Canon LBP3250 Series, Service Manual, Page: 28 / 98

Chapter 2
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2.4.1.3 Static Latent Image Formation Block
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This block is comprised of two steps and forms static latent images on the photosensitive drum.
When the final step of this block completes, negative charge remains at dark areas on the drum surface where laser beam has not been exposed, and negative charge
is eliminated from bright areas on the drum surface with laser beam exposed. The images on the drum with negative charge are called static latent images because
human eyes cannot detect them.
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Step 1: Primary charging
For preparation of latent image formation, the surface of photosensitive drum is charged with even negative potential. In this primary charging, the charge is applied
from the primary charging roller directly to the photosensitive drum.
DC bias is applied to the primary charging roller to maintain an even potential on the surface of the photosensitive drum.
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Step 2: Laser beam exposure
In this step, static latent images are formed on the photosensitive drum with laser beam.
When laser beams are scanned on the photosensitive drum negatively charged, bright areas lose their charges, eliminating negative potential on the surface of the
photosensitive drum; on those portions, static latent images are formed.
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0
Time (t)
Surface
potential
(V)
Laser
beam
exposure
(step 2)
Transfer
(step 4)
Primary
charging
(step 1)
Primary
charging
(step 1)
Exposed area
Unexposed area
Primary charging roller
Photosensitive drum
DC bias
Laser beam
Exposed
area
Unexposed
area