Controlling The Fixing File Bias Temperature; Controlling The Fixing Film Bias - Canon iR1200 Series Service Manual

- Paper Passage Temperature Control
While printing is taking place, the fixing heater temperature is controlled so that it is identical with the paper passage
control temperature target.
- Sheet-to-Sheet Temperature Control
To prevent overheating of areas not covered by paper (between sheets), the fixing heater temperature is controlled to
a level relatively lower than the paper passage control temperature
target.
- Rest Heating Temperature Control
While the machine is at rest, the fixing pressure roller is heated so that the toner collecting on it is melted and moved
to the fixing film, thereby ridding the roller of toner.
The rest heating control mechanism is used to control the temperature of the fixing heater to a level lower than the
paper passage target level when LTR or larger paper is used for printing.
The control temperature targets are switched in reference to the following 4 conditions:
- paper type (as indicated by a command during printing)
- type of control (cover paper or between sheets)
- change in fixing temperature control (OFF -> start-up -> paper passage, etc.)
- count of prints in continuous mode

8.2.2 Controlling the Fixing File Bias Temperature

8.2.2.1 Controlling the Fixing Film Bias

The machine is equipped with a fixing film bias control mechanism which is controlled by the CPU on the DC
controller PCB. The fixing film bias is used to prevent displacement of toner deposits; i.e., when the primary
charging roller DC bias is applied, a bias of the same polarity as the toner is applied to the fixing film so as to create
a magnetic field between the paper and the film.
DC controller PCB
CPU
Primary charging
roller
AC bias drive circuit
Primary charging
roller
DC bias drive circuit
J205
Superposition
J206
F-8-4
Primary
charging
roller
Photosensitive
drum
Fixing film
Chapter 8
0006-2979
8-3