Abstract:
A developing device includes: a casing; a developing roller rotatably supported to the casing; a resiliently deformable blade supported to the casing and extending in an axial direction of the developing roller; and a regulation portion. The developing roller is rotatable in a rotational direction and to carry a layer of developer thereon. The blade has a first surface facing the developing roller. The regulation portion is configured to be in contact with the developing roller to regulate a thickness of the layer of the developer. The blade is formed with a through-hole to allow a material of the regulation portion to pass therethrough to form the regulation portion, the through-hole being exclusively formed in a central area in the axial direction assuming that the blade were divided into three areas each having an identical length in the axial direction with each other.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority from Japanese Patent Application No. 2012-011393 filed Jan. 23, 2012. The entire content of the priority application is incorporated herein by reference. 
       TECHNICAL FIELD 
       [0002]    The present invention relates to a developing device provided with a thickness regulation blade for regulating a thickness of developer. 
       BACKGROUND 
       [0003]    An electrophotographic image forming apparatus uses a developing device having a casing and a developing roller rotatably supported thereto. On a surface of the developing roller, a thin layer of toner having a uniform thickness needs to be formed. To this effect, the developing device is provided with a thickness regulation blade configured to be in contact with the surface of the developing roller for flattening toner provided thereon. 
         [0004]    There are two types of thickness regulation blades: “against-type” and “with-type.” Assuming that a thickness regulation blade has a base end fixed to the casing of the developing device and a distal end in contact with the surface of the developing roller, the thickness regulation blade is called as “against-type” when a direction from the base end toward the distal end is opposite to a rotation direction of the developing roller; and the thickness regulation blade is called as “with-type” when the direction from the base end toward the distal end is coincident with the rotation direction of the developing roller. There is also known a conventional thickness regulation blade having a portion provided with a regulating portion made of a rubber material, the portion being in contact with the surface of the developing roller. 
       SUMMARY 
       [0005]    Incidentally, in the “against-type” thickness regulation blade, contact pressure against the developing roller can be ensured relatively easy since the distal end of the thickness regulation blade is brought into pressure contact with the surface of the developing roller by friction between the distal end and the developing roller. On the other hand, in the “with-type” thickness regulation blade, contact pressure against the developing roller is harder to be obtained, compared to the “against-type”. 
         [0006]    In order to form the regulating portion in the “with-type” thickness regulation blade, a through-hole may be formed in a longitudinal end portion of the blade so that a material for forming the regulating portion can be injected through the through-hole to be provided on the blade. However, forming the through-hole in the blade may reduce rigidity of the blade (resiliency of the blade) partially in the vicinity of the through-hole, preventing the toner layer from being formed uniformly on the surface of the developing roller. 
         [0007]    It is an object of the present invention is to provide a developing device having a with-type thickness regulation blade that enables a toner layer to be formed uniformly on a surface of a developing roller. 
         [0008]    In order to achieve this and other objects of the present invention, there is provided a developing device including: a casing; a developing roller rotatably supported to the casing; a resiliently deformable blade supported to the casing; and a regulation portion. The developing roller defines an axis extending in an axial direction and is configured to rotate in a rotational direction and to carry a layer of developer thereon. The blade extends in the axial direction and has a first surface facing the developing roller. The regulation portion is configured to be in contact with the developing roller to regulate a thickness of the layer of the developer carried on the developing roller. The blade is formed with a through-hole to allow a material of the regulation portion to pass therethrough in order to form the regulation portion on the blade, the through-hole being exclusively formed in a central area in the axial direction assuming that the blade were divided into three areas each having a length in the axial direction equal to each other. 
         [0009]    According to another aspect of the present invention, there is provided a developing device including: a casing; a developing roller rotatably supported to the casing; a resiliently deformable blade supported to the casing; a regulation portion; and a reinforcing plate. The developing roller defines an axis extending in an axial direction and is configured to rotate in a rotational direction and to carry a layer of developer thereon. The blade has a first surface facing the developing roller and a second surface opposite to the first surface. The regulation portion is provided on the first surface at a downstream side thereof in the rotational direction, the regulation portion being configured to be in contact with the developing roller to regulate a thickness of the layer of the developer carried on the developing roller. The reinforcing plate is provided on the second surface for reinforcement of the blade. The reinforcing plate includes: a main body portion extending in the axial direction and positioned at an upstream side of the second surface in the rotational direction, the main body portion having axial end portions in the axial direction; and a reinforcing portion extending from each axial end portion toward a downstream side of the second surface in the rotational direction, the reinforcing portion having a length in the axial direction. The blade is formed with a through-hole to allow a material of the regulation portion to pass therethrough in order to form the regulation portion on the blade, the through-hole being exclusively formed within a region having a length in the axial direction identical to the length of the reinforcing portion in the axial direction. 
         [0010]    According to still another aspect of the present invention, there is provided a developing device including: a casing; a developing roller rotatably supported to the casing; a resiliently deformable blade supported to the casing; and a regulation portion. The developing roller defines an axis extending in an axial direction and is configured to rotate in a rotational direction and to carry a layer of developer thereon. The blade extends in the axial direction and has a first surface facing the developing roller. The regulation portion is configured to be in contact with the developing roller to regulate a thickness of the layer of the developer carried on the developing roller. The blade is formed with a through-hole and the through-hole is exclusively formed in a central area in the axial direction assuming that the blade were divided into three areas each having a length in the axial direction equal to each other. The regulation portion has a contact portion configured to regulate the thickness of the layer of the developer, and a flat plate portion integral with the contact portion and extending along the first surface and in contact therewith, the flat plate portion having a protruding part protruding into the through-hole. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The particular features and advantages of the invention as well as other objects will become apparent from the following description taken in connection with the accompanying drawings, in which: 
           [0012]      FIG. 1  is a cross-sectional view showing a general configuration of a color LED printer as an image forming apparatus incorporating a developing device according to an embodiment of the present invention; 
           [0013]      FIG. 2  is an enlarged cross-sectional view of the developing device of  FIG. 1  and in the vicinity thereof; 
           [0014]      FIG. 3  is an exploded perspective view of the developing device according to the embodiment, the developing device including a thickness regulation blade; 
           [0015]      FIG. 4  is a cross-sectional view of the thickness regulation blade according to the embodiment taken along a line IV-IV shown in  FIG. 3 ; 
           [0016]      FIG. 5  is a plan view of the thickness regulation blade according to the embodiment; 
           [0017]      FIG. 6  is a plan view of a thickness regulation blade according to a variation of the present invention; and 
           [0018]      FIG. 7  is a plan view showing positions of through-holes formed as examples of the embodiment and comparative examples thereof. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    An electro-photographic type color LED printer  1  as an example of an image forming apparatus incorporating a developing device according to an embodiment of the present invention will be described with reference to  FIGS. 1 to 7 . 
         [0020]    Throughout the specification, the terms “upward”, “downward”, “upper”, “lower”, “above”, “below”, “beneath”, “right”, “left”, “front”, “rear” and the like will be used assuming that the color LED printer  1  is disposed in an orientation in which it is intended to be used. In use, the color LED printer  1  is disposed as shown in  FIG. 1 . Specifically, in  FIG. 1 , a left side, a right side, a near side and a far side of the color LED printer  1  are referred to as a front side, a rear side, a right side and a left side, respectively. Further, the top and bottom of the color LED printer  1  will be based on a vertical direction in  FIG. 1 . 
       Overall Structure of Color LED Printer 
       [0021]    As illustrated in  FIG. 1 , a color LED printer  1  includes a main casing  10 , within which disposed are a sheet supply section  20  configured to supply sheets S, an image forming section  30  configured to form images onto the supplied sheets S, and a sheet discharge section  90  configured to discharge the image-formed sheets S. 
         [0022]    An upper cover  12  is provided at an upper end portion of the main casing  10 . The upper cover  12  is pivotally movable about a rear side thereof so as to open and close in a vertical direction. The upper cover  12  has an upper surface serving as a sheet discharge tray  13  onto which the sheets S discharged from the main casing  10  is placed. The upper cover  12  has a lower surface on which four holding portions  14  are provided each for pivotally movably supporting an LED unit  40  to be described later. 
         [0023]    The sheet supply section  20  is provided at a lower end portion of the main casing  10 . The sheet supply section  20  includes a sheet supply tray  21  configured to accommodate a stack of the sheets S, and a sheet supply mechanism  22  configured to supply each sheet S from the sheet supply tray  21  to the image forming section  30 . The sheets S accommodated in the sheet supply tray  21  are separated one by one by the sheet supply mechanism  22  and supplied to the image forming section  30 . 
         [0024]    The image forming section  30  includes four LED units  40 , four photosensitive units  50 , four developing devices  60 , a transfer unit  70 , and a fixing unit  80 . 
         [0025]    The LED units  40  are arranged in a front-rear direction below the upper cover  12 . The LED units  40  are disposed to face respective photosensitive drums  52  from above thereof when the upper cover  12  is closed. Each LED unit  40  includes a head portion  41  and a support portion  42  that supports the head portion  41 . The head portion  41  has a tip end portion on which a plurality of not-illustrated light-emitting portions (LEDs) is arranged in a left-right direction. The support portion  42  is attached to the upper cover  12  through the corresponding holding portion  14 . In the LED unit  40  having the above configuration, the light-emitting portions are configured to blink based on image data so as to expose a surface of a corresponding charged photosensitive drum  52 . 
         [0026]    The photosensitive units  50  are juxtaposed in the front-rear direction between the upper cover  12  and sheet supply section  20 . Each photosensitive unit  50  includes a drum casing  51 , a photosensitive drum  52 , and a charger  53 . 
         [0027]    The developing devices  60  are arrayed in the front-rear direction at substantially the same height as the LED units  40  in the vertical direction. The developing units  60  can be attached to/detached from the main casing  10  when the upper cover  12  is opened. Each developing unit  60  includes a casing  61 , a developing roller  62 , a supply roller  63 , a thickness regulation blade  100 , and a toner chamber  65  that accommodates toner as an example of developer (also see  FIG. 2 ). 
         [0028]    The transfer unit  70  is provided between the sheet supply section  20  and the photosensitive units  50  in the vertical direction. The transfer unit  70  includes a drive roller  71 , a follow roller  72 , an endless conveying belt  73 , four transfer rollers  74 , and a cleaning section  75 . The endless conveying belt  73  is mounted on the drive roller  71  and the follow roller  72  in a taut state, and has an outer peripheral surface configured to be in contact with each of the photosensitive drums  52 . The conveying belt  73  defines an internal space in which the four transfer rollers  74  are disposed such that the conveying belt  73  is nipped between each transfer roller  74  and corresponding photosensitive drum  52 . 
         [0029]    The fixing unit  80  is disposed rearward of the photosensitive units  50 . The fixing unit  80  includes a heat roller  81 , and a pressure roller  82  opposing the heat roller  81  so as to apply pressure to the same. 
         [0030]    In the image forming section  30 , the surface of each photosensitive drum  52  is uniformly charged by the charger  53  and then exposed by the corresponding LED unit  40 , thereby an electrostatic latent image being formed on the surface of the photosensitive drum  52  based on image data. The toner in each toner chamber  65  is supplied to the developing roller  62  through the supply roller  63 , and then enters between the developing roller  62  and the thickness regulation blade  100  so as to be carried on the developing roller  62  as a thin layer having a constant thickness. 
         [0031]    The toner carried on each developing roller  62  is then supplied to the corresponding photosensitive drum  52  on which the electrostatic latent image has been formed to develop the electrostatic latent image into a visible toner image. Thereafter, the sheet S supplied from the sheet supply section  20  is conveyed between each photosensitive drum  52  and the conveying belt  73  (corresponding transfer roller  74 ), whereby the toner images formed on the respective photosensitive drums  52  are sequentially superimposed onto the sheet S to form a color toner image. The sheet S onto which the color toner image has been formed is then conveyed between the heat roller  81  and the pressure roller  82 , whereby the color toner image is thermally fixed onto the sheet S. 
         [0032]    The sheet discharge section  90  includes a sheet discharge path  91  and a plurality of conveying rollers  92  configured to convey the sheet S. The sheet discharge path  91  is formed so as to extend upward from an outlet of the fixing unit  80  and turn its direction frontward, and a plurality of conveying rollers  92  that convey the sheet S. The sheet S onto which the toner image has been thermally fixed is conveyed along the sheet discharge path  91  by the conveying rollers  92  and discharged onto the sheet discharge tray  13  outside the main casing  10 . 
       Detailed Configuration of Developing Device 
       [0033]    A detailed configuration of the thickness regulation blade  100  and portions adjacent thereto in each developing device  60  will be described. In the following description, directions with respect to the developing unit  60  are different from those defined in  FIG. 1 . That is, directions with respect to the developing unit  60  (top, bottom, left, right, front, rear) will be referred to as defined in  FIG. 3 . 
         [0034]    As illustrated in  FIG. 3 , the casing  61  of the developing device  60  has a front end portion in which an opening  61 A is formed. The developing roller  62  is mounted in the casing  61  so as to substantially close the opening  61 A (also see  FIG. 2 ). The casing  61  has left and right side walls  61 W each having a front end portion in which a groove  61 B is formed for supporting the developing roller  62 . Further, the casing  61  has an upper wall constituting an upper edge of the opening  61 A, and the upper wall has an upper surface  61 C serving as a support surface  61 C that supports the thickness regulation blade  100 . The support surface  61 C has left and right end portions in each of which a screw hole  61 D is formed for fixing the thickness regulation blade  100  by screws  130 . 
         [0035]    The developing roller  62  is a roller elongated in the left-right direction and has an outer peripheral surface made of a rubber. The developing roller  62  includes a shaft extending in an axial direction (i.e., left-right direction of the color LED printer  1 ) and the shaft has both axial ends provided with bearings  62 A respectively. The bearings  62 A are engaged with the respective grooves  61 B of the casing  61  and fixed to the casing  61  by screws (not shown). As a result, the developing roller  62  is rotatably supported by the casing  61 . The developing roller  62  is configured to rotate in a clockwise direction in  FIGS. 2 and 3 . 
         [0036]    The thickness regulation blade  100  includes a blade  110  and a reinforcing plate  120 . 
         [0037]    The blade  110  is formed of a thin metal plate elongated in the axial direction of the developing roller  62 . The blade  110  is thus resiliently deformable. The blade  110  has a rear end portion (base end portion) fixed to the support surface  61 C of the casing  61 , as will be described later. 
         [0038]    The blade  110  has an inner surface  110 A (first surface) configured to face the developing roller  62 , and an outer surface  110 B (second surface) opposite to the inner surface  110 A. 
         [0039]    The inner surface  110 A has a front end portion (distal end portion) on which a regulating portion  111  made of a rubber-like material is provided. In other words, the regulating portion  111  is provided at a downstream side of the inner surface  110 A in the rotation direction of the developing roller  62 . The regulating portion  111  has a substantially semi-circular shape in cross section (see  FIG. 2 ) and extends in the axial direction of the developing roller  62 . When the blade  110  is fixed to the casing  61 , the regulating portion  111  is configured to contact the outer peripheral surface of the developing roller  62 , while the blade  110  is slightly being resiliently deformed, as shown in  FIG. 2 . Due to the resilient deformation of the blade  110 , the regulating portion  111  can contact the outer peripheral surface of the developing roller  62  at a predetermined pressure and spread out (or flatten) the toner retained between the regulating portion  111  and the outer peripheral surface of the developing roller  62 , thereby regulating a thickness of the toner layer. 
         [0040]    Further, the blade  110  has left and right end portions in each of which a mounting hole  112  is formed at a position corresponding to each of the screw holes  61 D. 
         [0041]    The reinforcing plate  120  is mounted on the outer surface  110 B of the blade  110 . The reinforcing plate  120  is formed of a metal plate having a larger thickness and a higher rigidity than the metal plate of the blade  110 . As illustrated in  FIG. 3 , the reinforcing plate  120  includes a main body portion  121  and two reinforcing portions  122 . The main body portion  121  extends in the axial direction of the developing roller  62 . The main body portion  121  has left and right end portions in each of which a mounting hole  123  is formed at a position corresponding to each screw hole  61 D and each mounting hole  112 . 
         [0042]    Each of the two reinforcing portions  122  extends frontward from each axial end portion of the main body portion  121 . That is, each reinforcing portion  122  extends toward downstream in the rotation direction of the developing roller  62 . 
         [0043]    As illustrated in  FIG. 2 , the main body portion  121  is disposed on a rear end portion (base end portion) of the outer surface  110 B of the blade  110 , that is, at an upstream side of the outer surface  110 B in the rotation direction of the developing roller  62 , when assembled to the casing  61 . Hence, the reinforcing plate  120  can bring the base end portion of the blade  110  in close contact with the support surface  61 C and reinforce the blade  110  from outward (above) such that the distal end portion of the blade  110  can resiliently deform substantially uniformly in the axial direction of the developing roller  62 . 
         [0044]    The blade  110  has a central portion in the left-right direction in which a through-hole  113  is formed. More specifically, the through-hole  113  is positioned rearward of the regulating portion  111 , but closer to the regulating portion  111  than to the base end portion in the front-rear direction. The through-hole  113  is a hole through which the rubber-like material for forming the regulating portion  111  is adapted to penetrate in order to form of the regulating portion  111 . Specifically, as illustrated in  FIGS. 3 and 4 , the regulating portion  111  is formed with a flat-plate portion  111 A extending to cover the through-hole  113 . The flat-plate portion  111 A extends along the inner surface  110 A, and penetrates into the through-hole  113  to fill the same. In a metal die used to form the regulating portion  111  by injection molding, one of cavities serves to form a path connecting between the through-hole  113  and the regulating portion  111 . The rubber-like material entering this path and remaining intact after completion of injection molding corresponds to the flat-plate portion  111 A. 
         [0045]    The above-described blade  110  is assembled with the reinforcing plate  120  and is then fixed to the casing  61  by screwing the screws  130  into the respective screw holes  61 D of the casing  61  via the mounting holes  123  and  112 . 
         [0046]    The developing device  60  according to the present embodiment is attached to the main casing  10  of the color LED printer  1  for use. When a print command is received at the color LED printer  1 , the developing roller  62  and the supply roller  63  are rotated to supply the toner from the supply roller  63  to the developing roller  62 . The toner entering between the thickness regulation blade  100  and the developing roller  62  is flattened by the regulating portion  111  so as to be borne on the peripheral surface of developing roller  62  as a thin layer. 
         [0047]    Inherently, the blade  110  has a higher rigidity at its center portion relative to its both end portions in the axial direction. Therefore, if the through-hole  113  is formed near an axial end portion of the blade  110 , rigidity of the axial end portion, which is originally low, may become further lower. As a result, pressing force of the regulating portion  111  near the through-hole  113  against the developing roller  62  would become weaker, thereby making the toner layer on the peripheral surface of the developing roller  62  thicker only in that portion corresponding to and adjacent to the through-hole  113 . 
         [0048]    However, in the developing device  60  according to the present embodiment, the through-hole  113  is formed on the blade  110  at the central portion in the longitudinal direction thereof (axial direction). Therefore, a reduction in rigidity attributed to formation of the through-hole  113  is not significant. The regulating portion  111  can thus contact the developing roller  62  at a generally uniform pressure in the longitudinal direction, leading to formation of the toner layer having a generally uniform thickness on the developing roller  62 . 
         [0049]    It should be noted that, the through-hole  113  need not be formed at a position exactly center of the blade  110  in the longitudinal direction thereof. Referring to  FIG. 5 , assuming that the blade  110  is divided equally into three areas A 1 , A 2  and A 3  in the longitudinal direction thereof, the through-hole  113  may be formed at any position within the area A 2 . As long as the through-hole  113  is formed within the central area A 2  on the blade  110 , rigidity of the blade  110  is not affected significantly due to the existence of the through-hole  113 . Hence, the toner can be carried on the peripheral surface of the developing roller  62  with a generally uniform thickness. 
         [0050]    Various modifications are conceivable. 
         [0051]      FIG. 6  shows a through-hole  213  formed on a blade  210  according to a variation of the embodiment. In  FIG. 6 , regions on the blade  210  each having a length in its longitudinal direction identical to that of each reinforcing portion  122  of the reinforcing plate  120  are labeled as areas A 4  and A 5 , respectively. In this variation, the through-hole  213  may be formed only in the area A 5  or in the area A 5 . Since the both reinforcing portions  122  reinforce the longitudinal end portions of the blade  110 , forming the through-hole  213  in the longitudinal end portions of the blade  110  (in the area A 4  or A 5 ) could have little impact on the rigidity of the blade  210 . Therefore, the toner can be carried on the developing roller  62  as a layer having a generally uniform thickness. 
         [0052]    Further, the reinforcing plate  120  may not necessarily have the two reinforcing portions  122 . The reinforcing portion  122  may be dispensed with. That is, the reinforcing plate  120  may be configured of the main body portion  121  only. 
       Examples and Comparative Examples 
       [0053]    The inventors of the present invention have conducted several experiments in order to confirm technical advantages of the present invention. 
         [0054]    Specifically, the inventors prepared four pairs of the blade  110  formed of a stainless (entire length: 241 mm, width: 18.3 mm, and thickness: 0.1 mm) and the reinforcing plate  120  having a sufficient rigidity. Each blade  110  was attached to a developing device of an existing image forming apparatus (TN-290 manufactured by Brother Industries, Ltd.). 
         [0055]    As shown  FIG. 7 , in each blade  110 , a through-hole having a diameter of 6 mm was formed such that: each through-hole is positioned spaced away from one end of the blade  110  by 120.5 mm, or by 81.5 mm, or by 62 mm, or by 42.5 mm in the longitudinal direction. Each through-hole is spaced away from the tip end of the blade  100  equally by 6.5 mm. 
         [0056]    The developing device to which each blade  110  was attached was mounted in the above-identified image forming apparatus and initial operations were performed thereafter. Once the developing device was removed, the inventors visually confirmed the thickness of the toner layer formed by each blade  110 . Note that, in the experiments, a portion corresponding to the flat-plate portion  111 A was not provided. 
         [0057]    Followings results have been discovered from the experiments. 
         [0058]    With regard to the through-holes formed at positions separated by 120.5 mm and 81.5 mm from the one end of the blade  110  in the longitudinal direction (formed as examples of the embodiment), the thickness of the toner layer was found to be substantially uniform. However, with regard to the through-holes formed at 62 mm and 42.5 mm from the one end of the blade  110  (formed as comparative examples), the thickness of the toner layer was not uniform: the thickness was increased only at a portion around each through-hole. 
         [0059]    The same experiment was conducted for another set of the blade  110  and the reinforcing plate  120  having two reinforcing portions  122 . In this experiment, the reinforcing portions  122  were provided at longitudinal end portions of the reinforcing plate  120  respectively and each reinforcing portion  122  has a length of 7.2 mm in the longitudinal direction. The blade  110  was formed with a through-hole having a diameter of 6 mm at a position spaced away from one end of the blade  110  by 6.6 mm in the longitudinal direction. That is, the through-hole is positioned in an area corresponding to one of the reinforcing portions  122  in the longitudinal direction. Obtained results are that, the toner layer has a uniform thickness. 
         [0060]    While the invention has been described in detail with reference to the embodiments thereof, it would be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit and scope of the invention.