Patent Publication Number: US-2019168978-A1

Title: Rotary member support structure, transport device, charging device, and image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2017-233292 filed Dec. 5, 2017. 
     BACKGROUND 
     Technical Field 
     The present invention relates to a rotary member support structure, to a transport device, to a charging device, and to an image forming apparatus. 
     SUMMARY 
     According to an aspect of the invention, there is provided a rotary member support structure including: a rotary member including a shaft; a bearing that rotatably supports the shaft of the rotary member; a pressing member that presses the bearing in one direction; and a support that supports the bearing such that the bearing is movable in a pressing direction of the pressing member. When the rotary member is not rotating, the bearing and the pressing member are in contact with each other such that the bearing is rotatable about the shaft. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein: 
         FIG. 1  is a schematic diagram showing the structure of an image forming apparatus; 
         FIG. 2  is an enlarged schematic diagram showing an output transport path near a fixing device in the image forming apparatus in  FIG. 1 ; 
         FIG. 3  is a partial schematic cross sectional view showing the structure of a pair of first output rollers in the output transport path in  FIG. 2  (the structure includes support structures); 
         FIG. 4A  is a schematic diagram showing a support structure for a driven roller in the pair of output rollers in  FIG. 3  in exemplary embodiment 1; 
         FIG. 4B  is a schematic cross-sectional view taken along line IVB-IVB in  FIG. 4A ; 
         FIG. 5A  is an enlarged schematic diagram showing the support structure for the driven roller in  FIG. 4A ; 
         FIG. 5B  is a schematic diagram showing a contact state of a protrusion in the support structure in  FIG. 5A ; 
         FIG. 6A  is a schematic diagram showing a state when the driven roller in the support structure in  FIG. 5A  is not rotating; 
         FIG. 6B  is a schematic diagram showing a state during rotation of the driven roller in the support structure in  FIG. 6A ; 
         FIG. 7A  is an exploded perspective view showing the structure of a pressing member including the protrusion in the support structure in  FIG. 5A ; 
         FIG. 7B  is a schematic cross-sectional view showing the pressing member in  FIG. 7A ; 
         FIG. 8A  is an enlarged schematic diagram showing a support structure for the driven roller in exemplary embodiment 2; 
         FIG. 8B  is a schematic diagram showing a contact state of a protrusion in the support structure; 
         FIG. 9A  is a schematic diagram showing a state when the driven roller in the support structure in  FIG. 8A  is not rotating; 
         FIG. 9B  is a schematic diagram showing a state during rotation of the driven roller in the support structure in  FIG. 9A ; 
         FIG. 10A  is a schematic perspective view showing the structure of the protrusion in the support structure in  FIG. 8A ; 
         FIG. 10B  is a schematic perspective view showing another example of the structure of the protrusion in the support structure; 
         FIG. 11A  is an enlarged schematic diagram showing a support structure for the driven roller in exemplary embodiment 3; 
         FIG. 11B  is a schematic diagram showing a contact state of a protrusion in the support structure; 
         FIG. 12A  is a schematic diagram showing a state when the driven roller in the support structure in  FIG. 11A  is not rotating; 
         FIG. 12B  is a schematic diagram showing a state during rotation of the driven roller in the support structure in  FIG. 12A ; 
         FIG. 13  is an enlarged schematic diagram showing a support structure for a charging roller in exemplary embodiment 4; 
         FIG. 14A  is a schematic diagram showing a state when the charging roller in the support structure in  FIG. 13  is not rotating; 
         FIG. 14B  is a schematic diagram showing a state during rotation of the charging roller in the support structure in  FIG. 14A ; 
         FIG. 15A  is an enlarged schematic diagram showing a comparative support structure for the driven roller; 
         FIG. 15B  is a schematic diagram showing a contact state between a pressing member and a bearing in the support structure; 
         FIG. 16A  is a schematic diagram showing a state when the driven roller in the support structure in  FIG. 15A  is not rotating; and 
         FIG. 16B  is a schematic diagram showing a state during rotation of the driven roller in the support structure in  FIG. 16A . 
     
    
    
     DETAILED DESCRIPTION 
     Exemplary embodiments of the present invention will next be described with reference to the drawings. 
     EXEMPLARY EMBODIMENT 1 
       FIGS. 1 and 2  show exemplary embodiment 1 of the invention.  FIG. 1  shows the structure of an image forming apparatus  1  according to exemplary embodiment 1.  FIG. 2  is an enlarged illustration of an output transport path in the image forming apparatus  1  in  FIG. 1 . 
     &lt;General Structure of Image Forming Apparatus&gt; 
     In the image forming apparatus  1 , an image based on the information about an image including letters, photographs, diagrams, etc. is formed using a developer on a recording paper sheet  9  that is an example of a transportation object or a recording medium. 
     As shown in  FIG. 1 , the image forming apparatus  1  includes: a housing  10  serving as an apparatus body; an image forming unit  2  that forms a toner image using a toner serving as the developer by, for example, electrophotography and transfers the toner image onto a recording paper sheet  9 ; a paper feeder  3  that holds a prescribed number of recording paper sheets  9  and feeds a recording paper sheet  9  to a transfer position of the image forming unit  2 ; and a fixing device  4  that fixes the toner image transferred onto the recording paper sheet  9 . The image forming unit  2 , the paper feeder  3 , and the fixing device  4  are disposed inside the housing  10 . 
     The housing  10  is composed of various members such as structural members and exterior materials. An output tray  11  for placing ejected recording paper sheets  9  with images formed thereon is provided in an upper portion of the housing  10 . The output tray  11  is formed as a collecting surface having an inclined surface disposed below a paper outlet  12  of the housing  10  and is configured to collect recording paper sheets  9  ejected from the paper outlet  12 . 
     The image forming unit  2  includes a photoreceptor drum  21  that is a driving drum and rotates in a direction indicated by arrow A and further includes a charging device  22 , an exposure device  23 , a developing device  24 , a transfer device  25 , and a cleaning device  26  that are disposed in this order around the photoreceptor drum  21 . 
     The charging device  22  is, for example, a contact charging device that electrically charges the circumferential surface (the outer circumferential surface serving as an image-forming region) of the photoreceptor drum  21  to a prescribed potential with a prescribed polarity. The exposure device  23  irradiates the circumferential surface of the charged photoreceptor drum  21  with light (indicated by a chain double-dashed arrow) in response to image information (signals) inputted in various forms to the image forming apparatus  1  to thereby form an electrostatic latent image. The developing device  24  supplies a charged toner used as a developer to develop the electrostatic latent image on the photoreceptor drum  21 , and a toner image is thereby formed. The transfer device  25  is, for example, a contact transfer device that electrostatically transfers the toner image on the photoreceptor drum  21  onto a recording paper sheet  9 . The cleaning device  26  cleans the photoreceptor drum  21  by removing undesired substances such as the toner remaining on the circumferential surface of the photoreceptor drum  21 . 
     The paper feeder  3  includes: a paper tray  31  that holds plural recording paper sheets  9  having a prescribed size and a prescribed type and used for image formation, the recording paper sheets  9  being stacked on a sheet stacking plate  32 ; and a delivery unit  33  that delivers the recording paper sheets  9  held in the paper tray  31  one by one. 
     The paper tray  31  is attached to the housing  10  such that the paper tray  31  can be pulled out of the housing  10 , and plural paper trays  31  may be provided depending on use conditions. The recording paper sheets  9  used are, for example, recording mediums cut into a prescribed size such as plain paper sheets, coated paper sheets, or thick paper sheets. 
     The fixing device  4  includes a housing  40  having an inlet for a recording paper sheet  9  and a paper outlet and further includes a heating rotary body  41  and a pressurizing rotary body  42  that are disposed inside the housing  40  and rotate while in contact with each other. 
     As shown in  FIGS. 1 and 2  etc., the heating rotary body  41  is a driving rotary body and rotates in a direction indicated by an arrow. The heating rotary body  41  is a fixing member for heating and is in a roller form or a belt-pad form, and the circumferential surface of the heating rotary body  41  is heated to a prescribed temperature by a heater  43 . The pressurizing rotary body  42  is a fixing member for pressurization that is in a roller form or a belt-pad form and is disposed so as to be aligned substantially along the axial direction of the heating rotary body  41 . The pressurizing rotary body  42  is in contact with the heating rotary body  41  at a prescribed pressure and is rotated by the heating rotary body  41 . In the fixing device  4 , the contact portion between the heating rotary body  41  and the pressurizing rotary body  42  serves as a fixing treatment section FN through which a recording paper sheet  9  with a non-fixed toner image transferred thereon passes to thereby subject it to prescribed fixing treatment (heating, pressurization, etc.). 
     &lt;Structure of Transport Path&gt; 
     In the image forming apparatus  1 , as shown by a chain double-dashed line in  FIG. 1 , a transport path Rt for transportation of a recording paper sheet  9  is provided in the housing  10 . The transport path Rt includes a supply transport path Rt 1 , a relay transport path Rt 2 , and an output the transport path Rt 3 . 
     As shown in  FIG. 1 , the supply transport path Rt 1  connects the delivery unit  33  of the paper feeder  3  to the transfer position (a portion of the photoreceptor drum  21  that faces the transfer device  25 ) of the image forming unit  2 . The supply transport path Rt 1  is composed of a pair of transport rollers  34  and unillustrated plural transport guide members. 
     The pair of transport rollers  34  are composed of so-called resist rollers. The resist rollers in a non-rotating state have the function of correcting the inclination of a transported recording paper sheet  9 . The resist rollers start rotating at the timing of transfer, and the rotating resist rollers have the function of feeding a recording paper sheet  9  to the transfer position. 
     As shown in  FIG. 1 , the relay transport path Rt 2  connects the transfer position of the image forming unit  2  to the fixing treatment section of the fixing device  4 . The relay transport path Rt 2  is composed of a prescribed guide member  35 . 
     As shown in  FIGS. 1 and 2  etc., the output transport path Rt 3  connects the fixing treatment section FN of the fixing device  4  to the paper outlet  12 . The output transport path Rt 3  is composed of a pair of first output rollers  36 , a pair of second output rollers  37 , plural output guiding members  38  and  39 , etc. 
     The pair of first output rollers  36  is disposed on the paper outlet side of the housing  40  of the fixing device  4  and includes a driving roller  361  and a driven roller  362  that is pressed against the driving roller  361  and driven to rotate by the driving roller  361 . The pair of second output rollers  37  is disposed at the paper outlet  12  and includes a driving roller  372  and a driven roller  371  that is in contact with the driving roller  372  and is driven to rotate by the driving roller  372 . A support structure for the pair of first output rollers  36  will be described later. 
     The output guiding members  38  are a pair of members  38   a  and  38   b  that face each other so as to form a transport space through which a recording paper sheet  9  subjected to fixation is guided to the pair of first output rollers  36 . The output guiding members  39  are a pair of members  39   a  and  39   b  that face each other so as to form a transport space through which a recording paper sheet  9  discharged from the pair of first output rollers  36  is guided to the pair of second output rollers  37 . 
     &lt;Image Forming Operation by Image Forming Apparatus&gt; 
     In the image forming apparatus  1 , an image is formed as described below. An image forming operation for forming an image on one side of a recording paper sheet  9  will be described. 
     First, when an unillustrated controller in the image forming apparatus  1  receives an image formation request, the image forming unit  2 , the paper feeder  3 , and the fixing device  4  are actuated. 
     Then, in the image forming unit  2 , the photoreceptor drum  21  starts rotating. The charging device  22  charges the circumferential surface of the photoreceptor drum  21  to a predetermined potential with a predetermined polarity (a negative polarity in this embodiment), and then the exposure device  23  exposes the charged circumferential surface of the photoreceptor drum  21  to light according to image information to thereby form an electrostatic latent image having a prescribed pattern. Next, the developing device  24  supplies a toner serving as a developer and charged to a prescribed polarity (a negative polarity in this embodiment) to the electrostatic latent image formed on the circumferential surface of the photoreceptor drum  21  to develop the electrostatic latent image, and the electrostatic latent image is thereby converted to a visible toner image. 
     Next, in the image forming unit  2 , the rotating photoreceptor drum  21  transfers the toner image to the transfer position facing the transfer device  25 . The delivery unit  33  of the paper feeder  3  feeds a recording paper sheet  9  to the supply transport path Rt 1  according to transfer timing, and the pair of resist rollers  34  in the supply transport path Rt 1  delivers the recording paper sheet  9  to the transfer position. Then, in the image forming unit  2 , the transfer device  25  transfers the toner image on the photoreceptor drum  21  onto one side of the recording paper sheet  9  through electrostatic action at the transfer position. In the image forming unit  2 , after the image transfer, the cleaning device  26  cleans the circumferential surface of the photoreceptor drum  21  and other portions to prepare for the next image forming process. 
     Next, in the image forming unit  2 , the rotational force of the rotating photoreceptor drum  21  causes the recording paper sheet  9  with the toner image transferred thereon to be delivered to the relay transport path Rt 2  and transported to the fixing device  4 . In the fixing device  4 , the recording paper sheet  9  is introduced into the fixing treatment section FN between the heating rotary body  41  and the pressurizing rotary body  42  driven to rotate by the heating rotary body  41 . When the recording paper sheet  9  passes through the fixing treatment section FN, the toner image on the recording paper sheet  9  is heated and fused under pressure and is thereby fixed to the recording paper sheet  9 . 
     Finally, the recording paper sheet  9  subjected to fixation is transported through the output transport path Rt 3  to the paper outlet  12  of the housing  10  and then ejected and placed in the output tray  11 . 
     In this case, as shown in  FIGS. 1 and 2 , the recording paper sheet  9  subjected to fixation is guided by the output guiding members  38  and the output guiding members  39  in the output transport path Rt 3 , held between the pair of first output rollers  36  and then between the pair of second output rollers  37 , and transported by the transportation force of the rollers. 
     A single-color toner image is thereby formed on one side of the recording paper sheet  9 , and the single-side image formation operation is completed. When an instruction to perform the image forming operation plural times is issued, the above series of operations is repeated the plural times. 
     &lt;Support Structure for Pair of First Output Rollers and Transport Device Using the Same&gt; 
     In the image forming apparatus  1 , a support structure shown in  FIGS. 3 to 6B  etc. is used as the support structure supporting the pair of first output rollers  36  disposed in the output transport path Rt 3 . 
     First, as shown in  FIG. 3  etc., in the pair of first output rollers  36 , a rotary member  5 A including a rotating shaft  51  serving as a shaft and roller bodies  53  disposed on the outer circumferential surface of the rotating shaft  51  is used as the driving roller  361 . The driving roller  361  in exemplary embodiment 1 is a roller having a structure including the plural roller bodies  53  disposed on the rotating shaft  51  at prescribed intervals. 
     As shown in  FIG. 3  etc., in the pair of first output rollers  36 , a rotary member  5 B including a rotating shaft  52  serving as a shaft and a roller body  54  disposed on the outer circumferential surface of the rotating shaft  52  is used as the driven roller  362 . The driven roller  362  in exemplary embodiment 1 is a roller having a structure including one roller body  54  disposed on the rotating shaft  52 . 
     The pair of first output rollers  36  has a structure in which the rotating shafts  51  and  52  are rotatably supported by prescribed support members  70  through bearings  55  and  56 , respectively, such that the roller bodies  53  and  54  of the driving roller  361  and the driven roller  362 , respectively, forming the rotary members  5 A and  5 B rotate while in contact with each other. 
     The support members  70  are plate members such as synthetic resin plates or metallic plates fixed to prescribed positions. 
     As shown in  FIGS. 1 to 3  etc., the pair of first output rollers  36  forms a transport device  7  that transports a recording paper sheet  9 , which is an example of a transportation object. Specifically, the recording paper sheet  9  is transported while sandwiched between the driving roller  361  and the driven roller  362  driven to rotate by the driving roller  361 . 
     As shown in  FIG. 3 , the driving roller  361  is driven to rotate in a prescribed direction by rotating power transmitted to the rotating shaft  51  from a rotation driving device  77 . The rotating power is transmitted from the rotation driving device  77  to the driving roller  361  (to its rotating shaft  51 ) using an unillustrated rotation transmitting mechanism such as a gear train. 
     In the driving roller  361  in the above support structure, the bearings  55  rotatably supporting the rotating shaft  51  are fixed to respective stationary attachment members  71  disposed in the support members  70 , and the driving roller  361  is thereby attached to the support members  70 . 
     The stationary attachment members  71  include, for example, holes or recesses into which the bearings  55  are partially fitted and members which fix the bearings  55 . The bearings  55  are, for example, sliding bearings. 
     As shown in  FIGS. 3 to 5B  etc., in the driven roller  362  in the above support structure, the bearings  56  rotatably supporting the rotating shaft  52  are attached to movable attachment members  72  disposed in the support members  70  so as to be movable by a given distance toward the driving roller  361  as shown by double-pointed arrows E 1 -E 2 . 
     Each of the movable attachment members  72  includes a support  73  that supports a corresponding bearing  5  for the driven roller  362  movably with respect to the rotating shaft  51  of the driving roller  361 . The supports  73  are attached and fixed to the respective support members  70 . The bearings  56  are, for example, sliding bearings. The supports  73  may be formed as portions of the support members  70  and integrated therewith. 
     In the driven roller  362 , the bearings  56  supporting the rotating shaft  52  are supported by the movable attachment members  72  so as to be pressed by respective pressing members  57  in a direction E 1  directed toward the rotating shaft  51  of the driving roller  361 . 
     As described above, in the pair of first output rollers  36 , the driving roller  361  (the rotary member  5 A) is rotatably supported by the support members  70  (their stationary attachment members  71 ) while the position of the driving roller  361  is fixed. The driven roller  362  (the rotary member  5 B) is rotatably supported by the supports  73  (the movable attachment members  72 ) of the support members  70  so as to be movable toward the driving roller  361  and is also supported by the pressing members  57  through the bearings  56  so as to be pressed in the direction E 1  directed toward the rotating shaft  51  of the driving roller  361 . 
     In particular, as shown in  FIGS. 3, 4A, and 4C , in the pair of first output rollers  36 , the driven roller  362  (the rotary member  5 B) employs a support structure  6  including: the bearings  56  that rotatably support the rotating shaft  52 ; the pressing members  57  that press the respective bearings  56  in the direction E 1  directed toward the rotating shaft  51  of the driving roller  361 ; and the supports  73  that support the respective bearings  56  so as to be movable in the direction E 1  in which the bearings  56  are pressed by the pressing members  57 . 
     As shown in  FIGS. 4A and 4B , each of the bearings  56  in the support structure  6  includes a plate-shaped body  56   a  having a substantially rectangular side portion. Each body  56   a  includes: a bearing hole  56   b  located at substantially the center and passing through the body  56   a ; a step portion  56   c  that is disposed in an upper outer portion of the body  56   a  and extends in the moving direction E 1 -E 2 ; and a pressure receiving portion  56   d  that receives the pressure of a corresponding pressing member  57  on one side. 
     As shown in  FIGS. 4A and 4B , each support  73  in the support structure  6  includes a body  74  having a holding portion  74   a  that accommodates a corresponding bearing  56  such that upper and lower portions of the bearing  56  are held so as to be movable in the direction E 1 -E 2 . The body  74  includes: a lower guiding portion  74   b  that holds and guides the lower side surface of the bearing  56  when it moves; an upper guiding portion  74   c  that holds and guides the upper side surface (the step portion  56   c ) of the bearing  56  when it moves; and an abutting portion  74   d  against which part of the pressing member  57  abuts to fix the pressing member  57 . 
     As shown in  FIGS. 4A and 4B , each of the pressing members  57  in the support structure  6  is composed of a member that can elastically press a corresponding bearing  56  in the direction E 1  directed toward the rotating shaft  51  of the driving roller  361 . Each of the pressing members  57  in exemplary embodiment 1 includes a coil spring. 
     Each of the coil springs of the pressing members  57  is disposed between the pressure receiving portion  56   d  of a corresponding bearing  56  and the abutting portion  74   d  of a corresponding support  73  and is used such that the bearing  56  is pressed by prescribed pressing force F toward the rotation center ( 02 ) of the rotating shaft  52  of the driven roller  362 . 
     As shown in  FIG. 4A , in the abutting portion  74   d  of the support  73  in exemplary embodiment 1, a protrusion holding portion  74   e  that holds one end of the coil spring used as the pressing member  57  is provided. The protrusion holding portion  74   e  is fitted into an internal space at the one end of the coil, and the coil spring is thereby held. Since the one end of the coil spring is held by the protrusion holding portion  74   e , the position of the coil spring is unlikely to be displaced. 
     &lt;Problems with Support Structure for Pair of First Output Rollers&gt; 
     Generally, as exemplified in  FIG. 15A , in the support structure  6  for the driven roller  362  of the pair of first output rollers  36 , each coil spring included in a corresponding pressing member  57  is disposed such that its end portion opposite to the abutting portion  74   d  of a corresponding support  73  is pressed against part of a corresponding bearing  56 . 
     The support structure  6  shown in  FIG. 15A  is a comparative support structure  60 . Both ends of the coil spring serving as the pressing member  57  are assumed to be parallel to each other and have a substantially flat annular shape, unless otherwise specifically stated. Symbol L 1  for a chain dashed line in  FIG. 15A  etc. represents a virtual straight line (virtual line) connecting the rotation center  02  of the driven roller  362  to the rotation center  01  of the driving roller  361 . Symbol L 2  for a chain dashed line represents the direction (the axial line) of the rotating shaft  52  of the driven roller  362 . 
     In the comparative support structure  60 , the coil spring serving as the pressing member  57  is disposed such that a central portion  57   a  of an end of the coil spring that is pressed against part of the bearing  56  substantially coincides with a position P 1  at which the virtual line L 1  intersects a pressure receiving surface  56   e  of the bearing  56  and is in contact with the pressure receiving surface  56   e .  FIG. 15B  shows a portion  57   b  in which an end portion of the coil spring serving as the pressing member  57  is in contact with the pressure receiving surface  56   e  of the bearing  56  and also shows the state of the portion  57   b . In this support structure  60 , the coil spring serving as the pressing member  57  is attached on the assumption that the pressing force F of the coil spring acts toward the rotation center  02  of the rotating shaft  52 . 
     As shown in  FIG. 15A , in this support structure  60 , when the driving roller  361  is rotated in a direction indicated by a chain double-dashed arrow at its operating timing, the driven roller  362  is driven to rotate in a rotation direction C indicated by a chain double-dashed arrow. 
     In this case, as shown in  FIG. 15A , a rotational force (moment) Mr and a rotational drag force (moment) Mb are generated and act on the bearing  56 . The rotational force Mr urges the bearing  56  to rotate in the rotation direction C through the frictional force such as the sliding force between the bearing  56  and the rotating shaft  52  of the driven roller  362 . The rotational drag force Mb is caused by the pressing member  57  pressed against the bearing  56  and urges the bearing  56  to rest against the rotational force Mr. 
     In fact, in the support structure  60 , the coil springs serving as the pressing members  57  may have different pressing characteristics (may have their own unique pressing characteristics) depending on the attachment states of the coil springs, their individual differences, etc. In this case, as shown  FIGS. 16A and 16B , each bearing  56  may rotate about the rotating shaft  52  and come to rest while in contact with part of the holding portion  74   a  of the support  73  and inclined within a movable space in the support  73 . 
       FIG. 16A  shows a state (J 1 ) in which the bearing  56  slides within the holding portion  74   a  of the support  73  in a direction opposite to the rotation direction C of the driven roller  362  and is thereby inclined and at rest.  FIG. 16B  shows a state (J 2 ) in which the bearing  56  slides within the holding portion  74   a  of the support  73  in the rotation direction C of the driven roller  362  and is thereby inclined and at rest. 
     In this support structure  60 , during rotation of the driven roller  362 , the sliding friction between the bearing  56  and the rotating shaft  52  may change instantaneously, and the rotational force Mr may increase or decrease. Specifically, when a reduction in the sliding friction occurs, the rotational force Mr decreases. In this case, the rotational force Mr can be substantially equal to the rotational drag force Mb (Mr≅Mb). 
     When these forces are substantially equal to each other, the bearing  56  is unstable and can easily rotate about the rotating shaft  52  during rotation of the driven roller  362 . Therefore, the bearing  56  rotates back and forth repeatedly between the above two states (J 1  and J 2 ). 
     Therefore, in the support structure  60 , the bearing  56  repeatedly collides with portions of the support  73 , and this causes unwanted noise and vibration. When a transport device  7  is formed using this support structure  60 , unwanted noise and vibration are generated during transfer of a recording paper sheet  9  by the transport device  7 . 
     &lt;Detailed Structure of Support Structure for Pair of First Output Rollers&gt; 
     Accordingly, in exemplary embodiment 1, as the support structure  6  that supports the driven roller  362  of the pair of first output rollers  36 , a support structure  6 A shown in  FIGS. 4A and 5A  is employed. In the support structure  6 A, when the driven roller  362  serving as the rotary member is not rotating, the bearing  56  and the pressing member  57  are in contact with each other while the bearing  56  is rotatable about the rotating shaft  52 . 
     The state in which the bearing  56  is rotatable is an unstable state. Specifically, for example, when the driven roller  362  is not rotating, the bearing  56  can easily rotate about the rotating shaft  52  in the rotation direction C of the driven roller  362  (or its rotating shaft  52 ) and also in a direction opposite to the rotation direction C, as shown in  FIG. 6A . Symbol L 1  for a chain dashed line in  FIG. 6A  represents a virtual line connecting the rotation center  02  of the driven roller  362  to the rotation center  01  of the driving roller  361 , as does the virtual line L 1  described above. 
     In the support structure  6 A for the driven roller  362  in exemplary embodiment 1, each pressing member  57  has a protrusion  81 , and the protrusion  81  is in contact with a corresponding bearing  56 . When the driven roller  362  is not rotating, the bearing  56  can rotate about the rotating shaft  52 . 
     Moreover, in the support structure  6 A for the driven roller  362 , during rotation of the driven roller  362 , the bearing  56  is held in a state in which it is rotated in the rotation direction C of the driven roller  362 , as shown in  FIG. 6B . 
     The phrase “the bearing  56  is held in a state in which it is rotated in the rotation direction C of the driven roller  362 ” means that, for example, the bearing  56  rotated in the rotation direction C of the driven roller  362  comes into contact with part of the holding portion  74   a  of the support  73  and is thereby inclined and at rest and the inclined state is maintained during the rotation of the driven roller  362 , as shown in  FIG. 6B . The phrase also encompasses the following case. 
     Specifically, during the rotation of the driven roller  362  in the rotation direction C, the bearing  56  is brought to the inclined state described above. Then the bearing  56  in the inclined state slightly rotates continuously back and forth in the rotation direction C of the driven roller  362  and its reverse rotation direction. In other words, in this state, during the rotation of the driven roller  362  in the rotation direction C, the bearing  56  is prevented from rotating in the reverse rotation direction beyond the position at which the bearing  56  is unstable and rotatable when the driven roller  362  is not rotating ( FIG. 6A ). 
     The protrusion  81  disposed in the pressing member  57  is formed as a structural member having a spherical surface portion that comes in to contact with the pressure receiving surface  56   e  of the pressure receiving portion  56   d  of the bearing  56 . 
     As shown in  FIG. 5B , the protrusion  81  formed as the spherical surface-shaped structural member is in point contact with the pressure receiving surface  56   e  of the pressure receiving portion  56   d  of the bearing  56 . This allows the bearing  56  to be easily rotatable when the driven roller  362  is not rotating. 
     Symbol  81   a  in  FIG. 5B  represents a portion of the protrusion  81  that is in contact with the bearing  56 . The contact portion  81   a  substantially corresponds to the apex of the spherical surface-shaped protrusion  81 . A chain dashed line L 2  in  FIG. 5B  indicates the direction (axial line) of the rotating shaft  52  of the driven roller  362  as described above. 
     In fact, the term “point contact” also encompasses the case in which the shape of the contact portion  81   a  is a dot-like shape (a small circular shape) with a certain diameter (width) w 1  on condition that shape of the contact portion  81   a  is maintained in the above-described rotatable state as shown in  FIG. 5B . The pressure receiving surface  56   e  of the pressure receiving portion  56   d  of the bearing  56  is a flat surface. However, the pressure receiving surface  56   e  may be a curved surface with a small curvature so long as the point contact with the protrusion  81  can be maintained. 
     As shown in  FIGS. 7A and 7B , the pressing member  57  provided with the protrusion  81  includes a coil spring  571  having a first end  571   a  to which a component  85  having the protrusion  81  is attached. 
     The component  85  having the protrusion  81  has an attachment recess  85   c  into which the first end  571   a  of the coil spring  571  is fitted. The protrusion  81  may be integrated with the component  85 , or the protrusion  81  formed separately may be later integrated with the component  85 . 
     The pressing member  57  provided with the protrusion  81  is disposed such that the protrusion  81  is pressed toward the rotation center  02  of the rotating shaft  52  of the driven roller  362 . Specifically, as shown in  FIG. 6A , the pressing member  57  is disposed such that its pressing force F acts toward the rotation center  02  of the rotating shaft  52 . 
     In this case, the coil spring  571  serving as the pressing member  57  may be attached such that a second end  571   b  of the coil spring  571  is fitted onto and held by the protrusion holding portion  74   e  ( FIG. 4A ) provided in the abutting portion  74   d  of the support  73 . 
     &lt;Operational Advantages of Support Structure for Pair of First Output Rollers&gt; 
     As shown in  FIGS. 5A and 6A , in the support structure  6 A supporting the driven roller  362  of the pair of first output rollers, when the driven roller  362  is not rotating (is in a non-rotating state), the bearing  56  is in point contact with the protrusion  81  disposed in the pressing member  57 . 
     In the support structure  6 A in this state, the bearing  56  is rotatable about the rotating shaft  52  within the movable space in the holding portion  74   a  of the support  73 . In this case, only the pressing force F exerted by the pressing member  57  and directed to the rotation center  02  of the rotating shaft  52  acts on the bearing  56 . Therefore, the bearing  56  is in an unstable state in which it can easily rotate about the rotating shaft  52  in the rotation direction C of the driven roller  362  and also in the reverse rotation direction. 
     As shown in  FIG. 6B , in the support structure  6 A, when the driven roller  362  is rotating during, for example, transportation of a recording paper sheet  9  (during rotation of the driven roller  362 ), the rotational force Mr in the rotation direction C of the driven roller  362  acts on the bearing  56 , as described above for the comparative support structure  60 . 
     Therefore, in the support structure  6 A, the bearing  56  that is rotatable when the driven roller  362  is not rotating is maintained in a state in which the bearing  56  is rotated in the rotation direction C of the driven roller  362  within the movable space in the holding portion  74   a  of the support  73 . 
     Specifically, as shown in  FIG. 6B , the bearing  56  in this case is rotated in the rotation direction C of the driven roller  362  within the movable space in the holding portion  74   a  of the support  73 . Then part (a corner) of the bearing  56  comes into contact with part of the holding portion  74   a , and the bearing  56  comes to rest, so that the bearing  56  is slightly inclined. 
     Also in this support structure  6 A, during rotation of the driven roller  362 , the sliding friction between the bearing  56  and the rotating shaft  52  may change instantaneously, and the rotational force Mr may increase or decrease, as described above for the comparative support structure  60 . Specifically, when a reduction in the sliding friction occurs, the rotational force Mr decreases. In this case, the rotational force Mr and the rotational drag force Mb may become substantially equal to each other (Mr≅Mb). 
     However, in the support structure  6 A, the protrusion  81  in the pressing member  57  is in point contact with the bearing  56 . Since the pressing member  57  is disposed such that its pressing force F acts toward the rotation center  02  of the rotating shaft  52 , the vector of the load generated by the protrusion  81  is directed toward the rotation center  02  of the rotating shaft  52 . Therefore, in the support structure  6 A, the rotational drag force (moment) Mb itself that is caused by the pressing member  57  pressed against the bearing  56  and urges the bearing  56  to rest against the rotational force Mr is unlikely to be generated. 
     Therefore, in the support structure  6 A, the rotational drag force Mb is unlikely to increase to a level comparable to the rotational force Mr, and the relation between the rotational force Mr and the rotational drag force Mb is easily maintained such that the rotational force Mr is larger than the rotational drag force Mb (Mr&gt;Mb). 
     In this support structure  6 A, during rotation of the driven roller  362  (and the driving roller  361 ), the bearing  56  is easily maintained in a state in which it is rotated in the rotation direction C of the driven roller  362  within the holding portion  74   a  of the support  73 . In this case, the bearing  56  is prevented from rotating in the reverse rotation direction opposite to the rotation direction C beyond the position at which the bearing  56  is in the rotatable state when the driven roller  362  is not rotating and from rotating back and forth repeatedly around the above position. 
     Therefore, in the support structure  6 A, generation of noise and vibration caused by repeated rotation of the bearing  56  within the movable space in the support  73  can be prevented or reduced, as described above for the comparative support structure  60 . 
     In the support structure  6 A, the generation of noise and vibration that occurs during rotation of the driven roller  362  in the comparative support structure  60  is prevented or reduced. Therefore, in a transport device  7  produced using the support structures  6 A, a recording paper sheet  9  can be smoothly transported without generation of noise and vibration. 
     In the structural example shown in exemplary embodiment 1, the protrusion  81  in point contact with the pressure receiving portion  56   d  of the bearing  56  is a structural component having a spherical surface shape. However, this structural example is not a limitation. For example, the protrusion  81  may be a structural component in which the portion in contact with the pressure receiving portion  56   d  of the bearing  56  has a cone shape or a pyramid shape. 
     In the support structure  6  in which the protrusion  81  in point contact with the bearing  56  is used, even when the driven roller  362  is rotated in the rotation direction C and the reverse rotation direction in a switchable manner, the bearing  56  is rotated in the direction of rotation of the driven roller  362  (the rotation direction C or the reverse rotation direction). 
     In the support structure  6 A, even when the driven roller  362  is rotated in the forward and reverse directions in a switchable manner, the generation of noise and vibration caused by repeated rotation of the bearing  56  as described above is prevented. 
     EXEMPLARY EMBODIMENT 2 
       FIGS. 8A and 8B  show a support structure  6 B for the driven roller  362  in exemplary embodiment 2. 
     The support structure  6 B according to exemplary embodiment 2 has the same structure as the support structure  6 A according to exemplary embodiment 1 except that the protrusion  81  is replaced with a protrusion  82  having a different structure. Therefore, in the support structure  6 B, the same components as the support structure  6 A are denoted by the same symbols in  FIGS. 8A and 8B  and subsequent figures, and their description will be omitted in principle. 
     As shown in  FIGS. 8A and 8B , in the support structure  6 B, the protrusion disposed in the pressing member  57  is a protrusion  82  in line contact along the axial line L 2  of the rotating shaft  52  with the pressure receiving surface  56   e  of the pressure receiving portion  56   d  of the bearing  56 . Therefore, as shown in  FIGS. 8A, 8B, and 9A , when the driven roller  362  is not rotating, the bearing  56  is rotatable about the rotating shaft  52 . 
     Also in this support structure  6 B, as in the support structure  6 A according to exemplary embodiment 1, during rotation of the driven roller  362 , the bearing  56  is held in a state in which it is rotated in the rotation direction C of the driven roller  362 , as shown in  FIG. 9B . 
     The protrusion  82  is formed as a structural component in which its portion coming into contact with the pressure receiving surface  56   e  of the bearing  56  can be in line contact along the axial line L 2  of the rotating shaft  52 . As shown in  FIG. 10A , the protrusion  82  is formed as, for example, a horizontally extending triangular prism-shaped structural component having an edge line  82   a  that comes into contact with the bearing  56 . 
     As shown in  FIG. 8B , the protrusion  82  having the portion capable of line contact comes into line contact with the pressure receiving surface  56   e  of the pressure receiving portion  56   d  of the bearing  56 . 
     In this case, when the driven roller  362  is not rotating, the bearing  56  can be easily brought to the above-described rotatable state. When the protrusion  82  in line contact along the axial line L 2  of the rotating shaft  52  is used, the bearing  56  is further prevented from being inclined accidentally in a direction intersecting the axial line L 2 , as compared to the case when the protrusion  81  in point contact is used. Therefore, the posture of the bearing  56  in the direction of the axial line L 2  is stabilized. 
     The term “line contact” encompasses the case in which the contact portion  82   a  of the protrusion  82  has a continuous or discontinuous rectangular shape with a certain width w 2  on condition that the bearing  56  is maintained in the above-described rotatable state, as shown in  FIG. 8B . In this case, the width w 2  is shorter than the length k 1  of the contact portion  82   a  along the axial line L 2  of the rotating shaft  52  (w 2 &lt;k 1 ). 
     The pressing member  57  provided with the protrusion  82  includes a coil spring  571  having an end to which a component  85  having the protrusion  82  is attached (e.g.,  FIG. 8A ), as is the pressing member  57  provided with the protrusion  81  ( FIGS. 7A and 7B ). 
     &lt;Operational Advantages of Support Structure for Pair of First Output Rollers&gt; 
     As shown in  FIGS. 8A, 8B, and 9A , in the support structure  6 B supporting the driven roller  362 , when the driven roller  362  is not rotating, the bearing  56  is in line-contact with the protrusion  82  in the pressing member  57 . 
     In the support structure  6 B in this case, as in the support structure  6 A, the bearing  56  is rotatable about the rotating shaft  52  within the movable space in the holding portion  74   a  of the support  73 . In this case, the bearing  56  is in an unstable state in which it can easily rotate in the rotation direction C of the driven roller  362  and also in the reverse rotation direction. However, the posture of the bearings  56  along the axial line L 2  of the rotating shaft  52  is in a stable state. 
     As shown in  FIG. 9B , in the support structure  6 B, when the driven roller  362  is rotating, the rotational force Mr in the rotation direction C of the driven roller  362  acts on the bearing  56 , and therefore the bearing  56  is held in a state in which it is rotated in the rotation direction C of the driven roller  362  within the movable space in the holding portion  74   a  of the support  73 . 
     Specifically, as shown in  FIG. 9B , the bearing  56  in this case is rotated in the rotation direction C of the driven roller  362  within the movable space in the holding portion  74   a  of the support  73 . Then part (a corner) of the bearing  56  comes into contact with part of the holding portion  74   a , and the bearing  56  comes to rest, so that the bearing  56  is slightly inclined. 
     In this the support structure  6 B, as in the support structure  6 A, during rotation of the driven roller  362 , the sliding friction between the bearing  56  and the rotating shaft  52  may change instantaneously, and the rotational force Mr may increase or decrease. For example, the rotational force Mr and the rotational drag force Mb may become substantially equal to each other (Mr≅Mb). 
     However, in the support structure  6 B, the protrusion  82  in the pressing member  57  is in line contact with the bearing  56 . Since the pressing member  57  is disposed such that its pressing force F acts toward the rotation center  02  of the rotating shaft  52 , the vector of the load generated by the protrusion  82  is directed toward the rotation center  02  of the rotating shaft  52 . Therefore, in the support structure  6 B, as in the support structure  6 A, the rotational drag force Mb itself that is caused by the pressing member  57  pressed against the bearing  56  and urges the bearing  56  to rest against the rotational force Mr is unlikely to be generated. 
     Therefore, also in the support structure  6 B, as in the support structure  6 A, the rotational drag force Mb is unlikely to increase to a level comparable to the rotational force Mr, and the relation between the rotational force Mr and the rotational drag force Mb is easily maintained such that the rotational force Mr is larger than the rotational drag force Mb (Mr&gt;Mb). 
     Also in this support structure  6 B, during rotation of the driven roller  362 , the bearing  56  is easily maintained in a state in which it is rotated in the rotation direction C of the driven roller  362  within the holding portion  74   a  of the support  73 . In this case, the bearing  56  is prevented from rotating in the reverse rotation direction opposite to the rotation direction C beyond the position at which the bearing  56  is in the rotatable state when the driven roller  362  is not rotating and from rotating back and forth repeatedly around the above position. 
     Therefore, also in this support structure  6 B, as in the support structure  6 A, generation of noise and vibration caused by repeated rotation of the bearing  56  within the movable space in the support  73  can be prevented or reduced. 
     In exemplary embodiment 2, the protrusion  82  in line contact may be, for example, a structural body including a semicylindrical member having an apex portion (ridge line)  82   b  extending substantially linearly in a lengthwise direction, as shown in  FIG. 10B . This structural body may be disposed such that the apex portion  82   b  comes into contact with the bearing  56 . 
     In this case, the apex portion  82   b  of the protrusion  82  is less worn due to contact with the bearing  56  than the protrusion  82  of the structural body shown in  FIG. 10A , and the bearing  56  can be maintained in a desirable state for a long time. 
     EXEMPLARY EMBODIMENT 3 
       FIG. 11  shows a support structure  6 C for the driven roller  362  in exemplary embodiment 3. 
     The support structure  6 C according to exemplary embodiment 3 has the same structure as the support structure  6 A according to exemplary embodiment 1 except that the protrusion  81  is disposed in the bearing  56 . Therefore, in the support structure  6 C, the same components as the support structure  6 A are denoted by the same symbols in  FIGS. 11A and 11B  and subsequent figures, and their description will be omitted in principle. 
     In the support structure  6 C, the protrusion disposed in the bearing  56  is a protrusion  83  that comes into point contact with one end of a coil spring serving as the pressing member  57 , as shown in  FIGS. 11A and 11B . Therefore, as shown in  FIGS. 11A, 11B, and 12A , when the driven roller  362  is not rotating, the bearing  56  is rotatable about the rotating shaft  52 . 
     Also in this support structure  6 C, as in the support structure  6 A according to exemplary embodiment 1, during rotation of the driven roller  362 , the bearing  56  is held in a state in which it is rotated in the rotation direction C of the driven roller  362 , as shown in  FIG. 12B . 
     The protrusion  83  disposed in the bearing  56  is formed as a structural component in which its portion coming into contact with one end of the pressing member  57  has a spherical surface shape, as is the protrusion  81  in the support structure  6 A. In this case, the pressing member  57  is formed as, for example, a coil spring  571  to which a component  85  having a flat surface serving as a portion  85   a  to be in contact with the protrusion  83  is attached to the one end. 
     As shown in  FIG. 11B , the protrusion  83  formed as the spherical surface-shaped structural body comes into point contact with the one end of the coil spring  571  serving as the pressing member  57  (the flat portion  85   a  of the component  85 ). In this manner, when the driven roller  362  is not rotating, the bearing  56  can be easily brought to the above-described rotatable state. 
     Symbol  83   a  in  FIG. 11B  represents a portion of the protrusion  83  that is in contact with the one end of the coil spring  571  serving as the pressing member  57 . The contact portion  83   a  substantially corresponds to the apex of the spherical surface-shaped protrusion  83 . 
     In the support structure  6 C, as in the support structure  6 A, the pressing member  57  is disposed so as to be pressed toward the rotation center  02  of the rotating shaft  52  of the driven roller  362 . Specifically, as shown in  FIG. 12A , the pressing member  57  is disposed such that its pressing force F acts toward the rotation center  02  of the rotating shaft  52 . 
     &lt;Operational Advantages of Support Structure for Pair of First Output Rollers&gt; 
     As shown in  FIGS. 11A, 11B, and 12A , in this support structure  6 C, when the driven roller  362  is not rotating, the protrusion  83  disposed in the bearing  56  is in point contact with the one end of the pressing member  57 . 
     In the support structure  6 C in this case, substantially as in the support structure  6 A, the bearing  56  is rotatable about the rotating shaft  52  within the movable space in the holding portion  74   a  of the support  73 . In this case, the bearing  56  is in an unstable state in which it can easily rotate in the rotation direction C of the driven roller  362  and also in the reverse rotation direction. However, the posture of the bearing  56  along the axial line L 2  of the rotating shaft  52  is in a stable state. 
     As shown in  FIG. 12B , in the support structure  6 C, when the driven roller  362  is rotating, the rotational force Mr in the rotation direction C of the driven roller  362  acts on the bearing  56 . Therefore, the bearings  56  is held in a state in which it is rotatable in the rotation direction C of the driven roller  362  within the movable space in the holding portion  74   a  of the support  73 . 
     Specifically, as shown in  FIG. 12B , the bearing  56  in this case is rotated in the rotation direction C of the driven roller  362  within the movable space in the holding portion  74   a  of the support  73 . Then part (a corner) of the bearing  56  comes into contact with part of the holding portion  74   a , and the bearing  56  comes to rest, so that the bearing  56  is slightly inclined. 
     In the support structure  6 C, as in the support structure  6 A etc., during rotation of the driven roller  362 , the sliding friction between the bearing  56  and the rotating shaft  52  may change instantaneously, and the rotational force Mr may increase or decrease. Therefore, for example, the rotational force Mr and the rotational drag force Mb may become substantially equal to each other (Mr≅Mb). 
     However, in this support structure  6 C, the protrusion  83  in the bearing  56  is in point contact with the pressing member  57 . Since the pressing member  57  is disposed such that its pressing force F acts toward the rotation center  02  of the rotating shaft  52 , the vector of the load generated by the protrusion  83  is directed toward the rotation center  02  of the rotating shaft  52 . Therefore, in the support structure  6 C, the rotational drag force Mb itself that is caused by the pressing member  57  pressed against the bearing  56  and acts against the rotational force Mr is unlikely to be generated. 
     Therefore, also in the support structure  6 C, because of substantially the same reason as in the support structure  6 A etc., the rotational drag force Mb is unlikely to increase to a level comparable to the rotational force Mr, and the relation between the rotational force Mr and the rotational drag force Mb is easily maintained such that the rotational force Mr is larger than the rotational drag force Mb (Mr&gt;Mb). 
     Also in this support structure  6 C, during rotation of the driven roller  362 , the bearing  56  is easily maintained in a state in which it is rotated in the rotation direction C of the driven roller  362  within the holding portion  74   a  of the support  73 . In this case, the bearing  56  is prevented from rotating in the reverse rotation direction opposite to the rotation direction C beyond the position at which the bearing  56  is in the rotatable state when the driven roller  362  is not rotating and from rotating back and forth repeatedly around the above position. 
     Therefore, also in the support structure  6 C, substantially as in the support structure  6 A, generation of noise and vibration caused by repeated rotation of the bearing  56  within the movable space in the support  73  can be prevented or reduced. 
     In exemplary embodiment 3, the protrusion  83  in point contact may be, for example, a different structural member such as that described in exemplary embodiment 1. 
     In exemplary embodiment 3, the protrusion  82  in line contact as exemplified in exemplary embodiment 2 may be used instead of the protrusion  83  in point contact. 
     EXEMPLARY EMBODIMENT 4 
       FIG. 13  shows a support structure  6 D for a charging roller  220  in exemplary embodiment 4 and the charging device  22  using the support structure  6 D. 
     This support structure  6 D supports the charging roller  220  in the charging device  22  of the image forming unit  2 . For example, the support structure  6 A according to exemplary embodiment 1 ( FIGS. 4A, 4B, 5A, 5B , etc.) is used as the support structure  6 D. 
     The charging roller  220  is a rotary member  5 C including, for example: a rotating shaft  221  to which a charging voltage is supplied; and a roller body  222  disposed on the rotating shaft  221  and having a multilayer structure including an elastic layer, a surface layer, etc. The charging roller  220  is in contact with the circumferential surface of the photoreceptor drum  21  rotating in the direction of arrow A and is driven to rotate by the photoreceptor drum  21  in a direction indicated by chain double-dashed arrow D, and the circumferential surface of the photoreceptor drum  21  is thereby charged. 
     A chain dashed line L 3  in  FIG. 13  etc. represents a virtual straight line (virtual line) connecting the rotation center  03  of the photoreceptor drum  21  to the rotation center  04  of the charging roller  220 . A double-pointed arrow denoted by symbols E 3  and E 4  indicates moving directions when the support  73  movably supports the bearing  56  of the charging roller  220 . 
     As shown in  FIG. 13 , in the support structure  6 D supporting the charging roller  220 , substantially as in the support structure  6 A according to exemplary embodiment 1, the protrusion  81  disposed in the pressing member  57  is in point contact with the pressure receiving surface  56   e  of the pressure receiving portion  56   d  of the bearing  56  (see, for example,  FIG. 6B ). In this case, as shown in  FIG. 14A , when the charging roller  220  is not rotating, the bearing  56  is rotatable about the rotating shaft  221 . 
     As shown in  FIG. 14B , also in this support structure  6 D, substantially as in the support structure  6 A according to exemplary embodiment 1, when the charging roller  220  is rotating, the bearing  56  is maintained in a state in which it is rotated in the rotation direction D of the charging roller  220 . 
     &lt;Operational Advantages of Support Structure for Charging Roller&gt; 
     As shown in  FIGS. 13 and 14A , in the support structure  6 D for the charging roller  220 , when the charging roller  220  is not rotating, the bearing  56  is in point contact with the protrusion  81  disposed in the pressing member  57 . 
     In the support structure  6 D in this case, as in the support structure  6 A, the bearing  56  is rotatable about the rotating shaft  221  within the movable space in the holding portion  74   a  of the support  73 . 
     As shown in  FIG. 14B , in the support structure  6 D, when the charging roller  220  is rotating, the rotational force Mr in the rotation direction D of the charging roller  220  acts on the bearing  56 . Therefore, the bearing  56  is held in a state in which it is rotatable in the rotation direction D within the movable space in the holding portion  74   a  of the support  73 . 
     Specifically, as shown in  FIG. 14B , the bearing  56  in this case is rotated in the rotation direction D of the charging roller  220  within the movable space in the holding portion  74   a  of the support  73 . Then part (a corner) of the bearing  56  comes into contact with part of the holding portion  74   a , and the bearing  56  comes to rest, so that the bearing  56  is slightly inclined. 
     Also in the support structure  6 D, as in the support structure  6 A, during rotation of the charging roller  220 , the sliding friction between the bearing  56  and the rotating shaft  221  may change instantaneously, and the rotational force Mr may increase or decrease. For example, the rotational force Mr and the rotational drag force Mb may become substantially equal to each other (Mr≅Mb). 
     However, in the support structure  6 D, because of the same reason as in the support structure  6 A, the rotational drag force Mb is unlikely to increase to a level comparable to the rotational force Mr, and the relation between the rotational force Mr and the rotational drag force Mb is easily maintained such that the rotational force Mr is larger than the rotational drag force Mb (Mr&gt;Mb). 
     Also in this support structure  6 D, during rotation of the charging roller  220 , the bearing  56  is easily maintained in a state in which it is rotated in the rotation direction D of the charging roller  220  within the holding portion  74   a  of the support  73 . In this case, the bearing  56  is prevented from rotating in the reverse rotation direction opposite to the rotation direction C beyond the position at which the bearing  56  is in the rotatable state when the charging roller  220  is not rotating and from rotating back and forth repeatedly around the above position. 
     Therefore, also in the support structure  6 D, as in the support structure  6 A, generation of noise and vibration caused by repeated rotation of the bearing  56  within the movable space in the support  73  can be prevented or reduced. 
     In the support structure  6 D, the generation of noise and vibration during rotation of the charging roller  220  is prevented or reduced. Therefore, in the charging device  22  formed using the support structure  6 D, charging can be performed desirably without generation of noise and vibration. 
     OTHER EXEMPLARY EMBODIMENTS 
     In the structural examples shown in exemplary embodiments 1 to 3, one of the support structures  6 A to  6 C is used as the structure for supporting the driven roller  362  (the rotary member  5 B) of the pair of first output rollers  36 . However, any of them may be used as a structure for supporting the driving roller  361  (the rotary member  5 A) of the pair of first output rollers  36 . 
     In the pair of first output rollers  36 , the driving roller  361  may be replaced with an elastic roller having the function of correcting curl of a recording paper sheet  9 . The elastic roller is, for example, a continuous single roller such as the driven roller  362 , and an elastic body is used as its roller body. 
     Each of the support structures  6 A to  6 C exemplified in exemplary embodiments 1 to 3 can be used for a transport device including a pair of transport rollers (rotary members) that are in pressure contact with each other and are rotated and transport a recording paper sheet  9  held therebetween. Specifically, each of the support structures  6 A to  6 C can be used as a support structure for at least one of the pair of transport rollers. 
     Each of the support structure  6 A to  6 C exemplified in exemplary embodiments 1 to 3 can be used as the support structure  6 D for the charging roller  220  in the charging device  22  of the image forming unit  2  exemplified in exemplary embodiment 4, but this is not a limitation. Each of the support structures  6 A to  6 C may be used as the support structure for a different rotary member. Examples of such a rotary member include a transfer roller and fixing roller. 
     Each of the support structures  6 A to  6 C may be used as the support structure for a pressing roller pressed against a portion of an endless belt that is not supported by a support roller. In this case, a rotary member in contact with the pressing roller is a portion of the rotating belt that is not supported by the support roller. 
     Moreover, an image forming apparatus including the rotary member using one of the support structures  6 A to  6 D and the transport device  7  or the charging device  22  is not limited to the apparatus forming a monochrome image using a single-color toner as exemplified in exemplary embodiments 1 to 4. Image forming apparatuses of different types may be used. 
     Examples of the image forming apparatuses of different types include: an image forming apparatus that forms a multicolor image using a combination of plural color toners; and an image forming apparatus that forms an image by jetting ink droplets. 
     The rotary member and the transport device  7  that use any of the support structures  6 A to  6 C may be a rotary member and a transport device of an apparatus other than the image forming apparatus. 
     The foregoing description of the exemplary embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.