Abstract:
A fixing device and an image forming apparatus including the fixing device are supplied capable of preventing life of roller from shortening due to big shearing warp. 
     In the fixing device to fix a toner image that is transferred on a record medium though using an endless belt heated by a heating member, the endless belt is extended by a first pressing member and the heating member; a second pressing member and the first pressing member sandwich and hold the endless belt to press the endless belt; and a rotating member is externally contacted with the endless belt and drives the endless belt to move.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to a fixing device used in a copying apparatus, a printer, a facsimile apparatus or the like, and relates to an image forming apparatus using the fixing device. 
       FIELD OF THE INVENTION 
       [0002]    In recent years, as a purpose to save electric power or to shorten rising time, an image forming apparatus having a fixing device that uses an endless belt, is utilized (refer to patent document 1). Here, regarding the fixing device that uses the endless belt, its summary will be explained. 
         [0003]      FIG. 7  is an explanatory diagram of a fixing device that uses a conventional endless belt. 
         [0004]    As shown by  FIG. 7 , “ 2 ” is a pressing roller. The pressing roller  2  has a metal shaft  2   a  and an elastic layer  2   b,  and is a roller for receiving a rotation drive force from a drive source (not shown) via the metal shaft  2   a . “ 3 ” is a fixing roller. The fixing roller  3  has a metal shaft  3   a  and an elastic layer  3   b,  and is a roller that is pressed by the pressing roller  2  to form a nip part N. A fixation belt  4  is an endless belt, as shown by  FIG. 7 , is a cylinder-shaped belt which is extended by the fixing roller and a supporting body  5 . “ 6 ” is a heat source. The heat source  6  is a surface shape and is contacted with an inner surface of the fixation belt  4 . 
         [0005]    In the fixing device that uses the conventional endless belt and has the above-mentioned structure, the pressing roller  2  is driven to rotate by the drive source (not shown). When the pressing roller  2  is driven to rotate, the fixing roller  3  is driven to rotate through a friction force between the pressing roller  2  and the fixation belt  4  and through a friction force between the fixation belt  4  and the fixing roller  3 . When the fixing roller  3  is driven to rotate, the fixation belt  4  is driven to move while resisting to a friction force between the fixation belt  4  and the supporting body  5 . The fixation belt  4  is maintained at a predetermined temperature by the heat source  6 . A record sheet (not shown) is conveyed by the fixation belt  4  which is maintained at the predetermined temperature by the heat source  6 , and passes the nip part N. As a result, toner is heated and is pressed so as to be fixed on the record sheet. Here, because the pressing roller  2  presses the fixing roller  3  to form the nip part N, so it is possible to supply the record sheet and toner with sufficient heat amount. 
         [0006]    Patent document 1: Japan patent application No. 2006-154823. 
         [0007]    As stated above, in the fixing device that uses the conventional endless belt, it is necessary to increase the rotation drive force and the pressure of the pressing roller  2  in order to make the fixation belt  4  drive to move while resisting to the friction force between the fixation belt  4  and the supporting body  5 . As a result, in the elastic layer  2   b  of the pressing roller  2  and in the elastic layer  3   b  of the fixing roller  3  (especially, in the elastic layer  2   b  of the pressing roller  2 ), a shearing warp in a rotation direction becomes big, thus, life is shortened. 
       SUMMARY OF THE INVENTION 
       [0008]    It is, therefore, an object of the invention to provide a fixing device and an image forming apparatus capable of solving the above problem. 
         [0009]    An aspect of the invention is to provide a fixing device. The fixing device to fix a toner image that is transferred on a record medium though using an endless belt heated by a heating member, comprises a first pressing member; a second pressing member; and a rotating member, wherein the endless belt is extended by the first pressing member and the heating member; the second pressing member and the first pressing member sandwich and hold the endless belt to press the endless belt; and the rotating member is externally contacted with the endless belt and drives the endless belt to move. 
         [0010]    Another aspect of the invention is to provide an image forming apparatus. The image forming apparatus comprises a fixing device to fix a toner image that is transferred on a record medium though using an endless belt heated by a heating member, includes: wherein the fixing device includes: a first pressing member; a second pressing member; and a rotating member, wherein the endless belt is extended by the first pressing member and the heating member; the second pressing member and the first pressing member sandwich and hold the endless belt to press the endless belt; the rotating member is externally contacted with the endless belt and drives the endless belt to move. 
       EFFECT OF THE PRESENT INVENTION  
       [0011]    Through having the rotating member that is externally contacted with the endless belt and drives to move the endless belt, the rotating member shares a driving force for making the endless belt drive to move, therefore, shearing warp in a rotation direction, that occurs inside of the first pressing member and the second pressing member is greatly reduced. As a result, it is possible to prevent a life shortening of both members. 
         [0012]    The above and other objects and features of the present invention will become apparent from the following detailed description and the appended claims with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is an explanatory diagram of an image forming apparatus of the present invention; 
           [0014]      FIG. 2  is an explanatory diagram of a fixing device in embodiment 1; 
           [0015]      FIG. 3  is an explanatory diagram of an endless belt; 
           [0016]      FIG. 4  is an explanatory diagram of a heat source; 
           [0017]      FIG. 5  is an explanatory diagram of a heat source of other example; 
           [0018]      FIG. 6A  is a part explanatory diagram for showing a contact state of the fixation belt  4  and the heat source  6  in embodiment 1; 
           [0019]      FIG. 6B  is an explanatory diagram for showing a structure of a fixing device in embodiment 2; 
           [0020]      FIG. 7  is an explanatory diagram of a fixing device that uses a conventional endless belt. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0021]      FIG. 1  is an explanatory diagram of an image forming apparatus of the present invention. 
         [0022]    As the image forming apparatus of the present invention, it will be explained through using a color printer serving as an example. As shown by  FIG. 1 ,  40 K,  40 Y,  40 M and  40 C are developing apparatuses that develop through using respective colors of black, yellow, magenta and cyan. “ 50 ” is a fixing device. A structure of the developing apparatus of each color is the same, therefore, it will be to only explained the black developing apparatus  40 K as an example. 
         [0023]    The black developing apparatus  40 K has a image carrying body  41 K, a charging section  42 K, a latent image forming section  43 K, a developing section  44 K and a transferring section  45 K. The image carrying body  41 K is a photosensitive drum. The charging section  42 K charges a surface of the image carrying body  41 K negatively. The latent image forming section  43 K irradiates with light the surface of the image carrying body  41 K that is charged negatively, and forms an electrostatic latent image. The developing section  44 K supplies the electrostatic latent image with toner, and develops the electrostatic latent image. The developed toner image is transferred on a record medium by the transferring section  45 K. Further, the toner image that is transferred on the record medium, is transferred on the record medium by the fixing device  50  and is ejected. Embodiment explained below is about the fixing device  50 . The following is to explain embodiment of the present invention in detail through using drawings. 
       Embodiment 1  
       [0024]      FIG. 2  is an explanatory diagram of a fixing device in embodiment 1. 
         [0025]    As shown by  FIG. 2 , the fixing device  50  of embodiment 1 comprises a pressing roller  2 , a fixing roller  3 , a fixation belt  4 , a supporting body  5 , a heat source  6  and a drive use assisting roller  7 . 
         [0026]    The pressing roller  2  has a metal shaft  2   a  and an elastic layer  2   b . Further, the pressing roller  2  is a roller whose diameter is 20 mm˜40 mm, and which forms a nip part N through providing a pressure F to the fixing roller  3  which is opposite to the pressing roller  2 . Here, the metal shaft  2   a  is a shaft formed from iron material or the like, and is axis-supported rotation-freely by a shaft holding portion (not shown). And, the elastic layer  2   b  is formed concentrically on a circumference surface of the metal shaft  2   a ; and is a heat-resistant elastic member whose thickness is 1 mm˜10 mm formed from, for example, a silicon rubber or the like. Further, on the surface, fluorine series resin is accumulated 10 μm˜50 μm as a mold release layer. 
         [0027]    The fixing roller  3  has a metal shaft  3   a  and an elastic layer  3   b . Further, the fixing roller  3  is a roller whose diameter is 20 mm˜40 mm, and which forms the nip part N through being provided a pressure F by pressing roller  2 . As well as the press roller  2 , the metal shaft  3   a  is a shaft formed from iron material or the like, and is axis-supported rotation-freely by the shaft holding portion (not shown). And, the elastic layer  3   b  is formed concentrically on a circumference surface of the metal shaft  3   a ; and is a heat-resistant elastic member whose thickness is 1mm˜10 mm formed from, for example, a silicon rubber or the like. Further, on the surface, fluorine series resin is accumulated 10 μm˜50 μm as a mold release layer. 
         [0028]    The fixation belt  4 , as shown by  FIG. 2 , is an endless belt that is extended by the fixing roller  3  and the supporting body  5 . Here, regarding the fixation belt  4 , it will be explained in detail through using other diagram. 
         [0029]      FIG. 3  is an explanatory diagram of an endless belt. 
         [0030]    As shown by  FIG. 3 , the endless belt (the fixation belt  4 ) is formed by accumulating thin silicon rubber or fluorine series resin to serve as an elastic layer  4   b  on a circumference surface of a base member  4   c  formed from a thin board of nickel, polyimide, stainless or the like. Further, as a mold release layer  4   b,  PFA (perfluoro alkoxyl alkane), PTFE (polytetrafluoroethylene), FEP (fluorinated ethylene propylene copolymer) or the like is accumulated thin on the surface of the elastic layer  4   b . These materials are excellent in heat-resistant. From the point of strength or heat-resistant, the size of the base member  4   c  is desirable 30 μm˜150 μm; the thickness of the elastic layer  4   b  is desirable about 50 μm˜300 μm; and the thickness of the mold release layer  4   b  is desirable 10 μm˜50 μm. 
         [0031]    As shown by  FIG. 2 , the supporting body  5  is a part that extends the fixation belt  4  with the fixing roller  3 . The part is formed from resin having high heat-resistant such as PPS (polyphenylene sulfide), PEEK (polyetheretherketone), LCP (Liquid Crystal Polymer) or the like. In consideration of a transform or a breakage due to heat, the part can also be formed by adopting material such as glass fiber, glass beads or the like for strengthening. Moreover, it is possible to provide fluorine grease to between the fixation belt  4  and the supporting body  5  in order to reduce friction. 
         [0032]    The heat source  6  is contacted with the inner surface of the fixation belt  4 , and is a surface-shaped heat source that heats the fixation belt  4 . The heat source  6 , as shown by  FIG. 2 , is furnished on upstream side from the nip part N with respect to a movement direction of the fixation belt  4 . Further, the heat source  6  is also furnished on upstream side from the nip part N with respect to a movement direction of the medium. Here, regarding a structure of the heat source  6 , it will be explained in detail through using other drawing. 
         [0033]      FIG. 4  is an explanatory diagram of a heat source. 
         [0034]    As shown by  FIG. 4 , the heat source  6  is formed to include an electricity insulating layer  6   b  that is formed from glass material on a base member  6   a  that is formed from a board of stainless or ceramic; a resistance heating element  6   c  that is formed from nickel chromium alloy, silver palladium alloy or the like on the electricity insulating layer  6   b ; and a protection layer  6   d  that is formed from glass, fluorine series resin (PFA, PTFE, FEP). Moreover, an outer surface of the heat source  6  is desirable to be formed by a same curvature as that of the fixation belt  4  in the state that the fixation belt  4  is extended by the fixing roller  3  and the supporting body  5 . 
         [0035]    The heat source  6  stated above is an example. Here, regarding other example of a heat source, it will be explained. 
         [0036]      FIG. 5  is an explanatory diagram of a heat source of other example. 
         [0037]    As shown by  FIG. 5 , it is possible to furnish a halogen heater serving as a heat source inside a metallic pipe P, to heat the fixation belt  4  via the metallic pipe P. 
         [0038]    As shown by  FIG. 2 , the drive use assisting roller  7  has a metal shaft  7   a  and an elastic layer  7   b . Further, the drive use assisting roller  7  is a roller that sandwiches and holds the fixation belt  4  with the supporting body  5 ; presses the fixation belt  4  from the outer surface to generate a nip part Nk; receives rotation drive force from the drive source (not shown); and make the fixation belt  4  drive to move. Here, when the fixation belt  4  is driven to move while resisting to a friction force between the fixation belt  4  and the supporting body  5 , the drive force is conducted to the fixing roller  3  via friction force between the fixation belt  4  and the fixing roller  3 , thus, the fixing roller  3  is driven to rotate. Further, the friction force makes the pressing roller  2  be drive to rotate via friction force between the pressing roller  2  and the fixation belt  4 . 
         [0039]    The drive use assisting roller  7  contacts with the fixation belt  4  on upstream side from a position that the fixation belt  4  contacts with the surface-shaped heater and is heated, along a movement direction of the fixation belt  4 . Therefore, it is possible to prevent an influence on the temperature of the fixation belt  4  heated by the surface-shaped heater. 
         [0040]    The drive use assisting roller  7  is formed by accumulating a heat-resistant elastic layer  7   b  whose thickness is 0.5 mm˜2 mm on the circumference surface of the metal shaft  7   a . The heat-resistant elastic layer  7   b  is formed from a silicon rubber or the like, and the metal shaft  7   a  is formed from iron material or the like. 
         [0041]    Moreover, it is possible to use other metal such as aluminum and the like instead of the iron material stated above as the metal shaft  2   a  of the pressing roller  2 , the metal shaft  3   a  of the fixing roller  3  and the metal shaft  7   a  of the drive use assisting roller  7 . Further, it is possible to use other elastic material such as silicon sponge, fluorine rubber and the like instead of the silicon rubber stated above. Moreover, the fixing roller  3 , the fixation belt  4 , the supporting body  5 , the heat source  6  and the drive use assisting roller  7  are generally unified as a fixation belt assembly  1 . 
         [0042]    A fixing device  50 A of embodiment 1 explained above operates as follows. 
         [0043]    As shown by  FIG. 2 , when the drive use assisting roller  7  receives rotation drive force from the drive source (not shown), the fixation belt  4  receives the drive force via the nip part Nk; and moves while sliding with respect to the supporting body  5  and the heat source  6 . 
         [0044]    When electric power is supplied to the heat source  6 , the heat source  6  generates heat, and the fixation belt  4  is heated via a sliding surface with the fixation belt  4 . A surface temperature of the fixation belt  4  is detected by a temperature detecting means (not shown), and according to the detected temperature, the supplying electricity to the heat source  6  is controlled by a control of a controlling system. As a result, the surface temperature of the fixation belt  4  is maintained at a proper temperature. 
         [0045]    The pressing roller  2  sandwiched and holds the fixation belt  4  with the fixing roller  3  which is furnished opposite to the pressing roller  2 , further, provides the pressure F with respect to the fixing roller  3 . By the pressure F, the friction force between the pressing roller  2  and the fixation belt  4 , and the friction force between the fixation belt  4  and the fixing roller  3  are obtained. At the same time, the nip part N is formed. 
         [0046]    As a result, a record medium  9  on which non-fixation toner  8  is transferred is conveyed to pass through the nip part N between the fixation belt  4  and the pressing roller  2 . At that time, the non-fixation toner  8  on the record medium  9  is fixed through heat of the fixation belt  4  and through pressure of the pressing roller  2 . Here, it becomes obvious experimentally that the fixation belt  4  is desirable to be extended by the fixing roller  3  and the supporting body  5  through a force of about 0.5 kg˜2 kg. 
         [0047]    According to the above explanation, in embodiment 1, by providing the drive use assisting roller  7 , the drive force for making the fixation belt  4  be driven to move while resisting to the friction force between the fixation belt  4  and the supporting body  5 , is shared with the drive use assisting roller  7 , therefore, it is unnecessary to increase the pressure F of the pressing roller  2 . Further, the pressing roller  2  drives to rotate, therefore, it is unnecessary to supply with drive force for making the fixation belt  4  be driven to move while resisting to the friction force between the fixation belt  4  and the supporting body  5 . Accordingly, the shearing warp that occurs in the elastic layer  2   b  (and the elastic layer  3   b ) in rotation direction is greatly reduced. As a result, it is possible to prevent a shortening of life of both rollers. 
         [0048]    Moreover, in the above explanation, only such case is explained that the fixation belt  4  is driven to rotate only by the drive use assisting roller  7 , however, the present invention is not limited by the example. That is, through making one of the fixing roller  3  and the pressing roller  2  or both of them rotate in a rotation number that almost synchronize with a movement speed of the fixation belt  4 , it is also possible to make the fixation belt  4  and the record medium  9  move more stably. In the case, the pressing roller  2  does not need to supply with excessive drive force for making the fixation belt  4  be driven to move while resisting to the friction force between the fixation belt  4  and the supporting body  5 , so it is possible to obtain the same effect as above. 
       Embodiment 2  
       [0049]      FIG. 6A  is a part explanatory diagram for showing a contact state of the fixation belt  4  and the heat source  6  in embodiment 1;  FIG. 6B  is an explanatory diagram for showing a structure of a fixing device in embodiment 2. 
         [0050]    As explained by using  FIG. 3  in embodiment 1, the fixation belt  4  moves along an arc surface of the supporting body  5 . And the heat source  6  is furnished in concave place on the arc surface of the supporting body, and is formed in plane shape ( FIG. 4 ). Accordingly, a touch state of the fixation belt  4  and the heat source  6  in embodiment 1, as shown by  FIG. 6A , an aperture “t” exists between the fixation belt  4  and the heat source  6 , therefore, there are possibilities that a heat conduction is impeded or that the heat source  6  is damaged because a temperature of itself rises too much. The purpose of the embodiment is to prevent the above inconvenience. 
         [0051]    As shown by  FIG. 6A , in a fixing device  50 B of embodiment 2, the drive use assisting roller  7  is furnished in a position opposite to the heat source  6 , the drive use assisting roller  7  and the heat source  6  sandwich and hold the fixation belt  4 . Accordingly, because the fixation belt  4  is pressed by the heat source  6  by the drive use assisting roller  7 , so the aperture does not occur between the fixation belt  4  and the heat source  6 . 
         [0052]    By adopting the above explained structure, in the embodiment, it becomes possible to secure stability of touch of the heat source  6  and the fixation belt  4 , therefore, it becomes possible to attempt stabilization of heat conduction characteristic. Further, by attempting stabilization of heat conduction characteristic, it becomes possible to prevent a breakage of the heat source  6  due to overheat of the heat source  6 . 
       The Utilization Possibility in Industry: 
       [0053]    In the embodiment 1 and the embodiment 2, only such case is explained that the fixing device of the present invention is applied to a color electronic printer serving as an image forming apparatus. However, the present invention is not limited by the case. That is, the present invention also can be applied to an image forming apparatus such as copying apparatus, facsimile and the like. In the case, it is possible to use the fixing device of the present invention as a means/an apparatus that forms toner formed from resin having heating fusion characteristic by using an image forming processing means such as a color electronic printer; and performs a heating/pressure fixing process of non-fixation toner corresponding to the desired image information. 
         [0054]    The present invention is not limited to the foregoing embodiments but many modifications and variations are possible within the spirit and scope of the appended claims of the invention.