Device for controlling focus of an optical disk apparatus

Details Device for controlling focus of an optical disk apparatus Device for controlling focus of an optical disk apparatus

1994-06-22

1997-06-24

Tran, Thang V.

Dynamic information storage or retrieval

With servo positioning of transducer assembly over track...

Optical servo system

369 4429, 369 4435, G11B 709

Patent

active

056423403

ABSTRACT:
A focusing control device for use in an optical disk apparatus of the present invention is provided with: an error-signal generation circuit for generating a focus error signal; a detection circuit for detecting the quantity of light derived from a light beam reflected from an optical disk in order to form a light signal; a voltage-generating circuit for generating an offset signal whose polarity is suitable for an out-focus state based on the difference between a reference signal and the light signal, only when the light signal is smaller than the reference signal, that is, only during the out-focus state; an addition amplifier for adding the offset signal to the focus error signal; and a control circuit for controlling the position of a lens in response to the output of the addition amplifier. With this arrangement, the focus error signal is added by the offset signal so as to be shaped only during the out-focus state. The lens is always driven toward the just-focus position by the use of the focus error signal thus shaped; this eliminates failure in the focus pull-in operation.

REFERENCES:
patent: 4669074 (1987-05-01), Hsich et al.
patent: 4683560 (1987-07-01), Takeuchi et al.
patent: 4730294 (1988-03-01), Funada

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