Drum Unit; Photosensitive Drum; Primary Charger; Transfer Roller - Brother MFC8440D Service Manual

7/13/2019
CHAPTER 3 THEORY OF OPERATION
2.5

Drum Unit

2.5.1

Photosensitive drum

Generates the latent electrostatic image and develops the image on the drum surface.
2.5.2

Primary charger

Forms a uniform charge on the drum surface.
(1) Corona wire
Generates the ion charge on the drum.
(2) Grid
Spreads the ion charge evenly over the drum surface.
2.5.3

Transfer roller

Transfers the toner image to the paper from the drum surface.
2.5.4

Cleaner

Removes the paper dust or dirt on the surface of the photosensitive drum.
2.6

Toner Cartridge

Develops the electrostatic latent image on the photosensitive drum with toner and forms the
visible image.
2.7

Print Process

2.7.1

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
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.
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Brother 8840D Service Manual
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Corona wire
Fig. 3-35
3-22
Aluminum drum sleeve
Organic photoconductor layer
Grid
HVPS
Photosensitive
drum
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