Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Patent
1989-08-10
1991-05-21
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
369 4441, G01J 120, G11B 700
Patent
active
050177680
ABSTRACT:
Light is condensed on a recording medium by an objective lens, and light reflected from the recording medium passes through the objective lens and is split into light along two optical paths via a condenser lens and beam splitter. A light-receiving surface having an area smaller than that of the irradiation pattern of the returned light when the objective is focused is disposed on the inner side of a focal point on one optical path, and an identical light-receiving surface is disposed on the outer side of a focal point on the other optical path. The arrangement is such that the photoelectric outputs of the two light-receiving surfaces coincide when the objective lens is focused. Preferably, the light-receiving surface is divided into four portions by a straight line, which is obtained by projecting the track direction of the recording medium, and a region having line symmetry with respect to the straight line and an area smaller than that of the irradiation pattern when the objective is focused. A tracking error signal of the objective lens is obtained by correcting a difference signal between light-receiving surfaces on the inner side by a low-frequency component of a difference signal between light-receiving surfaces on the outer side.
REFERENCES:
patent: 4724533 (1988-02-01), Ohara et al.
patent: 4742218 (1988-05-01), Nakamura et al.
patent: 4764912 (1988-08-01), Ando et al.
patent: 4801794 (1989-01-01), Kowalski et al.
patent: 4843603 (1989-06-01), Prikryl
patent: 4862442 (1989-08-01), Tadokoro et al.
Copal Company Limited
Fujitsu Limited
Messinger Michael
Nelms David C.
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