Canon LBP-3000 Service Manual Download

Page: 38 / 118

HTTP://WWW.FIXCLUB.COM.CN

Chapter 2

2-12

F-2-15

2.4.2.2 Generation of the Primary Charging Bias

0008-0113

The primary charging bias )PR1 is used to charge the surface of the photosensitive drum to a negative potential by way of preparing the surface for the

formation of images.

The primary charging bias may be a primary charging DC negative bias generated by the primary charging bias generation circuit of the high-voltage power

supply circuit )or a primary charging AC bias. The level of the bias that consists of these 2 types of biases is changed in relation to the developing DC

negative bias according to the image density information coming from the video controller.

2.4.2.3 Generation of the Developing Bias

0008-0115

The developing bias (DEV) is used to attract toner to the static (latent) image formed on the surface of the photosensitive drum. The developing bias may

be a developing DC negative bias generated by the developing bias generation circuit of the high-voltage power supply circuit or a developing AC bias. A

bias that consists of these 2 types of biases is applied to the developing cylinder of the cartridge at such times as programmed in advance.

The level of the developing negative bias is varied in relation to the primary charging DC negative bias according to the image density information arriving

from the video controller.

2.4.2.4 Generation of the Transfer Charging Bias

0008-0117

The transfer charging bias (TRS) is used to transfer toner from the surface of the photosensitive drum to print paper.

The transfer charging bias may be a transfer charging DC positive bias generated by the transfer charging bias generation circuit of the high-voltage power

supply circuit )or a transfer charging DC negative bias). The transfer charging DC positive bias is applied to the transfer charging roller at time of toner

transfer; on the other hand, the transfer charging DC negative bias is applied to the transfer charging roller at such times as when the roller needs to be

cleaned.

The transfer charging bias generation circuit serves to apply the transfer charging biases to the transfer charging roller in keeping with the selected sequence

of printing operation.

The following shows the type of bias applied for a specific printing sequence:

* Printing Bias

It is a transfer charging DC positive bias used to move the toner from the surface of the photosensitive drum to print paper during printing sequence.

* Sheet-to-Sheet Bias

It is a low level transfer charging DC positive bias applied to the transfer charging roller to prevent adhesion of toner remaining on the surface of the

photosensitive drum to the transfer charging roller.

* Cleaning Bias

It is a bias used to return the residual toner sticking to the transfer charging roller at time of warm-up or last rotation to the surface of the photosensitive

drum. This bias is a transfer charging DC negative bias, and is applied to the toner charging roller.

The level of the transfer charging DC positive bias is varied according to the instructions from the engine controller. The machine performs constant current

control by charging the voltage level of the transfer charging DC positive bias according to the transfer current feedback signal (TRCRNT).

PR1

TRS

DEV

IC902

CPU

DVAC

TRNDC

TRCRNT

TRPDC

PRAC

PRPWM