Device for detecting focussing error in an optical reader head

Details Device for detecting focussing error in an optical reader head Device for detecting focussing error in an optical reader head

1975-07-22

1977-05-24

Nelms, David C.

Radiant energy

Photocells; circuits and apparatus

Photocell controls its own optical systems

1791003V, 250204, 358127, G01J 120

Patent

active

040257843

ABSTRACT:
A device for detecting the error in focussing a read-out beam on the impression. Two photodetector cells located respectively in front of and behind the optical axis of the system, in relation to the direction of transfer, produce two electrical signals the difference between which is the read-out signal, a control signal being obtained by a comparison of the phases of the two signals, one of which is phase-shifted so that the optimum focussing point corresponds to zero phase-shift.

REFERENCES:
patent: 3876841 (1975-04-01), Kramer et al.
patent: 3913076 (1975-10-01), Lehureau et al.
patent: 3924063 (1975-12-01), Simons
patent: 3925603 (1975-12-01), Naruse et al.
patent: 3932700 (1976-01-01), Snopko

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