GB2225149A

GB2225149A - Video apparatus

Info

Publication number: GB2225149A
Application number: GB8922759A
Authority: GB
Inventors: Jacob Ezra; Richard Alexander Smith
Original assignee: Individual
Current assignee: Individual
Priority date: 1988-10-10
Filing date: 1989-10-10
Publication date: 1990-05-23
Also published as: GB8922759D0

Abstract

Apparatus for recording and/or playing back video signals has a spinning drum containing a plurality of magnetic recording and/or playback heads and a tape drive mechanism for causing a magnetic tape to pass over the surface of the drum along a helical path. To allow recording or playback of two video signals simultaneously the drum contains heads (12A, 12B, 126, 12D) at two or more different levels which are spaced apart axially with respect to the axis of rotation (20), the heads at each level scanning a respective band of the tape. The apparatus is of particular use in storing 3D video images. Also disclosed is a 3D video projector having a backlit screen and a retractable inclined mirror (Figures 10 and 11). <IMAGE>

Description

VIDEO APPARATUS This invention relates to video recording and/or playback apparatus, and in particular to apparatus for recording and/or playing back video signals for three dimensional television or other uses.

A number of attempts have been made in the past to produce systems for recording and viewing three-dimensional images, but they have met with limited success largely due to the complexity and expense of the apparatus involved or the difficulty in obtaining an image which is of satisfactory quality and which can be viewed easily. There is a long history of experiments with three dimensional projection of images in the cinema, including techniques in which two images formed with light polarised perpendicularly with respect to each other are projected on to a screen which preserves the polarisation of each image, and in which the viewer is provided with a simple pair of spectacles having orthogonal polarising filters, one for each eye. The system achieves good image definition and colour and has been used extensively.

The popularity more recently of video tape as an image storage medium has led to the investigation of methods of providing three-dimensional television viewing. There is a tendency to favour the use of systems in which two television images are multiplexed in time on a simple television screen, the viewer being provided where necessary with spectacles having electronically controlled optical shutters allowing light from the screen to pass alternately to one eye then the other in synchronisation with the multiplexing of the images on the screen.

To record the images, signals from two cameras are time-division multiplexed and recorded on video-tape. This multiplexing technique has the disadvantage of complexity and expense due particularly to the need for optical shutters using, for example, liquid crystal shutters. In addition, the number of viewers is restricted, and the image does flicker unless a very high multiplex switching rate can be achieved.

The alternative technique of retaining separate signals for each image and recording them separately on video tapes, discs or other recording media has not been satisfactorily achieved due to the difficulty of synchronising the images to the accuracy necessary for viewing moving scenes.

It is an object of this invention to provide means whereby a three-dimensional image or images of a scene can be recorded and displayed to the viewer without the disadvantages of the multiplexing system referred to above.

According to this invention, apparatus for recording and/or playing back video signals has a plurality of magnetic heads mounted on a rotatable member such as a spinning drum, and means for moving a magnetic storage tape relative to the heads and the rotatable member at an oblique angle relative to the axis of rotation of the rotatable member, wherein the heads are mounted on the rotatable member at at least two levels which are spaced apart in the axial direction of the rotatable member, whereby the or each head at each level scans a respective longitudinal band on the tape along obliquely angled tracks. In this way, two or more video signals may be recorded or played back simultaneously in synchronisation from respective tracks on the tape, the heads all scanning the same frame of the composite picture at the same time.The resulting multiple channel recording allows two or more video signals (representing for instance a three-dimensional image) to be stored separately on a single tape so that parallel but separate processing of playback signals can be carried out for display by separate respective display projectors or cathode ray tubes. In the case of a three-dimensional system the displayed images may then be orthogonally polarised and combined for viewing with spectacles with polarising filters, thereby avoiding the need for spectacles with complex, expensive and heavy shutter devices.

Since in the preferred embodiments of the invention each video signal is recorded without multiplexing of the signals, the images produced on playback, as well as being synchronised, are free of flicker.

The invention also includes viewing apparatus comprising a plurality of colour video image projector arrays, polarising means for polarising the beams from each array differently from the other array or arrays, and a screen arranged so that the beams are incident upon it to form focused images with the polarisation of each image maintained. Preferably, the apparatus comprises two arrays each of three projectors, and each projector has a polarising filter so that the beams of one array are all orthogonally polarised to those of the other array. The screen may be of a translucent material if back-projected, or silvered for front projection, but in both cases the optical surfaces must be such as to preserve polarisation so that viewers wearing spectacles with filters polarised at right angles to each other may view different images with different eyes.In this way, if the projector arrays are fed with stereo signals, the viewer can receive a stereo or three-dimensional picture.

The invention will now be described by way of example with reference to the drawings in which : Figure 1 is plan view of a rotatable drum of a video recording and playback apparatus, shown in conjunction with a tape cassette; Figure 2 is a simplified side view of the rotatable drum in accordance with the invention; Figure 3 is a diagram of a section of magnetic tape showing a pattern of tracks produced by the arrangement of Figures 1 and 2; Figure 4 is a diagrammatic axial section through the drum of Figures 1 and 2; Figure 5 is a simplified diagrammatic axial section of the drum of Figures 1 and 2 showing a second transformer; Figure 6 is a side view showing an alternative transformer arrangement; Figure 7 is a diagrammatic side view of a drum and drive motor for an alternative embodiment of the invention; Figure 8 is a perspective view of the components shown in Figure 6;; Figure 9 is a diagram of a further transformer arrangement for four channel apparatus; Figure 10 is a sectioned side view of viewing apparatus for producing a three-dimensional video image; Figure 11 is a view corresponding to that of Figure 10 with the apparatus in an operative configuration; Figure 12 is a block diagram of an alternative playback stage; and Figure 13 is a timing diagram illustrating the operation of the playback stage of Figure 12.

Referring to Figure 1, a typical video recording and playback apparatus includes a rotatable drum 10 with magnetic record/playback heads 12 and positioned such that the tape 14 from a tape cassette 16 inserted in the apparatus may be drawn out of the cassette by rollers 18 to wrap the tape around the drum 10 as shown. Normally the area of contact between the tape 14 and the drum 10 subtends an angle of 1800 or a little greater at the axis of rotation 20 of the drum.The conventional drum 10 has a single pair of heads 12 located in a common plane perpendicular to the axis of rotation 20, the speed of rotation of the drum and the rate of passage of the tape 14 over it being such that the heads 12 record along alternate tracks at an oblique angle to the edges of the tape (the axis of rotation 20 of the drum being angled so that the tape follows a spiral path over the drum surface).

In apparatus in accordance with the present invention, the drum 10 has two or more pairs of heads at axially spaced positions.

A drum 10 housing two pairs of heads is shown in Figure 2, the heads being labelled 12A to 12D respectively, the first pair of heads 12A, 12B being at a lower level than the second pair 12C, 12D.

By suitably arranging the axial spacing of the two pairs of heads, the angle of inclination of the head axis 20, and the tape speed, the two video signals can be recorded simultaneously in synchronism on separate bands 22, 24 of the tape 14 as shown in Figure 3, with room for audio and control tracks 26 adjacent the tape edges and a guard band 28 between the two video bands 22, 24.

In the Figure, one recorded track 30 is shown within each band.

In the preferred embodiment of the invention the heads of the first pair are directly in registry with those of the second pair, but it will be appreciated that an angular separation between the two diameters defined by each respective pair of heads does still allow synchronisation between the two video signals to be achieved.

Referring to Figure 4, the drum 10 is mounted on a motor spindle 32 which is hollow to allow the passage of connecting wires. The drum has body parts 10A, 10B on which are mounted plates 34 and 35 carrying the magnetic recording and playback heads 12A to 12D.

Signals received from or transmitted to the lower pair of heads 12A, 12B are passed between the rotatable drum and the stationary parts of the apparatus via transformer windings 36A, 36B embedded in a ring of insulative material 38. Tracking of the heads 12A to 12D in registry with the recorded tracks is controlled by altering the tape speed or drum rotation speed in response to signals picked up by the heads and fed separately to the stationary parts of the apparatus via slip rings, one set (40) of which is visible in Figure 4. The signal paths between the lower pair of heads 12A, 12B and the slip rings 40 includes conductors 42 adjacent the head mounting plate, spring contacts 44 and wire links 46.Similar signals picked up by the upper pair of heads 12C, 12D are transmitted via similar conductors 48, and spring contacts 50, the latter being connected to wires 52 which are threaded through the hollow spindle 32. Also threaded through the spindle 32 are wires 54 connecting the upper pair of heads 12C, 12D with a second transformer assembly (not shown in Figure 4) as described below.

The second transformer assembly is shown in the simplified crosssection of Figure 5, which indicates the relationship between the drum 10 and the top part of a motor housing 60. The coils 36A, 36B are the two primary windings of a first transformer assembly having secondary windings 62A, 62B mounted on a top portion 60A of the motor body 60. The second transformer assembly has concentric primary windings 36C, 36D mounted on a wheel 64 attached by a bush 64A to the spindle 32 so as to rotate with the spindle. Holes 66 drilled in the spindle 32 beneath the wheel 6 allow the wires 52, 54 from the upper pair of heads and tracking contacts 50 to be brought out to primary windings 36C, 36D and to a second set of rotating slip rings 68 respectively.The secondary windings 62C, 62D of the second transformer assembly are moulded on a lower part 60B of the motor body 60 so as to be directly beneath and coaxial with the primary windings 36C, 36D.

Tracking signals from the two sets of slip rings 40, 68 are fed to control circuitry of the apparatus via sets of brushes 70 and 72 mounted between the transformer secondary windings and the spindle 32.

In an alternative arrangement of drum and motor, the transformer parts are mounted separately from the drum 10 on the spindle 32 Oand motor body 60 as shown in Figure 6. The first transformer assembly 74 has a rotatable part A mounted on the spindle 32 which is connectable via conductors (not shown) inside the spindle 32 to one set of heads 12A, 12B in the drum 10, and a stationary part B rigidly coupled to the motor body 60. The second transformer assembly 76 is similarly mounted and connected. Separation of the transformer assemblies from the drum in this way allows for relatively simple replacement of heads and improves the stability of the gaps between the primary windings and the secondary windings.

Yet a further alternative arrangement is illustrated in the exploded diagrams of Figures 7 and 8. The same reference numerals are used as before. In this arrangement a single transformer assembly 78 serves for transmitting all video information signals between the heads 12A to 12D and the connected circuitry (not shown). This is achieved by locating the four primary windings 36A to 36D in a single rotating support 80 which is easily detachable from the drum 10 by bolts 82, and by arranging the windings coaxially and, if necessary, in a stepped configuration with one pair of windings axially displaced with respect to the other pair to minimise crosstalk. The rotating support 80 has a hollow central bush for the connections 81 to the heads.

The secondary windings 62A to 62D are arranged in a matching coaxial and stepped configuration on the motor body 60. No hollow motor spindle is required since the rotating support 80 is mounted on the end of the motor spindle 132 and there are no stationary parts intervening between the support 80 and the drum.

Slip rings and brushes for the tracking signals are not shown in Figures 7 and 8, but are preferably mounted on the opposing faces of the drum 10 and motor body 60 outwardly of the rotating support 80.

There are instances where it is useful to extend the capabilities of the apparatus described above to allow simultaneous and synchronous recording and playback of more than two video signals.

Simultaneous front or rear projection of four images produced by four projectors spaced apart by distances corresponding to eye separation, the projection being onto a lenticular screen (i.e.

a directionally selective screen), offers the possibility of three-dimensional viewing without the need for separately restricting the images reaching each eye of the viewer using, for example, polarising spectacles. To record four video signals, the spinning drum of the apparatus has four pairs of heads each at a different one of four axially spaced positions. The transformer arrangement may be a development of those shown in Figures 5 and 6 with several stacked transformers or, preferably, is as is shown in Figure 9 in which the stepped air gap configuration of Figure 7 is extended over an increased diameter. The width of the magnetic tape needed to record four signals at full TV bandwidth is larger than with the two channel arrangement. Typically, the tape width is increased from 12.5mm to 25mm.

Referring now to Figures 10 and 11, an exemplary projection apparatus for two channel viewing of two simultaneously and synchronously played back video signals comprises two projector arrays 86, 88. Each array has three projectors (for red, green and blue components of the respective image), only one of which is visible in the Figures.

The apparatus has a cabinet 90 with an inoperative configuration and an operative configuration as shown in Figures 10 and 11 respectively. In the inoperative configuration the top of the cabinet 90 is closed with the top panel 92 resting on the front and rear panels. The top panel 92 carries a vertical screen 94 and a swivellable mirror 96 which both lie vertical one behind the other in the inoperative configuration. In use, the top panel 92 is lifted upwards as shown in Figure 11 to expose the screen 94, and the mirror 96 is pivoted rearwards on a telescopic mount 98 so that its lower edge is adjacent the rear of the cabinet.

The projector arrays 86, 88 are arranged to direct beams of light upwardly towards the mirror 96 on converging paths to coincide in focus on the screen 94. Each projector has an individual polarising filter (not shown) so that the beams of the one array are all polarised in one direction while those of the other array are polarised in an orthogonal direction. The screen 94 is made of a translucent material which preserves the polarisation of the partly scattered light projected towards the viewers so that each viewer, if provided with spectacles having polarising filters arranged with corresponding respective orthogonal polarising directions, sees a stereo picture.

Polarising filters and spectacles may be dispensed with if a lenticular screen are used, as referred to above.

As an alternative to optical polarisation as a means of separating the left and right images of the displayed picture, a time division multiplexing system has been devised which avoids some of the disadvantages of prior multiplexing systems, the main one being the flickering of the image due to a refresh rate of only 25Hz. The conventional television receiver using the PAL colour system has 625 horizontal lines which are scanned 50 times a second. These lines are arranged as two interlaced sets of lines which are alternately scanned. By constructing the receiver to scan at double the conventional rate, i.e. at 100Kz, is possible for left and right images to be alternately displayed while maintaining the 50Hz refresh rate of the conventional single channel receiver.

Referring to Figures 12 and 13, this may be achieved by feeding the left and right signals obtained, after amplification, from the tape to a series of frame stores 100A to lOOD via switching devices 102A and 102B arranged to switch in phase after each complete frame of 625 lines has been recorded. During each switching interval of the switching devices 102A, 102B only two of the frame stores are receiving picture signals. The other two frame stores are transmitting previously stored picture signals at double the rate at which they were written in to a timedivision multiplexer 104 via second switching devices 106A, 106B.

By appropriate timing of the read-outs from each frame store 100 to 100D, and appropriate switching of the multiplexer 104, the multiplexer output signal is arranged to present interlaced left and right fields alternately for feeding to a single monitor or projection unit (not shown) which scans the picture at double the rate of scanning of the images stored on the tape.

The timing of the multiplexer output signals is shown by way of example in Figure 13, in which the first line 108 represents the output of one pair of heads (the left channel) over the time T for playing back a complete frame, while the second line 110 represents the output of the other pair of heads (the right channel). The interlaced fields are labelled La, Lb for the left channel and Ra, Rb for the right channel. The width of the diagram corresponds to one complete scan n of each picture. Thus, if the switching devices 102A, 102B are in the position shown in Figure 12 during scan n, the interlaced left channel fields Lan and Lbn are written into frame store 100A while the right channel fields Ran and Rbn are written to frame store lOOC.

Simultaneously, the signals from the previous scan (n-l) are read to the multiplexer 104 at double the write rate, as shown by line 112 in Figure 13 in the sequence La(n-1), Lb(n-l), Ra(n-l), Rb(n1), the left fields being read from store 100B and the right fields from store 100D.

The same technique as described with reference to Figure 12 may be used with a 100Hz monitor or projection array for playing back either one or with simultaneously of two video signals which do not form a composite image but which are separate. Indeed, by arranging for the drum 10 to have heads at additional levels, as many TV signals as there are head levels niay be recorded, and according to the switching and timing arrangement and the number of monitors, any number of these signals would be played back as required.

It will be appreciated that when viewing a multiplexed threedimensional picture switching spectacles can be used for viewing the left and right channels alternately to give the viewer the impression of a composite, largely flicker-free, three-dimensional picture. The spectacles (not shown) preferably use liquid-crystal screens controlled by a switching signal synchronised with the multiplexer 104 via a control output 114 (Figure 12) to adopt alternate transparent and opaque states with the left and right screens oppositely phased with respect to each other.

Alternatively, where the composite multiplexed image appears on a screen, a electronically controllable liquid crystal polarising filter may be placed over the picture screen. Such polarising filters are dynamically alterable to switch between two substantially orthogonal polarisations, and can therefore be switched in synchronism with the time-division multiplexer 104 to polarise the left and right images differently. In this case the viewer is required only to wear passive orthogonally polarised spectacles.

Claims

1. Apparatus for recording and/or playing back video signals comprising a plurality of magnetic recording and/or playback heads mounted on a rotatable member, and means for moving a magnetic storage tape relative to the heads and the rotatable member at an oblique angle relative to the axis of rotation of the rotatable member, wherein the heads are mounted on the rotatable member at at least two levels which are spaced apart in the axial direction of the rotatable member, whereby the or each band at each level scans a respective longitudinal band on the tape along obliquely angled tracks, and wherein the apparatus includes means for feeding different video signals simultaneously to and/or receiving such signals simultaneously from the heads at different levels.

2. Apparatus according to claim 1, wherein the rotatable member is a drum having a plurality of heads located at each of the different levels.

3. Apparatus according to claim 2, wherein the heads at each level are in registry with the heads at the or each other level.

4. Apparatus according to any preceding claim, including a plurality of transformers located at different levels with respect to the axis of rotation for conducting video signals between the heads and associated electronic circuitry.

5. Apparatus according to claim 4, wherein each transformer comprises a first coil mounted for rotation with the shaft and a second coil mounted on a stationary support member and located so as to be magnetically coupled to the first coil when the rotatable member is rotating, and wherein the rotatable member is mounted on a hollow shaft and electrical connections between the transformer furthest from the rotatable member and the respective head or heads pass through the hollow shaft.

6. Apparatus according to any of claims 1 to 3, including a plurality of transformers each having a first part mounted on a shaft for rotation with the rotatable member and a second stationary part mounted adjacent the first part and magnetically coupled thereto, wherein the rotatable member is detachable from the shaft.

7. Apparatus according to any of claims 1 to 3 or 6, having a transformer assembly with a first part containing a plurality of first coils mounted for rotation with the rotatable member, and a stationary second part containing a plurality of second coils located adjacent to and magnetically coupled to the first coils, wherein the first coils are concentric with respect to each other and the axis of rotation and of differing diameters, and the second coils are similarly concentric with respect to each other in registry with the first coils, and wherein the first and second transformer parts have corresponding stepped surfaces defining an air gap therebetween, with one or more coil pairs, each comprising a first coil and a second coil, being axially raised with respect to other coil pairs.

8. Apparatus according to any preceding claim, including means for adjusting the said oblique angle between the axis of rotation of the rotatable member and the tape to allow the heads of one of the said levels to move over substantially the whole width of the tape.

9. Apparatus according to any preceding claim for playing back video signals representing a composite three-dimensional picture, wherein the apparatus further comprises a pair of display units each having at least one display device, each display unit being coupled to receive a different one of the video signals and having a polarising filter arranged such that the picture displayed by one unit is orthogonally polarised with respect to the picture displayed by the other unit.

10. Apparatus according to claim 9, wherein the display units comprise a plurality of colour video image projector arrays each having three display devices in the form of three projectors arranged to project images of different respective colours.

11. Apparatus according to any of claims 1 to 8 for playing back at least first and second video signals recorded on a single magnetic tape, wherein the apparatus further comprises means for storing signals representative of video signals received from the heads at a first scanning rate, switching means operable for receiving previously stored signals from the storage means at a second scanning rate which is a multiple of the first scanning rate, and a display unit coupled to the switching means for displaying images corresponding respectively one or both of the first and second video signals.

12. Apparatus according to claim 11, wherein the first and second signals represent a composite three-dimensional picture, and wherein the switching means comprise a time-division multiplexer, the display unit being arranged to receive the stored signals corresponding to both first and second video signals alternately.

13. Apparatus according to claim 11, wherein the storage means are operable during each scanning interval n to store in a first part thereof interlaced left channel fields Lan, Lbn and right channel fields Ran, Rbn while at the same time reading from another part thereof the interlaced left and right channel fields stored during the previous scanning interval (n-1) on a single channel at double the rate at which they were stored.

14. Apparatus according to claim 13, wherein stored fields of the previous scanning interval (n-l) are read out in the sequence La(n-l), Lb(n-l), Ra(n-l), Rb(n-l).

15. Apparatus according to any preceding claim, having electrical circuit means for receiving and/or transmitting two or more video signals each representing a complete television picture of the same scene, the pictures being viewable together to form a composite three-dimensional picture of the scene, wherein the circuit means are arranged such that the signals are recorded and/or played back simultaneously and in synchronism, the heads scanning the same frame of the composite picture at the same time.

16. Stereo television picture viewing apparatus comprising a plurality of colour video image projector arrays, polarising means for polarising the beams from each array differently from the other array or arrays, and a screen arranged so that the beams are incident upon it to form focused images with the polarisation maintained.

17. Apparatus according to claim 16, wherein the screen is formed of a translucent material for back projection, the material being of a type which substantially preserves the difference in polarisation between the beams of the first array and the beams of the second array.

18. Apparatus according to claim 16, wherein the screen is formed of a silvered material for front projection, the material being of a type which substantially preserves the difference in polarisation between the beams of the first array and the beams of the second array.

19. Apparatus according to claim 17, including a mirror for reflecting light projected from the arrays.

20. Apparatus according to claim 19, wherein the projector arrays are housed in a cabinet and the mirror is movable between a retracted position in which it is disposed substantially vertically within the cabinet and an extended position in which it projects above the cabinet in an inclined orientation.

21. Apparatus according to claim 20, wherein the cabinet has a front wall, side walls and a rear wall, and wherein the mirror is pivotally mounted at or adjacent is upper edge on a mirror support which is movable into and out of the cabinet in such a manner that in the retracted position the mirror is between the front wall of the cabinet and the projector arrays, and that in its extended position the mirror has its upper edge raised above the front wall of the cabinet, the pivoting of the mirror allowing inclination of the mirror in the extended position to reflect beams from the projector arrays in a forward direction.

22. Apparatus according to claim 21, wherein the screen is vertically slidable with the mirror support from a retracted configuration between the front wall of the cabinet and the projector arrays, and a substantially vertical extended configuration above the front wall.

23. Apparatus according to claim 22, wherein the mirror support also carries a lid for the cabinet.

24. Apparatus for recording and/or playing back video signals, the apparatus being constructed and arranged substantially as herein described and shown in the Figures 2 to 9, 12 and 13 of the drawings.

25. Stereo television picture viewing apparatus constructed and arranged substantially as herein described and shown in Figures 10 and 11 of the drawings.