Dynamic information storage or retrieval – Control of storage or retrieval operation by a control... – Mechanism control by the control signal
Patent
1988-07-15
1990-01-30
Psitos, Aristotelis M.
Dynamic information storage or retrieval
Control of storage or retrieval operation by a control...
Mechanism control by the control signal
250201, 350 9611, G11B 709
Patent
active
048978280
ABSTRACT:
A focusing error detecting apparatus having a first photo-detector of which the light receiving portion is halved to provide first and second light receiving portions asymmetrical with respect to the center of a beam spot of a bundle of incident laser beams, the first photo-detector being located in the optical path ahead of the focusing point of the bundle of the incident laser beams, a second photo-detector of which the light receiving portion is halved to provide first and second light receiving portions asymmetrical with respect to the center of a beam spot of a bundle of incident laser beams, the second photo-detector being located in the optical path behind a focussing point of the bundle of the incident laser beams and a calculating circuit for calculating a difference between a difference of detected outputs from the first and second light receiving portions of the first photo-detector and a difference of detected outputs from the first and second light receiving portions of the second photo-detector, thereby to derive a focusing error signal from the output of the calculating circuit.
REFERENCES:
patent: 4011400 (1977-03-01), Simons et al.
patent: 4654519 (1987-03-01), Ando
patent: 4725725 (1988-02-01), Ando
patent: 4823331 (1989-04-01), Yoshitoshi et al.
Kume Hidehiro
Matsumoto Yoshiyuki
Mitsumori Koji
Oinoue Hiroshi
Yamamoto Etsufumi
Psitos Aristotelis M.
Shaw, Jr. Philip M.
Sony Corporation
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