CA1150834A - Time base error - Google Patents

Abstract

ABSTRACT

A time base error correction system for use in an appara-tus for recovering a signal from a track recorded on a disc, wherein the signal includes a periodic synchronizing signal that defines a time base, and the apparatus includes optical system for directing a source beam of radiation to follow along the track and a spindle servo device for rotating the disc relative to the source beam, to produce a modulated beam of radiation containing the signal, the optical system device further direct-ing the modulated beam to a signal recovery device for recover-ing the signal from the modulated beam, the time base error correcting system comprising: a separator for separating the synchronizing signal from the signal recovered from the modu-lated beam; a reference signal generator for generating a reference signal having a prescribed frequency; a phase detec-tor for detecting the relative phase between the synchronizing signal and the reference signal; and for generating a control signal representative of error in relative phase; a radial location detector for detecting the radial location of the source beam relative to the disc; a control signal adjustor for adjusting the control signal as a function of the radial location of the source beam relative to the disc; and tangential beam steerer responsive to the control signal for steering the source beam tangentially along the information track to vary the rate of relative movement between the source beam and the disc in a manner correcting for time base errors in the signal re-covered from the modulated beam.

Description

115083~

VIDEO DISC PLAYER
TECHNICAL FIELD
The present invention relates to the method 2nd means ~or reading a frequency modulated video signal stored in the form Or successively positioned reflectlve and non-re~lective regions on a plurality o~ informa~ion tracks carried by a video disc. More specifically, an optical system i~ employed for directing a reading be~m to impinge upon the in~ormation track and for gather~ng 10 ~the reflected signals modulated by the re~lective and non-reflective regions of the information track. A
~requency modulated electrical signal is recovered from the reflected light modulated signal. m e recovered ~requency mGdulated electrical slgnal is ap~lied to a signal processing sectlon wherein the recovered fre-quency modulated signal is prepared for application to a standard television receiver and/or monitor. me recovered light modulated signals are applied to a plurality of servo systems for providing control signals which are employed ror keeping the lens at the optimum focus position with relation tothe in~ormation bearing sur~ace of the video disc and to maintaln the ~ocused light beam in a position such that the focused light spot lmpinges at the center of the in~ormation track.
~RIE~ ~U~ R~ OF THE INVE~T~ON
The present lnvention is dlrected to a video disc player operatlng to recover rrequency modulated video slgnals ~rom an inrormation bearing surface o~ a vldeo disc. m e ~req~ency modulated video in~ormaticn , is stored in a plurality of concentric circles or a single spiral extending over an information bearing portion of the video disc surface. The frequency modu-lated video slgnal is represented by indicia arranged in track-like fashion on the information bearing surface portion of the video disc. The indicia comprise suc-cessively positioned reflective and non-reflective reglons 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 approxi-mately the same as the width of the indicia positioned 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 impingin~ 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 of the lens to its fullest. In this relationship, the lens acts as a low pass filter. In the gathering of the reflected light and passing the reflected light through the lens when operating at the maximum resolution of the lens, the gathered light assumes a sinusoidal-shaped llke modulat~
beam representing the frequency modulated video signals contained on tlle 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 tracklng errors and focus errors.
The information bearing portion of the recovered fre-quency modulated video signal is applied to an FM
3~ processing system for preparation prior to transmission to a standard TV receiver and/or a TV mon tor.
The control portion of the recovered frequency modulated video signal is applied to a plurality of servo subsystems for controlling the position o~ the .

reading beam on the center of the information track and for controlllng the placing o~ the lens for gathering the maximum reflected light when the lens is positioned at its optimum focused position. A tangentlal servo subsystem is employed for determining the time base error introduced into the reading process due to the mechanics of the reading system. This time base errcr appears as a phase error in the recovered frequency modulated video signal.
The phase error is detected by comparing a selected portion of the recovered frequency modulated signal with an internally generated signal having the correct phase relationship with the predetermined por-tion o~ the recovered frequency modulated video signal.
The predetermined relationship is established durlng the original recording on the video disc. In the pre-ferred embodiment, the predetermined ~rtion of the recovered frequency modulated video slgnal is the color burst signal. The internally generated reference frequency is the color subcarrier frequency. The color burst signal was originally recorded on the video disc under control of an identical color subcarrier fre-quency. The phase error detected in this comparison process is applied to a mirror moving in the tangential direction which adjusts the location at which the focused spot impinges upon the information track. The tangential mirror causes the spot to move along the information track either in the ~orward or reverse direction for providing an adjustment equaltothe phase error detected ln the comparison process. The tangential mlrror ln its broadest sense is a means for ad~usting the time base of the signal read from the vldeo disc member to ad~ust ~or time base errors in~ected by the mechanics of the reading system.
3~ In an alternatlve form of the invention, the predetermined port on of the recovered frequency modu-lated video signal is added to the total recorded frequency modulat~d video signal at the time of record-lng and the same frequency is employed as the operating point for the highly controlled crystal oscillator used in the comparison process.
In the preferred embodiment when the video disc player is recovering frequency modulated video signals representing television pictures, the phase error comparison procedure is performed for each line of television information. The phase error is used for the entire line of television information for correcting the time base error for one full line of television informa-tlon. In this manner, incremental changes are appliedto correct for the time base error. These are con-stantly being recomputed for each line of television information.
A radial tracking servo subsystem is employed 15 for maintaining radial tracking of the focused light spot on one information track. The radial tracking servo subsystem responds to the control signal portion of the recovered frequency modulated signal to develop an error signal indicating the offset from the preferred center of track position tothe actual position. This - tracking error is employed for controlling the movement of a radial tracking mirror to bring the light spot back into the center of track position.
The radial tracking servo subsystem operates in a closed loop mode of operation and ~n an 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 contlnuously applied through the radial tracking mirror to bring the focus spot back to the center of track position. In the open loop mode o~ operation, the differential tracking error is temporarily removed from controlling the operation of radial tracking mirror. In the open loop mode of operation, various combinations of signals take over control of the movement of the radial track-ing mirror for directing the point of impingement of the focused spot from the preferred center of track positlon on a first track to a center of track position on an adjacent track. A first control pu~.~c causes the ; :

11~83~ ( tracking mirror to move the focused spot of llght from the center of track positlon on a first track and move tow~rds a next adjacent track. This ~irst control pulse terminates at a point prior to the focused spot reaching the center of trac~: position in the next adjacent track.
After the termination of the rirst control pulse, a second control pulse is applied to the radial tracking mirror to compensate for the additional energy added to the tracking mirror by the first control pulse. The second control pulse is employed for bringing the focused spot into the preferred center o~ track focus position as soon as possible. The second control pulse is also employed for peventing oscillat~on of the read spot about the second information track. A residual portion of the differential tracking ~rror is also applied to the radial tracking mirror at a point cal-culated to assist *he second control pulse in bringing the focused spot to rest at the center of track ~ocus ~ 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 ~he tracking servo subsystem to achieve - the movement of a focused spot tracking the center of a first information track to a separate and spaced loca-tion in which the spot begins tracking the center of the next adjacent information track. me stop motion subsystem performs its function by detecting a predeter-mined signal recovered from the frequency modulated video signal which indicates tl~e proper position within the recovered frequency modulated video signal at which time the ~umping operation should be initiated. This detection function is achieved, in part, by internally generating a gating clrcuit indicating that portion of the recovered rrequency modulated video signal within whlch the predetermined signal should be located.
In response to the predetermine~ signal, which is called in the rererred embodiment a white flag, the stop motlon servo subsystem generates a first control signal for application to the tracking servo subsystem fcr temporarily interrupting the applicaticn of the differential tracking error to the radial tracklng mirrors. The top motion subs~rstem generates a second control signal for application tothe radial tracking mirrors for causing the radial tracking mirrors to leave the center of tracking position on a first information track and jump to an adjacent information track. The stop motion subsystem terminates the second control signal prior to the focus spot reaching the center of the focus position on the next adjacent in~ormation 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 compensating for the effects on the radial tracking mirror which were added to the radial tracking mirror by the second control pulse. While the second control pulse is necessary to ~ have the reading beam move from a first information track to an adjacent information 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 h~ving 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 lt 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 through to the radial tracking mirror at a time calculated for the gated portion of the differential tracking error to assist the compensation pulse in bringing the focus spot under control upon the center of track position of the next ad~acent information tracl~.
The video disc player employs a spindle servo subsystem for rotating the video disc member positloned upon the spindle at a predetermlned frequency. In the . - .

" 1 1 ~ 8 3 pre~erred embodiment the predetermined rrequency ls 1799.1 revolutions per minute. In one revolution of the video disc, a complete rrame Or televislon lnforma-tior. is read from the vldeo disc~ processed in elec-tronic portion of the video disc player and applied to a standard television receiver and/or television monitor in a form acceptable to each such unit, respectively.
~oth the television receiYer and the television monitor handle the signals applied thereto by standard internal circuitry and display the color3 or black and white signal, on the receiver or monitor.
The spindle servo subsystem achieves the accur-ate speed of rotation by comparlng the actual speed of rotation with a motor reference frequency. The motor reference frequency ls derlved from the color sub-carrier frequency which is also used tc correct for time base errors as described hereinbefore. ~y utiliz-ing the color subcarrier frequency as the source of the ~ motor rererence signal, the spindle motor ltself removes all fixed time base errors which arise from 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 maJor portion of time base error. While the color subcarrier frequency is shown as the preferred source in generating the motor reference frequency, other highly controlled frequency signals can be used in controlling the writing and reading of frequency modulated video signal on the vldeo disc.
A carriage servo subsystem operates ln a close loop mode Or operation to move the carriage assembly to the specific location under the direction of a plurallty of current generators. The carriage servo subsystem controls the relative posi1;icning of ~he vldeo disc and the optical system used to form the read beam.
A plurality Or individual current sources are indlvidually activated by command signals from the :

function generator for directlng the movement of the carriage servo.
A first command signal can direct the carriage servo subsystem to move the carriage assembly to a predetermined location such that the read beam inter-sects a predetermined portion of the information bear-ing surface of the video disc member. A second current source provides a continuous bias current ror directing the carriage assembly to move in a fixed direction at a predetermined speed. A fùrther current source generates a current signal of fixed magnitude and variable length for moving the carriage assembly at a high rate of speed in a predetermined direction.
A carriage tachometer current generating means is mechanically connected to the carriage motor and is employed for generating a current indicating the instantaneous position and speed of the carriage motor.
The current from the carriage tachometer is compared ~ with the sum of the currents being generated in the current sources in a summation circult. The summation clrcuit 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 from the following more partlcular descrlption of a preferred 3 embodiment of the invention as illustrated in the accompanying drawings wherein:
FIGURE 7 shows a generalized block diagram of a video disc piayer;
FIGURE 2 shows a schematic diagram of the opti~
cal system employed with reference to the video disc player shown in Figure l;
FIGURE 3 shows a block diagram of the spindle servo subsystem employed in the video disc player shown in Figure l;

g FIGURE 4 shows a block diagram of the carriage servo subsystem employed in the video disc player shown in Fiæure l;
FIGURE 5 shows a block diagram of the focus servo subsystem employed in the video disc player shown in Figure l;
FIGURES 6a, 6b, and 6c show various waveforms illustr~ing the operation of the servo subsystem sho~ln in Figure 5;
FIGURE 7 shows a partly schematic and partly block diagram view of the signal recovery subsystem employed in the video disc player shown in Figure l;
FIGURE 8 shows a plurality of waveforms and one sectional view used in explaining the operation of the signal recovery subsystem shown in Figure 7;
FIGURE 9 shows a block diagra~ of the tracking servo used in the video disc player shown in Figure l;
FIGURE 10 shows a plurality Or 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 employed in the video disc p}ayer shown in Figure l;
FIGURE 12 shows a block diagram of the stop motion subsystem utilized in the video disc player of Figure l;
FIGURES 13A, 13B, and 13C show waveforms gen-erated in the stop motion 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 in the FM processing circuit shown in Figure 14;
FIGURE 15 shows a plurality of ~aveforms and one transfer function utilized in explaining the opera-tion of the FM corrector shown in Figure 15;
FIGURE 17 is a block dlagram of the FM

detector used in the FM processing circuit shown ln Fi6ure 14;
FIGU~E l& shows a plurality of waveforms used in explaining the operation of the FM detector shown with reference to Figure 17;
FIGUR~ 19 shows a block diagram of the audio processing circuit utilized in the video disc player sho~n with reference to Figure l;
FIGURE 20 shows a block diagram Or 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 use~ul in explaining the operation of the audio demodulator shown with reference to Figure 20;
FIGURE 22 shows a block diagram of the audio voltage controlled oscillator utilized in the audio processing circuit shown with reference to Figure 19;
~ FIGURE 23 shows a plurality of waveforms avail-20 able in the audio voltage controlled oscillator sho~,1n 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-25 lized in the explanation of the RF modulator shown with reference to Figure 24;
FIGURE 26 shows a schematic view of a video disc member illustrating the eccentricity effect of uneven cooling on the disc;
FIGURE 27 is a schematic view of a video disc lllustrating the eccentricity effect of an off-center relationship of the information tracks to the central aperture;
FIGURE 28 is a logic diagram demonstrating the normal acquire focus mode of operation of the focus servo emploJed in the video disc shol~n ~r Figure l; and FIGURE 29 is a logic diagram demonstrating other modes of operation of the foc~s servo sho~n with reference to ~igure l;

_ 11~1834 DETAIIED DESCRIPTION OF THE IN~'ENTION
T~le same numeral will be used in the several views to represent the same element.
Referring to Figure 1, there is shown a sche-matic block diagram of a video disc player system in-dicated generally at 1. The player 1 employs an optical system indicated at 2 and shown in greater detail in Figure 2.
Referring collectively to Figures 1 and 2, the optical system 2 includes a read laser 3 employed for generating a read beam 4 which is used for reading a frequency modulated encoded signal stored on a video disc 5. The read beam 4 is polarlzed ln a predetermln.ed dlrection. The read beam 4 is dlrected to the vldeo disc 5 by the optical system 2. An additional function of the optical system 2 is to focus the light beam dc .ln to a spot 6 at its point of impingement with the video dlsc 5.
~ A portion of an information bearing surface 7 of the video disc 5 is shown enlarged within a circle 8.
A plurality of information tracks 9 are formed on the video disc 5. Each track is formed with successive light reflective regions 10 and light non-reflective regions 11. The directlon of reading is indlcated by an arrow 12. The read beam 4 has two degrees of movemer.t, the first of which is in the radial directlon 2s indl-cated by a double headed arrow 13; the second of whi^h ls the tangential directlon as indicated by a double headed arrow 14. The double heads of each of the arro~s 13 and 14 indicate:that the read beam 4 can move in both dlrections in each of the radial degree and tan-gential degree.
Referring to Figure 2, the optical system ccm-prises a lens 15 employed for shaping the beam to fully 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 impingement with the video disc 5. Improved results have been found when the entrance aperture 16 is overfilled by the liS0834 readin2 beam ~. This results in maximum llght lntenslty at the spot 6.
After the beam 4 ls properly f~rmed by the lens 15, it passes through a difractlon grating 18 which splits the read beam into three separate beams (not sho;~n). ~o of the beams are employed for developing a radial ~racking error and the other is used for develop-ing both a focus error slgnal and the inrormatlon signal.
These three Deams are treated identlcally by the remain-ing portinn of the optical system. Therefore, they arecollectively referred to as the read beam 4. The output for the diffraction grating 18 is applied to a beam splitting prism ~0. The axis of the prism 20 ls slightly offset from the path of the beam 4 for reasons that are explained with reference to the descriptlon of the performance of the optlcal system 2 as lt relates to a reflected beam 4'. The transmitted portlon of the beam 4 is applied through a quarter wave plate 22 which pro-~v~es a for~y-~lve degree shift in polarizatlon of the li~ht forming the beam 4. The rear beam 4 next impinges upon a fixed mirror 24 which re-directs the read beam 4 to a ~irst articulated mirror 26. The functlon of the first articulated mirror 26 is to move the light beam in a first degree of motion which is tangential to the 25 surface (f the video disc 5.to correct for time base error errors introduced into the reading beam 4 because of eccentricities in the manufacture of the dlsc 5.
The tangential direction is in the forward and/or back-ward direction of the information track on the video disc 5 as illdicated by the double headed arrow 14. The read beam 4 now impinges upon the entrance aperture 16, as previously described, and is focused to a spot 6 upon the information bearing track 9 of the video dlsc 5 by the lens 17.
The first articulated mirror 26 directs the light beam to a second articulated mirror 28. The second articulated mirror 28 is employed as a tracking mirror. It is the function of the tracking mirror 28 to respond to tracking error signals so as to slightly 1150834 ~

change its physical position to direct the polnt Or impingement S Or the read beam 4 so as to radially tracl; the information carrying indicia on the surface of the video disc 5. The second articulated mirror 28 has one degree of movement which moves the light beam in a radial direction over the surface of the video disc 5 or indicated by the double headed arrow 13.
In normal playing mode, the focused beam of light impinges upon successively positioned light reflective regions 10 and light non-reflective regions 11 representing the frequency modulated information.
In the preferred embodiment, the light non-reflective regions 11 are light scattering elements carried by the video disc 5. The modulated light beam ls a light equivalent of the electrical f~equenc~J modulated signal ccntaining all the recorded information. This modulated light beam is generated by the microscopic objective lens 17 by gathering as much reflected light from the successively positioned light reflective region 10 and light non-reflective regions 11 on the video disc 5. The reflected portion o the read beam is indicated at 4'. The reflected read beam 4' retraces the same path previously explained by impinging in sequence upon the second articulated mirror 28, the first arti-culated mirror 26, and the fixed mirror 24. The re-flected read beam 4' next passes through the quarter-wave plate 22. The quarterwave plate 22 provides an additional forty-five degree polarization shift re-sulting in a total of ninety degrees in shift of polar-ization to the reflected read beam 4'. me reflectedread beam 4' now impinges upon the beam splitting prism 20, which prism diverts the reflected read beam 4' to lmpinge upon a signal recovery subsystem indicated generally at 30.
3~ The function of the beam splitting prism is to pre ent the total reflected read beam 4' from re-entering the laser 3. The effect of the returning read beam 4' upon the laser 3 would be to upset the mecAanism whereby the laser oscillates in its predetermined mode 1150834 ' of operat~on. ~ccordingly, the beam splittlng prism 20 redire~ts a slgnificant portion of the reflected read be~m 4' for preventing feedback into the laser 3 when t~le laser 3 would be affected by this feedback portlon of the reflected read beam 4'. For those solid state lasers which are unaffected by the feedback of the re-flected light beam 4', the beam splitting prism 20 is unnecessary. The solid state laser 3 can function as the photo detector portion of the signal recovery sub-system 30 to be described hereinafter.
Referring to Figure 1, the normal operatingmode of the signal recovery subsystem 30 is to provide a plurality of informational signals to the remaining portion of the player 1. These informational signals fall generally into two types, an informational signal itself ~hich represents the stored information. A
second type of signal is a control signal derived from the informational signal for controlling various por-~ tions of the player. The lnformational signal is a frequency modulated signal representing the information stored on the video disc 5. This informational signal is applied to an FM processing subsyste~ indicated at 32 over a line 34. A first contrPl signal generated by the signal recovery subsystem 30 is a differential focus error signal applied to a focus servo subsystem lndica-ted at 36 over a line 38. A second type Or control signal generated by the signal recovery subsystem 30 is a differential tracking error signal applied to a track-ing servo subsystem 40 over a line 42. The dlfferential 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 of 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~

control Or a s~ndle servo subsystem 50. A splndle tachometer (not shown) is mounted relative to the spindle 49 to generate electrical signals showing the present speed of rotation o~ 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. ~ecause 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 o~ 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 subs~Jstem 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 Or 1799.1 revolutions per minute allo~ls 30 frames of television information to be displayed on a standard television receiver.
The next major functioning ~ the video disc player 1 is the activation of a carriage servo sub-system 55. As previously mentioned, the reading of thefrequency modulated encoded information from the video disc 5 is achieved by directing and focusing a read beam 4 to impinge upon the successively positioned light reflective region 10 and a light non-reflective region 11 3 cn the vide~ disc ~ 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 betlYeen the combined ~tical system 2 and the video disc 5. Either the video disc 5 can move under the fixed laser read beam 4 or the optical s~stem 2 can move relative to the fixed video disc 5. In this embodiment, the optical system 2 is held stationary and the video disc 5 is moved under the reading beam 4. The carriage servo 1150~34 ~

subsystem controls this lelative movement between the ~ideo disc ~ and the optical system 2.
As completely descrlbed hereinafter, the carriage servo subsystem adds a degree of flexibility to the overall functioning of the video disc player 1 by directing the aforementioned relative movement in a number of different modes of operation. In its first mode of operation the carriage servo subsystem 55 re-sponds to the player enable signal applied to it over the line 54 to move a carriage assembly 56 such that the read beam 4 impinges upon the video disc 5 perpendi-cular to the information bearing surface of the video disc 5. At this time it would be important to note that the term carriage assembly is used to identify the 1 structural member upon which the video disc is carried, This also includes the spindle motor 48, the spindle 49, the spindle tachometer (not shown) a carriage motor 57 and a carriage tachometer generator 58. For the purpose ~ of not unduly complicating the broad block diagram shown in Figure 1, the carriage assembly is not shown in great detail. For an understanding of the summarized opera-tion of a vldeo disc player, it is important to note at this time that the function of the carriage servo subsystem is to move the carriage to its inltial posi-tion at which the remaining player functions will beinitiated in sequence. Obviously, the carrlage servo subsyste~ can position the carriage at any number of fixed locations relative to the vldeo disc pursuant to the design requirements of the system, but for the purposes of this description the carriage is positioned at the beginning of the frequency modulated encoded - information carried by the video disc. The carriage motor 57 provides the driving ~orce to move the carrlage assembly 56. The carriage tachometer generator 58 is a current source for generating a current lndicating the instantaneous speed and direction ~ movement of the carriage assembly.
The spindle servo subsystem 50 has bro~ght the spindle speed up to its operational rotational rate of 17~ 1 rpm at ~JIlich tlme the player ena~le signal ls gellerated on the line 5l~ The player enable si~nal on t~ie line 54 is applied to the carriage servo subsystem 55 for controlling the relative motlon between the carriage assembly 56 and the optional system 2. The next sequence in the PLAY operation is for the ~ocus servo subsystem 36 to control the movement of the lens 17 relative to the video disc 5. The focusing opera-tion includes a coil, (not shown), moving the lens 17 under the direction of a plurality of separate elec-trical waveforms which are summed within the coil itself.
These waveforms are completely described ~ith reference to the description ~iven for the focus servo subsystem in F ~ ures 6a, 6b and 6c. A voice coil arrangement as found in a standard loud speaker has been found to be suitable for controlling the up and down motion of the lens 17 relative to the video disc 5. The electrical signals for controllil~ the voice coil are generated by ~ the focus servo subsystem 36 for application to the coil over a line 64.
The inputs to the focus servo subsystem are applied from a plurality of locations. The first of which is applied from the signal recovery subsystem 30 over the line 38 as previously descrlbed. The second input signal is from the FM processing circuit 32 over a line 66. The FM processing subsystem 32 provides the frequency modulated signal read from the surface of the video disc 5. A third input signal to the focus servo subsystem 36 is the ACQUIRE FOCUS enabling logic signal 30 generated by the act of putting the player into its play mode by selection of a function PLAY button within the function generator 47.
The function of the focus servo subsystem 36 is to position the lens 17 at the optimum distance from 35 the video disc 5 such that the lens 17 is able to gather and/or collect the maxi!~um li~hv reflected ~ro~, the video disc 5 and modulated by the successively posi-tioned ~ight reflective region 10 and light non-reflective region 11. This optimum range is approxi-1150~3.~
mately ~3 microlls in len~th and is located at a distanceof one mlcron above the top surface of the video disc 5.
~he focus servo subsystem 36 has several modes of oper-ation all of wl~ich are descrlbed hereinafter ln greater detail with reference to Figures 5, oa, ~b 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. The differential focus error signal from the signal recovery subsystem 30 provides an electrical representation of the relative distance between the lens 17 and the video disc 5. Un-fortunately, the differential focus error signal is relatively small in amplitude and has a wave shape containing a number of positions thereonJ each of which indicate that the proper point has been reached. All but one of such positions are not the true optimum focusing positions but rather carry false information.
~ Accordingly, the differential focus error signal itself is not the onl~ signal employed to indicate the optimum focus condition. I~hile the use of differential focus error itself can oftentimes result inthe selection of the optimum focus position, it cannot do so reliably on every focus attempt. Hence, the combination of the differential focus error signal ~ith the signal indica-tive of reading a frequency modulated signal from the video disc 5 provides enhanced operation over the use of using the differential focus error signal itself.
Durlng the focus acquiring mode of operation, 3 the lens 17 is moving at a relatively high rate of speed towards the video disc 5. An uncontrolled lens detects a frequency modulated siGnal from the information carried by the video disc 5 in a very narrow spaclal range. This very narrow spacial range is the optimum focusing ra~ge. Accordingly, the combination of the detected frequency modulated signal and the differential focus error signal provides a reliable system for ac-quiring focus.
The focus servo subsystem 36 hereinafter 11~0834 described co;ltains additional improvements. One Ort~lese improvements is an addition of a further fixed si~nal to those alraady described ~hich further helps the focus servo subsystem 36 acquire proper focus on the initial attempt to acquire focus. This 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 kickback pulse is combined with the previously discussed signals and applied to the voice coil so as to independently cause the lens to physically move back through the region at ~hich a frequency modulated signal was read from the disc 5. This internally generated fixed kickback pulse signal gives the lens 17 the opportunity to pass through the critical optimum focusin~ point a number of times during the first transversing of the lens 17 to~Jards the video disc 5.
Further improvements are described for handling momentary loss of focus during the play mode of opera-tion caused by i~perfection 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 subsyste~ 36 over the line 66.
A tangential servo subsystem 80 receives its first input signal from the FM processing subsystem 32 over a line 82. The input signal present on the line 82 is the frequency modulated signal detected from the sur-face of the video disc 5 by the lens 17 as amplified 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. The second input signal to the tangential servo subsystem c~O is over a line 84. The signal on the line 84 is a varlable DC signal generated by a carria~e pos~tion po'entiom2ter. }1e amplituc~e of the variable voltage signal on the line 84 indicates the relative position of the point of impact of the reading spot S over the radial distance indicated by a " 1150834 double headed arrow 85 as drawn upon the surface of the vldeo disc 5. This variable voltage ad~usts the gain of an internal circuit for ad~usting its operating charac-teristics to track tlle relative position of the spot as lt transverses the radial position as indicated by the length of the line 86.
The function of the tangential time base error correction subsystem 80 is to adjust the slgnal detected from the video disc 5 for tangential errors caused by eccentricity of the information tracks 9 on the disc 5 and other errors introduced into the detected signal due to any ph~sical imperfection of the video dlsc 5 itself. The tangential tlme base error correction subsystem 80 performs its function by comparing a signal read from the disc 5 with a locally generated slgnal.
The difference between the two signals is indicative of the instantaneous error in the signal being read by the player 1. More specially, the signal read from the disc ~ 5 is one whic'.l was carefully applied to the disc with a predetermined amplitude and phase relative to other signals recorded therewith. For a color television FM
signal this is the color burst portion of the video signal. The locally generated signal is a crystal con-trolled oscillator operating at the color subcarrier

2~ frequenc~r of 3.579545 megahertz. The tangential time base error ~orrection subsystem 80 compares the phase difference between the color burst signal and the color subcarrier oscillator frequency and detects any differ-ence. This difference is then employed for ad~ustlng the phase ~ the remaining portlon of the llne of FM
lnformation which contained the color burst signal.
The phase difference of each succeeding line is gener-ated in exactl~ the same manner for providing continuous tangential time base error correction for the entire signal read from the disc.
In other embodiments storing informatlon signals which do not have a portion thereof comparable to a color ~urst signa~ such a51~nal having predeter-mined amplitude and phase relative to the remaining 115U~33~

si~nals on the disc 5 can be perlodically added to the information when recorded on the disc 5. In the play mode, this portion of the recorded information can be selected out and compared witll a locally generated signal comparabl~ 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 theinformation track, in the direction of the double headed arrow 14, to correct for the time base error injected due to an imperfection from a manufacture of the video disc 5 and/or the reading t~,erefrom. Another output signal from the tangential time base error cor-rection subsystem 80 is applied to the stop motion sub-system 44 over a line 92. This signal, as completely described hereinafter, is the composite sync signal which is generated in the subsystem 80 by separating the composite sync signal from the remaining video signal.
It has been found convenient to locate the sync pulse separator in the tangential time base error correction subsystem 80. This sync pulse separator could be located in an~j 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 conveniei~t because of the presence of the color subcarrier oscillator frequency used in the comparison operation as previously described. This color subcarrier oscillator frequency is an accurately ~i~0834 ( ~, geller?.ted signal. It is divided down to a motor refer-ence freque2lcy used in the control of the spindle servo speed. ~- utili~ing the color su~carrier frequency as a control frequency for the speed of the splndle, the speed of the spindle is efl~ectively locked to this color subcarrie- frequency causing the spindle to rotzte at t'ne precise frame frequency rate required for maximu~.
fidelity in the display of the in~ormatio.l detected from the video disc 5 on either a televisicn rec~iver indicated at 95 and/or a TV monitor indi_ated at 98.
The tracking servo subsystem 40 receives a plurality of input si~nals, one of which is the pre-viously descri~ed differential tracking error signal generated by a signal recovery subsystem 30 as applied thereto over a line 42. A second input signal to the tracking servo s~bsystem ~0 is generated in a functio~
generator 47 over a line 102. For the purpose of clar-ity~ the ~u~ction generator 47 is sllo~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 thc ^onsole of the video disc player 1. The specific functions so ~enerated are described in more detzil in the detailed description ol the carriage servo sub-system 55 contained hereinafter.
The signal contained on the line 102 is a - signal which operates to disable the normal ~unctioning of the tracking servo 40 during certain functions initiated by the function generator 47. For example, the f~nction generator 47 is capable of generating a signal for causin~ tne relative move~ent of the carriage assembly 5G over the video disc 5 to be in the fast for~ard or fast reverse condition. ~y definition, the lens is traversing the video disc 5 in a radial direction as represented by the arrol~ 13, rapidly sklpping over the tracks at the rate of 11~000 tracks per inch and trackin~
is not expected in this condition. Hence, the signal from the functlon generator 47 on the line 102 disables the tracking servo 40 so that it does not attempt to operate in .. . .. . _ __ 115~834 its normal tracklng mode.
A third input signal to the tracking servo subsystem 40 is the stop motion compensation pulse gene~
ated in the stop motion subsystem 44 and applled over a llne 104. An additional lnput signal ~pplled to tracking servo subsystem 40 ls the subsystem loop interrupt signal generated by the stop motion subsystem 44 and applied over a line 10Z. A third input signal to the tracking servo subsystem 40 is the stop motion pulse generated by the stop motion subsystem 44 and applied over a line 108.
The output signals from the tracking servo sub-system 40 include a first radial mirror tracking signal over a line 110 and a second radial mirror control on a line 112. The mirror control signalson the line 110 and 112 are applied to the second articulated mirror 28 which is employed for radial tracking purposes. The control signals on the lin~s 110 and 112 move the second articulated mirror 28 such that the reading beam 4 impinglng thereupon is moved in the radial direction and - becomes centered on the information track 9 illuminated by the focused spot 6.
A further output signal from the tracking servo subsystem 40 is applied to an audio processing subsystem 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-cation to the loud speakers contained in the TV receiver 96, and to a pair of audio jacks 117 and 118 respec-

3 tively and to an audio accessory block 120. The audio ~acks 117 and 118 are a convenient point at which exter-nal equipment can be interconnected with the video disc player 1 for recelpt of two audio channels for stereo application.
A further output signal from the tracking servo subsystem 40 is applied to the carriage servo subsystem 55 over a line 130. The control signal present on the line 130 is the DC component ~ the tracking correctlon signal which is employed by the carriage servo subsystem 1~S0834 ~

for provldin~ a further carrlage control signal lndica-tive Or ho~ closely the tracking servo subsystem 40 ls following the directions glven by the functlon generator 47. For example, lf the function generator 47 gives an lnstructioll to the carrlage servo 55 to provide carriage movement calculated to operate with a slow forward or slow reverse movement, the carriage ser~o subsystem 55 has a further control slgnal for determlnlng how well it is operating so as to cooperate with the electronlc control signals generated to carry out the lnstruction from the function generator 47.
The stop motion subsystem 44 is equipped with a plurallty of input signals one of which is an output signal of the function generator 47 as applied over a line 132. The control signal present on the line 132 is a STOP enabling signal indicating that the video disc player 1 should go into a stop motion mode of operation.
A second input slgnal to the stop motion subsystem 40 is the frequency modulated sigl~l read off ~f the video disc and generated b~ the FM processing subsystem 32.
The video slgnal from the FM processing subsystem 32 is applied to the s~op motion subsystem 44 over a line 134.
Another input signal to the stop motion subsystem 44 is the dif~erential tracking error as detected by the 2~ signal recovery subsystem 30 over the line 46.
The tangential servo system 80 ls equipped with a plurality of other output signals in addition to the ones previously identified. The first of which is applied to the audio processing subsystem 114 over a 3o line 140. The signal carried by the line 140 is the color subcarrier oscillator frequency generated in the tanential servo subsystem 80. An additional output signal from the tangential servo 80 is applied to the FM processing subsystem 32 over a line 142. The signal carried by the line 142 ~s the chroma portion of the video signal generated in the chroma separator filter portion of the tangential servo subsystem 80. An addi-tional output signal from the tangential servo 80 is applied t~ the FM processing subsystem 32 over a line 14-~. The sigral carrled by tlle line 144 is a gate enab-ling signal generated by a first gate separat~r portion of the tangential servo system 80 which indicates the instantaneous presence of the burst ~ime period in the 5 received video signal.
The focus servo receives its ACQUIR~ FOCUS
signal on a line 145.
The power output from the spindle servo sub-system 50 is applied to the spindle motor 48 over a line 14~.
The power generated in the carriage servo 55 for driving the carriage motor 57 iS applied thereto over a line 150. The current generated in the carriage tachometer generator 58 for application to the carriage 15 servo subsystem 55 indicative of the instantaneous speed and direction of the carriage, is applied to the carriage servo subsystem ~5 over a line 152.
The FM processing unit 32 has an additional plurality of output signals other than those already described. A first output signal from the FM processing subsystem 32 is applied to a data and C10Ck recovery subsystem 152 over a line 154. The data and clock re-co~ery circuit is of standard design and it is employed to read address information contained in a predetermined 25 portion of the information stored in each spiral and/or circle contained on the surface of the video.disc 5.
The address information detected in the video signal furnished by the FM processing unit 32 iS applied to the function generator 47 from the data and clock recovery subsystem 152 over a line 15D. The C10Cking information detected by the data and C10Ck recovery subsystem is applied to the function generator over a llne 158. An additional output signal from the FM processing unit 32 is applied to the audio processing subsystem 114 over a line 160. The signal carried by the line 160 is a fre-quency modulated video signal from the FM distribution amplifiers contained in the FM processir.g unit 32. An additional outpu~ signal ~rom the FM processing subsystem 32 is applied to an RF modulator 152 over a line 164.

. .

_cf~_ The line 154 carries a video output si~nal from the FM
detector pOrtiO`l O~ the FM processing unit 32. A final output signal from the FM processin6 unlt 32 is applled to the TV monitor 98 over a line 166. The line 166 c~rries a video signal of the type displa~able in a standard TV r,lonitor ~8.
The ~udio processing system 114 receives an additional input signal from the function generator 47 over 2 line 170. The signals carried by the line 170 from the function generator 47 are such as to switch the discriminated audio signals to the various audio accessory systems used herewith. The audio contained in the FM modulated signal recovered from the video disc 5 contains a~pluralit-~r of separate audio signals.
More specifically, one or two channels of 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 signals - contained on the line 170 control the selection at which the audio channel is to be utilized.
Tne audio processing system 114 is equipped with an additional output signal for application to the RF
modulator lS2 over a line 172. The signal applied to the RF 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 rrequency selected for use with one channel of the TV receiver. This modulated channel frequency oscillator is applied to a standard TV receiver 96 such that the internal circuitry of the TV receiver demodulates the audio contained in the modulated channel ~requency si~nal in its standard mode of oper-ation.
The audio signals applied to the audio acces-sory unit 120 and the audio ~acl~s 117 and 118 lies within the normal audio range suitable for driving a -~7-loudspea~er b~l mealls Or the audio jacks 117 and 118.
The same audio frequencies can be the ir.put to a stereophon~c audio amplifier when such is employed as the audio accessory 120.
In the preferred embodiment, the output ~rom the audio processing system 114 modulates the channel 3 frequency oscillatDr before applicaticn to a standard TV receiver 96. llhile Channel 3 has been conveni-ently selected for this purpose, the oscillating ~re-quency Or the channel frequency oscillator can be adapted for use with any channel of the standard TV
receiver 96. The output of the RF modulator 162 is applied to the TV receiver 96 over a line 174.
An additional output signal frcm the function generator 47 is applied to the carriage servo subsystem 55 over a line 180. The line 180 represents a plural-ity o~ individual lines. Each individual line is nct sho;~n in order to keep the main block diagram as clear as possible. Eac]l of the individual lines, schematic-ally indicated by the single line 180, represents an ~ instruction from the function generator instructing the carriage servo to move in a predetermined direction at a predetermined speed. This is described in greater detail when describing the detailed operation o~ the carriage servo 55.
NORMAL PLAY MODE - SEQVENCE OF OPERATION
The depression of the play button generates a PLAY signal rrom the function generator followed by an ACQUIRE FOCUS signal. The PLAY signal is applied to the laser 3 by a line 3a for generating a read beam 4.
The PLAY signal turns on the spindle motor subsystem 50 and starts the spindle rotating. After the spindle servo subsystem accelerates the spindle motor to its proper rotational speed of 1799.1 revolutions per minute~ the spindle servo subsystem 50 generates a PLAYER ENABLE signal for application to the carriage servo subsystem 55 ~or controlling the relative move-ment between the carriage assembly and the optical assembly 2. The carriage servo subsystem 55 directs 11S0834~
-2~-the mQvement Or the carriage such that the read beam

4 is positioned to impin~e upon the beginning portion of the in~orm~tion stored on the video disc record 5.
Once the carriage servo subsystem 55 reaches the approx-imate be~inning of the recorded informa~ion, the lensfocus servo subs~stem 35 automatically moves the 1~n9 17 towards the video disc surface ~. The movement of the lens is calculated to ~ass the lens through a point at which optimum focusing is acllieved. The ~ens servo system preferably achieves optim~m focus in combina-tion with other control signals generated by reading information recorded on the video disc surface 5. In the preferred embodiment, the lens servo subsystem has a built-in program triggered by information read from the ~isc whereby the lens is caused to move through the optimum focusing point several times by an oscilla-tor~J type microscopic retracing of the lens path as the lens 17 moves through a single lens focusing acquiring procedure. As the lens moves through the optimum focusing point, it automatically ac~uires information ~ from the video disc. This information consists of a total Fr~i signal as recorded on the video disc 5 and additionally includes a differential focus error sig~l 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 36 that the correct point of focus has been success-full~J located. When the point of optimum focus has been located, the focus servo loop is closed and the 3 mechanicall~ initiated acquire focus procedure is terminated. The radial tracking mirror 28 is now responding to the dirferential tracking error generated from the informaticn gathered by the reading lens 17.
The radial tracking error is causinG the radial track-ing mirror 28 to follow the in~ormation track andcorrect for an~J radial decartul-ec from a perfect spiral or circle track configuration. Electronic processing of the detected video FM signal generates a tangential error signal which is applied to the tangential ~.irror " 1151~834 ~5 for correcting phase error in the reading process caused by small physical deformaties in the surface of the video disc 5. Durin~ the normal play mode, the servo subsystems hereinbefore described continue their normal mode of operation to maintain the read b~am 4 properly in the center of the information track and to maintain the lens at the optimum focusing point such t'nat the light gathered by the lens generates a high quality signal 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 fideliJ~J durin~ the display in the television receiver 9~ and/or television monitor 9~.
Immediately upon recovery from the video disc surface, the frequency modulated video signal is applied to a tangential servo subsystem 80 for detecting any phase difference ~esent in the recovered video signal and caused b~J the mecllanics of the reading process.
The detected phase difference is employed for driving a tangential mirror 26 and ad~ustin~ 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 lntro-duced into the reading process. The recovered videosignal is Fr~ 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 rrequency end of the video spectrum is atten-uated morc by the reading lens than the low frequency portion of the frequency spectrum of the freqllency modulated slgnal read from the video disc. This equalization ls achieved through amplif~Jing the higher frequency portion more than the lower Irequency por-tion. After the frequencJ modulation correction is achieved, the detected signal is sent to a discrimina-tor board whereby the discriminated video is produced -3o -~or applicaticn to the remaining portions cr the board.
Referring to Fi~ure 3, there is shol~n a gen-erali~ed blocl; diagram of the spindle servo subsystem illdicated at 50. One of the runctions of the spindle servo subsystem is to mai.ltain the speed o~ rotation of the spindle 49 by the spindle motor 48 at a constan~
speed of 1799.1 rpm. Obviously, this figure has been selected to be compatible with the scanning ~requency of a standard television receiver. The standard tele-vision receive-~ receives 30 rrames per second and the in~ormat~on is recorded on the video disc such that one complete fra~e of television information is con-tained in one spiral and/or track. Obviously~ when the time requirements Or a television receiver or tele-vision monitor differ from this standard, then thefunctioll o~ the spindle servo subsyste~ is 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 from the first tachometer element is applied to a Schmitt trig-ger 200 over the line 51. The tac~o~.eter input signal pulse train from the second tachometer element is applied to a second Schmitt trigger 202 over the line 52. A 9.33 ~z motor reference frequency is applied to a third Schmitt trigger 204 from the tangential servo subsystem 80 over a line 94.
The output from the Schmitt trigger 200 is applied to an edge generator circuit 206 through a divide by two network 208. The output ~rcm 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 35 of the edge generators 20c, 210 and 214 is employed ror ger.erating a s,larp pulse colre~polldlrg tc both the positive going eclge and the negati~e going edge of the signal applied respectively rrom the divided by two net~orks 208, 212 and 215.

li~;O834 ~1 The output from the ed~e generator 214 is applied as the reference phase signal to a ~irst ph~3e detectQr 21~ and to a second phase detector 220. The phase detector 218 has as its second input signal the output 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 detectors operate to indicate any phase difference between the tachometer input si~nals and the motor reference frequency. The output from the phase detector 218 is applied to a summation circuit 222. And the output from the phase 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 po~er amplifier 22~. The function of the lock detector 224 is to indicate when the spindle speed has reached a predetermined rotational speed. This can be done by sensing the output signals from tlle summation circuit 222.
In the preferred embodiment is has been deter-mined that the rotational speed of the spindle motor should reach a predetermined speed before the carriage assembly is placed in motion. When a video disc is brou~ht to a relatively high rDtational speed, the disc rides on a cushion of air and rises sli2htly vertical against the force of gravity. Additionally, the centrifugal force of the video disc causes the video disc to somewhat flatten considerably. It has been found that the vertical movement a~ainst gravity caused b~ tl1e disc riding on a cushion of air and the vertical rise caused by the centrifugal force both llft the video disc from its position at rest to a stabilized position spaced from its initial rest posi-tion and at a predetermined position with reference to other internal fixed members of the video disc pla~er cabinet. The d~-namics c~ a spinnin~ disc at 1799.1 rpm wit'l1 a predeterr"ined weight and density can be calculated such as to insure that the disc is spaced from all internal components and is not in ;

~ ,:

. .

115083~
,, contact Witil anJ such internal components. An~J con-tact between the disc and the player cabinet causes rubbing, ~nd the rubbin~ causes damage to the video disc throu~h abrasion.
In the preferred embodiment~ the lock detector 224 has been set to generate a PLAYER ENAE~E pulse on the line 5~ when the spindle speed is up to its full 1799.1 rpm speed. A speed less than the full rota-tional speed can be selected as the point at which the player enable signal is generated provided that the video disc has moved sufficiently from its initial position and has attained a position spaced from the internal components of the video disc player cabinet.
In an alternate embodiment, a fixed dela~-, after apDly-ing the STAR.T slgnal to the spindle motor, is used tostart t'ne carriage assembly in motion.
During the normal operating mode of the video disc player 1 the tachometer input si~n21s ar~ con-tinuously applied to the Schmi~t triggers 200 and 202 over the lines 51 and 52, respectively. These actual ta^hometer input signals are compared against the moto~
reference signal and any de~Jiation therefrom is detected in the summation circuit 222 for application to the po-"er ampllfier 226. The power amplifler 226 prov1des the driving force to the spindle motor 48 to maintain the required rotational speed of the spindle 49.
Referring to Figure 4, there ls shown a sche-matic block dia~ram of the carriage servo subsystem 55.
The carriage servo subsystem 55 comprises a plurality of current sources 230 through 235. The function of each of these current sources is to provude a predeter-mined value of current in response to an 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~ comprises a plurality of in-dividual lines. For the purposes of this description, each of these lines will be identified as l&Oa through l~Oe. Tlle ou~puts of the current sources 230 through 235 are applied to a summatioll circuit 238. The 1150834 ' output fro~ the summation circuit 238 is applied to a p^wer amplifier 240 over a linc 242. The output from ~he power ampli ier 240 is applied to the carriage motor 57 over the line 150. A dashed line 244 extending between t'ne carriage motor 57 and the carriage tachometer .member 58 indicates that these units are mechanically connected. The output from the carria~e tachometer 58 is applied to the summation circuit by the line 152.
The STAP~T pulse is applied to the current source 232~ over a line 180al. The current source 232a functions to provide a predetermined current for moving the carriage assembly from its initial rest posltion to the desired start of track position. As previously mentioned the carriage assembly 56 and the optical system 2 are moved relative one to the other. In the standard PLA~' mode of operation, the optical s~Tstem 2 and carriage assembly 5~ are moved such that the read beam 4 from the laser 3 is caused to impinge UpOIl the start Or the recorded information. Accordingly, the current source 232 generates the current for applica-tion to the summation circuit 238. The summation circuit 238 functions to sense the several incremental amounts of current being generated b~T the ~arious current sources 230 through 235 and compares this sum of the currents against the current being fed into the summation circuit 238 from the carriage tachometer system 58 over the line 152. It has been previously mentioned that the current generated b~J the carriage tachometer 58 indicates the instantaneous speed and position of the carriage assembly 55. This current on the line 152 is compared with the currents being generated by the current sources 230 through 235 and the resulting difference current is applied to the power amplifier 240 over the line 242 for generating the pol~er required to move the carriage motor 57 to the desircd locatio;l.
Only for purposes of e~;ample, the carriage tachometer 58 could be generatil~ a r.egative current indicating that the carriage assembly 56 is positioned ~iS083~

at ~ first location. The currellt source 2,2a would generate a second current indicati!~ the desired posi-tiOIl for the c~rriage assembly 56 to reach for start-up time. The summ~tion circuit 23~ compares the two currents and 6enerates a resulting difference current on th2 line 242 for applicaticn to the po~er amplifier 240. The output from the amplifier 240 is applied to the carriage motor 57 for driving the carriage motor and mo~ing 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~Jn by the line 244. As its position changes, the carriage tachometer 58 generates a nel~ and differ-ent signal on the line 152. ~en the carri~ge tachom-eter 58 indicates that it is at the same position asindicated b~T the output signal from the current source 232a, the sum~ation circuit 238 indicates a COr~PARE
EQUAL condition. No signal is applied to the po-~er amplifier 240 and no additional power is applied to the carriage motor 57 causing the carria~e motor 57 o stop.
The START signal on the line 180al causes the carriage motor 57 to move to its START position. When the spindle servo subs~Jstem 50 has brought the speed of rotation of the spindle 49 up to its reading speed, a PLAY ENAELE signal is generated by the spindle servo subsystem 50 for application to a current source 230 over a line 54. The current source 230 generates a constant bias current sufficient to move the carriage assembly 56 a distance of 1.6 microns for each revolu-tion of the disc. This bias current is applied to the summation circuit 238 for providing a constant current input signal to the poiler amplifier for driving the carriage motor 57 at the indicated distance per revo-luticn. This constant input bias currer.t f~cm thecurrQnt source 230 is f-ur~her ideni;irled as a ~i st fixed bias control signal to the carriage motor 57.
The current source 231 receives a FAST FORWARD
E~A~LE signal from the functicn generator 47 over the 115083~

line 18~`o. The fast fort~ard current source 231 ~ener-ates an o~ltpU~ current signal for application to the summation circuit 238 and the po~1er amplifier 240 for activating the carria~e motor 57 to move the carriage

5 assembl~ 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 as indicated by the double headed arrow 13 shown in Fi~re 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 subsyste~ is capable of providing relative motion between the carriage assembly and the optical s~Jstem 2 such as to traverse the typically four inch wide band of informatio:l bearing surface ~ the video disc 5 in approximately four seconds fro.~ the outer periphery to the inner peripher~. The average speed is one inch per second. During the four second period, the reading head moves across appro~imatel~ forth-four thousand tracks. The video disc is revolving at nearly thirty revolutions per second and hence, under idealized con-ditions, t'ne video disc 5 rotates one hundred and t~enty times while the carriage servo subsystem 55 provides the relative motion from the outer periphery to the inner peripher~J. Hence~ the absolute point of 3o impact of the reading beam upon the rotatin~ video disc is a spirally shaped llne having one hundred and twenty 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 doublc headed line lo.
The currer.t source 23~ receives its ~A~ FE-VERSE EN~BIE signal from the function generator 47 over the line 180c. The fast reverse current source 233 pr~-vides its output directly ~o tlle summation ci.cuit 238.

1~S0834 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 ~r~
~ 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 nGrmal mode of operation. A second current source operates as a means for generating a current of the same but greater amplitude to direct the carriage assembly to move at a higher rate of speed in the same direction as the bias current. This second type of current ceases to operate when the carriage assembly reaches its predetermined position.
An additional current source is available for generating a current value of opposite polarity when compared with the permanently available bias current for causing the carriage motor to move in a direction opposite to that direction moving under the influence of the permanently available bias current.
A summation circuit is employed for summing the currents available from the plurality of current sources for generating a signal for giving directions to the carriage motor. The summation circuit also sums the output current from the carriage tachometer indi-cating the instantaneous speed and location of the carriage assembly as the carriage assembly move pur-suant to the various commands from the input current generators. The summation circuit provides a differ-ence output signal to a power amplifier for generating the power required to move the carriage assembly such ,~

that the currellt getl~rated in the carriage tachometer matches the current generated from input current sources.
Rererring collectivel-~ to Figure 5 and Figures oA through 6F there ls shown and described a schematic block diagram Or the focus servo subs~Jstem 36 a plur-ality of d~fferent waveforms which are employed with the focus servo subs~stem and a plurality of single lo~ic diagrams showing the sequence of steps used in 10 the focus servo to operate in a plurality of different modes of operation. The focus error signal from the signal recovery subsystem 30 is applied to an ampli~ier and loop compensation circuit 250 over the line 38.
The output fromthe amplifier and loop compensation cir-suit 250 is applied to a kicl~back pulse generator 252over a line 25~ and to a focus servo loop switch 256 over the line 254 and a second line 258. The output from the kickback pulse generator 252 is applied to a driver circuit 260 over a line 202. The output from the focus servo loop switch 255 is applied to the - driver circuit 260 over a line 264.
The FM video signal is applied from the dis-tribution amplifier portion of the FM processing sub-system 32 to a FM level detector 270 over the line 66. The output from the Fr~ le~el detector 270 is ap-plied 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 focus logic circuit is applied to the focus servo loop switch 256 over a line 276. A second output signal from the acquire focus logic circuit 272 is applied to a ramp generator clrcuit 278 over a line 280. The acquire focus logic circuit 272 has as its second input signal the acquire focus enable signal generated by the functioll generator l~7 over the line 146. The output of the ramp generator 278 is applied to the driver circuit 260 over a line 281.
The acquire focus enable si nal applied to the 115~834 acquire foc~ls logic 272 over the line 145 is shown on line A of FiOure 6A. Easically~ this si~nal is a two-le~el signal generated by the function generator 47 and havin~ a disabling lower condition indicated at ~82 and an enabling conditioll indicated ger.erally at 28~. The function generator produces this pulse when the video disc player 1 is in one Or its play modes and it is neccssary to read the information stored on the video disc 5.
Referring to line ~ of Figure 5A, there is shol~n a typical ramping voltage waveform generated by the ramp generator circuit 278. During the period of time corresponding to the disabling portion 282 of the acquire focus si~nal, the focus ramp wave~orm is in a quiescent condition. Coincidental ~ith the turning on of the acquire focus enable si~nal, the ramp generator 278 generates its rampin~ voltage waveform shown as a sawtooth type output waveform going frcm a higher position at 286 to a lo~ler position at 288. This is sho~m as a linearly changin~ 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 operat-lng modes of the video disc 25 player. Prior to the generation of the acquire focus enabie signal, the lens is generally in a retracted position indicated generally at 290. Upon the receipt of the acquire focvs enable signal, the lengs begins to move in a path indicated by the dash/dot line 292.
30 The dash/dot line 292 begins at a point identified as the upper limit of lens travel and moves through an intersection with a dotted line 294. This point of intersection is identified as the lens in focus posi-tion 293 . I~hell focus is not acquired on the first 35 attempt, the lens continues along the dash/dot line 292 to a p~int 295 ident ~ ie~ a5 lO~Jer limi~v of lens travel. I~en the lens reaches point 295, the lens remains at the lower limit cr lens travel through the portinn of the line indicated generally at 296. The 1150834 `

lens continues to follo~ the dash/dot line to a point in~icated at 297 identified as the RAMP R~SET polnt.
T',~is is also shown on line A as 28~. During the ramp reset ti~e th2 lens is drawn back to the up~er limit of lens travel portion of the waveform as indicated at 298.
In this first mode of operation the lens fails in its f~rst atte~pt at acquiring focus. The lens passes through the lens in focus position as indicated by the dotte~ 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 limit Or lens travel position are sensed by li~it switches in the lens driver sul~assembly not shown.
During a successful attempt to acquire focus, the path of lens travel changes to the dotted line indicated at 294 and remains there until focus is lost.
The lens is ~rmally one micron above the video disc 5 when in the focus position. Also, the i~-focus posi-~ tion can vary over a range of 0.3 microns.
The out~ut signal from the ramp generator 278 to the driver 260 on the line 281 has the configuration sho~ln on line ~ of Figure 6A.
The waveform shown on line G Or Figure 6A
shows the wave shape of the signal applied to the FM
level detector 270 over the line 56. The waveform shown on line G illustrates two principal conditions. The open double sided sharp pulse indicated generally at 30 300 is generated b~J the signal recovery subsystem 30 as the lens passes through focus. This is shown by the vertical line 301 connecting the top of the pulse 300 with the point on line 292 indicating that the lens has passed throu~h ~he ln-focus position as indicated by its intersection with the dotted line 294. Correspond-ing to the description previously given ~lith reference to line C of Figure 5A, the lens passes through focus and the sharp pulse retracts to its no activity level indicated generally at 302.

1150834 ( --4 i--In the second illustration, the waveform shown on line G of Figure 6A illustrates the output from the F~l distribution amplifier on the line 56 wher. the lens acquires focus. This is indicated by the envelope generall~y represented by the crossed hatched sections between lines 304 and 306.
Referring to the waveform shown on line H of Figure 6A, there is shown a dash/dot line 30~ 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 sho~s the loss of the FM signal by the detector 270.
The solid line 312 shows the presence of an FM signal detected by the FM level detector when the lens ac-quires focus. The continuing portion of the waveform at 312 indicates that a FM signal is available in the focus servo subsystem 35.
Referring to line I of Figure 6A, there is ~ shown the output characteristic of the focus servo loop switch 255. In the portion of its cperating character-istics generally indicated by the portion of the line indicated at 314, the switch is in the ofl 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 focus is acquired. The operating mode of the Yideo disc player ~uring the critical period of acquiring focus is more full~J described with reference to the waveforms shown in Figure 6C. Line A of Figure 6C
represents a corrected differential focus error gener-ated by the signal recovery system 30 as the lens follows its physical path as previousl~- described with reference to line C of Figure 6A. At point 319 of the waveform A shown in ~igure 5C, the differe~ al focus error corresponds to a portion Or the lens ~ravel du~ing which no focus errors are available. At the region indicated at 320, the first false in-focus error signal ~15G 834 is availa~le, The~ is first a mQmentary rise ln focuserrcr to a first maximum initlal level at polnt 322.
.~t point 3?~, the differential focus error begins to rlse in the opposite direction until it peaks at a point 5 32~. T`.le differenti~l focus error begins to drop to a second but opposite maximum at a point 325. At a point 328, halfwaJ between the points 324 and 325, is the optimum in-focus position for the lens. At this point 328, the lens gathers maximum reflected light from the video disc surface. Continuing past point 326, the differential focus error begins to fall towards a second false in-focus condition represented at this point 330. The differential focus error rises past the in-~ocus position to a lower maximum at 332 prior 15 to falling back to the position at 333 where no focus error informatioll 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 presentl~
20 bathing 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 towards the video disc 5 in an 25 attempt to acquire focus. It should be noted that the frequency modulated signal from the video disc 5 is detected only over a small distance as the lens reaches optimum focus, and then passes 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 ~hen focus is missed.
I~,'hlle focus can be achieved using only the differential focus error signal shown with reference to line A of Figure 6C, one embodiment Or the present invention utilizes the dir~erential fscus error signal as shown on line A of Figure 6C ln combination with the signal shown on line ~ Or Figure 6C to achieve more reliable acquisition of focus during each attempt at 1150834 ~

~ocus .
Fisure C of line 6C shows an inverted ideal-i~ed focus error si~nal. This ideallzed error signal is then differentiated and the results shown on llne D
of Figure 6C~ The differentiation of the idealized focus error signal is represented by the line 339.
Small portions of this line 339 shown at 340 and 342 lyin~ above the zero point indicated at 344 give false indication of proper focusing regions. The region 346 falling under the line 339 and above the zero ccndi~ion represented by the line 34L~ indicates the range within which the lens should be positioned to obtain proper and optimum focus. The region 346 repre-sents approximately 0.3 microns of lens travel and corresponds to the receipt of an Fr~ input to the FM
level detector as shown in line ~. It should be noted that no F~ is shown on line ~ correspondin~ to regions 340 and 3~'2. Hence, ~he 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 foc~s.
The signal representing the differentiation Or the idealized ~ocus error is applied to the gener-25 ator 252 ror activating the generator 252 to generate its kickback waveform. The output from the FM level detector 270 is an alternative input to the kickback generator for generating the ki~kback waverorm for application to the driver 260.
Referrlng 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 range. This is a sawtooth signal and it is calculated to move the lens s~oothly through the point at which F~1 is detected by the FM level detector 270 as indi-cated by the waveform on line H. In a flrst mode of operation, the rOcus ramp follows a dot-dash portion .....

- 1151)834`

23ï of the waverorm to a p~)int 2~7a corresponding to the time at which the output of the FM level detector sho-~;s the acquisition of ~ocus ~y ~enerating the si~nal level at 312a in line ~I. The output signal from the acquire focus logic bloclc 272 turns orf the ramp gen-erator over the line 280 indicating that fccus has been acquired. llhen focus is acquired, the output from the ramp generator follows the dash line porticn at 287b indicating that focus has been acquired.
Referring to line A of Figure 6E, a portion of the focus ramp is shown extending between a first upper voltage at 286 and a second lower voltage at 288. The optimum focus point is located at 287a and corresponds with the peak of the FM signal applied to the FM
level detector 270 as shown on line C of Fi~ure 6~.
Line ~ is 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 function line 290 extends between an upper limit Or lens travel indicated at point 292 and a lower limit of lens travel indicated at point 295. The optimum lens focus position is indicated by a line 295.
The optimum lens focus point is therefore located at 299.
Referring to line D of Figure 6~, there is shown the superimposing of a kickback sawtooth wave-form indicated generally in the area 300 upon the lens position transfer line 292. This indicates that in the top portion of the three kickback pulses are located at 302, 304 and 306. The lower portion of the three klckback pulses are located at 308, 310 and 312, re-spectively. The line 296 again shows the point of optimum ~ocus. The intersection of the line 296 with the line 292 at points 296a, 296b, 295c and 296d shows that the lens itself passes through the optlmum lens focus position a plurality of times durin~ one acquire focus enable function.
Referring to line E of Figure 6~, the input to the FM level ~etector indicates that during an oscillaior,~ mo1~ioll of the lens tllrough the optlmum focus positlon as shown by the combined lens travel function cllaracteristic shown in Fi~ure D, the lens has the opportunity to acquire focus Or the FM signal at four locations indicated at the peaks of waveforms 314, 316, 318 and 320.
The ~Javeforms shown with reference to Fi~ure 6Pi demonstrate that the addl~ion of a high frequency oscillating sawtooth kickback pulse upon the ramping signal generated by the ramp generator 278 causes the lens to pass through the optimum lens focus position a plurality of times for each attempt at acquiring lens focus. This improves the reliability of achieving proper lens focus during each attempt.
The focus servo system employed in the present invention functions to position the lens at the place calculated to provide optimum focusing of the reflected read spot arter impinging upon the information track.
In a first mode Or operation, the lens servo is moved under a ramp voltage waveform from its retracted posi~ion towards its fully down position. When focus is not acquired during the traverse of this distance, means are provided for automatically returning the ramping voltage to its original position and retracing the lens to a point corresponding to the start of th~
ramping voltage. Thereafter, the lens automatically moved through its focus acquire mode of operation and through the optimum focus position at which focus is acquired.
ln a third mode of operation, the fixed ramp-ing waveform is used in combination 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 bearing surface o~ the video disc and an output is indicated at an r'~il detector. In a further embodimentj an oscillatory waveform is superimposed upon the ramping vol~age to help the lens acquire proper focus. The oscillatory waveform is triggered ` liS0~34( by a number Or alternative input slgnals. A first such input si~nal is the output from the ~M detector indicating that the lens has reached the optimum focus point. A second trl~ering signal occurs a fixed time after the beginning Or the ramp voltage ~aveform. A
third alternative input signal is a derivation of the differential tracking er~r indicating the point at which the lens is best calculated to lie within the range at which optimum focus can be achieved. In a further 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 in focus even though there is a momentary loss of detected frequency modulated signal. This is achieved by constantly monitoring the presence of FM signal detected from the video disc.
Upon the sensing of a momentary loss of frequenc~
modulated signal, a timing pulse is generated which is calculated to restart the focus acquire mode ~ oper-ation. However, i~f the frequency modulated signalsare detected prior to the termination of this fixed period of timej the pulse terminates and the acquire focus mode is skipped. If FM is lost for a period of time lon~er than 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.
~OCUS 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 untll the objective lens 17 acquires optimum focus of the light modulated signal being refl2cted from the surface of the video disc 5. Due to the re-solving power of the lens 17, the optimum focus point is located approximately one mlcrGn from the disc surface. The range of ler.s traYel at Wh~C';l optlmu~
focus can be achieved is 0.3 microns. The information bearing surface of the video disc member 5 upon which the light reflective and light non-reflective members :
. _ '` 1150834 ( ~4~,-are positioned, are o~tentimes distorted due to imper-fections in the manufacture of the video disc 5. The video disc 5 is manufactured according to standards t~llich l`~ill make availa~le 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 subsystem 35 responds to an enabling signal telling the lens driver mechanism when to attempt to acquire focus.
A ramp generator is a means for generating a ramping voltage for directing the lens to move from its upper retracted position down towards the video disc member 5. Unless interrupted by external signals, the ramping 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 voltage. The full lens down position can also be indicated by a limit switch which closes when the lens reaches this position.
~ The lens acquire period equals the time of the ramping voltage. At the end of the rampin2 voltage period, automatic means are provided for automatically resetting the ramp generator to its initial positicn at the start of the ramping period. Operator interven-tion is not required to reset the lens to its lens acquire mode in the preferred embodiment after focus was not achieved during the first attempt at acquiring focus.
In the recovery of F.M video information from the video disc surface 5, lmperfections on the disc surface can cause a momentary loss of the FM signal being recovered. A gating means is provided in the lens servo subsystem 36 for detecting this loss FM
from 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-s~Jstem 3~ for a predetermlned time. Du,ing th~s pre-determined time, the reacquisition of the FM signal prevents the FM detector means from causing the servo subsystem to restart the acquire focus mode of operation.

834 ( ~ ,~
In the everlt that F~l is not detected during thls first predetermined time the FM detector means reactivates the ramp generator for generat~ng the ramping slgnal which causes the lens to follow through the acquire focus procedure. At the end of the ramp generator period) 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 upon it an oscillatory sequence of pulses. The oscillatory sequence of pulses are added to the standard ramping voltage in response to the sensing of recovered F~
from the video disc surface 5. ~he combination of the oscillatory waveform upon the standard ramping voltage is to drive the lens through the optimum focus position in t~e 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 focus ramp signal. ~lile this is not as efficient as using the Fi~ level detector output signal as the means for triggering the oscilla-tor~r waveform ger.erator it provides reasonable and reliabl~ results.
In a third embodiment, the oscillatory wave-form is triggered by the compensated tracking error signal.
Referring to Figure 7, there is shown a schematic block diagram of the signal recovery sub-system 30. The waveforms shown in Flgure 8, lines ~, C and D, lllustrate certain of the electrical waveforms available within the signal recovery subsystem 30 during the normal operation of the player. P.eferring to Figure 7, the reflected light beam is indicated at 4' and is divided into three principal beams. A first beam impinges upon a first trac~ing photo detector indicated at 380, a second portion of the read beam ~' 0~33~
impinges UpOIl a second tracking photo detector 382 and the central ~nformation beam is shown impi~glng upon a concentric ring detector indicated generally at 384.
The concentric ring detector 384 has an lnner portion at 38~ and an outer portion at 388, respectively.
The output from the first tracking photo de-tector 380 is applied to a first tracking preamp 390 over a line 392. The output from the second tracking photo detector 382 is applied to a second tracking preamp 394 over a line 395. The output from the inner portion 386 of the concentric ring detector 384 is applied to a first focus preamp 398 over a line 400.
The output from the outer portion 388 of the concen-tric rin~ detector 384 is applied to a second focus pre-amp 402 over a line 404. The output frcm both portions386 and 388 of the concentric ring focusing element 384 are applied to a ~ide band amplifier 405 over a line 405. Al alternative embodiment to that sho~n would include a summation of the signals on the lines 400 20` and 404 and tlle application of this sum to the wide band amplifier 405. The showing of the line 405 is schematic in nature. The output from the wide band amplifier 405 is the time base error corrected fre-quency modulated signal for application to the FM
processing subsystem 32 over the line 34.
~ The output from the first focus preamp 398 is applied as one input to a differential amplifier 408 over a line 410. The output from the second focus preamplifier 402 forms the second input to the differ-3 ential amplifier 408 over the line 412. The outputfrom the differential amplifier 408 ls the differential focus error si~nal applied to the focus servo 36 over the line 38.
The output from the first tracking preampli-fier 390 forms one input to a differential amplifier 414 over a line 415. The o~ltput fromthe second track-ing preamplifier 394 form~ a secona inpu~ to tne diffe~
ential amplifier 414 over a line 418. The output from the differential amplifier 414 is a differential track-liS083 --5(~ -ing error signal applied to the tracking servo system over the line 4. and applled to the stop motion sub-syste!n over the line 42 and an addltional line 45.
Line A of Figure 8 SIlOwS a cross-sectlonal view taken in a radial direction across a video disc member 5. Light non-re~lective elements are shown at 11 and intertr~ck re~ions are shown at lOa. Such inte~-track regions lOa are similar in shape to light re-flective elements 10. The light reflective regions 10 10 are planar in nature and normally are hiGhly polished surfaces. such as a thin aluminum layer. The light n2r.
reflective regions 11 in the preferred embodiment are light scatterillg and appear as bumps or elevations above the planar surface represented by the light re-flective regions 10. The lengths of the line indicatedat 420 and 421 shows the center to center spacing of tl~10 adjacently positioned tracks 422 and 423 about a center tracl~ 424. A point 425 in the line 420 and a point 425 in the line 421 represents the crossover point 20` between each of the adjacent tracks 422 and 423 ~hen - leaving the central track 424 respectively. The cross-over points 425 and 425 are each exactly halfway be-tween the central track 424 and the tracks 422 and 423 respectively. The end points of line 420 represented at 427 and 428 represellt the center of information tracks 422 and 424, respectively. The end of line 421 at 429 represents the center of information track 423.
The waveform shown in line B of Figure 8 represents an idealized form of the frequency modulated signal output derived from the modulated light beam 4' during radial movement of the read beam 5 across the tracks 422, 424 and 423. This shows that a maximum frequency modulated signal is available at the area indicated generally at 430a, 430b and 430c which correspond to the centers 427, 42~ and 429 of the in-formation tracks 422J 424 and 423, res~,ectivel~y. A
minimum frequency modulated signal is available at 431a and 431b wllich corresponds to the crossover poi-.ts 425 and 425. The waveform shown on line ~ of Figure 3 is generaled by radially movlng a focused lens across the surface Or a video disc 5.
Referriilg to line C of Fi~ure 8, there ls shown the differential tracking error signal generated in the differential amplifier 414 shown in Figure 7.
The differential tracking error signal is the same as thai shown in lille A of Figure 6C e~cept for the details shown in the Figure 6C for purposes of explanation of the focus servo subs~stem peculiar to that mode of operation.
Referring again to Figure C of line 8, the differential trac~ing error signal output shows a first maximum tracking error at a pOillt indicated at 432a and ~32b which is intermediate the center 428 of an information 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 intermediate the crossover points 425 and 425 between the information track 424 and the next adjacent tracks 422 and 423. Minimum focus error is shown in line C at 440a, 440b and 440c corresponding to the center of the information tracks 422, 424 and 423, respectivel~r. 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 ~f identi-~ying which of the minimum differential trackin~ error signal outputs corresponds with the center Or 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 o, there is shown the differential focus error signal output wave-form generated b~ tlle differenti~l amplifier 408. The waveform is indicated generallJ- b~ a line 442 which moves in quadrature with the differenti~l tracking error signal shown with reference to line C of Figure 8.

5~
Rel'erring to Flgure 9J there is shown a schemat1c block diagram of the tracking servo subsystem 40 emplo~red ln the video disc pla~er 1. The dlf-eren-tial trackin~ error is applled to a track~n~ servo loop interrupt swltch 480, over the llne 4~ from the signal recovery system 30. The loop lnterrupt signal is ap-plied to a ~ate 482 over a line 108 from the stop motion subsystem 44. An open fast loop command signal is applied to an open loop fast gate 484 over a line 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 180b is diagra~matically shown as the samR signal applied to the carriage servo fast forward current generator over a line 180b. The console s~Jitch is s'nown enterin~ an open loop fast gate 48~ over the line 180b'. The fast reverse command from the remote con-trol portion of the function ~enerator 47 is appliedto the open loop fast gate 4~4 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 gate 484 is applied to an or gate 488 over a line 490.
The output from the open loop fast gate 486 is applied to the or ~ate 488 over a llne 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 is 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 llne 505 and an amplifier and fre-quenc~r compensation net~:ork 510. The other end of the resistor 498 is connected 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 l~SOW~

signal from the stop motion subsystem 44 over the line lOo. The signal on the line 106 is a stop motlon eom-pensation pulse.
The function of the amplifier 510 is to provide a DC eomponent of the traelcing error, developed over the combination of the resistor 498 and eapaeitor 502, to the carriage servo system 55 durin~ normal tracking periods o~er a line 130. The DC component from the junction 496 is gated to the carriage servo 55 by the play enabling signal from the funetion generator 47.
The push/pull amplifier circuit 500 generates a first traeking A signal for tlle radial tracking mirror 28 over the line 110 and generates a seeond tracking B output signal to the radial tracking mirror 28 over the line 112. The radial mirror requires a maximu~. of 600 volts across the mirror for maximum operating e~fieieney when bimorph type mirrors are used. Accordingly, the push/
pull amplifier circuit 500 comprises a pair of ampli-fier circuits, eaeh one providing a three hundred voltage swing for driving the tracking mirror 28.
~ Together, theJ 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 eombined with the detalled descrip-tion of the operation of the stop motion subsys~em 44 shown with reference to Figure 12 and the waveforms shown in Figures 13A, 13~ and 13C.
TRACKING SERVO SU~SYSTEM - NO~MAL MODE OF OPERATION
-The video dise member 5 being played on the video disc player 1 contains approximately eleven thousand information tracks per ineh. The distanee from the center of one information traek to the next ad~acent information trae~ ls in the range cf 1.6 microns. The informaticn indici~ aligned n an informa-tion track is approximately 0.5 microns in width. This leaves approximatel~ one micron of empty and open space between the cutermost regions of the indicia positioned in adjaccrlt irirormation bearing tracl;s.
The function of the tracklng servo ls to direct the impinement of a focused spot of light to imp~ct directly upon the center of an lnformatlon track.
The focused spot of light is approxlmately the same width as the information bearing sequence of indicia which form an information track. Obviously, maximum signal recovery ls achieved when the focused beam of light is caused to travel such that all or most of the light spot impinges upon the successively positioned light reflective and light non-reflective regions of the information track.
The tracking servo is further identified as the radial tracking servo because the departures from 15 the information track occur in the radial direction upon the disc surface. The radial tracking servo is continuously operable in the normal play mode.
The radial tracking servo system is interrup~ed or released from the differential tracking error signal 20 generated from the FM video information signal recov-ered from tile video disc 5 in certain modes of opera-tion. In a first mode ~ operation, when the carriage servo is causing the focused read beam to radially traverse the 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 jump back mode of operation wherein the 30 focused reading beam 4 is caused to jump from one track to an adjacent track, the differential tracking error is removed from the radial tracking servo loop for eliminating a signal from the tracking mirror drivers which tend to unsettle the radial mirror and tend to 35 require a longer period of time prior for the radial tracking ser~o subsys'em to reacnuire proper tracking of the nex.t adjacent informatioll track. In this embod-iment of operation where the differential tracking error is removed from the tracking mirror drivers, a substitute ,, .
. . .~

-5~-pulse is generated for giving a clean unambiguous signal to the trackin~ m~rror drivers to direct the 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 of pre-emphasis at the beginning and end of the stop motion pulse which are tailored to direct the tracking mirror drivers to move the focused spot to the predetermined next track location and to help maintain the focused spot in the proper trackin~ position. In review, one mode of operation of the video disc player removes the differential tracking error signal from application to the trac'~ing mirror drivers and no additional signal is substituted therefor. In a further embodiment of operation of the video disc player, the differential tracking error signal is replaced by a particularly shaped stop motion pulse.
In a still further mode of opera'ion of the tracking mirror servo subsystem 40, the stop motion pulse which is employed for directing the focused beam to leave a f~rst information track and depart for a second adjacent information track is used in combina-tion with a compensation signal applied directly to the radial tracking mirrors to direct the mlrrors to main-tain focus on the next adjacent track. In the preferr~embodiment, the compensation pulse is applied to the tracking mirror drivers after the termination of the stop motion pulse.
In a still further embodiment of the tracking servo subsystem 4~s the differential tracking error signal is interrupted for a period less than the time necessary to perform the stop motion mode of operation and the portion of the differential tracking error allowed to pass into the tracking mirror drivers is calculated to assist the radial tracking mirrors to achieve proper radial tracking.
Referring to Figure 11, there is shown a block diagram of the tangential servo subsystem 80. A first input signal to the tangential servo subsysiem 80 is ~150834 ( --,6--applied from the FM processing system 32 over the line 62. The signal present on the line 82 is the video signal available frcm the vodeo distribution ampl~-fiers as contained in the FM processing system 32, The video signal on the line 82 is applied to a sync pulse separator circuit 520 over a line 522 and to a chroma separator filter 523 over a line 524. The 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 subsystem 44 over the line 92. The lunction of the chroma separator filter 523 ~s to separate the chroma portion fro~ the total video signal received from t~le FM processing circuit 32.
The output from the chroma separator filter 523 is ap-plied to the FM corrector portion of the FM process-~ ing circuit 32 over the line 142. The output signal from the chroma separator filter 523 is a}so appliedto a burst phase detector circuit 52~ over a line 52~.
The burst phase detector circuit 526 has a second input signal from a color subcarrier oscillator circuit 530 over a line 532. The p~rpose of the burst phase de-tector circuit 52~ is to compare the instantaneousphase of the color burst signal with a very accurately generated color subcarrier oscillator slgnal generated in the oscillator 530. The phase dif`ference detected in the burst phase detector circuit 525 is applied to a sample and hold circuit 534 over a line 535. The function of the sample and hold circuit is to store a voltage equivalent of the phase difference detected in the burst phase detector circuit 526 for the time during which the f'ull line of` video inf'ormation containing that color burst signal, used in generating the phase difference, is read f`rom the disc 5.
The purpose cf the burst gate separator 525 ls to generate an enabling signal indicating the time during which the color bu-st portion of the video 334 ( ~aveform is received from the FM processing unit 32.
The output signal from the burst gate separator 525 is applied to tile FM corrector portion of the FM
processin~ system 32 over a line 144. The same burst gate timin~ signal is applied to the sample and hold circuit ~4 over a line 538. The enabling signal on the line 53S gates the input from the burst phase de-tector 52~ into the sample and hold circuit 534 durin~
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 subcarrier oscillator circuit 530 supplies the color subcarrier frequency to a divide circuit 540 over a line 541 which dlvldes the color subcarrier frequency by three hundred and eighty-four for generating the motor reference frequency. The motor reference fre-quency signal is applied to the spindle servo subsystem 50 over the line 94.
The output from the sample and hold circuit - 531' ls applied to an automatic gain 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 25 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 lnside track to the outside track and/or conversely when 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 re~ions 10 and non-reflective regions 11 w~th difrerent dimensions from the outisde track to the inside track. The purpose of the constant rotational speed rrom the spindle motor 48 is to turn the disc 5 through nearly thirty revol~tions per second to provide thirty frames of in~ormation tothe television receiver 96. The length of a track at the outermost circum-ference is much longer than the len~th of a track at -5~
tlle innermost circumrerence. Since the sa~e amount Or infornation is stored in one revolution at ~cth the inner and outer circumference, the si~e of the reflec-tive and non-reflective regions 10 and 11, respectively, are adjusted from the inner radius to the outer radius.
Accordin~ly, this change in si7e requires that certain adjustments in the ~rocessing of the detected signal read from ihe video disc 5 are made for optimum opera-tion One of the required adjustments is to adjust the gain of the amplifier 542 which adjusts for the time base error as the reading poi-nt radially changes from an ins~de 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 54~. The compensation net-r~orlc 545 is employed for preventing any system oscillations and instabilit~J. The output from the compensation net~ork 545 is applied to a tangential mirror drlver circuit 500 over a line 550. The tangential mirror driver circuit ~00 was described with reference to Figure 9.
The circuit 500 comprises a pair of push/pull ampli-fiers. The output from one ~ the push/pull amplifiers (not shown) is applied to the tangential mirror 26 over a line 88. The output fromthe second push/pull amplifier (not shown) is applied to the tangential mirror 26 over a line 90.
TIi~E ~ASE ERROR CORPECTION MODE OF OPERATION
The recovered FM video sigilal, from the surface of the video disc 5 is corrected, for ti~e base errors introduced by the mechanlcs of the reading process, in the tangential servo subsystem 80. Time base errors are introduced into the reading process due to theminor imperfections in the video disc 5. A time base error introduces a slight phase change into the re-covered Fr~l video signal. A typical time base error base correction system includes a highly accurate 1 15~
oscillator for generating 3 source of slgnals used as a phase standard for comparison purposes. In the pre-ferred embodiment, the accurate osclllator is conven-iently chosen to oscillate at the color subcarrier frequellcy. T:~e color subcarrier frequency is also used during the wrlting process for controlling the speed of revolution of the writing disc during the ~riting process. In this manner~ the reading process is phase controlled by the same highly accurate oscil-lator as ~as 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 signal forms a small portion of the recovered FM video signal. A color burst signal ls repeated in each llne 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 with 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 si~nal or its equivalent, but may be sampled at randomly or pre-determined locations in the recovered signal contain~ng the recorded equivalent of the color burst signal.
~hen the recorded inform~tion is not so highly sensi-tive to phase error, the comparison may occur at greater spaced locations. In general, ~e phase difference bet~een the recorded signal and the locally generated signal is repetitively sensed at spaced locations on the recording surface for adjusting for phase errors in the recovered signal. In the preferred embodiment this repetitive sensing for phase error occurs on each line of the FM video signa.

.:

1150834 `
~,~
The detected phase error ls stored for a period of time extending to the next sampling process.
This phase error is used to adjust the reading posi-tiCIl of ~le reading beam so as to impinge upon the video disc at a location such as to correct for the phase error.
Repetitive comparison of the recorded signal with the locally generated, highly accurate frequency, continuousl~ ad~usts for an incremental portion of the recovered video signal recovered during the sampling periods.
In the preferred embodiment, the phase error changes as the reading beam radially tracks across the information bearin2 surface portion of the video disc 5.
In this embodiment, a further signal is required for adjusting the phase error according to the lnstan-taneous location of the reading beam to ad~ust the phase error according to its instantaneous location on the information bearing portion of the video disc 5 This additional signal is caused by the change in physical size of the indicia contained on the video disc surface as the radial tracking position changes from the inner location to the outer location. The same amount of information is contained at an inner radius as at an outer radius and hence the indicia must be smaller at the inner radius when compared to the indicia at the outer radius.
In an alternative embodiment, when the size of the indicia is the same at the inner radius and at the outer radius, this additional signal for ad~usting for instantaneous radial position is not required.
Such an embodiment would be operable with video disc members which are in strip form rather than in dlsc form and when the information is recorded using indicia of the same size on a video disc member.
In the preferred embGdiment, a tangential mirror 26 is t}le mechanism selected for correcting the time base errors introduced by the mechanics cf the reading system. Such a mirror is electronically liS0834 i controlled and is a means for changing the phase ~ the recovered video signal read from the disc by changing the time base on which the signals are read from the disc. This is achieved by directing the mirror to read the information from the disc at an incremental point earlier or later in tine ~hen compared to the time and sp~cial location during which the phase error .~as detected. The amount of phase error determines the degree of change in location and hence time in which 10 t'ne information ~s read.
I~en no phase error is detected in the time base corr4cting system the point of impingement of the read beam with the video disc surface 5 is not moved.
'~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 fro~ the video disc is available for processing at a point in time earlier or later when compared to ~ the comparison period. In the preferred embodiment, this is achieved by changing the spacial location of the point of intersection of the read beam with the video disc surface 5.
Referring to Figure 12J there is shown a block diagram of the stop motion subsystem 44 employed in 25 the video disc player 1. The ~aveform shown with reference to Figures 13A, 13B and 13C are used in con~unction with the block diagram shown in Figure to explain the operation of the stop motion system.
The video signal from the FM processing unit 32 is 30 applied to an input buffer stage 551 over the llne 134.
The output signal from the buffer 551 is applied to a DC restorer 552 over a line 554. The function of the DC restorer 552 is to set the blanking voltage level at a constant uniform level. Variations in signal 35 recording and recover~J oftentimes result in video signals available on the line 134 with different blank-ing levels. The output from the DC restorer 552 is applied to a wllite flag detector circuit 550 over a line 558. The function of the white flag detector 555 115~834 ~
-~2-is to idelltif~ the presence Or ar all white 'evel video signal existing during an entire line of one or both fields colltained in a frame of television information.
`~'hile the white flag detector has been described as 5 being detecting an all white video si~nal during a complete line interval of a frame of television in-formatioll, the white flag may take otller forms. One such form would be a special number stored ln a line.
Alternatively, the white flag detector can respond to the address indicia found in each video frame for the same purpose. Other indicia can also be 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 rnost reliable.
The vertical sync signal from the tangential servo 80 is applied to a delay circuit 560 over a line 92. The output from the dela~J circuif, 560 is supplied to a vertical ~indow generator 552 over a line 504.
~ The function of the window generator 552 is to gener-20 ate an enabling signal for application tothe white flag detector 55~ over the line 556 to coincide with that line interval in which the white flag signal ha~ been stored. The output signal from t'ne generator 552 gates the predetermined ~rtion of the video signal 2~ from the FM detector and generates an output white flag pulse whenever the white flag is contained in the portion of the video signal under surveillance. The output from the white flag detector 556 is applied to a stop motion pulse generator 567 over a line 5583 a gate 569 and a further line 570. The gate 569 has as a second input signal, over the line 132, the STOP MOTION
r~ODE enabling signal from the function generator 47.
The differential tracking error from the signal recovery subsystem 30 is applied to a zero crossing 35 detector and delay circuit 571 over the lines 42 and 45. The function of 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 and 423.

115~834 ~`
-~3-It ~ important to note that the differentlal trackin~
sl~nal out.put also indicates the same level signal at point 44~c which identifies the optimum focusing point at which the tracking servo system 40 seeks to position the lens in perfect tracking aligrlment on the mid-point 429 of the track 423 wilen the tracking suddenly ~umps ~rom track 424 to track 423. Accordingl~, a means must be provided for recogni7ing the dif~erence between points 441b and 440c on the differential error signal 10 shown in line C of ~igure 8.
The output of the zero crossing detector and delay circuit 571 is applied to the stop motion pulse generator 567 over a line 572. The stop motion pulse generated in the generator 567 is applied to a plurality of locations tlle first o~ which is as a loop lnterrupt pulse to the tracking servo 40 over the line 108. A
second output signal from the stop motion pulse ~ener-ator 5~7 is applied to a stop motion compensation se-quence generator 573 over a line 574a. The function of the stop mO~iOIl compensation sequence generator 573 is to generate a compensation pulse waveform for appli-cation to the rad~al 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~.
With reference to line A of Figure 8, the center to center distance, indicated by the line 420, between adjacent tracks is presently fixed at 1.6 microns. The tracking servo mirror gains sufficient inertia upon receiving a stop motion pulse that the focused spot from the mirror ~umps from one track to the next adjacent track. The inertia of the tracking mirror under normal operation conditions causes the mirror to swing past the one track to be ~umped.
Brie~ , the stop motion ~ulse on the line 104 causes the rad~al tracking mirror 2~ to leave the track on which it is tracking and ~ump to the next sequential track. A short time later, the radial tracking mirror 083~
-51~

recei~es a stop motion compensation pulse to remove the added inertia and direct the trackin~ mirror into tracking the next adjacent track withcut skipping one or more tracks berore selectin~ a track for tracking.
In order to insure the optimum cooperation bett~een 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 differential trackirg error signal from being applied to the track-ing error amplifiers 500 during the period of time that the mirror is purposely caused to leave one track unde~r d~rection of the stop motion pulse from the generator 557 and to settle upon a next adjacent track under the direction of the stop motlon compensation pulse from the generator 573.
As an introduction to the detail understand-ing of the interaction between the stop motion system 4~ and the trackin~ servo system 40, the waveform shown in Figures 13A, 13~ and 13C are described.
Refer ing to line A of Figure 13A, there is sho~^~n the normal tracking mirror drive signals to the radial trackillg mirror 28. As previously discussed, there are two driving signals applied to t~e tracking mirror 2~. The radial tracking A signal represented by a line 574 and a radial tracking ~ signal represented by a line 575. Since the lnformation track is normally in the shape of a spiral, there is a continuous track-ing control signal being applied to the radial tracking mirror for follot~1ing 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 c~mplete revolution of the disc.
A typical normal tracking mirror drive s_gnal waveform for a single revolution of the disc is represented by the lengt!l of the line indicated at 57~. The two dis-continuities shown at 578 and 580 on waveforms 574 and 575, respectively, indicate the ~ortlon of the normal tracking period at which a stop motion pulse is given.

1150834( -~
, ~ 5 The stop ~otlon pulse is also referred to as a ~ump bac~ signal and these two terms are used to describe the output from the generator 567. The stoo motlor.
pulse ls represented b~ the small vertical'y dispose~
dlscontinul-y present in the llnes 574 and 575 at polnts 578 and 580, respectlvely. The rem2~ni~g wave-forms contained in Figures 13A, 13~ and 13C are on an expanded time base and represent those electrical slgnals whlch occur ~ust before the beginning of thls ~ump back perlod, through the ~ump back perlod and contlnulng a short duration beyond the ~ump back period.
The stop motlon pulse generated by tne stop motion pulse generator 567 and applled to the tracking servo system 40 over the llne 104 ls represented on 15 line C of Figure 13A. The stop motion pulse ls ideally not a squarewave but has areas of pre-emphasis located generally at 58~ and 584. These areas of pre-emphasis insure ~tlmum reliabllity ln the stop motion system 44. The stop motion pulse can be descrlbed as rlsing 20 to a flrst hlgher voltage level during the initial period of the stop motion pulse period. Ne~t, the stop motlcn pulse gradually falls off to a second voltage level, as at 583. The level at 583 is main-tained during the duratlon o`f the stop motion pulse 25 period. At the termlnation of the stop motior. pulse, the waveform falls to a negative voltage le~el at 5~5 below the zero voltage level at 586 and rises grad~ally to the zero voltage level at 586.
Line D of Figure 13 represents the differen-3 tial tracklng error signal recelved from the recover~system 30 over the lines 42 and 46. The waveform shown on llne D of Figure 13A ls a compensated differ-ential trackin~ error achieved through the use of the combinatlon of a stop motion pulse and a stop .~otlon 35 compens~tlon pulse applled to the radlal trac~ing mirror 28 according to the teaching of the present inventlcn.
Llne G of Flgure 13A represents the loop inte~
rupt pulse generated by the stop ~otion pulse 2enera~or 115083~ ( 567 and applied to the tracl;ill~ servo subsystem 40 over the line 108. As previously mentioned, it is best to remove tlle differential tracking error signal as repre-sented b~r the ~aveform on line D from application to the radial tracking mirror 28 during the stop motion interval period. The loop interrupt pulse shown on line G achieves this gating funcrion. Ho-Y~ever, by inspectionj it can be seen that the differential tracking error signal lasts for a period longer than the loop interrupt pulse shown on line G. The waveform shown o~ line E is the portion of the differential tracking error signal shown on line D ~hich survives the gating by the loop interrupt pulse sho~!n on line G.
The waveform shown on line E is the compensated track-in~ error as interrupted by the loop interrup~ pulsewhich is applied to the tracking mirror 28. Referring to line F, the high frequency signal represented gener-ally under the bracket 590 indicates tne output waveform of the zero crossing detector circuit 571 in the stop motion system 44. A zero crossing pulse is generated each time the differential error tracking signal shown in line D of Figure 13A crosses through a zero bias level. Ilhile t~le information shown under the bracket 590 is helpful in maintaining a radial tracklng mirror 28 in tracking a single information track, such in-formation must be gated off at the beginning of the stop motion interval as indicated by the dashed lines 592 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 referring again to line D, the differential tracking error signal rises to a first maximum at 594 and falls to a second opposite but e~ual maximum at 596. At point 59~ e tracking mirror is passing over the zero crossing point 426 between two ad~acent track~ 424 and 423 as s~lown witll rel'erence r O line .~, of ~igure 8.
This means tllat the mirror has traveled half way from the first track 424 to tile second track 423. At this point indicated by Ihe nu~er 598, t~le zerc crossing ~150834 ^~67-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 ~150834 (

-6~-inrormation tracl;, is S~OW`.l at the re~ion 510 of Line A.
Tlle tracking error represents the slight side to side (radial) motion of the read beam 4 to the successively positioned reflec~ive and non-reflective regions on the disc 5 as previously described. A point 612 represents the start of a stop motion pulse. The uncompensated tracking error is increasing to a first maximum indi-cated at 514. The region between 612 and 614 shows an increase in tracking error indlcating the departure of the read beam from the track bein~ read. Fro~ point 614, the dirferential tracking error signal drops to a pcint indicated at 616 which represents the mid-point of an information track as shown at point 426 in line A
Or Figure 8. However, the distance traveled by the 15 read beam bet~een points 512 and 616 on curve A in Figure 13~ is a movement of o.8 microns and is equal to lengtll of line 617. The uncompensated radial track-ing error rises to a second maximum at point 618 as the read bea~ begins to approach the neYt ad~acent track 423. The tracking error reaches zero at point 622 but is unable to stop and continues to a new maximum at 624. The radial tracking mirror 28 possesses suffi-cient inertia so that it is not able to instantaneously stop in ~esponse to the differential tracking error 25 sig!lal 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 polnt indicatcd at 524 wherein the closed loop servo-ing erfect of tl1e tracking servo subsystem slows the mirror do~n and brings the read beam back towards the lnformation track represented by the zero crosslng dif-ferential tracking error as indicated at point 625.
Additional peaks are identified at 626 and 6c8. These show a gradual damping of the differential tracking error as the radial tracking mirror becomes graduall~r positiGned 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 portion of the waveform sho~n in line A

1150834 ~

e~isting arter point 632 shows a gradual return Or the ra~ tracliing error to its zero positlon as the read spot gra~uall~ comes to rest on the ne~t adjacent track 423.
Point 615 represents a false indication of ~ero tracki!lg error as the read beam passes over the cenver 425 of the region between adJacent tracks 424 and 423.
For optimum operation in a stop motion situa-tion wnerein the read beam jumps 'o the next adjacent track, the ti.~e allowed for the radial tracking m~rror 28 to reacquire proper radial tracking is 300 micro-seccnds. This is indicated by the length c~ the line 634 shown on line ~. ~y observation, it can be seen that the radial tracking mirror 28 has not yet reac-quired zero radial error position at the expiration of the 300 microsecond time period. Obviously, if more time were available to achieve tllis result, the wave-~ form shown wlth reference to Figure A would be suitable for those syster.1s having more tirne for the radialtracking mirrol to reacquire zero differential trackin~
error on the center of the next adjacent track.
Referring briefly to line D of 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 showrl with reference to line A. The compensated di~ferential tracking error shown in line D is capable of achieving proper radial tracking by the tracking servo subsystem within the 3 time frame allowed for proper operation of the video dlsc pla~yer 1. Referring briefl~ to line E of Figure 13A, the remaining trackin~ error signal available after interruption b~y the loop interrupt pulse is of the proper direction to cooperate with the stop motion compensation pulses described herelnarter to bring the radial tracl;~ng mirror to its optimllm ra~ial vrackin~
position as soon as possible.
The stop motion compensation generator 573 shown with reference to Figure 12, applies the waveform `" 11S~l 334( '10 sl~own in line E Ot Figure 13~ to the ra~3ial tracking ~irror 2~ b~! way of the line l0S and the amplifier 500 shown in Figure 9. The stop motion pulse directs the radial tracl;ing mirror 28 to leave the tracking of one 5 information tracl; and begin to seek the tra^king of the next ad,~acent track, In response to the pulse from the zero crossinE~ detector 571 shown in Figure 12, the stop motion pulse generator 5~57 is caused to generate the stop motion compensation pulse shown in line E.
Referring to line E of Figure 13~, the stop mo.,ion corr.pensation pulse waveform comprises a plural-it~J of individual and separate regions indicated at 540, 542 and 544, respectively. The fir~t region 540 of the stop mo'cion 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 cross~ng situation.
At this time, the stop motiorl pulse generator 557 generates the first portion 540 of the compensation 20 pulse which is applied directlJ to the tracking mirror 28. The generation of the first portion 540 of the stop motion cornpensation pulse has the effect of re-ducing the peak 624 to a lower radial tracking displace-ment as represented by the new peak 524' as shown in 25 line 1~. It should be kept in mind that the waveforms shown in Figure 13~ are schematic only to show the overall interrelationship of the various pulses used in the tracking servo subsystem and the stop motion subs~ stem to cause a read beam to jump from one track 30 to the next adjacent track. Since the peak error 624' ls not as high as the error at peak 624, this has the effect of reduciilg the error at peak error point 526' and generally shifting the remaining portion of the waveform to the left such that the ~ero crossings at 35 o25', 630 ' and 532' all occur sooner than they would have occurred ~r~itllout the pre sence of the stop motion compensation pulse.
Referring back to llne E of Figure 13~, the second portion 542 of the stcp motlon compensat~on . .

1~l5083~ `, 'ri--pulse is of a secolld polarity when compared to the fi,~st region 540. The second portion 54~ of the stop motion compensation pulse occurs at a point in time to compensate for the traclcing error shown at 626' of line ~. This results in ar. even smaller radial track-ing error beinO generated at that time and this smaller radial traclcing error is represented as point 52~" on line C. Since the degree of the radial trac~ing error represented by the point 626" of line C is si~nificantly smaller than that shown with reference to point 526' ol iine ~, the maximum error in the opposite direction shown at poir.t ~25' is again significantly smaller than that represented at point ~26 of line A. This counteractin~ of the natural tendency of the radial trackinO mirror 28 to oscillate back and forth over the information track is further dampened as indicated by the further movement to the left of points 628" and 525 with reference to their relative locations shown in lir.es ~ and A.
Referring again to line E of Figv.re 13~ and the third region ~44 of the stop motion compensation pulse, this region 544 occurs at the time calculated to dampen the remaining long term tracking error as represented that portion of the error signal to the right of the zero crossing 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 ~44 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 of the light beam as it is caused to depart ~rom one information track being read to the ne,{t adjacent tracl{ under the control of a stop motion pulse and a stop motion compensation pulse. It should be noted that the wavefol~m shown in line-D of ~igure 13~ can rep~esellt the movement in either direction although the polarity of various signals would be changed to represent the different direction of movement.

~50834 `
The cooperation ~etween the stop ~'otion sub-s~-stem 44 and t`ne tracking se;vo subsystem 40 durin~ a stop motion period will now be described .:ith reference to Fi~u es 9 and 12 and their related wave-'orms. Re-ferring to Figure 9A, the tracking ser~o s~s~Jstem 40is in oper~tion just prior to the initiati~n of a stop mction mode to maintain the radial tr~cking mirror 28 ln its position centered directly atop of information track. In order to maintain this position, the di~fer-10 ential tracking 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 tracl~ing servo loop switch 480, the a.-?lifier 510 15 and the push/pull amplifiers 500. That pcrtion of the wav2form shown a~ 591 on line D of Figure 13A as being traversed.
The function generator 47 generates a stop motion mode signal for applica'ion to the stop motion mode gate 5S9 over a line 132. The ~unct'~n of the stop motion mode gate 569 is to ~enerate a pulse in response to the proper location in a tele.~ision frame for the stop motion mode to occur. This pcint is de-tected b~J the combined operation of the total video signal from the FM processing board 32 bei~.g applied to the white flag detector 555 over a line 134 in com-bLnation with the vertical sync pulse developed in the tangential servo system 80 and applied ~er a line ~?.
The windo~ gener~tor 562 provides an enabling signal which corresponds with a predetermined portion of the video signal containing the white flag indicator. The ~hite flag pulse applied to the stop moticn mode gate 569 is gated to the stop motion pulse generator 557 in response to the enablillg signal received Lrom the function generatGr 47 over the line 13~. The enabling signal ~rom the stop motion mode gate 559 '~ltiates the stop motion pulse as shown ~Yith reference to line C
of Figure 13A. The output from t'ne zero crossing de-tector 571 indic2tes the end of the stop motion pulse ~73 ~
period by application of a signal to the stop motion pulse ger.erator ~57 over the line 572. The stop motion p~lse from the ~enerator 567 is applied to the trackin~ servo loop interrupt SWitCil ~30 b~- way of the gate 482 and the line 108. The function of the track-ing servo loop interrupt switch 480 is to remove t'ne differential tracking error currently being generated in the signal recovery subsystem 30 frcm the pusy/pull am?lifiers 500 driving the radial tracki,.g mirror 2~.
Accordingly, the switch 480 opens and the differential tracking error is no longer applied to the amplifiers 50~ for driving the radial tracking mirror 28. Simul-taneouslyj the stop motion pulse from the generator 5G7 is applied to the amplifiers 500 over the line 104.
15 The stop motion pulse, in essence, is substituted for the differential trac`~ing error and provides a driving signal to t,-he push/pull amplifiers 500 for starting the read spot to move to the next adjacent information track to be read.
The stop motion pulse from the ~enerator 567 is also applied to the stop motion compensation sequence generator 573 wherein the waveform shown ~ith reference to line H of Figure 13A and line E o~ Figure ~ is generated. ~y inspection of line H, it is to be noted that the ccmpensation pulse shown on line H occurs at the termination of the loop interrupt pulse on line G, which loop interrupt pulse is triggered by the start of the stop motion pulse shown on line C. The compensa-tlon pulse is applied to the push/pull amplifiers 500, 3 over the line 10~ shown in Figures 9 and 12~ for damp-ing out any oscillation in the operation of radial tracking mirror 28 caused by the applicatlon of the stop motion pulse.
As previously mentloned~ the compensation pulse is initiated at the termination Or the loop interrupt signal. Occurring slmultaneousl~ with the generation Or the compensation pulse~ the trackin~
servo loop in~errupt switch 480 closes and allows the differential tracking error to be reapplied to the _ ` 1151~834`

p;lsh,~pull amplifiers 500. The typical waverorm avail-able at this poii.t is showll in line E Or Figure 13A
~hich cooperates with the stop motion compensation pulse to ~uiclcly bring the radial tracking mirror 28 into suitable radial tracking aligllment.
Referrii~ brierly to line A of ~7igure 13C, two rrames o~ televisicn video in~ormation bein~ read from the video disc 5 are shown. Line A represents the differential traclcing errcr signal havin~ abrupt dis-coniinuities located at 650 and 652 representing thes~op motion mode of operation. Discontinuities of smaller amplitude are shown at 554 and 656 to show the effect o~ errors on the surface of the video disc surface in the dilferential track~ng error signal.
Line k of Figure 13C shows the FM envelope as lt is read from the video disc surface. The stop motion periods at 653 and 660 show that the F~ envelope is temporarily interrupted as the readin~ spot jumps tracks. Changes in the FM envelope at 662 and 664 show the tempcrary loss of Fil as trackin6 errors cause the trackin~ beam to temporarily leave the informat~on track.
In review o~ the stop motion mode of opera-tion, the following combinations occur in the prefer-ed embodiment. In a first embodiment, the differential tracking error slgnal is removed from the tracking mirror 28 and a stop motion pulse is substituted there~or to cause the radial tracking mirror to ~ump one track fromthat track being tracked. In this 3 embodiment, the stop motion pulse has areas of pre-emphasis such as to help the radial tracking mirror to regain tracking of the ne~ track to which it has been positioned The differential tracking error is re-applied into the tracking servo subsystem and cooperate with the stop motion pul5e applled to the radial track-ing mirror ~o reacquir2 ra~ial trac3c_n~. The ~ifferen-tial tracking error can be re-entered into the tracking servo system ~or optimum results. In this embodiment, the duration of the loop interrupt pulse is varied ~or gatitlg ofi` the application of the differential track-ing error into the push/pull amplifiers 500. The stop motion pulse is of fixed length in this embodiment.
Al alternative to this fixed length of the stop motion p~lse is to initiate the end of the stop motion pulse at the first zero crossing detected after the ~eginning of the stop motion pulse was initiated. Suitable delays can be entered into this loop to remove any extraneous sigIlals that may slip through due to mis-alignment of the beginnil~ of the stop motion pulseand the detection of zero crossings in the detector ~71.
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 compensation se-quence is initiated with the termination of the loop lnterrupt period. Coincidental IJith the termination of the loop interrupt period, the differential track-20~ ing error is reapplied into the tracking servo sub-- s~Jstem 40. In a further embodiment, the stop motion compensation pulse can be entered into the tracking servo subsystem over the line 106 at a ~eriod fixed in time from the beginning of the stop motion pulse as opposed to the ending of the loop interrupt pulse. The stop motion compensation sequence comprises a plurallty of separate and distinct regions. In the preferred embodiment, the first region opposes the tendency of the tracking mirror to overshoot the next adjacent track and directs the mirror bacl; into radial tracking Or that next adjacent 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 spof again over-shoots the center portion of the next adjacent trackbut in $he opposite direction. ~re thi~d region o~
tile stop motioi compensation sequence is of the same polarity as the first region, but of si,nificantly lol~er amplitude to further compensate any tendency of -` 1150~334 the radial tracking mirror having the focus spot again leave the inrormation track.
lhile in the preferred embodiment, the various resions of the stop motion sequence are shown to consist of separate individual regions. It is possible for these re~ions to be themselves broken do~.Jn into in-dividual pulses. It has been found by experimenc that the various regions can provide enhanced operation when separated by ~ero level signals. More specific-ally, a zero level condition exists between regionone and region two allowing the radial tracking mirror to move under its own inertia without the constant ap~lication of a portion of the compensation pulse.
It has also been found by experiment that this quiescent 17 period of the compensation sequence can coincide with the reapplication of the differential trackinz error to the radial tracking mirrors. In this sense, region one, sho~m at 640, of the compensation sequence cooper-ates with the portion ~04 sho~Jn in line E of Figure 13A
from the di-ferential trackln~ error input into tlle tracking loop.
~ y observation o~ the compensation waveform shc~n in line E of Figure 13~, lt can be observed that the various regions tend to begin at a high amplitude and fall off to ~ery low compensation signals. It can also be observed that the period of the various regions begin at a first relatively short ti~e period and ~radually become longer in duration. This coin-cides with the energy contained in the ~racking mirror as it seeks to regain radial tracking. Initially in the track ~umping sequence, tl~e energy is high and the early portions of the compensation pulse are appro-priately high to counterac'c this energy. Thereafter, as energy is removed rrom the tracking mirror, the corrections become less so as to bring the radial tracking mirror back into radial ali~nment as SOOil as possible.
Refe rin~ to Figure 14, there is shown a block diagram of ~he F~ processing system 32 employed in the video disc player l. The frequency modulated video signal recovered ~rom the dlsc 5 forms the input to the F.~i processing U?lit 32 over the line 34. The frequency modulated vldeo signal is applied to a dis-t-ibution amplifier 670. The distributicn amplifier provides three equal unloaded representations ~ the received signal. The first output signal from the distribution amplifier is applied to a FM corrector circuit 572 over a line 673. The FM corrector circuit 672 oper~tes to provide variable gain amplilication to the received freauency mcdulated video signal to compensate for the mean transler function of the lens 17 as it reads the frequency modulated video signal from the disc. The lens 17 is opera~ing close to its a~solute resolving po~ler and as a re.sult recovers the frequency modulated video signal with difrerent ampli-tudes correspGnding to different frequencies.
Tl.e output from the FM corrector 672 is applied to an Flq detector 574 over a line 675. The FM detector enerates discriminated video for applica-tion to the remaining circui~s requiring such dis-crimirated video in the video disc player. A second output signal from the distribution amplifier ~70 is applied to the tangential servo subsystem 80 over a line 82. A further output signal from the distribu-tion amplifier 670 is applied to the stop motion sub-system 44 over the line 134.
Referring to Figure 15 there is shown a more detailed block diagram of the FM corrector 672 sho~m in 3 Figure 14. The FM video signal from the amplifier 570 is applied to an audio subcarrier trap circuit 576 over the line 673. The ~unction of the su~carrier trap circuit 675 is to remove all audio components ~rom the frequency modulated video signal prior to application to a frequency selective variable gain ampli~ier 678 over l~:e 58~.
The control signals for operating the ampli~ier 678 inslude a first burst gate detector 582 having a plurality of input signa s. A first input signal is the ` ~ ~ ~ 8 3 ~

chroma portion of the FM video s~ænal as applied over a line 1"~. The second input signal to tlle bu.st gate 682 is the burst gate enable signal from the tanger.tial servo system 80 over the line 144. The function of the burst gate 682 is to gate into an amplitude detector 684 over a line 685 that portion of the chroma signal corresponding to the color burst signal. The output from the amplitude detector ~84 is 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 function of the amplitude detector 584 is to determine the first order lol~er chroma side band vector and apply it as a current representation to the summation circuit 15 688. The burst level ad~ust signal on the line 694 from the potentiometer 692 operates in con~unction lith this vector to develop a control signal to an amplifier 696. The output from the summation circuit is applied to the amrlifier 695 over tne line 698. The output from the amplifier 695 is a control voltage for applica-tio.. to the amplifier 678 over a line 700.
~ eferring to Figu~e 15~ there is sho~ln a numoer of waveforms lelpful in understand~lg the operation OT~
the FM corrector sho~n ir- Figure 15. The waveform repre-25 sented by the line 701 represents the FM correctortransfer function in generating control voltages for application to the amplifier 678 over the line 700.
- The line 702 includes four sect-lons of the curve indi-cated generall~J at 702~ 704, 706 and 708. These 3 segments 702~ 704~ 70O and 708 represent the various control voltages generated in response to the com-parison with the instantaneous color burst signal amplitude and the pre-set level.
Line 710 represents the mean transfer function Or the objective lens 17 employed for reading the successive li~ht reflective re~ions ~ ar.d light non-reflective re~ions 11. It c~n ~e seen upon inspection that the gain versus frequenc~J response of the lens fall~ off as the lens reads the rrequency modulated ' ,~

represelltatiol~s Or the vidco signal. ~eferrin~ to t~le ren.air.i.lV portion of Figure 15, there is sho~n the frequencv spectrum of the frequency modulated signals as read from the video disc. ThiS indic~tes that the video sigllals are located principally between the 7.5 and 9.~ megahert~ region at which ~he frequenc~J 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. ~nthis manner the effective frequency response of the lens is brought into a normalized or uniform region.
FM CORRECTOR SU~SYSTEM - NORr~L MODE OF OPERATIOM
The FM corrector subsystem functi~ns to adjust the FM video signal received from the disc such that all recovered FM signals over the entire frequenc-~spectra of the recovered FM signals are all amplified to a level, relative one to the other to reacquire their substantially identical relationships one to the other as they exis'cea 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 the 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 from which the FM video signal is recovered. This is achieved by ~easuring the color burst signal in the lower chroma side band and storing a representation of its amplitude. This lower chroma side band signal functions as a reference ampli-tude.
The FM video si~nal is recovered from the video disc as previously described. The chrominance signal is removed from the FM video signal and the burst gate enable signal gates the color burst signal present on eacll line of ~r~ video information into a ~15V83(4 -~o -ccmparison operation. The comparison operation ef~ec-tively operates for sensing the difference between t~le actu~l amplitude of the color burst signal re-covered rrom the video dlsc surface with a reference amplitude. The reference amplitude has been ad~usted to the correct level and the comparison process indi-cates an error signal between the recovered amplitude of the color burst signal and the reference color burst signal indicating the difference in amplitude between the two signals. The error signal generated in this comparison operation can be identified as the color burst error amplitude signal. This color burst error amplitude signal is employed for adjusting the gain of a variable gain amplifier to amplify the signal presently being recovered from the video disc 5 to amplify the chrom~nance signal more than the luminance signal. This variable amplification provides a var-iable gain over the frequency spectrum. The higher frequencies are amplified more than the lo~ier fre-quencies. Since the chrominance si~nals are at thehigher frequencies, they are amplified more than the luminance signals. This variable amplification of signals results in effectively ~aintaining the correct ratio Or the luminance signal to the chrominance signal as the reading process radially moves from the outer periphery to the inner periphery. As previously men-tioned, the lndicia representing the FM video signal on the video disc 5 change in size from the outer periphery to the inner periphery. At the inner periphery they are smaller than at the outer periphery. The smallest size indicia are at the absolute resolution power of the lens and the lens recovers the FM signal represented by this smallest size indicia at a lower amplitude value than the lower frequency members which are larger in size and spaced farther apart.
In a preferred mode of operation, the audio signals contained in the FM video signal are removed from the FM video signal before application to the variable gain amplifier. The aud~o information is , . .

~1~)83 contained around a number Or FM subcarrier signals and it has been found by experience that the removal of these FM subcarrier audio signals provides enhanced correction of ~he remainin~ video FM signal in the var-iable gain amplifier.
In an alternati~e mode of operation thefrequency band width applied to the variable gain amplifier is that band width which is affected by the mean transfer function of the ob~ective lens 17. More specifically, when a portion of the total FM recovered from the video disc lies in a range not affected by the mean transfer function, then this portion of the total waveform can be removed from that portion of the FM signal applied to the variable gain amplifier. In this manner, the operation of the variable gain ampli-fier is not complicated by signals having a frequency which need not be corrected because of the resolution characteristics of the objective lens 17.
The FM corrector functions to sense the ab-solute value of a signal recovered from the video disc,which signal is kno~,m to suffer an amplitude change due to the resolution power of the objective lens 17 used in the video disc signal. This known signal ls then compared against a reference signal lndicating the amplltude that the known signal should have. The out-put from the comparison is an indication of the addi-tional amplification required for all of the signals lying in the frequency spectra affected by the resolv-ing power of the lens. The amplifier is designed to provide a varia~le gain over the frequency spectra.
Furthermore, the variable gain is further selective based on the amplitude of the error signal. Stated another way for a first error signal detected between the signal recovered from the disc and the reference frequency, the variable gain amplifier is operated at a first level of variable amplification over the entire frequency range of the affected signal. For a second level of error signal, the gain across the frequency spectra is ad~usted a different amount when compared ( ~ 50~3 ~ 8~ -ror the first color burst error amplitude signal.
~ eferring to Figure 17, there is shown a block dia~ram of the FM detector circuit 674 shown with refer-ence to Fisure 14. The corrected frequency modulated signal rrom the FM corrector 572 is applied to a li~iter 720 over the line 675. The output ~rom the limiter is applied to a drop-out detector and compen-sation circuit 722 over a line 724. It is the function of the limiter to change the corrected FM video signal into a discriminated video slgnal. The output from the drop-out detector 722 is applied to a low pass filter 725 over a line 728. The output from the low pass filter 726 is applied to a wide band video dis-tribution amplifier 730 whose function is to provide a plurality of output signals on the line 66, 82, 134, 154, 156, 164 and 16S, as previously described. The function of the FM detector is to change the frequency modulated video signal into a discriminated video signal as sho~n 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 wit~in the zero to one volt range suitable for display on the television monitor 98 over the line 166.
Referring to Figure 19, there is shown a block diagram of the audio processing circuit 114. The frequency modulated video signal from the distribution 3 amplifier 670 of the FM processing unit 32, as shown with reference to Figure 14, applies one of its inputs to an audio demodulator circuit 740. The audio demodu-lator clrcuit provides a plurality of output signals, one of which is applied to an audio variable controlled 35 oscillator circuit 742 over a line 744. A first audio output is available on a line 74;~ ~or application to the audio accessory unit 120 and a second audio output signal is available on a line 747 for appllcation to the audio accessory unit 120 and/or the audio ~acks ') Y . , - - .

1 1~083~
~, 117 and 11~. The output from the audio volta~e con-trolled oscillat`or is a 4.5 megahert~ signal for appli-cation to the RF modulator 162 over the line 172.
Referring to Figure 20, there is sho~ln a block diagram of the audio demodulator circuit 740 shown with rererence to Figure 19. The frequency modulated video si~nal 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 ~ilter 752 over the line 160 and a second line

7~4~ The first band pass filter 750 strips the first audio channel from the FM video signal, appiies it to an audio FM discriminator 755 over a line 758~ The 15 audio FM discriminator 756 provides an audio signal in the audio range to a SWitCi~ g circuit 760 over a line 752~
The second band pass filter 752 h2ving a central frequenc~ of 2.8 megahert~ operates to strip the second audio channel from the Frl video input signal - and applies this frequenc-~ spectra of the total FM
signal to a second video FM discriminator 764 over a li.ne 765~ The second audio channel in the audio fre-quency range applied to the switching circuit 750 over 25 a line 768~
The switching circuit 760 is provided with a plurality of additional lnput signals. A first of which is the audio squelch signal from the tracking servo subsystem as applied thereto over the line 116~
3 The second input signal is a selection command signal from the function generator 47 as applied thereto over the line 170~ The output frcm the switching circuit is applied to a first amplifier circult 770 over a line 771 and to a second amplifier circuit 772 over a 35 line 773~ The lines 771 and 773 are also connected to a su~mation circuit indicated at 774~ The output from the summation circuit 774 is applied to a third ampli-fier circuit 775 The output rrom the first ampllfier 770 is the cnannel one audio signal for application to

8 3 -~4-the audio jack 117. The output from the second ampli-fier 772 is the second channel audio signal for application tothe audio jaclc 113. The output from the thlrd amplifler 776 is the audio signal to the audio VC0 742 over the line 744. Referring briefly to Figure 21, there is shown on line A the frequency modulated envelope as recelved from the distribution amplifier in the FM processin~ unit 32. The output of the audio FM discriminator for one channel is sho~n on line ~. In this manner, the FM signal is changed an audio frequency signal for applicatlon to the switch-ing circuits 760~ as previously descrlbed.
Xeferring to Figure 22, there is shown a block diagram of the audio voltage controlled oscilla-15 tor 742 as shown with reference to Figure 19. Theaudio signal from the audio demodulator is applied to a band pass filter 780 over the line 741~. The band pass filter passes the audio frequency si~nals to a summation circuit 782 by way of a pre-emphasis circuit 20 784 and a first line 78~ and a second line 788.
The 3.58 megahertz color subcarrier frequency rrom the tangentlal servo system 80 is applied to a divide circuit 790 over the line 140. The divide circuit 790 divides the color subcarrier frequency by 25 2048 and applies the output signal to a phase detector 792 over a line 794. The phase detector has a second input signal from the 4.5 megahertz voltage controlled oscillator circuit as applied to a second divide cir-cuit 798 and a first line 800 and 802. The divide 3 circuit 798 divides the output of the VC0 796 by 1144.
The output from the phase detector ls applied to an amplitude and phase compensatlon circuit 804. The output from the circuit 804 is applied as a third input to the summation circuit 782. The output from the voltage controlled oscillator 796 is also applied to a low pass filter 806 by the line 800 and a æcond line 808. The output from the filter 806 is the 4.~
megahertz frequency modulated signal for application to the RF modulator 182 by the line 172. The function 8 3~ ( of the audio voltage controlled oscillator clrcult ls to prepare the audio signal received from the audio demod~
ulator 740 to a frequency which can be applied to the ~F modulato.~ 16~ so as to be processed by a standa~d television receiver 96.
Referring briefly to Figure 23, there can be seen on line A a waveform representing the audio signal received from the audio demodulators and available on the line 744. Line ~ of Figure 23 represents the 4.5 megahertz carrier frequency. Line C of Figure 23 represents the 4.5 megahertz modulated audio carrier ~hich is generated in the VC0 circuit 796 for applica-tion to the RF modulator 152.
Referring to Figure 24, there is shown a block diagram of the RF modulator 162 employed in the video disc player. me video information signal from the FM processing circuit 32 is applied to a DC re-storer 81~ over the line 154. The DC restorer 810 read~usts the blanking level of the received video signal. The output from the restorer 810 is applied to a first b21anced modulator 812 over a line 814.
The 4.5 megahertz modulated signal from the audio VC0 is applied to a second balanced modulator 816 over the~line 172. An oscillator circuit 818 functions 25 to generate a suitable carrier frequency corresponding to one of the channels of a standard television re-ceiver 96. In the preferred embodiment, the Channel 3 frequency ls selected. The output from the oscillator 818 is applied to the first balanced modulator 812 over 30 a line 820. The output from the oscillator 818 is applied to the second balanced modulator 816 over the line 822. The output from the modulator 812 is ap-plied to a summation clrcuit 824 over a line 826. The output from the second balanced modulator 816 is 35 applied to the summation clrcuit 824 over the line 828. Referring briefly to the wave~orm sho~Jn in Figure 25, line A shows the 4.5 megahertz frequcncy modulated signal received from the audio VC0 over the line 172. Line P of Figure 25 shows the video signal i liS0834 received frol~l the FM processing circuit 32 over theline 154. The ou'put from the summation circuit 824 is sho~n on line C~ The si3nal shown on line C is suita~le for processing by a standard television re-ceiver. The signal shown on line C is such as to causethe standard television receiver 96 to display the sequential fra~e information as applied thereto.
Referring briefly to F~gure 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 trac~ at the outside radius demonstrates 15 an eY.treme degree of eccentricity arising from the effect of uneven cooling of the video disc 5.
Referring briefly to Figure 27, there is shown a schematic view of a video disc 5 having contained ~thereon an in'~ormation track at an outside radius -20 represented b~ the numeral 834. An information track at an inside radius is represented by the numeral 836.
This Figu-re 27 shows the eccentricity effect of an off-center rela~ionship of the tracks to a central aperture indicated generally at 838. More specifically, the off-center aperture effectively causes the distance . represented by a line 840 to be effectively different from the length of the line 842. Obviously, one can be larger than the otter. This represents the off-centered position of the center aperture hole 838.
Referring to Figure 28, there is shown a logic diagram representing the first mode of operation of the focus servo 36.
The lcgic diagram shown with reference to Figure 28 comprises a plurality of AND function gates shown at 850, 852, 854 and 855. The AND function gate 850 has a pluralit~T of input signals~ the first of which is the L~NS ~'i`iAPI-~ applied over a line 858. The second input signal to the AND gate 850 is the FOCUS
SIGNAL applied over a line 860. The AND gate 852 has ..
~_ .

50 8 3 ~ `
-~7 -a plur lit-~ of input signals, the first o~ which is the ~U~ SIGNAL applied thereto for the line 860 and a seccnd lille ~G2. The second input signal to the AND
function gate 852 ~s the lens enable signal on a line 8~4. The output from the AND function gate 852 is the ramp enable signal ~hich 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 function gate 854 over a line lO 866. The AND function gate 854 has a second input signal applied over the line 868. The signal on the line 868 is the FM detected signal. The output from the AND function gate 854 is the focus acquire signal.
This focus acquire signal is also applied to the ramp generator 278 for disalbin~ the ramping waveform at that ~int. The AND function gate 85S is equipped with a plurality of input signals, tlle first of which is the FOCUS SIGNAL applied thereto over the line 860 ~and an additional lire 870. The second input signal to the AND function gate 855 is a ramp and signal applied over a line 872. The output signal from the AND function gate 856 is the withdraw lens enabling signal. ~riefly~ the logic circuitry shown ~ith refer-ence to FigUI'e 2~ generates the basic mode of operation of the lens servo. Prior to the function generator 47 generating a lens enable signal, the LENS ENA~LE signal is applied to the AND function gate 850 along with the FOCUS SIGNAL. This indicates that the player is in an inactivated condition and the output signal from the 3 AND runction gate indicates that the lens is in the fully with~rawn position.
~ hen the function generator generates a lens enable signal for application to the AND gate 852, the second input signal to thc AND gate 852 lndicates that the video disc pla~Je~ 1 is not in the focus mode.
AccGraingl~, the output sig~al 1'rom the AND g~te 852 is the ramp enable signal which initiates the ramping waveform shown with reference to line P of Figu.e 6A.
The ramp enable signal also indicates that the focus ' _ -8~-servo is i~l the acqulre rOcus mode ~ operatlon andthis enablill~ signal ~orms a first lnput to the AND
~unction gate 854. The second input signal to the AND
fur.ction gate 854 indicates that FM has been success-fully detected and the output from the AND functiongate 8~4 is the focused acquire signal indicating that the normal play mode has been successfully entered and frequency modulated video signals are being recovered from the surface of the video disc. The output from 10 the AND function ~ate 855 indicates that a successful acquisition of focus was not achieved in the first focus attempt. The ramp end signal on the lir.e 872 indicates that the lens has been fully extended towards the video disc surface. The FOCUS SIGNAL on the line 15 870 indicates that focus was noi successfully acquired.
Accordinglv, the output from the Al~D function gate 855 ~ithdraws the lens to its upper position at which time a focus acauire operation can be reattempted.
Referring to Figure 29, there is sho~n a logic 20 diagram illustrating the additional mcdes of operation of the lens servo. A first AND gate 880 is equipped witll a plurality of input signals, the first of which is the focus signal generated by the A~D gate 854 and applied to the AND gate 880 over a line 859. The 25 FM DETEC~' SIGNAL is ap,plied to the AND gate 880 over a line 882. The output from the AND gate 880 is applled to an OR gate 84 over a line 886. A second input signal is applied to th4 OR gate 884 over a line 888.
The output from the OR functlon gate 884 is applied to 30 a first one-shot circuit shown at 890 over a line 8g2 to drive the one-shot into its state for generating an output signal on the line 894. T~e output signal on tlle line 894 is applied to a delay circuit ~95 over a second line 898 and to a second AND function gate 900 over a line 902. The Ai~D function gate 9CO is equipped with a second input signal on which the FM detect signal is applied over a line 904. The output from the AND function gate 900 is applied to reset the first one-shot 890 over a line 90o.

. .~ - .. . .. . .. . .

sg Tlle output from the delay circuit 895 is ap-plied as a first input signal to a third AND function gate 908 o~er a line 910. The AND function gate 908 is equipped with a second input signal which is t~e ~A~iY ~ ;IGi~lA~ 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 input signal to the AND function gate 918 is the output signal from the first one-shot 890 over the line 894 and a second line 922. The output from 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 t~e timing period of tile focus ramp voltage shown on line ~ of Figure 6A. The input signal on line 925 activates the one-shot 924 to generate its output signal on a line 928 for application to a dela~-circuit 930. The output from the delay circuit 930 forms one input to a sixth AI~TD function gate 932 over a line 934. The AND function gate 932 has as its second ir.put signal the FOCUS SIGi~AL available on a line 936.
The output from the AND function gate 9 32 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 is also applied to a third ane-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 mentionedJ the output ~rom the delay circuit 942 i s applied to the OR function 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 ~.~. T~.e second one-shG~ 92l! is e~nployed ~or generating a waveform shown on line ~ of Figure oA.
The third one-shot 940 is employed for generating the waveform shown on line F of Figure 6A.

~o In one form of operation, the logic circultry shown in Fi~ure 29 operates to dela~r the attempt to reacquire focus due to momentary losses cr FM caused by imperfections on the video disc. This is achieved in tl~e followlng manner. The Al~D functlon gate 880 gener-ates an output signal on the line 885 only when the video disc player ls ln the ~ocus mode and there is a temporary loss of F~ as indicated by the ~M -DE~.~CT SIGNAL
on line 882. T'~e output slgnal on the llne 885 trlggers the first one-shot to generate a timin~ period of pre-determined short length durlng whlch the vldeo dlsc -player will be momentarily stopped from reattempting to acquire lost focus superficially indlcated by the avallability of the FM DE~CT SIGNAL on the line 882.
The output from the first one-shot forms one lnput to the AND functiol gate 900. If the FM detect signal available on 9~4 reappears prior to the timln~ ou~ of the time period Or the first one-shot, the output from the AND circuit 900 resets the flrst one-shot 890 and the video disc player continues reading the reacquired FM signal. Assuming that the first one-shot is not reset, then the following sequence Or operation occurs.
The output from the delay circuit 895 is gated through the AND functlon gate 908 by the RAMP RESET SIGNAL
avallable on line 912. The RAMP ~ESET SIGNAL is avail-able in the normal focus play mode. The outp~t from the AND gate 908 ls applied to the OR gate 914 for gen-erating the reset slgnal causing the lens to retrack and begin its focus operation. The output from the OR
gate 914 is also applled to a turn on the second one-shot which establishes the shape of the ramping wavefo~
shown in Figure ~. The output from the second one-shot 924 ls essential coextensive in time with the ramping period. Accordingly, when the o~tput from the second one-shot is generated~ the machine is caused to return to the attempt to acquire focus. ~rlhen fccus is success-fully acquired, t~le ~'OCU~ ~IGl~AL on l~ne 936 does not gate the output from the delay circuit 930 through to the OR function gate 914 to restart the automatic focus .

~1~083~ ( procedure. Howe~er, when the video disc player does not acquire focus the FOCUS SIGNAL on line 936 gates the output from the delay circuit 930 to restart auto-matically the focus acquire mode. When focus is success-fully acquired, the output from the delay line is notgated through and the player continues in its focus mode.
l~ile the invention has been particularly shown and described with reference to a preferred embod-iment a~d 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 (22)

92

1. A time base error correction system for use in an apparatus for recovering an information signal from an information track recorded on disc-shaped information bear-ing surface, wherein the information signal includes a periodic synchronizing signal that defines a time base, and the apparatus includes optical system means for directing a source beam of radiation to follow along the information track and spindle servo means for rotating the information bearing surface relative to the source beam, to produce a modulated beam of radiation containing the information signal, the optical system means further directing the modulated beam to signal recovery means for recovering the information signal from the modulated beam, the time base error correcting system comprising:
separation means for separating the synchronizing signal from the information signal recovered from the modu-lated beam;
reference signal means for generating a reference signal having a prescribed frequency;
phase detection means for detecting the relative phase between the synchronizing signal and the reference signal; and for generating a control signal representative of error in relative phase;
radial location detection means for detecting the radial location of the source beam relative to the disc;
control signal adjusting means for adjusting the control signal as a function of the radial location of the source beam relative to the disc; and tangential beam steering means responsive to the control signal for steering the source beam tangentially along the information track to vary the rate of relative movement between the source beam and the information bearing surface in a manner correcting for time base errors in the information signal recovered from the modulated beam.

2. A time base error correction system as set forth in Claim 1, wherein the synchronizing signal has a highly accurate frequency and is recorded as a portion of the recorded information signal, the synchronizing signal having a predetermined amplitude and phase relative to the remainder of the information signal on the information bear-ing surface.

3. A time base error correction system as set forth in Claim 1, wherein the synchronizing signal is of relatively short duration and occurs at periodic intervals in the information signal, and the phase error detection means includes means for establishing the control signal during the occurrence of the synchronizing signal, and further includes means for maintaining the control signal at a constant level until the next occurring synchronizing signal.

4. A time base error correction system as set forth in Claim 3, wherein the means to maintain the control signal at a constant level comprises a sample and hold circuit.

5. A time base error correction system as set forth in Claim 1, wherein the spindle servo means is respon-sive to the reference signal means for rotating the disc at a prescribed angular rate of rotation.

6. A time base error correction system as set forth in Claim 5, wherein the spindle servo means compromises:
spindle motor means for rotating the disc;
spindle tachometer means for generating a spindle tachometer signal indicative of the actual angular rate of rotation of the spindle motor means; and spindle error means responsive to both the refer-ence signal means and the spindle tachometer means for con-trolling the angular rate of rotation of the spindle motor means.

7. A time base error correction system as set forth in Claim 6, and further including:
a frequency divider coupled to the reference signal means for dividing the frequency of the reference signal and for coupling the divided reference signal to the spindle motor drive means to establish a direct relationship between the frequency of the reference signal and the rate of angular rotation of the disc.

8. A time base error correction system as set forth in Claim 1, wherein the control signal adjusting means varies the control signal as a direct function of the radial location of the source beam relative to the disc.

9. A time base error correction system as set forth in Claim 8, wherein the control signal adjusting means includes a variable gain controlled amplifier, and the radial location detection means includes means for adjusting the gain of the amplifier as a function of the radial loca-tion of the source beam relative to the disc.

10. A time base error correction system as set forth in Claim 9, and further including carriage means for translating the disc and the source relative to one another along a radius of the disc, and wherein the means for alter-ing the gain of the amplifier comprises a potentiometer coupled to and actuated by the carriage means.

11. A time base error correction system for use in a video disc player for deriving video information from a frequency modulated signal stored in an information track arranged spirally on a disc, wherein the video information includes a color subcarrier having a color burst synchro-nizing signal, and the player includes spindle servo means for rotating the disc, optical system means for directing a source beam of radiation to follow along the information track and for directing a frequency modulated beam of radiation containing the video information to signal re-covery means for recovering the frequency modulated signal from the frequency modulated beam, and the player further includes video detector means for verifing the video infor-mation from the frequency modulated signal recovered from the frequency modulated beam, the time base error correction system comprising:
color burst separation means for separating the color burst synchronizing signal from the video information;
color subcarrier reference oscillator means for generating a color subcarrier reference signal;
phase error detection means for detecting the relative phase difference between the color burst synchro-nizing signal and the color subcarrier reference signal, and for generating a control signal representative of error in relative phase;
radial location detection means for detecting the radial location of the source beam relative to the disc;
control signal adjusting means for adjusting the control signal as a function of the radial location of the source beam relative to the disc; and beam steering means responsive to the control signal for steering the source beam along the information track to vary the rate of relative movement between the source beam and the disc in a manner correcting for time base errors in the video information.

12. A time base error correction system as set forth in Claim 11, wherein the phase error detection means includes means for establishing the control signal during the occurrence of the color burst synchronizing signal, and further includes means for maintaining the control signal at a constant level until the next occurring color burst synchronizing signal.

13. A time base error correction system as set forth in Claim 12, wherein the means to maintain the con-trol signal at a constant level compreses a sample and hold circuit.

14. A time base error correction system as set forth in Claim 11, wherein the spindle servo means is responsive to the color subcarrier reference oscillator means for rotating the disc at a prescribed angular rate of rotation.

15. A time base error correction system as set forth in Claim 14, wherein the spindle servo means com-prises:
spindle motor means for rotating the disc;
spindle tachometer means for generating a spindle tachometer signal indicative of the actual angular rate of rotation of the spindle motor means; and spindle error means responsive to both the refer-ence signal means and the spindle tachometer means for con-trolling the angular rate of rotation of the spindle motor means.

16. A time base error correction system as set forth in Claim 15, and further including:
a frequency divider coupled to the color subcar-rier reference signal and for coupling the divided refer-ence signal to the spindle motor drive means to establish a direct relationship between the frequency of the color subcarrier reference signal and the rate of angular rotation of the disc.

17. A time base error correction system as set forth in Claim 11, wherein the control signal adjusting means varies the control signal as a direct function of the radial location of the source beam relative to the disc.

18. A time base error correction system as set forth in Claim 17, wherein the control signal adjust-ing means includes a variable gain controlled amplifier, and the radial location detection means includes means for adjusting the gain of the amplifier as a function of the radial location of the source beam relative to the disc.

19. A time base error correction system as set forth in Claim 18, and further including carriage means for translating the disc and the source relative to one another along a radius of the disc and wherein the means for altering the gain of the amplifier comprises a poten-tiometer coupled to and actuated by the carriage means.

20. A method of time base error correction for use in an apparatus for deriving an information signal from an information track arranged tangentially on a disc, wherein the information signal includes a synchronizing signal, and the apparatus includes optical system means for directing a source beam of radiation to follow along the information track and means for imparting relative movement between the disc and the source beam in a direc-tion along the information track to produce a modulated beam of radiation containing the information signal, and the optical system means further directing the modulated beam to signal recovery means for recovering the informa-tion signal from the modulated beam, the method comprising the steps of:
separating the synchronizing signal from the information signal recovered from the modulated beam;
generating a reference signal having a pre-scribed frequency;
detecting the relative phase between the syn-chronizing signal and the reference signal;

generating a reference signal having a pre-scribed frequency;
detecting the radial location of the source beam on the information track relative to the disc;
adjusting the control signal as a function of such radial location; and steering the source beam along the informa-tion tracks as a function of the control signal such that the error in phase between the synchronizing signal and the reference signal is reduced.

21. A method of time base error correction as set forth in Claim 20, wherein the adjusting step comprises varying the control signal as an inverse function of such radial location.

22. A method of time base error correction as set forth in Claim 20, wherein the disc is rotated at a prescribed angular rate of rotation controlled by the reference signal.