Patent Publication Number: US-8995876-B2

Title: Drum unit, development cartridge detachably attachable to the drum unit, and image forming apparatus having the drum unit and the development cartridge

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority under 35 U.S.C. §119 from Japanese Patent Application No. 2010-124277 filed on May 31, 2010. The entire subject matter of the application is incorporated herein by reference. 
     BACKGROUND 
     1. Technical Field 
     The following description relates to one or more process units, each of which includes a drum unit and a development cartridge, for an image forming apparatus such as a laser printer. 
     2. Related Art 
     In an example of an image forming apparatus such as a laser printer, a drum cartridge holding a photoconductive drum is detachably attached into a main body of the apparatus. Further, the drum cartridge includes a development cartridge attached thereto that supports a development roller. The drum cartridge having the development cartridge attached thereto constitutes a process cartridge. 
     In a state where the development cartridge is attached to the drum cartridge, the development roller contacts the photoconductive drum. In order to make the development roller contact the photoconductive drum under a predetermined pressing force, the drum cartridge includes a pressing member by which the development cartridge is pressed against the photoconductive drum. Specifically, the pressing member is urged by a compression spring. The development cartridge includes a development-side boss. When the development cartridge is attached to the drum cartridge, the pressing member contacts the development-side boss, and the pressing member is pressed against the development-side boss by an urging force of the compression spring so as to establish a pressure-contact between the development roller and the photoconductive drum. 
     SUMMARY 
     A user may attach the process cartridge into the main body of the image forming apparatus swiftly with a great force. In the main body, a positioning member is provided to position the process cartridge. When the process cartridge is attached into the main body, a drum-side boss provided to the drum cartridge engages with the positioning member such that the process cartridge is positioned. Therefore, when the process cartridge is attached into the main body swiftly with a great force, the development cartridge might be detached from the drum cartridge by an impact at the time when the drum-side boss engages with the positioning member. 
     In order to prevent the development cartridge from being improperly detached from the drum cartridge, the drum cartridge is provided with a lock lever. When the development cartridge is attached to the drum cartridge, the lock lever comes into contact with the development-side boss from an upstream side in the attaching direction. Thereby, the development cartridge is restrained from moving toward the upstream side in the attaching direction, and thus the development cartridge is prevented from being improperly detached from the drum cartridge. 
     However, the configuration of the drum cartridge provided with the lock lever causes problems such as a complicated configuration and a larger number of parts of the process cartridge (the drum cartridge). 
     Aspects of the present invention are advantageous to provide one or more improved techniques for a process unit including a drum unit and a development cartridge, which techniques make it possible to prevent the development cartridge from being improperly detached from a frame of the drum unit, even with a simple configuration of the process unit. 
     According to aspects of the present invention, a drum unit is provided, which includes a frame configured such that a development cartridge is detachably attached thereto, wherein the development cartridge includes a pressed portion and a developer holding body configured to hold and carry thereon development agent, a photoconductive body held by the frame, the photoconductive body having a surface supplied with the development agent from the developer holding body, and a pressing member provided to the frame. The frame is configured such that the development cartridge is movable relative to the frame between a pressed state where the pressed portion is pressed by the pressing member when the development cartridge is attached to the frame and a released state where the pressed portion is released from pressing of the pressing member when the development cartridge is attached to the frame. The pressing member includes a pressing section configured to contact and press the pressed portion when the development cartridge is in the pressed state, and a restriction section that is disposed in a different position from a position of the pressing section and configured to restrict movement of the pressed portion in a released direction when the development cartridge is in the pressing state, the released direction being a direction in which the pressed portion moves when the development cartridge moves from the pressing state to the released state. 
     According to aspects of the present invention, further provided is an image forming apparatus, which includes a main body casing, a drum unit attached into the main body casing to be movable between a first position where the process unit is inside the main body casing and a second position where the process unit is outside the main body casing, the drum unit including a frame, a photoconductive body held by the frame, and a pressing member provided to the frame, and a development cartridge detachably attached to the frame of the drum unit, the development cartridge including a pressed portion, and a developer holding body configured to hold and carry thereon development agent to be supplied to a surface of the photoconductive body. The development cartridge is movable between a pressed state where the pressed portion is pressed by the pressing member when the development cartridge is attached to the frame and a released state where the pressed portion is released from pressing of the pressing member when the development cartridge is attached to the frame. The pressing member includes a pressing section configured to contact and press the pressed portion when the development cartridge is in the pressed state, and a restriction section that is disposed in a different position from a position of the pressing section and configured to restrict movement of the pressed portion in a released direction when the development cartridge is in the pressing state, the released direction being a direction in which the pressed portion moves when the development cartridge moves from the pressing state to the released state. 
     According to aspects of the present invention, further provided is a development cartridge, which includes a pressed portion, and a developer holding body configured to hold and carry thereon development agent. The development cartridge is detachably attachable to a frame of a drum unit. The drum unit includes a photoconductive body held by the frame, the photoconductive body having a surface supplied with development agent from the developer holding body, and a pressing member provided to the frame. The development cartridge is movable relative to the frame between a pressed state where the pressed portion is pressed by the pressing member when the development cartridge is attached to the frame and a released state where the pressed portion is released from pressing of the pressing member when the development cartridge is attached to the frame. The pressing member includes a pressing section configured to contact and press the pressed portion when the development cartridge is in the pressed state, and a restriction section that is disposed in a different position from a position of the pressing section and configured to restrict movement of the pressed portion in a released direction when the development cartridge is in the pressing state, the released direction being a direction in which the pressed portion moves when the development cartridge moves from the pressing state to the released state. The pressed portion includes a first pressed section configured to be pressed by the pressing section, and a second pressed section configured to, after contacting the restriction section, be pressed by the restriction section. 
    
    
     
       BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS 
         FIG. 1  is a cross-sectional side view schematically showing a configuration of a color printer in an embodiment according to one or more aspects of the present invention. 
         FIG. 2  is a perspective view showing a drawer unit for the color printer in the embodiment according to one or more aspects of the present invention. 
         FIG. 3A  is a right-side view of the drawer unit (in which a drawer frame is not shown) before a development cartridge is attached thereto in the embodiment according to one or more aspects of the present invention. 
         FIG. 3B  is a right-side view of the drawer unit (in which the drawer frame is not shown) in the middle of the development cartridge being attached thereto in the embodiment according to one or more aspects of the present invention. 
         FIG. 3C  is a right-side view of the drawer unit (in which the drawer frame is not shown) after the development cartridge is attached thereto in the embodiment according to one or more aspects of the present invention. 
         FIG. 3D  is a right-side view of the drawer unit (in which the drawer frame is not shown) in a state where a pressed boss comes in contact with a restriction section in the embodiment according to one or more aspects of the present invention. 
         FIG. 3E  is a right-side view of the drawer unit (in which the drawer frame is not shown) in a state where a pressing member is operated by a user&#39;s finger in the embodiment according to one or more aspects of the present invention. 
         FIG. 3F  is a right-side view of the drawer unit (in which the drawer frame is not shown) in a state where the development cartridge is in a released state (takes a released posture) in the embodiment according to one or more aspects of the present invention. 
         FIG. 3G  is a right-side view of the drawer unit (in which the drawer frame is not shown) in a state where the development cartridge is lifted up in the embodiment according to one or more aspects of the present invention. 
         FIG. 4  is a right-side view illustrating in an enlarged manner a part of the drawer unit shown in  FIG. 3D  in a state where the pressed boss contacts the restriction section in the embodiment according to one or more aspects of the present invention. 
         FIG. 5  is a right-side view of a drawer unit including a pressing member and a pressed boss in a first modification according to one or more aspects of the present invention. 
         FIG. 6  is a right-side view illustrating in an enlarged manner a part of the drawer unit shown in  FIG. 5  in a state where the pressed boss contacts a restriction section in the first modification according to one or more aspects of the present invention. 
         FIG. 7  is a right-side view of a development cartridge including a pressing member and a pressed boss in a second modification according to one or more aspects of the present invention. 
         FIG. 8  is a right-side view of a development cartridge including a pressing member and a pressed boss in a third modification according to one or more aspects of the present invention. 
         FIG. 9  is a right-side view showing a pressing member and a pressed boss in a fourth modification according to one or more aspects of the present invention. 
         FIG. 10  is a right-side view showing a pressing member and a pressed boss in a fifth modification according to one or more aspects of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     It is noted that various connections are set forth between elements in the following description. It is noted that these connections in general and, unless specified otherwise, may be direct or indirect and that this specification is not intended to be limiting in this respect. 
     Hereinafter, an embodiment according to aspects of the present invention will be described with reference to the accompany drawings. 
     1. Configuration of Color Printer 
     As shown in  FIG. 1 , a color printer  1  is a tandem-type color printer. The color printer  1  includes a main body casing  2 . Further, a drawer unit  3  is attached into the main body casing  2 . A front cover  4  is provided to a front face of the main body casing in an openable and closable manner. In a state where the front cover  4  is opened, the drawer unit  3  is movable horizontally between a housed position where the drawer unit  3  is inside the main body casing  2  (see  FIG. 1 ) and a pulled position where the drawer unit  3  is outside the main body casing  2  (not shown). 
     It is noted that in the following description, a side where the front cover  4  is disposed will be defined as a front side of the color printer  1  (see  FIG. 1 ). Additionally, an up-to-down direction and a left-to-right direction for the color printer  1  will be as defined when the color printer  1  is viewed from the front side thereof. Further, each direction for the drawer unit  3  will, unless specified otherwise, be defined in conformity to the directions for the color printer  1  in a state where the drawer unit  3  is attached into the color printer  1 . 
     The drawer unit  3  includes a drawer frame  5  that has a substantially rectangle shape in a top view. The drawer frame  5  includes two side plates that face each other across a predetermined distance in the left-to-right direction, a front beam  6  provided to bridge respective front ends of the two side plates, and a rear beam  7  provided to bridge respective rear ends of the two side plates. 
     In the drawer frame  5 , four photoconductive drums  8  are supported to be rotatable around respective rotational axes extending in the left-to-right direction. The four photoconductive drums  8  are provided for four colors, i.e., black, yellow, magenta, and cyan, respectively, and arranged parallel to each other at intervals of a constant distance along the front-to-rear direction in the order of black, yellow, magenta, and cyan from the front side. 
     Further, in the drawer frame  5 , four electrification devices  9  are held between the two side plates. The four electrification devices  9  are provided to correspond to the four photoconductive drums  8 , respectively. Each electrification device  9  is disposed in a position that is behind and higher than a corresponding one of the photoconductive drums  8 . For instance, each electrification device  9  is a scorotron type charger having a wire and a grid. 
     The drawer unit  3  includes four development cartridges  10  configured to be detachably attached to the drawer frame  5 . The four development cartridges  10  are provided to correspond to the four photoconductive drums  8 , respectively. Each development cartridge  10  is attached from an upper side of the drawer frame  5  in a state where the drawer unit  3  is pulled out up to the pulled position, and disposed in an upper front position relative to a corresponding one of the photoconductive drums  8 . 
     Each development cartridge  10  includes a development housing  11  and a development roller  12  supported by the development housing  11 . The development roller  12  is provided rotatably around a rotational axis extending in the left-to-right direction, and a part of a circumferential surface of the development roller  12  is exposed out of the development housing  11 . When the development cartridge  10  is attached to the drawer frame  5 , the circumferential surface of the development roller  12  contacts an upper front side of a circumferential surface of the photoconductive drum  8 . 
     In the main body casing  2 , an exposure device  13  is disposed above the drawer unit  2  and configured to emit four laser beams that correspond to the four colors, respectively. 
     In response to the rotation of the photoconductive drum  8 , the circumferential surface of the photoconductive drum  8  is selectively exposed to the laser beam from the exposure device  13  after being evenly charged by the electrification device  9  discharging. By the exposure, charges are removed selectively from the circumferential surface of the photoconductive drum  8  such that an electrostatic latent image is formed on the circumferential surface of the photoconductive drum  8 . When facing the development roller  12 , the electrostatic latent image is supplied with toner from the development roller  12 . Thereby, a toner image is held and carried on the circumferential surface of the photoconductive drum  8 . 
     It is noted that instead of the exposure device  13 , four LED arrays may be provided to correspond to the photoconductive drums  8 , respectively. 
     At a bottom of the main body casing  2 , a feed cassette  14  is disposed that accommodates one or more sheets P. Each sheet P placed on the feed cassette  14  is fed onto a conveying belt  15  by various rollers. The conveying belt  15  is disposed in a position lower than the four photoconductive drums  8 , such that an upper-side surface thereof faces the four photoconductive drums  8 . Transfer rollers  16  are disposed in positions to face the photoconductive drums  8  across the upper-side of the conveying belt  15 , respectively. The sheet P fed on the conveying belt  15  passes through between the conveying belt  15  and each photoconductive drum  8 , while being conveyed on the conveying belt  15  traveling. A toner image formed on each photoconductive drum  8  is transferred onto the sheet P when facing the sheet P between the photoconductive drum  8  and a corresponding one of the transfer rollers  16 . 
     A fixing unit  17  is disposed in a downstream position relative to the conveying belt  15  in a feeding direction for feeding the sheet P. The sheet P with the toner image transferred thereon is fed to the fixing unit  17 . The fixing unit  17  is configured to fix the toner image onto the sheet P by heating and pressing the sheet P. The sheet P with the toner image fixed thereon is ejected by various rollers onto a catch tray  18  which is formed on an upper surface of the main body casing  2 . 
     2. Drawer Unit 
     (1) Cartridge Guide 
     A shown in  FIGS. 2 , and  3 A to  3 G, cartridge guides  21  are formed on an inner surface of each side plate (not shown) of the drawer frame  5  of the drawer unit  3 . Each cartridge guide  21  is configured to guide a corresponding one of the four development cartridges  10  when the development cartridge  10  is attached to or detached from the drawer frame  5 . More specifically, on the inner surface of each side plate, projection rails (rib-shaped walls)  22  are formed that protrude toward the inside of the drawer frame  5 . Each projection rail  22  is formed substantially in a shape of the character “U” that is open upward. Each cartridge guide  21  is formed with an inside section partitioned by the projection rail  22 . 
     A lower end portion of the projection rail  22  extends along a straight line connecting a rotational center of the photoconductive drum  8  and a rotational center of the development roller  12  in the state where the development cartridge  10  is attached to the drawer frame  5 . Then, the lower end portion of the projection rail  22  bends toward an upper rear side at an angle of  90  degrees at the lowest end, further bends toward au upper front side at an angle of  90  degrees point, and again extends along the aforementioned straight line. Namely, the lower end portion of the projection rail  22  is formed in a shape of an angular “C.” Further, a lower end section of the cartridge guide  21 , which is formed with the C-shaped portion, extends to be parallel to the straight line connecting the rotational center of the photoconductive drum  8  and the rotational center of the development roller  12 . In addition, a width of the lower end section of the cartridge guide  21  is as long as an outer diameter of a below-mentioned shaft cover  45 . 
     (2) Pressing Member 
     Further, each side plate (not shown) of the drawer frame  5  is provided with four pressing members  31  each of which is configured to press a corresponding one of the four development cartridges  10 . Each pressing member  31  is formed substantially in a fan shape with a circumferential surface portion being partially removed from a fan with a central angle of 60 degrees when viewed in the left-to-right direction. More specifically, the pressing member  31  has a shape formed with a half-arc surface  32 , a crank-shaped surface  33 , a linear surface  34 , and a protruding surface  35 . The half-arc surface  32  is formed in a half-arc shape when viewed in the left-to-right direction. The crank-shaped surface  33  is formed in a crank shape extending from one end of the half-arc surface  33  when viewed in the left-to-right direction. The linear surface  34  is formed in a linear shape extending from the other end of the half-arc surface  33  when viewed in the left-to-right direction. The protruding surface  35  is continuous with the crank-shaped surface  33  and the linear surface  34  and protrudes to be farther from the half-arc surface  32 . 
     At each side of each development cartridge  10  in the left-to-right direction, a shaft  36  extending in the left-to-right direction is disposed in such a position as to face an upper front end of the development cartridge  10 . Each shaft  36  is un-rotatably held by the side plates of the drawer frame  5 . 
     Then, a distal end of the shaft  36  is inserted into a portion that is a center of the half-arc surface  32  of the pressing member  31 , so as to be rotatable relative to the pressing member  31 . Thereby, the pressing member  31  is supported by the shaft  36  to be swingable (rotatable) around the shaft  36 . As depicted in  FIG. 3G , the pressing member  31  is provided such that the crank-shaped surface  33  thereof extends in non-contact with the development cartridge  10  so as to be inclined slightly rearward relative to the vertical direction. 
     Further, as illustrated in  FIG. 2 , a linear spring  37  is wound around the shaft  36 . One end of the linear spring  37  extends downward from the shaft  36  and is fixed to the side plate of the drawer frame  5 . The other end of the linear spring  37  is fixed to the pressing member  31 . The pressing member  31  is urged clockwise by the linear spring  37  when viewed from the right side. 
     When viewed in the left-to-right direction, the linear surface  34  of the pressing member  31  bends at an angle of 90 degrees, slightly extends toward a lower rear side, further bends, and then extends toward the protruding surface  35 . Thereby, at an end of the linear surface  34  that is closer to the protruding surface  35 , a restriction section  38  is formed substantially in a right-triangle shape when viewed in the left-to-right direction. A section of the linear surface  34  other than a section where the restriction section  38  is formed is defined as a pressing section  39  for pressing a below-mentioned a pressed boss  41 . 
     3. Development Cartridge 
     The development housing  11  of the development cartridge  10  is formed substantially in a triangle shape with a lower portion thereof being narrower downward when viewed in the left-to-right direction. At an upper front end of each side face of the development housing  11 , a pressed boss  41  is disposed that protrudes outward. The pressed boss  41  is formed substantially in a cylindrical shape. A portion of the pressed boss  41  that faces the restriction section  38  of the pressing member  31  is formed with an L-shaped notch  42  recessed toward a lower rear side when viewed in the left-to-right direction. Thereby, as shown in  FIG. 4 , the pressed boss  41  includes, in the notch  42 , a first flat surface  42 A inclined slightly forward relative to the up-to-down direction (the vertical direction) and a second flat surface  42 B that is perpendicular to the first flat surface  42 A and inclined slightly toward an upper rear side relative to the front-to-rear direction (the horizontal direction) (for example, see  FIG. 4 ). 
     The development roller  12  is held by a lower end of the development housing  11 . Specifically, the development roller  12  includes a roller main body  43  formed in a cylindrical shape around as a central axis line extending in the left-to-right direction, and a development roller shaft  44  inserted into the roller main body  43  along the central axis line. Both ends of the development roller shaft  44  in the left-to-right direction protrude from both end faces of the roller main body  43  in the left-to-right direction, and penetrate both side faces of the development housing  11 , respectively, so as to be rotatably supported by the development housing  11 . A cylindrical shaft cover  45  is attached to a portion of the development roller shaft  44  that protrudes from the development housing  11 . 
     4. Attaching and Detaching of Development Cartridge 
     When the development cartridge  10  is attached to the drawer frame  5 , the drawer frame  5  (the drawer unit  3 ) is pulled to the pulled position outside the main body casing  2 . Then, the development cartridge  10  is placed above the drawer frame  5 , and the development cartridge  10  is moved toward the photoconductive drum  8  with the development roller  12  being directed downward. In the middle of this movement, the shaft cover  45  on each end of the development roller shaft  44  is inserted into the cartridge guide  21  from above. After that, in response to the movement of the development cartridge  10 , the shaft cover  45  is guided by the cartridge guide  21  such that the development roller  12  moves in such a direction as to approach the photoconductive drum  8 . Thereafter, when the shaft cover  45  reaches the lower end section of the cartridge guide  21 , a further movement of the development cartridge toward the photoconductive drum  8  is restricted. 
     In this state, as shown in  FIG. 3A , the pressed boss  41  of the development cartridge  10  contacts the lower end of the protruding surface  35  of the pressing member  31 . 
     After that, an upper end of the development cartridge  10  is pushed forward. Thereby, the pressed boss  41  moves toward the linear surface  34  while sliding in contact with the protruding surface  35 . Then, as depicted in  FIG. 3B , the pressed boss  41  slides under the linear surface  34  from a position on the protruding surface  35  so as to push up the pressing member  31 . 
     Further, the pressed boss  41  moves toward the half-arc surface  32  while sliding in contact with the linear surface  34 , and gets over the restriction section  38 . Then, as shown in  FIG. 3C , the pressed boss  41  moves to such a position as to be slightly away from the restriction section  38 . Thereafter, when the development housing  11  comes into contact with a supporting portion  101  of the drawer frame  5  from a rear side so as to restrict a further tilting movement of the development cartridge  10 , the attachment of the development cartridge  10  to the drawer frame  5  is completed. In this state, the pressing section  39  of the pressing member  31  contacts the pressed boss  41  from an upper front side, so as to urge the pressed boss  41  in a direction substantially parallel to a direction in which the photoconductive drum  8  presses the development roller  12 . 
     After the development cartridge  10  is attached to the drawer frame  5 , the drawer frame  5  is moved to the housed position inside the main body casing  2 . At this time, when the drawer frame  5  is moved swiftly with a great force, a rearward force may be applied to an upper end of the development cartridge  10  due to an impact generated when the movement of the drawer frame  5  is stopped in the housed position. 
     When such a force is applied to an upper end of the development cartridge  10 , the development cartridge  10  is tilted rearward. Thereby, the pressed boss  41  moves toward the restriction section  38  while sliding in contact with the pressing section  39 . When the pressed boss  41  moves to such a position as to contact the restriction section  38 , the restriction section  38  gets into the notch  42  of the pressed boss  41 , as shown in  FIG. 3D . Then, the restriction section  38  contacts the first flat surface  42 A of the pressed boss  41 . 
     At this time, as illustrated in  FIG. 4 , a straight line L 1  intersects a tangential line L 2 , so as to form an acute angle at a downstream side relative to the straight line L 1  in the direction in which the pressing section  39  presses the pressed boss  41 , when viewed from the right side. It is noted the straight line L 1  is a line extending in a released direction that is a moving direction of the pressed boss  41  through a contact point between the restriction section  38  and the first flat surface  42 A. Further, the tangential line L 2  is a tangential line that touches both the restriction section  38  and the first flat surface  42 A at the contact point. Additionally, the tangential line L 2  intersects a straight line L 3 , so as to form an acute angle at a downstream side relative to the straight line L 3  in the direction in which the pressing section  39  presses the pressed boss  41 , when viewed from the right side. It is noted that the straight line L 3  is a line passing through the center line of the shaft  36  and the contact point between the restriction section  38  and the first flat surface  42 A. 
     Therefore, after contact is established between the restriction section  38  and the first flat surface  42 A of the pressed boss  41 , the force that the restriction section  38  receives from the pressed boss  41  is changed into a force in such a direction that the pressing section  39  presses the pressed boss  41 , as indicated by an arrow in  FIG. 3D . As a result, the movement of the pressed boss  41  in the released direction is restricted, such that the pressed boss  41  is prevented from getting over the restriction section  38  to be away from the linear surface  34 . 
     When the development cartridge  10  is detached from the drawer frame  5 , the drawer frame  5  (the drawer unit  3 ) is pulled out to the pulled position outside the main body casing  2 . Then, as shown in  FIG. 3E , when the pressing member  31  is turned forward by a user&#39;s finger against the clockwise urging force by the linear spring  37  when viewed from the right side, the pressing section  39  is separated from the pressed boss  41 . At this time, the restriction section  38  is placed out of a path on which the pressed boss  41  moves in the released direction. 
     After that, an upper end of the development cartridge  10  is pushed rearward while keeping the posture of the pressing member  31 . Thereby, as illustrated in  FIG. 3F , when the pressed boss  41  is behind the pressing member, the development cartridge  10  is placed in a released state (takes a released posture). When the development cartridge  10  is in the released state, the development cartridge  10  is lifted up and completely detached from the drawer frame  5 , as depicted in  FIG. 3G . 
     5. Effects 
     (1) Effect 1 
     As described above, the development cartridge  10  includes the pressed boss  41  and the development roller  12 . Further, when attached to the drawer frame  5  that holds the photoconductive drum  8 , the development cartridge  10  can move between a pressed posture (a pressed state) where the pressed boss  41  is pressed by the pressing member  31  and the released state where the pressed boss  41  is released from the pressing of the pressing member  31 . The pressing member  31  is provided to the drawer frame  5  and provided with the pressing section  39  and restriction section  38 . The pressing section  39  contacts and presses the pressed boss  41  when the development cartridge  10  is in the pressed state. The restriction section  38  is disposed in a different position from that of the pressing section  39  and configured to restrict the movement of the pressed boss  41  in the pressing state in the released direction of the pressed boss  41  (i.e., the moving direction in which the pressed boss  41  moves when the development cartridge  10  moves from the pressing state to the released state). 
     As the restriction section  38  restricts the movement of the pressed boss  41  in the released direction, it is possible to prevent the development cartridge  10  from being improperly detached from the drawer frame  5 . The restriction section  38  is provided not separately from but to the pressing member  31 . Thus, with such a simple configuration it is possible to prevent the development cartridge  10  from being improperly detached from the drawer frame  5 . 
     (2) Effect 2 
     The pressing section  39  and the restriction section  38  are arranged in the aforementioned order in the released direction. Namely, the pressing section  39  is disposed upstream relative to the restriction section  38  in the released direction. Therefore, it is possible to certainly restrict the movement of the pressed boss  41  (from the pressed state to the released state) in the released direction. Consequently, it is possible to prevent in a favorable manner the development cartridge  10  from being improperly detached from the drawer frame  5 . 
     (3) Effect 3 
     In addition, when moves in the released direction, the pressed boss  41  comes in contact with the restriction section  38  such that the movement thereof is restricted. After contact is established between the pressed boss  41  and the restriction section  38 , the force that the restriction section  38  receives from the pressed boss  41  is changed into a pressing force in the pressing direction in which the pressing section  39  presses the pressed boss  41 . 
     In the color printer  1 , the straight line L 1  (which extends in the released direction through the contact point between the restriction section  38  and the first flat surface  42 A when contact is established therebetween) and the tangential line L 2  (which touches both the restriction section  38  and the first flat surface  42 A at the contact point) form an acute angle at a downstream side relative to the straight line L 1  in the direction in which the pressing section  39  presses the pressed boss  41 . Thereby, the force that the restriction section  38  receives from the pressed boss  41  is certainly changed into the pressing force after contact is established between the pressed boss  41  and the restriction section  38 . 
     As a result, the force with which the pressing member  39  presses the pressed boss  41  rises, and thereby it is possible to more certainly restrict the movement of the pressed boss  41 . Thus, it is possible to prevent in a more favorable manner the development cartridge  10  from being improperly detached from the drawer frame  5 . 
     (4) Effect 4 
     The restriction section  38  is disposed in a position where the restriction section  38  can be separated from the pressed boss  41  when the development cartridge  10  is in the pressing state. Thereby, the restriction section  38  is generally separated from the pressed boss  41  when the development cartridge  10  is in the pressing state. Hence, since there is no risk that the restriction section  38  might exert any influence on the pressed boss  41 , the pressing section  39  can press the pressed boss  41  in favorable manner. 
     (5) Effect 5 
     The pressed boss  41  includes its circumferential surface and the first flat surface  42 A. The circumferential surface of the pressed boss  41  receives a force from the pressing section  39 . The first flat surface  42 A receives a force from the restriction section  38  after establishing a contact with the restriction section  38 . The pressed boss  41  includes the notch  42  formed to be recessed in the opposite direction to the released direction. The first flat surface  42 A faces the notch  42 . In the pressed boss  41 , the circumferential surface that receives a force from the pressing section  39  is different from the first flat surface  42 A that receives a force from the restriction section  38 . Thereby, it is possible to design the pressing section  39  and the restriction section  38  separately, and thus to design the pressing member  31  more flexibly. 
     (6) Effect 6 
     The pressing member  31  is rotatably supported by the shaft  36  provided to the drawer frame  5 , and urged against the development cartridge  10  by the linear spring  37  (see  FIG. 2 ). With such a simple configuration, it is possible to allow the pressing section  39  of the pressing member  31  to press the pressed boss  41 . 
     (7) Effect 7 
     When the pressed boss  41  contacts the restriction section  38  at the contact point, the tangential line L 2  (which touches both the restriction section  38  and the first flat surface  42 A at the contact point) and the straight line L 3  (which passes through the center line of the shaft  36  and the contact point) form an acute angle at a downstream side relative to the straight line L 3  in the direction in which the pressing section  39  presses the pressed boss  41  when viewed from the right side. Thereby, it is possible to prevent the pressing member  31  from turning in such a direction that the pressing section  39  is farther from pressed boss  41  when the pressed boss  41  contacts the restriction section  38 . Thus, it is possible to restrict the movement of the pressed boss  41  by the restriction section  38  in a more favorable manner. 
     (8) Effect 8 
     The pressing member  31  includes the protruding surface  35 . The protruding surface  35  serves as a guide surface for guiding the pressed boss  41 , which is in non-contact with the pressing section  39 , to such a position as to contact the pressing section  39 . Accordingly, when the development cartridge  10  is attached to the drawer frame  5 , it is possible to guide the pressed boss  41  by the protruding surface  35  into the position to contact the pressing section  39 . Therefore, it is possible to easily place the pressed boss  41  into the position to contact the pressing section  39 . 
     Hereinabove, the embodiment according to aspects of the present invention has been described. The present invention can be practiced by employing conventional materials, methodology and equipment. Accordingly, the details of such materials, equipment and methodology are not set forth herein in detail. In the previous descriptions, numerous specific details are set forth, such as specific materials, structures, chemicals, processes, etc., in order to provide a thorough understanding of the present invention. However, it should be recognized that the present invention can be practiced without reapportioning to the details specifically set forth. In other instances, well known processing structures have not been described in detail, in order not to unnecessarily obscure the present invention. 
     Only an exemplary embodiment of the present invention and but a few examples of their versatility are shown and described in the present disclosure. It is to be understood that the present invention is capable of use in various other combinations and environments and is capable of changes or modifications within the scope of the inventive concept as expressed herein. For example, the following modifications are feasible. 
     6. Modifications 
     (1) First Modification 
     Instead of the restriction section  38  provided to the pressing section  31  as shown in  FIG. 4 , for instance, as illustrated in  FIG. 5 , a restriction section  51  that is a projection smaller than the restriction section  38  may be formed at an end, closer to the protruding surface  35 , of the linear surface  34 . Further, as illustrated in  FIG. 5 , the pressed boss  41  may not necessarily formed with the notch  42 . 
     When a rearward force is applied to an upper end of the development cartridge  10  after the development cartridge  10  is attached to the drum frame  5 , the pressed boss  41  moves toward the restriction section  51  while sliding in contact with the pressing section  39 . When the pressed boss  41  moves to a contact position where it contacts the restriction section  51 , the pressed boss  41  contacts the restriction section  51  as shown in  FIG. 6 . At this time, a straight line L 1  (which extends in a released direction that is a moving direction of the pressed boss  41  through a contact point between the restriction section  51  and the pressed boss  41 ) intersects a tangential line L 2  (which touches both the restriction section  51  and the pressed boss  41  at the contact point) so as to form an acute angle at a downstream side relative to the straight line L 1  in a direction in which the pressing section  39  presses the pressed boss  41 , when viewed from the right side. Further, the tangential line L 2  intersects a straight line L 3  (which passes through the center line of the shaft  36  and the contact point between the restriction section  51  and the pressed boss  41 ) so as to form an acute angle at a downstream side relative to the straight line L 3  in the direction in which the pressing section  39  presses the pressed boss  41 , when viewed from the right side. 
     Therefore, the force that the restriction section  51  receives from the pressed boss  41  after contact is established between the restriction section  51  and the pressed boss  41  is changed into a force in a direction in which the pressing section  39  presses the pressed boss  41 . Consequently, the movement of the pressed boss  41  in the released direction is restricted, such that the pressed boss  41  is prevented from getting over the restriction section  51  to be away from the linear surface  34 . 
     (2) Second Modification 
     Additionally, as illustrated in  FIG. 7 , an unguiform restriction section  61  may be formed at an end, closer to the protruding surface  35 , of the linear surface  34 . The restriction section  61  has a forward-facing surface that forms an acute angle with the pressing section  39  (the linear surface  34 ) and is smaller than the restriction section  38  shown in  FIG. 4 . 
     In this case, a projection  62  may be formed on the circumferential surface of the pressed boss  41 . When the pressed boss  41  moves rearward, the projection  62  may contact a corner formed between the pressing section  39  and the restriction section  61 . Thereby, the pressing member  31  is turned clockwise by a force that the restriction section  61  receives from the projection  62  after contact is established between the projection  62  and the corner, when viewed from the right side. Consequently, a force in a direction in which the pressing section  39  presses the pressed boss  41  rises. 
     Thus, the drawer unit  3  configured as above in the second modification can provide the same effects as those described in the aforementioned embodiment and the first modification. 
     (3) Third Modification 
     Additionally, when the pressing member  31  is formed with the restriction section  61 , the pressed boss  41  may be formed in a teardrop shape with a pointed projection  71  when viewed in the left-to-right direction, as shown in  FIG. 8 . In this case, when the pressed boss  41  moves rearward, the projection  71  may contact the corner formed between the pressing section  39  and the restriction section  61 . 
     Thus, the drawer unit  3  configured as above in the second modification can provide the same effects as those described in the second modification in which the pressed boss  41  is formed with the projection  62  (see  FIG. 7 ). 
     (4) Fourth Modification 
     Instead of the pressing member  31  formed substantially in a fan shape when viewed in the left-to-right direction, a pressing member  81  shaped as shown in  FIG. 9  may be employed. The pressing member  81  may be formed as an arm extending rearward from the shaft  36 . Specifically, the pressing member  81  may be formed integrally with a pressing section  82  (which has a base end supported rotatably by the shaft  36 , slightly extends toward an upper rear side, and then bends and extends rearward) and a restriction section  83  (which is formed in a rectangle shape when viewed in the left-to-right direction). The shaft  36  and the pressed boss  41  face each other in the front-to-rear direction. Further, a forward-facing surface of the restriction section  83  extends substantially in the up-to-down direction (the vertical direction) in a state where the pressing section  82  presses the pressed boss  41 . 
     According to this configuration, when the pressed boss  41  moves rearward, the pressed boss  41  comes in contact with the restriction section  83 . Consequently, the movement of the pressed boss  41  is restricted. At this time, the pressed boss  41  does not provide the restriction section  83  with any force for turning the pressing member  81 . Thus, it is possible to prevent the development cartridge  10  from being improperly detached from the drawer frame  5 . 
     (5) Fifth Modification 
     Instead of the pressing member  31  formed substantially in a fan shape when viewed in the left-to-right direction, a pressing member  91  shaped as shown in  FIG. 10  may be employed. The pressing member  91  may be formed as an arm extending rearward from the shaft  36 . Specifically, the pressing member  91  may be formed integrally with a pressing section  92  (which has a base end supported rotatably by the shaft  36 , slightly extends toward an upper rear side, and then bends and extends rearward) and a restriction section  93  (which is formed in a trapezoidal shape when viewed in the left-to-right direction). The shaft  36  and the pressed boss  41  face each other in the front-to-rear direction. Further, a forward-facing surface of the restriction section  93  is tilted rearward with respect to the vertical direction, in a state where the pressing section  92  presses the pressed boss  41 . 
     According to this configuration, when the pressed boss  41  moves rearward, the pressed boss  41  comes in contact with the restriction section  93 . Consequently, the movement of the pressed boss  41  is restricted. At this time, the pressed boss  41  provides the restriction section  93  with a force directed toward a lower rear side. Accordingly, the pressing member  91  is turned clockwise when viewed from the right side. Consequently, a force in a direction in which the pressing section  92  presses the pressed boss  41  rises. Thus, it is possible to certainly prevent the development cartridge  10  from being improperly detached from the drawer frame  5 . 
     In the aforementioned embodiment, the pressing section  39  is provided to the drawer frame  5  that includes a plurality of development cartridges  10  detachably attached thereto. However, such an aspect of the present invention may be applied to a monochrome-type drum cartridge.