| 摘要 |
PURPOSE:To prevent a fixing unit from being damaged uselessly by rapidly detecting a fault without depending on the rise and fall of the temperature of the fixing unit even when a heater gets into a consecutive turning-on state because of the fault of a fixing temperature control circuit. CONSTITUTION:A heater turning-on signal Sa generated from a microcomputer 21 on an engine board 9 side is superposed on an energizing stop signal Sb outputted from a timer circuit constituted of a timer IC 35, resistances R1 and R2, and a capacitor C1 in an energizing stop signal generation circuit 31 by an inversion input NAND gate 36, and a cycle and the off-period of a duty ratio which are decided by the resistances R1 and R2 and the capacitor C1 are added to the signal, then the signal is outputted to a power source unit 10 as a heater turning-on signal Sc. Therefore, when the signal Sa is 'L', the signal Sc is changed to be 'H' for 0.5 seconds in the cycle of five seconds with the signal Sb. Meanwhile, heater driving voltage impressed on the heater 5b is fetched as a pulsating current signal Sd on a power source unit 10 side and the turning-on state of the heater is monitored. |
