JP2010066543A - Fixing device and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device and an image forming device capable of preventing surely and early local abnormal heating of a heating roller or a fixing belt, caused by abnormal stop of the heating roller in a constitution wherein a temperature sensor for detecting the temperature of the heating roller is provided on a position separated from an induction heating position of the heating roller. <P>SOLUTION: The fixing device has a constitution, equipped with a gate power source control circuit 73 for blocking power supply to an induction coil 54a, on the condition that the stop of the heating roller 53 be detected by a pulse detection circuit 81, a fixing high-temperature detection circuit 75 for blocking power supply to the induction coil 54a, on the condition that the detected temperature by a thermistor 78 reaches an upper limit set temperature which is set beforehand or higher; and an upper limit set temperature changing circuit 90 for setting the upper limit set temperature, when stoppage of the heating roller 53 is detected by the pulse detection circuit 81 to be lower than an upper limit, set temperature when the rotation of the heating roller 53 is detected by the pulse detecting circuit 81. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an induction heating type fixing device and an image forming apparatus including the same, and more particularly to a technique for forcibly stopping induction heating when abnormal heating occurs.

Conventionally, an image forming apparatus such as a printer, a copying machine, a facsimile machine, or a complex machine of these is heated by a fixing belt stretched between a heating roller and a fixing roller, and the fixing belt is pressed against a sheet of paper. A fixing device that melts and fixes toner on paper may be used.
Further, the fixing belt in the fixing device is provided with an induction coil and a magnetic core that inductively heat the heating roller and the fixing belt by applying an induction current to a rotating heating roller and a part of the fixing belt. An electromagnetic induction heating device is used. Here, in a general fixing device, the temperature of the heating roller is detected by a temperature sensor or the like, and abnormal heating is prevented by stopping induction heating when the detected temperature reaches or exceeds a preset upper limit temperature. is doing.
Further, when induction heating is performed in such a fixing device, if the fixing belt or the heating roller does not rotate due to some abnormality, the fixing belt or the heating roller may be locally concentrated and heated. Therefore, for example, in Patent Document 1, when it is detected that the rotation of the heating roller or the fixing belt is stopped, abnormal heating can be prevented by stopping the inverter circuit and stopping the power supply to the induction coil. Proposed. Specifically, in Patent Document 1, the output of the inverter circuit is stopped by stopping the input of the pulse signal input to the inverter circuit or by an enable signal for switching the enable / disable of the inverter circuit. Thereby, abnormal heating due to the rotation of the heating roller and the fixing belt being stopped during induction heating can be prevented at an early stage.
JP 2004-279661 A

However, as disclosed in Patent Document 1, when the rotation of the heating roller or the fixing belt stops abnormally, the output of the inverter circuit is stopped by stopping the pulse signal or enable signal input to the inverter circuit. In the configuration, the output of the inverter circuit cannot be stopped if an abnormality has occurred in the control circuit that outputs the pulse signal or the enable signal. For this reason, the safety measures against abnormal heating were not perfect.
Therefore, as described above, it may be possible to take a double safety measure by configuring the induction heating to stop even when the temperature detected by the temperature sensor reaches the upper limit set temperature or more. Thereby, abnormal heating is prevented by any one of the safety measures.
However, in a configuration in which an induction coil and a magnetic core used for induction heating are arranged so as to cover a predetermined area on the outer periphery of the heating roller (see, for example, FIG. 2), the temperature sensor is connected to the induction on the surface of the heating roller. It cannot be placed in contact with the position where heating is performed, and is placed at a position away from the position where induction heating is performed. In this case, when the heating roller is stopped, the temperature sensor indirectly detects the temperature of the induction heating position in the heating roller by the heat conduction in the heating roller. For this reason, when the temperature detected by the temperature sensor reaches the upper limit set temperature or higher and the induction heating is stopped, the temperature at the induction heating position of the heating roller has already exceeded the upper limit set temperature, resulting in a lack of safety. There is.
Accordingly, the present invention has been made in view of the above circumstances, and its object is to provide a temperature sensor for detecting the temperature of the heating roller at a position away from the induction heating position in the heating roller. It is an object of the present invention to provide a fixing device and an image forming apparatus that can reliably and quickly prevent local abnormal heating of the heating roller and the fixing belt due to abnormal stopping of the heating roller.

In order to achieve the above object, the present invention provides a fixing roller that is rotationally driven by a predetermined driving means, and a driving force transmitted from the fixing roller via a fixing belt stretched between the fixing roller. A heating roller that is rotationally driven, an induction heating unit that is disposed so as to cover a predetermined area on the outer periphery of the heating roller, and that receives electric power to inductively heat the heating roller and / or the fixing belt; Roller rotation detection means for detecting rotation and stop, and first power supply shut-off means for cutting off power supply to the induction heating means on condition that the roller rotation detection means detects the stop of the heating roller. And a fixing device comprising the following (1) to (3).
(1) Roller temperature detection means for detecting the temperature of the heating roller at a position away from a position where induction heating of the heating roller and / or the fixing belt by the induction heating means is performed.
(2) Second power supply shut-off means for shutting off power supply to the induction heating means on condition that the temperature detected by the roller temperature detecting means has reached a preset upper limit temperature or higher.
(3) The upper limit set temperature when the roller rotation detecting unit detects the stop of the heating roller is higher than the upper limit set temperature when the roller detecting unit detects the rotation of the heating roller. Upper limit temperature changing means for setting low. For example, the upper limit set temperature changing means includes a first upper limit set temperature set in advance corresponding to the rotation of the heating roller and the first upper limit set temperature set in advance corresponding to the stop of the heating roller. The lower second upper limit set temperature is switched according to the detection result by the roller rotation detecting means.

According to the present invention, when the heating roller abnormally stops, some abnormality has occurred in the first power supply cutoff means, and the first power supply cutoff means supplies power to the induction heating means. Even if not shut off, the second power supply shut-off means supplies power to the induction heating means based on the upper limit set temperature corresponding to the time when the heating roller is stopped after being changed by the upper limit set temperature changing means. Therefore, local abnormal heating of the heating roller and the fixing belt by the induction heating means can be prevented reliably and early, and safety can be improved.
Here, one of the first power supply cutoff means and the second power supply cutoff means is a path cutoff means for blocking the power supply path to the induction heating means, and the other is It is desirable that the switching driving stop means stop the switching signal to the switching means for controlling the power supplied to the induction heating means. That is, it is desirable that the first power supply shut-off means and the second power supply shut-off means are different methods and cut off the power supply to the induction heating means. Even if there is a situation where the supply cannot be cut off, the power supply can be cut off by the other method.
By the way, the present invention can also be understood as an image forming apparatus including the fixing device.

  According to the present invention, when the heating roller abnormally stops, some abnormality has occurred in the first power supply cutoff means, and the first power supply cutoff means supplies power to the induction heating means. Even if not cut off, the second power supply cut-off means supplies power to the induction heating means on the basis of the upper limit set temperature corresponding to when the heating roller is stopped after being changed by the upper limit set temperature changing means. Therefore, local abnormal heating of the heating roller and the fixing belt by the induction heating means can be prevented reliably and early, and safety can be improved.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings so that the present invention can be understood. The following embodiment is an example embodying the present invention, and does not limit the technical scope of the present invention.
1 is a block diagram showing a schematic configuration of the copying machine X according to the embodiment of the present invention, FIG. 2 is a block diagram showing a schematic configuration of the fixing device 5 according to the embodiment of the present invention, and FIG. 6 is a circuit diagram for explaining an example of an upper limit set temperature changing circuit 90 provided in the fixing device 5 according to the embodiment of the present invention. FIG.
First, a schematic configuration of the copying machine X according to the embodiment of the present invention will be described with reference to FIG.
As shown in FIG. 1, a copying machine X according to an embodiment of the present invention includes an operation display unit 1, an image reading unit 2, an image processing unit 3, an image forming unit 4, a fixing device 5, a control unit 6, and the like. In general, it is structured. The copying machine X has various other constituent elements that a general electrophotographic copying machine has, but since these are not different from the conventional ones, description thereof is omitted here. The present invention is not limited to the copying machine X, and can also be applied to, for example, an electrophotographic image forming apparatus such as a printer apparatus, a facsimile apparatus, and a multifunction machine having these functions and a scanner function.

The control unit 6 includes a CPU and peripheral devices such as a ROM and a RAM, and controls the copier X in an integrated manner by executing processing according to a predetermined program stored in the ROM.
The operation display unit 1 includes a liquid crystal display that displays various types of information according to instructions from the control unit 6, a touch panel for performing operation input to the control unit 6, and the like.
The image reading unit 2 reads an image of a document set on a document table or an ADF (automatic conveyance device), and the image data read by the image reading unit 2 is input to the image processing unit 3. The
The image processing unit 3 performs various operations on image data of a document read by the image reading unit 2 and image data of a document input from an information processing apparatus (not shown) via a communication network such as a LAN. Image processing is performed. The image data that has been subjected to image processing by the image processing unit 3 is input to the image forming unit 4.
The image forming unit 4 includes a photosensitive drum, a charger, a developing device, an LSU, and the like. A toner image (developer) is applied to a sheet based on image data of a document input from the image processing unit 3. To form.
The fixing device 5 melts and fixes the toner image on the paper on which the toner image is formed by the image forming unit 4. The copying machine X according to the embodiment of the present invention is characterized by the configuration and operation related to the fixing device 5 and will be described in detail below.

As shown in FIG. 2, the fixing device 5 includes a fixing roller 51 and a pressure roller that rotate while pressing a sheet conveyed on the sheet conveying path 50 after the toner image is transferred in the image forming unit 4. 51a and a heating roller 53 that is rotationally driven by a driving force transmitted from the fixing roller 51 via a fixing belt 52 stretched between the fixing roller 51, and induction that heats the heating roller 53 An induction heating unit 54 (an example of induction heating means) having a coil 54a and a magnetic core 54b and a heating control unit 7 for controlling the heating operation by the induction heating unit 54 are provided.
The fixing roller 51 is connected to predetermined driving means such as a stepping motor (not shown), and is rotationally driven by the predetermined driving means. When the fixing roller 51 is rotationally driven, the fixing belt 52 travels by the driving force, and the heating roller 53 rotates by the driving force transmitted from the fixing belt 52.

Here, the heating roller 53 is made of a magnetic material. The induction coil 54 a and the magnetic core 54 b of the induction heating unit 54 are formed to have substantially the same width as the longitudinal width of the heating roller 53, and a predetermined area (see FIG. 2 (see reference 2, upper semicircular region). As a result, a magnetic circuit (magnetic path) for guiding the magnetic flux generated by the induction coil 54a is formed between the magnetic core 54b and the surface of the heating roller 53.
In the fixing device 5, a magnetic flux generated by passing an alternating current through the induction coil 54 a acts on a magnetic circuit formed between the magnetic core 54 b and the heating roller 53, thereby causing the heating roller 53 to move. The heating roller 53 is heated (induction heating) by the eddy current (induction current) generated on the surface. As a result, the fixing belt 52 stretched around the heating roller 53 is heated by heat conduction from the heating roller 53, and the adhered toner is melted and fixed on the paper contacting the fixing belt 52. When the fixing belt 52 is made of a magnetic member, the fixing belt 52 is induction-heated by a magnetic flux acting from the magnetic core 54b.

On the other hand, the heating control unit 7 includes a CPU 71, an IGBT gate drive circuit 72, a gate power supply control circuit 73, an IGBT 74 (insulated gate bipolar transistor, an example of switching means), a fixing high temperature detection circuit 75, a relay coil 76, a relay contact 77, A thermistor 78 (an example of roller temperature detection means), a rotary encoder 80, a pulse detection circuit 81, and an upper limit set temperature change circuit 90 are included.
In the heating control unit 7, the CPU 71 executes predetermined control processing (arithmetic processing) based on a control program and various parameters stored in a ROM or RAM (not shown) to control each component. Is done. The CPU 71 controls a heating operation in the fixing device 5 based on a control instruction from the control unit 6. Further, the processing function of the CPU 71 may be achieved by the control unit 6 and the CPU 71 may be omitted.

The rotary encoder 80 outputs a pulse signal as the heating roller 53 rotates, and the pulse signal is input to the pulse detection circuit 81. For example, the rotary encoder 80 outputs a pulse signal in response to detection of each of an encoder mounted on the rotating shaft of the heating roller 53 and rotating in synchronization with the heating roller 53 and a slit formed in the encoder. And a photo interrupter.
The pulse detection circuit 81 detects the rotation and stop of the heating roller 53 depending on whether or not a pulse signal is input from the front rotary encoder 80. Here, the pulse detection circuit 81 that performs such detection is an example of roller rotation detection means. The roller rotation detecting means is not limited to this, and any means capable of detecting the rotation and stop of the heating roller 53 may be used. The pulse detection circuit 81 may detect that the heating roller 53 is rotating on condition that the pulse signal input from the rotary encoder 80 is stabilized at a predetermined frequency.
The pulse detection circuit 81 inputs the detection result of rotation and stop of the heating roller 53 to the CPU 71, the gate power supply control circuit 73, and the upper limit set temperature changing circuit 90. For example, the pulse detection circuit 81 outputs an “H” signal when the rotation of the heating roller 53 is detected, and an “L” signal when the stop is detected.

  For example, when the CPU 71 performs control for rotating the fixing roller 51 by a predetermined driving means, and the pulse detection circuit 81 detects the stop of the heating roller 53, the fixing roller 51. Therefore, it is determined that an abnormality has occurred in the transmission system of the driving force to the heating roller 53. At this time, the CPU 71 executes a process for displaying the fact on the operation display unit 1 and a process for stopping the input of the switching signal to the IGBT gate drive circuit 72.

The IGBT gate drive circuit 72 is a transistor, FET, IGBT, or the like, and switches whether or not a switching signal is input from the CPU 71 to the IGBT 74. The IGBT 74 is a switching means for performing a switching operation for switching whether or not a DC voltage supplied from a primary power supply (not shown) is supplied to the induction coil 54a according to a switching signal input from the CPU 71. A transistor or FRT may be used instead of the IGBT 74.
The gate power supply control circuit 73 switches the establishment of the power supply path from a predetermined power supply to the IGBT gate drive circuit 72 according to the detection result input from the pulse detection circuit 81, thereby switching the IGBT gate. The drive circuit 72 switches whether or not a switching signal is input to the IGBT 74. Specifically, the gate power supply control circuit 73 blocks the power supply path to the IGBT gate drive circuit 72 on condition that the stop of the heating roller 53 is detected by the pulse detection circuit 81. The input of the switching signal to the IGBT 74 by the IGBT gate driving circuit 72 is stopped.
Therefore, in the fixing device 5, when the heating roller 53 is stopped due to some abnormality, the input of the switching signal from the IGBT gate drive circuit 72 to the IGBT 74 is stopped, and the power supply to the induction coil 54a is stopped. By being cut off, local abnormal heating of the heating roller 53 is prevented. Here, the IGBT gate drive circuit 72 and the gate power supply control circuit 73 are examples of first power supply cutoff means and switching drive stop means.

In addition, the heating control unit 7 detects the abnormality of the heating roller 53 by cutting off the power supply to the induction coil 54a when the temperature of the heating roller 53 reaches a preset upper limit temperature or higher. A configuration for preventing heating is also employed. Hereinafter, the configuration will be described.
In the fixing device 5, since the heating roller 53 is induction heated by the induction heating unit 54 disposed so as to cover a predetermined area on the outer periphery of the heating roller 53, a position where the induction heating is performed (hereinafter referred to as “induction”). The thermistor 78 cannot be disposed in the vicinity of the “heating position”.
Therefore, the thermistor 78 is disposed at a position away from the induction heating position of the heating roller 53, and detects the temperature of the heating roller 53 at the position. Specifically, the thermistor 78 is disposed on the outer periphery of the heating roller 53 on the opposite side of the induction heating position and not covered with the induction heating unit 54. The thermistor 78 is a contact-type temperature sensor that detects the temperature of the heating roller 53 by bringing a heat sensitive part into contact with the outer peripheral surface of the heating roller 53.

The temperature of the heating roller 53 detected by the thermistor 78 is input to the CPU 71 and the fixing high temperature detection circuit 75. The CPU 71 executes fixing temperature control for maintaining the temperature of the fixing belt 52 at a predetermined fixing temperature by controlling a switching signal output to the IGBT 74 based on the temperature detected by the thermistor 78.
On the other hand, the fixing high temperature detection circuit 75 determines whether or not the temperature of the heating roller 53 detected by the thermistor 78 has reached a preset upper set temperature or higher, and has reached the upper set temperature or higher. On the condition that the relay coil 76 is energized, the power supply to the induction coil 54a is cut off. Here, the fixing high temperature detection circuit 75 when performing such control is an example of a second power supply cutoff means. The upper limit set temperature is set in advance as a temperature for detecting an abnormal heating state of the heating roller 53.
The relay coil 76 is connected to a relay contact 77 provided on a power supply path that continues from the primary power source (not shown) through the IGBT 74 to the induction coil 54a, depending on whether or not energization is controlled by the fixing high temperature detection circuit 75. ON / OFF is switched to establish / cut off the power supply path.
The fixing high temperature detection circuit 75 may be any circuit that can forcibly cut off the power supply to the induction coil 54a, and is not limited to that described here. For example, the switching of the input path of the switching signal from the IGBT gate driving circuit 72 to the IGBT 74 is switched to control the driving of the IGBT 74 and to switch the power supply to the induction coil 54a. There may be.

By the way, the upper limit set temperature, which is a determination index for switching the presence / absence of power supply to the induction coil 54a in the fixing high temperature detection circuit 75, normally assumes the case where the heating roller 53 is rotating normally. Is set.
However, when the heating roller 53 is rotating normally, a portion heated at the induction heating position of the heating roller 53 reaches the thermistor 78, but the heating roller 53 stops due to some abnormality. In other words, the same part of the heating roller 53 is locally heated at the induction heating position of the heating roller 53. In this case, abnormal heating is detected until the temperature of the heating roller 53 detected at the installation position of the thermistor 78 by heat conduction from the induction heating position of the heating roller 53 reaches the upper limit set temperature. Therefore, there is a problem that the discovery of the abnormal heating is delayed.
Therefore, in the fixing device 5 of the copying machine X according to the embodiment of the present invention, when the heating roller 53 stops due to some abnormality, abnormal heating of the heating roller 53 is detected at an early stage to the induction coil 54a. The upper limit set temperature changing circuit 90 is provided in order to cut off the power supply and stop the induction heating of the heating roller 53.

The upper limit set temperature changing circuit 90 changes the upper limit set temperature which is a determination index in the fixing high temperature detection circuit 75 according to the detection result by the pulse detection circuit 81. Specifically, the upper limit set temperature changing circuit 90 determines the upper limit set temperature when the pulse detection circuit 81 detects the stop of the heating roller 53, and the pulse detection circuit 81 rotates the heating roller 53. Is set lower than the upper limit set temperature when. Here, the upper limit set temperature changing circuit 90 when performing such setting is an example of the upper limit set temperature changing means.
For example, when the fixing temperature control is performed by the CPU 71 so that the temperature of the heating roller 53 detected by the thermistor 78 is 180 ° C., the upper limit set temperature changing circuit 90 sets the upper limit set temperature to When the heating roller 53 is rotating, the temperature is set to 250 ° C., and when the heating roller 53 is stopped, the temperature is set to 200 ° C.

Here, a specific configuration example of the fixing high temperature detecting circuit 75 and the upper limit set temperature changing circuit 90 will be described with reference to FIG.
As shown in FIG. 3, the fixing high temperature detection circuit 75 corresponds to a detection voltage corresponding to the temperature of the heating roller 53 detected by the thermistor 78 and the upper limit set temperature input from a predetermined power source Vcc. When the detected voltage of the thermistor 78 reaches the reference voltage or higher, it is determined that the temperature of the heating roller 53 has reached the upper limit set temperature or higher, and a detection signal is sent to the relay coil 76. Is a comparator that outputs.
On the other hand, the upper limit set temperature changing circuit 90 is a voltage dividing circuit having three resistors R1 to R3 for dividing an input voltage from the predetermined power source Vcc. In the upper limit set temperature changing circuit 90, a voltage value inputted as the reference voltage to the fixing high temperature detecting circuit 75 from between the resistor R1 and the resistor R2 is inputted between the resistor R2 and the resistor R3. It changes according to the output signal of the pulse detection circuit 81. Specifically, the upper limit set temperature changing circuit 90 detects the stop of the heating roller 53 as compared with the case where the rotation of the heating roller 53 is detected and the “H” signal is input from the pulse detection circuit 81. When the “L” signal is input from the pulse detection circuit 81, the reference voltage value input to the fixing high temperature detection circuit 75 becomes lower.
As described above, the upper limit set temperature changing circuit 90 is configured so that the reference voltage input to the fixing high temperature detecting circuit 75 when the heating roller 53 is rotated and the heating roller 53 are set according to the detection result of the pulse detecting circuit 81. By switching the reference voltage input to the fixing high temperature detection circuit 75 at the time of stopping, the upper limit setting temperature in the fixing high temperature detection circuit 75 is set to a first upper limit setting that is set in advance corresponding to the rotation of the heating roller 53. The temperature is switched between a temperature (for example, 250 ° C.) and a second upper limit set temperature (for example, 200 ° C.) that is lower than the first upper limit set temperature that is set in advance when the heating roller 53 is stopped.

As described above, in the fixing device 5, when the heating roller 53 stops abnormally, thereafter, the upper limit set temperature serving as a determination index in the fixing high temperature detection circuit 75 is higher than that during the rotation of the heating roller 53. Since it is set low, abnormal heating of the heating roller 53 can be detected at an early stage to prevent the abnormal heating from continuing.
Therefore, in the fixing device 5, even if some abnormality occurs in the gate power supply control circuit 73, the IGBT gate drive circuit 72, etc., and the power supply to the induction coil 54 a is not cut off by them, the upper limit set temperature Based on the upper limit set temperature corresponding to when the heating roller 53 is stopped after being changed by the changing circuit 90, the fixing high temperature detecting circuit 75 cuts off the power supply to the induction coil 54a. Therefore, local abnormal heating of the heating roller 53 and the fixing belt 52 by the induction coil 54a can be reliably and early prevented, and safety can be improved.

1 is a block diagram showing a schematic configuration of a copier according to an embodiment of the present invention. 1 is a schematic configuration diagram showing a schematic configuration of a fixing device according to an embodiment of the present invention. FIG. 3 is a circuit diagram for explaining an example of an upper limit set temperature changing circuit provided in the fixing device according to the embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Operation display part 2 ... Image reading part 3 ... Image processing part 4 ... Image forming part 5 ... Fixing device 51 ... Fixing roller 51a ... Pressure roller 52 ... Fixing belt 53 ... Heating roller 54 ... Induction heating part (induction heating means) Example)
54a ... induction coil 54b ... magnetic core 6 ... control unit 7 ... heating control unit 71 ... CPU
72 ... IGBT gate drive circuit 73 ... Gate power supply control circuit (an example of first power supply cutoff means)
74 ... IGBT (an example of switching means)
75. Fixing high temperature detection circuit (example of second power supply cutoff means)
76: Relay coil 77 ... Relay contact 78 ... Thermistor (an example of roller temperature detecting means)
80: Rotary encoder 81: Pulse detection circuit (an example of roller rotation detection means)
90 ... Upper limit set temperature changing circuit (an example of upper limit set temperature changing means)
X: Copier (an example of an image forming apparatus)

Claims (4)

A fixing roller that is rotationally driven by a predetermined driving means; a heating roller that is rotationally driven by a driving force transmitted from the fixing roller via a fixing belt stretched between the fixing rollers; and the heating roller An induction heating means which is arranged so as to cover a predetermined area on the outer periphery of the paper and receives the power supply to induction-heat the heating roller and / or the fixing belt; and a roller rotation detection means for detecting rotation and stop of the heating roller; A fixing device comprising: a first power supply shut-off means for shutting off the power supply to the induction heating means on the condition that the stop of the heating roller is detected by the roller rotation detecting means,
Roller temperature detecting means for detecting the temperature of the heating roller at a position separated from a position where induction heating of the heating roller and / or the fixing belt by the induction heating means is performed;
Second power supply shut-off means for shutting off power supply to the induction heating means on condition that the temperature detected by the roller temperature detecting means has reached or exceeded a preset upper limit set temperature;
The upper limit set temperature when the roller rotation detecting unit detects the stop of the heating roller is set lower than the upper limit set temperature when the roller detecting unit detects the rotation of the heating roller. Means for changing the upper limit set temperature;
A fixing device comprising:   The upper limit set temperature changing means is set to be higher than a first upper limit set temperature preset corresponding to the rotation of the heating roller and the first upper limit preset temperature preset corresponding to the stop of the heating roller. The fixing device according to claim 1, wherein the second upper limit set temperature is switched according to a detection result by the roller rotation detection unit.   Either one of the first power supply cutoff means and the second power supply cutoff means is a path cutoff means for blocking the power supply path to the induction heating means, and the other is for the induction heating means. The fixing device according to claim 1, wherein the fixing device is a switching drive stop unit that stops a switching signal to a switching unit that controls supply power.   An image forming apparatus comprising the fixing device according to claim 1.

Images