| 摘要 |
PURPOSE:To detect a fault in turning on and off a heater, by photodetecting the light emission of the heater and generating a one-shot pulse when it is turned on and off, and then resetting and restarting a timer by the one-shot pulse. CONSTITUTION:In normal use, an IC timer U6 is checked with a time constant (R11+R12)XC11 determined by resistances R11 and R12 and a capacitor C11 until a heat fixing device is powered up and rises in temperature up to a prescribed value, and then a heater 15 turned on and off according to the temperature rise and drop of the fixing device. The timer U6 is reset and restarted repeatedly by the one-shot pulses of AND gate circuit U13 and U14 generated when the light emission output is turned on and off. The Q output signal A of a D type FF is a reloading signal for processing the display showing that copying is in readiness, and the Q output signal D of a J-K type FF, U8 goes up to a high level in case of the occurrence of a fault and is inputted to a control circuit, which performs fault processing, waring, etc. |
