| 摘要 |
PURPOSE:To prevent stains on a background by setting a developing bias value from a suspension period and a developer fatigue degree and gradually lowering said value in accordance with the number of copies produced from the start of a copying machine. CONSTITUTION:A developer-based copy quantity detection circuit 11 counts the number of copies from the time of feeding a fresh developer, and sends its signal to a bias control circuit 12. A copy quantity detection circuit 13 is cleared when a copying machine is suspended, and starts to count when it starts operation, and sends its signal to the circuit 12. A suspension time detection circuit 14 detects a length of time from the suspension of the machine or the stop of agitation of the developer to the restart, and sends its digitized value to the circuit 12. The circuit 12 receives these signals, sets a correct bias voltage value, and applies it to a developing roller 17. A toner is triboelectrified in polarity opposite to an electrostatic latent image by agitation with a blade wheel 19. The polarity of the bias voltage is opposite to that of the toner, lower than potential at the image part, and somewhat higher than potential at the background. Therefore, the toner adheres to the image part but not to the background part, thus preventing background stains. |
