Xerox DocuPrint N2125 Service Manual page 266

Figure 3 Side View Block Diagram of the Drum Charge Process
2. Exposure
The Raster Output Scanner (Laser) generates an invisible beam of cohesive light, called
a laser beam. Image data received from the print controller 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 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 is less negative, relative to
the surrounding negative charge.
3. Development (Figure 4)
The toner in the Print Cartridge has a magnetic property that causes it to adhere to the
Magnetic Roll. The Charge Metering Blade (CM Blade) spreads the toner into a very thin
layer on the Magnetic Roll. Friction between the Magnetic Roll and the CM Blade gener-
ates 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 PWB supplies the Magnetic Roll 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
Roll to the surface of the drum. The AC voltage agitates the toner on the Magnetic Roll
and makes toner transfer easier.
General Procedures / Information
GP 3.1
The Magnetic Roll 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 rel-
ative 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, or positive, relative to the
negative charge on the Magnetic Roll.
The toner adhering to the Magnetic Roll is always in contact with the drum surface. When
a less negative point on the drum (a discharged area) comes in contact with the more
negative charged toner on the Magnetic Roll, toner transfers from the Magnetic Roll to
that point on the drum. At this point there is now a visible toner image on the drum sur-
face.
Figure 4 Side View Block Diagram of the Development Process
4. Transfer (Figure 5)
The Bias Transfer Roll (BTR) applies a positive charge to the back side of the printing
paper as the paper travels between the BTR and the drum surface. This positive charge
transfers the negative charged toner image from the drum surface to the front of the
paper. The toner image is now on the paper and the paper is now stuck to the drum sur-
face due to the relative electrical differences.
02/2000
6-26
Initial Issue
DocuPrint N2125