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Chapter 2

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2.3.2 Driving and Controlling the High-Voltage System

2.3.2.1 Outline

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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.

F-2-27

2.3.2.2 Primary Charging Bias Generation

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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

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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

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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.

Primary
transfer

roller

Developing

cylinder

High-voltage

power supply circuit

Pressure roller

DCNT Board

Primary transfer