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Chapter 2
2.4.3.4 Image halftone corrective control (D-half control)
LBP5000 / LBP5100
The machine uses the video controller PCB to execute gradation control based on the measurements of the halftone density taken by the DC controller PCB.
When D-max control ends, the DC controller PCB and the video controller PCB executes D-half control in the following sequence:
1. The DC controller measures the density patterns of individual colors drawn on the ETB using the optimum primary charging bias and developing bias determined
by D-max control, sending the result to the video controller PCB in the form of density data.
2. The video controller PCB executes gradation control based on the density data so that ideal halftone images may be obtained.
2.4.3.5 Image density detection control
LBP5000 / LBP5100
The machine executes image density detection to enable D-max control and D-half control.
The machine shines light on the 4-color image density patterns formed on the ETB, and measures the intensity of the reflected light to identify the density of the
patterns.
The density of an image is measured by the DC controller PCB using the reflection type/density sensor (SR10) mounted on the ETB.
If the light-receiving segment does not receive a sufficient amount of light at time of image density detection, the DC controller will indicate 'E020' in the status
window. If the reading by the color displacement/density sensor (SR10) is outside a specific range, on the other hand, the DC controller sets the image density to
the density control value used before the execution of the image density detection or the initial value, and indicate the presence of an "image measurement error"
for the color in question.
2.4.3.6 Overview of Color Misregistration Corrective Control
LBP5000 / LBP5100
The machine corrects displacement of color caused by the variation that may exist among individual laser/scanner units and cartridges. The types of displacement
corrected by this mechanism are the following:
- main scanning direction write start position
- main scanning direction magnification
- sub scanning direction write start position
The color displacement correction mechanism is executed by the DC controller PCB through control of the color displacement/density sensor (SR10) and the color
displacement sensor (SR11) for the following conditions:
- when the power is turned on or the door is closed after a cartridge has been replaced
- when a specific number of prints have been made (on a job basis)
- when the user requests the execution of calibration
The machine uses the following sequence when executing the mechanism:
1) The DC controller identifies the degree of displacement of individual colors based on the patterns drawn on the ETB, and sends the result to the video controller
in the form of color displacement information.
2) In response, the video controller controls the video signals of the individual colors based on the color displacement information it has received to adjust the main
scanning direction write start position, main scanning direction magnification, and sub scanning direction write start position.
On the printer engine side, the DC controller PCB controls the speed of the scanner motor to correct any displacement of color in sub scanning direction.
Scanning Magnification
The term "scanning magnification" refers to the size of an image in main scanning direction.
The machine's photosensitive drums are independent among individual colors, and the possible variation between drums leads to different optical paths. The fact
in turn means variation in the imaging area in main scanning direction among colors, causing color displacement along the image edge if left unattended.
2.4.3.7 Color misregistration detection
LBP5000 / LBP5100
The machine checks the position of the 4 color displacement patterns (colors) formed on the ETB.
When color displacement correction control is executed, the DC controller PCB controls the color displacement/density sensor (SR10) and the color displacement
sensor (SR11). The color displacement/density sensor (SR10) and the color displacement sensor (SR11) are located on the ETB, and each consists of 2 segments
(i.e., light-emitting LED and light-receiving phototransistor).
The machine uses the following sequence to execute color displacement detection:
1) The DC controller PCB turns on the LED, and checks the light reflected by the ETB. At this time, the intensity of the reflected light differs depending on the
2-16
Density sensor
Direction of
belt rotation
Density pattern image
F-2-20
ETB
0010-6077
0010-7371
0010-6078
0010-6079
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