Optical recording/playback apparatus having a focusing control s

Details Optical recording/playback apparatus having a focusing control s Optical recording/playback apparatus having a focusing control s

1984-06-11

1987-04-28

Cardillo, Raymond F.

Dynamic information storage or retrieval

With servo positioning of transducer assembly over track...

Optical servo system

369 46, 250202, G11B 712, G11B 2100, G11B 7095

Patent

active

046619445

ABSTRACT:
The disclosed apparatus for recording and/or reading information in or from a track of a radiation-reflecting record carrier by means of a light beam includes an objective system for focusing the light beam so as to form a light spot on the record carrier in dependence on a control signal (S.sub.f). The control signal is generated by a focusing-error detection system having an astigmatic element and four detectors (D.sub.1 to D.sub.4). The output signals S.sub.1 to S.sub.4 of the four detectors are combined in an electric circuit arranged to produce a control signal satisfying the formula: ##EQU1## This control signal drastically reduces the influence on the focusing of offset of the light spot on the four detectors.

REFERENCES:
patent: 4123652 (1978-10-01), Bouwhuis
patent: 4163149 (1979-07-01), Sawano et al.
patent: 4293944 (1981-10-01), Izumuta et al.
patent: 4467462 (1984-08-01), Shibata
patent: 4544838 (1985-10-01), Musha et al.

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