| 摘要 |
PURPOSE:To eliminate the need for providing separately a sensor for detecting an original size by detecting the original size by the signal from a means for detecting the surface potential of a photosensitive drum. CONSTITUTION:A surface potential sensor 13 for detecting the surface potential on a photosensitive drum 11 is provided to control the stabilization of the surface potential of the photosensitive body and to detect the density of the original. The characteristic of the surface potential sensor 13 is so adjusted that the output voltage proportional to the surface potential of the drum 11 can be obtd. Light is not projected to the drum 11 by as much as the length of the original while the original is imposed on an original platen. The length of the original is detectable from the time (distance) when the surface potential pattern of the pattern formed on an original cover is continuously obtd. up to the rear end of the image region of the original platen before the rear end of the image region of the original platen. |
