CA1150836A - Focus servo system for optical player apparatus - Google Patents

Abstract

ABSTRACT

A focus servo system for use in a player apparatus for deriving information from an information bearing surface, the player apparatus including an optical device for directing a source beam of radiation along a prescribed optical path to the surface, the focus servo system comprising: an objective lens for focusing the source beam on the information bearing sur-face; a focus error detector for detecting the position of the objective lens relative to the information bearing surface; a lens driver, selectively responsive to the focus error detector, for moving the objective lens relative to the information bearing surface along the path of the source beam; a focus acquisition signal device, selectively generating an output to the lens driver in a focus acquisition mode, for driving the objective lens in a first direction through a predetermined range of travel that includes an optimum focusing position; and a kick-back signal device, responsive to the focus error de-tector means, for providing an additional ouptut to the lens driver means to intermittently drive the objective lens in a direction opposite to the first direction, whereby the objec-tive lens scans back and forth past the optimum focusing posi-tion; an objective lens focusor for focusing the source beam on the information bearing surface; a focus error detector for detecting the position of the objective lens relative to the information bearing surface; a lens driver, selectively respon-sive to the focus error detector, for moving the objective lens relative to the information bearing surface along the path of the source beam; focus acquisition signal device in a focus acquisition mode, for driving the objective lens in a first direction through a predetermined range of travel that includes an optimum focusing position; and a kick-back signal device, responsive to the focus error detector, for providing an addi-tional output to the lens driver to intermittently drive the objective lens in a direction opposite to the first direction, whereby the objective lens scans back and forth past optimum focusing position.

Description

VIDEO DISC PLAYER
TECHNICAL FIELD
The present invention relates to the method 2nd means for reading a frequency modulated video signal stored in the form of successively positioned reflectlve and non-reflective regions on a plurality of lnformation tracks carried by a video disc. More specifically, an optical system is employed for directlng a reading be~m to impinge upon the information track and for gather'ng 10 ~the reflected signals modulated by the reflective and non-reflective regions of the information track. A
frequency modulated electrical signal ls recovered fr~m the reflected llght modulated ~lgnal. The recovered frequency mGdulated electrical slgnal ls applied to a signal processing section wherein the recovered fre-quency modulated signal is prepared for appllcatlon to a standard television receiver and/or monitor. me recovered light modulated signals are applied to a plurality of servo systems for providing control 8ign~1s which are employed for keeplng the lens at the optim~m focus positlon with relation tothe information beari-.g surface Or the video disc and to maintain the focuse~
llght beam ln a position such that the focused llght spot implnges at the center Or the lnformatlon track.
BRIE~ 5~ OF THE INVENT~ON
The present lnvention is dlrected to a video dlsc player operating to recover rrequencY modulated video signals from an information bearing surrace Or a vldeo disc. The frequency modulated video informaticn .

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is stored in a plursllty of concentric circles or a single splral extending over an informatlon bearing portion of the video disc surface. The frequency modu-lated video signal ls represented by lndicia arranged in track-like fashion on the inrormation bearing surface portlon Or the video dlsc. The indicia comprise suc-cessively positioned reflective and non-reflective regions in the inrormation 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 approxl-mately the same as the width Or the indicla positloned in the information track. A microscopic ob~ective lens is used for focusing the read beam to a spot and for gathering up the reflected light caused by the spot impinging upon successively positioned light reflective and light non-reflective regions. The use of the microscopically small indicia typically 0.5 microns in ~ width and ranging between one micron and 1.5 microns in length taxes the resolving power Or the lens to its fullest. In this relationship, the lens acts as a low pass filter. In the gathering of the rerlected light and passing the reflected light through the lens when operating at the maximum resolution of the lens, the gathered light assumes a sinusoldal-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 ~irst as an information bearing light member and second as a control signal source for generating radial tracking errors and focus errors.
The information bearing portion of the recovered fre-quency modulated video slgnal is applied to an FM
processing system for preparation prior to transmission to a standard TV rece~ver and/or a TV mon tor.
The control portlon of the recovered freQuency modulated video slgnal is applied to a plurality of servo subsystems for controlling the position of the t -3~ 836 reading beam on the center of the in~ormatlon track and for controlling the placing of the lens for gatherlng the maximum reflected li~ht when the lens is posltloned at its optimum focused posltion. A tangentlal servo subsystem ls employed ror determining the time base error introduced into the readin~ process due to the mechanics of the reading system. This time base error appears as a phase error in the recovered frequency modulated video signal.
The phase error is detected by comparing a selected portion of the reco~ered 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 t,he pre-ferred embodiment, the predetermined ~rtion of the recovered frequency modulated video signal ls the color burst signal. The internally generated reference rrequency ls 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 ad~usts the location at which the focused spot impinges upon the information track. The tangential mirror causes the spot to move along the lnformation track either in the forward or reverse direction for providing an ad~ustment equaltothe phase error detected ln the comparison process. The tangential mirror in lts broadest sense is a means for ad~usting the time base of the signal read from the video disc member to ad~ust for time base errors in~ected by the mechanics of the reading system.
3~ In an alternatlve ~orm of the invention, the predetermined port;on of the recovered frequency modu-lated video signal is added to the total recorded frequency modulated video signal at the time of record-lng and the same frequency is employed as the operating J

4 1~50B36 point for the hi~hly controlled crystal oscillator used in the comparison process.
In the preferred embodiment when the vldeo disc player is recovering frequency modulated vldeo slgnals representins television pictures, the phase error comparison procedure is performed for each line of television information. m e phase error ls used for the entire line of television information for correcting the time base error for one full line of television infor~a-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 llght 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 in all op~n loop 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 ~ack to the center of track position. In the open loop mode of operation, the differentlal tracklng error is temporarily removed from controlling the operation of radial tracking mirror. In the open loop mode of operation, various combinations of slgnals take over control o~ the movement of the radial track-ing mirror for directing the point of impingement Or the focused spot from the preferred center of track ; position on a first track to a center of track position on an adjacent track. A first control pU~.C causes the 115~836 trac~ing mirror to move the focused spot Or llght rrom the center of track position on a ~irst track and move towards a next adjacent track. This rirst control pulse terminates at a point prior to the rocused sp~t reaching the center Or track position in the next adjacent track.
After the termination Or the rirst 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 ls employed for bringing the focused spot into the preferred center Or track rOcus position as soon as possible. The second control pulse is also employed for peventing oscillation of the read spot about the second inrormation track. A residual portion of the difrerential tracking error is also applied to the radial tracking mirror at a point cal-culated to assist the second control pulse ln 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 Or the next adjacent information track. The stop motion subsystem performs its function by detectlng a predeter-mined signal recovered from the frequency modulated video signal which indicates the proper position wlthin the recovered frequency modulated video signal at whlch time the ~umping operatlon should be lnitiated. This detection function ls achieved, in part, by internally generating a gatlng circuit indicating that portlon of the recovered frequency modulated vldeo slgnal within whlch the predetermlned s~gnal should be located.
In response to the predetermlned signal, whlch is called ln the re~erred embodiment a white ~lag, the stop motion servo subsystem generates a first control slgnal ror appllcatlon to the tracking servo subsystem ~ 150836 fcr temporarily interrupting the appllcation of the differential tracking error to the radial tracking mirrors. The top motion subsystem generates a second control signal for appllcation tothe radial tracking mirrors for causing the radial tracklng mirrors to leave the center of tracklng position on a first information track and ~ump 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 inrormation track.
In the preferred embodiment, a third control signal is generated by the stop motion subsystem at a time spaced from the termination of 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. ~ile the second control pulse is necessary to ~ have the reading beam move from a first information track to an ad~acent lnformation track, the spaces in-volved are so small that the ~umping operation cannot al~ays reliably be achieved using the secor.d control signal alone. In a preferred embodiment haYlng an im-proved reliable mode of operation, the third control signal is employed for compensating for 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 adjacent information track. A further em-bodiment gates the differential error signal throu~h to the radial tracking mirror at a tlme calculated for the gated portion of the differential tracking error to assist the compensation pulse in bringlng the focus spot under control upon the center of track position of the - next ad~acent information track.
The video disc player employs a splndle servo subsystem for rotating the video disc member positioned upon the spindle at a predetermined frequency. In the .t .

~lSV836 preferred embodlment the predetermined frequency is 1799.1 revolutions per minute. In one revolution of the video disc, a complete frame of television informa-tior. is read from the video disc, processed in elec-tronic portion of the video disc player and applied to astandard television recelver 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 slgnal, 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 sub-carrier frequency which is also used to correct for time base errors as described hereinbefore. Py utlliz-ing the color subcarrier frequency as the source of the ~ motor reference slgnal, the spindle motor itself removes all fixed time base errors which arise ~rom a mismatch-ing of the recording speed with the playback speed. The recording speed is 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 ma~or portion of time base error. While the color subcarrier rrequency is shown as the preferred source in generating the motor reference frequency~ other highly controlled rrequency signals can be used in controlling 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 carriage assembly to the specific location under the direction of a plurality of current generators. The carriage servo subsystem con~rols the relative posit;icning of 'he video disc and the optical system used to form the read beam.
A plurality of individual current sources are indlvldually activated by command signals from the functlon generator for directlng the movement Or the carriage servo.
A first command slgnal can direct the carriage servo subsystem to move the carrlage assembly to a predetermined location such that the read beam lnter-sects a predetermined portion of the informatlon bear-ing surface of the vldeo dlsc member. A second current source provides a continuous blas current for directing the carriage assembly to move ln a fixed direction at a predetermined speed. A further current source generates a current signal of fixed magnitude and variable length for moving the carriage assembly at a high rate of speed ln a predetermined direction.
A carriage tachometer current ~eneratlng means ls 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 from the carriage tachometer ls compared ~ with the sum of the currents being generated in the current sources in a summation circuit. The summation circuit detects the difference between the current sources and the carriage tachometer and applies a different signal to a power amplifier for moving the carrlage assembly under the control of the current generators.
~RIEF DESCRIPTION OF THE DRA~NGS
The foregoing and other ob~ects, features and advantages of the invention will be apparent rrom the following more particular descrlptlon of a preferred 3 embodiment of the inventlon as lllustrated ln the accompanying drawlngs whereln:
FIGURE ~ shows a generallzed block dlagram of a video dlsc player;
FIGURE 2 shows a schematic diagram of the opti~
3~ cal system employed with reference to the video disc player sho~Jn ir, Figure l;
FIGURE 3 shows a block diagram of the spindle servo subsystem employed in the video dlsc player shown ln Figure l;

1150836 ~

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 dlagram of the focus servo subsystem employed in the vldec disc player shown in Figure l;
FIGURES 6a, 6b, and 6c show various waveforms illustr~ing the operation of the servo subsystem shown ln Figure 5;
FIGURE 7 shows a partly schematic and partly block diagram vlew of the signal recovery subsystem employed ln the video disc player shown in ~lgure l;
FIGURE 8 shows a plurallty of waveforms and one sectional vlew used ln explaining the operation of the signal recovery subsystem shown in Flgure 7;
FIGURr 9 shows a block dlagra~ of the tracking servo used in the video disc player shown in Figure l;
FIGURE 10 shows a plura~.ity of waveforms ~ utilized in the explanation of the operation of the 20 tracking servo shown in Figure 9;
FIGURE 11 shows a block diagram of the tangen-tial servo emplo~red 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;
FIGUP~.S 13A, 13~, and 13C show waveforms gen-erated in the stop motlon subsystem shown with reference to Figure 12;
FIGURE 14 is a generalized block diagram of the FM processing subsystem utilized in the video disc player shown with reference to Figure l;
FIGURE 15 is a block dlagram of the FM correc-tor circuit utilized ln the FM processing clrcuit shown in Figure 14;
FIGURE 15 shows a plural~ty Or waveforms and one transfer runction utilized in explaining the opera-tion of the FM corrector shown in Figure 15;
FIGURE 17 is a block diagram Or the FM

11~0836 detector used in the FM processing circuit shown ln Figure 14;
FIGU~E 18 shows a plurality Or waveforms used in explaining the operation of the FM detector shown with reference to Figure 17;
FIGU~ 19 shows a block diagram of the audlo processing circuit utilized in the video disc player shown with reference to Figure l;
FIGURE 20 shows a block diagram of the audio demodulator employed in the audio processing circuit utilized in the video disc player shown with reference to Figure 19;
FIGUR~ 21 shows a plurality of waveforms useLul in e~plaining the operation of the audio demodulator sho~n with reference to ~igure 20;
FIGURE 22 shows a block diagram of the audic voltage controlled oscillator utilized ln 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 ~F modulator shown withreference to Figure 24;
FIGURE 26 shows a schematic view of a video dlsc member illustrating the eccentricity effect of uneven cooling on the disc;
FIGU~E 27 is a schematic view o~ a video disc illustrating the eccentricity effect of an orf-center relationship Or the information tracks to the central aperture;
FIGURE 28 is a logic diagram demonstrating the 3~ normal acquire focus mode of operation of the focus servo employed in the video disc sh~n in Figure l; and FIGURE 29 is a logic diagram demonstrating other modes of operation of the focus servo shown with reference to Figure l;

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_ 11~0133S

D~TAILED DESCRIPTION OF THE I~TENTION
The same numeral will be used in the several vlews to represent the same element.
Referring to Figure 1, there ls shown a sche-matic block diagram of a video disc player system in--dicated generally at 1. The player 1 employs an optical system lndlcated at 2 and shown in greater detail ln Figure 2.
Referring collectlvely to Figures 1 and 2, ~he optical system 2 includes a read laser 3 employed for generating a read beam 4 which ls used for readin~ a frequency modulated encoded signal stored on a video disc 5. The read beam 4 is polarized in a predetermined direction. The read beam 4 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 lmpingement with the video 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 d~sc 5. Each track is formed with successive light reflective regions 10 and light non-reflective regions 11. The direction of reading is lndlcated by an arro~ 12. The read beam 4 has two degrees o~ movemer.', the first of which is in the radial direction ~s indi-cated by a double headed arrow 13; the ~econd of wh ^h is the tangential direction as indicated by a double headed arro~.~ 14. The double heads of each of the arrows 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.
Referrlng to Figure 2, the optical system ccm-prises a lens 15 employed for shaping the beam to fully flll an entrance aperture 16 of a microscopic ob~ectlve lens 17. The ob~ective lens is employed for forming the spot 6 of light at its point of lmpingement with the video disc 5. Improved results have been found when the entrance aperture 16 is overfllled by the 1150~336 readlng beam 4. Thls results in maximum light intenslty at the spct 6.
After the beam 4 ls properly formed by the lens 15, it passes through a di~raction grating 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 is used for develop-ing both a focus error signal and the information signal.
These three oeams are treated ldentically by the remaln-ing portiDn of the optical system. Therefore, they arecollectively referred to as the read beam 4. The output for the di~fraction grating 18 is applied to a beam splltting prism 20. The axis of the prism 2Q ls slightly offset from the path of the beam 4 for reasons that are explalned with reference to the descriptlon of the performance of the optical system 2 as it 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 forty-~1ve 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 artlculated 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 s urface ~ the video dlsc 5.to correct for time base error errors introduced into the reading beam 4 because of eccentricities in the manufacture of the disc 5.
The tangential direction is in the forward and/or back-ward direction o~ 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 foc~sed 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 lighf beam to a second articulated mirror c8. The second articulated mirror 28 is employed as a tracking mirror. It is the function of the tracklng mirror 28 to respond to tracking error signals so as to sli~htly ` 1150836 change its physical posltlon to dlrect the polnt of impingement S of the read beam 4 so as to radlally tracl; the lnformatlon carrylng lndlcla on the surface of the video dlsc 5. The second artlculated mlrror 28 has one degree of movement whlch moves the llght beam ln a radial dlrection over the surface o~ the video dlsc ~ or indlcated by the double headed arrow 13.
In normal playing mode, the focused beam of llght lmplnges upon successively positioned llght reflective regions 10 and light non-reflectlve regions 11 representlng the frequency modulated lnformation.
In the preferred embodlment, the llght non-reflectlve reglons 11 are light scatterlng elements carrled by the vldeo disc 5. The modulated llght beam ls a light equivalent of the electrlcal fsequenc~ modulated slgnal ccntaining all the recorded lnformation. This modulated light beam is generated by the mlcroscopic objectlve lens 17 by gat~ering as much reflected light from the ~ successlvely positloned llght reflective region 10 and light non-reflective regions 11 on the vldeo disc 5. The re~lected portion of the read beam is lndicated at 4'. The reflected read beam 4' retraces the same path previously explained by impinging ln sequence upon the second articulated mirror 28, the first arti-culated mirror 26, and the fixed mlrror 24. The re-flected read beam 4' next passes through the quarter-wave plate 22. The quarterwave plate 22 provldes an additional forty-five degree polarization shift re-sultlng ln a total of nlnety degrees in shift of polar-ization to the reflected read beam 4'. The reflectedread beam 4' now impinges upon the beam splitting prism 20, which prism dlverts the reflected read beam 4' to lmpinge upon a signal recovery subsystem indicated generally at 30.
The function of the beam splitt~ng prism ls to prevent the total reflected read beam 4' rrom re-entering the laser 3. The efrect o~ the returnlng read beam 4' upon the laser 3 would be to upset the mecAanism whereby the laser oscillates ln lts predetermlned mode 1150836 ( of operation. Accordingly, the beam splitting prlsm 20 redirects a significant 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 portlon o~ 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 itself ~:hich represents the stored lnformation. A
second type Or signal is a control slgnal derived frcm the informational signal for controlllng various por-~ tions of the player. The informational signal is a cO ~requency modulated signal representing the lnformatlon stored on the video disc 5. This informational signal is applied to an FM processing subsystem indicated at 32 over a line 34. A flrst contrpl signal generated by the signal recovery subsystem 30 is a differentlal focus error signal applied to a focus servo subsystem indica-ted at 3~ over a line 38. A second type of control signal ger,erated by the signal recovery subsystem 30 is a differential tracking error signal applied to a track-lng 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 function o~ the video 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 splndle 49, as provided by the spindle motor 48, is under the 115083~ f control of a spindle servo subsystem 50. A splndle tachometer (not shown) ls 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 tachometer 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 50. A line 52 carries the tachometer pulses from the second tachometer element to the spindle servo subsystem 50. Wher 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 allo~s 30 frames of television in~ormation 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 is achieved by dlrecting and focusing a read beam 4 to impinge upon the successively positioned light reflective region 10 and a lig'nt non-re~lective region 11 3 on the vid~ disc 5. For optimum results, the read beam 4 should impinge upon the plane carrying the encoded information at right angles. To achieve this geometric configuration requires relative movement between the combined ~tical system 2 and the Yideo disc 5. Either the video disc 5 can move under the fixed laser read beam 4 or the optical system 2 can move relative t~ 'ne fixed video disc 5. In this embodiment, the optical system 2 is held stationary and the video disc 5 ls moved under the reading beam 4. The carrlage servo su~system controls this relative movement between the video disc 5 and the optical system 2.
As completely described hereina~ter, the carriage servo subsystem adds a degree Or flexibility to the overall functioning of the video disc player 1 by dlrecting the aforementioned relatlve movement in a number Or different modes o~ operation. In its ~irst 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 UpOil 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 ls not shown in great detall. For an understandlng of the summarized opera-tlon of a vldeo dlsc player, it ls 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 which the remaining player functions will beinitiated in sequence, Obviously, the carriage servo subsystem can position the carriage at any number of fixed locations relative to the vldeo disc pursuant to the deslgn requlrements of the system, but for the purposes ~ this description the carriage is posltloned at the beginning of the frequency modulated encoded - information carried by the video disc. The carriage motor 57 provides the driving force to move the carriage assembly 56. The carriage tachometer ger.erator 58 is a current source for generating a current lndicating the instantaneous s~eed and direction ~ movement of the carriage assembly.
The spindle servo subsystem 50 l~as brought the spindle speed up to its operational rotational rate of 1793.1 rpm at ~hich tlme the player ena~le slgnal is generated on the line 54. The player enable slgnal on the llne 54 is applied to the carrlage servo subsystem 55~for controlling the relative motlon between the carrlage assembly 56 and the optlonal system 2. The next sequence in the PLAY operation is for the focus servo subsystem 36 to co-,ltrol the movement of the lens 17 relative to the video disc 5. The focusing opera-tlon includes a coil (not shown) moving the lens 17 under the direction of a plurallty of separate elec-trlcal waveforms which are summed within the coil ltself.
These waveforms are completely descrlbed ~ith reference to the descriptlon ~iven for the focus servo subsystem in Figures 6a 6b and 6c. A volce coll arrangement as found ln a standard loud speaker has been found to be suitable for controlllng the up and do~n motlon of the lens 17 relati e to the video disc 5. The electrlcal signals for controllil~ the volce coll are generated by ~ the focus servo subsystem 36 for appllcation to the coil over a ~ine 64.
The inputs to the focus servo subsystem are applled from a plurallty of locations. The first of hich is applied from the slgnal recovery subsystem 30 over the line 38 as previously descrlbed. The second input signal is from the FM processing circuit 32 over a llne 66. The FM processing subsystem 32 provides the frequency modulated slgnal read from the surface of the video disc 5. A third input signal to the focus servo subsystem 36 is the ACQUIRE FOCUS enabling loglc signal 30 generated by the act of puttlng the player lnto its pla~y mode by selectlon of a functlon PIAY 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 collcct the maximum lig;lt reflected from the video disc 5 and modulated by the successively posi-tioned light reflective region 10 and light non -reflective region 11. This optimum range is approxi-11~;083~i 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-at~on all of which are descrlbed hereinafter ln greater detail with reference to Figures 5, ~a, .ib and ~c.
At the present time it is important to note that the focus servo subsystem 36 utilizes its three input signals in various combinations to achieve an enhanced focusing arrangement. me dlfferential focus error signal from the signal recovery subsystem 30 provides an electrical representatlon of the relative distance between the lens 17 and the video disc 5. Un-fortunately, the dlfferential focus error signal ls relatively small in amplitude and has a uave shape containing a number of positlons thereonJ each of which lndicate that the proper point has been reached. All but one o~ such positions are not the true optlmum focusing positions but rather carry false information.
~ Accordingly, the dlfferentlal focus error slgnal ltself is not the only signal emplo~Jed to indicate the optlmum focus condition. I~hile the use of differential focus error itself can oftentimes result ~nthe selectlon of the optlmum ~ocus positlon, lt cannot do so rellably on every focus attempt. Hence, the combination of the dlfferential focus error slgnal with the slgnal indica-tive of reading a frequency modulated slgnal from the vldeo disc 5 provldes enhanced operatlon over the use of uslng the dlfferentlal focus error slgnal ltself.
Durln~ the focus acquiring mode of operation, 3 the lens l7 is moving at a relatlvely high rate of speed towards the video disc 5. An uncontrolled lens detects a frequency modulated sl~nal from the informatlon carried by the video disc 5 in a very narrow spaclal range. This very narrow spaclal range ls the optimum focusing range. Accordlngly, the combination of the detected frequenc~J modulated slgnal and the differential focus error signal provides a reliable system for ac-qulring focus.
The focus servo subsystem 36 herelnafter 11S083`f~ ~

described cont2ins additional improvements. One Or these improvements is an additioll of a further fixed signal to those alraady described whicll further helps the focus servo subsystem 36 acquire proper focus on the initial attempt to acquire focus. Thls addi-tional signal is an internally generated kickback signal ~hich is initiated at the time when a frequency modulated signal is detected by the FM processing subsystem 32. This internally generated klckback pulse is combined with the previously discussed signals and applied to the voice coil so as to independently cause the lens tc physically move back through the region at ~hich ~ frequency modulated signal was read f~om the disc 5. This internally generated fixed kickback pulse signal gives the lens 17 the opportunity to p2SS through the critical optimum focusing point a number of times during the first transversing of the lens 17 to~ards the video disc 5.
F~rther improvements are described for handling momentary loss of focus during the play mod~ of opera-tion caused `D~J 1mperfection in the encoded frequency 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 subsystem 36 over the line 66.
A tangential servo subsystem 80 receives its first input signal from the FM processlng subsystem 32 over a line 82. The input signal present on the line 82 is the frequency modulated signal detected from the sur-face of the video disc 5 by the lens 17 as ampliried inthe 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. me second input signal to the tangential servo subsystem 80 is over a line 84. The signal on the line 84 is a variable DC signal generated by a carri~e position potenti3met2r. T~e amplitude of the variable voltage signal on the line 84 indicates the relative position of the point Or impact of the readlng spot S over the radial distance indicated b~ a double headed arrow 86 as drawn upon the surrace of the video disc 5. This variable voltage adJusts the gain of an internal circuit for ad~usting lts operatlng charac-teristics to track the relative position Or the spot as it transverses the radial positlon as indicated by the length of the line 85.
The function of the tangential tlme base error correction subsystem 80 is to adjust the signal detected from the video disc 5 for tangential errors caused by eccentricity of the informatlon tracks 9 on the disc 5 and other errors introduced into the detected signal due to any physical imperfection of the video disc 5 itself. The tangential time base error correction subsystem 80 performs its runction by comparing a signal read from the disc 5 wlth a locally generated slgnal.
The difference between the two signals ls lndlcatlve of the instantaneous error in the signal being read by the player 1. More specially, the signal read from the disc ~ 5 ls one which was carefully applied to the dlsc with a predetermined amplitude and phase relative to other signals recorded therewith. For a color televislon FM
signal this is the color burst portion of the vldeo signal. The locally generated signal is a crystal con-trolled oscillator operating at the color subcarrier frequenc~T of 3.579545 megahertz. The tangentlal time base error correction subsystem 80 compares the phase dlfference between the color burst slgnal and the color subcarrier oscillator frequency and detects any differ-ence. ~his dlfference ls then employed for ad~ustlng the phase ~ the remainlng portion of the llne of FM
lnformation which contalned the color burst signal.
The phase difference of each succeeding ~ine is gener-ated in exactl~ the same manner for providlng continuous tangential tlme base error correction for the entire signal read from the disc.
In other embodlments storing in~ormation signals which do not have a portlon thereof comparable to a color ~urst slgna~ such ~8~ ~ having predeter-mlned amplitude and phase relative to the remalning ` 1150836 ~

slgnals on the disc 5 can be periodlcally added to the information when recorded on the dlsc 5. In the play mode, this portion of the recorded lnformation can be selected out and compared witll a locally generated sisnal comparable to the color subcarrier oscillator.
In thls manner, tangential time 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 5 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 26 so as to re-direct the read beam 4 forward and backwards along thelnformation track, in the dlrection 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 ti~e base error cor-rection subsystem 80 is applied to the stop ~otion sub-system 44 over a line 92. Thls 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 remainlng video slgnal.
It has been found convenient to locate the sync pulse separator in the tangential time bsse error correction subsystem 80. This æync pulse separator could be located in any other portion of the player at a point where the complete video signal is available from the FM processing subsystem 32.
A further 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 motor reference frequency in the tangentialsubsystem 80 is convenient because of the presence of the color subcarrier osclllator frequency used in the comparison operation as previously described. This color subcarrier oscillator frequency is an accurately 115U836 ( . ~
gener2ted signal. It is dlvided down to a motor re~er-ence frequenc~t used in the control of the spindle servo speed. ~- utili~ing the color subcarrier frequency as a control frequency for the speed Or the spindle, the speed of the spindle is erfectively locked to this color subcarrie- frequency causing the spindle to rotate at the precise frame frequency ra~e required for maximu~.
fidelity 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 indi-ated at 98.
The tracking servo subsystem 40 receives a plurality of input signals, one of which is the pre-viously descri~ed differential tracking error signal generated by a signal recsvery subsystem 30 as applied thereto over a line 42. A second input signal to the tracking servo subsystem 40 is generated in a function generator 47 over a line 102. For the purpose of clar-ity, the function ge!lerator 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 generated are described in ~ore detail in the detailed description Or the carriage servo sub-system $5 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 initi~ted by the function generator 47. For example, the function generator 47 is capable Or generating a signal for causing the relative move~.ent of the carriage assembly 56 over the video disc 5 to be in the rast for~ard 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 o~ 11,000 tracks per inch and tracking is not expected in this condition. Hence, the slgnal from the functlon generator 47 on the line 102 disables the tracking servo 40 so that it does not attempt to operate in ..... ... _ _ .
.

` 11S0836 ( its normal tracking mode.
A thlrd input signal to the tracking servo subsystem 40 is the stop motion compensation pulse gene~
ated in the stop motion subsystem 44 and applied over a line 104. An additional input sigr.al applled 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 thlrd lnput slgnal to the tracking servo subsystem 40 ls the stop motion pulse generated by the stop motion subsystem 44 and applied over a line 108.
The output slgnals from the tracking servo sub-system 40 include a first radial mirror tracking signal over a llne 110 and a second radial mlrror control on a line 112. The mirror control signalson the line 110 and 112 are applied to the second articulated mirror 28 which is emplo~ed for radial traclcing purposes. The control signals on the lin~s 110 and 112 move the second articulated mirror 28 such that the reading beam 4 impinging thereupon ls moved in the radial direction and - becomes centered on the information track 9 illuminated by the ~ocused spot 6.
A further output signal from the tracking servo subsystem 40 is applied to an audio processing subsystem 114 over a line 116. The audio squelch signal on the line 116 causes the audio processing subsystem 114 to stop transmitting audio signals for the ultimate appli-catlon to the loud speakers contained in the TV receiver 96, and to a pair o~ audio ~acks 117 and 118 respec-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 lnterconnected with the video disc player 1 ~or recelpt of two audio channels for stereo applicatlon.
A further output signal from the ~racking servo subsystem 40 is applied to the carriage servo subsystem 55 over a line 130. The control signal present on the llne 130 is the DC component ~ the tracking correctlon signal which is employed by the carriage servo subsystem for providlns 8 rurther carriage control slgnal indica-tive o~ now closely the tracking servo subsystem 40 ls following the directions glven by the ~unction generator 47. For example, if the function generator 47 glves an instruction to the carriage servo 55 to provide carriage movement calculated to operate with a slo~ forward or slow reverse movementJ the carriage servo subsystem 55 has a further control signal for determining how well it is operatlng so as to cooperate with the electronic control signals generated to carry out the instruction from the function generator 47.
The stop motion subsystem 44 ls equlpped with a plurality of input signals ~ne of which ls an output signal o~ the function generat~r 47 as applied over a 1~ line 132. The control signal present on the llne 132 ls a STOP enabling signal lndicating 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 off ~f the vldeo disc and generated by the FM processing subsystem 32.
The video si~nal from the FM processing subsystem 32 ls applied to the stop motlon subsystem 44 over a line 134.
Another lnput slgnal to the stop motion subsystem 44 ls the dlfferentlal tracklng error as detected by the

2~ signal recovery subsystem 30 over the llne 45.
The tangential servo system 80 ls equipped with a plurality of other output signals in addition to the ones previously ldentifled. The first of which is applled to the audio processing subsystem 114 over a llne 140. The signal carried by the line 140 is the color subcarrier oscillator frequency generated in the tanentlal servo subsystem 80. An additlonal output signal from the tangential servo 80 is applied to the FM processing subsystem 32 over a llne 142. The signal

3~ carried by the line 142 ~s the chroma portlon of the vldeo slgnal generated ln the chroma separator fllter portion of the tangentlal ~ervo subsystem 80. An addi-tlonal output slgnal from the tangentlal servo 80 is applied to the FM processlng subsystem 32 over a line 1~508(36 1~4. The signal carried by the line 144 ls a gate enab-ling signal generated by a first gate separator portion Or the tangential servo system ~0 wllich indlcates the instan~neous presence o~ the burst ~ime period in the received video signal.
The focus servo receives its ACQUIRE FOCUS
signal on a line 14~.
me 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 i~ the carriage tacnometer generator 58 for application to the carriage 15 servo subs~Jstem 55 indicative of the instantaneous speed and direction of the carriage, is applied to the carriage servo subsystem 55 over a line 152.
The FM processing unit 32 has an additional plurality of output signals other than those already described. A ~irst output signal from the Fr~ processing subsystem 32 is applied to a data and cloc~ recovery subsystem 152 over a line 1~4. The data and clock re-covery circuit is of standard deslgn and it is employed to read address information contained ln a predetermined 25 portion of the in~ormation stored in each spiral and/or circle contained on the sur~ace of the vldeo.dlsc 5.
The address information detected in the video signal ~urnished by the FM processing unit 32 ls applied to the runction generator 47 ~rom the data and clock recovery subsystem 152 over a line 15~. The clocki~g lnformation detected by the data and clock recovery subsystem is applied to the function generator over a line 158. An additional output signal from the FM processir.g unit 32 ls applied to the audio processing subsystem 114 over a line 1~0. The signal carried by the line 160 is a fre-quency modulated video signal from the FM dlstribution ampliflers contained in the Frl processir.g unit 32. An addltional outpu~ signal from the Fi~ processing subsystem 32 is applied to an RF modulator 152 over a line 164.

-~6- 11S083~
The line 16', carries a video output signal from the FM
detector portion of the FM processins unlt 32. A final output signal from the FM processin~ unit 32 ls applied to the TV monitor 9& over a line 155. ~he llne 166 c~rries a video signal o~ the type displayable in a standard TV monitor 98.
The audio processing system 11~ receives an additional input signal from the function generator 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 Fr~ modulated signal recovered from the video disc 5 contains a~plurality of separate audio signals.
More specifically, one or two channels Or audio 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 explaining 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 witl an additional output signal for application to the RF
modulator 1~2 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 wlth one channel of the TV receiver. This modulated channel ~requency oscillator is applied to a standard TV receiver 96 such that the internal circuitry of the TV recelver demodulates the audio contained in the modulated 3~ channel frequency signal in its standard mode of oper-ation.
The audio signals applied to the audio acces-sory unit 120 and tlle audio ~acks 117 and 118 lies ~ithin the normal audio ran6e suiiable for driving a loudspea~er b~ mealls Or the audio jacks 117 and 118.
The same audio ~requencies can be the ir.put to a stereophonic audio ampll~ier when such is employed as the audio accessory 120.
In the pre~erred embodiment, the output ~rom the audio processing system 114 m~dulates the channel 3 frequency oscillatDr be~ore applicaticn to a standard TV receiver 96. l~hile Channel 3 has been conveni-ently selected ror this purpose, the oscillating ~re-quency of the channel frequency oscillator can be adapted f~r use with any channel of the standard TV
receiver 96. The output o~ the RF modulator 162 is zpplled to the rrv receiver 96 over a line 174.
An additional output slgnal ~rcm the function generator 47 is applied to the carrlage servo subsystem 55 over a llne 180. The llne 180 represents a plural-it~J of individual lines. Each individual line is not shcwn 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, represents an ~ lnstruction ~rom the ~unction generator lnstructlng the carrlage servo to move ln a predetermined direction at a predetermined speed. Thls is described ln greater detail when describing the detailed operation of the carriage servo 55.
NORMAL PLAY MODE - SEQI~ENCE OF OPERATION
The depression of the play button generates a PLhY slgnal from the runctlon generator followed by an ACQUIRE FOCUS slgnal. The PLAY signal is applied to the laser 3 by a line 3a ~or generating a read beam 4.
The PLAY signal turns on the spindle motor subsystem 50 and starts the splndle rotatlng. After the spindle servo subsystem accelerates the splndle motor to its proper rotational speed of 1799.1 revolutions per minute, tlle spindle servo subsystem 50 generates a PLAYER ENA~LE signal for appllcation to the carriage servo subsystem 55 ~or controlling the relative move-ment between the carriage assembly and the optlcal assembly 2. The carriage servo subs~stem 55 dlrects 1151~836 the movement of the carriage such that the read beam

4 is positioned to impinge upon the beglnning portion of the inform~tion stored on the video disc record 5.
Once the carriage servo subsystem 55 reaches the approx-imate beginnins Of the recorded information, the lensrOcus servo subsystem 3~ automatically moves the 1~n9 17 towards the video disc surface 5. The mo-~ement of the lens is calcul~ted to pass the lens through a point at which optimum focusing is acllieved. The lens ser~o system preferably achieves optimum focus in com~ina-tion with other control signals generated by reading information recorded on the video disc surface ~. In the preferred embodi~ent, the lens servo subsystem has a built-in program triggered by information read from the disc ~lhereby the lens is caused to move tllrough the opti~um ~ocusing point several times by an oscilla-tor~ 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 focusing 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 lnformation signal read from the disc is used as a feedback signal to tell the lens servo subsystem 35 that the correct point of focus has been success-full~J located. ~hen the point of optlmum focus has been located, the focus servo loop is closed and the 3 mechanically initiated acquire focus procedure ls terminated. The radial tracking mirror 28 is now responding to the di~ferential trackin~ error generated from the informaticn gathered by the reading lens 17.
The radial tracking error is causing the radial track-ing m~rror 2~ to follow the information track andcorrect for any radial de~artures fro~ 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 " 115()8~6 26 for correctin~ phase error in the reading process caused by small physical deformatles in the surface of the video disc 5. Durin~ the normal play mode, the servo subsystems hereinbefore described continue their normal mode Or operation to maintain the read beam 4 properly in the center of the informa~ion track and to maintain the lens at the optimum focusing point such that the light gathered by the lens generates a high quality si~nal for display on a standard television receiver cr in a television monitor.
The frequency modulated signal read from the disc needs additional processing to achieve optimum fideliJy during the display in the television receiver 9~ and/or television monitor 98.
Immediately upon recovery from the video disc surface, the frequency modulated video signal is applied to a tan~ential servo subsystem 80 for detectlng any phase difference Eresent in the recovered video signal and caused by the mechanics of the reading process.
The detected phase difference is employed for driving a tangential mirror 26 and ad~ustin6 for this phase difference. The movement of the tangential mirror 26 functions for changing the phase of the recovered video signal and eliminating time base errors intro-duced into the reading process. The recovered videosignal is F~ 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 the FM video spectra to correct for the mean transfer function of the readin~ lens 17. More specifically, the high frequency end of the video spectrum is atten-uated more by the reading lens than the lo~ frequency portion of the frequency spectrum of the frequency modulated slgnal read from the video disc. This equalization ls achieved through amplif~v~ing the higher frecluency portion more than the lower frequency por-tion. After the frequency modulation correction is achieved, the detected signal is sent to a discrimina-tor board whereby the discrimil~ted video is produced 1150~336 3o-~or applicaticn to the remaini;~ portions Or the board.
Rererring to Figure 3 there ls sho~n a gen-erali~ed blocl~ diagram Or the spindle servo subsystem indicated at ~0. One o~ the ~unctlons o~ the spindle servo subsystem is to maintain the speed o~ rotation o~ the spindle 4g by the spindle motor 48 at a constant speed of 1799.1 rpm. Obviously this ~i~ure has beei~
selected to be compatible with the scanni~g rrequency Or a standard television receiver. me standard tele-vision receive~ receives 30 rrames per second and theln~ormation is recorded on the video disc such that one complete ~rame of television in~ormation is con-tained in one spiral and/or track. ObviouslyJ when the time requirements Or a television receiver or tele-vision moritor differ rrom this standard then thefunction o~ the spindle servo subsyste~ ls 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 begins to turn the tachometer input sig~l pulse train ~rom the first tachometer element is applied to a Schmitt trig-ger 200 over the line 51. The tacho~.eter lnput signal pulse train rrom the second tachometer element is applied to a second Schmitt trigger 202 over the line 25 52. A 9.33 KHz motor reference ~requency is applied to a third Schmitt trigger 204 ~rom the tangential servo subsystem 80 over a line 94.
The output from the Schmitt trigger 200 is applied to an edge generator Cil'CUit 206 through a 30 divide by t~o network 208. The output rrcm the Schmitt trigger 202 is applied to an edge generator 210 through a divided by two network 212. Tlle output from the Schmitt trigger 204 is applied to an edge generator circuit 214 througll a divided by two network 216. Each 3~ o~ the edge generators 206 210 and 214 is employed ror gererqting -q sllarp pulse corres?ond}ng to bo~h the positive gOiilg e~e and the negative ~oing edge o~ the signal applied respectively fro~ the divlded by two net-,~orks 208 212 and 215.

1150836 ~

The output from the ed~e generator 214 is ap~iied as the reference phase si~nal to a rirSt ph~3e detector 218 and to a second phase detector 220. The phase detector 218 has as lts second input signal the OUtp~lt from the edge generator 206. The phase genera-tor 220 has as its second input signal the output of the edge generator 210. The phase de'ectors operate to lndicate any phase difference between the tachometer input signals 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 power amplifier 22S. The function of the lock detector 224 is to indicate when the splndle speed has reached a predetermined rotational speed. This can be done by sensing the output signals from the summ~tion circuit 222.
In tne preferred embodiment ls has been deter-mlned 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 brou~ht to a relatively high rDtational speed, the disc rides on a cushion of air and rises slightly vertical against the force of gravity. Additionally, the centrifugal force of the vldeo disc causes the video disc to some~ at 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 centrirugal force both lift the video disc from its position at rest to a stabillzed position spaced from its lnitial rest posi-tion and at a predetermined p~sition with reference to other internal fixed members of the video disc player cabinet. The dynamics ol a spinnin~ disc at 1799.1 rpm Wit~1 a predetermined weight and density can be calculated such as to insure that the dlsc ls spaced from all lnternal components and ls not ln ,, contact ~itll anJ such i~lternal components. An~J con-tact between the disc and the player cabinet causes rubbing, an~ the rubbing causes dama~e to the video disc throu~h abrasion.
In the preferred embodiment, the lock detector 224 has been set to generate a PIAYER 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-tlonal speed can be selected as the point at which the player enable si~nal 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 ~ixed dela~-, after apply-ing the START signal to the spindle motor, is used tostart t'ne carriage assembly in motion.
During the normal operating mode of the vi~eo disc player l; the tachometer input si~nals are con-tinuously applie~ to the Schmitt triggers 200 and 202 over the lines 51 and 52, respectively. These actual ta~hometer input signals are compared against the moto~
reference si~nal and any deviation therefrom is detected in the summation circuit 222 for applic~tion to the poJer amplifier 225. The power amplifler 226 provides 2~ 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 ~5.
The carriage servo subsystem ~ comprises a plurality of current sources 230 through 235. The function of each Or these current sources is to provude a predeter-mined value of current in response to an input signal from the function generator 47 over the line 180. It was previously described that the line 180, shown with reference to Figure 1, comprlses a plurality of in-dividual llnes. For the pur?oses of ~his description, each of these lines will be identlfied as 180a through l~Oe. The outputs of the current sources 230 throu~h 23~ are applied to a summation circuit 238. The ~150836 ~

ouiput from the summation clrcuit 23~ is applied to a p^wer ampli~ier 240 over a line 242. The output from the power ampll~ier 240 is applied to the carriage motor 57 over t~le line 150. A dashed line 244 extending between the carriage motor 57 and the carriage tachometer member 58 indicates that these units are mechanically connected. The output ~rom the carriage tachometer 58 is applied to the summation circuit by the line 152.
The STAP~T pulse is applied to the current so~rce 232a 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 tracl~ position. As previously mentioned, the carriage assembly 55 and the optical 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 informatlon. Accordingly, the current source 232 generates the c~rrent for applica-tion to the summation circuit 238. The summ~tion circuit 238 runctions to sense the several incremental amounts Or current being generated by the ~arious current sources 230 through 235 and compares this sum 25 of the currents against the current being ~ed into the summation circuit 238 from the carriage tachometer s~Jstem 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 position of the carriage assembly 5S. 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 applled to the po~Jer ampli~ier 240 over the line 242 fo~ generating 35 the power required to move the carriage motor 57 to the desircd locatio.l.
Onl~J for purposes of example, the carriage tachometer 58 could be generatil~ a negative current indicating that the carriage assembly 56 is positioned ~15083~
-3~-at a first location. The current source 232a ~ould gener2te a SeCOlld cu~rent indicati~.~ the desired posi-tion for the carriage assembly 56 to reacn for start-up time. The summation circuit 23~ compares the two currents and 6enerates a resulting difrerence current on the line 2~2 for application to the pol~er amplifier 240. The output from the amplifier 240 is applied to the carriage motor 57 for driving the carriage motor and moving the carriage assembly to the indicated position. As the carriage motor 57 moves, the carriage tachometer 58 also moves as indicated by the mechanical linkage sho~n by the line 244. As its pos ~ion changes, the carriage tachometer 58 generates a nell 2nd differ-ent signal on t',le line 152. When the carri~ge tachom-eter 58 indicates that it is at the same position asindicated b~ the output signal from the cur ent source 232a~ the summation circuit 238 indicates a COr~PAR~
E~UAL condition. No signal is applied to the po-.~ler amplifier 240 and no additional power is applied to the carriage motor 57 causing the carria~e motor 57 ~o stop.
The START sign21 on t'ne line 180al causes the carriage motor 57 to move to its START positlon. When the spindle servo subs~Jstem 50 has brought the speed of rota~ion of the spindle 49 up to its reading 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 cor.stant current input signal to the po~er amplifier for driving the carriage motor 57 at the indicated distance per revo-lution This constant input bias currer.t frcm thecurrPnt so-,rce 230 is fur~her ~delli;ifled as a first fiY~ed bias control signal to the carriage motor 57.
The current source 231 receives a FAST FORtJARD
E~APLE signal from the functicn generator 47 over the 115~836 ~5 llne 180`o. ~ne ~ast for~l~.d current source 231 gener-aies an output current signal for applicatlon to the summation circuit 238 and the power amplifier 240 for activating the carriage motor 57 to move the carriage assembly 56 in the fast forl~ard direction. For clari-fication, the directions referred to in this section of the description refer to the relative movement of t'..e carriage assembly and the reading beam 4. These movements are directed generally in a radial direction 0 2S 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 high rotational speed and hence the radial tracking dces not occur in a straight line across the tracks as indicated by the double arrow 13. More specifically, the ca-riage servo subsystem ls capable of providing relative motion between the carria~e assembly and the optical s~Jstem 2 such as to traverse the typically four inch wide band of infcrmatio:l bearing surtace ~ the video disc 5 in approximately four secon~s from the outer periphery to the inner periphery. The average speed is one inch per second. During the four second period, the reading head moves ac;oss appro~imately forth-four thousand tracks. The video disc is revolving at nearly thirty revolut~ons per second and hence, under idealized con-ditions, the video disc 5 rotates one hundred and t~enty times while the carriage servo subsystem 55 provides the rela~ive motion from the outer periphery to the inner periphery. 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 t~lenty spirals. The net effect of this movement is a radial movement of the point of impingement of the reading beam 4 ~ith the video disc 5 in a radial direction as indicated by a double headed line 1~.
The current source 23, receives its ~ T ~E-VERSE E~J~LE signal from the function generator 47 over the line 180c. The fast reverse current source 233 pr~-vides its output directly to tl.e summation ci,cuit 238.

115~836 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 the 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 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 mo~e 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 ffr ~

that the current generated in the carrlage tachometer matches the current generated from input current sources.
Referring collectlvely to Flgure 5 and Figures

5 oA through 6F, there ls shown and described a schematlc block diagram of the focus servo subsystem 36, a plur-ality of d~r~erent wave~orms which are employed wlth the rOcus servo subsystem and a plurallty of single logic dia~rams showlng the sequence of steps used in 10 the focus servo to operate in a plurality of different modes of operation. The rOcus error signal from the slgnal recovery subsystem 30 ls applied to an ampll~ier and loop compensatlon circuit 250 over the line 38.
The output ~romthe ampli~ler and loop compensatlon cir-15 suit 250 is applied to a kiclcback pulse generator 252over a llne 25~ and to a focus servo loop switch 256 over the line 254 and a second l~ne 258. The output ~rom the kickback pulse generator 252 ls applied to a driver circult 260 over a line 202. The output ~rom the focus servc loop switch 256 is applied to the - driver circuit 260 over a llne 264.
The FM vldeo slgnal is applled from the dls-tribution amplifler portlon o~ the FM processing sub-system 32 to a FI~ level detector 270 over the llne 25 66. The output from the FM level detector 270 is ap-plled to an acquire focus logic circuit 272 over line 274. The output of the FM 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 30 ~ocus logic clrcult is applled to the ~ocus servo loop swltch 256 over a llne 276. A second output slgnal from the acquire focus loglc clrcuit 272 ls applled to a ramp generator clrcuit 278 over a llne 280. The acquire ~ocus loglc clrcuit 272 has as its second input 35 signal the acquire ~ocus enable signal generated by the ~unctioll generator 1,7 over the line 146. The output o~ the ramp generator 278 is applied to the drlver clrcult 260 over a line 281.
The acquire focus enable signal applied to the 1150~336 acquire rOc-ls logic 272 over the line 145 is shown o., line A of Figure 6A. ~asicall~, this signal ls a two-le~el sigial generated by the function generator 47 and haYi~ a disabling lo~ler condition indicated at 282 and an enabli,lg condition indicated ger.erally at 284. The functiorl generator produces this pulse when the video disc player 1 is in one of its play modes and it is necessary to read the information stored on the video disc 5.
Referring to line ~ of Figure 6A, there is shol-~n a typical ramping voltage waveform generated by the ramp generator circuit 2~8. 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 ~ocus enable si~nal, the ramp generator 2~8 generates its ramping voltage waveform shown as a sa-.~Jtooth type output waveform going from a higher position at 286 to a lo~er position at 288. ThiS is sholn as a linearl~ cnanging 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 25 player. Prior to the generation of the acquire focus enabie signal, the lens is generally in a retracted positlon indicated generally at 290. Upon the receipt of the acqulre focus enable slgnal, the lengs begins to move ln a path indicated by the dash/dot line 292.
30 The dash/dot line 292 begins at a point identifled as the upper limit of lens travel and moves through an intersection with a dotted line 294. This point of intersection ls identifled as the lens in focus posi-tlon 293. Whell focus is not acquired on the first 35-attempt, the lens continues along th~ dash/dot line 292 to a p~int 295 identi e~ a5 10~Jer lir`~i t Or lens travel. lJhen the lens reaches point 295, the lens remains at the lower limit cr lens travel throu~h the portinn o~ t~.e line indicated generally at 296. The 115083~
~o-lens continues to follow the dash/dot line to a point ~ndicated at 297 ldentified as the RAMP R~SET point~
This is also shown on line A as 288. ~ur lng the ramp reset ti~e the lens is drawn back to the upper limit of lens travel portion Or the waveform as indicated at 298.
In this first mode of operation the lens fails in its firs~ attempt at acqulring focus. The lens passes through the lens in rOcus 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 before retracting to its upper limit of lens travel indicated at 298. The upper limit of lens travel position and the lower li~.it Or lens travel position are sensed by limit switches in tlle lens driver subassembly not shown.
Duri~g a successful attempt to acquire focus the path of lens travel changes to the dotted line indicated at 294 znd remains there until focus is lost.
The lens is ~ormally one micron above the video disc 5 20 ~hen in the focus position Also the in-focus posi-~ tion can varT over a range of 0.3 microns.
The output signal fro~ the ramp generator 278to the driver 250 on the line 281 has the configuration shown on line ~ of Figure 6A.
2~ The ~aveform 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 ~lave~orm shown on line G illustrates two principal conditions. The open double sided sharp pulse indicated generally at 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 indicatlng that the lens has passed through the in~focus position as indicated by its intersection with the dotted line 294. Correspond-ing to the description previously given ~ith reference to line C of Figure 6A the lens passes through focus and the sharp pulse retracts to its no activity level indicated generally at 302.

-4;-I~ the second illustration, the waveform shownon line G Or Flgure 6A lllustrates the output from the F~ distribution amplirier on t`ne line 56 ~hen the len~
acquires ~ocus. This is indicated by the envelope generally represented by the crossed hatched sections between lines 304 and 30S.
Referring to the waveform shown on line H of Figure 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 294 of line C of Figure 6~. The output of the level detector represented by the dotted iine 311 shows the loss of the FM signal by the detector 270.
1~ The solid line 312 shows the presence of an FM slgnal detected by the FM level detector when the lens ac-quires focus. The continuing portlon of the waveform at 312 indicates that a Frl signal ls available in the focus servo subsystem 35.
Referring to line I of Figure 6A, there is ~ shown the output char~cteristic of the focus servo loop switch 255. In the portion of its cperating character-istics generally indicated by the portion Or the line indicated at 314, the switch is in the Or, condition representing the unfocused condition. The position of the line 316 represents the focused condition. The vertical transition at 318 indicates the time at which rOcus is acquired. The operating mode of the video disc player ~uring the critical period Or acquiring focus is more ~ullJ described with reference to the waveforms shown in Figure 6C. Line A of Flgure 6C
represents a corrected differential focus error gener-ated by the signal recovery system 30 as the lens follows its physical path as previously described with 3~ reference to line C 3f Figure ~A. At point 319 Or the waveform A shown in Figure 5C, the difrerential focus error corresponds to a portivn Or the lens ~ravel during which no focus errors are available. At the region indicated at 320, the first false in-focus error signal 15~83 is available~ There is ftrst a momentary rise in focus error to a first maximum initial level at point 322.
.'~t pOillt 3~2, the differential rOcus error begins to rlse in ~he opposlte direction until it peaks at a point 5 324. ~rhe difrerenti~l focus error begins to drop to a second but opposite maximum at a point 325. 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 athers 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 p~int 330. The differential focus error rises past the ln-focus position to a lower maximum at 332 prior to falling back to the position at 333 where no focus error inrorma~ioll iS available. No focus error in-formation is available because the lens is so close to the video disc surface as to be unable to distinguish a difference of the diffused illumination presently 20 bat~ng the two focus detectors.
Referring to line ~, there is shown a waveform representing the frequency modulated signal detected from the video disc surface 5 through the lens 17 as the lens is moving tol~Jards the video disc 5 ln an attempt to acquire focus. It should ~e 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 through optimum focus.
This small distance is represented by sha~p peaks 334a and 334b of the FM detected video as the lens 17 moves through this preferred in-focus position ~Ihen focus is missed.
I~Jhlle focus can be achieved using only the differential focus error signal shown with reference to line A of Fi~ure 6C, one embodiment of the present invention utili~es the differential focus error signal as shown on line A of Figure 6C in combination with the signal shown on line ~ of Figure Gc to achieve more reliable acquisition of focus during each attempt at 1~5~836 -~i3 -f~us.
Figure ~ of line 6C shows an lnverted ideal-i~ed focus error signal. This ldealized error signal is tilen differentiated and the results shown on llne D
Or Fi~ure 6C. The differentiation of the ideallzed focus error signal is represented by the line 339.
Small portions of this line 339 shown at 340 and 342 lyinO above the zero point indicated at 344 give false indication of proper focusing regions. The region 345 falling under the line 339 and above the zero ccndition represented by the llne 344 indicates the range wiihin which the lens should be positioned to obtain proper and optimum focus. The region 346 repre-sents approximately 0.3 mlcrons of lens travel and 1~ corresponds to the receipt of an FM input to the FM
level detector as shown in line B. It should be noted that no Fl'i is shown on line ~ correspondi~ to regions 340 and 342. Xence~ 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 focu~.
The signal representing the differentiation cr the idealized focus error is applied to the gener-ator 252 for activating the generator 252 to generate its kickback waveform. The output from the F~ level detector 270 is an alternative input to the kickback generator for generating the ki~kbacl{ waveform ~or application to the driver 260.
Referring back to line ~ of Figure 6A and continuing the description of the waveform shown there-on, the dot/dash portion beginning at 285 represents the start of the output signal from the ramp generator 27~ for moving the lens through the optimum focusing 3~ range. This is a sawtooth signal and it is calculated to move the lens smoothly through the point at which Fr1 is detected b~ the FM level detector 270 as lndi-cated by the waveform on line H. In a flrst mode of operation, the focus ramp follows a dot-dash portion - 1~50836 ?8/ of the waveform to a p~lnt 287a corresponding to the ti~e at which the output of the FM level detector shows the acquisition of ~ocus b~ generatlng the sisnal le~el at 312a in line I~. The output si~nal from the 5 acquire ~ocus lo~;ic bloclc 272 turns off the ramp ~;en-erator over the line 280 indicatin~ that rccus has been acquired. Uhen focus is acquired, the output from t'ne ra~p generator follows the dash line porticn at 287b indicating that focus has been acquired.
Referring to line A of Figure 6~, a portion o~7 the focus ramp is shown extending between a first upper voltage at 285 and a second lower voltage at 288. The optimum 170cus point is located at 287a and corresponds with the pe2k of the FM signal applied to the FM
level detector 270 as shown on line C of Fi~ure 6~.
Line P ls a simplified version of the lens position transfer function 290 as shown more specifically With reference to line C of Figure 6A. The lens position transfer func'~io, line 290 extends between an u~per limlt of lens travel indicated at point 292 and a lower llr~it of lens travel indicated at point 295. The optimum lens focus position is indicated b~T a line 295.
The optimum lens focus point is therefore located at 299 .
Referring to line D of Figure 6E, there is shown the superlmposing of a kickback sawt~oth wave-form indicated generally ln the area 300 upon the lens posltion 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 295 again shows the point of optimum focus. The intersection of the line 296 with the line 292 at points 296a, 296~, 295c and 296d shows that the lens itself passes through the optimu~, lens focus position a plurall'~T of ti~es dul71rlct one acquire focus enable function.
Referring to line E of Figure 6P, the input to the FM level oetector indicates that during an ~;

_ .

oscillaior~ motlon Or the lens through the optimum ~ocus position as shown by the combined lens travel functlon characteristic shown in Figure D, the lens has the opportunity to acquire focus Or t~.e FM si~nal at rour locations indicated at the peaks Or waveforms 314, 316, 318 and 320.
The waveforms shown with rererence to Figure

6~ demonstrate that the addition Or a high frequenc~
oscillatln~ sawtooth klckback 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. This lmproves the reliability of achieving proper lens ~ocus during each attempt.
The rOcus servo system employed in the present invention functions to position the lens at the place calculated to provide optimum focusing Or the reflected read spot a~ter impinging upon the information track.
In a first mode of operation, tlle lens servo is moved under a ramp voltage waveform from its retracted position 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 tl~e lens to a point corresponding to the start of the ramping voltage. Thereafter, the lens automatlcally moved through lts focus acquire mode of operation and through the optimum focus position at which focus is acquired.
In a third mode Or operation, the fixed ramp-ing waveform ls used in comblnation with the output rrom an FM detector to stabilize the mirror at the optimum focus position which corresponds to the point at which a frequency modulated signal is recovered from the information bearin~ surface Or the video disc and an output is indicated at an Fi;i detector. In a further embodiment an oscillatory waveform is superimposed upon the ramping voltage to help the lens acquire proper focus. The oscillatory waveform is triggered `` ` 115083 by a num~er of alternative input signals. A first such illpUt si~nal is the output from the ~M detector indicating that the lens has reac~led the optimum focus point. A second tri6gering signal occurs a fixed time after the beginning of the ramp voltage ~aveform. A
third alternative input signal is a derivation of the differential tracking err~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 embodiment of the present invention, the focus servo is constantly monitoring the presence of FM
in the recovered frequency modulated signal. The focus servo can maintain the lens ln focus even though there is a momentary loss of detected frequency modulated signal. This is achieved by constantly monitoring the presence o~ FM signal detected rom the video disc.
Upon the sensing of a momentary loss of ~requency modulated signal, a timing pulse is generated which is calculated to restart the focus acquire mode of oper-ation. However, i~f the frequency modulated signalsare detected prior to the termination of this fixed perlod of time the pulse terminates and the acquire focus mode is skipped. If FM is lost for a period of time lon~er thall this pulse, then the focus acquire mode is automatically entered. The focus servo con-tinues to attempt to acquire focus until successful acquisition is achieved.
FOCUS SERVO SU~SYSTEM - NORMAL MODE OF OPERATION
The principal function of the focus servo sub-system is to drive the lens mechanism towards the video disc 5 until the ob~ective lens 17 acquires optimum focus of the light modulated signal bein~ 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 ler.s travel at wllich optimum focus can be achieved is 0.3 microns. The information bearing surface of the vldeo disc member 5 upon which the light reflective and light non-reflective members _. _ -47~-are pcsitioned, are ortentimes distorted due to imper-fections in tihe manufacture of the video disc 5. The video disc 5 is manufactured according to standards which ~ill make available for use on video disc players those video disc members 5 having errors which can be handled by the focus servo system 36.
In a first mode of operation, the focus servo su~system 3~ 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 rampins voltage for directlng the lens to move from its upper retracted position down towards the video disc member 5. Unless interrupted by external signals, the ramcing voltage continues to move the lens through the optimum focus position to a full lens down position correspond-ing to the end of the ramping voitage. The full lens do~n position can also be indicated by a limit switch which closes ~1'nen the lens reaches this position.
~ The lens acqulre period equals the time 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 posltlcn at the start of the ramping period. Operator interven-tion is not required to reset the lens to lts lens acquire mode in the preferred embodiment after focus was not achieved during the flrst attempt at acqulring focus.
In the recovery of FM video information from the video dise surface ~, lmperfections on the dlsc surface can cause a momentary loss of the FM signal being recovered. A gating means is provlded ln the lens servo subsystem 36 ~or detecting this loss FM
~rom the recovered FM video signal. This FM detecting means momentarily delays the reactivation of the ac-quire focus mode of operation of the lens servo sub-system 35 fcr a predetermlned time. Duri:;g this pre-determined time, the reacquisition of the FM slgnal prevents the FM detector means from causing the servo subsystem to restart the acquire focus mode of operation.

11~0836 ~ ,~
In the event that F~l ls not detected during this flrst predetermiiled time the FM detector means reactivates the ramp generator for generating the ramping signal which causes the lens to rollow through the acquire fccus procedure. At the end of the ramp generator period J the FM detector means provides a further signal for resetting the ramp generator to its initial position and to follow through the ramping and acquire focus procedure.
In a third embodiment, the ramping voltage generated by the ramp generator has superimpcsed upcn it an oscillatory sequence of pulses. me 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 focus procedure.
In a further embodiment, the generation of the oscillatory waveform is triggered a fixed time after the initiation of the ~ocus ramp signal. ~nile this is not as efficient as USillg the Fi~ level detector output signal as the means for triggering the oscilla-tor~r waveform ger.erator it provides reasonable and reliable results.
In a third embodiment, the osclllatory wave-form is triggered by the compensated tracklng error signal.
Referring to Figure 7, there is shown a schematic block diagram of the signal recovery sub-system 30. The waveforms shown in Flgure 8, lines P, C and D, illustrate certain of the electrical waveforms available within the signal recovery subsystem 30 during the normal operation of the player. Re~erring to Figure 7, the reflected light beam is indlcated at 4' and is divided into three principal beams. A first beam impinges upon a first tracking photo detector lndicated at 330, a second portion o~ the read beam 4' ~150~36`
4~
l~pinges UpOIl a second trackin~ photo detector 382 and the central information beam ls shown impinglng upon a concentric rin~ detector indicated generally at 384.
The concentric ring detector 384 has an inner portion at 386 and an outer portion at 388, respectively.
The output from the first track~n~ photo de-tector 380 is applied to a first trackin~ 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 ls applled 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 portions 386 and 388 of the concentric rin~ focusing element 384 are applied to a wide band amplifier 405 over a line 405. Al alternative embodiment to that sho~n would include a summation of the signals on the llnes 400 20~ and 404 and tne appllcation of this sum to the wide band ampllfier 405. The showlng of the llne 405 is schematic in nature. The output from the wide band ampllfier 405 is the time base error corrected fre-quency modulated slgnal 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 dlfferentlal ampllfier 408 over a line 410. The output from the second focus preamplifier 402 forms the second lnput to the differ-3 ential amplifier 408 over the line 412. The outputfrom the difrerential ampllfier 408 is the differential focus error signal applied to the focus servo 36 over the line 38.
The output from the first tracking preampll-fier 390 forms one input to a differentlal amplifier414 over a line 415. The output ~'romthe second track-ing preamplifier 394 forms a secona in,out to trle diffe~
ential amplifier 414 over a line 418. The output from the differential amplifier 414 is a differentlal track--5~- 1150836 in~ error si~nal applied to the trackln~ servo syste-, o~er the line 4 and applled to the s~op m~tion sub-system over the line 42 and an additional line 45.
Line A of Fi~ure 8 shows a cross-sectlonal view taken in a radial directlon across a video dlsc member 5. Light non-reflective elements are shown a' 11 and intertr~ck regions are shown at lOa. Such int~
traclc re~ions lOa are slmilar ln shape to llght re-flective elements 10. The ligh~ reflectlve regions 10 10 are planar in nature and normally are hi~hly polished surfaces, such as a thin aluminum layer. The light n~
reflective regions 11 in the preferred embodiment are light scattering and appear as bumps or elevations above the ~7anar surf~ce represented oy the light re-flective regions 10. The lengths of the line indicatedat 420 and 421 shows the center to center spacing of two adjacently positioned tracks 422 and 423 about a center traclc 424. A point 425 ln the line 420 and a polnt 425 in the llne 421 represents the crossover pclnt 20` between each of the adjacent tracks 422 and 423 ~hen - leavlng the central track 424 respectively. The cross-over polnts 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 lnformation tracks 422 and 424, respectively. The end Or line 421 at 429 represents the center of information track 423.
The waveform shown in line B o~ Figure 8 represents an idealized form Or the ~requency modulat~d si~nal output derived from the modulated light beam "' during radlal movement of the read beam 5 across the tracks 422, 424 and 423. This shows that a maximum frequency modulated signal ls avallable at the area indicated generally at 430a, 430b and 430c which correspond to the centers 427, 42~ and 429 of the in-formation tracks 422S 42~ an~ 423, reslJectively. A
minimum ~requency modulated si~nal ls av~ilable at 431a and 431b which corresponds to the crossover points 42~ and 426. The waveform shown on line ~ o~ Flgure 3 ` ` ` ~150836 -51_ ls generaied by radially moving a focused lens across the surface Or a vldeo disc 5.
Referrillg to line C of Figure 8, there ls shown the dlfferentlal tracking error signal generated ln the differentlal amplifier 414 shown ln Flgure 7.
The differential tracklng error signal ls the same as that shown ln lil~e A of Figure 6C e~cept for the detalls shown ln the Figure 6C for purposes Or explanation of the focus servo subsystem peculiar to that mode of operation.
Referrlng again to Flgure C of line 8, the differential tracking error signal output shows a first maximum traching error at a pOillt indicated at 432a and 432b which is intermediate the center 428 of an lnformaticn traclc 424 and the crossover point indi-cated at 425 or 426 depending on the direction of beam travel frcm the central track 424. A second maximum tracking erro~ is also shown at 434a and 434b corres-ponding to a track location interm~dlate the crossover points 425 and 425 between the informa'ion track 424 and the next adjacent tracks 422 and 423. Minlmum focus error is shown in line C at 440a, 440b and 440c corresponding to the center of the information tracks 422, 424 and 423, respectively. 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 description given with reference to Figure 6C as to the importance ~ ldenti-fying which of the minimum differentlal 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 ls shown the differential focus error si~nal output wave-form generated by the differenti~l amplifier 408. The waveform is indicated generally by a line 442 which moves in quadrature with tne differential tracking error signal silown with reference to line C of Figure 8.

115(~836 --5~--Rel'erring to Fl~ure 9, there ls shown a schematic block dia~ram of the tracking servo subsystem 40 emplo~red ln the vldeo disc pla~er 1. The dlfferen-tial trackins error ls applled to a trackln~ servo loop 5 lnterrupt swltch 4SO, over the llne 46 fro~ the signal recovery system 30. The loop lnterrupt signal ls ap-plied to a gate 482 over a llne 108 from the stop motion subsystem 44. An open fast loop command slgnal ls applied to an open loop fast gate 484 over a line 180~ 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 15 180b is diagra~matically shown as the sa~e signal applled to the carriage servo fast forward current generator over a line 180b. The console s~itch is shown entering an open loop fast gate 48~ over the line ~ 180b ' . The fast reverse command from the remote con-20 trol portion of the function generator 47 is appliedto the open loop ~ast gate 484 over the line 180b.
The fast reverse command from the console portlon of the function generator 47 is applied to the open loop fast gate 486 over the line 180b ' . The output from the 25 gate 484 is applied to an or gate 488 over a line 490.
The output from the open loop fast gate 480 is applied to the or gate 488 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 the or gate 488 ls applied to the gate 482 as a gating signal. The output from the tracking servo open loop switch 480 is applied to a ~unction 496 connected to one side ~ a resistor 498 and as an input to a tracking mirror amplifier driver 500 over a line 505 and an ampllfier and fre-quenc~r compens~t1on network 510. The other end of th~
resistor 498 is c onnected to one side of a capacitor 502. The other side of the capacitor 502 is connected to ground. The amplifier 5C0 receives a second input 115~)836 si~r.al from the stop motion subsystem 44 over the llne 106. The slnal on tne line 106 is a stop motlon com-pensation pulse.
The fuilction of the amplifier 510 is to provide a DC component of the trackln~ error, developed over the combination of the resistor 498 and capacitor 502, to the carriage servo system 55 during normal tracking periods over a line 130. The DC component from the junction 496 is gated to the carriage servo 55 by the play enabling signal from the function generator 47.
The push/pull amplifier circuit 500 generates a first trac~ing A signal for tlle radial tracking mirror 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 maximum operating efficiency when bimorph type mirrors are used. Accordingly, the pùsh/
pull amplifier circuit 500 comprises a pair of ampli-fier circuits, each one providing a three hundred volta~e swing for driving the tracking mirror 28.
~ Together, they represent a maximum of six hundred volts peak to peak signal for application over the lines 110 and 112 for 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 detalled 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.
TRACKING SERVO SUPSYSTEM - NO~MAL MODE OF OPERATION
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~ is in the range ~ 1.6 microns. The informalion indicia al~gned n an informa-tion track is approximately 0.5 microns in width. This leaves approximately one micron of empty and open space bet~een the cutermost reGions of the indicia positioned 54 llS0836 in adjacent ir.formation bearing tracks.
The function of the tracklng servo ls to direct the impin~ement of a focused spot of llght to impact directl~J upon the center Or an information track.
5 The focused spot of light ls approximately the same wl~th as the inrormation bearing sequence of lndlcia which form an information track. Obviousl~, maximum signal recovery ls achieved when the focused beam of llght ls caused to travel such that all or most of the light spot impinges upon the successively positioned light reflective and light non-reflectlve regions of the lnformation track.
The tracking servo is further identified as the radlal tracking servo because the departures from 15 the lnformation 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 frcm the differential tracking error signal 20 generated from the FM video information signal recov-ered from t;le video disc 5 in certain modes of oper~-tion. In a first mode ~ operation, when the carriage servo is causing the focused read beam to radially traverse t'ne information bearing portion of the video 25 disc 5, 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 3 focused reading beam 4 is caused to ~ump from one track to an ad~acent track, the differential tracking error is removed from the radial tracking ser~-o loop for ellminating a signal from the tracking mirror drivers which tend to unsettle the radlal mirror and tend to 35 require a longer period of time prior for the radizl trqc~{ing ~ervo subs~Jstem to reacquire proper tracking of the neYt adjacent informatioll track. In this embod-iment of operation where the differential tracking error is removed from the tracking mirror drivers, a substitute _55_ 1~50836 pulse is genera~ed for giving a clean unambiguous slgnal to t!le tracking mirror drivers to direct tl~e tracking mirror to move to itS next assigned location. This signal in the preferred embodiment is identified as the stop motion pulse and comprises regions Or 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 review, one mode ~ operation Or the video disc player removes the differential tracking error signal from application to the trac~cing mirror drivers and no additionPl signal is substituted therefor. In a further embodiment of operation o~ 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 flrst information traclc and depart for a second adjacent information track is used in combina-tion with a compensatlon signal applied directly to the radial tracking mirrors to direct the mlrrors to main-~ain focus on the next adjacent track. In the preferr~embodir,ent, 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 40s 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 Or the differential tracking error allowed to pass into the tracking mirror drivers is calculated to assist the radial traclcing mlrrors to achie~Je proper radial tracking.
Re~erring to Figure 11, there is shown a block diagram of the tangential servo subsystem 80. A first input signal to the tangential servo subs~Jstem 80 is 115~836 --,6--applled from the FM processing system 32 over the line 82. 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 chrom~
separa~or filter 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 signal. The vertical sync signal is applied to the stop motion su~system 44 over the line 92. The function of the chroma separator filter 523 's to separate the chroma portion fro~ the total video si~nal received from the Fl~ processing circuit 32, The output from the chroma separator filter 523 is ap-plled 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 applied to a burst phase detector circuit 526 over a line 52~.
The burst phase detector circuit 526 has a second input signal from a color subcarrler oscillator circuit 530 over a llne 532. The p~rpose of the burst phase de-tector circuit 526 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 circult 526 is applied to a sample and hold circuit 534 over a line 535. The function Or 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 tlme during which the f'ull line of video information containing that color burst signal, used in generatin~ the phase difference, is read from the disc 5.
The purpose of the burst gate separator 525 ls to generate an enabling signal lndicating the time during which the color bu-st portion Or the video l tS0836 waverorm is received from the FM processing unit 32.
The output ignal from the burst gate separator 52 is applied to the FM corrector portion Or the FM
processing system 3~ over a llne 144. The same burst 5 ~ate timinG sig~al is applied to the sample and hold circuit 54 over a line 538. The enabling signal on the line 53S gates the input from the burst phase de-tector 526 into tlle sample and hold circuit 534 during the color burst 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 color s~bcarr~er oscillator circuit 530 supplies the color subcarrier frequency 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 ~0 over the line 94.
The output from the sample and hold circuit ~ 53l' is applied to an automatic ~ain contrclled ampli-fier circuit 542 over a line 544. The automatic gain controlled amplifier 542 has a second input signal from the carriage position potentiometer as applled thereto over the line 84. The function of the signal on the line 84 is to change the gain of the amplifier 542 as the reading beam 4 radially moves from the inside track to the outside track and/or conversely h~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-reflective regions 11 with different dimensions from the outisde track to the lnside track. The purpose of the const~nt rotational speed from the spindle motor 48 is to turn the disc 5 t'nrough nearly thirty revol~tions per second to provide thlrty frames of in~ormation tothe television receiver 96. me length of a track at the outermost circum-ference is much longer than the length of a track at li501~36 -5~
tlle innermost circumrerence. Since the same amount of lnformation is stored in one revolution at ~cth the inner and outer circumfere~ce~ the si~e Or the reflec-tive and non-reflective re~ions 10 and 11, respectively~
are adjusted from the inner radius to the outer radius.
Accordingly, this change in size requires ~hat certain adjustmentsin the processing of the detected signal read from ihe video disc 5 are made for optimum opera-tion. 0ne of the required adjustments is to adjust the gain of the amplifier 542 which adjusts for the time b~se 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 5~6. The compensation netv:ork 545 is employed for preventing any system oscillations and instability. 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 ampll-fiers. The output from one ~ the push/pull amplifiers (not shown) is applied to the tangential mirror 26 over a line 88. The output fromthe second push/pull ampllf~er (not sho~1n) ls applied to the tangential mirror 2~ over a llne 90.
TIME ~ASE ERROR CORPECTION MODE: OF OPERATION
, The recovered FM video signal, from the surfaceof the video disc 5 is corrected, for time base errors introduced by the mechanics Or the reading process, in the tangential servo subsystem 80. Time base errors 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 F~ video signal. A typical tlme base error base correction system includes a highly accurate 115(~836 oscillator for generating a source of slgnals used as a phase standard for comparlson purposes. In the pre-ferred embodimentJ the accurate oscillator is conven-iently chosen to oscillate at the color subcarrier frequency. T:~e color subcarrier rrequency is also used during the wrlting process for controlling the speed of revolution of the writing disc during the writing process. In this manner, the reading process is phase controlled by the same highl~J accurate oscil-lator as was used in the writing process. The outputfrom the highly controlled oscillator is compared with the color burst signal of a Fr~ color video signal. An alternative system records a highly accurate frequency at any selected frequency during the writing process.
During the reading process, this frequency would be compared ~ith a highly accurate oscillator in the player and the phase difference between the t~o signals is sensed and is employed for the same purpose.
The color burst slgnal 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 highly accurate subcarrier oscillator signal for detecting the presence of any phase error.
In a different 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-determined locations in the recovered signal containing the recorded equivalent of the color burst signal.
~en the recorded information is not so highly sensi-tive to phase error, the comparison may occur at greater spaced locations. In general, the phase di~ference between the recorded signal and the locally generated signal is repetitively sensed at spaced locations on the recording surface for adjusting for phase rrors in the recovered signal. In the preferred embodiment this repetitive sensing for phase error occurs on each line of the FM video signa.

~1~W836 -6~-The detected phase error ls stored for a period of time extendin~ to the next sampllng process.
This phase error ls used to ad~ust the readlng posl-ticn of ~le reading beam so as to lmpinge upon the vldeo dlsc st a locatlon such as to correct for the phase error.
Repetitlve comparison of the recorded signal with the locally generated, highly accurate frequency, contlnuousl~ ad~usts for an incremental portion of the recovered video signal recovered durlng the sampllng periods.
In the preferred embodiment, the phase error changes as the reading beam radially tracks across the information bearing surface portion of the video disc 5.
In this embodiment, a further si~nal is required for ad~usting the phase error according to the lnstan-taneous location of the reading beam to adjust the phase error according to its lnstantaneous locatlon on the lnformation bearlng portion of the video disc 5.
This addltional signal ls caused by the change ln ph~Jsical slze of the lndicia contalned on the video disc surface as the radlal tracking posltion changes from the inner location to the outer locztion. The same amount of informatlon is contained ~t an inner radius as at an outer radlus and hence the lndicia must be smaller at the inner radius when compared to the lndlcia at the outer radlus.
In an alternatlve embodiment, when the size of the indlcia ls the same at the lnner radlus and at the outer radius, this additlonal slgnal for adjustlng for lnstantaneous radlal positlon ls not required.
Such an embodiment ~ould be operable with vldeo disc members which are in strip form rather than ln disc form and when the informatlon ls recorded uslng lndicla 3~ of the same size on a vldeo dlsc member.
In the pre~erred embodiment, a tangentlal mirror 26 ls t~le mechanism selected for correcting the time base errors introduced by the mechanlcs ~ the reading system. Such a m~rror is electronically -5:1-controlled and ls a means for changlng the phase ~ the recovered video signal read from the dlsc 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 ln tine when compared to the time and spacial location during which the phase error ~:~as detected. The amount of phase error determines the degree of chan~e in location and hence time in which 10 the information ls read.
~ hen no phase error is detected in the time base corr4cting system the point Or i~pingement of the read beam with the video disc surrace 5 is not moved.
l~hen 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 rOr processing at a point in time earlier or later when compared to ~ the comparison perlod. In the preferred embodiment, this is achieved by changing the spacial location of the point of intersection of the read beam ~ith the video disc surface 5.
Re~erring 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, 13B and 13C are used in conJunction with the block diagram shown in Flgure ~2 to explain the operation of the stop motlon system.
The video signal from the FM processing unit 32 is 3 applied to an input buffer stage 551 over the line 134.
The output signal from the burrer 551 is applied to a DC restorer 552 over a line 554. The function Or the DC restorer 552 is to set ~he blanking voltage level at a constallt uniform level. Variations in signal recording and recover~J oftentimes result in video signals available on the line 134 with dirrerent blank-ing levels. The output from the DC restorer 552 is applied to a wllite flag detector circuit 55O over a line 558. The runction Or the wnite flag detector 556 11$~836 is to idellti~ the presence of ar. all whlte 'evel v~deo s~gn~l existin~ during an entire line of one or both fields contained in a frame Or television information.
'~'hile the white 1'1ag detector has been described 2S
being detectin~ an all white video signal durlng a complete line interval of a frame of television in-formation, the white flag may take otller forms. Cne such form would be a special number stored in a line.
Alternativel~, the white flag detector can respond to the address indicia found in each video frame for the same purpose. Other indicia can also be employed. How-ever, the use of 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 from the delay circuif 560 is supplied to a vertical window generator 552 over a line 5~4.
~ The function of the window Oenerator 5S2 is to gener-20 ate an enabling signal for application tothe white flag detector 55~ over the line 55~ to coincide with that line interval in which the white flag signal ha~ been stored. The output signal from the generator 5~2 gates the predetermined ~rtion of the video sign 1 from-the Fl~ 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 30 569 and a further line 570. The gate 569 has as a second input signal, over the line 132, the STOP MOTION
~ODE enabling signal from the function generator 47.
The differential tracking error from the signal recovery subsystem 30 is applied to a zero crossing detector and delay circuit 571 over the lines 42 and 45. The function o~ the zero crossing detector circuit 571 is to identify when the lens crosses the mid-points 425 and/or 425 between two ad~acent tracks 424 ~nd 423.

~ :1508~6 -~3 -It ~ important to note that the dlrferentlal tracklnG
si~nal output also indlcates the same level signal at polnt 440c which identifies the optlmum focusing point at which the tracking servo system 40 seeks to position the lens in perfect tracking aligrlment on the mid-point 429 Or the track 423 when the tracklng suddenly ~umps from track 42~ to track 423. Accordingly, a means must be pro-~ided for recogni~ing the dif~erence between points 4~1b 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 ~he stop motion pulse generator 5~7 over a line 572. The stop motion pulse genera~ed in tlle generator 567 is applied to a plurality o~ locati~ns the first Or ~Jhich is as a loop interrupt pulse to the trackin~ 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 motio!l 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 theline 10~.
~ ith reference to line A of Figure 8, the center to center dlstance, 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 t~e mirror to s~ing past the one track to be ~umped.
Briefl-~J, the stop motion ~uise on the line 104 causes the radial tracking mirror 2~ to leave the track on hich it is tracking and ~ump ~o the next sequential track. A short time later, the radial tracking mirror ilsds~6 -~4-re~eives a stop motion compensation pulse to remove the added inertia and direct the tracklng mlrror into tra~king the next aàjacent track wl~hcut skipping one or more tracks before selecting a track for tracking.
In order to insure the optimum cooperation betlleen the stop motion pulse from the generator 567 and the stop motion compensation pulse frcm the gener-ator 573 the loop interrupt pulse on line 108 is sent to the tracking servo to remove the di~rerential trackil2 error signal from being applied to the track-ing error amplifiers 500 during the period of time that the mirrcr is purposely caused to leave one track und~r direction of the stop motion pulse from the generator 5~7 and to settle upon a ne;~t adjacent track under the direction of the stop motion compensation pulse from the generator 573.
As an i~.troduction to the detail understand-ing of the interaction between the stop motion system ~ 44 and the tracking servo system 40 the waveform s~lown 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 trackin& mirror 28. As previously discussed there are two driving si~nals applied to the tracking mirror 28. The radial tracking A signal represented by a line 574 and a radial tracking ~ signal represented by a line 575. Since the information track is normally in the shape Or a spiral there is a continuous track-lng control signal being applied to the radial tracking mirror for following 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.
A typlcal normal tracking mirror drive signal waveform for a single revolution of the disc is represented by the lengt!l of the line indicated at 57~. The two dis-continuities s~owll at ~78 and 580 on waveforms 574 and 575 respectively indicate the portlon of the normal trackin~ period at which a stop motion pulse is given.

liS083~
. , .
-s5-The stop motlon pulse is also referred to as a Jump back slænal and these two terms are used to describe the outpu~ rom the gener tor 567. me stoo motion pulse is represented b~J the small vertical'~ dlspose~
discontinuity present in the llnes 574 and 575 at polnts 578 and 580, respectively. The rem2~n ~g wave-forms contained in Figures 13A, 13~ and 13C are on an expanded time base and represent those electrlcal signals which occur ~ust before the beginning of thls Jump back perlod, through the ~ump back perlod and continulng a short duration beyond the ~ump back period.
The stop motion pulse generated by tne stop motlon pulse generator 5S7 and applled to the tracking servo system 40 over the llne 104 ls represented or.
line C o~ Figure 13A. The stop motion pulse ls ide~lly not a squarewa~e but has areas of pre-emphasis located generall-~ at 582 and ~84. These areas o~ p.e-emphasls insure ~timum reliability ln the stop motion system 44. The stop motion pulse can be described as rlsing to a first higher voltage level during the inltlal period of the stop motion pulse perlod. Next, the stop motlon pulse gradually falls o~f to a second voltage level, as at 583. m e level at 583 is ma'n-tained during the duratlon o`f the stop motion pulse period. At the termination o~ the stop motion pulse, the waveform falls to a negztive voltage level at 585 below the zero voltage level at 586 and rises gradually to the zero voltage level at 586.
Line D of Flgure 13 represents the d~f~eren-3 tial tracking error signal received ~rom the recover~system 30 over the llnes 42 and 46. The wave~orm shown on line D of Figure 13A is a compensated differ-entlal trackin~ error achieved through the use o~ the comblnatlon of a stop motion pulse and a stop motlon compensatlon pulse applied to the radial trac~ing mirror 28 according to the teachlr.g o~ the present lnventlcn.
Line G o~ Figure 13A represents the loop inte~
rupt pulse generated by the stop motlon pulse 2enerator ~,, l iS~)836 5~7 and applied to the tracl;ills servo subs~stem 40 over the line loS. A~ previously mentioned, lt ls best to remove the differentlal tracking error sign~l as repre-sented b~ the waveform on line D from appllcatlon to the radial tracking mirror 28 during the stop motion interval period. The loop lnterrupt pulse shown line G achieves this gatlng function. However, by lnspection, it can be seen that the differential tracking error slgnal lasts for a period longer than the loop interrupt pulse shown on line G. The waveform sho~n on line E is the portion of the differential tracking error signal shown on line D which survives the gatlng by the loop interrupt pulse shown on line G.
~he waveform shown on line E is the compensated track-ing error as ir.terrupted by the loop interrup~ pulsewhich is applied to the tracking mirror 28. Referrlng 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 in the stcp motion system 44. A zero crossing pulse is generated each time the di ferential error tracking slgnal sho~n in line D of Figure 13A crosses through a zero bias level. I~ile the information shown under the bracket 590 is helpf ul in maintaining a radial tracking mirror 28 in traclsing a slngle information track, such in-formation must be gated off at the beginning of the stop motion interval as indicated by the dashed lines 592 connecting 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 referrin~ again to line D, the differential tracking error signal rises to a first maximum at 594 and falls to a second opposite but equal maximum at 596. At point 598, ~IIe tracking mirror is passing over the zero crossing point 426 between two ad~acent tracks 424 and 423 as shown witll re~erence f o line .~ of Fi~ure 8.
This means that the mirror has traveled half way ~rom the first track 424 to tlle second track 423. At thls point indlcated by ~he number 598, the zerc crossin~

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 lSV~3 6 -5~ -i~formatio~l tracl;~ ls sho~n at the region 610 Or Llne A.
- The tracking error represents the slight side to side (radial) ~otion of the read beam 4 to the successively positiored reIlective and non-reflecti~e reglons on the disc 5 as prevlously described. A point 612 represents the star~ of a stop motion pulse. The uncompensated trac~ing error 1~ increasing to a first maximum indi-cated at 514. The region between 612 and 614 shows an increase in tracking error ind~cating the departure of the read beam from the track being read. From point 61~ the dirferential tracking error signal drops to a pcint indicated at 616 which represents the mid-poir.t of an information track as shown at point ~2s in line A
Or Figure 8. Hot~ever the distance traveled by the read beam between poi.nts 512 and 616 on curve A in Figure 13E is a movement o~ o.8 microns and is equal to lengtll of line 617. The uncompensated radial trao~:-ing error rises to a second ma.~imum at point 618 as the read beam begins to approach the neY~t 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 624. The radial track~ng mirror 28 possesses suffi-cient inertia so that it is not able to instantaneously stop in response to the differential trackir.g error signal detecting a zero error at point 622 as the read beam crosses the next adjacent information track.
Accordingly the raw tracking error increases to a point indicatcd at 624 wherein the closed loop servo-ing effect of the tracking servo subsystem slows the 30 mirror do~n and brings the read beam back towards the lnformation track represented by the zero crossing dif-ferential tracking error as indica~ed at point 625.
Addltional peaks are ldentifled at 626 and 628. These show a gradual damping of the differential tracking 35 error as the radial tracklng mirror becomes graduall~
positicned in its proper location to generate a zero tracking error such as at points 612 622, 625. Addi-tlonal zero crossing locations are indicated at 630 and 632. The po~tion of tne wavefo~m shot~n in line A

1~5081~6 e.~isting arter point 632 shows a gradual return of the raw tracking error to its ~ero positlon as the read spot gradually comes to rest on the next ad~acent track 423.
Point ~16 represents a ralse indication of ~ero tracki!l~ error as the read beam passes over the cer.ter 425 of t'ne region between ad~acent tracks 42 anà 423.
For optimum operation in a stop motion situa-tior. wnerein the read beam ~umps 'o the ne~t adjacent trac~, the time allowed for the radial tracking mirror 28 to reacquire proper radial tracking is 300 micro-seconds. This is indicated b~r the length of the line 634 sho~ln on line ~. ~y observation, it can be seen that the radial tracklng mirror 28 has not yet reac-quired zero radial error position at the expiration of tlle 300 microsecond time period. Obviously, if more time ~ere available to achieve tllis result, the wave-~ ~crm shown wlth re~erence to Figure A would be suitable ~or those systeMs having more time ror the radialtrac~ing mirror to reacquire zero differential trackin~
error on the center of the next adjacent track.
Re~erring briefly to line D o~ Figure 13, line 634 is redrawn to lndicate 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 di~rerential tracl~ing error shown in line D is capable of achieving proper radial tracking by the tracking servo subsystem within the 3 time frame allowed ror proper operation Or the video disc player 1. Referring briefly to line E Or Figure 13A, the remaining tracking error signal available a~ter interruption b~y the loop interrupt pulse is o~ the proper direction to cooperate with the stop motion compensatlon pulses descrlbed hereinarter to brlng the radial ~rac';_ng mirrcr ~o ~ts op~imllm ra~ial trackin~
position as soon as possible.
The stop motion compens~tion generator 573 shown wlth reIerence to F~gure 12, applies the wave~orm

7~, ~150836 sho~n in line E of Figure 13E to the radlal trackin~
mirror 28 b~y ~ay of the line 10~ and the amplifier 500 sho~n ir. Figure 9. The stop motion pulse directs the radi~l tr~cking mirror 28 to leave the tracking of one information track and begin to seek the tracklng of the next ad~acent track. In response to the pulse from the zero crossing detector 571 sho~n in Figure 12, the stop motion pulse generztor 557 is caused to generate the stop motion compensation pulse s'nown in line E.
lC Referring to line E of Figure 13E, the stop motioll co~pensation pulse waveform comprises a plural-ity of individual and separate regions indicated at 540, 542 and 544, respectively. The fi~t region 540 of the stop motion compensation pulse begins as the 15 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 motiorl pulse generator 557 generates the first ~ortion 540 of the compensation 20 pulse ~.~hich is applied directly to the tracking mirror 2~. The generation of tl~e flrst portion 640 of the stop motion compensation pulse has the effect of re-ducing the peak 624 to a lo~ler radial tracking displace-ment as represented by the ne~ peak 524 ~ as shown in line ~. It should be kept ln mind that the waveforms sholln in Figure 13B are schematic only to show the overall lnterrelationship of the various pulses used in the tracking servo subsystem and the stop motion subsystem to cause a read beam to ~ump from one track 30 to the next adjacent track. Since the peak error 624 is not as high as the error at peak 624, this has the effect of reducii~ the error at peak error point 526 and generally shifting the remainlng portlon of the ~Javeform to the left such that the rero crossings at 35 ~2~', 630' and 632' all occur sooner than they would have occurred ~Jit;lout the presence of the stop motion compensation pulse.
~ eferring back to llne E of Fl~ure 13~, the second portion 642 of the stop motion compensatlon . .. .

8 3 6 -7i-pulse is of a second polarlty when compared to the rirst region S40. The second portlon 642 of ~he stop motion compensation pulse occurs at a polnt in time to compensate for the tracking error shown at 626' of line ~. This results in ar. eYen smaller radial track-ing error being generated at that time and this smaller radial tracking error is represen~ed as point 526" on line C. Since the degree of the radial tracking error represented by the point 626" of line C is significantly smaller than that sllown with reference to point 626' Or ;ine ~, the maximum error in the opposite direction shown at poir.t 525' is again significantly smaller than that represented at point 625 of line A. This counteracting of the natural tendency of the radial trackinO mirrcr 2~ to oscillate baclc and forth over the information track ls furtller dampened as indicated b~ the furth2r movement to the left of points 628" and 525 with reference to their relative locations show in lines P and A.
Referring again to line E of ~igure 13~ and the t'ni~d region 544 of the stop motion compensation pulse, this region 644 occurs at the time calculated to dampen the remaining long term traclcing error as represented that portion of the error signal to the ri~ht of the zero crossin~ point 532" shown in 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 the motion Or the light beam as it is caused to depart from one information track being read to tlle next adjacent traclc 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 Figure 13~ can represent the movement in either directLon although tlle polarity of various signals would be changed to represent the difrerent direction of movement.

-` ~150836 ~ he cooperatlon ~etwee.l the stop motion sub-system 44 and the tracking se;vo subsystem 40 duril~ a stop motion period wlll now be described r:~th reference to Figures 9 and 12 and their rela~ed wave~orms. Re-fe ring to ~igure 9A the tracking servo su~s~stem 40ls in operation ~ust prior to the initiaticn of a stop mction mode to maintain the radial tr~cking mlrror ~8 in its position centered directly atop o~ infor~ation track. In order to maintain this position the di~fer-10 ential traclcing error is detected in the s~gnal recoverJsubsystem 30 and applied to the tracking servo subsystem 40 by the line 42. In this present operating mode the differential tracking error passes di-ectly thro~gh the tr-c~.ing servo loop s~itch 480 the a~?lifier 510 15 and the pusll/pull amplifiers 500. Th~t pc-tion of the waveform showr. a' 591 on line D of Figure 13A as being traversed.
Tl-e function generator 47 gener2tes a stop motion mode signal for applica~ion to the stop motion mode gate 5S9 over a line 132. The function of the stop motion mode gate 569 is to generate ~ pulse in response to t`ne proper location in a televlsion frame for the stop motion mode to occur. This pcint is de-tected bJ the combined operation of the total video signal from the FM processing board 32 be~ng applied to the white flag detector 556 over a line 134 ln com-blnation with the vertical sync pulse developed in the tangential servo system 80 and applied ~er a ltne 9~.
The wlndo~; gener~tcr 562 provides an enabling signal which corresponds with a predetermined po-tion of the vldeo signal containing the white flag indicator. The ~hite flag pulse applied to the stop motion mode gate 569 is gated to the stop motion pulse generator 567 in response to the enablillg signal received rom the function generatcr 47 over the line 132. The enabling slgnal from the stop motion mode gate ~59 nltiates the stop motion pulse as shown with reference to line C
of Figure 13A. The output from the zero crossing de-tector 571 indicates the end of the stop ~otion pulse .

l.t~0~36 period by application Or a si~nal to the stop motion pulse ~er.erator ~57 over the line 57~. The stop ~otion pulse rrom the generator 567 is applied to the traclcing servo loop interrupt switc`ll 430 by way Or the gate 482 and the line 108. The function of the track-in~ servo loop interrupt swi ch ~80 is to remove tlle dilferential tracking error currently being generated in the signal recovery subsystem 30 ~rcm the pusy/pull am?li~iers 500 driving the radial tracking mirror 2~.
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 rrom the generator 567 is applied to the ampli~iers 500 over the line 104.
The stop motion pulse, in essence, is substituted for the difrerential tracking error and provides a driving si~nal to the push/pull amplifiers 500 ror starting the read spot to move to the next adjacent information track to be read.
Tlle stop motion pulse ~rom the generator 567 is also applied to the stop motion compensation sequence generator 573 wnerein the waveform shown ~i'h reference to line H of Figure 13A and line r~ of Figure BR iS
generated. ~y inspection of line H, it is to be noted that the ccmpensation pulse sholYn 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. me compensa-tion pulse is applied to the push/pull amplifiers 500, 3 over the line lOZ shown in Figures 9 and 12, for damp-ing out any oscillation in the operation of radial tracking mirror 28 caused by the applicatlon of the stop motion pulse.
As previously mentioned, the compensation pulse is initiated at the termination of the loop interrupt signal. Occurring simultaneousl~r wit'n the generation Or the compensation pulse, the tracking servo loop interrupt switch 480 closes and allows the di~ferential tracking error to be reapplied to the ~ 3 ~

push/pull amplifiers 500. The typical waverorm avall-a`cle at this point is shol~n in line E of ~igure 13A
which cooperates ~th the stop motion com~ensatlon pulse to ~uickly bring the radial tracking mirror 28 into suitable radial tracking alignment.
Referring briefly to line A of Fig~lre 13C, two frames of televisicn video information beinO read from the video disc 5 are shown. Line A represents the differential tracking errcr signal hav~ng a~rupt dis-con~inuitles located at 550 and 652 representing thestop motion mode of operation. Discontinuities of smaller amplitude are shown at 654 and 656 to show the effect of errors on the surface of the video disc sur~ace in the differential track~ng error signal.
Line B of Figure 13C shows the FM envelo~e as it is read from the video disc surface. The stop motion periods at 653 and 660 show that the FM envelope is temporarily interrupted as the reading spot jumps tracks. Changes in the FM envelope at 662 and 664 show the tempcrary loss of FM as tracking errors cause the trackillg beam to temporarily leave the informatlon track.
In review Or the stop motlon mode of opera-tion, the following combinatio~s occur in the preferred 2~ embodiment. In a first embodiment, the differential tracklng error signal ls removed from the tracking mirror 28 and a stop motion pulse is substltuted therefor to cause the radial tracking mirror to ~ump one track fromthat track belng tracked. In this 3 embodlment, the stop motlon pulse has areas of pre-emphasis such as to help the radlal tracking mirror to regain tracking of the new track to which it has been positioned. The differential tracking error is re-applied into the tracking servo subsystem and cooperate 3~ with the ~top motion pulse applied to the radial track-inO mirror to reacquire radial tracl~in~. The dif~eren-tlal tracking error can be re-entered into the tracklng servo system for optimum results. In this e~bodiment, the duration of the loop lnterrupt pulse is varied for gating crr the a~plicatlon of the differential track-in~ error into the push/pull ampliflers 500. The stop motlon pulse is of fixed lenr~th ln thls embodiment.
Al alternative to thls fixed lengtll of the stop motion pulse is to lnitiate the end of the stop motion pulse at the flrst zero crossing detected after the ~eginning of the stop motion pulse was initiated. Suitable del~ys can be entered into this loop to remove an~
extraneous signals that may slip throu3h due to mis-alignment of the beginnil~ of the stop motion pulseand the detection of zero crossings in the detector 571.
A further embodiment includes any one of the above combinations and further includes the generation of a stop motion aompensation sequence. In the pre-ferred embodiment, the stop motion compensatlon se-quence is initiated with the terminatlon of the loop interrupt period. Coincldental with the termination Or the loop interrupt period, the differential track-20~ ing error is reapplied into the tracking servo sub-- system 40. In a further embodiment~ the stop motion compensation pulse can be entered into the tracking servo subsystem over the line 106 at a period 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 plurality of separate and distinct regions. In the preferred embodiment, the first region opposes the tendency of the tracking mirror to overshoot the next adjacent track and directs the mirror bacl; lnto radial tracking of that next ad~acent particular track. A second region is of lower amplitude than the first region and of opposite polarity to further compensate the motion of the radial tracking mirror as the spot again over- -shoots the center portion of the next adjacent track but in the opposite direction. ~he third re~ion sf the stop moiivn compensation sequence is of the same polarit~ as the first region, but Or si~nificantly lower amplitude to further compensate any te~dency of 75 ~ 836 the radial trackillg mlrror having the rOcus spot again leave the in~ormation track.
lhile in the preferred embodlment, the various resions of the stop motion sequence are sho~Yn to consist of separ~te individual regions. It is possible for these re&ions to be themselves broken down into in-dividual pulses. It has been found by experiment that the various regions can provide enhanced operation when separated by sero level signals. More specific-ally, a zero level condition exists between re~ionone and region tl~o allowing the radial tracking mirror to move under its own inertia without the constant appllcation of a portion of the compensation pulse.
It has also been found by experiment that this quiescent 1~ period of the compensation sequence can coincide with the reapplication of the differential trackin2 error to the radial tracking mirrors. In this sense, region one, showll at 640~ of the compensation sequence cooper-ates with the pcrtion ~04 sho~n in line E of Figure 13A
from the dirrerential trackin~ error input into the tracking loop.
~ y observatlon of the compensation waveform shcwn 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. Tt can also be observed that the period of the various regions begin at a first relatively short time period and gradually become longer in duratlon. Thls coin-cides with the energy contained in the ~raclcln~ mirror as it seeks to regain radial trackin~. Initially ln the track ~umping sequence, tlle energy is high and the early portions of the compensation pulse are appro-priately hi~h to counterac'c this energy. ~hereafter, as energy is removed ~rom the tracking mirror, the correcticns become less so as to bring the radial tracking mirror back into radial al~gnment as soon as possible.
P.efe-rin~ to Flgure 1~, there is shown a block diagram of the F~l processing system 32 employed 77 1~5083~
in the videQ disc pla-~er 1. The frequency modulated video sign~l recovered from the dlsc 5 fo ms the input to the F~l processing unit 32 over the line 34. The frequency modulated video slgnal is applied to a dis-tribution amplifler 670. The distributicn amplifierprcvides 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 F~ corrector circult 672 operates to provide variable gain amplification to the received freauency mcdulated video signal to compensate for the mean transfer function of the lens 17 as it reads the frequency modulated vldeo slgnal from the disc. The lens 17 is operating close to its absolute resolving po:~er and as a result, recovers the frequency modulated video signal with dif~erent ampli-tudes correspGnding to different frequencies.
The output froM the FM corrector 672 is applied to an Fl~ detector 574 over a llne 675. The FM detector gellerates discrimi,lated video for applica-tio.. to the remainlng circuits requiring such dis-crimirated video in the video disc player. A second output slgnal from the distribution amplifier 670 is applied to the tangential servo subsystem 80 over a line 82. A rurther output signal from the distrlbu-tion ampli~ier 670 is applied to the stop motion sub-system 44 over the line 134.
Referrlng to Figure 15, there is shown a more detalled block diagram of the FM corrector 672 sho~ln ln 3 Figure 14. The FM video signal from the amplifler 570 is applied to an audio subcarrier trap circult 576 over the line 673. The ~unction of the subcarrler trap circuit 676 is to remove all aud~o components ~rom the frequency modulated video slgnal prior to appl~cation to a ~requency selectlve variable gain amplifier 678 o~ e 5~.
The control signals ror operating the amplit'ler 678 include a first burst gate detector 582 having a plurality of input slgna's. A first input slgnal is the -78- 115083~
chro~ portion Or the FM video siænal as applied over a llne 1~. The second lnpu slgnal to the burst gate 682 ls the burst gate enable signal ~rom the tanger.tial servo system 80 over the llne 144. The function Or the burst gate 582 is to gate lnto an amplitude detector 68~ over a line 685 that portion o r the chroma signal corresponding to the color burst slgnal. 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 ~92 over a line 594. The runction Or the amplitude detector 584 is to deter~ine the first order lol~er chroma side band vector and apply it as a c~rrent representation to the summation circuit 15 688. The burst level ad~ust si~nal on the line 694 from the potentiometer 692 operates in conJunction l1ith this vector to develop a control signal to an ampli~ier 696. The output from the summation circuit is applied to the amnlifier 595 over the line 698. ~ne output from the amplifier 696 ls a control voltage for applica-tion to tlle ampli~ier 678 over a line 700.
Rererrins to Figu~e 15 there is shown a numoer Or wave~or~s helpful in understanding the operation of the FM corrector sh~n in Figure 15. The ~aveform repre-sented by the line 701 represents the FM correctortransfer ~unction in generating control vol~ages ~or application to the amplifier 678 over the line 700.
- The line 702 includes four sections Or the curve indi-cated generally at 702 ~ 7~4 706 and 708. These segments 702, 704~ 70~ and 708 represent the various control voltages generated in response to the com-parison with the instan aneous color burst signal amplitude and the pre-set level.
Line 710 represents the mean trans~er ~unction 3~ Or the objective lens 17 emplo-~-ed ror re~ding the successive li~ht rerlective regions ~ ar.d li~ht non-reflective reOions 11. It can be seen up~n inspection that the gain versus frequency response o~ the lens falls o~ as the lens reads the rrequency modulated .. . .

rep~eselltatlons of the vldeo signal. ~eferrin~ to the remair.lng portion of Flgure 16, there ls sho~n the frequenc~- spectrum of the frequency modul~ted sigr.als as read from the video disc. Thls lndicates that the 5 video sigllals are located prlncipally between the 7.5 and 9.2 megahertz region at which the frequenc~l re-sponse Or the lens shown on line 710 is showing a sig-nificant decrease. Accordingly, the control voltage from the amplifier 696 is variable in nature to com-pensate for the frequency response of the lens. Inthis m~nner the effective frequency respcnse of the lens is brought into a normalized or uniform region.
FM CORR~CTOR 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 entlre ~requency spectra of the recovered FM signals are all amplified to a level, relative one to the other to reacquire thelr substantially identlcal relationships one to the other as they existea during the recording process.
The microscopic lens 17 employed in the video disc player 1 has a mean transfer characteristic such that it attenuates the higher frequencies more than it attenuates t!le lower 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 signal such that the ratio of the luminance sig-nal to the chrominance signal is maintained regardless of the position on the disc ~rom which the FM video slgnal is recovered. This is achieved by measuring the color burst signal in the lower chroma side band and storing a representation of lts amplitude. This lo~.ler chroma side band signal functions as a reference ampli-tude.
The FM video signal is recovered from the vide~ disc as previously described. The chrominance signal is removed from the FM video signal and the burst gate er.able signal gates the color burst signal present on each line of Frl video information into a _ . . .

-80- ~ ~ ~ ~ 6 ccmparison operatio!l. The comparlson opera~lon e~rec-tively operates for sensing the dir~erence between tlle actual amplitude Or the color burst signal re-covered from the video disc surface with a reference amplitude. The reference amplitude has been ad~usted to the correct level and the comparlson process indi-cates an errcr slgnal between the recovered amplltude Or the color burst signal and the reference color burst signal indicating the difrerence in ampl~tude between the two signals. The error signal generated in this comparison operation can be identi~ied as the color burst error amplitude signal. This color burst error amplitude signal is employed for ad~usting the gain of a variable gain amplifier to amplify the signal presently being recovered from the video disc 5 to ampli~y the chrominance signal more than the luminance signal. This variable amplification provides a var-iable gain over the ~requency spectrum. mhe higher frequencies are ampli~ied more than the lower fre-quencies. Since the chrominance signals are at thehlgher frequencies, they are amplified more than the luminance signals. This variable amplification of signals results in e~fectively maintaining the correct ratio Or the luminance signal to the chrominance signal as the reading process radially moves ~rom the outer periphery to the inner periphery. As previously men-tioned, the lndicia representing the FM video signal on the video disc 5 change ln size from the outer periphery to the lnner periphery. At the lnner periphery they 3 are smaller than at the outer perlphery. The smallest size lndicia are at the absolute resolution power of the lens and the lens recovers the FM si~nal represented by thls smallest size lndicla at a lower amplltude value than the lower frequency members which are larger ln slze and spaced farther apart.
In a preferred mode of operation, the audlo signals contained in the F:~ video signal are removed from the FM vldeo signal be~ore application to the variable gain amplifier. The aud~o inrormation ls 8 1 :lS0~36 contqined around a number Or FM subcarrier slgnals and it has ~een found by experlence that the removal Or these FM subcarrler audlo slgnals provides enhanced correction Or the remainin~ video FM signal in the var-iable gain amplifier.
In an alternatl~e mode of operation thefrequency band width applied to the variable galn amplifier is that band width which is affected by the mean transfer function Or the ob~ective lens 17. More specifically, when a portion of the total FM recovered from the video disc lies in a range not affected by the mean transfer functlon, then this portion of the total waveform can be removed from that portlon of the F~l signal applied to the variable gain amplifier. In this manner, the operation of the variable ~ain ampli-fier is not complicated by signals having a frequency which need not be corrected because of the resolution characteristics of the objective lens 17.
The Fl~q corrector functions to sense the ab-solute value of a signal recovered from the video disc,which signal is known 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 ls an lndlcation of the addl-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 varlable gain is ~urther selective based on the amplitude Or 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 afrected signal. For a sec~nd level of error signal, the gain across the frequency spectra is ad~usted a different amount when compared ~50836 for the first color burst error amplitude signal.
~ eferring to Fi6ure 17, there ls sho~n a block di~gram of the FM detector circuit 674 shown with refer-ence to Figure 14. The corrected frequency modulated slgnal from the FM corrector 672 is applied to a llmiter 720 over the line 675. The output from the limiter is applied to a drop-out detector and compen-satlon circuit 722 over a line 724. It is the function of the limiter to change the corrected FM video signal into a discriminated video signal. The output from the drop-out detector 722 is applied to a lo~ pass filter 725 over a line 728. The output from the low pass fllter 726 is applied to a wide band video dis-tribution amplifier 730 ~hose function is 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 video 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.
Referrlng to Figure 19, there ls shown a block diagram of the audio processing circuit 114. The frequency modulated video slgnal from the distribution 3 amplifier 670 of the FM processing unit 32, as shown with reference to Figure 14, applies one of lts lnputs to an audio demodulator clrcuit 740. The audio demodu-lator circuit provides a plurality of output signals, one of which is applled to an audio variable controlled 3~ oscillator circuit 742 over a line 744. A first audio output is available on a llne 74;~ for application to the audio accessory unit 120 and a second audio output signal is available on a line 747 for application to the audio accessor~J unit 120 and/or the audio ~acks .

-8,- li50836 117 and 11~. The output from the audio volta6e con-trolled osclllator is a 4.5 megahert~ signal for appli-c~tion to the RF modulator 162 over the line 172.
Referring to Figure 20, there is shown a block diagram of the audio demodulator circuit 740 shown with reference 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~J 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 audio F~ discriminator 75~ provides an audio signal in the audio range to a SWitCi~ g circuit 760 over a line 752.
The second band pass filter 752 havin2 a central frequenc~T of 2.8 megahert~ operates to strip 20 the second audio channel from the FM video input signal - and applies this frequenc~ spectra Or the total FM
signal to a second video FM discriminator 764 over a line 765. The second audio channel in the audio fre-quenc~J range applied to the switching circuit 750 over a line 768.
The s~itching circuit 760 is provided with a plurality of additional input signals. A first of which is the audio squelch signal from the trackin~
servo subsystem as applie~ thereto over the line 116.
3 Thc second input signal ls a selection command signal from the function generator 47 as applied thereto over the line 170. The output from the switc~ g circuit ls applied to a first amplifier circuit 770 over a line 771 and to a second amplifier circuit 772 over a line 77~. The lines 771 and 773 are also connected to a summation 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 channel one audio signal for application to ` 1150836 the audio jack 117. The output from the second ampli-fier 772 is the second channel audio slgnal ~or application tothe audio ~ack 118~ The output rrom the thlrd amplifier 776 is the audio si~nal to the audio VC0 742 over the llne 744. Referring briefly to Fi~ure 21, there is shown on line A the rrequenc~J
modulated envelope as received from the distribution amplifier in the F~ processing unit 32. me output of the audio FM discriminator for one channel ls shown on line ~. In th~s manner, the FM signal is changed an audio frequency signal for applicatlon to the switch-lng circuits 760, as previously descrlbed.
Xeferring to Figure 22, there is shown a block diagram of the audio voltage controlled ~scilla-tor 742 as shown with reference to Figure 19. Theaudio signal ~rom the audio demodulator is applied to a band pass ~ilter 780 over the llne 744. The band pass filter passes the audio frequency signals to a summation circuit 782 by way of a pre-emphasis circuit 784 and a first line 786 and a second line 788.
The 3.58 megahertz color subcarrier frequency from the tangentlal servo system 80 is applled to a divide circuit 790 over tne line 140. The divide circuit 790 divides the color subcarrier frequency by 2048 and applies the output signal to a phase detector 792 over a line 794. The phase detector has a second lnput slgnal from the 4.5 megahertz voltage controlled oscillator circuit as applied to a second divide clr-cuit 798 and a flrst line 800 and 802. The divlde 3 circuit 798 divides the output of the VC0 796 by 1144.
The output from the phase detector ls applied to an amplitude and phase compensatlon clrcuit 804. The output from the clrcult 804 is applled as a thlrd input to the summation circult 782. The output from the voltage controlled oscillator 796 ls also applied to a low pass filter 806 ~ the line 800 and a ~cond line 806. ~he output from the filter 806 ls the 4.5 megahertz ~requency modulated slgnal for appllcatlon to the RF modulator 182 by the line 172. The function 115~836 oI' the audio voltage controlled osclllator clrcult is to prepare the audio signal received rrom the audio demod-ulator 740 to a frequency wi~ich can be applied to the ~F modulato~ 152 so as to be processed by a standard televislon recelver 9S.
Referring brlefly to Figure 23, there can be seen on line A a waveform representlng the audio signal received from the audio demodulators and available on the llne 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 ln the VC0 circuit 796 for applica-tion to the RF modulator 152.
Re~erring to Figure 24, there ls shown a 15 block diagram of the RF modulator 162 employed in the video disc player. The video information signal from the Frl 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 signal. The output from the restorer 810 is applled to a first balanced modulator 812 over a line 814.
The 4.5 megahertz modulated signal from the audio VC0 is applied to a second balanced modulator 81O
over the~llne 172. An osclllator circuit 818 functlons 25 to generate a suitable carrier frequency corresponding to one of the channels of a standard televislon re-celver 96. In the preferred embodiment, the Channel 3 frequency is selected. The output rrom 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 o~tput from the modulator 812 is ap-plied to a summation clrcuit 824 over a llne 826. The output from the second balanced modulator 816 ls 35 applied to the summatlon circuit 824 over the llne 828. Referring briefly to the wave~orm shown in Figure 25, llne A sho~s the 4.5 megahertz frequellcy modulated signal received rrom the audlo VC0 over the llne 172. Line ~ o~ Figure 25 shows the vldeo signal 115~36 -8~-received fro~ the FM processing clrcuit 32 over the line 154. The output from the summation circuit 824 is showll on line C. The signal shown on line C ls suitable for processing by a standard television re-ceiver. me signal shown on line C is such as to causethe standard television receiver 96 to display the sequential ~rame in~ormation as applied thereto.
Rererring 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 infor~ation track at the outside radius demonstrates 15 an eY.treme degree of eccentrlcity arising from the effect of uneven cooling of the video disc 5.
Referring briefly to Figure 27, there is shown a schematic view o r a video disc 5 having contained ~thereon an in~ormation track at an outside radius - 20 represented bJ the numeral 834. An information track at an inside radius is represented by the numeral 836.
This Figure 27 shows the eccentricity efI'ect of an off-center relationship of the tracks to a central aperture indicated generally at 838. More specifically, 25 the off-center aperture effectively causes the dlstance represented by a llne 840 to be effectively different from the length of the llne 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 ~ operation Or the focus servo 36.
The logic diagram shown wlth reference to Figure 28 comprises a plurality oi AND functlon gates 35 shown at 850, 852, 854 and 856. The AND function gate 850 has a pluralit~ of inpu~ signals3 ~!le first of which is the r~N~ JA~L~ applied over a line 858. The second input signal to the AND gate 850 is the ~OCUS
SIGNAL applied over a llne 860. The AND gate 852 has .

-87- 1 1S~B3 6 a plur21it-~ of input si~nals, the ~irst Or whlch is the FOCUS SI~i~AL applied thereto ~or the line 860 and a second lille 862. The second input si&nal to the AND
function gate 852 is the lens enable sigilal on a llne 5 804. The output rrom the AND runction gate 852 is the ramp enable signal which is available for the entire period the ramp signal is being generated. The output frcm the AND function gate 852 is also applied as an input signal to the AND runction gate 854 over a line lo 866. The AND ~unction gate 854 has a second input signal applied over the llne 868. The signal 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 generator 278 for disalbing the ramping wave~orm at that ~int. The AND function gate 856 is equipped with a pluralit~J of input signals, the first of which is the FOCUS ~IGi~lAL applied thereto over the line 860 ~nd an additional lire 870. The second input signal 20 to the A~D function gate 855 is a ramp and signal applied over a line 872. The output signal from the AND ~unction gate 856 is the withdraw lens enabling signal. ~rierly, the logic circuitry shown with refer-ence to Figure 28 generates the basic mode o~ operation 25 o~ the lens servo. Prior to the function generator 47 generating a lens enable signal, the LENS ENA~LE signal is applied to the AND ~unction ~ate 850 along wlth the FOCUS SIGNAL. This indicates that the player is in an inactivated condition and the output si~nal from the 3 AND runction gate indicates that the lens is ln the fully withdrawn position.
~ en the ~unction generator generates a lens enable signal for application to the AND gate 852, the second input signal to the AND gate 852 indicates that the video disc pla~e. 1 is not in the focus mode.
AccGrdingl~, the output signal rrom the .~ND gate 852 is the ramp enable signal which initiates the ramping waveform shown with re~erence to l~ne P of Figu-e 6A.
The ramp enable signal also indicates that the focus ~- ~0836 -8~ -ser~o is in the acqulre focus mode ~ operatlon and this enabli2~ signal forms a flrst lnput to the AND
function gate 85~. The second input slgnal to the AND
function gate 854 indicates that ~M has been success-rully detected and the output from the A~TD ~unctiongate 854 is the focused acquire signal indicatir~ that the normal play mode has been successfully entered and frequency modulzted video signals are being recovered rrom the surface of the vldeo dlsc. The output from 10 the AND function &ate 856 lndicates that a successful acquisitlon 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 FOC~tS SIGI~qL on the llne 15 870 indicates tilat focus was not successfully acquired.
Accordingl~, the output from the AND function gate 855 ~ithdraws the lens to its uppe~ position at whlch time a focus acquire operation can be reattempted.
Referring to Figure 29, there is sho,1n a logic 20 dlagram illustrating the additional mcdes o~ operation of the lens servo. A first AND gate 880 is equipped witll ~ pluralit~J of input signals, the first Or which ~s the focus signal generated by the A~ gate 854 and applied to the AND gate 880 over a line 853. The 25 FM DETECl' SIGNAL is applied to the AND gate 880 over a line 8~2. 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 llne 888.
The output from the OR function gate 884 is applied to 30 a first one-shot circuit shown at ~90 over a line 892 to drive the one-shot into its state for generating an output signal on the line 894. Tlle output slgnal on the line 894 is applied to a delay circuit ~96 over a second line ~98 and to a second AND function gate 900 35 over a line 902. The AND function gate 9CO ls equlpped with a second input signal on whic~l the FM detect signal is applied over a line 90l~. The output from the AND function gate-900 is applied to reset the first one-shot ~90 over a line 90S.

_.. ~ . ... . .. . .. .

1'150836 sg -The output from the delay circuit 895 ls ap-plied as a first input signal to a third AND f~nction g~te 908 over a line 910. The AND function gate 908 is equipped with a second input signal which is the RAriP KE~ IGi~L applied 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 applied at least a fourth AND functlon gate 918 over a line 920. The second inpu~ sl~nal to the AN~ function gate 918 is the output signal from the rirst one-shot 890 over the line 894 and a secon~ 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 the timing period of t~le focus ramp voltage sho;wn on line B of Figure 6A. The lnput signal on line 925 activates the one-s'not 924 to generate its output signal on a line 928 for application to a delay circuit 930. The output from the delay circult 930 forms one input to a sixth A~ function gate 932 over a line 934. The AI~D function gate 932 has as its second irput signal the FOCUS SIGiJAL available on a line 936.
The output fro~ 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 functlon gate 884 over the line 888.
The one-shot 890 is the circuit employed for generating the timing waveform shown on lir.e D of Figure 6Q. The second one-shG~ 9211 is employ d ~or generatin~ a waveform shown on line ~ of Figure oA.
The third one-shot 940 is employed for generating the waverorm shown on line F of Figure 6A.

~o llS0836 In one form of operation, the logic circultry shown in Fig ure 29 operates to delay the attempt to reac~uire focus due to momentary losses cf FM caused by imperfections on the video disc. This ls achieved in 5 tlle following manner. The AND function gate 880 gener-ates an output signal on the line 885 only when the video disc player is in the focus mode and there ls a temporary loss of FM as lndicated by the FM DEr~CT SIGl~AL
on llne 882. The output signal on the llne 885 triggers 10 the first one-shot to generate a tim~ng perlod of pre-determined short length during which the video disc player will be momentarily stopped from reattemptin~;
to acquire lost focus superficially indicated by the availability of the FM DEl`~CT SI~NAL on the line 882.
15 The output from the first one-shot forms one lnput to t;le AND function gate 900. If the FM detect signal ava~lable on 9~4 reappears prior to the timlng out of the tlme period of the first one-shot, the output from the Ai~D circuit 900 resets the first one-shot 890 and 20 the video disc player continues reading the reacquired FM signal. Assuming that the first one-shot is not reset, 'chen the following sequence of operation occurs.
The output from the delay circuit 895 is gated through the AND function gate 908 by the ~AMP R~:SET SIGNAL
25 available on line 912. The RAMP RESET SIGNAL ls avail-able in the normal focus play mode. The output 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 lts focus operation. The output from the OR
30 gate 914 is also applied to a turn on the second one-shot which establishes the -shape of the ramping wavefo~m shown in Figure B. The output from the second one-shot 924 is essential coextensive in tine with the ramping period. Accordingly, when the ot~tput from the second 35 one-shot is generated, t;he machine is ca-;sed to return to the attempt to acquire ~ocus. When fecus is success-fully acquired, tlle ~()CU~ ~LGi~lAI. on 1 Lne 936 does not gate the output from the delay circuit 930 through to the OR function gate 914 to restart the automatlc focus ~1 ;~

.

1150~36 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 rOcus acquire mode. When focus is success-fully acquired, the output from the delay line 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 (28)

92

1. A focus servo system for use in a player apparatus for deriving information from an information bearing surface, said player apparatus including optical means for directing a source beam of radiation along a prescribed optical path to said surface, said focus servo system comprising:
objective lens means for focusing the source beam on the information bearing surface;
focus error detection means for detecting the position of said objective lens means relative to the information bearing surface;
lens driver means, selectively responsive to said focus error detection means, for moving said objec-tive lens means relative to the information bearing sur-face along the path of the source beam;
focus acquisition signal means, selectively generating an output to said lens driver means in a focus acquisition mode, for driving said objective lens means in a first direction through a predetermined range of travel that includes an optimum focusing posi-tion; and kick-back signal means, responsive to said focus error detection means, for providing an additional output to said lens driver means to intermittently drive said objective lens in a direction opposite to said first direction, whereby said objective lens means scans back and forth past said optimum focusing position.
objective lens means for focusing the source beam on the information bearing surface;
focus error detection means for detecting the position of said objective lens means relative to the information bearing surface;
lens driver means, selectively responsive to said focus error detection means, for moving said objec-tive lens means relative to the information bearing sur-face along the path of the source beam;

focus acquisition signal means in a focus acquisition mode, for driving said objective lens means in a first direction through a predetermined range of travel that includes an optimum focusing position; and kick-back signal means, responsive to said focus error detection means, for providing an additional output to said Iens driver means to intermittently drive said objective lens in a direction opposite to said first direction, whereby said objective lens means scans back and forth past said optimum focusing position.

2. A focus servo systemas defined in Claim 1, and further including:
information detection means for detecting said information as said objective lens means reaches said optimum focusing position and for disabling said focus acquisition signal means in response to detection of said information.

3. A focus servo system as defined in Claim 2, and further including restart means for restarting said focus acquisition mode if said focus acquisition signal means drives said objective lens means through said predetermined range of travel without said infor-mation detection means detecting said information.

4. A focus servo system as defined in Claim 3, wherein said restart means is responsive to said information detection means to restart said focus acqui-sition mode, even after once disabling said focus acqui-sition signal means in response to detection of said information, if said information detection means does not continue to detect said information.

5. A focus servo system as defined in Claim 1, and further including:

focus servo switching means for selectively establishing open and closed loop modes of operation, said switching means disconnecting said lens driver means from said focus error detection means in said open loop mode and connecting said lens driver means to said focus error detection means in said closed loop mode.

6. A focus servo system as defined in Claim 5, wherein said focus servo switching means establishes sais open loop mode of operation during said focus acquire mode.

7. A focus servo system for use in a video player apparatus in which video information is derived from information tracks on a video disc surface, said video player apparatus including optical means for dir-ecting a source beam of radiation along a prescribed path to said disc surface, said focus servo system comprising:
objective lens means for focusing the source beam on the surface;
focus error detection means for detecting the position of said objective lens means relative to the disc surface;
lens driver means, selectively responsive to said focus error detection means, for moving said objective lens means relative to the disc surface along the path of the source beam;
focus acquisition signal means, selectively generating an output to said lens driver means in a focus acquisition mode, for driving said objective lens in a first direction through a predetermined range of travel that includes an optimum focusing position loca-ted a prescribed distance from the disc surface; and kick-back signal means, responsive to said focus error detection means, for providing another output to said lens driver means to intermittently drive said objective lens in a direction opposite to said first direction, whereby said objective lens means scans back and forth past said optimum focusing posi-tion as said focus acquisition dignal means tends to drive said objective lens means through said range of travel.

8. A focus servo system as defined in Claim 7, wherein said kick-back signal means includes differ-entiation means for differentiating an output signal from said focus error detection means.

9. A focus servo system as defined in Claim 7, and further including:
information detection means for detecting said information as said objective lens means reaches said optimum focusing position and for disabling said focus acquisition signal means in response to detection of said information.

10. A focus servo system as defined in Claim 9, and further including restart means for restarting said focus acquisition mode if said focus acquisition signal means drives said objective lens means through said predetermined range of travel without said infor-mation detection means detecting said information.

11. A focus servo system as defined in Claim 10, wherein said restart means is responsive to said information detection means to restart said focus acqui-sition mode, even after once disabling said focus acqui-sition signal means in response to detection of said information, if said information detection means does not continue to detect said information.

12. A focus servo system as defined in Claim 11, and further including:
delay means for delaying said restart means for a predetermined period of time in the event said information detection means does not continue to detect said information, after previously disabling said focus aquisition signal means in response to detection of said information.

13. A focus servo system as defined in Claim 9, and further including:
focus servo switching means for selectively establishing open and closed loop modes of operation, said focus servo switching means disconnecting said lens driver means from said focus error detection means in said open loop mode and connecting said lens driver means to said focus error detection means in said closed loop mode.

14. A focus servo system as defined in Claim 13, wherein said focus servo switching means establishes said open loop mode of operation during said focus acquire mode.

15. A focus servo system for use in a video player apparatus in which video information is derived from information tracks on a surface of a video disc, said video player apparatus including optical system means for directing a source beam of radiation along a prescribbed path to said disc surface, and spindle means for rotating said disc at a predetermined angular rate of rotation, said focus servo system comprising:
objective lens means for focusing the source beam on the surface;

focus error detection means for detecting the position of said objective lens means relative to the disc surface;
lens driver means, selectively responsive to said focus error detection means, for moving said objec-tive lens means relative to the disc surface along the path of the source beam;
focus acquisition drive signal means, selec-tevely generating an output to said lens driver means in a focus acquisition mode, for driving said objective lens toward an optimum focusing position located a pre-scribed distance from the disc surface; and spindle lock detector means, responsive to the spindle means, for detecting the angular rate of rotation of the disc, said spindle lock detector means inhibiting said focus acquisition signal means if the rotation rate of the disc is less than a predetermined rotation rate.

16. A focusing method for use in a player apparatus for deriving information from an information bearing surface, said player apparatus including optical means for directing a source beam of radiation along a prescribed optical path to said surface, said method comprising the steps of:
directing the source beam through an objective lens means onto the information bearing surface;
detecting the position of said objective lens means relative to the information bearing surface;
driving said objective lens in a first direc-tion through a predetermined range of travel that inc-ludes an optimum focusing position; and intermittently driving said objective lens in a direction opposite to said first direction, whereby said lens driver means scans back and forth past said optimum focus ing position.

17. A focusing method as defined in Claim 16, and including the further step of:
detecting the information as said objective lens means passes through said optimum focusing position and for halting said objective lens means in response to detection of said information.

18. A focus servo system for use in a player apparatus for deriving information from an information bearing surface carrying a spiral-shaped information track in the form of a lineal series of first and sec-ond regions, each of the first regions is a planar-shaped region and each of the second regions is in the form of a discontinuity out of the plane of the first region, comprising:
a radiation source for emitting a reading light beam having an optical axis;
a lens driver and objective lens means;
said objective lens means including an objec-tive lens for focusing said reading beam at a fixed dist-ance spaced from said lens and a single coil for moving said lens to a preferred position at which said read beam is focused on an individual turn of the spiral-shaped information track;
said lens driver being connected to said coil;
said lens driver means being selectively responsive to at least one drive signal for moving said objective lens means relative to the information track along the path of said reading beam;
first control means for generating a first drive signal for application to said lens driver means to move said objective lens means along a distance be-tween an upper out-of-focus position and a down beyond-focus position;
second control means for generating a second drive signal for application to said lens driver means to move said objective lens means along a predetermined portion within the range of the first control means;
focus acquisition signal means having a least first and second modes of operation;
said first mode of operation being employed for enabling said first control means and for disabling said second control means;
said second mode of operation being employed for disabling said first control means and for anabling said second control means;
signal means for generating a lens enabling control signal for application to said focus acquisition signal means for causing said focus acquisition means to be initially placed in its first mode of operation and said first drive signal moves said objective lens towards its down position; and information detection means for detecting the preferred position of said objective leans means rela-tive to the information-bearing surface to indicate that the information track is at the in-focus position and for generating an in-focus control signal for applica-tion to said focus acquisition signal means for changing its mode of operation from its first mode of operation to its second mode of operation whereby said first con-trol means is disabled and said second control means is enabled for controlling the movement of said objective lens means during the in-focus position.

19. A focus servo system for use in a player apparatus for deriving information from an information bearing surface carrying a spiral-shaped information track in the form of a lineal series of first and second regions, each of the first regions is a planar-shaped region and each of the second regions is in the form of a discontinuity out of the plane of the first region, comprising:

a radiation source for emitting a reading light beam having an optical axis;
a lens driver and objective lens means;
said objective lens means including an objec-tive lens for focusing said reading beam at a fixed distance spaced from said lens and a single coil for moving said lens to a preferred position at which said read beam is focused on an individual turn of the spiral-shaped information track;
said lens driver being connected to said coil;
said lens driver means being selectively re-sponsive to at least one drive signal for moving said objective lens means relative to the information track along the path of said reading beam;
first control means for generating a ramp shaped first drive signal for application to said lens driver means to move said objective lens means along a distance between an upper out-of-focus position and a down beyond-focus position;
second control means for generating a focus error second drive signal for application to said lens driver means to move said objective lens means at a preferred focus position within the range of the first control means to maintain said read beam focused upon the information track;
focus servo switching means for selectively establishing mutually exclusive open and closed loop modes of operations;
said open loop mode of operation being employed for enabling said first control means and for disabling said second control means;
said closed loop mode of operation being em-ployed for disabling said first control means and for enabling said second control means;
signal means for generating a lens enabling control signal for application to said focus servo switching means for causing said focus servo switching means to be initially placed in its open loop mode of operation and said first drive signal moves said objective lens towards its down position; and tracking error detection means for detecting the preferred position of said objective lens means rela-tive to the information-bearing surface to indicate that the information track is at the in-focus position and for generating an in-focus control signal for application to said focus servo switching signal means for changing its mode of operation from its open loop mode of operation to its closedloop mode of operation whereby said first control means is disabled and said second control means is enabled for controlling the movement of said objec-tive lens means during the in-focus position.

20. A focus servo system for use in a player apparatus for deriving information from an information bearing surface carrying a spiral-shaped information track in the form of a lineal series of first and second regions, each of the first regions is a planar-shaped region and each of the second regions is in the form of a discontinuity out of the plane of the first region, comprising:
a radiation source for emitting a reading light beam having an optical axis;
a lens driver and objective lens means;
said objective lens means including an objec-tive lens for focusing said reading beam at a fixed distance spaced from said lens and a single coil for moving said lens to a preferred position at which said read beam is focused on an individual turn of the spiral-shaped information track;
said lens driver being connected to said coil;
said lens driver means being selectively re-sponsive to at least one drive signal for moving said objective lens means relative to the information track along the path of said reading beam;
first control means for generating a first drive signal for application to said lens driver means to move said objective lens means along a distance between an upper out-of-focus position and a down beyond-focus position;
focus error detection means for generating a focus error signal as a second drive signal for appli-cation to said lens driver means to move said objective lens means along a predetermined portion within the range of first drive signal;
focus servo switching means for selectively establishing mutually exclusive open and closed loop modes of operations;
said open loop mode of operation being em-ployed for connecting said first drive signal to said lens driver means and for disconnecting said second drive signal from said lens driver means;
said closed loop mode of operation being em-ployed for disconnecting said first drive signal from said lens driver means and for connecting said second drive signal to said lens driver means;
said closed loop mode of operation being em-ployed for disabling said first control means and for enabling said second control means;
signal means for generating a lens enabling control signal for application to said focus servo switching signal means for causing said focus servo switching means to be initially placed in its open loop mode of operation and said first drive signal moves said objective lens towards its down position; and information detection means for detecting the preferred position of said objective lens means relative to the information bearing surface to indicate that the information track is at the in-focus position and for generating an in-focus control signal for application to said focus servo switching means for changing its mode of operation from its open loop mode of operation to its closed loop mode of operation whereby said first control means is disabled and said second control means is enabled for controlling the movement of said objec-tive lens means during the in-focus position.

21. A focus servo system as recited in Claim 20, wherein said information detection means includes said focus error detection means for generating an in-focus control signal for indicating an optimum focusing position.

22. A focus servo system as recited in Claim 20, wherein said information detection means includes a tracking error detection means for indicating an optimum focusing position.

23. A focus servo system for use in a player apparatus for deriving information from an information bearing surface carrying a spiral-shaped information track in the form of a lineal series of first and sec-ond regions, each of the first regions is a planar-shaped region and each of the second regions is in the form of a discontinuity out of the plane of the first region, comprising:
a radiation source for emitting a reading light beam having an optical axis;
a lens driver and objective lens means;
said objective lens means for focusing said reading beam on an individual turn of the spiral-shaped information track;
said lens driver means being selectively re-sponsive to at least one drive signal for moving said objective lens means relative to the information track along the path of said reading beam;
first control means for generating a first drive signal for application to said lens driver means for moving said objective lens means along a distance between an upper out-of-focus position and a down beyond-focus position;
said first control means having at least a first and a second mode of operation;
said first mode of operation of said first control means being employed for driving said objective lens means from said upper out-of-focus position towards a lower beyond-focus position at a first rate of speed;
said second mode of operation of said first control means being employed for driving said objective lens means from said lower beyond-focus position to said upper out-of-focus position at a second rate of speed greater than said first rate of speed;
focus error detection means for generating a focus error signal as a second drive signal for appli-cation to said lens driver means for meving said objec-tive lens means along a predetermined portion within the range of the first control means;
focus acquisition signal means having at least first, second and third modes of operation;
said first mode of operation of said focus acquisition signal means being employed for enabling said first mode of operations of said first control means and for disabling said second control means;
said second mode of operation of said focus acquisition signal means being employed for disabling said first control means and for enabling said second control means;
signal means applied to said focus acquisition signal means for causing said focus acquisition means to be initially placed in its first mode of operation where-by said first drive signal moves said objective lens towards its down position;

information detection means for indicating the position of said objective lens means relative to the information-bearing surface and said detection means having a first output signal and a second output signal;
said first output signal indicating that the information track is at the infocus position, and said second output signal indicating that the information track is not in-focus;
means for sensing at least the position of said objective lens means at a lower limit of lens travel position and for generating a lower limit of lens travel control signal;
said third mode of operation of said focus acquisition signal means being responsive to said lower limit of lens travel control signal and said second out-put signal of said detection means for generating a third control signal;
said first control means being responsive to said third control signal for changing into its second mode of operation and automatically retracting said objec-tive lens from its lower limit of travel to its upper limit of travel; and means responsive to said signal means and to said second output signal of said detection means for changing said first control means back to its first mode of operation whereby said lens driver moves said objec-tive lens along said optical axis of said radiation source until said detection means generates said first output signal for activating said second control means.

24. A focus servo system as recited in Claim 23, wherein said information detection means includes said focus error detection means for generating an in-focus control signal for indicating an optimum focusing position.

25. A focus servo system as recited in Claim 23, wherein said information detection means includes a tracking error detection means for indicating an optimum focusing position.

26. A focus servo system for use in a player apparatus for deriving information from an information bearing surface carrying a spiral-shaped information track in the form of a lineal series of first and second regions, each of the first regions is a planar-shaped region and each of the second regions is in the form of a discontinuity out of the plane of the first region, comprising:
a radiation source for emitting a reading light beam having an optical axis;
a lens driver and objective lens means;
said objective lens means for focusing said reading beam on an individual turn of the spiral-shaped information track;
said lens driver means being selectively re-sponsive to at least one drive signal for moving said objective lens means relative to the information track along the path of said reading beam;
first control means for generating a first drive signal for application to said lens driver means to move said objective lens means along a distance between an upper out-of-focus position and a down beyond-focus position;
said first control means having at least a first and a second mode of operation;
said first mode of operation of said first control means being employed for driving said objective lens means from said upper out-of-focus position to-wards a lower beyond-focus position at a first rate of speed;

said second mode of operation of said first control means being employed for retracting said objec-tive lens means from its current position to said upper out-of-focus position at a second rate of speed greater than said first rate of speed;
second control means for generating a second drive signal for application to said lens driver means to move said objective lens means along a predetermined portion within the range of the first control means;
focus acquisition signal means having at least first, second and third modes of operation;
said first mode of operation being employed for enabling said first control means and for disabling said second control means;
said second mode of operation being employed for disabling said first control means and for enabling said second control means;
signal means for generating a lens enabling control signal for application to said focus acquisition signal means for causing said focus acquisition means to be initially placed in its first mode of operation and said first drive signal moves said objective lens towards its down position;
information detection means for indicating the position of said objective lens means relative to the information-bearing surface and said detection means having at least a first output signal and a second output signal;
said first output signal indicating that the information track is at the in-focus position, and said second output signal indicating that the information track is not in-focus;
said focus acquisition signal means being responsive to at least said first output signal from said detection means for changing its mode of operation from its first mode of operation to its second mode of operation whereby said first control means is disabled and said second control means is enabled for control-ling the movement of said objective lens means while said objective lens means is in the in-focus position;
said information detection means further generating a continuous detect information output sig-nal indicating that said detection means is success-fully detecting information at said preferred position;
loss of signal detection means responsive to said detect information output signal for generating a signal indicating that said detection means has ceased detecting said information signal for a predetermined period of time;
said third mode of operation of said focus acquisition signal means being responsive to at least said output signal from said loss of signal detection means for generating a lens retract signal;
said first control means being responsive to at least said lens retract signal for changing into its second mode of operation and automatically retracting said objective lens to said upper out-of-focus position;
lens position sensing means for sensing at least the position of said objective lens means at an upper out-of-focus position and for generating an upper out-of-focus control signal; and said first control means being responsive to said upper out-of-focus control signal for changing back into its first mode of operation and said first drive signal moves said objective lens towards its down position.

27. A focus servo system as recited in Claim 26, wherein said information detection means includes a focus error detection means for indicating an optimum focusing position.

28. A focus servo system as recited in Claim 26, wherein said information detection means includes a tracking error detection means for indicating an optimum focusing position.