| 摘要 |
PURPOSE:To prevent toner from sticking to a no-image area by controlling the DC component of the developing bias of the no-image area so that the DC component is larger in absolute value than a development start voltage when a positive image is formed and smaller in absolute value than the development start voltage when a negative image is formed. CONSTITUTION:A switch S1 is changed over to a contact (e) in the no-image area and a switch S2 is changed over to a contact (f) during positive image information to apply the specific developing bias 16. No-image areas (h) and (k) are areas where parimary electrostatic charging is not performed and held at about 0V and while no-image areas (i) and (j) are held at a photosensitive body potential of -200V by exposure for charge erasure, a DC voltage of -350V is applied as the developing bias to the no-image areas (i) and (j). The potential contrast between the no-image areas of a photosensitive body and the developing bias is -150V and reversal neither normal development nor reverse fogging occurs. Consequently, much toner is prevented from sticking to no-image areas of the photosensitive body and no waste of toner consumption and no contamination in the device are caused, so that excellent images are obtained. |
