| 摘要 |
PURPOSE:To give always an optimum bias voltage independently of variance of the environment of a photosensitive drum and the secular change, by compensating the change of the charging characteristic owing to the temperature near a recording material and the change of moisture absorption characteristic of the recording material during charging or the pause of charging. CONSTITUTION:A resistance value variable temperature sensor 13 is provided in a proper position around a photosensitive drum 1. An AC bias of about 1,000Hz 1VRMS is applied to the sensor 13 from an oscillating circuit 11 through a resistance R8 and a capacitor C2. This AC bias is converted to a DC by a rectifying circuit 14 and is inputted to a time constant circuit. In the time constant circuit, an electronic switch 16 is short-circuited during charging and a time constat tau1 is reduced to C1(R1XR2/R1+R2), and the switch 16 is opened during the pause of charging and a time constant tau2 is reduced to C1.R1, thus compensating the charge restoration characteristic and the charge degradation characteristic. Thus, an optimum bias value is always applied to a developing roller 8 at a charging start time as well as a charging restart time. |
