CA1150833A - Spindle servo system - Google Patents

Abstract

ABSTRACT

A spindle servo system for in an apparatus for recovering a signal from a track on the surface of a disc, wherein the signal includes a signal defining a time base, and the system includes optical system for directing a source beam of radiation to the track and for directing a modulated beam of radiation containing the signal to a signal recovery device for recovering the signal from the modulated beam, the spindle servo system comprising: a spindle motor for rotating the disc whereby relative motion between the disc and the source beam produces the modulated beam; a spindle tachometer including first and second tachometer elements coupled to the spindle motor, for producing first and second spindle tachometer signals, indica-tive of the actual angular rate of rotation of the spindle motor; a spindle reference signal generator for producing a spindle reference signal representing a desired angular rate of rotation of the spindle motor; a device for comparing each of the first and second spindle tachometer signals with the spindle reference signal, to produce first and second error signals representative of the detected differences therebetween;
and an adder for summing together the first and second error signals to produce a spindle motor control signal for coupling to the spindle motor to produce the desired angular rate of rotation.

Description

VIDEO DISC PLAYER
TECHNICAL FTFLD
The present invention relates to the method ~nd means for reading a frequency modulated video signal stored in the form Or successively positioned reflect1ve and non-reflective regions on a plurality Or informa~on tracks carried by a video disc. More specifically, an optical system is employed for directing a reading be_~-to impinge upon the lnformation track and for gatheri~g 10 ~the reflected signals modulated by the rerlective and non-re~lective regions of the information track. A
~requency modulated electrical signal is recovered from the re~lected light modulated signal. The recovered requency mGdulated electrical slgnal is applied to a signal processing section wherein the recovered fre-quency modulated signal is prepared for application to , a standard television receiver and/or monitor. The - recovered light modulated signals are applled to a plurality of servo systems for providing control 5ign~1s which are employed for keeping the lens at the optlmum focus position with relation tothe in~ormatlon beari~.g sur~ace of the video disc and to maintain the focused light beam in a position such that the foc~sed light spot impinges at the center o~ the lnrormatlon track.
BRIEF ~ A;R~ OF THE INVE~T~ON
The present invention is directed to a video disc player operatlng to recover frequency modulated video signals ~rom an information bearing sur~ace of a vldeo disc. The rrequency modulated video inrormaticn .~.
!

liSVW3 ( is stored in a plurality of concentric circles or a single spiral extendlng over an information bearing portion of the video disc surface. The rrequency modu-lated video signal is represented by indicia arranged in track-like fashion on the information bearing sur~ace portion of the video disc. The indicia co~prise suc-cessively positioned reflective and non-re~lective regions in the information track.
A laser is used as the source of a coherent light beam and an optical system is employed for focus-: ing the light beam to a spot having a diameter approxi-mately the same as the width of the indicia positioned in the information track. A microscopic o~ective lens is used for focusing the read beam to a spot and for 1~ gathering up the reflected light caused by the spot impinging upon successively positioned light reflective and li~ht non-re~lective regions. The use of the microscopically small indicia typically 0.5 microns in ~ width and ranging between one micron and 1.~ microns in length taxes the resolvlng power of the lens to its fullest. In this relationship, the lens acts as a low pass filter. In the gathering of the re~lected light and passing the reflected light through the lens when operating at the maximum resolution of the lens, the gathered light assumes a sinusoidal-shaped like modulat~
beam representing the frequency modulated video signals contained on the video disc member.
The output from the microscopic lens is ap-plied to a signal recovery system wherein the reflected 3 light beam is employed first as an inrormation bearing light member and second as a control signal source for generating radial tracking errors and ~ocus errors.
The information bearing portion of the recovered fre-quency modulated video signal is applied to an FM
3~ processing system for preparation prior to transmission to a standard TV receiver and/or a TV mon tor.
The control portion of the recovered ~requency modulated video signal is applied to a plurality of servo subsystems ~or controlllng the position of the 1~50833 ( readin6 beam on the center of the information track and for controlling the placing of the lens for gathering the maxim~lm reflected light when the lens is positloned at lts optlmum focused position. A tangential servo subsystem is employed for determining the time base error introduced into the reading process due to the mechanics of the reading system. This time base error appears as a phase error in the recovered frequency modulated video slgnal.
The phase error is detected by comparing a selected portion of the recovered frequency modulated signal with an internally generated signal having the correct phase relationship with the predetermined por-tion of the recovered frequency modulated video signal.
The predetermined relationship is established during the original recording on the video disc. In the pre-ferred embodiment, the predetermined ~rtion of the recovered frequency modulated video signal is the color ~burst signal. The internally generated reference frequency is the color subcarrier frequency. The color burst signal ~as originally recorded on the video disc under control of an identical color subcarrier fre-quency. The phase error detected in this comparison process is applied to a mirror moving in the tangential direction which adjusts the location at which the ~ocused spot impinges upon the information track. The tangential mirror causes the spot to move along the information track either in the rorward or reverse direction for providing an ad~ustment equal tothe phase error detected in the comparison process. The tangential mirror in its broadest sense is a means for ad~usting the time base of the signal read from the video disc memb~r to ad~ust ~or time base errors in~ected by the mechanics Or the reading system.
In an alternative form of the lnvention, the predetermined port on of the recovered ~requency modu-lated video signal is added to the total recorded frequency modulated video signal at the time of record-ing and the same frequency is employed as the operating -``` 1150833 point for the highly controlled crystal oscillator used in the comparison process.
In the preferred embodiment when the video disc player is recovering frequency modulated video slgnals representing television pictures, the phase error comparison procedure is performed for each line of television information. The phase error is used for the entire line of television information for correcting the time base error for one full line of television inform~-tion. In this manner, incremental changes are appliedto correct for the time base error. These are con-stantly being recomputed for each line of television information.
A radial tracking servo subsystem is employed 15 for maintaining radial tracking of the focused light spot on one information track. The radial tracking servo subsystem responds to the control signal portion of the recovered frequency modulated signal to develop an error signal indicating the offset from the preferred center of track position tothe actual position. This - tracking error is employed for controlling the movement of a radial tracking mirror to bring the light spot back into the center of track position.
The radial tracking servo subsystem operates in a closed loop mode o~ operation and ln all op~n 1GOP
mode of operation. In the closed loop mode of operation, the diff~rential tracking error derived from the re-covered frequency modulated video signal is continuously applied through the radial tracking mirror to bring the focus spot back to the center of track position. In the open loop mode Or operation, the differential tracking error is temporarily removed from controlling the operation of radial tracking mirror. In the open loop mode of operation, various combinations of signals take over control of the movement of the radial track-lng mirror for directing the point of impingement of the focused spot from the preferred center of track ~; position on a first track to a center of track posltion on an adjacent track. A first control pU;l.C causes the .
;

`` ` liS0833 tracking mirror to move the focused spot of light from the center of track positlon on a first track and move towards a next adjacent track. This first control pulse terminates at a point prior to the focused spot reaching the center o~ trac~ position in the next adjacent track.
After the termination of the first control pulse, a second control pulse is applied to the radial tracking mlrror to compensate for the additional energy added to the tracking mirror by the first control pulse. The second control pulse is employed for bringing the focused spot into the preferred center of track focus position as soon as possible. The second control pulse is also employed for peventing oscillation of the read spot about the second information track. A residual portion of the differential tracking error is also applied to the radial tracking mirror at a point cal-culated to assist *he second control pulse in bringing the focused spot to rest at the center of track focus position in the next ad~acent track.
A stop motion subsystem is employed as a means for generating a plurality of control signals for application to the tracking servo subsystem to achieve the movement of a focused spot tracking the center of a first information track to a separate and spaced loca-tion in which the spot begins tracking the center of the next adjacent information track. The stop motion subsystem performs its function by detecting a predeter-mined signal recovered from the frequency modulated video signal which indlcates the proper position within the recovered frequency modulated video signal at which time the Jumping operation should be initiated. Thls detection function is achieved, in part, by internally generating a gating circuit lndicating that portion of the recovered frequency modulated video signal within which the predetermined signal should be located.
In response to the predetermined signal, which is called in the referred embodiment a white flag, the stop motlon servo subsystem generates a first control signal for applicatlon to the tracking servo subsystem s~

-11~0833 fcr temporarily interrupting the applicaticn of the differential tracking error to the radial tracking mirrors. ~le top motion subsystem generates a second control signal for application tothe radial tracking mirrors for causing the radial tracking mirrors to leave the center of tracking position on a first information track and jump to an adjacent information track. The stop motion subsystem terminates the second control signal prior to the focus spot reaching the center of the focus position on the next adjacent information track.
In the preferred embodiment, a third control signal is generated by the stop motion subsystem at a time spaced from the termination o~ the second control pulse. The third control pulse is applied directly to the radial tracking mirrors for compensatlng for the effects on the radial tracking mirror which were added to the radial tracking mirror by the second control pulse. While the second control pulse is necessary to ~ have the reading beam move from a first in'ormation track to an adjacent information track, the spaces in-- volved are so small that the ~umping operation cannot altlays reliably be achieved using the secor.d control signal alone. In a preferred embodlment having an im-proved reliable mode of operation, the third control signal is employed for compensating ~or the effects of the second control ~ump pulse on the radial tracking mirror at a point in time when it is assured that the focus spot has, in fact, left the first information track and has yet to be properly positioned in the center of the next ad~acent information track. A further em-- bodiment gates the differential error signal through to the radial tracking mirror at a time calculated for the gated portion of the differential tracking error to assist the compensation pulse in bringing the focus spot under control upon the center of track position of the - next adjacent information track.
The video disc player employs a spindle servo subsystem for rotating the video disc member positioned upon the spindle at a predetermined frequency. In the ~iS0833 preferred embodiment the predetermlned rrequency is 1799.1 revolutlons per minute. In one revolutlon of the vldeo disc, a complete ~rame of televlslon lnforma-tior is read from the video disc, processed in elec-tronic portion of the video disc player and applled to astandard television receiver and/or television monitor in a form acceptable to each such unit, respectively.
~oth the television receiver and the television monitor handle the signals applied thereto by stan~ard internal circuitry and display the color, or black and white signal, on the receiver or monitor.
The spindle servo subsystem achieves the accur-ate speed of rotation by comparing the actual speed of rotation with a motor reference frequency. The motor reference frequency is derived from the color sùb-carrier frequency which ls also used tc correct for time base errors as described hereinbe~ore. Ey utiliz-ing the color subcarrier frequency as the source of the . motor reference slgnal, the spindle motor itself removes all flxed tlme base errors which arise from a mismatch-ing of the recording speed with the playback speed. The recording speed ls also controlled by the color fre-quency subcarrier frequency. The use of a single highly controlled frequency in both the recording mode and the reading back mode removes the maJor portlon of time ; base error. While the color subcarrier rrequency ls shown as the preferred source ln generatlng the motor reference frequency, other highly controlled frequency signals can be used ln controlllng the writing and reading of frequency modulated video signal on the video disc.
A carriage servo subsystem operates in a close loop mode of operation to move the carrlage assembly to the specific location under the direction of a plurality of current generators. The carriage servo subsys'em controls the relative posii;icning of ~he vid~o disc and the optical system used to form the read beam.
A plurality of individual current sources are lndivldually activated by command slgnals from the :, functlon generator for dlrectlng the movement Or the carrlage servo.
A first command sl~nal can dlrect the carrlage servo subsystem to move the carrlage assembly to a 5 predetermlned locatlon such that the read beam lnter-sects a predetermined portion of the lnformatlon bear-ing surface Or the video disc member. A second current source provides a contlnuous blas current for directing the carriage assembly to move ln a fixed dlrectlon at a 10 predetermlned speed. A rurther current source generates J a current signal of fixed magnitude and varlable length for moving the carrlage assembly at a high rate of speed in a predetermined direct~on.
A carriage tachometer current generatlng means 15 is mechanically connected to the carriage motor and is employed for generating a current indicating the instantaneous position and speed of the carriage motor.
The current ~rom the carriage tachometer is compared , with the sum of the currents being generated ln the 20 current sources in a summation circult. The summation circuit detects the difference between the current - sources and the carriage tachometer and applles a different slgnal to a power amplifier for moving the carriage assembly under the control of the current 25 generators.
-' PRIEF DESCRIPTION OF THE DRA~INGS
,~ .
The foregoing and other objects, ~eatures and advantages of the inventlon will be apparent from the following more particular description of a preferred 3 embodiment of the invention as illustrated in the accompanying drawings wherein:
FIGURE ~ shows a generalized block diagram o~
a video disc player;
FIGURE 2 shows a schematlc diagram of the opti~
35 cal system employed wit'~ reference to the video disc pl~yer shown in Fi~ure l;
FIGURE 3 shows a block diagram Or the spindle servo subsystem employed in the video dlsc player shown in Figure l;
'~ .
~ r 115(~833 g FIGURE 4 shows a block diagram of the carriage servo subsystem employed in the video disc player shown in Flgure l;
FIGURE 5 shows a block diagram of the focus servo subsystem employed ln the video disc player shown in Figure l;
FIGURES 5a, 6b, and 6c show vari~us waveforms illustr~lng the operation of the servo subsystem sho~1n ln Figure 5;
FIGURE 7 shows a partly schematic and partly ~' block diagram view of the signal recovery subsystem employed in the video disc player shown in Figure l;
FIGURE 8 shows a plurality of waveforms and one sectional view used in explaining the operation of the signal recovery subsys~em shown in Figure 7;
FIGURE 9 shows a block diagram o~ the tracking servo used in the video disc player shown ln Figure l;
FIGURE 10 shows a plurality Or wave~orms ~ utilized in the explanatlon o~ the operation of the tracking servo shown in Figure 9;
FIGURE 11 shows a block diagram of the tangen-tial servo employed in the video disc player shown in Figure l;
FIGUR~ 12 shows a block diagram of the stop motion subsystem utilized in the video disc player of Figure l;
FIGURES 13A, 13~, and 13C show waveforms gen-: erated in the stop motion subsystem shown with reference to Figure 12;
: 30 FIGURE 14 is a generalized block diagram of - the FM processing subsystem utilized in the video disc player shown witl1 reference to Figure l;
FIGURE 15 is a block diagram of the FM correc-tor circuit utilized in the FM processing circuit shown - 35 in Figure 14;
FIGURE 15 shows a plurality of waverorms and one transfer function utilized in explaining the opera-; tion of the FM corrector shown in Figure 15;.. FIGURE 17 is a block dlagram of the FM

.

detector used ln the FM processlng circuit shown lnFigure 14;
FIGURE 18 shows a plurallty of waveforms used in explaining the operation of the FM detector shown wlth reference to ~igure 17;
FIGURE 19 shows a block dia~ram of the audio processing circuit utilized in the video disc player ; sho~n ~ith reference to Figure l;
FIGURE 20 shows a block diagram of the audio demodulator emplo~-ed in the audio processing circuit utilized in the video disc player shown with reference !' to Figure 19;
FIGURE 21 shows a plurality of waveforms useful in e,~plaining the operation of the audio demodulator shown with reference to ~igure 20;
FIGU~E 22 shows a block diagram Or the audio voltage controlled oscillator utilized in the audio processing circuit shown with reference to Figure 19;
, FIGURE 23 shows a plurality of waveforms avail-able in the audio voltage controlled oscillator sho~"n with reference to Figure 22;
FIGU~E 24 shows a block diagram of the RF modul~-tor utilizing the video disc player shown in Figure l;
FIG~E 25 shows a plurality of waveforms uti-lized in the explanation of the RF modulator shown with reference to Figure 24;
FIGURE 26 shows a schematic view of a video disc member illustrating the eccentricity effect of uneven cooling on the disc;
30 FIGURE 27 is a schematic view of a video disc illustrating the eccentricity effect of an off-center relationship of the information tracks to the central aperture;
FIGURE 28 is a logic diagram demonstrating the norma' acquire focus mode o~ operation of the focus serl~o emplojed in the video disc shol~n ~n Figure l; and FIGUR~ 29 is a logic diagram demonstrating ., other modes Or operation Or the focus servo shot~n with reference to Figure l;

llSOW3 --1i--DETAILED Drscp~IpTIoN OF THE I~'ENTION
The same numeral will be used in the several views to represent the same element.
Referring to Figure 1, there is shown a sche-matic block diagram of a video disc player system in-dicated generally at 1. The player 1 employs an optical system indicated at 2 and shown in greater detail in Figure 2.
Referring collectively to Figures 1 and 2, ~he optical system 2 includes a read laser 3 employed for generating a read beam 4 which is used for reading a frequency modulated encoded signal stored on a video disc 5. The read beam 4 is polarized in a predeterm ned direction. The read beam ~ is directed to the video disc 5 by the optical system 2. An additional function of the optical system 2 is to focus the light beam dc~n to a spot 6 at its point of impingement with the viceo disc 5.
A portion of an information bearing surface 7 of the video disc 5 is shown enlarged within a circle 8.
A plurality of information tracks 9 are formed on the video disc 5. Each track is formed with successive light reflective regions 10 and light non-reflective regions 11. The direction of reading is indicated by an arrow 12. The read beam 4 has two degrees of movemer.t the first of which is in the radial direction ~s indi-cated by a double headed arrow 13; the second of wh ^h is the tangential direction as indicated by a double headed arro~ 14. The double heads of each of the arro~s 3 13 and 14 indicate that the read beam 4 can move in both directions in each of the radial degree and tan-gential degree.
Referring to Figure 2, the optical system ccm-prises a lens 15 employed for shaping the beam to fully 3~ fill an entrance aperture 16 of a microscopic objective lens 17. The objective lens ls employed for forming the spot ~ of light at its point of impingement with the video disc 5. Improved results have been found when the entrance aperture 16 is overfilled by the :

`` 1150833 re~ding beam 4.- Thls results ln maximum light lntensity at the spct 6.
After the beam 4 is properly formed by the lens 15, it passes tllrough a dlfraction gratlng 18 which splits the read beam into three separate beams (not shown). T~o of the beams are employed for developing a radial ~racking error and the other ls used for develop-ing both a focus error signal and the information slgnal.
These three Deams are treated ident~cally by the remain-ing portinn of the optical system. Therefore, they are ; collectively referred to as the read beam 4. The output for the diffraction grating 18 is applied to a beam splitting prism 20. The axis of the prism 20 is slightly offset from the path of the beam 4 for reasons that are explained wlth reference to the descrlption ofthe performance of the optical system 2 as lt relates to a reflected beam 4'. The transmitted portion of the beam 4 is applied through a quarter wave plate 22 which prc-~Vldes a for~y-flve degree shift in polarization of the light forming the beam 4. The rear beam 4 next impinges upon a fixed mirror 24 which re-directs the read beam 4 to a first articulated mirror 26. The function of the first articulated mirror 26 is to move the light beam in a first degree of motion which is tangential to the 25 surface cf t'ne video disc 5.to correct for time base error errors introduced into the reading beam 4 because of eccentricities in the manufacture of the dlsc 5.
The tangential direction is in the forward and/or back-ward direction of the information track on the video disc 5 as indicated by the double headed arrow 14. The read beam 4 now impinges upon the entrance aperture 16, as previously described, and is focused to a spot 6 upon the information bearing track 9 of the video disc 5 by the lens 17.
The first articulated mirror 26 directs the light beam to a second articulated mirror ~8. The second articulated mirror 28 is employed as a tracking mirror. It is the function of the tracking mirror 28 to respond to tracking error signals so as to slightly .i~
.

cilange its physical posltion to direct the point of impingement S Or the read beam 4 so as to radially tracl; the information carrying indicia on the surface of the ~ideo disc 5. The second articulated mirror 28 has one degree of movement which moves the light beam in a radial direction over the surface of the video disc 5 or indicated by the double headed arrow 13.
In normal playing mode, the focused beam of light impinges upon successively positioned light reflective regions 10 and light non-reflective regions 11 representing the frequency modulated information.
In the preferred embodiment, the light non-reflective regions 11 are light scattering elements carried by the video disc 5. The modulated light beam is a light equivalent of the electrical f~equency modulated signal ccntaining all the recorded information. This modulated light beam is generated by the microscopic ob~ective lens 17 by gatnering as much reflected light from the successively positioned light reflective region 10 and light non-reflective re~ions 11 on the video disc 5. The reL`lected portion of the read beam is indicated at 4'. The reflected read beam 4' retraces the same path previously explained by impinging ir. sequence upon the second articulated mirror 28~ the first arti-culated mirror 26, and the fixed mirror 24. The re-flected read beam 4' next passes through the quarter-~ave plate 22. The quarterwave plate 22 provides an addltional forty-five degree polarizatlon shift re-sulting in a total of ninety degrees in shift of polar-ization to the reflected read beam 4'. The reflected read beam 4' now impinges upon the beam splitting prism 20, which prism diverts the reflected read beam 4' to impinge upon a signal recovery subsystem indicated generally at 30.
The function of the beam splitting prism is to pre~ent the total reflecte(3 read `l~eam 4' from re-entering the laser 3. The effect of the returning read beam 4' upon the laser 3 would be to upset the mecAanism whereby the laser oscillates in its predetermined mcde .~ .

" ~150833 of operat~on. Accordingly, the beam splitting prism 20 redirects a si~nificant portion of the reflected read beam 4' for preventing feedback into the laser 3 when the laser 3 would be affected by this feedback portion of the reflected read beam 4'. For those solid state lasers which are unaffected by the feedback of the re-flected light beam 4', the beam splitting prism 20 is unnecessary. The solid state laser 3 can function as the photo detector portion of the signal recovery sub-system 30 to be described hereinafter.
Referring to Figure 1, the normal operatingmode of the signal recovery subsystem 30 is to provide a plurality of informational signals to the remaining portion of the player 1. These informational signals fall generally into two types, an informational signal itsel~ ~hich represents the stored information. A
second type of signal is a control signal derived from the informational signal for controlling various por-~ tions of the player. The inform~tional signal is a frequency modulated signal representing the information ; stored on the video disc 5. This informational signal is applied to an FM processing subsystem indicated at 32 over a line 34. A first contrpl signal generated by the signal recovery subsystem 30 is a differential focus error signal applied to a focus servo subsystem indica-ted at 3~ over a line 38. A second type Or control signal generated by the signal recovery subsystem 30 is a differential tracking error signal applied to a track-ing servo subsystem 40 over a line 42. The differential tracking error signal from the signal recovery sub-system 30 is also applied to a stop motion subsystem indicated at 44 over the line 42 and a second line 46.
Upon receipt of the START pulse generated in a function generator 47, the first ~unction of the vldeo disc player 1 is to activate the laser 3, activate a spindle motor 48, causing an integrally attached spindle 49 and its video disc member 5 mounted thereon to begin spinning. The speed of rotation of the spindle 49, as provided by the spindle motor 48, is under the `i control of a s~indle servo subsystem 50. A spindle : tachometer (not sho~n) is mounted relatlve to the - spindle 49 to generate electrical signals showing the present speed of rotation of the spindle 49. The tachometer comprises two elements which are located one hundred eighty degrees apart with reference to the spindle 49. Each of these tacl~ometer elements generates an output pulse as is common in the art. Because they are located one hundred eighty degrees out of phase with each other, the electrical signals generated by each are one hundred eighty degrees out of phase with each other. A line 51 carries the sequence of pulses gener-ated by the first tachometer elements to the spindle servo subsystem ~0. A line 52 carries the tachometer pulses from the second tachometer element to the spindle servo subsystem 50. ~her the spindle servo subsystem 50 reaches its predetermined rotational velocity of 1799.1 revolutions per minute, it generates a player enable signal on a line 54. The accurate rotational speed of 1799.1 revolutions per minute allows 30 frames of television information to be displayed on a standard television receiver.
The next major functioning ~ the video disc player 1 is the activation of a carriage servo sub-system 55. As previously mentioned, the reading of thefrequency modulated encoded information from the video disc 5 ls achieved by directing and focusing a read beam 4 to impinge upon the successively positioned light reflective region 10 and a light non-reflective region 11 3 ~n the vid~ disc ~. For optimum results, the read beam 4 should impinge upon the plane carrying the encoded information at right a~gles. To achieve this geometric configuration requires relatlve movement between the combined ~tical system 2 and the video disc 5. Either 3~ the video disc 5 can move under the fixed laser read beam 4 or the opt~cal system 2 can move relative to ~ne fixed video disc 5. In this embodimen$, the optical - system 2 is held stationary and the video dlsc 5 is moved under the reading beam 4. The carriage servo .~ .
i 1150~33 subsystem controls this relative movement bet~een thevideo disc 5 and the optical system ~.
As com~letely described hereina~ter~ the carriage servo subsystem adds a degree of flexibility to the overall functioning of the video disc player 1 by directing the aforementioned relative movement in a number of different modes of operation. In its first mode of operation the carriage servo subsystem 55 re-sponds to the player enable signal applied to it over the line 54 to move a carriage assembly 56 such that the read beam 4 impinges upon the video disc 5 perpendi-cular to the information bearing surface of the video disc 5. At this time it would be important to note that the term carriage assembly is used to identify the structural member upon which the video disc is carried.
This also includes the spindle motor 48, the spindle 49, the spindle tachometer (not shown) a carriage motor 57 and a carriage tachometer generator 58. For the purpose of not unduly complicating the broad block diagram shown in Figure 1, the carriage assembly is not shown in great ~ detail. For an understanding of the summarized opera-tion of a video disc player, it is important to note at this time that the function of the carriage servo subsystem is to move the carriage to its initial posi-tion at w'nich the remaining player functions ~ill be i: initiated in sequence. Obviously, the carriage servo subsystem can position the carriage at any number of fixed locations relative to the video disc pursuant to the deslgn requirements of the system, but for the purposes ~ this des~ription the carriage is positioned at the beginning of the frequency modulated encoded information carried by the video disc. The carrlage motor 57 provides the driving force to move the carriage assembly 56. The carriage tachometer generator 58 is - 35 a current source for generating a current lndicating the instantaneous s~eed and direction cf movement of the carriage assembly.
The spindle servo subsystem 50 has brough~ the ; spindle speed up to its operational rotati~nal rate of 1 ~

1799.1 rpm at ~hich time the player enable slgnal is generated on the line 54. The player enable signal on tlle line 54 is applied to the carriage servo subsystem 55 for controlling the relative motion between the carriage assembly 56 and the optional system 2. The next sequence in the PLAY operation is for the focus servo subsystem 36 to control the movement of the lens 17 relative to the video disc 5. The focusing opera-tion includes a coil, (not shown), moving the lens 17 under the direction of a plurality of separate elec-trical waveforms which are summed within the coil itself.
These waveforms are completely described ~ith reference to the description ~iven for the focus servo subsystem in Figures 6a, 6b and 6c. A voice coil arrangement as found in a standard loud speaker has been found to be suitable for controlling the up and down motion o~ the lens 17 relative to the video disc 5. The electrical signals for controlling the voice coil are generated by the focus servo subsystem 36 for application to the coil over a l~ine 64.
The inputs to the focus servo subsystem are applied from a plurality of locations. The first of whlch is applied from the signal recovery subsystem 30 over the line 38 as previously described. The second input signal is from the FM processing circuit 32 over ;, a line 65. The FM processing subsystem 32 provides the frequency modulated signal read from the surface of the video disc 5. A tllird input signal to the focus servo subsystem 36 is the ACQUIRE FOCUS enabling logic signal 30 generated by the act of putting the player into its play mode by selection of a function PLAY button within the function generator 47.
The function of the focus servo subsystem 36 is to position the lens 17 at the optimum distance from 35 the video disc 5 such that the lens 17 is able to gather and/or collect the maximum light reflected rrom the video disc 5 and modulated by the successively posi-tioned light reflective region 10 and llght non-reflective reglon 11. This optimum range is approxl-``` 1150833 mately .3 microns in length and is located at a distance of one micron above the top surface of the video disc 5.
The focus servo subsystem 36 has several modes of oper-ation all of which are described hereinafter in greater detail with re~erence to Figures 5, ja, I~b and 6c.
At the present time it is lmportant to note that the focus servo subsystem 36 utilizes its three input signals in various combinations to achieve an enhanced focusing arrangement. The differential focus error signal from the signal recovery subsystem 30 provides an electrical representation of the relative distance between the lens 17 and the video disc 5. Un-fortunately, the differential focus error signal is relatively small in amplitude and has a wave shape containing a number of positions thereon, each of ~Jhich indicate that the proper point has been reached. All but one of such positions are not the true optimum focusing positions but rather carry false information.
~ Accordingly, the differential focus error signal itself 20 i5 not the only signal emplo~ed to indicate the optimum focus condition. ljhile the use of differential focus error itself can oftentimes result inthe selection of the optimum focus position, it cannot do so reliably on every ~ocus attempt. Hence, the combination of the differential focus error signal with the signal indica-tlve of reading a frequency modulated signal from the video disc 5 provides enhanced operation over the use of using the differential focus error signal itself.
During the focus acquiring ~ode Or operation, 3 the lens 17 is moving at a relatively high rate of speed towards the video disc 5. An uncontrolled lens detects a frequency modulated siGnal from the information carried by the video disc 5 in 2 very narrow spacial range. This very narrow spacial range is the optimum focusing range. Accordingly, the combination of the detected frequency modulated signal and the differential focus error signal provides a reliable system for ac-quiring focus.
The focus servo subsystem 36 hereinafter , .

l i ~ ~ 3 descri~ed cont.~ ins additional lmprovements. One Or these improvements is an addition of a further fixed signal to those alraady described whicll further helps the rOcus servo subsystem 36 acquire proper focus 5 on the initial sttempt to acquire focus. This addi-tional si~nal is an internally generated kickbacl~
signal which is initiated at the time when a frequency modulated signal is detected by the FM processing subsystem 32. This internally generated kickback 10 pulse is combined with the previously discussed signals t and applied to the voice coil so as to independently cause the lens to physically move back through the region at ~hich a frequency modulated signal was read from the disc 5. This internally generated fixed 15 kickback pulse signal gives the lens 17 the opportunity to pass through the critical optimum focus~ng point a number of times during the first transversing of the lens 17 to~ards the video disc 5.
Further improvements are described for handling 20 momentary loss of focus during the play mode of opera-tion caused by imperfection in the encoded frequenc~J
modulated signal which caused a momentary loss of the frequency modulated signal as detected by the FM
processing subsystem 32 and applied to the focus servo 25 subsystem 36 over the line 66.
A tangential servo subsystem 80 recelves its first input signal from the FM processing subsystem 32 over a line 82. The input signal present on the line 82 is the frequency modulated signal detected from the sur-30 face of the video disc 5 by the lens 17 as amplified in : the signal recovery subsystem 30 and applied to the FM
processing subsystem 32 by a line 34. The signal on the line 82 is the video signal. The second input signal to the tangential servo subsystem 80 is over a line 84. The 35 signal on the line 84 is a variable DC si~nal generated b~J a carriage pos~tion potentiolnet2r. ~lle amplitude o~
the variable voltage signal on the line 84 indicates - the relative position of the point of impact of the reading spot ~ over the radial distance indicated by a dou~le headed arrow ~6 as drawn upon the surface of the - video disc 5. This variable voltage ad~usts the gain of an internal circuit for ad~ustlng lts operatlng charac-teristics to track tlle relative position of the spot as it transverses the radial position as indicated by the lensth of the line ~5.
The function of the tangential time base error correction subsystem 80 is to adjust the signal detected from the video disc 5 for tangential errors caused by eccentricity of the information tracks 9 on the disc 5 and other errors introduced into the detected signal due to any physical imperfection of tl~e video disc 5 itself. The tangential time base error correction subsystem 80 performs its function by comparing a signal read from the disc 5 with a locally generated signal.
The difference between the two signals is indicative of the instantaneous error in the signal being read by the player 1. More specially, the signal read from the disc ~ 5 is one which was carefully applied to the disc ~ith a predetermined amplitude and phase relative to other signals recorded therewith. For a color television FM
signal this is the color burst portion of the video signal. The locally generated signal is a crystal con-trolled oscillator operating at the color subcarrier frequency of 3.579545 megahertz. The tangential time base error correction subsystem 80 compares the phase difference between the color burst signal and the color subcarrier oscillator frequency and detects any differ-ence. This difference ls then employed for ad~usting the phase cf the remaining portion of the line of FM
information which contained the color burst signal.
The phase difference of each succeeding line is gener-ated in exactly the same manner for providing continuous tangential time base error correction for the entire signal read from the disc.
In other embodiments storing information signals which do not have a portion thereof comparable to a color ~urst signa~ such ~3ienal having predeter-mined amplitude and phase relative to the remaining ~, 1~50833 si~nals on the disc 5 can be periodlcall~y added to the information when recorded on the disc 5. In the play mode, this portion of the recorded lnformation can be selected out and compared witll a locally generated signal comparable to the color subcarrier oscillator.
In this manner, tangential tlme base error correction can be achieved for any signal recorded on a video disc member.
The error signal so detected in the comparison of the signal read from the video disc ~ and the inter-nally generated color subcarrier oscillator frequency is applied to the first articulated mirror 25 over lines 88 and 90. The signals on lines 88 and 90 operate to move the first articulated mirror 25 so as to re-direct the read beam 4 forward and backwards along theinformation track, in the direction of the double headed arrow 14, to correct for the time base error injected due to an imperfection from a manufacture of the video disc 5 and/or the reading therefrom. Another output signal from the tangential time base error cor-rection subsystem 80 is applied to the stop motion sub-system 44 over a line 92. This signal, as completely described hereinafter, is the composite sync signal which is generated in the subsystem 80 by separating the composite sync signal from the remaining video signal.
It has been found convenient to locate the sync pulse separator in the tangential time base error correctlon subsystem 80. This sync pulse separatGr could be located in any other portion of the player at a point where the complete vldeo signal is available from the FM processing subsystem 32.
A f~rther output signal from the tangential subsystem is a motor reference frequency applied to the spindle servo subsystem 50 over a line 94. The genera-tion of the mGtOr reference frequency in the tangentialsubsys~em 80 is convenieilt because of the presence of the color subcarrier oscillator frequency used in the comparison operation as previously descrlbed. This color subcarrier oscillator frequency is an accurately 1150833 ~
, , genera~ed signal. It is divided down to a motor re~er-ence frequeslc~T used in the control Or the spindle servo speed. ~- utili~ing the color su~carrier frequency as a control frequency for the speed of the spindle, the speed of the spindle is effectively locked to this color subcarrier frequency causing the spindle to rotate at t`ne precise fram.e frequency rate required for maximum - fidelit-~ in the display of the information detected from the video disc 5 on either a televisicn receiver indicated at 95 and/or a TV monitor indicated at 98.
The tracking servo subsystem 40 receives a I plurality of input signals, one of which is the pre-viously descri~ed differential tracking error signal generated by a signal recovery subsystem 30 as applied thereto over a line 42. A second input signal to the tracking servo s~lbsystem ~0 is generated in a function generator 47 over a line 102. For the purpose of clar-ity9 the function ge!~erator 47 is sho~n as a single block. In the preferred embodiment, the function gener-ator 47 includes a remote control function generatorand a series of switches or buttons permanently mounted on the ^onsole of the video disc player 1. The specific functions so ~enerated are described in more detail in the detailed description Or the carriage servo sub-system 55 contained hereinafter.
The signal contained on the line 102 is asignal which operates to disable the normal functionin~
of the tracking servo 40 during certain functions initiated by the function generator 47. For example, the function generator 47 is capable of generating a signal for causing t'ne relative movement of the carriage assembly 56 over the video disc 5 to be in the fast for~Jard or fast reYerse condition. By definiticn, the lens is traversing the video disc 5 in a radial direction as represented by the arrow 13, rapidly sklpping over the tracks at the rate of 11,000 tracks per inch and tracking is not expected in this condition. Hence, the signal from the function generator 47 on the line 102 disables the ~, tracking servo 40 so that it does not attempt to operate in r llS0833 its normal tracking mode.
A third input signal to the tracklng servo subsystem 40 is the stop motion compensation pulse gene~
ated in the stop motion subsystem 44 and applied over a 5 line 104. An additional lnput signal applied to tracking servo subsystem 40 is the subsystem loop interrupt signal generated by the stop motion subsystem 44 and applied over a line 10~. A third input si~;nal to the tracking servo subsystem 40 is the stop motion pulse 10 generated by the stop motion subsystem 44 and applied over a line 108.
! The ~utput signals from the tracking servo sub-system 40 include a first radial mirror tracking signal over a line 110 and a second radial mirror control on 15 a line 112. The mirror control signals on the line 110 and 112 are applied to the second articulated mlrror 28 which is employed for radial tracldng purposes. The c ontrol signals on the lin~s 110 and 112 move the second articulated mirror 28 such that the reading beam 4 20 impinging thereupon is moved in the radial direction and - becomes centered on the information track 9 illuminated by the focused spot 6.
A further output signal from the tracking servo subsystem 40 is applied to an audio processing subsystem 25 114 over a line 116. The aud io squelch slgnal on the line 116 causes the audio processing subsystem 114 to S top transmitting audio signals for the ultimate appli-cation to the loud speakers contained in the TV receiver 96, and to a pair of audio jacks 117 and 118 respec-3 tlvely and to an audio accessory block 120. The audio ~acks 117 and 118 are a convenient point at which exter-nal equipment can be interconnected with the video disc player 1 for receipt of two audio channels for stereo application.
A further output signal from the tracklng servo subsystem 40 is applied to the carriage servo subsystem 55 over a line 130. The control signal present on the line 130 is the DC component of the tracking correction signal which is employed by the carriage servo subsystem .

__ .

1150833 ( for providing a ~urther carriage control signal indica-: tive of now closely the tracking servo subsystem 40 ls following the directions glven by the function generator 47. For example, lf the function generator 47 gives an instruction to the carriage servo 55 to provide carriage ` movement calculated to operate with a slow forward or slow reverse movement, the carriage serY~ subsystem 5~
has a further control signal for determining how well it is operating so as to cooperate with the electronic control signals generated to carry out the instructionfrom the function generator 47.
The stop motion subsystem 44 is equlpped with a plurality ol input signals one o~ which is an output signal of the function generator 47 as applied over a line 132. The control signal present on the line 132 is a STOP enabling signal indicating that the video disc player 1 should go into a stop motion mode of operation.
A second input signal to the stop motion subsystem 40 is the frequency modulated signal read o~f ~f the video disc and generated by the FM processing subsystem 32.
The video signal from the FM processing subsystem 32 i5 applied to the stop motion subsystem ~4 over a line 134.
Another input signal to the stop motion subsystem 44 is the differential tracking error as detected by the signal recovery subsystem 30 over the line 46.
The tangential servo system 80 ls equipped with a plurality of other output signals ln additlon to the ones previously ldentifled. The flrst Or which is applied to the audio processing subsystem 114 over a line 140. The slgnal carried by the line 140 is the color subcarrier oscillator frequency generated ln the tanential servo subsystem 80. An additional output : signal from the tangential ser~io 80 ls applied to the FM processing subsystem 32 over a llne 142. The slgnal carrled by the llne 142 ~s the chroma portion of the vldeo signal generated in the chroma separator filter portion of the tangential servo subsystem 80. An addi-tional output signal from the tangential servo 80 is applied to the FM processing subsystem 32 over a line .~.
.;~

-' 1150833 14". The sigrlal carried by tlle line 144 is a gate enab-ling signal generated by a first gate separator portion o~ t'ne tangential servo system 80 which indicates the instantaneous presence of the burs~ ~ime period in the received video signal.
The focus servo receives its ACQUIRE FOCUS
signal on a line 145.
The power output from the spindle servo sub-system 50 is applied to the spindle motor 48 over a line 14~.
The power generated in the carriage servo 55 for driving the carriage motor 57 is applied thereto over a line 150. The current generated in the carriage tachometer generator 58 for application to the carriage servo subsystem 55 indicative of the instantaneous speed and direction of the carriage, is applied to the carriage servo subsystem 55 over a llne 152.
The F~ processing unit 32 has an additional pluralit~ of output signals other than those already described. A first output signal from the FM processing ~ SUbS~JStem 32 is applied to a data and clock recovery subsystem 152 over a line 154. The data and clock re-cover~ circuit is of standard design and it is emplo~ed to read address information contained in a predetermined 25 portion of the information stored in each spiral and/or circle contained on the surrace of the video.disc 5.
The address information detected in the video signal furnished by the FM processing unit 32 is applied to the function generator 47 from the data and clock recovery subsystem 152 over a line 15D. The clocking information detected by the data and clock recovery subsystem is applied to the function generator over a line 158. An additional output slgnal from the FM processir.g unit 32 is applied to the audio processing subsystem 114 over a line 150. The signal carried by the line 160 is a fre-quency modulated video signal from the FM distribution amplifiers contained in the FM processir,g unit 32. An additional output signal from the FM processing subs~stem 32 is applied to an RF modulator 152 over a line 164.
a . :

``` ~150833 -~6 -The line 154 carrles a video output si~nal from the FM
detector portion of the FM processing unit 32. A final output signal from ~he FM processing unit 32 is applied to the TV monitor 98 over a line 155. The line 166 carries a video signal of the type displa~-able in a standard TV r"onitor 98.
The audio processing system 11~ receives an additional input signal from the function ~enerator 47 over a line 170. The signals carried by the line 170 from the function generator 47 are such as to switch the discriminated audio signals to the various audio ; accessory systems used herewith. The audio contained in the FM modulated signal recovered from the video disc 5 contains a~plurality of separate audio signals.
~ore s~ecifically, one or two channels of àudio can be contained in the FM modulated signal. These audio channels can be used in a stereo mode of operation. In one of the preferred modes of operations each channel contains a different language explainin~ the scene shown on the TV receiver 96 and/or TV monitor 98. The si~nals - contained on the line 170 control the selection at ~hich the audio channel is to be utilized.
The audio processing system 114 is equipped wit ; an additional output signal for application to the RF
modulator 162 over a line 172. The signal applied to the R~ modulator 152 over the line 172 is a 4.5 mega-hertz carrier frequency modulated by the audio informa-tion. The modulated 4.5 megahert~ carrier further modulates a channel frequency oscillator having its center frequency selected for use with one channel of the TV receiver. This modulated channel frequency oscillator is applied to a standard TV receiver 96 such that the internal circuitry of the TV receiver demodulates the audio contained in the modulated channel frequency signal in its standard mode of oper-ation.
The audio signals appl~ed to the aùdio acces-sory unit 120 and the audio ~acks 117 and 118 lies ~ithin the normal audio ran~e sui~able for driving a loudspeal;er b~l mealls o~ the audio jacks 117 and 118.
The same audio frequencies can `oe the ir.put to a stereophonic audio amplifier when such is employed as the audio accessory 120.
In the preferred embodiment, the output from the audio processing system 114 modulates the channel 3 frequency oscillatDr before applicaticn to a standard TV receiver 96. l~hile Channel 3 has been conveni-ently selected for this purpose, the oscillating fre-quency of the channel frequency oscillator can be adapted for use with any channel of the standard TV
receiver 96. The output of the RF modulator 162 is applied to the TV receiver 96 over a line 174.
An additional output signal frcm the function generator 47 is applied to the carriage servo subsystem 55 over a line 180. The line 180 represents a plural-ity of individual lines. Each individual line is not shc.~n in order to keep the main block dia~ram as clear as possible. Each of the individual lines, schematic-ally indicated by the single line 180, represen~s an ~ instruction from the function generator instructing the carriage servo to move in a predetermined direction at a predetermined speed. This is described in greater detail when describing the detailed operation of the carriage servo 55.
NORMAL PLAY r~ODE - SEQUENCE OF OPERATION
The depression of the play button generates a PLAY signal from the function generator followed by an ACQUIRE FOCUS signal. The PLAY signal is applied to the laser 3 by a line 3a for generating a read beam 4.
The PLAY slgnal turns on the spindle motor subsystem 50 and starts the splndle rotating. After the spindle servo subsystem accelerates the spindle motor to its proper rotational speed of 1799.1 revolutions per minute, the spindle servo subsystem 50 generates a PLAYER ENABLE signal for application to the carriage servo subsystem 55 for controlling the relative move-ment between the carriage assembly and the optical assembly 2. The carriage servo subsystem 55 directs : ' ..

115l)833

-2~-the movement of the carriage such that th~ read beam 4 is positioned to lmpinge upon the beginning portion o~ the information stored on the video disc record 5.
Once the carriage servo subsystem 5~ reaches the approx-im~te beginning of the recorded information, the lensrOcus servo subs~stem 35 automatically moves the l~n9 17 towards the video disc surface 5. The movement of the lens is calculated to pass the lens through a point at which op~imum focusing is acilieved. The lens servo system preferably achieves optimum focus in combina-tion with other control signals generated by reading information recorded on the video disc surface 5. In the preferred embodiment, the lens servo subsystem has a built-in program triggered by information read from the ~isc whereby the lens is caused to move through the optimum focusing point several times by an oscilla-tory type microscopic retracing of the lens path as the lens 17 moves t'nrough a single lens focusing acquiring procedure. As the lens moves through the optimum focusi~lg point, it automatically acquires information ~ from the video disc. This information consists of a total FM signal as recorded on the video disc 5 and additionally includes a differential focus error signal and a differential tracking error signal. The size of the video information signal read from the disc is used as a feedback signal to te~l the lens servo subsystem ;~ 36 that the correct point of focus has been success-fully located. When the point of optlmum focus has been located~ the focus servo loop is closed and the

3 mechanicall~ initiated acquire focus procedure is terminated. The radial tracking mirror 28 is now responding to the differential trackln& error generated from the informaticn gathered by the reading lens 17.
The radial tracking error is causing the radial track-ing mirror 28 to follow the information track andcorrect for any radial departures from a ~erfect spiral or circle track configuration. Electronic processing of the detected video FM signal generates a tangential error signal which is applied to the tangential mirror " ` 115083 ~9 2~ for correctin~ phase error in the reading process caused by small physical deformaties in the surface of the video disc 5. Duri~g the normal play mode, the servo subsystems hereinbefore described continue their normal mode of operation to maintain tlle read beam 4 properly in the center of the information track and to maintain the lens at the optimum focusing point such that the light ~athered by the lens generates a high quality si~nal ~or display on a standard television receiver ~r in a television monitor.
The frequency modulated signal read from the I disc needs additional processing to achieve optimum fideliJy durin~ the display in the television receiver 95 and/or television monitor 9~.
Immediately upon recovery from the video disc surface, the frequency modulated video signal is applied to a tangential servo su~system 80 for detecting any phase difference Eresent in the recovered video signal and caused by the mechanics of the readin~ process.
The detected phase difference is employed for driving a tangential mirror 26 and ad~usting for this phase difrerence. The movement of the tangential mirror 26 functions for changing the phase ~ the recovered video signal and eliminating time base errors intro-duced into the reading process. The recovered videosignal is FM corrected for achieving an equal amplitude FM signal over the entire FM video spectra. This re-quires a variable amplification of the FM signal over tlle ~M video spectra to correct for the mean transfer function of the readin~ lens 17. More specifically, the high frequeilcy end of the video spectrum is atten-uated more by the reading lens than the lo~ rrequency portion Or the frequency spectrum of the frequencJ
modulated signal read from the video disc. This equalization ls achieved through ampli~vring the higher frequency portion more tha!l the loJer frequency por-tion. A~ter the ~requency modulation correction is - achieved, the detected signal is sent to a discrimina-tor board whereby the discriminated video is produced .~

11~0833 ~or application to the remaining portions o~ the board.
Re~erring to Figure 3, there is sho~m a gen-erali~ed blocl~ diagram Or the spindle servo subsystem indicated at 50~ One Or the functions of the spindle servo subsystem is to maintain the speed of rotatlon of the spindle 49 by the spindle motor ~8 at a constant speed of 1799.1 rpm. Obviously, this figure has been selected to be compatible with the scanning frequency of a standard television receiver. The standard tele-vision receive~ receives 30 ~rames per second and thelnformation is reccrded on the video disc such that one complete ~ra~e of television in~ormation is con-tained in one spiral and/or track. Obviously, when the time requirements o~' a television recei~rer or tele-vision moritcr differ from this standard, then thefunctiotl o~ the spindle servo subsyste~ ~s to maintain the rotational speed at the new standard.
The function ger.erator 47 provides a START
pulse to the spindle motor. As the motor beg,ns to turn, the tachometer input sig~l pulse train from the firs' tachometer element is applied to a Schmitt trig-ger 200 over the line 51. The tacho~.eter input signal pulse train from the second tachometer element is applied to a second Schmitt trigger 202 over the line 52. A 9.33 l~z mo~or reference frequency is applied to a third Schmitt trigger 204 from the tangential servo subsystem 80 over a line 94.
The output from the Schmitt trigger 200 is applied to an edge generator circuit 206 through a 30 divide by two network 208. The output frcm the Schmitt trigger 202 is applied to an edge generator 210 tllrough a dlvided by two network 212. Tlle output from the Schmitt trigger 204 is applied to a~ edge generator circuit 214 ~hrougll a divided by two networlc 216. Each 35 o~ the edge generators 206, 210 and 21!L ~s employed ror ger.erating a s'llarp pulse correspvndLrg tc bo~h the positive goin~ edge and the negative ~oing edge Or the sign~l applied respectively rro~ the divided by two net~orks 208, 212 and 215.

~150833 The output from tlle ed~e generator 214 is applied as the reference phase signal to a rlrst ph~3e detector 218 and to a second phase detect~r 220. The phase detector 21S has as its second input signal the outp-lt from tlle edge generator 206. The phase genera-tor 220 has as its second input signal the output of the edge generator 210. The phase detectors operate to indicate any phase difference between the tachometer input si~nals and the motor reference frequency. The output from the phase detector 218 is applied to a summation circuit 222. And the output from the ph~se detector 220 is also applied as a second input to the summation circuit 222. The output from the summation circuit 222 is applied to a lock detector 224 and to a poller amplifier 22~. The function of the lock detector 224 is to indicate when the spindle speed has reached a predetermined rotational speed. This can be done by sensing the output signals from the summation circuit 222.
I~ the preferred embodi~ent is has been deter-mined that the rotational speed of the spindle motor should reach a predetermined speed before the carriage assembly is placed in motion. When a video disc is brought to a relatively high r~tational speed, the disc rides on a cushion of air and rises slightly vertical against the force of gravity. Additionally, the centrifugal force of the video disc causes the video disc to somewhat flatten considerably. It has been - found that the vertical movement against gravity caused by the disc riding on a cushion of air and the vertical rise caused by the centrifugal force both lift the video disc from its position at rest to a stabillzed position spaced from its initial rest posi-tion and at a predetermined position with reference to other internal fixed members of the video disc player cabinet. The d~-namics of a sp nnin~ disc at 1799.1 rpm Wit~l a predetermined weight and density can be calculated such as to insure that the disc is spaced ~rom all internal components and is not ln ~.
~ . ~

....

, ~
contact ;~ith anY SUCh internal components. An~J con-tact between the disc and the pla-yer cabinet causes rubbing, and the rubbing causes dama~e to the video disc throu~h abrasion.
In the preferred embodiment, the lock detector 224 has been set to Benerate a PLAYER ENAELE pulse on the line 54 when the spindle speed is up to its full 1799.1 rpm speed. A speed less than the full rota-tional speed can be selected as the point at which the player enable signal is generated provided that the video disc has moved sufficiently from its initial position and has attained a position spaced from the internal components of the video disc player cabinet.
In an alternate embodiment, a fixed dela~j, after apply-lng the STAR.T signal to the spindle motor, is used tostart the carriage assembly in motion.
During the normal operating mo~e of the vi~eo disc player lj the tachometer input signals are con-tinuously applie~ to the Schmitt trig~ers 200 and 202 over the lines 51 and 52, respectively. These actual tachometer input signals are compared against the moto-reference signal and any deviation therefrom is detected in the summation circuit 222 for application to the po~er amplifier 226. The power amplifler 226 prov~des the driving force to the spindle motor 48 to maintain the required rotational speed of the spindle 49.
Referring to Figure 4, there is shown a sche-matic block diagram of the carriage servo subsystem 55.
The carriage servo subsystem 55 comprises a plurality of current sources 230 through 235. The function of each of these current sources is to provude a predeter-mined value of current in response to an lnput signal from the function generator 47 over the llne 180. It ~as previously described that the line lo, shown with reference to ~igure 1, comprises a plurality of in-dividual lines For the pur?ose~ of tl1~S deSCriPtiOn) each of thesr7 lines will be identified as 180a through l~Oe. The outputs of the current sources 230 through 235 are applied to a summation circuit 238. The , 115083;3 o~rput from the summatlon circuit 238 ls applled to a p^~er amplifier 240 over a line 2~2. The output from ~he po~er amplifier 240 is applied to the carriage motor 57 over the line 150. A dashed line 244 extending 5 bet~leen the carriage motor 57 and the carriage tachometer member 58 indicates that these units are mechanically connected. The output from the carriage tachometer 58 is applied to the summation circuit by the line 152.
The STAP~T pulse is applied to the current source 23~a over a line 180al. The current source 232a functions to provide a predetermined current for moving the carriage assembly from its initial rest position to the desired start of track position. As previously mentioned the carriage assembly 56 and the optical 15 system 2 are moved relative one to the other. In the standard PLAY mode of operation, the optical system 2 and carriage assembly 56 are moved such that the read beam 4 from the laser 3 is caused to impinge upon the ~ start Or the recorded information. Accordingly, the current source 232 generates the current for applica-tion to the summation circuit 238. The summation circu~t 238 functions to sense the several incremental amounts of current being generated b~T the various current sources 230 throush 235 and compares this sum 25 of the currents against the current being fed into the summation circuit 238 from the carriage tachometer system 58 over the line 1~2. It has been previously mentioned that the current generated by the carria~e tachometer 58 indicates the instantaneous speed and 30 posltion of the carriage assembly 55. This current on the line 152 is compared with the currents being generated by the current sources 230 through 235 and the resulting difference current is applied to the po~er amplifier 240 over the line 242 for generating 35 the pol~ter req~lired to move the carriage motor 57 to the ~esired locatio:.
Only for purposes of example, the carriage tachometer 58 could be generatil~ a negative current indicating tllat the carr~age assembly 56 is positioned at 3 firsi location. The current source 2~2a would generate a second current lndicatil~ the desired posi-tion for the c~rriage assembly 56 to reach for start-up time. The summation circuit 23~ compares the t~o currents and ~enerates a resultin,~ difference current on the line 242 for application to the po~:er amplifier 240. The output from the amplifier 240 is applied to the carriage motor 57 for drivin~ the carriage motor and movin~ the carriage assembly to the indicated position. As the carriage motor 57 moves, the carria~e tachometer 58 also moves as indicated by the mechanical linkage sho~n b~J the line 244. As its pos~tion changes, the carriage tachometer 58 generates a ne~ ~nd differ-ent signal on the line 152, ~hen the carriage tachom-eter 58 indicates that it is at the same position asindicated b'Vr the output signal from the current source 232a, the summation circuit 238 indicates â COMPARE
EQUAL condition. No signal is applied tc the po~.~er amplifier 240 and no additional power is applied to the carria~e motor 57 causing the carrlage motor 57 to stop, The START signal on the line 180al causes the carriage motor 57 'co move to its START position. When the spindle servo subs~Jstem 50 has brought the speed of' rota~ion of th~ spindle 49 up to its readin~ speed, a PLAY ENA~LE signal is generated by the spindle servo subsystem 50 for application to a current source 230 over a line 54, The current source 230 generates a constant bias current sufficient to move the carriage assembly 56 a distance of 1.6 microns for each revolu-tion of the disc. This bias current is applied to the summation circuit 238 for providing a constant current input signal to the po~1er amplifier for driving the carriage motor 57 at the indica~ed distance per revo-lution. This constant input bias currer.t ~cm thecurrent so-lrce 23~ is f~ur~her ideni;irled as a ~irst fixed bias control signal to the carria~e motor 57.
The current source 231 receives a FAST FORlJARD
E~A~LE slgnal from the functicn generato~r 47 over the --~5--line l~Ob. The fast forl~ard current sourcc 231 gener-ates an output current sir~nal for applicati~n to the summation circuii 238 and the po~er amplif~er 240 for activating the carriage motor 57 to move the carriage assembl~ 5~ in the fast forward direction. For clari-fication, the directions referred to in this section of the description refer to the relative movement of the carriage assembly and the reading beam 4. These movements are directed generally in a radial airection as indicated by the double headed arrow 13 shown in Figure 1. In the fast forward mode of operation~ the video disc 5 is rotating at a very hi~n rot~tional speed and hence the radial trac~ing dces not OCCUI' in a straight line across the tracks as indicated by the double arrow 13. More specifically, the ca.riage servo subsyste~ is capable of providing relative motion between the carriage assembly and the optical s~Jstem 2 such as to traverse the typically four inch wide band of lnformation bearing surface cf the video disc 5 in approximately four secon~s from ~he outer periphery to the inner periphery. The average speed is one inch per second. During the four second period, the reading head moves ac-l~oss appro~imatel-~ forth-four thousand tracks. The video disc is revolving at nearly thirty revolutions per second and hence; under idealized con-ditions, the video disc 5 rotates one hundred and ~Jenty times while the carriage servo subsystem 55 provides the relative motion from the outer periphery to the inner peripher~J. Hence, the absolute point of 3o impact of the reading beam upon the rotatin~ video disc is a spirally shaped line having one hundred and twenty spirals. The net effect of this ~ovement is a radial movement of the point of impingement of the reading beam 4 l~ith the video disc 5 in a radial direction as indicated by a double headed line 13.
The current source 23, receivcs its ~ASr.~
VERSE ENABLE signal from the function generator 47 over the line 180c. The fast reverse current source 233 pr~-vides its output directl~J to tlle summation ci.cuit 238.

li~833 The current source 234 is a SLOW FORWARD cur-rent source and receives its SLOW FORWARD ENABLE input signal from the function generator 47 over a line 180d.
The output signal from the slow forward current source 234 is applied to the summation circuit 238 through an adjustable potentiometer circuit 246. The function of the adjustable potentiometer circuit 246 is to vary the output from the slow forward current source 234 so as to select any speed in the slow forward direction.
The current source 235 is a SLOW REVERSE cur-rent source which receives its SLOW REVERSE ENABLE
signal from the function generator 47 over the line 180e. The output from the slow forward current source 235 is applied to the summation circuit 238 through an adjustable potentiometer circuit 248. The adjust-able potentiometer circuit 248 functions in a similar manner with the circuit 246 to adjust the output signal from the slow reverse current source 235 such that the carriage servo subsystem 55 moves the carriage assembly 56 at any speed in the slow reverse direction.
The DC component of the tracking correction signal from the tracking servo subsystem 40 is applied to the summation circuit 238 over the line 130. The function of this DC component of the tracking correc-tion signal is to initiate carriage assembly movement when the tracking errors are in a permanent off-tracking situation such that the carriage servo sub-system should provide relative motion to bring the relative position of the video disc 5 and the read beam 4 back within the range of the tracking capability of the tracking mirrors. The DC component indicates that thje tracking mirrors have assumed a position for a substantial period of time which indicates that they are attempting to acquire tracking and have been unable to do so.
CARRIAGE SERVO - NORMAL MODE OF OPERATION
The carriage servo sybsystem 55 is the means for controlling the relative movement between the carriage assembly on which the video disc 5 is located 1~50833 and the optical system in which the reading laser 3 is located. A carrige tachometer is mechanically linked to the carriage motor and operates as a means for generating a highly accurate current value representing the instantaneous speed and direction of the movement of the carriage assembly 56.
A plurality of individually activated and variable level current sources are employed as means for generating signals for directing the direction and speed of movement of the carriage assembly. A first current source for controlling the direction of the carriage motor generates a continuous reference current for controlling the radial tracking of the read beam relative to the video disc as the read beam radially trakcs from the outer periphery to the inner periphery in the normal mode of operation. A second current source operates as a means for generating a current of the same but greater amplitude to direct the carriage assembly to move at a higher rate of speed in the same direction as the bias current. This second type of current ceases to operate when the carriage assembly reaches its predetermined position.
An additional current source is available for generating a current value of opposite polarity when compared with the permanently available bias current for causing the carriage motor to move in a direction opposite to that direction moving under the influence of the permanently available bias current.
A summation circuit is employed for summing the currents available from the plurality of current sources for generating a signal for giving directions to the carriage motor. The summation circuit also sums the output current from the carriage tachometer indi-cating the instantaneous speed and location of the carriage assembly as the carriage assembly move pur-suant to the various commands from the input current generators. The summation circuit provides a differ-ence output signal to a power amplifier for generating the power required to move the carriage assembly such 3~

1150~333 ~hat the currellt ~enerated in the carriage tachometer mqtclles the current generated from input current sources.
Rererring collectivel~ to Figure 5 and Figures 6A through 6FJ there is shown and described a schematic block diagram of the focus servo subsystem 36, a plur-ality of difrerent waveforms which are employed with the focus servo subsystem and a plurality of single logic diagrams showing the sequence of steps used in 10 the focus servo to operate in a plurality of different modes of operation. The focus error signal from the signal recovery subsystem 30 is applied to an amplifier and loop compensation circuit 250 over the line 38.
The output fro~the amplifier and loop compensation cir-suit 250 is applied to a kicl~back pulse generator 252over a line 254 and to a focus servo loop s~Jitch 256 over the line 254 and a second line 258. The output from the kiclc'~ack pulse generator 252 is applied to a driver circuit 260 over a line 262. The output from the focus servo loop switch 256 is applied to the - driver circuit 260 over a line 264.
The FM video signal is applied from the dis-tribution amplifier portion of the FM processin~ sub-system 32 to a FM level detector 270 over the line 66. The output from the FM level detector 270 is ap-plied to an acquire focus logic circuit 272 over line 274. The output Or the ~M level detector 270 is ap-plied as a second alternative input signal to the gener-ator 252 over a line 275. The output from the acquire focus logic circuit is applied to the focus servo loop switch 256 over a line 276. A second output signal from the acquire focus logic circuit 272 is applied to a ramp generator circuit 278 over a line 280. The acquire focus logic circuit 272 has as its second input signal the acquire rOcus enable signal generated by the function generator 1~7 over t`ne line 1"6. The output of the ramp generator 278 is applied to t~le driver circuit 260 over a line 281.
The acquire focus enable signal applied to the acquire focus lo~ic 272 over tlle line 14~ is shown o~
line A of Figure 6A. ~asic~ , this si~al is a t~o-le~el signal generated by the function generator 47 and havil~ a disabling lo~er condition indicated at 282 and an ena~ling conditioll indicated ger.erally at 284. The function generator produces this pulse when the video disc pla~Jer 1 is in one Or its play modes and it is necessary to read the information stored on the video disc 5.
Referring to line ~ of Figure 5A, there is shol-~n a typical ramping voltage waveform generated by the ramp generator circuit 278. During the period of time corresponding to the disabling portion 282 of the acquire focus signal, the focus ramp wave~orm is in a quiescent condition. Coincidental ~ith the turning on of the acquire focus enable si~nal, the ramp generator 278 generates its ramping voltage waveform shown as a sawtooth type output waveform going frcm a higher position at 286 to a lower position at 288. This is shown as a linearly changing signal and has been found ~ to be the most useful waveform for this purpose.
Referring to line C of Figure 6A, there is shown a representation of the motion of the lens itself during a number of operatlng modes of the video disc player. Prior to the generation of the acquire focus enabie signal, the lens is generally in a retracted position indicated generally at 290. Upon the receipt of the acquire focus enable signal, the lengs begins to move in a path indicated by the dash/dot line 292.
The dash/dot line 292 begins at a point identified as the upper limit of lens travel and moves through an intersection with a dotted line 294. This point of lntersection is identified as the lens in focus posi-tion 293. lJhell focus is not acquired on the first 35 attempt, the lens continues along the dash/dot line 292 to a p~int 295 ident ~ied as lo~er li~i~ of lens travel Ilhen the lens reaches pvint 295, the lens remains at the lower limit cr lens travel through the portinn of the line indicated generally at 296. The -4t)-lens continues to follo~ the da~h/dot line to a point illdicate~ at 297 identified as the RAMP R~SET point.
This is also shown on line A as 288. Du-ing the ramp reset til~e the lens is drawn back to the up~er limit of lens travel portion of the waveform as indicated at 298.
In this first mode of operation the lens fails in its first attempt at acquiring focus. The lens passes through the lens in focus position as indicated by the dotted line 294. After failing to acquire focus the lens then moves all the way to its lower limit of lens travel at 296 ~efore retracting to its upper limit of lens travel indicated at 298. The upper limit of lens travel position and the lower limit Or lens travel position are sensed by limit switches in the lens driver subassembly not shown.
During a successful attempt to acquire focus the path of lens travel changes to the dotted line indicated at 294 and remains there until ~ocus is lost.
The lens is r.ormally one micron above the video disc 5 uhen in the focus position. Also the in-focus posi-~ tion can vary over a range of 0.3 microns.
The output signal from the ramp generator 278 to the driver 260 on the line 281 has the configuration shoun on line ~ of Figure 6A.
The waveform shown on line G of Figure 6A
shows the wave shape of the signal applied to the FM
level detector 270 over the line 66. The uaveform shown on line G lllustrates two principal conditions. The open double sided sharp pulse indicated generally at 30 300 is generated by the signal recovery subsystem 30 as the lens passes through focus. This is shown by the vertical line 301 connecting the top of the pulse 300 with the point on line 292 indicating that the lens has passed through the ln-focus position as indicated by its intersection with the dotted line 294. Correspond-ing to the description previously given uith reference to line C of Figure 5A the lens passes through focus and the sharp pulse retracts to its no activity level indicated generally at 302.

1~50~33 4l--In the second illustration, the waveform sho~1n on line G Or Figure 6A illustrates the output ~rom the F~ d_stributioll amplifier on the line 56 when the lens acquires focus. This is in~icated by the envelope generally represented by the crossed hatched sections between lines 304 and 30~.
Re~erring to the waveform shown on line H of Fi~ure 6A, there is shown a dash/dot line 308 repre-senting the output from the FM level detector 270 corres-ponding to that situation when the lens does not acquirefocus in its first pass through the lens in focus posi-tion by line 29~ of line C of Figure 6~. The output of the level detector represented by the dotted line 311 shows the loss of the FM signal by the detector 270.
The solid line 312 shows the presence of an FM signal detected by the FM level detector when the lens ac-quires focus. The continuing portion of the waveform at 312 indicates that a Frq signal is available in the focus servo subsystem 36.
Referring to line I of Figure 6A, there is - shown the output characteristic cr the focus servo loop switch 256. In the portion of its cperating character-istics generally indicated by the portion of the line indicated at 314, the switch is in the ofl conditlon representing the unfocused condition. The posltion of the iine 316 represents the focused condition. The vertical transition at 318 indicates the time at which focus is acquired. The operating mode of the video disc player ~uring the critical period of acquiring focus is more fully described with reference to the waveforms shown in Figure 6C. Line A of Figure 6C
represents a corrected differential focus error gener-ated by the signal recovery system 30 as the lens follows its ph~sical path as previously described with reference to line C of Figure 5A. At point 319 of the waverorm A shown in ~igure ~C, the di~ eren.~ial focus error corresponds to a porti~n oI` the lens travel du~ing which no focus errors are available. At the region indicated at 320, the first false in-focus error signal 1~50833

4~-is available. There is first a momentary rise in focus errcr to a first maximum initial level at point 322.
.~t point 3~, the differential focus error begins to rise i21 ~he opposite direction until it peaks at a point 324. T`ne difrerential focus error begins to drop to a second but opposite maximum at a point 326. At a point 328, halfway between the points 324 and 325, is the optimum in-focus position for the lens. At this point 328, the lens gathers maximum reflected light from the video disc surface. Continuing past point 326, the differential focus error begins to fall towards a second false in-focus condition represented at this point 330. The differential focus error rises past the in-focus position to a lower maximum at 332 prior to falling back to the position at 333 where no focus error information is available. No focus error in-formatior is available because the lens is so close to the video disc surface as to be unable to distinguish ~ difference of the diffused illumination presently bath~ng the two focus detectors.
Referring to line ~, there is shown a wavefor~
representing the frequency modulated signal detected from the video disc surface 5 through the lens 17 as the lens is moving towards the video disc 5 in an atte~pt to acquire focus. It should be noted that the frequency modulated signal from the video disc 5 is detected only over a small distance as the lens reaches optimum focus, and then passes tilrough optimum rOcus.
This small distance is represented by ~ha~p peaks 334a and 334b of the FM detected video as the lens 17 moves through this preferred in-focus position when focus is missed.
lihlle focus can be achieved using only the dif~erential focus error signal shown with reference to line A of Figure 6C, one embodiment of the present invention utili~es the differential focus error signal as shown on line A of Figure 6C in combination wi~h the signal shown on line ~ of Figure 6C to achieve more reliable acquisition of focus during each attempt at . ~

_ 1j3 focu~.
Figure C of line 6C shows an inverted ideal-i~ed focus error signal. Tlis idealized error signal is then dlrferentiated and the results shown on line D
of Figure 6C. The differentiation of the idealized focus error signal is represented by the line 339.
Small portions of this line 339 shown at 340 and 342 lyin~ above the zero point indicated at 344 give false indication of proper focusing regions. The region 346 falling under t~e line 339 and above the zero condition represented by the line 341~ indicates the range within which the lens should be positioned to obtain proper and optimum focus. The re~ion 346 repre-sents approximately 0.3 microns of lens travel and corresponds to the receipt of an F~ input to the F~I
level detector as shown in line B. It should be noted that no ~ is shown on line ~ corresponding to regions 340 and 342. Hence~ the FM pulse shown on line ~ is used as a gating signal to indicate when the lens has been positioned at the proper distance above the ~ video disc 5 at which it can be expected to acquire focus.
The signal representing the differentiation of the idealized focus error is applied ~o the gener-25 ator 252 for activating the generator 252 to generate its kickback waveform. The output from the FM level detector 270 is an alternative input to the kickback generator for generating the ki~kback wave~orm for application to the driver 260.
Referring back to line ~ of Fi~ure 6A and continuing the description of the waveform shown there-on, tlle dot/dash portion beginning at 285 represents the start of the output signal from the ramp generator 27~ for moving the lens through the optimu~ ~ocusing 3~ range. This is a sawtooth signal and it is calculated to move the lens smoothly through the point at which FM is detected by the FM level detector 270 as indi-cated by the waveform on line H. In a flrst mode of operation, the rocus ramp follows a dot-dash portion _ ... . . ..... .

` 11~833' -44_ 2~ Or the ~aveform to a p~int 287a corresponding to tlle ti~e at which th2 output of the Frl level detector shows the acq~.lisition of ~ocus b~ ~enerating the si~nal le~el at 312a in line l~. The output si~nal from the acquire focus logic block 272 turns ofl the ramp gen-erator over the line 280 indicatin~ that ~ccus has been acquired. ~lhen focus is acquired, the output from the ramp generator follows the dash line portion at 287 indicating that focus has been acquired.
Referring to line A of Figure 6~, a portion of the focus ramp is shotln extending between a first upper voltage at 285 and a second lower voltage at 288. The optimum focus point is located at 287a and corresponds with the peak of the FM signal applied to the FM
level detector 270 as shown orl line C of Figure 6E.
Line ~ is a simplified version of the lens position transfer functior 290 as shown more specifically with reference to line C of Figure 6A. The lens position transfer function line 290 extends between an u~per limit Or lens travel indicated at point 292 and a lower limit of lens travel indicated at point 295. The optimum lens focus position is indic~ted by a line 296.
The optimum lens focus point is therefore located at 299.
Referring to line D of Figure 6~, there is shown the superimposing of a kickback sawtooth wave-form indicated generally in the area 300 upon the lens position transfer line 292. This indicates that in the top portion of the three kickback pulses are located at 302, 304 and 306. The lower portion of the three kickback pulses are located at 308, 310 and 312, re-spectively. The line 296 again shows the point of optimum focus. The intersection Or the line 296 with the line 292 at points 29Ga, 296b, 295c and 296d shows that the lens itself passes through the optimum lens focus position a pluralit~r of times durir~g one acquire focus enable function.
Referring to line E of Figure 6~, the input tc the F~ level detector indicates that during an 11~0833 oscilla~or~r mo~lon of the lens tllrough the optlmum focus positlon as shown by the combined lens travel function characteristic shown in Fi~ure D, the lens has the opportunity to acquire focus of t~.e FM sigilal at four locations indicated at the peaks of waveforms 314, 316, 318 and 320.
The ~aveforms shown with reference to Figure 6~ demonstrate that the addition of a high frequency oscillating sawtooth kickback pulse upon the ramping signal generated by the ramp generator 278 causes the lens to pass through the optimum lens focus position a plurality of times or each attempt at acquiring lens focus. Th~s improves the reliability of achieving proper lens focus during each attempt.
The focus servo system employed in the present invention functions to position the lens at the place calculated to provide optimum focusing of the reflected read spot after impinging upon the information track.
In a first mode of operation, the lens servo is moved under a ramp voltage waveform from its retracted posltion towards its fully down position. When focus is not acquired during the traverse of this distance, means are provided for automatically returning the ramping voltage to its original position and retracing the lens to a point corresponding to the start of the ramping voltage. Thereafter, the lens automatically moved through its focus acquire mode of operation and through the optimum focus position at which focus is acquired.
In a third mode of operation, the fixed ramp-ing waveform is used in combination with the output from an FM detector to stabillze the mirror at the optimum focus positlon ~hich corresponds to the point at which a frequency modulated signal is recovered from the information bearing surface of the video disc and an output is indicated at an F;i; detector. In a further embodiment, an osc~llatory waverorm is superimposed upon the ramping vol~age to help the lens acquire proper focus. The oscillatory waveform is triggered ( liS~8~' by a num`~er of alternative input signals. A first such input signal ls the output from the FM detector lndicatin~ that the lens has reached the optlmum focus point. A second triggering signal occurs a fixed time after the beginning of the ramp voltage ~aveform. A
third alternatlve input signal is a derivation of the differential tracking er~r indicating the point at which the lens is best calculated to lie within the range at which optimum focus can be achieved. In a further e.mbodiment of the present invention, the focus servo is constantly monitoring the presence of FM
in the recovered frequency modulated signal. The focus servo can mai-ntain the lens in focus even though there is a momentary loss of detected frequency modulated signal. This is achieved by constantly monitoring the presence of Fl~ signal detected from the video disc.
Upon the sensing of a momentary loss of frequenc~J
modulated signal, a timing pulse is generated which is calculated to resta,t the focus acquire mode of oper-2~ ation. However, i~ the frequency modulated signalsare detected prior to the termination of this fixed period of timej the pulse terminates and the acquire focus mode is skipped. If FM is lost for a period of time longer than this pulse, then the focus acquire mode is automatically entered. Tlle focus servo con-tinues to a~tempt to acquire focus until successful acquisition is achieved.
FOCUS SERVO SU~SYSTEM - NORMAL MODE OF OPERATIO~
-The principal functlon of the focus servo sub-system is to drive the lens mechanism towards the video dlsc 5 until the objective lens 17 acquires optimum focus of the light modulated signal being refl2cted from the surface of the video disc 5. Due to the re-solving power of the lens 17, the optimum focus point is located approximately one micron from the disc surface. The range of lens travel at ~hich optimum focus can be achieved is 0.3 microns. The information bearing surface of the video disc member 5 upon which the light reflective and light non-reflective members -47l-are positioned, are oftentimes distorted due to imper-fectlons in tne manufacture of the video disc 5. The video disc 5 is manufactured accordin~ to standards which ~Jill make available for use on vldeo disc players those video disc members 5 havin~ errors which can be handled by the focus servo system 36.
In a first mode of operation, the focus servo subsystem 36 responds to an enabling signal telling the lens driver mechanism when to attempt to acquire focus.
A ramp generator is a means for generating a ramping voltage for directing the lens to move from its upper retracted position down towards the video disc member

5. Unless interrupted by external signals, the ramolng voltage continues to move the lens throu~h the optimum focus position to a full lens down position correspond-ing to the end of the ramping voltage. The full lens down position can also be indicated by a limit switch which closes ~hen the lens reaches this position.
~ The lens acquire period equals the tlme of the ramping voltage. At the end of the ramping voltage period, automatic means are provided for automatically resetting the ramp generator to its initial positicn at the start of the ramping period. Operator interven-tion is not required to reset the lens to its lens acquire mode in the preferred embodiment after focus was not achieved during the flrst attempt at acquiring focus.
In the recovery of FM video information from the video disc surface 5, lmperfections on the dlsc surface can cause a momentary loss of the FM signal being recovered. A gatlng means ls provlded in the lens servo subsystem 36 for detecting this-loss FM
from the recovered FM video signal. Thls FM detectin~
means momentaril~ delays the reactivation of the ac-quire focus mode of operation of the lens servo sub-system 3~ for a predetermlned time. Duri:;g this pre-determined time, the reacquisition of the FM signal prevents the FM detector means from causir.g the servo subsystem to restart the acquire focus mode of operation.

1150833 ( ~ ,~
In the event that F~l is not detected during this first predetermined ti!ne the FM detector means reactivates the ramp generator for generating the ramping slgnal which causes tl~e lens to follow throu~h the acquire focus procedure. At the end of the ra~p generator period, the FM detector means provides a further signal for resetting the ramp generator to its initial pOsitiOIl and to follow through the ramping and acquire ~ocus procedure.
In a third embodiment, the ra~ping voltage generated by the ramp generator has super~mpcsed upon it an oscillatory sequence of pulses. The oscillatory sequence of pulses are added to the standard ramping voltage in response to the sensing of recovered F~
from the video disc surface 5. The combination of the oscillatory waveform upon the standard ramping voltage is to drive the lens through the optimum focus position in the direction towards the disc a number of times during each acquire ~ocus procedure.
In a further embodiment, the generation of the oscillatory waveform ls triggered a fixed time after the initiation of the focus ramp si~nal. ~nile this is not as efficient as using the Fi~ level detector output sisnal as the means for triggering the oscilla-tory waveform ger.erator it provides reasonable and reliable results.
In a third embodiment, the oscillatory wave-form is triggered by the compensated tracking error signal.
Referring to Figure 7, there is shown a schematic block diagram of the signal recovery sub-system 30. The wave~orms shown in Figure 8, lines ~, G and D, lllustrate certain of the electrical waveforms available within the signal recovery subsystem 30 during the normal operation of the player. Referring to Figure 7, the reflected light beam is indicated at 4' and is divided into three principal beams. A ~irst beam impinges upon a first tracking photo detector indicated at 380, a second portion of the read beam 4' li50833 impin~es UpO!l a second tracking photo detector 382 and the central information beam is shown impinging upon a concentric ring detector indicated generally at 384.
The concentric ring detector 384 has an lnner portion at 385 and an outer portion at 38&, respectively.
The output from the first tracking photo de-tector 380 is applied to a first tracking preamp 390 over a line 392. The output from the second tracking photo detector 382 is applied to a second tracking preamp 394 over a line 395. The output from the inner portion 386 of the concentric ring detector 384 is zpplied to a first focus preamp 398 over a line 400.
The output from the outer portion 388 of the concen-tric ring detector 384 is applied to a second focus pre-amp 402 over a line 404. The output frcm both portions385 and 388 of the concentric ring focusing element 384 are applied to a wide ban~ amplifier 405 over a line 405. Al alternative embodiment to that sho~n would include a summation of the signals on the lines 400 20` and 404 and the application of this sum to the wide band amplifier 405. The showing of the line 40~ is schematic in nature. The cutput from the wide band amplifier 405 is the time base error corrected fre-quency modulated signal for application to the FM
25 processing subsystem 32 over the line 34.
The output from the first focus preamp 398 is applied as one input to a differential amplifier 408 over a line 410. The output from the second focus preamplifier 402 forms the second input to the differ-3 ential amplifier 408 over the line 412. The outputfrom the differential amplifier 408 is the differential focus error signal applied to the focus servo 36 over the line 38.
The output from the first tracking preampli-35 fier 390 forms one input to a differential amplifier414 over a line 415. The output fromthe second track-ing preamplifier 394 forms a second inpu~ to the diffe~
ential amplifier 414 over a line 418. The output from the differential amplifier 414 is a differential track-1~5()833 -5n-ln~ error signal applie~ to the tracking servo syste-over the line 42 and applied to the stop motlon sub-s~stem over the line 42 and an additional line 45.
Line A of Figure 8 shows a cross-sectional view talcen in a radial direction across a video disc meMber 5. Light non-re~lective elements are shown at 11 and intertr~c~ regions are shown at lOa. Such inte~-traclc regions lOa are similar in shape to light re-flective elements 10. The light reflective regions 10 10 are planar in nature and normally are highly polished surfaces such as a thin aluminum layer. The light nor.
reflective regions 11 in the preferred embodiment are light scattering and appear as bumps or elevations above the ~lanar surface represented by the light re-flective regions 10. The lengths Or the line indicatedat 420 and 421 shows the center to center spacing of two adjacently positioned tracks 422 and 423 about a center tracl~ 424. A point 425 in the line 420 and a polnt 425 in the line 421 represents the crossover point 20` between each of the adjacent tracks 422 and 423 l~hen - leaving the central track 424 respectively. The cross-over points 425 and 425 are each exactly halfway be-tween the central track 424 and the tracks 422 and 423 respectively. The end points of line 420 represented at 427 and 428 represent the center of information tracks 422 and 424, respectively. The end of line 421 at 429 represents the center of information track 423.
The waveform shown in line B of Figure 8 represents an idealized form of the frequency modulated signal output derived from the modulated light beam 4' during radial movement of the read beam 5 across the tracks 422, 424 and 423. This shows that a maximum frequency modulated signal is available at the area indicated generally at 430a, 430b and 430c which correspond to the centers 4279 42~ and 429 of the in-; formation tracl~s 4225 424 alld 423, res~ectively. A
minimum frequellcy modulated signal is available at 431a and 431b wl~ich correspon~s to the crossover points 425 and 426. The wavefolm shown on line ~ of Figure 3 I

1~ 833 _51_ ls generaled by radially movlng a focused lens acrossthe surrace of a video disc 5.
Referring to line C of Figure 8, there is shown the difrerential tracklng error signal generated in the differen~ial amplifier 414 shown in Figure 7.
Tl~e differential tracking error signal ls the same as that shol~Jn in lille A of Figure 6C e~cept for the details shown in the Figure 6C for purposes of explanation of the focus servo subs~rstem peculiar to that mode of operation.
Referring again to Figure C of line 8, the differential tracking error signal output shows a first maximum tracking error at a pOillt indicated at 432a and 432b which is intermediate the center 428 of an information track 424 and the crossover point indi-cated at 425 or 426 depending on the direction of beam travel from the central track 424. A second maximum tracking error is also shown at 434a and 434b corres-ponding; to a track location intermedlate the crossover points 425 and 425 between the information track 424 and the next adjacent tracks 422 and 423. Minimum focus error is shown in line C at 440a, 440b and 4~0c corresponding to the center of the information tracks 422, 424 and 423, respectiveljr. Minimum tracking error signals are also shown at 441a and 441b corresponding to the crossover points 425 and 426, respectively. This corresponds with the detailed descriptlon given with reference to Figure 6C as to the importance ~ identi-fying which of tlle minimum differential tracking error signal outputs corresponds with the center of track location so as to insure proper focusing on the center of an information track and to avoid attempting to focus upon the track crossovers.
Referring to line D of Figure 8, there is shown the differential focus error signal output wave-form generated by the differential amplifier 408. The waveform is indicated generally by a line 442 which moves ln quadrature with tne different~al tracking error signal silown with reference to line C of Figure 8.

~lSC~833 5~
Rel'erring to Fl~ure 9, there is shown a schematic block diagram of the tracking servo subsystem ~0 emplo~red in the video disc pla~rer 1. The difleren-tial trackin~ error is applied to a trac~in~ servo loop lnterrupt switch 4~0, over the line 4~ from the signal recovery system 30. The loop interrupt signal is ap-plied to a ~ate 482 over a line 108 from the stop motion subsystem 44. An open fast loop command signal is applied to an open loop fast gate 484 over a line 180b from the function generator 47. As previously mentioned, the function generator includes both a re-mote control unit from which commands are received and a set of console switches from which commands can be received. Accordingly, the command signal on line 180b is diagrammatically shown as the same signal applied to the carriage servo fast forward current generator over a line 180b. The console switch is shown entering an open loop fast gate 486 over the line 180b'. The rast reverse command from the remote con-trol portion of the function generator 47 is appliedto the open loop fast gate 484 over the line 180b.
The fast reverse command from the console portion of the function generator 47 is applied to the open loop fast gate 486 over the line 180b'. The output from the gate 484 is applied to an or gate 488 over a line 490.
The output from the open loop fast gate 486 is applied to the or gate 4~8 over a line 492. The first output from the or gate 488 is applied to the audio processing system 114 to provide an audio squelch output signal on 3 the line 116. A second output from tlle or gate 488 is applied to the gate 482 as a gating signal. The output from the tracking servo open loop switch 480 is applied to a junction 496 connected to one side ~ a resistor 498 and as an input to a trac~in~ mirror amplifier driver 500 over a line 505 and an amplifier and fre-quenc~r compensation network 510. The other end Or the resistor 498 is connected to one side of a capacitor 502. The ot'.ler side of the capacitor 502 is connected to ground. The amplifier 500 receives a second input llS0833 signal from the s~op motion subsystem ~4 over the line lOo. The slgnal on the llne 106 ls a stop motlon com-pensation pulse.
The function of the amplifler 510 is to provide a DC component of the trackin~ error, developed over the comblnatlon of the resistor 498 and capacitor 502, to the carriage servo system 55 durlng normal tracklng periods over a line 130. The DC component from the junction 49~ is gated to the carrlage servo 55 by the play enabling slgnal from the function generator 47.
The push/pull amplifier circult 500 generates a first trac~ing A signal for the radial tracking mlrror 28 over the line 110 and generates a second tracking ~ output signal to the radial tracking mirror 28 over the line 112. The radial mirror requires a maximum of 600 volts across the mirror for maxlmum operating efficiency when bimorph t~ype mirrors are used. Accordingly, the push/
pull ampllfler circuit 500 comprises a pair of ampli-fier circuits~ each one providing a three hundred voltage swing for drivlng the tracking mirror 2~.
~ Together, they represent a maximum of six hundred volts peak to peak slgnal for appllcatlon over the lines 110 and 112 fGr controlling the operation of the radial tracking mirror 28. For a better understanding of the tracking servo 40, the description of its detailed mode of operation is combined with the detailed descrip-tion of the operation of the stop motion subsystem 44 shown with reference to Figure 12 and the waveforms shown in Figures 13A, 13~ and 13C.
TRACKI~G SERVO SU~SYSTEM - NORMAL MODE OF OPERAT~ON
The video disc member 5 being played on the video disc player 1 contains approximately eleven thousand information tracks per inch. The distance from the center of one information track to the next ad~acent information trac~ ls in the range ~ 1.6 microns. The information indicia alig:led ln an informa-tion track is approximately 0.5 microns in width. This leaves approximately one micron of empty and open space between the cutermost regions of the indicia positioned #33 -~4-in adJ`acent information bearing tracks.
The function of the tracking servo is to direct the impin~ement of a focused spot of light to imp~ct directly upon the center of an information track.
The focused spot of light is approximately the same width as the information bearing sequence of indicia which form an information track. Obviously, maximum si~nal recovery is achieved when the focused beam of light is caused to travel such that all or most of the light spot impinges upon the successively positioned light reflective and light non-reflective regions of the information track.
The traclcing servo is further identified as the radial tracking servo because the departures from the information track occur in the radial direction upon the disc surface. The radial tracking servo is continuously operable in the normal play mode.
The radial tracking servo system is interrupted or released from the differential tracking error signal 20 generated from the FM video information signal recov-ered from the video disc 5 in certain modes of opera-tion. In a first mode cf operation, when the carria~e servo is causing the focused read beam to radiall~J
traverse the information bearing portion of the video 25 disc 5J the radial tracking servo system 40 is released from the effects of the differential tracking error signal because the radial movement of the reading beam is so rapid that tracking is not thought to be neces-sary. In a ~ump back mode of operation wherein the 30 focused reading beam 4 is caused to jump from one track to an adjacent track, the difrerential tracking error is removed from the radial tracking servo loop for eliminating a signal from the tracking mirror drivers which tend to unsettle the radial mirror and tend to 35 require a longer period of time prior for the radial tracking servo subsyJtem to reac~u~re pro,er tracking of the next ad~acent informatioll track. In this embod-iment of operation where the differential tracking error is removed from the trackillg mirror drivers, a substitute 1~50833 -5~-pulse is genera ed for givin~ a clean unambiguous signal to the tracking mirror drivers to direct tlle tracking mirror to move to its next assigned locaticn. This signal in the preferred embodiment is identified as the stop motion pulse and comprises regions of pre-emphasis at the beginning and end of the stop motion pulse which are tailored to direct the tracking mirror drivers to move the focused spot to the predetermined next traclc location and to help maintain the focused spot in the proper tracking position. In revlew, one mode of operation of the video disc player removes the differential tracking error signal from application to the tracking mirror drivers and no addition~l signal is substituted therefor. In a further embodiment of operation of the video disc player, the differential tracking error signal is replaced by a particularly shaped stop motion pulse.
In a still further mode of opera'ion of the tracking mirror servo subsystem 40, the stop motion pulse which is employed for directing the focused beam to leave a first information traclc and depart for a second adjacent information track is used in combina-tion wi'h a compensation signal applied directly to the radial tracking mirrors to direct the mirrors to main-tain focus on the next adjacent track. In the preferr~embodiment, the compensation pulse is applied to the tracking mirror drivers after the termination of the stop motion pulse.
In a still further embodiment of the tracking servo subsystem 40J the differential tracking error signal is interrupted for a period less than the time necessary to perform the stop motion mode of operation and the portion of the differential tracking error allowed to paGs into the tracking mirror drivers is calculated to assist the radial traclcing mirrors to achiel~e proper radial tracking.
Referring to Figure 11, there is shown a block diagram of the tangential servo subsystem 80. A first input signal to the tangential servo subsys~em 80 is 1 ~ ~ 8 3 -,6-applled from the Fr~ processlnG system 32 over the line 8~. The signal present on the line 82 is the video signal available frcm the vodeo distribution ampli-fiers as contained in the FM processing system 32~ The video sigllal on the line 82 is applied to a sync pulse separator circuit 520 over a line 522 and to a chroma separator fil~er 523 over a line 524. me video signal on the line 82 is also applied to a burst gate separa-tor circuit 525 over a line 525a.
The function of the vertical sync pulse separ-ator circuit 520 is to separate the vertical sync signal from the video sign~l. The vertical sync signal is applied to the stop motion subsystem 44 over the line 92. The function Or the chroma separator filter 523 's to separate the chroma portion fro~ the total video signal received from the FM processing circuit 32.
The output from the chroma separator filter 523 is ap-plied to the FM corrector portion of the FM process-~ ing circuit 32 over the line 142. The output signal from the chroma separator filter 523 is also appliedto a burst phase detector circuit 526 over a line 528.
The burst phase detector circuit 526 has a second input signal from a color subcarrier oscillator circuit 530 over a line 532. The p~rpose of the burst phase de-tector circuit 525 is to compare the instantaneousphase of the color burst signal with a very accurately generated color subcarrier oscillator signal generated in the oscillator 530. The phase difference detected in the burst phase detector circuit 52~ is applied to a sample and hold circuit 534 over a line 535. ~he function of the sample and hold circuit is to store a voltage equivalent of the phase difference detected in the burst phase detector circuit 526 for the time during - which the f'ull line of video information containing that color burst signal, used in generating the phase difference, is read from the disc 5.
The purpose of the burst gate separator 525 is to generate an enabling signal indicating the time during which the color burst portion of the video ~ ~ ~ ~ 3( waverorm is received from the FM processin~ unit 32.
The output signal frQm the burst gate separator 525 is ap~lied to the FM corrector portion Or the FM
processing system 32 over a line 144. The same burst gate timil~ signal is applied to the sample and hold circuit ~ over a line 538. ~he enabling signal on the line 53S gates the input from the burst phase de-tector 526 into the sample and hold circuit 53~ during the color b~rst portion of the video signal.
The color subcarrier oscillator circuit 530 applies the color subcarrier frequency to the audio processing circuit 114 over a line 140. The coior subcarrier oscillator circult 530 supplies the color subcarrier frequenc~J to a divide circuit 540 over a line 541 which divides the color subcarrier frequency by three hundred and eighty-four for generating the motor reference frequency. The motor reference fre-quency signal is applied to the spindle servo subsystem 50 over the line 94.
The output from the sample and hold circuit ~ 53L' is applied to an automatic gain contrclled ampli-ri er circuit 542 over a line 544. The automatic gain controlled amplifier 542 has a second input signal from the carriage position potentiometer as applied thereto over the line 84. The function of the signal on the line 84 is to change the gain of the amplirler 542 as the readinG beam 4 radially moves from the inslde track to the outside track and/or conversely ~hen the reading beam moves from the outside track to the inside track.
The need for this adjustment to change with a change in the radial position is caused by the formation of the reflective regions 10 and .~on-rerlective regions 11 with different dimensions from the outisde tr~ck to the inside track. The purpose of the const?nt rotational speed from the spin~le motor 48 is to turn the disc 5 through nearly thirty revolut~ons per second to provide thirty rrames of in~ormation tothe television receiver 96. The length of a track at the outermost circum-ference is much lon~er than the length Or a track at ~150833 i -5~
the innermost circumference. Since the sa~e amount of inlormation is stored in one revolution at ~cth the inner and outer circumference~ the si~e of the reflec-tive and non-reflective re~ions 10 and 11, respectively~
are adjusted from the inner radius to the outer radius.
Accordin~ly, this change in size requires that certain adjustmen~ in the processing of the detected signal read from the video disc 5 are made for optimum opera-tion. One of the required adjustments is ~o adjust the gain of the amplifier 542 which adjusts for the time base error as t!!~e reading pOiilt radially changes from an inside to an outside circumference. The carriage position potentiometer (not shown) generates a suffi-ciently accurate reference voltage indicating the radial position of the point of impingement of the reading beam 4 onto the video disc 5. The output from the amplifier 542 is applied to a compensation circuit 545 over a line 546. The compensation net-v~orlc 545 is employed for preventing any system oscillations and instabilit~J. The output from the compensation network 545 is applied to a tangential mirror dr~ver circuit 500 over a line 550. The tangential mirror driver circuit ~00 was described with reference to Figure 9.
The circuit 500 comprises a pair of push/pull ampli-fiers. The output from one ~ the push/pull ampllfiers (not shown) is applied to the tangential mirror 26 over a line 88. The output fromthe second push/pull ampl-lfier (not sho~n) is applied to the tangential mirror 2~ over a llne 90.
TIME ~ASE ERROR CORP~CTION r~ODE OF OPERATION
The recovered FM video signal, from the surface of the video disc 5 is corrected~ for time base errors introduced ~y the mechanics of the reading process, in the tangential servo subsystem 80. Time base errors 3~ are introduced into the reading process due to the minor imperfections in the video disc 5. A time base error introduces a slight phase change into the re-covered FM video signal. A typical time base error base correction system includes a highly accurate 5~.
oscillator for generatlng ~ source Or signals used as a phase standard for comparison purposes. In the pre-ferred embodiment) the accurate oscillator is conven-iently chosen to oscillate at the color subcarrier frequency. T~e color subcarrier frequency is also used during the wrlting process for controlling the speed of revolution of the writing disc during the riting process. In this manner~ the reading process is phase controlled by the same highly accurate oscil-lator as was used in the writing process. The outputfrom the highly controlled oscillator is co~pared with the color burst signal of a FM color video signal. An alternative system records a highly accurate frequency at any selected frequency during the writing process.
During the readin~ process, this frequency would be compared with a highly accurate oscillator in the player and the phase difference between the t~lO signals is sensed and is employed for the same purpose.
The color burst signal forms a small portion of the recovered FM video signal. A color burst signal is repeated in each line of color T.V. video information in the recovered FM video signal. In the preferred embodiment, each portion of the color burst signal is compared ~ith the hlghly accurate subcarrier oscillator signal for detecting the presence of any phase error.
In a dif~erent embodiment, the comparison may not occur during each availability of the color burst signal or its equivalent, but may be sampled at randomly or pre-determir,ed locations in the recovered signal containing the recorded equivalent of the color burst signal.
~hen the recorded information is not so highly sensi-tlve to phase error, the comparison may occur at greater spaced locations. In general, the phase difference between the recorded signal and the locally generated signal is repetitively sensed at spaced locations on the recording surrace for adjusting for phase errors in the recovered signal. In the preferred embodiment this repe~itive sensing for phase error occurs on each line of the FM video signa.

115V~333`

The detected phase error is stored for a period of time extending to the next sampling process.
Tllis phase error is used to adjust the reading posi-tiCII Or ~le reading beam so as to impinge upon the video disc at a location such as to correct for the phase error.
Repetitive comparison of the recorded signal ~ith the locally generated, highly accurate frequency, continuousl~ ad~usts for an incremental portion of the recovered videG signal recovered during the sampling periods.
In the preferred embodiment, the phase error changes as the reading beam radially tracks across the information bearin~ surface portion of the video disc 5.
In this embodiment, a further signal is required for adjusting the phase error according to the lnstan-taneous location of the reading beam to adjust the phase error according to its instantaneous location on the information bearing portion of the video disc 5.
This additional signal is caused by the change in physical size of the indicia contained on the video disc surface as the radial tracking position changes from the inner location to the outer location. The same amount of information is contained at an inner radius as at an outer radius and hence the indicia must be smaller at the inner radius when compared to the indicia at the outer radius.
In an alternative embodiment, when the size of the indicia is the same at the inner radius and at the outer radius, this additional signal for ad~usting for instantaneous radial position is not required.
Such an embodiment would be operable with video disc members which are in strip form rather than ln disc form and when the information is recorded using indicia of the same size on a video disc member.
In tile preferred embGdi!nent, a tangential mirror 26 is tlle mechanism selected for correcting the time base errors introduced by the mechanics ~ the reading system. Such a mirror is electronically ~51)833 controlled and ~s a me~ns for changing the phase ~ the recovered video signal read ~'rom the disc by changing the time base on which the signals are read from the disc, This is achieved by directing the mirror to read the information from the disc at an incremental point earlier or later in tine when comp2red to the time and spacial location during which the phase error :~as detected. The amount of phase error determines the degree of change in location and hence time in which 10 t~ne inrormation is read.
I~hen no phase error is detected in the time base corr4cting system the point of impingement of the read beam with the video disc surface 5 is not moved.
l~lhen a phase error is detected during the comparison 15 period, electronics signals are generated for changing the point of impingement so that the recovered informa-tion from the video disc is available for processing at a point in time earlier or later when compared to ~ the comparison period. In the preferred embodiment, this is achieved by changing the spacial location of the point of intersection of the read beam with the video disc surface 5.
Referring to Figure 12, there is shown a block diagram of the stop motion subs~stem 44 employed in the video disc player 1. The ~aveform shown with reference to Figures 13A, 13~ and 13C are used in con~unction with the block diagram shown in Figure ~2 to explain the operation of the stop motion system.
The video signal from the FM processing unit 32 is applied to an input buffer stage 551 over the llne 134.
The output signal from the buffer 551 is applied to a DC restorer 552 over a line 554. The function of the DC restorer 552 is to set the blanking voltage level at a constant uniform level. Varlations in signal recording and recover~J oftentimes result in video signals available on the line 134 with different blank-ing levels. The output from the DC restorer 552 is applied to a w~lite flag detector circuit 55~ over a line 558. The function of the white flag detector 55 11~()83;B

is to identir~ the presence of ar all white kvel video signal existing during an entire line of one or both fields contained in a frame of television infor~ation.
I~'hile the white ~lag detector has been described as bein~ detecting an all white video signal during a complete line interval of a frame of television in-formation, the white flag may take other forms. Cne such form wo~lld be a special number stored in a line.
Alternatively, the white flag detector can respond to the address indicia found in each video frame for the same purpose. Other indicia can also be e~ployed. How-ever the use Or an all white level signal during an entire line interval in the television frame of in-formation has been found to be the most reliable.
The vertical sync signal from the tangential servo 80 is applied to a delay circuit 550 over a line 92. The output frorn the dela~J circuit 550 is supplied to a vertical ~indow generator 552 over a line 5~.
~ The function of the window generator 552 is to gener-ate an enabling signal for application tothe white flag detector 55~ over the line 566 to coincide with that line interval in which the white flag signal has been stored. The output signal from the generator 552 gates the predeterrnined ~rtion of the video signal from the FM detector and generates an output white flag pulse whenever the white flag is contained in the portion of the video signal under surveillance. The output from the white flag detector 556 is applied to a stop motion pulse generator 567 over a line 558, a gate 569 and a further line 570. The gate 569 has as a second input signal, over the line 132, the STOP MOTION
MODE enabling signal from the function generator 47.
The differential tracking error from the signal recovery subsystern 30 is applied to a zero crossing detector and delay circuit 571 over the lines 42 and 45. The function of the ~ero crossing detector circuit 571 is to identiry when the lens crosses the mid-points 425 and/or 425 between two ad~acent tracks 424 and 423.

~150833 ~
-s3 -It is important to note that the differential tracking si~nal output also indicates the same level signal at point 44~c which identifies the optlmum focusing point at wtlich the tracking servo system 40 seeks to positlon the lens in perfect tracking aligrlment on the mid-point 429 o~ the track 423 w`nen the tracking suddenly ~umps from track 424 to track 423. Accordingl~, a means must be provided for recogni~ing the difference between points 441b and 440c on the differential error signal 10 shown in line C of Figure 8.
The output of the zero crossing detector and delay circuit 571 is applied to the stop motion pulse generator 567 over a line 572. The stop motion pulse generated in the generator 5~7 is applied to a plurality of locations the first of which is as a loop lnterrupt pulse to the tracking servo 40 over the line 108. A
second output sigr.al from the stop motion pulse gener-ator 5~7 is applied to a stop motion compensation se-quence generator 573 over a line 574a. The function of the stop motion compensation sequence generator 573 ~ is to generate a compensation pulse waveform for appli-cation to the radial tracking mirror to cooperate with the actual stop motion pulse sent directly to the track-ing mirror over the line 104. The stop motion compen-sation pulse is sent to the tracking servo over the line 10~.
~ ith reference to line A of Figure 8, the center to center distance, indicated by the line 420, between adjacent tracks is presently fixed at 1.6 microns. The tracking servo mirror gains sufficient inertia upon receiving a stop motion pulse that the focused spot from the mirror ~umps from one track to the next ad~acent track. The inertia of the tracking mirror under normal operation conditions causes the mirror to swin~ past the one track to be jumped.
~riefl~, the stop motion ~uise on the line 104 causes t~le radial tracking mirror 2~ to leave the track on whlch it is tracking and Jump to the next sequential track. A short time later~ the radial tracking mirror ~150833 receives a stop motion co~pensation pulse to remove the added inertia and direct the trackin~ mirror into t.a~killg the next adjacent track ~ithcut skipping one or more tracks ~efore selecting a track for tracking.
In order to insure the optimum cooperation between the stop motion pulse fro~ the generator 567 and the stop motion compensation pulse rrcm the gener-ator 573, the loop interrupt pulse on line 108 is sent to the tracking servo to remove the difrerential tracking error signal from being applied to the track-ing error amplifiers 500 during the period of time that the mirrcr is purposely caused to lea~!e one track und~ direction of the stop motion pulse from the generator 557 and to settle upon a next adjacent track under the direction of the stop motion compensation pulse from the generator 573.
As an introduction to the detail understand-ing of the interaction between the stop motion system ~ 44 and the tracking servo system 40, the waveform shown in Figures 13A, 13~ and 13C are described.
Refer ing to line A of Figure 13A, there is shown the normal tracking mirror drive signals to the radial tracking mirror 28. As previously discussed, there are two clriving signals applied to the tracking mirror 28. The radial tracking A signal represented by a line 574 and a radial tracking B signal represented by a line 575. Since the information track is normally in the shape of a spiral, there is a continuous track-ing control signal being applied to the radial tracking mirror ~or follo~ing the spiral shaped configuration of the information track. The time frame of the information shown in the waveform shown in line A
represents more than a complete revolution of the disc.
~ typical normal tracking mirror drive signal waveform for a single revolution o~ the disc is represented by the lengt!1 of the line in~icated at 575. The two dis-continuities shown at 578 and 580 on waveforms 574 and 575, respectively~ indicate the portion of the normal tracking period at which a stop motion pulse is given.

-~5-The stop motion pulse ls also rererred to as a ~ump back slgnal and these two terms are used to descrlbe the output from the generator 567. The sto~ motlon pulse is represented by the small vertically dlspose dlscon~inui' ~y present ln the llnes 574 and 575 at polnts 578 and 580, respectlvely. The remaining wa e-forms contained in Flgures 13A, 13B and 13C a~e on an expanded tlme base and represent those electrical signals which occur ~ust before the beginnlng of this ~ump back period, through the ~ump back period and continuing a short duration beyond tne ~ump back period.
The stop motion pulse generated by the stop motion pulse generator 567 and applied to the tracklng servo system 40 over the line 104 ~s represented or llne C of Flgure 13A. The stop motlon pulse is ideally not a squarewave but has areas of pre-emphPsis located generally at 582 and 584. These areas of pre-emphasls lnsure ~timum reliabillty in the stop motion system 44. The stop motlon pulse can be described as rlsing to a first higher voltage level during the initial perlod of the stop motion pulse period. Next, the stop moticn pulse gradually falls off to a second voltage level, as at 583. The level at 583 is ma~n-talned during the duratlon o`f the stop motion pulse period. At the termination of the stop motion pulse, the waveform falls to a neg~tive voltage level at 585 below the zero voltage level at 586 and rises gradually to the zero voltage level at 586.
Line D of Figure 13 represents the differen-3 tlal tracking error signaI recelved from the recoverysystem 30 over the llnes 42 and 46. The waveform shown on line D of Figure 13A is a compensated differ-entlal tracking error achieved through the use of t~.e combinatlon of a stop motion pulse and a stop motlon compensation pulse applied to the radial trac~lng mlrror 28 according to the teaching of the present lnventlcn.
Line G of Flgure 13A represents the loop inte~
rupt pulse generated by the stop motion pulse generator 1150833 ( ,,;
~o7 and applied to the tracl;ill~ servo sub~stem 40 over the llne 108. ~s previously mentioned, lt is best to remove the diffelentlal trackin~ error signal as repre-sented by the l~aveform on line D from application to the radial trackil~ mirror 28 during the stop motion lnterval period. The loop interrupt pulse shown on line G achieves this gating function. However, by inspectionj it can be seen that the differential tracking error signal lasts for a period longer than ttle loop interrupt pulse shown on line G. The waveform shown on line E is the portion of the differential tracking error signal shown on line D which survives the gating by the loop interrupt pulse shown on line G.
The waveform shown on line E is the compensated track-in~ error as interrupted by the loop interrup- pulse which is applied to the tracking mirror 28. Referring to line F, the high frequency signal represented gener-ally under the bracket 590 indicates the output waveform of the zero crossing detector circuit 571 1~ the stop motion system 44. A zero crossing pulse is generated each time the differential error tracking signal shown in line D of Figure 13A crosses t~rough a zero bias level. Ilhile the information shown under the bracket 590 is helpful in maintaining a radial tracklng mirror 28 in tracking a single information track, such in-formation must be gated off at the beginning of the stop motion interval as indicated by the dashed lines 592 connectin~ the start of the stop motion pulse in line C of Figure 13A and the absence of zero crossing 3 detector pulses shown on line F of Figure 13A. ~y referring again to llne D, the differential tracking error signal rises to a first maximum at 594 and falls to a second opposite but e~ual maximum at 596. At point 59~, the tracking mlrror is passing over the zero crossing point 426 between two ad~acent tracks 424 and 4~3 as shown witll relerence f o line .~ of Figure 3.
This means ttlat the mirror has traveled half way from the first track 424 to tlle second track 423. At this point indicated by ~he num~er 598, t~e zerc crossing 1~5~833 detector generates an output pulse indicated at 600.
The output pulse 600 terminates the stop motion pulse shown on line C as represented by the vertical line segment 602. This termination of the stop motion pulse starts the negative pre-emphasis period 584 as pre-viously described. The loop interrupt pulse is not affected by the output 600 of the zero crossing de-tector 571. In the preferred embodiment, improved performance is achieved by presenting the differential tracking error signal from being applied to the radial tracking mirror 28 too early in the jump back sequence before the radial tracking mirror 28 has settled down and acquired firm radial tracking of the desired track.
As shown b reference to the waveform shown in line F, the zero crossing detector again begins to generate zero crossing pulses when the differential tracking error signal reappears as indicated at point 604.
Referring to line H of Figure 13A, thereis shown a waveform representing the stop motion compensation sequence which begins coincidental with the end of the loop interrupt pulse shown on line G.
Referring to Figure 13B, there is shown a plurality of waveforms explaining the relationship between the stop motion pulse as shown on line C of Figure 13A, and the stop motion compensation pulse waveform as shown on the line H of Figure 13A and re-peated for convenience on line E of Figure 13E. The compensation pulse waveform is used for generating a differential compensated tracking error as shown with reference to line D of Figure 13E.
Line A of Figure 13B shows the differential uncompensated tracking error signal as developed in the signal recovery subsystem 30. The waveform shown om Figure A represents the radial tracking error signal as the read beam makes an abrupt departure from an information track on which it was tracking and moves towards one of the adjacent tracks positioned on either side of the track being read. The normal tracking error signal, as the beam oscillates slightly down the liS0833 lnfcrmatioll tracl~, is sho~n at the region ~10 Or Line A
The tracking error represen~s the slight side to side (radial) motion of the read beam 4 to the successively positior.ed reflec~ive and non-reflective regions on the disc 5 as previously described. A point 612 represents t~le start of a stop motion pulse. The uncompensated tracking error is increasing to a first m~ximum indi-cated at 514. The region between 612 and 614 shows an increase in tracking error ind~cating the departure of ~he read beam from the track being read. From point 61~, the differential tracking error signal drops to a pcint indicated at 616 which represents the mid-poir.t of an information track as shown at point 426 in line A
of Figure 8. However, the distance traveled by the read beam between points 512 and 616 on curve A in Figure 13E is a movement of o.8 microns and is equal to length of line 617. The uncompensated radial track-ing error rises to a second ~aximum at point 618 as tne read beam begins to approach th~ neYt ad~acent track 20 423. The tracking error reaches zero at point 622 but is unable to stop and continues to a new maximum at 524. The radial tracking mirror 28 possesses suffi-cient inertia so that it is not able to instantaneously stop in response to the differential tracking error 25 sig!lal detecting a zero error at point 'o22 as the read beam crosses the next adjacent information track.
Accordingly~ the raw tracking error increases to a pOillt indicated at 524 wherein the closed loop servo-ing effect of the tracking servo subsystem slows the 30 mirror down and brings the read beam back towards the information track represented by the zero crossing dif-ferential tracking error as indicated at point 625.
Additional peaks are identified at 626 and 628. These shol~ a gradual damping of the differential tracking error as the radial tracking mirror becomes graduall~T
positiGned iin its proper location to gener~te a zero tracking error, such as at points 612, 622, 625. Addi-tional zero crossing locations are indicated at 630 and 632. The portion of the ~aveform sho~n in line A

~150833 ( .59 e~isting arter point ~32 shows a gradual return of the raw tracking error to its zero position as the read spot gra~uall~ comes to rest o~l the ne~t adjacent track 423.
Point 616 represents a ralse indication of ~ero traekin~ error as the read beam passes over the cen~er 425 of tlle region between adJacent tracks 42' and 423.
For optimum operation in a stop motion situa-tior. wnerein the read beam ~umps to the next adjacent track, the time allowed for the radial tracking mirror 28 to reacquire proper radial tracking is 300 micro-seccnds. This is indicated by the length o~ the line 634 sho~ln on line ~. ~y observation, it can be seen that the radial tracking mirror 28 has not yet reac-quired zero radial error position at the expiration of the 300 microsecond time period. Obviously, if more time l~ere available to achieve this result, the wave-~orm shown ~with reference to Figure A would be suitable for those syster.1s having more time for the radial tracking mirror to reacquire zero differential trackin~
error on the center of the next adjacent track.
Referring briefly to line D of Figure 13, line 63l~ is redrawn to indicate that the compensated radial tracking error signal shown in line D does not include those large peaks shown with re~erence to line A. The compensated difrerential tracking error shown in line D is capable Or achieving proper radial traclcing by the tracking servo subsystem within the 3 time frame allowed for proper operation of the video disc player 1. Referring briefly to line E of Figure 13A, the remaining trac~ing error signal available after interruption b~y the loop interrupt p~lse is of the proper direction to cooperzte ~Jith the stop motion compensation pulses descri~ed ~lereinafter to bring the radial 'rac'-~ ng mirror ~o ~ts Op~i.mllm radial 'racking position as soon as possible.
The stop motion compensation generator 573 shown witll re~erence to Figure 12, applies the waveform ~150833 ~
-~lo -shown in line E of Figure 13~ to the radial trackinG
~irror 2S b~J way of the li~e loS a~d the a~plifier 500 shown in Figure 9. The stop motion pulse directs the radial tracl;ing mirror 28 to leave the tracking of one informatioll track and begin to seek the tracking of the next ad~acent track. In response to the pulse from the zero crossing detector 571 shown in Figure 12, the stop motion pulse generator 557 is caused to generate the stop motion compensation pulse shown in line E.
Referring to line E of Figure 13~, the stop motion co~.pensation pulse waveform comprises a plural-ity of individual and separate re~ions indicated at 540, 542 and 544, respectively. The fir~t region 540 of the stop motion compensation pulse begins as the differential uncompensated radial tracking error at point 515 cross the zero reference level indicating that the mirror is in a mid-track crossing situation.
At this time, the stop motior. pulse generator 557 generates the first portion 540 of the co~pensation pulse which is applied directlJ- to the tracking mirror 2~. The generation of the first portion 640 of the stop motion compensation pulse has the effect of re-ducing the peak 624 to a lower radial tracking displace-ment as represented by the new pealc 524' as shown in line ~. It should be kept in mind that the waveforms shown in Figure 13~ are schematic only to show the overall interrelationship of the various pulses used in the tracking servo subsystem and the stop motion subsystem to cause a raad beam to jump from one track to the next adjacent track. Since the peak error 624' is not as high as tlle error at peak 624, this has the effect of reducii~ the error at peak error point 526' and generally shifting the remaining portion of the waveform to the left such that the ~ero crossings at 35 525', 630' and 632' all occur sooner than they would have occurred WitllOUt the presence of the stop motion compensation pulse.
Referring back to llne E of Figure 13~, the second ~ortion 542 of the stop motion compensation , , i-pulse is of a second polarity when compared to the first region 540. The second portion 642 of ~he stop motion compensation pulse occurs at a point in time to compensate for the tracking error shown at 626' of line ~. This results in ar. even smaller radial track-ing error beinO generated at that time and this smaller radial tracking error is represented as point 526" on line C, Since the degree of the radial tracking error represented by the point 626" of line ~ is significantly smaller than that shown with reference to point 526' of iine ~, the maximum error in the opposite direction sho~,~n at poir.t 525' is again significantly smaller than that represented at point ~26 of line A. This counteracting of the natural tendency of the radial trackinO mirror 23 to oscillate back and forth over the information track is further dampened as indicated by the further movement to the left of points 628" and ~25 with reference to their relative locations shown in lines ~ and A.
Referring again to line E of Figu.re 13~ and the t'nird region o44 of the stop motion compensation pulse, tllis region 544 occurs at the time calculated to dampen the remaining long term tracking error as represented that portion of the error signal to the ri~ht of the zero crossing point 532" shown ln line C.
Region 644 is shown to be approximately equal and opposite to this error signal which would exist if the portion 644 of compensation pulse did not exist. Re-ferring to line D of Figure 13~, there is shown the differential and compensated radial tracking error representative of t'ne motion Or the light beam as it is caused to depart ~rom one information 'rack being read to the ne~t adjacent track under the control of a stop motion pulse and a stop motion compensation pulse. It should ~e noted that the waveform shown in line-D of ~igure 13~ can represent the movement in either direction althouh the polarity of various signals would be changed to represent t~.e different direction of movement.

11501~33 Thc cooperatior. ~etweeil the stop -otion sub-system 44 and t`ne tracking servo s~lbsystem 4n during a stop motion period will now be described ~:ith reference to Flgures 9 and 12 and tileir related wave:-orms. Re-ferring to Fi~ure 9A, the tracking ser~o su~s~Jstem 40is in operation just prior to the initiation of a stop motion mode to maintain the radial tracking mirror 28 in its position centered directly atop o~ information track. In order to maintain this position, the differ-ential tracl~ing error is detected in the s~gnal recove~subsystem 30 and applied to the trackir~ servo subsystem 40 by the line 42. In this present operating mode, the differential tracking error passes di-ectly thro~gh the trac~ing servo loop switch 480, the a.plifier 510 15 and the pus~l/pull amplifiers 500. That pc~tion of the wa~eform shown at 591 on line D of Figure 13A as being traversed.
The function generator 47 generates a stop motion mode signal for applica~ior. to the stop motion mode gate 559 over a line 132. The funct'~n of the stop motioll mode gate 569 is to generate ~ pulse in response to t`ne proper location in a tele.~ision frame for the stop motion mode to occur. This pcint is de-tected b~J the combined operation of the total video signal from the FM processing board 32 bein.g applied to the white flag detector 55~ over a line 134 in com-bination ~ith the vertical sync pulse developed in the tangential servo system 80 and applied ~er a llne ~
The wlndo~ generator 562 prov,ides an enabling signal which corresponds with a predetermined pcrtion of the video signal containing the white flag indicator. The white flag pulse applied to the stop motion mode gate 569 is gated to the stop motion pulse generator 557 in response to the enabling signal received 'rom the function ~eneratcr 47 over the line 132. The enablin~
signal from the stop motion mode gate 569 inltiates the stop motion pulse as shown with reference to line C
of F~gure 13A. The output from the zero crossing de-tector 571 indicates the end of the stop ~otion pulse , ..
-l3-period ~y application of a signal to the stop mot'on pulse gererator ~57 over the line 572. The stop ~otion pulse from the ~enerator 567 is applied to the tracl{ing servo loop interrupt SWitCil 4~0 b~- way of the gate 48~ and the line 10~. The function of the track-in~ servo loop interrupt s~itch 480 is to remo-~e tne di.ferential trackin~ error currently being generated in the signal recovery subsystem 30 frcm the pusy/pull am~lifiers 500 driving the radial trackin~ mirror 28.
10 Accordingly, the switch 480 opens and the differential tracking error is no longer applied to the amplifiers 500 for driving the radial tracking mirror 28. Simul-taneously, the stop motion pulse from the generator 56( is applied to the amplifiers 500 over tlle line 104.
The stop motion pulse~ in essence, is substituted for the differenti21 traclcing error and provides a driving signal to tl-le push/pull ampliflers ~00 for starting the read spot to move to the next ad~acent information track to be read.
The stop moiion pulse from the 3enera~or 567 is also applied to the stop motion compensation sequence generator 573 s1herein the waveform shown with reference to line H of Figure 13A and line E of Figure ~ is generated. ~y inspection of line H, it is to be noted that the ccmpensation pulse shown on line H occurs at the termination of the loop interrupt pulse on line G, which loop interrupt pulse is triggered by the start of the stop motion pulse shown on line C. The compensa-tion pulse is applied to the push/pull amplifiers 500, 3 over the line 10~ shown in Figures 9 and 12~ for damp-ing out any oscillation in the operation of radial tracking mirror 28 caused by the applicat-lon of the stop motion pulse.
As previously mentioned, the co~pensation pulse is initiated at the termination of the loop interrupt signal. Occurring slmultaneously Wit'fl the generation of ~he compensation pulse, the tracking servo loop interrupt switch 480 closes and allows the differential tracking error to be reapplied to the .. .

~ 3 ~

push~ull amplifiers ~00. The typical wa~erorm avail-able at tllis pOiil~ iS shown in line E Or ~igure 13A
~hich cooperates with the stop motion com~ensation pulse to ~uickly bring the radial tracking mirror 28 into suitable radial tracking aligllment.
Referring briefly to line A Or Figure 13C, two rrames of television video information ~eing read from the video disc 5 are sho~n. Line A represents the differential tracking errcr signal havin~ aDrupt dis-continuities located at 550 and 652 representing thestop motion mode of operation. Discontinuities of smaller amplitude are shown at 554 and 556 to show the effect of errors on the surface of tile video disc surface in the dilferential tracking error signal.
Line ~ of ~igure 13C shows the FM envelope as it is read frcm the video disc surface. The stop motion periods at 658 and 660 show that the FM envelope is temporarily interrupted as the readin~ spot jumps tracks. Changes in the FM envelope at 662 and 664 sho~ the tempcrary loss of Fil as tracking errors cause the tracking '~eam to temporarily leave t~.e informatlon track.
In review of the stop motion mode of opera-tion, the following combinations occur in the preferred embodiment. In a first embodiment, the differential tracking error signal is removed from the trac~ing mirror 28 and a stop motion pulse is substituted therefor to cause the radial trackit~ mirror to ~ump one track fromthat track being tracked. In this 3 embodiment, the stop motion pulse has areas of pre-emphasis such as to help the radial tracking mirror to regain tracking of the new track to which it has been positioned The differential tracking error is re-applied into the track~ng servo subsystem and cooperate with the stop motion pulst? applied to the radial track-ir.g mirror to reacquir2 radial tracl{ing. T'.e differ?n-tial tracking error can be re-entered into the tracking servo system for optimum results. In this embodiment, the duration of the loop interrupt pulse is varied for gati:lg ofl` tlle applica'vion of the differential track-ing error into the push/pull amplifiers 500. The stop motion pulse is of fixed length in this embodiment.
Al alternative to this fixed length of the stop motion pulse is to initiate the end of the stop motion pulse at the first zero crossin~ detected after the ~eginning of the stop motion pulse was initiated. Suitable delays can be entered into this loop to rem~ve any extraneous si~nals that may slip throu~h due to mis-alignment of the beginning of the stop motion pulseand the detection of zero crossings in the detector A further embodiment includes any ~ne of theabove combinations and further includes the generation of a stop motion ~ompensation sequence. In the pre-ferred embodiment, the stop motion compensation se-quence is initiated with the termination of the loop interrupt period. Coincidental with the termination of the loop interr~pt period, the differential track-20~ ing error is reapplied into the tracking servo sub-- sJstem 40. In a further embodiment, the stop motion compensation pulse can be entered into the trac~ing ser~o subsystem over the line 106 at a ~eriod fixed in time from the beginnin~ of the stop motion pulse as opposed to the ending of the loop interrupt pulse. The stop motion compensation sequence comprises a plurallty of separate and distinct regions. In the preferred embodiment, the first region opposes the tendency of the tracking mirror to overshoot the ne~t adJacent track and directs the mirror bacl; into radial tracking of that next adjacent particular track. A second region is Or lower amplitude than the first region and of opposite polarity to further compensate the motion of the radial tracking mirror as the spct again over-shoots the center portion of the next adjacent trackbut in the opposite direc'ion. ~he third region of the stop mo~v~on compensa~ion sequence is of the same polarit~J as the rirst region~ bu~v of sisniricantly lo~er amDlitude to further compensate any tendency of -75- llS0833 tl~e radial trackillg mlrror having the focus spot again leave the in~orm~tion track.
lhile in the preferred embodiment, the various resions of the stop motion sequence are sho-~n to consist o~ separate individual regions. It is possible for these re~ions to be themselves broke1l down into in-dividual pulses. It has been found by experiment that the various regions can provide enhanced operation when separated by ~ero level signals. More specific-ally, a zero level condition exists between reOionone and region two allowing the radial tracking mirror to move under its own inertia without the constant application of a portlon of the compensation pulse.
It has also been found by experiMent thac this quiescent period of the compensation sequence can coincide with the rcapplica~ion of the differential trackin~ error to the radial tracking mirrors. In this sense, region one, shown at ~40, of the compensation sequence cooper-ates with the porti~n S04 sho~Jn in line E of Figure 13A
from the di ferential tracklng error input into the tracking loop.
~ y observation of the compensation waveform shcl~n in line E of Figure 13~, lt can be observed that the various regions tend to begin at a high amplitude and fall off to very low compensation signals. It can also be observed that the period of the various regions begin at a first relatively short time period and gradually become longer in duration. This coin-cides with the energy contained in the ~rackin~ mirror as it seeks to regain radial tracking. Initially ln the track ~umping sequence, the energy is hi~h and the early portions of the compensation pulse are appro-priately high to counterac'c this energy. Thereafter, as energy is removed from the tracking mirror, the ~5 corrections become less so as to bring the radia' tracking mirror back into radial alignment as soon as possible.
P.eferring to Figure 1~, there is shown a block diagram of the F?~ processing system 32 employed ..

11~0833 in the video disc pla~er 1. The frequency modulatedvideo signal recovered from the disc 5 forms the input to the F~l processing unit 32 over the line 34. The frequency modulated video signal is applied to a dis-tribution amplifier 670. The distributicn amplifierprovides three equal unloaded representations ~ the received signal. The first output signal from the distribution amplifier is applied to a FM corrector circuit 572 over a line 673. The FM corrector circuit 572 oper~tes to provide variable gain amplification to the received freauency mcdulated video signal to compensate for the mean trans'er function of the lens 17 as it reads the frequency modulated video signal from the disc. The lens 17 is operating close to its absolute resolving po~èr and as a result, recovers the frequency modulated video signal with different ampli-tudes corresponding to different frequencies.
Tl,e output from the FM corrector 672 is applied to an Fll detector 574 over a line 675. The FM detecfor Generates discrimi:lated video for applica-tion to the remailllng circuits requirin~ such dis-crimirated video in the video disc player. A second output signal from the distribution amplifier o70 is applied to the tangential servo subs~Jstem 80 over a line 82. A further output signal from the distribu-tion amplifier 670 is applied to the stop motion sub-system 44 over the line 134.
Rcferring to Figure 15, there is shown a more detalled block dlagram of the FM corrector 672 sho~Jn ln 3 Figure 14. The FM video slgnal from the amplifier 570 is applied to an audio subcarrier trap circult 576 over the line 673. The ~unction of the su~carrier trap circuit 675 is to remove all a~ldio components from the frequency modulated video signal prior to application to a rrequencvr selectlve variable gaiil amplirier 678 over a line 53~.
The control signals for operating the amplifier 678 include a first burst gate detector 582 havlng a plurality of input sl~nals. A first input signal is the _ ~ 5~V~3 3 chroma portion of the F~ video si~nal as applied ove~ a line 1~ The second inpul signal to the burst gate 68~ is tlle burst gate enable signal from the tanger.~ial servo system 80 over the line 144. The function of the burst gate 582 is to gate into an amplitud_ detector 684 over a line 685 that portion of the chroma signal corresponding to the color burst signal. The output from the amplitude detector 684 i s applied to a summa-tion circuit 588 over a line 690. A second input to 10 the summation circuit 588 is from a variable burst level adjust potentiometer 692 over a line 594. The function of the amplitude detector 584 is to deter~ine the first order lo~er chroma side band vector and apply it as a current representation to the summation circuit 688. The burst level adjust si~nal on the line 694 from the potentiometer 692 operates in con~unction l~ith this vector to develop a control signal to an ampli~ier 696. The output from the summation circuit is applied to the amplifier 595 over the line 698. The output from the amplifier 695 is a control voltage for applica-tior. to the amplifier 678 over a line 700.
Referrinx to Figu~e 153 there is sho~n a nu~ber of wave~orms l~elpful in understanding the operation of the FM corrector sho~n ir Figure 15. The ~laveform repre-sented by the line 701 represents the FM correctortransfer function in generating control voltages ~or application to the amplifier 678 over the line 700.
- The line 702 includes four sections of the curve indi-cated generally at 70~, 704, 706 and 708. These 3 segments 702, 704~ 70~ and 708 represent the various control voltages generated in response to the com-parison with the instantaneous color burst signal amplitude and the pre-set level.
Line 710 represents the mean transfer function Or the objective lens 17 emplo~ed for reading the successive li~ht reflective re~ions ~ ar.d li~ nor-reflective re~ions 11. It c~n be seen upon inspection that the gaill versus frequencJ response of the lens falls off as the lens reads the frequency ~odulated representatlo~?s o~ the video signal. ~eferrin~ to the remair.ing portion of Flgure 16, there ls sho~ln the frequenc~,- spectrum of the fre~uency modul~ted signals as read from the video disc. This indicates that the ~ideo si~nals are located principally between the 7.5 and 9.2 megahertz region at which the frequenc~J re-sponse of the lens shown on line 710 is showing a sig-nificant decrease. Accordingly, the con~rol voltage frcm the amplifier 696 is variable in nature to com-pensate for the frequency response of the lens. Inthis m~nner the effective frequency response of the lens is brought into a normalized or uniform region.
FM 5QRRECTOR SU~SYSTEM - NORr~L MODE OF OPERATIOM
The FM corrector subsystem functions to adjust the FM video signal received from the disc such that all recovered Frl signals over the entire frequency spectra of the recovered FM signals are all amplified to a level~ relative one to the other to reacquire their substantially identical relationships one to the other as they existed during the recording process.
The microscopic lens 17 employed in the video disc player 1 has a mean transfer cllaracteristic such that it attenuates the higher frequencies more than it attenuates tlle lo~Jer frequencies. In this sense, the lens 17 acts similar to a low pass filter. The function of the FM corrector is to process the received FM
video si~nal such that the ratlo of the luminance sig-nal to the chrominance signal is maintained regardless of the position on the disc from which the FM video signal is recovered. This is achieved by measuring the color burst signal in the lo~Yer chroma side band and storing a representation of its amplitude. This lo~qer chroma side band signal functions as a re~erence ampli-tude.
The FM video signal is recovered from the video disc as previously described. The chrominance signal is removed from the FM video signal and the burst gate enable signal gates the color burs~ signal present on each line of FM video information into a li~833 comparison op2ration. The comparison operatlon effec-tively operates for senslng tlle difference between tlle actu~l amplitude of the color burst signal re-covered rrom the video disc surlace with a reference amplitude~ The reference amplitude has been ad~usted to the correct level and the comparison process indi-cates an error signal between the recovered amplitude of the color burst signal and the reference color burst signal indicating the difference in amplitude between the two signals. The error signal generated in this comparison operation can be identified as the color burst error amplitude signal. This color burst error amplitude signal is employed for adjusting the gain of a variable gain amplifier to amplify the signal presently being recovered from the video disc 5 to amplify the chrominance sisnal more than the luminance signal. This variable amplification provides a var-iable gain over the frequency spectrum. The higher frequencies are amplified more than the lo~er fre-quencies. Since the chrominance signals are at thehigher frequencies, they are amplified more than the luminance signals. This variable amplification of signals results in effectively maintaining the correct ratio Or the luminance signal to the chrominance signal as the reading process radially moves from the outer peripher~ to the inner periphery. As previously men-! tioned, the lndicia representing tlle FM video signal onthe video disc 5 change in size from the outer periphery to the inner periphery. At the inner periphery they 3 are smaller than at the outer periphery. The smallestsize indicia are at the absolute resolution power of the lens and the lens recovers the FM signal represented by this smallest size indicia at a lower amplitude value than the lower frequency mem~ers which are larger in size and spaced farther apart.
In a preferred mode of operation, the audio signals contained in the F~ video signal are removed from the FM video signal before application to the variable gain amplifier. The aud~o information ls ~i~0833 ( ccntained around a number of FM subcarrier signals and it has been found by experience that the removal of these Fibl subcarrier audio signals provides enhanced correction of ~he remaining video FM signal in the var-iable gain amplifier.
In an alternati~e mode of operation thefrequency band width applied to the variable gain amplifier is that band width which is affected by the mean transfer function of the ob~ective lens 17. More specifically, when a portion of the total FM recovered from the video disc lles in a range not affected by the mean transfer function, then this portion of the total waveform can be removed from that portion of the FM signal applied to the variable gain amplifier. In this manner, the operation of the variable gain ampli-fier is not complicated by signals having a frequency which need ~ot be corrected because of the resolution characteristics of the objective lens 17.
The FM corrector functions to sense the ab-solute value of a signal recovered from the vldeo disc, ~ ~1hich signal is kno~,m to suffer an amplitude change due to the resolution power of the objective lens 17 used in the video disc signal. This known signal is then compared against a reference signal indicating the amplitude that the known signal should have. The out-put from the comparison is an indication of the addi-tional amplification required for all of the signals lying in the frequency spectra affected by the resolv-ing power of the lens. The amplifier is designed to provide a variable gain over the frequency spectra.
Furthermore, the variable gain is further selective based on the amplitude of the error signal. Stated another way for a first error signal detected between the signal recovered from the disc and the reference frequency, the variable gain amplifier is operated at a first level of variable amplification over the entire frequency range of the affected signal. For a second level of error signal, the gain across the frequency spectra is ad~usted a different amount when compared _, . . . ,,.. , _ .

115~33 ~or the first color burst error amplitude signal.
~ eferrin~ to Figure 17, there is shown a block diagram Or the FM detector circuit 674 shown with refer-ence to Fi~ure 14. The corrected frequenc~y modulated slgnal fro~ the F~ corrector 672 is applied to a li~iter 720 over the line 67~. The output from the limiter is applied to a drop-out detector and compen-sation circuit 722 over a line 724. It is the function of the limiter to change the corrected FM video signal into a dlscriminated video signal. The output from the drop-out detector 722 is applied to a low pass filter 725 over a line 728. The output from the low pass filter 726 is applied to a wide band vldeo dis-tribution amplifier 730 whose function ls to provide a plurality of output signals on the line 66, 82, 134, 154, 156, 164 and 16~, as previously described. The function of the FM detector is to change the frequency modulated video signal into a discriminated video signal as shown with reference to lines A and ~ of Figure 18. The frequency modulated vi~eo signal is ~ represented by a carrier frequency having carrier variations in time changing about the carrier fre-quency. The discriminated video signal is a voltage varying in time signal generally lying within the zero to one volt range suitable for display on the television monltor 98 over the line 166.
Referring to Figure 19, there is shown a block diagram of the audio processing circuit 114. The frequency ~odulated video signal from the distribution 3 amplifier 670 of the FM processing unit 32, as shown with reference to Figure 14, applies one of its lnputs to an audio demodulator circuit 740. The audio demodu-lator circuit provides a plurality of output signals, one of which is applied to an audio variable controlled oscillator circuit 742 over a line 744. A first audio output is available on a line 74', ~or application to the audio accessory unit 120 an~ a second audio output signal is available on a line 747 for application to the audio accessory unit 120 and/or the audio ~acks _ . . .

~, 117 alld 11~. The output from the audio volta~e con-trolled oscillat:or is a 4.5 megahert~ signal for appli-cation to the RF modulator 162 over the line 172.
Referrin~ to Figure 20, there is shosln a block diagram of the audio demodulator circuit 740 shown with re~erence to Figure 19. The frequency modulated video signal is applied to a first band pass filter 750 having a central band pass frequency of 2.3 mega-hert , over the line 160 and a second line 751. The 10 frequenc~ modulated video signal is applied to a second band pass filter 752 over the line 160 and a second line 754. The first band pass filter 750 strips the first audio channel from the FM video signal, applies it to an audio FM discriminator 755 over a line 758. The 15 audio FM discriminator 756 provides an audio signal in the audio range to a switc`ning circuit 760 over a line 752.
The second band pass filter 752 having a central frequenc~r of 2.8 meGahert~ operates to strip 20 the second audio channel from the FM video input signal - and applies t'l~is frequenc~J spectra of the total FM
signal to a second video FM discriminator 764 over a line 765. The second audio channel in the audio fre-quency range applied to the switching circuit 750 over 25 a line 768.
The switching circuit 760 is provided with a plurality of additional input signals. A first of which is the audio squelch signal from the tracking servo subsystem as applied thereto over the line 116.
3 The second input signal is a selection command signal from the function generator 47 as applied thereto over the line 170. The output from the switclling circuit is applied to a first arnplifier circuit 770 over a line 771 and to a second amplifier circuit 772 over a line 773. The lines 771 and 773 are also connected to a surr.mation circuit indicated at 774. The output from the summation circuit 774 is applied to a third ampli-fier circuit 7'(5. The output from the first amplifier 770 is the cilannel one audio signal for application to ,.~

.---~4 -the audio j~ck 117. The output from the second ampli-fier 772 is the second channel audio signal ~or application tothe audio jack 118. The output from the third amplifier 776 ls the audio signal to the audio VC0 742 over the line 744. Referring briefly to Figure 21, there is shown on line A the frequenc~J
modulated envelope as received from the distribution amplifier in the FM processin~ unit 32. The output of the audio FM discriminator for one channel is shown on line ~. In this manner, the FM signal is c~anged an audio frequency signal for application to the switch-lng circuits 760, as previously described.
Xeferring to Figure 22, there is shown a bloc~ diagram of the audio voltage controlled oscilla-tor 742 as shown with reference to Figure 19. Theaudio signal from the audio demodulator is applied to a band pass filter 780 over the line 744. The band pass filter passes the audio frequency signals to a summation circuit 782 by way of a pre-emphasis circuit 20 784 and a first line 786 and a second line 788.
The 3.58 me~ahertz color subcarrier frequency from the tangent-lal servo system 80 is applled to a divide circuit 790 over the line 140. The divide circuit 790 divides the color subcarrier frequency by 25 2048 and applies the output signal to a phase detector 792 over a line 794. The phase detector has a second input signal from the 4.5 megahertz voltage controlled oscillator circuit as applied to a second divide cir-cuit 798 and a first line 800 and 802. The divide 3 circuit 798 divides the output of the VC0 796 by 1144.
The output from the phase detector is applied to an amplitude and phase compensation circuit 804. The output ~rom the circuit 804 is applied as a third input to the summation circuit 782. The output from the voltage controlled oscillator 796 is also applied to a low pass filter 806 by the line 800 and a æcond line 808. The output from the filter 806 ls the 4.5 megahertz frequency modulated signal for application to the RF modulator 182 by the line 172. The function s 1~5S~833 ~

of the audio voltage controlled oscillator circuit is to prepare tlle audio signal received from the audio demod-ulator 740 to a frequency which can be applied to the fiF modulator 162 so as to be processed by a standard 5 television receiver 95.
Referriilg briefl~; to Figure 23, there can be seen on line A a waveform representing the audio signal received from the audio demodulators and available on the line 744. Line ~ of Figure 23 represents the 4.5 megahertz carrier frequency. Line C of Figure 23 represents the 4.5 megahertz modulated audio carrier ~hich is generated in the VC0 circult 796 for applica-tion to the RF modulator 152.
Referring to Figure 243 there is shown a 15 block diagram of the RF modulator 162 employed in the video disc player. The video information signal from the FM processing circuit 32 is applied to a DC re-storer 81~ over the line 154. The DC restorer 810 read~usts the blanking level of the received video 20 Signal. The output from the restorer 810 is applied to a first balallced modulator 812 over a line 814.
The 4.5 megahertz modulated signal from the audio VC0 is applied to a second balanced modulator 810 over the~line 172. An oscillator circuit 818 functions 25 to generate a suitable carrier frequency corresponding to one of the channels of a standard television re-ceiver 96. In the preferred embodiment, the Channel 3 frequency is selected. The output from the oscillator 818 is applied to the first balanced modulator 812 over a line 820. The output from the oscillator 818 is applied to the second balanced modulator 816 over the line 822. The output from the modulator 812 is ap-plied to a summation circuit 824 over a line 826. The output from the second balanced modulator 816 is 35 applied to the summation circuit 824 over the line 828. Referring briefly to the waveform s~own in Figure 25, line A shows the 4.5 megahertz frequency modulated signal received from the audio VC0 over the line 172. Line ~ of Figure 25 silows the video signal llSV~
-8~-received from the FM processing circuit 32 over the line 154. The output from the summation circuit 824 is shcwn on line C~ The signal shown on line C is suitable for processing by a standard television re-ceiver. The signal shown on line C is such as to causethe standard television receiver 96 to display the sequential frame information as applied thereto.
Referring briefly to Figure 26, there is shown a video disc 5 having contained thereon a schematic 10 representation of an information track at an outside radius as represented by the numeral 830. An informa-tion track schematically shown at the inside radius is shown by the numeral 832. The uneven form of the information track at the outside radius demonstrates 15 an extreme degree of eccentricity arising from the effect of uneven cooling of the video disc 5.
Referring briefly to Figure 27, there is shown a schematic view of a video disc 5 having contained ~thereon an information track at an outside radius - 20 represented by the numeral 834 . An information track at an inside radius is represented by the numeral 836.
This Figure 27 shows the eccentricity effect of an off-center relationship of the tracks to a central aperture indlcated generally at 838. More specifically, the off-center aperture effectively causes the distance represented by a line 840 to be effectively different from the length of the line 842. Obviously, one can be larger than the ot~er. This represents the off-centered position of the center aperture hole 838.
Referring to Figure 28, there is shown a logic diagram representing the first mode of operation of the focus servo 36.
The logic diagram shown wittl reference to Figure 28 comprises a plurality of AND function gates 35 shown at 850, 852, 854 and 856. The AND function gate 850 has a plurality of input signalsj t!le first of which is the r~N~ ~NA~L~ applied over a line 858. The second input slgnal to the AND gate 850 is the FOCUS
SIGNAL applied over a line 860. The AND gate 852 has &

- a pluralit-~ of input signals, the first of which is the FOCUS SIGl~hL applied thereto for the line 860 and a second liile 862. The second input signal to the AND
function gate 852 ~s the lens enable sigllal on a line 5 864. The output ~rom the AND function gate 852 is the ramp enable signal which i~s available for the entire period the ramp signal is being generated. The output from the AND function gate 852 is also applled as an input signal to the AMD function gate 854 over a line 10 866. The AND function gate 854 has a second input signal applied over the line 868. The slgnal on the line 868 is the FM detected signal. The output from the AND function gate 854 ~s the focus acquire signal.
This focus acquire signal is also applied to the ramp 15 generator 278 for disalblng the ramping waveform at that ~int. The AND function gate 856 is equipped with a plurality of input signals, tlle first of which is the FOCUS SIGNAL applied thereto over the line 860 ~nd an additional lir,e 870. The second input signal to the AND func~ion ~ate 856 is a ramp and signal applied over a line 872. The output signal from the AND function gate 856 is the withdraw lens enabling signal. Briefly, the logic circuitry shown with refer-ence to Figure 2~ generates the basic mode of operation 25 of the lens servo. Prior to the function generator 47 generating a lens enable signal, the LENS ENA~LE signal is applied to the AND function gate 850 along with the FOCUS--SIGNAL. This indicates that the player is in an inactivated condition and the output signal from the 3 AND function gate indicates that the lens ls in the fully withdrawn position.
~ en the function generator generates a lens enable signal ~or application to the AND gate 852, the second input signal to the AND gate 852 indicates 35 that the video disc player 1 is not in the focus mode.
Accordingly, the output signal from tile AND gate 8~2 ls the ramp enable signal which initiates the ramping waveform shown with reference to line B of Figure 6A.
The ramp enable signal also indicates that the focus ~i51~333 -8~-servo is in the acquire focus mode ~ operation and this enablil~ signal ~orms a first lnput to the AND
~unction gate 85~. The second input slgnal to the AND
function gate 854 indicates that FM has been success-fully detected and the output from the AND functiongate 854 is the focused acquire signal indicati~ that the normal play mode has been successfully entered and frequency modulated video signals are being recovered from the surface of t'ne video disc. The output from 10 the AND function gate 856 indicates that a successlul acquisition of focus was not achieved in the first focus attempt. The ramp end signal on the lir.e 872 indicates that the lens has been fully extended towards the video disc surface. The FOCUS SIGN.~L on the line 15 870 indicates tilat focus was not successfully acquired.
Accordingly, the output from the AND ~unction gate 856 withdraws the lens to its upper position at which ti~e a focus acquire operation can be reattempted.
~ Referring to Figure 29, there is sho~1n a logic 20 diagram illustrating the additional mcdes of operation of the lens servo. A first AND gate 880 is equipped with a plural-Lty of input signals, the first of which is the focus signal generated by the A~ gate 854 and applied to the AND gate 880 over a line 859. The 25 Fi~ DETECT SIG~lAL is applied to the AND gate 880 over a line 882. The output from the AND gate 880 is applied to an OR gate 84 over a line 886. A second input signal is applied to th4 OR gate ~84 over a line 888.
The output from the OR function gate 884 is applied to 30 a first one-shot circuit shown at o90 over a line 892 to drive the one-shot into its state for generating an output signal 011 the line 894. T~le ~utput signal on the line 894 is applied to a delay circuit 396 over a second line ~98 and to a second AND function gate 900 35 over a line 902. The AND function gate 9CO is e~uipped with a second input signal on whic~ the FM detect signal is applied over a line gol~. The output from the AND function gate 900 is applied to reset the first one-shot o90 over a line 90~.
i,.

. .

11~0833 ~
-ss -Tlle output from the delay circuit 896 is ap-plled as a first input signal to a third AND runction g.~te 908 over a line 910. m e AND function gate 908 is equipped l~itl^~ a second input signal which is the RAMP RE~ Gi~AL applie~ to the AND function gate 908 over a line 912. The output from the AND function gate 908 is applied as a first input signal to an OR circuit 914 over a line 916.
The output from the OR function gate 914 is the ramp reset enabling signal which is applled at least a fourth AND functlon gate 918 over a line 920. The second input sigilal to the ~ND function gate 918 is the output signal from the first one-shot 890 over the line 894 and a second line 922. The output f,om the AND
function gate 918 is applied to a second one-shot cir-cuit 924 over a line 926. The output from the second one-shot indicates tl1e timing period of the focus ramp voltage shown on line ~ of Figure 6A. The input signal on llne 925 activates the one-shot 924 to generate its output signal on a line 928 for application to a delay circuit 930. The output from the delay circuit 930 forms one input to a sixth A~ function gate 932 over a line 934. The AND function gate 932 has as its second ir.put signal the FOCUS -SIGi~AL available on a line 936.
The output from the AND function gate 932 is applied as the second input signal to the OR function gate 914 over a line 938. The output from the AND function gate 932 ls also applied to a third ~e-shot circuit 940 over a line 942. The output from the third one-shot 3 is applied to a delay circuit 942 over a line 944. As previously rnentioned, the output from the delay clrcuit 942 is applied to the OR function gate 884 over the line 888.
The one-shot 890 is the circuit employed for 3~ generating the timing waveform shown on lir.e D of ~ig~lre ~1~. The second one-shG~ 924 is emplo~Jed ~or generating a waveform shown on line E of Figure 6A.
The third one-shot 940 is employed for generating the waveform shown on line F of Figure 6A.

~50833 -,qo _ In one form of operation, the logic circuitry shown in Fi~ure 29 operates to dela~ the attempt to reacquire rOcus due to momentary losses cf FM caused by imperfections on the video disc. This is achieved in tlle followin~ manner. The AI~D function gate 880 gener-ates an output slgnal on the line 885 only when the video disc player is in the focus mode and there is a temporar~J loss of FM as indicated by the ~M DE'l~CT SIGNAL
on line 882. The output signal on the line 88~ triggers the first one-shot to generate a timin~ period of pre-determined short length during which the video disc -player will be momentarily stopped from reattempting to acquire lost focus superficially indicated by the availability of the FM DE~CT SIG~AL on the line 8&2.
1~ The output from the first one-shot forms one input to the AND functioll gate 900. If the FM detect signal available on 9~4 reappears prior to the timing oùt of the time period of the first one-shot, the output from the AND circuit 900 resets the first one-shot 890 and the video disc player cont~nues reading the reacquired Fr~ signal. Assuming that the first one-shot is not reset, then the following sequence Or operation occurs.
The output from the delay circuit 895 is gated through the AND function gate 908 by the ~AMP P~SET SIGNAL
available on line 912. The RAMP ~ESET-SIG-NAL is avail-able in the normal focus play mode. The outp~t from the AND gate 908 is applied to the OR gate 914 for gen-erating the reset signal causing the lens to retrack and begin its focus operation. The output from the OR
gate 914 is also applied to a turn on the second one-shot which establishes the shape of the ramplng wavefo~
shown in Figure B. The output from the second one-shot 924 is essential coextensive in time ~ith the ramping period. Accordingly, when the output from the second one-shot is generated, the ~achine is caused to return to the attempt to acquire fvcus. I~en focus is success-fully acquired, the ~IOCU~ ~LGNAL on lir.e 936 does not gate the output from the delay circuit 930 through to the OR function gate 914 to restart the automatic rOcus (` li508;~3 ( procedure. HoweYer, when the video disc player does not acquire focus the FOCUS SIGNAL on line 935 gates the output from the delay circuit 930 to restart auto-matically the focus acquire mode. When focus is success-fully acquired, the output from the delay llne is notgated through and the pla~er continues in its focus mode.
While the invention has been particularly shown and described with reference to a preferred embod-iment and alterations thereto, it would be understood bythose skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention.

Claims (7)

92

1. A spindle servo system for use in an appara-tus for recovering an information signal from an information track arranged on an information bearing surface of a disc, wherein the information signal includes a signal defining a time base, and the apparatus includes optical system means for directing a source beam of radiation to the information track and for directing a modulated beam of radiation con-taining the information signal to signal recovery means for recovering the information signal from the modulated beam, the spindle servo system comprising:
spindle motor means for rotating the disc to impart relative motion between the disc and the source beam and thereby produce the modulated beam;
spindle tachometer means including first and second tachometer elements coupled to the spindle motor means, for producing first and second spindle tachometer signal indicative of the actual angular rate of rotation of the spindle motor means;
spindle reference signal means for producing a spindle reference signal representing a desired angular rate of rotation of the spindle motor means;
means for comparing each of the first and second spindle tachometer signals with the spindle reference signal, to produce first and second error signals represen-tative of the detected differences therebetween; and means for summing together the first and second error signals to produce a spindle motor control signal for coupling to the spindle motor means to produce the desired angular rate of rotation.

2. A spindle servo system as set forth in claim 1, wherein:
the first and second spindle tachometer signals both have frequencies indicative of the actual angular rate of rotation of the spindle motor means, the spindle reference signal has a frequency repre-senting the desired angular rate of rotation of the spindle motor means, and the means for comparing comprises phase detection means for detecting the relative phase angles of such sig-nals.

3. A spindle servo system as set forth in claim 2, wherein the information signal includes a color video signal, and the reference signal means comprises a color subcarrier oscillator and divider means for dividing the color subcarrier to produce the reference signal having a frequency representing the desired angular rate of rotation.

4. A spindle servo system as set forth in claim 3, wherein the color subcarrier oscillator is the sole source of the spindle reference signal, whereby fixed errors in the time base of the information signal recovered from the modulated beam are prevented.

5. A spindle servo system as set forth in claim 1, wherein the apparatus includes focus means for moving an objective lens along a prescribed path to focus the source beam on the disc, and the spindle servo system further com-prises lock detection means, responsive to the spindle motor control signal, for enabling the focus means only when the spindle motor means is rotating at the desired angular rate of rotation.

6. A spindle servo system as set forth in claim 1, wherein the apparatus includes carriage means for trans-lating the disc and the optical system means relative to one another along a radius of the disc, and the spindle servo system further comprises lock detection means responsive to the spindle motor control signal, for enabling the carriage means only when the spindle motor means is rotating at the desired angular rate of rotation.

7. A spindle servo system as set forth in claim 1, wherein the apparatus includes beam steering means for steering the source beam to follow a path defined by the information track, and the spindle servo system further com-prises lock detection means, responsive to the spindle motor control signal, for enabling the beam steering means only when the spindle motor means is rotating at the desired angular rate of rotation.