JP2014219585A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device capable of surely detecting and outputting an abnormal state, when abnormality occurs, and to provide an image forming apparatus including the fixing device.SOLUTION: A control part 8 includes an arithmetic part 54, a load detection part 61 detecting the driving voltage of a motor 57, and an abnormality determination part 62. The load detection part 61 detects the driving voltage of the motor 57 and outputs it to the abnormality determination part 62. The abnormality determination part 62 includes a window comparator 67 and determines whether or not an input voltage Vin from the load detection part 61 is within a range from a reference voltage Va to a reference voltage Vb. When the input voltage Vin is within the range, a normal signal is outputted. When the input voltage Vin is out of the range, an abnormal signal is outputted.

Description

  The present invention provides a fixing device capable of determining an abnormal state in the fixing device and an image forming apparatus including the fixing device.

  The electrophotographic image forming apparatus includes a fixing device that fixes the toner image transferred to the printing paper on the printing paper. The fixing device includes a heating device such as a heater, a heating roller (rotary body) whose surface is heated by the heating device, and a pressure roller that is pressed against the heating roller and driven. The heating roller is rotatably supported by a fixing device, and is driven to rotate when a rotational driving force is transmitted from an electric motor such as a DC motor. When the printing paper is conveyed to the nip formed between the heating roller and the pressure roller, the toner image on the printing paper is melted by the heating roller while the printing paper is conveyed by the heating roller and the pressure roller. And is fixed to the printing paper by the pressure applied by the pressure roller. Further, in the fixing device, the surface temperature of the heating roller is detected using a temperature sensor, and the heating device is controlled to be heated so that the temperature at the nip portion becomes a fixing temperature at which fixing is possible based on the detection result.

  In this type of fixing device, there may occur an abnormality such that the printing paper is clogged in the nip portion or the printing paper is wound around the heating roller. In this case, the rotation of the heating roller is stopped, and the heating roller is locally heated to a high temperature, which may cause the printing paper to ignite. To solve this problem, conventionally, when the heating roller is heated to an abnormal temperature higher than a predetermined reference temperature, the control unit of the image forming apparatus performs stop control to stop the heating control of the heating apparatus.

JP 2007-212502 A JP 2009-109525 A

  However, in the conventional stop control, when the CPU of the control unit is in a state in which determination processing cannot be performed, it becomes impossible to detect the temperature of the heating roller, and heating is performed even if an abnormality occurs in the fixing device. The heating by the apparatus cannot be stopped. In order to solve this problem, Patent Document 1 and Patent Document 2 disclose a technique in which heating of a heated object by a heating device is interrupted by a circuit in which a CPU is not interposed. However, each of the techniques described in the above-mentioned patent documents uses the temperature of a heated object detected by a temperature sensor such as a thermistor. For this reason, when the temperature sensor fails, heating of the heating device cannot be stopped even if an abnormality occurs in the fixing device.

  The present invention has been made in view of the above circumstances, and a purpose thereof is a fixing device capable of reliably detecting and outputting an abnormal state when an abnormality occurs in heating of the fixing device, and the fixing device. The present invention provides an image forming apparatus.

The fixing device of the present invention includes a rotating body, a load detection unit, and an abnormality determination unit. The rotating body rotates by receiving a rotational driving force transmitted from a predetermined electric motor. The load detector is for detecting and outputting a load applied to the electric motor. The abnormality determination unit outputs an abnormality signal when the output from the load detection unit is outside a set range from a predetermined lower threshold value to an upper threshold value.
The image forming apparatus according to the present invention includes the fixing device.

  According to the present invention, when an abnormality occurs such as a load applied to the rotating body due to an abnormally high temperature of the rotating body, the abnormal state can be reliably detected and output. Is possible.

1 is a diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram illustrating a configuration of a control unit included in the image forming apparatus illustrated in FIG. 1. It is a figure which shows the structure of the load detection part and abnormality determination part of the control part shown in FIG. It is a timing chart which shows the state of the input voltage and output voltage in the abnormality determination part shown in FIG. It is a flowchart which shows the procedure of the abnormality determination process performed by the control part shown in FIG.

  Embodiments of the present invention will be described below with reference to the drawings as appropriate. In addition, the following embodiment is only an example which actualized this invention, and does not limit the technical scope of this invention.

[Image forming apparatus 10]
FIG. 1 is a schematic diagram showing a configuration of an image forming apparatus 10 (an example of the image forming apparatus of the present invention) according to an embodiment of the present invention. As shown in FIG. 1, the image forming apparatus 10 forms an image on printing paper based on the read image data of an original or image data input from the outside, and reads the image of the original on the top. A scanner 12 is provided, and an electrophotographic image forming unit 14 is provided below. A specific example of the image forming apparatus 10 according to the embodiment of the present invention is, for example, a printer, a copier, a facsimile, or a multifunction machine having these functions.

  The image forming unit 14 forms an image on a print sheet based on a print job such as image data read by the scanner 12 or image data input from the outside. The image forming unit 14 mainly includes a paper feed tray 16 capable of holding print paper, a transport roller 19, a transfer device 15 that transfers a toner image to the print paper fed from the paper feed tray 16, and a print paper. A fixing device 18 (an example of the fixing device of the present invention) that fixes the transferred toner image on the printing paper, an operation display unit (not shown), and a motor 57 that supplies rotational driving force to the heating roller 38 of the fixing device 18 (An example of the electric motor of the present invention, see FIG. 2) and a control unit 8 (see FIG. 2) for controlling these operations. These components are arranged inside a casing 20 that constitutes a housing of the image forming unit 14. Between the upper part of the casing 20 and the scanner 12, a paper discharge space 21 that is open at the front is provided. A paper discharge tray 23 is disposed on the lower surface of the paper discharge space 21. The printing paper fed from the paper feed tray 16 is conveyed by the conveyance roller 19 along the conveyance path 20A provided in the casing 20, and the toner image is transferred to the printing paper by the transfer device 15 in the conveyance process. The The toner image transferred to the printing paper is fixed to the printing paper by being heated and melted when passing through the fixing device 18. The printing paper that has passed through the fixing device 18 is discharged to the paper discharge space 21 and held on the paper discharge tray 23.

[Fixing device 18]
The fixing device 18 includes a frame 34, a heating roller 38 supported by the frame 34, a pressure roller 39 that is pressed against the heating roller 38 and is driven to rotate, a heating device 42, and a temperature sensor 44. . The heating roller 38 and the pressure roller 39 are supported by the frame 34 so as to be rotatable.

  In the fixing device 18, the heating roller 38 is heated by the heating device 42 in order to melt the toner. The outer peripheral surface of the heating roller 38 is heated from one direction by a heating device 42 provided on the upper portion thereof. In the present embodiment, the heating by the heating device 42 is controlled by the control unit 8 so that the surface temperature of the heating roller 38 is heated to a preset temperature (for example, 175 ° C.). More specifically, the heating roller 38 is heated by the heating device 42 so that the temperature of the nip portion 82 between the heating roller 38 and the pressure roller 39 becomes the set temperature.

  The heating device 42 is a device that generates heat on the heating roller 38 by an induction heating method using electromagnetic induction. The heating device 42 is provided so as to cover the circumferential surface of the heating roller 38 through a gap. The heating roller 38 generates Joule heat under the influence of magnetic lines of force from the heating device 42 and self-heats. In the present embodiment, the induction heating type heating device 42 is illustrated, but other heating devices such as a halogen heater may be applied instead of the heating device 42.

  The heating roller 38 rotates in response to the rotational driving force transmitted from the motor 57. The heating roller 38 is connected to a motor 57 that is driven and controlled by a motor driver 56 of the control unit 8 via a gear transmission mechanism (not shown). For this reason, when the motor 57 is rotationally driven, the heating roller 38 is rotated in a predetermined direction by transmitting the rotational driving force via the gear transmission mechanism. Further, the heating roller 38 conveys the printing paper while sandwiching the printing paper at the nip portion 82 with the pressure roller 39 as described later. When the heating roller 38 is driven and controlled by the motor driver 56, the printing paper is conveyed at the nip portion 82 at a predetermined conveyance speed. Such control of the motor 57 is realized by outputting a drive signal corresponding to the conveyance speed to the motor driver 56 in the control unit 8.

  The pressure roller 39 is disposed to face the heating roller 38. The pressure roller 39 is pressed against the heating roller 38 by a spring or the like. Thereby, a nip portion 82 is formed between the pressure roller 39 and the heating roller 38. In the fixing device 18, the printing paper is conveyed so as to pass through the nip portion 82 from right to left in FIG. When the printing paper passes through the nip portion 82 with the heating roller 38 heated, the toner image carried on the printing paper is melted and fixed on the printing paper.

  A temperature sensor 44 for detecting the temperature of the outer peripheral surface of the heating roller 38 is provided around the heating roller 38. As the temperature sensor 44, a general-purpose product and a small and low-cost thermistor is used. Of course, the temperature sensor 44 may be of any type as long as it can detect the surface temperature of the heating roller 38, a contact type that utilizes changes in thermoelectromotive force, electrical resistance, and magnetism, and brightness and color.・ A non-contact type that measures temperature with infrared intensity is also applicable.

[Control unit 8]
The control unit 8 controls the image forming apparatus 10 in an integrated manner. That is, the control unit 8 controls the transport operation by the transport roller 19, the transfer operation by the transfer device 15, the fixing operation by the fixing device 18, and the like in the image forming apparatus 10. As shown in FIG. 2, the control unit 8 includes a calculation unit 54 including a CPU 51, a ROM 52, and a RAM 53, a motor driver 56, a heater driver 55, a load detection unit 61, an abnormality determination unit 62, and the like. In the arithmetic unit 54, the CPU 51 executes heating control and fixing operation control, which will be described later, according to a predetermined program stored in the ROM 52. The heating control and the fixing operation control by the control unit 8 are not limited to those executed by the CPU 51 and may be realized by an electronic circuit such as an integrated circuit (ASIC).

  The calculation unit 54 is electrically connected to the temperature sensor 44. A detection signal from the temperature sensor 44 is input to the calculation unit 54. The calculation unit 54 calculates the temperature of the heating roller 38 based on the detection signal from the temperature sensor 44, controls the heater driver 33 according to the calculation result, and performs heating by the heating device 42. Specifically, the calculation unit 54 controls the heating device 42 so that the temperature of the nip portion 82 between the heating roller 38 and the pressure roller 39 is constant at the set temperature necessary for fixing the toner.

  The motor driver 56 is a drive circuit that supplies a drive current to the motor 57 to drive the motor 57 to rotate. The motor driver 56 is configured by, for example, an electronic circuit such as an integrated circuit (ASIC) or an internal memory. The motor driver 56 is electrically connected to the motor 57, and drives and controls the motor 57 based on a drive signal from the calculation unit 54. Thereby, the heating roller 38 rotates. The motor driver 56 is not limited to an electronic circuit such as an integrated circuit (ASIC), and may be realized by executing a predetermined program by the CPU 51, for example.

  The motor 57 is a DC motor, for example. The DC motor has a characteristic that the starting torque is large, the rotational speed is linearly proportional to the input voltage (applied voltage), and the output torque is linearly proportional to the input current. Control is easy and the cost is low. In the present embodiment, a DC motor is described as an example of the motor 57. However, the present invention is not limited to a DC motor, and any motor can be applied as long as it can detect a load applied to the motor 57. is there.

  The heater driver 55 is a drive circuit that supplies a drive current to the heating device 42 and controls heating performed using the heating device 42. Similar to the motor driver 56, the heater driver 55 is a drive circuit configured by an electronic circuit such as an integrated circuit (ASIC) or an internal memory. The heater driver 55 is electrically connected to the heating device 42 and performs heating control using the heating device 42 based on a drive signal from the calculation unit 54. Thereby, the heating roller 38 is heated. The heater driver 55 may be realized, for example, by a predetermined program being executed by the CPU 51.

  The load detection unit 61 is for detecting and outputting the magnitude of the load applied to the motor 57, and is an example of the load detection unit of the present invention. Specifically, the load detection unit 61 is a voltage detection circuit that can detect the load voltage (applied voltage) of the motor 57. As shown in FIG. 3, the load detection unit 61 includes an internal resistor 61 </ b> A provided in series with the − terminal of the motor 57 and a DC power supply 61 </ b> B that outputs a voltage Vc. One end of the internal resistor 61A is connected to the-terminal of the motor 57, and the other end is connected to the + electrode of the DC power supply 61B. Further, the negative electrode of the DC power supply 61B is connected to a frame or the like, and is set to a ground potential (GND potential). A transistor 64 is connected to the + terminal of the motor 57, and when a motor drive signal is input from the motor driver 56 to the transistor 64, the drive voltage Vcc is applied to the + terminal of the motor 57, and When the motor drive signal is lost, the drive voltage Vcc is not applied to the + terminal of the motor 57.

  The negative terminal of the motor 57 is input to a window comparator 67 of the abnormality determination unit 62 described later. That is, the voltage at the negative terminal of the motor 57 is an output from the load detection unit 61, and the voltage is input to the window comparator 67 as the input voltage Vin. In the present embodiment, since the load detection unit 61 is provided with the DC power supply 61B, even if the drive voltage Vcc is not applied to the + electrode of the motor 57, the load detection unit 61 detects the input voltage Vin. A voltage Vc which is the lowest possible voltage is input to the window comparator 67.

  The abnormality determination unit 62 outputs an abnormality signal when the output from the load detection unit 61 is outside the set range from a predetermined lower limit threshold to an upper limit threshold, and is an example of the abnormality determination unit of the present invention. It is. Here, the lower limit threshold is a reference voltage Vb input to a comparison circuit 67B described later, and the upper limit threshold is a reference voltage Va input to a comparison circuit 67A described later. Specifically, the abnormality determination unit 62 outputs a LOW level voltage signal (hereinafter referred to as “LOW voltage signal”) when the load voltage of the motor 57 output from the load detection unit 61 is outside the set range. It is a comparison circuit that outputs as Vout. This LOW voltage signal is a voltage signal having a voltage value lower than a predetermined reference value. In this embodiment, the LOW voltage signal is handled as an abnormal signal. In addition, the abnormality determination unit 62 outputs a voltage signal at the HI level (hereinafter referred to as “HI voltage signal”) as the output voltage Vout when the load voltage of the motor 57 detected by the load detection unit 61 is within the set range. This is a comparison circuit. This HI voltage signal is a voltage signal having a voltage value higher than a predetermined reference value. In the present embodiment, the HI voltage signal is handled as a normal signal.

  As shown in FIG. 3, the abnormality determination unit 62 includes a window comparator 67 and a reference voltage switching circuit 68. The window comparator 67 includes a comparison circuit 67A (an example of the second comparison circuit of the present invention) and a comparison circuit 67B (an example of the first comparison circuit of the present invention). A reference voltage Va is input to the comparison circuit 67A as a comparison reference. This reference voltage Va has a voltage value higher than a reference voltage Vb described later. The comparison circuit 67A outputs the LOW voltage signal when the input voltage Vin output from the load detection unit 61 and input to the comparison circuit 67A is higher than the reference voltage Va. Further, the reference voltage Vb is input to the comparison circuit 67B as a comparison reference. The comparison circuit 67B outputs the LOW voltage signal when the input voltage Vin input to the comparison circuit 67B output from the load detection unit 61 is lower than the reference voltage Vb. In other words, when the input voltage Vin is between the reference voltage Vb and the reference voltage Va, the window comparator 67 outputs the HI voltage signal as a normal signal instead of the LOW voltage signal. Note that the reference voltage Va and the reference voltage Vb are both higher than the voltage Vc output from the DC power supply 61B.

  The reference voltage switching circuit 68 is a circuit that changes the reference voltage Vb in accordance with the presence or absence of a motor drive signal that drives the motor 67, and is an example of a lower limit threshold change circuit of the present invention. Specifically, the reference voltage switching circuit 68 makes the reference voltage Vb lower than the voltage Vc of the DC power supply 61B, which is the lowest voltage that can be detected by the load detection unit 61 when the input of the motor drive signal is lost. It is configured as follows. In the present embodiment, the reference voltage switching circuit 68 changes the reference voltage Vb to the ground potential (GND potential) when the motor drive signal is not input. In contrast, when the motor drive signal is input to the abnormality determination unit 62, the reference voltage switching circuit 68 restores the reference voltage Vb.

  As shown in FIG. 3, the reference voltage switching circuit 68 includes a DC power supply 70 that outputs a voltage Vb connected to the negative pole of the comparison circuit 67 </ b> B, and a transistor 71 connected to the negative pole of the DC power supply 70. . The emitter terminal of the transistor 71 is set to the ground potential. The reference voltage switching circuit 68 has an internal resistor 73, one of which is connected to the negative pole of the comparison circuit 67B and the other of which is set to the ground potential. With this configuration, when the motor drive signal is input to the base of the transistor 71, a current flows between the collector and the emitter, and the reference voltage Vb is input to the negative pole of the comparison circuit 67B. On the other hand, when there is no input of the motor drive signal, the collector-emitter is not conductive, and the negative pole of the comparison circuit 67B becomes the ground potential.

  Since the load detection unit 61 and the abnormality determination unit 62 are configured in this way, as shown in FIG. 4, when the motor drive signal becomes HI and the drive current is supplied to the motor 57, the reference voltage switching is performed. The circuit 68 changes the reference voltage of the lower threshold value from the ground potential (GND potential) to the voltage Vb (see time point T1). In this state, the window comparator 67 compares and determines whether or not the input voltage Vin is between the reference voltage Vb and the reference voltage Va. For example, as shown at times T1 to T2, when the input voltage Vin is between the reference voltage Vb and the reference voltage Va, the output voltage Vout becomes HI. Further, as shown at times T2 to T3, when the input voltage Vin becomes higher than the reference voltage Va, the output voltage Vout changes from HI to LOW. On the other hand, when the input voltage Vin becomes lower than the reference voltage Vb as shown at times T4 to T5, the output voltage Vout also changes from HI to LOW in this case. When the motor drive signal becomes LOW and no drive current is supplied to the motor 57, the reference voltage switching circuit 68 changes the lower limit threshold reference voltage from Vb to the ground potential (GND potential) (time points T6 to T7). reference). In this state, the window comparator 67 compares and determines whether or not the input voltage Vin is between the ground potential (GND potential) and the reference voltage Va. As described above, even if the drive voltage is not applied to the motor 57, the voltage Vc of the DC power supply 61B is input as the input voltage Vin as the minimum voltage. Therefore, the window comparator 67 always determines that the input voltage Vin is between the ground potential (GND potential) and the reference voltage Va from time T6 to T7, and maintains the output voltage Vout at HI.

  Next, an example of the procedure of the abnormality determination process executed by the control unit 8 will be described with reference to the flowchart of FIG. In the figure, S11, S12,... Represent processing procedure (step) numbers. Processing in each step is performed by the control unit 8, more specifically, by the CPU 61 of the calculation unit 64 executing a program in the ROM 62. Here, in this embodiment, the stop control part of this invention is implement | achieved when the control part 8 performs an abnormality determination process. In the following description, it is assumed that the image forming apparatus 10 is in the power saving mode at the time of step S11.

  First, in step S <b> 11, the control unit 8 determines whether a print instruction is input to the image forming apparatus 10. When a printing instruction is input, the control unit 8 switches the operation mode of the image forming apparatus 10 from the power saving mode to the printing operation mode. Specifically, a motor drive signal is output to the motor driver 56 to drive the stopped motor 57 (S12). Further, a drive signal is output to the heater driver 55, and heating of the heating roller 38 using the heating device 42 that has been stopped is started (S13).

  In the next step S <b> 14, the control unit 8 determines whether the measured temperature is abnormal based on the temperature detected using the temperature sensor 44. With this determination, it can be determined whether or not the fixing device 18 is abnormal. For example, when printing paper is jammed in the fixing device 18 or printing paper is wound around the heating roller 38 or the pressure roller 39, the rotation of the heating roller 38 is slowed or stopped. At this time, the heat of the heating roller 38 is not taken away by the printing paper, and the heating roller 38 is in a high temperature state that the printing paper is ignited. In such a state, the control unit 8 determines that the fixing device 18 is abnormal when the measured temperature detected using the temperature sensor 44 is equal to or higher than a reference value (temperature threshold that can be determined as abnormal). To do. Here, if it is determined that the fixing device 18 is abnormal, the control unit 8 stops the motor 57 in the next step S18, and further stops the heating of the heating roller 38 using the heating device 42.

  If the temperature sensor 44 is broken and the surface temperature of the heating roller 38 cannot be measured accurately, the determination in step S14 is not performed accurately. Even in this case, according to the abnormality determination process of the present embodiment, the abnormality determination of the fixing device 18 can be accurately performed by performing the determination of step S15.

  If it is determined in step S14 that the measured temperature is not abnormal, the control unit 8 determines whether or not the output voltage Vout from the abnormality determination unit 62 is HI (S15). Here, when the output voltage Vout is LOW, it can be determined that the motor 57 is overloaded. That is, it can be determined that the printing paper is clogged or caught up, which is the cause of the excessive load on the motor 57. In this case, the process proceeds to step S18, the motor 57 is stopped, and the heating of the heating roller 38 using the heating device 42 is further stopped.

  On the other hand, when the control unit 8 determines that the output voltage Vout is HI in step S15, it can be determined that an excessive load is not applied to the motor 57. That is, it can be determined that the printing paper is not jammed or caught up, which is the cause of the excessive load on the motor 57. In this case, the process proceeds to step S16, and the printing operation is started on the printing paper. When the printing operation is finished, the operation mode of the image forming apparatus 10 is again shifted to the power saving mode, and a series of processes is finished (S19). Note that when the operation mode of the image forming apparatus 10 is the power saving mode in step S19, the motor drive signal to the motor driver 56 is stopped. In this case, as described above, the reference voltage switching circuit 68 of the abnormality determination unit 62 changes the reference voltage of the comparison circuit 67B from the voltage Vb to the ground potential. Therefore, even if the input voltage Vin decreases to the voltage Vc, the output voltage Vout maintains HI. Therefore, even when a printing instruction is input as in step S11 and the mode is shifted from the power saving mode to the printing operation mode, it is possible to immediately perform control for heating the heating roller 38 using the heating device 42.

  By performing such abnormality determination processing, even if the abnormality of the fixing device 18 cannot be determined at the temperature detected by the temperature sensor 44, the abnormality of the fixing device 18 is determined based on the output voltage Vout of the window comparator 67 in step S15. The presence or absence of can be accurately determined.

  In the above-described embodiment, the example in which the CPU 61 of the calculation unit 64 determines based on the voltage signal of the output voltage Vout has been described, but the present invention is not limited to this. For example, if the output voltage Vout is used as a drive signal for the heater driver 55, even if the CPU 61 fails and an accurate determination cannot be made, if the abnormality occurs in the fixing device 18, the heating device 42 is surely obtained. The heating of the heating roller 38 using can be stopped.

  In the above-described embodiment, the image forming apparatus 10 including the fixing device 18 is illustrated. However, the present invention can be applied to a single product including only the fixing device 18.

8: Control unit 10: Image forming apparatus 18: Fixing device 64: Calculation unit 38: Heating roller 39: Fixing roller 42: Heating device 44: Temperature sensor 57: Motor 61: Load detection unit 62: Abnormality determination unit 67: Window comparator Generator 68: Reference voltage switching circuit

Claims (8)

A rotating body that rotates by receiving a rotational driving force transmitted from a predetermined electric motor;
A load detection unit for detecting and outputting a load applied to the electric motor;
And an abnormality determination unit that outputs an abnormality signal when an output from the load detection unit is outside a predetermined range from a predetermined lower limit threshold value to an upper limit threshold value. The load detection unit is a voltage detection circuit for detecting and outputting a load voltage of the electric motor,
The abnormality determination unit outputs the abnormality signal that is a voltage signal lower than a predetermined reference value when the output from the load detection unit is outside the setting range, and the output from the load detection unit is the setting range. 2. The fixing device according to claim 1, wherein the fixing device outputs a normal signal that is a voltage signal higher than the reference value.   The abnormality determination unit includes a first comparison circuit that outputs a voltage signal lower than the reference value when an output from the load detection unit is lower than the lower limit threshold, and an output from the load detection unit is the upper limit threshold. The fixing device according to claim 2, further comprising: a second comparison circuit that outputs a voltage signal lower than the reference value when higher than the reference value.   4. The fixing device according to claim 3, wherein the first comparison circuit includes a lower limit threshold changing circuit that changes the lower limit threshold depending on whether or not a drive signal for driving the electric motor is input.   The fixing device according to claim 4, wherein the lower limit threshold changing circuit lowers the lower limit threshold lower than a minimum voltage that can be detected by the load detection unit when the input of the drive signal is lost.   The fixing device according to claim 2, wherein the comparison circuit is a window comparator. A heating device for heating the rotating body;
The fixing device according to claim 1, further comprising: a stop control unit that receives the abnormality signal output from the abnormality determination unit and stops driving the heating device. An image forming apparatus comprising the fixing device according to claim 1.

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