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CHAPTER II -21
2.5.2 Exposure Stage
After the drum is positively charged, it is exposed to the light emitted from the laser unit.
Fig. 2.26
The area exposed to the laser beam is the image to be printed. The surface potential of the
exposed area is reduced forming the electrostatic image to be printed.
1 Cycle of drum
Surface Potential (V)
+1000
+700
+400
+300
123
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. 2.27
Drum
Paper
Laser beam
f lens
Pol
yg
on mirror
Motor
Lens
Laser diode
Laser detector
Laser Beam