User manual

95.08.23.11.29
Color LaserWriter 12/600 PS Basics & Theory 1–66
For full-color transfer, the transfer force weakens as the number of
negatively charged toner particles on the paper increases as the transfer
step proceeds with the first color, second color and so on. To counteract
this effect, the transfer bias is gradually increased for the second and
subsequent colors. Also, the transfer bias control signal (
/TRPWM) is
changed according to the temperature/humidity sensing system so as to
apply an appropriate print bias.
The between-colors bias, with a voltage value smaller than that of the
print bias, is applied between colors to minimize the damage to the
photosensitive drum.
When the drum motor begins to rotate, the high-voltage control IC
(IC1003) on the high-voltage power supply board is charged with the
transfer bias by setting the transfer voltage drive signal (
/HVTR) to “L.”
At the same time, the print bias and between-colors bias for each color
are applied by varying the
/TRPWM signal.
Voltage to
Attraction
Roller
For full-color transfer, the high-voltage control IC (IC1003) on the
high-voltage power supply board applies the attraction voltage to the
attraction roller by setting the attraction voltage drive signal (
/HVATR)
to “L” before transference of the first color image. Also, an appropriate
attraction bias is applied by varying the attraction bias value control
signal (
/ATRPWM) according to the environment detected by the
temperature/humidity sensing system. After the attraction roller
contacts the transfer drum for a specified period of time, the
/HVATR
signal is set to “H,” and the attraction bias is set to off.
Voltage to
Discharge
Roller
When the paper is separated, the high-voltage control IC (IC1003) on
the high-voltage power supply board applies the discharge bias, which
is output in response to the combination of the discharge bias (AC)
select signals (
/HVSEAC0, /HVSEAC1), to the discharge roller in order to
discharge the transfer drum surface.
Based on values sensed by the temperature/humidity sensing system,
the discharge bias changes the combination of the
/HVSEAC0 and
/HVSEAC1 signals to switch the discharge bias value.
OFF
Discharge Bias: Low
/HVSEAC0
H
L
H
L
/HVSEAC1
H
H
L
L
Discharge Bias: Middle
Discharge Bias: High