Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Patent
1976-12-22
1979-01-23
Demeo, Palmer C.
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
355 68, G01J 132, G03B 708, G03B 2774
Patent
active
041362772
ABSTRACT:
An automatic exposure system for a copying machine comprising a scanning optical system having an imaging period and a calibrating period, including a lamp illumination control loop for providing a calibrated control signal, said control loop comprising means for supplying a reference control signal to the lamp means during the calibration period, a multiplying digital to analogue convertor arranged to respond to the output of a light intensity detector positioned to receive light reflected during the calibration period from a document to be copied, a comparator for comparing the output of the digital to analogue convertor and the reference control signal and for controlling the countdown of a digital counter to equalize the convertor output and reference control signal, and circuit means for maintaining said counter output constant during a subsequent imaging period and for supplying a predetermined input to the digital to analogue convertor to generate as its output said calibrated control signal.
REFERENCES:
patent: 3914049 (1975-10-01), Basu et al.
patent: 3947117 (1976-03-01), Basu et al.
patent: 3986022 (1976-10-01), Hyatt
DeMeo Palmer C.
Taylor Ronald L.
Xerox Corporation
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