Abstract:
An image drum cartridge includes supporting walls, on which a photoconductive drum rotates, a position selector, a developing roller that rotates relative to the position selector, a developing blade that forms a thin layer of toner on the developing roller, and a slideable member that urges the developing blade against the developing roller. The position selector is mounted on the supporting walls and movable between first and second positions. The position selector causes the developing roller to move to an operative position where a nip is formed between the photoconductive drum and the developing roller. The position selector causes the developing roller to move to an inoperative position where no nip is formed between the photoconductive drum and the developing roller. The developing roller has a first rotational axis and the position selector has a second rotational axis away from the first rotational axis.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention generally relates to an image drum cartridge and a developing unit. 
   2. Description of the Related Art 
   A conventional image forming apparatus such as a printer, a facsimile machine, and a copying machine incorporates a photoconductive drum (i.e., image drum). There are provided a charging roller, an exposing unit, a developing roller, a transfer roller, and a cleaning roller in this order around the photoconductive drum. The charging roller charges the surface of the photoconductive drum uniformly. The exposing unit illuminates the charged surface to form an electrostatic latent image on the photoconductive drum. The developing roller applies toner to the electrostatic latent image to develop the electrostatic latent image into a toner image. The transfer roller transfers the toner image onto a recording medium. The recording medium having the toner image thereon passes through a fixing unit where the toner image is fused into a permanent image. 
   Structural elements such as the photoconductive drum, charging roller, developing roller, and cleaning roller have relatively short lives. Additionally, toner is a consumable item. Thus, a recent trend is that these structural elements including a toner cartridge are integrally assembled into a unitary construction, i.e., an image drum cartridge, so that the whole assembly can be quickly replaced for a new, unused one. 
     FIG. 25  illustrates the positional relationship between a photoconductive drum  23  and a developing roller  24  of a conventional art. 
   The rotational axes of the photoconductive drum  23  and the developing roller  24  are spaced apart by a predetermined distance in such a way that the developing roller  24  is in pressure contact with the photoconductive drum  23  to create a nip D between them. 
   With the conventional image forming apparatus, the nip D is present between the photoconductive drum  23  the developing roller  24  even when they are at rest. The presence of the nip D at all times causes a mark of the nip D to be left on the photoconductive drum  23  or causes the surface of the developing roller  24  to deform. Thus, when a print operation is performed after a long time storage of the apparatus, lines appear in a printed image, the lines extending in a direction in which the nip D extends. 
   SUMMARY OF THE INVENTION 
   The present invention solves the aforementioned problems of the conventional image forming apparatus. An object of the invention is to provide an image drum cartridge and developing unit where lines in the direction of a nip are eliminated and print quality is maintained. 
   An image drum cartridge includes a supporting member, an image drum, a bearing, and a rotative body. The image drum is rotatably supported on the supporting member. The bearing is mounted on the supporting member. The bearing is rotatable about a first rotational axis (sh2) relative to the supporting member and movable between a first position and a second position. The rotative body is rotatable about a second rotational axis (sh1) away from the first rotational axis (sh2). When the bearing rotates to the first position, the bearing causes the rotative body to move to an operative position where a nip is formed between the image drum and the rotative body. When the bearing rotates to the second position, the bearing causes the rotative body to move to an inoperative position where no nip is formed between the image drum and the rotative body. 
   The image drum cartridge further includes an operating member for operating the bearing, so that the bearing moves between the first position and the second position. 
   The operating member is detachably attached to the bearing. 
   When the operating member is attached to the image drum cartridge, the operating member causes the bearing to move to the second position. When the operating member is detached from the image drum cartridge, the operating member causes the bearing to move to the first position. 
   The image drum cartridge further includes a positioning member for selectively positioning the bearing at the first position and the second position. 
   A developing unit includes a bearing and a developing roller. The bearing is rotatable about a first rotational axis (sh2) relative to the supporting member and movable between a first position and a second position. The developing roller is rotatable about a second rotational axis (sh1) away from the first rotational axis (sh2). When the bearing rotates to the first position, the bearing causes the developing roller to move to an operative position. When the bearing rotates to the second position, the bearing causes the developing roller to move to an inoperative position. 
   The developing unit further includes a developing blade that is in contact with the developing roller when the developing roller is at the operative position. When the bearing moves from the first position to the second position, the developing roller moves in such a direction as to be away from the developing blade. 
   An image drum cartridge includes an image drum, a position-selecting member, and a developing roller. The position-selecting member is movable between a first position and a second position relative to the image drum. When the position-selecting member moves from the first position to the second position, the developing roller moves in such a direction as to be away from a developing blade. When the position-selecting member moves to the first position, the position-selecting member causes the developing roller to move to an operative position where the developing roller is out of engagement with the image drum and the developing blade. When the position-selecting member moves to the second position, the position-selecting member causes the developing roller to move to an inoperative position where the developing roller is in engagement with the image drum and the developing blade. When the developing roller is at the operative position, the developing roller rotating in contact with the developing blade. 
   The image drum cartridge further includes an operating member for operating the position-selecting member so that the position-selecting member moves between the first position and the second position. 
   The operating member is detachably attached to the position-selecting member. 
   When the operating member is pushed into the image drum cartridge, the operating member causes the position-selecting member to move to the second position. When the operating member is pulled out of the image drum cartridge, the operating member causes the position-selecting member to move to the first position. 
   The image drum cartridge further includes a supporting member on which the image drum is rotatably supported. The developing roller is rotatable about a first rotational axis (sh1) away from a second rotational axis (sh2). The position-selecting member is a bearing rotatable about a second rotational axis (sh2) relative to the supporting member. 
   The image drum cartridge further includes a positioning member for selectively positioning the bearing at the first position and the second position. 
   An image drum cartridge includes an image drum, a position-selecting member, a position-selecting member, an operating member, and a rotative body. The image drum is rotatably supported on a supporting member. The position-selecting member is mounted on the supporting member. The position-selecting member is movable between a first position and a second position relative to the supporting member. The operating member is attached to the image drum cartridge to operate the position-selecting member so that the position-selecting member moves between the first position and the second position. The operating member is detached from the image drum cartridge after operating the position selecting member. The rotative body is rotatable relative to the position-selecting member. When the position-selecting member moves to the first position, the position-selecting member causes the rotative body to move to an operative position where a nip is formed between the image drum and the rotative body. When the position-selecting member moves to the second position, the position-selecting member causes the rotative body to move to an inoperative position where no nip is formed between the image drum and the rotative body. 
   When the operating member is attached to the image drum cartridge, the operating member causes the position-selecting member to move to the second position (inoperative position). When the operating member is detached from the image drum cartridge, the operating member causes the position-selecting member to move to the first position (operative position). 
   An image drum cartridge includes a developing roller, a developing blade, and a slidable member. The developing blade has a first end portion at which the developing blade is fixedly supported and a second end portion at which the developing blade is movable to engage the developing roller. The slidable member slidably moves between an operative position and a non-operative position. When the slidable member moves to the operative position, the slidable member urges the second end of the developing blade against the developing roller. When the slidable member moves to the non-operative position, the slidable member does not urge the second end of the developing blade against the developing roller. 
   The slidable member is caused to move between the operative position and the non-operative position by a cam mechanism. 
   The image drum cartridge further includes an operating member that operates the slidable member to slide between the operative position and the non-operative position. 
   The operating member is attached to the image drum cartridge when the operating member operates the slidable member, and can be detached from the image drum cartridge when the operating member does not operate the slidable member. 
   A developing apparatus includes a developing roller, a developing blade, and a slidable member. The developing blade has a first end portion at which the developing blade is fixedly supported and a second end portion at which the developing blade is movable to engage the developing roller. The slidable member slidably moves between an operative position and a non-operative position. When the slidable member moves to the operative position, the slidable member urges the second end of the developing blade against the developing roller. When the slidable member moves to the non-operative position, the slidable member does not urge the second end of the developing blade against the developing roller. 
   The slidable member is caused to move between the operative position and the non-operative position by a cam mechanism. 
   The developing apparatus further includes an operating member that operates the slidable member to slide between the operative position and the non-operative position. 
   The operating member is attached to the image drum cartridge when the operating member operates the slidable member and can be detached from the image drum cartridge when the operating member does not operate the slidable member. 
   Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limiting the present invention, and wherein: 
       FIG. 1  is a perspective view of an image drum cartridge according to the first embodiment; 
       FIG. 2  is a perspective view, illustrating a pertinent portion of an image drum cartridge; 
       FIG. 3  is an enlarged view of an image drum cartridge; 
       FIG. 4  is a perspective view, illustrating a bearing according to a first embodiment when the bearing is assembled to the apparatus; 
       FIG. 5  is a front perspective view of the bearing; 
       FIG. 6  is a second perspective view of the bearing; 
       FIG. 7  is a first view of the bearing; 
       FIG. 8  is a rear view of the bearing; 
       FIGS. 9-11  illustrate the operation of the bearing when an operating rod is operated; 
       FIGS. 12A-12C  are enlarged views, illustrating the operation of the bearing; 
       FIG. 13  illustrates the positional relationship between a photoconductive drum and a developing roller according to the first embodiment; 
       FIG. 14  is an exploded perspective view, illustrating a bearing according to a second embodiment; 
       FIG. 15  is a perspective view, illustrating the bearing after it is assembled; 
       FIG. 16  is a perspective view, illustrating a left side wall according to the second embodiment; 
       FIG. 17  is a perspective view, illustrating the bearing; 
       FIGS. 18A and 18B  illustrate a modification to the operating rod; 
       FIG. 19  illustrates a modification of the first embodiment that has a pressing mechanism for pressing a developing blade against the developing roller; 
       FIG. 20  illustrates the detail of the pressing mechanism; 
       FIG. 21  is a perspective view, illustrating the detail of a handle; 
       FIGS. 22A and 22B  are side views, illustrating the pressing member and the developing blade; 
       FIG. 23  is a front view of a cam and the pressing member; 
       FIGS. 24A and 24B  and  FIGS. 24C and 24D  illustrate modifications of the cam; and 
       FIG. 25  illustrates the positional relationship between a photoconductive drum and a developing roller of a conventional art. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   First Embodiment 
   {Construction} 
     FIG. 1  is a perspective view of an image drum cartridge  10  according to a first embodiment. 
   Referring to  FIG. 1 , the image drum cartridge  10  includes a left side wall  11  and a right side wall  12  assembled integrally with a main body  13  between the left and right side walls  11  and  12 . The main body  13  includes a photoconductive drum  23  ( FIG. 2 ) and a charging roller, not shown. A transfer roller, not shown, is provided directly below the image drum cartridge  10 . The charging roller charges the surface of the photoconductive drum  23  uniformly. An exposing unit, (LED head), not shown, illuminates the charged surface of the photoconductive drum  23  to form an electrostatic latent image. A developing roller  24  ( FIG. 2 ) applies toner to the electrostatic latent image to form a toner image. The transfer roller transfers the toner image onto a recording medium. The recording medium having the toner image thereon is advanced to a fixing unit, not shown, where the toner image is fused into a permanent image. 
     FIG. 2  is a perspective view, illustrating a pertinent portion of the image drum cartridge  10 . 
     FIG. 3  is an enlarged view of the image drum cartridge  10  in FIG.  2 . 
   Referring to  FIGS. 2 and 3 , there are provided the left side wall  11 , the right side wall  12 , the photoconductive drum  23 , and the developing roller  24 . The left and right side walls  11  and  12  also have holes  16  ( FIG. 4 ) a predetermined distance away from projections  25  (FIG.  4 ). The holes  16  receive bearings  17  that support the developing roller  24 . 
     FIG. 4  is a perspective view, illustrating a bearing  15  according to a first embodiment when the bearing  15  is assembled to the apparatus. 
   Referring to  FIG. 4 , each of the left and right side walls  11  and  12  is formed with the projection  25  and the hole  16  therein. The projection  25  and hole  16  are spaced apart a predetermined distance. A bearing  15  is rotatably received in each hole  16 . The developing roller  24  is rotatably supported by means of bearings  17  disposed in the bearings  15  in such a way that the developing roller  24  is rotatable relative to the left and right side walls  11  and  12 . The projections  25  project from surfaces of the left and right side walls  11  and  12  that oppose each other. The photoconductive drum  23  is also rotatably supported on the projections  25  by means of bearings. 
   A through-hole  41  is formed in each of the left and right side walls  11  and  12  between the projection  25  and the hole  16 . The through-hole  41  receives an operating rod  43  inserted thereinto. The operating rod  43  is formed with a rack  44  in mesh with a gear  35 . Moving the operating rod  43  vertically allows the bearing  15  to rotate. 
     FIG. 5  is a first perspective view of the bearing. 
     FIG. 6  is a second perspective view of the bearing. Referring to  FIGS. 5 and 6 , the bearing  15  includes a substantially disk-like plate  29  and first and second cylindrical sleeves  31  and  32  that project from the disk-like plate  29  away from each other. Thus, the disk-like plate  29  closes the first and second cylindrical sleeves  31  and  32  at their one end. The second cylindrical sleeve  32  of the bearing  15  is fitted into the holes  16 , so that the bearing  15  is rotatable with respect to the left and right side walls  11  and  12 . 
     FIG. 7  is a front view of the bearing. 
     FIG. 8  is a rear view of the bearing. 
   Referring to  FIGS. 7 and 8 , a first axis Sh1 and a second axis Sh2 are spaced apart by a predetermined distance, so that the first cylindrical sleeve  31  and the second cylindrical sleeve  32  are eccentric to each other. The disk-like plate  29  and the first cylindrical sleeve  31  form a space in which the bearing  17  is received. The first axis Sh1 serves as a rotational axis about which the developing roller  24  rotates. The second axis Sh2 serves as a rotational axis about which the bearing  15  rotates. 
   The disk-like plate  29  is formed with a through-hole  34  centered at the first axis Sh1. The first cylindrical sleeve  31  has a thick wall  37  that extends around the disk-like plate  29  circumferentially over about 180°. A gear  35  is formed in the outer circumferential surface of the thick wall  37 , extending over about 90° on a circumference centered at the second axis Sh2. The gear  35  has an arcuate flange  36  that is centered at the second axis Sh2 and extends angularly across 90°. The thick wall  37  and the flange  36  have locking recesses  45  and  46  formed therein, respectively, for positioning the bearing  15  at a predetermined rotational position. 
   {Operation of Bearing} 
   The operation of the bearing  15  will be described. 
     FIG. 9  illustrates the bearing  15  when the operating rod  43  is moved to a position P. 
     FIG. 10  illustrates the bearing  15  when the operating rod  43  is moved to a position Q. 
   Referring to  FIGS. 9 and 10 , the bearing  15  is in mesh with the rack  44  of the operating rod  43 . When the operating rod  43  is moved vertically, the bearing  15  is rotated so that the bearing  15  can be positioned at a predetermined position. For example, moving the operating rod  43  in a direction shown by a white arrow in  FIG. 10 , the gear  35  rotates in a direction shown by an arrow to move to a position in FIG.  10 . 
     FIG. 11  illustrates the positional relationship between the photoconductive drum  23 , bearing  15 , and locking pins  51  and  52 . 
     FIG. 12A  is an enlarged view of FIG.  11 . 
     FIGS. 12B and 12C  are enlarged views, illustrating the positional relationship between the bearing  15  and the photoconductive drum  23 . 
   The second cylindrical sleeve  32  is centered at the second axis Sh2. When the second cylindrical sleeves  32  are fitted into the holes  16  formed in the left side wall  11  and right side wall  12 , respectively, the bearings  15  are supported by the left side wall  11  and right side wall  12 . Therefore, each bearing  15  rotates about the second axis Sh2. 
   Referring to  FIG. 11 , the left and right side walls  11  and  12  have locking pins  51  and  52  projecting therefrom. When the operating rod  43  in  FIG. 9  is moved to a position P (FIG.  10 ), the bearing  15  rotates to a first adjustment position where the locking pin  51  drops in the locking recess  46  as shown in  FIGS. 12A and 12B . 
   When the operating rod  43  is moved to a position Q (FIG.  9 ), the bearing  15  rotates to a second adjustment position where the locking pin  52  drops in the locking recess  45  as shown in  FIGS. 12A and 12C . 
   As shown in  FIG. 12B , when the bearing  15  rotates to the position P, the first axis Sh1 moves to a first axis position A. When the first axis Sh1 is at the first axis position A, the developing roller  24  is at its operative position, so that a nip having a size of Ba is created between the photoconductive drum  23  and the developing roller  24 . When the bearing  15  rotates to the position Q, the first axis Sh1 moves to a second axis position B. 
   As shown in  FIG. 12C , when the bearing  15  rotates to the position Q, the first axis Sh1 moves to the second axis position B. When the first axis Sh1 is at the second axis position B, the developing roller  24  is at its non-operative position where a gap having a size of Bb is formed between the photoconductive drum  23  and the developing roller  24 . This operation brings the developing roller  24  to its non-operative position. 
     FIGS. 18A and 18B  illustrate a modification to the operating rod  43 . 
   An operating rod  81  is made of plastics and has a ring shaped finger hold  81   a  formed at one end portion, a rack  81   c  formed at another end portion, and a flexible straight portion between the finger hold  81   a  and the rack  81   c . The operating rod  81  also has a guide  81   b  formed near the rack  81   c , which is slidingly guided in a narrow groove formed in an inner surface of the through-hole  41  when the operating rod  81  is inserted into the groove. 
   Referring to  FIG. 18A , when the image drum cartridge  10  is installed in the office, the operator can pull the finger hold  81   a  with his finger in a direction shown by arrow E. Thus, the rack  81   c  moves out of meshing engagement with the gear  35  to cause the gear  35  to rotate in a direction shown by arrow F. Thus, the developing roller  24  moves into pressing engagement with the photoconductive drum  23 . 
   Referring to  FIG. 18B , when the operating rod  81  is inserted into the through-hole  41 , the operator pushes a portion  81   d  into the through-hole  41  in a direction shown by arrow G. Thus, the rack  81   c  moves into meshing engagement with the gear  35  to cause the gear  35  to rotate in a direction shown by arrow H. This causes the developing roller  24  to move out of engagement with the photoconductive drum  23 . 
     FIG. 13  illustrates the positional relationship between the photoconductive drum  23  and the developing roller  24  according to the first embodiment. 
   Referring to  FIG. 13 , a developing unit includes the developing roller  24 , a toner supplying roller  71 , and a developing blade  72 . The developing roller  24  is a resilient body made of a synthetic rubber such as silicone and urethane and is in pressure contact with the photoconductive drum  23  to form a nip between the developing roller  24  and the photoconductive drum  23 . The photoconductive drum  23  is a hollow cylindrical drum made of an aluminum alloy with a layer of a photoconductive material coated thereon. The toner-supplying roller  71  takes the form of a sponge roller and rotates in pressure contact with the developing roller  24  to supply toner, not shown, to the developing roller  24 . The developing blade  72  is made of a thin metal plate such as a stainless plate bent into an L-shape. When the developing blade  72  is urged against the developing roller  24 , the developing blade  72  is resiliently deformed to press the surface of the developing roller  24 , thereby forming a thin layer of toner on the developing roller  24 . A seal sponge  73  is disposed at each longitudinal end portion of the developing roller  24  so as to prevent the toner from spilling from the developing unit. 
   When the image drum cartridge  10  ( FIG. 1 ) is not in operation, the developing roller  24  is moved to its non-operative position shown in a solid line in FIG.  13 . When the image drum cartridge  10  is attached into the image forming apparatus, the developing roller  24  is moved to its operative position shown in a dotted line in FIG.  13 . 
   When the first axis Sh1 moves in a direction parallel to a line tangent to the photoconductive drum  23 , i.e., from the first axis position A to the second axis position B, the developing roller  24  is moved from the operative position (dotted line) to the non-operative position (solid line). In other words, as the bearing  15  moves from the position P (solid line in  FIG. 12B ) to the position Q (dot-dot-dash line in FIG.  12 C), the developing roller  24  moves away from the photoconductive drum  23  and developing blade  72 . Thus, the photoconductive drum  23  and the developing roller  24  are completely separated from each other. This operation prevents the surface of the developing roller  24  from remaining deformed by the photoconductive drum  23  and developing blade  72  when no printing is performed. 
   When the first axis Sh1 moves in a direction parallel to a line tangent to the photoconductive drum  23 , i.e., from the second axis position B to the first axis position A, the developing roller  24  is moved from the non-operative position (solid line) to the operative position (dotted line). In other words, as the bearing  15  moves from the position Q to the position P, the developing roller  24  approaches the toner-supplying roller  71  so that the developing roller  24  presses the toner supplying roller  71  with a larger force. The toner-supplying roller  71  is made of a sponge material having a very low hardness. Therefore, the surface of the developing roller  24  is not deformed as the pressing force increases. 
   As described above, the developing roller  24  can be positioned selectively at the non-operative position and at the operative position. Therefore, when the developing roller  24  is at rest, no nip is formed between the photoconductive drum  23  and developing roller  24 . This prevents the surface of the developing roller  24  from deforming or the mark of a nip from being left on the photoconductive drum  23  over time. The elimination of the mark of the nip and the deformation of the developing roller  24  prevents lines from resulting in printed images when printing is performed after a long-time storage of the apparatus. Thus, good print quality can be maintained. 
     FIG. 19  illustrates a modification of the first embodiment that has a pressing member  77  for pressing a developing blade  79  against the developing roller  24 . 
     FIG. 20  illustrates the detail of the pressing member  77 . 
     FIG. 21  is a perspective view, illustrating the detail of a handle  75 . 
   Referring to  FIG. 19 , an image drum cartridge  10  has a toner cartridge  74  attached to it. Referring to  FIG. 20 , a developing blade  79  is fixedly supported by a bracket  80  at a few locations. Guides  78  have slits  78   a  formed therein in which the pressing member  77  is slidably guided in directions shown by arrows L and M. The pressing member  77  is urged in the direction shown by arrow L by an urging means, not shown. The handle  75  has an engagement portion  75   a  that fits into an engagement hole  76   a  of a cam  76 . Operating the handle  75  in directions shown by arrow K and I causes the cam  76  to slide in the L direction and M direction. The handle  75  can be detached from the cam  76  after operating the cam  76 . 
     FIGS. 22A and 22B  illustrate the positional relation between the pressing member  77  and the developing blade  79 . 
   When the handle  75  is turned in a direction shown by arrow K by a 90° angle, the cam  76  rotates by a 90° angle in the direction shown by arrow K so that the pressing member  77  moves in the M direction. When the handle  75  is turned in a direction shown by arrow I by a 90° angle from a position shown in  FIG. 20 , the cam  76  rotates by a 90° angle in the direction shown by arrow I so that the pressing member  77  moves in the L direction. 
     FIGS. 22A and 22B  are side views, illustrating pressing member  77  and the developing blade  79 . 
   When the pressing member  77  moves in the L direction as shown in  FIG. 22A , the pressing member  77  does not push the developing blade  79  so that the developing blade  79  does not deform to press the developing roller  24 . 
   When the pressing member  77  moves in the M direction as shown in  FIG. 22B , the pressing member  77  pushes the developing blade  79  so that the developing blade  79  resiliently deforms to press the developing roller  24 . 
     FIG. 23  is a front view of the cam  76  and the pressing member  77 . 
   Referring to  FIG. 23 , at least two cams  76  are provided. When the cams  76  are rotated by a 90° angle in the K direction, the cam  76  rotates in the K direction from the solid line position to the dotted line position, the pressing member  77  moves in the M direction to push the developing roller  24 . When the cams  76  are rotated by a 90° angle in the opposite direction, the cam  76  rotates back in the opposite direction from the dotted line position to the solid line position, so that the pressing member  77  moves back in the L direction. 
     FIGS. 24A and 24B  and  FIGS. 24C and 24D  illustrate modifications of the cam  76 . 
     FIGS. 24A and 24B  illustrate a cam  76 A having flat portions that contact the pressing member  77 . When the cam  76 A in  FIG. 24B  is rotated by 90° in the K direction, the cam  76 A stands on the pressing member  77  in a stable manner as shown in FIG.  24 A. 
   Referring to  FIGS. 24C and 24D , a cam  76 B has four projections so that the cam  76 B can stand on the pressing member  77  in a stable manner in  FIGS. 24C and 24D . 
   Second Embodiment 
     FIG. 14  is an exploded perspective view, illustrating a bearing  55  according to a second embodiment. 
     FIG. 15  is a perspective view, illustrating the bearing  55  after it is assembled. 
     FIG. 16  is a perspective view, illustrating a left side wall  42  according to the second embodiment. 
   Referring to  FIGS. 14-16 , the bearing  55  has a disk-like plate, not shown, a cylindrical space, a cylindrical receiving sleeve  61 , and a cylindrical control  62 . The cylindrical space is centered at a third axis Sh3. The cylindrical sleeve  61  is centered at a fourth axis Sh4 and projects forwardly from the disk-like plate. The cylindrical control  62  is also centered at the fourth axis Sh4 and projects rearwardly from the disk-like plate. The third and fourth axes Sh3 and Sh4 are defined a predetermined distance away from each other, so that the cylindrical control  62  is eccentric to the cylindrical space. The cylindrical space receives the bearing  54  therein. The developing roller  24  ( FIG. 13 ) rotates about the third axis Sh3. In other words, the third axis Sh3 serves as an axis about which the developing roller  24  rotates while the fourth axis Sh4 serves as an axis about which the bearing  55  rotates. 
   The left side wall  42  and the right side wall (not shown) each have a hole  66  formed therein in which the bearing  55  is rotatably received. The cylindrical controls  62  extend through the holes  66  to the outer side of the left side wall  42  and the right side wall, respectively. 
     FIG. 17  is a perspective view, illustrating a lever  67 . 
   As shown in  FIG. 17 , the lever  67  can be used in place of the cylindrical control  62 , in which case a shaft  62   a  in line with the fourth axis Sh4 projects through the hole  66  from the left side wall  42  and the lever  67  is attached to the shaft  62   a.    
   The use of the lever  67  facilitates adjustment of rotation of the bearing  55 . 
   The bearing  55  can be rotated by a variety of means. A wire may be wound on the bearing  55  and pulled to rotate the bearing  55 . Alternatively, a friction member may be attached to the bearing  55  and moved straight or rotated, thereby causing the bearing  55  to rotate. 
   The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art intended to be included within the scope of the following claims.