Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Patent
1991-09-27
1993-07-27
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
369 4423, G01J 120
Patent
active
052312801
ABSTRACT:
A focusing error detection apparatus for detecting a focusing error of a converging light beam on a surface of a recording medium in an image forming system. The apparatus includes a pair of mutually opposed first and second knife edges placed adjacent to the recording medium, a photodetector for outputting a signal indicative of a quantity of light received by the photodetector, a differentiation circuit for outputting a signal proportional to a derivative of the signal inpuuted from the photodetector with respect to time, a detection circuit having a first peak voltage part outputting a first signal indicative of a first peak voltage and a second peak voltage part outputting a second signal indicative of a second peak voltage, and a comparison circuit for comparing the first peak voltage with the second peak voltage, so that a deviation of the converging light beam from an intended position on the surface of the recording medium is detected on the basis of a difference between the first and second peak voltages.
REFERENCES:
patent: 4357085 (1982-11-01), Niwa et al.
patent: 4378491 (1983-03-01), Lehman
patent: 4517666 (1985-05-01), Ando 250201.5
Allen S.
Nelms David C.
Ricoh & Company, Ltd.
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