Brother HL-7050 Service Manual page 113

CHAPTER 3 THEORY OF OPERATION
2.6 Print Process
2.6.1 Charging
The drum is charged to approximately 975V 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 100V.
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.
Laser detector
Laser diode
Fig. 3-17
Drum
Paper
Laser beam
f lens
Polygon mirror
Motor
Lens
Fig. 3-18
3-18
Laser beam