Patent Publication Number: US-2022229381-A1

Title: Developing cartridge including blade and blade holder for supporting end portion of blade

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 16/951,122, filed Nov. 18, 2020, which is a continuation of U.S. patent application Ser. No. 16/458,340, filed Jul. 1, 2019, now U.S. Pat. No. 10,845,728, which claims priority from Japanese Patent Application No. 2018-183058 filed Sep. 28, 2018. The entire content of the aforementioned applications are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to a developing cartridge. 
     BACKGROUND 
     There has been conventionally known an electro-photographic type image forming apparatus including a frame having a photosensitive drum, and a cartridge attachable to and detachable from the frame. A conventional image forming apparatus including a cartridge is disclosed in prior art. The cartridge disclosed in the prior art includes a developing roller. During a printing process of the image forming apparatus, the developing roller is driven to rotate so that toner accommodated in the cartridge is carried on an outer circumferential surface of the developing roller. The photosensitive drum rotates in a state where the photosensitive drum contacts the developing roller, thereby transferring a toner image from the photosensitive drum onto a printing sheet. 
     The cartridge disclosed in the prior art includes a first frame, a second frame, the developing roller, a blade, and a support member. The first frame is assembled with the second frame by means of welding to constitute a casing in which toner is accommodatable. The developing roller is supported by the casing so as to be rotatable about a rotational axis extending in a first direction. The blade extends in the first direction and a second direction, and has a first end portion in the second direction that is positioned close to the outer circumferential surface of the developing roller. Further, the blade is configured to regulate a thickness of a toner layer carried on the outer circumferential surface of the developing roller. The support member is fixed to an outer surface of the casing by a plurality of threads to support a second end portion in the second direction of the blade. 
     SUMMARY 
     In a structure where the support member supporting the blade is fixed to the outer surface of the casing only by the plurality of threads as described in the prior art, a reinforcing rib connecting the first frame to the second frame is required in an interior of the casing in order to restrain deflection of the casing which may occur when external force is applied to the casing. However, providing the reinforcing rib may reduce an internal capacity of the casing, and also reduce a space for positioning a component such as an agitator within the casing. 
     In view of the foregoing, it is an object of the present disclosure to provide a developing cartridge capable of restraining deflection of a casing without the necessity of reducing the internal space of the casing. 
     In order to attain the above and other objects, according to one aspect, the disclosure provides a developing cartridge including: a casing; a developing roller; a blade; and a blade holder. The casing is configured to accommodate toner therein. The casing has a groove recessed inward of the casing. The developing roller is rotatable about a rotational axis extending in a first direction. The developing roller has an outer circumferential surface. The blade is configured to regulate a thickness of a layer of toner formed on the outer circumferential surface of the developing roller. The blade extends in a second direction toward the outer circumferential surface of the developing roller and having one end portion and another end portion in the second direction. The another end portion of the blade is positioned away from the one end portion of the blade in the second direction. The another end portion of the blade is positioned farther from the outer circumferential surface of the developing roller than the one end portion of the blade is from the outer circumferential surface of the developing roller. The blade holder supports the another end portion of the blade. The blade holder includes: a first plate extending in the second direction and supporting the another end portion of the blade; and a second plate extending from the first plate in a third direction crossing the second direction. The second plate has a distal end portion positioned within the groove. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The particular features and advantages of the embodiment(s) as well as other objects will become apparent from the following description taken in connection with the accompanying drawings, in which: 
         FIG. 1  is a schematic diagram of an image forming apparatus including a developing cartridge according to one embodiment of the present disclosure; 
         FIG. 2  is a perspective view of the developing cartridge according to the embodiment; 
         FIG. 3  is a cross-sectional view of the developing cartridge according to the embodiment taken along a plane perpendicular to a first direction; 
         FIG. 4  is a perspective view of the developing cartridge according to the embodiment in which a portion of the developing cartridge is exploded; and 
         FIG. 5  is an enlarged view of a portion of the developing cartridge according to the embodiment illustrated in  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION 
     &lt;1. Image Forming Apparatus&gt; 
     Hereinafter, an image forming apparatus  100  including developing cartridges  2  according to one embodiment of the present disclosure will be described with reference to  FIGS. 1 to 5 . 
     In the following description, in a state where the developing cartridge  2  is attached to a drum unit  1 , a direction in which a rotational axis of a developing roller  22  extends will be referred to “first direction”. Further, a direction in which a layer thickness regulation blade  24  extends toward an outer circumferential surface of the developing roller  22  and a direction opposite thereto will be collectively referred to as “second direction”. The first direction and the second direction cross each other. Preferably, the first direction and the second direction are perpendicular to each other. A direction crossing the first direction and the second direction will be referred to as “third direction”. Preferably, the third direction is perpendicular to the first direction and the second direction. 
       FIG. 1  is a schematic diagram of the image forming apparatus  100 . The image forming apparatus  100  is an electro-photographic type printer. For example, the image forming apparatus  100  may be a laser printer or an LED printer. As illustrated in  FIG. 1 , the image forming apparatus  100  includes a main casing  101 , a controller  102 , the drum unit  1 , and four developing cartridges  2 . Each of the developing cartridge  2  is attachable to the drum unit  1 . Further, the drum unit  1  to which four developing cartridges  2  are attached is attachable to and detachable from the main casing  101 . 
     Four developing cartridges  2  accommodate therein developing agents (for example, toners) of colors different from one another (for example, cyan, magenta, yellow, and black). The image forming apparatus  100  is configured to form images on recording surfaces of printing sheets using toners supplied from four developing cartridges  2 . Note that the number of the developing cartridges  2  attachable to the drum unit  1  may be one to three, or more than five. 
     The controller  102  is positioned in the main casing  101 . The controller  102  is configured of, for example, a circuit board. The controller  102  includes a processor such as a CPU, and various memories. The controller  102  is configured to execute various processes in the image forming apparatus  100  by operating the processor in accordance with programs. 
     &lt;2. Drum Unit&gt; 
     The drum unit  1  illustrated in  FIG. 1  includes four photosensitive drums  11  and a frame  12 . Each of the photosensitive drums  11  is configured to transfer toner supplied from the corresponding one of the developing cartridges  2  to the printing sheets. The four photosensitive drums  11  are arranged to be spaced apart from one another. 
     Each photosensitive drum  11  has a cylindrical-shaped outer circumferential surface and extends in the first direction. The outer circumferential surface of each photosensitive drum  11  is coated with photosensitive material. Further, each photosensitive drum  11  is rotatable about a rotational axis extending in the first direction. 
     The frame  12  is configured to hold the four photosensitive drums  11 . The frame  12  includes four cartridge-holding portions  120 . The four cartridge-holding portions  120  are arrayed with each other with an interval between neighboring cartridge-holding portions  120 . Each of the cartridge-holding portions  120  is configured to receive the corresponding one of the developing cartridges  2 . 
     &lt;3. Developing Cartridges&gt; 
       FIG. 2  is a perspective view of the developing cartridge  2 .  FIG. 3  is a cross-sectional view of the developing cartridge  2  as viewed in the first direction.  FIG. 4  is a perspective view of the developing cartridge  2  in which a portion of the developing cartridge  2  is exploded.  FIG. 5  is an enlarged view of a portion of the developing cartridge  2  illustrated in  FIG. 3 . As illustrated in  FIGS. 2 through 5 , each of the developing cartridges  2  includes a casing  21 , the developing roller  22 , a supply roller  23 , the layer thickness regulation blade  24  as an example of a blade, a first agitator  25 , and a second agitator  26 . 
     The casing  21  is a container configured to accommodate toner therein. The casing  21  is made of resin. The casing  21  is configured of a first frame  201  and a second frame  202 . As illustrated in  FIGS. 2 through 4 , the first frame  201  has a lid-like shape. The second frame  202  has a box shape and faces the first frame  201  in the second direction. By assembling the second frame  202  with the first frame  201 , the casing  21  is configured as a container. The casing  21  has one end portion  203  in the first direction, and another end portion  204  spaced apart from the one end portion  203  in the first direction. Further, the first frame  201  has an opening  205  at one end portion thereof in the third direction. Detailed configuration of the first frame  201  will be described later. 
     The developing roller  22  is rotatable about its rotational axis extending in the first direction. The developing roller  22  has one end portion in the first direction supported by the one end portion  203 , and another end portion in the first direction supported by the other end portion  204 . The developing roller  22  is positioned at the opening  205  of the casing  21 . Hence, a portion of the outer circumferential surface of the developing roller  22  is exposed to an outside of the casing  21 . Upon attachment of each developing cartridge  2  to the corresponding cartridge-holding portion  120  of the drum unit  1 , an outer circumferential surface of the photosensitive drum  11  and the outer circumferential surface of the corresponding developing roller  22  are in contact with each other. 
     The supply roller  23  illustrated in  FIGS. 3 and 5  is rotatable about a rotational axis extending in the first direction. The supply roller  23  has one end portion in the first direction supported by the one end portion  203 , and another end portion in the first direction supported by the other end portion  204 . The supply roller  23  is positioned between the first agitator  25  and the developing roller  22  in the third direction. The supply roller  23  is positioned adjacent to the developing roller  22 . A portion of the supply roller  23  having an outer circumferential surface of the supply roller  23  is made from, for example, a rubber having elasticity. The outer circumferential surface of the supply roller  23  and the outer circumferential surface of the developing roller  22  are in contact with each other. Hence, toner can be supplied from the supply roller  23  to the outer circumferential surface of the developing roller  22 . 
     The layer thickness regulation blade  24  is configured to regulate thickness of a layer of toner formed on the outer circumferential surface of the developing roller  22  so that the thickness of the layer of toner is formed to a constant thickness. The layer thickness regulation blade  24  extends in the second direction toward the outer circumferential surface of the developing roller  22 . The layer thickness regulation blade  24  is positioned between the one end portion  203  and the other end portion  204  of the casing  21  in the first direction. The layer thickness regulation blade  24  is positioned opposite to the supply roller  23  with respect to the developing roller  22  in the second direction. 
     The layer thickness regulation blade  24  has one end portion in the second direction positioned adjacent to the developing roller  22  and in contact with the outer circumferential surface of the developing roller  22 . Further, the layer thickness regulation blade  24  has another end portion in the second direction positioned away from the one end portion of the layer thickness regulation blade  24 . The other end portion of the layer thickness regulation blade  24  is positioned farther from the outer circumferential surface of the developing roller  22  than the one end portion of the layer thickness regulation blade  24  is from the outer circumferential surface of the developing roller  22 . An acting portion  24   a  made from rubber is provided at the one end portion in the second direction of the layer thickness regulation blade  24 . The contact of the acting portion  24   a  with the toner layer on the outer circumferential surface of the developing roller  22  regulates the thickness of the toner layer. A portion of the layer thickness regulation blade  24  other than the acting portion  24   a  is formed of a metal plate. 
     The other end portion in the second direction of the layer thickness regulation blade  24  is supported by the first frame  201  of the casing  21  through the first blade holder  250  and a second blade holder  260  (described later). A detailed configuration for supporting the other end portion of the layer thickness regulation blade  24  will be described later. 
     The first agitator  25  illustrated in  FIG. 3  is configured to agitate toner accommodated in an internal space of the casing  21 . The first agitator  25  is rotatable about a rotational axis extending in the first direction. The first agitator  25  includes a blade  25   a  in a form of a film. The blade  25   a  has a distal end portion in contact with an inner surface of the casing  21 . The rotation of the first agitator  25  about its rotational axis causes the blade  25   a  to rotate. Upon rotation of the blade  25   a,  the toner accommodated in the casing  21  is agitated. 
     The second agitator  26  is also configured to agitate the toner accommodated in the internal space of the casing  21 . Specifically, the second agitator  26  is configured to mainly agitate toner positioned in a region in the internal space in which toner is not sufficiently agitated by the first agitator  25 . The second agitator  26  is positioned between the supply roller  23  and the first agitator  25  in the third direction. The second agitator  26  is rotatable about its rotational axis extending in the first direction. The second agitator  26  is positioned closer to the supply roller  23  than to the developing roller  22  in the third direction. With this configuration, toner agitated by the second agitator  26  can be efficiently supplied to the supply roller  23 . 
     In the image forming apparatus  100  configured as described above, the outer circumferential surface of the photosensitive drum  11  is exposed to laser beam after the outer circumferential surface is uniformly charged, so that an electrostatic latent image is formed on the outer circumferential surface of the photosensitive drum  11  on a basis of inputted print data. Toner accommodated in the casing  21  is supplied to the supply roller  23  while the toner is agitated by the first agitator  25  and the second agitator  26 , and is then supplied to the developing roller  22  from the supply roller  23 . More specifically, toner is entered into a portion between the developing roller  22  and the layer thickness regulation blade  24  in accordance with the rotation of the developing roller  22 , and the toner is carried on the outer circumferential surface of the developing roller  22  as the thin toner layer having constant thickness. 
     The toner carried on the outer circumferential surface of the developing roller  22  is supplied to the electrostatic latent image formed on the outer circumferential surface of the photosensitive drum  11 , thereby causing the electrostatic latent image to become a visible image to form a toner image on the outer circumferential surface of the photosensitive drum  11 . The formed toner image is transferred to the recording surface of the printing sheet and is then thermally fixed thereto, whereupon the printing process is terminated. 
     &lt;4. Structure for Supporting Layer Thickness Regulation Blade&gt; 
     A structure for supporting the layer thickness regulation blade  24  will be described while mainly referring to  FIGS. 4 and 5 . The layer thickness regulation blade  24  is attached to and supported by the first frame  201  of the casing  21  using the support structure according to the embodiment. Specifically, the support structure is configured by the first blade holder  250 , the second blade holder  260 , a plurality of grooves  207 , a first thread  209  as an example of a first fastening member, a second thread  210  as an example of second fastening member, and a plurality of third threads  208 . 
     The first blade holder  250  illustrated in  FIGS. 3 to 5  is configured to support the other end portion in the second direction of the layer thickness regulation blade  24 . The first blade holder  250  is made of metal. Although it is preferable that the metal contains iron, the first blade holder  250  may be made from stainless steel. The first blade holder  250  includes a first plate  251  and a second plate  252 . The first plate  251  has a flat plate shape that extends in the first direction and the second direction. The first plate  251  has one end portion in the second direction closer to the developing roller  22  than another end portion in the second direction of the first plate  251  is to the developing roller  22 . The first plate  251  has a pair of opposing surfaces crossing the third direction. One of the opposing surfaces that faces a third plate  263  (described later) of the second blade holder  260  is in contact with the layer thickness regulation blade  24 . 
     The second plate  252  extends in the third direction from the other end portion in the second direction of the first plate  251 . The second plate  252  extends perpendicularly to the first plate  251  in the present embodiment. The second plate  252  has a flat plate shape extending in the first direction and the third direction. The second plate  252  has a base end portion connected to the other end portion in the second direction of the first plate  251 , and a distal end portion extending toward the plurality of grooves  207 . 
     The second blade holder  260  is configured to support the other end portion of the layer thickness regulation blade  24  in cooperation with the first blade holder  250 . The second blade holder  260  is made from metal preferably containing iron. However, the second blade holder  260  may be made from stainless steel. The second blade holder  260  includes the third plate  263  and a fourth plate  264 . The third plate  263  has a flat plate shape extending in the first direction and the second direction. The third plate  263  has one end portion in the second direction closer to the developing roller  22  than another end portion in the second direction of the third plate  263  is to the developing roller  22 . The third plate  263  has a pair of opposing surfaces crossing the third direction. One of the opposing surfaces facing the first plate  251  is in contact with the layer thickness regulation blade  24 . That is, the layer thickness regulation blade  24  is nipped between the first plate  251  and the third plate  263  to be supported thereby in the present embodiment. 
     The fourth plate  264  extends in the third direction from the other end portion in the second direction of the third plate  263 . In the present embodiment, the fourth plate  264  extends perpendicularly relative to the third plate  263 . The fourth plate  264  has a flat plate shape extending in the first direction and the third direction. The fourth plate  264  has a base end portion connected to the other end portion in the second direction of the third plate  263 , and a distal end portion extending toward the grooves  207 . 
     Each of the plurality of grooves  207  is provided at the first frame  201  of the casing  21 . Each groove  207  extends in the first direction and is recessed inward of the casing  21  in the third direction. In the present embodiment, the grooves  207  extend from the one end portion  203  to the other end portion  204  in the first direction. As illustrated in  FIGS. 4 and 5 , the first frame  201  includes a groove bottom wall  207   a,  an inner wall  207   b,  and a plurality of outer walls  207   c  those constituting the grooves  207 . 
     The groove bottom wall  207   a  is a plate like portion extending in the first direction, and has a constant width (groove width) in the second direction. The groove bottom wall  207   a  has the groove width greater than a total of thicknesses of the second plate  252  and the fourth plate  264 . In the present embodiment, the groove bottom wall  207   a  extends in the first direction over the one end portion  203  and the other end portion  204 . 
     The inner wall  207   b  is a plate like portion that extends in the first direction and the third direction. Specifically, the inner wall  207   b  extends in the first direction over the one end portion  203  and the other end portion  204 . The inner wall  207   b  extends in the third direction from one end in the second direction of the groove bottom wall  207   a  toward the first plate  251 . The first frame  201  includes a rib  211  positioned on an inner surface of the inner wall  207   b.  The inner wall  207   b  is supported and reinforced by the rib  211 . 
     Each of the plurality of outer walls  207   c  extends in the first direction and the third direction. As illustrated in  FIG. 4 , the plurality of outer walls  207   c  are arrayed in the first direction with a prescribed interval between neighboring outer walls  207   c.  That is, the plurality of grooves  207  are arrayed in the first direction with an interval between neighboring grooves  207 . Each of the outer walls  207   c  extends toward an outside of the casing  21  in the third direction from another end in the second direction of the groove bottom wall  207   a.  That is, the inner wall  207   b  and the outer walls  207   c  face each other in the second direction with a gap corresponding to the groove width of the groove bottom wall  207   a  therebetween. 
     The first thread  209 , the second thread  210 , and the plurality of third threads  208  are fastening members for fixing the first blade holder  250  and the second blade holder  260  to the first frame  201 . The Number of the plurality of third threads  208  is smaller than the number of the plurality of outer walls  207   c  by one. Each of the second plate  252  and the fourth plate  264  has a plurality of through-holes allowing the corresponding third threads  208  to be inserted therethrough. Further, the inner wall  207   b  has a plurality of threaded holes with which the corresponding third threads  208  threadingly engage. 
     Each of the first plate  251  and the third plate  263  has one end portion in the first direction having through-holes allowing the first thread  209  to be inserted therethrough, and another end portion in the first direction having through-holes allowing the second thread  210  to be inserted therethrough. Further, one end portion in the first direction of the first frame  201  has a threaded hole with which the first thread  209  threadingly engages, and another end portion in the first direction of the first frame  201  has a threaded hole with which the second thread  210  threadingly engages. 
     With this support structure, the other end portion in the second direction of the layer thickness regulation blade  24  is nipped between the first plate  251  and the third plate  263 . In this state, the second plate  252  and the fourth plate  264  are overlapped with each other, and distal end portions of the second plate  252  and the fourth plate  264  are positioned within the grooves  207 . In this case, each of the through-holes of the second plate  252  is overlapped with the corresponding one of the through-holes of the fourth plate  264  and the corresponding one of the intervals formed between neighboring outer walls  207   c.  Each of the third threads  208  is inserted into the overlapped through-holes and the interval, and threadingly engages with the corresponding threaded hole formed in the inner wall  207   b.    
     Further, the through-hole formed in the one end portion in the first direction of the first plate  251  and the through-hole formed in the one end portion in the first direction of the third plate  263  are overlapped with each other. The first thread  209  is inserted into the overlapped through-holes, and threadingly engages with the threaded hole formed in the one end portion in the first direction of the first frame  201 . 
     Similarly, the through-hole formed in the other end portion in the first direction of the first plate  251  and the through-hole formed in the other end portion in the first direction of the third plate  263  are overlapped with each other. The second thread  210  is inserted through the overlapped through-holes, and threadingly engages with the threaded hole formed in the other end portion in the first direction of the first frame  201 . 
     In this way, the layer thickness regulation blade  24  is attached to and supported by the first frame  201  of the casing  21 . In this case, the distal end portion of the second plate  252  of the first blade holder  250  and the distal end portion of the fourth plate  264  of the second blade holder  260  are positioned within the grooves  207  of the first frame  201 . With this configuration, the first frame  201  can be reinforced with the second plate  252  and the fourth plate  264 . Accordingly, deflection and deformation of the casing  21  can be restrained even if an external force that may reduce the internal space of the casing  21  in the second direction is applied to the casing  21 , thereby restraining leakage of toner accommodated in the casing  21  in spite of the application of the external force to the casing  21 . 
     Further, the first blade holder  250  and the second blade holder  260  function not only to reinforce the casing  21  but also to hold the layer thickness regulation blade  24 . Therefore, the numbers of parts and components in the developing cartridge  2  can be reduced. 
     Further, as illustrated in  FIG. 5 , the distal end portions of the second plate  252  and the fourth plate  264  are positioned within the grooves  207  such that gaps in the second direction are positioned between the second plate  252  and the inner wall  207   b,  and between the fourth plate  264  and the outer walls  207   c.  Therefore, even if the casing  21  is deflected or deformed due to the application of the external force that reduces the internal space of the casing  21  in the second direction, the deflected casing  21  (the deflected first frame  201 ) is brought into abutment against the second plate  252  of the first blade holder  250  and the fourth plate  264  of the second blade holder  260 , thereby restraining further deflection or deformation of the casing  21 . Hence, excessive deflection or deformation of the casing  21  does not occur. As a result, leakage of toner from the internal space of the casing  21  can be suppressed in spite of the application of the external force to the casing  21 . 
     Further, the plurality of grooves  207  are positioned at a position between the one end portion  203  and the other end portion  204  of the casing  21  in the first direction. In other words, the grooves  207  are positioned at least at an intermediate portion between the one end portion  203  and the other end portion  204 , where deflection more likely to occur among an entire region of the casing  21  in the first direction. Since the distal end portion of the second plate  252  of the first blade holder  250  and the distal end portion of the fourth plate  264  of the second blade holder  260  are positioned within these grooves  207 , deflection or deformation of the casing  21  can be restrained well. 
     Further, because the first blade holder  250  and the second blade holder  260  are made of metal, the casing  21  can be firmly reinforced with the metallic first blade holder  250  and the second blade holder  260 . Therefore, deflection or deformation of the casing  21  can be desirably restrained. Further, the casing  21  itself may have insufficient rigidity, since the casing  21  is made of resin. However, reinforcement of the casing  21  by the metallic first blade holder  250  and the second blade holder  260  can enhance rigidity of the casing  21 . 
     Further, in the developing cartridge  2  according to the above-described embodiment, the third threads  208  are arrayed in the first direction with prescribed gap therebetween such that each third thread  208  is positioned at the corresponding interval between neighboring outer walls  207   c  in the first direction. Therefore, at least a portion of each third thread  208  is positioned between the corresponding interval between neighboring grooves  207  in the first direction. Thus, the first blade holder  250  and the second blade holder  260  can be stably attached to the casing  21 . 
     Further, as illustrated in  FIG. 2 , each third thread  208  has a head portion positioned in the corresponding interval formed between neighboring outer walls  207   c  in the first direction. Thus, the head portion of each third thread  208  is exposed to an outside of the grooves  207 . Hence, a shaft portion of each third thread  208  can be inserted into the through-holes of the second plate  252  and the fourth plate  264 , so that a tip end portion of the shaft portion of each third thread  208  can threadingly engages with the threaded hole of the inner wall  207   b.    
     Further, in the developing cartridge  2  according to the above-described embodiment, the other end portion in the second direction of the layer thickness regulation blade  24  is supported by nipping the other end portion between the first plate  251  of the first blade holder  250  and the third plate  263  of the second blade holder  260 . This configuration can more stably support the layer thickness regulation blade  24 . 
     Further, in the developing cartridge  2  according to the above-described embodiment, the first plate  251  and the third plate  263  are fastened to the casing  21  by the first thread  209  and the second thread  210 . Accordingly, the layer thickness regulation blade  24  nipped between the first plate  251  and the third plate  263  can be stably supported by the casing  21 . Further, in a case where the image forming apparatus  100  is a laser printer, the first thread  209  and the second thread  210  do not interfere with laser beam emitted toward the outer circumferential surface of the photosensitive drum  11 , since the first thread  209  and the second thread  210  are positioned at end portions in the first direction of the first blade holder  250  and the second blade holder  260 . 
     Further, in the developing cartridge  2  according to the above-described embodiment, a conventional structure for restraining deflection or deformation of the second frame toward the first frame, such as a rib disposed in the internal space of the casing and connecting an inner surface of the first frame to an inner surface of the second frame, is not provided. Hence, reduction in internal capacity of the casing  21  can be avoided while restraining deflection or deformation of the casing  21 . Consequently, the second agitator  26  can be positioned closer to the supply roller  23  than to the developing roller  22 . Since the second agitator  26  can be provided at a position adjacent to the supply roller  23 , sufficiently agitated toner can be continuously supplied from the supply roller  23  to the developing roller  22 . 
     &lt;5. Modifications&gt; 
     While the description has been made in detail with reference to the specific embodiment, it would be apparent to those skilled in the art that many modifications and variations may be made thereto. Various modifications to the above embodiment will be briefly described below. 
     For example, the second plate  252  of the first blade holder  250  extends perpendicularly to the first plate  251  in the above-described embodiment. That is, an angle defined between the first plate  251  and the second plate  252  is right angle. However, the angle between the first plate  251  and the second plate  252  may be acute angle or obtuse angle. Similarly, in the second blade holder  260  of the above-described embodiment, the fourth plate  264  extends perpendicularly to the third plate  263 . However, an angle defined between the third plate  263  and the fourth plate  264  may be acute angle or obtuse angle. 
     In the above-described embodiment, the other end portion in the second direction of the layer thickness regulation blade  24  is supported by both the first blade holder  250  and the second blade holder  260 . However, one of the first blade holder  250  and the second blade holder  260  may be dispensed with. In this case, the other end portion in the second direction of the layer thickness regulation blade  24  may be attached to the first plate  251  of the first blade holder  250  or the third plate  263  of the second blade holder  260  by welding means such as spot welding. 
     In the above-described embodiment, the grooves  207  are provided substantially over the entire region between the one end portion  203  and the other end portion  204  of the first frame  201 . However, the grooves  207  may be positioned only at a center portion in the first direction of the first frame  201  instead. Here, among the entire region of the casing  21  in the first direction, deflection most likely occurs at the center portion of the casing  21  in the first direction. In this case, since the grooves  207  is positioned at the center portion of the casing  21  in the first direction and the distal end portions of the second plate  252  of the first blade holder  250  and the fourth plate  264  of the second blade holder  260  are positioned inside the grooves  207 , deflection of the casing  21  can be efficiently restricted. Further, by forming the grooves  207  only at the center portion in the first direction of the casing  21 , a region at which the grooves  207  is positioned can be reduced, thereby causing material cost and machining cost to be reduced. 
     The first blade holder  250  and the second blade holder  260  may be formed of a material other than metal. In the latter case, sufficient rigidity of the first blade holder  250  and the second blade holder  260  may be obtained by increasing thickness thereof. 
     The second agitator  26  may be dispensed with. 
     Further, the detailed configuration of the image forming apparatus and the developing cartridge may be suitably modified without departing from the scope of the present disclosure. Further, various features appearing in the above embodiment and the above modifications may be suitably combined together avoiding conflicting combination.