Patent Publication Number: US-8543025-B2

Title: Fixing device and image forming apparatus incorporating same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is based on and claims priority to Japanese Patent Application No. 2010-052768, filed on Mar. 10, 2010, in the Japan Patent Office, which is hereby incorporated herein by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Exemplary aspects of the present invention 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 including 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 an image carrier; an optical writer emits a light beam onto the charged surface of the image carrier to form an electrostatic latent image on the image carrier according to the image data; a development device supplies toner to the electrostatic latent image formed on the image carrier to make the electrostatic latent image visible as a toner image; the toner image is directly transferred from the image carrier onto a recording medium or is indirectly transferred from the image carrier onto a recording medium via an intermediate transfer member; a cleaner then cleans the surface of the image carrier after the toner image is transferred from the image carrier onto the recording medium; 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. 
     The fixing device used in such image forming apparatuses may include an endless fixing belt formed into a loop and a resistant heat generator provided inside the loop formed by the fixing belt to heat the fixing belt, to shorten a warm-up time or a time to first print (hereinafter also “first print time”). Specifically, the resistant heat generator faces the inner circumferential surface of the fixing belt across a slight gap. A pressing roller presses against a contact member also provided inside the loop formed by the fixing belt via the fixing belt to form a nip between the fixing belt and the pressing roller through which the recording medium bearing the toner image passes. As the recording medium bearing the toner image passes through the nip, the fixing belt heated by the resistant heat generator and the pressing roller apply heat and pressure to the recording medium to fix the toner image on the recording medium. 
     In the nip in the fixing device, since heavy pressure is exerted at a position between the fixing member and the pressing member, torque may be generated during a startup time and a recovery time from standby state. If the torque is strong, motors may be locked or gears may be broken. 
     To counteract this effect, it is possible to improve rotation and reduce friction resistance, a lubricant, such as grease, may be applied to an inner circumferential face of the endless fixing belt, at a portion facing a support member or the contact member. 
     However, viscosity of the lubricant is dependent on temperature, and thus the viscosity is significantly higher in a cooled state, due (for example) to the ambient temperature of the fixing device. Torque failure often occurs when the fixing device starts up in a state in which the ambient temperature is cool. 
     In order to prevent torque failure from occurring, the entire fixing device may be heated as the endless belt remains motionless to warm the lubricant on the endless belt. Then, rotation of the endless belt is restarted after the viscosity of the lubricant is sufficiently decreased by warming. 
     However, if the endless belt is heated in a non-rotation condition until the lubricant is warmed sufficiently, heating is time consuming and start-up time increases. More particularly, the start-up time of the endless belt under low-temperature conditions is significantly longer. 
     In addition, in a fixing device in which the heating member for the fixing member heats the fixing member not entirely and uniformly but only locally, it is difficult to transmit the heat to the lubricant covering the entire fixing device (particularly in the nip), and as result, the heating time until the fixing member start rotating is further increased. 
     SUMMARY OF THE INVENTION 
     This specification describes below an improved fixing device. In one exemplary embodiment of the present invention, a fixing device includes an endless belt-shaped fixing member, a pressing member, a driver, a contact member, and a heating member. The fixing member rotates in a predetermined direction, formed in a loop, having an inner circumferential face of which coated with a lubricant. The pressing member contacts an outer circumferential surface of the fixing member, to press against the fixing member. The driver drives and rotates the pressing member. The contact member is provided inside the loop formed by the fixing member and is pressed against the pressing member via the fixing member to form a nip between the pressing member and the fixing member through which the recording medium bearing the toner image passes. The heating member heats the fixing member, provided inside the loop formed by the fixing member. When the fixing device starts up, the pressing member drives and rotates the fixing member less than 360 degrees to move a warmed range of the fixing member heated by the heating member to the nip. 
     Another embodiment of the present invention provides an image forming apparatus that includes a latent image carrier on which a latent image is formed, and the fixing device described above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the invention 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 schematic view of an image forming apparatus according to an exemplary embodiment of the present invention; 
         FIG. 2  is a vertical sectional view of a fixing device included in the image forming apparatus shown in  FIG. 1 ; 
         FIG. 3  is a vertical sectional view of a fixing device including a halogen heater included in the image forming apparatus shown  FIG. 1   
         FIG. 4A  is a perspective view of a fixing sleeve included in the fixing device shown in  FIG. 2 ; 
         FIG. 4B  is a vertical sectional view of the fixing sleeve shown in  FIG. 4A ; 
         FIG. 5  is a horizontal sectional view of a laminated heater included in the fixing device shown in  FIG. 2 ; 
         FIG. 6  is a perspective view of the laminated heater shown in  FIG. 5  and a heater support included in the fixing device shown in  FIG. 2 ; 
         FIG. 7  is a perspective view of the laminated heater shown in FIG.  5 , the heater support shown in  FIG. 6 , and a terminal stay included in the fixing device shown in  FIG. 2 ; 
         FIG. 8  is a partial perspective view of the laminated heater shown in  FIG. 5 , the heater support shown in  FIG. 6 , the terminal stay shown in  FIG. 7 , and power supply wiring included in the fixing device shown in  FIG. 2 ; 
         FIG. 9  is a partial sectional view of the fixing device shown in  FIG. 2 ; 
         FIG. 10  is a horizontal sectional view of the heater support shown in  FIG. 6 , the laminated heater shown in  FIG. 5 , and the fixing sleeve shown in  FIG. 4A  illustrating edge grooves included in the laminated heater; 
         FIG. 11  is a horizontal sectional view of the heater support shown in  FIG. 6 , the laminated heater shown in  FIG. 5 , and the fixing sleeve shown in  FIG. 4A  illustrating edge grooves included in the heater support; 
         FIGS. 12A and 12B  are schematic diagrams illustrating operation of the fixing device shown in  FIG. 2 ; 
         FIG. 12C  is diagram illustrating a start-up process of operation in the fixing device in the states shown in  FIGS. 12A and 12B ; 
         FIGS. 13A through 13C  are schematic diagrams illustrating another operation the fixing device shown in  FIG. 2 ; 
         FIG. 13D  is diagram illustrating a start-up process of operation in the fixing device in the states shown in  FIGS. 13A through 13C ; 
         FIG. 14A  is a plan view of a laminated heater as one variation of the laminated heater shown in  FIG. 5 ; 
         FIG. 14B  is a lookup table of a matrix showing regions on the laminated heater shown in  FIG. 14A ; 
         FIG. 15  is a plan view of a laminated heater as another variation of the laminated heater shown in  FIG. 5 ; 
         FIG. 16  is a plan view of a laminated heater as yet another variation of the laminated heater shown in  FIG. 5 ; 
         FIG. 17  is an exploded perspective view of a laminated heater as yet another variation of the laminated heater shown in  FIG. 5 ; 
         FIG. 18A  is a sectional view of a fixing sleeve support, a laminated heater, and a contact member included in the fixing device shown in  FIG. 2  illustrating the laminated heater provided inside the fixing sleeve support; 
         FIG. 18B  is a sectional view of a fixing sleeve support, a laminated heater, and a contact member included in the fixing device shown in  FIG. 2  illustrating the laminated heater provided outside the fixing sleeve support; 
         FIG. 18C  is a sectional view of a fixing sleeve support as one variation of the fixing sleeve support shown in  FIG. 18B ; 
         FIG. 18D  is a sectional view of a fixing sleeve support as another variation of the fixing sleeve support shown in  FIG. 18B ; 
         FIG. 18E  is a sectional view of a resin support provided inside the fixing sleeve support shown in  FIG. 18D ; 
         FIG. 19  is a vertical sectional view of a fixing device according to another exemplary embodiment of the present invention; 
         FIG. 20  is a perspective view of a fixing sleeve support included in the fixing device shown in  FIG. 19 ; 
         FIG. 21A  is a partial vertical sectional view of the fixing device shown in  FIG. 19 ; and 
         FIG. 21B  is a perspective view of the fixing device shown in  FIG. 21A . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In describing exemplary 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, in particular to  FIG. 1 , an image forming apparatus  1  according to an exemplary embodiment of the present invention is explained. 
       FIG. 1  is a schematic view of the image forming apparatus  1 . As illustrated in  FIG. 1 , the image forming apparatus  1  may be a copier, a facsimile machine, a printer, a multifunction printer having at least one of copying, printing, scanning, plotter, and facsimile functions, or the like. According to this exemplary embodiment of the present invention, the image forming apparatus  1  is a tandem color printer for forming a color image on a recording medium. 
     As illustrated in  FIG. 1 , the image forming apparatus  1  includes an exposure device  3 , image forming devices  4 Y,  4 M,  4 C, and  4 K, a controller  10 , a paper tray  12 , a fixing device  20 , an intermediate transfer unit  85 , a second transfer roller  89 , a feed roller  97 , a registration roller pair  98 , an output roller pair  99 , a stack portion  100 , and a toner bottle holder  101 . 
     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, chargers  75 Y,  75 M,  75 C, and  75 K, development devices  76 Y,  76 M,  76 C, and  76 K, and cleaners  77 Y,  77 M,  77 C, and  77 K, respectively. 
     The fixing device  20  includes a fixing sleeve  21  and a pressing roller  31 . 
     The intermediate transfer unit  85  includes an intermediate transfer belt  78 , first transfer bias rollers  79 Y,  79 M,  79 C, and  79 K, an intermediate transfer cleaner  80 , a second transfer backup roller  82 , a cleaning backup roller  83 , and a tension roller  84 . 
     The toner bottle holder  101  includes toner bottles  102 Y,  102 M,  102 C, and  102 K. 
     The toner bottle holder  101  is provided in an upper portion of the image forming apparatus  1 . The four toner bottles  102 Y,  102 M,  102 C, and  102 K contain yellow, magenta, cyan, and black toners, respectively, and are detachably attached to the toner bottle holder  101  so that the toner bottles  102 Y,  102 M,  102 C, and  102 K are replaced with new ones, respectively. 
     The intermediate transfer unit  85  is provided below the toner bottle holder  101 . The image forming devices  4 Y,  4 M,  4 C, and  4 K are arranged opposite the intermediate transfer belt  78  of the intermediate transfer unit  85 , and form yellow, magenta, cyan, and black toner images, respectively. 
     In the image forming devices  4 Y,  4 M,  4 C, and  4 K, the chargers  75 Y,  75 M,  75 C, and  75 K, the development devices  76 Y,  76 M,  76 C, and  76 K, the cleaners  77 Y,  77 M,  77 C, and  77 K, and dischargers surround the photoconductive drums  5 Y,  5 M,  5 C, and  5 K, respectively. Image forming processes including a charging process, an exposure process, a development process, a transfer process, and a cleaning process are performed on the photoconductive drums  5 Y,  5 M,  5 C, and  5 K to form yellow, magenta, cyan, and black toner images on the photoconductive drums  5 Y,  5 M,  5 C, and  5 K, respectively. 
     A driving motor drives and rotates the photoconductive drums  5 Y,  5 M,  5 C, and  5 K clockwise in  FIG. 1 . In the charging process, the chargers  75 Y,  75 M,  75 C, and  75 K uniformly charge surfaces of the photoconductive drums  5 Y,  5 M,  5 C, and  5 K at charging positions at which the chargers  75 Y,  75 M,  75 C, and  75 K are disposed opposite the photoconductive drums  5 Y,  5 M,  5 C, and  5 K, respectively. 
     In the exposure process, the exposure device  3  emits laser beams L onto the charged surfaces of the photoconductive drums  5 Y,  5 M,  5 C, and  5 K, respectively. In other words, the exposure device  3  scans and exposes the charged surfaces of the photoconductive drums  5 Y,  5 M,  5 C, and  5 K at irradiation positions at which the exposure device  3  is disposed opposite the photoconductive drums  5 Y,  5 M,  5 C, and  5 K to irradiate the charged surfaces of the photoconductive drums  5 Y,  5 M,  5 C, and  5 K to form thereon electrostatic latent images corresponding to yellow, magenta, cyan, and black colors, respectively. 
     In the development process, the development devices  76 Y,  76 M,  76 C, and  76 K render the electrostatic latent images formed on the surfaces of the photoconductive drums  5 Y,  5 M,  5 C, and  5 K visible as yellow, magenta, cyan, and black toner images at development positions at which the development devices  76 Y,  76 M,  76 C, and  76 K are disposed opposite the photoconductive drums  5 Y,  5 M,  5 C, and  5 K, respectively. 
     In the transfer process, the first transfer bias rollers  79 Y,  79 M,  79 C, and  79 K transfer and superimpose the yellow, magenta, cyan, and black toner images formed on the photoconductive drums  5 Y,  5 M,  5 C, and  5 K onto the intermediate transfer belt  78  at first transfer positions at which the first 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 via the intermediate transfer belt  78 , respectively. Thus, a color toner image is formed on the intermediate transfer belt  78 . After the transfer of the yellow, magenta, cyan, and black toner images, a slight amount of residual toner, which has not been transferred onto the intermediate transfer belt  78 , remains on the photoconductive drums  5 Y,  5 M,  5 C, and  5 K. 
     In the cleaning process, cleaning blades included in the cleaners  77 Y,  77 M,  77 C, and  77 K mechanically collect the residual toner from the photoconductive drums  5 Y,  5 M,  5 C, and  5 K at cleaning positions at which the cleaners  77 Y,  77 M,  77 C, and  77 K are disposed opposite the photoconductive drums  5 Y,  5 M,  5 C, and  5 K, respectively. 
     Finally, dischargers remove residual potential on the photoconductive drums  5 Y,  5 M,  5 C, and  5 K at discharging positions at which the dischargers are disposed opposite the photoconductive drums  5 Y,  5 M,  5 C, and  5 K, respectively, thus completing a single sequence of image forming processes performed on the photoconductive drums  5 Y,  5 M,  5 C, and  5 K. 
     The intermediate transfer belt  78  is supported by and stretched over three rollers, which are the second transfer backup roller  82 , the cleaning backup roller  83 , and the tension roller  84 . A single roller, that is, the second transfer backup roller  82 , drives and endlessly moves (e.g., rotates) the intermediate transfer belt  78  in a direction D 1 . 
     The four first 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  to form first transfer nips, respectively. The first 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 toner forming the yellow, magenta, cyan, and black toner images on the photoconductive drums  5 Y,  5 M,  5 C, and  5 K, respectively. Accordingly, the yellow, magenta, cyan, and black toner images formed on the photoconductive drums  5 Y,  5 M,  5 C, and  5 K, respectively, are transferred and superimposed onto the intermediate transfer belt  78  rotating in the direction D 1  successively at the first transfer nips formed between the photoconductive drums  5 Y,  5 M,  5 C, and  5 K and the intermediate transfer belt  78  as the intermediate transfer belt  78  moves through the first transfer nips. Thus, a color toner image is formed on the intermediate transfer belt  78 . 
     The paper tray  12  is provided in a lower portion of the image forming apparatus  1 , and loads a plurality of recording media P (e.g., transfer sheets). The feed roller  97  rotates counterclockwise in  FIG. 1  to feed an uppermost recording medium P of the plurality of recording media P loaded on the paper tray  12  toward a roller nip formed between two rollers of the registration roller pair  98 . 
     The registration roller pair  98 , which stops rotating temporarily, stops the uppermost recording medium P fed by the feed roller  97  and reaching the registration roller pair  98 . For example, the roller nip of the registration roller pair  98  contacts and stops a leading edge of the recording medium P. The registration roller pair  98  resumes rotating to feed the recording medium P to a second transfer nip, formed between the second transfer roller  89  and the intermediate transfer belt  78 , as the color toner image formed on the intermediate transfer belt  78  reaches the second transfer nip. 
     At the second transfer nip, the second transfer roller  89  and the second transfer backup roller  82  sandwich the intermediate transfer belt  78 . The second transfer roller  89  transfers the color toner image formed on the intermediate transfer belt  78  onto the recording medium P fed by the registration roller pair  98  at the second transfer nip formed between the second transfer roller  89  and the intermediate transfer belt  78 . Thus, the desired color toner image is formed on the recording medium P. After the transfer of the color toner image, residual toner, which has not been transferred onto the recording medium P, remains on the intermediate transfer belt  78 . 
     The intermediate transfer cleaner  80  collects the residual toner from the intermediate transfer belt  78  at a cleaning position at which the intermediate transfer cleaner  80  is disposed opposite the intermediate transfer belt  78 , thus completing a single sequence of transfer processes performed on the intermediate transfer belt  78 . 
     The recording medium P bearing the color toner image is sent to the fixing device  20 . In the fixing device  20 , the fixing sleeve  21  and the pressing roller  31  apply heat and pressure to the recording medium P to fix the color toner image on the recording medium P. 
     Thereafter, the fixing device  20  feeds the recording medium P bearing the fixed color toner image toward the output roller pair  99 . The output roller pair  99  discharges the recording medium P to an outside of the image forming apparatus  1 , that is, the stack portion  100 . Thus, the recording media P discharged by the output roller pair  99  are stacked on the stack portion  100  successively to complete a single sequence of image forming processes performed by the image forming apparatus  1 . 
     Referring to  FIGS. 2 to 9 , the following describes the structure of the fixing device  20 . 
       FIG. 2  is a vertical sectional view of the fixing device  20 . As illustrated in  FIG. 2 , the fixing device  20  further includes a laminated heater  22 , a heater support  23 , a terminal stay  24 , a power supply wiring  25 , a contact member  26 , and a core holder  28 . As illustrated in  FIG. 2 , the fixing sleeve  21  is a rotatable endless belt serving as a fixing member or a rotary fixing member. The pressing roller  31  serves as a pressing member or a rotary pressing member that contacts an outer circumferential surface of the fixing sleeve  21 . The contact member  26  is provided inside a loop formed by the fixing sleeve  21 , and is pressed against the pressing roller  31  via the fixing sleeve  21  to form a nip N between the pressing roller  31  and the fixing sleeve  21  through which the recording medium P passes. The laminated heater  22  is provided inside the loop formed by the fixing sleeve  21 , and contacts or is disposed close to an inner circumferential surface of the fixing sleeve  21  to heat the fixing sleeve  21  directly or indirectly. The heater support  23  is provided inside the loop formed by the fixing sleeve  21  to support the laminated heater  22  at a predetermined position in such a manner that the heater support  23  and the fixing sleeve  21  sandwich the laminated heater  22 . According to this exemplary embodiment, the laminated heater  22  contacts the inner circumferential surface of the fixing sleeve  21  to heat the fixing sleeve  21  directly. 
     In addition, the controller  10  and a driver  35 , and a thermistor  33  are provided in the fixing device  20 . The driver  35  is formed by, for example, a motor, a gear, and so on. The controller  10  controls the driver  35 . The thermistor  33 , serving as a temperature detector, is provided close to the fixing sleeve  21 . The controller  10  also controls the heating in the laminated heater  22  based on the detection result detected by the thermistor  33 . The controller  10  may be a computer including a central processing unit (CPU) and associated memory units (e.g., ROM, RAM, etc.). The computer performs various types of control processing by executing programs stored in the memory. It is to be noted that the controller  10  and the driver  35  may be provided in the image forming apparatus  1 , instead of the interior of the fixing device. 
     In the fixing device  20  shown in  FIG. 2 , when the fixing device  20  starts up, the fixing sleeve  21  (fixing member) is rotated less than 360 degrees by rotating the pressing roller  31  (pressing member), and an area of the fixing sleeve  21  heated by the laminated heater  22  (heating member) is moved to the nip N. 
     laminated heater  22  functions as a heating member, the heating member is not limited to a laminated heater. For example, as shown in  FIG. 3 , a halogen heater  32  can be also adapted as the heating member. Similarly to the laminated heater  22  shown in  FIG. 2 , the halogen heater  32  does not heat the fixing sleeve  21  (fixing member) uniformly but locally. Further, the heating member may be formed by an induction heater (IH). 
     In addition, as shown in  FIG. 3 , the fixing device  20  may further include a metal pipe  30  that guides the rotary fixing member (fixing sleeve  21 ) at a predetermined position. In this configuration, the heating sleeve  21  and the metal pipe  20  together serve as fixing members. 
       FIG. 4A  is a perspective view of the fixing sleeve  21 .  FIG. 4B  is a sectional view of the fixing sleeve  21 . As illustrated in  FIG. 4A , an axial direction of the fixing sleeve  21  corresponds to a long axis of the pipe-shaped fixing sleeve  21 . As illustrated in  FIG. 4B , a circumferential direction of the fixing sleeve  21  extends along a circumference of the pipe-shaped fixing sleeve  21 . The fixing sleeve  21  is a flexible, pipe-shaped endless belt having a width in the axial direction of the fixing sleeve  21 , which corresponds to a width of a recording medium P passing through the nip N between the fixing sleeve  21  and the pressing roller  31 . For example, the fixing sleeve  21  is constructed of a base layer and at least a release layer provided on the base layer. The base layer is made of a metal material and has a thickness in a range of from about 30 μm to about 50 μm. The fixing sleeve  21  has an outer diameter of about 30 mm. The base layer of the fixing sleeve  21  includes a conductive metal material such as iron, cobalt, nickel, or an alloy of those. 
     The release layer of the fixing sleeve  21  is a tube covering the base layer, and has a thickness of about 50 μm. The release layer includes a fluorine compound such as tetrafluoroethylene-perfluoroalkylvinylether copolymer (PFA). The release layer facilitates separation of toner of a toner image T on the recording medium P, which contacts the outer circumferential surface of the fixing sleeve  21  directly, from the fixing sleeve  21 . 
     The pressing roller  31  depicted in  FIG. 2  is constructed of a metal core including a metal material such as aluminum or copper; a heat-resistant elastic layer provided on the metal core and including silicon rubber (e.g., solid rubber); and a release layer provided on the elastic layer. The pressing roller  31  has an outer diameter of about 30 mm. The elastic layer has a thickness of about 2 mm. The release layer is a PFA tube covering the elastic layer and has a thickness of about 50 μm. A heat generator, such as a halogen heater, may be provided inside the metal core as needed. A pressing mechanism presses the pressing roller  31  against the contact member  26  via the fixing sleeve  21  to form the nip N between the pressing roller  31  and the fixing sleeve  21 . For example, a portion of the pressing roller  31  contacting the fixing sleeve  21  causes a concave portion of the fixing sleeve  21  at the nip N. Thus, the recording medium P passing through the nip N moves along the concave portion of the fixing sleeve  21 . 
     A driving mechanism drives and rotates the pressing roller  31 , which presses the fixing sleeve  21  against the contact member  26 , clockwise in  FIG. 2  in a rotation direction R 2 . Accordingly, the fixing sleeve  21  rotates in accordance with rotation of the pressing roller  31  counterclockwise in  FIG. 2 , in a rotation direction R 1 . 
     A long axis of the contact member  26  corresponds to the axial direction of the fixing sleeve  21 . At least a portion of the contact member  26  that is pressed against the pressing roller  31  via the fixing sleeve  21  includes a heat-resistant elastic material such as fluorocarbon rubber. The core holder  28  holds and fixes the contact member  26  at a predetermined position inside the loop formed by the fixing sleeve  21 . A portion of the contact member  26  that contacts the inner circumferential surface of the fixing sleeve  21  may include a slidable and durable material such as a Teflon® sheet. 
     In addition, in order to improve rotation of the fixing sleeve  21  with the contact member  26 , a lubricant such as grease, oil is applied on an inner circumferential face of the fixing sleeve  21 . 
     The core holder  28  is made of sheet metal, and has a width in a long axis thereof corresponding to the width of the fixing sleeve  21  in the axial direction of the fixing sleeve  21 . The core holder  28  is a rigid member having an H-like shape in cross-section, and is provided at substantially a center position inside the loop formed by the fixing sleeve  21 . 
     The core holder  28  holds the respective components provided inside the loop formed by the fixing sleeve  21  at predetermined positions. For example, the core holder  28  includes a first concave portion facing the pressing roller  31 , which houses and holds the contact member  26 . In other words, the core holder  28  is disposed opposite the pressing roller  31  via the contact member  26  to support the contact member  26 , with the fixing sleeve  21  disposed therebetween. Accordingly, even when the pressing roller  31  presses the fixing sleeve  21  against the contact member  26 , the core holder  28  prevents substantial deformation of the contact member  26 . In addition, the contact member  26  protrudes from the core holder  28  slightly toward the pressing roller  31 . Accordingly, the core holder  28  is isolated from and does not contact the fixing sleeve  21  at the nip N. 
     The core holder  28  further includes a second concave portion disposed back-to-back to the first concave portion, which houses and holds the terminal stay  24  and the power supply wiring  25 . The terminal stay  24  has a width in a long axis thereof corresponding to the width of the fixing sleeve  21  in the axial direction of the fixing sleeve  21 , and is T-shaped in cross-section. The power supply wiring  25  extends on the terminal stay  24 , and transmits power supplied from an outside of the fixing device  20 . A part of an outer circumferential surface of the core holder  28  holds the heater support  23  that supports the laminated heater  22 . In  FIG. 2 , the core holder  28  holds the heater support  23  in a lower half region inside the loop formed by the fixing sleeve  21 , that is, in a semicircular region provided upstream from the nip N in the rotation direction R 1  of the fixing sleeve  21 . The heater support  23  may be adhered to the core holder  28  to facilitate assembly. Alternatively, the heater support  23  need not be adhered to the core holder  28  to prevent heat transmission from the heater support  23  to the core holder  28 . 
     The heater support  23  supports the laminated heater  22  in such a manner that the laminated heater  22  either contacts the inner circumferential surface of the fixing sleeve  21  or the laminated heater  22  is disposed close to the inner circumferential surface of the fixing sleeve  21  across a predetermined gap. Accordingly, the heater support  23  includes an arc-shaped outer circumferential surface having a predetermined circumferential length and disposed along the inner circumferential surface of the circular fixing sleeve  21  in cross-section. 
     The heater support  23  may have a heat resistance that resists heat generated by the laminated heater  22 , a strength sufficient to support the laminated heater  22  without being deformed by the fixing sleeve  21  when the rotating fixing sleeve  21  contacts the laminated heater  22 , and sufficient heat insulation so that heat generated by the laminated heater  22  is not transmitted to the core holder  28  but which does transmit the heat to the fixing sleeve  21 . For example, the heater support  23  may be a molded foam including polyimide resin. When the laminated heater  22  is configured to contact the inner circumferential surface of the fixing sleeve  21 , the rotating fixing sleeve  21  applies a force that pulls the laminated heater  22  to the nip N to the laminated heater  22 . To address this force, the heater support  23  may include the molded foam including polyimide resin that provides the heater support  23  with a strength sufficient to support the laminated heater  22  without being deformed. Alternatively, a supplemental solid resin member may be provided inside the molded foam including polyimide resin to improve rigidity. 
       FIG. 5  is a sectional view of the laminated heater  22 . As illustrated in  FIG. 5 , the laminated heater  22  includes a heat generation sheet  22   s . The heat generation sheet  22   s  includes a base layer  22   a  having insulation, a resistant heat generation layer  22   b  provided on the base layer  22   a  and including conductive particles dispersed in a heat-resistant resin, an electrode layer  22   c  provided on the base layer  22   a  to supply power to the resistant heat generation layer  22   b , and an insulation layer  22   d  provided on the base layer  22   a . The heat generation sheet  22   s  is flexible, and has a predetermined width in the axial direction of the fixing sleeve  21  depicted in  FIG. 2  and a predetermined length in the circumferential direction of the fixing sleeve  21 . 
     The insulation layer  22   d  insulates one resistant heat generation layer  22   b  from another adjacent resistant heat generation layer  22   b  of a different power supply system, and insulates an edge of the heat generation sheet  22   s  from an outside of the heat generation sheet  22   s.    
     The heat generation sheet  22   s  has a thickness in a range of from about 0.1 mm to about 1.0 mm, and has a flexibility sufficient to wrap around the heater support  23  depicted in  FIG. 2  at least along an outer circumferential surface of the heater support  23 . 
     The base layer  22   a  is a thin, elastic film including a certain heat-resistant resin such as polyethylene terephthalate (PET) or polyimide resin. For example, the base layer  22   a  may be a film including polyimide resin to provide heat resistance, insulation, and a certain level of flexibility. 
     The resistant heat generation layer  22   b  is a thin, conductive film in which conductive particles, such as carbon particles and metal particles, are uniformly dispersed in a heat-resistant resin such as polyimide resin. When power is supplied to the resistant heat generation layer  22   b , internal resistance of the resistant heat generation layer  22   b  generates Joule heat. The resistant heat generation layer  22   b  is manufactured by coating the base layer  22   a  with a coating compound in which conductive particles, such as carbon particles and metal particles, are dispersed in a precursor including a heat-resistant resin such as polyimide resin. 
     Alternatively, the resistant heat generation layer  22   b  may be manufactured by providing a thin conductive layer including carbon particles and/or metal particles on the base layer  22   a  and then providing a thin insulation film including a heat-resistant resin such as polyimide resin on the thin conductive layer. Thus, the thin insulation film is laminated on the thin conductive layer to integrate the thin insulation film with the thin conductive layer. 
     The carbon particles used in the resistant heat generation layer  22   b  may be known carbon black powder or carbon nanoparticles formed of at least one of carbon nanofiber, carbon nanotube, and carbon microcoil. 
     The metal particles used in the resistant heat generation layer  22   b  may be silver, aluminum, or nickel particles, and may be granular or filament-shaped. 
     The insulation layer  22   d  may be manufactured by coating the base layer  22   a  with an insulation material including a heat-resistant resin identical to the heat-resistant resin of the base layer  22   a , such as polyimide resin. 
     The electrode layer  22   c  may be manufactured by coating the base layer  22   a  with a conductive ink or a conductive paste such as silver. Alternatively, metal foil or a metal mesh may be adhered to the base layer  22   a.    
     The heat generation sheet  22   s  of the laminated heater  22  is a thin sheet having a small heat capacity, and is heated quickly. An amount of heat generated by the heat generation sheet  22   s  is arbitrarily set according to the volume resistivity of the resistant heat generation layer  22   b . In other words, the amount of heat generated by the heat generation sheet  22   s  can be adjusted according to the material, shape, size, and dispersion of conductive particles of the resistant heat generation layer  22   b . For example, the laminated heater  22  providing heat generation per unit area of 35 W/cm 2  outputs a total power of about 1,200 W with the heat generation sheet  22   s  having a width of about 20 cm in the axial direction of the fixing sleeve  21  and a length of about 2 cm in the circumferential direction of the fixing sleeve  21 , for example. 
     If a metal filament, such as a stainless steel filament, is used as a laminated heater, the metal filament causes asperities to appear in the surface of the laminated heater. Consequently, when the inner circumferential surface of the fixing sleeve  21  slides over the laminated heater, the asperities of the laminated heater abrade the surface of the laminated heater easily. To address this problem, according to this exemplary embodiment, the heat generation sheet  22   s  has a smooth surface without asperities as described above, providing improved durability in particular against wear due to sliding of the inner circumferential surface of the fixing sleeve  21  over the laminated heater  22 . Further, a surface of the resistant heat generation layer  22   b  of the heat generation sheet  22   s  may be coated with fluorocarbon resin to further improve durability. 
     In  FIG. 3 , the heat generation sheet  22   s  faces the inner circumferential surface of the fixing sleeve  21  in a region in the circumferential direction of the fixing sleeve  21  between a position on the fixing sleeve  21  opposite the nip N and a position upstream from the nip N in the rotation direction R 1  of the fixing sleeve  21 . Alternatively, the heat generation sheet  22   s  may face the inner circumferential surface of the fixing sleeve  21  in a region in the circumferential direction of the fixing sleeve  21  between the position on the fixing sleeve  21  opposite the nip N and a position of the nip N in the rotation direction R 1  of the fixing sleeve  21 . Yet alternatively, the heat generation sheet  22   s  may face the entire inner circumferential surface of the fixing sleeve  21  in the circumferential direction of the fixing sleeve  21 . 
     Referring to  FIGS. 6 to 9 , the following describes assembly processes for assembling the fixing device  20 , that is, steps for putting together the components provided inside the loop formed by the fixing sleeve  21 .  FIG. 6  is a perspective view of the laminated heater  22  and the heater support  23 .  FIG. 7  is a perspective view of the laminated heater  22 , the heater support  23 , and the terminal stay  24 .  FIG. 8  is a perspective view of the laminated heater  22 , the heater support  23 , the terminal stay  24 , and the power supply wiring  25 . 
     As illustrated in  FIG. 6 , the laminated heater  22  further includes electrode terminal pairs  22   e  and an attachment terminal  22   f . The electrode terminal pair  22   e  includes electrode terminals  22   e   1  and  22   e   2 . 
     As illustrated in  FIG. 6 , the heat generation sheet  22   s  of the laminated heater  22  is adhered to the heater support  23  with an adhesive along the outer circumferential surface of the heater support  23 . The adhesive may have a small heat conductivity to prevent heat transmission from the heat generation sheet  22   s  to the heater support  23 . 
     The electrode terminal pair  22   e  is connected to the electrode layer  22   c  (depicted in  FIG. 5 ) at an end of the heat generation sheet  22   s  in a long axis of the laminated heater  22  parallel to the axial direction of the fixing sleeve  21 , and sends power supplied from the power supply wiring  25  (depicted in  FIG. 8 ) to the electrode layer  22   c.    
     The plurality of electrode terminal pairs  22   e , which are connected to the electrode layer  22   c , is provided on one end of the laminated heater  22  in the circumferential direction of the fixing sleeve  21 . In  FIG. 6 , the electrode terminal pairs  22   e  are provided on an edge of one end of the laminated heater  22  disposed opposite another end of the laminated heater  22  provided closer to the nip N and the pressing roller  31  in the circumferential direction of the fixing sleeve  21 . The electrode terminal pair  22   e  including the electrode terminals  22   e   1  and  22   e   2  is provided on each of lateral ends of the laminated heater  22  in the axial direction of the fixing sleeve  21 . 
     The following describes the reason for the above-described arrangement of the electrode terminal pairs  22   e.    
     The laminated heater  22  includes at least two electrode terminal pairs  22   e  to supply power to the resistant heat generation layer  22   b  depicted in  FIG. 5 . For example, when one electrode terminal pair  22   e  is provided on each end of the heat generation sheet  22   s  in the circumferential direction of the fixing sleeve  21 , a power source harness for power supply is connected to each electrode terminal pair  22   e . However, the heat generation sheet  22   s  itself is a thin film with little rigidity. Accordingly, a terminal block that connects the harness to the electrode terminal pair  22   e  is provided on each end of the heat generation sheet  22   s  in the circumferential direction of the fixing sleeve  21 , upsizing the fixing device  20 . To address this problem, according to this exemplary embodiment, the two electrode terminal pairs  22   e  are provided on one end of the heat generation sheet  22   s  in the circumferential direction of the fixing sleeve  21  to downsize the fixing device  20 . 
     Alternatively, the electrode terminal pair  22   e  may be provided on one end of the heat generation sheet  22   s  in the axial direction of the fixing sleeve  21 . However, when the heat generation sheet  22   s  is attached to the heater support  23  along the outer circumferential surface of the heater support  23 , the electrode terminal pair  22   e  is bent, resulting in deformation of the electrode terminal pair  22   e  when the electrode terminal pair  22   e  is secured with a screw, complication of the electrode terminals  22   e   1  and  22   e   2 , and complicated assembly. To address those problems, according to this exemplary embodiment, the plurality of electrode terminal pairs  22   e  is provided on one end of the heat generation sheet  22   s  in the circumferential direction of the fixing sleeve  21 . Accordingly, even when the heat generation sheet  22   s  is attached to the heater support  23  along the outer circumferential surface of the heater support  23 , the electrode terminal pairs  22   e  are not bent, facilitating assembly processes. 
     In next step, as illustrated in  FIGS. 7 and 8 , the heat generation sheet  22   s  is bent along the edge of the heater support  23  near the electrode terminal pairs  22   e  in such a manner that the electrode terminal pairs  22   e  are directed to a center of the circular loop formed by the fixing sleeve  21 . Then, each of the electrode terminals  22   e   1  and  22   e   2  is connected to the power supply wiring  25  on the terminal stay  24 , and secured to the terminal stay  24 . For example, the electrode terminals  22   e   1  and  22   e   2  are secured to the terminal stay  24  with screws, respectively, as illustrated in  FIG. 8 . 
     As illustrated in  FIG. 6 , the attachment terminal  22   f  is provided on and protrudes from a center of the edge of the heat generation sheet  22   s  in the long axis of the laminated heater  22 . The attachment terminal  22   f  is also secured to the terminal stay  24  with a screw. 
       FIG. 9  is a partial sectional view of the fixing device  20  illustrating the inner components provided inside the fixing sleeve  21 . In this step, as illustrated in  FIG. 9 , the core holder  28  is attached to the terminal stay  24  in such a manner that the second concave portion of the core holder  28  houses the terminal stay  24 . Further, the contact member  26  is attached to the core holder  28  in such a manner that the core holder  28  houses the contact member  26 , thus completing assembly of the inner components to be provided inside the loop formed by the fixing sleeve  21 . 
     Finally, the assembled components are inserted into the loop formed by the fixing sleeve  21  at a position illustrated in  FIG. 2 , completing assembly of the fixing sleeve  21  and the inner components provided inside the fixing sleeve  21  of the fixing device  20 . 
     When the heat generation sheet  22   s  is not adhered to the heater support  23  with an adhesive, the electrode terminal pairs  22   e  and the attachment terminal  22   f , which are provided at a fixed end of the heat generation sheet  22   s  opposite a free end of the heat generation sheet  22   s  provided near the nip N in the circumferential direction of the fixing sleeve  21 , are secured to the terminal stay  24  with the screws, respectively. The rotating fixing sleeve  21  pulls the free end of the heat generation sheet  22   s  toward the nip N to tension the heat generation sheet  22   s . Accordingly, the heat generation sheet  22   s  contacts the inner circumferential surface of the fixing sleeve  21  stably in a state in which the heat generation sheet  22   s  is sandwiched between the heater support  23  and the fixing sleeve  21 . Consequently, the heat generation sheet  22   s  heats the fixing sleeve  21  effectively. 
     However, when the heat generation sheet  22   s  is not adhered to the heater support  23  and therefore is separated from the heater support  23 , the fixing sleeve  21  rotating back to allow removal of a jammed recording medium P may lift and shift the heat generation sheet  22   s  from its proper position. Moreover, the moving heat generation sheet  22   s  may twist and deform the electrode terminal pairs  22   e , breaking them. To address these problems, the heat generation sheet  22   s  is preferably adhered to the heater support  23  to prevent the heat generation sheet  22   s  from shifting from the proper position. 
     Conversely, when the entire inner surface of the heat generation sheet  22   s  facing the heater support  23  is adhered to the heater support  23 , heat generated by the heat generation sheet  22   s  moves from the entire inner surface of the heat generation sheet  22   s  to the heater support  23  easily. To address this problem, lateral end portions of the heat generation sheet  22   s  in the axial direction of the fixing sleeve  21 , which correspond to a non-conveyance region on the fixing sleeve  21  through which the recording medium P is not conveyed, are adhered to the heater support  23  to prevent the heat generation sheet  22   s  from shifting from the proper position. Further, a center portion of the heat generation sheet  22   s  in the axial direction of the fixing sleeve  21 , which corresponds to a conveyance region on the fixing sleeve  21  through which the recording medium P is conveyed, that is, a maximum conveyance region corresponding to a width of the maximum recording medium P, is not adhered to the heater support  23  and therefore is isolated from the heater support  23 . Accordingly, heat is not transmitted from the center portion of the heat generation sheet  22   s  in the axial direction of the fixing sleeve  21  to the heater support  23 . As a result, heat generated at the center portion of the heat generation sheet  22   s  is used effectively to heat the fixing sleeve  21 . 
     The heat generation sheet  22   s  may be adhered to the heater support  23  with a liquid adhesive for coating. Alternatively, a tape adhesive (e.g., a double-faced adhesive tape), which provides adhesion on both sides thereof and includes a heat-resistant acryl or silicon material, may be used. Accordingly, the laminated heater  22  (e.g., the heat generation sheet  22   s ) is adhered to the heater support  23  easily. Further, if the laminated heater  22  malfunctions, the laminated heater  22  can be replaced easily by peeling off the double-faced adhesive tape, facilitating maintenance. 
     It is to be noted that, if the heat generation sheet  22   s  and the heater support  23  merely sandwich the double-faced adhesive tape, the lateral end portions of the heat generation sheet  22   s  in the axial direction of the fixing sleeve  21 , which are adhered to the heater support  23 , are lifted by a thickness of the double-faced adhesive tape. Accordingly, the center portion of the heat generation sheet  22   s  in the axial direction of the fixing sleeve  21 , which is not adhered to the heater support  23 , does not contact the fixing sleeve  21  uniformly, decreasing heating efficiency for heating the fixing sleeve  21  and varying temperature distribution of the fixing sleeve  21  in the axial direction of the fixing sleeve  21 . To address this problem, the lateral end portions of the heat generation sheet  22   s  in the axial direction of the fixing sleeve  21 , which are adhered to the heater support  23  with the double-faced adhesive tape, have a thickness decreased by the thickness of the double-faced adhesive tape. 
       FIG. 10  is a sectional view of the heater support  23 , the laminated heater  22 , and the fixing sleeve  21 . As illustrated in  FIG. 10 , the laminated heater  22  further includes edge grooves  22   g  and double-faced adhesive tapes  22   t . The edge grooves  22   g  are provided at lateral edges, which correspond to the non-conveyance region on the fixing sleeve  21  through which the recording medium P is not conveyed, of the heat generation sheet  22   s  in the axial direction of the fixing sleeve  21 , respectively, on a surface of the base layer  22   a  (depicted in  FIG. 5 ) of the heat generation sheet  22   s  that faces the heater support  23 , and extend in the circumferential direction of the fixing sleeve  21 . Each of the edge grooves  22   g  has a depth equivalent to the thickness (e.g., about 0.1 mm) of the double-faced adhesive tape  22   t.    
     The double-faced adhesive tapes  22   t  are adhered to the edge grooves  22   g  of the heat generation sheet  22   s , respectively, and then adhered to the heater support  23 . In other words, the heat generation sheet  22   s  is adhered to the heater support  23  at predetermined positions on the heater support  23  via the double-faced adhesive tapes  22   t . Accordingly, when the heat generation sheet  22   s  is adhered to the heater support  23 , a surface of the heat generation sheet  22   s  that faces the fixing sleeve  21  is planar in the axial direction of the fixing sleeve  21 . Consequently, the heat generation sheet  22   s  uniformly contacts the fixing sleeve  21  at the center portion of the heat generation sheet  22   s  corresponding to the conveyance region on the fixing sleeve  21  over which the recording medium P is conveyed, providing improved heating efficiency for heating the fixing sleeve  21  and uniform temperature distribution of the fixing sleeve  21  in the axial direction of the fixing sleeve  21 . 
     Alternatively, edge grooves may be provided in the heater support  23  instead of in the heat generation sheet  22   s .  FIG. 11  is a sectional view of the heater support  23 , the laminated heater  22 , and the fixing sleeve  21 . As illustrated in  FIG. 11 , the heater support  23  includes edge grooves  23   g.    
     The edge grooves  23   g  are provided at lateral edges of the heater support  23  in the axial direction of the fixing sleeve  21 , which correspond to the non-conveyance region on the fixing sleeve  21  through which the recording medium P is not conveyed, heater support, on a surface of the heater support  23  that faces the heat generation sheet  22   s , and extend in the circumferential direction of the fixing sleeve  21 . Each of the edge grooves  23   g  has a depth equivalent to the thickness of the double-faced adhesive tape  22   t . The double-faced adhesive tapes  22   t  are adhered to the edge grooves  23   g  of the heater support  23 , respectively, and then the heat generation sheet  22   s  is adhered to the heater support  23  via the double-faced adhesive tapes  22   g . Accordingly, when the heat generation sheet  22   s  is adhered to the heater support  23 , the surface of the heat generation sheet  22   s  that faces the fixing sleeve  21  is planar in the axial direction of the fixing sleeve  21 . Consequently, the heat generation sheet  22   s  uniformly contacts the fixing sleeve  21  at the center portion of the heat generation sheet  22   s  corresponding to the conveyance region on the fixing sleeve  21  over which the recording medium P is conveyed, providing improved heating efficiency for heating the fixing sleeve  21  and uniform temperature distribution of the fixing sleeve  21  in the axial direction of the fixing sleeve  21   
     Referring back to  FIG. 2 , the following describes basic operation of the fixing device  20  having the above-described structure. 
     When the image forming apparatus  1  receives an output signal, for example, when the image forming apparatus  1  receives a print request specified by a user by using a control panel or a print request sent from an external device, such as a personal computer, the pressing roller  31  is pressed against the contact member  26  via the fixing sleeve  21  to form the nip N between the pressing roller  31  and the fixing sleeve  21 . 
     Thereafter, an external power source or an internal capacitor supplies electric power to the laminated heater  22  via the power supply wiring  25  to cause the heat generation sheet  22   s  to generate heat. The heat generated by the heat generation sheet  22   s  is transmitted effectively to the fixing sleeve  21  contacting the heat generation sheet  22   s , so that the fixing sleeve  21  is heated quickly. 
     Then, the controller  10  causes the driver  35  to drive and rotate the pressing roller  31  clockwise in  FIG. 2  in the rotation direction R 2 . Accordingly, the fixing sleeve  21  rotates counterclockwise in  FIG. 2  in the rotation direction R 1  in accordance with rotation of the pressing roller  31 . At this time, the laminated heater  22  supported by the heater support  23  contacts the inner circumferential surface of the fixing sleeve  21 , and the fixing sleeve  21  slides over the laminated heater  22 . 
     The temperature detector  33  is provided at a position upstream from the nip N in the rotation direction R 1  of the fixing sleeve  21 . For example, the temperature detector  33  may be provided outside the loop formed by the fixing sleeve  21  to face the outer circumferential surface of the fixing sleeve  21  with or without contacting the fixing sleeve  21 . Alternatively, the temperature detector  33  may be provided inside the loop formed by the fixing sleeve  21  to face the heater support  23  with or without contacting the heater support  23 . The thermistor  33  (temperature detector) detects a temperature of the fixing sleeve  21  or the heater support  23  to control heat generation of the laminated heater  22  based on a detection result provided by the thermistor  33  so as to heat the nip N up to a predetermined fixing temperature. When the nip N is heated to the predetermined fixing temperature, the fixing temperature is maintained, and a recording medium P is conveyed to the nip N. 
     In the fixing device  20  according to this exemplary embodiment, the fixing sleeve  21  and the laminated heater  22  have a small heat capacity, shortening a warm-up time and a first print time of the fixing device  20  while saving energy. Further, the heat generation sheet  22   s  is a resin sheet. Accordingly, even when rotation and vibration of the pressing roller  31  applies stress to the heat generation sheet  22   s  repeatedly, and bends the heat generation sheet  22   s  repeatedly, the heat generation sheet  22   s  is not broken due to wear, and the fixing device  20  operates for a longer time. 
     When the image forming apparatus  1  does not receive an output signal, the pressing roller  31  and the fixing sleeve  21  do not rotate and power is not supplied to the laminated heater  22 , to reduce power consumption. However, in order to restart the fixing device  20  immediately after the image forming apparatus  1  receives an output signal, power can be supplied to the laminated heater  22  while the pressing roller  31  and the fixing sleeve  21  do not rotate. For example, power in an amount sufficient to keep the entire fixing sleeve  21  warm is supplied to the laminated heater  22 . 
     Next, operation of the fixing device  20  is described in further detail below, with reference  FIGS. 12A through 13D .  FIGS. 12A ,  12 B,  13 A,  13 B, and  13 C are schematic diagrams illustrating a warmed range of the fixing device  20 .  FIG. 12A  shows a state in which the fixing device  20  is not operated (stopped state or non-rotation state) and a range indicated by arrow A (hereinafter “warmed range A”) is heated by the laminated heater  22  (heating member) (shown in  FIG. 2). 12B  a state in which the fixing sleeve  21  is stopped after being rotated through a predetermined angle indicated by arrow C by rotation of the pressing member  31 , and a range indicated by arrow B (hereinafter “warmed range B”) is heated by the laminated heater  22  (heating member) (shown in  FIG. 2 ). At this time, the warmed range A of the fixing sleeve  21  is moved to the nip N side (right side) shown in  FIG. 12B . 
       FIG. 12C  shows processes of start-up operation in the fixing device  20  in the states shown in  FIGS. 12A and 12B . Referring to  FIGS. 12A through 12C , the processes of the start-up operation in the fixing device  20  is described below. 
     Initially, at step S 101 , when the fixing device  20  in the image forming apparatus  1  receives the output signal, the fixing device  20  begins the start-up process. During start-up process in the fixing device  20 , at step S 102 , the external power source or the internal capacitor supplies electrical power to the laminated heater  22  via the power supply wiring  25  (see  FIG. 2 ) to cause the heat generation sheet  22   s  (see  FIG. 5 ) of the laminated heater  22  to generate heat. 
     Thereafter, at S 103 , the laminated heater  22   s  heats the range A of the fixing sleeve  21 , and the lubricant in the warmed range A is melted. Accordingly, in the warmed range A of the fixing sleeve  21  heated by the laminated heater  22 , the viscosity of the lubricant (e.g., grease) applied on the inner circumferential surface of the fixing sleeve  21  is decreased. 
     Then, at step S 104 , the controller  10  causes the driver  35  to drive the pressing roller  31 , and the fixing sleeve  21  is rotated less than 360 degrees by driving the pressing roller  31 . Accordingly, the warmed range A of the fixing sleeve  21  heated by the laminated heater  22  is moved to the nip N facing the pressing roller  31 . 
     After that, the fixing sleeve  21  starts rotating in a state in which the lubricant in the nip N is melted by moving the warmed range A thus heated to the nip N, that is, the fixing device  20  starts fixing process at step S 105 . Accordingly, the fixing sleeve  21  can start rotating (starts continuously rotating) without occurring torque failure. 
     Therefore, even when the viscosity of the lubricant is high under low-temperature conditions, the fixing device  20  starts up in a state in which the lubricant in the nip N is melted. Therefore, the failure of the torque can be prevented. 
     Further, it is preferable that the above-described control is performed not only in a start-up state during which the fixing device  20  starts up under low-temperature conditions but also in a standby state (heat retention state) in which the fixing sleeve  21  is at a predetermined warned temperature. In the standby state in which the fixing device  20  recovers to the fixing process, the above-described processes are performed similarly shown in  FIGS. 12A through 12C . 
     As described above, in the standby state, the fixing sleeve  21  is similarly rotated by driving the pressing roller  31  less than 360 degrees, and the warmed range of the fixing sleeve  21  heated by the laminated heater  22  is moved to the nip N facing the pressing roller  31 . As a result, for example, a failure occurring when the fixing sleeve  21  is locally heated can be prevented, and entire fixing device  20  can be warmed. In addition, a recovery time in a case in which the print request is received can be shortened. 
     As described above, in order to move the warmed range of the fixing sleeve  21  heated by the laminated heater  22  in the non-rotation state (start-up state and standby state) to the nip N, that is, the position facing the contact member  26 , the pressing roller  31  drives and rotates the fixing sleeve  21  at least one time less than 360 degrees. Thus, the lubricant in the nip N can be warmed. As a result, the failure caused by the torque is prevented, and rapid starting up is achieved, which can enhance useful life of the fixing device  20 . 
     Further, it is preferable that the rotation angle of the fixing sleeve  21  by which the pressing roller  31  rotates from initial state to reaching the warmed range of the fixing nip N be not any divisor of 360. In a case in which the rotation angle is not divisors of 360, the fixing sleeve  21  can avoid stopping repeatedly at the same positions when the pressing roller  31  rotation repeatedly by repeating the start-up state and standby state. Accordingly, permanent strain of the fixing sleeve  21  caused by stopping many times at the same positions can be prevented. 
     In addition, as shown in  FIGS. 12A through 12C , a rotation velocity of the pressing roller  31  during rotation in the start-up state and standby state may be set slower than a rotation velocity of the pressing roller  31  during normal fixing process. In this state, the pressing roller  31  and the fixing sleeve  21  can be rotated in a condition in which the torque is reduced. 
     Further, a temperature detector  34 , such as a thermistor, that detects temperature in the pressing roller  31 , may be provided close to the pressing roller  31 , as shown in  FIG. 12B . In this configuration, because the temperature of the pressing roller  31  can be regarded as similar to the temperature at the position of the nip N, the pressing roller  31  may rotate in the start-up state and standby state so that the temperature detected by the temperature detector  34  is kept above a predetermined temperature (e.g., fixing temperature). 
     Thus, by controlling the temperature of the pressing roller  31  by using the temperature detector  34  that detects the temperature of the pressing roller  31 , the temperature of the nip N can be maintained at a desired temperature with a high degree of accuracy. Accordingly, the fixing device  20  can performed in an energy-efficient manner and the working life of the fixing device can be extended. 
     Herein, in order to reduce the torque further, as shown in  FIGS. 13A through 13C , it is preferable that the pressing roller  31  perform intermittent rotation in which the pressing roller  31  alternately rotates and stops. In  FIG. 13A , when the fixing sleeve  21  is not rotating, the warmed range indicated by arrow A is heated.  FIG. 13B  shows the fixing device  20  in which the fixing sleeve  21  is stopped after being rotated a predetermined angle indicated by arrow C 1  by intermittent rotation of the pressing roller  31 . The warmed range A is moved to the right shown in  FIG. 13B . 
     Further,  FIG. 13C  shows the fixing device  20  in which the fixing sleeve  21  is stopped after being further rotated at a predetermined angle indicated by arrow C by intermittent rotation of the pressing roller  31 . The warmed range A is further moved to the right shown in  FIG. 13C . In  FIG. 13C , a range indicated by solid arrow B is a range in which the fixing sleeve  21  is currently heated. 
     More specifically,  FIG. 13D  shows processes of a start-up operation in the fixing device  20  when the pressing roller  31  rotates intermittently in the states shown in  FIGS. 13A through 13C . Referring to  FIGS. 13A through 13D , the processes of the start-up operation in the fixing device  20  is described below. 
     Similarly to  FIG. 12C , initially, at step S 201  in  FIG. 13D , when the fixing device  20  in the image forming apparatus receives the output signal, the fixing device  20  begins the start-up process. During start-up process in the fixing device  20 , at step S 202 , the external power source or the internal capacitor supplies electrical power to the laminated heater  22  via the power supply wiring  25  to cause the heat generation sheet  22   s  to generate heat. 
     Then, at S 203 , the laminated heater  22   s  heats the range A (first warmed range) of the fixing sleeve  21 , and the lubricant in the warmed range A is melted. 
     Subsequently, at step S 204 , the controller  10  causes the driver  35  to drive the pressing roller  31  to rotate intermittently. That is, the fixing sleeve  21  is rotated at a predetermined angle (less than 360) by driving the pressing roller  31 . 
     Then, at step S 205 , the driver  35  stops driving the pressing roller  31  to rotate, and the rotation of the fixing sleeve  21  is stopped. At step S 206 , the laminated heater  22   s  heats the range B (another warmed range) of the fixing sleeve  21 , and the lubricant in the warmed range B is melted. 
     After that, at step S 207 , the fixing sleeve  21  is re-rotated at a predetermined angle (less than 360) by driving the pressing roller  31 . 
     By repeating theses processes steps S 205  through S 207 , the warmed range A (first warmed range) of the fixing sleeve,  21  heated by the laminated heater  22  is moved to the nip N facing the pressing roller  31 . 
     After the first warmed range reaches the nip, (Yes at step S 208 ), the fixing sleeve  21  starts rotating in a state in which the lubricant in the nip N is melted, that is, the fixing device  20  smoothly starts the fixing process at step S 209 . Accordingly, the fixing sleeve  21  can start rotating (starts continuously rotating) without occurring torque failure. 
     In addition, similarly to  FIGS. 12A through 12D , it is preferable that the rotation angle of the fixing sleeve  21  of the pressing roller  31  during intermittent rotation be small. When the rotation angle of the pressing roller  31  is small and the intermittent rotation is performed little by little, the fixing sleeve  21  can be rotated at low torque. 
     Further, it is preferable that the rotation angle by which the pressing roller  31  rotates each intermittent rotation be not any divisor of 360. In a case in which the rotation angle is not divisors of 360, the fixing sleeve  21  can avoid stopping repeatedly at the same positions when the pressing roller  31  repeats intermittent rotation. Accordingly, permanent strain of the fixing sleeve  21  caused by stopping many times at the same positions can be prevented. 
     In addition, as shown in  FIGS. 13A through 13D , a rotation velocity of the pressing roller  31  during intermittent rotation may be set slower than a rotation velocity of the pressing roller  31  during normal fixing process. In this state, the pressing roller  31  and the fixing sleeve  21  can be rotated in a condition in which the torque is reduced. 
     Further, a temperature detector  34 , such as a thermistor, that detects temperature in the pressing roller  31 , may be provided close to the pressing roller  31 , as shown in  FIG. 12B . In this configuration, because the temperature of the pressing roller  31  can be regarded as similar to the temperature at the position of the nip N, the pressing roller  31  may intermittently rotate so that the temperature detected by the temperature detector  34  is kept above a predetermined temperature (e.g., fixing temperature). 
     Thus, by controlling the temperature of the pressing roller  31  by using the temperature detector  34  that detects the temperature of the pressing roller  31 , the temperature of the nip N can be maintained at a desired temperature with a high degree of accuracy. Accordingly, the fixing device  20  can performed in an energy-efficient manner and the working life of the fixing device can be extended. 
     Referring to  FIGS. 14A ,  14 B,  15 , and  16 , the following describes variations of the heat generation sheet  22   s  of the laminated heater  22 . 
     In the heat generation sheet  22   s , the resistant heat generation layer  22   b  is provided on the entire surface or a part of the surface of the base layer  22   a . Alternatively, the resistant heat generation layer  22   b  may be divided among a plurality of regions zoned arbitrarily on the surface of the base layer  22   a  in such a manner that each resistant heat generation layer  22   b  generates heat independently. 
       FIG. 14A  is a plan view of a laminated heater  22 U as one variation of the laminated heater  22 . As illustrated in  FIG. 14A , the laminated heater  22 U includes a heat generation sheet  22   s U. The heat generation sheet  22   s U includes resistant heat generation layers  22   b   1  and  22   b   2 . The other elements of the laminated heater  22 U are equivalent to the elements of the laminated heater  22  depicted in  FIG. 5 . 
       FIG. 14A  is a plan view of the laminated heater  22 U spread on a flat surface before the laminated heater  22 U is adhered to the heater support  23  depicted in  FIG. 2 . A horizontal direction in  FIG. 14A  is a width direction of the laminated heater  22 U corresponding to the axial direction of the fixing sleeve  21 . A vertical direction in  FIG. 14A  is a circumferential direction of the laminated heater  22 U corresponding to the circumferential direction of the fixing sleeve  21 . 
     As illustrated in  FIG. 14A , the heat generation sheet  22   s U is divided into three regions on the surface of the heat generation sheet  22   s U in the width direction of the heat generation sheet  22   s U, that is, in the axial direction of the fixing sleeve  21 . Further, the heat generation sheet  22   s U is divided into two regions on the surface of the heat generation sheet  22   s U in the circumferential direction of the heat generation sheet  22   s U and the fixing sleeve  21 . Thus, in total, the heat generation sheet  22   s U is divided into six regions. 
       FIG. 14B  is a lookup table of a matrix with two rows in the circumferential direction of the fixing sleeve  21  and three columns in the axial direction of the fixing sleeve  21 , referred to as a 2-by-3 array of 6 elements corresponding to the six regions. The resistant heat generation layer  22   b   1  having a predetermined width and length is provided in the element ( 1 ,  2 ) corresponding to the region provided at a lower center portion of the heat generation sheet  22   s U in  FIG. 14A  in the axial direction of the fixing sleeve  21 . The resistant heat generation layers  22   b   2  having a predetermined width and length are provided in the elements ( 2 ,  1 ) and ( 2 ,  3 ) corresponding to the regions provided at upper lateral end portions of the heat generation sheet  22   s U in  FIG. 14A  in the axial direction of the fixing sleeve  21 , respectively. 
     The electrode layers  22   c  connected to the resistant heat generation layer  22   b   1  are provided in the elements ( 1 ,  1 ) and ( 1 ,  3 ) corresponding to the regions provided at lower lateral end portions of the heat generation sheet  22   s U in  FIG. 14A  in the axial direction of the fixing sleeve  21 , respectively. Each of the electrode layers  22   c  is connected to the electrode terminal  22   e   1  that protrudes from one edge, that is, a lower edge in  FIG. 14A , of the heat generation sheet  22   s U, forming a first heat generation circuit. 
     The electrode layer  22   c  connected and sandwiched between the two resistant heat generation layers  22   b   2  is provided in the element ( 2 ,  2 ) corresponding to the region provided at an upper center portion of the heat generation sheet  22   s U in  FIG. 14A  in the axial direction of the fixing sleeve  21 . Each of the two resistant heat generation layers  22   b   2  is connected to the electrode layer  22   c  that extends to the lower edge of the heat generation sheet  22   s U in  FIG. 14A  in the circumferential direction of the heat generation sheet  22   s U. Each of the electrode layers  22   c  is connected to the electrode terminal  22   e   2  that protrudes from the lower edge of the heat generation sheet  22   s U, forming a second heat generation circuit. 
     The insulation layer  22   d  is provided between the first heat generation circuit and the second heat generation circuit to prevent a short circuit of the first heat generation circuit and the second heat generation circuit. 
     In the laminated heater  22 U having the above-described configuration, when the electrode terminals  22   e   1  supply power to the heat generation sheet  22   s U, internal resistance of the resistant heat generation layer  22   b   1  generates Joule heat. By contrast, the electrode layers  22   c  do not generate heat due to their low resistance. Accordingly, only the region of the heat generation sheet  22   s U shown by the element ( 1 ,  2 ) generates heat to heat the center portion of the fixing sleeve  21  in the axial direction of the fixing sleeve  21 . 
     On the other hand, when the electrode terminals  22   e   2  supply power to the heat generation sheet  22   s U, internal resistance of the resistant heat generation layers  22   b   2  generates Joule heat. By contrast, the electrode layers  22   c  do not generate heat due to their low resistance. Accordingly, only the regions of the heat generation sheet  22   s U shown by the elements ( 2 ,  1 ) and ( 2 ,  3 ), respectively, generate heat to heat the lateral end portions of the fixing sleeve  21  in the axial direction of the fixing sleeve  21 . 
     When a small size recording medium P having a small width passes through the fixing device  20 , power is supplied to the electrode terminals  22   e   1  to heat only the center portion of the heat generation sheet  22   s U in the axial direction of the fixing sleeve  21 . By contrast, when a large size recording medium P having a large width passes through the fixing device  20 , power is supplied to the electrode terminals  22   e   1  and  22   e   2  to heat the heat generation sheet  22   s U throughout the entire width thereof in the axial direction of the fixing sleeve  21 . Thus, the fixing device  20  provides desired fixing according to the width of the recording medium P with reduced energy consumption. 
     The controller  10  depicted in  FIG. 2  controls an amount of heat generated by the laminated heater  22 U according to the size of the recording medium P. Accordingly, even when the small size recording media P pass through the fixing device  20  continuously, the lateral end portions of the heat generation sheet  22   s U corresponding to the non-conveyance regions of the fixing sleeve  21  over which the recording medium P is not conveyed, respectively, are not overheated, thus preventing stoppage of the fixing device  20  to protect the components of the fixing device  20  and decrease of productivity of the fixing device  20 . The single, divided laminated heater  22 U provides varied regions of the heat generation sheet  22   s U, reducing temperature variation of the laminated heater  22 U in the axial direction of the fixing sleeve  21  compared to a plurality of separate, laminated heaters. 
     Edges of each of the resistant heat generation layers  22   b   1  and  22   b   2  contacting the insulation layers  22   d  or the electrode layers  22   c  having a relatively high heat conductivity generate a smaller amount of heat due to heat transmission from the resistant heat generation layers  22   b   1  and  22   b   2  to the insulation layers  22   d  or the electrode layers  22   c . Accordingly, in the configuration illustrated in  FIG. 14A , in which a border between the center, resistant heat generation layer  22   b   1  and the adjacent electrode layer  22   c  and a border between the lateral, resistant heat generation layer  22   b   2  and the adjacent electrode layer  22   c  are provided on an identical face, when power is supplied to the electrode terminals  22   e   1  and  22   e   2 , such borders have a decreased temperature, varying temperature distribution of the laminated heater  22 U in the axial direction of the fixing sleeve  21 . As a result, a faulty toner image is formed due to faulty fixing. 
     To address this problem,  FIG. 15  illustrates a laminated heater  22 V as another variation of the laminated heater  22 .  FIG. 15  is a plan view of the laminated heater  22 V. As illustrated in  FIG. 15 , the laminated heater  22 V includes a heat generation sheet  22   s V. The heat generation sheet  22   s V includes a resistant heat generation layer  22   b   1 V replacing the resistant heat generation layer  22   b   1  depicted in  FIG. 14A . The other elements of the laminated heater  22 V are equivalent to the elements of the laminated heater  22 U depicted in  FIG. 14A . 
     The resistant heat generation layer  22   b   1 V has a longer width in the axial direction of the fixing sleeve  21 . Accordingly, the resistant heat generation layer  22   b   1 V partially overlaps each of the resistant heat generation layers  22   b   2  in a width direction of the heat generation sheet  22   s V, that is, in the axial direction of the fixing sleeve  21 , to form an overlap region. Accordingly, when power is supplied to the electrode terminals  22   e   1  and  22   e   2 , temperature decrease is prevented at a border between the resistant heat generation layer  22   b   1 V and the electrode layer  22   c  and a border between the resistant heat generation layer  22   b   2  and the electrode layer  22   c.    
       FIG. 16  is a plan view of a laminated heater  22 W as yet another variation of the laminated heater  22 . As illustrated in  FIG. 16 , the laminated heater  22 W includes a heat generation sheet  22   s W. The heat generation sheet  22   s W includes resistant heat generation layers  22   b   1 W and  22   b   2 W replacing the resistant heat generation layers  22   b   1 V and  22   b   2  depicted in  FIG. 15 , respectively. The other elements of the laminated heater  22 W are equivalent to the elements of the laminated heater  22 V depicted in  FIG. 15 . 
     The resistant heat generation layer  22   b   1 W partially overlaps each of the resistant heat generation layers  22   b   2 W to form an overlap region. In each overlap region, a border between the resistant heat generation layer  22   b   1 W and the adjacent electrode layer  22   c  is tapered with respect to the circumferential direction of the heat generation sheet  22   s W in a direction opposite a direction in which a border between the resistant heat generation layer  22   b   2 W and the adjacent electrode layer  22   c  is tapered with respect to the circumferential direction of the heat generation sheet  22   s W. Thus, an amount of overlap of the resistant heat generation layer  22   b   1 W and the resistant heat generation layer  22   b   2 W is adjusted. 
     With the configuration shown in  FIG. 15 , a width of the overlap region in which the resistant heat generation layer  22   b   1 V overlaps the resistant heat generation layer  22   b   2  in the width direction of the heat generation sheet  22   s V, that is, in the axial direction of the fixing sleeve  21 , is unchanged. Accordingly, if the width of the overlap region varies, an amount of heat generated by the heat generation sheet  22   s V varies. To address this problem, with the configuration shown in  FIG. 16 , the width of the overlap region changes in the circumferential direction of the heat generation sheet  22   s W. For example, the width of the overlap region of the resistant heat generation layer  22   b   1 W and the width of the overlap region of the resistant heat generation layer  22   b   2 W decrease at a predetermined rate in a downward direction in  FIG. 16 . Accordingly, heat generation distribution is adjusted to reduce adverse effects of production errors of the laminated heater  22 W. As a result, the laminated heater  22 W provides uniform temperature throughout the axial direction of the fixing sleeve  21 . 
     In the laminated heater  22 U depicted in  FIG. 14A , portions on the surface of the base layer  22   a  on which the resistant heat generation layers  22   b   1  and  22   b   2  are to be provided are exposed and coated to form the resistant heat generation layers  22   b   1  and  22   b   2 . Then, portions on the surface of the base layer  22   a  on which the insulation layers  22   d  are to be provided are exposed and coated to form the insulation layers  22   d  formed of heat-resistant resin. Thereafter, portions on the surface of the base layer  22   a  on which the electrode layers  22   c  are to be provided are exposed and coated with a conductive paste to form the electrode layers  22   c . In other words, exposure of the portions on the surface of the base layer  22   a  on which the resistant heat generation layers  22   b   1  and  22   b   2  are to be provided is adjusted to form the resistant heat generation layers  22   b   1  and  22   b   2  having an arbitrary shape. Similarly, the resistant heat generation layers  22   b   1 V and  22   b   2  of the laminated heater  22 V depicted in  FIG. 15  and the resistant heat generation layers  22   b   1 W and  22   b   2 W of the laminated heater  22 W depicted in  FIG. 16  are formed. 
     The laminated heater (e.g., the laminated heater  22 ,  22 U,  22 V, or  22 W) may include a plurality of layered heat generation sheets in each of which one or more resistant heat generation layers are provided on an arbitrary portion on the surface of the base layer  22   a  in such a manner that the resistant heat generation layers generate heat independently from each other.  FIG. 17  illustrates a laminated heater  22 X including a plurality of heat generation sheets. 
       FIG. 17  is an exploded perspective view of the laminated heater  22 X. As illustrated in  FIG. 17 , the laminated heater  22 X includes a first heat generation sheet  22   s   1 , an insulation sheet  22   sd , and a second heat generation sheet  22   s   2 . The first heat generation sheet  22   s   1  includes the resistant heat generation layer  22   b   1  and the electrode layers  22   c . The insulation sheet  22   sd  includes the insulation layer  22   d . The second heat generation sheet  22   s   2  includes the resistant heat generation layers  22   b   2  and the electrode layers  22   c.    
     The first heat generation sheet  22   s   1  is provided on the insulation sheet  22   sd  provided on the second heat generation sheet  22   s   2 . 
     The first heat generation sheet  22   s   1  is divided into three regions on a surface of the first heat generation sheet  22   s   1  in a width direction of the first heat generation sheet  22   s   1 , that is, in the axial direction of the fixing sleeve  21 . The resistant heat generation layer  22   b   1  is provided in the center region on the surface of the first heat generation sheet  22   s   1 . The electrode layers  22   c , which are connected to the resistant heat generation layer  22   b   1 , are provided in the lateral-end regions on the surface of the first heat generation sheet  22   s   1 , respectively. 
     The second heat generation sheet  22   s   2  is divided into five regions on a surface of the second heat generation sheet  22   s   2  in a width direction of the second heat generation sheet  22   s   2 , that is, in the axial direction of the fixing sleeve  21 . The resistant heat generation layers  22   b   2  are provided in the second and fourth regions from left to right in  FIG. 17 , respectively. The electrode layers  22   c , which are connected to the resistant heat generation layers  22   b   2 , are provided in the first, third, and fifth regions from left to right in  FIG. 17 , respectively. 
     The first heat generation sheet  22   s   1  is provided on the second heat generation sheet  22   s   2  via the insulation sheet  22   sd  in such a manner that the first heat generation sheet  22   s   1  and the second heat generation sheet  22   s   2  sandwich the insulation sheet  22   sd . Thus, an independent first heat generation circuit is provided in the first heat generation sheet  22   s   1 , and another independent second heat generation circuit is provided in the second heat generation sheet  22   s   2 . 
     When power is supplied to the first heat generation circuit, internal resistance of the resistant heat generation layer  22   b   1  generates Joule heat, and the center region on the surface of the first heat generation sheet  22   s   1  in the width direction of the first heat generation sheet  22   s   1  generates heat to heat the center portion of the fixing sleeve  21  in the axial direction of the fixing sleeve  21 . When power is supplied to the second heat generation circuit, internal resistance of the resistant heat generation layers  22   b   2  generates Joule heat, and the lateral-end regions on the surface of the second heat generation sheet  22   s   2  in the width direction of the second heat generation sheet  22   s   2  generate heat to heat the lateral end portions of the fixing sleeve  21  in the axial direction of the fixing sleeve  21 . 
     If the laminated heater  22 X is divided in a circumferential direction of the laminated heater  22 X as in the laminated heaters  22 U,  22 V, and  22 W depicted in  FIGS. 14A ,  15 , and  16 , respectively, the laminated heater  22 X needs to have an increased area to provide a desired heat generation amount, and therefore is not installed inside the small fixing sleeve  21  having a small diameter. To address this problem, the laminated heater  22 X includes the plurality of heat generation sheets layered in a thickness direction, that is, the second heat generation sheet  22   s   2  and the first heat generation sheet  22   s   1  provided on the second heat generation sheet  22   s   2  in such a manner that the resistant heat generation layer  22   b   1  of the first heat generation sheet  22   s   1  is shifted from the resistant heat generation layers  22   b   2  of the second heat generation sheet  22   s   2  in the width direction of the laminated heater  22 X as illustrated in  FIG. 17 . Accordingly, the laminated heater  22 X provides varied heat generation distribution in the axial direction of the fixing sleeve  21  like the laminated heaters  22 U,  22 V, and  22 W depicted in  FIGS. 14A ,  15 , and  16 , respectively, providing an increased output of heat while saving space and downsizing the fixing device  20 . 
     As illustrated in  FIG. 2 , when the fixing sleeve  21  rotates, the pressing roller  31  pulls the fixing sleeve  21  at the nip N. Accordingly, the pressing roller  31  applies tension to an upstream portion of the fixing sleeve  21  provided upstream from the nip N in the rotation direction R 1  of the fixing sleeve  21 . Consequently, the inner circumferential surface of the fixing sleeve  21  slides over the laminated heater  22  in a state in which the fixing sleeve  21  is pressed against the heater support  23 . By contrast, the pressing roller  31  does not apply tension to a downstream portion of the fixing sleeve  21  provided downstream from the nip N in the rotation direction R 1  of the fixing sleeve  21 . Accordingly, the downstream portion of the fixing sleeve  21  remains slack, a situation that is exacerbated if the fixing sleeve  21  rotates faster and destabilizing the rotation of the fixing sleeve  21 . 
     To address this problem, the fixing device  20  may include a fixing member support provided inside the loop formed by the fixing sleeve  21  to support at least the downstream portion of the fixing sleeve  21 .  FIGS. 18A ,  18 B,  18 C,  18 D, and  18 E illustrate such fixing member support. 
       FIG. 18A  is a sectional view of a fixing sleeve support  27 A, the laminated heater  22 , and the contact member  26 . The fixing sleeve support  27 A is a metal member serving as a fixing member support, for example, a thin, stainless steel pipe. The laminated heater  22  is provided on an inner circumferential surface of the fixing sleeve support  27 A, and an outer circumferential surface of the fixing sleeve support  27 A supports the fixing sleeve  21  depicted in  FIG. 2 , providing stable rotation of the fixing sleeve  21 . Further, the rigid, metal fixing sleeve support  27 A supports the fixing sleeve  21 , facilitating assembly of the fixing device  20 . The fixing sleeve  21  does not slide over the laminated heater  22  by contacting the laminated heater  22 , preventing wear of a protective layer (e.g., a sliding layer) and an insulation layer provided on the surface of the laminated heater  22  which may be caused by the fixing sleeve  21  sliding over the laminated heater  22 . Accordingly, electric conductors, such as the resistant heat generation layers  22   b   1  and  22   b   2  and the electrode layers  22   c , are not exposed, preventing short circuiting. However, the metal fixing sleeve support  27 A has a substantial heat capacity, providing a slower speed at which the temperature of the fixing sleeve  21  increases during warm-up than the structure shown in  FIG. 2  that does not include the fixing sleeve support  27 A. 
       FIG. 18B  is a sectional view of the fixing sleeve support  27 A, the laminated heater  22 , and the contact member  26  as a variation of the structure shown in  FIG. 18A . As illustrated in  FIG. 18B , the laminated heater  22  is provided on the outer circumferential surface of the fixing sleeve support  27 A to transmit heat to the fixing sleeve  21  more quickly than the laminated heater  22  provided on the inner circumferential surface of the fixing sleeve support  27 A shown in  FIG. 18A . However, heat is adversely transmitted from an inner circumferential surface of the laminated heater  22  facing the fixing sleeve support  27 A to the fixing sleeve support  27 A. 
     To address this problem, the fixing device  20  may include a fixing sleeve support  27 B, instead of the fixing sleeve support  27 A, which has a heat conductivity smaller than that of the metal fixing sleeve support  27 A as in  FIG. 18B .  FIG. 18C  is a sectional view of the fixing sleeve support  27 B, the laminated heater  22 , and the contact member  26 . The fixing sleeve support  27 B, serving as a fixing member support, includes solid resin having a heat conductivity smaller than that of the metal fixing sleeve support  27 A, suppressing heat transmission from the inner circumferential surface of the laminated heater  22  facing the fixing sleeve support  27 B to the fixing sleeve support  27 B. However, a heat resistance of resin is generally smaller than that of metal, and resin having a high heat resistance is expensive, resulting in increased manufacturing costs. 
     To address this problem, the fixing device  20  may include a fixing sleeve support  27 C instead of the fixing sleeve support  27 B. The fixing sleeve support  27 C is formed of polyimide resin foam that provides heat insulation and rigidity.  FIG. 18D  is a sectional view of the fixing sleeve support  27 C, the laminated heater  22 , and the contact member  26 . The fixing sleeve support  27 C serves as a fixing member support. 
       FIG. 18E  is a sectional view of the fixing sleeve support  27 C, the laminated heater  22 , the contact member  26 , and a resin member  27 D for enhanced rigidity. The resin member  27 D is formed of polyimide foam, and is provided inside the fixing sleeve support  27 C in such a manner that the resin member  27 D contacts an inner circumferential surface of the fixing sleeve support  27 C, providing an improved rigidity. 
     Referring to  FIG. 19 , the following describes a fixing device  20 Y according to another exemplary embodiment.  FIG. 19  is a sectional view of the fixing device  20 Y. As illustrated in  FIG. 19 , the fixing device  20 Y includes the fixing sleeve  21 , the laminated heater  22 , the heater support  23 , the terminal stay  24 , the power supply wiring  25 , the contact member  26 , the fixing sleeve support  27 A, the core holder  28 , an insulation support  29 , and the pressing roller  31 . In other words, the fixing device  20 Y has the structure shown in  FIG. 2  and the structure shown in  FIG. 18A . 
     The pipe-shaped fixing sleeve support  27 A is provided inside the loop formed by the fixing sleeve  21 . The insulation support  29  is provided inside a loop formed by the fixing sleeve support  27 A and downstream from the nip N in the rotation direction R 1  of the fixing sleeve  21 . The insulation support  29  contacts an outer surface of the H-shaped core holder  28 . 
     The fixing sleeve support  27 A is, for example, a thin metal pipe having a thickness in a range of from about 0.1 mm to about 1.0 mm, and includes iron, stainless steel, and/or the like. An outer diameter of the fixing sleeve support  27 A is smaller than an inner diameter of the fixing sleeve  21  by a length in a range of from about 0.5 mm to about 1.0 mm. The fixing sleeve support  27 A is cut along a long axis of the fixing sleeve support  27 A parallel to the axial direction of the fixing sleeve  21 , and therefore includes an opening facing the nip N. Cut ends of the fixing sleeve support  27 A are folded in toward the core holder  28 , so that the cut ends of the fixing sleeve support  27 A do not contact the inner circumferential surface of the fixing sleeve  21  at the nip N. 
     The insulation support  29  is provided downstream from the nip N in the rotation direction R 1  of the fixing sleeve  21 . The insulation support  29  has a heat resistance that resists heat applied by the fixing sleeve  21  via the fixing sleeve support  27 A, a heat insulation that prevents heat transmission from the fixing sleeve support  27 A contacting the fixing sleeve  21  to the insulation support  29 , and a strength that supports the fixing sleeve support  27 A in such a manner that the fixing sleeve support  27 A is not deformed by the fixing sleeve  21  that rotates and slides over the fixing sleeve support  27 A. The insulation support  29  includes polyimide resin foam like the heater support  23 . 
       FIG. 20  is a perspective view of the fixing sleeve support  27 A. As illustrated in  FIG. 20 , the fixing sleeve support  27 A includes a window  27   w .  FIG. 21A  is a partial sectional view of the fixing device  20 Y.  FIG. 21B  is a partial perspective view of the fixing device  20 Y. 
     As illustrated in  FIG. 20 , a predetermined region on a circumferential surface of the fixing sleeve support  27 A provided upstream from the nip N in the rotation direction R 1  of the fixing sleeve  21  is cut away to provide the window  27   w . Accordingly, when the components provided inside the loop formed by the fixing sleeve  21  are arranged as illustrated in  FIG. 21A  and are inserted into the fixing sleeve  21 , the entire outer circumferential surface of the laminated heater  22  is exposed through the window  27   w  as illustrated in  FIG. 21B . Consequently, the laminated heater  22  is disposed close to the inner circumferential surface of the fixing sleeve  21 . 
     The laminated heater  22  (e.g., the heat generation sheet  22   s ) is supported by the heater support  23 , and is disposed close to the inner circumferential surface of the fixing sleeve  21  with a predetermined gap δ provided therebetween. The predetermined gap δ is smaller than the thickness of the fixing sleeve support  27 A, that is, greater than 0 mm but not greater than 1 mm. Accordingly, the laminated heater  22  heats the fixing sleeve  21  quickly and effectively. 
     In both of the fixing devices  20  or  20 Y depicted in  FIGS. 2 and 19 , respectively, the fixing sleeve  21  and the laminated heater  22  have a small heat capacity, shortening a warm-up time and a first print time while saving energy. The heat generation sheet  22   s  of the laminated heater  22  is a resin-based sheet. Accordingly, even when rotation and vibration of the pressing roller  31  stress the heat generation sheet  22   s  repeatedly and bend the heat generation sheet  22   s  repeatedly, the heat generation sheet  22   s  is not broken by wear, providing long-duration operation. The laminated heater  22  generates heat in various portions thereof in the axial direction of the fixing sleeve  21 , providing effective temperature control of the fixing sleeve  21  according the size of the recording medium P passing through the fixing device  20 . Further, in addition to the fixing sleeve support  27 A, the insulation support  29  is added as needed, improving stable rotation of the fixing sleeve  21  and suppressing formation of a faulty toner image even when the fixing sleeve  21  rotates at a higher speed. The fixing sleeve support  27 A, which conducts heat in the axial direction of the fixing sleeve  21 , is provided to facilitate uniform temperature of the fixing sleeve  21  in the axial direction of the fixing sleeve  21 . Accordingly, the fixing sleeve  21  provides a desired fixing property even when the fixing sleeve  21  rotates at a higher speed. 
     The image forming apparatus  1  (depicted in  FIG. 1 ) that includes either the fixing device  20  or  20 Y provides a shortened warm-up time and a shortened first print time. Even when the size of the recording medium P varies, the image forming apparatus  1  forms a desired toner image on the recording medium P while reducing energy consumption. Further, even when the image forming apparatus  1  forms a toner image at a higher speed, the fixing device  20  or  20 Y suppresses formation of a faulty toner image. 
     In the fixing devices  20  and  20 Y according to the above-described exemplary embodiments, the pressing roller  31  is used as a pressing member. Alternatively, a pressing belt, a pressing pad, or a pressing plate may be used as a pressing member to provide effects equivalent to the effects provided by the pressing roller  31 . 
     Further, the fixing sleeve  21  is used as a fixing member. Alternatively, an endless fixing belt or an endless fixing film may be used as a fixing member. 
     The present invention has been described above with reference to specific exemplary 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 exemplary embodiments may be combined with each other and/or substituted for each other within the scope of the present invention.