Patent Publication Number: US-9423721-B2

Title: Developing device, visible-image-forming device, and image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2014-183458 filed Sep. 9, 2014, and Japanese Patent Application No. 2015-065270 filed Mar. 26, 2015. 
     BACKGROUND 
     Technical Field 
     The present invention relates to a developing device, a visible-image-forming device, and an image forming apparatus. 
     SUMMARY 
     According to an aspect of the invention, there is provided a developing device including a developer container that contains developer; a developer carrier provided in the developer container and that is rotatable while carrying the developer on a surface, the developer carrier facing an image carrier on which a latent image is to be formed; a first transporting member including a rotating shaft and a transporting blade supported by the rotating shaft, the first transporting member transporting the developer in the developer container while stirring the developer; and a second transporting member including a rotating shaft and a transporting blade supported by the rotating shaft, the second transporting member being provided side by side with the first transporting member, the second transporting member transporting the developer, while stirring the developer, in a direction opposite to a direction of transport by the first transporting member. The rotating shaft of the first transporting member is positioned in an area of projection defined by projecting the developer carrier from an upper side in a gravitational direction. Supposing that a first virtual tangent to an outer surface of the developer carrier extends in the gravitational direction on a side of the developer carrier opposite the image carrier and that a second virtual tangent to an outer edge of the transporting blade of the first transporting member extends in the gravitational direction on a side of the first transporting member opposite the image carrier, the second virtual tangent is farther from the image carrier in a horizontal direction than the first virtual tangent. Letting a distance in the horizontal direction between the first virtual tangent and the second virtual tangent be a first distance, and a distance in the horizontal direction between the first virtual tangent and an inner surface of the developer container on the side of the developer carrier opposite the image carrier be a second distance, the first distance is shorter than the second distance. A developer guiding member that guides the developer moving along the developer carrier is provided on a downstream side in a direction of rotation of the developer carrier with respect to a facing area where the developer carrier faces the image carrier. The developer guiding member faces the outer surface of the developer carrier with a gap interposed between the developer guiding member and the outer surface of the developer carrier. The developer guiding member includes an inclined portion that inclines from an upstream side in the direction of rotation of the developer carrier toward a downstream side in the direction of transport by the first transporting member. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein: 
         FIG. 1  illustrates an image forming apparatus according to a first exemplary embodiment; 
         FIG. 2  illustrates relevant parts of the image forming apparatus according to the first exemplary embodiment; 
         FIG. 3  illustrates a developing device according to the first exemplary embodiment; 
         FIG. 4  is a sectional view taken along line IV-IV illustrated in  FIG. 3 ; 
         FIG. 5  illustrates the positional relationship among relevant elements according to the first exemplary embodiment and corresponds to  FIG. 3 ; 
         FIG. 6  illustrates a guiding-fin member according to the first exemplary embodiment; 
         FIG. 7A  illustrates the distribution of magnetic forces acting on a developing roller according to the first exemplary embodiment; 
         FIG. 7B  illustrates the distribution of the magnetic forces with respect to the position of the guiding-fin member; 
         FIG. 8A  illustrates a movement of developer in a case where the guiding-fin member is provided; 
         FIG. 8B  illustrates a movement of developer in a comparative case where the guiding-fin member is not provided; 
         FIG. 9A  illustrates the pitch of fins of the guiding-fin member and the amount of developer in the first exemplary embodiment; 
         FIG. 9B  illustrates the pitch of the fins of the guiding-fin member and the amount of developer in a comparative case where the pitch of the fins is larger than the pitch of turns in a transporting blade of a supply auger; 
         FIG. 10A  illustrates the pitch of the fins and the way the developer is returned to a supply chamber in the first exemplary embodiment; 
         FIG. 10B  illustrates a state where the supply auger according to the first exemplary embodiment has transported the developer by moving from the position illustrated in  FIG. 10A ; 
         FIG. 10C  illustrates the pitch of the fins and the way the developer is returned to the supply chamber in a comparative case where the pitch of the fins is larger than the pitch of turns in the transporting blade of the supply auger; 
         FIG. 10D  illustrates a state where the supply auger according to the comparative case has transported the developer by moving from the position illustrated in  FIG. 10C . 
         FIG. 11A  is a graph illustrating the difference in toner concentration with respect to the amount of developer in Experimental Example 1-1 and Comparative Example 1-1 in each of which the process speed is 126 mm/s; 
         FIG. 11B  is a graph illustrating the difference in toner concentration with respect to the amount of developer in Experimental Example 1-2 and Comparative Example 1-2 in each of which the process speed is 63 mm/s; 
         FIG. 12A  is a graph illustrating the difference in toner concentration with respect to the amount of developer in Comparative Examples 1-1 and 1-2 in each of which the angle of inclination of each fin is 0 degrees; 
         FIG. 12B  is a graph illustrating the difference in toner concentration with respect to the amount of developer in Experimental Examples 1-1 and 1-2 in each of which the angle of inclination of each fin is 40 degrees; 
         FIG. 13  is a graph illustrating the results of experiments conducted in Experimental Examples 2-1 and 2-2 and Comparative Examples 2-1 and 2-2; 
         FIG. 14A  illustrates the position of a guiding-fin member according to a second exemplary embodiment; 
         FIG. 14B  is a bottom view of the guiding-fin member according to the second exemplary embodiment; 
         FIG. 15  illustrates a developing device according to a third exemplary embodiment and corresponds to  FIG. 3  illustrating the developing device according to the first exemplary embodiment; 
         FIG. 16  is a perspective view of relevant parts included in a guiding-fin member according to the third exemplary embodiment; and 
         FIG. 17  is a bar graph illustrating the results of experiments conducted in Experimental and Comparative Examples 3, with the horizontal axis representing the length of transport of the developer in the axial direction of the developing roller. 
     
    
    
     DETAILED DESCRIPTION 
     Exemplary embodiments of the present invention will now be described with reference to the drawings. Note that the present invention is not limited to the following exemplary embodiments. 
     For easy understanding, directions and sides to be mentioned hereinafter referring to the drawings are defined as follows: the anteroposterior direction corresponds to the X-axis direction, the horizontal direction corresponds to the Y-axis direction, and the vertical direction corresponds to the Z-axis direction. Furthermore, arrows X, −X, Y, −Y, Z, and −Z point toward the front side, the rear side, the right side, the left side, the upper side, and the lower side, respectively. 
     A circle with a dot illustrated in each of relevant drawings represents an arrow pointing toward the near side from the far side of the drawing, and a circle with a cross illustrated in each of relevant drawings represents an arrow pointing toward the far side from the near side of the drawing. 
     Elements that are negligible in the following description are not illustrated in the drawings, for easy understanding. 
     First Exemplary Embodiment 
       FIG. 1  illustrates an image forming apparatus according to a first exemplary embodiment of the present invention. 
       FIG. 2  illustrates relevant parts of the image forming apparatus according to the first exemplary embodiment. 
     Referring to  FIG. 1 , a copier U as an exemplary image forming apparatus according to the first exemplary embodiment includes a printer unit U 1  as an exemplary recording unit and as an exemplary image recording device. The printer unit U 1  supports a scanner unit U 2  as an exemplary reading unit and as an exemplary image reading device. The scanner unit U 2  supports an automatic feeder U 3  as an exemplary document transporting device. The scanner unit U 2  according to the first exemplary embodiment also supports a user interface UI as an exemplary input unit. An operator operates the copier U by inputting relevant information on the user interface UI. 
     The automatic feeder U 3  includes a document tray TG 1  as an exemplary medium holder that is provided at the top thereof. The document tray TG 1  holds a stack of plural pages of document Gi to be copied. The automatic feeder U 3  also includes a document output tray TG 2  as an exemplary document output portion that is provided below the document tray TG 1 . Pairs of document transporting rollers U 3   b  are provided between the document tray TG 1  and the document output tray TG 2  and along a document transport path U 3   a.    
     The scanner unit U 2  according to the first exemplary embodiment includes a platen glass PG as an exemplary transparent document table that is provided on the upper surface thereof, and a reading optical system A provided below the platen glass PG. The reading optical system A according to the first exemplary embodiment is supported in such a manner as to be movable in the horizontal direction along the lower surface of the platen glass PG. The reading optical system A is normally stationary at an initial position illustrated in  FIG. 1 . 
     An imaging device CCD as an exemplary imaging member is provided on the right side of the reading optical system A. The imaging device CCD is electrically connected to an image processing unit GS. 
     The image processing unit GS is electrically connected to a drawing circuit DL included in the printer unit U 1 . The drawing circuit DL is electrically connected to light-emitting-diode (LED) heads LHy, LHm, LHc, and LHk as exemplary latent-image-forming devices. 
     Photoconductor drums PRy, PRm, PRc, and PRk as exemplary image carriers are provided above the respective LED heads LHy, LHm, LHc, and LHk. 
     Charging rollers CRy, CRm, CRc, and CRk as exemplary charging devices are provided facing the respective photoconductor drums PRy, PRm, PRc, and PRk. A charging voltage is applied from a power supply circuit E to each of the charging rollers CRy, CRm, CRc, and CRk. The power supply circuit E is controlled by a controller C as an exemplary controller. The controller C performs control operations by transmitting and receiving signals to and from the image processing unit GS, the drawing circuit DL, and other associated elements. 
     The LED heads LHy, LHm, LHc, and LHk apply drawing beams to the surfaces of the photoconductor drums PRy, PRm, PRc, and PRk in drawing areas Q 1   y , Q 1   m , Q 1   c , and Q 1   k , respectively. The drawing areas Q 1   y , Q 1   m , Q 1   c , and Q 1   k  are defined on the downstream side with respect to the charging rollers CRy, CRm, CRc, and CRk in a direction of rotation of the photoconductor drums PRy, PRm, PRc, and PRk, respectively. 
     Developing devices Gy, Gm, Gc, and Gk are provided facing the surfaces of the photoconductor drums PRy, PRm, PRc, and PRk in development areas Q 2   y , Q 2   m , Q 2   c , and Q 2   k , respectively. The development areas Q 2   y , Q 2   m , Q 2   c , and Q 2   k  are defined on the downstream side with respect to the drawing areas Q 1   y , Q 1   m , Q 1   c , and Q 1   k  in the direction of rotation of the photoconductor drums PRy, PRm, PRc, and PRk, respectively. Combinations of the photoconductor drums PRy, PRm, PRc, and PRk and the developing devices Gy, Gm, Gc, and Gk are regarded as process cartridges PRy+Gy, PRm+Gm, PRc+Gc, and PRk+Gk, respectively, as exemplary visible-image-forming devices. 
     First transfer areas Q 3   y , Q 3   m , Q 3   c , and Q 3   k  are defined on the downstream side with respect to the development areas Q 2   y , Q 2   m , Q 2   c , and Q 2   k  in the direction of rotation of the photoconductor drums PRy, PRm, PRc, and PRk, respectively. The photoconductor drums PRy, PRm, PRc, and PRk are in contact with an intermediate transfer belt B as an intermediate transfer body in the respective first transfer areas Q 3   y , Q 3   m , Q 3   c , and Q 3   k . First transfer rollers T 1   y , T 1   m , T 1   c , and T 1   k  as exemplary first transfer devices are provided in the respective first transfer areas Q 3   y , Q 3   m , Q 3   c , and Q 3   k  and across the intermediate transfer belt B from the respective photoconductor drums PRy, PRm, PRc, and PRk. 
     Drum cleaners CLy, CLm, CLc, and CLk as exemplary image-carrier-cleaning devices are provided on the downstream side with respect to the first transfer areas Q 3   y , Q 3   m , Q 3   c , and Q 3   k  in the direction of rotation of the photoconductor drums PRy, PRm, PRc, and PRk, respectively. 
     A belt module BM as an exemplary intermediate transfer device is provided above the photoconductor drums PRy, PRm, PRc, and PRk. The belt module BM includes the intermediate transfer belt B. The intermediate transfer belt B is rotatably supported by a driving roller Rd as an exemplary driving member, a tension roller Rt as an exemplary stretching member, a walking roller Rw as an exemplary meandering correcting member, an idler roller Rf as an exemplary follower member, a backup roller T 2   a  as an exemplary counter member provided in a second transfer area, and the first transfer rollers T 1   y , T 1   m , T 1   c , and T 1   k.    
     A second transfer roller T 2   b  as an exemplary second transfer member is provided across the intermediate transfer belt B from the backup roller T 2   a . A combination of the backup roller T 2   a  and the second transfer roller T 2   b  is regarded as a second transfer device T 2 . An area where the second transfer roller T 2   b  and the intermediate transfer belt B are in contact with each other is regarded as a second transfer area Q 4 . 
     A combination of the first transfer rollers T 1   y , T 1   m , T 1   c , and T 1   k , the intermediate transfer belt B, the second transfer device T 2 , and other associated elements is regarded as a transfer device T 1 +T 2 +B according to the first exemplary embodiment that transfers images formed on the photoconductor drums PRy, PRm, PRc, and PRk to a medium. 
     A belt cleaner CLb as an exemplary cleaning device for the intermediate transfer body is provided on the downstream side with respect to the second transfer area Q 4  in a direction of rotation of the intermediate transfer belt B. 
     Cartridges Ky, Km, Kc, and Kk as exemplary developer containers are provided above the belt module BM. The cartridges Ky, Km, Kc, and Kk contain developers to be supplied to the developing devices Gy, Gm, Gc, and Gk, respectively. The cartridges Ky, Km, Kc, and Kk and the developing devices Gy, Gm, Gc, and Gk are connected to each other with developer supplying devices (not illustrated), respectively. 
     Sheet trays TR 1  to TR 3  as exemplary medium containers are provided at the bottom of the printer unit U 1 . The sheet trays TR 1  to TR 3  are each supported by guide rails GR as exemplary guide members in such a manner as to be detachable in the anteroposterior direction. The sheet trays TR 1  to TR 3  each contain sheets S as exemplary media. 
     A pickup roller Rp as an exemplary medium pickup member is provided on the upper left side of each of the sheet trays TR 1  to TR 3 . A pair of separating rollers Rs as an exemplary separating member is provided on the left side of the pickup roller Rp. 
     A transport path SH along which each sheet S is transported extends upward on the left side of the sheet trays TR 1  to TR 3 . Plural pairs of transporting rollers Ra as exemplary medium transporting members are provided along the transport path SH. A pair of registration rollers Rr as an exemplary feeding member is provided in a downstream portion of the transport path SH and on the upstream side with respect to the second transfer area Q 4  in the direction of transport of the sheet S. 
     A fixing device F is provided above the second transfer area Q 4 . The fixing device F includes a heat roller Fh as an exemplary heating member, and a pressure roller Fp as an exemplary pressing member. An area where the heat roller Fh and the pressure roller Fp are in contact with each other is regarded as a fixing area Q 5 . 
     A pair of output rollers Rh as an exemplary medium transporting member is provided obliquely above the fixing device F. An output tray TRh as an exemplary medium output portion is provided on the right side of the pair of output rollers Rh. 
     Description of Image Forming Operation 
     Plural pages of document Gi held on the document tray TG 1  sequentially pass through a document reading position on the platen glass PG and are sequentially outputted to the document output tray TG 2 . 
     If the document Gi is automatically transported and copied through the automatic feeder U 3 , the reading optical system A is stationary at the initial position and applies light to each of the pages of the document Gi that passes through the document reading position on the platen glass PG. 
     If the operator manually copies the document Gi by sequentially placing the plural pages of document Gi onto the platen glass PG, the reading optical system A moves in the horizontal direction while applying light to each of the pages of the document Gi that is placed on the platen glass PG, thereby scanning each of the pages of the document Gi. 
     Light reflected by the page of the document Gi travels through the reading optical system A and is focused on an imaging surface of the imaging device CCD. The imaging device CCD converts the light reflected by the page of the document Gi and focused on the imaging surface thereof into electrical signals for red R, green G, and blue B. 
     The image processing unit GS converts the electrical signals for R, G, and B inputted thereto from the imaging device CCD into pieces of image information for black K, yellow Y, magenta M, and cyan C and temporarily stores the pieces of image information. The image processing unit GS outputs the temporarily stored pieces of image information as pieces of image information for latent image formation to the drawing circuit DL at a predetermined timing. 
     If the image on the page of the document Gi is a monochrome image, only the piece of image information for black K is inputted to the drawing circuit DL. 
     The drawing circuit DL includes driving circuits (not illustrated) for the respective colors of Y, M, C, and K and outputs signals based on the pieces of image information inputted thereto to the LED heads LHy, LHm, LHc, and LHk for the respective colors at a predetermined timing. 
     The surfaces of the photoconductor drums PRy, PRm, PRc, and PRk are charged by the respective charging rollers CRy, CRm, CRc, and CRk. The LED heads LHy, LHm, LHc, and LHk form electrostatic latent images on the surfaces of the photoconductor drums PRy, PRm, PRc, and PRk in the drawing areas Q 1   y , Q 1   m , Q 1   c , and Q 1   k , respectively. The developing devices Gy, Gm, Gc, and Gk develop the electrostatic latent images on the surfaces of the photoconductor drums PRy, PRm, PRc, and PRk into toner images as exemplary visible images in the development areas Q 2   y , Q 2   m , Q 2   c , and Q 2   k , respectively. As the developers contained in the developing devices Gy, Gm, Gc, and Gk are consumed, fresh developers are supplied to the developing devices Gy, Gm, Gc, and Gk from the cartridges Ky, Km, Kc, and Kk, respectively, in accordance with the amounts of consumption. 
     The toner images on the surfaces of the photoconductor drums PRy, PRm, PRc, and PRk are transported to the respective first transfer areas Q 3   y , Q 3   m , Q 3   c , and Q 3   k . The power supply circuit E applies a first transfer voltage to each of the first transfer rollers T 1   y , T 1   m , T 1   c , and T 1   k  at a predetermined timing. The first transfer voltage is of the opposite polarity to a toner contained in the developer. Hence, the first transfer voltage causes the toner images on the photoconductor drums PRy, PRm, PRc, and PRk to be sequentially transferred to the intermediate transfer belt B in the first transfer areas Q 3   y , Q 3   m , Q 3   c , and Q 3   k , respectively, such that the toner images are superposed one on top of another. If a monochrome image in the K-color is to be formed, only the toner image in the K-color is transferred from the photoconductor drum PRk for the K-color to the intermediate transfer belt B. 
     The toner images on the photoconductor drums PRy, PRm, PRc, and PRk are transferred for the first transfer to the intermediate transfer belt B as an exemplary intermediate transfer body by the respective first transfer rollers T 1   y , T 1   m , T 1   c , and T 1   k . Residual substances adhering to the surfaces of the photoconductor drums PRy, PRm, PRc, and PRk that have undergone the first transfer are removed by the respective drum cleaners CLy, CLm, CLc, and CLk. The surfaces of the photoconductor drums PRy, PRm, PRc, and PRk that have been thus cleaned are recharged by the respective charging rollers CRy, CRm, CRc, and CRk. 
     One of the sheets S contained in the sheet trays TR 1  to TR 3  is picked up by a corresponding one of the pickup rollers Rp at a predetermined timing of sheet feeding. If plural sheets S are picked up at a time by the pickup roller Rp, one of the sheets S is separated from the others by the pair of separating rollers Rs. The sheet S thus passed through the pair of separating rollers Rs is transported to the pair of registration rollers Rr by the plural pairs of transporting rollers Ra. 
     The pair of registration rollers Rr feeds the sheet S synchronously with the transport of the toner images on the intermediate transfer belt B to the second transfer area Q 4 . 
     When the sheet S thus fed from the pair of registration rollers Rr passes through the second transfer area Q 4 , a second transfer voltage is applied to the second transfer roller T 2   b , whereby the toner images on the surface of the intermediate transfer belt B are transferred to the sheet S. 
     Residual toner on the surface of the intermediate transfer belt B that has passed through the second transfer area Q 4  is removed by the belt cleaner CLb. 
     The sheet S that has passed through the second transfer area Q 4  then passes through the fixing area Q 5 , where the fixing device F applies heat and pressure to the toner images, thereby fixing the toner images. 
     The sheet S having the toner images fixed thereto is discharged to the output tray TRh by the pair of output rollers Rh. 
     Description of Developing Device 
       FIG. 3  illustrates one of the developing devices Gy, Gm, Gc, and Gk according to the first exemplary embodiment. 
       FIG. 4  is a sectional view taken along line IV-IV illustrated in  FIG. 3 . 
     The developing devices Gy, Gm, Gc, and Gk according to the first exemplary embodiment of the present invention will now be described. The developing devices Gy, Gm, Gc, and Gk for the respective colors all have the same configuration. Therefore, the developing device Gy for the Y-color will be described in detail herein, and detailed description of the other developing devices Gm, Gc, and Gk is omitted. 
     Referring to  FIGS. 3 and 4 , the developing device Gy provided facing the photoconductor drum PRy includes a developer container V that contains a two-component developer composed of a toner and a carrier. Referring to  FIG. 3 , the developer container V includes a lower container body  1 , and a container covering  2  as an exemplary covering member that is provided over the lower container body  1 . 
     Referring to  FIGS. 3 and 4 , the lower container body  1  provides a developing-roller chamber  4  as an exemplary developer-carrier housing that is provided in an upper left part thereof, and a supply chamber  6  as an exemplary first chamber that is provided below the developing-roller chamber  4 . The supply chamber  6  is continuous with the developing-roller chamber  4 . A stirring chamber  7  as an exemplary second chamber is provided on the right side of the supply chamber  6 . 
     The supply chamber  6  and the stirring chamber  7  are separated from each other by a partition wall  8  as an exemplary partition member. Referring to  FIG. 4 , the partition wall  8  has a first port  8   a  as an exemplary first connecting portion that is provided in a front part thereof. The first port  8   a  connects the supply chamber  6  and the stirring chamber  7  to each other. In the first exemplary embodiment, the first port  8   a  is provided on the front side with respect to the front end of the developing-roller chamber  4 . The partition wall  8  also has a second port  8   b  as an exemplary second connecting portion that is provided in a rear part thereof. The second port  8   b  also connects the supply chamber  6  and the stirring chamber  7  to each other. 
     The developing-roller chamber  4  houses a developing roller R 0   y  as an exemplary developer carrier. The developing roller R 0   y  is positioned such that an upper left portion of the outer surface thereof faces the photoconductor drum PRy. The developing roller R 0   y  includes a magnet roller  11  as an exemplary magnet member. Referring to  FIG. 4 , the magnet roller  11  is unrotatably supported by the developer container V. Referring to  FIGS. 3 and 4 , a developing sleeve  12  as an exemplary rotating body is provided around the magnet roller  11 . The developing sleeve  12  is rotatably supported by the developer container V. A gear G 0  as an exemplary driving-force-transmitting member is supported at the rear end of the developing sleeve  12 . The gear G 0  receives a driving force from a motor (not illustrated) as an exemplary drive source. When the developing device Gy according to the first exemplary embodiment receives the driving force transmitted from the motor, the developing sleeve  12  rotates in a direction the same as a direction in which the surface of the photoconductor drum PRy moves in the development area Q 2   y  as an exemplary facing area. 
     A trimmer  13  as an exemplary layer-thickness-regulating member is provided in a lower part of the developing-roller chamber  4 . The trimmer  13  according to the first exemplary embodiment has a round columnar shape extending in the anteroposterior direction. The trimmer  13  is unrotatably supported with a predetermined gap provided with respect to the developing sleeve  12 . 
     The magnet roller  11  has a development magnetic pole S 1  at a position corresponding to the development area Q 2   y , and a trimming magnetic pole N 2  as an exemplary layer-thickness-regulating magnetic pole at a position facing the trimmer  13 . The trimming magnetic pole N 2  is of the opposite polarity to the development magnetic pole S 1 . The magnet roller  11  also has a transport magnetic pole N 1  and a pick-off magnetic pole S 2 . The transport magnetic pole N 1  is of the opposite polarity to the development magnetic pole S 1  and is provided on the downstream side with respect to the development magnetic pole S 1  in the direction of rotation of the developing sleeve  12 . The pick-off magnetic pole S 2  is an exemplary developer-release magnetic pole and is provided on the downstream side with respect to the transport magnetic pole N 1  in the direction of rotation of the developing sleeve  12 . The pick-off magnetic pole S 2  is of the opposite polarity to the transport magnetic pole N 1 . The magnet roller  11  also has a pickup magnetic pole S 3  as an exemplary developer-attracting magnetic pole. The pickup magnetic pole S 3  is provided on the downstream side with respect to the pick-off magnetic pole S 2  and on the upstream side with respect to the trimming magnetic pole N 2  in the direction of rotation of the developing sleeve  12 . The pickup magnetic pole S 3  is of the same polarity as the pick-off magnetic pole S 2  but is of the opposite polarity to the trimming magnetic pole N 2 . 
     Referring to  FIGS. 3 and 4 , the supply chamber  6  houses a supply auger  16  as an exemplary first transporting member. The supply auger  16  includes a rotating shaft  16   a  extending in the anteroposterior direction, a helical transporting blade  16   b  provided around the rotating shaft  16   a , and a gear G 1  as an exemplary driving-force-transmitting member that is supported at the rear end of the rotating shaft  16   a.    
     The stirring chamber  7  houses a stirring auger  17  as an exemplary second transporting member. As with the supply auger  16 , the stirring auger  17  includes a rotating shaft  17   a , a transporting blade  17   b , and a gear G 2 . 
     The gear G 1  included in the supply auger  16  is in mesh an intermediate gear G 3 , which is in mesh with the gear G 0 . The gear G 2  of the stirring auger  17  is in mesh with the gear G 1  of the supply auger  16 . 
     Referring to  FIG. 4 , the stirring chamber  7  has a supply port  7   a  in a rear part thereof. The developer is supplied from the cartridge Ky to the stirring chamber  7  through the supply port  7   a.    
     Function of Developing Device 
     In each of the developing devices Gy, Gm, Gc, and Gk configured as described above, when the image forming operation is started, the motor is activated and causes a corresponding one of the developing rollers R 0   y , R 0   m , R 0   c , and R 0   k  to rotate. Accordingly, the augers  16  and  17  rotate. In the first exemplary embodiment, when the supply auger  16  rotates, the supply auger  16  transports the developer in the supply chamber  6  from the first port  8   a  toward the second port  8   b , as illustrated by arrow Ya representing the direction of transport, while stirring the developer. The developer that has reached the second port  8   b  flows through the second port  8   b  into the stirring chamber  7 . When the stirring auger  17  rotates, the stirring auger  17  transports the developer in the stirring chamber  7  from the second port  8   b  toward the first port  8   a , as illustrated by arrow Yb, while stirring the developer. The developer that has reached the first port  8   a  flows through the first port  8   a  into the supply chamber  6 . Thus, a combination of the supply chamber  6  and the stirring chamber  7  is regarded as a circulation chamber  6 + 7 . 
     The developer in the supply chamber  6  is attracted to the developing sleeve  12  with the magnetic force exerted by the pickup magnetic pole S 3 . When the developer thus attracted to the developing sleeve  12  goes past the trimmer  13 , only a predetermined amount of developer is allowed to pass through the gap between the trimmer  13  and the developing sleeve  12 . The developer that has gone past the trimmer  13  is used for the development of the latent image on the photoconductor drum PRy, PRm, PRc, or PRk in the development area Q 2   y , Q 2   m , Q 2   c , or Q 2   k . Some of the developer that has not been used for the development is further transported while being kept attracted to the surface of the developing sleeve  12  by the effect of a magnetic field produced between the development magnetic pole S 1  and the transport magnetic pole N 1 , a magnetic field produced between the transport magnetic pole N 1  and the pick-off magnetic pole S 2 , and the like. In an area between the pick-off magnetic pole S 2  and the pickup magnetic pole S 3  that are of the same polarity, the magnetic force that attracts the developer to the developing sleeve  12  is reduced. Hence, the developer on the surface of the developing sleeve  12  is released from the developing sleeve  12  in the area between the pick-off magnetic pole S 2  and the pickup magnetic pole S 3  and returns to the circulation chamber  6 + 7 . In the first exemplary embodiment, a position Q 11  where the magnetic force that attracts the developer to the developing sleeve  12  is smallest is defined above a virtual horizontal line L 0  passing through the center of rotation of the developing sleeve  12 . Hence, the developer that has been released from the developing sleeve  12  tends to slide along the outer surface of the developing sleeve  12  and then falls off the developing sleeve  12 . 
     Description of Individual Elements of Developing Device 
       FIG. 5  illustrates the positional relationship among relevant elements of the developing device Gy (or Gm, Gc, or Gk) according to the first exemplary embodiment, and corresponds to  FIG. 3 . 
     Referring to  FIG. 5 , in the developing device Gy according to the first exemplary embodiment, the rotating shaft  16   a  of the supply auger  16  is positioned in an area of projection A 1  defined by projecting the developing roller R 0   y  from the upper side in the gravitational direction. 
     As illustrated in  FIG. 5 , a tangent to the outer surface of the developing roller R 0   y  that is on a side of the developing roller R 0   y  opposite the photoconductor drum PRy and extends in the gravitational direction is denoted as a first virtual tangent L 1 . Furthermore, a tangent to the outer edge of the transporting blade  16   b  of the supply auger  16  that is on a side of the supply auger  16  opposite the photoconductor drum PRy and extends in the gravitational direction is denoted as a second virtual tangent L 2 . In the developing device Gy according to the first exemplary embodiment, the second virtual tangent L 2  is farther from the photoconductor drum PRy than the first virtual tangent L 1  in the horizontal direction. 
     As illustrated in  FIG. 5 , the horizontal-direction distance between the first virtual tangent L 1  and the second virtual tangent L 2  is denoted as a first distance K 1 . Furthermore, on the side of the developing roller R 0   y  opposite the photoconductor drum PRy, the horizontal-direction distance between the first virtual tangent L 1  and the inner surface of the developer container V is denoted as a second distance K 2 . In the developing device Gy according to the first exemplary embodiment, the first distance K 1  is shorter than the second distance K 2 . 
     Hence, in the developing device Gy according to the first exemplary embodiment, the positions of the developing roller R 0   y  and the supply auger  16  in the horizontal direction substantially coincide with each other. Accordingly, the developing device Gy according to the first exemplary embodiment has a smaller size than related-art developing devices. 
       FIG. 6  illustrates a guiding-fin member  21  according to the first exemplary embodiment. 
     Referring to  FIGS. 5 and 6 , the guiding-fin member  21  as an exemplary developer guiding member is provided on the side of the developing roller R 0   y  opposite the photoconductor drum PRy. The guiding-fin member  21  according to the first exemplary embodiment is supported by the inner surface of the developer container V. The guiding-fin member  21  includes plural fins  22  as exemplary inclined portions. The fins  22  each project upright from the inner surface of the developer container V and are arranged side by side at a predetermined pitch P 1  in the axial direction of the developing roller R 0   y . The fins  22  each incline from the upstream side thereof in the direction of rotation of the developing roller R 0   y  toward the downstream side in the direction of transport Ya by the supply auger  16 . That is, the fins  22  according to the exemplary embodiment each incline from the upper side thereof toward the downstream side of the supply chamber  6 . 
     Referring to  FIGS. 3 and 5 , the tip of each of the fins  22  in the direction of projection thereof curves in an arc shape conforming to the developing sleeve  12 , with a gap H 1  provided with respect to the developing sleeve  12 . In the first exemplary embodiment, the gap H 1  is larger than a gap H 2  between the trimmer  13  and the outer surface of the developing sleeve  12 . The fins  22  are arranged within an area corresponding to the length of the outer surface of the developing sleeve  12  in the axial direction, i.e., the anteroposterior direction. While the first exemplary embodiment concerns a case where the fins  22  are arranged within the area corresponding to the length of the outer surface of the developing sleeve  12 , the present invention is not limited to such a case. The fins  22  may be arranged in an area wider than the length of the developing sleeve  12 . 
       FIGS. 7A and 7B  illustrate the position of the guiding-fin member  21  according to the first exemplary embodiment.  FIG. 7A  illustrates the distribution of magnetic forces acting on the developing roller R 0   y  according to the first exemplary embodiment.  FIG. 7B  illustrates the distribution of the magnetic forces with respect to the position of the guiding-fin member  21 . 
       FIG. 7A  is a graph illustrating the distribution of the magnetic forces exerted by the respective magnetic poles S 1 , S 2 , S 3 , N 1 , and N 2  of the magnet roller  11  of the developing roller R 0   y  according to the first exemplary embodiment in the direction of rotation of the developing sleeve  12 . In the graph, the magnitude of the magnetic forces in a direction normal to the surface of the magnet roller  11  corresponds to the length of the graph area in the radial direction of the developing roller R 0   y . The broken line illustrated in  FIG. 7A  represents the outer circumference of the developing sleeve  12 . The farther the graph extends from the developing sleeve  12  in the radial direction, the larger the magnitude of the magnetic force becomes. Referring to  FIGS. 7A and 7B , the magnetic force of the pick-off magnetic pole S 2  becomes a maximum value T 1  at a position Q 21  and becomes a half value T 1 /2 of the maximum value T 1  at each of a position Q 22  and a position Q 23  that are on the upstream side and the downstream side, respectively, of the position Q 21  in the direction of rotation of the developing sleeve  12 . In this specification and in the appended claims, the width of an area between the position Q 22  and the position Q 23  is referred to as half-value width W. Referring to  FIG. 7B , an upper end  22   a , as an exemplary upstream end in the direction of guiding of the developer, of each of the fins  22  of the guiding-fin member  21  according to the first exemplary embodiment is positioned within the area defined by the half-value width W. That is, the upper end  22   a  faces a position on the outer surface of the developing sleeve  12  in the area defined by the half-value width W. In addition, a lower end  22   b , as an exemplary downstream end in the direction of guiding of the developer, of the fin  22  according to the first exemplary embodiment is positioned on the lower side with respect to the position Q 11  where the magnetic force is smallest. 
     Referring now to  FIGS. 5 and 6 , the fins  22  of the guiding-fin member  21  according to the first exemplary embodiment are arranged at the pitch P 1 , which is shorter than a pitch P 2  of turns in the transporting blade  16   b  of the supply auger  16 . Referring to  FIG. 6 , the fins  22  each incline with respect to a direction orthogonal to the axial direction of the developing roller R 0   y  by an angle of inclination θ 1 , which is set to, for example, 30 degrees. While the first exemplary embodiment concerns a case where the angle of inclination θ 1  is 30 degrees, the present invention is not limited to such a case. The angle of inclination θ 1  may be set to any angle, as long as the fins  22  each incline from the upstream side thereof in the direction of rotation of the developing roller R 0   y  toward the downstream side in the direction of transport Ya by the supply auger  16 . In such a configuration, the angle of inclination θ 1  may be set to 20 degrees or about 20 degrees or larger and smaller than or equal to the complementary angle of the angle of repose of the developer. If the angle of inclination θ 1  is smaller than 20 degrees, the fin  22  extends almost orthogonally to the axial direction of the developing roller R 0   y , making it difficult to guide the developer toward the downstream side in the direction of transport Ya. On the other hand, if the angle of inclination θ 1  is larger than the complementary angle of the angle of repose of the developer, the developer may accumulate on the fin  22 , increasing the probability that the transport of the developer may be hindered. 
     Hence, the angle of inclination θ 1  is more preferably 30 degrees or larger and smaller than or equal to the complementary angle of the angle of repose of the developer. If the angle of inclination θ 1  is 30 degrees or larger, the amount of developer to be guided toward the downstream side in the direction of transport Ya tends to become larger than in a case where the angle of inclination θ 1  is smaller than 30 degrees. Note that the angle of repose of the developer varies with the kind of the developer and conditions, such as the temperature and the humidity, of the environment in which the developer is used. In the first exemplary embodiment, a developer whose angle of repose is 35 degrees is employed, for example. Hence, in the first exemplary embodiment, the complementary angle of the angle of repose of the developer is 55 degrees, which is obtained by subtracting 35 degrees from the right angle. The fin  22  has a length λ 1 , which is set such that λ 1 ·(sin θ 1 ) is larger than the pitch P 2  of the turns in the transporting blade  16   b  of the supply auger  16 . That is, the length λ 1  of the fin  22  according to the first exemplary embodiment satisfies a relationship of λ 1 &gt;P 2 /(sin θ 1 ). 
     Referring to  FIG. 5 , the developing device Gy according to the first exemplary embodiment includes a guide member  31  as an exemplary second developer guiding member. The guide member  31  is provided at the upper end of the partition wall  8  and guides the developer in a direction orthogonal to the axial direction of the developing roller R 0   y . That is, the guide member  31  is provided across the developing roller R 0   y  from the photoconductor drum PRy. 
     The guide member  31  according to the first exemplary embodiment has an inclined surface  32  that inclines toward the rotating shaft  16   a  of the supply auger  16  from an upper end  31   a  thereof toward the lower side. The upper end  31   a  of the guide member  31  is positioned on the lower side with respect to a lower end  33  of the developing roller R 0   y  in the gravitational direction. 
     A lower end  31   b  of the guide member  31  in the gravitational direction is positioned on the upper side with respect to the rotating shaft  16   a  of the supply auger  16 . That is, the lower end  31   b  of the guide member  31  is at a position higher than the rotating shaft  16   a  of the supply auger  16 . In the first exemplary embodiment, the position of the lower end  31   b  is lower than an upper edge  16   c  of the transporting blade  16   b  of the supply auger  16 . 
     In the first exemplary embodiment, the lower end  31   b  of the guide member  31 , i.e., the lower end  31   b  of the inclined surface  32 , is positioned nearer to the inner surface of the developer container V in the horizontal direction than the second virtual tangent L 2 . 
     In the first exemplary embodiment, an angle of inclination θ 2  of the inclined surface  32  of the guide member  31  with respect to the horizontal direction is set to a value larger than or equal to the angle of repose of the developer and smaller than 90 degrees, more specifically, 35 degrees or larger and smaller than 90 degrees. 
     Function of Guiding-Fin Member 
     In the developing device Gy according to the first exemplary embodiment that is configured as described above, when the augers  16  and  17  rotate, the developer is transported and circulates in the circulation chamber  6 + 7 . In the supply chamber  6 , the supply auger  16  rotates, whereby the developer is transported in the direction of transport Ya. Some of the developer in the supply chamber  6  is attracted to the developing sleeve  12  with the magnetic force exerted by the pickup magnetic pole S 3 . The rest of the developer in the supply chamber  6  is further transported toward the downstream side in the direction of transport Ya. The developer attracted to the developing sleeve  12  is carried by the developing sleeve  12  that rotates. With the rotation of the developing sleeve  12 , the developer passes through the development area Q 2   y , whereby the latent image on the photoconductor drum PRy is developed, and the toner contained in the developer is consumed. The resulting developer whose toner has been consumed is further carried with the rotation of the developing sleeve  12  toward the position Q 11  where the magnetic force acting on the developing roller R 0   y  is smallest. Since the magnetic force that attracts the developer to the developing sleeve  12  is reduced near the position Q 11 , the developer whose toner has been consumed is released from the developing sleeve  12 . 
     The developer thus released from the developing sleeve  12  jumps, with a force of inertia, toward the guiding-fin member  21  provided on the right side of the position Q 11  and above the supply chamber  6 . The fins  22  of the guiding-fin member  21  each incline such that the lower end  22   b  thereof is positioned on the downstream side with respect to the upper end  22   a  in the direction of transport Ya. Hence, the developer that has entered the guiding-fin member  21  is guided along the fins  22  toward the downstream side in the direction of transport Ya while moving downward with the gravitational force or the like. Thus, the developer that has entered the guiding-fin member  21  passes through the guiding-fin member  21  while moving toward the downstream side in the direction of transport Ya with respect to the position of release. That is, in the first exemplary embodiment, the developer returns to the supply chamber  6  after being transported toward the downstream side in the direction of transport Ya. In the first exemplary embodiment, the guide member  31  is provided below the guiding-fin member  21 . The guide member  31  receives the developer dropping from the guiding-fin member  21  and guides the dropped developer into the supply chamber  6 . The developer that has returned to the supply chamber  6  is mixed with a mass of developer transported from the upstream side and the like, and the mixture is further transported in the direction of transport Ya. 
     The upper end  22   a  of each of the fins  22  of the guiding-fin member  21  according to the first exemplary embodiment is positioned in the area defined by the half-value width W. Hence, even if the position of the pick-off magnetic pole S 2  is displaced because of any dimensional errors, the guiding-fin member  21  is positioned on the lateral side of the position Q 11 . Therefore, in the first exemplary embodiment, the developer that has been released from the developing sleeve  12  tends to enter the guiding-fin member  21 , regardless of the dimensional errors of the associated elements. In the first exemplary embodiment, the gap H 1  is provided between the guiding-fin member  21  and the developing sleeve  12 . Hence, the wear of the developing sleeve  12  is suppressed more than in a case where the guiding-fin member  21  is in contact with the developing sleeve  12 . Particularly, in the first exemplary embodiment, the gap H 1  is larger than the gap H 2 . Hence, the guiding-fin member  21  according to the first exemplary embodiment is less likely to come into contact with the developer that is carried by the developing sleeve  12 . Consequently, in the first exemplary embodiment, the scattering of the developer, i.e., the generation of developer cloud, is suppressed. 
     The developer that has been attracted to the developing sleeve  12  and whose toner has been consumed in the development area Q 2   y  is released from the developing sleeve  12  and returns to the supply chamber  6 . The developer that has returned to the supply chamber  6  is transported toward the downstream side in the direction of transport Ya by the supply auger  16 . The developer that has been transported to the downstream side in the direction of transport Ya is attracted to the developing sleeve  12  again. Then, after the toner contained in the developer is consumed in the development area Q 2   y , the developer returns to the supply chamber  6 . Thus, while the developer is transported from the upstream side to the downstream side of the supply chamber  6 , the above cycle is repeated in which the developer is attracted to the developing sleeve  12 , the toner of the developer is consumed in the development area Q 2   y , and the developer returns to the supply chamber  6 . Hence, the consumption of toner from the developer in the supply chamber  6  increases toward the downstream side in the direction of transport Ya, resulting in a difference between the toner concentration of the developer on the upstream side and the toner concentration of the developer on the downstream side. If the difference in the toner concentration of the developer becomes large, the density of the developed image may become nonuniform, deteriorating the quality of the resulting image. 
       FIGS. 8A and 8B  illustrate the movement of the developer.  FIG. 8A  illustrates a case where the guiding-fin member  21  is provided.  FIG. 8B  illustrates a comparative case where the guiding-fin member  21  is not provided. 
     In the comparative case illustrated in  FIG. 8B  where the guiding-fin member  21  is not provided, a position Q 031  of the supply chamber  6  from which the developer is attracted to the developing sleeve  12  and the position Q 032  of the supply chamber  6  to which the developer that has been released from the developing sleeve  12  returns are substantially the same in the direction of transport Ya. In contrast, according to the first exemplary embodiment illustrated in  FIG. 8A , the developer that has been released from the developing sleeve  12  is guided by the guiding-fin member  21  and returns to a position Q 32  of the supply chamber  6  that is on the downstream side in the direction of transport Ya with respect to a position Q 31  of the supply chamber  6  from which the developer has been attracted to the developing sleeve  12 . Thus, according to the first exemplary embodiment, the developer is transported toward the downstream side in the direction of transport Ya not only by the supply auger  16  but also by the guiding-fin member  21 . Therefore, in the first exemplary embodiment, the developer tends to be transported quickly from the upstream side to the downstream side of the supply chamber  6 , and the number of times for which the developer is attracted to the developing sleeve  12  tends to be small, correspondingly. Consequently, the consumption of toner from the developer tends to be small even on the downstream side of the supply chamber  6  in the direction of transport Ya. Accordingly, the difference between the toner concentration of the developer on the upstream side and the toner concentration of the developer on the downstream side, i.e., the difference in the toner concentration of the developer in the direction of transport Ya, tends to be small. Thus, according to the first exemplary embodiment, the difference in the toner concentration of the developer is made smaller than in a case where the developer that has passed through the development area is not moved in the direction of transport Ya. 
     The guiding-fin member  21  according to the first exemplary embodiment includes the fins  22  each inclining at the angle of inclination θ 1  and that are arranged side by side at the pitch P 1  in the direction of transport Ya. Hence, the distribution of the amount of developer guided by the guiding-fin member  21  according to the first exemplary embodiment is more even than in related-art developing devices in which the angle of inclination of guiding members varies with the positions of the guiding members. Moreover, the distribution of the number of fins  22  according to the first exemplary embodiment in the direction of transport Ya is more even than in the related-art developing devices. Therefore, in the first exemplary embodiment, the developer that has been released from the developing sleeve  12  is more likely to be transported toward the downstream side in the direction of transport Ya, regardless of the position in the axial direction of the developing roller R 0   y , before returning to the supply chamber  6 . Thus, the probability that the developer whose toner has been consumed may return concentratedly to a certain area is reduced in the first exemplary embodiment. Accordingly, in the first exemplary embodiment, the probability that the toner concentration of the developer on the downstream side may be reduced so much as to make a noticeable variation in the toner concentration is smaller than in the related-art developing devices. 
     Furthermore, in the first exemplary embodiment, the angle of inclination θ 1  is set to 30 degrees, which is smaller than or equal to the complementary angle of the angle of repose of the developer. Hence, in the first exemplary embodiment, the developer that is guided in the direction of transport Ya is less likely to accumulate on the fins  22  and to clog between adjacent ones of the fins  22 . 
       FIGS. 9A and 9B  illustrate the pitch P 1  of the fins  22  of the guiding-fin member  21  and the amount of developer.  FIG. 9A  illustrates the first exemplary embodiment.  FIG. 9B  illustrates a comparative case where the pitch P 1  of the fins  22  of the guiding-fin member  21  is larger than the pitch P 2  of the turns in the transporting blade  16   b  of the supply auger  16 . 
     In the first exemplary embodiment, the pitch P 1  of the fins  22  is smaller than the pitch P 2  of the turns in the transporting blade  16   b  of the supply auger  16 . 
     An amount of developer that corresponds to the size of the pitch P 1  drops into the gap between adjacent ones of the fins  22  of the guiding-fin member  21 . In the first exemplary embodiment, the lower end  22   b  of each of the fins  22  is positioned on the downstream side in the direction of transport Ya with respect to an area B 1  into which the developer that has entered the guiding-fin member  21  drops. Hence, the developer that has entered the gap between adjacent ones of the fins  22  drops while being guided in the direction of transport Ya along one of the adjacent fins  22  and returns to a position of the supply chamber  6  that faces the lower end  22   b  of the fin  22 . 
     Therefore, as the pitch P 1  of the fins  22  becomes larger, a larger amount of developer enters the gap between adjacent ones of the fins  22  and the amount of developer guided by each fin  22  tends to increase. Moreover, as the pitch P 1  becomes larger, positions of the supply chamber  6  to each of which the developer returns tend to become farther apart from one another. Hence, as the pitch P 1  becomes larger, a larger amount of developer whose toner has been consumed tends to return to each of fewer positions of the supply chamber  6 . Accordingly, it tends to take a long time for the toner concentration of the developer to be evened out, and the toner concentration of the developer is more likely to vary in the direction of transport Ya. 
       FIGS. 10A to 10D  illustrate the pitch P 1  of the fins  22  and the way the developer is returned to the supply chamber  6 .  FIG. 10A  illustrates the first exemplary embodiment.  FIG. 10B  illustrates a state where the supply auger  16  has transported the developer by moving from the position illustrated in  FIG. 10A .  FIG. 10C  illustrates an exemplary case where the pitch P 1  of the fins  22  is larger than the pitch P 2  of the turns in the transporting blade  16   b  of the supply auger  16 .  FIG. 10D  illustrates a state where the supply auger  16  has transported the developer by moving from the position illustrated in  FIG. 10C . 
     Particularly, in a case where the pitch P 1  of the fins  22  is larger than the pitch P 2  of the turns in the transporting blade  16   b  of the supply auger  16  as illustrated in  FIGS. 10C and 10D , the developer may return to only one of two adjacent spaces  16   b   1  and  16   b   2  each defined by one turn of the transporting blade  16   b , without returning to the other. The adjacent spaces  16   b   1  and  16   b   2  are separated from each other by the transporting blade  16   b . When the supply auger  16  rotates, the spaces  16   b   1  and  16   b   2  move while being kept separated from each other. Therefore, the developer in the space  16   b   1  and the developer in the space  16   b   2  are less likely to be mixed together. Hence, if the developer returns to only one of the two adjacent spaces  16   b   1  and  16   b   2 , the height of the mass of developer or the toner concentration of the developer may become different between that in the space  16   b   1  and that in the space  16   b   2 . Consequently, defective attraction of the developer to the developing sleeve  12  or defective development on the photoconductor drum PRy that deteriorates the quality of the resulting image may occur depending on the length, i.e., the pitch P 2 , of the adjacent spaces  16   b   1  and  16   b   2 . 
     In contrast, according to the first exemplary embodiment illustrated in  FIGS. 9A, 10A, and 10B , the pitch P 1  of the fins  22  is smaller than the pitch P 2  of the turns in the transporting blade  16   b  of the supply auger  16 . Since the pitch P 1  is not too large, the developer tends to return to more positions of the supply chamber  6  by a smaller amount for each of the positions. That is, the developer whose toner has been consumed is distributed more evenly before returning to the supply chamber  6 . Accordingly, the variation in the toner concentration of the developer in the direction of transport Ya is reduced. 
     Particularly, in the first exemplary embodiment in which the pitch P 1  is smaller than the pitch P 2 , the developer is more likely to be distributed to each of the spaces  16   b   1  and  16   b   2  each defined by one turn of the transporting blade  16   b  of the supply auger  16 . Therefore, in the first exemplary embodiment, the height of the mass of developer or the toner concentration of the developer is less likely to vary, and image quality is less likely to be deteriorated than in the case where the pitch P 1  is larger than the pitch P 2 . 
     In the first exemplary embodiment, referring to  FIG. 3 , the developer that has passed through the guiding-fin member  21  tends to return to a side of the supply chamber  6  that is farther from the developing roller R 0   y  than the rotating shaft  16   a  of the supply auger  16  in the horizontal direction. According to the first exemplary embodiment, in a sectional view taken orthogonally to the axial direction of the rotating shaft  16   a , the supply auger  16  rotates in such a direction that the developer is transported sequentially from a position on the side farther from the developing roller R 0   y , to a position facing the bottom of the supply chamber  6 , to a position on a side nearer to the developing roller R 0   y , and to a position where the developer is attracted to the developing sleeve  12 . Hence, the developer just returned to the supply chamber  6  with its toner consumed is less likely to be supplied to the developing sleeve  12  before being mixed with the mass of developer in the supply chamber  6 . 
     EXAMPLES 
     Experiments for demonstrating the effects produced by the first exemplary embodiment are conducted as follows. 
     The following experiments are conducted on several models of a printer called DocuCentre SC2020 of Fuji Xerox Co., Ltd. that have been modified for the experiments. 
     Experimental Example 1-1 
     In Experimental Example 1-1, modified developing devices Gy are used. Specifically, two developing devices Gy are prepared, with the amount of developer that is present around the augers  16  and  17  and the developing roller R 0   y , i.e., the amount of developer sump, being set to 135 g and 90 g, respectively. Each of the developing devices Gy includes the guiding-fin member  21 . The length λ 1  of each of the fins  22  of the guiding-fin member  21  is 25 mm. The pitch P 1  of the fins  22  is 10 mm. The angle of inclination θ 1  of each fin  22  is 40 degrees. Then, the difference in toner concentration ΔTC (%) in the supply chamber  6  is measured for each of the two developing devices Gy containing different amounts of developer. Specifically, an image with a density of 100%, i.e., a solid image, intended for size A3 is formed and is printed on twenty sheets S successively. Then, after the printing on the twenty sheets S is complete, the difference in toner concentration ΔTC (%) in each of the developing devices Gy is measured. More specifically, the toner concentration is measured at each of two predetermined positions of the supply chamber  6  that are space apart from each other in the direction of transport Ya, and the difference between the two measured values is taken as the difference in toner concentration ΔTC (%). In Experimental Example 1-1, the process speed is set to 126 mm/s. That is, the speed at which each sheet S passes through the second transfer area Q 4  is set to 126 mm/s. Furthermore, the speed of rotation of the developing roller R 0   y , i.e., the speed of rotation of the developing sleeve  12 , is set to 214.2 mm/s. 
     Experimental Example 1-2 
     In Experimental Example 1-2, the process speed is set to 63 mm/s. That is, the speed at which each sheet S passes through the second transfer area Q 4  is set to 63 mm/s, and the speed of rotation of the developing sleeve  12  is set to 107.1 mm/s. The other conditions and the measurement method are the same as those employed in Experimental Example 1-1. 
     Comparative Example 1-1 
     In Comparative Example 1-1, the angle of inclination θ 1  of each fin  22  is set to 0 degrees for each of three developing devices Gy that contain different amounts of developer of 135 g, 100 g, and 85 g, respectively. The other conditions and the measurement method are the same as those employed in Experimental Example 1-1. 
     Comparative Example 1-2 
     In Comparative Example 1-2, the angle of inclination θ 1  of each fin  22  is set to 0 degrees for each of three developing devices Gy that contain different amounts of developer of 135 g, 100 g, and 85 g, respectively. The other conditions and the measurement method are the same as those employed in Experimental Example 1-2. 
     Results of Experiments in Experimental Examples 1-1 and 1-2 and Comparative Examples 1-1 and 1-2 
       FIGS. 11A and 11B  are graphs illustrating the results of the experiments conducted in Experimental Examples 1-1 and 1-2 and Comparative Examples 1-1 and 1-2.  FIG. 11A  illustrates the difference in toner concentration with respect to the amount of developer in Experimental Example 1-1 and Comparative Example 1-1 in each of which the process speed is 126 mm/s.  FIG. 11B  illustrates the difference in toner concentration with respect to the amount of developer in Experimental Example 1-2 and Comparative Example 1-2 in each of which the process speed is 63 mm/s. 
       FIGS. 12A and 12B  are graphs illustrating the results of the experiments conducted in Comparative Examples 1-1 and 1-2 and Experimental Examples 1-1 and 1-2.  FIG. 12A  illustrates the difference in toner concentration with respect to the amount of developer in Comparative Examples 1-1 and 1-2 in each of which the angle of inclination θ 1  is 0 degrees.  FIG. 12B  illustrates the difference in toner concentration with respect to the amount of developer in Experimental Examples 1-1 and 1-2 in each of which the angle of inclination θ 1  is 40 degrees. 
     In the graphs illustrated in  FIGS. 11A to 12B , the horizontal axis represents the amount of developer (g), and the vertical axis represents the difference in toner concentration ΔTC (%). The graphs illustrated in  FIGS. 11A to 12B  are plotted by obtaining measured values of the difference in toner concentration ΔTC (%) for the different amounts of developer in the respective developing devices Gy in each of Experimental Examples 1-1 and 1-2 and Comparative Examples 1-1 and 1-2. Thus, the relationship between the amount of developer and the difference in toner concentration is illustrated by an approximate line. 
     In general, in each of the developing devices Gy, Gm, Gc, and Gk, as the amount of developer contained therein becomes larger, the influence of toner consumption tends to become smaller and the difference in toner concentration ΔTC (%) therefore tends to become smaller. This tendency is understood from the fact that the gradients of the approximate lines obtained in Experimental Examples 1-1 and 1-2 and Comparative Examples 1-1 and 1-2 graphed in  FIGS. 11A to 12B  are all negative. That is, there is less problem with the difference in toner concentration ΔTC (%) if the amount of developer is large. Hence, the difference in toner concentration ΔTC (%) in the case where the amount of developer is small is desired to be close to the difference in toner concentration ΔTC (%) in the case where the amount of developer is large, and the change in the difference in toner concentration ΔTC (%) with respect to the change in the amount of developer is desired to be small. Referring to  FIGS. 11A to 12B , the gradients of the approximate lines obtained in Experimental Examples 1-1 and 1-2 in which the angle of inclination θ 1  of the fin  22  is 40 degrees are gentler than those obtained in Comparative Examples 1-1 and 1-2 in which the angle of inclination θ 1  of the fin  22  is 0 degrees. That is, the change in the difference in toner concentration ΔTC (%) with respect to the change in the amount of developer is smaller in Experimental Examples 1-1 and 1-2 than in Comparative Examples 1-1 and 1-2. Accordingly, if the developing device Gy, Gm, Gc, or Gk has a small size and a correspondingly small capacity, the increase in the difference in toner concentration ΔTC (%) is suppressed by providing the guiding-fin member  21  including the inclined fins  22 . 
     Furthermore,  FIGS. 12A and 12B  show that, in the case where the guiding-fin member  21  including the inclined fins  22  is provided, the difference in toner concentration ΔTC (%) tends to become smaller as the process speed is increased. This is because of the following reason. When the process speed is increased, the speed of rotation of the developing sleeve  12  increases. Accordingly, the centrifugal force that acts on the developer on the developing sleeve  12  increases, and the speed at which the developer is released from the developing sleeve  12  tends to increase. Hence, when the developer is released from the developing sleeve  12 , the developer easily reaches the guiding-fin member  21  and is easily guided along the guiding-fin member  21 . Therefore, in the case where the process speed is high, the proportion of developer that returns to the supply chamber  6  after being guided along the guiding-fin member  21  is much larger than the proportion of developer that returns to the supply chamber  6  by vertically dropping downward with the gravitational force. Consequently, the difference in toner concentration ΔTC (%) of the developer is further reduced. 
     Experimental Example 2-1 
     In Experimental Example 2-1, a developing device Gy in which the amount of developer that is present around the augers  16  and  17  and the developing roller R 0   y  is set to 180 g is used. The developing device Gy includes the guiding-fin member  21 . The angle of inclination θ 1  of each of the fins  22  is set to 50 degrees. In Experimental Example 2-1, the influence of the inclined fins  22  upon the length of transport of the developer in the direction of transport Ya is measured. Specifically, a solid image intended for size A3 is formed, whereby the developing device Gy is activated. In this image forming operation, an image of the developing sleeve  12  is taken with a video camera as an exemplary observation member from the side of the photoconductor drum PRy. In Experimental Example 2-1, another developer having a color different from the Y-color is added to a predetermined position of the developing sleeve  12 . Then, after a predetermined period of time, any positions where the colors of the two developers are mixed on the developing sleeve  12  are observed on the image taken with the video camera. In other words, the length of transport of the developer in the axial direction of the developing roller R 0   y  is measured on the basis of the position where the other developer has been added, the time elapsed, and any positions where the mixture of the two developers has appeared on the developing sleeve  12 . In Experimental Example 2-1, the process speed is set to 126 mm/s. That is, the speed at which the sheet S passes through the second transfer area Q 4  is set to 126 mm/s, and the speed of rotation of the developing sleeve  12  is set to 214.2 mm/s. The other conditions and the measurement method are the same as those employed in Experimental Example 1-1. 
     Experimental Example 2-2 
     In Experimental Example 2-2, the process speed is set to 63 mm/s. That is, the speed at which the sheet S passes through the second transfer area Q 4  is set to 63 mm/s, and the speed of rotation of the developing sleeve  12  is set to 107.1 mm/s. The other conditions and the measurement method are the same as those employed in Experimental Example 2-1. 
     Comparative Example 2-1 
     In Comparative Example 2-1, the angle of inclination θ 1  of each of the fins  22  included in the guiding-fin member  21  is set to 0 degrees. The other conditions and the measurement method are the same as those employed in Experimental Example 2-1. 
     Comparative Example 2-2 
     In Comparative Example 2-2, the angle of inclination θ 1  of the fin  22  is set to 0 degrees. The other conditions and the measurement method are the same as those employed in Experimental Example 2-2. 
     Results of Experiments in Experimental Examples 2-1 and 2-2 and Comparative Examples 2-1 and 2-2 
       FIG. 13  is a graph illustrating the results of the experiments conducted in Experimental Examples 2-1 and 2-2 and Comparative Examples 2-1 and 2-2. 
     Referring to  FIG. 13 , the length of transport of the developer in the direction of transport Ya is about 10 to 11 mm in each of Comparative Examples 2-1 and 2-2, in which the angle of inclination θ 1  is 0 degrees. In contrast, the length of transport of the developer in the direction of transport Ya is about 12 mm in Experimental Example 2-2, in which the angle of inclination θ 1  is 50 degrees and the process speed is 63 mm/s. Furthermore, the length of transport of the developer in the direction of transport Ya is about 16 mm in Experimental Example 2-1, in which the angle of inclination θ 1  is 50 degrees and the process speed is 126 mm/s. That is, it is found that the developer moves in the direction of transport Ya by a larger length in the case where the angle of inclination θ 1  is large at 50 degrees than in the case where the angle of inclination θ 1  is 0 degrees. This is interpreted as that the developer is more likely to be guided in the direction of transport Ya in the case where the fins  22  of the guiding-fin member  21  incline. 
     In each of Experimental Examples 2-1 and 2-2, the angle of inclination θ 1  is 50 degrees. In Experimental Example 2-2 in which the process speed is 63 mm/s, the length of transport of the developer is about 12 mm. On the other hand, in Experimental Example 2-1 in which the process speed is 126 mm/s, the length of transport of the developer is about 16 mm, which is larger than 12 mm. This means that, if the angle of inclination θ 1  is the same, the length of transport of the developer in the direction of transport Ya becomes larger by increasing the process speed. 
     According to the results of the experiments conducted in Experimental Examples 1, as the angle of inclination θ 1  becomes larger and as the process speed becomes higher, the difference in toner concentration ΔTC (%) in the direction of transport Ya tends to become smaller. That is, the results of the experiments in Experimental Examples 1 and 2 show a tendency that the larger the amount of developer guided in the direction of transport Ya, the smaller the difference in toner concentration ΔTC (%) of the developer in the direction of transport Ya. 
     In Experimental Examples 2-1 and 2-2 and in Comparative Examples 2-1 and 2-2, the length of transport of the developer on the developing sleeve  12  is observed. Hence, the sum of the length by which the guiding-fin member  21  has guided the developer and the length by which the supply auger  16  has transported the developer is measured. Therefore, considering the result of the measurement in Comparative Example 2-2, the length by which the supply auger  16  transports the developer in Experimental Example 2-2 in which the process speed is 63 mm/s is estimated to be about 10 mm. Furthermore, considering the result of the measurement in Comparative Example 2-1, the length by which the supply auger  16  transports the developer in Experimental Example 2-1 in which the process speed is 126 mm/s is estimated to be about 11 mm. 
     Second Exemplary Embodiment 
     A second exemplary embodiment of the present invention will now be described. Elements corresponding to those described in the first exemplary embodiment are denoted by the corresponding ones of the reference numerals used in the first exemplary embodiment, and detailed description thereof is omitted. 
     The second exemplary embodiment is basically the same as the first exemplary embodiment, except the following points. 
       FIGS. 14A and 14B  illustrate a guiding-fin member  21 ′ included in a developing device Gy′ according to the second exemplary embodiment.  FIG. 14A  illustrates the position of the guiding-fin member  21 ′.  FIG. 14B  is a bottom view of the guiding-fin member  21 ′. 
     Referring to  FIGS. 14A and 14B , the guiding-fin member  21 ′ as an exemplary developer guiding member according to the second exemplary embodiment is provided above the developing roller R 0   y , not on the lateral side of the developing roller R 0   y . Fins  22 ′ included in the guiding-fin member  21 ′ according to the second exemplary embodiment each have an arc shape conforming to the developing sleeve  12 , with a gap H 1 ′ provided with respect to the outer surface of the developing sleeve  12 . A left end  22   a ′, as an exemplary upstream end in the direction of guiding of the developer, of each fin  22 ′ is positioned in correspondence with the transport magnetic pole N 1 . In the second exemplary embodiment, the left end  22   a ′ is positioned, in the direction of rotation of the developing sleeve  12 , on the downstream side with respect to an opening  2   a  of the developer container V and near and on the upstream side with respect to the transport magnetic pole N 1 . A right end  22   b ′, as an exemplary downstream end in the direction of guiding of the developer, of the fin  22 ′ faces the pick-off magnetic pole S 2 . 
     The gap H 1 ′ (mm) according to the second exemplary embodiment is set to a value smaller than the thickness of a developer layer to be formed on the developing sleeve  12 . Specifically, the gap H 1 ′ is set to a value smaller than the gap H 2  between the trimmer  13  and the outer surface of the developing sleeve  12 . Particularly, in the second exemplary embodiment, letting the tight bulk density of the developer be P (g/mm 3 ) and the preset amount of developer per unit area that is to be carried by the developing sleeve  12  be M (g/mm 2 ), the gap H 1 ′ is set to a value that satisfies the relationship of M/P&gt;H 1 ′. The term “tight bulk density” refers to the density of powder (the developer) that has been charged tightly into a container while being tapped. For reference, the density of powder that has been charged loosely into a container without being tapped is referred to as “loose bulk density.” 
     Function of Guiding-Fin Member According to Second Exemplary Embodiment 
     In the developing device Gy′ according to the second exemplary embodiment that is configured as described above, as the developing sleeve  12  rotates, the developer that has been attracted to the developing sleeve  12  from the supply chamber  6  is transported toward the downstream side in the direction of rotation of the developing sleeve  12 . Specifically, the developer attracted to the developing sleeve  12  passes through the development area Q 2   y  and is transported to the transport magnetic pole N 1  and then to the pick-off magnetic pole S 2 . The guiding-fin member  21 ′ of the developing device Gy′ according to the second exemplary embodiment extends from a position on the upstream side with respect to the transport magnetic pole N 1  to a position facing the pick-off magnetic pole S 2 . Hence, in the second exemplary embodiment, the developer that has passed through the development area Q 2   y  and whose toner has been consumed enters the guiding-fin member  21 ′ from the left ends  22   a ′ of the fins  22 ′. Subsequently, the developer that has passed through the guiding-fin member  21 ′ is released from the developing sleeve  12  at the position Q 11  and drops into the supply chamber  6 . In this process, the developer that is dropping may be guided by the guide member  31 , occasionally. 
     The guiding-fin member  21 ′ according to the second exemplary embodiment includes plural fins  22 ′ each incline from the upstream side thereof in the direction of rotation of the developing sleeve  12  toward the downstream side in the direction of transport Ya, i.e., the axial direction of the developing roller R 0   y . Therefore, the developer that has entered the guiding-fin member  21 ′ comes into contact with the fins  22 ′ while moving toward the downstream side in the direction of rotation of the developing sleeve  12 . Then, the developer that tends to move toward the downstream side in the direction of rotation of the developing sleeve  12  is guided toward the downstream side in the direction of transport Ya along the fins  22 ′. Hence, the developer that has passed through the guiding-fin member  21 ′ tends to exit the guiding-fin member  21 ′ from a position on the downstream side in the direction of transport Ya with respect to the position of entry into the guiding-fin member  21 ′. Thus, in the second exemplary embodiment, the developer tends to be released from the developing sleeve  12 , before returning to the supply chamber  6 , at a position on the downstream side in the direction of transport Ya with respect to the position of attraction to the developing sleeve  12 . Therefore, in the second exemplary embodiment, the developer whose toner has been consumed easily move toward the downstream side in the direction of transport Ya before returning to the supply chamber  6 , as in the first exemplary embodiment. Consequently, in the developing device Gy′ according to the second exemplary embodiment that has a small size, the difference in toner concentration ΔTC (%) of the developer in the axial direction of the developing roller R 0   y  tends to be suppressed, as in the first exemplary embodiment. 
     The guiding-fin member  21 ′ according to the second exemplary embodiment is configured to guide the developer on the developing sleeve  12  in the direction of transport Ya. In the first exemplary embodiment, the guiding-fin member  21  is provided on the lateral side of the developing roller R 0   y , and the developer that has been released from the developing sleeve  12  is introduced into and is guided by the guiding-fin member  21 . In general, if the process speed is changed and the speed of rotation of the developing sleeve  12  is therefore changed, the centrifugal force that acts on the developer changes and the position and the speed of release of the developer from the developing sleeve  12  also change, accordingly. Consequently, the position from which the developer released from the developing sleeve  12  enters the guiding-fin member  21  and the amount of developer that enters the guiding-fin member  21  change. That is, in the first exemplary embodiment, the length by which the developer is guided in the direction of transport Ya and the amount of developer that is guided by the guiding-fin member  21  may change with the process speed. On the other hand, the guiding-fin member  21 ′ according to the second exemplary embodiment is held above the developing sleeve  12  and comes into contact with and guides the developer that is moving toward the downstream side in the direction of rotation of the developing sleeve  12 . Hence, even if the process speed is changed, the amount of developer that enters the guiding-fin member  21 ′ is less likely to change. Moreover, the axial-direction position of entry of the developer into the guiding-fin member  21 ′ and the length of guiding of the developer in the direction of transport Ya are less likely to change. Hence, in the second exemplary embodiment, the length of guiding of the developer in the direction of transport Ya and the amount of developer to be guided are more stabilized for a wider range of process speed than in the case where the developer is guided after being released from the developing sleeve  12 . 
     In the second exemplary embodiment, the gap H 1 ′ between the guiding-fin member  21 ′ and the developing sleeve  12  is set on the basis of the tight bulk density P of the developer. The guiding-fin member  21 ′ according to the second exemplary embodiment needs to come into contact with the developer on the developing sleeve  12 . Hence, in the second exemplary embodiment, the gap H 1 ′ between the guiding-fin member  21 ′ and the developing sleeve  12  is set to a value smaller than the thickness of the developer layer to be formed on the developing sleeve  12 . Particularly, the guiding-fin member  21 ′ according to the second exemplary embodiment is positioned such that the gap H 1 ′ satisfies the relationship of M/P&gt;H 1 ′, where P denotes the tight bulk density of the developer, and M denotes the preset amount of developer per unit area of the developing sleeve  12 . That is, the gap H 1 ′ is set to a value smaller than M/P, which is the thickness of the developer layer based on a tight bulk density. In general, a centrifugal force and so forth act on the developing sleeve  12 , and the developer that is present on the developing sleeve  12  has a larger thickness than the thickness based on the tight bulk density. Therefore, if the gap H 1 ′ satisfies the relationship of M/P&gt;H 1 ′, the guiding-fin member  21 ′ assuredly comes into contact with the developer. Thus, in the second exemplary embodiment, the guiding-fin member  21 ′ assuredly comes into contact with the developer on the developing sleeve  12 , and the developer is easily guided by the guiding-fin member  21 ′. 
     Third Exemplary Embodiment 
     A third exemplary embodiment of the present invention will now be described. Elements corresponding to those described in the first exemplary embodiment are denoted by the corresponding ones of the reference numerals used in the first exemplary embodiment, and detailed description thereof is omitted. 
     The third exemplary embodiment is basically the same as the first exemplary embodiment, except the following points. 
       FIG. 15  illustrates a developing device Gy according to the third exemplary embodiment and corresponds to  FIG. 3  illustrating the first exemplary embodiment. 
       FIG. 16  is a perspective view of relevant parts included in a guiding-fin member  21 ″ according to the third exemplary embodiment. 
     Referring to  FIGS. 15 and 16 , the guiding-fin member  21 ″ according to the third exemplary embodiment is provided with a guiding wall  42  as an exemplary stopping member that extends over downstream ends  41 , in the direction of rotation of the developing roller R 0   y , of the respective fins  22  thereof. The guiding wall  42  according to the third exemplary embodiment has a plate-like shape that is flat in the vertical direction and in the anteroposterior direction. 
     A lower end  42   a  of the guiding wall  42  is positioned at a distance longer than the radius of the rotating shaft  16   a  from the center of rotation of the supply auger  16  in the horizontal direction. 
     Referring to  FIG. 15 , a lower end portion of each of the fins  22  of the guiding-fin member  21 ″ according to the third exemplary embodiment includes a left end  46  and a lowest end  47 . The left end  46  is nearer to the developing roller R 0   y  and is at a higher position than the lowest end  47 . 
     As illustrated in  FIG. 15  in a sectional view taken perpendicularly to the axial direction of the supply auger  16 , the lowest end  47  of each of the fins  22  of the guiding-fin member  21 ″ according to the third exemplary embodiment is positioned on the right side, on which the transporting blade  16   b  of the supply auger  16  moves from the upper side toward the lower side in the gravitational direction. 
     The lowest end  47  of each of the fins  22  of the guiding-fin member  21 ″ according to the third exemplary embodiment is positioned above a top surface  48  of the mass of developer that is formed when the supply auger  16  is rotating. 
     Function of Guiding-Fin Member According to Third Exemplary Embodiment 
     In the developing device Gy according to the third exemplary embodiment that is configured as described above, the developer that has been released from the developing roller R 0   y  is guided by the guiding-fin member  21 ″ toward the downstream side in the direction of transport Ya by the supply auger  16 . In this process, as the speed of rotation of the developing roller R 0   y  increases, the centrifugal force that acts on the developer increases. Accordingly, when the developing sleeve  12  rotates at a high speed, the developer is easily released from the developing sleeve  12 . 
     If the sheet S is a cardboard, the sheet S is transported at a low speed so that, for example, the occurrence of defective fixing is suppressed. Correspondingly, the developing sleeve  12  rotates at a low speed. In such a case, the centrifugal force that acts on the developer is reduced. Consequently, the developer is less likely to be released from the developing sleeve  12 , and the position of release of the developer is shifted toward the pickup magnetic pole S 3 . 
     That is, if the guiding wall  42  is not provided, the position from which the developer that has been released from the developing sleeve  12  drops off the developing sleeve  12  is shifted toward the position from which the developer is picked up. Such a situation tends to increase the amount of developer that is reattracted to the supply auger  16  after dropping off the developing sleeve  12  without being transported by a satisfactory length in the axial direction of the supply auger  16 . Accordingly, the average length of transport of the developer tends to be insufficient. 
     In the third exemplary embodiment, however, since the guiding wall  42  is provided, the developer that has been released from a position nearer to the pickup magnetic pole S 3  is also guided downward by the guiding wall  42 . Therefore, the position from which the developer drops is satisfactorily far from the position of pickup of the developer. Accordingly, the developer is more easily transported in the axial direction of the supply auger  16  before being reattracted to the developing sleeve  12 . Thus, in the third exemplary embodiment, the difference between the toner concentration of the developer on the upstream side and the toner concentration of the developer on the downstream side in the direction of transport Ya is smaller than in the first exemplary embodiment. 
     Particularly, in the third exemplary embodiment, the lower end  42   a  of the guiding wall  42  is positioned at a distance longer than the radius of the rotating shaft  16   a  from the center of rotation of the supply auger  16  in the horizontal direction. That is, the developer that has been guided by the guiding wall  42  drops onto the right side of the supply auger  16 . The developer that has dropped onto the right side of the supply auger  16  moves along with the rotation of the supply auger  16  sequentially from the right side, to the lower side, to the left side, and to the upper side of the rotating shaft  16   a . Hence, the developer tends to be transported by a long length in the direction of transport by the supply auger  16  before being reattracted to the developing sleeve  12 . 
     In the third exemplary embodiment, each fin  22  of the guiding-fin member  21 ″ has the left end  46  that is at a higher position than the lowest end  47  thereof. Such a shape allows the guiding-fin member  21 ″ to extend up to a lower position than in the first exemplary embodiment where the lower end of the guiding-fin member  21  extends horizontally. Therefore, the length of guiding of the developer by the guiding-fin member  21 ″ is longer than in the first exemplary embodiment. Accordingly, the length of guiding of the developer toward the downstream side in the axial direction of the supply auger  16  is longer than in the first exemplary embodiment. Consequently, it becomes much easier to reduce the difference in toner concentration of the developer than in the case of the guiding-fin member  21  including the fins  22  that each do not have the lowest end  47  and the left end  46 . 
     The lowest end  47  of the fin  22  of the guiding-fin member  21 ″ according to the third exemplary embodiment is positioned above the top surface  48  of the mass of developer that is formed when the supply auger  16  is rotating. If the lowest end  47  of the fin  22  of the guiding-fin member  21 ″ is positioned below the top surface  48  of the mass of developer, the guiding-fin member  21 ″ hinders the transport of the developer. In the third exemplary embodiment, however, the guiding-fin member  21 ″ is prevented from hindering the transport of the developer. 
     When the supply auger  16  is rotating, the top surface  48  of the mass of developer inclines as illustrated in  FIG. 15  along with the rotation of the supply auger  16 . When the supply auger  16  is not rotating, the mass of developer has a top surface  48 ′ that is substantially horizontal. Even if the guiding-fin member  21 ″ comes into contact with the developer when the supply auger  16  is not rotating, there is no problem. In the third exemplary embodiment, the lowest end  47  of the fin  22  of the guiding-fin member  21 ″ is positioned above the top surface  48  of the mass of developer that is formed when the supply auger  16  is rotating and below the top surface  48 ′ of the mass of developer that is formed when the supply auger  16  is not rotating. Therefore, the lowest end  47  of the fin  22  of the guiding-fin member  21 ″ is positioned much lower than in a case where the lowest end  47  of the fin  22  of the guiding-fin member  21 ″ is positioned above the top surface  48 ′ of the mass of developer that is formed when the supply auger  16  is not rotating. 
     Examples 3 
     Experiments for demonstrating the effects of providing the guiding wall  42  according to the third exemplary embodiment are conducted in Experimental Examples 3 and in Comparative Examples 3. 
     Experimental Examples 3 are basically the same as Experimental Examples 2, except that the amount of developer sump in each of the developing devices Gy is 90 g. 
     Experimental Example 3-1 
     In Experimental Example 3-1, the developing device Gy includes the guiding wall  42 , the angle of inclination θ 1  of the fin  22  is set to 50 degrees, and the process speed is set to 126 mm/s. 
     Experimental Example 3-2 
     In Experimental Example 3-2, the developing device Gy includes the guiding wall  42 , the angle of inclination θ 1  of the fin  22  is set to 50 degrees, and the process speed is set to 63 mm/s. 
     Experimental Example 3-3 
     Experimental Example 3-3 is based on the same conditions as Experimental Example 2-1. That is, the developing device Gy does not include the guiding wall  42 , the angle of inclination θ 1  of the fin  22  is set to 50 degrees, and the process speed is set to 126 mm/s. 
     Experimental Example 3-4 
     Experimental Example 3-4 is based on the same conditions as Experimental Example 2-2. That is, the developing device Gy does not include the guiding wall  42 , the angle of inclination θ 1  of the fin  22  is set to 50 degrees, and the process speed is set to 63 mm/s. 
     Comparative Example 3-1 
     Comparative Example 3-1 is based on the same conditions as Comparative Example 2-1. That is, the developing device Gy does not include the guiding wall  42 , the angle of inclination θ 1  of the fin  22  is set to 0 degrees, and the process speed is set to 126 mm/s. 
     Comparative Example 3-2 
     Comparative Example 3-2 is based on the same conditions as Comparative Example 2-2. That is, the developing device Gy does not include the guiding wall  42 , the angle of inclination θ 1  of the fin  22  is set to 0 degrees, and the process speed is set to 63 mm/s. 
     The results of the experiments are illustrated in  FIG. 17 . 
       FIG. 17  is a bar graph illustrating the results of experiments conducted in Experimental and Comparative Examples 3, with the horizontal axis representing the length of transport of the developer in the axial direction. 
     Referring to  FIG. 17 , the results of Experimental Examples 3-1 and 3-3 show that, if the process speed is high, the length of transport of the developer is substantially the same, that is, there is substantially no effect of providing the guiding wall  42 . In contrast, the results of Experimental Examples 3-2 and 3-4 show that, if the process speed is low, the length of transport of the developer increases by providing the guiding wall  42 . Furthermore, the results of Experimental Examples 3-2 and 3-4 and Comparative Examples 3-1 and 3-2 show that providing the guiding-fin member  21 ″ increases the length of transport of the developer as in Experimental Examples 2, and that providing the guiding wall  42  further increases the length of transport of the developer. 
     Modifications 
     While some exemplary embodiments of the present invention have been described above in detail, the present invention is not limited to the above exemplary embodiments. Various modifications may be made to the above exemplary embodiments within the scope of the present invention that is defined by the appended claims. Exemplary modifications (H01) to (H010) of the present invention will now be described below. 
     Modification (H01) 
     While each of the above exemplary embodiments concerns a case where the image forming apparatus is a copier, the present invention is not limited to such a case. For example, the image forming apparatus may be a printer or a facsimile, or a multifunction machine having plural or all of the functions of the foregoing apparatuses. 
     Modification (H02) 
     While each of the above exemplary embodiments concerns a case where the copier U uses developers having four respective colors, the present invention is not limited to such a case. For example, the present invention is also applicable to a monochrome image forming apparatus or to a multicolor image forming apparatus using five or more colors or three or less colors. 
     Modification (H03) 
     While each of the first and second exemplary embodiments concerns a case where either the guiding-fin member  21  or the guiding-fin member  21 ′ is provided, the present invention is not limited to such a case. The developing device Gy or Gy′ may include both the guiding-fin member  21  and the guiding-fin member  21 ′. In that case, the guiding-fin member  21  and the guiding-fin member  21 ′ may be combined as an integral body, instead of being provided as separate members. 
     Modification (04) 
     In each of the above exemplary embodiment, the pitch P 1  of the fins  22  or  22 ′ is desired to be smaller than the pitch P 2  of the turns in the transporting blade  16   b  of the supply auger  16 . However, the present invention is not limited to such a case. If the total amount of developer to be transported in the supply chamber  6  is satisfactorily larger than the amount of developer to be guided by the fins  22  or  22 ′, the pitch P 1  may be larger than the pitch P 2 . 
     Modification (H05) 
     In each of the above exemplary embodiments, the angle of inclination θ 1  is desired to be 20 degrees or about 20 degrees or larger and smaller than or equal to the complementary angle of the angle of repose of the developer. However, the present invention is not limited to such a case. For example, the angle of inclination θ 1  may be larger than the complementary angle of the angle of repose of the developer if the developer is less likely to accumulate on the fins  22  and the movement of the developer in the guiding-fin member  21 ,  21 ′, or  21 ″ is less likely to be hindered, owing to a certain level of force of inertia that releases the developer from the developing sleeve  12  or a force of transporting the developer that is exerted by the developing sleeve  12 . 
     Modification (H06) 
     In the first exemplary embodiment, the guiding-fin member  21  is desired to be provided such that the upper end  22   a  thereof is positioned in the area defined by the half-value width W of the distribution of the magnetic force exerted by the pick-off magnetic pole S 2 . Alternatively, the upper end  22   a  may be provided on the outside of the area defined by the half-value width W. 
     Modification (H07) 
     While the first exemplary embodiment concerns a case where the gap H 1  provided between the guiding-fin member  21  and the outer surface of the developing sleeve  12  is larger than the gap H 2  provided between the trimmer  13  and the outer surface of the developing sleeve  12 , the present invention is not limited to such a case. The guiding-fin member  21  may be in contact with the developer on the developing sleeve  12 . 
     Modification (H08) 
     While the third exemplary embodiment concerns a case where the guiding wall  42  is flat in the vertical direction, the present invention is not limited to such a case. For example, the guiding wall  42  may incline with respect to the vertical direction. Moreover, the guiding wall  42  is not limited to have a flat shape and may have a curved shape. 
     Modification (H09) 
     In the third exemplary embodiment, the lower end  42   a  of the guiding wall  42  is desired to be positioned at a distance longer than the radius of the rotating shaft  16   a  from the center of rotation of the supply auger  16  in the horizontal direction. Depending on the position of the pickup magnetic pole S 3  and other factors, the position of the lower end  42   a  may be changed to a position exactly above the rotating shaft  16   a , or the like position. 
     Modification (H010) 
     In the third exemplary embodiment, the lowest end  47  of each fin  22  of the guiding-fin member  21 ″ is desired to be positioned below the top surface  48 ′ of the mass of developer that is formed when the supply auger  16  is not rotating. However, the present invention is not limited to such a case. The lowest end  47  may be positioned above the top surface  48 ′. 
     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.