Patent Publication Number: US-9846388-B2

Title: Developing device including a guide portion and an image forming apparatus provided with the same

Description:
INCORPORATION BY REFERENCE 
     This application is based upon and claims the benefit of priority from the corresponding Japanese Patent Application No. 2016-039528 filed on Mar. 2, 2016, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     The present disclosure relates to a developing device and an image forming apparatus. 
     In general, a developing device of an electrophotographic system includes a storage portion that stores developer, a developer carrying member of a cylindrical shape, a magnet disposed in a hollow portion of the developer carrying member, a stirring portion configured to stir the developer, and a layer thickness restricting portion configured to restrict the layer thickness of the developer on the developer carrying member. 
     The stirring portion is of a screw feeder type and includes a shaft portion and a blade portion spirally extending outward from the shaft portion. The developer carrying member is referred to as a magnetic roller, a magnetic sleeve or the like. 
     It is known that, on the surface of the developer carrying member, streaky density unevenness of the developer may be formed along the blade portion of the stirring portion. In particular, in a case where the developer includes toner of a low-melt-type whose melting point is low, the density unevenness is likely to occur due to the stirring portion. 
     In addition, it is known that a restriction plate facing the outer circumferential surface of the developer carrying member may be provided on the upstream side of the layer thickness restricting portion in the rotation direction of the developer carrying member, and that a projection portion is formed on the surface of the restriction plate. 
     The restriction plate compresses the developer carried by the developer carrying member by gradually narrowing the passage of the carried developer. The projection portion moderates the density unevenness of the developer on the outer circumferential surface of the developer carrying member. 
     SUMMARY 
     A developing device according to an aspect of the present disclosure includes a storage portion, a developer carrying member, a stirring portion, a layer thickness restricting portion, and a guide portion. The storage portion stores developer including toner. The developer carrying member is of a cylindrical shape, has a magnet in an inside thereof, and rotates in the storage portion while carrying the developer on an outer circumferential surface thereof. The stirring portion includes a blade portion spirally extending outward, the stirring portion facing the developer carrying member with a first gap therebetween and stir the developer in the storage portion by rotating. The layer thickness restricting portion is located on a downstream side of the stirring portion in a rotation direction of the developer carrying member. The layer thickness restricting portion faces the developer carrying member with a second gap therebetween and restricts a layer thickness of the developer carried by the developer carrying member. The guide portion is disposed between the stirring portion and the layer thickness restricting portion. The guide portion includes a first guide surface and a second guide surface. On the first guide surface, a plurality of convex portions or a plurality of concave portions are formed. The first guide surface faces the stirring portion with, between them, a third gap that is a passage through which the developer passes toward the first gap. The second guide surface faces the developer carrying member with, between them, a fourth gap that is a passage through which the developer passes toward the second gap. 
     An image forming apparatus according to another aspect of the present disclosure includes an image carrying member, the developing device, a transfer device, and a fixing device. On a surface of the image carrying member, an electrostatic latent image is formed. The developing device develops, as a toner image, the electrostatic latent image on the surface of the image carrying member. The transfer device transfers the toner image to a sheet. The fixing device heats the toner image transferred to the sheet. 
     This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description with reference where appropriate to the accompanying drawings. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Furthermore, the claimed subject matter is not limited to implementations that solve any or all disadvantages noted in any part of this disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a configuration diagram of an image forming apparatus including a developing device according to a first embodiment. 
         FIG. 2  is a configuration diagram of the developing device according to the first embodiment. 
         FIG. 3  is a front view of a stirring screw and a guide portion included in the developing device according to the first embodiment. 
         FIG. 4  is a front view of the guide portion included in the developing device according to the first embodiment. 
         FIG. 5  is a front view of a guide portion included in the developing device according to a second embodiment. 
         FIG. 6A  and  FIG. 6B  are, respectively, a front view and a cross-sectional view of a guide portion included in the developing device according to a third embodiment. 
         FIG. 7A  and  FIG. 7B  are, respectively, a front view and a cross-sectional view of a guide portion included in the developing device according to a fourth embodiment. 
         FIG. 8  is a front view of a guide portion included in the developing device according to a fifth embodiment. 
         FIG. 9  is a front view of a guide portion included in the developing device according to a sixth embodiment. 
         FIG. 10  is a front view of a guide portion included in the developing device according to a seventh embodiment. 
         FIG. 11  is a front view of a guide portion included in the developing device according to an eighth embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The following describes embodiments of the present disclosure with reference to the accompanying drawings. It should be noted that the following embodiments are examples of specific embodiments of the present disclosure and should not limit the technical scope of the present disclosure. 
     First Embodiment: Configuration of Image Forming Apparatus  10   
     First, a description is given of a configuration of an image forming apparatus  10  including a developing device  43  according to the first embodiment of the present disclosure, with reference to  FIG. 1 . 
     The image forming apparatus  10  forms an image on a sheet by an electrophotographic system using developer  9 . The sheet is a sheet-like image formation medium such as a sheet of paper or an envelope. The developer  9  is two-component developer that includes toner  9   a  and carrier  9   b . The carrier  9   b  is a granular material having magnetism. 
     The image forming apparatus  10  includes a sheet supply portion  2 , a sheet conveying portion  3 , an image forming portion  40 , and a toner supply portion  400 . The image forming portion  40  includes image forming units  4 , a laser scanning portion  46 , and a fixing device  49 . The image forming portion  40  executes a print process to form an image on the sheet. 
     In the sheet supply portion  2 , a sheet feed portion  22  feeds sheets one by one from a sheet cassette  21  that stores a plurality of sheets, to a conveyance path  30 . Furthermore, the sheet conveying portion  3  conveys the sheet along the conveyance path  30 , and discharges the sheet with an image formed thereon from the conveyance path  30  onto a discharge tray  101 . 
     The image forming units  4  perform a developing process using the powdery developer  9  and a primary transfer process. The image forming apparatus  10  shown in  FIG. 1  is a tandem-type image forming apparatus and is a color printer. The image forming apparatus  10  thus includes a plurality of image forming units  4  that respectively correspond to colors of cyan, magenta, yellow, and black, an intermediate transfer belt  47 , a secondary transfer device  48 , and a secondary cleaning device  470 . 
     Each of the image forming units  4  includes a photoconductor  41 , a charging device  42 , a developing device  43 , a primary transfer device  44 , and a primary cleaning device  45 . 
     In each of the image forming units  4 , the drum-like photoconductor  41  rotates and the charging device  42  uniformly charges the surface of the photoconductor  41 . The laser scanning portion  46  writes an electrostatic latent image on the charged surface of the photoconductor  41  by scanning a laser beam thereon. It is noted that the photoconductor  41  is an example of the image carrying member on which the electrostatic latent image is formed. 
     The developing device  43  develops the electrostatic latent image on the photoconductor  41  as an image of the toner  9   a , by using the two-component developer  9 . The toner supply portion  400  is provided for each color of the toner  9   a , and supplies the toner  9   a  to a corresponding one of the developing devices  43 . 
     The primary transfer device  44  transfers the image of the toner  9   a  from the surface of the photoconductor  41  to the intermediate transfer belt  47 . The primary cleaning device  45  removes the toner  9   a  that has remained on the surface of the photoconductor  41 . 
     The secondary transfer device  48 , in the conveyance path  30 , transfers the toner image formed on the intermediate transfer belt  47  to the sheet. The secondary cleaning device  470  removes the toner  9   a  that has remained on the intermediate transfer belt  47 . 
     It is noted that the primary transfer device  44 , the intermediate transfer belt  47 , and the secondary transfer device  48  constitute the transfer device that transfers the toner image on the photoconductor  41  to the sheet. 
     The fixing device  49  heats the toner image transferred to the sheet to fix the toner image to the sheet. The fixing device  49  includes a fixing roller that rotates while contacting the toner image formed on the sheet, and a heater that heats the fixing roller. 
     A low-melt-type toner may be adopted as the toner  9   a  of the developer  9 , wherein the melting point of the low-melt-type toner is less than 150° C. In that case, in the fixing device  49 , the set temperature for the heat control of the fixing roller by the heater may be equal to or less than 150° C. This contributes to reduction of the power consumption of the fixing device  49 . 
     [Configuration of Developing Device  43 ] 
     The developing device  43  shown in  FIG. 2  is of a so-called interactive touch down system. The developing device  43  includes a storage portion  4300 , a developing roller  430 , a magnetic roller  431 , a magnet  432 , a first stirring screw  433 , a second stirring screw  434 , a blade  435 , and a guide portion  436 . The magnet  432  is disposed in a hollow portion of the cylindrical magnetic roller  431 . 
     In the storage portion  4300  storing the developer  9 , the developing roller  430 , the magnetic roller  431 , the first stirring screw  433 , and the second stirring screw  434  rotate. The first stirring screw  433  and the second stirring screw  434  cyclically conveys the developer  9  in the storage portion  4300  while stirring it. The toner  9   a  is electrically charged by being stirred. 
     As shown in  FIG. 3 , the second stirring screw  434  is a stirring portion of a screw feeder type, and includes a shaft portion  434   a  and a blade portion  434   b  of a spiral shape. The second stirring screw  434  rotates around the shaft portion  434   a . The blade portion  434   b  spirally extends outward from the shaft portion  434   a . It is noted that the first stirring screw  433  has the same structure as the second stirring screw  434 . 
     The second stirring screw  434  is disposed to face the magnetic roller  431  with a first gap G 1  therebetween and rotates at the position. It is noted that the second stirring screw  434  is an example of the stirring portion that stirs the developer  9  in the storage portion  4300 . 
     The second stirring screw  434  conveys the developer  9  to the first gap G 1  while stirring the developer  9 . This allows the developer  9  to be supplied to the magnetic roller  431 . 
     The magnetic roller  431  having the magnet  432  in its inside rotates in a predetermined forward rotation direction R 0  while carrying the two-component developer  9  on its outer circumferential surface. The magnetic roller  431  is configured to supply only the toner  9   a  among the developer  9  it carries, to the developing roller  430 . It is noted that the magnetic roller  431  is an example of the developer carrying member. 
     The blade  435  is disposed on the downstream side of the second stirring screw  434  in the forward rotation direction R 0  of the magnetic roller  431 , to face the magnetic roller  431  with a second gap G 2  therebetween. The blade  435  is disposed between the developing roller  430  and the second stirring screw  434  in the surrounding of the magnetic roller  431 . 
     The magnet  432  includes a first magnetic pole portion  432   a , a second magnetic pole portion  432   b , a third magnetic pole portion  432   c , and a fourth magnetic pole portion  432   d , wherein the second magnetic pole portion  432   b  is adjacent to and on the downstream side of the first magnetic pole portion  432   a  in the forward rotation direction R 0 , the third magnetic pole portion  432   c  is adjacent to and on the downstream side of the second magnetic pole portion  432   b  in the forward rotation direction R 0 , and the fourth magnetic pole portion  432   d  is adjacent to and on the downstream side of the third magnetic pole portion  432   c  in the forward rotation direction R 0 . 
     The magnetic roller  431  carries the developer  9  by the magnetic force of the magnet  432  that is in the inside of the magnetic roller  431 . That is, the first magnetic pole portion  432   a  magnetically attracts the developer  9 , and the developer  9  is drawn up from the periphery of the second stirring screw  434  onto the outer circumferential surface of the magnetic roller  431  by the magnetic force of the first magnetic pole portion  432   a.    
     The first magnetic pole portion  432   a  is disposed on the upstream side of the blade  435  in the forward rotation direction R 0  of the magnetic roller  431 . A part of the first magnetic pole portion  432   a  faces the second stirring screw  434  with the first gap G 1  therebetween. 
     The blade  435  restricts the layer thickness of the developer  9  carried by the magnetic roller  431 . By passing through the second gap G 2 , the layer thickness of the developer  9  on the outer circumferential surface of the magnetic roller  431  becomes approximately equal to the height of the second gap G 2 . It is noted that the blade  435  is an example of the layer thickness restricting portion. 
     The second magnetic pole portion  432   b  is disposed on the upstream side of a position on the magnetic roller  431  facing the developing roller  430 , in the forward rotation direction R 0  of the magnetic roller  431 . A part of the second magnetic pole portion  432   b  faces the blade  435  with the magnetic roller  431  therebetween. The magnetic pole of the second magnetic pole portion  432   b  is different from the magnetic pole of the first magnetic pole portion  432   a.    
     The developing roller  430  rotates while carrying, on its outer circumferential surface, the toner  9   a  supplied from the magnetic roller  431 . Furthermore, the developing roller  430  supplies the toner  9   a  to the electrostatic latent image formed on the surface of the photoconductor  41 . In this way, the developing roller  430  develops, as the toner image, the electrostatic latent image on the surface of the photoconductor  41 . 
     The third magnetic pole portion  432   c  faces the developing roller  430  with the magnetic roller  431  therebetween. The magnetic pole of the third magnetic pole portion  432   c  is the same as the magnetic pole of the first magnetic pole portion  432   a . In addition, the magnetic pole of the fourth magnetic pole portion  432   d  is different from the magnetic pole of the first magnetic pole portion  432   a.    
     The carrier  9   b  on the magnetic roller  431  forms a magnetic brush by the magnetic field of the magnet  432 . The magnetic brush comes to contact the outer circumferential surface of the developing roller  430 . Upon contact, the toner  9   a  that has adhered to the carrier  9   b  transitions from the magnetic roller  431  to the developing roller  430 . 
     The toner  9   a  then transitions from the developing roller  430  to the photoconductor  41  when the layer of the toner  9   a  carried by the developing roller  430  faces the electrostatic latent image on the photoconductor  41 . The toner  9   a  that has remained on the developing roller  430  without transitioning to the photoconductor  41 , is collected into the storage portion  4300 . 
     Meanwhile, it is known that, on the outer circumferential surface of the magnetic roller  431 , streaky density unevenness of the developer  9  is formed along the blade portion  434   b  of the second stirring screw  434 . The density unevenness of the developer  9  occurs since the blade portion  434   b  of the second stirring screw  434  generates thickness distribution of the layer of the developer  9  in the axial direction of the magnetic roller  431 . 
     In addition, there is known a conventional apparatus in which a restriction plate is disposed on the upstream side of the blade  435  in the forward rotation direction R 0  of the magnetic roller  431 , to face the outer circumferential surface of the magnetic roller  431 , and a projection portion is formed on the surface of the restriction plate. 
     The restriction plate compresses the developer  9  carried by the magnetic roller  431 . The projection portion moderates the density unevenness of the developer  9  on the outer circumferential surface of the magnetic roller  431 . 
     There may be a case where, due to the miniaturization of the developing device  43 , a passage of the developer  9  that is long enough to eliminate the density unevenness of the developer  9  cannot be secured between the magnetic roller  431  and the restriction plate. 
     It is noted that the toner  9   a  of the low melt type is likely to be deteriorated upon compression. Accordingly, it is preferable to moderate the density unevenness of the developer  9  on the outer circumferential surface of the magnetic roller  431  by applying as little pressure as possible to the developer  9 . 
     The developing device  43  has a configuration that can moderate the density unevenness of the developer  9  due to the second stirring screw  434  on the outer circumferential surface of the magnetic roller  431 , even if the peripheral space of the magnetic roller  431  is narrow. The following describes the configuration. 
     [Guide Portion  436 ] 
     The guide portion  436  is disposed between the second stirring screw  434  and the blade  435 . In the example shown in  FIG. 2 , the guide portion  436  is attached to the blade  435  on a surface on the side of the second stirring screw  434 . The guide portion  436  includes a first guide surface  436   a  facing the second stirring screw  434 , and a second guide surface  436   b  facing the magnetic roller  431 . 
     The first guide surface  436   a  faces the second stirring screw  434  with a third gap G 3  therebetween. The third gap G 3  is a passage through which the developer  9  passes toward the first gap G 1 . The first guide surface  436   a  guides, to the first gap G 1 , the developer  9  that is moved by the rotation of the second stirring screw  434 . 
     The second guide surface  436   b  faces the magnetic roller  431  with a fourth gap G 4  therebetween. The fourth gap G 4  is a passage through which the developer  9  from the first gap G 1  passes toward the second gap G 2 . 
     The fourth gap G 4  gradually narrows from the first gap G 1  side to the second gap G 2  side. That is, the passage through which the developer  9  carried by the magnetic roller  431  passes toward the second gap G 2  is made narrower by the second guide surface  436   b . With this configuration, in the first gap G 1 , the second guide surface  436   b  guides the developer  9  that has moved from the peripheral of the second stirring screw  434  to the outer circumferential surface of the magnetic roller  431 , to the second gap G 2 . 
     In the following description, a direction that is perpendicular to the longitudinal direction of the rotation shaft of the second stirring screw  434  and directs to the magnetic roller  431  when viewed from the front side of the first guide surface  436   a , is referred to as a developer supply direction D 1 . When viewed from the front side of the first guide surface  436   a , the blade portion  434   b  on its side facing the first guide surface  436   a  is displaced in the developer supply direction D 1 . 
     As shown in  FIG. 4 , a plurality of convex portions  436   z  are formed on the first guide surface  436   a . The plurality of convex portions  436   z  are formed in an area of the first guide surface  436   a  that extends from a position close to one of opposite ends of the rotation shaft of the second stirring screw  434  in the longitudinal direction of the rotation shaft, to a position close to the other end. 
     In the present embodiment, each of the plurality of convex portions  436   z  is formed in the tapered shape in which the width gradually narrows from the upstream side to the downstream side in the developer supply direction D 1 , along the developer supply direction D 1  when viewed from the front side of the first guide surface  436   a.    
     The plurality of convex portions  436   z  are arranged at intervals in alignment along the longitudinal direction of the rotation shaft of the second stirring screw  434 , when viewed from the front side of the first guide surface  436   a . It is noted that the height position of each of the plurality of convex portions  436   z  is constant in the developer supply direction D 1 . 
     In  FIG. 4 , the blade portions  434   b  of the second stirring screw  434  facing the first guide surface  436   a  are represented by an imaginary line. As shown in  FIG. 4 , the blade portions  434   b  facing the first guide surface  436   a  are slanted with respect to the developer supply direction D 1 , when viewed from the front side of the first guide surface  436   a.    
     In the following description, a direction in which the blade portions  434   b  facing the first guide surface  436   a  are slanted with respect to the developer supply direction D 1 , is referred to as a blade slant direction D 2 . 
     Each of the plurality of convex portions  436   z  forms steps with respect to the first guide surface  436   a  at edges of opposite sides thereof, the steps extending in a direction intersecting the blade slant direction D 2 . With this configuration, when the developer  9  passes through the third gap G 3 , the developer  9  is stirred by the plurality of convex portions  436   z  in a direction where the density distribution of the developer  9  that would become high along the blade portion  434   b  is made substantially uniform. 
     Due to the above-described action of the plurality of convex portions  436   z , the density unevenness of the developer  9  due to the second stirring screw  434  on the outer circumferential surface of the magnetic roller  431  is moderated. In addition, the configuration makes it possible to secure an enough length of the plurality of convex portions  436   z  in the developer supply direction D 1  even when the peripheral space of the magnetic roller  431  is narrow, namely, even when the distance between the first gap G 1  and the second gap G 2  is short. 
     Second Embodiment 
     Next, a description is given of a developing device  43 A according to the second embodiment that is applicable to the image forming apparatus  10 , with reference to  FIG. 5 . In  FIG. 5 , components that are the same as those shown in  FIG. 1  to  FIG. 4  are assigned the same reference signs. 
     A plurality of convex portions  436   y  are formed on the first guide surface  436   a  of the guide portion  436  of the developing device  43 A. The plurality of convex portions  436   y  are formed in an area of the first guide surface  436   a  that extends from a position close to one of opposite ends of the rotation shaft of the second stirring screw  434  in the longitudinal direction of the rotation shaft, to a position close to the other end. 
     The plurality of convex portions  436   y  are different in shape and arrangement from the plurality of convex portions  436   z  formed on the first guide surface  436   a  of the guide portion  436  of the developing device  43 . This is the difference between the developing device  43 A and the developing device  43 . 
     In the developing device  43 A, the plurality of convex portions  436   y  are formed in a staggered arrangement on the first guide surface  436   a  of the guide portion  436 . For example, the height position of each of the plurality of convex portions  436   y  may be equal. 
     In the example shown in  FIG. 5 , each of the convex portions  436   y  is cylindrical. It is noted that each of the convex portions  436   y  may have a polygonal shape in cross section. 
     Each of the plurality of convex portions  436   y , in major portions of its outer circumference, forms a step with respect to the first guide surface  436   a , and the steps are aligned along a direction intersecting the blade slant direction D 2 . With this configuration, when the developer  9  passes through the third gap G 3 , the developer  9  is stirred by the plurality of convex portions  436   y  in a direction where the density distribution of the developer  9  that would become high along the blade portion  434   b  is made substantially uniform. 
     Due to the above-described action of the plurality of convex portions  436   y , the density unevenness of the developer  9  due to the second stirring screw  434  on the outer circumferential surface of the magnetic roller  431  is moderated. 
     Third Embodiment 
     Next, a description is given of a developing device  43 B according to the third embodiment that is applicable to the image forming apparatus  10 , with reference to  FIG. 6A  and  FIG. 6B . In  FIG. 6A  and  FIG. 6B , components that are the same as those shown in  FIG. 1  to  FIG. 4  are assigned the same reference signs. 
     A plurality of convex portions  436   x  are formed on the first guide surface  436   a  of the guide portion  436  of the developing device  43 B. The plurality of convex portions  436   x  are formed in an area of the first guide surface  436   a  that extends from a position close to one of opposite ends of the rotation shaft of the second stirring screw  434  in the longitudinal direction of the rotation shaft, to a position close to the other end. 
     The plurality of convex portions  436   x  are different in shape from the plurality of convex portions  436   z  formed on the first guide surface  436   a  of the guide portion  436  of the developing device  43 . 
     In the developing device  43 B, when viewed from the front side of the first guide surface  436   a , the plurality of convex portions  436   x  are formed along an inversely slanted direction D 3  that is slanted toward the opposite side of the blade slant direction D 2  on the basis of the developer supply direction D 1 . The plurality of convex portions  436   x  are, as a whole, an example of the inversely slanted portion. 
     As shown in  FIG. 6B , each of the plurality of convex portions  436   x  is formed in a taper shape in which the height thereof is gradually reduced from the upstream side to the downstream side in the developer supply direction D 1 . The developing device  43 B produces substantially the same effect as the developing device  43  or  43 A. 
     Fourth Embodiment 
     Next, a description is given of a developing device  43 C according to the fourth embodiment that is applicable to the image forming apparatus  10 , with reference to  FIG. 7A  and  FIG. 7B . In  FIG. 7A  and  FIG. 7B , components that are the same as those shown in  FIG. 1  to  FIG. 4  are assigned the same reference signs. 
     A plurality of convex portions  436   w  are formed on the first guide surface  436   a  of the guide portion  436  of the developing device  43 C. The plurality of convex portions  436   w  are formed in an area of the first guide surface  436   a  that extends from a position close to one of opposite ends of the rotation shaft of the second stirring screw  434  in the longitudinal direction of the rotation shaft, to a position close to the other end. 
     The plurality of convex portions  436   w  are different in shape from the plurality of convex portions  436   z  formed on the first guide surface  436   a  of the guide portion  436  of the developing device  43 . 
     In the developing device  43 C, when viewed from the front side of the first guide surface  436   a , the plurality of convex portions  436   w  are formed along the inversely slanted direction D 3  on the basis of the developer supply direction D 1 , as is the case with the plurality of convex portions  436   x . The plurality of convex portions  436   w  are, as a whole, an example of the inversely slanted portion. 
     As shown in  FIG. 7B , the plurality of convex portions  436   w  are constant in height in the developer supply direction D 1 . The developing device  43 C produces substantially the same effect as the developing device  43 ,  43 A or  43 B. 
     Fifth Embodiment 
     Next, a description is given of a developing device  43 D according to the fifth embodiment that is applicable to the image forming apparatus  10 , with reference to  FIG. 8 . In  FIG. 8 , components that are the same as those shown in  FIG. 1  to  FIG. 4  are assigned the same reference signs. 
     A plurality of convex portions  436   v  are formed on the first guide surface  436   a  of the guide portion  436  of the developing device  43 D. The plurality of convex portions  436   v  are formed in an area of the first guide surface  436   a  that extends from a position close to one of opposite ends of the rotation shaft of the second stirring screw  434  in the longitudinal direction of the rotation shaft, to a position close to the other end. 
     The plurality of convex portions  436   v  are different in shape from the plurality of convex portions  436   z  formed on the first guide surface  436   a  of the guide portion  436  of the developing device  43 . 
     In the developing device  43 D, each of the plurality of convex portions  436   v  is formed in the shape of a wave that extends in the longitudinal direction of the rotation shaft of the second stirring screw  434 . When viewed from the front side of the first guide surface  436   a , the plurality of convex portions  436   v  are formed at intervals in the developer supply direction D 1 . 
     The plurality of convex portions  436   v  are constant in height position in the longitudinal direction of the rotation shaft of the second stirring screw  434 . The developing device  43 D produces substantially the same effect as the developing device  43 ,  43 A,  43 B or  43 C. 
     Sixth Embodiment 
     Next, a description is given of a developing device  43 E according to the sixth embodiment that is applicable to the image forming apparatus  10 , with reference to  FIG. 9 . In  FIG. 9 , components that are the same as those shown in  FIG. 1  to  FIG. 4  are assigned the same reference signs. 
     A plurality of convex portions  436   u  are formed on the first guide surface  436   a  of the guide portion  436  of the developing device  43 D. The plurality of convex portions  436   u  are formed in an area of the first guide surface  436   a  that extends from a position close to one of opposite ends of the rotation shaft of the second stirring screw  434  in the longitudinal direction of the rotation shaft, to a position close to the other end. 
     The plurality of convex portions  436   u  are different in shape from the plurality of convex portions  436   z  formed on the first guide surface  436   a  of the guide portion  436  of the developing device  43 . 
     When viewed from the front side of the first guide surface  436   a , the plurality of convex portions  436   u  are formed at intervals in the longitudinal direction of the rotation shaft of the second stirring screw  434 . 
     In the developing device  43 E, each of the plurality of convex portions  436   u  includes a first portion  436   p  and a second portion  436   q . When viewed from the front side of the first guide surface  436   a , the first portion  436   p  of each convex portion  436   u  is formed along the inversely slanted direction D 3  that is slanted on the basis of the developer supply direction D 1 . The first portion  436   p  of each convex portion  436   u  is an example of the inversely slanted portion. 
     When viewed from the front side of the first guide surface  436   a , the second portion  436   q  of each convex portion  436   u  is formed along the developer supply direction D 1 . The plurality of convex portions  436   u  are constant in height in the developer supply direction D 1 . The developing device  43 E produces substantially the same effect as the developing device  43 ,  43 A,  43 B,  43 C or  43 D. 
     Seventh Embodiment 
     Next, a description is given of a developing device  43 F according to the seventh embodiment that is applicable to the image forming apparatus  10 , with reference to  FIG. 10 . In  FIG. 10 , components that are the same as those shown in  FIG. 1  to  FIG. 4  are assigned the same reference signs. 
     A plurality of convex portions  436   t  are formed on the first guide surface  436   a  of the guide portion  436  of the developing device  43 F. The plurality of convex portions  436   t  are formed in an area of the first guide surface  436   a  that extends from a position close to one of opposite ends of the rotation shaft of the second stirring screw  434  in the longitudinal direction of the rotation shaft, to a position close to the other end. 
     The plurality of convex portions  436   t  are different in shape from the plurality of convex portions  436   z  formed on the first guide surface  436   a  of the guide portion  436  of the developing device  43 . 
     When viewed from the front side of the first guide surface  436   a , the plurality of convex portions  436   t  are formed at intervals in the longitudinal direction of the rotation shaft of the second stirring screw  434 . 
     In the developing device  43 F, when viewed from the front side of the first guide surface  436   a , each of the plurality of convex portions  436   t  is formed along a curved line that intersects the blade slant direction D 2 . For example, the plurality of convex portions  436   t  are constant in height in the developer supply direction D 1 . The developing device  43 F produces substantially the same effect as the developing device  43 ,  43 A,  43 B,  43 C,  43 D or  43 E. 
     Eighth Embodiment 
     Next, a description is given of a developing device  43 G according to the eighth embodiment that is applicable to the image forming apparatus  10 , with reference to  FIG. 11 . In  FIG. 11 , components that are the same as those shown in  FIG. 1  to  FIG. 4  are assigned the same reference signs. 
     A plurality of convex portions  436   s  are arranged in a lattice shape on the first guide surface  436   a  of the guide portion  436  of the developing device  43 G. That is, the plurality of convex portions  436   s  include portions that form vertical frames of the lattice along the developer supply direction D 1 , and portions that form horizontal frames of the lattice along the longitudinal direction of the rotation shaft of the second stirring screw  434 . 
     It may be said that the first guide surface  436   a  of the developing device  43 G is composed of a plurality of rectangular concave portions that are formed along the longitudinal direction of the rotation shaft of the second stirring screw  434 , and along the developer supply direction D 1 . 
     The plurality of convex portions  436   s  are formed in an area of the first guide surface  436   a  that extends from a position close to one of opposite ends of the rotation shaft of the second stirring screw  434  in the longitudinal direction of the rotation shaft, to a position close to the other end. 
     The developing device  43 G produces substantially the same effect as the developing device  43 ,  43 A,  43 B,  43 C,  43 D,  43 E or  43 F. 
     [Results of Evaluation Experiment] 
     The following describes results of an evaluation experiment in which a comparison was made between a comparative device whose first guide surface  436   a  and second guide surface  436   b  of the guide portion  436  are flat, and the developing devices  43 ,  43 A,  43 B,  43 C,  43 D,  43 E,  43 F and  43 G. 
     In general, when the amount of the developer  9  in the storage portion  4300  becomes small, the density unevenness of the developer  9  due to the second stirring screw  434  is likely to occur. Furthermore, the density unevenness of the developer  9  due to the second stirring screw  434  is more likely to occur when the print process has been executed a number of times and the developer  9  has been deteriorated, than when the developer  9  is new. 
     In the evaluation experiment, a test printing was performed under a plurality of conditions where the set amount of the developer  9  in the storage portion  4300  was gradually reduced by 10 grams, so as to detect, among conditions under which a print with no density unevenness due to the second stirring screw  434  was obtained, a condition with the smallest amount of the developer  9 . Hereinafter, the amount of the developer  9  set for the detected condition is referred to as a “limit amount”. Here, it can be said that the smaller the limit amount is, the less the density unevenness due to the second stirring screw  434  is likely to occur. 
     In addition, the evaluation experiment was conducted in an initial state where the developer  9  was new, and in a 100,000-sheets printed state where the print process had been performed on 100,000 sheets. 
     When the limit amount of the developer  9  in the comparative device in the initial state was 100%, the limit amounts of the developing devices  43 ,  43 A,  43 B,  43 C,  43 D,  43 E,  43 F and  43 G were, respectively, 77%, 82%, 82%, 86%, 86%, 82%, 82%, and 91%. 
     In addition, when the limit amount of the developer  9  in the comparative device in the 100,000-sheets printed state was 100%, the limit amounts of the developing devices  43 ,  43 A,  43 B,  43 C,  43 D,  43 E,  43 F and  43 G were, respectively, 79%, 79%, 79%, 83%, 83%, 83%, 83%, and 88%. 
     The results of the evaluation experiment indicate that, in the developing devices  43 ,  43 A,  43 B,  43 C,  43 D,  43 E,  43 F and  43 G, compared to the comparative device, the density unevenness due to the second stirring screw  434  is difficult to occur even when the amount of the developer  9  in the storage portion  4300  becomes small. 
     It is noted that when the limit amount of the developer  9  in the comparative device in the initial state was 100%, the limit amount of the developer  9  in the comparative device in the 100,000-sheets printed state was 109%. 
     First Application Example 
     In the developing devices  43 ,  43 A,  43 B,  43 C,  43 D,  43 E,  43 F and  43 G, the plurality of convex portions  436   z ,  436   y ,  436   x ,  436   w ,  436   v ,  436   u ,  436   t  and  436   s  may be further formed on the second guide surface  436   b  of the guide portion  436 . In that case, the direction oriented from the first gap G 1  to the second gap G 2  on the second guide surface  436   b  corresponds to the developer supply direction D 1 . 
     Second Application Example 
     In the developing devices  43 ,  43 A,  43 B,  43 C,  43 D,  43 E,  43 F and  43 G, the plurality of convex portions  436   z ,  436   y ,  436   x ,  436   w ,  436   v ,  436   u ,  436   t  and  436   s  form convexes and concaves on the first guide surface  436   a.    
     On the other hand, when viewed from the front side of the first guide surface  436   a , a plurality of concave portions having the same outline shapes as the plurality of convex portions  436   z ,  436   y ,  436   x ,  436   w ,  436   v ,  436   u ,  436   t  and  436   s  may be formed on the first guide surface  436   a  instead of the plurality of convex portions  436   z ,  436   y ,  436   x ,  436   w ,  436   v ,  436   u ,  436   t  and  436   s.    
     Furthermore, in the present application example, the plurality of concave portions may be formed on both the first guide surface  436   a  and the second guide surface  436   b.    
     In the case where the plurality of concave portions are formed on the first guide surface  436   a , concaves and convexes are formed on the first guide surface  436   a . This case, too, produces substantially the same effect as the cases where the developing devices  43 ,  43 A,  43 B,  43 C,  43 D,  43 E,  43 F or  43 G are adopted. 
     For example, a plurality of groove-like concave portions extending along the inversely slanted direction D 3  may be formed on the first guide surface  436   a  instead of the plurality of convex portions  436   x  shown in  FIG. 6A . In this case, each of the plurality of groove-like concave portions may be formed in the shape of a groove that becomes shallow gradually from the upstream side to the downstream side in the developer supply direction D 1 . 
     It is noted that the developing device and the image forming apparatus of the present disclosure may be configured by freely combining, within the scope of claims, the above-described embodiments and application examples, or by modifying the embodiments and application examples or omitting a part thereof. 
     It is to be understood that the embodiments herein are illustrative and not restrictive, since the scope of the disclosure is defined by the appended claims rather than by the description preceding them, and all changes that fall within metes and bounds of the claims, or equivalence of such metes and bounds thereof are therefore intended to be embraced by the claims.