Canon MF8580Cdw Service Manual page 60

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Technical Overview > Fixing System > Controls > Protective Control
■ Fixing temperature control
The fixing control circuit controls temperatures of the fixing heater to attain the respective
target temperatures.
The figure below shows this circuit schematically.
Fixing assembly
Fixing film unit
Fuse
FU901
FU1
RL901
TH
ixing heater
Pressure
drive circuit
roller
FU1：Temperature fuse
TH：Thermistor Fixing control circuit
The DC controller monitors the fixing heater temperature detection signal (MAINTH) to
output the respective fixing heater drive signals (FSRD+, FSRD-) depending on the detected
temperatures. The fixing heater drive circuit controls the fixing heater based on the output
signal to attain the target temperature in the fixing heater.
1) Start-up temperature control
This controls the fixing heater warm-up to the target temperature.
Different temperatures are targeted depending on elapsed time after the last print job,
paper types or the environment.
2) Printing temperature control
This controls the fixing film temperature during printing to maintain the target.
Different temperatures are set in the fixing film depending on paper types.
3) Sheet-to-sheet temperature control
This control lowers the sheet-to-sheet fixing heater temperature during continuous printing
in the low-speed mode to prevent temperature rise on the pressure roller.
Different sheet-to-sheet temperatures are set depending on sheet intervals or paper types.
2 Technical Overview > Fixing System > Controls > Protective Control
/RLD+
Relay
/RLD-
drive
circuit
DC controller
FSRD+
FSRD-
Fixing heater
safety circuit
MAINTH
F-2-33
■ Protective Control
his control is to detect abnormal temperature rise in the fixing assembly to shut off power
supply to the fixing heater.
This product has the following 3 protective controls to prevent abnormal temperature rise in
the fixing assembly.
• DC controller
• Fixing heater safety circuit
• Temperature fuse
The descriptions below are the details of each protective control.
1) DC controller
When DC Controller monitors temperature of the central thermistor of the fixing heater
and exceeds the pre-defined temperature, which is thought abnormally high temperature,
therefore the drive signal (FSRD+, FSRD-) of the fixing heater is stopped outputting and
the relay is turned off and the power distribution to the heater is stopped.
2) Fixing heater safety circuit
This circuit detects abnormal temperatures in the center of the fixing heater to shut off
power supply to the heater.
3) Temperature fuse
When the temperature of the fixing heater abnormally rises, the temperature fuse is open
to shut off power supply to the heater.
• 226 deg C or higher detected at the temperature fuse.
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