Xerox WorkCentre Pro 412 Service Manual Download Page 54

Page: 54 / 192

Circuit Description

WorkCentre Pro 412

Launch Issue

5-28

August 2001

5-5-7. High Voltage Power Supply

5-5-7-1. Summary

It is the high voltage power supply that has DC+24V/DC+5V (used for the image forming device in OA digital
picture developing method) as the rated inputs. It supplies electrifying voltage (MHV), supply voltage (SUP-
PLY), developing voltage (DEV), blade voltage (BLADE) and transferring voltage (THV).
Each high voltage supply shows the voltage required in each digital picture process.

5-5-7-2. Digital Picture Process

Digital picture developing method is widely used by copy machine, laser beam printer and fax paper.
The process is comprised of electrification, exposure, develop, transfer and fixing.

First, in the electrification process, retain constant charge at approx. -900V for the electric potential on the
OPC surface by electrifying OPC drum at approx. -1.4KV through the electrification roller.
The electrified surface of OPC is exposed responding to the video data by the LSU that received print com-
mand due to rotation. The unexposed non-video section will retain the original electric potential of -900V, but
the electric potential of the image area exposed by LSU will be approx. -180V that it will form the electrostatic
latent image. The surface of the photo-conductive drum where the electrostatic latent image is formed
reaches the developer as the drum rotates. Then the electrostatic latent image formed on the OPC drum is
developed by the toner supplied to the developing roller by supplying roller and it is transformed into visible
image. It is the process to change the afterimage on the OPC drum surface formed by LSU into visible image
by the toner particles.
While the supply roller energized with -450V by HVPS and the developer roller energized with -300V rotate
in the same direction, it keeps the toner particles between two rollers supplied to OPC drum in negative state
by the friction between two rollers.
The toner supplied to the developer roller is biased to bias electric potential by the developer roller and trans-
ferred to the developing area. After (-) toner is attached to the developer roller, it will move to the exposed high
electric potential surface (-180V) rather than to the unexposed low electric potential surface (-900V) of the
developer roller and OPC drum. Eventually the toner will not settle in the low electric potential surface to form
the visible image.
Later, the OPC drum continues to rotate and reaches to transfer location in order to accomplish the transfer
process.
This process transfers the (-)toner on the transfer roller to the printing paper by the transfer roller. The (-)toner
attached to the OPC drum will be energized to hundreds to thousands of the (+)transfer voltage by HVPS.
The (+)electrostatic force of the transfer roller generated has higher adhesiveness than the (-)toner OPC drum
and thus it moves to the surface of the paper passing through the transfer roller.
The toner transferred to the paper with weak electrostatic force is fixed to the paper by the pressure and heat
of the fixer composed of pressure roller and heat roller.
The toner attached to the paper is melted by applying the heat (approx. 180°C) from the heat roller and the
pressure (approx. 4kg) from the pressure roller. After the fixing process, the paper is sent out of the set to fin-
ish the printing process.