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Photoconduction Section
The photoreceptor drum surface is exposed to light, and toner adheres to the portions
of the drum where the charge is neutralized (latent image formation), so that visible
images are formed (developed). This section describes the three phases of
photoconduction: discharge, main charging, and exposure.
Discharge
The discharge phase uniformly discharges the drum before exposure. This is
accomplished by the LED discharge lamp, which neutralizes the residual charge by
exposing the drum surface to light.
Main Charging
The selenium photoconductive drum serves as the image transfer medium for the
printer. The drum is a cylinder with special properties. The material of the drum
surface is an insulator when in the dark and a conductor when exposed to light.
Before beginning the printing process, the drum must be electrically charged. The
neutral photoconductive drum rotates past the main charger, which causes the drum
surface to undergo a corona discharge, to ensure that the surface contains uniform
positive charges.
A single tungsten wire is centered in a metal channel over the drum. The channel has
a wire grid between the lower open end of the channel and the surface material of the
drum. The air around the wire is ionized by the high positive potential on the wire.
The grid of the channel is maintained at a voltage "less positive" than that on the
tungsten wire.
Principles of Operation
LED Discharge lamp
Residual Charge
Photoreceptor Drum
5–7
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