Advertisement
-
2. COPYING PROCESS
E. Step 3 Scanning Exposure
Optical image
Figure 2-7
Light from the original is projected onto
the drum surface.
Charges
in these
light
areas on the drum are neutralized
by drum
photosensitive
effects.
F. Step 4 Developing
} $$Jp'"Q
Figure 2-8
As shown in Figure 2-8, the developing
assembly
consists of a developing
cylinder
(a stationary
magnet
surrounded
by a
rotating
sleeve)
and
a blade
made
of
magnetic
material.
Black toner is a single
component
type consisting
of a fine powder
of mixed
magnetite
and resin binder.
The
toner
has insulating
properties
and is
charged
to a positive
potential
by friction
with the rotating cylinder.
Color
developer
is a two-component
type consisting
of iron powder (carrier) and
toner mixed
together
in a fixed ratio. The
main component
of the toner is resin. The
/---
toner is charged
to a positive
potential and
,
the iron powder
to a negative
potential
by
'
friction with the rotating cylinder.
Figure
2-9
A concentrated
magnetic field develops
between
the magnet
and the edge of the
_
blade.
This
field
attracts
the
charged
developer.
The developer
is held virtually immobile
by the magnetic
field,
forming
a curtain
along the edge of the blade. As the cylinder
rotates, this curtain skims the toner particles
on its surface to a thin uniform layer.
An AC bias plus a negative
DC bias are
applied
simultaneously
to the developing
cylinder
so that
the
waveform
of the
developing
bias
has a larger
negative
excursion than positive.
.q++fjyg
DC bias
Figure 2~10
During copying toner is attracted
to the
drum by the charges
on the drum surface
and by repulsion due to the developing
bias
(during the positive excursion),
transforming
the latent electrostatic
image into a visible
image. Excess toner particles are attracted
back to the cylinder
from the drum due to
the charges
on the drum surface
and the
developing
bias
(during
the
negative
excursion).
The DC bias affects copy density
and
_'
fogging:
As the DC bias
becomes
less
negative
(approaching
OV), the density and
_
degree of fogging both increase.
Advertisement
