Canon LBP5000 Series Service Manual Download

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Chapter 2

2-15

- Print Bias (positive DC bias)

While printing sequence is under way, the machine uses the print bias to transfer the toner from the surface of the photosensitive drum to print paper.

- Sheet-to-Sheet Bias (positive DC bias)

While continuous printing is under way, the machine uses the sheet-to-sheet bias to make sure that the residual toner on the photosensitive drum will not move

to the surface of the ETB.

- Cleaning Bias (negative DC bias)

The machine uses the cleaning bias to move the toner sticking to the ITB back to the photosensitive drum.

The level of the transfer bias varies according to the instructions from the DC controller PCB.

The DC controller PCB adjusts the output of the transfer bias according to the transfer current feedback signal (TRS) from the transfer bias generation circuit to

maintain a specific level of transfer efficiency (constant current control).

2.4.2.6 Generation of the Fixing Bias

0010-6085

LBP5000 / LBP5100

The machine uses the fixing bias (FSR) to prevent the movement of toner from the print paper to the fixing film before fixing.

The fixing bias may be a positive DC bias or a negative DC bias generated by the fixing high-voltage generation circuit of the high-voltage power supply PCB. The

machine applies the fixing bias to the fixing pressure roller at specific timing.

2.4.2.7 Electrostatic eliminate bias

0015-7917

LBP5100

The electrostatic eliminate bias is added for decreasing an electrical potential on paper surface, which became too high due to the transfer bias.

This bias is the DC positive bias generated in the electrostatic eliminate high-voltage generation circuit in the high-voltage power supply PCB. It is applied to the

electrostatic eliminator unit just for the period where the leading edge of paper separates from the ETB until the delivery operation is completed.

2.4.2.8 ETB drive roller bias

0015-7918

LBP5100

The ETB drive bias is added for toner holding enhancement onto force of paper which electrical potential is decreased due to the electrostatic eliminator unit.

This bias is the DC positive bias generated in the sub high-voltage power supply PCB. It is applied to the ETB drive roller just for the period where the leading edge

of paper separates from the ETB until the trailing edge of paper passes through the fixing unit.

2.4.3 Image Stabilizaton Control

2.4.3.1 Overview of the Image Stabilization Control Mechanism

0010-6074

LBP5000 / LBP5100

The machine uses its image stabilization control mechanism to prevent lowering of image quality (e.g., in the form of a faulty image) otherwise caused by changes

in the environment or deterioration of the photosensitive drum or toner.

The machine's image stabilization control mechanism may be any of 4 types: Environment corrective control, Image density corrective control (D-max control),

Image halftone corrective control (D-half control), Color Misregistration Corrective Control.

T-2-2

2.4.3.2 Environment corrective control

0010-6075

LBP5000 / LBP5100

The DC controller checks the site environment with reference to the temperature/humidity information from the environment sensor (SR12), and controls the var-

ious high-voltage biases so as to ensure the production of optimum images.

The machine executes environment control at the following timing:

- when the power is turned on

- when a cartridge has been replaced

- when there has been an appreciable change in the environment

2.4.3.3 Image density corrective control (D-max control)

0010-6076

LBP5000 / LBP5100

The machine executes image density correction to stabilize the image density by controlling the printer engine.

When a specific condition exists, the DC controller executes D-max control in the following sequence:

1. It measures the density patterns of individual colors drawn on the ETB.

2. It controls the primary charging bias and the developing bias based on the measurements of the individual patterns to ensure optimum density.