Patent Publication Number: US-8977169-B2

Title: Toner supply system for image forming apparatus development device

Description:
This application is based on Japanese Patent Application No. 2011-257523 and Japanese Patent Application No. 2011-257524, filed with the Japan Patent Office on Nov. 25, 2011, the contents of which are incorporated herein by reference. 
     BACKGROUND 
     The present disclosure relates to a development device that can be installed suitably in an image forming apparatus such as a copier or a printer, and an image forming apparatus including the development device. 
     A conventional development device includes a development housing having a development roller and a stirring screw, and a toner container that replenishes toner and is attached to the development housing detachably. A toner discharge port that can be opened and closed is provided in a bottom portion of the toner container, and a toner replenishment port is provided in the development housing in a position corresponding to the toner discharge port. When the toner container is attached to the development housing and both the toner discharge port and the toner replenishment port are opened, toner in the toner container is supplied to a predetermined circulatory conveyance passage formed in the development housing. 
     The circulatory conveyance passage is constituted by an outward conveyance passage corresponding to the toner replenishment port and a return conveyance passage corresponding to the development roller. A stirring screw in which a spiral vane is disposed around a rotary shaft is mounted in each circulatory conveyance passage. The toner is conveyed in circulatory fashion between the outward conveyance passage and the return conveyance passage by the respective stirring screws. 
     In a conventional development device having this type of configuration, a conveyance ability suppressing portion may be provided on the stirring screw provided in the outward conveyance passage on a downstream side of the toner replenishment port in order to reduce a conveyance ability locally. A toner accumulation portion is formed by the conveyance ability suppressing portion in the vicinity of the toner replenishment port on an upstream side of the conveyance ability suppressing portion. When a large amount of toner exists in the accumulation portion, the toner in the accumulation portion blocks the toner replenishment port. Further, when the amount of toner in the accumulation portion is small, a gap is formed between the toner replenishment port and the toner accumulation portion such that toner flows into the development housing from the toner container side. Thus, an amount of replenishment toner supplied to the development housing from the toner container is regulated in accordance with the amount of accumulated toner in the accumulation portion. 
     When determining an interior layout of an image forming apparatus main body installed with the development device described above, it may be desirable to connect the toner container to an end portion of the development housing in an extension direction of the rotary shaft. In this case, the toner replenishment port is disposed in an end portion of the outward conveyance passage. However, a connecting passage connecting the outward conveyance passage to the return conveyance passage is close to this end portion, and therefore developer accumulates easily therein. Hence, when the toner replenishment port is disposed in the end portion of the outward conveyance passage, developer accumulation in the vicinity of the connecting passage affects the accumulation portion formed by the conveyance ability suppressing portion, and as a result, toner replenishment regulation becomes unstable. 
     An object of the present disclosure is to provide a development device in which replenishment developer is supplied from a replenishment developer housing portion as an amount of developer in a developer accumulation portion decreases, with which the replenishment developer can be supplied with stability even when a developer introduction port is disposed in the vicinity of a connecting passage of a developer conveyance passage. 
     SUMMARY 
     A development device according to an aspect of the present disclosure includes a casing that houses a developer, a replenishment developer housing portion, a developer conveyance path, a developer introduction port, a developer conveyance portion, a first conveyance ability suppressing portion, and a connecting conveyance portion. 
     The replenishment developer housing portion is attached to the casing detachably and houses replenishment developer supplied to the casing. 
     The developer conveyance path is formed in the casing and includes a first conveyance passage through which the developer is conveyed in a first direction, a second conveyance passage which is disposed alongside the first conveyance passage, and through which the developer is conveyed in a second direction, which is an opposite direction to the first direction, a first connecting passage which connects a downstream side of the first conveyance passage to an upstream side of the second conveyance passage in a third direction that intersects the first direction, and a second connecting passage which connects a downstream side of the second conveyance passage to an upstream side of the first conveyance passage in a fourth direction, which is an opposite direction to the third direction. 
     The developer introduction port is provided in the casing to oppose a first direction downstream side position of the first conveyance passage, and the replenishment developer is introduced into the developer conveyance path from the replenishment developer housing portion through the developer introduction port. 
     The developer conveyance portion is disposed in the first conveyance passage to convey the developer in the first direction so that the developer passes the position in which the developer introduction port opposes the first conveyance passage. 
     The first conveyance ability suppressing portion is disposed on the developer conveyance portion on a downstream side of the developer introduction port in said first direction in order to partially suppress a developer conveyance ability of the developer conveyance portion such that a developer accumulation portion for regulating an introduction amount of the replenishment developer is formed in a position opposing the developer introduction port, and such that a first direction downstream side thereof opposes the first connecting passage in the third direction. 
     The connecting conveyance portion is joined to the first direction downstream side of the first conveyance ability suppressing portion in the developer conveyance portion and opposes the first connecting passage in the third direction in order to pass the developer from the first conveyance passage to the second conveyance passage. 
     An image forming apparatus according to another aspect of the present disclosure includes an image carrier having a surface on which an electrostatic latent image is formed, wherein the electrostatic latent image is formed into a visible developer image using a developer, and a development device that supplies the developer to the image carrier. The development device is configured as described above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view illustrating an internal structure of an image forming apparatus according to an embodiment of the present disclosure; 
         FIG. 2  is a plan view of a development device according to an embodiment of the present disclosure; 
         FIG. 3  is a sectional view of a toner replenishment portion; 
         FIG. 4  is a perspective view of a stirring screw; 
         FIG. 5  is a plan view of the development device; 
         FIG. 6  is a plan view of a development device according to another embodiment of the present disclosure; 
         FIG. 7  is a plan view of a development device according to another embodiment of the present disclosure; 
         FIG. 8  is a plan view of a development device according to a comparative example; 
         FIG. 9  is a plan view of a development device according to a comparative example; 
         FIG. 10  is a plan view of a development device according to a comparative example; 
         FIG. 11  is a plan view of a conventional volume replenishment type development device; 
         FIG. 12  is a plan view of a conventional volume replenishment type development device; 
         FIGS. 13A and 13B  are pattern diagrams showing volume replenishment type toner replenishment; and 
         FIGS. 14A and 14B  are pattern diagrams showing toner replenishment according to an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure will be described below on the basis of the drawings.  FIG. 1  is a schematic sectional view showing a configuration of an image forming apparatus  1  including a development device  20  according to an embodiment of the present disclosure. The image forming apparatus  1  includes an optical scanning device  11 , the development device  20 , a toner container  30  (a replenishment developer housing portion), a charger  13 , a photosensitive drum  14  (an image carrier), a transfer roller  15 , a fixer  16 , and a sheet feeding cassette  17 . 
     The photosensitive drum  14  is a cylindrical member having a peripheral surface on which an electrostatic latent image and a toner image are formed. The photosensitive drum  14  is rotated in a clockwise direction of  FIG. 1  upon reception of driving force from a motor, not shown in the drawing. The charger  13  charges a surface of the photosensitive drum  14  substantially uniformly. 
     The optical scanning device  11  includes a light source such as a laser diode, a deflector, a scanning lens, an optical element, and so on. The optical scanning device  11  forms an electrostatic latent image of image data by irradiating the peripheral surface (a scanned surface) of the photosensitive drum  14  substantially uniformly charged by the charger  13  with laser light corresponding to the image data. 
     The development device  20  forms a toner image by supplying toner to the peripheral surface of the photosensitive drum  14  on which the electrostatic latent image is formed. The development device  20  includes a development roller that carries the toner and a stirring screw that stirs and conveys the toner. The toner image formed on the photosensitive drum  14  is transferred onto a sheet that is fed from the sheet feeding cassette  17  and conveyed along a conveyance path P. The development device  20  is replenished with toner from the toner container  30 . The development device  20  will be described in detail below. 
     The toner container  30  is a box-shaped member that houses toner in its interior. The toner container  30  supplies toner to the development device  20 . The toner container  30  is attached to the development device  20  detachably. 
     The transfer roller  15  is disposed below and opposite the photosensitive drum  14  such that a transfer nip portion is formed therebetween. The transfer roller  15  is constituted by a conductive rubber material or the like. Further, a transfer bias is applied to the transfer roller  15  by bias applying means, not shown in the drawing. The transfer roller  15  transfers the toner image formed on the photosensitive drum  14  onto the sheet. 
     The fixer  16  includes a fixing roller  160  having an inbuilt heater, and a pressurizing roller  161  provided in a position opposing the fixing roller  160 . The fixer  16  conveys the sheet formed with the toner image while heating the sheet such that the toner image formed on the sheet is fixed. 
     &lt;Description of Development Device&gt; 
       FIG. 2  is a plan view showing an internal structure of the development device  20 . The development device  20  includes a development housing  210  (a casing) having an elongated box shape that extends in one direction (an axial direction of a development roller  21 ). The development housing  210  includes an interior space  220  and a toner replenishment port  25 . The development roller  21 , a first stirring screw  23  (a developer conveyance portion), and a second stirring screw  24  are disposed in the interior space  220 . When a single component development method is employed, toner is filled into the interior space  220  as a developer. When a two component development method is employed, a mixture of toner and a carrier constituted by a magnetic body is filled as the developer. The toner is conveyed through the interior space  220  while being stirred, and supplied to the photosensitive drum  14  successively from the development roller  21  in order to develop the electrostatic latent image. 
     The development roller  21  has a cylindrical shape that extends in an elongation direction of the development housing  210 , and includes a sleeve part that is driven to rotate on an outer periphery thereof. When the single component development method is employed, toner carrying a charge due to frictional electrification is adhered to the sleeve part from the second stirring screw  24 . When the two component development method is employed, a magnetic field formed by a magnetic pole disposed fixedly in a sleeve interior causes the carrier constituted by the magnetic body to adhere to a sleeve surface from the second stirring screw  24  together with the toner, which is adhered by electrostatic force. The toner (developer) carried on the sleeve surface is conveyed to an opening portion (not shown) provided in the development housing  210 , and supplied to the opposing photosensitive drum  14 . 
     The interior space  220  of the development housing  210  is covered by a top plate, not shown in the drawing, and divided by a partition plate  22  extending in a left-right direction into a first conveyance passage  221  and a second conveyance passage  222  that are parallel to each other and formed in an elongated shape extending in the left-right direction. The partition plate  22  is shorter than a left-right direction width of the development housing  210  such that a first connecting passage  223  and a second connecting passage  224  connecting the first conveyance passage  221  to the second conveyance passage  222  are formed respectively on a left end and a right end of the partition plate  22 . As a result, a circulation path (a developer conveyance path) constituted by the first conveyance passage  221 , the first connecting passage  223 , the second conveyance passage  222 , and the second connecting passage  224  is formed in the interior space  220 . The toner is conveyed along the circulation path in a clockwise direction in  FIG. 2 . Hence, the first connecting passage  223  connects a downstream side of the first conveyance passage  221  in a toner conveyance direction to an upstream side of the second conveyance passage  222 , while the second connecting passage  224  connects a downstream side of the second conveyance passage  222  to an upstream side of the first conveyance passage  221 . 
     The toner replenishment port  25  (a developer introduction port) is an opening portion perforated into the top plate and disposed above the vicinity of a left end of the first conveyance passage  221  ( FIG. 2 ). The toner replenishment port  25  is disposed to face the circulation path described above, and functions to introduce replenishment toner (replenishment developer) supplied from the toner container  30  into the circulation path (the interior space  220 ). 
     The first stirring screw  23  is disposed in the first conveyance passage  221 . The first stirring screw  23  includes a first rotary shaft  23   a  (a rotary shaft), and a first spiral vane  23   b  (a screw vane) that projects in a spiral shape from a periphery of the first rotary shaft  23   a . The first stirring screw  23  is driven to rotate about the first rotary shaft  23   a  (arrow R 2 ) in order to convey the toner in a direction of an arrow D 1  in  FIG. 2  (a first direction). The first stirring screw  23  conveys the developer so that the developer passes the position in which the toner replenishment port  25  opposes the first conveyance passage  221 . The first stirring screw  23  thus has a function for mixing the toner conveyed through the first conveyance passage  221  with new toner flowing in through the toner replenishment port  25 , and passing the mixed toner to the second conveyance passage  222  side. 
     A first paddle  23   c  (a connecting conveyance portion) is disposed on a downstream side of the first stirring screw  23  in the toner conveyance direction (the D 1  direction). The first paddle  23   c  is a plate-shaped member disposed on the first rotary shaft  23   a  so as to face the first connecting passage  223 . The first paddle  23   c  rotates together with the first rotary shaft  23   a  in order to pass the toner from the first conveyance passage  221  to the second conveyance passage  222  in a direction of an arrow D 3  in  FIG. 2  (a third direction). 
     The second stirring screw  24  is disposed in the second conveyance passage  222 . The second stirring screw  24  includes a second rotary shaft  24   a , and a second spiral vane  24   b  that projects in a spiral shape from a periphery of the second rotary shaft  24   a . The second stirring screw  24  is driven to rotate about the second rotary shaft  24   a  (arrow R 1 ) in order to convey the toner in a direction of an arrow D 2  in  FIG. 2  (a second direction). The second stirring screw  24  conveys the toner through the second conveyance passage  222  and supplies the toner to the development roller  21 . A second paddle  24   c  is disposed on a downstream side of the second stirring screw  24  in the toner conveyance direction (the D 2  direction). The second paddle  24   c  is a plate-shaped member disposed on the second rotary shaft  24   a.  The second paddle  24   c  rotates together with the second rotary shaft  24   a  in order to pass the toner from the second conveyance passage  222  to the first conveyance passage  221  in a direction of an arrow D 4  in  FIG. 2  (a fourth direction). 
     The toner container  30  is disposed above the toner replenishment port  25  of the development housing  210 . The toner container  30  includes an interior toner conveyance passage  30   a  through which the toner is conveyed, a toner conveyance member  321 , and a toner discharge port  33 . The toner container  30  is incorporated into the development device  20  such that a lengthwise direction (a formation direction of the toner conveyance passage  30   a ) of the toner container  30  is positioned in an orthogonal direction to a lengthwise direction (the developer conveyance direction of the first stirring screw  23 , i.e. the arrow D 1  direction) of the development device  20 . 
     The toner discharge port  33  is provided in a bottom portion of the toner container  30  so as to oppose the toner replenishment port  25  of the development device  20 . The toner conveyance member  321  includes a shaft portion and a vane portion that rotates about the shaft portion (see  FIG. 3 ), and conveys replenishment toner in the toner conveyance passage  30   a  toward the toner discharge port  33 . Toner that falls through the toner discharge port  33  is supplied to the development device  20  via the toner replenishment port  25 . 
     &lt;Toner Conveyance Ability Suppressing Portion&gt; 
     The first stirring screw  23  includes a conveyance ability suppressing portion, in which a toner conveyance ability is suppressed in comparison with other parts, in two separate locations in an axial direction of the first rotary shaft  23   a.  More specifically, the first stirring screw  23 , when disposed in the first conveyance passage  221 , includes a first conveyance ability suppressing portion  26  positioned on a downstream side of the toner replenishment port  25  in the toner conveyance direction (the D 1  direction), and a second conveyance ability suppressing portion  28  positioned on an upstream side of the toner replenishment port  25 . The first conveyance ability suppressing portion  26  partially suppresses the toner conveyance ability such that a toner accumulation portion  27  for regulating a toner introduction amount is formed in a position facing the toner replenishment port  25 . The second conveyance ability suppressing portion  28  partially suppresses the toner conveyance ability such that an upstream side accumulation portion  29  in which the toner accumulates is formed on the upstream side of the toner replenishment port  25 . The accumulation portions  27 ,  29  will be described in detail below. 
     &lt;Re: Accumulation Portions&gt; 
     To describe the accumulation portion  27 , first, a flow of the toner newly introduced through the toner replenishment port  25  will be described.  FIG. 3  is a sectional view showing the vicinity of the toner replenishment port  25  provided in the development device  20  and the toner discharge port  33  provided in the toner container  30 . Note that for descriptive purposes, the toner container  30  has been rotated 90 degrees in a horizontal direction in  FIG. 3 . In actuality, the toner conveyance member  321  in the toner container  30  extends frontward toward a paper surface such that the first stirring screw  23  and the toner conveyance member  321  in the toner container  30  have a mutually orthogonal positional relationship. 
     Replenishment toner T 2  supplied through the toner discharge port  33  in the toner container  30  falls into the first conveyance passage  221  so as to intermix with existing toner T 1 , whereupon the mixed toner T 1 , T 2  is conveyed in the arrow D 1  direction (the first direction) by the first stirring screw  23 . At this time, the toner T 1 , T 2  is stirred and electrified. 
     As described above, the first conveyance ability suppressing portion  26  in which the toner conveyance ability is partially suppressed is provided on the first stirring screw  23  on the downstream side of the toner replenishment port  25  in the toner conveyance direction. In this embodiment, the first conveyance ability suppressing portion  26  is formed by removing the first spiral vane portion  23   b  of the first stirring screw  23  (see  FIG. 4 ). The first conveyance ability suppressing portion  26  therefore corresponds to a partial axial direction part in which only the first rotary shaft  23   a  exists. In this case, the first conveyance ability suppressing portion  26  does not have an ability to convey the toner in the axial direction of the first rotary shaft  23   a . Hence, in the first conveyance passage  221 , toner conveyed from an upstream side of the first conveyance ability suppressing portion  26  begins to accumulate in the first conveyance ability suppressing portion  26 . The toner accumulates up to a position directly on the upstream side of the first conveyance ability suppressing portion  26  where the toner replenishment port  25  opposes the first conveyance passage  221 , and as a result, the toner accumulation portion  27  (developer accumulation portion) is formed in the vicinity of an inlet of the toner replenishment port  25 . 
     Note that in a case where the first stirring screw  23  of the development device  20  is controlled to different rotation speeds depending on operation conditions of the image forming apparatus  1 , the first conveyance ability suppressing portion  26  is preferably constituted by a region in which only the first rotary shaft  23   a , and not the first spiral vane  23   b , is formed, as in this embodiment. In this case, the toner conveyance ability is suppressed irrespective of the rotation speed of the first stirring screw  23 , and therefore the accumulation portion  27  is formed with stability. 
     When the replenishment toner T 2  is supplied through the toner replenishment port  25  such that an amount of toner in the interior space  220  increases, the accumulated toner in the accumulation portion  27  blocks (seals) the toner replenishment port  25  such that further toner replenishment is suppressed. When the toner in the interior space  220  is consumed via the development roller  21  thereafter such that the amount of accumulated toner in the accumulation portion  27  decreases, the toner blocking the toner replenishment port  25  decreases such that a gap forms between the accumulation portion  27  and the toner replenishment port  25 . As a result, the replenishment toner T 2  flows into the interior space  220  through the toner replenishment port  25  again. Hence, this embodiment employs a volume replenishment type toner replenishment method in which the amount of introduced replenishment toner is adjusted as the amount of accumulated toner in the accumulation portion  27  decreases. 
       FIG. 11  shows a conventional development device  20 J 1  employing the volume replenishment type toner replenishment method. The development device  20 J 1  includes a circulation path constituted by a first conveyance passage  421 , a first connecting passage  401 , a second conveyance passage  422 , and a second connecting passage  402 . Toner is conveyed in circulatory fashion in directions of arrows D 11 , D 41 , D 21 , and D 31  by first and second stirring screws  23 J 1 ,  24 J 1 . A toner replenishment port  25 J 1  is provided in a substantially central portion of the first conveyance passage  421  in an axial direction. An accumulation portion  27 J 1  formed by a conveyance ability suppressing portion  26 J 1  of the first stirring screw  23 J 1  is formed in a position of the first conveyance passage  421  opposing the toner replenishment port  25 J 1 , and the amount of replenishment toner supplied from the toner container  30  is regulated by increasing and decreasing the accumulation portion. 
     Here, when determining an interior layout of a main body of the image forming apparatus  1  installed with the development device described above, it may be desirable to connect the toner container  30  to an end portion of the development housing  212  in a rotary shaft extension direction.  FIG. 12  shows a conventional development device  20 J 2  employing the volume replenishment type toner replenishment method. The development device  20 J 2  includes a circulation path constituted by a first conveyance passage  521 , a first connecting passage  501 , a second conveyance passage  522 , and a second connecting passage  502 . Toner is conveyed in circulatory fashion in the directions of the arrows D 11 , D 41 , D 21 , and D 31  by first and second stirring screws  23 J 2 ,  24 J 2 . A toner replenishment port  25 J 2  is provided in an upstream side end portion of the first conveyance passage  521  in the toner conveyance direction (the arrow D 11 ), and the toner container  30  (not shown) is disposed to face the toner replenishment port  25 J 2 . In this case, an accumulation portion  27 J 2  is formed by a conveyance ability suppressing portion  26 J 2  of the first stirring screw  23 J 2  so as to oppose the toner replenishment port  25 J 2 . 
     The connecting passage  502  that connects the first conveyance passage  521  to the second conveyance passage  522 , meanwhile, is disposed in the upstream side end portion of the first conveyance passage  521  in which the toner replenishment port  25 J 2  is provided. Hence, toner passed from the second conveyance passage  522  to the first conveyance passage  521  impinges on the accumulation portion  27 J 2  while being conveyed in the arrow D 11  direction by the first stirring screw  23 J 2 . The flow of the toner is therefore obstructed by the accumulation portion  27 J 2 . As a result, a toner blockage occurs in a region T in  FIG. 12 . 
     As shown in  FIG. 2 , to prevent this problem, the toner replenishment port  25  may be provided in the first conveyance passage  221  on the downstream side of the first direction (the arrow D 1  direction) and the toner container  30  may be disposed in accordance with this position. In this case, the accumulation portion  27  formed by the first conveyance ability suppressing portion  26  is near to the first connecting passage  223  for passing the toner from the first conveyance passage  221  to the second conveyance passage  222 . When the first paddle  23   c  is not provided, the toner conveyed in the first direction by the first stirring screw  23  impinges on a side wall  210   a  of the development housing  210  so as to form an accumulation. Toner overflowing from the accumulation gradually passes through the first connecting passage  223 , whereby the toner is passed as described above. Therefore, toner accumulation during the passage may affect the nearby accumulation portion  27 , leading to instability in replenishment toner regulation. 
     To solve the problem described above, occurring in relation to the accumulation portion  27  when the toner replenishment port  25  is provided in the first conveyance passage  221  on the downstream side of the first direction (the arrow D 1  direction), in this embodiment, a unique innovation is implemented in relation to the arrangement of the first paddle  23   c  and the first conveyance ability suppressing portion  26 . This point will be described in detail below. 
       FIG. 5  is a view illustrating a first embodiment in which the arrangement of the first paddle  23   c  and the first conveyance ability suppressing portion  26  is set favorably. In the drawing, A represents a width of the second connecting passage  224  in the second direction, B represents a width of the first connecting passage  223  in the first direction, and C represents a first direction length of the first paddle  23   c . Further, X represents a length of the first conveyance ability suppressing portion  26  in the first direction, and Z represents a first direction distance from a first direction downstream end of the toner replenishment port  25  to a first direction upstream end of the first connecting passage  223 . 
     In this embodiment, shapes and arrangements of the respective members are set such that B, X, and Z satisfy a relational expression Z&lt;X&lt;B (see  FIG. 5 ). Thus, a first direction downstream side of the first conveyance ability suppressing portion  26  and the first paddle  23   c  (connecting conveyance portion) constituted by a plate-shaped member are disposed to face the first connecting passage  223  in the third direction (the arrow D 3  direction). 
     The length C of the rotating first paddle  23   c  is included within the width B of the first connecting passage  223  in the first direction. Accordingly, toner positioned in the downstream end portion of the first conveyance passage  221  receives rotary force from the first paddle  23   c  so as to be passed actively to the upstream side of the second conveyance passage  222 . As a result, the toner positioned in the downstream end portion of the first conveyance passage  221  is prevented from flowing back to the periphery of the first conveyance ability suppressing portion  26 . 
     Further, the first direction downstream side of the first conveyance ability suppressing portion  26  opposes the first connecting passage  223  in the third direction. Therefore, even when excessive toner accumulates on the periphery of the first conveyance ability suppressing portion  26 , the toner on the periphery of the first conveyance ability suppressing portion  26  can flow directly into the first passage  223  without passing through the first paddle  23   c , as shown by an arrow Fl in the drawing. Hence, excessive toner in the accumulation portion  27  quickly flows out to the second conveyance passage  222  side. As a result, toner accumulation in the accumulation portion  27  is stable, and therefore the amount of supplied replenishment toner is regulated favorably. 
     Furthermore, since the first paddle  23   c  is constituted by a plate-shaped member, a barrier is formed between a right end portion (a first direction upstream side end portion) of the first paddle  23   c  and the first conveyance ability suppressing portion  26  when the first paddle  23   c  rotates. As a result, the toner is dammed easily, and therefore the first direction downstream side end portion (a starting end portion) of the accumulation portion  27  is secured reliably, while the toner in the accumulation portion  27  required to regulate the supply of replenishment toner is prevented from flowing out to the first connecting passage  223  side in an excessive amount. 
     Further, in this embodiment, the length of the first paddle  23   c  is set such that a relational expression C&gt;(B−C) is satisfied ( FIG. 5 ). Accordingly, a length (B−C) by which the first connecting passage  223  and the first conveyance ability suppressing portion  26  overlap in the first direction is set to be shorter than the first direction length C of the first paddle  23   c.  Hence, the accumulated toner in the accumulation portion  27  does not flow out into the first connecting passage  223  from the overlapping part in a large amount, and therefore only the excess toner in the accumulation portion  27  flows out to the second conveyance passage  222  side through the first connecting passage  223 . As a result, the amount of toner in the accumulation portion  27  remains stable. 
     Furthermore, in this embodiment, the respective first direction widths of the first connecting passage  223  and the second connecting passage  224  are set such that a relational expression B&lt;A is satisfied. Accordingly, a pressure of the toner is higher in the first connecting passage  223  than in the second connecting passage  224 , and therefore the toner is prevented from accumulating in a large amount on the second connecting passage  224  side. As a result, toner accumulation on the circulation path can be limited to a region extending from the accumulation portion  27  to the first connecting passage  223 . 
     Next, a second embodiment of the first conveyance ability suppressing portion will be described on the basis of  FIG. 6 . In this embodiment, similarly to the first embodiment, a first conveyance ability suppressing portion  26   a  is provided on the first direction downstream side of the toner replenishment port  25 , and a first paddle  231   c  is provided on a first direction downstream side of the first conveyance ability suppressing portion  26   a . Further, the first direction downstream side part of the first conveyance ability suppressing portion  26   a  and the first paddle  231   c  oppose a first connecting passage  223   a  in the third direction. On the other hand, in the second embodiment, the relationships between B, C, X, and Z differ from those of the first embodiment, and therefore this point will be described in detail, while description of other points will be omitted. 
     In the second embodiment, the shapes and arrangements of the respective members are set such that relational expressions Z&lt;B&lt;X and C&lt;B are satisfied. In this case, a first direction overlapping part (B−C) between the first connecting passage  223   a  and the first conveyance ability suppressing portion  26   a  is set to be larger than that of the first embodiment. In this embodiment, therefore, toner on the periphery of the first conveyance ability suppressing portion  26   a  flows to the first connecting passage  223   a  side more easily, and as a result, an accumulation portion  27   a  is less likely to form. In other words, the toner flows to the first connecting passage  223   a  side easily in a case where excessive toner is likely to accumulate in the accumulation portion  27   a  due to a fluidity, environmental conditions, and so on of the used toner, and therefore regulation of the replenishment toner supply is realized favorably. 
     Next, a third embodiment of the first conveyance ability suppressing portion will be described on the basis of  FIG. 7 . In this embodiment, similarly to the first embodiment, a first conveyance ability suppressing portion  26   b  is provided on the first direction downstream side of the toner replenishment port  25 , and a first paddle  232   c  is provided on a first direction downstream side of the first conveyance ability suppressing portion  26   b . Further, the first direction downstream side part of the first conveyance ability suppressing portion  26   b  and the first paddle  232   c  oppose a first connecting passage  223   b  in the third direction. On the other hand, in the third embodiment, the relationships between B, C, X, and Z differ from those of the first embodiment, and therefore this point will be described in detail, while description of other points will be omitted. 
     In this embodiment, the shapes and arrangements of the respective members are set such that relational expressions B&lt;Z&lt;X and C&lt;B are satisfied. In this case, in comparison with the first embodiment, the first conveyance ability suppressing portion  26   b  is set to be longer in the first direction and an accumulation portion  27   b  is formed over a longer first direction range. Further, a first direction overlapping part between the first connecting passage  223   b  and the first conveyance ability suppressing portion  26   b  is set to be smaller than a first direction length of the accumulation portion  27   b . As a result, in this embodiment, the toner in the accumulation portion  27   b  is less likely to flow to the first connecting passage  223   b  side. In other words, the accumulation portion  27   b  is formed by the first conveyance ability suppressing portion  26   b  even in a case where a toner accumulation is unlikely to form due to the fluidity, environmental conditions, and so on of the used toner, and therefore regulation of the replenishment toner supply is realized favorably. 
     Next, referring to  FIG. 8 , a first comparative example not including the configuration of the present disclosure will be described. In this comparative example, similarly to the first embodiment, a first conveyance ability suppressing portion  26   c  is provided on the first direction downstream side of the toner replenishment port  25 , and a first paddle  233   c  is provided on a first direction downstream side of the first conveyance ability suppressing portion  26   c . However, the first direction downstream side part of the first conveyance ability suppressing portion  26   c  does not oppose a first connecting passage  223   c  in the third direction. Further, in this comparative example, the relationships between B, C, X, and Z differ from those of the first embodiment, and therefore this point will be described in detail, while description of other points will be omitted. 
     In the first comparative example, the shapes and arrangements of the respective members are set such that relational expressions B&lt;X&lt;Z and B&lt;C are satisfied. This case differs from the first embodiment in that, as described above, the first direction downstream side part of the first conveyance ability suppressing portion  26   c  does not oppose the first connecting passage  223   c  in the third direction. Therefore, toner in an accumulation portion  27   c  cannot pass through the first connecting passage  223   c  without passing through the first paddle  233   c . Further, the first direction width B of the first connecting passage  223   c  is set to be smaller than the first direction length C of the first paddle  233   c . Hence, a problem occurs in that excessive toner accumulates in a region M of  FIG. 8 . As a result, in the first comparative example, a large amount of toner accumulates regardless of whether or not replenishment toner is required, and therefore regulation of the replenishment toner supply is not realized favorably. 
     Next, referring to  FIG. 9 , a second comparative example will be described. In the second comparative example, similarly to the first embodiment, a first conveyance ability suppressing portion  26   d  is provided on the first direction downstream side of the toner replenishment port  25 , and a first paddle  234   c  is provided on a first direction downstream side of the first conveyance ability suppressing portion  26   d . However, the first direction downstream side part of the first conveyance ability suppressing portion  26   d  does not oppose a first connecting passage  223   d  in the third direction. In this comparative example, the relationships between B, C, X, and Z differ from those of the first embodiment, and therefore this point will be described in detail, while description of other points will be omitted. 
     In the second comparative example, the shapes and arrangements of the respective members are set such that relational expressions X&lt;B&lt;Z and B&lt;C are satisfied. This case differs from the first embodiment in that, as described above, the first direction downstream side part of the first conveyance ability suppressing portion  26   d  does not oppose the first connecting passage  223   d  in the third direction. Therefore, toner in an accumulation portion  27   d  cannot pass through the first connecting passage  223   d  without passing through the first paddle  234   c . Further, the first direction length C of the first paddle  234   c  is set to be greater than the first direction width B of the first connecting passage  223   d , with the result that the first conveyance ability suppressing portion  26   d  is set to be short. Accordingly, a part (C−B) in which the first paddle  234   c  projects from the first connecting passage  223   d  in the second direction (the arrow D 2  direction) is so long that a flow of toner through the first conveyance passage  221  in the first direction is obstructed when this part rotates. Hence, the toner on the circulation path gathers on the periphery of the first paddle  234   c  such that the amount of toner in other regions decreases. As a result, the toner replenishment port  25  is sealed by the accumulation portion  27   d  at all times such that the replenishment toner cannot flow into the first conveyance passage  221 . Moreover, when, in this condition, images are output continuously at a high printing rate in the image forming apparatus  1 , partial toner deficiencies occur on the development roller  21 , leading to image quality defects. Therefore, with the second comparative example, regulation of the replenishment toner supply is not realized favorably, and moreover, a toner balance on the circulation path is disturbed, causing image quality defects. 
     Next, referring to  FIG. 10 , a third comparative example will be described. In the third comparative example, similarly to the first embodiment, a first conveyance ability suppressing portion  26   e  is provided on the first direction downstream side of the toner replenishment port  25 , and a first paddle  235   c  is provided on a first direction downstream side of the first conveyance ability suppressing portion  26   e . However, the first direction downstream side part of the first conveyance ability suppressing portion  26   e  does not oppose a first connecting passage  223   e  in the third direction. In the third comparative example, the relationships between B, C, X, and Z differ from those of the first embodiment, and therefore this point will be described in detail, while description of other points will be omitted. 
     In the third comparative example, the shapes and arrangements of the respective members are set such that relational expressions X&lt;Z&lt;B and B&lt;C are satisfied. This case differs from the first embodiment in that, as described above, the first direction downstream side part of the first conveyance ability suppressing portion  26   e  does not oppose the first connecting passage  223   e  in the third direction. Therefore, toner in an accumulation portion  27   e  cannot pass through the first connecting passage  223   e  without passing through the first paddle  235   c . Further, the first direction length C of the first paddle  235   c  is set to be slightly greater than the first direction width B of the first connecting passage  223   e , and the first conveyance ability suppressing portion  26   e  is set to be short. As a result, the amount of toner in the accumulation portion  27   e  formed by the first conveyance ability suppressing portion  26   e  is small, whereby excessive replenishment toner flows into the first conveyance passage  221 . Moreover, a part (C−B) in which the first paddle  235   c  projects from the first connecting passage  223   e  in the second direction (the arrow D 2  direction) is short, and therefore the first paddle  235   c  possesses little force for blocking the toner conveyed in the first direction. As a result, the circulation path does not include a region where the toner gathers and accumulates, and therefore an amount of toner distributed over the entire circulation path increases, leading to an increase in a drive torque of a development device  20   h . Hence, with the third comparative example, regulation of the replenishment toner supply is not realized favorably, and moreover, the toner balance on the circulation path is disturbed, causing defects in the drive torque of the development device  20   h.    
     As described above, in the first to third embodiments, the first conveyance ability suppressing portion  26  ( 26   a ,  26   b ) is provided on the first direction downstream side of the toner replenishment port  25 , and the first paddle  23   c  ( 231   c ,  232   c ) is provided on the first direction downstream side of the first conveyance ability suppressing portion  26  ( 26   a ,  26   b ). Further, the first direction downstream side part of the first conveyance ability suppressing portion  26  ( 26   a ,  26   b ) and the first paddle  23   c  ( 231   c ,  232   c ) oppose the first connecting passage  223  ( 223   a ,  223   b ) in the third direction. Therefore, in contrast to the first to third comparative examples, the toner accumulates in the accumulation portion  27  ( 27   a ,  27   b ) with stability such that regulation of the replenishment toner supply is realized favorably. 
     &lt;Re: Upstream Side Accumulation Portion&gt; 
     Next, the upstream side accumulation portion  29  formed by the second conveyance ability suppressing portion  28  will be described. First, a reason why the second conveyance ability suppressing portion  28  needs to be provided in the development device  20  including the first conveyance ability suppressing portion  26  that forms the accumulation portion  27  will be described. 
     In the volume replenishment type toner replenishment method described above, when the amount of replenishment toner T 2  housed in the toner container  30  varies rapidly, the replenishment toner T 2  may flow rapidly into the interior space  220  of the development housing  210 . This phenomenon occurs particularly strikingly when a residual amount of toner in the toner container  30  attached to the development device  20  decreases such that the toner container  30  is replaced with a new toner container  30  by a user. This phenomenon will be described below with reference to  FIGS. 13A and 13B . 
       FIGS. 13A and 13B  are sectional views showing the first passage  221  in the development housing  220  from the horizontal direction. In both drawings, toner flows into a right end of the first conveyance passage  221  in the drawings from the second connecting passage  224 . The toner conveyed through the first conveyance passage  221  by the first stirring screw  23  is passed to the second conveyance passage  222  side on a left end of the first conveyance passage  221  in the drawings by the first paddle  23   c.  Further, in both  FIG. 13A  and  FIG. 13B , the toner container  30 , not shown in the drawings, is disposed above the toner replenishment port  25  provided on the downstream side of the first conveyance passage  221 .  FIGS. 13A and 13B  show a manner in which a toner distribution in the first conveyance passage  221  varies in accordance with differences in the amount of toner in the toner container  30 . 
       FIG. 13A  shows a condition of the first conveyance passage  221  when the amount of toner in the toner container  30  is small.  FIG. 13B  shows a condition in which the toner container  30  has been replaced with a new toner container  30  from the condition shown in  FIG. 13A . In  FIG. 13A , the amount of replenishment toner T 2  that can fall through the toner discharge port  33  is small, and therefore a downward pressure applied by the replenishment toner T 2  to the accumulation portion  27  is small (arrow Y 21 ). Accordingly, a pressure required for the accumulation portion  27  to seal the toner replenishment port  25  from below is also small. Hence, the replenishment toner T 2  and the toner in the accumulation portion  27  press against each other by a small pressure such that equilibrium is maintained therebetween, and as a result, the toner replenishment port  25  is sealed. At this time, the toner T 1  in the first conveyance passage  221  is distributed between the accumulation portion  27  covering the toner replenishment port  25 , a first upstream portion  100   b  distributed directly upstream of the toner replenishment port  25  and having an inclined surface, and a second upstream portion  100   c  distributed further upstream and having a substantially horizontal, stable draft surface. 
     Here, when the residual amount of toner in the toner container  30  decreases, the user is warned thereof by display means, not shown in the drawings, provided on the image forming apparatus  1 . At an appropriate time, the user detaches the old toner container  30  and attaches a new toner container  30  to the development device  20 . A large amount of toner is housed in the interior of the new toner container  30 , and therefore the amount of replenishment toner T 2  attempting to fall through the toner discharge port  33  toward the toner replenishment port  25  increases rapidly when the toner container  30  is replaced. 
     Accordingly, the downward pressure applied by the replenishment toner T 2  to the accumulation portion  27  in the toner replenishment port  25  increases (arrow Y 22 ). Moreover, the downward pressure applied by the replenishment toner T 2  to the accumulation portion  27  in the toner replenishment port  25  exceeds an upward pressure applied by the accumulation portion  27  to the replenishment toner T 2 . As a result, the replenishment toner T 2  advances through the first conveyance passage  221  to the first upstream portion  100   b  side (arrow  100   d ) where a pressure (a sealing pressure) exerted on the toner replenishment port  25  is weak. The advancing toner forms a sudden toner inflow that is outside the regulation range, and differs from the flow of replenishment toner flowing in through the toner replenishment port  25  in that the amount of developer in the accumulation portion  27  decreases relative to the amount of toner consumed via the development roller  21 . 
     When, following replacement of the toner container  30 , the development device  20  is controlled to rotate the first stirring screw  23  and the second stirring screw  24 , the toner distribution in the interior space  220  varies due to the inflowing replenishment toner T 2  described above. In other words, as shown in  FIG. 13B , when the amount of toner in the interior space  220  increases rapidly, the amount of toner accumulated by the first conveyance ability suppressing portion  26  also increases. As a result, the accumulation portion  27  spreads to the upstream side of the toner replenishment port  25  such that the second accumulation portion  27 B is formed. Further, the first upstream portion  100   b  and the second upstream portion  100   c  respectively shift to the upstream side in the toner conveyance direction (the arrow D 1  direction) such that a third upstream portion  100   e  and a fourth upstream portion  100   f  are formed. The second accumulation portion  27 B blocks the toner replenishment port  25  from both the upstream side and the downstream side by a larger amount of toner than the accumulation portion  27 , and therefore, eventually, advancement of the replenishment toner T 2  flowing in immediately after replacement of the toner container  30  is suppressed. 
     Hence, when a toner container  30  housing a small amount of toner in its interior is replaced with a new toner container  30  housing a large amount of toner, the pressure exerted by the replenishment toner T 2  in the toner replenishment port  25  varies such that a large amount of replenishment toner T 2  flows into the first conveyance passage  221  rapidly. In this case, the replenishment toner T 2  and the toner T 1  housed in the first conveyance passage  221  cannot be stirred and mixed together quickly, and therefore unevenness occurs in the toner charge. Unevenly charged toner causes toner fogging on the photosensitive drum  14  following development. 
     To solve the problem described above, in which a large amount of toner flows rapidly to the development device  20  side when the amount of toner in the toner container  30  varies, in this embodiment, the first stirring screw  23  includes the second conveyance ability suppressing portion  28  (to be referred to hereafter as a suppression paddle  28 ) in a position in the first conveyance passage  221  on the upstream side of the toner replenishment port  25  in the toner conveyance direction (the arrow D 1  direction) (see  FIGS. 2 ,  4 , and so on). 
     The suppression paddle  28  is a plate-shaped rib member that spans two adjacent first spiral vanes  23   b  in the arrow D 1  direction so as to extend in a rotation radius direction of the first rotary shaft  23   a . The suppression paddle  28  rotates in the arrow R 2  direction in accompaniment with the rotation of the first stirring screw  23  so as to convey the toner T 1  conveyed through the first conveyance passage  221  in the R 2  direction. Hence, the ability to convey the toner T 1  in the arrow D 1  direction is suppressed on a periphery of the suppression paddle  28  such that the toner T 1  accumulates. The upstream side accumulation portion  29  is formed in the first conveyance passage  221  directly upstream of the toner replenishment port  25  by the accumulated toner T 1 . 
     Referring to  FIGS. 14A and 14B , the toner distribution through the development device  20  including the suppression paddle  28  according to this embodiment will be described.  FIGS. 14A and 14B  are sectional views showing the first conveyance passage  221  in the development housing  220  from the horizontal direction.  FIG. 14A  shows a condition of the interior space  220  when the amount of toner in the toner container  30  is small.  FIG. 14B  shows a condition in which the toner container  30  has been replaced with a new toner container  30  from the condition shown in  FIG. 14A . In  FIG. 14A , the accumulation portion  27  is formed in the first conveyance passage  221  by the first conveyance ability suppressing portion  26  in a position opposing the toner replenishment port  25 , as described above. Further, the upstream side accumulation portion  29  is formed directly upstream of the toner replenishment port  25  by the suppression paddle  28 . 
     The upstream side accumulation portion  29  accumulates so as to block the first conveyance passage  221  on the upstream side of the toner replenishment port  25 . When the amount of toner in the toner container  30  is small, the downward pressure applied by the replenishment toner T 2  to the accumulation portion  27  in the toner replenishment port  25  is small (arrow Y 23 ). In this case, the accumulation portion  27  and the upstream side accumulation portion  29  block the periphery of the toner replenishment port  25  on the first conveyance passage  221  side such that upward pressure is exerted on the replenishment toner T 2 . As a result, the replenishment toner T 2  stops in the vicinity of the toner replenishment port  25  rather than flowing into the interior space  220 . 
     When the toner container  30  is replaced with a new toner container  30 , the amount of toner housed therein is large, and therefore the downward pressure applied by the replenishment toner T 2  to the accumulation portion  27  in the toner replenishment port  25  increases. In this embodiment, however, the accumulation portion  27  and the upstream side accumulation portion  29  apply upward pressure to the replenishment toner T 2  in the toner replenishment port  25  likewise in this case, and therefore the replenishment toner T 2  does not flow rapidly into the first conveyance passage  221  ( FIG. 14B ). In particular, the upstream side of the toner replenishment port  25 , to which the replenishment toner T 2  advances easily when the suppression paddle  28  is not provided, is sealed by the upstream side accumulation portion  29 , and therefore the replenishment toner T 2  is prevented from flowing rapidly into the first conveyance passage  221 . 
     Hence, the suppression paddle  28  has a function for forming the upstream side accumulation portion  29 , and the upstream side accumulation portion  29  has a function for sealing the upstream side of the toner replenishment port  25 . Furthermore, the suppression paddle  28  is disposed in an outermost position in a radial direction of the first spiral vane  23   b , and therefore the rotating suppression paddle  28  forms a barrier directly upstream of the toner replenishment port  25  in a region in the vicinity of an inner peripheral surface of the development housing  210  on an orthogonal cross-section to the first rotary shaft  23   a . As a result, the replenishment toner T 2  is prevented from flowing to the upstream side of the toner replenishment port  25  following replacement of the toner container  30  even more reliably. 
     The toner in the interior space  220  is consumed on the photosensitive drum  14  side via the development roller  21 , and when the amount of developer in the accumulation portion  27  and the upstream side accumulation portion  29  decreases, the replenishment toner T 2  flows into the interior space  220  (the first conveyance passage  221 ). 
     As described above, with the development device  20  according to this embodiment, rapid toner inflow into the development housing  210 , which is likely to occur following replacement of the toner container  30 , is suppressed. Therefore, a stirring deficiency between the rapidly inflowing toner and the toner in the development housing  210  is unlikely to occur, and as a result, toner fogging on the photosensitive drum  14  is suppressed. 
     The development device  20  according to an embodiment of the present disclosure was described above, but the present disclosure is not limited thereto, and the following modified embodiments, for example, may be employed. 
     (1) In the embodiment described above, a part in which the first spiral vane  23   b  is removed from the first stirring screw  23  is used as the first conveyance ability suppressing portion  26 . Alternatively, a rod member that is parallel to the first rotary shaft  23   a  may be disposed on a peripheral edge portion of the first spiral vane  23   b  of the first stirring screw  23 , and a part to which the rod member is annexed may be used as the first conveyance ability suppressing portion  26 . The toner conveyance ability is suppressed by the rod member annexed to the first spiral vane  23   b  such that the toner accumulates in the first conveyance passage  221 . 
     (2) In the embodiment described above, a plate-shaped member disposed on the first rotary shaft  23   a  is used as the first paddle  23   c . However, the present disclosure is not limited thereto, and instead, a rod-shaped member disposed parallel to the first rotary shaft  23   a  may be disposed on the first rotary shaft  23   a . Further, a tip end of the plate-shaped member may be bent into a dogleg shape in order to improve the toner passing ability, and so on. 
     (3) In the embodiment described above, the suppression paddle  28  serves as the second conveyance ability suppressing portion to form the upstream side accumulation portion  29 . However, the present disclosure is not limited thereto, and instead, for example, the second conveyance ability suppressing portion may be formed by partially providing only the first rotary shaft  23   a , or in other words partially removing the first spiral vanes  23   b . In this case, the toner conveyance ability in the direction of the first rotary shaft  23   a  (the arrow D 1  direction) decreases such that the upstream side accumulation portion  29  is formed similarly. The second conveyance ability suppressing portion may also be formed by partially reducing an outer diameter of the first spiral vane  23   b.    
     Although the present disclosure has been fully described by way of example with reference to the accompanying drawings, it is to be understood that various changes and modifications will be apparent to those skilled in the art. Therefore, unless otherwise such changes and modifications depart from the scope of the present disclosure hereinafter defined, they should be construed as being included therein.