Canon PC430 Service Manual - Page 68

CHPTER 4 IMAGE FORMATION SYSTEM E. Transfer Charging Control Circuit 1. Outline Figure 4-101E shows the circuit that controls transfer charging, and the circuit has the following functions: • Controls the constant current in measurement mode. • Controls the constant voltage of the DC bias. • Switches the polarities of the DC bias (cleaning mode). The internal resistance of the transfer corona roller tends to vary from one roller to another or because of changes in the environment. The copier sends constant current to the transfer charging roller so that the microprocessor can check the changes in terms of voltage (measurement mode). Based on the measured voltage, the microprocessor corrects the DC bias. Further, the copier is equipped with a cleaning mechanism (cleaning mode) that prevents adhesion of toner to the transfer charging roller. In cleaning mode while the drum is rotating, except during transfer, a DC bias is applied to the transfer charging roller with a reversed polarity, thereby returning the toner to the photosensitive drum. Measurement mode Transfer (negative DC bias) Cleaning mode (positive DC bias) 4-10 COPYRIGHT © 1998 CANON INC. CANON PC400/420/430,FC200/220 REV.0 JAN.1998 PRINTED IN JAPAN (IMPRIME AU JAPON)