Patent Publication Number: US-8977172-B2

Title: Fixing apparatus having an air blowing mechanism

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a fixing apparatus which fixes a toner image on a sheet. The fixing apparatus can be used, for example, in an image forming apparatus like a copying machine, a printer, a facsimile (FAX), and a multifunction peripheral having a plurality of such functions. 
     2. Description of the Related Art 
     An image forming apparatus using an electrophotographic method conventionally includes a fixing apparatus which fixes a toner image formed on recording material (sheet) at a nip portion between two fixing members (first and second fixing rotatable members). A lot of toners with improved fusibility have recently been developed. With improved fusibility, toner can be uniformly and favorably melted by a fixing apparatus. This makes the fixed toner layer more uniform and smoother for improved image glossiness. 
     As a result, an image having higher glossiness and higher image quality than heretofore can be formed on high gloss recording material such as coated paper. 
     As the fixing apparatus repeats fixing processing, the fixing members tend to be deteriorated in surface properties by edge portions of recording material (both ends in a direction orthogonal to a conveyance direction of the recording material) as compared to other areas. Specifically, the areas touched by the edge portions of recording material tend to be roughened in the surface as compared to the other areas. Such uneven surface properties of the fixing members can appear on the fixed image as uneven image glossiness. 
     An apparatus discussed in Japanese Patent Application Laid-Open No. 2008-040363 includes a roughing roller (rubbing rotatable member) which rubs the surface of a fixing member. Specifically, the roughing roller rubs the fixing member to make a deteriorated state (surface roughness) of the areas touched by the edge portions of recording material less noticeable as compared to the other areas. 
     When the roughing processing by the roughing roller finishes and the roughing roller is separated from the fixing member, a line of shavings produced by the roughing processing can appear on the fixing member. Such shavings interfere with favorable fixing processing next time. Specifically, a line of shavings can appear on an image to cause a decrease in image quality. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a fixing apparatus that can diffuse a line of shavings produced by rubbing processing. 
     The present invention is further directed to a fixing apparatus that can suppress a decrease in image quality due to a line of shavings produced by the rubbing processing. 
     According to an aspect of the present invention, a fixing apparatus includes first and second fixing rotatable members configured to fix a toner image on a sheet at a nip portion therebetween, a rubbing rotatable member configured to rub an outer surface of the first fixing rotatable member, a moving mechanism configured to move the rubbing rotatable member between a contact position, in which the rubbing rotatable member is in contact with the outer surface of the first fixing rotatable member, and a separate position, in which the rubbing rotatable member is away from the outer surface of the first fixing rotatable member, and an air blowing mechanism configured to blow air to between the rubbing rotatable member and the first fixing rotatable member at least when the rubbing rotatable member moves from the contact position to the separate position. 
     Further features and aspects of the present invention will become apparent from the following detailed description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary embodiments, features, and aspects of the invention and, together with the description, serve to explain the principles of the invention. 
         FIG. 1  is a sectional view illustrating an image forming apparatus according to a first exemplary embodiment. 
         FIG. 2  is a perspective view illustrating an appearance of a fixing apparatus according to the first exemplary embodiment. 
         FIG. 3  is a cross-sectional left side view of essential parts of the fixing apparatus (when a lower belt assembly is in a pressure state). 
         FIG. 4  is a cross-sectional left side view of essential parts of the fixing apparatus (when the lower belt assembly is in a separate state). 
         FIG. 5  is a left side view of essential parts of the fixing apparatus (when the lower belt assembly is in the pressure state). 
         FIG. 6  is a perspective view of a belt deviation control mechanism portion. 
         FIG. 7A  is a flowchart illustrating vertical movement control of the lower belt assembly, and  FIG. 7B  is a block diagram illustrating a control system. 
         FIG. 8A  is a flowchart illustrating fixing operation control of the fixing apparatus, and  FIG. 8B  is a block diagram illustrating a control system. 
         FIG. 9A  is a flowchart illustrating fixing belt temperature control, and  FIG. 9B  is a block diagram illustrating a control system. 
         FIGS. 10A and 10B  are explanatory diagrams illustrating a roughing mechanism (surface property recovery mechanism). 
         FIG. 11A  is a control flowchart of the roughing mechanism, and  FIG. 11B  is a block diagram illustrating a control system. 
         FIG. 12A  is a flowchart illustrating a surface property recovery operation, and  FIG. 12B  is a block diagram illustrating a control system. 
         FIG. 13  is a schematic diagram illustrating a blowing mechanism. 
         FIG. 14  is a perspective view of the blowing mechanism. 
         FIG. 15  is a diagram illustrating diffusion of foreign substances in a roughing operation in detail. 
         FIG. 16  is a control flowchart illustrating the surface property recovery operation (roughing operation). 
         FIGS. 17A ,  17 B,  17 C, and  17 D are schematic diagrams illustrating an arrangement of a roughing member and a blowing unit in a fixing apparatus according to a second exemplary embodiment. 
         FIGS. 18A and 18B  are schematic diagrams illustrating an arrangement of the roughing member and the blowing unit in the fixing apparatus according to the second exemplary embodiment. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Various exemplary embodiments, features, and aspects of the invention will be described in detail below with reference to the drawings. 
     (1) Image Forming Apparatus 
       FIG. 1  is a schematic block diagram of an image forming apparatus  1  according to the present exemplary embodiment.  FIG. 1  illustrates a schematic sectional view taken along a conveyance direction V of a sheet (recording material) S. The image forming apparatus  1  is a full color electrophotographic printer (hereinafter, referred to as a printer) using an intermediate transfer member. The printer  1  can form an image corresponding to image data (electrical image information) input from an external host apparatus  23  on the sheet S to output an image formation product. The external host apparatus  23  is connected to a printer control unit (hereinafter, referred to as a central processing unit (CPU))  10  via an interface  22 . 
     The CPU  10  is a control unit that controls an operation of the printer  1  in a comprehensive manner. The CPU  10  exchanges various electrical information signals with the external host apparatus  23  and a printer operation unit  24 . The CPU  10  further processes electrical information signals input from various process devices and sensors, processes command signals for various process devices, and performs predetermined initial sequence control and predetermined image forming sequence control. Examples of the external host apparatus  23  include a personal computer, a network, an image reader, and a facsimile. 
     The printer  1  includes first to fourth, four image forming units U (UY, UM, UC, and UK) which are arranged in parallel from left to right in the diagram. The image forming units UY, UM, UC, and UK are electrophotographic image forming mechanisms having similar configurations, with the only difference in that their developing units  5  contain developers or toners of different colors, namely, yellow (Y), magenta (MA), cyan (C), and black (BL), respectively. 
     Each image forming unit U includes an electrophotographic photosensitive member (hereinafter, referred to as a drum)  2 , and process units acting on the drum  2 , including a charging roller  3 , a laser scanner  4 , a developing unit  5 , and a primary transfer roller  6 . 
     The drums  2  of the image forming units U are driven to rotate in the respective arrowed counterclockwise directions at a predetermined speed. A Y color toner image corresponding to a Y color component image of a full color image to be formed is formed on the drum  2  of the first image forming unit UY. An MA color toner image corresponding to an MA color component image is formed on the drum  2  of the second image forming unit UM. A C color toner image corresponding to a C color component image is formed on the drum  2  of the third image forming unit UC. A BL color toner image corresponding to a BL color component image is formed on the drum  2  of the fourth image forming unit UK. The toner images are formed on the drums  2  of the image forming units U by known forming processes and principles. A description thereof will thus be omitted. 
     An intermediate transfer belt unit  7  is arranged below the image forming units U. The intermediate transfer belt unit  7  includes a flexible endless intermediate transfer belt  8  serving as an intermediate transfer member. The intermediate transfer belt  8  is wound and stretched across three rollers, including a drive roller  11 , a tension roller  12 , and a secondary transfer counter roller  13 . The drive roller  11  is driven to move the intermediate transfer belt  8  to circulate in the arrowed clockwise direction at a speed corresponding to the rotation speed of the drums  2 . A secondary transfer roller  14  is put into contact with the secondary transfer counter roller  13  by a predetermined pressing force with the intermediate transfer belt  8  therebetween. A contact portion between the intermediate transfer belt  8  and the secondary transfer roller  14  forms a secondary transfer nip portion. 
     The primary transfer rollers  6  of the image forming units U are arranged inside the intermediate transfer belt  8 , and are in contact with lower surfaces of the respective drums  2  via the intermediate transfer belt  8 . In each image forming unit U, a contact portion between the drum  2  and the intermediate transfer belt  8  forms a primary transfer nip portion. A predetermined primary transfer bias is applied to the primary transfer rollers  6  at predetermined control timing. 
     The Y color toner, MA color toner, C color toner, and BL color toner formed on the drums  2  of the respective image forming units U are successively superimposed and primary-transferred onto the surface of the moving and circulating intermediate transfer belt  8  at the respective primary transfer nip portions. As a result, a four-color superimposed, unfixed full color toner image is combined and formed on the intermediate transfer belt  8 . The unfixed full color toner image is conveyed to the secondary transfer nip portion. 
     One of sheets S accommodated in a first or second sheet cassette  15  or  16  is separated and fed by an operation of a sheet feeding mechanism and conveyed to a registration roller pair  18  through a conveyance path  17 . The registration roller pair  18  once receives the sheet S, and if the sheet S is skewed, straightens the sheet S. The registration roller pair  18  conveys the sheet S to the secondary transfer nip portion in synchronization with the full color toner image on the intermediate transfer belt  8 . 
     While the sheet S is pinched and conveyed by the secondary transfer nip portion, a predetermined secondary transfer bias is applied to the secondary transfer roller  14 . The entire full color toner image on the intermediate transfer belt  8  is thereby secondary-transferred to the sheet S in order. The sheet S past the secondary transfer nip portion is separated from the surface of the intermediate transfer belt  8 , passed through a conveyance path  19 , and introduced into an image heating and fixing apparatus (hereinafter, referred to as a fixing apparatus)  100  serving as an image processing apparatus. The fixing apparatus  100  heats and presses the sheet S to fix the unfixed full color toner image into a fixed image. The sheet S past the fixing apparatus  100  is conveyed and discharged by a discharge roller pair  20  to a discharge tray  21  as a full color image formation product. 
     (2) Fixing Apparatus  100   
       FIG. 2  is a perspective view illustrating an appearance of the fixing apparatus  100  according to the present exemplary embodiment.  FIG. 3  is a cross-sectional left side view of essential parts of the fixing apparatus  100 .  FIG. 3  illustrates a case where a lower belt assembly B is in a pressure state.  FIG. 4  is a cross-sectional left side view of essential parts of the fixing apparatus  100 .  FIG. 4  illustrates a case where the lower belt assembly B is in a pressure-released state.  FIG. 5  is a left side view of essential parts of the fixing apparatus  100 .  FIG. 5  illustrates the case where the lower belt assembly B is in the pressure state.  FIG. 6  is a perspective view of a belt deviation control mechanism portion. 
     As employed herein, a longitudinal direction (longitudinal length) or width direction (width) of the fixing apparatus  100  or a member constituting the fixing apparatus  100  refers to a direction (or a dimension in the direction) that is parallel to a direction orthogonal to the conveyance direction V of a sheet S in the plane of the sheet conveyance path of the fixing apparatus  100 . A lateral direction (lateral length) refers to a direction (or a dimension in the direction) that is parallel to the conveyance direction V of the sheet S in the plane of the sheet conveyance path of the fixing apparatus  100 . 
     A front of the fixing apparatus  100  refers to a plane on a sheet inlet side. A back of the fixing apparatus  100  refers to a plane on a sheet outlet side. The right and left refer to the right and left of the fixing apparatus  100  when seen from the front, respectively. In the present exemplary embodiment, the left side is referred to as a near side, and the right side a far side. Above and below refer to above and below in the direction of the gravitational force, respectively. Upstream and downstream refer to upstream and downstream in the conveyance direction V of the sheet S, respectively. The width of a belt or sheet S refers to the dimension in the direction orthogonal to the conveyance direction V of the sheet S. 
     The fixing apparatus  100  according to the present exemplary embodiment is an image heating apparatus of a belt nip method, an electromagnetic induction heating (IH) method, or an oilless fixing method. 
     The fixing apparatus  100  includes an upper belt assembly A serving as a heating unit and the lower belt assembly B serving as a pressure unit. The fixing apparatus  100  further includes a pressure-separation mechanism (contacting/separating unit) for pressing and separating the lower belt assembly B against/from the upper belt assembly A. The fixing apparatus  100  further includes an IH heater (magnetic flux generation unit)  170 , a deviation control mechanism of the fixing belt  105 , and a roughing mechanism (surface property recovery mechanism). The IH heater  170  is a heating mechanism that heats the fixing belt  105  of the upper belt assembly A. The roughing mechanism recovers surface properties of the fixing belt  105 . Such components will be described in order below. 
     (2-1) Upper Belt Assembly A and IH Heater  170   
     The upper belt assembly A is arranged between right and left upper side plates  140  of an apparatus casing. The upper belt assembly A includes a flexible fixing belt (endless belt)  105 . The fixing belt  105  includes a release layer (parting layer) on its surface and serves as a fixing rotatable member (fixing member) located opposite an image bearing surface of the sheet S. The upper belt assembly A further includes a plurality of belt stretching members across which the fixing belt  105  is stretched. The belt stretching members include a drive roller (support roller)  131 , a steering roller  132 , and a pad stay  137 . The steering roller  132  also serves as a tension roller. 
     The drive roller  131  is arranged on the sheet outlet side between the right and left upper side plates  140 . Right and left shaft portions  131   a  of the drive roller  131  are rotatably supported between the right and left upper side plates  140  via respective bearings (not illustrated). 
     Steering roller support arms  154  are arranged onside the right and left upper side plates  140 , respectively. The steering roller support arms  154  extend from the side of the drive roller  131  to the sheet inlet side. The right steering roller support arm  154  (not illustrated) is fixed to the right upper side plate  140  (not illustrated). Referring to  FIG. 6 , the left steering roller support arm  154  is supported by the left shaft portion  131   a  of the drive roller  131  via a bearing  154   a . The left steering roller support arm  154  is vertically swingable about the left shaft portion  131   a . A pin  151  is formed on a free end of the left steering roller support arm  154 . A shaft  160  is formed on an outside surface of the left upper side plate  140  on the sheet inlet side. 
     A worm wheel (helical gear)  152  is rotatably supported by the shaft  160 . A fork plate  161  having a U-shaped groove  161   a  is integrally formed on the worm wheel  152 . The pin  151  of the left steering roller support arm  154  is engaged with the groove  161   a  of the fork plate  161 . A stepping motor  155  is arranged on the upper side plate  140 . A worm  157  fixed to a rotation shaft of the stepping motor  155  meshes with the worm wheel  152 . 
     The stepping motor  155  is driven forward or backward to rotate the fork plate  161  upward or downward via the worm  157  and the worm wheel  152 . In response, the left steering roller support arm  154  rotates upward or downward about the shaft portion  131   a.    
     The steering roller  132  is arranged on the sheet inlet side between the right and left upper side plates  140 . Right and left shaft portions  132   a  of the steering roller  132  are rotatably supported by the right and left steering roller support arms  154  via bearings  153 , respectively. The bearings  153  are supported by the steering roller support arms  154  slidably and movably in a belt tension direction. The bearings  153  are biased by tension springs  156  to move in a direction away from the drive roller  131 . 
     The pad stay  137  is a member made of stainless steel (SUS material), for example. Both right and left ends of the pad stay  137  are fixed to the right and left upper side plates  140 . The pad stay  137  is thereby supported inside the fixing belt  105 , close to the drive roller  131  between the drive roller  131  and the steering roller  132 , with its pad surface downward. 
     The fixing belt  105  laid across the drive roller  131 , the steering roller  132 , and the pad stay  137  undergoes predetermined tension (tensile force) from the movement of the steering roller  132  in the belt tension direction, caused by the biasing forces of the tension springs  156 . In the present exemplary embodiment, a tension of 200 N is applied to the fixing belt  105 . An inner surface of a descending belt portion of the fixing belt  105  is put in contact with the downward pad surface of the pad stay  137 . 
     Any fixing belt  105  that can be heated by the IH heater  170  and has heat resistance may be selected as appropriate. For example, a nickel metal layer, stainless steel layer, or other magnetic metal layer having a thickness of 75 μm, a width of 380 mm, and a circumferential length of 200 mm, coated with a 300-μm-thick silicon rubber and covered with a perfluoroalkoxy (PFA) tube as a surface layer (release layer), is used. 
     An example of the drive roller  131  is a solid roller made of stainless steel with an outer diameter of φ18, surfaced with a heat-resistant silicon rubber elastic layer formed by integral molding. The drive roller  131  is arranged on the sheet outlet side of a nip area of a fixing nip portion N which is formed between the fixing belt  105  and the pressure belt  120  serving as a second fixing rotatable member to be described below. The elastic layer is elastically distorted by a predetermined amount by pressure contact of a pressure roller  121 . 
     In the present exemplary embodiment, the drive roller  131  and the pressure roller  121  form a nip of generally straight shape with the fixing belt  105  and the pressure belt  120  therebetween. However, the drive roller  131  and the pressure roller  121  may have various crown shapes. For example, the drive roller  131  and the pressure roller  121  may be intentionally configured with a concave crown shape to control buckling of the sheet S ascribable to differences in the speed of the sheet S within the fixing nip portion N. 
     An example of the steering roller  132  is a hollow roller of stainless steel with an outer diameter of φ20 and an inner diameter of φ18 or so. The steering roller  132  functions as a tension roller that stretches and tensions the fixing belt  105 . The deviation control mechanism to be described below controls a tilt of the steering roller  132 , whereby the steering roller  132  functions as a steering roller for adjusting deviations of the fixing belt  105  in the width direction orthogonal to the moving direction of the fixing belt  105 . 
     A drive input gear G is coaxially fixed and arranged on the left side of the left shaft portion  131   a  of the drive roller  131 . A drive motor  301  ( FIG. 2 ) inputs a drive to the drive input gear G through a drive transmission unit (not illustrated), whereby the drive roller  131  is driven to rotate in the arrowed clockwise direction in  FIG. 4  at a predetermined speed. 
     The rotation of the drive roller  131  conveys the fixing belt  105  to circulate in the arrowed clockwise direction at a speed corresponding to the speed of the drive roller  131 . The steering roller  132  rotates to follow the circulation and conveyance of the fixing belt  105 . The inner surface of the descending belt portion of the fixing belt  105  slides and moves over the downward pad surface of the pad stay  137 . For stable conveyance of the sheet S at the fixing nip portion N to be described below, the fixing belt  105  and the drive roller  131  reliably transmit a drive therebetween. 
     The IH heater  170  serves as a heating unit for heating the fixing belt  105 . The IH heater  170  is an induction heating coil unit including an excitation coil, a magnetic core, and a holder which holds the excitation coil and the magnetic coil. The IH heater  170  is arranged above the upper belt assembly A. The IH heater  170  is fixed to the right and left upper side plates  140  so that the IH heater  170  is located opposite the fixing belt  105 , or more specifically, an upper surface portion of the fixing belt  105  and a portion where the steering roller  132  lies, at a predetermined distance without contact. 
     An alternating current is supplied to the excitation coil of the IH heater  170  to generate an alternating-current magnetic flux. The alternating-current magnetic flux is introduced into the magnetic core to generate eddy currents in the magnetic metal layer of the fixing belt  105  serving as an induction heat generation member. The eddy currents generate Joule heat based on the specific resistance of the induction heat generation member. A thermistor  220  detects a temperature of the surface layer of the fixing belt  105 . Based on temperature information from the thermistor  220 , the alternating current supplied to the excitation coil is controlled so that the surface temperature of the fixing belt  105  is adjusted to approximately 140° C. to 200° C. (target temperature). 
     (2-2) Lower Belt Assembly B and Pressure-Separation Mechanism 
     The lower belt assembly B is arranged under the upper belt assembly A. The lower belt assembly B is built on a lower frame (pressure frame)  306 . The lower frame  306  is vertically rotatably supported about a hinge shaft  304  which is fixed to right and left lower side plates  303  on the sheet outlet side of the fixing apparatus  100 . 
     The lower belt assembly B includes the flexible pressure belt (endless belt)  120  serving as a fixing rotatable member (pressure member) which forms the fixing nip portion N with the fixing belt  105  of the upper belt assembly A. The lower belt assembly B further includes the pressure roller (pressure roller)  121 , a tension roller  122 , and a pressure pad  125 , which serve as a plurality of belt suspension members across which the pressure belt  120  is suspended with tension. 
     Right and left shaft portions  121   a  of the pressure roller  121  are rotatably supported between right and left side plates of the lower frame  306  via respective bearings  159 . Right and left shaft portions  122   a  of the tension roller  122  are rotatably supported by the right and left side plates of the lower frame  306  via bearings  158 , respectively. The bearings  158  are supported by the lower frame  306  slidably and movably in a belt tension direction. The bearings  158  are biased by tension springs  127  to move in a direction away from the pressure roller  121 . 
     An example of the pressure pad  125  is a member made of silicon rubber. Both right and left ends of the pressure pad  125  are fixed and supported between the right and left side plates of the lower frame  306 . The pressure roller  121  lies on the sheet outlet side between the right and left side plates of the lower frame  306 . The tension roller  122  lies on the sheet inlet side between the right and left side plates of the lower frame  306 . The pressure pad  125  is not-rotatably supported and arranged inside the pressure belt  120 , close to the pressure roller  121  between the pressure roller  121  and the tension roller  122 , with its pad surface upward. 
     The pressure belt  120  laid across the pressure roller  121 , the tension roller  122 , and the pressure pad  125  undergoes predetermined tension (tensile force) from the movement of the tension roller  122  in the belt tension direction, caused by the biasing forces of the tension springs  127 . In the present exemplary embodiment, a tension of 200 N is applied to the pressure belt  120 . An inner surface of an ascending belt portion of the pressure belt  120  is put in contact with the upward pad surface of the pressure pad  125 . 
     Any heat-resistant pressure belt  120  may be selected as appropriate. For example, a nickel metal layer having a thickness of 50 μm, a width of 380 mm, and a circumferential length of 200 mm, coated with a 300-μm-thick silicon rubber and covered with a PFA tube as a surface layer (release layer), is used. An example of the pressure roller  121  is a solid roller made of stainless steel with an outer diameter of φ20. An example of the tension roller  122  is a hollow roller made of stainless steel with an outer diameter of φ20 and an inner diameter of φ18 or so. 
     The lower belt assembly B is controlled to rotate vertically about the hinge shaft  304  by the pressure-separation mechanism serving as a contacting/separating unit. More specifically, when the lower belt assembly B is rotated and lifted up by the pressure-separation mechanism, the lower belt assembly B moves to a pressure position as illustrated in  FIG. 3 . When the lower belt assembly B is rotated and lifted down, the lower belt assembly B moves to a separate position as illustrated in  FIG. 4 . 
     When the lower belt assembly B is moved to the pressure position, the pressure roller  121  and the pressure pad  125  are pressed against the drive roller  131  and the pad stay  137  of the upper belt assembly A, respectively, by a predetermined pressure force with the pressure belt  120  and the fixing belt  105  therebetween. As a result, the fixing belt  105  of the upper belt assembly A and the pressure belt  120  of the lower belt assembly B form therebetween the fixing nip portion N having a predetermined width in the conveyance direction V of the sheet S. When moved to the separate position, the lower belt assembly B stops being pressed against the upper belt assembly A and is separated from the upper belt assembly A without contact. 
     The pressure-separation mechanism according to the present exemplary embodiment will be described. A pressure spring unit is arranged on the lower frame  306  at a side opposite from the hinge shaft  304 . The pressure spring unit includes a pressure spring  305  for elastically pressing the lower belt assembly B against the upper belt assembly A. 
     A pressure camshaft  307  is rotatably supported between lower portions of the right and left lower side plates  303  via bearings. A pair of eccentric pressure cams  308  having the same shape and the same phase are fixed and arranged on the right and left sides of the pressure camshaft  307 . The eccentric pressure cams  308  support the bottom surface of the lower frame  306 . A pressure gear  309  ( FIG. 2 ) is coaxially fixed and arranged on the right end of the pressure camshaft  307 . A pressure motor  302  inputs a drive to the pressure gear  309  through a drive transmission unit (not illustrated), whereby the pressure camshaft  307  is driven to rotate. 
     The pressure camshaft  307  is controlled to rotate to a first rotation angle position and a second rotation angle position. In the first rotation angle position, the eccentric pressure cams  308  are situated with their large protrusions upward as illustrated in  FIGS. 3 and 5 . In the second rotation angle position, the eccentric pressure cams  308  are situated with their large protrusions downward as illustrated in  FIG. 4 . 
     When the pressure camshaft  307  is rotated to and stopped at the first rotation angle position, the large protrusions of the eccentric pressure cams  308  lift up the lower frame  306  on which the lower belt assembly B is mounted. The lower belt assembly B makes contact with the upper belt assembly A while compressing the pressure spring  305  of the pressure spring unit. As a result, the lower belt assembly B is elastically pressed and biased to the upper belt assembly A with a predetermined pressure (for example, 400 N) resulting from a compression reactive force of the pressure spring  305 . The lower belt assembly B is held in the pressure position illustrated in  FIG. 3 . 
     The pressure contact of the pressure roller  121  with the drive roller  131  warps and deforms the drive roller  131  by several hundreds of millimeters in a direction opposite from the contacting direction to the pressure roller  121 . The warpage of the drive roller  131  can cause a pressure drop in the center of the fixing nip portion N in the longitudinal direction. To avoid the pressure drop, the drive roller  131  or both the drive roller  131  and the pressure roller  121  is/are configured with a crown shape so that the drive roller  131  and the pressure roller  121  form a nip of generally straight shape. In the present exemplary embodiment, the drive roller  131  has a convex crown shape of 300 μm. 
     When the pressure camshaft  307  is rotated to and stopped at the second rotation angle position, the large protrusions of the eccentric pressure cams  308  are directed downward and the small protrusions face the bottom surface of the lower frame  306 , whereby the lower belt assembly B is lifted down. In other words, the lower belt assembly B is held in the separate position illustrated in  FIG. 4 , where the lower belt assembly B stops being pressed against the upper belt assembly A and is separated from the upper belt assembly A by a predetermined distance without contact. 
     Vertical movement control of the lower belt assembly B will be described with reference to a control flowchart illustrated in  FIG. 7A  and a block diagram of a control system illustrated in  FIG. 7B . 
     The lower belt assembly B is normally held in the separate position illustrated in  FIG. 4 . In step S 13 - 001 , if the CPU  10  issues a pressure command (YES in step S 13 - 001 ), then in step S 13 - 002 , the CPU  10  rotates the pressure motor  302  by a predetermined number of rotations, or N turns, in a clockwise (CW) direction via a motor driver  302 D. As a result, the pressure camshaft  307  is driven to rotate by a half turn. In step S 13 - 003 , the eccentric pressure cams  308  are switched from the second rotation angle position illustrated in  FIG. 4  to the first rotation angle position illustrated in  FIGS. 3 and 5 , and the lower belt assembly B is rotated and lifted up so that the pressure roller  121  and the pressure pad  125  move to the pressure position. 
     More specifically, the pressure roller  121  and the pressure pad  125  are pressed against the drive roller  131  and the pad stay  137  of the upper belt assembly A by a predetermined contact pressure with the pressure belt  120  and the fixing belt  105  therebetween. In step S 13 - 004 , the fixing belt  105  and the pressure belt  120  form therebetween the fixing nip portion N having a predetermined width in the conveyance direction V of the sheet S. 
     If the lower belt assembly B is held in the pressure position illustrated in  FIG. 3  and the CPU  10  issues a separation command (YES in step S 13 - 005 ), then in step S 13 - 006 , the CPU  10  rotates the pressure motor  302  by a predetermined number of rotations, or N turns, in a counterclockwise (CCW) direction via the motor driver  302 D. As a result, the pressure camshaft  307  is driven to rotate by a half turn. In step S 13 - 008 , the eccentric pressure cams  308  are switched from the first rotation angle position illustrated in  FIGS. 3 and 5  to the second rotation angle position illustrated in  FIG. 4 . In other words, the lower belt assembly B is rotated and lifted down so that the pressure roller  121  and the pressure pad  125  move to the separate position. In step S 13 - 009 , the formation of the fixing nip portion N is released. 
     (2-3) Fixing Operation and Temperature Adjustment Control 
     Next, a fixing operation of the fixing apparatus  100  will be described with reference to a control flowchart illustrated in  FIG. 8A  and a block diagram of a control system illustrated in  FIG. 8B . When the fixing apparatus  100  is in a standby state, the lower belt assembly B is held in the separate position illustrated in  FIG. 4 . The drive motor  301  stops being driven. Power supply to the IH heater  170  is also stopped. 
     The CPU  10  starts predetermined image forming sequence control based on input of a print job start signal. The CPU  10  drives the pressure motor  302  of the fixing apparatus  100  via the motor driver  302 D at predetermined control timing, whereby the pressure camshaft  307  is driven to rotate by a half turn. This moves the lower belt assembly B from the separate position illustrated in  FIG. 4  to the pressure position illustrated in  FIG. 3 . In step S 16 - 001 , the fixing belt  105  and the pressure belt  120  form the fixing nip portion N therebetween. 
     Next, the CPU  10  drives the drive motor  301  via a motor driver  301 D to input a drive to the drive input gear G. As a result, the drive roller  131  of the upper belt assembly A is driven as described above, and the fixing belt  105  starts to rotate. 
     A rotational force of the drive input gear G is also transmitted to the pressure roller  121  of the lower belt assembly B through a drive gear train (not illustrated), whereby the pressure roller  121  is driven to rotate in the arrowed counterclockwise direction in  FIG. 3 . In step S 16 - 002 , the pressure belt  120  starts to rotate in the arrowed counterclockwise direction because of the rotation of the pressure roller  121  and a frictional force of the rotating fixing belt  105 . In the fixing nip portion N, the fixing belt  105  and the pressure belt  120  move in the same direction at almost the same moving speed. 
     Next, the CPU  10  supplies power to the IH heater  170  via a heater controller  170 C and a heater driver  170 D ( FIG. 9B ). The CPU  10  thereby heats the fixing belt  105  by electromagnetic induction heating up to a predetermined target temperature and performs temperature adjustment control. More specifically, in step S 16 - 003 , the CPU  10  starts temperature adjustment control to increase and maintain the temperature of the fixing belt  105  to a target temperature of 140° C. to 200° C. according to the grammage or paper type of a sheet S to be passed. 
     After the formation of the fixing nip portion N, the rotation of the fixing belt  105  and the pressure belt  120 , and the temperature increase and temperature adjustment of the fixing belt  105 , a sheet S on which the image forming units U have formed an unfixed toner image t ( FIG. 3 ) is introduced into the fixing apparatus  100 . An inlet guide  184  arranged on a sheet inlet portion of the fixing apparatus  100  guides the sheet S to enter the fixing nip portion N, which is the pressure contact portion between the fixing belt  105  and the pressure belt  120 . A flag sensor  185  including a photointerrupter is arranged on the inlet guide  184 . The flag sensor  185  detects passing timing of the sheet S. 
     The fixing nip portion N pinches and conveys the sheet S with the image bearing surface of the sheet S located opposite the fixing belt  105  and the opposite side of the sheet S located opposite the pressure belt  120 . The unfixed toner image t is fixed to the sheet surface as a fixed image by heat and a nip pressure from the fixing belt  105 . The sheet S past the fixing nip portion N is separated from the surface of the fixing belt  105 , and comes out from the sheet outlet side of the fixing apparatus  100 . The discharge roller pair  20  ( FIG. 1 ) conveys and discharges the sheet S to the discharge tray  21 . 
     If the conveyance of a sheet or sheets S in a print job for a predetermined single sheet or plurality of consecutive sheets has finished, then in step S 16 - 004 , the CPU  10  ends the heating and temperature adjustment control of the fixing belt  105  and turns off the power supply to the IH heater  170 . In step S 16 - 005 , the CPU  10  turns off the drive motor  301  to stop rotating the fixing belt  105  and the pressure belt  120 . 
     The CPU  10  drives the pressure motor  302  via the motor driver  302 D, whereby the pressure camshaft  307  is driven to rotate by a half turn. This moves the lower belt assembly B from the pressure position illustrated in  FIG. 3  to the separate position illustrated in  FIG. 4 . In step S 16 - 006 , the fixing nip portion N between the fixing belt  105  and the pressure belt  120  is thus released. In such a state, the CPU  10  waits for the input of a next print job start signal. 
     Temperature control of the fixing belt  105  will be described with reference to a control flowchart illustrated in  FIG. 9A  and a block diagram of a control system illustrated in  FIG. 9B . The upper belt assembly A includes the thermistor  220 , which serves as a temperature detection member for detecting the surface temperature of the fixing belt  105 . In step S 17 - 001 , the CPU  10  applies power to the IH heater  170  via the heater controller  170 C and the heater driver  170 D at predetermined control timing based on the input of a print job start signal. The IH heater  170  increases the temperature of the fixing belt  105  by electromagnetic induction heating. 
     The thermistor  220  detects the temperature of the fixing belt  105 , and inputs detection temperature information (electrical information about temperature) to the CPU  10 . If the temperature detected by the thermistor  220  becomes higher than or equal to a predetermined prescribed value (target temperature) (YES in step S 17 - 002 ), then in step S 17 - 003 , the CPU  10  stops the power to the IH heater  170 . Subsequently, if the temperature detected by the thermistor  220  becomes lower than the predetermined prescribed value (NO in step S 17 - 004 ), then in step S 17 - 001 , the CPU  10  resumes the application of the power to the IH heater  170 . 
     The CPU  10  repeats the foregoing steps S 17 - 001  to S 17 - 004  to adjust and maintain the temperature of the fixing belt  105  to the predetermined target temperature. Such fixing belt temperature adjustment control is performed until a print job for a predetermined single sheet or plurality of consecutive sheets finishes (YES in step S 17 - 005 ). 
     (2-4) Belt Deviation Control Mechanism 
     The fixing belt  105 , when rotating, causes a phenomenon of moving closer to one side or the other in the width direction orthogonal to the conveyance direction V of the sheet S. Such a phenomenon will be referred to as a belt deviation movement. The pressure belt  120 , pressed into contact with the fixing belt  105  to form the fixing nip portion N, also makes a deviation movement with the fixing belt  105 . 
     In the present exemplary embodiment, swing deviation control is performed to stabilize the deviation movement of the fixing belt  105  within a predetermined deviation range. The swing deviation control refers to a method for tilting the steering roller  132  in a direction opposite to the direction of the deviation movement of the fixing belt  105  when the belt position is detected to have moved more than a predetermined amount from the center in the width direction. Such swing deviation control can be repeated to periodically move the fixing belt  105  from one side to the other in the width direction. This enables stable control of the deviation movement of the fixing belt  105 . In other words, the fixing belt  105  is configured to be capable of reciprocations in the direction orthogonal to the conveyance direction V of the sheet S. 
     The upper belt assembly A includes a sensor unit (not illustrated) for detecting an end position of the fixing belt  105 . The sensor unit is located on the left side (near side) of the fixing belt  105 , close to the steering roller  132 . The CPU  10  detects the end position (belt deviation movement position) of the fixing belt  105  by using the sensor unit, and rotates the stepping motor  155  by a predetermined number of rotations in a forward direction (CW) or reverse direction (CCW) accordingly. 
     As a result, the left steering roller support arm  154  is rotated upward or downward about the shaft portion  131   a  by a predetermined amount of control via the foregoing mechanisms  157 ,  152 ,  161 , and  151  illustrated in  FIGS. 5 and 6 . In response, the tilt of the steering roller  132  changes to perform deviation control of the fixing belt  105 . 
     (2-5) Roughing Mechanism of Fixing Belt  105   
     Next, the roughing mechanism (surface property recovery mechanism) for recovering surface properties of the fixing belt  105  will be described with reference to  FIGS. 10A and 10B . In the present exemplary embodiment, a roughing roller  400  is arranged above the drive roller  131  of the upper belt assembly A. The roughing roller  400  serves as a rubbing rotatable member (roughing member) which rubs an outer surface of the fixing belt  105  to recover surface properties of the fixing belt  105 . As described above, the roughing roller  400  is effective when areas of the fixing belt  105  touched by the edge portions of a sheet S are locally roughened in the surface as compared to other areas. More specifically, the roughing roller  400  rubs almost the entire longitudinal area of the fixing belt  105 . The roughing roller  400  thereby makes the areas locally roughened in the surface and the other areas have approximately the same surface roughness so that a deteriorated state becomes less noticeable. As employed in the present exemplary embodiment, making a deteriorated state less noticeable in this way is referred to as recovering surface properties. Specifically, in the present exemplary embodiment, the surface of the fixing belt  105  locally roughened to a surface roughness Rz of approximately 2.0 is recovered to a surface roughness Rz of 0.5 to 1.0 by the roughing processing (rubbing processing) of the roughing roller  400 . 
     While the roughing roller  400  is so called in the present exemplary embodiment, the role of the roughing roller  400  is to maintain the surface roughness of the fixing belt  105  sufficiently low for a long period of time. This suppresses uneven glossiness of an image as well as a decrease in image glossiness. 
     The roughing roller  400  is rotatably supported between a pair of right and left roughing (RF) support arms  141  via bearings (not illustrated). The right and left RF support arms  141  are rotatably supported by fixed shafts  142  which are coaxially fixed to the right and left upper side plates  140  of the apparatus casing, respectively. 
     The roughing roller  400  includes a φ12-mm core of stainless steel. Abrasive grains are densely bonded to the surface of the core via an adhesive layer. Abrasive grains of #1000 to #4000 in mesh scale (granularity) can be used according to target glossiness of an image. Abrasive grains of #1000 in mesh scale (granularity) have an average grain size of approximately 16 μm. Abrasive grains of #4000 in mesh scale (granularity) have an average grain size of approximately 3 μm. The abrasive grains are alumina-based ones (commonly called “Alundum” or “Morundum”). Alumina grains are the most widely used in industries, and have significantly high hardness as compared to that of the surface of the fixing belt  105  and an acute grain shape for excellent abrasive performance. In the present exemplary embodiment, abrasive grains with a mesh scale (granularity) of #2000 (an average grain size of 7 μm) are used. 
     (2-6) Contacting/Separating Mechanism for Contacting and Separating Roughing Roller 
     In the present exemplary embodiment, the fixing apparatus  100  includes a contacting/separating mechanism (moving mechanism) for contacting and separating the roughing roller  400  against/from the fixing belt  105 . The contacting/separating mechanism will be described in detailed below. 
     The roughing roller  400  is configured so that its shaft portions at both longitudinal ends are pressed toward the fixing belt  105  by a pressing mechanism during rubbing processing. In the present exemplary embodiment, the right and left RF support arms  141  play the role of the pressing mechanism. 
     RF cams (eccentric cams)  407  are arranged above the respective right and left RF support arms  141 . The right and left RF cams  407  have the same shape and are fixed to an RF camshaft  408  with the same phase. The RF camshaft  408  is rotatably supported between the right and left upper side plates  140  of the apparatus casing via bearings. RF separation shafts  406  are fixed to the respective right and left upper side plates  140 . RF separation springs  405  are respectively stretched between the RF separation shafts  406  and arm ends of the right and left RF support arms  141  at the side opposite from where the roughing roller  400  is supported. 
     The right and left RF support arms  141  are constantly biased by the tensile forces of the RF separation springs  405  to rotate about the respective fixed shafts  142  in a direction to lift up the roughing roller  400 . The top surfaces of the right and left RF support arms  141  are elastically pressed to the bottom surfaces of the corresponding right and left RF cams  407 . As illustrated in  FIG. 10B , an RF attachment/detachment gear  409  is fixed to the left end of the RF camshaft  408 . The RF attachment/detachment gear  409  meshes with an RF motor gear  411  of an RF pressure motor  410 . 
     In the present exemplary embodiment, the right and left RF cams  407  are normally stopped at a first orientation of an rotational angle where the large protrusions of the right and left RF cams  407  are directed upward as illustrated in  FIGS. 3 and 4 . In such a state, the right and left RF support arms  141  are in contact with the small protrusions of the respective corresponding RF cams  407 . As a result, the roughing roller  400  is held in a separate position at a predetermined distance from the fixing belt  105 . In other words, the roughing roller  400  is lifted above the fixing belt  105  and will not act on the fixing belt  105 . 
     If the right and left RF cams  407  are rotated by 180° from the foregoing first orientation, the right and left RF cams  407  are turned into and held in a second orientation of the rotational angle where the large protrusions are directed downward as illustrated in  FIG. 10A . In such a state, the right and left RF support arms  141  are pressed down about the fixed shafts  142  by the respective corresponding RF cams  407  against the RF separation springs  405 . As a result, the roughing roller  400  is turned into and held in a pressure position (contact position) where the roughing roller  400  is in touch (contact) with the surface of the fixing belt  105  at a belt wound portion of the drive roller  131  with a predetermined pressing force and forms a roughing nip portion R. 
     An RF gear  403  fixed to an end of the roughing roller  400  meshes with an RF drive gear  401  fixed to an end of the drive roller  131 . The rotational force of the drive roller  131  is then transmitted to the roughing roller  400  through the RF drive gear  401  and the RF gear  403 , whereby the roughing roller  400  is rotated in a direction reverse to the fixing belt  105 . The roughing roller  400  having the abrasive layer on its surface has the function of rotating with a circumferential speed difference with respect to the fixing belt  105  in the width direction (direction in which the surfaces both move) to evenly roughen the surface (smoothen the surface) of the fixing belt  105 . 
     In other words, the roughing roller  400  serving as a rubbing member is a roller member that rotates with a circumferential speed difference with respect to the fixing belt  105 . To switch the position of the roughing roller  400  between the separate position and the pressure position, the RF pressure motor  410  switches the orientation of the right and left RF cams  407  between the first orientation and the second orientation via the RF motor gear  411 , the RF attachment/detachment gear  409 , and the RF camshaft  408 . In  FIG. 10A , the lower belt assembly B pressed against the upper belt assembly A to form the fixing nip portion N is omitted. 
       FIG. 11A  is a flowchart illustrating operation control of the foregoing roughing mechanism. As described above, the right and left RF cams  407  of the roughing mechanism are normally stopped at the first orientation of the rotational angle where the large protrusions are directed upward as illustrated in  FIGS. 3 and 4 . The roughing roller  400  is held in the separate position at a predetermined distance from the fixing belt  105 . 
     If the CPU  10  issues a pressure command at predetermined pressure control timing (YES in step S 15 - 001 ), then in step S 15 - 002 , the CPU  10  rotates the RF pressure motor  410  by a predetermined number of rotations, or M turns, in a CW direction via a motor driver  410 D ( FIG. 11B ). In step S 15 - 003 , the right and left RF cams  704  are switched from the first orientation ( FIGS. 3 and 4 ) to the second orientation ( FIG. 10A ), whereby the roughing roller  400  is moved from the separate position (first position) to the pressure position (second position). In step S 15 - 004 , with the roughing roller  400  moved to the pressure position, the fixing belt  105  and the roughing roller  400  are pressed to form the roughing nip portion R. 
     If the CPU  10  issues a separation command at predetermined separation control timing (YES in step S 15 - 005 ), then in step S 15 - 006 , the CPU  10  rotates the RF pressure motor  410  by a predetermined number of rotations, or M turns, in a CCW direction via the motor driver  410 D. In step S 15 - 007 , the right and left RF cams  407  are switched back from the second orientation ( FIG. 10A ) to the first orientation ( FIGS. 3 and 4 ), whereby the roughing roller  400  is moved from the pressure position to the separate position. In step S 15 - 008 , with the roughing roller  400  moved to the separate position, the fixing belt  105  and the roughing roller  400  are separated to release the roughing nip portion R. 
     Next, timing to enter a surface property recovery operation of the fixing belt  105  by the roughing roller  400  will be described with reference to  FIGS. 12A and 12B . As illustrated in the block diagram of  FIG. 12B , in the present exemplary embodiment, the CPU  10  uses a counter W to count the number of sheets S on which the fixing apparatus  100  has performed the fixing processing during the execution of a print job, and stores the cumulative value into a memory Z. 
     If the cumulative value has reached a predetermined number N of sheets (in the present exemplary embodiment, 3000), the CPU  10  finishes the print job in process or suspends the execution of the print job (fixing processing) before performing the surface property recovery operation of the fixing belt  105  by the roughing roller  400 . After the end of the surface property recovery operation, the CPU  10  resets the cumulative value stored in the memory Z to zero. If the print job has been suspended, the CPU  10  resumes the remaining print job after the execution of the surface property recovery operation of the fixing belt  105 . 
       FIG. 12A  is a flowchart illustrating the foregoing surface property recovery operation. If the cumulative number of sheets passed is greater than or equal to the predetermined number of passed sheets N (YES in step S 18 - 001 ), then in step S 18 - 002 , the CPU  10  finishes the print job in process or suspends the print job. In step S 18 - 003 , the CPU  10  starts the surface property recovery operation. The CPU  10  also resets the counter W to zero. After the end of the surface property recovery operation, the CPU  10  enters a wait for a next print job. If there is a print job suspended, then in step S 18 - 004 , the CPU  10  resumes the suspended print job, and enters a wait for a next print job after the end of the print job. 
     The present exemplary embodiment has dealt with the case of entering the surface property recovery operation of the fixing belt  105  by the roughing roller  400  after the fixing apparatus  100  has performed the fixing processing on a predetermined number of sheets. This is not restrictive. The CPU  10  may count the number of specific sheets alone. The CPU  10  may perform the surface property recovery operation of the fixing belt  105  on a timely basis like before a print job for a certain type of sheet or in response to a user&#39;s operation or instruction from the printer operation unit  24  ( FIG. 1 ) during a print wait. 
     (2-7) Blowing Mechanism 
     As described above, when the roughing roller  400  is moved to the pressure position, the fixing belt  105  is rubbed to recover its surface properties. Here, shavings of the surface layer of the fixing belt  105  can be produced in the roughing nip portion R. The shavings may remain on the fixing belt  105  in a line, and the line of shavings extending in the axial direction of the fixing belt  105  may adhere to an image immediately after the roughing operation. Since the image immediately after the roughing operation has high glossiness, the shavings of the surface layer of the fixing belt  105  can appear particularly noticeably, causing a decrease in image quality. 
     To prevent the shavings of the surface layer of the fixing belt  105  produced by the roughing roller  400  from remaining on the fixing belt  105  in a line and to make shavings appearing on an image immediately after the roughing operation less noticeable, a blowing mechanism is used to diffuse the shavings of the surface layer of the fixing belt  105  during the roughing operation. A shaving diffusing configuration using the blowing mechanism will be described in detail. 
       FIG. 13  is a schematic diagram illustrating the blowing mechanism according to the present exemplary embodiment.  FIG. 14  is a perspective view of the blowing mechanism.  FIG. 15  is a schematic diagram illustrating the blowing mechanism. The blowing mechanism includes fans  601  and a duct  602 . The CPU  10  serving as a controller controls an operation of the fans  601 . When the roughing roller  400  is moved to the pressure position, the fans  601  blow air to the roughing nip portion (contact portion) R between the roughing roller  400  and the fixing belt  105  through the duct  602  so that the air can be blown to the entire longitudinal area (the entire area in the belt width direction) of the fixing belt  105 . 
     In the present exemplary embodiment, when the roughing roller  400  is pressed against (put into contact with) the fixing belt  105 , the fans  601  are driven to blow air through the duct  602  at a wind velocity of Vw (for example, 10 m/s) to near the roughing nip portion R formed between the fixing belt  105  and the roughing roller  400 . Shavings of the surface layer of the fixing belt  105  occurring during the roughing operation are thereby diffused. This can prevent the shavings of the surface layer of the fixing belt  105  produced by the roughing roller  400  from remaining on the fixing belt  105  in a line, and make shavings appearing on an image immediately after the roughing operation less noticeable. 
     In the present exemplary embodiment, the roughing roller  400  is located opposite the drive roller  131 , which is one of the plurality of support rollers rotatably supporting the fixing belt  105  from inside. The roughing operation is performed by pressing the roughing roller  400  against the drive roller  131  with the fixing belt  105  therebetween. 
     A description will be given with reference to  FIG. 15 . In the present exemplary embodiment, the fans  601  are configured to blow air from an upstream side to a downstream side in the rotational direction of the fixing belt  105 . The duct  602  is configured to have a blowing opening  602   a  within the range of 45°≦θ≦60°, where θ is the angle formed between a line J passing through the two rotation centers (axial centers) of the drive roller  131  and the roughing roller  400  and a wind direction K of the blown air. The duct  602  is thus configured to blow air to the roughing nip portion R. This improves the effect for diffusing the shavings of the surface layer of the fixing belt  105  occurring in the roughing operation. 
     The blowing opening  602   a  of the duct  602  is installed within a distance a=14 mm, where a is the distance between a nip line ML of the roughing nip portion R formed between the drive roller  131  and the roughing roller  400  and a line T that is drawn in parallel to the nip line ML on a side away from the drive roller  131 . Such installation improves the effect for diffusing the shavings of the surface layer of the fixing belt  105  occurring in the roughing operation. As employed herein, the nip line ML refers to a line that connects an inlet portion and an outlet portion of the roughing nip portion R in the width direction of the roughing nip portion R (the rotational direction of the drive roller  131 ). 
     Next, the surface property recovery operation (roughing operation) of the fixing belt  105  will be described in detail with reference to  FIG. 16 . In step S 12 - 1 , the CPU  10  initially starts to drive the fans  601  to blow air. In step S 12 - 2 , the CPU  10  moves the roughing roller  400  from the separate position (first position) to the pressure position (second position) to form the roughing nip portion R with the fixing belt  105 . 
     Next, the CPU  10  turns on the drive motor  301  to rotate for a predetermined time T 1 . In other words, in step S 12 - 3 , the CPU  10  rotates the fixing belt  105  for the predetermined time T 1 . The fans  601  blow air to diffuse shavings produced in the roughing nip portion R, thereby avoiding deposition of the shavings and preventing damage of the roughing roller  400  and the fixing belt  105 . 
     If the predetermined time T 1  has elapsed (YES in step S 12 - 3 ), then in step S 12 - 4 , the CPU  10  moves the roughing roller  400  to the separate position to release the formation of the roughing nip portion R with the fixing belt  105 . This ends the processing of the surface property recovery operation (rubbing processing) on the surface layer of the fixing belt  105 . In the meantime, the fans  601  continue blowing air. Even after the release of the roughing nip portion R, the CPU  10  drives the drive motor  301  to rotate for a predetermined time T 2  (for example, 2 sec) to further diffuse shavings remaining on the surface layer of the fixing belt  105 . Finally, the CPU  10  stops rotating the drive motor  301  to end the surface property recovery operation of the fixing belt  105 . 
     In the foregoing description, the fans  601  blow air from immediately before the start of the rubbing processing by the roughing roller  400  to immediately after the end of the rubbing processing. However, the blowing of the fans  601  is not limited to such an example. The following configuration may be employed instead. 
     The present exemplary embodiment is intended to diffuse shavings that may remain on the fixing belt  105  in a line in the longitudinal direction of the fixing belt  105 . The fans  601  therefore have only to blow air at least when the roughing roller  400  moves from the pressure position (contact position) to the separate position. The fans  601  may continue blowing air for a predetermined time even after the roughing roller  400  has move from the pressure position to the separate position. This can further diffuse shavings. The fans  601  may start to blow air at timing before the timing when the roughing roller  400  starts to move from the pressure position to the separate position. This can diffuse a certain amount of shavings in advance. 
     Like the first exemplary embodiment, a fixing apparatus according to a second exemplary embodiment is a fixing apparatus of a belt heating method. The second exemplary embodiment is applied to a belt-type fixing apparatus. In the first exemplary embodiment, the arrangement of the fans  601  and the duct  602  illustrated in  FIG. 13  diffuses foreign substances occurring in the roughing operation over the fixing belt  105 . As a result, the foreign substances can be made less visible on an image but may still remain on the fixing belt  105 . 
     The present exemplary embodiment defines the positional relationship of the roughing roller  400  with the fans  601  and the duct  602  to sweep away the foreign substances occurring in the roughing operation and prevent the foreign substances from remaining on the fixing belt  105 . 
       FIGS. 17A to 17D  each are a schematic diagram illustrating an arrangement of the roughing roller  400  and the duct  602  in a belt-type fixing apparatus in which the fixing belt  105  is suspended across three suspension rollers  701  serving as a plurality of suspension members. 
     Like the first exemplary embodiment, the roughing roller  400  is located opposite a suspension roller  701  corresponding to the drive roller  131  and is in contact with the fixing belt  105 . Suppose two common tangents U 1  and U 2  to the suspension roller  701  and the roughing  400  are drawn not to intersect a line J that connects the axial centers of the two rollers  701  and  400 . With respect to the line J connecting the axial centers of the two rollers  701  and  400 , an area where either one of the common tangents U 1  and U 2  intersects the fixing belt  105  will be referred to as D. An area where neither of the common tangents U 1  and U 2  intersects the fixing belt  105  will be referred to as E. The fans  601  and the duct  602  are arranged on the D side and blow air to the E side. 
     More specifically, the fans  601  and the duct  602  are arranged in the area (area D) where a common tangent intersects the fixing belt  105 . With such a configuration, any of the arrangements illustrated in  FIGS. 17A to 17D  can sweep away the foreign substances occurring in the roughing operation and prevent the foreign substances from remaining on the fixing belt  105 . 
     If the two common tangents U 1  and U 2  of the suspension roller  701  and the roughing roller  400  both intersect the fixing belt  105  as illustrated in  FIGS. 18A and 18B , the foreign substance sweeping effect can be obtained in the following case. Take, as illustrated in  FIG. 18A , a coordinate system with respect to the axis of the suspension roller  701  located opposite the roughing roller  400 . If the roughing roller  400  lies in the third or fourth quadrant of the coordinate system, the air blowing provides a favorable foreign substance sweeping effect. The duct  602  may be arranged in either of the third and fourth quadrants. 
     If the roughing roller  400  lies in the first or second quadrant of the foregoing coordinate system as illustrated in  FIG. 18B , foreign substances are not able to be swept off the fixing belt  105 . Such an arrangement shall be avoided. 
     As described above, even in the present exemplary embodiment, shavings of the surface layer of the fixing belt  105  produced by the roughing roller  400  can be prevented from remaining on the fixing belt  105  in a line. Shavings appearing on an image immediately after a roughing operation can thus be made less noticeable. 
     While the exemplary embodiments of the present invention have been described above, various configurations described above may be replaced with known ones without departing from the scope of the concept of the present invention. 
     For example, the foregoing exemplary embodiments have been described by using the fixing belt  105  as an example of the member for the roughing roller  400  to perform the rubbing processing on. However, an exemplary embodiment of the present invention is not limited thereto, and may be similarly applied to a case where a roughing roller  400  performs rubbing processing on the pressure belt  120 . Such an application is particularly effective when images are formed on both sides of a sheet S. 
     The foregoing exemplary embodiments have been described by using a fixing apparatus including the fixing belt  105  and the pressure belt  120  as an example. However, an exemplary embodiment of the present invention is not limited thereto, and may be similarly applied to cases where a fixing roller is used instead of the fixing belt  105 , and where a pressure roller or a nonrotating pad having a small surface friction coefficient is used instead of the pressure belt  120 . 
     The foregoing exemplary embodiments have been described by using a fixing apparatus that fixes an unfixed toner image to a sheet S as an example. However, an exemplary embodiment of the present invention is not limited thereto, and may be similarly applied to an apparatus that heats and presses a toner image that has been temporarily fixed to a sheet (even in such a case, the apparatus is referred to as a fixing apparatus). 
     The foregoing exemplary embodiments have dealt with a heating mechanism of electromagnetic induction heating method. However, an exemplary embodiment of the present invention is not limited thereto, and may be similarly applied to cases where heating mechanisms of other methods such as a halogen heater are used. Specifically, for example, a heating mechanism such as a halogen heater may be arranged inside the drive roller  131  and/or the pressure roller  121 . 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all modifications, equivalent structures, and functions. 
     This application claims priority from Japanese Patent Application No. 2012-087255 filed Apr. 6, 2012, which is hereby incorporated by reference herein in its entirety.