Patent Publication Number: US-6912371-B2

Title: System for regulating the sliding force of a fusing belt in an image forming apparatus

Description:
FIELD OF THE INVENTION 
   The present invention relates generally to image processing and, more particularly, to a system and method for regulating the sliding force of a fusing belt in an image forming apparatus. 
   BACKGROUND OF THE INVENTION 
   A conventional image forming apparatus includes a fusing unit, which fuses a latent image onto a document. The fusing unit typically includes a heat roller, a fusing roller, a fusing belt stretched across the heat roller and the fusing roller, and a press roller proximate to either the heat roller or the fusing roller. The latent image is fused on the document when it passes between the press roller and the fusing belt on either the heat roller or the fusing roller. 
   The fusing belt rotates by rotation of the heat and fusing rollers. This fusing belt rotation results in a sliding force that may move the fusing belt away from its central position on the rollers towards the edge of the rollers. This sliding can result in improper fusion of the latent image to the document. 
   To avoid this sliding, a regulating part is placed on an edge of the rollers. In the conventional image forming apparatus, the regulating part is place over an edge portion of the roller and is fixed to a wall or other fixed (non-moving) portion of the image forming apparatus.  FIG. 1  shows a portion of a fusing unit in an image forming apparatus including a conventional regulating part. As shown in  FIG. 1 , the fusing unit includes a roller  1 , a fusing belt  2 , a regulating part  3 , and a fixed portion  4 . The regulating part  3  is coupled to the fixed portion  4  by a fixing element  5 , such as a screw. The fixed portion  4  is also coupled to a bridge portion  6  positioned at the end of the roller  1  to enable roller  1  to rotate. 
   Although the regulating part  3  counteracts the sliding force and maintains the fusing belt  2  in its proper position on roller  1 , the conventional design of  FIG. 1  results in other drawbacks. With the fixed regulating part  3 , the fusing belt  2  contacts the regulating part  3  when the roller  1  rotates, generating a friction force between the moving fusing belt  2  and the fixed regulating part  3 . The generated friction force damages the fusing belt  2 , requiring replacement of the fusing belt, which increases the costs for operating the image forming apparatus, and increases the down time of the image forming apparatus. 
   In addition, the image forming apparatus typically drives either the fusing roller or the heat roller with a motor, and the other roller is left free standing. This design results in a high tension force on one side of the fusing belt  2 , i.e., the side being pulled toward the motorized roller. The high tension force causes the portion of the regulating part  3  on the side corresponding to the high tension force to be carved deeply. As a result, the regulating part needs to be replaced as well. 
   Accordingly, it would be desirable to have a regulating part which improves the operation of the fusing apparatus and the life cycle of the fusing belt. 
   SUMMARY OF THE INVENTION 
   According to an aspect of the invention, an image forming apparatus includes a roller having a central portion and an outer edge portion, a fusing belt positioned over at least a portion of the central portion of the roller, and a belt regulating part, positioned on the outer edge portion of the roller, that impedes the fusing belt from moving onto the outer edge portion of the roller. The belt regulating part includes a first portion having a surface adjacent to the central portion of the roller and an edge of the fusing belt. The first portion is configured to contact the fusing belt if the fusing belt moves toward the outer edge portion of the roller. The belt regulating part also includes a second portion coupled to the first portion, the second portion having an interior surface that contacts with the outer edge portion of the roller during operation of the image forming apparatus to cause the regulating part to rotate in conjunction with the rotation of the roller and the fusing belt. 
   Further features, aspects and advantages of the present invention will become apparent from the detailed description of preferred embodiments that follows, when considered together with the accompanying figures of drawing. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a diagram of a portion of a fusing unit in an image forming apparatus having a conventional regulating part. 
       FIG. 2  is a diagram of a fusing unit of an image forming apparatus consistent with the present invention. 
       FIG. 3  is a diagram of a portion of the fusing unit of FIG.  2 . 
       FIG. 4  is a diagram of a regulating part consistent with the present invention. 
       FIG. 5  is a perspective view of the regulating part of FIG.  4 . 
       FIG. 6  is a diagram of the regulating part of  FIG. 4  deformed by the expansion of a roller during the operation of the image forming apparatus. 
       FIGS. 7A and 7B  are diagrams of another regulating part consistent with the present invention. 
       FIG. 8  is a diagram of another regulating part consistent with the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 2  is a diagram of a fusing unit of an image forming apparatus consistent with the present invention. As shown in  FIG. 2 , the fusing unit includes a regulating part  10 , a fusing belt  20 , a roller  30 , a roller  40 , and a press roller  50 . In the embodiment as illustrated, roller  30  is a heat roller, and roller  40  is a fusing roller, though they can be interchanged. 
   In operation, the roller  30  is driven by a motor, which causes the fusing belt  20  to rotate around the rollers  30  and  40 . A document, or other medium for receiving a latent image, is passed between the press roller  50  and the fusing belt  20 , to fuse the latent image to the medium. 
   As described above, the rotation of the fusing belt  20  results in a sliding force that may move the fusing belt  20  away from its central position on the roller  30  and toward one edge of the heat roller  30 . To maintain the fusing belt  20  in its proper position, the regulating part  10  is positioned on the edge of the roller  30 . The maintenance of the position of the fusing belt  20  is shown more particularly in FIG.  3 . 
     FIG. 3  is a diagram of a portion of the fusing unit of FIG.  2 . As shown in  FIG. 3 , the regulating part  10  (which can be on one or both ends of the roller) includes a first portion  12  and a second portion  14 . In addition, the fusing unit also includes a stopper  60  positioned over the edge of the roller  30 . The stopper  60  keeps the regulating part  10  from sliding off of the roller  30 . 
   The first portion  12  of the regulating part  10  has an external circumference greater than an external circumference of the second portion  14 . In this embodiment, the external circumference of the first portion  12  also exceeds the combined external circumference of the fusing belt  20  over the central wider portion of the roller  30 . If during operation the fusing belt  20  slides toward the edge of the roller  30 , the surface of the first portion  12  facing the fusing belt  20  keeps the fusing belt  20  from sliding off its proper position on the roller  30 . 
   The regulating part  10  is not secured to any fixed portion of the image forming apparatus. As a result, the regulating part can rotate in conjunction or synchronously with the rollers  30  and  40  and the fusing belt  20 . By rotating in conjunction with the rollers  30  and  40  and the fusing belt  20 , the regulating part  10  can avoid the wearing down of the fusing belt  20  otherwise caused by friction between the moving fusing belt  20  and a stationary regulating part, as well as the wearing down of the regulating part  10  itself due to this friction and the high tension force derived from driving the roller  30  (and/or roller  40 ). 
   When the rollers  30  and  40  are rotating and moving the fusing belt  20 , the roller implemented as the heat roller, such as roller  30 , can be heated by a heater, which is typically located within the roller. When the heater is off, there is a clearance between the internal surface of the regulating part  10  and the external surface of the edge portion of the roller  30 . Due to this clearance, the rotation of the roller  30  does not necessarily cause the regulating part  10  to rotate. However, the rotation of the rollers  30  and  40  produces a sliding force on the fusing belt  20 . The sliding of the fusing belt  20  moves the belt toward the surface of the first portion  12  of the regulating part  10  that faces the fusing belt  20 . When the fusing belt  20  contacts this surface, the regulating part  10  can move slightly laterally, but is kept from further lateral movement by the stopper  60 . Then, the friction force between the edge of the fusing belt  20  and the surface of the first portion  12  of the regulating part  10 , as well as the friction force between the stopper  60  and a surface of the second portion  14  of the regulating part  10 , causes the regulating part  10  to rotate in conjunction or synchronously with the rollers  30  and  40  and the fusing belt  20 . 
   When the heater is on, it causes the heat roller (in this example, roller  30 ), to thermally expand. The heater also causes the regulating part  10  to thermally expand. The regulating part  10  and the roller  30  may be made from different materials with different thermal expansion properties. For example, the regulating part  10  may be formed from a material such as polyphenylene sulfide or polyether ether keton, and the roller  30  may be made from a material such as aluminum or stainless steel. If the roller  30  thermally expands more than the regulating part  10 , then the expansion of the roller  30  causes the external surface of the edge portion of the roller  30  to contact the internal surface of the regulating part  10 , and eliminate any clearance between them. With this expansion and elimination of the clearance, regulating part  10  will rotate synchronously with the roller  30 . 
   The increased diameters (or equivalently circumferences) of the roller  30  and regulating part  10  can be monitored using a temperature detection device. The temperature detection device can implemented, for example, as a thermistor in the fusing unit. By monitoring temperature, the image forming apparatus can calculate the number of rotations of the regulating part  10  to thereby judge whether or not the roller  30  is driving it. If the regulating part is not being driven by the roller  30 , then an appropriate message can be displayed on the image forming apparatus, such as on an LCD control panel. A message that the regulating part  10  is not rotating may indicate that the fusing unit is not operating properly. 
   To facilitate the rotation of the regulating part  10 , it is preferable to increase the surface roughness on the external surface of the edge portion of the roller  30  where the regulating part  10  is positioned. The surface roughness can be increased by applying an appropriate coating on part or all of the surface of the roller  30 . 
   When the roller  30  and the regulating part  10  are made from different materials, the regulating part  10  may crack due to the larger and faster thermal expansion of the roller  30  resulting from the different coefficient of thermal expansion and thermal conductivity of the different materials. To avoid such cracking, the regulating part  10  is preferably designed to accommodate the larger and faster thermal expansion of the roller  30 .  FIG. 4  is a diagram of an exemplary regulating part consistent with the present invention. 
   As shown in  FIG. 4 , the regulating part  10  includes a plurality of ribs  16 . The number of ribs  16  shown is three, although the number of ribs may be more or less than three. Three or more ribs preferably reduces the likelihood of the regulating part  10  tilting with respect to the roller  30 . The diagram of  FIG. 4  shows the regulating part  10  and roller  30  in a cooled state, i.e., where the heater is off. Although no clearance is shown between the ribs  16  and the roller  30 , it is possible for there to be some clearance between them, or at least insufficient contact for the regulating part  10  to be rotated by the roller  30 . 
     FIG. 5  is a perspective view of the regulating part of FIG.  4 . The regulating part  10  includes the first portion  12  and the second portion  14 , as well as the ribs  16 . As shown in  FIG. 5 , the ribs  16  are only formed in the interior surface of the second portion  14 . The interior surface of the first portion  12  proximate to the second portion  14  slopes away from the interior surface of the second portion  14 , making it unnecessary to extend the ribs  16  to the first portion  12 . If the interior surface of the first portion  12  is configured to have the same diameter (or equivalently circumference) as the interior surface of the second portion  14 , then the ribs  16  may extend to the first portion  12 . The sloped design of the interior surface of the first portion  12  preferably matches a sloped design of the exterior surface of the roller  30  at a location where the edge portion of the roller  30  having the smaller diameter meets the central portion of the roller  30  having the larger diameter. 
   When the roller  30  and regulating part  10  are formed with different materials such that the roller  30  thermally expands a greater amount and faster than the regulating part  10 , the roller  30  causes the regulating part to deform.  FIG. 6  is a diagram of the regulating part of  FIG. 4  exemplifying how it may be deformed by the expansion of a roller during the operation of the image forming apparatus. As shown in  FIG. 6 , the roller  30  contacts the ribs  16  of the regulating part, causing the shape of the regulating part to deform. In particular, relief portions  18  are formed between each of the ribs  16 . To ensure that the regulating part  10  does not crack, it is preferable that any weld lines for making the regulating part are located on the ribs  16  and not on the relief portions  18  as the relief portions  18  are likely to have greater deformation than the ribs  16 . 
   The regulating part  10  can have alternative configurations that also are capable of rotating synchronously with the rollers  30  and  40  and the fusing belt  20  while maintaining the position of the fusing belt  20 .  FIGS. 7A and 7B  are diagrams of an alternative regulating part consistent with the present invention. As shown in  FIG. 7A , the regulating part  10  includes an external portion  22 , and internal portion  24 , and a bridge portion  26  coupling the external portion  22  to the internal portion  24 . 
   The internal portion  24  is preferably made of a material that is expandable that can tolerate the thermal expansion of the roller  30 . The internal portion  24  can be made of a material such as polyphenylene sulfide or polyether ether keton. Conversely, the bridge portion  26  is preferably made of a compressible material that can similarly tolerate the thermal expansion of the roller  30 . The bridge portion  26  can be made of a material such as polyphenylene sulfide or polyether ether keton. The bridge portion  26  can be a continuous ring formed between the external portion  22  and the internal portion  24 . Alternatively, the bridge portion  26  can comprise one or more sections or pieces connecting the external portion  22  to the internal portion  24 . 
   When the heater is off, the interior surface of the internal portion  24  can be snugly in contact with the exterior surface of the roller  30  or there can be a some clearance between them. When the heater is on, the thermal expansion of the roller  30  causes the exterior surface of the edge portion of the roller  30  to contact the interior surface of the interior portion  24 , thereby causing the interior portion  24  to expand in a radial direction. When the internal portion  24  expands, the bridge portion  26  is compressed. In addition, the snug contact of the roller  30  to the internal portion of the regulating part  10  causes the regulating part  10  to rotate synchronously with the roller  30 . By using an expandable material for the internal portion  24  and a compressible material for the bridge portion  26 , the regulating part  10  can accommodate the thermal expansion of the roller  30  without cracking, and rotate synchronously with the roller  30 . 
     FIG. 8  is a diagram of another alternative regulating part consistent with the present invention. As shown in  FIG. 8 , the roller  30  includes a rib portion  32 , and the regulating part  10  similarly includes a rib portion  28 . When the roller  30  rotates during the operation of the image forming apparatus, the rib portion  32  of the roller  30  contacts the rib portion  28  of the regulating part  10 , which causes the regulating part  10  to rotate synchronously with the roller  30 . 
   Any other form of contact regions can exist between the roller and the regulating part, such as respective ribs, dots, or protrusions. The shape of the regulating part can even have areas of recess that will contact the roller. 
   The foregoing description of a preferred embodiment of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and modifications and variations are possible in light in the above teachings or may be acquired from practice of the invention. The embodiments (which can be practiced separately or in combination) were chosen and described in order to explain the principles of the invention and as practical application to enable one skilled in the art to utilize the invention in various embodiments and with various modifications are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.