| 摘要 |
PURPOSE:To compensate the influence by contamination of photodetectors by providing the two photodetectors in prescribed positions, determining the output signal ratio of the respective photodetectors, and compensating the detected value of the light reflected from an original detected by the 2nd photodetector during copying operation. CONSTITUTION:A reference density plate 10 is disposed in the place of the leading end part in the optical scanning direction of contact glass 22 where there are virtually no contaminations by the toners and the like, and the 1st photodetector 11 constituted of a photodiode, phototransistor or the like is installed near said plate 10. The reflected light from an exposure lamp 3 by the plate 10 is detected by the 1st photodetector 11. The 2nd photodetector 12 for detecting the reflected light from the plate 10 and the reflected light from the original 1 is provided to near a photodetector 9. The signals of both elements 11, 12 are operated by an error detector 13, and the errors owing to the contamination of the 2nd photodetector 12 near the photoreceptor 9 are corrected by a correcting circuit 15. |
