Specifications

Principles of Operation Function of Major Components - 29
Fusing and Paper Exit
Fuser Assembly
The major parts contained within the fuser assembly include the fuser heater bulb, fuser
roller, thermostat, fuse, and temperature sensor assembly.
The fuser heater bulb is located inside the fuser roller. Power to the bulb is switched on
and off so that the temperature of the fuser roller surface is kept constant. When the
temperature of the fuser rises to the predetermined upper limit temperature, the power
supply is switched off. This safeguard is known as first-stage overheat protection.
The fuser roller applies the heat for melting and fusing the toner to paper. It is connected to
the frame ground through a diode so that negative charge flows, thereby preventing the
toner image from being disturbed during the fusing process.
The thermostat is a part of the fuser bulb circuit and provides the second-stage overheat
protection. If the first-stage overheat protection fails to prevent overheat and the
thermostat reaches the predetermined temperature, the contacts of the thermostat open to
break the circuit between the fuser bulb and the power supply.
The fuse is also a part of the fuser bulb circuit and provides the third-stage overheat
protection. If the first and second stage protection both fail to prevent overheat and the fuse
reaches the predetermined temperature, the fuse melts to open the circuit between the
fuser and the power supply.
The temperature sensor is a resistor whose resistance varies rapidly with temperature. It
is positioned in contact with the surface of the fuser roller. Power to the fuser bulb is
switched on and off so that the temperature of the surface of the fuser roller is kept
constant.
Fuser Pressure Roller
The fuser pressure roller is a sponge roller covered with a tube. It is located beneath the
fuser assembly and is spring-loaded to apply pressure against the fuser roller as paper
passes. The fuser pressure roller is not mechanically driven.
Fuser Exit Sensor/Actuator
The fuser exit sensor is actuated as paper exits the fuser assembly but before paper reaches
the paper deflector guide.
Delivery Sensor/Actuators
The delivery sensor is actuated as paper reaches the delivery rollers.
Delivery Roller Shaft
The delivery roller shaft holds three fixed delivery rollers that feed paper through to the
output tray on the top of the printer.