Brother HL-1240, Service Manual

Page: 60 / 333

CHAPTER 3 THEORY OF OPERATION
3-22
2.6 Print Process
2.6.1 Charging
The drum is charged to approximately 870V by an ion charge which is generated by the
primary charger. The charge is generated by ionization of the corona wire, which has a DC
bias from the high-voltage power supply applied to it. The flow of the ion charge is controlled
by the grid to ensure it is distributed evenly on the drum surface. The aluminum drum sleeve
in the photosensitive drum is grounded.
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Organic Photoconductor layer
Aluminum drum sleeve
Photosensitive
Drum
HVPS
870V
Voltage
Regulator
Grid
Corona wire
Fig. 3-28
The primary charge uses a corona wire, but since the drum is positively charged, only less
than 1/10 of the usual quantity of ozone is generated compared with the negatively charged
drum. The level of ozone expelled from the printer is therefore not harmful to the human body.
Applicable safety standards have been complied with.
2.6.2 Exposure stage
After the drum is positively charged, it is exposed to the light emitted from the laser unit.
Fig. 3-29
Drum
Lens
Laser beam
Polygon mirror
Paper
Laser detector
Laser diode
Motor
Laser beam
f lens