| 摘要 |
PURPOSE:To obtain a high-quality fog-free picture having a high contrast by controlling a primary charger at the surface potential of lst-stage irradiation and by controlling a development bias at the surface potential of 2nd-stage intense irradiation by switching an LED by two stages. CONSTITUTION:Between an entire-surface exposure lamp 68 and a developing device 62, a surface electrometer 67 and an LED70 irradiating an exposed part with light are provided, and an in- mirror lens 52 is provided with a shutter 82. In this constitution, the LED70 is turned on with the shutter 82 closed to measure the potential of a dark part on a drum surface which is not irradiated and that of a light part, a target value voltage for obtaining a predetermined high contrast is subtracted to multiply the result by a set coefficient for the calculation of a correction current value, and a charger 51 is controlled by the calculated value to stabilize the surface potentials. Then, the quantity of light equivalent to that when a white original is irradiated with light from the LED70 is set to measure the surface potentials, and a development bias is controlled with a voltage obtained by adding the target value of the light-part potential to the measured value, thereby preventing a fog. Consequently, potential variations due to fluctuations of the temperature of a photoreceptor and a secular change are compensated to stabilize the potentials, and consequently a fog is prevented to obtain pictures of good quality. |
