Abstract:
A developing apparatus including a first chamber; a second chamber forming a circulation path for the developer; a rotatable shaft in the first chamber; a first blade provided on the rotation shaft to feed the developer in a predetermined direction in the first chamber; a second blade provided on the rotation shaft to feed the developer fed by the first blade in a direction opposite the predetermined direction; a discharging portion provided downstream of the second blade to discharge the developer in the first chamber; and a regulating member having a regulating surface continuously extending in a rotational moving direction of the rotation shaft, the regulating member being provided on the rotation shaft in a region between the first blade and the second blade, a region connecting with a downstream end of the first blade, or a connecting with a downstream end of the second blade.

Description:
FIELD OF THE INVENTION AND RELATED ART 
       [0001]    The present invention relates to a developing apparatus which is mounted in an electrophotographic image forming apparatus or the like to develop an electrostatic image on an image bearing member into a toner image, with the use of developer which contains toner and carrier. 
         [0002]    There have been widely used an image forming apparatus such as a copying machine, a printer, and a facsimile, the developing device of which develops an electrostatic image formed on an image bearing member such as a photosensitive drum, into a toner image, with the use of developer which contains toner and carrier. 
         [0003]    Referring to  FIG. 3 , the background technologies of an image forming apparatus of the abovementioned type is described. A developing device ( 1 ) circularly moves developer through a development chamber ( 14 ) and a stirring chamber ( 15 ), which are in connection to each other through openings ( 7   a ,  7   b ), by rotating a conveyance screw ( 5 ) and a stirring screw ( 6 ). As the developer in the developing device ( 1 ) is continuously stirred for a substantial length of time, the developer in the developing device ( 1 ) deteriorates. Thus, as an image forming operation continues, the developer container ( 2 ) is continuously replenished with developer little by little, while causing the developer in the developer container ( 2 ) to overflow from the developer container ( 2 ) by the amount by which the amount of the developer in the developer container ( 2 ) was made excessive by the replenishment of the developer container ( 2 ) with carrier (Japanese Laid-open Patent Application 2010-256701). 
         [0004]    In the case of the developing device ( 1 ) disclosed in Japanese Laid-open Patent Application 2010-256701, a return screw ( 10 ) which is opposite in the developer conveyance direction from the stirring screw ( 6 ) is disposed on the downstream side of the stirring chamber ( 15 ), in order to discharge the developer through a developer discharge opening ( 8 ) as the developer flows downstream of the stirring chamber ( 15 ) over the return screw  10 . 
         [0005]    In the case of the developing apparatus disclosed in Japanese Laid-open Patent Application 2010-237329, a disc-shaped member is provided on the upstream side of the return screw ( 10 ), in terms of the developer conveyance direction of the return screw ( 10 ), that is, the downstream side of the stirring chamber ( 15 ) in terms of the downstream side of the developer conveyance direction of the stirring chamber ( 15 ), to prevent the developer from flowing downstream of the stirring chamber ( 15 ) over the return screw ( 10 ) by an excessive amount. 
         [0006]    It has been discovered that in the case of the developing apparatus ( 1 ) which uses the return screw ( 10 ) to regulate the discharging of the developer, the amount by which the developer is discharged changes in synchronism with the rotational period of the return screw ( 10 ), or the rotational period of the conveyance screw ( 5 ) which rotates in the development chamber ( 14 ) which is located next to the stirring chamber ( 15 ). It has also been discovered that as the stirring screw ( 6 ) is switched in rotational speed, and/or as developer changes in fluidity, the amount by which the developer is discharged changes. 
       SUMMARY OF THE INVENTION 
       [0007]    The primary object of the present invention, which relates to a developing apparatus which uses a return screw to regulate the amount by which developer is discharged, is to provide a developing apparatus which is stable in the effects of the regulation, being therefore smaller in the change in the amount of developer discharge, and therefore, is stable in developer discharge. 
         [0008]    According to an aspect of the present invention, there is provided a developing apparatus comprising a first chamber in which a developer including toner and carrier is fed; a second chamber in fluid communication with said first chamber to form a circulation path for the developer; a rotation shaft rotatable in said first chamber; a first blade member provided on said rotation shaft and configured to feed the developer in a predetermined direction in said first chamber; a second blade member provided on said rotation shaft and configured to feed the developer fed by said first blade member in a direction opposite the predetermined direction; a discharging portion provided downstream of said second blade member with respect to the predetermined direction and configured to discharge the developer in said first chamber; and a regulating member having a regulating surface continuously extending in a rotational moving direction of said rotation shaft and configured to regulate the developer fed by said first blade member, said regulating member being provided on said rotation shaft in a region between said first blade member and said second blade member, a region connecting with a downstream end of said first blade member, or a connecting with a downstream end of said second blade member. 
         [0009]    Further features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings). 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a drawing for describing the structure of the image forming apparatus in the first embodiment of the present invention. 
           [0011]      FIG. 2  is a sectional view of the developing apparatus, at a plane which is perpendicular to the axial lines of the rollers of the apparatus. It is a drawing for describing the structure of the apparatus. 
           [0012]      FIG. 3  is a perspective view of the developing apparatus. 
           [0013]      FIG. 4  is a sectional view of the stirring chamber at a plane which is perpendicular to the lengthwise direction of the chamber. It is for describing the stirring chamber. 
           [0014]      FIG. 5  is a perspective view of the stirring screw. 
           [0015]      FIG. 6  is an enlarged view of a comparative return screw. 
           [0016]      FIG. 7  is a drawing for describing the gap between the peripheral edge of the return screw and the inward surface of the stirring chamber. 
           [0017]      FIG. 8  is a plan view of the adjacencies of the return screw of the comparative developing apparatus. 
           [0018]      FIG. 9  is perspective view of the adjacencies of the return screw of the comparative developing apparatus. 
           [0019]      FIG. 10  is a plan view of the adjacencies of the return screw of the developing apparatus in the first embodiment. 
           [0020]      FIG. 11  is a perspective view of the adjacencies of the return screw of the developing apparatus in the first embodiment. 
           [0021]      FIG. 12  is a perspective view of the adjacencies of the return screw of a developing apparatus which has no blade-free portion between its regulatory portion and stirring screw. 
           [0022]      FIG. 13  is a plan view of the adjacencies of the return screw of the developing apparatus in the second embodiment. 
           [0023]      FIG. 14  is a perspective view of the adjacencies of the return screw of the developing apparatus in the second embodiment. 
           [0024]      FIG. 15  is a drawing for describing a return screw having a tapered portion. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0025]    Hereinafter, preferable embodiments of the present invention are described in detail with reference to appended drawings. 
       (Image Forming Apparatus) 
       [0026]      FIG. 1  is a drawing for describing the structure of the image forming apparatus in the first embodiment. Here, the overall structure and operation of the image forming apparatus in the first embodiment are described. 
         [0027]    Referring to  FIG. 1 , the image forming apparatus  100  is an electrophotographic full-color printer having four image formation sections, which correspond one for one to the four primary colors, more specifically, yellow, magenta, cyan and black. 
         [0028]    The image forming apparatus  100  is capable of forming a full-color image (based on four primary color) on a sheet of recording medium (recording paper, plastic film, fabric, etc.), in response to image formation signals it receives from an image reading apparatus which is in connection to the main assembly of the apparatus  100 , or a host apparatus, such as a personal computer, connected to the main assembly so that communication is possible between the image forming apparatus  100  and host apparatus. 
         [0029]    The image formation sections  110 Y,  110 M,  110 C and  110 Bk form yellow, magenta, cyan, and black toner images, with the use of photosensitive drums  29 Y,  29 M,  29 C and  29 Bk, respectively. They place the four toner images in layers on an intermediary transfer belt  86 . 
         [0030]    Meanwhile a sheet P of recording medium stored in a recording medium storage cartridge (unshown) is conveyed to a secondary transfer section T2 with the use of a supply roller  84  and a conveyer belt  88 , with the same timing as the timing with which the toner images are conveyed to the secondary transfer section T2. Then, the four toner images, different in color, on the intermediary transfer belt  86  are transferred together (secondary transfer) onto the sheet P of recording medium on the conveyer belt  88 , by the application of transfer bias to a secondary transfer roller  33 . 
         [0031]    After the transfer of the toner images onto the sheet P of recording medium from the intermediary transfer belt  86 , the sheet P is separated from the conveyer belt  88 , and is conveyed to a fixing device  70 , which thermally fixes the toner images to the sheet P by applying heat and pressure to the sheet P onto which the toner images were transferred. Thus, the toner images on the sheet P are melted and mixed, becoming a permanent full-color image. Thereafter, the sheet P is discharged from the image forming apparatus  100 . 
         [0032]    The toner which remained on the intermediary transfer belt  86  in the secondary transfer section T2 is removed by a belt cleaning apparatus  18 . Not only can the image forming apparatus  100  form a full-color image, but also, a monochromatic image of a desired color, and a multicolor image having two or more colors, with the use of only the desired image formation section, or sections. 
       (Image Formation Section) 
       [0033]    Referring to  FIG. 1 , the four image formation sections  110 Y,  110 M,  110 C and  110 Bk are practically the same in structure, although they are different in developer color. That is, in the first embodiment, the developing devices  1 Y,  1 M,  1 C and  1 Bk which correspond to yellow, magenta, cyan and black, respectively, are the same in structure. In the following description of the developing devices, therefore, suffixes Y, M, C and Bk which indicate which image formation section each structural component, and portions thereof, belong, are left out to describe the four image formation sections together. 
         [0034]    Generally speaking, a photosensitive drum  29  (photosensitive member) which is an example of image bearing member is an electrophotographic photosensitive member which is in the form of a rotatable drum. A charge roller  35  (charging process) uniformly charges the photosensitive drum  29  to preset polarity and potential level. An exposing device  37  (exposing process) is an information writing means which forms an electrostatic image on the charged photosensitive drum  29 . A developing device  1  (developing process) develops the electrostatic image formed on the photosensitive drum  29 , into a toner image, with the use of the toner in developer. A transferring device  34  (transferring process) transfers the toner image onto the intermediary transfer belt  86  from the peripheral surface of the photosensitive drum  29 . A drum cleaning device  40  (cleaning process) moves a small amount of toner (residual developer, transfer residual toner) remaining on the photosensitive drum  29  after the transfer of the toner image from the photosensitive drum  29 , to clean the peripheral surface of the photosensitive drum  29 . The photosensitive drum  29  is repeatedly subjected to electrophotographic processes (charging process, exposing process, developing process, transferring process and cleaning process) to form toner images. 
         [0035]    The photosensitive drum  29  is a cylindrical photosensitive component. It is rotationally driven in the direction indicated by an arrow mark R29 in the drawing. The charge roller  35 , developing device  1 , primary transfer roller  34 , and drum cleaning device  40  are disposed in the adjacencies of the peripheral surface of the photosensitive drum  29 . There is also disposed an exposing device  37  which employs a laser scanner disposed above the photosensitive drum  29 . 
         [0036]    The intermediary transfer belt  86  is disposed so that it is pinched by the photosensitive drum  29  and primary transfer roller  34 . It is circularly driven by a driver roller  89  in the direction indicated by an arrow mark R86 to convey the toner images to the secondary transfer section T2 in which the toner images are transferred onto a sheet P of recording medium. 
         [0037]    As an image forming operation begins, first, the peripheral surface of the rotating photosensitive drum  29  is uniformly charged by the charge roller  35 . During this process of charging the photosensitive drum  29 , charge bias is applied to the charge roller  35  from a charge bias power source. Next, the photosensitive drum  29  is exposed by a beam of laser light emitted by the exposing device  37  while being modulated with image formation signals. Consequently, an electrostatic image (latent image) is effected on the photosensitive drum  29 . 
         [0038]    The electrostatic image on the photosensitive drum  29  is developed into a visible image by the toner stored in the developing device  1 . In the case of the developing device  1  in this embodiment, a reversal developing method is used. Thus, toner adheres to the points (areas) of the peripheral surface of the photosensitive drum  29 , which have just been exposed to the beam of laser light. After the formation of a toner image on the photosensitive drum  29  by the developing device  1 , the toner image is transferred onto the intermediary transfer belt  86  (primary transfer). The transfer residual toner, that is, the toner remaining on the photosensitive drum  29  after the primary transfer is removed by the drum cleaning device  40 . 
       (Developing Device) 
       [0039]      FIG. 2  is a sectional view of the developing device  1 , at a plane which is perpendicular to the axial lines of the rollers of the developing device  1 . It is for describing the developing device  1 .  FIG. 3  is a perspective view of the developing device  1 . The developing device  1  uses a two-component developing method, which uses a mixture of toner and carrier, as its developer. A two-component developing method is advantageous in terms of the image quality stability, apparatus durability, etc., over other developing methods which are presently proposed. 
         [0040]    Referring to  FIG. 2 , the developing device  1  stores two-component developer made up of toner (nonmagnetic) and carrier (magnetic), in its developer container  2 . The ratio of mixture between the toner and carrier is roughly 1:9 in weight. This ratio is to be properly adjusted according to the amount of toner charge, carrier particle diameter, structure of the image forming apparatus  100 , etc. The ratio should not be limited to the abovementioned numerical value. 
         [0041]    The developing device  1  has an opening, which corresponds in position to the development area of the developing device  1 , which faces the photosensitive drum  29 . It has also a development sleeve  3  and a magnet  4 . The development sleeve  3  is disposed so that it is partially exposed from the developer container  2  through the opening. The magnet  4  is disposed in the hollow of the development sleeve  3 . 
         [0042]    The development sleeve  3  is formed of a nonmagnetic substance. During a developing operation, it is rotated in the direction indicated by an arrow mark A. It holds in a layer the two-component developer in the developer container  2 , and conveys the layer of developer to the development area, in which it supplies the photosensitive drum  29  with the developer to develop the electrostatic image on the photosensitive drum  29 . After the development of the electrostatic image, the developer is recovered into the developer container  2  by the rotation of the development sleeve  3 . 
         [0043]    Next, referring to  FIG. 3 , the interior of the developer container  2  has a development chamber  14  which is the second chamber in which the development sleeve  3  and developer are storable, and a stirring chamber  15  which is the first chamber in which the developer is storable. The two chambers  14  and  15  are divided by a partition wall  7 . There are disposed a conveyance screw  5  and a stirring screw  6  in the development chamber  14  and stirring chamber  15 , respectively. The developer in the developer container  2  is circularly conveyed in the developer container  2  by the conveyance screw  5  and stirring screw  6  while being stirred and mixed by the conveyance screw  5  and stirring screw  6 . 
         [0044]    The above-mentioned partition wall  7  is between the conveyance screw  5  and stirring screw  6 . The rear portion of the partition wall  7  is provided with an opening  7   a , whereas the front portion of the partition wall  7  is provided with an opening  7   b , in order to ensure that while the developer is circularly conveyed in the developer container  2 , the developer is allowed to smoothly move between the development chamber  14  and stirring chamber  15 . The openings  7   a  and  7   b  connect the development chamber  14  and stirring chamber  15 , making up parts of the developer circulation passage. 
         [0045]    The developer in the development chamber  14  is conveyed in the direction indicated by an arrow mark B, whereas the developer in the stirring chamber  15  is conveyed in the direction indicated by an arrow mark C. That is, the developer is circularly moved in the developer container  2  by being conveyed in the direction indicated by the arrow mark B, and then, in the direction indicated by the arrow mark C. 
       (Automatic Developer Replacement Method) 
       [0046]      FIG. 4  is a sectional view of the stirring chamber  15 , at a vertical plane parallel to the lengthwise direction. It is for describing the stirring chamber  15 .  FIG. 5  is a perspective view of the stirring screw  6 . 
         [0047]    In the case of the developing device  1  which uses a two-component developing method, it is impossible for the developing device  1  to escape from the developer deterioration, in particular, carrier deterioration, which is attributable to the continuous and extended usage of the device  1 . Thus, a method for automatically replacing developer is employed. An automatic developer replacement method replenishes the developing device  1  with replenishment developer which contains toner, by the amount by which toner was consumed by the developing operation of the developing device  1 . It discharges the excessive amount of developer in the developing device  1 , into an external recovery container  114 . As the replenishment developer, such developer that contains carrier by a preset ratio (roughly 10% in weight) is used. 
         [0048]    Also in the case of an automatic developer replacement method, the excessive amount of developer in the developing device  1  is automatically discharged at roughly the same time as the replenishment of the developing device  1  with replenishment toner. The usage of this method, therefore, makes it possible to keep stable the developer in the developing device  1  in overall properties, without requiring an image forming apparatus to be increased in size and/or cost. Further, the developer replacement operation is automatically carried out as an image forming operation continues. Thus, this method makes unnecessary an operation for entirely replacing the developer in the developing device  1 , or replacing the developing device  1  itself. Thus, this method makes it possible to improve a developing device in terms of maintenance, and also, to reduce a developing device in operational cost. 
         [0049]    Referring to  FIG. 2 , a developer replenishment section  11  delivers replenishment developer to the upstream side of the stirring screw  6 , in terms of the developer conveyance direction of the stirring screw  6 , in the stirring chamber  15 . As a replenishment screw  112  is rotated, such developer that contains toner by the amount by which toner was consumed by image formation is delivered to the developer container  2 . 
         [0050]    The toner in developer is consumed by image formation. However, the carrier delivered to the developing device  1  is not consumed by image formation. Thus, it remains in the developer container  2 . Therefore, as the developer container  2  is continuously replenished with replenishment developer to keep stable, in toner density, the developer in the developer container  2 , the developer in the developer container  2  gradually increases, as an image forming operation continues. 
         [0051]    Next, referring to  FIG. 4 , there is provided a developer discharge passage  13  on the downstream side of the stirring screw  6  in terms of the developer conveyance direction. The discharge passage  13  extends from the developer conveyance passage  12  (part of developer circulation passage) in which the stirring screw  6  is disposed. The developing device  1  is designed so that the bottom surface  13   a  of the discharge passage  13  is positioned higher than the bottom surface  12   a  of the conveyance passage  12 . Further, the bottom surface  13   a  of the discharge passage  13  is provided with a developer discharge opening  8 . The rotational shaft  10   a  of the stirring screw  6  is rotatably disposed, extending through the conveyance passage  12  and discharge passage  13 . It rotates the return screw  10  and developer discharge screw  9  together. 
         [0052]    Referring to  FIG. 5 , the return screw  10  is disposed on the downstream side of the stirring screw  6  in terms of the conveyance direction of the stirring screw  6 . The developer conveyance direction of the return screw  10  is opposite from the developer conveyance direction Ha of the stirring screw  6 . The developer discharge screw  9  is disposed on the downstream side of the return screw  10  in terms of the developer conveyance direction of the stirring screw  6 . The developer conveyance direction of the developer discharge screw  9  is the same as the developer conveyance direction Ha of the stirring screw  6 . 
         [0053]    Referring to  FIG. 4 , the developer discharge screw  9  conveys the excessive amount of developer in the discharge passage  13  to the developer discharge opening  8 , and discharges the developer through the opening  8 . As the developer in the developer container  2  is increased by the repetition of the replenishment of the developing device  1  with the replenishment developer, the developer in the stirring chamber  15  starts to flow into the discharge passage  13  over the return screw  10 , and be conveyed to the developer discharge opening  8 , and discharged from the opening  8 , by the developer discharge screw  9 . As the developer is discharged through the developer discharge opening  8 , it is recovered by the recovery container ( 114  in  FIG. 3 ), and is stored therein. 
         [0054]    As described above, in the case of an automatic developer replacement method, the developing device  1  is automatically and gradually replenished with replenishment developer in such a manner that the developer container  2  remains stable in the amount of the developer therein. That is, the developing device  1  is replenished with toner by the amount by which toner was consumed by an image forming operation, by the replenishment of the developing device  1  with the replenishment developer, while discharging the developer in the developer container  2 , which has become excessive in carrier content. 
       (Comparative Developing Device) 
       [0055]      FIG. 6  is an enlarged view of the return screw  10 H of the comparative developing device  1 .  FIG. 7  is a drawing for describing the gap between the peripheral edge of the return screw  10 H and inward surface of the stirring chamber  15 .  FIG. 8  is a plan view of the adjacencies of the return screw  10 H of the comparative developing device  1 . By the way, in  FIGS. 8 and 9 , the portion of the developer container  2 , which covers the top side of the developer container  2 , is not illustrated, in order to show the internal structure of the developing device  1 . 
         [0056]    Referring to  FIG. 6 , across the downstream end portion of the stirring screw  6  in terms of the developer conveyance direction, the developer is conveyed in the direction indicated by an arrow mark P. A certain amount of developer flows over the return screw  10 H as indicated by an arrow mark Q. Then, it is conveyed to the developer discharge opening  8  in  FIG. 4 ) by the discharge screw  9 , and is discharged through the developer discharge opening  8 . 
         [0057]    If the most upstream end of the blade of the return screw  10 H in terms of the developer conveyance direction of the return screw  10 H has a break as disclosed in Japanese Laid-open Patent Application 2010-237329, the developer periodically moves through the break. Thus, the developing device  1  is likely to become unstable in developer discharge. Thus, in the case of the return screw  10 H of the comparative developing device, the most upstream end of the return screw  10 H is provided with a regulatory portion  10   h , which is a disc-shaped developer damming plate, in order to eliminate the break to prevent the developer from being discharged through the blade break. 
         [0058]    Referring to  FIG. 7 , in order to prevent the return screw  10  and developer container  2  from contacting each other, a small amount (roughly 2.0 mm) of gap, which is arc-shaped in cross-section ( FIG. 7 ), is provided between the peripheral edge of the return screw  10 H and inward surface of the developer container  2 . Across the downstream end portion of the return screw  10 H in terms of the conveyance direction in the stirring chamber  15 , the developer is present across both the upstream and downstream portions of the return screw  10 H. Therefore, the developer in the arc-shaped gap S will have lost its fluidity by being compressed. Thus, it is rare that the developer in the arc-shaped gap S leaks into the discharge passage ( 13  in  FIG. 4 ) and then, is discharged. 
         [0059]    However, on the upstream side of the return screw  10 H in terms of conveyance direction, there is no developer. Thus, if the blade has a break on the upstream side of the return screw  10 H in terms of the conveyance direction, no regulatory portion on the upstream side of the return screw  10 H, the developer is not pressed, and therefore, it becomes fluid again, being therefore likely to leak into the discharge passage ( 13  in  FIG. 4 ). 
         [0060]    In the case of the comparative developing device, a disc-shaped regulatory portion  10   h  is provided at the upstream end of the return screw  10 H in terms of the conveyance direction, in order to prevent the blade from having a break, in order to prevent the problem that the developer simply goes through the arc-shaped gap S, and is discharged through the developer discharge opening  8 . 
         [0061]    Referring to  FIG. 8 , in the case of the comparative developing device  1 H, the developer in the developer container  2  is circularly conveyed through the development chamber  14  and stirring chamber  15  by the rotation of the conveyance screw  5  and stirring screw  6 . While the developer is conveyed by the stirring screw  6 , it is not stable in speed. That is, it turns into a developer flow indicated by an arrow mark P1, which periodically changes in speed in synchronism with the rotational phase of the blade of the stirring screw  6 . Then, as a certain amount of developer flows over the return screw  10 H, and leaks to the discharge passage  13 . The surface of this flow of developer tends to be made to periodically rise like waves, by the developer flow indicated by the arrow mark P1, which periodically changes in speed. 
         [0062]    Further, as the developer is delivered from the stirring chamber  15  into the development chamber  14  through the opening  7   a , a part of the developer is pushed back into the stirring chamber  15  through the opening  7   a  as the blade of the conveyance screw  5  is rotated. That is, it flows in the direction indicated by an arrow mark P2. The developer flow in the direction indicated by the arrow mark P2 periodically changes in speed in synchronism with the rotational phase of the conveyance screw  5 . Thus, the developer flows over the return screw  10 H and leaks into the discharge passage  13 , with the same timing as that with which the developer flow indicated by the arrow mark P2 periodically changes in speed, and therefore, flows in the manner of succession of waves, that is, the same timing as that with which the developer surfaces rises. 
         [0063]    Also in the developing device  1 H, the developer flow indicated by the arrow marks P1 and P2, which periodically changes in speed like succession of waves collide with the developer which is being conveyed by the return screw  10 H, at the developer return line L which the blade of the return screw  10 H forms. Therefore, the developer return line L substantially changes in position in terms of the developer conveyance direction in response to the rotational phase of the downstream end of the blade of the return screw  10 H. The range in which the position of the developer return line L changes is as large as a single pitch of the spiral blade of the return screw  10 H. 
         [0064]    Referring to  FIG. 9(   a ), therefore, as the developer return line L retracts, the collision between the developer and the blade of the return screw  10 H is delayed, and also, the developer flow indicated by the arrow marks P1 and P2 slips by the return screws  10 H through the break of the blade of the return screw  10 H, which is at the end surface of the return screw  10 H. As the surface of the developer flow indicated by the arrow marks P1 and P2 which flows into the return screw  10 H rises with the latest timing with which the blade of the return screw  10 H pushed back the developer flow indicated by the arrow marks P1 and P2, the developer suddenly leaks into the discharge passage ( 13  in  FIG. 4) . Further, the higher the conveyance screw  5  and stirring screw  6  in rotational speed, the greater the pulsation of the developer flow indicated by the arrow marks P1 and P2, and the changes in the height of the developer flow surface. Therefore, the higher the operational speed of the developing device  1 H, the more conspicuous the periodic leakages of the developer. 
         [0065]    By the way, the developer flow indicated by the arrow marks P1 and P2 changes in height (surface height). Further, the blade of the return screw  10 H periodically changes in its ability to prevent, by its blade, the developer flow indicated by the arrow marks P1 and P2 from leaking out. Therefore, it is reasonable to think that the relationship in terms of rotational phase among the discharge screw  9 , stirring screw  6 , and return screw  10 H should be optimized according to the change in the height of the surface of the developer flow indicated by the arrow marks P1 and P2. That is, in order to optimize the above described relationship in rotational phase, the timing with which the developer surface of the developer flow indicated by the arrow marks P1 and P2 becomes highest should be offset by 180° in rotational phase so that the developer return line L which the blade of the return screw  10 H forms becomes farthest from the discharge passage ( 13  in  FIG. 4 ) when the developer surface becomes highest. 
         [0066]    Referring to  FIG. 9(   b ), in terms of the rotational phase of the return screw  10 H, the developing device  1 H is designed so that the return screw  10 H pushes back each wave of developer flow by its most downstream end portion, in synchronism with the timing with which each wave of developer flow arrives at the most downstream end portion of the return screw  10 H. With the developing device  1 H being designed as described above, it is possible to prevent the problem that the force which pushes back the developer flow reduces in strength, and also, the problem that developer slips by the return screw  10 H through the blade break which is at the end surface of the return screw  10 H. This design is theoretically possible in a case where the developing device  1 H is always driven at a preset rotational speed. 
         [0067]    However, in the case of a developing device which is to be mounted in an image forming apparatus which can be operated in one of multiple preset speeds, that is, an image forming apparatus switchable in operational speed, it has to be operatable in various speeds. Therefore, it cannot be designed as described above, because it is difficult to design a developing device so that the point in time at which the pulsation of the developer flow, which is caused by the stirring screw  6  and/or conveyance screw  5 , arrives at the most downstream end portion of the return screw  10 , synchronize with the rotational phase of the most downstream end portion of the blade of the return screw  10 H, regardless of the operational speed of the developing device  1 H (rotational speed of return screw  10 H), because as the developing device  1 H is switched in operational speed, the developer which flows to the return screw  10 H, changes in the timing with which its surface rises. 
         [0068]    In the following embodiments of the present invention, therefore, a structure for damming up the developer as the developer flows to the return screw  10  from the upstream side of the stirring chamber  15  is disposed on the downstream side of the return screw  10  in terms of the conveyance direction, in order to enable the developing device  1  to properly push back the developer at the same position, regardless of the rotational phase of the return screw  10 . 
       Characteristic Portions of Developing Device in Embodiment 1 
       [0069]      FIG. 10  is a plan view of the adjacencies of the return screw  10  of the developing device  1  in the first embodiment.  FIG. 11  is a perspective view of the adjacencies of the return screw  10  of the developing device  1  in the first embodiment.  FIG. 12  is a drawing for describing a developing device, which has an area which has no blade between the regulatory portion and stirring screw  6 . By the way, in  FIGS. 10 and 11  which show the internal structure of the developing device  1 , the portion of the developing device  1 , which covers the top side of the developer container  2 , is not illustrated. 
         [0070]    Referring to  FIG. 10 , the stirring chamber  15  which is an example of the first chamber, and the development chamber  14  which is an example of the second chamber, are in connection to each other through the opening  7   a , making up a passage through which the developer circulates. The stirring screw  6  which is an example of the first member with a blade conveys the developer in a preset direction, whereas the return screw  10  which is an example of the second member with a blade conveys the developer in the opposite direction from the preset developer conveyance direction of the stirring screw  6 , as the developer is conveyed to the return screw  10  by the stirring screw  6 . The discharge passage  13  which is an example of a passage for discharging the developer is disposed on downstream side of the return screw  10  in terms of the preset developer conveyance direction of the stirring screw  6  to discharge the developer in the stirring chamber  15 . 
         [0071]    The regulatory portion  10   b  which is an example of regulatory component is disposed between the stirring screw  6  and return screw  10 . It has a regulatory surface which has no break in terms of the rotational direction of the regulatory portion  10   b . It regulates the developer as the developer conveyed by the stirring screw  6  flows to the return screw  10 . The regulatory portion  10   b  is shaped so that it has no break in terms of its rotational direction. The regulatory surface of the regulatory portion  10   b  is round and flat. The regulatory portion  10   b  is connected to the downstream end of the return screw  10  in terms of the conveyance direction. It is in the form of a disc, and is the same in external diameter as the return screw  10 . By the way, the regulatory portion  10   b  may be connected to the downstream end of the stirring screw  6 , or the downstream end of the return screw  10 . 
         [0072]    The regulatory portion  10   b  which is in the form of a disc and is continuous in terms of its circumferential direction is disposed at the downstream end of the blade of the return screw  10 . It is connected to the downstream end of the blade. The surface of the regulatory portion  10   b , which faces the developer flow indicated by the arrow marks P1 and P2, is flat. Thus, the end surface of the return screw  10 , that is, the first surface with which the developer flow generated in the direction (downstream direction) indicated by the arrow mark P1 in the stirring chamber  15  by the stirring screw  6  collides is the flat surface which is in the form of a disc. Further, the end surface of the blade of the return screw  10 , that is, the first surface with which the reversal developer flows, indicated by the arrow mark P2, which flows back into the stirring chamber  15  from the development chamber  14  through the opening  7   a , is also a flat surface and in the form of a disc. Therefore, the regulatory portion  10   b  can always push back the developer at the same position in terms of the conveyance direction of the return screw  10 , regardless of the rotational speed of the screw and developer conveyance speed, as the developer begins to flow to the return screw  10 . 
         [0073]    Further, the regulatory portion  10   b  is greater in external diameter than the rotational shaft  10   a  of the return screw  10 . Therefore, it can prevent the developer flow indicated by the arrow mark P1 from periodically flowing to the return screw  10  through the break which the blade has in terms of its circumferential direction. 
         [0074]    Further, in terms of the direction parallel to the rotational axis of the return screw  10  or stirring screw  6 , the regulatory portion  10   b  is disposed away from the downstream end of the stirring screw  6  in terms of the conveyance direction. There is an area A in which only the rotational shaft  10   b  is present, between the flat surface of the regulatory portion  10   b  and the blade of the stirring screw  6 . Therefore, the oscillatory changes in the height of the surface of the developer layer in the developer container  2 , which is caused by the rotational of the stirring screw  6 , attenuates in the area A. That is, the developer layer arrives at the return screw  10  after it is reduced in the oscillatory changes in the height of its top surface. Further, referring to  FIG. 12 , a phenomenon that a triangular space, which is formed by the blade and regulatory portion in a case where the blade of the stirring screw  6  is in connection to the regulatory portion  10   b  as indicated by an arrow mark E, enables the developer to flow over the regulatory portion  10   b  by scooping up the developer, does not occur. Therefore, the developer flow is prevented from pulsatively flowing, and/or changing in the height of its top surface, and therefore, the amount by which the developer periodically flows to the return screw  10  reduces. 
         [0075]    Further, in terms of a preset direction, the regulatory portion  10   b  is disposed so that it overlaps with the opening  7   a  which is on the downstream side of the stirring screw  6  in terms of the conveyance direction of the stirring screw  6 . Therefore, the rising of the surface of the developer flow, which is caused by the collision of the developer flow indicated by the arrow mark P1 with the regulatory portion  10   b , can be utilized to efficiently deliver the developer from the stirring chamber  15  to the development chamber  14 . Further, the rising of the surface of the developer flow, which is caused by the collision of the developer flow indicated by the arrow mark P1 can be utilized to push back the reversal developer flow, indicated by the arrow mark P2, from the stirring chamber  15  into the development chamber  14 , in order to reduce the reverse developer flow. 
         [0076]    By the way, the return screw  10  is provided with a regulatory portion  10   h  like the return screws  10 H of the comparative developing device  1 H. The regulatory portion  10   h  also is in the form of a disc, and is disposed at the upstream end of the blade of the return screw  10  in terms of the conveyance direction. As described above, this structural arrangement is for preventing the amount by which the developer leaks toward the discharge passage ( 13  in  FIG. 4 ) from the return screw  10 , from changing, regardless of the rotational phase of the return screw  10 . 
         [0077]    As described above, in the case of the developing device  1  in the first embodiment, its regulatory portion  10   b  reliably pushes back the developer, regardless of the rotational phase of the return screw  10 . Therefore, it can prevent the developer from being discharged by an excessive amount, regardless of the rotational speed of the developing device  1  which can be driven at one of the multiple rotational speeds with which the developing device  1  is provided. Since it can prevent the developer from being discharged by an excessive amount, it can minimize the changes in the amount of the developer in the developer container  2 , being therefore capable of always keeping the amount of the developer in the developer container  2  at a proper value. 
       Effects of Embodiment 1 
       [0078]    In recent years, carrier has been improved in terms of its deterioration attributable to the operation of the developing device  1 , and also, has been reduced in the amount of toner required for image formation. With the presence of such background, it is desired to reduce the amount by which developer is recovered and stored in the recovery container ( 114  in  FIG. 3 ), by reduction in the amount by which carrier is supplied to the developing device  1 , in order to reduce the image forming apparatus  100  in operational cost, and also, the amount of waste. However, as the amount by which carrier is supplied to a developing device ( 1 ) is reduced, the changes in the amount of the developer in the developer container ( 2 ), which is attributable to the periodic developer leakage, increases. In comparison, in the case of the developing device  1  in the first embodiment, the periodic developer leakage attributable to the rotation of the return screw  10  is unlikely to occur. Therefore, it is unlikely to occur that as the developing device  1  is driven, the amount of the developer in the developer container  2  falls below a preset minimum value, due to the excessive amount of developer discharge. Therefore, the developing device  1  in this embodiment is unlikely to suffer from the nonuniformity in image density, which is attributable to the unsatisfactory coating of the development sleeve  3  with the developer, which occurs as the amount of the developer in the developer container  2  falls below the minimum value. 
         [0079]    Also in recent years, a developing device has been reduced in size, being therefore likely to be reduced in the amount by which its developer container is to be filled with developer. As the amount by which the developer container is to be filled is reduced, the change in the amount of the developer container, which is attributable to the periodic developer leakage, also increases. In comparison, in the case of the developing device  1  in this embodiment, the amount of the developer in the developer container  2  can be stabilized by the prevention of the periodic developer leakage. That is, the present invention can realize a developing device which is light, and small in the amount by which its developer container is to be filled with developer. 
         [0080]    In the first embodiment, the regulatory portion  10   b  pushes back the developer flow in a proper manner, on the downstream side of the return screw  10 , to prevent the developer from invading into the upstream side of the return screw  10 . Therefore, it is unlikely for the developer to suddenly leak by an excessive amount. Thus, it is unlikely for the amount of the developer in the developer container  2  to reduce enough for it to fall below the minimum value. 
         [0081]    In the first embodiment, on the downstream side of the return screw  10  in terms of the conveyance direction, the positional relationship between the developer having reversely flowed from the stirring screw  6  and development chamber  14  through the opening  7   a , and the regulatory portion  10   b  which is the first object with which the developer collides, is not affected by the rotational phase of the stirring screw  6 . Therefore, it is unlikely for the developer to flow to the return screw  10  through the blade break which is at the end surface of the return screw  10 . 
         [0082]    In the first embodiment, even if there occurs such a developer flow that the developer delivered from the stirring chamber  15  to the development chamber  14  through the opening  7   a  is partially made by the rotation of the conveyance screw  5  to flow back from the development chamber  14  to the stirring chamber  15 , it can be dammed up by the regulatory portion  10   b . Therefore, the reverse flow can be dealt with without designing a developing device so that the timing with which the developer wave arrives at the most downstream portion of the return screw  10  synchronizes with the rotational phase of the blade of the return screw  10 . With the provision of the regulatory portion  10   b , the periodic changes in the amount by which the developer flows to the return screw  10  reduces, regardless of the rotational speed of the developing device even if the developing device  1  has multiple rotational speeds. With the provision of the regulatory portion  10   b , the return screw  10  can be designed with no attention to the length of time for the developer flow pulsation caused by the blade of the stirring screw  6  and/or conveyance screw  5  to reach the most downstream portion of the return screw  10 . 
         [0083]    The developing device  1  which uses a developer replacement method and has multiple developer conveyance speeds is prevented from excessively discharging the developer, and therefore, is capable of keeping the developer in the developer container  2  proper in amount, regardless of the developer conveyance speed. Even in the case of the steering roller  6  which is high in rotational speed, and therefore, tends to cause the developer to move in a pulsative manner, and increase the changes in the height of the developer surface, it is possible to prevent the developing device  1  from excessively discharging developer. Therefore, it is capable of keeping the developer in the developer container  2  always proper in amount. 
       Embodiment 2 
       [0084]      FIG. 13  is a plan view of the adjacencies of the return screw of the developing device in the second embodiment of the present invention.  FIG. 14  is a perspective view of the adjacencies of the return screw of the developing device in the second embodiment.  FIG. 15  is a drawing for describing a return screw provided with a tapered portion. The developing device in the second embodiment is the same in structure as the developing device  1  in the first embodiment, except that its return screw  10  is provided with a tapered portion. Therefore, the structural components, and portions thereof, of the developing device  1  shown in  FIGS. 13-15 , which are the same in structure as the counterparts shown in  FIGS. 9 and 10 , are given the same referential codes as those given to the counterparts, and are not described here in order not to repeat the same descriptions. 
         [0085]    Referring to  FIG. 13 , in the second embodiment, the return screw  10  is provided with a regulatory portion  10   d , which is located on the downstream end of the return screw  10  in terms of the conveyance direction. The downstream portion of the rotational shaft  10   a  of the regulatory portion  10   d  is greater in diameter than the upstream end of the rotational shaft  10   a  of the regulatory portion  10   d . More specifically, the external diameter of the rotational shaft  10   a  of the return screw  10   d  is largest at the downstream end of the rotational shaft  10   a  in terms of the developer conveyance direction of the return screw  10 , and gradually reduces toward the upstream end. The portion of the rotational shaft  10   a , across which its diameter gradually reduces toward the upstream end in terms of the conveyance direction, overlaps with at least a part of the return screw  10 . 
         [0086]    Referring to  FIG. 14 , the end surface  10   c  of the regulatory portion  10   d  is in the form of a disc and is flat. Therefore, the regulatory portion  10   d  is as effective as the regulatory portion  10   b  in the first embodiment to dam up the developer as the developer is conveyed by the stirring screw  6 . 
         [0087]    Next, referring to  FIG. 15(   a ), the regulatory portion  10   d  is also provided with a tapered portion  10   e , which is located next to the stirring screw  6 , and across which the diameter of the rotational shaft  10   a  gradually increases toward the regulatory portion  10   d  in the pattern of a hyperbolic curve. The tapered portion  10   e  gradually increases in diameter in the adjacencies of the downstream end of the return screw  10 , and steplessly connects to the peripheral portion of the regulatory portion  10   d.    
         [0088]    Referring to  FIG. 14 , the lower the rotational speed, the gentler the developer flow indicated by an arrow mark P1 which is generated as the developer is conveyed toward the regulatory portion  10   b , the pulsation of the developer flow indicated by an arrow mark P2 which occurs as the developer is reversely conveyed from the development chamber  14 , and the changes in the height of the developer flow surface. Further, even if the rotational speed of the return screw  10  is slow, the developer having flowed over the regulatory portion  10   d  is pushed back toward the stirring screw  6  by the rotation of the spiral blade of the return screw  10 . 
         [0089]    Generally speaking, in a case where developer is conveyed by a screw which has a spiral blade, the developer is subjected to such a force that is generated by the centrifugal force and the inclination of the surface of the spiral blade which extends upstream, and also, that pushes the developer outward in terms of the radius direction of the screw. Therefore, in a case where the regulatory portion  10   b  is provided as in the first embodiment as shown in  FIG. 10 , the centrifugal force which acts on the developer is substantial as long as the rotational speed is substantial. Therefore, the developer is pushed back toward the stirring screw  6  with no problem. 
         [0090]    However, in a case where the rotational speed is low, the centrifugal force is insufficient. Therefore, as the developer flows to the return screw  10  over the regulatory portion  10   b , the force generated by the return screw  10  is sometimes insufficient to cause the developer to flow over the regulatory portion  10   b  and return to the stirring screw  6 . The portion of the developer flow, which fails to flow to the stirring screw  6  over the regulatory portion  10   b , is pushed toward the discharge passage  13  and is discharged. 
         [0091]    Referring to  FIG. 15(   b ), in the second embodiment, therefore, the rotational shaft  10   a  is shaped so that it gradually increases in diameter toward its downstream end in terms of the conveyance direction to steplessly connect to the peripheral edge of the end surface  10  of the return screw  10 . With the provision of this structural arrangement, the developer flow from the stirring screw  6  is regulated by the end surface  10   c , and the developer having flowed over the end surface  10   c  is pushed up by the tapered portion  10   e  of the return screw  10 , and therefore, is returned to the stirring screw  6 . 
         [0092]    Referring to  FIG. 15 , by the way, the return screw  10  is structured so that its tapered surface  10   e  is hyperbolically contoured. More specifically, the tapered portion  10   e  is smallest in diameter at roughly the center of the return screw  10  in terms of the direction parallel to the rotational axis of the return screw  10 , and gradually increases in diameter toward the most downstream end of the return screw  10 , and becomes the same as that of the return screw  10  (diameter of spiral blade) at the most downstream end. However, the same effect as the effect obtainable by this embodiment can be obtained by shaping the rotational shaft  10   a  in such a manner that it gradually increases in diameter toward the downstream end of the return screw  10  in terms of the conveyance direction. That is, this embodiment is not intended to limit the present invention in scope in terms of the shape of the return screw  10 . 
       (Miscellanies) 
       [0093]    The present invention is applicable to developing devices which are partially or entirely different in structure from those similar to the developing devices  1  in the preceding embodiments, as long as they are structured so that a developer damming member which is circularly continuous in terms of the rotational direction of the conveyance screw  5  is disposed between the two conveyance screws which are opposite in the developer conveyance direction. That is, the preceding embodiments are not intended to limit the present invention in scope in terms of the measurement, material, and shape of the structural components, and the positional relationship among the structural components, unless specifically noted. They are not intended to limit the weight ratio of the carrier of the replenishment developer to 10%. The regulatory portions  10   b  and  10   b  may be angled. Further, the regulatory portions  10   b  and  10   d  may be provided with slits, holes, etc., as long as they can prevent the amount by which developer is discharged, from changing. 
         [0094]    Further, in the preceding embodiments, the regulatory portion  10   b  and return screw  10  were continuous. However, they may be separated from each other in terms of the direction parallel to their axial line. 
         [0095]    Further, the present invention is applicable to a developing device, regardless of whether the image forming apparatus which employs the developing device is of the single drum type or tandem type, of the single-component developer type or two-component developer type, and intermediary transfer type or direct transfer type. Further, the present invention is applicable to a developing device, regardless of the image bearing member count, image bearing member charging method, electrostatic image forming method, developing method, transferring method, fixing method, etc., of the image forming apparatus by which the developing device is employed. In the foregoing, only the portions of the image forming apparatus, which are essential to the formation and transfer of a toner image were described. However, the present invention is also compatible with image forming apparatuses other than those in the preceding embodiment. For example, it is compatible with various printers, copying machines, facsimile machines, multifunction machines capable of performing two or more of the preceding machines, etc., which are a combination of the image forming apparatus in the preceding embodiments, and additional devices, equipments, casing, etc. 
         [0096]    According to the present invention which is related to a developing device, as the first bladed member causes developer to flow to the second bladed member, the regulatory member regulates the developer flow regardless of its rotational phase. Therefore, it is prevented that the amount, by which developer is discharged, changes in synchronism with the rotational period of the second bladed member. Therefore, a developing device which regulates its developer discharge with the use of the second bladed member can be stabilized in the effect of regulatory member to minimize the change in the amount of developer discharge. Therefore, it is possible to reliably discharge developer. 
         [0097]    While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
         [0098]    This application claims priority from Japanese Patent Application No. 240731/2013 filed Nov. 21, 2013, which is hereby incorporated by reference.