Abstract:
An image fixing apparatus includes a heater including a substrate, a first electrode provided on one side of the substrate and a second electrode provided on the other side of the substrate; and a connector, connected with the heater, for receiving electric power, the connector including an electrically insulative housing, and a contact terminal provided inside the housing and having first spring contact contacted to the first electrode and a second spring contact contacted to the second electrode, wherein the first spring contact and the second spring contact are disposed at positions different as seen in a direction perpendicular to a surface of the substrate.

Description:
FIELD OF THE INVENTION AND RELATED ART 
       [0001]    The present invention relates to a connector for supplying a heater made up of a dielectric substrate and a heat generating member formed on the substrate, with electric power. It also relates to a fixing apparatus having such a connector. 
         [0002]    A fixing apparatus having an endless belt and a ceramic heater which is in contact with the inward surface of the endless belt has been put to practical use as a fixing apparatus for thermally fixing a toner image formed on a sheet of recording medium, to the sheet of recording medium. A ceramic heater has a ceramic substrate, a heat generating member, and electrodes which are in electrical connection with the heat generating member. The heater is held by a heater holder. A connector for supplying the heater with electric power is connected to the electrodes of the heater. The connector is provided with a pair of contact terminals. In order to ensure that the contact terminals of the power supply connector remain satisfactorily connected with the electrodes of the heater, it is necessary for a preset amount of contact pressure to be maintained between the contact terminals of the power supply and the heater electrodes. 
         [0003]    Some ceramic heaters are structured so that a heater (or heaters) is placed on both surfaces of their ceramic substrate. In the case of these ceramic heaters, therefore, it is possible that they may have an electrode (or electrodes) on both surfaces of their ceramic substrate (heater having a heater (or heaters) on both of its surfaces may be referred to simply as “two-sided heater”). Thus, a power supply connector for a ceramic heater having an electrode (or electrodes) on both surfaces of its ceramic substrate has to be structured so that as it is connected to (engaged with) the ceramic heater, the spring contacts of the power supply connector come into contact with the electrodes of the ceramic heater, on both surfaces of the ceramic heater. This structural arrangement for the power supply connector is problematic for the following reason: 
         [0004]    That is, if a ceramic heater is reduced in the thickness of its ceramic substrate in order to reduce the heater in thermal capacity, for example, the amount by which the spring contacts of the power supply connector are bent when the connector is engaged with the ceramic heater (electrodes of ceramic heater), also reduces, making it difficult to provide the interface between the electrodes of the ceramic heater and the spring contacts of the power supply connector, with a satisfactory amount of contact pressure. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention is made in consideration with the above described issue. Thus, the primary object of the present invention is to provide a fixing apparatus (device) and the connector therefor, which are capable of ensuring that the satisfactory electrical connection is maintained between the electrodes of the heater (ceramic heater, for example) of the fixing apparatus and the power supply connector for the heater of the fixing apparatus. 
         [0006]    According to an aspect of the present invention, there is provided an image fixing device for heating and fixing an unfixed image formed on a recording material, comprising a heater including a substrate, a first electrode provided on one side of said substrate and a second electrode provided on the other side of the substrate; and a connector, connected with said heater, for receiving electric power, said connector including an electrically insulative housing, and a contact terminal provided inside said housing and having first spring contact contacted to said first electrode and a second spring contact contacted to said second electrode, wherein said first spring contact and said second spring contact are disposed at positions different as seen in a direction perpendicular to a surface of said substrate. 
         [0007]    According to another aspect of the present invention, there is provided an electrical connector for electric power supply, said connector comprising electrically insulative housing; and a contact terminal provided inside said housing and including a first spring contact for contacting to a first electrode provided on one side of a heater substrate and a second spring contact for contacting to a second electrode provided on the other side of the substrate, wherein said first spring contact and said second spring contact are disposed at positions different from each other as seen in a direction perpendicular to a surface of said substrate. 
         [0008]    According to a further aspect of the present invention, there is provided an image fixing apparatus for heating and fixing an unfixed image formed on a recording material, comprising a heater including a substrate, a first electrode provided on one side of said substrate and a second electrode provided on the other side of the substrate; and a connector, connected with said heater, for receiving electric power, said connector including an electrically insulative housing, a first contact terminal provided inside said housing and having first spring contact contacted to said first electrode, and a second contact terminal provided inside said housing and having a second spring contact contacted to said second electrode. 
         [0009]    According to a further aspect of the present invention, there is provided an electrical connector for electric power supply, said connector comprising electrically insulative housing; and a first contact terminal provided inside said housing and including a first spring contact for contacting to a first electrode provided on one side of a heater substrate; and a second contact terminal provided inside said housing and including a second spring contact for contacting to a second electrode provided on the other side of the heater substrate. 
         [0010]    Further features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings). 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a sectional view of a typical fixing apparatus (device) to which the present invention is applicable. 
           [0012]      FIGS. 2A ,  2 B, and  2 C are drawings for illustrating the structure of the heater in the first embodiment of the present invention. 
           [0013]      FIGS. 3A ,  3 B, and  3 C are drawings for showing how the heater is supported by the heater supporting member, in the first embodiment of the present invention. 
           [0014]      FIG. 4  is a drawing for showing how the power supply connector attaches itself to the electrode portion of the heater, in the first embodiment. 
           [0015]      FIG. 5  is a perspective view of the contact terminals of the power supply connector in the first embodiment, and illustrates the shape of the contact terminals. 
           [0016]      FIG. 6  is a sectional view of the power supply connector in the first embodiment. 
           [0017]      FIGS. 7A and 7B  are sectional views of the power supply connector in the first embodiment after the mating of the power supply connector with the heater supporting member, at planes parallel and perpendicular, respectively, to the direction in which the connector is engaged. 
           [0018]      FIGS. 8A ,  8 B, and  8 C are drawings for showing how the heater is supported by the heater supporting member, in the second embodiment of the present invention. 
           [0019]      FIG. 9  is a drawing for showing how the power supply connector attaches itself to the electrode portion of the heater, in the second embodiment. 
           [0020]      FIG. 10  is a perspective view of the contact terminals of the power supply connector in the second embodiment, and illustrates the shape of the contact terminals. 
           [0021]      FIG. 11  is a sectional view of the power supply connector in the second embodiment. 
           [0022]      FIG. 12  is a sectional view of the combination of the heater electrode and the power supply connector, in the second embodiment, after the mating of the connector with the heater supporting member. 
           [0023]      FIG. 13  is a perspective view of the contact terminals of the power supply connector in the third embodiment, and illustrates the shape of the contact terminals. 
           [0024]      FIG. 14  is a sectional view of the power supply connector, in the third embodiment. 
           [0025]      FIGS. 15A and 15B  are sectional views of the power supply connector in the third embodiment after the mating of the power supply connector with the heater supporting member, at planes parallel and perpendicular, respectively, to the direction in which the connector is engaged. 
           [0026]      FIGS. 16A ,  16 B, and  16 C are drawings for showing how the heater is supported by the heater supporting member, in the fourth embodiment of the present invention. 
           [0027]      FIG. 17  is a drawing for showing the lengthwise end portion of the heating unit after the attachment of the supporting member which backs up the heater shown in  FIG. 16(   a ). 
           [0028]      FIG. 18  is a drawing for showing how the power supply connector attaches itself to the electrode portion of the heater, in the fourth embodiment. 
           [0029]      FIGS. 19A and 19B  are top and bottom, respectively, plan views of the combination of the electrode portion of the ceramic heater and the power supply connector, in the fourth embodiment, after the attachment of the connector to the electrode portion. 
           [0030]      FIGS. 20A and 20B  are sectional views of the combination of the power supply connector and the electrode portion of the ceramic heater, in the fourth embodiment, after the attachment of the power supply connector to the electrode portion, at planes parallel and perpendicular, respectively, to the direction in which the connector is engaged, after the attachment of the connector to the heater supporting member. 
           [0031]      FIG. 21  is a schematic sectional view of a typical image forming apparatus with which the present invention is compatible. 
           [0032]      FIGS. 22A-22E  are drawings for showing the structure of the ceramic heater and the power supply connector for the heater, in the fifth embodiment of the present invention. 
           [0033]      FIG. 23  is a perspective view of the connector terminal in the sixth embodiment. 
           [0034]      FIGS. 24A ,  24 B, and  24 C are drawings of the connector in the sixth embodiment. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0035]    Hereinafter, embodiments of the present invention are described in detail with reference to the appended drawings. 
       Embodiment 1 
     (General Structure of Image Forming Apparatus) 
       [0036]      FIG. 21  is a drawing for showing the general structure of a typical image forming apparatus with which the present invention is compatible. This image forming apparatus is an electrophotographic printer. 
         [0037]    The printer  100  receives the information of an image to be formed, from an external host computer or the like (unillustrated), and forms on a sheet S of recording medium, an image which is in accordance with the received information of the image to be formed. 
         [0038]    As soon as the printer  100  receives a print signal, the photosensitive drum  71  of the printer  100  begins to be rotationally driven in the clockwise direction, at a preset peripheral velocity. While the photosensitive drum  71  is rotationally driven, its peripheral surface is charged to a preset potential level by the charge roller  72  of the printer  100 , to which a preset bias is being applied. 
         [0039]    Then, the charged portion of the peripheral surface of the photosensitive drum  71  is scanned (exposed) by the laser scanner  73  of the printer  100 , in accordance with the information of the image to be formed, which was received from the unshown host computer or the like. As a result, an electrostatic latent image, which reflects the information of the image to be formed, is effected on the charged portion of the peripheral surface of the photosensitive drum  71 . Then, the electrostatic latent image is developed by the developing device  74  of the printer  100 , into a toner image, which is a visible image formed of toner, on the peripheral surface of the photosensitive drum  71 . 
         [0040]    Meanwhile, one of the sheets S of recording medium, which are in a sheet feeder cassette of the printer  100  is fed into the main assembly of the printer  100 , by the sheet feeder roller  75  of the printer  100 , while being separated from the rest in the cassette. Then, the sheet S is conveyed, with a preset control timing, by the pair of registration rollers  76  of the printer  100 , to the transfer nip N which is formed between the photosensitive drum  71  and the transfer roller  77  of the printer  100 . Then, while the sheet S is conveyed through the transfer nip N, remaining pinched by the transfer nip N, the toner image on the photosensitive drum  71  is transferred onto the sheet S as if it is peeled away from the photosensitive drum  71 . 
         [0041]    After the transfer of the toner image onto the sheet S, the sheet S is conveyed through the fixing device  1  of the printer  100 . While the sheet S is conveyed through the fixing device  1 , the toner image on the sheet S is thermally fixed to the sheet. Then, the sheet S is discharged from the printer  100  by the pair of discharge rollers  79  of the printer  100 . 
         [0042]    The transfer residual toner, that is, the toner remaining on the peripheral surface of the photosensitive drum  71  after the transfer of the toner image onto the sheet S, is removed by the cleaning device  80  of the printer  100 , ending the image formation process sequence. 
         [0043]    The photosensitive drum  71 , charge roller  72 , laser scanner  73 , developing device  74 , transfer roller  77 , and cleaning device  80  make up the image forming means of the printer  100 . 
       (Structure of Fixing Device) 
       [0044]    Next, referring to  FIG. 1 , the general description of the fixing device  1  is given.  FIG. 1  is a sectional view of the fixing device  1  in this embodiment. 
         [0045]    The fixing device  1  is made up of a heating unit  2 , a pressure roller  3 , a pair of sheet conveyance rollers  4 , a sheet guiding portion, and a housing. The heating unit  2  is made up of a heater  5 , and a heater supporting member  6  (substrate holder). As the heater  5  is supplied with electric power, it generates heat. The heater  5  is kept pressed toward the pressure roller  3  by a pressure generating means (unshown). The pressure roller  3  rotates by being externally driven. The heating unit  2  has a cylindrical film  7  (endless belt), which is circularly moved by the rotation of the pressure roller  3 . As the sheet S, on which an unfixed toner image is borne, is conveyed to the area of contact between the heating unit  2  and pressure roller  3 , the toner in the unfixed toner is fixed to the sheet S, by the heat and pressure applied by the combination of the heating unit  2  and pressure roller  3 . Thereafter, the sheet S is conveyed out of the fixing device  1 , and is discharged into the delivery tray (unshown) of the printer  100 , by the pair of sheet conveyance rollers  4  of the fixing device  1 . 
       (Structure of Heating Unit) 
       [0046]    Next, referring to  FIGS. 2-5 , the heating unit  2  in this embodiment is described. 
         [0047]    First, referring to  FIG. 2 , the general structure of the heater  5  is described.  FIG. 2(   a ) is a sectional view of the heater  5 .  FIG. 2(   b ) is a plan view of the heater  5  as seen from the direction indicated by an arrow mark b in  FIG. 2(   a ). It shows the surface (first surface) of the heater  5 , which has a heat generating member  8 , which is greater in dimension in terms of the lengthwise direction of the heater  5  than the heat generating member  8  on the other surface of the heater  5 .  FIG. 2(   c ) is a plan view of the heater  5  as seen from the direction indicated by an arrow mark a in  FIG. 2(   a ). It shows the surface (second surface) of the heater  5 , which has the heat generating member  8 , which is less in dimension in terms of the lengthwise direction of the heater  5  than the heat generating member  8  on the first surface. The two surfaces shown in  FIGS. 2(   b ) and  2 ( b ), respectively, are parallel to each other. 
         [0048]    The heater  5  has a dielectric substrate  9  made of ceramic material. The abovementioned heat generating member  8 , which generates heat as electric current flows through it, is on the surface of this dielectric substrate  9 . The heater  5  is also provided with electrodes  10 ,  10   f  and  10   r , and leads  11 . More specifically, the electrodes  10 ,  10   f  and  10   r  are for supplying the heat generating member  8  with electric power. Each of the leads  11  is in connection to one of the lengthwise ends of the heat generating member  8  and the corresponding the electrode to provide electrical connection between the electrode and heat generating member  8 . The heater  5  is also provided with a protective layer  12  which is made of glass or the like substance, and is placed on the dielectric substrate, heat generating member  8 , and leads  11 , to protect the heat generating member  8  and leads  11 . The combination of the electrodes  10  and  10   f  is on the first surface of the dielectric substrate  9 , and the combination of the electrodes  10  and  10   r  is on the second surface of the dielectric substrate  9 . 
         [0049]    The heat generating member  8  on the first surface of the substrate  9  and the heat generating member  8  on the second surface of the substrate  9  are made different in dimension in terms of the lengthwise direction of the heater  5 , in order to enable the heater  5  to accommodate various sheets which are different in size. As the heat generating member  8  is supplied with electric power through a connector  13  (which will be described later), electrodes  10 ,  10   f  and  10   r , and the leads  11 , each heat generating member  8  generates heat by the amount proportional to the amount of the supplied electric power. Thus, the amount by which heat is generated by the heater  5  can be controlled by controlling the amount of electric power supply to the heater  5 , more specifically, by simultaneously supplying both heat generating members  8  with electric power, or supplying only one of the heating members  8  with electric power. 
         [0050]    It is desired that the electrodes  10  and  10   f  to be grounded are positioned on the first surface of the substrate  9  in such a manner that they will be symmetrically positioned with reference to the center of a sheet S of recording medium, in terms of the direction perpendicular to the recording medium conveyance direction, when the sheet S is conveyed through the fixing device  1 , and also, that the electrodes  10  and  10   r  to be grounded are positioned on the second surface of the substrate  9  in such a manner that they will be symmetrically positioned with reference to the center of the sheet S, in terms of the direction perpendicular to the recording medium conveyance direction. It is also desired that the heat generating members  8  are positioned on the first and second surfaces, one for one, of the substrate  9 , in such a manner that the center of the heater  5 , in terms of their lengthwise direction, coincides with the center of the sheet S in terms of the direction perpendicular to the recording medium conveyance direction when the sheet S is conveyed through the fixing device  1 , for the following reason. That is, the electrodes  10 ,  10   f  and  10   r , and the heat generating members  8  are positioned as described above to make the heat distribution of the heater  5  symmetrical with reference to the center of the sheet S in terms of the direction perpendicular to the recording medium conveyance direction (lengthwise direction of heater  5 ), in order to prevent the end portions of the heater  5  from excessively increasing in temperature. 
         [0051]    Next, referring to  FIGS. 3 and 4 , how the connector  13  is attached to the heating unit  2  is described. 
         [0052]      FIG. 3  shows how the heater  5  is supported by the heater supporting member  6 .  FIG. 3(   a ) shows the entirety of the combination of the heater  5  and heater supporting member  6 .  FIG. 3(   b ) shows the side of the heater  5 , which contacts the film  7 .  FIG. 3(   c ) shows the end portion of the heater supporting member  6 , which faces the heater  5  and has a cutaway. The heater supporting member  6  supports the heater  5 , by holding the heater  5  in its groove which extends in its lengthwise direction of the heater (heater supporting member  6 ). It controls the film  7  in terms of the lateral movement of the film  7  as the film  7  is circularly moved. The cutaway portion of the heater supporting member  6  is positioned so that the electrode  10   f , for example, is exposed through the cutaway. The electrodes  10   f  and  10   r  are connected to the connector  13  which has a pair of spring contacts. However, the two electrodes  10 , which are on the other lengthwise ends of the heater supporting member  6  from the electrodes  10   f  and  10   r  are connected to two connectors  13 , which are independent from each other. That is, in terms of the electrical circuit, the heating unit  2  in this embodiment is structured to use three connectors to enable the two heat generating members  8  to be independently controlled from each other. 
         [0053]    In a case where the electrode  10   r  is on the heater supporting side of the heater supporting member  6 , the cutaway portion of the heater supporting member  6  is positioned so that the side of the electrode  10   f , which is exposed through the cutaway, is on the heater supporting surface side of the heater supporting member  6 . 
         [0054]      FIG. 4  is a drawing which shows how the connector  13  mates with the heater  5 . The connector  13  is moved toward the lengthwise end portion of the heater supporting member  6  in the direction indicated by an arrow mark so that it attaches itself to the portion of the heater supporting member  6 , which is on the outward side of the track of the film  7 . That is, the connector  13  is connected to the lengthwise end portion of the heater  5 . 
       (Structure of Connector) 
       [0055]    Next, referring to  FIGS. 5 and 6 , the structure of the connector  13  is described. 
         [0056]      FIG. 5  is a drawing which shows the shape of the terminal  14  of the connector  13 . The connector terminal  14  is shaped so that its cross section appears roughly U-shaped. It is made of stainless steel, titanium alloy, or the like material, and is plated. It is provided with a pair of spring contacts, more specifically, spring contacts  16   f  and  16   r  (first and second spring contacts, respectively), which extend into the space of the connector  13 , which corresponds in position to the void of the U-shaped portion. As the connector  13  is made to attach itself to the abovementioned lengthwise end of the heater  5 , the spring contacts  16   f  and  16   r  (first and second spring contacts) come into contact with the electrodes  10   f  and  10   r  of the heater  5 . The first spring contact  16   f  is provided with the first point  16   fc  of contact, which contacts the first electrode  10   f  on the substrate  9 , and the second spring contact  16   r  is provided with the second point  16   c  of contact, which contacts the second electrode  10   r  on the substrate  9 . These spring contacts  16   f  and  16   r  are resiliently bendable in the direction intersectional to the heater supporting surface of the dielectric substrate  9 . Thus, as the connector  13  is engaged with the heater  9  and the heater supporting member  9 , the points  16   fc  and  16   rc  of contact of the spring contacts  16   f  and  16   r  come into contact with the electrodes  10   f  and  10   r , respectively, while the spring contacts  16   r  and  16   r  are made to resiliently bend in the abovementioned direction. 
         [0057]    The connector terminal  14  is in connection to a lead  17  which is made up of a bundle of fine wires and is crimped to one end of the terminal  14 . It is in connection to the control chip (unshown) through the lead  17 . 
         [0058]      FIG. 6  is a sectional view of the connector  13 . The connector  13  has a dielectric housing  15 , and a terminal  14  held in the housing  15 . The housing  15  of the connector  13  is roughly U-shaped in cross section, like the terminal  14 . The connector terminal  14  is held in the housing by being forcefully inserted into the housing  15  from the opposite side of the housing  15  from the opening of the housing  15 , which corresponds in position to the open end of a letter U. The points  16   fc  and  16   rc  of contact (first and second points of contact) are offset from each other in the direction perpendicular to the direction (indicated by arrow mark in  FIG. 5 ) in which the connector  13  is to be attached to the heater  5  and heater supporting member  6 . That is, the first and second points  6   fc  and  16   rc  of contact are positioned so that when they are displaced by the bending of the spring contacts  16   f  and  16   r , they do not interfere with each other. Thus, the spring contacts  16   f  and  16   r  are allowed to be bent in the direction (indicated by arrow mark in  FIG. 6 ) perpendicular to the electrodes  10   f  and  10   r  without interfering with each other. That is, the two spring contacts  16   f  and  16   r  are different in position in terms of the direction parallel to the heat generating member supporting surface of the substrate  9 . 
         [0059]    When the connector  13  is in engagement with the heating unit  2 , the spring contacts  16   f  and  16   r  remain overlapped with each other by a distance g in terms of the direction (in which spring contacts are bent) in which the points  16   fc  and  16   rc  of contact are displaced (distance g can be changed within range in which points of contact do not come into contact with housing  15  or the like). 
         [0060]      FIG. 7  is a sectional view of the combination of the connector  13  and the lengthwise end portion of the heater  5 , after the connector  13  has been mated with the heater supporting member  6  on which the heater  5  is present.  FIG. 7(   a ) is a sectional view of the combination at a plane parallel to the direction in which the connector  13  was made to attach itself to the heater  5  and heater supporting member  6 , and  FIG. 7(   b ) is sectional view of the combination at a plane parallel (as shown in  FIG. 7(   a )) to the lengthwise direction the heater  5 . The heater supporting member  6  is not shown, for the simplification of the description of the connector  13 . Referring to these drawings, as the connector  13  is made to attach itself to the heater  5  and heater supporting member  6 , the spring contacts  16   f  and  16   r  are resiliently bent. Thus, a preset amount of contact pressure is generated between the points  16   fc  and  16   rc  and the electrodes  10   f  and  10   r , respectively. 
         [0061]    That is, the spring contacts  16   f  and  16   r  are resiliently bendable in the direction perpendicular to the surface of the heater  5 . Thus, as the connector  13  is made to engage with the heater  5 , the points  16   fc  and  16   rc  are made to press on the electrodes  10   f  and  10   r , by the resiliency of the spring contacts  16   f  and  16   r , respectively. 
         [0062]    The connector  13  is structured so that the vertical projections of the points  16   fc  and  16   rc  of contact upon the surface of the heater  5  are different in position. Further, the connector  13  is structured so that when the connector  13  is not in engagement with the heater  5 , the spring contacts  16   f  and  16   r  overlap with each other as seen from the direction perpendicular to the direction in which the connector  13  is engaged with the heater  5 . Further, the heater  5  is in the form of a long and narrow rectangle, and the vertical projections of the points  16   fc  and  16   rc  of contact upon the surface of the heater  5  are offset from each other in the lengthwise direction of the heater  5 . 
         [0063]    The heater  5  is in the form of a long and narrow rectangle as described above. Therefore, structuring the connector  13  so that the points  16   fc  and  16   rc  of contact are offset in position from each other in terms of the lengthwise direction of the heater  5  makes it possible to provide the connector  13  with spring contacts which are greater in size than a spring contact with which the connector  13  can be provided in a case where the connector  13  is structured so that the points  16   fc  and  16   rc  of contact are offset from each other in the widthwise direction of the heater  5 . Further, It can reduce the connector  13  in the amount of the friction which occurs between the points  16   fc  and  16   rc  of contact and the electrodes of heater  5  when the connector  13  is engaged with the heater  5 , and also, makes it possible for the heater  5  to remain reliably in contact with the points  16   fc  and  16   rc  of contact. In other words, it makes it possible to narrow the heater  5  to reduce the heating unit  2  in size, without reducing the electrodes in size. 
         [0064]    That is, in the case of the connector  13  in this embodiment, there is nothing to interfere with the resilient bending of the spring contacts  16   f  and  16   r . Thus, the distance by which the points  16   fc  and  16   rc  of contact of the spring contacts  16   f  and  16   r , respectively, are displaced in the direction intersectional to the surface of the heater  5  is hardly affected by the thickness t of the heater  5 . Therefore, it is ensured that as the connector  13  is engaged with the heater  5  and heater supporting member  6 , the preset amount of contact pressure is generated and maintained between the points  16   fc  and  16   rc  of contact and the electrodes  16   f  and  16   r , respectively. Further, it does not occur that the points  16   fc  and  16   rc  of contact of the connector terminal  14  rub against each other when the connector  13  is moved around and/or the printer  100  (image forming apparatus) is moved around. Therefore, the contact failure attributable to the rubbing of the points  16   fc  and  16   rc  of contact against each other is unlikely to occur. 
       Embodiment 2 
       [0065]    Next, referring to  FIGS. 8-12 , the second embodiment of the present invention is described. 
         [0066]    Here, the portions of the connector  13  and heating unit  2  in this embodiment, which are the same as the counterparts in the first embodiment are not going to be described. This embodiment is different from the first embodiment in the direction in which the connector  13  is moved to be made to attach itself to the heater  5  and heater supporting member  6 , and also, the shape of the connector terminal  14 . 
         [0067]    First, referring to  FIGS. 8 and 9 , how the connector  13  is attached to the heater  5  and heater supporting member  6  is described. 
         [0068]      FIG. 8  illustrates how the heater  5  is supported by the heater supporting member  6 .  FIG. 8(   a ) shows the entirety of the combination of the heater  5  and heater supporting member  62  (substrate holder).  FIG. 8(   b ) shows the film contacting side of the heater  5 .  FIG. 8(   c ) shows the end portion of the heater supporting member  62 , which faces the heater  5  and has a cutaway. The heater supporting member  62  supports the heater  5 , by holding the heater  5  in its groove which extends in its lengthwise direction. It controls the film  7  in terms of the lateral movement of the film  7  as the film  7  is circularly moved. The cutaway portion of the heater supporting member  62  is positioned so that the electrode  10   f , for example, is exposed through the cutaway. 
         [0069]    In a case where the electrode  10   r  is on the heater supporting side of the heater supporting member  62 , the cutaway portion of the heater supporting member  62  is positioned so that the side of the electrode  10   f , which is exposed through the cutaway, is on the heater supporting surface side of the heater supporting member  62 . 
         [0070]      FIG. 9  is a drawing which shows how the connector  23  attaches itself to the heater  5 . The connector  23  is moved toward the lengthwise end portion of the heater supporting member  62  in the direction indicated by an arrow mark so that it engages with the lengthwise end of the heater  5  and heater supporting member  62 . 
         [0071]    Next, referring to  FIGS. 10 and 11 , the structure of the connector  23  is described.  FIG. 10  shows the shape of the terminal  24  of the connector  23 . The terminal  24  is shaped so that its cross section appears roughly U-shaped. It is made of stainless steel, titanium alloy, or the like material, and is plated. It is provided with a pair of spring contacts, more specifically, spring contacts  16   f  and  16   r , which extend into the internal space of the connector  23 , which corresponds in position to the void of the U-shaped portion of the connector  23 . As the connector  23  engages with the abovementioned lengthwise end of the heater  5 , the spring contacts  16   f  and  16   r  come into contact with the electrodes  10   f  and  10   r  of the heater  5 , and are made to resiliently bend in the abovementioned direction. The terminal  14  is in connection to a lead  17  which is made up of a bundle of wires and is crimped to one end of the terminal  14 . It is in connection to the control chip (unshown) through the lead  17 . In this embodiment, the electrodes  10   f  and  10   r  are in connection to each other through a common lead. 
         [0072]      FIG. 16  is a sectional view of the connector  23 . The connector  23  has a housing  15 , and a terminal  14  held in the housing  15 . The housing  15  of the connector  23  is roughly U-shaped in cross section, like the terminal  14 . The connector terminal  14  is held in the housing  15  by being forcefully inserted into the housing  15  from the opposite side of the housing  15  from the opening of the housing, which corresponds in position to the open end of the U-shaped portion of the housing  15 . The spring contacts  16   f  and  16   r  are offset from each other in the direction parallel to the direction (indicated by arrow mark in  FIG. 10 ) in which the connector  23  is to be engaged with the heater  5  and heater supporting member  62 . That is, the spring contacts  16   f  and  16   r  are positioned so that when they are resiliently bent in the direction perpendicular to the electrodes  10   f  and  10   r , they do not interfere with each other. The connector  23  is structured so that the vertical projections of the points  16   fc  and  16   rc  of contact upon the surface of the long and narrow rectangular heater  5  are different in position. That is, the connector  23  is structured so that when the connector  23  is engaged with the heater  5  and heater supporting member  62 , the first and second points  16   fc  and  16   rc  of the spring contacts  16   f  and  16   r , respectively, are not made to come into contact with each other, by the bending of the spring contacts  16   f  and  16   r.    
         [0073]    Further, the connector  23  is structured so that the spring contacts  16   f  and  16   r  overlap with each other by a distance g as seen from the direction parallel to the direction in which the connector  23  is engaged with the heater  5 . The distance g may be changed, provided that the change does not cause the points  16   fc  and/or  16   rc  of contact to come into contact with the housing  15  or the like. 
         [0074]      FIG. 12  is a sectional view of the combination of the connector  23  and the lengthwise end portion of the heater  5 , after the connector  23  attached itself to the heater supporting member  62  on which the heater  5  is present. As is evident from  FIG. 12 , as the connector  23  attaches itself to the heater supporting member  62 , the spring contacts  16   f  and  16   r  come into contact with the electrodes  10   f  and  10   r , respectively, and are made to resiliently bend by the electrodes  10   f  and  10   r , providing thereby a preset amount of contact pressure between themselves and the electrodes  10   f  and  10   r , respectively. 
         [0075]    That is, in the case of the connector  23  in this embodiment, there is nothing to interfere with the resilient bending of its spring contacts  16   f  and  16   r . Thus, the distance by which the points  16   fc  and  16   rc  of contact of the spring contacts  16   f  and  16   r , respectively, are displaced is hardly affected by the thickness t of the heater  5 . Therefore, it is ensured that as the connector  23  is engaged with the heater  5  and heater supporting member  62 , the preset amount of contact pressure is generated and maintained between the points  16   fc  and  16   rc  of contact and the electrodes  10   f  and  10   r , respectively. Further, it does not occur that the points  16   fc  and  16   rc  of contact of the connector terminal  14  rub against each other when the connector  23  is moved around and/or the printer  100  (image forming apparatus) is moved around. Therefore, the contact failure attributable to the rubbing of the points  16   fc  and  16   rc  of contact against each other is unlikely to occur. 
         [0076]    As will be evident from the description of the second embodiment of the present invention given above, even in a case where the present invention is applied to the fixing device structured so that the connector  23  is to be made to attach itself to the heater  5  and heater supporting member  62  in the direction parallel to the lengthwise direction of the heater  5 , the effect of the present invention are the same as those obtained by the second embodiment. Further, in this embodiment, the points of contact of the connector  23 , which contact the front and rear sides of the heater substrate, are offset from each other in the direction parallel to the lengthwise direction of the substrate. Therefore, it is unnecessary to increase the heater in width, making it unnecessary to increase the heating unit in size. 
       Embodiment 3 
       [0077]    Next, referring to  FIGS. 13-15 , the third embodiment of the present invention is described. 
         [0078]    Here, the portions of the fixing device  1  in this embodiment, which are the same as the counterparts in the first embodiment are not going to be described. This embodiment is different from the first one in the shape of the spring contacts. 
         [0079]    First, referring to  FIGS. 13 and 14 , the structure of the connector  33  is described. 
         [0080]      FIG. 13  shows the shape of the terminal  34  of the connector  33 . The terminal  34  is shaped so that its cross section appears roughly U-shaped. It is made of stainless steel, titanium alloy, or the like material, and is plated. It is provided with a pair of spring contacts  161   f  and  162   f , which contact the electrode  10   f , and a pair of spring contacts  161   r  and  162   r , which contact the electrode  16   r . These spring contacts extend into the internal space of the connector  33 , which corresponds in position to the void of the U-shaped portion of the connector  33 . The pair of spring contacts  161   r  and  162   r  are between the spring contact  161   f  and  161   r  in terms of the direction indicated by an arrow mark. The connector terminal  34  is in connection to a lead  17  which is made up of a bundle of fine wires and is crimped to one end of the terminal  34 . It is in connection to the control chip (unshown) through the lead  17 . 
         [0081]      FIG. 14  is a sectional view of the connector  33 . The connector  33  has a housing  15 , and a terminal  34  held in the housing  15 . The housing  15  of the connector  33  is roughly U-shaped in cross section, like the terminal  34 . The connector terminal  34  is held in the housing  15  by being forcefully inserted into the housing  15  from the opposite side of the housing  15  from the opening of the housing, which corresponds in position to the open end of the U-shaped portion of the connector  33 . The spring contacts  161   f ,  162   f ,  161   r  and  162   r  are offset from each other in the direction perpendicular to the direction (indicated by arrow mark in  FIG. 13 ) in which the connector  33  is attached to the heater  5  and heater supporting member  62 . That is, the spring contacts  161   f ,  162   f ,  161   r  and  162   r  are positioned so that when they are made to resiliently bend in the direction (indicated by arrow mark in  FIG. 13 ) perpendicular to the electrodes  10   f  and  10   r , they do not interfere with each other. 
         [0082]    Further, the connector  33  is structured so that the points  161   fc ,  162   fc ,  161   rc  and  162   rc  of contact of the spring contacts  161   f ,  162   f ,  161   r  and  162   r , respectively, overlap with each other by a distance g as seen from the direction parallel to the direction in which the connector  33  is engaged with the heater  5 . The value of the distance g is optional, provided that the change in the value does not cause the points of contact to come into contact with the housing  15  or the like. 
         [0083]      FIG. 15  is a sectional view of the combination of the connector  33  and the lengthwise end portion of the heater  5 , after the connector  33  attached itself to the heater supporting member  62  on which the heater  5  is present.  FIG. 15(   a ) is a sectional views of the combination of the connector  34  and the lengthwise end portion of the heater  5 , at a plane parallel to the direction in which the connector  34  is made to attach itself to the heater  5  and heater supporting member  62 , and  FIG. 15(   b ) is a sectional view of the combination at a plane parallel (as shown in  FIG. 15(   a )) to the lengthwise direction of the heater  5 . For the simplification of the description of the combination, the heater supporting member  62  is not shown in the drawings. As will be evident from the drawing, as the connector  33  is made to attach itself to the heater  5  and heater supporting member  62 , the spring contacts  161   f  and  162   f  contact the electrode  10   f , and the spring contact  161   r  and  162   r  contact the electrode  10   r . That is, each electrode is contacted by two spring contacts. Further, the spring contacts  161   f  and  162   f  are symmetrically positioned with reference to the centerline L of the connector terminal  34 , and the spring contacts  161   r  and  162   r  also are symmetrically positioned with reference to the centerline L of the connector terminal  34  ( FIG. 15(   b )). 
         [0084]    Incidentally, the spring contacts  161   f  and  162   f  make up the first electrode portion of the connector  33 , and the spring contacts  161   r  and  162   r  make up the second electrode portion of the connector  33 . 
         [0085]    As the connector  33  is connected to the heater  5 , the spring contacts  161   f  and  162   f  come into contact with the electrode  10   f  by their points  161   fc  and  162   fc  of contact (two points of contact), and the spring contacts  161   r  and  162   r  come into contact with the electrode  10   r  by their points  161   rc  and  162   rc  of contact (two points of contact). The connector  33  is structured so that the points  161   fc ,  162   fc ,  161   rc  and  162   rc  are different in the position of their vertical projection upon the surface of the heater  5 . 
         [0086]    Therefore, there is nothing to interfere with the resilient bending of its spring contacts  161   f ,  162   f ,  161   r  and  162   r . Thus, the distance by which the points  161   fc ,  162   fc ,  161   rc  and  162   rc  of contact are displaced by the bending of the spring contacts is hardly affected by the thickness t of the heater  5 . Therefore, it is ensured that as the connector  33  is engaged with the heater  5 , the preset amount of contact pressure is generated and maintained between the points of contact and the corresponding electrode. 
         [0087]    Further, it does not occur that the points  161   fc ,  162   fc ,  161   rc  and  162   rc  of contact of the connector terminal  34  rub against each other when the connector  33  is moved around and/or the printer  100  (image forming apparatus) is moved around. Therefore, the contact failure attributable to the rubbing of the points of contact against each other is unlikely to occur. 
         [0088]    In addition, in the case of this embodiment, a single electrode is contacted by the pair of symmetrically positioned spring contacts in such a manner that one of the symmetrically positioned spring contact contacts the front side of the electrode, whereas the other contacts the rear side of the electrode. Therefore, the connector terminal  34  is kept stable in attitude. Therefore, it is unlikely to occur that the contact pressure between the point of contact of a springy electrode and the corresponding electrode of the heater is reduced by the change in the attitude of the connector  33 . 
         [0089]    Further, the spring contact  161   f  is positioned closest to the lengthwise end of the heater  5  among the four spring contacts. Therefore, the reactive force from the spring contact  161   f  is caught by the heater supporting member, whereby the shearing stress to which the lengthwise end portion of the heater  5  is subject is reduced. Further, the lengthwise end portion of the heater  5  is sandwiched by the heater supporting member and the spring contact  161   f . That is, the heater  5  remains securely supported. 
       Embodiment 4 
       [0090]    Next, referring to  FIGS. 16-20 , the fourth embodiment of the present invention is described. 
         [0091]    Here, the portions of the fixing device in this embodiment, which are the same as the counterparts in the first and third embodiments are not described. It is in the shape of the heater supporting member that this embodiment is different from the first and third embodiments. 
         [0092]    First, referring to  FIGS. 16 and 17 , how the connector  13  is engaged with the heating unit  2  is described. 
         [0093]      FIG. 16  shows how the heater  5  is supported by the heater supporting member  63  (substrate holder).  FIG. 6(   a ) shows the entirety of the combination of the heater  5  and heater supporting member  63 .  FIG. 16(   b ) shows the side of the heater  5 , which contacts the film  7 .  FIG. 16(   c ) shows the end portion of the heater supporting member  63 , which faces the heater  5  and has a cutaway. The heater supporting member  63  supports the heater  5 , by holding the heater  5  in its groove which extends in its lengthwise direction. It controls the film  7  in terms of the lateral movement of the film  7  as the film  7  is circularly moved. The cutaway portion of the heater supporting member  63  is positioned so that the electrode  10   f , for example, is exposed through the cutaway. 
         [0094]    In a case where the electrode  10   r  is on the heater supporting side of the heater supporting member  63 , the cutaway portion of the heater supporting member  6  is positioned so that the side of the electrode  10   f , which is exposed through the cutaway, is on the heater supporting surface side of the heater supporting member  63 . 
         [0095]      FIG. 17  shows the lengthwise end of the heating unit  2  after the attachment of a supporting member  20  (shown in  FIG. 16(   a )) which supports the heater  5 , to the heating unit  2 . The connector  33  in the third embodiment attaches itself to the lengthwise end portion of the heating unit  2  which is in the state in which the heater  5  is remaining sandwiched by the heater supporting member  63  and a supporting member  20 . 
         [0096]      FIG. 18  is a drawing which shows how the connector  33  attaches itself to the heater  5 . The connector  33  attaches itself to the heater supporting member  63  by being moved in the direction indicated by an arrow mark, on the outward side of the lateral edge of the film  7 . 
         [0097]    Next,  FIG. 19  shows the state of the combination of the connector  33  and the lengthwise end portion of the heating unit  2  after the connector  33  attached itself to the heater  5 . Here, the housing  15  is not illustrated for the simplification of the description.  FIG. 19(   a ) is a plan view of the abovementioned combination as seen from the side on which the heater  5  contacts the film  7 . The supporting member  20  is positioned between the spring contact  161   f  and  162   f .  FIG. 19(   a ) is a plan view of the combination as seen from the rear side of  FIG. 19(   a ). 
         [0098]      FIG. 20  is a sectional view of the combination of the connector  33  and the lengthwise end portion of the heating unit  2  after the connector  33  attached itself to the heater supporting member  63  on which the heater  5  is present.  FIG. 20(   a ) is a sectional view of the combination at a plane parallel to the direction in which the connector  33  is made to attach itself to the heater  5 , and  FIG. 20(   b ) is a sectional views of the combination at plane parallel (shown in  FIG. 20(   a )) to the lengthwise direction of the heater  5 . 
         [0099]    As will be evident from these drawings, the heating unit  2  is structured so that the actual supporting portions  63   a  and  63   b  of the heater supporting member  63  are positioned on the opposite side of the heater  5  from the spring contacts  161   f  and  162   f , respectively, and back up the heater  5  against the contact pressure generated by the spring contacts  161   f  and  162   f . Further, the spring contact  161   f  is positioned closest to the lengthwise end of the heater  5  among the four spring contacts  161   f ,  162   f ,  161   r  and  162   r , and the reactive force generated by the spring contact  161   f  is caught by the actual supporting portion  63   b  of the supporting member  63 . Therefore, the heating unit  2  in this embodiment is smaller in the amount of the shearing stress to which the lengthwise end portion of the heater  5  is subjected, than any heating unit in accordance with the prior art. 
         [0100]    Further, the supporting member  20  is positioned on the opposite side of the heater  5  from the spring contacts  161   r  and  162   r , and backs up the heater  5  against the contact pressure generated by the spring contacts  161   r  and  162   r.    
         [0101]    Therefore, this embodiment has not only the effect which the third embodiment has, but also, is smaller in the amount of the shearing stress to which the heater  5  is subjected by the contact pressure generated by the spring contacts  161   f ,  162   f ,  161   r  and  162   r . Therefore, this embodiment makes it possible to reduce the heater  5  in thickness. 
       Embodiment 5 
       [0102]    Next, the fifth embodiment of the present invention is described. The heater  200  in this embodiment is provided with three heat generating members  201 , and three power supply lines. Thus, the three heat generating members  201  connected to the three power supply lines, one for one, can be independently driven from each other. Further, each of the two connectors in this embodiment has two terminals (which are similar to the one shown in  FIG. 13 ), which are in the housing of the connector. 
         [0103]    Referring to  FIG. 22(   a ), the front surface of the heater  5  is provided with two heat generation lines (heat generating members  201   a  and  201   b ), and the back surface of the heater is provided with one heat generation line (heat generating member  201   c ). The three heat generating members are different in heat generation amount distribution. More concretely, the front surface of the heater  5  are provided with two heat generating members  201   a  and  201   b , which are in parallel to each other and extend in the lengthwise direction of the heater  5 . The heat generation amount distribution of the heat generating member  201   a  is such that the closer it is to the center of the heat generating member  201   a , the greater the amount by which heat is generated by the heat generating member  201   a , whereas the heat generation distribution of the heat generating member  201   b  is such that the farther it is from the lengthwise center of the heat generating member  201   b , the greater the amount by which heat is generated by the heat generating member  201   b . The heat generation amount distribution of the heat generating member  201   c  is similar to that of the heat generating member  201   a , that is, the closer to the lengthwise center of the heat generating member  201   c , the greater the amount by which heat is generated by the heat generating member  201   c . However, the heat generating member  201   c  is shorter than the heat generating member  201   a , as shown in  FIG. 22(   a ). These heat generating members are integrated with an electric power supply circuit as shown in  FIG. 22(   e ). Thus, the heater  5  is changed in heat distribution by controlling switches  240   a - 240   c . That is, the heater  5  can be changed in heat distribution so that the heat distribution of the heater  5  matches recording medium size, for example. 
         [0104]    Referring to  FIG. 22 , the heater  200  is provided with five electrodes  210   a - 210   e . Each of these electrodes is connected to a connector. The heating unit  2  in this embodiment is structured so that the circuit shown in  FIG. 22(   e ) can be completed simply by connecting two connectors ( 230 A and  230 B) to the heater  5 . The housing of the connector  230 A contains two terminals which are similar to those shown in  FIG. 13 . That is, the heating unit  2  in this embodiment has four terminals ( 220   a - 220   c ). However, it is only in the case of the terminal  220   a  that all the spring contacts come into contact with one of the electrodes of the heater  5  as shown  FIG. 22(   c ); the portions of the heater  5 , which correspond in position to the other terminals  220  ( 220   b ,  220   c  and  220   e ) than the terminal  220   a , one for one, have an electrode on only the front or back surface. 
         [0105]    The four terminals  220   a - 220   e  are the same in shape. That is, the two connectors  230 A and  230 B in this embodiment are designed to be connected to the lengthwise ends of a two-sided heater, one for one, and yet, are the same in structure. That is, this connector design can reduces the connectors  230 A and  230 B in cost. Further, they can be further reduced in cost by being made the same in the shape of their housings  230 A and  230 B. 
         [0106]    The connector terminals in this embodiment are practically the same in structure as the one shown in  FIG. 13 . Therefore, they can assure that a proper amount of contact pressure is generated and maintained between their spring contacts and the corresponding electrodes of the heater. 
       Embodiment 6 
       [0107]    Next, referring to  FIGS. 23 and 24 , the sixth embodiment of the present invention is described. This embodiment is different from the preceding embodiments in that unlike the connectors in the preceding embodiments, the connector  333  in this embodiment has two terminals  34   a  and  34   b  which are electrically independent from each other, and the spring contacts of which are in the top and bottom portions of the connector housing. 
         [0108]      FIG. 23  is a perspective view of the connector terminal  34  in this embodiment. The connector terminal  34  has two sub-terminals  34   a  and  34   b . The sub-terminal  34   a  has two spring contacts  161   f  and  162   f , and is in connection to a lead  17   a . The sub-terminal  34   b  has two spring contacts  161   r  and  162   r , and is in connection to a lead  17   b . “ 161   fc ,  162   fc ,  161   rc  and  162   rc ” stand for the points of contact of the spring contacts, one for one. 
         [0109]      FIG. 24(   a ) shows the state of the combination of the lengthwise end portion of the heating unit  2  after the attachment of the connector  333  to the heater holder  6  which holds the heater  5 .  FIG. 24(   b ) a sectional view of the connector  333 , at a plane (b)-(b) in  FIG. 24(   a ), after the disengagement of the connector  333  from the heater. “t” stands for the thickness of the heater  5 . The connector sub-terminals  34   a  and  34   b  are solidly attached to terminal anchorages  14 A and  14 B, respectively, with which the connector housing  315  is provided. Referring to  FIG. 24(   b ), when the connector  333  is not in engagement with the heater  5 , the spring contacts  161   f  and  162   f  of the connector sub-terminal  34   a , and the spring contacts  161   r  and  162   r  of the connector sub-terminal  34   b , overlap as seen from the direction perpendicular to the direction in which their points of contact are displaced. 
         [0110]    The connector in this embodiment also can ensure that a proper amount of contact pressure is generated and maintained between the point of contact of each spring contact and the corresponding electrode of the heater, regardless of the thickness t of the heater  5 . 
         [0111]    By the way, a substantial distance is sometimes required between the top and bottom terminals when the two terminals are differently used in terms of polarity. The method for providing a proper amount of distance between the top and bottom terminals is as follows: 
         [0112]    In the case of this embodiment, a pair of insulating projections  350  are provided in the housing  315 . The insulating projections  350  are also given the function of guiding the connector sub-terminals  34   a  and  34   b  when the sub-terminals  34   a  and  34   b  are fitted into the housing  315 . Referring to  FIG. 24(   b ), the insulating projections  350  are positioned so that they will be between the connector sub-terminals  34   a  and  34   b  after the fitting of the sub-terminals  34   a  and  34   b  into the housing  315 . The housing  315  is structured so that the insulating projections  350  project toward the center of the housing  315 . 
         [0113]      FIG. 24(   c ) is an enlarged view of the area of  FIG. 24(   b ), which is encircled by a dotted line D. There is a clearance y between the top end of the insulating projection  350  and spring contact  161   f , which prevents the top end from coming into contact with the spring contact  161   f . The distance provided between the connector sub-terminals  34   a  and  34   b  to insulate them from each other can be expressed as (a+b+c) in  FIG. 24(   c ). Thus, a satisfactory amount of insulation distance can be provided by structuring the connector so that Inequality (insulation distance&lt;(a+b+c) is satisfied. 
         [0114]    While the present invention has been described with reference to the exemplary embodiments, it is not to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
         [0115]    This application claims priority from Japanese Patent Applications Nos. 108115/2012 and 066154/2013 filed May 10, 2012 and Mar. 27, 2013, respectively, which are hereby incorporated by reference.