Xerox Phaser 6200B, Service Manual

Page: 331 / 386

Theory of Operation 313
Fuser Control
Fuser temperature control
During fuser temperature control the printer’s target temperature is set. The heat roller
surface temperature is controlled to match the target temperature by turning the heater
lamp on/off.
The heat roller surface temperature is detected by the thermistor sensor. The logic
detects the resistance value alternately at 40ms cycles. The temperature is detected at
80ms cycles and if the detection result is high, the heater lamp is turned off. If the
detection result is low, the heater lamp is turned on.
For the target temperature, different temperatures are set for standby, printing, and
process control. The target temperature is also changed according to the inside
temperature detected with the temperature/humidity sensor, print count, print mode,
input power supply voltage and paper type.
Cool down
During printing, the temperature distribution of the heat roller becomes uneven
between paper and non-paper. To make the heat roller temperature as even as
possible, a wait time is provided and the heater lamp is kept off. This is called the cool
down.
A cool down is executed according to the number of sheets continuously printed
when a set, printing with a certain type and size of paper is completed, and when the
paper type or size is changed. The cool down occurs evenly in the middle of several
hundred sheets of continuous printing.
As a simple cool down, the Pages Per Minute Down is provided. This function idles
the fuser during printing, without feeding paper, to improve temperature distribution
on the heat roller.
The pages per minute execution timing is determined depending on the paper size and
type.