Patent Publication Number: US-9423736-B2

Title: Heater and image heating apparatus including the same

Description:
FIELD OF THE INVENTION AND RELATED ART 
     The present invention relates to a heater for heating an image on a sheet and an image heating apparatus provided with the same. The image heating apparatus is usable with an image forming apparatus such as a copying machine, a printer, a facsimile machine, a multifunction machine having a plurality of functions thereof or the like. 
     An image forming apparatus is known in which a toner image is formed on the sheet and is fixed on the sheet by heat and pressure in a fixing device (image heating apparatus). As for such a fixing device, a type of fixing device is recently proposed (Japanese Laid-open Patent Application 2012-37613) in which a heat generating element (heater) is contacted to an inner surface of a thin flexible belt to apply heat to the belt. Such a fixing device is advantageous in that the structure has a low thermal capacity, and therefore, the temperature rise to allow the fixing operation is quick. 
     Japanese Laid-open Patent Application 2012-37613 discloses a structure of a fixing device in which a heat generating region width of a heat generating element (heater) is controlled in accordance with a width size of the sheet.  FIG. 11  is a circuit diagram of the heater disclosed in Japanese Laid-open Patent Application 2012-37613. As shown in  FIG. 11 , the fixing device comprises electrodes  1027  ( 1027   a - 1027   f ) arranged in a longitudinal direction of a substrate  1021  and heat generating resistance layers  1025 ), and the electric power supply is supplied through the electrodes to the heat generating resistance layers  1025  ( 1025   a - 1025   e ) so that the heat generating resistance layer generates heat. 
     In this fixing device, each electrode is electrically connected with an electroconductive line layers  1029  ( 1029   a ,  1029   b ) formed on the substrate. More specifically, the electroconductive line layer connected with the electrode  1027   b  and the electrode  1027   d  extends toward one longitudinal end of the substrate. The electroconductive line layer  1029   a  connected with the electrode  1027   c  and the electrode  1027   e  extends toward another longitudinal end of the substrate. In the one end portion of the substrate with respect to the longitudinal direction, the electrode  1027   a  and the electroconductive line layer  1029   b  are connectable with respective electroconductive members. In the other end portion of the substrate with respect to the longitudinal direction, the electrode  1027   f  and the electroconductive line layer  1029   a  are connectable with respective electroconductive members. In more detail, the opposite longitudinal end portions of the substrate is not coated with an insulation layer for protecting the electroconductive lines, and the electroconductive line layers  1029   a    1029   b  and the electrodes  1027   a ,  1027   f  are exposed. Therefore, the heater  1006  is connected to a voltage supply circuit by the electroconductive member contacted to exposed stations of electroconductive line layers  1029   a ,  1029   b  and electrodes  1027   a ,  1027   f . The voltage supply circuit includes an AC voltage source and switches  1033  ( 1033   a ,  1033   b ,  1033   c ,  1033   d ), by combinations of the actuations of which heater energization pattern is controlled. In other words, the electroconductive line layers  1029   a ,  1029   b  are selectively connected with a voltage source contact  1031   a  or a voltage source contact  1031   b  in accordance with the intended connection pattern. With such a structure, the fixing device disclosed in Japanese Laid-open Patent Application 2012-37613 thereby changes the width size of the heat generating region of the heat generating resistance layer  1025  in accordance with the width size of the sheet to be heated. 
     Here, for simplicity, the exposed portion of the electroconductive line layer  1029   a  will be called electrical contact A, the exposed portion of the electroconductive line layer  1029   b  is called electrical contact B, the exposed portion of the electrode  1027   a  will be called electrical contact C, and the exposed portion of the electrode  1027   f  will be called electrical contact D. With the structure disclosed in Japanese Laid-open Patent Application 2012-37613 in which the electrical contacts An and D and electrical contacts B and C are arranged in the widthwise direction of the substrate, the length of the substrate can be reduced as compared with the structure in which the electrical contacts are arranged in the longitudinal direction of the substrate. 
     As shown in part (a) of  FIG. 11 , when the heater  1006  generates heat for the maximum width sheet, the electrical contacts An and C are connected with the voltage source contact  1031   a , and the electrical contacts B and D are connected with the voltage source contact  1031   b . That is, the electrical contacts A and D which are adjacent to each other in the widthwise direction of the substrate are connected with different voltage source contacts, and the electrical contacts B and C which are adjacent to each other in the widthwise direction of the substrate are connected with different voltage source contacts. Therefore, a short circuit attributable to creepage discharge tends to occur between the electrical contacts A and D, and between the electrical contacts B and C. In order to prevent the short circuit, it is required to provide a sufficiently wide clearance between the electrical contacts A and D and between the electrical contacts B and C. 
     However, if sufficiently wide gaps are provided between the electrical contacts arranged in the widthwise direction of the substrate  1021 , the substrate  1021  is required to have a sufficiently large width. As a result, the substrate  1021  increases in size in the widthwise direction which leads to an increase in cost. 
     A heater in which a width size of the heat generating region is changeable is desired to suppress an increase of the width of the substrate resulting from the arrangement of the electrical contacts in the widthwise direction of the substrate. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a heater having a relatively smaller width. 
     It is another object of the present invention to provide an image heating apparatus having a relatively smaller width. 
     According to an aspect of the present invention, there is provided a heater usable with an image heating apparatus including an electric energy supplying portion provided with a first terminal and a second terminal, and an endless belt for heating an image on a sheet. The heater is contactable to the belt to heat the belt. The heater comprises: a substrate; a first connecting portion electrically connectable with the first terminal; a second connecting portion electrically connectable with the second terminal and provided adjacent to the first connecting portion with a gap in a longitudinal direction of said substrate; a third connecting portion electrically connectable with the second terminal; a fourth connecting portion electrically connectable with the second terminal and provided adjacent to the third connecting portion with a gap in the widthwise direction of said substrate; and a plurality of heat generating portions arranged in the longitudinal direction of the substrate. The heat generating portions include at least one heat generating portion capable of generating heat by electric energy supplied from the first connecting portion and the second connecting portion, at least one heat generating portion capable of generating heat by electric energy supplied from the first connecting portion and the third connecting portion, and at least one heat generating portion capable of generating heat by electric energy supplied from the first connecting portion and the fourth connecting portion. A gap between the third connecting portion and the fourth connecting portion in the widthwise direction is smaller than a gap between the first connecting portion and the second connecting portion in the longitudinal direction. 
     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 
         FIG. 1  is a section of view of the image forming apparatus according to an Embodiment 1 of the present invention. 
         FIG. 2  is a sectional view of an image heating apparatus according to an Embodiment 1 of the present invention. 
         FIG. 3  is a front view of an image heating apparatus according to Embodiment 1 of the present invention. 
         FIG. 4  illustrates a structure of a heater Embodiment 1. 
         FIG. 5  illustrates the structural the relationship of the image heating apparatus according to an Embodiment 1. 
         FIG. 6  illustrates mounting of a connector. 
         FIG. 7  illustrates a contact terminal. 
         FIG. 8  illustrates an arrangement of the electrical contacts in Embodiment 1. 
         FIG. 9  illustrates the structural the relationship of the image heating apparatus according to an Embodiment 1. 
         FIG. 10  illustrates an arrangement of the electrical contacts in Embodiment 2. 
         FIG. 11  is a circuit diagram of a conventional heater. 
         FIG. 12  is an illustration (a) of heat generating type used with a heater, and an illustration (b) of a switching type for a heat generating region used with the heater. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Embodiments of the present invention will be described in conjunction with the accompanying drawings. In this embodiment, the image forming apparatus is a laser beam printer using an electrophotographic process as an example. The laser beam printer will be simply called printer 
     Embodiment 1 
     Image Forming Apparatus 
       FIG. 1  is a sectional view of the printer  1 , which is the image forming apparatus of this embodiment. The printer  1  comprises an image forming station  10  and a fixing device  40 , in which a toner image formed on the photosensitive drum  11  is transferred onto a sheet P, and is fixed on the sheet P, by which an image is formed on the sheet P. Referring to  FIG. 1 , the structures of the apparatus will be described in detail. 
     As shown in  FIG. 1 , the printer  1  includes image forming stations  10  for forming respective color toner images Y (yellow), M (magenta), C (cyan) and), Bk (black). The image forming stations  10  include respective photosensitive drums  11  ( 11 Y,  11 M,  11 C,  11 Bk), corresponding to Y, M, C, Bk colors, arranged in the order named from the left side. Around each drum  11 , similar elements are provided as follows: a charger  12  ( 12 Y,  12 M,  12 C,  12 Bk); an exposure device  13  ( 13 Y,  13 M,  13 C,  13 Bk); a developing device  14  ( 14 Y,  14 M,  14 C,  14 Bk); a primary transfer blade  17  ( 17 Y,  17 M,  17 C,  17 Bk); and a cleaner  15  ( 15 Y,  15 M,  15 C,  15 Bk). The structure for the Bk toner image formation will be described as a representative example, and the descriptions for the other colors are omitted for simplicity by assigning the like reference numerals. So, the elements will be simply called the photosensitive drum  11 , the charger  12 , the exposure device  13 , the developing device  14 , the primary transfer blade  17  and the cleaner  15  with these reference numerals. 
     The photosensitive drum  11  as an electrophotographic photosensitive member is rotated by a driving source (unshown) in the direction indicated by an arrow (counterclockwise direction in  FIG. 1 ). Around the photosensitive drum  11 , the charger  12 , the exposure device  13 , the developing device  14 , the primary transfer blade  17  and the cleaner  15  are provided in the order named. 
     A surface of the photosensitive drum  11  is electrically charged by the charger  12 . Thereafter, the surface of the photosensitive drum  11  exposed to a laser beam in accordance with image information by the exposure device  13 , so that an electrostatic latent image is formed. The electrostatic latent image is developed into a Bk toner image by the developing device  14 . At this time, similar processes are carried out for the other colors. The toner image is transferred from the photosensitive drum  11  onto an intermediary transfer belt  31  by the primary transfer blade  17  sequentially (primary-transfer). The toner remaining on the photosensitive drum  11  after the primary-image transfer is removed by the cleaner  15 . By this, the surface of the photosensitive drum  11  is cleaned so as to be prepared for the next image formation. 
     On the other hand, the sheets P contained in a feeding cassette  20  are placed on a multi-feeding tray  25  and picked up by a feeding mechanism (unshown) and fed to a pair of registration rollers. The sheet P is a member on which the image is formed. Specific examples of the sheet P are plain paper, a thick sheet, a resin material sheet, an overhead projector film or the like. The pair of registration rollers  23  once stops the sheet P to correct oblique feeding. The registration rollers  23  then feed the sheet P into between the intermediary transfer belt  31  and the secondary transfer roller  35  in timed relation with the toner image on the intermediary transfer belt  31 . The roller  35  functions to transfer the color toner images from the belt  31  onto the sheet P. Thereafter, the sheet P is fed into the fixing device (image heating apparatus)  40 . The fixing device  40  applies heat and pressure to the toner image T on the sheet P to fix the toner image on the sheet P. 
     [Fixing Device] 
     The fixing device  40 , which is the image heating apparatus used in the printer  1 , will be described  FIG. 2  is a sectional view of the fixing device  40 .  FIG. 3  is a front view of the fixing device  40 .  FIG. 5  illustrates a structural relationship of the fixing device  40 . 
     The fixing device  40  is an image heating apparatus for heating the image on the sheet by a heater unit  60  (unit  60 ). The unit  60  includes a flexible thin fixing belt  603  and a heater  600  contacted to the inner surface of the belt  603  to heat the belt  603  (low thermal capacity structure). Therefore, the belt  603  can be efficiently heated, so that a quick temperature rise at the start of the fixing operation is accomplished. As shown in  FIG. 2 , the belt  603  is nipped between the heater  600  and the pressing roller  70  (roller  70 ), by which a nip N is formed. The belt  603  rotates in the direction indicated by the arrow (clockwise in  FIG. 2 ), and the roller  70  is rotated in the direction indicated by the arrow (counterclockwise in  FIG. 2 )  29  to nip and feed the sheet P supplied to the nip N. At this time, the heat from the heater  600  is supplied to the sheet P through the belt  603 , and therefore, the toner image T on the sheet P is heated and pressed by the nip N, so that the toner image it fixed on the sheet P by the heat and pressure. The sheet P having passed through the fixing nip N is separated from the belt  603  and is discharged. In this embodiment, the fixing process is carried out as described above. The structure of the fixing device  40  will be described in detail in conjunction with the accompanying drawings. 
     Unit  60  is a unit for heating and pressing an image on the sheet P. A longitudinal direction of the unit  60  is parallel with the longitudinal direction of the roller  70 . The unit  60  comprises a heater  600 , a heater holder  601 , a support stay  602  and a belt  603 . 
     The heater  600  is a heating member for heating the belt  603 , slidably contacting with the inner surface of the belt  603 . The heater  600  is pressed to the inside surface of the belt  603  toward the roller  70  so as to provide a desired nip width of the nip N. The dimensions of the heater  600  in this embodiment are 5-20 mm in the width (the dimension as measured in the left-right direction in  FIG. 2 ), 350-400 mm in the length (the dimension measured in the front-rear direction in  FIG. 2 ), and 0.5-2 mm in the thickness. The heater  600  comprises a substrate  610  elongated in a direction perpendicular to the feeding direction of the sheet P (widthwise direction of the sheet P), and a heat generating resistor  620  (heat generating element  620 ). 
     The heater  600  is fixed on the lower surface of the heater holder  601  along the longitudinal direction of the heater holder  601 . In this embodiment, the heat generating element  620  is provided on the back side of the substrate  610  is not in slidable contact with the belt  603 , but the heat generating element  620  may be provided on the front surface of the substrate  610  is in slidable contact with the belt  603 . However, the heat generating element  620  is preferably provided on the back side of the substrate  610 , by which a uniform heating effect to the substrate  610  is accomplished, from the standpoint of preventing non-uniform heat application which may be caused by a non-heat generating portion of the heat generating element  620 . The details of the heater  600  will be described hereinafter. 
     The belt  603  is a cylindrical (endless) belt (film) for heating the image on the sheet in the nip N. The belt  603  comprises a base material  603   a , an elastic layer  603   b  thereon, and a parting layer  603   c  on the elastic layer  603   b , for example. The base material  603   a  may be made of metal material such as stainless steel or nickel, or a heat resistive resin material such as polyimide. The elastic layer  603   b  may be made of an elastic and heat resistive material such as a silicone rubber or a fluorine-containing rubber. The parting layer  603   c  may be made of fluorinated resin material or silicone resin material. 
     The belt  603  of this embodiment has dimensions of approx. 30 mm in the outer diameter, approx. 330 mm in the length (the dimension measured in the front-rear direction in  FIG. 2 ), approx. 30 μm in the thickness, and the material of the base material  603   a  is nickel. The silicone rubber elastic layer  603   b  having a thickness of approx. 400 μm is formed on the base material  603   a , and a fluorine resin tube (parting layer  603   c ) having a thickness of approx. 20 μm coats the elastic layer  603   b.    
     The belt contacting surface of the substrate  610  may be provided with a polyimide layer having a thickness of approx. 10 μm as a sliding layer  603   d . When the polyimide layer is provided, the rubbing resistance between the fixing belt  603  and the heater  600  is low, and therefore, the wearing of the inner surface of the belt  603  can be suppressed. In order to further enhance the slidability, a lubricant such as grease may be applied to the inner surface of the belt. 
     The heater holder  601  (holder  601 ) functions to hold the heater  600  in the state of urging the heater  600  toward the inner surface of the belt  603 . The holder  601  has a semi-arcuate cross-section (the surface of  FIG. 2 ) and functions to regulate a rotation orbit of the belt  603 . The holder  601  may be made of heat resistive resin material or the like. In this embodiment, it is Zenite 7755 (tradename) available from Dupont. 
     The support stay  602  supports the heater  600  by way of the holder  601 . The support stay  602  is preferably made of a material which is not easily deformed even when a high pressure is applied thereto, and in this embodiment, it is made of SUS304 (stainless steel). 
     As shown in  FIG. 3 , the support stay  602  is supported by left and right flanges  411   a  and  411   b  at the opposite end portions with respect to the longitudinal direction. The flanges  411   a  and  411   b  may be simply called flange  411 . The flange  411  regulates the movement of the belt  603  in the longitudinal direction and the circumferential direction configuration of the belt  603 . The flange  411  is made of heat resistive resin material or the like. In this embodiment, it is PPS (polyphenylenesulfide resin material). 
     Between the flange  411   a  and a pressing arm  414   a , an urging spring  415   a  is compressed. Also, between a flange  411   b  and a pressing arm  414   b , an urging spring  415   b  is compressed. The urging springs  415   a  and  415   b  may be simply called urging spring  415 . With such a structure, the elastic force of the urging spring  415  is applied to the heater  600  through the flange  411  and the support stay  602 . The belt  603  is pressed against the upper surface of the roller  70  at a predetermined urging force to form the nip N having a predetermined nip width. In this embodiment, the pressure is approx. 156.8 N at one end portion side and approx. 313.6 N (32 kgf) in total. 
     As shown in  FIG. 3 , connectors  700   a ,  700   b  are provided as an electric energy supply member electrically connected with the heater  600  to supply the electric power to the heater  600 . The connectors  700   a ,  700   b  may be simply called connector  700 . The connector  700   a  is detachably provided at one longitudinal end portion of the heater  600 . The connector  700   b  is detachably provided at one longitudinal end portion of the heater  600 . The connector  700  is easily detachably mounted to the heater  600 , and therefore, assembling of the fixing device  40  and the exchange of the heater  600  or belt  603  upon damage of the heater  600  is easy, thus providing good maintenance property. Details of the connector  700  will be described hereinafter. 
     As shown in  FIG. 2 , the roller  70  is a nip forming member which contacts an outer surface of the belt  603  to cooperate with the belt  603  to form the nip N The roller  70  has a multi-layer structure on the metal core of metal material, the multi-layer structure including an elastic layer  72  on the metal core  71  and a parting layer  73  on the elastic layer  72 . Examples of the materials of the metal core  71  include SUS (stainless steel), SUM (sulfur and sulfur-containing free-machining steel), Al (aluminum) or the like. Examples of the materials of the elastic layer  72  include an elastic solid rubber layer, an elastic foam rubber layer, an elastic porous rubber layer or the like. Examples of the materials of the parting layer  73  include fluorinated resin material. 
     The roller  70  of this embodiment includes a metal core of steel, an elastic layer  72  of silicone rubber foam on the metal core  71 , and a parting layer  73  of fluorine resin tube on the elastic layer  72 . Dimensions of the portion of the roller  70  having the elastic layer  72  and the parting layer  73  are approx. 25 mm in outer diameter, and approx. 330 mm in length. 
     A thermistor  630  is a temperature sensor provided on a back side of the heater  600  (opposite side from the sliding surface side. The thermistor  630  is bonded to the heater  600  in the state that it is insulated from the heat generating element  620 . The thermistor  630  has a function of detecting the a temperature of the heater  600 . As shown in  FIG. 5 , the thermistor  630  is connected with a control circuit  100  through an A/D converter (unshown) and feed an output corresponding to the detected temperature to the control circuit  100 . 
     The control circuit  100  comprises a circuit including a CPU operating for various controls, a non-volatilization medium such as a ROM storing various programs. The programs are stored in the ROM, and the CPU reads and execute them to effect the various controls. The control circuit  100  may be an integrated circuit such as ASIC if it is capable of performing the similar operation. 
     As shown in  FIG. 5 , the control circuit  100  is electrically connected with the voltage source  110  so as to control is electric power supply from the voltage source  110 . The control circuit  100  is electrically connected with the thermistor  630  to receive the output of the thermistor  630 . 
     The control circuit  100  uses the temperature information acquired from the thermistor  630  for the electric power supply control for the voltage source  110 . More particularly, the control circuit  100  controls the electric power to the heater  600  through the voltage source  110  on the basis of the output of the thermistor  630 . In this embodiment, the control circuit  100  carries out a wave number control of the output of the voltage source  110  to adjust an amount of heat generation of the heater  600 . By such a control, the heater  600  is maintained at a predetermined temperature (approx. 180 degree C., for example). 
     As shown in  FIG. 3 , the metal core  71  of the roller  70  is rotatably held by bearings  41   a  and  41   b  provided in a rear side and a front side of the side plate  41 , respectively. One axial end of the metal core is provided with a gear G to transmit the driving force from a motor M to the metal core  71  of the roller  70 . As shown in  FIG. 2 , the roller  70  receiving the driving force from the motor M rotates in the direction indicated by the arrow (clockwise direction). In the nip N, the driving force is transmitted to the belt  603  by the way of the roller  70 , so that the belt  603  is rotated in the direction indicated by the arrow (counterclockwise direction). 
     The motor M is a driving portion for driving the roller  70  through the gear G. As shown in  FIG. 5 , the control circuit  100  is electrically connected with the motor M to control the electric power supply to the motor M. When the electric energy is supplied by the control of the control circuit  100 , the motor M starts to rotate the gear G. 
     The control circuit  100  controls the rotation of the motor M. The control circuit  100  rotates the roller  70  and the belt  603  using the motor M at a predetermined speed. It controls the motor so that the speed of the sheet P nipped and fed by the nip N in the fixing process operation is the same as a predetermined process speed (approx. 200 [mm/sec], for example). 
     [Heater] 
     The structure of the heater  600  used in the fixing device  40  will be described in detail.  FIG. 4  illustrates a structure of a heater Embodiment 1.  FIG. 6  illustrates a connector. Part (a) of  FIG. 12  illustrates a heat generating type used in the heater  600 . Part (b) of  FIG. 12  illustrates a heat generating region switching type used with the heater  600 . 
     The heater  600  of this embodiment is a heater using the heat generating type shown in parts (a) and (b) of  FIG. 12 . As shown in part (a) of  FIG. 11 , electrodes A-C are electrically connected with the A-electroconductive-line, and electrodes D-F are electrically connected with B-electroconductive-line. The electrodes connected with the A-electroconductive-lines and the electrodes connected with the B-electroconductive-lines are interlaced (alternately arranged) along the longitudinal direction (left-right direction in part (a) of  FIG. 11 ), and heat generating elements are electrically connected between the adjacent electrodes. When a voltage V is applied between the A-electroconductive-line and the B-electroconductive-line, a potential difference is generated between the adjacent electrodes. As a result, electric currents flow through the heat generating elements, and the directions of the electric currents through the adjacent heat generating elements are opposite to each other. In this type heater, the heat is generated in the above-described the manner. As shown in part (b) of  FIG. 12 , between the B-electroconductive-line and the electrode F, a switch or the like is provided, and when the switch is opened, the electrode B and the electrode C are at the same potential, and therefore, no electric current flows through the heat generating element therebetween. In this system, the heat generating elements arranged in the longitudinal direction are independently energized so that only a part of the heat generating elements can be energized by switching a part off. In other words, with the system, the heat generating region can be changed by providing a switch or the like in the electroconductive line. In the heater  600 , the heat generating region of the heat generating element  620  can be changed using the above-described system. 
     The heat generating element generates heat when energized, irrespective of the direction of the electric current, but it is preferable that the heat generating elements and the electrodes are arranged so that the currents flow along the longitudinal direction. Such an arrangement is advantageous over the arrangement in which the directions of the electric currents are in the widthwise direction perpendicular to the longitudinal direction (up-down direction in part (a) of  FIG. 11 ) in the following manner. When joule heat generation is effected by the electric energization of the heat generating element, the heat generating element generates heat corresponding to the resistance value thereof, and therefore, the dimensions and the material of the heat generating element are selected in accordance with the direction of the electric current so that the resistance value is at a desired level. The dimension of the substrate on which the heat generating element is provided is very short in the widthwise direction as compared with that in the longitudinal direction. Therefore, if the electric current which flows in the widthwise direction, it is difficult to provide the heat generating element with a desired resistance value, using a low resistance material. On the other hand, when the electric current flows in the longitudinal direction, it is relatively easy to provide the heat generating element with a desired resistance value, using the low resistance material. In addition, when a high resistance material is used for the heat generating element, a temperature non-uniformity may result from non-uniformity in the thickness of the heat generating element when it is energized. For example, when the heat generating element material is applied on the substrate along the longitudinal direction by screen printing or like, a thickness non-uniformity of about 5% may result in the widthwise direction. This is because a heat generating element material painting non-uniformity occurs due to a small pressure difference in the widthwise direction by a painting blade. For this reason, it is preferable that the heat generating elements and the electrodes are arranged so that the electric currents flow in the longitudinal direction. 
     In the case that the electric power is supplied individuality to the heat generating elements arranged in the longitudinal direction, it is preferable that the electrodes and the heat generating elements are disposed such that the directions of the electric current flow alternates between adjacent ones. As to the arrangements of the heat generating members and the electrodes, it would be considered to arrange the heat generating elements each connected with the electrodes at the opposite ends thereof, in the longitudinal direction, and the electric power is supplied in the longitudinal direction. However, with such an arrangement, two electrodes are provided between adjacent heat generating elements, with the result of the likelihood of a short circuit. In addition, the number of required electrodes is large with the result of large non-heat generating portion. Therefore, it is preferable to arrange the heat generating elements and the electrodes such that an electrode is made common between adjacent heat generating elements. With such an arrangement, the likelihood of a short circuit between the electrodes can be avoided, and the non-heat generating portion can be made small. 
     In this embodiment, a common electroconductive line  640  corresponds to A-electroconductive-line of part (a) of  FIG. 12 , and opposite electroconductive lines  650 ,  660   a ,  660   b  correspond to B-electroconductive-line. In addition, common electrodes  642   a - 642   g  correspond to electrodes A-C of part (a) of  FIG. 12 , and opposite electrodes  652   a - 652   d ,  662   a ,  662   b  correspond to electrodes D-F. Heat generating elements  620   a - 620   l  correspond to the heat generating elements of part (a) of  FIG. 12 . Hereinafter, the common electrodes  642   a - 642   g  are simply common electrode  642 . The opposite electrodes  652   a - 652   e  are simply called opposite electrode  652 . The opposite electrodes  662   a - 662   e  are simply called opposite electrode  662 . The opposite electroconductive lines  660   a ,  660   b  are simply called opposite electroconductive line  660 . The heat generating elements  620   a - 620   l  are simply called heat generating element  620 . The structure of the heater  600  will be described in detail referring to the accompanying drawings. 
     As shown in  FIGS. 4 and 6 , the heater  600  comprises the substrate  610 , the heat generating element  620  on the substrate  610 , an electroconductor pattern (electroconductive line), and an insulation coating layer  680  covering the heat generating element  620  and the electroconductor pattern. 
     The substrate  610  determines the dimensions and the configuration of the heater  600  and is contactable to the belt  603  along the longitudinal direction of the substrate  610 . The material of the substrate  610  is a ceramic material such as alumina, aluminum nitride or the like, which has high heat resistivity, thermo-conductivity, electrical insulative property or the like. In this embodiment, the substrate is a plate member of alumina having a length (measured in the left-right direction in  FIG. 4 ) of approx. 400 mm, a width (up-down direction in  FIG. 4 ) of approx. 8 mm and a thickness of approx. 1 mm. 
     On the back side of the substrate  610 , the heat generating element  620  and the electroconductor pattern (electroconductive line) are provided through a thick film printing method (screen printing method) using an electroconductive thick film paste. In this embodiment, a silver paste is used for the electroconductor pattern so that the resistivity is low, and a silver-palladium alloy paste is used for the heat generating element  620  so that the resistivity is high. As shown in  FIG. 6 , the heat generating element  620  and the electroconductor pattern are coated with the insulation coating layer  680  of heat resistive glass so that they are electrically protected from leakage and a short circuit. 
     As shown in  FIG. 4 , there are provided an electrical contact  641  (one of a grounding contact and a non-grounding contact) and an electrical contact  661   a  (the other of the grounding contact and the non-grounding contact) as a part of the electroconductor pattern in one end portion side of the substrate  610  with respect to the longitudinal direction. In the other end portion side  610   b  of the substrate  610  with respect to the longitudinal direction, there are provided the electrical contacts  651  (the other of the grounding contact and the non-grounding contact),  661   b  (the other of the grounding contact and the non-grounding contact) as a part of the electroconductor pattern. In a central region  610   c  of the substrate  610  with respect to the longitudinal direction, the heat generating element  620  and the common electrode  642  and the opposite electrodes  652 ,  662  as a part of the electroconductor pattern are provided. In one end portion side  610   d  of substrate  610  beyond the heat generating element  620  with respect to the widthwise direction, the common electroconductive line  640  as a part of the electroconductor pattern is provided. In the other end portion side  610   e  of the substrate  610  beyond the heat generating element  620  with respect to the widthwise direction, the opposite electroconductive lines  650  and  660  are provided as a part of the electroconductor pattern. 
     The heat generating elements  620  ( 620   a - 620   l ) are resistors for generating joule heat upon electric power supply thereto. The heat generating element  620  is one heat generating element member extending in the longitudinal direction on the substrate  610 , and is disposed in the region  610   c  ( FIG. 4 ) adjacent to the center portion of the substrate  610 . The heat generating element  620  has a desired resistance value, and has a width (measured in the widthwise direction of the substrate  610 ) of 1-4 mm, a thickness of 5-20 μm. The heat generating element  620  in this embodiment has the width of approx. 2 mm and the thickness of approx. 10 μm. A total length of the heat generating element  620  in the longitudinal direction is approx. 320 mm, which is enough to cover a width of the A4 size sheet P (approx. 297 mm in width). 
     On the heat generating element  620 , seven common electrodes  642   a - 642   g  which will be described hereinafter are laminated with intervals in the longitudinal direction. In other words, the heat generating element  620  is isolated into six sections by common electrodes  642   a - 642   g  along the longitudinal direction. The lengths measured in the longitudinal direction of the substrate  610  of each section are approx. 53.3 mm. On central portions of the respective sections of the heat generating element  620 , one of the six opposite electrodes  652 ,  662  ( 652   a - 652   d ,  662   a ,  662   b ) are laminated. In this manner, the heat generating element  620  is divided into 12 sub-sections. The heat generating element  620  divided into 12 sub-sections can be deemed as a plurality of heat generating elements  620   a - 620   l . In other words, the heat generating elements  620   a - 620   l  electrically connect adjacent electrodes with each other. Lengths of the sub-section measured in the longitudinal direction of the substrate  610  are approx. 26.7 mm. Resistance values of the sub-section of the heat generating element  620  with respect to the longitudinal direction are approx. 120Ω. With such a structure, the heat generating element  620  is capable of generating heat in a partial area or areas with respect to the longitudinal direction. 
     The resistivities of the heat generating elements  620  with respect to the longitudinal direction are uniform, and the heat generating elements  620   a - 620   l  have substantially the same dimensions. Therefore, the resistance values of the heat generating elements  620   a - 620   l  are substantially equal. When they are supplied with electric power in parallel, the heat generation distribution of the heat generating element  620  is uniform. However, it is not inevitable that the heat generating elements  620   a - 620   l  have substantially the same dimensions and/or substantially the same resistivities. For example, the resistance values of the heat generating elements  620   a  and  620   l  may be adjusted so as to prevent temperature lowering at the longitudinal end portions of the heat generating element  620 . At the positions of the heat generating element  620  where the common electrode  642  and the opposite electrode  652 ,  662  are provided, the heat generation of the heat generating element  620  is substantially zero. However, the heat uniforming function of the substrate  610  makes the influence on the fixing process negligible if the width of the electrode is not more than 1 mm, for example. In this embodiment, the width of each electrode is not more than 1 mm. The common electrodes  642  ( 642   a - 642   g ) are a part of the above-described electroconductor pattern. The common electrode  642  extends in the widthwise direction of the substrate  610  perpendicular to the longitudinal direction of the heat generating element  620 . In this embodiment, the common electrode  642  is laminated on the heat generating element  620 . The common electrodes  642  are odd-numbered electrodes of the electrodes connected to the heat generating element  620 , as counted from a one longitudinal end of the heat generating element  620 . The common electrode  642  is connected to one contact  110   a  of the voltage source  110  through the common electroconductive line  640  which will be described hereinafter. 
     The opposite electrodes  652 ,  662  are a part of the above-described electroconductor pattern. The opposite electrodes  652 ,  662  extend in the widthwise direction of the substrate  610  perpendicular to the longitudinal direction of the heat generating element  620 . The opposite electrodes  652 ,  662  are laminated on the heat generating element  620 . The opposite electrodes  652 ,  662  are the other electrodes of the electrodes connected with the heat generating element  620  other than the above-described common electrode  642 . That is, in this embodiment, they are even-numbered electrodes as counted from the one longitudinal end of the heat generating element  620 . 
     That is, the common electrode  642  and the opposite electrodes  662 ,  652  are alternately arranged along the longitudinal direction of the heat generating element. The opposite electrodes  652 ,  662  are connected to the other contact  110   b  of the voltage source  110  through the opposite electroconductive lines  650 ,  660  which will be described hereinafter. 
     The common electrode  642  and the opposite electrode  652 ,  662  function to supply the electric power to the heat generating element  620 . 
     In this embodiment, the odd-numbered electrodes are common electrodes  642 , and the even-numbered electrodes are opposite electrodes  652 ,  662 , but the structure of the heater  600  is not limited to this example. For example, the even-numbered electrodes may be the common electrodes  642 , and the odd-numbered electrodes may be the opposite electrodes  652 ,  662 . 
     In addition, in this embodiment, four of the all opposite electrodes connected with the heat generating element  620  are the opposite electrode  652 . In this embodiment, two of the all opposite electrodes connected with the heat generating element  620  are the opposite electrode  662 . However, the allotment of the opposite electrodes is not limited to this example, but may be changed depending on the heat generation widths of the heater  600 . For example, two may be the opposite electrode  652 , and four may be the opposite electrode  662 . 
     The common electroconductive line  640  is a part of the above-described electroconductor pattern. The common electroconductive line  640  extends along the longitudinal direction of the substrate  610  toward the one end portion side  610   a  of the substrate in the one end portion side  610   d  of the substrate. The common electroconductive line  640  is connected with the common electrodes  642  which is in turn connected with the heat generating element  620 . The common electroconductive line  640  is connected to the electrical contact  641  which will be described hereinafter. In this embodiment, in order to assure the insulation of the insulation coating layer  680 , a gap of approx. 400 μm is provided between the common electroconductive line  640  and each opposite electrode. 
     The opposite electroconductive line  650  is a part of the above-described electroconductor pattern. The opposite electroconductive line  650  extends along the longitudinal direction of substrate  610  toward the other end portion  610   b  of the substrate in the other end portion side  610   e  of the substrate. The opposite electroconductive line  650  is connected with the opposite electrode  652  which is in turn connected with the heat generating element  620 . The opposite electroconductive line  650  is connected to the electrical contact  651  which will be described hereinafter. 
     The opposite electroconductive line  660  ( 660   a ,  660   b ) is a part of the above-described electroconductor pattern. The opposite electroconductive line  660   a  extends along the longitudinal direction of substrate  610  toward the one end portion side  610   a  of the substrate in the other end portion side  610   e  of the substrate. The opposite electroconductive line  660   a  is connected with the opposite electrode  662   a  which is in turn connected with the heat generating element  620  ( 620   a ,  620   b ). The opposite electroconductive line  660   a  is connected to the electrical contact  661   a  which will be described hereinafter. The opposite electroconductive line  60   b  extends along the longitudinal direction of substrate  610  toward the other end portion  610   b  of the substrate in the other end portion side  610   e  of the substrate. The opposite electroconductive line  660   b  is connected to an opposite electrode  662   b  which is in turn connected with the heat generating element  620  ( 620   k ,  620   l ). The opposite electroconductive line  660   b  is connected to the electrical contact  661   b  which will be described hereinafter. In this embodiment, an approx. 400 μm gap is provided between the opposite electroconductive line  660   a  and the common electrode  642  and between the opposite electroconductive line  660   b  with common electrode  642  so that the electrical insulation is assured by the insulation coating layer  680 . In addition, between the opposite electroconductive lines  600   b  and  650 , an approx. 100 μm gap is provided. 
     The electrical contacts  641 ,  651 ,  661   a ,  661   b  are a part of the above-described electroconductor pattern. In one end portion side  610   a  of the substrate, the electrical contacts  641 ,  661   a  are provided. In other end portion side  610   b  of the substrate, the electrical contacts  651 ,  661   b  are provided. As shown in  FIG. 6 , the portion including the electrical contacts  641 ,  651 ,  661   a ,  661   b  is not coated with the insulation coating layer  680 , so that the electrical contacts  641 ,  651 ,  661   a ,  661   b  are exposed. Therefore, the electrical contacts  641 ,  661   a  function as a connecting portion for contacting to and electrically connecting to the connector  700   a . Therefore, the electrical contacts  651 ,  661   b  function as a connecting portion for contacting to and electrically connecting to the connector  700   b.    
     When voltage is applied between the electrical contact  641  and the electrical contact  651  through the connection between the heater  600  and the connector  700 , a potential difference is produced between the common electrode  642  ( 642   b - 642   f ) and the opposite electrode  652  ( 652   a - 652   d ). Therefore, through the heat generating elements  620   c ,  620   d ,  620   e ,  620   f ,  620   g ,  620   h ,  620   i ,  620   j , the currents flow along the longitudinal direction of the substrate  610 , and the directions of the currents through the adjacent heat generating elements are substantially opposite to each other. The heat generating elements  620   c ,  620   d ,  620   e ,  620   f ,  620   g ,  620   h ,  620   i  as a first heat generating region generate heat, respectively. 
     When voltage is applied between the electrical contact  641  and the electrical contact  661   a  through the connection between the heater  600  and the connector  700 , a potential difference is produced between the common electrode  642   a - 642   b ) and the opposite electrode  662   a . Therefore, through the heat generating elements  620   a ,  620   b , the currents flow along the longitudinal direction of the substrate  610 , and the directions of the currents through the adjacent heat generating elements are substantially opposite to each other. The heat generating elements  620   a ,  620   b  as a second heat generating region adjacent the first heat generating region generate heat. 
     When voltage is applied between the electrical contact  641  and the electrical contact  661   a  through the connection between the heater  600  and the connector  700 , a potential difference is produced between the common electrode  642   f ,  642   g  and the opposite electrode  662   b  through the common electroconductive line  640  and the opposite electroconductive line  660   b . Therefore, through the heat generating elements  620   k ,  620   l , the currents flow along the longitudinal direction of the substrate  610 , and the directions of the currents through the adjacent heat generating elements are substantially opposite to each other. By this, the heat generating elements  620   k ,  620   l  as a third heat generating region adjacent to the first heat generating region generate heat. 
     In this manner, by selecting the electrical contacts supplied with the voltage, the desired one or ones of the heat generating elements  620   a - 620   l  can be selectively energized. In this embodiment, the first heat generating region, the second heat generating region and the third heat generating region include a plurality of heat generating elements, respectively, but they may include one heat generating element, respectively. 
     [Connector] 
     The connector  700  used with the fixing device  40  will be described in detail.  FIG. 7  is an illustration of a terminal  710 . The connectors  700   a  and  700   b  of this embodiment includes terminals (which may be called terminal)  710 ,  720   a ,  720   b ,  730 , which are electrically connected with the heater  600  by being mounted to the heater  600 . More particularly, as shown in  FIG. 6 , the connector  700   a  includes the terminal  710  contactable to and electrically connectable to the electrical contact  641 , and the terminal  720   a  contactable to and electrically connectable to the electrical contact  661   a . The terminals  710 ,  720   a  are contained in a housing  750   a . The connector  700   b  includes a terminal  720   b  contactable to and electrically connectable to the electrical contact  661   b , and a terminal  730  contactable four and the electrically connectable to the electrical contact  651 . The terminals  720   b ,  730  are contained in a housing  750   a . By the connectors  700   a ,  700   b  being mounted to the heater  600  to sandwich the heater  600 , the terminals are connected with the corresponding electrical contacts. In the fixing device  40  of this embodiment having the above-described the structures, no soldering or the like is used for the electrical connection between the connectors and the electrical contacts. Therefore, the electrical connection between the heater  600  and the connector  700  rise in temperature during the fixing process operation can be accomplished and maintained with high reliability. In the fixing device  40  of this embodiment, the connector  700  is detachably mountable relative to the heater  600 , and therefore, the belt  603  and/or the heater  600  can be replaced without difficulty. The structure of the connector  700  will be described in detail. 
     As shown in  FIG. 6 , the connector  700   a  provided with the terminals  710 ,  720   a  of metal is mounted to the heater  600  from an end portion with respect to the widthwise direction of the substrate  610  in the one end portion side  610   a  of the substrate. The connector  700   b  provided with the terminals  720   b ,  730  is mounted to the heater  600  from a longitudinal end portion of the substrate  610  in the other end portion side  610   b  of the substrate. 
     The terminals  710 ,  720   a ,  720   b ,  730  will be described taking the terminal  710   a  as an example. The terminal  710   a  electrically connects the electrical contact  641  with a switch SW 643  which will be described hereinafter. As shown in  FIG. 7 , the contact terminal  710   a  is provided with a cable  712  for the electrical connection between the switch SW 643  and the electrical contact  711  for contacting to the electrical contact  641 . The contact terminal  710  has a channel-like configuration, and by moving in the direction indicated by an arrow in  FIG. 6 , it can receive the heater  600 . The portion of the connector  700   a  which contacts the electrical contact  641  is provided with the electrical contact  711  which contacts the electrical contact  641 , by which the electrical connection is established between the electrical contact  641  and the contact terminal  710 . The electrical contact  711  has a leaf spring property, and therefore, contacts the electrical contact  641  while pressing against it. Therefore, the contact  710  sandwiches the heater  600  between the front and back sides to fix the position of the heater  600 . 
     Similarly, the contact terminal  720   a  functions to contact the electrical contact  661   a  with the switch SW 663  which will be described hereinafter. The contact terminal  720   a  is provided with the electrical contact  721   a  for contacting to the electrical contact  661   a  and a cable  722   a  for the electrical connection with the switch SW 643 . 
     Similarly, the contact terminal  720   b  functions to contact the electrical contact  661   b  with the switch SW 663  which will be described hereinafter. The contact terminal  720   b  is provided with a cable  722   b  for the electrical connection between the switch SW 643  and the electrical contact  721   b  for contacting to the electrical contact  661   b.    
     Similarly, the contact terminal  730  functions to contact the electrical contact  651  with the switch SW 663  which will be described hereinafter. The contact terminal  730  is provided with a cable  722   a  for the electrical connection between the switch SW 643  and the electrical contact  731  for contacting to the electrical contact  651 . 
     The terminals  710 ,  720   a  of metal are supported by the housing  750   a  of the resin material. The terminals  710 ,  720   a  are disposed in the housing  750   a  with a gap therebetween so as to connect with the electrical contacts  641 ,  661   a  when the connector  700   a  is mounted to the heater  600 . Between the terminals, a partition is provided to assure the electrical insulation between the terminals. 
     The terminals  720   b ,  730  of metal are supported by the housing  750   b  of the resin material. The terminal  720   b ,  730  are disposed with a gap therebetween in the housing  750   b  so as to contact with the electrical contacts  661   b ,  651 , respectively, when the connector  700   b  is mounted to the heater. Between the terminals, a partition is provided to assure the electrical insulation between the terminals. 
     In the above-described example, the connector  700   a  is mounted to the end portion with respect to the widthwise direction of the substrate  610 , and the connector  700   b  is mounted to the substrate  610  in the longitudinal end portion of the substrate, but this is not limiting to the present invention, and another combination of the mounting directions of the connector  700  to the substrate  610 . For example, the connector  700   b  may also be mounted to the heater from the end portion with respect to the widthwise direction of the substrate, similarly to the connector  700   a.    
     [Electric Energy Supply to Heater] 
     An electric energy supply method to the heater  600  will be described. The fixing device  40  of this embodiment is capable of changing the a width of the heat generating region of the heater  600  by controlling the electric energy supplied to the heater  600  in accordance with the width size of the sheet P. With such a structure, the heat can be efficiently supplied to the sheet P. In the fixing device  40  of this embodiment, the sheet P is fed with the center of the sheet P aligned with the center of the fixing device  40 , and therefore, the heat generating region extends from the center portion. The electric energy supply to the heater  600  will be described in conjunction with the accompanying drawings. 
     The voltage source  110  is a circuit for supplying the electric power to the heater  600 . In this embodiment, the commercial voltage source (AC voltage source) of approx. 100V in effective value (single phase AC). The voltage source  110  of this embodiment is provided with a voltage source contact  110   a  and a voltage source contact  110   b  having different electric potential. The voltage source  110  may be DC voltage source if it has a function of supplying the electric power to the heater  600 . 
     As shown in  FIG. 5 , the control circuit  100  is electrically connected with switch SW 643 , switch SW 653 , and switch SW 663 , respectively to control the switch SW 643 , switch SW 653 , and switch SW 663 , respectively. 
     Switch SW 643  is a switch (relay) provided between the voltage source contact  110   a  and the electrical contact  641 . The switch SW 643  connects or disconnects between the voltage source contact  110   a  and the electrical contact  641  in accordance with the instructions from the control circuit  100 . The switch SW 653  is a switch provided between the voltage source contact  110   b  and the electrical contact  651 . The switch SW 643  connects or disconnects between the voltage source contact  110   a  and the electrical contact  641  in accordance with the instructions from the control circuit  100 . The switch SW 653  is a switch provided between the voltage source contact  110   b  and the electrical contact  651 . The switch SW 643  connects or disconnects between the voltage source contact  110   a  and the electrical contact  641  in accordance with the instructions from the control circuit  100 . 
     When the control circuit  100  receives the execution instructions of a job, the control circuit  100  acquires the width size information of the sheet P to be subjected to the fixing process. In accordance with the width size information of the sheet P, a combination of ON/OFF of the switch SW 643 , switch SW 653 , switch SW 663  is controlled so that the heat generation width of the heat generating element  620  fits the sheet P. At this time, the control circuit  100 , the voltage source  110 , switch SW 643 , switch SW 653 , switch SW 663  and the connector  700  functions as an electric energy supplying portion for supplying the electric power to the heater  600 . 
     When the sheet P is a large size sheet (an usable maximum width size), that is, when A3 size sheet is fed in the longitudinal direction or when the A4 size is fed in the landscape fashion, the width of the sheet P is approx. 297 mm. Therefore, the control circuit  100  controls the electric power supply to provide the heat generation width B ( FIG. 5 ) of the heat generating element  620 . To effect this, the control circuit  100  renders ON all of the switch SW 643 , switch SW 653 , switch SW 663 . As a result, the heater  600  is supplied with the electric power through the electrical contacts  641 ,  661   a ,  661   b ,  651 , and all of the 12 sub-sections of the heat generating element  620  generate heat. At this time, the heater  600  generates the heat uniformly over the approx. 320 mm region to meet the approx. 297 mm sheet P. 
     When the size of the sheet P is a small size (narrower than the maximum width), that is, when an A4 size sheet is fed longitudinally, or when an A5 size sheet is fed in the landscape fashion, the width of the sheet P is approx. 210 mm. Therefore, the control circuit  100  provides a heat generation width A ( FIG. 5 ) of the heat generating element  620 . Therefore, the control circuit  100  renders ON the switch SW 643 , switch SW 663  and renders OFF the switch SW 653 . As a result, the heater  600  is supplied with the electric power through the electrical contacts  641 ,  651 , so that 8 sub-sections of the 12 sub-sections of the heat generating element  620  generate heat. At this time, the heater  600  generates the heat uniformly over the approx. 213 mm region to meet the approx. 210 mm sheet P. 
     [Disposition of Electrical Contact] 
     The disposition or arrangement of the electrical contacts will be described.  FIG. 8  shows the arrangement of the electrical contacts in this embodiment. In this embodiment, adjacent electrical contacts connected to the same voltage source contact are arranged in the widthwise direction of the substrate  610 , and the adjacent to electrical contacts connected to the different voltage source contact are arranged in the longitudinal direction of the substrate  610 . With such an arrangement, sufficient gaps can be provided between the adjacent electrical contacts connected to the different voltage source contacts. By providing narrow gaps between the electrical contacts connected to the same voltage source contact, the enlargement of the width of the substrate can be suppressed. By the electrical contacts connected to the same voltage source contact being arranged in the widthwise direction, the number of the electrical contacts arranged in the longitudinal direction can be reduced, and therefore, the increase of the length of the substrate can be suppressed. 
     In this embodiment, in the one end portion side  610   a  of the substrate, the electrical contact  641  connecting to the voltage source contact  110   a  and the electrical contact  661   a  connecting to the voltage source contact  110   b  are arranged in the longitudinal direction. In addition, in the other end portion side  610   b  of the substrate, the electrical contacts  651 ,  661   b  connecting to the voltage source contact  110   b  are arranged in the widthwise direction of the substrate  610 . A description will be provided in detail in conjunction with the accompanying drawings. 
     As described hereinbefore, in this embodiment, the electrical contacts  641 ,  661   a  are disposed in the one end portion side  610   a  of the substrate, and the electrical contacts  651 ,  661   b  are disposed in other end portion side  610   b  of the substrate. Each electrical contact has a size of not less than 2.5 mm×2.5 mm (widthwise direction and longitudinal direction of the substrate) so as to receive the electric energy from the terminal assuredly, and the area thereof is preferably lives. In this embodiment, the dimensions of the electrical contact  641  are approx. 7 mm×approx. 3 mm, that of the electrical contact  661   a  are approx. 5 mm×approx. 3 mm, and that of the electrical contact  661   b  and  651  are approx. 5 mm×approx. 3 mm. 
     As described hereinbefore, the portion of the substrate  610  provided with the electrical contacts  641 ,  651 ,  661   a ,  661   b  is not coated with the insulation coating layer. That is, the electrical contacts are exposed, and therefore, the provision of the gaps between adjacent electrical contacts is desirable to prevent the electrical leakage and/or short circuit. With the increase of the insulation distance, the risk of the leakage and/or a short circuit decreases, but on the other hand, the substrate  610  is increased in size. Therefore, proper sizes of the gaps between the adjacent electrical contacts are desirable. 
     In this embodiment, the electrical contact  641  is connected to the voltage source contact  110   a , and the electrical contact  661   a  is connected to the voltage source contact  110   b . In other words, the electrical contacts  641  and  661   a  which are connected to the different (opposite polarities) voltage source contacts are adjacent to each other, with the result of large potential difference therebetween. In order to prevent a short circuit due to creepage discharge, it is preferable to provide a sufficiently large insulation distance between the electrical contact  641  and the electrical contact  661   a . Japanese Electrical Appliance and Material Safety Law (annex Table of attached Table) stipulates that in a charging portion or other position of different polarities where a voltage between the lines 50V-150V, the required space distance (creeping distance) is approx. 2.5 mm. In this embodiment, taking mounting tolerances of the connector  700  and/or the thermal expansion of the substrate  610  into account, the gap E is approx. 4.0 mm. When the gap between the electrical contacts  641  and  661   a  is not constant because of non-parallelism between the electrical contacts  641  and  661   a , a minimum value of the gap is deemed as the gap E. 
     In this embodiment, the electrical contacts  651 ,  661   b  are connected to the voltage source contact  110   b . That is, the electrical contacts  651  and  661   b  which are adjacent to each other are connected to the same voltage source contact (same polarity), and therefore no large potential difference is produced therebetween. Therefore, a short circuit due to the creepage discharge hardly occurs between the electrical contacts  651  and  661   b  (gap F). Therefore, as long as a function of insulation for normal operation of the heater  600  is provided, the gap F can be made minimum. However, in consideration of the mounting tolerances of the connector  700  and the thermal expansion of the substrate  610 , the gap F in this embodiment is approx. 1.5 mm. When the gap between the electrical contacts  641  and  661   a  is not constant because of non-parallelism between the electrical contacts  641  and  661   a , a minimum value of the gap is deemed as the gap F. Gap E&gt;gap F. The gap between the electrical contact  661   a  and the electrical contact  651  is less than gap E in the entirety, by which the width required by the electrical contacts can be reduced. Therefore, the width of the electrical contacts in total in the other end portion side  610   b  of the substrate is approx. 7.5 mm, and therefore, the electrical contacts can be accommodating in the substrate  610  having the width of approx. 8 mm. If the electrical contacts  651  and  661   b  are connected with different voltage source contacts, the width of the electrical contacts in total is approx. 10 mm. Therefore, the electrical contacts are not provided in the substrate  610  of the width of approx. 8 mm, which necessitates enlargement of the width of the substrate  610 . 
     That is, by arranging the electrical contacts connected to the different voltage source contacts are arranged in the longitudinal direction of the substrate  610 , the gap between the electrical contacts can be made sufficient. In addition, by arranging the electrical contacts connected to the same voltage source contact are arranged in the widthwise direction of the substrate, the number of the electrical contacts arranged in the longitudinal direction of the substrate can be reduced. Even though the electrical contacts connected to the same voltage source contacts are arranged in the widthwise direction of the substrate, the increase of the width of the substrate  610  can be suppressed by reducing the gap therebetween. 
     Embodiment 2 
     A heater according to Embodiment 2 of the present invention will be described.  FIG. 9  is an illustration of a structure relation of the image heating apparatus of this embodiment.  FIG. 9  shows the arrangement of the electrical contacts in this embodiment.  FIG. 8  shows the arrangement of the electrical contacts in this embodiment. In Embodiment 1, the heat generating element  620  is supplied with the electric energy from the electrical contacts disposed in the opposite longitudinal end portions of the substrate  610 . In Embodiment 2, the heat generating element  620  it is supplied with the electric energy from the electrical contacts provided one longitudinal end portion of the substrate  610 . More particularly, the electrical contacts  661   a ,  661   b  (electrical contact  661 ) in Embodiment 1 are concentrated in one end portion side  610   a  of the substrate. That is, all the electrical contacts  641 ,  651 ,  661  are in the one end portion side  610   a  of the substrate. With this structure of this embodiment, the length of the substrate is reduced. The details of the heater  600  of this embodiment will be described in conjunction with the drawings. The structures of the fixing device  40  of Embodiment 2 are fundamentally the same as those of Embodiment 1 except for the structures relating to the heater  600 . In the description of this embodiment, the same reference numerals as in Embodiment 1 are assigned to the elements having the corresponding functions in this embodiment, and the detailed description thereof is omitted for simplicity. 
     As shown in  FIG. 9 , in the heater  600  of this embodiment, the heat generating element  620  is supplied with the electric power through the electrical contacts  641 ,  651 ,  661  provided in one end portion side of the substrate  610  with respect to the longitudinal direction. The electrical contact  661  is disposed adjacent to the electrical contact  641  with a gap therebetween, and they are arranged in the longitudinal direction of the substrate  610 . The electrical contact  661  is disposed adjacent to the electrical contact  641  with a gap therebetween, and they are arranged in the longitudinal direction of the substrate  610 . The electrical contact  661  disposed adjacent to the electrical contact  651  with a gap therebetween, and are arranged in the widthwise direction of the substrate. 
     In the heater  600  of this embodiment, the opposite electroconductive lines  660   a  and  660   b  extend so as to surround the electrical contact  651 . With such a structure, the opposite electroconductive lines  660   a  and  660   b  are connected to the electrical contact  661 . The  661  electrical contact functions as the electrical contacts  661   a  and  661   b  of Embodiment 1. 
     In this embodiment, the dimension of the electrical contact  641  is approx. 7 mm×approx. 3 mm, and the dimension of the electrical contacts  661   a  and  651  are approx. 3 mm×approx. 3 mm. 
     The opposite electroconductive line  650  extends along the longitudinal direction of the substrate  610  toward the one end portion side  610   a  of the substrate in another end portion side with respect to the widthwise direction substrate  610  beyond the heat generating element  620 . The opposite electroconductive line  650  is connected to the electrical contact  651 . 
     In this embodiment, the electrical contact  641  is connected to the voltage source contact  110   a , and the electrical contact  661  is connected to the voltage source contact  110   b . In other words, the electrical contacts  641  and  661  which are connected to the different voltage source contacts are adjacent to each other, with the result of large potential difference therebetween. In order to prevent a short circuit due to creepage discharge, it is preferable to provide a sufficiently large insulation distance between the electrical contact  641  and the electrical contact  661 . The desired space distance (creeping distance) is approx. 2.5 mm. In consideration of the mounting tolerances of the connector  700  and the thermal expansion of the substrate  610 , the gap E in this embodiment is approx. 4 mm. 
     Since the electrical contact  651  is connected to the voltage source contact  110   b , a sufficient insulation distance is desirably provided between the electrical contact  641  and the electrical contact  661 . Therefore, the gap E between the electrical contacts  641  and  651  is approx. 4.0 mm in this embodiment. 
     Since the electrical contacts  651  and  661  are contacted to the voltage source contact  110   b , no large potential difference is produced therebetween. Therefore, a short circuit due to the creepage discharge hardly occurs between the electrical contacts  651  and  661   a  (gap F). Therefore, as long as a function of insulation for normal operation of the heater  600  is provided, the gap F can be made minimum. However, in consideration of the mounting tolerances of the connector  700  and the thermal expansion of the substrate  610 , the gap F in this embodiment is approx. 1.5 mm. Thus, gap E&gt;gap F. 
     Therefore, the width of the electrical contacts in total in the other end portion side  610   b  of the substrate is approx. 7.5 mm, and therefore, the electrical contacts can be accommodating in the substrate  610  having the width of approx. 8 mm. If the electrical contacts  651  and  661   b  are connected with different voltage source contacts, the width of the electrical contacts in total is approx. 10 mm, and therefore, the electrical contacts are not provided in the substrate  610  of the width of approx. 8 mm. 
     This, according to this embodiment, by arranging the electrical contacts connected to the different voltage source contacts are arranged in the longitudinal direction of the substrate  610 , the gap between the electrical contacts can be made sufficient. In addition, by arranging the electrical contacts connected to the same voltage source contact are arranged in the widthwise direction of the substrate, the number of the electrical contacts arranged in the longitudinal direction of the substrate can be reduced. Even though the electrical contacts connected to the same voltage source contacts are arranged in the widthwise direction of the substrate, the increase of the width of the substrate  610  can be suppressed by reducing the gap therebetween. The heaters per se of the foregoing embodiments can be summarized as follows: 
     A heater comprising: 
     a substrate; 
     a first connecting portion electrically connectable with one of grounding and non-grounding sides of a power source; 
     a second connecting portion electrically connectable with the other of the grounding and non-grounding sides and provided adjacent to the first connecting portion with a gap in a longitudinal direction of the substrate; 
     a third connecting portion electrically connectable with the other of the grounding and non-grounding sides; 
     a fourth connecting portion electrically connectable with the other of the grounding and non-grounding sides and provided adjacent to the third connecting portion with a gap in the widthwise direction of the substrate; 
     a plurality of heat generating portions arranged in the longitudinal direction of the substrate, the heat generating portions including at least one heat generating portion capable of generating heat by electric energy supplied from the first connecting portion and the second connecting portion, at least one heat generating portion capable of generating heat by electric energy supplied from the first connecting portion and the third connecting portion, and at least one heat generating portion capable of generating heat by electric energy supplied from the first connecting portion and the fourth connecting portion; 
     a gap between the third connecting portion and the fourth connecting portion in the widthwise direction is smaller than a gap between the first connecting portion and the second connecting portion in the longitudinal direction. 
     OTHER EMBODIMENTS 
     The present invention is not restricted to the specific dimensions in the foregoing embodiments. The dimensions may be changed properly by one skilled in the art depending on the situations. The embodiments may be modified in the concept of the present invention. 
     The electric energy supply to the heat generating element  610  is not limited to that in the longitudinal direction of the substrate. For example, by sandwiching the heat generating element in the widthwise direction by electrodes, the electric current may flow in the widthwise direction of the substrate. With such a structure, the present invention is applicable if there are provided an electrical contact connected to one of the terminals of the voltage source and a plurality of electrical contacts connected to the other terminal of the voltage source. In such a case, the electrical contacts connected to the same polarity are arranged in the widthwise direction of the substrate, and the electrical contacts connected to the opposite polarities are arranged in the longitudinal direction of the substrate, so that the gap between the electrical contacts connected to the same polarity is reduced, by which the increase of the width of the substrate can be suppressed. 
     The heat generating region of the heater  600  is not limited to the above-described examples which are based on the sheets are supplied with the center thereof aligned with the center of the fixing device. Alternatively, the heat generating regions of the heater  600  may be modified so as to meet the case in which the sheets are supplied with one end thereof aligned with an end of the fixing device. More particularly, the heat generating elements corresponding to the heat generating region A are not heat generating elements  620   c - 620   j  but are heat generating elements  620   a - 620   e . With such an arrangement, when the heat generating region is switched from that for a small size sheet to that for a large size sheet, the heat generating region does not expand at both of the opposite end portions, cone. The heat generating region in the one end portion side may be enlarged. 
     The number of patents of the heat generating region of the heater  600  is not limited to two. For example, three or more patents may be provided. 
     The forming method of the heat generating element  620  is not limited to those disclosed in Embodiments 1, 2. In Embodiment 1, the common electrode  642  and the opposite electrodes  652 ,  662  are laminated on the heat generating element  620  extending in the longitudinal direction of the substrate  610 . However, the electrodes are formed in the form of an array extending in the longitudinal direction of the substrate  610 , and the heat generating elements  620   a - 620   l  may be formed between the adjacent electrodes. 
     The number of the electrical contacts limited to three or four. Five or more electrical contacts may be provided if the electrical contacts connected to the same voltage source contact are arranged in the widthwise direction of the substrate. For example, in Embodiment 1, in one end portion side  610   a  of the substrate, an electrical contact different from the electrical contacts  641 ,  661   a  may be provided, and the other end portion side  610   b  of the substrate, an electrical contact different from the electrical contacts  661   b , and  651  may be provided. 
     The electrical contact connected to the voltage source contact  110   a  is not limited to the electrical contact  641 . For example, in the one end portion side  610   a  of the substrate, an electrical contact which is different from the electrical contact  641  and which is connected to the voltage source contact  110   a  may be provided. Furthermore, this electrical contact may be provided adjacent to the electrical contact  641  with a gap therebetween in the widthwise direction of the substrate  610 . 
     The belt  603  is not limited to that supported by the heater  600  at the inner surface thereof and driven by the roller  70 . For example, so-called belt unit type in which the belt is extended around a plurality of rollers and is driven by one of the rollers. However, the structures of Embodiments 1-4 are preferable from the standpoint of low thermal capacity. 
     The member cooperative with the belt  603  to form of the nip N is not limited to the roller member such as a roller  70 . For example, it may be a so-called pressing belt unit including a belt extended around a plurality of rollers. 
     The image forming apparatus which has been a printer  1  is not limited to that capable of forming a full-color, but it may be a monochromatic image forming apparatus. The image forming apparatus may be a copying machine, a facsimile machine, a multifunction machine having the function of them, or the like, for example. 
     The image heating apparatus is not limited to the apparatus for fixing a toner image on a sheet P. It may be a device for fixing a semi-fixed toner image into a completely fixed image, or a device for heating an already fixed image. Therefore, the fixing device  40  as the image heating apparatus may be a surface heating apparatus for adjusting a glossiness and/or surface property of the image, for example. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2014-108593 filed on May 26, 2014, which is hereby incorporated by reference herein in its entirety.