Brother International HL-720 Service Manual - Page 46

Exposure stage, Fig. 2.32, area is recreated forming an electrostatic image to be printed.

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2.5.2 Exposure stage After the drum is positively charged, it is exposed to the light emitted from the laser unit. Drum Paper Laser Beam Laser detector Laser diode Laser beam f lens Polygon mirror Motor Lens Fig. 2.32 The exposed area is the part to be printed. The surface potential of the exposed area is recreated forming an electrostatic image to be printed. Surface Potential (V) +1000 +700 1 Cycle of drum 1 2 34 (a) (b) +400 Drum +300 Sleeve 1 Primary charging 2 Laser beam exposure and developing (a) Unexposed area ( Non image area ) (b) Exposed area ( Image area ) 3 Transfer the image to paper 4 Erase the residual potential Time Fig. 2.33 II-29

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II-29
2.5.2
Exposure stage
After the drum is positively charged, it is exposed to the light emitted from the laser
unit.
Fig. 2.32
The exposed area is the part to be printed. The surface potential of the exposed
area is recreated forming an electrostatic image to be printed.
1 Cycle of drum
Surface Potential (V)
+1000
+700
+400
+300
1
2
3
4
(a)
(b)
Time
1
2
3
4
Primary charging
Laser beam exposure and developing
(a)
Unexposed area
( Non image area )
(b)
Exposed area
( Image area )
Transfer the image to paper
Erase the residual potential
Drum
Sleeve
Fig. 2.33
Laser Beam
Drum
Paper
Laser beam
f
lens
Polygon mirror
Motor
Lens
Laser diode
Laser detector