Patent Publication Number: US-2013236225-A1

Title: Fixing device and image forming apparatus incorporating same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This patent application is based on and claims priority pursuant to 35 U.S.C. §119 to Japanese Patent Application No. 2012-053106, filed on Mar. 9, 2012, in the Japanese Patent Office, the entire disclosure of which is hereby incorporated by reference herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Example embodiments generally relate to a fixing device and an image forming apparatus, and more particularly, to a fixing device for fixing a toner image on a recording medium and an image forming apparatus incorporating the fixing device. 
     2. Description of the Related Art 
     Related-art image forming apparatuses, such as copiers, facsimile machines, printers, or multifunction printers having at least one of copying, printing, scanning, and facsimile functions, typically form an image on a recording medium according to image data. Thus, for example, a charger uniformly charges a surface of a photoconductor; an optical writer emits a light beam onto the charged surface of the photoconductor to form an electrostatic latent image on the photoconductor according to the image data; a development device supplies toner to the electrostatic latent image formed on the photoconductor to render the electrostatic latent image visible as a toner image; the toner image is directly transferred from the photoconductor onto a recording medium or is indirectly transferred from the  photoconductor onto a recording medium via an intermediate transfer belt; finally, a fixing device applies heat and pressure to the recording medium bearing the toner image to fix the toner image on the recording medium, thus forming the image on the recording medium. 
       FIG. 1  illustrates one example of such fixing device. As shown in  FIG. 1 , a fixing device  20 R 1  includes a fixing belt  1   j  stretched across a heating roller  1   d  and a fixing roller  1   b.  A pressing roller  1   a  is pressed against the fixing roller  1   b  via the fixing belt  1   j  to form a fixing nip N between the pressing roller  1   a  and the fixing belt  1   j.  The fixing belt  1   j  is heated by a heater  1   f  disposed inside the heating roller  1   d.  As the pressing roller  1   a  rotating clockwise and the fixing belt  1   j  rotating counterclockwise in  FIG. 1  convey a recording medium P bearing a toner image T through the fixing nip N, the fixing belt  1   j  and the pressing roller  1   a  apply heat and pressure to the recording medium P, thus fixing the toner image T on the recording medium P. 
     However, since the fixing roller lb incorporates a rubber layer having an increased thermal capacity that draws heat from the fixing belt  1   j,  it takes substantial time to warm up the fixing belt  1   j  to a given fixing temperature to fix the toner image T on the recording medium P. 
     To address this problem, a fixing device incorporating a ceramic heater having a reduced thermal capacity is proposed.  FIG. 2  illustrates a fixing device  20 R 2  incorporating a ceramic heater  2   f  that presses against a pressing roller  2   a  via a fixing belt  2   j  to form a fixing nip N between the fixing belt  2   j  and the pressing roller  2   a.  As the pressing roller  2   a  rotating clockwise and the fixing belt  2   j  rotating counterclockwise in  FIG. 2  convey a recording medium P bearing a toner image T through the fixing nip N, the fixing belt  2   j  and the pressing roller  2   a  apply heat and pressure to the recording medium P, thus fixing the toner image T on the recording medium P. Since the ceramic heater  2   f  having a reduced thermal capacity directly heats the fixing belt  2   j,  that is, a film also having a reduced thermal capacity, the fixing belt  2   j  is heated to the fixing temperature quickly with reduced power. 
     However, since the fixing belt  2   j  is heated by the ceramic heater  2   f  at the fixing nip N only, the fixing belt  2   j  is cool at a position immediately upstream from the fixing nip N in the direction of rotation of the fixing belt  2   j.  Accordingly, at an entry to the fixing nip N, the fixing belt  2   j  may not be heated to the fixing temperature, resulting in fixing failure that may arise due to a decreased temperature of the fixing belt  2   j.    
     To address this problem, a configuration in which a heater disposed inside a fixing belt heats the fixing belt entirely is proposed. For example, a tubular metal thermal conductor disposed inside the fixing belt presses against a pressing roller via the fixing belt. The heater is disposed inside the metal thermal conductor. As the metal thermal conductor is heated by the heater disposed inside it, the metal thermal conductor disposed opposite the entire inner circumferential surface of the fixing belt heats the entire fixing belt quickly. 
     On the other hand, the fixing devices described above may include a separator situated downstream from the fixing nip N in the direction of rotation of the fixing belt to contact and separate the recording medium P discharged from the fixing nip N from the fixing belt. For example, the separator should be spaced apart from the fixing belt with a given interval therebetween to facilitate separation of the recording medium P from the fixing belt without damaging the fixing belt. However, the interval may be uneven or eliminated as the fixing belt is deformed by fluctuations in operation and environment of the fixing device. Accordingly, the recording medium P may be wound around the fixing belt or the separator may come into contact with the fixing belt, resulting in faulty separation of the recording medium P from the fixing belt and damage to the fixing belt. 
     SUMMARY OF THE INVENTION 
     At least one embodiment may provide a fixing device that includes a flexible endless belt rotatable in a given direction of rotation. A nip formation pad is disposed opposite an inner circumferential surface of the endless belt. A pressing body is pressed against the nip formation pad via the endless belt to form a fixing nip between the pressing body and the endless belt through which a recording medium is conveyed. A flange contacts and supports the endless belt. A separator is movably supported by the flange to contact and separate the recording medium discharged from the fixing nip from the endless belt. The separator includes a center plate disposed opposite a center of the endless belt in an axial direction thereof to contact the recording medium and a lateral end plate disposed opposite each lateral end of the endless belt in the axial direction thereof and including a contact portion projecting beyond the center plate toward the endless belt and contacting the endless belt to produce a given interval between the center plate and the endless belt. 
     At least one embodiment may provide an image forming apparatus including the fixing device described above. 
     Additional features and advantages of example embodiments will be more fully apparent from the following detailed description, the accompanying drawings, and the  associated claims. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       A more complete appreciation of example embodiments and the many attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
         FIG. 1  is a vertical sectional view of a first related-art fixing device; 
         FIG. 2  is a vertical sectional view of a second related-art fixing device; 
         FIG. 3  is a schematic vertical sectional view of an image forming apparatus according to an example embodiment of the present invention; 
         FIG. 4  is a vertical sectional view of a fixing device according to a first example embodiment of the present invention that is installed in the image forming apparatus shown in  FIG. 3 ; 
         FIG. 5  is a perspective view of the fixing device shown in  FIG. 4 ; 
         FIG. 6  is a partial perspective view of a fixing device according to a second example embodiment of the present invention that is installable in the image forming apparatus shown in  FIG. 3 ; 
         FIG. 7  is a vertical sectional view of a fixing device as a variation of the fixing device shown in  FIG. 4 ; and 
         FIG. 8  is a vertical sectional view of a fixing device as another variation of the fixing device shown in  FIG. 4 . 
     
    
    
     The accompanying drawings are intended to depict example embodiments and should not be interpreted to limit the scope thereof. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted. 
     DETAILED DESCRIPTION OF THE INVENTION 
     It will be understood that if an element or layer is referred to as being “on”, “against”, “connected to”, or “coupled to” another element or layer, then it can be directly on, against, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, if an element is referred to as being “directly on”, “directly connected to”, or “directly coupled to” another element or layer, then there are no intervening elements or layers present. Like numbers refer to like elements throughout. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     Spatially relative terms, such as “beneath”, “below”, “lower”, “above”, “upper”, and  the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or  “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, term such as “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated  90  degrees or at other orientations) and the spatially relative descriptors used herein are interpreted accordingly. 
     Although the terms first, second, etc. may be used herein to describe various elements, components, regions, layers and/or sections, it should be understood that these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are used only to distinguish one element, component, region, layer, or section from another region, layer, or section. Thus, a first element, component, region, layer, or section discussed below could be termed a second element, component, region, layer, or  section without departing from the teachings of the present invention. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present invention. As used herein, the singular forms “a”, “an”, and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “includes” and/or “including”, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     In describing example embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner. 
     Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, particularly to  FIG. 3 , an image forming apparatus  1  according to an example embodiment is explained. 
       FIG. 3  is a schematic vertical sectional view of the image forming apparatus  1 . The image forming apparatus  1  may be a copier, a facsimile machine, a printer, a multifunction printer (MFP) having at least one of copying, printing, scanning, plotter, and facsimile functions, or the like. According to this example embodiment, the image forming apparatus  1  is a tandem color printer that forms a toner image on a recording medium P by electrophotography. 
     Four toner bottles  102 Y,  102 M,  102 C, and  102 K containing yellow, magenta, cyan, and black toners, respectively, are detachably attached to a bottle holder  101  situated in an upper portion of the image forming apparatus  1 . 
     Below the bottle holder  101  is an intermediated transfer unit  85  accommodating an intermediate transfer belt  78  rotatable in a rotation direction R 1 . The intermediate transfer belt  78  is disposed opposite four image forming devices  4 Y,  4 M,  4 C, and  4 K aligned in the rotation direction R 1  of the intermediate transfer belt  78  to form yellow, magenta, cyan, and black toner images, respectively. The image forming devices  4 Y,  4 M,  4 C, and  4 K include photoconductive drums  5 Y,  5 M,  5 C, and  5 K surrounded by chargers  75 Y,  75 M,  75 C, and  75 K, development devices  76 Y,  76 M,  76 C, and  76 K, cleaners  77 Y,  77 M,  77 C, and  77 K, and dischargers, respectively. On the photoconductive drums  5 Y,  5 M,  5 C, and  5 K, image forming processes including a charging process, an exposure process, a development process, a primary transfer process, and a cleaning process are performed to form yellow, magenta, cyan, and black toner images on the photoconductive drums  5 Y,  5 M,  5 C, and  5 K, respectively. 
     For example, as a driver (e.g., a motor) drives and rotates the photoconductive drums  5 Y,  5 M,  5 C, and  5 K clockwise in  FIG. 3  in a rotation direction R 2 , the chargers  75 Y,  75 M,  75 C, and  75 K uniformly charge an outer circumferential surface of the respective photoconductive drums  5 Y,  5 M,  5 C, and  5 K in the charging process. Then, an exposure device  3  situated below the image forming devices  4 Y,  4 M,  4 C, and  4 K emits laser beams onto the charged outer circumferential surface of the respective photoconductive drums  5 Y,  5 M,  5 C, and  5 K according to yellow, magenta, cyan, and black image data sent from an external device such as a client computer, thus forming electrostatic latent images on the photoconductive drums  5 Y,  5 M,  5 C, and  5 K, respectively, in the exposure process. 
     As the electrostatic latent images formed on the photoconductive drums  5 Y,  5 M,  5 C, and  5 K reach a position disposed opposite the respective development devices  76 Y,  76 M,  76 C, and  76 K, the development devices  76 Y,  76 M,  76 C, and  76 K visualize the electrostatic latent images into yellow, magenta, cyan, and black toner images, respectively, in the development process. 
     Primary transfer bias rollers  79 Y,  79 M,  79 C, and  79 K are disposed opposite the photoconductive drums  5 Y,  5 M,  5 C, and  5 K, respectively, via the intermediate transfer belt  78 . As the yellow, magenta, cyan, and black toner images formed on the photoconductive drums  5 Y,  5 M,  5 C, and  5 K reach a position disposed opposite the respective primary transfer bias rollers  79 Y,  79 M,  79 C, and  79 K, the primary transfer bias rollers  79 Y,  79 M,  79 C, and  79 K primarily transfer the yellow, magenta, cyan, and black toner images onto the intermediate transfer belt  78  in the primary transfer process. After the primary transfer of the yellow, magenta, cyan, and black toner images, residual yellow, magenta, cyan, and black toners in a slight amount failed to be transferred onto the intermediate transfer belt  78  remain on the photoconductive drums  5 Y,  5 M,  5 C, and  5 K, respectively. To address this circumstance, a cleaning blade of the respective cleaners  77 Y,  77 M,  77 C, and  77 K mechanically removes the residual toners from the respective photoconductive drums  5 Y,  5 M,  5 C, and  5 K in the cleaning process. 
     Finally, the dischargers discharge the outer circumferential surface of the respective photoconductive drums  5 Y,  5 M,  5 C, and  5 K, eliminating residual potential from the photoconductive drums  5 Y,  5 M,  5 C, and  5 K. Thus, a series of image forming processes performed on the respective photoconductive drums  5 Y,  5 M,  5 C, and  5 K is completed. The yellow, magenta, cyan, and black toner images primarily transferred from the photoconductive drums  5 Y,  5 M,  5 C, and  5 K onto the intermediate transfer belt  78  are superimposed on a same position on the intermediate transfer belt  78 . Thus, a color toner image is formed on the intermediate transfer belt  78 . 
     The intermediate transfer unit  85  includes the intermediate transfer belt  78 , the four primary transfer bias rollers  79 Y,  79 M,  79 C, and  79 K, a secondary transfer backup roller  82 , a cleaning backup roller  83 , a tension roller  84 , and an intermediate transfer belt cleaner  80 . The intermediate transfer belt  78  is stretched across and supported by the three rollers, that is, the secondary transfer backup roller  82 , the cleaning backup roller  83 , and the tension roller  84 . As the secondary transfer backup roller  82  rotates counterclockwise in  FIG. 3 , it drives and rotates the intermediate transfer belt  78  in the rotation direction R 1 . The primary transfer bias rollers  79 Y,  79 M,  79 C, and  79 K and the photoconductive drums  5 Y,  5 M,  5 C, and  5 K sandwich the intermediate transfer belt  78 , forming primary transfer nips between the photoconductive drums  5 Y,  5 M,  5 C, and  5 K and the intermediate transfer belt  78 , respectively. The primary transfer bias rollers  79 Y,  79 M,  79 C, and  79 K are applied with a transfer bias having a polarity opposite a polarity of yellow, magenta, cyan, and black toners of the yellow, magenta, cyan, and black toner images formed on the photoconductive drums  5 Y,  5 M,  5 C, and  5 K. 
     As the intermediate transfer belt  78  rotating in the rotation direction R 1  travels through the primary transfer nips, the yellow, magenta, cyan, and black toner images are primarily transferred from the photoconductive drums  5 Y,  5 M,  5 C, and  5 K onto the intermediate transfer belt  78  in such a manner that the yellow, magenta, cyan, and black toner images are superimposed on the same position on the intermediate transfer belt  78 . Thus,  the color toner image is formed on the intermediate transfer belt  78 . Thereafter, the color toner image formed on the intermediate transfer belt  78  reaches a secondary transfer roller  89 . The secondary transfer roller  89  sandwiches the intermediate transfer belt  78  together with the secondary transfer backup roller  82 , forming a secondary transfer nip between the secondary transfer roller  89  and the intermediate transfer belt  78 . As a recording medium P is  conveyed through the secondary transfer nip, the color toner image is secondarily transferred from the intermediate transfer belt  78  onto the recording medium P in a secondary transfer process. After the secondary transfer of the color toner image, residual toner failed to be transferred onto the recording medium P remains on the intermediate transfer belt  78 . To address this circumstance, the intermediate transfer belt cleaner  80  removes the residual toner from the intermediate transfer belt  78 . Thus, a series of transfer processes, that is, the primary transfer process and the secondary transfer process, performed on the intermediate transfer belt  78  is completed. 
     The recording medium P is conveyed to the secondary transfer nip from a paper tray  12  situated in a lower portion of the image forming apparatus  1  through a feed roller  97  and a registration roller pair  98 . The paper tray  12  loads a plurality of recording media P (e.g., transfer sheets). As the feed roller  97  rotates counterclockwise in  FIG. 3 , it picks up and feeds an uppermost recording medium P toward a nip formed between two rollers of the registration roller pair  98 . As the recording medium P comes into contact with the registration roller pair  98 , the registration roller pair  98  that stops its rotation halts the recording medium P temporarily. At a time when the color toner image formed on the intermediate transfer belt  78  reaches the secondary transfer nip, the registration roller pair  98  resumes its rotation to convey the recording medium P toward the secondary transfer nip. Thus, the color toner image is secondarily transferred from the intermediate transfer belt  78  onto the recording medium P. Thereafter, the recording medium P bearing the color toner image is conveyed to a fixing device  20  where a fixing belt  21  and a pressing roller  31  apply heat and pressure to the recording medium P, thus fixing the color toner image on the recording medium P. Then, the recording medium P bearing the fixed color toner image is conveyed to an output roller pair  99  that discharges the recording medium P onto an outside of the image forming apparatus  1 , that is, an output tray  100  where the recording medium P is stacked. Thus, a series of image forming processes performed by the image forming apparatus  1  is completed. 
     With reference to  FIG. 4 , a description is provided of a construction of the fixing device  20  according to a first example embodiment of the present disclosure that is incorporated in the image forming apparatus  1  described above. 
       FIG. 4  is a vertical sectional view of the fixing device  20 . As shown in  FIG. 4 , the fixing device  20  (e.g., a fuser) includes the fixing belt  21  formed into a loop and serving as an endless belt rotatable in a rotation direction R 3 ; the pressing roller  31  serving as a pressing body contacting an outer circumferential surface of the fixing belt  21  and rotatable in a rotation direction R 4  counter to the rotation direction R 3  of the fixing belt  21 ; a metal pipe  22  contactably disposed in proximity to an inner circumferential surface of the fixing belt  21 ; and a heater  40  (e.g., a halogen heater set) disposed inside the loop formed by the fixing belt  21 . The heater  40  heats the metal pipe  22  that in turn heats the fixing belt  21 . The fixing device  20  further includes a nip formation pad  41  disposed inside the loop formed by the fixing belt  21  and supported by the metal pipe  22 . The pressing roller  31  is pressed against the nip formation pad  41  via the fixing belt  21  to form a fixing nip N between the pressing roller  31  and the fixing belt  21 . Accordingly, the inner circumferential surface of the fixing belt  21  comes into direct contact with and slides over the nip formation pad  41 . Alternatively, the inner circumferential surface of the fixing belt  21  may come into indirect contact with the nip formation pad  41  via a slide sheet and may slide over the slide sheet. According to this example embodiment shown in  FIG. 4 , the pressing roller  31  and the nip formation pad  41  produce the curved fixing nip N that is concave along an outer circumference of the pressing roller  31 . Alternatively, the fixing nip N may be planar or have other shapes. However, the concave fixing nip N is preferable because it facilitates separation of the recording medium P from the fixing belt  21  and thereby prevents jamming of the recording medium P by directing a leading edge of the recording medium P discharged from the fixing nip N toward the pressing roller  31 . 
     A detailed description is now given of a construction of the pressing roller  31 . 
     The pressing roller  31  is constructed of a hollow metal roll; a silicone rubber layer coating the metal roll; and a surface release layer coating the silicone rubber layer. The release layer is made of tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) or polytetrafluoroethylene (PTFE) that facilitates separation of the recording medium P from the pressing roller  31 . As the pressing roller  31  receives a driving force from a driver (e.g., a motor) located inside the image forming apparatus  1  depicted in  FIG. 3  through a gear train, the pressing roller  31  rotates in the rotation direction R 4 . The pressing roller  31  is pressed by a spring against the nip formation pad  41  via the fixing belt  21 . As the spring presses the pressing roller  31  against the nip formation pad  41 , the silicone rubber layer of the pressing roller  31  deforms and produces the fixing nip N having a given length in a recording medium conveyance direction A 1 . Alternatively, the pressing roller  31  may be a solid roller. However, it is preferable that the pressing roller  31  is a hollow roller that has a reduced thermal capacity. If the pressing roller  31  is the hollow roller, a heater such as a halogen heater may be situated inside the pressing roller  31 . The silicone rubber layer of the pressing roller  31  may be made of solid rubber. However, it is preferable that the silicone rubber layer is made of sponge rubber if no heater is situated inside the pressing roller  31 . In this case, the sponge rubber achieves an enhanced insulation that draws less heat from the fixing belt  21 . 
     A detailed description is now given of a construction of the fixing belt  21 . 
     The fixing belt  21  is a metal belt made of nickel or stainless steel or a sleeve belt or a film made of resin such as polyimide. The fixing belt  21  is constructed of a base layer and a surface release layer. The release layer is made of PFA or PTFE that facilitates separation of toner of a toner image T on a recording medium P. Alternatively, an elastic layer made of silicone rubber may be interposed between the base layer and the release layer. If the pressing roller  31  does not incorporate the elastic layer, the pressing roller  31  has a reduced thermal capacity that improves fixing performance of being heated to a given fixing temperature quickly. However, as the pressing roller  31  and the fixing belt  21  sandwich and  press the toner image T on the recording medium P passing through the fixing nip N, slight surface asperities of the fixing belt  21  may be transferred onto the toner image T on the recording medium P, resulting in formation of a faulty solid toner image, that is, an orange peel image. To address this problem, the pressing roller  31  includes the elastic layer having a thickness not smaller than about  100  micrometers. Such relatively thick elastic layer deforms and absorbs slight surface asperities of the fixing belt  21 , preventing formation of an orange peel image. 
     A detailed description is now given of a configuration of the metal pipe  22 . 
     The metal pipe  22  is made of metal such as aluminum, iron, and stainless steel. According to this example embodiment shown in  FIG. 4 , the metal pipe  22  is substantially circular in cross-section. Alternatively, the metal pipe  22  may be rectangular or may have other shapes. A support  42  supporting the nip formation pad  41  is situated inside a substantial loop formed by the metal pipe  22 . The support  42  supports the nip formation pad  41  against pressure from the pressing roller  31 , preventing bending of the nip formation pad  41  and thereby facilitating the nip formation pad  41  to produce the even fixing nip N throughout an axial direction of the fixing belt  21 . The nip formation pad  41  and the support  42  are mounted on and positioned by a flange  43  at each lateral end of the nip formation pad  41  and the support  42  in a longitudinal direction thereof parallel to the axial direction of the fixing belt  21 . The flange  43  also contacts and supports the fixing belt  21  at each lateral end in the axial direction thereof, thus guiding the fixing belt  21  rotating in the rotation direction R 3 . A surface of the support  42  may be insulated or mirror finished, preventing itself from being heated by heat radiated from the heater  40  and thereby minimizing waste of energy. 
     According to this example embodiment, the heater  40  includes a plurality of halogen heaters. Alternatively, the heater  40  may be at least one halogen heater, induction heater, resistant heat generator, carbon heater, or the like. According to this example embodiment,  the fixing belt  21  is driven and rotated by an external roller, that is, the pressing roller  31 . For example, as a driver drives and rotates the pressing roller  31  in the rotation direction R 4 , the fixing belt  21  is rotated in the rotation direction R 3  by a driving force transmitted from the pressing roller  31  at the fixing nip N. Alternatively, a driver is connected to the fixing belt  21  through a gear train and the flange  43  to drive and rotate the fixing belt  21 . Yet alternatively, a driver is connected to each of the pressing roller  31  and the fixing belt  21 . 
     The fixing belt  21  is rotated by the pressing roller  31  rotated by the driver by friction between the fixing belt  21  and the pressing roller  31  at the fixing nip N. Conversely, at a position other than the fixing nip N, the fixing belt  21  is guided by the flange  43  so that the rotation locus of the fixing belt  21  is spaced apart from the heater  40  within a given distance.  An interface between the fixing belt  21  and the metal pipe  22  is applied with a lubricant such as silicone oil and fluorine grease. Thus, the entire fixing belt  21  is warmed up quickly and maintained at a given temperature stably at reduced costs. 
     Alternatively, the fixing device  20  may not incorporate the metal pipe  22 . If the metal pipe  22  is eliminated, the fixing belt  21  is heated by the heater  40  directly, shortening a warm-up time of the fixing belt  21  and thereby saving energy. 
     With reference to  FIG. 4 , a description is provided of a configuration of the flange  43  and a separator  32  coupled with the flange  43 . 
     The flange  43  supports the fixing belt  21  at each lateral end of the inner circumferential surface of the fixing belt  21  in the axial direction thereof in such a manner that the fixing belt  21  is slidable over the flange  43 . The flange  43  includes a groove that engages the separator  32  (e.g., a separation plate). Thus, the flange  43  supports the separator  32  through the groove. The nip formation pad  41  situated inside the loop formed by the fixing belt  21  is supported by the support  42 . The support  42 , the flange  43 , and the heater  40  are supported by a belt unit stay mounted on a frame of the fixing device  20 . A torsion coil spring  33  serving as a biasing member is interposed between the separator  32  and the flange  43 . For example, the torsion coil spring  33  is anchored to the separator  32  and the flange  43  to exert a bias to the separator  32  that constantly biases the separator  32  downward against the fixing belt  21 . 
       FIG. 5  is a perspective view of the fixing device  20  seen from above the pressing roller  31 . As shown in  FIG. 5 , the separator  32  is constructed of a center plate  32   b  disposed opposite a center of the fixing belt  21  in the axial direction thereof over which the recording medium P is conveyed and a lateral end plate  32   a  disposed opposite each lateral end of the fixing belt  21  in the axial direction thereof over which the recording medium P is not conveyed. That is, the center plate  32   b  is disposed opposite a passage region PR on the outer circumferential surface of the fixing belt  21  where the recording medium P passes. 
     Conversely, the lateral end plate  32   a  is disposed opposite a non-passage region NP on the outer circumferential surface of the fixing belt  21  where the recording medium P does not pass. The center plate  32   b  is integrally molded with the lateral end plates  32   a  into a unit. The lateral end plate  32   a  is constructed of a body  32   a   1  contiguous to the center plate  32   b  and disposed at each lateral end of the separator  32  in a longitudinal direction thereof parallel to the axial direction of the fixing belt  21  and a contact portion  32   a   2  projecting from the body  32   a   1  toward the fixing belt  21 . For example, the contact portion  32   a   2  of the lateral end plate  32   a  projects beyond the center plate  32   b  toward the fixing belt  21 . 
     Each of the contact portions  32   a   2  is constantly in contact with the outer  circumferential surface of the fixing belt  21  in the non-passage region NP thereof where the recording medium P does not pass. Thus, the contact portions  32   a   2  produce a desired interval I depicted in  FIG. 4  between the center plate  32   b  and the fixing belt  21  in the passage region PR thereof where the recording medium P passes. Hence, the interval I facilitates separation of the recording medium P from the fixing belt  21  by the center plate  32   b.  The torsion coil spring  33  depicted in  FIG. 4  exerts a bias to the separator  32  that is great enough to bring each contact portion  32   a   2  into constant contact with the outer circumferential surface of the fixing belt  21  and small enough to prevent deformation of the fixing belt  21 . 
     With the configuration of the separator  32  described above, the contact portions  32   a   2  produce the desired constant interval I between the center plate  32   b  and the fixing belt  21  that facilitates separation of the recording medium P from the fixing belt  21 . Accordingly, even if the fixing belt  21  is deformed by fluctuations in operation and environment of the fixing device  20 , the contact portions  32   a   2  constantly produce the desired interval I between the center plate  32   b  and the fixing belt  21  uniformly in the axial direction of the fixing belt  21 , thus preventing failures that may arise as the recording medium P is accidentally wound around the fixing belt  21  or as the center plate  32   b  accidentally comes into contact with the fixing belt  21 . 
     Since each contact portion  32   a   2  contacts the fixing belt  21  in the non-passage region NP thereof where the recording medium P does not pass, the contact portion  32   a   2  does not come into contact with the recording medium P. Accordingly, the contact portion  32   a   2  does not adversely affect the recording medium P by damaging the recording medium P and obstructing conveyance of the recording medium P, for example, thus facilitating stable separation of the recording medium P from the fixing belt  21 . Further, a user can arbitrarily move the separator  32  upward to enlarge the interval I between the separator  32  and the fixing belt  21 . Accordingly, even if the recording medium P is jammed between the separator  32  and the fixing belt  21 , the user can remove the jammed recording medium P from between the separator  32  and the fixing belt  21  readily by moving the separator  32  upward. Additionally, compared to a configuration in which a separator is rotatably supported by a support shaft mounted on a side plate that supports the flange  43 , according to this example embodiment, the separator  32  is supported by the flange  43  that supports the fixing belt  21 , positioning the separator  23  relative to the fixing belt  21  more precisely. 
     With reference to  FIG. 6 , a description is provided of a configuration of a fixing device  20 S according to a second example embodiment of the present disclosure. 
       FIG. 6  is a partial perspective view of the fixing device  20 S. Unlike the fixing device  20  shown in  FIG. 5 , the fixing device  20 S incorporates a flange  43 S including a regulator  43   a  instead of the flange  43  that does not include the regulator  43   a.    
     As shown in  FIG. 6 , the flange  43 S is constructed of a regulator support  43   b  and the arm-shaped regulator  43   a  integrally molded with the regulator support  43   b  and projecting from the regulator support  43   b  toward the lateral end plate  32   a  of the separator  32  in the axial direction of the fixing belt  21 . Although  FIG. 6  illustrates the flange  43 S situated at one lateral end of the fixing belt  21  in the axial direction thereof, another flange  43 S is situated at another lateral end of the fixing belt  21  in the axial direction thereof. For example, the regulator  43   a  is constructed of a fixed end  43   a   1  contiguous to and mounted on the regulator support  43   b  and a free end  43   a   2  extending from the fixed end  43   a   1  toward the lateral end plate  32   a  of the separator  32 . The free end  43   a   2  is situated in a travel path through which the lateral end plate  32   a  of the separator  32  moves downward. Thus, the regulator  43   a,  by contacting the lateral end plate  32   a  of the separator  32 , regulates movement of the separator  32  in a direction to reduce the interval I between the separator  32  and the fixing belt  21 . Accordingly, even if the contact portion  32   a   2  of the separator  32  in contact with the fixing belt  21  is subject to downward movement, the lateral end plate  32   a  comes into contact with the free end  43   a   2  of the regulator  43   a  that regulates or prevents downward movement of the contact portion  32   a   2 . Consequently, the contact portion  32   a   2  does not press against the fixing belt  21  with substantial pressure, minimizing failures such as damage to the fixing belt  21 . 
     According to the second example embodiment depicted in  FIG. 6 , the regulator  43   a  is  molded with the regulator support  43   b.  Alternatively, the regulator  43   a  may be manufactured separately from the regulator support  43   b.    
     The fixing device  20  depicted in  FIG. 4  incorporates the plurality of halogen heaters serving as the heater  40 . Alternatively, other heaters may be employed, for example, a ceramic heater disposed opposite the fixing nip N, a flexible laminated heater in contact with the inner circumferential surface of the fixing belt  21 , and an induction heater disposed opposite the fixing belt  21  as shown in  FIG. 7 . 
       FIG. 7  is a vertical sectional view of a fixing device  20 T incorporating an induction heater  37  instead of the heater  40 , that is, the halogen heaters, depicted in  FIG. 4 . As shown in  FIG. 7 , the induction heater  37  is disposed opposite the outer circumferential surface of the fixing belt  21  to heat the fixing belt  21  by induction heating. Alternatively, the induction heater  37  may be disposed opposite the inner circumferential surface of the fixing belt  21  or both the inner circumferential surface and the outer circumferential surface of the fixing belt  21 . 
     Additionally, the heater  40  incorporated in the fixing device  20  depicted in  FIG. 4  is  substantially housed by the support  42 . Alternatively, a heater may be disposed downstream from a support in the rotation direction R 3  of the fixing belt  21  as shown in  FIG. 8 .  FIG. 8  is a vertical sectional view of a fixing device  20 U incorporating a heater  40 ′ disposed downstream from a support  42 ′ in the rotation direction R 3  of the fixing belt  21 . 
     With reference to  FIGS. 4 to 8 , a description is provided of advantages of the fixing devices  20 ,  20 S,  20 T, and  20 U described above. 
     The fixing device (e.g., the fixing devices  20 ,  20 S,  20 T, and  20 U) includes a flexible endless belt (e.g., the fixing belt  21 ) rotatable in the rotation direction R 3 ; the nip formation pad  41  contactably disposed opposite the inner circumferential surface of the endless belt; a pressing body (e.g., the pressing roller  31 ) pressed against the nip formation pad  41  via the endless belt to form the fixing nip N between the pressing body and the endless belt through which a recording medium P bearing a toner image T is conveyed; a flange (e.g., the flanges  43  and  43 S) contacting and rotatably supporting the endless belt; and the separator  32  movably supported by the flange to separate the recording medium P discharged from the fixing nip N from the endless belt by contacting the recording medium P. The separator  32  includes the center plate  32   b  disposed opposite the center of the endless belt in the axial direction thereof and the lateral end plate  32   a  disposed opposite each lateral end of the endless belt in the axial direction thereof. The lateral end plate  32   a  includes the contact portion  32   a   2  projecting beyond the center plate  32   b  toward the endless belt and contacting the endless belt to produce the given interval I between the center plate  32   b  and the outer circumferential  surface of the endless belt. 
     With this configuration of the separator  32 , the given interval I is retained between the center plate  32   b  and the outer circumferential surface of the endless belt, facilitating separation of the recording medium P from the endless belt. Accordingly, even if the endless belt is deformed by fluctuations in operation and environment of the fixing device, the contact  portions  32   a   2  constantly produce the desired interval I between the center plate  32   b  and the endless belt uniformly in the axial direction of the endless belt, thus preventing failures that may arise as the recording medium P is accidentally wound around the endless belt or as the center plate  32   b  accidentally comes into contact with the endless belt. 
     According to the example embodiments described above, the pressing roller  31   serves as a pressing body disposed opposite the fixing belt  21 . Alternatively, a pressing belt, pressing pad, a pressing plate, or the like may serve as a pressing body. 
     The present invention has been described above with reference to specific example embodiments. Note that the present invention is not limited to the details of the embodiments described above, but various modifications and enhancements are possible without departing from the spirit and scope of the invention. It is therefore to be understood that the present invention may be practiced otherwise than as specifically described herein. For example, elements and/or features of different illustrative example embodiments may be combined with each other and/or substituted for each other within the scope of the present invention.