Xerox DocuPrint N2025 Service Manual page 284

Print Process Description
1. Charge
This step places a uniform negative electric charge on the drum surface (the outside sur-
face of the photoconductive layer, to be exact*). Figure 3
The charge is given by the BCR (Bias Charge Roll) in the Print Cartridge. The BCR is a
conductive roll disposed in direct contact with the drum surface. A discharge voltage is
applied to the BCR from the HVPS. The discharge voltage is an AC voltage with a nega-
tive DC bias voltage superimposed. The AC voltage is controlled by constant-current reg-
ulation. The discharge occurs in the very small gaps between the BCR and the drum
surface.
Any unevenness in the charge on the drum surface resulting from the previous cycle is
leveled by the AC discharge between the BCR and the drum surface, and the drum sur-
face is uniformly charged again to the same voltage as the DC bias voltage with respect to
the inner conductor of the drum.
*The drum is an aluminum cylinder with a coating of photoconductive material on the sur-
face.
General Procedures / Information
GP 5.1
2. Exposure
This step scans the negative charged drum surface with a thin beam of laser light. Figure
4
The laser light beam is emitted by the laser diode in the Laser (Raster Output Scanner)
and shines onto the drum surface being moved from one side to the other by means of the
rotating polygon mirror and mirrors and lenses in the Laser.
02/2000
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Figure 3 Charge
DocuPrint N2025/N2825
Initial Issue