Xerox M20 - WorkCentre B/W Laser, Service Manual

Page: 258 / 314

December 2006
6-52 WorkCentre M20, 4118, FaxCentre 2218 Family
GP 16
General Procedures and Information
It receives motor enable signal (2 phase) from CPU and generates bipolar pulse (constant-
current) and sends its output to stepping motor input.
High Voltage Power Supply
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 volt-
age (MHV), supply voltage (SUPPLY), developing voltage (DEV), blade voltage (BLADE) and
transferring voltage (THV). Each high voltage supply shows the voltage required in each digital
picture process.
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. Refer
to Figure 1.
Figure 1 Process
First, in the electrification process, retain constant charge at approximately -900V for the elec-
tric potential on the OPC surface by electrifying OPC drum at approximately -1.4KV through
the electrification roller. The electrified surface of OPC is exposed responding to the video data
by the LSU that received print command 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 approximately -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 sup-
plied 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 transferred 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 (approximately 180C) from the
heat roller and the pressure (approximately 4kg) from the pressure roller. After the fixing pro-
cess, the paper is sent out of the set to finish the printing process.
Organization of the Device
The HVPS is comprised of electrification output unit, bias output unit and transfer output unit.
Refer to Figure 2, Figure 3, Figure 4 and Figure 5.
1. Input Unit.
2. Electrification Output (Enable) Unit: MHV (Main High Voltage).
3. Bias Output (Enable) Unit: DEV (Development Voltage)/Supply (Supply Voltage)/BLADE
(Blade Voltage).
4. Transfer ‘+’ Output (Enable) Unit: THV (+) (Transfer High V)).
5. Transfer ‘-’ Output (Enable) Unit: THV (-) (Transfer High Voltage(-)).
6. Switching Unit.
7. Feedback Unit.
8. Regulation Unit.
9. Output Unit.