Fusing Section - Epson EPL N2700 Service Manual

EPL-N2700

2.1.6.5 Fusing Section

The power from the transport motor (M2) is transmitted to the upper
fusing roller so that the toner-transferred paper is fed from the transfer
section to the fusing section.
The paper is heated to melt the toner by the upper fusing roller and
pressed by the upper and lower fusing rollers. The upper fusing roller is
heated by the fusing roller heater lamp (H1) which is built in it. The
fusing roller thermistor (TH1) is attached to the upper fusing roller for
controlling the heater temperature. Also, the fusing roller thermostat
(TH1) and fusing roller heater lamp fuse (TF1) are attached to the upper
fusing roller as shown on the next page. The thermostat (TH1) and lamp
fuse (TF1) are connected in series to the heater lamp (H1). The heater
lamp (H1) is heated when an AC voltage is applied.
Thermostat
Thermistor
Temperature fuse
Upper Fusing Roller
(Heater Lamp)
Figure 2-26. Fusing Section
Operating Principles
Lower Fusing Roller
Paper
Printer Mechanism Operating Principles


Temperature control using the thermistor
The resistance of the thermistor (TH1) attached to the upper fusing
roller varies with temperatures. When temperature rises, the
resistance of the thermistor (TH1) decreases, and vice versa. As
shown in the circuit diagram, the thermistor output is connected to
an analog port of the CPU on the main board.
The input level to the analog port of the CPU decreases as the
temperature rises. The CPU performs A/D (Analog-to-Digital)
conversion for the input level to know the current temperature.
To heat the upper fusing roller, the CPU set the Heater Remote 1
output to ON ("L") state. Then, the triac on the power supply unit
turns ON and an AC voltage is applied to the fusing roller heater
lamp (H1) and the upper fusing roller is heated. The CPU monitors
the output from the thermistor and controls ON/OFF of the triac to
control the temperature of the upper fusing roller.
When the upper fusing roller temperature becomes abnormal and
the output from the thermistor lowers than the predetermined level,
the abnormal-heater-temperature detecting circuit is activated and
the triac is forcibly turned OFF, resulting in shutting off an AC
voltage application to the heater lamp.
Figure 2-27. Temperature Control Using the Thermistor
Revision A
72