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Chapter 8

8-3

8.2.2 Controlling the Fixing Film Temperature

8.2.2.1 Outline

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The surface temperature of the fixing heater is detected to control the fixing heater drive signal so that the fixing heater temperature becomes the target temperature.

The temperature of the fixing heater is detected by the thermistor (TH1/TH2) provided on the fixing heater. If the surface temperature rises, the resistance of the

thermistor lowers and the voltage of the fixing heater temperature detection signal (M_TH/S_TH) also lowers.

The CPU on the DC controller monitors the voltage of the M_TH/S_TH signal to control the fixing heater 1 drive signal (H1DRV) and fixing heater 2 drive signal

(H2DRV). These two voltages are generated based on the zero crossing detection signal which is output from the heater control circuit. The CPU controls these two

signals to adjust the fixing heater temperature to the prescribed value.

8.2.2.2 Controlling the Fixing Film Temperature

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This machine performs fixing temperature control according to the fixing heater temperature as mentioned below.

1) Warm-up temperature control

Upon receipt of a print command from the DC controller, the fixing heater heats to the temperature below the target paper-present section temperature.

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

between sheets.

4) Down sequence

The temperature may detect an abnormally high temperature during continuous printing. If the sub-thermistor detects a temperature equal to or higher than 275

deg C, the sheet-to-sheet distance is increased to prevent the paper-absent section temperature from rising. If the sub-thermistor detects a temperature equal to

or lower than 220 deg C in the down sequence, normal control resumes.

5) Cooling mode

If printing is performed using wider sheets (*1) after printing is performed using narrower sheets in the continuous print mode, fixing offset may occur due to

the difference in temperature between the edge and center. If the sub-thermistor detects a temperature equal to or higher than 130 deg C, paper feed and printing

stop to prevent the temperature from rising at the edge. If the sub-thermistor detects a temperature equal to or lower than 130 deg C or two or more minutes lapse,

normal control resumes.

*1: The large size is a paper of which the width is 10 mm larger than the previous job.

8.2.2.3 Target Temperatures by Mode

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This machine controls the fixing temperature according to the "media type" selected in the user mode and the "target temperature" set in the "special mode."

The correspondence between each mode and target temperature is as follows:

*1: Target fixing temperature at startup. When the initial temperature of the fixing unit is high, the target temperature is lowered. In the continuous copy mode, the

target temperature is lowered in 5 deg C steps.

*2: Number of sheets controlled at the initial target temperature. If it is exceeded, the target temperature is lowered. The prescribed number of sheets varies with

the paper size.

Fixing mode

Paper type

Target initial fixing
temperature (*1)

Initial number of
sheets (*2)

Condition

Normal

Plain paper (colored paper/recycled paper/
label sheet (64-80 g/m2)

190 deg C

1-9 (A4/LTR)

Special Mode P: OFF

185 deg C