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E.
Controlling
the Developing
Bias
1.
Outline
The
copier
controls
the copy density
by
varying the voltage of the developing
bias (DC
component)
according
to the following
set-
tings:
.
EXPOSURE
CONTROL
lever (manual density
control)
.
AE sensor
output
(automatic
density
con-
trol)
*
Density correction
knob
Deterioration
of
the
drum
brings
about
shifts in the drum sensitivity and, such shifts,
in turn, can produce
foggy
image. The prob-
lem can be corrected
by changing the DC bias
using the density correction
knob.
Figure 3-17
shows
changes
in the devel-
oping bias (DC component)
initiated by the ex-
posure
lever
(manual
density
control),
and
Figure 3-18
shows changes
in the developing
bias (DC component)
in the automatic
density
control.
2.
Mechanism
The circuit shown in Figure 3-l 9 serves to
control
the developing
bias and has the fol-
lowing functions:
Controls ON/OFF of the developing bias (AC
component)
Controls ON/OFF of the developing bias (DC
component)
Controls
the voltage
level of the
DC bias
according to the settings made by the copy
density lever.
Controlling ON/OFF
of the Developing
Bias
(AC component)
The
square
wave
generation
circuit
re-
mains activated as long as power is availa-
ble.
When ACBON is 'I',
AC bias switch circuit is ON,
L
Square wave generation
circuit is OFF.
This condition deprives the developing
cyl-
inder of the AC bias.
When ACBON is '0'.
AC bias switch circuit is OFF.
The above condition causes the output of
the square
wave
generation
circuit to be
sent to the Tl
drive circuit, increased
to
1300
VAC,
and
sent
to the
developing
cylinder.
The
output
of
the
AC
high-voltage
transformer,
on the other hand, is rectified
in the rectifier circuit and sent also to the
static charge eliminator (about 3.0 kV).
Developmg
bias
IV.
DC component1
Figure 3-l 7 Manual
Density
Control
,-
'\
--200--
--3oo--
--4oo--
-500
Ilight)
-600
T
Figure 3-l B Automatic
Density
Control
3-16
coPvAlOHT @loaO
CNHON INC.
CllNOH
UP-1010
RN.0
OEC. 1980 PRINIEO
IN JAPAN
IIMPRIME
1U J1POll
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