| 摘要 |
PURPOSE:To accurately detect the surface potential of a photosensitive body and to obtain stable image quality without making th device expensive and complicating it only by calibrating a surface potential detector. CONSTITUTION:A photosensitive belt 5 starts moving while a reference voltage is impressed on the Al substrate 5a of the belt 5 from a developing bias power source 32 by switching a relay switch 30 so that a normally closing contact (b) is opened and a normally opening contact (a) is closed. Then, a surface potential sensor (surface potential detector) 21 is calibrated by regarding the measured value of potential obtained from the sensor 21 at that time as a reference value. In such a case, the measured values of the potential obtained from the sensor 21 while the belt 5 makes a round are successively sampled at prescribed intervals and the respective measured values are averaged. It is recommended that the averaged value is used as the reference value. Besides, it is recommended that the belt 5 is turned at a lower speed than that at the time of forming an image when the sensor 21 is calibrated. |
