Patent Publication Number: US-8532527-B2

Title: 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. 2009-209365 filed Sep. 10, 2009. 
     BACKGROUND 
     (i) Technical Field 
     The present invention relates to an image-forming apparatus. 
     (ii) Related Art 
     An image-forming unit (image-forming member assembly) that is detachably attached to an apparatus body of an image-forming apparatus, such as a printer, is known. The image-forming unit includes a photosensitive drum (an example of a photosensitive member) and a developing roller (an example of a developing unit). The image-forming unit is used while being attached to the apparatus body of the image-forming apparatus. 
     SUMMARY 
     According to an aspect of the invention, there is provided an image-forming apparatus including an image-forming member assembly including a photosensitive member that has a shaft and allows an electrostatic latent image to be formed thereon, a developing unit that supplies the photosensitive member with a developer and develops the electrostatic latent image, and a rotating unit that has a rotating shaft, receives a driving force, and rotates the developing unit; a driving unit that drives the rotating unit; a positioning member having a positioning hole in which the shaft of the photosensitive member is rotatably supported and positioned at two points; and a support member having a support hole that has a guide side to guide the movement of the rotating shaft and supports the rotating shaft of the rotating unit in a direction in which the rotating shaft is moved toward and away from the positioning hole. When a force received by the rotating shaft while the driving unit drives the rotating unit is divided into a first component force along the guide side and a second component force orthogonal to the guide side, the first component force has a direction in which a contact force of the shaft of the photosensitive member against an edge of the positioning hole is increased. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiment(s) of the present invention will be described in detail based on the following figures, wherein: 
         FIG. 1  is a perspective view of the appearance of a printer serving as an image-forming apparatus according to an exemplary embodiment of the present invention; 
         FIG. 2  is an explanatory view of the inner configuration of the printer in  FIG. 1 ; 
         FIG. 3  illustrates the inner configuration of the printer in  FIG. 1  when an outer panel and an inner panel of the printer are open; 
         FIG. 4  is a perspective view illustrating the relationship between a photosensitive drum and the inner panel of the printer in  FIG. 1 ; 
         FIG. 5  is a perspective view showing an image-forming unit and a bracket of the printer in  FIG. 1 ; 
         FIG. 6  illustrates the relationship between the image-forming unit and the bracket; 
         FIG. 7  explains the force that a rotating shaft of an idler gear receives at a support hole; 
         FIG. 8  explains the force that the rotating shaft of the idler gear receives at the support hole; 
         FIG. 9  explains the force that the rotating shaft of the idler gear receives at the support hole; 
         FIG. 10  explains the force that the rotating shaft of the idler gear receives at the support hole; 
         FIG. 11  is a side view showing the image-forming unit of the printer in  FIG. 1 ; and 
         FIG. 12  explains the relationship between tangents of the support hole respectively passing through two points at which a shaft of the photosensitive drum contacts a positioning hole and a guide side of the support hole. 
     
    
    
     DETAILED DESCRIPTION 
     An exemplary embodiment as an example of the present invention will be described below in detail with reference to the drawings. In the drawings explaining the exemplary embodiment, like reference numerals basically refer like components and repeated explanation will be omitted. 
     A printer PR 1  as an image-forming apparatus according to an exemplary embodiment of the present invention will be described. 
     In  FIGS. 1 and 2 , the printer PR 1  includes a storage section that stores printing sheets serving as recording media, a conveying mechanism for the printing sheets, and an image-forming unit that forms images on the printing sheets. A printing operation is executed by using toners of four colors including yellow (Y), magenta (M), cyan (C), and black (K) in accordance with image data that is sent from, for example, a personal computer or a scanner. 
     The printer PR 1  includes four image-forming units SY, SM, SC, and SK (examples of image-forming member assemblies) that respectively form toner images of the colors including yellow (Y), magenta (M), cyan (C), and black (K). The image-forming units SY, SM, SC, and SK are individually attachable and detachable. 
     The four image-forming units SY, SM, SC, and SK have similar configurations to one another except for the colors of images formed thereby. The image-forming units SY, SM, SC, and SK include photosensitive drums  10  ( 10 Y,  10 M,  10 C,  10 K) (examples of photosensitive members) that are rotated at a predetermined speed; charging rollers  11  ( 11 Y,  11 M,  11 C,  11 K) that electrically charge the surfaces of the photosensitive drums  10 Y,  10 M,  10 C, and  10 K; developing devices  12  ( 12 Y,  12 M,  12 C,  12 K) that develop electrostatic latent images formed on the photosensitive drums  10 Y,  10 M,  10 C, and  10 K with toners (examples of developers) of corresponding colors; and cleaning devices  13  ( 13 Y,  13 M,  13 C,  13 K) that clean off toners remaining on the photosensitive drums  10 Y,  10 M,  10 C, and  10 K after transferring images. 
     Toner cartridges  8 Y,  8 M,  8 C, and  8 K are arranged above the image-forming units SY, SM, SC, and SK so as to be detachable and attachable. The toner cartridges  8 Y,  8 M,  8 C, and  8 K contain the toners that are used by the developing devices  12 Y,  12 M,  12 C, and  12 K for the development of the electrostatic latent images formed on the photosensitive drums  10 Y,  10 M,  10 C, and  10 K. 
     The developing devices  12 Y,  12 M,  12 C, and  12 K include developing rollers  12 - 2  ( 12 Y- 2 ,  12 M- 2 ,  12 C- 2 ,  12 K- 2 ) (examples of developing units) that supply the photosensitive drums  10 Y,  10 M,  10 C, and  10 K with the toners. The toners each including one component or two components and contained in the toner cartridges  8 Y,  8 M,  8 C, and  8 K are supplied to the developing rollers  12 Y- 2 ,  12 M- 2 ,  12 C- 2 , and  12 K- 2  while the toners are stirred. The toners supplied to the developing rollers  12 Y- 2 ,  12 M- 2 ,  12 C- 2 , and  12 K- 2  are conveyed to development regions facing the photosensitive drums  10 Y,  10 M,  10 C, and  10 K while the layer thicknesses of the toners are regulated. The toners are used to develop the electrostatic latent images formed on the surfaces of the photosensitive drums  10 Y,  10 M,  10 C, and  10 K. 
     Accordingly, the developing devices  12 Y,  12 M,  12 C, and  12 K develop the electrostatic latent images formed on the photosensitive drums  10 Y,  10 M,  10 C, and  10 K as toner images of the colors including yellow (Y), magenta (M), cyan (C), and black (K). 
     An exposure device  14  is arranged below the image-forming units SY, SM, SC, and SK. The exposure device  14  exposes the electrically charged surfaces of the photosensitive drums  10 Y,  10 M,  10 C, and  10 K to light in accordance with images of corresponding colors, and forms electrostatic latent images. 
     A unitized intermediate transfer belt  15  is provided between the image-forming units SY, SM, SC, and SK and the toner cartridges  8 Y,  8 M,  8 C, and  8 K. The toner images formed on the photosensitive drums  10 Y,  10 M,  10 C, and  10 K are transferred (an example of primary transferring) onto the intermediate transfer belt  15 . The intermediate transfer belt  15  is in contact with the photosensitive drums  10 Y,  10 M,  10 C, and  10 K. The intermediate transfer belt  15  is detachably attached to a casing  1 , and supported by three rollers  16   a ,  16   b , and  16   c  (one of the rollers is a driving roller, and the other rollers are driven rollers). The rollers  16   a ,  16   b , and  16   c  rotate the intermediate transfer belt  15  in a direction indicated by an arrow in  FIG. 2 . The toner images formed on the photosensitive drums  10 Y,  10 M,  10 C, and  10 K are superposed on top of one another and transferred onto the intermediate transfer belt  15 . Thus, a full-color toner image is formed on the intermediate transfer belt  15 . 
     A cleaner  22  is arranged at a position at which the cleaner  22  faces the roller  16   c  with the intermediate transfer belt  15  interposed therebetween. The cleaner  22  removes the toners remaining on the intermediate transfer belt  15 . 
     Primary transfer rollers  16  ( 16 Y,  16 M,  16 C,  16 K) are arranged such that the primary transfer rollers  16 Y,  16 M,  16 C, and  16 K and the photosensitive drums  10 Y,  10 M,  10 C, and  10 K nip the intermediate transfer belt  15  therebetween. The primary transfer rollers  16 Y,  16 M,  16 C, and  16 K transfer the toner images formed on the photosensitive drums  10 Y,  10 M,  10 C, and  10 K onto the intermediate transfer belt  15 . The primary transfer rollers  16 Y,  16 M,  16 C, and  16 K are assembled with the unitized intermediate transfer belt  15 , and hence are attached and detached together with the intermediate transfer belt  15 . 
     A secondary transfer roller  17  is provided at a position at which the secondary transfer roller  17  faces the roller  16   a  such that the secondary transfer roller  17  and the roller  16   a  define a nip portion N. The intermediate transfer belt  15  is nipped at the nip portion N. The secondary transfer roller  17  transfers the full-color toner image, which has been transferred on the intermediate transfer belt  15 , onto a sheet P serving as a recording medium. 
     A feed cassette  18  is arranged in a lower section of the casing  1 . Sheets P are stacked in the feed cassette  18 . A pickup roller  19  picks up the sheets P one by one from the feed cassette  18 . A picked-up sheet P is conveyed through a conveyance path R that extends from the feed cassette  18 , through the nip portion N and a fixing device  20 , to an ejection tray  24  that is formed above the casing  1 . When the sheet P is conveyed to the nip portion N at a certain timing by a pair of registration rollers  23 , the full-color toner image on the intermediate transfer belt  15  is transferred onto the sheet P by the secondary transfer roller  17 . The transferred toner image is fixed by the fixing device  20 . Then, the sheet P is ejected onto the ejection tray  24 . 
     A manual feed tray  21  is provided in a side portion of the casing  1 . Sheets P are also conveyed through the conveyance path R from the manual feed tray  21 . 
     A control unit is disposed in the casing  1 . The control unit is, for example, an image processing device that performs image processing on image data. 
     The image processing device successively outputs image data of the respective colors including yellow (Y), magenta (M), cyan (C), and black (K) to the exposure device  14 . The exposure device  14  emits four laser beams in accordance with the image data, scans the photosensitive drums  10 Y,  10 M,  10 C, and  10 K, and exposes the photosensitive drums  10 Y,  10 M,  10 C, and  10 K to the beams. Hence the electrostatic latent images are formed. 
     Referring to  FIG. 1 , an outer panel  2  is provided in a side surface (a front surface in  FIG. 1 ) of the casing  1 . The outer panel  2  is manually opened and closed. 
     When the outer panel  2  is open, the inner portion of the casing  1  is exposed to the outside. Referring to FIGS.  1  and  3 , the unitized intermediate transfer belt  15  and the four image-forming units SY, SM, SC, and SK are mounted in the inner portion of the casing  1  so as to be attachable and detachable. In this exemplary embodiment, the mounting positions of the four image-forming units SY, SM, SC, and SK in the casing  1  are slightly different from one another in the vertical direction. The image-forming unit SY is mounted at the highest position. The mounting positions of the image-forming units SM, SC, and SK are progressively lower in that order. 
     Referring to  FIG. 1 , the intermediate transfer belt  15 , and the image-forming units SY, SM, SC, and SK are covered with an inner panel  3 . The inner panel  3  is attached to an inner wall  5  that has an opening  5   a , through which the intermediate transfer belt  15  and the image-forming units SY, SM, SC, and SK are attached and detached. The inner panel  3  is opened and closed while a lower portion thereof serves as a support point. The inner panel  3  closes the opening  5   a  when the inner panel  3  is closed. 
     Referring to  FIG. 1 , two release levers  4  are provided on the inner panel  3 . Each release lever  4  is moved between a position at which the closed inner panel  3  is locked relative to the inner wall  5  and a position at which the closed inner panel  3  is unlocked relative to the inner wall  5 . 
     Referring to  FIG. 4 , the photosensitive drums  10 Y,  10 M,  10 C, and  10 K, the charging rollers  11 Y,  11 M,  11 C, and  11 K, the developing devices  12 Y,  12 M,  12 C, and  12 K, and the primary transfer rollers  16 Y,  16 M,  16 C, and  16 K are arranged such that the longitudinal direction of these components are aligned with the mounting direction of these components. In addition, transmission mechanisms (for example, gears and couplings) that transmit torques to the photosensitive drums  10 Y,  10 M,  10 C, and  10 K, the charging rollers  11 Y,  11 M,  11 C, and  11 K, the developing devices  12 Y,  12 M,  12 C, and  12 K, and the primary transfer rollers  16 Y,  16 M,  16 C, and  16 K are arranged at positions on the forward side in the mounting direction of the image-forming units SY, SM, SC, and SK (that is, the far side of the casing  1 ). In this exemplary embodiment, the photosensitive drums  10 Y,  10 M,  10 C, and  10 K are driven by using the couplings. Thus, the rotating shafts of the photosensitive drums  10 Y,  10 M,  10 C, and  10 K are prevented from being displaced when the photosensitive drums  10 Y,  10 M,  10 C, and  10 K are driven. 
     Idler gears  12 - 1   a  ( 12 Y- 1   a ,  12 M- 1   a ,  12 C- 1   a ,  12 K- 1   a ) (examples of rotating units) are arranged at positions on the backward side in the mounting direction of the image-forming units SY, SM, SC, and SK (that is, the near side of the casing  1 ) (see  FIGS. 5 and 6 ). The idler gears  12 Y- 1   a ,  12 M- 1   a ,  12 C- 1   a ,  12 K- 1   a  transmit driving forces to developing-roller-rotating gears that rotate the developing rollers  12 Y- 1 ,  12 M- 1 ,  12 C- 1 , and  12 K- 1 . 
     Referring to  FIGS. 4 and 5 , the inner panel  3  includes a bracket  30  (an example of a positioning member) having positioning holes  30   a  (examples of positioning holes). The positioning holes  30   a  rotatably support the shafts  10   a  of the photosensitive drums  10 Y,  10 M,  10 C, and  10 K. Each of the positioning holes  30   a  has a V-shaped lower portion to allow the shaft  10   a  to contact the positioning hole  30   a  at two points for positioning. The release levers  4  provided on the inner panel  3  include spring members (not shown). When the release levers  4  are operated to be moved to the positions at which the inner panel  3  is locked to the inner wall  5 , the spring members press the shafts  10   a  of the photosensitive drums  10 Y,  10 M,  10 C, and  10 K against edges of the positioning holes  30   a  in association with the operation. When the release levers  4  are operated, each of the shafts  10   a  of the photosensitive drums  10 Y,  10 M,  10 C, and  10 K is pressed to the corresponding positioning hole  30   a  at the two points for positioning. 
     The shafts  10   a  of the photosensitive drums  10 Y,  10 M,  10 C, and  10 K each include a rotating shaft  10   a - 1  that rotates with the drum body and a bearing  10   a - 2  that rotatably supports the rotating shaft  10   a - 1 . The shaft  10   a - 2  does not rotate but is merely supported by the positioning hole  30   a . The rotating shaft  10   a - 1  supported by the bearing  10   a - 2  rotates. 
     The shafts  10   a  of the photosensitive drums  10  and the idler gears  12 - 1   a  are supported by support frames SY- 1 , SM- 1 , SC- 1 , and SK- 1  that are attached at positions on the backward side in the mounting direction of the image-forming units SY, SM, SC, and SK (see  FIG. 11 ). 
     The lower portions of the positioning holes  30   a  of the photosensitive drums  10 Y,  10 M,  10 C, and  10 K do not have to have V shapes, and the lower portions may have any shapes as long as the photosensitive drums  10 Y,  10 M,  10 C, and  10 K can be positioned. 
     Referring to  FIGS. 5 and 6 , the bracket  30  (an example of a support member) also has support holes  30   b  (examples of support holes) that support rotating shafts  12 - 1   aa  ( 12 Y- 1   aa ,  12 M- 1   aa ,  12 C- 1   aa ,  12 K- 1   aa ) of the idler gears  12 - 1   a  ( 12 Y- 1   a ,  12 M- 1   a ,  12 C- 1   a ,  12 K- 1   a ). 
     The support holes  30   b  are long holes that are elongated toward the positioning holes  30   a . Since the rotating shafts  12 - 1   aa  are supported by the support holes  30   b , the idler gears  12 - 1   a  can be moved toward and away from the positioning holes  30   a.    
     Transmission gears  32  are rotatably attached to a body frame  31 . The transmission gears  32  transmit torques from drive sources (examples of driving units, not shown) to the idler gears  12 - 1   a . The idler gears  12 - 1   a  mesh with the drive sources through the transmission gears  32 . When the drive sources rotate the transmission gears  32 , the torques are transmitted to the idler gears  12 - 1   a  and the idler gears  12 - 1   a  are rotated. The developing rollers  12 - 2  are rotated accordingly, and the developing rollers  12 - 2  supply the photosensitive drums  10  with the toners. 
     Referring to  FIG. 6 , a direction, in which the idler gears  12 - 1   a  are driven by the torques when the idler gears  12 - 1   a  receive the torques from the transmission gears  32 , is a pressure angle acting direction D. In this exemplary embodiment, forces F received by the rotating shafts  12 - 1   aa  at the support holes  30   b  when the idler gears  12 - 1   a  are rotated by forces in the pressure angle acting direction D will be described below. 
     Referring to  FIGS. 7 to 10 , a guide side  30   b - 1  defines a side of each of the support holes  30   b . The guide side  30   b - 1  guides the movement of the corresponding rotating shaft  12 - 1   aa  in the support hole  30   b . When the force F is divided into a first component force F 1  along the guide side  30   b - 1  and a second component force F 2  orthogonal to the guide side  30   b - 1 , in this exemplary embodiment, the direction of the first component force F 1  is a direction in which the contact force of the shaft  10   a  of the photosensitive drum  10  against the edge of the positioning hole  30   a  is increased, as shown in  FIGS. 7 and 8 . 
     When the direction of the first component F 1  is the direction in which the contact force of the shaft  10   a  of the photosensitive drum  10  against the edge of the positioning hole  30   a  is increased, a force f acts in a direction in which the rotating shaft  12 - 1   aa  of the idler gear  12 - 1   a  is moved away from the positioning hole  30   a  during the operation of the apparatus as shown in  FIGS. 7 and 8 . When the idler gear  12 - 1   a  is rotated, a force in the direction in which the image-forming unit SY, SM, SC, or SK is moved away from the positioning hole  30   a  is not exerted on the image-forming unit SY, SM, SC, or SK, to which the idler gear  12 - 1   a  is attached. 
     In contrast, referring to  FIGS. 9 and 10 , if the direction of the first component F 1  is a direction in which the contact force of the shaft  10   a  of the photosensitive drum  10  against the edge of the positioning hole  30   a  is decreased, for example, although a force F is exerted toward the lower side as shown in  FIG. 9 , a force f toward the positioning hole  30   a  acts on the rotating shaft  12 - 1   aa  of the idler gear  12 - 1   a  during the operation of the apparatus. Then, when the idler gear  12 - 1   a  is rotated, a force in the direction in which the image-forming unit SY, SM, SC, or SK is moved away from the positioning hole  30   a  is exerted on the image-forming unit SY, SM, SC, or SK, and hence the shaft  10   a  of the photosensitive drum  10  may be lifted from the positioning hole  30   a.    
     In this exemplary embodiment, as described above, the force in the direction in which the image-forming unit SY, SM, SC, or SK is moved away from the positioning hole  30   a  is not exerted on the image-forming unit SY, SM, SC, or SK. The shaft  10   a  of the photosensitive drum  10  is not lifted from the positioning hole  30   a  and is reliably positioned with respect to the positioning hole  30   a . Accordingly, color misregistration and banding failure due to variation in the position of the photosensitive drum  10  can be prevented. 
     Since a force that lifts the shaft  10   a  of the photosensitive drum  10  is not exerted, the spring force that causes the shaft  10   a  of the photosensitive drum  10  to be pressed against the edge of the positioning hole  30   a  is decreased. The image-forming unit SY, SM, SC, or SK can be detached from the apparatus body by a small operating force. 
     Referring to  FIG. 11 , the center of gravity G of the image-forming unit SY, SM, SC, or SK may be located within a rectangular or square region, or a substantially rectangular or square region defined by a segment L 1  serving as a diagonal that connects the shaft  10   a  of the photosensitive drum  10  and the rotating shaft  12 - 1   aa  of the idler gear  12 - 1   a , and by horizontal lines L 2  passing through both ends of the segment L 1 . Since the center of gravity G is located within that region, a force in the direction in which the image-forming unit SY, SM, SC, or SK is moved away from the positioning hole  30   a  during the operation of the apparatus is further reliably prevented from being exerted on the image-forming unit SY, SM, SC, or SK. 
     The exemplary embodiment of the invention made by the inventor has been specifically described above, however, all components and techniques of the exemplary embodiment disclosed in the specification are merely examples, and hence it is to be noted that the invention is not limited to the disclosed components and techniques. In particular, the technical scope of the present invention should not be interpreted in a limited manner on the basis of the explanation in the exemplary embodiment, but should be interpreted on the basis of the scope of the claims. The present invention includes all modifications without departing from techniques equivalent to the techniques described in the scope of the claims and the concept of the scope of the claims. 
     For example, in this exemplary embodiment, the bracket  30  has the positioning hole  30   a  and the support hole  30   b . However, the bracket  30  may be divided into a positioning member having the positioning hole  30   a  and a support member having the support hole  30   b.    
     If the bracket  30  has the positioning hole  30   a  and the support hole  30   b  like in the exemplary embodiment, the shaft  10   a  of the photosensitive drum  10  and the rotating shaft  12 - 1   aa  of the idler gear  12 - 1   a  are accurately positioned. A force in the direction in which the image-forming unit SY, SM, SC, or SK is moved away from the positioning hole  30   a  during the operation of the apparatus is further reliably prevented from being exerted on the image-forming unit SY, SM, SC, or SK. 
     Also, referring to  FIG. 12 , when θ 1  and θ 2  are angles respectively defined by a tangent L 3  and the horizontal line and by a tangent L 4  and the horizontal line (θ 1 &lt;θ 2 ), the tangents L 3  and L 4  passing through the two points at which the shaft  10   a  of the photosensitive drum  10  contacts the positioning hole  30   a ; and θ 3  is an angle defined by the guide side  30   b - 1  of the support hole  30   b  and the horizontal line, the angles may be set such that the angle θ 3  is equal to or greater than the angle θ 1  and is equal to or smaller than the angle θ 2  (θ 1 ≦θ 3 ≦θ 2 ). 
     Accordingly, the shaft  10   a  of the photosensitive drum  10  reliably contacts the positioning hole  30   a  at the two points. A force in the direction in which the image-forming unit SY, SM, SC, or SK is moved away from the positioning hole  30   a  is further reliably prevented from being exerted on the image-forming unit SY, SM, SC, or SK. 
     In the above description, the printer serving as the image-forming apparatus is a full-color printer. However, the printer may be a color printer that is not a full-color printer, or may be a black and white printer. 
     Also, the image-forming apparatus may be, for example, a facsimile machine. Further, the image-forming apparatus may have plural functions including a function of a printer and a function of a facsimile machine. 
     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.