Image Gradation Correction Control (D-Half Control); Color Displacement Correction Control; Toner Cartridge; Developing Roller Engagement/Disengagement Control - Canon LBP5050 Series Service Manual

- When a customer requests the calibration
MEMO:
- When the calibration is executed, sheet counter reading and elapsed time timer are cleared.
- Calibration is not executed in sleep mode.
- At power ON, calibration is suspended until the initial print process is completed and the machine is ready or until 15 min passes after the power ON. The time
setting can be changed from option > Device settings > printer start setting in printer status window.

2.4.3.3 Image gradation correction control (D-half control)

LBP5050N / LBP5050
This is a control that main controller PCB executes the gradation correction based on result of the halftone density measurement that is executed by DC controller
PCB.
After D-max control, DC controller PCB and main controller PCB execute the D-half control in the following procedure.
1. DC controller PCB measures the each color density detection pattern on ITB that is made by the appropriate primary charge bias that is determined at D-max
control and developing bias, and sends the density data to main controller PCB.
2. Main controller PCB executes the gradation correction to realize the ideal halftone image based on the data.

2.4.3.4 Color displacement correction control

LBP5050N / LBP5050
This control is to correct the color displacement that appears due to the variation of laser scanner unit or toner cartridge.
The following objects are controlled by this color displacement correction.
- Write start position in main scanning direction
- Magnification in main scanning direction
- Write start position in sub scanning direction
When one of the following conditions is met, DC controller PCB controls the color displacement/density sensor and displacement sensor.
- At power ON
- When the door is closed after replacing the toner cartridge
- After printing, the specified time (100 min and 300 min) elapses
- After the previous color displacement correction control, when the number of print exceeds 100
- When a customer requests the calibration
MEMO:
- When the calibration is executed, sheet counter reading and elapsed time timer are cleared.
- Calibration is not executed in sleep mode.
- At power ON, calibration is suspended until the initial print process is completed and the machine is ready or until 15 min passes after the power ON. The time
setting can be changed from option > Device settings > printer start setting in printer status window.
The following is the sequences of this control.
1) DC controller calculates the degree of each color displacement by the color displacement detection pattern made on ITB and sends the color displacement infor-
mation to main controller.
2) Main controller controls the each color video signal according the color displacement data and adjusts the write start position in main scanning direction, the
magnification in main scanning direction and the write start position in sub scanning direction.
At printer engine side, DC controller PCB also controls the scanner motor speed to correct the color displacement in sub scanning direction.
Scanning magnification
This indicates the image size in the main scanning direction.
Since this machine is equipped with the independent photosensitive drum for each color, the photosensitive drum position differs due to the toner cartridge variation
and that leads to the laser wave length difference. Thus, image range differs depending on a color in main scanning direction so that the color displacement occurs
at the edge of the image.

2.4.4 Toner Cartridge

2.4.4.1 Developing roller engagement/disengagement control

LBP5050N / LBP5050
The developing roller engagement/disengagement control engages the required developing roller with the photosensitive drum according to the print mode, full-
color mode or monochrome mode.
The necessary developing roller is engaged with the photosensitive drum only when required, preventing a deterioration of the drums and making maximum use of
the life.
The engagement/disengagement of the developing roller is controlled by the DC controller rotating the main motor and changing the direction of the developing
disengagement cam. The DC controller controls the developing roller state, whether engaged or disengaged, by counting the main motor rotation after it detects the
signal from the developing homeposition sensor.
All four colors' developing rollers disengage from the photosensitive drums when the printer is turned on and when a print operation is completed. All four colors'
developing rollers engage with the photosensitive drums when the full-color mode is designated. Only black's developing roller engages with the photosensitive
drum when the monochrome mode is designated.
The DC controller determines an abnormality of the developing roller engagement/disengagement function and notifies the main controller when it does not sense
the signal from the developing homeposition sensor for a specified period during the developing roller engagement/disengagement operation.

2.4.5 Transfer Unit

2.4.5.1 Pad transfer

LBP5050N / LBP5050
The printer has a pad transfer method for the primary transfer operation.
The pad transfer method stabilizes an image compared to the conventional separation roller method. The features for the pad transfer method are as follows:
The wider nip width between the transfer pad and the photosensitive drum improves the transfer performance.
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