Patent Publication Number: US-9411273-B1

Title: Fixing device and image forming apparatus

Description:
INCORPORATION BY REFERENCE 
     This application is based on Japanese Patent application No. 2014-072991 filed on Mar. 31, 2014, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     The present disclosure relates to a fixing device configured to fix a toner image onto a recording medium and an image forming apparatus including the fixing device. 
     Conventionally, an electrographic image forming apparatus, such as a copying machine or a printer, includes a fixing device configured to fix a toner image onto a recording medium, such as a sheet. For the fixing device, a heat roller manner is widely used. The heat roller manner is a manner to form a fixing nip by using a pair of rollers, which are made of metal, such as aluminum or iron, for example. 
     On the other hand, a fixing manner is being shifted from the above-mentioned heat roller manner to a belt manner to shorten a warm-up time. The belt manner is a manner to form a fixing nip by using a fixing belt. The fixing belt has a smaller heat capacity than a pair of the rollers and is made of metal, such as SUS (stainless steel), for example. 
     For example, there is a fixing device including a fixing belt, a pressuring member coming into pressure contact with the fixing belt so as to form a fixing nip, a heat source arranged at an inside in a radial direction of the fixing belt, a reflecting member reflecting a radiant heat from the heat source and a supporting member supporting the reflecting member. 
     In the fixing device as described above, there is a case where the reflecting member and the supporting member are fastened to each other with a screw. However, if the reflecting member and the supporting member are fastened to each other with a screw, there is a problem that the weaker of the reflecting member and the supporting member (normally, the reflecting member) is deformed when they are heated, in a case where a linear expansion coefficient of the reflecting member is different from that of the supporting member. 
     Further, in the fixing device as described above, when the fixing device is assembled, the heat source, the reflecting member and the supporting member have to be inserted into the fixing belt which has flexibility. Therefore, there is a problem that it is difficult to assemble the fixing device. 
     SUMMARY 
     In accordance with an embodiment of the present disclosure, a fixing device includes a fixing belt, a pressuring member, a heat source, a reflecting member, a supporting member and a retaining member. The fixing belt is configured to be rotatable around a rotation axis. The pressuring member is configured to be rotatable and to come into pressure contact with the fixing belt so as to form a fixing nip. The heat source is arranged at an inside in a radial direction of the fixing belt and configured to radiate a radiant heat. The reflecting member is configured to reflect the radiant heat radiated from the heat source to an inner circumference face of the fixing belt. The supporting member is configured to support the reflecting member from a side of the fixing nip. The retaining member includes a contact part and a holding part. The contact part is configured to come into contact with the reflecting member from a side opposite to the fixing nip. The holding part is configured to hold the heat source. 
     In accordance with an embodiment of the present disclosure, an image forming apparatus includes the above-mentioned fixing device. 
     The above and other objects, features, and advantages of the present disclosure will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present disclosure is shown by way of illustrative example. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram showing an outline of a printer according to an embodiment of the present disclosure. 
         FIG. 2  is a sectional view showing a fixing device of the printer according to the embodiment of the present disclosure. 
         FIG. 3  is a perspective view showing the fixing device of the printer according to the embodiment of the present disclosure. 
         FIG. 4  is an exploded perspective view showing an upper frame part and a fixing belt, in the fixing device of the printer according to the embodiment of the present disclosure. 
         FIG. 5  is an exploded perspective view showing a heater, a reflecting member, a supporting member, a pressing member and a retaining member, in the fixing device of the printer according to the embodiment of the present disclosure. 
         FIG. 6  is an exploded perspective view showing the supporting member and the pressing member, in the fixing device of the printer according to the embodiment of the present disclosure. 
         FIG. 7  is a front view showing the heater, the reflecting member, the supporting member, the pressing member and the retaining member, in the fixing device of the printer according to the embodiment of the present disclosure. 
         FIG. 8  is a plan view showing the heater, the reflecting member, the supporting member and the retaining member, in the fixing device of the printer according to the embodiment of the present disclosure. 
         FIG. 9  is a perspective view showing the heater, the reflecting member, the supporting member and the retaining member, in the fixing device of the printer according to the embodiment of the present disclosure. 
         FIG. 10  is an exploded perspective view showing the reflecting member, the supporting member and the retaining member, in the fixing device of the printer according to the embodiment of the present disclosure. 
         FIG. 11  is a sectional view showing a fixing device according to another embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     First, with reference to  FIG. 1 , the entire structure of a printer  1  (an image forming apparatus) will be described. 
     The printer  1  includes a box-like formed printer main body  2 . In a lower part of the printer main body  2 , a sheet feeding cartridge  3  storing sheets (recording mediums) is installed and, in a top face of the printer main body  2 , an ejected sheet tray  4  is formed. To the top face of the printer main body  2 , an upper cover  5  is openably/closably attached at a lateral side of the ejected sheet tray  4  and, below the upper cover  5 , a toner container  6  is installed. 
     In an upper part of the printer main body  2 , an exposure device  7  composed of a laser scanning unit (LSU) is located below the ejected sheet tray  4 . Below the exposure device  7 , an image forming part  8  is arranged. In the image forming part  8 , a photosensitive drum  10  as an image carrier is rotatably arranged. Around the photosensitive drum  10 , a charger  11 , a development device  12 , a transfer roller  13  and a cleaning device  14  are located along a rotating direction (refer to an arrow X in  FIG. 1 ) of the photosensitive drum  10 . 
     Inside the printer main body  2 , a conveying path  15  for the sheet is arranged. At an upstream end in the conveying path  15 , a sheet feeding part  16  is positioned. At an intermediate stream part in the conveying path  15 , a transferring part  17  composed of the photosensitive drum  10  and transfer roller  13  is positioned. At a downstream part in the conveying path  15 , a fixing device  18  is positioned. At a downstream end in the conveying path  15 , a sheet ejecting part  19  is positioned. Below the conveying path  15 , an inversion path  20  for duplex printing is arranged. 
     Next, the operation of forming an image by the printer  1  having such a configuration will be described. 
     When the power is supplied to the printer  1 , various parameters are initialized and initial determination, such as temperature determination of the fixing device  18 , is carried out. Subsequently, in the printer  1 , when image data is inputted and a printing start is directed from a computer or the like connected with the printer  1 , image forming operation is carried out as follows. 
     First, the surface of the photosensitive drum  10  is electrically charged by the charger  11 . Then, exposure corresponding to the image data is carried out to the photosensitive drum  10  by a laser light (refer to a two-dot chain line P in  FIG. 1 ) from the exposure device  7 , thereby forming an electrostatic latent image on the surface of the photosensitive drum  10 . Subsequently, the development device  12  develops the electrostatic latent image to a toner image by a toner. 
     On the other hand, a sheet picked up from the sheet feeding cartridge  3  by the sheet feeding part  16  is conveyed to the transferring part  17  in a suitable timing for the above-mentioned image forming operation, and then, the toner image on the photosensitive drum  10  is transferred onto the sheet in the transferring part  17 . The sheet with the transferred toner image is conveyed to a downstream side in the conveying path  15  to be inserted to the fixing device  18 , and then, the toner image is fixed onto the sheet in the fixing device  18 . The sheet with the fixed toner image is ejected from the sheet ejecting part  19  to the ejected sheet tray  4 . The toner remained on the photosensitive drum  10  is collected by the cleaning device  14 . 
     Next, the fixing device  18  will be described in detail. Hereinafter, it will be described so that the front side of the fixing device  18  is positioned at the near side of  FIG. 2 , for convenience of explanation. An arrow Y of  FIG. 2  a conveying direction of the sheet (in the present embodiment, left and right direction). Arrow Fr of each figure indicates a front side of the fixing device  18 . An arrow I of each figure indicates an inside in a front and rear direction and an arrow O of each figure indicates an outside in the front and rear direction. 
     As shown in  FIG. 2  or the like, the fixing device  18  includes a box-like formed fixing frame  21 , a fixing belt  22  housed in an upper part of the fixing frame  21 , a pressuring roller  23  (a pressuring member) housed in a lower part of the fixing frame  21 , a heater  24  (a heat source) arranged at an inside of the fixing belt  22  in a radial direction, a reflecting member  25  arranged at the inside of the fixing belt  22  in the radial direction and at a lower side of the heater  24 , a supporting member  26  arranged at the inside of the fixing belt  22  in the radial direction and at a lower side of the reflecting member  25 , a pressing member  27  arranged at the inside of the fixing belt  22  in the radial direction and at a lower side of the supporting member  26  and retaining members  28  (In  FIG. 2 , only a rear side retaining member  28  is shown) respectively arranged at both front and rear end sides of the fixing belt  22 . 
     The fixing frame  21  is made of a plate metal. As shown in  FIG. 3  or the like, the fixing frame  21  is composed of an upper frame part  31  and a lower frame part  32  connected to each other. 
     The upper frame part  31  of the fixing frame  21  includes a pair of front and rear upper side end plates  33  and a top plate  34  connecting upper end parts of the upper side end plates  33 . 
     As shown in  FIG. 4  or the like, to an outer face of each upper side end plate  33  of the upper frame part  31 , a heater attachment plate  35  is fixed. To an inner face of each upper side end plate  33 , a belt attachment base  36  is fixed. An arc-like belt supporting part  37  is arranged at an end part inside in the front and rear direction of each belt attachment base  36 . Around outer circumference of the belt supporting part  37 , annular meandering restriction ring  38  is arranged. 
     To the top plate  34  of the upper frame part  31 , a pair of front and rear first thermistors  40  are fixed. As shown in  FIG. 3  or the like, each first thermistor  40  comes into contact with a center part and a rear part of an outer circumference face of the fixing belt  22 . 
     The lower frame part  32  of the fixing frame  21  includes a pair of front and rear lower side end plates  41  and a bottom plate  42  connecting lower parts of the lower side end plates  41 . 
     At an inside in the front and rear direction of each lower side end plate  41  of the lower frame part  32 , swing frames  43  are arranged. At a right end side of each swing frame  43 , a spindle  44  is arranged and each swing frame  43  is configured to swing around each spindle  44  as a fulcrum. At a rear side (outside in the front and rear direction) of the rear lower side end plate  41 , an input gear  45  is arranged coaxially with each spindle  44 . The input gear  45  is connected to a drive source  46  composed of a motor or the like. 
     As shown in  FIG. 2  or the like, to the lower frame part  32 , a second thermistor  47  is fixed. The second thermistor  47  comes into contact with an outer circumference face of the pressuring roller  23 . At the lower frame part  32 , an entry guide  48  and an ejecting guide  49  is arranged. 
     The fixing belt  22  is formed in a roughly cylindrical shape elongated in the front and rear direction. The fixing belt  22  has flexibility and is formed in an endless shape in a circumferential direction. The fixing belt  22  includes, for example, a base material layer and a release layer covering the base material layer. The base material layer of the fixing belt  22  is made of, for example, metal, such as steel special use stainless (SUS). Incidentally, the base material layer of the fixing belt  22  may be made of resin, such as polyimide (PI). The release layer of the fixing belt  22  is made of, for example, perfluoro alkoxy alkane (PFA) tube. Each figure shows the respective layers (the base material layer and the release layer) of the fixing belt  22  without especially distinguishing. 
     Into both front and rear end parts of the fixing belt  22 , the belt supporting part  37  (refer to  FIG. 4  or the like) arranged at each belt attachment base  36  of the upper frame part  31  is inserted. Thereby, the fixing belt  22  is rotatably supported by the upper frame part  31 . The fixing belt  22  is rotatable around a rotation axis A (refer to  FIG. 4  or the like) extending in the front and rear direction. That is, in the present embodiment, the front and rear direction is a rotation axis direction of the fixing belt  22 . Both front and rear end faces of the fixing belt  22  are arranged at an inside in the front and rear direction of the meandering restriction ring  38  arranged in each belt attachment base  36  of the upper frame part  31 . Thereby, meandering (movement to an outside in the front and rear direction) of the fixing belt  22  is restricted. 
     The pressuring roller  23  (refer to  FIG. 2  or the like) is formed in a roughly columnar shape elongated in the front and rear direction. The pressuring roller  23  is composed of, for example, a columnar core material  50 , an elastic layer  51  provided around the core material  50  and a release layer (not shown) covering the elastic layer  51 . The core material  50  of the pressuring roller  23  is made of, for example, metal, such as iron. The elastic layer  51  of the pressuring roller  23  is made of, for example, silicone rubber. The release layer (not shown) of the pressuring roller  23  is made of, for example, PFA tube. 
     The pressuring roller  23  is arranged at a lower side (an outside) of the fixing belt  22 . The pressuring roller  23  comes into pressure contact with the fixing belt and, between the fixing belt  22  and the pressuring roller  23 , a fixing nip  52  is formed. Incidentally, the conveying direction of the sheet is, for example, a conveying direction when the sheet passes through the fixing nip  52 . The pressuring roller  23  is rotatably supported by a center part in a longitudinal direction (in the present embodiment, a center part in the left and right direction) of each swing frame  43  of the fixing frame  21 . Each swing frame  43  is configured to swing around each spindle  44  to move the pressuring roller  23  in the upper and lower direction so that the pressure of the fixing nip  52  is shifted. 
     As shown in  FIG. 3 , to a rear end part of the pressuring roller  23 , a drive gear  53  is fixed. The drive gear  53  is meshed with the input gear  45  and connected to the drive source  46  via the input gear  45 . 
     The heater  24  (refer to  FIG. 5  or the like) is composed of, for example, a halogen heater. As shown in  FIG. 2  or the like, a lower end part (an end part of the fixing nip  52  side) of the heater  24  is arranged at an upper side (a further side from the fixing nip  52 ) than upper end parts (end parts far from fixing nip  52  side) of the pressing member  27 , the supporting member  26  and the reflecting member  25 . Both front and rear end parts of the heater  24  are attached to the heater attachment plate (refer to  FIG. 4 ) of the upper frame part  31  of the fixing frame  21 . As shown in  FIG. 5  or the like, both front and rear end parts of the heater  24  are connected with a thermostat  54 . 
     The heater  24  includes a radiating part  55  and held parts  56  arranged at both front and rear sides (outsides in the front and rear direction) of the radiating part  55 . The radiating part  55  is configured to generate heat by energizing of the heater  24  so as to radiate a radiant heat. The held parts  56  are arranged at both front and rear end parts of the heater  24 . Each held part  56  is formed in a lateral columnar shape and has a larger diameter than the radiating part  55 . 
     The reflecting member  25  is formed in a shape elongated in the front and rear direction. The reflecting member  25  is made of a metal, such as an aluminum alloy for brightening. The reflecting member  25  is arranged between the heater  24  and the supporting member  26 . A top face of the reflecting member  25  (a face at a side of the heater  24 ) is a reflecting face (mirror face) which reflects a radiant heat radiated from the radiating part  55  of the heater  24 , to an inner circumference face of the fixing belt  22 . The reflecting member  25  is arranged to cover an upper side (the side of the heater  24 ) of the supporting member  26 , thereby preventing the radiant heat radiated from the radiating part  55  of the heater  24  from being directly radiated on the supporting member  26  so as to prevent the temperature of the supporting member  26  from rising. 
     As shown in  FIG. 2  or the like, the reflecting member  25  includes a first reflecting part  61 , a second reflecting part  62  which is provided at a left side (a downstream side in the sheet conveying direction) of the first reflecting part  61  and a third reflecting part  63  which connects the first reflecting part  61  with the second reflecting part  62 . 
     The first reflecting part  61  inclines to a lower side (a side of the supporting member  26 ) toward a right side (an upstream side in the sheet conveying direction). The second reflecting part  62  inclines to a lower side (the side of the supporting member  26 ) toward a left side (the downstream side in the sheet conveying direction). The third reflecting part  63  is arranged along the left and right direction (the sheet conveying direction). The third reflecting part  63  faces the radiating part  55  of the heater  24  at an interval. 
     The reflecting member  25  is bent so as to project toward an upper side (a side of the heater  24 ). In other words, the reflecting member  25  is bent so as to dent toward a lower side (a side of the supporting member  26 ). Hence, at a lower side (a side of the supporting member  26 ) of the reflecting member  25 , a concave part  66  is formed so as to be covered by the first reflecting part  61 , the second reflecting part  62  and the third reflecting part  63 . 
     As shown in  FIG. 5  or the like, at both front and rear end parts of the first reflecting part  61 , engagement pieces  64  extending horizontally toward a right side (the upstream side in the sheet conveying direction) are arranged. At both front and rear end parts of the second reflecting part  62 , engagement pieces  65  extending horizontally toward a left side (the downstream side in the sheet conveying direction) are arranged. 
     The supporting member  26  is formed in a shape elongated in the front and rear direction. The supporting member  26  includes an upstream side stay  71  and a downstream side stay  72 . The upstream side stay  71  and the downstream side stay  72  are made of sheet metals, such as SECC (galvanized steel sheet), for example. An upper part of the supporting member  26  is inserted into the concave part  66  formed at the lower side of the reflecting member  25 . 
     As shown in  FIGS. 5 to 7  or the like, the upstream side stay  71  includes an upstream side base plate  73  which extends in upper and lower direction, an upstream side support plate  74  which is bent from a lower end part of the upstream side base plate  73  to the right side (the upstream side in the sheet conveying direction), an upstream side guide plate  75  which is bent from a right end part of the upstream side support plate  74  to an upper right side and upstream side fixing pieces  76  protruded from both front and rear end parts of the upstream side guide plate  75  to an upper side and extending toward outsides in the front and rear direction. 
     In a left side face (an inside face in the left and right direction) of each upstream side fixing piece  76 , a pair of front and rear fixing protrusions  77  are arranged. At an inside end part of each upstream side fixing piece  76  in the front and rear direction, an engagement groove  78  (an engagement part) is arranged. 
     As shown in  FIGS. 5 to 7  or the like, the downstream side stay  72  includes a downstream side base plate  80  which extends in the upper and lower direction, a downstream side support plate  81  which is bent from a lower end part of the downstream side base plate  80  to the left side (the downstream side in the sheet conveying direction), a downstream side guide plate  82  which is bent from a left end part of the downstream side support plate  81  to an upper left side and downstream side fixing pieces  83  protruded from both front and rear end parts of the downstream side guide plate  82  to an upper side and extending toward outsides in the front and rear direction. 
     The downstream side base plate  80  is fixed to the upstream side base plate  73  with a plurality of screws  84  arranged at intervals in the front and rear direction. At a lower end part of the downstream side base plate  80 , a plurality of fitting holes  85  are arranged at intervals in the front and rear direction. 
     In a right side face (an inside face in the left and right direction) of each downstream side fixing piece  83 , a fixing protrusion  86  is arranged. At an inside end part of each downstream side fixing piece  83  in the front and rear direction, an engagement groove  87  (an engagement part) is arranged. 
     As shown in  FIGS. 8 and 9  or the like, with the engagement grooves  78 ,  87  arranged at the upstream side stay  71  and the downstream side stay  72 , the engagement pieces  64 ,  65  arranged at the first reflecting part  61  and the second reflecting part  62  of the reflecting member  25  are engaged. By such a configuration, the reflecting member  25  is supported by the supporting member  26  from a lower side (a side of the fixing nip  52 ). 
     As shown in  FIG. 6  or the like, the pressing member  27  is formed in a plate-like shape elongated in the front and rear direction. The pressing member  27  is made of a heat resistant resin such as LCP (Liquid Crystal Polymer). 
     In an upper face of the pressing member  27 , a plurality of fitting protrusions  88  are arranged at intervals in the front and rear direction. Each fitting protrusion  88  fits into each fitting hole  85  arranged at the downstream side base plate  80  of the downstream side stay  72  of the supporting member  26 . 
     As shown in  FIG. 7  or the like, a top face of the pressing member  27  comes into contact with a bottom face of the supporting member  26  (more specifically, the bottom face of the upstream side support plate  74  of the upstream side stay  71  and the bottom face of the downstream side support plate  81  of the downstream side stay  82 ). Thus, the pressing member  27  is supported by the supporting member  26 , and a warp (deformation caused by a fixing load) of the pressing member  27  is suppressed. 
     As shown in  FIG. 2  or the like, the bottom face of the pressing member  27  inclines to a lower side (a side of the pressuring roller  23 ) from the right side (the upstream side in the sheet conveying direction) toward the left side (the downstream side in the sheet conveying direction). The bottom face of the pressing member  27  presses the fixing belt  22  to the lower side (the side of the pressuring roller  23 ). 
     Between the bottom face of the pressing member  27  and the inner circumference face of the fixing belt  22 , a sheet member  90  is interposed. The sheet member  90  is made of a fluorine-based resin, such as PTFE, and has a lower friction coefficient than that of the pressing member  27 . In addition, between the bottom face of the pressing member  27  and the inner circumference face of the fixing belt  22 , a lubricant (grease) may be applied. 
     As shown in  FIGS. 9 and 10  or the like, each retaining member  28  includes a main body plate  91  and both side plates  92  arranged at both left and right sides of the main body plate  91 . 
     The main body plate  91  of each retaining member  28  extends in a horizontal direction. At an inside end part of the main body plate  91  in the front and rear direction (a first end part in the front and rear direction), a roughly rectangular contact part  93  is arranged. The contact part  93  is protruded from a center in the left and right direction of an inside edge part of the main body plate  91  in the front and rear direction toward an inside in the front and rear direction. The contact part  93  comes into contact with each of both front and rear end parts of the third reflecting part  63  of the reflecting member  25  from an upper side (a side opposite to the fixing nip  52 ). As shown in  FIG. 8  or the like, the contact part  93  overlaps partially with the engagement grooves  78 ,  87  of the supporting member  26  with regard to a location in the front and rear direction. 
     As shown in  FIGS. 9 and 10  or the like, in the center part of the main body plate  91  in the front and rear direction, a notch part  94  formed in a rectangular shape by a plan view is arranged. At an outside end part of the main body plate  91  in the front and rear direction (a second end part in the front and rear direction), a holding part  95  is arranged at an outside of the notch part  94  in the front and rear direction. The holding part  95  is curved in an arc shape to a lower side (a side of the fixing nip  52 ). On the holding part  95 , each held part  56  of the heater  24  is placed (held). At both left and right edge parts of the main body plate  91 , rectangular slits  96  are arranged. 
     Each side plate  92  of each retaining member  28  is bent from each of the both left and right edge parts of the main body plate  91  to a lower side. At each side plate  92 , a protruding piece  97  protruding upward is arranged from a front part to a rear part. 
     At an inside part of each side plate  92  in the front and rear direction, a first fixing hole  98  with a precise circular shape is arranged so as to overlap partially with the protruding piece  97 . With the first fixing hole  98  of the right side plate  92 , the fixing protrusion  77  arranged at an inside in the front and rear direction of the upstream side stay  71  of the supporting member  26  is engaged. At an outside part of each side plate  92  in the front and rear direction, a second fixing hole  99  with an elongated hole shape elongated in a lateral direction is arranged so as to overlap partially with the protruding piece  97 . With the second fixing hole  99  of the right side plate  92 , the fixing protrusion  77  arranged at an outside in the front and rear direction of the upstream side stay  71  of the supporting member  26  is engaged. With the second fixing hole  99  of the left side plate  92 , the fixing protrusion  86  of the downstream side stay  72  of the supporting member  26  is engaged. By above-mentioned configuration, each side plate  92  is fixed to the supporting member  26 . 
     To fix a toner image to a sheet in the fixing device  18  to which the above configuration is applied, the drive source  46  is driven. When the drive source  46  is driven in this way, a rotation of the drive source  46  is transmitted to the pressuring roller  23  via the input gear  45  and the drive gear  53 , and the pressuring roller  23  rotates as indicated by arrow B in  FIG. 2 . When the pressuring roller  23  rotates in this way, as indicated by arrow C in  FIG. 2 , the fixing belt  22  which comes into pressure contact with the pressuring roller  23  is driven and rotated in a direction opposite to that of the pressuring roller  23 . When the fixing belt  22  rotates in this way, the fixing belt  22  slides against the pressing member  27  and the sheet member  90 . 
     Further, to fix a toner image to a sheet, the heater  24  is activated (turned on). When the heater  24  is activated in this way, the radiating part  55  of the heater  24  radiates a radiant heat. As indicated by arrow D in  FIG. 2 , a part of the radiant heat radiated from the radiating part  55  of the heater  24  is directly radiated on the inner circumference face of the fixing belt  22 , and is absorbed. Further, as indicated by arrow E in  FIG. 2 , another part of the radiant heat radiated from the radiating part  55  of the heater  24  is reflected to the inner circumference face of the fixing belt  22  by the upper face of the reflecting member  25  and is absorbed by the inner circumference face of the fixing belt  22 . According to the above function, the heater  24  heats the fixing belt  22 . When a sheet passes through the fixing nip  52  in this state, a toner image is heated and then melts, and then the toner image is fixed to the sheet. 
     In the present embodiment, as described above, a manner to directly heat the fixing belt  22  by the heater  24  is applied. However, it is impossible to directly heat the fixing belt  22  by the heater  24  in an area where the reflecting member  25  and the supporting member  26  exist (an area of a side of the fixing nip  52 ). Accordingly, there is a problem that heating efficiency of the fixing belt  22  is deteriorated. 
     However, in the present embodiment, the reflecting member  25  is provided with the first reflecting part  61  and the second reflecting part  62  so that the reflecting member  25  is formed in a shade-like shape, and a center part in the left and right direction (the upstream side base plate  73  and the downstream side base plate  80 ) of the supporting member  26  is made higher than both left and right side parts (the upstream side guide plate  75  and the downstream side guide plate  82 ) of the supporting member  26  (refer to  FIG. 2  or the like). By applying such a configuration, it is possible to broaden an area, of the fixing belt  22 , directly heated by the heater  24 . Accordingly, it is possible to rise the heating efficiency of the fixing belt  22 . 
     Also, the reflecting member  25  further includes the third reflecting part  63  configured to connect the first reflecting part  61  with the second reflecting part  62 . Accordingly, it is possible to easily separate the heater  24  from the reflecting member  25 , thereby preventing the temperature of the reflecting member  25  from rising. 
     On the other hand, if the center part in the left and right direction of the supporting member  26  is made higher than the both left and right side parts of the supporting member  26  as described above, it becomes difficult to place the heater  24  on the supporting member  26  because the parts of the same height in an upper face of the supporting member  26  is reduced. Accompanying to this, there is a concern that it becomes difficult to assemble the fixing device  18 . Accordingly, in the present embodiment, the fixing device  18  is assembled in the following way. 
     Firstly, the reflecting member  25  is placed on the supporting member  26  while the engagement pieces  64 , of the reflecting member  25  are engaged with the engagement grooves  78 ,  87  of the supporting member  26 . Next, the fixing protrusions  77 ,  86  of the supporting member  26  are engaged with the first and second fixing holes  98 ,  99  of each side plate  92  of each retaining member  28 . According to this, each side plate  92  is fixed to the supporting member  26  and each retaining member  28  is attached to each of both front and rear end parts of the supporting member  26 . Accompanying to this, the contact part  93  of each retaining member  28  comes into contact with each of both front and rear end parts of the third reflecting part  63  of the reflecting member  25  from the upper side. According to this, a shift of the reflecting member  25  is securely prevented. 
     Next, each held part  56  of the heater  24  is placed on the holding part  95  of each retaining member  28 . In this state, the heater  24 , the reflecting member  25 , the supporting member  26  and the pressing member  27  are inserted into the fixing belt  22 . 
     In the present embodiment, as described above, each held part  56  of the heater  24  is placed (held) on the holding part  95  of each retaining member  28  when the fixing device  18  is assembled. Accordingly, it is possible to easily assemble the fixing device  18 . 
     Also, in the fixing device  18  with above-mentioned configuration, if the reflecting member  25  and the supporting member  26  are fastened to each other with a screw, there is a concern that the reflecting member  25  which is weaker than the supporting member  26  is deformed when they are heated because of the difference between a linear expansion coefficient of the reflecting member  25  and that of the supporting member  26 . Thus, in the present embodiment, the reflecting member  25  is supported by the supporting member  26  from the lower side (the side of the fixing nip  52 ) and the contact part  93  of each retaining member  28  comes into contact with each of both front and rear end parts of the third reflecting part  63  of the reflecting member  25  from an upper side (the side opposite to the fixing nip  52 ). By applying such a configuration, it is possible to sandwich the reflecting member  25  between the supporting member  26  and the contact part  93  and to fix the reflecting member  25  to the supporting member  26  without fastening the reflecting member  25  to the supporting member  26  with a screw. Accordingly, it is possible to prevent the reflecting member  25  from deforming when the reflecting member  25  and the supporting member  26  are heated. 
     Also, each retaining member  28  includes a main body plate  91  including the contact part  93  and the holding part  95  and the both side plates  92  arranged at both sides of the main body plate  91 , and the both side plates  92  are fixed to the supporting member  26 . By applying such a configuration, it is possible to securely fix each retaining member  28  to the supporting member  26 . 
     Also, the contact part  93  is arranged at the inside end part of the main body plate  91  in the front and rear direction and the holding part  95  is arranged at the outside end part of the main body plate  91  in the front and rear direction. By applying such a configuration, it is possible to separate the contact part  93  which comes into contact with the third reflecting part  63  of the reflecting member  25  from the holding part  95  on which each held part  56  of the heater  24  is placed (held), as far as possible. Accompanying to this, it is possible to prevent the reflecting member  25  and the heater  24  from coming into contact with each other when the fixing device  18  is assembled. 
     Also, the supporting member  26  includes the engagement grooves  78 ,  87  with which the engagement pieces  64 ,  65  of the reflecting member  25  are engaged, and the contact part  93  overlaps partially with the engagement grooves  78 ,  87  with regard to the location in the front and rear direction. By applying such a configuration, it is possible to sandwich the reflecting member  25  between the engagement grooves  78 ,  87  and the contact part  93 . Accordingly, it is possible to securely prevent the shift of the reflecting member  25 . 
     Also, the heater  24  includes the radiating part  55  configured to radiate the radiant heat and the held parts  56  arranged at the outsides of the radiating part  55  in the front and rear direction and placed on the holding part  95 . By applying such a configuration, it is possible to prevent a temperature of each retaining member  28  from rising due to heat transmission from the heater  24 , compared with a case where the radiating part  55  is placed on the holding part  95 . 
     Also, each held part  56  is formed in the lateral columnar shape and the holding part  95  is curved in the arc shape to the lower side. By applying such a configuration, it is possible to securely hold each held part  56  by the holding part  95 . 
     Also, the fixing device  18  includes a pressing member  27  configured to press the fixing belt  22  to the lower side (the side of the pressuring roller  23 ). By applying such a configuration, it is possible to securely fix the toner image onto the sheet in the fixing nip  52 . 
     Also, in the present embodiment, the heater  24  heats the fixing belt  22 , so that it is possible to reduce a heat capacity of a member heated by the heater  24 , compared with a case where the heater  24  heats a fixing roller. Accompanying to this, it is possible to shorten a warm-up time of the fixing device  18 . 
     Also, in the present embodiment, the reflecting member  25  is bent so as to project to the upper side (the side of the heater  24 ), so that it is possible to broaden the area, of the fixing belt  22 , directly heated by the heater  24 . Accordingly, it is possible to promptly rise the temperature of the fixing belt  22 . 
     Also, in the present embodiment, the reflecting member  25  includes the third reflecting part  63 , so that it is possible to easily separate the heater  24  from the reflecting member  25 . Therefore, it is possible to prevent the temperature of the reflecting member  25  from rising. Also, the contact part  93  of each retaining member  28  comes into contact with the third reflecting part  63 , so that it is possible to securely prevent the shift of the reflecting member  25 . 
     In the present embodiment, the reflecting member  25  is bent so as to project to the upper side (the side of the heater  24 ). In another embodiment, the reflecting member  25  may be curved so as to project to the upper side (the side of the heater  24 ). In still another embodiment, as shown in  FIG. 11 , the reflecting member  25  may include a first plate part  101  arranged along an upper and lower direction (a direction crossing (orthogonal) to the sheet conveying direction) and arranged at a right side (an upstream side in the sheet conveying direction) of the supporting member  26 , a second plate part  102  arranged along the upper and lower direction (the direction crossing (orthogonal) to the sheet conveying direction) and arranged at a left side (a downstream side in the sheet conveying direction) of the supporting member  26  and a third plate part  103  configured to connect upper end parts (end parts of a side far from the fixing nip  52 ) of the first plate part  101  and the second plate part  102 . By applying such a configuration, the reflecting member  25  may be formed in a U shape, thereby making a large space at a lower side (a side of the supporting member  26 ) of the reflecting member  25 . Accompanying to this, it is possible to enhance flexibility of a layout of the supporting member  26 . 
     In the present embodiment, the first reflecting part  61  and the second reflecting part  62  of the reflecting member  25  are connected by the third reflecting part  63 . In another embodiment, the first reflecting part  61  and the second reflecting part  62  of the reflecting member  25  may be directly connected with each other without the third reflecting part  63 . In such a case, the reflecting member  25  may be formed in a roughly V shape and it is preferable to form the contact part  93  of each retaining member  28  in a V shape so that the form of the contact part  93  corresponds to that of the reflecting member  25 . By applying such a configuration, it is possible to securely prevent the shift of the reflecting member  25 . 
     In the present embodiment, one heater  24  is arranged at the inside in the radial direction of the fixing belt  22 . In another embodiment, a plurality of heaters  24  may be arranged at the inside in the radial direction of the fixing belt  22 . 
     In the present embodiment, the halogen heater is used as the heater  24 . In another embodiment, a ceramic heater or the like may be used as the heater  24 . 
     In the present embodiment, the configuration of the present disclosure is applied to the printer  1 . In another embodiment, the configuration of the present disclosure may be applied to another image forming apparatus, such as a copying machine, a facsimile or a multifunction peripheral. 
     While the present disclosure has been described with reference to the particular illustrative embodiments, it is not to be restricted by the embodiments. It is to be appreciated that those skilled in the art can change or modify the embodiments without departing from the scope and spirit of the present disclosure.