Exposure - Lexmark C935 Service Manual

Exposure

The Printhead generates a beam of laser light. Image data received from the RIP card assembly modulates this
beam, turning it on and off according to image information that is received from the host computer and software.
Through the use of a series of rotating and stationary mirrors within the Printhead, the beam scans the negative
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 slightly less
negative than the surrounding negative charge. The less negative areas are considered positive. This
discharge/no discharge process creates an invisible, electrostatic image on the surface of the drum. This image
is called a latent image.
DRUM
Development
The toner contained within the PC Cartridge has a magnetic property that causes it to adhere to the Magnetic
Roll. The Metering Blade spreads the toner into a very thin layer on the Magnetic Roll. Friction between the
Magnetic Roll and the CM Blade generates a small electrical charge that is transferred to the toner.
The surface of the Magnetic Roll is made up of a thin sheet of conductive material. The HVPS supplies the
Magnetic Roll with two voltages: a DC voltage and an AC voltage. The DC voltage is used to transfer toner from
the Magnetic Roll to the surface of the drum. The AC voltage agitates the toner on the Magnetic Roll, making
toner transfer easier.
The Magnetic Roll maintains a negative DC electrical potential. Negative charged areas of the drum have a
lower electrical potential, or higher relative negative value than the Magnetic Roll. Discharged areas of the drum
have a higher electrical potential, or lower relative negative value, than the Magnetic Roll. A discharged point on
the surface of the drum now appears less negative in relation to the negative charge on the Magnetic Roll.
Modulated
Laser Beam
Printhead
Drum Surface
Image
Laser Beam
0V
Invisible Latent Image
Drum Surface
Voltage
Laser Beam
Discharge
Level
General information
5057-XXX
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