Printing System Models - Control of Color Imaging Systems: Analysis and Design - page 557

10.2.1 C HARGING M ODEL
With the aid of a corotron or a scorotron device (Figures 10.1 and 10.2), charge is
uniformly deposited on the photoconductor surface (in the dark). In the corotron
setup, corona wires are placed above a photoconductive plate, whereas in the
scorotron system, a metallic grid is inserted between the corotron wires and the
photoconductor. When electric field strength in the vicinity of a thin corotron wire

becomes suf ciently large to ionize the gas molecules in the air surrounding the

photoconductor, corona discharge occurs. The corona discharge produces ionized
gas molecules that flow to the surface of the photoconductor which absorbs them,

generating a charge distribution on its surface. A uniform surface charge is created
on the whole photoconductor when it moves with a constant velocity through a
stationary corotron that is steadily emitting corona ions. Corona wires are generally
maintained at a high potential (

10 kV) throughout the charging process. To
improve the uniformity of the charge distribution in the scorotron, a metallic grid is

5 -

Shield

Wire

V w

V s

y

Bare plate
(substrate)

L

x

V e

FIGURE 10.1 Corotron charging system.

Shield

Wire

V w

V s

y

Grid

Photoconductor
(plate)

x

V g

V p

FIGURE 10.2 Scorotron charging system.