Optical scanning apparatus for a multi-layer record carrier, inc

Details Optical scanning apparatus for a multi-layer record carrier, inc Optical scanning apparatus for a multi-layer record carrier, inc

1996-07-30

1998-08-11

Hindi, Nabil

Dynamic information storage or retrieval

With servo positioning of transducer assembly over track...

Optical servo system

369 4429, 369 94, G11B 700

Patent

active

057937214

ABSTRACT:
An optical beam in a scanning device is focused on an information layer of a multi-layer optical record carrier. A focus control circuit keeps the focal point of the beam on the information layer. When the focal point jumps to another information layer, the focus control circuit does not monitor the so-called central aperture signal in order not to depend on the presence of information in the information layers. During the jump the characteristics of the feedback loop of the focus control unit are modified to avoid instabilities in the movement of the focal point during the jump. The characteristics of the feedback loop are restored after a predetermined period of time, then the focal point is near the designated layer and the restored control loop focuses the focal point on the designated layer.

REFERENCES:
patent: 4023033 (1977-05-01), Bricot et al.
patent: 4724533 (1988-02-01), Ohara et al.
patent: 5189293 (1993-02-01), Leenknegt
patent: 5263011 (1993-11-01), Maeda et al.
patent: 5321676 (1994-06-01), Van Velthoven et al.
patent: 5511057 (1996-04-01), Holtslag et al.
patent: 5608715 (1997-03-01), Yokogawa et al.

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