Tracking system for a reading beam

Claim 2

A tracking system for a reading beam (11) reading a selected recorded track (37) on a record (13) including a recovery device (25) arranged to derive a tracking error signal (51) for the reading beam after encountering the record, and beam steering means (21) responsive to the tracking error signal, characterised by a monitor (41) of the tracking error signal, and disabling means (43) arranged in response to the monitor recognising an abnormality in the tracking error signal, to render the beam steering means temporarily irresponsive to the tracking error signal.

Claim 3

A tracking system as claimed in Claim 1 in which the monitor produces a disable signal in response to the tracking error signal going beyond a set threshold.

Claim 4

A tracking system as claimed in Claim 1 in which the monitor includes first and second threshold detectors (47,49) arranged to produce respective first and second signals in response to the tracking error signal exceeding respective positive and negative threshold values, and in which a disable signal is produced in response to the appearance of the first signal, and in response to the appearance of the second signal.

Claim 5

A system as claimed in Claim 2 or Claim 3 in which the disable signal lasts for as long as the threshold value is exceeded.

Claim 6

A system as claimed in Claim 2 or Claim 3 including monostable means for producing the disable signal, which lasts for a preset time.

Claim 7

A system as claimed in Claim 5 for use with a disc record in which the preset time is substantially less than the time for the reading beam to cover one complete revolution of the recorded track on the disc. surface.

Claim 8

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 record medium defect of a type that causes the selected track to deviate momentarily from its normal position, and for producing a corresponding disable signal: 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.

Claim 9

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 record medium defect of a type that causes the selected track to deviate momentarily from its normal position, and for producing a corresponding disable signal: 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.

Claim 10

Tracking apparatus for positioning a reading beam in alignment with a selected track of a plurality of substantially circular and concentric recording tracks on a rotatable video disc, comprising: means for determining the location of the reading beam relative to the centerline of the selected track on the video disc, and for producing a corresponding tracking error signal: beam steering beams for controllably positioning the reading beam in accordance with the tracking error signal, whereby the reading beam is positioned in alignment with the selected track; first threshold detector means for comparing the tracking error signal to a first prescribed threshold, to produce a first signal whenever the first threshold is exceeded; second threshold detector means for comparing the tracking error signal to a second prescribed threshold, to produce a second signal whenever the second threshold is exceeded: means for combining the first and second signals in a prescribed fashion, to produce a disable signal indicating that the reading beam is impinging on a video disc defect of a prescribed type; and switch means responsive to the disable signal, for selectively uncoupling the tracking error signal from the beam steering means, whereby the reading beam is maintained substantially in its current position whenever it impinges on a video disc defect of the prescribed type.

Claim 11

Tracking apparatus for positioning a reading beam in alignment with a selected track of a plurality of substantially circular and concentric recording tracks on a rotatable video disc, comprising: means for determining the location of the reading beam relative to the centerline of the selected track on the video disc, and for producing a corresponding tracking error signal: beam steering beams for controllably positioning the reading beam in accordance with the tracking error signal, whereby the reading beam is positioned in alignment with the selected track; first threshold detector means for comparing the tracking error signal to a first prescribed threshold, to produce a first signal whenever the first threshold is exceeded; second threshold detector means for comparing the tracking error signal to a second prescribed threshold, to produce a second signal whenever the second threshold is exceeded: means for combining the first and second signals in a prescribed fashion, to produce a disable signal indicating that the reading beam is impinging on a video disc defect of a prescribed type; and switch means responsive to the disable signal, for selectively uncoupling the tracking error signal from the beam steering means, whereby the reading beam is maintained substantially in its current position whenever it impinges on a video disc defect of the prescribed type.

Claim 12

.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 accordance with the tracking error signal, to align the beam in the prescribed position relative to the selected track; monitoring the tracking error signal and determining when the reading beam is scanning a record medium defect of a type that causes the selected track to deviate momentarily from its normal position, and producing a corresponding disable signal; and interrupting the step of controllably positioning in accordacne with the disable signal, whereby the reading beam is maintained in its current position relative to the record medium.

Claim 13

.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 accordance with the tracking error signal, to align the beam in the prescribed position relative to the selected track; monitoring the tracking error signal and determining when the reading beam is scanning a record medium defect of a type that causes the selected track to deviate momentarily from its normal position, and producing a corresponding disable signal; and interrupting the step of controllably positioning in accordacne with the disable signal, whereby the reading beam is maintained in its current position relative to the record medium.

Claim 14

In a system utilising a beam to scan a record medium, a combination comprising: first means for controllably adjusting a prescribed characteristic of the beam relative to the record medium; second means for monitoring the performance of the first means and detecting deviations from normal operation; and third means, responsive to the detection of deviations by the second means, for shifting the first means to a different operational state.

Claim 15

In a system utilising a beam to scan a record medium, a combination comprising: first means for controllably adjusting a prescribed characteristic of the beam relative to the record medium; second means for monitoring the performance of the first means and detecting deviations from normal operation; and third means, responsive to the detection of deviations by the second means, for shifting the first means to a different operational state.