Image forming apparatus
View Patent ↗An image forming apparatus includes a heating element that generates heat, a temperature detector that detects a temperature of the heating element, a resistor that divides a detection result of the temperature detector and a predetermined reference voltage, a disconnection detector that detects a disconnection of the temperature detector, a converter that converts the divided voltage value into a digital signal and outputs the digital signal to a controller, a comparing unit that inverts its output on the basis of a predetermined threshold, a delay circuit that delays an increase in an output voltage of the comparing unit, a discharge circuit that quickly discharges the output voltage of the comparing unit, a latch circuit connected to an output of the discharge circuit, and a power supply path connecting and disconnecting unit that is connected to the latch circuit and connects and disconnects a power supply path to the heating element.
1. An image forming apparatus comprising:
a heating element configured to generate heat when a current is applied thereto;
a temperature detector that is disposed in the vicinity of the heating element and is configured to detect a temperature of the heating element;
a resistor configured to divide a detection result of the temperature detector and a predetermined reference voltage;
a disconnection detector that is connected in parallel to the resistor, and is configured to detect a disconnection of the temperature detector;
a converter configured to convert the divided voltage value into a digital signal and to output the digital signal to a controller;
a comparing unit configured to invert an output of the comparing unit on the basis of a comparison between the divided voltage value and a predetermined threshold, and a comparison between an output of the disconnection detector and the predetermined threshold;
a delay circuit configured to delay an increase in an output voltage of the comparing unit;
a discharge circuit configured to quickly discharge the output voltage of the comparing unit;
a latch circuit that includes a flip-flop connected to an output of the discharge circuit; and
a power supply path connecting and disconnecting unit that is connected to the latch circuit, and is configured to connect and disconnect a power supply path to the heating element.
2. The image forming apparatus according to claim 1 , wherein a delay time of the delay circuit and the discharge circuit is greater than time taken to switch from temperature detection to disconnection detection.
3. The image forming apparatus according to claim 1 , wherein the delay circuit and the discharge circuit include a capacitor and a resistor.
4. The image forming apparatus according to claim 1 , wherein the delay circuit and the discharge circuit include a reset circuit.
5. The image forming apparatus according to claim 1 , wherein:
the comparing unit is configured to compare an input, input to the comparing unit, to the predetermined threshold, to output a first output of a first level when the input is less than the predetermined threshold, and to output a second output of a second level when the input is greater than the predetermined threshold, and
wherein the input is either of the divided voltage value and a disconnection detection voltage, corresponding to the detected disconnection by the disconnection detector.
6. The image forming apparatus according to claim 5 , wherein the input to the comparing unit is repeatedly switched, at a predetermined time interval, between the divided voltage value and the disconnection detection voltage.
7. The image forming apparatus according to claim 6 , wherein a delay time of the delay circuit and the discharge circuit is greater than the predetermined time interval.
8. The image forming apparatus according to claim 6 , wherein the delay time of the delay circuit and the discharge circuit is greater than the predetermined time interval such that:
when the disconnection detection voltage is less than the predetermined threshold and the divided voltage value is greater than the predetermined threshold, the latch circuit does not operate to control the power supply path connecting and disconnecting unit to disconnect the power supply path to the heating element; and
when the disconnection detection voltage is less than the predetermined threshold and the divided voltage value is less than the predetermined threshold, the latch circuit operates to control the power supply path connecting and disconnecting unit to disconnect the power supply path to the heating element.
9. The image forming apparatus according to claim 1 , wherein the disconnection detector comprises a transistor and a resistor.
10. The image forming apparatus according to claim 1 , wherein the power supply path connecting and disconnecting unit is configured to connect and disconnect the power supply path to the heating element according to a signal from the latch circuit.