Patent Publication Number: US-8126377-B2

Title: Developer cartridge, developing device, and process cartridge

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from Japanese Patent Application No. 2007-258574 filed on Oct. 2, 2007, the entire subject matter of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to a developer cartridge having a supply opening for supplying developer in a cartridge to a developing chamber and a return opening for returning developer from the developing chamber to the inside of the cartridge, and more particularly, to a developing device having the developer cartridge and a process cartridge. 
     BACKGROUND 
     In general, an image processing apparatus such as an image forming apparatus includes a photosensitive drum having electrostatic latent images formed thereon, a process cartridge having a developing roller for supplying toner to the photosensitive drum, and a toner cartridge (developer cartridge) having toner accommodated therein. As an example of the image forming apparatus, JP-A-9-319202 discloses a configuration including a supply opening for supplying toner in a toner cartridge to a developing chamber, a toner cartridge having formed therein a return opening for returning toner from the developing chamber to the inside of the toner cartridge, an agitator having blades for agitating the interior of the toner cartridge, and an auger capable of conveying toner within the developing chamber at a supply opening side toward a return opening side. In the image forming apparatus, when the agitator is rotated, the blades of the agitator are rotated so that the blades pass through a position opposite the supply opening from the below to the above, whereby the toner accumulated in the lower half portion of the toner cartridge is pushed upward by the blades of the agitator to be delivered through the supply opening at the above and is discharged through the supply opening. The toner is then conveyed toward the return opening side by the auger and circulated in such a manner that the toner is returned back through the return opening into the toner cartridge. Therefore, fresh toner can be always supplied to the developing chamber from the cartridge. 
     SUMMARY 
     Aspects of the present invention provide a developer cartridge, a developing device, and a process cartridge capable of improving circulation of developer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side sectional view of an image forming apparatus according to a first example of the invention; 
         FIG. 2  is an enlarged sectional view of a developer cartridge; 
         FIG. 3A  is a perspective view of the developer cartridge in a closed state, and  FIG. 3B  is a perspective view of the developer cartridge in an open state; 
         FIG. 4A  is a perspective view of an agitator showing the state where a plate-shaped portion is detached therefrom, and  FIG. 4B  is a perspective view of the agitator showing the state where the plate-shaped portion is attached thereto; 
         FIGS. 5A to 5D  are diagrams showing an operation of the agitator, in which  FIG. 5A  is a front view showing a state where an oblique agitation blade is positioned at a lower half portion of an inside housing,  FIG. 5B  is a front view showing a state where developer is conveyed toward a supply opening side by the oblique agitation blade,  FIG. 5C  is a front view showing a state where a delivery agitation blade is positioned at the lower half portion of the inside housing, and  FIG. 5D  is a front view showing a state where developer slips off from the delivery agitation blade and is delivered through the supply opening into the developing chamber; 
         FIGS. 6A to 6D  are sectional views taken along the line VI-VI in  FIG. 5A , in which  FIG. 6A  is a sectional view showing the state where the oblique agitation blade is positioned at the lower half portion of the inside housing,  FIG. 6B  is a sectional view showing the state where developer is conveyed toward the supply opening side by the oblique agitation blade,  FIG. 6C  is a sectional view showing the state where the delivery agitation blade is positioned at the lower half portion of the inside housing, and  FIG. 6D  is a sectional view showing the state where developer slips off from the delivery agitation blade and is delivered through the supply opening into the developing chamber; 
         FIGS. 7A to 7D  are sectional views taken along the line VII-VII in  FIG. 5A , in which  FIG. 7A  is a sectional view showing the state where the oblique agitation blade is positioned at the lower half portion of the inside housing,  FIG. 7B  is a sectional view showing the state where developer is conveyed toward the supply opening side by the oblique agitation blade,  FIG. 7C  is a sectional view showing the state where the delivery agitation blade is positioned at the upper half portion of the inside housing, and  FIG. 7D  is a sectional view showing the state where developer is returned through the return opening into the developing chamber; 
         FIG. 8  is a perspective view of an agitator according to a second example of the invention; 
         FIG. 9  is an exploded perspective view of the agitator shown in  FIG. 8 ; 
         FIG. 10A  is an exploded perspective view of a gear mechanism, and  FIG. 10B  is a sectional view taken along the line X-X in  FIG. 8 ; 
         FIGS. 11A and 11B  are diagrams showing conveyance of developer by the delivery agitation blade, in which  FIG. 11A  is a sectional view showing the state the delivery agitation blade is positioned at the lower half portion of the inside housing, and  FIG. 11B  is a sectional view showing the state where developer is pushed through the supply opening into the developing chamber by the delivery agitation blade; and 
         FIG. 12  is a sectional view showing a modified example of the inside housing. 
     
    
    
     SUMMARY 
     &lt;General Overview&gt; 
     According to an aspect of the present invention, there is provided a developer cartridge comprising: a housing configured to accommodate developer; a rotation shaft that is rotatably supported by the housing and passes across an inside of the housing; a supply opening that is formed in a wall of the housing opposite in a diameter direction of the rotation shaft and is configured to supply the developer to an outside of the housing; a return opening that is formed in a wall of the housing at a position displaced from the supply opening in an axial direction of the rotation shaft and is configured to return the developer to the inside of the housing; a first agitation blade that is supported by the rotation shaft and is configured to pass through a position opposite the return opening along an inner surface of the housing by rotation of the rotation shaft; and a second agitation blade that is supported by the rotation shaft and is configured to pass through a position opposite the supply opening along an inner surface of the housing by the rotation of the rotation shaft, wherein the first agitation blade is configured to pass through the position opposite the return opening from an above to a below of the position opposite the return opening along with the rotation of the rotation shaft. 
     According to another aspect of the present invention, there is provided a developing device comprising: the developer cartridge according to the above aspect; a developing chamber to which developer is supplied through the supply opening of the developer cartridge; a supply roller provided in the developing chamber; and a developing roller to which the developer is supplied from the supply roller. 
     According to still another aspect of the present invention, there is provided a process cartridge comprising: the developing device according to the above aspect; and a photosensitive drum to which the developer is supplied from the developing roller. 
     Exemplary Embodiments 
     Exemplary embodiments of the invention will be described with reference to the drawings. 
     The above described related art apparatus has some disadvantages. For example, the agitator is rotated such that the blades of the agitator pass through the position opposite the supply opening from the below to the above. In this case, when the blades are also provided at the return opening side, the toner accumulated in the lower half portion of the cartridge is pushed upward by the return opening-side blades, and the toner is pushed through the return opening into the developing chamber. Thus, the toner may not circulate smoothly. 
     Aspects of the present invention provide a developer cartridge, a developing device, and a process cartridge capable of improving circulation of developer. 
     FIRST EXAMPLE 
       FIG. 1  is a side sectional view of an image forming apparatus according to a first example of the invention. 
     (1) Image Forming Apparatus 
     As shown in  FIG. 1 , an image forming apparatus  1  includes a body casing  2 , a feeder unit  4  for conveying sheet  3 , an image forming unit  5  for forming images on the sheet  3 , and the like. 
     (2) Feeder Unit 
     The feeder unit  4  includes a sheet feed tray  6 , a sheet pressing plate  7 , and various rollers  11 . In the feeder unit  4 , the sheet  3  in the sheet feed tray  6  is moved upward by the sheet pressing plate  7  and conveyed to an image forming unit  5  by the various rollers  11 . 
     (3) Image Forming Unit 
     The image forming unit  5  includes a scanner unit  16  as an example of an exposure unit, a process cartridge  17 , a fixing unit  18 , and the like. 
     (4) Scanner Unit 
     The scanner unit  16  includes a laser emitting part (not shown), a polygon mirror, lenses, and a reflection mirror (not denoted by reference numeral). In the scanner unit  16 , a laser beam travels along a path indicated by a chain line in the drawing and is scanned and irradiated onto the surface of a photosensitive drum  27  of the process cartridge  17 . 
     (5) Process Cartridge 
     The process cartridge  17  is detachably attached to the body casing  2  by opening a front cover  2   a . The process cartridge  17  includes a developing cartridge  28  as an example of a developing device, and a drum unit  51 , etc. 
     The developing cartridge  28  is configured to be detachable from the body casing  2  in a state where it is attached to the drum unit  51 . The developing cartridge  28  may be configured to be detachable from the drum unit  51  that is fixed to the body casing  2 . 
     The developing cartridge  28  includes a developing roller  31 , a thickness regulation blade  32 , a supply roller  33 , and an auger  34 . A developer cartridge  100  (which will be described later) is detachably attached to the developing cartridge  28 . The developer in the developer cartridge  100  is agitated by an agitator  200  and is supplied to the developing roller  31  by the supply roller  33 . At this time, the developer is positively charged by friction while being rubbed between the supply roller  33  and developing roller  31 . Subsequently, with the rotation of the developing roller  31 , the developer supplied onto the developing roller  31  is moved between the thickness regulation blade  32  and the developing roller  31 , where the developer is then carried as a thin layer of a predetermined thickness on the developing roller  31 . 
     The drum unit  51  includes a photosensitive drum  27 , a scorotron charger  29 , and a transfer roller  30 . In the drum unit  51 , the surface of the photosensitive drum  27  is uniformly charged with positive charges by the scorotron charger  29  and is thereafter exposed by the laser beam fast-scanned from the scanner unit  16 . With this exposure, the electric potential at the exposed portion decreases and thus electrostatic latent images based on image data are formed on the exposed portion. Here, the term, “electrostatic latent images,” refers to an exposed portion which is exposed by the laser beam and the electric potential of which is decreased, among portions on the surface of the photosensitive drum  27  which is uniformly charged with positive charges. Next, when the developer carried on the surface of the developing roller  31  is brought into opposing contact with the photosensitive drum  27  by the rotation of the developing roller  31 , the developer carried on the surface of the developing roller  31  is supplied to the electrostatic latent images formed on the surface of the photosensitive drum  27 . Then, the developer is selectively carried on the surface of the photosensitive drum  27  and changed to a visible image, whereby a developer image is formed by reversal development. 
     Thereafter, the photosensitive drum  27  and a transfer roller  30  are rotated to convey the sheet  3  pinched between them, and when the sheet  3  is conveyed while being pinched between the photosensitive drum  27  and the transfer roller  30 , the developer image carried on the surface of the photosensitive drum  27  is transferred onto the sheet  3 . 
     (6) Fixing Unit 
     The fixing unit  18  includes a heating roller  41  and a pressure roller  42 . In the fixing unit  18 , the developer transferred onto the sheet  3  is thermally fixed during the passage of the sheet  3  between the heating roller  41  and the pressure roller  42 . Moreover, the sheet  3  thermally fixed in the fixing unit  18  is delivered to a sheet discharge tray  46  by a sheet discharge roller  45  disposed on the downstream side of the fixing unit  18 . 
     (7) Developer Cartridge 
     Next, the detailed structure of the developer cartridge  100  as an example of a developer cartridge according to the present invention will be described. In the drawings,  FIG. 2  is an enlarged sectional view illustrating a detailed structure of a developer cartridge.  FIG. 3A  is a perspective view of the developer cartridge in a closed state, and  FIG. 3B  is a perspective view of the developer cartridge in an open state. 
     As shown in  FIG. 2 , the developer cartridge  100  constitutes the process cartridge  17  together with the developing cartridge  28  and the drum unit  51  described above, and the developer cartridge  100  is detachably attached to the developing cartridge  28 . Specifically, the developer cartridge  100  includes an inside housing  110  configured to accommodate developer T therein, an outside housing  120  configured to be displaced relative to the inside housing  110 , and the agitator  200 . 
     The inside housing  110  has a hollow, cylindrical shape, and is rotatably supported by a substantially cylindrical, inner circumferential surface of the outside housing  120 . Moreover, a supply opening  111  for supplying the developer T to the inside of the developing cartridge  28  is formed in a portion at the side of the developing cartridge  28  of an outer circumferential wall (a wall opposite a rotation shaft  210  of the agitator  200  in the diameter direction) of the cylindrical shape of the inside housing  110 . Moreover, as shown in  FIG. 3B , the supply opening  111  is formed at a center portion in the axial direction of the inside housing  110 . Furthermore, return openings  112  for returning the developer T from a developing chamber  28 A (see  FIG. 2 ) in the developing cartridge  28  to the inside of the developer cartridge  100  are formed at both the left and right sides (opposite positions in the axial direction of the inside housing  110 ) of the supply opening  111 . 
     The outside housing  120  has a substantially hollow, cylindrical shape, and at corresponding portions at the side of the developing cartridge  28  of an outer circumferential wall of the cylindrical shape of the outside housing  120 , a supply opening  121  communicating with the supply opening  111  of the inside housing  110  and return openings  122  communicating with the return openings  112  of the inside housing  110 . That is, the supply opening  121  and the return openings  122  of the outside housing  120  are formed at positions corresponding to the supply opening  111  and the return openings  112  of the inside housing  110 , the three ports being arranged in the axial direction. 
     A gear part  130  is disposed on an end surface at one end side of the outside housing  120 , the gear part  130  being fixed at an end portion of a rotation shaft  210  of the agitator  200  that is rotatably provided to the inside housing  110  and the outside housing  120 . When driving force is transmitted from the side of the body casing  2  to the gear part  130 , the agitator  200  is rotated. 
     The inside housing  110  and the outside housing  120  having the above-described construction are configured such that when developer cartridge  100  is attached to the developing cartridge  28 , the outside housing  120  is fixed to the developing cartridge  28  and the inside housing  110  is rotated relative to the outside housing  120 . The rotation structure is well known: to briefly describe, a projection  113  having a circular arc shape formed at an end portion of the inside housing  110  shown in  FIG. 3A  engages with a lever (not shown) and is moved along the circular arc shape by a lever operation, whereby the inside housing  110  is rotated relative to the outside housing  120 . Moreover, in a state shown in  FIG. 3A  where the developer cartridge  100  is not attached thereto, the supply opening  111  and the return openings  112  of the inside housing  110  are closed by the circumferential wall of the outside housing  120 . Meanwhile, in a state shown in  FIG. 3B  where the developer cartridge  100  is attached and the inside housing  110  is rotated, the supply opening  111  and the return openings  112  of the inside housing  110  are communicated with the supply opening  121  and the return openings  122  of the outside housing  120  so that the developer T can be supplied through the ports. 
     As shown in  FIGS. 4A and 4B , the agitator  200  includes the rotation shaft  210 , a support wall  220 , an oblique agitation blade  230 , which is an example of the first agitation blade, and a delivery agitation blade  240 , which is an example of the second agitation blade. 
     As shown in  FIG. 3B , the rotation shaft  210  is rotatably supported by the inside housing  110  and the outside housing  120  and is configured to pass across the inside of the inside housing  110  (specifically, the rotation shaft  210  is coaxial to the center axis of the inside housing  110 ). 
     The support wall  220  is formed integral with the rotation shaft  210  and includes a first support frame portion  221  that extends from the rotation shaft  210  toward one side in the diameter direction and a second support frame portion  222  that extends from the rotation shaft  210  toward a side opposite to the extending direction of the first support frame portion  221 . The first support frame portion  221  is shorter than the second support frame portion  222  in the axial direction of the rotation shaft  210 , and a portion of the support wall  220  opposite the return openings  112  (see  FIGS. 3A and 3B ) of the inside housing  110  has a notch shape. In addition, the first support frame portion  221  and the second support frame portion  222  have a lattice shape, and a plurality of openings  225  are formed in the support wall  220 . 
     The oblique agitation blade  230  has a distal end thereof formed along the inner circumferential surface of the inside housing  110 , and is oblique to the rotation shaft  210  over portions of the support wall  220  from the distal end of the first support frame portion  221  to the distal end of the second support frame portion  222 . Specifically, two oblique agitation blades  230  (four in total) are provided on the support wall  220  with the supply opening  111  disposed between them so that an end portion  232  at the backward side in the rotation direction of the rotation shaft  210  is positioned closer to the supply opening  111  (see  FIG. 3 ) of the inside housing  110  than an end portion  231  at the forward side in the rotation direction of the rotation shaft  210 . More specifically, the end portion  231  of the oblique agitation blade  230  at the forward side in the rotation direction is integrally formed on the second support frame portion  222 , and the end portion  232  at the backward side in the rotation direction is integrally formed on the first support frame portion  221 . Moreover, among the four oblique agitation blades  230 , the oblique agitation blades  230  at both end sides in the axial direction of the rotation shaft  210  are configured to pass through a position opposite the return openings  112  from the above to the below along the inner circumferential surface of the inside housing  110  when the rotation shaft  210  is rotated in the arrow direction shown in  FIG. 4A . 
     As shown in  FIG. 4B , the delivery agitation blade  240  is provided at a side of the support wall  220  opposite to the oblique agitation blades  230 , specifically at the side of the first support frame portion  221  of the support wall  220 . The delivery agitation blade  240  includes a plate-shaped portion  241  that is obliquely provided to the support wall  220  and guide walls  242  that are provided at both sides of the plate-shaped portion  241  in the axial direction of the rotation shaft  210 . 
     The plate-shaped portion  241  is supported by four, triangular ribs  243  (only three of them are illustrated) shown in  FIG. 4A , whereby when a front end thereof  241 A at the forward side in the rotation direction is opposed to the supply opening  111  of the inside housing  110  as shown in  FIG. 2 , a rear end thereof  241 B at the backward side in the rotation direction is positioned above the front end  241 A. Incidentally, the rear end  241 B in this example is always positioned above the front end  241 A when the front end  241 A is positioned at each of the positions from the lower end to the upper end of the supply opening  111 . Alternatively, the rear end  241 B may not be always positioned at each of the positions as long as the rear end  241 B is positioned above the front end  241 A (i.e., the lower end of the supply opening  111 ) when the front end  241 A is positioned at least at the lower end of the supply opening  111 . 
     As shown in  FIG. 4A , the guide walls  242  are formed so as to extend from the support wall  220  toward the outer side in the diameter direction of the rotation shaft  210 . A distal end thereof protrudes further outward in the diameter direction of the rotation shaft  210  than the plate-shaped portion  241  and is formed along the inner circumferential surface of the inside housing  110 . The delivery agitation blade  240  having the construction described above is provided to the rotation shaft  210  integral with the support wall  220  and is thus rotated in the same direction as the oblique agitation blade  230  (that is, the delivery agitation blade  240  passes through a position opposite the supply opening  111  from the above to the below along the inner circumferential surface of the inside housing  110 ). 
     As shown in  FIG. 2 , flexible film  300  that extends toward the rotation shaft  210  is provided at the lower end of the supply opening  111  of the inside housing  110 . Specifically, the flexible sheet  300  has such a length that it does not make abutting contact with the front end  241 A of the plate-shaped portion  241  of the rotating agitator  200 . 
     Next, the operation of the agitator  200  according to the present invention will be described. In the drawings,  FIGS. 5A to 5D  are diagrams showing an operation of the agitator, in which  FIG. 5A  is a front view showing a state where an oblique agitation blade is positioned at a lower half portion of an inside housing,  FIG. 5B  is a front view showing a state where developer is conveyed toward a supply opening side by the oblique agitation blade,  FIG. 5C  is a front view showing a state where a delivery agitation blade is positioned at the lower half portion of the inside housing, and  FIG. 5D  is a front view showing a state where developer slips off from the delivery agitation blade and is delivered through the supply opening into the developing chamber.  FIGS. 6A to 6D  are sectional views taken along the line VI-VI in  FIG. 5A .  FIGS. 7A to 7D  are sectional views taken along the line VII-VII in  FIG. 5A . In  FIGS. 7A to 7D , the oblique agitation blade  230  is schematically illustrated without being taken along the line VII-VII in  FIG. 5A  for the sake of explanation. 
     As shown in  FIGS. 5A and 6A , when the agitator  200  is rotated from the state where the oblique agitation blade  230  is positioned at the lower half portion of the inside housing  110  so that the oblique agitation blade  230  is positioned at a side opposite the supply opening  111  with the rotation shaft  210  disposed therebetween as shown in  FIG. 6B , developer T slips off from the oblique agitation blade  230  as shown in  FIG. 5B  and is conveyed from the side of the return openings  112  to the side of the supply opening  111  (toward the center of the inside housing  110  in the axial direction). 
     Subsequently, when the agitator  200  is rotated further, as shown in  FIGS. 5C and 6C , the developer T conveyed to the center in the axial direction of the inside housing  110  is taken upward by the delivery agitation blade  240  and conveyed by the delivery agitation blade  240 . Moreover, as shown in  FIGS. 5D and 6D , when the front end  241 A of the plate-shaped portion  241  of the delivery agitation blade  240  is moved to a position opposite the supply opening  111  of the inside housing  110 , the developer T slips off from the plate-shaped portion  241  and is delivered through the supply opening  111  to the developing chamber  28 A. Moreover, at this time, the developer T is supported by the flexible film  300  that is provided so as to cover a gap between the inner surface of the inside housing  110  and the front end  241 A of the plate-shaped portion  241 . Therefore, the developer T can be delivered through the supply opening  111  to the developing chamber  28 A without falling in the lower half portion of the inside housing  110 . 
     In this manner, when the developer T is delivered through the supply opening  111 , the amount of the developer T in the developing chamber  28 A becomes a predetermined amount or more, and the overflowing developer T is returned through the return openings  112  to the inside of the developer cartridge  100 . At this time, since the notch portion (see  FIGS. 4A and 4B ) of the support wall  220  is disposed at the position opposite the return openings  112 , the developer T can be efficiently returned through the return openings  112  to the inside of the inside housing  110 . 
     Moreover, the oblique agitation blade  230  disposed at a position opposite the return openings  112  conveys the developer T to the side of the supply opening  111  as shown in  FIGS. 7A and 7B  and thereafter passes through the upper half portion of the inside housing  110  as shown in  FIG. 7C . At this time, since the developer T falls through the openings  225  of the support wall  220 , as shown in  FIG. 7D , when the oblique agitation blades  230  pass through the return openings  112 , the developer T in the inside housing  110  is not discharged through the return openings  112  to the developing chamber  28 A. Furthermore, since the oblique agitation blades  230  pass through the return openings  112  from the above to the below, as shown in  FIGS. 7C and 7D , the developer T returned through the return openings  112  to the inside of the inside housing  110  is scraped by the oblique agitation blades  230  and received in the inside housing  110 . For this reason, it is possible to suppress the developer T from being forced back toward the developing chamber  28 A by the oblique agitation blades  230 , and the developer T is efficiently returned to the inside of the inside housing  110 . 
     According to the configuration described above, the following advantages can be obtained. 
     Since the oblique agitation blades  230  are rotated so that they pass through the return openings  112  from the above to the below, the developer T can be efficiently returned through the return openings  112  to the inside of the inside housing  110 , and circulation of the developer T can be improved. 
     Since the plate-shaped portion  241  that is disposed oblique to the support wall  220  is configured to deliver the developer T through the supply opening  111  to the developing chamber  28 A, it is possible to efficiently deliver a lot of developer T to the developing chamber  28 A when the delivery agitation blade  240  passes through the supply opening  111  from the above to the below. 
     Since the guide walls  242  are provided at both sides of the plate-shaped portion  241 , it is possible to suppress the developer T on the plate-shaped portion  241  from overflowing from both sides of the plate-shaped portion  241 . Accordingly, a large amount of developer T can be conveyed to the supply opening  111 . 
     Since the flexible film  300  is provided at the lower end of the supply opening  111 , it is possible to suppress the developer T from overflowing from the delivery agitation blade  240  and falling in the lower half portion of the inside housing  110 . Accordingly, a larger amount of developer T can be conveyed to the supply opening  111 . 
     SECOND EXAMPLE 
     Next, a second example of the present invention will be described in detail by appropriately referring to the attached drawings. In the second example, the structure of the agitator according to the first example is modified, and the same components as the first example will be denoted by the same reference numerals and will not be described. In the drawings,  FIG. 8  is a perspective view of an agitator according to the second example.  FIG. 9  is an exploded perspective view of the agitator shown in  FIG. 8 .  FIG. 10A  is an exploded perspective view of a gear mechanism, and  FIG. 10B  is a sectional view taken along the line X-X in  FIG. 8 . 
     As shown in  FIG. 8 , the agitator  400  according to the second example includes a rotation shaft  410 , a pair of oblique agitation blade units  420 , a delivery agitation blade unit  430 , and a gear mechanism  440 , which is an example of a driving unit. 
     As shown in  FIG. 9 , the rotation shaft  410  has one end portion thereof  411  that is connected to the gear part  130  (see  FIGS. 3A and 3B ), whereby the rotation shaft  410  is rotated when driving force is transmitted thereto from the side of the one end portion  411 . Moreover, at the other end portion of the rotation shaft  410 , one (first oblique agitation blade unit  420 A) of the pair of oblique agitation blade units  420  is integrally formed. Meanwhile, a pair of latching protrusions  412  is formed at corresponding portions closer to the one end side than the center of the rotation shaft  410  so as to protrude outward in the diameter direction. The latching protrusions  142  are configured to latch the other (second oblique agitation blade unit  420 B) of the pair of oblique agitation blade units  420  and a first gear  441  described later. 
     The oblique agitation blade units  420  includes the first oblique agitation blade unit  420 A that is integrally formed with the rotation shaft  410  and the second oblique agitation blade unit  420 B that is rotatably supported by the rotation shaft  410 . 
     The first oblique agitation blade unit  420 A includes a support frame  421  and two oblique agitation blades  422 , which are an example of the first agitation blade. The support frame  421  generally has a rectangular frame shape and a center portion thereof in the diameter direction of the rotation shaft  410  is integrally formed with the rotation shaft  410 . Each of the oblique agitation blades  422  is integrally formed with the support frame  421  and the rotation shaft  410  in the same shape and posture as the oblique agitation blades  230  according to the first example. That is, the oblique agitation blades  422  are arranged such that end portions thereof  422 B at the backward side in the rotation direction of the rotation shaft  410  are positioned closer to the supply opening  111  (see  FIGS. 3A and 3B ) of the inside housing  110  than end portions thereof  422 A at the forward side in the rotation direction. 
     The second oblique agitation blade unit  420 B includes substantially the same support frame  421  and the same two oblique agitation blades  422  as the first oblique agitation blade unit  420 A and further includes an approximately cylindrical shaft portion  423  configured to rotatably engage with the rotation shaft  410 . Moreover, a key groove  423 A is formed in an end portion of the shaft portion  423  close to the first oblique agitation blade unit  420 A so as to engage with the latching protrusions  412  of the rotation shaft  410 . For this reason, the second oblique agitation blade unit  420 B is integrally rotated with the rotation shaft  410  when the key groove  423 A is engaged with the latching protrusions  412  of the rotation shaft  410 . 
     The delivery agitation blade unit  430  includes a support frame  431 , a delivery agitation blade  432 , which is an example of the second agitation blade, and a shaft portion  433  that is integrally formed with the support frame  431 . The support frame  431  generally has a rectangular frame shape and a center portion thereof in the diameter direction of the rotation shaft  410  is integrally formed with the shaft portion  433 . The delivery agitation blade  432  is generally rectangular flexible sheet, and one end thereof is fixed to one end of the support frame  431  in the diameter direction of the rotation shaft  410 , whereby the other end thereof is bent to make sliding contact with the inner circumferential surface of the inside housing  110 . The shaft portion  433  generally has a C shape (approximately cylindrical shape) and is configured to rotatably engage with the rotation shaft  410 . Moreover, at an end portion of the shaft portion  433  close to the gear mechanism  440 , a pair of latching protrusions  433 A configured to latch a second gear  442  in the rotation direction are formed so as to protrude toward the gear mechanism  440 . Furthermore, in the inner circumferential surface of the shaft portion  433 , a relief groove  433 B (see  FIG. 10A ) is formed for preventing the delivery agitation blade unit  430  from interfering with the latching protrusions  412  of the rotation shaft  410  when the delivery agitation blade unit  430  is inserted from the one end side of the rotation shaft  410 . The delivery agitation blade unit  430  having the construction described above is configured to be rotated in the backward direction by the gear mechanism  440  in a manner independent from the oblique agitation blade unit  420 . Moreover, delivery opening portions  433 C are formed at both end sides of the lower portion of the shaft portion  433  in order to deliver developer entering into the shaft portion  433  to the outside. With such a configuration, it is possible to prevent the developer entering into a gap between the shaft portion  433  and the rotation shaft  410  from sticking thereto, whereby the delivery agitation blade unit  430  can be efficiently rotated. 
     The gear mechanism  440  is disposed between the delivery agitation blade unit  430  and the second oblique agitation blade unit  420 B at one end side of the rotation shaft  410  (see  FIG. 8 ). The gear mechanism  440  includes the first gear  441 , the second gear  442 , a third gear  443 , and a gear holding member  444 . Here, the first gear  441 , the second gear  442  and the third gear  443  have the same structure, and therefore, only the structure of the first gear  441  will be described. In the second example, since the first gear  441 , the second gear  442  and the third gear  443  have same structure, the number of components can be decreased. Alternatively, the first gear  441 , the second gear  442  and the third gear  443  may have mutually different structures. 
     As shown in  FIG. 10A , the first gear  441  has a cylindrical rotating cylinder portion  441 A formed at the center thereof to which the rotation shaft  410  is inserted and a gear tooth portion  441 B formed in the outer circumferential surface thereof. In the rotating cylinder portion  441 A, a pair of key grooves  441 C is formed at both sides of the center of the rotating cylinder portion  441 A so as to be communicated with each other from the inner circumferential surface side to the outer circumferential surface side and from one end side thereof to the other end side thereof. Moreover, the key grooves  441 C are configured to engage with the latching protrusions  412  of the rotation shaft  410  shown in  FIG. 9 . For this reason, the first gear  441  is integrally rotated with the rotation shaft  410  and the oblique agitation blade unit  420  in a state where the key grooves  441 C are engaged with the latching protrusions  412  of the rotation shaft  410 . Moreover, a pair of relief grooves  441 D are formed in the rotating cylinder portion  441 A at positions displaced by about 90 degrees from the key grooves  441 C so as to be communicated with each other from one end side of the rotating cylinder portion  441 A to the other end side. For this reason, even when developer enters into the rotating cylinder portion  441 A, the developer can be delivered to the outside through the relief grooves  441 D. 
     The second gear  442  includes a rotating cylinder portion  442 A, a gear tooth portion  442 B, key grooves  442 C, and relief grooves  442 D, all of which have the same structure as those of the first gear  441 . The key grooves  442 C of the second gear  442  are configured to engage with the latching protrusions  433 A of the delivery agitation blade unit  430  shown in  FIG. 9 . For this reason, the second gear  442  is integrally rotated with the delivery agitation blade unit  430  in a state where the key grooves  442 C are engaged with the latching protrusions  433 A of the delivery agitation blade unit  430 . Moreover, the relief grooves  442 D of the second gear  442  are in agreement with the relief grooves  433 B of the delivery agitation blade unit  430  when the key grooves  442 C of the second gear  442  engage with the latching protrusions  433 A of the delivery agitation blade unit  430 . For this reason, the delivery agitation blade unit  430  can be inserted into the rotation shaft  410  from one end side to the center portion in a state where the second gear  442  is set to the delivery agitation blade unit  430 . Moreover, even when developer enters into the rotating cylinder portion  442 A, the developer can be delivered to the outside through the relief grooves  442 D. 
     The third gear  443  includes a rotating cylinder portion  443 A, a gear tooth portion  443 B, key grooves  443 C, and relief grooves  443 D, all of which have the same structure as those of the first gear  441 . In the third gear  443 , the key grooves  443 C do not have any special function, and the relief grooves  443 D contribute to the discharge of developer entering into the rotating cylinder portion  443 A. The third gear  443  is held by the gear holding member  444 , whereby as shown in  FIG. 10B , the third gear  443  is disposed above the rotation shaft  410  and rotated in a circumferential direction perpendicular to the rotation shaft  410  so as to engage with the first gear  441  and the second gear  442 . 
     The first gear  441 , the second gear  442  and the third gear  443  having the construction described above have the respective gear tooth portions  441 B,  442 B and  443 B having a spur gear shape with a large tooth gap. Accordingly, the first gear  441 , the second gear  442  and the third gear  443  make point contact with each other in order to transmit power. 
     The gear holding member  444  is disposed between the first gear  441  and the second gear  442  and includes a rotation shaft support portion  444 A and a gear support portion  444 B. The rotation shaft support portion  444 A has an approximately C-shaped section and is rotatably engaged with the rotation shaft  410  as shown in  FIG. 10B . The gear support portion  444 B is integrally formed with the rotation shaft support portion  444 A so as to protrude upward (a direction perpendicular to the axial direction) from a center portion in the axial direction of the rotation shaft support portion  444 A. The gear support portion  444 B includes a large diameter portion  444 C, a small diameter portion  444 D, and an engagement portion  444 E, which are sequentially arranged from the side of the rotation shaft support portion  444 A. The large diameter portion  444 C has a diameter larger than the diameter of a hole formed in the rotating cylinder portion  443 A of the third gear  443 , whereby the large diameter portion  444 C supports the third gear  443  from the below. The small diameter portion  444 D has a substantially the same diameter as that of the hole formed in the rotating cylinder portion  443 A of the third gear  443 , whereby the small diameter portion  444 D rotatably supports the third gear  443 . The engagement portion  444 E extends upward from an end surface of the small diameter portion  444 D and is configured to engage with an engagement hole  110 A formed in an upper portion of the inner circumferential surface of the inside housing  110  as shown in  FIG. 10B . Moreover, a discharge opening portion  444 F is formed at the center of the lower portion of the rotation shaft support portion  444 A in order to discharge developer entering into the rotation shaft support portion  444 A to the outside. With such a configuration, it is possible to prevent the developer entering into a gap between the rotation shaft support portion  444 A and the rotation shaft  410  from sticking thereto, whereby the rotation shaft  410  can be efficiently rotated. 
     Next, the operation of the agitator  400  according to the second example will be described. In the drawings,  FIGS. 11A and 11B  are diagrams illustrating the conveyance of developer by the delivery agitation blade, in which  FIG. 11A  is a sectional view showing the state the delivery agitation blade is positioned at the lower half portion of the inside housing, and  FIG. 11B  is a sectional view showing the state where developer is pushed through the supply opening into the developing chamber by the delivery agitation blade. 
     When a driving device (not shown) of the image forming apparatus  1  is activated, the driving force is transmitted to the one end portion  411  of the agitator  400  shown in  FIG. 8 , whereby the rotation shaft  410  and the oblique agitation blade unit  420  are rotated in the arrow direction (a direction of passing through the return openings  112  from the above to the below). The driving force is transmitted to the delivery agitation blade unit  430  while the direction of the driving force is reversed via the gear mechanism  440 , whereby the delivery agitation blade unit  430  is rotated in a direction opposite to the rotation direction of the oblique agitation blade unit  420 . 
     For this reason, as shown in  FIGS. 11A and 11B , the delivery agitation blade  432  can push up the developer T accumulated in the lower half portion of the inside housing  110  to the supply opening  111  so that the developer T is efficiently discharged through the supply opening  111  to the developing chamber  28 A. Moreover, the oblique agitation blades  422  of the oblique agitation blade unit  420  pass through the return openings  112  from the above to the below in a manner similar to the oblique agitation blades  230  according to the first example (see  FIGS. 7A to 7D ) in order to return the developer T through the return openings  112  efficiently. 
     According to the second example, following advantages can be provided. 
     Since the oblique agitation blades  422  are rotated so that they pass through the return openings  112  from the above to the below, it is possible to efficiently return the developer T through the return openings  112  to the inside of the inside housing  110 . Accordingly, circulation of the developer T can be improved. 
     Since the delivery agitation blade  432  is rotated so that it passes the supply opening  111  from the below to the above, the developer T accumulated in the lower half portion of the inside housing  110  can be efficiently discharged through the supply opening  111 . 
     Since the rotation direction of the driving force transmitted to the delivery agitation blade  432  is reversed via the gear mechanism  440  having such a simple structure as to be received into the inside housing  110 , it is possible to miniaturize the developer cartridge  100  and to realize the miniaturization of the image forming apparatus  1 . 
     Since the first gear  441 , the second gear  442  and the third gear  443  are configured to make point contact with each other in order to transmit power, it is possible to prevent the developer T from being entangled between the gears  441 ,  442  and  443 , whereby the delivery agitation blade  432  can be efficiently rotated in a direction opposite to the rotation direction of the oblique agitation blades  422 . 
     Since the third gear  443  is provided above the rotation shaft  410 , the portions of the third gear  443  engaging with the first gear  441  and the portions of the third gear  443  engaging with the second gear  442  can be isolated from the developer T accumulated in the lower half portion of the inside housing  110 . For this reason, it is possible to more efficiently prevent the developer T from being entangled between the gears  441 ,  442  and  443 . Moreover, since the third gear  443  is not buried in the developer T accumulated in the lower half portion of the inside housing  110 , the flow of the developer T in the inside housing  110  is not interfered. Accordingly, circulation of the developer T can be improved. 
     Since the gear mechanism  440  is disposed between the delivery agitation blade unit  430  and the second oblique agitation blade unit  420 B that is disposed at a side to which the driving force of the rotation shaft  410  is transmitted, it is possible to prevent distortion of the rotation shaft  410 . 
     Although the present invention has been described based on the above-described exemplary embodiments, the present invention is not limited to the above-described exemplary embodiments. It will be understood that the present inventive concept may be subjected to various improvements and modifications within the scope of the present invention. 
     In the first example, the supply opening  111  of the inside housing  110  is disposed at a position overlapping with the rotation shaft  210  in the horizontal direction (see  FIGS. 6A to 6D ). Alternatively, the supply opening  111  may be provided below the rotation shaft as shown in  FIG. 12 . According thereto, the developer T can more efficiently slip off from the plate-shaped portion  241  of the delivery agitation blade  240 . 
     In the first example, the pair of guide walls  242  of the delivery agitation blade  240  is arranged in parallel. Alternatively, the gap between the pair of guide walls may be gradually decreased as they go toward the return opening side of the inside housing. According thereto, the developer can be more efficiently flown into the supply opening. 
     In the second example, although the gear mechanism  440  is used as the driving unit, the present invention is not limited to this. For example, the driving unit may have a structure in which the first gear  441  is detached from the gear mechanism  440  shown in  FIG. 8 , the upper end of the gear holding member  444  protrudes out to the outside of the developer cartridge, and a driving force of which the direction is opposite to the direction of the driving force transmitted to the rotation shaft  410  is transmitted to the upper end of the gear holding member  444 . 
     In the above-described exemplary embodiments, although the present inventive concept have been described in relation to a laser printer, the present inventive concept is not limited to any specific type of laser printer. Rather, the present inventive concept can be applied to other image forming apparatuses such as a copying machine or a multi-functional device. 
     Further, in the above-described exemplary embodiments, the scanner unit  16  is employed as the exposure unit. Alternatively, an LED head may be used for example. Moreover, the structure of the conveying unit or the fixing unit may be appropriately modified. 
     Still further, in the above-described exemplary embodiments, although a single supply opening  111  ( 121 ) and two return openings  112  ( 122 ) are provided, the number of ports can be arbitrary. For example, one supply opening may be provided at one end side of the developer cartridge and one return opening may be provided at the other end side of the developer cartridge. 
     Still further, in the above-described exemplary embodiments, the oblique agitation blades  230  and  422  formed of material such as resin that is not likely to bend are used as the first agitation blade. Alternatively, flexible sheet may be used for the oblique agitation blades  230  and  422 . Further, in the first example, the delivery agitation blade  240  formed of material such as resin that is not likely to bend is used as the second agitation blade. Alternatively, the flexible sheet may be used for the second agitation blade. Still further, in the second example, the delivery agitation blade  432  formed of flexible sheet is used as the second agitation blade. Alternatively, the delivery agitation blade may be formed of material such as resin that is not likely to bend or non-flexible material. In such a case, a distal end of the delivery agitation blade may be slightly separated from the inner surface of the inside housing without sliding contact with the inside housing. 
     In the first example, although a plurality of openings  225  is formed on the entire surface of the support wall  220 , the openings may be formed in a portion of the support wall, or the openings may not be formed. Moreover, although the rectangular support frames  421  and  431  having a rectangular opening at the center thereof are used in the second example, the openings formed by the support frames  421  and  431  may be appropriately covered by a plate-shaped member. 
     In the second example, the delivery agitation blade unit  430  is inserted into the rotation shaft  410  in the axial direction from one end thereof. Alternatively, the delivery agitation blade unit  430  (specifically, the C-shaped shaft portion  433 ) may be fitted to the rotation shaft  410  by being pressed in the diameter direction of the rotation shaft  410 .