Abstract:
An image forming device includes a casing, photosensitive bodies, developing devices, developer accommodating devices, and a retaining member. The developer accommodating devices includes a first developer accommodating device that is individually replaceable and separable from the corresponding developing device and a second developer accommodating device that is replaceable together with the corresponding developing device. The retaining member retains the photosensitive bodies arranged in an arrangement direction, the developing devices, and the developer accommodating devices at fixed positions within the casing. The retaining member is capable of being pulled out from the casing and is movable between a housed position and a withdrawn position. One of the developer accommodating devices located at a most downstream side in the arrangement direction is the first developer accommodating device, and each of the developer accommodating devices other than the one of the developer accommodating devices is the second developer accommodating device.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority from Japanese Patent Application No. 2010-012054 filed Jan. 22, 2010. The entire content of this priority application is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates in general to an image-forming device for forming images on recording sheets, and more particularly to an image-forming device having a plurality of photosensitive members arranged in tandem and retained together with corresponding developing devices and developer-accommodating devices at fixed positions in a retaining member that can be withdrawn from a body of the image-forming device along the juxtaposed direction of the photosensitive members. 
     BACKGROUND 
     An image-forming device such as a laser printer for forming color images on recording sheets is well known in the art. One such image-forming device has a plurality of photosensitive members and a plurality of corresponding developer cartridges (each integrally formed of a developing device and a developer-accommodating device) arranged in tandem and held at fixed positions within a retaining member. Parts, consumables, and the like in the photosensitive members and the developer cartridges can be replaced by pulling the retaining member out from a body of the image-forming device along the direction in which the photosensitive members are juxtaposed. 
     SUMMARY 
     In order to keep down running costs in a laser printer or other image-forming device, it is beneficial to be able to separate the developer-accommodating devices (toner cartridges) from the developing devices and the photosensitive members so that the developer-accommodating devices can be replaced individually. However, when developing devices having such individually detachable toner cartridges are employed in an image-forming device configured with a retaining member that is pulled out of the image-forming device in the direction of the juxtaposed photosensitive members, the force applied to the extracted retaining member as a result of operations performed to open and close shutters in the toner cartridge when mounting and removing the toner cartridge can potentially damage the retaining member or cause the image-forming device to overturn. 
     It is an object of the present invention to provide an image-forming device having photosensitive members arranged in tandem in a retaining member that can be pulled out of a body of the image-forming device along the juxtaposing direction of this tandem arrangement, whereby one of the developing devices provided in the retaining member has an individually detachable toner cartridge for reducing running costs and the configuration eliminates the risk of damaging the retaining member and overturning the body of the image-forming device due to forces applied to the retaining member when the retaining member is partially withdrawn from the body. 
     In order to attain the above and other objects, the present invention provides an image forming device. The image forming device includes a casing, a plurality of photosensitive bodies, a plurality of developing devices, a plurality of developer accommodating devices, and a retaining member. The casing is formed with a first opening. The plurality of developing devices respectively corresponds to the plurality of photosensitive bodies. The plurality of developer accommodating devices accommodates and supplies developer respectively to the plurality of developing devices. The plurality of developer accommodating devices includes a first developer accommodating device that is individually replaceable and separable from the corresponding developing device and a second developer accommodating device that is replaceable integrally together with the corresponding developing device. The retaining member retains the plurality of photosensitive bodies arranged in an arrangement direction, the plurality of developing devices, and the plurality of developer accommodating devices at fixed positions within the casing. The retaining member is capable of being pulled out from the casing in the arrangement direction through the first opening and is movable between a first position where the plurality of photosensitive bodies, the plurality of developing devices, and the plurality of developer accommodating devices are inside the casing and a second position where one of the plurality of developer accommodating devices located at a most upstream side in the arrangement direction is replaceable. Another one of the plurality of developer accommodating devices located at a most downstream side in the arrangement direction is the first developer accommodating device accommodating black developer, and each of the developer accommodating devices other than the another one of the plurality of developer accommodating devices is the second developer accommodating device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The particular features and advantages of the invention as well as other objects will become apparent from the following description taken in connection with the accompanying drawings, in which: 
         FIG. 1  is a cross-sectional view showing a color multifunction device according to a first embodiment of the present invention; 
         FIG. 2  is a cross-sectional view illustrating an operation in which a black toner cartridge is removed from a developing device; 
         FIG. 3  is a cross-sectional view illustrating an operation in which the black toner cartridge is attached to the developing device; 
         FIG. 4  is a cross-sectional view illustrating an operation in which a developing device and a developer accommodating device disposed on a farthest side of a retaining member are replaced; 
         FIG. 5  is a perspective view showing the toner cartridge and the developing device when shutters are at a closed position; 
         FIG. 6  is a perspective view showing the toner cartridge and the developing device when the shutters are at an open position; 
         FIG. 7  is an explanatory diagram illustrating a circulation of toner in a process unit; 
         FIG. 8  is a cross-sectional view illustrating a feature of a developing roller provided in the developing device corresponding to the black toner cartridge; and 
         FIG. 9  is a cross-sectional view illustrating an operation in which a black toner cartridge is attached to a developing device according to a second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Next, preferred embodiments of the present invention will be described while referring to the accompanying drawings. The following description first covers the overall structure of a color multifunction device of a first embodiment according to the present invention and subsequently includes a detailed description of a process unit having a developer-accommodating device accommodating black developer. 
     As shown in  FIG. 1 , a color multifunction device  1  has a main body  10  and a flatbed scanner  20  disposed above the main body  10 . Within the main body  10 , the color multifunction device  1  primarily includes a sheet-feeding unit  30  for supplying sheets of a paper P, an image-forming unit  40  for forming images on sheets of paper P supplied by the sheet-feeding unit  30 , and a sheet-discharging unit  90  for discharging the sheets of paper P after images have been formed thereon. 
     In the following description, directions related to the color multifunction device  1  will refer to directions seen from the perspective of an operator when operating the color multifunction device  1 . Specifically, the right side of the color multifunction device  1  in  FIG. 1  will be referred to as the “front” or the “near side”; the left side as the “rear” or the “far side”; the near side in  FIG. 1  as “left”; and the far side in  FIG. 1  as “right.” Also, the upper and lower sides along the vertical in  FIG. 1  will be referred to as “upper” and “lower” in the description. 
     The flatbed scanner  20  disposed above the main body  10  is a document-reading device well known in the art. During a copy operation and the like, the flatbed scanner  20  generates image data by irradiating light onto an original document placed in the flatbed scanner  20  and reads the image from the original document. 
     The sheet-feeding unit  30  is disposed in a bottom section of the main body  10  and includes a paper tray  31  for accommodating sheets of paper P, and a paper-feeding mechanism  32  for conveying sheets of paper P from the paper tray  31  to the image-forming unit  40 . The paper-feeding mechanism  32  separates and conveys the paper P accommodated in the paper tray  31  to the image-forming unit  40  one sheet at a time. 
     The image-forming unit  40  primarily includes an exposure unit  50 , four process units including a process unit  61  and three process units  62 , a transfer unit  70 , and a fixing unit  80 . 
     The exposure unit  50  is provided in a top section of the main body  10  and includes a laser light source, a polygon mirror, lenses, reflecting mirrors, and the like (not shown in the drawings). Laser beams emitted from the laser light source are reflected off the polygon mirror and the reflecting mirrors, pass through the lenses, and are scanned at a high speed over surfaces of photosensitive drums described later. 
     The process unit  61  and the process units  62  are disposed between the sheet-feeding unit  30  and the exposure unit  50  and are juxtaposed (arranged in tandem) in the front-to-rear direction. The process units  61  and  62  are held in a retaining case  65 . 
     The retaining case  65  has a bottomless frame-like structure, for example, and is capable of moving between a first position where the retaining case  65  is mounted in the main body  10  (see  FIG. 1 ) and a second position where the retaining case  65  is removed forwardly from the main body  10  (see  FIG. 4 ). Guide rails  10 R (see  FIG. 4 ) are formed on inner sides of the main body  10  for guiding the retaining case  65  in the front-to-rear direction. A front cover  11  is provided on a front side of the main body  10  over a first opening  11   a  formed in the main body  10  and can be pivotally rotated downward to expose the first opening  11   a  or upward to cover the first opening  11   a . A handle  65 H is provided on a front end of the retaining case  65 . By opening the front cover  11  and pulling on the handle  65 H, an operator can pull the retaining case  65  out of the main body  10  in a pull-out direction, i.e., moves the retaining case  65  to the second position, as illustrated in  FIG. 4 . Once the retaining case  65  has been positioned at the second position, the operator can replace components of the process units  62  that, during their normal operating state, are positioned far side (rearward) of the main body  10 . That is, the second position indicates the position of the retaining case  65  at which the process unit  61  disposed nearest side of the retaining case  65  among the four process units  61  and  62  with respect to the pull-out direction can be accessed and replaced. 
     An upper cover  12  can open and close a second opening  12   a  formed at a position immediately above the first opening  11   a  and penetrating the main body  10  in top-to-bottom direction. The upper cover  12  is provided on an upper front portion of the main body  10  (immediately above the front cover  11 ). As shown in  FIGS. 2 and 3 , the process unit  61  disposed on the nearest side of the retaining case  65  can be accessed through the second opening  12   a  by opening the upper cover  12 , without pulling the retaining case  65  out of the main body  10 , enabling the operator to mount or replace a toner cartridge  100  (described later in greater detail) in the process unit  61 . 
     As shown in  FIG. 1 , the process unit  61  disposed on the nearest side of the retaining case  65  among the four process units includes a photosensitive drum  61 A, a charger  61 B, the toner cartridge  100  accommodating black toner, and a developing device  200 . The developing device  200  includes a developing roller  61 C, a supply roller  61 D, a thickness-regulating blade  61 E, and an auger  61 F. Specifically, the supply roller  61 D is disposed closer to the near side than the developing roller  61 C and the auger  61 F is disposed closer to the near side than the supply roller  61 D as shown in  FIG. 1 . The toner cartridge  100  is disposed above the auger  61 F. The structure of the process unit  61  will be described later in greater detail. 
     The photosensitive drum  61 A and the charger  61 B of the process unit  61  may be configured so that they are mounted in and removed from the retaining case  65  together (i.e., replaceable as a unit) or may be fixed to the retaining case  65  to form a single unit therewith. Alternatively, the developing roller  61 C, the supply roller  61 D, the thickness-regulating blade  61 E, and the auger  61 F constituting the developing device  200  may be configured as an integrated unit that is mounted in and removed from the retaining case  65 , or may be fixed to the retaining case  65  together with the photosensitive drum  61 A and the charger  61 B and formed as a single unit with the retaining case  65 . If the developing device  200  is detachably mounted in the retaining case  65 , the photosensitive drum  61 A and the charger  61 B may be configured to be detachably mounted as a unit or to be mounted and removed separately. 
     Each of the three process units  62  among the four process units disposed farther rearward in the retaining case  65  includes a photosensitive drum  62 A, a charger  62 B, a developing roller  62 C, a supply roller  62 D, a thickness-regulating blade  62 E, and a developer-accommodating device  62 G. The developer-accommodating devices  62 G of these process units  62  accommodate toner in one of the colors cyan, magenta, and yellow, respectively. A developing device  62 H of each process unit  62  is configured of the developing roller  62 C, the supply roller  62 D, and the thickness-regulating blade  62 E and is integrally configured with the developer-accommodating device  62 G and detachably mounted in the retaining case  65  (see  FIG. 4 ). 
     As with the photosensitive drum  61 A and the charger  61 B of the process unit  61 , the photosensitive drum  62 A and the charger  62 B of the process unit  62  may be configured to be detachably mounted in the retaining case  65  (i.e., replaceable) or fixed to the retaining case  65  to form a single unit therewith. The process unit  62  (i.e., the photosensitive drum  62 A, the charger  62 B, the developing roller  62 C, the supply roller  62 D, the thickness-regulating blade  62 E, and the developer-accommodating device  62 G) may be detachably mounted in the retaining case  65  as a unit. 
     The transfer unit  70  is disposed between the sheet-feeding unit  30  and the process units  61  and  62 . The transfer unit  70  primarily includes a drive roller  71 , a follow roller  72 , an endless conveying belt  73  stretched taut about the rollers  71  and  72 , and four transfer rollers  74 . The outer surface of the conveying belt  73  is in contact with each of the photosensitive drums  61 A and  62 A and is pinched between the transfer rollers  74  disposed on the inner side of the conveying belt  73  and the photosensitive drums  61 A and  62 A. 
     A cleaning unit  75  is disposed beneath the conveying belt  73 . The cleaning unit  75  contacts the conveying belt  73  for removing toner, paper dust, and other deposited matter from the conveying belt  73  and for recovering this deposited matter. 
     The fixing unit  80  is disposed rearward of the process units  61  and  62  and the transfer unit  70 . The fixing unit  80  primarily includes a heating roller  81 , and a pressure roller  82  disposed in confrontation with the heating roller  81  and applying pressure to the same. 
     In the image-forming unit  40 , the chargers  61 B and  62 B apply a uniform charge to the respective surfaces of the photosensitive drums  61 A and  62 A, after which the surfaces are exposed to laser beams emitted from the exposure unit  50  in a high-speed scan to form electrostatic latent images on the charged surfaces of the photosensitive drums  61 A and  62 A based on image data. Toner accommodated in the toner cartridge  100  and the developer-accommodating devices  62 G is supplied respectively to the developing rollers  61 C and  62 C via the supply rollers  61 D and  62 D. As the developing rollers  61 C and  62 C rotate, toner carried on the surfaces of the same is regulated to a prescribed thickness by the respective thickness-regulating blades  61 E and  62 E. 
     The toner layers of uniform thickness carried on the developing rollers  61 C and  62 C are supplied to the electrostatic latent images formed on the photosensitive drums  61 A and  62 A, respectively, whereby the electrostatic latent images are developed into visible toner images on the photosensitive drums  61 A and  62 A. Subsequently, as a sheet of paper P carried on the conveying belt  73  is sequentially conveyed between the photosensitive drums  61 A and  62 A and the conveying belt  73  (the transfer rollers  74 ), the toner images carried on the photosensitive drums  61 A and  62 A are sequentially transferred onto and superposed on the sheet of paper P. When the sheet of paper P is then conveyed between the heating roller  81  and the pressure roller  82 , the toner images transferred on the sheet are fixed to the sheet by heat. 
     The sheet-discharging unit  90  primarily includes a paper-discharge path  91  for guiding sheets of paper P upward in the main body  10  from the exit side of the fixing unit  80  while inverting the sheets, and a discharge roller  92  for discharging the inverted sheets onto a discharge tray  15  formed on top of the main body  10 . Thus, after the toner images are fixed to a sheet of paper P by heat in the fixing unit  80 , the sheet is conveyed from the fixing unit  80  into the paper-discharge path  91 , and the discharge roller  92  discharges the sheet onto the discharge tray  15 . 
     Next, the structure of the process unit  61  (the toner cartridge  100  and the developing device  200 ) will be described in detail and contrasted with the process units  62  while referring primarily to  FIGS. 5 and 6 .  FIGS. 5 and 6  show a bottom view of the toner cartridge  100  and a top view of the developing device  200 . 
     As shown in  FIGS. 2 and 3 , the toner cartridge  100  of the process unit  61  is detachably mounted on the developing device  200 . When mounted on the developing device  200 , the toner cartridge  100  is positioned above and adjacent to the developing device  200 . 
     As shown in  FIGS. 5 and 6 , the toner cartridge  100  is a substantially cylindrical container with side walls  110  closing both left and right ends thereof. The cylindrically shaped wall of the toner cartridge  100  are formed with a first supply opening  111  for supplying toner from the toner cartridge  100  to the developing device  200 , and first return openings  112  for returning toner from the developing device  200  to the toner cartridge  100  (see  FIG. 7 ). 
     A cylindrical first shutter  120  is provided on the toner cartridge  100  around the cylindrical wall of the toner cartridge  100 . By rotating the first shutter  120  in a circumferential direction relative to the toner cartridge  100 , the shutter  120  can open and close the first supply opening  111  and the first return openings  112 . Specifically, a first shutter supply opening  121  and the first shutter return openings  122  are formed in the first shutter  120  at positions that perfectly overlap the respective first supply opening  111  and the first return openings  112  formed in the toner cartridge  100  when the first shutter  120  is in an open position illustrated in  FIG. 6 . When the first shutter  120  is rotated a prescribed stroke in the circumferential direction relative to the toner cartridge  100  to a closed position illustrated in  FIG. 5 , the first shutter  120  completely blocks the first supply opening  111  and the first return openings  112 . 
     A ridge part  110 P is provided on each of the left and right side walls  110  of the toner cartridge  100 . The ridge parts  110 P extend radially from the center of the side walls  110  to the outer edge thereof and have a rectangular cross section. Protruding parts  120 P having the same cross-sectional shape as the ridge parts  110 P are provided on longitudinal ends of the first shutter  120 . 
     When the first shutter  120  is set in the closed position as shown in FIG.  5 , the protruding parts  120 P are aligned with the outer ends of the corresponding ridge parts  110 P, forming continuous guide rails for guiding the toner cartridge  100  when the toner cartridge  100  is mounted on the developing device  200  described later. When the first shutter  120  is rotated to the open position while the toner cartridge  100  is attached to the developing device  200 , the protruding parts  120 P move circumferentially within second groove parts R 2  (described later in greater detail) formed in side walls of the developing device  200  so that the toner cartridge  100  is engaged (interlocked) with the developing device  200  (see  FIG. 6 ). 
     A handle  120 H is provided on the peripheral surface of the first shutter  120 . The handle  120 H extends horizontally rearward from an upper portion of the first shutter  120  when the toner cartridge  100  is mounted on the developing device  200  (i.e., when the first shutter  120  is in the open position), as shown in  FIG. 1 . When the operator grips the handle  120 H and rotates the handle  120 H from this horizontal position upward relative to the mounted toner cartridge  100 , the first shutter  120  is rotated to the closed position, disengaging (unlocking) the toner cartridge  100  from the developing device  200  so that the toner cartridge  100  can be removed (see  FIG. 2 ). 
     Further, an agitator  140  well known in the art is provided inside the toner cartridge  100  (see  FIG. 1 ). As shown in  FIG. 7 , the agitator  140  is primarily configured of a rotational shaft  141  rotatably supported in the left and right side walls  110 , and a plurality of sheet-like agitating blades  143 . The agitating blades  143  are formed of a flexible material and are fixed to the rotational shaft  141 . The agitating blades  143  are formed such that their dimension along the radial direction away from the rotational shaft  141  varies along the axial direction of the rotational shaft  141 . Specifically, the radial length of the agitating blades  143  is longer toward the center region of the rotational shaft  141  at which the first supply opening  111  is located than toward the ends at which the first return openings  112  are located. However, the agitating blade  143  positioned opposite the first supply opening  111  is formed with a uniform radial length. 
     A motor (not shown) provided in the main body  10  applies a drive force to the rotational shaft  141  for rotating the agitator  140  in the toner cartridge  100 . When the rotational shaft  141  rotates, the distal edges of the agitating blades  143  slanted relative to the rotational shaft  141  scrape against the inner surface of the toner cartridge  100 , agitating toner in the toner cartridge  100  and conveying this toner from the left and right ends at which the first return openings  112  are formed toward the center region at which the first supply opening  111  is formed as indicated by arrows in  FIG. 7 . 
     As shown in  FIG. 7 , the auger  61 F is configured to convey toner supplied through the central first supply opening  111  (and a second supplying opening  211  described later) toward the left and right first return openings  112  (and second return openings  212  described later). The auger  61 F may be configured of a screw-type auger, as in the example shown in  FIG. 7 , which is primarily configured of a rotational shaft rotatably supported in the left and right walls of the developing device  200 , and helical bits wound in a spiral shape around this rotational shaft. As shown in  FIG. 6 , an accommodating recessed part  210 S is formed at a position adjacent to the auger  61 F for accommodating the toner cartridge  100 . 
     As shown in  FIGS. 5 and 6 , the second supplying opening  211  and the second return openings  212  are formed in a curved wall of the developing device  200  forming the arch shape (arc-shaped in a cross section) of the accommodating recessed part  210 S at positions respectively corresponding to the first supply opening  111  and first return openings  112  formed in the toner cartridge  100  (see also  FIG. 7 ). The second supplying opening  211  functions to supply toner from the toner cartridge  100  to the developing device  200 , while the second return openings  212  function to return toner from the developing device  200  to the toner cartridge  100 . 
     Hence, when toner is supplied into the developing device  200  through the first supply opening  111  of the toner cartridge  100  and the second supplying opening  211 , the auger  61 F conveys this toner from the center region of the developing device  200  (conveying start region) toward the left and right longitudinal end regions (conveying end regions), as indicated by arrows in  FIG. 7 . Through this conveying process, residual toner in the developing device  200  that the supply roller  61 D did not supply to the developing roller  61 C is circulated back through the second return openings  212  and the first return openings  112  formed on both ends of the toner cartridge  100  and recovered in the toner cartridge  100 . 
     A second shutter  220  is also provided in the developing device  200  around the arch-shaped wall of the accommodating recessed part  210 S. By rotating in a circumferential direction relative to the accommodating recessed part  210 S, the second shutter  220  can open and close the second supplying opening  211  and second return openings  212  formed in the accommodating recessed part  210 S. More specifically, a second shutter supply opening  221  and second shutter return openings  222  are formed in the second shutter  220  at positions that are perfectly aligned with the second supplying opening  211  and the second return openings  212  formed in the developing device  200  when the second shutter  220  is in an open position (see  FIG. 6 ). By rotating the second shutter  220  a prescribed stroke in the circumferential direction relative to the developing device  200  to a closed position, the second shutter  220  completely blocks the second supplying opening  211  and the second return openings  212  (see  FIG. 5 ). 
     A grooved part  210 R is formed on the inside surface of each of the left and right walls of the accommodating recessed part  210 S. The grooved part  210 R includes a first groove part R 1  extending radially downward from the center of curvature of the accommodating recessed part  210 S, a second groove part R 2  following circumferential directions (both forward and rearward) from the bottom end of the first groove part R 1 , and a funnel-shaped part R 3  formed at the top of the first groove part R 1  in a funnel shape that widens toward the top in order to facilitate insertion of the ridge part  110 P and the protruding part  120 P when mounting the toner cartridge  100  in the accommodating recessed part  210 S. 
     An inner circumferential protruding part  220 P is formed on each of the left and right ends of the second shutter  220  for slidably engaging in the second groove parts R 2 . A notched part  220 Q is formed in the inner circumferential protruding part  220 P in the portion opposing the bottom end of the first groove part R 1  when the second shutter  220  is at the closed position so that the protruding part  120 P can be inserted into the notched part  220 Q when mounting the toner cartridge  100  (see  FIG. 5 ). 
     The process unit  61  in the first embodiment is arranged with the supply roller  61 D forward of the developing roller  61 C and the auger  61 F forward of the supply roller  61 D. Further, in a comparison between the process unit  61  and the process unit  62  as illustrated in  FIG. 8 , an angle β formed by a plane passing through the rotational shaft of the developing roller  61 C and the rotational shaft of the photosensitive drum  61 A and a horizontal plane passing through the rotational shaft of the photosensitive drum  61 A is smaller than a similar angle α formed in the process unit  62  (α&gt;β). Thus, the position of the developing roller  61 C has been shifted farther forward in relation to the photosensitive drum  61 A than the position of the developing roller  62 C in relation to the photosensitive drum  62 A. 
     By arranging the components of the developing device  200  in this way, the toner cartridge  100  mounted above the auger  61 F is farther forward and separated from the position of the photosensitive drum  61 A with respect to the front-to-rear direction. As a result, the toner cartridge  100  can be disposed in a position that in a plan view is not overlapped by the exposure unit  50  used to expose the photosensitive drum  61 A from above (see  FIG. 1 ). 
     Hence, unlike the process units  62  positioned farther back in the retaining case  65 , the process unit  61  positioned nearest forward can be accessed from above without interference from the exposure unit  50 , even when the retaining case  65  is fully accommodated in the main body  10  (i.e., when the retaining case  65  is at the first position), in order to mount or replace the toner cartridge  100 . Further, since the toner cartridge  100  can be accessed by opening the upper cover  12 , the operator can mount or remove the toner cartridge  100  through the second opening  12   a  while appropriately opening the shutters  120  and  220  simply by gripping and operating the handle  120 H, and need not open the front cover  11 . 
     Further, the developing roller  61 C of the process unit  61  is configured of a larger roller than the developing roller  62 C of the process unit  62 . Specifically, the developing roller  61 C has a diameter D 1  that is greater than a diameter D 2  of the developing roller  62 C (D 1 &gt;D 2 ). Hence, the supply roller  61 D and the auger  61 F are shifted farther forward in their layout arrangement, enabling the toner cartridge  100  to be disposed in a position that facilitates mounting and removal operations from above. 
     Generally, the developing roller  61 C is provided with sealing members that is disposed at both width ends surface thereof in order to prevent toner from leaking from the developing roller  61 C. Since the surface of the developing roller  61 C has a smaller curvature due to the larger diameter, it is possible to use a sealing member that has a simple structural design and is suitable for long-term use. 
     Consequently, the developing device  200  of the process unit  61 , which can be mounted and removed separately from the toner cartridge  100 , may be configured to have a longer lifespan than the developing device  62 H of the process unit  62 , which has the developer-accommodating device  62 G integrally provided with the developing device  62 H. Accordingly, the effects of using the toner cartridge  100  in the process unit  61  to reduce running costs can be better exploited. 
     While chemical toner is used for the color toner accommodated in the developer-accommodating devices  62 G of the process units  62  in the first embodiment, pulverized toner is used for the black toner accommodated in the toner cartridge  100  of the process unit  61 . 
     Here, “chemical toner” denotes toner that is manufactured according to chemical processes, in contrast to the traditional toners that are manufactured through a mechanical pulverizing process. Chemical toner can be produced through a variety of methods, including emulsion polymerization and aggregation, suspension polymerization, emulsion aggregation, and dissolution suspension. “Pulverized toner” includes not only traditional toner manufactured according to a mechanical pulverizing process, but also to the same toner that has been chemically treated to produce rounder toner particles. 
     By employing pulverized toner, which has lower fluidity than chemical toner, it is possible to reduce the likelihood of toner leaking from the developing device  200  and to extend the service life of the developing device  200  in terms of the number of printed sheets, since the service life is greatly dependent on the lifespan of the toner leakage preventing seal. 
     Next, operations for replacing the toner cartridge  100  in the process unit  61  having the above construction will be described. 
     When the process unit  61  is positioned as shown in  FIG. 1 , the toner cartridge  100  is engaged with the developing device  200 , and the first shutter  120  and the second shutter  220  are at the open position. In other words, as shown in  FIG. 6 , the protruding part  120 P of the first shutter  120  is at a position offset from the ridge part  110 P and is inset in the second groove part R 2 . Thus, the mounted toner cartridge  100  is firmly and inseparably fixed to the developing device  200 . 
     When the toner cartridge  100  is out of black toner or needs to be replaced for any reason, the operator first opens the upper cover  12  and then rotates the handle  120 H rearward (counterclockwise direction in  FIG. 1 ). When the handle  120 H is rotated in this way, the first and second shutters  120  and  220  on the toner cartridge  100  and developing device  200  are closed and the toner cartridge  100  is disengaged from the developing device  200 . Next, the operator extracts the toner cartridge  100  upward through the second opening  12   a , i.e., in a direction indicated by the arrow in  FIG. 2 . 
     More specifically, the operation to rotate the handle  120 H rearward shifts the first shutter  120  and the second shutter  220  from the position shown in  FIG. 6  to the position shown in  FIG. 5 , causing the first shutter  120  and the second shutter  220  to shift to the closed position and the protruding parts  120 P of the first shutter  120  to arrive at a position aligned with the ridge parts  110 P. Consequently, the protruding parts  120 P can pass through the respective first groove parts R 1  which are the portion of the grooved parts  210 R that extend radially, thereby enabling the operator to pull the toner cartridge  100  upward, as illustrated in  FIG. 2 . 
     When mounting a new toner cartridge  100  in the process unit  61 , the operator opens the upper cover  12  to expose the second opening  12   a , as shown in  FIG. 3 . Next, the operator inserts the toner cartridge  100  through the second opening  12   a , in the direction indicated by an arrow in  FIG. 3 , and sets the toner cartridge  100  in the process unit  61 . 
     During this operation, the operator aligns the ridge parts  110 P and the protruding parts  120 P on left and right sides of the toner cartridge  100  in the state shown in  FIG. 5  with the grooved parts  210 R on the left and right sides of the developing device  200  and inserts the ridge parts  110 P and the protruding parts  120 P in the corresponding grooved parts  210 R until the entire toner cartridge  100  is seated in the accommodating recessed part  210 S of the developing device  200 . Subsequently, the operator rotates the handle  120 H forward (clockwise direction in  FIG. 3 ), moving the first shutter  120  and the second shutter  220  to their open positions shown in  FIG. 6 . 
     Through this operation, the protruding parts  120 P of the first shutter  120  enter the respective second groove parts R 2  of the grooved parts  210 R and move to a position offset from the respective ridge parts  110 P. Accordingly, the mounted toner cartridge  100  is firmly fixed to and inseparable from the developing device  200 . 
     Since the second shutter  220  of the developing device  200  opens and closes the second supplying opening  211  and the second return openings  212  in association with the handle  120 H opening and closing the first shutter  120 , both the first shutter  120  and the second shutter  220  are easily opened and closed through a single operation. Further, the toner cartridge  100  is disengaged from the developing device  200  in association with the operation of the handle  120 H to switch these shutters  120  and  220  to their closed positions and is engaged with the developing device  200  in association with the operation of the handle  120 H to switch the shutters  120  and  220  to their open positions, thereby achieving both safety and simplicity of operations. 
     When one of the developer-accommodating devices  62 G of the process units  62  must be replaced together with the developing device  62 H (i.e., the developing roller  62 C, the supply roller  62 D, and the thickness-regulating blade  62 E) because the developer-accommodating device  62 G has run out of cyan, magenta, or yellow toner, for example, the operator opens the front cover  11 , grips the handle  65 H, and pulls the retaining case  65  forward to move the second position and replace the relevant components, as illustrated in  FIG. 4 . Here, the retaining case  65  may be completely separately removed from the main body  10  before replacing the components of the process units  62 . 
     As shown in  FIG. 4 , guide grooves  65 G are formed in the inner surfaces of both side walls constituting the retaining case  65 . The guide grooves  65 G function to guide the vertical sliding movement of the developer-accommodating devices  62 G and the developing devices  62 H when they are mounted in the retaining case  65  and to maintain the mounted developing devices  62 H (particularly the developing rollers  62 C) at a fixed position in the bottom ends of the guide grooves  65 G. This construction for mounting and removing the developer-accommodating devices  62 G and the developing device  62 H facilitates the smooth replacement of components in the process units  62 . 
     The color multifunction device  1  according to the first embodiment having the construction described above primarily produces the following advantages and effects. 
     In the color multifunction device  1  of the first embodiment, the process unit  61  is mounted in the retaining case  65  at a position closest to the near side relative to the pull-out direction of the retaining case  65 . Further, the toner cartridge  100  accommodating black toner is detachably provided in the process unit  61 . Accordingly, the toner cartridge  100  accommodating black toner can be replaced easily and safely without pulling the retaining case  65  outward while reducing running costs for the color multifunction device  1 , thereby eliminating the risk of damaging the retaining case  65  and overrunning the main body  10  due to forces applied to the retaining case  65  when the retaining case  65  is partially pulled out from the main body  10 . Further, the process units  62  whose developing devices  62 H and corresponding developer-accommodating devices  62 G accommodating color toners can be integrally separated from the retaining case  65  as a unit are arranged toward the far side of the retaining case  65  relative to the pull-out direction. This structure of the process units  62  eliminates the opening and closing of shutters in the developer-accommodating devices  62 G, thereby making replacement of the process units  62  easy and safe. 
     Among the developer accommodating devices  62 G and the toner cartridge  100 , the toner cartridge  100  can be replaced separately from the process unit  61 . Since the toner cartridge  100  accommodates black toner, which is generally consumed faster than the color toners, this configuration can greatly reduce running costs. 
     In the process unit  61  provided with the separable toner cartridge  100 , the auger  61 F is provided in the developing device  200 . Accordingly, the openings formed in the toner cartridge  100  and the developing device  200  (the openings  111 ,  112 ,  211 , and  212  in the first embodiment) that is opened and closed by the shutters  120  and  220  in order to supply toner from the toner cartridge  100  to the supply roller  61 D need not be provided across the entire longitudinal surface of the toner cartridge  100  and the developing device  200 , thereby reducing the size of the openings. 
     Sponge-like seals for preventing toner leakage are generally provided around the edges of the openings formed in the toner cartridge  100  and the developing device  200 , which openings are opened and closed by the shutters  120  and  220 . The risk of toner leakage increases as the size of these openings increases. Further, increasing the region of the seals that is slidingly contacted by the shutters  120  and  220  makes the shutter operations heavier and more cumbersome. Hence, in order to improve operations of the shutters  120  and  220  and the performance of the seals, it is desirable to reduce the size of the openings formed in the toner cartridge  100  and the developing device  200  and to reduce the size of the seals required around the periphery of the openings. 
     Since the configuration of the first embodiment reduces the size of the openings  111 ,  112 ,  211 , and  212  and the size of the seals provided around the edges of these openings, the seals can be expected to prevent toner leakage reliably over a long lifespan, and operations of the shutter  120  are accomplished easily and smoothly. Further, by reducing the size of the openings, the stiffness of the toner cartridge  100  and the developing device  200  is increased. 
     In the first embodiment, in addition to the supply openings  111  and  211  for receiving toner supplied from the toner cartridge  100  into the developing device  200 , the return openings  112  and  212  are provided as exits for toner returning from the developing device  200  to the toner cartridge  100 . Since toner is circulated between the toner cartridge  100  and the developing device  200  via these openings, the toner can be uniformly agitated and conveyed, thereby improving image quality. 
     The supply roller  61 D is positioned closer to the near side with respect to the pull-out direction than the developing roller  61 C, and the auger  61 F is positioned closer to the near side with respect to the pull-out direction than the supply roller  61 D. Accordingly, the toner cartridge  100  positioned above the auger  61 F is also on the near side while the retaining case  65  is accommodated in the main body  10  (at the first position), whereby the toner cartridge  100  can easily be mounted, removed, or replaced. 
     The angle β formed by a plane passing through the rotational shaft of the developing roller  61 C and the rotational shaft of the corresponding photosensitive drum  61 A and a plane along the pull-out direction is smaller than the angle α formed by a plane passing through the rotational shaft of the developing roller  62 C and the rotational shaft of the corresponding photosensitive drum  62 A and a plane along the pull-out direction. Accordingly, the toner cartridge  100  positioned above the auger  61 F is also on the near side while the retaining case  65  is accommodated in the main body  10  (at the first position), whereby the toner cartridge  100  can easily be mounted, removed, or replaced. 
     Since the toner cartridge  100  can be accessed from above and replaced while the retaining case  65  is accommodated in the main body  10  (first position) with this construction, the toner cartridge  100  can easily be replaced without opening the front cover  11  and removing the retaining case  65 . 
     More specifically, the toner cartridge  100  is disposed in a position that is not overlapped vertically by the exposure unit  50 , which exposes the photosensitive drums  61 A and  62 A from above, while the retaining case  65  is accommodated in the main body  10  (at the first position). Hence, the exposure unit  50  does not interfere with operations to access the toner cartridge  100  from above. Therefore, the toner cartridge  100  can easily be replaced, without opening the front cover  11  and pulling out the retaining case  65 . 
     The main body  10  has the upper cover  12  positioned above the front cover  11  that can be opened and closed independently of the front cover  11 . Accordingly, the toner cartridge  100  can be mounted, removed, and replaced simply by opening the upper cover  12  and without opening the front cover  11 , which operation requires that sufficient space is allocated in front of the main body  10 . 
     Next, a color multifunction device  1 ′ serving as an image-forming device according to a second embodiment of the present invention will be described with reference to  FIG. 9 . In the color multifunction device  1 ′ according to the second embodiment, the components of a process unit  61 ′ are arranged differently from the process unit  61  described in the first embodiment, and these differing arrangements will be contrasted in the following description, where like parts and components are designated with the same reference numerals to avoid duplicating description. 
     The features of the second embodiment that differ from those in the first embodiment are found in the arrangement of the process unit  61 ′ provided with a toner cartridge  100 ′ accommodating black toner, and a developing device  200 ′. In the second embodiment, a photosensitive drum  61 A′, a developing roller  61 C′, and a supply roller  61 D′ have substantially the same arrangement as the photosensitive drum  62 A, the developing roller  62 C, and the supply roller  62 D in the process units  62 . Further, the supply roller  61 D′ is positioned forward of the developing roller  61 C′, as described in the first embodiment. 
     The size and positioning of the developing roller  61 C shown in  FIG. 8  are not applied to the developing roller  61 C′ in the second embodiment. Further, the auger  61 F is disposed forward of the supply roller  61 D in the first embodiment, whereas an auger  61 F′ is disposed above the developing roller  61 C′ and the supply roller  61 D′ in the second embodiment. 
     In the second embodiment, the toner cartridge  100 ′ is positioned closer to the near side in the pull-out direction than the auger  61 F′ (diagonally above the auger  61 F′). Accordingly, the toner cartridge  100 ′ is disposed in substantially the same position in the main body  10  as the toner cartridge  100  of the first embodiment when the toner cartridge  100 ′ is mounted in the accommodating recessed part  210 S of the developing device  200 ′ and the retaining case  65  is accommodated in the main body  10  (first position). Therefore, the toner cartridge  100  can easily be mounted, removed, and replaced simply by opening the upper cover  12  while the retaining case  65  remains in the first position. 
     When the retaining case  65  is accommodated in the main body  10 , the toner cartridge  100 ′ is disposed at a position that is not overlapped by the exposure unit  50  that exposes the photosensitive drum  61 A′ and the photosensitive drums  62 A from above. Therefore, the exposure unit  50  does not interfere with operations to access the toner cartridge  100 ′ from above. Thus, the toner cartridge  100 ′ can easily be replaced without having to open the front cover  11  and pull out the retaining case  65 . 
     While the invention has been described in detail with reference to the first and second embodiments thereof, it would be apparent to those skilled in the art that many modifications and variations may be made therein without departing from the spirit of the invention, the scope of which is defined by the attached claims. 
     In the first and second embodiments described above, a conveying member for conveying toner along the axial direction of the supply roller is a screw-type auger  61 F ( 61 F′) having helical bits, but the present invention is not limited to this type of conveying member. Any conventional conveying means (such as means that conveys with blades) may be employed as the conveying member, provided that the member can convey toner supplied from the developer-accommodating device (toner cartridge) from the conveying start position to the conveying end position along the axis of the supply roller. 
     Further, the process unit  61  in the first and second embodiments has return openings  112  and  212  for recovering toner from the developing device  200  back into the toner cartridge  100  ( 100 ′) and includes a mechanism for circulating this toner, but the present invention is not limited to this configuration. In a developing device having a separable toner cartridge that does not circulate toner, the size of the supply openings for supplying toner from the toner cartridge  100  into the developing device  200  can still be decreased by providing a conveying member in the developing device for conveying toner along the axis of the supply roller, thereby achieving the advantages of the present invention described above. 
     While the recording sheets described in the first and second embodiments are paper P, such as normal paper or postcards, the recording sheets may also be transparencies or the like. 
     The specific structure and arrangement of other components constituting the image-forming device, such as the exposure device, retaining member, photosensitive drums, developer-accommodating devices, and operating member (handle), may be modified as desired and are not limited to the description in the above-mentioned embodiments. 
     Further, while the image-forming device with process units according to the present invention is a color multifunction device  1  and  1 ′ in the first and second embodiments, the image-forming device may also be a photocopier, printer, or the like. Also, the image-forming device of the first and second embodiments includes four process units  61  and  62 , but the present invention may be applied to any image-forming device having a plurality of developer-accommodating devices, including one that accommodates black developer.