Photoconductive Section; Discharge; Main Charging - Printronix L5535 Maintenance Manual

Chapter 8

Photoconductive Section

Photoconductive Section
In the electrophotographic system, the photoconductive photoreceptor drum
surface is exposed to light, and toner adheres to portions 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.
Residual Charge

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.
This voltage differential controls the ions flying from the drum and past the
grid. The ion flow sets up a potential of approximately +580 volts on the
surface of the drum as it rotates under the metal channel. The drum surface
potential is then monitored after the ensuing exposure step, and the main
charger current is controlled according to the results of that monitoring.
II–114
LED Discharge Lamp
+
-
-
+
-
+
Photoreceptor Drum