Patent Publication Number: US-10775714-B2

Title: Developing device

Description:
BACKGROUND OF THE DISCLOSURE 
     Field of the Disclosure 
     The present disclosure relates to a developing device including a resin-made regulating blade. 
     Description of the Related Art 
     A developing device includes a developing device frame, a rotatable developer bearing member that bears developer for developing an electrostatic latent image formed on an image bearing member, and a regulating blade serving as a developer regulating member for regulating an amount of the developer born on the developer bearing member. The regulating blade is provided opposing the developer bearing member with a predetermined gap (hereinafter, referred to as an SB gap) interposed between the regulating blade and the developer bearing member along a rotational axis direction of the developer bearing member. The SB gap refers to a shortest distance between the developer bearing member and the regulating blade. The amount of the developer conveyed to a developing region where the developer bearing member faces the image bearing member is adjusted by adjusting the size of the SB gap. 
     A developing device including a resin-made developer regulating member molded from resin and a resin-made developing device frame molded from resin has recently been known (see Japanese Patent Application Laid-Open No. 2014-197175). 
     A developing device including a resin-made regulating blade and a resin-made developing device frame may have a structure in which the resin-made regulating blade is mounted and fixed onto a blade mounting portion of the resin-made developing device frame. 
     A length of a region in a longitudinal direction of the regulating blade (maximum image region of the regulating blade) corresponding to a maximum image region in an image region that can be formed on the image bearing member increases as a width of a sheet on which an image is formed increases. In addition, a length in the longitudinal direction of a surface on which the regulating blade is mounted (the surface is hereinafter referred to as a blade mounting surface) of the blade mounting portion of the developing device frame increases as the length in the longitudinal direction of the maximum image region of the regulating blade increases. 
     If the developing device frame with a long length in the longitudinal direction of the blade mounting surface of the developing device frame is molded from resin, unevenness of the blade mounting surface of the developing device frame is more likely to increase, so that the flatness (Japanese Industrial Standards (JIS) B0021) of the blade mounting surface of the developing device frame is liable to increase. This is because, in general, a variation in flatness in the longitudinal direction of a resin molded product is liable to occur as the length in the longitudinal direction of the resin molded product increases. 
     In the case of mounting and fixing the regulating blade onto the blade mounting surface of the developing device frame, an orientation of the developing device frame is converted so as to make the blade mounting surface of the developing device frame substantially parallel to an installation surface (horizontal surface) of a mounting device of the regulating blade, and the developing device frame is installed in the mounting device of the regulating blade. In this case, the inclination of the blade mounting surface of the developing device frame with respect to the installation surface (horizontal surface) of the mounting device of the regulating blade tends to be greater when the flatness of the blade mounting surface is large than when the flatness of the blade mounting surface is small. In addition, there is a possibility that the position of the regulating blade relative to a developing sleeve when the regulating blade is mounted on the blade mounting surface may vary as the inclination of the blade mounting surface with respect to the installation surface (horizontal surface) of the mounting device of the regulating blade increases. The position of the regulating blade relative to the developing sleeve includes a position where the regulating blade comes closest to the developing sleeve. 
     On the other hand, the size of the SB gap in a state where the regulating blade is fixed to the blade mounting surface is more likely to vary in the longitudinal direction of the developing sleeve as the amount of variation in the position of the regulating blade relative to the developing sleeve when the regulating blade is mounted on the blade mounting surface increases. Further, if the size of the SB gap varies in the longitudinal direction of the developing sleeve, there is a possibility that unevenness may occur in the amount of the developer to be born on the surface of the developing sleeve in the longitudinal direction of the developing sleeve. 
     Accordingly, there is a demand for preventing a variation in the position of the regulating blade relative to the developing sleeve, including the position where the regulating blade comes closest to the developing sleeve, when the regulating blade is mounted on the blade mounting surface, regardless of the flatness of the blade mounting surface of the developing device frame. 
     SUMMARY OF THE DISCLOSURE 
     The present disclosure is directed to a developing device capable of preventing a variation in a position where a resin-made regulating blade comes closest to a rotatable developing member when the regulating blade is mounted on a resin-made developing device frame. 
     According to an aspect of the present disclosure, a developing device includes a rotatable developing member configured to bear and feed a developer including toner and carrier toward a position where an electrostatic image formed on an image bearing member is developed. A resin-made regulating blade is provided opposing the rotatable developing member and configured to regulate an amount of the developer born on the rotatable developing member, and a resin-made developing device frame provided separately from the regulating blade and including a mounting portion to mount the regulating blade. A recessed portion for gripping the regulating blade is formed, when the developing device is viewed in a section perpendicular to a rotational axis of the rotatable developing member, on an upstream side of the regulating blade with respect to a closest position where the regulating blade is closest to the rotatable developing member in a rotation direction of the rotatable developing member, and wherein a length of the recessed portion in a direction vertical to a straight line passing through the closest position and a rotation center of the rotatable developing member is 0.5 mm or more. 
     Further features and aspects of the present disclosure will become apparent from the following description of example embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional view illustrating a structure of an image forming apparatus according to a first example embodiment. 
         FIG. 2  is a perspective view illustrating an example structure of a developing device. 
         FIG. 3  is a perspective view illustrating the structure of the developing device. 
         FIG. 4  is a sectional view illustrating the structure of the developing device. 
         FIG. 5  is a perspective view illustrating a structure of a resin-made doctor blade (alone). 
         FIG. 6  is a perspective view illustrating a structure of a resin-made developing device frame (alone). 
         FIG. 7  is a schematic view illustrating rigidity of the resin-made doctor blade (alone). 
         FIG. 8  is a schematic view illustrating the rigidity of the resin-made developing device frame (alone). 
         FIG. 9  is a schematic view illustrating straightness of the resin-made doctor blade (alone). 
         FIG. 10  is a perspective view illustrating deformation of the resin-made doctor blade due to a temperature change. 
         FIG. 11  is a sectional view illustrating deformation of the resin-made doctor blade due to a developer pressure. 
         FIG. 12  is a sectional view illustrating a structure of a developing device according to the first example embodiment. 
         FIG. 13  is an enlarged view illustrating the structure of the developing device according to the first example embodiment. 
         FIG. 14  is a schematic view illustrating a structure of a mounting device of the resin-made doctor blade. 
         FIG. 15  is an enlarged view illustrating an orientation of the resin-made doctor blade when the doctor blade is mounted. 
         FIG. 16  is an enlarged view illustrating the orientation of the resin-made doctor blade when the doctor blade is mounted. 
         FIGS. 17A and 17B  are enlarged views each illustrating the orientation of the resin-made doctor blade when the doctor blade is mounted. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Example embodiments, features and various aspects of the present disclosure will be descried in detail below with reference to the accompanying drawings. The following example embodiments are not intended to limit the present disclosure described in the claims, and not all combinations of features described in the following example embodiments are essential to the solving means of the present disclosure. The present disclosure can be implemented in various applications such as a printer, various printing machines, a copying machine, a facsimile (FAX) machine, and a multi-function peripheral. 
     &lt;Example Structure of Image Forming Apparatus&gt; 
     First, a structure of an image forming apparatus according to a first example embodiment of the present disclosure will be described with reference to a sectional view illustrated in  FIG. 1 . As illustrated in  FIG. 1 , an image forming apparatus  60  includes an endless intermediate transfer belt  61  as an intermediate transfer member, and four image forming units  600 , which are provided in a range from an upstream side to a downstream side along a rotation direction (direction indicated by an arrow C in  FIG. 1 ) of the intermediate transfer belt  61 . The image forming units  600  form toner images of yellow (Y), magenta (M), cyan (C), and black (Bk), respectively. 
     Each image forming unit  600  includes a rotatable photosensitive drum  1  as an image bearing member. Each image forming unit  600  also includes a charging roller  2  as a charging unit, a developing device  3  as a developing unit, a primary transfer roller  4  as a primary transfer unit, and a photosensitive drum cleaner  5  as a photosensitive drum cleaning unit, which are disposed along a rotation direction of the photosensitive drum  1 . 
     Each developing device  3  is attachable to and detachable from the image forming apparatus  60 . Each developing device  3  includes a developer container  50  that contains two-component developer (hereinafter simply referred to as developer) including a nonmagnetic toner (hereinafter simply referred to as toner) and a magnetic carrier. Toner cartridges containing toner of Y, M, C, and Bk, respectively, are attachable to and detachable from the image forming apparatus  60 . The toner of each of Y, M, C, and Bk is supplied to the corresponding developer container  50  through a toner conveyance path. The developing device  3  will be described in detail below with reference to  FIGS. 2 to 4 , and the developer container  50  will be described in detail below with reference to  FIG. 5 . 
     The intermediate transfer belt  61  is stretched around a tension roller  6 , a driven roller  7   a , the primary transfer roller  4 , a driven roller  7   b , and a secondary inner transfer roller  66 , and is moved in the direction indicated by the arrow C in  FIG. 1 . The secondary inner transfer roller  66  also functions as a drive roller that drives the intermediate transfer belt  61 . The intermediate transfer belt  61  is rotated in the direction indicated by the arrow C in  FIG. 1  along with the rotation of the secondary inner transfer roller  66 . 
     The intermediate transfer belt  61  is pressed by the primary transfer roller  4  from a back surface of the intermediate transfer belt  61 . The intermediate transfer belt  61  is brought into contact with the photosensitive drum  1 , thereby forming a primary transfer nip portion as a primary transfer portion between the photosensitive drum  1  and the intermediate transfer belt  61 . 
     An intermediate transfer member cleaner  8  serving as a belt cleaning unit contacts the intermediate transfer belt  61  at a position opposing the tension roller  6  via the intermediate transfer belt  61 . A secondary outer transfer roller  67  serving as a secondary transfer unit is disposed at a position opposing the secondary inner transfer roller  66  via the intermediate transfer belt  61 . The intermediate transfer belt  61  is nipped between the secondary inner transfer roller  66  and the secondary outer transfer roller  67 . In this way, a secondary transfer nip portion serving as a secondary transfer portion is formed between the secondary outer transfer roller  67  and the intermediate transfer belt  61 . In the secondary transfer nip portion, a toner image is adsorbed on a surface of a sheet S (e.g., paper or a film) by applying a predetermined pressing force and a transfer bias (electrostatic load bias). 
     Sheets S are stored in a sheet storage portion  62  (e.g., a sheet feed cassette or a sheet feed deck) in a stacked state. A sheet feed unit  63  feeds a sheet S at an image formation timing using, for example, a frictional separation method including a sheet feed roller. The sheet S fed by the sheet feed unit  63  is conveyed to registration rollers  65  disposed in the middle of a conveyance path  64 . After the registration rollers  65  perform a skew correction or a timing correction, the sheet S is conveyed to the secondary transfer nip portion. In the secondary transfer nip portion, a secondary transfer operation is performed in a matched state of the timing of the sheet S and the timing of the toner image. 
     A fixing device  9  is disposed on a downstream side of the secondary transfer nip portion in a conveyance direction of the sheet S. A predetermined pressure and a predetermined amount of heat are applied from the fixing device  9  to the sheet S conveyed to the fixing device  9 , thereby melting and fixing the toner image onto the surface of the sheet S. In this manner, the sheet S having the image fixed thereon is directly discharged to a discharge tray  601  by a forward rotation of discharge rollers  69 . 
     In a case of double-sided image formation, the sheet S is conveyed until a trailing edge of the sheet S passes through a switching flapper  602  by a forward rotation of the discharge rollers  69 . Then, the discharge rollers  69  are rotated reversely. As a result, leading and trailing edges of the sheet S are reversed and the sheet S is conveyed to a duplex conveying path  603 . After that, the sheet S is conveyed to the conveyance path  64  again by a re-feed roller  604  in synchronization with the next image forming timing. 
     &lt;Example Image Forming Process&gt; 
     During image formation, the photosensitive drum  1  is rotationally driven by a motor. The charging roller  2  uniformly charges the surface of the rotationally driven photosensitive drum  1  in advance. An exposure device  68  forms an electrostatic latent image on a surface of the photosensitive drum  1  electrically charged by the charging roller  2  based on an image information signal input to the image forming apparatus  60 . The photosensitive drum  1  is capable of forming a plurality of sizes of electrostatic latent images. 
     The developing device  3  includes a rotatable developing sleeve  70  as a developer bearing member that bears the developer. The developing device  3  develops the electrostatic latent image formed on the surface of the photosensitive drum  1  by using the developer born on the surface of the developing sleeve  70 . As a result, the toner is attached to an exposure portion on the surface of the photosensitive drum  1  to thereby form a visible image. A transfer bias (electrostatic load bias) is applied to the primary transfer roller  4  to transfer the toner image formed on the surface of the photosensitive drum  1  onto the intermediate transfer belt  61 . A small amount of the toner remaining on the surface of the photosensitive drum  1  after the primary transfer (transfer residual toner) is collected by the photosensitive drum cleaner  5 , to thereby prepare for the next image forming process again. 
     Image formation processes for the respective colors performed by parallel processing using the image forming units  600  for the respective colors of Y, M, C, and Bk are carried out at a timing when the images are sequentially superimposed on the toner image having an upstream color primarily transferred onto the intermediate transfer belt  61 . As a result, a full-color toner image is formed on the intermediate transfer belt  61 , and the toner image is conveyed to the secondary transfer nip portion. A transfer bias is applied to the secondary outer transfer roller  67 , and the toner image formed on the intermediate transfer belt  61  is transferred onto the sheet S conveyed to the secondary transfer nip portion. A small amount of the toner remaining on the intermediate transfer belt  61  after the sheet S passes through the secondary transfer nip portion (transfer residual toner) is collected by the intermediate transfer member cleaner  8 . The fixing device  9  fixes the toner image transferred onto the sheet S. The sheet S subjected to the fixing process by the fixing device  9  is discharged onto the discharge tray  601 . 
     A series of image forming processes described above is completed to prepare for the next image forming operation. 
     &lt;Example Structure of Developing Device&gt; 
     A general structure of a developing device will be described with reference to a perspective view illustrated in  FIG. 2 , a perspective view illustrated in  FIG. 3 , and a sectional view illustrated in  FIG. 4 .  FIG. 4  is a sectional view of the developing device  3  taken along a section H illustrated in  FIG. 2 . 
     The developing device  3  includes a resin-made developing device frame molded from resin (hereinafter simply referred to as developing device frame  30 ), and the developer container  50  formed of resin-made cover frame  40  (hereinafter, simply referred to cover frame  40 ) that is formed separately from the developing device frame  30  from resin.  FIGS. 2 and 4  each illustrate a state where a cover frame  40  is mounted on the developing device frame  30 .  FIG. 3  illustrates a state where the cover frame  40  is not mounted on the developing device frame  30 . The structure of the developing device frame  30  (alone) will be described in detail below with reference to  FIG. 6 . 
     The developer container  50  is provided with an opening at a position corresponding to a developing region where the developing sleeve  70  faces the photosensitive drum  1 . The developing sleeve  70  is disposed rotatably with respect to the developer container  50  so that a part of the developing sleeve  70  is exposed at the opening of the developer container  50 . Bearings  71 , which are bearing members, are respectively provided at both ends of the developing sleeve  70 . 
     The inside of the developer container  50  is divided (partitioned) into a developing chamber  31  as a first chamber and a stirring chamber  32  as a second chamber by a vertically extending partition wall  38 . The developing chamber  31  and the stirring chamber  32  are connected to each other at both longitudinal ends through two communicating portions  39  of the partition wall  38 . Accordingly, the developer can communicate between the developing chamber  31  and the stirring chamber  32  through the communicating portions  39 . The developing chamber  31  and the stirring chamber  32  are arranged side by side (at right and left sides) in a horizontal direction. 
     A plurality of magnetic poles is provided along a rotation direction of the developing sleeve  70  in the developing sleeve  70 . A magnet roll serving as a magnetic field generation unit, which generates a magnetic field for bearing the developer on the surface of the developing sleeve  70 , is disposed in a fixed manner. The developer in the developing chamber  31  is scooped up by the influence of the magnetic field of the magnetic pole of the magnetic roll, and is supplied to the developing sleeve  70 . Since the developer is supplied from the developing chamber  31  to the developing sleeve  70 , the developing chamber  31  is also referred to as a supply chamber. 
     In the developing chamber  31 , a first conveyance screw  33  serving as a conveyance unit for stirring and conveying the developer in the developing chamber  31  is provided opposing the developing sleeve  70 . The first conveyance screw  33  includes a rotational shaft  33   a  as a rotatable shaft portion and a helical blade portion  33   b  as a developer conveying portion provided along an outer periphery of the rotational shaft  33   a , and is supported rotatably relative to the developer container  50 . Bearing members are respectively provided at both end portions of the rotational shaft  33   a.    
     The stirring chamber  32  is provided with a second conveyance screw  34  as a conveyance unit for stirring the developer in the stirring chamber  32  and conveying the developer in a direction opposite to a developer conveyance direction of the first conveyance screw  33 . The second conveyance screw  34  includes a rotary shaft  34   a  as a rotatable shaft portion and a helical blade portion  34   b  as a developer conveying portion provided along an outer periphery of the rotary shaft  34   a , and is rotatably supported relative to the developer container  50 . Bearing members are respectively provided at both end portions of the rotary shaft  34   a . The first conveyance screw  33  and the second conveyance screw  34  are rotationally driven, thereby forming a circulating path in which the developer is circulated between the developing chamber  31  and the stirring chamber  32  through the communicating portions  39 . 
     A regulating blade (hereinafter referred to as a doctor blade  36 ) as a developer regulating member for regulating an amount of the developer (also referred to as a developer coating amount) born on the surface of the developing sleeve  70  is attached to the developer container  50  in such a manner that the regulating blade opposes the surface of the developing sleeve  70  without being in contact with the surface of the developing sleeve  70 . The doctor blade  36  includes a coating amount regulating surface  36   r  as a regulating portion for regulating the amount of the developer born on the surface of the developing sleeve  70 . The doctor blade  36  is a resin-made doctor blade molded from resin. The structure of the doctor blade  36  (alone) will be described below with reference to  FIG. 5 . 
     The doctor blade  36  is provided opposing the developing sleeve  70  via a predetermined gap (hereinafter referred to as an SB gap G) interposed between the doctor blade  36  and the developing sleeve  70  in the longitudinal direction of the developing sleeve  70  (i.e., a rotational axis direction of the developing sleeve  70 ). Assume herein that the SB gap G is a minimum distance between a maximum image region of the developing sleeve  70  and a maximum image region of the doctor blade  36 . The maximum image region of the developing sleeve  70  refers to a region of the developing sleeve  70  corresponding to a maximum image region in an image region in which an image can be formed on the surface of the photosensitive drum  1  in the rotational axis direction of the developing sleeve  70 . The maximum image region of the doctor blade  36  refers to a region of the doctor blade  36  corresponding to the maximum image region of the image region in which an image can be formed on the surface of the photosensitive drum  1  in the rotational axis direction of the developing sleeve  70 . In the first example embodiment, electrostatic latent images having a plurality of sizes can be formed on the surface of the photosensitive drum  1 . Accordingly, the maximum image region refers to an image region corresponding to a largest size (e.g., A3 size) among the plurality of sizes of image regions that can be formed on the surface of the photosensitive drum  1 . On the other hand, in a modified example in which an electrostatic latent image having only one size can be formed on the surface of the photosensitive drum  1 , the maximum image region indicates an image region having the only one size in which the electrostatic latent image can be formed on the surface of the photosensitive drum  1 , instead thereof. 
     The doctor blade  36  is disposed substantially opposing a peak position of a magnetic flux density of the magnetic pole of the magnet roll. The developer supplied to the developing sleeve  70  is influenced by the magnetic field of the magnetic pole of the magnet roll. Further, the developer regulated and scraped off by the doctor blade  36  tends to stagnate at a portion upstream of the SB gap G. As a result, a developer stagnating portion is formed on the upstream side of the doctor blade  36  in the rotational direction of the developing sleeve  70 . Then, a part of the developer stagnating at the developer stagnating portion is conveyed through the SB gap G along with the rotation of the developing sleeve  70 . In this case, a layer thickness of the developer passing through the SB gap G is regulated by the coating amount regulating surface  36   r  of the doctor blade  36 . In this way, a thin layer of the developer is formed on the surface of the developing sleeve  70 . 
     Then, a predetermined amount of the developer born on the surface of the developing sleeve  70  is conveyed to the developing region along with the rotation of the developing sleeve  70 . Therefore, the amount of the developer to be conveyed to the developing region is adjusted by adjusting the size of the SB gap G. In the first example embodiment, when the magnitude of the SB gap G is adjusted, a target size of the SB gap G (i.e., target value of the SB gap G) is set to about 300 μm. 
     The developer conveyed to the developing region is magnetically raised in the developing region, so that a magnetic brush is formed. The magnetic brush contacts the photosensitive drum  1 , thereby supplying the toner in the developer to the photosensitive drum  1 . Then, the electrostatic latent image formed on the surface of the photosensitive drum  1  is developed into a toner image. The developer on the surface of the developing sleeve  70  after passing through the developing region and supplying the toner to the photosensitive drum  1  (hereinafter, this developer is referred to as developer obtained after a development process) is scraped off from the surface of the developing sleeve  70  by a repelling magnetic field formed between the identical-polarity magnetic poles of the magnet roll. The developer obtained after the development process, which is scraped off from the surface of the developing sleeve  70 , drops into the developing chamber  31 , and is collected in the developing chamber  31 . 
     As illustrated in  FIG. 4 , the developing device frame  30  is provided with a developer guide portion  35  for guiding the developer to be conveyed toward the SB gap G. The developer guide portion  35  and the developing device frame  30  are integrally formed, and the developer guide portion  35  and the doctor blade  36  are formed separately from each other. The developer guide portion  35  is formed inside the developing device frame  30  and is disposed on the upstream side of the coating amount regulating surface  36   r  of the doctor blade  36  in the rotation direction of the developing sleeve  70 . A flow of the developer is stabilized by the developer guide portion  35  to adjust the density of the developer to a predetermined developer density, thereby defining the weight of the developer at a position where the coating amount regulating surface  36   r  of the doctor blade  36  comes closest to the surface of the developing sleeve  70 . 
     As illustrated in  FIG. 4 , the cover frame  40  is formed separately from the developing device frame  30  and is mounted on the developing device frame  30 . Further, the cover frame  40  covers a part of an opening of the developing device frame  30  to cover a part of an outer peripheral surface of the developing sleeve  70  over an entire area of the developing sleeve  70  in the longitudinal direction. In this case, the cover frame  40  covers a part of the opening of the developing device frame  30  so that the developing region of the developing sleeve  70  opposing the photosensitive drum  1  is exposed. The cover frame  40  is fixed to the developing device frame  30  by ultrasonic bonding. However, as a method for fixing the developing device frame  30  to the cover frame  40 , any one of screw fastening, snap fitting, bonding, welding, and the like may be used. As for the cover frame  40 , as illustrated in  FIG. 4 , the cover frame  40  may be formed using a single part (resin molded product), or may be formed using a plurality of parts (resin molded products). 
     &lt;Example Structure of Resin-Made Doctor Blade&gt; 
     The structure of the doctor blade  36  (alone) will be described with reference to a perspective view illustrated in  FIG. 5 . 
     During an image forming operation (development operation), the pressure of the developer generated from a flow of the developer (hereinafter, this pressure is referred to as a developer pressure) is exerted on the doctor blade  36 . As the rigidity of the doctor blade  36  decreases, the doctor blade  36  is more likely to be deformed and the size of the SB gap G is more likely to vary when the developer pressure is exerted on the doctor blade  36  during the image forming operation. During the image forming operation, the developer pressure is applied in a widthwise direction (direction indicated by an arrow M in  FIG. 5 ) of the doctor blade  36 . Accordingly, in order to prevent a variation in the size of the SB gap G during the image forming operation, the doctor blade  36  is desirably made resistant to deformation in the widthwise direction of the doctor blade  36  by increasing the rigidity of the doctor blade  36  in the widthwise direction. 
     As illustrated in  FIG. 5 , the doctor blade  36  is formed into a plate shape from the viewpoint of mass production and cost. Further, as illustrated in  FIG. 5 , a sectional area of a side surface  36   t  of the doctor blade  36  is made small, and a length t 2  in a thickness direction of the doctor blade  36  is made smaller than a length t 1  in the widthwise direction of the doctor blade  36 . In this way, the doctor blade  36  (alone) has a structure in which the doctor blade  36  is more likely to be deformed in the direction (direction indicated by the arrow M in  FIG. 5 ) perpendicular to a longitudinal direction (direction indicated by an arrow N in  FIG. 5 ) of the doctor blade  36 . Accordingly, in order to correct the straightness of the coating amount regulating surface  36   r , the doctor blade  36  is fixed to a blade mounting portion  41  of the developing device frame  30  in a state where at least a part of the doctor blade  36  is flexed in the direction indicated by the arrow M in  FIG. 5 . The correction of the straightness of the doctor blade  36  will be described in detail below with reference to  FIG. 9 . 
     &lt;Structure of Resin-Made Developing Device Frame&gt; 
     The structure of the developing device frame  30  (alone) will be described with reference to a perspective view illustrated in  FIG. 6 .  FIG. 6  illustrates a state where the cover frame  40  is not mounted on the developing device frame  30 . 
     The developing device frame  30  includes the developing chamber  31  and the stirring chamber  32  that is partitioned from the developing chamber  31  by the partition wall  38 . The partition wall  38  is molded from resin. The partition wall  38  may be formed separately from the developing device frame  30 , or may be formed integrally with the developing device frame  30 . 
     The developing device frame  30  includes sleeve supporting portions  42  for rotatably supporting the developing sleeve  70  by supporting the bearings  71  provided at both end portions of the developing sleeve  70 . The developing device frame  30  also includes the blade mounting portion  41  that is formed integrally with the sleeve supporting portions  42  and is used to mount the doctor blade  36 .  FIG. 6  illustrates a virtual state where the doctor blade  36  is caused to float from the blade mounting portion  41 . 
     In a state where the doctor blade  36  is mounted on the blade mounting portion  41 , an adhesive A coated on a blade mounting surface  41   s  of the blade mounting portion  41  is cured, so that the doctor blade  36  is fixed to the blade mounting portion  41 . 
     &lt;Rigidity of Resin-Made Doctor Blade&gt; 
     The rigidity of the doctor blade  36  (alone) will be described with reference to a schematic view illustrated in  FIG. 7 . The rigidity of the doctor blade  36  (alone) is measured in a state where the doctor blade  36  is not fixed to the blade mounting portion  41  of the developing device frame  30 . 
     As illustrated in  FIG. 7 , a concentrated load F 1  is exerted in the widthwise direction of the doctor blade  36  with respect to a central portion  36   z  of the doctor blade  36  in the longitudinal direction of the doctor blade  36 . In this case, the rigidity of the doctor blade  36  (alone) is measured based on an amount of flexure of the doctor blade  36  in the widthwise direction at the central portion  36   z  of the doctor blade  36 . 
     For example, assume that the concentrated load F 1  of 300 gf is exerted in the widthwise direction of the doctor blade  36  with respect to the central portion  36   z  of the doctor blade  36  in the longitudinal direction of the doctor blade  36 . In this case, the amount of flexure of the doctor blade  36  in the widthwise direction at the central portion  36   z  of the doctor blade  36  is 700 μm or more. In this case, the amount of deformation on a section of the central portion  36   z  of the doctor blade  36  is 5 μm or less. 
     &lt;Example Rigidity of Resin-Made Developing Device Frame&gt; 
     The rigidity of the developing device frame  30  (alone) will be described with reference to a schematic view illustrated in  FIG. 8 . The rigidity of the developing device frame  30  (alone) is measured in a state where the doctor blade  36  is not fixed to the blade mounting portion  41  of the developing device frame  30 . 
     As illustrated in  FIG. 8 , the concentrated load F 1  is exerted in the widthwise direction of the blade mounting portion  41  with respect to a central portion  41   z  of the blade mounting portion  41  in the longitudinal direction of the blade mounting portion  41 . In this case, the rigidity of the developing device frame  30  (alone) is measured based on the amount of flexure in the widthwise direction of the blade mounting portion  41  at the central portion  41   z  of the blade mounting portion  41 . 
     For example, assume that the concentrated load F 1  of 300 gf is exerted in the widthwise direction of the blade mounting portion  41  with respect to the central portion  41   z  of the blade mounting portion  41  in the longitudinal direction of the blade mounting portion  41 . In this case, the amount of flexure in the widthwise direction of the blade mounting portion  41  at the central portion  41   z  of the blade mounting portion  41  is 60 μm or less. 
     Assume that the concentrated load F 1  of the same magnitude is exerted on each of the central portion  36   z  of the doctor blade  36  and the central portion  41   z  of the blade mounting portion  41  of the developing device frame  30 . In this case, the amount of flexure of the central portion  36   z  of the doctor blade  36  is 10 times or more as high as the amount of flexure of the central portion  41   z  of the blade mounting portion  41 . Therefore, the rigidity of the developing device frame  30  (alone) is 10 times or more as high as the rigidity of the doctor blade  36  (alone). For this reason, in a state where the doctor blade  36  is mounted on the blade mounting portion  41  of the developing device frame  30  and the doctor blade  36  is fixed to the blade mounting portion  41  of the developing device frame  30 , the rigidity of the developing device frame  30  is dominant over the rigidity of the doctor blade  36 . Further, in a case where the doctor blade  36  is fixed to the developing device frame  30  over an entire area of the maximum image region of the doctor blade  36 , the rigidity of the doctor blade  36  in a case where the doctor blade  36  is fixed to the developing device frame  30  is higher than that in a case where only the both end portions in the longitudinal direction of the doctor blade  36  are fixed. 
     The magnitude of the rigidity of the developing device frame  30  (alone) is greater than the magnitude of the rigidity of the cover frame  40  (alone). Accordingly, in a state where the cover frame  40  is mounted on the developing device frame  30  and the cover frame  40  is fixed to the developing device frame  30 , the rigidity of the developing device frame  30  is dominant over the rigidity of the cover frame  40 . 
     &lt;Example Correction of Straightness of Resin-Made Doctor Blade&gt; 
     As the width of the sheet S on which an image is formed increases (e.g., the width of the sheet S is an A3 size), the length of the maximum image region in the image region in which an image can be formed on the surface of the photosensitive drum  1  increases in the rotational axis direction of the developing sleeve  70 . Accordingly, the length of the maximum image region of the doctor blade  36  increases as the width of the sheet S on which an image is formed increases. In a case where a doctor blade with a long length in the longitudinal direction is molded from resin, it is difficult to ensure the straightness of the coating amount regulating surface of the resin-made doctor blade molded from resin. This is because, in the case where the doctor blade with a long length in longitudinal direction is molded from resin, when the thermally expanded resin thermally contracts, a portion where the thermal contraction advances and a portion where the thermal contraction is delayed are liable to be generated depending on the position in the longitudinal direction of the doctor blade. 
     Accordingly, in the resin-made doctor blade, as the length of the doctor blade in the longitudinal direction increases, the SB gap is liable to vary in the longitudinal direction of the developer bearing member due to the straightness of the coating amount regulating surface of the doctor blade. When the SB gap varies in the longitudinal direction of the developer bearing member, there is a possibility that unevenness may occur in the amount of the developer born on the surface of the developer bearing member in the longitudinal direction of the developer bearing member. 
     For example, in a case where a resin-made doctor blade having a longitudinal length corresponding to an A3 size (this doctor blade is hereinafter referred to as an A3-size compatible resin-made doctor blade) is manufactured with a general resin molded product accuracy, the straightness of the coating amount regulating surface is about 300 μm to 500 μm. Even if the A3-size compatible resin-made doctor blade is manufactured with a high accuracy by using a high-accuracy resin material, the straightness of the coating amount regulating surface is about 100 μm to 200 μm. 
     In the first example embodiment, the size of the SB gap G is set to about 300 μm, and a tolerance of the SB gap G (i.e., a tolerance with respect to a target value of the SB gap G) is set to ±10% or less. Therefore, in the first example embodiment, this means that an adjustment range of the SB gap G is 300 μm±30 μm and that an allowable tolerance of the SB gap G is 60 μm at maximum. For this reason, even when the A3-size compatible resin-made doctor blade is manufactured with a general resin molded product accuracy, or is manufactured with a high accuracy by using a high-accuracy resin material, a resultant value exceeds an allowable range as the tolerance of the SB gap G only by the accuracy of the straightness of the coating amount regulating surface. 
     In the developing device including the resin-made doctor blade, the SB gap G desirably falls within a predetermined range in the rotational axis direction of the developer bearing member in a state where the doctor blade is fixed to the mounting portion of the developing device frame, regardless of the straightness of the coating amount regulating surface. Accordingly, in the first example embodiment, even when the resin-made doctor blade in which the straightness of the coating amount regulating surface is low is used, the straightness of the coating amount regulating surface is corrected. With this correction, in a state where the doctor blade is fixed to the mounting portion of the developing device frame, the SB gap G is set to fall within the predetermined range in the rotational axis direction of the developing sleeve  70 . 
     The straightness of the coating amount regulating surface  36   r  of the doctor blade  36  will now be described with reference to a schematic view illustrated in  FIG. 9 . The straightness of the coating amount regulating surface  36   r  is represented by an absolute value of a difference between a maximum value and a minimum value of the outer shape of the coating amount regulating surface  36   r  based on a predetermined location of the coating amount regulating surface  36   r  in the longitudinal direction of the coating amount regulating surface  36   r . For example, assume that a central portion of the coating amount regulating surface  36   r  in the longitudinal direction of the coating amount regulating surface  36   r  is defined as an origin of an orthogonal coordinate system, a predetermined straight line passing through the origin is defined as an X-axis, and a straight line vertical to the X-axis from the origin is defined as a Y-axis. In this orthogonal coordinate system, the straightness of the coating amount regulating surface  36   r  is represented by an absolute value of a difference between a maximum value and a minimum value at Y-coordinates of the outer shape of the coating amount regulating surface  36   r.    
     As illustrated in  FIG. 9 , in the resin-made doctor blade (alone), the shape of the central portion of the coating amount regulating surface  36   r  of the doctor blade  36  in the longitudinal direction of the doctor blade  36  is greatly flexed. Therefore, the straightness of the doctor blade  36  needs to be corrected by reducing a difference between the positions of leading end portions  36   e  ( 36   e   1  to  36   e   5 ) of the doctor blade  36  illustrated in  FIG. 5 . In view of an allowable value of the tolerance of the SB gap G, a mounting accuracy of the doctor blade  36  with respect to the developing device frame  30 , and the like, the straightness of the coating amount regulating surface  36   r  of the doctor blade  36  needs to be corrected to 50 μm or less. Considering that the accuracy of the straightness of a doctor blade made of metal by a secondary cutting process is 20 μm or less, it is more preferable to correct the straightness of the coating amount regulating surface  36   r  of the resin-made doctor blade  36  to 20 μm or less. In view of the actual mass-production process, a setting value for correcting the straightness of the coating amount regulating surface  36   r  of the doctor blade  36  is set to about 20 μm to 50 μm. 
     Accordingly, a force (also referred to as a straightness correction force) for flexing at least a part of the maximum image region of the doctor blade  36  is applied to the doctor blade  36 , to thereby flex at least a part of the maximum image region of the doctor blade  36 . Thus, the straightness of the coating amount regulating surface  36   r  of the doctor blade  36  is corrected to 50 μm or less. 
     In an example illustrated in  FIG. 9 , the straightness correction force is applied to each of the leading end portions  36   e   2 ,  36   e   3 , and  36   e   4  in a direction indicated by an arrow I in  FIG. 9  so that the outer shapes of the leading end portions  36   e   2 ,  36   e   3 , and  36   e   4  are adjusted based on the outer shapes of the leading end portions  36   e   1  and  36   e   5  of the doctor blade  36 . As a result, the shape of the coating amount regulating surface  36   r  of the doctor blade  36  is corrected from a coating amount regulating surface  36   r   1  to a coating amount regulating surface  36   r   2 , so that the straightness of the coating amount regulating surface  36   r  of the doctor blade  36  can be corrected to 50 μm or less. In the example illustrated in  FIG. 9 , the outer shape of each leading end portion  36   e  of the doctor blade  36  is adjusted based on the outer shapes of the leading end portions  36   e   1  and  36   e   5  (both end portions in the longitudinal direction of the coating amount regulating surface  36   r ), but instead may be adjusted based on the outer shape of the leading end portion  36   e   3  (the central portion in the longitudinal direction of the coating amount regulating surface  36   r ). In this case, the straightness correction force is applied to the doctor blade  36  so that the outer shapes of the leading end portions  36   e   1 ,  36   e   2 ,  36   e   4 , and  36   e   5  are adjusted based on the outer shape of the leading end portion  36   e   3  of the doctor blade  36 . 
     In this manner, in order to correct the straightness of the doctor blade  36 , the rigidity of the doctor blade (alone) needs to be reduced so that at least a part of the maximum image region of the coating amount regulating surface  36   r  is flexed when the straightness correction force is applied to the doctor blade  36 . 
     &lt;Example Method for Adjusting SB Gap&gt; 
     The SB gap G is adjusted by moving the position of the doctor blade  36  with respect to the developing device frame  30  so as to adjust the position of the doctor blade  36 , which is mounted on the blade mounting portion  41 , relative to the developing sleeve  70  supported by the sleeve supporting portions  42 . At a predetermined position of the blade mounting portion  41  that is determined by adjusting the SB gap G, the flexed doctor blade  36  obtained by flexing at least a part of the maximum image region of the flexed doctor blade  36  is fixed with the adhesive A coated in advance over an entire maximum image region of the blade mounting surface  41   s . The maximum image region of the blade mounting surface  41   s  refers to a region of the blade mounting surface  41   s  corresponding to the maximum image region in the image region in which an image can be formed on the surface of the photosensitive drum  1  in the rotational axis direction of the developing sleeve  70 . In this case, in the maximum image region of the doctor blade  36 , the region flexed to correct the coating amount regulating surface  36   r  is fixed to the blade mounting portion  41 . The adhesive A need not necessarily be coated on a part of the blade mounting surface  41   s , as long as a region that receives a force for flexing at least a part of the maximum image region of the doctor blade  36  is fixed to the blade mounting portion  41  with the adhesive A. In this regard, if the adhesive A is coated over the entirety of the maximum image region of the blade mounting surface  41   s , the following condition is satisfied. The condition is such that the adhesive A is coated on a region of 95% or more of the maximum image region of the blade mounting surface  41   s , including the region flexed to correct the straightness of the coating amount regulating surface  36   r  in the region corresponding to the maximum image region of the doctor blade  36 . 
     Thus, it is possible to prevent the region flexed to correct the straightness of the coating amount regulating surface  36   r  in the maximum image region of the doctor blade  36  from being recovered from the flexed state to the non-flexed original state. With this structure, the doctor blade  36  is fixed to the blade mounting portion  41  in a state where the straightness of the coating amount regulating surface  36   r  is corrected to 50 μm or less. 
     The size of the SB gap G is measured (calculated) by the following method. The size of the SB gap G is measured in a state where the developing sleeve  70  is supported by the sleeve supporting portions  42  of the developing device frame  30 , the doctor blade  36  is mounted on the blade mounting portion  41  of the developing device frame  30 , and the cover frame  40  is fixed to the developing device frame  30 . 
     To measure the size of the SB gap G, a light source (e.g., a light-emitting diode (LED) array or a light guide) is inserted into the developing chamber  31  along the longitudinal direction of the developing chamber  31 . The light source inserted into the developing chamber  31  emits light from the inside of the developing chamber  31  to the SB gap G. In addition, cameras for capturing light beams emitted from the SB gap G to the outside of the developing device frame  30  are disposed at five locations respectively corresponding to the leading end portions  36   e  (i.e.,  36   e   1  to  36   e   5 ) of the doctor blade  36 . 
     To measure the positions of the leading end portions  36   e  ( 36   e   1  to  36   e   5 ) of the doctor blade  36 , the cameras provided at the five locations, respectively, capture light beams emitted from the SB gap G to the outside of the developing device frame  30 . In this case, each camera detects the position where the developing sleeve  70  comes closest to the doctor blade  36  on the surface of the developing sleeve  70  and the leading end portions  36   e  ( 36   e   1  to  36   e   5 ) of the doctor blade  36 . Next, the size of the SB gap G is calculated by converting each pixel value from image data read and generated by the camera into a distance. If the calculated size of the SB gap G does not fall within a predetermined range, the SB gap G is adjusted. Then, when the size of the calculated SB gap G falls within the predetermined range, the obtained position is determined to be a position where the doctor blade  36  obtained by flexing at least a part of the maximum image region of the doctor blade  36  is fixed to the blade mounting portion  41  of the developing device frame  30 . 
     Whether the SB gap G falls within the predetermined range in the rotational axis direction of the developing sleeve  70  is determined by the following method. First, the maximum image region of the doctor blade  36  is divided into four or more segments at equal intervals, and the SB gap G is measured at five or more locations in each segment of the doctor blade  36  (including both end portions and the center portion of the maximum image region of the doctor blade  36 ). Then, a maximum value of the SB gap G, a minimum value of the SB gap G, and a median value of the SB gap G are extracted from samples of the measurement value of the SB gap G measured at five or more locations. 
     In this case, an absolute value of a difference between the maximum value of the SB gap G and the median value of the SB gap G may have to be 10% or less of the median value of the SB gap G, and an absolute value of a difference between the minimum value of the SB gap G and the median value of the SB gap G may have to be 10% or less of the median value of the SB gap G. In this case, assume that the tolerance of the SB gap G is ±10% or less, and the SB gap G falls within a predetermined range in the rotational axis direction of the developing sleeve  70 . For example, if the median value of the SB gap G is 300 μm based on the samples of the measurement value of the SB gap G measured at five or more locations, the maximum value of the SB gap G may have to be set to 330 μm or less and the minimum value of the SB gap G may be set to 270 μm or more. In other words, in this case, the adjustment range of the SB gap G is 300 μm±30 μm and an allowable tolerance of the SB gap G (i.e., a tolerance with respect to the target value of the SB gap G) is 60 μm at maximum. 
     &lt;Linear Expansion Coefficients&gt; 
     Next, deformation of each of the doctor blade  36  and the developing device frame  30  caused by a temperature change due to heat generated during the image forming operation will be described with reference to a perspective view illustrated  FIG. 10 . Examples of the heat generated during the development operation include heat generated when the rotational shaft of the developing sleeve  70  and the bearings  71  are rotated, heat generated when the rotational shaft  33   a  of the first conveyance screw  33  and the bearing member thereof are rotated, and heat generated when the developer passes through the SB gap G. A temperature in the vicinity of the developing device  3  changes due to such heat generated during the image forming operation, so that the temperature of each of the doctor blade  36 , the developing device frame  30 , and the cover frame  40  also changes. 
     As illustrated in  FIG. 10 , an elongation amount of the doctor blade  36  caused by a temperature change is set as H [μm], and an elongation amount of the blade mounting surface  41   s  of the blade mounting portion  41  of the developing device frame  30  caused by a temperature change is set as I [μm]. Also, assume that a linear expansion coefficient α 1  of the resin forming the doctor blade  36  is different from a linear expansion coefficient α 2  of the resin forming the developing device frame  30 . In this case, the amount of deformation caused by a temperature change is different between the developing device frame  30  and the doctor blade  36  due to the difference between the linear expansion coefficients α 1  and α 2 . To compensate for the difference between H [μm] and I [μm], the doctor blade  36  is deformed in a direction indicated by an arrow J in  FIG. 10 . The deformation of the doctor blade  36  in the direction indicated by the arrow J in  FIG. 10  is hereinafter referred to as deformation in a warp direction of the doctor blade  36 . The deformation in the warp direction of the doctor blade  36  causes a variation in the size of the SB gap G. In order to prevent a variation in the size of the SB gap G due to heat, the linear expansion coefficient α 2  of the resin forming the blade mounting portion  41  and the sleeve supporting portions  42  of the developing device frame  30  (alone) and the linear expansion coefficient α 1  of the resin forming the doctor blade  36  (alone) are related. More specifically, when the linear expansion coefficient α 1  of the resin forming the doctor blade  36  is different from the linear expansion coefficient α 2  of the resin forming the developing device frame  30 , the amount of deformation caused by a temperature change varies due to the difference between the linear expansion coefficients α 1  and α 2 . 
     In general, a resin material has a linear expansion coefficient larger than that of a metal material. When the doctor blade  36  is made of a resin material, warping deformation occurs in the doctor blade  36  due to a temperature change caused by heat generated during the image forming operation, and the longitudinal central portion of the doctor blade  36  is easily flexed. As a result, in the developing device in which the resin-made doctor blade  36  is fixed to a resin-made development frame, the size of the SB gap G is liable to vary as the temperature changes during the image forming operation. 
     At least a part of the maximum image region of the doctor blade  36  is flexed to correct the straightness of the coating amount regulating surface  36   r  within 50 μm or less. In addition, a method for fixing the doctor blade  36 , which is obtained by flexing at least a part of the maximum image region of the doctor blade  36 , to the blade mounting portion  41  of the developing device frame  30  with the adhesive A over the entire maximum image region of the doctor blade  36 , is employed. 
     In this case, if there is a large difference between the linear expansion coefficient α 2  of the resin forming the developing device frame  30  and the linear expansion coefficient α 1  of the resin forming the doctor blade  36 , the difference causes the following issue when a temperature change occurs. That is, when a temperature change occurs, the amount of deformation (amount of expansion/contraction) of the doctor blade  36  caused by the temperature change is different from the amount of deformation (amount of expansion/contraction) of the developing device frame  30  caused by the temperature change. As a result, even if the SB gap G is adjusted with a high accuracy to determine the position where the doctor blade  36  is mounted on the blade mounting surface  41   s  of the developing device frame  30 , the size of the SB gap G varies due to a temperature change during the image forming operation. 
     Since the doctor blade  36  is fixed to the blade mounting surface  41   s  over the entire maximum image region, a variation in the size of the SB gap G due to a temperature change during the image formation operation may be desirably prevented. In general, in order to prevent unevenness in the amount of the developer born on the surface of the developing sleeve  70  in the longitudinal direction of the developing sleeve  70 , a variation amount of the SB gap G due to heat needs to be reduced to ±20 μm or less. 
     A difference between the linear expansion coefficient α 2  of the resin forming the developing device frame  30  including the sleeve supporting portions  42  and the blade mounting portion  41  and the linear expansion coefficient α 1  of the resin forming the doctor blade  36  is hereinafter referred to as a linear expansion coefficient difference α 2 −α 1 . A change in the maximum flexure amount of the doctor blade  36  caused by the linear expansion coefficient α 2 −α 1  is described with reference to Table 1. The maximum flexure amount of the doctor blade  36  was measured when a temperature change from a room temperature (23° C.) to a high temperature (40° C.) is applied in a state where the doctor blade  36  is fixed to the blade mounting portion  41  of the developing device frame  30  over the entire maximum image region of the doctor blade  36 . 
     Assume that the linear expansion coefficient of the resin forming the developing device frame  30  including the sleeve supporting portions  42  and the blade mounting portion  41  is represented by α 2  [m/° C.] and the linear expansion coefficient of the resin forming the doctor blade  36  is represented by α 1  [m/° C.]. In addition, the maximum flexure amount of the doctor blade  36  was measured by changing a parameter of the linear expansion coefficient difference α 2 −α 1 . Table 1 illustrates the result of the measurement. In Table 1, when the absolute value of the maximum flexure amount of the doctor blade  36  is 20 μm or less, the maximum flexure amount is denoted by “∘”, and when the absolute value of the maximum flexure amount of the doctor blade  36  is more than 20 μm, the maximum flexure amount is denoted by “x”. 
     
       
         
           
               
               
             
               
                 TABLE 1 
               
               
                   
               
             
            
               
                   
                 Linear Expansion Coefficient Difference 
               
               
                   
                 α2 − α1 [×10 −5  m/° C.] 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                   
                 0 
                 +0.20 
                 +0.40 
                 +0.50 
                 +0.54 
                 +0.55 
                 +0.56 
                 +0.57 
                 +0.60 
               
               
                   
               
               
                 Maximum Flexure 
                 ∘ 
                 ∘ 
                 ∘ 
                 ∘ 
                 ∘ 
                 ∘ 
                 x 
                 x 
                 x 
               
               
                 Amount of Doctor Blade 
               
               
                   
               
            
           
           
               
               
            
               
                   
                 Linear Expansion Coefficient Difference 
               
               
                   
                 α2 − α1 [×10 −5  m/° C.] 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                 0 
                 −0.20 
                 −0.40 
                 −0.44 
                 −0.45 
                 −0.46 
                 −0.47 
                 −0.50 
               
               
                   
               
               
                 Maximum Flexure 
                 ∘ 
                 ∘ 
                 ∘ 
                 ∘ 
                 ∘ 
                 x 
                 x 
                 x 
               
               
                 Amount of Doctor Blade 
               
               
                   
               
            
           
         
       
     
     As seen from Table 1, in order to reduce the amount of variation of the SB gap G due to heat to ±20 m or less, the linear expansion coefficient difference α 2 −α 1  needs to satisfy the following relational expression (1).
 
−0.45×10 −5  [m/° C.]≤α2−α1≤0.55×10 −5  [m/° C.]  (1)
 
In this regard, the resin forming the developing device frame  30  and the resin forming the doctor blade  36  may need to be selected so that the linear expansion coefficient difference α 2 −α 1  is in a range from −0.45×10 −5  [m/° C.] to 0.55×10 −5  [m/° C.]. If the same resin is selected as the resin forming the developing device frame  30  and the resin forming the doctor blade  36 , the linear expansion coefficient difference α 2 −α 1  becomes zero.
 
     When the adhesive A is coated on the doctor blade  36  or the developing device frame  30 , the linear expansion coefficient of the doctor blade  36  or the developing device frame  30  coated with the adhesive A varies. However, the volume of the adhesive A coated on the doctor blade  36  or the developing device frame  30  is extremely small, and thus the influence on a dimensional variation in the thickness direction of the adhesive A caused by a temperature change is negligible. Accordingly, when the adhesive A is coated on the doctor blade  36  or the developing device frame  30 , deformation in the warp direction of the doctor blade  36  caused by a variation of the linear expansion coefficient difference α 2 −α 1  is negligible. 
     Similarly, since the cover frame  40  is fixed to the developing device frame  30 , if the deformation amount of the developing device frame  30  is different from the deformation amount of the cover frame  40  due to a temperature change, deformation of the cover frame  40  in the warp direction causes a variation in the size of the SB gap G. Assume that the linear expansion coefficient of the resin forming the developing device frame  30  including the sleeve supporting portions  42  and the blade mounting portion  41  is represented by α 2  [m/° C.], and the linear expansion coefficient of the resin forming the cover frame  40  is represented by α 3  [m/° C.]. In addition, a difference between the linear expansion coefficient α 3  of the resin forming the cover frame  40  and the linear expansion coefficient α 2  of the resin forming the developing device frame  30  including the sleeve supporting portions  42  and the blade mounting portion  41  is hereinafter referred to as a linear expansion coefficient difference α 3 −α 2 . In this case, the linear expansion coefficient difference α 3 −α 2  needs to satisfy the following relational expression (2) as in Table 1.
 
−0.45×10 −5  [m/° C.]≤α3−α2≤0.55×10 −5  [m/° C.]  (2)
 
In this regard, the resin forming the developing device frame  30  and the resin forming the cover frame  40  may only need to be selected so that the linear expansion coefficient difference α 3 −α 2  is in a range from −0.45×10 −5  [m/° C.] to 0.55×10 −5  [m/° C.]. If the same resin is selected as the resin forming the developing device frame  30  and the resin forming the cover frame  40 , the linear expansion coefficient difference α 3 −α 2  becomes zero.
 
&lt;Example Developer Pressure&gt;
 
     Next, deformation of the doctor blade  36  caused by the developer pressure that is generated from a developer flow during the image forming operation and is applied to the doctor blade  36  will be described with reference to a sectional view illustrated in  FIG. 11 .  FIG. 11  is a sectional view illustrating the developing device  3  in a section (section H illustrated in  FIG. 2 ) perpendicular to the rotational axis of the developing sleeve  70 . FIG.  11  also illustrates a structure in the vicinity of the doctor blade  36  fixed to the blade mounting portion  41  of the developing device frame  30  with the adhesive A. 
     As illustrated in  FIG. 11 , a line connecting a closest position of the doctor blade  36  and the developing sleeve  70  in the coating amount regulating surface  36   r  and a rotation center of the developing sleeve  70  is defined as the X-axis. In this case, the doctor blade  36  has a long length in the X-axis direction and a high rigidity at a section in the X-axis direction. Further, as illustrated in  FIG. 11 , a proportion of a sectional area T 1  of the doctor blade  36  to a sectional area T 2  of a wall portion  30   a  of the developing device frame  30  located in the vicinity of the developer guide portion  35  is small. 
     As described above, the rigidity of the developing device frame  30  (alone) is 10 times or more as high as the rigidity of the doctor blade  36  (alone). Accordingly, the rigidity of the developing device frame  30  with respect to the doctor blade  36  is dominant over the rigidity of the doctor blade  36  in a state where the doctor blade  36  is fixed to the blade mounting portion  41  of the developing device frame  30 . As a result, during the image forming operation, a displacement (maximum flexure amount) of the coating amount regulating surface  36   r  of the doctor blade  36  when the doctor blade  36  receives the developer pressure is substantially equivalent to a displacement (maximum flexure amount) of the developing device frame  30 . 
     During the image forming operation, the developer scooped up from the first conveyance screw  33  is conveyed to the surface of the developing sleeve  70  through the developer guide portion  35 . After that, the doctor blade  36  receives the developer pressure from various directions also when the layer thickness of the developer is defined to match the size of the SB gap G by the doctor blade  36 . As illustrated in  FIG. 11 , assuming that a direction perpendicular to the X-axis direction (a direction in which the SB gap G is defined) is a Y-axis direction, the development pressure in the Y-axis direction is applied in the direction perpendicular to the blade mounting surface  41   s  of the developing device frame  30 . In other words, the developer pressure in the Y-axis direction becomes a force in a direction in which the doctor blade  36  is detached from the blade mounting surface  41   s . Therefore, a bonding force of the adhesive A may need to be sufficiently larger than the developer pressure in the Y-axis direction. In this regard, an adhering area or a coat thickness of the adhesive A on the blade mounting surface  41   s  is optimized in consideration of the force of detaching the doctor blade  36  from the blade mounting surface  41   s  by the developer pressure, and the adhesive force of the adhesive A. 
     &lt;Example Structure of Developing Device According to First Example Embodiment&gt; 
     As described above, the developing device including the resin-made doctor blade  36  and the resin-made developing device frame  30  may have a structure in which the resin-made doctor blade  36  is mounted in a fixed manner on the blade mounting portion  41  of the resin-made developing device frame  30 . 
     Further, as described above, the length in the longitudinal direction of the maximum image region of the doctor blade  36  increases as the width of the sheet S on which an image is formed increases. The length in the longitudinal direction of the blade mounting surface  41   s  increases as the length in the longitudinal direction of the maximum image region of the doctor blade  36  increases. 
     In a case where the developing device frame  30  having a longer length in the longitudinal direction of the blade mounting surface  41   s  is molded from resin, unevenness of the blade mounting surface  41   s  is more likely to increase, so that the flatness (Japanese Industrial Standards (JIS) B0021) of the blade mounting surface  41   s  is liable to increase. This is because, in general, a variation in flatness in the longitudinal direction of a resin molded product is liable to occur as the length in the longitudinal direction of the resin molded product increases. 
     In the first example embodiment, when the doctor blade  36  is mounted and fixed (bonded) onto the blade mounting surface  41   s  with the adhesive A, the mounting device for the doctor blade  36  (hereinafter referred to as a blade mounting device) is used. Further, in the first example embodiment, an orientation of the developing device frame  30  is converted so as to make the blade mounting surface  41   s  be substantially parallel to an installation surface (horizontal surface) of the blade mounting device, and the developing device frame  30  is installed in the blade mounting device. In this case, the inclination of the blade mounting surface  41   s  with respect to the installation surface (horizontal surface) of the blade mounting device tends to be greater when the flatness of the blade mounting surface  41   s  is large than when the flatness of the blade mounting surface  41   s  is small. In addition, there is a possibility that the position of the doctor blade  36  relative to the developing sleeve  70  when the doctor blade  36  is mounted on the blade mounting surface  41   s  may vary as the inclination of the blade mounting surface  41   s  with respect to the installation surface (horizontal surface) of the blade mounting device increases. The position of the doctor blade  36  relative to the developing sleeve  70  includes a position where the doctor blade  36  comes closest to the developing sleeve  70 . 
     On the other hand, the size of the SB gap G in a state where the doctor blade  36  is fixed (bonded) to the blade mounting surface  41   s  is liable to vary in the longitudinal direction of the developing sleeve  70  as a variation amount of the position of the doctor blade  36  relative to the developing sleeve  70  increases. Further, when the size of the SB gap G varies in the longitudinal direction of the developing sleeve  70 , there is a possibility that unevenness may occur in the amount of the developer born on the surface of the developing sleeve  70  in the longitudinal direction of the developing sleeve  70 . 
     Accordingly, a variation in the position of the doctor blade  36  relative to the developing sleeve  70  may be desirably prevented when the doctor blade  36  is mounted on the blade mounting surface  41   s , regardless of the flatness of the blade mounting surface  41   s  of the developing device frame  30 . 
     According to the first example embodiment, it is possible to provide a developing device having a structure in which a variation in a position where a resin-made regulating blade comes closest to a developer bearing member when the regulating blade is mounted on a resin-made developing device frame is prevented and the SB gap G is set to fall within a predetermined range in the longitudinal direction of the developer bearing member. The developing device will be described in detail below. 
     The structure of the developing device according to the first example embodiment will be described with reference to a sectional view illustrated in  FIG. 12  and an enlarged view illustrated in  FIG. 13 .  FIG. 12  is a sectional view of a developing device  300  taken along a section perpendicular to the rotational axis of the developing sleeve  70 .  FIG. 13  is an enlarged view of the developing device  300  in a sectional region C (in the vicinity of a doctor blade  360 ) illustrated in  FIG. 12 . Components in  FIGS. 12 and 13  that are identical to those in  FIGS. 2, 3, and 4  are denoted by the same reference symbols. Differences between the structure of the developing device  300  according to the first example embodiment and the structure of the developing device  3  described above with reference to  FIGS. 2, 3, and 4  will be mainly described below. 
     In the first example embodiment, in the case of mounting and fixing the doctor blade  360  onto the blade mounting surface  41   s , a developing device frame  310  is installed in the device with such an orientation that the blade mounting surface  41   s  is substantially parallel to the installation surface (horizontal surface) of the blade mounting device. 
     The structure of the blade mounting device will now be described with reference to a schematic view illustrated in  FIG. 14 . The orientation of the doctor blade  360  (i.e., the position of the doctor blade  360  relative to the developing sleeve  70  when the doctor blade  360  is mounted on the blade mounting surface  41   s ) at the time of mounting the doctor blade  360  will be described with reference to enlarged views illustrated in  FIGS. 15, 16, 17A, and 17B .  FIGS. 15, 16, 17A, and 17B  each illustrate a sectional view of the developing device  300  along a section perpendicular to the rotational axis of the developing sleeve  70 .  FIGS. 15, 16, 17A, and 17B  each illustrate a state where the orientation of the developing device frame  310  is converted so that the blade mounting surface  41   s  illustrated in the sectional view of  FIG. 12  is substantially parallel to the installation surface (horizontal surface) of the blade mounting device. 
     As illustrated in  FIG. 14 , the blade mounting device includes cameras  100  provided at five locations, respectively, in the rotational axis direction of the developing sleeve  70 . The cameras  100  provided at five locations, respectively, can measure the size of the SB gap G at leading end portions  360   e  ( 360   e   1  to  360   e   5 ) of the doctor blade  360  at the respective positions of the cameras  100 . The leading end portions  360   e  ( 360   e   1  to  360   e   5 ) of the doctor blade  360  are disposed at a closest position where the doctor blade  360  comes closest to the developing sleeve  70  when the doctor blade  360  is mounted on the blade mounting surface  41   s.    
     An installation axis of each camera  100  is placed substantially perpendicular to a straight line M connecting a rotation center  70   a  of the developing sleeve  70  and the leading end portion  360   e  (closest position where the doctor blade  360  comes closest to the developing sleeve  70 ) of the doctor blade  360 . Thus, each camera  100  measures the size of the SB gap G. A straight line M is substantially parallel to the installation surface (horizontal surface) of the blade mounting device. 
     As illustrated in  FIG. 14 , the blade mounting device includes grip units  101 , each of which is composed of a first grip member  101   a  and a second grip member  101   b  and used to grip the doctor blade  360 , at positions respectively corresponding to the five cameras  100 . As illustrated in  FIG. 15 , the first grip member  101   a  grips a first vertical surface  360   a  of the doctor blade  360  that is perpendicular to the straight line M. The second grip member  101   b  grips a second vertical surface  360   b  of the doctor blade  360  that is perpendicular to the straight line M. The first vertical surface  360   a  is provided substantially parallel to the second vertical surface  360   b . Further, the first vertical surface  360   a  is provided at a location closer to the developing sleeve  70  than the second vertical surface  360   b . The first vertical surface  360   a  and the second vertical surface  360   b  of the doctor blade  360  are respectively nipped by the grip member  101   a  and the grip member  101   b  of the grip unit  101 , thereby gripping the doctor blade  360 . 
       FIG. 14  illustrates an example in which five cameras  100  and five grip units  101  are installed at certain intervals in the rotational axis direction of the developing sleeve  70  in the blade mounting device. The number of cameras  100  and the number of grip units  101  are not particularly limited thereto and may be appropriately set depending on the required accuracy of the SB gap G. 
     As for the doctor blade  360  gripped by each grip unit  101 , the surface of the developing sleeve  70  and the leading end portion  360   e  of the doctor blade  360  are detected by each of the five cameras  100  and the size of the SB gap G at each of the five locations is calculated based on the position measurement. Further, based on the result of calculating the size of the SB gap G, each of the five grip units  101  moves in the direction of the straight line M and is adjusted to a desired size (300 μm in the first example embodiment) of the SB gap G. The process of adjusting the size of the SB gap G is desirably performed immediately before a mounted surface (attached surface)  360   s  of the doctor blade  360  is mounted on (contacts) the blade mounting surface  41   s , in terms of the accuracy of adjusting the size of the SB gap G. This is because, if the cameras  100  have different focal lengths between the surface of the developing sleeve  70  and the leading end portion  360   e  of the doctor blade  360 , a position measurement error occurs. This results in deterioration of the accuracy of adjusting the size of the SB gap G. The first example embodiment illustrates an example in which the cameras  100  are each used as a unit that measures the size of the SB gap G. Alternatively, the size of the SB gap G may be measured by a sensor or a thickness gauge, instead of using the cameras  100 . 
     The doctor blade  360 , adjusted to the desired size of the SB gap G by performing the process of adjusting the size of the SB gap G as described above, is pressed with a predetermined load and bonded to the blade mounting surface  41   s , which is coated with the adhesive A in advance. However, even if the size of the SB gap G is adjusted to the desired size by the process of adjusting the SB gap G, there is a factor that varies the size of the SB gap G when the blade mounting surface  41   s  of the developing device frame  310  and the mounted surface  360   s  of the doctor blade  360  are pressed and bonded. The factor will be described below. 
     As described above, the doctor blade  360  is made of a resin material and the developing device frame  310  is also made of a resin material. Thus, the mounted surface  360   s  of the doctor blade  360  and the blade mounting surface  41   s  of the developing device frame  310  are a part of a resin component. As long as each of the doctor blade  360  and the developing device frame  310  is formed with a general resin molded product accuracy, the mounted surface  360   s  of the doctor blade  360  and the blade mounting surface  41   s  of the developing device frame  310  are not necessarily substantially parallel to each other depending on a resin molding condition and a contraction condition. 
     For example, assume that the blade mounting surface  41   s  is inclined at a predetermined angle with respect to the straight line M as illustrated in  FIG. 16 . In this case, the mounted surface  360   s  of the doctor blade  360  mounted on the blade mounting surface  41   s  having an inclination with respect to the straight line M is bonded to the developing device frame  310  with a predetermined inclination with respect to the straight line M along with the inclination of the blade mounting surface  41   s . Accordingly, even if the size of the SB gap G is adjusted, the doctor blade  360  is fixed (bonded) to the blade mounting surface  41   s  with an inclination of a predetermined angle with respect to the straight line M. As a result, the orientation of the doctor blade  360  is inclined and the position of the leading end portion  360   e  of the doctor blade  360  (the position of the doctor blade  360  relative to the developing sleeve  70 ) varies. Further, the adjusted size of the SB gap G is different from the value of the SB gap G after bonding. 
     As the inclination of the blade mounting surface  41   s  with respect to the straight line M increases, a variation amount of the position of the doctor blade  360  relative to the developing sleeve  70  increases when the doctor blade  360  is mounted on the blade mounting surface  41   s . This means that the size of the SB gap G generated when the doctor blade  360  is mounted on the blade mounting surface  41   s  varies as the inclination of the blade mounting surface  41   s  with respect to the straight line M increases. In this case, the varying size of the SB gap G is defined as “ΔG”. Further, an angle of rotation of the doctor blade  360  along with the blade mounting surface  41   s  around the first grip member  101   a  when the doctor blade  360  is mounted and bonded onto the blade mounting surface  41   s  having an inclination with respect to the straight line M is defined as an “angle θ”. 
     A relationship between the “angle θ” and “ΔG” when the doctor blade  360  is mounted on the blade mounting surface  41   s  having an inclination with respect to the straight line M will now be described with reference to  FIGS. 17A and 17B . 
       FIG. 17A  illustrates an example (comparative example) in which a grip position of a doctor blade  3600  to be gripped by the first grip member  101   a  is disposed at a position apart from the straight line M. On the other hand,  FIG. 17B  illustrates an example in which a grip position of the doctor blade  360  to be gripped by the first grip member  101   a  is disposed on the straight line M. The size of the “angle θ” illustrated in  FIG. 17A  is the same as the size of the “angle θ” illustrated in  FIG. 17B . However, even if the size of the “angle θ” illustrated in  FIG. 17A  is the same as the size of the “angle θ” illustrated in  FIG. 17B , “ΔG” illustrated in  FIG. 17B  is smaller than “ΔG” illustrated in  FIG. 17A . This means that, at the same angle θ, “ΔG” with respect to the inclination of the blade mounting surface  41   s  in the structure in which the grip position of the doctor blade to be gripped by the first grip member  101   a  is disposed on the straight line M is smaller than that in the structure in which the grip position is disposed at a position apart from the straight line M. 
     The first example embodiment has a feature that, as illustrated in  FIG. 17B , a recessed portion (recessed portion  360   c ) for the first grip member  101   a  to grip the doctor blade  360  is formed on the doctor blade  360 . The recessed portion  360   c  is formed on the upstream side of the doctor blade  360  with respect to the closest position (the leading end portion  360   e  of the doctor blade  360 ) where the doctor blade  360  comes closest to the developing sleeve  70  in a rotation direction R of the developing sleeve  70 . Further, a plurality of recessed portions  360   c  of the doctor blade  360  is formed at intervals in the rotational axis direction (the longitudinal direction of the doctor blade  360 ) of the developing sleeve  70 . The reason that the recessed portions  360   c  are formed on the doctor blade  360  will now be described below. 
     Regardless of the flatness of the blade mounting surface  41   s , when the doctor blade  360  is mounted on the blade mounting surface  41   s , a variation in the position where the doctor blade  360  comes closest to the developing sleeve  70  is prevented. To prevent the variation, the grip position of the doctor blade  360  to be gripped by the first grip member  101   a  and the grip position of the doctor blade  360  to be gripped by the second grip member  101   b  are disposed on the straight line M. 
     Accordingly, a position of the doctor blade  360  on the straight line M is used as a target of the grip position of the doctor blade  360  to be gripped by the first grip member  101   a . However, there is a possibility that the first grip member  101   a  may grip a position away from the position of the doctor blade  360  on the straight line M by a predetermined distance due to a positional accuracy of the first grip member  101   a . For this reason, the shape of the doctor blade  360  may have to be designed in consideration of the positional accuracy of the first grip member  101   a  when the grip position of the doctor blade  360  to be gripped by the first grip member  101   a  is disposed on the straight line M of the doctor blade  360 . 
     Therefore, as illustrated in  FIG. 17B , the recessed portion  360   c  is formed on the doctor blade  360  and a length L of a predetermined region of the recessed portion  360   c  is set. The length L of the predetermined region of the recessed portion  360   c  indicates a vertical direction length that is vertical to the straight line M at a portion on the upstream side of the doctor blade  360  with respect to the position where the doctor blade  360  comes closest to the developing sleeve  70  in the rotation direction R of the developing sleeve  70  in the recessed portion  360   c . When the recessed portion  360   c  of the doctor blade  360  is gripped by the first grip member  101   a , a mark is formed on the recessed portion  360   c  after being gripped by the first grip member  101   a . The mark formed after gripping can be recognized by conducting an analysis using a three-dimensional measuring instrument. Accordingly, it can be verified that the first grip member  101   a  has gripped the recessed portion  360   c  in the case of gripping the doctor blade  360 . 
     In the first example embodiment, a lower limit of the length L of the predetermined region of each recessed portion  360   c  provided on the doctor blade  360  is set to 0.5 mm in consideration that a minimum value of a thickness of a resin molded product in resin molding is locally 0.5 mm. In other words, in the first example embodiment, the length L of the predetermined region of each recessed portion  360   c  is 0.5 mm or more. 
     Further, the lower limit of the length L of the predetermined region of each recessed portion  360   c  formed on the doctor blade  360  is desirably set as follows, as needed. Specifically, depending on the inclination of the blade mounting surface  41   s  with respect to the installation surface (horizontal surface) of the blade mounting device, an allowable size that satisfies the positional accuracy of the first grip member  101   a  when the grip position of the doctor blade  360  to be gripped by the first grip member  101   a  is disposed on the straight line M is taken into consideration. In addition, depending on a size allowed as a deviation in adjustment of the SB gap G, an allowable size that satisfies the positional accuracy of the first grip member  101   a  when the grip position of the doctor blade  360  to be gripped by the first grip member  101   a  is disposed on the straight line M is taken into consideration. 
     For example, assume that the angle of the inclination of the blade mounting surface  41   s  with respect to the installation surface (horizontal surface) of the blade mounting device is ±5 degrees and the size allowed as a deviation in adjustment of the SB gap G is ±10 μm. In this case, ±0.3 mm is allowed as the positional accuracy of the first grip member  101   a  when the grip position of the doctor blade  360  to be gripped by the first grip member  101   a  is disposed on the straight line M. Thus, a position at a distance of 0.3 mm on the upstream side of the doctor blade  360  with respect to the closest position where the doctor blade  360  comes closest to the developing sleeve  70  in the rotation direction R of the developing sleeve  70  is set as a start point. A position at a distance of 0.3 mm on the downstream side of the doctor blade  360  with respect to the closest position where the doctor blade  360  comes closest to the developing sleeve  70  in the rotation direction R of the developing sleeve  70  is set as an end point. In the range from the start point to the end point in the rotation direction R of the developing sleeve  70 , the first grip member  101   a  is allowed to grip the doctor blade  360 . In other words, the first grip member  101   a  may have to grip the doctor blade  360  on the position at a distance of 0.3 mm on the upstream side of the doctor blade  360  with respect to the closest position where the doctor blade  360  comes closest to the developing sleeve  70  in the rotation direction R of the developing sleeve  70 . To this end, the length L of the predetermined region of each recessed portion  360   c  is desirably set to 0.6 mm or more in consideration of a thickness balance margin (±0.3 mm) in resin molding. 
     For example, assume that the angle of the inclination of the blade mounting surface  41   s  with respect to the installation surface (horizontal surface) of the blade mounting device is ±8 degrees and a size allowed as a deviation in adjustment of the SB gap G is ±30 μm. In this case, ±0.5 mm is allowed as the positional accuracy of the first grip member  101   a  when the grip position of the doctor blade  360  to be gripped by the first grip member  101   a  is disposed on the straight line M. In other words, a position at a distance of 0.5 mm on the upstream side of the doctor blade  360  with respect to the closest position where the doctor blade  360  comes closest to the developing sleeve  70  in the rotation direction R of the developing sleeve  70  is set as a start point. A position at a distance of 0.5 mm on the downstream side of the doctor blade  360  with respect to the closest position where the doctor blade  360  comes closest to the developing sleeve  70  in the rotation direction R of the developing sleeve  70  is set as an end point. In the range from the start point to the end point in the rotation direction R of the eloping sleeve  70 , the first grip member  101   a  is allowed to grip the doctor blade  360 . In other words, the first grip member  101   a  may need to grip the doctor blade  360  on the position at a distance of 0.5 mm on the upstream side of the doctor blade  360  with respect to the closest position where the doctor blade  360  comes closest to the developing sleeve  70  in the rotation direction R of the developing sleeve  70 . To this end, the length L of the predetermined region of each recessed portion  360   c  is desirably set to 0.8 mm or more in consideration of a thickness balance margin (±0.3 mm) in resin molding. 
     As described above, in the first example embodiment, the doctor blade  360  is flexed to correct the straightness of the doctor blade  360 . Accordingly, the length of a basic thickness of the doctor blade  369  is set in a range from 1.0 mm to 3.0 mm to reduce the rigidity of the doctor blade  360  (alone) so that the doctor blade  360  can be flexed. In consideration of this, an upper limit of the length L of the predetermined region of each recessed portion  360   c  of the doctor blade  360  is desirably set to be shorter than the length of the basic thickness of the doctor blade  360  and is desirably set to 1.0 mm or less. 
     In this manner, the length L of the predetermined region of each recessed portion  360   c  of the doctor blade  360  is designed in consideration of the allowance of the positional accuracy of the first grip member  101   a  when the grip position of the doctor blade  360  to be gripped by the first grip member  101   a  is disposed on the straight line M of the doctor blade  360 . The allowance of the positional accuracy of the first grip member  101   a  is determined based on the angle of the inclination of the blade mounting surface  41   s  with respect to the installation surface (horizontal surface) of the blade mounting device and the size allowed as a deviation in adjustment of the SB gap G. 
     In the first example embodiment, as described above with reference to  FIG. 17B , a position of the doctor blade  360  on the straight line M is used as a target of the grip position of the doctor blade  360  to be gripped by the first grip member  101   a . Further, in the first example embodiment, the doctor blade  360  is provided with the recessed portions  360   c  described above with reference to  FIG. 17B . Furthermore, in the first example embodiment, in consideration of the positional accuracy of the first grip member  101   a , the first grip member  101   a  can grip a position away from the position of the doctor blade  360  on the straight line M by the predetermined distance on the upstream side in the rotation direction R of the developing sleeve  70 . 
     Thus, it is possible to prevent a variation in the position of the regulating blade relative to the developing sleeve, including the position where the regulating blade comes closest to the developing sleeve, when the regulating blade is mounted on the blade mounting surface, regardless of the flatness of the blade mounting surface of the developing device frame. According to the first example embodiment as described above, it is possible to prevent a variation in the position where the resin-made regulating blade comes closest to the developer bearing member when the regulating blade is mounted on the resin-made developing device frame, and it is also possible to set the SB gap to fall within a predetermined range in the longitudinal direction of the developer bearing member. 
     In the first example embodiment descried above, an example is described where the blade mounting surface  41   s  has an inclination with respect to the installation surface (horizontal surface) of the blade mounting device when the regulating blade is mounted on the blade mounting surface. However, it is not limited thereto. The present disclosure is also applicable to a case where, when the regulating blade is mounted on the blade mounting surface, not only the blade mounting surface  41   s , but also the mounted surface  360   s  of the doctor blade  360  has an inclination with respect to the installation surface (horizontal surface) of the blade mounting device. In this case, even if a deviation occurs in a relative surface accuracy between the mounted surface  360   s  of the doctor blade  360  and the blade mounting surface  41   s , ΔG (the variation amount of the position of the doctor blade  360  relative to the developing sleeve  70 ) can be reduced. 
     OTHER EXAMPLE EMBODIMENTS 
     The present disclosure is not limited to the example embodiments described above. Various modifications (including any organic combination of example embodiments) can be made based on the gist of the present disclosure, and these modifications are within the scope of the present disclosure. 
     In the example embodiments described above, an example is described where, as illustrated in  FIG. 1 , the image forming apparatus  60  has a structure in which the intermediate transfer belt  61  is used as the intermediate transfer member. However, it is not limited thereto. The present disclosure is also applicable to an image forming apparatus having a structure in which recording materials are sequentially brought into direct contact with the photosensitive drum  1 . 
     Further, in the example embodiments described above, an example is described where the developing device  300  is configured as a single unit. However, advantageous effects similar to those described above can be obtained also in the form of a process cartridge in which the image forming unit  600  (see  FIG. 1 ) including the developing device  300  are integrated into a unit and the unit is configured to be attachable to and detachable from the image forming apparatus  60 . The present disclosure is also applicable to any types of image forming apparatus, such as a monochrome or color image forming apparatus, as long as the image forming apparatus functions as the image forming apparatus  60  including the developing device  300  or the process cartridge. 
     While the present disclosure has been described with reference to example embodiments, it is to be understood that the disclosure is not limited to the disclosed example embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2018-220915, filed Nov. 27, 2018, which is hereby incorporated by reference herein in its entirety.