Canon    LBP3310, Service Manual

Page: 53 / 114

Chapter 2
2-25
3) Between-sheets temperature control
This control maintains the temperature of the fixing heater below the normally targeted temperature during the continuous printing in order to prevent the
temperature rise of betweensheets.
The temperature of the fixing heater is detected by the thermistor (TH1) on the fixing heater.
If the surface temperature rises, the resistance value of the thermistor decreases, which allows the voltage of the FIXING HEATER TEMPERATURE signal
(FSRTH) to decrease.
The CPU (IC201) on the engine controller monitors the voltage of the FSRTH signal. It outputs the FIXING HEATER DRIVE signal (FSRD) depends on the
voltage and turns the phototriac coupler (SSR101) ON/OFF to maintain the temperature at specified temperature. The CPU starts the fixing heater temperature
control to rise the temperature at 100 deg C once the power switch is turned ON. This brings the grease melt enough, because the viscosity of the grease in the
fixing unit is high, and prevents the fixing film from the breakage. This control is not operated if the temperature is over 100 deg C when the power switch is
turned ON.
4) down sequence; during continuous printing so as to prevent overheating of the edges of the heater.
In this control, the CPU of the engine controller checks the length and width of paper; if the size of the paper matches a specific set of conditions, the machine
is shifted to long narrow mode (Note) or small paper mode regardless of the settings of the driver.
In this mode, the CPU forces the printing speed to decrease conversely increasing the distance between sheets, thereby increasing the sensitivity of the thermistor
located in the middle of the fixing heater and, consequently, preventing the edges of the heater from overheating.
The following shows the relationship between the printing speed and the conditions used to make a shift to this mode:
T-2-5
The term "long narrow paper" refers to a type of paper that is narrow in width and long in length.
2.8.2.2 Protective Functions
2.8.2.2.1 Protective function
0018-3139
LBP3370 / LBP3310
The printer utilizes the following three protective functions to prevent the abnormal temperature rise of the fixing heater.
- CPU
- Fixing heater safety circuit
- Thermoswitch
1) Protective function by the CPU
The CPU constantly monitors the voltage of the thermistor. The CPU interrupts a power supply to the fixing heater when the fixing temperature abnormally
exceeds the specified value.
The CPU puts the FIXING HEATER DRIVE signal (FSRD) into "L" and turns the phototriac coupler (SSR101) OFF to interrupt the power supply to the fixing
heater, when the temperature of the fixing heater rises abnormally high and the voltage of the thermistor is lower than approx. 0.9 V (equivalent to 220 deg C).
2) Protective function by the fixing heater safety circuit
The fixing heater safety circuit constantly monitors the voltage of the thermistor. This circuit interrupts a power supply to the fixing heater regardless of the
commands from the CPU when the fixing temperature abnormally exceeds the specified value.
The comparator (IC501) outputs "L" and the transistor (Q103) is turned OFF, when the temperature of the fixing heater rises abnormally high and the thermistor
voltage gets under approx. 0.5 V (equivalent to 280 deg C). Then the relay (RL101) is turned OFF, regardless of the RELAY DRIVE signal (RLYD) output from
the CPU, in order to interrupt the power supply to the fixing heater.
3) Protective function by the thermoswitch
The contact point of the thermoswitch gets broken and the AC voltage supply to the fixing heater is cut off, when the temperature of the fixing heater rises
abnormally high and the temperature of the thermoswitch exceeds approx. 230 deg C. It results in the interruption of the power supply to the fixing heater.
2.8.2.2.2 failure detection
0018-3140
LBP3370 / LBP3310
If the printer meets any of following conditions, the CPU determines the fixing unit failure and notifies it to the video controller.
1) The temperature of the fixing unit does not exceed 45 deg C within 1.39 sec. after the temperature control is started.
2) The temperature of the fixing unit does not reach the targeted temperature -10 deg C within 63 sec. after the wait sequence is started.
3) The fixing unit temperature is monitored every 5 msec., and the temperature exceeds 220 deg C for 30 times continuously.
4) The thermistor voltage is monitored every 5 msec., and the temperature is lower than 100 deg C during the normal temperature control or lower than 55 deg
C during the between-sheets temperature control or the cleaning mode for 240 times continuously.
5) The temperature of the fixing unit is monitored every 200 msec., and the counter reaches 150 by the following sequences; +1 to the counter if the temperature
is -100 deg C below of its targeted temperature, -1 to the counter if the temperature is -100 deg C over of its targeted temperature.
6) The temperature of the thermistor is detected every 5 msec. during the control and it shows under 20 deg C for 100 times continuously after the temperature
of the fixing unit exceeds 50 deg C at least once.
Heavy paper 2 210 to 200 deg C
Transparency 190 to 185 deg C
Envelop 205 to 195 deg C
Label 210 to 200 deg C
Down-sequence mode Paper length Paper width Printing speed (ppm)
Small size paper mode 272mm or less - 10-->6-->4
Long narrow paper mode 272mm or more 197mm or more 4
Paper type selected for driver Fixing target temperature