Canon LBP-860 Service Manual page 59

Reference: Toner projection development
but lo simplify the explanation, the drum potential is shown as positive when it is higher [less
than the developing cylinder potential.
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Toner movmmmi and elerlrir potenlials
Description
potential between the drum
surface and Lhe cylinder is
sufficient to overcome Lhe
of loner projected depends
the DC bias volta@ on
the cylinder.
When the potential dif-
ference between Ihe drum
surface and the developing
cylinder is reduced, the
resulting weak electric field
combines with the magnelic
from the drum to the
cylinder. This removes any
excessive toner adhering to
the drum. and improves the
contrast finished
the
print.
The drum surface potential
is only slightly higher than
the cylinder potential, so th,
cylinder is greater than the
electrostatic attraction to
the drum. Therefore, only a
small amount of toner is
projected toward the drum.
cylinder bias and the
magnetic force now
combine to strongly allrart
the toner to the cylinder,
removing the excessive
toner from the unexposed
the drum and
preventing fogging.