Patent Publication Number: US-7583923-B2

Title: Bearing structure and fusing device for image forming apparatus employing the bearing structure

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit under 35 U.S.C § 119(a) of Korean Patent Application Nos. 10-2004-0031666, filed on May 6, 2004 and 10-2004-0033101, filed on May 11, 2004, in the Korean Intellectual Property Office, the entire disclosures of both of which are hereby incorporated by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a bearing structure that rotatably supports a roller and a fusing device for an image forming apparatus employing the bearing structure. More particularly, the present invention relates to a bearing structure that reduces friction between a roller and a bearing under pressure and a fusing device for an image forming apparatus employing the bearing structure. 
   2. Description of the Related Art 
   In general, bearing structures are employed to rotatably support a roller on a fixed frame. That is, bearing structures are installed at both sides of a roller to be connected between the roller and the frame, and to rotatably support the roller. 
   Bearing structures are divided into a ball bearing type, which rotatably supports a roller by balls that roll between an inner wheel and an outer wheel, and a sliding bearing type, which is made of plastic material and rotatably supports a roller by allowing the roller to slide. The ball bearing is superior in performance to the sliding bearing, but has a complex structure, thereby increasing the number of assembling processes and manufacturing costs. Accordingly, the sliding bearing, which can be mass produced easily at low costs, is widely used. 
   In general, electrophotographic image forming apparatuses print an image on a sheet of paper by emitting light to a photosensitive medium charged at a predetermined potential to form an electrostatic latent image, developing the electrostatic latent image with toner of a predetermined color to form a toner image, and transferring and fusing the toner image. The image forming apparatuses employ a fusing device in a printing path to fuse the transferred image on the sheet of paper. 
   Referring to  FIGS. 1 and 2 , a conventional image forming apparatus includes a frame  1 , a fusing roller  11  installed for being rotatable on a frame  1 , a heater  15  embedded in the fusing roller  11  for heating a surface of the fusing roller  11 , a pressure roller  21  rotatably installed on the frame  1  for pressing a printing paper P with the fusing roller  11 , and bearing structures  30  for rotatably supporting the fusing roller  11  and the pressure roller  21 . 
   Each of the bearing structures  30  includes a sliding bearing  31  installed on the frame  1 , and an elastic member  35  for supporting elastically the sliding bearing  31 . The sliding bearing  31  is made of plastic material, and has a bearing groove  33  into which the fusing roller  11  or the pressure roller  21  is rotatably inserted. Here, a clearance is formed between an inner surface of the bearing groove  33  and an outer surface of each of the fusing roller  11  and the pressure roller  21 . A fluid is injected into the clearance, and guides the fusing roller  11  and the pressure roller  21 , thereby helping them to slide during their rotation. The elastic member  35  elastically supports the sliding bearing  31  in a predetermined direction, and the pressure roller  21  presses the fusing roller  11 . 
   In this manner, if the fusing roller  11  and the pressure roller  21  are rotatably supported while pressure is applied therebetween in a predetermined direction, a predetermined area on the inner surface of the bearing groove  33 , that is, an area A formed in a direction opposite to the direction in which the pressure is applied, has a narrower clearance than other areas, such that the area A directly contacts the fusing roller  11  or the pressure roller  21  with a higher load. 
   With the increase in the load, the sliding bearing  31  may be worn, and the system may operate wrongly or halt. Further, foreign substances C generated during the wear may remain inside the bearing groove  33 , thereby causing the bearing to operate abnormally. 
   In the meantime, it can be considered that the fusing device can employ a ball bearing. However, since the ball bearing is large and a mold bearing should be used inside the ball bearing, the ball bearing has a complex structure and increases the number of assembling processes and manufacturing costs as compared to the sliding bearing. 
   Further, since the ball bearing is made of metal material stronger than the plastic material of the sliding bearing, even when the fusing roller is heated by the heater installed thereinside to an abnormally high temperature where plastic material may be deformed, the ball bearing is not deformed. In the meanwhile, a general fusing device employs a fuse, which determines whether the bearing is overheated based on the degree of deformation of the heated bearing and stops the heating if it is determined to be overheated. Accordingly, if the fusing device constructed as above employs the ball bearing, the bearing is not deformed at an abnormally high temperature, thereby increasing the possibility of fires. Thus, the fusing device employing the fuse cannot be used. 
   SUMMARY OF THE INVENTION 
   The present invention provides a bearing structure having a sliding bearing to substantially prevent a friction during operation, and a fusing device for an image forming apparatus employing the bearing structure. 
   According to an aspect of the present invention, there is provided a bearing structure installed between a frame and a rotary shaft for rotatably supporting the rotary shaft on the frame. The bearing structure has a bearing body having a fitting part in which the rotary shaft is rotatably fitted. A rolling support unit is installed on at least one portion inside the fitting part for contacting the rotary shaft in a rolling manner. 
   According to another aspect of the present invention, a fusing device for an image forming apparatus has a fusing roller in which a heater is embedded and a pressure roller that faces the fusing roller and cooperates with the fusing roller in pressing a sheet of paper passing therebetween. Bearing structures rotatably support the fusing roller and the pressure roller on a frame. Each of the bearing structures has a bearing body, which has a fitting part in which at least one of the fusing roller and the pressure roller is rotatably fitted; and a rolling support unit installed on at least one portion inside the fitting part for contacting the fitted roller in a rolling manner. 
   Other objects, advantages and salient features of the invention will become apparent from the following detailed description, which, taken in conjunction with the annexed drawings, discloses preferred embodiments of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
       FIG. 1  is a schematic sectional view of a conventional fusing device for an image forming apparatus; 
       FIG. 2  is a schematic sectional view illustrating the operation of the fusing device shown in  FIG. 1 ; 
       FIG. 3  is an exploded perspective view of a bearing structure according to a first embodiment of the present invention; 
       FIG. 4  is a schematic sectional view of the bearing structure of  FIG. 3 ; 
       FIG. 5  is an exploded perspective view of a bearing structure according to a second embodiment of the present invention; 
       FIG. 6  is a schematic sectional view of a fusing device for an image forming apparatus according to a first embodiment of the present invention; 
       FIG. 7  is a schematic sectional view illustrating the operation of the fusing device of  FIG. 6 ; 
       FIG. 8  is an exploded perspective view of a bearing structure according to a third embodiment of the present invention; 
       FIG. 9  is a schematic sectional view of the bearing structure of  FIG. 8 ; 
       FIG. 10  is an exploded perspective view of a bearing structure according to a fourth embodiment of the present invention; 
       FIG. 11  is a schematic sectional view of a fusing device for an image forming apparatus according to a second embodiment of the present invention; 
       FIG. 12  is a schematic sectional view illustrating the operation of the fusing device shown in  FIG. 11 ; 
       FIG. 13  is an exploded perspective view of a bearing structure according to a fifth embodiment of the present invention; and 
       FIG. 14  is a schematic sectional view of a fusing device for an image forming apparatus having the bearing structure of  FIG. 13 , according to a fifth embodiment of the present invention. 
   

   Throughout the drawings, like reference numerals will be understood to refer to like parts, components and structures. 
   DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
   The present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. 
   Referring to  FIGS. 3 and 4 , a bearing structure  50  according to an exemplary embodiment of the present invention is installed between a frame  41  and a rotary shaft  45 , and rotatably supports the rotary shaft  45  on the frame  41 . The bearing structure  50  includes a bearing body  51  having a fitting part  53  in which the rotary shaft  45  is rotatably fitted, and a rolling support unit  60  installed inside the fitting part  53  for contacting the rotary shaft  45  in a rolling manner. 
   The frame  41  has a space  43  in which the bearing structure  50  is installed. The bearing structure  50  has guide grooves  52  formed on both upper and lower sides thereof so that the bearing structure  50  may be slidably inserted into the space  43 . Accordingly, both extensions of the frame  41  formed by the space  43  are inserted into the guide grooves  52 , such that the bearing structure  50  may be installed on the frame  41 . Here, the method of coupling the bearing structure  50  to the frame  41  is exemplary, and various modifications may be made. 
   Preferably, an elastic member  57  is interposed between the bearing body  51  and the frame  41 . The elastic member  57  elastically presses the bearing body  51  to the frame  41  in a predetermined direction. Accordingly, if the bearing structure  50  rotatably supports the rotary shaft  45  while the elastic member  57  presses the bearing body  51  in the predetermined direction, a predetermined pressure may be applied to the rotary shaft  45  due to an elastic biasing force of the elastic member  57 . 
   The bearing structure  50  is a type of sliding bearing, and is made of a plastic material that preferably has a high resistance to heat and friction caused during its rotatably supporting function. That is, the rotary shaft  45  is slidably fitted in the fitting part  53  formed on the bearing body  51  so as to freely rotate. 
   A clearance is formed between an inner wall of the fitting part  53  and the rotary shaft  45 . A fluid may be injected into the clearance to facilitate rotation of the rotary shaft  45 . In the meantime, when the rotary shaft  45  is pressed in the predetermined direction, the clearance becomes eccentric to one direction such that a specific portion has a narrower clearance. 
   The rolling support unit  60  is installed on the specific portion with the narrower clearance, and contacts the rotary shaft  45  in a rolling manner. 
   An installation groove  54  is formed within at least one area of the fitting part  53 , for example, within the portion with the narrower clearance, to receive the rolling support unit  60 . Here, the bearing body  51  has side walls  55  of a predetermined thickness extending along both sides of the installation groove  54 , and a plurality of coupling grooves  56  are formed on the side walls  55 . 
   The rolling support unit  60  includes a plurality of bushings  61 , a plurality of guide shafts  63  freely rotatably coupled to the bushings  61 , respectively, and a support belt  65  surrounding the guide shafts  63 . 
   The plurality of bushings  61  are attached to the side walls  55  of the fitting part  53 , and rotatably support the guide shafts  63 , respectively. The plurality of guide shafts  63  are placed on predetermined positions inside the fitting part  53 , and both ends of each guide shaft  63  are rotatably installed on each bushing  61 . Accordingly, the guide shafts  63  may freely rotate inside the fitting part  53  when an external force is applied to the guide shafts  63 . 
   The support belt  65  surrounds the plurality of guide shafts  63 . That is, in the state where the support belt  65  is disposed inside the installation groove  54 , the guide shafts  63  pass through the support belt  65  to be coupled to the bushings  61 , as shown in  FIG. 4 . 
   exposed surface  65   a  of the support belt  65  mounted in the fitting part  53  directly contacts the rotary shaft  45 . Accordingly, the support belt  65  is operatively connected to the rotary shaft  45  such that the support belt  65  is moved in a rotational direction of the rotary shaft  45 . At this time, since the guide shafts  63  are rotatably coupled to the bushings  61 , the guide shafts  63  facilitate movement of the support belt  65 . 
   Referring to  FIG. 5 , a bearing structure  70  according to another exemplary embodiment of the present invention is installed between the frame  41  and the rotary shaft  45  and rotatably supports the rotary shaft  45  on the frame  41 . The bearing structure  70  includes a bearing body  71  having a fitting part  73  in which the rotary shaft  45  is rotatably fitted. A rolling support unit  80  is installed inside the fitting part  73  for contacting the rotary shaft  45  in a rolling manner. 
   The bearing structure  70  of the exemplary embodiment illustrated in  FIG. 5  is different from the bearing structure  50  according to the previous embodiment described with reference to  FIGS. 3 and 4  in that the rolling support unit  80  has a separate independent structure and may be installed on the fitting part  73 . Accordingly, an explanation will be given focusing on the difference, and a detailed explanation of other elements will not be given. 
   To this end, the bearing body  70  has a space part  74  formed on at least one area inside the fitting part  73 . The rolling support unit  80 , which is a single body, is mounted in the space part  74 . 
   The rolling support unit  80  includes a housing  87  having a dented inner space formed thereon, a plurality of bushings  81 , a plurality of guide shafts  83 , and a support belt  85 . 
   the state where the plurality of bushings  81 , the plurality of guide shafts  83 , and the support belt  85  are assembled, the housing  87  is mounted in the space part  74 . Here, the housing  87  may be mounted in the space part  74  by bonding means, e.g., an adhesive, screws, or hooks. For example, the housing  87  may be mounted in the space part  74  using guide grooves  74   a  and guide rails  87   a,  which are correspondingly formed on the space part  74  and the housing  87 , respectively, as shown in  FIG. 5 . 
   The housing  87  has side walls extending along both sides of the dented inner space thereof, and a plurality of coupling grooves  89  are formed on the side walls  88 . The bushings  81  are inserted into the coupling grooves  89 , respectively. The guide shafts  83  are rotatably coupled to the bushings  81 , respectively, and guide the support belt  85  to facilitate rotation. 
   An exposed surface of the support belt  85  mounted in the fitting part  73  directly contacts the rotary shaft  45  in a rolling manner, such that the support belt  85  is operatively connected to the rotary shaft  45  and thus is moved in a rotational direction of the rotary shaft  45 . 
   Referring to  FIGS. 6 and 7 , a fusing device for an image forming apparatus according to an exemplary embodiment of the present invention includes a fusing roller  111 , and a pressure roller  121  rotatably installed in contact with the fusing roller  112 . Bearing structures  130  rotatably support the fusing roller  111  and the pressure roller  121  on a frame  101 . 
   The fusing roller  111  is rotatably installed on the frame  101  through the bearing structure  130 . A heater  115  is embedded inside the fusing roller  111 . Accordingly, the fusing roller  111  cooperates with the pressure roller  121  to fuse an image transferred to a printing paper P at high temperature and high pressure. The fusing roller  111  and the pressure roller  121  rotate while mutually pressing the printing paper P passing therebetween, areas are formed in directions opposite to the directions in which pressures are applied when the respective bearing structures  130  are coupled to the fusing roller  111  and the pressure roller  121  that have a narrower clearance than other areas. 
   Each of the bearing structures  130  includes a bearing body  131  having a fitting part  133  in which one of the fusing roller  111  and the pressure roller  121  is rotatably fitted, and a rolling support unit  140  installed on at least one portion inside the fitting part  133  for contacting the fusing roller  111  or the pressure roller  121  in a rolling manner. The rolling support unit  140  includes a support belt  145 , which directly contacts the fusing roller  111  or the pressure roller  121  in a rolling manner, and is disposed on an area with a narrower clearance on an inner surface of the fitting part  133 , thereby facilitating smooth rotation of the fusing roller  111  or the pressure roller  121 . 
   The bearing structures  130  illustrated in  FIGS. 6 and 7  are substantially similar in structure and function to the bearing structures according to the previous embodiments described with reference to  FIGS. 3 through 5 , such that a detailed explanation thereof will not be given. 
   Alternatively, although the bearing structures including the rolling support unit support both the fusing roller and the pressure roller in the present embodiment, it is just exemplary, and the bearing structures may support either the fusing roller or the pressure roller. 
   As described above, since the rolling support unit  140  is employed in the specific portion with a narrower clearance to contact the roller in a rolling manner, not in a frictional manner, a friction between the bearing body  131  and the fusing roller  111  and the pressure roller  121  may be reduced. 
   Referring to  FIGS. 8 and 9 , a bearing structure  250  according to another exemplary embodiment of the present invention is installed between a frame  241  and a rotary shaft  245 , and rotatably supports the rotary shaft  245  on the frame  241 . The bearing structure  250  includes a bearing body  251  having a fitting part  253  in which the rotary shaft  245  is rotatably fitted, and a rolling support unit  260  is installed inside the fitting part  253  for contacting the rotary shaft  245  in a rolling manner. 
   The frame  241  has a space  243  in which the bearing structure  250  is installed. The bearing structure  250  has guide grooves  252  formed on both upper and lower sides thereof so that the bearing structure  250  may be slidably installed in the space  243  through the guide grooves  252 . Accordingly, both extensions of the frame  241  formed by the space  243  are inserted into the guide grooves  252 , such that the bearing structure  250  may be installed on the frame  241 . Here, the method of coupling the bearing structure  250  to the frame  241  is exemplarily shown, and various modifications may be made thereto. 
   Preferably, the bearing structure  250  further includes an elastic member  257  that is disposed between the bearing body  251  and the frame  241 . The elastic member  257  elastically presses the bearing body  251  to the frame  241  in a predetermined direction. Accordingly, if the bearing structure  250  rotatably supports the rotary shaft  245  while the elastic member  257  presses the bearing body  251  in the predetermined direction, a predetermined pressure may be applied to the rotary shaft  245  due to an elastic biasing force of the elastic member  257 . 
   The bearing structure  250  is a type of sliding bearing, and is made of a plastic material that preferably has a high resistance to heat and friction caused during its rotatably supporting function. That is, the rotary shaft  245  is slidably fitted in the fitting part  253  formed on the bearing body  251  to rotate freely. 
   A clearance is formed between an inner wall of the fitting part  253  and the rotary shaft  245 . A fluid may be injected into the clearance to facilitate rotation of the rotary shaft  245 . When the rotary shaft  245  is pressed in the predetermined direction, the clearance becomes eccentric to one direction such that a specific portion has a narrower clearance. 
   The rolling support unit  260  is installed on the portion with the narrower clearance, and contacts the rotary shaft  245  in a rolling manner. 
   An installation groove  254  is formed within at least one area of the fitting part  253 , for example, within the portion with the narrower clearance, to receive the rolling support unit  260 . The bearing body  251  has side walls of a predetermined thickness along both sides of the installation groove  254 , and a plurality of coupling grooves  256  are formed on the side walls  255 . 
   The rolling support unit  260  includes a plurality of bushings  261 , a plurality of shafts  263  that are freely rotatably coupled to the bushings  261 , respectively, and a plurality of convex parts  265  formed on outer peripheries of the shafts  263 . 
   The plurality of bushings  261  are attached to the side walls  255  of the fitting part  253 , and rotatably support the shafts  263 . Both ends of each shaft  263  are rotatably installed on each bushing  261  in the state where the plurality of shafts  263  are placed on predetermined positions inside the fitting part  253 . Accordingly, the plurality of shafts  263  may freely rotate inside the fitting part  253  when an external force is applied to the shafts  263 . 
   Each of the convex parts  265  is formed on a portion of an outer periphery of each of the shafts  263 . That is, the convex parts  265  are integrally formed with the shafts  263 , or are coupled as separate members to the outer peripheries of the shafts  263 . 
   Exposed surfaces of the convex parts  265  mounted in the fitting part  253  directly contact the rotary shaft  245 . Accordingly, the convex parts  265  are operatively connected to the rotary shaft  245  such that the convex parts  265  rotate together with the shafts  263  in a rotational direction of the rotary shaft  245 . 
   Referring to  FIG. 10 , a bearing structure  270  according to another exemplary embodiment of the present invention is installed between the frame  241  and the rotary shaft  245 , and rotatably supports the rotary shaft  245  on the frame  241 . The bearing structure  270  includes a bearing body  271  having a fitting part  273  in which the rotary shaft  245  is rotatably fitted, and a rolling support unit  280  installed inside the fitting part  273  for contacting the rotary shaft  245  in a rolling manner. 
   The bearing structure  270  according to the present embodiment illustrated in  FIG. 10  is different from the bearing structure  250  according to the previous embodiment described with reference to  FIGS. 8 and 9  in that the rolling support unit  280  has a separate independent structure and may be installed on the fitting part  273 . Accordingly, an explanation will be given focusing on the difference, and a detailed explanation of other elements will not be given. 
   The bearing structure  270  has a space part  274  formed on at least one area inside the fitting part  273 . The rolling support unit  280 , which is a single body, is mounted in the space part  274 . 
   The rolling support unit  280  includes a housing  287  having a dented inner space, a plurality of bushings  281 , a plurality of shafts  283 , and a plurality of convex parts  285 . 
   The bushings  281 , the shafts  283 , and the convex parts  285  are assembled inside the housing  287 , which is mounted in the space part  274 . The housing  287  may be mounted in the space part  274  by bonding means, e.g., an adhesive, screws, or hooks. For example, the housing  287  may be mounted in the space part  274  using guide grooves  274   a  and guide rails  287   a,  which are correspondingly formed on the space part  274  and the housing  287 , respectively, as shown in  FIG. 10 . 
   The housing  287  has side walls  288  extending along both sides of the dented inner space thereof, and a plurality of coupling grooves  289  are formed on the side walls  288 . The bushings  281  are inserted into the coupling grooves  289 , respectively, and the shafts  283  are freely rotatably coupled to the bushings  281 , respectively. 
   Exposed surfaces of the convex parts  285  mounted in the fitting part  273  directly contact the rotary shaft  245 . Accordingly, the convex parts  285  are operatively connected to the rotary shaft  245  such that the convex parts  285  are moved in a rotational direction of the rotary shaft  245 . 
   Referring to  FIGS. 11 and 12 , a fusing device for an image forming apparatus according to another exemplary embodiment of the present invention includes a fusing roller  311 , and a pressure roller  321  rotatably installed in contact with the fusing roller  311 . Bearing structures  330  for rotatably supporting the fusing roller  311  and the pressure roller  321  on a frame  301 . 
   The fusing roller  311  is rotatably installed on the frame  301  through the bearing structure  330 . A heater  315  is embedded inside the fusing roller  311 . Accordingly, the fusing roller  311  cooperates with the pressure roller  321  to fuse an image transferred to a printing paper P at high temperature and high pressure. The fusing roller  311  and the pressure roller  321  rotate while mutually pressing the printing paper P passing therebetween, areas are formed in directions opposite to directions in which pressures are applied when the respective bearing structures  330  are coupled to the fusing roller  311  and the pressure roller  321  that have a narrower clearance than other areas. 
   Each of the bearing structures  330  includes a bearing body  331  having a fitting part  333  in which the fusing roller  311  or the pressure roller  321  is rotatably fitted, and a rolling support unit  340  installed on at least one portion inside the fitting part  333  for contacting the fusing roller  311  or the pressure roller  321  in a rolling manner. The rolling support unit  340  includes convex parts  345 , which directly contact the fusing roller  311  and the pressure roller  321  in a rolling manner, and is disposed on an area with a narrower clearance on an inner surface of the fitting part  333 , thereby helping the fusing roller  311  or the pressure roller  321  to rotate smoothly. 
   The bearing structures  330  illustrated in  FIGS. 11 and 12  are substantially similar in structure and function to the bearing structures described with reference to  FIGS. 8 through 10 , and a detailed explanation thereof will not be given. 
   The bearing structures including the rolling support unit according to this exemplary embodiment support both the fusing roller and the pressure roller, and thus, it is possible that the bearing structure supports either the fusing roller or the pressure roller. 
   As described above, since the rolling support unit  340  is employed in the specific portion with the narrower clearance to contact the roller in a rolling manner, not in a frictional manner, friction between the bearing body  331  and the fusing roller  311  and the pressure roller  321  may be reduced. 
   Referring to  FIG. 13 , a bearing structure  450  according to a further embodiment of the present invention is installed between a frame  441  and a rotary shaft  445  and rotatably supports the rotary shaft  445  on the frame  441 . The bearing structure  450  includes a bearing body  451  having a fitting part  453  in which the rotary shaft  445  is rotatably fitted, and a rolling support unit  460 , which is installed inside the fitting part  453  for contacting the rotary shaft  445  in a rolling manner. 
   The bearing structure  450  according to the exemplary embodiment illustrated in  FIG. 13  is different from the bearing structure  250  according to the previous embodiment described with reference to  FIGS. 8 and 9  in the structure of the rolling support unit  460 . Accordingly, an explanation will be given focusing on the difference, and a detailed explanation of other elements will not be given. 
   To this end, the bearing body  451  has an installation groove  454  formed within at least one area of the fitting part  453 . The rolling support unit  460  is inserted into the installation groove  454 . Two installation grooves  454  may be installed as shown in  FIG. 13 , and one, or three or more installation grooves may also be installed. 
   The rolling support unit  460  includes at least one ball member  465 , which is freely rotatably inserted into the installation groove  454 . The ball member  465  directly contacts the rotary shaft  445  to guide the rotary shaft  445  to rotation. Preferably, the rolling support unit  460  further includes a cap member  467 . The cap member  467  is attached to the installation groove  454  and prevents the ball member  465  from being removed from the installation groove  454 . Preferably, the installation groove  454  extends at a lateral surface of the bearing body  451  in a longitudinal direction of the rotary shaft  445  in  FIG. 13 . That is, the installation groove  454  may be formed inside the bearing body  451  in a direction in which the rotary shaft  445  is pressed. 
   An exposed surface of the ball member  465  inserted into the installation groove  454  directly contacts the rotary shaft  445 , thereby facilitating smooth rotation of the rotary shaft  445 . 
   Referring to  FIG. 14 , a fusing device for an image forming apparatus according to another exemplary embodiment of the present invention includes a fusing roller  411 , and a pressure roller  421  rotatably installed in contact with the fusing roller  411 . Bearing structures rotatably support the fusing roller  411  and the pressure roller  421  on a frame  401 . 
   Since the fusing device illustrated in  FIG. 14  is substantially similar to the fusing device of the previous embodiment described with reference to  FIGS. 11 and 12  in the structure of the bearing structures  470 , a detailed explanation of the fusing roller  411  and the pressure roller  421  will not be given. 
   Each of the bearing structures  470  includes a bearing body  471  having a fitting part  473  in which the fusing roller  411  or the pressure roller  421  is rotatably fitted, and a rolling support unit  480  installed on at least one portion inside the fitting part  473  for contacting the fusing roller  411  or the pressure roller  421  in a rolling manner. The rolling support unit  480  includes a ball member  485 , which directly contacts the fusing roller  411  or the pressure roller  421  in a rolling manner, and is disposed on an area with a narrower clearance on an inner surface of the fitting part  473 , thereby facilitating smooth rotation of the fusing roller  411  or the pressure roller  421 . The bearing structure  470  is substantially identical in structure and function to the bearing structure of the previous embodiment described with reference to  FIG. 13 , such that a detailed explanation thereof will not be given. 
   Although the bearing structures including the rolling support unit according to this exemplary embodiment supports both the fusing roller and the pressure roller, the bearing structures may support either the fusing roller or the pressure roller. 
   As described above, since the rolling support unit  470  is employed in the specific portion with a narrower clearance to contact the roller in a rolling manner instead of frictionally, friction between the bearing body  431  and the fusing roller  411  and the pressure roller  421  may be reduced. 
   Since the bearing structure according to exemplary embodiments of the present invention employs the support belt, the convex part, or the ball member, which is operatively connected to the roller and rotates, friction between the roller and the bearing under a pressure may be reduced. 
   Further, if the rolling support unit of the bearing structure is manufactured as a separate independent member of the bearing body and then is coupled to the bearing body, the rolling support unit may be assembled and installed more easily, thereby reducing the number of assembling processes. 
   Moreover, since the fusing device for an image forming apparatus employs a modified sliding bearing instead of a ball bearing, problems caused when the ball bearing is employed may be solved fundamentally. In addition, since the rolling support unit includes the support belt, the convex part, or the ball member that contacts the bearing body in a rolling manner, friction may be reduced at portions under a high pressure, and foreign substances generated due to the friction are substantially prevented. 
   While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.