| 摘要 |
PURPOSE:To execute satisfactorily copying without causing a failure by detecting a reflecting density of a ground of a copying original prior to execution of a copying work, determining an optimum developing bias by this detecting output, and executing by a constant optimum developing bias in the course of an operation of the copying stage. CONSTITUTION:A sensor 19 for detecting a ground density of a copying original 12 to be fed is provided on the lower side in the copying original feeding direction of an original feed roller 22 of an automatic original feed device. Basing on a detecting output of this sensor 19, developing bias voltage is determined. Subsequently, voltage of a developing bias voltage source is controlled to developing bias voltage corresponding to a reflecting density of a ground of the copying original 12. In this way, copying is executed by an optimum developing bias based on a reflecting density of a ground of the copying original, which is detected prior to execution of a copying work, therefore, the copying can be executed satisfactorily without causing a failure. |
