Patent Publication Number: US-2011070005-A1

Title: Cylindrical heating element and fixing device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This invention is based on Japanese patent application No. 2009-216711 filed in Japan on Sep. 18, 2009, the entire content of which is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a heating element which can be used as a rotating member for heating or a part thereof in a fixing device employed in an image forming device operated by an electrophotographic system, electrostatic recording system and other systems, that is, a fixing device which fixes, on a recording medium such as a recording paper sheet, a toner image formed in an image forming portion of the image forming device and transferred onto the recording medium by passing the recording medium (on which an unfixed toner image is held) through a nip formed by the rotating member for heating and a rotating member for pressurizing which is pressed against the rotating member for heating with heating under pressure, and further to a fixing device using such a cylindrical heating element. 
     2. Description of Related Art 
     Fixing devices employed in image forming devices operated by the electrophotographic system, electrostatic recording system or like system generally comprise a rotating member for heating  91  and a rotating member for pressurizing  92  which is pressed against the rotating member for heating  91 , as shown in  FIG. 22  as an example. 
     The rotating member for heating  91  is usually constituted by providing an elastic material layer  912  made of elastic material such as a silicon rubber around a hollow metal shaft  911  and disposing a heater H such as a halogen lamp heater inside the metal shaft  911 . The elastic material layer  912  is covered with a fluorine-based wear-resistant film  913  in some cases. 
     The rotating member for pressurizing  92  is formed by providing an elastic material layer  922  around a shaft  921 . The elastic material layer  922  is covered with a fluorine-based wear-resistant film  923  in some cases. 
     This type of fixing device is described in Japanese Unexamined Patent Publication Nos. H05-158369 (JP05-158369,A) and H05-210336 (JP05-210336,A). 
     However, in the above-mentioned conventional fixing device, the hollow metal shaft  911  having the heater H incorporated therein for the rotating member for heating  91  has large heat capacity because it is thickly formed so that it has sufficient strength as the shaft for the rotating member and for other reasons. Therefore, according to the heat-source portion comprising the hollow metal shaft  911  having the heater H incorporated therein, it takes much time to heat the surface of the rotating member for heating  91  to a temperature at which the toner image is fused with heating and is fixed onto the recording medium (a so-called warm-up time is long), and therefore it has been difficult to meet the demand for shortening the warm-up time of fixing devices for the ease of use of the devices and thus of image forming devices, and the recent demand for energy saving. 
     SUMMARY OF THE INVENTION 
     A first object of the present invention is to provide a heating element with high heating efficiency which can be utilized as a heat source for a rotating member for heating in a fixing device which is employed in an image forming device operated by an electrophotographic system, electrostatic recording system or like system, and passes a recording medium on which an unfixed toner image is held through a nip formed by the rotating member for heating and a rotating member for pressurizing which is pressed against the rotating member for heating to fix the toner image onto the recording medium with heating under pressure. 
     A second object of the present invention is to provide a fixing device which is employed in an image forming device operated by an electrophotographic system, electrostatic recording system or like system, and passes a recording medium on which an unfixed toner image is held through a nip formed by a rotating member for heating and a rotating member for pressurizing which is pressed against the rotating member for heating to fix the toner image on the recording medium with heating under pressure, the fixing device being capable of quickly and efficiently heating the rotating member for heating to a temperature at which the toner image can be fixed, compared with a conventional fixing device which employs a heat source comprising a hollow metal shaft having a heater incorporated therein as a heat source for a rotating member for heating, so that it can meet the demand for a reduced warm-up time of the fixing device for the ease of use of the fixing device and thus of the image forming device, and the recent demand for energy saving. 
     In order to achieve the first object, one aspect of the present invention provides a cylindrical heating element comprising: 
     a cylindrical member; and 
     a metallic pattern being capable of generating heat by being electrified provided on at least one of inner and outer circumferential surfaces of the cylindrical member. 
     In order to achieve the second object, another aspect of the present invention provides a fixing device which passes a recording medium on which an unfixed toner image is held through a nip formed by a rotating member for heating and a rotating member for pressurizing which is pressed against the rotating member for heating to fix the toner image on the recording medium with heating under pressure, the rotating member for heating comprising the above-mentioned cylindrical heating element. 
     The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments when taken in conjunction with accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1(A)  is a perspective view of an example of a cylindrical heating element, and  FIG. 1(B)  is a perspective view of a state that an electric insulation film which covers a metallic pattern has been removed in the cylindrical heating element shown in  FIG. 1(A) . 
         FIG. 2  is a front view of an example of a fixing device. 
         FIG. 3  is a perspective view of another example of a cylindrical heating element. 
         FIG. 4  is a view showing another example of a fixing device. 
         FIG. 5  is a view showing still another example of a fixing device. 
         FIG. 6  is a front view of still another example of a cylindrical heating element. 
         FIG. 7(A)  is a perspective view of an example of a flexible resin sheet on which a metallic pattern is formed;  FIG. 7(B)  is a perspective view which shows how the resin sheet is wound on a roll; and  FIG. 7(C)  is a view which shows how a rolled resin sheet is inserted into a cylindrical member and adhered onto its inner circumferential surface. 
         FIG. 8  is a view showing an example of a heating roller for a fixing device, including a cylindrical heating element formed by the technique shown in  FIGS. 7(A) to 7(C) . 
         FIG. 9  is a view showing a modification to the heating roller of  FIG. 8 . 
         FIG. 10  is a view showing still another example of a fixing device. 
         FIG. 11  is a perspective view of an example of a flexible resin sheet on which metallic patterns are divisionally formed. 
         FIG. 12(A)  is a perspective view of another example of a flexible resin sheet on which a metallic pattern is formed;  FIG. 12(B)  is a view showing how the resin sheet is adhered on an outer circumferential surface of a cylindrical member; and  FIG. 12(C)  is a sectional view which shows an example of a heating roller for a fixing device, including a cylindrical heating element formed by the technique of  FIGS. 12(A) and 12(B) . 
         FIG. 13  is a sectional view of still another example of a heating roller. 
         FIG. 14  is a view showing still another example of a fixing device. 
         FIG. 15  is a front view of still another example of a fixing device. 
         FIG. 16(A)  is a sectional view of a part of a power supplying device to the heating roller in the fixing device shown in  FIG. 15 , and  FIGS. 16(B) and 16(C)  are views which show first and second portions of the power supplying device seen from direction X and direction Y in  FIG. 15 , respectively. 
         FIG. 17  is a schematic perspective view of still another example of a cylindrical heating element. 
         FIG. 18  is a view showing an example of a flexible resin sheet on which resistive patterns for detecting temperature are formed. 
         FIG. 19  is a view showing an example of a heating roller for fixing devices, including the cylindrical heating element in  FIG. 17 . 
         FIG. 20  is a view showing another example of a flexible resin sheet on which resistive patterns for detecting temperature are formed. 
         FIG. 21  is a view showing still another example of a heating roller for fixing devices. 
         FIG. 22  is a view showing an example of conventional fixing devices. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention will be described below. 
     Cylindrical heating elements of the embodiments of the present invention include the following cylindrical heating element. 
     &lt;Cylindrical Heating Element&gt; 
     A cylindrical heating element comprising: 
     a cylindrical member; and 
     a metallic pattern provided on at least one of inner and outer circumferential surfaces of the cylindrical member and being capable of generating heat by being electrified. 
     Fixing devices of the embodiments of the present invention include the following fixing device. 
     &lt;Fixing Device&gt; 
     A fixing device which passes a recording medium on which an unfixed toner image is held through a nip formed by a rotating member for heating and a rotating member for pressurizing which is pressed against the rotating member for heating to fix the toner image onto the recording medium with heating under pressure, and the rotating member for heating comprising a cylindrical heating element according to the present invention. 
     In this fixing device, any of the following cases is included in the mode of pressing the rotating member for pressurizing against the rotating member for heating.
     (1) The case where the rotating member for pressurizing whose rotation shaft is movable is pressed against the rotating member for heating whose rotation shaft is in place,   (2) On the contrary, the case where the rotating member for heating whose rotation shaft is movable is pushed with respect to the rotating member for pressurizing whose rotation shaft is in place, whereby the rotating member for pressurizing is pushed relatively toward the rotating member for heating,   (3) The case where the rotating member for heating and the rotating member for pressurizing are pressed against each other, whereby the rotating member for pressurizing is relatively pressed against the rotating member for heating.   

     The cylindrical heating element can be utilized as a heat source or the like of a rotating member for heating in a fixing device which is employed in an image forming device operated by an electrophotographic system, electrostatic recording system or like system, and passes a recording medium on which an unfixed toner image is held through a nip formed by the rotating member for heating and a rotating member for pressurizing which is pressed against the rotating member for heating to fix the toner image on the recording medium with heating under pressure. 
     Furthermore, the cylindrical heating element is, for example, a heating element for constituting at least a part of the rotating member for heating of a fixing device which passes the recording medium on which the unfixed toner image is held through a nip formed by the rotating member for heating and the rotating member for pressurizing which is pressed against the rotating member for heating to fix the toner image on the recording medium with heating under pressure. 
     In any case, the cylindrical heating element has, provided thereon, the metallic pattern being capable of generating heat by being electrified on at least one of the inner and outer circumferential surfaces of the cylindrical member. Therefore, heat can be efficiently generated directly from the metallic pattern by supplying the metallic pattern with electric current (in other words, by supplying an electric power to the metallic pattern), and the cylindrical member can be formed to have low heat capacity, whereby heat can be generated from the entire cylindrical heating element including the metallic pattern and the cylindrical member provided with the same with high efficiency, and energy saving can be achieved accordingly. 
     Since the above-mentioned fixing device comprises the rotating member for heating having the cylindrical heating element which can efficiently generate heat, it can quickly and efficiently heat the rotating member for heating to a temperature at which the toner image can be fixed, compared with a conventional fixing device which employs a heat source comprising a hollow metal shaft having a heater incorporated therein as a heat source for the rotating member for heating. Therefore, it can meet the demand for a reduced warm-up time of the fixing device for the ease of use of the fixing device and thus of the image forming device, and the recent demand for energy saving. 
     In the cylindrical heating element, the metallic pattern may be provided directly on at least one of the outer and inner circumferential surfaces of the cylindrical member. 
     In this case, the cylindrical member may be formed of, for example, a heat-resistant resin (e.g., a phenol-based resin, a polyimide-based resin and like thermosetting resin), but may be also formed of, for example, a metal such as nickel, iron and copper. When a cylindrical member made of a conductive metal is employed as the cylindrical member, for example, the cylindrical member may have an electric insulation film (e.g., a polyimide-based film, etc.) on a circumferential surface thereof on which the metallic pattern is to be provided may be employed. The metallic pattern may be covered with an electric insulation film (e.g., a polyimide film, a varnish such as a polyimide-based varnish, etc.) from the side opposite to the circumferential surface of the cylindrical member. 
     The metallic pattern may be provided by disposing a flexible resin sheet with the metallic pattern being capable of generating heat by being electrified formed on a surface of the sheet on at least one of the outer and inner circumferential surfaces of the cylindrical member. The mode of disposition of the flexible resin sheet with the metallic pattern formed thereon onto the circumferential surface of the cylindrical member may be attachment using an adhesive (including sticky materials), or simple disposition or others not by an adhesion or the like as long as it causes no inconvenience. 
     The flexible resin sheet in this case may be also made of a heat-resistant resin, as an example of other possible cases. Examples of such a resin sheet include a sheet made of a thermosetting resin such as a polyimide-based resin. 
     In addition, the adhesive employed in the case where the resin sheet provided with the metallic pattern is adhered onto the circumferential surface of the cylindrical member may be also a heat-resistant adhesive. For example, epoxy-based adhesives and polyimide-based adhesives having heat resistance can be used. 
     The metallic pattern formed on the resin sheet may be covered with an electric insulation film (a polyimide-based film and a varnish such as a polyimide-based varnish) from the side opposite to the sheet. 
     In order that the cylindrical heating element is used as at least a part of a rotating member for heating of a fixing device, the cylindrical member provided with the metallic pattern may be a cylindrical member incorporated into an elastic material layer (elastic material cylinder) [e.g., an elastic material layer (elastic material cylinder) made of a silicon resin] (in other words, a cylindrical member having an elastic material layer attached on an outer circumferential surface of the cylindrical member), and the elastic material layer may be further covered with a wear-resistant film such as a fluorine-based resin film. In addition, the elastic material layer may contain heat conductive particles (e.g., carbon particles and metal particles such as nickel particles) mixed thereinto to achieve uniform heat distribution. In any case, the cylindrical member may also contain heat conductive particles mixed thereinto to achieve uniform heat distribution. 
     In order that the cylindrical heating element is used as at least a part of a rotating member for heating of a fixing device, the cylindrical member provided with the metallic pattern may be a cylindrical member which fits onto the elastic material layer (elastic material cylinder) [e.g., an elastic material layer (elastic material cylinder) made of a silicon resin] (in other words, a cylindrical member having an elastic material layer attached on an inner circumferential surface of,the cylindrical member). When the elastic material layer is provided on the inner circumferential surface side of the cylindrical member in such a manner, the elastic material layer may be attached onto a core (e.g., a core functioning as a rotation shaft rod). 
     In order for the cylindrical heating element to be used as at least a part of a rotating member for heating of a fixing device, the cylindrical member provided with the metallic pattern may have an engaging portion which is formed at an end portion of the cylindrical member and can be engaged with a rotary drive portion of a rotary drive mechanism. 
     In order for the cylindrical heating element to be used as at least a part of a rotating member for heating, the metallic pattern may be divided into a plurality of patterns for providing a plurality of divided heat generation zones (e.g., a heat generation zone for A4-sized recording medium and heat generation zone for A3-sized recording medium). 
     In any case, examples of materials of the metallic pattern include copper, iron, aluminum and an alloy of two or more metals selected from copper, iron and aluminum. The thickness of the metal line constituting the metallic pattern is, for example, about 12.5 μm to 50 μm. 
     In any case, by selecting the thickness, width and length of the metal line constituting the metallic pattern, selecting the power fed to the metallic pattern and by other means, the temperature of the heat generated by the metallic pattern, and thus the temperature of the heat generated by the cylindrical heating element can be readily controlled. 
     Cylindrical heating elements, fixing devices and other components will be described below with reference to drawings. 
       FIG. 1(A)  is a perspective view of an example of a cylindrical heating element. 
     The cylindrical heating element  1 A in  FIG. 1(A)  comprises a cylindrical member  11   a  and a metallic pattern  12   a  being capable of generating heat by being electrified provided on an outer circumferential surface  111   a  of a cylindrical member  11   a , and the metallic pattern  12   a  is covered with an electric insulation film  13   a .  FIG. 1(B)  is a perspective view of a state that an electric insulation film which covers a metallic pattern has been removed in the cylindrical heating element shown in  FIG. 1(A) . 
     Herein, the term “metallic pattern” means a pattern comprising a metal line which can generate heat by supplying it with an electric current (in other words, an electric power). 
     The metallic pattern  12   a  herein is a pattern comprising a plurality of portions extending parallel to each other in the longitudinal direction of the cylindrical member  11   a  and extending in a zigzag pattern as a whole. 
     Ring-shaped electrode portions  141   a ,  142   a  for receiving electricity, which are electrically continuous with the metallic pattern  12   a , are disposed on the outer circumferential surface at both end portions of the cylindrical member  11   a . In this example, these ring-shaped electrode portions are formed integrally with the metallic pattern, and one end of the metallic pattern  12   a  is connected to one electrode portion  141   a , while the other end of the metallic pattern  12   a  is continuous with the other electrode ring portion  142   a.    
     The electric insulation film  13   a  covers the metallic pattern  12   a  in the area inside the ring-shaped electrode portions  141   a ,  142   a:    
     The ring-shaped electrode portions may be provided separately from the metallic pattern  12   a  and then electrically connected with the metallic pattern  12   a . Silver solder and so-called eyelets may be used as such an electrical connecting means. The ring-shaped electrode portions provided separately from the metallic pattern  12   a  may be reinforcements of the cylindrical member  11   a.    
     At both ends of the cylindrical member  11   a , a pair of engaging portions (engaging recesses)  113   a  which engage with end members  15   a  (see  FIG. 2 ) for rotatably supporting this cylindrical heating element  1 A, which are described later, are formed at each of both ends of the cylindrical member  11   a  at an interval of 180 degrees in central angle. As will be described later, the end member  15   a  to the left in  FIG. 2  is a rotationally driven member, and therefore, in the example in  FIG. 2 , the cylindrical heating element  1 A is a rotationally driven member in the fixing device  2 A. However, when it is used to freely rotate by following the rotation of the rotating member for pressurizing without being driven (e.g., when used as shown in  FIGS. 10 ,  14 , etc.), the engaging portions  113   a  can be marks for alignment, and in some cases, the engaging portions  113   a  can be dispensed with. 
     The fixing device  2 A in  FIG. 2  is a fixing device which can be employed in image forming devices operated by electrophotographic system, electrostatic recording system and other systems. In this example, the fixing device  2 A comprises a rotating member for heating  21   a  (hereinafter referred to as a heating roller  21   a ) in the form of a roller, and a rotating member for pressurizing  22   a  (hereinafter referred to as pressurizing roller  22   a ) in the form of a roller placed opposite to the rotating member for heating  21   a.    
     The heating roller  21   a  uses the cylindrical heating element  1 A in  FIG. 1(A) . That is, the heating roller  21   a  can rotate by fitting the end member  15   a  onto each of the end portions of the cylindrical member  11   a  of the cylindrical heating element  1 A and rotatably supporting a rotation shaft sa of each of the end members  15   a  by a frame Fa. 
     The end member  15   a  comprises an outer disk portion  151  and an inner disk portion  152  having a slightly smaller diameter than the outer disk portion  151  which are stacked integrally in two layers with their centers aligned, and the rotation shaft sa integrally provided to protrude from the center of the outer surface of the outer disk portion  151 . The inner disk portion  152  has a pair of projections  153  on its circumferential surface. Each of the end members  15   a  is attached to an end of the cylindrical member  11   a  at the inner disk portion  152 , and the projection  153  is engaged with the engaging portion  113   a  of the cylindrical member  11   a.    
     The pressurizing roller  22   a  comprises an elastic material layer  222  attached to a rotation shaft  221 . The rotation shaft  221  is rotatably supported by the frame Fa, whereby the entire pressurizing roller  22   a  is rotatably supported by the frame. The elastic material layer  222  of the pressurizing roller  22   a  is pressed against the heating roller  21   a , whereby a nip Na is provided between the heating roller  21   a  and pressurizing roller  22   a.    
     The nip Na is a nip having a width (a length in the direction of passing of the recording medium) required for heating, melting and fixing the unfixed toner image onto the recording medium. 
     The shaft sa of one of the end members  15   a  of the heating roller  21   a  (the left shaft of the member  15   a  in  FIG. 2 ) is connected to a rotary drive mechanism  161  comprising an electric motor (not illustrated), and the heating roller  21   a  can be rotated by the drive mechanism  161 . At this time, one of the end members  15   a  of the cylindrical heating element  1 A of the heating roller  21   a  is a rotational member rotated by the mechanism  161 , and the heating roller  21   a  can be rotated by the rotation of the end member  15   a.    
     The pressurizing roller  22   a  is rotationally driven by the drive mechanism  161  via a transmission mechanism  162  comprising gears and other parts in the direction opposite to the heating roller. 
     In this manner, the heating roller  21   a  and the pressurizing roller  22   a  can be rotated in such a direction that the recording medium is passed through the nip Na. 
     Power supply rollers e 1   a , e 2   a , which are examples of electrode portions for power supply, are in contact with the ring-shaped electrode portions  141   a ,  142   a  attached to the end portions of the cylindrical member  11   a  of the cylindrical heating element  1 A constituting the heating roller  21   a  in a manner of allowing rolling contact. Power supply electrodes which are in sliding contact with the electrode portions  141   a ,  142   a  can be also employed in place of the power supply rollers. 
     The power supply rollers e 1   a , e 2   a  are electrically connected to a variable-output power supply unit PWa. 
     According to the fixing device  2 A described above, the toner image can be fixed onto the recording medium with heating under pressure by supplying an electric power from the power supply unit PWa to the metallic pattern  12   a  of the cylindrical heating element  1 A of the heating roller  21   a  to cause the cylindrical heating element  1 A to generate heat; further raising the temperature of the surface of the heating roller  21   a  to the toner image fixing temperature; rotating the heating roller  21   a  and the pressurizing roller  22   a  by the drive mechanism  161 ; and passing the recording medium on which the unfixed toner image is held (not illustrated in  FIG. 2 ) with the surface of the recording medium on which the unfixed toner image is held facing the heating roller  21   a.    
     The cylindrical heating element  1 A constituting a main part of the heating roller  21   a  is provided with the metallic pattern  12   a  being capable of generating heat by being electrified on the outer circumferential surface of the cylindrical member  11   a . Heat can be efficiently generated directly from the metallic pattern  12   a  by supplying power from the power supply unit PWa to the metallic pattern  12   a . In addition, the cylindrical member  11   a  can be formed to have low heat capacity, whereby heat can be generated from the entire cylindrical heating element  1 A including the metallic pattern  12   a  and the cylindrical member  11   a  provided with the same with high heating efficiency. Accordingly, the temperature of the heating roller  21   a  can be increased to a toner image fixing temperature quickly and efficiently, thereby meeting the demand for reduced warm-up time for the ease of use of the fixing device  2 A and thus of the image forming device and recent demand for energy saving. 
     Although the cylindrical heating element  1 A in  FIG. 1  comprises the metallic pattern  12   a  provided on the outer circumferential surface  111   a  of the cylindrical member  11   a , a metallic pattern may be provided on the inner circumferential surface of the cylindrical member, and metallic patterns being capable of generating heat by being electrified may be provided on both the inner and outer circumferential surfaces of the cylindrical member. 
       FIG. 3  shows a cylindrical heating element  1 B constituted by providing a metallic pattern  12   b  on an inner circumferential surface  112   a  of a cylindrical member  11   a  in a zigzag pattern. The cylindrical member  11   a  in this example is the same as that of the cylindrical heating element  1 A. The metallic pattern  12   b  is covered with an electric insulation film  13   b . Ring-shaped electrode portions  141   b ,  142   b  are provided on the outer circumferential surface at both end portions of the cylindrical member  11   a . The metallic pattern  12   b  is electrically connected to these electrode portions. 
       FIG. 4  shows an example of the fixing device  2 B employed in image forming devices operated by electrophotographic system, electrostatic recording system and other systems. The fixing device  2 B comprises a heating roller  21   b  and the pressurizing roller  22   b  placed opposite to the roller  21   b.    
     The heating roller  21   b  uses the cylindrical heating element  1 B in  FIG. 3 . 
     That is, the heating roller  21   b  is constituted by providing an elastic material layer  211  on the outer circumferential surface  111   a  of the cylindrical member  11   a  of the cylindrical heating element  1 B in the area inside the ring-shaped electrode portions  141   b ,  142   b  while these electrode portions  141   b ,  142   b  are left exposed, covering the surface of the elastic material layer  211  by a wear-resistant film  212 , and further attaching end members (not illustrated) similar to the end members  15   a  shown in  FIG. 2  at both ends of the cylindrical member  11   a  to rotatably support the cylindrical member  11   a  on a frame, which is not illustrated, by a shaft sa protruding from the end members. 
     Although not restrictive, such an elastic material layer  211  can be obtained by, for example, resin molding, and the wear-resistant film  212  can be provided by, for example, covering the layer  211  with a tube made of a wear-resistant material. 
     The pressurizing roller  22   b  is constituted by attaching an elastic material layer  222 ′ on a rotation shaft  221 ′, and is rotatably supported by a frame, which is not illustrated. The pressurizing roller  22   b  is pressed against the heating roller  21   b  so that a nip Nb required for fixing an unfixed toner image T onto a recording medium S is formed. 
     The heating roller  21   b  and the pressurizing roller  22   b  can be driven to rotate by using a drive mechanism and a transmission mechanism similar to those in the case of the fixing device  2 A in  FIG. 2 . 
     Ring-shaped electrode portions  141   b ,  142   b  are formed on the outer circumferential surface at both end portions of the cylindrical member  11   a . These are electrically connected to a metallic pattern  12   b . Power supply roller electrodes e 1   a , e 2   a  are in contact with the electrodes  141   b ,  142   b  in a manner of allowing rolling contact, and these roller electrodes are connected to a variable-output power supply unit, which is not illustrated. 
     According to the fixing device  2 B, the toner image T can be fixed onto the recording medium S with heating under pressure by supplying an electric power to the metallic pattern  12   b  from the power supply unit via the roller electrodes e 1   a , e 2   a  and the ring-shaped electrode portions  141   b ,  142   b  of the cylindrical heating element  1 B of the heating roller  21   b  to cause the cylindrical heating element  1 B to generate heat and further increasing the temperature of the surface of the heating roller  21   b  to the toner image fixing temperature, and rotating the heating roller  21   b  and the pressurizing roller  22   b  to pass the recording medium S holding the unfixed toner image T through the nip Nb. 
       FIG. 5  shows still another example, fixing device  2 C. The fixing device  2 C is constituted by replacing the heating roller  21   b  in the fixing device  2 B with the heating roller  21   c , and is substantially the same as the fixing device  2 B in the other respects. 
     The heating roller  21   c  is constituted by disposing a rotation shaft  213  within the cylindrical member  11   a  of the cylindrical heating element  1 B in  FIG. 3  and providing an elastic material layer  214  on the shaft to support the cylindrical heating element  1 B by the rotation shaft  213  on a frame, which is not illustrated, so that it can be rotatably driven. In the roller  21 C, the engaging portions  113   a  at both end portions of the cylindrical member  11   a  can be dispensed with. 
     When the heating roller  21   c  is employed, the cylindrical member  11   a  of the cylindrical heating element  1 B may be formed thin enough to be deformed so that a nip having a more sufficient width for fixing the toner image is formed in contact rotation between the heating roller  21   c  and the pressurizing roller  22   b.    
     Each of the metallic patterns  12   a ,  12   b  in the cylindrical heating elements  1 A,  1 B described above is a single continuous pattern, and uniformly generates heat throughout the entire of the cylindrical heating element, except both end portions of the cylindrical heating element. 
     However, when the cylindrical heating element is used as at least a part of the rotating member for heating of the fixing device, a heat generation zone or heat generation zones of the heating element may be varied depending on the size of recording medium to achieve energy saving and for other purposes because recording medium of various sizes are applied to the fixing device. 
     A cylindrical heating element  1 C shown in  FIG. 6  is an example of such a cylindrical heating element. The cylindrical heating element  1 C is constituted by providing a zigzag metallic pattern  121   c  on the inner circumferential surface of the cylindrical member  11   a  at the center potion thereof and providing metallic patterns  122   c ,  123   c  having the same zigzag pattern on both sides of the pattern  121   c  on the inner circumferential surface of the cylindrical member  11   a.    
     To one end portion of the outer circumferential surface of the cylindrical member  11   a  are attached the followings: 
     a ring-shaped electrode portion  141   c  electrically connected to one end of the pattern  121   c;    
     a ring-shaped electrode portion  142   c  electrically connected to one end portion of the pattern  122   c ; and 
     a ring-shaped electrode portion  143   c  electrically connected to one end portion of the pattern  123   c.    
     To the other end portion of the outer circumferential surface of the cylindrical member  11   a , a common ring-shaped electrode portion  144   c  electrically connected to the other ends of the patterns  121   c ,  122   c  and  123   c  is attached. 
     In a fixing device which employs a heating roller using this cylindrical heating element, when a A4-size recording medium is passed through the fixing device in londitudinal orientation, only the pattern  121   c  is energized, while when a A3-size recording medium is passed through the fixing device in longitudinal orientation, all of the patterns  121   c ,  122   c  and  123   c  can be energized to generate heat. 
     Formation of the metallic patterns or further the ring-shaped electrode portions formed integrally with the metallic patterns in the cylindrical heating elements  1 A,  1 B,  1 C described above can be performed, for example, by drawing or printing such patterns or electrode potions on at least one of the outer and inner circumferential surfaces of the cylindrical member  11   a  with a conductive paste (e.g., copper paste, silver paste) comprising a metallic material for forming the patterns or electrode portions. 
     As another method, the metallic patterns or electrode portions can be also formed by providing a conductive metal film on at least one of the outer and inner circumferential surfaces of the cylindrical member  11   a  on which the metallic patterns or the electrode portions are to be provided, forming resist patterns corresponding to the metallic patterns or electrode portions to be formed on the metal film, and etching the metal film with the portions covered with the resist left unetched. 
     In any case, the metallic patterns and electrode portions themselves can be formed by pattern formation techniques already known in the field of the formation of printed circuit boards and other devices. 
     The cylindrical heating element can be also produced by the method shown in  FIGS. 7(A) to 7(C) . The basic manufacturing method of the cylindrical heating element shown in  FIGS. 7(A) to 7(C)  is as follows: 
     That is, a heat generating sheet  17 D is formed by forming a metallic pattern  12   d  on a flexible resin sheet  171  (FIG.  7 (A)), and this heat generating sheet  17 D is rolled, inserted into a cylindrical member  172 , and disposed on an inner circumferential surface of the cylindrical member  172  [refer to  FIGS. 7(B) and 7(C) ]. In this example, although not restrictive, the heat generating sheet  17 D is rolled, inserted into the cylindrical member  172 , and adhered onto the inner circumferential surface of the cylindrical member with an adhesive (it may be a sticky material). 
     More specifically, the flexible resin sheet  171  in this example is a sheet having a pair of tongue-shaped pieces  171   d  in an extending manner, and the pair of tongue-shaped pieces  171   d  is integrally provided to extend from a set of parallel side portions  171 ′,  171 ′ of two set of parallel side portions of the sheet  171 . The metallic pattern  12   d  is formed on this sheet  171 , while strip electrode portions (precursors of the ring-shaped electrode portions)  141   d ,  142   d  are formed on areas neighboring to the pattern  12   d . The metallic pattern  12   d  may be covered with an electric insulation film. At this time, the electrode portions  141   d ,  142   d  are left exposed. 
     Meanwhile, a core roll  30  ( FIG. 7(B) ) is prepared by attaching an elastic material layer  32  to a shaft  31 . The heat generating sheet  17 D is wound onto the circumferential surface of the elastic material layer  32  of this core roll with its metallic pattern  12   d  facing inward and with the strip electrode portions  141   d ,  142   d  lying further out than opposite ends of the elastic material layer  32 . Each of the tongue-shaped pieces  171   d  is adhered onto the outer circumferential surface of the side portion (lug portion)  171 ′ of the sheet  171  with an adhesive. In this manner, as shown in  FIG. 8  as an example, a cylindrical heating element  1 D which can be used as a part of a heating roller  21   d  of a fixing device can be obtained. 
     In the cylindrical heating element  1 D, the strip electrode portions  141   d ,  142   d  are rolled to form ring-shaped electrode portions. 
     In addition, the lug portions  171 ′ of the sheet over which the tongue-shaped pieces  171   d  are overlaid in the cylindrical heating element  1 D are located further out than the region through which the recording medium passes in the heating roller  21   d , so that the smoothness of the area through which the recording medium passes is maintained. Furthermore, the portions overlaid in such a manner also serve as a reinforcement of the end portion of the cylindrical heating element  1 D. 
     In the heating roller  21   d  shown in  FIG. 8 , the cylindrical heating element  1 D may be adhered to the elastic material layer  32  of the roller  30 . The cylindrical heating element  1 D may be merely disposed by attachment to the outside of the elastic material layer  32  without being adhered onto the same as long as it causes no inconvenience, e.g., its position is not changed on the roller  30 . The heating roller  21   d  can be rotatably supported on a frame of the fixing device by the roller shaft  31 , and can be used for fixing an unfixed toner image onto a recording medium in combination with a pressurizing roller supported by the frame. At this time, for example, electrodes for power supply e 1   d , e 2   d  can be brought into rolling contact or sliding contact with the rotating ring-shaped electrode portions  141   d ,  142   d , as shown in  FIG. 8 , to electrify the metallic pattern  12   d  via these electrodes and cause the cylindrical heating element  1 D to generate heat, so that the temperature of the heating roller  21   d  can be increased to a toner image fixing temperature. 
     As shown in  FIG. 9 , an elastic material layer  33  can be attached onto the outer circumferential surface of the cylindrical member  172  of the cylindrical heating element  1 D in the heating roller  21   d  in  FIG. 8  (e.g., attached by resin molding), and its surface can be covered with a wear-resistant film  34 . By providing the elastic material layer  33  in such a manner, a sufficient nip contributing to fixing a toner image on a recording medium can be easily obtained between the heating roller  21   d  and a pressurizing roller which is pressed against the roller  21   d.    
     After the cylindrical heating element  1 D is formed by the step shown in  FIGS. 7(A) to 7(C) , the roll  30  can be withdrawn from the heating element  1 D, and the remaining cylindrical heating element  1 D can be used as a part of the rotating member for heating of the fixing device. 
       FIG. 10  shows a schematic constitution of still another example, a fixing device  2 E. The fixing device  2 E is a fixing device which uses a belt-shaped heating rotation member  21   e  constituted by attaching an elastic material layer  33 ′ onto the cylindrical heating element  1 D from which the roll  30  is withdrawn by resin molding or other method, and covering the surface of the layer  33 ′ with a wear-resistant film  34 ′. 
     The rotation belt  21   e  for heating is supported from inside by a rotatable roller Re, and a pressurizing roller  22   e  is pressed against the belt  21   e  in a manner of pinching the belt  21   e  between the roller  22   e  and the support roller Re. The pressurizing roller  22   e  is constituted by attaching an elastic material layer  222 ′ onto a shaft  221 ′, and can be driven to rotate in the counterclockwise direction in  FIG. 10  by a driving mechanism, which is not illustrated. 
     According to the fixing device  2 E, power is supplied from the ring-shaped electrode portions  141   d ,  142   d  and electrode portions for power supply (not illustrated) which are in contact with the ring-shaped electrode portions  141   d ,  142   d  to the metallic pattern  12   d  of the cylindrical heating element  1 D of the belt  21   e  for heating, whereby the heating element  1 D generates heat and the temperature of the belt  21   e  is raised to the fixing temperature. In addition, the pressurizing roller  22   e  is rotationally driven and the belt  21   e  for heating is rotated by following rotation in a state that the belt  21   e  for heating is supported by the support roller Re. 
     By passing a recording medium S retaining an unfixed toner image T through a nip Ne between the rotation belt for heating  21   e  and the pressurizing roller  22   e  in such a state, the toner image can be fixed on the recording medium S. 
     The roller Re may be also rotationally driven. In addition, a pad (not illustrated) which presses the belt  21   e  from inside against the pressurizing roller  22   e  can be also employed in place of the roller Re. At this time, the width of the nip Ne can be changed by selecting the size of the pad. 
     The cylindrical heating elements  1 A,  1 B,  10  described above can be also used as at least a part of a belt for heating by forming the cylindrical member  11   a  thinly enough to be bent. 
     When the cylindrical heating element is pressed to the pressing roller side from inside by a inner roller, pad or the like, in order to make a contact action between the inner roller, pad or the like and the cylindrical heating element smoother, the metallic pattern for heat generation may be provided on the outer circumferential surface of the cylindrical member. When a heat generating sheet provided with the metallic pattern is employed, the heat generating sheet may be disposed on the outer circumferential surface of the cylindrical member. 
     The metallic pattern  12   d  in the cylindrical heating element  1 D is formed of a single continuous line, and uniformly generates heat approximately throughout its entire length. Accordingly, the cylindrical heating element  1 D is uniformly heated except opposite end portions thereof. However, when the cylindrical heating element is used as at least a part of the rotating member for heating of the fixing device, the recording medium passing through the fixing device have various sizes. Therefore, heat generation zone(s) in the cylindrical heating element may be varied depending on the size of the recording medium to achieve energy saving and for other purposes. 
     Examples of the heat generating sheet for providing such a cylindrical heating element include that shown in  FIG. 11 . A heat generating sheet  17 E shown in  FIG. 11  is constituted by providing a metallic pattern  121   d  in a zigzag pattern in a central portion of a flexible resin sheet  171  similar to the resin sheet shown in  FIG. 7(A) , and providing metallic patterns  122   d ,  123   d  in a zigzag pattern at both sides of the pattern  121   d.    
     On the side opposite to the surface on which the metallic patterns are provided at one of the two end portions of the flexible resin sheet  171  are formed a strip electrode portion  141   e  electrically connected to one end portion of the pattern  121   d , 
     a strip electrode portion  142   e  electrically connected to one end portion of the pattern  122   d , and 
     a strip electrode portion  143   e  electrically connected to one end portion of the pattern  123   d . On the side opposite to the surface on which the metallic patterns are provided at the other end portion of the sheet  171  is formed a common strip electrode portion  144   e  electrically connected to the other ends of the patterns  121   d ,  122   d  and  123   d.    
     According to this heat generating sheet  17 E, the cylindrical heating element can be also obtained by rolling this and adhering or merely disposing this at the inner circumferential surface of the cylindrical member or by other means. 
     The cylindrical heating element can be also produced by the method shown in  FIGS. 12(A) to 12(C) . The basic manufacturing method of the cylindrical heating element shown in  FIGS. 12(A) to 12(C)  is as follows: 
     That is, a metallic pattern  12   f  is formed on a flexible resin sheet  171   f  to form a heat generating sheet  17 F (FIG.  12 (A)), and rolling this heat generating sheet  17 F and disposing this on an outer circumferential surface of a cylindrical member  11   a  ( FIG. 12(B) ). At this time, the heat generating sheet  17 F may be adhered to the outer circumferential surface of the cylindrical member  11   a  with an adhesive, or may be merely disposed without adhering, as long as it causes no inconvenience, for example, there is no possibility that the sheet is shifted relative to the cylindrical member. 
     Explained in further detail, the metallic pattern  12   f  is formed on the surface of the flexible resin sheet  171   f  in the shape of a quadrangle shape, and strip electrode portions (precursors of the ring-shaped electrode portions)  141   f ,  142   f  are formed on both outer sides of the pattern  12   f . Thus, the heat generating sheet  17 F is obtained. The metallic pattern  12   f  may be covered with an electric insulation film. At this time, the electrode portions  141   f ,  142   f  are left exposed. 
     This heat generating sheet  17 F is wound onto the outer circumferential surface of the cylindrical member  11   a  and adhered thereto with an adhesive, or securely wound and disposed thereon without adhering. In such a way, the cylindrical heating element  1 F is obtained. In this example, in order to use the heating element  1 F as the rotating member for heating of the fixing device, an elastic material layer  35  is attached to the cylindrical heating element  1 F by resin molding or other means as shown by the broken chain line in  FIG. 12(B) , and as shown in  FIG. 12(C) . The surface of the elastic material layer  35  is covered with a wear-resistant film  36 , such as a wear resistance film tube. 
     As shown in  FIG. 13 , the following constitution may be also employed: an elastic material layer  37  is attached onto the outer circumferential surface of the cylindrical member  11   a ; the heat generating sheet  17 F is wound thereon to form a cylindrical heating element  1 F′; an elastic material layer  35 ′ is attached further thereon. The layer  35 ′ may be covered with a wear-resistant film  36 ′. 
     The heat generating sheet disposed on the outer circumferential surface of the cylindrical member is not limited to that in  FIG. 12(A) , and may be such that is provided with more than one groups of the metallic patterns, such as the heat generating sheet  17 E shown in  FIG. 11 . 
     In any case, the cylindrical member  11   a  is the same as the cylindrical member  11   a  used in the cylindrical heating element  1 A in  FIG. 1 . Therefore, as in the case of the cylindrical heating element  1 A, the cylindrical member can be used as a main portion of the rotating member for heating of the fixing device by attaching end members  15   a  at their both ends or by other means. 
     However, the cylindrical member on which the heat generating sheet is disposed need not be the cylindrical member  11   a , and may be a cylindrical member having no engaging portion  113   a . Its thickness may be also small so that it exhibits flexibility. 
       FIG. 14  shows still another example, a fixing device  2 G. The fixing device  2 G comprises a rotating member for heating  21 G and a pressurizing roller  22 G which is rotated while it is in contact with this rotating member for heating. The rotating member for heating  21 G is constituted by winding a flexible heat generating sheet  17 F shown in  FIG. 12(A)  on an outer circumferential surface of the cylindrical member thinly formed and exhibiting flexibility, and adhering the sheet thereon to form the rotating member  21 G for heating in the form of a belt. 
     The pressurizing roller  22 G is constituted by attaching an elastic material layer  222   g  to a rotation shaft  221   g . The rotation belt for heating  21 G is wound on guide rollers r 1 , r 2 , r 3 , and is pressed by a pad Pd between the guide rollers r 1  and r 2  on the pressurizing roller to form a wide nip Ng between itself and the pressurizing roller  22 G. By passing a recording medium on which an unfixed toner image is retained through this nip Ng, the toner image can be fixed onto the recording medium. 
       FIG. 15  shows still another example, a fixing device  2 H. The fixing device  2 H comprises a heating roller  21   h  and a pressurizing roller  22   h  pressed against the heating roller  21   h.    
     The heating roller  21   h  is a modification of the heating roller shown in  FIG. 9  mentioned previously. Furthermore, the heating roller  21   h  uses a cylindrical heating element  1 D′ formed by omitting the ring-shaped electrode portions  141   d ,  142   d  at both end portions in the cylindrical heating element  1 D constituting the heating roller  21   d ′ in  FIG. 9 , that is, the cylindrical heating element  1 D constituted by rolling the heat generating sheet  17 D comprising the flexible resin sheet  171  on which the metallic pattern  12   d  is provided and adhering it onto the inner circumferential surface of the cylindrical member  172 . 
     An elastic material layer  33  is attached to the cylindrical member  172  of the cylindrical heating element  1 D′ as in the cylindrical heating element  1 D, and its surface is covered with a wear-resistant film  34 . End members  211   h ,  212   h  are attached to both end portions of the cylindrical member  172 . The end members  211   h ,  212   h  have such a constitution that their disc-like portions are integrally stacked in two layers as the end members  15   a  of the heating roller  21   a  of the fixing device  2 A shown in  FIG. 2 , and the small-diameter disc-like portion is fitted into the end portion of the cylindrical heating element  1 D′. 
     The heating roller  21   h  is rotatably supported on a fixing device frame Fh by a shaft  211   s  protruding from the end member  211   h  and a shaft  212   s  protruding from the end member  212   h.    
     The pressurizing roller  22   h  is constituted by attaching an elastic material layer  222   h  onto the shaft  221   h , and is rotatably supported on the frame Fh and pressed against the heating roller  21   h , forming a nip Nh between itself and the heating roller  21   h.    
     One of the shafts  212   s  of the heating roller  21   h  can be driven to rotate by a rotary drive, which is not illustrated, and the pressurizing roller  22   h  can be driven to rotate by the rotary drive via a transmission mechanism, which is not illustrated. 
     The fixing device  2 H comprises a power supply device  18  which electrify the metallic pattern  12   d  of the cylindrical heating element  1 D′.  FIG. 16(A)  is a sectional view showing an essential part of the power supply device  18 . The device  18  comprises, as shown in  FIGS. 15 and 16(A) , a first portion  181 , and a second portion  182  which is the same as the first portion but facing the first portion  181  symmetrically. 
     The first portion  181  is constituted by disposing a primary coil  181   c  on a disc-like first core member  181 ′ in a manner of winding, while the second portion  182  is constituted by disposing a secondary coil  182   c  on a disc-like second core member  182 ′ in a manner of winding. The core members  181 ′,  182 ′ are formed of a material (which can be a core for an electromagnet), that is, magnetic substance (ferrite in this example). 
     The first portion  181  is supported on a fixedly positioned frame Fh′ by a shaft  181   s  protruding toward opposite to the second portion  182  from the core member  181 ′, and is statically disposed. The shaft  211   s  protruding from the end member  211   h  of the heating roller  21   h  is connected to and fixed on a side opposite to the first portion  181  of the core member  182 ′ of the second portion  182 . In this manner, in a state that the central axes of the first portion  181  and the second portion  182  are aligned, the first portion  181  and the second portion  182  oppose each other at a gap ds between flat planes on which those core members face each other. 
     Although not restrictive, the areas of the portions of the flat planes of the core members are the same in this example. 
       FIG. 16(B)  is a view showing the first portion  181  seen along the direction of arrow X shown in  FIG. 15 , while  FIG. 16(C)  is a view showing the second portion  182  seen along the direction of arrow Y shown in  FIG. 15 . 
     On each of the core member planes opposing each other of the first and second portions  181 ,  182 , a circular groove  180  having the same size as the first and second portions is formed with its center aligned with the center axes of the shafts  181 S,  211   s  and same size, and the coil is wound in this circular groove  180 . 
     The coil  181   c  wound on the core member  181 ′ of the first portion  181  is a primary coil. Both end portions  181   e ,  181   e ′ of this coil are drawn from the first portion  181  opposite to the second portion  182 , and are connected to a variable-output alternating-current power supply unit PWh. 
     The coil  182   c  wound on the core member  182 ′ of the second portion  182  is a secondary coil. Both end portions  182   e ,  182   e ′ of the this coil are drawn from the second portion opposite to the first portion  181  through the second portion  182 , further guided to a hollow portion of the end member shaft  211   s , reaches the inside of the cylindrical heating element  1 D′ through the hollow portion, and are connected to a metallic pattern  12   d.    
     The first portion  181  provided with the primary coil  181   c  and the second portion  182  provided with the secondary coil  182   c  are, so to speak, separating transformers formed by separating a transformer in a middle potion thereof. An induced current flows to the secondary coil  182   c  of the second portion  182  by mutual induction by flowing an alternating current from the power supply unit PWh to the primary coil  181   c , whereby the metallic pattern  12   d  is energized; the cylindrical heating element  1 D′ generates heat; and the temperature of the surface of the heating roller  21   h  is raised to such a temperature at which an unfixed toner image can be fixed onto a recording medium. 
     The temperature control of the heating roller may be performed by detecting the temperature of the surface of the heating roller  21   h  with an appropriate temperature sensor TS such as a thermistor, and adjusting the output of the power supply unit PWh, based on the difference between a detected temperature and a target temperature (e.g., about 180° C.), so that the detected temperature is changed toward the target temperature. 
     In general, the output of the power supply unit PWh is not critical as long as it is an alternating-current power. Examples include currents at frequencies ranging from about 50 Hz to 60 Hz (90V to 240V) from commercial power sources to about 100 kHz. However, employing a high-frequency power enables the first and second portions to be smaller since their volumes, which are affected by the core member and the winding number of the coils, can be reduced. Therefore, in order to reduce the sizes of the first and second portions  181 ,  182  (especially the sizes of the core members  181 ′,  182 ′), and in consideration of power transfer efficiency; the frequency can be controlled, for example, within a range from 1 kHz to 100 kHz. In this example, the frequency can be controlled within a range from 20 kHz to 40 kHz as a more preferably range. 
     The control of the output of the unit PWh may be conducted by varying the duty ratio of waveforms by PWM control. 
     In any case, fine control of the temperature can be performed. 
     Generally speaking, the gap ds between the flat planes of the first and second core members  181 ′,  182 ′ may be, for example, 0.1 mm or more to avoid contact between both members. In addition, although depending on the winding numbers of the primary and secondary coils, the materials of the core member  181 ′,  182 ′ and other conditions, the gap between the flat planes of the first and second core members may be, for example, about 10 mm at most in general, in order to cause the secondary coil  182   c  to generate an induced current which can change the temperature of the surface of the heating roller toward a predetermined temperature. 
     Although depending on the winding numbers of the primary and secondary coils, the materials of the core members  181 ′,  182 ′, and the gap(interval) between the members  181 ′,  182 ′, the proportion of the portion in the flat plane of the first core member  181 ′ which faces the second core member  182 ′ to the entire area of the flat plane (and the proportion of the portion in the flat plane facing the first core member  181 ′ of the second core member  182 ′ to the entire area of the flat plane) maybe, for example,  50 % or higher in general, in order to generate an induced current which can change the temperature of the surface of the heating roller toward a predetermined temperature more securely and efficiently. 
     Inside the cylindrical heating element  1 D′ of the heating roller  21   h  may be provided a supporting elastic material made of a sponge or the like in a position corresponding to the passage area of the recording medium by resin molding or other means. A power supply device similar to the power supply device  18  described above can be also applied, as shown in  FIG. 15 , not only for energization of the metallic pattern  12   d  of the cylindrical heating element  1 D′ of the heating roller  21   h , but also for energization of metallic patterns of other cylindrical heating elements described in this specification and metallic patterns of similar cylindrical heating elements, as long as no inconvenience is caused, for example, in terms of structure. 
       FIG. 17  shows still another example, a cylindrical heating element  1 J. The cylindrical heating element  1 J is constituted by providing a metallic pattern  12   j   1  on the center and metallic patterns  12   j   2 ,  12   j   3  on its both side on the outer circumferential surface of a cylindrical member  11   j , attaching ring-shaped electrode portions  141   j ,  142   j ,  143   j ,  144   j  on the outer circumferential surface of one side of the cylindrical member  11   j , and also providing a resistive pattern for detecting temperature (resistive pattern whose electric resistance varies depending on changes in temperature comprising a conductive line such as copper line) on the inner circumferential surface of the cylindrical member  11   j.    
     Although not illustrated, components on the outer circumferential surface of the cylindrical member are each connected in the following manner: 
     the ring-shaped electrode portion  141   j  is connected to one end of the metallic pattern  12   j   1 ; 
     the ring-shaped electrode portion  142   j  is connected to one end of the metallic pattern  12   j   2 ; 
     the ring-shaped electrode portion  143   j  is connected to one end of the metallic pattern  12   j   3 ; and 
     the ring-shaped electrode portion  144   j  is connected to the other end of the each metallic pattern. 
     The resistive pattern for detecting temperature on the inner circumferential surface of the cylindrical member  11   j  is, but is not limited to, provided as follows in this example: 
     As shown in  FIG. 18 , a central resistive pattern sj 1  is formed and resistive patterns sj 2 , sj 3  are formed on both its sides on one side of a flexible resin sheet  19 ; strip electrode portions  1   s ,  2   s ,  3   s ,  4   s  are formed on one end portion of the other side of the sheet; the resin sheet  19  is rolled with the side on which the resistive patterns are provided facing outside and is inserted into the cylindrical member  11   j  to dispose the sheet on the inner circumferential surface of the cylindrical member  11   j . In this example, the resin sheet  19  is adhered onto the inner circumferential surface of the cylindrical member  11   j  with an adhesive, but it may be merely disposed inside the cylindrical member as long as it causes no inconvenience, e.g., there is no possibility of dispositioning. 
     The resistive patterns sj 1 , sj 2 , sj 3  are all patterns comprising metal line whose electric resistance vary depending on changes in temperature in this example. 
     In a state that the resin sheet  19  is disposed on the inner circumferential surface of the cylindrical member  11   j  in such a manner, the resistive pattern sj 1  corresponds to the metallic pattern  12   j   1 ; the resistive pattern sj 2  to the metallic pattern  12   j   2 ; and the resistive pattern sj 3  to the metallic pattern  12   j   3 . 
     The strip electrode portions  1   s ,  2   s ,  3   s ,  4   s  serve as ring-shaped electrode portions in a state that the resin sheet  19  is rolled and disposed on the inner circumferential surface of the cylindrical member  11   j , which are left exposed. 
     Although not illustrated, on the inner circumferential surface side of the cylindrical member  11   j , 
     the electrode portion  1   s  is connected to one end of the resistive pattern sj 1 ; 
     the electrode portion  2   s  is connected to one end of the resistive pattern sj 2 ; 
     the electrode portion  3   s  is connected to one end of the resistive pattern sj 3 ; and 
     the electrode portion  4   s  is connected to the other end of each resistive pattern. 
     When the cylindrical heating element  1 J is used as a part of a heating roller for fixing devices, a rotatable heating roller  21   j  can be obtained, for example, as shown in  FIG. 19 , by attaching an elastic material layer  41  to the cylindrical heating element  1 J, covering its surface with a wear-resistant film  42 , attaching appropriate end members to the end portions of the cylindrical heating element  1 J, and supporting this on a frame of the fixing device by a shaft. In this case, the end members may be attached at the farther side of these electrode portions  1   s  to  4   s  so that electrodes for detecting the electric resistance can be brought into contact with the ring-shaped electrode portions  1   s  to  4   s  from outside. 
     Depending on the size of the recording medium subjected to fixing of a toner image, at least one of the metallic patterns  12 J 1  to  12 J 3  is electrified by a variable-output power supply unit (not illustrated) via some of the electrodes for power supply (not illustrated) and the ring-shaped electrode portions  141   j  to  144   j  to cause a predetermined range of the cylindrical heating element  1 J to generate heat, whereby the temperature of a predetermined range of the heating roller  21   j  can be raised toward the toner image fixing temperature. 
     Heat generation is caused by energization of at least one of the metallic patterns  12   j   1  to  12   j   3 . The variation of electric resistance of each resistive pattern caused by changes in temperature of the metallic pattern, corresponding to the resistive pattern, which generate heat can be detected by a resistance detector via at least some of the ring-shaped electrode portions  1   s  to  4   s  and the detecting electrodes for detecting electric resistance which are brought into contact with the electrode portions  1   s  to  4   s , which are not illustrated. Accordingly, the temperature of the portion of the heating roller  21   j  heated by the heat generated by the metallic pattern(s) can be grasped. Therefore, power supplied from the power supply unit to the metallic patterns can be controlled in a control unit which receives detection information corresponding to temperature from the resistance detector, which is not illustrated, based on a difference between the temperature detected by the resistive pattern(s) and a target temperature, by frequency control, PWM control or other means, and the temperature of the heating roller  21   j  can be controlled finely, precisely and stably toward a predetermined fixing temperature in a predetermined range. 
     When the frequency of the power supply unit output is controlled, the resistance of the resistive patterns may be grasped by converting the resistance of the resistive patterns to frequency in advance, and by converting the variation of the resistance of the resistive patterns into the variation of frequency. 
     The flexible resin sheet shown in  FIG. 20  is constituted by print-forming, on the sheet surface of the resin sheet  19 , a resistive pattern sj 1 ′ so as to correspond to the metallic pattern  12   j   1 , a resistive pattern sj 2 ′ so as to correspond to the metallic pattern  12   j   2 , and a resistive pattern sj 3 ′ so as to correspond to the metallic pattern  12   j   3 , instead of forming a group of resistive patterns sj 1 , sj 2  and sj 3  by wiring on the surface of the flexible resin sheet  19 . Each of the resistive patterns sj 1 ′, sj 2 ′, sj 3 ′ herein is a strip pattern made by coating with a conductive paste such as copper paste and silver paste whose electric resistance varies depending on changes in temperature. 
     On the end portion of the opposite side surface of the sheet  19  on which the resistive patterns sj 1 ′, sj 2 ′ and sj 3 ′ are not formed, strip electrode portions  1   s ′ to  4   s ′, which are to be ring-shaped electrode portions electrically connected to the resistive patterns sj 1 ′, sj 2 ′ and sj 3 ′, are formed. 
     This sheet can be also rolled with the surface on which the resistive patterns sj 1 ′ to sj 3 ′ are provided facing outside, inserted into the cylindrical member  11   j , and disposed on the inner circumferential surface of the cylindrical member  11   j  by adhesion with an adhesive, by mere disposition or by other means to form a cylindrical heating element  1 J′ (see  FIG. 21 ). Furthermore, a heating roller  21   j ′ as shown in  FIG. 21  can be formed by attaching an elastic material layer  41  onto an outer circumferential surface of the cylindrical heating element  1 J′, and covering its surface with a wear-resistant film  42 . 
     In this heating roller  21   j ′, the heat generation is caused by electrifying at least one of the metallic patterns  12 J 1  to  12 J 3 . The variation of electric resistance of the resistive patterns caused by changes in temperature in response to heat generation of the metallic patterns can be detected via at least some of the ring-shaped electrode portions  1   s  to  4   s  and detection electrodes (not illustrated) brought into contact with these electrode portions. Accordingly, the temperature of the portion of the heating roller  21   j  heated by the heat generated by the metallic pattern(s) can be grasped. Therefore, power supplied from the power supply unit to the metallic patterns can be controlled based on a difference between the temperature detected by the resistive patterns and a target temperature, and the temperature of the predetermined range of the heating roller  21   j ′ can be precisely controlled toward a predetermined fixing temperature. 
     The resistive patterns for detecting temperature (patterns provided by wiring, patterns of coated strips, etc.) can be provided not only on the cylindrical heating elements  1 J,  1 J′ described above, but also on other cylindrical heating elements described in the specification and similar cylindrical heating elements, as long as no inconvenience is caused, so that the resistive patterns can be used to control the temperature of the cylindrical heating elements and the rotating bodies for heating of the fixing devices using the same. In any case, the resistive patterns for detecting temperature can be also formed directly on the inner circumferential surface of the cylindrical member, or can be formed on an electric insulation film by covering the metallic patterns with an electric insulation film. 
     Generally speaking, the cylindrical members in the cylindrical heating elements such as the cylindrical heating elements  1 A ( FIG. 1 ),  1 B ( FIG. 3 ),  1 C ( FIG. 6 ),  1 D ( FIG. 8 , etc.),  1 F (FIG.  12 (B)),  1 F′ ( FIG. 13 ),  1 D′ ( FIG. 15 ),  1 J ( FIG. 17 , etc.) and  1 J′ ( FIG. 21 ) described above, among others, that is, the cylindrical members such as the cylindrical members  11   a  ( FIG. 1 , etc.),  172  ( FIGS. 7(A) ,  7 (B) and  7 (C) to  9 , etc.) and  11   j  ( FIG. 17 , etc.), among others, can be formed of thermosetting resins such as polyimide-based resins and phenol-based resins exhibiting such heat resistance, in order to impart heat resistance for withstanding heat generation of the metallic patterns. 
     The cylindrical member constituting the cylindrical heating element may be made of a metal. For example, it may use a metallic material comprising nickel, copper or iron as a main ingredient. 
     However, the cylindrical members  11   a  ( FIG. 1 , etc.),  172  ( FIGS. 7(A) ,  7 (B) and  7 (C) to  9 , etc.),  11   j  ( FIG. 17 , etc.) and other cylindrical members in the cylindrical heating elements described with reference to the drawings are made of a polyimide resin. 
     The thickness of the cylindrical member may be suitably selected depending on whether the cylindrical heating element is used as a component of the rotating member for heating in the form of a roller or as a component of the rotating member for heating in the form of a flexible belt, and depending on the materials of the cylindrical member and other conditions. 
     The cylindrical members constituting the cylindrical heating element [cylindrical member  11   a  ( FIG. 1 , etc.),  172  ( FIGS. 7(A) ,  7 (B) and  7 (C) to  9 , etc.),  11   j  ( FIG. 17 , etc.), among others] may comprise heat conductive particles, e.g., carbon particles and metal particles such as nickel particles dispersed therein, in order to achieve uniform heat distribution. 
     When the cylindrical member contains heat conductive particles having electric conductivity, for safety, for example, the components which are electrified, such as the metallic patterns and resistive patterns for detecting temperature, may be disposed so as not to come into direct contact with the cylindrical member. 
     Generally speaking, the metallic patterns which are capable of generating heat by being electrified in each of the cylindrical heating elements such as the cylindrical heating elements  1 A ( FIG. 1 ),  1 B ( FIG. 3 ),  1 C ( FIG. 6 ),  1 D ( FIG. 8 , etc.),  1 F (FIG.  12 (B)),  1 F′ ( FIG. 13 ),  1 D′ ( FIG. 15 ),  1 J ( FIG. 17 , etc.) and  1 J′ ( FIG. 21 ), among others, that is, the metallic patterns  12   a  ( FIG. 1 , etc.),  12   b  ( FIGS. 3 ),  121   c  to  123   c  ( FIG. 6 ),  12   d  ( FIG. 7(A) , etc.),  121   d  to  123   d  ( FIG. 11 ),  12   f  ( FIG. 12(A) , etc.),  12   j   1  to  12   j   3  ( FIG. 17 ), among others, comprise, for example, copper, iron, aluminum or an alloy of two or more metals selected from copper, iron and aluminum, but the metallic patterns in the cylindrical heating elements described with reference to the drawings mainly comprise copper (including those formed of copper). 
     Formation of the metallic patterns can be formed by etching a copper film formed previously, printing with a conductive paste mainly comprising copper and by other means. 
     The materials (especially conductivity) of the metallic patterns and the thickness, width and overall length of lines which provide the metallic patterns and are capable of generating heat by being electrified can be selected depending on the target temperature of the heat generated by the metallic patterns. In other words, the conductivity, thickness, width and length of lines which are capable of generating heat by being electrified and provide the metallic patterns can be factors for controlling the temperature of the heat generated, in addition to the power supplied to the metallic patterns, whereby the temperature of the heat generated can be controlled with ease accordingly. 
     Even when these are taken into consideration, from the perspective of keeping the surface on which the metallic patterns are formed as smooth as possible, the thickness of lines which are capable of generating heat by being electrified and provide the metallic patterns is, for example, in the range from about 12.5 μm to 50 μm. 
     Examples of the electric insulation film for covering the metallic patterns and, in some cases, the resistive patterns for detecting temperature include, in general, thermosetting resin films having high heat resistance such as polyimide films and varnish films having high heat resistance such as polyimide-based varnishes. A polyimide-based varnish is employed for covering the metallic patterns in the cylindrical heating elements and the like described above. 
     In any case, the thickness of the electric insulation film is, for example, about 10 μm or more to ensure electric insulation effect. Meanwhile, the thickness of the electric insulation is, in order to prevent it from being uselessly thick, or in order not to hinder the flexibility of the cylindrical heating element when flexibility is required, for example, about 50 μm or less. 
     As shown in FIGS.  7 (A),(B) and (C) as an example, when the cylindrical heating element (e.g.,  1 D) is formed by forming a metallic pattern (e.g.,  12   d ) on the flexible resin sheet (e.g.,  171 ), and rolling this sheet and adhering it onto the inner circumferential surface of the cylindrical member (e.g.,  172 ) with an adhesive or disposing without adhering, or when the cylindrical heating element (e.g.,  1 F) is formed by, as shown in  FIG. 12(A)  to  FIG. 12(C)  as an example, forming the metallic pattern (e.g.,  12   f ) on the flexible resin sheet (e.g.,  171   f ), and adhering this sheet onto the outer circumferential surface of the cylindrical member (e.g.,  11   a ) with an adhesive or disposing thereon without adhering, examples of the flexible resin sheet include, generally speaking, resin sheets comprising a thermosetting resin such as polyimide-based resins exhibiting heat resistance which can withstand heat generation of the metallic patterns. The cylindrical heating elements  1 D,  1 F described above, among others, employ a polyimide film as the flexible resin sheet for forming the metallic patterns. 
     The thickness of the flexible resin sheet is, for example, about 12.5 μm or more to ensure strength and electric insulation in order to a certain degree, and is about 50 μm or less in order to maintain flexibility. 
     The flexible resin sheet  19  (refer to  FIGS. 18 and 20 ) employed to form the resistive patterns for detecting temperature may be also a resin sheet similar to that for forming the metallic patterns. 
     Examples of the adhesive which can be employed when the resin sheet is adhered onto the circumferential surface of the cylindrical member include heat-resistant adhesives which can withstand the heat generation of the metallic patterns, such as epoxy-based adhesive and polyimide-based adhesive. 
     In the elastic material layers [ 211  ( FIG. 4 ),  214  ( FIG. 5 ),  32  ( FIGS. 7(B)  and (C) to  9 ),  33  ( FIG. 9 ),  33 ′ ( FIG. 10 ),  35  (FIG.  12 (B)),  35 ′ and  37  ( FIG. 13 ),  41  ( FIG. 19 ,  FIG. 21 ), etc.] in the rotating members for heating [ 21   b  ( FIG. 4 ),  21   c  ( FIG. 5 ),  21   d ′ ( FIG. 9 ),  21   e  ( FIG. 10 ),  21   f  (FIG.  12 (C)),  21   f ′ ( FIG. 13 ),  21   h  ( FIG. 15 ),  21   j  ( FIG. 19 ),  21   j ′ ( FIG. 21 ), etc.] of the fixing devices using the cylindrical heating elements, examples of the heat resistant elastic material layer include elastic material layers comprising a silicon resin (e.g., silicone rubber). Among such elastic material layers, the elastic material layers ( 211  ( FIG. 4 ), etc.) located further on the outer circumferential side than the metallic pattern may contain heat conductive particles, e.g., carbon particles and metal particles such as nickel particles, mixed and dispersed therein, in order to achieve uniform heat distribution. 
     When the surface of the elastic material layer is covered with a wear-resistant film, [film  212  ( FIG. 4 ), film  34  ( FIG. 9 ,  FIG. 15 ), film  34 ′ ( FIG. 10 ), film  36  (FIG.  12 (C)), film  36 ′ ( FIG. 13 ) and film  42  ( FIG. 19 ,  FIG. 21 ), among others], examples of the wear-resistant film include resin films having heat resistance which can withstand the temperature of the rotating member for heating, for example, films and tubes made of fluoride resin such as PTFE and PFA. 
     With respect to the ring-shaped electrode portions which supply power to the metallic patterns which are capable of generating heat by being electrified in each of the cylindrical heating elements such as the above-mentioned cylindrical heating elements  1 A ( FIG. 1 ),  1 B ( FIG. 3 ),  1 C ( FIG. 6 ),  1 D ( FIG. 8 , etc.),  1 F (FIG.  12 (B)),  1 F′ ( FIG. 13 ),  1 D′ ( FIG. 15 ),  1 J ( FIG. 17 , etc.),  1 J′ ( FIG. 21 ), and with respect to the ring-shaped electrode portions which detects the variation in resistance from the resistive patterns for detecting temperature in the cylindrical heating elements having such resistive patterns, the ring-shaped electrode portions may be provided integrally with the metallic patterns or resistive patterns, but may be also formed separately from the metallic patterns or resistive patterns and then connected to those patterns by electrical connecting means (material or member) such as silver solder and eyelets. The ring-shaped electrode portions formed separately may also serve as reinforcing members of the end portions of the cylindrical heating element. 
     In any case, when the ring-shaped electrode portions are connected to the metallic patterns, in order to keep the contact resistance with the power supply electrodes which are brought into contact with the ring-shaped electrode portions low for as long as possible, and when the ring-shaped electrode portions are connected to the resistive patterns, in order to keep the contact resistance with the electrodes for detecting resistance which are in contact with the ring-shaped electrode portions low for as long as possible, the surfaces of the electrode portions are preferably formed of at least one conductive material selected from nickel, gold, rhodium and conductive carbon. 
     Such a layer part can be obtained by, for example, plating or applying such a material or a paste containing such a material, or by other means. 
     Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.