of the main walls of the cassette has a comparatively large opening this still provides satisfactory protection of the magnetic tape. However, dust can still rather easily reach the magnetic tape, and the tape can readily be damaged by the ridge if the stretched portion of the magnetic tape in the cassette is not sufficiently taut.

In the case of reversible magnetic tape cassettes this solution cannot be adopted. If the housing of a reversible magnetic tape cassette has cut-outs in the main walls for withdrawal of the magnetic tape from the magnetic-tape cassette, the cut-outs should be formed in both main walls. From German Offenlegungsschrift No. 2,552,063, to which U.S. Pat. No. 4,021,006 corresponds, a reversible magnetic tape cassette of this type is known, having two cassette covers which partly extend along the front of the cassette housing: a first cassette cover on the side near the first main wall of the cassette housing, and a second cassette cover on the side near the second main wall of the cassette housing. When the cassette covers are closed a part of the first cassette cover is situated in the plane of the first main wall and a part of the second cassette cover is situated in the plane of the second main wall. At the front of the magnetic tape cassette perpendicular to these parts, half-height front cover portions extend parallel to the rear of the cassette housing, and are thus perpendicular to the first-mentioned parts of the cassette covers. The first cassette cover is pivotable about a first pivoting axis disposed near the first main wall of the cassette housing and the second cassette cover is pivotable about a second pivoting axis disposed near the second main wall of the cassette housing. The two pivoting axes are parallel to each other and parallel to the main walls. The two cassette covers also have gear-segments which engage with each other. When the one cassette cover is pivoted the second cassette cover is thus pivoted simultaneously and to the same extent. Each cassette cover covers the front of the cassette housing over half its height.

When this known magnetic-tape cassette is placed on a cassette apparatus, a unit on the deck of the cassette apparatus partly opens the two cassette covers, after which the magnetic heads are brought into contact with the magnetic tape through the slot between the two cassette covers. The magnetic tape cassette has cut-outs in the main walls for bringing the magnetic tape into contact with two pressure rollers by means of two capstans on either side of the magnetic head, which capstans are situated behind the magnetic tape.

A disadvantage of this known cassette is that both in the first and in the second position of the magnetic tape cassette on a cassette apparatus the two cassette covers must be opened. One of the two cassette covers is then always pivoted into a position in which it moves toward and faces the cassette apparatus. In the cassette apparatus the magnetic tape cassette should therefore be supported in such a way that there is sufficient clearance between the main wall of the magnetic tape cassette which faces the cassette apparatus and the parts of the apparatus near that wall. Another drawback is that the opened cassette covers constitute an obstruction to the device which withdraws the magnetic tape from the cassette, unless the cassette covers are opened very far. This last alternative demands a still greater clearance. Otherwise both sides adjacent the cassette covers must have cut-outs formed which open towards the front, as in the known cassette, so that the magnetic tape is exposed at these locations. The spaced required above the cassette for the opened cassette cover is comparatively large, because the cassette cover portion which is disposed in the main wall also pivots upwards. This is a drawback because the overall height of a cassette apparatus should be minimized for obvious reasons.

Therefore, the known magnetic tape cassette is less suitable for application where the magnetic tape is to be withdrawn from the cassette housing. Moreover, unless openings are formed in the main walls of the cassette housing on both sides of the cassette covers for the passage of the tape withdrawal elements of a cassette apparatus, which means that there will be locations on both sides of the cassette covers where the magnetic tape can be touched and damaged, the two cassette covers should be pivoted into their open positions before the magnetic tape cassette is moved to an operating position over the withdrawal elements of the cassette apparatus. However, for thus swinging open the cassette covers before the magnetic tape consists is completely in its operating position, the known magnetic tape cassette is less suitable because of the actuation elements for the cassette covers which are then required. Further, the part of the cassette cover which faces the deck of the cassette apparatus and which is situated at the front of the cassette housing constitutes an obstruction for the withdrawal elements even if the cassette covers are swung open very far.

SUMMARY OF THE INVENTION

It is the object of the invention to provide a magnetic tape cassette which may be inverted or flipped over, and which provides good protection against dust or accidental touching when closed, but does not require excessive clearance between the cassette and the apparatus.

Covers

In accordance with the invention a single cassette cover substantially covers the entire front of the cassette housing; and on both sides the cassette cover is provided with pivoting arms which extend along the side walls of the cassette housing toward the rear of the cassette housing in the closed position, from its closed position the cassette cover being pivotable into either of two different open positions, one towards the first main wall of the cassette housing and the other towards the second main wall of the cassette housing.

In the cassette in accordance with the invention the entire front of the cassette housing is covered, so that if the main walls have cut-outs which extend to the front of the cassette housing, the tape is protected to some extent against inadvertent touching. As the cassette cover is movable in either of two pivoting directions, a magnetic tape cassette is obtained which on its side which faces a cassette apparatus has no obstacles which impair placing of the cassette on the cassette apparatus or the insertion of elements of the apparatus into the cassette. Above the magnetic tape cassette a certain clearance is required for the swung-open cassette cover. However, this clearance may be comparatively small and need not be greater than the height dimension of the magnetic tape cassette, but may even be smaller.

In most cassette equipment, the magnetic tape cassette is not placed directly onto the deck by hand, but is slid into a movable cassette holder, after which the cassette holder is moved towards the deck. The magnetic tape cassette in accordance with the invention is particularly suitable for such applications, because the movement of the magnetic tape cassette towards the deck allows provisions to be made on the deck for opening the cassette cover during the movement of the cassette holder. The cassette cover which is thus opened during the movement of the cassette holder does not impede insertion into the magnetic tape cassette of elements such as capstans, pressure rollers, magnetic tape retaining elements or elements for withdrawing the magnetic tape from the cassette.

Single Pivot

In a simple embodiment of the invention pivotal bearing means are disposed midway between the first and the second main wall and the cassette cover is pivotable in its first and its second pivoting directions about a single pivoting axis midway between the two main walls. This embodiment reduces the likelihood of the cassette cover touching the portion of the magnetic tape which is tensioned along the front of the magnetic tape cassette, during the pivotal movement of the cover, if the pivoting axis is situated somewhat to the rear of the magnetic tape cassette.

Double Pivot

In a preferred embodiment of the invention the pivotal bearing means comprise a first pivotal bearing means disposed nearer the side of the first main wall for pivoting the cassette cover in its first pivoting direction about a first pivoting axis which is also nearer the side of the first main wall, as well as a second pivotal bearing means disposed nearer the side of the second main wall for pivoting the cassette cover in its second pivoting direction about a second pivoting axis which is likewise nearer the side of the second main wall. This embodiment has the advantage that the distance between the stretched portion of the magnetic tape, which extends along the front of the magnetic tape cassette, and the inner side of the cassette cover, which faces the magnetic tape, can be reduced and that moreover the pivoting axes can be situated nearer the front of the cassette housing, without the risk of the magnetic tape being damaged. Thus smaller cassette dimensions are obtained. A further advantage of this embodiment is that the cassette cover can be pivoted into a position in which the front side of the cassette cover extends parallel to the main walls of the cassette housing without occupying much room in the apparatus, so that optimum accessibility of elements of the cassette apparatus to the magnetic tape is obtained.

Bearing constructions which enable a component to be pivoted into two different pivoting directions about two different parallel pivoting axes are known. Examples of these are the known hinge construction for swing doors, while there are also constructions comprising crosswise arranged straps.

A simple bearing construction which is suitable for a magnetic tape cassette is obtained with an embodiment of the invention in which the first pivotal bearing means include fist bearing journals as well as parts of the magnetic tape cassette which define first bearing recesses which receive the first bearing journals, and the second pivotal bearing means include second bearing journals as well as parts of the magnetic tape cassette which define second bearing recesses which receive the second bearing journals. These bearing recesses each have an opening at their circumference to allow movement of the first bearing journals out of the first bearing recesses during pivotal movement of the cassette cover about the second pivoting axis, and to allow movement of the second bearing journals out of the second bearing recesses during pivotal movement of the cassette cover about the first pivoting axis.

In this embodiment it is necessary to prevent the cassette cover in its closed or swung open positions, or during its pivotal movement, from becoming detached from the cassette housing by movement of the bearing journals out of the bearing recesses. In a further preferred embodiment parts of the magnetic tape cassette define arcuate first guide slots which each terminate in the respective openings in the circumference of the first bearing recesses, for guiding the first bearing journals with play during the pivotal movement of the cassette cover in its second pivoting direction; and parts of the magnetic tape cassette define arcuate second guide slots which each terminate in the respective openings in the circumference of the second bearing recesses, for guiding the second bearing journals with play during the pivotal movement of the cassette cover in its first pivoting direction. These parts of the magnetic tape cassette consist of parts of the side walls of the cassette housing if the bearing journals are disposed on the pivoting arms of the cassette cover, or consist of parts of the pivoting arms if the bearing journals are disposed on the side walls of the cassette housing.

The two guide slots intersect each other midway between the two main walls of the cassette housing. At the location of the intersection there is a possibility that a bearing journal does not move in the corresponding guide slot, so that the cassette cover could assume a wrong position. It is therefore advantageous to use an embodiment in which the bearing recesses have an at least partly circular cross-section with a diameter equal to the maximum transverse dimension of the associated bearing journal plus the play; the bearing journals have an elongate shape with a width dimension which is smaller than the length dimension; and the arcuate slots have a width dimension which is adapted to the width dimension of the associated bearing journal and is smaller than the diameter of the associated bearing recess. This embodiment prevents movements of the cassette cover other than in the first or the second pivoting direction in every position of the cassette cover, by cooperation of the bearing journals and parts of the cassette housing.

If the bearing journals are disposed on the pivoting arms and the guide slots are disposed in the side walls of the cassette housing, in another preferred embodiment providing a simple mounting of the cassette cover, each side wall of the cassette housing has mounting slots which extend in the direction of the bearing recesses and which intersect the guide slots at intersections, for mounting the bearing journals in the bearing recesses. The mounting slots each have an open entry side to allow unimpeded entry of the bearing journal into the mounting slot, and furthermore have a bottom with a profile which extends from a level at which there is play between the cassette cover and the cassette housing to a level at which the cassette cover is slightly bent by an interference fit between the bearing journals and the bottom of the mounting slots. Thus, when the cassette cover is being mounted, the cassette cover is slightly bent until the bearing journals engage with the bearing recesses, after which the bearing journals snap into the bearing recesses as a result of the resilient action of the cassette cover itself.

In order to obtain well-defined open positions of the cassette cover in a magnetic tape cassette of the types described above having first and second pivoting axes, according to another preferred embodiment of the invention in which the bearing journals are disposed on the pivoting arms of the cassette cover, the cassette housing is provided with stops which are adapted to cooperate with the second bearing journals so as to limit the pivotal movement of the cassette cover in its first pivoting direction, and with stops which are adapted to cooperate with the first bearing journals so as to limit the pivotal movement of the cassette cover in its second pivoting direction. In the embodiment in which guide slots for the bearing journals are formed in the side walls of the magnetic tape cassette, each of the guide slots at its end which is remote from the corresponding bearing recess may terminate at a portion of the side wall of the cassette housing, which portion functions as one of the stops which is adapted to cooperate with the bearing journals so as to limit the pivotal movements of the cassette cover.

Slide Plates

The invention is suitable both for audio and for video cassettes, both when they are not provided with cut-outs in the main walls which are open towards the front of the cassette housing and when such cut-outs are provided. However, it is a further object of the invention to provide a magnetic tape cassette having maximum fields of application. For such an objective it is necessary to form large cut-outs in the main walls of the cassette housing to permit the passage of elements of cassette apparatus of different types. In the case in which large cut-outs in the main walls of the cassette housing extend to the front, there is an increased risk of the magnetic tape being damaged and of dust and dirt penetrating into the interior of the cassette.

An embodiment of the invention, which satisfies this object, includes a first and a second slide plate respectively disposed near the first and second main walls, each slide plate being movable between a retracted position nearer the rear of the cassette housing and a closing position nearer the front of the cassette housing. Each slide plate leaves the respective openings in the corresponding main wall clear in its retracted position, and closes these openings at least partly and preferably completely in the closing position. Thus it is possible to provide magnetic tape cassettes which, once they have been removed from the cassette apparatus, are almost completely closed, except of course for the openings in the main walls for the passage of drive spindles for the magnetic tape reels; but which, once they have been placed on a cassette apparatus, first of all have a fully open front, and secondly also provide satisfactory access behind (to the back side of) the magnetic tape to allow passage of elements of a cassette apparatus through the cut-outs in the main walls.

An embodiment is preferred in which the two slide plates are part of a single slide member which is bodily movable between the retracted position and the closing position, which member also includes two side walls which extend along the side walls of the cassette housing and which interconnect the slide plates. The slide member may then be formed as a unitary component which is integrally manufactured from a plastic. These embodiments have the advantage that easy guidance and journalling of the slide plates on the cassette housing is assured.

Alternatively, according to another preferred embodiment, the slide member comprises two identical parts which are integrally manufactured from a plastic, which parts are provided with snap-connection means and are interconnected thereby through a snapped connection. As the two parts of the slide member are identical only one tool is required for manufacturing the slide member. The advantage of this embodiment mainly resides in the simplified mounting of the slide member. By using the snapped connection, the member can readily be mounted on the cassette housing after the magnetic tape reels and the cassette cover have been mounted in and on the cassette housing respectively. If the two pivoting arms of the cassette cover are located on the outside of the cassette housing, in a still further preferred embodiment the side walls of the slide member cover the pivoting arms in the closed position of the cassette cover. Thus, the pivoting arms are well protected when the magnetic tape cassette is removed from a cassette apparatus, so that the comparatively vulnerable bearing means of the cassette cover are protected against mechanical damaging. Moreover, a magnetic tape cassette is thus obtained with a clean-cut and smooth appearance, because the bearing constructions are covered by the side walls of the slide member.

Spring Restraints

For specific uses of the magnetic tape cassette in accordance with the invention it may be of importance that, once a cassette cover is open, it does not swing back to its closed position under the influence of gravity. An embodiment of the invention which is of interest in this respect includes resilient means which load the cassette cover relative to other parts of the magnetic tape cassette, the cassette cover being in a stable balanced position under the influence of the resilient load in its first and in its second open position for any orientation of the cassette relative to the direction of the force of gravity. The resilient means may for example act on the cassette cover and on the slide member and urge these components towards each other. Leaf spring constructions are also possible which cooperate with non-round bearing journals of the cassette cover. However, it is not always desirable to subject the cassette cover to a resilient load, because the bistable positions which the cassette cover can assume under the influence of the resilient menas require that the cassette apparatus include means for closing the cassette cover against the resilient load.

Comparatively simple means on the cassette apparatus are sufficient for moving the slide plates. Since the slide plates slide over the main walls of the cassette housing they are easily opened during the operation of inserting the magnetic tape cassette into a cassette holder. Preferably, resilient means are provided which act both on the cassette housing and on the slide plates so as to urge the slide plates towards their closing positions. With the aid of these resilient means the slide plates are always automatically moved towards their closed positions when the magnetic tape cassette is removed from the cassette apparatus. Moreover, the resilient means enable automatic ejection or at least partial ejection of a magnetic tape cassette from a cassette holder.

Accommodating the resilient means in the magnetic tape cassette may be a problem in view of the limited space which is available. When a slide member which is bodily movable is used, an embodiment is therefore of interest which makes optimum use of the space available in a magnetic tape cassette. In this embodiment the first and the second slide plates of the slide member are interconnected halfway between its two side walls and behind the magnetic tape by means of a connecting member, and the resilient means for loading the slide member towards the closed position comprise a pressure spring between the connecting member and the cassette housing. Thus, in the cassette housing a space exists halfway between its side walls and between the two circular reels, which can readily accommodate a helically wound pressure spring, so that the available and generally unused room can be utilized. A further advantage of this embodiment is that owing to the connection between the two slide plates at a location between the two side walls of the slide member the slide member is given a higher rigidity. If the slide member consists of a unitary component which is integrally manufactured from a plastic, it is advantageous to manufacture the slide member and the connecting member together as a single integrally manufactured component. As the connecting member is located behind the magnetic tape, mounting of such a slide member may be difficult. In an embodiment which overcomes this problem the unit comprising the slide member and the connecting member is made of two identical parts which are integrally manufactured from a plastic and provided with snap-connection means, the parts being interconnected by a snapped connection. After the magnetic tape reels have been mounted in the cassette housing and, as the case may be, also after mounting the cassette cover, the slide member can be fitted onto the cassette housing by moving the two parts of the slide member towards each other in a direction perpendicular to the main walls of the cassette housing and interconnecting them by means of a snapped connection. Subsequently, the pressure spring can be mounted between the cassette housing and the slide member.

Cover/Slide Movement

When a bodily movable slide member is used, in yet another preferred embodiment the slide member and the cassette cover are provided with cooperating parts for pivoting the cassette cover towards its closed position, no matter which of its two open positions the cassette cover occupies. The advantage of this embodiment is that the movement of the slide member to its closing position and the pivotal movement of the cassette over from an open position to its closed position can proceed in a single operation, when the slide member is moved towards its closing position. Furthermore, it is advantageous if the slide member and the cassette cover are provided with cooperating latching means which prevent the cassette cover from moving to the open position when the slide member is in the closing position. Thus, the cassette cover will always stay closed as long as the slide member is in its closing position.

For moving the slide member and subsequently opening the cassette cover when the magnetic tape cassette is placed on the cassette apparatus, in yet another preferred embodiment the edge of each of the side walls of the slide member remote from the rear of the cassette housing is arranged to be clear of the cassette cover, at least at locations which are disposed near the main walls. This edge may then be used as a stop means for moving the slide member to its retracted position when the magnetic tape cassette is placed in a cassette holder of the cassette apparatus. For opening the cassette cover after the cassette has been inserted and for moving the slide member in the cassette holder, in a different preferred embodiment the corresponding edge of each of the side walls of the slide member which is remote from the rear of the cassette housing has a recess formed at a location midway between the main walls of the cassette housing. The cassette cover is then provided with lateral projections which engage the recesses when the cassette cover is closed. These projections may be used to open the cassette cover by engaging elements on a cassette apparatus during movement of the cassette holder to an operating position.

In a magnetic tape cassette in accordance with the invention each of the slide plates will have a length dimension which is roughly equal to the distance between the side walls of the cassette housing; and transverse thereto, a width dimension which is substantially smaller. This occurs because the width dimension must be limited so that when the slide plate is in its retracted position the plate does not interfere with the drive means for the magnetic tape reels. The comparatively great length/width ratio of the slide plates is apt to cause the plates to jam if a slide plate or a slide member does not perform a purely translational movement between its closing position and its retracted position, but rather twists slightly about an axis parallel to the axes of rotation of the magnetic-tape reels. Since jamming of the slide plates or the bodily movable slide member is obviously undesirable, in another preferred embodiment of the invention each of the side walls of the cassette housing, at the location of the side walls of the slide member when this member is in its retracted position, is provided with a curved profile with a radius of curvature which is substantially equal to the distance between the two side walls of the cassette housing. This profile enables the slide member to twist a little relative to the cassette housing, such that one side wall of the slide member is nearer the rear of the cassette housing than the other side wall of the slide member, without the slide member becoming jammed on the cassette housing.

In a different embodiment which is adapted to eliminate jamming effects, each of the side walls of the slide member comprises a portion which protrudes towards the rear of the cassette housing, so arranged that in the closing position of the slide member each side wall of the slide member extends beyond the location occupied by those sides of the slide plates of the slide member facing the rear of the cassette housing when the slide member is in its retracted position. That location, as previously stated, is dictated by the fact that the slide plates should not interfere with the drive means for the magnetic tape reels. However, the side walls of the slide member may extend further towards the rear of the cassette housing, so that a favorable ratio is obtained between the length of the slide member and its width at the location of the side walls. A further advantage is the improved appearance obtained by the use of the protruding portions, when the slide member is in the closed position; that is, the outward appearance viewed at a main wall is not spoiled by a stepwise change required because of the thickness of the slide member.

In many cases, especially if the slide member is loaded towards its closing position by resilient means, it is advantageous if the slide member and the housing are provided with cooperating stop means to prevent a slide member, once it has been mounted, from sliding off the cassette housing when the cassette cover has not yet been mounted or has been removed. This embodiment provides greater ease of handling the magnetic tape cassette during assembly. In addition, if the cassette includes resilient means for loading the slide member towards the closing position, a further advantage is obtained from this embodiment if, while the slide member is in the closing position, the stop means engage the slide member and transmit at least the greater part of the resilient load imposed by the resilient means to the cassette housing. When this embodiment is used the cassette cover, and thus the bearing means for the pivotal movements of the cassette cover, are not loaded by the resilient means.

BRIEF DESCRIPTION OF THE DRAWING

The invention will now be described in more detail with reference to the drawing, in which:

FIG. 1 is a view at a first main surface of a magnetic tape cassette having a cassette cover which is pivotable about a single axis,

FIG. 2 is a side view at the cassette cover of the magnetic tape cassette in accordance with FIG. 1,

FIG. 3 is a view at a second main surface of the cassette of FIG. 1.

FIG. 4 is a side view of the magnetic tape cassette in accordance with the preceding Figures,

FIG. 5 is a detail of FIG. 4, showing the cassette cover swung open in a first pivoting direction, and a dashed line showing the cassette cover in a second open position in a second pivoting direction,

FIG. 6 is a view similar to FIG. 1, but of a magnetic tape cassette having a cassette cover pivotable about two pivoting axis and a slide member for closing the openings in the main walls,

FIG. 7 is a front view of the magnetic tape cassette of FIG. 6,

FIG. 8 is a view in accordance with FIG. 6, but now at a different main surface of the magnetic tape cassette,

FIG. 9 is a perspective view of the cassette in accordance with FIGS. 6 to 8, the slide member being in its closing position and the cassette cover being in its closed position,

FIG. 10 is similar to FIG. 9, but with the slide member in its retracted position and the cassette cover opened in a first pivoting direction,

FIG. 11 is similar to FIG. 10, but with the cassette cover opened in a second pivoting direction,

FIG. 12 is a partial exploded view of a magnetic tape cassette in accordance with FIGS. 6 to 11,

FIG. 13 shows a detail of one of the side walls of the cassette in accordance with FIGS. 6 to 12, the position of the bearing journals being shown relative to the bearing recesses and the guide slots when the cassette cover is closed,

FIG. 14, shows the same detail as FIG. 13, but with the cassette cover opened in a first pivoting direction,

FIG. 15 is a sectional view in accordance with the arrows XV--XV in FIG. 14,

FIG. 16 is a cross-section across the center of the slide member and in accordance with the arrows XVI--XVI in FIG. 12,

FIG. 17 is a partial cross-section in accordance with the arrows XVII--XVII in FIG. 16,

FIGS. 18, 19 and 20 are views of a connecting member for interconnecting the slide plates of the slide member in the magnetic tape cassette in accordance with FIGS. 6 to 12,

FIG. 21 shows an integrally manufactured plastic version of a slide member for a magnetic tape cassette in accordance with FIGS. 6 to 12,

FIG. 22 shows a slide member consisting of two plastic components which have been snapped together for the magnetic tape cassette in accordance with FIGS. 6 to 12,

FIG. 23 shows a detail of one of the snap connections for interconnecting the parts of the slide member in accordance with FIG. 22,

FIG. 24 and FIG. 25 illustrate the principle of an embodiment in which a slide member and a cassette cover are loaded relative to each other by means of a tension spring, FIG. 24 representing the situation with the cassette cover closed and FIG. 25 the situation with the cassette cover open,

FIG. 26 is similar to FIG. 8, but with the slide member in a twisted position,

FIG. 27 is a similar view as in FIG. 9 of a modified embodiment, with a slide member which has portions protruding towards the rear of the cassette housing,

FIG. 28 is a view at a main wall of the magnetic tape cassette in accordance with FIG. 27,

FIG. 29 schematically shows a part of a cassette apparatus with a hinged cassette holder containing a cassette in accordance with the invention, the slide member being moved into its more retracted position during insertion of the cassette, and

FIG. 30 is similar to FIG. 29, but with the cassette holder in its operating position and the cassette cover being opened by means provided on the deck of the cassette apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Single Pivot

The magnetic tape cassette 1 in accordance with FIGS. 1 to 3 is adapted to cooperate with a cassette apparatus in a first position, as is shown in FIG. 1, and in a reversed second position, as shown in FIG. 3. As is customary with such so-called reversible cassettes, the two main walls are provided with designations "1" and "2" respectively, for the user. The magnetic tape cassette has a first and a second adjacently disposed reel hub 2 and 3 respectively, which are rotatable about parallel spaced axes of rotation, not shown. These hubs each have a central opening 4 and 5 respectively for engagement by a reel hub drive spindle which belongs to the cassette apparatus. Around the central openings 4 and 5 a number of openings 6 and 7 respectively are formed for a reel hub carrier pin of the cassette apparatus. The cassette 1 housing includes a first main wall 8 and, parallel thereto, a main wall 9. The main wall 8 has a first opening 10 coaxial with the first reel hub 2 to allow passage of a reel drive spindle, and a similar second opening 11 for the second reel hub 3. The second main wall 9 has corresponding first and second openings 12 and 13 respectively. The main walls 8 and 9 are interconnected by side walls 14 and 15 at their short sides, and by a rear wall 16. The reel hubs 2 and 3 have reel flanges 17 and 18 respectively. A length of magnetic tape 19 is connected to the reel hubs 2 and 3 at its two ends, so as to enable it to be wound back and forth between the first reel 2 and the second reel 3. Near a front opening 20, opposite the rear 16 of the cassette, a portion 21 of the tape 19 is stretched in a position where it can be engaged by parts of a cassette apparatus. To keep the stretched tape position 21 taut along the front of the cassette housing two guide rollers 22 and 23 are located between the two main walls 8 and 9 of the cassette housing. In the main wall 8 three cut-outs 24, 25 and 26 are formed, which are open towards and extend to the front opening 20 of the cassette housing, for the passage of components of a cassette apparatus behind the stretched tape portion 21 and to allow withdrawing the magnetic tape from the cassette housing. The main wall 9 has a corresponding cut-outs 27, 28 and 29 which also extend to the front opening 20.

A cassette cover 30 is connected to the cassette housing and is pivotable relative thereto about a pivoting axis 31 parallel to the main walls, between a closed position, shown in FIGS. 1 to 4, and an open position which is obtained by a pivotal movement in a pivoting direction towards a main surface of the cassette housing. The cassette cover covers substantially the entire front opening 20 of the cassette housing.

On both sides the cassette cover is provided with pivoting arms 32 and 33 having free ends 34 and 35 respectively, the arms extending along the respective side walls 14 and 15 of the cassette housing, toward the housing rear when in the closed position. The pivoting arms have free ends 34 and 35 respectively which face the rear 16 of the cassette housing in the closed position. The side walls 14 and 15 of the cassette housing and the pivoting arms 32 and 33 of the cassette cover 30 are provided with pivotal bearing means which cooperate with each other near the free ends 34 and 35 of the pivoting arms 32 and 33. As is shown in FIG. 5 the cassette cover 30 is pivotable from its closed position into two different opened positions. Solid lines in FIG. 5 represent a first open position of the cassette cover 30, which is reached by pivoting the cassette cover in a first pivoting direction indicated by an arrow 36 towards the first main wall 8 of the cassette housing. Dashed lines represent a second open position of the cassette cover reached by pivoting the cassette cover in a second pivoting direction in accordance with an arrow 37 towards the second main wall 9. The main wall 8 has slots 38 and 39 which are open towards the front 20 of the cassette housing for the passage of the pivoting arms 32 and 33 when the cassette cover 30 is pivoted in its first pivoting direction 36. The main wall 9 has corresponding slots 40 and 41 for pivoting in the second pivoting direction 37. The bearing means for the pivotal bearing of the cassette cover comprise two bearing journals 42 and 43 near the free ends 34 and 35 of the pivoting arms 32 and 33 and corresponding recesses in the side walls 14 and 15 of the cassette housing. An example of such a recess is the recess 44 in FIGS. 4 and 5.

The bearing journals 42 and 43 have a square cross-section and the recess 44 as well as the corresponding recess, not shown, in the side wall 15 of the cassette housing has a semicircular cross-section. In the side walls at the location of the bearing journals 42 and 43 leaf springs 45 provide a simple spring restraint for loading the bearing journals towards the rear 16 of the cassette housing. Because of the resilience of the leaf springs loading the square cross-section of the bearing journals of the cassette cover, the cassette cover will be held in a stable balanced position, both in its closed position and in its two open positions for any orientation of the magnetic tape cassette relative to the direction of the force or gravity.

Double Pivots

FIGS. 6 to 20 relate to a different embodiment of the invention. The magnetic tape cassette 47 is largely identical to the magnetic tape cassette 1 of FIGS. 1 to 5. The cassette includes reel hubs 48 and 49 with central openings 50 and 51 and additional openings 52 and 53 arranged around the central openings. The cassette housing comprises a first main wall 54 and a second main wall 55 with first openings 56 and 57 respectively, and with second openings 58 and 59 respectively, for the reel hubs 48 and 49. The main walls 54 and 55 are interconnected by side walls 60 and 61 and a rear wall 62. Opposite the rear wall there is located a front opening 63, see FIGS. 10 to 12. The cassette housing accommodates a magnetic tape 64 with a stretched tape portion 65 near the front 63.

A cassette cover 66 substantially covers the entire front 63 of the cassette housing. On both sides the cover 66 has pivoting arms 67 and 68 which extend along the sides walls 60 and 61 and which have free ends 69 and 70. In the closed position the arms 67 and 68 extend toward, and the free ends face, the rear 62 of the cassette housing. The side walls 61 and 62 and the pivoting arms 67 and 68 have cooperating pivotal bearing means near the free ends 69 and 70 of the pivoting arms. The cassette cover 66 is pivotable from its closed position, see FIGS. 6 to 8, into two different open positions; namely, a first open position, by pivoting in a first pivoting direction 71 (FIG. 10) towards the first main wall 54, and a second open position, by pivoting in a second pivoting direction 72 (FIG. 11) towards the second main wall 55 of the cassette housing.

In the magnetic tape cassette 47 the pivotal bearing means comprise first pivotal bearing means situated nearer the 66 in its first direction 71 about a first pivoting axis 73 which is situated nearer the side of the first main wall 54; and second pivotal bearing means situated nearer the side of the second main wall 55, for pivoting the cassette cover in the second pivoting direction 72 about a second pivoting axis 74 spaced from the first axis and situated nearer the side of the second major wall. The first pivotal bearing means comprise first bearing journals 75 and 76 formed on the arms 67 and 68 respectively as well as parts of the cassette housing side walls 60 and 61 which define first bearing recesses 77 which receive the first bearing journals. For clarity, only the first bearing for cooperation with the bearing journal 75 is shown, in FIGS. 11 and 12. The second pivotal bearing means comprise second bearing journals 78 and 79 also formed on the arms 67 and 68 respectively, and parts of the cassette housing side walls 60 and 61 which define second bearing recesses 80 for receiving these bearing journals. Similarly, only the second bearing recess for receiving the bearing journal 78 is shown in FIGS. 10 and 12.

Each of the bearing recesses has an opening at its circumference, for moving the bearing journals 75 and 76 out of the corresponding bearing recesses when the cassette cover is pivoted about the second pivoting axis 74 and for moving the bearing journals 78 and 79 out of the corresponding bearing recesses when the cassette cover 66 is pivoted about the first pivoting axis 73.

Actuate first guide slots 81 (only one shown in FIGS. 11 and 12) each terminate in the respective opening in the circumference of the first bearing recesses 77 for guiding the first bearing journals 75 and 76 with play when the cassette cover 66 is pivoted in its second pivoting direction 72. Arcuate second guide slots 82 (again, only one shown) each terminate in the respective opening in the circumference of the second bearing recesses 80 for guiding the second bearing journal 78 with play when the cassette cover 66 is pivoted in its first pivoting direction 71.

As is in particular apparent from FIGS. 13 to 15 the bearing recesses 77 and 80 have, as shown, an at least partly circular cross-section with a diameter equal to the length (maximum transverse dimension) L of the associated bearing journals 75 or 78 plus some play. The bearing journals have an elongated shape with a width dimension T which is smaller than the length dimension L. The arcuate guide slots have a width dimension W which is adapted to the width dimension T of the associated bearing journal and which is smaller than the diameter of the associated bearing recess. In this way movements of the cassette cover 66 other than in the first or the second pivoting directions 71 and 72 are prevented in any position of the cassette cover by cooperation of the bearing journals and the parts of the side walls 60 and 61 which surround the bearing recesses. The bearing journals are also arcuate, so that they always engage with the associated guide slots in a comparatively accurate manner.

The side walls 60 and 61 also have mounting slots 83 to 86 for mounting the bearing journals in the bearing recesses. FIGS. 13 and 14 show that the mounting slots 83 and 84 respectively intersect the guide slots 82 and 81 at the location of the intersections C1 and C2 respectively. The mounting slots each have an open entry side for the free entry of the bearing journal into the mounting slots. The bottom of each mounting slot has a profile which extends between a level N1 at which there is play between the cassette cover 66 and the cassette housing, and a level N2 at which the cassette cover is slightly bent by forces between the bearing journals and the bottoms of the mounting slots. As is apparent in particular from the detailed section view (FIG. 15) of the slots shown in FIG. 14 the cassette cover in its first open position is prevented from moving in a direction other than the pivoting direction by cooperation of the first bearing journals (such as the bearing journal 75) with the walls of the associated first bearing recesses 77. At the same time the second bearing journals, such as the bearing journal 78, engage the side walls of the second guide slots 82 in the pivoted position of the cassette cover. The levels N1 and N2 of the mounting slots have been selected in such a way that, if a bearing journal is situated at the location of an intersection C1 and C2, it is guided by the side walls of the relevant guide slot.

In order to limit the pivotal movements of the cassette cover 66 the side walls 60 and 61 of the cassette housing are provided with stops which cooperate with the bearing journals. It can be seen from FIGS. 13 and 14 that the guide slots 82 and 81 are closed at the ends 87 and 88 which are remote from their respective bearing recesses 80 and 77. At these locations ungrooved portions of the side walls 60 and 61 of the cassette housing constitute stops for the bearing journals.

Both main walls 54 and 55 of the magnetic tape cassette 47 have cut-outs 89 and 90 which extend to (open towards) the front opening of the cassette housing for the pasage of elements of a cassette apparatus behind the stretched tape portion 65. In order to minimize the penetration of dust into the magnetic tape cassette, even when the cassette cover is open, the cassette is provided with a closed front wall 91 at the rear of the cut-outs 89 and 90. The wall 91 has two openings 92 and 93, at a location of two tape guide rollers 94 and 95 respectively, just large enough to permit withdrawing the magnetic tape 64.

Slide Plates

Near the first and near the second main wall there are respectively located a first slide plate 96 and a second slide plate 97, which are slidable between a retracted position (FIGS. 10, 11) nearer the rear 62 of the cassette housing and a closing position (FIGS. 6-9) nearer the front 63 of the cassette housing. In the retracted position the slide plates 96 and 97 leave the cut-outs 89 and 90 in the corresponding main walls 54 and 55 free. In the closed position the cut-outs are completely closed.

The two slide plates 96 and 97 form part of a single slide member 98 (hereinafter referred to as slide 98) which is bodily movable between a retracted position (see FIGS. 10 and 11) and a closing position (see FIGS. 6 to 9). The slide 98 includes the two slide plates 96 and 97 as well as two side walls 99 and 100 which extend along the side walls 60 and 61 of the cassette housing and which interconnect the slide plates.

In this preferred embodiment, the slide 98 is manufactured from a plastic as a unitary molding. It is alternatively possible to use a two-part slide 101 as shown in FIG. 22, which comprises slide plates 102 and 103 and side walls 104 and 105. This slide comprises two identical unitary molded plastic parts, the one part comprising the slide plate 102 and the side wall 104 and the other part the slide plate 103 and the side wall 105. The parts are connected to each other by means of snap connections. FIG. 23 shows a cross-section across the snap-connection means, which connect the slide plate 102 to the side wall 104. The connection means comprise a pin 106 with a thickened frustoconical upper end 107. At the location of the pin 106 the slide plate 102 has a hole 108, and counterbore 109 which receives the conical end 107 of the pin 106. This conical end has a diameter which is slightly larger than the hole 108, so that when the slide plate 102 is mounted on the side wall 104 the conical end is slightly elastically deformed as it passes through the hole 108 until the counterbore 109 is reached. The slide 101 operates in an identical manner as the slide 98.

In the magnetic tape cassette 47 the two pivoting arms 67 and 68 of the cassette cover 66 are located outside the cassette housing. When the slide 98 is in its closing position the arms 67 and 68 are covered by the side walls 99 and 100 of the slide, so that when the magnetic tape cassette is removed from a cassette apparatus the pivoting arms and thus the bearing means are satisfactorily protected against mechanical damage. Moreover, a clean-cut appearance is thus obtained.

Spring Restraint

The complete slide 98 is loaded towards its closing position by a pressure spring 110 (FIGS. 6 and 8). For this purpose the slide plates 96 and 97 are interconnected by a connecting plate 111 halfway between the side walls 99 and 100, behind the stretched tape portion 65. The pressure spring 110 is fitted around a pin 112 extending rearward from the plate 111, and bears against the connecting plate 111 and against the bottom of a blind hole 113 in the cassette housing midway between its side walls 60 and 61 (FIG. 12). The connecting member, also see FIGS. 18 to 20, not only serves as a point of attachment for the pressure spring 110, but also stiffens the slide 98. Without this stiffening, the comparatively thin slide plates 96 and 97 can readily be bent. The connecting plate 111 has two slots 114 and 115 which engage two ridges 116 and 117 on the rear center of the slide plates 96 and 97.

Instead of a slide 98 with a separate connecting plate 111, it is alternatively possible to employ a slide 118 which is integrated with a connecting plate 119, as shown in FIG. 21. The slide plates 120 and 121, as well as the side walls 122 and 123, the connecting plate 119 and the pin 124 extending from the plate are integrally manufactured from a suitable plastic by injection molding. When such a slide is used the various components of the cassette must be assembled in such a sequence that the stretched tape portion 65 along the front of the cassette does not obstruct fitting of the slide. In order to facilitate the mounting of the pressure spring a pin may be used which is substantially shorter then the pin 124. Instead of the pin a local recess in the surface of the connecting plate may be used in order to prevent undesired lateral movements of the end of the pressure spring.

The two-part slide 101 in accordance with FIG. 22 enables the slide to be mounted after the magnetic tape has been placed in the cassette housing. This slide comprises a connecting plate 125 consisting of two parts 125A and 125B, which are integral with the slide plate 102 and the slide plate 103 respectively. The part 125B is connected to the slide plate 102 by a snap connection of the type of FIG. 23 and the part 125A is connected to the slide plate 103 by means of a similar snap connection. The pin 173 also consists of two parts, but is otherwise the same as the pin 124 described in the preceding paragraph.

Cover/Slide Movement

The pressure spring 110 ensures that the slide 98 is normally in its closing position when the cassette is not placed on a cassette apparatus, and thus covers the openings 89 and 90 in the main walls of the cassette housing. In its closing position the slide also covers any other openings in the main walls, such as the customary locating openings 126 to 129 (FIGS. 6 and 8) for locating the cassette relative to a cassette apparatus with the aid of locating pins provided on the deck of the apparatus. However, the pressure spring 110 also has another function, namely the closure of the cassette cover 66 when the slide 98 is moved to its closing position. For this purpose the slide 98 and the cassette cover 66 are provided with cooperating parts which cause the cassette cover to pivot to its closed position from either of its two open positions. As shown in FIGS. 10 and 11, the edges of the pivoting arms 67 and 68 and parts of the slide plates 96 and 97 engage in a sliding fashion to provide this cooperation.

The slide 98 and the cassette cover 66 are provided with a cooperating latch for preventing the cassette cover 66 from moving to an open position if the slide 98 is in its closing position, so that a magnetic tape cassette which has been removed from an apparatus cannot readily be opened. This is possible only after at least partly moving back the slide 98 toward its retracted position against the force of the pressure spring 110. The latching means again are formed by the edges of the pivoting arms 67 and 68 of the cassette cover 66 and parts of the slide plates 96 and 97 of the slide 98, namely those parts of the slide plates which, when the slide is in its closing position, cover the pivoting arms 67 and 68 together with the side walls 99 and 100. The latching means also include two projections 130 and 131 on either side of the cassette cover 66, which engage corrsponding notches in the walls 99 and 100 of the slide 98.

As is clearly shown especially in FIG. 7 and also in FIG. 9 the cassette cover 66 leaves the front edges 132 and 133 of the side walls 99 and 100 of the slide 98, which are remote from the rear 62 of the cassette housing, free at locations which are disposed nearer the main walls 54 and 55 of the cassette housing. This has been done to provide an abutment for moving the slide 98 to its retracted position when the magnetic tape cassette is placed in a cassette holder of a cassette apparatus, as shown in FIGS. 29 and 30. These figures show a part of a cassette apparatus 134 in cross-section at the location of a cassette holder 135. The cassette holder is pivotable about a hinge pin 136 and is thus movable from a cassette insertion position shown in FIG. 29 to an operating position shown in FIG. 30.

At its front the cassette holder 135 has a cassette insertion opening. By means of tension springs 139 levers 138 urge a cassette against a partly open bottom plate 140, which is provided with upward projections 141 at each side. During insertion of a cassette these projections engage the front edges 132 and 133 of the slide 98. When the cassette 47 is inserted into the cassette holder 135 the slide 98 is thus readily moved from its closing position to its more retracted position.

The side walls 99 and 100 of the slide 98 have notches 142 and 143 which can receive the lateral projections 130 and 131 of the cassette cover in the closed position. As described above, these projections and notches latch the cassette cover in its closed position. However, the projections also enable simple opening of the cassette cover after the cassette has been inserted into a cassette holder of a cassette apparatus. For this purpose a cassette apparatus 134 may include a cover opener 144 which is mounted to the deck of a cassette apparatus 134 by a pin 146 slidable in a slotted hole 147 against upward force of a spring 145. In FIG. 29 the slide 98 already occupies its more retracted position, so that the cassette cover 66 can be pivoted. The cassette cover is pivoted when the cassette holder 135 is moved downwards, during which movement the top of the cover opener 144 engages the projection 130 on the cassette cover 66. The opposite projection 131 can similarly be engaged by a symmetrically located cover opener.

FIG. 26 is similar to FIG. 8 except that the side wall 100 of the slide 98 is now moved towards the more retracted position, while the side wall 99 is still in a position corresponding to the closing position of the slide. In such a situation the slide 98 can readily become jammed on the cassette housing. In order to prevent such an undesired situation the side walls 60 and 61, at the location of the side walls 99 and 100 of the slide 98 when they are in their more retracted positions, have been given a curved profile P with a radius of curvature R which is substantially equal to the distance between the two side walls 60 and 61 of the cassette housing. Thus, at least a limited twisting of the position of the slide 98 relative to the cassette housing is possible without the slide becoming jammed on the cassette housing. For the sake of simplicity FIG. 26 only shows a single radius R, i.e. of the profile P of the side wall 60.

Another embodiment which prevents jamming of the slide is shown in FIGS. 27 and 28. These figures show a magnetic tape cassette 148 which is substantially identical to the magnetic tape cassette shown in FIGS. 6 to 12, except for a slightly different shape of the slide member and the side walls of the cassette housing. For simplicity, only the differences of the cassette 148 will be described in full detail. It comprises a bodily movable slide member 149 with side walls 150, 151 having prolonged portions 153 and 154 respectively, which extend toward the rear 152 of the cassette housing. In the closing position of the slide each side wall of the slide 149 extends rearward beyond the location of the rear edges 155 and 156 of the slide plates when the slide 149 is in its more retracted position. This location is near two ridges 157 and 158 on the cassette housing. The side walls 159 and 160 of the magnetic tape cassette 148 have corresponding grooves 161 for guiding the prolonged portions of the side walls of the slide 149. The prolonged portions 153 and 154 not only prevent the slide 149 from becoming jammed, but, as is shown in FIG. 28, a smoother appearance of the cassette is obtained, which is aesthetically desirable.

In the cassette 47 the slide 98 and the cassette housing are provided with cooperating stop means to prevent a slide, once mounted, from sliding off the cassette housing, when the cassette cover 66 has not yet been mounted or has been removed. The slide has two inwardly facing bosses 162 and 163 (see FIGS. 12, 16 and 17), and the side walls 60 and 61 of the housing have grooves 164 in which the bosses may move (only one groove shown, in FIGS. 9 and 12). As shown in FIG. 12, the end 165 of the groove 164 serves as a stop for the boss 162. The side wall 61 has a similar groove and end stop for the boss 163. These ends are located so that the bosses abut the respective ends in the closing position of the slide 98. As a result, in the closing position the pressure of the spring 110 is transmitted to the side walls 60 and 61 of the cassette housing by the bosses 162 and 163. The cassette cover 66 and, in particular, the bearing journals 75 to 79 are not loaded by the pressure spring 110 in the closing position of the slide 98, because there is always some clearance between the cassette cover 66 and the slide 98 in its closing position.

Alternative Spring Restraint

FIGS. 24 and 25 schematically show a part of a magnetic tape cassette which is largely identical to the magnetic tape cassette in accordance with FIGS. 6 to 12, but which includes resilient means for loading the cassette cover and the slide member relative to each other. A cassette cover 166 is shown, having a pivoting arm 167 which is journalled on a side wall 168 of the magnetic tape cassette. Furthermore, the cassette includes a slide 169, on which a pin 170 is located. The side wall 167 of cassette cover 136 carries a pin 171. Between the two pins a tension spring 172 is mounted. The bearing arrangement of the pivoting arm 167 includes two bearing journals 173 and 174, bearing recesses 175 and 176, as well as guide slots 177 and 178.

In the situation shown in FIG. 24 the cassette cover 166 is in the closed position and the slide 169 is in the closing position. The slide 169 is pulled towards the cassette cover 166 by the tension spring 172, the assembly being in a stable balanced position. Similarly, in the situation of FIG. 25, in which the cassette cover 166 is in one of its open positions and the slide 169 has been moved into its more retracted position, the cassette cover 166 is in a stable position under the influence of the force exerted on it. The connecting line between the pins 177 and 171 extends on such a side of the bearing journal 173 that the cassette cover tends to swing open further. However, this is prevented by abutment of the bearing journal 174 with the end of its guide slot 178. By suitably dimensioning the spring 172, allowance being made for the weight of the cassette cover 166, the cassette cover is in a stable balanced position for any orientation of the cassette relative to the force of gravity.

PHILIPS VR2350 STEREO MATCH LINE VIDEO2000 SYSTEM Tape guide in a helical scan cassette recorder:

 A helical scan cassette tape recorder including tape guide means for pulling part of the tape out of the cassette and laying it on a surface of the recorder drum. The guide means includes a curved guide rail and a support which moves on the rail along a curved path defined by the rail and carries a tape guide element which engages the tape during threading and operation. Grooves in the rail may cause the support to tilt during its longitudinal movement on the rail.

 

 1. A helical scan tape cassette recording and/or playback apparatus having a deck plate adapted so that a cassette may be disposed thereon, a cylindrical head drum supported on the deck plate, and tape guide means for guiding a tape along a path on a cylindrical surface of the drum, said means including a tape guide element for engaging a tape in a cassette disposed on the deck plate, pulling part of the tape out of the cassette and laying the tape on the cylindrical surface of the drum,
wherein the tape guide means includes a guide rail on the deck plate defining a longitudinal at least partly curved guide path, and
a support mounting said tape guide element, including a carriage having a U-shaped cross-section having a central portion and two side portions adjoining the central portion and situated on opposite sides of the guide rail, arranged for longitudinal movement on the guide rail along said path, and means cooperatively engaging between at least an inner side of one of said side portions and the respective side of said guide rail for positioning said carriage with respect to said rail along at least one direction transverse to said longitudinal movement.


2. An apparatus as claimed in claim 1 wherein said means for positioning cooperatively engages between the inner side of each of said portions and the respective side of the rail, to position the carriage in both directions transverse the longitudinal movement.

3. An apparatus as claimed in claim 1 wherein said means for positioning cooperatively engages between the inner side of each of said side portions and the respective side of the rail, and said means for positioning further includes means for tilting the carriage about an axis perpendicular to said longitudinal movement as said carriage is moved along said rail.

4. An apparatus as claimed in claim 1, wherein said cooperatively engaging means includes at least one pin projecting inwardly from an inner side of one of said side portions, and the guide rail has a longitudinal guide groove in the side facing said one side portion, the pin engaging slidably in the groove.

5. An apparatus as claimed in claim 4 wherein the end of said pin which engages the guide groove is ball-shaped.

6. An apparatus as claimed in claim 4 wherein said pin is connected to the carriage side portion by a screw-threaded connection for adjusting the distance through which the pin projects into the groove.

7. An apparatus as claimed in claim 3, wherein said cooperatively engaging means includes two pins projecting inwardly from an inner side of one of said side portions and the guide rail has a longitudinal guide groove in a side facing said one side portion, said pins engaging slidably in said groove, said pins being spaced longitudinally from one another in the direction of carriage movement along the rail; and the carriage includes a single pin projecting inwardly from the inner side of the other side portion and the guide rail has a longitudinally extending guide groove in an opposite side of the guide rail facing said other side portion, said single pin engaging slidably in said other guide groove in a transverse plane which lies between said two pins.

8. An apparatus as claimed in claim 7 wherein the end of each pin which engages in a respective guide groove is ball-shaped.

9. An apparatus as claimed in claim 8 wherein each pin is connected to the respective carriage side portion by a screw threaded connection so that the distance through which the pin projects from the respective side portion and engages the corresponding groove can be adjusted.

10. An apparatus as claimed in claim 3, wherein said cooperatively engaging means includes two pins projecting inwardly from an inner side of one of said side portions and the guide rail has two longitudinal guide grooves in a side facing said one side portion, said pins engaging slidably in respective grooves, said pins being spaced longitudinally from one another in the direction of carriage movement along the rail; and the carriage includes a single pin projecting inwardly from the inner side of the other side portion and the guide rail has a longitudinally extending guide groove in an opposite side of the guide rail facing said other side portion, said single pin engaging slidably in said other guide groove in a transverse plane which lies between said two pins.

11. An apparatus as claimed in claim 10 wherein the end of each pin which engages in a respective guide groove is ball-shaped.

12. An apparatus as claimed in claim 10 wherein each pin is connected to the respective carriage side portion by a screw threaded connection so that the distance through the pin projects from the respective side portion and engages the corresponding groove can be adjusted.

Description:

BACKGROUND OF THE INVENTION
The invention relates to an apparatus for recording and/or playing back signals on a magnetic tape carried on two rotatable spools in a cassette. The invention relates particularly to a recording and/or playback apparatus of the kind (hereinafter referred to as "a helical scan recorder") comprising a deck plate, at least one drive spindle for driving one of the spools in the cassette to wind the tape onto that spool and unwind it from the other spool, means for supporting the cassette on the deck plate in a position such that the spool to be driven is coaxial with the drive spindle, a rotary magnetic recording and/or playback head supported for rotation relative to the deck plate, a guide drum for the tape, which drum is supported on the deck plate with its axis coinciding with the axis of rotation of the rotary magnetic head, and tape guide means for pulling part of the tape between the spools out of the cassette and laying it in the cylindrical surface of the guide drum and for subsequently guiding the tape along a helical path around part of said surface of the drum so that the rotary magnetic head can record and/or playback signals on the tape which are arranged in tracks extending obliquely relative to the longitudinal direction of the tape.
The term "guide drum" is to be understood herein to include a drum composed of separate coaxial parts.
In a known helical scan recorder which is described in U.S. Pat. No. 3,660,614, a guide slot is formed in a base plate to define a guide path for a tape guide element which pulls part of the tape out of the cassette and lays it on the surface of the guide drum. It has been found to be of particular importance that the tape guide arrangement ensures that the magnetic tape is guided along a path such that, when the tape is pulled out of the cassette and is laid on the surface of the guide drum, the tape guide element exerts no irregular forces on the tape. Such an arrangement prevents deformation of the tape, which is apt to occur in particular at the edges. Therefore, jerky movements of the tape guide element should also be avoided. These requirements cannot be met, or can be met only inadequately, by means of a guide slot formed in a base plate.

SUMMARY OF THE INVENTION
According to the present invention the tape guide means in a helical scan recorder comprise a tape guide element which is engageable with the tape and which, during a threading operation of the tape guide means to pull part of the tape out of the cassette and lay it on the cylindrical surface of the guide drum, moves along a guide path which is at least partly curved and which is defined by a guide rail mounted on the deck plate, the tape guide element being carried by a support which is movable along the guide rail.
In one embodiment of the invention the distance of the guide path from a plane perpendicular to the axis of the drive spindle varies over at least part of the length of the guide path so that in this part the path extends obliquely relative to the deck plate.
In a preferred embodiment, the support of the tape guide element includes a carriage of U-shaped cross-section, having two side portions which adjoin a central portion and which are situated on opposite sides of the guide rail.
Preferably, at least one pin projects inwardly from the inner side of one of the side portions of the carriage and engages slidably in a longitudinal guide groove in the facing side of the guide rail.
According to a first preferred embodiment, two longitudinally spaced pins project from the inner side of one of side portions of the carriage and engage slidably in a longitudinal guide groove in the facing side of the guide rail, the pins thus being aligned in the direction of movement of the carriage along the rail, and a single pin projects from the inner side of the other side portion of the carriage and engages slidably in a guide groove in the corresponding facing side of the guide rail, the latter guide groove also extending longitudinally of the rail and the single pin being situated in a traverse plane which lies between the two pins.
In a second preferred embodiment, two longitudinally spaced pins project from the inner side of one of the side portions of the carriage and engage slidably in two respective parallel guide grooves in the facing side of the guide rail, the grooves extending longitudinally in the direction of movement of the carriage along the rail, and a single pin projects from the inner side of the other side portion of the carriage and engages slidably in a corresponding longitudinal guide groove in the adjacent facing side of the guide rail, the single pin again being situated in a transverse plane between the two pins.
In a different aspect of the invention, the end of each pin which engages in a respective guide groove may be shaped like a ball. Further, each pin may be connected to the respective side portion of the carriage by means of a screwthreaded connection so that the distance through which the pin projects inwardly from the respective side portion can be adjusted.

BRIEF DESCRIPTION OF THE DRAWING

A helical scan recorder according to embodiments of the invention in which the tape guide arrangement includes two movable tape guide elements will now be described with reference to the accompanying drawings, in which
FIG. 1 is a plan view of those parts of the apparatus which are relevant to the invention,
FIG. 2 is a sectional view, taken on the line II--II in FIG. 1, of one of the tape guide elements and the associated guide rail,
FIG. 3 is a side view of the tape guide element and guide rail shown in FIG. 2,
FIG. 4 is a sectional view, taken on the line IV--IV in FIG. 1, of the other tape guide and associated guide rail,
FIG. 5 shows the tape guide element of FIG. 4 in side view at a position on the associated guide rail which is indicated by the arrow V in FIG. 1, and
FIG. 6 is a side view of the guide rail of FIGS. 4 and 5 at the location indicated by the arrow VI in FIG. 1.


DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring first to FIG 1, the tape handling mechanism of a helical scan video recorder is shown, having a deck plate 1 on which is disposed a cassette 2 which contains a magnetic tape 3 carried on two spools 4 and 5 which are rotatable about parallel axis 4a and 5a respectively. The spools may be formed with or without flanges. When

the apparatus is in operation the tape is unwound from one spool and wound onto the other. When the cassette is not in use, a part of the tape which extends between two guide rollers 6 and 7 in the cassette passes across an opening 8 in the cassette housing, as indicated by the dotted line 3a in FIG. 1. This part of the tape 3 has to be pulled out of the cassette 2 and laid on the cylindrical surface of a guide drum 9 mounted on the deck plate 1. At this location rotary magnetic heads (not shown), which are coaxial with the drum 9 and which are supported for rotation relative to the deck plate, cooperate with the tape in the operation of the apparatus. For pulling the tape out of the cassette and laying it on the surface of the guide drum 9, two tape guide elements in the form of pins 10 and 11 each move along an associated guide path from a rest position, in which the pins extend behind the tape 3 at the location of the opening 8 in the cassette housing, into an operating position. In FIG. 1 these two tape guide pins 10 and 11 are represented by uninterrupted lines in the operating position and by broken lines in the rest position. The part of the tape 3 which is pulled out of the cassette and laid on the surface of the guide drum is also represented by uninterrupted lines.

When the tape guide pins 10 and 11 are in the operating position, the tape 3 extends from the guide roller 6 in the cassette, around the tape guide pin 10, past an erase head 12, around the guide drum 9 and the rotating magnetic heads, past a tape drive capstan 13 and a playback head 14, around the tape guide pin 11 and past a guide pin 15 to the guide roller 7 in the cassette. For driving the tape 3, a pressure roller 16 presses the tape against the capstan 13. A drive spindle (not shown) is provided for driving the spool onto which the tape is to be wound. Means not shown are provided for supporting the cassette on the deck plate in a position such that this spool is coaxial with the drive spindle. The guide drum 9, the capstan 13, the playback head 14, the tape guide pin 11 and the guide pin 15 are arranged obliquely relative to the deck plate in such positions that the tape travels along a helical path around part of the cylindrical surface of the guide drum and is subsequently returned into the cassette. The guide path for the tape guide 10 should be parallel to the deck plate 1 because the tape 3 travels from the cassette 2 to the guide drum 9 in directions which are parallel to the deck plate. The tape guide pin however, should be guided from the rest position into the operating position along a path which is oblique relative to the deck plate because the tape 3 leaves the guide drum 9 in a direction which is oblique relative to the deck plate 1 and, after passing round the tape guide pin 11, moves gradually upwards in the direction of the cassette. The guide path for the pin 11 also twists about its longitudinal axis so that the tape guide pin 11 is tilted to one side as it travels along the guide path. As can be seen from FIG. 1, the guide paths for the tape guide pins 10 and 11 are at least partly curved and extend partly around the guide drum 9.
The guide paths for the tape guide pins 10 and 11 are defined by guide rails 17 and 18 respectively, which are secured fixedly to the deck plate 1 by screws 17A and 18A respectively. The tape guide pins 10 and 11 are carried by supports constituted by carriages 19 and 20 respectively which are slidable along the rails 17 and 18 respectively. The carriage 19 is moved by means of a pivotable arm 21 which is situated below the deck plate and which has a slot 22 which engages a pin 23 extending downwardly from the carriage 19, which pin is movable in a slot 24 formed in the deck plate 1 adjacent the guide rail 17. In a similar way the carriage 20 is moved by means of a pivotable arm 25 which has a slot 26 which engages a pin 27 extending downwardly from the carriage 20, which pin is movable in a slot 28 formed in the deck plate 1 adjacent the guide rail 18. The carriages 19 and 20 are moved along the guide rails 17 and 18 by pivoting the arms 21 and 25 respectively. The carriages may alternately be moved by means other than those shown, for example by means of a cable.
As can be seen from FIGS. 2 and 3, the carriage 19 for the tape guide pin 10 has a U-shaped cross-section and has side portions 29 and 30 which adjoin a central portion and which extend downwardly at opposite sides of the guide rail 17, which has a rectangular cross-section. The guide rail 17 has longitudinally extending guide grooves 31 and 32 in its sides, and engaging slidably in these grooves are pins which project inwardly from the inner sides of the side portions 29 and 30 of the carriage 19. In the present example two pins 33 and 34 extend from the side portion 29 into the guide groove 31, and from the side portion 30 one pin 35 extends into the guide groove 32. The pins 33 and 34 which extend from the side portion 29 are spaced longitudinally from each other in the direction of movement of the carriage 19 along the guide rail 17, and the pin 35 which is connected to theeside portion 30 is situated in a transverse plane which lies between the two pins 33 and 34. In this way three-point guiding is provided for the carriage 19, ensuring perfect alignment of the carriage along the guide rail 17.
The pins 33, 34 and 35 are connected to the side portions 29 and 30 of the carriage 19 by screw-threaded connections so that the distance from the free end of each pin to the respective side portion 29 or 30, and thus the penetration depth of the pin into the respective guide groove 31 and 32, can readily be adjusted. Furthermore, the free ends of the pins 33, 34 and 35 are pointed so as to minimize friction if the free end of any of the pins contacts the bottom of the respective guide groove. Furthermore, the clearances between the side portions 29 and 30 of the carriage 19 and the guide rail 17 and between the pins 33, 34 and 35 and the walls of the guide grooves 31 and 32 are adapted to the curvature of the rail 17 so that the carriage can be moved along the guide rail in a smooth and uniform manner. If desired, the shape of the side portions 29 and 30 of the carriage may also be adapted to the curvature of the guide rail 17. The side portions 29 and 30 need not extend the whole length of the carriage; the side portion 30 may be a narrow portion of sufficient width for the connection thereto of the pin 35, and the side portion 29 may be divided into two such narrow portions to which the pins 33 and 34 can be connected.
As previously stated, the carriage 20 for the tape guide pin 11 has to be moved from the rest position into the operating position in such a way that the distance between the guide path and a plane perpendicular to the axis of rotation of the drive spindle varies, and moreover, when the operating position of the tape guide pin 11 is reached, the pin must have been tilted away from the guide drum 9 so that it occupies the correct position oblique to the deck plate 1 for guiding the tape. For this purpose the carriage 20, as it is moved along the guide rail 18, should perform a tilting movement. This tilting movement is obtained through the shape of the guide path defined by guide grooves in the rail 18, as will now be described.
As shown in FIGS. 4, 5 and 6, the height of the guide rail 18, which has a U-shaped cross-section, relative to the deck plate 1 decreases from the location indicated by the arrow VI in FIG. 1 to the location of the section shown in FIG. 4. The carriage 20 has a U-shaped cross-section and has side portion 36 and 37 situated one on each side of the guide rail 18. Projecting from the inner side of the side portion 36 is a pin 39 which engages slidably in a longitudinally extending guide groove 38 in the adjacent side of the guide rail 18. Two pins 42 a

nd 43 project from the inner side of the side portion 37 and engage slidably in two respective parallel longitudinally extending guide grooves 40 and 41 in the adjacent side of the rail 18. The two pins 42 and 43 are spaced longitudinally from each other in the direction of movement of the carriage 20 along the guide rail 18 and are situated at different levels relative to the guide rail to suit the spacing between the two guide grooves 40 and 41. The pin 39 is situated in a transverse plane which lies between the two pins 42 and 43. In this way particularly reliable three-point guiding for the carriage 20 is provided, which guiding also allows the carriage to be tilted to one side. In conformity with the decreasing height of the guide rail 18 the guide grooves 40, 41 and 38, viewed from the cassette, also have a downward slope relative to the deck plate 1 so that the required gradual descent of the carriage 20 to the operating position of the tape guide pin 11 is obtained. The guide groove 38, however, has a less steep downward slope than the guide grooves 40 and 41. This is apparent from FIG. 6, wherein the guide groove 38 is disposed near the level of the guide groove 41, and from FIG. 4, where the guide groove 38 is situated at a level approximately midway between the guide grooves 40 and 41. This results in the carriage 20 being tilted about an axis extending in the longitudinal direction of the guide rail 18, as is shown in FIG. 4, so that the tape guide pin 11 performs a tilting movement away from the guide drum 9 as it moves from the rest position into the operating position, the tilting movement being adapted so that the tape 3 is pulled out of the cassette 2 and laid on the guide drum 9 as gently as possible and without deformation. The guide grooves in the rail 18, which together define the guide path for the tape guide pin 11, can be shaped to produce any desired movement of the pin 11. As is shown in FIG. 4, the pins 39, 42 and 43 are also secured in the side portions 36 and 37 of the carriage 20 by screw-threaded connections so as to enable the penetration depth of the pins into the guide grooves to be readily adjusted. In the first example the free end of each of the guide pins is shaped like a ball so that a uniform movement of the carriage along the guide rail 18 is ensured despite the tilting movement of the carriage. The free ends of the pins 33, 34 and 35 of the carriage 19 may also be ball-shaped. The clearances between side portions 36 and 37 of the carriage 20 and the guide rail 18 and between the pins 39, 42 and 43 and the walls of the guide grooves 38, 40 and 41 are adapted to the curvatures of the rail 18 so that the carriage 20 can be moved along the rail in a smooth and uniform manner. If, required, the depth of the guide grooves may also be varied so as to ensure a reliable three-point guidance in all cases. As the guide grooves in the rail 18 have a comparatively complex shape, the rail is preferably manufactured from a plastic material, so that the desired shape of the guide grooves can be readily obtained. The cross-sectional shape of the guide grooves may also be adapted to other requirements; for example, the grooves may be given a trapezoidal cross-section. The fixing screws 17A and 18A allow the guide rails 17 and 18 to be adjusted slightly relative to the desk plate or, if necessary, to be replaced by other guide rails.

PHILIPS VR2350 STEREO MATCH LINE  SYSTEM VIDEO2000 Helical scan cassette recorder with improved tape threading:

 A tape threading device for a helical scan tape cassette recorder, having pivotal levers each having a tape guide for withdrawing and wrapping the tape about a guide drum. The levers overlap each other at an area of instantaneous overlap at which they are coupled to each other by a mechanism including a sliding block which is guided by a carrier device along a path which extends in the area of overlap. The sliding block is in force-sustained engagement with a link-motion surface on at least one of the levers.


1. A helical scan cassette recorder for use with a cassette containing a record carrier tape and having at least one aperture for withdrawing the tape from the cassette after the cassette has been inserted into the recorder, comprising
a tape guide drum having a circumferential surface, and a tape guide device comprising two levers each supporting a respective tape guide which levers are pivotable about two parallel pivotal axes, and are arranged to overlap each other at an area of overlap which varies as the levers are pivoted, a driving device for pivoting said levers between a rest position and an operating position, and a coupling device which acts directly on said levers for coordinating their pivotal movements; in the rest position said guides being located behind the tape within the cassette at the location of the aperture in said cassette; during movement from the rest position to the operating position, said guides pulling a length of the tape from within the cassette and wrapping said length of tape around the tape guide drum; and in the operating position said tape guides keeping the record carrier wrapped around said drum;

characterized in that the coupling device includes a link-motion mechanism comprising a sliding block which extends in the same direction as the pivotal axes of the two levers, a carrier device arranged to be movable transversely of the pivotal axes, a link-motion surface on a least one of said levers, means for urging the sliding block against the link-motion surface, and means for maintaining said sliding block in force-sustained cooperation with said carrier device,
said carrier device moving said sliding block along a path of movement defined by the carrier device and extending through an area of instantaneous overlap of said two levers,
said sliding block being in force-sustained engagement with said two levers at the location of the area of instantaneous overlap, engagement of the block with said one lever being provided by said means for urging said carrier device moving said sliding block along a path of movement which is defined by the carrier device and which extends through the area of instantaneous overlap of the two levers.


2. A recorder as claimed in claim 1, characterized in that the link-motion surface is formed on a side wall of said at least one lever.

3. A recorder as claimed in claim 1, characterized in that said sliding block is a cylindrical pin.

4. A recorder as claimed in claim 1, characterized in that the sliding block comprises a rotatable roller arranged to cooperate with at least one link-motion surface.

5. A recorder as claimed in claim 1, characterized in that the link-motion surface with which the sliding block is in force-sustained engagement is formed on one lever, and the carrier device for the sliding block is formed by the other of the two levers.

6. A recorder as claimed in claim 5, characterized in that the link-motion surface is formed on a side wall of said one lever.

7. A recorder as claimed in claim 1, characterized in that each of said levers includes a slot forming a link-motion surface, the slot having a shape substantially corresponding to a portion of a circular involute whose base circle is concentric with the pivotal axis of the respective lever, the base circles being tangent to each other at a line which extends perpendicularly to a plane in which the two pivotal axes lie, a ratio of the diameters of said two base circles being inversely proportional to a ratio of the pivoting angles of the two levers; said slots overlapping each other at the area of instantaneous overlap of the two levers, and said sliding block floating in said slots in said area of overlap.

8. A recorder as claimed in claim 7, characterized in that the sliding block is a cylindrical pin.

9. A recorder as claimed in claim 3, characterized in that the sliding block comprises a rotatable roller arranged to cooperate with at least one link-motion surface.

10. A recorder as claimed in claim 1, characterized by comprising two said link-motion surfaces, one formed on each respective laver, said surfaces overlapping each other at the location of the area of instantaneous overlap of the levers; and in that said carrier device is a separate actuating member which is movable relative to the two levers, and the sliding block is in force-sustained engagement with the two link-motion surfaces at said location of area of overlap.

11. A recorder as claimed in claim 10, characterized in that said separate actuating element is a sliding member slidable along a guide.

12. A recorder as claimed in claim 10, characterized in that said separate actuating member is a pivotally journalled arm.

13. A recorder as claimed in claim 12, characterized in that, as viewed along the pivotal axes, the arm is disposed between the two levers, and the sliding block extends through the arm and has two free ends, each in force-sustained engagement with a respective one of said link-motion surfaces.

14. A recorder as claimed in claim 13, characterized in that the link-motion surfaces are formed on respective side/walls of said levers.

15. The recorder as claimed in any one of claims 1 2, 5, 6, 10, 11, 12, 13 or 14, characterized in that the link-motion surface is formed by a slot in the lever on which said surface is formed, said sliding block extending through said slot.

16. A recorder as claimed in claim 15, characterized in that said sliding block is a cylindrical pin.

17. A recorder as claimed in claim 15, characterized in that the sliding block comprises a rotatable roller arranged to cooperate with at least one link-motion surface.

Description:

BACKGROUND OF THE INVENTION
The invention relates to a recording and/or reproducing apparatus for use in conjunction with a record carrier in the form of a tape contained in a cassette which has at least one aperture for withdrawing the record carrier from said cassette and which can be inserted into the apparatus. The apparatus comprises a tape-guide drum around whose circumferential surface the record carrier, which has been withdrawn from the cassette, can be wrapped at least partly and a tape-guide device for withdrawing the record carrier from the cassette and wrapping it around the tape-guide drum. This kind of apparatus will be referred to as a helical scan cassette recorder.
More particularly, the invention relates to such an apparatus in which the tape-guide device comprises two levers which are pivotable about two parallel pivotal axes. The levers overlap each other in an area of overlap which varies as they are pivoted. Each carries at least one tape guide which is adapted to cooperate with the record carrier, and can be pivoted, by means of a driving device, between a rest position, in which the tape guides are located behind the record carrier in the cassette at the location of the aperture in said cassette, and an operating position, in which the tape guides keep the record carrier, which is taken along when the levers are pivoted from their rest positions to their operating positions, wrapped around the tape-guide drum. The levers are coupled to each other by a coupling device which acts directly on the levers for coordinating their pivotal movements. Such a helical scan cassette recorder is for example known from U.S. Pat. No. 4,323,936.
The coordination of the pivotal movements of the two levers is important because the two levers and the tape guides which they carry should be moved between their rest positions and their operating positions with a coordinated movement which is as uniform as possible. Smooth motion is required to ensure that the record carrier is not subjected to an undesired load during movement of the levers. Also, to guarantee a correct and undisturbed operation they must reach their operating positions or their rest positions at the same time. In the apparatus described in U.S. Pat. No. 4,323,936 the two levers are therefore coupled to each other by a coupling device comprising a cable, the cable being connected to the two levers at fixed points of attachment. When such a coupling device is used, as a result of the constant length of the cable and the fixed points of attachment of the cable to the two levers, the two levers behave similarly in each stage of their actuating movements, so that their pivotal movements cannot be adapted to each other arbitrarily. Further, mounting such a cable is comparatively intricate and ageing of the cable may have an adverse effect on the reliability of operation.

SUMMARY OF THE INVENTION
An object of the invention is to provide a particularly simple and reliable coupling device between the two levers for the tape guides in a helical scan cassette recorder.
Another object is to couple the two levers so that their movements can be adapted to each other in the desired manner in all movement stages.
In accordance with the invention, the coupling device comprises a link-motion mechanism which comprises a sliding block which extends in the same direction as the pivotal axes of the two levers. The block is in force-sustained engagement with the two levers at the location of their area of instantaneous overlap, and is in force-sustained cooperation with a carrier device which is movable transversely of the pivotal axes. The carrier device moves the sliding block along a path of movement which is defined by the carrier device. The path extends through the area of instantaneous overlap of the two levers, the force-sustained engagement of the sliding block with at least one of the two levers being obtained through a link-motion surface on that lever. The link-motion surface extends within the area of instantaneous overlap and corresponds to the path of movement of the sliding block, the sliding block being urged against the link-motion surface as it moves along the surface. This provides a simple and reliable coupling between the two levers. Further, the shape of the path of movement of the sliding block and the shape of the link-motion surface along which the sliding block moves during actuation the two levers permit arbitrary adaptation of the pivotal movements of the two levers to each other. Such a coupling device comprising a link-motion mechanism also has the advantage that it can be mounted simply and rapidly.
It is found to be advantageous if the carrier device for the sliding block is a separate actuating member which is movable relative to the two levers, each of the two levers comprises a link-motion surface, which surfaces also overlap each other at the location of the area of instantaneous overlap of the two levers, and the sliding block is in force-sustained engagement with the two link-motion surfaces at the location of the area of overlap. The use of a separate actuating member as the carrier device for the sliding block permits the path of movement for the sliding block to be optimized so as to ensure a correct and undisturbed force transmission between the sliding block and the two link-motion surfaces. The path of movement of the sliding block, relative to each of the two link-motion surfaces during actuation of the levers, has a comparatively short length as a result of its arrangement on a separate actuating member and its movement relative to two link-motion surfaces so that the link-motion surfaces themselves may be comparatively short. This arrangement is advantageous in view of the required space, and it permits compact construction of the levers.
The separate actuating member may, for example, be constructed as a rotatable disk or ring. However, it is found to be particularly advantageous if the separate actuating member for the sliding block is a pivotally journalled arm. This results in a particularly simple and compact construction.
In this respect it is also advantageous if, viewed along the pivotal axes, the arm is situated between the two levers and if the sliding block extends through the arm and each of its two free ends is in force-sustained engagement with one of the two link-motion surfaces. This permits the arm, which serves as actuating member, and its bearing arrangement to be loaded uniformly, which is of advantage for a correct operation and a long life.
According to a further advantageous embodiment, the separate actuating member for the sliding block is a sliding member which is slidable along a guide. This results in a very stable construction.
In another preferred embodiment the carrier device for the sliding block is formed by one of the two levers and the other one of the two levers comprises the link-motion surface with which the sliding block is in force-sustained engagement. Since one of the two levers itself is also utilized as carrier device for the sliding block, a separate actuating member for the carrier device may be dispensed with and a particularly simple and compact construction is obtained.
In order to obtain a very simple construction it is found to be advantageous if the link-motion surface is formed on a side wall of the relevant lever.
In a different preferred embodiment, the link-motion surface is formed by a slot in the relevant lever, through which slot the sliding block extends. This guarantees a correct and reliable cooperation of the sliding block with the link-motion surfaces during each movement of the two levers.
Moreover, it is preferable if the carrier device for the sliding block is formed by both levers. Each lever has a slot for the formation of a link-motion surface, the two slots also overlap each other in the area of instantaneous overlap of the two levers, and the sliding block floats in these slots in the area of overlap. The shape of each slot substantially corresponds to a portion of a circular involute whose base circle is centered relative to the pivotal axis of the relevant lever, the two base circles being tangent to each other at a tangent line which extends perpendicularly to the plane in which the two pivotal axes lie, and the ratio of the diameters of the two base circles being inversely proportional to the ratio of the pivoting angles of the two levers. In this way a separate actuating member may be dispensed with and the sliding block is guided accurately along a path of movement by the two levers themselves during their movement, the travel of the sliding block relative to each of the two slot-shaped link-motion surfaces during the movement of the levers being only short as a result of the movement of this block relative to two link-motion surfaces. This arrangement permits the slots themselves to be very short, which is of advantage for a compact construction of the levers. Since the shape of each of the two slots corresponds to a portion of a specific circular involute, the carrier device for the sliding block, which device is formed by the two levers, defines a rectilinear path of movement for the block. As a result of the rectilinear path of movement of the sliding member and the circularly involute shape of the two slots, the pivotal movements of the two levers are coordinated in such a way that the two levers, which are coupled to each other via the link-motion mechanism, each perform a similar pivotal movement which corresponds to a rolling movement of the two base circles of the circular involutes on each other. Further, during the pivotal movement of the two levers the forces between the sliding block and the slots which serve as link-motion surfaces are always directed perpendicularly to the bounding walls of the slots, which is of advantage for a smooth and correct force transmission.
In a simple advantageous embodiment the sliding block is a cylindrical pin.
Furthermore, it is found to be advantageous if the sliding block comprises a rotatable roller which is adapted to cooperate with at least one link-motion surface. As a result, the sliding block can perform a rolling movement relative to the link-motion surface. This type of movement produces a low friction of the link-motion mechanism.
Six embodiments of the invention will now be described in more detail, by way of non-limitative example.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic plan view of the relevant parts of a first embodiment of a helical scan cassette apparatus in accordance with the invention, the two levers being shown in their rest positions.
FIG. 2 is a similar view of the apparatus shown in FIG. 1, the two levers of the tape-guide device being shown in their operating positions.
FIG. 3 is a schematic plan view of the relevant parts of a second embodiment of the invention, having a sliding block formed as a pin and a movably guided sliding member, the rest positions of the lever being shown in broken lines and their operating positions in solid lines.
FIG. 4, in the same way as FIG. 3, shows the relevant parts of a third embodiment, in a pin which serves as a sliding block.
FIG. 5, similarly shows the relevant parts of a fourth embodiment in which the carrier device for a rotatable roller is formed by one of the two levers and in which only the other lever has a slot which receives the roller.
FIG. 6 similarly, shows the relevant part of a fifth embodiment in which the carrier device for a pin-shaped sliding block is formed by the two levers, which each have a link-motion slot with a circularly involute shape.
FIG. 7 is a sectional view, on an enlarged scale, of the floating link-motion pin of the embodiment of FIG. 6 and taken on the line VII--VII.
FIG. 8, in the same way as FIG. 3, shows the relevant parts of a sixth embodiment, in which the sliding block comprises two rollers on a pivotable arm serving as carrier device, which are each independently rotatable and cooperate with a lever side wall which serves as a link-motion surface.
FIG. 9 is an enlarged sectional view, taken on the line IX--IX in FIG. 8, of the sliding block.

DESCRIPTION OF THE PREFERRED EMBODIMENTS:
FIGS. 1 and 2 schematically

show a video cassette recorder using a magnetizable record carrier 1 in the form of a tape (the carrier is hereinafter referred to as "tape"). The apparatus comprises a tape-guide drum 2, around whose circumferential surface the tape 1 can be wrapped in a helical path through an angle of substantially 180°. Inside the tape guide drum 2 two schematically shown rotary magnetic heads 3 and 4 are arranged, which heads cooperate with the tape 1 wrapped around the drum through a gap which is formed in the drum 2 and which divides the drum substantially into two drum halves, which heads scan the moving tape along tracks which are inclined relative to the longitudinal direction of the tape, the magnetic heads 3 and 4 recording television signals on or reproducing said signals from the tape. For the transport of the tape 1 which has been wrapped around the tape-guide drum 2 the apparatus comprises a capstan 5, against which the tape can be pressed by means of a pressure roller 6 which is arranged on the apparatus so as to be movable, in a manner not shown.
Further, the apparatus comprises a stationary magnetic head 7 by means of which a track which extends in the longitudinal direction of the tape 1 can be scanned in order to record or reproduce an audio signal associated with the television signals. Adjacent the magnetic head 7 a further stationary magnetic head 8 is arranged, by means of which the same track as scanned by the magnetic head 7 can be scanned in order to erase audio signals recorded in this track. A further stationary magnetic head 9 enables both the television signals recorded in the inclined tracks and the associated audio signals recorded in the longitudinal track of the tape to be erased simultaneously.
As can be seen in FIGS. 1 and 2, the tape 1 is contained in a substantially rectangular cassette 10 which can be inserted into the apparatus and whose cassette housing c

omprises two major walls and four side walls and, for taking up the tape, contains two adjacent rotatable reels 11 and 12 between which the tape extends. The tape 1 extends in the cassette from the first reel 11, which serves as supply reel, over a first guide roller 13, along the side wall 14, and over a second guide roller 15 to the second reel 12, which serves as a take-up reel. In the side wall 14 the cassette 10 is formed with an aperture 16 through which the tape can be withdrawn from the cassette in order to wrap it around the tape-guide drum 2. In its center the aperture 16 continues as a trough-shaped recess 17 in a major wall of the cassette housing. In order to protect the exposed length of the tape 1 at the location of the aperture 16 in the side wall 14 of the cassette housing the cassette 10 comprises a cassette cover which is movable relative to the cassette housing, which cover automatically exposes the length of tape upon insertion of the cassette into the apparatus and which for the sake of clarity and simplicity is not shown, because it is not relevant to the present invention.
For withdrawing the tape 1 from the cassette 10 and wrapping it around the tape-guide drum 2 the apparatus comprises a tape-guide device 18. When the tape 1 has been wrapped around the tape-guide drum 2 by the tape-guide device 18 and the pressure roller 6 has been moved towards the capstan 5, which movement may be derived from and controlled by the movement of the tape-guide device 18, the tape can cooperate with the magnetic heads 7, 8 and 9, with the capstan 5, and with a tape-guide post 19. The tape-guide device 18 comprises two plate-shaped levers 22 and 23 which are each pivotable about a pivotal axis 20 and 21 respectively and which overlap each other in an area of overlap which varies during the pivotal movements. The area of overlap of the two levers is that area in which the two levers--viewed along the parallel pivotal axes 20 and 21--overlap each other. This area of overlap changes during the pivotal movements of the two levers, as can be seen in FIGS. 1 and 2. In this embodiment the area of overlap of the two levers 22 and 23 in the position shown in FIG. 1 is smaller than in the position shown in FIG. 2.
At its free end each of the two levers is formed with a rectangular aperture 24 and 25 respectively, receiving a U-shaped bracket 26 and 27 respectively, which is spring-loaded towards the free end of the respective lever 22 or 23 by a pressure spring 28 or 29 respectively which acts on the lever 22 or 23 respectively. One of the two limbs of each U-shaped bracket 26 and 27 carries two tape guides 30, 31 and 32, 33 respectively, shown schematically in FIGS. 1 and 2. The tape guides 30 and 33 are, for example, constructed as rotatable rollers and the tape guides 31 and 32 as stationary pins. The two limbs of each U-shaped bracket 28 and 27 respectively are positioned against the plate-shaped levers 22 and 23 respectively on both sides, so that the position of each bracket and the tape guides arranged thereon in the axial direction of the tape guide rollers 30 and 33 is defined. For the sake of completeness it is to be noted that the pins 31 and 32 and the tape guide drum 2 are inclined relative to the other parts which cooperate with the tape, in order to obtain the desired helical path of the tape 1 around the tape guide drum 2, which for the sake of simplicity and clarity is not shown.
By means of a driving device to be described in more detail hereinafter the levers 22 and 23 of the tape-guide device 18 are pivotable between a rest position, which is shown in FIG. 1 and in which the tape guides 30, 31, 32 and 33 are located behind the tape 1 in the cassette 10 at the location of the aperture 16, the tape guides being introduced into the cassette through the trough-shaped opening 17, and an operating position, which is shown in FIG. 2 and in which the tape guides keep the tape 1, which has been taken along during the pivotal movement of the two levers from the rest position to their operating position, wrapped around the tape-guide drum 2. In the rest position of the two levers 22 and 23 the main body of each U-shaped bracket 26 and 27 bears against that bounding wall of the rectangular aperture 24 or 25, respectively, which faces the free end of the relevant lever 22 or 23, respectively, under the influence of the pressure springs 28 and 29 respectively. In the operating position of the two levers the free end of each bracket, which ends each have a wedge-shaped projection 34 and 35 respectively, bears against a positioning block 38 and 39 respectively formed with a V-shaped groove 36 and 37 respectively, the wedge-shaped projections 34 and 35 engaging the V-shaped grooves 36 and 37. This ensures an accurate positioning of the brackets 26 and 27 and the tape guides 30, 31, 32 and 33 on these brackets in the operating position of the two levers 22 and 23. As can be seen in FIG. 2, the main bodies of the brackets 26 and 27 are then lifted off those bounding walls of the apertures 24 and 25 which face the free ends of the levers against the action of the pressure springs 28 and 29, which is simply achieved in that the two levers are moved from their rest position into their operating position with a specific overtravel. In this way the pressure springs 28 and 29 keep the free ends of the brackets 26 and 27 urged against the positioning blocks 38 and 39.
When the two levers are pivoted between their rest position, and their operation position it is essential that they perform a uniform and accurately coordinated movement, in order to prevent the tape guides on the levers from exerting an undesired load on the tape and in order to ensure that the two levers and the tape guides on these levers always reach their rest positions and operating positions at the same time. This synchronization ensures that in the rest position of the levers the tape guides are always located behind the tape and in the operating position of the levers the tape is correctly and exactly wrapped around the tape-guide drum. In order to coordinate the pivotal movements of the two levers 22 and 23 to each other these levers are coupled to each other by a coupling device which acts directly on these levers. The coupling device is constructed as a particularly simple, stable and reliable link-motion mechanism 40.
The link-motion mechanism 40 comprises a sliding block which extends in the same direction as the pivotal axes 20 and 21 of the two levers 22 and 23, which is in force-sustained engagement with the two levers in the instantaneous area of overlap of these levers and which is simply formed by a cylindrical pin 41. A carrier device, which is movable transversely of the pivotal axes 20 and 21 of the two levers 22 and 23, is in force-sustained cooperation with the pin 41 and moves the pin 41 along a path which extends through the instantaneous area of overlap of the two levers. The path is defined by the carrier device during the pivotal movement of the two levers between their rest position and their operating position. The carrier device for the pin 41 used as sliding block is formed by a separate actuating member which is a plate-shaped arm 43. The arm 43 is pivotable about a spindle 42 in the apparatus which is movable relative to the two levers 22 and 23, which carries the stationary pin 41, and which guides the pin 41 along a circular path which extends through the instantaneous area of overlap of the two levers. As can be seen in FIG. 2, the plate-shaped arm 43 used as carrier device for the pin 41 is situated between the two plate-shaped levers 22 and 23 viewed along of the pivotal axes, the pin 41 extending through the arm 43 and its free ends each being disposed on one side of the arm 43.
Each of the two levers 22 and 23 is formed with a slot 44 and 45 respectively of substantially arched shape, the slot being a link-motion surface for the link-motion mechanism 40. The slots 44 and 45 extend in the instantaneous area of overlap, correspond to the path of movement of the pin 41 used as sliding block, and also overlap each other in the instantaneous area of overlap of the two levers. The slots 44 and 45 are each disposed in a plane perpendicular to the pivotal axes 20 and 21 of the two levers and to the pin 41. The pin 41 extends in the same direction as the pivotal axes and through the arm 43 and has free ends which each extend through one of the two slots 44 and 45 in the levers. The pin 41 slides along the slots during the pivotal movement of the two levers between their rest position and their operating position and ensures that the pivotal movements of the two levers are accurately coordinated to each other and the two levers always reach their operating position or rest position at the same time. In the present case the clearance between the pin used as sliding block and the slots used as link-motion surfaces may be the same over the entire length of each slot in order to ensure a smooth sliding movement. However, in practice it is found to be effective if the clearance at the ends of the slots is smaller than in the remainder of the slots, because this accurately define the positions of the two levers in their rest position and their operating position. As a result of the choice of the length of the arm 43 and the position of its pivot 42, the path of movement of the pin 41 is a circular path during a pivotal movement of the two levers between their rest and their operating position. This path is such that the force transmission between the pin 41 and the slots 44 and 45 takes place substantially perpendicularly to the bounding walls of these slots, thereby guaranteeing a smooth sliding movement of the pin in the slots and a correct force transmission without the risk of jamming. In the present case the circular path of movement of the pin 41, and the shapes of the slots 44 and 45 are selected in conformity with each other in such a way that pivotal movements of the two levers are so coordinated that the two levers are pivoted uniformly and steadily during each stage of the movement. This steady movement ensures that the tape is guided in a reliable and gentle manner by the tape guides on the levers.
For moving the two levers 22 and 23 between their rest and their operating position, as already stated, a motor driving device 46 comprises a motor 47 whose direction of rotation is reversible. The motor 47 is connected to a rotatable control disk 49 through a self-braking transmission 48, which is for example formed by a self-braking worm gear and is represented symbolically as a dash-dot line. The control disk 49 is formed with a control groove 50 in one major surface. The control groove 50 is engaged by a control pin 51 carried by a control lever 52, which is rigidly connected to the spindle 21 of the lever 23.
In order to pivot the two layers from their rest position to their operating position, for withdrawing the tape 1 from the cassette 10, the control lever 52 should be pivoted counterclockwise, which is effected when the control disk 49 is rotated counterclockwise out of the position shown in

FIG. 1. For this purpose the motor 47 is connected to a power supply V through a first switching device 53. Upon actuation of the first switching device 53 the motor 47 is driven in a first direction of rotation, thereby rotating the control disk 49 out of the position shown in FIG. 1 in the counterclockwise direction through the self-braking transmission 48. The control lever 52 is then also pivoted counterclockwise by the control groove 50 via the control pin 51, so as to cause a corresponding pivotal movement of the lever 23. As a result of the coupling of the lever 23 to the lever 22 via the link-motion mechanism 40, the lever 22 is also pivoted in an accurately coordinated manner, the arm 43 carrying the pin 41 is also being moved and thereby moves and guides the pin along a circular path. Just before the operating position of the two levers is reached the U-shaped brackets 26 and 27 butt against the positioning blocks 38 and 39, so that the brackets cannot be moved any further and the pressure springs 28 and 29 acting between the levers and the brackets are compressed. If upon a continued movement the two levers 22 and 23 reach their operating positions, which happens at the same instant as a result of the accurately coordinated movement, a projection 54 on the control disk 49 actuates a first end-position switch 55, which interrupts the circuit for the motor 47 closed by the first switching device 53. As a result of this, the motor 47 stops and the two levers 22 and 23 are maintained in their operating positions via the self-braking transmission 48. During the movement of the two levers from their rest positions to their operating positions the tape guides 30, 31, 32 and 33 on these levers move the tape 1 along, the tape being withdrawn smoothly and gently from the cassette 10 and being wrapped around the tape-guide drum 2. It is obvious that at least one of the two reels 11 and 12 should then be allowed to rotate, in order to enable the tape 1 to be unwound. When the two levers 22 and 23 are in their operating positions, the tape 1 path is as shown in FIG. 2, namely from the first reel 11 via the guide roller 13, the magnetic head 9, the tape guides 30 and 31, the tape-guide drum 2, the tape guides 32 and 33, the magnetic heads 8 and 7, the capstan 5 and the pressure roller 6, the tape-guide pin 19 and the guide roller 15 to the second reel 12. In this situation it is then possible to record signals on or reproduce signals from the tape 1.
In order to return the tape 1 into the cassette 10, the two levers should be moved from their operating positions to their rest positions. For this purpose the motor 47 is connected to the power supply V via a second switching device 56. Upon actuation of the second switching device 56 the motor 47 is driven in a direction of rotation which is opposite to the afore-mentioned first direction of rotation, so that the control disk 49 is rotated clockwise out of the position shown in FIG. 1. This rotation results in a corresponding movement of the control lever 52 and, consequently, a movement of the two levers 22 and 23 from their operating positions to their rest positions via the link-motion mechanism 40. Upon leaving the operating position the pressure spring 28 or 29 acting on each U-shaped bracket 26 or 27, respectively, urges the main body of the relevant bracket against that bounding wall of the rectangular aperture 24 or 25 which faces the free end of the relevant lever. When the two levers reach their rest position, which takes place at the same instant because of the accurately coordinated movement obtained by means of the link-motion mechanism 40, the projection 54 on the control disk 49 actuates a second end-position switch 57, which interrupts the circuit for the motor 47 closed upon an actuation of the second switching device 56. The motor 47 then stops and the two levers are maintained in their rest positions via the self-braking transmission 48.
Upon the pivotal movement of the two levers from their operating positions to their rest positions the tape guides carried by the levers return to their positions inside the recess 17 in the cassette 10, the tape 1 being returned into the cassette 10. It is evident that at least one of the two reels 11 and 12 should then be driven to take up the tape. In this situation the cassette may then be removed from the apparatus and, if desired, replaced by another cassette, upon which the tape guides are again located behind the tape of the other cassette in an absolutely reliable manner.
The driving device 46 for pivoting the two levers 22 and 23 may also act on the arm 43 in a similar manner, in which case the two levers 22 and 23 will also be pivoted in an accurately coordinated manner because the arm 43 is driven via the pin 41 and the slots 44 and 45 of the link-motion mechanism 40.
As will be apparent from the foregoing description, the use of a link-motion mechanism with a sliding block pin on a pivotal arm, which pin passes through a slot, used as a link-motion surface, in a lever for carrying the tape guides provides a particularly simple, stable and reliable coupling between the two levers, which always guarantees an accurately coordinated movement of the two levers and which ensures that the two levers always reach their operating positions or their rest positions at the same time. Since such a pin which slides in slots is subject to hardly any wear, an exact and reliable coupling between the two levers for coordinating their movements is also guaranteed after prolonged use of the apparatus. The use of a pivotal arm as carrier device for the pin is also very simple and results in a compact construction. Since the arm guides the pin along a path which extends substantially perpendicularly to the slots, the force transmission between the pin and the slots of the link-motion mechanism also takes place substantially perpendicularly to the bounding walls of the slots, which guarantees that always a correct and smooth force transmission is obtained. The two slots are each short, which is of advantage for the required space and consequently for a compact construction of the levers of the tape-guide device. By constructing the link-motion surfaces as slots, through which the pin used as sliding block extends, the pin cannot inadvertently be lifted off the link-motion surfaces, this link-motion mechanism being operative both during the movement of the levers to their operating positions and the movement of the levers to their rest positions.
FIG. 3 is even further simplified in comparison with FIGS. 1 and 2 and for the sake of simplicity only shows the tape-guide device 18 for removing the tape 1 from the cassette 10 and fo

r wrapping the tape around the tape-guide drum 2, all the other parts which cooperate with the tape not being shown. In the present case each lever 22 and 23 carries a tape-guide roller 30 and 33 respectively and the driving device 46 for moving the two levers comprises a gear wheel 58 which is rigidly mounted on the spindle 21 of the lever 23 and which can be driven with a constant speed by the motor 47 via the transmission 48 whilst in the present case, an overload clutch is arranged between the motor 47 and the transmission 48. In the same way as in the apparatus shown in FIGS. 1 and 2 the two rollers 30 and 33 may be arranged on the levers 22 and 23 so as to be movable against a spring force, the geometrical positions of the two rollers in the operating position of the two levers being also adjustable by means of a positioning device.
As carrier device for the sliding-block pin 41 of the link-motion mechanism 40 there is again provided a separate actuating member, which is now formed by a sliding member which is slidably guided in a rectilinear guide 60, namely between two positions defined by the ends of the guide 60, in which the two levers 22 and 23, which are coupled to each other via the pin 41 of the link-motion mechanism 40 which extends through the slots 44 and 45 used as link-motion surfaces, occupy their rest positions indicated by the dotted lines and their operating positions indicated by solid lines. As soon as the sliding member 59 butts against one end of its guide the overload clutch arranged between the motor 47 and the transmission 48 of the driving device 46 becomes operative and thereby disengages the drive of the sliding member by the motor. The sliding member 59 is maintained in its positions defined by the ends of the guide as a result of the self-braking action of the transmission 48. The sliding member 59 ensures that the pin 41 of the link-motion mechanism 40 is driven and guided along a rectilinear path in a stable and reliable manner upon a movement of the two levers. In this respect it is to be noted that such a sliding member used as carrier device may also be movably guided along a curved guide, in which case the path of the pin may simply be adapted to specific requirements, for example as regards a smooth and reliable force transmission or a specific coordination of the pivotal movements of the two levers.
As can be seen in FIG. 3, the slot 45 in the lever 23 is simply a straight slot. Further, the rectilinear path of movement of the pin 41 and the shapes of the two slots 44 and 45 have been selected to coordinate the pivotal movements so that similar movements of the two levers 22 and 23 are achieved. In other words, each slot of the link-motion mechanism 40 may be selected so that its shape, its arrangement on the levers and the shape of the path of movement of the pin 41 of the link-motion mechanism are such that each of the two levers performs a substantially similar movement, which guarantees a particularly steady and smooth movement of the two levers.
In this apparatus the two levers are also coupled via a simple link-motion system in an accurate and reliable manner, the two levers each performing accurately coordinated and similar pivotal movements. Since the levers and consequently the tape guides carried by these levers perform similar movements, a particularly smooth, steady and gently withdrawal from or return of the tape into the cassette is achieved. The sliding block formed by a simple pin is then guided in a stable and reliable manner by means of a sliding member which acts as carrier device.
In the apparatus shown in FIG. 4 each lever 22 or 23 carries a tape-guide pin 31 or 32, respectively, which pins may each be arranged so as to be movable on the relevant lever. The driving device 46 for moving the two levers is adapted to cooperate with the carrier device formed by the sliding member 59 for the pin 41. For this purpose the motor 47 again drives a gear wheel 61 via an overload clutch and the transmission 48, which gear wheel drives a lead-screw 62. The lead-screw cooperates with a threaded bore in the sliding member 59 which is slidably guided by the guide 60, so that by driving the lead-screw in the opposite directions of rotation the sliding member can be moved in opposite directions, the levers 22 and 23, which are coupled to each other via the pin 41 on the sliding member and the slots 44 and 45 of the link-motion mechanism 40, being pivotable in an accurately coordinated manner between their rest positions shown in dotted lines and their operating positions shown in solid lines.
In this embodiment the slots 44 and 45 of the link-motion mechanism 40 are simply rectilinear slots. As a result of the straight slots and the straight path of movement of the pin used as a sliding block the pivotal movements of the two levers are coordinated in such a way that upon the pivotal movements of the two levers the levers are initially accelerated and are then braked again. In this way a steady and accurately coordinated movement of the two levers is obtained, which again results in the tape being guided in a reliable and gentle manner and which guarantees that the levers again reach their operating positions or their rest positions at the same time.
In the apparatus shown in FIG. 5 each lever 22 or 23 carries a tape-guide pin 31 or 32, respectively, and the driving device 46 is constructed in the same way as tha
t of the apparatus shown in FIG. 3, but in the present case a gear wheel 63 is rigidly mounted on the spindle 20 of the lever 22 and driven by the driving device 46.
In this apparatus the carrier device for the sliding block of the link-motion mechanism 40 is simply constituted by the lever 23 itself. The sliding block is constructed as a rotatable roller 64, which is rotatably journalled on the lever 23. The roller 64 extends through an arched slot 44 in the other lever 22, which slot serves as link-motion surface. Upon the movement of the two levers between their rest positions and their operating positions the roller 64 rolls on the bounding walls of the slots 44. Such a rolling movement guarantees a minimal friction and thus a smooth actuation of the two levers. Again the slot 44 and the path of movement of the pin 41, which is again arcuate, are selected to coordinate the pivotal movements of the two levers to each other in such a way that similar movements of the levers 22 and 23 are obtained.
Also in this apparatus a very simple and accurate coupling between the two levers and thus accurately coordinated movements of these levers are achieved. The similar movements of the two levers again guarantee a particularly gentle withdrawal of the tape from or return into the cassette. By arranging the roller used as sliding block on one of the two levers a separate carrier device may be dispensed with. By constructing the sliding block as a roller it rolls on the link-motion surface during the movement of the two levers, which is of advantage for a minimal friction and consequently a smooth movement.
In the apparatus shown in FIG. 6 each of the levers 22 and 23 carries a tape-guide pin 31 or 32, respectively, which is arranged so as to be movable on the relevant lever 22 or 23 in the same way as in the apparatus shown in FIGS. 1 and 2, in order to guarantee an accurate positioning of the pin by means of a positioning device when the levers are in their operating positions, in the same way as in the apparatus shown in FIGS. 1 and 2. However, for the sake of simplicity this is not shown, because this is not essential for the present invention. A driving device for driving the two levers 22 and 23, which is not shown for the sake of simplicity, may be constructed in exactly the same way as in the apparatus shown in FIGS. 1 and 2 and drive one of the two levers. For driving the two levers there may also be provided a motor-driven gear wheel on one of the two spindles 20 and 21 in the same way as in the apparatus shown in FIGS. 3 and 5.
For coordinating their pivotal movements the two levers 22 and 23 are coupled to each other via a link-motion mechanism 40, whose sliding block is constituted by a cylindrical pin 65. The carrier device for the sliding block formed by the pin 65 is now constituted by one of the two levers 22 and 23 themselves, so that a separate carrier device may be dispensed with. The two levers 22 and 23 are each formed with a slot 44 and 45, respectively, as a link-motion surface. The two slots 44 and 45 overlap each other in the instantaneous area of overlap of the two levers and the pin 65 floats in these slots in this area of overlap, which will be described in detail with reference to FIG. 7. The shape of each slot 44 or 45 corresponds substantially to a portion of a circular involute, E₁ or E₂, respectively, whose base circles, C₁ and C₂ respectively, are centered on the pivotal axes 20 and 21, respectively, of the relevant levers, 22 and 23, respectively, in which the slots 44 and 45, respectively are formed. The two base circles C₁ and C₂ of the circular involutes E₁ and E₂ are a tangent to each other in a plane 66, which extends perpendicularly to the two pivotal axes 20 and 21 and which is represented by a dash-dot line in FIG. 6, along a tangent line which is also indicated by a dash-dot line, and the ratio of their diameters D₁ and D₂ is inversely proportional to the ratio of the pivoting angles β₁ and β₂ of the levers 22 and 23, respectively. In the present case the central portions of the two portions of the circular involutes E₁ and E₂ each comprise in good approximation by a portion of a circle of curvature of the circular involutes, because this simplifies the formation of these slots. The centres of these two circles of curvature are designated 68 and 69 in FIG. 6 their radii, shown as dash-dot lines, are designated R₃ and R₄.
The sliding block formed by the pin 65 floats in the two slots 44 and 45. The pin 65 is movable along the slots 44 and 45 and is guided by the two levers 22 and 23 themselves in their axial directions. As is shown in FIG. 7, one end of the pin 65 comprises a portion 70 of larger diameter and on the other end of the pin a retaining ring 71 is fitted. Between the portion 70 of the pin 65 and the lever 23 and between the lever 22 and the retaining ring 71 a washer 72 and 73 respectively, is fitted onto the pin in order to minimize the friction.

As a result of the slots of the previously described circularly involute shape, it is achieved that the forces acting between the pin 65 and each of the slots 44 and 45, respectively, are always such that the slots 44 and 45 move the pin 65 along the said tangent line 67 during the pivotal movements of the levers 22 and 23. In other words, the levers 22 and 23 formed with the slots serve as carrier device for the sliding block and always move and guide this block accurately along the rectilinear path defined by the tangent line 67. As a result of the rectilinear path of the pin 65 and the circularly involute shape of the slots 44 and 45 used as link-motion surfaces the pivotal movements of the two levers 22 and 23 are coordinated in such a way that during the pivotal movements of the levers which are coupled to each other via the link-motion mechanism 40 these levers each perform a similar pivotal movement corresponding to a rolling movement of the two base circles C₁ and C₂ of the circular involutes E₁ and E₂ relative to each other. Moreover, by the choice of the path of the sliding block and the shape of the slots which serve as link-motion surfaces it is achieved that during the pivotal movements of the two levers the forces acting between the sliding block and the slots are always directed perpendicularly to the bounding walls of the slots, so that always a smooth and correct force transmission via the link-motion mechanism is guaranteed. In this way it is also ensured that in the present apparatus the movements of the two levers 22 and 23 of the tape-guide device 18 are coordinated accurately, so that a reliable, uniform and gentle guidance of the tape 1 by the tape guides 31 and 32 is ensured and the two levers always reach their operating positions or rest positions at the same time. Since the two levers also function as a carrier device for the sliding block, a separate carrier device may be dispensed with, thus providing a simple and compact construction. As the path of the sliding block movement is short relative to the two slots which are each formed in one of the levers, the slots themselves may also be short so that these levers have a compact construction and do not occupy much space.

In the apparatus shown in FIG. 8 the link-motion mechanism 40 for coupling the two levers 22 and 23 has a link-motion surface on each lever, which surface is now simply formed on a side wall, 74 and 75, respectively, of the relevant levers 22 and 23. The two side walls 74 and 75 each have the shape of an arc of circle. The sliding block 76 of the link-motion mechanism 40 in this apparatus comprises a rotatable roller 77 and 78, respectively, for cooperation with each of the side walls, 74 and 75 respectively, serving as link-motion surfaces, as can be seen from FIG. 9. The two rollers 77 and 78 are rotatably mounted on a common spindle 81 by means of two retaining rings 79 and 80. The central portion of the spindle 81 is rigidly mounted in an arm 43 which is pivotal about a pivotal axis 42, the spindle 81 extending through the arm 43 and a washer, 82 and 83 respectively, being slid onto the spindle 81 between the arm 43 and each of the two rollers, 77 and 78 respectively.
The arm 43 again forms the carrier device for the sliding block 76, which guides the member accurately and reliably along a predetermined path, namely a circular path. As can be seen in FIG. 9, the arm 43 is situated between the two levers 22 and 23, viewed along the pivotal axes 20 and 21. The sliding block 76 extends through the arm 43 with its spindle 81, as already stated, and its roller 77 and 78 which are mounted on each of the two free ends and which are rotatable about the spindles 81 are in force-sustained engagement with the two side walls 74 and 75 of the two levers which acts as link-motion surfaces, so that substantially symmetrical forces obtain relative to the arm.
For driving the two levers 22 and 23 which are coupled to each other via the link-motion mechanism 40 the motor-drive device 46 comprises a motor 47, which drives a gear wheel 84 on the spindle 42 of the arm 43 via an overload clutch and the self-braking transmission 48. For stopping the motor 47 when the two levers 22 and 23 reach their operating positions or their rest positions, it is for example possible, in the same way as in construction used in the apparatus shown in FIGS. 1 and 2, to employ two end-position switches, which cooperate with a projection on the gear wheel 84. Alternatively, there may be provided two end-position switches which cooperate with the arm 43.
When the gear wheel 84 is driven in the counter clockwise direction, the arm 43 is also pivoted counterclockwise, thereby moving and guiding the sliding block 76 along a circular path. Via the two rollers 77 and 78 of the sliding block, which are in force-sustained engagement with the side walls 74 and 75 of the two levers, the two levers 22 and 23 are moved along and pivoted from their rest positions to their operating positions. The two rollers 77 and 78 then roll on the side walls 74 and 75 of the two levers in opposite directions of rotation, which is of advantage for a minimal friction of the link-motion mechanism and thus for a smooth operation of the two levers. As a result of the coupling via the link-motion mechanism the pivotal movements of the two levers are accurately coordinated to each other.
In the present apparatus the choice of the path of movement of the sliding block and the shape of each of the two side walls forming the link-motion surfaces results in such a coordination of the pivotal movements of the two levers that during the pivotal movements from the rest positions into the operating positions the lever 23 is initially moved slightly faster than the lever 22 so that the lever 23 has a slide lead relative to the lever 22, and at the end of this pivotal movement the lever 23 is moved slightly more slowly than the lever 22, so that the lever 22 again lags relative to the lever 23, the two levers 22 and 23 reaching their operating positions at the same time at the end of this pivotal movement. During this pivotal movement of the levers 22 and 23 from their rest positions to their operating positions the tape guides 31 and 32 again withdraw the tape 1 from the cassette 10 in a smooth and gentle manner and keep it wrapped around the tape-guide drum 2 in a reliable manner when the operating position of the two levers is reched.
In order to return the two levers 22 and 23 from their operating positions to their rest positions, the gear wheel 84 is driven in the clockwise direction, which results in a clockwise pivotal movement of the arm 43. The arm 43 carries a pin 85 which extends through this arm and whose two free ends are in force-sustained engagement with the side walls 86 and 87 of the levers 22 and 23 when the arm is pivoted clockwise. As a result of this, the two levers 22 and 23 are returned from their operating positions to their rest positions via the pin 85 which is driven by the arm 43 and which cooperates with the side walls 86 and 87 of these levers.
It is evident that also in the apparatus shown in FIG. 8 the pivotal movement of the two levers are accurately coordinated and thereby ensure a smooth and gently withdrawal of the tape from the cassette and a correct wrapping of this tape around the tape-guide drum. As the side walls of the levers are also used as link-motion surfaces a very simple and stable construction of the levers is obtained. Since the sliding block rolls on the relevant link-motion surfaces a particularly favourable friction of the link-motion mechanism is obtained, which is of advantage for a smooth operation. Since the two rollers of the sliding block are each disposed on one side of the arm, symmetrical forces obtain in the cooperation of the sliding block with the levers, so that the arm and its pivot are not subjected to torsional loads. It is to be noted that the two rollers of the sliding block may also be journalled rotatably on separate spindles, which may then be arranged non-coaxially. If desired, the two rollers of the sliding block may have different diameters.
As appears from the embodiments described in the foregoing differently coordinated pivotal movements of the two levers are obtained by a corresponding choice of the paths of movement of the sliding blocks and the shapes of the link-motion surfaces. It will be appreciated that other arbitrarily coordinated movements can be obtained, for example in such a way that one lever is accelerated during one stage of the movement and the other lever moves uniformly or is slowed down.

PHILIPS VR2350 STEREO MATCH LINE  VIDEO2000 High speed scanning arrangement for video tape recorder:

 In a helical scan video recorder in which the magnetic heads are arranged on bimorph piezoelectric actuators it may be desirable, in order to counteract depolarization of the piezoelectric elements, to bias these elements. This is possible without the use of additional slip rings if the electrode to which the drive voltage is applied is connected, via a diode, to the electrode to which the bias is applied and the bias is applied, alternately with the drive voltage, at instants at which the associated magnetic head is not used. If the (lower) drive voltage is applied the diode is cut off and the bias is isolated from the drive.

 1. An apparatus for recording and/or reproducing information on a record carrier in the form of a tape in tracks which are inclined relative to the longitudinal axis of the record carrier, which apparatus comprises
a first magnetic head,
a first electro-mechanical actuator on which said magnetic head is arranged for controlling the position of said magnetic head in a direction transverse to the tracks, said actuator comprising two piezoelectric transducers which are each arranged on one side of a common electrode and which are each provided with an electrode on the side which is remote from said common electrode,
a rotatable body, on which said actuator is mounted, for moving the magnetic head in the track direction,
a tracking signal generator for supplying a signal to the actuator for controlling the position of the magnetic head relative to the tracks,
a drive signal input which is coupled to electrodes of the piezoelectric transducers in such a way that the transducer deflects as a function of the signal applied to said drive signal input, and
a first rotary signal-coupling means for coupling the drive signal generator to the drive signal input of actuator, characterized by
a bias voltage input for applying a bias voltage so that both piezoelectric elements are biased in the direction of polarization, at least during periods in which they are driven by the drive signal,
a buffer element for buffering said bias voltage during said periods,
a first voltage isolator between the bias voltage input and the drive voltage input, and
switching means arranged between the tracking signal generator and the signal coupling means, for alternately connecting the drive signal input to the tracking signal generator and a source of bias voltage via said signal coupling means.


2. An apparatus as claimed in claim 1, comprising a second electro-mechanical actuator of the same type as the first actuator, which second actuator carries a second magnetic head, is also mounted on the rotatable body, and is connected to the tracking signal generator via a second rotary signal coupling means and switching means, characterized in that the bias voltage input of said second actuator is connected to the bias voltage input of the first actuator, both bias voltage inputs have a common connection to the buffer element, and a second voltage isolator is arranged between the drive voltage input of the second actuator and the bias voltage input of said second actuator.

3. An apparatus as claimed in claim 1 or 2, characterized in that the buffer element comprises a capacitor.

4. An apparatus as claimed in claim 3, characterized in that the first or the second voltage isolator comprises a diode which is poled in the forward direction between the relevant drive voltage input and the relevant signal voltage input.

5. An apparatus as claimed in claim 4, characterized in that the two piezoelectric elements arranged on both sides of the common electrode are biased in opposite directions relative to said common electrode, the drive voltage input is connected to the other electrode of one piezoelectric element and the other electrode of the other piezoelectric element is coupled to earth.

Description:

The invention relates to an apparatus for recording and/or reproducing information on a record carrier in the form of a tape in tracks which are inclined relative to the longitudinal axis of the record carrier, which apparatus comprises
a first magnetic head,
a first electro-mechanical actuator on which said magnetic head is arranged for controlling the position of said magnetic head in a direction transverse to the tracks, said actuator comprising two piezoelectric transducers which are each arranged on one side of a common electrode and which are each provided with an electrode on the side which is remote from said common electrode,
a rotatable body, on which said actuator is mounted for moving the magnetic head in the track direction,
a tracking-signal generator for applying a signal to the actuator for controlling the position of the magnetic head relative to the tracks,
a drive-signal input which is coupled to electrodes of the piezoelectric transducers in such a way that the transducer deflects as a function of the signal applied to said drive-signal input, and
a first rotary signal-coupling means for coupling the tracking-signal generator to the drive-signal input of the actuator.
Such apparatus is used in commercially available video recorders of the well-known V2000 system. Such a video recorder is very suitable to be provided with a mode of operation in which the pictures can be reproduced at a substantially higher speed in order to locate a specific passage. The reproduction in this mode remains excellent because the electromechanical actuator ensures that the head follows the track correctly. The maximum reproduction speed is dictated by the maximum deflection of the actuator, which maximum deflection depends on the maximum driving voltage. The maximum driving voltage depends on the depolarization limit of the piezoelectric elements. It is known, inter alia from German Patent Application No. 27 11 691, which has been laid open to public inspection, that the application of a bias counteracts depolarization, so that the maximum deflection can be increased by applying a bias. This means that the maximum reproduction speed can be increased by applying a bias voltage. Moreover, each actuator (the afore-mentioned video recorder comprises two such actuators) would require the use of an additional signal-coupling means, such as a slip ring.
The invention aims at providing an apparatus of the type mentioned in the opening paragraph which allows a bias voltage to be applied without the use of additional signal-coupling means and to this end it is characterized by
a bias-voltage input for applying a bias so that both piezoelectric elements are biased in the direction of polarization, at least during periods in which they are driven by the drive signal,
a buffer element for buffering said bias voltage during said periods,
a first voltage isolator between the bias-voltage input and the drive-voltage input, and
switching means arranged between the tracking-signal generator and the signal-coupling means, for alternately connecting the drive-signal input to the tracking-signal generator and a source of bias voltage via said signal-coupling means.
The invention is based on the recognition of the fact that it is thus possible to apply a voltage pulse, for example at times when the head is not used (for example during the period in which the second head follows the track). This voltage pulse is applied to the buffer via the voltage isolator. If subsequently the drive signal, whose amplitude is lower, is applied the voltage isolator isolates the buffer from the drive signal input.
In an apparatus comprising a second electro-mechanical actuator of the same type as the first actuator, which second actuator carries a second magnetic head, is also mounted on the rotatable body, and is connected to the tracking-signal generator via a second rotary signal coupling means and switching means, the invention may further be characterized in that the bias-voltage input of said second actuator is connected to the bias-voltage input of the first actuator, both bias-voltage inputs have a common connection to the buffer element, and a second voltage isolator is arranged between the drive-voltage input of the second actuator and the bias-voltage input of said second actuator.
With respect to the buffer element the invention may further be characterized in that the buffer element comprises a capacitor.
With respect to the voltage isolator the invention may further be characterized in that the first or the second voltage isolator comprises a diode which is poled in the forward direction between the relevant drive-voltage input and the relevant signal-voltage input.
A preferred embodiment of the invention may further be characterized in that the two piezoelectric elements arranged on both sides of the common electrode are biased in opposite directions relative to said common electrode, the drive-voltage input is connected to the other electrode of one piezoelectric element and the other electrode of the other piezoelectric element is coupled to earth.
The invention will now be described in more detail, be way of example, with reference to the drawing, in which
FIG. 1 shows an embodiment of the invention,
FIG. 2 shows some signal waveforms to explain the operation of the apparatus in accordance with the invention, and
FIG. 3 shows an alternative to a part of the embodiment shown in FIG. 1.

FIG. 1 shows an embodiment of the invention. On a rotatable body 1, shown schematically, two electro-mechanical actuators 2 and 3 are arranged diame

trally opposite each other, which actuators carry video heads 4 and 5, respectively. Via means, not shown, for example a rotary transformer, these video heads are connected to the non-rotating part of the apparatus. This assembly rotates within a drum around which a magnetic head is wrapped along a helical path over 180° (in said V2000 system). The heads 4 and 5 then alternately follow an inclined track on the magnetic tape. The electro-mechanical actuators 2 and 3 control the heads 4 and 5 in directions indicated by arrows T, i.e. in directions transverse to the direction of the tracks followed by these heads owing to the rotation of the body 1.
The electro-mechanical actuators 2 and 3 each have a common electrode 6, two piezoelectric elements 7 and 8 on both sides of the electrode 6, electrodes 9 and 10 being arranged on both sides of said elements which are remote from the electrode 6, so that the piezoelectric element 7 is arranged between the electrodes 6 and 9 and the piezoelectric element 8 between the electrodes 6 and 10. Both piezoelectric elements are polarized in the direction indicated by P.
In the present example the electrode 10 is connected to earth via the body 1. The common electrode 6 of the actuator 2 or 3 is connected to a drive-signal input, 11 and 12 respectively, which via a slip ring, 13 and 14 respectively, and switching means 15 is connected to a source 18 of tracking signals. Via a capacitor 25 the electrode 9 of the actuator, 2 and 3 respectively, is connected to earth and to a bias-voltage input, 21 and 22 respectively. Via a voltage isolator, in the present example a diode 23 or 24, this bias voltage input, 21 or 22, is connected to the corresponding drive-voltage input 11 or 12. The switching means 15, which may be electronic means, may be regarded as two change-over switches 16 and 17 which under control of a device 19 alternately connect the tracking signal generator 18 to one of the slip rings 13 and 14 and which connect a direct voltage source 20 to the other slip ring in phase opposition.
The operation of the apparatus shown in FIG. 1 will be explained with reference to FIG. 2 which shows the signals S₁ and S₂ on the slip rings 13 and 14, respectively, as a function of time.
Between the instants t₁ and t₂ a tracking signal is applied to the slip ring 13. If it is assumed that capacitor 25 carries a higher direct voltage (E), the diode 23 will be cut off. The common electrode 6 of the actuator 2 then receives a signal which appears in parallel across both piezoelements, as indicated by the dashed arrows S, because the electrode 10 is connected directly and the electrode 9 is connected indirectly, via capacitor 25 and via diode 24 and source 20, to earth. In one element the polarity of the signal has the same direction as the polarization (P) and in the other element it is directed oppositely, so that the transducer 2 deflects in conformity with the signal S₁. The voltage E across capacitor 25 also appears on the electrode 9. Since the common electrode 6 is connected to the tracking signal source and the electrode 10 is connected to earth, this bias voltage is distributed uniformly as indicated by the arrows V between the two piezoelements in accordance with the polarization P. As a result of this, the neutral level of the actuator (no deflection) is obtained when the voltage on the common electrode 6 is 1/2E (electrode 9 is then at E and electrode 10 at 0 V). The steady-state d.c. level of the tracking signal should then also be 1/2E.
At the same time the direct voltage E from source 20 will appear on slip ring 14 (signal S₂). If the charge on capacitor 25 is not sufficient, capacitor 25 will be charged substantially to the voltage E (but for one diode voltage) via the diode 24 which then conducts. The voltage on electrode 9 of element 3 and, via drive signal input 12, on the common electrode 6 is then E volts. This results in a substantial deflection of the actuator in conformity with the drive signal of E volts, but this is no problem because the head 5 is inoperative during this period. At the instant t₂ the signal S₂ on slip ring 14 changes over from the direct voltage E to the tracking signal. Diode 24 is then cut off. The tracking signal then appears on the common electrode 6 and capacitor 25 is charged.
The same happens between the instants t₂ and t₃ but now actuators 2 and 3 are interchanged.
It is to be noted that a system is conceivable in which both heads are operative simultaneously, for example in the case of a tape-wrapping angle of 210°, the additional 30° wrap being used for audio recording. Switches 16 and 17 must then be operated so that the voltage E is transferred during a shorter period, for example after the instant t₄ as shown in FIG. 2. The switching means 15 must then be modified so that each of the drive inputs 11 and 15 can receive an independent drive signal, at least when both heads are driven simultaneously.
In principle it is also possible to re-charge the capacitor 25 with shorter voltage pulses. The invention may, in principle, also be employed in single-head video recorders.
FIG. 3 shows a possible variant to the device shown in FIG. 1, in which both piezoelectric elements 7 and 8 are polarized in the same direction viewed from the common electrode 6. The drive signal must then be applied to electrodes 9 and 10 in phase opposition in order to obtain a deflection and the bias-voltage input 21 must be connected to the mean voltage across the buffer capacitor 25. Instead of the diode 25 active voltage isolators may then be used.

PHILIPS VR2350 STEREO MATCH LINE  Arrangement for the recording and reproduction of wide frequency band video signal:
 


 Method of recording and reproduction of wide frequency band video signals onto or from a magnetizable recording carrier, carried out by the following means: means for separating of the video frequency signals into first and second signals of lower and upper frequency range respectively, for converting said second signal into a third signal the frequency range of which equaling that of said first signal, for frequency modulating a carrier wave frequency by said first and third signals and for recording the frequency modulated signals by means of a twin head, for reproducing the recorded signals by means of a twin head and for amplifying, limiting and demodulating the recorded signals and reconverting the third signal into its original frequency range and combining the so reconverted third signal and said first signal.

 1. An apparatus for the recording and reproducing of wide frequency band color video signals onto or from two adjacent tracks of a magnetizable recording carrier, whereat the color video signal to be recorded is separated into a lower and upper frequency range, said lower frequency range frequency modulating a carrier wave, said apparatus further comprising:
a. means for converting said upper frequency range into said lower frequency range;
b. means for frequency modulating said carrier wave by said converted upper frequency range;
c. twin head means for simultaneously recording both said frequency modulated signals; and,
d. means for reproducing the recorded signals encoding the twin head, means for amplifying, limiting and demodulating the recorded signals and for reconverting the converted upper frequency range into its original frequency range and for combining the reconverted signal and the lower frequency range signal.


2. The apparatus in accordance with claim 1 wherein the mixing frequency used for the converting and reconverting of the upper frequency range is an integral multiple of the line frequency.

3. The apparatus in accordance with claim 1 wherein the individual recording heads of the twin head have azimuth-angles which are different from zero and are equal in value but oppositely inclined.

Description:

BACKGROUND OF THE INVENTION
In view of the limited band width of the frequency band of simple tape video recording and reproducing apparatuses for home use a color television signal can be recorded only with losses in quality and after a considerable transformation of the original video signals.
For example, in a widely used European system of recording and reproduction, the brightness and chrominance signals are separated from each other. A carrier frequency located at about 4 MHz is frequency-modulated with the brightness signal, which is limited to 2.7 MHz. The chrominance signal is moved out of its original frequency position into a new frequency range, which is located lower than that of the lower side bands of the frequency-modulated brightness signals. Thereafter the frequency-converted color signals are added and recorded.
Japanese systems, which also were developed especially for home use, use essentially the same principle. Both systems suffer from serious disadvantages. The procedure is intricate and includes many possibilities for error, if the luminance and chrominance signals are separated, processed in a different manner and then put together again. The frequency band width of the brightness signal must be narrowed. Since a portion of the tape recorded information is contained in the amplitude, the advantage of frequency modulation largely is lost. The track width cannot be reduced below a certain minimum figure and the color information is recorded at a relatively large wave length. The danger of cross-talk and especially cross-color disturbances between neighboring tracks exists just where it is most conspicuous. This can be avoided by the provision of guard bands between the tracks, but because the guard bands do not carry any information a large amount of tape is needed.
If guard bands between adjacent tracks are omitted, adjacent tracks are recorded and read at different azimuth angles, and the polarity of the color information is changed from line to line, which requires not only additional electronics but requires a radically different lay-out of the whole electronic circuit, depending upon whether the apparatus is to be used for NTSC, PAL or SECAM.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a recording and reproducing arrangement for wide frequency band video signals onto or from a magnetizable carrier, which avoids the above described faults and which especially permits the recording of the full video frequency band with small and inexpensive apparatuses and without additional tape consumption at full utilization of the advantages of frequency modulation. The color television system (NTSC, PAL or SECAM) does not influence the recording, so that the same apparatus can be used for all systems, except of course, for different power supply frequencies.
The inventive combination is new and brings out a surprising result. For example, the frequency transformation of a portion of the color television signal is known. U.S. Pat. No. 3,234,323 discloses the method of modulation onto a carrier frequency for the brightness and the color and to record each in parallel tracks. German Pat. No. 1,935,109 discloses means to record on adjacent tracks without leaving space in between, but with different azimuth angles. In comparison, none of the known arrangements permits recording of the full color television signal frequency band with small and inexpensive apparatus independently of the color transmission system and with full utilization of the advantages of frequency modulation and without additional tape consumption and loss of quality.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1 and 2 taken together provide a diagrammatic showing of the subject invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT
An embodiment of the in

vention is shown in the FIGS. in which for example the mean track spacing amounts to 187 μm, the width of a track itself is 130 μm, the frequency modulation deviation ranges from 3.1 MHz to 4.5 MHz, and at this condition video signals up to 2.7 MHz with 10 dB loss can be recorded. If now, according to the invention, the mean track spacing is divided into two tracks each of 93.5 μm track width lying parallel and adjacent to one another without interspace, and if, from the signal which is introduced at connection 1, a lower frequency range extending up to 2.7 MHz is separated by a low-pass filter 2, then this lower frequency range may be frequency modulated in a modulator 3 and after appropriate amplification in an amplifier 4 be recorded by a magnetic transducer head 5, just as well as in the aforementioned original state. Simultaneously, the line synchron impulses are separated at 6 and an upper frequency range of the color television signal from 2.7 MHz to 5.5 MHz is made available over the high-pass filter 7. The frequency of the output voltage of a voltage controlled oscillator (VCO) 8 with a nominal frequency of about 2.6 MHz is divided in a divider 9 by, for example, 166 and compared with the line synchron impulses in a phase comparator 10; the difference signal synchronizes the oscillator 8 to a frequency which is an integral multiple of the line frequency. The mixing of the output voltages of the oscillator 8 and of the high-pass filter 7 in a mixing unit 11 and the limiting by a low-pass filter 12, whose cut-off frequency may lie a little higher than those of 2, effects a transposition of the upper video frequencies into the same frequency range as is behind the low-pass filter 2; the signals applied to the frequency modulators 3 and 13, may also be treated in the same manner, especially with respect to a possible pre-emphasis and the modulation itself; the last is indicated by a common carrier wave oscillator 16. The signal, which is frequency modulated in 13, is applied by way of an amplifier 14 to a further magnetic head 15, which is preferably combined with the magnetic head 5 to form a twin head, recording simultaneously with head 5 parallel tracks without any interspace. Technologically, the amplifiers 4 and 14 and the heads 5 and 15 are of equal design; as later will be explained, only the azimuth angles of the gaps of heads 5 and 15 differ from each other.
In the play-back apparatus according to

FIG. 2, the amplifiers 17, the limiters 18 and the demodulators 19, which are following the heads 5 and 15, are once more built wholly alike; the blocks 6, 8, 9, 10 and 11 are the same for recording, according to FIG. 1 and for reproducing, according to FIG. 2. The output voltage of the mixing unit 11 is taken through a band-pass filter 20, which filters out the upper side band of the mixing product, and transfers it to an adder stage 21, which also receives the demodulated signals read by head 5. If necessary, there may be inserted frequency-response corrections at suitable places, deemphasis on offset compensators, and this in both channels.
The synchronization to the line frequency of the mixing frequency of the oscillator 8, which is required for the frequency shift, proves to be especially advantageous, because by this, large time basis deviations are compensated for. The upper cut-off frequency of the demodulated signal, which head 5 picks up, is thus shifted exactly as much as the lower cut-off frequency behind the band-pass filter 20, so that the crossover positions between the two ranges of video frequencies are not changed relative to each other.
As a result, compared with the original shape, the upper useful video frequency can be doubled without loss of playing time or quality, and this, without having to extract the chrominance signal out of the color television signal and without having information carried by the amplitude of the magnetization, which exists at the tape. For this latter reason, the width of the tracks may be further decreased, and in this way, the playing time can be again increased.
Compared with the aforementioned Japanese system, it is true that this system also uses the advantage of abutting tracks. But instead of this, another advantage is obtained in that the very complicated and from television system to television system very different processing of the color signal is avoided; also the disadvantage of a chrominance sub-carrier transposed into a low frequency range, namely the therewith associated danger of cross-talk from track to track is very greatly reduced. For example: the converted chrominance sub-carrier frequency is normally of the order of 600 kHz. If there is a track width without interspace of 55 μm, a head to tape speed of 6000 mm/s and an azimuth-angle of 8° Which is contrarotating from track to track (which means 16° effective for each head), and the scanning head deviates by 9% of the track width out of its track, the cross-talk results in a signal to noise ratio of 20.4 dB. This ratio is too small and must therefore be further diminished by complicated and expensive electronic means with the help of comb filters. According to the invention all recorded frequencies are located at 4 MHz; under otherwise equal circumstances the cross-talk ratio now amounts to 45 dB, which requires no additional distortion suppressing means.
The invention is not limited to the specific oblique track recording, but can also be used at the transverse track, or the longitudinal track methods using rotating magnetic heads. The advantages derived from the invention is independent of the shape (form) of the record carrier and of the track.

PHILIPS VR2350 STEREO MATCH LINE  Method and device for tracking video signals on a magnetic VIDEO2000 SYSTEM tape by detecting phase jumps:

 A method and device for maintaining an exact track when playing back video ignals, which are recorded on a magnetic tape in oblique parallel tracks with different azimuth angles.

 1. A device for adjusting the exact position of the track when replaying video signals which are recorded in oblique parallel tracks on a magnetic tape, said oblique tracks being alternately recorded and replayed by two rotating heads, the gaps of which have opposite equal azimuth angles causing phase jumps of the line frequency of the scanned video signal during track changes in case of mistracking, said device including means for detecting said phase jumps, and means for applying said phase jumps to said rotating heads to readjust the rotating video heads to the exact track position by control of the tape speed.

2. A device in accordance with claim 1 further comprising means for measuring the phase jumps of the line frequency for changes from an even numbered to an odd numbered track and for changes from an odd numbered to an even numbered track.

3. A device in accordance with claim 2 in which the phase jumps of the line frequency of the video signal with respect to a reference frequency during subsequent track changes are detected by different sample and hold circuits, the outputs of said sample and hold circuits being fed to the input of a differential amplifier to form an error signal, said error signal controlling the tape speed so as to minimize said error signal.

4. A device according to claim 2 further comprising a phase locked loop to produce the reference frequency synchronized to the line frequency of the scanned video signal, said phase locked loop containing a phase comparator, a voltage controlled oscillator and a low pass filter therebetween, said low pass filter causing the control time constant of the voltage controlled oscillator to equal at least the scanning time of one track.

5. A device according to claim 3 in which the separated line pulses from the scanned video signal are fed through gate circuits to the sample and hold circuits, and which are alternately opened for about two line intervals by pulses which are derived from the position signals of the head wheel each time a video head starts to scan a new track.

6. A device according to claim 5 in which the error signal of the differential amplifier is added to or subtracted from the rectified voltage of the tacho generator of the tape feed motor and in which by comparing the sum or difference, respectively, with a given reference voltage the rotation of the tape feed motor is controlled so as to minimize the error voltage produced by the differential amplifier.

7. A device according to claim 6 in which a low pass filter is provided at the output of the differential amplifier.

Description:

BACKGROUND OF THE INVENTION
When recording video signals in oblique parallel tracks cross-talking from track to track can be kept to a minimum if the tracks are separated by guard bands. However, such guard bands are a poor way of using the available recording face.
Another possibility for minimizing cross-talk is to record with azimuth angles which differ from track to track. In such a case the guard bands can be eliminated. However, in such a system the requirement for exactly scanning the recorded track is increased.
Methods and devices for an automatical tracking during play-back of video signals in oblique tracks are known, but were never attractive for incorporation into devices for home use. For example it has been suggested to use the time difference which occurs simultaneously with a migration as a measure of the lateral migration of the replay head from the magnetic track. This method can be accomplished by very simple circuitry but poses high demands with respect to the precision and the timely constancy of such circuits, because very small and continuously changing time intervals must be measured.
SUMMARY OF THE INVENTION
The subject invention provides a device and a method wherein an exact tracking is made possible without expensive equipment and without significant requirements for precision, durability and constancy of the circuit elements.
The invention is related to video tape recorders where the video signals are recorded in oblique parallel tracks which are alternately recorded and replayed by two rotating video heads with gaps having opposite azimuth angles. The migration of the video heads from the exact track position is determined by the phase jump which occurs during track change.
The invention is based on the realization that the sudden change of a magnitude is easier to measure than a continuous change.
BRIEF DESCRIPTION OF THE FIGURES
FIG. 1 is a diagrammatic representation of two oblique tracks with the tape scanning and tape feeding directions indicated;
FIG. 2 is a schematic diagram utilizing the subject invention; and
FIG. 3 is a schematic diagram illustrating a further embodiment of the invention.
DESCRIPTION OF A PREFERRED EMBODIMENT
FIG. 1 sho

ws two oblique tracks 1 and 2. For track 1 the recording and replay gap of the magnet head is turned from the vertical position counterclockwise through angle α and for track 2 in a clockwise direction through an equal angle α . If during replay the heads are displaced from the nominal position 3, 4 into position 3', 4' by an amount h perpendicular to the track direction, an additional phase change occurs in addition to the reduction of the signal to noise ratio. With the scanning and tape feeding directions and with the azimuth angles of FIG. 1 head 3' scans the video signal by an amount (h) (tan α) earlier and head 4' by an amount (h) (tan α) later than at nominal position. Therefore, during the change from track 1 to track 2 a sudden phase jump takes place corresponding to (2) (h) (tan α) rearwardly and from track 2 to track 1 forwardly. However, if heads 3 and 4 are not migrating upwardly as shown in FIG. 1 but rather downwardly, the sudden phase jump takes place with the magnitude (2) (h) (tan α) forwardly and from track 2 to track 1 rearwardly. Therefore, the magnitude of the phase jump is a measure of the magnitude of migration of the video heads from the track, while the sign of the phase jump determines the direction of migration.
In the invention the phase jump is measured at the line frequency with respect to a reference oscillation which is synchronized to the line frequency but which cannot follow sudden phase jumps or rapid frequency changes. For this purpose a voltage controlled oscillator 8 is provided as can be seen in FIG. 2 which oscillates at about double the line frequency and which is synchronized by means of phase comparator 6 and low pass filter 7 to the line pulses fed at 5 and separated from the scanned video signal. The double line frequency is chosen because of the frequency of the equalizing pulses of the vertical signal, and the low pass filter 7 prevents oscillator 8 from following immediately the occuring phase jumps.
Simultaneously, the scanned line pulses are fed to gate circuits 12 and 13 which open for a short time for about two line durations after each second head change. The necessary opening pulses are fed at 14 and 15 and are derived from the position pulse of the head wheel, so that gate 12 opens when changing from track 1 to track 2, for example, while gate 13 opens when changing from track 2 to the next track.
It is useful to transform the output voltage of oscillator 8 into a trapezoidal wave by pulse former 9 the output of which is fed as a reference to the sample and hold circuits 10 and 16 or 11, 16, respectively. The output signals of 10 and 11 are coupled to the input of differential amplifier 17.
The error signal which is generated at the output of the differential amplifier 17 may be used for making an exact track adjustment for the video heads. For example, the error signal may influence the recovery time of a monostable multivibrator 18 to which the reference pulses for the servo control circuit 20 of the tape transport motor are fed at 19. Another possibility exists in the immediate adjustment of the rotating video heads in axial direction by means of piezoceramic elements which are excited by the error signal of differential amplifier 17.

Since the maintaining of the track and the transport speed for the tape are unmistakeably correlated in accordance with the invention the reference pulses which are fed at 19 may be omitted in accordance with a further embodiment of the invention. In other words, the usual synchronous track is not necessary.
In accordance with FIG. 3, the servo control circuit of band feeding motor 21 includes tacho generator 22 which is coupled with motor 21, and the output voltage of the generator after being rectified at 23 is coupled to the input of a differential amplifier 24. The other input of differential amplifier 24 is coupled to a reference voltage 25. This control loop controls the tape feeding speed approximately to the nominal value, while the output voltage of the differential amplifier 17 which is fed into the summing element 26 provides the exact adjustment of the tape speed with respect to the exact track adjustment.
The additional low pass filter 27, 28 is only necessary for the start of the tape movement and elimates the big alternating phase jumps generated during the acceleration of the magnetic tape.

PHILIPS VR2350 STEREO MATCH LINE   Method for dynamic track adjustment in SYSTEM VIDEO2000 video recorders:. 

 1. Method for dynamic equidistant track adjustment in magnetic helical-scan video recording with the aid of rotating magnetic video heads which are adjustable by a servosystem perpendicularly to the direction of movement, the servosystem being controlled by a control signal (burst) of a particular frequency keyed in each case at the beginning of the track and the area of reproduction of a new track being located immediately adjacent to the area of recording of the preceding track, characterized in that the order of recording and reproduction for the control signal (burst) keyed in arbitrary length, relative to the scanning movement of the magnetic video head, takes place alternatingly from track to track and, relative to the beginning of the track, offset in time and geometry from track to track.

VERFAHREN ZUR DYNAMISCHEN SPUREINSTELLUNG BEI VIDEORECORDERN PATENTANSPR·UCHE

1. Verfahren zur dynamischen ·aquidistanten Spureinstellung bei der magnetischen Schr·agspur-Videoaufzeichnung mit Hilfe von rotierenden Video-Magnetk·opfen, die senkrecht zur Bewegungsrichtung durch ein Servosystem verstellbar sind, wobei die Ansteuerung des Servosystems durch ein jeweils am Spuranfang eingetastetes Steuersignal (Burst) bestimmter Frequenz erfolgt, d a d u r c h g e k e n n z e i c h n e t dass die Reihenfolge der Aufzeichnung und Wiedergabe f·ur das in beliebiger L·ange eingetastete Steuersignal (Burst) bezogen auf die Abtastbewegung des Video Magnetkopfes von Spur zu Spur alternierend und bezogen auf den Spuranfang von Spur zu Spur zeitlich und geometrisch versetzt erfolgt, derart, dass der Wiedergabebereich einer neuen Spur dem Aufzeichnungsbereich der vorangegangenen Spur unmittelbar benachbart ist.

2. Verfahren nach Anspruch 1, d a d u r c h g e k e n n z e i c h n e t , dass in jeder zweiten Spur zwischen dem Aufzeichnungs- und Wiedergabebereich des Steuersignals (Burst) eine L·ucke mit der L·ange des doppelten Spurversatzes eingef·ugt ist.

3. Verfahren nach Anspruch 1, d a d u r c h g e k e n n z e i c h n e t , dass in jeder zweiten Spur die Summe der zeitlichen und geometrischen L·ange des Aufzeichnungs- und Wiedergabebereichs f·ur das Steuersignal (Burst) um den doppelten Spurversatz vergr·ossert wird.

Description:

VERFAHREN ZUR DYNAMISCHEN SPUREINSTELLUNG BEI VIDEORECORDERN BESCHREIBUNG Die Erfindung betrifft ein Verfahren, mit dem bei der magnetischen Videoauf zeichnung die ohne Zwischenraum aneinandergrenzenden, winkelentkoppelten Schr·ag spuren auf konstanten Abstand gebracht werden k·onnen.
Die Anwendung des Verfahrens setzt voraus, dass die aufzeichnenden bzw. wiedergebenden rotierenden Video Magnetk·opfe senkrecht zu ihrer Abtastrichtung gesteuert bewegbar sind. Die gesteuerte Bewegbarkeit, wie sie z.B. beim System ~Video 2000" angewendet wird, dient prim·ar der Spurfindung bei der Wiedergabe. Hierzu werden zus·atzlich zum Luminanz- und Chrominanzsignal beispielsweise vier Hilfsfrequenzen aufgezeichnet, die unterhalb des Chrominanzsignals und Luminanzsignals liegen und die bei der Wiedergabe in einer Servoschaltung derart verarbeitet werden, dass der Wiedergabekopf immer so eingestellt wird, dass er auf der gewunschten Magnetspur l·auft.
Einzelheiten ·uber dieses Verfahren sind beispielsweise aus WGrundig Technische lnforma- tonen", Heft 3/198Q, Seite 111 ff. und "Grundig Technische Infonmationen", Heft 3/1981, Seite 105 ff. zu entnehmen.
Die M·oglichkeit der Steuerung der Magnetk·opfe senkrecht zur Spurrichtung wird ausser zur Spurfindung bei der Wiedergabe aber auch bei der Aufnahme dazu benutzt, um die aufeinanderfolgenden Spuren ·aquidistant zu schreiben.
Hierzu wird ein Schwingungszug, auch Burst genannt, am jeweiligen Spuranfang mit einer weiteren Hilfsfrequenz aufgezeichnet. Unmittelbar nach der Aufzeichnung des Burstsignals, dessen Dauer nach dem Stand der Technik dem von Spur zu Spur entstehenden Spurversatz entspricht, wird der rotierende Magnetkopf auf Wiedergabe umgeschaltet und tastet das Burstsignal der vorhergehenden Spur ab. Die Amplitude des dabei gewonnenen Signals ist ein Mass f·ur den Spurabstand und kann zur Einstellung des rotierenden Magnetkopfes am Spuranfang benutzt werden, derart, dass die Spurabst·ande konstant sind.
Die Bezugsgr·osse bei diesem Regelvorgang wird beim Stand der Technik dadurch gewonnen, dass einer der beiden rotierenden Video-Magnetk·opfe auf dem Kopf rad hinsichtlich seiner Einstellung senkrecht zur Abtasteinrichtung eine feste Vorgabe erh·alt und nur der zweite Kopf so geregelt wird, dass ·aquidistante Spuren entstehen. Es ist prinzipiell aber auch m·oglich, jeweils bei Beginn einer Aufzeichnung die erste Spur mit fest eingestelltem rotierenden Video-Magnetkopf zu schreiben und anschliessend beide Video-Magnetk·opfe fortlaufend auf konstanten Spurabstand einzuregeln.
F·ur die exakte Spureinstellung darf dabei das Burstsignal nicht zu kurz sein, da mit der nachfolgenden Auswerteschaltung und auch mit der Umschaltung Aufnahme/ Wiedergabe Einschwingvorg·ange mit bestimmter Zeitdauer verbunden sind.
Wird die Aufzeichnung des Burstsignals nach de

m Stand der Technik entsprechend der Dauer des Spurversatzes gew·ahlt, dann liegen die Aufzeichnungsabschnitte in benachbarten Spuren geometrisch treppenf·ormig zueinander wie aus Figur 1 ersichtlich. Der rotierende Magnetkopf kann dann sofort nach der Aufzeichnungsperiode f·ur den Burst auf Wiedergabe umgeschaltet und nach Massgabe des aus der vorhergehenden Spur abgetasteten Burstsignals auf exakten Spurabstand eingestellt werden.
Bei geringer Spurbreite bzw. Bandgeschwindigkeit und entsprechend geringer Spurneigung kann der Spurversatz auf sehr kleine Werte absinken. Entsprechend den oben geschilderten Zusammenh·angen wird dann nach dem Stand der Technik die Dauer des Burstsignals ebenfalls auf einen geringen Wert reduziert. Es besteht dann die Gefahr, dass dieses zeitlich verk·urzte Burstsignal mit R·ucksicht auf die mit der Kopfregelung verbundenen Einschwing- und Urnschaltvorg·ange f·ur eine st·orsichere Regelung nicht mehr ausreicht.
Man k·onnte daran denken, das Burstsignal zeitlich ·uber den Spur versatz hinaus zu verl·angern, um wieder eine sichere Auswertung zu erreichen. Dann aber wandert die geometrische und zeitliche Position des Burstsignals von Spur zu Spur immer weiter auf der Aufzeichnungsspur voran und w·urde schliesslich den Videosignal-Austastbereich verlassen bzw. in den Bildsignalbereich gelangen. Dies ist zur Vermeidung von St·orungen unzul·assig.
Ausserdem l·asst sich bei zunehmender Entfernung der Burstaufzeichnung vom Spuranfang das gew·unschte Ziel der Spureinstellung im Sinne eines konstanten Spurabstandes am Spuranfang nicht mehr befriedigend erreichen.
Aufgabe der Erfindung ist es, bei der magnetischen Video aufzeichnung in Schr·agspuren auch bei geringem Versatz von Spur zu Spur ein Burstsignal f·ur die Einstellung des Spurabstandes aufzuzeichnen und wiederzugeben, das in seiner zeitlichen Ausdehnung so gew·ahlt werden kann, dass eine sichere Auswertung mit Hilfe der Regeleinrichtung f·ur die Verstellung des Magnetkopfes senkrecht zur Abtastrichtung im Sinne der Erreichung ·aquidistanter Spuren m·oglich ist.
Die erfindungsgem·asse L·osung dieser Aufgabe ist aus Figur 2 ersichtlich. Wird n·amlich die zeitliche Folge der Aufzeichnung und Wiedergabe des Burstsignals von Spur zu Spur alternierend gew·ahlt, dann kann das Burstsignal zeitlich ausgedehnt werden, ohne dass die unerw·unschte Erscheinung der Wanderung innerhalb der Spur in Abtastrichtung auftritt. Im dargestellten Beispiel nach Figur 2 ist in der ersten Spur die geometrische und zeitliche L·ange der Burstaufzeichnung beliebig gew·ahlt. In der folgenden Spur wird nun die Burstaufzeichnung bezogen auf den Spuranfang um die Burstl·ange zuz·uglich des Spurversatzes verschoben und der Lesevorgang vor den Schreibvorgang gelegt. Damit wird der zeitlich verl·angerte Burst vollst·andig ausgewertet und ein neuer Burst mit der gleichen L·ange aufgezeichnet.
In der dritten Spur schliesslich setzt die Burstaufzeichnung bezogen auf den Spuranfang wieder so ein wie in der ersten Spur, w·ahrend der Lesevorgang gegen·uber der Aufzeichnung um die Burstl·ange zuz·uglich des doppelten Spurversatzes verschoben ist. Durch Vertauschung der Reihenfolge von Schreiben und Lesen sowie durch Einf·ugen einer L·ucke zwischen Schreiben und Lesen in jeder zweiten Spur um die Dauer des doppelten Spurversatzes wird also sichergestellt, dass bei verl·angerter Burstdauer das Burstsignal in voller L·ange gelesen werden kann und trotzdem der Schreib- und Lesevorgang am Spuranfang verbleibt, wie es f·ur die wirkungsvolle und st·orsichere Regelung des Spurabstandes n·otig ist.
Ausserdem wird durch die erfindungsgem·asse Auf zeichnungs- Wiedergabe-Geometrie f·ur das Steuersignal (Burst) erreicht, dass jedem der beiden Magnetk·opfe ein konstanter zeitlicher Ablauf f·ur Aufzeichnung und Wiedergabe zugeordnet ist. Mit anderen Worten, der erste Videokopf (ungeradzahlige Spuren) zeichnet in festem Abstand oder zeitlicher Dauer vom Spuranfang auf, dann folgt eine L·ucke entsprechend dem doppelten Spurversatz, danach der Wiedergabebereich f·ur das Steuersignal (Burst).
Der zweite Videokopf (geradzahlige Spuren) gibt in festem Abstand oder zeitlicher Dauer vom Spuranfang wieder und zeichnet ohne l·ucke anschliessend auf.
Zum besseren Verst·andnis des Verfahrens sei noch angemerkt, dass die Wiedergabe des Steuersignals (Burst) aus der vorhergehenden Spur trotz Winkelentkopplung auch dann noch m·oglich ist, wenn der Video-Magnetkopf die vorhergehende Spur nicht mehr unmittelbar trifft.
Dies erkl·art sich daraus, dass die Frequenz des Steuersignals bezogen auf das Video signal verh·altnism·assig niedrig gew·ahlt wird, so dass die Winkelentkopplung unwirksam wird und das Streufeld ·uber die Spurbreite hinaus wirkt.




PHILIPS VR2350 STEREO MATCH LINE  DEVICE FOR ROTATING ANNULAR TRANSFORMERS IN A VIDEO SET:

 1. Arrangement of rotating toroidal transformers (10, 11) for the inductive transmission of high-frequency oscillations in a video recording and playback machine with at least two signal recording and playback heads (5, 6), which are preferably arranged offset by 180 degrees on a rotating head wheel (2) in a head drum, the transformers each having one rotating (10', 11') toroidal part and one fixed (10", 11") toroidal part, each signal head (5, 6) being assigned the rotating part of a transformer in a certain way, and the transformers (10, 11) being arranged axially one above the other, characterized in that the transformers (10, 11) have different ring sizes such that they do not radially overlap.

ANORDNUNG VON ROTIERENDEN RINGF·ORMIGEN TRANSFORMATOREN IN EINEM VIDEOGER·AT PATENTANSPR·UCHE

1. Anordnung von rotierenden ringf·ormigen Transformatoren zur induktiven ·Ubertragung hochfrequente

r Schwingungen in einem Video-Auf zeichnungs- und -Wiedergabeger·at mit wenigstens zwei Signal-Aufzeichnungs- und Wiedergabek·opfen, die vorzugsweise um 180 versetzt auf einem rotierenden Kopfrad in einer Kopftrommel angeordnet sind, und jedem Signalkopf der rotierende Teil eines Transformators in bestimmter Weise zugeordnet ist, d a d u r c h g e k e n n z e i c h n e t , dass ein Transformator (10) mit rotierendem und feststehendem ringf·ormigem Teil des ersten Signalkopfes (5) gegen·uber dem anderen rotierenden Transformator (11) des zweiten Signalkopf es (6) axial verschoben und durch verschiedene Ringgr·ossen radial und axial nicht ·uber schneidend in der Kopftrommel (1) angeordnet ist.

2. Anordnung nach Anspruch 1, d a d u r c h g e k e n n z e i c h n e t , dass das Kopfrad (2) einen hochgezogenen Flansch (13) aufweist, auf den ein rotierender Trafoteil (11) aufgesetzt ist, w·ahrend der andere rotierende Trafoteil mit der geringeren Ringgr·osse (10') auf der inneren Planseite des Kopfrades (14) angeordnet ist, und die H·ohe des Flansches wenigstens der gesamten Querschnittsh·ohe eines Transformators entspricht.

3. Anordnung nach Anspruch 2, d a d u r c g e k e n n z e i c h n e t , dass die H·ohe des Flansches des Kopfrades der halben Querschnittsh·ohe des kompletten Transformators entspricht.

Description:

ANORDNUNG VON ROTIERENDEN RINGF·ORMIGEN TRANSFOXMATQREN IN EINEM VIDEOGER·AT BESCHREIBUNG Die Erfindung betrifft eine Anordnung von rotierenden ringf·ormigen Transformatoren zur induktiven Ubertragung hochfrequenter Schwingungen in einem Video-Aufzeichnungs- und Wiedergabeger·at mit wenigstens zwei Signal-Aufzeichnungs- und Wiedergabek·opfen, die vorzugsweise um 1800 versetzt auf einem rotierenden Kopfrad in einer Kopftrommel angeordnet sind, und jedem Signalkopf der rotierende Teil eines Transformators in bestimmter Weise zugeordnet ist.
Bei den meisten bekannten magnetischen Bild-Aufzeichnungs- und Wiedergabeger·aten mit bandf·ormigem Aufzeichnungsmedium erfolgt die Aufzeichnung und Wiedergabe der Video signale auf das Magnetband mittels sogenannter Schr·agspuraufzeichnung bzw. Abtastung ·uber auf einem rotierenden Kopfrad angeordnete Videok·opfe.
Es ist bekannt, dass hierbei die hochfrequenten Schwingungen mit Hilfe eines rotierenden Transformators induktiv ·ubertragen werden. Da vorzugsweise mit zwei um 1800 auf dem Kopfrad versetzt angeordneten Videok·opfen gearbeitet wird, sind auch hierzu zwei getrennte rotierende Transformatoren erforderlich. Das Kopfrad mit den beiden Videok·opfen ist mit den rotierenden Transformatoren in einer vom Magnetband teilweise umschlungenen zweigeteilten Kopftrommel integriert, wobei wenigstens ein Teil der Kopftrommel feststeht. Die Unterbringung der beiden rotierenden Transformatoren erfolgt in bekannter Weise in der Kopftrommel derart, dass diese entweder axial ·ubereinander angeordnet sind, oder sich mit verschiedenen Radien der einzelnen ·Ubertragerringe in einer Ebene befinden.
Ein wesentlicher Unterschied dieser verschiedenen Anordnungen ergibt sich in der Bewertung der Ubersprechd·ampfung von einem zum anderen rotierenden Transformator. Eine messwertm·assig grosse Obersprechd·ampfung ist bei Ger·aten der geschilderten Art in zunehmender Weise w·unschenswert, da inzwischen auch das Stereo-Tonsignal im Schr·agspurverfahren aufgezeichnet bzw. abgetastet wird.
Es kann somit in Videoaufzeichnungsger·aten ein PCM Tonsignal in einer Zusatzumschlingung vor oder nach der Video spur aufgezeichnet werden. Besonders hohe Anforderungen an die ·Ubersprechd·ampfung zwischen den beiden rotierenden Signal·ubertragern (Transformatoren) werden dann noch gestellt, wenn bei dieser genannten Technik eine Nachvertonung gew·unscht wird, denn dann ist es erforderlich, dass ein Videokopf mit dem PCM Schreibstrom angesteuert wird, w·ahrend der andere Videokopf das frequenzmodulierte Videosignal ausliest Die hierf·ur erforderliche hohe Ubersprechd·ampfung ist nach den bisher bekannten Anordnungen von rotierenden Transformatoren in der Kopftrommel eines Videoaufzeichnungsger·ates nicht gegeben.
Aufgabe der Erfindung ist es daher, eine Anordnung und Ausf·uhrung von wenigstens zwei rotierenden Transformatoren in Videoaufzeichnungsger·aten zu schaffen, die einerseits ein gutes ·Ubersprechverhalten sicherstellt und andererseits einen einfachen konstruktiven Einbau der rotierenden Transformatoren in die Kopftrommel des Ger·ates gew·ahrleistet.
Diese Aufgabe wird erfindungsgem·ass durch die im kennzeichnenden Teil des Anspruchs 1 angegebenen Merkmale gel·ost.
Vorteilhafte Ausgestaltungen des erfindungsgem·assen Aufbaus eines rotierenden ringf·ormigen Transformators in einer Kopftrommel f·ur Videoaufzeichnungsger·ate ergeben sich aus den Unteranspr·uchen.
Ein Ausf·uhrungsbeispiel wird nachfolgend anhand einer schematischen Zeichnung n·aher erl·autert.
Die im Schnitt dargestellte Figur zeigt eine Kopftrommel 1 mit eingesetztem Kopfrad 2. Der obere Teil 3 der Kopftrommel ist mit dem Kopfrad drehbar in einem unteren Teil 4 der Kopftrommel gelagert. Auf beiden Seiten um 180 versetzt, sind die Signalk·opfe 5 und 6 auf dem Kopfrad angeordnet. Auf einer nur teilweise dargestellten Welle 7 ist das Kopfrad aufgezogen und ·uber zwei Kugellager 8 in der Kopftrommel gelagert. Zur Vereinfachung der dargestellten Figur ist der Antrieb der Kopftrommel nicht gezeichnet, ebenso ist der Chassisteil 9, auf dem die Kopftrommel befestigt ist, nur zeichnungsm·assig angedeutet. Die beiden rotierenden Transformatoren 10 und 11 sind versetzt in der Kopftrommel angeordnet, wobei der Transformator 10 dem Signalkopf 5 und der Transformator 11 dem Signalkopf 6 zugeordnet ist.
Die Anschl·usse der Signalk·opfe werden jeweils ·uber eine Kontaktplatte 12, die sich im oberen Teil der Kopftrommel befindet, zu den Transformatoren 10 und 11 gef·uhrt. Die rotierenden Transformatoren bestehen, wie bekannt, aus zwei Ringkernh·alften mit eingelegten Wicklungen, wobei der jeweils rotierende Teil 10' und 11' an dem Kopfrad und der feststehende Teil 10'' und 11'' am unteren Teil der Kopftrommel befestigt ist. Die beiden Ringteile sind durch einen sehr kleinen Luftspalt getrennt. Die Anschl·usse der feststehenden Trafo-Ringteile werden in einfachster Weise ·uber Bohrungen, die sich im unteren Teil der Kopftrommel befinden, an eine nicht n·aher dargestellte Schaltungsplatte gef·uhrt.
Nach der Zeichnung ist der Transformator 10, der dem ersten Signalkopf 5 zugeordnet ist, gegen·uber dem anderen Transformator 11, der dem zweiten Signalkopf 6 zugeordnet ist, axial verschoben und durch verschiedene Ringgr·osse radial und axial nicht ·uberschneidend in der Kopftrommel angeordnet. Um diese Anordnung zu erreichen, weist das Kopfrad 2 einen ·ausseren hochgezogenen Flansch 13 auf, an dem der rotierende Trafoteil 11' des Trafos 11 (mit grossem Ringdurchmesser) befestigt ist. Der rotierende Trafoteil 10' mit der geringeren Ringgr·osse befindet sich hingegen auf der inneren Planseite 14 des Kopfrades. Die H·ohe des Flansches entspricht bei dieser Anordnung wenigstens der gesamten Querschnittsh·ohe eines kompletten Transformators.
Eine andere nicht dargestellte Anordnung sieht eine Flanschh·ohe vor, die etwa nur der halben Querschnittsh·ohe des Transformators entspricht.







PHILIPS VR2350 STEREO MATCH LINE  System for extending the playing time of video cassettes in VIDEO2000 SYSTEM.


 A system is provided for extending the playing time of standardized video cassettes. The system utilizes a rotating head drum having mounted thereon a first set of video heads displaced 180° with respect to each other, a second set of video heads displaced by a certain amount from 180° with respect to each other, a rotating winding of a transformer, and relays to interconnect the heads of either the first or second set of heads with the rotating winding as the head drum rotates. The relays are controlled by stationary coils and logic to respond to the setting of switches to enable the system to operate at normal tape speed via the first set of heads or reduced tape speed via the second set of heads without requiring any change in the speed of rotation of the head drum.

1. In a video tape record/playback machine of the type including a tape transport, a tape transport drive, a rotating head drum, means for rotating said head drum, a first pair of video heads mounted on said head drum and displaced from each other by 180°, and a transformer having a rotating winding mounted to said head drum and a stationary winding; the improvement comprising: a second pair of video heads mounted to said head drum and displaced from each other by an angle slightly different from 180° and control means to interconnect said first pair of video heads and said rotating winding when said tape transport drive is operated at a normal speed and to interconnect at least one of the video heads of said second pair and said rotating winding when said tape transport drive is operated at a lower, extended play speed.

2. The machine in accordance with claim 1 wherein said control means comprises: a first polarized relay affixed to said head drum for rotation therewith, said first relay having a first position interconnecting said first pair of video heads to said rotating winding and a second position interconnecting said second pair of video heads to said rotating winding;
first and second stationary exciter coils in controlling relationship with said first relay to drive said first relay to said first or second position;
switch means having a "normal" position and a "long play" position; and
logic circuit means responsive to the "normal" or "long play" position of said switch means to activate said exciter coils to drive said first relay to said first or second position respectively.


3. The machine in accordance with claim 2 wherein said second pair of video heads comprises a record/playback head and a playback only head; said switch means further has a "record" position and a "playback" position and further comprising
a second polarized relay affixed to said head drum for rotation therewith and having a "playback" position interconnecting both heads of said second pair of video heads with said rotating winding and a "record" position interconnecting only said record/playback head with said rotating winding;
said first and second stationary exciter coils are in controlling relationship with said second relay to drive said second relay to said "record" or "playback" position; and
said logic circuit means is responsive to said "record" or "playback" position of said switch to activate said exciter coils to drive said second relay to said "record" or "playback" position respectively.


4. The machine in accordance with claim 3 wherein said switch means further includes a "start" position indicating that said tape transport drive has been activated and said logic circuit means is responsive to said "start" position of said switch to activate said exciter coils to drive said first relay to said first position regardless of whether said switch is in said "normal" or "long play" position.

5. The machine in accordance with claim 1 further comprising a servo control connected to said tape transport drive, a tachometer generator secured to said tape transport drive adapted to generate pulses responsive to the rotational speed of said drive; a tape transported past said head drum by said tape transport, said tape having thereon first and second slant tracks, and the nominal output of said tachometer generator at said normal and lower speeds are integral multiples of the frame frequency of said slant tracks.

6. The machine in accordance with claim 5 further comprising: a divider connected to the output of said tachometer generator, said divider having a first state to divide the output of said tachometer generator by a first fixed integer to reduce it to the frame frequency when said tape transport operates at normal speed and a second state to divide the output of said tachometer generator by a second fixed integer to reduce it to the frame frequency when said tape transport operates at a lower speed;
a comparator having a first input from said divider, a second input from a reference pulse source, and an output in controlling relationship with said servo control;
a reference pulse source; and
means for switching said reference pulse source between a first state to generate reference pulses corresponding to said normal speed and a second state to generate reference pulses corresponding to said lower speed.


7. Video tape cassette recorder provided for the use of standardized video cassettes and for extending the playing time of said video cassettes, said recorder including a tape transport mechanism capable of driving the tape at a normal standardized speed and at essentially half the standardized speed, a rotating head drum with a first pair of video heads displaced from each other by 180° and with a second pair of video heads displayed from each other by an angle slightly different from 180° and displaced from said first pair by a suitable angle; a transformer with one stationary winding and one rotating winding mounted to said head drum, said head drum being equipped with a first polarized relay to connect said first or said second pair of video heads to said rotating transformer winding and with a second polarized relay to connect one or both of said second pair of video heads to said rotating transformer winding; said first and said second polarized relays being displaced from each other by 180° and being actuated in both positions by first and second stationary coils excited through logic circuits under the control of position pulses of said head drum and of the switching mode of operative switches, said operative switches being shiftable between normal or long play or record or playback positions.

8. A video tape cassette recorder in accordance with claim 7 wherein said operative switches include a special switch for the start and the stop of the tape transport drive; said special switch being interconnected with said logic circuits so as to connect in the stop position of said special switch said first pair of video heads to said rotating transformer winding regardless of whether said respective operative switch is in the normal or in the long play mode position.

9. A video tape cassette recorder in accordance with claim 7 further comprising a tachometer generator and a frequency divider for the output pulses of said tachometer generator; said tachometer generator being secured to and producing a plurality of pulses per revolution of said tape transport drive; the frequency of said tachometer generator output pulses being an integral multiple of the frame frequency of the video signal at both the rated normal and the rated low speed of said tape transport drive; and said frequency divider being switchable between two division factors so as to divide to frame frequency the frequency of said tachometer generator output pulses at both, the rated normal and the rated low speed of said tape transport drive.

Description:

BACKGROUND OF THE INVENTION
The present invention relates to video tape recording and more particularly to a system for extending the playing time of standardized video cassettes in which each of two rotating video heads, displaced relative to each other by 180°, records or scans one slant track per television field.
In the standard video cassette intended for home use, a magnetic tape located in a cassette is utilized. When the cassette is positioned in the video equipment, the tape is pulled from the cassette and positioned for operation. In order to permit interchangeability of the cassette (i.e., in order to insure that a cassette recorded on one machine can be played back on another machine) certain system standards have been established which are adhered to by the industry. These standards include the geometry of the slant tracks, the speed of rotation of the head drum, the number of video heads mounted on the drum, and the transport speed of the tape past the head drum. In one popular cassette system two video heads are mounted on the head drum 180° apart from each other and displaced to record or scan along one slant track. With 50 fields per second (as is common in most European countries) the head drum must therefore rotate at 1500 RPM. In order that the common line interlace of 312.5 lines per field is recorded and reproduced correctly, a tape speed must be chosen so that the spacing between the tracks (in the lengthwise direction of the tape) corresponds to an odd multiple of half lines. In the aforementioned system, this multiple was chosen as 11.
As a result of the above established standards, the maximum playing time of a cassette is limited to about an hour utilizing the thinnest tapes available. This playing time is not sufficient for certain forms of desired programs (e.g., such as full-length motion pictures). Thus, a considerable need exists for a system to extend the playing time of a standard cassette while maintaining provision for normal recording and playback capabilities.

It has heretofore been proposed (in German Pat. No. 1,437,141 for example) that the playing time of a given length of tape could be extended through the slant track method by recording only the even or odd television fields but scanning them twice during playback with the tape transport moving at roughly half the normal speed. In practice, a head drum which rotates at 1500 RPM and carries two video heads is utilized. The magnetic tape is looped 180° over the head drum. For recording, only one of the heads operates while for playing back both heads scan the same track. It is also known that in this case the two heads must no longer be precisely 180° apart from each other but the additional head position must be displaced by a slight amount from 180°. In practice this displacement distance is on the order of a millimeter and thus, it would not be practical to mount an additional head displaced by this slight amount.
The principal object of the present invention is to provide an improved video cassette machine capable of functioning in both a standard normal mode and an extended play mode.
A further object is to provide such a machine which can be readily switched from one mode to the other without requiring any intervention with the drive mechanism of the head drum.

SUMMARY OF THE INVENTION
The above and other beneficial objects and advantages are attained in accordance with the present invention by providing an improved video tape record/playback machine capable of normal as well as extended play operation. Video tape record/playback machine includes a tape transport, a tape transport drive, a rotating head drum, a motor for rotating the head drum, a first pair of video heads mounted on the head drum and displaced from each other by 180° of arc, and a transformer having a rotating winding mounted to the head drum and a stationary winding. In addition to the above, the present device further includes a second pair of video heads mounted to the head drum and displaced by an angle slightly different from 180°. In addition, means are provided to interconnect the first pair of video heads and the rotating winding when the tape transport drive is operated at a normal speed and to interconnect at least one of the video heads of the second set and the rotating winding of the transformer when the tape transport drive is operated at a lower, extended play speed. The control means includes a set of polarized relays affixed to the head drum for rotation therewith as well as stationary exciter coils which activate the relays. The exciter coils, in turn, are activated through a control logic circuit which is governed by switches set at the desired operational mode.


BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings:
FIG. 1 is a schematic of the head drum and its control logic;
FIG. 2 is a circuit diagram of the switching arrangement between the normal and long playing heads; and
FIG. 3 is a schematic of the tape speed switching arrangement.
DETAILED DESCRIPTION OF THE PREPARED EMBODIMENT
Reference is now made to the drawings wherein similar components bear the same reference numeral throughout the several views.

In FIG. 1, a rotating drum head 1 is shown carrying a first set of heads N₁ and N₂ displaced 180° apart from each other f₁ could theoretically be used with another head displaced slightly apart from N₂ by a distance on the order of 1 millimeter. Since this is not practical to effect, a second set of heads L₁ and L₂ is mounted to the head drum with the displacement between heads L₁ and L₂ being off slightly from 180° as shown. The arrows adjacent to the heads N₁, N₂, L₁ and L₂ depict their operability. Accordingly, heads N₁, N₂ and L₁ are designed for record and playback operation while head L₂ is designed for playback operation only.


or normal (N mode) operation. For long playing (L mode) operation head N
Referring briefly to FIG. 2, it can be seen that a rotating transformer 2 is provided with one rotating winding and one stationary winding. Since rotating multiple transformers are expensive, only a simple transformer 2 is provided. As shown in FIG. 1, a small polarized relay 3 rotates with the head drum and serves to connect the rotating winding of the transformer with heads N₁ -N₂ or L₁ -L₂ as required. To this end, the relay 3 is switched by stationary exciter coils 4 and 5 as the head drum rotates. A second polarized relay 6 is also provided to connect both heads L₁ and L₂ to the transformer winding during L mode-playback but only head L₁ to the transformer winding during L mode-record. The electrical contacts of the polarized relays 3 and 6 are shown in FIG. 2.
The logic and switches for the control of the polarized relays 3 and 6 is depicted in FIG. 1. Thus, as shown, coil 4 is energized by the output of AND gates 7 or 8. Coil 5 is energized by the output of AND gates 9 or 10. In turn, each of the AND gates 7, 8, 9 and 10 has an input from the function switches 11 used to determine (a) L or N mode; (b) record or playback; and (c) whether the tape transport is operative or not.
In addition to the above, gates 7 and 9 each have another input connected to a position pickup 13. Pickup 13 comprises a simple transducer designed to generate a pulse each time a small permanent magnet 14 which rotates with the head drum rotates past the pickup. Thus, the polarized relay 3 is activated through coils 4 or 5 each time the magnet 14 moves past the position pickup and is therefore controlled by either the gates 7 or 9 depending on whether switch 11 is in the "L" or "N" position.
The output of pickup 13 is also delayed 20 ms through delay means 12 and then applied to gates 8 and 10. 20 ms corresponds to the time it takes for the drum head 1, rotating at 1500 RPM, to rotate through 180°. Thus, 20 ms or half a head drum rotation after relay 3 is excited by coils 4 or 5, relay 6 is excited by coils 4 or 5.
In N mode (i.e., switch 11 at N position) the electrical contacts of relay 3 are switched to N thereby connecting the heads N₁ and N₂ in series with the rotating transformer. The position of the contacts of relay 6 is immaterial since in N position relay 3 shunts past heads L₁ and L₂. The operation of the cassette system then proceeds in a conventional manner.
In L mode -- record, (switch 11 at L and "record") the electrical contacts of relay 3 are switched to the L position via the AND gate 15, the OR gate 16 and AND gate 9. After 20 ms, relay 6 is energized via gates 15 and 8 and the head L₁ is thereby connected to rotating transformer 2.
In L mode -- playback (switch 11 at L and "playback") one must differentiate between the tape in the running or stopped condition. The latter would occur, for example, for the reproduction of still pictures. It has been found that with the magnetic tape stopped, even when in the "L" mode, the N heads must be utilized since the L heads will incorrectly scan the tracks resulting in phase shift and poor signal to noise ratio. Thus, if switch 11 is in the L mode -- playback position but the tape drive is not started, relay 3 is switched to the N position via inverted AND gate 17, AND gate 18, and AND gate 7.
When the tape drive is started (and switch 11 is thus in the L mode -- playback, tape start position) the relay 3 is switched to the L position via AND gate 19, OR gate 16 and AND gate 9. In addition 20 ms later relay 6 is energized to the playback position via AND gate 10 so that the two heads L₁ and L₂ are connected in series with the transformer coil 2.
In both the N and L modes of operation the start of each slant track has to coincide with the start of a field and hence phase control of the head drum 2 is required. This is accomplished by means of a phase comparator 20 which compares pulses from the pickup 13 with reference pulses from an outside reference source 21. The reference pulses could, for example, comprise the vertical synchronous pulses separated from the video signal. The output of the comparator 21 is fed to an amplifier 22 which feeds the drive motor 23 of the head drum 1.
A phase shifter 24 is provided between the comparator 20 and pickup 13 to compensate for tolerances of the apparatus. The phase difference corresponding to the angle α in FIG. 1 which occurs in the transition from N to L operation is compensated for via switch 25.
Usually, during recording, the servo control of the tape transport motor compares the frequency and phase of the actual values of a tachometer generator coupled with the transport shaft with reference values which generally are derived from the frame frequency and which are simultaneously recorded on the magnetic tape as a separate synchronization track. Here the control accuracy of the tape transport becomes greater, the larger the number of pulses which are delivered by the tachometer generator per revolution of the transport shaft. The previously mentioned conditions for the mutual spacing of the slant tracks recorded on the tape and the dependence of this spacing on line duration also applies analogously to L-operation. However, since in L-operation only every other field is recorded the track spacing, as measured in the lengthwise direction of the tape, must now correspond to an odd multiple of whole lines. The result is that the transport velocity of the magnetic tape in L-operation must not be exactly equal to one-half of that in N-operation, but may be somewhat greater or smaller.
In the present case with a track spacing in N-operation corresponding to 11 half-lines, a track spacing corresponding to five whole lines must therefore be chosen in L-operation, i.e., the speed of rotation of the transport shaft must be reduced in the ratio of 5:11. The frequency of the pulses delivered by the tachometer generator is thereby also decreased in the ratio of 5:11.
In order to carry out the switching of the speed between N- and L- operation as simply as possible and, also, by purely electrical means, the number of tachometer pulses per revolution of the transport shaft is chosen so that the tachometer pulse frequencies which occur at the desired speed of the magnetic tape in N- and L- operation are integral multiples of the frame frequency. If, therefore, Z is the number of tachometer pulses per revolution of the transport shaft, and if n_N and n_L are its speed of rotation in N- and L-operation, the following is to apply: Z ^. n_N = p . 25 and Z ^. n_L = q ^. 25,
where p and q are integral numbers and 25 Hz is the frame frequency. Since the ratio of the speeds of rotation is the same as that of the line numbers corresponding to the track spacings, therefore, in the example above n_N /n_L = 11/5 and p/q = 11/5.

FIG. 3 shows the circuit diagram of the transport shaft control and of the transport speed switching arrangement. For simplicity, only the recording operation is shown. Motor 26 drives the magnetic tape in the direction of the arrow via the transport shaft 27 and a rubber pressure roller (not shown). A tachometer generator is coupled to the transport shaft. This may consist of a ferromagnetic gear 29 and a pickup 30 which generates pulses in response to rotation of the gear. The tachometer pulses are fed via an amplifier 31 to a frequency comparator 32 and a switchable frequency divider 33. The time constant of an R-C circuit or the charging time of a capacitor can serve as the reference for comparator 32. Both of these can be adjusted by simple means via the double-throw switch 34 to the pulse frequencies coming from pickup 30 in N- or L-operation. A divider 33 divides the tachometer pulse frequency down to the frame frequency, where the division ratio can be changed by means of switch 35 from p:1 in N-operation to q:1 in L-operation. The actual frame frequency appearing at the output of divider 33 is phase-compared in comparator 36 with the reference frame frequency and the error signal so produced also serves as an input to control the frequency comparator 32.
The reference frame frequency is obtained in the frequency divider 37 by halving the vertical blanking frequency, which is separated from the video signal to be recorded and is fed to the terminal 38. This frame frequency is recorded at the same time on the tape 28 as the sychronization track 40 via the stationary magnetic head 39. The resulting error signal produced in 32 controls the motor 26 via the control amplifier 41.
With the numbers given above, the number of teeth of the ferromagnetic gear tachometer 29 can, for example, be chosen as 110. If the desired speed of rotation of the motor 26 is 750 RPM in N-operation, p = 55 and q = 25 for the divider 33.
The switches 34 and 35 shown in FIG. 3 can be ganged to operate together with the N/L switch 11. To prevent operating errors, it is advisable, however, to operate the switch 25 via the control logic rather than manually.
Thus in accordance with the above, the aforementioned objectives are effectively attained.

 PHILIPS VR2350 STEREO MATCH LINE  Device for the track following of rotating magnetic heads SYSTEM VIDEO2000.(DYNAMIC TRACK FOLLOWING)

1. Device for the track following of rotating magnetic heads (2, 3) in magnetic tape devices, in which piezoelectric elements (4, 5) are used as carriers of the magnetic heads, are clamped at one end firmly in a rotating holder and are connected at their deflectable end to the magnetic head, the free length (b) of the piezoelectric elements (4, 5) running at an angle to the joining line between assigned magnetic head and point of rotation of the rotating holder, to increase the deflection, characterized in that the free length (b) of the piezoelectric elements (4, 5) extends up to approximately level with the point of rotation and in that, to compensate for azimut errors, the piezoelectric elements (4, 5) are clamped into the rotating holder (1) at such an angle that the clamping lengths (a1 , a2 ) at the edges of the respective piezoelectric element are of different sizes. 

 

EINRICHTUNG F·UR DIE SPURNACHESHRUNG VON ROTIERENDEN MAGNETK·OPFEN PATENTANSPR·UCHE

1. Einrichtung f·ur die Spurnachf·uhrung von rotierenden Magnetk·opfen in Magnetbandger·aten, bei der als Tr·ager der Magnetk·opfe Piezoelemente verwendet sind, die an einem Ende fest in einer rotierenden Halterung eingespannt und an ihrem auslenkbaren Ende mit dem Magnetkopf verbunden sind, d a d u r c h g e k e n n z e i c h n e t , dass zur Erh·ohung der Auslenkung die freie L·ange (b) der Piezoelemente (4, 5) schr·ag zur Verbindungslinie (6, 7) zwischen zugeordnetem Magnetkopf (2, 3) und Drehpunkt (8) der rotierenden Halterung (1) bis etwa in der H·ohe dieses Drehpunktes verl·auft, und dass zur Kompensation von Azimutfehlern die Piezoelemente schr·ag (a1, a2) in die rotierende Halterung eingespannt sind.

2. Einrichtung nach Anspruch 1, d a d u r c h g e k e n n z e i c h n e t , dass die rotierende Halterung der Piezoelemente fest mit einem rotierenden Kopfrad (1) verbunden ist.

Description:

EINRICHTUNG F·UR DIE SPURNACHF·UHRUNG VON ROTIERENDEN MAGNETK·OPFEN BESCHREIBUNG Die Erf

indung betrifft eine Einrichtung f·ur die Spurnachf·uhrung von rotierenden Magnetk·opfen in Magnetbandger·aten, bei der als Tr·ager der Magnetk·opfe Piezoelemente verwendet sind, die an einem Ende fest in einer rotierenden Halterung eingespannt und an ihrem auslenkbaren Ende mit dem Magnetkopf verbunden sind.
Seit einiger Zeit werden beispielsweise in Videorecordern zur Spurnachf·uhrung Piezoelemente (in diesem Zusammenhang auch "Aktuatoren" oder Bimorphe" genannt) verwendet, an deren freischwingenden Enden die Magnetk·opfe befestigt sind. Die Piezoelemente weisen die Eigenschaft auf, dass sie beim Anlegen einer Spannung je nach Polarit·at in die eine oder andere Richtung ausgelenkt werden, so dass die Magnet k·opfe senkrecht zur Abtastrichtung bewegt werden k·onnen. Steuert man die Piezoelemente mit einer Regelspannung entsprechend dem Spurfehler an, so folgen die Videok·opfe genau den vorgesehenen Spuren.
An ihren anderen Enden sind die Piezoelemente fest in einen Piezoeiementhalter eingespannt, der entweder selbst rotiert oder starr mit dem rotierenden Kopfrad des Videorecorders verbunden ist. Die freischwingende L·ange des Piezoelementes ist ein Mass f·ur die erreichbare Kopfauslenkung.

Die Figuren 1 und 2 zeigen bekannte Anordnungen zur Spurnachf·uhrung in Videorecordern. Die Magnetk·opfe 2 und 3 sind an den freischwingenden Enden der Piezoelemente 4 und 5 befestigt (z. B. aufgeklebt). Die freischwingenden L·angen der Piezoelemente sind mit b bezeichnet. An ihren anderen Enden sind die Piezoelemente in einen Piezoelementhalter 1 eingespannt, der entweder selbst als rotierendes Teil ausgebildet oder mit dem rotierenden Kopfrad des Videorecorders starr verbunden ist. Die Einspannl·ange der Piezoelemente in die Piezoelementhalter ist mit a bezeichnet.
Neuere Trends in der Video technik f·uhren zu immer kleineren Kopf r·adern, was zur Folge hat, dass die freischwingenden L·angen der Piezoelemente und damit auch die erreichbare Kopfauslenkung immer kleiner wird.
Der vorliegenden Erfindung liegt deshalb die Aufgabe zugrunde, eine Einrichtung zur Erh·ohung der Piezoelementauslenkung zu schaffen, die sich insbesondere f·ur kleine Magnetbandger·ate eignet, billig ist und eine praktisch azimutfehlerfreie Wiedergabe der magnetisch aufgezeichneten Signale erm·oglicht.
Diese Aufgabe wird nach der vorliegenden Erfindung dadurch gel·ost, dass die Piezoelemente schr·ag zur Verbindungslinie zwischen zugeordnetem Magnetkopf und Drehpunkt der rotierenden Halterung bis etwa in die H·ohe dieses Drehpunktes verlaufen und dass die Piezoelemente zur Vermeidung von Azimutfehlern schr·ag in die rotierende Halterung eingespannt sind.
Die Vorteile der Erfindung liegen darin, dass insbesondere bei Magnetbandger·aten mit kleinen Kopfr·adern die freischwingenden L·angen der Piezoelemente und damit die erreichbare Auslenkung vergr·ossert wird.
Im folgenden wird ein Ausf·uhrungsbeispiel f·ur die vorliegende Erfindung mit Hilfe der Figur 3 n·aher erl·autert. Die Magnetk·opfe 2 und 3 sind an den freischwingenden Enden der Piezoelemente 4 und 5 befestigt. Die freischwingenden L·angen'der Piezoelemente sind mit b bezeichnet.
Durch die Anordnung der Piezoelemente 4, 5 schr·ag zur Verbindungslinie 6, 7 zwischen zugeordnetem Magnetkopf 2, 3 und Drehpunkt 8 der rotierenden Halterung 1 bis etwa in H·ohe dieses Drehpunktes wird die freischwingende L·ange jedes Piezoelementes vergr·ossert. An ihren anderen Enden sind die Piezoelemente in den Piezoelementhalter 1 eingespannt.
Diese Einspannung erfolgt im Gegensatz zum Stand der Technik schr·ag, um die sonst bei der Auslenkung der Piezoelemente zu erwartenden Azimutfehler der Magnetk·opfe zu kompensieren. Damit wird eine praktisch azimutfehlerfreie Wiedergabe der magnetisch aufgezeichneten Signale erm·oglicht. Die Einspannl·ange, unter der hier der Mittelwert der Strecken al und a2 verstanden wird, ist mit a bezeichnet.
Mit einer Anordnung nach der vorliegenden Erfindung wird erreicht, dass im Vergleich zum Stand der Technik bei sonst gleichen Bedingungen (insbesondere bei gleicher Regelspannung)die erreichbare Auslenkung der Piezoelemente vergr·ossert wird.
Die Erfindung ist nicht auf das vorliegende Ausf·uhrungsbeispiel beschr·ankt. Beispielsweise spielt es keine Rolle, welcher Art die Verbindungen zwischen Magnetkopf und Piezoelement sowie Piezoelement und Piezoelementhalter sind.

  PHILIPS VR2350 STEREO MATCH LINE  SYSTEM VIDEO2000 Scan tracking arrangement for videorecorders using piezoelectric elements. 

 1. Scan tracking arrangement in video recorders having a rotating head wheel, in which arrangement the magnetic heads are attached to piezoelectric elements and each head has a tape contact phase and a non-contact phase during one full revolution of the head wheel, and in which arrangement a voltage which holds the head on the intended track is applied to the piezoelectric element of a head which is in tape contact at that time, and in which arrangement a decaying alternating voltage for eliminating hysteresis effects of the piezoelectric element is applied ot the piezoelectric element of a head which is not in tape contact at that time, characterized by the following features : the decaying alternating voltage is rectangular and the frequency of the decaying alternating voltage for eliminating hysteresis effets of the piezoelectric element is just below the frequency of mechanical renonance of the piezoelectric element.

 

1. ANORDNUNG ZUR SPURNACHF·UHRUNG IN VIDEORECORDERN UNTER VERWENDUNG VON PIEZOELDIENTEN PATENTANS PRUCH Anordnung zur Spurnachf·uhrung in Videorecordern mit einem rotierenden Kopfrad, wobei die Magnetk·opfe an Piezoelementen befestigt sind und jeder Kopf w·ahrend einer Vollumdrehung des Kopfrades eine Bandeingriffphase und eine Nichteingriffphase hat, und wobei an das Piezoelement eines Kopfes, der gerade im Bandeingriff steht, eine Spannung angelegt wird, die den Kopf auf der vorgesehenen Spur h·alt, und wobei an das Piezoelement eines Kopfes, der gerade nicht im Bandeingriff steht, eine abklingende Wechselspannung zur Beseitigung von Hystereseeffekten des Piezoelementes angelegt wird, gekennzeichnet durch die folgenden Merkmale: : - die abklingende Wechselspannung ist rechteckf·ormig und - die Frequenz der abklingenden Wechselspannung zur Beseitigung von Hystereseeffekten des Piezoelemen tes liegt knapp unterhalb der mechanischen Reso nanzfrequenz des Piezoelementes.

Description:

ANORDNUNG ZUR SPURNACHF·UHRUNG IN VIDEORECORDERN UNTER VERWENDUNG VON PIEZOELEMENTEN BESCHREIBUNG Die Erfindung betrifft eine Anordnung zur Spurnachf·uhrung in Video
recordern mit einem rotierenden Kopfrad, wobei die Magnetk·opfe an Piezoelementen befestigt sind und jeder Kopf w·ahrend einer Vollumdrehung des Kopfrades eine Bandeingriffphase und eine Nichteingriffphase hat, und wobei an das Piezoelement eines Kopfes, der gerade imBandeingriff steht, eine Spannung angelegt wird, die den Kopf auf der vorgesehenen Spur h·alt, und wobei an das Piezoelement eines Kopfes, der gerade nicht im Bandeingriff steht, eine abklingende Wechselspannung zur Beseitigung des Hystereseeffektes des Piezoelementes angelegt wird.
Seit einiger Zeit werden in Videorecordern zur exakten Spurhaltung Piezoelemente (in diesem Zusammenhang auch "Aktuatoren" oder Eimorphe" genannt) verwendet, auf denen die Magnetk·opfe befestigt sind. Die Piezoelemente weisen die Eigenschaft auf, dass sie beim Anlegen einer Spannung je nach Polarit·at in die eine oder in- die andere Richtung ausgelenirwerden, so dass die Magnetk·opfe senkrecht zur Abtastrichtung bewegt werden k·onnen. Steuert man die Piezoelemente mit einer Regelspannung entsprechend dem Spurfehler an, so folgen die Videok·opfe genau den vorgesehenen Spuren.
Aus der europ·aischen Offenlegungsschrift mit der Publikationsnummer 0091 750 ist eine Anordnung zur Spursteuerung bekannt, bei der ein auf einem Piezoelement befestigter Magnetkopf w·ahrend der Bandeingriffsphase durch das Anlegen einer positiven oder negativen Gleichspannung an eine vorgegebene Stelle gebracht wird. Nach dem Abschalten dieser Gleichspannung am Beginn der Nichteingriffsphase kehrt die Kopf-Piezoelement-Einheit nicht wieder exakt in ihre Ausgangsposition zur·uck, da aufgrund des Hystereseeffektes im Piezoelement eine Restauslenkung verbleibt, die die Nullpunktlage der Kopf-Piezoelement-Einheit ver·andert. Demzufolge werden bei der n·achsten Bandeingriffsphase dieses Kopfes Spurfehler auftreten.
Um diese m·oglichst schnell auszuregeln, ·uberlagert man der an das Piezoelement angelegten Gleichspannung w·ahrend der Nichteingriffsphase eine abklingende sinusf·ormige Wechselspannung. Nach dem Abklingen dieser sinusf·ormigen Wechselspannung liegt am Piezoelement die Spannung an, die die jeweils geforderte Ablenkung des Magnetkopfes bewirkt.
Des weiteren ist aus der europ·aischen Offenlegungsschrift mit der Publikationsnummer 0091 764 eine Vorrichtung bekannt, die ebenso wie der Erfindungsgegenstand zur Spurregelung den Piezoeffekt ausnutzt.
Bei der bekannten Vorrichtung sind zwei um 180 Grad versetzte Magnetk·opfe an Piezoelementen befestigt, die ihrerseits fest mit dem Kopfrad verbunden sind.

Zur Vermeidung eines Spurfehlers bei im Vergleich zur Aufzeichnung unterschiedlicher Wiedergabegeschwin digkeit wird an die beiden Piezoelemente w·ahrend des jeweilyFn Bandeingriffs ein dreieckf·ormiges Spurkorrektursignal angelegt. W·ahrend des Nicht eingriffs beh·alt das Piezoelement und damit auch der daran befestigte Magnetkopf eine Restauslenkung, so dass auch bei dieser Anordnung die Nullpunktlage der Kopf Piezoelement-Einheit ver·andert wird, was am Beginn der n·achsten Bandeingriffsphase des Magnetkopfes zu einem Spurfehler f·uhrt.
Zur Vermeidung dieses Spurfehlers am Beginn der n·achsten Bandeingriffsphase wird dem Piezoelement w·ahrend der Nichteingriffsphase eine abklingende sinusf·ormige Wechselspannung zugef·uhrt, die die fehlerhafte Nullpunktlage der Kopf Piezoelement-Einheit beseitigt, d. h. die Restauslenkung des Kopfes r·uckg·angig macht, so dass der Kopf am Beginn der n·achsten Bandeingriffsphase genau die jewei1ige Soll-Spur ·ubereckt. Die bekannte Vorrich tung enth·alt weiterhin eine Umpolvorrichtung, die in Abh·angigkeit davon, ob das Piezoelement in die eine oder in die andere Richtung ausgelenkt wurde, d. h.
die Wiedergabegeschwindigkeit kleiner oder gr·osser als die Aufzeichnungsgeschwindigkeit war, dem Piezoelement eine geeignet gepolte Spannung zur Beseitigung von Hystereseefekten zuf·uhrt. Es zeigt sich also, dass der Versuch, die Hystereseefekte ohne Verwendung, einer Umpolvorrichtung f·ur die abkleme Weckselspannung zu beseitigen, noch keine zufried stellenden Ergebnisse bringt.
Ausgehend von diesem Stand der Technik liegt der vorliegenden Erfindung die Aufgabe zugrunde, eine verbesserte Anordnung zur Beseitigung von Hysterese- effekten einer Kopf-Piezoelement-Einheit zu schaffen, mit der auch ohne Verwendung einer Umpolvorrichtung die Hystereseefekte der Kopf-Piezoelement- Einheit vollst·andig beseitigt werden.
Die L·osung dieser Aufgabe erfolgt durch die kennzeichneneden Merkmale des Patentanspruchs.

Die Vorteile der Erfindung liegen nicht nur darin, dass die Videnkopfe am beginn ihrer n·achsten Bandeingriffsphase an ihrer Sollposition stehen, sondern in der mehrere auch darin dass eine Desensibilizierung der Piezoelment verwenden wird, also keine Verringerung der Empfindlichkeit gegen·uber der angeleg ten Spannung auftritt, was bei einem l·angeren Anlie gen einer Spannung (insbesondere einer hohen Gleich spannung) an einem Piezoelement der Fall sein k·onnte.
im folgenden wird die Erfindung an einem Ausf·uhrungs beispiel n·aher erl·autert. Dabei zeigen: Fig. 1 ein Blockschaltbild mit allen f·ur die Erfindung wesentlichen Bauteilen und Fig. 2 ein Diagramm, das die Verl·aufe der an die Piezoelemente angelegten Spannun gen als Funktion der Zeit zeigt.
Im Ausf·uhrungsbeispiel von Figur 1 wird dem Eingang A eines Microcomputers 1 eine auf bekannte Art und Weise erzeugte digitale, impulsbreitenvariable Regelspan nung zugef·uhrt, die eine genaue Auskunft ·uber die Ab weichung des jeweiligen Magnetkopfes von der Soll spurlage gibt. Eine detaillierte Beschreibung der Er zeugung einer derartigen Regelspannung kann beispielsweise der Zeit schrift "Grundig Technische Informationen" 3/81, S. 110 - 116, entnommen werden.
Der Microcomputer 1 erzeugt an seinem Ausgang B vom jeweiligen Betriebszustand (Aufzeichnung, Wiedergabe, Zeitlupe, Zeitraffer) abh·angige digitale Regelsignale f·ur die ?iezemente. Diese Regelsignale werden in einem Digital/Analog-Wandler 2 digital-/analog-gewan delt und zwei Schaltern 3 und 4 zugef·uhrt. Die ·Offnungs- und Schliesszeiten dieser Schalter sowie der Schalter 5 und 6 werden von den an den Ausg·angen C und D des Microcomputers 1 anliegenden Steuersignalen gesteuert. Der Schalter 3 ist immer dann geschlossen, wenn der am Piezoelement 1 befestigte Kopf im Bandeingriff steht.
Der Schalter 5 befindet sich w·ahrend dieser Zeitspanne in der Stellung b, so dass die am Ausgang des D/A-Wandlers 2 anliegende Regelspannung ·uber die Schalter 3 und 5 an das Piezoelement 1 weitergegeben wird und der am Piezoelement 1 befestigte Magnetkopf der durch die Regelspannung vorgegebenen Spur folgt.
Ist die Kopf-Piezoelement-Einheit 1 im Bandeingriff, dann befindet sich die Kopf-Piezoelement-Einheit 2 in ihrer Nichteingriffsphase. Diese Zeitspanne wird ausgenutzt, um dem Piezoelement 2 ·uber den Schalter 6, der sich hierbei in der Stellung b befindet, eine abklingende rechteckf·ormige Spannung von einem vom Microcomputer 1 gesteuerten Generator 7 zuzuf·uhren.
Damit wird eine eventuelle Restauslenkung des zugeharigen Magnetkopf es, die ihre Ursache in der Hysterese im Piezoelement 2 hat, vollst·andig beseitigt. Besonders wirkungsvoll ist gem·ass einem Merkmal der Erfindung die Beseitigung der Hystereseeffekte des Piezoelementes dann, wenn die Frequenz der angelegten Rechteckspannung knapp unterhalb der mechanischen Resonanzfrequenz (ungef·ahr 1 kHz) des Piezoelementes liegt, also beispielsweise in der Gr·ossenordnung von 700 Hz.
Hat der Magnetkopf 1 die Spur zuende gelesen bzw.
geschrieben, -so findet eine vom Microcomputer gesteuerte Kopfumschaltung statt. Jetzt wird eine am Ausgang des D/A-Wandlers 2 anliegende analoge Regelspannung durch den geschlossenen Schalter 4 und den Schalter 6, der sich in der Stellung a befindet, an das Piezoelement 2 weitergeleitet, so dass der am Piezoelement 2 befestigte Magnetkopf der ihm durch die Regelspannung aufgepr·agten Spur folgt.
Der Schalter 3 ist in dieser Phase ge·offnet. Gleichzeitig dazu wird dem Piezoelement 1 ·uber den Schalter 5, der sich in dieser Phase in der Stellung a befindet, eine abklingende Rechteckspannung von einem vom Microcomputer 1 gesteuerten Generator 8 zur vollst·andigen Beseitigung des Hystereseeffektes des Piezoelementes 1 zugef·uhrt, die eine eventuelle Restauslenkung der Kopf-Piezoelement-Einheit 1 beseitigt, so dass der Magnetkopf 1 am Beginn seines n·achsten Bandeingriffes an der richtigen Stelle steht.
Figur 2 gibt einen ·Uberblick ·uber

die an die Piezoelemente 1 und 2 angelegten Spannungen. Dabei entsprechen die Zeitintervalle [ t1, t2 ] , [ t3 > t4 ] > [ t5, t6 ] , den Bandeingriffsphasen der Kopf-Piezoelement-Einheit 1 und den Nichteingriffsphasen der Kopf-Piezoelement Einheit 2 und die Zeitintervalle [ t2, t3 ] [ t4, t5 [ t6, t7 ] , den Bandeingriffsphasen der Kopf-Piezoelement-Einheit 2 und den Nichteingriffsphasen der Kopf-Piezoelement-Einheit 1.
Die obengenannten Zeitintervalle, die f·ur die Beseitigung der Hystereseeffekte der Piezoelemente 1 bzw.
2 zur Verf·ugung stehen, liegen bei Verwendung von zwei um 180 Grad versetzten Magnetk·opfen im Normalbetrieb bei 20 msec. Es hat sich ·uberraschenderweise gezeigt, dass eine Beseitigung der Hystereseeffekte der Piezoelemente besonders wirkungsvoll ist, wenn die-Frequenz der Spannung zur Beseitigung der Hystereseeffekte knapp unterhalb der mechanischen Resonanzfrequenz der Piezoelemente gew·ahlt wird, die in der Gr·ossenordnung von 900 - 1200 Hz liegt, und eine abklingende Rechteckspannung verwendet wird. Bei der Wahl der Frequenz muss lediglich darauf geachtet werden, dass keine st·orenden Resonanzerscheinungen auftreten, d. h. dass die Frequenz nicht zu nahe bei der mechanischen Resonanzfrequenz der Piezoelemente liegt.
W·ahlt man beispielswelse 700 Hz, dann betr·agt die Dauer einer Schwingung 1,4 msec. In der zur Verf·u gung stehenden Zeitspanne von 20 msec. w·are somit eine Beseitigung der Hystereseeffekte mit ca. 14 Schwingungen m·oglich.
Der exakte Verlauf des Abklingvorganges (Verlauf der Einh·ullenden der abklingenden Rechteckspannung) richtet sich nach den physikalischen Eigenschaften des jeweils verwendeten Aktuatormaterials. Es ist in jedem Fall darauf zu achten, dass die Amplitude der letzten Rechteckschwingung hinreichend klein gew·ahlt wird.
Bei einigen neueren Entwicklungen im Videobereich (z. B. Kamerarecorder) werden immer kleinere Kopfr·ader verwendet und es liegt eine ·Uberumschlingung des Magnetbandes um das Kopfrad vor. Demzufolge werden die Nichteintauchphasen der Kopf-Piezoelement Einheiten und damit die zum Beseitigen der Hystereseeffekte zur Verf·ugung stehenden Zeitintervalle kleiner. Auch werden bei einigen neueren Trends die Zeitintervalle, in denen Spannungen (insbesondere Gleichspannungn) an den Piezoelementen anliegen, und/oder die Amplituden der an die Piezoelemente angelegten Spannungen gr·osser.
Dies kann eine Desensibilisierung der Piezoelemente gegen·uber der angelegten Spannung zur Folge haben, d. h. die Piezoelemente k·onnen dann, wenn ·uber einen l·angeren Zeitraum eine hohe Gleichspannung--an ihnen anliegt-, gegen·ubn der angelegten Spannung unempfindlich werden, so dass Spurfehler entstehen. Auch dieser Nachteil wird durch eine Beseitigung der Hystereseeffekte nach der vorliegenden Erfindung in vorteilhafter Weise vermieden.

PHILIPS VR2350 STEREO MATCH LINE SYSTEM VIDEO2000 Method for distortion-free still picture reproduction with magnetic video tape:

 A method for distortion-free still picture reproduction from magnetic video tape slant tracks wherein the tracks are recorded and scanned without any guard band therebetween by means of two video heads which rotate in a common plane with different azimuth angles. During still picture recording, two adjacent slant tracks are continuously or repetitively scanned by two rotating video hands which have different azimuth angles with one head displaced axially by one slant track width with respect to the other. During still mode reproduction, the two adjacent slant tracks are continuously scanned by mechanically deflecting the two rotating video heads by way of plungers following a ring. 

 1. A device for the recording, reproduction, and distortion-free reproduction of slant tracks recorded on magnetic video tape without any intermediate spacing between adjacent tracks, said device comprising: a drum; two video heads mounted in said drum and adapted to rotate in a common plane with different azimuth angles; a pair of spring leaves, each of said heads being mounted to one of said springs; a pair of plungers, each plunger having one end engaging one of said springs and an opposite end; and an axially adjustable ring mounted in said drum, said ring having an upper surface which rises linearly for half the width of a slant track about half its circumference and declines linearly over the remaining half of its circumference, said ring being adjustable between a first position out of contact with said plungers and a second position wherein said plungers' opposite ends engage said ring upper surface; and one of said plungers is shorter than the other of said plungers by the width of a slant track.

Description:

BACKGROUND OF THE INVENTION
The present invention relates to video recording and in particular to reproducing still pictures recorded along slant tracks on magnetic video tape.
When reproducing still pictures recorded on slant tracks on magnetic tape it is common practice to repeatedly scan the same slant track with the rotating head or heads. This is particularly true for the widely used devices wherein a field is recorded per slant track with two 180° offset video heads. The two video heads scan the same slant track in sequence and repeatedly. However, the signal-to-noise ratio with such devices is reduced when the magnetic tape is idle as compared to when the tape is moving since the scanning device of the video heads is not in conformity with the recorded tracks. This is illustrated in FIG. 1 wherein tracks 2 and 3 depict the tracks recorded (or scanned) by a video head when the tape is in motion and track 4 depicts a track recorded (or scanned) when the tape is stopped.
Heretofore, several proposals to eliminate the error resulting from the above have been proposed. For example, the angle of inclination of the total slant track cylinder may be changed so that the video heads follow the recorded tracks 2 and 3, even when the tape is idle. This is suggested in U.S. Pat. No. 3,375,331. French Pat. No. 2,107,066 suggests the vertical adjustment of the tape feed at the slant track cylinder. IBM Technical Disclosure Bulletin, June 1969, pages 33/34 suggests reciprocal movement of the video heads axially during each rotation of the head. Unfortunately, none of the above can be employed if for tape saving purposes, the slant tracks are recorded immediately adjacent to each other without any guard band and if they are recorded with different azimuth angles in order to eliminate cross talk. For example, a known device uses two video heads for recording and reproducing, wherein the azimuth angle of the gap of the one video head is 15° in clockwise direction and the azimuth angle of the gap of the other video head is 15° in counterclockwise direction. With this embodiment it is impossible to obtain a distortion-free still picture recording by means of repeated scanning of the same track, even if one of the above mentioned means for compensating for the differing angle between the scanning direction of the heads and the inclination of the recorded track is used.
In view of the above, it is an object of the present invention to provide a method to permit distortion-free still picture reproduction with such slant track devices, wherein adjacent slant tracks are recorded and scanned without a guard band therebetween and with different azimuth angles.

SUMMARY OF THE INVENTION
The above and other beneficial objects are attained in accordance with the present invention by providing a method for the distortion-free reproduction of slant track magnetic video tape wherein adjacent tracks, each containing a field, are recorded and scanned without any guard band therebetween by means of two video heads which rotate in a common plane with different azimuth angles. One of the video heads is displaced axially with respect to the other head by a distance equal to one slant track width of the magnetic tape.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:
FIG. 1 is a plan view of a length of magnetic tape having slant tracks immediately adjacent to one another recorded thereon;
FIG. 2 is a simplified schematic drawing of a mounting arrangement for video heads in accordance with the present invention;
FIG. 3 is a wind up of the ring of FIG. 2; that is, FIG. 3 sets forth the height of ring 13 as a function of angular displacement proceeding for a full 360° about the ring;
FIG. 4 is a block diagram of a circuit for carrying out the present invention electronically; and,
FIG. 5 is a waveform diagram of various outputs of the circuit of FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
In accordance with the present invention, an arrangement is provided to compensate for the different angles o

f the slant track when the tape is idle or moving. Reference is made to FIG. 2 wherein a first embodiment of the invention is depicted schematically. Two video heads 5 and 6 which differ in their azimuth angles are mounted on the head wheel 7 on spring plates 8 and 9. The video heads 5 and 6 are adjusted by screws 10 and 11 to their desired position, that is, so that they lie in a common rotational plane for the normal operation. A ring 13 is provided in the lower stationary slant track cylinder 12. Ring 13 can be shifted from the solid line position of FIG. 2 to the position of FIG. 2 as shown in the dotted lines, when the device is switched from normal picture reproduction to still picture reproduction. The ring 13 is divided, as shown in FIG. 3, so that its upper edge rises linearly through half its circumference. The amount of change, which is denoted by the letter "X" is equal to the width of a slant track on the magnetic tape. Plungers 14 and 15 engage the upper edges of ring 13. The distance "X" corresponds to an axial displacement of one track width taking into consideration the lever transmission on springs 8 and 9. Plunger 15 is shorter by the distance X than plunger 14. As a result, the video head 5 is displaced with respect to video head 6 by a complete track width when the ring 13 is displaced into the position indicated by the dotted lines. When rotating the head wheel 7 both video heads move axially in accordance with the upper edge of ring 13 and thereby follow the recorded tracks 2 and 3 of FIG. 1.

A circuit for carrying out the inventive method with purely electronic means is shown in FIG. 4. In this embodiment the axial adjustment of the one video head by one track width

and the subsequent axial guiding of both video heads in accordance with the recorded tracks is carried out in a commonly known manner wherein the video heads are mounted on electromechanical transducers, for example, piezoceramic elements. The control voltages for the piezoceramic must be obtained from the scanned video signals. Accordingly, the tracks must be provided with suitable signals which, on the one hand should not interfere with the chrominance signals, and on the other hand must be readable for a video head with the "wrong" azimuth angle. For these reasons only very low frequencies are used for the signal frequencies. The frequencies should be beneath the chrominance subcarrier.
In accordance with this embodiment of the invention, synchronizing pulses of the video signal are applied to the terminal 16 (see FIG. 4) and are separated in separator 17 and fed to a filter 18 which supplies constant line pulses. A voltage controlled oscillator 19 oscillates at a median frequency of, for example, 16 times line frequency, and synchronizes the line pulse received from filter 18 across the dividers 20, 21 and 22 through phase comparator 23. A further divider 24 is coupled to the inverting output of 20. The inverted and noninverted outputs of 21 and 24 are fed to a multiplexer 25 which multiplexes the outputs by approximately 90° with respect to each other in the sequence of D₁, D₂, D₃ and D₄ as shown in FIG. 5.
Vertical blanking pulses received from separator 17 are filtered in the filter device 26 (which separates the ver

tical signal) and are converted to regular frame signals in 27. The frame signals are fed to the multiplexer 25 (input A) and are also fed to divider 28, the output of which is also fed to the multiplexer (input B).
Multiplexer 25 operates as a quadruple converter and switches the D-voltages in series in accordance with logical orders from its A and B inputs. This is shown schematically in FIG. 5. The output voltage of multiplexer 25 is filtered in filter 29 and fed to the center top of switch 30. This voltage may then be fed to a terminal 31 through switch 30 and from there the output voltage is added to the frequency modulated video signal before recordation. Since each halfwave of voltage A corresponds to a field and thereby to a slant track, a voltage of quadruple line frequency is superimposed to the frequency modulated video signal and the phase of the superimposed signal changes from slant track to slant track by about 90°. Simultaneously, the divided frame pulses in 28 are fed to a pulse shaper 32 wherein they are converted as shown in FIG. 5 in such a manner that when they are added to the video signal across terminal 33, one or a plurality of follow up equalizing pulses in the vertical signal of the first field of every second frame is blanked out. In this manner each slant track is coded by virtue of the phase of the D-voltage which superimposes the frequency modulated video signal and the start of each second frame by gating the follow up equalizing pulses. The frequency of the code signals is lower than the frequency ranges for chrominance and brightness and is locked to the line frequency.
During the reproduction of a still picture, switch 30 is positioned with its center tap connecting with terminal W, switch 34 is closed and the scanned demodulated video signal is at terminal 16. The scanned frequency modulated video signal from which the code frequency is filtered out through band pass filter 36, is applied at terminal 35 and is fed to a phase comparator 38 through limiter 37. The vertical signals which are present at output 26 are tested in pulse comparator 39 by means of a time circuit to determine if follow up equalizing pulses are gated. If so, a reset (flip-flop) signal is fed to divider 28, so that in accordance with the sketch in FIG. 5 only phases D₁ and D₂ are discharged from the multiplexer 25 and fed to the comparator 38. The error signal of comparator 38 controls an amplifier 40, the output of which is fed to a terminal 42 across a switch 41. The electro-mechanical converters (which comprise, for example, piezoceramic elements which are not shown) are coupled to the terminal and the video heads are mounted to the piezoceramic. During recording, switch 41 is in position A and the electromechanical converters are fed with a constant bias, so that they rotate in a common plane.