Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Patent
1982-09-29
1985-10-01
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
369 44, G05B 100
Patent
active
045448388
ABSTRACT:
A tracking error of a light spot focused on an optical record disc by means of an objective lens with respect to an information track recorded on the disc is detected by processing outputs from a light detector arranged in a far field of the track and having four light receiving regions on which a light reflected by the disc is incident. A tracking error signal of a differential detection system, i.e. a difference between two sums of outputs from two pairs of two regions aligned in a direction tangential to the track is derived, and a push-pull signal, i.e. a difference between two sums of outputs of two pairs of two light receiving regions aligned in a radial direction is also obtained. Zero crossings of the push-pull signal are detected to produce sampling pulses and the tracking error signal of differential system is sampled by the sampling pulses to derive a tracking error signal which is substantially free from disturbance due to a possible shift of the light impinging upon the light detector with respect to the optical axis of objective lens.
REFERENCES:
patent: 3381086 (1968-04-01), Moss et al.
patent: 4025784 (1977-05-01), Lehureau et al.
patent: 4051528 (1977-09-01), Takeda et al.
patent: 4057833 (1977-11-01), Braat
patent: 4410969 (1983-10-01), Maeda
Ito Ken-ichi
Musha Toru
Gatto J.
Nelms David C.
Olympus Optical Co,. Ltd.
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