Patent Publication Number: US-8526861-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. 2011-071130 filed Mar. 28, 2011. 
     BACKGROUND 
     Technical Field 
     The present invention relates to an image forming apparatus. 
     SUMMARY 
     According to an aspect of the invention, there is provided an image forming apparatus including: image forming units that are detachably mounted on an apparatus body, each of the image forming units including an image holding body where an electrostatic latent image is formed on a surface of the image holding body and a developing unit provided with a developing member that is disposed with a gap between the developing member and the image holding body and supplies a developer to the electrostatic latent image formed on the surface of the image holding body while rotating; shaft members that are provided at the image forming units and rotatably support the developing units so that the developing members approach or are separated from the image holding bodies when seen in a direction of a rotation axis of the developing member, a direction of a rotation axis of each shaft member being parallel to the rotation axis of the developing member; urging members that are provided at the image forming units and urge the developing members toward the image holding bodies, one end of each of the urging members being fixed to each of the developing units; supply devices that are disposed adjacent to the developing units and supply developers to the developing units when seen in the direction of the rotation axis of the developing member; transport passages of which base end portions are connected to body parts of the supply devices, through which developers stored in the body parts are transported to the developing units, and which are provided so as to extend toward the developing members and the image holding bodies when seen in the direction of the rotation axis of the developing member, the developers being transported to the developing units from supply ports formed at leading end portions of the transport passages through receiving ports of the developing units connected to the supply ports; and elastic members each of which forms a part of the transport passage and is extensibly deformed so as to absorb the deviation of the relative position between the supply port and the receiving port. 
    
    
     
       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 side view of an image forming unit and the like used in an image forming apparatus according to an exemplary embodiment of the invention; 
         FIG. 2  is an enlarged perspective view of a toner supply device used in the image forming apparatus according to the exemplary embodiment of the invention; 
         FIG. 3  is an enlarged perspective view of a leading end portion of a toner transport passage of a toner supply device used in the image forming apparatus according to the exemplary embodiment of the invention; 
         FIG. 4  is an enlarged perspective view of the leading end portion of the toner transport passage of the toner supply device used in the image forming apparatus according to the exemplary embodiment of the invention; 
         FIGS. 5A ,  5 B, and  5 C are cross-sectional views showing a mounting portion of a developing unit used in the image forming apparatus according to the exemplary embodiment of the invention and a mounting object portion of the toner transport passage; 
         FIG. 6  is a side view showing the image forming units and the toner supply devices used in the image forming apparatus according to the exemplary embodiment of the invention; 
         FIG. 7  is a cross-sectional view of an intermediate passage of the toner supply device used in the image forming apparatus according to the exemplary embodiment of the invention; and 
         FIG. 8  is a schematic configurational diagram of the image forming apparatus according to the exemplary embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     An example of an image forming apparatus according to an exemplary embodiment of the invention will be described with reference to  FIGS. 1 to 8 . Meanwhile, an arrow V shown in the drawings shows a vertical direction and an arrow H shows a horizontal direction. 
     (Entire Configuration) 
     A view of an image forming apparatus  10 , which is seen from the back surface (the surface opposite to the surface corresponding to a user operating the apparatus), is shown in  FIG. 8 . As shown in  FIG. 8 , an image processing unit  12 , which performs the image processing of image data to be input, is provided in an apparatus body  10 A of the image forming apparatus  10 . 
     The image processing unit  12  processes input image data into gray scale data corresponding to four colors, that is, yellow (Y), magenta (M), cyan (C), and black (K). An exposure device  14 , which receives the processed gray scale data and performs image exposure using laser beams LB, is provided at the central portion in the apparatus body  10 A. 
     Further, four image forming units  16 Y,  16 M,  16 C, and  16 K corresponding to yellow (Y), magenta (M), cyan (C), and black (K) are disposed above the exposure device  14  at intervals in the direction inclined to the horizontal direction, and are detachably mounted on the apparatus body  10 A. Meanwhile, when Y, M, C, and K do not need to be distinguished from each other in the description, reference letters Y, M, C, and K may be omitted. 
     All of these four image forming units  16 Y,  16 M,  16 C, and  16 K have the same configuration. Each of the image forming units includes a columnar image holding body  18 , a charging member  20  for primary charging, a developing unit  22 , and a cleaning blade (not shown). The columnar image holding body is rotationally driven at a predetermined speed. The charging member  20  for primary charging charges the outer peripheral surface of the image holding body  18 . The developing unit  22  visualizes an electrostatic latent image, which is formed on the charged outer peripheral surface of the image holding body  18 , as a toner image by developing the electrostatic latent image with a predetermined color toner through the image exposure of the above-mentioned exposure device  14 . The cleaning blade cleans the outer peripheral surface of the image holding body  18 . 
     Moreover, toner supply devices  68 , which supply toners to the developing units  22 , are provided on the right side of the developing units  22  in the horizontal direction shown in  FIG. 8  so as to be adjacent to the developing units  22 . Meanwhile, the image forming units  16  and the toner supply devices  68  will be described in detail below. 
     Further, the exposure device  14  is provided with four semiconductor lasers (not shown) that have the configuration common to the four image forming units  16 Y,  16 M,  16 C, and  16 K. Laser beams LB-Y, LB-M, LB-C, and LB-K are emitted from these semiconductor lasers in accordance with gray scale data. 
     Meanwhile, the laser beams LB-Y, LB-M, LB-C, and LB-K emitted from the semiconductor lasers are radiated to a polygon mirror  26 , which is a rotating polygon mirror, through a cylindrical lens (not shown) and are deflected and scanned by the polygon mirror  26 . Further, the laser beams LB-Y, LB-M, LB-C, and LB-K, which are deflected and scanned by the polygon mirror  26 , are scanned and exposed obliquely from below to exposure points on the image holding bodies  18  through an imaging lens and plural mirrors (not shown). 
     Furthermore, since the exposure device  14  scans and exposes images on the image holding bodies  18  from below, there is a concern that toners and the like fall onto the exposure device  14  from the developing units  22  and the like of the four image forming units  16 Y,  16 M,  16 C, and  16 K positioned on the upper side. For this reason, the periphery of the exposure device  14  is sealed by a rectangular parallelepiped frame  28 . Moreover, windows  30 Y,  30 M,  30 C, and  30 K, which are made of transparent glass and transmit four laser beams LB-Y, LB-M LB-C, and LB-K toward the image holding bodies  18  of the respective image forming units  16 Y,  16 M,  16 C, and  16 K, are provided on the upper portion of the frame  28 . 
     Meanwhile, a primary transfer unit  21  as an example of a transfer device is provided above the respective image forming units  16 Y,  16 M,  16 C, and  16 K. Further, the primary transfer unit  21  includes an intermediate transfer belt  32  as an example of an endless member; a driving roll  36  where the intermediate transfer belt  32  is wound and which is rotationally driven and revolves the intermediate transfer belt  32  in the direction of an arrow; a tensioning roll  40  as an example of a tensioning member where the intermediate transfer belt  32  is wound and which applies tension to the intermediate transfer belt  32 ; a driven roll  66  that is provided above the tensioning roll  40  and rotationally driven together with the intermediate transfer belt  32 ; and primary transfer rolls  34 Y,  34 M,  34 C, and  34 K as an example of transfer members that are disposed on one side of the intermediate transfer belt  32  opposite to the image holding bodies  18 Y,  18 M,  18 C, and  18 K with the intermediate transfer belt  32  interposed therebetween. 
     Furthermore, the respective color toner images, which correspond to yellow (Y), magenta (M), cyan (C), and black (K) and are sequentially formed on the image holding bodies  18  of the image forming units  16 Y,  16 M,  16 C, and  16 K, are multiply transferred to the intermediate transfer belt  32  by the four primary transfer rolls  34 Y,  34 M,  34 C, and  34 K. 
     In addition, a cleaning blade  38 , which cleans the outer peripheral surface of the intermediate transfer belt  32 , is provided on one side of the intermediate transfer belt  32  opposite to the driving roll  36  with the intermediate transfer belt  32  interposed therebetween. 
     Further, a secondary transfer roll  42  is provided on one side of the intermediate transfer belt  32  opposite to the driven roll  66  with the intermediate transfer belt  32  interposed therebetween. The respective color toner images, which correspond to yellow (Y), magenta (M), cyan (C), and black (K) and are multiply transferred to the intermediate transfer belt  32 , are transported by the intermediate transfer belt  32 , are interposed between the driven roll  66  and the secondary transfer roll  42 , and are secondarily transferred to a sheet member P as a recording medium to be transported along a sheet transport path  56 . 
     Furthermore, a fixing device  44 , which fixes the toner images transferred to the sheet member P to the sheet member P by heat and pressure, is provided on the downstream side of the secondary transfer roll  42  in the transport direction of the sheet member P (hereinafter, simply referred to as the downstream side). 
     Moreover, discharge rolls  46 , which discharge the sheet member P to which the toner images have been fixed to a discharge section  48  provided at the upper portion of the apparatus body  10 A of the image forming apparatus  10 , are provided on the downstream side of the fixing device  44 . 
     Meanwhile, a sheet feeding member  50  in which sheet members P are stacked is provided on the lower side in the apparatus body  10 A of the image forming apparatus  10 . In addition, a sheet feeding roll  52 , which feeds the sheet members P stacked in the sheet feeding member  50  to the sheet transport path  56 , is provided and a separation roll  54 , which separates and transports the sheet members P one by one, is provided on the downstream side of the sheet feeding roll  52 . Further, a positioning roll  58 , which adjusts a transport timing, is provided on the downstream side of the separation roll  54 . Accordingly, a sheet member P supplied from the sheet feeding member  50  is fed to a position (secondary transfer position), where the intermediate transfer belt  32  and the secondary transfer roll  42  come into contact with each other, at a predetermined timing by the rotating positioning roll  58 . 
     Furthermore, transport rolls  60 , which do not discharge a sheet member P where toner images have been fixed to one surface by the fixing device  44  onto the discharge section  48  by the discharge rolls  46  as it is and transport the sheet member to a sheet transport path  62  for double-sided printing, are provided near the discharge rolls  46 . Accordingly, the sheet member P, which is transported along the sheet transport path  62  for double-sided printing, is transported to the positioning roll  58  again while having been inverted. This time, toner images are transferred and fixed to the back of the sheet member P and the sheet member P is then discharged onto the discharge section  48 . 
     An image is formed on the sheet member P as described below due to this configuration. 
     First, gray scale data corresponding to the respective colors are sequentially output to the exposure device  14  from the image processing unit  12 , and laser beams LB-Y, LB-M, LB-C, and LB-K, which are emitted from the exposure device  14  in accordance with the gray scale data, are scanned and exposed to the outer peripheral surfaces of the image holding bodies that are charged by the charging members  20 , so that electrostatic latent images are formed on the outer peripheral surfaces of the image holding bodies  18 . The electrostatic latent images formed on the image holding bodies  18  are visualized as the respective color toner images, which correspond to yellow (Y), magenta (M), cyan (C), and black (K), by the developing units  22 Y,  22 M,  22 C, and  22 K, respectively. 
     Moreover, the respective color toner images, which correspond to yellow (Y), magenta (M), cyan (C), and black (K) and are formed on the image holding bodies  18 , are multiply transferred to the revolving intermediate transfer belt  32  by the primary transfer rolls  34  of the primary transfer unit  21  that are disposed over the respective image forming units  16 Y,  16 M,  16 C, and  16 K. 
     Further, the respective color toner images, which have been multiply transferred to the revolving intermediate transfer belt  32 , are secondarily transferred to the sheet member P, which is transported to the sheet transport path  56  from the sheet feeding member  50  at a predetermined timing by the sheet feeding roll  52 , the separation roll  54 , and the positioning roll  58 , by the secondary transfer roll  42 . 
     Furthermore, the sheet member P to which the toner images have been transferred is transported to the fixing device  44 . The toner images transferred to the sheet member P are fixed to the sheet member P by the fixing device  44 . After the toner images are fixed to the sheet member, the sheet member P is discharged onto the discharge section  48 , which is provided at the upper portion of the apparatus body  10 A of the image forming apparatus  10 , by the discharge rolls  46 . 
     Meanwhile, when images are to be formed on both surfaces of a sheet member P, a sheet member P, where toner images have been fixed to one surface by the fixing device  44 , is transported to the sheet transport path  62  for double-sided printing through the transport rolls  60  after the switching of the transport direction of the sheet member without being discharged onto the discharge section  48  as it is by the discharge rolls  46 . Further, the sheet member P is transported along the sheet transport path  62  for double-sided printing, so that the sheet member P is inverted. Then, the sheet member P is transported to the positioning roll  58  again. This time, the sheet member P is discharged onto the discharge section  48  by the discharge rolls  46  after toner images are transferred and fixed to the back of the sheet member P. 
     (Configuration of Main Parts) 
     Next, the image forming units  16  and the toner supply devices  68  will be described. 
     As shown in  FIG. 1 , each of the image forming units  16 , which are detachably mounted on the apparatus body  10 A (see  FIG. 8 ), is provided with an image holding body housing  70  where the columnar image holding body  18  is rotatably supported and the above-mentioned developing unit  22 . 
     Further, the developing unit  22  is provided with a developing roller  72  as an example of a columnar developing member that is disposed with a gap (A shown in  FIG. 1 ) between itself and the image holding body  18  and supplies a toner to the electrostatic latent image formed on the surface of the image holding body  18  while rotating. 
     In detail, a developer unit housing  74  where the developing roller  72  is rotatably supported is provided, and the direction of the rotation axis of the developing roller  72  (hereinafter, simply referred to as the direction of the rotation axis) is parallel to the direction of the rotation axis of the image holding body  18 . 
     In addition, the image holding body housing  70  and the developer unit housing  74  are attached to each other by a shaft member  76 , of which the axis extends along the direction of the rotation axis of the developing roller  72 , so as to rotate relative to each other. Meanwhile, when the image forming unit  16  is mounted on the apparatus body  10 A, the image holding body housing  70  is fixed to the apparatus body  10 A and the developing unit  22  is supported so as to be rotatable relative to the image holding body housing  70 . 
     Further, cylindrical roller members  78 , which have a diameter larger than the diameter of the developing roller  72 , are provided at both end portions of the developing roller  72  in the direction of the rotation axis. Furthermore, there are provided springs  90  that urge the roller members  78  so that the roller members  78  come into contact with both end portions of the image holding body  18 . The springs  90  are provided at both ends of the developing roller  72  in the direction of the rotation axis. One end of each spring  90  is fixed to the image holding body housing  70  and the other end of each spring  90  is fixed to the developer unit housing  74 . 
     The outer peripheral surfaces of the roller members  78  come into contact with both end portions of the image holding body  18  due to this configuration, so that a predetermined gap (A shown in  FIG. 1 ) is formed between the outer surface of the image holding body  18  and the outer surface of the developing roller  72 . 
     Further, an agitating member  80 , which agitates the toner supplied to the developing unit  22  from the toner supply device  68  while rotating and of which the axial direction of a rotating shaft  80 A is parallel to the direction of the rotation axis of the developing roller  72 , is provided on the right side of the shaft member  76  in the horizontal direction shown in  FIG. 1 . Specifically, a spiral blade portion BOB is formed on the periphery of the rotating shaft  80 A, and the toner is agitated by the rotation of the blade portion  80 B. 
     Furthermore, a receiving port  84 , through which the toner supplied from the toner supply device  68  is fed into the developer unit housing  74 , is formed at the developer unit housing  74  above the agitating member  80  in the vertical direction and near one end portion of the agitating member  80  in the direction of the rotation axis. Specifically, the receiving port  84  is formed at a mounting portion  82  of the developer unit housing  74  that is mounted on a mounting object portion  108  to be described below (see  FIG. 3 ). 
     As described above, the shaft member  76  is disposed below the developing roller  72  and the receiving port  84  is disposed parallel to the shaft member  76  in the horizontal direction. 
     Further, a shutter  86 , which closes the receiving port  84  formed at the developer unit housing  74  when the image forming unit  16  is separated from the apparatus body  10 A as shown in  FIG. 3 , is slidably provided. 
     In detail, the shutter  86  is adapted to be slidable relative to the developer unit housing  74  in the attachment/detachment direction of the image forming unit  16  (which is the depth direction of the apparatus body  10 A and is the direction of an arrow D shown in  FIG. 3 ), and is adapted to move between an open position (see  FIG. 5C ) where the receiving port  84  is opened and a closed position (see  FIG. 5A ) where the receiving port  84  is closed. 
     In addition, springs  88 , which urge the shutter  86  to the closed position, are provided between the shutter  86  and the developer unit housing  74 . Meanwhile, two springs  88  are provided so as to urge the both end portions of the shutter  86  in the horizontal direction. 
     Further, a protruding portion  92 , which comes into contact with a columnar portion  118  (see  FIGS. 5A to 5C ) of a toner transport passage  98  to be described below when the image forming unit  16  is mounted on the apparatus body  10 A, is formed on the outer surface of the developer unit housing  74 . Specifically, the protruding portion  92  is formed so as to protrude from a back wall  74 A of the developer unit housing  74 , which faces the back surface of the apparatus body  10 A, in the above-mentioned attachment/detachment direction. 
     Meanwhile, as shown in  FIG. 6 , the toner supply devices  68 , which correspond to the respective colors and supply toners to the developing units  22  corresponding to the respective colors, are provided on the right side of the image forming units  16 , which correspond to the respective colors, in the horizontal direction shown in  FIG. 6 . 
     Each of the toner supply devices  68  includes a body part  96  in which a toner is stored, and a toner transport passage  98  as a tubular member which is provided so as to extend from the lower surface of the body part  96  toward the developing unit  22  and through which the toner stored in the body part  96  is transported to the developing unit  22 . Further, when seen in the direction of the rotation axis of the developing roller  72 , as shown in  FIGS. 1 and 6 , the toner transport passages  98 M,  98 C, and  98 K except for the toner transport passage corresponding to yellow (Y) extend along a straight line G that connects the rotation axis of the shaft member  76  with the rotating shaft  80 A of the agitating member  80 . That is, when seen in the direction of the rotation axis of the developing roller  72 , the straight line G is parallel to the center lines J of each of the toner transport passages  98 M,  98 C, and  98 K. 
     Moreover, the leading end portion of each of the toner transport passages  98  extends toward the developing roller  72  and the image holding body  18 . In addition, when seen in the direction of the rotation axis of the developing roller  72 , a spring  90  is provided on one side of the center line J opposite to the shaft member  76  with the center line J of the toner transport passage  98 , which extends in the extending direction of the toner transport passage  98 , interposed therebetween. 
     Meanwhile, as shown in  FIG. 2 , an intermediate passage  100 , of which the base end portion is fixed to the lower surface of the body part  96  and the leading end portion is fixed to the base end portion of the toner transport passage  98 , is provided on the lower surface of the body part  96 . Further, the toner stored in the body part  96  is transported to the base end portion of the toner transport passage  98  through the inside of the intermediate passage  100 . 
     Furthermore, as shown in  FIG. 4 , a crank-shaped holding portion  104 , which is formed by cutting and raising a back panel  102  inward, is formed on the back panel  102  of the apparatus body  10 A. In addition, an inverted U-shaped hook portion  106 , which is caught by the holding portion  104  from above, is formed at the leading end portion of the toner transport passage  98  facing the back panel  102  of the apparatus body  10 A. The hook portion  106  is caught by the holding portion  104  due to this configuration, so that the leading end portion of the toner transport passage  98  is temporarily held on the apparatus body  10 A. 
     Further, a supply port  110  is formed at the lower portion of the leading end portion of the toner transport passage  98  in the vertical direction. A toner is supplied to the developing unit  22  through the supply port  110  and the receiving port  84  that is formed at the mounting portion  82  of the developer unit housing  74 . 
     Furthermore, as shown in  FIGS. 3 and 4 , a mounting object portion  108  is provided at the lower portion of the supply port  110  in the vertical direction. When the image forming unit  16  is moved in the direction of the arrow D and mounted on the apparatus body  10 A, the mounting portion  82  formed at the developer unit housing  74  is mounted on the mounting object portion  108 . 
     In detail, a holding portion  120 , which holds a flange portion  112  (see  FIG. 1 ) formed at the mounting portion  82  from below, is formed at the mounting object portion  108 . In addition, a shutter  114 , which closes the supply port  110  when the image forming unit  16  is separated from the apparatus body  10 A, is slidably provided at the holding portion. 
     The shutter  114  is adapted to be slidable relative to the toner transport passage  98  in the attachment/detachment direction of the image forming unit  16  (which is the depth direction of the apparatus body  10 A and is the direction of the arrow D shown in  FIG. 3 ), and is adapted to move between an open position (see  FIG. 5C ) where the supply port  110  is opened and a closed position (see  FIG. 5A ) where the supply port  110  is closed. 
     Moreover, as shown in  FIG. 5A , the mounting object portion  108  is provided with a coil-like spring  116  that urges the shutter  114  at the closed position. Further, a columnar portion  118 , which supports the spring  116  from the inside, is provided at the mounting object portion  108 . 
     When the mounting portion  82  of the developer unit housing  74  is mounted on the mounting object portion  108  of the toner transport passage  98 , the columnar portion  118  comes into contact with the protruding portion  92  of the developer unit housing  74  and the receiving port  84  faces the supply port  110  due to this configuration as shown in  FIGS. 5A ,  5 B, and  5 C. Further, in this state, the shutter  114  is pressed against the back wall  74 A of the developer unit housing  74  and moved to the open position from the closed position, and the shutter  86  is pressed against a side wall  98 A formed at the toner transport passage  98  and moved to the open position from the closed position. 
     Furthermore, as shown in  FIG. 6 , a bellows-like rubber tube  122  as an example of an elastic member, which is made of an elastic material, is provided at a portion of each toner transport passage  98  that is closer to the base end portion than the mounting object portion  108 . When the relative position between the receiving port  84  and the supply port  110  is deviated, the rubber tube  122  is deformed and absorbs the deviation of the relative position. 
     In addition, as shown in  FIGS. 1 and 7 , a transport member  124 , which transports the toner stored in the body part  96  toward the supply port  110  while rotating and of which the direction of the rotation axis is parallel to the extending direction of the toner transport passage  98 , is provided in each toner transport passage  98 . The transport member  124  includes a columnar rotating shaft  124 A and a blade portion  124 B that is formed on the periphery of the rotating shaft  124 A, and the toner is transported toward the supply port  110  by the rotation of the blade portion  124 B. 
     Further, the transport member  124  is supported in cantilever state at the base end portion of the toner transport passage  98  (see  FIG. 7 ). Furthermore, the base end portion of the rotating shaft  124 A of the transport member  124 , which is supported in cantilever state, is connected to a gear group  126  (see  FIG. 2 ) that is provided on the outside of the toner transport passage  98 . A driving force from a motor (not shown) is transmitted to the transport member  124  through the gear group  126 , so that the transport member  124  is rotated. 
     In addition, at least a portion of the transport member  124 , which is positioned closer to the leading end of the toner transport passage  98  than the rubber tube  122 , is made of an elastically deformable resin material. 
     (Operation of Configuration of Main Parts) 
     Next, the operations of the image forming units  16 , the toner supply device  68 , and the like will be described. 
     As shown in  FIG. 6 , the toners stored in the body parts of the toner supply devices  68  corresponding to the respective colors are supplied to the developing units  22  through the toner transport passages  98 . 
     Specifically, as shown in  FIGS. 2 and 7 , the toner stored in the body part  96  enters the base end portion of the toner transport passage  98  through the intermediate passage  100 . The toner, which has entered the base end portion of the toner transport passage  98 , is transported toward the leading end portion of the toner transport passage  98  by the blade portion  124 B of the transport member  124  that is rotated by a driving force transmitted through the gear group  126 . 
     As shown in  FIG. 1 , the toner, which has been transported toward the leading end portion of the toner transport passage  98 , is supplied to the developing unit  22  through the supply port  110  and the receiving port  84  by gravity. 
     The toner supplied to the developing unit  22  is agitated by the rotating agitating member  80 . The toner, which has been agitated by the agitating member  80 , is transferred to the rotating developing roller  72 . 
     The rotating developing roller  72  supplies the toner to the image holding body  18  through a gap between itself and the image holding body  18 , and develops an electrostatic latent image formed on the outer peripheral surface of the image holding body  18  (visualizes the electrostatic latent image as a toner image). 
     Here, the developer unit housing  74 , which supports the developing roller  72 , is rotatably mounted on the image holding body housing  70 , which is fixed to the apparatus body  10 A, by the shaft member  76 . Further, the springs  90  of which one ends are fixed to the developer unit housing  74  urge the roller members  78  so that the roller members  78  come into contact with both end portions of the image holding body  18 . Accordingly, the size of the gap (A shown in  FIG. 1 ), which is formed between the developing roller  72  and the image holding body  18  and through which the toner is transferred, is in a predetermined range. 
     Meanwhile, when the image forming unit  16  is separated from the apparatus body  10 A for maintenance or the like, a maintenance door (not shown) provided on the front of the apparatus body lap, is opened first. 
     Moreover, as shown in  FIG. 3 , the image forming unit  16  is moved to the front side (the front side of the apparatus body  10 A) in the attachment/detachment direction of the image forming unit  16  (which is the depth direction of the apparatus body  10 A and is the direction of the arrow D shown in  FIG. 3 ). 
     When the image forming unit  16  is moved to the front side in the attachment/detachment direction as shown in  FIGS. 5A ,  5 B, and  5 C, the shutter  114 , which is pressed against the back wall  74 A of the developer unit housing  74  and disposed at the open position (see  FIG. 5C ), is moved to the closed position (see  FIG. 5A ) by the urging force of the spring  116 . Accordingly, the toner, which is supplied to the developing unit  22  from the toner supply device  68 , is prevented from being scattered to the outside. 
     Further, the shutter  86 , which is pressed against the side wall  98 A of the toner transport passage  98  and disposed at the open position (see  FIG. 5C ), is moved to the closed position (see  FIG. 5A ) by the urging force of the springs  88 . Accordingly, the toner, which is stored in the developing unit  22 , is prevented from being scattered to the outside. 
     In contrast, when the image forming unit  16  is mounted on the apparatus body  10 A after maintenance or the like is finished, the maintenance door (not shown) provided on the front of the apparatus body  10 A is opened first. 
     Moreover, as shown in  FIG. 3 , the image forming unit  16  is moved to the back side (the back side of the apparatus body  10 A) in the attachment/detachment direction of the image forming unit  16  (which is the depth direction of the apparatus body  10 A and is the direction of the arrow D shown in  FIG. 3 ). 
     When the image forming unit  16  is moved to the back side in the attachment/detachment direction as shown in  FIGS. 5A ,  5 B, and  5 C, the shutter  114 , which is disposed at the closed position (see  FIG. 5A ) by the urging force of the spring  116 , is pressed against the back wall  74 A of the developer unit housing  74  and moved to the open position (see  FIG. 5C ). Further, the protruding portion  92  formed at the developer unit housing  74  comes into contact with the columnar portion  118  formed at the mounting object portion  108  of the toner transport passage  98 , so that the developer unit housing  74  is stopped. 
     Furthermore, the shutter  86 , which is disposed at the closed position (see  FIG. 5A ) by the urging force of the springs  88 , is pressed against the side wall  98 A of the toner transport passage  98  and moved to the open position (see  FIG. 5C ). 
     Here, when the relative position between the receiving port  84  of the developing unit  22  and the supply port  110  of the toner transport passage  98  is deviated as shown in  FIG. 1 , the rubber tube  122  provided at the toner transport passage  98  is elastically deformed or the entire toner transport passage  98  is rotated about the base end portion of the toner transport passage  98  as a center, so that the deviation of the relative position between the receiving port  84  and the supply port  110  is absorbed. 
     Further, since only the base end portion of the transport member  124  is supported, the leading end portion of the transport member  124 , which is disposed in the toner transport passage  98 , is moved together with the toner transport passage  98  as the toner transport passage  98  is moved. 
     Accordingly, the mounting portion  82  of the developing unit  22  is mounted on the mounting object portion  108  (see  FIG. 3 ) of the toner transport passage  98  as shown in  FIG. 1 , so that a toner is supplied to the developing unit  22  from the toner supply device  68  through the supply port  110  and the receiving port  84 . 
     As described above, the leading end portion of the toner transport passage  98  extends toward the developing roller  72  and the image holding body  18  when the image forming unit  16  is mounted on the apparatus body  10 A. The relative position between the receiving port  84  of the developing unit  22  and the supply port  110  of the toner transport passage  98  is deviated, and the rubber tube  122  may contract in the extending direction of the toner transport passage  98  in order to absorb the deviation of the relative position. 
     In this case, since the leading end portion of the toner transport passage  98  extends toward the developing roller  72  and the image holding body  18  as described above so that the rubber tube  122  is elastically restored, the roller members  78  are pressed against the image holding body  18  by the force applied to the developing unit  22 . For this reason, when the image forming unit  16  is mounted on the apparatus body  10 A, the variation of the size of the gap formed between the image holding body  18  and the developing roller  72  is suppressed. In particular, if the intersection between parts is set so that the rubber tube  122  contracts when the above-mentioned relative position is deviated, the configuration is particularly effective in that the variation of the size of the gap is suppressed. 
     Further, if the structure that suppresses the variation of the size of the gap set between the image holding body  18  and the developing roller  72  is employed, the size of the rubber tube  122  is reduced as compared to the case where this structure is not employed. 
     Furthermore, according to the above-mentioned exemplary embodiment, each of the toner transport passages  98  is disposed so that the center line J of each toner transport passage  98  passes between the shaft member  76  and the spring  90  when seen in the direction of the rotation axis of the developing roller  72 . For this reason, as compared to the case where the center line J of the toner transport passage  98  does not pass between the shaft member  76  and the spring  90 , a moment, which causes the developer unit housing  74  to rotate about the shaft member  76  as a center, is reduced by a force that is generated due to the deviation of the relative position between the receiving port  84  and the supply port  110 . Accordingly, the variation of the size of the gap formed between the image holding body  18  and the developing roller  72  is effectively suppressed. 
     Moreover, according to the above-mentioned exemplary embodiment, the straight line G, which connects the rotation axis of the shaft member  76  with the rotating shaft  80 A, of the agitating member  80 , is parallel to the center line J of each of the toner transport passages  98 M,  980 , and  98 K when seen in the direction of the rotation axis of the developing roller  72 . Accordingly, the displacement transmitted to the developer unit housing  74  from the toner transport passage  98  is reduced as compared to the case where the straight line G crosses the center line of each toner transport passage. Therefore, the variation of the size of the gap formed between the image holding body  18  and the developing roller  72  is effectively suppressed. 
     Further, according to the above-mentioned exemplary embodiment, the transport member  124  is supported in cantilever state at the base end portion of the toner transport passage  98 . Accordingly, even though the leading end portion of the toner transport passage  98  is moved due to the deviation of the relative position between the receiving port  84  of the developing unit  22  and the supply port  110  of the toner transport passage  98 , the transport member  124  is moved so as to follow the movement of the leading end portion of the toner transport passage  98 . 
     Furthermore, according to the above-mentioned exemplary embodiment, at least a portion of the transport member  124 , which is positioned closer to the leading end of the toner transport passage  98  than the rubber tube  122 , is made of an elastically deformable resin material. Accordingly, the rubber tube  122  is elastically deformed when the relative position between the receiving port  84  and the supply port  110  is deviated, and the leading end portion of the transport member  124  is elastically deformed even when the portion of the toner transport passage  98 , which is positioned closer to the leading end of the toner transport passage  98  than the rubber tube  122 , is moved. As a result, the strong friction between the inner wall of the toner transport passage  98  and the transport member  124  is suppressed, so that the generation of a problem such as a mass of a toner (toner grid) is suppressed. 
     Moreover, according to the above-mentioned exemplary embodiment, as shown in  FIG. 3 , two springs  88 , which urge the shutter  86 , are provided so as to urge the both end portions of the shutter  86  in the width direction of the shutter. For this reason, the shutter  86  stably slides as compared to the case where one spring is provided. 
     Meanwhile, the specific exemplary embodiment of the invention has been described in detail. However, the invention is not limited to the exemplary embodiment of the invention, and it is apparent to those skilled in the art that the invention may have various exemplary embodiments within the scope of the invention. For example, at least a portion of the transport member  124 , which is positioned closer to the leading end of the toner transport passage  98  than the rubber tube  122 , has been made of an elastically deformable resin material in the above-mentioned exemplary embodiment. However, the diameter of a portion of the shaft member corresponding to the leading end portion of the transport member may be reduced so that the leading end portion of the transport member can be elastically deformed. 
     Further, the straight line G has been parallel to the center line J of each of the toner transport passages  98 M,  980 , and  98 K in the above-mentioned exemplary embodiment. However, the straight line G may also be parallel to the center line of the toner transport passage  98 Y. Furthermore, a toner has been supplied to the developing unit  22  in the exemplary embodiment of the invention. However, a developer, which is a mixture of a toner and a carrier, may be supplied to the developing unit. Moreover, an electrophotographic image forming apparatus has been described in the exemplary embodiment of the invention, but the invention may also be applied to image forming apparatuses using other developers such as an inkjet 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.