JPS55117156A - Copying control method - Google Patents

Abstract

PURPOSE:To prevent ground stains by controlling developing bias voltage, exposure lamp light quantity and charging voltage at the time of copying the original of large light transmittance without using original retaining plate. CONSTITUTION:The developing device 4 which develops electrostatic latent images is of wet type and consists of a developing solution feed pump 4a, surface potential detecting electrodes 291-293 and developing electrode 27. The developing devide 4 is controlled by the automatic developing bias circuit constituted by an operational amplifier 35 or the like, whereby the development of less ground stains is accomplished. However, ground stains occur with the original of high light transmittance with the retainer plate being held open. At such a time, a switch 13 closes when the retainer plate is opened and if a switch 14 is closed manually, a switch 15d shifts to the 15b side and the voltage further adding bias to the output of an ordinary operational amplifier 35 is applied to an electrode 27. As a result of this, the toner deposition on the ground part where the quantity of received light is less and surface potentials are high becomes less and the copy of less ground stains may be obtained.