Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Patent
1988-07-28
1989-12-19
Richardson, Robert L.
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
369 45, 369 46, 250201, G11B 700
Patent
active
048887528
ABSTRACT:
A focusing and tracking servo system for generating focusing and tracking error signals for use in driving a servo system which focuses and tracks an optical beam, such as a laser beam on an optical disk. The system includes a photosensor having two sub-photosensors arranged to be adjacent to each other and to have a common boundary, and the laser beam has a circular cross-section and an optical axis. The laser beam reflected by the optical disk is incident on the photosensor so that the optical axis is offset from the boundary between the sub-photosensors. Consequently, the optical spot formed on each sub-photosensor has a different area and the sub-photosensors generate different photoelectric currents. The output currents from the sub-photosensors are individually amplified by amplifiers having adjustable amplification factors, and the amplification factors are set so that they are inversely proportional to the output current of the sub-photosensors when the laser beam incident on the optical disk is in an in-focus state. When the laser beam incident on the optical disk is in an out-of-focus state the optical spot changes, and thus the relative output currents of the sub-photosensors change. A focusing error signal is generated in accordance with the difference of the output currents of the amplifiers. In another embodiment of the present invention a photosensor array having four sub-photosensors arranged in a quadrant matrix with two boundaries is utilized to generate both focusing and tracking error signals.
REFERENCES:
patent: 4455085 (1984-06-01), Kato et al.
patent: 4492856 (1985-01-01), Kimura
Patent Abstracts of Japan, vol. 9, No. 308, Dec. 4 , 1985 & JP-A-60 138748.
Patent Abstracts of Japan, vol. 7, No. 73, Mar. 25, 1983 & JP-A-58 3140.
Patent Abstracts of Japan, vol. 9, No. 221, Sept. 7, 1985 & JP-A-60 79537.
Patent Abstracts of Japan, vol. 8, No. 179, Aug. 17, 1984 & JP-A-59 71135.
Fujitsu Limited
Richardson Robert L.
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