Patent Publication Number: US-9423763-B2

Title: Exposure unit covering member configuration for an image forming apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority from Japanese Patent Application No. 2011-058463, filed on Mar. 16, 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 
     As an electrophotographic image forming apparatus, a color printer is known which includes four photosensitive drums for four colors, yellow, magenta, cyan, and black. 
     A color multifunction apparatus, which is proposed as an example of the color printer, may include process cartridges for each color, LED units, an intermediate transfer belt and a secondary transfer roller. The process cartridges may be arranged in tandem with each other horizontally. Each of the process cartridges may include a photosensitive drum and a developing unit. The developing unit may include a developing roller, a first supply roller, a second supply roller, a doctor blade, and a toner container. Each of the LED unit may be configured to expose a corresponding photosensitive drum from below. The intermediate transfer belt may extend horizontally such as to contact the photosensitive drums in the respective process cartridges from above. The secondary transfer roller may be disposed such as to contact the intermediate transfer belt from one horizontal direction. 
     In the above color multifunction apparatus, each LED unit may include an LED head uncovered. 
     As the LED head is uncovered, the LED head may get soiled by toner dropped from above or dust accumulated on the LED head. 
     SUMMARY 
     Illustrative aspects of the disclosure provide an image forming apparatus including a casing, a photosensitive drum disposed in the casing, and a developing cartridge facing the photosensitive drum, the image forming apparatus being configured to facilitate attachment and removal of the developing cartridge to and from the casing. 
    
    
     
       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 perspective view, looking from the front and right, of a process unit illustrated in  FIG. 1 , from which a part of a drawer frame is removed; 
         FIG. 3  illustrates the process unit illustrated in  FIG. 1  is being pulled out from a casing, wherein a developing cartridge is being removed from the process unit; 
         FIG. 4  is an enlarged perspective view in which the developing cartridge is being removed from the process unit; 
         FIGS. 5A and 5B  illustrate an LED cover is interlocked with attachment and removal of a developing cartridge, wherein  FIG. 5A  is an enlarged sectional view in which a developing cartridge is attached and an LED cover is located in an open position, and  FIG. 5B  is an enlarged sectional view in which the developing cartridge is removed and the LED cover is located in a closed position; 
         FIGS. 6A and 6B  illustrate that the LED cover is interlocked with the attachment and removal of the developing cartridge, wherein  FIG. 6A  is a sectional view of the process unit as viewed from a front side, illustrating that the developing cartridge is attached and the LED cover is in the closed position, and  FIG. 6B  is a sectional view of the process unit as viewed from the front side, illustrating that the developing cartridge is removed and the LED cover is in the open position; 
         FIGS. 7A and 7B  illustrate a printer according to a second embodiment, wherein  FIG. 7A  illustrates that the developing cartridge is attached and the LED cover is in the open position, and  FIG. 7B  illustrates that the developing cartridge is removed and the LED cover is in the closed position; 
         FIG. 8  illustrates a printer according to a third embodiment, in which the process unit is located inside the casing and handles of the developing cartridges are retracted downward; 
         FIG. 9  illustrates that the process unit is pulled out from the casing and the handles of the developing cartridges protrude upward; 
         FIG. 10  illustrates a printer according to a fourth embodiment, in which a top cover is located in an open position; and 
         FIGS. 11A and 11B  illustrate a printer according to a fifth embodiment, wherein  FIG. 11A  illustrates that the developing cartridge is attached and the LED cover is in the open position, and  FIG. 11B  illustrates that the developing cartridge is removed and the LED cover is in the closed 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 horizontally oriented and is of an intermediate transfer type. 
     The printer  1  is a multifunction apparatus integrally including a casing  2  as an example of a main body, and a flat bed scanner  3 , which is disposed above the casing  2  and configured to read image formation of a document. 
     The printer  1  may further include 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 to have the form of substantially a rectangle in a side view and accommodates the sheet supply section  4  and the image forming section  5  therein. One side wall of the casing  2  contains an opening  6  and a front cover  7  configured to pivot on its lower end portion between a closed position ( FIG. 1 ) to close the opening  6  and an open position ( FIG. 3 ) to open the opening  6 . 
     In the following descriptions, the side on which the front cover  7  is provided (the left side of  FIG. 1 ) is referred to as the front or front side, and the opposite side (the right side of  FIG. 1 ) is referred to as the rear or rear side. The left or left side and the right or right side are defined when the printer  1  is viewed from the front side. 
     The sheet supply section  4  may include a sheet supply tray  8  configured to store stack of sheets P therein. The sheet supply tray  8  may be 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  may include a pickup roller  10 , a sheet supply roller  11 , a sheet supply pad  12 , a pair of pinch rollers  13 , and a pair of registration rollers  14 . The pickup roller  10  is disposed in an upper rear portion of the sheet supply tray  8 . The sheet supply roller  11  is disposed behind the pickup roller  10 . The sheet supply pad  12  is disposed facing the sheet supply roller  11  from below. The pinch rollers  13  are arranged one above the other and contact the sheet supply roller  11  from the rear side. The registration rollers  14  are disposed facing each other in a front-rear direction above the sheet supply roller  11 . 
     The sheets P in the sheet supply tray  8  are fed between the sheet supply roller  11  and the sheet supply pad  12  by rotation of the pickup roller  10 , and separated one by one by rotation of the sheet supply roller  11 . By rotation of the sheet supply roller  11 , a separated sheet P passes between the sheet supply roller  11  and the pinch rollers  13 , and is fed to the registration rollers  14 . By rotation of the registration rollers  14 , the sheet P is supplied to the image forming section  5  (specifically, between an intermediate transfer belt  13  and a secondary transfer roller  27 ) at a specified time. 
     The image forming section  5  is disposed above the sheet supply section  4 , and includes a process unit  15  as an example of a movable unit, four light emitting diode (LED) units  16  as an example of an exposure member, a transfer unit  17 , and a fixing unit  18 . 
     The process unit  15  is disposed facing the sheet supply tray  8  from above, in front of the pickup roller  10  such as to overlap the pickup roller  10  when projected in the front-rear direction. The process unit  15  is configured to move, e.g., slide, along the front-rear direction between an inside position ( FIG. 1 ) where the process unit  15  is located inside the casing  2  and an outside position ( FIG. 3 ) where the process unit  15  is pulled out from and located outside the casing  2 . 
     When the process unit  15  is in the inside position, an intermediate transfer belt  30  and photosensitive drums  20  are disposed in a first relative position where they are disposed proximate to each other. When the process unit  15  is in the outside position, the intermediate transfer belt  30  and the photosensitive drums  20  are disposed in a second relative position where they are separated from each other. 
     The process unit  15  is configured to accommodate four photosensitive members, e.g., photosensitive drums  20 , provided for each color, four scorotron chargers  21  corresponding to the photosensitive drums  20 , and four developing units, e.g., developing cartridges  22 , corresponding to the photosensitive drums  20  therein. 
     Each of the photosensitive drums  20  has substantially a cylindrical shape, which extends in the left-right direction, and is disposed along the left-right direction. The photosensitive drums  20  are arranged in the front-rear direction. Specifically, a black photosensitive drum  20 K, a yellow photosensitive drum  20 Y, a magenta photosensitive drum  20 M, and a cyan photosensitive drum  20 C are arranged in this order from the front to the rear. 
     Each of the scorotron chargers  21  is disposed at the rear of and spaced apart from a corresponding one of the photosensitive drums  20 . 
     Each of the developing cartridges  22  is disposed at a lower front side of a corresponding one of the photosensitive drums  20 . The developing cartridges  22  are arranged in the front-rear direction. Each of the developing cartridges  22  includes a developer carrying member, e.g. a developing roller  23 . 
     Each developing roller  23  is rotatably supported in an upper end of a corresponding developing cartridge  22  such that the developing roller  23  is exposed from above and contacts a corresponding photosensitive drum  20  from below. 
     Each developing cartridge  22  includes a supply roller  24  configured to supply toner to the developing roller  23 , and a layer-thickness regulating blade  25  configured to regulate a thickness of toner supplied to the developing roller  23 . Each developing cartridge  22  contains a developer, e.g. toner of each color, in front of the supply roller  24 . 
     Each of the LED units  16  is disposed at the rear of a corresponding developing cartridge  22  so as to face a corresponding photosensitive drum  20  from below. Each LED unit  16  is configured to expose a surface of its corresponding photosensitive drum  20  based on image data and form a latent image on the surface. 
     The transfer unit  17  may include a belt unit  26  and a secondary transfer roller  27 . 
     The belt unit  26  may be disposed above the process unit  15  along the front-rear direction so as to face the photosensitive drums  20  from above. 
     The belt unit  26  may include a drive roller  28 , a driven roller  29 , an endless belt, e.g. an intermediate transfer belt  30 , and four primary transfer rollers  31 . 
     The drive roller  28  and the driven roller  29  are spaced apart from each other in the front-rear direction. 
     The intermediate transfer belt  30  is looped around the drive roller  28  and the driven roller  29  and disposed such that a lower side of the intermediate transfer belt  30  contacts the photosensitive drums  20 . The intermediate transfer belt  30  is configured to rotate upon rotation of the drive roller  28  in such a direction that the lower side contacting the photosensitive drums  20  moves from front to rear. 
     The primary transfer rollers  31  are disposed within the intermediate transfer belt  30  and above the respective photosensitive drums  20  such that the lower side of the intermediate transfer belt  30  is sandwiched between the primary transfer rollers  31  and the photosensitive drums  20 . 
     The secondary transfer roller  27  is disposed at the rear of the intermediate transfer belt  30  such that the intermediate transfer belt  30  is sandwiched between the secondary transfer roller  27  and the drive roller  28  of the belt unit  26 . 
     The fixing unit  18  is disposed above the secondary transfer roller  27 , and includes a heat roller  37  and a pressure roller  38  disposed facing the heat roller  37 . 
     In each developing cartridge  22 , toner 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. 
     The surface of the photosensitive drum  20  is uniformly and positively charged by the scorotron charger  21  along with rotation of the photosensitive drum  20 , and then exposed by the LED unit  16 . Thus, a latent image corresponding to an image to be formed on a sheet P is formed on the surface of the photosensitive drum  20 . 
     When the photosensitive drum  20  further rotates, positively charged toner carried on the surface of the developing roller  23  is supplied to the latent image formed on the surface of the photosensitive drum  20 . With this, the latent image on the photosensitive drum  20  is visualized, and a toner image is carried on the surface of the photosensitive drum  20  by reversal developing. In this manner, toner images are carried on the surfaces of the photosensitive drums  20 . 
     The toner images carried on the surfaces of the photosensitive drums  20  by reversal developing are primarily transferred to the lower side of the intermediate transfer belt  30  moving from the front to the rear. The toner images are sequentially overlapped one over the other to form a color image on the intermediate transfer belt  30 . 
     The color image formed on the intermediate transfer belt  30  is secondarily transferred to a sheet P supplied from the sheet supply section  4  when the color image formed on the intermediate transfer belt  30  passes a position facing the secondary transfer roller  27 . 
     The color image transferred to the sheet P is fixed at the fixing unit  18  while the sheet P passes between the heat roller  37  and the pressure roller  38 . 
     A top surface of the casing  2  contains an ejection tray  33  to which the sheet P is to be ejected. An upper rear end portion of the casing  2  protrudes upward from the ejection tray  33  and contains an ejection portion  39 . 
     The ejection portion  39  has an ejection opening  19  formed above the ejection tray  33 . The sheet P is ejected from the ejection opening  19 . The ejection portion  39  includes a plurality of, e.g., three, ejection rollers  32  disposed in the ejection opening  19  and configured to feed the sheet P to the ejection tray  33 . 
     The sheet P having the toner image fixed at the fixing unit  18  is ejected onto the ejection tray  33  by the ejection rollers  32 . 
     The flatbed scanner  3  is spaced from and above the ejection tray  33  and supported at an upper end portion of the ejection tray  39 . In the flatbed scanner  3 , a document is placed between a pressing cover  34  and a glass surface  35 , and then a CCD sensor  36  slides to read image information of the document. 
     As shown in  FIG. 1 , the process unit  15  includes a drawer frame  41 . 
     The drawer frame  41  is shaped like an open-topped rectangular box, and includes support mechanisms  42  (only one is shown in  FIG. 2 ), drum units  43 , the developing cartridges  22 , the LED units  16 , and a belt cleaning unit  44 . 
     The support mechanisms  42  are disposed facing each other inside the right and left sidewalls of the drawer frame  41 . 
     As shown in  FIG. 2 , each support mechanism  42  includes a support plate  45  and four holding members  46 . The support plate  45  is configured to support the drum units  43  and the developing cartridges  22 . The holding members  46  are configured to hold the respective drum units  43  in their retracted positions ( FIG. 4 ). 
     The support plate  45  is shaped like substantially a rectangle, extending in the front-rear direction. The support plate  45  has drum support grooves  47  for supporting the photosensitive drums  20 , unit supporting holes  48  for supporting the drums units  43 , and cartridge support grooves  49  for supporting the developing cartridges  22 . The support plate  45  also includes support bosses  50  for supporting the holding members  46 . 
     Four drum support grooves  47  are spaced apart from each other in the front-rear direction to correspond to the respective photosensitive drums  20 . Each of the drum support grooves  47  is recessed downward from an upper end of the support plate  45  to have a U-like shape, which is open upward, in a side view. Each of the drum support grooves  47  has a width (a length in the front-rear direction) sized to receive a flange member  56  of the corresponding photosensitive drum  20 . 
     Each of the unit support holes  48  is formed at the rear of a corresponding one of the drum support grooves  47  and at the upper end portion of the support plate  45 . Each of the unit support holes  48  extends through the support plate  45  in the right-left direction and is shaped like substantially a circle in a side view. Each of the unit support holes  48  has a diameter sized to receive a unit support boss  59  of the corresponding drum unit  43 . 
     Each of the cartridge support grooves  49  is formed in front of a corresponding one of the drum support grooves  47 . Each of the cartridge support grooves  49  is recessed downward from the upper end of the support plate  45  to have a U-like shape, which is open upward, in a side view. Each of the cartridge support grooves  49  has a width (a length in the front-rear direction) sized to receive a cartridge support boss  66  of the corresponding developing cartridge  22 . 
     Each of the support bosses  50  is disposed under a corresponding one of the cartridge support grooves  49 , and is shaped like substantially a cylinder, protruding outward from the support plate  45  in the right-left direction. 
     Each of the holding members  46  is shaped like a letter L in a side view, and extends in the front-rear direction and is bent downward at its rear end. The holding members  46  are arranged in the front-rear direction to correspond to the respective photosensitive drums  20 . 
     Each of the holding members  46  has a guide groove  52  for guiding a shaft  57  of a corresponding photosensitive drum  20 , and an insertion hole  51  into which a corresponding support boss  50  of the support plate  45 . The holding member  46  also includes a contact portion  40  to contact a cartridge support boss  66  of a corresponding developing cartridge  22 . 
     The guide groove  52  is shaped like substantially a letter L, in a side view, to correspond to the shape of the holding member  46  in a rear half of the holding member  46 . Specifically, the guide groove  52  has a straight portion  52 A extending in the front-rear direction substantially straightly and a bend portion  52 B which is bent downward continuously from a rear portion of the straight portion  52 A. 
     The insertion hole  51  is formed in a front end portion of the holding member  46  so as to extend through the holding member  46  in the right-left direction, and shaped like substantially a circle in a side view. 
     The contact portion  40  is disposed slightly at the rear of the insertion hole  51  in the front end portion of the holding member  46 , and is shaped like substantially a flat plate, extending inward in the right-left direction from an upper end portion of the holding member  46 . 
     The holding members  46  are arranged on an outer side of the support plate  45  in the right-left direction. In each holding member  46 , the holding member support boss  50  of the support plate  45  is inserted into the insertion hole  51  and screwed such that the holding member  46  is pivotable on the front end portion of the holding member  46 . 
     Each drum unit  43  includes a unit frame  58  configured to integrally hold the photosensitive drum  20  and a scorotron charger  21  ( FIG. 1 ). 
     The unit frame  58  is shaped like substantially a box, which extends in the right-left direction and is open toward the front side. The unit frame  58  includes unit support bosses  59  at an upper rear end portion thereof. 
     The unit support bosses  59  have substantially a cylinder shape, extending outward from right and left outer surfaces of the unit frame  58  in the right-left direction. Each unit support boss  59  has an outside diameter which is smaller than a diameter of the unit support hole  48 . 
     The photosensitive drum  20  is rotatably supported in a front end portion of the unit frame  58 . The photosensitive drum  20  includes a base tube  55 , a pair of right and left flange members  56 , and a shaft  57 . 
     The base tube  55  is shaped like substantially a cylinder extending in the right-left direction. The base tube  55  is covered with a photosensitive layer. 
     The flange members  56  extend in the right-left direction and are substantially cylindrically shaped and their outer sides in the right-left direction are closed. 
     The flange members  56  are engaged in both end portions of the base tube  55  in the right-left direction such as to have a central axis coincident with a central axis of the base tube  55  and so as not to rotate relative to the base tube  55 . The flange members  56  are rotatably supported by the unit frame  58 . 
     The shaft  57  is substantially cylindrically shaped and extends in the right-left direction. The shaft  57  has a central axis coincident with the central axis of the base tube  55 , and is inserted into each of the flange members  56  so as to protrude outward from each of the flange members  56  in the right-left direction and so as not to rotate relative to the flange members  56 . The shaft  57  has an outside diameter, which is smaller than a width of the guide groove  52  of the holding member  46 . The shaft  57  is coupled to the unit support boss  59  via a coupling member  54  ( FIG. 4 ). 
     The scorotron charger  21  is supported in a rear end portion of the unit frame  58  ( FIG. 1 ). 
     The unit support boss  59  of the unit frame  58  is inserted into the unit support hole  48  of the support plate  45  and screwed. The drum unit  43  is supported by the support plate  45  such that the drum unit  43  is configured to pivot around the unit support boss  59 . 
     The shaft  57  of the photosensitive drum  20  is inserted into the guide groove  52  of the holding member  46 . 
     As shown in  FIGS. 2 and 5A , when the developing cartridge  22  is attached to the drawer frame  41 , the drum unit  43  is located in an image formation position where the flange member  56  is engaged in the drum support groove  47  of the support plate  45  and the photosensitive drum  20  faces the developing roller  23  from above. When the drum unit  43  is in the image formation position, an image can be formed on the photosensitive drum  20 . 
     At this time, the holding member  46  is tilted in the front-rear direction, and the shaft  57  of the photosensitive drum  20  is inserted into a front end portion in the guide groove  52  of the holding member  46 . 
     When the photosensitive drum  20  is pressed from below, the flange member  56  is disengaged from the drum support groove  47 , and the drum unit  43  is pivoted around the unit support boss  59  clockwise in the right side view. 
     Concurrently, the holding member  46  is pressed upward by the shaft  57  of the photosensitive drum  20 , pivoted around the holding member support boss  50  counterclockwise in the right side view, and inclined upwardly from the front side to the rear side. 
     At this time, the shaft  57  of the photosensitive drum  20  is guided along the straight portion  52 A of the guide groove  52  of the holding member  46  and moved rearward in the guide groove  52 . In other words, the straight portion  52 A of the guide groove  52  functions as a guide portion configured to guide the drum unit  43  between the image formation position and the retracted position ( FIG. 4 ). 
     As shown in  FIG. 4 , when the drum unit  43  is rotated until the shaft  57  reaches a rear end portion in the guide groove  52 , the holding member  46  is raised such as to extend upward from the front side to the rear side. 
     When the holding member  46  is raised, the bend portion  52 B of the guide groove  52  extends substantially in the front-rear direction, and the contact portion  40  overlaps a lower end portion of the cartridge support groove  49  when projected in the right-left direction. 
     When the drum unit  43  is further rotated, the shaft  57  is engaged in the bend portion  52 B in the guide groove  52 . 
     As shown in  FIGS. 4 and 5B , the drum unit  43  is retracted upward and rearward from the image formation position where the photosensitive drum  20  is located above the developing roller  23 , and thus the photosensitive drum  20  is located in the retracted position where the photosensitive drum  20  is retracted from the developing roller  23 . 
     The drum unit  43  is stopped from rotating further counterclockwise when the shaft  57  contacts, from above, a wall defining a front side of the bend portion  52 B. In other words, the bend portion  52 B in the guide groove  52  functions as a stopper portion configured to engage and stop the photosensitive drum  20  in the retracted position. 
     To rotate the drum unit  43  from the retracted position to the image formation position, the holding member  46  is rotated clockwise in a right side view such that the shaft  57  is disengaged from the bend portion  52 B and engaged in the straight portion  52 A. 
     Then, the drum unit  43  is rotated counterclockwise in the right side view by its own weight, and located in the image formation position. 
     As shown in  FIGS. 1 and 4 , the developing cartridges  22  are detachably supported in the drawer frame  41 . Each developing cartridge  22  includes a cartridge frame  61 . The cartridge frame  61  supports a developing roller  23 , a supply roller  24 , and a layer thickness regulating blade  25 , and is configured to store toner therein. 
     The cartridge frame  61  is shaped like substantially a box, extending in the right-left direction. The cartridge frame  61  has an opening  62 , which is formed at a front-side upper end portion to have substantially a rectangular shape, in a plan view, extending in the right-left direction. The developing roller  23  is supported in the opening  62 . 
     The cartridge frame  61  also includes a handle  63  and a cartridge support portion  64 . 
     The handle  63  is disposed in a central portion of an upper end portion of the cartridge frame  61  in the right-left direction and shaped to have substantially an arc shape, protruding upward. 
     The cartridge support portion  64  includes an extending portion  65  and a cartridge support boss  66  as an example of an interference member. 
     The extending portion  65  extends upward from the upper end portion at an end of the cartridge frame  61  in the right-left direction. 
     The cartridge support boss  66  is shaped like substantially a cylinder, extending outward from an upper end portion of the extending portion  65  in the right-left direction. The cartridge support boss  66  has an outside diameter which is smaller than a width (a length in the front-rear direction) of the cartridge support groove  49 . 
     As shown in  FIGS. 5A and 5B , each LED unit  16  includes an LED array support member  71  extending between the right and left sidewalls of the drawer unit  41 , a light emitting element array, e.g. an LED array  72 , supported by the LED array support member  71 , a covering member, e.g. an LED cover  77  covering the LED array  72 , and a movable member  84  as an example of a cover operation mechanism configured to move the LED cover  77 . 
     The LED array support member  71  includes a support beam  73  and an LED array storing portion  74 . 
     The support beam  73  is shaped like substantially a cylinder extending in the right-left direction. The support beam  73  extends between both side plates of the drawer frame  41 . 
     The LED array storing portion  74  is shaped like an open-topped rectangular box, and a bottom wall of the LED array storing portion  74  is coupled to the support beam  73 . The LED array storing portion  74  has inside dimensions, in the front-rear direction and the right-left direction, substantially equal to or slightly greater than those of the LED array  72 . 
     The LED array  72  integrally holds a number of LEDs arranged in the right-left direction. The LED array  72  has a length in the right-left direction, which is shorter than a length in the right-left direction of the photosensitive drum  20  and longer than a length in the right-left direction in a paper passing area on the photosensitive drum  20  where a sheet P contacts the photosensitive drum  20 ). 
     The LED array  72  includes LED positioning members  75 , as an example of a protruding member, one by one at the right and left ends thereof. The LED positioning members  75  are configured to position the LED array  72  relative to the photosensitive drum  20 . 
     The LED positioning members  75  are rollers having substantially a circular plate shape, and disposed to protrude slightly upward at the left and right ends of the LED array  72 . The LED positioning members  75  contact the photosensitive drum  20  from below. Thus, the LED positioning members  75  are configured to position the LED array  72  at a distance (corresponding to a protrusion length of the LED positioning members  75 ) from the photosensitive drum  20  in face-to-face relationship with the photosensitive drum  20 . 
     The LED array  72  is stored in an upper end portion of the LED array storing portion  74  such that the LED array  72  is movable relative to the LED array storing portion  74 . A lower end portion of the LED array  72  is resiliently supported via a compression spring  76  by a bottom wall of the LED array storing portion  74 . 
     Specifically, the compression spring  76  is connected at one end to the bottom wall of the LED array storing portion  74  and at the other end to the lower end portion of the LED array  72 . Thus, the LED array  72  is resiliently supported via the compression spring  76  by the bottom wall of the LED array storing portion  74 . 
     The LED cover  77  integrally includes a cover portion  78  that covers the LED array  72 , support portions  79  at which the LED cover  77  is supported to the LED array support member  71 , and drive gears  80  that apply a drive force to the LED cover  77 . 
     The cover portion  78  has substantially a flat plate shape extending in the right-left direction in a plan view. The cover portion  78  is curved to have an upward arc shape when projected in the right-left direction. 
     The support portions  79  extend inside in a radial direction of the cover portion  78  from the left and right ends of the cover portion  78 . 
     Each of the drive gears  80  has substantially a circular plate shape, having thickness in the right-left direction. The drive gear  80  has gear teeth around its peripheral surface. The drive gear  80  is disposed outside of each of the right and left support portions  79  so as not to rotate relative to the support portions  79 . The drive gear  80  is located such that a center of rotation of the drive gear  80  overlaps a free end of each support portion  79  which is disposed inside in the radial direction of the cover portion  78 . 
     The LED cover  77  is rotatably supported by the LED array support member  71  at the free ends (lower ends) of the support portions  79  such that the cover portion  78  is disposed upward. 
     The LED cover  77  is configured to move, e.g., pivot around the lower ends of the support portions  79 , between an open position (or a retracted position shown in  FIG. 5A ) where the cover portion  78  is retracted from between the LED array  72  and the photosensitive drum  20  and a closed position (or a cover position shown in  FIG. 5B ) where the cover portion  78  covers the LED array  72  between the LED array  72  and the photosensitive drum  20 . The LED cover  77  may be held in the open position at least when the LED unit  16  forms a latent image on the photosensitive drum  20 . 
     As shown in  FIGS. 5A, 5B, 6A and 6B , the movable member  84  includes an interference portion  81  as an example of an engaging portion, input gears  82 , and compression springs  83 . The interference portion  81  is configured to engage the lower end portion of the developing cartridge  22 . The input gears  82  are configured to engage the drive gears  80  of the LED cover  77 . The compression springs  83  are configured to urge the interference portion  81  upward. 
     The interference portion  81  is shaped like a flat plate, extends in the right and left direction ( FIGS. 6A and 6B ), and is disposed below the developing cartridge  22 . 
     Each of the input gears  82  extends continuously from each of the right and left ends of the interference portion  81  ( FIGS. 6A and 6B ), and is shaped like a sector, in a side view, regarding a rear end portion of the interference portion  81  as the center. The input gear  82  extends rearward and upward to have substantially a 120-degree center angle ( FIGS. 5A and 5B ). The input gear  82  has gear teeth on a circumferential surface in the arc portion of the input gear  82  to engage the gear teeth of the drive gear  80 . 
     The rear end of the interference portion  81  is supported at a bottom wall of the drawer frame  41  such that the movable member  84  is rotatable. 
     Thus, the movable member  84  is configured to move between a first position ( FIG. 5A ) where the interference portion  81  extends in the front-rear direction along the bottom wall of the drawer frame  41  and a second position ( FIG. 5B ) where the interference portion  81  is inclined upward toward the front side. 
     The movable member  84  is located in the first position as the interference portion  81  is pressed from above by the lower end portion of the developing cartridge  22  when the developing cartridge  22  is attached to the drawer frame  41 . In other words, the lower end portion of the developing cartridge  22  functions as an engaging portion configured to engage the movable member  84  from above. 
     When the movable member  84  is in the first position, a rear end portion of the input gear  82  engages the drive gear  80  of the LED cover  77  located in the open position. 
     Each of the compression springs  83  is interposed between the interference portion  81  and the bottom wall of the drawer frame  41 , and is connected at one end to the lower surface of the interference portion  81  and at the other end to the bottom wall of the drawer frame  41 . Thus, the movable member  84  is urged clockwise in the right side view around the rear end portion of the interference portion  81 . 
     The movable member  84  is urged clockwise in the right side view to move the LED cover  77  to the closed position. 
     As shown in  FIG. 5A , when the LED cover  77  is in the open position, the movable member  84  is located in the first position, and the front end portion of the cover portion  78  is disposed at the rear of the upper end portion of the LED positioning member  75 . 
     As shown in  FIG. 5B , when the movable member  84  is rotated clockwise in the right side view by the urging force of the compression spring  83 , a drive force having counterclockwise direction in the right side view is input to the drive gear  80  of the LED cover  77  via the input gear  82  of the movable member  84 , and the drive gear  80  is rotated counterclockwise in the right side view. 
     Then, the counterclockwise drive force is input from drive gear  80  to the LED cover  77 , and the LED cover  77  is rotated counterclockwise in the right side view from the open position. 
     When the LED cover  77  is rotated counterclockwise in the right side view from the open position, the front end portion of the cover portion  78  of the LED cover  77  is brought in contact with the upper end portion of the LED positioning member  75  from the rear. 
     When the LED cover  77  is further rotated, the cover portion  78  is moved frontward while pressing the circumferential surface of the LED positioning member  75  downward. 
     With this, the LED array  72  is retracted downward against the urging force of the compression spring  76 , and the LED cover  77  is located in the closed position. 
     When the movable member  84  is rotated counterclockwise in the right side view against the urging force of the compression spring  83  under the situation where the movable member  84  is located in the second position and the LED cover  77  is located in the closed position ( FIG. 5B ), a clockwise drive force in the right side view is input via the input gear  82  of the movable member  84  to the drive gear  80  of the LED cover  77 , and the drive gear  80  is rotated clockwise in the right side view. 
     Then, the clockwise drive force is input from the drive gear  80  to the LED cover  77  and the LED cover  77  is rotated clockwise from the closed position in the right side view. 
     When the LED cover  77  is rotated clockwise in the right side view from the closed position, the cover portion  78  is moved rearward. 
     When the front end portion of the cover portion  78  is retracted rearward from the upper end portion of the LED positioning member  75 , the LED cover  77  is located in the open position, and the LED array  72  is moved upward by the urging force of the compression spring  76 . 
     As shown in  FIG. 1 , the belt cleaning unit  44  includes a waste toner storing portion  91 , a scrape roller  92 , a scrape blade  93 , and a belt cleaning roller  94 . 
     The waste toner storing portion  91  is shaped like substantially a box having an opening  95  at its upper end portion. 
     The scrape roller  92  is disposed facing the opening  95  of the waste toner storing portion  91  from above. 
     The scrape blade  93  has the shape of substantially a flat plate extending in the front-rear direction, and a front end portion (base end portion) of the scrape blade  93  is fixed to a front end defining the opening  95  of the waste toner storing portion  91  such that a rear end portion (free end portion) thereof contacts the scrape roller  92  from below. 
     The belt cleaning roller  94  is rotatably supported at the upper end portion of the belt cleaning unit  44  such as to contact the scrape roller  92  from above. 
     The belt cleaning unit  44  is disposed such that the belt cleaning roller  94  contacts the lower side of the intermediate transfer belt  30  from below. The belt cleaning unit  44  is configured to cause the belt cleaning roller  94  to remove dirt, e.g. residual toner, from the intermediate transfer belt  30 . The toner held by the belt cleaning roller  94  is transferred to the scrape roller  92 , the toner transferred to the scrape roller  92  is scraped by the scrape blade  93 , and then stored in the waste toner storing portion  91 . 
     When the developing cartridge  22  is removed from the casing  2 , the front cover  7  is released, and the process unit  15  is pulled out frontward and located in the outside position as shown in  FIG. 3 . 
     The handle  63  of the developing cartridge  22  is held, and pulled upward from the drawer frame  41 . 
     Along with upward movement of the developing cartridge  22 , the developing roller  23  presses the photosensitive drum  20  from below. 
     When the photosensitive drum  20  is pressed from below, the drum unit  43  is rotated around the unit support boss  59  clockwise in the right side view as described above. 
     As shown in  FIGS. 4, 5A and 5B , when the developing cartridge  22  is pulled further upward, the drum unit  43  is rotated further clockwise in the right side view, and is retracted upward and rearward from the position where the photosensitive drum  20  is located above the developing roller  23  and thus located in the retracted position. At this time, the shaft  57  is engaged in the bend portion  52 B in the guide groove  52 , and thus the drum unit  43  is stopped in the retracted position. 
     When the developing cartridge  22  is pulled further upward, the developing cartridge  22  is removed upward through a space formed when the drum  43  is retracted. 
     In this way, the developing cartridge  22  is removed from the casing  2 . 
     As shown in  FIG. 5B , when the developing cartridge  22  is removed from the casing  2 , the pressing of the interference portion  81  by the lower end portion of the developing cartridge  22  is cancelled. 
     As described above, the movable member  84  is rotated clockwise in the right side view by the urging force of the compression spring  83 , and the LED cover  77  is moved from the open position to the closed position. 
     When the developing cartridge  22  is attached to the casing  2 , the process unit  15  is located in the outside position, such that the drum unit  43  is stopped in the retracted position. In this state, the handle  63  of the developing cartridge  22  is held such that the developing roller  23  is located rearward and exposed upward, to position the developing cartridge  22  above the drawer frame  41  in front of the drum unit  43 . 
     The developing cartridge  22  is inserted into the drawer frame  41  from above such that the cartridge support boss  66  of the developing cartridge  22  is engaged in the cartridge support groove  49  of the drawer frame  41 . 
     Then, the developing roller  23  of the developing cartridge  22  arrives in the drawer frame  41 , and then the cartridge support boss  66  of the developing cartridge  22  is engaged in the cartridge support groove  49  of the drawer frame  41 . 
     When the cartridge support boss  66  is engaged in lower end portion of the cartridge support groove  49 , the cartridge support boss  66  contacts the contact portion  40  of the holding member  46 . 
     As the cartridge support boss  66  contacts the contact portion  40 , the holding member  46  is rotated about the holding member support boss  50  clockwise in the right side view. 
     The shaft  57  is disengaged from the bend portion  52 B, and engaged in the straight portion  52 A. Namely, engagement of the shaft  57  in the bend portion  52 B is released. 
     Then, the drum unit  43  is rotated counterclockwise in the right side view from the retracted position by its own weight, and thus located in the image formation position. 
     In this way, the developing cartridge  15  is attached to the process unit  15 . 
     When the developing cartridge  22  is attached to the process unit  15 , as shown in  FIG. 5A , the interference portion  81  of the movable member  84  is pressed from above by the lower end portion of the developing cartridge  22 , and the movable member  84  is rotated counterclockwise in the right side view against the urging force of the compression spring  83 . 
     Then, the LED cover  77  is rotated clockwise in the right side view from the closed position and located in the open position. At this time, the cover portion  78  is moved rearward such that it is retracted from a path along which the developing cartridge  22  is attached or removed. 
     When the LED cover  77  is located in the open position, the LED array  72  is moved upward by the urging force of the compression spring  76 , and is brought in contact with the photosensitive drum  20  in the LED positioning member  75 . 
     According to the printer  1 , the drum unit  43  is configured to move between the image formation position where an image is formed on the photosensitive drum  20  and the retracted position where the photosensitive drum  20  is retracted from the developing roller  23 , as shown in  FIGS. 5A and 5B . 
     With this structure, as the drum unit  43  is moved to the retracted position, a path through which the developing cartridge  22  is attached and removed is opened. Thus, the developing cartridge  22  can be attached and removed through the path. 
     Thus, the developing cartridge  22  can be easily detachably attachable, only by rotating the drum unit  43  from the image formation position to the retracted position. 
     According to the printer  1 , as shown in  FIG. 4 , the holding member  46  that holds each drum unit  43  in the retracted position is provided. 
     With the holding member  46 , when the developing cartridge  22  is removed, the drum unit  43  can be held in the retracted position. 
     As a result, when the developing cartridge  22  is attached, there is no need to move the drum unit  43  to the retracted position, and thus the developing cartridge  22  can be easily attached. 
     According to the printer  1 , as shown in  FIG. 4 , the guide groove  52  of the holding member  46  into which the shaft  57  of the drum unit  43  is inserted includes the straight portion  52 A along which the drum unit  43  is guided between the image formation position and the retracted position and the bend portion  52 B in which the drum unit  43  is stopped in the retracted position. 
     Thus, the shaft  57  of the drum unit  43  can be guided along the straight portion  52 A and then smoothly stopped in the bend portion  52 B. 
     As a result, the drum unit  43  can be moved from the image formation position to the retracted position and then smoothly stopped in the retracted position. 
     According to the printer  1 , as shown in  FIGS. 2 and 4 , the developing cartridge  22  includes the cartridge support boss  66  that interferes with the holding member  46  and releases the engagement of the drum unit  43  in the bend portion  52 B in the guide groove  52  while the developing cartridge  22  is attached to the casing  2 . 
     While the developing cartridge  22  is removed from the casing  2 , the developing roller  23  presses the drum unit  43  from below, and thus the drum unit  43  is moved from the image formation position to the retracted position. In addition, while the developing cartridge  22  is attached to the casing  2 , the engagement of the drum unit  43  in the bend portion  52 B of the guide groove  52  is released and thus the drum unit  43  is moved from the retracted position to the image formation position. 
     Thus, the drum unit  43  can be reliably moved to the retracted position by removing the developing cartridge  22 , and reliably moved to the image formation position by attaching the developing cartridge  22 . 
     According to the printer  1 , as shown in  FIGS. 1 and 3 , the process unit  15  is provided which holds the drum units  43  and is configured to move along the front-rear direction between the inside position where the process unit  15  is disposed inside the casing  2  and outside position where the process unit  15  is pulled out outside the casing  2 . 
     Thus, the printer  1  provides a front access design in which the process unit  15  is pulled frontward to detachably attach the developing cartridge  22  to the process unit  15 . 
     As a result, even when the printer  1  is installed in a space limited vertically, the developing cartridge  22  can be detachably attached to the process unit  15  without great difficulty. 
     According to the printer  1 , as shown in  FIG. 1 , the process unit  15  includes the belt cleaning unit  44  which cleans the intermediate transfer belt  30 . 
     Thus, the need to increase the physical size of the printer  1  can be obviated compared with a case where a part for cleaning the intermediate transfer belt  30  is provided separately from the process unit  15 . 
     According to the printer  1 , as shown in  FIG. 1 , an intermediate transfer type is employed in which a toner image carried on each photosensitive drum  20  is primarily transferred to the intermediate transfer belt  30 . 
     Thus, a toner image can be transferred onto a sheet P without the need to pass the sheet P between each photosensitive drum  20  and the belt unit  26 , compared with a direct tandem type where a toner image carried on each photosensitive drum  20  is directly transferred to a sheet P. 
     As a result, a path along which the sheet P is fed can be simplified. 
     According to the printer  1 , as shown in  FIG. 1 , the LED units  16  are provided which expose the photosensitive drums  20 . 
     Thus, as the size of each LED unit  16  is small compared with a scanner which emits laser beams to expose the photosensitive drums  20 , the need to increase the physical size of the printer  1  can be obviated. 
     According to the printer  1 , as shown in  FIG. 5A , when the developing cartridge  22  is attached to the casing  2  and at least when the LED unit  16  forms a latent image on the photosensitive drum  20 , the cover operation mechanism is configured to hold the LED cover  77  in the open or retracted position where the LED cover  77  is retracted from between the photosensitive drum  20  and the LED array  72 . 
     Thus, while the developing cartridge  22  is attached to the casing  2 , the LED array  72  can be covered by the LED cover  77  except during image formation. 
     According to the printer  1 , as shown in  FIG. 5A , when the developing cartridge  22  is attached to the casing  2 , the LED cover  77  is located in the open position where the LED cover  77  is retracted from between the photosensitive drum  20  and the LED array  72 . In addition, as shown in  FIG. 5B , when the developing cartridge  22  is removed from the casing  2 , the LED cover  77  is located in the closed position where the LED cover  77  covers the LED array  72  between the photosensitive drum  20  and the LED array  72 . 
     Thus, when the developing cartridge  22  is removed from the casing  2 , the LED array  72  can be covered by the LED cover  77 . 
     As a result, for example, the potential that the LED array  72  gets soiled by toner dropped from the photosensitive drum  20  can be minimized. 
     According to the printer  1 , as shown in  FIG. 5A , when the developing cartridge  22  is attached to the process unit  15 , the interference portion  81  of the movable member  84  is pressed by the lower end portion of the developing cartridge  22 . In addition, as shown in  FIG. 5B , when the developing cartridge  22  is removed from the process unit  15 , the interference portion  81  is released from being pressed by the lower end portion of the developing cartridge  22 . 
     Thus, with a simple structure, attachment and removal of the developing cartridge  22  to and from the process unit  15  can be interlocked with the movement of the LED cover  77 . 
     According to the printer  1 , as shown in  FIGS. 5A and 5B , the movable member  84  is urged such that the LED cover  77  is moved to the closed position. 
     Thus, when the developing cartridge  22  is removed from the process unit  15 , the LED cover  77  can be reliably moved to the closed position. 
     According to the printer  1 , as shown in  FIGS. 5A and 5B , the movable member  84  includes the input gears  82  that engage the drive gears  80  of the LED cover  77 , and the compression springs  83 , and is urged by the urging force of the compression springs  83  such that the LED cover  77  is moved to the closed position. 
     With a simple structure, when the developing cartridge  22  is removed from the process unit  15 , the LED cover  77  can be moved to the closed position. 
     According to the printer  1 , as shown in  FIG. 5A , the LED cover  77  is moved to the open position such that it is retracted from a path along which the developing cartridge  22  is attached or removed. In other words, the LED cover  77  located in the open position is opening the path. 
     Thus, the developing cartridge  22  can be attached to or removed from the process unit  15  without interference of the LED cover  77 . 
     According to the printer  1 , as shown in  FIGS. 5A and 5B , the LED array  72  of the LED unit  16  is urged toward the photosensitive drum  20 . When the LED cover  77  is in the open position, the LED positioning member  75  of the LED array  72  is brought into contact with the photosensitive drum  20 , thereby the LED array  72  is disposed facing the photosensitive drum  20  at a specified distance. When the LED cover  77  is in the closed position, the LED cover  77  contacts the LED positioning member  75 , thereby the LED array  72  is disposed facing the cover portion  78  of the LED cover  77  at a specified distance. 
     Thus, when the LED cover  77  is in the open position, the LED array  72  can be disposed facing the photosensitive drum  20  at a specified distance, and when the LED cover  77  is moved to the closed position, the LED array  72  can be disposed facing the cover portion  78  of the LED cover  77  at a specified distance. 
     As a result, with a simple structure, the LED array  72  can be positioned relative to the photosensitive drum  20 , and the LED cover  77  can be prevented from interfering with the photosensitive drum  20 . 
     According to the printer  1 , as shown in  FIGS. 1 and 5A , the LED array  72  is disposed under the photosensitive drum  20 . 
     However, the LED cover  77  can minimize the potential that the LED array  72  gets soiled by toner dropped from the photosensitive drum  20 . 
     According to the printer  1 , as shown in  FIG. 1 , the four photosensitive drums  20  are spaced apart from each other in the front-rear direction perpendicular to an up and down direction (where the developing cartridge  22  is attached to or removed from the process unit  15 ). 
     Thus, the printer  1  is structured of a color printer having the photosensitive drums  20  corresponding to each color. 
     A second illustrative embodiment will be described with reference to  FIGS. 7A and 7B . It is noted that elements similar to or identical with those shown and described in the first embodiment are designated by similar numerals, and thus the description thereof can be omitted for the sake of brevity. 
     According to the first embodiment, the LED cover  77  is provided with the drive gears  80 , and the movable member  84  disposed under the developing cartridge  22  is provided with the input gears  82  that engage the drive gears  80 . With the engagement of the drive gears  80  with the input gears  82 , the LED cover  77  is moved to the open position along with the attachment of the developing cartridge  22 , and moved to the closed position along with the removal of the developing cartridge  22 . 
     In the second embodiment, however, as shown in  FIGS. 7A and 7B , the developing cartridge  22  includes, at its lower rear end portion, an engaging portion  101  protruding reward, as an example of a cover operation mechanism, and the LED cover  77  includes, at its front end portion, an engaging portion  102  protruding frontward, as an example of a cover operation mechanism. The LED cover  77  does not include the drive gears  80 . 
     When the developing cartridge  22  is attached, the engaging portion  101  is brought in contact with the engaging portion  102  from above, and thereby the LED cover  77  is rotated counterclockwise in a right side view and located in the open position. When the developing cartridge  22  is removed, the engaging portion  101  is brought in contact with the engaging portion  102  from below, and thereby the LED cover  77  is rotated clockwise in the right side view and located in the closed position. 
     Specifically, in the second embodiment, the engaging portion  101  is shaped like substantially a flat plate protruding rearward from a lower rear end portion of the cartridge frame  61 . 
     The LED cover  77  includes the engaging portion  102 , a pair of right and left support plates  104  as an example of a cover operation mechanism, and a cover portion  105  extending between the support plates  104 . 
     The support plates  104  are shaped like a sector in the right side view. 
     The cover portion  105  has substantially a flat plate shape in a plan view. The cover portion  105  is curved to correspond to an arc shape of the support plates  104  in a side view. 
     The engaging portion  102  extends frontward from the front end portion of the support plate  104  when the LED cover  77  is in the closed position (shown in  FIG. 7B ). 
     The LED cover  77  is supported by the LED array support member  71  such that the cover portion  105  is disposed upward and pivotable around a center angle portion (a lower end portion) of each support plate  104 . 
     The LED cover  77  is rotated between an open position (or retracted position,  FIG. 7A ) where the cover portion  105  is retracted from between the LED array  72  and the photosensitive drum  20  and a closed position (or cover position,  FIG. 7B ) where the cover portion  105  covers the LED array  72  between the LED array  72  and the photosensitive drum  20 . 
     The LED cover  77  is urged clockwise in the right side view by a coil spring  103  as an example of a cover operation mechanism. Specifically, the coil spring  103  is fixed at one end to the support plate  104  of the LED cover  77 , and at the other end to the LED array storing portion  74 . 
     When the developing cartridge  22  is attached, the LED cover  77  is located in the open position ( FIG. 7A ) where the cover portion  105  is retracted in front of the LED array  72  against an urging force of the coil spring  103 . Then, the engaging portion  102  is brought in contact with a rear wall of the cartridge frame  61 , and thereby the LED cover  77  is secured at the open position. 
     In the second embodiment, when the developing cartridge  22  is removed from the process unit  15 , the engaging portion  101  is brought in contact with the engaging portion  102  from below, and thereby the LED cover  77  is rotated clockwise in the right side view and then located in the closed position. 
     When the developing cartridge  22  is attached to the process unit  15 , the engaging portion  101  is brought in contact with the engaging portion  102  from above, and thereby the LED cover  77  is rotated counterclockwise in the right side view and then located in the open position. 
     According to the second embodiment, the LED cover  77  includes the engaging portion  102  and the support plates  104 . 
     Thus, with a simple structure, attachment and removal of the developing cartridge  22  to and from the process unit  15  can be interlocked with the movement of the LED cover  77 . 
     Even with the second embodiment, it is clear that effects similar to those brought about by the first embodiment can be appreciated. 
     A third illustrative embodiment will be described with reference to  FIGS. 8 and 9 . It is noted that elements similar to or identical with those shown and described in the first embodiment are designated by similar numerals, and thus the description thereof can be omitted for the sake of brevity. 
     In the first embodiment described above, the arc-shaped handle  63  extending upward is disposed in the central portion of the upper end portion of each cartridge frame  61  in the right-left direction. In the third embodiment, the handles  63  are configured to move up and down. As shown in  FIG. 8 , when the process unit  15  is disposed inside the casing  2 , the handles  63  are retracted inside or downward in the respective cartridge frames  61 . As shown in  FIG. 9 , when the process unit  15  is pulled out from the casing  2 , the handles  63  protrude outside or upward from the respective cartridges  61 . 
     Specifically, in the third embodiment, as shown in  FIGS. 8 and 9 , the casing  2  includes inside a pair of rail members  111  as an example of a contact member, which are configured to press the handles  63  downward. 
     The rail members  111  are shaped like substantially a flat plate extending in the front-rear direction. The rail members  111  are disposed outside the base tubes  55  of the photosensitive drums  20  in the right-left direction, and are spaced apart from each other in the right-left direction to sandwich the belt unit  26  therebetween. The rail members  111  are fixed to an upper wall of the casing  2  at their upper end portions. 
     Each developing cartridge  22  includes a handle storing portion  112  in which the handle  63  is stored. The developing cartridge  22  includes a compression spring  113  as an example of an urging member that urges the handle  63  upward. 
     The handle storing portion  112  is defined at the upper end portion of the cartridge frame  61  to have the shape of substantially a rectangle extending vertically in a side view. 
     The handle  63  is stored in the handle storing portion  112  slidably in the up and down direction. 
     The coil spring  113  is connected at one end to a bottom wall of the handle storing portion  112  and at the other end to the lower end portion of the handle  63 . Thus, the handle  63  is urged upward. 
     In the third embodiment, as shown in  FIG. 8 , when the process unit  15  is disposed inside the casing  2 , an upper end portion of each handle  63  contacts a lower end portion of the rail members  111 , and each handle  63  is pressed by the rail members  11  from above. 
     Thus, each handle  63  is retracted downward into the handle storing portion  112  of the cartridge frame  61  against the urging force of the compression spring  113  such that upper end portion of the handle  63  is disposed below the upper end portion of the photosensitive drum  20 . 
     As shown in  FIG. 9 , when the process unit  15  is pulled out from the casing  2 , the handles  63  are separated from the rail members  111  and released from being pressed by the rail members  111 . 
     Each handle  63  is pressed upward from the handle storing portion  112  of the cartridge frame  61  by the urging force of the compression spring  113  such that the upper end portion of the handle  63  is located above the upper end portion of the photosensitive drum  20 . 
     According to the third embodiment, as shown in  FIGS. 8 and 9 , the handles  63  are configured to be retracted below the upper end portions of the photosensitive drums  20  when the process unit  15  is disposed inside the casing  2 , and to protrude above the upper end portions of the photosensitive drums  20  when the process unit  15  is pulled out from the casing  2 . 
     Thus, when the process unit  15  is pulled out from the casing  2 , the handles  63  protrude above the photosensitive drums  20 , facilitating pickup and installation of the developing cartridge  22  relative to the process unit  15 . 
     As a result, the developing cartridge  22  can be smoothly attached and removed. 
     According to the third embodiment, as shown in  FIGS. 8 and 9 , each developing cartridge  22  includes the compression spring  113  that urges the handle  63  upward, while the casing  2  includes the rail members  111  that contact the handle  63  from above when the process unit  15  is disposed inside the casing  2 . 
     Thus, when the process unit  15  is inserted into the casing  2 , each handle  63  is configured to contact the rail members  111  from below and withdraw downward against the urging force of the compression spring  113 . When the process unit  15  is pulled out from the casing  2 , each handle  63  is configured to protrude upward by the urging force of the compression spring  113 . 
     As a result, with a simple structure, the vertical movement of the handles  63  can be interlocked with sliding movement of the process unit  15  relative to the casing  2 . 
     In addition, even with the third embodiment, it is clear that effects similar to those brought about by the first embodiment can be appreciated. 
     A fourth illustrative embodiment will be described with reference to  FIG. 10 . It is noted that elements similar to or identical with those shown and described in the first embodiment are designated by similar numerals, and thus the description thereof can be omitted for the sake of brevity. 
     In the first embodiment described above, the printer  1  is designed with front access structure. By releasing the front cover  7 , which is disposed in the front end portion of the casing  2 , the process unit  15  is pulled out from the casing  2 . 
     In the fourth embodiment, as shown in  FIG. 10 , the casing  2  includes a top cover  120 , as an example of a movable unit, at the upper end portion. By releasing the top cover  120 , the developing cartridge  22  is attached to or removed from the casing  2 . 
     Specifically, the top cover  120  is provided at the upper wall and an upper end portion of the rear wall of the casing  2 . 
     The top cover  120  is configured to pivot about a middle portion of the rear wall of the casing  2  (a rear side of the fixing unit  18 ). The top cover  120  supports the belt unit  26  and the fixing unit  18  via a support mechanism, which is not shown. 
     The top cover  120  is pivoted along with the belt unit  26  and the fixing unit  18  such that the upper end portion of the casing  2  is fully released. 
     When the top cover  120  is released, the upper end portion of the process unit  15  is exposed from above and access to the developing cartridge  22  is available from above. 
     For attachment and removal of each developing cartridge  22  to and from the casing  2 , the top cover  120  is pivoted upward such that the upper end portion of the casing  2  is released. Then, each developing cartridge  22  is attached to or removed from the casing  2  from the released upper end portion of the casing  2 . 
     In addition, even with the fourth embodiment, it is clear that effects similar to those brought about by the first embodiment can be appreciated. 
     A fifth illustrative embodiment will be described with reference to  FIG. 11 . It is noted that elements similar to or identical with those shown and described in the first embodiment are designated by similar numerals, and thus the description thereof can be omitted for the sake of brevity. 
     In the first embodiment described above, the drawer frame  41  of the process unit  15  holds the drum units  43 , and the developing cartridges  22  are configured to be attached to and removed from the process unit  15 . In the fifth embodiment, as shown in  FIGS. 11A and 11B , a process cartridge  131  integrally including a developing unit  132  and the drum unit  43  is configured to be attached to and removed from the process unit  15 . The developing unit  132  is identical in structure to the developing cartridge  22  of the first embodiment. 
     Even with the fifth embodiment, it is clear that effects similar to those brought about by the first embodiment can be appreciated. 
     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.