Image Stabilization Control - Canon CLBR 460ps Service Manual

D. Image Stabilization Control
1. Outline
This printer conducts the stabilization density control in order to prevent variations in the image
density caused by environmental changes, deteriorated photosensitive drum or toner.
The image stabilization control consists of the image density ajustment control and the gra-
dation adjustment control. Each control is conducted as needed.
a. Image density ajustment control (Developing bias control)
The DC controller forms the maximum density pattern on the photosensitive drum for the each
color in the specified cases. The density sensor detects the density of the pattern. The optimum
developing bias and primary charging bias that stabilize the density of the each color are deter-
mined based on the detected density.
The image density adjustment control is conducted in the following cases:
• When the power is turned ON.
• After a specified number of sheets is printed.
• When the toner cartridge door is opened and closed.
• When the drum cartridge is replaced.
• When the video controller sends a command to conduct the control.
When the value detected by the density sensor does not fall within the specified range, the
DC controller sets the image density to the default value and notifies the video controller of an
abnormal density sensor warning.
b. Gradation adjustment control (controller density control)
The function of the gradution adjustment control is to send the density data required for the
video controller to perform gradation adjustment.
The DC controller forms density detection pattern for each color on the photosensitive drum
with the appropriate developing bias and the primary charging bias set by the image density
adjustment control based upon the image data sent from the Video controller. Then, the DC
controller detects the density detection pattern with the density sensor and sends back the den-
sity data to the Video controller. The Video controller executes the gradation control to obtain
the appropriate half-tone image based upon the data.
The Video controller executes the control by sending command, and the printer does not con-
trol by itself.
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