Dynamic information storage or retrieval – Condition indicating – monitoring – or testing – Including radiation storage or retrieval
Patent
1987-09-29
1989-03-28
Sikes, William L.
Dynamic information storage or retrieval
Condition indicating, monitoring, or testing
Including radiation storage or retrieval
369 44, 369 46, 369 48, 369 58, 369 59, 371 57, 371 61, 371 62, G11B 509, G06F 1100
Patent
active
048170771
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a device for detecting a defect of a disc-shaped record medium, which generates a defect detection output signal at the time when the defect of the disc-shaped record medium comes to a reading position during reproduction of an information signal recorded in a spiral recording track on the disc-shaped record medium.
TECHNICAL BACKGROUND
In a disc player for reproducing an information signal from an optical disc, such as an optical digital audio disc, on which the information signal is recorded in the form of small pits arranged in a spiral track, a light beam is used for reading the information signal from the spiral track. The light beam is emitted from an optical head which is moved in the direction of the radius of the optical disc so as to scan the spiral track on the optical disc which is in a state of revolutions at a predetermined speed, and the light beam is required to trace correctly the spiral track and to be focused correctly on the surface of the optical disc on which the spiral track is formed. To make the light beam comply with these requirements, tracking servo-control and focus servo-control are performed. In the tracking servo-control, the position of a beam spot formed by the light beam on the optical disc in relation to the spiral track is detected to produce a tracking detection output and an optical element, such as a focusing lens, in the optical head or the optical head in its entirety is moved in the direction of the radius of the optical disc in response to the tracking detection output so as to cause the position of the beam slot to be placed correctly on the spiral track. In the focus servo-control, a focus condition of the light beam on the optical disc is detected to produce a focus detection output and the focusing lens in the optical head or the optical head in its entirety is moved in the direction of an axis of rotation of the optical disc in response to the focus detection output so as to cause the light beam to be focused correctly on the optical disc.
The tracking detection output is obtained in the form of a tracking error signal representing deviations of the beam spot on the optical disc from the center of the spiral track and the focus detection output is obtained in the form of a focus error signal representing defocus of the light beam on the optical disc. The tracking error signal and the focus error signal are usually derived from an information signal reproducing section together with a reproduced information signal. In the information signal reproducing section, a reading light beam, which comes from a portion of the optical disc on which the light beam emitted from the optical head is caused to impinge and modulated in intensity, is detected by a plurality of light detecting elements forming together a photodetector and detection output signals obtained from the light detecting elements in the photodetector are calculated at a signal processing circuit. Then, control signals are produced respectively based on the tracking error signal and the focus error signal which are derived from the information signal reproducing section containing the photodetector and the signal processing circuit, and supplied to driving means for moving the optical element such as the focusing lens in the optical head or the optical head in its entirety in the direction of the radius of the optical disc or the direction of the axis of rotation of the optical disc. As a result, the optical element such as the focusing lens in the optical head or the optical head in its entirety is moved in the direction of the radius of the optical disc or the direction of the axis of rotation of the optical disc in response to each of the tracking error signal and the focus error signal.
When the information signal is reproduced from the spiral track on the optical disc under the tracking servo-control and the focus servo-control performed as mentioned above in the disc player, and in the case where the optical disc has a defect where the surface o
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Eslinger Lewis H.
Healy Brian M.
Maioli Jay H.
Sikes William L.
Sony Corporation
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