Sharp FO-3150 Service Manual page 91

2) Protect against overheat
Though the heater lamp ON signal (HLON) is normal, if triac PD101 and
T2 are kept ON, overheat may result.
To prevent against this, temperature fuses are used.
When the fusing roller surface temperature exceeds about 187 degrees
C, the temperature fuse blows off to open the 12V power line which
drives the power relay RY101, opening the power line for the photo triac
PD101 and triac T2. Therefore, the power is not supplied to the heater
lamp.
A temperature fuse is also provided in the heater lamp power line. In
case of overheating, the heater lamp power line is opened directly.
3) Timing of temperature detection and heater control
As shown by the following timings, four values of software thermistor
voltage are input as A/D conversion values. The mean value of two
medians among these four is regarded as the newest thermistor value
(temperature).
• The value is compared with the temperature (155 C) control value
every 100 ms.
• If the value is higher than 155 C, the heater becomes OFF. If lower,
the heater becomes ON.
• The heater ON timing is in accordance with the timing of Power Zero
Cross interrupt.
Heater ON/OFF Control
Timings of thermistor value input and heater control
Fig. 18
4) Heater control (Temperature control)
Control method
1 Base machine printing (Copy, List, Receiving)
• Temperature control is started when data to be printed are produced
(or when slips are to be prepared).
• Temperature is controlled at 155 C. (Heater OFF over 155 C. Heater
ON below 155 C.)
• After printing, temperature is not controlled. (Heater is not turned
ON.)
• Fan motor starts revolving from the beginning of temperature control
and stops 120 seconds after printing is finished.
2 PC printing
• Temperature control is started when PC starts printing.
• Temperature is controlled at 155 C. (Heater OFF over 155 C. Heater
ON below 155 C.
Heater ON/OFF Control
T (x 10ms)
Inputting thermistor values
• After printing, temperature is not controlled.
• Fan motor starts revolving from the beginning of temperature control
and stops 120 seconds after printing is finished.
Temperature control is not started from the start of printing because the
first copying time should be within 28 seconds.
155 C
HLON
FAN
CDPAGE
(Base machine Printing started)
Printing started
155 C
Printing started
HLON
FAN
CDPAGE
(PC printing started)
The Heater ON timing is set during Zero Cross interrupt.
5 – 18
FO-3150U/C
In case of the base machine printing
120s
(Single sheet continuous printing)
Printing finished
Preparation of printing
data started
Temperature control started
Fig. 19
In case of PC printing
120s
(Single sheet/continuous)
Printing finished
Temperature control started
Fig. 20
OFF
OFF