Dynamic information storage or retrieval – Control of storage or retrieval operation by a control... – Mechanism control by the control signal
Patent
1986-12-03
1989-06-20
McElheny, Jr., Donald
Dynamic information storage or retrieval
Control of storage or retrieval operation by a control...
Mechanism control by the control signal
369 45, G11B 713
Patent
active
048415090
ABSTRACT:
An apparatus and method for identifying focus and tracking errors in an optical disk apparatus is provided. Reflections from the disk are generated using a conventional laser light source to produce an optical image including zero and first order diffraction rays. A cylindrical lens converges the image along a single axis to form an elliptical optical image having a major and minor axis and having first and second interference portions aligned along the major axis. A half-mirror type beam splitter splits the image into first and second images which are detected at first and second photodetectors each including first, second, third, and fourth photoreceptive portions. The first and second photoreceptor portions are spaced along the minor axis, the first and fourth photoreceptor portions are spaced along the major axis. The photoreceptors are spaced forward and behind a converging focus point so that the image is converging towards one photodetector and diverging at the second photodetector. Differences that are identified in photoreception between the first and second photoreceptive portions as representative of focus error and differences in photoreception between the third and fourth photoreceptive portions are representative of tracking error.
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Kamisada Toshimasa
Saito Akira
Hitachi , Ltd.
McElheny Jr. Donald
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