Abstract:
A developing device for an electrophotographic image forming apparatus includes a developing roller of a developing portion for developing an electrostatic latent image on an electrophotographic photosensitive drum, a developer accommodator, a supply opening, between the developing portion and the accommodator, and a stirring member including a support rotatably provided on the accommodator and a stirrer on the support. The stirrer&#39;s length is longer than the opening&#39;s length in a longitudinal direction of a mount mounted to the support and the length of the stirrer&#39;s end portion is shorter than the supply opening&#39;s length. When the stirrer is rotated, an end thereof enters the opening to feed the developer from the accommodator through the opening to the developing portion and then through the supply opening back to the developer accommodating portion.

Description:
FIELD OF THE INVENTION AND RELATED ART 
     The present invention relates to a developing apparatus used by an electrophotographic image forming apparatus. It also relates to an electrophotographic image forming apparatus in which a process cartridge is removably mountable. 
     A “process cartridge” means a cartridge in which an electrophotographic photosensitive drum, and at least one among the processing means, more specifically, a developing means, a cleaning means, and a charging means, which act one the electrophotographic photosensitive drum, are integrally disposed. A “process cartridge” is removably mounted into the main assembly of an electrophotographic image forming apparatus by a user. 
     An “image forming apparatus” is an apparatus which forms an image on recording medium with the use of an electrophotographic image forming method. Some of the examples of an electrophotographic image forming apparatus are an electrophotographic copying machine, an electrophotographic printer (LED printer, laser beam printer, etc.), a facsimile apparatus, a wordprocessor, etc. 
     The abovementioned recording medium is any medium on which an image is formable. Some examples of the recording medium are a sheet of ordinary paper, a sheet for an OHP, etc. 
     The “main assembly” of an electrophotographic image forming apparatus is what remains after the removable of a process cartridge or process cartridges from the electrophotographic image forming apparatus. 
     In the field of an electrophotographic image forming apparatus, it has been a common practice to use a process cartridge system, which integrally disposes an electrophotographic photosensitive drum and one or more processing means (which act on electrophotographic photosensitive drum), in a cartridge which is removably mountable in the main assembly of an electrophotographic image forming apparatus. 
     A process cartridge system makes it possible for a user to maintain an image forming apparatus himself or herself, that is, without relying on a service person. Thus, it can drastically improve an image forming apparatus in operational efficiency in terms of maintenance. 
     Regarding a developing apparatus disposed in a process cartridge such as those described above, a developing apparatus having a developer storage portion, a development roller, a development portion, and a blade, has been put to practical use. The developer storage portion (which hereafter may be referred to as toner chamber) is a portion in which developer is stored. A development station (which hereafter may be referred to as development chamber), is a portion in which toner is supplied to a development roller. 
     Japanese Laid-open Patent Application 2000-330365 discloses a process cartridge which has a stirring member made up of a stirring portion and a stirring portion supporting portion. The stirring portion supporting portion is rotatably attached to the frame of the process cartridge. The stirring portion is firmly attached to the supporting portion. Further, the process cartridge is structured so that as the supporting portion is rotated, the toner in the toner chamber is conveyed to the development chamber by the stirring portion. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a developing apparatus and an electrophotographic image forming apparatus in which the developer stored in the developer storage portion can be satisfactorily moved in a circulatory manner between the developer storage portion and development portion. 
     It is another object of the present invention to provide a developing apparatus and an image forming apparatus in which not only is it possible to satisfactorily convey the developer in the developer storage portion, to the development portion, but also, to satisfactorily return the developer from the development portion to the developer storage portion. 
     It is a further object of the present invention to provide a developing apparatus and an electrophotographic image forming apparatus in which not only is it possible to satisfactorily convey the developer from the developer storage portion, deeper into the development portion, but also, to satisfactory return the developer from the developer portion, deeper into the development storage portion, than any of the prior arts. 
     According to an aspect of the present invention, there is provided a developing device for an electrophotographic image forming apparatus, said developing device comprising a developing roller for developing an electrostatic latent image formed on said electrophotographic photosensitive drum; a developing portion in which said developing roller is provided; a developer accommodating portion for accommodating the developer to be used for development of the electrostatic latent image by said developing roller; a supply opening, provided between said developing portion and said developer accommodating portion, for supplying the developer from said developer accommodating portion; and a stirring member including a supporting portion rotatably provided on said developer accommodating portion, and a stirring portion provided on said supporting portion, wherein a stirring portion has a length measured in a longitudinal direction of a mounting portion mounted to said supporting portion, which is longer than a length of said supply opening in the longitudinal direction, and wherein said stirring portion has an end portion having a length which is shorter than the length of said supply opening, wherein when said stirring member is rotated, an end of said stirring portion enters said supply opening by a rotation toward said supply opening to feed the developer from said developer accommodating portion through said supply opening to said developing portion, and wherein the developer thus fed through said supply opening is fed said developer accommodating portion. 
     According to another aspect of the present invention, there is provided an electrophotographic image forming apparatus to which a process cartridge is detachably mountable, said apparatus comprising i) a process cartridge including, an electrophotographic photosensitive drum, a developing roller for developing an electrostatic latent image formed on said electrophotographic photosensitive drum, a developing portion in which said developing roller is provided, a developer accommodating portion for accommodating the developer to be used for development of the electrostatic latent image by said developing roller, a supply opening, provided between said developing portion and said developer accommodating portion, for supplying the developer from said developer accommodating portion, and a stirring member including a supporting portion rotatably provided on said developer accommodating portion, and a stirring portion provided on said supporting portion, wherein a stirring portion has a length measured in a longitudinal direction of a mounting portion mounted to said supporting portion, which is longer than a length of said supply opening in the longitudinal direction, and wherein said stirring portion has an end portion having a length which is shorter than the length of said supply opening, wherein when said stirring member is rotated, an end of said stirring portion enters said supply opening by a rotation toward said supply opening to feed the developer from said developer accommodating portion through said supply opening to said developing portion, and wherein the developer thus fed through said supply opening is fed said developer accommodating portion; and ii) a transfer roller for transferring a developed image formed on said electrophotographic photosensitive drum onto a recording material; feeding means for feeding the recording material. 
     These and other objects, features, and advantages of the present invention will become more apparent upon consideration of the following description of the preferred embodiments of the present invention, taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional view of the combination of the main assembly of the image forming apparatus, and process cartridge in the main assembly, in the preferred embodiment of the present invention. 
         FIG. 2  is an enlarged sectional view of the process cartridge in the preferred embodiment. 
         FIG. 3  is a perspective view of the process cartridge, which is for describing the structure of the process cartridge. 
         FIG. 4  is an exploded perspective view of the latent image formation unit. 
         FIG. 5  is an exploded perspective view of the development unit. 
         FIG. 6  is also an exploded perspective view of the development unit. 
         FIG. 7  is a perspective view of the stirring member, which is for showing the structure of the stirring member. 
         FIG. 8  is a sectional view of the development unit after the installation of the stirring member into the development unit. 
         FIGS. 9(   a )- 9 ( c ) are sectional views of the development unit, which are for describing the stirring member movement and circulatory movement of the toner in the development unit. 
         FIGS. 10(   a ) and  10 ( b ) are also sectional views of the development unit, which are for describing the stirring member movement and circulatory movement of the toner in the development unit. 
         FIGS. 11(   a ),  11 ( b ), and  11 ( c ) are horizontal sectional views of the development unit, left end portion of the stirring member and its adjacencies, and right end portion of the stirring member and its adjacencies, respectively, which are for showing the positional relationship between the stirring member and the developer delivery hole, in terms of the lengthwise direction of the stirring member. 
         FIG. 12  is a perspective view of the lengthwise right end portion of the stirring member, and its adjacencies, which is for showing the shape of the lengthwise end portion of the stirring member. 
         FIGS. 13(   a ) and  13 ( b ) are horizontal sectional views of one of the modified versions of the development unit in the preferred embodiment, right end portion of its stirring member, and its adjacencies, respectively, which are for showing the positional relationship between the stirring member, and its developer delivery hole, which are for showing the positional relationship between the stirring member and the toner delivery hole, in terms of the lengthwise direction of the stirring member. 
         FIGS. 14(   a ) and  14 ( b ) are a top plan view of the entirety of the modified version of the stirring member in the preferred embodiment, and an enlarged top view of the right end portion of the stirring member and its adjacencies, respectively, which are for showing the structure of the stirring member. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, the preferred embodiment of the present invention will be described with reference to an electrophotographic image forming apparatus, and a process cartridge used by the image forming apparatus. The preferred embodiment will be described assuming the process cartridge is removably mountable in the main assembly of the electrophotographic image forming apparatus. It is also assumed that the developing apparatus and electrophotographic photosensitive drum are integrally disposed in the process cartridge, which is removably mountable in the main assembly of the electrophotographic image forming apparatus. 
     However, the preferred embodiment is not intended to limit the present invention in scope. That is, the present invention is also applicable to a built-in developing apparatus of the main assembly of an electrophotographic image forming apparatus, and a developing apparatus (so-called development cartridge) designed to be removably mountable in the apparatus main assembly. 
     (Overall Structure) 
       FIG. 1  is a sectional view of the combination of the main assembly  1  of the image forming apparatus (which hereafter may be referred to simply as apparatus main assembly  1 ), and process cartridge  2  (which hereafter may be referred to simply as cartridge  2 ) in the main assembly, in the preferred embodiment of the present invention.  FIG. 2  is an enlarged sectional view of the cartridge  2 . Next, referring to  FIGS. 1 and 2 , the general structure of the image forming apparatus in this embodiment, and the image formation process carried out by the image forming apparatus, will be described. 
     This image forming apparatus is a laser beam printer structured so that the cartridge  2  is removably mountable in the apparatus main assembly  1 . Further, the image forming apparatus is structured so that when the cartridge  2  is in its image forming position in the main assembly  1 , the exposing apparatus  3  is on the top side of the cartridge  2 , and also, a sheet tray  4 , in which sheets of recording medium P (which hereafter may be referred to simply as sheet P), is on the bottom side of the cartridge  2 . Further, the apparatus main assembly  1  is provided with a pickup roller  5   a , a pair of sheet feeding-and-conveying rollers  5   b , two pairs of sheet conveying rollers  5   c , a sheet transfer guide  6 , a transfer charge roller  7 , a sheet conveyance guide  8 , a fixing apparatus  9 , a pair of sheet discharging rollers  10 , a delivery tray  11 , etc. In terms of the direction in which the sheet P is conveyed through the apparatus main assembly  1 , they are arranged in the order in which they are listed. The charge roller  7  is a roller for transferring an image formed of developer on a photosensitive drum  10 , onto the sheet P. Incidentally, the pickup roller  5   a , sheet feeding-and-conveying rollers  5   b , sheet conveying rollers  5   c , and sheet discharging rollers  10 , etc., make up a conveying means for conveying the sheet P. 
     (Description of Image Formation Process) 
     Next, the image formation process of this image forming apparatus will be described. 
     First, a print start signal is to be inputted. As a print start signal is inputted, the electrophotographic photosensitive drum  20  (which hereafter will be referred to simply as drum  20 ) begins to be rotationally driven in the direction indicated by an arrow mark R 1  at a preset peripheral velocity (process speed). The peripheral surface of the drum  20  is in contact with a charge roller  12 . Thus, the peripheral surface of the drum  20  is uniformly charged by the charge roller  12 . 
     Then, a beam of laser light L is outputted from the exposing apparatus  3  while being modulated with picture element signals, which reflect the information regarding the image to be formed. The beam of laser light L is projected into the cartridge  2  through an opening  53 , with which the top wall of the cartridge  2  is provided. As the beam of laser light L is projected into the cartridge  2 , it scans the charged portion of the peripheral surface of the drum  20 . As a result, an electrostatic latent image, which is in accordance with the information regarding the intended image, is formed on the charged portion of the peripheral surface of the drum  20 . This electrostatic latent image is developed by developer T (which hereafter may be referred to as toner T), into a visible image, that is, an image formed of toner. The developer T is stored in a developing apparatus unit  40 . 
     To describe in more detail, the charge roller  12 , which is a charging means, is in contact with the drum  20 , and charges the drum  20 . It is rotated by the rotation of the drum  20 . The development unit  40  develops the latent image on the drum  20 , by supplying the portion of the peripheral surface of the drum  20 , which has the latent image, with toner T. The unit  40  has a toner chamber (developer storing portion), a stirring member  43 , and a development chamber (latent image developing portion). The unit  40  has also a development roller  41  (developer bearing member), and a development blade  42 . 
     The development chamber  44  (latent image developing portion) is one of the spaces created by partitioning the interior of the process cartridge  2 . It is the chamber in which the development roller  41  is located. 
     The toner T is in a toner chamber  45  (developer storage portion) is sent out to the development chamber  44  by the rotation of the stirring member  43 . As the development roller  41 , which internally holds a magnetic roller  41  (stationary magnet), is rotated, a layer of frictionally charged toner particles is formed on the peripheral surface of the development roller  41  by a development blade  42 . The charged toner particles in this layer of toner are transferred onto the drum  20  in the pattern of the latent image on the drum  20 . As a result, a visible image is formed of toner on the peripheral surface of the drum  20 . The development blade  42  is a blade for regulating the amount by which the toner is coated on the peripheral surface of the drum  20  per unit area, and also, for frictionally charging the toner. That is, the development roller  41 , which is a latent image developing means, develops the electrostatic latent image on the drum  20 , with the use of the toner T. 
     Meanwhile, the sheet P stored in the bottom portion of the apparatus main assembly  1 , is fed into the apparatus main assembly  1  from the sheet tray  4  by the pickup roller  5   a , sheet feeding-and-conveying rollers  5   b , and sheet conveying rollers  5   c , in synchronism with the timing with which the beam of laser light L begins to be outputted. Then, the sheet P is conveyed to the transfer portion, that is, the interface between the drum  20  and transfer charge roller  7 , by way of the transfer guide  6 . Then, the sheet P is conveyed through the transfer portion. As the sheet P is conveyed through the transfer portion, the image formed of toner (which hereafter will be referred to simply as toner image) on the drum  20  is transferred from the drum  20  onto the sheet P as if it were peeled away from the drum  20 . 
     After the transfer of the toner image onto the sheet P, the sheet P is separated from the drum  20 , and then, is conveyed to the fixing apparatus  9  along the conveyance guide  8 . Then, the sheet P is conveyed through the nip (interface) between a fixation roller  9   a  and a pressure roller  9   b , of which the fixing apparatus  9  is made up. In this nip, the toner particles, of which the toner image is formed, are subjected to heat and pressure. As a result, the toner image becomes fixed to the sheet P. After the fixation, the sheet P is conveyed to the pair of discharge rollers  10 , and then, is discharged into the delivery tray  11  by the pair of discharge rollers  10 . 
     After the transfer of the toner image from the drum  20 , the toner particles remaining on the peripheral surface of the drum  20  are removed by a cleaning blade  52 . Then, the cleaned portion of the peripheral surface of the drum  20  is used again for the above described image formation process, which begins with the charging step. The toner removed from the drum  20  is stored in a toner chamber  51   e  for the removed toner, which is a part of the latent image formation unit  50 . 
     In the case of the electrophotographic image forming apparatus in this embodiment, the charge roller  12  (charging means), development roller  41  (developing means (developing apparatus)), cleaning blade  52 , etc., are the processing means which act on the drum  20 . 
     (Structure of Process Cartridge) 
       FIG. 3  is a perspective view of the cartridge  2 , which is for describing the structure of the cartridge  2 . Next, the structure of the cartridge  2  will be described with reference to  FIGS. 2 and 3 . 
     Referring to  FIG. 2 , the drum  2 , charge roller  12 , and cleaning blade  52  are integrally attached to the portion of the frame of the cartridge  2 , which supports the drum  20 . They make up the latent image formation unit  50 . That is, the unit  50  has the drum  20 , charge roller  12 , and blade  52 . 
     On the other hand, the development unit  40  is made up of the toner chamber  45  for storing toner, toner storage container  40   a , and lid  40   b . The wall of the container  40   a  and the lid  40   b  make up the frame of the development unit  40 . They are unitized by welding or the like method. 
     Next, referring to  FIG. 3 , the units  50  and  40  are connected to each other by a pair of pins  54  (connecting members), making up the cartridge  2 , in such a manner that they are allowed to rotationally move relative to each other. 
     Also referring to  FIG. 3 , the unit  40  is provided with a pair of lateral members  55  ( 55 L and  55 R), which make up the end portions, one for one, of the unit  40  in terms of the lengthwise direction (which is parallel to axial line of development roller  41 ) of the unit  40 . The lateral members  55  ( 55 L and  55 R) are provided with arm portions  55   a  ( 55   a L and  55   a R), respectively. The end portion of each of the arm portions  55  is provided with a through hole  55   b  ( 55   b L or  55   b R), which is parallel to the development roller  41 . The arm portions  55   a  ( 55   a L and  55   a R) are inserted into a pair of specific portions of the frame  51  of the latent image formation unit  50 . On the other hand, the frame  51  of the unit  50  is provided with a pair of holes  51   a  ( 51   a L and  51   a R), through which the pair of connecting members  54  ( 54 L and  54 R) are put (left hole  51   a L is not shown in drawing). The holes  51   a  are positioned in such a manner that as the arm portions  55   a  of the unit  40  are inserted into the abovementioned specific portions of the frame  51  of the unit  50 , one for one, they align with the holes  55   a  of the unit  40 . After the insertion of the arm portions  55   a  into the abovementioned specific portions of the frame  51  of the unit  50 , the connective members  54  ( 54 L and  54 R) are put through both the holes  55   b  ( 55   b L and  55   b R) and holes  51   a  ( 51   a L and  51   a R), respectively. With the insertion of the connective members  54 , the units  50  and  40  are connected to each other in such a manner that they are allowed to rotationally move relative to each other about the connective members  54 . 
     The cartridge  2  is provided with a pair of compression coil springs  46 , which are attached to the base portions of the arm portions  55   a  ( 55   a L and  55   a R), respectively, in such a manner than after the unitization of the two units  40  and  50 , the compression coil springs  45  are in contact with the frame  51  of the latent image formation unit  50 . Thus, the unit  40  remains pressed downward by the force generated by the resiliency of the springs  46 , ensuring that the development roller  41  ( FIG. 2 ) is kept pressed toward the drum  20 . Further, the lengthwise end portions of the development roller  41  are fitted with a pair of gap maintaining members (unshown), one for one. Thus, a preset amount of distance is maintained between the development roller  41  and drum  20 . 
     (Latent Image Formation Unit) 
     Next, referring to  FIGS. 2 and 4 , the latent image formation unit  50  will be described.  FIG. 4  is a perspective view of the latent image formation unit  50 . 
     The toner image developed by the unit  40  (unit having development roller  41 ) is transferred onto the sheet P in the transfer portion as described above. The toner remaining on the drum  20  after the transfer is scraped down by the blade  52 , and then, is scooped into the aforementioned toner chamber  51   e  by a scooping sheet  14   a , and remains stored therein. 
     The blade  52  is a means for removing the toner remaining on the drum  20  after the transfer. In order to prevent the toner from leaking from the toner chamber  51   e , the latent image formation unit  51  is provided with a first sealing member  14   b  (unshown) and a second sealing member  14   c , which are securely attached to the predetermined portions of the latent image formation unit  51 , with the use of a piece of two-sided adhesive tape or the like. The first and second sealing members  14   b  and  14   c  are for preventing the toner from leaking from the rear side of the corresponding lengthwise ends of the rubber portion of the blade  52 . 
     The blade  52  is firmly attached to a predetermined portion of the latent image formation unit  51 , with a pair of small screws  58 . The latent image formation unit  51  is also provided with a third sealing member  14   d , which is a member for preventing the toner from leaking from the lengthwise ends of the rubber portion of the blade  52 , and also, for wiping way the substances, such as toner, having adhered to the drum  20 . Further, the abovementioned scooping sheet  14   a , which is a sheet for scooping up the toner removed from the drum  20 , is also firmly attached to the latent image formation unit  51  with the use of a piece of two-sided adhesive tape or the like. 
     Further, the latent image formation unit  51  is fitted with an electrode  15 , a pair of charge roller bearings  13  ( 13 L and  13 R); the electrode  15  and charge roller bearings  13  are embedded in the frame portion of the latent image formation unit  51 . The shaft portions  12   a  ( 12   a L and  12   a R) are fitted in the bearings  13  ( 13 L and  13 R), respectively. 
     The electrophotographic photosensitive member assembly  21  (which hereafter will be referred to simply as drum assembly  21 ) is provided with a drum flange  151 , which makes up one of the lengthwise ends of the drum assembly  21 . The drum flange  151  has a rotational force receiving member  150 , through which the drum assembly  21  receives rotational force from the apparatus main assembly  1 . The method for attaching the drum flange  151  to the drum  20  is crimping, bonding, welding, or the like method. The drum assembly  21  is also provided with a drum flange  152 , which is attached to the other lengthwise end of the drum  20 , that is, the lengthwise end, from which the drum  20  is not driven. The drum flange  152  is provided with a ground contact, etc., which are integral with the drum flange  152 . 
     The drum assembly  21  is fitted into the latent image formation unit slot in the latent image formation unit frame  51  in such a manner that the drum flange  151  attached to one of the lengthwise end of the drum  20  rotatably fits into the bearing member  158 . At the other lengthwise end of the latent image formation unit frame  51 , not only is a drum shaft  159  pressed through the drum shaft hole of the latent image formation unit frame  51  so that the drum shaft  159  is firmly attached to the latent image formation unit frame  51 , but also, through the hole  152   a  of the drum flange  152  (drum flange on the side from which latent image formation unit is not driven), in such a manner that the drum flange  152  (drum assembly  21 ) is allowed to rotate about the drum shaft  159 . 
     Further, the unit  50  is provided with a protective member  101  and a pressure application spring  102 . The protective member  101  is for shielding the drum  20  from light, and also, for protecting the drum  20 . The spring  102  is attached to one  101   a L of the lengthwise ends of the shaft portion of the protective member  101 . The protective member  101  is attached to the latent image formation unit frame  51  (drum supporting frame) by fitting the shaft portion  101   a L and  101   a R of the protective member  101  into the bearing portions  51   d  ( 51   d L and  51   d R), respectively, of the drum supporting frame  51 , which are roughly U-shaped in cross section. 
     (Developing Apparatus Unit) 
     Next, referring to  FIGS. 5 and 6 , the development unit  40  will be described.  FIG. 5  is a perspective view of the toner chamber portion of the development unit  40 , which is for describing the structure of the toner chamber  45 .  FIG. 6  is an exploded perspective view of the development unit  40 . 
     Referring to  FIG. 5 , the stirring member  43  is in the toner chamber  43 . More specifically, one of the lengthwise ends of the stirring member  43  is supported by a helical gear  28  (which hereafter will be referred to as stirring gear) attached to the wall of the toner storage container  40   a  from outside the container  40   a , whereas the other lengthwise end of the stirring member  43  is directly supported by the wall of the toner storage container  40   a . The stirring gear  28  rotates by receiving rotational force from the apparatus main assembly  1 . The stirring member  43  is rotated by the rotation of the stirring gear  28 . As the rotational force is transmitted to the stirring gear  28  from the apparatus main assembly  1 , the stirring gear  28  is thrust toward the other lengthwise end of the stirring member  43 , and therefore, the stirring member  43  is thrust toward the other lengthwise end of the stirring member  43 . 
     Next, referring to  FIG. 6 , the development unit  40  has a first gear  30  and a second gear  29 , which are rotatably attached to the toner storage container  40   a . The first and second gears  30  and  29  are in mesh with each other. Thus as the first gear  30  is rotated, the rotational force (driving force) is transmitted from the first gear  30  to the second gear  29 , and then, from the second gear  29  to the stirring gear  28 . 
     The toner storage container  40   a , the walls of which function as the frame portion of the development unit  40  having the toner chamber  45  and development chamber  44 , integrated with the lid  40   b  by ultrasonic welding as described above. 
     There is a toner delivery hole  37  between the development chamber  44  ( FIG. 2 ) and toner chamber  45 . The toner delivery hole  37  is the hole for moving the toner in the toner chamber  45 , from the toner chamber  45  to the development chamber  44 . Referring to  FIG. 5 , the toner delivery hole  34  is has a long and narrow rectangular shape. Designated by a referential code  37   a  are the top and bottom fringe portions of the toner delivery hole  37 , which are perpendicular to the direction in which the toner T is advanced into the development chamber  44 . Next, referring to  FIG. 6 , until the cartridge  2  is put to use for the first time, the toner delivery hole  37  remains sealed with a toner seal, which is thermally and removably bonded to the fringe portions  37   a  of the toner delivery hole  37  to keep hole  37  sealed. Thus, if the cartridge  2  is brand-new, a user is to pull out the toner seal  27  to open the toner delivery hole  37 . The toner seal  27  is pasted to the fringe portions  37   a  of the toner delivery hole  37 , which face the development chamber  44  (developing portion), as described above. As for the method for attaching the toner seal  27  to the fringe portions  37   a , any method may be employed as fits. As the user pulls out the toner seal  27 , the toner delivery hole  37  becomes open, allowing the toner T in the toner chamber  45 , to be delivered to the development chamber  44  so that the toner T comes into contact with the development roller  41 . 
     In practical terms, the toner delivery hole  37  is rectangular. That is, in some cases, because of the errors which occur during the manufacturing of the cartridge  2 , the hole  37  may not be perfectly rectangular; all four corners may not be properly angled (by 90°), or may be rounded. 
     Next, referring to  FIG. 6 , the development unit  40  has the toner storage container  40   a , lid  40   b , first lateral member  55 L, second lateral member  55 R, development roller  41 , and development blade  42 . It also has the components for supplying the development roller  41  with electricity, additional sealing members for preventing toner leakage, etc. 
     The development blade  42  is attached, along with a pair of cleaning members  38 , to the toner storage container  40   a , by its lengthwise ends, with the use of a pair of screws  59 . The cleaning members  38  are disposed in contact with the lengthwise end portions of the peripheral surface of the development roller  41 , one for one, and clean the portions of the peripheral surface of the development roller  41 , with which they are in contact. 
     Further, a development roller assembly  39  is fitted into a predetermined position of the development unit  40 . Incidentally, the development roller assembly  39  has a magnetic roller  41   a , which was inserted into the development roller  41  through the opening with which one of the lengthwise ends of the development roller  41  is provided. The development roller assembly  39  is also provided with a development roller flange  41   b , which is solidly attached to the abovementioned lengthwise end of the development roller assembly  39  by being pressed into the abovementioned hole. 
     The lengthwise end portions of the development roller  41  are fitted with a pair of gap maintaining member  48  ( 48 L and  48 R), one for one, which are for maintain a preset amount of distance between the peripheral surface of the drum  20  and that of the development roller  41 . The lengthwise end portions of the development roller  41  are also fitted with a pair of bearing members  47  ( 47 L and  47 R), one for one. 
     Further, one of the lengthwise ends of the development roller  41  is fitted with a development roller gear  49 . The gear  49  is in mesh with a gear  151   c  ( FIG. 4 ), with which the flange  151  attached to the corresponding lengthwise end of the drum  20 . The gear  49  transmits rotational force to the development roller  41 . The gear  49  is also in mesh with the abovementioned gear  30 . 
     Further, the development unit  40  has the first and second lateral members  55 L and  55 R, which are firmly attached to the second and first lengthwise ends, respectively, of the toner storage container  40   a . The bearing members  47  ( 47 L and  47 R) are precisely positioned by the lateral members  55 L and  55 R. The development roller  41  is rotatably supported by the bearing members  47 . Incidentally, the bearing members  47  ( 47 L and  47 R) make up the left and right lengthwise end portions of the development roller assembly  39 , respectively. 
     (Toner Conveying Mechanism) 
     Next, referring to  FIGS. 7-13 , the toner conveying mechanism, with which the development unit  40  is provided, will be described.  FIGS. 7(   a ) and  7 ( b ) are perspective views of the stirring member  43 , and show the structure of the stirring member  43 .  FIG. 8  is a sectional view of the development unit  40  after the proper attachment of the stirring member  43  to the unit  40 .  FIGS. 9(   a )- 9 ( c ), and  FIGS. 10(   a ) and  10 ( b ), are sectional views of the unit  40 , which are for describing the movement of the stirring member  43 , and the circulatory movement of the toner T.  FIGS. 11(   a ) and  11 ( b ) are sectional views of the stirring member  43  and its adjacencies, and show the positional relationship between the stirring member  43  and toner delivery hole  37 , in terms of their lengthwise direction.  FIG. 12  is a perspective view of one of the lengthwise end portion of the stirring member  43 , and its adjacencies, and shows the shape of the lengthwise end portion.  FIGS. 13(   a ) and  13 ( b ) are sectional views of one of the lengthwise end portions of the modified version of the stirring member  43  in the preferred embodiment, which is different in shape from the one in the preferred embodiment. They show the positional relationship between the modified version of the stirring member  43  and the toner delivery hole  37 , in terms of their lengthwise direction. 
     First, referring to  FIGS. 7(   a ),  7 ( b ), and  8 , the toner conveying mechanism will be described regarding its structure. 
     Referring to  FIG. 7(   a ), the stirring member  43  has a supporting portion  43   a  and a stirring portion  43   a . The supporting portion  43   a  is rotatably supported in the toner chamber  45  by the wall of the toner chamber  45 . The stirring portion  43   b  is attached to the supporting portion  43   a . Designated by a referential code  43   f  is one of the lengthwise edges of the stirring portion  43   b , by which the stirring portion  43   b  is attached to the supporting portion  43   a . This edge hereafter will be referred to as the attachment edge  43   f . Designated by a referential code  43   e  is the opposite lengthwise edge of the stirring portion  43   b  from the attachment edge  43   f . Further, the supporting portion  43   a  is provided with multiple projections  43   c , which are aligned in the direction parallel to the lengthwise direction of the supporting portion  43   a , with the provision of present intervals, whereas the attachment portion  43   f  is provided with multiple holes  43   d , which are also aligned in the direction parallel to the lengthwise direction of the stirring member  43 , with the presence of preset intervals equal to those of the supporting portion  43   a . Thus, the stirring portion  43   b  is firmly attached to the supporting portion  43   a  by positioning the stirring portion  43   b  relative to the supporting portion  43   a , in such a manner that the projection  43   c  fit into the holes  43   d , one for one, and then, melting the projections with the application of heat to prevent the projections from coming out of the holes  43   d  ( FIG. 7(   b )). 
     The stirring portion  43   b  is an elastic and resilient sheet, being therefore capable of flexing when it is conveying the toner, as will be described later in more detail. In this embodiment, a sheet made of polyphenyl sulfide (PPS), which is 50 μm in thickness, is used as the material for the stirring portion  43   b . It should be noted here that the material for the stirring portion  43   b  does not need to be limited to a sheet of PPS. For example, a sheet of polyethylene-terephthalate (PET) or the like can be used to obtain the same effects as those obtained by the sheet of PPS. 
     Next, referring to  FIG. 8 , the stirring member  43  is located next to the toner delivery hole  37  of the toner chamber  45 . It is rotated in the direction indicated by an arrow mark Y, by the rotation of the stirring gear  38  ( FIG. 6 ). As it is rotated, it stirs the toner T (unshown) in the toner chamber  45 . 
     The stirring member  43  conveys the toner T in the toner chamber  45 , from the toner chamber  45  to the development chamber  45 , in which the development roller  41  is located, while stirring the toner T. 
     The bottom surface  45   a  of the toner chamber  45  is provided with a curvature, the center of which coincides with the rotational center of the stirring member  43 . The radius TR 2  of this bottom surface  45   a  is smaller than the radius TR 1  of the locus of the sweeping edge  43   e  (conveying edge, stirring edge) ( FIG. 7 ) of the stirring portion  43   b  when the stirring portion  43   b  is straight. Thus, when the stirring portion  43   b  conveys the body of toner T through the portion of the toner chamber, which is next to the curved portion of the bottom surface of the toner chamber  45 , it resiliently bends. 
     Next, referring to  FIGS. 9(   a )- 9 ( c ),  10 ( a ) and  10 ( b ), the operation of the toner conveying mechanism will be described.  FIGS. 9(   a )- 9 ( c ) show the state, in which the toner T and stirring member  43  are, when the stirring member  43  is conveying the toner T toward the development chamber  44 .  FIGS. 10(   a ) and  10 ( b ) show the state, in which the toner T and stirring member  43  are, when the stirring member  43  is conveying the toner T in the opposite direction from the development chamber  44 . 
     Referring to  FIG. 9(   a ), the stirring portion  43   b  is conveying the toner T from the toner chamber  45  toward the development chamber  44 , while being flexed by the bottom surface  45   a  of the toner chamber  45 . When the stirring  43  is in the state shown in  FIG. 9(   a ), it is conveying the body of toner T, which is between the stirring member  43  and toner chamber  45 , in a manner to pushing the body of toner T into the development chamber  44 . Incidentally, the lengthwise direction of the toner chamber  45  is parallel to the development roller  41  (cartridge  2 ). 
     Next, referring to  FIG. 9(   b ), as the abovementioned body of toner T is conveyed to the adjacencies of the development chamber  45 , it is moved into the development chamber  44  by the further rotational movement of the stirring portion  43   b  across the toner delivery hole  37 . 
     While the stirring portion  43   b  is moved from its position shown in  FIG. 9(   b ) to the position shown in  FIG. 9(   c ), the stirring portion  43   b  leaves the arcuate portion of the bottom surface  45   a  of the toner chamber  45 . Thus, the stirring portion  43   b , which was remaining flexed, is allowed to straighten. As a result, the sweeping edges portion ( 43   e ) enters the development chamber  44  through the toner delivery hole  37 . This is how the toner T in the toner chamber  45  is moved into the development chamber  44  through the toner delivery hole  37 . Further, it is also by the straightening of the stirring portion  45   b  that the toner T is moved from the toner chamber  45  into the development chamber  44 . The lengthwise end portions of the sweeping edge portion ( 43   e ) are shaped in such a manner that their edges are slanted relative to the lengthwise direction of the stirring member  43 ; the stirring portion  43   b  has slanted edges  43 R and  43 L ( FIG. 11) , as will be described later in more detail. Thus, even after the stirring portion  43   e  straightens after remaining flexed, the sweeping edge portion ( 43   e ) does not interferes with the lateral edges of the toner delivery hole  37 . 
     Next, referring to  FIG. 10(   a ), even after the toner T is conveyed from the toner chamber  45  into the development chamber  44  by the rotation of the stirring portion  43   b  (stirring member  43 ), the sweeping edge portion ( 43   e ) of the stirring portion  43   b  remains extending into the development chamber  44  through the toner delivery hole  37 . Therefore, even after the stirring member  43  begins to rotate in the direction to return from the development chamber  44  to the toner chamber  44 , the sweeping edge portion ( 43   e ) is still in the development chamber  44 . Thus, as the stirring member  43  rotates in the direction to return to the toner chamber  45 , the body of toner T, which is in the adjacent portion of the development chamber  44  to the toner delivery hole  37 , can be moved back into the toner chamber  45  (developer storage portion). 
     Next, referring to  FIG. 10(   b ), while the stirring member  37  is rotated in the direction to cause the stirring portion  43   b  to move from the development chamber  44  back into the toner chamber  45 , the sweeping edge portion ( 43   e ) of the stirring portion  43   b  remains in contact with the lengthwise edge  37   a   1  (top edge of toner delivery hole  37 ) of the top portion of the fringe portion  37   a  of the toner delivery hole  37 , being thereby flexed again (as shown in  FIG. 10(   b )). More specifically, the edge  37   a   1  of the top portion of the fringe portion  37   a  is the lengthwise edge of the toner delivery hole  37 , which is on the top side of the hole  37  when the cartridge  7  is in its image forming position in the apparatus main assembly  1 . 
     As the stirring member  43  further rotates, the sweeping edge portion ( 43   e ) of its stirring portion  43   b  leaves the lengthwise edge  37   a   1  of the toner delivery hole  37 . As the sweeping edge  43   e  leaves the lengthwise edge  37   a   1 , the stirring portion  37   b  is allowed to straighten, causing the toner T having adhered to the stirring portion  43   b , to be return into the toner chamber  45 . That is, not only is the toner T on the stirring portion  43   b  conveyed back into the toner chamber  45  by the rotation of the stirring member  43   b  (stirring member  43 ), but also, by the resiliency of the stirring portion  43   b , which causes the stirring portion  43   b  to snappingly straighten back into its natural shape (shape before it is flexed). Therefore, it is ensured that the body of toner T on the stirring portion  43   b  is moved back into the toner chamber  45 . 
     Thus, the toner T in the development unit  40  is satisfactorily moved in a circulatory manner, from the toner chamber  45  to the development chamber  44 , and then, from the development chamber  44  to the toner chamber  45 , and then, from the toner chamber  45  to the development chamber  44 , and so on. 
     If the toner T is moved only by the rotational movement of the stirring portion  43   b , which is shown in  FIGS. 9(   a ),  9 ( b ), and  9 ( c ), it is possible that the development chamber  44  will be excessively supplied with the toner T. If the development chamber  44  is excessively supplied with the toner T, some of the toner T in the development chamber  44  is likely to become stagnant in the portion of the development chamber  44  (space in development chamber  44 ) surrounded by the gap maintaining member  48 L, which is located at one (left end) of the lengthwise ends of the development chamber  44 , and the fringe portion  37   a  of the toner delivery hole  37 , and also, in the portion of the development chamber  44  (space in development chamber  44 ) surrounded by the gap maintaining member  48 R, which is located at the other (right end) lengthwise end of the development chamber  44 , and the fringe portion  37   a  of the toner delivery hole  37  ( FIG. 6) . Here, “excessively supplied with the toner T” means that the amount of the toner T moved into the development chamber  44  by the rotation of the stirring portion  43   b  (stirring member  43 ) exceeds the normal (proper) amount of the toner T, which is to be present in the development chamber  44  in order to properly develop a latent image. 
     As the development chamber  44  is supplied with an excessive amount of toner T, a substantial amount of toner T in the development chamber  44  becomes stagnant, that is, the toner T in the development chamber  44  has no place to go in the development chamber  45 , and therefore, it accumulates in the radius direction of the development roller  41 , in the adjacencies of the gap maintaining members  48 L and  48 R, which are at the lengthwise left and right ends of the development roller  41 . 
     In this embodiment, therefore, the toner returning operation, that is, the operation for returning the body of toner T having been conveyed into the development chamber  44  is partially returned from the development chamber  44  to the toner chamber  45 , which will be described next, is carried out ( FIGS. 10(   a ) and  10 ( b )). This embodiment makes it possible to efficiently convey the toner T backward, as will be described later. That is, it makes it possible to efficiently convey the toner T, in a circulatory manner, from the toner chamber  45  to the development chamber  44 , and then, from the development chamber  44  to the toner chamber  45 , and the, from the toner chamber  45  to the development chamber  44 , and so on. 
     Further, referring to  FIGS. 11 and 12 , the return conveyance of the toner T, that is, the conveyance of the toner T from the development chamber  44  to the toner chamber  44 , will be described in detail.  FIG. 11(   b ) is an enlarged view of the lengthwise right end portion of the stirring member  43  and its adjacencies, shown in  FIG. 11(   b ), and  FIG. 11(   c ) is an enlarged view of the lengthwise left end portion of the stirring member  43  and its adjacencies, shown in  FIG. 11(   a ). In the following portion of the description of this embodiment, “width” means the distance (length) from one lengthwise end of a given component to the other lengthwise end of the same component. Further, the abovementioned “lengthwise directions” means the direction parallel to the lengthwise directions of the toner delivery hole  37 , stirring portion  43   b , development chamber  44 , and toner chamber  45 , and therefore, are parallel to each other. 
       FIG. 11  is a drawing for showing the relationship among: the width L 4  of the toner chamber  45 ; width L 3  of the attachment edge portion  43   f  of the stirring portion  43   b , by which the stirring portion  43   b  is attached to the supporting portion  43   a ; the width L 2  of the other lengthwise edge  43   e  of the stirring portion  43   b ; and width L 1  of the toner delivery hole  37 . 
     The comparison of these portions of the development unit  40  reveals the following. The width L 4  of the toner chamber  45  is greater than the width L 1  of the toner delivery hole  37  and the width L 3  of the lengthwise edge  43   f . Further, the width L 3  of the lengthwise edge  43   f  is greater than the width L 1  of the hole  37 , and the width L 2  of the sweeping edge  43   e  is less than the width L 1  of the hole  37 . That is, L 4 &gt;L 3 &gt;L 1 &gt;L 2 . The width L 2  of the sweeping edge  43   e  of the stirring portion  43   b  is less than the width L 1  of the hole  37 . Further, the stirring member  43  is positioned so that its stirring portion  43   b  can extends by a preset length into the development chamber  44  through the hole  37 . Thus, as the stirring member  43  is rotated, the sweeping edge portion ( 43   e ) enters from the toner chamber  45  into the development chamber  44  through the hole  37 . Referring to  FIG. 11 , designated by referential codes  45 R and  45 L are the inward surface of the right lateral wall of the toner chamber  45 , and the inward surface of the left lateral wall of the toner chamber  45 , respectively. 
     Next, referring to  FIGS. 11 and 12 , the lengthwise end portions of the sweeping edge  43   e  are shaped so that it has a first slanted edge  43 R and a second slanted edge  43 L, which slant toward the supporting portion  43   a . To describe in more detail, referring to  FIGS. 11(   b ) and  12 , one of the lengthwise end portions, that is, one of the corner portions, of the sweeping edge portion ( 43   e ), is shaped in such a manner that the resultant edge  43 R is slanted toward the supporting portion  43   a . Further, referring to  FIG. 11(   c ), the other lengthwise end portion, that is, the other corner portion, of the sweeping edge portion ( 43   e ) is shaped in such a manner that the resultant  43 L is also slanted toward the supporting portion  43   a.    
     The lengthwise edge portion ( 43   e ), that is, the sweeping edge portion, of the stirring portion  43   b , and the lengthwise edge portion ( 43   f ) of the stirring portion  43   b , by which the stirring portion  43   b  is attached to the supporting portion  43   a , are parallel to each other. Further, the widthwise edges of the stirring portion  43   e  are practically parallel to each other. The expression “practically parallel” is used because they may not be perfectly parallel to each other due to the errors which occurred during the manufacturing of the process cartridge  2 . 
     The width L 2  of the sweeping edge  43   e  is less than the width L 1  of the toner delivery hole  37 . Thus, when the stirring member  43  is rotated, the first and second slanted edges  43 R and  43 L do not come into contact with the lateral edges  37   a  and  37   b  of the hole  37 , respectively (no contact). That is, when the stirring member  43  is conveying the toner T from the toner chamber  45  into the development chamber  44 , it can enter (extend) into the development chamber  44  through the toner delivery hole  37  without coming into contact with the lateral edges of the hole  37 . 
     In this embodiment, L 1  is roughly 205 mm, and L 2  is roughly 200 mm. L 3  is roughly 210 mm, and L 4  is roughly 215 mm. Further, the angle α of the first edge  43 R relative to the sweeping edge  34   e , and the angle α of the second edge  43 L relative to the sweeping edge  34   e , are roughly 135 degrees ( FIG. 11 ). 
     However, these values are not intended to limit the present invention in scope. That is, the size of each of the abovementioned components, and the angle of each of the abovementioned portions, have only to be selected as fit. 
     According to the preferred embodiment described above, the stirring member  43  has: the supporting portion  43   a  rotatably disposed in the toner chamber  45  (developer storage portion); and stirring portion  43   g  attached to the supporting portion  43   a  in such a manner that its lengthwise direction become parallel to that of the supporting member  43   a . The edge portion ( 43   f ) of the stirring portion  43   b , by which the stirring portion  43   b  is attached to the supporting portion  43   a , is greater in length than the toner delivery hole  37 . Further, the sweeping edge  43   e  of the stirring portion  43   b  is less in length than the toner delivery hole  37 . Further, when the stirring portion  43   b  is moving in the direction to convey the toner T into the development chamber  44 , the sweeping edge portion ( 43   e ) of the stirring portion  43   b  snappingly extends into the development chamber  44  through the toner delivery hole  37  to convey the toner T (developer) from the toner chamber  45  (developer storage portion) into the development chamber  44  (developing station) through the hole  37 , whereas when the stirring portion  43   b  is moving toward the toner chamber  45  (developer storage portion), the sweeping edge portion ( 43   e ) partially conveys back into the toner chamber  45 , the body of toner T which it moved into the development chamber  44  through the toner delivery hole  37  by its movement toward the development chamber  44 . 
     That is, according to the preferred embodiment described above, when the stirring portion  43   b  is moving toward the development chamber  44  while the stirring member  43  rotates, the sweeping edge portion ( 43   e ) of the stirring portion  43  conveys the toner T in the toner chamber  45  (developer storage portion), from the tone chamber  45 , into the development chamber  44  (developing portion) through the toner delivery hole  37  by extending into the development chamber  44  through the toner delivery hole  37  (toner supplying movement), whereas when the stirring portion  43   b  is moving toward the toner chamber  45  (developer storage chamber) while the stirring member  43  rotates, the sweeping edge portion ( 43   e ) partially conveys back into the toner chamber  45  (developer storage chamber), the body of toner T it conveyed into the development chamber  44  through the development delivery hole  37  by its movement toward the development chamber  44  (toner recovery movement). That is, for each full rotation of the stirring member  43 , the stirring portion  43   b  of the stirring member  43  conveys the toner T in the toner chamber  45 , to the development chamber  44 , and also, conveys the toner T in the development chamber  44 , to the toner chamber  45 . More specifically, according to this preferred embodiment, when the stirring portion  43   b  is rotationally moving from the toner chamber  45  to the toner delivery hole  37 , it conveys the toner T in the toner chamber  45 , to the development chamber  44 , whereas when it is rotationally moving from the development chamber  44  to the toner chamber  45 , it conveys the toner T in the development chamber  44 , to the toner chamber  45 . 
     Further, the distance between the inward surface of the right lateral wall  45 R of the toner chamber  45  and the inward surface of the left lateral wall  45 L is greater than the length of the toner delivery hole  37 . Further, the toner delivery hole  37  is made slightly shorter than the toner chamber  45  and development chamber  44  to leave a pair of small fringe portions  37   a  at its lengthwise ends, one for one. The small fringes portions  37   a  extend in the direction perpendicular to the direction in which the toner T is advanced into the development chamber  44 . 
     The presence of these fringe portions  37   a  makes it possible to removably attach the toner seal  28  to seal the toner delivery hole  37  in such a manner that it can be removed to reopen the hole  37 . As the stirring member  37  further rotates, the sweeping edge portion ( 43   e ) of the stirring portion  43   b  is flexed, and then, the sweeping edge  43   e  comes into contact with the lengthwise edge  37   a   1  of one of the fringe portions  37   a  of the toner delivery hole  37 , across the entirety of the edge  37   a   1 . Here, the lengthwise edge  37   a   1  is the lengthwise edge of the toner delivery hole  37 , which is on the top side when the cartridge  2  is in its image forming position in the apparatus main assembly  1 . 
     Then, as the sweeping edge  43   e  leaves the lengthwise edge  37   a   1 , it allows the stirring portion  43   b  to snappingly straighten. Thus, the toner T on the stirring portion  43   b  is flung back into the toner chamber  43  by this springy straightening of the stirring portion  43   b , which is caused by the resiliency of the stirring portion  43   b . Therefore, it is ensured that a part of the body of toner T conveyed into the development chamber  44  is conveyed back into the development chamber  44 . In other words, the toner T is satisfactorily moved in the cartridge  2  in a circulatory manner. 
     Further, the stirring portion  43   b  is shaped so that both of the lengthwise end portions of the sweeping edge portion ( 43   e ) of the stirring portion  43   b  slant toward the supporting portion  43   a  of the stirring member  43 ; there are the first and second slanted edges  43 R and  43 L. It is by the presence of these slanted edges  43 R and  43 L that the above described effects are obtained. 
     Further, when the stirring member  43  rotates, the first and second slanted edges  43 R and  43 L do not come into contact with the edges of the right and left fringe portions  37   a  of the toner delivery hole  37 . Therefore, it is ensured that the above-described effects are obtained. 
     The supporting portion  43   a  of the stirring member  43  is provided with multiple projections  43   c , which align in the lengthwise direction of the supporting portion  43   a  with the presence of the preset intervals, whereas the attachment portion  43   f  is provided with multiple holes  43   d , which are also aligned in the direction parallel to the lengthwise direction of the stirring member  43 , with the presence of preset intervals. Thus, the stirring portion  43   b  is attached to the supporting portion  43   a  by the following method. That is, the stirring portion  43   b  is positioned relative to the supporting portion  43   a  in such a manner that the projections  43   c  fit into the holes  43   d , one for one. Then, in order to prevent the projections  43   c  from coming out of the holes  43   d , the portion of each projection  43   c , which is extending beyond the stirring portion  43   b , is made greater in diameter than the corresponding hole  43   d , by applying heat to the extending portion, and then, cooling it (naturally or forcefully). This is how the stirring portion  43   b  is attached to the supporting portion  43   a . 
     That is, the stirring portion  43   b  is attached to the supporting portion  43   a  by thermally melting the projections  43   c  while keeping the projections  43   c  fitted in the holes  43   d.    
     In other words, the stirring member  43   b  can be easily attached to the supporting portion  43   a  without using an adhesive. 
     Further, the development unit  40  has the stirring gear  28  (helical gear), which is located outside one of the lateral wall  45 L of the toner chamber  45 . The stirring gear  38  rotates with the supporting portion  43   a . As the stirring gear  28  rotates, it generates a thrust directed toward the other lengthwise end of the supporting portion  43   a . Thus, while the stirring member  43  is rotated, the supporting portion  43   a  (stirring member  43 ) is kept pressed toward the other lengthwise end. 
     Next, referring to  FIG. 13 , the positional relationship between a stirring member  43 , which is different in shape from the stirring member  43  in the above described preferred embodiment of the present invention, and the toner delivery hole  37 , will be described.  FIG. 13(   a ) is a drawing for showing the positional relationship among the components of the toner conveying mechanism, and their portions, in terms of the lengthwise direction, in the preferred embodiment of the present invention.  FIG. 13(   b ) is a drawing for showing the positional relationship among the components of the toner conveying mechanism, and their portions, in terms of the lengthwise direction, in a comparative example of a toner conveying mechanism for a process cartridge. 
     In the case of the toner conveying mechanism shown in  FIG. 13(   a ), there is the following relationship among: the width L 4  of the toner chamber  45 ; width L 3  of the edge  43   f  of the attachment edge portion of the stirring portion  43   b , by which the stirring portion  43   b  is attached to the supporting portion  43   a ; the width L 2  of the other lengthwise edge, that is, the sweeping edge  43   e , of the stirring portion  43   b ; and width L 1  of the toner delivery hole  37 : L 4 &gt;L 3 &gt;L 1 &gt;L 2 . 
     On the other hand, in the case of the toner conveying mechanism shown in  FIG. 13(   b ), the relationship among: the width L 4  of the toner chamber  45 , width L 3  of the lengthwise edge  43   f  of the attachment portion of the stirring portion  43   b , by which the stirring portion  43   b  is attached to the supporting portion  43   a ; the width L 2  of the other lengthwise edge, that is, the sweeping edge  43   e , of the stirring portion  43   b ; and width L 1  of the toner delivery hole  37  is: L 4 &gt;L 1 &gt;L 3 =L 2 . That is, the stirring portion ( 43   b ) is practically rectangular. 
     It is evident from the comparison between  FIGS. 13(   a ) and  13 ( b ) that the shape of the stirring portion  43   b  in  FIG. 13(   a ) is such that the stirring portion  43   b  is narrowest at the sweeping edge  43   e , and widens toward the edge  43   f  of the attachment portion. Thus, the corner portion X of the stirring portion  43   b  in  FIG. 13(   a ) is higher in rigidity than the corner portion X of the stirring portion  43   b  in  FIG. 13(   b ). 
     Thus, when the sweeping edge portion ( 43   e ) bears the weight of the body of toner T, the corner portion X in  FIG. 13(   b ) is likely to more easily flex compared to the corner portion X in  FIG. 13(   a ), because the corner portion X in  FIG. 13(   b ) is lower in rigidity than the corner portion X in  FIG. 13(   a ). 
     Therefore, shaping the stirring portion ( 43   b ) as shown in  FIG. 13(   a ), which shows the stirring portion  43   b  in the preferred embodiment of the present invention, offers the following advantages over shaping the stirring portion ( 43   b ) as shown in  FIG. 13(   b ). That is, in a case where the stirring portion  43   b  is shaped as shown in  FIG. 13(   a ) which shows the stirring portion  43   b  in the preferred embodiment, it is ensured that when the stirring portion  43   b  is rotationally moving toward the toner chamber  45 , the body of toner T conveyed into the developer chamber  44  is partially conveyed back into the toner chamber  45  by being carried on the sweeping edge portion ( 43   e ) of the stirring portion  43   a , which has extended into the development chamber  44  through the toner delivery hole  37  as shown in  FIGS. 10(   a ) and  10 ( b ). The arrow marks R 2  in  FIGS. 13(   a ) and  13 ( b ) indicate the bodies of toner T, which have become stagnant in the lateral end portions of the development chamber  44 . 
     Further, a stirring portion  43   b  shaped as shown in  FIG. 13(   a ), which shows the stirring portion  43   b  in the preferred embodiment of the present invention, is greater in the amount by which the toner T is conveyed from the development chamber  44  to the toner chamber  45  than the stirring portion  43   b  shaped as shown in  FIG. 13(   b ). 
     Regarding the dimensional and positional relationship among the components in the toner chamber  45  and their portions, the smaller the difference between the width L 3  of the edge  43   f  of the stirring portion attachment portion and width L 4  of the toner chamber  45 , the smaller the gap S between the lateral wall  45 R of the toner chamber  45  and the corresponding lengthwise end of the stirring portion  43   b , and the gap S between the lateral wall  45 L and the adjacent lengthwise end of the stirring portion  43   b  ( FIGS. 13(   a ) and  13 ( b )). 
     Shaping the stirring portion  43   b  as shown in  FIG. 13(   a ) can make the gap S smaller than shaping the stirring portion  43   b  as shown in  FIG. 13(   b ). 
     The narrower the gap S, the closer to the inward surface of the lateral wall  45 R of the toner chamber  45  and the inward surface of the lateral wall  45 L of the toner chamber  45 , the stirring portion  43   b  can stir the toner T, and therefore, the wider the range, in terms of the lengthwise direction of the toner chamber  45 , in which the stirring portion  43   b  can convey the toner T while stirring it. 
     The gap S shown in  FIG. 13(   a ) is narrower than that shown in  FIG. 13(   b ). Therefore, the stirring portion  43   b  shaped as shown in  FIG. 13(   a ) can convey the toner T in a wider range, in terms of the lengthwise direction of the toner chamber  45 , while stirring the toner T, than the stirring portion  43   b  shaped as shown in  FIG. 13(   b ). 
     From the standpoint of the efficiency with which the toner T is conveyed in a circulatory manner in the development unit, that is, the toner is conveyed from the toner chamber  45  to the development chamber  44 , and then, from the development chamber  44  back into the toner chamber  45 , and so on, the shape for the stirring portion  43   b , which is shown in  FIG. 13(   a ), is superior to that shown in  FIG. 13(   b ). 
     Further, the lengths L 4 , L 3 , and L 2  of the toner chamber  45 , stirring portion  43   b , and toner delivery hole  37 , respectively, are set to satisfy the following relationship: L 4 &gt;L 3 &gt;L 1 &gt;L 2 . This arrangement can further improve the cartridge  2  in terms of the conveyance of the toner T from the toner chamber  45  into the development chamber  44 , and then, from the development chamber  44  back into the toner chamber  45 ; the toner T is more satisfactorily conveyed. That is, according to the preferred embodiment of the present invention, the toner T is efficiently conveyed in a circulatory manner in the cartridge  2 , that is, from the toner chamber  45  to the development chamber  44 , and then, from the development chamber  44  to the toner chamber  45 , and so on. 
     Also according to the preferred embodiment described above, the toner T in the toner chamber  45  can be stirred across a wider range of the toner chamber  45  in terms of its lengthwise direction. Further, since the toner T in the toner chamber  45  is conveyed from the toner chamber  45  to the development chamber while being stirred across the wider range of the toner chamber  45  in terms of its lengthwise direction, the entire range of the development roller  41  in terms of its lengthwise direction is more uniformly supplied with the toner T. Therefore, it becomes possible to reliably output high quality images, that is, images which are accurate in density across the entire range in terms of the direction parallel to the development roller  41 . 
     Further, the forward toner conveyance, that is, the toner conveyance from the toner chamber to the development chamber, the reverse toner conveyance, that is, the toner conveyance from the development chamber to the toner chamber, can be repeatedly carried out with improved efficiency. The alternate repetition of the forward toner conveyance and reverse toner conveyance can prevent supplying the development chamber with an excessive amount of toner, and also, can reduce the amount by which toner becomes stagnant in the development chamber. 
     Therefore, it is possible to prevent the following problem: as the development chamber  44  is continuously supplied with an excessive amount of toner, the stagnant toner in the development chamber  44  is robbed by the excessive amount of toner, of the place to go in the development chamber  44 , being thereby cornered into the lengthwise end portions of the development chamber  44 , and eventually, it accumulates at the lengthwise ends of the development roller  41 . 
       FIGS. 14(   a ) and  14 ( b ) are plan views of the stirring member  43 , which are for showing the structure of the stirring member  43 . 
       FIG. 14(   a ) shows the overall shape of another modified version of the stirring member  43  in the preferred embodiment, and  FIG. 14(   b ) shows the lengthwise right end portion of the stirring member  43 , and its adjacencies, after the installation of the stirring member  43  into the toner chamber  45 . 
     The stirring portion  43   b  shown in  FIG. 14(   a ) has a portion  43   g , which extends beyond the sweeping edge portion ( 43   e ) of the stirring portion  43   b  shown in  FIG. 13(   a ). More specifically, not only is this stirring portion  43   b  shaped in such a manner that the lengthwise right and left end portions of its sweeping edge portion ( 43   e ) have the abovementioned first and second slanted edges  43 R and  43 L, respectively, but also, its sweeping edge portion ( 43   e ) has the portion  43   g , which extends beyond the line connecting the inward ends of the first and second slanted edges  43 R and  43 L. Thus, in the case of this stirring portion  43   b , the sweeping edge  43   e  is the lengthwise edge of the portion  43   g . That is, in this modification of the preferred embodiment, the sweeping edge portion of the stirring portion  43   b  is shaped so that the portion  43   g , which is practically a long and narrow rectangular portion, is positioned between the inward end of the first slanted edge  43 R, and the inward end of the second slanted edge  43   l , in terms of the lengthwise direction of the stirring portion  43   b.    
     Next, referring to  FIG. 14(   b ), the relationship among: the width L 4  of the toner chamber  45 , width L 3  of the lengthwise edge  43   f  of the attachment portion ( 43   f ) of the stirring portion  43   b ; width L 2  of the sweeping edge  43   e ; and width L 1  of the toner delivery hole  37  is: L 4 &gt;L 3 &gt;L 1 &gt;L 2 . That is, it is the same as that in the preferred embodiment. Further, the width L 2  of the sweeping edge  43   e  of the stirring portion  43   b  is less than the width L 1  of the toner delivery hole  37 . Moreover, the stirring member  43  is positioned so that the sweeping edge portion ( 43   e ) of the stirring portion  43   b  extends farther into the development chamber  44  through the toner delivery hole  37 . 
     When the toner T is conveyed to the development chamber  44 , the above described practically rectangular portion  43   g  having the sweeping edge  43   e  does not come into contact with the lateral fringe portions  37   a  of the toner delivery hole  37 . Further, when the toner T is conveyed to the development chamber  44 , the sweeping edge portion ( 43   e ) of the stirring portion  43   b  reaches farther into the development chamber  44  through the toner delivery hole  37 . 
     Further, when the toner T is reversely conveyed, the sweeping edge portion ( 43   e ) of the stirring portion  43   b  can return some of the toner T in the development chamber  44  to the toner chamber  45 . 
     The greater the dimension of the protruding edge portion  43   g  in terms of the direction perpendicular to the lengthwise direction of the stirring member  43 , the farther the sweeping edge portion ( 43   e ) reaches into the development chamber  44 , and therefore, the greater the amount by which the toner T in the development chamber  44  is conveyed back into the toner chamber  45  during the reverse toner conveyance. 
     The dimension of the protruding edge portion  43   g  is set in consideration of the amount by which the toner T is conveyed from the toner chamber  45  to the development chamber  44 , and the amount by which the toner T is reversely conveyed, that is, from the development chamber  44  to the toner chamber  45 . 
     According to the above described preferred embodiment of the present invention and its modification, the toner T (developer) in the cartridge  2  can be satisfactorily conveyed in a circulatory manner, that is, from the toner chamber  45  (developer storage portion) to the development chamber  44 , and then, from the development chamber  44  to the toner chamber  45 , and then, from the toner chamber  45  to the development chamber  44 , and so on. 
     Also, according to the above described preferred embodiment and its modification, not only is it possible to satisfactorily convey the toner T in the toner chamber  45  to the development chamber  44 , but also, it is possible to satisfactorily return the toner T in the development chamber  44  to the toner chamber  45 . 
     Also, according to the above described preferred embodiment and its modification, not only is it possible to satisfactorily convey the toner T in the toner chamber  45  deeper into the development chamber  44 , but also, satisfactorily convey the toner from the development chamber  44  deeper into the toner chamber  45  than any of cartridges in accordance with the prior art. 
     Therefore, according to the above described preferred embodiment of the present invention and its modification, the toner T in the toner chamber  45  (cartridge  2 ) can be stirred across the wider range in terms of the lengthwise direction of the toner chamber  45  than that in any of cartridges in accordance with the prior art. Further, since the toner T in the toner chamber  45  is conveyed from the toner chamber  45  to the development chamber while being stirred across the wider range of the toner chamber  45  in terms of its lengthwise direction, the entire range of the development roller  41  in terms of its lengthwise direction is more uniformly supplied with the toner T. Therefore, it becomes possible to reliably output high quality images, that is, images which are accurate in density across its entire range in terms of the direction parallel to the development roller  41 . 
     Further, the forward toner conveyance, that is, the toner conveyance from the toner chamber  45  into the development chamber  44 , and the reverse toner conveyance, that is, the toner conveyance from the development chamber  44  into the toner chamber  45 , can be repeatedly carried out in a satisfactory manner. Therefore, the problem that the development chamber  44  is excessively supplied with the toner can be prevented by repeating the forward toner conveyance and reverse toner conveyance. Further, it is possible to minimize the amount by which the toner T becomes stagnant in the development chamber  44 . 
     Therefore, it is possible to prevent the occurrence of the phenomenon that the stagnant toner in the development chamber  44  is cornered into the lengthwise end portions of the development chamber, by the body of toner T, which is successively conveyed into the development chamber  44 , and eventually, the stagnant toner T cumulatively collect in the adjacencies of the lengthwise ends of the development roller  41 . 
     In the above described preferred embodiment of the present invention and its modification, the developing apparatus and electrophotographic photosensitive drum were integrally disposed in a cartridge to obtain a process cartridge which is removably mountable in the main assembly of an electrophotographic image forming apparatus. However, this structural arrangement is not intended to limit the present invention in scope. For example, a developing apparatus may be turned into a development cartridge which is removably mountable in the main assembly of an electrophotographic image forming apparatus. In a case where the developing apparatus is in the form of a development cartridge, a so-called process cartridge is made up of an electrophotographic photosensitive drum, and at least one processing means, more specifically, at least one of the cleaning means and charging means, which are integrally disposed in a cartridge. As for the developing apparatus, it may be in the forms of a development cartridge, or may be built in as a part of the main assembly of an electrophotographic image forming apparatus. 
     Further, the measurements, materials, and shapes of the structural components of the electrophotographic image forming apparatus in the above described preferred embodiment of the present invention and its modified version, and their positional relationship, should be altered as necessary, based on the structure of an apparatus to which the present invention is applied, and/or various factors which affect the operation of the apparatus. That is, the above-described preferred embodiment of the present invention is not intended to limit the present invention in scope, unless specifically noted. 
     While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth, and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims. 
     This application claims priority from Japanese Patent Application No. 198425/2008 filed Jul. 31, 2008 which is hereby incorporated by reference.