Canon iR C3380 series Service Manual page 214

Chapter 7
Step 1: primary charging
In this step, the surface of the photosensitive drum is charged to an even negative potential to prepare for the formation of an image. The machine uses a roller
charging method, in which charges are directly applied to the surface of the photosensitive drum.
The machine's primary charging roller is made from conducting rubber, and is given both AC and DC biases to keep the surface potential of the photosensitive drum
even.
Step 2: laser beam exposure
In this step, a static image is formed on the surface of the photosensitive drum.
The negatively charged surface of the photosensitive drum is exposed by a laser beam. As a result, those areas hit by the beam are neutralized (light area), thus
eliminating negative charges and consequently forming a static image on the surface.
7-4
Primary charging roller
F-7-4
Laser beam
Dark area Light area
F-7-5
Photosensitive drum
AC bias
DC bias