Canon ImageCLASS MF4690 Service Manual - page 71

Chapter 6

6-3

6.2 Driving and Controlling the High-Voltage System

6.2.1 Generation of Transfer Charging Bias

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The transfer charging bias (TRS) is output to transfer the toner on the photosensitive drum to papers.

There are transfer charging DC positive bias and transfer charging DC negative bias generated at the transfer charging bias generation circuit in the high-voltage

power supply circuit. The transfer charging DC positive bias is output to the transfer charging roller at transferring the toner. The transfer charging DC negative

bias is applied to the transfer charging roller at cleaning the transfer charging roller.

The transfer charging bias generation circuit applies these transfer charging biases to the transfer charging roller according to each print sequence.

The following are the biases for print sequences.

- Cleaning bias:

This is the bias for transferring the toner on the photosensitive drum to the paper at the time of print sequence. The transfer charging DC positive bias is applied to

the transfer charging roller.

- Sheet-to-sheet bias: 

This is the bias to prevent the residual toner on the photosensitive drum from being attracted to the transfer charging roller, at between sheets during continuous

printing. Faint transfer charging DC positive bias is applied to the transfer charging roller.

- Cleaning bias:

This is the bias to return the residual toner on the transfer charging roller to the photosensitive drum at the time of warm-up or last rotation sequence. The transfer

charging DC negative bias is applied to the transfer charging roller.

The transfer charging DC positive bias is changed due to the instruction of the DCNT board. To realize appropriate transfer density, the DCNT board changes the

voltage of the transfer charging DC positive bias for constant current control according to the transfer current feedback signal (TRCRNT) sent from the transfer

charging bias generation circuit.

6.3 Toner Cartridge

6.3.1 Toner Level Detection

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Overview

The toner sensor (magnetic sensor) detects the remaining toner level. When a toner cartridge is inserted, the toner sensor becomes in contact with the lower part of

the cartridge. The lower part of the cartridge being in contact with the toner sensor is made thin to achieve increased sensor sensitivity.

The toner sensor converts the magnetic force change in the cartridge filled with the toner made from magnetic body and resin into voltage.

The MPU of the DCNT board compares this output voltage of the toner sensor with the reference value, and detects the toner level.

Toner detections sequence

Detection is performed per 2.16 sec after 550 ms passing since the main motor was activated. The CPU of the DCNT board compares the output voltage of the toner

sensor with the reference value.

At initialize rotation after power-on and opening/closing the toner cover, it is detected once at 4.32 sec.