Patent Publication Number: US-2012034008-A1

Title: Separating device and image forming apparatus

Description:
CROSS REFERENCE 
     This Nonprovisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2010-174462 filed in Japan on Aug. 3, 2010, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a separating device including a separating claw for separating a recording medium winding around a roller or an endless belt, and to an image forming apparatus. 
     Conventionally, there is an image forming apparatus that transfers a toner image formed on a photoconductor drum to an intermediate transfer belt, and further transfers the toner image from the intermediate transfer belt to a paper sheet, so as to form an image on the paper sheet. Such an image forming apparatus is equipped with a separating claw disposed to be opposed to the intermediate transfer belt, so that the separating claw separates a paper sheet winding around the intermediate transfer belt when the toner image is transferred (see JP-A-2009-204768). 
     In addition, there is an image forming apparatus equipped with an intermediate transfer roller instead of the intermediate transfer belt, and a separating claw disposed to be opposed to the intermediate transfer roller (see JP-A-2006-91088). 
     In the image forming apparatus described in JP-A-2009-204768, as image forming apparatus  200  illustrated in  FIG. 1 , if a jam (paper jam) occurs in a fixing device  15 , for example, while a paper sheet P (illustrated by a dot line) is being conveyed, the paper sheet P is folded and presses a separating claw  21 , so that the tip of the separating claw  21  may be pressed to the outer circumferential surface of an intermediate transfer belt  6 . In this case, because the separating claw  21  has higher hardness than an intermediate transfer belt drive roller  62 , the intermediate transfer belt drive roller  62  may suffer damage such as a scratch or a dent. 
     This problem occurs also in the image forming apparatus described in JP-A-2006-91088 in the same manner. Specifically, when a jam occurs, the separating claw is pressed to the intermediate transfer roller, and the intermediate transfer roller is damaged. 
     An object of the present invention is to provide a separating device that does not damage the roller even if the separating claw for separating a recording medium contacts the opposed roller, and to provide an image forming apparatus equipped with the separating device. 
     SUMMARY OF THE INVENTION 
     A separating device of the present invention includes a roller and a separating claw. The roller is disposed in a convey path for conveying a recording medium. The separating claw is disposed to be opposed to the roller so as to separate a recording medium by the tip. In addition, a part of the roller to which the separating claw is opposed is made of material having higher hardness than the tip of the separating claw. 
     In the case where the separating claw is disposed to be opposed to the roller, if a jam occurs and a recording medium is folded, the recording medium presses the separating claw, so that the tip of the separating claw may be pressed to the roller. According to the structure of the present invention, a part of the outer circumferential surface of the roller, to which the separating claw is opposed, has higher hardness than the tip of the separating claw. Therefore, even if a jam occurs and the tip of the separating claw is pressed to the roller, the roller is not scratched or dented. Therefore, it is possible to prevent the roller from being damaged by the separating claw. 
     In an embodiment of the present invention, a part of the roller to which the separating claw is opposed is made of metal, while the tip of the separating claw is made of resin. 
     In this structure, when a jam occurs and the tip of the separating claw is pressed to the roller, the tip of the separating claw is deformed. Therefore, the roller is not scratched or dented. Thus, it is possible to prevent the roller from being damaged by the separating claw. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a conventional image forming apparatus, illustrating a state when a jam has occurred. 
         FIG. 2  is a schematic diagram of an image forming apparatus according to an embodiment of the present invention. 
         FIG. 3A  is a schematic diagram of a separating device according to the embodiment of the present invention, illustrating a normal state. 
         FIG. 3B  is a perspective view illustrating a positional relationship between the separating claw and the intermediate transfer belt drive roller. 
         FIG. 4A  is a front cross sectional view of the intermediate transfer belt drive roller. 
         FIG. 4B  is a front view illustrating an external appearance of the intermediate transfer belt drive roller illustrated in  FIG. 4A  and a positional relationship between the separating claw and the intermediate transfer belt. 
         FIG. 5A  is a front cross sectional view of an intermediate transfer belt drive roller of a different form from that illustrated in  FIGS. 4A and 4B . 
         FIG. 5B  is a front cross sectional view of the intermediate transfer belt drive roller illustrated in  FIG. 5A , in which a rubber layer is removed. 
         FIG. 5C  is a front view illustrating an external appearance of the intermediate transfer belt drive roller illustrated in  FIG. 5A  and a positional relationship between the separating claw and the intermediate transfer belt. 
         FIG. 6A  is a perspective view illustrating a positional relationship between the intermediate transfer belt drive roller and separating claws. 
         FIG. 6B  is a front view illustrating an external appearance of the intermediate transfer belt drive roller in the case where a plurality of separating claws are disposed and a positional relationship between the intermediate transfer belt and the separating claws. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     First, a schematic structure of an image forming apparatus  100  equipped with a separating device according to an embodiment of the present invention is described with reference to  FIG. 2 . Note that in the image forming apparatus  100 , the same components as in the image forming apparatus  200  illustrated in  FIG. 1  are denoted by the same numerals or symbols. 
     The image forming apparatus  100  is a tandem color image forming apparatus including a first image forming unit  1  for forming a yellow toner image, a second image forming unit  2  for forming a magenta toner image, a third image forming unit  3  for forming a cyan toner image, and a fourth image forming unit  4  for forming a black toner image. Hereinafter, the four image forming units of the image forming apparatus  100  are collectively referred to as an image forming unit group  5 . 
     In  FIG. 2 , an intermediate transfer belt (endless belt)  6  is disposed above the image forming unit group  5 . The intermediate transfer belt  6  runs around a support roller  61 , an intermediate transfer belt drive roller  62  (hereinafter referred to as a drive roller  62 ) like a loop in a tensioned state, and turns in the direction indicated by arrow R. The intermediate transfer belt  6  is made of polyimide material containing electron conductive material. The film thickness of the intermediate transfer belt  6  is 60 to 80 μm, for example. The polyimide material is a polymer that has highest heat resistance among organic materials and is superior in mechanical characteristic, electrical insulation, environmental stability, and chemical resistance. Therefore, the intermediate transfer belt  6  is superior in durability. 
     The image forming unit group  5  includes the first image forming unit  1 , the second image forming unit  2 , the third image forming unit  3 , and the fourth image forming unit  4 , arranged in this order along the intermediate transfer belt  6  in the direction of arrow R. 
     On the inner circumferential side of the intermediate transfer belt  6 , there are disposed primary transfer rollers  71 ,  72 ,  73 , and  74  for transferring single color toner images formed by the image forming unit group  5  to the intermediate transfer belt  6 . The primary transfer rollers  71 ,  72 ,  73 , and  74  sustain the intermediate transfer belt  6  in a tensioned state, and are respectively opposed to photoconductor drums (image carriers)  161 ,  162 ,  163  and  164  of the image forming unit group  5  via the intermediate transfer belt  6 . The single color toner images formed by the image forming unit group  5  are transferred (as primary transfer) onto the intermediate transfer belt  6  in a superposed manner, so that one color toner image is formed. The intermediate transfer belt  6  conveys the toner image after the primary transfer to the position where the drive roller  62  and a secondary transfer belt  310  described later are opposed to each other (a secondary transfer position). Hereinafter, in rotation direction R of the intermediate transfer belt  6 , a side of the support roller  61  is referred to as the upstream side, and a side of the drive roller  62  is referred to as the downstream side. 
     A secondary transfer unit  31  is disposed at the secondary transfer position that is opposed to the drive roller  62  via the intermediate transfer belt  6 . The color toner image formed on the intermediate transfer belt  6  is transferred to a paper sheet (corresponding to a recording medium) P by electrostatic force at the secondary transfer position where the drive roller  62  and the secondary transfer unit  31  are opposed to each other. At the secondary transfer position, the intermediate transfer belt  6  (the drive roller  62 ) is provided with a separating claw  21  for separating the paper sheet P when it winds around the same. A separating device  8  is constituted of the drive roller  62  and the separating claw  21 . 
     A belt cleaning unit  10  for cleaning the surface of the intermediate transfer belt  6  is disposed at the position opposed to the support roller  61  via the intermediate transfer belt  6 . The belt cleaning unit  10  includes a belt cleaning brush  11  disposed to contact with the intermediate transfer belt  6 , and a belt cleaning blade  12 , so as to remove the toner remaining on the intermediate transfer belt  6  without being transferred to the paper sheet P. 
     In  FIG. 2 , a tray  14  for housing paper sheets is disposed below the image forming unit group  5 . The paper sheet in the tray  14  is conveyed by a plurality of paper feed rollers  131  to  134 , in the paper sheet convey direction indicated by arrow Q to the secondary transfer position where the secondary transfer belt  310  is opposed to the intermediate transfer belt  6 . In this secondary transfer position, the color toner image on the intermediate transfer belt  6  is secondarily transferred to the paper sheet P. 
     The paper sheet P to which the color toner image is secondarily transferred is conveyed to a fixing unit  15 . Then, the color toner image is fixed to the paper sheet P by the fixing unit  15 , which is delivered by a delivery roller pair  135  to the outside of the image forming apparatus  100 . 
     Next, a specific structure of the separating device and periphery thereof is described.  FIG. 3A  illustrates a state where the image forming apparatus  100  normally conveys the paper sheet P (indicated by a dot line). 
     As illustrated in  FIG. 3A , the image forming apparatus  100  includes, in order from an upstream side to a downstream side in the convey path  130  opposed to one side P 1  of the paper sheet P that is conveyed in the direction of arrow Q in the convey path, a convey guide  171 , a roller  1341  of the paper feed roller pair  134 , a convey guide  173 , the drive roller  62  (the intermediate transfer belt  6 ) and the separating claw  21  of the separating device  8 , a support member  22 , a retreat convey guide  23 , a roller cover  153  of the fixing unit  15 , and a heat roller  151  of the fixing unit  15 . In addition, it includes, in order from the upstream side to the downstream side in the convey path  130  opposed to the other side P 2  of the paper sheet P, a convey guide  172 , a roller  1342  of the paper feed roller pair  134 , a convey guide  174 , a secondary transfer unit  31 , a convey guide  18 , and a pressure roller  152  of the fixing unit  15 . 
     The secondary transfer unit  31  includes the secondary transfer belt (the endless belt)  310 , a support roller  311 , a secondary transfer auxiliary roller  312 , a secondary transfer roller  313 , a secondary transfer belt drive roller  314 , and a support roller  315 . The secondary transfer belt  310  runs around the rollers  311  to  315  like a loop in a tensioned state. 
     The paper sheet P is conveyed by the paper feed roller pair  134 , by the intermediate transfer belt  6  and the secondary transfer belt  310 , and by the heat roller  151  and the pressure roller  152  of the fixing unit  15 , along the convey path  130 . 
     As illustrated in  FIG. 3A , the separating claw  21  is pivoted by a pin  220  in a swinging manner with respect to a separating claw holder  41 , and the tip thereof slightly contacts with the intermediate transfer belt  6 . The tip of the separating claw  21  is made of resin. It is preferred that the resin used for the tip of the separating claw  21  has flexibility and lower hardness than materials of a rubber layer  627  and a metal layer  637  that will be described later, like Esubea N9240 (produced by STARLITE Co., Ltd), for example. 
       FIG. 3B  illustrates an example in which one separating claw  21  is disposed at the middle portion in the rotation axis direction of the intermediate transfer belt  6 . When the toner image carried on the intermediate transfer belt  6  is transferred to the paper sheet (the recording medium) P, if the paper sheet P winds around the intermediate transfer belt  6 , the separating claw  21  separates the paper sheet P from the intermediate transfer belt  6  by the tip. 
     As illustrated in  FIGS. 4A and 4B , the drive roller  62  of the separating device  8  includes a cylindrical metal core part  621  and rubber layers  626  to  628  adhered to the outer circumferential surface of the metal core part  621 . Note that the intermediate transfer belt  6  is omitted in  FIG. 4B . 
     The metal core part  621  is constituted of a thin pipe made of an aluminum alloy (Al—Cu), the ends of which are sealed with disc lids  622  and  623  made of an aluminum alloy. At the centers of the disc lids  622  and  623 , rotation shafts  624  and  625  made of stainless steel are pressed in. The outer diameter of the metal core part  621  is 25 to 35 mm, for example. 
     The rubber layers  626  to  628  are made of EPDM blend rubber having electrical conductivity. The thickness t of the rubber layers  626  to  628  is 0.4 to 0.5 mm, for example. 
     The rubber layer  627  is adhered in a cylindrical manner to a part of the outer circumferential surface of the metal core part  621  to which the separating claw  21  is opposed. The rubber layer  627  has a width W 2  wider than a width W 1  of the separating claw  21  in the direction parallel to the center line C 1  connecting the rotation shaft  624  and the rotation shaft  625 . Thus, even if the separating claw  21  swings, the tip of the separating claw  21  can always contact with the rubber layer  627 . The rubber layer  627  is made of material having higher hardness than the tip of the separating claw  21 , that is, for example, a hardness of 60 degrees measured by JISA. 
     The rubber layer  626  is adhered to the outer circumferential surface of the metal core part  621  in a cylindrical manner from one end of the rubber layer  627  to one end of the metal core part  621 . The rubber layer  628  is adhered to the outer circumferential surface of the metal core part  621  in a cylindrical manner from the other end of the rubber layer  627  to the other end of the metal core part  621 .  FIGS. 4A and 4B  illustrate the case where the width of each of the rubber layers  626  and  628  is set to W 3 . 
     Hardness of the rubber layers  626  and  628  is not limited to a specific value. However, by using material having lower hardness than the intermediate transfer belt  6 , abrasion of the back surface of the intermediate transfer belt  6  can be reduced so that durability of the intermediate transfer belt  6  can be improved compared with the case where a high hardness material is used. However, if the hardness of the rubber layers  626  and  628  is excessively low, dimensional accuracy of the drive roller cannot be secured, and in particular, a problem such as color shift may occur when a color image is formed. Therefore, it is necessary to set the hardness of the rubber layers  626  and  628  regarding the dimensional accuracy as important. 
     In this way, in the separating device  8 , the rubber layer  627  having higher hardness than the tip of the separating claw  21  is disposed on the outer circumferential surface of the drive roller  62  to which the separating claw  21  is opposed, thereby a damage to the drive roller  62  can be prevented, even if a jam occurs and the separating claw  21  is pressed by the folded paper sheet P so that the tip of the separating claw  21  is pressed to the drive roller  62 . 
     In addition, by setting the hardness of the rubber layer  627  of the drive roller  62  to be higher than that of the separating claw  21  as described above, a damage to the intermediate transfer belt  6  can be prevented. Specifically, because the hardness of the rubber layer  627  of the drive roller  62  is higher than that of the separating claw  21 , the rubber layer  627  of the drive roller  62  and the intermediate transfer belt  6  are hardly deformed when being pressed by the separating claw  21  due to occurrence of a jam. Therefore, the intermediate transfer belt  6  is not dented so that no damage is caused to the intermediate transfer belt  6 . 
     Next, a separating device  8 ′ is described, which is equipped with an intermediate transfer belt drive roller having a different form from the separating device  8 . A part of the intermediate transfer belt drive roller to which the separating claw  21  is opposed can be made of metal. 
     As illustrated in  FIG. 5C , the separating device  8 ′ includes an intermediate transfer belt drive roller  63  (hereinafter referred to as drive roller  63 ) and the separating claw  21 . As illustrated in  FIG. 5A , the drive roller  63  includes a cylindrical metal core part  631 , a metal layer  637  disposed on the outer circumferential surface of the metal core part  631 , and rubber layers  636  and  638  adhered to the outer circumferential surface of the metal core part  631 . The rubber layers  636  and  638  are disposed adjacent to the metal layer  637 . 
     The metal core part  631  has the same structure as the metal core part  621  illustrated in  FIGS. 4A and 4B , which is constituted of a thin pipe made of an aluminum alloy (Al—Cu), and the ends thereof are sealed with disc lids  632  and  633  made of an aluminum alloy. 
     As illustrated in  FIG. 5B , the metal layer  637  is disposed in a cylindrical manner at a part of the outer circumferential surface of the metal core part  631  to which the separating claw  21  is opposed. The thickness t of the metal layer  637  is 0.4 to 0.5 mm, for example. The metal layer  637  has a width W 2  wider than a width W 1  of the separating claw  21  in the direction parallel to a center line C 2  connecting a rotation shaft  634  and a rotation shaft  635 . Thus, even if the separating claw  21  swings, the tip of the separating claw  21  can always contact with the metal layer  637 . The metal layer  637  may be formed as a separate body from the metal core part  631  like a metal sheet wound on the outer circumferential surface of the metal core part  631 , or may be formed integrally with the metal core part  631  around the outer circumference of the metal core part  631 . In addition, the type of metal material of the metal layer  637  is not limited as long as it has higher hardness than the tip of the separating claw  21 . If an aluminum alloy (2000 Al—Cu) is used for the metal layer  637 , for example, the hardness of the metal layer  637  is 95 to 105 by Brinell hardness HB. 
     The rubber layer  636  has the same structure as the rubber layer  626  illustrated in  FIGS. 4A and 4B , and is adhered to the outer circumferential surface of the metal core part  631  from one end of the metal layer  637  to one end of the metal core part  631  in a cylindrical manner. In addition, the rubber layer  638  has the same structure as the rubber layer  628  illustrated in  FIGS. 4A and 4B , is adhered to the outer circumferential surface of the metal layer  637  from the other end of the metal core part  631  to the other end of the metal core part  631  in a cylindrical manner. The rubber layers  636  and  638  are made of EPDM blend rubber having electrical conductivity.  FIG. 5C  illustrates the case where the widths of the rubber layers  636  and  638  of the separating device  8 ′ are set to W 3  each. The thickness t of the rubber layers  636  and  638  is 0.4 to 0.5 mm, for example. Note that the intermediate transfer belt  6  is omitted in  FIG. 5C . 
     In this way, in the separating device  8 ′, the metal layer  637  having high hardness than the tip of the separating claw  21  is disposed on the outer circumferential surface to which the separating claw  21  of the drive roller  63  is opposed, and the tip of the separating claw  21  is made of resin having flexibility and lower hardness than the metal material of the metal layer  637 . Thus, when a jam occurs and the tip of the separating claw  21  is pressed to the drive roller  63 , the tip of the separating claw  21  is deformed, but the drive roller  63  is not deformed. Therefore, it is possible to prevent the drive roller  63  or the intermediate transfer belt  6  from being damaged. 
     Next, a separating device  8 ″ is described, which is equipped with an intermediate transfer belt drive roller having a still different form. If the plurality of separating claws  21  are disposed to be opposed to the intermediate transfer belt  6 , it is preferred that rubber layers having higher hardness than the tip of the separating claw  21  are disposed on the outer circumferential surface of the intermediate transfer belt drive roller in the parts to which the separating claws  21  are opposed, respectively, in the same manner as illustrated in  FIGS. 4A and 4B . 
     For instance,  FIG. 6A  illustrates a case where three separating claws  211  to  213  are disposed to be opposed to the intermediate transfer belt  6  (an intermediate transfer belt drive roller  64  (hereinafter referred to as a drive roller  64 )). The separating device  8 ″ includes the drive roller  64  and the separating claws  211  to  213 . The separating claw  211  is pivoted by a pin  221  in a swinging manner with respect to a separating claw holder  411 . Similarly, the separating claw  212  is pivoted by a pin  222  in a swinging manner with respect to a separating claw holder  412 , and the separating claw  213  is pivoted by a pin  223  in a swinging manner with respect to a separating claw holder  413 . 
     In this structure, as illustrated in  FIG. 6B , rubber layers  646  to  648  having higher hardness than the tip of the separating claws  211  to  213  are adhered to the drive roller  64  in the parts to which the separating claws  211  to  213  are opposed (outer circumferential surface), respectively, in a cylindrical manner. Each of the rubber layers  646  to  648  has a width W 2  wider than a width W 1  of the separating claw  21  in the direction parallel to a center line C 3  connecting a rotation shaft  644  and a rotation shaft  645 . Thus, even if the separating claws  211  to  213  swing, the tips of the separating claws  211  to  213  can always contact with the rubber layers  646  to  648 , respectively. In addition, rubber layers  649  to  652  having any hardness are adhered to the drive roller  64  in the parts to which the separating claws  211  to  213  are not opposed (outer circumferential surface of the metal core part  641 ), in a cylindrical manner.  FIG. 6B  illustrates the case where the widths of the rubber layers  650  and  651  are set to W 5  each, and the widths of the rubber layers  649  and  652  are set to W 6  each. Note that the intermediate transfer belt  6  is omitted in  FIG. 6B . 
     Metal layers having higher hardness than the tips of the separating claws  211  to  213  may be disposed instead of the rubber layers  646  to  648  on the drive roller  64 , similarly to the case described above with reference to  FIG. 5 . 
     By constituting the separating device  8 ″ in this way, it is possible to prevent the intermediate transfer belt drive roller or the intermediate transfer belt from being damaged when a jam occurs, also in the case where a plurality of separating claws are disposed. 
     As described above, in the image forming apparatus, because the part of the outer circumferential surface of the intermediate transfer belt drive roller to which the separating claw is opposed has higher hardness than the tip of the separating claw, even if a jam occurs and the separating claw is pressed by the paper sheet so that the tip of the separating claw is pressed to the intermediate transfer belt drive roller, a damage to the intermediate transfer belt drive roller can be prevented. 
     Note that the description described above is about the structure in which the separating claw is disposed to be opposed to the intermediate transfer belt, but the present invention is not limited to this structure. The present invention can be also applied to a structure in which the separating claw is disposed to be opposed to an intermediate transfer roller. In addition, the present invention can be applied to other structures, as long as the separating claw is disposed to be opposed to a roller. For instance, the present invention can be applied to a fixing device in which the separating claw is disposed to be opposed to a pressure roller or a heat roller of the fixing device. In addition, if a conveying roller for paper is provided with a separating claw, the present invention can be applied to the conveying roller, too.