JP2006119386A - Image heating apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device of a heat induction system, which has a means for avoiding causing a paper non-passage section to rise in temperature due to the size of a recording material being passed along a heat roller. <P>SOLUTION: The image heating apparatus includes the fixing device of the induction heat system, and a shielding means for shielding from a magnetic flux. The shielding means is driven by a temperature difference between the middle and each end of the fixing device. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus including an induction heating type fixing device using heat generated by an eddy current generated in a conductive member by a magnetic field generated by energizing a coil.

  In an image forming apparatus such as a copying machine, a facsimile machine, or a printer, image information to be generated is optically converted into an electrostatic latent image on a photosensitive drum, developed on the latent image with toner, and the above-described toner image is formed on a recording material. An electrophotographic system in which an image is formed on a recording material by transferring and passing a fixing device that heats and pressurizes the recording material on which the toner image is placed is widely used.

  In the above-described fixing device, the recording material is sandwiched and conveyed through the recording material by passing the pressure on the recording material and pressurizing, and further, the roller has a heating means, and the heating means generates heat, so that the toner on the recording material is melted by heat. There are many image forming apparatuses having a configuration for fixing a toner image on a recording material. In particular, in an image forming apparatus that performs high-speed image formation with a large number of images formed per unit time, heat roller fixing using a halogen lamp is generally used.

  Conventionally, as the fixing unit, a heating unit such as a halogen lamp is disposed inside the roller, and the surface of the roller is heated by radiant heat from the heating unit (hereinafter referred to as a halogen method). ).

  However, the halogen type fixing means requires a relatively long time until the roller surface reaches an appropriate temperature. There are also several problems such as poor conversion efficiency between the electric power supplied to the heat generating means and the amount of heat generated.

  In order to solve these problems, an induction heating method (hereinafter referred to as IH method) fixing means has been proposed.

  The IH type fixing unit has a configuration in which a coil is disposed inside a fixing unit made of a metal conductor. A high-frequency current is passed through the aforementioned coil, and an induced eddy current is generated in the fixing means of the metal conductor by a high-frequency magnetic field generated by this high-frequency current. The induced eddy current generates heat in the fixing means itself due to the skin resistance of the metal conductor.

  Since this IH type fixing means generates heat directly, it is possible to raise the temperature of the fixing means in a relatively short time compared to indirect heating using a halogen lamp or the like. Further, there is a feature that energy loss due to heat generation or light leakage in portions other than the fixing unit is small, and conversion efficiency between the electric power supplied to the heating unit and the amount of heat generated is good.

  By the way, in the halogen type or IH type fixing means, when a recording material having a width smaller than the sheet passing width is continuously passed through the fixing means, the recording material passes through the area where heat is taken away by the recording material, and the recording material This occurs in areas where heat is not taken away. When the recording material is continuously passed, heat is supplied to the fixing means in order to improve the fixing property in the recording material passage portion. Similarly, heat is supplied to the non-sheet passing portion where the recording material is not deprived of heat. As a result, there arises a problem that the non-sheet passing portion overheats.

Therefore, in Japanese Patent Laid-Open No. 2002-40843, in order to prevent the temperature rise of the non-sheet passing portion of the fixing unit as described above, the coil is provided up to the end, and the amount of current flowing at the center and the end is approximately equal. In a heat fixing device, a configuration is disclosed in which a member that blocks a high-frequency magnetic field in a portion through which a recording material does not pass is installed between a fixing means of a metal conductor (hereinafter referred to as a shielding plate) and a coil.
JP 2002-40843 A

  Here, consider control of a fixing device adopting a configuration in which a member for blocking a high-frequency magnetic field in a portion where the recording material does not pass is installed between a fixing means of a metal conductor and a coil. At this time, when the shielding plate is driven in accordance with the paper width during the sheet passing, the shielding is continuously performed while the paper width narrower than the heating surface of the fixing device is continuously passing, so that the shielding is performed. The temperature of the part where it is is not raised easily. As a result, the temperature at the position shielded by the shielding plate by the fixing means is significantly lower than the fixing temperature. In such a situation, when a recording material having a paper width that passes through the shielding position passes, fixing failure occurs.

  Further, when the shielding plate is driven in accordance with the paper width of the recording material being passed in the image forming output process, when the recording material having different paper widths alternately passes through the fixing device, the shielding plate is controlled every time the paper width size is switched. It is necessary and processing becomes complicated. Further, since the number of times of driving the shielding plate increases, the life of the motor, which is a means for driving the shielding plate, and the shielding plate itself is consumed.

  As described above, in the configuration in which the operation of the shielding member is performed according to the size of the recording material that passes the sheet, problems such as poor fixing and shortening of the life occur. Therefore, if the operation is performed when the temperature rises, the fixing defect does not occur. The number of operations can be reduced, and the above problem can be solved.

  The present invention includes a heating member that has a conductive layer and heats an unfixed toner image on a recording material, and a coil that generates a magnetic field by energization. The conductive layer generates heat due to an eddy current generated by the magnetic field generated by the coil. The image heating apparatus includes a shielding unit that is located between the coil and the heating member and shields a magnetic field generated from the coil, and a plurality of temperature detectors that detect the surface temperature of the heating member at different positions. The shielding means is operated using a detection result obtained by any one of the temperature detectors.

  With this configuration, the temperature of the non-sheet passing portion can be increased with a small number of operations of the shielding plate by driving the shielding plate not by the paper width of the recording material during image formation output but by the surface temperature measured at different positions of the fixing unit. Can be prevented.

  Embodiments of the present invention will be specifically described below with reference to the drawings.

  FIG. 1 is an internal configuration diagram of an embodiment to which an image forming apparatus of the present invention is applied. The image processing apparatus includes an image output unit 10 that is an apparatus that outputs a document image on a recording material, an image input unit 11 that is an apparatus that reads image information from the document, and an automatic mounted on the image input unit 11. A document feeder 12 and a sorter 13 for sorting and ejecting copy sheets discharged from the image output unit 10 into a plurality of bins are provided.

  This image forming apparatus is a digital copying machine, which is pixelated by a CCD of an image input unit 11 which is an apparatus for reading image information from a document, and is read into the apparatus as image information. After necessary image processing is performed, an image memory Stored in The image information is transferred to the main body image output unit 10, and the image is reproduced and recorded on the recording material.

  The image input unit 11 includes a light source 21 that scans while irradiating a document placed on a document table on the upper surface of the input unit. The light source 21 obtains a driving force from an optical system motor (not shown) and reciprocates in the left-right direction in FIG. The light generated from the light source 21 is reflected by the stacked originals to obtain an optical image. The optical image is transmitted to the CCD 26 via the mirrors 22, 23 and 24 and the lens 25. The mirrors 22, 23, and 24 are driven integrally with the light source 21. The CCD 26 is composed of an element that converts light into an electrical signal, and an optical image transmitted by the function of the element is converted into an electrical signal and further converted into a digital signal.

  Each adjustment value in these image input devices is stored in a backup storage device.

  The image information of the read original is subjected to various correction processes and image processes desired by the user, and is stored in an image memory (not shown).

  Each adjustment value in these image processing apparatuses is stored in a backup storage device.

  The image output unit 10 reads the image information stored in the image memory, reconverts the digital signal into an analog signal, and further amplifies the output value to an appropriate output value by an exposure control unit (not shown). Is converted to The optical signal propagates through the scanner 28, the lens 29 and the mirror 30, and is irradiated onto the photosensitive drum 31 charged by the charging means for charging the surface of the photosensitive drum as an image carrier, thereby forming an electrostatic latent image. Is done. The electrostatic latent image is formed with a toner image by a developing unit that forms a toner image, and is transferred onto a recording material conveyed through the main body by a transfer unit that transfers the image from the photosensitive drum onto the recording material.

  The recording material to which the toner image has been transferred is conveyed to the fixing unit 32. The fixing unit 32 is a pressure roller that is a pressure member that forms a nip portion that sandwiches and conveys the recording material by contacting the heating roller with a heating roller that heats and fixes the toner image on the recording material with heat. It consists of. The fixing unit 32 includes a coil for induction heating. In addition, the toner image is fixed to the recording material by heating and pressurizing the recording material with the fixing unit and the pressure roller. Details of the fixing means 32 will be described with reference to FIG.

  After fixing, the recording material is conveyed to the sorter 13.

  The sorter 13 is a device installed on the left side of the main body image output unit 10, and performs a process of sorting the recording material output from the image output unit 10 to the paper discharge tray 33 and discharging the recording material. The paper discharge tray is controlled by the main body control unit (not shown), and the output recording material paper is discharged to an arbitrary paper discharge tray designated by the control unit.

  The paper feed trays 34 and 35 are located in the lower part of the main body, and can store recording materials to some extent. The control unit conveys the recording material accumulated from the paper feed trays 34 and 35 and outputs an image. The paper feed deck 36 is a device installed on the left side of the main body image output unit 10 and can store a large amount of recording materials. As with the paper feed trays 34 and 35, the recording material accumulated by the control unit is conveyed and an image is output.

  The paper is set on the paper feed trays 34 and 35 by the operator. At this time, the paper size and orientation are set, and this data is stored in the backup storage device.

  On the left side of the main body image output unit 10, a manual feed tray 37 that allows an operator to relatively easily feed a small number of arbitrary types of recording materials is installed. This manual feed tray is also used when special recording paper such as OHP sheet, thick paper, postcard size paper is used.

  The paper feed rollers 38, 39, 40, 41, and 42 are paper transport rollers, and each roller plays a role of actually transporting the recording material when paper is fed for image output processing.

  FIG. 2 is a diagram showing details of the fixing unit 32. However, only the portion (heating roller 104) that performs electromagnetic induction heating, which is a feature of the present invention, is shown.

  The fixing unit 32 includes a heating roller 104 and a pressure roller (not shown), and is driven to rotate by being supplied with a driving force from a fixing motor 220 that is a driving unit for driving the heating roller. Further, when the recording material on which the toner image is formed passes between the heating roller and the pressure roller, the toner image on the recording material is heated and pressurized, and the toner image is fixed on the recording material.

  Further, in order to reproduce a stable image on the recording material, the surface temperature of the heating roller 104 is required to be an optimum temperature for the fixing action. For this reason, in order to detect the surface temperature of the heating roller 104, the first thermistor 312 which is the first temperature detecting body for detecting the temperature of the heating roller at the center of the heating roller 104 and the end of the heating roller 104 are heated. A second thermistor 314 is installed as a second temperature detector for detecting the temperature of the roller. In the present embodiment, it is assumed that the second thermistor 314 is disposed outside the area where the recording material can pass.

  The first thermistor 312 and the second thermistor 314 are devices that detect the temperature at the installation position of the heating roller 104, respectively.

  FIG. 3 is a view showing details of the inside of the heating roller 104.

  First, the heating roller 104 will be described. The heating roller of this embodiment has a two-layer structure, and a release layer comprising a metal layer such as iron as a conductive layer in the lower layer and a fluororesin or the like having a high release property with respect to the toner in the upper layer of the metal layer Consists of layers. In order to increase the heat capacity, an elastic layer such as rubber may be provided between the metal layer and the release layer.

  Here, in the image forming apparatus of the present embodiment, the conveyance control is executed so that the center of the recording material is along the center of the fixing unit 32 with the center of the fixing unit 32 as a reference.

  When a high frequency current is input to the coil 108 by energization means, a magnetic flux is generated from the coil 108. The generated magnetic flux is guided to the heating roller 104 along the core 106 such as ferrite, and an induced eddy current is generated by the magnetic flux in the metal layer in the heating roller 104. Due to this induced eddy current and the surface resistance of the heating roller 104, the heating roller 104 itself generates heat.

  Further, the above-described ferrite core 106 is installed with substantially the same length as the heating surface of the heating roller 104 so as to uniformly heat the heating roller 104.

  For this reason, when a recording material having approximately the same size as the width of the heat generating surface of the heating roller due to the induced eddy current passes through the fixing means 32, the amount of heat generated in the non-sheet passing area is small. However, when a recording material having a size smaller than the width of the heat generating surface of the heating roller 104 passes through the fixing unit 32, the heat at the center of the fixing unit 32 is taken away by the passage of the recording material, but both ends where the recording material does not pass. Continues to rise in temperature due to heating of the induced eddy current. The reason is that in the present embodiment, since the coil flows current to heat both the central portion and the end portion, when the same amount of heat is generated in the heating roller, the central portion is deprived of heat by the recording material. This is because the end portion which is a non-sheet passing portion takes less heat than the central portion.

  Therefore, when the image forming apparatus continuously passes a recording material having a size smaller than the width of the heating surface of the heating roller 104, the temperature of the fixing unit 32 becomes non-uniform. If the recording material passes through the fixing means 32 in this non-uniform state, it causes wrinkles on the recording material.

  On the other hand, a shielding member made of aluminum, copper or the like will be described. The shielding member generates an eddy current due to the magnetic flux, but is preferably a low-resistance metal in order to reduce the amount of heat generated by the generated eddy current. The reason is that even if the magnetic flux is shielded, a large amount of heat is transmitted to the heating roller due to the heat generated by the shielding member itself. Therefore, it is desirable that the resistance value of the shielding member is lower than the resistance value of the conductive layer of the heating member. In this embodiment, if the aluminum shielding plate 110 is processed and placed between the heating roller 104 and the ferrite core 108, the passage of magnetic flux is hindered. As a result, the generation of eddy currents in the metal layer in the heating roller 104 can be suppressed, and the heat generation of the heating roller 104 can be reduced.

  As shown in the figure, the shielding plate 110 made of aluminum has a concave shape corresponding to a predetermined paper width. The shielding plate 110 is driven by shielding member driving means such as a stepping motor 210.

  As a result, the shielding plate 110 is driven by the stepping motor 210 when the above-described temperature rise at the end of the fixing unit, which occurs when the recording material having a relatively narrow paper width is continuously fixed, is shielded. The plate 110 can shield the gap between the ferrite core 106 and the heating roller 104 and prevent the end from being heated.

  Reference numeral 410 denotes a position detection sensor as a shielding plate position detector for detecting the position of the shielding plate, and 420 denotes a slit. The slit 420 is driven in synchronization with the shielding plate 110, and when the slit 420 comes on the position detection sensor 410, the shielding plate 110 is in a position where the ferrite core 106 is not completely shielded (hereinafter referred to as home position position). That is, the position detection sensor 410 can detect the home position by detecting the slit 420.

  FIG. 4 is a graph showing the surface temperature distribution of the heating roller 104 when the recording material having a paper width narrower than the heating range of the heating roller 104 is conveyed without driving the shielding plate in the image forming apparatus.

  As shown in the drawing, the surface temperature distribution of the heating roller 104 when the recording material having a paper width narrower than the heating range of the heating roller 104 is conveyed without driving the shielding plate is as follows. However, the non-sheet passing portion becomes higher. This is because the way in which heat is deprived differs between the central portion and the end portion.

  Incidentally, in order to fix the toner image formed on the recording material to the recording material as a stable image, it is necessary to keep the temperature of the sheet passing range 1004 constant at the target temperature.

  Therefore, the temperature is detected by the first thermistor 312 installed in the center of the heating roller 104, the amount of heat supplied to the heating roller 104 is calculated from the difference from the target temperature, and the coil is energized from the calculation result. Predetermined energization is performed by energization control means for controlling the energization amount.

  However, the coil 108 and the ferrite core 106 are arranged so that the heating roller 104 heats not only the central part but also the end part. Therefore, if temperature control is executed in accordance with the temperature of the sheet passing range 1004, the non-sheet passing portion becomes high as shown in the figure.

  Such a high temperature state of the non-sheet passing portion may cause a failure of the fixing device itself or a device around the fixing device. In such a situation, when recording materials having different paper widths are passed, the fixing temperature is uneven, which may cause a negative effect on the fixed image on the recording material.

  FIG. 5 is a graph showing a temperature difference between the central portion and the end portion of the heating roller 104 when a recording material having a paper width narrower than the heating range of the heating roller 104 is conveyed in the image forming apparatus. The temperature of the central portion of the heating roller 104 is detected by the first thermistor 312. The end temperature is detected by the second thermistor 314. Here, ΔT is the difference in temperature between the second thermistor 314 and the first thermistor 312.

  As shown in the figure, when the recording material having a paper width narrower than the heating range of the heating roller 104 is continuously conveyed to the fixing device, the end temperature of the heating roller 104 increases as time passes. As a result, the value of ΔT, which is the temperature difference between the end and the center, also increases.

  In the control of the fixing device of the present invention, when ΔT exceeds the reference temperature T3 indicated by 1108, control is performed to drive the shielding plate 110 to a position between the ferrite core 106 and the heating roller 104. In this embodiment, the temperature difference from the second thermistor is used as a reference for the operation of the shielding plate. However, when the temperature of the end thermistor becomes a predetermined temperature higher than the target temperature of the heating roller, the shielding plate is operated. There is no problem.

  When the shielding plate 110 is positioned between the ferrite core 106 and the heating roller 104, the amount of heat supplied to the shielding portion is dramatically reduced. For this reason, the temperature at the end of the heating roller 104 gradually decreases, and ΔT also decreases accordingly.

  When the shielding plate 110 is located between the ferrite core 106 and the heating roller 104 and ΔT decreases and becomes lower than the reference temperature T4 lower than T3 indicated by 1110, the shielding plate 110 is moved to the ferrite core 106. And the drive to retract from between the heating roller 104 are executed. The reason is that if the temperature of the end portion is low, the heat in the central portion moves to the end portion side, so that the necessary heat generation amount is increased, resulting in thermal inefficiency. In this embodiment, the temperature difference from the thermistor 2 is used as a reference for the operation of the shielding plate. However, the shielding plate is operated when the temperature of the end thermistor falls below a predetermined temperature lower than the target temperature of the heating roller. There is no problem.

  Control of equalizing the temperature of the heating roller 104 is performed by driving the shielding plate 110 based on the temperature difference between the central portion and the end portion of the heating roller 104.

  FIG. 6 is a flowchart showing a control flow of the shielding plate 110. This process is executed after the start of print output by the image forming apparatus, and is executed at regular intervals. After the processing starts, the process proceeds to step 102.

  In step 102, a process of reading the temperature of the first thermistor 312, that is, the temperature of the central portion of the heating roller 104 is executed and stored in the variable Tmain. After processing, go to step 104.

  In step 104, a process of reading the temperature of the second thermistor 314, that is, the temperature of the central portion of the heating roller 104 is executed and stored in the variable Tsub. After the processing, the process proceeds to step 106.

  In step 106, a temperature difference ΔT between the temperature Tmain of the first thermistor 312 and the temperature Tsub of the second thermistor 314 is calculated. After the calculation, the process proceeds to step 108.

  In step 108, ΔT is compared with the threshold value T3, and the process is branched. That is, if ΔT is larger than T3, it is determined that the shielding plate 110 should be moved to the magnetic flux shielding position, and the process proceeds to step 112. If ΔT is equal to or less than T3, the process proceeds to step 110.

  In step 110, ΔT is compared with the threshold value T4, and the process is branched. That is, if ΔT is smaller than T4, it is determined that the shielding plate 110 should be retracted from the magnetic flux shielding position, and the process proceeds to step 114. If ΔT is equal to or greater than T4, this process ends.

  In step 112, the process is branched depending on whether or not the shielding plate 110 is at the magnetic flux shielding position. If the shielding plate 110 is not in the shielding position, the process proceeds to step 116, and a process for moving the shielding plate 110 to the magnetic flux shielding position is called. After the process, this process ends.

  In step 114, the processing is branched depending on whether or not the shielding plate 110 is in the non-magnetic flux shielding position. If the shielding plate 110 is in the shielding position, the process proceeds to step 118, and a process for retracting the shielding plate 118 from the magnetic flux shielding position is called. After the process, this process ends.

  This process is called at regular intervals while the image forming apparatus prints out, and the drive control of the shielding plate is executed.

  FIG. 7 is a flowchart showing a drive control flow of the shielding plate 110. This process is executed when the shielding plate control in steps 116 and 118 described in FIG. 6 is called. After the start of this process, the process proceeds to step 202.

  In step 202, a process for setting the number of drive pulses for driving the stepping motor 210 up to the motor drive position is called. Here, by setting the number of pulses supplied to the stepping motor 210, it is possible to control the shielding plate to stop at a specified position. After setting, go to step 204.

  In step 204, driving of the stepping motor 210 is started. The driving direction differs depending on whether the shielding position of the shielding plate or the retracting position of the shielding plate. After starting the motor drive, the process proceeds to step 206.

  In step 206, the processing is kept waiting until the driving for the number of drive pulses of the stepping motor 210 set in step 202 is completed. After the time corresponding to the number of drive pulses has elapsed, the process proceeds to step 208.

  In step 208, the process is branched depending on whether or not the slit 420 is detected by the position detection sensor 410. In other words, if the slit 420 is detected by the position detection sensor 410, the process proceeds to step 210. If the slit 420 is not detected by the position detection sensor 410, the process proceeds to step 212.

  In step 210, a process for notifying the control unit that the driving of the stepping motor 210 has been completed normally is performed. After the processing, this control is finished.

  In step 212, the position detection sensor 410 cannot detect the slit 420 even though the stepping motor 210 is driven and controlled by the drive pulse. Therefore, it is determined that the drive control of the shielding plate has not been performed correctly. The process of notifying the alarm is performed. After the processing, this control is finished.

  In the second embodiment, the basic configurations of the image forming apparatus and the fixing apparatus are the same.

  FIG. 8 is a diagram illustrating details of the fixing unit 32 in the second embodiment.

  As shown in the figure, a third thermistor 316 is installed in the fixing means 32 of the second embodiment. In the control of the shielding plate 110 in the second embodiment, either the second thermistor 314 or the third thermistor 316 is selected as the detection target of the temperature difference of the fixing unit described with reference to FIGS. In the present embodiment, either the second thermistor 314 or the third thermistor 316 is selected depending on the width of the recording material passing through the fixing unit 32. In this embodiment, the second thermistor is disposed outside the range of the recording material that can be passed, and the third thermistor is a non-sheet-passing portion area of a predetermined recording material width. Arranged within the range.

  That is, when a recording material having a paper width narrower than the first thermistor 312 and the third thermistor 316 installed at the center passes, the third thermistor 316 is selected. That is, a thermistor that is a non-sheet-passing portion region of the recording material that is being passed through and is located near the end in the width direction of the recording material is selected.

  This is because the temperature distribution in the sheet passing region of the recording material is desired to be as constant as possible, so that the detection accuracy of the temperature change in the portion near the end of the recording material is increased.

  Further, when a recording material having a paper width wider than the first thermistor 312 and the third thermistor 316 installed in the center passes, the second thermistor 314 is selected.

  The reason is that the third thermistor 316 serves as a paper passing area, and therefore it is desired to detect the temperature of the non-paper passing area.

  The drive control of the shielding plate 110 is the same as in FIGS.

  Also in the third embodiment, the basic configurations of the image forming apparatus and the fixing apparatus are the same.

  FIG. 9 is a diagram illustrating details of the inside of the heating roller 104 in the third embodiment.

  As shown in the figure, the shape of the shielding plate 110 is a shape capable of shielding between the ferrite core 106 and the heating roller 104 with an arbitrary width.

  Positioning control of the shielding plate 110 is executed such that the shielding plate SP described with reference to FIG. 6 has an optimum shielding width according to the width size of the recording material in the sheet.

  In the above-described embodiments, the black and white image forming apparatus has been described. However, there are a plurality of developing units, and there is an intermediate transfer member that is intermediately transferred before the toner image on the photosensitive member is transferred to the recording material. The present invention is naturally effective even in an image forming apparatus that has a color such that a toner image is transferred from a transfer member to a recording material.

  In the embodiment, the roller has been described. However, the same effect can naturally be obtained even with a belt configuration.

1 is an internal configuration diagram of an embodiment to which an image forming apparatus of the present invention is applied. 3 is a diagram showing details of a fixing unit 32. FIG. FIG. 4 is a diagram showing details of the inside of a heating roller 104. 3 is a graph showing a surface temperature distribution of a heating roller 104. 6 is a graph showing a temperature difference between a central portion and an end portion of the heating roller 104. It is the flowchart which showed the control flow of the shielding board 110. FIG. 5 is a flowchart showing a drive control flow of a shielding plate 110. FIG. 6 is a diagram illustrating details of a fixing unit 32 in Embodiment 2. FIG. 6 is a diagram illustrating details of the inside of a heating roller 104 in Embodiment 3.

Explanation of symbols

32 Fixing means 104 Heating roller 110 Shielding plate 312 First thermistor 312
314 Second thermistor

Claims (4)

  An image heating apparatus that includes a heating member that heats an unfixed toner image on a recording material and a coil that generates a magnetic field by energization, and the conductive layer generates heat due to an eddy current generated by the magnetic field generated by the coil The movable shielding means that is located between the coil and the heating member and shields the magnetic field generated from the coil, and a plurality of temperature detectors that detect the surface temperature of the heating member at different positions, An image heating apparatus, wherein the shielding means is operated using a detection result of any one of the temperature detectors.   2. The image heating apparatus according to claim 1, wherein the operation of the shielding unit is performed by a difference in detected temperatures between any two of the plurality of temperature detecting bodies.   3. The image heating apparatus according to claim 1, wherein a temperature detection body to be used is selected depending on a size of the recording material to be conveyed. The image heating apparatus according to any one of claims 1 to 3, wherein the shielding means changes a position using a detection result of the temperature detection body.

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