Brother International HL 1240 Service Manual - Page 60

CHAPTER 3 THEORY OF OPERATION 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. Voltage Regulator +++-+--+--+- 870V - + -- - ++ + - + + + + + + + ++ + + Aluminum drum sleeve Photosensitive Organic Photoconductor layer Drum Grid HVPS 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. Drum Laser beam Laser detector Paper Laser beam f lens Polygon mirror Laser diode Lens Motor Fig. 3-29 3-22