PHILIPS VIDEO CASSETTE RECORDER VCR N1502 CHASSIS DECK INTERNAL VIEW.

The cassette deck is concerned with the physical mechanics of moving and scanning the tape.

The first item that should be mentioned in the picture below is the lacing motor. When a cassette is loaded into the VCR and the machine is switched on, it is this motor and it's associated mechanics which drag the tape out of the cassette housing and wrap it around the drum and guide posts by rotating the entire drum assembly 200 orso degrees clockwise. The guide posts, being on the inside of the tape, pull the tape out of the cassette as they themselves are pulled round the drum.

The main circular item at the top of the picture is the drum assembly. This is divided into two sections, one stationary and the other that rotates. The stationary part (The lower drum) is the part of the assembly which sets the lower position tape as it is played. It has a special high-precision guide called the "Ruler-Edge" which, with the guide posts, ensures that the tape is positioned in exactly the correct place to be scanned by the video heads on the upper-drum. The lower drum also has the end-of-tape sensor mounted on it. This, as the name suggests, stops the tape when it has reached the end of it's travel. It detects the end of the tape by means of a foil strip on the tape which shorts out two contacts as it passes the sensor. On top of the lower drum, is the rotating part (The upper drum). This has the video heads mounted on it 180 degrees apart. The video heads read the picture information as they scan the moving tape.

The capstan and pinch-wheel combine to pull the tape from the supply spool, past the video heads and audio / control heads and back onto the take-up spool. In the play and record modes, the take-up spool carrier has just enough torque to provide drive to take up the slack between the capstan and the take-up spool without actually dragging the tape through the mechanism itself.

Apart from the video heads, there are three more heads in the VCR. The full erase head on the left hand side erases the entire cross section of the tape before fresh audio and video are recorded. If this head is not working, then when a fresh recording has been made,vague images of the previously recorded program will be seen underneath the new recording. The audio and control heads are mounted on the same assembly on the right hand side of the VCR. The audio head records the sound on the bottom of tape and plays it back in the same way as an audio tape recorder. The control head records and picks up pulses to accurately control the position of the tape, and these are recorded on the top of the tape.

The idler on the bottom right of the picture is used to direct power from the motor to the take-up or the supply spools during fast forward or rewind.

The Servo Board (Hinged Up)

The servo board accurately controls the speed and position of the drum and the tape relative to one another during record and playback.

If the picture is to be free of noise bars and tracking-errors, it is imperative that the VCR knows exactly the speed and the relative position of the tape and the heads during record and playback. This is where the servo board comes in. The VCR employs a series of sensors to control phase-locked-loops which accurately set the position and speed of the tape and the heads. The modules in the picture control various aspects of this job and are switched in and out depending on the positions of the record and play switches. (These switches are mechanically linked to the play and record buttons on the front of the VCR).

The digital lock-in circuit makes sure the upper drum is rotating at the correct speed as quickly as possible after the VCR is switched on.

The FM Board (Under the Signals Board)

The FM processor board is mounted underneath the signals board on the right hand side of the N1700 / N1702 VCR. In playback it demodulates and processes the FM video signal which is supplied by the video heads via the video head amplifier. In record mode, the video signal is fed to the FM modulator and then passed as an FM signal to the video heads, again via the video head amplifier.

The FM processor board also contains a recycling drop-out-compensator (DOC). The blue delay line you can see at the bottom of the picture stores one line of video information, so in the event of a drop-out (loss of FM signal due to bad tape or clogged heads etc.), the last good line of video can be displayed instead of a white blip on the screen.

The Signals Board

The signals board is the most complicated board in the N1500 / N1502 VCR. It performs several tasks related to signal processing.

In record mode, the signals board takes an RF signal from the antenna socket, demodulates it using circuits very similar to most television sets, and converts it into it's component luminance (Y) signal and composite chrominance signals (C). The Y and C signals are then amplifies and processed before being passed to the video heads for recording on to the tape.

In playback mode, the signals board takes the signal from the head, recovers the seperate Luminance and Chrominance signals, demodulates them and then combines them to form a recognisable composite video signal. This signal is then modulated and sent out as an RF signal through the antenna socket to the television.

The antenna amplifier unit amplifies the RF signals coming in to the video recorder from the television aerial and then passes them to the RF output socket.

PHILIPS VIDEO CASSETTE RECORDER  VCR  N1502 TAPE DIVERTING DEVICE IN A TAPE RECORDER APPARATUS WITH DRUM SHIFT DURING TAPE ENGAGEMENT:

An apparatus for recording and/or playback of signals having a wide frequency spectrum carried on a tape carrier accommodated on a cassette. The cassette is provided with an opening across which the tape extends when not being played or not in an operative condition. The tape cassette is placed on the apparatus in a playback position on a supporting base. The apparatus has a cylindrically shaped drum mounted adjacent the cassette having its longitudinal axis at an angle to the axis normal to the principal plane of the cassette. A tape diverting device having a support member mounted for rotational movement about said drum and having at least one tape guide stud mounted thereon and projecting through the opening in the cassette when the cassette is placed on the apparatus for engaging the tape as the tape diverting device is rotated about the drum. Rotation of the supporting member of the tape diverting device will cause the tape guide stud to engage the tape and draw the tape out of the cassette and wind it, in a helical path, around the cylindrical surface of the drum to thereby place the tape in an operative position for playback in contact with transducer heads.

1. In an apparatus for recording and/or playback of signals having a wide frequency spectrum carried on a tape carrier accommodated in a cassette, said cassette having an opening across which said tape will extend when not in the operative playback condition, said apparatus comprising a base for supporting thereon said cassette, a drum having a cylindrical surface supported on said base adjacent said cassette, said tape being helically wound thereabout when in an operative position, a tape diverting device movable between an inoperative condition and an operative condition for engaging and drawing a portion of said tape out of said cassette and around part of said drum surface in a helical path, said device comprising a support member formed integrally with said drum and being arranged on said apparatus for pivotal movement about an axis of rotation which is parallel to the longitudinal axis of said drum and offset therefrom, said longitudinal axis of said drum being shifted from a position further from the cassette than the axis of said supporting member prior to moving the tape diverting device to the operative condition to a position closer to said cassette than the axis of said supporting member when said supporting member and drum have been pivoted about said supporting member axis and said tape has been wound about the surface of said drum, and at least one tape guide stud mounted on said support member, said stud projecting through said cassette opening when said cassette is placed in a position on said apparatus for playback, whereby said tape stud will engage said tape and draw said tape out of the cassette and wrap said tape about a portion of said drum as said support member is pivoted about said axis of rotation so that said tape will be wound about said drum in a helical path

2. The apparatus according to claim 1 further comprising a tape guide member located on said drum for guiding the tape along an edge thereof which faces said base of the apparatus, whereby the tape will bear upon said tape guide member when the cassette is placed on the apparatus with the tape diverting device in the inoperative condition, in which condition said tape guide stud will project through the opening of said cassette and

3. The apparatus according to claim 1 wherein said tape diverting device comprises two tape guide studs mounted on said supporting member, said studs projecting through said cassette opening for engagement with said tape when said cassette is placed on said apparatus, one of said tape guide studs engaging said tape for guiding the tape in one direction about said drum when said diverting device is rotated in that direction, the other of said studs engaging said tape in the same direction for maintaining said tape in a spaced relation between said first mentioned

4. The apparatus according to claim 1 wherein said tape is wrapped no more

5. The apparatus according to claim 1 wherein said axis of rotation about which said supporting member is pivoted is arranged normal to the principal plane of the cassette when the cassette is placed in the

6. The apparatus according to claim 5 wherein the axis of said drum is inclined at an angle to the axis normal to the principal plane of the

7. The apparatus according to claim 1 further comprising means for rotating said tape diverting device, means for driving said tape when said tape has been drawn out around said drum into the operative playback condition and means for engaging said tape when said tape is in the operative playback

8. The apparatus according to claim 7 wherein said means for rotating said

9. The apparatus according to claim 7 wherein said means for rotating said tape diverting device comprises a handle mounted on said support and

10. The apparatus according to claim 7 wherein said means for picking up

11. The apparatus according to claim 1 further comprising locking members mounted on said apparatus for locking said cassette in its playback position on the apparatus when said tape has been wound about said drum and means cooperating with said tape diverting device for actuating said

12. The apparatus according to claim 11 wherein said locking members operate to prevent further cassettes from being placed on the apparatus when said tape diverting device has been moved to the operative position.

13. The apparatus according to claim 12 wherein said locking members comprise a pair of bolts pivotally mounted on said apparatus, spring means attached to said bolts and link-members cooperating with said tape

14. The apparatus according to claim 1 further comprising means for preventing operation of said apparatus during the rotational movement of said tape diverting device, said apparatus being allowed to operate when said tape has been moved to an operative playback condition by said tape

15. The apparatus according to claim 14 wherein said means for preventing operation of said apparatus comprises a switch mounted on said apparatus, and projecting means mounted on said support member of said diverting device for engagement with said switch whereby said switch is closed to allow operation of the apparatus when said supporting member has been

16. The apparatus according to claim 15 further comprising means for terminating operation of the apparatus which may have been initiated at the beginning of the rotational movement of said tape diverting device.

17. The apparatus according to claim 16 wherein said means for terminating operation of said apparatus comprises a lever pivotally mounted on said apparatus for engaging the operative switches of said apparatus and projecting means mounted on said support member for engaging said lever and displacing said lever for returning said switches to their inoperative positions.

Description:

The invention relates to a tape recording and/or play-back apparatus. It is intended for use with signals having a wide frequency spectrum. In such a device a record carrier is accommodated in a cassette and can be brought out from the cassette and wound along a helical path around part of the cylindrical outer surface of a drum by means of a displaceable tape diverting device having at least one tapeguide stud. When the cassette is placed on the apparatus the tape guide stud projects into an opening in the cassette and engages a portion of the tape which extends in the region of the cassette opening. In such apparatus it has already been proposed to provide a tape diverting device with two tapeguide studs which are adapted to be displaced in a direction at right angles to the path of the tape in the cassette and which, with the tape wound about the drum, are located diametrically opposite one another laterally of the drum.

According to the invention, in an apparatus of the aforementioned kind, the tape diverting device is arranged so as to be pivotable along an arc of a circle away from the cassette, when the latter has been placed on the apparatus, about part of the drum, whilst during the pivoting movement of the tape diverting device the tape is engaged by the tape guide and is wound around the cylindrical outer surface of the drum. The steps according to the invention ensure a particularly simple and reliable construction which permits a satisfactory control of the tolerances in respect of the relative positions of the tape diverting device and the drum which have to satisfy stringent requirements.

The pivotal movement of the tape diverting device can be effected in a variety of manners. Advantageously the tape diverting device includes a support carrying the tape guide stud, which support is pivotable about an axis arranged at right angles to the principal plane of the cassette. It has been found to be particularly advantageous for the tape diverting device to be provided with a support which carries the tape guide stud and is pivotable about an axis extending in the same direction as the drum axis. In this case a particularly accurate construction is obtainable by designing the support and the drum as an integral unit adapted to pivot about the axis of the support. An arrangement which is particularly advantageous is obtained if, with the tape wound around the drum, the drum axis is closer to the cassette than is the pivoting axis of the tape diverting device.

Obviously, there are several manners in which the tape diverting device can be pivoted. For example, it may be effected by means of a separate control member which actuates the tape diverting device through a toothed gearing. It has proved advantageous to use a servo motor for pivoting the tape diverting device. A simple construction which is highly effective for operating the apparatus is obtained when the tape diverting device is pivoted by means of a handle having a part which extends above the drum and preferably acts as a cover for the drum.

An advantageous starting position for winding the tape around the drum and a particularly accurate winding operation is obtained if a tape guide arrangement is provided on the drum and is caused to bear the tape on the tape guide when the cassette is placed in the operative position.

Further, it has proved highly advantageous for the tape diverting device to have two tape guide studs which when the cassette is placed on the apparatus engage the tape. One of these studs, with the tape wound on the drum, guides the tape with respect to the drum, whilst the other stud holds the part of the tape travelling between the said one stud and the cassette spaced away from the drum and may, if required, divert the tape.

To obtain a high degree of reliability, the following features have been found to be of advantage. The first feature is that the on/off switch of the apparatus can be operated when the tape diverting device is pivoted. Further, the tape diverting device may operate a locking device which, with the tape wound around the drum, locks the cassette in its position on the apparatus. In this case the locking device preferably also acts to prevent cassettes from being placed on the apparatus when the tape guide stud has been pivoted towards the drum. Also, it has proved of advantage that when the tape diverting device is being pivoted, preferably at the beginning of its movement, any mode of operation of the apparatus can be stopped, for example by actuation of an automatic stop or by returning the mode switch to its inoperative position.

The invention will now be described more fully with reference to the accompanying drawings in which:

FIG. 1 is a top plan view and

FIG. 2 is a part sectional view, part side elevation of an apparatus in which the tape, which is accommodated in a cassette containing two coaxially arranged reels, is wound by means of a tape guide stud of the tape diverting device around the cylindrical outer surface of a drum for a part of the drum circumference equal to an arc of 120°;

FIGS. 3 and 4 show the two operative conditions of a tape diverting device having two tape guide studs, permitting the tape to be wound around the cylindrical outer surface of the drum through 180°;

FIGS. 5 to 8 show further modifications of the embodiment shown in FIGS. 3 and 4;

FIGS. 9 and 10 show the two operational positions of a tape diverting device similar to the embodiment shown in FIGS. 3 and 4 in which, however, only one tape guide stud is used; and

FIGS. 11 and 12 show diagrammatically a top plan view and a side elevation respectively of a tape diverting device having two tape guide studs, which is shown in the operative position co-operating with a tape cassette containing two tape reels arranged side by side in one plane.

Referring now to FIGS. 1 and 2, a cassette 1 is adapted to be placed on a base plate 2 of an apparatus. When the cassette is placed in position the tape reels 3 and 4, which are coaxially arranged in the cassette one above the other, are coupled with winding spindles 5 and 6 respectively of the apparatus. The drive of the tape 7 is effected in a conventional manner by means of a capstan 9 which projects into an opening 8 in the cassette and engages the tape and to which a pressure roller 10 can be urged. The two Figures show the arrangement in the operative condition in which the pressure roller has been pivoted into engagement with the capstan. The tape is brought out from a shorter side 11 of the cassette at the level of the lower reel 4, travels past, for example, two magnetic heads 12 and 13, subsequently reaches a tape guide stud 14 and then is helically wound around a drum 15 and finally re-enters the cassette at the shorter side 11 at the level of the second reel 3 along a path parallel to that of the tape part leaving the cassette.

The drum 20 is mounted on a support 15 secured to the base plate 2, the drum axis 17 being inclined at an angle to the normal to the main plane of the cassette, so that in known manner the tape is caused by the co-operation of the drum with the tape guide stud 14, which in this embodiment is conical and is inclined at an appropriate angle to the drum to be wound around the cylindrical outer surface of the drum along a helical path, in this embodiment through an angle α of 120°. At the area at which the tape is wound around the drum the signal recording takes place by means of a magnetic head assembly rotating within a gap 18 in the drum.

It is an object of the present invention to provide a tape diverting device 19 which enables a tape to be guided from the cassette into the afore-described operative position in a simple manner but with a high degree of accuracy. For this purpose the tape diverting device 19, which carries the aforementioned tape guide stud 14 by means of a support 20, is arranged so as to be pivotable in an arc of a circle away from the cassette placed on the apparatus and about part of the drum. In this embodiment the support 20 comprises an annular member which is adapted to pivot about the pedestal 16 and which is guided so as to pivot about an axis 23 normal to the principal plane of the cassette by means of a plurality of tags 22 which are arranged along the circumference of the annular member and project into a slit 21 in the pedestal.

In the inoperative position of the tape diverting device the tape guide stud is in a position 14' shown by broken lines in FIG. 1. When the cassette is placed on the apparatus the tape guide stud enters and opening 24 in the casette and engages the part 7' of the tape adjacent the said opening and shown by broken lines in FIG. 1. When the tape diverting device is pivoted in the direction indicated by an arrow 25 in order to take up the operative position shown in FIGS. 1 and 2, the tape guide stud 14 engages the tape 7 and winds it around the cylindrical outer surface of the drum so that it occupies the desired travelling position. Since this movement is performed along a circular path around the drum, the tape is wound along the required path around the cylindrical outer surface of the drum with a high degree of accuracy, which is of great importance for such an apparatus. This is ensured in particular by the fact that with such a construction the relative positions of the tape diverting device and the drum can be accurately controlled.

To enable the pivoting movement of the tape diverting device the support 20 is provided with teeth along its circumference which mesh with a pinion 26 which advantageously can be driven by a servo-motor, not shown, arranged to be switched by an operating member of the apparatus. A ball detent 27 provided on the support 20 determines the inoperative and operative positions of the tape diverting device. Obviously, the pivoting movement of the support 20 may be performed in a different manner, for example, by means of a toothed rack actuated by an operating member or by means of a rope or chain.

In

the embodiment shown in FIGS. 3 and 4 the support 20 of the tape diverting device 19 is arranged to pivot about an axis 23 parallel to the drum axis 17. The two axes, which are inclined at an angle to a normal to the principal plane of the cassette, are shown symbolically by crosses in the Figure. The two axes are parallel but spaced so that the drum 15 is arranged eccentrically with respect to the support 20. Advantageously the support 20 and the drum 15 form an integral structure arranged to pivot about the axis 23 of the support. As will be seen from FIG. 4, which shows the tape diverting device in its operative condition, the relative positions of the two axes 17 and 23 are chosen so that with the tape wound around the drum the drum axis is closer to the cassette than is the pivoting axis of the tape diverting device. This ensures that when the tape diverting device 19 is pivoted in the direction of the arrow 25 from the inoperative position shown in FIG. 3 into the operative position, the drum follows this pivotal movement and engages the tape so that the tape is securely wound around the drum, especially in the case in which the drum is provided with a tape guide for the tape edge facing the base plate, as will be described more fully hereinafter. By arranging the drum close to the part of the tape in the inoperative position of the tape diverting device and by the fact that the drum moves into the path of the tape when the tape diverting device is pivoted, a particularly compact construction is obtained.

In the embodiment under consideration the tape is to be wound around the drum through 180°. For this purpose the tape diverting device has two tape guide studs 14 and 28 which when the cassette is placed on the apparatus engage the tape. Stud 14 guides the tape with respect to the drum, whilst the other stud (18) maintains the tape travelling between the first-mentioned tape guide stud 14 and the cassette spaced away from the drum. The aforementioned choice of the axis 17 and 23 of the drum and the tape diverting device ensures, as is shown in FIG. 4, that in order for the tape to be wound around the drum through 180°, owing to the movement of the drum into the path of the tape a pivotal movement of the tape diverting device through an angle of less than 180°, namely of about 165°, is required, which is advantageous for the operation of the arrangement.

Obviously, with respect to the choice of the relative positions of the axes 17 and 23 many modifications of the embodiment described are possible, one of which will be described, by way of example, with reference to FIGS. 9 and 10. In this embodiment, the drum moves into the path of the tape through a greater distance and the tape is wound around the drum through 180° by means of a single tape guide stud 14.

Returning to the embodiment shown in FIGS. 3 and 4, some further advantageous features will now be mentioned. The support 20 of the tape diverting device is formed with a projection 29 by means of which the on/off switch 30 of the apparatus can be operated in a manner such that in the inoperative position of the tape diverting device the switch is open. This ensures that in the inoperative condition of the tape diverting device, in which condition a cassette can be placed in the apparatus, no mode of operation of the apparatus can be initiated, thus preventing the tape from being damaged. Obviously it may be ensured in known manner that it is impossible to place a cassette on the apparatus when the pressure roller is urged to the capstan.

In order to avoid damage to the tape during the pivotal movement of the tape diverting device, advantageously any mode of operation of the apparatus which is being performed will be stopped when the tape diverting device is pivoted, preferably at the beginning of this movement. For this purpose the support 20 of the tape diverting device is formed with a further projection 31, which, when the tape diverting device is pivoted from its inoperative position, briefly displaces lever 32, which in turn displaces a holding bar 33 into which mode switches 34, 35 and 36, for example for advance, fast forward and fast return of the tape respectively, snap in known manner in their closed positions so that, when the tape diverting device is pivoted, any mode switch which may be in the closed position returns to its open position. The lever 32 is so disposed relative to the support 20 that at the beginning of the pivotal movement of the tape diverting device from the operative position to the inoperative position the aforementioned projection 29 for operating the on/off switch also operates the lever 32, so that in this case also any switched-in mode is switched out. Obviously, switching out the modes may be effected in a different manner, for example, by the lever 32 operating a conventional automatic stop.

An apparatus equipped with a tape-diverting device according to the embodiment shown in FIGS. 3 and 4 is schematically shown in top plan view in FIG. 5

with the tape diverting device in the inoperative position and in FIG. 7 with said device in the operative position, FIGS. 6 and 8 showing corresponding sectional views taken on the lines VI -- VI and VIII -- VIII respectively. In this embodiment there is provided for pivoting the tape-diverting device 19, which forms an integral structure with the drum, a handle 37 which has a part 38 which extends as a cover above the drum and is connected to the support 20 of the tape diverting device by a brace 39 extending along the side of the drum. The support 20 is formed with a groove 40 into which lugs 41, secured to the apparatus project, so that the support is pivotable. Thus the handle for pivoting the tape diverting device at the same time forms a cover capable of fitting into the cover plate 42 of the apparatus.

The cassette 1 can be inserted into an opening 43 in the cover plate 42, in which position the tape guide studs 14 and 28 engage the tape. In order to wind the tape around the drum the handle 37 must simply be pivoted through an angle of about 165°. To lock the cassette in its position on the apparatus in this operative condition of the tape diverting device, a locking arrangement 44 is provided which can be operated by the tape diverting device. This locking arrangement comprises two bolts 46 which are pivotably mounted one on either side of the opening 43 and are acted upon by springs 45 and which are linked to a system of levers 47 supported by the edge of the part 38. Since when the tape diverting device is pivoted the edge of the part 38 performs an eccentric movement, the bolts can be operated by means of the lever system. As FIGS. 5, 7 and 8 show, in the inoperative condition of the tape diverting device the bolts have been pivoted out of the area of the opening 43, so that a cassette can be inserted, but in the operative condition of the tape diverting device they engage the top of a cassette which may be accommodated in the opening 43 and thereby lock it in position. At the same time this locking arrangement prevents the insertion of a cassette when the tape diverting device is in its operative condition, since the bolts will then project into the opening.

As FIGS. 5, 6 and 7 show, the drum 15 is in known manner provided with a tape guide member 48 in the form of a strip which is helically wound around the drum and guides the tape along the edge which faces the base plate 2. In the inoperative condition of the tape diverting device this tape guide member is located just within the range of the tape part 7 which extends in the opening 24 in the cassette, so that when the cassette has been placed on the apparatus the tape engages the guide member. As a result, when the tape is wound around the drum this guide member ensures accurate positioning.

In the embodiment shown in FIGS. 11 and 12 the cassette 1 contains tape reels 3 and 4 arranged side by side in a single plane. The tape diverting device 19 and the drum 15 have a common axis 49 which is inclined at an angle to the normal to the principal plane of the cassette, in other words, the axes of the drum and the tape diverting device designated 17 and 23 hereinbefore coincide. The tape diverting device again comprises a support 20, which in this embodiment is arranged to pivot about the drum, which is rigidly secured to the apparatus, and is provided with two tape guide studs 14 and 28. In FIG. 11 the positions which the tape guide studs occupy in the inoperative condition of the tape diverting device and the path along which the tape travels in this condition are shown by broken lines.

In the operative condition of the tape diverting device the tape guide stud 28 and the tape guide stud 14 are required to divert the tape, and the stud 28 also maintains the tape part between and the cassette and the tape guide stud 14 spaced away from the drum. The tape guide studs divert the tape leaving the cassette to a higher level, after which the stud 14 guides the tape tangentially towards the drum, around the cylindrical outer surface of which it describes a helical path through an arc of 180°, and the tape finally re-enters the cassette at the same level at which another part of the tape leaves the cassette and parallel to this part. For this purpose the tape guide studs have been given suitable conical shaped and are skewed to one another and to the drum axis.

Although in the embodiments shown the axis of the drum (15) is inclined at an angle to the normal to the principal plane of the cassette, this is not necessary, but embodiments of the apparatus according to the invention are possible in which the axis of the drum is normal to the main plane of the cassette and the tape is caused to be helically wound around the drum by appropriately designed tape guide studs.

 

PHILIPS VIDEO CASSETTE RECORDER  VCR  N1502 Device for extracting and positioning video tape from a cassette to around a slit head drum:

 A tape extraction apparatus for wrapping magnetic video tape from a two spool cassette to span helically and at least 360° circumferentially around a slit head drum. The apparatus has an upper and a lower kidney-shaped pair of arcuate grippers driven in arcuate paths pushing the tape out of the cassette around the head drum. In the end position around the head drum, the upper gripper rests on the lower. A clamping device holds them in position. A mechanism for driving the grippers is disclosed.

 1. An apparatus for the recording and reproduction of signals, particularly video signals, on a magnetic tape (16) which is disposed in a cassette (1) on spools (11, 12) which lie concentrically one above the other, and having means whereby it is adapted to be laid, in two loops moving in opposite directions towards one another, against the periphery of a slit head drum (35), in which at least one magnetic head rotates, comprising a tape extraction device having a pair of grippers (38, 39) initially positioned within the cassette on the side of the tape remote from the drum, said device being mounted on a chassis plate, said grippers (38, 39) being disposed in different planes in their end position in which the magnetic tape (16) spans helically and contacts over an angle of at least 360° circumferentially around the head drum (35), the head drum having means whereby it is obliquely adjustable in relation to the chassis plate, one of said grippers being an upper gripper and said upper gripper (38) being in the form of an arcuate tape guide body and being disposed at a greater normal distance from the chassis plate (50), and having an upper edge (40) for positioning the upper edge of the tape, and the other gripper being a lower gripper (39) being disposed at a lesser normal distance from the chassis plate and being likewise in the form of an arcuate tape guide body and having a lower guide edge (41) for positioning the bottom edge of the tape, the vertical height of each gripper (38, 39) is slightly greater than the width of the magnetic tape (16), said upper gripper (38) in said end position being supported by a portion of its lower edge on a portion of the upper edge of the lower gripper (39), and the horizontal length of said tape guide bodies defined by said grippers (38, 39) holds at a distance from the periphery of the head drum the tape loops guided towards and away from the head drum (35).

2. An apparatus according to claim 1, wherein said the tape guide bodies formed by said grippers (38,39) have a curvature in the direction of their length, and are at least partly kidney-shaped in plan view.

3. The apparatus according to claim 2, wherein said tape guide bodies formed by said grippers (38,39) have a cylindrical surface on their tape guide surface which in the end position faces the head drum (35), which cylindrical surface merges into a deflecting surface rounded roughly in kidney shape in order to divert the magnetic tape from the periphery of the head drum.

4. The apparatus according to claim 3, wherein said the grippers (38,39) each have at least one vertically disposed cylinder (44) and/or a roller which is connected to the other vertical tape guide surfaces of the grippers (38,39).

5. The apparatus according to one of claims 1-4, wherein said grippers (38,39) are provided with equalizing slopes which on the extraction of the tape project beyond the otherwise vertical tape guide surfaces of the grippers, projecting progressively downwards starting from the top guide edge on said upper gripper (38), and progressively upwards starting from the bottom guide edge on said lower gripper (39), and that the equalizing slopes, formed by equalizing springs (87,88) are drawn back again behind the tape guide surfaces of the grippers in the end position.

6. The apparatus according to one of claims 1-4, wherein said grippers (38, 39) are supported in the end position against a stop pin (93) on the side of the head drum remote from the cassette and which projects upwards from said chassis plate (50).

7. The apparatus according to claim 6, further comprising there is additionally provided a clamp lever device (90) having two locking levers (94,95) pressing the grippers (38,39) from outside onto the stop pin (93) on operation of the record or playback function.

8. The apparatus according to claim 7, wherein said clamp lever device (90) additionally has a clamp plate (98) which is coupled to said locking levers (94,95) and which on operation of the record or playback function presses horizontal stop surfaces (99,100) of said grippers (38,39) from above onto said chassis plate (50).

9. The apparatus according to claim 1, wherein the guide path of each gripper (38,39) during its movement, starting from its position in an appertaining cutout (36,37) in the cassette (10) and as far as the head drum (35), first has a tangential path element, an adjoining curved path element, and finally a path element, which adjoins the curved path element, for applying the magnetic tape (16) against the periphery of the head drum and directed radially in relation to the head drum (35).

10. The apparatus according to claim 9, further comprising in the guide path of said upper gripper (38) there is provided on the chassis plate (50), in the region of the transition from the curved to the radial path element, a slide lifter (48) which has a vertical height gradually increasing to a maximum in the direction of movement and then decreasing again, and by which said upper gripper (38) is guided above and at a distance from said lower gripper (39) with a lift height corresponding to the maximum.

11. The apparatus according to claim 10, wherein said grippers (38,39) engage crossingly one over the other by their tape guide surfaces in their extracted end position, so that the bottom tape loop is guided by said lower gripper (39) and the lower face of said upper gripper (38), and the top tape loop is guided by said upper gripper (38) and the upper face of said lower gripper (39).

12. The apparatus according to claim 1, wherein each gripper (38,39) is disposed at the front end of a rocking lever (51,52;76,77) whose rocking axis (72;78,79) lies in the region of the other end of the rocking lever and is guided in a straight guide (73) parallel to the tape extraction device each rocking lever having so as to form a lever arm in relation to the rocking axis (72;78,79), a guide pin (80,81) guided along a curved guide path (82,83).

13. The apparatus according to claim 12, wherein the curved guide path (74) is in the form of a rail or curved slot (82,83).

14. The apparatus according to claim 13, wherein the curved slots (82,83) are disposed in said chassis plate (50), said guide pins (80,81) are guided in the curved slots at the rear end of the rocking levers (76,77) which at their front end carry said grippers (38,39), the rocking axes (78,79) of said rocking levers (76,77) lie approximately in the center between the two ends of these levers and are carried by a slide plate (55), and said slide plate is guided for sliding in slide rails (75) provided on the chassis plate parallel to the tape extraction direction.

15. The apparatus according to claim 14, further comprising a bow spring (84) fastened by one end to said chassis plate (50) and by its other end to said slide plate (55) and has a length such that in the two end positions of the sliding movement of said slide plate said guide pins (80,81) are pulled or pressed under the action of said bow spring (84) to the ends of curved slots (82,83).

16. The apparatus according to one of claims 9 to 15, further comprising a drive means for driving the tape extraction device comprising a rack frame (55), in the form of a slide plate having two racks (56,57) which are disposed parallel to the tape extraction device and are spaced apart from one another by a distance which is greater than the diameter of a continuously rotating gear (59) which is associated with them as driver and which can be selectively brought by a jump spring system into engagement with one or the other of the racks and at the ends of the rack opening (58), which is formed by the two racks (56,57), runs in each case from the rack in engagement with it into a widened cut-out in which it remains out of engagement with both racks until the jump spring system is operated again.

17. The apparatus according to claim 1, wherein the spools (11,12) of the cassette (10) are each provided with a tape plate (13,14) which on its periphery is formed as a gear and is associated with a driving gear (21,22) which through a cutout (17,18) in a side surface of the cassette (10) can be brought into driving engagement with the tape plate (13,14).

18. The apparatus according to claim 17, wherein the drive gears (21,22) for the upper tape plate (13) and the lower tape plate (14) are mounted with their driving spindles (19,20) on a common rocking lever (27) which for the purpose of adaptation to different sizes of cassette (10,10') is arranged for rocking about the vertical axis approximately in the middle of a side surface of the cassette.

19. The apparatus according to claim 1, wherein the head drum is fastened on a carrier plate (60) which has four-point mounting and which in one bearing point is pressed by a pressure spring against said chassis plate (50), in two other bearing points is pressed away from said chassis plate, and in a fourth bearing point is provided with an adjusting screw (68) for adjusting the inclination of the head drum axis (61).

20. The apparatus according to claim 19, wherein said bearing points are distributed around the periphery of the head drum (35).

Description:

BACKGROUND OF THE INVENTION
The invention relates to an apparatus for recording and reproducing signals, particularly video signals, on a magnetic tape which is disposed in spools lying one above the other concentrically in a cassette and is adapted to be laid by a tape extracting device with a pair of grippers engaging behind the magnetic tape, in two tape loops running towards one another in opposite directions, against the periphery of a slit head drum in which at least one magnetic head rotates.
For the recording of picture signals and their reproduction on a magnetic tape, many diverse methods and apparatuses are known. The methods can be divided into longitudinal, transverse, and inclined trace recording. In longitudinal trace recording, the tape feed or speed is equal to the scanning speed. In order to achieve adequate playblack times for a predetermined length of magnetic tape the scanning speed must be kept low. However, the attainable upper frequency limit and consequently the quality of the television picture are thereby impaired. The process is therefore not suitable for small, inexpensive video recorders. In the transverse trace method the video signal is recorded in transverse tracks lying side by side. Although the tape speed is reduced in this process, nevertheless it is not possible to accommodate a television frame on a transverse track. The transverse trace method can therefore be put into practice technically only at great expense and is consequently also out of the question for inexpensive video recorders. Thus only the inclined trace method remains for such recorders.
The inclined trace or helical scan method has a number of advantages, which particularly affect the construction of inexpensive video recorders. These advantages include the low tape speed, which is between 4.75 and 19.05 centimeters per second, the good utilisation of the tape by means of inclined tracks, since an inclined track can accommodate an entire television frame, and also the relatively low electronic expense for the magnetic head and magnetic tape servo control. Finally, the good picture quality which can be achieved is also not to be ignored.
In order to achieve the necessary high relative speed between the magnetic head and the magnetic tape, the video heads rotate on a head disc inside a slit head drum around which the magnetic tape is slung helically. The video heads extend about 50 microns over the periphery of the head drum. The tape traction ensures good contact between the magnetic tape and the magnetic heads.
The speed of rotation of the head disc depends on the number of magnetic heads. In two-head systems, the head disc must rotate at 25 revolutions per second, and in single-head systems at 50 revolutions per second (in the NTSC system 30 and 60 revolutions per second respectively).
In addition to the number of video heads and the width of the magnetic tape, the angle of contact of the magnetic tape around the head drum is also of decisive importance for the functioning of the apparatus. In this respect a distinction is made between alpha-wrap covering 360° and omega-wrap covering slightly more than 180°. In the case of 360° wrap of the head drum only one rotating magnetic head is required. The track recorded by it contains a complete television picture, so that a stationary picture can also be scanned with good picture quality. It is however extremely difficult to achieve 360° wrap of the magnetic tape around the head drum. This difficulty is even greater when a video recorder has to work with cassettes. It is true that numerous tape extraction devices for cassette video recorders are already known. None of these however is able to lay the magnetic tape around the periphery of the head drum over an angle of 360° or more. Techniques known from spool apparatus cannot be applied to cassette apparatus. In addition, they are usually expensive.

SUMMARY OF THE INVENTION
The problem underlying the invention is therefore that of supplementing the apparatus of the kind first defined above by an inexpensive and simple tape extraction and guide device which can be used in a simple, small video recorder which works with cassettes and can apply the single-head inclined trace method with 360° wrap.
As a solution according to the invention it is proposed that at least in their end position, in which the magnetic tape is wrapped helically over at least 360° around the head drum adjusted obliquely to the plane of the apparatus, the grippers are disposed in different planes, that the upper gripper, which is in the form of a tape guide member and disposed at a greater distance from the chassis plate, should have a guide edge for the upper edge of the tape and the lower gripper, which is likewise in the form of a tape guide member, should have a guide edge for the lower edge of the tape, that the vertical height of each gripper should be slightly greater than the width of the magnetic tape, that in the end position the upper gripper should be supported by its lower side on the upper side of the lower gripper, and that the horizontal length of the tape guide members formed by the grippers should hold the tape loops, which are guided to and from the head drum by means of the grippers, at a distance from the periphery of the head drum.
It can be seen that the grippers used here are tape guide bodies which in their end position, in which they bear against the magnetic tape on the periphery of the head drum, mutually overlap in different planes and during playback and recording themselves press the magnetic tape against the periphery of the head drum. The angle of wrap thus achieved amounts to more than 360°, usually about 390° to 400°. Because of the length of the grippers those tape loops which make the connection between the tape loop guided around the head drum and the spools in the cassette are nevertheless held at a distance from the head drum. Because of the manner in which the tape is guided on the grippers, which in their end position are supported on one another, accurate positioning of the magnetic tape is in addition achieved with simple means. The entire tape extraction device is situated under the cassette trough or grouped around the head drum on the chassis plate. Despite the simple construction, which provides a good picture quality, a very compact construction of the video recorder is also achieved thereby. With simple, inexpensive means it has therefore been made possible to use the single-head inclined trace method with a 360° angle of wrap around the head drum in a video cassette recorder. Further details of the invention are explained more fully in the following description of the drawings and in the patent claims.

BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be explained more fully below with the aid of some examples of embodiment which are illustrated in the drawings, in which:
FIG. 1 shows diagrammatically a section through the cassette with laterally disposed drive spindles,
FIG. 2 is a plan view of the embodiment shown in FIG. 2.
FIG. 3 is a view similar to FIG. 2, the gear drive of the spindles being shown more clearly,
FIG. 4 shows diagrammatically a plan view similar to FIGS. 2 and 3 in order to show the compatibility of the drive system with different sizes of cassettes,
FIG. 5 is a plan view of two drive spindles combined on a single rocking lever,
FIG. 6 is an elevation for more detailed explanation of the drive spindle arrangement shown in FIG. 5,
FIG. 7 is a plan view of a cassette with tape guide elements at the tape outlet points,
FIG. 8 is an end view of the cassette shown in FIG. 7,
FIG. 9 is a partial view, corresponding to FIG. 7, with a different form of construction of a tape guide element,
FIG. 10 shows on a larger scale an elevation of a tape guide element according to FIG. 9,
FIG. 11 is a cross-section through the tape guide element shown in FIG. 10,
FIG. 12 is a section through a corner of a cassette with tape guide elements in the form of conical surfaces,
FIG. 13 shows in side view a tape guide element in the form of a slide body disposed in a cassette cutout,
FIGS. 14a to 14f show in side view a tape extraction device with a bottom gripper, in perspective two grippers disposed one above the other in the end position, a top gripper in side view, another form of construction of a gripper consisting of two cylinders, shown in side view, a plan view of this form of construction, and a plan view of the cassette inserted into the apparatus and of the head drum in various relative positions of the grippers and of the tape in relation to the cassette and the head drum,
FIGS. 15a and 15b are elevations of the grippers, respectively in their end position shown in FIG. 14b and before this end position is reached,
FIG. 16 shows a form of construction of the mechanism for guiding the grippers,
FIGS. 17a, 17b, and 17c show diagrammatically an elevation of the head drum with adjusting device, a plan view, and a section respectively,
FIGS. 18a and 18b show diagrammatically an indication of the track path for correct and incorrect adjustment of the latter respectively,
FIG. 19 shows another example for the guide mechanism of the tape extraction device,
FIG. 20 another example of a guide mechanism for the grippers,
FIGS. 21 to 24 show another example of construction of the guide mechanism of the tape extraction device in various operating positions, and
FIGS. 25 and 26 show two views in perspective of the tape extraction device with the tape partially and completely extracted.

DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 shows a cassette 10 in which two spools 11 and 12 are disposed coaxially one above the other, these spools both having a tape plate 13, 14 and being mounted by their hubs on a common spindle 15 supported by the cassette. A magnetic tape 16 is guided from one spool to the other by means of suitable guide rollers and grippers.
The front side of the cassette 10 is open or provided with a hinged lid which opens automatically when the cassette is inserted into the apparatus. In addition, the cassette is provided in another side wall with cutouts 17,18 through which drive gears 21,22 mounted on drive spindles 19,20 (FIG. 6) are introduced into the cassette 10 and brought into engagement with tape plates 13,14 formed as toothed discs by teeth provided on their periphery. For the actual driving of the tape there are provided a tape drive shaft 23 and a rubber pressure roller 24, which is mounted, for swivelling about an articulation point 26, on a lever 25 on the other side of the magnetic tape 16, opposite the tape drive shaft 23. The tape drive shaft 23 and the rubber pressure roller 24 can also be inserted into the cassette through corresponding cutouts in the bottom and side wall of the cassette respectively. Details of the guiding of the tape and of the tape drive by means of the tape drive shaft 23 and the rubber pressure roller 24 are familiar to the specialist and do not need to be explained here. Furthermore, the mechanism by which the drive gears 21,22 are brought into mesh with the periphery of the tape plates 13,14 in dependence on operating requirements is not shown in detail.

It is however of decisive importance that here the periphery of the tape plates 13,14 is provided with a toothed rim and also that the drive is effected by means of drive gears 21,22. It is likewise important that the the drive spindles 19,20 of the drive gears 21,22 are mounted on a common rocking lever 27 (FIG. 5). In the first place it is thus possible, through a simple movement controlled by the mechanism, for only one drive gear at a time, namely that one of the two drive gears 21,22 rotating in opposite directions which is required in each particular case, to be brought into engagement with the toothed rim on the periphery of the appertaining tape plate 13,14. Secondly, as illustrated in FIG. 4, it is thereby possible to use one and the same drive system for the spools 11,12 for different sizes of cassette. Thus, FIG. 4 shows on the one hand a cassette 10 of standard size, but on the other hand a cassette 10' having a considerably larger spool diameter. As indicated in the drawing, the drive gears 21,22 can also be brought without difficuly by means of the rocking lever 27 into engagement with the toothed rims on the periphery of the tape plates. This is obviously also true when the drive gears 21,22 or their drive spindles 19,20 are each brought separately to the periphery of the tape plates by the mechanism, and not by means of a common rocking lever 27 rockable about a vertical axis, provided only that the two drive gears are slightly offset laterally in relation to one another and disposed approximately in the middle of a side face of the cassette 10. Since the spools 11,12 lie one above the other in the cassette 10 and the magnetic tape 16 has to be guided from the bottom to the top spool and vice versa, diagonal guiding of the magnetic tape is necessary. If the magnetic tape 16 is guided over the head drum, this diagonal guiding is achieved by inclining the head drum (see FIG. 17). For operations of rewinding the magnetic tape inside the cassette 10, however, so called "piping" occurs. In order to prevent this, fixed tape guide elements 28,29 having conically shaped surfaces are provided in the open side surface of the cassette.
In FIG. 7 it can be seen that these guide elements 28,29 are disposed in the corners of the open side face of the cassette 10. In an elevation viewed from the open side,

FIG. 8 clearly shows that the conical tape guide element 28 is situated at the height of the bottom spool 12 in one corner of the opening, and the conical tape guide element 29 at the height of the top spool 11 in the other corner of the open side face of the cassette 10. The path followed by the magnetic tape 16 is shown in broken lines. An additional non-conical tape guide element 30 lying roughly in the centre of the open side of the cassette 10 can also be seen.
FIGS. 10, 11, and 13 show in detail the construction of the tape guide element 30. FIG. 12 shows on a larger scale the conical shape of the tape guide elements 28 and 29. It can clearly be seen that the tape guide elements 28,29 form inclined surfaces which in the region of the cassette top and bottom are at the shortest distance from the spindle 15, while in the horizontal centre plane of the cassette 10, that is to say on both sides of the tape plate 13 of the upper spool, the distance from the spindle 15 is at its maximum. Like the tape guide elements 28,29, the tape guide element 30 is also in the form of a slide member.


In FIG. 10 the magnetic tape 16 is once again shown in dash-lines. It is guided by the tape guide element 30 after the style of an inclined groove which is bounded at the top by an inclined tape guide edge 31 at a slight angle to the horizontal, and at the bottom by a tape guide edge 32 parallel to the tape guide edge 31. These tape guide edges 31,32 are expediently slightly grooved in the longitudinal direction of the magnetic tape 16, so that by means of a certain retaining power they prevent the magnetic tape from passing out through the open side opening in the cassette 10.

On the other hand, the grooves must be so flat that the retaining force is sufficiently slight to be overcome by the tape extraction device without damaging the edges of the tape. The tape guide edges 31,32 are in addition extended in each case by a respective tape catcher 33,34 opening in the direction of the outside of the cassette. It is thereby ensured that when the magnetic tape, which has been laid around the head drum by the tape extraction device, returns into the cassette 10, it will reliably enter between the tape guide edges 31,32.
It is expedient for the tape guide element 30 not to lie exactly on the line connecting the tape guide elements 28 and 29, but at the tip of the isosceles triangle formed by the line connecting the tape guide elements 28,29 and the tape guide element 30, the tip of which points towards the exterior of the cassette 10 (FIG. 9).
After the above explanation of the cassette 10 and of its construction, the tape extraction device will now be explained in greater detail. A basic requisite is that this device should be one for cassette operation in which the magnetic tape must be wrapped around the head drum over an angle of 360°. With an angle of wrap of 360° the magnetic tape is thus wound helically around the head drum. A complete 360° wrap makes it necessary to use, in the tape extraction device, grippers which finally ensure a certain overlap, that is to say an angle of wrap around the head drum of more than 360°.

FIGS. 14a to 14f now show details of the tape extraction device which is suitable for this purpose. FIG. 14f shows the cassette 10 of FIG. 1 in a plan view (or view from below). The magnetic tape 16 is shown in four different phases of wrapping around a head drum 35. The top and bottom faces of the cassette are provided with cutouts 36 and 37 respectively. When the cassette is inserted into the apparatus, grippers 38,39 automatically penetrate into these cutouts and thus engage behind the magnetic tape 16 in the cassette 10. For recording and playback the tape extraction device now comes into operation with an actuating and guide mechanism when the apparatus is correspondingly operated; the grippers 38 and 39 are moved towards the head drum 35 until finally the magnetic tape 16 is completely wrapped around it. The individual phases of the operation are indicated in the Figure. Each of the grippers 38, 39 performs a movement which lays the magnetic tape, drawn by it out of the cassette 10, around the head drum 35 over an angle of slightly more than 180°. In the end position of the grippers 38,39 they lie one above the other in contact, as can clearly be seen in FIG. 14b. In the end position therefore the tape loops are guided by both grippers.
For the purpose of guiding the magnetic tape 16 the grippers are additionally provided with guide plates. Thus, the upper gripper 38 has on its upper side a guide plate 40, and the lower gripper 39 has on its lower side a guide plate 41. The guide plates are distinguished in that in plan view they project slightly beyond the outer periphery of the gripper bodies themselves, and thus can form a stop edge for the side edge of the magnetic tape 16. In addition, the outer edges of the guide plates 40, 41, projecting beyond the periphery of the gripper bodies, are also bent away from the gripper body, out of the plane in which they are in contact with the gripper body, thereby facilitating the re-gripping of the magnetic tape in the event of the loss of the tape tension. Furthermore, auxiliary plates 42,43 may also be provided. As can be seen in FIGS. 2a and 2c, the auxiliary plate 42 is fastened at the bottom on the upper gripper 38, and the auxiliary plate 43 is fastened at the top on the lower gripper 39. The auxiliary plates are similar in construction to the guide plates 40, 41. However, they extend only over that portion of the mutually facing sides of the grippers which in the end position shown in FIG. 14b is not in contact with the respective other gripper body. Moreover, the auxiliary plates 42,43 are frequently completely unnecessary because, as can clearly be seen in FIGS. 14b and 14f, in the end position the grippers lie one on the other, forming an angle, to the extent of about half in each case, so that the surfaces of the grippers 38,39 lying one on the other project in each case beyond the contour of the respective other gripper and can thus themselves serve as guide edges for the magnetic tape 16. By suitable selection of the height of the grippers 38,39, and therefore of the distance between the surfaces lying one on the other and the other guide edges formed by the guide plates 40,41, it is reliably ensured that the side edges of the magnetic tape 16 helically guided around the head drum 35 will lie side by side without a gap being formed.
The grippers 38,39 are expediently in the form of roughly kidney-shaped solid bodies of metal. Their shape can clearly be seen from the drawings. Instead, it is also possible, as shown in FIGS. 14d and 14e for the upper gripper 38, for the grippers to be composed of two cylinders 44,45 disposed upright and spaced apart parallel to one another, these cylinders being joined at the top by the guide plate 40, while the outer cylinder 44 carries at the bottom the auxiliary plate 42. Instead of cylinders, it is also possible to use one or two rollers.
A form of construction comprising the two shapes explained above in combination is particularly advantageous for the grippers: the gripper body is in the form of a solid body of metal, which at its front end, which pulls the tape furthest around the head drum 35, is made straight, while at its rear end, which lies further outwards to the side, it is provided with the cylinder 44, which itself can be provided with a tape guide flange 46 (see FIGS. 25 and 26).
For the purpose of achieving the contact-msntioned above in connection with FIG. 14b-between the upper gripper 38 and the lower gripper 39 in the end position, it is expedient to provided a compression spring 47. This spring is disposed above the upper gripper 38, behind the head drum 35 (viewing from the cassette 10), at the point where the grippers 38,39 engage one over the other.
FIG. 15a shows how in this position the compression spring 47 applies to the gripper 38 a pressure force indicated by an arrow, and thus applies the said gripper against the surface of the lower gripper 39, which in turn is supported on a chassis plate of the apparatus.

FIG. 15b shows the grippers 38,39 in a position just before they come to lie one on the other. As indicated by a broken line representing the bottom plane of the upper gripper 38 and a broken line representing the top plane of the lower gripper 39, the two grippers are here a short distance apart owing to the fact that the upper gripper 38 is slightly raised by a sliding lifter 48 (see FIGS. 22a and 22b) shortly before the end position is reached. It is thereby ensured that the end position shown in FIG. 15a can be reliably reached and that the side surfaces of the grippers will not in any circumstances run over one another.
The magnetic tape 16 is guided on the gripper bodies 38 and 39 by the guide plates 40, 41 and optionally by the auxiliary plates 42,43. The distance between these guide edges on the grippers 38,39 is slightly, but only very slightly, larger than the standard with of the magnetic tape 16. Tolerances in the width of the tape can thus be accepted. On the other hand, however, the clean positioning of the grippers one on the other as shown in FIG. 15a and the achievement of the distances indicated ensure that in the end position, which corresponds to recording or playback, the edges of the tape will lie one against the other without a gap. The difficulties which otherwise occur with a 360° angle of wrap as the result of overlapping of the edges of the tape, the bending-over of the edges of the tape, or gaps between the edges of the tape, are reliably avoided. The good positioning of the magnetic tape 10 in the operating position for recording and playback is therefore achieved through the fact that the grippers 38,39 are each provided, on their sides remote from the respective other gripper, with guide edges which are formed by the guide plates 40,41, and that the upper gripper 38, on reaching the end position, makes a slight movement perpendicularly to the direction of transport of the magnetic tape 16, in the direction of the lower gripper 39 if the two grippers 38,39 already overlap.
FIG. 16 shows a guide mechanism which is incorporated in the apparatus and which permits the movement of the gripper referred to above. A chassis plate 50 of the apparatus carries a mechanical linkage of the tape extraction device. This linkage consists of two roughly parallel rods 51,52, which extend generally in the tape extraction direction (see the large arrows in FIG. 16). The rods 51,52 are connected at their ends not provided with grippers 38,39 to reversing levers 53,54 which extend transversely to the rods 51,52 and connect the latter to a toothed rack frame 55. Given suitable articulation of the grippers 38,39 or of their rods to the remainder of the mechanism, the reversing levers 53,54 can be combined with the toothed rack frame 55 to form a plate (FIG. 19).

It is essential in every case that the rack frame 55 should have an elongated opening 58 extending parallel to the tape extraction direction, the longitudinal edges of the said opening being formed by two toothed racks 56,57 lying opposite one another. The rack 56 extends from the upper end (in FIG. 16) of the rack opening 58 in the rack frame 55 nearly but not quite as far as the bottom end. Furthermore, the rack 57 extends from the bottom end almost but not quite as far as the upper end of the rack opening 58. The portions left free by the racks 56,57 at the bottom and top ends respectively of the rack opening 58 are rather larger than the diameter of a gear 59 which lies in the plane of the rack opening. In addition, the distance between the racks 56 and 57 transversely to the tape extraction direction, or perpendicularly to their own longitudinal direction, is greater than the diameter of the gear 59.
The gear 59 is mounted on a vertical drive spindle perpendicular to the plane of FIG. 16) and rotates continuously. By means of a jump spring system, which is not illustrated but which is familiar to the specialist, it can be brought into engagement with either the rack 56 or the rack 57 as desired by movement in the direction of the double arrow over the rack frame 55. The gear rotates in the direction of the arrow. If therefore the gear 59 has been brought into engagement with the rack 56 by means of the spring system, the rack frame 55 and thus, through the action of the reversing levers 53,54 and the racks 51,52 or the grippers carried by them, the magnetic tape are brought out of the cassette. This operation is continued until the gear 59 runs into the free portion at the bottom end of the rack opening 58 and thus no longer applies a driving force. By means of suitable guide slots, which however are not shown in detail in FIG. 16, an additional movement of the grippers 38, 39 is brought about in the transverse direction of the large arrows in FIG. 16, the grippers having now reached their end position shown at the top in FIG. 16.
If the tape is to be pulled in again for high speed forward or reverse movement or for removal of the cassette, it is sufficient for the gear 59 to be brought into engagement with the rack 57 by means of the aforesaid spring system. The entire tape extraction device then returns into the position shown in FIG. 16. The lateral or curved guiding of the grippers will be explained more fully below with reference to FIG. 20. In principle, through this kind of mechanical guidance of the grippers 38,39 an extremely flat configuration can be given to the mechanical linkage, which nevertheless ensures defined guiding of the tape in every position of the apparatus. For the correct guiding of the magnetic tape 16, applied by the grippers 38,39 against the head drum 35, on the latter, however, the correct inclined position of the head drum 35 in relation to the plane defined by the chassis plate 50 is necessary.

FIGS. 17a to 17c show a simple adjusting device for the inclined position of the head drum 35. The latter is constructed on a supporting plate 60, on which the head drum axis 61 lies perpendicularly. In order that the head drum spindle 61 may form in relation to the vertical line 62 on the chassis plate 50 the angle clearly visible in FIG. 17a, the carrier plate 60 must therefore also form the same angle with the chassis plate 50. In order now to be able to adjust this angle to the correct value, the carrier plate 60 of the head drum 35 has four-point mounting.
The four-point mounting consists firstly of a back-pressure bearing 63, which is disposed on the side remote from the cassette, behind the head drum, and is constructed as follows: a vertical pin 64 is carried by the chassis plate 50. At its bottom end is provided an abutment plate 65. The vertical pin 64 also passes through an oversize hole in the carrier plate 60, which is thus mounted so as to be freely displaceable on the vertical pin. Between the carrier plate 60 and the abutment plate 65 a compression spring 66 is inserted. The latter presses the carrier plate 60 into contact against the lower face of the chassis plate 50. A height adjusting bearing 67 is disposed on each side of the head drum 35 in the arrangement shown in FIG. 17b. The height adjusting bears 67 urge the carrier plate 60 away from the chassis plate 50. They thus also apply a back pressure to the compression spring 66. The actual adjustment of the inclination of the head drum axis 61 is effected however by means of an adjusting screw 68, which is disposed, in relation to the axis of the head drum, diametrically opposite the back-pressure bearing 63, on the side of the head drum facing the cassette, so that the four-point mounting consists of four bearing points uniformly distributed around the head drum 35. The adjusting screw 68 is a threaded screw which passes through a threaded hole in the carrier plate 60. Since the head of the adjusting screw 68 is accessible above the chassis plate 50 (see FIG. 17a), it is thus possible with simple means to effect extremely accurate adjustment of the head drum axis 61. This is particularly important when magnetic tapes which have been played on different types of apparatus are played on the apparatus described.
FIG. 18 illustrates the manner in which the magnetic tape 16 is recorded with an apparatus of this kind. The present apparatus is one in which recording or playback is effected with the aid of the single-head inclined trace method. A magnetic head rotates in the slit head drum 35. The magnetic head records in each case a complete television picture and/or frame on a single inclined track 69. For this to be possible the 360° angle of wrap of the magnetic tape 16 around the head drum 35 is necessary in the manner already explained above. The recording is effected in the inclined track 69 in a quality such that without tape feed a stationary picture can without difficulty be scanned with good picture quality by the single inclined track 69. For this purpose, however, accurate adjustment is necessary, as shown in FIG. 18a. Defective adjustment may result in a track path of the kind shown in FIG. 18b: the ends of the inclined track are remote from the edge of the magnetic tape at the bottom. At the top a part of the track and consequently a part of the information are lost. By simple operation of the height adjusting bearing 67 by means of round-headed screws, which are accessible on the chassis plate 50, accurate adjustment as shown in FIG. 18a can be achieved.
Individual forms of construction of the guide mechanism of the tape extraction device will now be described below in greater detail. FIG. 19 shows a form of construction which is very similar to FIG. 16, but in which the rods 51,52 are articulated direct to the correspondingly widened, plate-like rack frame 55, as previously indicated in the description of FIG. 16.

FIG. 20 shows a guide mechanism fo the gripper 39, with the aid of which the said gripper can be applied against the head drum 35 in the manner explained above. The gripper 38 obviously has a corresponding guide mechanism of the same kind. This guide mechanism consists of a guide lever 70 of the Indian club shape shown in FIG. 20. The guide lever 70 lies roughly parallel to the tape extraction direction shown in dash-dot lines in the Figure. At its front end facing the head drum 35 it carries the gripper 39. At its other end, which is widened in the shape of an Indian club, the lever is provided with a guide pin 71 and a driving pin 72. The driving pin 72 combines the function of guidance with the function of a force application point on the guide lever 70, to which for example the driving force for the tape extraction movement is here transmitted by the rack control system previously explained. The guide lever 70 consists of a flat metal plate, which in turn is laid on the chassis plate 50 or another auxiliary plate of the guide mechanism. This chassis plate 50 or the auxiliary plate now has a straight guide slot 73 as guide for the driving pin 72 and a curved guide path 74 as guide for the guide pin 71. The straight guide slot 73 is at least almost parallel to the tape extraction direction shown in dash-dot lines. The curved guide path 74 is roughly parallel to the tape extraction direction in its portion farthest from the head drum 35, but moves increasingly away from that direction as it approaches the head drum 35. In addition, the guide pin 71 and the driving pin 72 are so constructed, in the manner shown in the Figure, that the guide pin 71 is disposed at the outermost bottom end of the guide lever 70 but the driving pin 72 is disposed between the guide pin 71 and the gripper 39 and can be at a distance from the said gripper which is three times its distance from the guide pin 71.
If the guide lever 70 in FIG. 20 is now moved in the tape extraction direction, and if through the force of a spring the guide pin 71 is continuously held bearing against the curved guide path 74, in the movement towards the head drum 35 the entire guide lever 70 is rocked about the driving pin, which is guided in the straight guide slot, in such a manner that the gripper 39 finally comes into the position behind the head drum 35 as shown in FIG. 14f.

FIGS. 21 to 26 will serve to explain another embodiment. FIGS. 21 to 24 show the guide mechanism in this embodiment similarly to FIGS. 16 and 19, while in the view in perspective shown in FIGS. 25 and 26 the direction of viewing is over the head drum 35 towards the cassete 10.
FIG. 21 shows a rack frame 55, which is once again in the form of a plate and which lies under and parallel to the chassis plate 50, being guided in a parallel guide consisting of slide rails 75 and mounted from below on the chassis plate 50, for a movement in the tape extraction direction. The drive for this movement is effected once again in the manner already described above by means of the gear 59 carried by the spring system and selectively brought into engagement with one or the other of the racks 56,57. The grippers 38,39 are remotely triangular in shape. The inner corners of the triangle, which in the end position overlap behind the head drum 35, are rounded in kidney shape. The base side facing the head drum, as tape guide surface, is curved in the form of an arc of a circle, like the kidney-shaped grippers 38,39, in accordance with the embodiment described above. The corner of the grippers 38,39 lying opposite this base side carries in each case a cylinder 44, the periphery of which projects slightly beyond the contour line of the gripper body and serves to deflect the portion of tape passing into the cassette.
The grippers 38,39 are disposed at the front end of rocking levers 76,77, which are of Indian club shape, as shown in the Figure. The rocking levers 76,77 are connected to the rack frame 55 on pivot pins 78,79. They may be disposed on the side of the rack frame 55 remote from the chassis plate 50. Since however the rack frame 55 is slightly lifted off the chassis plate 50 by the slide rails 75, the rocking levers 76,77 are expediently disposed in the gap between the surface of the chassis plate 50 and the bottom face of the rack frame 55. Since the pivot pins 78,79 are fastened to the plate-shaped rack frame 55, which in turn is guided in the slide rails 75 parallel to the tape extraction direction, separate straight guidance of the kind explained above in connection with the straight guide slot 73 in FIG. 20 is not required in the present case. However, a guide system corresponding to the curved guide path 74 and comprising guide pins 80, 81, which are fastened to the rocking levers 76,77, is necessary. The guide pins 80, 81 have the form of cylindrical pins which project downwards from the rocking levers 76,77 and run in curved slots 82,83 which are formed in the chassis plate 50.
The relative position shown in FIG. 21 of the pivot pins 78,79 and guide pins 80,81 on the rocking levers 76,77 has in turn the effect that when the gear 59 is correspondingly operated the tape extraction device first guides out of the cassette the magnetic tape 16 running over the grippers 38,39, then guides it in front of and finally behind the head drum 35, around which the magnetic tape is finally laid with an angle of wrap of more than 360°. The individual steps are explained separately below with the aid of the following Figures.
FIG. 22a first shows an embodiment, which has been slightly modified or supplemented in relation to FIG. 21, in the starting position which is also shown in FIG. 21.
Here there is additionally provided a bow spring 84, which is fastened at a fastening point 85 on the chassis plate 50 and at a fastening point 86 on the plate-shaped rack frame 55. The fastening point 85 on the chassis plate slies directly next to a slide rail 75 and roughly at the centre of the longer side, lying in the tape extraction direction, of the plate-shaped rack frame in the starting position of the latter. The fastening point 86 on the plate-shaped rack frame lies at the side of the rack 57, on the side remote from the fastening point 85 of the rack opening 58, approximately one-third along the total length of the rack 57, nearer its end remote from the head drum 35. The fastening point 86 thus lies in the starting position nearer the bottom edge (at the bottom in FIG. 22a) of the plate-shaped rack frame than the fastening point 85. Given a suitable length of the bow spring 84, the latter is thus able to give to the plate-shaped rack frame two defined end positions in its slide guide formed by the slide rails 75.
On end position, the bottom end position, is shown in FIG. 22a. The bow spring 84 pulls the slide plate into this end position, in which the guide pins 80,81 run onto the bottom ends of the curved slots 82,83 and thus form stops for a defined end position. The other (upper) end position is shown in FIG. 24. Here again the bow spring 84 pushes the plate-shaped rack frame 55 so far upwards onto the head drum that the guide pins 80,81 run onto the upper ends of the curved slots 82,83 and thus clearly define an end position. In the intermediate positions the bow spring 84 scarcely applies a force to the plate-shaped rack frame 55, since then the fastening points 85,86 lie more or less at the same height. The drive for the movement therefore does not have to overcome additional forces. The bow spring, acting as jump spring, thus ensures that the plate-shaped rack frame and all parts connected to it always have an accurately defined end position both when retracted and when extended. These accurately defined end positions are necessary not only in respect of the grippers, but also because of the continuously rotating gear 59 and its disconnection from the racks 56,57 in the end positions.
FIGS. 22a and 22b show another expedient development, which has already been briefly discussed above. This relates to the slide lifter 48. As shown in FIG. 22a, this component is disposed in the path of movement of the upper gripper 38 behind the head drum 35, just before the end position. FIG. 22b shows the cross-sectional shape of the slide lifter. It can be seen that both at its run-on end and at its run-off end the slide lifter has a diminishing height, so that the gripper 38 can run onto the slide lifter without difficulty from the surface of the chassis plate 50 serving as guide for it. The upper gripper is lifted out within the clearance available in the guide mechanism, so that between its lower face and the upper face of the bottom gripper 39 the distance shown in FIG. 15b is obtained. The height of lift achieved by the slide lifter 48 thus ensures that at the moment when the overlapping of the paths of the grippers 38,39 commences the lower face of the gripper 38 definitely lies above the upper face of the gripper 39. The maximum height of lift is obtained about 30° before the end position, if the periphery of the drum 35 is taken as reference point. As can be seen in FIG. 22b, the height of lift is thereupon reduced again, so that shortly before the end position is reached the gripper 38 is placed from above over the gripper 39 and makes contact with it.
It has been stated above that the guide mechanism must have a certain play. This play is indispensable for the movements explained, since otherwise excessive forces would be necessary. On the other hand, however, play in the end position is undesirable. Here it is on the contrary important that the grippers, which in this end position still serve, as previously, as tape guide elements, should have a constant, reliably reproducible position. For this reason a clamp lever device 90 is provided in order to hold the grippers 38,39 without play in the end position. For this purpose the front ends of the rocking levers 76,77 carrying the grippers are of a special shape. As can be seen in detail in the Figures, they have front flanks 91,92 which in the end position shown in FIG. 24 lie parallel to the tape extraction direction and a short distance apart on both sides of the longitudinal plane of symmetry of the tape extraction device. (see dash-dot line in FIG. 20), which plane passes through the axis of the head drum. In the longitudinal plane of symmetry of the entire belt extraction device there is now provided at this point, behind the head drum 35, a stop pin 93 onto which the front flanks 91,92 of the rocking levers 76,77 run from both sides in the end position. An accurately defined end position is thus also ensured for the rocking levers with the simplest means. From this end position the grippers could however still be lifted laterally through the action of forces transmitted to them through the magnetic tape. The clamp lever device is therefore additionally provided with two locking levers 94,95. These are in the form of angle levers and are rockable about a vertical pivot disposed at the angle and carried by the chassis plate 50, as indicated by double arrows in the Figures. That arm of the locking levers 94,95 which lies nearer the head drum 35 is provided with a nose which extends parallel to the other arm and whose locking surface is however parallel to the arm itself. Corresponding to these locking surfaces, steps 96,97 are provided on the side of the rocking levers 76,77 which is remote from the front flanks 91,92 or head drum 35 or stop pin 93, in the region carrying the grippers 38,39. The locking surfaces of the steps 96,97 lie parallel to the front flanks 91,92. When, as can best be seen in FIG. 24, the arms of the locking levers 94,95 on the head drum side engage behind the step surfaces 96,97, the rocking levers are pressed without play on to the stop pin 93, and can no longer lift off laterally from the said pin. The grippers 38 and 39 are then also fixed with their circular surfaces on the periphery of the head drum 35, without being able to lift off the latter.
The clamp lever device 90 is in addition provided with a clamp plate 98 suitably connected to the locking levers 94,95. This clamp plate is so constructed that in pivoted positions of the locking levers 94,95 which are shown in FIG. 22a and FIG. 23 their end pointing towards the head drum 35 points obliquely upwards. In the end position the clamp plate 98 however lies at the top on stop surfaces 99,100 at the front end of the rocking levers 76,77 when the locking levers 94,95 have been pivoted behind the steps 96,97. These stop surfaces 99,100 are horizontal surfaces and on their edges are provided with the steps 96, 97 on the side remote from the head drum 35. Through the pressure applied in the end position from above to the stop surfaces 99,100 (as indicated by an arrow in FIG. 24), the rocking levers 76,77 are pressed onto the chassis plate 50 and thus held at an accurately defined vertical height in relation to the head drum 35 likewise fastened on the chassis plate 50.
By means of the clamp lever device 90 therefore a working position which is always identical and free from play is fixed for recording and playback in the end position. Since locking is required only in this case, the clamp lever device 90 is operated, on operation of the recording or playback lever, by means of a linkage known to the specialist or by means of an electromechanical control arrangement also familiar to the specialist.
A reference has previously been made to the tape guide elements 28,29 in connection with FIG. 7 and subsequent Figures, particularly FIG. 12, these guide elements having a conical shape in order to prevent "piping" of the tape. It is however possible to prevent this by means of the oppositely conical tape guide elements 28,29 only when the magnetic tape 16 is completely retracted into the cassette, so that it runs over these tape guide elements and is suitably supported by them. However, piping may again occur while the magnetic tape is being pulled out of the cassette and thus is at least to a substantial extent lifted off the tape guide elements 28,29. In these intermediate positions, although the tape is not driven, so that piping does not give rise to any considerable difficulties in respect of locally concentrated tape stress, nevertheless accurate contact between the magnetic tape 16 and the periphery of the head drum 35 is essential. If because of the piping some loose portions of tape are formed during the transfer of the magnetic tape from the tape guide elements to the periphery of the head drum, accurate laying of the magnetic tape by means of the grippers 38,39 against the drum may be made difficult. This disadvantage is now overcome by providing the grippers with equalising slopes which act progressively during the operation of extracting the tape and which always maintain a uniform tape tension over the entire width of the tape.
FIGS. 22c and 22d show the arrangement of the equalizing slopes for the bottom gripper 39 and the top gripper 38 with the aid of equalizing springs 87 and 88 respectively.

It can clearly be seen from FIGS. 22c and 22d how the equalizing springs 87,88 are arranged: a rear end of the springs is bent over and mounted in the plate-shaped rack frame 55, in the direct proximity of the pivot pins 78,79 which connect the rack frame 55 to the rocking levers 76,77. The equalizing springs 87,88 then extend over the rocking levers as far as the grippers 38,39 which have a slot guide through which the equalizing springs 87, 88 pass. The front end of the equalizing springs 87,88 can pass out of the slot guide from the guide surface of the grippers 38,39 and into the region between their kidney-shaped guide noses, which point towards one another, and the cylinders 44. As can clearly be seen in FIGS. 22c and 22d, the front end of the equalizing springs is in each case formed by an upwardly bent loop, of which one vertical side remains inside the guide slot while the other side, lying further out, projects conically upwards in the case of the bottom equalizing spring 88, and conically downwards in the case of the top equalizing spring 87. The resulting angles correspond to the angles of the conical tape guide elements 28,29. These equalizing points for straightening pipes formed in the tape may also be disposed elsewhere on the grippers.

In the starting position shown in FIG. 22a the equalizing springs project beyond the periphery of the grippers in the manner only indicated in FIG. 22a but clearly shown in FIGS. 22c and 22d. If the tape extraction device is now operated, the grippers will lift the magnetic tape 16 off the tape guide elements 28,29 by means of the projecting portions of the equalizing springs, so that the formation of pipes is prevented and the magnetic tape is subjected at all points to uniform tape tension. As the plate-shaped rack frame continues to pass out, the equalizing springs 87,88 continuously move out to an ever increasing extent. When however finally the rocking levers 76,77 swing behind the head drum 35, the distance from the points of articulation of the equalizing springs on the rack frame 55 to the outlet surface increases, so that the equalizing springs are pulled back into the interior of the grippers. In the end position shown in FIG. 24 the equalizing springs are completely contained inside the grippers and do not impair the uniform guiding of the tape for the purpose of recording and playback. However, during the operations of extracting and retracting the tape the equalizing springs 87,88 prevent any formation of pipes in the magnetic tape.
FIG. 25 corresponds in the form of a view in perspective to FIG. 23, but the direction of viewing is over the clamp lever device 90 and the head drum 35 towards the cassette 10. With the same direction of viewing, FIG. 26 corresponds to the end position which is shown in plan view in FIG. 24.

 PHILIPS VIDEO CASSETTE RECORDER  VCR  N1502, Servo system for controlling the position of a reading head:

 A servo system for controlling the position of a magnetic reading head relative to the center of a selected information track. During recording a long-wave positioning signal is recorded below the data signal in the tracks. Upon reading out, the head not only reads the information of the selected track but, as result of cross-talk, also the positioning signals of the adjacent tracks. After filtering out and processing the positioning signals, a control signal for controlling the head is obtained.

 1. A servo system for controlling the position of a magnetic reading head relative to the center of a selected data track in a magnetizable layer of a recording medium that is relatively movable with respect to the reading head and is provided with a plurality of spaced tracks extending parallel to each other, said system comprising means for receiving short wave information signals and at least two ordered long-wave positioning signals, each of said long-wave positioning signals having a different frequency, means for recording said information signals in successive tracks and for successively superimposing each ordered position signal in separate ones of said data tracks in longitudinal alignment with said short-wave information signals in the magnetizable layer in which the data tracks are recorded, said positioning signals having a wavelength of a magnitude sufficient to produce crosstalk in a reading head placed over said selected data track, the wavelength of said short-wave information signals being of a magnitude insufficient to produce a crosstalk signal in said reading head placed over said selected data track, the spacing between tracks in which adjacent longwave positioning signals are recorded being at most equal to twice the spacing between the tracks in which the short-wave information signals are recorded, the adjacent recorded long-wave positioning signals having different frequencies, a magnetic reading head having a gap width substantially equal to the width of each track so as to scan the full width of a selected track and to simultaneously read all signals in said selected track and only the long-wave positioning signals in the tracks on either side thereof, said reading head producing during reading a composite signal, frequency sensitive electronic means for separating the two positioning signals read from the tracks on either side of the selected tracks from the composite signal, means for effecting a frequency comparison between the positioning signals and producing a servo signal which is a function of the deviation of the reading head from the center of the selected track and means responsive to the servo signal for adjusting the relative position between said reading head and said magnetic medium to align said reading head with said selected data track.

2. A servo system as claimed in claim 1 further comprising a helical scan video recorder, said magnetic reading read being mounted in said video recorder, said servo system being connected to said video recorder to keep said magnetic reading head centrally on a selected track, and wherein the frequencies of the positioning signals are coupled to the line frequency of the video signal.

3. A servo system as claimed in claim 2, wherein the frequencies of the positioning signals are an odd number of times half the line frequency.

4. A servo system as claimed in claim 2, characterized in that the frequencies of the positioning signals are an odd number of times half the line frequency of the video signal.

5. A servo system as claimed in claim 1, wherein the wavelength of the positioning signals is at least of the same magnitude as the distance between the tracks.

6. A servo system as claimed in claim 1, wherein the signal recording means receives positioning signals of a first, a second and a third wavelength, respectively for separately recording in every three successive tracks, the separating means comprising three frequency-selective filters for separating the positioning signals read from the selected track and from the two tracks on either side thereof from the composite signal and the comparison means comprising means for effecting an amplitude comparison of the three positioning signals.

7. A servo system as claimed in claim 1, in which the same magnetic head having a gap width which is substantially equal to the width of the tracks is included in both said signal recording means and said reading head.

8. A servo system as claimed in claim 1, wherein said electronic separating means connected to the output of the reading head comprises a frequency-selective filter for separating the positioning signals from the composite signal and a device for deriving a servo signal from the positioning signals.

9. In a servo system as recited in claim 1, wherein said long-wave positioning signals have two different frequencies, the long-wave positioning signals of each frequency being recorded in separate tracks, the track spacing between said recorded long-wave positioning signals being equal to twice the track spacing between the recorded short-wave information signals.

10. A servo system as claimed in claim 9, wherein said electronic separating means connected to the output of the reading head comprises two frequency-selective filters for separating the positioning signals of the tracks present beside a selected track from the composite signal, as well as an electronic circuit from which a servo signal is obtained by comparison of the amplitudes of the positioning signals.

11. A servo system for controlling the position of a magnetic recording head relatively to the center of a selected data track in a magnetizable layer of a recording medium that is relatively movable with respect to the reading head and is provided with a plurality of spaced tracks entending parallel to each other, said system comprising means for receiving shortwave information signals and two ordered long-wave positioning signals, each of said long-wave positioning signals having the same frequency and a different phase, means for recording said information signals in successive tracks and for successively superimposing each ordered positioning signals in separate ones of said data tracks in longitudinal alignment with said short-wave information signals in the magnetizable layer in which the data tracks are recorded, said positioning signals having a wavelength of a magnitude sufficient to produce crosstalk in a reading head placed over said selected data track, the wavelength of said short-wave information signals being of a magnitude insufficient to produce a crosstalk signal in said reading head placed over said selected data track, the spacing between tracks in which adjacent long-wave positioning signals are recorded being equal to twice the spacing between the tracks in which the short-wave information signals are written, the adjacent recorded long-wave positioning signals having different phases, a magnetic reading head having a gap width substantially equal to the width of each track so as to scan the full width of a selected track and to simultaneously read all signals in said selected tracks and only the long-wave positioning signals in the tracks on either side thereof, said reading head producing during reading a composite signal, frequency sensitive electronic means for separating the two positioning signals read from the tracks on either side of the selected track from the composite signal, means for effecting a phase comparison between said positioning signals and for producing a servo signal which is a function of the deviation of the reading head from the center of the selected track, and means responsive to the servo signal for adjusting the relative position between said reading head and said magnetic medium to align said reading head with said selected data track.

12. Apparatus as recited in claim 11, wherein the wavelength of the positioning signals is at least of the same magnitude as the distance between the tracks.

Description:

This invention relates to a servo system for controlling the position of a magentic reading head relative to the center of a selected track on a magnetizable recording medium which is relatively movable with respect to the head and has a plurality of juxtaposed tracks, said system comprising a reading head for reading information on a selected track which is suitable for simultaneously detecting information on tracks present on either side thereof so that a composite signal is obtained, a circuit which is connected to the output of the reading head and serves to separate the composite signal and to generate a servo signal which is a function of the deviation of the reading head from the center of the selected track, and head positioning means controlled by the servo signal.
In magnetic devices in which information is recorded in and read out from tracks on a magnetizable recording medium by means of magnetic heads, it is of great importance that during reading out the reading head be positioned accurately above the selected track. The degree of accuracy with which the reading head can be positioned determined the distance necessary between adjacent tracks and hence influences to a considerable extent the storage efficiency, that is the number of information units which can be stored per unit of surface area of the recording medium. For increasing the track accuracy, several servo systems for controlling the position of reading heads have been proposed, both servo systems for centering a head to the track in a video recorder, and servo systems for positioning the head in a magnetic disc memory.
A device of the kind mentioned in the preamble and which is destined in particular for positioning the head in a magnetic disc memory is known from the U.S. Pat. No. 3,491,347. The device known from this patent specification has as a particularity that the buffer zones between the tracks have been eliminated so that a larger information density is obtained. Upon reading a selected track, the signals of the adjacent tracks crosstalk as a result of the absence of the buffer zones. By means of a device for filtering and logically handling the overall read signal, a centering signal is obtained which corresponds in value and sign with the difference in amplitude of the adjacent tracks. In order to be able to perform this, the tracks present beside a selected track should have distinguishable characteristics, which is realized in the known device by modulating the data signals of every three successive tracks on three different carrier waves. The carrier waves may differ either in frequency or in phase. A drawback hereof is that for providing distinguishable characteristics, the carrier wave frequencies should differ by at least a factor 11/2, so that a limit is imposed upon the shortest frequency which can still be written (and hence on the information density). When using carrier waves of different phases, the distinction of the signal of a selected track from that of the adjacent tracks is rather difficult. This involves not only that it is difficult to generate a centering signal, but also that it is difficult to prevent crosstalk of the data signals. A further difficulty is that,when comparatively short-wave signals are used - as is described in the said patent -- the crosstalk on which the whole system is based, is small, while, owing to the absence of buffer zones, there will be 100% crosstalk of the signal of one of the adjacent racks as soon as the head is positioned with a substantial part of its width over the adjacent track in question.
It is the object of the present invention to provide a servo system which does not exhibit the drawbacks associated with the above-mentioned systems. For that purpose, the servo system according to the invention is characterized in that a device is present to write long-wave positioning signals on the tracks and that the reading head is suitable to simultaneously read the information content of a selected track and the long-wave positioning signals on the tracks present on either side thereof.
The system according to the invention is based on the recognition of the fact that upon reading out a given track the condition is used that the low frequency (long-wave) positioning signals of the adjacent tracks cross-talk to the reading head and are hence also read out, while the high frequency (short-wave) information signals of the adjacent tracks do not cross-talk and are hence not read out. For a good operation of the system it is of importance that the wave-length of the positioning signals be at least of the same magnitude as the distance between the tracks.
Within the scope of the invention there are several possibilities for the positioning signal form.
A first preferred embodiment of the system according to the invention is characterized in that a device is present to write on the tracks alternately a positioning signal of a first and a second wavelength and having such a phase that the tracks present beside a selected track always comprise positioning signals of the same wavelength but in opposite phases, the circuit connected to the output of the reading head comprising at least two frequency-selective filters for separating the two individual positioning signals from the composite signal and a device for deriving a servo signal from the individual positioning signals.
The above-described measuring system has the advantage that it comprises a zero method. However, there are certain circumstances in which it does not prove readily possible to record the servo signals of the adjacent tracks sufficiently accurately in opposite phases on the recording medium. In those cases an amplitude measuring system may advantageously be used.
For that purpose, a further preferred embodiment of the system according to the invention is characterized in that a device is present to write on at least every three successive tracks positioning signals of a first, a second and a third wavelength, respectively, the circuit connected to the output of the reading head comprising a corresponding number of frequency-selective filters for separating the positioning signals from the selected track and from the adjacent tracks, as well as a corresponding number of electronic circuits from which a servo signal is obtained by mutual comparison of the amplitudes of the three positioning signals.
The system according to the invention is particularly suitable for use in video recorders, since an "alien" signal, in this case a positioning signal, can easily be written "under" the video signal. In addition, the frequency of the positioning signals can simply be derived from the line frequency of the video signal.
Although in the above-described measuring systems measurements are performed on every track so as to obtain servo information, this is not necessary in all cases. It has been found, for example, that it is sufficient for a reasonably fast servo circuit that measurements are performed every other track to obtain servo information.
Therefore, a second preferred embodiment of the system according to the invention is characterized in that a device is present to write in the tracks a positioning signal every other track.
An advantage hereof is that simpler circuits than in the first-mentioned case will suffice.
In this case also there are several possibilities for the positioning signals.
A further preferred embodiment of the system according to the invention is characterized in that a device is present to write in every other information track positioning signals having a fixed wavelength but in mutually opposite phases, the circuit connected to the output of the reading head comprising a frequency-selective filter for separating the positioning signals from the composite signal and a device for deriving a servo signal from the positioning signals.
The above measuring system as well as one of the other above measuring systems has the advantage that it comprises a zero method. However, there are certain circumstances in which it proves not to be readily possible to record positioning signals every other track sufficiently accurately in opposite phases on the recording medium.
Therefore, yet another preferred embodiment of the system according to the invention is characterized in that a device is present to write in every other information track positioning signals of a first and a second wavelength, respectively, the circuit connected to the output of the reading head comprising two frequency-selective filters for separating the positioning signals of the tracks present beside a selected track from the composite signal, as well as an electronic circuit from which a servo signal is obtained by mutual comparison of the amplitudes of the positioning signals.

The invention will be described in greater detail with reference to the drawing.

FIG. 1a shows diagrammatically a magnetic head and the tape guide with the tape guide means and driving means in a helical scan video recorder.
FIG. 1b shows a block diagram of a servo system for controlling the position of the head of FIG. 1a relative to its track.
FIGS. 2 and 3 show various guide signal forms which can be used for generating a servo signal.
FIG. 4 is a block diagram of a writing circuit which may be used within the scope of the invention with the recorder shown in FIG. 1a.
FIG. 5 is a block diagram of a circuit associated with the circuit shown in FIG. 4 with which the control voltage for controlling the head position is derived.
FIG. 6 is a block diagram of another writing circuit which may be used with the recorder shown in FIG. 1a.
FIG. 7 is a block diagram of a circuit associated with the circuit of FIG. 6 with which the control voltage for controlling the head position is derived.
FIG. 8 is a block diagram of yet another writing circuit which may be used with the recorder shown in FIG. 1a.
FIG. 9 is a block diagram of a circuit associated with the circuit shown in FIG. 8 with which the control voltage for controlling the head position is derived.

FIG. 1a shows a video drum 3 in which a head disc 4 is present. A video head 1 is mounted on it. The magnetic tape 2 is unwound from the reel 8, laid in a loop about the drum 3, and wound on the reel 9. Such a tape guide is used in helical scan video recorders. However, the invention is not restricted to the use in (helical scan) video recorders but can very readily be explained with reference to the problems occurring in video recorders in general. With each (half) revolution of the head disk 3 the video head 1 writes a track with a length of-in a certain case -- 47 cm and a width of 150 to 250 microns. This comparatively large length/width ratio of the tracks give rise to positioning errors during scanning the tape 2 by the head 1 as a result of which annoying interferences in the displayed picture occur in that the adjacent track is also read partly. For correcting the position of the head 1 relative to a track written on the magnetic tape 2, it is within the scope of the invention to control the speed of the magnetic tape 2 which is driven by the capstan 7 and unwound from the reel 8 and wound on the reel 9.
For this purpose serves the servo circuit shown diagrammatically in FIG. 1b in which the same reference numerals are used for corresponding components as in FIG. 1a. The track detection circuit D connected to the magnetic head 1 makes a servo signal upon reading, which signal is used to control the reference source B. The switch S then is in the position 1 (= reading). The signal of the reference source B is compared by the comparison circuit V with the velocity-proportional signal of the tachometer T obtained via the frequency detector F. The output signal of V controls the servo amplifier A which ultimately controls the speed of the motor M which drives the tape 2 via the capstan 7. During writing, the switch S is in the position 2 (= writing). The tape speed is then maintained constant by means of the signal of the reference source C which is compared with the tacho signal in the phase discriminator E.
In order to obtain a servo system for automatically keeping the head 1 centered on the track, said system should comprise a measuring system which can provide a positioning signal which is a measure of the deviation from the center of the track and which indicates the direction in which the position should be readjusted. For that purpose, according to the invention, long-wave positioning information is recorded in the information tracks themselves, as is shown in

FIGS. 2 and 3. The head should be capable of also reading the long-wave positioning information of the tracks present beside the track to be followed.
FIG. 2 shows diagrammatically the situation in which the two adjacent tracks n-1 and n+1 of the information track n to be followed comprise positioning signals of equal wavelength λ₁ but in opposite phases and with an essentially longer wavelength than the information signals. The length direction of the tracks is parallel to the X axis of the system of axes shown. The variation of the magnetization M in the tracks represents the positioning information. For a reasonably fast servo circuit it is sufficient that every other track is measured to obtain servo information.
Synchronous detection of the sum of the positioning signals of the adjacent tracks read by the head 10, to be distinguished from the information track of the track n to be followed by means of a frequency-selective filter, then provides a control voltage which indicates both the direction and the value of the deviation of the head 10 relative to the line c centrally between the adjacent tracks n-1 and n+1.
FIG. 3 shows diagrammatically the situation in which both adjacent tracks n-1 and n+1 of the track n to be followed comprise positioning signals of different wavelengths λ₁ and λ₂. In this case also the starting point is that it is sufficient for a reasonably fast servo circuit to perform the measurement every other track to obtain servo information. After frequency-selective filtering of the positioning signals read by the head 11 and amplitude detection, the required control voltage is obtained from the difference of the detected adjacent signals.

FIG. 4 shows a block diagram for the writing part of a measuring system which is suitable to write the configuration of positioning signals shown in FIG. 2 on a recording medium. In this case the measuring system forms part of a helical scan video recorder. The frequency of the positioning signal to be written is coupled to the line frequency of the video signal so as to minimize mutual cross-talk. In the present case the selected frequency is 2.5 times the line frequency and is obtained as follows. The sync. separator SS separates the line synchronization signal of frequency f_L and the frame synchronization signal of frequency f_r from the complete video signal to be recorded. The frequency-controllable oscillator OSC generates a signal the frequency of which is made exactly equal to 5 times the line frequency f_L by means of a frequency divider FD1 and a phase discriminator PD. The positioning frequency 2.5 f_L is obtained by means of the frequency divider FD2 connected to the output of the oscillator OSC. Since the track pattern on the tape has already been chosen to be so that on either side of a line on the tape always either even or odd lines are present, the polarity of the signal should be reversed every two frames so as to ensure that the adjacent tracks have opposite polarities. This is done as follows. From the frame synchronization signal f_r switching signals are obtained by means of two-dividers FD4 and FD5 for controlling the electronic switches S1 and S2 which reverse the polarity of the positioning signal in the correct sequence and supply said signal to the head every other track. By means of the filter F1 a sinusoidal signal is made out of the block-shaped positioning signal which appears at the output of the switch S1. This signal is supplied to the input of the write amplifier SV together with the complete video signal modulated by the frequency modulator MOD. The output of the write amplifier SV is connected to the electric winding of the writing/reading head K.

FIG. 5 shows a block diagram for the associated reading part. A read amplifier LV amplifies the composite signal which originates from the writing/reading head K. The positioning signal of frequency 2.5 f_L is separated from the composite signal by means of band pass filter BF. The output of the filter is connected to an input 1 of an analog multiplier AV. The other input 2 of the analog multiplier is connected to the output of the switch S1. The signal present at the output of the switch S1 is derived from the reproduced video signal by means of a circuit which is identical to that sub-circuit shown in FIG. 4 with which the signal present at the switch S1 is derived from the video signal to be recorded.
After analog multiplication of the signals of the bandpass filter BF and the switch S1 by means of the analog multiplier AV, the signal passes through a lowpass filter LF and a direct voltage signal V_r remains which is proportional to the deviation of the head K relative to the centre of the selected track. This direct voltage signal may be used to control an arm on which the head is mounted but is preferably used to control the speed of the motor which moves the tape and hence to keep the head centrally on the selected track as is shown in FIGS. 1a and 1b.

FIG. 6 shows a block diagram for the writing part of a measuring system which is suitable to write positioning signals in every information track of a recording medium. In this case also the measuring system forms part of a helical scan (or transversal scan) video recorder. The frequencies of the two positioning signals to be written-in are coupled to the line frequency of the video signal so as to minimize mutual cross-talk. The frequencies chosen in the present case are 1.5 times and 2.5 times the line frequency and are obtained as follows. The synchronous separator SS separates the line synchronisation signal of frequency f_L and the frame synchronisation signal of frequency f_r from the complete video signal to be recorded. The frequency-controllable oscillator OSC generates a signal, whose frequency is made exactly equal to 15 times the line frequency f_L by means of a frequency divider FD1 and a phase discriminator PD. The two positioning frequencies 1.5 f_L and 2.5 f_L are obtained by means of the frequency dividers FD 2 and FD 3 connected to the output of the oscillator OSC. Since the track pattern on the tape has already been chosen to be so that on either side of a line on the tape always either even or odd lines are present and the selected positioning signals then have the same phase, the polarity of both positioning signals should also be reversed every two frames so as to ensure that the adjacent tracks have opposite polarities. This is carried out as follows. From the frame synchronisation signal f_r switching signals are obtained by means of two-dividers FD 4 and FD 5 and a synchronous delay multivibrator MV, which signals serve to control the electronic switches S₁, S₂ and S₃ which reverse and select the polarity of the guide signals in the correct sequence. By means of the filters F₁ and F₂ sinusoidal signals are made out of the block-shaped positioning signals which appear at the outputs of the switches S₁ and S₂. These are applied to the input of the write amplifier SV together with the complete video signal modulated by the frequency modulator MOD. The output of the write amplifier V is connected to the electric winding of the read-write head K.

FIG. 7 shows a block diagram for the associated reading circuit. A reading amplifier LV amplifies the composite signal which is received from the writing/reading head K. The two positioning signals of frequency 1.5 f_L and 2.5 f_L, respectively, are separated from the signal by means of bandpass filters BF 1 and BF 2. The outputs of the two filters are connected to an analog multiplier AV 1. This is proportioned so that each output operates as a limiter for larger signals so that the output voltage is proportional to the smaller of the two (= sum of adjacent signals) while the output frequency is equal to the line frequency f_L so that this signal can be detected synchronously by means of the line frequency f_L transmitted by the video signal. For that purpose, the output of the read amplifier LV is coupled, via a highpass filter HF, an fm demodulator DEM, a sync. separator SS and a phase discriminator PD, to an oscillator OSC which generates a signal of frequency f_L. Since the polarity of the resulting control signal would vary per track, its polarity should previously be reversed. For that purpose, the amplitudes of the two positioning signals are compared by means of detectors DET 1 and DET 2 and a comparator COMP, and the output signal of the comparator is multiplied analogously with the output signal of the analog multiplier AV 1 by means of the analog multiplier AV 2. By means of the bandpass filter BF 3 it is ensured that only the part having frequency f_L of the output signal of the analog multiplier AV 2 is passed. After analog multiplication of the output signals of the bandpass filter BF 3 and the oscillator OSC by means of the analog multiplier AV 3, the signal passes through a lowpass filter LF and a direct voltage signal V_r remains which is proportional to the deviation of the head K relative to the centre of the selected track. Said direct voltage signal may be used to control an arm on which the head is mounted, but it is also possible to use it to control the speed of the motor which moves the tape and hence to keep the head centrally on the selected track.

FIG. 8 shows a block diagram for the writing part of another measuring system which is suitable to write positioning signals in every information track of a recording medium. In this case also the measuring system forms part of a helical scan (or transversal scan) video recorder, and, in order to prevent cross-talk, the frequencies of the positioning signal in this case also are coupled to the line frequency of the video signal. In the present case the selected frequencies are 1.5 times, 2.5 times and 3.5 times the line frequency. The sync. separator SS separates the line synchronisation signal of frequency f_L and the frame synchronisation signal of frequency f_r from the complete video signal to be recorded. The frequency-controllable oscillator OSC generates a signal whose frequency is made exactly equal to 105 times the line frequency f_L by means of a frequency divider FD 1 and a phase discriminator PD. The three required positioning frequencies are obtained by means of the frequency dividers FD 2, FD 3 and FD 4 connected to the output of the oscillator. By means of the filters F₁, F₂ and F₃ sinusoidal signals are made out of the block-shaped positioning signals which appear at the outputs of the frequency dividers. In a manner similar to FIG. 4 switching signals are derived from the frame synchronisation signal by means of the circuit D to control the electronic switch S which selects the positioning signals. These are applied to the input of the writing amplifier SV together with the complete video signal modulated by the frequency modulator MOD, the output of said amplifier being connected to the electric winding of the writing/reading head K.
FIG. 9 shows a block diagram for the associated reading circuit. A reading amplifier LV amplifies the composite signal which is received from the writing/reading head K. The three positioning signals are separated from the signal by means of bandpass filters BF 1, BF 2 and BF 3. Amplification then takes place by means of logarithmic amplifiers log V 1, log V 2 and log V 3 and subsequent rectification by means of the rectifiers G 1, G 2 and G 3. The logarithmic amplifiers ensure that the dynamic of the signals applied to the rectifiers is decreased while as a result of this a substantially linear relationship is also obtained between the control voltage to be obtained and the deviation of the head from the centre of the two adjacent tracks. The rectified signals are subtracted from each other in the difference amplifiers DIF V 1, DIF V 2 and DIF V 3. The control voltage is then obtained from a correct choice of one of the three difference voltages. Said choice is made by means of the comparator COMP which determines the largest of the three positioning signals (that is the positioning signal of the selected track) and then controls that switch of the electronic switches S 1, S 2 and S 3 which is connected to the output of the difference amplifier of the two other positioning signals, so that the difference of two adjacent signals always provides the control signal V_r.

PHILIPS VIDEO CASSETTE RECORDER  VCR  N1502  UNITS  AND  CIRCUITS  VIEW.