The fixing heater is equipped with 2 thermistor: a main thermistor in the middle and a sub thermistor at the end. The main thermistor is used to control the temper-

ature of the fixing heater and to detect its overheating, while the sub thermistor is used to detect an error temperature on the end of the fixing heater.

The CPU on the DC controller PCB monitors the main thermistor signal (FSRTH) and the sub thermistor signal (SUBTH) from the thermistors for control of the

fixing heater drive signal (FSRD0) and the relay drive signal (RLYD), thus varying the supply of power to the heater and, ultimately, controlling the temperature

of the fixing heater.

9.2.2 Controlling the Fixing Film Temperature

9.2.2.1 Controlling the Fixing Film Temperature

The CPU on the DC controller PCB executes the following 6 types of fixing temperature control:

1. Startup Temperature Control

Upon input of a print command from the image processor PCB, the fixing heater is heated up to the temperature lower than the target temperature of paper pass

temperature control according to the fixing temperature control mode and the number of prints made previously.

2.Paper-present section temperature control

The fixing heater temperature is adjusted to the target paper-present section temperature according to the combination of the paper size, number of sheets fed, fixing

mode, and temperature detected by the fixing main thermistor.

3.Sheet-to-sheet temperature control

The fixing heater temperature is held relatively below the target paper-present section temperature to prevent the paper-absent section temperature from rising be-

tween sheets.

4.Target temperature for the distance between sheets during duplex printing

To prevent the temperature rise of the no-paper pass unit for the distance between sheets during duplex printing, the fixing heater temperature is controlled as fol-

lows.

For the first to third prints, the fixing heater temperature is lowered by 25 deg C from the target temperature of paper pass temperature control.

For the fourth and succeeding prints, the fixing heater temperature is lowered by 35 deg C from the target temperature of paper pass temperature control

5. Control at Time of Down Sequence

When prints are made in the continuous print mode, the sub-thermistor in the no-paper pass unit may rise extremely. To prevent this, the print head and paper clear-

ance is widen when the sub-thermistor detects a temperature equal to or higher than 250/255/260 deg C. The down sequence is performed in three steps according

to the detected temperature. If the sub-thermistor detects a temperature equal to or lower than 180 deg C in the down sequence, the normal temperature control

resumes.

Reference:

A5/STMT throughputs in three down sequence steps are as follows:

Down sequence 1 (Detection of 250oC): A5/STMT plain paper 8 pppm

Down sequence 2 (Detection of 255oC): A5/STMT plain paper 3 pppm

Down sequence 3 (Detection of 260oC): A5/STMT plain paper 2 pppm

6. Cooling Mode

If prints are made on large-size (*1) paper after making prints on small-size (*1) paper in the continuous print mode, a fixing offset can occur due to the difference

in temperature between the edge and center of paper. To prevent this, the main motor is driven for 40 seconds after continuous printing on small-size paper or down-

sequence control, thus lowering the temperature detected by the sub-thermistor to a temperature below 160 deg C. When the following heater cooling time lapses

after stop of the main motor, normal control resumes.

*1 Large-size paper: 270 mm or longer Small-size paper: 215.9 mm or longer

Print count (sheets)

Heater cooling time (s)

After printing on small-size paper.

1-10

11-20

21 and more

T-9-2

After the throughput of printing on large-size paper has

reduced.

Any number of prints