EP0011990A1
Expired / Lapsed
EP
⏱️ 0.0 years remaining
System and apparatus for centering a light beam on an information track
Assignee: Discovision Associates
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Filing: 1979-11-22
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Granted: —
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Expires: 1999-11-22
Abstract
Abstract A servo control system for maintaining an information detection device, such as a light beam, centered on a moving information track, such as a spiral recording track on a video disc. The system of the invention includes a dither signal generator (60), a bandpass filter (68) for deriving an inter- mediatesignal indicative of the effect of dither on the detected signal derived from the information track, and switching circuitry for deriving an error signal from the intermediate signal and the polarity of the dithersignal. In one embodiment of the invention, the switching circuitry includes an inverter (72), and a switch (74) for selecting either the intermediate signal or the inverted intermediate signal, in accordance with the polarity of the dither signal. The error signal thus derived is low-pass filtered and has a positive value when thecenter position of the beam moves to one side of the track, and a negative value when the center position ofthe beam moves to the other side. In an alternate embodiment, a pulse generator provides two trains of pulses occurring at the positive and negative peaks of the dither signal, respectively, and the pulse trains are employed to control two sample-to-hold circuits, respectively supplied with the intermediate signal and its inverse.
Inventors
- 👤 Lawrence S. Canino
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-31 21:33
CPC Classifications
G; G11; G11B; G11B21/00; G11B21/02; G11B21/10; G11B21/106; G11B7/00; G11B7/08; G11B7/09
Claims Analysis
Total Claims: 22
Claim 1
Independent Claim
191 words
For use in an information storage and retrieval system having a detection means for deriving an information signal from an information track, apparatus for controlling the position of the detection means to follow the information track, said apparatus composing: first transducer means for moving the detection means transversely with respect to the information track; second transducer means for deriving an information signal from the detection means; means for generating an oscillatory dither signal for application to said first transducer means; means for bandpass filtering said information signal to obtain .an intermediate signal indicative of the effect of dither on said information signal; means for correcting the phase of said dither signal to obtain a phase-corrected dither signal for correlation with said intermediate signal; means for deriving an error signal from said intermediate signal and the polarity of said phase-corrected dither signal, wherein said error signal at any instant has a magnitude derived from said intermediate signal and a polarity derived from the product of the intermediate signal polarity and the phase-corrected dither'signal polarity; and means for combining said error signal and said dither signal for application to said first transducer means.
Claim 2
Dependent Claim
191 words
For use in an information storage and retrieval system having a detection means for deriving an information signal from an information track, apparatus for controlling the position of the detection means to follow the information track, said apparatus composing: first transducer means for moving the detection means transversely with respect to the information track; second transducer means for deriving an information signal from the detection means; means for generating an oscillatory dither signal for application to said first transducer means; means for bandpass filtering said information signal to obtain .an intermediate signal indicative of the effect of dither on said information signal; means for correcting the phase of said dither signal to obtain a phase-corrected dither signal for correlation with said intermediate signal; means for deriving an error signal from said intermediate signal and the polarity of said phase-corrected dither signal, wherein said error signal at any instant has a magnitude derived from said intermediate signal and a polarity derived from the product of the intermediate signal polarity and the phase-corrected dither'signal polarity; and means for combining said error signal and said dither signal for application to said first transducer means.
Claim 3
Dependent Claim
43 words
Apparatus as set forth in claim 1, wherein said means for deriving an error signal includes: means for inverting said intermediate signal; and switch means responsive to the polarity of said phase-corrected dither signal for selecting between said intermediate signal and its inverse.
Claim 4
Dependent Claim
102 words
Apparatus as set forth in claim 1, wherein said means for deriving an error signal includes: means for inverting said intermediate signal; first and second sample-and-hold means connected to sample said intermediate signal and its inverse, respectively; pulse generation means responsive to said phase-corrected dither signal to generate a first train of pulses corresponding to positive peaks of said phase-corrected dither signal and a second train of pulses corresponding to negative peaks of said phase-corrected dither signal, said first and second trains of pulses being coupled to said first and second sample-and-hold means, respectively, whereby said sample-and-hold means supply said error signal.
Claim 5
Dependent Claim
192 words
For use in a video disc record player having a reading beam for deriving a modulated light signal from an information track on a video disc record, a system for controlling beam position to follow the information track, said system comprising: first transducer means for moving the beam radially; second transducer means for deriving a modulated light signal from energy reflected from the disc; means for generating an oscillatory dither signal for application to said first transducer means; means for bandpass filtering said modulated light signal to obtain an intermediate signal indicative of the effect of dither on said modulated light signal; means for correcting the phase of said dither signal to obtain a phase-corrected dither signal for correlation with said intermediate signal; means for deriving an error signal from said intermediate signal and the polarity of said phase-corrected dither signal, wherein said error signal at any instant has a magnitude derived from said intermediate signal and a polarity derived from the product of the intermediate signal polarity and the phase-corrected dither signal polarity; and means for combining said error signal and said dither signal for application to said first transducer means.
Claim 6
Dependent Claim
192 words
For use in a video disc record player having a reading beam for deriving a modulated light signal from an information track on a video disc record, a system for controlling beam position to follow the information track, said system comprising: first transducer means for moving the beam radially; second transducer means for deriving a modulated light signal from energy reflected from the disc; means for generating an oscillatory dither signal for application to said first transducer means; means for bandpass filtering said modulated light signal to obtain an intermediate signal indicative of the effect of dither on said modulated light signal; means for correcting the phase of said dither signal to obtain a phase-corrected dither signal for correlation with said intermediate signal; means for deriving an error signal from said intermediate signal and the polarity of said phase-corrected dither signal, wherein said error signal at any instant has a magnitude derived from said intermediate signal and a polarity derived from the product of the intermediate signal polarity and the phase-corrected dither signal polarity; and means for combining said error signal and said dither signal for application to said first transducer means.
Claim 7
Dependent Claim
45 words
A system as set forth in claim 4, wherein said means for deriving an error signal includes: means for inverting said intermediate signal; and . switch means responsive to the polarity of said phase-corrected dither signal for selecting between said intermediate signal and its inverse.
Claim 8
Dependent Claim
39 words
. 6. A system as set forth in claim 5, wherein said means for deriving an error signal further includes low-pass filter means for removing from said error signal components corresponding to the dither signal frequency and higher frequencies.
Claim 9
Dependent Claim
26 words
A system as set forth i.n claim 6, and further including phase compensation means, to compensate for phase shifts in said first and second transducer means.
Claim 10
Dependent Claim
103 words
A system as set forth in claim 4, wherein said means for deriving an error signal includes: means for inverting said intermediate signal; first and second sample-and-hold means connected to sample said intermediate signal and its inverse, respectively; pulse generation means responsive to said phase-corrected dither signal to generate a first train of pulses corresponding to positive peaks of said phase-corrected dither signal and a second train of pulses corresponding to negative peaks of said phase-corrected dither signal, said first and second trains of pulses being coupled to said first and second sample-and-hold means, respectively, whereby said sample-and-hold means supply said error signal.
Claim 11
Dependent Claim
37 words
A system as set forth in claim 8, wherein said means for deriving an error signal further includes low-pass filter means for removing from said error signal components corresponding to the dither signal frequency and higher frequencies.
Claim 12
Dependent Claim
26 words
A system as set forth in claim 9, and further including phase compensation means, to compensate for' phase shifts in said first and second transducer means.
Claim 13
Dependent Claim
144 words
For use in a video disc record player having a reading beam for deriving. a modulated light signal from an information track on the disc, a method for centering the beam' as closely as possible to the center of the track, said method comprising the steps of: generating an oscillatory dither signal for application to a transducer to dither the beam radially; bandpass filtering the modulated light signal to obtain an intermediate signal indicative of the effect of the dither signal on the modulated light signal; shifting the phase of the dither signal to obtain a phase-corrected dither signal for correlation with the intermediate signal; . deriving an.error signal from the intermediate signal and the phase-corrected dither signal polarity; low-pass filtering the error signal; and combining the filtered error signal with the dither signal for application to the transducer to control radial beam position.
Claim 14
Dependent Claim
144 words
For use in a video disc record player having a reading beam for deriving. a modulated light signal from an information track on the disc, a method for centering the beam' as closely as possible to the center of the track, said method comprising the steps of: generating an oscillatory dither signal for application to a transducer to dither the beam radially; bandpass filtering the modulated light signal to obtain an intermediate signal indicative of the effect of the dither signal on the modulated light signal; shifting the phase of the dither signal to obtain a phase-corrected dither signal for correlation with the intermediate signal; . deriving an.error signal from the intermediate signal and the phase-corrected dither signal polarity; low-pass filtering the error signal; and combining the filtered error signal with the dither signal for application to the transducer to control radial beam position.
Claim 15
Dependent Claim
37 words
A method as set forth in claim 11, wherein said deriving step includes: inverting the intermediate signal; and selecting the intermediate signal or the inverted intermediate signal, as determined by the polarity of the phase-corrected dither signal.
Claim 16
Dependent Claim
38 words
A method as set forth in claim 11, wherein .said deriving step includes: inverting the intermediate signal; and sampling and holding the intermediate signal or the inverted intermediate signal, as determined by the polarity of the phase-corrected dither.signal.
Claim 17
Dependent Claim
147 words
For use in a storage and retrieval system having a detection means for deriving an information signal from an information track, a method for centering the detection means as closely as possible to the center of the track, said method comprising the steps of: generating an oscillatory dither signal for application to a transducer to dither the detection mean: transversely with respect to the track; bandpass filtering the information signal to obtain an intermediate signal indicative of the effect of the dither signal on the information signal; shifting the phase of the dither signal to obtain a phase-corrected dither signal for correlation with the intermediate signal; deriving an error signal from the intermediate signal and the phase-corrected dither signal polarity; and low-pass filtering the error signal and combining it with the dither signal for application to the transducer to control the transverse position of the detection means.
Claim 18
Dependent Claim
147 words
For use in a storage and retrieval system having a detection means for deriving an information signal from an information track, a method for centering the detection means as closely as possible to the center of the track, said method comprising the steps of: generating an oscillatory dither signal for application to a transducer to dither the detection mean: transversely with respect to the track; bandpass filtering the information signal to obtain an intermediate signal indicative of the effect of the dither signal on the information signal; shifting the phase of the dither signal to obtain a phase-corrected dither signal for correlation with the intermediate signal; deriving an error signal from the intermediate signal and the phase-corrected dither signal polarity; and low-pass filtering the error signal and combining it with the dither signal for application to the transducer to control the transverse position of the detection means.
Claim 19
Independent Claim
94 words
A system for retrieving information from an information track by detection of a signal of radiation reflected from the track from a reading beam of radiation which moves along the track, in which the reading beam is caused to dither radially by a dither signal, the reflected signal is bandpass filtered, alternate half cycles of the filtered reflected signal are reversed in phase to produce an error signal, and the error signal is combined with the dither signal, whereby the reading beam tends to be centered to dither about the axis of the track.
Claim 20
Independent Claim
94 words
A system for retrieving information from an information track by detection of a signal of radiation reflected from the track from a reading beam of radiation which moves along the track, in which the reading beam is caused to dither radially by a dither signal, the reflected signal is bandpass filtered, alternate half cycles of the filtered reflected signal are reversed in phase to produce an error signal, and the error signal is combined with the dither signal, whereby the reading beam tends to be centered to dither about the axis of the track.
Claim 21
Dependent Claim
120 words
.16. A method of centering a reading beam in relation to an information track to be read by relative longitudinal movement of the beam, in which an oscillatory movement is:superimposed on the beam transversely of the track, at a dither frequency; the dither frequency component is extracted from the output from the reading beam; an error signal - in phase with, or in phase opposite with, the dither signal is derived from the extracted component with a mean amplitude dependent on the amount of mean transverse displacement between the track and the beam and a phase dependent on the sense of the mean transverse displacement; and the error signal is combined with the dither signal for establishing the oscillatory movement.
Claim 22
Dependent Claim
120 words
.16. A method of centering a reading beam in relation to an information track to be read by relative longitudinal movement of the beam, in which an oscillatory movement is:superimposed on the beam transversely of the track, at a dither frequency; the dither frequency component is extracted from the output from the reading beam; an error signal - in phase with, or in phase opposite with, the dither signal is derived from the extracted component with a mean amplitude dependent on the amount of mean transverse displacement between the track and the beam and a phase dependent on the sense of the mean transverse displacement; and the error signal is combined with the dither signal for establishing the oscillatory movement.
References Cited (Backward Citations)
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