Xerox Phaser 4500, Service Manual

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2-2 Phaser 4500 Service Manual
Overview of the Phaser 4500 Laser Printer
Summary of the Printing Process
The Phaser 4500 print process consists of the following steps:
1.
Charge – The Print Cartridge contains a Bias Charge Roller that uniformly
distributes a negative electrical charge over the photoconductive drum surface.
2. Exposure – The Laser Assembly scans the surface of the photoconductive drum,
which is located inside the Print Cartridge. The Laser Diode Assembly produces
a laser beam which is turned on and off according to a data signal. A 12-sided
polygonal mirror in the Scanner Assembly is rotated at a specified speed. The
laser beam is reflected off of the mirror and onto the drum surface through a
series of lenses and mirrors. The laser beam scans the drum surface from one end
to the other, neutralizing the negative charge to create one line of a latent image
on the surface. The drum is rotated and the scan process is repeated to form an
image on the drum surface.
3.
Development – A magnetic roller in the Print Cartridge carries a thin layer of
toner supplied by an agitator in the cartridge's toner compartment. The Charging
and Metering (CM) Blade inside the cartridge applies a negative charge to the
toner and spreads the toner onto the magnetic roller. The negatively charged toner
is transferred to the Areas of the drum surface that have been discharged.
4. Paper Transport – Paper size sensors determine the length and width of the
media. Four tabs (one fixed, three movable) located in the paper tray indicate the
location of the length guide. Switches located in the left tray guides detect the
position of four tabs located on the paper tray. The Phaser 4500 uses a three-
roller system to pick paper. Two springs raise the tray's lift plate, along with the
paper stack, against the pick roller of the paper feeder assembly. To pick paper,
the nudger roller advances the top sheet to the feed roller and retard roller. The
retard roller prevents multi-picks. The feed roller advances the paper to the turn
pinch rollers, which feed it to the registration rollers. The registration sensor is
the first sensor to detect paper.
5. Transfer – The Transfer Roller is driven by a gear on the print cartridge. The
pressure of the Transfer Roller against the drum assists in driving the paper
through the transfer area. The Transfer Roller applies a positive charge to the rear
surface of the paper. The negatively charged toner image on the drum is attracted
to the positive charge on the rear surface of the paper, causing the image to be
transferred from the surface of the drum onto the paper.
6. Discharge –
The Detack Saw, located on the Transfer Roller assembly, helps to
separate the paper by partially neutralizing the charge holding the paper to the
drum. A cleaning blade in the Print Cartridge scrapes any remaining toner from
the surface of the drum. Then, the photoconductive drum is neutralized to prepare
the drum for the next print cycle.
7. Fusing – The paper is driven into the fuser, which uses heat and pressure rolls to
melt and bond the toner onto the surface of the paper. Heat Roller fingers inside
the fuser peel off the leading edge of the paper from the Heat Roller to prevent
the paper from becoming wound around it. An exit sensor detects paper exiting
from the fuser.