cording to the detected temperature. The fixing heater drive circuit controls the fixing heater depending on the signals so that the heater remains at the targeted

temperature.

1) Warm up temperature control

This control is to warm up the fixing heater until the fixing temperature reaches the required fixing temperature.

Warm up temperature differs depending on the elapsed time from the previous print, paper type or environment.

2) Print temperature control

This control is to keep the fixing sleeve temperature at a targeted temperature during printing.

Target temperature of fixing sleeve differs, depending on the paper type.

3) Paper interval temperature control

This control is to bring the fixing heater temperature lower than the fixing temperature at paper interval to prevent the pressure roller from overheating during

continuous printing in low speed mode at paper interval.

Temperature during paper interval is changed corresponding to the distance and paper type.

2.6.3 Protective Functions

2.6.3.1 Protective function

The protective function detects an abnormal temperature rise of the fixing unit and interrupts power supply to the fixing heater.

The following three protective components prevent an abnormal temperature rise of the fixing heater:

- DC controller

- Fixing heater safety circuit

- Thermal fuse

1) DC controller

The DC controller monitors the detected temperature of the thermistor located at the center of the fixing heater. The DC controller sets the FIXING HEATER

DRIVE (FSRD+, FSRD-) signals to inactive and releases the relay to interrupt power supply to the fixing heater under the following condition:

- Thermistor: 230 deg C or higher

2) Fixing heater safety circuit

The fixing heater safety circuit monitors the detected temperature of the thermistor located at the center of the fixing heater. The fixing heater safety circuit

releases the relay to interrupt power supply to the fixing heater under the following condition:

- Thermistor: 240 deg C or higher

3) Thermal fuse

When the temperature of the fixing heater rises abnormally high and the detected temperature of the thermal fuse is the following condition, the fuse blows to

interrupt power supply to the fixing heater:

- Thermal fuse: 226 deg C or higher

2.6.3.2 Fixing unit failure detection

The DC controller determines a fixing unit failure, sets the FIXING HEATER DRIVE (FSRD+, FSRD-) signals to inactive, releases the relay to interrupt power

supply to the fixing heater and notifies the main controller of a fixing unit failure when it encounters the following conditions:

1) Start-up failure

- If the detected temperature of the thermistor does not reach 40 deg C within a specified period from the heater energization during the wait period.

FU1

TH802

Fixing

heater

(H801)

roller

Fuse

FU901

Relay

drive

RL901

circui