Patent Publication Number: US-11640124-B2

Title: Developing device and image forming apparatus incorporating same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This patent application is based on and claims priority pursuant to 35 U.S.C. § 119(a) to Japanese Patent Application No. 2020-152727, filed on Sep. 11, 2020 in the Japan Patent Office, the entire disclosure of each of which is hereby incorporated by reference herein. 
     BACKGROUND 
     Technical Field 
     This disclosure generally relates to a developing device to develop a latent image formed on a surface of an image bearer such as a photoconductor drum, and an image forming apparatus including the developing device, such as a copier, a printer, a facsimile machine, or a multifunction peripheral (MFP) having at least two of such functions. 
     Related Art 
     As a developing device included in an image forming apparatus such as a copier and a printer, a developing device employing a two-component developing method is widely used that includes a developing roller in which a magnetic field generator such as a magnet is disposed. 
     SUMMARY 
     This specification describes an improved developing device that includes a developing roller, a developing case, and a support. The developing roller includes a sleeve and a magnetic field generator. The sleeve is rotatable and includes a hollow shaft at an axial end of the sleeve. The magnetic field generator is irrotationally disposed inside the sleeve and includes a non-rotating shaft at an axial end of the magnetic field generator. The non-rotating shaft penetrates through the hollow shaft and projects outward. The developing case is configured to store developer and rotatably supports the hollow shaft. The support includes a fitting portion into which the non-rotating shaft of the magnetic field generator is irrotationally fitted. The support is supported on the developing case using the fitting portion as a main-positioning portion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
         FIG.  1    is a schematic view of a configuration of an image forming apparatus according to an embodiment of the present disclosure; 
         FIG.  2    is a cross-sectional view of an image forming unit of the image forming apparatus of  FIG.  1   ; 
         FIG.  3    is a schematic cross-sectional view of a developing device and a photoconductor drum of the image forming unit of  FIG.  2    as viewed along a longitudinal direction of the developing device; 
         FIG.  4    is a schematic enlarged view of an end portion of the developing device of  FIG.  3    in an axial direction of a developing roller; 
         FIG.  5    is a schematic enlarged view of the end portion of the developing device, a support, and a gear holder when the support and the gear holder are removed from the developing device of  FIG.  4   ; 
         FIG.  6    is a schematic view of the gear holder of  FIG.  5    viewed from a direction A in  FIG.  5   ; 
         FIG.  7 A  is a schematic view of the support of  FIG.  5    viewed from the direction A in  FIG.  5   ; 
         FIG.  7 B  is a schematic view of the support of  FIG.  5    viewed from a direction B in  FIG.  5   ; 
         FIG.  8 A  is a schematic enlarged view of an end portion of the developing device according to a comparative embodiment in the axial direction of a developing roller; 
         FIG.  8 B  is a schematic view of a support of the developing device according to the comparative embodiment of  FIG.  8 A ; 
         FIG.  9 A  is a schematic view of the support according to a first variation viewed from the direction A of  FIG.  5   ; 
         FIG.  9 B  is a schematic view of the support according to the first variation viewed from the direction B of  FIG.  5   ; 
         FIG.  10 A  is a schematic view of the support according to a second variation viewed from the direction A of  FIG.  5   ; 
         FIG.  10 B  is a schematic view of the support according to the second variation viewed from the direction B of  FIG.  5   ; 
         FIGS.  11 A and  11 B  are schematic views of the support according to a third variation; 
         FIG.  12    is an enlarged view of the support and a D-cut portion of a non-rotating shaft, illustrating a positional relationship of the support and the D-cut portion in the axial direction of the shaft; and 
         FIGS.  13 A and  13 B  are schematic views of the support according to a fourth variation. 
     
    
    
     The accompanying drawings are intended to depict embodiments of the present disclosure and should not be interpreted to limit the scope thereof. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted. Also, identical or similar reference numerals designate identical or similar components throughout the several views. 
     DETAILED DESCRIPTION 
     In describing embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner and achieve similar results. 
     Referring now to the drawings, embodiments of the present disclosure are described below. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. Identical reference numerals are assigned to identical components or equivalents and a description of those components is simplified or omitted. 
     Initially with reference to  FIG.  1   , a configuration and operation of an image forming apparatus  1  according to an embodiment of the present disclosure is described below. 
     The image forming apparatus  1  according to the present embodiment is a tandem multicolor image forming apparatus in which process cartridges  20 Y,  20 M,  20 C, and  20 BK are arranged in parallel to each other, facing an intermediate transfer belt  40 . In each of the process cartridges  20 Y,  20 M,  20 C, and  20 BK, a developing device  26  is disposed to face a photoconductor drum  21  as illustrated in  FIG.  2   . 
     In  FIG.  1   , the image forming apparatus  1 , which is a color copier in the present embodiment, includes a document conveyance device  2 , a scanner  3  as a document reading device, and an exposure device  4  as a writing device. The document conveyance device  2  conveys a document to the scanner  3 . The scanner  3  reads image data of the document. 
     The exposure device  4  emits a laser beam based on input image data. 
     In addition, the image forming apparatus  1  includes the process cartridges  20 Y,  20 M,  20 C, and  20 BK to form yellow, magenta, cyan and black toner images on respective surfaces of the photoconductor drums, respectively, and an intermediate transfer belt  40  on which the yellow, magenta, cyan and black toner images are transferred and superimposed. 
     The image forming apparatus  1  further includes a sheet feeder  61  to accommodate sheets P such as paper sheets, a secondary transfer roller  65  to transfer the toner image formed on the intermediate transfer belt  40  onto the sheet P, a fixing device  66  to fix the unfixed toner image on the sheet P, and toner containers  70  to supply toners of respective colors to the developing devices  26  of the corresponding process cartridges  20 Y,  20 M,  20 C, and  20 BK. 
     Each of the process cartridges  20 Y,  20 M,  20 C, and  20 BK includes the photoconductor drum  21  as an image bearer, a charging device  22 , and a cleaning device  23 , which are united as a single unit as illustrated in  FIG.  2   . Each of the process cartridges  20 Y,  20 M,  20 C, and  20 BK, which is expendable, is replaced with a new one when depleted in a body of the image forming apparatus  1 . 
     In each of the process cartridges  20 Y,  20 M,  20 C, and  20 BK, the developing device  26  is disposed to face the photoconductor drum  21 . The developing device  26  is expendable and replaced with a new one when depleted in the body of the image forming apparatus  1 . An operator can independently perform an installation and removal operation of the developing device  26  with respect to the body of the image forming apparatus  1  and an installation and removal operation of the process cartridges  20 Y,  20 M,  20 C, and  20 BK with respect to the body of the image forming apparatus  1  as different operations. 
     In the process cartridges  20 Y,  20 M,  20 C, and  20 BK, yellow, magenta, cyan, and black toner images are formed on the respective photoconductor drums  21  as the image bearers. 
     A description is provided of image forming processes of the image forming apparatus  1  to form a color toner image on a recording medium. 
     A conveyance roller of the document conveyance device  2  conveys a document on a document table onto a platen (exposure glass) of the scanner  3 . The scanner  3  optically scans image data for the document on the platen. 
     The yellow, magenta, cyan, and black image data are transmitted to the exposure device  4 . The exposure device  4  irradiates the photoconductor drums  21  (see  FIG.  2   ) of the corresponding process cartridges  20 Y,  20 M,  20 C, and  20 BK with laser beams (as exposure light) L based on the yellow, magenta, cyan, and black image data, respectively. 
     Each of the four photoconductor drums  21  rotates clockwise in  FIGS.  1  and  2   . The surface of the photoconductor drum  21  is uniformly charged at a position where the photoconductor drum  21  faces the charging device  22  that is a charging roller, which is referred to as a charging process. Thus, the surface of the photoconductor drum  21  is charged to a certain potential. When the charged surface of the photoconductor drum  21  reaches a position to receive the laser beam L emitted from the exposure device  4 , an electrostatic latent image based on the image data is formed on the surface of the photoconductor drum  21 , which is referred to as an exposure process. 
     The laser beam L corresponding to the yellow image data is directed to the surface of photoconductor drum  21  in the process cartridge  20 Y, which is the first from the left in  FIG.  1    among the four process cartridges  20 Y,  20 M,  20 C, and  20 BK. A polygon mirror that rotates at high velocity deflects the laser beam L for yellow along the rotation axis direction of the photoconductor drum  21  (i.e., the main-scanning direction) so that the laser beam L scans the surface of the photoconductor drum  21 . Thus, an electrostatic latent image for yellow is formed on the surface of the photoconductor drum  21  charged by the charging device  22 . 
     Similarly, the laser beam L corresponding to the cyan image data is directed to the surface of the photoconductor drum  21  in the second process cartridge  20 C from the left in  FIG.  1   , thus forming an electrostatic latent image for cyan on the surface of the photoconductor drum  21 . The laser beam L corresponding to the magenta image data is directed to the surface of the photoconductor drum  21  in the third process cartridge  20 M from the left in  FIG.  1   , thus forming an electrostatic latent image for magenta on the photoconductor drum  21 . The laser beam L corresponding to the black image data is directed to the surface of the photoconductor drum  21  in the fourth process cartridge  20 BK from the left in  FIG.  1   , thus forming an electrostatic latent image for black on the photoconductor drum  21 . 
     Then, the surfaces of the photoconductor drums  21  having the respective electrostatic latent images reach positions opposed to the corresponding developing devices  26  (see  FIG.  2   ). The developing device  26  deposits toner of each color onto the surface of the photoconductor drum  21  and develops the electrostatic latent image on the photoconductor drum  21  into a toner image, which is referred to as a development process. 
     After the development process, the surfaces of the photoconductor drums  21  reach positions facing the intermediate transfer belt  40 . The primary transfer rollers  24  are disposed at the positions where the photoconductor drums  21  face the intermediate transfer belt  40  and in contact with an inner circumferential surface of the intermediate transfer belt  40 , respectively. At the positions of the primary transfer rollers  24 , the toner images on the photoconductor drums  21  are sequentially transferred to and superimposed on the intermediate transfer belt  40 , forming a multicolor toner image thereon, which is referred to as a primary transfer process. 
     After the primary transfer process, the surface of the photoconductor drum  21  reaches a position opposite the cleaning device  23 . The cleaning device  23  collects untransferred toner remaining on the photoconductor drum  21 , which is referred to as a cleaning process. 
     Subsequently, a residual potential of the surface of the photoconductor drum  21  is removed at a position opposite the discharger, and a series of image forming processes performed on the photoconductor drum  21  is completed. 
     Meanwhile, the surface of the intermediate transfer belt  40 , onto which the single-color toner images on the photoconductor drums  21  are superimposed, moves in the direction indicated by arrow in  FIG.  1    and reaches a position opposite the secondary transfer roller  65 . The secondary transfer roller  65  secondarily transfers the multicolor toner image on the intermediate transfer belt  40  to the sheet P, which is referred to as a secondary transfer process. 
     After the secondary transfer process, the surface of the intermediate transfer belt  40  reaches a position opposite a belt cleaning device. The belt cleaning device collects untransferred toner on the intermediate transfer belt  40  to complete a series of transfer processes on the intermediate transfer belt  40 . 
     The sheet P is conveyed from the sheet feeder  61  to the position of the secondary transfer roller  65  via a registration roller pair  64 . 
     Specifically, a sheet feed roller  62  feeds the sheet P from top of multiple sheets P accommodated in the sheet feeder  61 , and the sheet P is conveyed to a registration roller pair  64  through a sheet feed path. The sheet P that has reached the registration roller pair  64  is conveyed toward the position of the secondary transfer roller  65 , timed to coincide with the arrival of the multicolor toner image on the intermediate transfer belt  40 . 
     Subsequently, the sheet P, onto which the multicolor image is transferred, is conveyed to the fixing device  66 . The fixing device  66  includes a fixing roller and a pressure roller pressing against each other. In a nip between the fixing roller and the pressure roller, the multicolor image is fixed on the sheet P. 
     After the fixing process, an output roller pair  69  ejects the sheet P as an output image to the exterior of the image forming apparatus  1 , and the ejected sheet P is stacked on an output tray  5  to complete a series of image forming processes. 
     Next, with reference to  FIGS.  2  and  3   , the image forming units of the image forming apparatus  1  are described in detail below. 
     The four image forming units in the body of the image forming apparatus  1  have a similar configuration except the color of the toner used in the image forming processes. Therefore, parts of the image forming unit such as the process cartridge and the developing device are illustrated without suffixes Y, M, C, and BK, which denote the color of the toner, in the drawings. 
     As illustrated in  FIG.  2   , the process cartridge  20  mainly includes the photoconductor drum  21  as the image bearer, the charging device  22 , and the cleaning device  23 , which are stored in a case of the process cartridge  20  as a single unit. 
     The photoconductor drum  21  is an organic photoconductor designed to be charged with a negative polarity and includes a photosensitive layer formed on a drum-shaped conductive support. 
     The charging device  22  is the charging roller including a conductive core and an elastic layer of moderate resistivity coated on the conductive core. A power supply applies a predetermined voltage to the charging device  22  that is the charging roller, and the charging device  22  uniformly charges the surface of the photoconductor drum  21  opposite the charging device  22 . 
     The cleaning device  23  includes a cleaning blade  23   a  and a cleaning roller  23   b  that contact the photoconductor drum  21 . For example, the cleaning blade  23   a  is made of rubber, such as urethane rubber, and contacts the surface of the photoconductor drum  21  at a predetermined angle with a predetermined pressure. The cleaning roller  23   b  is a brush roller in which brush bristles are provided around a core. 
     As illustrated in  FIGS.  2  and  3   , the developing device  26  mainly includes a developing roller  26   a  as a developer bearer, a first conveying screw  26   b   1  as a first conveyor facing the developing roller  26   a , a partition  26   e , a second conveying screw  26   b   2  as a second conveyor facing the first conveying screw  26   b   1  via the partition  26   e , and a doctor blade  26   c  as a developer regulator facing the developing roller  26   a  to regulate an amount of developer borne on the developing roller  26   a.    
     The developing device  26  stores a two-component developer including carrier and toner. 
     The developing roller  26   a  is opposed to the photoconductor drum  21  with a small gap, thereby forming a developing range. As illustrated in  FIG.  3   , the developing roller  26   a  includes stationary magnets  26   a   1  as magnetic field generators, which are fixed not to rotate, inside and a sleeve  26   a   2  that rotates around the magnets  26   a   1 . The magnets  26   a   1  generate multiple poles (magnetic fields) around the outer circumferential surface of the developing roller  26   a.    
     The doctor blade  26   c  is above the developing roller  26   a  and is opposed to the developing roller  26   a  with a small gap as a doctor-gap DG to suitably adjust the amount of the developer carried on the developing roller  26   a.    
     The first conveying screw  26   b   1  and the second conveying screw  26   b   2  convey the developer stored in the developing device  26  in the longitudinal direction of the developing device  26 , thereby establishing a circulation path indicated by the dashed arrow in  FIG.  3   . That is, the first conveying screw  26   b   1  establishes a first conveyance path B 1 , and the second conveying screw  26   b   2  establishes a second conveyance path B 2 . The circulation path of the developer includes the first conveyance path B 1  and the second conveyance path B 2 . 
     The partition  26   e  is an inner wall and separates the first conveyance path B 1  from the second conveyance path B 2 , and the first and second conveyance paths B 1  and B 2  communicate with each other via first and second communication openings  26   f  and  26   g  disposed at both ends of the first and second conveyance paths B 1  and B 2  in the longitudinal direction. Specifically, with reference to  FIG.  3   , in a conveyance direction of the developer, an upstream end of the first conveyance path B 1  communicates with a downstream end of the second conveyance path B 2  via the first communication opening  26   f . Additionally, in the conveyance direction of the developer, a downstream end of the first conveyance path B 1  communicates with an upstream end of the second conveyance path B 2  via the second communication opening  26   g . That is, the partition  26   e  is disposed along the circulation path in the longitudinal direction except both ends of the circulation path. 
     The first conveying screw  26   b   1  in the first conveyance path B 1  is opposite the developing roller  26   a , and the second conveying screw  26   b   2  in the second conveyance path B 2  is opposite the first conveying screw  26   b   1  in the first conveyance path B 1  via the partition  26   e . The first conveying screw  26   b   1  supplies developer to the developing roller  26   a  and collects the developer that separates from the developing roller  26   a  after the development process while conveying the developer in the longitudinal direction of the developing device  26  (that is the lateral direction in  FIG.  3    and an axial direction of the first conveying screw). The second conveying screw  26   b   2  stirs and mixes the developer after the development process conveyed from the first conveyance path B 1  with a fresh toner supplied from a replenishing port  26   d  while conveying the developer in the longitudinal direction of the developing device  26 . 
     In the present embodiment, the first and second conveying screws  26   b   1  and  26   b   2  are horizontally arranged in parallel. Each of the first and second conveying screws  26   b   1  and  26   b   2  includes a shaft and a screw blade wound around the shaft. 
     A further detailed description is given of the image forming processes described above, focusing on the development process. 
     The developing roller  26   a  as the developer bearer rotates clockwise in a direction indicated by arrow in  FIG.  2   . As illustrated in  FIGS.  2  and  3   , the first conveying screw  26   b   1  and the second conveying screw  26   b   2  are disposed facing each other with the partition  26   e  interposed therebetween and rotate in directions indicated by arrows in  FIGS.  2  and  3   . Toner is supplied from the toner container  70  to the replenishing port  26   d  via a toner supply path. As the first conveying screw  26   b   1  and the second conveying screw  26   b   2  rotate in the respective directions in  FIG.  2   , the developer stored in the developing device  26  circulates in the longitudinal direction of the developing device  26 , that is, the direction indicated by the dashed arrow in  FIG.  3   , and the supplied toner is stirred and mixed with the developer circulating. 
     Stirring the developer causes the toner to be charged by friction with carrier in the developer and electrostatically attracted to the carrier. A magnetic force is generated on the developing roller  26   a  to scoop up the carrier. The magnetic force that is called as a developer scooping pole scoop up the carrier with the toner on the developing roller  26   a . The developer borne on the developing roller  26   a  is conveyed in the counterclockwise direction indicated by arrow in  FIG.  2    to a position opposite the doctor blade  26   c . The doctor blade  26   c  adjusts an amount of the developer on the developing roller  26   a  at the position. Subsequently, rotation of the sleeve  26   a   2  conveys the developer to a developing range in which the developing roller  26   a  faces the photoconductor drum  21 . The electric field formed in the developing range deposits toner on the electrostatic latent image formed on the photoconductor drum  21 . As the sleeve  26   a   2  rotates, the developer remaining on the developing roller  26   a  reaches above the first conveyance path B 1  and separates from the developing roller  23   a . In the developing range, a predetermined voltage as a developing bias is applied to the developing roller  26   a  by a development power supply, and a surface potential as a latent image potential is formed on the photoconductor drum  21  in the charging process and the exposure process. The developing bias and the latent image potential form an electric field in the developing range. 
     In the present embodiment, the developing roller  26   a  and the photoconductor drum  21  do not move in the same direction in the developing range. The developing roller  26   a  moves in the opposite direction (counter direction) of the movement direction of the photoconductor drum  21  in the developing range. This configuration can satisfactorily develop the latent image on the photoconductor drum  21  even if the linear velocity difference between the photoconductor drum  21  and the developing roller  26   a  in the developing range is small. 
     The toner in the toner container  70  is supplied through the replenishing port  26   d  to the developing device  26  as the toner in the developing device  26  is consumed. The toner consumption in the developing device  26  is detected by a toner concentration sensor that magnetically detects a toner concentration in the developer (i.e., a ratio of toner to the developer) in the developing device  26 . 
     The replenishing port  26   d  is disposed above an end of the second conveying screw  26   b   2  in the second conveyance path B 2  in the longitudinal direction that is the left and right direction in  FIG.  3   . 
     The configuration and operation of the developing device  26  according to the present embodiment are described in further detail below. 
     As described above with reference to  FIGS.  2  and  3   , the developing device  26  includes a developing roller  26   a  as the developer bearer facing the photoconductor drum  21  and develops the latent image formed on the surface of the photoconductor drum  21  as the image bearer. 
     The developing roller  26   a  includes a sleeve  26   a   2  that is rotatable and magnets  26   a   1  as the magnetic field generator that is irrotationally fixed inside the sleeve  26   a   2 . The sleeve  26   a   2  is a cylindrical member and has hollow shafts  26   a   20  at both ends in an axial direction of the sleeve  26   a   2  that is the lateral direction in  FIG.  3   . The magnets  26   a   1  is a columnar member and has non-rotating shafts  26   a   10  at both ends in an axial direction of the magnets  26   a   1  that is the lateral direction in  FIG.  3   . 
     A developing case  26   k  is a housing to store the developer inside, rotatably supports the developing roller  26   a , the first conveying screw  26   b   1 , and the second conveying screw  26   b   2 , and holds the doctor blade  26   c.    
     In particular, in the present embodiment, the developing case  26   k  rotatably supports the hollow shafts  26   a   20  formed at the axial ends of the sleeve  26   a   2  via ball bearings. 
     In addition, as illustrated in  FIGS.  3  and  4   , bearings  26   r  as gap forming members are disposed on the hollow shafts  26   a   20  of the sleeve  26   a   2  to contact the photoconductor drum  21 . The bearings  26   r  set a gap between the photoconductor drum  21  and the developing roller  26   a  that is a development gap PG illustrated in  FIG.  2   . 
     Specifically, the bearings  26   r  are disposed at the hollow shafts  26   a   20  at both ends of the developing roller  26   a  and contact non-image formation areas of the surface of the photoconductor drum  21 . The outer circumferential surfaces of the bearings  26   r  are made of low friction material. Abutting the bearings  26   r  against the surface of the photoconductor drum  21  determines a distance between the center axis of the developing roller  26   a  and the surface of the photoconductor drum  21  to set the development gap to a target value. 
     Accurately setting the development gap PG to the target value optimizes the electric field formed in the developing range, which enables suitably performing the development process. 
     Preferably, a biasing member is disposed to bias the developing device  26  toward the photoconductor drum  21  so that the bearings  26   r  reliably contact the photoconductor drum  21 . 
     The developing case  26   k  holds the doctor blade  26   c  so as to be able to adjust the doctor gap DG that is a gap between the developing roller  26   a  and the doctor blade  26   c  (see  FIG.  2   ). 
     When the doctor gap DG is accurately set to a target value, the doctor blade  26   c  optimizes an amount of the developer borne on the developing roller  26   a  that is supplied to the developing range in the development process, which enables suitably performing the development process. 
     As illustrated in  FIGS.  4  to  7 B , the developing device  26  according to the present embodiment includes supports  26   m  and gear holders  26   n  at both ends in the axial direction of the sleeve  26   a   2  that is the lateral direction in  FIGS.  3  to  5    and a direction perpendicular to a plane on which  FIGS.  6  and  7    are illustrated. 
     In addition, the developing device  26  includes the non-rotating shafts  26   a   10  at both ends of the magnets  26   a   1  as the magnetic field generator disposed inside the developing roller  26   a . The non-rotating shaft  26   a   10  penetrates through the hollow shaft  26   a   20  of the sleeve  26   a   2  and projects outward, that is, right side in  FIG.  4   . As illustrated in  FIG.  5   , the non-rotating shaft  26   a   10  has a D-cut portion  26   a   11  on a part of the non-rotating shaft  26   a   10  that is a predetermined area extending from the axial end toward the center. The D-cut portion  26   a   11  is made by a milling process so as to form a planar portion on the non-rotating shaft  26   a   10 , that is, so that a cross section of the D-cut portion  26   a   11  orthogonal to the axial direction has a D-shape. 
     The support  26   m  has a D-shaped hole  26   m   20  (see  FIGS.  7 A and  7 B ) as a fitting portion into which the non-rotating shaft  26   a   10  of the magnets  26   a   1  as the magnetic field generator is fitted so as not to rotate. 
     The support  26   m  is supported by the developing case  26   k , and the D-shaped hole  26   m   20  (the fitting portion) becomes a main-positioning portion. 
     Specifically, the support  26   m  includes a base plate  26   m   1  as a main support and an electrode  26   m   2  as a conductor fixed on the base plate  26   m   1 . The base plate  26   m   1  is made of a non-conductive material such as resin. The electrode  26   m   2  is a plate made of a conductive material such as metal to apply a developing bias to the developing roller  26   a  via the non-rotating shaft  26   a   10 . 
     As illustrated in  FIGS.  7 A and  7 B , the base plate  26   m   1  as the main support has a hole  26   m   11  having a hole diameter larger than a shaft diameter of the non-rotating shaft  26   a   10 . The non-rotating shaft  26   a   10  passes through the hole  26   m   11  without contacting the base plate  26   m   1 . 
     In addition, the base plate  26   m   1  has a notch  26   m   13 . The developing case  26   k  includes a boss  26   k   1  (see  FIGS.  4  and  5   ) including a small diameter portion formed at the tip of the boss  26   k   1 . The small diameter portion is fitted into the notch  26   m   13 . The notch  26   m   13  serves as a sub-positioning portion when the support  26   m  is disposed and positioned on the developing case  26   k.    
     Additionally, the base plate  26   m   1  has two holes  26   m   12  to fix the support  26   m  with screws  90  (that is, screw fastening). The support  26   m  is positioned on the developing case  26   k  by using the D-shaped hole  26   m   20  serving as the main positioning portion and the notch  26   m   13  serving as the sub-positioning portion. The hole diameter of the holes  26   m   12  is sufficiently larger than the outer diameter of the external threads of the screw  90 . 
     On the other hand, as illustrated in  FIGS.  7 A and  7 B , the electrode  26   m   2  as the conductor has a D-shaped hole  26   m   20  as a fitting portion into which the D-cut portion  26   a   11  of the non-rotating shaft  26   a   10  is fitted. The D-shaped hole  26   m   20  serves as the main-positioning portion when the support  26   m  is fixed on the developing case  26   k  as described above. As illustrated in  FIG.  7 A , the D-shaped hole  26   m   20  of the electrode  26   m   2  is exposed from the hole  26   m   11  of the base plate  26   m   1  when viewed from the inside of the developing device  26 , that is, viewed from the direction A in  FIG.  5   . 
     In addition, as illustrated in  FIG.  7 B , the electrode  26   m   2  has a thermal caulking hole  26   m   23  serving as the main-positioning portion and a thermal caulking slot  26   m   24  serving as the sub-positioning portion. Bosses formed on the base plate  26   m   1  pass through the thermal caulking hole  26   m   23  and thermal caulking slot  26   m   24  and are thermally melted, respectively, which is thermal caulking processing, to fix the electrode  26   m   2  on the base plate  26   m   1 . 
     The electrode  26   m   2  comes in contact with or separates from a terminal disposed in the body to the image forming apparatus  1  in conjunction with the attachment/detachment operation of the developing device  26  with respect to the main body of the image forming apparatus  1 . When the electrode  26   m   2  comes in contact with the terminal, a power supply in the body of the image forming apparatus  1  supplies a predetermined developing bias to the developing roller  26   a  via the terminal, the electrode  26   m   2 , and the non-rotating shaft  26   a   10 . 
     The electrode  26   m   2  has a cut-and-bent portion  26   m   21  (see  FIGS.  4  and  7 B ) in the vicinity of the D-shaped hole  26   m   20  in order to ensure contact with the non-rotating shaft  26   a   10 . The cut-and-bent portion  26   m   21  prevents failure in applying the developing bias from the electrode  26   m   2  to the non-rotating shaft  26   a   10 . 
     Referring to  FIGS.  4  to  6   , the gear holder  26   n  includes a support shaft  26   n   5  and an idler gear  26   y  rotatably held by the support shaft  26   n   5 . The idler gear  26   y  meshes with a drive gear  26   x  disposed on the hollow shaft  26   a   20  and rotating together with the sleeve  26   a   2 . In the present embodiment, the gear holder  26   n  is a bracket made of metal. 
     The drive gear  26   x  disposed on the developing roller  26   a  (specifically, the hollow shaft  26   a   20  of the sleeve  26   a   2 ) meshes with or separates from a motor gear of a drive motor disposed in the body to the image forming apparatus  1  in conjunction with the attachment/detachment operation of the developing device  26  with respect to the main body of the image forming apparatus  1 . The drive motor drives the drive gear  26   x  to drive and rotate the developing roller  26   a , and the driving force of the drive motor is transmitted to the gear train including the idler gear  26   y  to drive the first conveying screw  26   b   1  and second conveying screw  26   b   2 . 
     The developing case  26   k  supports the gear holder  26   n  together with the support  26   m.    
     Specifically, the support shaft  26   n   5  of the gear holder  26   n  is fitted into a depression formed in the tip of the boss  26   k   2  disposed on the developing case  26   k  (see  FIGS.  4  and  5   ). The support shaft  26   n   5  serves as the main-positioning portion when the gear holder  26   n  is disposed and positioned on the developing case  26   k.    
     In addition, as illustrated in  FIG.  6   , the gear holder  26   n  has a notch  26   n   3 . The small diameter portion formed at the tip of the boss  26   k   1  (see  FIGS.  4  and  5   ) on the developing case  26   k  is fitted into the notch  26   n   3 . The notch  26   n   3  serves as the sub-positioning portion when the gear holder  26   n  is disposed and positioned on the developing case  26   k.    
     Additionally, the gear holder  26   n  has two holes  26   n   2  to fix the gear holder  26   n  on the developing case  26   k  with screws  90  (that is, screw fastening). The gear holder  26   n  is positioned on the developing case  26   k  by using the support shaft  26   n   5  serving as the main positioning portion and the notch  26   n   3  serving as the sub-positioning portion. The hole diameter of the holes  26   n   2  is sufficiently larger than the outer diameter of the external threads of the screw  90 . The screws  90  to fix the gear holder  26   n  on the developing case  26   k  are used together with the screw fastening to fix the support  26   m  on the developing case  26   k . In other words, the gear holder  26   n  is sandwiched between the support  26   m  and the developing case  26   k , and the gear holder  26   n  and the support  26   m  are screwed together on the developing case  26   k . (The gear holder  26   n  and the support  26   m  are assembled from the state illustrated in  FIG.  5    to the state as illustrated in  FIG.  4   .) 
     As described above, the developing device  26  according to the present embodiment has a configuration in which the non-rotating shaft  26   a   10  of the magnets  26   a   1  is fitted into the D-shaped hole  26   m   20  serving as the main-positioning portion to support the support  26   m  on the developing case  26   k.    
     The above-described configuration can more accurately and stably position the developing roller  26   a  than a configuration in which another part serves as the main-positioning portion to support the support  26   m  on the developing case  26   k.    
     With reference to  FIGS.  8 A and  8 B , a developing device  126  according to a comparative embodiment is described below. The developing device  126  includes a support  126   m  including a boss  126   m   1  as the main-positioning portion at a position away from the developing roller  26   a . The developing device  126  includes a boss  126   k   2  disposed on the developing case  26   k  and having a recess at the top of the boss  126   k   2 . The boss  126   m   1  as the main-positioning portion is fitted into the recess to support the support  126   m  on the developing case  26   k . In the above-described configuration, accumulated tolerance of dimensions of parts and errors during assembling are likely to shift the position of the developing roller  26   a  from a target position. 
     The hollow shaft  26   a   20  of the developing roller  26   a  is supported on the developing case  26   k  through a ball bearing, but the non-rotating shaft  26   a   10  of the developing roller  26   a  is supported by the support  126   m . Accordingly, the non-rotating shaft  26   a   10  displaced from a target position with respect to the developing case  26   k  generates force that bends the developing roller  26   a  in a direction perpendicular to the axial direction of the developing roller  26   a . Driving force transmission from the drive gear  26   x  disposed on the hollow shaft  26   a   20  to the idler gear  26   y  disposed on the gear holder  126   n  generates a reaction force acting on the drive gear  26   x  so as to bend the developing roller  26   a  in the direction perpendicular to the axial direction. 
     Accordingly, positions of the developing rollers  26   a  (that is, the non-rotating shafts  26   a   10 ) vary in the developing devices  126  according to the comparative embodiment (or each time the support  126   m  is attached to the developing case  26   k ) and frequently shift from the target position. Variation in the positions of the developing rollers  26   a  causes variation in developing gaps PG between developing rollers  26   a  and the photoconductor drums  21  and variation in doctor gaps DG between developing rollers  26   a  and the doctor blades  26   c , which causes formation of an image having a large image density difference. 
     In contrast, the developing device  26  according to the present embodiment has the configuration in which the non-rotating shaft  26   a   10  of the developing roller  26   a  is fitted into the D-shaped hole  26   m   20  serving as the main-positioning portion to fix the support  26   m  on the developing case  26   k . This configuration easily positions the non-rotating shaft  26   a   10  to the target position with respect to the developing case  26   k . As a result, the above-described configuration is not likely to cause the disadvantage that accumulated tolerance of dimensions of parts and errors during assembling shift the position of the developing roller  26   a  (that is, the non-rotating shaft  26   a   10 ) from a target position and causes bending of the developing roller  26   a  in the direction perpendicular to the axial direction. In the above-described configuration, the developing roller  26   a  is not easily bent even when the driving force transmission from the drive gear  26   x  disposed on the hollow shaft  26   a   20  to the idler gear  26   y  disposed on the gear holder  126   n  generates the reaction force acting on the drive gear  26   x.    
     Accordingly, positions of the developing rollers  26   a  (that is, the non-rotating shafts  26   a   10 ) do not vary in the developing devices  26  according to the present embodiment (or each time the support  26   m  is attached to the developing case  26   k ), and the developing roller  26   a  (that is, the non-rotating shaft  26   a   10 ) is accurately and stably positioned to the target position. As a result, the developing gap PG between the developing roller  26   a  and the photoconductor drum  21  and the doctor gap DG between the developing roller  26   a  and the doctor blade  26   c  are not likely to vary, and the image having the target image density and a stable image density difference is formed. 
     In particular, the developing roller  26   a  and the photoconductor drum  21  in the present embodiment do not move in the same direction in the developing range. The developing roller  26   a  moves in the opposite direction (counter direction) of the movement direction of the photoconductor drum  21  in the developing range. In this configuration, the variation in the developing gap PG and the variation in the doctor gap DG are likely to cause an image density variation. Accordingly, the present disclosure is helpful. 
     Note that  FIGS.  4  to  13 B  illustrate one end portion of the developing device  26  in the axial direction, but the other end portion of the developing device  26  in the axial direction may have the same configuration. Similar to the one end portion of the developing device  26  in the axial direction, the other end portion of the developing device  26  may include the support  26   m  and the gear holder  26   n.    
     The present inventors performed experiments to confirm variations in the developing gaps PG, the doctor gaps DG, and the image density differences when the support  26   m  was attached to developing case  26   k  to complete the developing device  26  according to the present embodiment in several times, and the support  126   m  was attached to developing case  26   k  to complete the developing device  126  illustrated as the comparative embodiment in  FIGS.  8 A and  8 B  in several times. 
     As a result, unacceptable variations in the developing gaps PG, the doctor gaps DG, and the image density differences occurred in the developing devices  126  according to the comparative embodiment. In contrast, all variations in the developing gaps PG, the doctor gaps DG, and the image density differences in the developing devices  26  according to the present embodiment were acceptable levels. 
     The above-described experimental results confirmed the effect of the above-described embodiment. 
     Next, a first variation is described. 
     As illustrated in  FIGS.  9 A and  9 B , the support  26   m  in a first variation includes the base plate  26   m   1  as the main support having a hole  26   m   11  different from the hole illustrated in  FIG.  7 A . The hole  26   m   11  has a substantially same hole diameter as the shaft diameter of the non-rotating shaft  26   a   10 . The non-rotating shaft  26   a   10  penetrates the hole  26   m   11  and contacts the base plate  26   m   1 . 
     In addition, similar to the electrode as illustrated in  FIGS.  7 A and  7 B , the electrode  26   m   2  as the conductor of the support  26   m  has the D-shaped hole  26   m   20  as the fitting portion into which the D-cut portion  26   a   11  of the non-rotating shaft  26   a   10  is fitted. 
     In the support  26   m  configured as described above, the hole  26   m   11  of the base plate  26   m   1  positions the non-rotating shaft  26   a   10  in addition to the D-shaped hole  26   m   20  of the electrode  26   m   2 , which is different from the support illustrated in  FIGS.  7 A and  7 B . Accordingly, the above-described configuration can more accurately and stably position the developing roller  26   a  than the configuration as illustrated in  FIGS.  7 A and  7 B . 
     The present inventors performed experiments to confirm variations in the developing gaps PG, the doctor gaps DG, and the image density differences when the support  26   m  was attached to developing case  26   k  to complete the developing device  26  according to the first variation and the present embodiment including the support  26   m  as illustrated in  FIGS.  7 A and  7 B  in several times. As a result, all variations in the developing gaps PG, the doctor gaps DG, and the image density differences in the developing devices  26  according to the first variation were smaller than those in the developing device  26  including the support  26   m  as illustrated in  FIGS.  7 A and  7 B . 
     In the first variation, the main-positioning portion of the electrode  26   m   2  with respect to the base plate  26   m   1  illustrated in  FIG.  9 B , that is, the boss inserted into the thermal caulking hole  26   m   23  may be removed. Removing the boss enables easily sliding the electrode  26   m   2  on the base plate  26   m   1  so that the non-rotating shaft  26   a   10  penetrates the electrode  26   m   2  and the base plate  26   m   1  even when the position of the shaft penetrating the hole  26   m   11  of the base plate  26   m   1  is relatively shifted from the position of the shaft penetrating the D-shaped hole  26   m   20 . In addition, designing a center line of the thermal caulking slot  26   m   24  serving as the sub-positioning portion of the electrode  26   m   2  so as to pass through the center of the D-shaped hole  26   m   20  can improve a positional accuracy of the D-cut portion  26   a   11  with respect to the non-rotating shaft  26   a   10 . 
     Next, a second variation is described. 
     As illustrated in  FIGS.  10 A and  10 B , the support  26   m  in a second variation includes the base plate  26   m   1  as the main support having a D-shaped hole  26   m   11  different from the holes illustrated in  FIGS.  7 A and  9 A , and the D-cut portion  26   a   11  of the non-rotating shaft  26   a   10  is fitted into the D-shaped hole  26   m   11  as the fitting portion. 
     In addition, the electrode  26   m   2  as the conductor of the support  26   m  has a circular hole  26   m   22  having a hole diameter substantially equal to or larger than the shaft diameter of the non-rotating shaft  26   a   10 , which is different from the electrodes illustrated in  FIGS.  7 B and  9 B . 
     In the support  26   m  configured as described above, the hole  26   m   11  of the base plate  26   m   1  positions the non-rotating shaft  26   a   10  without rotation. As a result, the developing roller  26   a  is accurately and stably positioned. 
     A third variation is described. 
     As illustrated in  FIG.  11 A , the D-cut portion  26   a   11  formed on the non-rotating shaft  26   a   10  of the developing roller  26   a  (that is, the magnets  26   a   1 ) in the developing device  26  according to the third variation faces the photoconductor drum  21  in a cross section perpendicular to the axial direction of the non-rotating shaft  26   a   10 . 
     Specifically, in the cross section perpendicular to the axial direction, a flat portion of the fitting portion (that is the D-shaped hole  26   m   20  formed on the electrode  26   m   2  in  FIG.  11 A ) of the support  26   m  into which the D-cut portion  26   a   11  is fitted, that is, the flat portion facing the flat portion of the D-cut portion  26   a   11  is orthogonal to an imaginary line passing through the center axis of the photoconductor drum  21  and the center axis of the developing roller  26   a . In addition, the flat portion is disposed farther than the center axis of the developing roller  26   a  from the photoconductor drum  21 . 
     Alternatively, as illustrated in  FIG.  11 B , the D-cut portion  26   a   11  formed on the non-rotating shaft  26   a   10  of the developing roller  26   a  (that is, the magnets  26   a   1 ) in the developing device  26  according to another embodiment of the third variation faces the idler gear  26   y  disposed on the gear holder  26   n  in a cross section perpendicular to the axial direction of the non-rotating shaft  26   a   10 . 
     Specifically, in the cross section perpendicular to the axial direction, a flat portion of the fitting portion (that is the D-shaped hole  26   m   20  formed on the electrode  26   m   2  in  FIG.  11 B ) of the support  26   m  into which the D-cut portion  26   a   11  is fitted, that is, the flat portion facing the flat portion of the D-cut portion  26   a   11  is orthogonal to an imaginary line passing through the center axis of the idler gear  26   y  (that is, the support shaft  26   n   5 ) and the center axis of the developing roller  26   a . In addition, the flat portion is disposed farther than the center axis of the developing roller  26   a  from the idler gear  26   y.    
     The configurations illustrated in  FIGS.  11 A and  11 B  enable easily setting the posture of the magnets  26   a   1  fixed not to rotate in the developing device  26  (that is, the angle of the magnets  26   a   1 ) in the rotation direction of the developing roller  26   a  with respect to the photoconductor drum  21  or the doctor blade  26   c . Specifically, as the developing device  26  is driven, the developing roller  26   a  receives a pressure from the photoconductor drum  21  via the developer and receives a reaction force from the idler gear  26   y . The pressure and the reaction force at this time are forces pushing the D-cut portion  26   a   11  of the non-rotating shaft  26   a   10  to the flat portion of the D-shaped hole  26   m   20  of the electrode  26   m   2 . Accordingly, the flat portion of the D-shaped hole  26   m   20  of the electrode  26   m   2  accurately determines the posture (that is, the angle) of the non-rotating shaft  26   a   10  in the rotation direction of the developing roller  26   a.    
     With reference to  FIG.  12   , a configuration regarding the D-cut portion  26   a   11  of the non-rotating shaft  26   a   10  in the third variation (or the second variation and the fourth variation described below) is described. Preferably, the D-cut portion  26   a   11  of the non-rotating shaft  26   a   10  is formed a range W in the axial direction from the middle of the hole  26   m   11  of the base plate  26   m   1  as the main support to a tip of the non-rotating shaft  26   a   10  via the D-shaped hole  26   m   20  as the fitting portion of the electrode  26   m   2  as the conductor. 
     In the above-described configuration, at least a part of a hole of the base plate  26   m   1  into which the non-rotating shaft  26   a   10  is fitted is a cylindrical hole. In other words, at least a part of the hole  26   m   11  of the base plate  26   m   1  into which the D-cut portion  26   a   11  is fitted is the cylindrical hole. In addition, the D-cut portion  26   a   11  is fitted into the electrode  26   m   2  at a position at which the D-cut portion  26   a   11  on the non-rotating shaft  26   a   10  starts to extend. 
     A cylindrical portion of the non-rotating shaft  26   a   10  has a higher dimensional accuracy than the D-cut portion  26   a   11 . Since the above-described configuration receives the cylindrical portion of the non-rotating shaft  26   a   10  on the base plate  26   a   1 , the above-described configuration can accurately set the developing gap PG. Since the D-cut portion  26   a   11  is formed by performing secondary processing (milling processing) on the cylindrical portion of the non-rotating shaft  26   a   10 , in general, the D-cut portion  26   a   11  has a larger tolerance than the cylindrical portion, and the dimensional accuracy of the D-cut portion  26   a   11  is inferior to that of the cylindrical portion. 
     If the D-cut portion  26   a   11  of the non-rotating shaft  26   a   10  penetrates an entire portion of the hole  26   m   11  of the base plate  26   m   1  in the axial direction, in other words, if the D-cut portion  26   a   11  of the non-rotating shaft  26   a   10  penetrates the hole  26   m   11  that is a cylindrical hole extending in the base plate  26   m   1  in the axial direction and is supported by the base plate  26   m   1 , in addition to the tolerance of the non-rotating shaft  26   a   10  and the tolerance of the hole  26   m   11 , a clearance generated by the D-cut portion  26   a   11  increases the variation of the developing gap PG that is affected by pressures applied from the photoconductor drum  21  and the idler gear  26   y . Disposing the D-cut portion  26   a   11  of the non-rotating shaft  26   a   10  in the part of the hole  26   m   11  in the axial direction as illustrated in  FIG.  12    can improve the disadvantage described above. 
     In the third variation, a plurality of magnetic poles generated by the magnets  26   a   1  are positioned to target positions in the rotational direction of the developing roller  26   a  with respect to a D-cut surface (that is a flat surface) of the D-cut portion  26   a   11  as a reference. The D-cut surface (that is the flat surface) of the D-cut portion  26   a   11  is suitable for the reference because the D-cut surface is easily visible not only in the state of the developing roller  26   a  alone but also in the state of being installed in the developing device  26  to confirm the positional relationship between the D-cut surface and the photoconductor drum  21  or the idler gear  26   y.    
     As a result, the above configurations reduce the variation of the postures of the magnets  26   a   1  (that is, the angles of the magnets  26   a   1 ) in the rotation direction of the developing roller  26   a  with respect to the photoconductor drum  21  or the doctor blade  26   c  and enable forming images having stable and good image qualities. 
     A fourth variation is described. 
     As illustrated in  FIG.  13 A , the D-cut portion  26   a   11  formed on the non-rotating shaft  26   a   10  of the developing roller  26   a  (that is, the magnets  26   a   1 ) in the developing device  26  according to the fourth variation also faces the photoconductor drum  21  in the cross section perpendicular to the axial direction of the non-rotating shaft  26   a   10 . However, the D-cut portion  26   a   11  is disposed at a position rotated from the D-cut portion illustrated in  FIG.  11 A  by approximately 180 degrees about the center axis of the non-rotating shaft  26   a   10 . 
     Specifically, in the cross section perpendicular to the axial direction, a flat portion of the fitting portion (that is the D-shaped hole  26   m   20  formed on the electrode  26   m   2  in  FIG.  13 A ) of the support  26   m  into which the D-cut portion  26   a   11  is fitted, that is, the flat portion facing the flat portion of the D-cut portion  26   a   11  is orthogonal to an imaginary line passing through the center axis of the photoconductor drum  21  and the center axis of the developing roller  26   a . In addition, the flat portion is disposed nearer to the photoconductor drum  21  than the center axis of the developing roller  26   a.    
     Alternatively, as illustrated in  FIG.  13 B , the D-cut portion  26   a   11  formed on the non-rotating shaft  26   a   10  of the developing roller  26   a  (that is, the magnets  26   a   1 ) in the developing device  26  according to another embodiment of the fourth variation also faces the idler gear  26   y  disposed on the gear holder  26   n  in a cross section perpendicular to the axial direction of the non-rotating shaft  26   a   10 . However, the D-cut portion  26   a   11  is disposed at a position rotated from the D-cut portion illustrated in  FIG.  11 B  by approximately 180 degrees about the center axis of the non-rotating shaft  26   a   10 . 
     Specifically, in the cross section perpendicular to the axial direction, a flat portion of the fitting portion (that is the D-shaped hole  26   m   20  formed on the electrode  26   m   2  in  FIG.  13 B ) of the support  26   m  into which the D-cut portion  26   a   11  is fitted, that is, the flat portion facing the flat portion of the D-cut portion  26   a   11  is orthogonal to an imaginary line passing through the center axis of the idler gear  26   y  (that is, the support shaft  26   n   5 ) and the center axis of the developing roller  26   a . In addition, the flat portion is disposed nearer to the idler gear  26   y  than the center axis of the developing roller  26   a.    
     The configurations illustrated in  FIGS.  13 A and  13 B  enable easily setting the posture of the magnets  26   a   1  fixed not to rotate in the developing device  26  (that is, the angle of the magnets  26   a   1 ) in the rotation direction of the developing roller  26   a  with respect to the photoconductor drum  21  or the doctor blade  26   c . Specifically, the plurality of magnetic poles generated by the magnets  26   a   1  are positioned to the target positions in the rotational direction of the developing roller  26   a  with respect to the D-cut surface (that is the flat surface) of the D-cut portion  26   a   11  as the reference. The D-cut surface (that is the flat surface) of the D-cut portion  26   a   11  is suitable for the reference because the D-cut surface is easily visible not only in the state of the developing roller  26   a  alone but also in the state of being installed in the developing device  26  to confirm the positional relationship between the D-cut surface and the photoconductor drum  21  or the idler gear  26   y.    
     As a result, the above configurations reduce the variation of the postures of the magnets  26   a   1  (that is, the angles of the magnets  26   a   1 ) in the rotation direction of the developing roller  26   a  with respect to the photoconductor drum  21  or the doctor blade  26   c  and enable forming images having stable and good image qualities. 
     As described above, the developing device  26  includes the developing roller  26   a . The developing roller  26   a  includes the rotatable sleeve  26   a   2  and the magnets  26   a   1  as the magnetic field generator irrotationally disposed in the sleeve  26   a   2 . In addition, the developing device  26  includes the developing case  26   k  to store the developer inside and rotatably support the hollow shaft  26   a   20  formed at the axial ends of the sleeve  26   a   2 . In addition, the non-rotating shafts  26   a   10  are attached to both ends of the magnets  26   a   1 . The non-rotating shaft  26   a   10  penetrates through the hollow shaft  26   a   20  and projects outward. The developing device  26  includes the support  26   m  having the hole  26   m   20  (the fitting portion). The non-rotating shaft  26   a   10  of the magnets  26   a   1  is fitted into the hole  26   m   20 . The support  26   m  is supported on the developing case  26   k  using the hole  26   m   20  as the main-positioning portion. 
     As a result, the developing roller  26   a  is accurately and stably positioned. 
     In the present embodiment, the process cartridge  20  does not include the developing device  26 , and the developing device  26  is a unit that can be independently installed in and removed from the body of the image forming apparatus  1 . In contrast, the developing device  26  may be one of the constituent members of the process cartridge  20 , and the process cartridge  20  may be configured to be integrally installed in and removed from the body of the image forming apparatus  1 . 
     In such a configuration, similar effects to those of the above-described embodiment and variations are also attained. 
     It is to be noted that the term “process cartridge” used in the present disclosure means a removable unit including an image bearer and at least one of a charging device to charge the image bearer, a developing device to develop latent images on the image bearer, and a cleaning device to clean the image bearer that are united together and is designed to be removably installed as a united part in the body of the image forming apparatus. 
     In the present embodiment according to the present disclosure, the developing device  26  includes two conveying screws  26   b   1  and  26   b   2  as the conveyors horizontally arranged in parallel and the doctor blade  26   c  disposed above the developing roller  26   a . The configuration of the developing device to which the present disclosure is applied is not limited to the above-described configurations. The present disclosure may be applied to other developing devices such as a developing device including two conveyers obliquely arranged, a developing device including two conveyers arranged in parallel in the vertical direction, a developing device including three or more conveyors arranged, a developing device including the doctor blade disposed below the developing roller, or a developing device in which the developing roller rotates in the same direction as the photoconductor drum rotates in the developing range. 
     Applying the present disclosure to the above developing devices can provide effects similar to the effects of the above-described embodiments and variations. 
     The above-described embodiments are illustrative and do not limit the present disclosure. Thus, numerous additional modifications and variations are possible in light of the above teachings. It is therefore to be understood that within the scope of the present disclosure, the present disclosure may be practiced otherwise than as specifically described herein. The number, position, and shape of the components described above are not limited to those embodiments described above. Desirable number, position, and shape can be determined to perform the present disclosure.