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COPY PROCESS AROUND THE DRUM
1. DRUM CHARGE
In the dark, the charge corona unit gives a uniform negative charge to the
organic photo conductive (OPC) drum. The charge remains on the surface of
the drum because the OPC layer has a high electrical resistance in the dark.
The amount of negative charge on the drum is proportional to the negative
grid bias voltage applied to the grid plate on the charge corona unit.
2. EXPOSURE
An image of the original is reflected to the OPC drum surface via the optics
assembly. The charge on the drum surface is dissipated in direct proportion
to the intensity of the reflected light, thus producing an electrical latent image
on the drum surface.
The amount of remaining charge as a latent image on the drum depends on
exposure lamp intensity controlled by the exposure lamp voltage.
3. ERASE
The erase lamp illuminates the areas of the charged drum surface that will
not be used for the copy image. The resistance of the drum in the illuminated
areas drops and the charge on those areas dissipates.
4. DEVELOPMENT
Positively charged toner is attracted to the negatively charged areas of the
drum, thus developing the latent image. (The positive triboelectric charge is
caused by friction between the carrier and toner particles.)
The development bias voltage applied to the development roller shaft
controls two things:
1) The threshold level if toner is attracted to the drum or toner remains on
the development roller.
2) The amount of toner to be attracted to the drum.
The higher the negative development bias voltage is, the less toner is
attracted to the drum surface.
5. PRE-TRANSFER LAMP (PTL)
The PTL illuminates the drum to remove almost all the negative charge from
the exposed areas of the drum. This prevents the toner particles from being
reattracted to the drum surface during paper separation and makes paper
separation easier.
1-8
12 February 1992
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