GB2056721A - Stylus position sensing apparatus for a disc record player - Google Patents

Abstract

In a video disc player, a stylus arm (24), carrying a track following stylus (20) at one end thereof, has its other end secured to a carriage by a compliant member (30). The carriage is translated along a path disposed radially of the disc record during playback. Pickup circuits (52) are employed for sensing the variations in a signal representative capacitance formed between an electrode incorporated in the pickup stylus and conductive material disposed in the record to recover pre- recorded information from a spiral track disposed on the record. A stylus position indicative capacitance (94, 98) established between a first electrode secured to the stylus arm and coupled to the pickup circuits and a second electrode mounted to the carriage in the vicinity of the first electrode, is provided. In an embodiment, the stylus position representative capacitance is formed between a signal coupling flylead (38) of the stylus and the second electrode which is mounted on a cartridge (32) housing the stylus in the carriage. Circuitry (108-112) is provided for sensing signals appearing at the output of the pickup circuits to generate a signal indicative of the position of the pickup stylus relative to the arm cage. The rate of translation of the carriage is varied (46) in response to the stylus position indicative signal to maintain a desired relationship between the pickup stylus and the arm cage. <IMAGE>

Description

SPECIFICATION Stylus position sensing apparatus for a disc record player This invention relates to an apparatus for sensing the relative position of a track-following stylus with respect to an independentlydriven arm carriage suitable for a disc record player.

In a certain high density information record system, signals are recorded in the form of geometric variations in the bottom of a smooth spiral groove disposed on a disc record, the surface of which comprises conductive material covered with a thin coating of dielectric material. The record player includes a stylus arm carrying a groove-engaging stylus at its free end, and having its other end secured by means of a compliant coupler to an arm carriage. A turntable is provided for rotatably supporting the record during playback. The arm carriage is subject to translation, independent of the laterial motion of the groove-engaging stylus, along a path disposed radially of the disc record during playback.

Pickup circuits are employed for sensing the variations in the signal representative capacitance established between an electrode incorporated in the pickup stylus and the record conductive material as the record is rotated to recover prerecorded signals. U. S. patent No.

3,842,194, issued to Clemens describes a capacitance pickup system of the abovementioned type.

In a high density information record system, it is desirable to house the stylus assembly in a protective cartridge of the type described in U. S. patent No. 4,030,124 (Allen). In the arrangement described in the Allen patent the stylus arm has its other end secured to the cartridge housing by a compliant coupler. A conductive leaf spring is interposed between the stylus electrode and a terminal disposed on the cartridge. The pickup cartridge is subject to reception in a compartment provided in the translatable arm carriage. An electrical contact is established between the cartridge terminal and the pickup circuits during containment of the cartridge in the carriage compartment. The stylus leaf spring is described in more detail in U. S. patent No. 4,077,050 (Dholakia).

In the playback of disc records having high groove densities (e.g., of the order of 3,500 to 4,000 groove convolutions percentimeter conditions are occasionally encountered when the presence of some form of discontinuity in the disc groove causes the pickup stylus to skip across groove convolutions rather than follow the successive convolutions of the spiral groove in a continuous progression. Depending on the nature of a defect, an encounter of the stylus with the defect may result in an inward deflection of the pickup stylus (i.e., forward skip) or an upward deflection thereof (i.e., backward skip). In some instances, the outward deflection of the stylus is repeated a number of times causing the stylus to retrace one or more previously traversed convolutions, and thereby producing repeat play with annoying effects on picture display and sound reproduction.Such a repeat traversal of groove convolutions is referred to hereinafter as a "locked groove" occurrence.

In systems of the foregoing type, it is desirable to make a provision for correction of the locked groove problems, for example, by causing inward displacement of the pickup stylus upon occurrence of a locked groove to relocate the stylus to a point along the continuation of the spiral groove beyond the particular defect causing backward groove skips.

The apparatus used for relocating the stylus from one groove convolution to another, in addition to its use for the locked groove correction function, is also suitable for providing such features as fast/slow forward motion, fast/slow reverse motion, repeat play and search. U. K. patent appln. serial No.

2034507A in the name of Simshauser describes an illustrative track skipper apparatus.

Effective operation of the track skipping systems of the type described above requires that a fixed spatial relationship be maintained between the pickup stylus and the arm carriage. To this end, a system for sensing the relative position of the stylus with respect to the arm carriage is described.

The system disclosed includes a pickup stylus position indicative capacitance formed between a first electrode secured to the stylus and a second electrode mounted to the carriage near the first electrode. The player signal pickup circuits also serve to sense the variations in the stylus position indicative capacitance to provide a signal representative of the stylus relative position.

The rate of translation of the carriage may be varied in response to the stylus position representative signal in a manner that maintains an advantageous spatial relationship between the stylus arm and the carriage. Illustrative dimensions are as follows: (1) the stylusmounted movable electrode = 0.013 X 0. 190 c.m.'s (2) the carriage-mounted stationary electrode = 0.050 X 0.250 c.m.'s and (3) the lateral electrode spacing = In accordance with an aspect of the present invention, the stylus flylead additionally serves as the movable electrode of the stylus position indicative capacitance.

Field adjustments in the spacing between the stylus-mounted first electrode and the carriage-mounted second electrode might become necessary subsequent to the installation of the pickup cartridge in the carriage compartment because of the fineness of the dimensions involved. Pursuant to a further feature of the invention, the second electrode is fixedly disposed in the cartridge housing. The spacing between the flylead and the cartridgemounted electrode in the apparatus can be factory adjusted and thus substantially avoid the need for further field adjustments.

IN THE DRAWINGS: Figure 1 is a diagrammatic representation of a capacitance type of video disc player incorporating the stylus position sensing apparatus; Figure 2 schematically illustrates the principles of the capacitance type of signal pickup system; Figure 3 presents a perspective view of a pickup cartridge suitable for use with the stylus position sensing apparatus of Fig. 1, the pickup cartridge being shown upside down to expose its features; Figure 4 depicts a perspective view of a portion of the upside-down pickup cartridge of Fig. 3, partially broken away to illustrate the details thereof; Figure 5shown in block diagram form the player electronics including circuitry for the stylus position sensing apparatus of Fig. 1; Figures 6 and 7 illustrate schematic circuit diagrams for realizing various functions of the stylus position sensing system of Fig. 5; and Figures 8-10show a stylus position sensing apparatus in accordance with the present invention, wherein Figs. 8-10 respectively correspond to Figs. 1, 3 and 4.

Fig. 1 diagrammatically illustrates a video disc player 10 having a turntable 12 for rotatably supporting a disc record 14. A motor drives the turntable to rotate at proper speed, U. S. patent No. 3,912,283, issued to Hammond, et al., describes a illustrative turntable drive system. Video signals are recorded, as schematically shown in Fig. 2, in the form of undulations of a smooth spiral groove 16 disposed on the disc record, the surface of " which comprises a thin coating of dielectric material 18 overlying conductive material 19.

A pickup stylus 20 incorporates a conductive electrode 22 which forms a signal representative capacitance with the record conductive material when the stylus is lowered on the record for playback. The signal representative capacitance varies in accordance with the sig nals recorded on the disc as stylus/record relative motion is established. The player employes pickup circuits repsonsive to the signal representative capacitance variations for reconstructing recorded signals.

The pickup stylus 20 is secured to the free end of a stylus arm 24 by means of a stylus holder 26 in the manner shown in Figs. 3 and 4. The other end of the stylus arm 24 is secured to a connector plate 28 by means of a compliant coupler 30. The connector plate is suspended in a pickup cartridge 32 by means of a flexible diaphragm 34. A U shaped spring 36 serves to retain the delicate stylus assembly within the confines of the cartridge body during its storage and handling. A conductive leaf spring 38 (i.e., flyhead) connects the pickup electrode 22 to a terminal 40 on the cartridge body. An extension 42 is disposed on the stylus holder for constraining side-to-side excursions of the stylus.

The player includes an arm carriage 44 which is subject to translation along a path disposed radially of the disc record 14 placed on the turntable 12. As shown schematically in Fig. 1, a variable speed, DC motor 46 causes translation of the carriage at an appropriate speed in the manner described subsequently.

The carriage 44 is provided with a compartment 48 for removably receiving the pickup cartridge 32. Placement of the cartridge in the carriage compartment establishes electrical contact between the cartridge terminal 40 and a terminal 50 of a pickup circuit 52. Mounted in the carriage is an armstretcher apparatus 54. When the cartridge is installed in the carriage and a lid 56 of the carriage is closed, a mechanism 58, responsive to the lid movement, pushes the armstretcher toward the cartridge to effect mechanical engagement between the cartridge connector plate 28 and a translatable support disposed on the armstretcher. The armstretcher 54 imparts translatory motion to the stylus in a manner that opposes cylical deviations in the stylus-record relative velocity during playback.The cylical deviations in the stylus/record relative velocity result from a number of sources, for example, eccentricity, warp, etc. U. S. patent No.

3,983,318 (Miller) describes an illustrative armstretcher apparatus.

Also disposed in the carriage is a stylus arm lifting/lowering apparatus 60. The lifting/ lowering apparatus serves (1) to gently lower the pickup stylus on the record for playback, (2) to lift the stylus away from the record in the pause mode of the player, and (3) to raise the stylus for allowing it to clear the record bead as the carriage moves from an off-record rest position to an on-record play position.

When the lid 56 is closed, a tab disposed thereon defeats the stylus arm retaining spring 36, permitting the stylus arm 24 to rest on a support member 62 of the lifting/lowering apparatus. The bottom wall of the carriage has an opening 64 through which the pickup stylus is lowered for playback. Reference may be made to U. S. patent No. 4,053,161 (Bleazey) for a more detailed description of the stylus arm lifting/lowering apparatus.

The Simshauser track skipper apparatus (U.K. patent appln. Serial No. 2034507A comprises a small, light-weight permanent magnet 66 secured on the back side of the extension 42, and a pair of large diameter, air-core coils 68 and 70 disposed about plastic bumpers 72 and 74 mounted in the car riage. It will be noted that the bumpers 72 and 74 limit the side-to-side excursions of the extension 42 disposed on the stylus arm. The skipper coils are connected such that upon energization, they generate aiding magnetic fields. The permanent magnet is so dimensioned that its north pole is interposed between the coils when the stylus is lowered for playback. The stylus arm is displaced inward or outward depending upon the polarity of the actuating pulse applied to the coils.As previously indicated, the track skipper apparatus serves a multitude of functions, such as locked groove clearance, special effects, active searches, etc.

Fig. 5 is a block diagram representation of player electronics including circuitry for the stylus position sensing apparatus. The circuitry employed to recover the signals recorded on the disc will be explained first. As shown in Fig. 5, the terminal 50 of the pickup circuit 52 is coupled to the conductive stylus electrode 22. The pickup circuit, responsive to the variations in the signal representative capacitance 53 formed between the stylus electrode 22 and the conductive material of the record 14, provides at the output terminal 76 thereof audio and video signals recorded on the disc.

Reference may be made to U.S. patents issued to Carlson, et al. No. 3,872,240 and Kawamoto, et al. No. 4,080,625 for descriptions of illustrative pickup circuits. The output of the pickup circuit 52 is delivered to a pair of bandpass filters 78 and 80. The picture carrier bandpass filter 78 has a relatively wide passband encompassing the deviation range of the high frequency picture carrier (e.g., 4.3 to 6.3 MHz) as well as the requisite adjacent sideband regions, and selectively passes the picture carrier component of the recorded signal to the relative exclusion of the sound carrier component thereof.The sound carrier bandpass filter 80 has a relatively narrow passband encompassing the deviation range of the low frequency sound carrier (e.g., 71 6 KHz + 55 KHz) as well as the requisite adjacent sideband regions, and selectively passes the sound carrier component of the recorded signal to the relative exlusion of the picture carrier component thereof.

The outputs of the respective bandpass filters 78 and 80 are passed to respective demodulators 82 and 84. The picture demodulator 82 develops at its output terminal the picture signal information inclusive of synchronizing components, and the sound demodulator 84 develops at its output terminal the audio signal information.

A picture signal processor 86, coupled to the picture demodulator, effects the separation of the chrominance information from the luminance information. A composite video signal generator 88 recombines the chrominance and the luminance information in accordance w#th, for example, the NTSC format. A transmitter circuit 90 processes the sound, luminance and the chrominance information to form a signal suitable for delivery to a conventional color TV receiver, wherein color image displays may be developed in accordance with the recorded information. U. S. patent No.

4,097,899, issued to J. P. Yu, describes an illustrative transmitter circuit.

The player electronics also includes circuits coupled to the output of the signal pickup for detecting the occurrence of the locked grooves on the record. An illustrative locked groove detection scheme is described in U. S.

patent No. 4,198,658 in the name of Palmer.

The locked groove correction signal is applied to the coils 68 and 70 to effect locked groove clearance.

The stylus position sensing apparatus includes a stylus position indicative capacitance 92 established between a first electrode 94 secured in fixed relation to the stylus arm 24 and electrically connected to the flylead 38, and a second electrode 96 coupled to a terminal 98 disposed on the arm carriage 44 in the vicinity of the first electrode as shown in Fig. 5. Illustratively, the electrodes have the dimensions already noted.

The stylus position indicative capacitance 92 is arranged in series with a varactor diode 100. The varactor diode is coupled to the output terminal 104 of a 260 KHz. reference oscillator 102 by means of a resistor 106.

The stylus position indicative capacitance 92 is modulated by the spacing between the stylus 20 and the carriage 44, the capacitance of the varactor diode 100 is modulated by the reference oscillator 102. A schematic circuit diagram suitable for generating the 260 KHz. reference carrier is shown in Fig. 6 and the values of various elements shown therein are presented hereinbelow in a table.

The signal pickup circuit 52 additionally serves to sense the variations in the capacitance formed by the stylus position indicative capacitance 92 and the capacitance of the varactor diode 100 disposed in series therewith. Those variations appear at the output terminal 76 thereof as a 260 KHz. signal having an amplitude which varies inversely with the spacing between the position sensing electrodes 94 and 96. This signal is separated from the rest of the signals appearing at the output terminal 76 of the pickup circuit by a.

bandpass filter 108 coupled thereto. The bandpass filter has a passband encompassing the requisite deviation range of the 260 KHz.

reference carrier. The separated 260 KHz.

signals are amplified by an amplifier 110. A peak detector 112, coupled to the amplifier 110, generates a signal at the output thereof which represents the relative position of the pickup stylus 20 with respect to the arm carriage 44. The peak detector output signal is supplied to the driver amplifier 114 which generates at the output terminal 116 thereof an error correction signal suitable for applica tion to the motor 46, which drives the carriage. The amplitude of the signal applied to the carriage motor is such that the spacing between the stylus and the carriage is maintained at a predetermined optimum level. A schematic circuit suitable for realizing the foregoing functions is illustrated in Fig. 7, and the values of various elements shown therein are also given in the attached table.

As previously indicated, it is desirable to eliminate field adjustments of the stylus position sensing capacitance. The instant sty#lus position representative capacitance not only makes field adjustments unnecessary, but it also eliminates the need for a separate stylusmounted electrode. An apparatus pursuant to this invention will now be described with reference to Figs. 8-10, which correspond to previously-described Figs. 1, 3 and 4. As can be seen from Fig. 10, an electrode 120 of the subject apparatus is fixedly disposed on the cartridge 32. A wire 122, threaded through an aperture 124 in the wall of the cartridge housing, electrically connects the cartridgemounted electrode 120 to a terminal 126 provided on the cartridge housing in the manner indicated in Figs. 9 and 10.The cartridge terminal 126 electrically engages the terminal 98 upon receipt of the cartridge in the carriage compartment as illustrated in Fig. 8.

Pursuant to an aspect of the invention, the stylus flylead 38, which serves to provide electrical connection between the stylus pickup electrode 22 and the pickup circuits 52 of the player, additionally serves as a second electrode of the instant stylus position representative capacitance when the stylus arm is lowered on the record for playback.

It is noted that although the instant stylus position sensing apparatus is utilized herein for varying the rate of translation of the arm carriage in the manner that maintains a desired spacing between the pickup stylus and the arm carriage, it is also suitable for other purposes, such as detection of locked grooves on the disc. Moreover, it is important to understand that while the description herein is in the context of grooved discs, it is equally applicable to flat discs. Various defects on flat discs can cause the pickup stylus to retrace the same track. The present system can be advantageously employed to clear such occurrences in the playback of flat discs.

TABLE OF VALUES Illustratively, the values of various elements utilized in Figs. 5-7 are specified below.

I. CAPACITORS: (1) C1 - 0.01 microfarad (2) C2 - 1,000 picofarad (3) C3 - 1.0 microfarad (4) C4 - 220 picofarad (5) C5 -- 0.01 microfarad (6) C6 - 2.2 microfarad (7) C7 - 10.0 microfarad II.RESISTORS: (1) R1 - 10.0 Kilohms (2) R2 - 10.0 Kilohms (3) R3 - 7.5 Kilohms (4) R4 - 100.0 Kilohms (5) R5 - 13.0 Kilohms (6) R6 - 4.7 Kilohms (7) R7 - 3.0 Kilohms (8) R8 - 39.0 Kilohms (9) R9 - 2.0 Kilohms (10) R10 - 4.3 Kilohms (11) R11 - 82.0 Ohms (12) R12 - 4.7 Kilohms (13) R13 - 10.0 Kilohms (14) R14 10.0 Kilohms (15) R15 - 62.0 Ohms (16) R16 - 510.0 Ohms (17) R17 - 7.5 Kilohms (18) R18 1 1;0 Kilohms (19) R19 - 5.0 Kilohms (20) R20 - 10.0 Kilohms Ill. DIODES: (1) VD1 - 1477949-1 (2) D2-3 - IN60 (3) D4-5 - IN914 IV. TRANSISTORS: (1) Q1 - 1417330-3 (2) Q2-5 - MPSA17 (3) Q6 - MPSUOS V. MISCELLANEOUS: (1) CF1 - 260 KHz. Ceramic resonator (2) CF2 - 260 KHz. Ceramic filter

Claims (9)

CLAIMS:

1. A system for recovering prerecorded signals from a disc record having information recorded thereon along a spiral track disposed on the surface thereof by means of a trackfollowing device; comprising: a carriage subject to translation along a path disposed radially of said disc record, compliant means for securing said device to said carriage; first means including a device position indicative capacitance defined by a first electrode secured in fixed relation to said device and a second electrode mounted to said carriage adjacent to said first electrode; and second means coupled to said first electrode for sensing variations in said device position indicative capacitance for generating a signal indicative of the relative position of said device with respect to said carriage along said path.

2. A system for recovering prerecorded signals from a disc record having information recorded thereon along a spiral track disposed on the surface thereof by means of a trackfollwing stylus incroporating a pickup electrode; said system including a carriage subject to translation along a path disposed radially of said disc record; compliant member for securing said stylus to said carriage; means for sensing a signal indicative capacitance formed between said pickup electrode and said record for providing said prerecorded signals at the output terminal thereof; a flylead for connecting said pickup electrode with said capacitance sensing means; a stylus position indicative capacitance defined by a first electrode secured to said stylus and a second electrode mounted to said carriage adjacent to said first electrode; said signal capacitance sensing means also serving to sense said stylus position indicative capacitance for generating stylus position representative signals at the output terminal thereof; wherein said flylead additionally serves as said first electrode of said stylus position indicative capacitance.

3. A system as defined in Claim 2 further including a cartridge for housing said trackfollowing stylus; said carriage having a compartment for removably receiving said stylus cartridge; wherein said compliant member secures said stylus to said cartridge; wherein said flylead has one end secured to said pickup electrode and the other end secured to a first terminal disposed on said cartidge; said first terminal engages a terminal disposed in said carriage for coupling said pickup electrode with said capacitance sensing means, when said cartridge is received in said carriage compartment; wherein said second electrode comprises an element fixedly mounted to said cartridge such that said element is properly disposed during playback in relation to said flylead; said cartridge further including a second terminal in contact with said element and subject to engagement with another terminal disposed in said carriage during containment said cartridge in said carriage compartment.

4. A system as defined in any preceding Claim, wherein said first means further includes means coupled to said second electrode and modulated at a given frequency rate and said modulated means includes a varactor diode coupled in series with a source of said given frequency oscillations.

5. A system as defined in any Claims 1-3, including a pickup circuit coupled to an electrode incorporated in said track following device or stylus (as the case may be) for sensing the variations in a signal representative capacitance formed by said pickup electrode and conductive material disposed in said record to recover said prerecorded signals at the output terminal thereof; wherein said first electrode is secured to said device or stylus and coupled to said pickup circuit; said first means further including means coupled to said second electrode and modulated at'a given frequency rate; and second means coupled to said pickup circuit output terminal for deriving signals at said given frequency to the relative exclusion of said prerecorded signals for generating said signal indicative of the relative position of said device or stylus with respect to said carriage along said path.

6. A system as defined in Claim 5, wherein said modulated means includes a varactor diode coupled in series with a source of said given frequency oscillations.

7. A system as defined in any preceding claim, including means responsive to said position indicative signal for varying the rate of translation of said carriage in a manner that maintains a desired lateral spacing between said device and said carriage.

8. A disc record playback system having a pickup device position sensing arrangement substantially as hereinbefore described with reference to Figs. 1, 3 and 4 or Figs. 8-10 of the accompanying drawings.

9. A system according to any preceding claim having an error correction signal producing circuit arrangement substantially as hereinbefore described with reference to Fig.

5 of the accompanying drawing.