Canon ImageCLASS MF4690 Service Manual - page 87
Chapter 8
8-1
8.1 Overview/Configuration
8.1.1 Specification/Control/Function List
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T-8-1
8.1.2 Overview
0016-1858
The fixing unit employees the on-demand fixing method, and it is composed of fixing film unit, in which the fixing heater, thermistor, and temperature fuse are
incorporated, and the pressure roller.
The pressure roller and the delivery roller are driven with the main motor (M1).
A paper separated from the photosensitive drum is fed to inside of the fixing assembly, and the toner is fixed on a paper with the fixing film and the pressure roller.
A paper being fixed is detected with the delivery sensor (PS803); then, delivered to outside of the machine via the delivery roller.
F-8-1
[1] Pressure roller
[2] Fixing film
[3] Delivery roller
H1: Fixing heater
PS803: Delivery sensor
The fixing heater is the heater (ceramic heater) that the heating pattern is deposited on the ceramic plate.
By heating the fixing film with the fixing heater, it gives heat to passing papers.
The thermistor (TH1) locates at the center of the fixing heater (H1), and detects the temperature of the heater.
The temperature fuse (TP1) locates at the top center of the fixing heater. If the temperature of the fixing heater increases abnormally, it blocks power supply to the
heater by meltdown.
The temperature control of the fixing assembly composed of the foregoing components is executed at the fixing control circuit on the DCNT board with the instruc-
tion of the CPU (IC902). There are the fixing heater drive circuit and the fixing heater safety circuit in the fixing control circuit.
Item Function/Method
Fixing method
On-demand fixing
Fixing heater
Flat heater
Fixing temperature detection
Thermistor (TH1): temperature control, detection of abnormality
Temperature fuse (TP1): detection of abnormality
Fixing temperature control
Temperature control at startup
Temperature control at normal times
Temperature control at sheet-to-sheet interval
Protection function
Temperature error detection with the thermistor
Temperature rise detection with the temperature fuse