Patent Publication Number: US-9891551-B2

Title: Roller member, roller supporting mechanism, and image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a Continuation of U.S. application Ser. No. 14/673,545, filed Mar. 30, 2015, which claims priority from Japanese Patent Application No. 2014-074540 filed Mar. 31, 2014, which are hereby incorporated by reference herein in their entireties. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     This disclosure relates to a roller member used for an image forming apparatus, a roller supporting mechanism provided with the roller member, and the image forming apparatus. 
     An image forming apparatus is an apparatus that forms images on recording media. Examples of an electrophotographic image forming apparatus include, for example, electrophotographic copying machines, electrophotographic printers (LED printers, laser beam printers), facsimile apparatuses, and word processors. 
     Description of the Related Art 
     In the related art, an electrophotographic image forming apparatus (hereinafter, referred to as an image forming apparatus) is provided with a process device having a photosensitive drum (electrophotographic photosensitive drum), which is an image bearing member and configured to act on the photosensitive drum. Examples of the process device include a voltage application apparatus configured to apply electric charge on the photosensitive drum, a developing device configured to supply developer (hereinafter, referred to as “toner”) to the photosensitive drum, and a cleaning device configured to clean toner failed to be transferred and remaining on a surface of the photosensitive drum. 
     Examples of a charging device in the voltage application apparatus include a roller charging system using a conductive roller. In the roller charging system, charging of the surface of the photosensitive drum is achieved by bringing a charging roller, which is a conductive resilient roller, into bias abutment with the photosensitive drum and applying a voltage thereto. The charging roller generally has a form having a resilient layer covering a metallic shaft over the entire area in a longitudinal direction other than both ends (Japanese Patent Laid-Open No. 2013-109209). Examples of the metallic shaft of the charging roller include a form using a cylindrical-shaped metallic shaft (Japanese Patent Laid-Open No. 2010-230748). 
     In the case of manufacturing the cylindrical-shaped metallic shaft by pressing a metallic plate, a mating portion (an opposing area where one end portion and the other end portion of the metallic plate oppose each other) extending in an axial direction is present on the metallic shaft. Here, in this configuration, in order to increase the strength of the metallic shaft, a configuration in which projections and depressions are provided alternately on the mating portion and one end portion and the other end portion of the metallic plate are engaged by the depressions and the projections is conceivable. 
     In this case, by providing the projections and the depressions on the mating portion (opposing area), dimensional accuracy in a radial and the longitudinal direction (axial direction) of the metallic shaft may be lowered at the time of manufacture of the metallic shaft. 
     Therefore, in the metallic shaft provided with the depressions and the projections in the opposing area of the metallic plate where the one end portion and the other end portion oppose each other, restraint of lowering of the dimensional accuracy of the metallic shaft is required. 
     SUMMARY OF THE INVENTION 
     A representative configuration disclosed in this application is a roller member used in an image forming apparatus including: a metallic shaft, the metallic shaft including: a cylindrical portion formed so that one end portion and the other end portion of a metallic plate oppose each other; and a projecting portion projecting from an end surface of the cylindrical portion outward in an axial direction of the metallic shaft, wherein the one end portion and the other end portion each include a straight portion, a plurality of projections, and a plurality of depressions, the projections on the one end portion engage the depressions on the other end portion, the depressions on the one end portion engage the projections on the other end portion, and the straight portion on the one end portion oppose the straight portion on the other end portion in an opposing area in which the one end portion and the other end portion oppose, a straight area in which the straight portion of the one end portion and the straight portion of the other end portion oppose is positioned on an end portion of the cylindrical portion, a projection and depression area in which the projections on the one end portion and the projections on the other end portion are arranged alternately is located adjacent to the straight area, and a projecting amount of the projection projecting with respect to the straight portion to which the projection arranged so as to be interposed between the straight portion and the depression is adjacent is smaller than a projecting amount of the projection projecting with respect to the depression to which the projection is adjacent. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view illustrating a charging roller of Example 1. 
         FIG. 2  is a cross-sectional view illustrating an image forming apparatus body and a process cartridge of an electrophotographic image forming apparatus of Example 1. 
         FIG. 3  is a cross-sectional view illustrating the process cartridge of Example 1. 
         FIG. 4  is a perspective view illustrating the image forming apparatus body and the process cartridge of Example 1 in a state in which an opening and closing door is opened. 
         FIG. 5  is an explanatory perspective view illustrating a configuration of the process cartridge of Example 1. 
         FIG. 6  is an explanatory perspective view illustrating a configuration of a cleaning unit of Example 1. 
         FIGS. 7A and 7B  are explanatory views illustrating the configuration of the cleaning unit of Example 1. 
         FIG. 8  is an explanatory cross-sectional view illustrating a processing process of a charging roller of Example 1. 
         FIGS. 9A and 9B  are explanatory views illustrating a shaft portion of the charging roller of Example 1. 
         FIG. 10  is an explanatory view illustrating the charging roller. 
         FIGS. 11A and 11B  are explanatory views illustrating the charging roller of Example 1. 
         FIGS. 12A and 12B  are explanatory views illustrating a charging roller of Example 2. 
         FIGS. 13A to 13C  are explanatory views illustrating a charging roller of Example 3. 
         FIG. 14  is a deployed layout drawing illustrating a metallic plate of Example 1. 
         FIGS. 15A and 15B  are process layout drawings illustrating a normal feed press work for forming the metallic plate into a cylindrical shape. 
         FIG. 16  is a detailed drawing illustrating an end portion of a shaft portion of the charging roller of Example 1. 
         FIG. 17  is a detailed drawing illustrating the end portion of the shaft portion of the charging roller of another form of Example 1. 
         FIG. 18A  is an enlarged view illustrating the metallic plate of Example 1. 
         FIG. 18B  is an enlarged view illustrating the metallic plate of a comparative example. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Example 1 
     An embodiment of this disclosure will be described with reference to the drawings in detail below. A direction of a rotational axis of an electrophotographic photosensitive drum is defined as a longitudinal direction. 
     In the longitudinal direction, a side where the electrophotographic photosensitive drum receives a drive force from an image forming apparatus body is defined as a driving side (on a drive force receiving portion  63   a  side in  FIG. 6 ), and a side opposite thereto is defined as a non-driving side. 
     With reference to  FIG. 2 ,  FIG. 3 , and  FIG. 4 , a general configuration and an image forming process will be described. 
       FIG. 2  is a cross-sectional view illustrating the image forming apparatus body (hereinafter, referred to as an apparatus body A) of the electrophotographic image forming apparatus and a process cartridge (hereinafter, referred to as a cartridge B) as an embodiment of this disclosure. 
       FIG. 3  is a cross-sectional view illustrating the cartridge B. 
     Here, the apparatus body A of the electrophotographic image forming apparatus is a portion of the electrophotographic image forming apparatus from which the cartridge B is removed. 
       FIG. 4  is a perspective view illustrating the image forming apparatus body A and the process cartridge B. 
     General Configuration of Electrophotographic Image Forming Apparatus 
     In  FIG. 2  and  FIG. 4 , the electrophotographic image forming apparatus is a laser beam printer using an electrophotographic technology in which the cartridge B is demountably mounted on the apparatus body A. When the cartridge B is mounted on the apparatus body A, an exposure unit  3  (laser scanner unit) is arranged in an upper side of the cartridge B. 
     Also, a sheet tray  4  in which a recording medium (hereinafter, referred to as a sheet material P) as a target of image formation (a medium on which an image is to be recorded) is stored on a lower side of the cartridge B is arranged. 
     In addition, the apparatus body A includes a pickup roller  5   a,  a feed roller pair  5   b,  a conveyance roller pair  5   c,  a conveyance guide  6 , a transfer roller  7 , a conveyance guide  8 , a fixing unit  9 , a discharging roller pair  10 , and a discharge tray  11  arranged in sequence along a direction of conveyance of the sheet material P. The fixing unit  9  includes a heat roller  9   a  and a pressurizing roller  9   b.    
     Image Forming Process 
     Subsequently, the image forming process is described schematically. On the basis of a print start signal, the electrophotographic photosensitive drum (hereinafter, referred to as a drum  62 ) is driven to rotate at a predetermined circumferential velocity (process speed) in a direction indicated by an arrow R. 
     A charging roller  66  to which a bias voltage is applied, comes into contact with an outer peripheral surface of the drum  62 , and charges the outer peripheral surface of the drum  62  uniformly and evenly. The charging roller  66  is a conductive roller member (conductive roller). 
     The exposure unit  3  outputs a laser beam L in accordance with image information. The laser beam L passes through an exposure window portion  74  on an upper surface of the cartridge B, and scans and exposes the outer peripheral surface of the drum  62 . 
     Accordingly, an electrostatic latent image corresponding to the image information is formed on the outer peripheral surface of the drum  62 . 
     In contrast, as illustrated in  FIG. 3 , in a developing device unit  20  as a developing apparatus, toner T in a toner chamber  29  is stirred and conveyed by a rotation of a conveyance member  43  and fed to a toner supply chamber  28 . The toner T is born on a surface of a developing roller  32  by a magnetic force of a magnet roller  34  (fixed magnet). The toner T is controlled in layer thickness on a peripheral surface of the developing roller  32  while being charged by friction by a developing blade  42 . 
     The toner T is transferred to the drum  62  in accordance with the electrostatic latent image, and is visualized as a toner image. The drum  62  is an image bearing member configured to bear images (a toner image, a developer image) on the surface thereof. The developing roller  32  is a developer bearing member configured to bear developer (toner) for developing a latent image formed on the drum  62  as a toner image (developer image). 
     As illustrated in  FIG. 2 , the sheet material P stored in a lower portion of the apparatus body A is fed from the sheet tray  4  by the pickup roller  5   a,  the feed roller pair  5   b,  and the conveyance roller pair  5   c  at the same timing as outputting of the laser beam L. The pickup roller  5   a,  the feed roller pair  5   b,  and the conveyance roller pair  5   c  are a conveyance mechanism configured to convey the recording medium (sheet material P). 
     Then, the sheet material P passes through the conveyance guide  6 , and is fed to a transfer position between the drum  62  and the transfer roller  7 . At this transfer position, the toner images are transferred in sequence from the drum  62  to the sheet material P. 
     The sheet material P to which the toner image is transferred is separated from the drum  62  and conveyed to the fixing unit  9  along the conveyance guide  8 . The sheet material P then passes through a nip portion between the heat roller  9   a  and the pressurizing roller  9   b  which constitute part of the fixing unit  9 . 
     At the nip portion, pressurization and heat-fixation are performed, so that the toner image is fixed to the sheet material P. The sheet material P subjected to the fixation of the toner image is conveyed to the discharging roller pair  10 , and is discharged to the discharge tray  11 . 
     In contrast, as illustrated in  FIG. 3 , residual toner on the outer peripheral surface of the drum  62  after the transfer is removed by a cleaning blade  77 , and the drum  62  is used for the image forming process again. The toner removed from the drum  62  is stored in a waste toner chamber  71   b  of a cleaning unit  60 . 
     In the above, the charging roller  66 , the developing roller  32 , and the cleaning blade  77  are process devices configured to act on the drum  62 . 
     General Configuration of Cartridge 
     Subsequently, a general configuration of the cartridge B will be described with reference to  FIG. 3  and  FIG. 5 . 
       FIG. 5  is an explanatory perspective view illustrating a configuration of the cartridge B. 
     The cartridge B includes the cleaning unit  60  and the developing device unit  20  combined with each other. 
     The cleaning unit  60  includes a cleaning frame member  71 , the drum  62 , the charging roller  66 , and the cleaning blade  77 . 
     In contrast, the developing device unit  20  includes a bottom member  22 , a developer container  23 , a first side member  26 L, a second side member  26 R, the developing blade  42 , the developing roller  32 , the magnet roller  34 , the conveyance member  43 , the toner T, and biasing members  46 . 
     The cartridge B is formed by coupling the cleaning unit  60  and the developing device unit  20  with a coupling member  75  so as to be rotatable with each other. 
     Specifically, rotary hole  26   b L and  26   b R, extending in parallel with the developing roller  32 , are formed at distal ends of arm portions  26   a L and  26   a R formed on the first side member  26 L and the second side member  26 R provided on the developing device unit  20  at both end portions thereof in a longitudinal direction (an axial direction of the developing roller  32 ). 
     Fitting holes  71   a  for fitting coupling members  75  are formed at both end portions of the cleaning frame member  71  in a longitudinal direction. 
     The arm portion  26   a L and  26   a R are aligned with predetermined positions of the cleaning frame member  71  to insert the coupling member  75  into the rotary holes  26   b L and  26   b R and the fitting hole  71   a.  Accordingly, the cleaning unit  60  and the developing device unit  20  are coupled so as to be rotatable about the coupling member  75  as a center. 
     At this time, the biasing members  46  mounted at roots of the arm portions  26   a L and  26   a R abut against the cleaning frame member  71 , thereby biasing the developing device unit  20  toward the cleaning unit  60  about the coupling members  75  as a center of rotation. 
     Accordingly, the developing roller  32  is reliably pressed in the direction of the drum  62 . 
     With distance retaining members (which are not illustrated) mounted on both end portions of the developing roller  32 , the developing roller  32  is retained at a predetermined distance from the drum  62 . 
     Configuration of Cleaning Unit 
     Subsequently, a configuration of the cleaning unit  60  will be described with reference to  FIG. 6 ,  FIGS. 7A and 7B , and  FIG. 8 . 
       FIG. 6  is an explanatory perspective view illustrating the configuration of the cleaning unit  60 . 
       FIG. 7A  is an explanatory front view illustrating the configuration of the cleaning unit  60 .  FIG. 7B  is a drawing of a supporting portion of the charging roller  66  viewed in a direction indicated by an arrow H.  FIG. 8  is a cross-sectional view illustrating a process of formation of a shaft portion  66   a  from a plate into a cylindrical shape. 
     The cleaning blade  77  includes a supporting member  77   a  formed of a plate and a resilient member  77   b  formed of a resilient material such as urethane rubber, and is arranged at a predetermined position in the cleaning frame member  71  by fixing both ends of the supporting member  77   a  with screws  91 . 
     Resilient member  77   b  comes into abutment with the drum  62 , and removes residual toner from the outer peripheral surface of the drum  62 . The removed toner is stored in a waste toner chamber  71   b  ( FIG. 3 ) of the cleaning unit  60 . 
     A first seal member  82 , a second seal member  83 , a third seal member  84 , and a fourth seal member  85  are fixed to predetermined positions of the cleaning frame member  71  with double-sided tape and the like. 
     The first seal member  82  is provided across the longitudinal direction and prevents wasted toner from leaking from a back side of the supporting member  77   a  of the cleaning blade  77 . 
     The second seal member  83  prevents wasted toner from leaking from both ends of the resilient member  77   b  of the cleaning blade  77  in the longitudinal direction. 
     The third seal member  84  wipes adhered substances such as toner on the drum  62  while preventing the wasted toner from the leaking out from the both ends of the resilient member  77   b  of the cleaning blade  77  in the longitudinal direction. 
     The fourth seal member  85  is provided in contact with the drum  62  across the longitudinal direction, and prevents the wasted toner from leaking out from the upstream side of the drum  62  in a direction of rotation with respect to the cleaning blade  77 . 
     An electrode plate  81 , a biasing member  68 , and charging roller bearings  67 L and  67 R are mounted on the cleaning frame member  71 . 
     A metallic shaft (hereinafter, referred to as the shaft portion  66   a ) of the charging roller  66  is fitted to the charging roller bearings  67 L and  67 R. 
     The charging roller  66  is biased by the biasing member  68  with respect to the drum  62 , and is rotatably supported by the charging roller bearings (bearing portions)  67 L and  67 R. The biasing member  68  is driven to rotate in association with the rotation of the drum  62 . In other words, the charging roller  66  is supported by the cleaning unit  60  via the charging roller bearings  67  ( 67 L and  67 R). The cleaning unit  60  is a roller supporting mechanism configured to support the charging roller  66 . 
     The charging roller  66  is configured by covering the hollow shaft portion  66   a  with a conductive resilient layer (covering layer, covering member)  66   b  over the entire area in the longitudinal direction except for both ends. The shaft portion  66   a  is a cylindrical portion having a cylindrical shape (roller shape). The shaft portion  66   a  is a metallic shaft formed of a metal and having conductivity. 
     The resilient layer  66   b  and the shaft portion  66   a  are joined by an adhesive agent. The shaft portion  66   a  is a member formed by shaping a conductive metallic plate such as a stainless steel plate or a galvanized steel plate into a cylindrical shape by a press work. 
     Here, using the hollow shaft portion  66   a  formed by a press work is used is to achieve a weight reduction of the charging roller  66 , the cartridge having the charging roller  66 , and the image forming apparatus by reducing the weight of the shaft portion  66   a.  If the shaft portion  66   a  can be formed by processing the metallic plate, a cost reduction of the shaft portion  66   a  is achieved. 
     The electrode plate  81 , the biasing member  68 , the charging roller bearing  67 L, and the shaft portion  66   a  have conductivity. The electrode plate  81  is in contact with a power feeding portion (which is not illustrated) of the apparatus body A. With these members using as a power feeding route, power is supplied to the charging roller  66 . 
     The drum  62  is coupled integrally with a flange  64  and a flange  63  to achieve an electrophotographic photosensitive drum unit (hereinafter, referred to as a drum unit  61 ). This coupling method uses caulking, adhesion, welding, and the like. 
     An earth contact point and the like (which is not illustrated) is coupled to the flange  64 . The flange  63  includes a drive force receiving portion  63   a  configured to receive a drive force from the apparatus body A and a flange gear portion  63   b  configured to transmit the drive force to the developing roller  32 . 
     A bearing member  76  is integrally fixed to a driving side of the cleaning frame member  71  with a screw  90 , and a drum shaft  78  is fixed to a non-driving side of the cleaning frame member  71  by press fitting. 
     The bearing member  76  fits the flange  63 , and the drum shaft  78  fits a hole  64   a  of the flange  64 . 
     Accordingly, the drum unit  61  is rotatably supported by the cleaning frame member  71 . 
     A protecting member  79  is rotatably supported by the cleaning frame member  71  so that protection (light-shielding) of the drum  62  and exposure are allowed. 
     A biasing member  80  is mounted on a shaft portion  79   a R on a driving side of the protecting member  79 , and biases the protecting member  79  in a direction to protect the drum  62 . 
     A shaft portion  79   a L on a non-driving side and the shaft portion  79   a R on the driving side of the protecting member  79  fit bearing portions  71   c L and  71   c R of the cleaning frame member  71 . 
     Configuration of Charging Roller 
     A configuration of the charging roller  66  will be described with reference to  FIG. 1 ,  FIG. 8 ,  FIGS. 9A and 9B ,  FIG. 10 ,  FIGS. 11A and 11B ,  FIG. 14 ,  FIGS. 15A and 15B ,  FIG. 16 ,  FIG. 17 , and  FIGS. 18A and 18B . 
       FIG. 1  is a perspective view illustrating the charging roller  66  and the charging roller bearing  67 L.  FIG. 9A  is a perspective view illustrating the shaft portion  66   a .  FIG. 9B  is a detailed drawing illustrating an end portion  66   d  of the shaft portion  66   a  of the charging roller  66 . 
       FIG. 10  is a perspective view illustrating the charging roller  66  and the charging roller bearing  67 L as the comparative example with respect to this example.  FIGS. 11A and 11B  are detailed drawings illustrating the end portion  66   d  of the shaft portion  66   a  of the charging roller  66 .  FIG. 14  is a developed layout drawing illustrating the shaft portion  66   a.    
       FIG. 15A  is a perspective view illustrating a process layout of a normal feed press work for forming the metallic plate into a cylindrical shape.  FIG. 15B  is a plan view illustrating the process layout of the normal feed press work for forming the metallic plate into the cylindrical shape. 
       FIG. 16  is a detailed drawing illustrating an end portion of the shaft portion  66   a  of the charging roller  66  of Example 1.  FIG. 17  is a detailed drawing illustrating the end portion of the shaft portion  66   a  of the charging roller of another form of Example 1.  FIG. 18A  is a partially enlarged view illustrating the metallic plate. 
     The shaft portion  66   a  of the charging roller  66  as illustrated in  FIG. 8  is a member formed by shaping into a cylindrical shape in outer diameter by pressing a conductive metallic plate  66   a   1 , and includes a mating portion  66   c  of the metallic plate in an axial direction C of the shaft portion  66   a.  The metallic plate  66   a   1  is bent so that a long side  66   y   1  at one end portion (first end portion) and a long side  66   y   2  at the other end portion (second end portion) so as to oppose each other and is formed into a cylindrical shape (roller shape). An area in which the long side  66   y   1  at the one end portion and the long side  66   y   2  at the other end portion oppose (opposing area) corresponds to the mating portion  66   c  in the shaft portion  66   a.  Detailed description will be given later. 
     Here, in this example, an outer diameter of the shaft portion  66   a  is φ6 mm, the entire length in the axial direction C is 252.5 mm. An outer diameter and the entire length required in terms of function may be selected as needed. 
     With the provision of a projection and depression area  66   c   1  including a plurality of depressions and projections on the mating portion  66   c,  a desired strength is provided on the shaft portion  66   a.  The larger the number of projections and depressions, the stronger the shaft portion becomes, which is preferable. However, the strength required in terms of the function of the product may be selected as needed. 
     Here, the mating portion  66   c  has the projection and depression area  66   c   1  and straight areas  66   c   3  as illustrated in  FIG. 9A  and  FIG. 9B . The straight areas  66   c   3  are provided on both sides (both end sides) of the shaft portion  66   a  in the axial direction C, and the projection and depression area  66   c   1  is provided between two of the straight areas  66   c   3 . 
     As illustrated in  FIG. 9B , in a vertical direction D with respect to the axial direction C of the shaft portion  66   a,  a relationship between a projecting amount (=depressing amount) E of the projection and depression area  66   c   1  of the mating portion  66   c  and a projecting amount F of the straight areas  66   c   3  is E&gt;F. 
     In this example, the value E of the shaft portion is 2 mm, and the value F is half the value E, which is 1 mm (F=E/2). However, the value E may be a desired value selected in a range from 1 to 3 mm, and the value F may be selected in accordance with the value E. 
     Here, as illustrated in  FIG. 1 , corner portions (portions at recessed corners of the depressions and portions at projecting corners of the projections)  66   c   2  of the projection and depression area  66   c   1  are arranged so as to be covered entirely with the resilient layer (covering member)  66   b.  With this arrangement, the corner portions  66   c   2  are not exposed to the end portions  66   d  of the shaft portions  66   a  which is not covered with the resilient layer  66   b.  Therefore, sliding portions  67   a  of the charging roller bearings  67 L and  67 R and the corner portions  66   c   2  do not overlap with each other. 
     If the corner portions  66   c   2  come into contact with the charging roller bearing  67  ( 67 R and  67 L), the corner portions  66   c   2  are caught by the charging roller  66 , which may cause abrasion of the charging roller bearing  67  or prevention of smooth rotation of the charging roller  66 . Therefore, in the configuration of this example, the corner portions  66   c   2  are not exposed. 
     Description of Metallic Plate  66   a   1   
       FIG. 14  is a plan view illustrating the metallic plate  66   a   1  as a base material of the shaft portion  66   a.  In order to manufacture the shaft portion  66   a,  as illustrated in  FIG. 14 , the metallic plate  66   a   1  having a width larger than the entire length in the axial direction C such as a cold rolling steel plate, a galvanized steel plate, or a stainless steel plate having a thickness on the order of 0.6 mm is used as a row material. The metallic plate is pressed (punched) to form the following portions. 
     In other words, (1) frame portions  66   x   1  extending along the direction of conveyance of the metallic plate, (2) belt shaped flat plates (portions formed into a cylindrical shape, cylindrical shaped portions)  66   a   2  extending in a direction which intersects the direction of conveyance, and (3) connecting portions  66   a   3  configured to connect the frame portions  66   x   1  and the cylindrical shaped portions  66   a   2 . Areas combining the frame portions  66   x   1  and the connecting portions  66   a   3  are referred to specifically as cross pieces  66   a   4 . 
     In this embodiment, the cylindrical shaped portions  66   a   2  have a substantially rectangular shape. The short sides  66   x   3  that an end surface of the shaft portion of the charging roller extend substantially parallel to the direction of conveyance of the metallic plate  66   a   1 . In contrast, long sides  66   y  of the cylindrical shaped portion  66   a   2  are substantially orthogonal to the direction of conveyance. The long sides  66   y  are provided with two sides ( 66   y   1  and  66   y   2 ) having depressions and projections respectively so as to form the projection and depression area  66   c   1  of the shaft portion  66   a  by punching the metallic plate  66   a   1 . 
     The numbers of the depressions and the projections on the long sides  66   y  ( 66   y   1  and  66   y   2 ) satisfy the following relationship. In other words, the number of the projections provided on the long side (one end portion of the cylindrical shaped portion  66   a   2 )  66   y   1  and the number of the projections provided on the long side (the other end portion of the cylindrical shaped portion  66   a   2 )  66   y   2  are equivalent (the same number). 
     Therefore, the number of the depressions of the long side  66   y   1  that engage the projections of the long side  66   y   2  and the number of the depressions of the long side  66   y   2  that engage the projections of the long side  66   y   1  are also equivalent. 
     In  FIG. 14 , the number of the projections provided on the long side  66   y   1  is 15, and the number of the projections provided on the long side  66   y   2  is 15. (In other words, the number of the depressions provided on the long side  66   y   1  and the long side  66   y   2  are 15 respectively). 
     Straight portions adjacent to the connecting portions  66   a   3  and forming the straight areas  66   c   3  (see  FIGS. 9A and 9B ) have the same shape and dimensions as the long side  66   y   1  and the long side  66   y   2 . 
     In this manner, in this example, the cylindrical shaped portion  66   a   2  and the connecting portions  66   a   3  are punched so as to have a shape close to symmetry with respect to a center line CL passing through a center of the cylindrical shaped portion  66   a   2 . 
     More specifically, the connecting portions  66   a   3  are positioned on the center line CL, and the volumes of the cylindrical shaped portion  66   a   2  on both sides of the center line CL are substantially the same (substantially equivalent). 
     The connecting portions  66   a   3  here are used as reference positions in the bending process to form the cylindrical shaped portion  66   a   2  into a cylindrical shape. In other words, the cylindrical shaped portion  66   a   2  is bent so that a pair of the connecting portions  66   a   3  provided on both ends of the cylindrical shaped portion  66   a   2  come to an intermediate position of bending. 
     The frame portions  66   x   1  are provided with positioning holes  66   x   2  on the center line CL. The positioning holes  66   x   2  are used for positioning the metallic plate  66   a   1  when conveying the metallic plate  66   a   1 . 
       FIGS. 15A and 15B  are drawings of the metallic plate  66   a   1  illustrating a process in which the metallic plate  66   a   1  is bent into a cylindrical shape by a press work in sequence and formed into the shaft portion  66   a  of the charging roller  66 . On the basis of  FIGS. 15A and 15B , a method of manufacturing the shaft portion  66   a  has been described with an example of the normal feeding process, which is a general method of press work. 
     By pressing the metallic plate  66   a   1  conveyed by the cross pieces  66   a   4  repeatedly, the cylindrical shaped portion  66   a   2  is punched and subsequently, is formed into the cylindrical shape in sequence from step to step. 
     As described above, when pressing and bending a center portion of the cylindrical shaped portion  66   a   2 , the connecting portion  66   a   3  is used as the reference position of bending. 
     The number of projections provided on the long side  66   y   1  and the number of projections of the long side  66   y   2  are the same. More specifically, all of the number of the depressions provided on the long side  66   y   1 , the number of the projections provided on the long side  66   y   1 , the number of the depressions provided on the long side  66   y   2 , and the number of the projections provided on the long side  66   y   2  are the same. 
     Since the number of the projections (depressions) are uniform (the same number) on the long sides  66   y   1  and  66   y   2 , the cylindrical shaped portion  66   a   2  may be bent evenly on the left side and the right side (lateral symmetry) with reference to the connecting portions  66   a   3 . 
     Since bending is performed evenly on the left side and the right side with reference to the connecting portions  66   a   3 , the shaft portion  66   a  is formed substantially parallel with respect to the center axis CL of the cylindrical shaped portion  66   a   2 . Therefore, when bending the cylindrical shaped portion  66   a   2 , the cylindrical shaped portion  66   a   2  is prevented from easily inclining and rotating. The cylindrical shaped portion  66   a   2  may be bent with high degree of accuracy and formed into a cylindrical shape. 
     In this example, the straight areas  66   c   3  of the mating portion  66   c  extend parallel to an axial line of the shaft portion  66   a  (see  FIG. 1 ). However, as the configuration illustrated in  FIGS. 11A and 11B , the straight areas  66   c   3  may be arranged obliquely with respect to the axial line. However, the straight areas  66   c   3  are preferably arranged in parallel as illustrated in  FIG. 1  in order to improve a symmetric property of the cylindrical shaped portion  66   a   2  (see  FIG. 14 ) and improve the degree of accuracy of the shaft portion  66   a.    
     Subsequently, a device of layout of the straight areas  66   c   3  (see  FIGS. 9A and 9B ) on the shaft portion  66   a  will be described in detail with reference to  FIG. 18A .  FIGS. 18A and 18B  are partial enlarged views illustrating the metallic plate  66   a   1  before being bent (enlarged view of the area corresponding to the end portion of the shaft portion). 
     The metallic plate  66   a   1  includes the long side  66   y   1  at one end portion thereof, and the long side  66   y   2  at the other end portion thereof. The metallic plate  66   a   1  is bent so that the long side  66   y   1  and the long side  66   y   2  oppose each other and formed into a cylindrical shape as described above. The mating portion  66   c  illustrated in  FIG. 8  is an opposing area formed by the long side  66   y   1  and the long side  66   y   2  opposing each other. 
     The long side  66   y   1  includes straight portions  66   y   11  located at ends, a plurality of projections  66   y   13 , and a plurality of depressions  66   y   14 . 
     In the same manner, the long side  66   y   2  includes straight portions  66   y   21  located at ends, a plurality of projections  66   y   23  and a plurality of depressions  66   y   24 . 
     The projections  66   y   13 , the depressions  66   y   24 , the projections  66   y   23 , and the depressions  66   y   14  provided on the long side  66   y   1  and the long side  66   y   2  respectively correspond to an projection and depression area  66   c   1  (see  FIGS. 9A and 9B ) of the shaft portion  66   a.  In other words, the projection and depression area  66   c   1  is an area in which the plurality of projections  66   y   13  of the long side  66   y   1  and the plurality of projections  66   y   23  of the long side  66   y   2  are arranged alternately. 
     In the same manner, an area in which the straight portions  66   y   11  provided on the long side  66   y   1  and the straight portions  66   y   21  provided on the long side  66   y   2  oppose each other correspond to a straight area  66   c   3  (see  FIGS. 9A and 9B ) of the shaft portion  66   a.    
     The straight portions  66   y   11 ,  66   y   12 ,  66   y   21 , and  66   y   22  which correspond to the straight area  66   c   3  (see  FIGS. 9A and 9B ) are provided in parallel to a center line C 1  of the cylindrical shaped portion  66   a   2 . 
     The positions of the straight portion  66   y   11  and the straight portion  66   y   12  are configured so as to extend in substantially symmetry with respect to the center line C 1  (a line so as to satisfy relationships D2=D2′, and D3=D3′) passing through the center of the cylindrical shaped portion  66   a   2  as follows. 
     A projecting amount F of the projections  66   y   13  projecting with respect to the long side  66   y   1  adjacent thereto is smaller than a projecting amount E of the projections  66   y   13  projecting with respect to the depressions  66   y   14  adjacent thereto (F&lt;E). In the same manner, a depression amount F of the depressions  66   y   24  depressed with respect to the straight portion  66   y   12  adjacent thereto is smaller than a depressing amount E of the depressions  66   y   24  depressed with respect to the projections  66   y   23  adjacent thereto. 
     In this configuration, a distance D 1  from the center line C 1  to the straight portion  66   y   11  and a distance D 1 ′ from the center line C 1  to the straight portion  66   y   12  become close values (substantially the same values). In other words, the arrangement of the straight portions  66   y   11  and  66   y   21  is symmetric with respect to the center line C 1 , and hence the degree of accuracy of processing when bending the cylindrical shaped portion  66   a   2  is stabilized. 
     In other words, if an attempt is made to bend the cylindrical shaped portion  66   a   2  by a die when the cylindrical shaped portion  66   a   2  is not symmetry, timing of coming into contact with the die may differ from each other between one side and the other side of the cylindrical shaped portion  66   a   2  with respect to the center line C 1 . If the cylindrical shaped portion  66   a   2  comes into contact with the die in such a case, the cylindrical shaped portion  66   a   2  may move with respect to the die. 
     In contrast, if the cylindrical shaped portion  66   a   2  is close to symmetry with respect to the center line C 1 , laterally uniform (lateral symmetry) bending with respect to the center line C 1  is achieved. 
     In comparison, a configuration in which the arrangement of the straight portion is different from this example in the metallic plate (comparative example) is illustrated in  FIG. 18B . A configuration of the charging roller  66  manufactured from the metallic plate illustrated in  FIG. 18B  is illustrated in  FIG. 10 . 
     In the configuration illustrated in  FIG. 18B , which is the comparative example, a straight portion  66   y   15  projects with respect to the depressions  66   y   14  by the projecting amount E. A straight portion  66   y   25  is depressed with respect to the projections  66   y   23  by the depressing amount E. Consequently, a distance D 5  from the center line C 1  to the straight portion  66   y   25  is smaller than a distance D 4  from the center line C 1  to the straight portion  66   y   15  (D4&gt;D5). 
     D4−D5=E is satisfied. 
     Consequently, in the comparative example in FIG.  18 B, a symmetric property of the cylindrical shaped portion  66   a   2  is lost and hence the balance cannot be kept easily at the time of processing. In other words, when a force is applied when bending the metallic plate  66   a   1 , the degree of accuracy of processing may be lowered due to the inclination of the cylindrical shaped portion  66   a   2 . 
     Therefore, instead of the configuration as described in comparative example ( FIG. 18B ), it is preferable to keep a stress balance at the time of processing by arranging the straight portions  66   y   11  and the straight portion  66   y   12  at positions close to symmetry as described in this example ( FIG. 18A ). 
     In the comparative example illustrated in  FIG. 10 , the ratio of surface areas between the depressions and the projections is different at the end portions of the shaft portion  66   a.  However, in view of improvement of the degree of accuracy of processing, it is preferable to keep the ratio of the surface areas between the depressions and the projections as uniform as possible. 
     Therefore, in the configuration of this example, as illustrated in  FIG. 14 , in the cylindrical shaped portion  66   a   2 , a sum of the surface areas of the projections  66   y   13  provided on the long side  66   y   1  and a sum of the surface areas of the projections  66   y   23  provided on the long side  66   y   2  are substantially equal. The expression “substantially equal” means that the sum of the surface areas of the projections  66   y   23  falls within ±4% of the sum of the surface areas of the projections  66   y   13 . 
     A surface area S of the projection  66   y   13  is a value obtained by multiplying a width G 1  (see  FIG. 18A ) of the projection  66   y   13  by the projecting amount E of the projections  66   y   13  (S=G1×E). The sum of the surface areas of the projections  66   y   13  is a sum of the surface areas of the respective projections  66   y   13 . 
     The sum of the surface area of the projections  66   y   23  is obtained in the same manner. 
     In this manner, if the cylindrical shaped portion  66   a   2  is formed in symmetry with respect to the center line C 1 , the posture of the metallic plate  66   a   1  is stabilized when the cylindrical shaped portion  66   a   2  is processed, and the degree of accuracy of processing is improved. The dimensional accuracy of the shaft portion  66   a  in the radial and the longitudinal directions is stabilized. By using the shaft portion  66   a  with high dimensional accuracy as described above is used as the charging roller, a charging roller having a desirable charging function (charging performance) may be obtained. 
     In other words, if the accuracy of processing of the metallic shaft is improved, a cross section of the charging roller may be brought to be closer to an accurate circle. With the charging roller obtained in this manner, a photosensitive member may be charged uniformly at the time of rotation. 
     What is the most preferable as the shape of the cylindrical shaped portion  66   a   2  is the case where the projecting amount E of the projections become substantially equal among the projections  66   y   13  and the projections  66   y   23 , and in addition, the value F becomes a substantially half the value E. 
     The expression “all of the projecting amounts E of the projections are substantially equal” means that when an average of the projecting amounts of the projections ( 66   y   13  and  66   y   23 ) is calculated, the projecting amounts of the respective projections with respect to the average value fall within a variation range of ±4% of the diameter of the shaft portion  66   a.    
     Suppose that the diameter of the shaft portion  66   a  is 6.00 mm, 4% thereof is 0.24 mm. If the average value of the projecting amounts of the projections ( 66   y   13  and  66   y   23 ) is 2.00 mm, the projecting amounts of the respective projections  66   y   13  and  66   y   23  may fall within a range of 2.00±0.24 mm. 
     The expression “the value of F becomes a substantially half the value of E” means that the dimension of the actual F falls within the variation range of ±4% of the diameter of the shaft portion  66   a  with respect to the value F obtained by F=E/2. 
     Suppose that the diameter of the shaft portion  66   a  is 6.00 mm, 4% thereof is 0.24 mm. If the projecting amount E of the projections  66   y   13  adjacent to the straight portion  66   y   11  is 2.00 mm, the depression amount F of the straight portion  66   y   11  with respect to the projections  66   y   13  may fall within a range of 1.00±0.24 mm. 
     After the cylindrical shaped portion  66   a   2  has become the cylindrical shape in the metallic plate  66   a   1  and shaping is completed, the cylindrical shaped portion  66   a   2  is divided from the cross pieces  66   a   4  by cutting the connecting portions  66   a   3  in the metallic plate and a single shaft portion  66   a  is achieved. 
     In this case, as illustrated in  FIG. 1 , the connecting portions  66   a   3  remain on both end surfaces of the shaft portion  66   a,  and become projections (projecting portion)  66   k  projecting from the end surfaces of the shaft portion (cylindrical portion)  66   a  of the charging roller outward in the axial direction. 
     When viewing a cross section (cross section perpendicular to the axial line) of the shaft portion  66   a  manufactured in this manner, as illustrated in  FIG. 8 , a root portion of the projection  66   k  as a remaining portion of the connecting portions  66   a   3  comes to an opposite side of the straight areas  66   c   3  of a mating portion  66   c  with respect to a center (the axial line of the shaft portion) CL of the shaft portion  66   a.    
     In other words, when viewing the shaft portion  66   a  from the axial direction of the shaft portion  66   a,  a straight line H connecting the straight areas  66   c   3  and the center (the axial line of the shaft portion) CL passes the projection  66   k.    
     Characteristic of Projection  66   k    
     Here, in this example, connecting surfaces  66   k   2  connecting an end surface  66   a   5  of the shaft portion of the charging roller and a projecting surface (end surface of the projection  66   k )  66   k   1  are formed into inclined surfaces as illustrated in  FIG. 16 . 
     Accordingly, even though the connecting surfaces  66   k   2  come into contact with the charging roller bearing (bearing portion)  67  when the charging roller  66  rotates, abrasion of the charging roller bearing  67  may be reduced. Here, in this example, an outer diameter of the shaft portion  66   a  is (φ6 mm, the entire length in the axial direction C is 252.5 mm. However, the outer diameter and the entire length required in terms of function may be selected as needed. 
     A height  66 L of the projecting surfaces from the end surface of the cylinder is 0.2 mm, a width  66 M of the projecting surfaces is 1.5 to 2.5 mm, and an angle  66 N of the inclined surfaces is 45 degrees. 
     However, these values may be selected as needed within a range of minimum dimensions which do not cause any problem in terms of manufacture. 
     As illustrated in  FIG. 17 , the connecting surfaces  66   k   2  configured to continuously connect the end surface  66   a   5  of the charging roller shaft portion and the projecting surface  66   k   1  projecting from the end surface of the charging roller shaft portion may be a combination of an inclined surface and a rounded surface. 
     In this case, the angle  66 N of the inclined surface was set to 45 degrees and a dimension  66 R of the rounded surface was R0.2 mm. 
     However, these values may be selected as needed within a range of dimensions which do not cause any problem in terms of manufacture. 
     Dimensions of  66 M,  66 N, and  66 R are dimensions when cutting the metallic plate  66   a   1  before being bent into a cylindrical shape, and may be changed to some extent at the time of bending into the cylindrical shape. The projection  66   k  may be provided only at one end of the direction of axial line C depending on the manufacturing method. 
     The inclined surfaces are preferably provided on both sides when adding a processing load balance at the time of the press work, and the productivity when selecting the direction at the time of manufacture. However, it may be only one side on the front side in the direction of rotation of the charging roller. 
     Example 2 
     Referring now to  FIGS. 12A and 12B , a configuration of Example  2  will be described.  FIG. 12A  is an explanatory view illustrating the shaft portion  66   a.    FIG. 12B  is a detailed drawing illustrating the end portion of the charging roller  66 . 
     Example 2 is the same as Example 1 in those other than the arrangement of the projection and depression area  66   c   1  of the mating portion in the axial direction C of the charging roller  66  and the dimensional relationship of a width  66   g.    
     Here, a width  66   f  of each one of the projections and depressions (depressions or projections that form the projection and depression area)  66   c   4  of the projection and depression area  66   c   1  of the mating portion in the axial direction C of the charging roller  66  is set to be the same, and the projection and depression portion  66   c   4  are arranged equidistantly. 
     In this manner, by equalizing the width  66   f,  the same strength is achieved irrespective of the direction of twisting of the shaft portion  66   a  in a direction indicated by an arrow J. Accordingly, the direction of the axial direction C of the shaft does not need to be selected to use, the process of selecting the direction of the shaft is eliminated at the time of assembly, so that the cost may be reduced. 
     Example 3 
     Referring now to  FIGS. 13A to 13C , a configuration of Example 3 will be described.  FIG. 13A  is an explanatory view illustrating the shaft portion  66   a.    FIG. 13B  is an explanatory view illustrating the projection and depression area  66   c   1 .  FIG. 13C  is a detailed drawing illustrating the end portion of the charging roller  66 . 
     Example 3 is the same as Example 2 in those other than the dimensional relationship between the width  66   g  of the projection and depression area  66   c   1  of the mating portion and the width  66   h  of the mating portion at the end portion in the axial direction C of the charging roller  66 . 
     Configuration of Charging Roller 
     When defining the length and the width along the axial direction C of the charging roller  66 , the width  66   h  of the straight areas  66   c   3  of the mating portion is longer than the width  66   g  of one projection (depression) of the projection and depression area  66   c   1 . 
     In this example, the width  66   h  of the straight area  66   c   3  is set to 16 mm, and the width  66   g  of one projection (depression) of the projection and depression area  66   c   1  is set to 10.5 mm. 
     The width  66   h  of the straight area  66   c   3  may be set to 4 to 30 mm and the width  66   g  of one depression (projection) of the projection and depression area  66   c   4  may be set to a desired value, which is smaller than the width  66   h  of the straight area  66   c   3 . 
     A width  66   j  of the end portion  66   d  illustrated in  FIG. 13C  is preferably at least on the order of 4 mm in order to secure the width of sliding movement with respect to the bearings  67 L and  67 R in the case where this part is used for manufacture or in terms of the product function. Therefore, the width  66   h  of the straight area  66   c   3  is also preferable to be at least 4 mm. 
     The projection and depression area  66   c   1  of the mating portion is inclined at the angle F with respect to the direction D perpendicular to the axial direction C of the shaft portion  66   a.  It is because that the projection and depression area can easily be mated in terms of manufacture. In this example, the value F is set to 3 degrees. However, a desired angle in a range from 0 to 10 degrees may be selected. 
     The outer diameter of the shaft portion  66   a  is φ6 mm, an inner diameter is φ4.8 mm. However, the outer diameter may be set as desired between 3 to 15 mm, and the inner diameter may be set as desired in a range obtained by subtracting a thickness (0.3 to 2 mm) of the metallic plate  66   a   1  from the outer diameter. The inner diameter does not have to be a circular shape if it is not required in terms of function of the product and manufacture. 
     The projecting amount (=depressing amount) E of the projection and depression area  66   c   1  and the projecting amount F of the straight areas  66   c   3  are the same in dimensional relationship and the value E is 2 mm, and the value F is 1 mm (not illustrated). 
     A projecting corner R, and a recessed corner R may be provided as needed at the corner portions  66   c   2 . Although a configuration having no gap in engagement of the projections and the depressions at the mating portion is preferable in terms of strength, a gap may be partly generated. 
     By setting the width  66   h  of the straight area  66   c   3  to be larger than the width  66   g  of one projection and depression portion  66   c   4  in this manner, the length of the end portion  66   d  may be increased, so that a wide (long in the axial direction C) sliding portion with respect to the bearing may be secured. 
     In Examples 1 to 3 described above, an example in which the charging roller of this disclosure is assembled to the process cartridge has been described. However, this disclosure is not limited thereto, and the charging roller may be assembled to the image forming apparatus body in which a cartridge system is not employed. A configuration in which a minimum unit of only the charging roller can be mounted on and demounted from the process cartridge or the image forming apparatus body is also applicable. 
     In the respective examples, the charging roller  66  has been exemplified as the roller member. However, this disclosure is not limited thereto. For example, the roller member in which Examples are employed may be the developing roller  32 . 
     The charging roller  66  and the developing roller  32  are conductive rollers (having an electric resistance of approximately 10 8 Ω or lower), and are applied with a voltage at the time of image formation. However, the roller members having the shaft portion  66   a  of Examples are not limited thereto. The roller members to which the voltage is not applied at the time of image formation is also applicable, and a roller member covered with an insulative resilient member on an outer periphery of the shaft portion  66   a.    
     In the charging roller  66 , the shaft portion  66   a  is covered with the resilient member (the covering member). However, such a covering member is not essential. In other words, the simple term “roller member” in this disclosure may include the case of indicating the shaft portion  66   a  itself. 
     There may be the case where the shaft portion  66   a  itself is used as the roller member in the image forming apparatus, and there may be the case where the shaft portion  66   a  provided with the covering member such as the resilient member mounted on the outer periphery thereof is used as the roller member. 
     In conclusion, summary of the common advantages of Examples described thus far will be described below. Therefore, according to a configuration of respective Examples disclosed in this application, in the metallic shaft provided with the depressions and the projections of the metallic plate in the opposing area where the one end portion and the other end portion oppose each other, restraint of lowering of the dimensional accuracy of the metallic shaft is achieved. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary 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.