Patent Publication Number: US-11662685-B2

Title: Image forming apparatus having a drawer

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation application of U.S. patent application Ser. No. 17/195,849, filed Mar. 9, 2021, which is a continuation application of U.S. patent application Ser. No. 16/907,546, filed Jun. 22, 2020 and claims priority from Japanese Patent Application No. 2019-123950, which was filed on Jul. 2, 2019, the entireties of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     The following disclosure relates to an image forming apparatus. 
     There has been known an electrophotographic image forming apparatus in which a process cartridge including a photoconductive drum and a developing roller is removably mounted to a drawer. The image forming apparatus of this type requires replacement of the process cartridge when the process cartridge becomes empty of toner. However, the photoconductive drum has not reached the end of its useful life at this time, and thus the photoconductive drum is discarded before the end of the useful life, resulting in increase in running costs. 
     To solve this problem, an image forming apparatus is devised in which the process cartridge is separated into a drum cartridge including the photoconductive drum and a developing cartridge including the developing roller to enable individual replacement of the drum cartridge and the developing cartridge. 
     In such an image forming apparatus, unfortunately, the drum cartridge is mounted to the drawer, and the developing cartridge is mounted to the drum cartridge, but the drum cartridge moves relative to the drawer in removal of the developing cartridge from the drum cartridge, making it difficult to remove the developing cartridge. 
     SUMMARY 
     Accordingly, an aspect of the disclosure relates to an image forming apparatus capable of making a drum cartridge immovable relative to a drawer when a toner cartridge is removed from the drum cartridge mounted to the drawer. 
     In one aspect of the disclosure, an image forming apparatus includes: a housing; a drum cartridge including a photoconductive drum; a developing cartridge including a developing roller; a drawer movable between an inner position and an outer position, the drum cartridge being located in the housing when the drawer is located at the inner position in a state in which the drum cartridge is mounted to the drawer, at least a portion of the drum cartridge being exposed to an outside of the housing when the drawer is located at the outer position in the state in which the drum cartridge is mounted to the drawer; and a lock member provided on the drawer and movable between a lock position at which the lock member locks the drum cartridge to the drawer in the state in which the drum cartridge is mounted to the drawer, and a release position at which a lock between the drum cartridge and the drawer is released. The lock member includes an operation portion for moving the lock member between the lock position and the release position. The developing cartridge includes a cover member that covers at least a portion of the operation portion in a state in which the drum cartridge is mounted to the drawer, and the developing cartridge is mounted to the drum cartridge. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The objects, features, advantages, and technical and industrial significance of the present disclosure will be better understood by reading the following detailed description of the embodiments, when considered in connection with the accompanying drawings, in which: 
         FIG.  1    is a central cross-sectional view of an image forming apparatus; 
         FIG.  2 A  is a side view of a developing cartridge; 
         FIG.  2 B  is a rear view of the developing cartridge; 
         FIG.  3 A  is a side view of a drum cartridge; 
         FIG.  3 B  is a cross-sectional view of the drum cartridge, viewed from a rear side and taken along a plane containing a rotation shaft of a photoconductive drum of the drum cartridge; 
         FIG.  4    is a cross-sectional view of a process unit, viewed from a rear side and taken along the plane containing the rotation shaft of the photoconductive drum in a state in which the developing cartridge is mounted on the drum cartridge; 
         FIG.  5    is a side elevational view in cross section, illustrating the image forming apparatus in a state in which the drawer is located at the inner position, and the drawer guides and the urging rails are located at their respective positioning positions; 
         FIG.  6    is a cross-sectional view of the image forming apparatus, viewed from a rear side and taken along the plane containing the rotation shaft of the photoconductive drum in the state in which the drawer is located at the inner position, and the drawer guides and the urging rails are located at their respective positioning positions; 
         FIG.  7    is a side elevational view in cross section, illustrating the image forming apparatus in a state in which the drawer is located at the inner position, and the drawer guides and the urging rails are located at their respective positioning cancel positions; 
         FIG.  8    is a side elevational view in cross section, illustrating the image forming apparatus in a state in which the drawer is located at an outer position, and the drawer guides and the urging rails are located at their respective positioning cancel positions; 
         FIG.  9    is a side elevational view in cross section, illustrating the drawer in a state in which the developing cartridge and the drum cartridge are mounted; 
         FIG.  10    is a partial cross-sectional view of the drawer in the state in which the developing cartridge and the drum cartridge are mounted; 
         FIG.  11 A  is a side view of a cover member according to the second embodiment; and 
         FIG.  11 B  is a side view of a cover member according to the third embodiment. 
     
    
    
     EMBODIMENTS 
     Hereinafter, there will be described embodiments by reference to the drawings. It is to be understood that the following embodiments are described only by way of example, and the disclosure may be otherwise embodied with various modifications without departing from the scope and spirit of the disclosure. 
     Overall Configuration of Image Forming Apparatus 
       FIG.  1    illustrates an image forming apparatus  1  according to one embodiment of the present disclosure. The image forming apparatus  1  is an electrophotographic tandem color printer configured to form an image on a sheet S in multiple colors. 
     In the following description, the left side in  FIG.  1    is defined as a front side of the image forming apparatus  1 , the right side in  FIG.  1    as a rear side of the image forming apparatus  1 , the front side of the sheet of  FIG.  1    as a right side of the image forming apparatus  1 , and the back side of the sheet of  FIG.  1    as a left side of the image forming apparatus  1 . The upper side and the lower side in  FIG.  1    are defined as an upper side and a lower side of the image forming apparatus  1 , respectively. 
     The image forming apparatus  1  includes: a housing  2 ; a sheet-supply tray  10  capable of supporting the sheet S; and an image forming device  5  configured to form an image on the sheet S. 
     The housing  2  has a substantially rectangular parallelepiped shape and houses the sheet-supply tray  10  and the image forming device  5 . A front surface  21  of the housing  2  has an opening  2 A. The housing  2  includes a front-surface cover  22  capable of exposing and closing the opening  2 A. 
     A pivot shaft  22   a  is provided at a lower end portion of the front-surface cover  22 . The front-surface cover  22  is pivotable about the pivot shaft  22   a . The opening  2 A is exposed and closed by pivotal movement of the front-surface cover  22  about the pivot shaft  22   a . A sheet-discharge tray  23   a  is provided on an upper surface  23  of the housing  2 . The sheet-discharge tray  23   a  is inclined so as to be lower at its rear portion than its front portion. 
     A conveyance path P for the sheet S is formed in the housing  2  so as to extend from the sheet-supply tray  10  to the sheet-discharge tray  23   a  via the image forming device  5 . Sheet-supply rollers  11 , separating rollers  12 , and a separator pad  12   a  are provided in the housing  2 . 
     The sheets S supported on the sheet-supply tray  10  are separated into one and the other by the sheet-supply rollers  11 , the separating rollers  12 , and the separator pad  12   a  and supplied one by one into the conveyance path P. The sheet S supplied into the conveyance path P is conveyed toward the image forming device  5 . 
     The image forming device  5  is disposed over the sheet-supply tray  10  and includes four process units  50  arranged side by side in the front and rear direction. The process units  50  are mountable and removable on and from the housing  2  and provided so as to correspond respectively to black, yellow, magenta, and cyan. 
     The housing  2  includes a drawer  60  that supports the process units  50 . Each of the process units  50  includes a drum cartridge  51  and a developing cartridge  52 . The drum cartridge  51  is removably mounted on the drawer  60 . The developing cartridge  52  is removably mounted on the drum cartridge  51 . 
     The drum cartridge  51  includes a photoconductive drum  54  and an electrically charged roller  58 . The photoconductive drum  54  has a substantially cylindrical shape with its axial direction coinciding with the right and left direction. The photoconductive drum  54  is rotatably supported by the drum cartridge  51 . The electrically charged roller  58  extends in the right and left direction and is held in contact with an upper rear portion of the photoconductive drum  54 . 
     The developing cartridge  52  includes a developing roller  55 , a supply roller  56 , and a toner container  57  containing toner as a developer. The developing roller  55  extends in the right and left direction and is provided so as to be exposed rearward from a rear end portion of the developing cartridge  52 . The developing roller  55  is held in contact with an upper front portion of the photoconductive drum  54 . 
     The supply roller  56  extends in the right and left direction and is held in contact with an upper front portion of the developing roller  55 . The toner container  57  is disposed over the supply roller  56 . The toner is supplied from the toner container  57  to the supply roller  56 . The supply roller  56  supplies the toner to the developing roller  55 . The developing roller  55  supplies the toner to the photoconductive drum  54 . 
     An exposing unit  53  is provided over the process units  50  to expose surfaces of the respective photoconductive drums  54 . 
     A belt  31  is provided under the photoconductive drums  54 , with the conveyance path P interposed therebetween. The belt  31  is opposed to the photoconductive drums  54 . The belt  31  is tensioned between a drive roller  32  and a driven roller  33  located in front of the drive roller  32 . Transfer rollers  34  are opposed to the respective photoconductive drums  54 , with the belt  31  interposed between each of the transfer rollers  34  and a corresponding one of the photoconductive drums  54 . A belt unit  30  is constituted by the belt  31 , the drive roller  32 , the driven roller  33 , and the transfer rollers  34 . 
     In the image forming device  5 , the surface of the photoconductive drum  54  is uniformly charged by the electrically charged roller  58 , and then selectively exposed by the exposing unit  53  based on predetermined image data. As a result, an electrostatic latent image based on the image data is formed on the surface of the photoconductive drum  54 . 
     The toner contained in the toner container  57  is positively charged between the supply roller  56  and the developing roller  55  and born on a surface of the developing roller  55 . The toner born on the developing roller  55  is supplied to the electrostatic latent image formed on the surface of the photoconductive drum  54 , a toner image is born on the surface of the photoconductive drum  54 . 
     When the sheet S conveyed toward the image forming device  5  has reached a position on the belt  31 , the sheet S is conveyed by the belt  31  so as to pass through positions each between the belt  31  and a corresponding one of the photoconductive drums  54 . When the toner image born on the surface of the photoconductive drum  54  faces the sheet S, the toner image is transferred to the sheet S by a transfer bias applied to the transfer roller  34 . Thus, the toner images born on the respective photoconductive drum  54  are transferred to the sheet S by the belt unit  30 . 
     In the present embodiment, the belt  31  is constituted by a conveyor belt for conveying the sheet S to which the toner images are to be transferred. However, the belt  31  may be constituted by an intermediate transfer belt. In this case, the toner images are transferred to the belt, and then the toner images transferred to the belt are transferred to the sheet S. 
     The sheet S to which the toner images are transferred is conveyed to a fixing device  16  disposed downstream of the image forming device  5 . The fixing device  16  includes a heat roller  17  and a pressure roller  18  held in pressing contact with the heat roller  17 . The toner images are thermally fixed to the sheet S conveyed to the fixing device  16 , while the sheet S is passing through a position between the heat roller  17  and the pressure roller  18 . 
     The sheet S to which the toner images are thermally fixed is conveyed downstream from the fixing device  16  in the conveying direction and discharged onto the sheet-discharge tray  23   a  by a sheet-discharge roller  19 . 
     Developing Cartridge 
     As illustrated in  FIG.  2   , each of the developing cartridges  52  includes a development frame  521  that supports a corresponding one of the developing rollers  55  rotatably. The developing roller  55  includes a roller shaft  55   a  that is supported by the development frame  521 . 
     Opposite end portions of the roller shaft  55   a  protrude outward from the development frame  521  in the right and left direction. The development frame  521  includes a cover member  522  that is a plate member protruding outward in the right and left direction. In the present embodiment, the cover member  522  is provided on a right end portion of the development frame  521 . 
     A handle  521 H is formed at a front portion of an upper end portion of the development frame  521 . A user is allowed to grasp the handle  521 H when removing the developing cartridge  52  from the drum cartridge  51 . 
     Drum Cartridge 
     As illustrated in  FIGS.  3 A and  3 B , each of the photoconductive drums  54  is disposed such that its axial direction coincides with the right and left direction orthogonal to the moving direction of the drawer  60 . The photoconductive drum  54  includes: a drum body  541 ; a first drum shaft  542 A protruding rightward from a right end portion of the drum body  541 ; and a second drum shaft  542 B protruding from a left end portion of the drum body  541 . The first drum shaft  542 A is disposed on a first end  54 A that is a right end of the photoconductive drum  54 . The second drum shaft  542 B is disposed on a second end  54 B that is a left end of the photoconductive drum  54 . 
     The drum cartridge  51  includes: a first drum frame  511 A that supports the first end  54 A of the photoconductive drum  54  rotatably; and a second drum frame  511 B that supports the second end  54 B of the photoconductive drum  54  rotatably. Specifically, the first drum frame  511 A supports the first drum shaft  542 A disposed at the first end  54 A, and the second drum frame  511 B supports the second drum shaft  542 B disposed at the second end  54 B. 
     The first drum frame  511 A includes: a first side wall  512 A extending in the up and down direction; and a first protruding portion  513 A extending rightward from the first side wall  512 A. A portion of the first side wall  512 A at which the first protruding portion  513 A is formed has a first support hole  514 A for supporting the first drum shaft  542 A rotatably. The first protruding portion  513 A is located at a first end  51 A of the drum cartridge  51 . 
     The second drum frame  511 B includes: a second side wall  512 B extending in the up and down direction; and a second protruding portion  513 B protruding leftward from the second side wall  512 B. A portion of the second side wall  512 B at which the second protruding portion  513 B is formed has a second support hole  514 B for supporting the second drum shaft  542 B rotatably. The second protruding portion  513 B is located at a second end  51 B of the drum cartridge  51 . 
     An inner left surface of the first side wall  512 A has a first guide groove  515 A extending substantially in the up and down direction. The first guide groove  515 A is located above the first support hole  514 A. An upper end of the first guide groove  515 A is open, and a right end portion of the roller shaft  55   a  of the developing roller  55  is insertable in the first guide groove  515 A from an upper side thereof. 
     An inner right surface of the second side wall  512 B has a second guide groove  515 B extending substantially in the up and down direction. The second guide groove  515 B is located above the second support hole  514 B. An upper end of the second guide groove  515 B is open, and a left end portion of the roller shaft  55   a  of the developing roller  55  is insertable in the second guide groove  515 B from an upper side thereof. 
     As illustrated in  FIG.  4   , the developing roller  55  is mountable to the drum cartridge  51  by inserting the roller shaft  55   a  of the developing roller  55  into the first guide groove  515 A and the second guide groove  515 B. 
     A first projecting portion  516 A is formed on an outer right surface of the first side wall  512 A so as to project rightward from the first side wall  512 A. The first projecting portion  516 A projects from the first drum frame  511 A so as to extend away from the second drum frame  511 B. The first projecting portion  516 A is one example of a projecting portion. 
     A second projecting portion  516 B is formed on an outer left surface of the second side wall  512 B so as to project leftward from the second side wall  512 B. The second projecting portion  516 B projects from the second drum frame  511 B so as to extend away from the first drum frame  511 A. 
     Drawer 
     As illustrated in  FIGS.  5  and  6   , the drawer  60  is a substantially rectangular frame member capable of supporting the four process units  50 . The drawer  60  includes: a first side frame  61 A disposed to the right of the process units  50  and extending in the front and rear direction; and a second side frame  61 B disposed to the left of the process units  50  and extending in the front and rear direction. 
     The first side frame  61 A has four first support grooves  62 A arranged in the front and rear direction and each extending substantially in the up and down direction. The second side frame  61 B has four second support grooves  62 B arranged in the front and rear direction and each extending substantially in the up and down direction. Each of the number of the first support grooves  62 A and the number of the second support grooves  62 B corresponds to the number of the process units  50  supported by the respective first support grooves  62 A and the respective second support grooves  62 B. 
     Upper ends of the respective first support grooves  62 A are open so as to allow the first protruding portions  513 A of the respective drum cartridges  51  to be inserted into the respective first support grooves  62 A from an upper side thereof. Upper ends of the respective second support grooves  62 B are open so as to allow the second protruding portions  513 B of the respective drum cartridges  51  to be inserted into the respective second support grooves  62 B from an upper side thereof. The drum cartridges  51  are mountable to the drawer  60  by inserting the first protruding portions  513 A into the respective first support grooves  62 A and inserting the second protruding portions  513 B into the respective second support grooves  62 B. 
     The first protruding portions  513 A of the respective drum cartridges  51  mounted to the drawer  60  protrude outward from the first side frame  61 A in the right direction. That is, the first protruding portions  513 A of the respective first drum frames  511 A protrude from the first side frame  61 A so as to extend away from the second side frame  61 B. 
     The second protruding portions  513 B of the respective drum cartridges  51  mounted to the drawer  60  protrude outward from the second side frame  61 B in the left direction. That is, the second protruding portions  513 B of the respective second drum frames  511 B protrude from the second side frame  61 B so as to extend away from the first side frame  61 A. 
     With this configuration, when the drum cartridge  51  is mounted to the drawer  60 , the first protruding portion  513 A is supported by the first side frame  61 A, and the second protruding portion  513 B is supported by the second side frame  61 B. That is, when the drum cartridge  51  is mounted to the drawer  60 , the first side frame  61 A supports the first end  51 A of the drum cartridge  51 , and the second side frame  61 B supports the second end  51 B of the drum cartridge  51 . 
     The first side frame  61 A has first guide grooves  63 A formed in front of the respective first support grooves  62 A and each extending substantially in the up and down direction. Upper ends of the respective first guide grooves  63 A are open so as to allow the first projecting portions  516 A of the respective drum cartridges  51  to be inserted into the respective first guide grooves  63 A from an upper side thereof. 
     The second side frame  61 B has second guide grooves  63 B formed in front of the respective second support grooves  62 B and each extending substantially in the up and down direction. Upper ends of the respective second guide grooves  63 B are open so as to allow the second projecting portions  516 B of the respective drum cartridges  51  to be inserted into the respective second guide grooves  63 B from an upper side thereof. 
     The first projecting portions  516 A are inserted in the respective first guide grooves  63 A, and the second projecting portions  516 B are inserted in the respective second guide grooves  63 B, making it possible to prevent the drum cartridges  51  mounted to the drawer  60  from pivoting about the first drum shaft  542 A and the second drum shaft  542 B. 
     The first side frame  61 A is provided with lock members  70  that prevent the first projecting portions  516 A inserted in the respective first guide grooves  63 A, from coming out of the respective first guide grooves  63 A. 
     Structure for Supporting Drum Cartridge and Drawer 
     As illustrated in  FIGS.  5  and  6   , the housing  2  includes vertical frames  24 A,  24 B each extending in the front and rear direction and the up and down direction. The vertical frame  24 A is disposed at a right end portion of the housing  2  in the housing  2 . The vertical frame  24 B is disposed at a left end portion of the housing  2  in the housing  2 . 
     The vertical frame  24 A has two lower guide holes  241 A and three upper guide holes  242 A. The vertical frame  24 B has two lower guide holes  241 B and three upper guide holes  242 B. Each of the lower guide holes  241 A,  241 B and the upper guide holes  242 A,  242 B is an elongated hole extending substantially in the front and rear direction and inclined so as to be higher at its front portion than at its rear portion. The two lower guide holes  241 A are located apart from each other in the front and rear direction. The two lower guide holes  241 B are located apart from each other in the front and rear direction. The three upper guide holes  242 A are formed over the lower guide holes  241 A and located apart from each other in the front and rear direction. The three upper guide holes  242 B are formed over the lower guide holes  241 B and located apart from each other in the front and rear direction. 
     A drawer guide  65 A is provided in the housing  2  at a position located on an inner left side of the vertical frame  24 A. A drawer guide  65 B is provided in the housing  2  at a position located on an inner right side of the vertical frame  24 B. Each of the drawer guides  65 A,  65 B is a rail member extending in the front and rear direction. The first side frame  61 A is supported on the drawer guide  65 A so as to be movable in the front and rear direction. The second side frame  61 B is supported on the drawer guide  65 B so as to be movable in the front and rear direction. 
     The drawer guide  65 A includes two guide pins  651 A protruding rightward and outward. The drawer guide  65 B includes two guide pins  651 B protruding leftward and outward. The guide pins  651 A are provided so as to correspond to the respective lower guide holes  241 A and slidably inserted in the respective lower guide holes  241 A. The guide pins  651 B are provided so as to correspond to the respective lower guide holes  241 B and slidably inserted in the respective lower guide holes  241 B. 
     Since the guide pins  651 A,  651 B are inserted in the respective lower guide holes  241 A,  241 B, the drawer guides  65 A,  65 B are supported by the respective vertical frames  24 A,  24 B. The drawer guide  65 A is movable in the front and rear direction and the up and down direction relative to the vertical frame  24 A within a region in which the guide pins  651 A are slidable in the respective lower guide holes  241 A. The drawer guide  65 B is movable in the front and rear direction and the up and down direction relative to the vertical frame  24 B within a region in which the guide pins  651 B are slidable in the respective lower guide holes  241 B. 
     An urging rail  66 A is provided in the housing  2  at a position located on an inner left side of the vertical frame  24 A. An urging rail  66 B is provided in the housing  2  at a position located on an inner right side of the vertical frame  24 B. Each of the urging rails  66 A,  66 B is a rail member extending in the front and rear direction and located above a corresponding one of the drawer guides  65 A,  65 B. 
     The urging rail  66 A includes three guide pins  661 A protruding rightward and outward. The urging rail  66 B includes three guide pins  661 B protruding leftward and outward. The guide pins  661 A are provided so as to correspond to the respective upper guide holes  242 A and slidably inserted in the respective upper guide holes  242 A. The guide pins  661 B are provided so as to correspond to the respective upper guide holes  242 B and slidably inserted in the respective upper guide holes  242 B. 
     Since the guide pins  661 A,  661 B are inserted in the respective upper guide holes  242 A,  242 B, the urging rails  66 A,  66 B are supported by the respective vertical frames  24 A,  24 B. The urging rail  66 A is movable in the front and rear direction and the up and down direction relative to the vertical frame  24 A within a region in which the guide pins  661 A are slidable in the respective upper guide holes  242 A. The urging rail  66 B is movable in the front and rear direction and the up and down direction relative to the vertical frame  24 B within a region in which the guide pins  661 B are slidable in the respective upper guide holes  242   b.    
     A coupling arm  67 A is disposed in front of the drawer guide  65 A and the urging rail  66 A. A coupling arm  67 B is disposed in front of the drawer guide  65 B and the urging rail  66 B. Front end portions of the drawer guide  65 A and the urging rail  66 A are coupled to the coupling arm  67 A. Front end portions of the drawer guide  65 B and the urging rail  66 B are coupled to the coupling arm  67 B. 
     A coupling pin  652 A protruding rightward and outward is formed on the front end portion of the drawer guide  65 A. A coupling pin  652 B protruding leftward and outward is formed on the front end portion of the drawer guide  65 B. A lower end portion of the coupling arm  67 A has a coupling hole  671 A in which the coupling pin  652 A is inserted. A lower end portion of the coupling arm  67 B has a coupling hole  671 B in which the coupling pin  652 B is inserted. 
     Each of the coupling holes  671 A,  671 B is elongated in the up and down direction. The coupling pins  652 A,  652 B are inserted in the respective coupling holes  671 A,  671 B so as to be slidable in the up and down direction. The drawer guides  65 A,  65 B are coupled to the respective coupling arms  67 A,  67 B so as to be movable in the up and down direction. The urging rails  66 A,  66 B are coupled and fixed to the respective coupling arms  67 A,  67 B. 
     An engaging pin  672 A protruding rightward and outward is formed on a front end portion of the coupling arm  67 A. An engaging pin  672 B protruding leftward and outward is formed on a front end portion of the coupling arm  67 B. The front-surface cover  22  of the housing  2  includes link arms  27 A,  27 B. Each of the link arms  27 A,  27 B has an arc shape curved rearward and downward from the front-surface cover  22 . The link arms  27 A,  27 B respectively have engaging holes  271 A,  271 B engageable with the respective engaging pins  672 A,  672 B. Each of the engaging holes  271 A,  271 B has an arc shape curved so as to be lower at its rear portion than at its front portion. 
     With this configuration, the drawer  60  is movable between an inner position (illustrated in  FIG.  5   ) and an outer position (illustrated in  FIG.  8   ) in the front and rear direction. That is, the moving direction of the drawer  60  coincides with the front and rear direction, and a side nearer to the outer position than to the inner position in the moving direction of the drawer  60  is a front side, and a side nearer to the inner position than to the outer position in the moving direction of the drawer  60  is a rear side. 
     As illustrated in  FIG.  5   , when the drawer  60  is located at the inner position in the state in which the drum cartridge  51  is mounted to the drawer  60 , the drum cartridge  51  and the developing cartridge  52  are contained in the housing  2 . 
     As illustrated in  FIG.  8   , when the drawer  60  is located at the outer position in the state in which the drum cartridge  51  is mounted to the drawer  60 , at least a portion of the drum cartridge  51  and the developing cartridge  52  is exposed to the outside of the housing  2 . When the drawer  60  is located at the outer position, the drum cartridge  51  and the developing cartridge  52  exposed to the outside of the housing  2  are mountable on and removable from the drawer  60 . 
     The drawer guides  65 A,  65 B and the urging rails  66 A,  66 B are movable in the front and rear direction between (i) their respective positioning positions (illustrated in  FIG.  5   ) at which the drum cartridges  51  are positioned with respect to the housing  2  and (ii) their respective positioning cancel positions (illustrated in  FIG.  7   ) at which the positioning of the drum cartridges  51  with respect to the housing  2  is canceled, and the drawer  60  is movable in the front and rear direction. 
     As illustrated in  FIG.  5   , when the front-surface cover  22  of the housing  2  is closed, the drawer  60  is located at the inner position, and the drawer guides  65 A,  65 B and the urging rails  66 A,  66 B are located at their respective positioning positions. 
     When the drawer guides  65 A,  65 B and the urging rails  66 A,  66 B are located at their respective positioning positions, the guide pins  651 A,  651 B are located at rear end portions of the respective lower guide holes  241 A,  241 B, and the guide pins  661 A,  661 B are located at rear end portions of the respective upper guide holes  242 A,  242 B. Thus, each of the drawer guides  65 A,  65 B and the urging rails  66 A,  66 B is located at a rear and lower portion of its movable region. 
     The housing  2  includes a horizontal frame  25  extending in the horizontal direction between the right and left vertical frames  24 A,  24 B. The horizontal frame  25  is disposed below the drawer guides  65 A,  65 B. A first support plate  26 A and a second support plate  26 B are provided upright on the horizontal frame  25 . Each of the first support plate  26 A and the second support plate  26 B is a plate member extending in the front and rear direction. 
     The first support plate  26 A is disposed on an inner side of the first side frame  61 A in the right and left direction and capable of supporting the first drum frames  511 A from a lower side thereof. The second support plate  26 B is disposed on an inner side of the second side frame  61 B in the right and left direction and capable of supporting the second drum frames  511 B from a lower side thereof. 
     An upper end of the first support plate  26 A has positioning recessed portions  261 A formed respectively at positions corresponding to the positions of the respective drum cartridges  51  in the front and rear direction. When the drawer guide  65 A and the urging rail  66 A are located at their respective positioning positions, the first side walls  512 A of the respective first drum frames  511 A are supported by the respective positioning recessed portions  261 A from below. 
     An upper end of the second support plate  26 B has positioning recessed portions  261 B formed respectively at positions corresponding to the positions of the respective drum cartridges  51  in the front and rear direction. When the drawer guide  65 B and the urging rail  66 B are located at their respective positioning positions, the second side walls  512 B of the respective second drum frames  511 B are supported by the respective positioning recessed portions  261 B from below. 
     The first support plate  26 A and the second support plate  26 B are sheet-metal members formed by press working using the same metal mold and having the same shape. This ensures high accuracy for aligning the positions of the positioning recessed portions  261 A of the first support plate  26 A and the positioning recessed portions  261 B of the second support plate  26 B which support the drum cartridges  51 . Thus, it is possible to reduce positional misalignment of the photoconductive drums  54  when the drum cartridges  51  are positioned. 
     The urging rail  66 A is provided with first pressing members  68 A respectively at positions corresponding to the positions of the respective drum cartridges  51  in the front and rear direction. The first pressing members  68 A are arranged on a right and outer side of the first side frame  61 A. When the drawer guide  65 A and the urging rail  66 A are located at their respective positioning positions, the first pressing members  68 A press the first protruding portions  513 A of the respective first drum frames  511 A downward. 
     The urging rail  66 B is provided with second pressing members  68 B respectively at positions corresponding to the positions of the respective drum cartridges  51  in the front and rear direction. The second pressing members  68 B are arranged on a left and outer side of the second side frame  61 B. When the drawer guide  65 B and the urging rail  66 B are located at their respective positioning positions, the second pressing members  68 B press the second protruding portions  513 B of the respective second drum frames  511 B downward. 
     Thus, when the drawer guides  65 A,  65 B and the urging rails  66 A,  66 B are located at their respective positioning positions, the drum cartridges  51  are held by the first support plate  26 A and the first pressing members  68 A from lower and upper sides and held by the second support plate  26 B and the second pressing members  68 B from lower and upper sides, thereby positioning the drum cartridges  51 . This configuration enables stable positioning of the drum cartridges  51  with respect to the housing  2 . 
     In this case, the first pressing members  68 A are disposed on a right and outer side of the first support plate  26 A, and the second pressing members  68 B are disposed on a left and outer side of the second support plate  26 B. Accordingly, the distance W 2  in the right and left direction between (i) the position at which each of the first pressing members  68 A contacts a corresponding one of the first protruding portions  513 A and (ii) the position at which each of the second pressing members  68 B contacts a corresponding one of the second protruding portions  513 B is greater than the distance W 1  in the right and left direction between the position at which the first support plate  26 A contacts the first drum frames  511 A and the position at which the second support plate  26 B contacts the second drum frames  511 B. 
     With this configuration, each of the drum cartridges  51  can be effectively pressed by the first support plate  26 A and a corresponding one of the first pressing members  68 A and by the second support plate  26 B and a corresponding one of the second pressing members  68 B, resulting in higher accuracy for positioning the drum cartridges  51 . 
     The first support plate  26 A supports the first side walls  512 A of the respective first drum frames  511 A from a lower side thereof in the present embodiment but may support the first protruding portions  513 A from a lower side thereof. Likewise, the second support plate  26 B supports the second side walls  512 B of the respective second drum frames  511 B from a lower side thereof in the present embodiment but may support the second protruding portions  513 B from a lower side thereof. 
     In this case, the image forming apparatus  1  may be configured such that positions at which the first support plate  26 A contacts the respective first protruding portions  513 A are located on an inner side, in the right and left direction, of positions at which the first pressing members  68 A contact the respective first protruding portions  513 A, and positions at which the second support plate  26 B contacts the respective second protruding portions  513 B are located on an inner side, in the right and left direction, of positions at which the second pressing members  68 B contact the respective second protruding portions  513 B. 
     That is, the image forming apparatus  1  may be configured such that the distance W 2  in the right and left direction between (i) the position at which each of the first pressing members  68 A contacts a corresponding one of the first protruding portions  513 A and (ii) the position at which each of the second pressing members  68 B contacts a corresponding one of the second protruding portions  513 B is greater than the distance in the right and left direction between the positions at which the first support plate  26 A contacts the respective first protruding portions  513 A and the positions at which the second support plate  26 B contacts the respective second protruding portions  513 B. This configuration enables effective pressing of the drum cartridges  51  to increase the accuracy for positioning the drum cartridges  51 . 
     When the front-surface cover  22  of the housing  2  is opened in the state illustrated in  FIG.  5   , as illustrated in  FIG.  7   , the link arms  27 A,  27 B are moved frontward, causing the engaging pins  672 A,  672 B to be engaged with rear edges of the respective engaging holes  271 A,  271 B, whereby the coupling arms  67 A,  67 B are pulled frontward. When the coupling arms  67 A,  67 B are pulled frontward, the drawer guides  65 A,  65 B and the urging rails  66 A,  66 B are moved frontward to their respective positioning cancel positions. 
     In this case, since the guide pins  651 A,  651 B are slid from the rear end portions to the front end portions of the respective lower guide holes  241 A,  241 B with frontward movement of the drawer guides  65 A,  65 B, the drawer guides  65 A,  65 B are also moved upward. Likewise, since the guide pins  661 A,  661 B are slid from the rear end portions to the front end portions of the respective upper guide holes  242 A,  242 B with frontward movement of the urging rails  66 A,  66 B, the urging rails  66 A,  66 B are also moved upward. 
     While an amount of upper movement of each of the urging rails  66 A,  66 B is set to be greater than an amount of upper movement of each of the drawer guides  65 A,  65 B when the front-surface cover  22  is opened, the drawer guides  65 A,  65 B are coupled to the respective coupling arms  67 A,  67 B so as to be movable in the up and down direction, making it possible to absorb a difference between the amount of upper movement of each of the urging rails  66 A,  66 B and the amount of upper movement of each of the drawer guides  65 A,  65 B. 
     When the drawer guides  65 A,  65 B are moved frontward and upward, the drawer  60  supported by the drawer guides  65 A,  65 B are moved upward with the drum cartridges  51 , thereby canceling the state in which the drum cartridges  51  are supported by the first support plate  26 A and the second support plate  26 B. 
     When the urging rails  66 A,  66 B are moved frontward and upward, each of the first pressing members  68 A and the second pressing members  68 B is moved from a position located over a corresponding one of the first protruding portions  513 A of the respective first drum frames  511 A and the second protruding portions  513 B of the respective second drum frames  511 B, to a position located in front of the corresponding one of the first protruding portions  513 A and the second protruding portions  513 B, thereby canceling the state in which each of the first pressing members  68 A and the second pressing members  68 B presses a corresponding one of the first protruding portions  513 A and the second protruding portions  513 B. 
     In this case, since the amount of upper movement of each of the urging rails  66 A,  66 B is set to be greater than the amount of upper movement of each of the drawer guides  65 A,  65 B, it is possible to smoothly cancel the state in which each of the first pressing members  68 A and the second pressing members  68 B presses a corresponding one of the first protruding portions  513 A and the second protruding portions  513 B. It is also possible to move the drawer  60  from the inner position to the outer position without collision or interference between each of the first pressing members  68 A and the second pressing members  68 B and a corresponding one of the first protruding portions  513 A and the second protruding portions  513 B. 
     Thus, when the drawer guides  65 A,  65 B and the urging rails  66 A,  66 B are located at their respective positioning cancel positions, the state in which the drum cartridges  51  are pressed by the respective first pressing members  68 A and the respective second pressing members  68 B and the state in which the drum cartridges  51  are supported by the first support plate  26 A and the second support plate  26 B are canceled. This cancels the positioning of the drum cartridges  51  with respect to the housing  2 , making the drawer  60  movable in the front and rear direction. 
     When the front-surface cover  22  is opened, the drawer  60  becomes movable in the front and rear direction. The user in this state can grasp a handle  64  of the drawer  60  and pull the drawer  60  frontward to move the drawer  60  to the outer position as illustrated in  FIG.  8   . In the state in which the drawer  60  is located at the outer position, the drum cartridges  51  and the developing cartridges  52  of the process units  50  exposed to the outside of the housing  2  are mountable to and removable from the drawer  60 . 
     The drawer  60  can be moved to the inner position by pressing the drawer  60  located at the outer position, rearward. When the front-surface cover  22  is closed in the state in which the drawer guides  65 A,  65 B and the urging rails  66 A,  66 B are located at their respective positioning cancel positions as a result of opening of the front-surface cover  22 , the engaging pins  672 A,  672 B are engaged with front edges of the respective engaging holes  271 A,  271 B, whereby the coupling arms  67 A,  67 B are pressed rearward. When the coupling arms  67 A,  67 B are pressed rearward, the drawer guides  65 A,  65 B and the urging rails  66 A,  66 B are moved rearward to their respective positioning positions. 
     Lock Member and Cover Member 
     As illustrated in  FIGS.  9  and  10   , each of the lock members  70  includes: a pivot shaft  71  pivotably supported by the first side frame  61 A of the drawer  60 ; a claw  72  and an operation portion  73  supported by the pivot shaft  71  so as to be pivotable together with the pivot shaft  71 ; and an urging spring  74  that urges the claw  72  and the operation portion  73 . 
     Each of the lock members  70  is movable between (i) a lock position at which a corresponding one of the drum cartridges  51  is locked in the drawer  60  in the state in which the drum cartridge  51  is mounted to the drawer  60  and (ii) a release position at which the lock between the drum cartridge  51  and the drawer  60  is released. 
       FIG.  9    illustrates a state in which each of the first, third, and fourth lock members  70  from the front is located at the lock position, and the second lock member  70  from the front is located at the release position. 
     When the lock member  70  is located at the lock position, the claw  72  is located above the first projecting portion  516 A protruding from the first drum frame  511 A and is engaged with the first projecting portion  516 A to be moved upward, thereby restricting the upward movement of the first projecting portion  516 A. 
     That is, since the lock member  70  located at the lock position locks the drum cartridge  51  in the drawer  60 , it is possible to prevent the drum cartridge  51  from being disengaged from the drawer  60  by the first projecting portion  516 A coming out of the first guide groove  63 A. Also, the restriction of the movement of the first projecting portion  516 A prevents the drum cartridge  51  from moving with respect to the drawer  60 . 
     When the lock member  70  is located at the release position, the claw  72  is located in front of the first projecting portion  516 A, allowing the first projecting portion  516 A to move upward without engaging the claw  72 . That is, the lock members  70  located at the release position releases the lock between the drum cartridge  51  and the drawer  60 , allowing the drum cartridge  51  to be disengaged from the drawer  60  by the first projecting portion  516 A coming out of the first guide groove  63 A. 
     The urging spring  74  urges the claw  72  and the operation portion  73  in a direction in which the lock member  70  moves toward the lock position. Without operation of the operation portion  73 , the lock members  70  is moved to the lock position by an urging force of the urging spring  74 , so that the operation portion  73  is moved to a relatively upper position. 
     When the operation portion  73  of the lock member  70  located at the lock position is operated and pressed downward, the operation portion  73  is moved to a relatively lower position against the urging force of the urging spring  74 , so that the lock member  70  is moved to the release position. Thus, the operation portion  73  is configured to switch the position of the lock member  70  between the lock position and the release position. 
     As illustrated in  FIG.  10   , a portion of the first side frame  61 A to which each of the lock members  70  is mounted is less in thickness in the right and left direction than the other portion, and the lock member  70  is disposed so as not to lie off a left surface of the first side frame  61 A toward an inner side in the right and left direction. A right end portion of the operation portion  73  protrudes to a position located on a right and outer side of the first side frame  61 A. That is, the operation portion  73  protrudes from the first side frame  61 A in a direction away from the second side frame  61 B in the right and left direction. 
     The cover member  522  provided on the development frame  521  of each of the developing cartridges  52  is a plate member extending in the horizontal direction. The cover member  522  covers at least a portion of the operation portion  73  of the lock members  70  which protrudes outward from the first side frame  61 A in the right and left direction in the state in which the corresponding drum cartridge  51  is mounted to the drawer  60 , and the developing cartridge  52  is mounted to the drum cartridge  51 . 
     In the present embodiment, the cover member  522  protrudes from the development frame  521  to a position located on a right and outer side of the first side frame  61 A above the operation portion  73 , and the cover member  522  covers substantially the entirety of an upper side of the operation portion  73 . That is, an area occupied by the cover member  522  overlaps an area occupied by the operation portion  73  in plan view. 
     To remove the developing cartridge  52  and the drum cartridge  51  of the process unit  50  mounted to the drawer  60 , the user first opens the front-surface cover  22  of the housing  2  and pulls the drawer  60  located at the inner position frontward to move the drawer  60  to the outer position as illustrated in  FIG.  9   . 
     The user then grasps the handle  521 H of the developing cartridge  52  from a front and upper side of the drawer  60  located at the outer position and lifts the developing cartridge  52  upward to remove the developing cartridge  52  from the drum cartridge  51 . It is noted that  FIG.  9    illustrates a situation in which the developing cartridge  52  is removed from the drum cartridge  51  in the third process unit  50  from the front. 
     In this case, the drum cartridge  51  is locked by the lock member  70  located at the lock position to prevent the drum cartridge  51  from moving with respect to the drawer  60 , making it easy to remove the developing cartridge  52 . 
     At least a portion (i.e., an upper portion) of the operation portion  73  of the lock member  70  is covered with the cover member  522  in the state in which the developing cartridge  52  is mounted to the drum cartridge  51 , making it difficult for the user to press the operation portion  73  down from a front and upper side of the drawer  60 , making it possible to keep the lock member  70  at the lock position. In the case where the user views the drawer  60  from a front and upper side thereof, the operation portion  73  is hidden by the cover member  522  and not visible to the user, thereby preventing the user from having an intension of operating the operation portion  73 . 
     This prevents the user from performing misoperation of the operation portion  73  of the lock member  70  and removing the drum cartridge  51  from the drawer  60  with the developing cartridge  52  when removing the developing cartridge  52  from the drum cartridge  51 . 
     When the user removes the drum cartridge  51  from the drawer  60  after removing the developing cartridge  52  from the drum cartridge  51 , the user can operate the operation portion  73  because an upper side of the operation portion  73  of the lock member  70  is not covered with the cover member  522 . 
     Accordingly, the user can remove the drum cartridge  51  from the drawer  60  by lifting the drum cartridge  51  upward after moving the lock member  70  from the lock position to the release position by pressing the operation portion  73  of the lock member  70  down. It is noted that  FIG.  9    illustrates a situation in which the second drum cartridge  51  from the front is removed from the drawer  60 . 
     The lock member  70  is provided on the first side frame  61 A of the drawer  60  and located on an outer side of the first side wall  512 A of the first drum frame  511 A of the drum cartridge  51  in the right and left direction. This configuration prevents the lock member  70  from interfering with mounting and removal of the drum cartridge  51  to and from the drawer  60  when compared with the case where the lock member  70  is disposed at another position. 
     In the drawer  60  configured to support the drum cartridge  51  between the first side frame  61 A and the second side frame  61 B, the operation portion  73  of the lock member  70  protrudes from the first side frame  61 A away from the second side frame  61 B. This configuration increases the size of a space around the operation portion  73 , making it easy for the user to operate the operation portion  73  to mount and remove the drawer  60  to and from the drum cartridge  51 . 
     The cover member  522  protrudes to a position located on an outer side of the first side frame  61 A in the right and left direction and covers substantially the entirety of an upper side of the operation portion  73 . This configuration increases the effect of preventing the user from performing misoperation of the operation portion  73  of the lock member  70  when removing the developing cartridge  52  from the drum cartridge  51 . 
     The first projecting portion  516 A of the first drum frame  511 A which is engaged with the claw  72  when the lock member  70  is located at the lock position protrudes from the first side wall  512 A of the first drum frame  511 A away from the second drum frame  511 B. This configuration facilitates designing a mechanism of engagement between the first projecting portion  516 A and the claw  72  of the lock member  70  provided on the first side frame  61 A. 
     In the present embodiment, the lock member  70  is provided on the first side frame  61 A, and the cover member  522  is provided at the right end portion of the development frame  521 . However, the image forming apparatus  1  may be configured such that the lock member  70  is provided on the second side frame  61 B, and the cover member  522  is provided at a left end portion of the development frame  521 . 
     Second Embodiment 
     The cover member  522  of the developing cartridge  52  may be configured as follows. For example, a cover member  522 A illustrated in  FIG.  11 A  is provided on a development frame  521 A of a developing cartridge  52 A and protrudes outward from a right end portion of the development frame  521 A in the right and left direction. 
     The cover member  522 A is disposed in front of the operation portion  73  of the lock member  70  in a state in which the developing cartridge  52 A is mounted to the drum cartridge  51 . The cover member  522 A protrudes outward from the first side frame  61 A of the drawer  60  in the right and left direction and covers substantially the entirety of a front side of the operation portion  73 . That is, an area occupied by the cover member  522 A overlaps an area occupied by the operation portion  73  in elevational view of the cover member  522 A. 
     Thus, also in the configuration in which the cover member  522 A is disposed in front of the operation portion  73 , it is difficult for the user to press the operation portion  73  down from a front and upper side of the drawer  60 , making it possible to keep the lock member  70  at the lock position. In the case where the user views the drawer  60  from a front and upper side thereof, the operation portion  73  is hidden by the cover member  522 A and not visible to the user, thereby preventing the user from having an intension of operating the operation portion  73 . 
     This prevents the user from performing misoperation of the operation portion  73  of the lock member  70  and removing the drum cartridge  51  from the drawer  60  with the developing cartridge  52 A when removing the developing cartridge  52 A from the drum cartridge  51 . 
     Third Embodiment 
     The cover member  522  of the developing cartridge  52  may be configured as follows. For example, a cover member  522 B illustrated in  FIG.  11 B  is provided on a development frame  521 B of a developing cartridge  52 B and protrudes outward from a right end portion of the development frame  521 B in the right and left direction. 
     The cover member  522 B is disposed on an upper side and a front side of the operation portion  73  of the lock member  70  in a state in which the developing cartridge  52 B is mounted to the drum cartridge  51 . The cover member  522 B protrudes outward from the first side frame  61 A of the drawer  60  in the right and left direction. The cover member  522 B extends upward and then rearward continuously and covers substantially the entirety of an upper side and a front side of the operation portion  73 . That is, an area occupied by the cover member  522 B overlaps an area occupied by the operation portion  73  in elevational view and plan view of the cover member  522 B. 
     Thus, also in the configuration in which the cover member  522 B is disposed on an upper side and a front side of the operation portion  73 , it is difficult for the user to press the operation portion  73  down from a front and upper side of the drawer  60 , making it possible to keep the lock member  70  at the lock position. In the case where the user views the drawer  60  from a front and upper side thereof, the operation portion  73  is hidden by the cover member  522 B and not visible to the user, thereby preventing the user from having an intension of operating the operation portion  73 . 
     This prevents the user from performing misoperation of the operation portion  73  of the lock member  70  and removing the drum cartridge  51  from the drawer  60  with the developing cartridge  52 B when removing the developing cartridge  52 B from the drum cartridge  51 .