Konica Minolta bizhub 40p, Service Manual

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Theory of operation V er. 1.0 Dec. 2007 10. Fusing section
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bizhub 40P
Composition/Operation
10.3 Operation
10.3.1 Overview
A. Heat roller
• This is a hollow metal tube having a coated surface. This tube is heated by the inside
Heater Rod. Heat is applied to the paper passing between this roller and the Pressure
roller. This heat fuses and fixes the toner on the paper.
B. Pressure roller
• This is a metal shaft coated with sponge rubber. Pressure is applied to the paper
between this roller and the Heat roller. This pressure presses the melted toner against
the paper.
C. Heater Assembly
• The Heater Assembly consists of a Heater Rod located in a Heat roller and a harness
connecting the Heater Rod to a terminal. The Heater Rod consists of heater coil inside a
quartz glass and heats up the Heat roller.
D. Thermistor
• This is a resistor (thermistor) having a known value of resistance that sensitively varies
with temperature. This sensor is mounted in contact with the surface of the Heat roller,
and monitors the temperature of the surface. The power supply of the Heater Rod is
turned O
N and OFF using the signal from this sensor, so that the surface temperature of
the Heat roller can be maintained within a specified range. This signal is also used to
provide a first stage of overheat protection.
E. Thermostat Sensor
• Two thermostat are installed. The thermostat are connected to the Heat roller in series.
• This provides a second stage of overheat protection. If the first stage does not prevent
the fusing from overheating, the Thermostat cuts off the power-supply circuit for the
Heater Rod. The thermostat operates as follows.
1. If the paper is set incorrectly, the Pressure roller may melt and adhere. As a coun-
termeasure against this, the power-supply circuit is cut off to cool down the roller, if
the detected temperature gets higher than a preset temperature.
2. If the temperatures increase at both sides of the Heat roller, both ends of the paper
may curl. As a countermeasure against this, the mode is switched to Short lamp
lighting to control the temperature rise, if the detected temperature exceeds the
preset temperature.
F. Heat roller Fingers
• These fingers peel off the leading edge of the paper from the Heat roller to prevent the
paper from getting wound around the Heat roller.
G. Heat roller Diode
• The negative charge accumulated on the Heat roller may deteriorate the toner image on
the paper during fixing. The Heat roller Diode discharges the charge to the frame ground.
H. Exit Sensor
• This sensor detects the arrival of the paper at a detection point in the exit area positioned
behind the fuser unit. This sensor also detects the discharge of the paper from this point.
When the sensor receives light (i.e., paper is present), /EXIT goes Low.