| 摘要 |
PURPOSE:To confirm the operation and accuracy of a photodetector without using a special reference surface by subjecting the value of the photocurrent generated by the photodetector to logarithmic conversion. CONSTITUTION:The photocurrent 5 generated from a photodetector 1 is subjected to logarithmic conversion by a current/voltage logarithmic converter 6 to be converted to output voltage 9. When a printing surface 2 is in an unprinted state, a central processing unit 11 receiving an inspection signal applies a light-out signal to a light source 4 usually lighting to irradiate the printing surface 2 through a flashing device 15. The reflected light 3 from the printing surface 2 is detected by the photodetector 1 and the voltage 9 obtained by converting the photocurrent 5 by the converter 6 is stored in a first memory 13 as a black signal. Subsequently, the processing unit 11 applies a lighting signal to the light source and the reflected light 3 from a white paper surface at this time is detected by the photodetector 1 and converted by the converter 6 to be stored in a second memory 14 as a white paper surface signal. The difference between the voltages stored in the memories 13,14 as the black signal and the white paper surface signal is taken by the processing part 11 and, for example, when the difference is a density value of 3 or more, a normal light detecting state is judged. |
