Various Control Mechanisms; Fixing Temperature Control - Canon LBP5000 Series Service Manual

Chapter 2

2.6.2 Various Control Mechanisms

2.6.2.1 Fixing Temperature Control

2.6.2.1.1 Fixing Temperature Control

LBP5000
The machine monitors the surface temperature of the fixing heater, and controls the drive signal of the fixing heater so that the temperature will be identical to the
target temperature.
Fixing unit
Thermal fuse (FU100)
Fixing film unit
Main thermistor
(TH1)
The temperature of the fixing heater is checked by 2 thermistors: main thermistor (TH1), sub thermistor (TH2).
TH1 is used for printing temperature detection and sheet-to-sheet temperature control, while TH2 is used to check for edge overheating.
The CPU (IC7) on the DC controller PCB monitors the voltage of these 2 thermistors, and generates the fixing heater drive signal (FSRD) according to the level of
the voltage.
The machine's fixing temperature control mechanism uses the following 5 sequences of operation:
1. Initial Multiple Rotation Temperature Control
The machine executes initial multiple rotation temperature control to prevent tears in the fixing film by melting the grease on the inner side of the film at power-
on for smoother belt movement.
If the reading of the sub thermistor is lower than 55 deg C at power-on, the CPU turns on the fixing heater for a specific period of time before it starts the fixing/
delivery motor.
2. Start-Up Temperature Control
The machine executes start-up temperature control to determine the start-up temperature for the fixing heater to suit the reading of the main thermistor detected
when turning on the heater. If the heater is turned on within 40 sec after the end of the previous print job, the previous printing temperature is used for the
upcoming print job.
3. Printing Temperature Control
The machine executes printing temperature control so that the temperature of the fixing heater will be identical to the target temperature during printing.
In continuous printing mode, the machine changes the target temperature in stages according to the specified number of prints
4. Sheet-to-Sheet Temperature Control
The machine executes sheet-to-sheet temperature control to prevent overheating of the fixing pressure roller between sheets in continuous mode (low-speed
mode). The temperature of the fixing heater is lowered between sheets.
The sheet-to-sheet temperature, further, is varied depending on the distance between sheets and the type of paper used.
5. Throughput Reduction Control
The machine executes throughput reduction control to prevent overheating of the edges of the fixing heater during continuous printing on narrow paper.
If the reading of the sub thermistor exceeds a specific level in continuous printing, if the paper width sensor does not detect paper, or if the width of paper is less
than 195 mm, the machine will increase the distance between sheets to decrease throughput
Mode
Plain paper Number of sheets passed
Initial rotation temperature
Sheet-to-sheet temperature
Heavy paper 1 Number of sheets passed
Initial rotation temperature
Sheet-to-sheet temperature
2-32
Fixing heater (H100)
Sub thermistor
(TH2)
Temperature
control 1
1-5
199
Printing temperature 194
194
1-2
160
Printing temperature 165
155
Zero crossing
circuit
+24V
RL901
Relay drive
circuit
Fixing heater
drive circuit
Fixing control circuit
Low-voltage power supply unit
F-2-36
T-2-5
Temperature Temperature
control 2
6-17
179
189
184
3-6
153
163
153
DC controller PCB
ZEROX
RLD+
RLD-
FSRD
Fixing heater
safety circuit
RLD
SUBTH
MAINTH
+3.3V
Temperature
control 3 control 4
18-37 38-73
167 161
182 176
177 171
7-13 14-25
150 145
160 155
150 145
0010-6160
IC7
CPU
+3.3V
Temperature
control 5
74-
154
169
164
26-
140
150
140