| 摘要 |
PROBLEM TO BE SOLVED: To decide an appropriate voltage to be applied to an electrostatic charging roller, in accordance with the change of an electrostatic capacity due to the shaving of a photoreceptor and the environment, etc., and in accordance with the ambient temperature, and to prevent the occurrence of surface staining and the reduction of image density. SOLUTION: Two kinds of voltage, V1 and V2 equal to or exceeding a discharge start voltage Vth are applied to the electrostatic charging roller, and then, flowing currents I1 and I2 are measured, and the discharge start voltage Vth is obtained from a voltage V when I=0 is established in an expression; I-I1=((I2-I1)/(V2-V1)}(V-V1). Besides, a temperature detecting means is arranged near the electrostatic charger, and the voltage Vc to be applied on the electrostatic charging roller is obtained in accordance with the detected temperature in order to obtain a desired photoreceptor surface potential Vd by using the inclinationαof the photoreceptor surface potential Vd with respect to the applied voltage experimentally obtained beforehand, that is, by using Vc=Vth+Vd/α, and then, the Vc is applied on the electrostatic charging roller so as to obtain a fixed photoreceptor surface potential Vd.
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