GB2137010A - Disc player - Google Patents

Abstract

The disc player has a record groove engaging stylus (200) for recovering information from a grooved disc and a kicker transducer (36) for radially translating the stylus across the groove wall during a freeze frame player operating mode to affect repeat play of selected information. A further transducer (40) is activated to place the stylus in a prow-up attitude (Fig. 4) during the freeze frame mode to facilitate traversal of the groove wall and minimize groove wall damage. The further transducer is deactivated during normal play of the disc to minimize stylus wear. <IMAGE>

Description

SPECIFICATION Disc Player This invention relates to a disc player.

An illustrative application of the invention is to video disc players for playing grooved video discs.

One may readily obtain special effects with optical video disc players. In one commercially available optical player, for example, two video fields are recorded for each disc convolution. Stop action is obtained by supplying control signals to the player radial tracking mirror transducer such that the signal recovery light beam repeatedly scans the same disc convolution. Since signal recovery does not involve physical contact with the disc, there is no damage to the disc and no wear concerned with the signal recovery transducer.

It is known generally that one may obtain stop action in a player of the capacitance (or pressure) sensing type by repeatedly playing the same convolution of the information track. The problem of disc damage becomes important in disc systems of the kind wherein the recorded information is stored in the form of topological variations of a spiral groove and recovered by means of a groove engaging stylus. In such grooved-disc systems, repeated "kicking" (radial translation) of the pick-up stylus during freeze frame operation may lead to groove wall damage.

The problem of groove wall damage also exists in certain other "special effect" player operating modes (e.g., "rapid scan", etc.) where the player "kicker" transducer is used to radially translate the stylus across-groove walls to rapidly preview or scan the recorded program.

It is desirable to provide a disc player in which track skipping induced groove wall damage is minimized. It is also desirable to minimize such groove wall damge without significantly degrading the wear characteristics of either the disc groove or the signal recovery stylus.

The present invention is specified in the accompanying Claims.

The invention may be applied, for example, to a video disc player of the type for playing a grooved disc and comprising a stylus adapted for engaging and tracking a spiral groove in the disc to recover information therefrom. Processor means responsive to the information provides the video output signal and a stylus kicker transducer responsive to signal pulses supplied thereto during a selected operating mode of the player radially translates the stylus across the wall of the groove at predetermined times to effect playback of selected fields of the video signal such, a disc player may be improved so as to minimize groove wall damage during the selected operating mode and to minimize stylus wear during a normal continuous play operating mode of the player by means of a further transducer and a control means.The further transducer means is operatively associated with the stylus and responsive when activated for effectively imparting a prow-up attitude to the stylus with respect to the disc to facilitate traversal of the groove wall. The control means activates the further transducer during at least a portion of the time of the selected operating mode and deactivates the further transducer means otherwise.

In the drawings: Figure 1 is a block diagram of a disc player embodying the invention; Figure 2 is a perspective view of a keel-tipped stylus engaging a grooved disc record and adapted for tip rotation in accordance with the invention Figures 3, 4 and 5 illustrate different attitudes of the stylus with respect to the disc of Figure 3; Figures 6, 7, 8 and 9 are mechanical drawings of stylus attitude control arrangements embodying the invention; and Figure 10 is a table summarizing test data. The video Figure 10 is a table summarizing test data.

The video disc player of Figure 1 comprises a player mechanism 10 having a turntable 12 for supporting and rotating a video disc record 14 thereon. Disc 14 may be of the kind proposed for example by Clemens in U.S. Patent No.

3,842,1 94 in which information is stored in the form of topological variations of a spiral groove and recovered by sensing capacitance variations between the groove and a stylus during playback of the record. It will be assumed for purposes of illustration that field identifying data for facilitating tracking of particular video fields is recorded on disc 14 in the form of a digital auxiliary information code (DAXI) as proposed in U.S. Patent No. 4,308,557 of C. B Dieterich which issued December 1981. Video disc records of such a form are commercially available, for example, from RCA Corporation.

The recorded video signal including its tracking data component is recovered from disc 14 by means of a stylus (shown subsequently) which is mounted in a cartridge 16. The cartridge in turn is mounted on a carriage assembly 18 which provides radial translation of a stylus-cartridge assembly across the disc as the disc is played to facilitate tracking of the spiral groove.

Capacitance variations representative of the recorded information which occur between the stylus in cartridge 16 and disc 14 are sensed by means of a pickup circuit 20 which provides an FM output signal S1 representative of the recorded information.

The FM output signal of pickup circuit 20 is applied to the input of a video processor 22 which includes a picture frequency bandpass filter demodulator and conversion circuitry for providing a baseband video output signal S2 of a standard television format such as NTSC or PAL.

Such processors are known, see for example U.S.

Patent No.4,247,866 of T. J. Christopher and J.

A. Wilbur which describes a suitable NTSC standard processor and U.S. Patent No.

4,314,273 of J. G. Amerywhich describes a PAL standard processor. The video output signal S2 (including its accompanying sound components) is supplied to the input of a TV modulator 24 which supplies an RF output signal S3 (inclusive of picture and sound components) to an RF output terminal 26 for connection to the antenna terminal of a conventional television receiver 28.

An integrated circuit suitable for use as TV modulator 24 and which may be selectively operated to provide an output signal on TV channels 3 or 4 for example is the model LM 1889N "TV video modulator" made by National Semiconductor Company Inc.

The tracking information (DAXI) data accompanying the recovered video signal is detected by means of a PCM detector 30 coupled to receive the baseband luminance signal components S4 from a filter in video processor 22. Detector 30 may be of the type described for example by C. B. Dieterich in U.S. Patent No.

4,275,416 which issued June 23, 1981. A player control unit 32 (preferably microprocessor based is described in the Dieterich patent as opposed to the alternative of being implemented with random logic) is coupled to receive the DAXI data signal S5 from PCM detector 30 and player mode control signals from a player control switch unit 34. Unit 34 includes user activated switches for initiating player operating mode functions such as play, pause, scan, stop action, etc. Upon closure of one of the user activated switches in unit 34, controller 32 addresses its internal read only memory (ROM) and fetches an appropriate sequence of instructions resident in the memory for effecting the desire to control function. For example, in the pause operating mode controller 32 produces a video squelch signal SQ and an audio muting signal AM and a stylus lift signal S6.

Signal S6 is applied to a transducer coupled to the stylus assembly in cartridge 16 for lifting the stylus during the pause mode of operation of the player and lowering the stylus during the normal play, stop action and scan modes. Signals SQ and AM are applied to video processor 22 for squelching the video and muting the audio output signals of the processor during certain player operating modes. For example, the video output is squelched during the pause mode of player operation. The audio output is muted during all nonplay operating modes of the player (e.g., the stop action, pause and scan operating modes).

Control unit 32 in addition to lifting and lowering the stylus also generates the stylus kick control signal S7 and a stylus attitude control signal S8. The kick control signal is applied to a stylus kicker transducer 36 which is magnetically coupled to the stylus arm within cartridge 16 for effecting groove-to-groove translation of the stylus when activated. This feature is used in certain operating modes of the player for effecting track error corrections and in another operating mode of the player for producing special effects such as stop action and rapid visual scanning. As an example, during the normal (continuous) play and special effects operating modes of the player control unit 32 monitors the recovered field identification numbers and compares the recovered numbers with expected or desired track numbers.During the play operating mode the progression of field numbers should be monotonic. If a track error occurs, for example, a skip backwards, then the error in the progression of field numbers will be sensed in controller 32 and the magnitude of the skip backwards will be determined whereupon the stylus kick control signal S7 will activate kicker transducer 36 to return the stylus to the proper groove convolution.

During the "stop action" or "freeze frame" operating modes control unit 32 supplies kick pulses to transducer 36 once each revolution of disc 14 thereby repeating the video fields recorded in one convolution of the disc to create a stop motion effect. In one form of commercially available video disc player there are four complete video frames per revolution of the disc. Hence, if the video information during the four frames of the one revolution is substantially the same and without motion, the signal readout appearing on television receiver 28 will appear as a still image.

If, however, the signal information during the four frames of the repeated convolution is that of an image in motion, then the repetitious playback of the four frames will show a continuous repeat of the motion occurring during the four frame interval. This type of motion display is particularly usefui when instructional information is recorded on the video disc such as a.tennis or golf lesson where it may be desirable to show a particular motion of, for example, a tennis or golf swing. In the "scan" special effects operating mode control unit 32 supplies kick pulses to kicker transducer 36 which radially translates the stylus in cartridge 16 several grooves in the forward or reverse direction thus skipping the intermediate grooves and causing the displayed image to appear speeded up in proportion to the number of video fields skipped.

In both the stop action and the rapid scan operating modes, the stylus is engaged with the groove in disc 14 and is translated by kicker transducer 36 across the groove wall. The repeated traversal of the groove wall is timed so as to occur when in the vertical interval of the recorded video fields on disc 14 and so is not visible to the user of the video disc player in normal operation. It has been found however, particularly with regard to the freeze frame mode of operation where the same groove is repeatedly traversed, that groove wall damage can occur under certain circumstances. This damage is minimized in accordance with the invention by placing the stylus in a "prow up" attitude during the stop action and/or scan operating modes of the player and returning the stylus to a normal "level" mode of operation during the normal "continuous" play operating mode. Specifically, the stylus attitude control signal S8 is produced in control unit 32 during the stop action and scan operating modes. Signal S8 is applied to an attitude control transducer 40 which is mechanically coupled to a member of the player mechanism or stylus cartridge 10 to alter the attitude of the signal recovery stylus.

The perspective view of the stylus and disc shown in Figure 2 illustrates the new motion imparted to the stylus tip in accordance with the invention to minimize groove wall damage and stylus tip wear. In Figure 2 a keel-tipped stylus 200 is shown with the tip thereof engaged in a groove 202 of video disc record 14. The stylus includes a beveled leading edge 204 known as the prow, a substantially flat record engaging portion shaped to the groove contour 206 extending from the leading edge or prow to the trailing edge which is a flat surface normal to the plane of the disc on which there is deposited a conductive electrode 208 which provides capacitive sensing. Fabrication of styli of this type is described for example in U.S. Patent Nos.

4,369,604 and 4,162,510.

In conventional video disc players such a stylus is subjected to three forms of motion. Specifically, the stylus is moved vertically with respect to the record in response to the stylus lifting lowering mechanism, it moves tangentially in the direction of the groove when playing a disc and it moves radially to traverse groove walls in response to the stylus kicker transducer action. In accordance with the invention, the stylus of the player of Figure 1 is subjected to a fourth form of motion, namely rotation about an axis lying in a plane parallel to the plane of the disc and aligned with the radius of the disc. During the normal continuous play operating mode of the player control unit 32 deactivates control transducer 40, which rotates stylus 200 so as to assume an attitude in which the shoe 206 of the stylus is level or fully engaged with groove 202.In this attitude the signal elements which comprise the information stored with groove 202 fully support the tip end or groove engaging portion of the stylus and represent minimum wear condition for the stylus. During the stop action and freeze frame operating modes, control unit 32 generates signal S8 which activates transducer 40 to rotate stylus 200 in a sense to assume a prow up operating condition. This facilitates traversal over the walls of groove 202 during the special effects operating modes.

Figures 3 and 4 provide further illustration of the stylus attitude during the normal play and special effects operating modes, respectively. It is important that the stylus attitude be different in these two operating modes to provide a balance between groove damage and stylus wear. In the normal or continuous play operating mode, the stylus is level with respect to the disc as shown in Figure 3, which minimizes stylus wear as previously mentioned because of the full support imparted to the stylus shoe by the signal elements recorded on the disc. The length "L" of the stylus shoe as shown is long as compared with the period between signal elements so that essentially the entire record engaging tip of the stylus is supported by the signal elements. When in this attitude, stylus wear is minimal.This represents the normal operating mode of the player and the optimum stylus attitude for recovering signals from the disc. The prow-up attitude illustrated in Figure 4 facilitates traversal of groove walls with minimum damage but reduces the contact of the stylus tip with the disc.

If the stylus were permanently fixed in this position the stylus would wear flat relatively quickly to assume the level condition shown in Figure 3. In accordance with the invention, the stylus is placed in the prow-up attitude only during the times special effects are desired so that the effect of the increased wear on the trailing edge of the stylus is minimal since this represents only a very small fraction of the normal playing time of the player. Figure 5 illustrates a stylus attitude to be avoided, namely a prowdown attitude. The relatively sharp prow seriously damages groove walls. Also, this attitude decreases the amount of signal which may be recovered since the signal sensing electrode on the trailing edge of the stylus is displaced farther from the signal elements on disc 14.

The table of Figure 10 illustrates the dramatic improvement in special effects playing time obtained in accordance with the invention. The first column of the table will be discussed subsequently in connection with Figures 6, 7, 8 and 9. Two tests were performed with the stylus in a level attitude such that the stylus shoe angle was essentially 00. As can be seen, playing times of 110 and 240 minutes without groove wall damage were obtained when repeatedly playing a single convolution of the disc in the freeze frame operating mode.When the stylus attitude was changed to prow-up, playing times without damage to the groove wall of 300 to 1,000 minutes were obtained with a shoe angle of 0.30 and playing times in excess of 3,000 minutes were obtained without damage when the shoe angle was a positive angle of 0.70. The level and prow-up attitudes correspond to those illustrated in Figures 3 and 4. When the stylus was operated with the prow-down attitude, as shown in Figure 5, playing times of 105 and 25 minutes were obtained for negative shoe angles of #0.70 and ~1.3 respectively.

Looking at the data as a whole it is clear that for positive shoe angles, that is a prow-up attitude of the stylus, there is a dramatic improvement in the playing time of the special effects mode of operation of the player and it is also clear that the prow-down attitude is a situation to be avoided.

There is a practical limit however, as to an improvement that may be obtained by operating the stylus in a prow-up attitude. The greater the prow angle in the positive sense the greater will be the wear on the aft or trailing end of the stylus.

A point will be reached where the wear is sufficient to cause accelerated wear of the stylus electrode. This point occurs for shoe angles greater than about +30. An optimum stylus attitude is approximately +0.70 which provides extended playing time with minimal visible effects on the image displayed in the television receiver.

Figures 6, 7, 8 and 9 illustrate four arrangements embodying the invention for altering the stylus attitude in accordance with the mode of operation of the player of Figure 1. In Figure 6 the attitude control transducer 40 comprises a rotary solenoid 600 having terminals 602 and 604 for receiving the stylus attitude control signal S8 and an output shaft 606 having screw threads thereon engaged with a fixed member (e.g., the motor board 608) of the video disc player mechanism 10. When the solenoid is activated the screw threads on the shaft rotate in a sense to lower ball bearing 610. Conversely, when splenoid 600 is deactivated a spring return in the solenoid rotates shaft 606 in a sense to raise ball bearing 610 (supported by the end of shaft 606).Bearing 610 provides support for the shaft 612 of turntable 12 whereby activation and deactivation of solenoid 600 causes a change in the turntable height AH as shown. This, in turn, varies the stylus angle as will now be explained.

Stylus 200 is mounted in a stylus holder 202 that is secured to one end of a stylus arm 204 (a tubular shaft). The other end of stylus arm 204 is coupled via a compliant member 206 to a magnetic end plate 208 commonly called the tail post of the stylus assembly. The tail post is suspended within the stylus cartridge 16 by means of a compliant member (not shown) and provides support for the stylus arm and stylus.

The tail post is magnetic and cooperates with a so-called "arm stretcher" transducer and imparting tangential motion to the stylus to facilitate time base correction. Pivoting of the stylus arm assembly occurs at a point in the vicinity of the compliant member 206. The stylus holder 202 includes a magnet 210 affixed thereto which cooperates with an electromagnetic coil 212 for affecting radial translation of the stylus 200 when coil 212 is energized. The coil terminals 214 and 216 are coupled to receive the stylus kick pulse signal S7 produced by control unit 32 during the special effects operating modes of the player, during times of track error correction and during the normal continuous play operating mode.

The height of the tail post 208 of the stylus assembly with respect to the turntable (or disc) determines the stylus shoe angle since the stylus arm assembly essentially pivots at the tail post location. As the turntable height is raised the angle of the arm relative to turntable decreases and this decreases the stylus shoe angle.

Conversely, as the turntable height is lowered the arm forms a less acute angle with the turntable thereby increasing the stylus shoe angle with respect to the disc 14. This change in turntable height AH is imparted to the turntable by means of rotary solenoid 600 as previously explained.

Referring to Figure 10 the turntable height will normally be adjusted to provide a stylus angle of 0 during the normal play operating mode of the player. For reference purposes AH would be 0.000 inches as indicated in column one of the table of Figure 10. The pitch of the threads on shaft 606 is selected to provide a positive displacement of bearing 610 when rotary solenoid 600 is activated for lowering the turntable thereby effectively increasing the tail post height with respect to the turntable and thus imparting a positive shoe angle to the stylus.

In the stylus attitude control arrangement of Figure 7, the turntable is maintained in a stationary vertical position and the stylus assembly tail post 208 is raised with respect to the turntable to effect a prow-up attitude. Here, a linear solenoid 700 has terminal 702 and 704 for receiving the stylus attitude control signal S8 and an output shaft 706 coupled to an arm carriage guide rail 708. The arm carriage 18 is provided with a roller 710 at one end thereof which rolls on guide rail 708 as the arm carriage is translated radially across disc 14. The other end of the arm carriage 1 8 is fixed to a sliding member 712 which slides on a round shaft 714 to guide the arm carriage. Activation of solenoid 700 lifts the guide rail 708 during the special effects operating modes thereby raising the tail post 208 with respect to disc 14 and imparting and prow-up attitude to the stylus 200.

Figure 8 illustrates a variation of the arrangement of Figure 7 wherein the height of the guide rail is controlled by means of a solenoid 800 having terminals 802 and 804 for receiving the stylus attitude control signal S8. Here the shaft 806 of solenoid 800 is coupled to an eccentric 808 which in turn rotates the arm carriage guide rail 714 when the rotary solenoid is activated. The other end of shaft 714 is coupled via a similar eccentric 810 to a stationary shaft 812 that is fixed to a member of the player mechanism 10 but free to rotate on its on axis.

The sliding member 712 of arm carriage assembly 18 is thus lifted or lowered with respect to the turntable in accordance with the state of solenoid 800. When the solenoid is activated shaft 806 rotates in a clockwise sense which lifts sliding member 712. This increases the height of the tail post 208 with respect to turntable 12.

Deactivation of solenoid 800 lowers member 712 returning the tail post to its original height to maintain the stylus attitude in its original level position. Since the stylus rotates about an axis near the electrode end, there is little discelectrode motion involved and thus activation of the tilting solenoid does not introduce any significant timebase errors in the recovered video signal.

In the example of Figure 9, the stylus cartridge 16 is tilted with respect to the arm carriage 18 to effect alteration of the attitude of stylus 200 and thus control the shoe angle of the stylus with respect to disc 14. The cartridge tilt is provided by means of a lever arm 900 which is pivoted about a point 902 on the lower surface of arm carriage 18. One end of the arm is engaged with the cartridge assembly 1 6 and the other end of the arm is provided with an electromagnet 904.

Magnet 904 is proximate a solenoid coil 906 having terminals 908 and 910 for receiving the stylus attitude control signal S8. When coil 906 is not energized cartridge 16 will be in a first (level) position corresponding to a stylus shoe angle of 00. This represents the normal continuous play operating mode of the player. When coil 906 is energized lever arm 900-lifts the end of catridge 16 thereby lifting tail post 208 with respect to disc 14. This rotates stylus 200 in a sense to create a prow-up attitude during the special effects operating mode.

It will be appreciated that various changes and modifications may be made to the embodiments of the invention herein shown and described. As an example, the various solenoids may be replaced by other suitable forms of transducers and may be coupled by other mechanical arrangements so as to impart a rotation to the stylus as described. It will also be appreciated that where the inertia of the stylus tilting mechanism permits one may activate the stylus tilter during track error correction modes of the video disc player to impart tilt to the stylus at any time the stylus is undergoing a radial translation. It will also be appreciated that in the various embodiments of the invention shown the record has been illustrated as being played from its upper surface. The principle of the invention, however, apply equally to players wherein the stylus engages the disc on its lower surface.

Claims (10)

1. A disc player for playing a grooved disc and comprising: a stylus for picking-up recorded information from a spiral groove in said disc; processor means responsive to said information for providing an output signal; a stylus kicker transducer responsive to signal pulses supplied thereto during a selected operating mode of said player for radially translating said stylus across the wall of said groove to effect playback of selected portions of said information; further transducer means operatively associated with said stylus and responsive when activated for effectively imparting an attitude to said stylus with respect to said disc in which the loading edge thereof is raised from the disc to facilitate traversal of said groove wall; and control means for activating said further transducer means during at least a portion of the time of the selected operating mode and for deactivating said further transducer means otherwise.

2. A disc player as recited in Claim 1 wherein the said attitude of said stylus corresponds to a predetermined shoe angle between said disc and a surface of said stylus which engages the disc when the further transducer is deactivated, said shoe angle lying within a range of about 0.3 degrees to about 3.0 degrees.

3. A disc player as recited in Claim 2 wherein said predetermined angle is approximately 0.7 degrees.

4. A disc player as recited in Claim 1, 2 or 3 wherein said further transducer means is coupled to a selected member of said player for effectively rotating said stylus about an axis, said axis being aligned radially with respect to said disc and lying in a plane substantially parallel with the plane defined by said disc.

5. A disc player as recited in Claim 1,2,3 or 4 wherein said further transducer means is coupled to a turntable of said player for controlling the turntable height.

6. A disc player as recited in Claim 1,2,3 or 4 wherein the said stylus is housed in a cartridge which is mounted in a carriage which is movable radially of the disc and said further transducer means is coupled to the carriage of said player for controlling the attitude of said stylus.

7. A disc player as recited in Claim 1,2,3 or 4 wherein the said stylus is housed in a cartridge and said further transducer melons is coupled to the cartridge for controlling the attitude of said stylus.

8. A disc player substantially as hereinbefore described with reference to Figure 1,6,7,8 or 9 of the drawings.

9. A video disc player according to any preceding claim.

10. A video disc player substantially as hereinbefore described with reference to Figures 1 and 2 and to Figure 6, 7, 8 or 9 of the drawings.