Patent Publication Number: US-2016246231-A1

Title: Fixing device and image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2015-033960 filed Feb. 24, 2015. 
     BACKGROUND 
     Technical Field 
     The present invention relates to a fixing device and an image forming apparatus. 
     SUMMARY 
     According to an aspect of the invention, there is provided a fixing device that fixes a toner image onto a sheet, which is transported while holding the toner image, by applying heat and pressure to the sheet, the fixing device including a fixing roller that is driven so as to rotate, an endless belt that forms a contact region between the fixing roller and the endless belt and that rotates as a result of being driven by the fixing roller, which rotates, a heating member that includes a heat source that heats the contact region, a support member that is disposed at a position in a space enclosed by the belt, the position facing the fixing roller, and that has a support surface, which has a substantially non-arc shape in a direction in which the belt rotates and which is in contact with an inner surface of the belt in such a manner that the belt is sandwiched between the support member and the fixing roller, and a pressing member that includes a pair of guiding members that support and guide end edge portions of the belt in a direction in which a rotation axis of the belt extends. Each of the guiding members is a member having a guiding groove that has an inner guiding wall that guides an edge of the belt in the direction in which the rotation axis of the belt extends from an area inside the belt, an outer guiding wall that guides the edge of the belt from an area outside the belt, and a bottom surface that extends around the rotation axis in such a manner as to have a substantially arc shape and along which an end surface of the belt slides. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An exemplary embodiment of the present invention will be described in detail based on the following figures, wherein: 
         FIG. 1  is a diagram illustrating an internal structure of a printer, which is an example of an image forming apparatus according to the exemplary embodiment of the present invention; 
         FIG. 2  is a diagram illustrating a configuration of a fixing unit, which is included in the printer illustrated in  FIG. 1 , in a state of being removed from the printer; 
         FIG. 3  is a perspective view illustrating one of guiding members in a state where an end portion of a pressure belt on one side in a direction in which a rotation axis of the pressure belt extends is fitted to the guiding member; 
         FIG. 4  is a perspective view illustrating a portion of the guiding member on the inner surface side into which the pressure belt is fitted; 
         FIG. 5  is a sectional view taken along line V-V of  FIG. 4 ; and 
         FIG. 6  is a diagram illustrating an inner surface of the guiding member. 
     
    
    
     DETAILED DESCRIPTION 
     An exemplary embodiment of the present invention will be described below. 
       FIG. 1  is a diagram illustrating an internal structure of a printer  100 , which is an example of an image forming apparatus according to the exemplary embodiment of the present invention. The printer  100  includes a fixing unit  200 , which is an example of a fixing device according to the exemplary embodiment of the present invention. 
     A drawer-type sheet tray  110  is disposed in a lower portion of the printer  100 , and sheets P, each of which is to be used for a print operation and each of which has not yet been used, are accommodated in the sheet tray  110  in such a manner as to be stacked on top of one another. When an image printing operation is performed, the sheets P in the sheet tray  110  are picked up one by one by a pickup roller  151  and transported by transport rollers  152 . Details of transportation of the sheets P will be described later. 
     Four image forming engines  130  are mounted in the printer  100 . The four image forming engines  130  are cartridge-type image forming engines and are individually removable from the printer  100 . The image forming engines  130  include image forming engines  130 Y,  130 M,  130 C, and  130 K. The image forming engines  130  contain different monochromatic color toners, and each of the image forming engines  130  forms a monochromatic color toner image by using the corresponding monochromatic color toner. 
     In the following description, when the image forming engines  130  are described in such a manner as to be distinguished in terms of toner color, the letters Y, M, C, and K, which represent the toner colors (yellow, magenta, cyan, and black), will be given to the reference numeral  130 , which represents each of the image forming engines. 
     In the present exemplary embodiment, the image forming engines  130  have the same configuration. Each of the image forming engines  130  includes a photoconductor  131  that rotates in the direction of arrow a, a charger  132 , an exposure unit  133 , a developing unit  134 , and a cleaner  135 . The charger  132 , the exposure unit  133 , the developing unit  134 , and the cleaner  135  are disposed around the photoconductor  131 . 
     Each of the chargers  132  uniformly charges a surface of the corresponding photoconductor  131 . 
     Each of the exposure units  133  radiates exposure light, which is modulated on the basis of image data, onto the corresponding photoconductor  131  so as to form an electrostatic latent image on the photoconductor  131 . Image data representing a monochromatic color image is input to each of the image forming engines  130 , the monochromatic color image being formed of the color toner contained in the corresponding image forming engine  130 . Then, exposure light, which is modulated on the basis of the image data representing the corresponding monochromatic color image, is radiated from each of the exposure units  133 , and an electrostatic latent image corresponding to the monochromatic color image is formed on the corresponding photoconductor  131 . 
     Each of the developing units  134  develops an electrostatic latent image on the corresponding photoconductor  131  with the corresponding toner and forms a monochromatic color toner image on the photoconductor  131 . Each of the developing units  134  includes a toner cartridge  134   a . Each of the toner cartridges  134   a  contains the monochromatic color toner for the corresponding developing unit  134 . The toner in each of the toner cartridges  134   a  is supplied to the corresponding developing unit  134  and used for formation of a toner image. Each of the toner cartridges  134   a  may individually be replaced and is to be replaced with a new toner cartridge  134   a  when the toner cartridge  134   a  is empty. 
     An intermediate transfer unit  160  is disposed above the image forming engines  130 . The intermediate transfer unit  160  includes an endless intermediate transfer belt  161 , plural support rollers  162  that support the intermediate transfer belt  161 , four first transfer rollers  163 , and a cleaner  164 . 
     The intermediate transfer belt  161  is supported by the plural support rollers  162  and moves circularly in the direction of arrow b while passing through a movement path extending along the four image forming engines  130 . 
     The four first transfer rollers  163  are disposed at positions facing the photoconductors  131  of the image forming engines  130  with the intermediate transfer belt  161  interposed between the first transfer rollers  163  and the photoconductors  131 , and each of the first transfer rollers  163  serves to transfer a toner image formed on the corresponding photoconductor  131  onto the intermediate transfer belt  161 . 
     Toner images that are formed on the photoconductors  131 , which are included in the four image forming engines  130 , are sequentially transferred onto the intermediate transfer belt  161 , which moves in the direction of arrow b, in such a manner as to be superposed with one another by operation of the first transfer rollers  163 . 
     After the toner images have been transferred, residual toner and the like that remain on the surfaces of the photoconductors  131  are removed by the corresponding cleaners  135 . 
     Each of the image forming engines  130  includes a memory  136 . In each of the memories  136 , various information items related to the corresponding image forming engine  130 , such as the color of the toner used in the image forming engine  130  and an accumulated operation time of the image forming engine  130  from the beginning of use are recorded. When the image forming engines  130  are mounted in the printer  100 , the contents of the memories  136  are read by the printer  100 , and the contents of the memories  136  are rewritten as necessary. 
     Toner images that have been sequentially transferred to the intermediate transfer belt  161  in such a manner as to be superposed with one another are transferred, by operation of a second transfer roller  170 , onto one of the sheets P that has been transported to the position of the second transfer roller  170  in accordance with the timing at which the toner images are delivered to the position of the second transfer roller  170 . The fixing unit  200  applies heat and pressure to the sheet P on which the toner images have been transferred, and as a result, an image formed of the toner images, which have been fixed to the sheet P, is printed on the sheet P. The sheet P is ejected to a sheet-exit tray  140  by sheet ejection rollers  155 . 
     On the other hand, after the toner images have been transferred, residual toner and the like that remain on a surface of the intermediate transfer belt  161  are removed by the cleaner  164 . 
     A transport path along which the sheets P are to be transported in a print operation will now be described. 
     When a print operation is performed, one of the sheets P is picked up from the sheet tray  110  by the pickup roller  151  and is transported in the direction of arrow c by the transport rollers  152  until an end of the sheet P reaches timing-adjustment rollers  154 . After that, the sheet P is sent out by the timing-adjustment rollers  154  so as to be delivered to the position of the second transfer roller  170  in accordance with the timing at which toner images, which have been transferred to the intermediate transfer belt  161 , are delivered to the position of the second transfer roller  170 , and the toner images are transferred onto the sheet P by operation of the second transfer roller  170 . The sheet P, to which the toner images have been transferred, is further transported in the direction of arrow d, and the toner images are fixed onto the sheet P by the fixing unit  200 . Then, the sheet P is ejected to the sheet-exit tray  140  by the sheet ejection rollers  155 . 
     In the case of performing two-sided printing in which an image is printed on both first and second surfaces of one of the sheets P, a portion of the sheet P having an image only printed on the first surface thereof is ejected to the sheet-exit tray  140  by the sheet ejection rollers  155 , and then, the portion of the sheet P, which has been ejected, is drawn into the printer  100  again as a result of the sheet ejection rollers  155  rotating in a reverse direction. 
     The sheet P, which has drawn in the printer  100 , is transported in the direction of arrow e by transport rollers  156  and further transported by the transport rollers  152 , and the other end of the sheet P reaches the timing-adjustment rollers  154 . A process that is to be subsequently performed is similar to that in the case of printing an image on the first surface of the sheet P, and the sheet P having an image printed on the second surface is ejected to the sheet-exit tray  140 . 
     The printer  100  includes a controller  190 , and the controller  190  performs overall control of the printer  100 . 
     The configuration of the fixing unit  200  will now be described. 
       FIG. 2  is a diagram illustrating the configuration of the fixing unit  200 , which is included in the printer  100  illustrated in  FIG. 1 , in a state of being removed from the printer  100 . 
     As described above, the fixing unit  200  is a device that applies heat and pressure to one of the sheets P that has been transported while holding toner images, which have been transferred thereto by operation of the second transfer roller  170  illustrated in  FIG. 1 , so as to fix the toner images onto the sheet P. The fixing unit  200  corresponds to an example of the fixing device according to the exemplary embodiment of the present invention. 
     The fixing unit  200  includes a heating member  210  and a pressing member  220 . 
     The heating member  210  includes a heating roller  211  and a heat source  212  that is disposed in a space enclosed by the heating roller  211 . The heating roller  211  is a roller that is configured to be driven so as to rotate in the direction of arrow R 1 . 
     The pressing member  220  includes an endless pressure belt  221  and a support member  222 . 
     The pressure belt  221  is an endless belt that is in contact with the heating roller  211  and that is driven and rotated in the direction of arrow R 2  as a result of receiving a rotational driving force from the heating roller  211 . 
     The support member  222  is disposed at a position in a space enclosed by the pressure belt  221 , the position facing the heating roller  211 , and is in contact with the inner surface of the pressure belt  221  in such a manner that the pressure belt  221  is sandwiched between the support member  222  and the heating roller  211 . In order to press the pressure belt  221  against the heating roller  211  in a necessary nip region, a support surface  222   a  of the support member  222  that is in contact with the inner surface of the pressure belt  221  is recessed, and the overall shape of the support surface  222   a  is a non-arc shape or a substantially non-arc shape. 
     Thus, although the pressure belt  221  is a belt that normally has a cylindrical shape, since the pressure belt  221  is pressed against the heating roller  211  by the support surface  222   a  of the support member  222 , which has a non-arc shape or a substantially non-arc shape, portions of the pressure belt  221  in the nip region, which is defined between the support member  222  of the pressure belt  221  and the heating roller  211 , and the peripheral regions are pressed and deformed in such a manner that the pressure belt  221  has a non-circular shape. 
     The pressure belt  221  may sometimes move in a serpentine manner in a direction in which the rotation axis thereof extends (direction perpendicular to  FIG. 1  and  FIG. 2 ) as a result of rotating, and thus, a pair of guiding members  230  that suppress such serpentine movement of the pressure belt  221  are disposed at positions corresponding to the ends of the pressure belt  221  in the direction in which the rotation axis of the pressure belt  221  extends (hereinafter referred to as rotation axis direction). The pair of guiding members  230  serve as stoppers that are brought into contact with end surfaces of the pressure belt  221  in the rotation axis direction such that the pressure belt  221  will not further move in a serpentine manner. 
     A feature of the present exemplary embodiment is the guiding members  230 , which will be described in detail below. 
       FIG. 3  is a perspective view illustrating one of the guiding members  230  in a state where an end portion of the pressure belt  221  on one side in the rotation axis direction is fitted to the guiding member  230 . The pressure belt  221  illustrated in  FIG. 3  is not pressed against the heating roller  211  (see  FIG. 2 ) and has a cylindrical shape. 
     The guiding member  230  has a cutout portion  230   a  (see also  FIG. 4 ) formed by cutting out the guiding member  230 , the cutout portion  230   a  facing the heating roller  211 , and the guiding member  230  excluding the cutout portion  230   a  has a shape that allows an end edge portion of the pressure belt  221  in the rotation axis direction to be fitted into the guiding member  230 . 
       FIG. 4  is a perspective view illustrating a portion of one of the guiding members  230  on the inner surface side into which the pressure belt  221  is fitted. 
       FIG. 5  is a sectional view taken along line V-V of  FIG. 4 . 
     A guiding groove  231  that has a bottom surface  231   a  extending around the rotation axis of the pressure belt  221  in such a manner as to have an arc shape or a substantially arc shape is formed in the guiding member  230 . The end edge portion of the pressure belt  221  is fitted into the guiding groove  231 , and the pressure belt  221  rotates while being guided by the guiding member  230 . 
     The guiding groove  231  has an inner guiding wall  231   b  that guides the end edge portion of the pressure belt  221  from an area inside the pressure belt  221  and an outer guiding wall  231   c  that guides the end edge portion of the pressure belt  221  from an area outside the pressure belt  221 . The end edge portion of the pressure belt  221  is fitted to the guiding groove  231  of the guiding member  230 , and when the pressure belt  221  moves in a serpentine manner toward the side on which the guiding member  230  is disposed, an end surface of the pressure belt  221  abuts against the bottom surface  231   a  of the guiding groove  231  and slides along the bottom surface  231   a , and as a result, a further serpentine movement of the pressure belt  221  toward the side on which the guiding member  230  is disposed is suppressed. 
     The inner guiding wall  231   b  of the guiding groove  231  is parallel to the rotation axis of the pressure belt  221  and has an arc shape. On the other hand, the outer guiding wall  231   c  is formed of a surface inclined with respect to the rotation axis in such a manner that the diameter thereof increases with increasing distance from the bottom surface  231   a . The outer guiding wall  231   c  is tapered in a direction away from the start of the guiding groove  231 . Thus, even when the pressure belt  221  has a non-circular shape as a result of being pressed against the heating roller  211 , the shape of the pressure belt  221  is naturally corrected to a circular shape in a direction from a center portion of the pressure belt  221  toward the end portion of the pressure belt  221  in the rotation axis direction, and the end surface of the pressure belt  221  is caused to have a circular shape and pressed against the bottom surface  231   a , which has an arc shape or a substantially arc shape. 
       FIG. 6  is a diagram illustrating the inner surface of one of the guiding members  230 . For ease of understanding, the tapered shape of the outer guiding wall  231   c  is exaggeratedly illustrated in  FIG. 6 . 
     The pressure belt  221  (not illustrated in  FIG. 6 ) rotates in the direction of arrow R 2 . Regarding the outer guiding wall  231   c  of the guiding groove  231  of the guiding member  230 , a portion of the outer guiding wall  231   c  on the side on which the pressure belt  221  passes through the cutout portion  230   a  and enters the guiding groove  231  as a result of rotating with respect to the rotation axis of the pressure belt  221  is formed of an inclined surface having an inclination angle larger than that of an inclined surface that forms a portion of the outer guiding wall  231   c  on the side on which the pressure belt  221  exits the guiding groove  231  to the cutout portion  230   a  with respect to the rotation axis of the pressure belt  221 . 
     In other words, as illustrated in  FIG. 6 , when the inner surface of the guiding member  230  is viewed from the rotation axis direction, a width (the distance between one end of the outer guiding wall  231   c  connected to the bottom surface  231   a  and the other end of the outer guiding wall  231   c  on the side opposite to the bottom surface  231   a  in a radial direction of the guiding member  230 ) W 1  of the pressure belt  221  on the side on which the pressure belt  221  enters the guiding groove  231  is larger than a width W 2  on the side on which the pressure belt  221  exits the guiding groove  231 . 
     Consequently, also in a rotation direction (direction of arrow R 2 ) of the pressure belt  221 , part of the end edge portion of the pressure belt  221 , which corresponds to the cutout portion  230   a  and still has a non-arc shape enters the guiding groove  231  while being naturally corrected so as to have an arc shape. 
     As described above, in each of the guiding members  230  according to the present exemplary embodiment, the bottom surface  231   a  against which an end surface of the pressure belt  221  abuts has an arc shape or a substantially arc shape that is less likely to cause buckling or deformation of the pressure belt  221 , and the outer guiding wall  231   c  is tapered in order to naturally correct the shape of the pressure belt  221  from a non-circular shape to a circular shape in a direction from a center portion of the pressure belt  221  toward the end portion of the pressure belt  221  in the rotation axis direction. In addition, the guiding groove  231  whose start through which the pressure belt  221  enters the guiding groove  231  is widened is formed in order to naturally correct the shape of an end edge portion of the pressure belt  221  from a non-circular shape to a circular shape in the rotation direction (direction of arrow R 2 ) of the pressure belt  221 . 
     Thus, the probability of buckling or breakage occurring in an end edge portion of the pressure belt  221  is significantly reduced compared with a structure in which an end surface of the pressure belt  221  abuts against the bottom surface  231   a  while having a non-circular shape. 
     Note that, although one guiding member  230  of the pair of guiding members  230 , each of which is disposed at the corresponding end of the pressure belt  221  in the rotation axis direction, has been described above, the other guiding member  230  is formed so as to be plane-symmetrical to the guiding member  230 , which has been described above, and the guiding groove  231  whose width on the side on which the pressure belt  221  enters the guiding groove  231  in the rotation direction of the pressure belt  221  is set to be large is formed in each of the guiding members  230 . 
     Note that, although the case where the present invention is applied to the printer  100  illustrated in  FIG. 1  has been described above, the present invention may be applied to a variety of image forming apparatuses, such as printers and copying machines each of which requires a fixing unit that fixes a toner image onto a sheet, which is transported while holding the toner image, by applying heat and pressure to the sheet. 
     The foregoing description of the exemplary embodiment of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiment was chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.