Oki B6200 - Fuser

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Chapter 6 Principle of Operation
5.4 Fuser
Heat Roll
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 roll and the Pressure Roll. This heat fuses and
fixes the toner on the paper.
Pressure Roll
This is a metal shaft coated with sponge rubber. Pressure is applied to the paper between this roll
and the Heat Roll. This pressure presses the melted toner against the paper.
Heater Assembly
The Heater Assembly consists of a Heater Rod located in a Heat Roll 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 Roll.
Temperature Sensor
This is a resistor (thermister) having a known value of resistance that sensitively varies with
temperature. This sensor is mounted in contact with the surface of the Heat Roll, and monitors the
temperature of the surface. The power supply of the Heater Rod is turned ON and OFF using the
signal from this sensor, so that the surface temperature of the Heat Roll can be maintained within a
specified range. This signal is also used to provide a first stage of overheat protection.
Thermostat Sensor (STS)
Two STS are installed in the 34PPM and one in the 24PPM. The STS are connected to the Heat
Roll in series for both 34PPM and 24PPM.
This provides a second stage of overheat protection. If the first stage does not prevent the Fuser
from overheating, the Thermostat cuts off the power-supply circuit for the Heater Rod. The STS
operates as follows.
(1) If the paper is set incorrectly, the Pressure Roll may melt and adhere. As a countermeasure
against this, the power-supply circuit is cut off to cool down the roll, if the detected
temperature gets higher than a preset temperature.
(2) If the temperatures increase at both sides of the Heat Roll, 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.
Heat Roll Fingers
These fingers peel off the leading edge of the paper from the Heat Roll to prevent the paper from
getting wound around the Heat Roll.
Heat Roll Diode
The negative charge accumulated on the Heat Roll may deteriorate the toner image on the paper
during fixing. The Heat Roll Diode discharges the charge to the frame ground.
Exit Sensor
This sensor detects the arrival of the paper at a detection point in the exit area positioned behind the
Fuser. 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.