Apparatus for reading information stored in a track pattern on a

Details Apparatus for reading information stored in a track pattern on a Apparatus for reading information stored in a track pattern on a

1981-06-30

1984-07-03

Nelms, David C.

Radiant energy

Photocells; circuits and apparatus

Photocell controls its own optical systems

369 45, G01J 136

Patent

active

044581440

ABSTRACT:
Apparatus for reading information stored in a track pattern on a radiation reflecting record comprises a source of radiation such as a laser for supplying at least a reading beam, an objective lens assembly for passing the reading beam to the record and for controllably focusing the reading beam at a plane of focus, a photodetector array disposed in an optical path with the lens assembly for sensing at least the recorded information and focusing errors, and an astigmatic element disposed in the optical path for producing an astigmatic image of the reading beam in which the photodetector array comprises a unitary data photodetector disposed for impingement thereon of a zero order reading beam component for sensing the recorded information, and a quadrant photodetector array adjacent to the unitary data photodetector and including separated sectors disposed along orthogonal axes for sensing relative differences of the astigmatic image along the orthogonal axes to provide at least focus error correction signals to the objective lens assembly.

REFERENCES:
patent: 3974327 (1976-08-01), Van Dijk
patent: 4006293 (1977-02-01), Bouwhuis et al.
patent: 4051527 (1977-09-01), Braat
patent: 4059841 (1977-11-01), Bricot et al.
patent: 4152586 (1979-05-01), Elliott et al.

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