| 摘要 |
PURPOSE:To prevent soiling of a drum and to prevent change in surface potential by fixing a range of potential difference of a non image part potential on the photosensitive drum and developing bias voltage to a specified amount and by providing a reference voltage generating device, and a drum surface potential controlling electrode. CONSTITUTION:An electrifying film of the photosensitive drum 1 is electrified to positive potential VO by an electrifying device 2, and when the electrifying film is neutralized by irradiating with a laser beam, VO is lowered to VR. When the bias voltage VBP given to a developing sleeve is lowered to less than VR, negative toner is stuck even to the part irradiated with the laser beam (non image part), causing surface fogging and soiling. To prevent this, VBP is made as close to VR as possible, and the attracting force against the positively electrified toner is weakened. In a standard developing, since there is little fluctuation of VR, VBP is set sufficiently close to VR. Then, if the difference between potential VO of non image part of the photosensitive drum and the developing bias potential VBN(VO - VBN) is selected between 50 to 300 volts, the electrophotographic device of a reverse developing method where soiling of the nonimage part does not generate is obtained. |
