Patent Publication Number: US-9904221-B2

Title: Preheating device, fixing system, and image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2016-115428 filed Jun. 9, 2016 and No. 2016-142971 filed Jul. 21, 2016. 
     BACKGROUND 
     (i) Technical Field 
     The present invention relates to a preheating device, a fixing system, and an image forming apparatus. 
     (ii) Related Art 
     In a known preheating device, before a continuous recording medium on which an unfixed image, such as a toner image, is formed is introduced into a fixing device, a back surface of the recording medium on which the unfixed image is not formed is preheated. 
     Besides, in a known turning bar device, when a web (continuous recording medium) constituted by a sheet material shaped like a long belt is transported, a transport state of the web is changed and adjusted by outputting the web in a state in which the web is wound around a turning bar disposed in a transport path. 
     SUMMARY 
     According to an aspect of the invention, there is provided a preheating device including two first inverting members disposed at different positions while obliquely intersecting a feeding direction of a continuous recording medium on which an unfixed image is formed, the first inverting members inverting the recording medium by passing a back surface of the recording medium, on which the unfixed image is not formed, therealong before a fixing operation, and at least one heating rotating body disposed at a position further on an outside than a side edge portion of the recording medium in the feeding direction to preheat the recording medium before the fixing operation by passing a portion of the back surface of the recording medium present between the two first inverting members so that the portion of the back surface is wound around the heating rotating body. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein: 
         FIG. 1  is a schematic explanatory view illustrating a configuration of an image forming apparatus according to a first exemplary embodiment; 
         FIG. 2  is a schematic explanatory view illustrating a structure of a fixing system in the image forming apparatus illustrated in  FIG. 1 ; 
         FIG. 3  is a schematic perspective view illustrating a structure of a preheating device in the fixing system illustrated in  FIG. 2 ; 
         FIG. 4  is a schematic perspective view illustrating a structure of an inverting device in the fixing system illustrated in  FIG. 2 ; 
         FIG. 5  is a schematic explanatory view illustrating a state of the fixing system of  FIG. 2  when viewed from above; 
         FIG. 6  is a schematic explanatory view illustrating a configuration of an image forming apparatus according to a second exemplary embodiment; 
         FIG. 7  is a schematic explanatory view illustrating a structure of a fixing system in the image forming apparatus illustrated in  FIG. 6 ; 
         FIG. 8  is a schematic perspective view illustrating a structure of a preheating device in the fixing system illustrated in  FIG. 7 ; 
         FIG. 9  is a schematic explanatory view illustrating a state of the fixing system of  FIG. 7  when viewed from above; 
         FIG. 10  is a schematic explanatory view illustrating a structure of a fixing system according to a third exemplary embodiment; 
         FIG. 11  is a schematic explanatory view illustrating a state of the fixing system of  FIG. 10  when viewed from above; 
         FIG. 12  is a schematic explanatory view illustrating a configuration of an image forming apparatus according to a fourth exemplary embodiment; 
         FIG. 13  is a schematic explanatory view illustrating a structure of a fixing system in the fourth exemplary embodiment; 
         FIG. 14  is a schematic explanatory view illustrating a state of the fixing system of  FIG. 13  when viewed from above; 
         FIG. 15  is a schematic explanatory view illustrating a structure of a fixing system according to a fifth exemplary embodiment; 
         FIG. 16  is a schematic explanatory view illustrating a state of the fixing system of  FIG. 15  when viewed from obliquely above; 
         FIG. 17  is a schematic explanatory view illustrating a state of the fixing system of  FIG. 15  when viewed from above; and 
         FIG. 18  is a schematic explanatory view illustrating another structure example of the preheating device in the fixing system illustrated in, for example,  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION 
     Modes for carrying out the present invention (hereinafter referred to as “exemplary embodiments”) will described below with reference to the drawings. 
     First Exemplary Embodiment 
       FIGS. 1 to 3  illustrate an image forming apparatus according to a first exemplary embodiment.  FIG. 1  illustrates a general outline of the image forming apparatus,  FIG. 2  illustrates a fixing system provided in the image forming apparatus, and  FIG. 3  illustrates a preheating device provided in the image forming apparatus or the fixing system. In the figures including  FIG. 1 , arrows with signs X, Y, and Z denote (the directions of) orthogonal coordinate axes representing the directions of width, height, and depth, respectively, of a three-dimensional space assumed in the figures. 
     [Overall Configuration of Image Forming Apparatus] 
     An image forming apparatus  1  according to the first exemplary embodiment forms an image made with toner of developer on continuous paper  9  serving as an example of a continuous recording medium wound in a roll form. 
     As schematically illustrated in  FIG. 1 , the image forming apparatus  1  includes a supply device  11  that supplies continuous paper  9 , an image forming device  2  that forms a toner image serving as an example of an unfixed image on the continuous paper  9  supplied from the supply device  11 , a fixing system  4  that performs a fixing operation of fixing the toner image formed on the continuous paper  9  in the image forming device  2  after preheating, before the fixing operation, a back surface  9   b  of the continuous paper  9  on which the toner image is not formed, and a storage device  16  that stores the continuous paper  9  after an image is formed thereon by the fixing operation in the fixing system  4 . 
     The supply device  11  includes a pay-out roller  12  that pays out the continuous paper  9  wound in a roll form, an adjusting mechanism  13  that adjust a pay-out operation of the pay-out roller  12 , and an introduction transport roller pair  14  that transports the continuous paper  9  paid out through the adjusting mechanism  13  and supplies the continuous paper  9  to the image forming device  2 . 
     The pay-out roller  12  is rotated in a pay-out direction by driving force received from an unillustrated driving device. The adjusting mechanism  13  includes two transport rollers  13   a  and  13   b  arranged in parallel and spaced from each other in a transport direction (feeding direction) A of the continuous paper  9 , an elevating roller  13   c  that moves up and down almost along the gravitational direction between the two transport rollers  13   a  and  13   b , and an unillustrated position sensor that detects that the elevating roller  13   c  reaches specified positions in the up-down direction. In the adjusting mechanism  13 , the continuous paper  9  is supported while being laid between the two transport rollers  13   a  and  13   b , and is transported in such a manner that the continuous paper  9  is pulled downward almost along the gravitational direction by the elevating roller  13   c  between the transport rollers  13   a  and  13   b  and then turns back. 
     The transport roller pair  14  is constituted of a rotating roller and a driven roller arranged in pressure contact with each other. The rotating roller is rotated in a direction corresponding to the transport direction A by driving force received from an unillustrated driving device, and the continuous paper  9  is thereby transported while passing through a pressure contact portion between these rollers. In practice, the transport roller pair  14  is disposed in the image forming device  2 . 
     In the supply device  11 , the continuous paper  9  is transported by the transport roller pair  14  when the pay-out roller  12  is stopped and the elevating roller  13   c  of the adjusting mechanism  13  is moved to the lower specified position. 
     On the other hand, when the continuous paper  9  is transported by the transport roller pair  14 , the elevating roller  13   c  starts moving up, and moves up to finally reach the upper specified position. In this stage, the pay-out roller  12  rotates to pay out the continuous paper  9 . When the continuous paper  9  is paid out from the pay-out roller  12 , the elevating roller  13   c  starts moving down, and moves down to finally reach the lower specified position. In this stage, the pay-out roller  12  is stopped to discontinue paying-out of the continuous paper  9 . The amount of continuous paper  9  supplied to the image forming device  2  corresponds to the rotation amount of the transport roller pair  14 . 
     As the continuous paper  9 , for example, a belt-shaped long continuous material made of paper such as high-quality paper or glassine paper, or synthetic resin, such as polypropylene, is used. Besides, for example, label paper having a structure in which a surface base material (image forming surface) is provided on release paper with an adhesive layer interposed between is also used as the continuous paper  9 . 
     The storage device  16  includes a take-up roller  17  that takes up the continuous paper  9  on which an image is formed, an adjusting mechanism  18  that adjusts a take-up operation of the take-up roller  17 , and an output transport roller pair  19  that transports the continuous paper  9  to the adjusting mechanism  18  after the image is formed on the continuous paper  9 . 
     The take-up roller  17  is rotated in a take-up direction by driving force received from an unillustrated driving device. The adjusting mechanism  18  is constituted of two transport rollers  18   a  and  18   b , an elevating roller  18   c , and a detector that detects upper and lower specified positions of the elevating roller  18   c , almost similarly to the adjusting mechanism  13  in the supply device  11 . The transport roller pair  19  has a structure almost similar to the transport roller pair  14  in the supply device  11 . In practice, the transport roller pair  19  is also disposed in the image forming device  2 , similarly to the transport roller pair  14 . 
     The image forming device  2  forms toner images by using some or all of toners of four colors of yellow (Y), magenta (M), cyan (C), and black (K) on the basis of image information input from the outside through various units, and transfers the toner images on the continuous paper  9 . 
     In the first exemplary embodiment, the image forming device  2  includes four image forming units  20 Y,  20 M,  20 C, and  20 K each of which forms a toner image of any one of the above four colors (Y, M, C, and K), and an intermediate transfer device  30  that holds color toner images formed by the image forming units  20  (Y, M, C, and K) and transports the color toner images to a second transfer position P 2  where the color toner images are finally transferred onto the continuous paper  9 . 
     Each of the image forming units  20  (Y, M, C, and K) includes a photoconductor drum  21  to be rotated in a predetermined direction (a direction shown by arrow B). Also, in each of the image forming units  20  (Y, M, C, and K), a charging device  22 , an exposure device  23 , a developing device  24 , and a cleaning device  26  are arranged around the photoconductor drum  21 . The charging device  22  charges a peripheral surface of the photoconductor drum  21 . The exposure device  23  forms an electrostatic latent image by exposing the charged peripheral surface of the photoconductor drum  21  to light based on the image information. The developing device  24  develops the electrostatic latent image formed on the peripheral surface of the photoconductor drum  21  with toner of developer to form a toner image. The cleaning device  26  removes and cleans off unwanted matter, such as toner, remaining on the peripheral surface of the photoconductor drum  21 . 
     The developing device  24  is provided as four developing devices  24 Y,  24 M,  24 C, and  24 K. Each of the developing devices  24 Y,  24 M,  24 C, and  24 K stores toner of any one of the above four colors (Y, M, C, and K), and develops an electrostatic latent image of the corresponding color with the toner. 
     The intermediate transfer device  30  is disposed below the four image forming units  20  (Y, M, C, and K). 
     In the first exemplary embodiment, the intermediate transfer device  30  includes an intermediate transfer belt  31  that rotates in a direction of arrow C while passing through first transfer positions at photoconductor drums  21  in the image forming units  20  (Y, M, C, and K), plural support rollers  32 A to  32 E that support the intermediate transfer belt  31  rotatably, and first transfer devices  33  that first-transfer toner images on the photoconductor drums  21  onto an outer surface of the intermediate transfer belt  31  by, for example, an electrostatic action by pressing the outer surface of the intermediate transfer belt  31  against the first transfer positions on the photoconductor drums  21  in the image forming units  20  (Y, M, C, and K). For example, the first transfer devices  33  are each shaped like a roller. The intermediate transfer device  30  further includes a second transfer device  35  shaped like, for example, a roller to second-transfer the toner images on the intermediate transfer belt  31  onto continuous paper  9  by, for example, an electrostatic action, and a cleaning device  36  that removes and cleans off unwanted matter, such as toner, remaining on the outer surface of the intermediate transfer belt  31 . 
     The support roller  32 A, the support roller  32 D, and the support roller  32 E are respectively structured as a driving roller, a tensioning roller, and a second-transfer backup roller. The second transfer device  35  is displaceable to move into contact with and apart from the intermediate transfer belt  31  supported by the second-transfer backup roller  32 E. Thus, for example, the second transfer device  35  moves to a position in contact with the intermediate transfer belt  31  only during a period in which a second transfer operation is performed, and moves to a position separate from the intermediate transfer belt  31  during other necessary periods. 
     The first transfer positions are positions where the photoconductor drums  21  are opposed to the first transfer devices  33  in the image forming units  20  (strictly, positions where the photoconductor drums  21  are in contact with the intermediate transfer belt  31 ). The second transfer position P 2  is a position where the intermediate transfer belt  31  is in opposed contact with the second transfer device  35  in the intermediate transfer device  30 . 
     [Structure of Fixing System] 
     As illustrated in, for example,  FIGS. 1 and 2 , the fixing system  4  includes a fixing device  40  that performs a fixing operation of fixing a toner image formed as an unfixed image on continuous paper  9  by passing the continuous paper  9  therethrough, and a preheating device  5  disposed at a position upstream of the fixing device  40  in the feeding direction A of the continuous paper  9  to preheat, before the fixing operation, a back surface  9   b  of the continuous paper  9  on which the toner image is not formed. 
     The fixing system  4  is disposed between (the second transfer position P 2  in) the image forming device  2  and the storage device  16 . The fixing device  40  in the fixing system  4  includes at least a heating rotating body  41  and a pressurizing rotating body  42 , as illustrated in  FIG. 1 . A two-dot chain line VL 1  in  FIG. 2  is an imaginary straight line that connects the second transfer position P 2  in the image forming device  2  and a fixing nip FN (to be described later) serving as a fixing portion in the fixing device  40  in the shortest distance. 
     As illustrated in  FIG. 2 , the fixing device  40  of the first exemplary embodiment adopts a belt-shaped heating rotating body  41  and a roller-shaped pressurizing rotating body (pressurizing roller)  42 . The belt-shaped heating rotating body  41  is constituted of an endless heating belt  43  serving as a heating member, a fixing roller  44  serving as a pressing member, a first support roller  45 , an inner heating roller  46 , and a second support roller  47 , which are disposed to support the heating belt  43  while being in contact with an inner peripheral surface of the heating belt  43 , and an outer heating roller  48  in contact with a portion of an outer peripheral surface of the heating belt  43  between the first support roller  45  and the inner heating roller  46  to press the portion toward the inner peripheral surface of the heating belt  43 . 
     In the fixing device  40 , the heating belt  43  of the heating rotating body  41  is in pressure contact with the pressurizing roller  42  at a portion of the heating belt  43  wound on an outer peripheral surface of the fixing roller  44 . Thus, the pressure contact portion between the heating belt  43  and the pressurizing roller  42  serves as a fixing nip FN for fixing the unfixed toner image formed on the continuous paper  9  by heating and pressurization. 
     The heating belt  43  is composed of a belt base made of, for example, polyimide resin or polyamide resin, an elastic layer stacked on an outer peripheral surface of the belt base and made of, for example, silicone rubber, and a release layer stacked on a surface of the elastic layer and made of, for example, a tetrafluoroethylene perfluoroalkyl vinylether copolymer (PFA). 
     The fixing roller  44  is constituted by a cylindrical member made of metal such as aluminum or stainless steel, and is rotated in a direction of arrow in  FIG. 2  by an unillustrated driving unit. A heat source  49 A, such as a halogen lamp, is disposed inside the fixing roller  44 , and heats the fixing roller  44  so that the surface temperature of the fixing roller  44  reaches a required temperature. 
     Almost similarly to the fixing roller  44 , the inner heating roller  46  is constituted by a cylindrical member made of metal such as aluminum or stainless steel. A heat source  49 B, such as a halogen lamp, is disposed inside the inner heating roller  46 , and heats the inner heating roller  46  so that the surface temperature of the inner heating roller  46  reaches a required temperature. Also, force is applied from an unillustrated elastic member, such as a spring, to the inner heating roller  46  so that the inner heating roller  46  is elastically displaceable from the inner side toward the outer side of the heating belt  43 , and this applies a required tension to the heating belt  43 . 
     Almost similarly to the fixing roller  44 , the outer heating roller  48  is constituted by a cylindrical member made of metal such as aluminum or stainless steel. A heat source  49 C, such as a halogen lamp, is disposed inside the outer heating roller  48 , and heats the outer heating roller  48  so that the surface temperature of the outer heating roller  48  reaches a required temperature. 
     The heating belt  43  stretched between the plural rollers is heated from the inner peripheral surface side and the outer peripheral surface side by the fixing roller  44 , the outer heating roller  48 , and the inner heating roller  46  while circularly rotating. The heating belt  43  is thereby heated so that the temperature of the outer peripheral surface thereof reaches a required temperature. 
     The pressurizing roller  42  is constituted of a cylindrical roller base made of metal such as aluminum or stainless steel, an elastic layer stacked on an outer surface of the roller base and made of, for example, silicone rubber, and a release layer stacked on a surface of the elastic layer and made of, for example, PFA. 
     [Structure of Preheating Device] 
     As illustrated in, for example,  FIGS. 2 and 3 , the preheating device  5  includes two first inverting members  51  and  52  and a heating roller  53  serving as an example of a heating rotating body. The two first inverting members  51  and  52  are disposed at different positions to obliquely intersect the feeding direction A of the continuous paper  9  on which the toner image is formed, and invert the continuous paper  9  by passing a back surface  9   b  of the continuous paper  9 , on which the toner image is not formed, therealong before the fixing operation. The heating roller  53  is disposed at a position further on an outside than side edge portions  9   c  and  9   d  of the continuous paper  9  in the feeding direction A, and preheats a portion of the back surface  9   b  of the continuous paper  9  located between the first inverting members  51  and  52  before the fixing operation by passing the portion of the back surface  9   b  along the heating roller  53  so that the portion of the back surface  9   b  is wound around the heating roller  53 . 
     For example, the two first inverting members  51  and  52  are cylindrical members made of metal. The upstream-side first inverting member  51  disposed on the upstream side in the feeding direction A of the continuous paper  9  inverts the continuous paper  9  transported to the first inverting member  51  so that the continuous paper  9  is transported with the back surface  9   b  being in contact with the outer peripheral surface of the heating roller  53 . The downstream-side first inverting member  52  disposed on the downstream side in the feeding direction A of the continuous paper  9  inverts the continuous paper  9  transported from the heating roller  53  to the first inverting member  52  so that the continuous paper  9  is transported with a front surface  9   a  being opposed to the heating rotating body  41  (heating belt  43 ) in the fixing device  40 . 
     The first inverting members  51  and  52  in the first exemplary embodiment are fixedly arranged to intersect the feeding direction A of the continuous paper  9  at an angle of 45 degrees. 
     Specifically, the upstream-side first inverting member  51  is disposed at a position on a relatively upper side of the downstream-side first inverting member  52  while intersecting the downstream-side first inverting member  52 . The upstream-side first inverting member  51  is used to introduce the continuous paper  9  sent in the preheating device  5  from the lower side thereof and to pass the continuous paper  9  on the upper side thereof. 
     The downstream-side first inverting member  52  is disposed at a position on a relatively lower side of the upstream-side first inverting member  51  to substantially orthogonally intersect the upstream-side first inverting member  51 . The downstream-side first inverting member  52  is used to introduce the continuous paper  9  sent from the heating roller  53  from the lower side thereof and to pass the continuous paper  9  on the upper side thereof. 
     Alternatively, for example, the first inverting members  51  and  52  may be shaped like a barrel as a whole and be curved with an arc-shaped cross section only in a portion to be in contact with the continuous paper  9 . The shapes of other inverting members to be described later are similar to the shape of the first inverting members  51  and  52 . 
     As illustrated in  FIGS. 3 and 5 , the heating roller  53  is disposed at a position spaced outward by a predetermined distance S 1  from one of the side edge portions  9   c  and  9   d  of the continuous paper  9  in the feeding direction A (the side edge portion  9   d  in the first exemplary embodiment) in a state in which the axial direction of the heating roller  53  is substantially parallel to the feeding direction A of the continuous paper  9 . 
     The heating roller  53  is constituted of a cylindrical roller base made of, for example, metal, and a heat source  54 , such as a halogen lamp, disposed in an internal space of the roller base. The roller base of the heating roller  53  is rotatably provided, and is driven to rotate along with the motion (transport movement) of the continuous paper  9  that passes while being wound around the heating roller  53 . In the first exemplary embodiment, the winding angle of the back surface  9   b  of the continuous paper  9  around the heating roller  53  is set to be 180 degrees or more, for example, from the viewpoint of reliably heating the back surface  9   b  of the continuous paper  9 . 
     However, even when the winding angle of the back surface  9   b  of the continuous paper  9  around the heating roller  53  is 90 degrees or more, this winding angle is more effective than when the winding angle is less than 90 degrees. That is, the winding angle less than 90 degrees is disadvantageous, for example, from the viewpoints of ensuring the heating length and restricting the installation space of the preheating device  5  from being increased by the difficulty in arranging the first inverting members  51  and  52  in a state in which the winding angle of the continuous paper  9  increases to an obtuse angle before and after winding around the heating roller  53 . This condition concerning the winding angle also applies to a heating rotating body such as a heating roller  57  to be described later. 
     A one-dot chain line E in, for example,  FIG. 5  shows almost the center position (center line) in the width direction of the continuous paper  9  that is being transported in the feeding direction A. 
     As illustrated in  FIGS. 1 and 2 , in the fixing system  4 , it is necessary to feed out the continuous paper  9  from the preheating device  5  to the fixing device  40  after inverting the continuous paper  9  so that the front surface  9   a  on which the toner image is formed, of the front and back surfaces, faces up. Hence, an inverting device  6  is disposed upstream of the preheating device  5  in the feeding direction A of the continuous paper  9 . 
     As illustrated in, for example,  FIGS. 2 and 4 , the inverting device  6  includes two second inverting members  61  and  62  and a relay roller  63  serving as an example of a relay rotating body. The second inverting members  61  and  62  are disposed at different positions further on the front side serving as the upstream side than the upstream-side first inverting member  51  of the preheating device  5  in the feeding direction A of the continuous paper  9  while obliquely intersecting the feeding direction A of the continuous paper  9 . The second inverting members  61  and  62  invert the continuous paper  9  by passing the back surface  9   b  of the continuous paper  9  therealong. The relay roller  63  is disposed at a position further on the outside than the side edge portions  9   c  and  9   d  of the continuous paper  9  in the feeding direction A, and passes a portion of the back surface  9   b  of the continuous paper  9  located between the second inverting members  61  and  62  so that the portion of the back surface  9   b  is wound around the relay roller  63 . 
     For example, the two second inverting members  61  and  62  are cylindrical members made of metal. The upstream-side second inverting member  61  disposed on the upstream side in the feeding direction A of the continuous paper  9  inverts the continuous paper  9  transported to the second inverting member  61  to transport the continuous paper  9  in a state in which the back surface  9   b  of the continuous paper  9  is in contact with an outer peripheral surface of the relay roller  63 . The downstream-side second inverting member  62  disposed on the downstream side in the feeding direction A of the continuous paper  9  inverts the continuous paper  9  transported from the relay roller  63  to the second inverting member  62  to transport the continuous paper  9  so that the front and back surfaces of the continuous paper  9  face in directions opposite from the directions when the continuous paper  9  is transported to the upstream-side second inverting member  61 . In the first exemplary embodiment, the second inverting member  62  inverts the continuous paper  9  so that the back surface  9   b  of the continuous paper  9  faces up. 
     In the first exemplary embodiment, the second inverting members  61  and  62  are fixedly arranged to intersect the feeding direction A of the continuous paper  9  at an angle of 45 degrees. 
     Specifically, the upstream-side second inverting member  61  is disposed at a position on a relatively lower side of the downstream-side second inverting member  62  while intersecting the downstream-side second inverting member  62 . The upstream-side second inverting member  61  is used to introduce the continuous paper  9  transported through the second transfer position P 2  in the image forming device  2  from the upper side of the second inverting member  61  and to pass the continuous paper  9  on the lower side thereof. 
     The downstream-side second inverting member  62  is disposed at a position on a relatively upper side of the upstream-side second inverting member  61  while substantially orthogonally intersecting the upstream-side second inverting member  61 . The downstream-side second inverting member  62  is used to introduce the continuous paper  9  sent from the relay roller  63  from the upper side of the second inverting member  62  and to pass the continuous paper  9  on the lower side thereof. 
     As illustrated in  FIGS. 4 and 5 , the relay roller  63  is disposed at a position spaced outward by a predetermined distance from one of the side edge portions  9   c  and  9   d  of the continuous paper  9  in the feeding direction A in a state in which the axial direction of the relay roller  63  is substantially parallel to the feeding direction A of the continuous paper  9 . 
     The relay roller  63  is constituted by a cylindrical roller base made of, for example, metal. The relay roller  63  is rotatable, and is driven to rotate along with the motion (transport movement) of the continuous paper  9  that passes while being wound around the relay roller  63 . 
     [Image Forming Operation (Including Preheating and Fixing)] 
     Next, an image forming operation of the image forming apparatus  1  including the preheating device  5  and so on will be described. Here, a description will be given of a case in which a multicolor (full-color) image is formed by combining toners of the above four colors (Y, M, C, and K). 
     First, a toner image is formed as an unfixed image and is transferred onto continuous paper  9  in the image forming device  2 . 
     As illustrated in  FIG. 1 , in each of the image forming units  20  (Y, M, C, and K), after the peripheral surface of the rotating photoconductor drum  21  is charged to a required polarity and a required potential by the charging device  22 , the charged peripheral surface is exposed by the exposure device  23  on the basis of a color component obtained from (multicolor) image information, so that an electrostatic latent image of the color component is formed. After that, the electrostatic latent image is developed with charged toner of the corresponding color by the developing device  24  (Y, M, C, or K), and is thereby visualized as a color toner image. 
     Next, color toner images formed on the photoconductor drums  21  in the respective image forming units  20  (Y, M, C, and K) are first-transferred in order onto the rotating intermediate transfer belt  31  of the intermediate transfer device  30  by the transfer action of the first transfer devices  33 , and are then transported to the second transfer position P 2 . 
     Finally, the toner images first-transferred on the intermediate transfer belt  31  are collectively second-transferred onto continuous paper  9  transported to the second transfer position P 2  by the transfer action of the second transfer device  35 . 
     The continuous paper  9  paid out from the supply device  11  is transported by the transport roller pair  14  toward the second transfer position P 2  in operative association with the toner-image forming operation in the image forming device  2 . At this time, in the supply device  11 , when the continuous paper  9  is transported by the transport roller pair  14 , the elevating roller  13   c  in the adjusting mechanism  13  starts moving up from the lower specified position, and moves up to finally reach the upper specified position, as described above. In this stage, the pay-out roller  12  rotates to pay out the continuous paper  9 . For example, the continuous paper  9  is continuously transported during the toner-image forming operation. 
     Next, the continuous paper  9  on which the toner image has been formed is sent out from the second transfer position P 2 , is transported toward the fixing system  4 , and is subjected to preheating and fixing of the toner image in the fixing system  4 . 
     As illustrated in  FIGS. 1 and 2 , in the fixing system  4 , the continuous paper  9  sent out from the second transfer position P 2  is transported to pass through the inverting device  6 , the preheating device  5 , and the fixing device  40  in this order. 
     First, as illustrated in  FIGS. 4 and 5 , the continuous paper  9  is sent into the inverting device  6  in a state in which the front surface  9   a  having the toner image formed thereon faces up. Then, the continuous paper  9  is inverted, and is sent out from the inverting device  6  with the back surface  9   b  facing up. 
     At this time, in the inverting device  6 , the continuous paper  9  passes while the back surface  9   b  is in contact with the surface of the upstream-side second inverting member  61  to be obliquely wound around the surface. The continuous paper  9  is thereby twisted 90 degrees and is inverted. In this state, the continuous paper  9  is sent out toward the relay roller  63 . After that, the continuous paper  9  is transported along with the rotation of the relay roller  63  while the back surface  9   b  is in contact with the relay roller  63  to be wound around the relay roller  63  from the lower side. Then, the continuous paper  9  is sent out to return to the downstream-side second inverting member  62 . Finally, the continuous paper  9  passes while the back surface  9   b  is in contact with the surface of the downstream-side second inverting member  62  to be obliquely wound around the surface. The continuous paper  9  is thereby twisted 90 degrees, and is inverted. In this state, the continuous paper  9  is sent out from the inverting device  6  with the back surface  9   b  facing up. After that, the continuous paper  9  is transported toward the preheating device  5  provided on the downstream side. 
     Subsequently, as illustrated in  FIGS. 3 and 5 , the continuous paper  9  inverted in the inverting device  6  is sent into the preheating device  5  in the state where the back surface  9   b  having no tone image faces up, and is preheated from the back surface  9   b  before the fixing operation. Also, the continuous paper  9  is inverted, and is sent out from the preheating device  5  with the front surface  9   a  facing up. 
     At this time, in the preheating device  5 , the continuous paper  9  is passed while the back surface  9   b  is in contact with the surface of the upstream-side first inverting member  51  to be obliquely wound therearound. The continuous paper  9  is thereby twisted 90 degrees and is inverted. In this state, the continuous paper  9  is sent out toward the heating roller  53 . After that, the continuous paper  9  is transported along with the rotation of the heating roller  53  in the direction of arrow in  FIG. 3  while the back surface  9   b  is in contact with the heating roller  53  to be obliquely wound therearound from the upper side, and is sent out to return toward the downstream-side first inverting member  52 . Finally, the heated continuous paper  9  is passed while the back surface  9   b  is in contact with the surface of the downstream-side first inverting member  52  to be obliquely wound therearound. The continuous paper  9  is thereby twisted 90 degrees and is inverted. In this state, the continuous paper  9  is sent out from the preheating device  5  with the front surface  9   a  facing up, and is transported toward the fixing device  40  provided on the downstream side. In the preheating device  5 , the continuous paper  9  is heated from the back surface  9   b  at a required temperature (for example, a temperature set within the range of 90° C. to 180° C.) by the heating roller  53 . 
     Subsequently, as illustrated in  FIGS. 2 and 5 , the continuous paper  9  preheated in the preheating device  5  is sent into (the fixing nip FN of) the fixing device  40  in the state where the front surface  9   a  having the toner image formed thereon faces up, is subjected to the fixing operation of the toner image, and is then sent out from the fixing device  40 . 
     At this time, the continuous paper  9  is introduced into and transported through the fixing nip FN in a state where the front surface  9   a  is in contact with the heating belt  43  of the heating rotating body  41 . Thus, the unfixed toner image on the continuous paper  9  is fixed by the fixing operation using heat and pressure at the fixing nip FN. In this fixing operation of the toner image at the fixing nip FN, since the continuous paper  9  is preheated from the back surface  9   b  in the preheating device  5 , the continuous paper  9  is subjected to a formal fixing operation at the fixing nip FN in a state where the toner image is starting to be melted by heating. Hence, fixing may be more quickly and reliably performed than when preheating is not performed. 
     After the unfixed toner image is fixed in the fixing system  4 , the continuous paper  9  is transported toward the storage device  16  by the transport roller pair  19 . At this time, when the continuous paper  9  is transported by the transport roller pair  19 , the elevating roller  18   c  of the adjusting mechanism  18  in the storage device  16  starts moving down from the upper specified position, and moves down to finally reach the lower specified position. In this stage, the take-up roller  17  rotates to take up the continuous paper  9 . Thus, the continuous paper  9  is stored. 
     By repeating the above operation, a full-color image formed by combining four color toners is continuously formed on one surface (front surface  9   a ) of the continuous paper  9 . 
     While the fixing system  4  includes the preheating device  5  in the image forming apparatus  1 , the heating roller  53  of the preheating device  5  is disposed further on the outside than the side edge portion  9   d  of the continuous paper  9  (see, for example,  FIG. 5 ). 
     Second Exemplary Embodiment 
       FIGS. 6 to 8  illustrate an image forming apparatus according to a second exemplary embodiment.  FIG. 6  illustrates a general outline of the image forming apparatus,  FIG. 7  illustrates a fixing system provided in the image forming apparatus, and  FIG. 8  illustrates a preheating device provided in the image forming apparatus or the fixing system. 
     As schematically illustrated in  FIG. 6 , an image forming apparatus  1 B according to the second exemplary embodiment includes a supply device  11 , an image forming device  2 , a fixing system  4 B, and a storage device  16 . Compared with the image forming apparatus  1  of the first exemplary embodiment, the fixing system  4 B is partly different in structure from the fixing system  4  of the first exemplary embodiment, but the supply device  11 , the image forming device  2 , and the storage device  16  have the same structures. 
     As illustrated in, for example,  FIGS. 6 and 7 , the fixing system  4 B of the second exemplary embodiment includes a fixing device  40 , a preheating device  5 B, and a guide roller  71 . Among these, the fixing device  40  has the same structure as that of the fixing device  40  in the fixing system  4  of the first exemplary embodiment ( FIG. 2 ). 
     [Structure of Preheating Device] 
     As illustrated in, for example,  FIGS. 7 and 8 , the preheating device  5 B includes two first inverting members  55  and  56  and a heating roller  57  serving as an example of a heating rotating body. The first inverting members  55  and  56  are disposed at different positions while obliquely intersecting the feeding direction A of continuous paper  9  on which a toner image is formed, and inverts the continuous paper  9  by passing a back surface  9   b  of the continuous paper  9 , which does not have the toner image, therealong before a fixing operation. The heating roller  57  is disposed at a position further on an outside than side edge portions  9   c  and  9   d  of the continuous paper  9  in the feeding direction A, and preheats a portion of the back surface  9   b  of the continuous paper  9  between the first inverting members  55  and  56  before the fixing operation by passing the portion of the back surface  9   b  so that the portion of the back surface  9   b  is wound around the heating roller  57 . 
     In  FIG. 7 , a one-dot chain line VL 2  is an imaginary straight line that connects a second transfer position P 2  in the image forming device  2  and a fixing nip FN in the fixing device  40  in the shortest distance. 
     The two first inverting members  55  and  56  have structures substantially similar to those of the first inverting member  51  and  52  in the preheating device  5  of the first exemplary embodiment. However, the first inverting members  55  and  56  are arranged in a slight different manner as follows because the guide roller  71  to be described later is disposed on the upstream side of the preheating device  5 B. 
     That is, while the first inverting members  55  and  56  in the second exemplary embodiment are fixedly arranged to intersect the feeding direction A of the continuous paper  9  at an angle of 45 degrees, the arrangement thereof is slightly different in the following points. 
     First, the upstream-side first inverting member  55  on the upstream side in the feeding direction A of the continuous paper  9  is disposed at a position on a relatively upper side of the downstream-side first inverting member  56  provided on the downstream side, and intersects the feeding direction A. The upstream-side first inverting member  55  is used to introduce continuous paper  9  sent into the preheating device  5 B from the lower side of the first inverting member  55  and to pass the continuous paper  9  on the upper side thereof. 
     In contrast, the downstream-side first inverting member  56  is disposed at a position on a relatively lower side of the upstream-side first inverting member  55  while being substantially parallel to the upstream-side first inverting member  55 . This is a different point. The downstream-side first inverting member  56  is used to introduce the continuous paper  9  sent from the heating roller  57  from the lower side of the first inverting member  56  and to pass the continuous paper  9  on the upper side thereof. Thus, as illustrated in, for example,  FIG. 8 , the continuous paper  9  inverted and sent out by the downstream-side first inverting member  56  is sent out in a feeding direction directly opposite from the feeding direction A of the continuous paper  9  when the continuous paper  9  is sent to the upstream-side first inverting member  55 . 
     As illustrated in  FIGS. 8 and 9 , the heating roller  57  is disposed at a position spaced outward by a predetermined distance S 2  from one of the side edge portions  9   c  and  9   d  of the continuous paper  9  in the feeding direction A (the side edge portion  9   d  in the second exemplary embodiment) in a state in which the axial direction of the heating roller  57  is substantially parallel to the feeding direction A. While the distance S 2  at this time is equal to the distance S 1  of the heating roller  53  in the preheating device  5  of the first exemplary embodiment, it may be set at a different value. 
     Similarly to the heating roller  53  in the preheating device  5  of the first exemplary embodiment, the heating roller  57  is constituted of a cylindrical roller base made of, for example, metal, and a heat source  58 , such as a halogen lamp, disposed in an internal space of the roller base. Also, similarly to the heating roller  53 , the roller base of the heating roller  57  is rotatable, and is driven to rotate along with the motion (transport movement) of the continuous paper  9  passing to be wound around the heating roller  57 . In the second exemplary embodiment, the winding angle of the back surface  9   b  of the continuous paper  9  around the heating roller  57  is also set to be 180 degrees or more from the viewpoint of reliably heating the back surface  9   b  of the continuous paper  9 . 
     As illustrated in  FIGS. 6 and 7 , the fixing system  4 B includes a guide roller  71  serving as an example of a guide rotating body on the upstream side of the preheating device  5 B. The guide roller  71  guides the continuous paper  9  in a different direction by passing the back surface  9   b  of the continuous paper  9  so that the back surface  9   b  is wound around the guide roller  71 . 
     The guide roller  71  is disposed at a front position upstream of the upstream-side first inverting member  55 , of the two first inverting members  55  and  56  of the preheating device  5 B, in the feeding direction A of the continuous paper  9  in a state in which the axial direction of the guide roller  71  orthogonally intersects the feeding direction A of the continuous paper  9 . For example, the guide roller  71  is a cylindrical member made of metal. Also, the guide roller  71  is rotatably disposed between the second transfer position P 2  in the image forming device  2  and the fixing device  40  and at a position closer to the fixing device  40 . The guide roller  71  in the second exemplary embodiment is used to guide and return the continuous paper  9  sent out from the second transfer position P 2  of the image forming device  2  toward the second transfer position P 2  by turning back and passing the continuous paper  9  while the back surface  9   b  is wound in contact with the guide roller  71 . 
     [Operation of Fixing System] 
     In this fixing system  4 B, as illustrated in  FIGS. 6 and 7 , the continuous paper  9  sent out from the second transfer position P 2  in the image forming device  2  is transported to pass through the guide roller  71 , the preheating device  5 B, and the fixing device  40  in this order. 
     First, as illustrated in, for example,  FIG. 7 , the continuous paper  9  is transported to the guide roller  71  in a state where the front surface  9   a  on which a toner image is formed faces up, and is passed along the guide roller  71  so that the back surface  9   b  is wound around the guide roller  71 . Thus, the continuous paper  9  is guided in a different direction that is directly opposite from the feeding direction A of the continuous paper  9  when the continuous paper  9  is sent out from the second transfer position P 2  and that returns the continuous paper  9  toward the second transfer position P 2  again (however, this direction is a part of the feeding direction A). 
     Next, as illustrated in  FIGS. 7 and 8 , the continuous paper  9  transported by the guide roller  71  to return toward the second transfer position P 2  is sent into the preheating device  5 B in a state where the back surface  9   b  on which the toner image is not formed faces up. In the preheating device  5 B, the continuous paper  9  is preheated from the back surface  9   b  before the fixing operation, and is inverted. The continuous paper  9  is then sent out from the preheating device  5 B with the front surface  9   a  facing up. 
     At this time, in the preheating device  5 B, the continuous paper  9  is passed while the back surface  9   b  is in contact with the surface of the upstream-side first inverting member  55  to be obliquely wound therearound, is twisted 90 degrees, and is inverted. In this state, the continuous paper  9  is sent out toward the heating roller  57 . After that, the continuous paper  9  is transported along with the rotation of the heating roller  57  in the direction of arrow in  FIGS. 7 and 8  while the back surface  9   b  is in contact with the heating roller  57  to be wound therearound from the upper side, and is then sent out to return toward the downstream-side first inverting member  56 . Finally, the heated continuous paper  9  is passed while the back surface  9   b  is in contact with the surface of the downstream-side first inverting member  56  to be wound therearound, is twisted 90 degrees, and is inverted. The continuous paper  9  is then sent out from the preheating device  5 B with the front surface  9   a  facing up, and is transported toward the fixing device  40  provided on the downstream side. In the preheating device  5 B, the continuous paper  9  is heated from the back surface  9   b  at a required temperature (for example, a temperature set within the range of 90° C. to 180° C.) by the heating roller  57 . 
     Finally, as illustrated in  FIGS. 7 and 9 , the continuous paper  9  preheated by the preheating device  5 B is sent into (the fixing nip FN of) the fixing device  40  in the state where the front surface  9   a  having the toner image thereon faces up, is subjected to the fixing operation of the toner image, and is then sent out from the fixing device  40 . 
     While the fixing system  4 B includes the preheating device  5 B in the image forming apparatus  1 B, the heating roller  57  in the preheating device  5 B is disposed further on the outside than the side edge portion  9   d  of the continuous paper  9  (see, for example,  FIG. 9 ). 
     Third Exemplary Embodiment 
       FIG. 10  illustrates a fixing system according to a third exemplary embodiment. 
     As illustrated in  FIG. 10 , a fixing system  4 C according to the third exemplary embodiment includes a fixing device  40 , a preheating device  5 C, an inverting device  6 B, a first guide roller  75 , and a second guide roller  76 . 
     Among these, the fixing device  40  has the same structure as that of the fixing device  40  ( FIG. 2 ) in the fixing system  4  of the first exemplary embodiment. The preheating device  5 C and the inverting device  6 B have the same structures as those of the preheating device  5  (for example,  FIG. 3 ) and the inverting device  6  (for example,  FIG. 4 ) in the first exemplary embodiment. Further, the first guide roller  75  has the same structure as that of the guide roller  71  (for example,  FIG. 7 ) in the second exemplary embodiment. 
     In  FIG. 10 , a one-dot chain line VL 3  is an imaginary straight line that connects a second transfer position P 2  in an image forming device  2  and a fixing nip FN in the fixing device  40  in the shortest distance. 
     The second guide roller  76  is disposed in a state in which the axial direction thereof orthogonally intersects the feeding direction A of continuous paper  9 . With reference to the first guide roller  75 , after the continuous paper  9  is guided by the first guide roller  75 , is returned toward the second transfer position P 2  again, and is inverted by passing through the inverting device  6 B, the second guide roller  76  passes the continuous paper  9  therealong so that the back surface  9   b  of the continuous paper  9  is wound around the second guide roller  76 , and finally guides the continuous paper  9  in a direction toward (the fixing nip FN) in the fixing device  40 . The second guide roller  76  is disposed in a state in which the direction of a rotation axis thereof is substantially parallel to the direction of a rotation axis of the first guide roller  75 . 
     Also, with reference to the preheating device  5 C, the second guide roller  76  is disposed further on the front side serving as the upstream side than the upstream-side first inverting member  51 , of the first inverting members  51  and  52  in the preheating device  5 C, in the feeding direction A of the continuous paper  9 . 
     Further, for example, the second guide roller  76  is a cylindrical member made of metal. The second guide roller  76  is rotatably disposed at a position closer to the second transfer position P 2  in the image forming device  2  between the second transfer position P 2  and the fixing device  40 . 
     [Operation of Fixing System] 
     In this fixing system  4 C, as illustrated in  FIGS. 10 and 11 , the continuous paper  9  sent out from the second transfer position P 2  in the image forming device  2  is transported to pass through the first guide roller  75 , the inverting device  6 B, the second guide roller  76 , the preheating device  5 C, and the fixing device  40  in this order. In  FIG. 11 , the inverting device  6 B is not illustrated. 
     As illustrated in, for example,  FIG. 10 , the continuous paper  9  is first transported to the first guide roller  75  in a state where the front surface  9   a  on which the toner image is formed faces up, and is passed while the back surface  9   b  is wound around the first guide roller  75 . Thus, the continuous paper  9  is guided in a different direction that is directly opposite from the feeding direction A of the continuous paper  9  when the continuous paper  9  is sent out from the second transfer position P 2  and that returns the continuous paper  9  toward the second transfer position P 2  again. 
     Next, as illustrated in  FIG. 10 , the continuous paper  9  transported by the first guide roller  75  to return toward the second transfer position P 2  is sent into the inverting device  6 B in a state where the back surface  9   b  on which the toner image is not formed faces up, is inverted, and is then sent out from the inverting device  6 B with the front surface  9   a  facing up. 
     At this time, in the inverting device  6 B, the continuous paper  9  is passed while the back surface  9   b  is in contact with the surface of an upstream-side second inverting member  61  to be obliquely wound around the surface of the second inverting member  61 . The continuous paper  9  is thereby twisted 90 degrees, is inverted, and is sent out toward a relay roller  63 , almost similarly to the inverting device  6  of the first exemplary embodiment. After that, the continuous paper  9  is transported along with the rotation of the relay roller  63  while the back surface  9   b  is in contact with the relay roller  63  to be wound around the relay roller  63  from the lower side, and is then sent out to return toward a downstream-side second inverting member  62 . Finally, the continuous paper  9  is passed while the back surface  9   b  is in contact with the surface of the downstream-side second inverting member  62  to be obliquely wound around the surface of the second inverting member  62 . The continuous paper  9  is thereby twisted 90 degrees and is inverted. Then, the continuous paper  9  is sent out from the inverting device  6 B with the back surface  9   b  facing up, and is transported toward the second guide roller  76  provided on the downstream side. 
     Next, as illustrated in  FIGS. 10 and 11 , the continuous paper  9  inverted by the inverting device  6 B is transported to the second guide roller  76  downstream of the inverting device  6 B, and is passed while the back surface  9   b  is wound around the second guide roller  76 . Thus, the continuous paper  9  is guided in a different direction (the original feeding direction A) which is directly opposite from the feeding direction of the continuous paper  9  when the continuous paper  9  is sent from the first guide roller  75  through the inverting device  6 B and which is directed toward the fixing nip FN in the fixing device  40 . 
     Next, the continuous paper  9  guided by the second guide roller  76  is sent into the preheating device  5 C in a state where the back surface  9   b  on which the toner image is not formed faces up, is preheated from the back surface  9   b  before the fixing operation, and is inverted. Then, the continuous paper  9  is sent out from the preheating device  5 C with the front surface  9   a  facing up. 
     At this time, in the preheating device  5 C, as illustrated in, for example,  FIGS. 3, 10, and 11 , the continuous paper  9  is passed while the back surface  9   b  is in contact with the surface of the upstream-side first inverting member  51  to be obliquely wound around the surface of the first inverting member  51  from the lower side. The continuous paper  9  is thereby twisted 90 degrees, and is inverted. In this state, the continuous paper  9  is sent out toward the heating roller  53 . After that, the continuous paper  9  is transported along with the rotation of the heating roller  53  in the direction of arrow in  FIG. 3  while the back surface  9   b  is in contact with the heating roller  53  to be wound around the heating roller  53  from the upper side, and is then sent out to return toward the downstream-side first inverting member  52 . Finally, the heated continuous paper  9  is passed while the back surface  9   b  is in contact with the surface of the downstream-side first inverting member  52  to be obliquely wound around the surface of the downstream-side first inverting member  52  from the lower side. The continuous paper  9  is thereby twisted 90 degrees, and is inverted. The continuous paper  9  is sent out from the preheating device  5 C with the front surface  9   a  facing up, and is transported toward the fixing device  40  provided on the downstream side. In the preheating device  5 C, the continuous paper  9  is heated from the back surface  9   b  at a required temperature by the heating roller  53 . 
     Finally, as illustrated in  FIGS. 10 and 11 , the continuous paper  9  preheated in the preheating device  5 C is sent into (the fixing nip FN in) the fixing device  40  while the front surface  9   a  on which the toner image is formed faces up, is subjected to the fixing operation of the toner image, and is then sent out from the fixing device  40 . 
     In this fixing system  4 C, the heating roller  53  in the preheating device  5 C is also disposed at the position spaced outward by a predetermined distance S 3  from a side edge portion  9   d  of the continuous paper  9  (see, for example,  FIG. 11 ). While the distance S 3  is set at the same value as the distance S 1  in the first exemplary embodiment, it may be set at a different value. 
     Fourth Exemplary Embodiment 
       FIGS. 12 to 14  illustrate an image forming apparatus according to a fourth exemplary embodiment.  FIG. 12  illustrates a general outline of the image forming apparatus,  FIG. 13  illustrates a fixing system provided in the image forming apparatus, and  FIG. 14  illustrates a preheating device provided in the image forming apparatus or the fixing system. 
     As schematically illustrated in  FIG. 12 , an image forming apparatus  1 C according to the fourth exemplary embodiment includes a supply device  11 , an image forming device  2 , a fixing system  4 D, and a storage device  16 . The structure of the fixing system  4 D is partly different from that of the fixing system  4  in the image forming apparatus  1  of the first exemplary embodiment, but the other devices, that is, the supply device  11 , the image forming device  2 , and the storage device  16  have the same structures. 
     As illustrated in  FIGS. 12 and 13 , the fixing system  4 D in the fourth exemplary embodiment includes a fixing device  40  and a preheating device  5 D. The fixing device  40  has the same structure as that of the fixing device  40  ( FIG. 2 ) in the fixing system  4  of the first exemplary embodiment. 
     [Structure of Preheating Device] 
     As illustrated in  FIGS. 13 and 14 , the preheating device  5 D includes two first inverting members  510  and  520  and two heating rollers  530 A and  530 B serving as an example of a heating rotating body. The first inverting members  510  and  520  are disposed at different positions while obliquely intersecting a feeding direction A of continuous paper  9  on which a toner image is formed, and invert the continuous paper  9  by passing a back surface  9   b  of the continuous paper  9 , on which the toner image is not formed, therealong before a fixing operation. The heating rollers  530 A and  530 B are disposed at positions further on an outside than a side edge portion  9   d  of the continuous paper  9  in the feeding direction A, and preheat the continuous paper  9  before the fixing operation by passing the continuous paper  9  while a portion of the back surface  9   b  of the continuous paper  9  between the first inverting members  510  and  520  is wound around the heating rollers  530 A and  530 B. 
     In  FIG. 13 , a one-dot chain line VL 1  is an imaginary straight line that connects a second transfer position P 2  in the image forming device  2  and a fixing nip FN in the fixing device  40  in the shortest distance. 
     The two first inverting members  510  and  520  have structures substantially similar to those of the first inverting members  51  and  52  in the preheating device  5  of the first exemplary embodiment. The first inverting members  510  and  520  are fixedly disposed to obliquely intersect the feeding direction A of the continuous paper  9  at an angle of 45 degrees. 
     Also, the two first inverting members  510  and  520  are arranged as follows in a manner slightly different from the first inverting members  51  and  52  in the preheating device  5  of the first exemplary embodiment because the two heating rollers  530 A and  530 B are arranged. 
     That is, since the two heating rollers  530 A and  530 B are arranged in a substantially horizontal state, the two first inverting members  510  and  520  are arranged so that upper ends (top portions) thereof are at the same height as the imaginary straight line VL 1  connecting the second transfer position P 2  in the image forming device  2  and the fixing nip FN in the fixing device  40  in the shortest distance, as illustrated in  FIG. 13 . There is no height difference between the first inverting members  510  and  520  and the imaginary straight line VL 1 . In this respect, the first inverting members  51  and  52  in the preheating device  5  of the first exemplary embodiment are arranged so that the upper ends thereof have a height difference from the imaginary straight line VL 1  ( FIG. 2 ). 
     Similarly to the heating roller  53  in the preheating device  5  of the first exemplary embodiment, the two heating rollers  530 A and  530 B are each constituted of a cylindrical roller base made of, for example, metal, and a heat source  540 , such as a halogen lamp, disposed in an internal space of the roller base. Also, similarly to the heating roller  53 , the roller bases of the heating rollers  530 A and  530 B are rotatably disposed, and are driven to rotate along with the motion (transport movement) of continuous paper  9  that passes while winding around the heating rollers  530 A and  530 B. 
     As illustrated in  FIG. 14 , the two heating rollers  530 A and  530 B are arranged at positions spaced outward by a predetermined distance S 4  from one of side edge portions  9   c  and  9   d  of the continuous paper  9  in the feeding direction A (side edge portion  9   d  in the fourth exemplary embodiment) in a state in which the axial directions of the heating rollers  530 A and  530 B obliquely intersect the feeding direction A of the continuous paper  9 . 
     Specifically, the first heating roller  530 A on the upstream side in the feeding direction of the continuous paper  9  is disposed so that the axial direction thereof obliquely intersects the feeding direction of the continuous paper  9  when the continuous paper  9  is sent out from the upstream-side first inverting member  510  at an angle of about 45 degrees. In other words, the first heating roller  530 A is disposed in such a relation that the axial direction thereof is parallel to the axial direction of the first inverting member  510 . The first heating roller  530 A is used to introduce the continuous paper  9  sent from the first inverting member  510  from the lower side, to wind the continuous paper  9  around the first heating roller  530 A, and to send out the continuous paper  9  from the upper side. At this time, the winding angle of the back surface  9   b  of the continuous paper  9  around the first heating roller  530 A is about 180 degrees. 
     The second heating roller  530 B downstream of the first heating roller  530 A in the transport direction of the continuous paper  9  is disposed so that the axial direction thereof obliquely intersects the feeding direction of the continuous paper  9  sent out from the first heating roller  530 A at an angle of about 45 degrees. In other words, the second heating roller  530 B is disposed in such a relation that the axial direction thereof is parallel to the axial direction of the downstream-side first inverting member  520 . The second heating roller  530 B is used to introduce the continuous paper  9  sent from the first heating roller  530 A from the upper side, to wind the continuous paper  9  around the peripheral surface of the second heating roller  530 B, and to send out the continuous paper  9  from the lower side. At this time, the winding angle of the back surface  9   b  of the continuous paper  9  around the second heating roller  530 B is also about 180 degrees. 
     [Operation of Fixing System] 
     In this fixing system  4 D, as illustrated in  FIGS. 13 and 14 , continuous paper  9  sent out from the second transfer position P 2  in the image forming device  2  is transported to pass through the preheating device  5 D and the fixing device  40  in this order. 
     First, as illustrated in, for example,  FIG. 13 , the continuous paper  9  is sent into the preheating device  5 D in a state where the front surface  9   a  on which a toner image is formed faces up, is preheated from the back surface  9   b  before the fixing operation, and is inverted. Then, the continuous paper  9  is sent out from the preheating device  5 D with the front surface  9   a  facing up. 
     At this time, in the preheating device  5 D, the continuous paper  9  is passed while the front surface  9   a  is in contact with the surface of the upstream-side first inverting member  510  to be obliquely wound around the surface from the upper side. The continuous paper  9  is thereby twisted 90 degrees, and is inverted. In this state, the continuous paper  9  is sent out from the lower side of the first inverting member  510  toward the first heating roller  530 A. 
     The continuous paper  9  sent out from the first inverting member  510  is transported along the driven rotation of the first heating roller  530 A and heated while the back surface  9   b  is in contact with the first heating roller  530 A to be wound around the first heating roller  530 A from the lower side. The continuous paper  9  is thereby twisted 90 degrees and is inverted. In this state, the continuous paper  9  is sent out from the upper side of the first heating roller  530 A toward the second heating roller  530 B. Also, the continuous paper  9  sent out from the first heating roller  530 A is transported along with the driven rotation of the second heating roller  530 B and heated while the back surface  9   b  is in contact with the second heating roller  530 B to be wound around the second heating roller  530 B from the upper side. The continuous paper  9  is thereby twisted 90 degrees and is inverted. In this state, the continuous paper  9  is sent out from the lower side of the second heating roller  530 B toward the downstream-side first inverting member  520 . 
     Finally, after heated by the two heating rollers  530 A and  530 B, the continuous paper  9  is passed while the back surface  9   b  is in contact with the surface of the downstream-side first inverting member  520  to be obliquely around the surface from the lower side. The continuous paper  9  is thereby twisted 90 degrees and is inverted. Then, the continuous paper  9  is sent out from the preheating device  5 D with the front surface  9   a  facing up, and is transported toward the fixing device  40  provided on the downstream side. 
     In the preheating device  5 D, the continuous paper  9  is heated from the back surface  9   b  at a required temperature (for example, a temperature set within the range of 90° C. to 180° C.) by the two heating rollers  530 A and  530 B. 
     Next, as illustrated in  FIG. 13 , the continuous paper  9  preheated by the preheating device  5 D is sent into (the fixing nip FN in) the fixing device  40  in a state where the front surface  9   a  on which the toner image is formed faces up, is subjected to the fixing operation of the toner image, and is then sent out from the fixing device  40 . 
     While the fixing system  4 D in the image forming apparatus  1 C includes the preheating device  5 D, the two heating rollers  530 A and  530 B in the preheating device  5 D are both disposed further on the outside than the side edge portion  9   d  of the continuous paper  9  (see, for example,  FIG. 14 ). 
     In the image forming apparatus  1 C, the two heating rollers  530 A and  530 B are arranged between the first inverting members  510  and  520  in the preheating device  5 D of the fixing system  4 D. Hence, preheating is performed by the preheating device  5 D while the back surface  9   b  of the continuous paper  9  is wound into contact with the peripheral surfaces of the two heating rollers  530 A and  530 B in order at an angle of about 180 degrees. 
     Further, in the image forming apparatus  1 C, as illustrated in  FIGS. 12 and 13 , the two first inverting members  510  and  520  and the two heating rollers  530 A and  530 B in the preheating device  5 D of the fixing system  4 D are all disposed almost along the imaginary straight line VL 1 , and are arranged with little height difference from the imaginary straight line VL 1 . 
     Fifth Exemplary Embodiment 
       FIGS. 15 to 17  illustrate a fixing system and so on according to a fifth exemplary embodiment.  FIG. 15  illustrates a general outline of the fixing system,  FIG. 16  illustrates a state of a preheating device provided in the fixing system, when viewed from obliquely above, and  FIG. 17  illustrates the preheating device and so on. 
     As illustrated in  FIG. 15 , a fixing system  4 E according to the fifth exemplary embodiment includes a fixing device  40  and a preheating device  5 E. The fixing device  40  has the same structure as that of the fixing device  40  ( FIG. 2 ) in the fixing system  4  of the first exemplary embodiment. 
     [Structure of Preheating Device] 
     As illustrated in, for example,  FIGS. 15 and 16 , the preheating device  5 E includes two first inverting members  510  and  520  and four heating rollers  530 C,  530 D,  530 E, and  530 F serving as an example of a heating rotating body. The two first inverting members  510  and  520  are disposed at different positions while obliquely intersecting a feeding direction A of continuous paper  9  on which a toner image is formed, and invert the continuous paper  9  by passing a back surface  9   b  of the continuous paper  9 , on which the toner image is not formed, therealong before a fixing operation. The four heating rollers  530 C,  530 D,  530 E, and  530 F are disposed at positions further on an outside than a side edge portion  9   d  of the continuous paper  9  in the feeding direction A, and preheat the continuous paper  9  before the fixing operation by passing and winding a portion of the back surface  9   b  of the continuous paper  9  between the first inverting members  510  and  520  around the heating rollers  530 C to  530 F. 
     In  FIG. 15 , a one-dot chain line VL 1  is an imaginary straight line that connects a second transfer position P 2  in an image forming device  2  and a fixing nip FN in the fixing device  40  in the shortest distance. 
     The two first inverting members  510  and  520  have structures substantially similar to those of the first inverting members  510  and  520  in the preheating device  5 D of the fourth exemplary embodiment, and are fixedly arranged to obliquely intersect the feeding direction A of the continuous paper  9  at an angle of 45 degrees. 
     Each of the four heating rollers  530 C,  530 D,  530 E, and  530 F is constituted of a cylindrical roller base made of, for example, metal and a heat source  540 , such as a halogen lamp, disposed in an internal space of the roller base, similarly to the two heating rollers  530 A and  530 B in the preheating device  5 D of the fourth exemplary embodiment. In each of the heating rollers  530 C,  530 D,  530 E, and  530 F, the roller base is rotatably disposed and is driven to rotate along with the motion (transport movement) of the continuous paper  9  that passes while winding around the heating roller  530 C,  530 D,  530 E, or  530 F, similarly to the above-described two heating rollers  530 A and  530 B. 
     As illustrated in  FIG. 17 , the four heating rollers  530 C,  530 D,  530 E, and  530 F are disposed at positions spaced outward by a predetermined distance S 5  from the side edge portion  9   d  of the continuous paper  9  in the feeding direction A in a state in which the axial directions thereof are parallel to the feeding direction A of the continuous paper  9  or obliquely intersect the feeding direction A. 
     Specifically, the first heating roller  530 C on the most upstream side in the transport direction of the continuous paper  9  is disposed in a state where the axial direction thereof exists in the same plane passing the axis of the upstream-side first inverting member  510  and the axial direction is substantially parallel to the feeding direction A of the continuous paper  9 . The first heating roller  530 C is used to introduce the continuous paper  9  sent from the first inverting member  510  from the lower side, to wind the continuous paper  9  around the peripheral surface of the first heating roller  530 C, and to vertically send out the continuous paper  9  from a rear side surface of the first heating roller  530 C. At this time, the winding angle of the back surface  9   b  of the continuous paper  9  around the first heating roller  530 C is about 90 degrees. 
     The second heating roller  530 D downstream of the first heating roller  530 C in the transport direction of the continuous paper  9  is disposed on the vertically upper side of the first heating roller  530 C in a state where the axial direction thereof exists in the same plane passing the rotation axis of the first heating roller  530 C, and is tilted at an angle of, for example, 45 degrees so that one end is located at a higher position than the other end. The second heating roller  530 D is used to introduce the continuous paper  9 , which is sent upward in the vertical direction from the first heating roller  530 C, from a rear side surface, to wind the continuous paper  9  around the peripheral surface of the second heating roller  530 D, and to send out the continuous paper  9  from a front side surface in a substantially horizontal direction (a direction along the imaginary straight line VL 1 ). At this time, the winding angle of the back surface  9   b  of the continuous paper  9  around the second heating roller  530 D is about 180 degrees. 
     The third heating roller  530 E downstream of the second heating roller  530 D in the transport direction of the continuous paper  9  is disposed in a state where the axial direction thereof exists in the same plane passing the rotation axis of the second heating roller  530 D, and is tilted at an angle of, for example, 45 degrees so that one end thereof is located at a higher position than the other end. The second heating roller  530 D and the third heating roller  530 E are arranged in a chevron form, when viewed from the front side. The third heating roller  530 E is used to introduce the continuous paper  9 , which is sent in an upright position from the second heating roller  530 D to move in a substantially horizontal direction, from a front side surface, to wind the continuous paper  9  around the peripheral surface of the third heating roller  530 E, and to send out the continuous paper  9  downward in the substantially vertical direction from a rear side surface. At this time, the winding angle of the back surface  9   b  of the continuous paper  9  around the third heating roller  530 E is about 180 degrees. 
     Further, the fourth heating roller  530 F downstream of the third heating roller  530 E in the transport direction of the continuous paper  9  is disposed in a state where the axial direction thereof exists in the same plane passing the axis of the downstream-side first inverting member  520  and the axial direction is substantially parallel to the feeding direction A of the continuous paper  9 . The fourth heating roller  530 F is used to introduce the continuous paper  9 , which is sent from the third heating roller  530 E, from a rear side surface, to wind the continuous paper  9  around the peripheral surface of the fourth heating roller  530 F, and to send out the continuous paper  9  from the lower side in a substantially horizontal direction. At this time, the winding angle of the back surface  9   b  of the continuous paper  9  around the fourth heating roller  530 F is about 90 degrees. 
     [Operation of Fixing System] 
     In this fixing system  4 E, as illustrated in  FIGS. 15 to 17 , the continuous paper  9  sent out from the second transfer position P 2  in the image forming device  2  is transported to pass through the preheating device  5 E and the fixing device  40  in this order. 
     First, as illustrated in, for example,  FIG. 16 , the continuous paper  9  is sent into the preheating device  5 E in a state where the front surface  9   a  on which the toner image is formed faces up, is preheated from the back surface  9   b  before the fixing operation, and is inverted. The continuous paper  9  is then sent out from the preheating device  5 E with the front surface  9   a  facing up. 
     At this time, in the preheating device  5 E, the continuous paper  9  is passed while the front surface  9   a  is in contact with the surface of the upstream-side first inverting member  510  to be obliquely wound around the surface from the upper side. The continuous paper  9  is thereby twisted 90 degrees and is inverted. In this state, the continuous paper  9  is sent out from the lower side of the first inverting member  510  toward the first heating roller  530 C. 
     The continuous paper  9  sent out from the first inverting member  510  is transported along with the driven rotation of the first heating roller  530 C and heated while the back surface  9   b  is in contact with the first heating roller  530 C to be wound around the first heating roller  530 C from the lower side. The feeding direction of the continuous paper  9  is thereby turned 90 degrees, and the continuous paper  9  is sent out upward in the vertical direction from the rear side surface toward the second heating roller  530 D. Subsequently, the continuous paper  9  is transported along with the driven rotation of the second heating roller  530 D and heated while the back surface  9   b  is in contact with the tilted second heating roller  530 D to be wound around the second heating roller  530 D from the rear side surface. The feeding direction of the continuous paper  9  is thereby twisted 90 degrees, and the the continuous paper  9  is inverted. In this state, the continuous paper  9  is sent out toward the third heating roller  530 E upward in the substantially horizontal direction. Next, the continuous paper  9  is transported along the driven rotation of the tilted third heating roller  530 E and heated while the back surface  9   b  is in contact with the third heating roller  530 E to be wound around the third heating roller  530 E from a front surface side. Thus, the feeding direction of the continuous paper  9  is twisted 90 degrees, and the continuous paper  9  is inverted. In this state, the continuous paper  9  is sent out downward in the vertical direction toward the fourth heating roller  530 F. 
     Finally, the continuous paper  9  heated by the four heating rollers  530 C,  530 D,  530 E, and  530 F in order is passed while the back surface  9   b  is in contact with the surface of the downstream-side first inverting member  520  to be obliquely wound around the surface from the lower side. Thus, the continuous paper  9  is twisted 90 degrees and is inverted. The continuous paper  9  is sent out from the preheating device  5 E with the front surface  9   a  facing up, and is then transported toward the fixing device  40  provided on the downstream side. 
     In this preheating device  5 E, the continuous paper  9  is heated from the back surface  9   b  at a required temperature (for example, a temperature set within the range of 90° C. to 180° C.) by the four heating rollers  530 C,  530 D,  530 E, and  530 F. 
     Next, as illustrated in  FIG. 17 , the continuous paper  9  preheated by the preheating device  5 E is sent into (the fixing nip FN in) the fixing device  40  in a state where the front surface  9   a  having the toner image thereon faces up, is subjected to the fixing operation of the toner image, and is then sent out from the fixing device  40 . 
     While the fixing system  4 E includes the preheating device  5 E in the image forming apparatus  1 C, the four heating rollers  530 C,  530 D,  530 E, and  530 F in the preheating device  5 E are all disposed further on the outside than the side edge portion  9   d  of the continuous paper  9  (see, for example,  FIG. 17 ). 
     In this fixing system  4 E, since the four heating rollers  530 C,  530 D,  530 E, and  530 F are arranged between the first inverting members  510  and  520  in the preheating device  5 E, preheating is performed by the preheating device  5 E while the back surface  9   b  of the continuous paper  9  is wound into contact with the peripheral surfaces of the four heating rollers  530 C to  530 F in order at an angle of about 90 degrees, an angle of about 180 degrees, an angle of about 180 degrees, and an angle of about 90 degrees, respectively. 
     Other Exemplary Embodiments 
     While the downstream-side first inverting member  52  is fixedly disposed to obliquely intersect the feeding direction A of the continuous paper  9  in the preheating device  5  of, for example, the first exemplary embodiment, the downstream-side first inverting member  52  of the two first inverting members  51  and  52  may be provided to be displaceable in a direction D (D 2  in this exemplary embodiment) which allows the downstream-side first inverting member  52  to conform to a transport reference registration position (for example, center registration (CR)) of continuous paper  9  in the fixing device  40 , as representatively illustrated in  FIG. 18 . 
     For example, this is effective for the image forming apparatus  1 , for example, when the supply device  11  and the image forming device  2  adopt side registration (SR) different from center registration (CR) as the transport reference registration position of the continuous paper  9 , whereas the fixing device  40  adopts center registration (CR). That is, in this case, the transport reference registration position in the supply device  11  and the image forming device  2  does not need to be changed to center registration (CR), but the supply device  11  and the image forming device  2  are combined with the fixing device  40  adopting center registration (CR) only by changing the position of one component (downstream-side first inverting member  52 ) in the preheating device  5 . 
     In this case, as illustrated in  FIG. 18 , the downstream-side first inverting member  52  in the preheating device  5  is displaced from an initial position (a position of a first inverting member  52 A displaced in the direction of arrow D 1 ) to a conforming position (a position of a first inverting member  52 B displaced in the direction of arrow D 2 ). 
     Thus, when continuous paper  9 A transported by side registration (SR) in the supply device  11  and the image forming device  2  passes around the downstream-side first inverting member  52 B displaced to the conforming position in the preheating device  5 , the continuous paper  9 A is sent out as continuous paper  9 B in a registration state changed from side registration (SR) to center registration (CR) in the fixing device  40 . As a result, the continuous paper  9 B changed to center registration (CR) and sent to the fixing device  40  passes through the fixing nip FN while being transported by center registration (CR) in the fixing device  40 . Hence, the fixing operation is normally performed. For convenience, a side edge portion  9   c  of the continuous paper  9 A transported by side registration (SR) to be regulated is slightly separate from a two-dot chain line representing side registration (SR) in  FIG. 18 . In practice, however, the continuous paper  9 A is transported in a state in which the side edge portion  9   c  extends along (is nearly aligned with) the two-dot chain line representing side registration (SR). 
     This structure in which the downstream-side first inverting member  52  in the preheating device  5  is displaceable to conform to the transport reference registration position of the continuous paper  9  in the fixing device  40  is similarly applied to the preheating devices  5 B to  5 E in the second to fifth exemplary embodiments. In the preheating device  5 B, the downstream-side first inverting member  56  is provided displaceably to conform to the transport reference registration position of the continuous paper  9  in the fixing device  40 . In the preheating devices  5 E and  5 F, the downstream-side first inverting member  520  is provided displaceably to conform to the transport reference registration position of the continuous paper  9  in the fixing device  40 . 
     In the fixing system  4  according to the first exemplary embodiment (for example,  FIG. 2 ), the relay roller  63  in the inverting device  6  may be structured as a heating roller (for example, a heat source is disposed in an internal space of the roller base of the relay roller  63 ) as required. 
     In the fixing system  4 B according to the second exemplary embodiment (for example,  FIG. 7 ), the guide roller  71  may also be structured as a heating roller as required. 
     Further, in the fixing system  4 C according to the third exemplary embodiment (for example,  FIG. 10 ), one or both of the structure in which the relay roller  63  in the inverting device  6 B serves as a heating roller and the structure in which at least one of the first guide roller  75  and the second guide roller  76  serves as a heating roller may be adopted. 
     When the other roller is structured as the heating rotating body in addition to the heating rollers  53  or  57  in the preheating device  5  ( 5 B or  5 C), as described above, the back surface of the continuous paper  9  may be more accurately and efficiently preheated. On the other hand, if heat exhausted from the added heating rotating body may have an adverse influence in this case, for example, the heating temperature of the added heating rotating body is set to be lower than the heating temperature of the heating rotating body, such as the heating roller  53 , in the preheating device  5 . The shape of the heating rotating body is not limited to the roller shape, but may be other shapes. For example, the heating rotating body may be a belt-shaped heating rotating body provided with plural support rollers on which a heating belt is stretched. This shape also applies to the guide rotating body such as the guide roller  71 . 
     In the fixing system  4 E according to the fifth exemplary embodiment ( FIGS. 15 to 17 ), the tilted second and third heating rollers  530 D and  530 E in the preheating device  5 E may be used as inverting members as required. In this case, the upstream-side first inverting member  510 , the first heating roller  530 C, and the inverting member (serving as the second heating roller  530 D) constitute one preheating device ( 5 Ea), and the other inverting member (serving as the third heating roller  530 E), the fourth heating roller  530 F, and the downstream-side first inverting member  520  constitute one preheating device ( 5 Eb). For this reason, the preheating device having this structure may be treated as a preheating device ( 5 Ea+ 5 Eb) in which two preheating devices ( 5 Ea and  5 Eb) are connected in series. 
     As the heating rollers ( 530 A to  530 F) arranged between the upstream-side first inverting member  510  and the downstream-side first inverting member  520 , the two heating rollers ( 530 A and  530 B) are provided in the fourth exemplary embodiment, and the four heating rollers ( 530 C to  530 F) are provided in the fifth exemplary embodiment. However, three heating rollers or five or more heating rollers may be arranged as required as long as transportation of the continuous paper  9  in the desired state and preheating of the back surface  9   b  of the continuous paper  9  are performed. 
     Further, while the fixing device  40  of the fixing system  4  include the belt-shaped heating rotating body  41  and the roller-shaped pressurizing rotating body  42 , for example, in the first and second exemplary embodiments, a belt-shaped or roller-shaped heating rotating body  41  and a roller-shaped or belt-shaped pressurizing rotating body  42  may be arbitrarily combined as the fixing device  40 . 
     Alternatively, in the image forming apparatus  1 , the image forming device  2  may form other multicolor images (the types and number of the image forming units  20  are changed), may form a single-color image (for example, a monochrome image) (only the image forming unit  20 K is used), or may form an image without using the intermediate transfer device  30 . The supply device  11  and the storage device  16  in the image forming apparatus  1  are not limited to the ones adopting the adjusting mechanisms  13  and  18  used in the first and second exemplary embodiments, and mechanisms using other methods may be adopted. For example, the mechanisms using other methods include a mechanism having a structure in which the transport amount of the continuous paper  9  is adjusted by the transport roller pair  14  in the supply device  11  and the tension applied to the continuous paper  9  is adjusted by driving the transport roller pair  19  in the storage device  16  at a fixed torque. Further alternatively, the image forming apparatus may form an unfixed image made of a material different from the toner. 
     The foregoing description of the exemplary embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.