Patent Publication Number: US-8983352-B2

Title: Fixing device and image forming apparatus provided with the same

Description:
This application is based on applications No. 2011-217661 and No. 2012-191523 filed in Japan, the contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The present invention relates to a fixing device based on electromagnetic induction heating and an image forming apparatus provided with the fixing device. 
     (2) Description of the Related Art 
     Image forming apparatuses such as printers are provided with a fixing device that fixes an unfixed image, formed on a sheet and constituted by toner and the like, to the sheet by heating and applying pressure to the unfixed image when passing the sheet through a fixing nip. The fixing device may, for example, be based on electromagnetic induction heating. In such a fixing device, an excitation coil is provided on the outside of the running path of a fixing belt that has an induction heating layer. Magnetic flux that is generated by allowing alternating current to flow through the excitation coil is channeled to the induction heating layer, thereby heating the fixing belt. 
     In a fixing device based on electromagnetic induction heating, the heat capacity of the fixing belt can be set to a small value, thus allowing for a reduction in the time required for the temperature of the fixing belt to rise to a predetermined fixing temperature (i.e. the warm-up period). 
     As the heat capacity of the fixing belt decreases, however, the rate of temperature increase per unit of input power increases. Therefore, continuous use of small, narrow sheets leads to the problem that, compared to a region of the fixing belt through which the sheet passes (corresponding to the width of the sheet, and hereinafter referred to as the “sheet conveyance region”), the temperature rises in a region through which the sheet does not pass (hereinafter referred to as the “non-sheet conveyance region”) on either side of the sheet conveyance region in the direction of width of the belt. This leads to thermal destruction and deterioration of surrounding components. 
     One method for controlling a rise in temperature of the non-sheet conveyance region is to provide a self-adjusting temperature control function that reduces the amount of heat in the non-sheet conveyance region. With this method, a plate member (hereinafter referred to as a “heat-control plate”) is provided on the inside of the running path of the fixing belt, so that the fixing belt is between the excitation coil and the heat-control plate. The heat control plate includes a magnetic shunt alloy layer having a Curie point of a predetermined temperature higher than the fixing temperature. When the temperature of the non-sheet conveyance region rises to the Curie point, which is higher than the fixing temperature, the portion of the magnetic shunt alloy layer in the heat-control plate corresponding to the non-sheet conveyance region loses its magnetism. 
     The heat-control plate is in sliding contact with the inner circumferential surface of the fixing belt during rotation of the fixing belt and receives the load in the circumferential direction of the frictional force generated between the heat-control plate and the fixing belt. So that the heat-control plate does not change shape due to this load, the heat-control plate is strengthened by increasing the thickness of the heat-control plate, and by extending the edges of the heat-control plate in the direction of width of the belt beyond the edges of the fixing belt and securing the heat-control plate to the housing of the fixing device. 
     Increasing the thickness of the heat-control plate, however, causes a corresponding increase in the heat capacity of the heat-control plate, thus lowering the rate of temperature increase of the heat-control plate. This facilitates thermal transfer from the fixing belt to the heat-control plate, which in turn allows heat to escape to the device housing, thereby reducing the capability of the belt to rise in temperature. 
     SUMMARY OF THE INVENTION 
     An aspect of the present invention is a fixing device based on electromagnetic induction heating that, when a sheet with an unfixed image formed thereon passes through a fixing nip, applies heat and pressure to the sheet in order to fix the unfixed image thereto, the fixing device comprising: an endless belt driven to rotate and including an induction heating layer; a pressing member pressing against a surface of the belt to form the fixing nip between the pressing member and the surface of the belt; a magnetic flux generator provided outside of a running path of the belt and generating magnetic flux to cause the induction heating layer to heat; a heat-control plate provided inside of the running path of the belt and including a magnetic shunt alloy layer that loses magnetism upon exceeding a predetermined temperature higher than a fixing temperature; and a support member supporting the heat-control plate, wherein the heat-control plate includes a first region facing the magnetic flux generator with the belt therebetween and second regions extending continuously in a circumferential direction of the belt from opposite edges of the first region, and inside the running path of the belt, the support member is in contact with the heat-control plate at the second regions and not at the first region so as to support the heat-control plate at the second regions. 
     Another aspect of the present invention is an image forming apparatus comprising: an unfixed image forming unit forming an unfixed image on a sheet; and a fixing device fixing the unfixed image to the sheet by applying heat and pressure to the sheet when the sheet passes through a fixing nip, the fixing device comprising: an endless belt driven to rotate and including an induction heating layer; a pressing member pressing against a surface of the belt to form the fixing nip between the pressing member and the surface of the belt; a magnetic flux generator provided outside of a running path of the belt and generating magnetic flux to cause the induction heating layer to heat; a heat-control plate provided inside of the running path of the belt and including a magnetic shunt alloy layer that loses magnetism upon exceeding a predetermined temperature higher than a fixing temperature; and a support member supporting the heat-control plate, wherein the heat-control plate includes a first region facing the magnetic flux generator with the belt therebetween and second regions extending continuously in a circumferential direction of the belt from opposite edges of the first region, and inside the running path of the belt, the support member is in contact with the heat-control plate at the second regions and not at the first region so as to support the heat-control plate at the second regions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other objects, advantages and features of the invention will become apparent from the following description thereof taken in conjunction with the accompanying drawings which illustrate specific embodiments of the invention. 
       In the drawings: 
         FIG. 1  illustrates the overall structure of the printer; 
         FIG. 2  is a perspective view illustrating the structure of a fixing unit in the printer; 
         FIG. 3  is a lateral cross-section diagram illustrating the structure of the fixing unit; 
         FIG. 4  illustrates a cross-section of a fixing belt and a heat-control plate; 
         FIG. 5  is a schematic perspective view illustrating the structure of the heat-control plate and a support member; 
         FIG. 6  is a plan view of the heat-control plate being supported by the support member as viewed from the direction indicated by the arrow H in  FIG. 5 ; 
         FIG. 7  is a cross-section diagram of the fixing unit along a line from F to Fin  FIG. 3 ; 
         FIG. 8  illustrates the results of an experiment on temperature rise characteristics of the fixing belt when adopting the structure of the heat-control plate in a working example and the structure of the heat-control plate in two comparative examples; 
         FIG. 9  is a cross-section diagram of one end of the fixing roller in a modification in which the heat-control plate and the support member are fastened with eyelets; 
         FIG. 10  is an exploded perspective view of the modification that adopts eyelets; and 
         FIG. 11  is an exploded perspective view of a modification in which the heat-control plate and the support member are fastened with rivets. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following describes an embodiment of a fixing device and an image forming apparatus according to the present invention, using a tandem-type color printer (hereinafter simply referred to as a “printer”) as an example. 
     1. Overall Structure of Printer 
       FIG. 1  illustrates the overall structure of a printer  1 . 
     As illustrated in  FIG. 1 , the printer  1  forms images using well-known electrophotography. The printer  1  is provided with an image forming unit  10 , a belt conveyance unit  20 , a feed unit  30 , and a fixing unit  40 . The printer  1  is connected to a network (such as a LAN). Upon receiving an instruction for a print job from an external terminal device (not shown in the figures), the printer  1  performs color image formation based on the instruction using the colors yellow (Y), magenta (M), cyan (C), and black (K). 
     The image forming unit  10  is provided with imaging units  10 Y through  10 K, corresponding to the colors Y through K. The imaging unit  10 Y is provided with a photoconductor drum  11 Y and, disposed around the photoconductor drum  11 Y, a charger  12 Y, an exposure unit  13 Y, a developer  14 Y, a first transfer roller  15 Y, a cleaner for cleaning the photoconductor drum  11 Y, and the like. A Y-color toner image is formed on the photoconductor drum  11 Y after completing well-known charging, exposure, and developing processes. The other imaging units  10 M through  10 K have a similar structure, and toner images of corresponding colors are formed on the photoconductor drums  11 M through  11 K. 
     The belt conveyance unit  20  is provided with an intermediate transfer belt  21  that rotates in the direction indicated by the arrow. 
     The feed unit  30  feeds recording sheets S from a paper cassette to a conveyance path  35  one sheet at a time. 
     At transfer positions on the photoconductor drums  11 Y through  11 K, the toner images formed on the photoconductor drums  11 Y through  11 K undergo primary transfer to the rotating intermediate transfer belt  21  due to the effect of an electrostatic force from the electrical field produced between the first transfer rollers  15 Y through  15 K and the respective photoconductor drums  11 Y through  11 K. The timing of this image creation for each color is shifted so that the toner images are overlapped on the same position along the intermediate transfer belt  21 . 
     In coordination with the timing of image creation, a sheet S is fed from the feed unit  30  and is transported while sandwiched between the intermediate transfer belt  21  and a secondary transfer roller  22  that presses against the intermediate transfer belt  21 . The toner images of various colors simultaneously undergo secondary transfer to the sheet S due to the effect of an electrostatic force from the electrical field produced by secondary transfer voltage applied to the secondary transfer roller  22 . The resulting toner image on the sheet S is an unfixed image. The image forming unit  10 , the belt conveyance unit  20 , and the secondary transfer roller  22  constitute an unfixed image forming unit  50  that faints the unfixed image on the sheet S. After secondary transfer, the sheet S is transported to the fixing unit  40 . 
     The fixing unit  40  is based on electromagnetic induction heating and is provided with a fixing belt  101 . The fixing unit  40  uses heat and pressure to fix the toner images of various colors formed on the sheet S by secondary transfer of the unfixed image. After fixing, the sheet S is ejected out of the device by a pair of discharge rollers  38  and is stored in a storage tray  39 . 
     2. Structure of Fixing Unit  40   
       FIG. 2  is a perspective view of the structure of the fixing unit  40 , and  FIG. 3  is a cross-section diagram of the structure of the fixing unit  40 . Note that in  FIG. 2 , for the sake of convenience, the fixing unit  40  is depicted with a portion thereof cut away. 
     As shown in  FIGS. 2 and 3 , the fixing unit  40  is provided with an endless fixing belt  101 , a fixing roller  102 , a pressing roller  103 , a magnetic flux generator  104 , a heat-control plate  105 , a support member  106 , and the like. 
     Structure of Fixing Belt  101   
     The fixing belt  101  is a shape-preserving tube that elastically deforms upon application of a certain force in the radial direction and that returns from the deformed state, through its own restorative force, to a tubular shape when application of the external force ceases. 
       FIG. 4  shows a cross-section of the fixing belt  101  along a line from E to E in  FIG. 3 . A releasing layer  111 , an elastic layer  112 , and an induction heating layer  113  are layered in this order from the surface of the fixing belt  101 . The releasing layer  111  is, for example, a 20 μm thick layer of PFA (tetrafluoroethylene perfluoroalkoxy vinyl ether copolymer). The elastic layer  112  is, for example, a 200 μm thick layer of silicone rubber, fluorine-containing rubber, or the like. 
     The induction heating layer  113  is, for example, a 40 μm thick layer of nickel or the like and heats up due to magnetic flux produced by the magnetic flux generator  104 . Note that the induction heating layer  113  is not limited to nickel. Another magnetic or non-magnetic material may be used, as long as the material is suitable for use with electromagnetic induction heating. 
     Returning to  FIG. 2 , the length of the fixing belt  101  in the direction of width (i.e. the axial direction of the fixing roller  102 , hereinafter referred to as the “direction of width of the belt”) is greater than the width of the maximum size sheet.  FIG. 2  shows a small sheet of paper, which is smaller than the maximum size, passing through a fixing nip N. 
     Structure of Fixing Roller  102   
     The fixing roller  102  is an elongated metal core  121  surrounded by an elastic layer  122  and is provided on the inside of the running path of the fixing belt  101  (the path along which the fixing belt  101  rotates, hereinafter referred to as the “belt running path”). 
     The metal core  121 , which acts as an axle, is for example formed from stainless steel, iron, aluminum, or the like. 
     The elastic layer  122  is provided to prevent heat of the fixing belt  101  from escaping to the metal core  121 . The elastic layer  122  is made from a heat resistant material with low thermal conductivity, such as a rubber or resin sponge. 
     When using a silicone sponge, the thickness may be in a range of 1 mm to 10 mm, or more preferably in a range of 2 mm to 7 mm. The hardness of the elastic layer  122  may, for example, be in a range of 20 degrees to 60 degrees in terms of Asker C hardness, or more preferably in a range of 30 degrees to 50 degrees. Note that the overall hardness of the fixing roller  102  is preferably in a range of 30 degrees to 90 degrees in terms of Asker C hardness. 
     Both ends of the metal core  121  of the fixing roller  102  in the shaft direction are rotatably supported by a device housing  191  ( FIG. 7 ) of the fixing unit  40  via bearings  125  ( FIG. 7 ) that act as a bearing member. 
     The outer diameter of the fixing roller  102  is smaller than the inner diameter of the fixing belt  101 . Since the fixing roller  102  and the fixing belt  101  are in contact at the fixing nip N, a gap  110  exists between the fixing roller  102  and the fixing belt  101  at all locations other than the fixing nip N. 
     By providing this gap  110 , the only region where the fixing belt  101  and the fixing roller  102  are in contact is the fixing nip N. Therefore, this structure reduces heat transfer loss that would occur in a structure without a gap, whereby a portion of the heat generated by the occurring when a portion of the heat emitted by the heating layer of the fixing belt  101  escapes through the metal core  121  of the fixing roller  102  to the device housing  191  that rotatably supports the metal core  121  at either edge. 
     Structure of Pressing Roller  103   
     The pressing roller  103  is an elongated metal core  131  surrounded by an elastic layer  132 , which is further surrounded by a releasing layer  133 . The pressing roller  103  is provided on the outside of the belt running path and presses against the fixing roller  102  with the fixing belt  101  sandwiched therebetween, thereby guaranteeing formation of the fixing nip N between the pressing roller  103  and the surface of the fixing belt  101 . 
     The metal core  131  is, for example, formed from stainless steel. The elastic layer  132  is, for example, formed from rubber. The releasing layer  133  is, for example, formed from a PFA tube. 
     Both ends of the metal core  131  of the pressing roller  103  in the shaft direction are rotatably supported by the device housing  191  ( FIG. 7 ) of the fixing unit  40  via a bearing member (not shown in the figures). Furthermore, the pressing roller  103  is rotated in the direction indicated by the arrow B in  FIG. 2  by transmission of a driving force from a driving motor (not shown in the figures). By rotation of the pressing roller  103 , the fixing belt  101  is driven to rotate in the direction indicated by the arrow A, and the fixing roller  102  is driven to rotate in the same direction. Note that alternatively, the fixing roller  102  may be the driving roller, with the fixing belt  101  and the pressing roller  103  being driven. 
     Structure of Magnetic Flux Generator  104   
     The magnetic flux generator  104  includes a coil bobbin  140 , an excitation coil  141 , and the like. The magnetic flux generator  104  is disposed on the outside of the running path of the fixing belt  101  at a position near the fixing belt  101  so as to face the fixing belt  101  along the direction of width of the belt. 
     The coil bobbin  140  is a plate-shaped member that includes an arc-shaped portion that curves along the circumferential direction of the fixing belt  101  (hereinafter referred to as the “circumferential direction of the belt”). Both ends of the coil bobbin  140  in the direction of width of the belt are fixed to the device housing  191 . 
     The position of the coil bobbin  140  is adjusted so that the gap between the coil bobbin  140  and the surface of the fixing belt  101  (the belt to bobbin distance) is a predetermined value within a range of 1 mm to 2 mm. At the opposite side of the coil bobbin  140  from the fixing belt  101 , a plurality of cores is provided. The cores are formed from ferrite, which has a high magnetic permeability, or the like. 
     The excitation coil  141  is elongated in the direction of width of the belt and is formed by a conducting wire wound around the coil bobbin  140 , with a cross-section of the excitation coil  141  being arc-shaped. The excitation coil  141  is slightly longer in the direction of length than the fixing belt  101  is in the direction of width of the belt. The excitation coil  141  is connected to an excitation coil drive circuit (not shown in the figures) that includes a well-known high-frequency inverter. Using AC power supplied by the excitation coil drive circuit, the excitation coil  141  generates magnetic flux for causing the induction heating layer  113  of the fixing belt  101  to heat up. 
     The magnetic flux generated by the excitation coil  141  is guided to the fixing belt  101  by the cores provided in the coil bobbin  140  and passes mainly through the portion of the induction heating layer  113  of the fixing belt  101  facing the magnetic flux generator  104 , producing an eddy current in this portion of the induction heating layer  113  and thereby causing the induction heating layer  113  to heat up. The amount of heat is set to be approximately even at any position along the width of a sheet. 
     The heat from this heated portion transfers to the pressing roller  103  and the like at the position of the fixing nip N due to rotation of the fixing belt  101 , thus causing the temperature of the fixing nip N region to rise. While not shown in the figures, a sensor for detecting the temperature of the fixing belt  101  is provided separately. The current temperature of the fixing belt  101  is detected via a detection signal from the sensor. Based on the detected temperature, the supply of power to the excitation coil  141  is controlled so that the temperature of the fixing nip N is maintained at a target fixing temperature, such as 180° C. When a sheet S is passed through the fixing nip N while the temperature of the fixing nip N is being maintained at the target fixing temperature, the unfixed toner image on the sheet S is thermally fixed to the sheet S by being heated and pressed. 
     Structure of Heat-Control Plate  105   
     The heat-control plate  105  is provided within the gap  110  between the fixing belt  101  and the fixing roller  102  at a position so as not to come into contact with the fixing roller  102 . The heat-control plate  105  is elongated in the direction of width of the belt, and the length thereof is approximately equal to the width of the fixing belt  101 . In addition to functioning as a heat-control member, the heat-control plate  105  also functions to guide the rotating fixing belt  101  in the circumferential direction by being in contact with the inner circumferential surface of the fixing belt  101 . 
     In the present embodiment, the heat-control plate  105  is in contact with the fixing belt  101  even while the fixing belt  101  is not rotating. Alternatively, a structure may be adopted wherein a slight gap exists between the heat-control plate  105  and the fixing belt  101  when the fixing belt  101  is not rotating, with the fixing belt  101  and the heat-control plate  105  coming into contact after the start of rotation due to vibration or the like of the fixing belt  101 . The heat-control plate  105  then guides the fixing belt  101  during such contact. 
     In the cross-section illustrated in  FIG. 3 , the heat-control plate  105  is formed as an arc that curves in the circumferential direction of the belt at approximately the same curvature as the fixing belt  101 . In the circumferential direction of the belt, the heat-control plate  105  includes a central region  150  (first region) and edge regions  151  and  152  (second regions) that extend continuously away from opposite edges of the central region  150  in the circumferential direction of the belt so as to sandwich the central region  150 . 
     The central region  150  of the heat-control plate  105  faces the magnetic flux generator  104  with the fixing belt  101  therebetween and is not in contact with the support member  106 . 
     The edge regions  151  and  152  of the heat-control plate  105  do not face the magnetic flux generator  104 . The edge region  151  is in contact with and is supported by an edge region  161  of the support member  106  in the circumferential direction of the belt. The edge region  152  is in contact with and is supported by an edge region  162  of the support member  106  in the circumferential direction of the belt. 
     As illustrated in  FIG. 4 , starting at the side of the heat-control plate  105  that is closer to the fixing belt  101 , a magnetic shunt alloy layer  115  and a low-resistance conductive layer  116  are layered in this order. The heat-control plate  105  is formed by a method such as plating or vapor deposition, but a method to mechanically bond the two layers may also be used. 
     The magnetic shunt alloy layer  115  is made from a material, such as permalloy, with a Curie point of a predetermined temperature higher than the fixing temperature. The magnetic shunt alloy layer  115  has a reversible magnetic property: the magnetic shunt alloy layer  115  changes from being magnetic to being non-magnetic (i.e. loses its magnetism) upon exceeding the Curie point and reverts to being magnetic once the temperature falls to the Curie point or below. 
     The relative permeability of the magnetic shunt alloy layer  115  may, for example, be in a range of 50 to 2000, or preferably in a range of 100 to 1000. The volume resistivity in a temperature range lower than the Curie point may, for example, be in a range of 2×10 −8  Ωm to 200×10 −8  Ωm, or preferably in a range of 5×10 −8  μm to 100×10 −8  μm. The thickness of the magnetic shunt alloy layer  115  may, for example, be in a range of 100 μm to 1000 μm, or preferably in a range of 200 μm to 600 μm. When the target fixing temperature is approximately 180° C., the Curie point may be in a range of 180° C. to 240° C., or preferably in a range of 190° C. to 220° C. The present embodiment uses a permalloy with a thickness of 400 μm and a Curie point of 220° C. 
     The Curie point can be adjusted by changing the ratio of the components of the permalloy, as well as by using an alloy that includes chrome, cobalt, molybdenum, or the like. Note that the material for the magnetic shunt alloy layer  115  is not limited to permalloy; another material may be used. 
     The low-resistance conductive layer  116  is formed from a material with a lower electrical resistance than the magnetic shunt alloy layer  115 , such as copper or aluminum. 
     The magnetic shunt alloy layer  115  and the low-resistance conductive layer  116  can prevent a rise in temperature when consecutively printing a number of small sheets. Specifically, consider portions P in  FIG. 2 , which are located at opposite edges of the fixing belt  101  in the direction of width of the belt and through which a small sheet S does not pass (i.e. non-sheet conveyance regions). During consecutive printing, when the temperature of the non-sheet conveyance regions P rises above the fixing temperature and reaches the Curie point, due to heat not being absorbed by the sheet S, the portions of the magnetic shunt alloy layer  115  corresponding to the non-sheet conveyance regions P change from being magnetic to being non-magnetic. When the portions of the magnetic shunt alloy layer  115  corresponding to the non-sheet conveyance regions P change to being non-magnetic, it becomes easier in the non-magnetic portions for magnetic flux from the magnetic flux generator  104  to flow from the induction heating layer  113  of the fixing belt  101  through the magnetic shunt alloy layer  115  of the heat-control plate  105  to the low-resistance conductive layer  116 . 
     At portions of the low-resistance conductive layer  116  that correspond to the non-sheet conveyance regions P, magnetic flux is generated in a direction to cancel the magnetic flux that passes through these corresponding portions. This generation of magnetic flux in a canceling direction represses the generation of heat in portions of the induction heating layer  113  in the fixing belt  101  that correspond to the non-sheet conveyance regions P (self-adjusting temperature control function). 
     Due to this self-adjusting temperature control function, the temperature at the portions corresponding to the non-sheet conveyance regions P does not greatly exceed the Curie point, thus preventing an excessive rise in temperature that would damage the fixing belt  101 . Note that while providing the low-resistance conductive layer  116  in combination with the magnetic shunt alloy layer  115  enhances the effectiveness of the self-adjusting temperature control function, a structure without the low-resistance conductive layer  116  may be adopted provided that the self-adjusting temperature control function is sufficiently effective without the low-resistance conductive layer  116 . 
     Structure of Support Member  106   
     As illustrated in  FIG. 3 , the support member  106  is provided in the gap  110  between the fixing belt  101  and the fixing roller  102  and has the function of supporting the heat-control plate  105 . The support member  106  touches neither the fixing belt  101  nor the fixing roller  102 . 
     The support member  106  is, for example, formed from stainless steel, iron, or aluminum. Any heat resistant material may be used, such as resin. 
     The support member  106  includes a central region  160  (third region) and edge regions  161  and  162  (fourth regions). A cross-section of the central region  160  is an arc that curves in the circumferential direction of the belt and has a smaller curvature than the heat-control plate  105 . The edge regions  161  and  162  extend continuously away from opposite edges of the central region  160  in the circumferential direction of the belt so as to sandwich the central region  160 . 
     The central region  160  of the support member  106  faces the central region  150  of the heat-control plate  105  and is farther from the magnetic flux generator  104  than the central region  150  of the heat-control plate  105  is. The central region  160  is not in contact with the central region  150  of the heat-control plate  105 . In other words, a gap  90  exists between the central region  150  of the heat-control plate  105  and the central region  160  of the support member  106 . 
     The edge regions  161  and  162  of the support member  106  support the edge regions  151  and  152  of the heat-control plate  105 . 
       FIG. 5  is a schematic perspective view illustrating the structure of the heat-control plate  105  and the support member  106  when only the heat-control plate  105  and the support member  106  are viewed in isolation from the direction indicated by the arrow G in  FIG. 3 . Note that  FIG. 5  only illustrates one side in the direction of width of the belt. While the other side is omitted from the figure, it has basically the same structure. 
     As illustrated in  FIG. 5 , the central region  150  of the heat-control plate  105  is curved in an arc, whereas the edge regions  151  and  152  are in the form of a flat plate. 
     Cuts  153  extending in the circumferential direction of the belt are made in the edge region  151  at a plurality of positions in the direction of width of the belt with a predetermined interval between adjacent cuts. The cuts  153  divide the edge region  151  into first sections  155  and second sections  156  that alternate in the direction of width of the belt. 
     Cuts are similarly formed in the other edge region  152 , dividing the edge region  152  into first sections  158  and second sections  159  that alternate in the direction of width of the belt. 
     The central region  160  of the support member  106  is curved in an arc, whereas the edge regions  161  and  162  are in the form of a flat plate. 
     The central region  160  is connected to one edge region  161  by a step  163 , and the central region and  160  is connected to the other edge region  162  by a step  164 . 
     Slits  165  elongated in the direction of width of the belt are bored into the step  163 , and slits  166  elongated in the direction of width of the belt are similarly bored into the step  164 . While a plurality of slits  165  and  166  are provided at intervals in the direction of width of the belt, only one of each is shown in  FIG. 5 . 
     In the above structure, with the first sections  155  of the heat-control plate  105  overlapping the upper surface of the edge region  161  of the support member  106 , and the second sections  156  of the heat-control plate  105  fit into the slits  165  of the support member  106 , the edge region  151  of the heat-control plate  105  is supported by the edge region  161  of the support member  106  by, for example, being bonded thereto. 
     Similarly, with the first sections  158  of the heat-control plate  105  overlapping the lower surface of the edge region  162  of the support member  106 , and the second sections  159  of the heat-control plate  105  fitted into the slits  166  of the support member  106 , the edge region  152  of the heat-control plate  105  is supported by the edge region  162  of the support member  106  by, for example, being bonded thereto. 
       FIG. 6  is a plan view of the edge region  151  of the heat-control plate  105  being supported by the edge region  161  of the support member  106  when viewed from the direction indicated by the arrow H in  FIG. 5 .  FIG. 6  also illustrates the positional relationship of the fixing roller  102 . In order to clearly illustrate how the edge region  151  of the heat-control plate  105  overlaps the edge region  161  of the support member  106 , the heat-control plate  105  and the support member  106  are depicted with different patterns. 
     As shown in  FIG. 6 , the first sections  155  within the edge region  151  of the heat-control plate  105  overlap the upper surface of the edge region  161  of the support member  106 . At the overlapping portions, the edge region  161  of the support member  106  is hidden from view by the edge region  151  of the heat-control plate  105 . The upper surface of the edge region  161  of the support member  106  can only be seen where the second sections  156  of the heat-control plate  105  are fitted into the slits  165  in the support member  106 . 
       FIG. 6  shows an example in which three second sections  156  are provided in the edge region  151  of the heat-control plate  105 , and three slits  165  corresponding to the three second sections  156  are provided in the support member  106 . While  FIG. 6  shows one edge region  151  of the heat-control plate  105  being supported by the edge region  161  of the support member  106 , the structure for the other edge region  152  of the heat-control plate  105  to be supported by the edge region  162  of the support member  106  is similar. 
     Returning to  FIG. 5 , L-shaped mounts  171  and  172  are provided at one end in the direction of width of the belt of the edge regions  161  and  162  of the support member  106 . These mounts  171  and  172  are fixed to the device housing  191  ( FIG. 7 ). 
       FIG. 7  is a cross-section diagram of the fixing unit  40  along a line from F to F in  FIG. 3 , showing one edge in the direction of width of the belt. 
     As shown in  FIG. 7 , the tips of the mounts  171  and  172  of the support member  106  are fixed by, for example, being bonded or screwed to the device housing  191 . The other end in the direction of width of the belt has the same structure. 
     This fixed support guarantees sufficient strength between the support member  106  and the device housing  191  so that the support member  106  will not deform due to friction that occurs between the fixing belt  101  and the heat-control plate  105  and that acts on the support member  106  via the heat-control plate  105 . 
     3. Working Example and Comparative Examples 
       FIG. 8  shows the results of an experiment on temperature rise characteristics of the fixing belt  101  when adopting the structure of the heat-control plate  105  in a working example and the structure of the heat-control plate in two comparative examples.  FIG. 8  shows the result of measuring the time it takes for the temperature at the central region of the fixing belt  101  in the direction of width of the belt to rise to 160° C. when the fixing belt  101  is rotated and the excitation coil  141  is supplied with 1400 W power. 
     In the working example, the magnetic shunt alloy layer  115  in the heat-control plate  105  is 0.4 mm thick, the low-resistance conductive layer  116  is 0.3 mm thick, and the support member  106  is 1.0 mm thick. 
     Comparative example 1 does not include the support member  106 ; instead, the low-resistance conductive layer also functions as a support member. In comparative example 1, the magnetic shunt alloy layer is 0.4 mm thick, and the low-resistance conductive layer is 0.8 mm thick, which is sufficient thickness to guarantee the strength of the heat-control plate. Both ends of the heat-control plate in the direction of width of the belt are fixed directly to the device housing  191 . 
     When both ends of the heat-control plate in the direction of width of the belt are fixed directly to the device housing  191  in this way (i.e. with a conventional structure), a moment that is the product of (i) the tension in the circumferential direction of the belt due to the friction between the rotating fixing belt and the heat-control plate and (ii) the length in the direction of width of the belt acts only on the ends of the heat-control plate in the direction of width of the belt. 
     When the action of the moment on the heat-control plate grows large, a force that twists the heat-control plate in the circumferential direction of the belt increases. Therefore, in order to prevent the heat-control plate from deforming, the thickness of the heat-control plate is increased. In comparative example 1, the heat-control plate is provided with increased strength by setting the thickness to 1.2 mm. 
     In comparative example 2, the heat-control plate  105  and the support member  106  of the working example are formed integrally (i.e. the gap  90  does not exist between the heat-control plate  105  and the support member  106 ). The magnetic shunt alloy layer, the low-resistance conductive layer, and the support member all have the same thickness as in the working example. 
       FIG. 8  clearly shows how the time for the temperature to rise is shorter for the working example than for comparative examples 1 and 2. 
     In comparative example 1, the heat capacity increases in correspondence with an increase, as compared to the working example, in the thickness of the low-resistance conductive layer in the heat-control plate. It can be inferred that the time for the temperature to rise increased in response to the increase in the heat capacity. 
     In comparative example 2, the magnetic shunt alloy layer, the low-resistance conductive layer, and the support member all have the same thickness as in the working example, but the heat-control plate and the support member are formed integrally, and no gap  90  exists between the central region  150  of the heat-control plate  105  (the portion facing the magnetic flux generator  104 ) and the central region  160  of the support member  106 . 
     When viewing the portion of the fixing belt  101  facing the magnetic flux generator  104  (the main region of heat generation), heat from the main region of heat generation of the fixing belt  101  transfers to the central region  150  of the heat-control plate  105  but does not easily transfer to the central region  160  of the support member  106  due to the gap  90  in the working example. On the other hand, in comparative example 2, the heat-control plate and the support member are integral, thus facilitating transfer of heat from the main region of heat generation of the fixing belt  101  to the support member via the heat-control plate. 
     In other words, whereas comparative example 2 includes a support member to which heat from the fixing belt  101  in the main region of heat generation of the fixing belt  101  is transferred, no such support member substantially exists in the working example. It can therefore be inferred that the heat capacity is greater in comparative example 2 than in the working example, thus causing the time for the temperature to rise to be longer in comparative example 2 than in the working example. 
     In the working example, the support member  106  that supports the heat-control plate  105  is not in contact with the heat-control plate  105  at the central region  150 , but rather supports the edge regions  151  and  152  of the heat-control plate  105 . Furthermore, the ends of the support member  106  in the direction of width of the belt are fixed to the device housing  191 . 
     Accordingly, in the main region of heat generation of the fixing belt  101 , the gap  90  between the heat-control plate  105  and the support member  106  makes it difficult for heat from the fixing belt  101  to transfer to the support member  106 . Substantially, then, the heat-control plate  105  becomes the only member that contributes to determining the heat capacity. As compared to comparative examples 1 and 2, the working example therefore has a reduced heat capacity and improved temperature rise characteristics. 
     Since the edge regions  151  and  152  of the heat-control plate  105  in the circumferential direction of the belt are supported by the support member  106 , the edge regions  151  and  152  are acted on by the tension in the circumferential direction of the belt due to the friction between the rotating fixing belt  101  and the heat-control plate  105 . This tension, however, is smaller than the above-described moment. It is therefore unnecessary to increase the strength of the heat-control plate  105  by increasing the thickness thereof, resulting in a thinner structure than comparative example 1. Furthermore, since the fixing belt  101  is elongated in the direction of width of the belt, the region of the heat-control plate  105  in the direction of width of the belt that is supported by the support member  106  can be expanded as compared to the structure of comparative example 1, in which the ends in the direction of width of the belt are supported by the device housing  191 . 
     This allows for a decrease in the thickness of the heat-control plate  105  within a range that both prevents deformation of the heat-control plate  105  and permits the self-adjusting temperature control function to operate. The overall result is a decrease in heat capacity while preventing deformation of the heat-control plate  105 . 
     Modifications 
     The present invention has been described based on the embodiment, but the present invention is of course in no way limited to the above embodiment. The following modifications are possible. 
     (1) In the above embodiment, the heat-control plate  105  is supported by the support member  106  by being bonded thereto, but any method of fastening the heat-control plate  105  and the support member  106  together may be used. For example, these two components may be fastened with eyelets. 
       FIG. 9  is a cross-section diagram of one end of a fixing roller  102  in a structure adopting fastening with eyelets, and  FIG. 10  is an exploded perspective view showing only the heat-control plate  105  and the support member  106 . As illustrated in  FIGS. 9 and 10 , the heat-control plate  105  and the support member  106  are provided with through-holes  211  and  212  through which eyelets  201  pass. 
     With the edge region  151  of the heat-control plate  105  and the edge region  161  of the support member  106  in overlap, the tip of each eyelet  201  is passed through the corresponding through-hole  211  of the heat-control plate  105  and the corresponding through-hole  212  of the support member  106  in this order. After a washer  202  is attached at the back side of the support member  106 , the tip of each eyelet  201  is then crimped in order to fasten the edge region  151  of the heat-control plate  105  and the edge region  161  of the support member  106  together. 
     Similarly, with the edge region  152  of the heat-control plate  105  and the edge region  162  of the support member  106  in overlap, the tip of each eyelet  201  is passed through the corresponding through-hole  211  of the heat-control plate  105  and the corresponding through-hole  212  of the support member  106  in this order. After a washer  202  is attached at the back side of the support member  106 , the tip of each eyelet  201  is then crimped in order to fasten the edge region  152  of the heat-control plate  105  and the edge region  162  of the support member  106  together. 
     The edge region  151  of the heat-control plate  105  and the edge region  161  of the support member  106  are fastened together with a gap of a predetermined size, for example approximately 0.1 mm, provided in the direction of thickness of the fastened portion (the edge regions  151  and  161 ). Such a gap is also provided between the edge region  152  of the heat-control plate  105  and the edge region  162  of the support member  106 . 
     Three fastening locations for the eyelets  201  are provided in the edge region  151  of the heat-control plate  105  and in the edge region  161  of the support member  106  at intervals in the direction of width of the belt. Similarly, three fastening locations are provided in the edge region  152  of the heat-control plate  105  and in the edge region  162  of the support member  106  at intervals in the direction of width of the belt. 
     Among these three fastening locations, the central fastening location is located at the center of the heat-control plate  105  in the direction of width of the belt, whereas the other two outer fastening locations are located equidistant from the central fastening location in the direction of width of the belt. 
     In  FIG. 10 , the central fastening location is labeled  200   a , and the outer fastening locations are labeled  200   b . The through-holes  211  and  212  for the central fastening location  200   a  are round, whereas the through-holes  211  and  212  for the outer fastening locations  200   b  are in the shape of an oval elongated in the direction of width of the belt. 
     Forming the through-holes for the outer fastening locations as ovals provides the through-holes with play in the direction of width of the belt. Furthermore, providing a gap (of 0.1 mm in the above example) between the heat-control plate  105  and the support member  106  provides play in the direction of thickness of the heat-control plate  105 . As compared to other methods of fastening, such as welding or using screws, providing play in the above locations compensates for distortion or deformation of components arising due to the difference in the coefficients of thermal expansion of the heat-control plate  105  (i.e. the magnetic shunt alloy layer  115  and the low-resistance conductive layer  116 ) and the support member  106 . Providing play in the above locations therefore reduces deformation of the heat-control plate  105  and the support member  106 . 
     A large amount of deformation of the heat-control plate  105  and the support member  106  accelerates wear of the fixing belt  101  due to the inner surface of the fixing belt  101  coming into contact during rotation with the edge regions  151  and  152  of the heat-control plate  105 . Such deformation also accelerates wear of the fixing roller  102  due to the surface of the fixing roller  102  coming into contact during rotation with the edge regions  161  and  162  of the support member  106 . The structure of the present modification, however, prevents wear of the fixing belt  101  and the fixing roller  102  and increases the durability of the fixing belt  101  and the fixing roller  102 . 
     Note that when fastening with eyelets, a head  201   a  of each eyelet  201  protrudes from the surface of the heat-control plate  105 , whereas the washers  202  protrude from the back surface of the support member  106 . 
     In the present modification, the washers  202  protrude to a greater degree than the head  201   a  of the eyelets  201 . The greater amount of protrusion thus faces the fixing roller  102 , so that the side of the heat-control plate  105  that has the smaller amount of protrusion from the head  201   a  faces the fixing belt  101 . 
     As illustrated in  FIG. 9 , let the gap between the fixing roller  102  and the edge regions  161  and  162  of the support member  106  be α, and let the gap between the fixing belt  101  and the edge regions  151  and  152  of the heat-control plate  105  be β. If the relationship α&gt;β holds, and the gap β is narrow, then it becomes easy for the fixing belt  101  to come into contact with the edge regions  151  and  152  of the heat-control plate  105  due to variations in the position of the fixing belt  101  resulting from vibration during rotation. Therefore, if the relationship α&gt;β holds, contact between the rotating fixing belt  101  and the edge regions  151  and  152  of the heat-control plate  105  can be avoided by fastening the heat-control plate  105  and the support member  106  with eyelets so that the side of the heat-control plate  105  having the smaller amount of protrusion from the head  201   a  faces the fixing belt  101 . 
     Note that the number and positions of the fastening locations for the eyelets, as well as the value of the gap between the heat-control plate  105  and the support member  106 , are not limited to the above values. Appropriate values are determined in accordance with the device structure. 
     Furthermore, while the through-holes  211  and  212  have been described as being either round or oval, depending on the fastening location, the through-holes  211  and  212  are not limited to these shapes. For example, if the effects of the difference in the coefficients of thermal expansion can be suppressed by providing the above gaps, all of the through-holes may be formed to be round. Moreover, as long as the effects of the difference in the coefficients of thermal expansion can be compensated for without providing a gap of a predetermined size, the gap may be omitted, with the heat-control plate  105  and the support member  106  being provided in close contact. 
     While a method of providing two components, i.e. an eyelet  201  and a washer  202 , has been described, one tubular eyelet may instead be adopted, for example with both ends of the eyelet being crimped. 
     Additionally, the fastening member that fastens the heat-control plate  105  to the support member  106  is not limited to the eyelets  201 . For example, instead of the eyelets  201 , rivets  221  as illustrated in  FIG. 11  may be used as the fastening member. 
     Fastening with rivets, as when fastening with eyelets, compensates for distortion arising due to the difference in the coefficients of thermal expansion of the heat-control plate  105  and the support member  106 , thereby achieving the advantageous effect of suppressing deformation of the heat-control plate  105  and the support member  106 . 
     (2) In the above embodiment, a cross-section of the central region  160  of the support member  106  is curved, but as long as the support member  106  does not come into contact with the central region  150  of the heat-control plate  105 , the central region  160  need not be curved. The central region  160  may, for example, have one or more corners. 
     Furthermore, while the example of the support member  106  described above has a central region  160  and edge regions  161  and  162 , the support member  106  is not limited in this way. For example, a structure without the central region  160  may be adopted. 
     If the central region  160  and the edge regions  161  and  162  are integrated as in the embodiment, the edge regions  161  and  162  are in contact with each other via the central region  160 . This both increases the strength of the support member  106  and facilitates assembly at the time of manufacturing of the fixing unit  40 , since it suffices to support the heat-control plate  105  with the support member  106  and insert the integral combination of these two components into the fixing belt  101 . On the other hand, providing only the edge regions  161  and  162  without providing the central region  160  saves on materials by eliminating the need for the central region  160 , thereby lowering costs. 
     (3) In the above embodiment, the method by which the support member  106  supports the heat-control plate  105  is to fit the second sections  156  and  159  of the edge regions  151  and  152  of the heat-control plate  105  into the slits  165  and  166  provided in the steps  163  and  164  of the support member  106 , and then to bond the edge regions  151  and  152  of the heat-control plate  105  to the edge regions  161  and  162  of the support member  106 . The support method, however, is certainly not limited to this example. If support can be maintained simply by fitting the second sections  156  and  159  into the slits  165  and  166 , bonding is unnecessary. Furthermore, whether or not steps are provided, another method such as welding or mechanical fixing may be used. 
     In addition, while the mounts  171  and  172  of the support member  106  are fixed to the device housing  191  in the above example, the mounts  171  and  172  need not be fixed when adopting a structure such that the heat-control plate  105  is in contact with the inner circumferential surface of the fixing belt  101  during rotation of the fixing belt  101 . For example, the following structure may be adopted. In order for the heat-control plate  105  to be moveable so as to come into contact with or separate from the inner circumferential surface of the fixing belt  101 , the support member  106  may be movably supported by the device housing  191 , and during rotation of the fixing belt  101 , the driving force from the actuator of a motor or the like may displace the support member  106  to a position at which the heat-control plate  105  comes into contact with the inner circumferential surface of the fixing belt  101 . 
     (4) In the above embodiment, an example is described in which the fixing roller  102  is disposed along the inside of the running path of the fixing belt  101 . The pressed member is not limited to being a roller, however, as long as the pressed member is pressed by a pressing member, such as the pressing roller  103 , from the outside of the running path of the fixing belt  101  so that the fixing belt  101  is sandwiched therebetween, thus guaranteeing formation of the fixing nip N. 
     For example, instead of a roller, a fixing pad may be used. If a fixing pad is used, then instead of the mounts  171  and  172  of the support member  106  being supported by the device housing  191  outside of the fixing belt  101 , the mounts  171  and  172  may be supported by the fixing pad on the inside of the running path of the fixing belt  101 . 
     Furthermore, a structure has been described wherein the pressing roller  103  is provided as the pressing member, but the pressing member is not limited in this way. Alternatively, a pressing pad or the like may be used. 
     (5) In the above embodiment, an example is described in which the region (first region) of the heat-control plate  105  facing the magnetic flux generator  104 , with the fixing belt  101  therebetween, is the central region  150  in the circumferential direction of the belt, from one end of the coil bobbin  140  to the other end in the circumferential direction of the belt, but the first region is not limited in this way. A portion that includes the excitation coil  141  along the coil bobbin  140  (the entire region over which the conducting wire is wound around the coil bobbin  140 ) and the cores may be considered to be the magnetic flux generator, and the region facing this portion may be considered the first region. Alternatively, the excitation coil  141  alone may be considered the magnetic flux generator, and the region facing the excitation coil  141  may be considered the first region. 
     (6) In the above embodiment, an example of adopting the fixing device and the image forming apparatus according to the present invention in a tandem-type color printer is described, but the present invention is not limited in this way. The present invention may be adopted in, for example, a photocopier, a facsimile device, a Multiple Function Peripheral (MFP), or the like, regardless of whether image formation is color or monochrome, as long as the present invention is embodied as a fixing device based on electromagnetic induction heating, or an image forming apparatus provided with the fixing device, that includes a magnetic flux generator on the outside of the running path of an endless belt that includes an induction heating layer, the magnetic flux generator generating magnetic flux for heating the induction heating layer of the belt, and that includes a heat-control plate on the inside of the running path of the belt, the heat-control plate having a magnetic shunt alloy layer that loses its magnetism upon exceeding a predetermined temperature (Curie point) that is higher that the fixing temperature. 
     Note that the measurements, shape, material, etc. of the fixing belt  101 , the fixing roller  102 , the heat-control plate  105 , the support member  106 , and other components are not limited to the above examples. The measurements, shape, and the like may of course be determined in accordance with the structure of the device. 
     The above embodiment and modifications may be combined with one another. 
     SUMMARY 
     The above embodiment and modifications are one aspect of the present invention for solving the problems discussed in the Description of the Related Art. The above embodiment and modifications may be summarized as follows. 
     A fixing device according to an aspect of the present invention is based on electromagnetic induction heating that, when a sheet with an unfixed image formed thereon passes through a fixing nip, applies heat and pressure to the sheet in order to fix the unfixed image thereto, the fixing device comprising: an endless belt driven to rotate and including an induction heating layer; a pressing member pressing against a surface of the belt to form the fixing nip between the pressing member and the surface of the belt; a magnetic flux generator provided outside of a running path of the belt and generating magnetic flux to cause the induction heating layer to heat; a heat-control plate provided inside of the running path of the belt and including a magnetic shunt alloy layer that loses magnetism upon exceeding a predetermined temperature higher than a fixing temperature; and a support member supporting the heat-control plate, wherein the heat-control plate includes a first region facing the magnetic flux generator with the belt therebetween and second regions extending continuously in a circumferential direction of the belt from opposite edges of the first region, and inside the running path of the belt, the support member is in contact with the heat-control plate at the second regions and not at the first region so as to support the heat-control plate at the second regions. 
     In the above fixing device according to an aspect of the present invention, a cross-section of the first region of the heat-control plate may be an arc that curves along an inner circumferential surface of the belt, and the support member may include: a third region located farther from the magnetic flux generator than the first region of the heat-control plate and facing the first region with a gap therebetween; and fourth regions extending continuously in a circumferential direction of the belt from opposite edges of the third region, one of the fourth regions coming into contact with and supporting one of the second regions of the heat-control plate, and the other one of the fourth regions coming into contact with and supporting the other one of the second regions of the heat-control plate. 
     In the above fixing device according to an aspect of the present invention, a cross-section of the third region of the support member may be an arc that curves along the first region of the heat-control plate. 
     The above fixing device according to an aspect of the present invention may further comprise: a housing; and a roller provided inside the running path of the belt and pressed against by the pressing member with the belt therebetween, wherein the support member is longer, in a direction of width of the belt, than the belt is, and an edge of the support member in a direction of length thereof is fixed to the housing at a location away from the belt in the direction of width of the belt. 
     In the above fixing device according to an aspect of the present invention, the first region of the heat-control plate may be in contact with an inner circumferential surface of the belt while the belt is driven to rotate. 
     In the above fixing device according to an aspect of the present invention, the support member may have a slit provided therein, and a portion of one of the second regions of the heat-control plate may be fitted into the slit. 
     In the above fixing device according to an aspect of the present invention, the heat-control plate and the support member may be fastened together by a fastening member at a plurality of locations in the second regions where the heat-control plate and the support member are in contact. 
     In the above fixing device according to an aspect of the present invention, the fastening member may be a rivet. 
     In the above fixing device according to an aspect of the present invention, the fastening member may be an eyelet. 
     An image forming apparatus according to an aspect of the present invention comprises: an unfixed image forming unit forming an unfixed image on a sheet; and a fixing device fixing the unfixed image to the sheet by applying heat and pressure to the sheet when the sheet passes through a fixing nip, the fixing device comprising: an endless belt driven to rotate and including an induction heating layer; a pressing member pressing against a surface of the belt to form the fixing nip between the pressing member and the surface of the belt; a magnetic flux generator provided outside of a running path of the belt and generating magnetic flux to cause the induction heating layer to heat; a heat-control plate provided inside of the running path of the belt and including a magnetic shunt alloy layer that loses magnetism upon exceeding a predetermined temperature higher than a fixing temperature; and a support member supporting the heat-control plate, wherein the heat-control plate includes a first region facing the magnetic flux generator with the belt therebetween and second regions extending continuously in a circumferential direction of the belt from opposite edges of the first region, and inside the running path of the belt, the support member is in contact with the heat-control plate at the second regions and not at the first region so as to support the heat-control plate at the second regions. 
     In the above image forming apparatus according to an aspect of the present invention, a cross-section of the first region of the heat-control plate may be an arc that curves along an inner circumferential surface of the belt, and the support member may include: a third region located farther from the magnetic flux generator than the first region of the heat-control plate and facing the first region with a gap therebetween; and fourth regions extending continuously in a circumferential direction of the belt from opposite edges of the third region, one of the fourth regions coming into contact with and supporting one of the second regions of the heat-control plate, and the other one of the fourth regions coming into contact with and supporting the other one of the second regions of the heat-control plate. 
     In the above image forming apparatus according to an aspect of the present invention, a cross-section of the third region of the support member may be an arc that curves along the first region of the heat-control plate. 
     In the above image forming apparatus according to an aspect of the present invention, the fixing device may further comprise: a housing; and a roller provided inside the running path of the belt and pressed against by the pressing member with the belt therebetween, wherein the support member is longer, in a direction of width of the belt, than the belt is, and an edge of the support member in a direction of length thereof is fixed to the housing at a location away from the belt in the direction of width of the belt. 
     In the above image forming apparatus according to an aspect of the present invention, the first region of the heat-control plate may be in contact with an inner circumferential surface of the belt while the belt is driven to rotate. 
     In the above image forming apparatus according to an aspect of the present invention, the support member may have a slit provided therein, and a portion of one of the second regions of the heat-control plate may be fitted into the slit. 
     In the above image forming apparatus according to an aspect of the present invention, the heat-control plate and the support member may be fastened together by a fastening member at a plurality of locations in the second regions where the heat-control plate and the support member are in contact. 
     In the above image forming apparatus according to an aspect of the present invention, the fastening member may be a rivet. 
     In the above image forming apparatus according to an aspect of the present invention, the fastening member may be an eyelet. 
     With the above structure, tension in the circumferential direction of the belt due to the friction between the belt and the heat-control plate acts on the portion of the heat-control plate supported by the support member. This tension, however, is less than the moment that acts on both ends of the heat-control plate in the direction of width of the belt in a conventional structure in which these ends are directly fixed to the device housing, such moment being the product of the tension in the circumferential direction of the belt and the length in the direction of width of the belt. As a result, it is not necessary in the above structure to increase the thickness of the heat-control plate in order to prevent deformation due to the action of the moment. The above structure is therefore thinner than a conventional structure. 
     Reducing the thickness of the heat-control plate allows for a reduction in the heat capacity of the heat-control plate, thereby reducing the transfer of heat from the belt. In a conventional structure, a thick heat-control plate results in a large heat capacity, which causes heat from the belt to escape directly to the device housing via the heat-control plate. As compared to this conventional structure, the transfer of heat, produced by electromagnetic induction, from the belt to the support member via the heat-control plate is reduced, thereby improving the capability of the belt to rise in temperature. 
     Although the present invention has been fully described by way of examples with reference to the accompanying drawings, it is to be noted that various changes and modifications will be apparent to those skilled in the art. Therefore, unless otherwise such changes and modifications depart from the scope of the present invention, they should be construed as being included therein.