Xerox Phaser 6180 Service Manual page 62

Theory of Operation
2-8
The Magnet Roll is covered by a thin semi-conductive sleeve over the surface.
The Developer Bias voltage is supplied to this semiconductor sleeve from the
High-Voltage Power Supply (HVPS). Developer Bias is negative Direct
Current (DC) voltage combined with Alternating Current (AC) voltage. The
Magnet Roll is kept at constant negative voltage against the photoreceptor
layer of the drum by DC voltage. Therefore, at the area on the drum surface
where the negative electric charge does not decrease, potential is lower than
the magnet roll, while the potential is higher than the magnet roll at the area
where the negative charge on the drum surface decreases. The AC voltage
shakes the Developer on the Magnet Roll surface, causing the toner to
transfer to the drum.
Thus, the negatively charged toner is attracted only by the area where the
negative charge has decreased on the drum surface from the Magnet Roll
(electrostatic latent image) and the toner image is formed on the drum. When
the toner is attached, the negative charge at the portion of the drum increases
where the toner is located increases, the potential decreases, and the force to
attract the toner decreases.
Drum Surface
Toner
Image
Electric Potential
on Drum
-V
Developing
Bias
0
s6180-446
Phaser 6180 Color Laser Printer Service Manual