EP0062465B1
Expired / Lapsed
EP
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Tracking system for optical record medium
Assignee: Discovision Associates
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Filing: 1982-03-26
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Granted: 1985-07-31
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Expires: 2002-03-26
Abstract
Abstract Tracking apparatus and related method for use in a playback system for recovering information from a selected recording track on an optical record medium such as a video disc. The tracking apparatus produces a tracking error signal representative of the deviation of a scanning reading beam from the centerline of the selected track, and couples this error signal to a movable tracking mirror to form a servo for controllably positioning the beam in alignment with the track. The tracking apparatus further includes a defect detection circuit for monitoring the tracking error signal and producing a pair of control signals that indicate when video disc defects of prescribed types are being scanned, and a threshold detector circuit for comparing the error signal to prescribed positive and negative thresholds that are selectively-variable in accordance with the pair of control signals. A tracking loop disable signal is produced whenever the magnitude of the error signal exceeds either threshold, and this disable signal is used to uncouple the tracking error signal from the tracking mirror, so that the reading beam is maintained at its current position until the dimple has been passed.
Inventors
- 👤 Robert M. Shoji
- 👤 John S. Chudy
- 👤 Carlyle J. Eberly
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-28 20:18
CPC Classifications
G; G11; G11B; G11B7/00; G11B7/08; G11B7/09; G11B7/0948
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
313 words
Tracking apparatus for aligning a scanning reading beam in a prescribed position relative to a selected recording track on a record medium, comprising: means (25) for determining the location of the reading beam relative to the selected track on the record medium, and for producing a corresponding tracking error signal (51); beam steering means (21), responsive to the tracking error signal, for controllably positioning the reading beam in the prescribed position relative to the selected track; threshold detector means (43, 49) for comparing the tracking error signal to a prescribed pair of tracking thresholds and for producing a disable signal (59) whenever either threshold is exceeded, the disable signal indicating that a record medium defect of a prescribed type is being scanned; and means (43) responsive to the disable signal, for selectively uncoupling the tracking error signal from the beam steering means (21), whereby the reading beam is maintained in its current position relative to the record medium whenever the reading beam scans a record medium defect of the prescribed type, characterized by: first monitoring means (61) for comparing the tracking error signal to a first, prescribed trigger threshold, to produce a first trigger signal (69) whenever the threshold is exceeded, the first trigger threshold having a prescribed polarity; and second monitoring means (63) for comparing the tracking error signal to a second, prescribed trigger threshold, to produce a second trigger signal (71) whenever the threshold is exceeded, the second trigger threshold having a polarity opposite that of the first trigger threshold, whereby the first trigger signal is indicative of a first type of defect and the second trigger signal is indicative of a second type of defect, and further characterized by means (81 and 83) responsive to said first and second trigger signals for setting the values of said pair of tracking thresholds dependent upon which type of defect is being scanned.
Claim 2
Dependent Claim
313 words
Tracking apparatus for aligning a scanning reading beam in a prescribed position relative to a selected recording track on a record medium, comprising: means (25) for determining the location of the reading beam relative to the selected track on the record medium, and for producing a corresponding tracking error signal (51); beam steering means (21), responsive to the tracking error signal, for controllably positioning the reading beam in the prescribed position relative to the selected track; threshold detector means (43, 49) for comparing the tracking error signal to a prescribed pair of tracking thresholds and for producing a disable signal (59) whenever either threshold is exceeded, the disable signal indicating that a record medium defect of a prescribed type is being scanned; and means (43) responsive to the disable signal, for selectively uncoupling the tracking error signal from the beam steering means (21), whereby the reading beam is maintained in its current position relative to the record medium whenever the reading beam scans a record medium defect of the prescribed type, characterized by: first monitoring means (61) for comparing the tracking error signal to a first, prescribed trigger threshold, to produce a first trigger signal (69) whenever the threshold is exceeded, the first trigger threshold having a prescribed polarity; and second monitoring means (63) for comparing the tracking error signal to a second, prescribed trigger threshold, to produce a second trigger signal (71) whenever the threshold is exceeded, the second trigger threshold having a polarity opposite that of the first trigger threshold, whereby the first trigger signal is indicative of a first type of defect and the second trigger signal is indicative of a second type of defect, and further characterized by means (81 and 83) responsive to said first and second trigger signals for setting the values of said pair of tracking thresholds dependent upon which type of defect is being scanned.
Claim 3
Dependent Claim
78 words
Tracking apparatus as defined in claim 1, further including: first monostable multivibrator means (73) for producing a first control signal for controlling said means (81), said first multivibrator means being triggered by the first trigger signal; and second monostable multivibrator means (75) for producing a second control signal for controlling said means (83), the second multivibrator means being triggered by the second trigger signal; and wherein the first and second control signals both have a prescribed, constant duration.
Claim 4
Dependent Claim
35 words
Tracking apparatus as defined in claim 2, wherein the durations of the first and second control signals are at least as long as the normal duration of the record medium defects of the prescribed type.
Claim 5
Dependent Claim
69 words
Tracking apparatus as defined in claim 2, wherein: the first multivibrator means (73) includes means for inhibiting output of the first control signal when the second control signal is present; and the second multivibrator means (75) includes means for inhibiting output of the second control signal when the first control signal is present; whereby only one of the first and second control signals can be present at a time.
Claim 6
Dependent Claim
79 words
Tracking apparatus as defined in claim 1, wherein; the pair of thresholds present in the threshold detector means are opposite in polarity; the magnitude of the second threshold in the pair is greater than the magnitude of the first threshold in the pair when the first trigger signal is present; and the magnitude of the first threshold in the pair is greater than the magnitude of the second threshold in the pair when the second trigger signal is present.
Claim 7
Independent Claim
275 words
A method for aligning a scanning reading beam in a prescribed position relative to a selected recording track on a record medium, comprising steps of: determining the location of the reading beam relative to the selected track on the record medium, and producing a corresponding tracking error signal; controllably positioning the reading beam in the prescribed position relative to the selected track in accordance with the tracking error signal; comparing the tracking error signal to a prescribed pair of tracking thresholds, and producing a disable signal whenever either threshold is exceeded, the disable signal indicating that a record medium defect of a prescribed type is being scanned; and selectively interrupting the step of controllably positioning, in accordance with the disable signal, whereby the reading beam is maintained in its current position relative to the record medium whenever the reading beam scans a record medium defect of the prescribed type, characterized by the steps of: comparing the tracking error signal to a first, prescribed trigger threshold, to produce a first trigger signal whenever the first trigger threshold is exceeded, the first trigger threshold having a prescribed polarity; and comparing the tracking error signal to a second, prescribed trigger threshold, to produce a second trigger signal whenever the second trigger threshold is exceeded, the second trigger threshold having a polarity opposite that of the first trigger threshold, the first trigger signal being indicative of a first type of defect, and the second trigger signal being indicative of a second type of defect, and further characterized by the step of setting the values of the pair of tracking thresholds dependent upon which type of defect is being scanned.
Claim 8
Independent Claim
275 words
A method for aligning a scanning reading beam in a prescribed position relative to a selected recording track on a record medium, comprising steps of: determining the location of the reading beam relative to the selected track on the record medium, and producing a corresponding tracking error signal; controllably positioning the reading beam in the prescribed position relative to the selected track in accordance with the tracking error signal; comparing the tracking error signal to a prescribed pair of tracking thresholds, and producing a disable signal whenever either threshold is exceeded, the disable signal indicating that a record medium defect of a prescribed type is being scanned; and selectively interrupting the step of controllably positioning, in accordance with the disable signal, whereby the reading beam is maintained in its current position relative to the record medium whenever the reading beam scans a record medium defect of the prescribed type, characterized by the steps of: comparing the tracking error signal to a first, prescribed trigger threshold, to produce a first trigger signal whenever the first trigger threshold is exceeded, the first trigger threshold having a prescribed polarity; and comparing the tracking error signal to a second, prescribed trigger threshold, to produce a second trigger signal whenever the second trigger threshold is exceeded, the second trigger threshold having a polarity opposite that of the first trigger threshold, the first trigger signal being indicative of a first type of defect, and the second trigger signal being indicative of a second type of defect, and further characterized by the step of setting the values of the pair of tracking thresholds dependent upon which type of defect is being scanned.
Claim 9
Dependent Claim
65 words
A method as defined in claim 6, wherein: the first step of comparing further includes a step of producing a first control signal in response to the first trigger signal; the second step of comparing further includes a step of producing a second control signal in response to the second trigger signal; and the first and second control signals both have a prescribed, constant duration.
Claim 10
Dependent Claim
35 words
A method as defined in claim 7, wherein the durations of the first and second control signals are at least as long as the normal duration of the record medium defects of the prescribed type.
Claim 11
Dependent Claim
71 words
A method as defined in claim 7, wherein: the first step of comparing includes a step of inhibiting output of the first control signal when the second control signal is present; and the second step of comparing includes a step of inhibiting output of the second control signal when the first control signal is present; whereby only one of the first and second control signals can be present at a time.
Claim 12
Dependent Claim
79 words
A method as defined in claim 6, wherein: the pair of thresholds used in the step of comparing are opposite in polarity; the magnitude of the second threshold in the pair is greater than the magnitude of the first threshold in the pair when the first trigger signal is present; and the magnitude of the first threshold in the pair is greater than the magnitude of the second threshold in the pair when the second trigger signal is present.
References Cited (Backward Citations)
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