Patent Publication Number: US-2021188578-A1

Title: Rotating device and image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This patent application is based on and claims priority pursuant to 35 U.S.C. § 119(a) to Japanese Patent Application No. 2019-230260, filed on Dec. 20, 2019, in the Japan Patent Office, the entire disclosure of which is hereby incorporated by reference herein. 
     BACKGROUND 
     Technical Field 
     Embodiments of the present disclosure relate to a rotating device and an image forming apparatus including the rotating device. 
     Related Art 
     There has been known a rotating device including a shaft member, a counterpart member having a shaft insertion portion into which the shaft member is inserted, a bearing interposed between the counterpart member and the shaft member and provided in the shaft insertion portion so that the counterpart member and the shaft member is rotatable relative to each other, and a retaining member attached to an end portion on one side of the shaft member in an axial direction of the shaft member. 
     SUMMARY 
     According to an aspect of the present disclosure, there is provided a rotating device that includes a shaft member, a counterpart member, a bearing, and a retaining member. The counterpart member includes a shaft insertion portion into which the shaft member is inserted. The bearing is disposed in the shaft insertion portion and interposed between the counterpart member and the shaft member. The bearing causes the counterpart member and the shaft member to be rotatable relative to each other. The retaining member is disposed on an end portion of the shaft member on one side in an axial direction of the shaft member. The counterpart member includes an opposing portion closer to the end portion of the shaft member on the one side in the axial direction than the bearing. The opposing portion faces the retaining member in the axial direction. 
     According to another aspect of the present disclosure, there is provided an image forming apparatus that includes the rotating device and an image forming device configured to form an image on a sheet. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the disclosure and many of the attendant advantages and features thereof can be readily obtained and understood from the following detailed description with reference to the accompanying drawings, wherein: 
         FIG. 1  is a schematic diagram illustrating an image forming apparatus according to an embodiment of the present disclosure; 
         FIG. 2  is a schematic perspective view of a sheet-ejection drive device; 
         FIG. 3  is a schematic configuration diagram of the sheet-ejection drive device viewed from a direction indicated by arrow A in  FIG. 2 ; 
         FIGS. 4A and 4B  are schematic configuration diagrams of a first relay pulley according to a comparative example; 
         FIGS. 5A and 5B  are diagrams of a first relay pulley according to another comparative example; 
         FIG. 6  is a schematic configuration diagram of a first ball bearing; 
         FIG. 7  is a diagram illustrating an inner diameter dimension of an outer ring of the first ball bearing; 
         FIG. 8  is a diagram illustrating a configuration in which an E ring is in contact with an outer ring of the first ball bearing; 
         FIGS. 9A and 9B  are schematic configuration diagrams illustrating the first relay pulley, a first support shaft, and the E ring in the embodiment; 
         FIG. 10  is a perspective view illustrating the first relay pulley, the first support shaft, and the E ring of  FIGS. 9A and 9B ; 
         FIG. 11  is a perspective view illustrating assembly of the first ball bearing and a second ball bearing to the first relay pulley; 
         FIG. 12  is a cross-sectional view illustrating assembly of the first ball bearing and the second ball bearing to the first relay pulley; 
         FIG. 13  is a perspective view illustrating assembly of the first relay pulley, to which the first ball bearing and the second ball bearing are assembled, to the first support shaft; 
         FIGS. 14A and 14B  are schematic configuration diagrams of a first variation; 
         FIG. 15  is a diagram illustrating assembly of a first relay pulley according to the first variation; 
         FIG. 16  is a schematic configuration diagram of a second variation; 
         FIG. 17  is a schematic configuration diagram of a third variation; and 
         FIG. 18  is a schematic configuration diagram of a fourth variation. 
     
    
    
     The accompanying drawings are intended to depict embodiments of the present disclosure and should not be interpreted to limit the scope thereof. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted. 
     DETAILED DESCRIPTION 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. 
     In describing embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that have a similar function, operate in a similar manner, and achieve a similar result. 
     A description is given hereinafter of an image forming apparatus  1000  according to an embodiment of the present disclosure. In the following embodiment, the image forming apparatus is described as a copier. However, an image forming apparatus according to an embodiment of the present disclosure is not limited to the copier and may be any other type of image forming apparatus. First, a description is given of the outline of the image forming apparatus  1000 , with reference to  FIG. 1 . The image forming apparatus  1000  has the function as a digital color copier that digitizes image data obtained by scanning and reading an original document, and uses the image data to form an image. Further, the image forming apparatus  1000  also has the function of a facsimile machine that sends and receives image data of an original document to/from a remote place, and the function of what is called a printer that prints, on a paper sheet, image data handled by a computer. 
     In  FIG. 1 , the image forming apparatus  1000  forms an image on a recording sheet in an intermediate transfer system using an intermediate transfer belt  11 , and is a tandem-type electrophotographic apparatus that forms a toner image of each color with its dedicated process cartridge. A multistage sheet feeding device  2  is provided in the lowermost part of the image forming apparatus  1000  in the vertical direction. Moreover, an image forming device  1  is provided above the sheet feeding device  2 , and a scanner  3  is provided further above the image forming device  1 . At each stage, the sheet feeding device  2  includes a sheet feed tray  21  and a sheet feed unit  21   a . The sheet feed tray  21  contains a sheet bundle including recording sheets such as plain paper, overhead projector (OHP) film sheet, or traced drawings. The sheet feed unit  21   a  feeds a sheet of the sheet bundle contained in the sheet feed tray  21 . The sheet feed unit  21   a  includes a pickup roller  21   a   1  and a sheet separation and conveyance unit  21   a   2 . The pickup roller  21   a   1  picks up and feeds a recording sheet from the sheet feed tray  21 . The sheet separation and conveyance unit  21   a   2  separates and conveys the recording sheet fed by the pickup roller  21   a   1 . 
     A transfer device  10  is arranged substantially in the middle of the image forming device  1 . In the transfer device  10 , multiple rollers are arranged inside an endless loop of the intermediate transfer belt  11  so that the intermediate transfer belt  11  is stretched around the multiple rollers. The intermediate transfer belt  11  rotates (the surface of the intermediate transfer belt  11  moves) in a clockwise direction in  FIG. 1 . Four process cartridges  40 Y,  40 M,  40 C, and  40 K that form toner images in yellow, magenta, cyan, and black are arranged above the intermediate transfer belt  11  along a direction of movement of the surface of the intermediate transfer belt  11 . Since the configurations of the four process cartridges  40 Y,  40 M,  40 C, and  40 K, each functioning as an image forming device, are identical to each other except for the color of toner, the suffixes “Y”, “M”, “C”, and “K” indicating respective colors may be omitted below as appropriate. Moreover, two optical writing units are provided above the four process cartridges  40 Y,  40 M,  40 C, and  40 K. The two optical writing units are a first writing unit  20   a  and a second writing unit  20   b , each functioning as a latent image writing unit. 
     The process cartridges  40 Y,  40 M,  40 C, and  40 K, respectively, include drum-shaped photoconductors  41 Y,  41 M,  41 C, and  41 K that function as latent image bearers. Each of the photoconductors  41 Y,  41 M,  41 C, and  41 K, which may be collectively referred to as the photoconductors  41  unless colors distinguished, is rotatable in a counterclockwise direction in  FIG. 1 . A charging device, a developing device, a photoconductor cleaning device, and a lubricant application device are provided around the photoconductor  41 . 
     In  FIG. 1 , the transfer device  10  includes the intermediate transfer belt  11 , a belt cleaning device  17 , and four primary transfer rollers  46 . A plurality of rollers including a tension roller  14 , a drive roller  15 , and a secondary transfer counter roller  16  stretch the intermediate transfer belt  11  with tension. A belt drive motor drives the drive roller  15  to rotate to endlessly move the intermediate transfer belt  11  in the clockwise direction in  FIG. 1 . 
     The four primary transfer rollers  46  are arranged to respectively contact an inner circumferential surface side of the intermediate transfer belt  11 . A power supply applies a primary transfer bias to the primary transfer rollers  46 . Moreover, the primary transfer rollers  46  presses the intermediate transfer belt  11  from the inner circumferential surface of the intermediate transfer belt  11  toward the photoconductors  41  to form respective primary transfer nips. The primary transfer roller  46  forms a primary transfer electric field between the photoconductor  41  and the primary transfer roller  46  at each primary transfer nip by the primary transfer bias. The primary transfer roller  46  primarily transfers a toner image on the photoconductor  41  onto the intermediate transfer belt  11  under the influence of the primary transfer electric field and the nip pressure. 
     Moreover, the transfer device  10  includes a secondary transfer unit  22 . The secondary transfer unit  22  is disposed below the intermediate transfer belt  11  and serves as a secondary transfer device. The secondary transfer unit  22  includes a secondary transfer roller  22   a  that contacts and presses the secondary transfer counter roller  16  via the intermediate transfer belt  11 . The secondary transfer roller  22   a  secondarily transfers toner images on the intermediate transfer belt  11  collectively onto a recording sheet conveyed to a secondary transfer nip region between the secondary transfer roller  22   a  and the intermediate transfer belt  11 . A belt cleaning device  17  is provided downstream from the secondary transfer counter roller  16  in the direction of movement of the surface of the intermediate transfer belt  11 . The belt cleaning device  17  removes residual toner remaining on the surface of the intermediate transfer belt  11  after image transfer. The belt cleaning device  17  further includes a lubricant applying mechanism. The lubricant applying mechanism applies lubricant to the surface of the intermediate transfer belt  11 . 
     A fixing device  25  is provided downstream from the secondary transfer roller  22   a  in a direction of conveyance of the recording sheet. The fixing device  25  fixes the toner image formed on the recording sheet, to the surface of the recording sheet. An endless fixing belt  26  is pressed against a fixing pressure roller  27 . An endless conveyance belt  24  is disposed between the secondary transfer unit  22  and the fixing device  25 . The endless conveyance belt  24  is stretched between a pair of rollers. The conveyance belt  24  conveys the recording sheet, on which the image has been transferred, to the fixing device  25 . Further, below the secondary transfer roller  22   a , a reverse conveyance device  28  is provided that conveys a sheet reversed when images are formed on both sides of the sheet. 
     A bypass sheet feeding device  4  is disposed on the right side of the image forming device  1  in  FIG. 1 . Furthermore, the bypass sheet feeding device  4  includes a bypass tray  51  and a bypass sheet feeding device  150 . The bypass tray  51  loads a recording sheet to be fed by a bypass sheet feeding operation. The bypass sheet feeding device  150  feeds the recording sheet loaded on the bypass tray  51 . The bypass sheet feeding device  150  includes a bypass pickup roller  52  and a bypass separation and conveyance unit  53 . The bypass pickup roller  52  picks up and feeds a recording sheet from the bypass tray  51 . The bypass separation and conveyance unit  53  separates and conveys the sheet fed from the bypass tray  51 . 
     When a color original document is copied with the image forming apparatus  1000  including the above-described configurations, the scanner  3  reads an image of the color original document placed on an exposure glass. Moreover, the intermediate transfer belt  11  is rotated to form a toner image on each photoconductor  41  by image forming processes of the image forming apparatus  1000 . Then, the toner images formed on the photoconductors  41 Y,  41 M.  41 C, and  41 K are sequentially overlaid to be primarily transferred onto the intermediate transfer belt  11 . Accordingly, a four-color composite toner image is formed on the intermediate transfer belt  11 . 
     In parallel with the image forming operations of the four-color composite toner images being transferred onto the intermediate transfer belt  11 , the sheet feed unit  21   a  separates and feeds recording sheets one by one from a selected one of the sheet feed trays  21  of the sheet feeding device  2 , and conveys the recording sheets toward a pair of registration rollers  29 . 
     Instead of feeding recording sheets from the sheet feed tray  21 , a recording sheet may be fed and conveyed by the bypass tray  51 . In this case, the recording sheets on the bypass tray  51  are separated and fed one by one from the bypass sheet feeding device  150 , toward the pair of registration roller  29 . 
     When the separated and conveyed recording sheet is brought into contact with a nip between the pair of registration rollers  29 , the pair of registration rollers  29  temporarily stop the conveyance of the separated and conveyed recording sheet and cause the recording sheet to stand by. The pair of registration rollers  29  resumes the rotation at a proper timing in such a manner as to set the positional relationship between the four-color composite toner image overlaid on the intermediate transfer belt  11  and a leading end of the recording sheet, to a given position. The pair of registration rollers  29  is rotated to convey the standby recording sheet again. The secondary transfer roller  22   a  secondarily transfers the four-color composite toner image on the intermediate transfer belt  11 , to the given position of the recording sheet. Thus, a full color toner image is formed on the recording sheet. 
     The conveyance belt  24  conveys the recording sheet on which the full-color toner image is formed in such a way to the fixing device  25  located downstream from the secondary transfer roller  22   a  in the conveyance path. The fixing device  25  fixes the full color toner image that has been secondarily transferred by the secondary transfer roller  22   a , to the recording sheet. 
     In a face-up mode in which the recording sheet is ejected with the surface on which the image is formed facing upward, the recording sheet on which the full-color toner image is fixed is conveyed by a pair of pre-ejection rollers  31 , and is discharged to the outside of the image forming apparatus  1000  by the pair of ejection rollers  30 . On the other hand, in a face-down mode in which the recording sheet is ejected with the surface on which the image is formed facing down, the recording sheet on which the full-color toner image is fixed is conveyed to a switchback conveyance device  33 . The switchback conveyance device  33  conveys the recording sheet in a switchback manner toward the pair of switchback pre-ejection rollers  32 , and the pair of switchback pre-ejection rollers  32  conveys the recording sheet toward the pair of ejection rollers  30 . The pair of ejection rollers  30  discharges the recording sheet to the outside of the image forming apparatus  1000 . 
     In a duplex printing mode of forming images on both sides of a recording sheet, when the recording sheet having the full-color toner image fixed on the first side is ejected from the fixing device  25 , the recording sheet is conveyed to the switchback conveyance device  33  instead of being conveyed to the pair of ejection rollers  30 . The switchback conveyance device  33  performs switchback conveyance of the recording sheet, reverses the recording sheet, and conveys the recording sheet to the reverse conveyance device  28 . The reverse conveyance device  28  re-conveys the recording sheet to the pair of registration rollers  29 . Thereafter, the image forming apparatus  1000  causes the recording sheet to pass through the secondary transfer roller  22   a  and the fixing device  25  to form a full-color image also on the second side of the recording sheet. 
       FIG. 2  is a schematic perspective view of the sheet-ejection drive device  100  as a rotating device that drives the pair of ejection rollers  30 , the pair of pre-ejection rollers  31 , and the pair of switchback pre-ejection rollers  32 .  FIG. 3  is a schematic configuration diagram of the sheet-ejection drive device  100  viewed from the direction indicated by arrow A in  FIG. 2 . In  FIG. 3 , the arrangement of members is slightly different from the arrangement of members in  FIG. 2  in order to facilitate understanding of the members of the sheet-ejection drive device  100 . 
     The drive roller  130  for the pair of ejection rollers  30  includes two roller portions  130   a  and a roller shaft  130   b . The two roller portions  130   a  are fixed to the roller shaft  130   b  at a predetermined interval in the axial direction of the roller shaft  130   b . A drive roller  131  for the pair of pre-ejection rollers  31  has the same configuration as the drive roller  130  for the pair of ejection rollers  30 . In other words, the drive roller  131  includes two roller portions  131   a  and a roller shaft  131   b . A drive roller  132  for the pair of switchback pre-ejection rollers  32  also has a similar configuration and includes two roller portions  132   a  and a roller shaft  132   b . A front plate  1   b  and a rear plate  1   a  support roller shafts  130   b ,  131   b , and  132   b , respectively, of the drive rollers  130 ,  131 , and  132  via bearings  120 ,  121 , and  122 . 
     The sheet-ejection drive device  100  is disposed on the rear side of the image forming apparatus  1000 , which is one side in the axial direction, and includes a sheet ejection motor  101  as a drive source. The sheet ejection motor  101  is attached to the real plate  1   a  of the image forming apparatus  1000  via studs  101   b . The sheet-ejection drive device  100  includes a reduction gear  102  that meshes with a motor gear  101   a  of the sheet ejection motor  101 . The reduction gear  102  is fixed to a rear end portion of the roller shaft  131   b  of the drive roller  131  for the pair of switchback pre-ejection rollers  32 . 
     The sheet-ejection drive device  100  includes a first timing belt  108 . The first timing belt  108  is wound around a drive pulley  103 , an input pulley portion  105   a  of a first relay pulley  105 , and a second relay pulley  107 . The sheet-ejection drive device  100  includes a tightener roller  104 . The tightener roller  104  is in contact with the outer circumferential surface of the first timing belt  108  to apply tension to the first timing belt  108 . 
     The tightener roller  104  is rotatably supported by a tightener support shaft  104   a  fixed to the rear plate  1   a . The tightener support shaft  104   a  is supported by the tightener holder  104   b . The tightener holder  104   b  is held by the rear plate  1   a  so that the tightener roller  104  is movable in directions in which the tightener roller  104  comes into contact with and separates from the first timing belt  108 . The tightener holder  104   b  is biased toward the first timing belt  108  by a spring  104   c  as a biasing member. The spring  104   c  biases the tightener holder  104   b  toward the first timing belt  108 , so that the tightener roller  104  applies a predetermined tension to the first timing belt  108 . 
     The drive pulley  103  is fixed to a roller shaft  131   b  of the drive roller  131  for the pair of pre-ejection rollers  31 . The first relay pulley  105  is rotatably supported by a first support shaft  115  fixed to the rear plate  1   a . The first relay pulley  105  includes an input pulley portion  105   a  and an output pulley portion  105   b . The first timing belt  108  is wound around the input pulley portion  105   a . The second timing belt  116  is wound around the output pulley portion  105   b . An E ring  113  serving as a retaining member is attached to a distal end portion of the first support shaft  115 . Attaching the E ring  113  to the distal end portion of the first support shaft  115  can prevent the first relay pulley  105  from coming off the first support shaft  115 . 
     The second timing belt  116  is narrower than the first timing belt  108 . The second timing belt  116  is wound around the first relay pulley  105  and an ejection output pulley  106 . The ejection output pulley  106  is fixed to the rear end portion of the roller shaft  130   b  of the drive roller  130  for the pair of ejection rollers  30 . An E ring  114  serving as a retaining member is fixed to the rear end portion of the roller shaft  130   b  of the drive roller  130  for the sheet pair of ejection rollers  30 . The E ring  114  prevents the ejection output pulley  106  from coming off the roller shaft  130   b.    
     The second relay pulley  107  around which the first timing belt  108  is wound is rotatably supported by a second support shaft  117  fixed to the rear plate  1   a . The second relay pulley  107  is an integrally molded product of resin and a relay gear  109  that meshes with an ejection output gear  110 . An E ring  112  serving as a retaining member is attached to a distal end of the second support shaft  117 . The E ring  112  prevents the integrally molded product including the second relay pulley  107  and the relay gear  109  from coming off the second support shaft  117 . 
     The ejection output gear  110  is fixed to the rear end portion of the roller shaft  132   b  of the drive roller  132  for the pair of switchback pre-ejection rollers  32 . An E ring  111  serving as a retaining member is fixed to the rear end portion of the roller shaft  132   b  of the drive roller  132  for the pair of switchback pre-ejection rollers  32 . The E ring  111  prevents the ejection output gear  110  from coming off the roller shaft  130   b.    
     The drive force of the sheet ejection motor  101  is transmitted from the motor gear  101   a  to the reduction gear  102 , so that the drive roller  131  of the pair of pre-ejection rollers  31  is driven to rotate. The drive force of the sheet ejection motor  101  is transmitted to the first relay pulley  105  via the drive pulley  103  and the first timing belt  108  that are disposed coaxially with the reduction gear  102 . The drive force transmitted to the first relay pulley  105  is transmitted to the ejection output pulley  106  via the second timing belt  116 . Thus, the drive roller  130  for the pair of ejection rollers  30  is driven to rotate. The drive force of the sheet ejection motor  101  is transmitted to the ejection output gear  110  via the first timing belt  108 , the second relay pulley  107 , and the relay gear  109 . Thus, the drive roller  132  for the pair of switchback pre-ejection rollers  32  is driven to rotate. 
     The first timing belt  108  is applied with three load torques of the pair of ejection rollers  30 , the pair of pre-ejection rollers  31 , and the pair of switchback pre-ejection rollers  32 . On the other hand, only the load torque of the pair of ejection rollers  30  is applied to the second timing belt  116 . As described above, since the first timing belt  108  is applied with a larger load torque than the second timing belt  116 , the belt width of the first timing belt  108  is set to be larger than the belt width of the second timing belt  116 . In addition, setting the belt width of the second timing belt  116  narrower than the belt width of the first timing belt  108  can restrain an increase in the total axial length of the sheet-ejection drive device  100 . 
       FIGS. 4A and 4B  are schematic configuration diagrams of a first relay pulley  105 A according to a comparative example. As illustrated in  FIGS. 4A and 4B , the first relay pulley  105 A includes a first deviation preventing projection  105   c  between an input pulley portion  105   a  and an output pulley portion  105   b . The first deviation preventing projection  105   c  stops the deviation of the first timing belt  108 . Further, the first relay pulley  105 A includes a second deviation preventing projection  105   d  at a rear end portion that is at one side in the axial direction. The second deviation preventing projection  105   d  stops deviation of the second timing belt  116 . The first timing belt  108  having a belt width wider than a belt width of the second timing belt  116  is wound around the input pulley portion  105   a . Therefore, the input pulley portion  105   a  is set to be longer than the output pulley portion  105   b  in the axial direction. 
     The first relay pulley  105 A includes the input pulley portion  105   a  and the output pulley portion  105   b  having different axial lengths from each other. The first relay pulley  105 A further includes the first deviation preventing projection  105   c  between the input pulley portion  105   a  and the output pulley portion  105   b . Accordingly, when the first relay pulley  105 A is assembled to the first support shaft  115  by reverse attachment, the first timing belt  108  and the second timing belt  116  cannot be wound around the first relay pulley  105 A. Note that the reverse attachment is an attachment which the first relay pulley  105 A is assembled in reverse to a normal attachment in which the output pulley portion  105   b  is positioned on the front side. 
     Therefore, in the comparative example, the reverse attachment of the first relay pulley  105 A is prevented by a configuration as illustrated in  FIG. 4B . For example, a first support shaft  115  is provided with a first small-diameter portion  115   a  and a second small-diameter portion  115   b . A first inner peripheral surface  105   h  and a second inner peripheral surface  105   i  are provided on a shaft insertion portion  105   g  of the first relay pulley  105 A. The first inner peripheral surface  105   h  is in contact with the outer peripheral surface of the first small-diameter portion  115   a . The second inner peripheral surface  105   i  is in contact with the outer peripheral surface of the second small-diameter portion  115   b . With such a configuration, when the first relay pulley  105 A is inserted in reverse to the first support shaft  115 , a downstream end portion of the second inner peripheral surface  105   i  in the insertion direction abuts against a downstream end portion of the first small-diameter portion  115   a  in the insertion direction. Thus, the first relay pulley  105 A cannot be assembled to the first support shaft  115 , and reverse attachment can be prevented. 
     In the first relay pulley  105 A of the comparative example illustrated in  FIG. 4 , when the drive force of the sheet ejection motor  101  is transmitted to the first relay pulley  105 A and the first relay pulley  105 A is driven to rotate, the first inner peripheral surface  105   h  and the second inner peripheral surface  105   i  slide on the first support shaft  115 . The first relay pulley  105 A is made of resin, and wear may occur depending on usage conditions. Therefore, the amount of wear of the first inner peripheral surface  105   h  and the second inner peripheral surface  105   i  due to sliding with the first support shaft  115  increases, depending on usage conditions such as a load applied to the first relay pulley  105 A. Accordingly, the product life of the first relay pulley  105 A might come to an end early. Further, a load due to sliding resistance between the first support shaft  115  and the first relay pulley  105 A is applied to the first timing belt  108  and the like. Accordingly, the product life of a drive transmission member such as the first timing belt  108  of the sheet-ejection drive device  100  may be shortened. 
       FIGS. 5A and 5B  are illustrations of another comparative example in which the first relay pulley  105 A of the comparative example illustrated in  FIGS. 4A and 4B  is modified. In order to improve a disadvantage of the configuration illustrated in  FIGS. 4A and 4B , another comparative example illustrated in  FIGS. 5A and 5B  has the following configuration. For example, a first ball bearing  141  as a bearing is press-fitted into a rear end portion (left side in  FIG. 5B ) of a shaft insertion portion  105   g  of a first relay pulley  105 B, and a second ball bearing  142  as a bearing is press-fitted into a front end portion (right side in  FIG. 5B ) of the shaft insertion portion  105   g  of the first relay pulley  105 B. The first ball bearing  141  is smaller in size than the second ball bearing  142  and has an inner diameter smaller than the inner diameter of the second ball bearing  142 . As described above, the inner diameter of the first ball bearing  141  is set to be smaller than the inner diameter of the second ball bearing  142 . With such a configuration, when the first relay pulley  105 B is attempted to be assembled in reverse to the first support shaft  115 , the first ball bearing  141  abuts against an end portion of a first small-diameter portion  115   a . Thus, the first relay pulley  105 B cannot be assembled to a first support shaft  115 , and reverse attachment of the first relay pulley  105 B can be prevented even in the comparative example of  FIGS. 5A and 5B . 
     In the comparative example of  FIGS. 5A and 5B , the first support shaft  115  as a shaft member rotatably supports the first relay pulley  105 B as a counterpart member via ball bearings  141  and  142 . Thus, the first relay pulley  105 B is driven to rotate without sliding on the first support shaft  115 . Accordingly, wear of the first relay pulley  105 B is restrained, thus enhancing the durability of the first relay pulley  105 B. Further, no sliding resistance is generated between the first relay pulley  105 B and the first support shaft  115 . Accordingly, as compared with the comparative example illustrated in  FIGS. 4A and 4B , the load applied to the drive transmission member such as the first timing belt  108  of the sheet-ejection drive device  100  can be reduced. 
       FIG. 6  is a schematic configuration diagram of the first ball bearing  141 . As illustrated in  FIG. 6 , the first ball bearing  141  includes an inner ring  141   a  made of metal, an outer ring  141   b  made of metal, and a ball  141   c  as a rolling element disposed between the inner ring  141   a  and the outer ring  141   b . The second ball bearing  142  has the same configuration as the first ball bearing  141 . 
     The outer ring  141   b  of the first ball bearing  141  rotates together with the first relay pulley  105 B. On the other hand, the inner ring  141   a  is in a stationary state together with the first support shaft  115  since the static friction force with the first support shaft  115  is greater than the friction force with the ball  141   c.    
     The E ring  113  as a retaining member attached to a distal end portion of the first support shaft  115  is preferably made of metal and is preferably in contact with only the inner ring  141   a  of the first ball bearing  141 . Accordingly, as illustrated in  FIG. 7 , the outer diameter of the E ring  113  is preferably smaller than the inner diameter L of the outer ring  141   b . The outer ring  141   b  rotates together with the first relay pulley  105 , and the E ring  113  attached to the first support shaft  115  does not rotate. Accordingly, as illustrated in  FIG. 8 , when the E ring  113  is configured to contact the outer ring  141   b , the E ring  113  slides on the outer ring  141   b . Since the E ring  113  and the outer ring  141   b  are made of metals, the sliding of the E ring  113  on the outer ring  141   b  causes sliding between metals, which may cause abnormal noise. In addition, when metals having no slidability are used, seizure might occur and cause the metals to stick each other depending on usage conditions. 
     As described above, the first ball bearing  141  is a ball bearing having a smaller size than the second ball bearing  142  in order to prevent the first relay pulley  105 B from being reversely attached. In order to prevent contact with the outer ring  141   b  of the first ball bearing  141  having a small size, the E ring  113  needs to have a size smaller than a general size. 
     As illustrated in  FIG. 3 , in the sheet-ejection drive device  100 , not only the E ring  113  is attached to the first support shaft  115  but also the E ring  112  is attached to the second support shaft  117 . In addition, the E ring  114  is attached to the roller shaft  130   b  of the drive roller  130  for the sheet pair of ejection rollers  30 , and the E ring  111  is attached to the roller shaft  132   b  of the drive roller  132  for the pair of switchback pre-ejection rollers  32 . 
     The E ring  111  attached to the roller shaft  132   b  of the drive roller  132  rotates together with the ejection output gear  110 . Accordingly, even in a configuration in which the E ring  111  contacts the ejection output gear  110 , the E ring  111  does not slide on the ejection output gear  110 . Thus, the E ring  111  attached to the roller shaft  132   b  of the drive roller  132  for the pair of switchback pre-ejection rollers  32  is not particularly limited, and an inexpensive E ring of a general size can be used. 
     Similarly, the E ring  114  attached to the roller shaft  130   b  of the drive roller  130  for the pair of ejection rollers  30  rotates together with the ejection output pulley  106  and does not slide on the ejection output pulley  106 . Accordingly, an E ring of a general size can be also used as the E ring  114  attached to the roller shaft  130   b  of the drive roller  130  for the sheet pair of ejection rollers  30 . 
     The E ring  112  fixed to the second support shaft  117 , which is fixed to the rear plate  1   a , slides on the relay gear  109  facing the E ring  112  in the axial direction. However, the relay gear  109  is made of a resin having slidability such as polyoxymethylene (POM). Such a configuration can prevent occurrence of abnormal noise even if the E ring  112  slides on the relay gear  109 . Thus, the E ring  112  attached to the second support shaft  117  is not particularly limited. 
     As described above, in the comparative example of  FIGS. 5A and 5B , inexpensive E rings of a general size can be used as the three E rings  111 ,  112 , and  114  among the four E rings  111 ,  112 ,  113 , and  114  used in the sheet-ejection drive device  100 . However, the E ring  113  fixed to the first support shaft  115  needs to be smaller than the other E rings  111 ,  112 , and  114 . As a result, it is necessary to manage two types of E rings of the E ring  113  fixed to the first support shaft  115  and the other E rings  111 ,  112 , and  114 . Such a configuration may lead to an increase in component management cost. 
     Further, in the comparative example of  FIGS. 5A and 5B , erroneous assembly of the E rings such as fixing of another E ring  111 ,  112 , or  114  to the first support shaft  115  might occur. In addition, it is necessary to check the size of an E ring and attach the E ring to the shaft so that erroneous assembly does not occur. As a result, assembly efficiency might be deteriorated. 
     In the comparative example of  FIGS. 5A and 5B , it is also conceivable to set the other E rings  111 ,  112 , and  114  to a small size, similarly to the E ring  113  fixed to the first support shaft  115 . However, when the size is small, assemblability to the shaft might be deteriorated, which might deteriorate assembly efficiency. 
     The sheet-ejection drive device  100  according to the present embodiment is an improvement of the other comparative example of  FIGS. 5A and 5B  described above. For example, even when an E ring having the same general size as the other E rings  111 ,  112 , and  114  is used as the E ring  113  fixed to the first support shaft  115 , the E ring  113  does not come into contact with the outer ring of the first ball bearing  141 . Hereinafter, the sheet-ejection drive device  100  according to the present embodiment is described in detail. 
       FIGS. 9A and 9B  are schematic configuration diagrams illustrating the first relay pulley  105 , the first support shaft  115 , and the E ring  113  in the present embodiment. FIG.  10  is a perspective view illustrating the first relay pulley  105 , the first support shaft  115 , and the E ring  113  according to the present embodiment. In the following description, characteristic portions are mainly described, and redundant descriptions of the configuration similar to the configurations illustrated in  FIGS. 4A and 4B and 5A and 5B  are appropriately omitted. 
     The first relay pulley  105  of the present embodiment has an opposing portion  105   e  that extends further toward the rear side, which is one side in the axial direction, than the first ball bearing  141 . The opposing portion  105   e  opposes the E ring  113  in the axial direction. In this way, the opposing portion  105   e  is provided in the first relay pulley  105 , and the E ring  113  comes into contact with the opposing portion  105   e  and does not come into contact with the first ball bearing  141 . The first relay pulley  105  is made of a resin having slidability such as POM. Thus, sliding of the E ring  113  with respect to the opposing portion  105   e  is sliding between metal and resin. Accordingly, unlike sliding between metals, generation of noise can be restrained. 
     Further, there is no restriction that the outer diameter of the E ring  113  is equal to or smaller than the inner diameter of the outer ring of the first ball bearing  141 . Thus, in the sheet-ejection drive device  100 , the E ring  113  fixed to the first support shaft  115  can be an inexpensive E ring of a general size having the same shape as the other E rings  111 ,  112 , and  114 . Such a configuration can prevent the occurrence of erroneous assembly that is a disadvantage in the comparative examples. Further, the component management cost can be reduced. Further, assembly efficiency can be improved. 
     As illustrated in  FIG. 9B , the first relay pulley  105  of the present embodiment has guide ribs  105   j , a first positioning portion  105   k , and a second positioning portion  105   f . As described later, the guide ribs  105   j  guide the first ball bearing  141 . The guide ribs  105   j  are provided on the inner peripheral surface of the shaft insertion portion  105   g  of the first relay pulley  105 . The first positioning portion  105   k  is to position the first ball bearing  141 . The second positioning portion  105   f  is to position the second ball bearing  142 . The second positioning portion  105   f  is a distal end surface orthogonal to the axial direction of the guide rib  105   j.    
     A rear end portion (left end in  FIG. 9B ) of the outer ring of the second ball bearing  142  abuts against the second positioning portion  105   f . Thus, the second ball bearing  142  is positioned in the front side of the first relay pulley  105 . A front end portion (right end in  FIG. 9B ) of the inner ring of the second ball bearing  142  abuts against a second step surface  115   d  of the first support shaft  115 . The second step surface  115   d  is a surface orthogonal to the axial direction, which is a step between the outer peripheral surface of the shaft and the second small-diameter portion  115   b . Thus, the second ball bearing  142  is sandwiched between the second step surface  115   d  of the first support shaft  115  and the second positioning portion  105   f  of the first relay pulley  105  in the axial direction. 
     A rear end portion (left end in  FIG. 9B ) of the outer ring of the first ball bearing  141  abuts against the first positioning portion  105   k  of the first relay pulley  105 . Thus, the first ball bearing  141  is positioned at the rear side of the first relay pulley  105 . A front end portion (right end in  FIG. 9B ) of the inner ring of the first ball bearing  141  abuts against the first step surface  115   c  of the first support shaft  115 . The first step surface  115   c  is a surface orthogonal to the axial direction, which is a step between the second small-diameter portion  115   b  and the first small-diameter portion  115   a . Thus, the first ball bearing  141  is sandwiched between the first step surface  115   c  of the first support shaft  115  and the first positioning portion  105   k  of the first relay pulley  105  in the axial direction. 
     The first relay pulley  105  is made of resin and thus has a large coefficient of thermal expansion. Accordingly, the first relay pulley  105  greatly varies in the radial direction when the temperature rises. The first ball bearing  141  and the second ball bearing  142  are press-fitted into the first relay pulley  105 . However, since the radial variation of the first relay pulley  105  is large when the temperature rises, the press-fitting force between the first relay pulley  105  and each of the first ball bearing  141  and the second ball bearing  142  may decrease due to thermal expansion of the first relay pulley  105 . When the press-fitting force between the first relay pulley  105  and each of the first ball bearing  141  and the second ball bearing  142  decreases, the first ball bearing  141  and the second ball bearing  142  become relatively movable in the axial direction relative to the first support shaft  115  and the first relay pulley  105 . In the present embodiment, as described above, each of the first ball bearing  141  and the second ball bearing  142  is assembled so as to be sandwiched between the first support shaft  115  and the first relay pulley  105  in the axial direction. Accordingly, even if the press-fitting force between the first relay pulley  105  and each of the first ball bearing  141  and the second ball bearing  142  decreases, the step surfaces  115   c  and  115   d  of the first support shaft  155  restrict the movement of each of the first ball bearing  141  and the second ball bearing  142  toward the fixed end portion of the first support shaft  115  with respect to the first relay pulley  105 . Thus, each of the first ball bearing  141  and the second ball bearing  142  can be prevented from coming off the press-fitting portion of the first relay pulley  105 . Further, each of the first ball bearing  141  and the second ball bearing  142  restricts the movement of the first relay pulley  105  toward the fixed end portion of the first support shaft  155 , so that the first relay pulley  105  can be positioned at a predetermined position. 
     As illustrated in  FIG. 9B , the inner diameter d of the opposing portion  105   e  of the first relay pulley  105  of the present embodiment is smaller than the outer diameter of the first ball bearing  141 . Accordingly, the first ball bearing  141  cannot be inserted from the rear side (left side in  FIG. 9B ) of the first relay pulley  105 . Therefore, the first ball bearing  141  is inserted from the front side (right side in  FIG. 9B ) of the first relay pulley  105 . 
       FIG. 11  is a perspective view illustrating assembly of the first ball bearing  141  and the second ball bearing  142  to the first relay pulley  105 .  FIG. 12  is a cross-sectional view illustrating assembly of the first ball bearing  141  and the second ball bearing  142  to the first relay pulley  105 . 
     As illustrated in  FIGS. 11 and 12 , a plurality of guide ribs  105   j  are provided on the inner peripheral surface of the shaft insertion portion  105   g  at predetermined intervals in the circumferential direction of the first relay pulley  105 . The diameters of inscribed circles connecting the top portions of the guide ribs  105   j  are substantially the same as the outer diameter of the first ball bearing  141 . The first ball bearing  141  is inserted into the shaft insertion portion  105   g  from the front side of the first relay pulley  105  so that the outer peripheral surface of the first ball bearing  141  contacts the top portions of the respective guide ribs  105   j.    
     While the first ball bearing  141  inserted into the shaft insertion portion  105   g  is guided by the plurality of guide ribs  105   j , the first ball bearing  141  is moved to the rear side until the outer ring abuts against the first positioning portions  105   k . Accordingly, the first ball bearing  141  is press-fitted into a first press-fitting portion  105   m  of the first relay pulley  105 , which is one step shorter than the inner peripheral surface of the shaft insertion portion  105   g . Thus, the first ball bearing  141  is assembled to the first relay pulley  105 . In this way, the first ball bearing  141  is assembled while being guided by the plurality of guide ribs  105   j . Thus, the first ball bearing  141  can be easily assembled to the first relay pulley  105  without causing a failure such as tilting of the first ball bearing  141  relative to the axial direction during assembly. 
     When the assembly of the first ball bearing  141  is completed, the second ball bearing  142  is press-fitted into the shaft insertion portion  105   g  from the front side of the first relay pulley  105  and abuts against the second positioning portion  105   f  at the distal end of the guide rib  105   j . Thus, the second ball bearing  142  is assembled to the first relay pulley  105 . 
       FIG. 13  is a perspective view illustrating assembly of the first relay pulley  105 , to which the first ball bearing  141  and the second ball bearing  142  have been assembled, to the first support shaft  115 . The first relay pulley  105  is moved in a direction indicated by arrow A in  FIG. 13 , and the distal end of the first support shaft  115  fixed to the rear plate  1   a  by caulking or the like is inserted into the shaft insertion portion  105   g  from the front side of the first relay pulley  105 . Then, the distal end of the first support shaft  115  passes through the first relay pulley  105 . The inner ring of the first ball bearing  141  abuts against the first step surface  115   c  of the first support shaft  115 . The inner ring of the second ball bearing  142  abuts against the second step surface  115   d  of the first support shaft  115 . Thus, the first relay pulley  105  is assembled to the first support shaft  115 . After the first relay pulley  105  is assembled, the E ring  113  is fitted into a groove portion  115   e  of the first support shaft  115 . 
     As described above, when the first relay pulley  105  is assembled to the first support shaft  115 , the inner ring of the first ball bearing  141  abuts against the first step surface  115   c  of the first support shaft  115 , and the first ball bearing  141  is pushed rearward by the first step surface  115   c . Accordingly, even when the outer ring of the first ball bearing  141  is not in contact with the first positioning portion  105   k  and is not correctly assembled, the outer ring of the first ball bearing  141  can be pushed by the first step surface  115   c  and brought into contact with the first positioning portion  105   k . Thus, the first ball bearing  141  can be correctly assembled to the first relay pulley  105 . 
     Similarly, even when the outer ring of the second ball bearing  142  is not in contact with the second positioning portion  105   f  and is not correctly assembled, the outer ring of the second ball bearing  142  can be pushed by the second step surface  115   d  and brought into contact with the second positioning portion  105   f . Thus, the second ball bearing  142  can be correctly assembled to the first relay pulley  105 . 
     In addition, the first relay pulley  105  of the present embodiment has the opposing portion  105   e  on the rear side. The opening on the rear side is clearly smaller than the opening on the front side. Thus, the front side and the rear side of the first relay pulley  105  can be easily visually determined, and the reverse attachment of the first relay pulley  105  is restrained. If the first relay pulley  105  is reversely attached to the first support shaft  115 , the inner ring of the first ball bearing  141  abuts against the first step surface  115   c  of the first support shaft  115 . Accordingly, the first relay pulley  105  cannot be inserted into the first support shaft  115  until the distal end of the first support shaft  115  passes through the first relay pulley  105 . Thus, the first relay pulley  105  can be prevented from being reversely attached. 
     First Variation 
       FIGS. 14A and 14B  are schematic configuration diagrams of a first variation of the first relay pulley  105 .  FIG. 15  is a diagram illustrating assembly of the first relay pulley  105  according to the first variation. In the first variation, a stepped screw  113 A is used as a retaining member for the first relay pulley  105 . In the first variation, a screw hole  115   f  in which a screw groove is formed on an inner peripheral surface is provided at a distal end of the first support shaft  115 . As illustrated in  FIG. 15 , similarly to the above-described embodiment, the first relay pulley  105  into which the first ball bearing  141  and the second ball bearing  142  are press-fitted is moved in the direction indicated by arrow A in  FIG. 15 . Thus, the first relay pulley  105  is assembled to the first support shaft  115 . Next, the stepped screw  113 A is fastened to the screw hole  115   f  of the first support shaft  115 . Thus, as illustrated in  FIGS. 14A and 14B , the head of the stepped screw  113 A faces the opposing portion  105   e  of the first relay pulley  105 . Accordingly, the stepped screw  113 A can stop the first relay pulley  105  from coming off the first support shaft  115 . 
     Since the stepped screw  113 A is made of metal, abnormal noise may be generated when the head of the stepped screw  113 A slides on the outer ring of the first ball bearing  141 . However, also in the first variation, since the first relay pulley  105  is provided with the opposing portion  105   e , the head of the stepped screw  113 A slides on the opposing portion  105   e  made of a resin material having slidability. Such a configuration can restrain the generation of abnormal noise. 
     Second Variation 
       FIG. 16  is a schematic configuration diagram of a second variation. The second variation is an example in which a two-stage gear  205  is employed in the above-described embodiment. The two-stage gear  205  as a counterpart member is made of a resin material having slidability such as POM and includes a large-diameter gear portion  205   a  and a small-diameter gear portion  205   b . Other configurations are similar to the configurations of the above-described embodiment. Specifically, the first ball bearing  141  and the E ring  113  are configured not to come into contact with each other, and the two-stage gear  205  is configured to be prevented from being reversely attached. 
     The reverse attachment of the two-stage gear  205  is prevented by the following configuration. For example, the first ball bearing  141  is press-fitted to one side (left side in  FIG. 16 ) in the axial direction of the shaft insertion portion  205   g  of the through-hole shape of the two-stage gear  205 . The second ball bearing  142  having a larger size than the first ball bearing  141  is press-fitted to the other side (right side in  FIG. 16 ). A support shaft  215  that supports the two-stage gear  205  via the first ball bearing  141  and the second ball bearing  142  includes a first small-diameter portion  215   a  and a second small-diameter portion  215   b  that is larger than the first small-diameter portion  215   a  from the distal end side of the support shaft  215 . 
     The configuration in which the first ball bearing  141  and the E ring  113  are not in contact with each other is a configuration in which the two-stage gear  205  extends further toward the one side in the axial direction beyond the first ball bearing  141  and includes the opposing portion  205   e  facing the E ring  113  in the axial direction. With such a configuration, also in the second variation, abnormal noise can be prevented from being generated when the two-stage gear  205  is driven to rotate. 
     Third Variation 
       FIG. 17  is a schematic configuration diagram of a third variation. The third variation is an example of a configuration in which the shaft member rotates and the counterpart member does not rotate. In the third variation, a bearing case  210  made of a resin material as the counterpart member is attached to the side plate  1   b  of the image forming apparatus  1000 . A ball bearing  120  is disposed between the bearing case  210  and the roller shaft  130   b  of the drive roller to rotatably support the roller shaft  130   b . An E ring  211  is fixed to one end of the roller shaft  130   b  as a retaining member to prevent the roller shaft  130   b  from coming off from the side plate  1   b . The bearing case  210  includes an opposing portion  210   e  that extends further toward one side in the axial direction beyond the ball bearing  120  and that opposes the E ring  113  in the axial direction. 
     In the third variation, the E ring  211  rotates together with the roller shaft  130   b . However, the outer ring of the ball bearing  120  is in a stationary state since the static friction force with the bearing case  210  is larger than the friction force with the balls. Accordingly, when the E ring  211  comes into contact with the outer ring of the ball bearing  120 , the E ring  211  slides on the outer ring. As a result, abnormal noise might be generated due to sliding between metals. However, in the third variation as well, providing the opposing portion  210   e  in the bearing case  210  made of resin, the E ring  211  slides on the opposing portion  210   e  made of resin. Thus, sliding between the resin and the metal occurs, and generation of noise can be restrained. 
     Fourth Variation 
       FIG. 18  is a schematic configuration diagram of a fourth variation. The fourth variation differs from the third variation illustrated in  FIG. 17  in the configuration of attachment of the ball bearing  120  and the bearing case  210  to the side plate  1   b . In the third variation, as illustrated in  FIG. 17 , the bearing case  210  made of resin is attached to the side plate  1   b  of the image forming apparatus  1000 . The ball bearing  120  is disposed between the bearing case  210  and the roller shaft  130   b  of the drive roller. The bearing case  210  rotatably supports the roller shaft  130   b . However, in the configuration in which the outer ring of the ball bearing  120  made of metal is directly supported by the bearing case  210  made of resin, it is difficult to obtain positional accuracy of the roller shaft  130   b . Accordingly, it is difficult to adopt the configuration of the third variation in a cane in which the rotation accuracy of the roller portion  130   a  is required. 
     Hence, in the fourth variation, as illustrated in  FIG. 18 , the outer ring of the ball bearing  120  is directly supported by the side plate  1   b  made of metal. The bearing case  210  made of resin is fixed to the side plate  1   b  by fastening members  212  such as screws. Such a configuration enhances the positional accuracy of the ball bearing  120 . Accordingly, the positional accuracy of the roller shaft  130   b  can be enhanced, and the rotational accuracy of the roller portion  130   a  can be enhanced. Thus, in a case in which the rotation accuracy of the roller portion  130   a  is required, adopting the configuration of the fourth variation can satisfy the requirement of the rotation accuracy of the roller portion  130   a  and restrain the generation of abnormal noise. 
     In the third variation and the fourth variation, the bearing case  210  made of resin is provided, and the opposing portion  210   e  facing the E ring  211  is provided in the bearing case  210 . However, in the case in which the side plate  1   b  is made of resin, the ball bearing  120  may be press-fitted into the side plate  1   b , and the opposing portion facing the E ring  211  may be provided in the side plate  1   b . In such a case, the bearing case  210  can be obviated. 
     The embodiments and variations described above are some examples and, for example, attain advantages described below in a plurality of aspects A to P. 
     Aspect 1 
     A rotating device, such as the sheet-ejection drive device  100 , includes a shaft member, such as the first support shaft  115 ; a counterpart member, such as the first relay pulley  105 , including a shaft insertion portion, such as the shaft insertion portion  105   g , into which the shaft member is inserted; a bearing, such as the first ball bearing  141  and the second ball bearing  142 , provided in the shaft insertion portion and interposed between the counterpart member and the shaft member to cause the counterpart member and the shaft member to be rotatable relative to each other; and a retaining member, such as the E ring  113 , fixed to an end portion of the shaft member on one side in an axial direction of the shaft member. The counterpart member includes an opposing portion, such as the opposing portion  105   e , disposed closer to the end portion of the shaft member on the one side in the axial direction than the bearing. The opposing portion faces the retaining member in the axial direction. 
     In a comparative example, an E ring serving as a retaining member is in contact with an end portion of a ball bearing, serving as a bearing, on one side in an axial direction of the ball bearing. The ball bearing includes an inner ring, an outer ring, and balls as rolling elements disposed between the inner ring and the outer ring. Typically, the outer ring and the inner ring are made of metal. The E ring is also typically made of metal. Accordingly, in the configuration in which the E ring is in contact with the end portion of the bearing on the one side in the axial direction of the bearing, the metals contact each other. The E ring rotates together with a paddle shaft relative to a bearing case. If the E ring is in contact with the outer ring of the ball bearing, the metals slide on each other, which might cause abnormal noise. 
     On the other hand, in Aspect 1, the opposing portion provided on the counterpart member facing the retaining member in the axial direction is positioned closer to the end portion of the shaft member on the one side in the axial direction of the shaft member than the bearing. Such a configuration allows the retaining member to be in contact with the opposing portion while preventing the retaining member from being in contact with the bearing. Such a configuration can prevent generation of abnormal noise due to sliding of the retaining member on the bearing. 
     Aspect 2 
     In Aspect 1, the shaft member, such as the first support shaft  115 , is received by a plurality of bearings, such as the plurality of ball bearings  141  and  142 , having different outer diameters. One bearing disposed on the one side in the axial direction has the smallest outer diameter among the plurality of bearings. According to such a configuration, as described in the above-described embodiment, the bearing disposed on the one side in the axial direction has the shortest outer diameter among the plurality of bearings. Accordingly, the inner diameter of the outer ring of the bearing is shorter than the outer diameter of the retaining member such as the E ring. In such a configuration, providing the opposing portion such as the opposing portion  105   e  in the counterpart member can prevent the retaining member from sliding on the outer ring of the bearing, without using a small-sized retaining member such as an E ring. 
     Aspect 3 
     In Aspect 2, the inner diameter of the opposing portion, such as the opposing portion  105   e , is smaller than the outer diameter of the bearing, such as the first ball bearing  141 , disposed on the one side in the axial direction. The inner peripheral surface of the shaft insertion portion, such as the shaft insertion portion  105   g , has a guide rib, such as the guide rib  105   j , to guide the bearing disposed on the one side in the axial direction. According to such a configuration, as described in the above-described embodiment, the inner diameter of the opposing portion, such as the opposing portion  105   e , is smaller than the outer diameter of the bearing, such as the first ball bearing  141 , disposed on the one side in the axial direction. Accordingly, the bearing disposed on the one side in the axial direction is inserted from the other side of the shaft insertion portion in the axial direction and positioned on the one side of the shaft insertion portion in the axial direction. In Aspect 3, the guide rib, such as the guide rib  105   j , is provided on the inner peripheral surface of the shaft insertion portion, such as the shaft insertion portion the  105   g . Such a configuration can easily move the bearing, which is to be disposed on the one side of the shaft insertion portion in the axial direction inserted from the other side of the shaft insertion portion in the axial direction, to the one side in the axial direction. Thus, the workability of assembling the bearing can be enhanced. 
     Aspect 4 
     In any one of Aspects 1 to 3, the end portion of the shaft member, such as the first support shaft  115 , on the one side in the axial direction is a small-diameter portion, such as the first small-diameter portion  115   a , having a smaller diameter than another portion of the shaft member. The bearings, such as the first ball bearing  141  and the second ball bearing  142 , having different inner diameters are press-fitted into one side and the other side of the shaft insertion portion, such as the shaft insertion portion  105   g , in the axial direction. The bearings are disposed in the small-diameter portion and a portion having a larger diameter than the small-diameter portion of the shaft member. As described in the above-described embodiment, such a configuration can prevent the counterpart member, such as the first relay pulley  105 , from being reversely attached to the shaft member such as the first support shaft  115 . 
     Aspect 5 
     In any one of Aspects 1 to 4, one end of the bearing, such as a ball bearing, abuts against a surface of the shaft member such as the first support shaft  115  (e.g., the first step surface  115   c  and the second step surface  115   d  in the above-described embodiment) that faces the bearing in the axial direction of the shaft member. The other end of the bearing abuts against a surface of the counterpart member such as the first relay pulley  105  (e.g., the first positioning portion  105   k  and the second positioning portion  105   f  in the above-described embodiment) that faces the bearing in the axial direction. According to such a configuration, as described in the above-described embodiment, the bearing can be prevented from moving relative to the counterpart member, such as the first relay pulley  105 , in the axial direction. The bearing can be prevented from coming off the counterpart member. 
     Aspect 6 
     In any one of Aspects 1 to 5, the counterpart member, such as the first relay pulley  105 , is not in contact with the shaft member such as the first support shaft  115 . Such a configuration can restrain a decrease in contact pressure between the bearing and the counterpart member. 
     Aspect 7 
     In any one of Aspects 1 to 6, the counterpart member is a drive transmission member such as the first relay pulley  105 . The shaft member is a support shaft such as the first support shaft  115  that supports the drive transmission member. As described in the above-described embodiment, such a configuration can restrain generation of abnormal noise during drive transmission. 
     Aspect 8 
     In any one of Aspects 1 to 7, the counterpart member such as the first relay pulley  105  is made of a resin material, and the bearing is a ball bearing. Such a configuration can prevent the retaining member, such as the E ring  113 , from sliding on the outer ring of the ball bearing that rotates relative to the retaining member. Further, the resin material serves as a sliding counterpart of the retaining member, and generation of abnormal noise can be restrained. 
     Aspect 9 
     An image forming apparatus includes the rotating device according to any one of Aspects 1 to 8 and forms an image on a sheet. Such a configuration can restrain generation of abnormal noise. 
     The above-described embodiments are illustrative and do not limit the present invention. Thus, numerous additional modifications and variations are possible in light of the above teachings. For example, elements and/or features of different illustrative embodiments may be combined with each other and/or substituted for each other within the scope of the present invention. 
     Any one of the above-described operations may be performed in various other ways, for example, in an order different from the one described above.