Driving And Controlling The High-Voltage System; Outline; Primary Charging Bias Generation; Developing Bias Generation - Canon MF8100 Series Service Manual

Chapter 2

2.3.2 Driving and Controlling the High-Voltage System

2.3.2.1 Outline

In this circuit, biases are applied to the primary charging roller, developing cylinder, primary transfer roller, secondary transfer roller, auxiliary ITB cleaning roller,
ITB cleaning roller, and fixing film. The CPU (IC101) in the DCNT Board controls the high-voltage power supply circuit and the sub high-voltage power supply
circuit through the ASIC (IC102) to generate the biases.
The block diagram of this circuit is illustrated below.

2.3.2.2 Primary Charging Bias Generation

The primary charging bias is output to apply uniformed negative potential to the photosensitive drum surface as a preparation for image formation.
Two kinds of the biases, DC negative bias and AC bias, are generated in the primary charging high-voltage generation circuit in the high-voltage power supply
circuit. These two biases are applied together to the primary charging roller in the drum cartridge with a specified timing.
The values of the DC negative bias vary interlocked with the developing bias according to image density information sent from the SCNT Board.
Auxiliary developing bias is output to charge toner that was not charged by friction.
The printer's auxiliary developing bias is DC minus bias generated at auxiliary developing bias generation circuit inside high-voltage printed circuit board. Auxiliary
developing bias is applied onto the blade in the toner cartridge at a specified timing.

2.3.2.3 Developing Bias Generation

The developing bias is output to adhere toner to an electrostatic latent image formed on the photosensitive drum.
This bias is a DC negative bias generated in the developing high-voltage generation circuit in the high-voltage power supply circuit. The bias is applied to the de-
veloping cylinder in the toner cartridge with specified timing.
The values of the developing bias vary according to image density information sent from the SCNT Board. This allows the adjustment of image density.
The developing bias is output to charge toner that was not charged by friction.
This bias is applied onto the blade in the toner cartridge at a specified timing.

2.3.2.4 Primary Transfer Bias Generation

The primary transfer bias is output to transfer a toner image on the photosensitive drum to the ITB in the drum cartridge.
Two kinds of the biases, DC positive bias and DC negative bias, are generated in the primary transfer high-voltage generation circuit in the high-voltage power
supply circuit. The DC positive bias is output to the primary transfer roller in toner transfer. The DC negative bias is out-put to it in ITB cleaning.
The high-voltage power supply circuit applies these primary transfer biases to the primary
transfer roller according to a sequence.
The following are the biases applied at each sequence:
- Print bias (Note) (DC positive):
This bias is applied to the primary transfer roller to transfer a toner image on the photosensitive drum to the ITB in a print sequence.
- Cleaning bias (DC negative):
This bias is applied to the primary transfer roller to return residual toners adhered on the ITB to the photosensitive drum in a warm-up or last rotation sequence.
The values of the primary transfer bias vary according to the DCNT Board.
The DCNT Board changes the amperage of the primary transfer bias according to the PRIMARY TRANSFER CURRENT FEEDBACK (TR1S) signal sent from
the primary transfer high-voltage generation circuit and performs rated current control.
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Developing
rotary
Developing
ITB cleaning roller
Auxiliary
ITB cleaning roller
Pressure roller
ITB cleaning high-
Fixing high-voltage
voltage generation
generation circuit
circuit
Auxiliary ITB cleaning
Developing high- high-voltage
voltage generation generation circuit
circuit
Sub high-voltage powe r
supply circuit
IC101
CPU
Photosensitive
drum Primary charging roller
Blade
cylinder
Secondary
transfer
roller
Primary transfer
high-voltage
generation circuit
Secondary transfer
high-voltage
generation circuit
IC102
ASIC
F-2-27
ITB
Primary
transfer
roller
Primary charging
high-voltage
generation circuit
High-voltage
power supply circuit
DCNT Board
0011-6381
0008-1695
0008-1696
0008-1697