| 摘要 |
PURPOSE:To prevent much toner from sticking in no-image area during positive image formation by setting the DC component of the developing bias of no-image areas larger in absolute value than a development start voltage during positive image formation and lower in absolute value during negative image formation. CONSTITUTION:When a positive image is formed, no-image areas (h) and (k) are areas where pirmary electrostatic charging is not performed and at about 0V and no-image areas (i) and (j) ar applied with a DC voltage of -950V as a developing bias although the photosensitive potential is still at -800V. Therefore, the potential contrast between no-image areas of a photosensitive body and the developing bias is -150V and neither a normal phenomenon nor a reverse fogging phenomenon occurs. When a negative image is formed, a DC voltage of -650V is applied in the no-image areas (i) and (j) as the developing bais and the potential contrast between the photosensitive body potential in the no-image area and the developing bias is +150V, so that no toner sticks. Thus, the absolute value is set larger than the development start voltage during the positive image formation and smaller than the development start voltage during the negative image formation. Consequently, excellent images are obtained without consuming unnecessary toner nor causing contamination, etc., in the device. |
