Patent Publication Number: US-9429901-B2

Title: Photosensitive drum access configuration for an image-forming apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 13/626,216 filed Sep. 25, 2012, which claims priority from Japanese Patent Application No. 2011-284469, filed on Dec. 26, 2011, the entire subject matter of which is incorporated herein by reference. 
    
    
     FIELD 
     Aspects of the disclosure relate to an electrophotographic image forming apparatus. 
     BACKGROUND 
     A known electrophotographic image forming apparatus includes a main body having an opening, an LED head, and a photosensitive member unit integrally including a photosensitive drum and a toner cartridge. The photosensitive member unit is configured to be detachably attachable to the main body through the opening. The LED head is configured to expose the photosensitive drum. 
     The main body includes a top cover to open and close the opening. The LED head is held on an inner surface of the top cover. 
     When the top cover is in a closed position to close the opening, the LED head is brought close to the photosensitive drum. When the top cover is in an open position to release the opening, the LED head is separated from the photosensitive drum. 
     Before the photosensitive member unit is attached to or removed from the main body, the top cover is located in the open position so that the LED head is separated from the photosensitive drum. 
     SUMMARY 
     In terms of maintenance and running cost reduction, it is to be desired that the toner cartridge and the photosensitive drum are separately provided. 
     However, if the toner cartridge and the photosensitive drum are separately provided in the above image forming apparatus, the photosensitive drum should be removed from the main body after the LED head is separated from the photosensitive drum and the toner cartridge is removed from the main body. 
     In other words, even if only the photosensitive drum is replaced, it is necessary to remove the toner cartridge from the main body, which makes it complicated to replace the photosensitive drum. 
     Illustrative aspects of the disclosure provide an image forming apparatus including a developer storing container and a photosensitive drum, which are provided separately, and being configured to improve maintenance of the photosensitive drum. 
     According to an aspect of the disclosure, an image forming apparatus includes a main body, a photosensitive drum detachably attached to the main body, a light exposure member configured to expose the photosensitive member to light, a developer container configured to store a developer to be supplied to the photosensitive drum, and a supporting member disposed in the main body and configured to support the light exposure member and to hold the developer container detachably. The supporting member is configured to, while holding the developer container, move between a light exposure position where the light exposure member is located proximate to the photosensitive drum and a separation position where the light exposure member is separated from the photosensitive drum while the supporting member holds the developer container. 
     According to another aspect of the disclosure, an image forming apparatus includes a main body, a plurality of photosensitive drums detachably attached to the main body, a plurality of light exposure members configured to expose the plurality of photosensitive members to light respectively, a plurality of developer containers each configured to store a developer to be supplied to a corresponding one of the plurality of photosensitive drums, and a supporting member disposed in the main body and configured to support the plurality of light exposure members and to hold the plurality of developer containers detachably. The supporting member is configured to, while holding the plurality of developer containers, move between a light exposure position where each of the plurality of light exposure members is located proximate to a corresponding one of the plurality of photosensitive drums and a separation position where the each of the plurality of light exposure members is separated from the corresponding one of the plurality of photosensitive drums. 
     According to another yet aspect of the disclosure, an image forming apparatus includes a first unit including a photosensitive drum detachably, and a second unit including a light exposure member configured to expose the photosensitive member to light and a developer container configured to store a developer to be supplied to the photosensitive drum. The second unit is configured to move relative to the first unit between a light exposure position where the light exposure member is located approximate to the photosensitive drum and a separation position where the light exposure member is separated from the photosensitive drum. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Illustrative aspects will be described in detail with reference to the following figures in which like elements are labeled with like numbers and in which: 
         FIG. 1  is a side sectional view of an illustrative image forming apparatus, e.g. a printer, according to a first embodiment; 
         FIG. 2  is a right side view of the printer shown in  FIG. 1 , from which a right side wall of a casing is omitted; 
         FIG. 3  is a left side view of the printer shown in  FIG. 1 , from which a left side wall of the casing is omitted; 
         FIG. 4  is a side sectional view of the printer shown in  FIG. 1 , in which a top cover is located in an open position; 
         FIG. 5  is a perspective view of the printer shown in  FIG. 1 , in which the top cover is located in the open position; 
         FIG. 6  is a perspective view of the printer shown in  FIG. 1 , from which developing cartridges and drum cartridges are removed; 
         FIG. 7  is a perspective view of the printer shown in  FIG. 1 , in which a developing cartridge holding frame is located in an upper position; 
         FIG. 8  is a perspective view of a printer according to a second illustrative embodiment, in which a top cover is located in an open position; 
         FIG. 9  is a perspective view of the printer shown in  FIG. 8 , in which a developing cartridge holding frame is located in an upper position; 
         FIG. 10  is a perspective view of a printer according to a third illustrative embodiment, from which a right side wall of a casing is omitted; 
         FIG. 11  is a perspective view of the printer shown in  FIG. 10 , in which an opening cover is located in an open position; and 
         FIG. 12  is a perspective view of the printer shown in  FIG. 10 , in which a supporting member is located in an upper position. 
     
    
    
     DETAILED DESCRIPTION 
     A first illustrative embodiment will be described in detail with reference to the accompanying drawings. 
     As shown in  FIG. 1 , an image forming apparatus according to aspects of the invention applies to a printer  1 , which is a direct tandem type color printer. 
     For ease of discussion, in the following description, the top or upper side, the bottom or lower side, the left or left side, the right or right side, the front or front side, and the rear or rear side are used to define the various parts when the laser printer  1  is disposed in an orientation in which it is intended to be used. In  FIG. 1 , the left side is referred to as the front or front side, the right side is referred to as the rear or the rear side, the up side is referred to as the top or upper side, and the down side is referred to as the bottom or lower side. 
     The printer  1  includes a casing  2  as an example of a main body, a sheet supply section  4  configured to supply a sheet P, and an image forming section  5  configured to form an image on the sheet P supplied from the sheet supply section  4 . 
     The casing  2  is box-shaped and accommodates the sheet supply section  4  and the image forming section  5  therein. An upper end portion of the casing  2  contains an opening  3 . 
     The upper end portion of the casing  2  also contains a top cover  6 , as an example of open-and-close member, which is configured to open and close the opening  3 . 
     As shown in  FIG. 2 , the top cover  6  is shaped like a flat plate, and includes a handle  7  at its front end portion and a hinge portion  8  at its rear end portion. 
     As shown in  FIG. 7 , the handle  7  is shaped like a letter U, and fixed to the top cover  6  such that it is located in a central portion of a front end of an upper surface of the top cover  6 . 
     The top cover  6  is configured to pivot on the hinge portion  8  between an open position ( FIG. 4 ) to open the opening  3  and a closed position ( FIG. 2 ) to close the opening  3 . 
     As shown in  FIG. 1 , the sheet supply section  4  includes a sheet supply tray  9  configured to store stack of sheets P therein. The sheet supply tray  9  is disposed in a lower portion of the casing  2  and non-destructively detachable from and attachable to the casing  2 . 
     The sheet supply section  4  further includes a pickup roller  10 , sheet supply rollers  11 , and registration rollers  12 . The sheets P in the sheet supply tray  9  are fed by rotation of the pickup roller  10 , and separated one by one by rotation of the sheet supply rollers  11 . By rotation of the sheet supply roller  11 , a separated sheet P passes to between the registration rollers  12 . By rotation of the registration rollers  12 , the sheet P is supplied to the image forming section  5  (specifically, between photosensitive drums  13  and a conveyor belt  14 ) at a specified time. 
     The image forming section  5  includes a process unit  16 , a plurality of light emitting diode (LED) units  17  as an example of an exposure member, a transfer unit  18 , and a fixing unit  19 . 
     The process unit  16  is disposed in an upper portion of the casing  2 , and includes a plurality of drum cartridges  20  and a plurality of developing cartridges  21  as an example of a developer container. 
     There are four drum cartridges  20 , which are prepared for respective colors of black, yellow, magenta, and cyan, and spaced apart from each other in the front-rear direction. 
     Each of the drum cartridges  20  includes a photosensitive drum  13  and a scorotron charger  22 . In other words, there are four photosensitive drums  13  prepared for colors of black, yellow, magenta, and cyan, respectively. 
     Each of the photosensitive drums  13  has substantially a cylindrical shape, which is elongated in the left-right direction ( FIG. 7 ). The photosensitive drums  13  are rotatably supported in the respective drum cartridges  20 . 
     Each of the scorotron chargers  22  is disposed at a small distance above and behind a corresponding one of the photosensitive drums  13 . 
     There are four developing cartridges  21 , each disposed opposite to a corresponding one of the photosensitive drums  13  at an upper front side thereof. The developing cartridges  21  include respective developing rollers  23 . 
     Each of the developing rollers  23  is rotatably supported in a lower end of a corresponding one of the developing cartridges  21  such that the developing roller  23  is exposed from below and rear and a corresponding photosensitive drum  13  contacts the developing roller  23  from the rear side. 
     Each developing cartridge  21  includes a supply roller  24  configured to supply toner to the developing roller  23 , a layer-thickness regulating blade  25  configured to regulate a thickness of toner supplied to the developing roller  23 , and a toner storing portion  26  disposed above the supply roller  24  and the layer-thickness regulating blade  25 . Each toner storing portion  26  contains a developer, e.g. toner of each color. 
     There are four LED units  17  disposed facing the respective photosensitive drums  13  from above. Each LED unit  17  is configured to expose a surface of its corresponding photosensitive drum  13  based on image data and form a latent image on the surface. 
     The transfer unit  18  is disposed above the sheet supply section  4  and under the process unit  16  and arranged along the front-rear direction. 
     The transfer unit  18  includes a drive roller  27 , a driven roller  28 , a conveyor belt  14 , and a plurality of, e.g., four, transfer rollers  29 . 
     The drive roller  27  and the driven roller  28  are spaced apart from each other and disposed facing each other in the front-rear direction. 
     The conveyor belt  14  is looped around the drive roller  27  and the driven roller  28  and disposed such that an upper side of the conveyor belt  14  contacts the photosensitive drums  13 . 
     The conveyor belt  14  is configured to rotate upon rotation of the drive roller  27  in such a direction that the upper side contacting the photosensitive drums  13  moves from the front side to the rear side. 
     The transfer rollers  29  are disposed within the conveyor belt  14  and opposite to the respective photosensitive drums  13  in the top-bottom direction such that the lower side of the conveyor belt  14  is sandwiched between the transfer rollers  29  and the respective photosensitive drums  13 . 
     The fixing unit  19  is disposed at the rear of the transfer unit  18  and includes a heat roller  30  and a pressure roller  31  disposed facing the heat roller  30 . 
     In each developing cartridge  21 , toner in the toner storing portion  26  is supplied to the supply roller  24  and then supplied from the supply roller  24  to the developing roller  23 . Toner supplied to the developing roller  23  is positively charged between the supply roller  24  and the developing roller  23  by friction with rotation of the developing roller  23 , regulated to a specified thickness by the layer-thickness regulating blade  25  and then carried on a surface of the developing roller  23  as a thin layer having a specified thickness. 
     The surface of the photosensitive drum  13  is uniformly charged by the scorotron charger  22  along with rotation of the photosensitive drum  13 , and then exposed by the LED unit  17 . Thus, an electrostatic latent image corresponding to an image to be formed on a sheet P is formed on the surface of the photosensitive drum  13 . 
     When the photosensitive drum  13  further rotates, the toner carried on the surface of the developing roller  23  is supplied to the electrostatic latent image formed on the surface of the photosensitive drum  13 . With this, the electrostatic latent image on the photosensitive drum  13  is visualized, and a toner image is carried on the surface of the photosensitive drum  13  by reversal developing. In this manner, toner images are carried on the surfaces of the respective photosensitive drums  13 . 
     The sheet P supplied from the sheet supply section  4  is conveyed from the front side to the rear side by the conveyor belt  14 . When the sheet P passes through a transfer position between each of the photo sensitive drums  13  and a corresponding one of the transfer rollers  29 , the toner images carried on the surfaces of the respective photosensitive drums  13  are sequentially transferred onto the sheet P and a color image is formed on the sheet P. 
     The color image transferred onto the sheet P in the transfer unit  18  is thermally fixed onto the sheet P through the application of heat and pressure while the sheet P passes between the heat roller  37  and the pressure roller  38 . 
     Then, the sheet P is conveyed such that it is u-turned toward an upper front side, and ejected to an ejection tray  32  disposed on the top cover  6 . 
     The process unit  16  will be described. 
     As shown in  FIG. 2 , the process unit  16  includes a process frame  35 . 
     The process frame  35  includes a developing cartridge holding frame  36 , as an example of a supporting member, and a drum cartridge holding frame  37 . The developing cartridge holding frame  36  is configured to hold the developing cartridges  21  detachably. The drum holding frame  37  is configured to hold the drum cartridge  20  detachably. 
     As shown in  FIG. 7 , the drum cartridge holding frame  37  is shaped in substantially a rectangle as viewed from the top, and includes a pair of left and right sidewalls  39 , which are disposed apart from each other in the left-right direction, and a front wall  38  extending between front end portions of the side walls  39 . 
     As shown in  FIG. 2 , each sidewall  39  is shaped in substantially a rectangle elongated in the front-rear direction, and a front end portion of each sidewall  39  is inclined diagonally upward toward the front side. 
     Each sidewall  39  has a plurality of, e.g., four, drum positioning grooves  44 , drum guide grooves  43 , and LED positioning grooves  40 . 
     The drum positioning grooves  44  are spaced in the front-rear direction such that each of the drum positioning grooves  44  corresponds to one of upper bosses  56  of the drum cartridges  20 . 
     Each of the drum positioning grooves  44  is shaped like a letter U, in a side view, which is recessed downward from an upper end of the sidewall  39 . Each drum positioning groove  44  has a width substantially equal to an outside diameter of the upper boss  56 . 
     Each of the drum guide grooves  43  is disposed at the rear of a corresponding one of the drum positioning grooves  44  such that each of the drum guide grooves  43  corresponds to one of lower bosses  52  of the drum cartridges  20 . 
     Each of the drum guide grooves  43  formed in the right sidewall  39  extends downward from the upper end of the right sidewall  39  at an upper portion thereof and is inclined rearward toward the bottom side at a lower portion thereof. 
     As shown in  FIG. 3 , each of the drum guide grooves  43  formed in the left sidewall  39  has substantially an arc shape recessed downward from the upper end of the left sidewall  39  at an upper portion thereof, and is inclined rearward toward the bottom side at a lower portion thereof. 
     Each of the drum guide grooves  43  has a width substantially equal to an outside diameter of a corresponding one of the lower bosses  52 , at the lower portion thereof. 
     As shown in  FIG. 2 , each of the LED positioning grooves  40  is formed at the rear of a corresponding one of the drum guide grooves  43  such that each of the LED positioning grooves  40  corresponds to one of positioning protrusions  85  of the LED units  17 . 
     Each of the LED positioning grooves  40  is recessed downward from the upper end of the sidewall  39  at an upper portion thereof, and has substantially a U-shape. A lower portion of each LED positioning groove  40  continues from the upper portion thereof and is bent inward in the front-rear direction, and then extends downward. 
     Each of the sidewalls  39  includes a boss receiving portion  41  and a frame supporting portion  60 . 
     The boss receiving portion  41  is formed corresponding to each end of a frame gripping portion  71  in the left-right direction, and is shaped in substantially a rectangle elongated upward from an upper end at a front side of the sidewall  39 . 
     The boss receiving portion  41  has a boss receiving groove  61  at an upper end thereof. The boss receiving groove  61  is shaped like a letter U, in a side view, which is recessed downward from an upper end of the boss receiving portion  41 . The upper end of the boss receiving portion  41  is shaped such that the boss receiving groove  61  gradually widens upward. 
     The frame supporting portion  60  is shaped in substantially a rectangle in a side view. The frame supporting portion  60  has a shaft insertion hole  62  having substantially a circular shape in a side view at a central portion of the frame supporting portion  60 . 
     The front wall  38  is shaped such that it is inclined upward toward the front side along a lower end of the front end of each of the sidewall  39 . The front wall  38  includes a fixing portion  46 . 
     The fixing portion  46  continues from the upper end of the front wall  38 , and is substantially L-shaped in a side view, which bends to the front side. A front end of the fixing portion  46  is fixed to a front wall of the casing  2 . 
     Thus, the drum cartridge holding frame  37  is fixed immovably relative to the casing  2 . 
     The developing cartridge holding frame  36  will be described. 
     As shown in  FIG. 6 , the developing cartridge holding frame  36  includes a pair of holding frame sidewalls  65  spaced apart from each other in the left-right direction, a frame gripping portion  71  extending between front ends of the holding frame sidewalls  65 , and LED supporting portions  74  disposed between the holding frame sidewalls  65  and spaced in parallel relative to each other in the front-rear direction. 
     In the following description, the top, bottom, front, rear, left and right direction of the developing holding frame  36  are defined based on a case where the developing cartridge holding frame  36  is located in a light exposure position ( FIGS. 1-6 ). 
     The holding frame sidewalls  65  extend in the front-rear direction. 
     As shown in  FIG. 7 , the frame gripping portion  71  is shaped like a flat plate elongated in the left-right direction, and has an opening  72  and engagement bosses  73 . 
     The opening  72  is formed through the frame gripping portion  71  in a central portion thereof in the left-right direction and has substantially rectangular shape as viewed from the front side. 
     The engagement bosses  73  are shaped substantially cylindrically, and protrude outward from left and right end surfaces of the frame gripping portion  71  in a lower portion thereof. 
     As shown in  FIG. 7 , the lower end portions of the left and right ends of the frame gripping portion  71  are connected to the front end portions of the holding frame sidewalls  65 . As shown in  FIG. 1 , the frame gripping portion  71  is inclined upward to the front side. 
     As shown in  FIG. 6 , the LED supporting portions  4  are shaped like a flat plate extending between the holding frame sidewalls  65 . There are four LED supporting portions  4  spaced apart from each other at the rear of the frame gripping portion  71  in the front-rear direction. 
     As shown in  FIG. 1 , front and rear end surfaces of the LED supporting portions  74  are inclined along the toner storing portions  26  of the developing cartridges  21  when the developing cartridges  21  held by the developing cartridge holding frame  36  are projected in the left-right direction. 
     The LED units  17  are supported on lower surfaces of the respective LED supporting portions  74 . 
     Each of the LED units  17  includes an LED array  80  and an LED frame  81  supporting the LED array  80 . 
     The LED array  80  is disposed in a lower end portion of each LED unit  17 . The 
     LED array  80  is shaped like a flat plate extending in the left-right direction, and integrally holds a number of LEDs arranged in rows parallel to each other in the left and right direction. 
     The LED frame  81  is disposed on top of the LED array  80 . The LED frame  81  is shaped in substantially a rectangle in a side view ( FIG. 4 ), and is elongated in the left-right direction. 
     The LED frame  81  includes a plurality of, e.g., two, positioning protrusions  85  ( FIGS. 2 and 3 ), and a plurality of, e.g., two, compression springs  83 . 
     As shown in  FIG. 7 , each of the positioning protrusions  85  is disposed on one of left and right end surfaces of the LED frame  81 . An upper part of each positioning protrusion  85  is shaped like a cylinder extending outward from one of the left and right end surfaces of the LED frame  81 , while a lower part of each positioning protrusions  85  is shaped in substantially a rectangle, as viewed from a left or right side, protruding downward from a lower end of the upper part of each positioning protrusion  85  ( FIG. 2 ). 
     As shown in  FIG. 1 , each compression spring  83  is wound in an air-cored coil form and disposed on one of left and right end portion of the LED frame  81  on an upper surface of the LED frame  81 . 
     The compression spring  83  is fixed at its lower end portion to the upper surface of the LED frame  81  and at its upper end portion to a lower surface of the LED supporting portion  74 . 
     Thus, the LED unit  17  is supported by the LED supporting portion  74  such that the LED array  80  is movable in the top-bottom direction. The LED frame  81  is urged downward by the compression spring  83  under normal conditions. 
     As shown in  FIG. 6 , the developing cartridge holding frame  36  has a plurality of, e.g., four, receiving openings  63  partitioned by the pair of holding frame sidewalls  65 , the frame gripping portion  71  and the four LED supporting portions  74 . 
     Specifically, the frontmost receiving opening  63  is defined by a rear end portion of the frame gripping portion  71 , the frontmost LED supporting portion  74  and the pair of holding frame sidewalls  65 . 
     The other three receiving openings  63  (except for the frontmost receiving opening  63 ) are defined by two adjacent LED supporting portions  74  and the pair of holding frame sidewall  65 . 
     Each of the receiving openings  63  is shaped in substantially a rectangle as viewed from the top side. Recessed portions  75  are formed at left and right sides of the receiving opening  63 . 
     The recessed portions  75  are shaped like a letter U, as viewed from the left and right sides, and recessed outward from inner surfaces of the holding frame side walls  65  in the left-right direction. 
     The left holding frame sidewall  65  has coupling insertion portions  76  corresponding to the receiving openings  63 . As shown in  FIG. 3 , the coupling insertion portions  76  are formed through the left holding frame sidewall  65  and have a circular shape. 
     As shown in  FIG. 5 , the developing cartridge holding frame  36  includes a rotating portion  70 . 
     The rotating portion  70  is disposed in a rear end portion of the developing cartridge holding frame  36 , and includes rotation shaft holding portions  67  and a rotation shaft  68 . 
     The rotation shaft holding portions  67  are shaped in substantially a flat plate which continues from left and right ends of the rear end of the rearmost LED supporting portion  74 , respectively, and protrudes downward to the rear side ( FIG. 1 ). 
     The rotation shaft  68  is shaped in a cylinder extending in the left-right direction, and left and right end portions of the rotation shaft  68  are supported by the rotation shaft holding portions  67  so as not to rotate relative to the rotation shaft holding portions  67 . Thus, the rotation shaft  68  does not rotate relative to the developing cartridge holding frame  36 . The left and right end portions of the rotation shaft  68  protrude outward from the respective rotation shaft holding portions  67  in the left-right direction. The rotation shaft  68  has a length in the left-right direction longer than a distance between the frame holding portions  60  spaced apart from each other in the left-right direction. 
     The left and right end portions of the rotation shaft  68  are inserted into shaft insertion holes  62  formed in the respective frame supporting portion  60  of the drum cartridge holding frame  37 , thereby the developing cartridge holding frame  36  is supported by the drum cartridge holding frame  37  (or the casing  2 ) so as to move relative thereto. 
     Specifically, the developing cartridge holding frame  36  is configured to pivot about the rotation shaft  68  between a light exposure position ( FIG. 1 ) where the LED arrays  80  are located in a location close to the respective photosensitive drums  13  and a separation position ( FIG. 7 ) where the LED arrays  80  are separated from the respective photosensitive drums  13 . 
     As shown in  FIG. 1 , when the developing cartridge holding frame  36  is located in the light exposure position, the LED arrays  80  of the LED units  17  are disposed facing the respective photosensitive drums  13  from above. 
     As shown in  FIGS. 2 and 3 , the positioning protrusions  85  of the LED units  17  are disposed in the respective LED positioning grooves  40 . This prevents movement of the LED units  17  in the front-rear direction relative to the drum cartridge holding frame  37 . 
     The engagement bosses  73  are received in the boss receiving grooves  61  of the drum cartridge holding frame  37 , and the lower end portions of the holding frame sidewalls  65  are disposed facing the upper ends of the sidewalls  39  with a slight distance. 
     The casing  2  includes couplings  98 . As shown in  FIG. 6 , the couplings  98  are disposed such that, when the developing cartridge holding frame  36  is located in the light exposure position, the couplings  98  are spaced apart from and face the respective coupling insertion portions  76  in the left-right direction. The couplings  98  are shaped in substantially a cylinder, and configured to move in the left-right direction. 
     As shown in  FIG. 7 , when the developing cartridge holding frame  36  is located in the separation position, the LED arrays  80  of the LED units  17  are separated from the respective photosensitive drums  13 , and the LED positioning protrusions  85  are disengaged from the respective LED positioning grooves  40 . The engagement bosses  73  are also disengaged from the respective boss receiving grooves  61 . 
     The drum cartridge holding frame  37  holds the drum cartridges  20  detachably. 
     Each of the drum cartridges  20  includes a drum frame  47 . 
     The drum frame  47  is shaped like a box of which lower portion is open ( FIG. 1 ). As shown in  FIGS. 4 and 7 , the drum frame  47  includes a pair of drum sidewalls  50  spaced apart from each other in the left-right direction and a drum front wall  54  connecting front portions of the drum sidewalls  50 . 
     Each of the drum sidewalls  50  is shaped in substantially a flat plate, and includes a LED receiving groove  51 , a boss guide groove  55 , a lower boss  52 , and an upper boss  56 , which are located in the same positions. 
     The LED receiving groove  51  is shaped like a letter U, in a side view, which is recessed downward from an upper end of the drum sidewall  50 . 
     The boss guide groove  55  is disposed at the front of the LED receiving groove  51  and is shaped like a letter U, in a side view, which is recessed downward from the upper end of the drum sidewall  50 . The boss guide groove  55  widens upward. 
     The lower boss  52  is disposed under the LED receiving groove  51  and shaped like a cylinder protruding outward in the left-right direction from an outer surface of the drum sidewall  50  ( FIG. 4 ). 
     The upper boss  56  is disposed in a front end of the drum side wall  50  and is shaped like a cylinder protruding outward in the left-right direction from the outer surface of the drum sidewall  50  ( FIG. 4 ). 
     As shown in  FIG. 7 , the drum front wall  54  is shaped in substantially a flat plate, which extends between the front end portions of the drum sidewalls  50  and is elongated in the left-right direction. 
     The drum front wall  54  integrally includes a drum gripping portion  57 . 
     The drum gripping portion  57  is shaped in a rectangle as viewed from the top side, which continues from a central portion of the upper end portion of the drum front wall  54  in the left-right direction and extends to the front side. 
     The drum cartridges  20  are held in the drum cartridge holding frame  37  such that the lower bosses  52  are disposed in lower ends of the respective drum guide grooves  43  and the upper bosses  56  are located in the respective drum positioning grooves  44  as shown in  FIGS. 2 and 3 . 
     As shown in  FIG. 5 , the developing cartridges  21  are detachably attached to the developing cartridge holding frame  36 . 
     Each of the developing cartridges  21  integrally includes a developing portion  90  and a toner storing portion  26  disposed on top of the developing portion  90 . 
     The developing portion  90  extends in the left-right direction, and is open toward the rear side ( FIG. 1 ). Left and right ends of the developing portion  90  are closed by a pair of developing sidewalls  92 . 
     As shown in  FIG. 4 , each of the developing sidewalls  92  is shaped in substantially a triangle narrowing downward in a side view, and a boss  93  is disposed in a rear part of the sidewall  92 . 
     As shown in  FIG. 5 , the boss  93  is shaped like a cylinder protruding outward in the left-right direction from an outer surface of the developing sidewall  92 . 
     As shown in  FIG. 3 , the left developing sidewall  92  of each developing cartridge  21  includes a drive input portion  94 . 
     As shown in  FIG. 1 , each developing portion  90  accommodates the developing roller  23 , the supply roller  24 , and the layer-thickness regulating blade  25 , and a rear part of the developing roller  23  is exposed outside from the developing portion  90 . 
     Each drive input portion  94  is configured to transmit a drive force to the developing roller  23  and the supply roller  24  via the coupling  98  when the drive force from the casing  2  is input. 
     As shown in  FIG. 5 , each of the toner storing portions  26  is substantially box-shaped to have the form of substantially a rectangle in a side view, and communicates with the developing portion  90  at a lower end thereof ( FIG. 1 ). 
     The toner storing portion  26  includes a cartridge gripping portion  95 . 
     The cartridge gripping portion  95  is shaped in substantially a flat plate that continues from the toner storing portion  26  and protrudes upward from a central portion in the left-right direction at an upper end of the toner storing portion  26 . 
     The toner storing portions  26  have a dimension in the front-rear direction longer than that of the respective receiving openings  63  ( FIG. 6 ), and a dimension in the left-right direction longer than that of the respective receiving openings  63  ( FIG. 6 ). 
     As shown in  FIG. 1 , the toner storing portions  26  store black, yellow, magenta, and cyan toners, respectively. 
     As shown in  FIG. 4 , the developing cartridges  21  are attached to the developing cartridge holding frame  36  such that the bosses  93  are fitted in the boss guide grooves  55  of the drum sidewalls  50  and the lower ends of the toner storing portions  26  are supported by peripheral portions of the receiving openings  63  (LED supporting portions  74  and the holding frame sidewalls  65 ). 
     As shown in  FIG. 3 , the drive input portions  94  of the left developing sidewall  92  are exposed outside from the left holding frame sidewall  65  through the respective coupling insertion portions  76 . The drive input portions  94  are coupled to the respective couplings  98  when the developing cartridges  21  are attached to the developing cartridge holding frame  36  and the developing cartridge holding frame  36  is located in the light exposure position. 
     As shown in  FIG. 1 , the toner storing portions  26  of the developing cartridges  21  are disposed such as to overlap the LED units  17  as viewed from the top side when the developing cartridges  21 , attached to the developing cartridge holding frame  36  located in the light exposure position, are projected in the top-bottom direction (or in a direction where the developing cartridges  21  are attached or removed). 
     Next, the following will describe attachment and removal of the developing cartridges  21  relative to the casing  2 . 
     As shown in  FIGS. 4 and 5 , in a case where a developing cartridge  21  is removed from the casing  2 , the handle  7  of the top cover  6  is held and raised, and the top cover  6  is located in the open position such that the opening  3  is open. 
     The cartridge gripping portion  95  of the developing cartridge  21  is held and raised to pull the developing cartridge  21  upward. 
     The bosses  93  of the developing cartridge  21  are guided through the boss guide grooves  55 , and the developing cartridge  21  is removed from the developing cartridge holding frame  36  along the top-bottom direction. 
     When the developing cartridge  21  is moved further upward, the developing cartridge  21  is removed from the casing  2  through the opening  3 . 
     In a case where the developing cartridge  21  is attached to the casing  2 , the above removal procedure is reversed. 
     In other words, the developing cartridges  21  are detachably attachable to the developing cartridge holding frame  36  via the opening  3  when the developing cartridge holding frame  36  is located in the light exposure position. 
     Next, the following will describe attachment and removal of the drum cartridges  20  relative to the casing  2 . 
     As shown in  FIG. 7 , in a case where a drum cartridge  20  is removed from the casing  2 , the top cover  6  is located in the open position, the frame gripping portion  71  of the drum cartridge  20  is held and raised such that the developing cartridge holding frame  36  holding the four developing cartridges  21  is pivoted from the light exposure position to the separation position. 
     The drum gripping portion  57  of the drum cartridge  20  is held and raised to pull the drum cartridge  20  upward. 
     The lower boss  52  of the drum frame  47  is guided through the lower portion of the drum guide groove  43 , and the drum cartridge  20  is moved to the upper front side. 
     When the lower boss  52  reaches the upper part of the drum guide groove  43 , the lower boss  52  is guided through the upper part of the drum guide groove  43 , and the drum cartridge  20  is moved upward. 
     Thus, the drum frame  47  is pulled upward from the drum cartridge holding frame  37 . 
     When the drum cartridge  20  is moved further upward, the drum cartridge  20  is removed from the casing  2  through the opening  3 . 
     In a case where the drum cartridge  20  is attached to the casing  2 , the above removal procedure is reversed. 
     Thus, the photosensitive drum  13  supported by the drum cartridge  20  is detachably attachable relative to the casing  2 . 
     As shown in  FIGS. 5 and 7 , the printer  1  is configured such that the developing cartridge holding frame  36  holding the four developing cartridges  21  is movable between the light exposure position and the separation position. As shown in  FIG. 5 , with the developing cartridge holding frame  36  in the light exposure position, the developing cartridges  21 , of which replacement is required with higher frequency than the photosensitive drums  13 , can be detachably attached relative to the casing  2  in complete isolation. 
     As shown in  FIG. 7 , with the developing cartridge holding frame  36  in the separation position, the LED units  17  can be separated from the photosensitive drums  13  and the developing cartridges  21  can be also separated from the photosensitive drums  13 . 
     In other words, only by locating the developing cartridge holding frame  36  in the separation position, both of the LED units  17  and the developing cartridges  21  can be separated from the photosensitive drums  13 . 
     Thus, only by locating the developing cartridge holding frame  36  in the separation position, the photosensitive drums  13  can be removed from the casing  2  without having to remove the developing cartridges  21  from the casing  2  in advance, which improves the efficiency of replacing the photosensitive drums  13 . 
     Thus, the developing cartridges  21  and the photosensitive drums  13  can be detachably attached relative to the casing  2  in complete isolation, which facilitates maintenance of the photosensitive drums  13 . 
     As shown in  FIG. 5 , when the top cover  6  is located in the open position and the developing cartridge holding frame  36  is located in the light exposure position, the developing cartridges  21  are detachably attachable to the developing cartridge holding frame  36  through the opening  3 . 
     Thus, the developing cartridge  21  can be detachably attached relative to the casing  2  with reliability. 
     This facilitates maintenance of the developing cartridges  21 . 
     The developing cartridge holding frame  36  is configured to pivot about the rotation shaft  68  disposed at the rear end of the developing cartridge holding frame  36  between the light exposure position and the separation position. 
     Thus, the developing cartridge holding frame  36  can be moved between the light exposure position and the separation position. 
     As shown in  FIG. 1 , there are four photosensitive drums  13  each corresponding to one color of black, yellow, magenta, and cyan, and there are four developing cartridges  21  each corresponding to one of the photosensitive drums  13 . 
     Each of the toner storing portions  26  of the developing cartridges  21  stores a toner of one color of black, yellow, magenta, and cyan. Thus, a full-color image can be formed. 
     As shown in  FIG. 4 , the developing cartridges  21  are detachably attachable relative to the casing  2 , with the developing cartridge holding frame  36  remaining in the light exposure or with the LED units  17  remaining located proximate to the respective photosensitive drums  13  ( FIG. 1 ). 
     Thus, there is no need to leave a space for moving the LED units  17  between adjacent toner storing portions  26 . 
     As a result, the physical size of the toner storing portions  26  can be increased, and thus the amount of toner stored in the toner storing portions  26  can be increased. 
     As shown in  FIG. 1 , the toner storing portions  26  of the developing cartridges  21  are disposed such as to overlap the LED units  17  as viewed from the top side when the developing cartridges  21 , attached to the developing cartridge holding frame  36  located in the light exposure position, are projected in the top-bottom direction (or in a direction where the developing cartridges  21  are attached or removed). 
     As the physical size of the toner storing portions  26  can be increased, the amount of toner stored in the toner storing portions  26  can be increased. 
     A second embodiment will be described with reference of  FIGS. 8 and 9 . 
     It is noted that, in  FIGS. 8 and 9 , elements similar to or identical with those shown and described with  FIGS. 1-7  are designated by similar numerals, and thus the description thereof can be omitted for the sake of brevity. 
     The first embodiment shows that the developing cartridge holding frame  36  includes the rotating portion  70  and is configured to pivot about the rotation shaft  68  as shown in  FIG. 5 . 
     As shown in  FIG. 8 , the second embodiment shows that the developing cartridge holding frame  36  includes arm portions  100  each coupling the developing cartridge holding frame  36  and the hinge portion  8  of the top cover  6 . The developing cartridge holding frame  36  is configured to pivot about the hinge portion  8 . 
     The arm portions  100  are shaped in substantially a flat plate continuing from left and right ends of the rearmost LED supporting portion  74  ( FIG. 6 ) and extending diagonally upward toward the rear side. 
     Rear ends of the arm portions  100  are rotatably coupled to the hinge portion  8  of the top cover  6 . 
     Thus, the developing cartridge holding frame  36  is configured to pivot about the hinge portion  8  between the light exposure position ( FIG. 8 ) and the separation position ( FIG. 9 ). In other words, the top cover  6  and the developing cartridge holding frame  36  share a rotation axis X. 
     The top cover  6  has a notched portion  102 . The notched portion  102  is shaped like a letter U, as viewed from the top side, which is recessed rearward from a central portion of the front end of the top cover  6  in the left-right direction. 
     The frame gripping portion  71  includes a handle  101  corresponding to the notched portion  102  of the top cover  6 . 
     The handle  101  is shaped like a letter U, which is open downward, as viewed from the front side, and is fixed to the frame gripping portion  71  so as to straddle a central portion of the upper end of the frame gripping portion  71 . 
     The handle  101  protrudes upward from the notched portion  102  of the top cover  6  when the top cover  6  is in the closed position. 
     When the handle  101  is held and raised such that the developing cartridge holding frame  36  is pivoted from the light exposure position to the separation position, as shown in  FIG. 9 , the top cover  6  is pressed upward by the upper end of the gripping portion  71  and pivoted, along with the developing cartridge holding frame  36 , from the closed position to the open position. 
     In other words, along with pivoting of the developing cartridge holding frame  36  from the light exposure position to the separation position, the top cover  6  is pivoted integrally with the developing cartridge holding frame  36 , from the closed position to the open position. 
     Thus, without having to move the top cover  6  and the developing cartridge holding frame  36  separately, the top cover  6  and the developing cartridge holding frame  36  can be simultaneously moved to the open position and the separation position, respectively. 
     Thus, this facilitates maintenance of the photosensitive drums  13 . 
     Even with the second embodiment, it is clear that effects similar to those brought about by the first embodiment can be appreciated. 
     A third embodiment will be described with reference to  FIGS. 10-12 . 
     It is noted that, in  FIGS. 10-12 , elements similar to or identical with those shown and described with  FIGS. 1-9  are designated by similar numerals, and thus the description thereof can be omitted for the sake of brevity. 
     The second embodiment shows that, as shown in  FIG. 8 , the top cover  6  and the developing cartridge holding frame  36  are prepared separately. The third embodiment shows that the top cover  6  and the developing cartridge holding frame  36  are provided as a single part as shown in  FIG. 12 . 
     Specifically, the upper end of the frame gripping potion  71  of the developing cartridge holding frame  36  is fixed to a lower surface of the front end of the top cover  6 , and the rear ends of the arm portions  100  of the developing cartridge holding frame  36  are coupled to the hinge portion  8  of the top cover  6 . 
     With this structure, the top cover  6  and the developing cartridge holding frame  36  are integrally formed as a supporting member  110 . The supporting member  110  is configured to pivot about the hinge portion  8  between the light exposure position ( FIG. 10 ) and the separation position ( FIG. 12 ). An upper wall of the supporting member  110  (corresponding to the top cover  6  of the first and second embodiments) is formed as an upper supporting wall  111 . 
     The upper supporting wall  111  has a plurality of, e.g., four, supporting member openings  112 , as an example of an opening. 
     As shown in  FIG. 11 , the supporting member openings  112  are formed through the upper support wall  111 , in the shape of substantially a rectangle as viewed from the top side, and are spaced in parallel relative to each other in the front-rear direction. 
     The upper support wall  111  includes a plurality of, e.g., four, covers  113  corresponding to the supporting member openings  112 . 
     Each of the covers  113  is shaped in substantially a flat rectangular plate, and includes a cover gripping portion  114  at a front end thereof and a hinge  115  at a rear end thereof. 
     The cover gripping portion  114  is shaped in substantially a flat plate, and protrudes upward from a central portion of the front end of the cover  113  in the left-right direction. 
     Each cover  113  is configured to pivot about the hinge  115 , which is fixed to an upper surface of the upper support wall  111 , between an open position ( FIG. 11 ) where the support member opening  112  is open and a closed position where the support member opening  112  is closed ( FIG. 10 ). 
     In the third embodiment, when a developing cartridge  21  to be replaced is removed from the casing  2 , as shown in  FIG. 11 , the cover gripping portion  114  of the cover  113 , which corresponds to the developing cartridge  21  to be replaced, is held and the cover  113  is moved to the open position such that the support member opening  112  is open. 
     Then, the cartridge gripping portion  95  of the developing cartridge  21  is held and raised to pull the developing cartridge  21  upward. 
     The developing cartridge  21  is pulled upward from the developing cartridge holding frame  36  of the supporting member  110 , and removed from the casing  2  through the support member opening  112 . 
     To attach a developing cartridge  21  to the casing  2 , the above removal procedure is reversed. 
     In other words, the developing cartridges  21  are detachably attachable to the developing cartridge holding frame  36  of the supporting member  110  via the respective support member openings  112  in a state that the supporting member  110  is located in the light exposure position. 
     Thus, even with the third embodiment, it is clear that effects similar to those brought about by the first embodiment can be appreciated. 
     Only one of the developing cartridges  21 , which needs replacing, can be removed and replaced relative to the developing cartridge holding frame  36  of the supporting member  110  via a corresponding one of the support member openings  212 . Thus, this structure facilitates maintenance of the developing cartridges  21 . 
     When a drum cartridge  20  is removed from the casing  2 , as shown in  FIG. 12 , the handle  7  of the supporting member  110  is held and raised such that the supporting member  110  is located in the separation position such that the opening  3  is open. 
     Thus, with the same removal procedure described in the first embodiment, the drum cartridges  20  can be removed from the casing  2  via the opening  3 . 
     The first, second, and third embodiments can be combined as appropriate. 
     While the features herein have been described in connection with various example structures and illustrative aspects, it will be understood by those skilled in the art that other variations and modifications of the structures and aspects described above may be made without departing from the scope of the inventions described herein. Other structures and aspects will be apparent to those skilled in the art from a consideration of the specification or practice of the features disclosed herein. It is intended that the specification and the described examples only are illustrative with the true scope of the inventions being defined by the following claims.