Abstract:
Provided is a developing device including a container that accommodates a developer, a developer holding member that develops the electrostatic latent image on the image holding member by delivering the developer to a position facing the image holding member, while rotating, a first transport member that extends in a direction of a rotary shaft of the developer holding member, and that transports the developer inside the container in a first direction, and a pushing-back member that pushes back the developer transported in the first direction by the first transport member in a direction opposite to the first direction, and that allows an amount of the developer beyond pushing-back capacity within the developer transported in the first direction, to exit from the container, wherein the container includes a control wall that controls passage of the developer.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2015-085647 filed Apr. 20, 2015. 
       BACKGROUND 
     Technical Field 
       [0002]    An exemplary embodiment of the present invention relates to a developing device and an image forming apparatus. 
       SUMMARY 
       [0003]    According to an aspect of the invention, there is provided a developing device including: 
         [0004]    a container that accommodates a developer; 
         [0005]    a developer holding member that is arranged so that a region close to an image holding member for holding an electrostatic latent image is exposed from the container, and that develops the electrostatic latent image on the image holding member by delivering the developer to a position facing the image holding member, while rotating; 
         [0006]    a first transport member that extends in a direction of a rotary shaft of the developer holding member, and that transports the developer inside the container in a first direction; and 
         [0007]    a pushing-back member that is arranged ahead of the first transport member in the first direction, that pushes back the developer transported in the first direction by the first transport member in a direction opposite to the first direction, and that allows an amount of the developer beyond pushing-back capacity within the developer transported in the first direction, to exit from the container, 
         [0008]    wherein the container includes a control wall that controls passage of the developer by protruding from an inner wall surface forming a space through which the developer passes, in a shape extending in a direction intersecting the first direction, in the space. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein: 
           [0010]      FIG. 1  is a schematic configuration diagram of a printer as an exemplary embodiment of an image forming apparatus according to an exemplary embodiment of the invention; 
           [0011]      FIG. 2  is a perspective view illustrating a state where a frame member is drawn out from a printer main body; 
           [0012]      FIG. 3  is an external perspective view of the frame member on which four image forming engines are mounted; 
           [0013]      FIG. 4  is a perspective view of one photoreceptor module; 
           [0014]      FIG. 5  is a perspective view of one developing device module; 
           [0015]      FIG. 6  is an exploded plan view of the developing device module; 
           [0016]      FIG. 7  is an enlarged sectional view which is taken along arrow A-A illustrated in  FIG. 6 , and which illustrates a sectional shape of a control wall; 
           [0017]      FIG. 8  is a graph for describing an operation of the control wall; 
           [0018]      FIG. 9  is a graph illustrating another experiment example; 
           [0019]      FIG. 10  is a view illustrating a state where respective phases of a first auger and a second auger are aligned with zero degree; 
           [0020]      FIG. 11  is a view illustrating a state where the respective phases of the first auger and the second auger are misaligned with each other; and 
           [0021]      FIG. 12  is a side view of the developing device module. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    Hereinafter, an exemplary embodiment of the invention will be described. 
         [0023]      FIG. 1  is a schematic configuration diagram of a printer as an exemplary embodiment of an image forming apparatus according to the exemplary embodiment of the invention. 
         [0024]    A printer  1  prints and outputs an image by using a so-called electrophotographic system. 
         [0025]    Two sheet trays  2   a  and  2   b  are arranged in a lower part of the printer  1 . The two sheet trays  2   a  and  2   b  are drawable, and sheets P are stacked and accommodated in the sheet trays  2   a  and  2   b . The sheets P inside the sheet trays  2   a  and  2   b  are drawn out one by one for printing, and are transported through a transporting path illustrated by an arrow A. 
         [0026]    Four image forming engines  3 Y,  3 M,  3 C, and  3 K are disposed in an upper part of the printer  1 . The four image forming engines  3 Y,  3 M,  3 C, and  3 K respectively forma toner image using each color of yellow (Y), magenta (M), cyan (C), and black (K). Hereinafter, in the description common to the respective image forming engines  3 Y,  3 M,  3 C, and  3 K, the reference numerals of Y, M, C, and K which represent each color will be omitted, and the image forming engines  3 Y,  3 M,  3 C, and  3 K are simply referred to as image forming engines  3 . In the drawings to be described later, the reference numerals of Y, M, C, and K which represent each color will also be omitted in some cases. The omission will be similarly applied to other configuration elements in addition to the image forming engines. 
         [0027]    Each of the image forming engines  3  includes a photoreceptor  21  which rotates in a direction of an arrow B, a charger (not illustrated) which is arranged around the photoreceptor  21 , a developing device, and a cleaner. The photoreceptor  21  is an example of an image holding member. An exposure device  4  is provided above the image forming engines  3 . Image data is input to the printer  1  from a personal computer (not illustrated). The exposure device  4  exposes the photoreceptor  21  to exposure light  4   a  modulated in accordance with the image data. 
         [0028]    Each photoreceptor  21  is charged by the charger, and an electrostatic latent image is formed by the exposure using the exposure device  4 . The electrostatic latent image is developed by a toner accommodated in the developing device and a developer supplied from a carrier, thereby forming a toner image on the photoreceptor  21 . Furthermore, the toner image is transferred by an operation of a primary transfer device  5  so as to be sequentially stacked on an intermediate transfer belt  6 . The intermediate transfer belt  6  circularly moves in a direction of an arrow C. An operation of a secondary transfer device  7  transfers the toner image on the intermediate transfer belt  6  onto the sheet P transported to the corresponding position. The sheet P on which the toner image is transferred is further transported, is fixed by a fixing machine  8  using heat and pressure, and exits to an exit tray  9 . 
         [0029]    The four image forming engines  3  are incorporated in one drawable frame member  10 , and have a structure in which the image forming engines  3  are accommodated so as to be integrally drawn out from a printer main body  1 A. 
         [0030]      FIG. 2  is a perspective view illustrating a state where the frame member is drawn out from the printer main body. 
         [0031]    Doors  1 B and  1 C which opens and closes in each direction of arrows x 1 -y 1  and x 2 -y 2  are disposed on a front surface of the printer main body  1 A. The frame member  10  is drawn out in a direction of an arrow F and is accommodated in a direction of an arrow R by opening the doors  1 B and  10 . As described above, the four image forming engines  3 Y,  3 M,  3 C, and  3 K are incorporated in the frame member  10 . 
         [0032]      FIG. 3  is an external perspective view of the frame member on which the four image forming engines are mounted. 
         [0033]    The four image forming engines  3  are mounted on the frame member  10 . The respective image forming engines  3  include a photoreceptor module  20  and a developing device module  30 . In  FIG. 3 , a side indicated by the arrow F represents a front side, and a side indicated by the arrow R represents a rear side (refer to the arrows F-R in  FIG. 2 ). In a case of the arrows F-R illustrated in  FIG. 4  and the subsequent drawings to be described below, the side indicated by the arrow F also represents the front side, and the side indicated by the arrow R also represents the rear side. 
         [0034]      FIG. 4  is a perspective view of one photoreceptor module. 
         [0035]    The photoreceptor  21 , a charger  22 , and a cleaner  23  are incorporated in the photoreceptor module  20 . The photoreceptor  21  rotates in a direction of an arrow B (refer to  FIG. 4  together with  FIG. 1 ) in response to an operation of the printer  1  (refer to  FIG. 1 ). The photoreceptor module  20  needs to be replaced since the photoreceptor  21  is worn while the printer  1  (refer to  FIG. 1 ) is used for a long period of time, and has a structure which may be replaced by a user of the printer  1  (refer to  FIG. 1 ). 
         [0036]    Distance regulating members  24 F and  24 R are respectively disposed on both sides of the photoreceptor module  20  in a direction of a rotary shaft of the photoreceptor  21 . The distance regulating members  24 F and  24 R regulates the photoreceptor  21  included in the photoreceptor module  20  and a developing roll  31  (refer to  FIGS. 6 and 7 ) incorporated in the developing device module  30  so as to have a constant distance therebetween. 
         [0037]    Ring-shaped knobs  25 F and  25 R are respectively disposed at both end upper portions in the photoreceptor module  20 . The knobs  25 F and  25 R may be rotated into an upright state. A finger may be inserted into rings so as to lift the rings. In this manner, the photoreceptor module  20  may be pulled out upward from the frame member  10  illustrated in  FIG. 3 . 
         [0038]    Guide portions  26 F and  26 R are respectively disposed on both end surfaces of the photoreceptor module  20 . The guide portions  26 F and  26 R are guided so as to fit into a guide groove (not illustrated) disposed in the frame member  10 , thereby allowing the photoreceptor module  20  to be mounted on the frame member  10 . 
         [0039]      FIG. 5  is a perspective view of one developing device module. 
         [0040]    The developing device module  30  is fixed to the frame member  10  so as not to be easily replaced. The developing roll  31  is incorporated in the developing device module  30 . The developing roll  31  is arranged so that a region close to the photoreceptor  21  incorporated in the photoreceptor module  20  in a state of being mounted on the frame member  10  is exposed from a container  32 . The developing roll  31  rotates so that a portion facing the photoreceptor  21  moves forward in the same direction as the photoreceptor  21 . In the developing device module  30 , distance regulating rollers  33 F and  33 R which freely rotate coaxially with the developing roll  31  are respectively disposed on both sides of the developing roll  31 . The distance regulating rollers  33 F and  33 R come into contact with the distance regulating members  24 F and  24 R (refer to  FIG. 4 ) disposed in the photoreceptor module  20 , thereby allowing a structure in which the photoreceptor  21  and the developing roll  31  always maintain a constant distance therebetween. The developing device module  30  corresponds to an example of a developing device, and the developing roll  31  corresponds to an example of a developer holding member. 
         [0041]    A toner supply port  321  through which a toner is supplied from a toner bottle (not illustrated) is disposed in the container  32  of the developing device module  30 . The toner supplied from the toner supply port  321  is delivered to a position close to the photoreceptor  21  by the developing roll  31 , and an electrostatic latent image formed on the photoreceptor  21  is developed by the toner, thereby forming a toner image on the photoreceptor  21 . A film-like sealing member  34  is disposed in the developing device module  30  so that the toner leaks out from a gap between the photoreceptor  21  and the developing roll  31 . 
         [0042]      FIG. 6  is an exploded plan view of the developing device module. 
         [0043]      FIG. 6  illustrates an internal structure of the developing device module  30  by detaching an upper cover  32   a  which partially configures the container  32  of the developing device module  30 . An inner surface of the upper cover  32   a  is also illustrated inside out. The upper cover  32   a  is aligned with a position located when the upper cover  32   a  is attached thereto in a longitudinal direction (direction of the arrows F-R). 
         [0044]    The developing device module  30  includes a first auger  35  and a second auger  36  in addition to the developing roll  31  and the container  32  including the upper cover  32   a.    
         [0045]    A developer containing the toner supplied from the above-described toner supply port  321  is accommodated inside the container  32 . The developer inside the container  32  is transported in the direction of the arrow R by the first auger  35 , and is transported in the direction of the arrow F by the second auger  36 . 
         [0046]    The container  32  includes a first chamber  322  in which the first auger  35  is arranged and a second chamber  323  in which the second auger  36  is arranged. A partition wall  324  which partitions the first chamber  322  and the second chamber  323  is disposed in the container  32 . The container  32  includes flow paths  325   a  and  325   b  for connecting the first chamber  322  and the second chamber  323  to each other in both end portions of the first auger  35  and the second auger  36 . Therefore, the developer inside the first chamber  322  is transported in the direction of the arrow R by the first auger  35 , and flows into the second chamber  323  from the flow path  325   a  on the left side in  FIG. 6 . The developer inside the second chamber  323  is transported in the direction of the arrow F by the second auger  36 , and flows into the first chamber  322  from the flow path  325   b  on the right side in  FIG. 6 . In this way, the developer inside the container  32  is agitated while being circularly transported inside the container  32 . Then, the developer agitated in this manner is delivered from the second chamber  323  to the developing roll  31 , thereby developing an electrostatic latent image on the photoreceptor  21  (refer to  FIGS. 1 and 4 ). 
         [0047]    The first auger  35  includes a first spindle  351  which extends in the direction of the rotary shaft of the developing roll  31 , and a first spiral vane  352  which is formed around the first spindle  351 . The first auger  35  transports the developer inside the first chamber  322  in the direction of the arrow R by using the rotation of the first spindle  351 . 
         [0048]    The second auger  36  is arranged parallel to the first auger  35 . Similarly to the first auger  35 , the second auger  36  includes a second spindle  361  which extends in the direction of the rotary shaft of the developing roll  31 , and a second spiral vane  362  which is formed around the second spindle  361 . Compared to the first spiral vane  352 , the second spiral vane  362  turns around the second spindle  361  in a direction opposite to that of the first spiral vane  352 . However, a turning cycle of the second spiral vane  362  (pitch of the second spiral vane  362 ) is the same as a turning cycle of the first spiral vane  352  (pitch of the first spiral vane  352 ). 
         [0049]    The second spindle  361  rotates in the same direction as the first spindle  351 . Therefore, the developer inside the second chamber  323  is transported in the direction of the arrow F which is the direction opposite to that of the developer inside the first chamber  322  by the second spiral vane  362 . 
         [0050]    The first auger  35  further includes a third spiral vane  353  which is formed around the first spindle  351 , ahead (left side in  FIG. 6 ) of the first spiral vane  352  in a direction (direction illustrated by the arrow R) in which the developer is transported by the first spiral vane  352 . 
         [0051]    The third spiral vane  353  turns around the first spindle  351  at a smaller pitch, compared to the first spiral vane  351 . The third spiral vane  353  turns around the first spindle  351  in a direction opposite to that of the first spiral vane  351  (that is, the same direction as the second spiral vane  362 ). 
         [0052]    That is, within the developer transported into the first chamber  322  in the direction of the arrow R by the first spiral vane  352  after the first spindle  351  is rotated, the developer attempting to move straight without any change instead of flowing into the second chamber  323  through the flow path  325   a  is pushed back in the opposite direction (direction of the arrow F) by the third spiral vane  353 . However, if the amount of the transported developer increases, the increased amount is beyond the pushing-back capacity of the third spiral vane  353 . Consequently, the third spiral vane  353  cannot push back the total amounts. The developer partially moves straight without any change through a gap between the third spiral vane  353  and an inner wall surface of the container  32  in a portion accommodating the third spiral vane  353 . The developer moving straight in this way exits outward from the container  32  through an exit port  326 . The developer which has exited therethrough is accumulated in a waste toner tank (not illustrated) installed inside the printer  1  (refer to  FIG. 1 ). The developing device module  30  adopts the above-described structure so that an excessive amount of the developer is not accommodated inside the container  32 . 
         [0053]    The first spindle  351  and the first spiral vane  352  which configure the first auger  35  correspond to an example of a first transport member, and the second spindle  361  and the second spiral vane  362  which configure the second auger  36  correspond to an example of a second transport member. The first spindle  351  and the third spiral vane  353  which configure the first auger  35  correspond to an example of a pushing-back member. That is, according to the exemplary embodiment, the first spindle  351  functions as a configuration element of both the first transport member and the pushing-back member. 
         [0054]    Next, the upper cover  32   a  which configures the container  32  will be described. Two control walls  327  are formed on an inner wall surface  32   b  of a portion for covering an upper portion of the first auger  35  in the upper cover  32   a.    
         [0055]      FIG. 7  is an enlarged sectional view which is taken along arrow A-A illustrated in  FIG. 6 , and which illustrates a sectional shape of the control walls. In  FIG. 7 , the control walls  327  are illustrated by a solid line. A one-dot chain line is illustrated for subsequent description. 
         [0056]    The control walls  327  are illustrated so as to be disposed in a direction protruding upward in accordance with the direction of the upper cover  32   a  illustrated in  FIG. 6 . However, in practice, the upper cover  32   a  is reversely attached thereto. Accordingly, the control walls  327  adopt a downward protruding posture. A portion where the control walls  327  is formed on the inner wall surface of the upper cover  32   a  has an arch shape in a sectional view. Accordingly, the control walls  327  also extend in the arc shape. 
         [0057]    The control walls  327  protrude from the inner wall surface of the container  32 , which forms a space in which the first auger  35  is arranged, in a shape of extending in a direction intersecting the direction (direction of the arrow R) in which the developer is transported by the first spiral vane  352 , inside the space thereof. 
         [0058]    Within the inner wall surface which forms the space in which the first auger  35  is arranged, the control walls  327  form a boundary region between both the first spiral vane  352  and the third spiral vane  353 . 
         [0059]    As illustrated in  FIG. 7 , the control walls  327  have a tilting surface which tilts to a downstream side in the transport direction (direction of the arrow R) of the developer, as a wall surface  327   a  on an upstream side in the direction (direction of the arrow R) in which the developer is transported by the first spiral vane  352  protrudes from the inner wall surface  32   b  of the container  32 . 
         [0060]    The control wall  327  is formed at multiple (two in the exemplary embodiment) locations by leaving a space therebetween in the transport direction (direction of the arrow R) of the developer. 
         [0061]    An operation of the control walls  327  will be described later. 
         [0062]      FIG. 8  is a graph for describing the operation of the control walls. 
         [0063]    The horizontal axis in  FIG. 8  represents a weight (g) of a developer inside a container. The vertical axis in the graph represents an exit amount of the developer per unit time from the exit port  326  (refer to  FIG. 6 ). 
         [0064]      FIG. 8  illustrates a graph a indicated by a solid line and a graph b indicated by a one-dot chain line. 
         [0065]    In recent years, in order to increase the number of prints per unit time, the printer  1  (refer to  FIG. 1 ) tends to be operated at fast speed. Without exception of the developing device module  30 , not only the first auger  35  but also the second auger  36  is rotated at fast speed in response to a fast operation of the printer  1 . Then, the developer is transported at fast speed. The following phenomenon occurs. Even if the amount itself of the developer to be transported by the first spiral vane  352  is the amount of the developer which the third spiral vane  353  is scheduled to push back, the developer exits from the exit port  326  without any change after slipping through the third spiral vane  353 . According to scrutinized observation of the present inventors, it is found that the following phenomenon occurs. If the developer transported at fast speed by the first spiral vane  352  moves close to the third spiral vane  353 , the developer scatters and rides over the third spiral vane  353  as if rushing waves have broken on the shore, for example. 
         [0066]    The graph a in  FIG. 8  represents an initially targeted exit amount. In contrast, the graph b in  FIG. 8  represents an exit amount of a developer when the control walls  327  are not provided. If cases are observed from a case where the amount of the developer is small inside the container  32  to a case where the amount of the developer is large inside the container  32  (from the left side to the right side in  FIG. 8 ), in a state where the amount of the developer increases to some extent, the exit amount increases, despite the fact that the amount of the developer does not yet reach the initially targeted exit amount. If the amount of the developer further increases, the excessive exit of the developer does not occur temporarily. The reason is that the amount of the developer increases in the container  32 , a volume of a portion through which the developer passes becomes almost full, and thus there is no more extra space where the developer scatters as described above. 
         [0067]    If the amount of the developer further increases inside the container  32 , similarly to the graph a, the graph b also shows that the exit amount increases rapidly. This shows a normal exit amount which is expected. If the above-described control walls  327  are disposed on the inner wall surface  32   b  of the upper cover  32   a , the graph b approximates to the graph a. Accordingly, the excessive exit as illustrated in the graph b is controlled. 
         [0068]    As described above, the control walls  327  according to the exemplary embodiment are formed in the boundary region where both the first spiral vane  352  and the third spiral vane  353  are arranged, within the inner wall surface which forms the space in which the first auger  35  is arranged. The present inventors investigate whether the excessive exit of the developer may be effectively controlled if the control walls  327  are formed at any position in the longitudinal direction of the first auger  35 . It is found that the best effect of controlling the excessive exit may be obtained if the control walls  327  are formed at the above-described position. 
         [0069]    As illustrated in  FIG. 7 , the control walls  327  according to the exemplary embodiment have the tilting surface which tilts to the downstream side in the transport direction (direction of the arrow R) of the developer, as the wall surface  327   a  on the upstream side in the direction (direction of the arrow R) in which the developer is transported by the first spiral vane  352  protrudes from the inner wall surface  32   b  of the container  32 . 
         [0070]    If the wall surface  327   a  is formed into a vertical wall surface instead of the tilting surface, the exit amount of the developer increases. The reason is considered that air flowing together with developer and abutting against the wall surface causes turbulence to occur, and that the scattering of the developer cannot be controlled due to the turbulence. However, even in a case of the vertical wall surface, the excessive exit of the developer may be controlled, compared to a case where the control walls  327  are not provided. 
         [0071]    According to the exemplary embodiment, the wall surface  327   a  is formed into the tilting surface. Therefore, the turbulence is less likely to occur, and the excessive exit of the developer may be more effectively controlled. 
         [0072]    The wall surface  327   b  on the downstream side of the control walls  327  in the transport direction (direction of the arrow R) of the developer may employ the vertical wall surface as in the exemplary embodiment, or may be formed into the tilting surface like the wall surface  327   b  illustrated by the one-dot chain line in  FIG. 7 . 
         [0073]    As described above, the control wall  327  is formed at the multiple (two in the exemplary embodiment) locations by leaving a space therebetween in the transport direction (direction of the arrow R) of the developer. 
         [0074]    If a case where only one control wall  327  is formed therein is compared with a case where the multiple control walls  327  are formed therein, the better effect of controlling the excessive exit of the developer may be obtained in the case of the multiple control walls  327 . 
         [0075]    If a control wall which is long in the direction of the arrows F-R as illustrated by a one-dot chain line  327   c  in  FIG. 7  is formed, the effect of controlling the excessive exit of the developer becomes worse, compared to a case where a short control wall is formed at multiple locations. The reason is considered that air delivered together with the developer flows adversely and thus causes turbulence to occur. However, even in this case, a considerably good effect may be obtained, compared to a case where no control wall is provided. 
         [0076]      FIG. 9  is a graph illustrating another experiment example. 
         [0077]    The horizontal axis in  FIG. 9  represents a phase difference (°) between the first auger  35  and the second auger  36 . The vertical axis in  FIG. 9  represents an exit amount of a developer per unit time. The amount of the developer inside the container  32  is aligned with a point G on the horizontal axis in  FIG. 8 . 
         [0078]    As illustrated in  FIG. 9 , due to the phase difference between the first auger  35  and the second auger  36 , the exit amount of the developer varies greatly. Accordingly, a phase region having a large exit amount and a phase region having a small exit amount are present.  FIG. 10  is a view illustrating a state where respective phases of the first auger  35  and the second auger  36  are aligned with zero degree. 
         [0079]      FIG. 11  is a view illustrating a state the respective phases of the first auger  35  and the second auger  36  are misaligned with each other. 
         [0080]    As described above, the first spiral vane  352  which configures the first auger  35  transports the developer inside the first chamber  322  in the direction of the arrow R. Therefore, if the first spiral vane  352  is observed at a fixed point, it seems that the first spiral vane  352  moves in the direction of the arrow R. Similarly, the second spiral vane  362  which configures the second auger  36  transports the developer inside the second chamber  323  in the direction of the arrow F. Therefore, if the second spiral vane  362  is observed at a fixed point, it seems that the second spiral vane  362  moves in the direction of the arrow F. 
         [0081]    An issue to be described herein is whether the first spiral vane  352  and the second spiral vane  362  are brought into a state where both of these are closest to each other at any position during the above-described movement. 
         [0082]    In  FIG. 10 , the first spiral vane  352  and the second spiral vane  362  are brought into a state where both of these are closest to each other on the arrow F side within the flow path  325   a . Here, the state is set to a phase difference 0°. 
         [0083]    In  FIG. 11 , the first spiral vane  352  and the second spiral vane  362  are brought into a state where both of these are closest to each other in the vicinity of the center of the flow path  325   a  in the direction of the arrows F-R. That is, the state shows a state where phases of the first auger  35  and the second auger  36  are misaligned with each other. 
         [0084]    According to the exemplary embodiment, the phase difference between the first auger  35  and the second auger  36  is adjusted to be approximately 0°. In the phases, both the first spiral vane  352  and the second spiral vane  362  simultaneously open a front surface of the flow path  325   a  on the third spiral vane  353  side. 
         [0085]      FIG. 12  is a side view of the developing device module. 
         [0086]      FIG. 12  illustrates a first gear  355  fixed to the first spindle  351  of the first auger  35 , a second gear  365  fixed to the second spindle  361  of the second auger  36 , and a driving gear  37  for transmitting a driving force to both the first gear  355  and the second gear  365 . A joint portion  351   a  of the first spindle  351  of the first auger  35  with the first gear  355  is formed into a D-cut shape as illustrated. Similarly, a joint portion  361   a  of the second spindle  361  of the second auger  36  with the second gear  365  is also formed into a D-cut shape as illustrated. The D-cut direction of the joint portion  351   a  of the first spindle  351  and the phase of the first spiral vane  352  are determined uniquely. Similarly, the D-cut direction of the joint portion  361   a  of the second spindle  361  and the phase of the second spiral vane  362  are also determined uniquely. Therefore, when the developing device module  30  is assembled, the first gear  355 , the second gear  365 , and the driving gear  37  are assembled together by adjusting the D-cut direction of both the first spindle  351  and the second spindle  361 . In this manner, the respective phases of the first auger  35  and the second auger  36  may be adjusted. 
         [0087]    According to the exemplary embodiment, in addition to the control walls  327  disposed as described above, the respective phases of the first auger  35  and the second auger are adjusted as described above. Accordingly, the excessive exit of the developer as illustrated by the graph b in  FIG. 8  is more effectively controlled. 
         [0088]    Hitherto, an example has been described in which a so-called tandem machine printer includes four image forming engines  3 . However, without being limited to the number of image forming engines, the exemplary embodiment of the invention may be applied to not only a monochrome machine including only one image forming engine, but also a printer including five or more image forming engines. 
         [0089]    The foregoing description of the exemplary embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.