Canon LBP-1120 Service Manual page 45

CHAPTER 2
Step 1: Primary charging
For preparation of latent image formation, a uniform negative potential is applied to the photosensitive drum surface.
Primary charging of this printer is performed by the method that directly charges the photosensitive drum.
The primary charging roller consists of semiconductive rubber. In addition to DC bias, AC bias is applied to the
primary charging roller to maintain the potential on the drum surface uniform. The DC bias changes with the developing
DC bias that changes according to the IMAGE DENSITY DATA signal sent from the interface controller.
This direct charging method has advantages such as the lower applied voltage and almost no ozone generation over
the conventional corona charging method.
Step 2: Scanning Exposure
When the laser beam scans onto the photosensitive drum surface, charges on the light area are neutralized to form an
electrostatic latent image.
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Primary charging
roller
AC bias
Photosensitive drum
DC bias
Figure 2-4-6
Laser beam
Dark area Light area
Figure 2-4-7