Abstract:
The image heating apparatus includes a flexible sleeve, a sliding member for sliding on the inner periphery of the sleeve, a back-up member for forming a nip portion together with the sliding member through the sleeve, wherein a recording material for bearing an image is heated while being held and conveyed by the nip portion and a regulation member set by facing the edge surface of the sleeve in the generatrix direction to regulate the movement of the sleeve in the generatrix direction, the regulation surface having a regulation surface with which the edge surface of the sleeve contacts when the sleeve moves in the generatrix direction, wherein the regulation surface of the regulation member has a curved-surface area in which a line when the regulation surface is cut at a virtual plane almost parallel with the nip portion is a curved line expanede toward the edge surface of the sleeve. Thereby, an image heating apparatus is provided which is able to restrain deterioration of the durability of the flexible sleeve.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an image heating apparatus for heating an image born by a recording material by passing the recording material through a fixing nip portion N between a heat member and a pressuring member to cause the material to be held and conveyed. Particularly, the present invention relates to an image heating apparatus to be preferably mounted on an image forming apparatus such as a copying machine or printer as an image heating-fixing device.  
         [0003]     More minutely, the present invention includes a flexible sleeve-shaped rotor, a sliding member set to the inside of the rotor to slide on the inner periphery of the rotor, a pressuring member for forming a nip portion together with the sliding member by holding the rotor and a regulation member set by facing the end of the rotor to regulate movement of the rotor in a generatrix direction, which heats a recording material bearing an image by the nip portion while conveying the recording material.  
         [0004]     2. Related Background Art  
         [0005]     The heating roller system shown in  FIG. 15  has been used so far as an image heating apparatus to be mounted on a copying machine or printer as a fixing device. This system is basically constituted of a metallic heating roller  202  including a halogen heater  201  and an elastic pressuring roller  203  pressure-welded to the heating roller  202 . Moreover, a recording medium S bearing an unfixed toner image t as a member to be heated is introduced into the fixing nip portion N (fixing nip portion) of the roller pair  202  and  203  to hold, convey and pass the recording medium S. Thereby, the toner image t is heated, pressured and fixed.  
         [0006]     However, because the fixing device according to the heating roller system requires a lot of time in order to raise the temperature of roller surface up to a fixing temperature because the rollers respectively have a large heat capacity. Therefore, to quickly execute the image output operation, it is necessary to keep the roller surface at a certain degree of temperature also when the apparatus is not used.  
         [0007]     Therefore, a film-heating-system heating apparatus for fixing a developer to a recording medium by using a film heated by a heater is proposed as an on-demand type heating apparatus.  
         [0008]     This film-heating-system heating apparatus normally has a thin heat-resistant film (e.g. polyimide) and a heater (heat generation member) fixed to one side of the film. Moreover, the apparatus has a pressure roller set to the other side of the film by facing a heater to contact a member to be heated with the heater through the film.  
         [0009]     Moreover, when using the pressure roller as a fixing device, a recording medium making the fixing nip portion N (fixing nip portion) formed by pressure welding between the heater and pressure roller at both sides of the film form and bear a toner image is introduced and passed. Thereby, the visualized image bearing body face of the recording medium is heated by the heater through the film, heat energy is supplied to an unfixed image, toner is softened and melted and the image is heated and fixed.  
         [0010]     In the case of the above film-heating-system heating apparatus, it is possible to use a low-heat-capacity heater as a heat generation member. Therefore, it is possible to save power and shorten the wait time compared to the case of a conventional heat-roller-system or belt-heating-system apparatus.  
         [0011]     Moreover, it is recently proposed to prevent luster irregularity of an image by setting an elastic layer to the outside of a fixing film and uniforming the contact between a recording material having minute irregularity and the film. Furthermore, an apparatus is proposed which secures the on-demand property of a fixing device by using a metallic film having a heat conductivity higher than that of the polyimide film (e.g. stainless steel) in order to prevent deterioration of heat conductivity caused as a harmful result of setting the elastic layer.  
         [0012]     In the case of these film-heating-system fixing devicees, lateral shift to the generatrix direction (thrust direction) may occur in a film and it is difficult to regulate the lateral shift force. Particularly, when a displacement of the parallelism between a pressure roller and the film or the right-left difference of applied pressure increases, a strong hook-approach force is generated and a strong stress is applied to the end of the film. Therefore, the end of the film may be damaged.  
         [0013]     Therefore, it is proposed to regulate lateral shift by loosely winding a film, decreasing the lateral shift force of the film, and receiving the film end by the film-edge part regulation surface (hereafter also referred to as “regulation face”) of a flange in Japanese Patent Application Laid-Open No. H04-044075 and Japanese Patent Application Laid-Open No. H04-204980. When a fixing film is flexible enough and loose pulling is possible, it is possible to avoid film damage by the configuration disclosed in the above documents. However, in the case of a fixing belt using a metallic film, the fixing film itself has a high stiffness and lacks in flexibility. Therefore, when the shift of parallelism between the above pressure rollers and film or the difference between right and left applied pressures arises and a strong lateral shift force is generated and a film locally receives a stress on the lateral shift regulation surface, cracks may arise from an end.  
       SUMMARY OF THE INVENTION  
       [0014]     The object of the present invention is to solve the above problem and its object is to provide an image heating apparatus capable of preventing deterioration of the durability of a flexible sleeve.  
         [0015]     Another object of the present invention is to provide an image heating apparatus including a flexible sleeve, a sliding member for sliding on an inner periphery of said flexible sleeve, a back-up member for forming a nip portion together with said sliding member through said flexible sleeve, wherein a recording material for bearing an image is heated while being held and conveyed by the nip portion, and a regulation member provided with opposing to the edge surface of said sleeve in a generatrix direction of said sleeve, for regulating a movement of said sleeve in the generatrix direction of said sleeve, said regulation member having a regulation surface with which the edge surface of said sleeve contacts when said sleeve moves in the generatrix direction, wherein the regulation surface of said regulation member has a curved-surface area in which a line when the regulation surface is cut in a virtual plane substantially parallel to the nip portion is a curved line convexed toward the edge surface of said sleeve.  
         [0016]     A further object of the present invention is to provide an image heating apparatus including a flexible sleeve, a sliding member for sliding on the inner periphery of said sleeve, a back-up member for forming a nip portion together with said sliding member through said sleeve, wherein a recording material for bearing an image is heated while being held and conveyed by the nip portion, and a regulation member provided with opposing to the edge surface of said sleeve in a generatrix direction of said sleeve, for regulating a movement of said sleeve in the generatrix direction of said sleeve, said regulation member having a regulation surface with which the edge surface of said sleeve contacts when said sleeve moves in the generatrix direction, wherein the regulation surface of said regulation member has a curved-surface area in which the generatrix direction of the regulation member intersects with a virtual plane including the nip portion.  
         [0017]     A still further object of the present invention will become apparent by reading detailed description while referring to the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]      FIG. 1  is a schematic view of an image forming apparatus which mounts an image heating apparatus of the present invention;  
         [0019]      FIG. 2  is an enlarged crossing side schematic view of an essential portion of a fixing device;  
         [0020]      FIG. 3  is an enlarged longitudinal front schematic view of a fixing device in which a part of the fixing device in the longitudinal direction is omitted;  
         [0021]      FIG. 4  is a sectional schematic view showing the layer configuration of a flexible sleeve;  
         [0022]      FIG. 5  is a perspective schematic view showing a state of separating a fixing flange  40  from a reinforcement stay  39 ;  
         [0023]      FIG. 6  is a perspective schematic view showing an engagement relation between a longitudinal groove portion  40   a  formed on the fixing flange  40  and the longitudinal marginal portion  34   b  of a longitudinal guide slit  34   a  formed on the side plate  34  of an apparatus frame;  
         [0024]      FIG. 7A  is a perspective view of a fixing flange in which a sleeve edge part regulation surface is a curved face;  
         [0025]      FIG. 7B  is a perspective view of a fixing flange in which a sleeve edge part regulation surface is a part of an elliptic cylinder surface and the sleeve edge part regulation surface is a curved surface;  
         [0026]      FIG. 7C  is an illustration for explaining a fixing flange in which the shape of a circular arc when cutting a sleeve edge part regulation surface at a plane almost parallel with a fixing nip is approximate to an ellipse or circle and the sleeve edge part regulation surface is a curved surface;  
         [0027]      FIG. 8  is an enlarged longitudinal section schematic view of a fixing device using a fixing flange whose sleeve edge part regulation surface is a curved surface at one edge surface;  
         [0028]      FIG. 9  is an illustration viewed from the direction of the arrow V 1  in  FIG. 8 , which shows how the force of a flexible sleeve is applied to the edge part regulation surface of a flange when the reinforcement stay  39  is curved;  
         [0029]      FIG. 10  is an illustration when viewing the longitudinal-directional edge surface of a fixing device from the direction of the arrow V 1  in  FIG. 8 , which shows how the force of a flexible sleeve is applied to the edge part regulation surface of a flange when a flexible sleeve and a pressure roller have a crossing angle;  
         [0030]      FIG. 11  is a perspective view of a conventional fixing flange whose sleeve edge part regulation surface is a plane;  
         [0031]      FIG. 12  is an enlarged longitudinal section schematic view of a fixing device using a fixing flange whose sleeve edge part regulation surface is a plane at one edge surface;  
         [0032]      FIG. 13  is an illustration viewed from the direction of the arrow V 1  in  FIG. 12 , which shows how the force of a flexible sleeve is applied to the edge part regulation surface of a flange when the reinforcement stay  39  is curved;  
         [0033]      FIG. 14  is an illustration viewing the longitudinal-directional edge surface of a fixing device from the direction of the arrow V 1  in  FIG. 12 , which shows how the force of a flexible sleeve is applied to the edge part regulation surface of a flange when a flexible sleeve and a pressure roller have a crossing angle; and  
         [0034]      FIG. 15  is a schematic view of a configuration of a heat-roller-system fixing device. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     Embodiment 1  
       [0000]     (1) Embodiment of Image Forming Apparatus  
         [0035]     An embodiment of an image forming apparatus using an image heating apparatus of the present invention as a fixing device is described below by referring to  FIG. 1 .  
         [0036]     The image forming apparatus of this embodiment is a full-color image forming apparatus using an electrophotographic system. The apparatus has four process stations  1   a  to  1   d  arranged on an substantial straight line in a substantial vertical direction to the setting face of the apparatus to form four different color images (magenta, cyan, yellow and black) and a conveying route  20  for conveying sheets S serving as recording materials (recording media).  
         [0037]     The process stations  1   a  to  1   d  have photosensitive drums  2   a  to  2   d  for bearing a latent image. Moreover, the process stations  1   a  to  1   d  have electrification rollers  3   a  to  3   d  for uniformly electrifying the photosensitive drums  2   a  to  2   d  and exposure devices  4   a  to  4   d  for applying a laser beam on the photosensitive drums  2   a  to  2   d  to form a latent image. Furthermore, the process stations  1   a  to  1   d  have developing means  5   a  to  5   d  for developing the latent image formed on the photosensitive drums  2   a  to  2   d  by toners of corresponding colors (magenta, cyan, yellow and black) to visualize it. Furthermore, the process stations  1   a  to  1   d  have cleaning devices  6   a  to  6   d  for removing remaining toners from the photosensitive drums  2   a  to  2   d . These are arranged around the photosensitive drums  2   a  to  2   d.    
         [0038]     The developing means  5   a  to  5   d  have developing sleeves  50   a  to  50   d  for bearing toners. The developing sleeves  50   a  to  50   d  are supported by keeping predetermined intervals from corresponding photosensitive drums  2   a  to  2   d . A developing bias is applied between the photosensitive drums  2   a  to  2   d  and developing sleeves  50   a  to  5   d.    
         [0039]     An intermediate transfer belt  7  is suspended and strained on a driving roller  8 , a driven roller  9  and belt tension rollers  10  and  11  under tension and rotated in the direction shown by arrows in  FIG. 1 . The intermediate transfer belt  7  is conveyed along the arrangement direction of the process stations  1   a  to  1   d . Toner images of various colors on the photosensitive drums  2   a  to  2   d  are successively transferred to the surface of the intermediate transfer belt by primary transfer means  14   a  to  14   d  through the stations. Thereby, an unfixed full-color toner image is synthesized and formed on the outer face of the intermediate transfer belt  7 .  
         [0040]     The sheets S are stored in a sheet feed cassette  15  set to the lower portion of the apparatus. Then, the sheets S are separated and sent one by one from the sheet feed cassette  15  by a sheet feed roller  16  and fed to a pair of registration rollers  17 . The pair of the registration rollers  17  sends the fed sheets S between the intermediate transfer belt  7  and a secondary transfer roller  12 .  
         [0041]     The secondary transfer roller  12  set so as to face the driven roller  9  contacts with the lowermost surface of the intermediate transfer belt  7 . The secondary transfer roller  12  holds and conveys the sheets S passing between the roller  12  and the intermediate transfer belt  7 . A bias is applied to the secondary transfer roller  12  from a high-voltage power supply  13  (bias means). Thereby, a toner image on the intermediate transfer belt is secondary-transferred to the sheets S passing between the secondary transfer roller  12  and the intermediate transfer belt.  
         [0042]     The sheets S to which a toner image is transferred are sent to a fixing device  18 . In the fixing device  18 , the above sheets S are thermally pressured and the toner image is fixed on the sheets S as a permanent fixed image.  
         [0043]     The sheets S to which an image is fixed by the fixing device  18  are discharged to a discharge tray  19  at the outside of the fixing device  18  from the fixing device  18 .  
         [0000]     (2) Fixing Device (Image Heating Apparatus)  18   
         [0044]      FIG. 2  is an enlarged crossing side schematic view of an essential portion of the fixing device  18  and  FIG. 3  is an enlarged longitudinal front schematic view of the fixing device  18  whose middle portion is omitted. For apparatus component members in the following description, a longitudinal direction or horizontally long denotes a direction orthogonal to the moving direction of a recording material in a recording-material conveying face. Width direction or width denotes the moving direction of a recording material.  
         [0045]     In the fixing device  18 , a film assembly  31  as a heating member (a fixing member) and a pressure roller  32  serving as a backup member are arranged in vertically parallel between right and left side plates  34  of an apparatus frame  33 .  
         [0046]     The pressure roller  32  is constituted of a cored bar  32   a  and an elastic layer  32   b  of silicone rubber or fluorocarbon rubber formed like a roller concentrically in the hell around the cored bar. It is also possible to form a mold release layer of PFA, PTFE or FEP on the elastic layer  32 . In the case of this pressure roller  32 , both edge surfaces of the cored bar  32   a  are rotatably supported between right and left side plates  34  of the apparatus frame  33  through a bearing member  35 . Reference character G denotes a drive gear fixed to one edge surface of the cored bar  32   a  of the pressure roller. A torque is transferred to the drive gear G from a not-illustrated driving mechanism portion and the pressure roller  32  is rotated.  
         [0047]     The film assembly  31  is an assembly of a flexible sleeve  36  serving as a flexible rotor, guide member  37  for guiding the flexible sleeve from the inside, ceramic heater  38  (hereafter referred to as heater) serving as heating means for heating the flexible sleeve  36 , reinforcement stay (fixing stay)  39  and right and left fixing flanges  40  serving as regulation members for regulating the generatrix (thrust) directional movement of the flexible sleeve  36 .  
         [0048]     In the case of this embodiment, as shown by the layer configuration schematic view in  FIG. 4 , the flexible sleeve  36  is flexible and constituted of a metallic film layer  36   a , elastic layer  36   b  and mold release layer  36   c  from the inside toward the outside. The heat capacity of the flexible sleeve  36  for unit area is approx. 0.1 J/cm 2 ·K.  
         [0049]     The guide member  37  is a horizontally long member having a tub shape with a generally semicircular cross section and having rigidity, heat resistance, and heat insulating property, and is formed of liquid-crystal polymer, phenol resin, PPS or PEEK. The guide member  37  serves as a rotational guide of the flexible sleeve  36  loosely outer-fitted to the guide member  37 . Moreover, the guide member  37  also serves as a heater holder for heat-insulating and holding the heater  38 . Furthermore, the guide member  37  serves as a pressure member.  
         [0050]     The heater  38  has a high-insulating and preferable heat-conductive ceramic substrate such as alumina or aluminum nitride (AlN) or high heat-resistant resin substrate of polyimide, PPS or liquid-crystal polymer as a heater substrate. Moreover, a current-carrying heat-generating resistor layer made of silver palladium (Ag/Pd), RuO 2  or Ta 2 N is formed like a line or thin band having a thickness of approx. 10 μm and a width of approx. 1-5 mm through screen printing or the like on the surface of the heater substrate along the longitudinal direction. The heater  38  is set along the longitudinal direction of the guide member below the guide member  37 . The temperature of the heater  38  quickly rises when power is supplied from a not-illustrated power feed portion to the current-carrying heat-generating resistor layer. Then, the heater temperature is detected by a not-illustrated temperature sensor and supply of power from the power feed portion to the current-carrying heat-generating resistor layer is controlled so that the heater is maintained at a predetermined temperature by a control portion (not illustrated).  
         [0051]     The reinforcement stay  39  is a horizontally-long rigid member having a U-shaped cross section.  
         [0052]     Then, the flexible sleeve  36  is loosely applied to the outside of the guide member  37  to whose lower face the heater  38  is set and the reinforcement stay  39  is inserted into the guide member  37 . Right and left fixing flanges  40  are fitted to right and left outward extension arm portions  39   a  of the reinforcement stay  39 . Thus, the film assembly  31  is assembled.  
         [0053]      FIG. 5  is a perspective view of the fixing flange  40  at one edge surface and right and left outward extension arm portions  39   a  of the reinforcement stay  39 .  
         [0054]     The film assembly  31  is set to the upper side of the pressure roller  32  in substantial parallel with the pressure roller  32  with the heater  38  side facing down to set the film assembly  31  between right and left side plates  34  of the apparatus frame  33 . In the case of the right and left fixing flanges  40 , the longitudinal groove portions  40   a  set to the right and left flanges  40  are engaged with longitudinal marginal portions  34   b  of longitudinal guide slits  34   a  set to the right and left side plates  34  of the apparatus frame  33  (refer to  FIG. 6 ).  
         [0055]     Then, a pressure spring  42  is set between pressure portions  40   b  of the right and left fixing flanges  40  and the pressure arm  41 . Thereby, the heater  38  is pressured at a predetermined pressure against the upper face of the pressure roller  32  at both sides of the flexible sleeve  36  through the right and left fixing flanges  40 , the reinforcement stay  39  and the guide member  37 . The fixing nip portion (nip portion) N having a predetermined width is formed by the pressure because the heater  38  is pressure-welded to the upper face of the pressure roller  32  at both sides of the flexible sleeve  36  against the elasticity of the flexible sleeve  36  and elasticity of the pressure roller  32 . In the case of the fixing nip portion N, the flexible sleeve  36  is held between the heater  38  and the elastic pressure roller  32  and bent in accordance with the flat face at the lower face of the heater  38  and the inside of the flexible sleeve  36  closely contacts with the flat face at the lower face of the heater  38 .  
         [0056]     Thus, a torque is transferred to the drive gear G of the pressure roller  32  from a not-illustrated driving mechanism portion and the pressure roller  32  is rotated at a predetermined speed clockwise in  FIG. 2 . A torque acts on the flexible sleeve  36  in accordance with the friction force between the pressure roller  32  and the flexible sleeve  36  at the fixing nip portion N in accordance with the rotation of the pressure roller  32 . Thereby, the inside of the flexible sleeve  36  rotates by following the rotation of the pressure roller  32  counterclockwise in  FIG. 2  around the guide member  37  while closely contacting with and sliding on the lower face of the heater  38  (pressure roller driving type).  
         [0057]     In the case of the fixing device of this embodiment, the above heater  38  is set inside the flexible sleeve  36  serving as a rotor, and is a sliding member for forming the nip portion together with the pressure roller  32  serving as a pressure member at both sides of the flexible sleeve  36 .  
         [0058]     When the flexible sleeve  36  is rotated in accordance with the rotation of the pressure roller  32 , the heater  38  is turned on, the heater temperature is raised to a predetermined temperature and the temperature is controlled, the sheet S serving as a recording material is introduced. That is, the sheet S bearing unfixed toner image t is introduced between the flexible sleeve  36  of the fixing nip portion N and the pressure roller  32  and the toner-image bearing side of the sheet S closely contacts with the outer face of the flexible sleeve  36  at the fixing nip portion N and the fixing nip portion N is held and conveyed together with the flexible sleeve  36 . In this holding and conveying process, the sheet S is heated by the heat of the flexible sleeve  36  heated by the heater  38  and the unfixed toner image t on the sheet S is heated and pressured on the sheet S and melted and fixed. The sheet passing through the fixing nip portion N is curvature-separated from the face of the flexible sleeve  36  and discharged and conveyed.  
         [0000]     (3) Fixing Flange  40   
         [0059]     The pressure roller  32  and flexible sleeve  36  to be set to the fixing device are not always parallel to each other but a crossing angle may be present between the two due to a tolerance for fabrication. For example, component tolerances of right and left pressure springs  41  are also one of the causes of generating the crossing angle and lead to the imbalance between right and left pressures applied to the fixing nip portion and a crossing angle arises between the pressure roller  32  and the flexible sleeve  36 . When fabricating components used for the fixing device and assembling these components, various tolerances are overlapped other than the component tolerance of the pressure spring  41 . Therefore, a crossing angle easily arises between the flexible sleeve  36  and the pressure roller  32  and a phenomenon (lateral shift) arises in which the flexible sleeve  36  rotates and slowly moves in the thrust direction due to the crossing angle. The lateral shift of the flexible sleeve  36  is received by the regulation surface A of a edge part (an edge surface) of the flexible sleeve of the fixing flange  40  to regulate the flexible sleeve position in the generatrix direction of the flexible sleeve.  
         [0060]     The case of a conventional fixing flange  40  is described below by referring to FIGS.  11  to  14 . In the case of the conventional fixing flange  40 , the edge part regulation surface A is plane as shown in  FIG. 11 . The edge part regulation surface A is not set nearby the fixing nip portion in the sleeve circumferential direction but it is set to an area farthest from the fixing nip portion. The portion of the fixing flange  40  corresponding to the vicinity of the sleeve-circumference-directional nip portion is more concaved than the regulation surface A as shown in  FIG. 11B  so that it does not contact with the flexible-sleeve edge surface E (refer to  FIG. 12 ). This is because the flexible sleeve  36  is strongly constrained by the nip portion formed by the pressure roller  32  and heater  38  at the nip portion but it has no flexibility. Therefore, when the flexible sleeve  36  is pressed against the flange  40  at this portion, a local deforming stress arises and edge-surface breakdown of the sleeve easily occurs.  
         [0061]     By the above reason, the flange  40  has the regulation surface A in only a portion facing a circular-arc area opposite to the fixing nip portion when almost halving the circular edge surface E on a virtual plane almost parallel with the face of the fixing nip portion N, that is, a circular-arc area farthest from the fixing nip portion in the sleeve circumference direction in the edge-surface E (circular) of the flexible sleeve  36 .  
         [0062]     However, there is a case in which not only a crossing angle to the pressure roller  32  of the flexible sleeve  36  but also the curvature of the reinforcement stay  39  due to the pressure of the pressure spring  42  or tilt of the fixing flange  40  may be present. In this case, it is found that a range in which the edge part regulation surface A contacts with the sleeve edge surface E is narrow and local as shown in  FIGS. 12, 13 , and  14  and edge-surface breakdown of the sleeve may occur.  FIG. 12  shows a state in which the reinforcement stay  39  is deflected by the force of the pressure spring  42 . Under this state, the edge surface E of the sleeve  36  and regulation surface A of the flange  40  become a state close to point contact.  FIG. 13  is an illustration viewed from the direction of the arrow V 1  in  FIG. 12 .  FIG. 14  shows a state in which the sleeve  36  does not vertically contact with the regulation surface A of the flange  40  because the crossing angle θ is present between the flexible sleeve  36  and the pressure roller  32  when viewed from the direction of the arrow V 1  in  FIG. 12 .  
         [0063]     Then, a mechanism is described in which edge-surface breakdown of the flexible sleeve  36  occurs.  
         [0064]     As described above, because of the crossing angle between the flexible sleeve  36  and the pressure roller  32 , a force approaching to the generatrix direction to the flexible sleeve  36  is generated and the flexible sleeve  36  is sent to right or left generatrix direction while rotating. The flexible sleeve  36  contacts with the planar edge part regulation surface A of the fixing flange  40  shown in  FIG. 11 , generatrix-directional movement stops and flexible sleeve  36  continuously rotates while receiving a certain force from the contact face.  
         [0065]      FIG. 12  shows an illustration in which the fixing flange  40  fitted and fixed to the reinforcement stay  39  due to the curvature of the reinforcement stay  39  tilts from the flexible sleeve  36  and under this state, the flexible sleeve  36  rotates while receiving a certain force F from the edge part regulation surface A. In this case, when the fixing flange  40  tilts as shown in  FIG. 12 , the planar edge part regulation surface A tilts, the contact between the flexible sleeve  36  and the edge part regulation surface A becomes local as shown in  FIG. 12  and contacts in the circumferential direction at a minute length.  
         [0066]      FIG. 13  viewed from the V 1  direction in  FIG. 12  shows a state in which the regulation surface A of the flange locally contacts with two places of the edge surface of the flexible sleeve  36 . When a force acting in the thrust direction of the flexible sleeve  36  is locally received by the regulation surface A, apprehensiveness that the flexible-sleeve edge surface is broken increases.  
         [0067]     Moreover,  FIG. 14  shows a contact state between the flexible sleeve  36  and the edge part regulation surface A when a crossing angle occurs between the flexible sleeve  36  and the pressure roller  32 . In  FIG. 13 , the flexible sleeve  36  contacts with the edge part regulation surface A at two places. However, because the flexible sleeve  36  tilts from the pressure roller  32 , the number of contact places becomes one. Therefore, a local internal stress arises at the sleeve edge surface compared to the case of  FIG. 13  and apprehensiveness of edge-surface breakdown of the flexible sleeve  36  increases.  
         [0068]     Moreover, also when the fixing flange  40  tilts from the longitudinal direction of the pressure roller due to assembling backlash of the fixing flange  40 , pressure is locally received at one point similarly to the case of  FIG. 14  (illustration is omitted).  
         [0069]     Therefore, this embodiment uses a configuration in which a local force does not easily act by curving the flexible-sleeve edge part regulation surface A of the fixing flange  40  like a circular arc (convex curved surface to flexible sleeve edge surface).  
         [0070]     That is, the edge part regulation surface A of the fixing flange  40  is formed like a circular arc as shown in FIGS.  5  to  10 . The flange is different from that shown in  FIG. 11  only in the shape of the regulation surface A.  
         [0071]      FIG. 7A  is a perspective view of the fixing flange  40 , showing edge part regulation surface A curved like a circular arc, contactable width w, and curved value d.  FIG. 7B  shows that the edge part regulation surface A is a part of the surface of an elliptic cylinder. That is,  FIG. 7B  shows that the shape of the edge part regulation surface is a part of a circular cylinder or elliptic cylinder almost vertically standing on a recording-sheet passing face (virtual plane including nip portion).  FIG. 7C  shows a cross section Pf obtained by cutting the regulation surface at a plane P (plane parallel with virtual plane) almost parallel with the face of the nip portion N shown in  FIG. 7B . That is,  FIG. 7C  shows that the cross section obtained by cutting the edge part regulation surface A at virtual plane almost parallel with the nip portion N is a part of the circumferential face of the circle B or ellipse C. The circular arc of the edge part regulation surface A shown by the cross section is approximate to a part of the ellipse C or circle B as shown in  FIG. 7C  and is constituted so as to coincide with a state when diagonally viewing the flexible sleeve  36 . Thus, the regulation surface A of the regulation flange (regulation member)  40  has a curved-surface area in which a line when cutting the regulation surface A at a virtual plane substantially parallel with the nip portion N becomes a curved line inflated toward the edge surface E of the flexible sleeve  36 . Moreover, the regulation surface A of the regulation flange  40  has a curved-surface area whose generatrix direction intersects with a virtual plane including the nip portion N.  
         [0072]     By using this configuration, even when the reinforcement stay  39  is curved and the fixing flange  40  tilts as shown in  FIGS. 8 and 9  or the flexible sleeve  36  has a crossing angle from the pressure roller  32  as shown in  FIG. 10 , it is possible to widen the contact range between the sleeve edge surface E and the regulation surface A. Therefore, the risk that the flexible sleeve  36  locally receives a stress decreases and it is possible to avoid the local deformation of flexible sleeve edge surface and prevent edge surface breakdown from occurring.  
         [0073]     Therefore, to set the curved value, experiments are performed. Table 1 shows experiment results.  
                                             TABLE 1                                       Number of durable               sheets reaching           Curved value d   edge part           (mm)   breakdown                                        Contactable   0   30k to 50k           width w = 20 (mm)   0.1    70k to 120k               0.2   200k to 250k               0.3   150k to 200k               0.4   100k to 150k                      
 
         [0074]     Table 1 shows a relation between the curved value d when setting the contactable width w to 20 mm and the service life of a fixing device until reaching edge part destruction of a sleeve. Reference characters w and d denote the lengths shown in  FIGS. 7A  to  7 C. To clarify the effect by an experiment, the curved value of the reinforcement stay  39 , tilt of the fixing flange  40 , and crossing angle with the pressure roller  32  of the flexible sleeve  36  are set to values larger than those of a product fabricated in accordance with the normal quality standard.  
         [0075]     From these results, it is clarified that a configuration curved like a circular arc realizes a more preferable service life to edge part destruction than a case where the edge part regulation surface A is a plane. However, a curved value depends on one of the contactable range w and curved value d, contour of the flexible sleeve  36 , deflection value of the reinforcement stay  39  due to pressure of a pressure spring and crossing angle with the pressure roller  32  generated in the flexible sleeve  36  and changes in accordance with one of these conditions. Moreover, when the curve value is too large, it is shown that the durability of a sleeve may lower and is excluded from values shown in this table.  
         [0076]     Moreover, it is shown by an embodiment that the edge part regulation surface A is a part of the surface of a circular cylinder or elliptic cylinder. However, the edge part regulation surface A can be applied to a part of a conical surface and a part of a spherical surface. Also in the case of these shapes, the regulation surface A of the regulation flange (regulation member)  40  has a curve-surface area in which a line when the regulation surface A is cut at a virtual plane almost parallel with the nip portion N becomes a curved line inflated toward the edge surface E of the flexible sleeve  36 .  
         [0077]     Moreover, in the case of the above embodiment, the flexible sleeve  36  uses a sleeve having a heat capacity for unit area of approx. 0.1 j/cm 2 ·K. However, the flexible sleeve  36  is not restricted to the above sleeve. It is also possible to use a polyimide film having a very small heat capacity (for example, thickness of 50 μm and heat capacity for unit area of 0.01 J/cm 2 ·K). Also in this case, it is possible to realize a long service life to sleeve edge part destruction.  
         [0000]     [Others] 
         [0078]     (1) The heating Means  37  for heating the flexible sleeve  36  serving as a rotor is not restricted to the ceramic heater of the above embodiment. It is also allowed to use heating means using a nichrome wire, electromagnetic-induction exothermic member such as an iron piece, or PTC exothermic body. It is not always necessary to set the heating means  37  to the fixing nip portion N. The flexible rotor  35  can be heated by optional heating means from the inside or outside of the rotor  35 . It is also possible to constitute the flexible rotor  35  itself so as to generate heat through electromagnetic induction.  
         [0079]     (2) The pressure-rotor  32  serving as a pressure member is not restricted to a roller. It is also possible to use a rotating endless belt.  
         [0080]     (3) An image heating apparatus of the present invention is not restricted to use as the image heating-fixing device of the embodiment. The image heating apparatus is also effective as a temporary fixing device for temporarily fixing an unfixed image to a recording material or image heating apparatus such as a surface reforming apparatus for reforming the image surface property such as luster by reheating a recording material bearing a fixed image. Moreover, it is a matter of course that the image heating apparatus is also effective as a heating apparatus for heating a member to be heated such as a heat press apparatus for removing creases from paper currency, heat laminate apparatus, heating drying apparatus for evaporating moisture from paper currency, or drying heating apparatus used for an ink-jet printer.  
         [0081]     The present invention is not restricted to the above embodiment but it includes modifications within technical idea.  
         [0082]     This application claims priority from Japanese Patent Application No. 2005-117199 filed Apr. 14, 2005, which is hereby incorporated by reference herein.