Patent Publication Number: US-2020278629-A1

Title: Fixing device capable of restricting increase of friction force that acts between heater and fixing belt, image forming apparatus

Description:
INCORPORATION BY REFERENCE 
     This application is based upon and claims the benefit of priority from the corresponding Japanese Patent Application No. 2019-036072 filed on Feb. 28, 2019, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     The present disclosure relates to an electrophotographic image forming apparatus, and to a fixing device provided in the image forming apparatus. 
     An electrophotographic image forming apparatus includes a fixing device that heats a sheet to which a toner image has been transferred, to fix the toner image to the sheet. For example, the fixing device includes a fixing belt, a pressure roller, and a heater. The pressure roller is mounted in contact with an outer peripheral surface of the fixing belt. The heater is mounted to face the pressure roller across the fixing belt, and pressed against the fixing belt. A lubricant is applied to a contact surface of the heater that comes in contact with the fixing belt. 
     In this type of fixing device, a friction force that acts between the contact surface of the heater and the fixing belt may increase when the lubricant applied to the contact surface reduces. When the friction force increases, a problem may occur such as a noise, a disorder of print images, or a step-out of a driving portion that drives the pressure roller. There is known, as a related technology, a fixing device that can restrict the increase of the friction force acting between the contact surface and the fixing belt, by rotating the pressure roller in the reverse direction to return the lubricant that has flowed out of the contact surface, to the contact surface. 
     SUMMARY 
     A fixing device according to an aspect of the present disclosure includes a fixing belt, a pressure roller, a heater, and a reserving portion. The pressure roller is provided in contact with an outer peripheral surface of the fixing belt. The heater is provided to face the pressure roller across the fixing belt and pressed against the fixing belt. The reserving portion is provided within a contact range of the heater and the fixing belt, and has a reserving space for reserving a lubricant, wherein at least a part of the reserving space on the fixing belt side is open. 
     An image forming apparatus according to another aspect of the present disclosure forms an image on a sheet by using the fixing device. 
     This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description with reference where appropriate to the accompanying drawings. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Furthermore, the claimed subject matter is not limited to implementations that solve any or all disadvantages noted in any part of this disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing a configuration of an image forming apparatus. 
         FIG. 2  is a diagram showing a configuration of a fixing device according to a first embodiment of the present disclosure. 
         FIG. 3  is a diagram showing a configuration of a heater according to the first embodiment of the present disclosure. 
         FIG. 4  is a diagram showing a configuration of the heater and a heater support portion according to the first embodiment of the present disclosure. 
         FIG. 5  is a diagram showing a configuration of a substrate of the heater according to the first embodiment of the present disclosure. 
         FIG. 6  is a diagram showing a configuration of a fixing device according to a second embodiment of the present disclosure. 
         FIG. 7  is a diagram showing a configuration of a heater and a heater support portion according to the second embodiment of the present disclosure. 
         FIG. 8  is a diagram showing a configuration of a fixing device according to a third embodiment of the present disclosure. 
         FIG. 9  is a diagram showing a configuration of a heater and a heater support portion according to the third embodiment of the present disclosure. 
         FIG. 10  is a diagram showing a modification of the fixing device according to the third embodiment of the present disclosure. 
         FIG. 11  is a diagram showing a configuration of a fixing device according to a fourth embodiment of the present disclosure. 
         FIG. 12  is a diagram showing a modification of the fixing device according to the fourth embodiment of the present disclosure. 
         FIG. 13  is a diagram showing a configuration of a fixing device according to a fifth embodiment of the present disclosure. 
         FIG. 14  is a diagram showing a modification of the fixing device according to the fifth embodiment of the present disclosure. 
         FIG. 15  is a diagram showing a configuration of a fixing device according to a sixth embodiment of the present disclosure. 
         FIG. 16  is a diagram showing a configuration of a heater and a heater support portion according to the sixth embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The following describes embodiments of the present disclosure with reference to the accompanying drawings. It should be noted that the following embodiments are examples of specific embodiments of the present disclosure and should not limit the technical scope of the present disclosure. 
     [Configuration of Image Forming Apparatus  100 ] 
     First, a description is given of a configuration of an image forming apparatus  100  with reference to  FIG. 1 . Here,  FIG. 1  is a cross-sectional diagram showing a configuration of the image forming apparatus  100 . 
     For the sake of explanation, an up-down direction D 1  is defined as a vertical direction in a state where the image forming apparatus  100  is installed usably (the state shown in  FIG. 1 ). In addition, a front-rear direction D 2  is defined on the supposition that the left-side surface of the image forming apparatus  100  shown in  FIG. 1  is a front side (front). Furthermore, a left-right direction D 3  is defined based on the image forming apparatus  100  in the installation state viewed from the front side. 
     The image forming apparatus  100  is a printer having a print function to form an image based on image data. It is noted that the present disclosure is applicable to image forming apparatuses such as a facsimile apparatus, a copier, and a multifunction peripheral. 
     As shown in  FIG. 1 , the image forming apparatus  100  includes an image forming portion  1  and a sheet conveying portion  2 . The image forming portion  1  and the sheet conveying portion  2  are stored in a housing  101  of the image forming apparatus  100 . The housing  101  is formed in an approximate shape of a rectangular parallelepiped. A sheet receiving portion  102  is formed in an upper portion of the housing  101 , wherein a sheet with an image formed thereon by the image forming apparatus  100  is discharged to the sheet receiving portion  102 . 
     The image forming portion  1  is configured to form an image by an electrophotographic method based on image data input from an external information processing apparatus such as a personal computer. As shown in  FIG. 1 , the image forming portion  1  includes a photoconductor drum  11 , a charging device  12 , a laser scanning unit  13 , a developing device  14 , a transfer roller  15 , a cleaning device  16 , and a fixing device  17 . 
     The photoconductor drum  11  is rotatably supported by the housing  101 . 
     Upon receiving a rotational driving force transmitted from a motor (not shown), the photoconductor drum  11  rotates in a direction indicated by an arrow in  FIG. 1 . An electrostatic latent image is formed on the surface of the photoconductor drum  11 . 
     The charging device  12  charges the surface of the photoconductor drum  11 . 
     The laser scanning unit  13  irradiates light onto the charged surface of the photoconductor drum  11  based on the image data. The laser scanning unit  13  forms an electrostatic latent image on the surface of the photoconductor drum  11 . 
     The developing device  14  develops, by using developer including toner, the electrostatic latent image formed on the surface of the photoconductor drum  11 . The developing device  14  forms a toner image on the surface of the photoconductor drum  11 . 
     The transfer roller  15  transfers the toner image formed on the surface of the photoconductor drum  11  to a sheet conveyed by the sheet conveying portion  2 . 
     The cleaning device  16  cleans the surface of the photoconductor drum  11  after the toner image is transferred therefrom by the transfer roller  15 . 
     The fixing device  17  heats the sheet to which the toner image has been transferred, and thereby fixes the toner image to the sheet. The fixing device  17  is any one of fixing devices  17 A,  17 B,  17 C,  17 D,  17 E, and  17 F that are described below. 
     The sheet conveying portion  2  conveys a sheet on which an image is formed by the image forming portion  1 . As shown in  FIG. 1 , the sheet conveying portion  2  includes a sheet feed cassette  21 , a sheet conveyance path  22 , a sheet feed unit  23 , a pair of registration rollers  24 , and a pair of sheet discharge rollers  25 . 
     The sheet feed cassette  21  stores sheets on which images are formed by the image forming portion  1 . As shown in  FIG. 1 , the sheet feed cassette  21  is provided in a bottom portion of the housing  101 . For example, the sheets stored in the sheet feed cassette  21  are sheet-like materials such as sheets of paper, sheets of coated paper, postcards, envelopes, and OHP sheets. The sheet feed cassette  21  includes a lift plate (not shown) for lifting a plurality of sheets stored therein. 
     The sheet conveyance path  22  is a sheet moving path that extends from the sheet feed cassette  21  to the sheet receiving portion  102 , via the transfer roller  15  and the fixing device  17 . A plurality of pairs of rollers, including the pair of registration rollers  24  and the pair of sheet discharge rollers  25 , are provided in the sheet conveyance path  22 . In the sheet conveyance path  22 , a sheet fed from the sheet feed cassette  21  by the plurality of pairs of rollers is conveyed in a conveyance direction D 4  (see  FIG. 1 ) toward the sheet receiving portion  102 . The sheet conveyance path  22  is formed by a pair of conveyance guide members provided in the housing  101 . 
     The sheet feed unit  23  feeds the sheets stored in the sheet feed cassette  21  one by one to the sheet conveyance path  22 . The sheet feed unit  23  includes a pickup roller, a sheet feed roller, and a retard roller. The pickup roller feeds a top sheet of the plurality of sheets lifted by the lift plate of the sheet feed cassette  21 , to the sheet feed roller by rotating while in contact with an upper surface of the top sheet. The sheet feed roller feeds the sheet fed by the pickup roller to the sheet conveyance path  22  by rotating while in contact with the upper surface of the sheet. The retard roller is disposed below the sheet feed roller and biased toward the sheet feed roller. When a plurality of overlapping sheets are fed by the pickup roller, the retard roller separates sheets other than the top sheet from the plurality of overlapping sheets. 
     The pair of registration rollers  24  convey a sheet to a transfer position where a toner image is transferred to the sheet by the transfer roller  15  such that the sheet reaches the transfer position at the same timing as the toner image that is formed on the surface of the photoconductor drum  11  and carried by the rotation of the photoconductor drum  11 . 
     The pair of sheet discharge rollers  25  discharge the sheet to which the toner image has been fixed by the fixing device  17 , to the sheet receiving portion  102 . 
     First Embodiment 
     Next, with reference to  FIG. 2  to  FIG. 5 , a description is given of a configuration of a fixing device  17 A according to a first embodiment of the present disclosure. Here,  FIG. 2  is a cross-sectional diagram showing a configuration of the fixing device  17 A.  FIG. 3  is a cross-sectional diagram showing a configuration of a heater  32 A.  FIG. 4  is a bottom diagram showing a configuration of the heater  32 A and a heater support portion  33 A.  FIG. 5  is a bottom diagram showing a configuration of a substrate  41 . It is noted that the dotted line in  FIG. 4  indicates a fixing belt  31 . In addition, the one-dot chain line in  FIG. 5  indicates a substrate  49  that has the same shape as the substrate  41 . 
     As shown in  FIG. 2 , the fixing device  17 A includes the fixing belt  31 , the heater  32 A, the heater support portion  33 A, a pressing member  35 , reserving portions  36 , and a pressure roller  51 . 
     The fixing belt  31 , while in a state of being heated by the heater  32 A, comes in contact with a sheet to which a toner image has been transferred, and thereby fixes the toner image to the sheet. The fixing belt  31  is flexible and has an endless shape. As shown in  FIG. 2 , the fixing belt  31  is held between the heater  32 A and the pressure roller  51  and runs in a running direction D 5  following the rotation of the pressure roller  51 . The fixing belt  31  is guided by a guide portion  332  of the heater support portion  33 A and a guide member (not shown), to run along a running path. 
     The heater  32 A heats the fixing belt  31  from an inner side of the fixing belt  31 . As shown in  FIG. 3 , the heater  32 A includes a substrate  41 , a heating element  42 , a protection layer  43 , and a sensor  44 . 
     As shown in  FIG. 3  and  FIG. 4 , the substrate  41  is formed in a shape of a flat plate elongated in the left-right direction D 3  that matches the width direction of the fixing belt  31 . The heating element  42  is mounted on a surface of the substrate  41 . As shown in  FIG. 3  and  FIG. 4 , the heating element  42  is formed in a shape of a flat plate elongated in the longitudinal direction of the substrate  41 . The heating element  42  is connected to a power supply (not shown) via a wiring pattern mounted on the substrate  41 . The heating element  42  is heated by the passage of an electric current supplied from the power supply. The protection layer  43  covers a surface of the substrate  41  on which the heating element  42  is mounted, thereby protecting the surface of the substrate  41 . The outer surface of the protection layer  43  constitutes a contact surface  321  (an example of a first surface of the present disclosure) of the heater  32 A that comes in contact with the fixing belt  31 . The sensor  44  is mounted on a surface of the substrate  41  that is opposite from the surface on which the heating element  42  is mounted. The sensor  44  outputs an electric signal that varies depending on the temperature of the heating element  42 . The electric signal output from the sensor  44  is input to a control portion (not shown). The control portion controls the temperature of the heating element  42  based on the electric signal input from the sensor  44 . 
     The heater  32 A is mounted on the inner side of the fixing belt  31  to face the pressure roller  51 . Specifically, the heater  32 A is mounted in a posture where the contact surface  321  faces the axial center of the pressure roller  51 . In addition, the heater  32 A is pressed by the pressing member  35  toward the pressure roller  51 , and pressed against an inner peripheral surface of the fixing belt  31 . This forms a nip region R 1  where a sheet that passes through between the fixing belt  31  and the pressure roller  51  is pressed thereby. It is noted that in the present description, the nip region R 1  is defined as a region where the fixing belt  31  and the pressure roller  51  are in contact with each other. A lubricant is applied to the contact surface  321  of the heater  32 A to reduce the friction coefficient between the contact surface  321  and the inner peripheral surface of the fixing belt  31 . For example, fluorine grease is used as the lubricant. 
     The heater support portion  33 A supports the heater  32 A. As shown in  FIG. 4 , the heater support portion  33 A is formed to be elongated in the left-right direction D 3 . A recessed portion  331  is formed on a lower surface of the heater support portion  33 A so that the heater  32 A is fitted in the recessed portion  331 . The recessed portion  331  includes a bottom surface of a rectangular shape and side walls respectively erected on the sides of the bottom surface. In a state where the heater  32 A is fitted in the recessed portion  331 , a supported surface  322  (an example of a second surface of the present disclosure) is in contact with the bottom surface of the recessed portion  331 , wherein the supported surface  322  is a surface of the substrate  41  on which the sensor  44  is mounted. In addition, as shown in  FIG. 4 , in the state where the heater  32 A is fitted in the recessed portion  331 , opposite end portions of the heater  32 A in the front-rear direction D 2  and opposite end portions of the heater  32 A in the left-right direction D 3  are in contact with the side walls of the recessed portion  331 . The recessed portion  331  is formed such that its depth is approximately the same as the thickness of the heater  32 A. As a result, in the state where the heater  32 A fitted in the recessed portion  331 , the contact surface  321  of the heater  32 A is approximately flush with the edge portion of the recessed portion  331 . 
     The heater support portion  33 A guides the fixing belt  31  to run along the running path. Specifically, guide portions  332  are provided at opposite ends of the heater support portion  33 A in the front-rear direction D 2 . The guide portions  332  come in contact with the inner peripheral surface of the fixing belt  31  to guide the fixing belt  31  to run along the running path. 
     The pressing member  35  presses the heater support portion  33 A toward the pressure roller  51 . The pressing member  35  is mounted in contact with an upper surface of the heater support portion  33 A, and elongated in the left-right direction D 3  that matches the width direction of the fixing belt  31 . In addition, opposite end portions of the pressing member  35  in the longitudinal direction are supported by a pair of side plates (not shown) provided in the housing  101  such that the pressing member  35  can move in the up-down direction D 1 . The pressing member  35  receives a downward biasing force, namely a biasing force toward the pressure roller  51 , from a biasing member (not shown). This causes the pressing member  35  to press the heater support portion  33 A toward the pressure roller  51 . As the heater support portion  33 A is pressed toward the pressure roller  51 , the heater  32 A supported by the heater support portion  33 A is also pressed toward the pressure roller  51 . 
     The pressure roller  51  is provided below the fixing belt  31  to be in contact with an outer peripheral surface of the fixing belt  31 . The pressure roller  51  includes a shaft portion  511  and an elastic layer  512 , wherein the shaft portion  511  is made of a metal, and the elastic layer  512  is elastic and formed on the outer periphery of the shaft portion  511 . The shaft portion  511  is rotatably supported by the pair of side plates. Upon receiving a rotational driving force from a motor (not shown), the pressure roller  51  rotates in a rotation direction D 6 . 
     Meanwhile, a friction force that acts between the contact surface  321  of the heater  32 A and the fixing belt  31  may increase when the lubricant applied to the contact surface  321  reduces. When the friction force increases, a problem may occur such as a noise, a disorder of print images, or a step-out of a driving portion that drives the pressure roller  51 . There is known, as a related technology, a fixing device that can restrict the increase of the friction force acting between the contact surface  321  and the fixing belt  31 , by rotating the pressure roller  51  in the reverse direction to return the lubricant that has flowed out of the contact surface  321 , to the contact surface  321 . 
     However, in the fixing device of the related technology, the rotation control of the pressure roller  51  is complicated. On the other hand, the fixing device  17 A according to the first embodiment of the present disclosure can restrict the increase of the friction force that acts between the contact surface  321  and the fixing belt  31 , without making the rotation control of the pressure roller  51  complicated, as described in the following. 
     The reserving portions  36  are provided within a contact range of the heater  32 A and the fixing belt  31 , each of the reserving portions  36  having a reserving space for reserving the lubricant, wherein at least a part of the reserving space on the fixing belt  31  side is open. Specifically, as shown in  FIG. 2  and  FIG. 4 , the reserving portions  36  are recessed portions formed by the recessed portion  331  of the heater support portion  33 A and cut portions  45  formed on the substrate  41 . 
     Here, as shown in  FIG. 4  and  FIG. 5 , a plurality of cut portions  45  are formed on the substrate  41  of the heater  32 A. Specifically, the plurality of cut portions  45  are formed in line along the left-right direction D 3  at an upstream end of the substrate  41  in the running direction D 5 . 
     As shown in  FIG. 4  and  FIG. 5 , each of the cut portions  45  includes a first cut portion  451  and a second cut portion  453 . As shown in  FIG. 4 , the first cut portion  451  includes a first wall surface  452  that faces in a direction between a direction opposite to the running direction D 5  and the left (an example of a first direction of the present disclosure). The first wall surface  452  is a flat surface. The second cut portion  453  includes a second wall surface  454  that faces in a direction between the direction opposite to the running direction D 5  and the right (an example of a second direction of the present disclosure). The second wall surface  454  is a flat surface. In the substrate  41 , the plurality of cut portions  45  are formed such that the first wall surface  452  and the second wall surface  454  continue alternately in the left-right direction D 3 . 
     In the fixing device  17 A, when the lubricant that has adhered to the inner peripheral surface of the fixing belt  31  flows from the upstream in the running direction D 5  to the contact surface  321 , the lubricant is scraped by the edge portions of the reserving portions  36  and is reserved in the reserving portions  36 . Specifically, the lubricant that has adhered to the inner peripheral surface of the fixing belt  31  is scraped by corner portions formed of the contact surface  321  and the first wall surfaces  452 , and corner portions formed of the contact surface  321  and the second wall surfaces  454 , and is reserved in the reserving portions  36 . In addition, in the fixing device  17 A, the fixing belt  31  supplies the lubricant reserved in the reserving portions  36  to the contact surface  321 . Specifically, the fixing belt  31  supplies the lubricant to the contact surface  321  by conveying the lubricant that has adhered to the inner peripheral surface thereof at a region facing the reserving portions  36 , toward the downstream in the running direction D 5 . This restricts reduction of the amount of the lubricant that has adhered to the contact surface  321 , the reduction accompanied by the increase of the number of prints, and restricts increase of the friction force that acts between the heater  32 A and the fixing belt  31 . 
     Here, in the fixing device  17 A, the reserving portions  36  are provided at an upstream end of the heater  32 A in the running direction D 5  of the fixing belt  31 . Specifically, the reserving portions  36  are formed of the recessed portion  331  of the heater support portion  33 A and an upstream end portion of the substrate  41  in the running direction D 5 . As a result, compared with a case where the reserving portions  36  are provided downstream of the upstream end of the heater  32 A in the running direction D 5  of the fixing belt  31 , it is possible to widen the range in which the reserving portions  36  supply the lubricant. It is noted that the reserving portions  36  may be hole portions formed in the upstream end portion of the substrate  41  in the running direction D 5 , or hole portions formed downstream of the end portion of the substrate  41 . In addition, the reserving portions  36  may be formed by reserving spaces formed inside the substrate  41 , and communication ports communicating the reserving spaces with the outside of the substrate  41 . 
     In addition, the substrate  41  includes the plurality of cut portions  45  formed in line along the left-right direction D 3  that matches the width direction of the fixing belt  31 , and a plurality of reserving portions  36  are formed by the plurality of cut portions  45 . This restricts an adhering amount of the lubricant on the contact surface  321  from being varied in the width direction of the fixing belt  31 . It is noted that the number of the cut portions  45  provided in the substrate  41  may be one. 
     In addition, the substrate  41  is obtained by cutting a large substrate along a triangular-wave cutting line, into two small substrates of the same shape. As a result, as shown in  FIG. 5 , a specific end portion of the substrate  41  including the plurality of cut portions  45  is fitted with the specific end portion of another substrate  49  that has the same shape as the substrate  41 . With the substrate  41  formed in this way, compared with a case where the cut portions  45  are formed by cutting an end portion of a flat-plate substrate, it is possible to avoid generating cut pieces that become waste. It is noted that the substrate  41  may be obtained by cutting a large substrate along a sine-wave cutting line or a rectangular-wave cutting line, into two small substrates of the same shape. In addition, the substrate  41  may be formed in a shape in which the specific end portion is not fitted with the specific end portion of another substrate. 
     In addition, as shown in  FIG. 4 , the fixing belt  31  and the heater  32 A are arranged in a positional relation where: the right end portion of the fixing belt  31  faces a corner portion that is formed of a surface of the substrate  41  (a surface on which the heating element  42  is mounted) and the first wall surface  452 ; and the left end portion of the fixing belt  31  faces a corner portion that is formed of the surface of the substrate  41  and the second wall surface  454 . With this configuration, the lubricant that has adhered to the inner peripheral surface of the fixing belt  31  at the right end is shifted to the inside of the fixing belt  31  by the corner portion that is formed of the surface of the substrate  41  and the first wall surface  452 , and is scraped off. In addition, the lubricant that has adhered to the inner peripheral surface of the fixing belt  31  at the left end is shifted to the inside of the fixing belt  31  by the corner portion that is formed of the surface of the substrate  41  and the second wall surface  454 , and is scraped off. Accordingly, it is possible to prevent the lubricant from flowing to the outside of the fixing belt  31  in the left-right direction D 3 . It is noted that the fixing belt  31  and the heater  32 A may be arranged in a positional relation different from the above-described positional relation. 
     Second Embodiment 
     Next, with reference to  FIG. 6  and  FIG. 7 , a description is given of a configuration of a fixing device  17 B according to a second embodiment of the present disclosure. Here,  FIG. 6  is a cross-sectional diagram showing a configuration of the fixing device  17 B.  FIG. 7  is a bottom diagram showing a configuration of a heater  32 B 1 , a heater  32 B 2 , and a heater support portion  33 B. 
     The fixing device  17 B has the same configuration as the fixing device  17 A except that it includes two heaters  32 B in place of the heater  32 A, the heater support portion  33 B in place of the heater support portion  33 A, and a reserving portion  37  in place of the reserving portions  36 . 
     Similar to the fixing device  17 A, the fixing device  17 B can restrict the increase of the friction force that acts between the heaters  32 B and the fixing belt  31 , without making the rotation control of the pressure roller  51  complicated. 
     Each of the heaters  32 B has the same configuration as the heater  32 A except that it is smaller than the heater  32 A in size in the front-rear direction D 2 . 
     As shown in  FIG. 6 , the two heaters  32 B are provided in line along the running direction D 5  inside the fixing belt  31 . In addition, the two heaters  32 B are mounted to face the pressure roller  51 . Specifically, the two heaters  32 B are mounted in a posture where the contact surfaces  321  thereof face the pressure roller  51  and are parallel to each other. The two heaters  32 B are pressed by the pressing member  35  toward the pressure roller  51 , and pressed against the inner peripheral surface of the fixing belt  31 . A lubricant is applied to the contact surfaces  321  of the two heaters  32 B. 
     The heater support portion  33 B has the same configuration as the heater support portion  33 A except that it includes a recessed portion  333  in place of the recessed portion  331 . The heater support portion  33 B supports both of the heaters  32 B. 
     The recessed portion  333  is formed to store the two heaters  32 B. The recessed portion  333  includes a bottom surface of a rectangular shape and side walls respectively erected on the sides of the bottom surface. As shown in  FIG. 7 , the length of the recessed portion  333  in the left-right direction D 3  is approximately the same as that of each of the heaters  32 B. In addition, the recessed portion  333  is formed such that its length in the front-rear direction D 2  is longer, by a predetermined distance, than twice the length of each of the heaters  32 B in the front-rear direction D 2 . 
     In a state where the two heaters  32 B are stored in the recessed portion  333 , the supported surfaces  322  of the substrates  41  are in contact with the bottom surface of the recessed portion  333 . In addition, as shown in  FIG. 7 , in the state where the two heaters  32 B are stored in the recessed portion  333 , opposite end portions of the heaters  32 B in the left-right direction D 3  are in contact with the side walls of the recessed portion  333  that face each other in the left-right direction D 3 . In addition, as shown in  FIG. 7 , in the state where the two heaters  32 B are stored in the recessed portion  333 , an end portion of the heater  32 B 1  is in contact with a front side wall  334  of the recessed portion  333 , wherein the heater  32 B 1  is one of the two heaters  32 B and is disposed on the upstream side in the running direction D 5 . In addition, as shown in  FIG. 7 , in the state where the two heaters  32 B are stored in the recessed portion  333 , an end portion of the heater  32 B 2  is in contact with a rear side wall  335  of the recessed portion  333 , wherein the heater  32 B 2  is the other of the two heaters  32 B and is disposed on the downstream side in the running direction D 5 . The recessed portion  333  is formed such that its depth is approximately the same as the thickness of each of the heaters  32 B. As a result, in the state where the two heaters  32 B are stored in the recessed portion  333 , the contact surfaces  321  of the heaters  32 B are approximately flush with the edge portion of the recessed portion  333 . 
     The reserving portion  37  has a reserving space for reserving the lubricant between the two heaters  32 B, and at least a part of the reserving space on the fixing belt  31  side is open. Specifically, as shown in  FIG. 6  and  FIG. 7 , the reserving portion  37  is a recessed portion that is formed by: two end portions of the two heaters  32 B that face each other; and the recessed portion  333  of the heater support portion  33 B. 
     In the fixing device  17 B, when the lubricant that has adhered to the inner peripheral surface of the fixing belt  31  passes a region where the fixing belt  31  faces the reserving portion  37 , the lubricant is scraped by an edge portion of the reserving portion  37  that is on the downstream side in the running direction D 5 , and is reserved in the reserving portion  37 . As is the case with the fixing device  17 A, this restricts reduction of the amount of the lubricant adhering to the contact surface  321 , the reduction accompanied by the increase of the number of prints, and restricts increase of the friction force that acts between the heater  32 A and the fixing belt  31 . In addition, in the fixing device  17 B, the reserving portion  37  is provided at a position facing the center of the nip region R 1 . As a result, compared with the fixing device  17 A in which the reserving portions  36  face the upstream portion of the nip region R 1  in the running direction D 5 , it is possible to increase the amount of the lubricant reserved in the reserving portion. 
     Here, in the fixing device  17 B, the reserving portion  37  is formed of; the two end portions of the two heaters  32 B that face each other; and the heater support portion  33 B. As a result, compared with a configuration where the reserving portion  37  is formed of only the heater support portion  33 B, it is possible to simplify the shape of the heater support portion  33 B. It is noted that the reserving portion  37  may be formed of only the heater support portion  33 B. 
     In addition, as shown in  FIG. 7 , the heater support portion  33 B includes two restriction portions  336 . The two restriction portions  336 , provided between the two heaters  32 B, restrict the two heaters  32 B from moving in directions along the running direction D 5 . Specifically, the two restriction portions  336  are projection portions that project from opposite side walls of the recessed portion  333  that face each other in the left-right direction D 3 , toward the inside in the left-right direction D 3 . This prevents the heaters  32 B from moving in the running direction D 5  and reducing the lubricant reserving space in the reserving portion  37 . It is noted that the heater support portion  33 B may not include the two restriction portions  336 . 
     In addition, the two restriction portions  336  restrict the two heaters  32 B from moving at outside the fixing belt  31  in the width direction of the fixing belt  31 . Specifically, as shown in  FIG. 7 , the two restriction portions  336  are provided at outside the fixing belt  31  in the width direction of the fixing belt  31 . This avoids the two restriction portions  336  from interfering with reserving of the lubricant in the reserving portion  37 . It is noted that the two restriction portions  336  may be provided inside the fixing belt  31  in the width direction of the fixing belt  31 . In this case, the number of the restriction portions  336  may be one or three or more. 
     It is noted that as shown in  FIG. 11 , in a configuration where three or more heaters are provided, the reserving portion  37  may be provided between two adjacent heaters. 
     Meanwhile, there is known, as a related technology, a fixing device that includes a nip forming member that is provided to face the pressure roller  51  across the fixing belt  31 , wherein a lubricant is applied to a contact surface of the nip forming member that comes in contact with the fixing belt  31 , and the lubricant is supplied from inside the nip forming member to the inner peripheral surface of the fixing belt  31 . 
     Here, in the fixing device according to the related technology, it may be possible to provide a heater between the nip forming member and the fixing belt  31  to improve the heating efficiency. However, in this case, the heater interferes with supply of the lubricant from the inside of the nip forming portion to the inner peripheral surface of the fixing belt  31 . On the other hand, the fixing device  17 C according to the third embodiment of the present disclosure can improve the efficiency of heating the fixing belt  31  without interfering with supply of the lubricant to the inner peripheral surface of the fixing belt  31 , as described in the following. 
     Third Embodiment 
     Next, with reference to  FIG. 8  and  FIG. 9 , a description is given of a configuration of a fixing device  17 C according to a third embodiment of the present disclosure. Here,  FIG. 8  is a cross-sectional diagram showing a configuration of the fixing device  17 C.  FIG. 9  is a bottom diagram showing a configuration of the heater  32 A and a heater support portion  33 C. 
     The fixing device  17 C has the same configuration as the fixing device  17 A except that it includes the heater support portion  33 C in place of the heater support portion  33 A, a reserving portion  38  in place of the reserving portions  36 , and supply paths  39 . 
     The heater support portion  33 C has the same configuration as the heater support portion  33 A except that it further includes a recessed portion  337 . 
     The recessed portion  337  is formed to be recessed from the bottom surface of the recessed portion  331  upward. The recessed portion  337  includes a bottom surface of a rectangular shape and side walls respectively erected on the sides of the bottom surface. As shown in  FIG. 8 , the recessed portion  337  is provided at an upstream end of the recessed portion  331  in the running direction D 5 . The recessed portion  337  is elongated in the left-right direction D 3 . 
     The reserving portion  38  is configured to reserve the lubricant. In the fixing device  17 C, the heater  32 A is provided between the reserving portion  38  and the fixing belt  31 . Specifically, the reserving portion  38  is formed by the recessed portion  337  of the heater support portion  33 C, and the supported surface  322  of the heater  32 A. The lubricant is reserved in the reserving portion  38  in advance. 
     The supply paths  39  form moving paths in which the lubricant moves from the reserving portion  38  toward the pressure roller  51 . Specifically, as shown in  FIG. 8  and  FIG. 9 , the supply paths  39  are formed by: the recessed portion  331  of the heater support portion  33 C; and the cut portions  45  formed on the substrate  41 . 
     In the fixing device  17 C, the lubricant reserved in the reserving portion  38  is supplied to the contact surface  321  via the supply paths  39  formed at the heater  32 A. This makes it possible to improve the heating efficiency of the fixing belt  31  without interfering with the supply of the lubricant to the inner peripheral surface of the fixing belt  31 . 
     Here, in the fixing device  17 C, the reserving portion  38  is formed of the recessed portion  337  of the heater support portion  33 C and the supported surface  322  of the heater  32 A. As a result, compared with a configuration where the reserving portion  38  is formed of only the heater support portion  33 C, it is possible to simplify the shape of the heater support portion  33 C. It is noted that the reserving portion  38  may be formed of only the heater support portion  33 C. In this case, the heater support portion  33 C may have paths that connect the reserving portion  38  to the supply paths  39 . 
     Here, in the fixing device  17 C, the supply paths  39  are provided at an upstream end of the heater  32 A in the running direction D 5  of the fixing belt  31 . Specifically, the supply paths  39  are formed of the recessed portion  331  of the heater support portion  33 C and an upstream end portion of the substrate  41  in the running direction D 5 . As a result, compared with a case where the supply paths  39  are provided downstream of the upstream end of the heater  32 A in the running direction D 5  of the fixing belt  31 , it is possible to widen the range in which the supply paths  39  supply the lubricant. It is noted that the reserving portions  36  may be hole portions  46  formed in the upstream end portion of the substrate  41  in the running direction D 5 . The hole portions  46  may be formed downstream of the upstream end portion of the substrate  41  in the running direction D 5 . 
     In addition, the substrate  41  includes the plurality of cut portions  45  that are formed in line along the left-right direction D 3  that matches the width direction of the fixing belt  31 . This restricts the adhering amount of the lubricant on the contact surface  321  from being varied in the width direction of the fixing belt  31 . It is noted that the number of the cut portions  45  provided in the substrate  41  may be one. 
     In addition, as shown in  FIG. 9 , the fixing belt  31  and the heater  32 A are arranged in a positional relation where: the right end portion of the fixing belt  31  faces a corner portion that is formed of a surface of the substrate  41  (a surface on which the heating element  42  is mounted) and the first wall surface  452 ; and the left end portion of the fixing belt  31  faces a corner portion that is formed of the surface of the substrate  41  and the second wall surface  454 . With this configuration, as is the case with the fixing device  17 A, it is possible to prevent the lubricant from flowing to the outside of the fixing belt  31  in the left-right direction D 3 . It is noted that the fixing belt  31  and the heater  32 A may be arranged in a positional relation different from the above-described positional relation. 
     Meanwhile, when a sheet is conveyed to be passed through the fixing device  17 A at a very high speed, the toner is insufficiently melted in the nip region R 1 , and quality of a print image on the sheet is degraded. With regard to this problem, the roller diameter of the pressure roller  51  may be increased so that the nip region R 1  is expanded in the sheet conveyance direction D 4 , and the heating time period and the pressing time period in the nip region R 1  are increased. However, this enlarges the fixing device  17 A. On the other hand, a fixing device  17 D according to a fourth embodiment of the present disclosure can increase the sheet conveyance speed without enlarging the device, as described in the following. 
     Fourth Embodiment 
     Next, with reference to  FIG. 11 , a description is given of a configuration of the fixing device  17 D according to the fourth embodiment of the present disclosure. Here,  FIG. 11  is a cross-sectional diagram showing a configuration of the fixing device  17 D. 
     The fixing device  17 D has the same configuration as the fixing device  17 A except that it includes three heaters  32 C in place of the heater  32 A, and a heater support portion  33 D in place of the heater support portion  33 A, and does not include the reserving portions  36 . 
     Each of the heaters  32 C has the same configuration as the heater  32 A except that it is smaller than the heater  32 A in size in the short direction. 
     As shown in  FIG. 11 , the three heaters  32 C are provided inside the fixing belt  31 , in line along the outer peripheral surface of the pressure roller  51 . In addition, each of the three heaters  32 C is mounted to face the axial center of the pressure roller  51 . That is, each of the three heaters  32 C is mounted in a posture where a straight line perpendicular to the contact surface  321  passes through the axial center of the pressure roller  51 . For example, each of the three heaters  32 C is mounted in a posture where a straight line that is perpendicular to the contact surface  321  and passes through a center of the contact surface  321  in the short direction, passes through the axial center of the pressure roller  51 . Each of the three heaters  32 C is pressed by the pressing member  35  toward the pressure roller  51 , and pressed against the inner peripheral surface of the fixing belt  31 . A lubricant is applied to the contact surfaces  321  of each of the three heaters  32 C. 
     The heater support portion  33 D has the same configuration as the heater support portion  33 A except that it includes recessed portions  338 ,  339 , and  340  in place of the recessed portion  331 . 
     The recessed portion  338  is configured to be fitted with a heater  32 C 1  that is, among the three heaters  32 C, positioned most upstream in the running direction D 5 . The recessed portion  338  includes a bottom surface of a rectangular shape and side walls respectively erected on the sides of the bottom surface. As shown in  FIG. 11 , the bottom surface of the recessed portion  338  is inclined to face the axial center of the pressure roller  51 , with respect to a plane that includes the front-rear direction D 2  and the left-right direction D 3 . In a state where the heater  32 C 1  is fitted in the recessed portion  338 , the supported surface  322  of the substrate  41  is in contact with the bottom surface of the recessed portion  338 . In addition, in the state where the heater  32 C 1  is fitted in the recessed portion  338 , opposite end portions in the longitudinal direction and opposite end portions in the short direction of the heater  32 C 1  are in contact with the side walls of the recessed portion  338 . The recessed portion  338  is formed such that its depth is approximately the same as the thickness of the heater  32 C 1 . As a result, in the state where the heater  32 C 1  is fitted in the recessed portion  338 , the contact surface  321  of the heater  32 C 1  is approximately flush with the edge portion of the recessed portion  338 . 
     The recessed portion  339  is configured to be fitted with a heater  32 C 2  that is adjacent to the heater  32 C 1  among the three heaters  32 C. The recessed portion  339  includes a bottom surface of a rectangular shape and side walls respectively erected on the sides of the bottom surface. As shown in  FIG. 11 , the bottom surface of the recessed portion  338  is approximately parallel to the plane that includes the front-rear direction D 2  and the left-right direction D 3  such that the bottom surface faces the axial center of the pressure roller  51 . In a state where the heater  32 C 2  is fitted in the recessed portion  339 , the supported surface  322  of the substrate  41  is in contact with the bottom surface of the recessed portion  339 . In addition, in the state where the heater  32 C 2  is fitted in the recessed portion  339 , opposite end portions in the longitudinal direction and opposite end portions in the short direction of the heater  32 C 2  are in contact with the side walls of the recessed portion  339 . The recessed portion  339  is formed such that its depth is approximately the same as the thickness of the heater  32 C 2 . As a result, in the state where the heater  32 C 2  is fitted in the recessed portion  339 , the contact surface  321  of the heater  32 C 2  is approximately flush with the edge portion of the recessed portion  339 . 
     The recessed portion  340  is configured to be fitted with a heater  32 C 3  that is, among the three heaters  32 C, positioned most downstream in the running direction D 5 . The recessed portion  340  includes a bottom surface of a rectangular shape and side walls respectively erected on the sides of the bottom surface. As shown in  FIG. 11 , the bottom surface of the recessed portion  340  is inclined to face the axial center of the pressure roller  51 , with respect to a plane that includes the front-rear direction D 2  and the left-right direction D 3 . In a state where the heater  32 C 3  is fitted in the recessed portion  340 , the supported surface  322  of the substrate  41  is in contact with the bottom surface of the recessed portion  340 . In addition, in the state where the heater  32 C 3  is fitted in the recessed portion  340 , opposite end portions in the longitudinal direction and opposite end portions in the short direction of the heater  32 C 3  are in contact with the side walls of the recessed portion  340 . The recessed portion  340  is formed such that its depth is approximately the same as the thickness of the heater  32 C 3 . As a result, in the state where the heater  32 C 3  is fitted in the recessed portion  340 , the contact surface  321  of the heater  32 C 3  is approximately flush with the edge portion of the recessed portion  340 . 
     In the fixing device  17 D, each of the three heaters  32 C is mounted in a posture where the contact surface  321  thereof faces the axial center of the pressure roller  51 . Thus the three heaters  32 C are arranged such that the three contact surfaces  321  thereof draw an arc along the outer peripheral surface of the pressure roller  51 . As a result, it is possible to expand the nip region R 1  in the sheet conveyance direction D 4  without increasing the roller diameter of the pressure roller  51 . Accordingly, it is possible to increase the sheet conveyance speed without enlarging the device. 
     Here, as shown in  FIG. 11 , in the fixing device  17 D, the heater  32 C 3  that is, among the three heaters  32 C, positioned most downstream in the rotation direction D 6 , is mounted in a posture intersecting the sheet conveyance direction D 4 . This increases the bending of the fixing belt  31  at a downstream end of the nip region R 1  in the conveyance direction D 4 , thereby promoting separation of the sheet from the fixing belt  31 . It is noted that the fixing device  17 D may not include the heater  32 C 3  and the recessed portion  340 . 
     It is noted that, as shown in  FIG. 12 , the fixing device  17 D may not include the heater  32 C 1  and the recessed portion  338 . In the configuration shown in  FIG. 12 , the heater  32 C 2 , one of the two heaters  32 C that is positioned most upstream in the rotation direction D 6 , is mounted in a posture being parallel to the sheet conveyance direction D 4 . This helps a sheet enter the nip region R 1  smoothly. 
     Meanwhile, there is known, as a related technology, a fixing device in which the peak of the nip pressure of the nip region R 1  is set to be downstream of a center of the nip region R 1  in the running direction D 5  of the fixing belt  31  so that an image with high glossiness can be output. 
     However, in the fixing device of the related technology, the peak of the nip pressure of the nip region R 1  is set to be downstream of the heater in the running direction D 5 , and the nip region R 1  extends from the heater toward the downstream in the running direction D 5 . This increases the roller diameter of the pressure roller  51  that forms the nip region R 1 . On the other hand, a fixing device  17 E according to a fifth embodiment of the present disclosure is configured to output an image with high glossiness without increasing the roller diameter of the pressure roller  51 , as described in the following. 
     Fifth Embodiment 
     Next, with reference to  FIG. 13 , a description is given of a configuration of the fixing device  17 E according to the fifth embodiment of the present disclosure. Here,  FIG. 13  is a cross-sectional diagram showing a configuration of the fixing device  17 E. 
     The fixing device  17 E has the same configuration as the fixing device  17 A except that it includes two heaters  32 B in place of the heater  32 A, and a heater support portion  33 E in place of the heater support portion  33 A, and does not include the reserving portions  36 . It is noted that the heaters  32 B included in the fixing device  17 E are the same as the heaters  32 B included in the fixing device  17 B. 
     The two heaters  32 B are arranged in line along the running direction D 5  to be pressed against the inner peripheral surface of the fixing belt  31  in a positional relation where the peak of the nip pressure of the nip region R 1  is downstream of a center of the nip region R 1  in the running direction D 5  of the fixing belt  31 . Specifically, as shown in  FIG. 13 , the two heaters  32 B are mounted in a posture where the contact surfaces  321  thereof face the pressure roller  51  and are parallel to each other. In addition, among the two heaters  32 B, a heater  32 B 2  is downstream of a heater  32 B 1  in the running direction D 5 , and the contact surface  321  of the heater  32 B 2  projects toward the pressure roller  51  more than the contact surface  321  of the heater  32 B 1 . The two heaters  32 B are arranged such that end portions of the two heaters  32 B facing each other are in contact with each other, and a contact portion where the end portions are in contact with each other is downstream of the axial center of the pressure roller  51  in the running direction D 5 . The two heaters  32 B are pressed by the pressing member  35  toward the pressure roller  51 , and pressed against the inner peripheral surface of the fixing belt  31 . A lubricant is applied to the contact surfaces  321  of the two heaters  32 B. 
     The heater support portion  33 E has the same configuration as the heater support portion  33 A except that it includes a recessed portion  341  (an example of a first support portion of the present disclosure) and a recessed portion  342  (an example of a second support portion of the present disclosure) in place of the recessed portion  331 . 
     The recessed portion  341  comes in contact with the supported surface  322  of the heater  32 B 1  to support the heater  32 B 1 . The recessed portion  341  is formed to store the heater  32 B 1 . The recessed portion  341  includes a bottom surface of a rectangular shape and side walls respectively erected on the sides of the bottom surface. As shown in  FIG. 13 , a side wall of the recessed portion  341  that is on the downstream side in the running direction D 5  continues to the bottom surface of the recessed portion  342 . The recessed portion  341  and the heater  32 B 1  have approximately the same length in the left-right direction D 3 . In addition, the recessed portion  341  and the heater  32 B 1  have approximately the same length in the front-rear direction D 2 . In a state where the heater  32 B 1  is stored in the recessed portion  341 , the supported surface  322  of the substrate  41  comes in contact with a bottom surface of the recessed portion  341 . In addition, in the state where the heater  32 B 1  is stored in the recessed portion  341 , opposite end portions in the longitudinal direction and opposite end portions in the short direction of the heater  32 B 1  are in contact with the side walls of the recessed portion  341 . 
     The recessed portion  342  comes in contact with the supported surface  322  of the heater  32 B 2  at a position more on the pressure roller  51  side than the recessed portion  341  to support the heater  32 B 2 . The recessed portion  342  is formed to store the heater  32 B 2 . The recessed portion  342  includes a bottom surface of a rectangular shape and side walls respectively erected on the sides of the bottom surface except for a side on the upstream side in the running direction D 5 . As shown in  FIG. 13 , the bottom surface of the recessed portion  342  projects toward the pressure roller  51  more than the bottom surface of the recessed portion  341 . The recessed portion  342  and the heater  32 B 2  have approximately the same length in the left-right direction D 3 . In addition, the recessed portion  342  and the heater  32 B 2  have approximately the same length in the front-rear direction D 2 . In a state where the heater  32 B 2  is stored in the recessed portion  342 , the supported surface  322  of the substrate  41  comes in contact with a bottom surface of the recessed portion  342 . In addition, in the state where the heater  32 B 2  is stored in the recessed portion  342 , opposite end portions in the longitudinal direction and opposite end portions in the short direction of the heater  32 B 2  are in contact with the side walls of the recessed portion  342 . 
     In the fixing device  17 E, the positional relation between the two heaters  32 B sets the peak of the nip pressure of the nip region R 1  to be downstream of the center of the nip region R 1  in the running direction D 5  of the fixing belt  31 . This configuration makes it possible to output an image with high glossiness without increasing the roller diameter of the pressure roller  51 . 
     It is noted that, as shown in  FIG. 14 , the fixing device  17 E may include a recessed portion  343  (an example of a support portion of the present disclosure) in place of the recessed portions  341  and  342 , and may further include a spacer  344 . The recessed portion  343  is formed by the recessed portion  341  and the recessed portion  342 , wherein the bottom surfaces of the recessed portion  341  and the recessed portion  342  are flush with each other. The spacer  344  is provided between the bottom surface of the recessed portion  343  and the heater  32 B 2 . This allows the contact surface  321  of the heater  32 B 2  to project toward the pressure roller  51  more than the contact surface  321  of the heater  32 B 1 . With this configuration, too, the peak of the nip pressure of the nip region R 1  is set to be downstream of the center of the nip region R 1  in the running direction D 5  of the fixing belt  31 . It is noted that instead of providing the spacer  344 , the heater  32 B 2  may be formed to be thicker than the heater  32 B 1 . 
     In addition, the two heaters  32 B may be mounted in a posture where the contact surfaces  321  thereof are not parallel to each other. For example, as shown in  FIG. 12 , the two heaters  32 B may be arranged in a posture where the contact surfaces  321  thereof respectively face the axial center of the pressure roller  51 . In this case, the heater  32 B 2  positioned on the downstream side in the running direction D 5  is mounted to project toward the pressure roller  51  more than the heater  32 B 1 . With this configuration, too, it is possible to set the peak of the nip pressure of the nip region R 1  to be downstream of the center of the nip region R 1  in the running direction D 5  of the fixing belt  31 . 
     Meanwhile, there is known, as a related technology, a fixing device in which the heating element  42  is divided in its longitudinal direction into a plurality of heating portions, and energization of each of the plurality of heating portions can be controlled. 
     Here, in the fixing device of the related technology, in order to execute a temperature control for each of the heating portions, it is necessary to provide as many sensors as the heating portions on the back surface of the substrate  41 . However, the number of sensors that can be arranged on the back surface of the substrate  41  is limited. As a result, in the fixing device of the related technology, since it is not possible to provides more heating portions than sensors that can be arranged on the back surface of the substrate  41 , the number of divisions of the heating element  42  is limited. On the other hand, in a fixing device  17 F according to a sixth embodiment of the present disclosure, it is possible to increase the number of divisions of the heating element  42 , as described in the following. 
     Sixth Embodiment 
     Next, with reference to  FIG. 15  and  FIG. 16 , a description is given of a configuration of the fixing device  17 F according to the sixth embodiment of the present disclosure. Here,  FIG. 15  is a cross-sectional diagram showing a configuration of the fixing device  17 F.  FIG. 16  is a bottom diagram showing a configuration of heaters  32 D,  32 E, and  32 F, and the heater support portion  33 D. 
     The fixing device  17 F has the same configuration as the fixing device  17 A except that it includes the heaters  32 D,  32 E, and  32 F in place of the heater  32 A, and the heater support portion  33 D in place of the heater support portion  33 A, and does not include the reserving portions  36 . It is noted that the heater support portion  33 D is the same as the heater support portion  33 D included in the fixing device  17 D. 
     The heaters  32 D,  32 E, and  32 F include heating portions  421  to  425  formed by dividing the heating element  42 . As shown in  FIG. 16 , in the fixing device  17 F, the heating portions are provided in the heaters  32 D,  32 E, and  32 F at different positions in the left-right direction D 3  that matches the width direction of the fixing belt  31 . 
     As shown in  FIG. 15 , the heaters  32 D,  32 E, and  32 F are provided inside the fixing belt  31 , in line along the outer peripheral surface of the pressure roller  51 . In addition, each of the heaters  32 D,  32 E, and  32 F is mounted to face the axial center of the pressure roller  51 . Each of the heaters  32 D,  32 E, and  32 F is pressed by the pressing member  35  toward the pressure roller  51 , and pressed against the inner peripheral surface of the fixing belt  31 . A lubricant is applied to the contact surfaces  321  of each of the heaters  32 D,  32 E, and  32 F. 
     The heater  32 D has the same configuration as the heater  32 A except that it is smaller than the heater  32 A in size in the short direction, and it includes a heating portion  421  in place of the heating element  42 , and a sensor  441  in place of the sensor  44 . The heating portion  421  is heated when energized. As shown in  FIG. 16 , the heating portion  421  is provided in a region of the substrate  41  that faces the fixing belt  31 , at the center of the region in the left-right direction D 3 . The sensor  441  corresponds to the heating portion  421 , and outputs an electric signal that varies depending on the temperature of the heating portion  421 . 
     The heater  32 E has the same configuration as the heater  32 A except that it is smaller than the heater  32 A in size in the short direction, and it includes heating portions  422  and  423  in place of the heating element  42 , and sensors  442  and  443  in place of the sensor  44 . Each of the heating portions  422  and  423  is heated when energized. As shown in  FIG. 16 , the heating portion  422  is provided in the region of the substrate  41  that faces the fixing belt  31 , at a position between the center of the region in the left-right direction D 3  and the left end of the region. The heating portion  423  is provided in the region of the substrate  41  that faces the fixing belt  31 , at a position between the center of the region in the left-right direction D 3  and the right end of the region. The sensor  442  corresponds to the heating portion  422 , and outputs an electric signal that varies depending on the temperature of the heating portion  422 . The sensor  443  corresponds to the heating portion  423 , and outputs an electric signal that varies depending on the temperature of the heating portion  423 . 
     The heater  32 F has the same configuration as the heater  32 A except that it is smaller than the heater  32 A in size in the short direction, and it includes heating portions  424  and  425  in place of the heating element  42 , and sensors  444  and  445  in place of the sensor  44 . Each of the heating portions  424  and  425  is heated when energized. As shown in  FIG. 16 , the heating portion  424  is provided in the region of the substrate  41  that faces the fixing belt  31 , at the left end of the region. The heating portion  423  is provided in the region of the substrate  41  that faces the fixing belt  31 , at the right end of the region. The sensor  444  corresponds to the heating portion  424 , and outputs an electric signal that varies depending on the temperature of the heating portion  424 . The sensor  445  corresponds to the heating portion  425 , and outputs an electric signal that varies depending on the temperature of the heating portion  425 . 
     As described above, in the fixing device  17 F, the heating portions  421  to  425  are arranged in distribution in the heaters  32 D,  32 E, and  32 F. With this configuration, compared with a configuration where all of heating portions formed by dividing the heating element  42  are arranged in one substrate, it is possible to increase the number of divisions of the heating element  42 . 
     Here, as shown in  FIG. 15 , in the fixing device  17 F, the heaters  32 D,  32 E, and  32 F are disposed along the rotation direction D 6  of the pressure roller  51  with a predetermined interval therebetween. With this configuration, compared with a configuration where the heaters  32 D,  32 E, and  32 F are disposed with no interval therebetween, it is possible to restrict reduction in detection accuracy of the sensors  441  to  445  (an example of a plurality of temperature sensors of the present disclosure) caused by heat transfer in the substrate  41 . It is noted that the heaters  32 D,  32 E, and  32 F may be disposed with no interval therebetween. 
     As shown in  FIG. 15 , in the fixing device  17 F, the heaters  32 D,  32 E, and  32 F are mounted in a posture where the contact surfaces  321  thereof face the axial center of the pressure roller  51 . With this configuration, it is possible to increase the number of heaters without increasing the roller diameter of the pressure roller  51 . 
     In addition, as shown in  FIG. 15 , in the fixing device  17 F, among the heaters  32 D,  32 E, and  32 F, the heater  32 F positioned most downstream in the rotation direction D 6  is mounted in a posture intersecting the sheet conveyance direction D 4 . This increases the bending of the fixing belt  31  at a downstream end of the nip region R 1  in the conveyance direction D 4 , thereby promoting separation of the sheet from the fixing belt  31 . It is noted that the heaters  32 D,  32 E, and  32 F may be disposed in a state where the contact surfaces  321  thereof are parallel to each other. In this case, among the heaters  32 D,  32 E, and  32 F, the heater  32 D positioned most upstream in the rotation direction D 6  is mounted in a posture being parallel to the sheet conveyance direction D 4 . This helps a sheet enter the nip region R 1  smoothly. 
     It is to be understood that the embodiments herein are illustrative and not restrictive, since the scope of the disclosure is defined by the appended claims rather than by the description preceding them, and all changes that fall within metes and bounds of the claims, or equivalence of such metes and bounds thereof are therefore intended to be embraced by the claims.