GB2061568A - Video disc preview apparatus - Google Patents

Abstract

A video disc player apparatus having a preview feature. A signal pickup stylus (24) assembly is compliantly mounted (45) in a carriage assembly (20) for translating the stylus radially across the record. A transducer (23) responsive to user operated player controls (68) imparts translatory motion to the stylus relative to the carriage assembly and directed radially across the record causing the stylus to translate a prescribed number or record grooves per impulse. A position sensor (60) secured to the carriage assembly proximate the stylus monitors the stylus position relative to the carriage. Signals (65) derived from the position sensor are applied to the carriage assembly motor drive to maintain the carriage speed consonant with the average radial translation of the stylus. The user controls (68) either energise or gate an oscillator (66) which provides pulses to the transducer (23) which may be synchronised with blanking periods in the video recording. <IMAGE>

Description

SPECIFICATION Video disc preview apparatus This invention relates to video disc playback systems and in particular to a means for previewing record disc information in a relatively short time.

In certain video disc systems, information is prerecorded on record discs having information bearing tracks eg spiral grooves. The information is recovered by a track-following stylus contoured to engage the track. The stylus is mounted to a stylus arm attached via a compliant coupling to a carriage assembly which is driven to translate the stylus radially across the disc. The compliant coupling permits limited relative motion between the stylus and the carriage assembly.

A desirable feature of such a system is the ability to scan a record to obtain a general insight as to its information content, or to be able to translate the stylus to a particular area from memory based on viewing short intervals of the video information. Early attempts to include a preview feature consisted of manually translating the stylus with a thumbwheel assembly to override the normal carriage translation. The stylus-stylus arm assembly engaged a stop or bumper on the carriage assembly and was forced across the tracks. Although this method proved to be effective for scanning the disc it occasionally manifested a tendency to score the disc.

A system whereby the stylus is disengaged from the disc before manually translating the carriage, and periodically reengaged to display a picture as the record is scanned is not a desirable system since too little information is transmitted to the viewer.

It has been demonstrated that a stylus can be translated across one or more disc grooves, with little or no damage to the disc, by a kicker mechanism as described in our U.S. Patent No.

3,993,863 entitled, "Disc Record Groove Skipper", or our U.S. Patent Specification No.

41 83059 in the name of R. C. Palmer entitled, "Track Skipper for A Video Disc Player".

The present invention utilizes this feature to effect a stylus-carriage translation for scanning purposes with minimal or no damage to the record disc.

In the present invention a signal pickup device is mounted in a carriage assembly with a pickup skipper mechanism and a position detector for monitoring the relative stylus-carriage relationship. A pulse generator activated by a scan switch energizes the skipper mechanism at a predetermined rate to translate the stylus a prescribed number of tracks per revolution of the record. The stylus advances radially across the record at a rate in excess of the normal play speed.

The position sensor, responsive to the relative stylus-carriage relationship controls a motive means to establish the carriage translational speed in accordance with the average radial translatory motion of the stylus.

In the drawings: FIGURE 1 is a diagrammatic representation of a video disc player incorporating a record preview mechanism pursuant to the present invention; FIGURE 2 is a diagrammatic representation of the mechanism for translating the player carriage assembly; FIGURE 3 is a schematic representation of a stylus skipper mechanism; and FIGURE 4 is a schematic representation of a record scanning/preview apparatus embodying the present invention.

The video disc player 10 shown in FIGURE 1 includes a stylus supporting carriage assembly 20 which is translated over a portion of the record disc 11 by the motor 32. Carriage assembly 20 having rollers 28 mounted thereon moves along the rigid channels 29 providing precisely ascertained translation of the assembly across the record disc. A record disc 11 having information bearing tracks is rotated by turntable 12 producing relative motion between the information tracks and the signal pickup stylus 24.

Pickup stylus 24 is mounted to the free end of a stylus arm 22, the other end of which is compliantly coupled to a cartridge 21 which is removably received in the carriage assembly 20.

Included within the cartridge is a position sensor 25 for determining the relative position of the stylus/stylus arm with respect to the carriage and/or its relaxed or non-mechanically biased position. Control circuitry 26 responsive to the signal provided by the position sensor 25 generates a drive signal to condition motor 32 to maintain the motion of the carriage assembly in consonance with the radial translation of the groove following stylus and tending to sustain the stylus arm in a substantially unbiased position relative to its relaxed position.

A pair of electromagnetic coils 23 are secured to the carriage assembly disposed on either side of the stylus arm, which coils áre selectively energized to generate a magnetic field therebetween. The coils are arranged so that a small permanent magnet secured to the stylus arm will be disposed within the magnetic field when the stylus is in the normal play position. The permanent magnet and the coils 23 constitute the stylus skipper transducer.

The mechanical coupling between carriage drive motor 32 and the carriage assembly 20 is exemplified in FIGURE 2. The carriage assembly 20 includes an extension 27, the bottom edge of which is configured with teeth 33. Sprocket 31 engaging the teeth 33 is driven by the shaft of motor 32 to produce linear motion of the carriage and thus translate the carriage 20 radially across the record disc 11.

A particular stylus/stylus arm-skipper arrangement is illustrated in the FIGURE 3. Stylus 24 is fixedly mounted at the free end of stylus arm 22 the other end of which is coupled to a cartridge or carriage assembly (not shown) by compliant coupling 45 permitting limited movement of the stylus relative to the cartridge/carriage in the three dimensions shown. A permanent magnet 46 is secured to stylus arm 22, disposed between selectively energized coils 23. Coils 23, mounted to the cartridge/carriage assembly, have non magnetic cores and are connected to produce aiding magnetic fields therebetween when energized. Selectively energizing the coils in a particular polarity with a particular drive pulse to generate a magnetic field of a particular strength will create a prescribed translation of the magnet 46 and thereby translation of stylus 24 along the "x" axis.

Electrical connection is made to the pickup stylus 24 through metallic flylead 47 secured to the carriage/cartridge assembly by ball 48 having a connection 49. An electrode 50 mounted to the cartridge/carriage proximate the flylead and having electrical connection 51 forms a capacitor with flylead 47. The value of the capacitance varies in accordance with the spacing between flylead 47 and electrode 50 which varies proportional to the "x" directed movement of the stylus relative to the cartridge/carriage assembly.

Sensing the relative value of capacitance relative to a non-mechanically biased position of the stylus provides an indication of the relative position of the stylus with respect to the carriage. A sensing apparatus useful for detecting this relative capacitance includes an oscillator for applying an oscillatory signal to one plate of the capacitor and a circuit for sensing the amplitude of the oscillatory signal coupled to the other plate of the capacitor which amplitude is indicative of the relative spacing between the plates. One such apparatus is more fully described in U.K. patent application No.8022160, inventor B. K. Taylor which features stylus position sensing apparatus.

In FIGURE 4, position sensor 60 generates a signal at connection 61 proportional to the relative position of the stylus 24 with respect to the sensor secured to the carriage. This signal is amplified and compared with a reference value by amplifier circuitry 62. The reference value corresponds to the relaxed position of the stylus arm 24. A position signal corresponding to the reference signal produces no output signal to connection 63 to driver circuitry 64. A stylus position nearer to the sensor or farther from the sensor relative to its relaxed position applied to ampiifier 62 generates a signal at connection 63 proportional to the stylus position to control the output signal of driver circuit 64 applied via connection 65 to the motor 32.

Driver circuit 64 produces a nominal output signal to drive the carriage at a rate predetermined to maintain the carriage translation in synchronism with the radial progression of the groove following pickup stylus. Signal applied to driver 64 via connection 63, increases or decreases its output signal thereby modulating the speed of motor 32 to compensate for carriage translational motion tending to create a mechanical bias in the stylus arm due to relative carriage-groove motion.

A record disc is previewed by energizing the stylus skipper transducer inclusive of coils 23 and magnet 46 at a prescribed rate established by oscillator circuit 66. The skipper forces a mechanical bias on the stylus arm causing the position sensor to generate a signal to condition the motor to increase or decrease the carriage speed, thereby tending to cause the carriage to "catch" the stylus.

The stylus skipper circuitry comprises a driver circuit 67 which generates an output signal appropriate to drive the particular stylus skipper transducer, an oscillator 66 to establish the rate at which drive signals will be applied to the transducer, and control circuitry 68.

Control circuitry 68 is typically part of the user operated player controls. The complexity of such controls are dependent upon the number of player options. For example, such controls may include means to control the direction of skipper induced stylus translation, the number of grooves translated per skip, the rate at which skips are induced, whether the oscillator operates synchronously with record rotation or asynchronously therewith, and in addition control of the carriage direction.

Oscillator 66 may be a free running multivibrator with its rate programmed by switching between timing capacitors in a simpler embodiment. On the other hand it may be embodied as a voltage controlled oscillator in a phase locked loop circuit for providing synchronization with, for example, vertical blanking signals from the recovered video signal.

In either case, the oscillator provides trigger signals applied to the skipper drive circuit 67 to initiate drive pulses at some predetermined rate. It is noted that to inhibit skipper action the oscillator 66 itself may be inhibited or the driver 67 may be inhibited with the oscillator allowed to continuously oscillate.

As a particular example, for forward (inward) scan operation, skipper induced stylus translations of 120 per second, translating two grooves per skip provides a reasonable scanning rate without undue displeasing video interference.

Claims (10)

1. In a video disc playback system for recovering recorded information from a record disc having information bearing tracks, including a pickup device mounted to a first end of a support member, the second end thereof being compliantly coupled to a carriage assembly for traversing said pickup device radially across the record, the velocity of said carriage assembly being determined by the mechanical bias of the support member with respect to the carriage assembly, a preview apparatus comprising:: translating means responsive to drive signals for translating the pickup device relative to the carriage assembly and directed radially across the record disc; circuit means for generating drive signals at a prescribed average repetition rate so that said translating means produces a time-average mechanical bias on the support member thereby determining the velocity of translation of the carriage assembly.

2. The apparatus set forth in claim 1 wherein the translating means comprises: a pair of electromagnetic coils responsive to said drive signals for selectively producing a magnetic field therebetween, having nonmagnetic cores and being fixedly attached to the carriage assembly; and a permanent magnet secured to the support member and disposed between said coils.

3. The apparatus set forth in claim 1 wherein the circuit means is synchronized with the information on the record disc so that said drive signals occur to impart pickup device translation at prescribed positions on the record disc.

4. The apparatus set forth in claim 1 wherein the circuit means generates drive signals to produce pickup device translations at random angular positions on the record disc.

5. The apparatus set forth in claim 3 or claim 4 wherein the drive signals occur at an average rate of 120 per second and the pickup device is caused to translate two tracks per translation.

6. In a video disc player system having a signal pickup stylus secured to a stylus arm, which is compliantly mounted in a carriage assembly arranged to translate the signal pickup stylus radially across a record disc at a prescribed rate; apparatus comprising transducer means responsive to transducer drive signals for translating the stylus relative to the carriage assembly in a direction radially across the record disc; circuitry responsive to player controls for generating the transducer drive signals to effect prescribed translations of said stylus; detection means associated with the carriage assembly for generating position signals proportional to the instantaneous position of the stylus relative to its mechanically unbiased position;; means responsive to said position signals for adjusting the rate of translation of the carriage assembly, whereby the rate of transducer induced stylus translations establishes the rate of carriage translation.

7. The apparatus set forth in claim 6 wherein the detector means comprises: a capacitor having an air dielectric with a first plate secured to the carriage assembly and a second plate arranged proximate the signal pickup stylus and constrained to move in conformance with the signal pickup stylus; means for applying an oscillatory signal to one of said first and second capacitor plates; and means for detecting the relative strength of said oscillatory signal coupled between said first and second capacitor plates, the signal strength being inversely proportional to the distance between the first and second capacitor plates.

8. The apparatus set forth in claim 6 wherein the transducer means comprises: a pair of electromagnetic coils responsive to said drive signals for selectively producing a magnetic field therebetween having nonmagnetic cores and being fixedly attached to the carriage assembly; and a permanent magnet secured to the stylus arm and disposed between said coils.

9. The apparatus set forth in claim 8 or 8 wherein the circuitry for generating transducer drive signals comprises: a pulse generator responsive to trigger signals for producing a drive signal of prescribed amplitude and duration, said drive signal being applied to the transducer means; means for selectively determining the polarity of the pulse generator drive signal and thereby the direction of stylus translation; and an oscillator for generating said trigger signals at a prescribed rate.

10. Tracked information disc preview apparatus having manually controlled radial translation of the pickup, substantially as hereinbefore described with reference to the drawings.