Developer-accommodating vessel and developing device

0001The present invention relates to a developer-accommodating vessel and a developing device provided in a laser printer or other image-forming device.

0002A toner box, such as that disclosed in Japanese Patent-Application Publication No.<patcit id="pcit0001" dnum="JP2008176215A"><text>2008-176215</text></patcit> and <patcit id="pcit0002" dnum="JP2007086324A"><text>2007-86324</text></patcit>, is a conventional example of a developer-accommodating vessel provided in an image-forming device for accommodating developer used in image formation. The toner boxes disclosed in above-mentioned Patent applications are detachably mounted in a process unit functioning as the developing device of a laser printer.

0003The developer-accommodating vessel includes an exterior casing having a first toner outlet formed therein, and an interior casing having a second toner outlet formed therein. The interior casing accommodates toner. An agitator is also provided in the interior casing for agitating the toner. The agitator rotates about a rotational shaft passing through the center of the circular interior casing. When the agitator is driven to rotate as the first toner outlet formed in the exterior casing is aligned with the second toner outlet formed in the interior casing, the toner agitated by the agitator in the interior casing is discharged sequentially through the second toner outlet and first toner outlet and is supplied to the process unit side.

0004A tandem type color printer, such as that disclosed in Japanese Patent-Application Publication No.<patcit id="pcit0003" dnum="JP2006184552A"><text>2006-184552</text></patcit>, is a type of image-forming device well known in the art having a plurality of photosensitive drums arranged in parallel and juxtaposed horizontally. This color printer includes a photosensitive drum unit comprising the plurality of photosensitive drums in one cohesive unit, a developing unit disposed below the photosensitive drum unit and functioning to form toner images on the photosensitive drums, and an intermediate transfer belt unit disposed above the photosensitive drum unit for receiving toner images transferred from the photosensitive drums.

0005The developing unit is provided with a number of developing devices equivalent to the number of photosensitive drums, which developing devices are arranged parallel to each other and juxtaposed horizontally. Each developing device includes a developer case for accommodating toner, and a developing roller disposed at the top of the developer case.

0006In order to perform maintenance on the photosensitive drum unit and developing unit with the printer, these units can be pulled out from the body of the printer in a horizontal direction following the juxtaposed direction of the photosensitive drums. Once the developing unit has been pulled out of the printer, the individual developing devices can be upwardly extracted from the developing unit.

0007In the toner boxes, toner that is supplied from the interior casing of the toner box to the process unit side initially passes through the second toner outlet. However, the second toner outlet is formed in a circumferential surface of the interior casing and does not lie in the rotating path of the agitator. The rotating agitator conveys toner in the interior casing primarily in a direction along the path of the agitator, i.e., the rotating direction of the agitator.

0008In other words, since the second toner outlet is not provided in the rotating path of the agitator, the agitator cannot efficiently supply toner from the interior casing to the process unit through the second toner outlet.

0009Further, replacing the developer case is a maintenance activity that is frequently performed in the printer. However, since the developer case, which must be accessed most frequently, is disposed in the bottom of each developing device, it is necessary to remove the developing roller and the like disposed in the top of the developing unit before refilling the developer case with toner or replacing the developer case. Thus, maintenance of the developer case is troublesome.

0010Further, when the photosensitive drum unit and developer unit are pulled out of the printer together, the photosensitive drum unit disposed on top of the developing unit must be removed in order to remove the developing roller and the like, as described above, making maintenance of the developer case even more troublesome.

0011Therefore, it is an object of the present invention to provide a developer-accommodating vessel capable of efficiently supplying developer externally, and an image-forming device having a structure in which a plurality of developing units are disposed below a plurality of photosensitive drums juxtaposed in parallel and that is capable of facilitating maintenance of the developer-accommodating vessels disposed in the developing unit for accommodating developer.

0012In order to attain the above and other objects, the invention provides a toner cartridge. The toner cartridge includes a first toner accommodating unit and an agitating member. The first toner accommodating unit has a peripheral surface in which an inner hollow space for accommodating a toner is formed. The agitating member is disposed in the first toner accommodating unit and rotates in a rotating direction to agitate the toner. The peripheral surface has a wall portion formed with a first supply-hole at an upstream side in the rotating direction. The wall portion is curved about a reference line as a center of curvature and depressed inward the first toner accommodating unit. The reference line is outside of the first toner accommodating unit in a radial direction of the agitating member and extending in a prescribed direction.

0013It is preferable that the toner cartridge further includes a toner shutter for opening and closing the first supply hole by moving along the wall portion

0014It is preferable that the toner shutter is supported by the first toner accommodating unit at multiple points along the prescribed direction.

0015According to another aspect of the present invention, the present invention provides a developing device. The developing device includes a casing, a supply roller, and the toner cartridge. The supply roller is mounted on the casing. The wall portion has an arc-shape conforming with a circumferential surface of the supply roller. The casing has an arc wall opposed to the wall portion and conforming with the arc-shape of the wall portion.

0016It is preferable that the process shutter is supported by the casing at multiple points along the prescribed direction.

0017It is preferable that wherein the toner cartridge further comprises a toner shutter for opening and closing the first supply-hole by moving along the peripheral surface and an operation part that engages with the toner shutter. The movement of the operation part is interlocked with the movement of the process shutter.

0018It is preferable that when the toner cartridge is mounted in the developing device, the toner cartridge is adjacent to the developing device in a horizontal direction. The wall portion is formed with a second supply hole at a position downstream side of the first supply hole in the rotating direction.

0019According to still another aspect of the present invention, the present invention provides an image forming device. The image forming device includes a casing, a photosensitive drum, a developing device, a toner cartridge, and a support frame. The photosensitive drum rotates about a rotational axis. The developing device is disposed beneath the photosensitive drum. The toner cartridge accommodates the toner and is detachably mounted on the developing device to supply the toner. The support frame is drawable from the casing while integrally supporting the developing device and the toner cartridge. The support frame has an allowing unit that allows the toner cartridge to be detached from the developing device while maintaining the developing device to be supported, when the support frame is drawn from the casing.

0020The 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: <ul id="ul0001" list-style="none" compact="compact"><li><figref idref="f0001">Fig. 1</figref> is a right side cross-sectional view of a color printer 1 according to a first embodiment of the present invention;</li><li><figref idref="f0002">Fig. 2</figref> is a schematic cross-sectional view of the color printer when a first front cover moves upward and a second front cover is open;</li><li><figref idref="f0003">Fig. 3</figref> is a right side cross-sectional view of the color printer in a state that a drawer unit is extracted;</li><li><figref idref="f0004">Fig. 4</figref> is an enlarged right side cross-sectional view of the color printer;</li><li><figref idref="f0005">Fig. 5A</figref> is a right-side cross-sectional view of a process cartridge with a toner shutter and a process shutter open;</li><li><figref idref="f0005">Fig. 5B</figref> is a right-side view of the process cartridge with the toner shutter and the process shutter open;</li><li><figref idref="f0005">Fig. 5C</figref> is a right-side view of the process cartridge in which a toner box is dismounted therefrom with the toner shutter and the process shutter open;</li><li><figref idref="f0006">Fig. 6A</figref> is a right side cross-sectional view of a process cartridge with the toner shutter and the process shutter close;</li><li><figref idref="f0006">Fig. 6B</figref> is a right-side view of the process cartridge with the toner shutter and the process shutter close;</li><li><figref idref="f0006">Fig. 6C</figref> is a right-side view of the process cartridge in which the toner box is dismounted therefrom with the toner shutter and the process shutter close;</li><li><figref idref="f0007">Fig. 7</figref> is a perspective view of a shutter unit as viewed from a right-front side;</li><li><figref idref="f0008">Fig. 8A</figref> is a perspective view of the toner box with the toner shutter close as viewed from the left-front side;</li><li><figref idref="f0008">Fig. 8B</figref> is a perspective view of the toner box with the toner shutter open as viewed from the left-front side;</li><li><figref idref="f0008">Fig. 8C</figref> is a perspective view of the toner box with the toner shutter close as viewed from the right-front side;</li><li><figref idref="f0008">Fig. 8D</figref> is a perspective view of the toner box with the toner shutter open as viewed from the right-front side;</li><li><figref idref="f0008">Fig. 8E</figref> is a partial cross-sectional view around a pawl of the toner box;</li><li><figref idref="f0009">Fig. 9A</figref> is a right side cross-sectional view of the process cartridge while rotating an agitator with the toner shutter and the process shutter open;</li><li><figref idref="f0009">Fig. 9B</figref> is a right side cross-sectional view of the process cartridge after passing a prescribed time from <figref idref="f0009">Fig. 9A</figref>;</li><li><figref idref="f0009">Fig. 9C</figref> is a right side cross-sectional view of the process cartridge after passing a prescribed time from <figref idref="f0009">Fig. 9B</figref>;</li><li><figref idref="f0009">Fig. 9D</figref> is a right side cross-sectional view of the process cartridge after passing a prescribed time from <figref idref="f0009">Fig. 9C</figref>;</li><li><figref idref="f0010">Fig. 10</figref> is a perspective view of a toner box as viewed from right-front side according to a modification of the first embodiment;</li><li><figref idref="f0011">Fig. 11</figref> is a schematic cross-sectional view of a laser printer provided with a developing unit according to a second embodiment of the present invention;</li><li><figref idref="f0012">Fig. 12</figref> is a schematic cross-sectional view of the developing unit;</li><li><figref idref="f0013">Fig. 13</figref> is an exploded perspective view of a toner cartridge as viewed from right-front side;</li><li><figref idref="f0014">Fig. 14A</figref> is a schematic illustration of a relationship among a toner shutter, a first supply hole, and a second supply hole in a state in which the toner shutter is close;</li><li><figref idref="f0014">Fig. 14B</figref> is a schematic illustration of a relationship among the toner shutter, the first supply hole, and the second supply hole in a state in which the toner shutter is open;</li><li><figref idref="f0015">Fig. 15</figref> is a schematic cross-sectional view of the developing unit showing an each room formed therein as viewed from top;</li><li><figref idref="f0016">Fig. 16</figref> is a schematic cross-sectional view of the toner cartridge taken along a line in which the second supply hole is formed as viewed from left side;</li><li><figref idref="f0017">Fig. 17</figref> is an exploded perspective view of the toner cartridge as viewed from left-front side;</li><li><figref idref="f0018">Fig. 18</figref> is an exploded perspective view of a developing device and a process cartridge;</li><li><figref idref="f0019">Fig. 19A</figref> is a schematic illustration of the developing unit when the toner shutter and a process shutter are close; and</li><li><figref idref="f0019">Fig. 19B</figref> is a schematic illustration of the developing unit when the toner shutter and a process shutter are open.</li></ul>

1. General structure of a color printer

0021<figref idref="f0001">Fig. 1</figref> is a right side cross-sectional view of a color printer 1 serving as the image-forming device according to a first embodiment of the present invention. <figref idref="f0002">Fig. 2</figref> shows the same view of the color printer 1 in <figref idref="f0001">Fig. 1</figref> when a unit-mounting opening 49 is open. <figref idref="f0003">Fig. 3</figref> shows the color printer 1 in <figref idref="f0001">Fig. 1</figref> when a drawer unit 14 has been pulled out from a main casing 2. <figref idref="f0004">Fig. 4</figref> is a right side view of the color printer 1 in the state shown in <figref idref="f0003">Fig. 3</figref>. For the sake of description, one process cartridge 16 is shown in <figref idref="f0004">Fig. 4</figref> after being extracted upward from the drawer unit 14.

0022As shown in <figref idref="f0001">Fig. 1</figref>, the color printer 1 includes a main casing 2 forming the body of the color printer 1. The main casing 2 is box-shaped and slightly elongated vertically. Within the main casing 2, the color printer 1 also includes a feeding unit 3 for supplying sheets of a paper P to be printed, an image-forming unit 4 for forming images on the paper P supplied from the feeding unit 3, and a discharge unit 5 for discharging the paper P from the main casing 2 after an image has been formed thereon. The main casing 2 is provided with a first front cover 31 and a second front cover 50 on a front wall thereof.

0023Unless otherwise specified, the orientation of the color printer 1 and the orientation of the individual components in the color printer 1 will be described in accordance with the directional arrows shown in the drawing. This holds true for <figref idref="f0001">Fig. 1</figref> as well as subsequent drawings. The directions specified herein are defined based on the perspective of a user standing in front of the color printer 1 while facing the color printer 1. Thus, the left side of the color printer 1 is the far side of the drawing in <figref idref="f0001">Fig. 1</figref>, while the right side is the near side. The left-to-right direction will also be referred to as the width direction, and both the left-to-right (width) direction and the front-to-rear direction are considered horizontal directions.

(1) Feeding unit

0024The feeding unit 3 includes a paper tray 6, a feeding mechanism 7, and a pair of registration rollers 8.

0025The paper tray 6 is disposed in the bottom section of the main casing 2 and extends in a horizontal direction. The paper tray 6 may be removed from the main casing 2 on the front side thereof. The paper tray 6 holds sheets of paper P in a stacked state. The feeding mechanism 7 is disposed at the rear end of the paper tray 6 and functions to feed sheets of paper P from the paper tray 6 toward the image-forming unit 4. The feeding mechanism 7 includes components well known in the art for which reference numerals have not been assigned in <figref idref="f0001">Fig. 1</figref>, including a feeding roller, a separating roller, a separating pad, a paper dust roller, and a paper-conveying path. With this configuration, the feeding mechanism 7 functions to separate and feed sheets of paper P accommodated in the paper tray 6 upward to the registration rollers 8 one sheet at a time.

0026When the leading edge of the sheet of paper P reaches the registration rollers 8, the registration rollers 8 adjust the registration of the sheet and subsequently convey the sheet of paper P to the image-forming unit 4 at a prescribed timing.

(2) Image-forming unit

0027The image-forming unit 4 includes a scanning unit 10, a process unit 11, a transfer unit 12, and a fixing unit 13.

(2-1) Scanning unit

0028The scanning unit 10 is disposed in the bottom section of the main casing 2 above the paper tray 6. The scanning unit 10 includes various components well known in the art for which reference numerals have not been assigned in <figref idref="f0001">Fig. 1</figref>, including a laser light-emitting unit, a polygon mirror, and a plurality of lenses and reflecting mirrors. The laser light-emitting unit of the scanning unit 10 emits laser beams based on image data inputted from a device external to the color printer 1 or from an image-reading unit 35 described later. The laser beams are guided along paths indicated by dotted lines in <figref idref="f0001">Fig. 1</figref> and are ultimately irradiated onto photosensitive drums 19 described later that are provided in the process unit 11.

(2-2) Process unit

0029The process unit 11 is disposed above the scanning unit 10 and includes a drawer unit 14.

0030The drawer unit 14 is detachably mounted in the main casing 2. As will be described later, the drawer unit 14 is mounted in and removed from the main casing 2 along the front-to-rear direction. The drawer unit 14 includes a hollow, box-shaped drawer frame 15 that functions as a support frame, and four process cartridges 16 disposed inside the drawer frame 15.

0031An opening 15A is formed in nearly the entire top surface of the drawer frame 15. The opening 15A provides communication between the interior of the drawer frame 15 and the region above the drawer frame 15. A plurality of through-holes 15B is formed in the bottom wall of the drawer frame 15. The laser beams irradiated by the laser light-emitting units in the scanning unit 10 pass through corresponding through-holes 15B before being irradiated on the photosensitive drums 19. Four circular exposure holes 15C (see <figref idref="f0004">Fig. 4</figref>) are formed in the right wall of the drawer frame 15 at positions aligned in the front-to-rear direction. The circular exposure holes 15C penetrate the right wall of the drawer frame 15 in the width direction so as to provide communication with the interior of the drawer frame 15. The circular exposure holes 15C function as an allowing unit.

0032The process cartridges 16 are detachably mounted in the drawer frame 15 via the opening 15A. When viewed along the width direction, the four process cartridges 16 mounted in the drawer frame 15 are arranged parallel to each other and juxtaposed at substantially equal intervals in the front-to-rear direction (almost horizontally). Each of the process cartridges 16 is disposed at a slight incline to the vertical, with the top positioned farther rearward than the bottom.

0033The following description of the process cartridges 16 will be based on the state of the process cartridges 16 when they are mounted in the drawer frame 15 and oriented at a slight incline to the vertical, with the top farther rearward from the bottom. Since the structure of the four process cartridges 16 is identical, the following description will focus on the forwardmost process cartridge 16 in <figref idref="f0001">Fig. 1</figref>.

0034Each process cartridge 16 is provided with an upper case 17 on the top side, and a lower case 18 on the bottom. Together, the upper case 17 and lower case 18 form a hollow box shape elongated in the width direction. The upper case 17 primarily accommodates a photosensitive drum 19 and a charger 20.

0035The photosensitive drum 19 has a central shaft 19A extending in the width direction. Hence, the axial direction of the photosensitive drum 19 corresponds to this width direction, and the photosensitive drum 19 is elongated in the width direction. The widthwise ends of the photosensitive drum 19 are rotatably supported in corresponding side walls constituting the widthwise side walls of the upper case 17. The top of the upper case 17 is open so that the upper peripheral surface of the photosensitive drum 19 is exposed in the top surface of the upper case 17 from a perspective above the upper case 17 (process cartridge 16). The upper peripheral surface of the photosensitive drum 19 is also exposed through the opening 15A of the drawer frame 15 from a perspective above the drawer frame 15 (drawer unit 14). When viewed from the top, the four photosensitive drums 19 are arranged parallel to each other and juxtaposed at substantially equivalent intervals in the front-to-rear direction (nearly horizontal).

0036The charger 20 is held between both widthwise side walls of the upper case 17 and is positioned to oppose the lower rear surface of the corresponding photosensitive drum 19 from a distance. The lower case 18 is coupled to the upper case 17 by means of a coupling shaft 21 inserted through the upper rear corners of the lower case 18 in the width direction as shown in <figref idref="f0004">Fig. 4</figref>. With the coupling shaft 21, the lower case 18 can move relative to the upper case 17, and more specifically, can pivot relative to the upper case 17 about the coupling shaft 21.

0037The lower case 18 primarily accommodates a developing roller 22, a supply roller 23, and a toner box 24. Central shafts for each of the developing roller 22 and supply roller 23 extend in the width direction. The lower case 18 has widthwise side walls in which both widthwise ends of the developing roller 22 and supply roller 23 are rotatably supported.

0038The developing roller 22 is disposed in the upper end of the lower case 18. The top of the lower case 18 is open so that the upper peripheral surface of the developing roller 22 is exposed in the top surface of the lower case 18 from a perspective above the lower case 18. The upper case 17 is also open on the bottom so that the upper peripheral surface of the developing roller 22 exposed in the top opening of the lower case 18 opposes and contacts the lower front peripheral surface of the photosensitive drum 19 through the bottom opening in the upper case 17. More specifically, urging members (not shown) are provided for urging the entire lower case 18 supporting the developing roller 22 upward toward the upper case 17 supporting the photosensitive drum 19 so that the developing roller 22 contacts the photosensitive drum 19.

0039The supply roller 23 is disposed in contact with the developing roller 22 on the lower front side thereof. The toner box 24 is disposed in an area of the lower case 18 below the supply roller 23 (a box-accommodating chamber 73 described later; see <figref idref="f0005">Fig. 5C</figref>). As will be described later, the toner box 24 is detachably mounted in the lower case 18. The toner box 24 is formed with an inner hollow space and has a substantially cylindrical shape that is elongated in the width direction. The toner box 24 accommodates toner in the inner hollow space in one of the corresponding colors cyan, magenta, yellow, or black.

0040The lower case 18 and the group of members accommodated in the lower case 18 (the developing roller 22, supply roller 23, toner box 24, and the like) are referred to as a developing unit 37. The number of developing units 37 is equivalent to the number of process cartridges 16 (four in the preferred embodiment), and each developing unit 37 is disposed below a corresponding upper case 17 (i.e., below the photosensitive drum 19 provided in the upper case 17). The drawer unit 14 including the process cartridges 16 and toner boxes 24 is described below in greater detail.

0041When forming images with this process unit 11, the charger 20 in each process cartridge 16 applies a uniform electrical charge to the peripheral surface of the corresponding photosensitive drum 19. Subsequently, the scanning unit 10 irradiates a laser beam (indicated by a dotted line in <figref idref="f0001">Fig. 1</figref>) onto the peripheral surface of the charged photosensitive drum 19 via the corresponding through-hole 15B formed in the bottom surface of the drawer frame 15, forming an electrostatic latent image on the peripheral surface of the photosensitive drum 19 that corresponds to an image to be formed on paper P.

0042In the meantime, components in the developing unit 37 of each process cartridge 16 supply toner from the toner box 24 downward to the supply roller 23 (this will be described later in greater detail). The supply roller 23 supplies the toner received from the toner box 24 to the developing roller 22. The developing roller 22 carries on its peripheral surface a thin layer of toner that has been regulated to a prescribed thickness. As the photosensitive drum 19 rotates, the electrostatic latent image formed on the peripheral surface of the photosensitive drum 19 rotates into a position opposite the developing roller 22, at which time the toner carried on the surface of the developing roller 22 is supplied to the electrostatic latent image, developing the latent image into a visible toner image of the prescribed color.

0043Thus, each developing unit 37 functions to develop an electrostatic latent image formed on the corresponding photosensitive drum 19. Further, the toner box 24 in each developing unit 37 accommodates toner used to develop the latent image on the corresponding photosensitive drum 19.

(2-3) Transfer unit

0044The transfer unit 12 includes a follow roller 25, a drive roller 26, an intermediate transfer belt 27, primary transfer rollers 28, a secondary transfer roller 29, and a cleaning unit 30.

0045The follow roller 25 and drive roller 26 are disposed parallel to each other and separated in the front-to-rear direction. The endless intermediate transfer belt 27 is looped over and pulled taut between the follow roller 25 and drive roller 26. In this state, the intermediate transfer belt 27 is adjacent to the top side of the drawer unit 14. When the drive roller 26 is driven to rotate, the intermediate transfer belt 27 moves circularly about the follow roller 25 and drive roller 26, while the follow roller 25 follows the rotation of the drive roller 26.

0046Four primary transfer rollers 28 are arranged inside the intermediate transfer belt 27 at intervals in the front-to-rear direction. Each primary transfer rollers 28 is positioned opposite a corresponding photosensitive drum 19 so as to pinch the lower portion of the intermediate transfer belt 27 against the photosensitive drum 19. The position at which the photosensitive drum 19 contacts the intermediate transfer belt 27 is referred to as a primary transfer position. A high voltage circuit board (not shown) applies a first transfer bias to the primary transfer rollers 28, causing the toner image on each photosensitive drum 19 to be transferred onto the intermediate transfer belt 27 at the corresponding primary transfer position. Toner images in four colors transferred from the four photosensitive drums 19 become superimposed on the intermediate transfer belt 27 to form a color toner image.

0047The secondary transfer roller 29 is disposed on the rear side of the drive roller 26 and applies pressure to the drive roller 26 via the intermediate transfer belt 27. The position at which the secondary transfer roller 29 contacts the drive roller 26 (intermediate transfer belt 27) is referred to as a secondary transfer position. A high voltage circuit board (not shown) applies a second transfer bias to the secondary transfer roller 29, causing the color toner image formed on the intermediate transfer belt 27 to be transferred onto a sheet of paper P at the secondary transfer position as the registration rollers 8 convey the sheet upward.

0048The cleaning unit 30 is disposed above the intermediate transfer belt 27. The cleaning unit 30 functions to recover toner remaining on the intermediate transfer belt 27 after the toner image has been transferred to the paper P and to retain the toner within. The cleaning unit 30 may be replaced by opening the first front cover 31 rotatably attached to the front wall of the main casing 2.

(2-4) Fixing unit

0049The fixing unit 13 is disposed on the downstream side of the transfer unit 12 with respect to the conveying direction of the paper P, and more specifically above the contact position between the drive roller 26 and secondary transfer roller 29 (second transfer position). The fixing unit 13 includes a heating roller 32 and a pressure roller 33 well known in the art. The pressure roller 33 contacts and applies pressure to the heating roller 32. As a sheet of paper P passes between the heating roller 32 and pressure roller 33, the toner image transferred onto the sheet is fixed to the sheet by heat and pressure.

(3) Discharge unit

0050The discharge unit 5 has a plurality of conveying rollers (not indicated with reference numerals in <figref idref="f0001">Fig. 1</figref>) for conveying a sheet of paper P discharged from the fixing unit 13 onto a discharge tray 34 formed on top of the main casing 2.

(4) Other components

0051An image-reading unit 35 is provided in the main casing 2 at a position covering the top of the discharge tray 34. The image-reading unit 35 takes in an original document and scans image data from the document. The color printer 1 can form images based on the image data scanned by the image-reading unit 35.

0052Thus, the color printer 1 can both read and form images and is therefore referred to as a multifunction peripheral. The color printer 1 is also referred to as an in-body paper discharge type device, since the sheets of paper P are discharged onto the discharge tray 34, which is located vertically midway in the main casing 2 (below the image-reading unit 35).

0053Next, the components of the color printer 1 will be described in greater detail.

2. Main casing

0054A unit-accommodating chamber 40 is formed in the main casing 2 for accommodating the drawer unit 14. The unit-accommodating chamber 40 is a space defined vertically by the intermediate transfer belt 27 and the scanning unit 10. As shown in <figref idref="f0003">Fig. 3</figref>, a pair of partitioning walls 41 is provided in the main casing 2 for defining the left and right boundaries of the unit-accommodating chamber 40. Only the left partitioning wall 41 is shown in <figref idref="f0003">Fig. 3</figref>.

0055A guide part 42 is provided inner surfaces of the partitioning walls 41 (the right surface in the case of the left partitioning wall 41 shown in <figref idref="f0003">Fig. 3</figref>). As shown in <figref idref="f0002">Figs. 2</figref> and <figref idref="f0003">3</figref>, the guide part 42 includes in order beginning from the front side, a first guiding roller 43, a first sloped wall 44, a first guiding rail 45, a second guiding roller 46, a second sloped wall 47, and a second guiding rail 48.

0056The first guiding roller 43 is rotatably disposed on the front end of the corresponding partitioning wall 41 (see <figref idref="f0002">Fig. 2</figref>). The first guiding rail 45 is formed in a plate shape that extends evenly in the front-to-rear direction (see <figref idref="f0003">Fig. 3</figref>). The front end of the first guiding rail 45 is in proximity with the rear side of the first guiding roller 43 (not illustrated in the drawings). The first guiding rail 45 is disposed at a vertical position that is substantially equivalent to the lower portion of the first guiding roller 43 (see <figref idref="f0002">Figs. 2</figref> and <figref idref="f0003">3</figref>).

0057When viewed along the width direction, the first sloped wall 44 is substantially triangular in shape, narrowing toward the rear side (see <figref idref="f0002">Fig. 2</figref>). The top surface of the first sloped wall 44 slopes downward from the top part of the first guiding roller 43 to the top surface of the first guiding rail 45 (see <figref idref="f0002">Figs. 2</figref> and <figref idref="f0003">3</figref>).

0058As shown in <figref idref="f0003">Fig. 3</figref>, the second guiding roller 46 is rotatably disposed on the rear end of the corresponding partitioning wall 41 adjacent to the rear end of the first guiding rail 45. The second guiding roller 46 is positioned so that its upper part is substantially equivalent in position to the first guiding rail 45 relative to the vertical.

0059The second guiding rail 48 is formed in a plate shape that extends evenly in the front-to-rear direction, and then curves upward on the rear end. The second guiding rail 48 is disposed at substantially the same position as the lower portion of the second guiding roller 46 with respect to the vertical. When viewed along the width direction, the second sloped wall 47 has a substantially triangular shape, tapering toward the rear. The top surface of the second sloped wall 47 slopes downward from the top portion of the second guiding roller 46 to the top surface of the second guiding rail 48.

0060As shown in <figref idref="f0001">Fig. 1</figref>, a unit-mounting opening 49 is formed in the front wall of the main casing 2. The unit-mounting opening 49 allows communication between the area on the front side of the color printer 1 and the unit-accommodating chamber 40 (see <figref idref="f0002">Figs. 2</figref> and <figref idref="f0003">3</figref>).

0061The second front cover 50 is provided on the front wall of the main casing 2 and is capable of opening and closing thereon. In the closed state shown in <figref idref="f0001">Fig. 1</figref> the second front cover 50 is in an erect orientation and blocks the unit-mounting opening 49 on the front side thereof. In this state of the second front cover 50, a rotational shaft 51 extending in the width direction penetrates the bottom edge of the second front cover 50. The second front cover 50 is coupled to the front wall of the main casing 2 via the rotational shaft 51 and is capable of pivotally rotating about the rotational shaft 51. When an operator pulls the second front cover 50 forward from the closed position shown in <figref idref="f0001">Fig. 1</figref>, the second front cover 50 rotates forward and downward about the rotational shaft 51 (see <figref idref="f0002 f0003 f0004">Figs. 2 through 4</figref>). At this time, the second front cover 50 is in the open state and the unit-mounting opening 49 is exposed on the front side of the color printer 1 (see <figref idref="f0002">Figs. 2</figref> and <figref idref="f0003">3</figref>).

0062A pivoting unit 52 is provided in the main casing 2 above the second front cover 50 when the second front cover 50 is in the closed state. The pivoting unit 52 is an integrated unit that includes the discharge tray 34 and various parts positioned beneath the discharge tray 34 (specifically the intermediate transfer belt 27, follow roller 25, drive roller 26, primary transfer rollers 28, and cleaning unit 30), as well as the first front cover 31 described earlier. The pivoting unit 52 is capable of pivoting about the drive roller 26 of the transfer unit 12 and a pivoting shaft 53 disposed on the rear side of the discharge tray 34 so that the front of the pivoting unit 52 moves vertically.

0063When the second front cover 50 is in the closed state shown in <figref idref="f0001">Fig. 1</figref>, the lower front end of the pivoting unit 52 is engaged with the top end of the second front cover 50, restricting forward rotation of the second front cover 50. Therefore, the second front cover 50 can be maintained in the closed state.

0064When the pivoting unit 52 is pivoted upward from the state shown in <figref idref="f0001">Fig. 1</figref> to the state shown in <figref idref="f0002">Fig. 2</figref>, the lower front end of the pivoting unit 52 disengages from the top end of the second front cover 50, allowing the second front cover 50 to be rotated forward and downward. By rotating the second front cover 50 downward on the front side, the operator can expose the unit-mounting opening 49 described above.

00653. Drawer unit

(1) Drawer frame

0066As shown in <figref idref="f0004">Fig. 4</figref>, the drawer frame 15 has a hollow box shape with the opening 15A formed in the top surface.

0067Four guiding grooves 60 are formed in the inner widthwise surface on each widthwise side walls of the drawer frame 15 (i.e., the widthwise surfaces of the drawer frame 15 facing inwardly). The guiding grooves 60 are formed in the upper end of the side walls at substantially equal intervals in the front-to-rear direction and extend downward along a forward slope from the top edge of the inner surface. The innermost part (bottom end) of each guiding groove 60 is rounded so that each guiding groove 60 has a substantial U-shape when viewed in the width direction.

0068A positioning shaft 61 is integrally provided on the upper front corner of each widthwise wall of the drawer frame 15, protruding outward in the width direction therefrom. The top edge of each widthwise wall of the drawer frame 15 is bent outward in the width direction to form a flange 62.

0069As shown in <figref idref="f0003">Fig. 3</figref>, a protruding piece 63 is integrally provided on the upper rear end of each widthwise wall in the drawer frame 15, protruding rearward. Two wheels 64 juxtaposed in the front-to-rear direction are provided on each protruding piece 63. Rotational shafts of the wheels 64 extend in the width direction and are supported in the protruding pieces 63. Thus, the wheels 64 are rotatably supported by the protruding pieces 63.

0070A rotational shaft 65 and a handle 66 are provided on the front wall of the drawer frame 15. The rotational shaft 65 extends in the width direction and is supported in the front wall of the drawer frame 15. The rotational shaft 65 is inserted through one end (the rear end in <figref idref="f0003">Fig. 3</figref>) of the handle 66, by which the handle 66 is capable of rotating about the rotational shaft 65 (see <figref idref="f0001 f0002 f0003 f0004">Figs. 1 through 4</figref>). The operator grips the handle 66 when mounting the drawer unit 14 in or removing the drawer unit 14 from the main casing 2.

(2) Process cartridges

0071<figref idref="f0005">Fig. 5</figref> shows one of the process cartridges 16 when a process shutter 83 and a toner shutter 112 described later are both in an open position. <figref idref="f0005">Fig. 5A</figref> is a right side cross-sectional view of the process cartridge 16; <figref idref="f0005">Fig. 5B</figref> is a right side view of the process cartridge 16; and <figref idref="f0005">Fig. 5C</figref> illustrates the process cartridge 16 when the toner box 24 is separated from all other parts of the process cartridge 16.

0072<figref idref="f0006">Fig. 6</figref> shows the process cartridge 16 when the process shutter 83 and the toner shutter 112 are both in a closed position. <figref idref="f0006">Fig. 6A</figref> is a right side cross-sectional view of the process cartridge 16; <figref idref="f0006">Fig. 6B</figref> is a right side view of the process cartridge 16; and <figref idref="f0006">Fig. 6C</figref> shows the process cartridge 16 when the toner box 24 is separated from all other parts of the process cartridge 16.

(2-1) Upper case and lower case

0073As shown in <figref idref="f0005">Fig. 5A</figref>, the upper case 17 of each process cartridge 16 has a hollow box shape elongated in the width direction and open on the top and bottom surfaces. The upper case 17 supports the photosensitive drum 19 and charger 20. Both widthwise ends of the central shaft 19A of the photosensitive drum 19 penetrate the corresponding side walls of the upper case 17 in the width direction and protrude outward from the upper case 17 in the width direction (see <figref idref="f0005">Fig. 5B</figref>).

0074A cleaning roller 70 is rotatably supported in the upper case 17 above the charger 20. The outer peripheral surface of the cleaning roller 70 contacts the outer surface of the photosensitive drum 19 on the rear side thereof. The cleaning roller 70 functions to remove the toner and other foreign matter from the peripheral surface of the photosensitive drum 19 after a toner image has been transferred from the photosensitive drum 19 to the intermediate transfer belt 27 (see <figref idref="f0001">Fig. 1</figref>).

0075As described above, the lower case 18 has a hollow box shape elongated in the width direction and is open on the top. While the lower case 18 can move relative to the upper case 17, which is coupled to the lower case 18 via the coupling shaft 21, as described above, the lower case 18 in <figref idref="f0005">Fig. 5A</figref> is fixed in position so that the developing roller 22 contacts the lower front side of the photosensitive drum 19.

0076When viewed along the width direction, the lower case 18 resembles a teardrop that is wider toward the bottom. Accordingly, the interior of the lower case 18 also grows wider in the front-to-rear direction toward the bottom side. The interior of the lower case 18 is partitioned into a developing chamber 71, a supply chamber 72, and a box-accommodating chamber 73 in order from top to bottom.

0077When viewed along the width direction, the developing chamber 71 appears to be shaped substantially like a parallelogram tilted downward to the rear. The developing chamber 71 is exposed from above (outside of the lower case 18) through the open top surface of the lower case 18.

0078Viewed in the width direction, the supply chamber 72 is substantially circular in shape and in communication with the lower front side of the developing chamber 71. An arced wall 74 forming part of the front wall of the lower case 18 corresponding to the supply chamber 72 bulges forward in an arc shape. A first protruding wall 75 integrally provided on the front wall of the lower case 18 protrudes continuously from the lower edge of the arced wall 74 in a rearward direction into the lower case 18 and at the same curvature as the arced wall 74. Viewed along the width direction, the first protruding wall 75 is substantially shaped like a letter U that has been flattened vertically so as to curve in an arc that is convex on the bottom side. The first protruding wall 75 functions as an arc wall. Viewed from the right side, the arced wall 74 and first protruding wall 75 together are shaped like the letter C with an opening in the rear side. The region within the C-shaped portion formed by the arced wall 74 and first protruding wall 75 is the supply chamber 72.

0079When viewed in the width direction, the box-accommodating chamber 73 is substantially circular in shape and more than twice the size of the supply chamber 72. More specifically, a portion of the circumference of the circularly shaped box-accommodating chamber 73 in a side view is depressed inwardly to form an arc shape that is concave on the top. The bottom wall of the lower case 18 (including the lower ends of the front wall and rear wall) is formed in an arc shape conforming to the shape of the box-accommodating chamber 73 that is convex on the bottom. A second protruding wall 76 integrally provided on the rear wall of the lower case 18 is formed continuously with the rear end on the bottom wall of the lower case 18 and protrudes upward and forward into the lower case 18 at the same curvature as the bottom wall. The second protruding wall 76 is arc-shaped when viewed in the width direction and extends upward and forward while bulging upward and rearward. The rear end of the first protruding wall 75 described above is connected to the front (top) end of the second protruding wall 76. The second protruding wall 76 defines the lower rear side of the developing chamber 71.

0080In a right side view, the bottom wall of the lower case 18 and the second protruding wall 76 are taken together form an approximate C-shape having a cutout part in the top. The first protruding wall 75 is provided in the cutout region of this C-shape and protrudes thereto. The box-accommodating chamber 73 is the region defined by the bottom wall of the lower case 18, the second protruding wall 76, and the first protruding wall 75. The toner box 24 (and the toner shutter 112 and an agitator 111 described later provided in the toner box 24) is accommodated in the box-accommodating chamber 73, as shown in <figref idref="f0005">Fig. 5A</figref>.

0081A box-mounting opening 84 that is substantially circular and is approximately the same shape as the box-accommodating chamber 73 when viewed along the width direction is formed in a portion of the right wall in the lower case 18 corresponding to the box-accommodating chamber 73 in the width direction. The box-accommodating chamber 73 is exposed on the right side of the lower case 18 through the box-mounting opening 84 (see <figref idref="f0005">Fig. 5C</figref>). The portion of the left wall of the lower case 18 aligned with the box-accommodating chamber 73 in the width direction is substantially circular in shape and approximately the same shape and size as the box-accommodating chamber 73 in the width direction. A coupling gear 85 is rotatably disposed in the center of this circular region (see <figref idref="f0005">Fig. 5C</figref>).

0082A single through-hole 77 is formed in the upper rear portion of the first protruding wall 75, which appears to be shaped substantially like the letter U (or a tray) that has been flattened vertically when viewed along the width direction. The through-hole 77 is a slit extending in the width direction that penetrates the first protruding wall 75 in the front-to-rear direction to provide communication between the supply chamber 72 and box-accommodating chamber 73. Specifically, the box-accommodating chamber 73 communicates with the lower rear portion of the supply chamber 72 via the through-hole 77. Since the through-hole 77 is formed in the upper rear side of the first protruding wall 75, part of the first protruding wall 75 is positioned lower than the lower edge defining the through-hole 77. This part is an accumulating part 75A.

0083With this configuration of the lower case 18, the developing roller 22 described earlier is disposed in the developing chamber 71, and the supply roller 23 is disposed in the supply chamber 72. The lower peripheral surface of the supply roller 23 opposes the first protruding wall 75 from above and follows the upper curved surface of the first protruding wall 75. The through-hole 77 formed in the first protruding wall 75 confronts the lower rear portion of the supply roller 23.

0084A thickness-regulating blade 78 is also disposed in the developing chamber 71. The thickness-regulating blade 78 is integrally provided with a leaf spring 79 formed in a thin plate shape elongated in the width direction, and a rubber pressing part 80 disposed on the front end of the leaf spring 79. The leaf spring 79 extends from the rear wall of the lower case 18 in a direction upward and forward along the second protruding wall 76 toward the bottom peripheral surface of the developing roller 22. The elastic force of the leaf spring 79 presses the pressing part 80 against the bottom peripheral surface of the developing roller 22. The gap between the leaf spring 79 and the second protruding wall 76 is filled by a seal 81. The gap between the front peripheral surface of the developing roller 22 and the front wall of the lower case 18 is filled by a seal 82.

0085The process shutter 83 is provided in the lower case 18 for opening and closing the through-hole 77. The process shutter 83 has a thin plate shape elongated in the width direction. In the width direction, the process shutter 83 is shaped substantially like a letter U that has been flattened vertically, similar to the first protruding wall 75 and is positioned along the bottom of the first protruding wall 75. The process shutter 83 can slide in a direction along the curved surface of the first protruding wall 75. The toner shutter 112 mentioned earlier is positioned immediately below the process shutter 83 in <figref idref="f0005">Fig. 5A</figref>.

0086In <figref idref="f0005">Fig. 5A</figref>, the entire process shutter 83 is positioned below the first protruding wall 75. This position is the open position in which the process shutter 83 is shifted downward and forward from the through-hole 77. When the process shutter 83 is in the open position, the through-hole 77 is open.

0087When the process shutter 83 is slid a prescribed amount from the open position upward and rearward along the lower surface of the first protruding wall 75, the process shutter 83 arrives in the closed position shown in <figref idref="f0006">Fig. 6A</figref>. In the closed position, the process shutter 83 blocks the entire through-hole 77 from the bottom rear side. The process shutter 83 is returned to the open position shown in <figref idref="f0005">Fig. 5A</figref> when slid a prescribed distance from the closed position along a downward and forward arc following the lower surface of the first protruding wall 75.

0088A support member 86 is disposed in the lower case 18 for supporting the process shutter 83. The support member 86 is formed integrally with the process shutter 83. Taken together, the process shutter 83 and support member 86 constitute a shutter unit 87. The support member 86 functions as a rotational member.

0089<figref idref="f0007">Fig. 7</figref> is a perspective view of the shutter unit 87 from a front right viewpoint. Next, the components of the shutter unit 87 will be described with reference to <figref idref="f0007">Fig. 7</figref>. The following description will be based on the orientation of the shutter unit 87 in <figref idref="f0007">Fig. 7</figref>. The support member 86 is integrally provided with a pair of left and right rotating plates 88 connected to corresponding widthwise ends of the process shutter 83, and a beam member 89 spanning between the top portions of the left and right rotating plates 88.

0090The rotating plates 88 are formed in thin plate shapes with the thin dimension corresponding to the width direction and appears substantially circular in shape when viewed along the width direction. A through-hole 90 is formed in the circular center position of each rotating plate 88.

0091A left protruding part 91 is integrally formed on the peripheral surface of the left rotating plate 88 at one location in the circumferential direction (the bottom of the rotating plate 88 in <figref idref="f0007">Fig. 7</figref>) and protrudes radially outward from the left rotating plate 88 (downward in <figref idref="f0007">Fig. 7</figref>). As with the rotating plates 88, the protruding part 91 is also formed thin in the width direction and is substantially shaped like the letter U following the lower peripheral edge of the left rotating plate 88 when viewed along the width direction (see <figref idref="f0005">Fig. 5C</figref>). Two left recess parts 92 are formed in the right surface of the protruding part 91 at positions along the circumferential direction of the left rotating plate 88 (see <figref idref="f0005">Fig. 5C</figref>).

0092A right protruding part 93 is integrally provided on the right side surface of the right rotating plate 88. The right protruding part 93 has a thin plate shape with the thin dimension corresponding to the width direction and has a circular shape when viewed in the width direction with a diameter smaller than that of the right rotating plate 88. The right protruding part 93 is concentric with the right rotating plate 88. The circular center of the right protruding part 93 is aligned with the circular center of the right rotating plate 88 in the width direction. Further, the through-hole 90 described above that is formed in the right rotating plate 88 penetrates both the right rotating plate 88 and the right protruding part 93 at the center thereof.

0093As shown in <figref idref="f0005">Fig. 5C</figref>, a protruding part 94 is integrally provided on the right side surface of the right rotating plate 88 at one location along the outer circumference thereof (the part on the rear side of the right protruding part 93 in <figref idref="f0007">Fig. 7</figref>). The protruding part 94 protrudes radially outward from the right rotating plate 88 (rearward in <figref idref="f0007">Fig. 7</figref>). The protruding part 94 protrudes farther outward than the peripheral surface of the right rotating plate 88 on the right side thereof (see <figref idref="f0005">Fig. 5C</figref>).

0094Two right recessed parts 95 are formed in the right surface of the right rotating plate 88 along the peripheral edge thereof and at positions different from the protruding part 94 with respect to the circumferential direction of the right rotating plate 88 (positions lower than the right protruding part 93 in <figref idref="f0007">Fig. 7</figref>). The right recessed parts 95 are arranged along the circumferential direction of the rotating plate 88 (see <figref idref="f0005">Fig. 5C</figref>).

0095A rack gear 96 is formed on the outer peripheral surface of the right protruding part 93 in a position corresponding to the right recessed parts 95 with respect to the circumferential direction of the right protruding part 93 (the rotating plate 88; near the bottom end of the right protruding part 93 in <figref idref="f0007">Fig. 7</figref>; see also <figref idref="f0005">Fig. 5C</figref>). The rack gear 96 has a plurality of gear teeth that are arranged along the circumference of the right protruding part 93.

0096The left end of the process shutter 83 is connected to a part of the left rotating plate 88 (the lower end of the left rotating plate 88 in <figref idref="f0007">Fig. 7</figref>) on which the protruding part 91 (and specifically the left recess parts 92) is provided, while the right end is connected to a part of the right rotating plate 88 (the lower end of the right rotating plate 88 in <figref idref="f0007">Fig. 7</figref>) in which the right recessed parts 95 are formed. In <figref idref="f0007">Fig. 7</figref>, the process shutter 83 spans between the lower ends of the left and right rotating plates 88. The two right recessed parts 95 are continuously formed in the process shutter 83 from the right rotating plate 85 (see <figref idref="f0005">Fig. 5C</figref>). In other words, it may be said that the right recessed parts 95 are provided in the process shutter 83. If the protruding part 91 is treated as part of the process shutter 83, then it may be considered that the left recess parts 92 formed in the protruding part 91 are provided in the process shutter 83. The left recess parts 92 and the right recessed parts 95 are functions as a second connection member.

0097The beam member 89 has a plate shape extending in the width direction and spans between outer peripheral surfaces of the left and right rotating plates 88 at a different position along the circumference of the rotating plates 88 than the process shutter 83. When viewed along the width direction, the beam member 89 is curved in an arc that follows the outer peripheral surfaces of the left and right rotating plates 88.

0098The shutter unit 87 having a construction described-above is rotatably supported by the lower case 18, as shown in <figref idref="f0005">Fig. 5C</figref>. More specifically, in the shutter unit 87 having this construction, the left rotating plate 88 is positioned farther leftward than the left side surface of the lower case 18 (not shown), while the right rotating plate 88 is positioned farther rightward than the right side surface of the lower case 18. In this state, the left and right rotating plates 88 are aligned in the width direction with the entire supply chamber 72 and the lower left portion of the developing chamber 71 formed in the lower case 18 (see <figref idref="f0005">Fig. 5A</figref>).

0099Further, the process shutter 83 of the shutter unit 87 is accommodated in the box-accommodating chamber 73 of the lower case 18, while the beam member 89 is positioned farther forward from the front side surface of the lower case 18 (the front wall portion of the lower case 18 in the vicinity of the arced wall 74; see <figref idref="f0005">Fig. 5A</figref>).

0100Hence, only the process shutter 83 of the shutter unit 87 is positioned within the lower case 18, while all other parts of the shutter unit 87 are disposed outside of the lower case 18 (or outside of the process cartridge 16).

0101A support shaft 97 is integrally provided on the outer surface of each widthwise side wall of the lower case 18 at a position aligned with the center of curvature of the first protruding wall 75 (see <figref idref="f0005">Fig. 5A</figref>). The support shafts 97 protrude outward in the width direction from their corresponding outer surfaces. Each support shaft 97 is inserted into the through-hole 90 formed in the rotating plate 88 on the same widthwise side of the shutter unit 87. The support shaft 97 is inserted from the inside of the through-hole 90 in the width direction.

0102With this construction, the entire shutter unit 87 can freely rotate about the support shafts 97 provided on widthwise side walls of the lower case 18 in either a clockwise or counterclockwise direction when viewing the shutter unit 87 on the right side. Thus, the support shafts 97 on the lower case 18 serve as the rotational center of the shutter unit 87. The shutter unit 87 can rotate freely within a range in which the process shutter 83 slides between the open position and closed position described above.

0103When the process shutter 83 is in the open position shown in <figref idref="f0005">Fig. 5A</figref>, the beam member 89 contacts a portion of the front wall of the lower case 18 near the upper end of the arced wall 74 from the front side thereof. This contact restricts the shutter unit 87 from rotating clockwise in a right side view.

0104When the process shutter 83 is in this open position, the shutter unit 87 is rotated counterclockwise in a right side view until the beam member 89 contacts the front wall of the lower case 18 near the lower end of the arced wall 74 from the upper front side, as shown in <figref idref="f0006">Fig. 6A</figref>. This contact restricts the shutter unit 87 from rotating farther in the counterclockwise direction in a right side view. At this point, the process shutter 83 is in the closed position.

(2-2) Toner box

0105<figref idref="f0008">Fig. 8A</figref> is a perspective view from the left front side of the toner box 24 when the toner shutter 112 is in the closed position. <figref idref="f0008">Fig. 8B</figref> is a perspective view from the left front side of the toner box 24 when the toner shutter 112 is in the open position. <figref idref="f0008">Fig. 8C</figref> is a perspective view from the right front side of the toner box 24 when the toner shutter 112 is in the closed position. <figref idref="f0008">Fig. 8D</figref> is a perspective view from the right front side of the toner box 24 when the toner shutter 112 is in the open position. <figref idref="f0008">Fig. 8E</figref> is a front cross-sectional view showing relevant parts of the toner box 24.

0106The toner box 24 is hollow with a substantially cylindrical shape elongated in the width direction, as described above. As shown in <figref idref="f0008">Fig. 8</figref>, a box casing 100 forms the outer shell of the toner box 24 and has a hollow, substantially cylindrical shape elongated in the width direction. The box casing 100 functions as a first toner accommodating unit. Hence, a cross section of the box casing 100 viewed along the width direction is substantially circular in shape (see <figref idref="f0005">Fig. 5A</figref>). The box casing 100 is closed on both widthwise ends and accommodates toner therein. The box casing 100 is integrally provided with a circumferential wall 101 forming the outer circumferential (peripheral) surface thereof, and a pair of side walls 102 covering both widthwise ends of the circumferential wall 101.

0107A curved wall 103 is formed along one peripheral portion (upper portion) of the circumferential wall 101, extending across the entire width of the circumferential wall 101 (box casing 100). The curved wall 103 is depressed inward toward the circular center of the circumferential wall 101 (toward the interior of the box casing 100) to form an arc-shaped curve. The curved wall 103 functions as a wall portion. When viewed along the width direction, the curved wall 103 is substantially U-shaped. In other words, as shown in <figref idref="f0005">Fig. 5C</figref>, the curved wall 103 is curved in an arc shape whose center of curvature is a reference line X extending in the width direction. The reference line X positions outside (above) the box casing 100 in a radial direction of the circular center of the circumferential wall 101 as viewed along width direction (a radial to an agitator shaft 107 described later). The curvature of the curved wall 103 is substantially identical to that of the first protruding wall 75 in the lower case 18 of the process cartridge 16 (see <figref idref="f0005">Fig. 5A</figref>). The curved wall 103 functions to guide the toner after passing through a supply hole 104 described later.

0108As shown in <figref idref="f0008">Fig. 8B</figref>, the side walls 102 have the same shape as the circumferential wall 101 when viewed along the width direction. That is, each side walls 102 is substantially circular in shape, with one portion of the outer peripheral edge cut out in an arc. Thus, the box casing 100 comprising the circumferential wall 101 and side walls 102 is hollow and substantially cylindrical in shape, with one region on the outer peripheral surface depressed inwardly in an arc that extends across the entire width direction. Consequently, the interior space of the box casing 100 is also substantially circular in shape, but has one portion in the outer peripheral edge cut out in an arc shape when viewed along the width direction.

0109A supply hole 104 elongated in the width direction is formed in and penetrates the outer surface of the curved wall 103 (the surface exposed on the outside) near the rear edge of the curved wall 103. The supply hole 104 functions as a first supply hole. The width dimension of the supply hole 104 is slightly smaller than that of the curved wall 103. The supply hole 104 provides communication between the interior and exterior of the box casing 100.

0110A right guide groove 105 is formed in the outer surface of the curved wall 103 at a position farther rightward than the supply hole 104 and is recessed toward the circular center of the circumferential wall 101 (toward the interior of the box casing 100). When viewed along the width direction, the right guide groove 105 forms an arc shape that follows the outer curved surface of the curved wall 103. A cross section of the right guide groove 105 forms a convex shape that grows narrower toward the outer surface of the curved wall 103. In other words, the width of the right guide groove 105 is wider at its deepest point than at the surface of the curved wall 103.

0111A left guide groove 106 is formed in the left side surface of the left side wall 102 in an area following the curved wall 103 and is recessed rightward. The left guide groove 106 has an arc shape that follows the curved wall 103 and is substantially U-shaped when viewed along the width direction. The agitator shaft 107 extending along the width direction spans between the center parts of the circular left and right side walls 102 and is rotatably supported in these side walls 102. The agitator shaft 107 functions as a rotational shaft. The left end of the agitator shaft 107 protrudes farther leftward than the left side surface of the left side wall 102. An input gear 108 is integrally provided on the left end of the agitator shaft 107 and protrudes leftward from this left end. The input gear 108 functions as a transmitting member.

0112As shown in <figref idref="f0005">Fig. 5A</figref>, a support part 109 is integrally provided on the outer peripheral surface of the agitator shaft 107 within the box casing 100 and protrudes radially outward from the agitator shaft 107. The support part 109 is formed of a hard material (hard resin or the like). When viewed in the width direction, the support part 109 grows narrower away from the agitator shaft 107 in the radial direction. The support part 109 functions as a support portion.

0113An agitating blade 110 is attached to the support part 109. The agitating blade 110 functions as an agitating portion. The agitating blade 110 is formed of a flexible material, such as film. The agitating blade 110 is supported on the support part 109 and extends outward from the support part 109 along the radial direction of the agitator shaft 107 to the inner surface of the circumferential wall 101 forming the box casing 100. The natural length of the agitating blade 110 with respect to the radial direction of the agitator shaft 107 is greater than the distance between the support part 109 and the inner surface of the circumferential wall 101. Accordingly, the agitating blade 110 contacts the inner surface of the circumferential wall 101 and is slightly bowed in the box casing 100. When viewed from the right side, as in <figref idref="f0005">Fig. 5A</figref>, the side of the agitating blade 110 toward the inner surface side of the circumferential wall 101 is bowed in a clockwise direction with respect to the support part 109.

0114The agitator shaft 107, support part 109, and agitating blade 110 together configure the agitator 111. Excluding the left end part of the agitator shaft 107, the agitator 111 is disposed entirely in the toner box 24 (and specifically the box casing 100). In a right side view, the agitator 111 can rotate in the counterclockwise direction about the agitator shaft 107.

0115In one rotation of the agitator 111, the agitating blade 110 passes over and contacts the entire inner surface of the circumferential wall 101 (including the curved wall 103). Since the agitator 111 rotates (and the agitating blade 110 passes over the circumferential wall 101) in the counterclockwise direction when viewed from the right side, the supply hole 104 formed at the rear end of the curved wall 103 is on the upstream side of the curved wall 103 with respect to the rotating direction of the agitator 111.

0116As shown in <figref idref="f0008">Fig. 8B</figref>, the toner shutter 112 is provided in the toner box 24. The toner shutter 112 is plate-shaped and elongated in the width direction. When viewed along the width direction, the toner shutter 112 is arc-shaped with approximately the same curvature as the curved wall 103 of the box casing 100 (see <figref idref="f0005">Fig. 5A</figref>). The widthwise dimension of the toner shutter 112 is approximately the same as that of the curved wall 103, while the dimension of the toner shutter 112 in the circumferential direction (the direction of the curved surface) is about half that of the curved wall 103.

0117A folded part 113 is integrally provided on the left end of the toner shutter 112. The folded part 113 is bent in a direction orthogonal to the width direction and away from the center of curvature of the toner shutter 112 (downward in <figref idref="f0008">Fig. 8B</figref>). The folded part 113 has a plate shape that is thin in the width direction and is connected to the left end of the toner shutter 112 along the entire periphery thereof.

0118Two left protrusions 114 are integrally provided on the left side surface of the folded part 113. The left protrusions 114 are spaced from each other in the circumferential direction of the toner shutter 112 and protrude leftward. A left guide rib 115 is integrally provided on the right side surface of the folded part 113. The left guide rib 115 protrudes rightward and extends along the circumferential direction of the toner shutter 112.

0119Two right protrusions 116 are integrally provided on the outer surface of the toner shutter 112 (the surface exposed externally from the toner box 24; the top surface in <figref idref="f0008">Fig. 8B</figref>) near the right end thereof. The right protrusions 116 are spaced an interval in the circumferential direction of the toner shutter 112 and protrude in a direction toward the center of curvature of the toner shutter 112 (upward in <figref idref="f0008">Fig. 8B</figref>). The right protrusions 116 and the left protrusions 114 function as a first connection member.

0120A right guide rib 117 is integrally provided on the underside surface of the toner shutter 112 (although not shown in <figref idref="f0008">Fig. 8B</figref>, the bottom surface of the toner shutter 112 the same drawing) and extends along the circumferential direction of the toner shutter 112 (see <figref idref="f0008">Figs. 8A and 8C</figref>). The right guide rib 117 protrudes in a direction orthogonal to the width direction and away from the center of curvature of the toner shutter 112 (downward in <figref idref="f0008">Fig. 8A</figref>).

0121The toner shutter 112 is supported in the curved wall 103 of the box casing 100. More specifically, the left guide rib 115 of the toner shutter 112 is fitted into the left guide groove 106 formed in the box casing 100 from the left side, while the right guide rib 117 is fitted into the right guide groove 105 of the box casing 100 from the top in <figref idref="f0008">Fig. 8B</figref>. With this construction, the toner shutter 112 is supported by the box casing 100 at multiple points along the width direction (i.e., at the left guide rib 115 and right guide rib 117).

0122In this state, the left guide rib 115 can freely slide within the left guide groove 106 along the circumferential direction of the curved wall 103, and the right guide rib 117 can freely slide within the right guide groove 105 along the circumferential direction of the curved wall 103. Using the drawing of <figref idref="f0008">Fig. 8A</figref> as a reference, the bottom surface of the toner shutter 112 is disposed over the outer surface (top surface) of the curved wall 103 and opposes this outer surface along substantially the entire width direction. In this state, the toner shutter 112 can freely slide along the circumferential direction of the curved wall 103 between the open position shown in <figref idref="f0008">Figs. 8B and 8D</figref> and the closed position shown in <figref idref="f0008">Figs. 8A and 8C</figref>.

0123In the open position, the toner shutter 112 is shifted to the front side of the supply hole 104 so that the entire supply hole 104 is exposed (open) on the outside (the top; see <figref idref="f0008">Figs. 8B and 8D</figref>). In the closed position, the toner shutter 112 is aligned with the supply hole 104, covering the entire supply hole 104 on the outside (see <figref idref="f0008">Figs. 8A and 8C</figref>). Thus, the supply hole 104 is opened and closed by shifting the toner shutter 112 along the circumferential direction of the curved wall 103.

0124As shown in <figref idref="f0008">Fig. 8D</figref>, an operating part 118 is provided in the toner box 24 on the right side surface of the right side wall 102. The operating part 118 is plate-shaped with its thin dimension corresponding to the width direction. The operating part 118 is circular-shaped in a right side view, with a smaller diameter than the side wall 102. The center of the circular operating part 118 is aligned with the center of the circular right side wall 102 (the agitator shaft 107); in the width direction (see <figref idref="f0005">Figs. 5A and 5C</figref>).

0125A grip part 119 is integrally provided on the right side surface of the operating part 118. The grip part 119 has a narrow square columnar shape that extends along a straight line passing through the center of the circular operating part 118 in a right side view. A rack gear 120 is formed on the outer peripheral surface of the operating part 118 at one location on the circumference thereof. With respect to <figref idref="f0008">Fig. 8D</figref> in which the grip part 119 extends vertically, the rack gear 120 is formed at a position shifted slightly counterclockwise from the top end of the grip part 119 in a right side view. The rack gear 120 has a plurality of gear teeth arranged along the circumferential direction of the operating part 118.

0126The operating part 118 is supported on the right side wall 102 and is capable of rotating freely about its own center. Bosses 121 are integrally provided on the right side surface of the right side wall 102 adjacent to the operating part 118 and at positions on either side of the curved wall 103 with respect to the circumferential direction of the substantially circular side wall 102 (see <figref idref="f0005">Fig. 5C</figref>). The bosses 121 are cylindrical in shape and protrude rightward.

0127With the operating part 118 rotatably supported by the right side wall 102, as described above, the rack gear 120 of the operating part 118 is disposed between the two bosses 121 with respect to the circumferential direction of the side wall 102 (or operating part 118). Accordingly, the operating part 118 may be rotated between a position in which the rack gear 120 contacts the forward boss 121, as shown in <figref idref="f0008">Fig. 8D</figref> (hereinafter referred to as the "forward position"), and a position in which the rack gear 120 contacts the rearward boss 121, as shown in <figref idref="f0008">Fig. 8C</figref> (hereinafter referred to as the "rearward position"). An operator rotates the operating part 118 by gripping and twisting the grip part 119.

0128When in the forward position, the operating part 118 can be moved to the rearward position by rotating the grip part 119 all the way clockwise in a right side view. From the rearward position, the operating part 118 can be returned to the forward position by rotating the operating part 118 all the counterclockwise in a right side view. When looking at the toner box 24 by itself, the toner shutter 112 and operating part 118 are not mechanically coupled together, and the toner shutter 112 slides independent of the rotation of the operating part 118. Therefore, the toner shutter 112 does not slide when the operating part 118 is rotated in a standalone toner box 24. The toner shutter 112 is in the closed position in this state (see <figref idref="f0008">Fig. 8C</figref>).

0129As shown in <figref idref="f0008">Fig. 8E</figref>, a recessed part 122 is formed at one location in the left peripheral edge of the operating part 118. A cylindrical pawl 123 elongated in the width direction is fitted into the recessed part 122. A spring 124 has one end coupled to the right end of the pawl 123 and another end coupled to the portion of the operating part 118 defining the bottom of the recessed part 122. The spring 124 urges the pawl 123 leftward.

0130When the operating part 118 is in the rearward position shown in <figref idref="f0008">Fig. 8C</figref>, the left end of the pawl 123 protrudes leftward from the recessed part 122, as shown in <figref idref="f0008">Figs. 8A and 8E</figref>. The left end of the pawl 123 contacts the right outer surface of the curved wall 103 near the rearward boss 121 from the upstream side with respect to the counterclockwise direction in a right side view. While the pawl 123 remains in contact with the curved wall 103 in this state, the operating part 118 cannot be rotated counterclockwise in a right side view.

0131On the other hand, when the operating part 118 is in the forward position shown in <figref idref="f0008">Fig. 8D</figref>, the pawl 123 does not catch on the curved wall 103, as described above, but is almost completely accommodated in the recessed part 122 (see <figref idref="f0008">Fig. 8E</figref>) while opposing the right side surface of the right side wall 102.

(2-3) Mounting and removal of the toner box with respect to the process cartridge

0132Next, the procedure for mounting the toner box 24 in and removing the toner box 24 from the process cartridge 16 (and specifically the developing unit 37) will be described.

0133Before mounting the toner box 24 in the process cartridge 16, the process shutter 83 is in the closed position in the lower case 18 of the process cartridge 16, as shown in <figref idref="f0006">Fig. 6C</figref> (see also <figref idref="f0006">Fig. 6A</figref>). In the toner box 24, the toner shutter 112 is in the closed position and the operating part 118 is in the rearward position, as shown in <figref idref="f0008">Figs. 8A and 8C</figref>.

0134In this state, the toner box 24 is oriented with the curved wall 103 on the top side and disposed on the right side of the box-mounting opening 84 formed in the right side wall of the lower case 18 (the near side in <figref idref="f0006">Fig. 6</figref>). From this position, the toner box 24 is pushed leftward so that the left end (the end with the input gear 108) of the toner box 24 enters the box-mounting opening 84 first. The toner box 24 is pushed through the box-mounting opening 84 until fully accommodated in the box-accommodating chamber 73, as shown in <figref idref="f0006">Fig. 6B</figref>.

0135When the toner box 24 is fully accommodated in the box-accommodating chamber 73, the operation for mounting the toner box 24 in the process cartridge 16 (in the lower case 18 of the developing unit 37) is complete.

0136As shown in <figref idref="f0006">Fig. 6A</figref>, the toner box 24 is almost a perfect fit in the box-accommodating chamber 73 at this time and is positioned lower than the supply roller 23 when viewed in the width direction. Further, the curved wall 103 of the toner box 24 opposes the bottom of the first protruding wall 75 provided in the lower case 18 and closely conforms to the shape of the first protruding wall 75. When both the process shutter 83 and the toner shutter 112 are in the closed position, the top surface (outer surface) of the toner shutter 112 closely contacts the bottom surface of the process shutter 83 in the closed position from the lower rear side. Further, the support shaft 97 of the lower case 18 (rotational center of the shutter unit 87) is aligned with the reference line X (a line extending in the width direction and passing through the center of curvature of the curved wall 103 provided in the toner box 24) in the width direction (see <figref idref="f0006">Fig. 6B</figref>).

0137At the same time, the right side surface of the toner box 24 (and particularly the operating part 118) is exposed through the box-mounting opening 84 (see <figref idref="f0006">Fig. 6C</figref>) in the right side of the lower case 18 (see <figref idref="f0006">Fig. 6B</figref>). Since the toner box 24 is mounted leftward into the developing unit 37, the operating part 118 on the right side surface of the toner box 24 is disposed on the upstream side of the toner box 24 relative to the mounting direction. However, since the input gear 108 (see <figref idref="f0008">Fig. 8A</figref>) is provided on the left side surface of the toner box 24, the input gear 108 is on the downstream side of the toner box 24 relative to the mounting direction.

0138The supply hole 104 of the curved wall 103 confronts the through-hole 77 in the first protruding wall 75 from the lower rear side with the process shutter 83 and toner shutter 112 interposed therebetween, since both the process shutter 83 and the toner shutter 112 are in the closed position. In this state, the supply hole 104 and through-hole 77 are not in communication with each other.

0139The input gear 108 of the toner box 24 (see <figref idref="f0008">Fig. 8A</figref>) is coupled with the coupling gear 85 provided on the left side wall of the lower case 18 (see <figref idref="f0006">Fig. 6C</figref>). When the process cartridge 16 is mounted in the main casing 2, the coupling gear 85 is coupled with a drive source (not shown) provided in the main casing 2. By coupling the input gear 108 to the coupling gear 85 in this case, the input gear 108 can be coupled to the main casing 2 via the coupling gear 85. Consequently, the input gear 108 can receive a drive force from the drive source in the main casing 2 and transfer this drive force to the agitator shaft 107 (and thereby to the agitator 111).

0140The left protrusions 114 provided on the toner shutter 112 (see <figref idref="f0008">Fig. 8A</figref>) are fitted from the right into the corresponding left recess parts 92 (see <figref idref="f0006">Fig. 6C</figref>) formed in the protruding part 91, which is disposed on the left rotating plate 88 (see <figref idref="f0007">Fig. 7</figref>) of the process shutter 83 (and specifically the shutter unit 87). Further, the right protrusions 116 provided on the toner shutter 112 (see <figref idref="f0008">Fig. 8A</figref>) are fitted from the right into the right recessed parts 95 provided on the right side of the process shutter 83 (see <figref idref="f0006">Fig. 6C</figref>).

0141When the toner box 24 is mounted in the lower case 18, the left protrusions 114 are engaged in the left recess parts 92 and the right protrusions 116 are engaged in the right recessed parts 95 within the developing unit 37. Through these engagements, the toner shutter 112 is coupled with the process shutter 83.

0142Further, when the toner box 24 is mounted in the corresponding process cartridge 16 (developing unit 37), the rack gear 120 provided on the operating part 118 of the toner box 24 meshes with the rack gear 96 provided on the right protruding part 93 of the shutter unit 87 from the bottom side thereof, as shown in <figref idref="f0006">Fig. 6B</figref>. Hence, the operating part 118 is engaged with the shutter unit 87 of the corresponding developing unit 37, thereby coupling the operating part 118 with the shutter unit 87 (process shutter 83).

0143Since the toner shutter 112 is coupled with the process shutter 83, as described above (see <figref idref="f0006">Fig. 6A</figref>), the operating part 118 is coupled with the toner shutter 112 via the process shutter 83 when the toner box 24 is mounted in the process cartridge 16.

0144The pawl 123 provided in the left surface of the operating part 118 (see <figref idref="f0008">Fig. 8E</figref>) contacts the right side surface of the right rotating plate 88 provided in the shutter unit 87 at a position lower than the right protruding part 93 so that the pawl 123 is completely accommodated in the recessed part 122 (see <figref idref="f0008">Fig. 8E</figref>) and does not catch on the curved wall 103 (not illustrated in the drawings). In this state, the operating part 118 in the rearward position can be rotated counterclockwise in a right side view.

0145When the operating part 118 is in the rearward position and the toner box 24 is mounted in the process cartridge 16, the operating part 118 can be rotated counterclockwise in a right side view. At this time, the shutter unit 87 coupled with the operating part 118 receives a drive force produced by rotating the operating part 118 via the rack gear 96. As a result, the shutter unit 87 rotates clockwise in a right side view about the support shaft 97 of the lower case 18 (the reference line X described above).

0146As the shutter unit 87 rotates clockwise in a right side view, the process shutter 83 of the shutter unit 87 and the toner shutter 112 coupled to the process shutter 83 rotate (slide) clockwise in a right side view. When the operating part 118 reaches the forward position shown in <figref idref="f0005">Fig. 5B</figref>, the process shutter 83 and the toner shutter 112 have rotated as far as possible clockwise in a right side view and have arrived in their respective open positions, as shown in <figref idref="f0005">Fig. 5A</figref>. When the process shutter 83 and toner shutter 112 are both in the open position, the supply hole 104 and the through-hole 77 are in communication with each other.

0147With the operating part 118 in the forward position, the protruding part 94 provided on the right rotating plate 88 of the shutter unit 87 is adjacent to the right side wall 102 of the toner box 24 from the right side thereof. Hence, the toner box 24 mounted in the process cartridge 16 cannot be pulled rightward (cannot be removed), thereby maintaining the mounted state of the toner box 24 in the process cartridge 16.

0148However, when the operating part 118 in the forward position is rotated clockwise in a right side view, the shutter unit 87 (process shutter 83) and the toner shutter 112 rotate (slide) counterclockwise in a right side view about the support shaft 97 of the lower case 18 (i.e., the reference line X) and are thus returned to their respective closed positions shown in <figref idref="f0006">Fig. 6A</figref>. As a result, the supply hole 104 and the through-hole 77 are no longer in communication.

0149Further, the protruding part 94 of the shutter unit 87 rotates together with the rotation of the shutter unit 87 and is thus shifted upward from the toner box 24 in a right side view, as illustrated in <figref idref="f0006">Fig. 6B</figref>. Consequently, the protruding part 94 is not in the way of the toner box 24 when the toner box 24 is moved rightward, allowing an operator to remove the toner box 24 from the process cartridge 16, as described above.

0150As described above, the operations of the toner shutter 112 to open and close the supply hole 104 are associated with the operations of the process shutter 83 to open and close the through-hole 77. The image-forming operation described above can be implemented when the toner box 24 is mounted in the process cartridge 16, as shown in <figref idref="f0005">Fig. 5A</figref>, and the process shutter 83 and toner shutter 112 are both in the open position.

0151<figref idref="f0009">Fig. 9</figref> is a right side cross-sectional view showing the process cartridge 16 when both the process shutter 83 and toner shutter 112 are in the open position, where <figref idref="f0009">Figs. 9A through 9D</figref> show the various rotational states of the agitator 111 over time. As shown in <figref idref="f0009">Fig. 9</figref>, during an image-forming operation, a drive force from the main casing 2 side is transmitted to the agitator 111 via the input gear 108 (see <figref idref="f0008">Fig. 8A</figref>) and the coupling gear 85 (see <figref idref="f0005">Fig. 5C</figref>). This drive force serves to rotate the agitator 111 counterclockwise in a right side view so that the agitator 111 agitates the toner (the dot filled regions indicated in <figref idref="f0009">Fig. 9</figref>). The rotating path of the support part 109 provided in the agitator 111 is indicated by a dotted line in <figref idref="f0001">Fig. 1</figref>.

0152Specifically, the agitating blade 110 of the rotating agitator 111 contacts the inner peripheral surface of the circumferential wall 101 constituting the box casing 100 in a somewhat bowed state and scrapes toner accumulated in the bottom of the box casing 100 upward along the rotating direction of the agitator 111, as illustrated in <figref idref="f0009">Fig. 9A</figref>. As the agitator 111 continues to rotate, the toner scraped upward by the agitating blade 110 approaches the supply hole 104 from the upstream side (rear side in <figref idref="f0009">Fig. 9B</figref>) with respect to the rotating direction of the agitator 111 (counterclockwise in a right side view), as illustrated in <figref idref="f0009">Fig. 9B</figref>.

0153As the agitator 111 continues to rotate, the agitating blade 110 pushes the toner confronting the supply hole 104, as described above, into the supply hole 104 from the upstream side in the rotating direction of the agitator 111, as illustrated in <figref idref="f0009">Fig. 9C</figref>. The toner pushed through the supply hole 104 is pushed further inward by successive quantities of toner that the agitating blade 110 pushes through the supply hole 104, as shown in <figref idref="f0009">Fig. 9D</figref>. Consequently, toner pushed through the supply hole 104 passes through the through-hole 77 in communication with the supply hole 104 enters the supply chamber 72 of the lower case 18 provided in the process cartridge 16, and accumulates on the accumulating part 75A, which is a portion on the top surface of the first protruding wall 75 positioned lower than the through-hole 77.

0154Thus, in addition to supplying toner into the supply chamber 72, the rotations of the agitator 111 suitably agitate the toner collected in the bottom of the box casing 100. Toner collected in the accumulating part 75A in the supply chamber 72, as described above, is subsequently supplied onto the supply roller 23 provided in the supply chamber 72. Thereafter, the supply roller 23 rotating clockwise in a right side view conveys this toner upward and supplies the toner to the developing roller 22 at the point of contact between the supply roller 23 and developing roller 22.

0155As the developing roller 22 rotates counterclockwise in a right side view, the toner supplied onto the developing roller 22 is conveyed between the outer peripheral surface of the developing roller 22 and the pressing part 80 on the thickness-regulating blade 78. The pressing part 80 regulates the thickness of toner carried on the outer peripheral surface of the developing roller 22 at a thin layer. This thin layer of toner is subsequently supplied to the photosensitive drum 19.

0156When more than the required amount of toner collects on the accumulating part 75A of the first protruding wall 75, the excess toner is shifted from the accumulating part 75A to the through-hole 77, sequentially passes through the through-hole 77 and the supply hole 104 and returns to the toner box 24. Hence, the toner circulates between the toner box 24 and the accumulating part 75A of the first protruding wall 75.

0157When both the process shutter 83 and the toner shutter 112 are in the open position, as described above, toner can move between the toner box 24 and the corresponding photosensitive drum 19. However, when the process shutter 83 and toner shutter 112 are both in the closed position, as shown in <figref idref="f0006">Fig. 6A</figref>, toner cannot move between the toner box 24 and the photosensitive drum 19 since both the supply hole 104 and the through-hole 77 are closed.

0158In this way, the process shutter 83 and the toner shutter 112 open and close between the toner box 24 and the corresponding photosensitive drum 19 to allow or restrict the movement of toner therebetween. The operating part 118 of the toner box 24 (see <figref idref="f0006">Fig. 6B</figref>) is operated in order to open and close the process shutter 83 and toner shutter 112.

(3) Mounting and removal of the process cartridges (toner boxes) with respect to the drawer frame

0159Next, operations for mounting the process cartridges 16 in and removing the process cartridges 16 from the drawer frame 15 of the drawer unit 14 will be described. The following description will assume that the drawer unit 14 is outside of the main casing 2.

0160The process cartridge 16 is placed above the drawer frame 15, as shown in <figref idref="f0004">Fig. 4</figref>. The front-to-rear position of the process cartridge 16 with respect to the drawer frame 15 (see <figref idref="f0001">Fig. 1</figref>) differs according to the color of toner accommodated in the toner box 24 of the process cartridge 16. Therefore, the process cartridge 16 is disposed at a prescribed position in the front-to-rear direction above the drawer frame 15.

0161At this time, the corresponding left and right guiding grooves 60 in the drawer frame 15 are positioned below the process cartridge 16. The process cartridge 16 is inserted into the drawer frame 15 by lowering the process cartridge 16 through the opening 15A formed in the top of the drawer frame 15. When the process cartridge 16 has been lowered a certain amount, the guiding grooves 60 receive the corresponding widthwise ends of the central shaft 19A provided in the photosensitive drum 19 of the process cartridge 16. As the central shaft 19A of the photosensitive drum 19 is guided in the guiding grooves 60, the process cartridge 16 proceeds downward at a forward slant that follows the extended direction of the guiding grooves 60.

0162When the central shaft 19A of the photosensitive drum 19 arrives at the deepest point (bottom) of the guiding grooves 60, as illustrated by the forwardmost process cartridge 16 in <figref idref="f0004">Fig. 4</figref>, the downward movement of the process cartridge 16 stops and the operation for mounting the process cartridge 16 in the drawer frame 15 is complete. Assembly of the drawer unit 14 is complete when all process cartridges 16 have been mounted in the drawer frame 15 according to the procedure described above. In this state, the drawer frame 15 supports the four process cartridges 16 (i.e., the four photosensitive drums 19 and developing units 37).

0163When mounting of the process cartridge 16 in the drawer frame 15 is complete, the entire right side surface of the toner box 24 in the process cartridge 16 is exposed outside the drawer frame 15 through the circular exposure holes 15C formed in the right wall of the drawer frame 15 at the same position as the toner box 24 with respect to the front-to-rear direction. Hence, the operator can manipulate the grip part 119 on the operating part 118 of the toner box 24 exposed through the circular exposure holes 15C when the process cartridge 16 is mounted in the drawer frame 15 in order to move the process shutter 83 and toner shutter 112 between the open and closed positions, as described above (see <figref idref="f0005">Figs. 5</figref> and <figref idref="f0006">6</figref>).

0164Further, by gripping the grip part 119 provided on the operating part 118 that is exposed in the circular exposure holes 15C, the operator can pull the toner box 24 through the circular exposure holes 15C and extract the toner box 24 from the process cartridge 16 (i.e., from the drawer frame 15).

0165Conversely, by inserting the toner box 24 through the circular exposure holes 15C formed on the right side of the drawer frame 15 and thus through the box-mounting opening 84 in the corresponding process cartridge 16 (see <figref idref="f0006">Fig. 6C</figref>) so that the toner box 24 is accommodated in the box-accommodating chamber 73, the operator can mount the toner box 24 in the process cartridge 16 (i.e., the drawer frame 15).

0166In this way, the operator can move the toner box 24 along the width direction through the circular exposure holes 15C while the process cartridge 16 is mounted in the drawer frame 15 in order to remove only the toner box 24 from or mount only the toner box 24 in the drawer unit 14.

0167Further, when the operator pulls a process cartridge 16 that is mounted in the drawer frame 15 upward until the entire process cartridge 16 is lifted above the opening 15A formed in the top of the drawer frame 15, removal of the process cartridge 16 from the drawer frame 15 is complete.

4. Mounting and removal of the drawer unit relative to the main casing

0168Next, the procedure for mounting the drawer unit 14 in and removing the drawer unit 14 from the main casing 2 will be described.

0169While the drawer unit 14 is not mounted in the main casing 2, as illustrated in <figref idref="f0003">Fig. 3</figref>, the operator first pivots the pivoting unit 52 upward and subsequently rotates the second front cover 50 downward on the front side to expose the unit-mounting opening 49, as described above. Next, the operator inserts the drawer unit 14 through the unit-mounting opening 49 into the unit-accommodating chamber 40. The drawer unit 14 is inserted substantially horizontally along the guide parts 42.

0170When inserting the drawer unit 14 into the unit-accommodating chamber 40, the wheels 64 on the rear end of the drawer unit 14 roll over the first guiding roller 43 (see <figref idref="f0002">Fig. 2</figref>), first sloped wall 44 (see <figref idref="f0002">Fig. 2</figref>), and first guiding rail 45 of the corresponding guide part 42 (i.e., the guide part 42 on the same widthwise side) as the drawer unit 14 progresses rearward. When the wheels 64 reach the corresponding first guiding rails 45, the flanges 62 of the drawer unit 14 (see <figref idref="f0004">Fig. 4</figref>) come to rest on the corresponding first guiding rollers 43 (see <figref idref="f0002">Fig. 2</figref>).

0171Thus, as the drawer unit 14 progresses rearward, the wheels 64 roll over the first guiding rails 45 while the flanges 62 (see <figref idref="f0004">Fig. 4</figref>) slide rearward over the rolling first guiding rollers 43 (see <figref idref="f0002">Fig. 2</figref>). Accordingly, the drawer unit 14 moves rearward in a stable state. Subsequently, the wheels 64 on the drawer unit 14 roll over the second guiding rollers 46, second sloped walls 47, and second guiding rails 48 before coming to a halt at the curved rear ends of the second guiding rails 48. Thus, the drawer unit 14 moves diagonally downward and rearward while remaining in a level state before halting in the position shown in <figref idref="f0002">Fig. 2</figref>.

0172Through this process, the drawer unit 14 is mounted in the main casing 2. At this time, the positioning shafts 61 on the drawer frame 15 contact the main casing 2 (more specifically the partitioning wall 41), which contact further fixes the position of the drawer unit 14 relative to the main casing 2.

0173Next, the operator closes the second front cover 50 by rotating the second front cover 50 upward and closes the pivoting unit 52 by pivoting the pivoting unit 52 downward, as shown in <figref idref="f0001">Fig. 1</figref>. Through this operation, the intermediate transfer belt 27 of the transfer unit 12 contacts the tops of the photosensitive drums 19 provided in the drawer unit 14.

0174To remove the drawer unit 14 from the main casing 2, the operator sequentially opens the pivoting unit 52 and second front cover 50 to expose the unit-mounting opening 49, as shown in <figref idref="f0002">Fig. 2</figref>, and subsequently pulls the drawer unit 14 forward through the unit-mounting opening 49 (see <figref idref="f0003">Fig. 3</figref>).

0175The drawer unit 14 is completely removed from the main casing 2 when the operator has pulled the drawer unit 14 forward in a substantially level state until the four circular exposure holes 15C formed in the right side wall of the drawer frame 15 are exposed on the right side, as shown in <figref idref="f0004">Fig. 4</figref>. Thus, the drawer unit 14 (drawer frame 15) can be removed from the main casing 2 along the front-to-rear direction (the juxtaposed direction of the four photosensitive drums 19 shown in <figref idref="f0001 f0002 f0003">Figs. 1 through 3</figref>).

0176While the drawer unit 14 (drawer frame 15) is pulled out of the main casing 2 in this way, the operator can remove toner boxes 24 from or insert toner boxes 24 into the process cartridges 16 (developing units 37) supported in the drawer unit 14 through the corresponding circular exposure holes 15C of the drawer frame 15 along the width direction, as described above. Further, by manipulating the operating part 118 of each toner box 24 in this state, the operator can move the process shutter 83 and toner shutter 112 between their respective open and closed positions (see <figref idref="f0005">Figs. 5</figref> and <figref idref="f0006">6</figref>).

5. Effects of the first embodiment

0177(1) In the toner box 24 shown in <figref idref="f0009">Fig. 9</figref>, the agitator 111 is disposed inside the box casing 100, which serves to accommodate toner. The agitator 111 agitates toner in the box casing 100 by rotating about its agitator shaft 107 extending in the width direction.

0178As described above, the box casing 100 has the curved wall 103. The curved wall 103 curves in an arc shape whose convex side faces the interior of the box casing 100 (see <figref idref="f0005">Fig 5C</figref>). The center of curvature of the curved wall 103 is the reference line X. Therefore, when the agitator 111 rotates inside the box casing 100, the agitating blade 110 can contact and pass over the curved wall 103 protruding into the box casing 100.

0179The supply hole 104 is formed in the upstream side of the curved wall 103 with respect to the rotating direction of the agitator 111 (the counterclockwise direction in a right side view) to provide communication between the interior and exterior of the box casing 100. Accordingly, the supply hole 104 through which toner accommodated in the box casing 100 passes when expelling the toner outside of the toner box 24 can be disposed along the rotating path of the agitator 111 so as to oppose the rotating agitator 111 on the downstream side with respect to the rotating direction of the agitator 111.

0180As a result, toner conveyed by the rotating agitator 111 in the rotating direction thereof is efficiently supplied to the supply hole 104. Hence, the configuration of the toner box 24 enables toner accommodated in the box casing 100 to be efficiently expelled therefrom.

0181(2) Since the toner shutter 112 moves along the circumferential direction of the curved wall 103 in order to open and close the supply hole 104 (see <figref idref="f0008">Figs. 8A through 8D</figref>), the toner shutter 112 can appropriately allow or restrict the passage of toner through the supply hole 104.

0182(3) The agitator 111 includes the support part 109 formed of a hard material and extending radially outward from the agitator shaft 107, and the flexible agitating blade 110 that is supported on the support part 109 and extends radially outward therefrom.

0183With this construction, the agitating blade 110 supported on the support part 109 bows a suitable amount when the agitator 111 rotates in order to convey a large amount of toner in the rotating direction of the agitator 111. Since the agitating blade 110 also flexes a suitable amount when passing over the curved wall 103 (see <figref idref="f0009">Fig. 9D</figref>), the agitating blade 110 does not get caught on the curved wall 103, enabling the agitator 111 to rotate smoothly.

0184(4) Since the cross section of the box casing 100 when viewed along the width direction is substantially circular in shape and substantially matches the rotating path of the agitator 111, the agitator 111 can convey toner within the box casing 100 in the rotating direction of the agitator 111 without toner leaking around the agitator 111. Accordingly, the agitator 111 can convey toner to the supply hole 104 with even better efficiency and can agitate all of the toner within the box casing 100 thoroughly.

0185(5) As shown in <figref idref="f0008">Fig. 8</figref>, the toner shutter 112 is supported by the box casing 100 at a plurality of locations along the width direction. Therefore, the toner shutter 112 can open and close the supply hole 104 in a more stable state than when the toner shutter 112 is supported at only one location.

0186(6) As shown in <figref idref="f0009">Fig. 9</figref>, the developing unit 37 includes the toner box 24, and the lower case 18 in which the toner box 24 is detachably mounted, as described above.

0187The first protruding wall 75 is disposed in the lower case 18 opposite the curved wall 103 of the toner box 24 and curves in an arc shape that conforms with the shape of the curved wall 103. That is, the first protruding wall 75 protrudes in an arc shape toward the curved wall 103 of the toner box 24.

0188The lower case 18 supports the developing roller 22, which carries toner to be supplied to an electrostatic latent image, and the supply roller 23, which supplies toner from the toner box 24 to the developing roller 22 in the developing unit 37 described above.

0189The supply roller 23 is supported in the lower case 18 such that the outer peripheral surface of the supply roller 23 follows the first protruding wall 75 and the curved wall 103. The supply roller 23 can be compactly disposed in the developing unit 37 so as to fit within the inner region of the first protruding wall 75, thereby enabling the entire developing unit 37 to be made more compact (smaller vertically in this case).

0190(7) In the developing unit 37 described above, the through-hole 77 is formed in the first protruding wall 75 at a position confronting the supply roller 23 opposite the supply hole 104 of the toner box 24. The process shutter 83 is provided to open and close the through-hole 77. Hence, when the process shutter 83 opens the through-hole 77 while the supply hole 104 is open, toner is allowed to move between the toner box 24 and supply roller 23 (see <figref idref="f0005">Fig. 5A</figref>). When the process shutter 83 closes the through-hole 77, toner is restricted from moving between the toner box 24 and supply roller 23 (see <figref idref="f0006">Fig. 6A</figref>).

0191(8) The support member 86 is provided in the lower case 18 of the developing unit 37 (see <figref idref="f0007">Fig. 7</figref>). The support member 86 can freely rotate about the reference line X that extends in the width direction and passes through the center of curvature of the curved wall 103 (see <figref idref="f0005">Figs. 5B</figref> and <figref idref="f0006">6B</figref>).

0192The rotational center of the support member 86 is the reference line X. Since the process shutter 83 is integrally formed with the support member 86, the rigidity of the entire shutter unit 87 is enhanced. Since the process shutter 83 is supported on the support member 86 (see <figref idref="f0007">Fig. 7</figref>), the process shutter 83 can be rotated to open and close the through-hole 77 through the simple operation of rotating the support member 86 (see <figref idref="f0005">Figs. 5A</figref> and <figref idref="f0006">6A</figref>).

0193(9) As shown in <figref idref="f0008">Fig. 8</figref>, the operating part 118 engaged with the support member 86 is provided on the toner box 24 (see <figref idref="f0005">Figs. 5B</figref> and <figref idref="f0006">6B</figref>). Hence, the operator can easily rotate the support member 86 and process shutter 83 by operating the operating part 118 in order to open and close the through-hole 77 (see <figref idref="f0005">Figs. 5A</figref> and <figref idref="f0006">6A</figref>).

0194(10) When the toner box 24 is mounted in the lower case 18, as shown in <figref idref="f0006">Fig. 6</figref>, the left protrusions 114 of the toner shutter 112 are engaged in the left recess parts 92 of the process shutter 83 and the right protrusions 116 of the toner shutter 112 are engaged in the right recessed parts 95 of the process shutter 83 (see <figref idref="f0006">Figs. 6C</figref>, <figref idref="f0008">8A, and 8B</figref>). In this way, the operations of the toner shutter 112 to open and close the supply hole 104 are associated with the operations of the process shutter 83 to open and close the through-hole 77. Hence, both the supply hole 104 and through-hole 77 can be opened and closed together, thereby simplifying the operation.

0195(11) As shown in <figref idref="f0009">Fig. 9</figref>, the supply roller 23 is disposed at a higher position than the toner box 24. Accordingly, toner accommodated in the toner box 24 must be conveyed upward to be supplied to the supply roller 23.

0196However, with the toner box 24 of the preferred embodiment, the toner accommodated in the box casing 100 can be efficiently supplied to the supply roller 23 through the supply hole 104 formed in the toner box 24, even though the toner is being supplied upward, because the supply hole 104 is formed at a position upstream of the curved wall 103 with respect to the rotating direction of the agitator 111.

0197(12) The first protruding wall 75 provided in the developing unit 37 is arc-shaped with the convex side on the bottom. With this configuration, the accumulating part 75A is formed in the top of the first protruding wall 75 at a position lower than the bottom end of the through-hole 77.

0198Therefore, when toner accommodated in the box casing 100 of the toner box 24 is conveyed upward through the supply hole 104 and arrives at the through-hole 77, rather than falling back into the box casing 100, the toner accumulates in the accumulating part 75A of the first protruding wall 75, which is adjacent to the supply roller 23 and positioned lower than the bottom edge of the through-hole 77 (see <figref idref="f0009">Fig 9D</figref>). Accordingly, toner can be efficiently supplied to the supply roller 23.

0199(13) In the color printer 1 shown in <figref idref="f0001">Fig. 1</figref>, a plurality of developing units 37 is disposed beneath the plurality of photosensitive drums 19 juxtaposed horizontally for developing electrostatic latent images formed on the corresponding photosensitive drums 19. Thus, each of the developing units 37 is disposed beneath a corresponding photosensitive drum 19. The drawer frame 15 provided for supporting the plurality of photosensitive drums 19 and developing units 37 is disposed in the main casing 2 of the color printer 1 and can be pulled out from the main casing 2 along the juxtaposed direction of the photosensitive drums 19 (see <figref idref="f0003">Fig. 3</figref>).

0200The toner box 24 is also disposed in each developing unit 37 for accommodating toner needed to develop the electrostatic latent image on the corresponding photosensitive drum 19.

0201As shown in <figref idref="f0004">Fig. 4</figref>, the toner boxes 24 can be mounted in and removed from the corresponding developing units 37 supported in the drawer frame 15 along the axial direction of the photosensitive drums 19 (width direction) while the drawer frame 15 is pulled out of the main casing 2. In this way, the toner boxes 24 can be easily mounted in and removed from the developing units 37 without troubling the operator to perform such operations as removing the photosensitive drums 19 above the developing units 37.

0202This construction has the effect of improving the ease of maintaining the toner boxes 24 provided in the developing units 37 when the developing units 37 are disposed beneath the photosensitive drums 19 juxtaposed in a horizontal direction.

0203(14) With the color printer 1 of the preferred embodiment, the process shutter 83 and toner shutter 112 shown in <figref idref="f0005">Figs. 5A</figref> and <figref idref="f0006">6A</figref> allow or restrict the movement of toner by opening and closing the passage between the toner boxes 24 and corresponding photosensitive drums 19.

0204The operating part 118 is provided on the upstream side (right side surface) of the toner box 24 with respect to the mounting direction in which the toner box 24 is mounted in the corresponding developing unit 37 (leftward and also referred as the "mounting direction" hereafter) in order to open and close the process shutter 83 and toner shutter 112. Hence, by operating the operating part 118 disposed on the upstream side of the toner box 24 with respect to the mounting direction, i.e., in an easily accessible location, the operator can easily open the shutters (see <figref idref="f0005">Figs. 5</figref> and <figref idref="f0006">6</figref>).

0205The input gear 108 is provided on the downstream side (left side surface) of the toner box 24 with respect to the mounting direction (see <figref idref="f0008">Figs. 8A and 8B</figref>). The input gear 108 is coupled to the main casing 2 (more accurately, to the coupling gear 85 provided on the left side wall of the lower case 18; see <figref idref="f0006">Fig. 6C</figref>) in order to receive a drive force from the main casing 2 and transmit this force to the agitator 111.

0206Accordingly, as illustrated in <figref idref="f0006">Fig. 6</figref>, the input gear 108 can be coupled with the main casing 2 (strictly speaking, the coupling gear 85; see <figref idref="f0006">Fig. 6C</figref>) when the toner box 24 is completely mounted in the developing unit 37. With this construction, the toner box 24 can be more smoothly mounted in the developing unit 37 than when the input gear 108 couples with the main casing 2 while the toner box 24 is partially mounted in the developing unit 37. Further, by providing the input gear 108 on the downstream side of the toner box 24 with respect to the mounting direction, sufficient space can be allocated for the operating part 118 provided on the upstream side of the toner box 24 with respect to the mounting direction (see <figref idref="f0008">Fig. 8A</figref>).

0207(15) The first protruding wall 75 provided in each developing unit 37 arcs downward so that the top portion of the first protruding wall 75 (the accumulating part 75A) is positioned lower than the bottom edge of the through-hole 77.

0208Therefore, when toner accommodated in the box casing 100 of the toner box 24 is conveyed upward through the supply hole 104 and arrives at the through-hole 77, rather than falling back down into the box casing 100, the toner accumulates in the accumulating part 75A of the first protruding wall 75 at a position adjacent to the supply roller 23 and lower than the bottom edge of the through-hole 77 (see <figref idref="f0009">Fig. 9D</figref>). Accordingly, toner can be efficiently supplied to the supply roller 23.

6. Variations of the first embodiment

0209<figref idref="f0010">Fig. 10</figref> shows a modification of the first embodiment applied to the toner box 24 in <figref idref="f0008">Fig. 8D</figref>.

0210In the preferred embodiment described above, a single supply hole 104 is formed in the curved wall 103 of the toner box 24 (see <figref idref="f0008">Fig. 8D</figref>). However, a plurality of supply holes 104 may be formed in the curved wall 103, as in the variation shown in <figref idref="f0010">Fig. 10</figref>. In this case, the through-hole 77 in the process cartridge 16 (see <figref idref="f0009">Fig. 9</figref>) should also be formed as a plurality of through-holes 77 equivalent to the number of supply holes 104 and formed at a position where the plurality of supply holes 104 confronts when the toner box 24 is mounted in the process cartridge 16. In the example shown in <figref idref="f0010">Fig. 10</figref>, three supply holes 104 are aligned in the width direction. The widthwise dimension of each supply hole 104 is approximately one-third that of the single supply hole 104 provided in the first embodiment (see <figref idref="f0008">Fig. 8D</figref>).

0211With this construction, toner within the toner box 24 (box casing 100) is supplied into the supply chamber 72 of the process cartridge 16 (see <figref idref="f0009">Fig. 9</figref>) via the center supply hole 104 and the center through-hole 77. Toner supplied into the supply chamber 72 that is not supplied onto the supply roller 23 falls by its own weight sequentially through the two through-holes 77 on the widthwise ends and the two supply holes 104 on the widthwise ends, and is returned to the toner box 24.

0212In this way, toner is circulated between the toner box 24 and supply chamber 72. In this example, a seal (not shown) may also be provided in the toner box 24 to prevent toner from leaking through the supply holes 104 between the curved wall 103, in which the supply holes 104 are formed, and the toner shutter 112. Generally, the seal is provided to fringe the edges of the supply holes 104 (not illustrated in the drawings).

0213If the size of each supply hole 104 is reduced by providing a plurality of supply holes 104, as in the present modification, the amount of sealing material required to fringe the supply holes 104 can be reduced. Reducing the amount of required sealing material reduces the resistance generated when the toner shutter 112 slides against the seal. Thus, the toner shutter 112 slides more smoothly.

7. Second embodiment

0214Next, a laser printer 201 according to a second embodiment of the present invention will be described while referring to <figref idref="f0011 f0012 f0013 f0014 f0015 f0016 f0017 f0018 f0019">Figs. 11 through 19</figref>. Before describing the features of the present invention, a brief description will be given for the general structure of the laser printer 201.

8. General structure of the laser printer

0215As shown in <figref idref="f0011">Fig. 11</figref>, the laser printer 201 includes a main casing 202, a feeding unit 203, and an image-forming unit 204.

0216The main casing 202 is formed in a hollow box shape and includes an opening 202A formed in the front wall thereof, and a front cover 221 disposed on the front wall and capable of pivoting forward and rearward to open and close the opening 202A. The top surface of the main casing 202 is configured as a discharge tray 222 for receiving and holding sheets of a paper P after printing.

0217The feeding unit 203 includes a paper tray 231 and a feeding mechanism 232. The feeding mechanism 232 of the feeding unit 203 separates and conveys the paper P accommodated in the paper tray 231 one sheet at a time to the image-forming unit 204. The image-forming unit 204 includes a scanning unit 241, a process cartridge 242, and a fixing unit 243.

0218The scanning unit 241 has a well-known construction that includes primarily a laser light-emitting unit (not shown), as well as a polygon mirror and a plurality of lenses and reflecting mirrors (not denoted with reference numerals in the drawings). The laser beam emitted from the laser light-emitting unit follows a path within the scanning unit 241 indicated by a two-dot chain line in <figref idref="f0011">Fig. 11</figref> and is irradiated in a high-speed scan over the surface of a photosensitive drum 251 provided in the process cartridge 242.

0219The process cartridge 242 is detachably mounted in the main casing 202 when the front cover 221 is opened. The process cartridge 242 includes a process cartridge 205, and a developing unit 206 pivotably held by the process cartridge 205.

0220The process cartridge 205 includes the photosensitive drum 251, a transfer roller 252, and a Scorotron charger 253.

0221As shown in <figref idref="f0012">Fig. 12</figref>, the developing unit 206 includes a developing device 207, and a toner cartridge 208 that is detachably mounted on the developing device 207. When mounted on the process cartridge 205, the developing unit 206 is supported on the side walls of the process cartridge 205 and is capable of moving in the front-to-rear direction within elongated holes 205A formed in the side walls. The developing unit 206 is also pressed against the photosensitive drum 251 by springs 205B that urge the developing unit 206 rearward via the toner cartridge 208 (see <figref idref="f0012">Fig. 12</figref>).

0222The developing device 207 includes a developing roller 271, a thickness-regulating blade 272, and a supply roller 273. The toner cartridge 208 accommodates toner internally and is capable of conveying this toner to the developing device 207. The developing device 207 and toner cartridge 208 will be described later in greater detail.

0223With the process cartridge 242 having this construction, the toner cartridge 208 conveys toner into the developing device 207, and the supply roller 273 of the developing device 207 supplies this toner onto the developing roller 271, at which time the toner is positively tribocharged between the supply roller 273 and developing roller 271. As the developing roller 271 rotates, the toner carried on the surface of the developing roller 271 passes between the thickness-regulating blade 272 and developing roller 271, at which time the thickness-regulating blade 272 regulates the layer of toner carried on the surface of the developing roller 271 to a prescribed thickness.

0224In the meantime, in the process cartridge 205 shown in <figref idref="f0011">Fig. 11</figref>, the Scorotron charger 253 applies a uniform positive charge to the surface of the photosensitive drum 251, after which the scanning unit 241 irradiates a laser beam in a high-speed scan to form an electrostatic latent image on the surface of the photosensitive drum 251 based on image data by reducing the electric potential in exposed areas. Next, the rotating developing roller 271 supplies toner to the electrostatic latent image formed on the surface of the photosensitive drum 251 as the toner carried on the developing roller 271 rotates into and contacts the photosensitive drum 251.

0225In this way, toner selectively attracted to the surface of the photosensitive drum 251 develops the latent image into a visible toner image through reverse development. Thereafter, the toner image carried on the surface of the photosensitive drum 251 is transferred onto a sheet of paper P as the sheet is conveyed between the photosensitive drum 251 and transfer roller 252.

0226The fixing unit 243 includes a heating roller 243A and a pressure roller 243B. The fixing unit 243 functions to fix toner transferred to a sheet of paper P with heat as the sheet passes between the heating roller 243A and pressure roller 243B. After the toner image has been fixed to the sheet in the fixing unit 243, discharge rollers 244 disposed downstream of the fixing unit 243 discharge the sheet onto the discharge tray 222.

9. Structure of the developing unit

0227Next, the developing device 207 and toner cartridge 208 constituting the developing unit 206 will be described in greater detail. First, a description of the toner cartridge 208 will be given.

10. Structure of the toner cartridge

0228As shown in <figref idref="f0012">Fig. 12</figref>, the toner cartridge 208 is provided with a first accommodating unit 281, a second accommodating unit 282, and a third accommodating unit 283 that each accommodate toner. The toner cartridge 208 also has a grip part 283A that protrudes forward from the third accommodating unit 283.

0229When the toner cartridge 208 is mounted on the developing device 207 (and specifically when the developing unit 206 is mounted in the main casing 202), the first accommodating unit 281 is positioned adjacent to the developing device 207 in a horizontal direction. The first accommodating unit 281 is formed in a substantially hollow cylindrical shape. Among the walls constituting the first accommodating unit 281 is an adjoining wall 281A adjoined with the developing device 207. The adjoining wall 281A has a concave shape that is depressed toward the interior of the first accommodating unit 281.

0230More specifically, the adjoining wall 281A is curved in an arc shape in a cross-sectional view. The center of the arc shape is a reference line BL (the rotational center of a process shutter S2 described later with reference to <figref idref="f0018">Figs. 18</figref> and <figref idref="f0019">19</figref>) provided rearward (outside) of the first accommodating unit 281 and extending in the left-to-right direction (parallel to the rotational axis of an agitating member described later. For convenience, the adjoining wall 28 1 A will also be referred to as a "first arc wall W1" in the following description. The first arc wall W1 functions as a wall portion.

0231As shown in <figref idref="f0013">Fig. 13</figref>, a first supply hole W11 and second supply holes W12 are formed in the first arc wall W1 so as to penetrate the interior of the first accommodating unit 281.

0232A single first supply hole W 11 is formed in the upper half of the first arc wall W1 at a position in the left-to-right center thereof. The two second supply holes W12 are formed in the lower half of the first arc wall W1, with one positioned at each of the left and right ends thereof. Hence, the second supply holes W12 are offset from the first supply hole W11 both in the left-to-right direction and the vertical direction.

0233By forming the first supply hole W 11 in the top half of the first arc wall W1, the first supply hole W11 is disposed above the second supply hole W12 and provides communication in a downward slope from the first accommodating unit 281 to the developing device 207. Further, by forming the second supply holes W12 in the lower half of the first arc wall W1, the second supply holes W12 are disposed lower than the first supply hole W11 and provide communication in an upward slope from the first accommodating unit 281 to the developing device 207.

0234Further, the second supply holes W12 are both positioned outside of a printing area PA (see <figref idref="f0014">Fig. 14A</figref>). The printing area PA denotes the maximum width (length in a direction orthogonal to the conveying direction of the paper P) for a toner image to be transferred onto the paper P. Providing the second supply holes W12 outside of the printing area PA in this way suppresses the accumulation of toner in the developing device 207 outside of the printing area PA.

0235As shown in <figref idref="f0013">Fig. 13</figref>, a toner shutter S 1 is disposed on the rear side of the first arc wall W1. The toner shutter S1 opens and closes the first supply hole W11 and second supply holes W12 by moving along the circumference of the first arc wall W1. The toner shutter S1 includes a thin metal plate S 11 formed in an arc shape that conforms to the first arc wall W1, and a pair of sliding pieces S12 disposed one on each of the left and right ends of the metal plate S11.

0236An opening S 13 that is larger than each of the second supply holes W12 is formed one on each of the left and right sides of the metal plate S11 in the upper half thereof. When the toner shutter S 1 is in the closed position shown in <figref idref="f0014">Fig. 14A</figref>, the first supply hole W11 is closed by a region of the metal plate S11 between the openings S 13, and the second supply holes W12 are closed by regions of the metal plate S11 below the respective openings S 13.

0237When the toner shutter S1 is moved downward from this closed position to the open position, as shown in <figref idref="f0014">Fig. 14B</figref>, the top edge of the S11 is moved lower than the first supply hole W11, thereby opening the first supply hole W11, and the openings S13 are positioned overlapping the second supply holes W 12, thereby opening the second supply holes W12.

0238As shown in <figref idref="f0013">Fig. 13</figref>, the sliding pieces S 12 are slidably supported on the toner cartridge 208. A plurality of protrusions S14 is formed on each sliding piece S12. The protrusions S14 protruding frontward engage with a plurality of depressions S23 (see <figref idref="f0018">Fig. 18</figref>) formed in engaging plates S22 of a process shutter S2 described later.

0239As shown in <figref idref="f0012">Fig. 12</figref>, a single first agitator A1 is provided in the first accommodating unit 281. The first agitator A1 functions as an agitating member. The first agitator A 1 rotates in the first accommodating unit 281 so as to scrape over the first arc wall W1 in a direction from top to bottom (counterclockwise in <figref idref="f0012">Fig. 12</figref>). The first agitator A1 is configured of a rotational shaft A11 rotatably supported in side walls 284 constituting the left and right walls of the toner cartridge 208 (first accommodating unit 281), a support part A12 extending radially outward from the rotational shaft A11, and an agitating blade A13 supported on the support part A12.

0240As shown in <figref idref="f0015">Fig. 15</figref>, the agitating blade A13 is configured of a first film A14 disposed in the left-to-right center thereof, and second films A15 disposed two on each of the left and right sides of the first film A14. The second films A15 functions as a transfer blade. Overall, the agitating blade A13 has a width capable of extending over both the first supply hole W11 and the second supply holes W12 (a sufficient width for sliding over both openings).

0241The first film A14 is a rectangular elastically deformable film formed at a width approximately equivalent to the width (left-to-right dimension) of the first supply hole W11. As shown in <figref idref="f0012">Fig. 12</figref>, the first film A14 is in a flexed state while contacting an opposed wall 281C formed between the first accommodating unit 281 and second accommodating unit 282 and having an arc-shaped cross section; and the first arc wall W1 (first supply hole W11), a top wall 281D, and a bottom wall 281E forming the first accommodating unit 281.

0242As shown in <figref idref="f0015">Fig. 15</figref>, the opposed wall 281C is erected for blocking a wide central opening that provides communication between the first accommodating unit 281 and second accommodating unit 282 (see also <figref idref="f0012">Figs. 12</figref> and <figref idref="f0016">16</figref>). More specifically, the opposed wall 281C is disposed opposite the first supply hole W 11 horizontally and is formed with a greater width than that of the first film A14. With this construction, toner can be suitably conveyed by the first film A14 upward between the first film A14 and opposed wall 281C and, thereafter, can be suitably conveyed toward the first supply hole W11 between the first film A14 and top wall 281D.

0243The second films A15 are elastically deformable films, each of which has a leading edge A 16 that slides in contact with the inner surface of the first accommodating unit 281. The second films A15 are configured so that their leading edges A16 slope toward the rotational center of the first agitator A1 (rotational shaft A11) as the leading edges A16 approach the first film A14 side. Specifically, by forming the second films A15 of a suitable shape and setting the orientation mentioned-above, the second films A15 can slide over the inner surface of the first accommodating unit 281 in such a way that the inner portion of the leading edge A16 in the left-to-right direction slides behind the outer portion in the left-to-right direction.

0244With the inner portions being behind the outer portions with respect to the left-to-right direction when the leading edges A16 of the second films A15 slide over the inner surface of the first accommodating unit 281, the second films A15 can convey toner from the second supply holes W12 formed in the left and right outer sides toward the first supply hole W11 formed in the center. Each of the second films A15 has a hole A17 formed in the center region thereof. The holes A17 are provided to ensure that the second films A15 do not push back more than the necessary amount of toner into the second accommodating unit 282 from among toner that was returned into the first accommodating unit 281 via the second supply holes W12.

0245As shown in <figref idref="f0012">Fig. 12</figref>, the second accommodating unit 282 is positioned adjacent to the first accommodating unit 281 in a horizontal direction when the toner cartridge 208 is mounted on the developing device 207 (and specifically when the developing unit 206 is mounted in the main casing 202). The main casing 202 has a substantially hollow, cylindrical shape. The rear end of the second accommodating unit 282 is in communication with the first accommodating unit 281 in all regions other than the opposed wall 281C described above, while substantially the entire front side is in communication with the third accommodating unit 283.

0246A second agitator A2 is disposed inside the second accommodating unit 282. The second agitator A2 functions to convey toner accumulated in the bottom of the second accommodating unit 282 toward the first accommodating unit 281 by rotating in a direction opposite the rotational direction of the first agitator A1 (clockwise in <figref idref="f0012">Fig. 12</figref>). The second agitator A2 functions as a transfer member A2. The second agitator A2 includes a rotational shaft A21 and a support part A22 having substantially the same structure as the first agitator A1 described above, and an agitating blade A23 having a different structure from that in the first agitator A1.

0247As shown in <figref idref="f0015">Fig. 15</figref>, the agitating blade A23 is configured of a pair of elastically deformable third films A24 disposed in the left-to-right center of the agitating blade A23, and rectangular elastically deformable fourth films A25 disposed two on both the left and right sides of the third films A24.

0248The third films A24 are juxtaposed in the left-to-right direction and fall within the width of the opposed wall 281C. Each third film A24 has a leading edge A26 for slidingly contacting the inner surface of the second accommodating unit 282. The leading edges A26 slope toward the rotational center of the second agitator A2 (rotational shaft A21) as the leading edges A26 approach the adjacent third film A24 side. Specifically, by forming the third films A24 in a suitable shape and suitably setting the orientation mentioned-above, the third films A24 can rotate so that the outer portions of the leading edges A26 in the left-to-right direction are behind the inner portions of the leading edges A26 in the left-to-right direction when sliding along the inner surface of the second accommodating unit 282.

0249With the outer portions of the leading edges A26 in the left-to-right direction sliding over the inner surface of the second accommodating unit 282 behind the inner portions of the same, the third films A24 can convey toner outward in the left and right directions. Hence, the third films A24 serve as blades that convey toner from the left-to-right center to the left and right outer sides. Accordingly, toner conveyed by the third films A24 gravitates to the fourth film A25 sides so as to avoid the opposed wall 281C disposed on the rear side of the third films A24. Subsequently, the fourth films A25 supply the toner into the first accommodating unit 281.

0250As shown in <figref idref="f0012">Fig. 12</figref>, the third accommodating unit 283 is disposed adjacent to the second accommodating unit 282 in a horizontal direction when the toner cartridge 208 is mounted on the developing device 207 (and specifically when the developing unit 206 is mounted in the main casing 202). The third accommodating unit 283 has a substantially hollow cylindrical shape, with substantially the entire rear portion in communication with the second accommodating unit 282.

0251A third agitator A3 is disposed inside the third accommodating unit 283. The third agitator A3 conveys toner that accumulates in the bottom of the third accommodating unit 283 toward the second accommodating unit 282 by rotating in a direction opposite the rotating direction of the first agitator A1 (clockwise in <figref idref="f0012">Fig. 12</figref>). The third agitator A3 includes a rotational shaft A31 and a support part A32 having substantially the same structure as the second agitator A2 described above, and an agitating blade A33 having a slightly different structure from the second agitator A2.

0252As shown in <figref idref="f0015">Fig. 15</figref>, the agitating blade A33 has a single fifth film A34 that is rectangular in shape and elastically deformable disposed in the left-to-right center of the agitating blade A33, and fourth films A25 identical to those in the support part A22 disposed two on each of the left and right sides of the fifth film A34.

0253As shown in <figref idref="f0013">Fig. 13</figref>, a first agitator gear AG1, a second agitator gear AG2, and a third agitator gear AG3 are coaxially and integrally provided on one end of the respective first agitator A1, second agitator A2, and third agitator A3. Further, two gears G are disposed between the first agitator gear AG1 and second agitator gear AG2, and a single gear G is disposed between the second agitator gear AG2 and third agitator gear AG3. A coupling part CP is formed over the central shaft of the third agitator gear AG3.

0254With this construction, when a drive force from a drive source provided in the casing 202 (not shown) is transmitted to the coupling part CP formed on the third agitator gear AG3, the third agitator gear AG3 rotates in the same direction as the second agitator gear AG2 (counterclockwise in <figref idref="f0013">Fig. 13</figref>) and in the opposite direction as the first agitator gear AG1 (clockwise in <figref idref="f0013">Fig. 13</figref>). All of the gears are covered with a gear case 285. The gear case 285 is detachably mounted on the right side wall 284 of the toner cartridge 208.

0255The gear case 285 has a hole 285A formed therein for inserting the coupling part CP described above, and a shaft part 285B formed thereon and protruding outward (rightward). The gear case 285 functions to pivotably support an operating member 286 that serves to open and close the toner shutter S 1 described above and a process shutter S2 described later (see <figref idref="f0018">Fig. 18</figref>) in association with each other.

0256The operating member 286 is disposed on the inner side of a cover member 287 that covers the outer side of the gear case 285. The operating member 286 primarily includes a base part 286A, an arm part 286B, and an operation engaging part 286C. The base part 286A has a circular plate shape with a hole 286D formed in the center thereof for rotatably engaging with the shaft part 285B. A plurality of protrusions 286E are formed along the rear edge of the base part 286A for engaging with a plurality of depressions S26 formed in a second engaging plate S25 described later (see <figref idref="f0018">Fig. 18</figref>).

0257The arm part 286B extends radially outward from the base part 286A (in approximately the forward direction. The operation engaging part 286C is disposed on the distal end of the arm part 286B and protrudes rightward therefrom. The operation engaging part 286C protrudes (is exposed) externally through an arc-shaped elongated hole 287A formed in the cover member 287.

0258In addition to the elongated hole 287A, a hole 287B for receiving the coupling part CP described above and a hole 287C for receiving the shaft part 285B are formed in the cover member 287. Further, the shaft part 285B, operating member 286, and cover member 287 having a construction similar to those described above are disposed on the left side of the toner cartridge 208, as shown in <figref idref="f0017">Fig. 17</figref>.

11 Structure of the developing device

0259As shown in <figref idref="f0012">Fig. 12</figref>, the developing device 207 further includes a developer case 276 in which the developing roller 271 is provided, a support case 277 that supports the process cartridge 205 from the underside thereof, a developing chamber 274 accommodating the developing roller 271 and the like described above, and an auger 275 disposed above the supply roller 273.

0260The front wall of the developing chamber 274 is a second arc wall W2 that opposes the first arc wall W1 of the toner cartridge 208 and curves in an arc-shape conforming with the first arc wall W1. The second arc wall W2 functions as an arc wall. A first through-hole W21 is formed in the upper half of the second arc wall W2 at a position in the left-to-right center thereof opposing the first supply hole W11 of the first arc wall W1. Second through-holes W22 are formed in the lower half of the second arc wall W2, with one in either left and right end thereof, at positions opposing the second supply holes W 12 formed in the first arc wall W1.

0261Hence, the first through-hole W21 is disposed higher than the second through-holes W22 and provided communication in a direction diagonally downward from the developer cartridge 208 to the developing device 207. The second through-holes W22 provide communication in a direction diagonally upward from the toner cartridge 208 to the developing device 207.

0262A process shutter S2 is provided on the front side of the second arc wall W2 form opening and closing the first through-hole W21 and second through-holes W22 by moving along the circumference of the second arc wall W2. As shown in <figref idref="f0018">Figs. 18</figref>, <figref idref="f0019">19A, and 19B</figref>, the process shutter S2 includes a metal plate S21, and a pair of engaging plates S22 disposed one on either left and right end of the metal plate S21.

0263The metal plate S21 is formed in the same shape as the metal plate S11 of the toner shutter S 1 described earlier. By moving similarly to the metal plate S 11, as shown in <figref idref="f0014">Figs. 14A and 14B</figref>, the metal plate S21 opens and closes the first through-hole W21 and second through-holes W22 described above.

0264Each of the engaging plates S22 is disc-shaped and has a plurality of depressions S23 formed in the rear edge thereof for engaging with the plurality of protrusions S 14 formed on the sliding piece S12 of the toner shutter S1. The left and right engaging plates S22 are also coupled together by two beam-like plates S24. The beam-shaped plates S24 ensure that the rigidity of the process shutter S2 is maintained.

0265A disc-shaped second engaging plate S25 is coaxially disposed on the outer surface of each engaging plate S22. A plurality of depressions S26 is formed in the rear edge of each second engaging plate S25 for engaging with the plurality of protrusions 286E on the operating member 286 described above.

0266An engaging hole S27 is formed in the center portions of each engaging plate S22 and second engaging plate S25. The engaging holes S27 rotatably engage with rotational shafts 276A protruding outward from the developer case 276 supporting the developing roller 271. Through this construction, the process shutter S2 can rotate relative to the developer case 276.

0267The support case 277 has support holes 277A formed one in either widthwise side wall thereof. The rotational shafts 276A of the developer case 276 penetrate and are supported in the support holes 277A. The support case 277 also has columnar-shaped protrusions 277B formed one on each widthwise side wall thereof so as to protrude outward. The protrusions 277B formed on the support case 277 and the rotational shafts 276A inserted through the support holes 277A are loosely supported in the elongated holes 205A of the process cartridge 205 so as to be capable of shifting slightly in the front-to-rear direction.

0268As shown in <figref idref="f0019">Figs. 19A and 19B</figref>, the process shutter S2 having the above construction is configured to open and close together with the toner shutter S 1 in association with the pivoting of the operating member 286. For convenience, the developing device 207 and toner cartridge 208 are shown separated in <figref idref="f0019">Figs. 19A and 19B</figref>.

0269In <figref idref="f0019">Fig. 19A</figref>, the toner shutter S1 and the process shutter S2 is in a closed position. Specifically, the first supply hole W11 and second supply holes W 12 are closed by the toner shutter S 1 and the first through-hole W21 and the second through-holes W22 are closed by the process shutter S2, at which time the operation member 286 is positioned downward. When the operation engaging part 286C of the operating member 286 is pivoted upward from the closed position, the protrusions 286E formed on the operating member 286 push the depressions S26 of the second engaging plate S25 downward, causing the process shutter S2 to rotate clockwise as shown in <figref idref="f0019">Fig. 19B</figref>. When the process shutter S2 is rotated in this way, the depressions S23 formed in the engaging plates S22 push the protrusions S 14 formed on the toner shutter S 1 in the clockwise direction of <figref idref="f0019">Fig. 19</figref>. Accordingly, the toner shutter S 1 rotates clockwise together with the process shutter S2.

0270Consequently, the first supply hole W11 and second supply holes W 12 are opened (see <figref idref="f0014">Figs. 14A and 14B</figref>). To close the first supply hole W11 and second supply holes W12, the operation engaging part 286C of the operating member 286 is pivoted downward, i.e., in the direction opposite that described above. Accordingly, the toner shutter S1 and process shutter S2 rotate counterclockwise in <figref idref="f0019">Fig. 19</figref> and close the first supply hole W11 and second supply holes W12.

0271As shown in <figref idref="f0015">Fig. 15</figref>, the auger 275 is configured to convey toner supplied through the first through-hole W21 toward the left and right second through-holes W22. Specifically, the auger 275 includes a rotational shaft 275A, and a first helical blade 275B and a second helical blade 275C wound in spiral shapes about the rotational shaft 275A.

0272The first helical blade 275B and second helical blade 275C are respectively disposed on right and left sides of the rotational shaft 275A, separated by the axial center thereof (a point near the first through-hole W21. The spiraling directions of the first helical blade 275B and second helical blade 275C are opposite each other, so that the first helical blade 275B conveys toner rightward and the second helical blade 275C conveys toner leftward.

12. The flow of toner

0273Next, the flow of toner in the developing unit 206 will be described. The third agitator A3 in the third accommodating unit 283 supplies toner from the third accommodating unit 283 into the second accommodating unit 282. The third films A24 of the second agitator A2 convey toner in the second accommodating unit 282 outward in the left and right directions, after which the fourth films A25 supply this toner into the first accommodating unit 281. As shown in <figref idref="f0012">Fig. 12</figref>, the agitating blade A13 of the first agitator A1 rotates and slidingly contacts the opposed wall 281C in the first accommodating unit 281, pushing toner within the first accommodating unit 281 upward. As the agitating blade A13 continues to rotate, the toner supported on the agitating blade A13 is conveyed along the top wall 281D and over the top of the first supply hole W 11.

0274Through this conveyance, the toner falls by its own weight in a downward slope through the open first supply hole W11 and first through-hole W21 and is supplied into the developing device 207. The auger 275 then conveys the toner supplied into the developing device 207 outward in the left and right directions, as shown in <figref idref="f0015">Fig. 15</figref>.

0275Through this process, the toner is spread over substantially the entire width of the supply roller 273, enabling the supply roller 273 to supply toner to the developing roller 271 effectively. Further, when toner agitated by the auger 275 in the developing device 207 migrates over the second through-holes W22, the toner drops by its own weight in downward slope through the second through-holes W22 and the second supply holes W12 and returns to the first accommodating unit 281.

0276When toner is returned to the first accommodating unit 281, the second films A15 of the first agitator A1 convey the toner toward the left-to-right center thereof, while the first film A14 supplies the toner back through the first supply hole W11, as shown in <figref idref="f0015">Fig. 15</figref>.

13. Operations and effects of the second embodiment

0277The following effects can be obtained by the laser printer 201 according to the second embodiment described above. As the first agitator A1 (first film A14) slides over the first arc wall W1 in a direction from top to bottom, i.e. the first supply hole W11 is formed on the upstream side of the first arc wall W1 with respect to the rotational direction of the first agitator A1, the first agitator A 1 can push toner through the first supply hole W11 and effectively supply toner to the developing device 207. Further, since the first agitator A1 (second films A15) rotate in a manner for pushing toner away from the second supply holes W12, the structure of the first agitator A1 inhibits toner that was returned into the first accommodating unit 281 through the second supply holes W12 from being pushed back into the developing device 207. Hence, this construction improves circulation of the toner.

0278Since the second agitator A2 rotates in a direction opposite the rotating direction of the first agitator A1, the second agitator A2 can supply toner from the bottom of the second accommodating unit 282 into the first accommodating unit 281, thereby effectively conveying toner from the second accommodating unit 282 to the first accommodating unit 281. Further, since the third agitator A3 rotates in the same direction as the second agitator A2, the third agitator A3 can effectively convey toner from the third accommodating unit 283 into the second accommodating unit 282.

0279By disposing the opposed wall 281C between the first accommodating unit 281 and second accommodating unit 282, toner can be retained between the first agitator A1 and opposed wall 281C, enabling the first agitator A1 to convey toner effectively to the first supply hole W11 disposed in the top of the first arc wall W1. Further, since the opposed wall 281C is formed with an arc-shaped cross section, the first agitator A1 can convey toner smoothly upward.

0280By providing the second films A15 on the first agitator A1 for conveying toner from the second supply holes W12 toward the first supply hole W11, toner returned into the first accommodating unit 281 can be conveyed back toward the first supply hole W11. Hence, this construction further improves circulation of the toner.

0281By forming the first supply hole W11 as an opening that slopes downward into the developing device 207 and the second supply holes W 12 as openings that slope upward toward the developing device 207, the weight of the toner can be used to supply toner into the developing device 207 and return toner from the developing device 207, thereby improving the circulation of toner between the developing device 207 and developer cartridge 208.

0282By forming the first supply hole W11 higher than the second supply holes W12, the second embodiment inhibits toner accumulated in the developing device 207 from flowing back into the first accommodating unit 281 through the first supply hole W11, while effectively encouraging the return of toner through the second supply holes W12 disposed lower than the first supply hole W11.

0283By forming the adjoining wall 281A of the first accommodating unit 281 as the first arc wall W1 having an arc-shaped cross section that is concave on the side facing the interior of the first accommodating unit 281, the first supply hole W11 and second supply holes W12 can be formed with a desired slope simply by forming holes in the upper half and lower half of the first arc wall W1. Therefore, circulation of toner can be improved through a simple construction.

0284By providing the toner shutter S 1 for opening and closing the first supply hole W11 and second supply holes W12, the second embodiment can prevent toner from leaking when the toner cartridge 208 is not mounted in the developing device 207. Further, the construction for moving the toner shutter S1 along the circumference of the first arc wall W1 is simpler than a construction for moving the shutter in the axial direction of the agitator. Further, having a toner shutter S1 with an arc-shaped cross section rotating about its center axis (the reference line BL), as described in the second embodiment, ensures stable opening and closing operations. Specifically, the shutter does not tilt during movement, as can occur when using a flat plate-shaped shutter that is moved linearly.

0285Since two second supply holes W 12 are provided in the second embodiment, toner in the developing device 207 can be more easily returned to the first accommodating unit 281.

0286The second embodiment further improves the circulation of toner by providing one first supply hole W11 in the left-to-right center of the first supply hole W11 and one second supply hole W12 on each of the left and right ends of the first arc wall W1, and by disposing the auger 275 in the developing device 207 for conveying toner from the center toward both left and right ends of the developing device 207.

0287Providing the second supply holes W12 outside of the printing area PA inhibits the accumulation of toner outside of the printing area PA more so than within the printing area PA. Accordingly, this construction can suppress the occurrence of light image densities caused when only a small amount of toner has accumulated within the printing area PA.

0288The auger 275 provided for conveying toner received through the first through-hole W21 toward the second through-holes W22 further improves the circulation of toner.

0289By providing the cover member 287 for covering the operating member 286 and exposing only a portion of the operating member 286 (the operation engaging part 286C) through the elongated hole 287A formed in the cover member 287, the construction of the second embodiment inhibits foreign matter from entering between the operating member 286 and the toner cartridge 208 more than a structure that does not include such a cover member, for example. Hence, this construction improves operability.

0290While the invention has been described in detail with reference to the embodiments thereof, it would be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention.

0291In the first embodiment described above, the intermediate transfer type color printer 1 shown in <figref idref="f0001">Fig. 1</figref> temporarily transfers a toner image in each color from the respective photosensitive drum 19 to the intermediate transfer belt 27, and subsequently transfers the entire color toner image onto a sheet of paper P. However, the present invention is not limited to an intermediate transfer type color printer. For example, the invention may be applied to a direction transfer type color printer in which toner images are transferred directly from each photosensitive drum 19 onto the sheet of paper.

0292Further, the curved wall 103 is depressed inward the circular center of the circumferential wall 101 to form an arc-shaped curve. However, the curved wall may not be a good "arc-shaped curve" if the toner shutter 112 can slide along the circumferential direction of the curved wall 103 between the open position and the close position.

0293Further, while the photosensitive drums 19 are exposed by laser beams emitted from the scanning unit 10 in the color printer 1 of the first embodiment, the photosensitive drums 19 may be exposed using LEDs (Light-Emitting Diode) instead of the scanning unit 10.

0294In the second embodiment described above, the first supply hole W11 is disposed above the second supply holes W12, but the vertical arrangement of the first supply hole W11 and second supply holes W12 may be reversed or, alternatively, the first supply hole W11 and second supply holes W12 may be arranged at the same vertical position. Further, the left-to-right positions and the numbers of the first and second supply holes are not limited to the description in the second embodiment, but may be set as desired.

0295While the present invention is applied to the laser printer 201 in the second embodiment described above, the present invention may be applied to other image-forming devices such as photocopiers or multifunction peripherals.