Exposure; Development - Xerox 4400DT - Phaser B/W Laser Printer Service Manual

Exposure

The Laser Assembly generates an invisible beam of cohesive light, called a laser
beam. Image data received from the Engine Logic Board modulates this beam,
turning it on and off according to image information.
Through the use of a series of rotating and stationary mirrors within the Laser
Assembly, the beam scans the negatively charged drum surface. Whenever the print
controller sends a command to print a black pixel, the laser switches on long enough
to shine onto the drum at a single pixel point. That point is now discharged and is less
negative, relative to the surrounding negative charge.

Development

The toner in the Print Cartridge has a magnetic property that causes it to adhere to the
Magnetic Roller. The Charge Metering Blade (CM Blade) spreads the toner into a
very thin layer on the Magnetic Roller. Friction between the Magnetic Roller and the
CM Blade generates a small electrical charge that is transferred to the toner.
The surface of the Magnetic Roller is made up of a thin sheet of conductive material.
The HVPS PWB supplies the Magnetic Roller with two voltages: a negative DC
voltage and an AC voltage. The DC voltage is the voltage that is used to transfer toner
from the Magnetic Roller to the surface of the drum. The AC voltage agitates the
toner on the Magnetic Roller and makes toner transfer easier.
The Magnetic Roller maintains an electrical potential relative to the charged surface
of the drum. Negative charged areas of the drum have a lower electrical potential, or
higher relative negative value, than the Magnetic Roller. Discharged areas of the
drum have a higher electrical potential, or lower relative negative value, than the
Magnetic Roller. A discharged point on the surface of the drum now appears less
negative, or positive, relative to the negative charge on the Magnetic Roller.
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