Fixing System; Overview; Controls - Canon MF720 Series Service Manual

Fixing System

Overview

The fixing power supply controls temperatures of the Fixing Assembly.
This product employs the on-demand fixing method in the Fixing Assembly. The figure below shows the structure schematically.
TH802
Pressure Roller
Fixing Film
Name
Fixing heater 100V
120V
230V
Main thermistor
Sub thermistor 1
Sub thermistor 2
Temperature fuse
The temperature fuse is attached to the center of the fixing heater.
When the fixing heater comes to be abnormally hot, the temperature fuse is open to shut off the power supply to the fixing heater.
The thermistor detects the fixing heater temperature to input the temperature detection signal to the DC controller. Note that
temperatures at heater ends are not detected in models of MF8200 series with slower print speed.
The temperatures in the whole fixing assembly are controlled by the fixing control circuit and the fixing heater safety circuit based
on commands from the DC controller.

Controls

■ Fixing Speed Control
● Reduction of Throughput Based on Detected Temperature of Sub Thermistor
Paper interval extension time is determined based on the detected temperature of the Sub Thermistor.
Paper interval extension time determined by the detected temperature of the Sub Thermistor is added to the paper interval
extension time derived from the paper width detection result and paper length detection result.
Detection of temperature by the Sub Thermistor is performed when the Delivery Sensor turns OFF.
When the Paper Width Sensor is ON, reduction of throughput based on the detected temperature of the Sub Thermistor is not
executed.
Tempreture of Sub Thermistor: Tx
TH803
FU1
H100
TH801
Symbol
H100
H120
H220
TH801
TH802
TH803
FU1
T1
T2
T3
T4
Fixing Power Supply
Fixing Control
Fixing Heater
Drive Signal
Fixing Temperature Signal
To heat the fixing film
To detect the fixing heater temperature (center of the heater, contact ther-
mistor)
To detect the fixing heater temperature (heater ends, contact thermistor)
To prevent abnormal temperature rise in the fixing heater
41
2. Technical Explanation
DC Controller
Circuit
Fixing Heater
Safety Circuit
Role
Paper interval (sec)
3
6
9
15