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Tracking system and method for video disc player |
| RE32051 |
Tracking system and method for video disc player
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| Patent Drawings: | |
| Inventor: |
Ceshkovsky, et al. |
| Date Issued: |
December 17, 1985 |
| Application: |
06/619,259 |
| Filed: |
June 11, 1984 |
| Inventors: |
Ceshkovsky; Ludwig (Fountain Valley, CA)
Dakin; Wayne R. (Costa Mesa, CA)
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| Assignee: |
Discovision Associates (Costa Mesa, CA) |
| Primary Examiner: |
Faber; Alan |
| Assistant Examiner: |
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| Attorney Or Agent: |
Clark; Ronald J. |
| U.S. Class: |
250/202; 360/77.06; 369/44.26; 369/44.28; 369/44.29; 386/113; 386/126 |
| Field Of Search: |
369/44; 369/30; 369/111; 250/202; 360/10.1; 360/77; 360/75; 360/72.1; 358/342; 358/147; 358/166; 318/592; 318/596; 318/577 |
| International Class: |
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| U.S Patent Documents: |
Re29963; 3381086; 3530258; 3854015; 3911211; 4037252; 4057832; 4137430 |
| Foreign Patent Documents: |
52-26802 |
| Other References: |
A Review of the MCA Disco-Vision System, from Information Display, vol. 12, No. 2, Apr. 1976.. |
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| Abstract: |
A video disc player is described for use with a video disc having frequency modulated video information recorded thereon in the form of a plurality of concentric circles or a single spiral. The information track comprises successively positioned light reflective and light non-reflective regions. A focused light beam is caused to be positioned over the center of an information track and the light reflected from the information track is gathered by an objective lens for application to electronic circuitry for recovering the recorded frequency modulated video signals. Radial tracking means are described for maintaining the focused light spot to impinge upon the center of an information track. Lens focusing means are described for positioning the objective lens at the optimum focused position above the information track for gathering the maximum amount of reflected light from the information track. FM processing means are described for reconstructing the recovered frequency modulated video information such that the ratio between the amplitude of the signals as recorded is essentially the same in the signals as recovered from the video disc member. Further servo means are described for handling the selective change of the intersection of the reading beam with the video disc member in a predetermined preferred mode of operation. |
| Claim: |
What is claimed is:
1. A method of tracking for use in a player for deriving information from spaced information tracks on an information bearing surface, the player including beam steering meanshaving tracking mirror means coupled to tracking error detection means, for following a path formed by any one of the tracks with a source beam of radiation, the method comprising the steps of:
uncoupling the tracking mirror means from the tracking error detection means to establish an open loop mode;
driving the tracking mirror means in the open loop mode to move the source beam from a first one of the tracks towards a second one of the tracks;
searching for a selected location of the source beam intermediate the first track and the second track; and
recoupling the mirror means to the tracking error detection means to establish a closed door mode and control the movement of the mirror means, in response to completeting the search for the selected location, as the mirror means approaches thesecond track, whereby the beam steering means then follows a path formed by the second track with the source beam.
2. A tracking system for use in a player for recovering information from a selected one of a plurality of spaced information tracks on an information-bearing surface, the player including means for providing a beam of radiation and means forimparting relative movement between the surface and the beam, the tracking system comprising:
beam steering means for directing the beam of radiation along a prescribed path to impinge on the information-bearing surface; and
control means for coupling a tracking error signal to the beam steering means, in a first mode of operation, to controllably position the beam of radiation in alignment with a first selected track on the surface;
the control means further operating, in a second mode of operation, to uncouple the tracking error signal from the beam steering means, and to couple a control pulse signal to the beam steering means, to controllably move the beam of radiationtoward a second selected track on the surface;
the control means including detector means for determining when the beam of radiation has been moved to a prescribed position intermediate the first track and the second track, and for terminating the control pulse signal at that time.Iadd.;
said control means recoupling the tracking error signal to the beam steering means before the beam of radiation reaches the second selected track.Iaddend..
3. A tracking system as defined in claim 2, wherein the detector means terminates the control pulse signal when the beam of radiation is located substantially midway between the first track and the second track.
4. A tracking system as defined in claim 2, wherein the control means recouples the tracking error signal to the beam steering means a prescribed time after terminating the control pulse signal. .[.5. A tracking system as defined in claim 4,wherein the control means recouples the tracking error signal to the beam steering means before the beam of
radiation reaches the second selected track..]. 6. A tracking system as defined in claim 2, wherein the control means includes compensating means for coupling a compensation pulse signal to the beam steering means, to
stabilize the beam steering means. 7. A tracking system as defined in claim 6, wherein the compensating means couples the compensation pulse signal to the beam steering means a prescribed time after the control
pulse signal begins. 8. A tracking system as defined in claim 6, wherein the compensating means couples the compensation pulse signal to the beam steering means a prescribed time after the control pulse signal
terminates. 9. A tracking system as defined in claim 6, wherein the compensating pulse signal includes a first portion of a first polarity, a second portion of a second polarity, opposite to the first polarity, and a third portion of the firstpolarity, the third portion having an amplitude substantially less than the amplitude of the first portion and having a
duration substantially longer than the duration of the first portion. 10. A tracking system as defined in claim 9, wherein the first, second and third portions of the compensation pulse signal are separated from each
other by zero level portions. 11. A tracking system for use in a player for recovering information from a selected one a plurality of substantially circular and concentric information tracks on a record disc, the player including means forproviding a beam of radiation and means for rotating the disc relative to the beam, the tracking system comprising:
beam steering means for directing the beam of radiation along a prescribed path to impinge on the record disc; and
means operable in a first mode of operation, for coupling a tracking error signal to the beam steering means, to controllably position the beam of radiation in alignment with a first selected track on the disc;
means operable, in a second mode of operation, for uncoupling the tracking error signal from the beam steering means and coupling a control pulse signal to the beam steering means, to controllably move the beam of radiation to a second selectedtrack on the disc;
detector means for determining when the beam of radiation is located midway between the first track and the second track, and for terminating the control pulse signal at that time;
compensating means for coupling a prescribed compensation pulse signal to the beam steering means a prescribed time after the control pulse signal is terminated, to stabilize the beam steering means;
means for recoupling the tracking error signal to the beam steering means a prescribed time after the control pulse signal is terminated and before
the beam of radiation reaches the second selected track. 12. A tracking method for use in a player for recovering information from a selected one of a plurality of spaced information tracks on an informaton-bearing surface, the playerincluding means for providing a beam of radiation, and means for imparting relative movement between the surface and the beam, the tracking method comprising steps of:
directing the beam of radiation along a prescribed path using beam steering means, to impinge on the information-bearing surfaces; and
coupling a tracking error signal to the beam steering means, in a first mode of operation, to controllably position the beam of radiation in alignment with a first selected track on the surface;
uncoupling the tracking error signal from the beam steering means, in a second mode of operation, and coupling a control pulse signal to the beam steering means, to controllably move the beam of radiation toward a second selected track on thesurface; and
determining when the beam of radiation has been moved to a prescribed position intermediate the first track and the second track, and terminating the control pulse signal at that time.Iadd.; and
recoupling the tracking error signal to the beam steering means before the
beam of radiation reaches the second selected track.Iaddend.. 13. A tracking method as defined in claim 12, wherein the step of determining and terminating terminates the control pulse signal when the beam of radiation has been moved to aposition substantially midway between the
first track and the second track. 14. A tracking method as defined in claim 12, and further including a step of recoupling the tracking error signal to the beam steering means a prescribed time after the control
pulse signal has been terminated. .[.15. A tracking method as defined in claim 14, wherein the step of recoupling the tracking error signal to the beam steering means before the beam of radiation reaches the second
selected track..]. 16. A tracking method as defined in claim 12, and further including a step of coupling a compensation pulse signal to the beam steering means.[., .]. to stabilize the beam.[.steering means.]..
A tracking method as defined in claim 16, wherein the compensation pulse signal is coupled to the beam steering means a prescribed time after
the control pulse signal begins. 18. A tracking method as defined in claim 16, wherein the compensation pulse signal is coupled to the beam steering means a prescribed time after the control pulse signal terminates. |
| Description: |
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the method and means for reading a frequency modulated video signal stored in the form of successively positioned reflective and non-reflective regions on a plurality of information tracks carried by a video disc. More specifically, an optical system is employed for directing a reading beam to impinge upon the information track and for gathering the reflected signals modulated by the reflective and non-reflective regions of the information track. A frequencymodulated electrical signal is recovered from the reflected light modulated signal. The recovered frequency modulated electrical signal is applied to a signal processing section wherein the recovered frequency modulated signal is prepared forapplication to a standard television receiver and/or monitor. The recovered light modulated signals are applied to a plurality of servo systems for providing control signals which are employed for keeping the lens at the optimum focus position withrelation to the information bearing surface of the video disc and to maintain the focused light beam in a position such that the focused light spot impinges at the center of the information track.
SUMMARY OF THE INVENTION
The present invention is directed to a video disc player operating to recover frequency modulated video signals from an information bearing surface of a video disc. The frequency modulated video information is stored in a plurality of concentriccircles or a single spiral extending over an information bearing portion of the video disc surface. The frequency modulated video signal is represented by indicia arranged in track-like fashion on the information bearing surface portion of the videodisc. The indicia comprise successively positioned reflective and non-reflective regions in the information track.
A laser is used as the source of a coherent light beam and an optical system is employed for focusing the light beam to a spot having a diameter approximately the same as the width of the indicia positioned in the information track. Amicroscopic objective lens is used for focusing the read beam to a spot and for gathering up the reflected light caused by the spot impinging upon successively positioned light reflective and light non-reflective regions. The use of the microscopicallysmall 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 reflectedlight and passing the reflected light through the lens when operating at the maximum resolution of the lens, the gathered light assumes a sinusoidal-shaped like modulated beam representing the frequency modulated video signals contained on the video discmember.
The output from the microscopic lens is applied to a signal recovery system wherein the reflected light beam is employed first as an information bearing light member and second as a control signal source for generating radial tracking errors andfocus errors. The information bearing portion of the recovered frequency modulated video signal is applied to an FM processing system for preparation prior to transmission to a standard TV receiver and/or a TV monitor.
The control portion of the recovered frequency modulated video signal is applied to a plurality of servo subsystems for controlling the position of the reading beam on the center of the information track and for controlling the placing of thelens for gathering the maximum reflected light when the lens is positioned at its optimum focused position. A tangential servo subsystem is employed for determining the time base error introduced into the reading process due to the mechanics of thereading system. This time base error appears as a phase error in the recovered frequency modulated video signal.
The phase error is detected by comparing a selected portion of the recovered frequency modulated signal with an internally generated signal having the correct phase relationship with the predetermined portion of the recovered frequency modulatedvideo signal. The predetermined relationship is established during the original recording on the video disc. In the preferred embodiment, the predetermined portion of the recovered frequency modulated video signal is the color burst signal. Theinternally 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 frequency. The phase error detected in this comparison processis 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 forward orreverse direction for providing an adjustment equal to the phase error detected in the comparison process. The tangential mirror in its broadest sense is a means for adjusting the time base of the signal read from the video disc member to adjust fortime errors injected by the mechanics of the reading system.
In an alternative form of the invention, the predetermined portion of the recovered frequency modulated video signal is added to the total recorded frequency modulated video signal at the time of recording and the same frequency is employed asthe 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 erroris used for the entire line of television information for correcting the time base error for one full line of television information. In this manner, incremental changes are applied to correct for the time base error. These are constantly beingrecomputed for each line of television information.
A radial tracking servo subsystem is employed 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 modulatedsignal to develop an error signal indicating the offset from the preferred center of track position to the actual position. This tracking error is employed for controlling the movement of a radial tracking mirror to bring the light spot back into thecenter of track position.
The radial tracking servo subsystem operates in a closed loop mode of operation and in an open loop mode of operation. In the closed loop mode of operation, the differential tracking error derived from the recovered frequency modulated videosignal is continuously applied through the radial tracking mirror to bring the focus spot back to the center of track position. In the open loop mode of operation, the differential tracking error is temporarily removed from controlling the operation ofradial tracking mirror. In the open loop mode of operation, various combinations of signals take over control of the movement of the radial tracking mirror for directing the point of impingement of the focused spot from the preferred center of trackposition on a first track to a center of track position on an adjacent track. A first control pulse causes the tracking mirror to move the focused spot of light from the center of track position on a first track and move towards a next adjacent track. This first control pulse terminates at a point prior to the focused spot reaching the center of track position in the next adjacent track. After the termination of the first control pulse, a second control pulse is applied to the radial tracking mirrorto compensate for the additional energy added to the tracking mirror by the first control pulse. The second control pulse is employed for bringing the focused spot into the preferred center of track focus position as soon as possible. The secondcontrol pulse is also employed for preventing oscillation of the read spot about the second information track. A residual portion of the differential tracking error is also applied to the radial tracking mirror at a point calculated to assist the secondcontrol pulse in bringing the focused spot to rest at the center of track focus position in the next adjacent track.
A stop motion subsystem is employed as a means for generating a plurality of control signals for application to the tracking servo subsystem to achieve the movement of a focused spot tracking the center of a first information track to a separateand spaced location in which the spot begins tracking the center of the next adjacent inforamtion track. The stop motion subsystem performs its function by detecting a predetermined signal recovered from the frequency modulated video signal whichindicates the proper position within the recovered frequency modulated video signal at which time the jumping operation should be initiated. This detection function is achieved, in part, by internally generating a gating circuit indicating that portionof the recovered frequency modulated video signal within which the predetermined signal should be located.
In response to the predetermined signal, which is called in the referred embodiment a white flag, the stop motion servo subsystem generates a first control signal for application to the tracking servo subsystem for temporarily interrupting theapplication of the differential tracking error to the radial tracking mirrors. The stop motion subsystem generates a second control signal for application to the radial tracking mirrors for causing the radial tracking mirrors to leave the center oftracking 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 focus position on the next adjacent informationtrack.
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 forcompensating 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 anadjacent information track, the spaces involved are so small that the jumping operation cannot always reliably be achieved using the second control signal alone. In a preferred embodiment having an improved reliable mode of operation, the third controlsignal is employed for compensating for the effects of the second control jump pulse on the radial tracking mirror at a point in time when it is assured that the focus spot has, in fact, left the first information track and has yet to be properlypositioned in the center of the next adjacent information track. A further embodiment 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 thecompensation pulse in bringing the focus spot under control upon the center of track position of the next adjacent information track.
The video disc player employs a spindle servo subsystem for rotating the video disc member positioned upon the spindle at a predetermined frequency. In the preferred embodiment the predetermined frequency is 1799.1 revolutions per minute. Inone revolution of the video disc, a complete frame of television information is read from the video disc, processed in electronic portion of the video disc player and applied to a standard television receiver and/or television monitor in a formacceptable to each such unit, respectively. Both the television receiver and the television monitor handle the signals applied thereto by standard internal circuitry and display the color, or black and white signal, on the receiver or monitor.
The spindle servo subsystem achieves the accurate speed of rotation by comparing the actual speed of rotation with a rotor reference frequency. The motor reference frequency is derived from the color subcarrier frequency which is also used tocorrect for time base errors as described hereinbefore. By utilizing the color subcarrier frequency as the source of the motor reference signal, the spindle motor itself removes all fixed time base errors which arise from a mismatching of the recordingspeed with the playback speed. The recording speed is also controlled by the color frequency 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 timebase 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 videosignal on the video disc.
A carriage servo subsystem operates in a close loop mode of operation to move the carriage assembly to the specific location under the direction of a plurality of current generators. The carriage servo subsystem controls the relative positioningof the video disc and the optical system used to form the read beam.
A plurality of individual current sources are individually activated by command signals from the function generator for directing 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 intersects a predetermined portion of the information bearing surface of the video disc member. Asecond current source provides a continuous bias current for directing the carriage assembly to move in a fixed direction at a predetermined speed. A further current source generates a current signal of fixed magnitude and variable length for moving thecarriage assembly at a high rate of speed in a predetermined direction.
A carriage tachometer current generating means is mechanically connected to the carrier motor and is employed for generating a current indicating the instantaneous position and speed of the carriage motor. The current from the carriagetachometer is compared with the sum of the currents being generated in the current sources in a summation circuit. The summation circuit detects the difference between the current sources and the carriage tachometer and applies a different signal to apower amplifier for moving the carriage assembly under the control of the current generators.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention as illustrated in the accompanying drawings wherein:
FIG. 1 shows a generalized block diagram of a video disc player;
FIG. 2 shows a schematic diagram of the optical system employed with reference to the video disc player shown in FIG. 1;
FIG. 3 shows a block diagram of the spindle servo subsystem employed in the video disc player shown in FIG. 1;
FIG. 4 shows a block diagram of the carriage servo subsystem employed in the video disc player shown in FIG. 1;
FIG. 5 shows a block diagram of the focus servo subsystem employed in the video disc player shown in FIG. 1;
FIGS. 6a, 6b, and 6c show various waveforms illustrating the operation of the servo subsystem shown in FIG. 5;
FIG. 7 shows a partly schematic and partly block diagram view of the signal recovery subsystem employed in the video disc player shown in FIG. 1;
FIG. 8 shows a plurality of waveforms and one sectional view used in explaining the operation of the signal recovery subsystem shown in FIG. 7;
FIG. 9 shows a block diagram of the tracking servo used in the video disc player shown in FIG. 1;
FIG. 10 shows a plurality of waveforms utilized in the explanation of the operation of the tracking servo shown in FIG. 9;
FIG. 11 shows a block diagram of the tangential servo employed in the video disc player shown in FIG. 1;
FIG. 12 shows a block diagram of the stop motion subsystem utilized in the video disc player of FIG. 1;
FIGS. 13A, 13B, and 13C show waveforms generated in the stop motion sybsystem shown with reference to FIG. 12;
FIG. 14 is a generalized block diagram of the FM processing subsystem utilized in the video disc player shown with reference to FIG. 1;
FIG. 15 is a block diagram of the FM corrector circuit utilized in the FM processing current shown in FIG. 14;
FIG. 16 shows a plurality of waveforms and one transfer function utilized in explaining the operation of the FM corrector shown in FIG. 15;
FIG. 17 is a block diagram of the FM detector used in the FM processing circuit shown in FIG. 14;
FIG. 18 shows a plurality of waveforms used in explaining the operation of the FM detector shown with reference to FIG. 17;
FIG. 19 shows a block diagram of the audio processing circuit utilized in the video disc player shown with reference to FIG. 1;
FIG. 20 shows a block diagram of the audio demodulator employed in the audio processing circuit utilized in the video disc player shown with reference to FIG. 19;
FIG. 21 shows a plurality of waveforms useful in explaining the operation of the audio demodulator shown with reference to FIG. 20;
FIG. 22 shows a block diagram of the audio voltage controlled oscillator utilized in the audio processing circuit shown with reference to FIG. 19;
FIG. 23 shows a plurality of waveforms available in the audio voltage controlled oscillator shown with reference to FIG. 22;
FIG. 24 shows a block diagram of the RF modulator utilizing the video disc player shown in FIG. 1;
FIG. 25 shows a plurality of waveforms utilized in the explanation of the RF modulator shown with reference to FIG. 24;
FIG. 26 shows a schematic view of a video disc member illustrating the eccentricity effect of uneven cooling on the disc;
FIG. 27 is a schematic view of a video disc illustrating the eccentricity effect of an off-center relationship of the information tracks to the central aperture;
FIG. 28 is a logic diagram demonstrating the normal acquire focus mode of operation of the focus servo employed in the video disc shown in FIG. 1; and
FIG. 29 is a logic diagram demonstrating other modes of operation of the focus servo shown with reference to FIG. 1.
DETAILED DESCRIPTION OF THE SHOWN EMBODIMENT
The same numeral will be used in the several views to represent the same element.
Referring to FIG. 1, there is shown a schematic block diagram of a video disc player system indicated generally at 1. The player 1 employs an optical system indicated at 2 and shown in greater detail in FIG. 2.
Referring collectively to FIGS. 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 polarized ina predetermined direction. The read beam 4 is directed to the video disc 5 by the optical system 2. An additional function of the optical system 2 is to focus the light beam down to a spot 6 at its point of impingement with the video disc 5.
A portion of an information bearing surface 7 of the video disc 5 is shown enlarged within a circle 8. A plurality of information tracks 9 are formed on the video disc 5. Each track is formed with successive light reflective regions 10 andlight non-reflective regions 11. The direction of reading is indicated by an arrow 12. The read beam 4 has two degrees of movement, the first of which is in the radial direction as indicated by a double headed arrow 13. The second of which is thetangential direction as indicated by a double headed arrow 14. The double heads of each of the arrows 13 and 14 indicate that the read beam 4 can move in both directions in each of the radial degree and tangential degree.
Referring to FIG. 2, the optical system comprises a lens 15 employed for shaping the beam to fully fill an entrance aperture 16 of a microscopic objective lens 17. The objective lens is employed for forming the spot 6 of light at its point ofimpingement with the video disc 5. Improved results have been found when the entrance aperture 16 is overfilled by the reading beam 4. This results in maximum light intensity at the spot 6.
After the beam 4 is properly formed by the lens 15, it passes through a diffraction grating 18 which splits the read beam into three separate beams (not shown). Two of the beams are employed for developing a radial tracking error and the otheris used for developing both a focus error signal and the information signal. These three beams are treated identically by the remaining portion of the optical system. Therefore, they are collectively referred to as the read beam 4. The output for thediffraction grating 18 is applied to a beam splitting prism 20. The axis of the prism 20 is slightly offset from the path of the beam 4 for reasons that are explained with reference to the description of the performance of the optical system 2 as itrelates to a reflected beam 4'. The transmitted portion of the beam 4 is applied through a quarter wave plate 22 which provides a forty-five degree shift in polarization of the light forming the beam 4. The read beam 4 next impinges upon a fixed mirror24 which re-directs the read beam 4 to a first articulated mirror 26. The function of the first articulated mirror 26 is to move the light beam in a first degree of motion which is tangential to the surface of the video disc 5, to correct for time baseerror errors introduced into the reading beam 4 because of eccentricities in the manufacture of the disc 5. The tangential direction is in the forward and/or backward direction of the information track on the video disc 5 as indicated by the doubleheaded arrow 14. The read beam 4 now impinges upon the entrance aperture 16, as previously described, and is focused to a spot 6 upon the information bearing track 9 of the video disc 5 by the lens 17.
The first articulated mirror 26 directs the light beam to a second articulated mirror 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 asto slightly change its physical position to direct the point of impingement 6 of the read beam 4 so as to radially track the information carrying indicia on the surface of the video disc 5. The second articulated mirror 28 has one degree of movementwhich 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 lightnon-reflective regions 11 are light scattering elements carried by the video disc 5. The modulated light beam is a light equivalent of the electrical frequency modulated signal containing all the recorded information. This modulated light beam isgenerated 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 of the read beam is indicatedat 4'. The reflected read beam 4' retraces the same path previously explained by impingement in sequence upon the second articulated mirror 28, the first articulated mirror 26, and the fixed mirror 24. The reflected read beam 4' next passes through thequarterwave plate 22. The quarterwave plate 22 provides an additional forty-five degree polarization shift resulting in a total of one hundred ninety degrees in shift of polarization to the reflected read beam 4'. The reflected read beam 4' nowimpinges upon the beam splitting prism 20, which prism diverts the reflected read beam 4' to impinge upon a signal recovery subsystem indicated generally at 30.
The function of the beam splitting prism is to prevent 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 mechanism whereby the laser oscillates in itspredetermined mode of operation. Accordingly, the beam splitting prism 20 redirects a significant portion of the reflected read beam 4' for preventing feedback into the laser 3 when the laser 3 would be affected by this feedback portion of the reflectedread beam 4'. For those solid state lasers which are unaffected by the feedback of the reflected 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 recoverysubsystem 30 to be described hereinafter.
Referring to FIG. 1, the normal operating mode 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, aninformational signal itself which represents the stored information. A second type of signal is a control signal derived from the informational signal for controlling various portions of the player. The informational signal is a frequency modulatedsignal representing the information stored on the video disc 5. This informational signal is applied to an FM processing subsystem indicated at 32 over a line 34. A first control signal generated by the signal recovery subsystem 30 is a differentialfocus error signal applied to a focus servo subsystem indicated at 36 over a line 38. A second type of control signal generated by the signal recovery subsystem 30 is a differential tracking error signal applied to a tracking servo subsystem 40 over aline 42. The differential tracking error signal from the signal recovery subsystem 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 5mounted thereon to begin spinning. The speed of rotation of the spindle 49, as provided by the spindle motor 48, is under the control of a spindle servo subsystem 50. A spindle tachometer (not shown) is mounted relative to the spindle 49 to generateelectrical signals showing the present speed of rotation of the spindle 49. The tachometer comprises two elements which are located one hundred eighty degrees apart with reference to the spindle 49. Each of these tachometer elements generate an outputpulse as is common in the art. Because they are located one hundred eighty degrees out of phase with each other, the electrical signals generated by each are one hundred eighty degrees out of phase with each other. A line 51 carries the sequence ofpulses generated by the first tachometer elements to the spindle servo subsystem 50. A line 52 carries the tachometer pulses from the second tachometer element to the spindle servo subsystem 50. When the spindle servo subsystem 50 reaches itspredetermined rotational velocity of 1799.1 revolutions per minute, it generates a player enable signal on a line 54. The accurate rotational speed of 1799.1 revolutions per minute allows 30 frames of television information to be displayed on a standardtelevision receiver.
The next major functioning of the video disc player 1 is the activation of a carriage servo subsystem 55. As previously mentioned, the reading of the frequency modulated encoded information from the video disc 5 is achieved by directing andfocusing a read beam 4 to impinge upon the successively positioned light reflective region 10 and a light non-reflective region 11 on the video disc 5. For optimum results, the read beam 4 should impinge upon the plane carrying the encoded informationat right angles. To achieve this geometric configuration requires relative movement between the combined optical system 2 and the video disc 5. Either the video disc 5 can move under the fixed laser read beam 4 or the optical system 2 can move relativeto 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 subsystem controls this relative movement between the video disc 5 and the optical system2.
As completely described 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 responds 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 perpendicular to the informationbearing surface of the video disc 5. At this time it would be important to note that the term carriage assembly is used to identify the structural member upon which the video disc is carried. This also includes the spindle motor 48, the spindle 49, thespindle 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 FIG. 1, the carriage assembly is not shown in great detail. For an understanding ofthe summarized operation of a video disc player, it is important to note at this time that the function of the carriage servo subsystem is to move the carriage to its initial position at which the remaining player functions will be initiated in sequence. Obviously, the carriage servo subsystem can position the carriage at any number of fixed locations relative to the video disc pursuant to the design requirements of the system, but for the purposes of this description the carriage is positioned at thebeginning of the frequency modulated encoded information carried by the video disc. The carriage motor 57 provides the driving force to move the carriage assembly 56. The carriage tachometer generator 58 is a current source for generating a currentindicating the instantaneous speed and direction of movement of the carriage assembly.
The spindle servo subsystem 50 has brought the spindle speed up to its operational rotational rate of 1799.1 rpm at which time the player enable signal is generated on the line 54. The player enable signal on the line 54 is applied to thecarriage servo subsystem 55 for controlling the relative motion between the carriage assembly 56 and the operational system 2. The next sequence in the PLAY operation is for the focus servo subsystem 36 to control the movement of the lens 17 relative tothe video disc 5. The focusing operation includes a coil, (not shown), moving the lens 17 under the direction of a plurality of separate electrical waveforms which are summed within the coil itself. These waveforms are completely described withreference to the description given for the focus servo subsystem in FIGS. 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 thevideo disc 5. The electrical signals for controlling the voice coil are generated by the focus servo subsystem 36 for application to the coil over a 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 described. The second input signal is from the FM processingcircuit 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 generated bythe 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 the video disc 5 such that the lens 17 is able to gather and/or collect the maximum light reflected from the video disc 5 and modulated by thesuccessively positioned light reflective region 10 and light non-reflective region 11. This optimum range is approximately 0.3 microns in length and is located at a distance of one micron above the top surface of the video disc 5. The focus servosubsystem 36 has several modes of operation all of which are described hereinafter in greater detail with reference to FIGS. 5, 6a, 6b and 6c.
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 recoverysubsystem 30 provides an electrical representation of the relative distance between the lens 17 and the video disc 5. Unfortunately, the differential focus error signal is relatively small in amplitude and has a wave shape containing a number ofpositions thereon, 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 isnot the only signal employed to indicate the optimum focus condition. While the use of differential focus error itself can oftentimes result in the selection of the optimum focus position, it cannot do so reliably on every focus attempt. Hence, thecombination of the differential focus error signal with the signal indicative of reading a frequency modulated signal from the video disc 5 provides enhanced operation over the use of using the differential focus error signal itself.
During the focus acquiring mode of operation, 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 verynarrow spacial range. This very narrow spacial range is the optimum focusing range. Accordingly, the combination of the detected frequency modulated signal and the differential focus error signal provides a reliable system for acquiring focus.
The focus servo subsystem 36 hereinafter described contains additional improvements. One of these improvements is an addition of a further fixed signal to those already described which futher helps the focus servo subsystem 36 acquire properfocus on the initial attempt to acquire focus. This additional signal is an internally generated kickback signal which is initiated at the time when a frequency modulated signal is detected by the FM processing subsystem 32. This internally generatedkickback 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 which a frequency modulated signal was read from the disc 5. Thisinternally generated fixed kickback pulse signal gives the lens 17 the opportunity to pass through the critical optimum focusing point a number of times during the first transversing of the lens 17 towards the video disc 5.
Further improvements are described for handling momentary loss of focus during the play mode of operation caused by imperfection in the encoded frequency modulated signal which caused a momentary loss of the frequency modulated signal as detectedby the FM processing subsystem 32 and applied to the focus servo subsystem 36 over the line 66.
A tangential servo subsystem 80 receives its first input signal from the FM processing subsystem 32 over a line 82. The input signal present on the line 82 is the frequency modulated signal detected from the surface of the video disc 5 by thelens 17 as amplified in the signal recovery subsystem 30 and applied to the FM processing subsystem 32 by a line 34. The signal on the line 82 is the video signal. The second input signal to the tangential servo subsystem 80 is over a line 84. Thesignal on the line 84 is a variable DC signal generated by a carriage position potentiometer. The amplitude of the variable voltage signal on the line 84 indicates the relative position of the point of impact of the reading spot 6 over the radialdistance indicated by a double headed arrow 86 as drawn upon the surface of the video disc 5. This variable voltage adjusts the gain of an internal circuit for adjusting its operating characteristics to track the relative position of the spot as ittransverses 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 signal detected from the video disc 5 for tangential errors caused by eccentricity of the information tracks 9 on the disc 5 and other errors introduced intothe detected signal due to any physical imperfection of the video disc 5 itself. The tangential time base error correction subsystem 80 performs its function by comparing a signal read from the disc 5 with a locally generated signal. The differencebetween the two signals is indicative of the instantaneous error in the signal being read by the player 1. More specially, the signal read from the disc 5 is one which was carefully applied to the disc with a predetermined amplitude and phase relativeto 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 controlled oscillator operating at the color subcarrier frequency of 3.579545megahertz. The tangential time base error correction subsystem 80 compares the pahse difference between the color burst signal and the color subcarrier oscillator frequency and detects any difference. This difference is then employed for adjusting thephase of the remaining portion of the line of FM information which contained the color burst signal. The phase difference of each succeeding line is generated in exactly the same manner for providing continuous tangential time base error correction forthe entire signal read from the disc.
In other embodiments storing information signals which do not have a portion thereof comparable to a color burst signal, such a signal having predetermined amplitude and phase relative to the remaining signals on the disc 5 can be periodicallyadded 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 with a locally generated signal comparable to the color subcarrier oscillator. In this manner, tangentialtime 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 internally generated color subcarrier oscillator frequency is applied to the first articulated mirror 26 over lines 88 and 90. The signals on lines88 and 90 operate to move the first articulated mirror 26 so as to re-direct the read beam 4 forward and backwards along the information track, in the direction of the double headed arrow 14, to correct for the time base error injected due to animperfection from a manufacture of the video disc 5 and/or the reading therefrom. Another output signal from the tangential time base error correction subsystem 80 is applied to the stop motion subsystem 44 over a line 92. This signal, as completelydescribed hereinafter, in 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 timebase error correction subsystem 80. This sync pulse separator could be located in any other portion of the player at a point where the complete video signal is available from the FM processing subsystem 32.
A further output signal from the tangential subsystem is a motor reference frequency applied to the spindle servo subsystem 50 over a line 94. The generation of the motor reference frequency in the tangential subsystem 80 is convenient becauseof the presence of the color subcarrier oscillator frequency used in the comparison operation as previously described. This color subcarrier oscillator frequency is an accurately generated signal. It is divided down to a motor reference frequency usedin the control of the spindle servo speed. By utilizing the color subcarrier frequency as a control frequency for the speed of the spindle, the speed of the spindle is effectively locked to this color subcarrier frequency causing the spindle to rotateat the precise frame frequency rate required for maximum fidelity in the display of the information detected from the video disc 5 on either a television receiver indicated at 96 and/or a TV monitor indicated at 98.
The tracking servo subsystem 40 receives a plurality of input signals, one of which is the previously described differential tracking error signal generated by a signal recovery subsystem 30 as applied thereto over a line 42, a second inputsignal to the tracking servo subsystem 40 is generated in a function generator 47 over a line 102. For the purpose of clarity, the function generator 47 is shown as a single block. In the preferred embodiment, the function generator 47 includes aremote control function generator and a series of switches or buttons permanently mounted on the console of the video disc player 1. The specific functions so generated are described in more detail in the detailed description of the carriage servosubsystem 55 contained hereinafter.
The signal contained on the line 102 is a signal which operates to disable the normal functioning of the tracking servo 40 during certain functions initiated by the function generator 47. For example, the function generator 47 is capable ofgenerating a signal for causing the relative movement of the carriage assembly 56 over the video disc 5 to be in the fast forward or fast reverse condition. By definition, the lens is traversing the video disc 5 in a radial direction, as represented bythe arrow 13, rapidly skipping over the tracks at the rate of 11,000 tracks per inch and tracking is not expected in this condition. Hence, the signal from the function generator 47 on the line 102 disables the tracking servo 40 so that it does notattempt to operate in its normal tracking mode.
A third input signal to the tracking servo subsystem 40 is the stop motion compensation pulse generated in the stop motion subsystem 44 and applied over a line 104. An additional input signal applied to the tracking servo subsystem 40 is thesubsystem loop interrupt signal generated by the stop motion subsystem 44 and applied over a line 106. 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 line108.
The output signals from the tracking servo subsystem 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 signals on the line 110 and 112 are applied to the secondarticulated mirror 28 which is employed for radial tracking purposes. The control signals on the lines 110 and 112 move the second articulated mirror 28 such that the reading beam 4 impinging thereupon is moved in the radial direction and becomescentered 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 signalsfor the ultimate application to the loud speakers contained in the TV receiver 96, and to a pair of audio jacks 117 and 118 respectively and to an audio accessory block 120. The audio jacks 117 and 118 are a convenient point at which external equipmentcan be interconnected with the video disc player 1 for receipt 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 of the tracking correction signal which is employed by thecarriage servo subsystem for providing a further carriage control signal indicative of how closely the tracking servo subsystem 40 is following the directions given by the function generator 47. For example, if the function generator 47 gives aninstruction to the carriage servo 55 to provide carriage movement calculated to operate with a slow forward or slow reverse movement, the carriage servo subsystem 55 has a further control signal for determining how well it is operating so as to cooperatewith the electronic control signals generated to carry out the instruction from the function generator 47.
The stop motion subsystem 44 is equipped with a plurality 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 indicatingthat the video disc player 1 should go into motion mode of operation. A second input signal to the stop motion subsystem 40 is the frequency modulated signal read off the video disc and generated by the FM processing subsystem 32. The video signal fromthe FM processing subsystem 32 is applied to the stop motion subsystem 44 over a line 134. Another input signal to the stop motion subsystem 44 is the differetial tracking error as detected by the signal recovery subsystem 30 over the line 46.
The tangential servo system 80 is 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 line 140. The signal carried by theline 140 is the color subcarrier oscillator frequency generated in the tangential 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 line142 is the chroma portion of the video signal generated in the chroma separator filter portion of the tangential servo subsystem 80. An additional output signal from the tangential servo 80 is applied to the FM processing subsystem 32 over a line 144. The signal carried by the 144 is a gate enabling signal generated by a first gate separator portion of the tangential servo system 80 which indicates the instantaneous presence of the burst time period in the received video signal.
The focus servo receives its ACQUIRE FOCUS signal on a line 146.
The power output from the spindle servo subsystem is applied to the spindle motor 48 over a line 148.
The power generated in the carriage servo 55 for driving the carriage motor 57 is applied thereto over a line 150. The current generated in the carriage tachometer generator 58 for application to the carriage servo subsystem 55 indicative of theinstantaneous speed and direction of the carriage, is applied to the carriage servo subsystem 55 over a line 152.
The FM processing unit 32 has an additional plurality of output signals other than those already described. A first output signal from the FM processing subsystem 32 is applied to a data and clock recovery subsystem 152 over a line 154. Thedata and clock recovery circuit is of standard design and it is employed to read address information contained in a predetermined portion of the information stored in each spiral and/or circle contained on the surface of the video disc 5. The addressinformation detected in the video signal furnsihed by the FM processing unit 32 is applied to the function generator 47 from the data and clock recovery subsystem 152 over a line 156. The clocking information detected by the data and clock recoverysubsystem is applied to the function generator over a line 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 frequency modulatedvideo signal from the FM distribution amplifiers contained in the FM processing unit 32. An additional output signal from the FM processing subsystem 32 is applied to an RF modulator 162 over a line 164. The line 164 carries a video output signal fromthe FM detector portion of the FM processing unit 32. A final output signal from the FM processing unit 32 is applied to the TV monitor 98 over a line 166. The line 166 carries a video signal of the type displayable in a standard TV monitor 98.
The audio processing system 114 receives an additional input singal from the function generator 47 over a line 170. The signals carried by the line 170 from the function generator 47 are such as to switch the discriminated audio signals to thevarious audio accessory systems used herewith. The audio contained in the FM modulated signal recovered from the video disc 5 contains plurality of separate audio signals. More specifically, one or two channels of audio can be contained in the FMmodulated 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. Thesignals contained on the line 170 control the selection at which the audio channel is to be utilized.
The audio processing system 114 is equipped with an additional output signal for application to the RF modulator 162 over a line 172. The signal applied to the RF modulator 162 over the line 172 is a 4.5 megahertz carrier frequency modulated bythe audio information. The modulated 4.5 megahertz carrier further modulates a channel frequency oscillator having its center frequency selected for use with one channel of the TV receiver. This modulated channel frequency oscillator is applied to astandard TV receiver 96 such that the internal circuitry of the TV receiver demodulates the audio contained in the modulated channel frequency signal in its standard mode of operation.
The audio signals applied to the audio accessory unit 120 and the audio jacks 117 and 118 lies within the normal audio range suitable for driving a loudspeaker by means of the audio jacks 117 and 118. The same audio frequencies can be the inputto a stereophonic audio amplifier when such is employed as the audio accessory 120.
In the preferred embodiment, the output from the audio processing system 114 modulates the channel 3 channel frequency oscillator before application to a standard TV receiver 96. While Channel 3 has been conveniently selected for this purpose,the oscillating frequency of the channel frequency oscillator can be adapted for use with any channel of the standard TV receiver 96. The output of the RF modulator 162 is applied to the TV receiver 96 over a line 174.
An additional output signal from the function generator 47 is applied to the carriage servo subsystem 55 over a line 80. The line 180 represents a plurality of individual lines. Each individual line is not shown in order to keep the main blockdiagram as clear as possible. Each of the individual lines, schematically 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 predeterminedspeed. This is described in greater detail when describing the detailed operation of the carriage servo 55.
NORMAL .[.PALY.]. .Iadd.PLAY .Iaddend.MODE-SEQUENCE OF OPERATION
The depression of the play button generates a PLAY signal from the function generator followed by an ACQUIRE FOCUS signal. The PLAY signal is applied to the laser 3 by a line 3a for generating a read beam 4. The PLAY signal turns on the spindlemotor 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 forapplication to the carriage servo subsystem 55 for controlling the relative movement between the carriage assembly and the optical assembly 2. The carriage servo subsystem 55 directs the movement of the carriage such that the read beam 4 is positionedto impinge upon the beginning portion of the information stored on the video disc record 5. Once the carriage servo subsystem 55 reaches the approximate beginning of the recorded information, the lens focus servo subsystem 36 automatically moves thelens 17 towards the video disc surface 5. The movement of the lens is calculated to pass the lens through a point at which optimum focusing is achieved. The lens servo system preferably achieves optimum focus in combination with other control signalsgenerated 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 disc whereby the lens is caused to move thorugh the optimumfocusing point several times by an oscillatory 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 acquiresinformation from th video disc. This information consists of a total FM signal as recorded on the video disc 5 and additionally includes a differential focus error signal and a differential tracking error signal. The size of the video informationsignal 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 successfully located. When the point of optimum focus has been located, the focus servo loop is closed and themechanically initiated acquire focus procedure is terminated. The radial tracking mirror 28 is now responding to the differential tracking error generated from the information gathered by the reading lens 17. The radial tracking error is causing theradial tracking mirror 28 to follow the information track and correct for any radial departures from a perfect spiral or circle track configuration. Electronic processing of the detected video FM signal generates a tangential error signal which isapplied to the tangential mirror 26 for correcting phase error in the reading process caused by small physical deformaties in the surface of the video disc 5. During the normal play mode, the servo subsystems hereinbefore described continue their normalmode of operation to maintain the read beam 4 properly in the center of the information track and to maintain the lens at the optimum focusing point such that the light gathered by the lens generates a high quality signal for display on a standardtelevision receiver or in a television monitor.
The frequency modulated signal read from the disc needs additional processing to achieve optimum fidelity during the display in the television receiver 96 and/or television monitor 98.
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 present in the recovered video signal and caused by the mechanics of thereading process. The detected phase difference is employed for driving a tangential mirror 26 and adjusting for this phase difference. The movement of the tangential mirror 26 functions for changing the phase of the recovered video signal andeliminating time base errors introduced into the reading process. The recovered video signal is FM corrected for achieving an equal amplitude FM signal over the entire FM video spectra. This requires a variable amplification of the FM signal over theFM video spectra to correct for the mean transfer function of the reading lens 17. More specifically, the high frequency end of the video spectrum is attenuated more by the reading lens than the low frequency portion of the frequency spectrum of thefrequency modulated signal read from the video disc. This equalization is achieved through amplifying the higher frequency portion more than the lower frequency portion. After the frequency modulation correction is achieved, the detected signal is sentto a discriminator board whereby the discriminated video is produced for application to the remaining portions of the board.
Referring to FIG. 3, there is shown a generalized block diagram of the spindle servo subsystem indicated at 50. One of the functions of the spindle servo subsystem is to maintain the speed of rotation of the spindle 49 by the spindle motor 48 ata constant speed of 1799.1 rpm. Obviously, this figure has been selected to the compatible with the scanning frequency of a standard television receiver. The standard television receiver receives 30 frames per second and the information is recorded onthe video disc such that one complete frame of television information is contained in one spiral and/or track. Obviously, when the time requirements of a television receiver or television monitor differ from this standard, then the function of thespindle servo subsystem is to maintain the rotational speed at the new standard.
The function generator 47 provides a START pulse to the spindle motor. As the motor begins to turn, the tachometer input signal pulse train from the first tachometer element is applied to a Schmitt trigger 200 over the line 51. The tachometerinput signal pulse train from the second tachometer element is applied to a second Scmitt trigger 202 over the line 52. A 9.33 KHz 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 ouptut from the Schmitt trigger 202 is applied to an edge generator 210 through a divided by two network 212. Theoutput from the Schmitt trigger 204 is applied to an edge generator circuit 214 through a divided by two network 216. Each of the edge generators 206, 210 and 214 is employed for generating a sharp pulse corresponding to both the positive going edge andthe negative going edge of the signal applied respectively from the divide by two networks 208, 212 and 216.
The output from the edge generator 214 is applied as the reference phase signal to a first phase detector 218 and to a second phase detector 220. The phase detector 218 has as its second input signal the output from the edge generator 206. Thephase generator 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 signals and the motor reference frequency. The output from the phasedetector 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 poweramplifier 226. The function of the lock detector 224 is to indicate when the spindle speed has reached a predetermined rotational speed. This can be done by sensing the output signals from the summation circuit 222.
In the preferred embodiment it has been determined that the rotational speed of the spindle motor should reach a predetermined speed before the carriage assembly is placed in motion. When a video disc is brought to a relatively high rotationalspeed, the disc rides on a cushion of air and rises slightly vertical against the force of gravity. Additionally, the centrifugal force of the video disc causes the video disc to somewhat flatten considerably. It has been found that the verticalmovement against gravity caused by the disc riding on a cushion of air and the vertical rise caused by the centrifugal force both lift the video disc from its position at rest to a stabilized position spaced from its initial rest position and at apredetermined position with reference to other internal fixed members of the video disc player cabinet. The dynamics of a spinning disc at 1799.1 rpm with a predetermined weight and density can be calculated such as to insure that the disc is spacedfrom all internal components and is not in contact with any such internal components. Any contact between the disc and the player cabinet causes rubbing, and the rubbing causes damage to the video disc through abrasion.
In the preferred embodiment, the lock detector 224 has been set to generate a PLAYER ENABLE pulse on the line 54 when the spindle speed is up to its full 1799.1 rpm speed. A speed less than the full rotational speed can be selected as the pointat 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, afixed delay, after applying the START signal to the spindle motor, is used to start the carriage assembly in motion.
During the normal operating mode of the video disc player 1, the tachometer input signals are continuously applied to the Schmitt triggers 200 and 202 over the lines 51 and 52, respectively. These actual tachometer input signals are comparedagainst the motor reference signal and any deviation therefrom is detected in the summation circuit 222 for application to the power amplifier 226. The power amplifier 226 provides the driving force to the spindle motor 48 to maintain the requiredrotational speed of the spindle 49.
Referring to FIG. 4, there is shown a schematic block diagram of the carriage servo subsystem 55. The carriage servo subsystem 55 comprises a plurality of current sources 230 through 235. The function of each of these current sources is toproduce a predetermined 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 FIG. 1, comprises a plurality of individual lines. For thepurposes of this description, each of these lines will be identified as 180a through 180e. The outputs of the current sources 230 through 235 are applied to a summation circuit 238. The output from the summation circuit 238 is applied to a poweramplifier 240 over a line 242. The output from the power amplifier 240 is applied to the carriage motor 57 over the line 150. A dashed line 244 extending between the carriage motor 57 and the carriage tachometer member 58 indicates that these units aremechanically connected. The output from the carriage tachometer 58 is applied to the summation circuit by the line 152.
The START pulse is applied to the current source 232a over a line 180a. The current source 232a functions to provide a predetermined current for moving the carriage assembly from its initial rest position to the desire 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 PLAY mode of operation, the optical system 2 and carriage assembly 56 are moved such that the read beam 4 from the laser 3 iscaused to impinge upon the start of the recorded information. Accordingly, the current source 232 generates the current for application to the summation circuit 238. The summation circuit 238 functions to sense the several incremental amounts ofcurrent being generated by the various 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 previouslymentioned that the current generated by the carriage tachometer 58 indicates the instantaneous speed and position of the carriage assembly 56. This current on the line 152 is compared with the currents being generated by the current sources 230 through235 and the resulting difference current is applied to the power amplifier 240 over the line 242 for generating the power required to move the carriage motor 57 to the desired location.
Only for purposes of example, the carriage tachometer 58 could be generating a negative current indicating that the carriage assembly 56 is positioned at a first location. The current source 232a would generate a second current indicating thedesired position for the carriage assembly 56 to reach for start-up time. The summation circuit 238 compares the two currents and generates a resulting difference current on the line 242 for application to the power amplifier 240. The output from theamplifier 240 is applied to the carriage motor 57 for driving the carriage motor and moving the carriage assembly to the indiciated position. As the carriage motor 57 moves, the carriage tachometer 58 also moves as indicated by the mechanical linkageshown by the line 244. As its position changes, the carriage tachometer 58 generates a new and different signal on the line 152. When the carriage tachometer 58 indicates that it is at the same position as indicated by the output signal from thecurrent source 232a, the summation circuit 238 indicates a COMPARE EQUAL condition. No signal is applied to the power amplifier 240 and no additional power is applied to the carriage motor 57 causing the carriage motor 57 to stop.
The START signal on the line 180a causes the carriage motor 57 to move to its START position. When the spindle servo subsystem 50 has brought the speed of rotation of the spindle 49 up to its reading speed, a PLAY ENABLE signal is generated bythe 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 revolution of the disc. Thisbias current is applied to the summation circuit 238 for providing a constant current input signal to the power amplifier for driving the carriage motor 57 at the indicated distance per revolution. This constant input bias current from the currentsource 230 is further identified as a first fixed bias control signal to the carriage motor 57.
The current source 231 receives a FAST FORWARD ENABLE signal from the function generator 47 over the line 180b. The fast forward current source 231 generates an output current signal for application to the summation circuit 238 and the poweramplifier 240 for activating the carriage motor 57 to move the carriage assembly 56 in the fast forward direction. For clarification, the directions referred to in this section of the description refer to the relative movement of the carriage assemblyand the reading beam 4. These movements are directed generally in a radial direction as indicated by the double headed arrow 13 shown in FIG. 1. In the fast forward mode of operation, the video disc 5 is rotating at a very high rotational speed andhence the radial tracking does not occur in a straight line across the tracks as indicated by the double arrow 13. More specifically, the carriage servo subsystem is capable of providing relative motion between the carriage assembly and the opticalsystem 2 such as to traverse the typically four inch wide band of information bearing surface of the video disc 5 in approximately four seconds from the outer periphery to the inner pheriphery. The average speed is one inch per second during the foursecond period, the reading head moves across approximately forty-four thousand tracks. The video disc is revolving at nearly thirty revolutions per second and hence, under idealized conditions, the video disc 5 rotates one hundred and twenty times whilethe carriage servo subsystem 55 provides the relative motion from the outer periphery to the inner periphery. Hence, the absolute point of impact of the reading beam upon the rotating video disc is a spirally shaped line having one hundred and twentyspirals. The net effect of this movement is a radial movement of the point of impingement of the reading beam 4 with the video disc 5 in a radial direction as indicated by a double headed line 13.
The current source 233 receives its FAST REVERSE ENABLE signal from the function generator 47 over the line 180c. The fast reverse current source 233 provides its output directly to the summation circuit 238.
The current source 234 is a SLOW FORWARD current 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 summationcircuit 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 current 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 238through an adjustable potentiometer circuit 248. The adjustable 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 55moves 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 correction signal is to initiate carriageassembly movement when the tracking errors are in a permanent off-tracking situation such that the carriage servo subsystem should provide relative motion to bring the relative position of the video disc 5 and the read beam 4 back within the range of thetracking 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 subsystem 55 is the means for controlling the relative movement between the carriage assembly on which the video disc 5 is located and the optical system in which the reading laser 3 is located. A carriage tachometer ismechanically 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 thedirection 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 tracks from the outer periphery to the inner periphery in the normal modeof 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 ofcurrent 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 underthe 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 carriagetachometer indicating the instantaneous speed and location of the carriage assembly as the carriage assembly moves pursuant to the various commands from the input current generators. The summation circuit provides a difference output signal to a poweramplifier for operating the power required to move the carriage assembly such that the current generated in the carriage tachometer matches the current generated from input current sources.
Referring collectively to FIG. 5 and FIGS. 6A through 6F, there is shown and described a schematic block diagram of the focus servo subsystem 36, a plurality of different waveforms which are employed with the focus servo subsystem and a pluralityof single logic diagrams showing the sequence of steps used in the focus servo to operate in a plurality of different modes of operation. The focus error signal from the signal recovery subsystem 30 is applied to an amplifier and loop compensationcircuit 250 over the line 38. The output from the amplifier and loop compensation circuit 250 is applied to a kickback pulse generator 252 over a line 254 and to a focus servo loop switch 256 over the line 254 and a second line 258. The output from thekickback pulse generator 252 is applied to a driver circuit 260 over a line 262. The output from the focus servo loop switch 256 is applied to the driver circuit 260 over a line 264.
The FM video signal is applied from the distribution amplifier portion of the FM processing subsystem 32 to a FM level detector 270 over the line 66. The output from the FM level detector 270 is applied to an acquire focus logic circuit 272 overline 274. The output of the FM level detector 270 is applied as a second alternative input signal to the generator 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. Asecond output signal from the acquire focus logic circuit 272 is applied to a ramp generator circuit 278 over a line 280. The acquire focus logic circuit 272 has as its second input signal the acquire focus enable signal generated by the functiongenerator 47 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 signal applied to the acquire focus logic 272 over the line 146 is shown on line A of FIG. 6A. Basically, this signal is two-level signal generated by the function generator 47 and having a disabling lower conditionindicated at 282 and an enabling condition indicated generally at 284. The function generator produces this pulse when the video disc player 1 is in one of its play modes and it is necessary to read the information stored on the video disc 5.
Referring to line B of FIG. 6A, there is shown a typical ramping voltage waveform generated by the ramp generator circuit 278. During the period of time corresponding to the disabling portion 282 of the acquire focus signal, the focus rampwaveform is in a quiescent condition. Coincidental with the turning on of the acquire focus enable signal, the ramp generator 278 generates its ramping voltage waveform shown as a sawtooth type output waveform going from a higher position at 286 to alower position at 288. This is shown as a linearly changing signal and has been found to be the most useful waveform for this purpose.
Referring to line C of FIG. 6A, there is shown a representation of the motion of the lens itself during a number of operating modes of the video disc player. Prior to the generation of the acquire focus enable signal, the lens is generally in aretracted position indicated generally at 290. Upon the receipt of the acquire focus enable signal, the lens begins to move in a path indicated by the dash/dot line 292. The dash/dot line 292 begins at a point identified as the upper limit of lenstravel and moves through an intersection with a dotted line 294. This point of intersection is identified as the lens in focus position 293. When focus is not acquired on the first attempt, the lens continues along the dash/dot line 292 to a point 295identified as lower limit of lens travel. When the lens reaches point 295, the lens remains at the lower limit of lens travel through the portion of the line indicated generally at 296. The lens continues to follow the dash/dot line to a pointindicated at 297 identified as the RAMP RESET point. This is also shown on line A as 288. During the ramp reset time the lens is drawn back to the upper limit of lens travel portion of the waveform as indicated at 298.
In this first mode of operation the lens fails in its first attempt at acquiring focus. The lens passes through the lens in focus position as indicated by the dotted line 294. After failing to acquire focus, the lens then moves all the way toits 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 of lens travel position are sensed by limit switches in the lens driver subassemblynot 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 normally one micron above the video disc 5 when in the focus position. Also,the in-focus position can vary over a range of 0.3 microns.
The output signal from the ramp generator 278 to the driver 260 on the line 281 has the configuration shown on line B of FIG. 6A.
The waveform shown on line G of FIG. 6A shows the wave shape of the signal applied to the FM level detector 270 over the line 66. The waveform shown on line G illustrates two principal conditions. The open double sided sharp pulse indicatedgenerally at 300 is generated by the signal recovery subsystem 30 as the lens passes through focus. This is shown by the vertical line 301 connecting the top of the pulse 300 with the point on line 292 indicating that the lens has passed through thein-focus position as indicated by its intersection with the dotted line 294. Corresponding to the description previously given with reference to line C of FIG. 6A, the lens passes through focus and the sharp pulse retracts to its no activity levelindicated generally at 302.
In the second illustration, the waveform shown on line G of FIG. 6A illustrates the output from the FM distribution amplifier on the line 66 when the lens acquires focus. This is indicated by the envelope generally represented by the crossedhatched sections between lines 304 and 306.
Referring to the waveform shown on line H of FIG. 6A, there is shown a dash/dot line 308 representing the output from the FM level detector 270 corresponding to that situation when the lens does not acquire focus in its first pass through thelens in focus position by line 294 of line C of FIG. 6A. The output of the level detector represented by the dotted line 311 shows the loss of the FM signal by the detector 270. The solid line 312 shows the presence of an FM signal detected by the FMlevel detector when the lens acquires focus. The continuing portion of the waveform at 312 indicates that a FM signal is available in the focus servo subsystem 36.
Referring to line I of FIG. 6A, there is shown the output characteristic of the focus servo loop switch 256. In the portion of its operating characteristics generally indicated by the portion of the line indicated at 314, the switch is in theoff 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 video disc player during thecritical period of acquiring focus is more fully described with reference to the waveforms shown in FIG. 6C. Line A of FIG. 6C represents a corrected differential focus error generated by the signal recovery system 30 as the lens follows its physicalpath as previously described with reference to line C of FIG. 6A. At point 319 of the waveform A shown in FIG. 6C, the differential focus error corresponds to a portion of the lens travel during which no focus errors are available. At the regionindicated at 320, the first false in-focus error signal is available. There is first a momentary rise in focus error to a first maximum initial level at point 322. At point 322, the differential focus error begins to rise in the opposite directionuntil it peaks at a point 324. The differential focus error begins to drop to a second but opposite maximum at a point 326. At a point 328, halfway between the points 324 and 326, is the optimum in-focus position for the lens. At this point 328, thelens 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 pastthe in-focus position to a lower maximum at 332 prior to falling back to the position at 333 where no focus error information is available. No focus error information is available because the lens is so close to the video disc surface as to be unable todistinguish a difference of the diffused illumination presently bathing the two focus detectors.
Referring to line B, 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 attempt to acquire focus. It should benoted 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 a sharp peak 334a and 344b of the FMdetected video as the lens 17 moves through this preferred in-focus position when focus is missed.
While focus can be achieved using only the differential focus error signal shown with reference to line A of FIG. 6C, one embodiment of the present inventions utilizes the diffential focus error signal as shown on line A of FIG. 6C in combinationwith the signal shown on line B of FIG. 6C to achieve more reliable acquisition of focus during each attempt at focus.
FIG. C of line 6C shows an inverted idealized focus error signal. This idealized error signal is then differentiated and the results shown on line D of FIG. 6C. The differentiation of the idealized focus error signal is represented by the line339. Small portions of this line 339 shown at 340 and 342 lying 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 condition represented by the line 344indicates the range within which the lens should be positioned to obtain proper and optimum focus. The region 346 represents approximately 0.3 microns of lens travel and corresponds to the receipt of an FM input to the FM level detector as shown in lineB. It should be noted that no FM is shown on line B corresponding to regions 340 and 342. Hence, the FM pulse shown on line B is used as a gating signal to indicate when the lens has been positioned at the proper distance above the video disc 5 at whichit can be expected to acquire focus.
The signal representing the differentiation of the idealized focus error is applied to the generator 252 for activating the generator 252 to generate its kickback waveform. The output from the FM level detector 270 is an alternative input to thekickback generator for generating the kickback waveform for application to the driver 260.
Referring back to line B of FIG. 6A and continuing the description of the waveform shown thereon, the dot/dash portion beginning at 286 represents the start of the output signal from the ramp generator 278 for moving the lens through the optimumfocusing range. This is a sawtooth signal and it is calculated to move the lens smoothly through the point at which FM is detected by the FM level detector 270 as indicated by the waveform of line H. In a first mode of operation, the focus ramp followsa dot/dash portion 287 of the waveform to a point 287a corresponding to the time at which the output of the FM level detector shows the acquisition of focus by generating the signal level at 312a in line H. The output signal from the acquire focus logicblock 272 turns off the ramp generator over the line 280 indicating that focus has been acquired. When focus is acquired, the output from the ramp generator follows the dash line portion at 287b indicating that focus has been acquired.
Referring to line A of FIG. 6B, 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 signalapplied to the FM level detector 270 as shown on line C of FIG. 6B. Line B is a simplified version of the lens position transfer function 290 as shown more specifically with reference to line C of FIG. 6A. The lens position transfer function line 290extends between an upper limit of 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 296. The optimum lens focus point is therefore located at 299.
Referring to line D of FIG. 6B, there is shown the superimposing of a kickback sawtooth waveform indicated generally in the area 300 upon the lens position transfer line 292. This indicates that in the top portion of the three kickback pulsesare located at 302, 304 and 306. The lower portion of the three kickback pulses are located at 308, 310 and 312, respectively. The line 296 again shows the point of optimum focus. The intersection of the line 296 with the line 292 at points 296a,296b, 296c and 296d shows that the lens itself passes through the optimum lens focus position a plurality of times during one acquire focus enable function.
Referring to line E of FIG. 6B, the input to the FM level detector indicates that during an oscillatory motion of the lens through the optimum focus position as shown by the combined lens travel function characteristic shown in FIG. D, the lenshas the opportunity to acquire focus of the FM signal at four locations indicated at the peaks of waveforms 314, 316, 318 and 320.
The waveforms shown with reference to FIG. 6B demonstrate that the addition of a high frequency oscillating sawtooth kickback pulse upon the ramping signal generated by the ramp generator 278 causes the lens to pass through the optimum lens focusposition 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 after impinging upon the information track. In a first mode of operation, thelens servo is moved under a ramp voltage waveform from its retracted position towards its fully down position. When focus is not acquired during the traverse of this distance, means are provided for automatically returning the ramping voltage to itsoriginal position and retracing the lens to a point corresponding to the start of the ramping voltage. Thereafter, the lens automatically moved through its focus acquire mode of operation and through the optimum focus position at which focus isacquired.
In a third mode of operation, the fixed ramping waveform is used in combination with the output from an FM detector to stabilize the mirror at the optimum focus position which corresponds to the point at which a frequency modulated signal isrecovered from the information bearing surface of the video disc and an output is indicated at an FM detector. In a further embodiment, an oscillatory waveform is superimposed upon the ramping voltage to help the lens acquire proper focus. Theoscillatory waveform is triggered by a number of alternative input signals. A first such input signal is the output from the FM detector indicating that the lens has reached the optimum focus point. A second triggering signal occurs a fixed time afterthe beginning of the ramp voltage waveform. A third alternative input signal is a derivation of the differential tracking error indicating the point at which the lens is best calculated to lie within the range at which optimum focus can be achieved. Ina 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 detectedfrequency 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 frequency modulated signal, a timing pulse is generated which is calculated to restartthe focus acquire mode of operation. However, if the frequency modulated signals are detected prior to the termination of this fixed period of time, the pulse terminates and the acquire focus mode is skipped. If FM is lost for a period of time longerthan this pulse, then the focus acquire mode is automatically entered. The focus servo continues to attempt to acquire focus until successful acquisition is achieved.
FOCUS SERVO SUBSYSTEM--NORMAL MODE OF OPERATION
The principal function of the focus servo subsystem is to drive the lens mechanism towards the video disc 5 until the objective lens 17 acquires optimum focus of the light modulated signal being reflected from the surface of the video disc 5. Due to the resolving power of the lens 17, the optimum focus point is located approximately one micron from the disc surface. The range of lens travel at which optimum focus can be achieved is 0.3 microns. The information bearing surface of the videodisc member 5 upon which the light reflective and light non-reflective members are positioned, are oftentimes distorted due to imperfections in the manufacture of the video disc 5. The video disc 5 is manufactured according to standards which will makeavailable 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 36 responds to an enabling signal telling the lens driver mechanism when to attempt to acquire focus. A ramp generator is a means for generating a ramping voltage for directing the lens tomove 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 corresponding to the endof 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 ramping voltage period, automatic means are provided for automatically resetting the ramp generator to its initial position at the start of the ramping period. Operator intervention 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 FM video information from the video disc surface 5, imperfections 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 thisloss FM from the recovered FM video signal. This FM detecting means momentarily delays the reactivation of the acquire focus mode of operation of the lens servo subsystem 36 for a predetermined time. During this predetermined time, the reacquisition ofthe FM signal prevents the FM detector means from causing the servo subsystem to restart the acquire focus mode of operation. In the event that FM is not detected during this first predetermined time, the FM detector means reactivates the ramp generatorfor generating the ramping signal 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 andto follow through the ramping and acquire focus procedure.
In a third embodiment, the ramping voltage generated by the ramp generator has superimposed upon it an oscillatory sequence of pulses. The oscillatory sequence of pulses are added to the standard ramping voltage in response to the sensing ofrecovered FM from the video disc surface 5. The combination of the oscillatory waveform upon the standard ramping voltage is to drive the lens through the optimum focus position in the direction towards the disc a number of times during each acquirefocus procedure.
In a further embodiment, the generation of the oscillatory waveform is triggered a fixed time after the initiation of the focus ramp signal. While this is not as efficient as using the FM level detector output signal as the means for triggeringthe oscillatory waveform generator it provides reasonable and reliable results.
In a third embodiment, the oscillatory waveform is triggered by the compensated tracking error signal.
Referring to FIG. 7, there is shown a schematic block diagram of the signal recovery subsystem 30. The waveforms shown in FIG. 8, lines B, C and D, illustrate certain of the electrical waveform available within the signal recovery subsystem 30during the normal operation of the player. Referring to FIG. 7, the reflected light beam is indicated at 4' and is divided into three principal beams. A first beam impinges upon a first tracking photo detector indicated at 380, a second portion of theread beam 4' impinges upon a second tracking photo detector 382 and the central information beam is shown impinging upon a concentric ring detector indicated generally at 384. The concentric ring detector is fully described in U.S. Pat. No. 4,152,586to James E. Elliott, which is a continuation-in-part of application Ser. No. 803,986 filed June 6, 1977, entitled "Optical Focusing Servo System". The concentric ring detector 384 has an inner portion at 386 and an outer portion at 388, respectively.
The output from the first tracking photo detector 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 396. The output fromthe 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 concentric ring detector 384 is applied to a second focus preamp 402 over a line 404. Theoutput from both portions 386 and 388 of the concentric ring focusing element 384 are applied to a wide band amplifier 405 over a line 406. An alternative embodiment to that shown would include a summation of the signals on the lines 400 and 404 and theapplication of this sum to the wide band amplifier 405. The showing of the line 406 is schematic in nature. The output from the wide band amplifier 405 is the time base error corrected frequency modulated signal for application to the FM processingsubsystem 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 differential amplifier 408 over the line 412. The output from the differential amplifier 408 is the differential focus error signal applied to the focus servo 36 over the line 38.
The output from the first tracking preamplifier 390 forms one input to a differential amplifier 414 over a line 416. The output from the second tracking preamplifier 394 forms a second input to the differential amplifier 414 over a line 418. The output from the differential amplifier 414 is a differential tracking error signal applied to the tracking servo system over the line 42 and applied to the stop motion subsystem over the line 42 and an additional line 46.
Line A of FIG. 8 shows a cross-sectional view taken in a radial direction across a video disc member 5. Light non-reflective elements are shown at 11 and intertrack regions are shown at 10a. Such intertrack regions 10a are similar in shape tolight reflective elements 10. The light reflective regions 10 are planar in nature and normally are highly polished surfaces, such as a thin aluminum layer. The light non-reflective regions 11 in the preferred embodiment are light scattering and appearas bumps or elevations above the planar surface represented by the light reflective regions 10. The lengths of the line indicated at 420 and 421 shows the center to center spacing of two adjacently positioned tracks 422 and 423 about a center track 424. A point 425 in the line 420 and a point 426 in the line 421 represents the crossover point between each of the adjacent tracks 422 and 423 when leaving the central track 424 respectively. The crossover points 425 and 426 are each exactly halfway betweenthe central track 424 and the tracks 422 and 423 respectively. The end points of line 420 represented at 427 and 428 represents the center of information tracks 422 and 424 respectively. The end of line 421 at 429 represents the center of informationtrack 423.
The waveform shown in line B of FIG. 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 6 across the tracks 422, 424 and 423. This shows that amaximum frequency modulated signal is available at the area indicated generally at 430a, 430b and 430c which corresponds to the centers 427, 428 and 429 of the information tracks 422, 424 and 423 respectively. A minimum frequency modulated signal isavailable at 431a and 431b which corresponds to the crossover points 425 and 426. The waveform shown on line B of FIG. 8 is generated by radially moving a focused lens across the surface of a video disc 5.
Referring to line C of FIG. 8, there is shown the differential tracking error signal generated in the differential amplifier 414 shown in FIG. 7. The differential tracking error signal is the same as that shown in line A of FIG. 6C except forthe details shown in the FIG. 6C for purposes of explanation of the focus servo subsystem peculiar to that mode of operations.
Referring again to FIG. C of line 8, the differential tracking error signal output shows a first maximum tracking error at a point indicated at 432a and 432b which is intermediate the center 428 of an information track 424 and the crossover pointindicated at 425 or 426 depending on the direction of beam travel from the central track 424. A second maximum tracking error is also shown at 434a and 434b corresponding to a track location intermediate the crossover points 425 and 426 between theinformation 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 respectively. Minimum tracking error signals are alsoshown at 441a and 441b corresponding to the crossover points 425 and 426 respectively. This corresponds with the detailed description given with reference to FIG. 6C as to the importance of identifying which of the minimum differential tracking errorsignal outputs corresponds with the center of track location so as to insure proper focusing on the center of an information track and to avoid attempting to focus upon the track crossovers.
Referring to line D of FIG. 8, there is shown the differential focus error signal output waveform generated by the differential amplifier 408. The waveform is indicated generally by a line 442 which moves in quadrature with the differentialtracking error signal shown with reference to line C of FIG. 8.
Referring to FIG. 9, there is shown a schematic block diagram of the tracking servo subsystem 40 employed in the video disc player 1. The differential tracking error is applied to a tracking servo loop interrupt switch 480, over the line 46 fromthe signal recovery system 30. The loop interrupt signal is applied to a gate 482 over a line 108 from the stop motion subsystem 44. An open fast loop command signal is applied to an open loop fast gate 484 over a line 180b from the function generator47. As previously mentioned, the function generator includes both a remote 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 diagrammaticallyshown as the same signal applied to the carriage servo fast forward current generator over a line 180b. The console switch is shown entering an open loop fast gate 486 over the line 180b'. The fast reverse command from the remote control portion of thefunction generator 47 is applied to the open loop fast gate 484 over the line 180b. The fast reverse command from the console portion of the function generator 47 is applied to the open loop fast gate 486 over the line 180b'. The output from the gate484 is applied to an or gate 488 over a line 490. The output from the open loop fast gate 486 is applied to the or gate 488 over a line 492. The first output from the or gate 488 is applied to the audio processing system 114 to provide an audio squelchoutput signal on 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 junction 496 connected to one side of a resistor 498 and as aninput to a tracking mirror amplifier driver 500 over a line 505 and an amplifier and frequency compensation network 51. 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 toground. The amplifier 500 receives a second input signal from the stop motion subsystem 44 over the line 106. The signal on the line 106 is a stop motion compensation pulse. The output from the amplifier and frequency compensation circuit 510 isapplied as a second input to the amplifier driver 500.
The function of the amplifier 510 is to provide a DC component of the tracking error, developed over the combination of the resistor 498 and capacitor 502, to the carriage servo system 55 during normal tracking periods over a line 130. The DCcomponent from the junction 496 is gated to the carriage servo 55 by the play enabling signal from the function generator 47. The push/pull amplifier circuit 500 generates a first tracking A signal for the radial tracking mirror 28 over the line 110 andgenerates a second tracking B output signal to the radial tracking mirror 28 over the line 112. The radial mirror requires a maximum of 600 volts across the mirror for maximum operating efficiency when bimorph type mirrors are used. Accordingly, thepush/pull amplifier circuit 500 comprises a pair of amplifier circuits, each one providing a three hundred voltage swing for driving the tracking mirror 28. Together, they represent a maximum of six hundred volts peak to peak signal for application overthe lines 110 and 112 for controlling the operation of the radial tracking mirror 28. For a better understanding of the tracking servo 40, the description of its detailed mode of operation is combined with the detailed description of the operation ofthe stop motion subsystem 44 shown with reference to FIG. 12 and the waveforms shown in FIGS. 13A, 13B and 13C.
TRACKING SERVO SUBSYSTEM--NORMAL MODE OF OPERATION
The video disc member 5 being played on the video disc player 1 contains approximately eleven thousand information tracks per inch. The distance from the center of one information track to the next adjacent information track is in the range of1.6 microns. The information indicia aligned in an information track is approximately 0.5 microns in width. This leaves approximately one micron of empty and open space between the outermost regions of the indicia positioned in adjacent informationbearing tracks.
The function of the tracking servo is to direct the impingement of a focused spot of light to impact directly upon the center of an information track. The focused spot of light is approximately the same width as the information bearing sequenceof indicia which form an information track. Obviously, maximum signal recovery is achieved when the focused beam of light is caused to travel such that all or most of the light spot impinges upon the successively positioned light reflective and lightnon-reflective regions of the information track.
The tracking servo is further identified as the radial tracking servo because the departures from the information track occur in the radial direction upon the disc surface. The radial tracking servo is continuously operable in the normal playmode.
The radial tracking servo system is interrupted or released from the differential tracking error signal generated from the FM video information signal recovered from the video disc 5 in certain modes of operation. In a first mode of operation,when the carriage servo is causing the focused read beam to radially traverse the | | | |
