| 摘要 |
PURPOSE:To prevent fogging and density change caused by the change of the layer thickness of a photosensitive body and to improve image quality by providing an electrostatic charging means for electrostatically charging the surface of the photosensitive body and a means for detecting a current flowing in the photosensitive body accompanied with the electrostatic charging and detecting the current. CONSTITUTION:Two varistors 12a and 12b are serially connected to the grid electrode 11 of an electrostatic charger C and one end thereof is grounded so that the surface potential V0 of a photosensitive drum 1 may be always kept constant. The connection point of the varistors 12a and 12b is grounded through a bypass circuit 13, and a switching means 13a for switching the circuit 13 to a conductive state or a non-conductive state is interposed in the circuit 13. The potential V0 is switched at two steps by the circuit 13 and two kinds of currents Ipc flowing in the drum 1 are detected. The detected result is arithmetically operated by a main control part 22 to calculate an appropriate light quantity for compensating the lowering of sensitivity accompanied with the change of the layer thickness, then a control command signal is outputted to an exposing lamp voltage impressing means 14. |
