Patent Publication Number: US-2003235445-A1

Title: Fixing apparatus

Description:
BACKGROUND OF THE INVENTION  
       [0001] The present invention relates to a fixing apparatus provided in an image forming apparatus.  
       [0002] In an image forming apparatus using electro-photography, a fixing apparatus, which fixes toner images formed on a recording sheet, is provided. An apparatus in which the heating roller method is adopted is used as this fixing apparatus. A fixing apparatus of this method comprises a heating roller and a pressure roller. By rotating these two rollers, a recording sheet is carried between the two rollers and toner images are fixed onto the recording sheet by being heated and pressed.  
       [0003] In a fixing apparatus of this method, part of a toner, which forms toner images, may sometimes come off from a recording sheet during fixing and adhere to the surface of the heating roller. As the toner that has adhered to the surface of the heating roller re-adheres to non-image area of the recording sheet, it debases the quality of toner images.  
       [0004] In order to solve this problem, this fixing apparatus performs the cleaning for the surface of the heating roller. That removes the toner, which has adhered to the surface of the heating roller, by wiping off the surface of the heating roller. In addition, the toner on the recording sheet is prevented from adhering to the surface of the heating roller by applying releasing agent to the surface of the roller.  
       [0005] In a conventional fixing apparatus, a belt-shaped sheet comprising a web is used as a cleaning member in order to clean the surface of the heating roller. The cleaning member has releasing agent, and this cleaning member moves as it is pressed against the surface of the heating roller. The cleaning member remove the toner from the surface of the heating roller, by coming into contact with the surface of the heating roller and being adhered the toner that has adhered to the surface of the heating roller. The cleaning member comes into contact with the surface of the heating roller and applies the releasing agent held by the cleaning member itself to the surface of the heating roller.  
       [0006] A conventional fixing apparatus as described above has the following problem. When the force for pressing the cleaning member is increased in order to raise the rate for adhering the toner to the cleaning member, the cleaning member sticks to the heating roller causing the releasing agent has congealed on the surface of the heating roller during the heating roller stops. When the heating roller starts to rotate, the movement of the cleaning member and the rotation of the heating roller are impeded. Since the cleaning member performs both the wiping the toner off and the applying the releasing agent onto the surface of the heating roller with which the cleaning member contacts, the toner hinders the releasing agent. Therefore the releasing agent cannot be satisfactorily applied to the surface of the heating roller.  
       BRIEF SUMMARY OF THE INVENTION  
       [0007] The purpose of the present invention provides a fixing apparatus in which the conventional problem is solved.  
       [0008] A fixing apparatus according to an aspect of the present invention comprises: a heating member, which is moved in a circumferential direction; a pressure member, which sandwiches and carries the recording sheet in cooperation with the heating member; a first cleaning unit, which comprises a first cleaning member that moves while being in contact with the surface of the heating member by being pressed; and a second cleaning unit, which comprises a second cleaning member that is provided side by side with reference to the first cleaning unit in the rotating direction of the heating member. The second cleaning member has a releasing agent thereon and moves while in contact with the surface of the heating member by being pressed.  
       [0009] Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. 
     
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
     [0010] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate presently preferred embodiments of the invention, and together with the general description given above and the detailed description of the preferred embodiments given below, serve to explain the principles of the invention.  
     [0011] The single FIGURE is a schematic view showing a fixing apparatus related to an embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0012] An embodiment of the present invention will be described below by referring to the drawing.  
     [0013] The FIGURE is a schematic view showing a fixing apparatus related to an embodiment of the invention. In an image forming apparatus, the fixing apparatus fixes toner images, which have been transferred from a photosensitive member to a recording sheet, on the recording sheet. The fixing apparatus is a type that fixes toner images on a recording sheet by heating and pressing.  
     [0014] The fixing apparatus comprises a heating roller  1 , which is an example of a heating member, and a pressure roller  2 , which is an example of a pressure member. The heating roller  1  is, for example, a hollow cylinder, which is horizontally disposed and rotatably supported. The pressure roller  2  is, for example, a solid cylinder, which is disposed beneath the heating roller  1  in parallel with the heating roller  1  and rotatably supported.  
     [0015] The heating roller  1  is heated by a heater  3  to a temperature necessary for fixing. As the pressure roller  2  is given a forward force by a member which is not shown, the pressure roller  2  is brought into contact with the heating roller  1  by being pressing. The heating roller  1  is rotated by a drive mechanism on the center axis of the heating roller  1  as the center of rotation in the direction of an arrow shown in the FIGURE. In other words, the heating roller  1  is an example of a heating member moved in a circumferential direction. The pressure roller  2  is rotated by the rotation of the heating roller  1  on the center axis of the pressure roller  2  as the center of rotation in the direction of an arrow shown in the FIGURE. In other words, the pressure roller  2  is moved in a circumferential direction.  
     [0016] A recording sheet  4  is conveyed in the direction of an arrow shown in the FIGURE, passing through a contact portion between the surface of the heating roller  1  and the surface of the pressure roller  2 . A toner image  5  is transferred onto the top surface of the recording sheet  4 . The toner image  5  on the recording sheet  4  is heated by the heating roller  1 , is pressed by the heating roller  1  and pressure roller  2 , and is fixed on the recording sheet  4 .  
     [0017] When the toner image  5  on the recording sheet  4  is fixed, part of the toner forming the toner image  5  detaches from the recording sheet  4  and adheres to the surface of the heating roller  1 . The toner, which has adhered to the surface of the heating roller  1 , deteriorates the quality by adhering to a non-image area of the recording sheet. The fixing apparatus according to the present invention comprises a first cleaning unit  11  and a second cleaning unit  12 , which clean the surface of the heating roller  1 , in order to cope with the phenomenon of the adherence of toner to the surface of the heating roller  1 .  
     [0018] The first cleaning unit  11  and second cleaning unit  12  are provided side by side in the rotating direction (moving direction) of the heating roller  1  surrounding the heating roller  1 . The first cleaning unit  11  is provided in a position on the upstream side of the rotating direction (moving direction) of the heating roller  1  with reference to the second cleaning unit  12 . The second cleaning unit  12  is provided on the downstream side of the rotating direction (moving direction) of the heating roller  1  with reference to the first cleaning unit  11 . A releasing agent controlling member  13  is provided in a position on the downstream side of the rotating direction (moving direction) of the heating roller  1  with reference to the second cleaning unit  12 .  
     [0019] The first cleaning unit  11  has a first cleaning member  21 . This first cleaning member  21  is a belt-shape sheet comprising a web. The first cleaning member  21  has a length of such a size that permits continuous use and a width that corresponds to the length of the heating roller  1 . The first cleaning member  21  has no releasing agent.  
     [0020] The first cleaning unit  11  has a feed roller  22 , a pressure roller  23 , a tension roller  24 , a rewind roller  25  and an auxiliary tension roller  26 .  
     [0021] The feed roller  22  is an example of a member which feeds the first cleaning member  21 . The feed roller  22  is provided parallel to the heating roller  1 . The feed roller  22  holds the first cleaning member  21  by winding the first cleaning member  21  in roll shape. The pressure roller  23  is an example of a member which brings the first cleaning member  21  into contact with the surface of the heating member  1  by pressing the first cleaning member  21  against the heating member  1 . The pressure roller  23  is provided parallel to the heating roller  1 . The pressure roller  23  can move in directions in which the pressure roller  23  approaches or comes away from the heating roller  1 . The pressure roller  23  is applied a force toward the heating roller  1  by a member which is not shown. The first cleaning member  21  is pressed with a force strong enough to wipe off the toner on the surface of the heating roller  21 .  
     [0022] The tension roller  24  supports the first cleaning member  21  which has passed by the pressure roller  23 . The tension roller  24  is provided parallel to the heating roller  1 . The rewind roller  25  is an example of a member that rolls up the first cleaning member  21 . The rewind roller  25  is provided parallel to the heating roller  1 . The auxiliary tension roller  26  supports the first cleaning member  21  between the feed roller  22  and the pressure roller  23 .  
     [0023] The rewind roller  25  is rotated by a mechanism not shown in the wind-up direction on the axis of the rewind roller  25  with the center axis thereof serving as the center of rotation in order to move the first cleaning member  21  in the direction of an arrow shown in the FIGURE. The feed roller  22 , pressure roller  23 , tension roller  24  and auxiliary tension roller  26  are rotated on the center axes thereof serving as the centers of rotation, for example, with the movement of the first cleaning member  21 .  
     [0024] The operation of the first cleaning unit  11  will be described below. The first cleaning member  21  is fed from the feed roller  22 , moves in the direction of an arrow shown in the FIGURE while being supported by the auxiliary tension roller  26 , and is brought into contact with the surface (external peripheral surface) of the heating roller  1  by being pressed by the pressure roller  23 . As shown in-the FIGURE, the first cleaning member  21  moves in the same direction as the rotating direction (moving direction) of the heating roller  1  and is brought into contact therewith. The first cleaning member  21  leaves from the surface of the heating roller  1  and moves in the direction of an arrow shown in the FIGURE while being supported by the tension roller  24 . The first cleaning member  21  is finally rolled up by the rewind roller  25  that rotates in the direction of an arrow shown in the FIGURE.  
     [0025] As the first cleaning member  21  is pressed against the surface of the heating roller  1  and moves while in contact with the surface of the heating roller  1 , the first cleaning member  21  wipes off the toner adhering to the surface of the heating roller  1  and removes the toner from the surface of the heating roller  1 . The first cleaning member  21  can easily wipe off the toner adhering to the surface of the heating roller  1  because the first cleaning member  21  moves in the same direction as the rotating direction (moving direction) of the heating roller  1  and comes into contact with the surface of the heating roller  1 . Since the first cleaning member  21  is pressed with a force strong enough to wipe off the toner adhering to the surface of the heating roller  1 , the first cleaning member  21  can sufficiently and positively remove the toner adhering to the surface of the heating roller  1 .  
     [0026] The moving speed of the first cleaning member  21  is lower than the peripheral speed of the heating roller  1 , i.e., the moving speed in a peripheral direction thereof. Owing to this difference in speed, the effect of wiping off of the toner of the heating roller  1  by the first cleaning member  21  is improved. Moreover, the speed at which the first cleaning member  21  wipes off the toner of the heating roller  1  is reduced and hence this is economical. Furthermore, the load on a motor included in the drive mechanism, which rotates the shaft of the rewind roller  25 , can be reduced because it is possible to reduce the speed at which the first cleaning member  21  is rolled up by the shaft of the rewind roller  25 .  
     [0027] The first cleaning member  21  is given tension while being supported by the auxiliary tension roller  26  in a position on the upstream side of the moving direction with reference to the position of contact between the heating roller  1  and the pressure roller  23  and supported by the tension roller  24  in a position on the downstream side. Therefore, the pressure roller  23  can positively press the first cleaning member  21  to the heating roller  1  keeping in a sufficiently tight condition.  
     [0028] The second cleaning member  12  comprises a second cleaning member  31 . This second cleaning member  31  is a belt-shape sheet comprising a web. The second cleaning member  31  has a length of such a size that permits continuous use and a width that corresponds to the length of the heating roller  1 . The second cleaning member  31  has a releasing agent to be applied to the heating roller  1 . This releasing agent is, for example, a liquid, with which the second cleaning member  31  is impregnated or which is applied to the second cleaning member  31 . For example, silicon oil is used as the releasing agent.  
     [0029] The second cleaning unit  12  has a feed roller  32 , a pressure roller  33 , the tension roller  24 , the rewind roller  25  and an auxiliary tension roller  34 .  
     [0030] The feed roller  32  is an example of a member which feeds the second cleaning member  31 , and this feed roller  32  is provided parallel to the heating roller  1 . The feed roller  32  holds the second cleaning member  21  by winding the second cleaning member  21  in roll shape. The pressure roller  33  is an example of a member that brings the second cleaning member  21  into contact with the surface of the heating member  1  by pressing. The pressure roller  33  is provided parallel to the heating roller  1 . The pressure roller  33  can move in directions in which the pressure roller  33  approaches or leaves from the heating roller  1 . The pressure roller  33  is applied a force toward the heating roller  1  by a member which is not shown. The position in which the pressure roller  33  comes into contact with the heating roller  1  is a position on the downstream side of the rotating direction (moving direction) of the heating roller  1  with reference to the position in which the pressure roller  23  comes into contact with the heating roller  1 . The force with which the pressure roller  33  presses the second cleaning member  31  against the heating roller  1  is a level at which the releasing agent of the second cleaning member  31  can be applied to the heating roller  1 . The force with which the second cleaning member  31  is pressed is smaller than the force with which the first cleaning member  21  is pressed.  
     [0031] The tension roller  24  supports the second cleaning member  31  which has passed by the pressure roller  33 . The tension roller used in the first cleaning unit  11  is shared by the second cleaning unit. The rewind roller  25  is an example of a member which rolls up the second cleaning member  31 , and the rewind roller used in the first cleaning unit  11  is shared for the second cleaning unit. The auxiliary tension roller  34  supports the second cleaning member  31  between the feed roller  32  and the pressure roller  33 .  
     [0032] As described above, the rewind roller  25  is rotated by a mechanism, which is not shown, in the rewind direction on the axis of the rewind roller  25  with the center axis thereof serving as the center of rotation. The feed roller  32 , pressure roller  33 , tension roller  24  and auxiliary tension roller  34  are rotated on the center axes thereof serving as the centers of rotation with the movement, for example, the movement of the second cleaning member  31 .  
     [0033] The operation of the second cleaning unit  12  will be described below. The second cleaning member  31  is fed from the feed roller  32 , moves in the direction of an arrow shown in the FIGURE while being supported by the auxiliary tension roller  34 , and is pressed against the surface (external peripheral surface) of the heating roller  1  by the pressure roller  33 . The second cleaning member  31  moves in the direction reverse to the rotating direction (moving direction) of the heating roller  1  and comes into contact with the heating roller  1 . The second cleaning member  31  leaves from the surface of the heating roller  1  and moves in the direction of an arrow shown in the FIGURE while being supported by the tension roller  24 . The second cleaning member  31  is finally rolled up by the rewind roller  25  which rotates in the direction of an arrow shown in the FIGURE.  
     [0034] In other words, when the second cleaning member  31  has moved to the tension roller  24 , the second cleaning member  31  moves while being supported by the tension roller  24 , layering with the first cleaning member  21  which has similarly moved to the tension roller  24 . Subsequently, the second cleaning member  31  is rolled up by the rewind roller  25  while being layered with the first cleaning member  21 .  
     [0035] As the second cleaning member  31  moves while being pressed against the surface of the heating roller  1 , the second cleaning member  31  applies the releasing agent held by the second cleaning member  31  itself to the surface of the heating roller  1 . When the heating roller  1  rotates in the direction of an arrow shown in the FIGURE, the releasing agent is continuously applied to the surface. In this place, the toner adhering to the surface of the heating roller  1  has already been removed. Therefore, it is necessary only that the second cleaning member  31  is pressed to the heating roller  1  with a force large enough to apply the releasing agent to the surface of the heating roller  1 . Thus it is unnecessary for the second cleaning member  31  to be pressed to the heating roller  1  with a large force necessary for wiping off the toner adhering to the heating roller  1 .  
     [0036] The releasing agent controlling member  13  controls the thickness of a releasing agent by coming into contact with the surface of the heating roller  1 . The releasing agent prevents the toner of the recording sheet  4  from adhering to the surface of the heating roller  1  at the contact portion between the heating roller  1  and the pressure roller  2 .  
     [0037] The first cleaning member  21  may sometimes cannot remove all toner adhering to the surface of the heating roller  1 , and may remain a small amount of toner remains. The small amount of remaining toner reaches the second cleaning member  31  due to the rotation of the heating roller  1 . Since the second cleaning member  31  moves during being pressed against the surface of the heating roller  1 , the second cleaning member  31  can remove all toner by wiping off the remaining toner. In this case, the second cleaning member  31  can wipe off the toner simply by being pressed with a force necessary for applying the releasing agent to the heating roller  1 .  
     [0038] The moving speed of the second cleaning member  31  is lower than the peripheral speed of the heating roller (the moving speed in a peripheral direction) that rotates. Owing to this difference in speed, the second cleaning member  31  can satisfactorily apply the releasing agent to the heating roller  1  and satisfactorily wipe off the toner remaining on the heating roller  1 .  
     [0039] The second cleaning member  31  is given tension by being supported by the auxiliary tension roller  34  in a position on the upstream side and supported by the tension roller  24  in a position on the downstream side in the moving direction of the second cleaning member  31  with reference to the portion of contact with the pressure roller  33 . Therefore, the pressure roller  34  can positively press the second cleaning member  31  to the heating roller  1  keeping in a sufficiently tight condition.  
     [0040] As the tension roller  24  is shared by the first cleaning unit  11  and the second cleaning unit  12 , the number of members can be reduced. The tension roller  24  has also the function of guiding the first cleaning member  21  and second cleaning member  31  to the rewind roller  25 . As the rewind roller  25  is shared by the first cleaning unit  11  and the second cleaning unit  12 , the number of members can be reduced.  
     [0041] The fixing apparatus first removes the toner adhering to the surface of the heating roller  1  by the first cleaning member  21  of the first cleaning unit  11  after the heating roller  1  rotates and the surface of the heating roller  1  passes by the portion of contact with the pressure roller  2 . The first cleaning member  21  can positively remove the toner by being pressed against the heating roller  1  with a force necessary for removing the toner without being stuck by the releasing agent.  
     [0042] Next, the second cleaning member  31  of the second cleaning unit  12  applies the releasing agent to the surface of the heating roller  1 . Therefore, the second cleaning member  31  can apply the releasing agent by being pressed against the heating roller  1  with a force necessary for applying the releasing agent without being interfered with by the toner.  
     [0043] The present invention is not limited to the above-described embodiment. For example, the heating member is not limited to a roller and can also be applied an endless belt that moves in a circumferential direction.  
     [0044] Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.