EP0062465A1
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: —
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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 (13). The tracking apparatus produces a tracking error signal representative of the deviation of a scanning reading beam (11) from the centerline of the selected track, and couples this error signal to a movable tracking mirror (21) to form a servo for controllably positioning the beam in alignment with the track. The tracking apparatus further includes a defect detection circuit (41) 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
2026-11-09 05:17
CPC Classifications
G; G11; G11B; G11B7/00; G11B7/08; G11B7/09; G11B7/0948
Claims Analysis
Total Claims: 17
Claim 1
Independent Claim
238 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 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; beam steering means, responsive to the tracking error signal, for controllably positioning the reading beam in the prescribed position relative to the selected track; first means for monitoring the tracking error signal to detect when the reading beam scans a first type of defect in the record medium, and for producing a corresponding first control signal; second means for monitoring the tracking error signal to detect when the reading beam scans a second type of defect in the record medium, and for producing a corresponding second control signal; threshold detector means for comparing the tracking error signal to a prescribed pair of thresholds that are fixed in accordance with the first and second control signals, and for producing a disable signal whenever either theshold is exceeded, the disable signal indicating that a record medium defect of a prescribed type is being scanned; and means, responsive to the disable signal, for selectively uncoupling the tracking error signal from the beam steering means, 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.
Claim 2
Dependent Claim
238 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 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; beam steering means, responsive to the tracking error signal, for controllably positioning the reading beam in the prescribed position relative to the selected track; first means for monitoring the tracking error signal to detect when the reading beam scans a first type of defect in the record medium, and for producing a corresponding first control signal; second means for monitoring the tracking error signal to detect when the reading beam scans a second type of defect in the record medium, and for producing a corresponding second control signal; threshold detector means for comparing the tracking error signal to a prescribed pair of thresholds that are fixed in accordance with the first and second control signals, and for producing a disable signal whenever either theshold is exceeded, the disable signal indicating that a record medium defect of a prescribed type is being scanned; and means, responsive to the disable signal, for selectively uncoupling the tracking error signal from the beam steering means, 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.
Claim 3
Dependent Claim
89 words
Tracking apparatus as defined in claim 1, wherein: the first monitoring means includes means for comparing the tracking error signal to a first, prescribed trigger threshold, to produce a first trigger signal whenever the threshold is exceeded, the first trigger threshold having a prescribed polarity; and the second monitoring means includes means for comparing the tracking error signal to a second, prescribed trigger threshold, to produce a second trigger signal whenever the threshold is exceeded, the second trigger threshold having a polarity opposite that of the first trigger threshold.
Claim 4
Dependent Claim
75 words
Tracking apparatus as defined in claim 2, wherein: the first monitoring means further includes first monostable multivibrator means for producing the first control signal, the first multivibrator means being triggered by the first trigger signal; the second monitoring means further includes second monostable multivibrator means for producing the second control signal, the second multivibrator means being triggered by the second trigger signal; and the first and second control signals both have a prescribed, constant duration.
Claim 5
Dependent Claim
35 words
Tracking apparatus as defined in claim 3, 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 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 control 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 control signal is present.
Claim 7
Dependent Claim
67 words
Tracking apparatus as defined in claim 1, wherein: the first monitoring means includes means for inhibiting output of the first control signal when the second control signal is present; and the second monitoring means 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 8
Dependent Claim
190 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 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; beam steering means, responsive to the tracking error signal, for controllably positioning the reading beam in the prescribed position relative to the selected track; means for monitoring the tracking error signal and determining when the reading beam is scanning a defect in the record medium, and for producing a corresponding control signal indicative of the type of defect being scanned; threshold detector means for comparing the tracking error signal to a prescribed threshold that is selectively-variable in accordance with the control signal, a disable signal being produced whenever the error signal exceeds the threshold; and means, responsive to the disable signal, for selectively uncoupling the tracking error signal from the beam steering means, 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 a prescribed type.
Claim 9
Dependent Claim
190 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 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; beam steering means, responsive to the tracking error signal, for controllably positioning the reading beam in the prescribed position relative to the selected track; means for monitoring the tracking error signal and determining when the reading beam is scanning a defect in the record medium, and for producing a corresponding control signal indicative of the type of defect being scanned; threshold detector means for comparing the tracking error signal to a prescribed threshold that is selectively-variable in accordance with the control signal, a disable signal being produced whenever the error signal exceeds the threshold; and means, responsive to the disable signal, for selectively uncoupling the tracking error signal from the beam steering means, 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 a prescribed type.
Claim 10
Dependent Claim
40 words
Tracking apparatus as defined in claim 7, wherein the monitoring means includes second threshold detector means for comparing the tracking error signal to a second prescribed threshold, the control signal being produced whenever the error signal exceeds the second threshold.
Claim 11
Dependent Claim
218 words
9 . 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; monitoring the tracking error signal to detect when the reading beam scans a first type of defect in the record beam, and producing a corresponding first control signal; monitoring the tracking error signal to detect when the reading beam scans a second type of defect in the record medium, and producing a corresponding second control signal; comparing the tracking error signal to a prescribed pair of thresholds that are fixed in accordance with the first and second control signals, 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.
Claim 12
Dependent Claim
218 words
9 . 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; monitoring the tracking error signal to detect when the reading beam scans a first type of defect in the record beam, and producing a corresponding first control signal; monitoring the tracking error signal to detect when the reading beam scans a second type of defect in the record medium, and producing a corresponding second control signal; comparing the tracking error signal to a prescribed pair of thresholds that are fixed in accordance with the first and second control signals, 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.
Claim 13
Dependent Claim
94 words
A method as defined in claim 9 , wherein: the first step of monitoring includes a step of comparing the tracking error signal to a first, prescribed trigger threshold, to produce a first trigger signal whenever the threshold is exceeded, the first trigger threshold having a prescribed polarity; and the second step of monitoring includes a step of comparing the tracking error signal to a second, prescribed trigger threshold, to produce a second trigger signal whenever the threshold is exceeded, the second trigger threshold having a polarity opposite that of the first trigger threshold.
Claim 14
Dependent Claim
65 words
A method as defined in claim 10, wherein: the first step of monitoring further includes a step of producing the first control signal in response to the first trigger signal; the second step of monitoring further includes a step of producing the second control signal in response to the second trigger signal; and the first and second control signals both have a prescribed, constant duration.
Claim 15
Dependent Claim
38 words
12 . A method as defined in claim 11 , 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 16
Dependent Claim
80 words
A method as defined in claim 9 , 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 control 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 control signal is present.
Claim 17
Dependent Claim
74 words
14 . A method as defined in claim 9 , wherein: the first step of monitoring includes a step of inhibiting output of the first control signal when the second control signal is present; and the second step of monitoring 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.
References Cited (Backward Citations)
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