PATENT ABSTRACT
A developing apparatus usable with an electrophotographic image forming apparatus, the apparatus including a developer accommodating container, a developer chamber including a developer carrying member carrying and feeding a developer supplied from the container to develop an electrostatic latent image formed on an electrophotographic photosensitive member, a stirrer stirring the developer in the chamber and supplying the developer from the container into the chamber through an opening in the container, a wall surface, provided in the container, for being contacted by a free end portion of the stirrer while the stirrer moves, and a detector detecting a remaining amount of the developer. The position where the free end portion of the stirrer separates from the wall surface is above the detector and inside the container.

PATENT DESCRIPTION
FIELD OF THE INVENTION AND RELATED ART 
       [0001]    The present invention relates to an electrophotographic image forming apparatus, a developing apparatus employed by an electrophotographic image forming apparatus, and a process cartridge removably mountable in an electrophotographic image forming apparatus. 
         [0002]    Here, an “electrophotographic image forming apparatus” means an apparatus which forms an image on recording medium, using an electrophotographic image forming method. Examples of an electrophotographic image forming apparatus include an electrophotographic copying machine, an electrophotographic printer (laser beam printer, LED printer, etc.), a facsimile apparatus, a wordprocessor, and a multifunction apparatus capable of performing two or more functions of the preceding apparatuses, etc. 
         [0003]    A “developing apparatus” means an apparatus which develops an electrostatic latent image on an image bearing member, such as an electrophotographic photosensitive drum, into a visible image, with the use of developer. 
         [0004]    The process cartridge means a cartridge in which at least a developing means and an electrophotographic photosensitive drum, are integrally disposed so that they can be removably mountable in the main assembly of an electrophotographic image forming apparatus. 
         [0005]    As has been known, an image forming apparatus, such as a copying machine, a printer, or a facsimile machine, forms an electrostatic latent image on an image bearing member, such as an electrophotographic photosensitive member, and develops the electrostatic latent image into a visible image, more specifically, a visible image formed of toner, with the use of a developing apparatus. 
         [0006]    In the past, in the field of an image forming apparatus employing an electrophotographic image formation process, a process cartridge system has long been in use, according to which an electrophotographic photosensitive member, and one or more process cartridges which act on the electrophotographic photosensitive member, are integrally disposed in a cartridge removably mountable in the main assembly of an image forming apparatus. A process cartridge system makes it possible for a user to maintain an electrophotographic image forming apparatus without relying on a service person. Therefore, it can drastically improve an electrophotographic image forming apparatus, in terms of operability. 
         [0007]    One of the primary reasons for process cartridge replacement is developer (toner) depletion. Thus, in order to prompt user of timely process cartridge replacement by giving in advance the user the information regarding the amount of toner remainder, some of recent electrophotographic image forming apparatuses are designed so that they detect the amount of the toner remaining in a process cartridge. There are various methods usable for detecting the amount of toner remainder. 
         [0008]    One of the methods for detecting the amount of the toner remainder is recorded in Japanese Laid-open Patent Application 2003-131479 (FIG. 5), according to which the amount of the toner remainder is detected based on the amount of light transmission. Here, the general concept of detecting the amount of the toner remainder based on the amount of light transmission will be described with reference to a developing apparatus  104  showing in  FIG. 13 . 
         [0009]    A beam of light for detecting the amount of the toner remainder (which hereafter may be referred to simply as detection light), which is emitted from a light emitting portion, such as an LED, attached to the main assembly of an image forming apparatus, is guided through a light guide (unshown) attached to the image forming apparatus or the toner container  141  of a process cartridge, and then, into the toner container  141  through a transparent window  173  of the toner container  141 . 
         [0010]    The toner container  141  is structured so that as the detection light L enters the toner container  141 , it comes out, or fails to come out, of the toner container  141  through another transparent window or the like. It depends on various factors such as the amount of toner in the toner container  141  whether or not the detection beam L comes out of the toner container  141 . As the detection light L of comes out of the light exit window, it is guided to a light receiving portion (unshown), such as a phototransistor, by a light guide (unshown), such as the abovementioned light guide, attached to the main assembly of the image forming apparatus, or the toner container  141 . The light receiving portion is attached to the main assembly of the image forming apparatus, or the like. 
         [0011]    Generally, there are a pair of rotational stirring members  171  and  172  in the toner container  141 . The stirring members  171  and  172  are for conveying the toner in the toner container toward a development roller  140  while stirring the toner. As the detection light L enters the toner container  141  while the stirring member  171  and  172  are rotated, it is blocked by the stirring members  171  and  172  and/or the toner. The smaller the amount of toner in the toner container  141 , the longer the length of time the detection light L is allowed to transmit through the toner container  141 . Thus, the amount of toner (toner remainder) in the toner container  141  can be estimated by measuring the length of time the detection light L is allowed to transmit through the toner container  141 . This method of detecting (estimating) the amount of the toner remainder in the toner container  141  is referred to as a toner remainder amount detecting method of the light transmission type. 
         [0012]    The present invention is the further development of the prior art described above. 
         [0013]    In the case of the prior art described above, as the stirring members  171  and  172  in the toner container  141  are rotated, the toner having adhered to the transparent windows  173  and  174  is removed by the stirring members  171  and  172 , allowing therefore the detection light L to transmit through the toner container  141  until the toner covers again the transparent windows  173  and  174  by returning to, and accumulating on, the windows  173  and  174 . If the amount of the light received by the light receiving portion, with which the main assembly of the image forming apparatus is provided, is expressed in the form of a graph, the vertical and horizontal axes of which represent the amount of the light received and the length of elapsed time, respectively, the amount of the light received by the light receiving portion changes as shown in  FIG. 23 ; a waveform shown in  FIG. 23  is obtained. As the control portion of the main assembly of the image forming apparatus receives, from the light receiving portion, the electric signals which correspond to the amount of the light received by the light receiving portion, it measures the length of the periods a 1 , a 2 , a 3 , . . . of time, in which the amount of the received light is no less than a preset value (threshold value). Then, based on the measured length of the periods of time, the control portion calculates (estimates) the amount of the toner remainder in the toner container  141 . 
         [0014]    However, the pattern of the changes in the amount of the light received by the light receiving portion, which is expressed in the waveform in  FIG. 23 , is affected by the shape of the toner container  141 , the positional relationship between the transparent windows  173  and  174  and stirring members  171  and  172 , etc. Therefore, the amount of the light which the light receiving portion receives does not always change in the same pattern (waveform). Thus, if the threshold value is set shown in  FIG. 23 , the periods a 1 , a 2 , a 3 , . . . become different in length, affecting thereby the accuracy with which the amount of the toner remainder in the toner container  141  can be detected. 
       SUMMARY OF THE INVENTION 
       [0015]    The present invention is made in consideration of the problem described above. Thus, the primary object of the present invention is to provide a developing apparatus, a process cartridge, and an electrophotographic image forming apparatus, the amount of the developer remainder in which can be precisely detected. 
         [0016]    According to an aspect of the present invention, there is provide a developing apparatus for use with an electrophotographic image forming apparatus, said developing device comprising a developer accommodating chamber for accommodating a developer; a developer chamber including the developer carrying member for carrying and feeding a developer supplied from said developer accommodating chamber to develop an electrostatic latent image formed on an electrophotographic photosensitive member; a developer stirring member, rotatably provided in said developer accommodating chamber, for stirring the developer in said developer chamber then, supplying the developer from said developer accommodating chamber into said developer chamber through an opening formed in an upper part of said developer accommodating chamber; a wall surface, provided in said developer accommodating chamber, for being contacted by a free end portion of said developer stirring member while said developer stirring member is moving, wherein said developer stirring member lifts the developer toward said opening along said wall surface in said developer accommodating chamber; a developer detecting member, provided at said wall surface, for detecting a remaining amount of the developer by transmitting detecting light detected light into said developer accommodating chamber; wherein a position where the free end portion of said developer stirring member separates from said wall surface is above said developer detecting member and inside said developer accommodating chamber. 
         [0017]    According to another aspect of the present invention, there is provide a process cartridge detachably mountable to a main assembly of an electrophotographic image forming apparatus, said process cartridge comprising an electrophotographic photosensitive member on which an electrostatic latent image is formed; a developer accommodating chamber for accommodating a developer; a developer chamber including the developer carrying member for carrying and feeding a developer supplied from said developer accommodating chamber to develop said electrostatic latent image formed on an electrophotographic photosensitive member; a developer stirring member, rotatably provided in said developer accommodating chamber, for stirring the developer in said developer chamber then, supplying the developer from said developer accommodating chamber into said developer chamber through an opening formed in an upper part of said developer accommodating chamber, when said process cartridge is mounted to the main assembly of the electrophotographic image forming apparatus; a wall surface, provided in said developer accommodating chamber, for being contacted by a free end portion of said developer stirring member while said developer stirring member is moving, wherein said developer stirring member lifts the developer toward said opening along said wall surface in said developer accommodating chamber; a developer detecting member, provided at said wall surface, for detecting a remaining amount of the developer by transmitting detecting light detected light into said developer accommodating chamber; wherein a position where the free end portion of said developer stirring member separates from said wall surface is above said developer detecting member and inside said developer accommodating chamber. 
         [0018]    According to a further aspect of the present invention, there is provided an electrophotographic image forming apparatus for forming an image on a recording material, said apparatus comprising: 
         [0019]    (i) a developing device including, a developer accommodating chamber for accommodating a developer, a developer chamber including the developer carrying member for carrying and feeding a developer supplied from said developer accommodating chamber to develop an electrostatic latent image formed on an electrophotographic photosensitive member, a developer stirring member, rotatably provided in said developer accommodating chamber, for stirring the developer in said developer chamber then, supplying the developer from said developer accommodating chamber into said developer chamber through an opening formed in an upper part of said developer accommodating chamber; a wall surface, provided in said developer accommodating chamber, for being contacted by a free end portion of said developer stirring member while said developer stirring member is moving, wherein said developer stirring member lifts the developer toward said opening along said wall surface in said developer accommodating chamber, a developer detecting member, provided at said wall surface, for detecting a remaining amount of the developer by transmitting detecting light detected light into said developer accommodating chamber, wherein a position where the free end portion of said developer stirring member separates from said wall surface is above said developer detecting member and inside said developer accommodating chamber; and 
         [0020]    (ii) feeding means for feeding the recording material. 
         [0021]    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 DRAWINGS 
         [0022]      FIG. 1  is a schematic sectional view of the image forming apparatus in the first embodiment of the present invention, showing the general structure of the apparatus. 
           [0023]      FIG. 2  is a cross-sectional view of the process cartridge in the first embodiment of the present invention, showing the general structure of the cartridge. 
           [0024]      FIG. 3  is a schematic perspective view of the toner stirring member. 
           [0025]      FIG. 4  is a top view of the transparent member. 
           [0026]      FIGS. 5(   a ) and  5 ( b ) are sectional views of the transparent member, at planes A-A and B-B, respectively, in  FIG. 4 . 
           [0027]      FIG. 6  is a schematic cross-sectional view of the process cartridge, showing the operation of the toner stirring member in the cartridge. 
           [0028]      FIG. 7  is a schematic cross-sectional view of the process cartridge, showing the operation of the toner stirring member in the cartridge. 
           [0029]      FIG. 8  is a schematic cross-sectional view of the process cartridge, showing the operation of the toner stirring member in the cartridge. 
           [0030]      FIG. 9  is a schematic cross-sectional view of the process cartridge, showing the operation of the toner stirring member in the cartridge. 
           [0031]      FIG. 10  is a schematic cross-sectional view of the process cartridge, showing the operation of the toner stirring member in the cartridge. 
           [0032]      FIG. 11  is a schematic cross-sectional view of the process cartridge, showing the operation of the toner stirring member in the cartridge. 
           [0033]      FIG. 12  is a schematic cross-sectional view of the process cartridge, showing the operation of the toner stirring member in the cartridge. 
           [0034]      FIG. 13  is a schematic cross-sectional view of a typical process cartridge in accordance with the prior art. 
           [0035]      FIG. 14  is a schematic cross-sectional view of the process cartridge in another (second) embodiment of the present invention, showing the general structure of the cartridge. 
           [0036]      FIG. 15  is a perspective view of the stirring member and transparent member cleaning member of the developing apparatus in accordance with the present invention. 
           [0037]      FIG. 16  is a schematic cross-sectional view of the developing apparatus, in the second embodiment, which is in the state in which the toner remainder amount detection light L is received by the light receiving portion. 
           [0038]      FIG. 17  is a schematic cross-sectional view of the developing apparatus in the second embodiment, which is in the state in which the toner remainder amount detection light L is not received by the light receiving portion. 
           [0039]      FIG. 18(   a ) is a horizontal sectional view a transparent member of the light transmission type, which is made up of a pair of transparent portions for detecting the amount of the toner remainder based on the amount of light transmission, and  FIG. 18(   b ) is a vertical sectional view (at plane parallel to front panel of apparatus) of the transparent member of the light transmission type, which is made up of a pair of transparent portions for detecting the amount of the toner remainder based on the amount of light transmission. 
           [0040]      FIG. 19(   a ) is a horizontal sectional view a transparent member of the light transmission type, which is made up of a pair of transparent portions for detecting the amount of the toner remainder, and  FIG. 19(   b ) is a vertical sectional view (at plane parallel to front panel of apparatus) of the transparent member of the light transmission type, which is made up of a pair of transparent portions for detecting the amount of the toner remainder. 
           [0041]      FIG. 20  is a cross-sectional view of the developing apparatus, which is in the state in which its light receiving portion does not receive the toner remainder amount detection light. 
           [0042]      FIG. 21  is a cross-sectional view of the transparent member, its adjacencies, stirring sheet, and wiping sheet of the development unit, showing the relationship between the stirring sheet and wiping sheet when the wiping member begins to clean the transparent member. 
           [0043]      FIG. 22  is a schematic sectional view (at vertical plane) of the transparent member and wiping sheet of the development unit, in the second embodiment, having a gap between the wall of the recessed portion and transparent member, when the transparent member is being cleaned, showing the developer on the wiping sheet. 
           [0044]      FIG. 23  is a graph showing the changes (waveform) in the relationship between the amount of the developer remainder amount detection light received by the light receiving portion of the image forming apparatus in accordance with the prior art, and the elapsed time. 
           [0045]      FIG. 24  is a graph showing the changes (waveform) in the relationship between the amount of the developer remainder amount detection light received by the light receiving portion of the image forming apparatus in the first embodiment of the present invention, and the elapsed time. 
           [0046]      FIG. 25  is a graph showing the changes (waveform) in the relationship between the amount of the developer remainder amount detection light received by the light receiving portion of the image forming apparatus when the amount of the toner remainder in the toner storage chamber is relatively large, and the elapsed time. 
           [0047]      FIG. 26  is a graph showing the changes (waveform) in the relationship between the amount of the developer remainder amount detection light received by the light receiving portion of the image forming apparatus when the amount of the toner remainder is the toner storage chamber is relatively small, and the elapsed time. 
           [0048]      FIG. 27  is a schematic sectional view (at vertical plane) of the transparent member and wiping sheet of the development unit, in a comparative embodiment, having no gap between the wall of the recessed portion and transparent member, when the transparent member is being cleaned, showing the developer on the wiping sheet. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0049]    Hereinafter, the developing apparatus, process cartridge, and electrophotographic image forming apparatus, which are in accordance with the present invention will be described in more detail with reference to the appended drawings. 
       Embodiment 1 
       [0050]      FIG. 1  is a schematic sectional view of the electrophotographic image forming apparatus in the first of the preferred embodiments of the present invention, and shows the general structure of the apparatus. The electrophotographic image forming apparatus shown in  FIG. 1  is an electrophotographic color image forming apparatus. However, the application of the present invention is not limited to an electrophotographic color image forming apparatus, such as the one shown in  FIG. 1 . That is, the present invention is also applicable to an electrophotographic monochromatic image forming apparatus, and various electrophotographic image forming apparatuses other than the apparatus shown in  FIG. 1 . 
         [0051]    First, the general structure of the electrophotographic color image forming apparatus in this embodiment will be described regarding its general structure. 
       [Image Forming Apparatus] 
       [0052]    Referring to  FIG. 1 , the electrophotographic color image forming apparatus  100  in this embodiment has four image bearing members, more specifically, four electrophotographic photosensitive members  1  which are in the form of a drum (which hereafter will be referred to as “photosensitive drums  1 ”). The multiple image bearing members are arranged side by side (juxtaposed) in parallel in a horizontal straight row. The photosensitive drum  1  is rotationally driven in the direction indicated by an arrow mark A in the drawing, by an unshown driving means. The image forming apparatus  100  is also provided with various processing means, which are in the adjacencies of the peripheral surface of the photosensitive drum  1  and are arranged in the rotational direction of the photosensitive drum  1 . 
         [0053]    More specifically, disposed in the adjacencies of the peripheral surface of each photosensitive drum  1  are a charging means  2  ( 2   a - 2   d ), such as a charge roller, for uniformly charging the peripheral surface of the photosensitive drum  1 , and a scanner unit  3  for forming an electrostatic latent image on the peripheral surface of the photosensitive drum  1 , by projecting a beam of laser light, while modulating the beam with pictorial information. Also disposed in the adjacencies of the peripheral surface of the photosensitive drum  1  are a development unit  4  ( 4   a - 4   d ) and an intermediary transfer belt  5 . The development unit  4  is a developing apparatus, which develops an electrostatic latent image on the peripheral surface of the photosensitive drum  1  into a visible image, that is, an image formed of toner. The intermediary transfer belt  5  is a belt for transferring the toner image on the photosensitive drum  1 , onto a sheet  12  of recording paper as recording medium. There is also a cleaning member  6  ( 6   a - 6   d ) in the adjacencies of the peripheral surface of the photosensitive drum  1 . The cleaning member  6  is for removing the toner (transfer residual toner) remaining on the peripheral surface of the photosensitive drum  1  after the toner image transfer from the photosensitive drum  1 . 
         [0054]    In this embodiment, the photosensitive drum  1 , and the processing means, more specifically, the charging means  2 , development unit  4 , and cleaning member  6 , which process the photosensitive drum  1 , are integrally disposed in a cartridge (process cartridge  7  ( 7   a - 7   d )), which is removably mountable in the main assembly A of the electrophotographic image forming apparatus. 
         [0055]    In this embodiment, the process cartridges  7  ( 7   a - 7   d ) are the same in shape, and store yellow, magenta, cyan, and black developers (which hereafter will be referred to as toner), respectively, which are nonmagnetic single component developers. 
         [0056]    The intermediary transfer belt  5 , which is an intermediary transferring apparatus, is located above the process cartridge bays of the main assembly A of the electrophotographic image forming apparatus, into which the process cartridges  7  ( 7   a - 7   d ) are mounted. The intermediary transfer belt  5  is in contact with the photosensitive drum  1  ( 1   a - 1   d ) of each process cartridge  7  ( 7   a - 7   d ), and rotates (circularly moves) in the direction indicated by an arrow mark B. 
         [0057]    On the inward side of the loop which the intermediary transfer belt  5  forms, four primary transfer rollers  8  ( 8   a - 8   d ), as primary transferring means, are arranged in parallel so that they oppose the four photosensitive drums  1 , one for one. To the primary transfer roller  8 , bias which is opposite in polarity to the normal polarity to which toner is charged is applied from an unshown high voltage power source. As the primary transfer bias is applied to the primary transfer roller  8 , the toner image on the photosensitive drum  1  is transferred (primary transfer) onto the intermediary transfer belt  5 . 
         [0058]    Meanwhile a recording medium  12  is conveyed, in synchronism with the movement of the intermediary transfer belt  5 , by sheet conveying means, such as a sheet feeder roller  12   a , sheet conveyance roller  12   b  and  12 , etc., to the secondary transfer portion, which has a secondary transfer roller  9  as secondary transferring means. In the secondary transfer portion, the second transfer roller  9  remains pressed upon the intermediary transfer belt  5  with the presence of the recording paper  12  between the second transfer roller  9  and intermediary transfer belt  5 . The secondary transfer roller  9  is the same in structured as the primary transfer roller  8 . To the secondary transfer roller  9 , bias which is opposite in polarity as the normal polarity to which the toner is charged, is applied from an unshown high voltage power source. As the bias is applied to the secondary transfer roller  9 , the four toner images, different in color, on the intermediary transfer belt  5  are transferred together (secondary transfer) onto the recording paper  12 . 
         [0059]    After the transfer of the four toner images, different in color, onto the recording paper  12 , the recording paper  12  is conveyed to the fixing apparatus  10 . In the fixing apparatus  10 , the toner images are fixed to the recording medium  12  by the application of heat and pressure. The residual toner remaining on the intermediary transfer belt  5  after the secondary transfer is removed by a cleaning apparatus  11 , which is an apparatus for cleaning the intermediary transfer belt  5 . 
       [Process Cartridge] 
       [0060]    Next, referring to  FIG. 2 , the process cartridge  7  ( 7   a - 7   d ) will be described regarding its general structure.  FIG. 2  is a schematic cross-sectional view of the process cartridge  7  which is in its image forming position in the main assembly  100 A of the electrophotographic image forming apparatus. 
         [0061]    In this embodiment, a cartridge  7   a , which contains yellow toner, a cartridge  7   b , which contains magenta toner, a cartridge  7   c , which contains cyan toner, and a cartridge  7   d , which contains black toner, are the same in structure. 
         [0062]    The process cartridge  7  has a photosensitive member unit  13  made up of the photosensitive drum  1 , etc., and the development unit  4  made up of the development roller  17 , as a developer bearing member, etc. Next, each unit will be described. 
         [0063]    To the cleaning means frame  14  of the photosensitive member unit  13 , the photosensitive drum  1  is rotatably attached with interposition of a pair of unshown bearings. In the adjacencies of the peripheral surface of the photosensitive drum  1 , the charge roller  2 , and cleaning member  6  are disposed. As the residual toner is removed from the peripheral surface of the photosensitive drum  1  by the cleaning member  6 , it falls into a toner chamber  14   a  for the removed residual toner. 
         [0064]    As the driving force from a driving motor (unshown) is transmitted to the photosensitive member unit  13 , the photosensitive drum  1  is rotationally driven in synchronism with the progression of the image forming operation. To the cleaning means frame  14 , a pair of charge roller bearings  15  are attached so that the bearings  15  are movable in the direction indicated by a double-headed arrow mark C, the theoretical extension of which coincides with the axial lines of the charge roller  2  and photosensitive drum  1 . The shaft  2   a  of the charge roller  2  is rotatably borne by the pair of charge roller bearings  15 , which are kept pressured toward the photosensitive drum  1  by a pair of compression springs  16 . 
         [0065]    The developing means frame  18  of the development unit  4  has a developer storage chamber  18   a  (which hereafter may be referred to as toner storage chamber) and a development chamber  18   b . The toner storage chamber  18   a  stores toner. There is a development roller  17 , as a developer bearing member, in the development chamber  18   b . The development roller  17  rotates in contact with the photosensitive drum  1 , in the direction indicated by an arrow mark D. 
         [0066]    In this embodiment, the development chamber  18   b  is above the developer storage chamber  18   a . The developer storage chamber  18   a  and development chamber  18   b  are in connection to each other, through a hole  18   c , with which the partition wall between the two chambers  18   b  and  18   a  is provided. 
         [0067]    The development roller  17  in the development chamber  18   b  is rotatably supported by a developing means frame  18 . More specifically, the development roller  17  is supported at its lengthwise end portions by a pair of bearing members (unshown) attached to the lengthwise ends of the developing means frame  18 . The development unit  4  is also provided with a developer supply roller  20  (which hereafter will be referred to as toner supply roller) and a development blade  21 , which are in the adjacencies of the peripheral surface of the development roller  17 . The toner supply roller  20  rotates in contact with the development roller  17  in the direction indicated by an arrow mark E. The development blade  21  is for regulating in thickness the toner layer on the peripheral surface of the development roller  17 . 
         [0068]    Further, the development unit  4  has a developer stirring member  22  (which hereafter will be referred to as toner stirring member) for stirring the toner in the toner storage chamber  18   a  while conveying the toner to the abovementioned toner supply roller  20 . The toner stirring member  22  is rotatably supported in the toner storage chamber  18   a.    
         [0069]    Referring to  FIG. 2 , the wall of the toner storage chamber  18   a  has a bottom portion W 1 , a first portion W 2 , a second portion W 3 , and a third portion W 4 . The bottom portion W 1  is the portion which is at the bottom when the cartridge is in its image forming position, that is, when the attitude of the cartridge is as shown in  FIG. 2 . In terms of the rotational direction G of the toner stirring member  22 , the first portion W 2  is on the downstream side of the bottom portion W 1 . It is in connection to the bottom portion W 1 , and is tilted toward the axial line of the toner stirring member  22 , relative to the vertical direction. The second portion W 3  is on the downstream side of the first portion W 2 , and extends from the first portion W 2  to the hole  18   c . The third portion W 4  is on the downstream side of the hole  18   c , and extends from the hole  18   c  to the bottom portion W 1 . 
         [0070]    While the toner stirring member  22  rotates in the toner storage chamber  18   a  across the portion of its sweeping areas, which correspond to the bottom portion W 1  and first portion W 2  of the wall W of the toner storage chamber  18   a , the sweeping edge portion of the toner stirring member  22  moves in contact with the bottom portion W 1  and first portion W 2 , respectively, of the toner storage chamber wall, as will be described later in detail. Thus, as the toner stirring member  22  rotates, the body of toner T in the toner storage chamber  18   a  is upwardly conveyed from the area corresponding to the bottom portion W 1  to the area corresponding to the first portion W 2 , and then, is guided to the hole  18   c  along the second portion W 3 . 
         [0071]    The portion of the body of toner T, which failed to be guided into the hole  18   c , falls down, or is guided inward of the toner storage chamber  18   a  along the third portion W 4 . 
         [0072]    The development unit  4  is pivotally connected to the photosensitive member unit  13 . More specifically, the lateral plates  19 R and  19 L of the development unit  4  are provided with holes  19 Ra and  19 La, respectively. Further, a pair of connective pins  23 R and  23 L are put through the holes  19 Ra and  19 La and the corresponding holes of the photosensitive member unit  13  so that the development unit  4  is pivotally movable relative to the photosensitive member unit  13 . As described above, the development unit  4  is under the pressure from compression springs  24  for pressing the development unit  4 . Therefore, when the process cartridge  7  is being used for image formation, and therefore, as an image forming operation begins, the process cartridge  7  is pivoted about the connective pins  23  in the direction indicated by an arrow mark F, whereby the development roller  17  is placed in contact photosensitive drum  1 . 
       [Structure Arrangement for Detecting Amount of Toner Remainder] 
       [0073]    Next, referring to  FIGS. 2-5 , the detection of the amount of the developer remainder in the toner storage chamber  18   a  (which hereafter may be referred to simply as toner remainder detection), in this embodiment, will be described. 
         [0074]    Referring to  FIG. 2 , the toner stirring member  22  is in the toner storage chamber  18   a  which stores toner. It conveys toner to the toner supply roller  20  by being rotated in the direction G. 
         [0075]    Referring to  FIG. 3 , the toner stirring member  22  is made up of a shaft  22   a  and a stirring sheet  22   b . The shaft  22   a  is molded of a resinous substance. The stirring sheet  22   b  is attached to the shaft  22   a  by one of the longer edges. It is the very portion of the toner stirring member  22  that stirs toner. It can be easily made of flexible resinous sheet, such as polyester film, polyphenylene sulfide film, or the like. The thickness of the stirring sheet  22   b  is desired to be in a range of 50-250 μm. 
         [0076]    In order to ensure that the stirring member  22  stirs and conveys even the toner in the bottom portion of the toner storage chamber  18   a , the length RO of the shorter edges of the stirring sheet  22   b  is made greater than the distances from the rotational axis O of the stirring member  22  to the internal wall of the toner storage chamber  18   a , in particular, the internal surfaces of the portions W 1 , W 2 , and W 3  of the toner storage chamber wall W. The length W 0  of the longer edges of the stirring sheet  22   b  is made to be the same as the distance between the internal surfaces of the lateral walls (end walls in terms of rotational axis of stirring member  22 ) of the toner storage chamber  18   a.    
         [0077]    The force for driving the stirring member  22  is transmitted to the stirring member  22  by a driver gear (unshown) attached to one of the lengthwise ends of the shaft  22   a ; the shaft of the driver gear is inserted in the hole  22   c  with which one of the lengthwise ends of the shaft  22   a  is provided, through the hole with which the lateral wall of the toner storage chamber  18   a  of the developing means frame  18  is provided. 
         [0078]    Further, the toner storage chamber  18   a  is provided with a toner remainder amount detecting means of the light transmission type, which is for detecting the amount of the toner remaining in the toner storage chamber  18   a . More specifically, referring to  FIGS. 4 ,  5 ( a ), and  5 ( b ), in this embodiment, the development unit  4  is provided with a pair of transparent members  40  and  41 , of which the toner remainder amount detecting means (developer amount detecting means) is made. The transparent members  40  and  41  are attached to the first portion W 2  of the wall of the toner storage chamber  18   a  of the developing means frame  18 , as will be described later. The transparent members  40  and  41  are aligned in the direction parallel to the lengthwise direction of the development roller  17 . It is preferred that the transparent members  40  and  41  are positioned above the horizontal plane which coincides with the rotational axis of the toner stirring member  22 . 
         [0079]    The transparent member  40  has a light exit portion  40   a , through which the detection light L exits from the transparent member  40 , whereas the transparent member  41  has a light entrance portion  41   a , through which the detection light L enters the transparent member  41 . 
         [0080]    The transparent member  40  has the light exit portion  40   a  and a light guide portion  40   b . The light guide portion  40   b  guides the detection light L emitted from an LED (unshown), as a light emitting portion, with which the main assembly  100 A of the electrophotographic image forming apparatus is provided. The light exit portion  40   a  and light guide portion  40   b  are integral portions of the transparent member  40 . 
         [0081]    The transparent member  41  has the light entrance portion  41   a  and a light guide portion  41   b . The light guide portion  41   a  guides the detection light L to a phototransistor (unshown), as a light receiving portion, with which the main assembly  100   a  of the electrophotographic image forming apparatus is provided, after the detection light L transmits through the toner storage chamber  18   a.    
         [0082]    Incidentally, referring to  FIG. 5(   a ), in order to guide the detection light L from the LED, into the toner storage chamber  18   a , the light guide portion  40   b  is provided with a reflective intermediary surface  40   b   1 . Further, referring to  FIG. 4 , the light exit surface  40   b   2  of the light guide portion  40   b  squarely faces the light entrance surface  41   b   2  of the light entrance portion  41   b . Similarly, the light guide portion  41   b  is provided with a reflective surface  41   b   1  so that the light having entered the light guide portion  41   b  through the light entrance surface  41   b   2  is guided to a phototransistor (unshown), as shown in  FIG. 5(   b ). 
       [Method for Detecting Amount of Toner Remainder] 
       [0083]    Next, referring to  FIGS. 6-12 , and  24 , the method for detecting the amount of toner remainder will be described in detail. 
         [0084]      FIG. 6  is a cross-sectional view of the development unit  4 , which is in the state in which the amount of the toner in the storage chamber  18   a  is greater than a preset value, and in which the toner stirring member  22  is above the portion H 2  of the top surface of the body of toner T in the toner storage chamber  18   a .  FIG. 24  shows the relationship between the amount of light received by the phototransistor, and the elapsed time. The phototransistor outputs to the control portion (unshown) of the image forming apparatus main assembly (unshown), electrical signals which correspond to the amount of light it receives. As the control receives the electrical signals, it measures the duration of the period of time in which the amount of light which the phototransistor received is greater than a preset value (threshold value). Then, it calculates (estimates) the amount of the toner remainder in the toner storage chamber  18   a  from the measured duration. 
         [0085]    The portion A of the waveform (pattern) of the graph, in  FIG. 24 , which shows the changes in the abovementioned relationship between the amount of light received by the phototransistor and the elapsed time, corresponds to the state of the development unit  4  shown in  FIG. 6 . That is, the top surface of the body of toner in the toner storage chamber  18   a  is below the vertical position of transparent members  40  and  41 . Therefore, the detection light L is allowed to transmit through the space between the transparent members  40  and  41 , in the toner storage chamber  18   a.    
         [0086]    As the stirring member  22  is rotated when the development unit  4  is in the state shown in  FIG. 6 , the stirring sheet  22   b  presses on the portion H 2  of the top surface of the body of toner T in the toner storage chamber  18   a , that is, the portion of the top surface of the body of toner T, which is on the right-hand side of the axial line of the stirring member  22 , in  FIG. 6 . Therefore, the portion H 1  of the top surface of the body of toner T, that is, the portion on the left-hand side of the axial line of the stirring member  22  rises. 
         [0087]    The portion H 1  of the top surface of the body of toner T rises along the portion W 2 , that is, the slanted portion, of the wall of the toner storage chamber  18   a , eventually reaching the transparent members  40  and  41  as shown in  FIG. 7 . 
         [0088]    Immediately after the portion H 1  of the top surface of the body of toner T reaches the transparent members  40  and  41 , the detection light L emitted from the LED (unshown) begins to be blocked by the body of toner T which enters the space between the pair of transparent members  40  and  41  which is attached to the wall of the toner storage chamber  18   a . As a result, the phototransistor (unshown) is prevented from receiving the detection light L (state corresponding to point (B) in graph in  FIG. 24 ). 
         [0089]    As the toner stirring member  22  is further rotated, the portion H 1  of the top surface of the body of toner T rises along the portion W 2  of the internal surface of the toner storage chamber  18   a , becoming thereby angled (V) relative to the horizontal plane. 
         [0090]    As the angle V of the portion H 1  of the top surface of the body of toner T being pressed by the toner stirring sheet  22   b  becomes as steep as shown in  FIG. 8 , the body of toner T begins to partially break away and fall from the toner stirring sheet  22   b , accumulating again in the bottom portion of the toner storage chamber  18   a.    
         [0091]    At the beginning of the breakaway of the body of toner T, there is still a part of the body of toner T, between the pair of transparent members  40  and  41  attached to the portion W 2  of the wall of the toner storage chamber  18   a , and therefore, the detection light L remains blocked as shown in  FIG. 24  (state corresponding to portion (C)). 
         [0092]    When the development unit  4  is in the state shown in  FIG. 9 , the stirring sheet  22   b  has just moved past the space between the transparent members  40  and  40  due to the rotation of the toner stirring member  22 . 
         [0093]    That is, when the development unit  4  is in the state shown in  FIG. 9 , the body of toner T, which has been pushed up along the internal surface of the portion W 2  of the wall of the toner storage chamber  18   a  by the rotation of the toner stirring member  22  partially remains on the stirring sheet  22   b . However, since the stirring sheet  22   b  has just moved past the space between the transparent members  40  and  41  with which the portion W 2  of the wall of the toner storage chamber  18   a  is provided, there is no toner between the two transparent members  40  and  41 , allowing thereby the detection light L to transmit through the space between the two transparent members  40  and  41  as shown in  FIG. 24  (state corresponding to portion (D) of graph). 
         [0094]    Incidentally, referring to  FIG. 10 , in this embodiment, the portion W 2  of the toner storage chamber wall is tilted toward the axial line of the toner stirring member  22  relative to the vertical plane. Further, in this embodiment, the portion W 2  is flat. However, the portion W 2  may be curved inward of the toner storage chamber  18   a.    
         [0095]    Thus, while the remaining body of toner T on the stirring sheet  22   b  is pushed up along the portion W 2  of the toner storage chamber wall, it does not occur, as shown in  FIG. 24 , that the remaining body of toner T blocks the detection light L by falling from the stirring sheet  22   b , that is, it does not occur that the falling body of toner T prevents the detection light L from transmitting through the space between the transparent members  40  and  41  (state corresponding to portion (E) of graph in  FIG. 24 ). 
         [0096]    In this embodiment, the length RO ( FIG. 3 ) of the shorter edges of the stirring sheet  22   b  (which is roughly the same as distance R 01  from rotational axis O of toner stirring member  22  to sweeping edge  22   b A of stirring sheet  22   b ), is greater than the distance from the axial line O of the stirring member  22  to the internal surface of the portion W 2  of the toner storage chamber wall, as described above. Therefore, the possibility that the body of toner T, which is on the stirring sheet  22   b , partially falls through the gap between the stirring sheet  22   b  and the internal surface of the portion W 2  of the toner storage chamber wall is minimized. 
         [0097]    Then, as the toner stirring member  22  is further rotated, the toner stirring sheet  22   b  continues to convey the toner along the portion W 2  of the toner storage chamber wall, until the sweeping edge  22   b A of the toner stirring sheet  22   b  separate from the portion W 2 , at a point P. 
         [0098]    As soon as the sweeping edge  22   b A ( FIG. 3 ) of the toner stirring sheet  22   b  moves past the point P, the distance R from the rotational axis of the toner stirring member  22  to the internal surface of the toner storage chamber wall W becomes greater than the radius RO 1  of the sweeping area of the toner stirring sheet  22   b . Thus, the toner stirring sheet  22   b , which has been rotated, while remaining elastically bent, instantly straightens, catapulting thereby the body of toner T on the toner stirring sheet  22   b  at the same time. 
         [0099]    According to this embodiment, the development unit  4  is structured so that when the process cartridge  7  is in its image forming position in the main assembly of the image forming apparatus, the point P is on the inward side of the toner storage chamber  18   a  relative to the vertical plane coinciding with the most inward edges of the transparent members  40  and  41  with which the portion W 2  of the toner storage chamber wall is provided. Therefore, it does not occur, as described above, that the remaining body of toner T on the toner stirring sheet  22   b  falls directly onto the transparent members  40  and  41 . Therefore, it does not occur that while the sweeping edge  22   b A of the toner stirring sheet  22   b  is moving across the portion of the internal surface of the toner storage chamber wall, which is between the transparent members  40  ( 41 ) and point P in terms of the rotational direction of the toner stirring member  22 , the detection light L remains blocked by the toner. That is, the amount by which the phototransistor receives the detection light L is unlikely to be affected by the falling toner, as will be evident from the pattern (waveform) of the changes in the relationship between the amount of the detection light L received by the light receiving portion, and the elapsed time, shown in the graph in  FIG. 24 . Therefore, the threshold value for precisely determine the amount of the toner remainder can be easily set. 
         [0100]    Next, referring to  FIGS. 11 and 12 , the changes in the length of time the detection light L remains blocked, which is caused by the changes in the amount of the toner remainder in the toner storage chamber  18   a , will be described. 
         [0101]      FIGS. 11(   a ) and  11 ( b ) correspond to the case in which the amount of the toner remaining in the toner storage chamber  18   a  is relatively large.  FIG. 25  shows the relationship (waveform) between the amount of detection light L which the phototransistor (unshown) receives when the amount of the toner remaining in the toner storage chamber  18   a  is relatively large, and the elapsed time. 
         [0102]      FIG. 11(   a ) is a cross-sectional view of the development unit  4 , which corresponds to a point T 1  ( FIG. 25)  in elapsed time, at which the body of toner T has just reached the transparent members  40  and  41  by being pushed by the toner stirring sheet  22   b . As will evident from  FIG. 25 , the point T 1  in elapsed time is the point in time at which the detection light L, which has been allowed to transmit through the space between the transparent members  40  and  41 , has just begun to be blocked by the body of toner T. 
         [0103]      FIG. 11(   b ) is a cross-sectional view of the development unit  4 , which corresponds to a point T 2  ( FIG. 25)  in elapsed time, at which the toner stirring sheet  22   b  has just moved past the space between the transparent members  40  and  41 . As will evident from  FIG. 25 , the point T 2  in elapsed time is the point in elapsed time at which the body of toner T on the toner stirring sheet  22   b  has just moved out of the space between the transparent members  40  and  41  with which the portion W 2  of the toner storage chamber wall is provided, that is, the point in elapsed time at which the detection light L has just begun to transmit again through the space between the transparent members  40  and  41 . 
         [0104]    While the state of the process cartridge  7  changes from the state shown in  FIG. 11(   a ) to the state shown in  FIG. 11(   b ), the toner stirring member  22   b  rotates by an angle θb. 
         [0105]      FIGS. 12(   a ) and  12 ( b ) correspond to the case in which the amount of toner remaining in the toner storage chamber  18   a  is half the amount of toner remaining in the toner storage chamber  18   a  when the development unit  4  is in the state shown in  FIGS. 11(   a ) and  11 ( b ).  FIG. 26  shows the relationship (waveform) between the amount of detection light L which the phototransistor (unshown) received when the amount of the toner remaining in the toner storage chamber  18   a  was as shown in  FIGS. 12(   a ) and  12 ( b ), and the elapsed time. 
         [0106]    The angle by which the toner stirring member  22  rotates during the period between a point T 3  in elapsed time ( FIG. 26 ) at which the detection light L begins to be blocked again as shown in  FIG. 12(   a ), and a point T 4  ( FIG. 26)  in elapsed time at which the detection light L begins to transmit again though the space between the transparent members  40  and  41  as shown in  FIG. 12(   b ) is θ. 
         [0107]    As described above, the amount of toner remaining in the toner storage chamber  18   a  is estimated based on the fact that the angle (θ) by which the toner stirring member  22  rotates from the moment the detection light L begins to be blocked to the moment the detection light L begins to be allowed to transmit again through the space between the transparent members  40  and  41  is affected by the amount of toner remaining in the toner storage chamber  18   a.    
         [0108]    According to the present invention, the body of toner T, which is being pushed up along the smooth inward surface of the portion W 2  of the toner storage chamber wall, being therefore stable in behavior, is used to block the detection light L, or allow the detection light L to transmit through the space between the transparent members  40  and  41 . Therefore, the length of time the detection light L remains blocked, and the length of time the detection light L is allowed to transmit through the space between the transparent members  40  and  41 , are stable. Therefore, the amount of the toner remainder can be more precisely detected. 
         [0109]    Further, in this embodiment, the detection light L which is transmitting through the space between the transparent members  40  and  41  is blocked by pushing up the toner in the toner storage chamber  18   a  along the portion W 2  of the wall of the toner storage chamber  18   a , which is tilted toward the axial line of the toner stirring member  22  relative to the vertical direction, by the rotational toner stirring member  22 . Further, the transparent members  40  and  41  are attached to the portion W 2  of the wall of the toner storage chamber  18   a , which is tilted toward the axial line of the toner stirring member  22 . Therefore, toner does not settle on the transparent members  40  and  41 . Moreover, referring to  FIG. 10 , the development unit  4  is structured so that when the process cartridge is in its image forming position in the main assembly of the image forming apparatus, the point P of the inward surface of the toner storage chamber wall, which corresponds to the point in elapsed time at which the sweeping edge of the stirring sheet  22   b  becomes freed from the portion W 2  of the toner storage chamber wall, is on the inward side of the vertical plane which coincides with the most inward edges of the transparent members  40  and  41 , that is, the point P is closer to the rotational axis of the toner stirring member  22  than the most inward edges of the transparent members  40  and  41 . Therefore, it does not occur that as the excessive portion of the body of toner T which is being conveyed by the toner stirring member  22  falls, it disturbs the detection light L. Therefore, it is ensured that the amount of the toner remainder in the toner storage chamber  18   a  is precisely detected. 
       Embodiment 2 
       [0110]    Next, the second embodiment of the present invention will be described. 
         [0111]    Incidentally, the portions of the process cartridge and image forming apparatus in this embodiment, the description of which will be the duplication of the description of the counterparts in the first embodiment, will not be described here. 
       [Process Cartridge] 
       [0112]    Referring to  FIG. 14 , the process cartridge  7  ( 7   a - 7   d ) in this embodiment will be described.  FIG. 14  is a schematic cross-sectional view of the process cartridge  7  ( 7   a - 7   d ) in this embodiment, which is in its image forming position in the main assembly  100  of the electrophotographic image forming apparatus ( FIG. 1 ). 
         [0113]    In this embodiment, a cartridge  7   a , which contains yellow toner, a cartridge  7   b , which contains magenta toner, a cartridge  7   c , which contains cyan toner, and a cartridge  7   d , which contains black toner, are the same in structure. 
         [0114]    The process cartridge  7  ( 7   a - 7   d ) is made up of a photosensitive member unit  26  ( 26   a - 26   d ) and a development unit  4  ( 4   a - 4   d ). Next, the two units  26  and  4  will be described. 
         [0115]    The photosensitive member unit  26  is provided with a photosensitive drum  1  ( 1   a - 1   d ), a charge roller  2  ( 2   a - 2   d ), and a cleaning member  6  ( 6   a - 6   d ). 
         [0116]    To the cleaning means frame  27  of the photosensitive member unit  26 , the photosensitive drum  1  is rotatably attached with interposition of a pair of unshown bearings. In the adjacencies of the peripheral surface of the photosensitive drum  1 , the charge roller  2 , and cleaning member  6  are disposed as descried above. As the residual toner is removed from the peripheral surface of the photosensitive drum  1  by the cleaning member  6 , it falls into a chamber  27   a  for the removed residual toner. As the driving force from a driving motor (unshown) is transmitted to the photosensitive member unit  26 , the photosensitive drum  1  is rotationally driven in the direction indicated by an arrow mark A in synchronism with the progression of the image forming operation. 
         [0117]    To the cleaning means frame  27 , a pair of charge roller bearings  28  are attached so that the bearings  28  are movable in the direction indicated by a double-headed arrow mark C, the theoretical extension of which coincides with the axial lines of the charge roller  2  and photosensitive drum  1 . The shaft  2   j  of the charge roller  2  is rotatably borne by the pair of charge roller bearings  28 , which are kept pressured toward the photosensitive drum  1  by a pair of pressure applying member  46 . 
         [0118]    The developing means frame  29  of the development unit  4  has a developer storage chamber  29   a  (which hereafter will be referred to as toner chamber) and a development chamber  29   b . The toner chamber  29   b  stores toner. There is a development roller  25 , as a developer bearing member, in the development chamber  29   b . The development roller  25  rotates in contact with the photosensitive drum  1 , in the direction indicated by an arrow mark D. 
         [0119]    In this embodiment, the development chamber  29   b  is above the toner chamber  29   a . The toner chamber  29   a  and development chamber  29   b  are in connection to each other, through a hole  29   c , with which the partition wall between the two chambers  29   b  and  29   a  is provided. 
         [0120]    The development roller  25  in the development chamber  29   b  is rotatably supported by a developing means frame  29 . More specifically, the development roller  25  is supported at its lengthwise end portions by a pair of bearings (unshown) attached to the lengthwise ends of the developing means frame  29 . 
         [0121]    The development unit  4  is also provided with a developer supply roller  34  (which hereafter will be referred to as toner supply roller) and a development blade  35 , which are in the adjacencies of the peripheral surface of the development roller  25 . The toner supply roller  34  rotates in contact with the development roller  25  in the direction indicated by an arrow mark E. The development blade  35  is a blade for regulating in thickness the toner layer on the peripheral surface of the development roller  25 . 
         [0122]    Further, the toner chamber  29   a  of the developing means frame  29  is provided with a recess  42  which is recessed outward from the toner chamber  29 , as will be described later in detail. This recess  42  is provided with a pair of transparent members  40  and  41  as developer remainder amount detecting members (which is means for detecting amount of developer (toner) remainder) for detecting the amount of the developer remaining in the toner chamber  29   a . The transparent members  40  and  41  are provided with a light exit portion  40   a , through which the detection light L exits from the transparent member  40 , whereas the transparent member  41  has a light entrance portion  41   a , through which the detection light L enters the transparent member  41 , respectively. 
         [0123]    Further, there is a developer stirring member  36  (which hereafter will be referred to as toner stirring member) for stirring the toner in the toner storage chamber  29   a  while conveying the toner to the abovementioned toner supply roller  34 . The toner stirring member  36  is provided with a cleaning member  39  (which hereafter may be referred to transparent member cleaning member) for cleaning the light exit portion  40   a  and light entrance portion  41   a.    
         [0124]    The development unit  4  is pivotally connected to the photosensitive member unit  26 . More specifically, the bearing members  32 R and  32 L are provided with holes  32 Rb and  32 La, and a pair of connective pins  37 R and  37 L are put through the holes  32 Ra and  32 La and the corresponding holes of the photosensitive member unit  26  so that the development unit  4  is pivotally movable relative to the photosensitive member unit  26 . When the process cartridge  7  is being used for image formation, the development unit  4  is under the pressure from compression springs  24  for pressing the development unit  4 . Therefore, during an image forming operation, the process cartridge  7  is pivoted about the connective pins  37 R and  37 L in the direction indicated by an arrow mark F, whereby the development roller  25  is placed in contact photosensitive drum  1 . 
         [0125]    [Structure of Toner Stirring Member, Structure of Member for Cleaning Light Exit and Entrance Portions, Toner Remainder Amount Detection Based on Amount of Light Transmission] 
         [0126]    Next, referring to  FIGS. 14-18 , the structure of the toner stirring member  36 , structure of the member for cleaning the light exit portion and light entrance portion of the transparent members  40  and  41 , respectively, and detection of toner remainder amount based on the amount of light transmission, will be described. 
         [0127]    Referring to  FIG. 14 , there is a toner stirring member  36  in the toner chamber  29   a  which stores toner. The toner in the toner chamber  29   a  is conveyed to a toner supply roller  34  through the hole  29   c , by rotating the stirring member  36  in the direction X. Incidentally, also in this embodiment, the development unit  4  is structured so that the point P at which the sweeping edge of the toner stirring member  36  is freed from the internal surface of the portion Wa of the toner storage chamber wall, is on the inward side of the vertical plane which coincides with the most inward edges of the transparent member  40  and  41 , that is, the vertical plane which coincides with the point P is closer to the rotational axis O of the toner stirring member  36  than the vertical plane coinciding with the most inward edges of the transparent members  40  and  41 . 
         [0128]    Referring to  FIG. 14 , the wall W of the toner chamber  29   a  has a bottom portion Wb and a lateral portion Wa, The bottom portion Wb is the portion which is at the bottom when the cartridge is properly set in its image forming position, that is, when the attitude of the cartridge is as shown in  FIG. 14 . In terms of the rotational direction of the toner stirring member  36 , the lateral Wa is on the downstream side of the bottom portion Wb. It is tilted toward the axial line of the toner stirring member  36 , relative to the vertical direction. It is the lateral portion Wa that is provided with the recess  42  which is provided with the pair of toner remainder amount detecting member, that is, the transparent members  40  and  41 , as will be described later in later. Further, the wall W of the toner chamber  29   a  has a portion Wc, that is, the rest of the wall W of the toner chamber  29   a , which is between the abovementioned tilted portion Wa (lateral portion) and portion Wb (bottom portion) in terms of the rotational direction of the toner stirring member  36 , and connects the two portions Wa and Wb of the wall W of the toner chamber  29   a.    
         [0129]    As the toner stirring member  36  is rotated in the toner chamber  29   a , the sweeping edge  36   b A moves in contact with the bottom portion Wb, lateral portions Wa (tilted portion), etc., as will be described later in detail. Thus, the toner T in the toner chamber  29   a  is guided to the hole  29   c  along the bottom portion Wb, and then, along the portion Wa. 
         [0130]    More specifically, as the toner stirring member  36  is rotated, a part of the body of toner T in the toner chamber  29   a  fails to be guided into the hole  29   c , that is, it falls from the toner stirring member  36  and settles back in the bottom portion of the toner chamber  29   a , whereas the other part is guided inward of the toner chamber  29   a , along the portion Wc of the toner storage chamber wall, by the toner stirring member  36 . 
         [0131]    Referring to  FIG. 15 , the toner stirring member  36  is made up of a shaft  36   a  and a stirring sheet  36   b . The shaft  36   a  is molded of a resinous substance. The stirring sheet  36   b  is the very portion of the toner stirring member  36  that stirs toner. It is a rectangular sheet made of flexible resinous sheet. Its longer edges, that is, the edges parallel to the lengthwise direction of the shaft  36   a , have a length of W 0 , and its shorter edges, that is, the edges parallel to the radius direction of the sweeping area of the stirring sheet  36   b , that is, the distance from the rotational axis of the shaft  36   a  to the sweeping edge of the stirring sheet  36   b , have a length of H 0 . The stirring sheet  36   b  is attached to the shaft  36   a  by one of the longer edges. 
         [0132]    In terms of the stirring member rotation direction, the cleaning member  39  for cleaning the light exit surface  40   a  and light entrance surface  41   a  is on the downstream side of the stirring sheet  36   b . The cleaning member  39  is made up of a wiping sheet  39   a  and an auxiliary wiping sheet  39   b . The wiping sheet  39   a  is a flexible sheet for wiping away the toner having adhered to the light exit surface  40   a , and the light entrance surface  41   a . The auxiliary wiping sheet  39   b  is a member which assists the wiping sheet  39   a  in cleaning the light exit surface  40   a  and light entrance surface  41   a . The auxiliary wiping sheet  39   b  is attached to the shaft  36   a  by one of its edges parallel to the shaft  36   a . It is also attached to the wiping sheet  39   a  by the other edge parallel to the shaft  36   a . That is, the auxiliary wiping sheet  36   b  plays the role of the supporting member for attaching the wiping sheet  39   a  to the shaft  36   a.    
         [0133]    Referring to  FIGS. 14 and 15 , in this embodiment, the shaft  36   a  is rectangular in cross section. The toner stirring member  36  (stirring sheet  36   b ) is attached to one of the surfaces of the shaft  36   a . The transparent member cleaning member  39  (more specifically, auxiliary wiping sheet  39   b ) is attached to the opposite surface of the shaft  36   a  from the surface to which the toner stirring member  36  is attached. Therefore, in terms of the rotational direction of the toner stirring member  36 , the transparent member cleaning member  39  is on the downstream side relative to the toner stirring member  36  by a distance equivalent to the measurement (d) of the shaft  36   a  ( FIG. 14 ). 
         [0134]    To describe in more detail, the wiping sheet  39   a  is in the form of an isosceles trapezoid. That is, the wiping edge  39   a B of the wiping sheet  39   a , that is, the outward edge in terms of the radius direction of the sweeping area of the toner stirring member  36  is narrower (W 1   a ) than the edge  29   a C, that is, the inward (other) edge (W 2   a ) in terms of the abovementioned radius direction, which is closer to the shaft  36   a  by the height H 1   a  (W 1   a &lt;W 2   a ). As will be described later in more detail, the pair of lateral edges  39   a A of the trapezoidal wiping sheet  39   a  wipe away the toner having adhered to the light exit surface  40   a  and light entrance surface  41   a , by coming into contact with the light exit surface  40   a  and light entrance surface  41   a . Further, the distance H 0   a  from the axial line of the shaft  36   a  to the wiping edge  39   a B of the wiping sheet  39   a  is roughly the same in value as the abovementioned measurement H 0  of the stirring sheet in terms of the radius direction of the sweeping area of the toner stirring member  36 . 
         [0135]    The stirring sheet  36   b  and wiping sheet  39   a  can be easily made of flexible resinous sheet, such as polyester film, polyphenylene sulfide film, or the like. The thickness of the stirring sheet  22   b  is desired to be in a range of 50-250 μm. 
         [0136]    The force for driving the stirring member  36  is transmitted to the stirring member  36  by a driver gear (unshown) attached to one of the lengthwise ends of the shaft  36   a ; the shaft of the driver gear is inserted in the hole  36   c , with which one of the lengthwise ends of the shaft  36   a  is provided, through the hole with which one of the lateral walls of the toner chamber  29   a  of the developing means frame  29  is provided. 
         [0137]    Further, referring to  FIGS. 14 and 18(   a ), the light exit surface  40   a  and light entrance surface  41   a  for detecting the amount of the toner remainder, based on the amount of light transmission, are positioned so that they oppose each other, in terms of the direction parallel to the rotational axis of the toner stirring member  36 . The light exit surface  40   a  is an integral part of the transparent member  40  which guide the detection light L in  emitted from the LED (unshown), as a light emitting portion, with which the main assembly  100 A of the electrophotographic image forming apparatus is provided, into the recess  42  (that is, toner chamber  29   a ). 
         [0138]    The light exit surface  41   a  is an integral part of the transparent member  41 , which guides the detection light L out  to the phototransistor (unshown), as the light receiving portion, with which the main assembly  100 A of the electrophotographic image forming apparatus is provided, after the detection light L transmits through the recessed portion  42 . Incidentally, the transparent members  40  and  41  may be integrated into a single component. 
         [0139]    As the cleaning member  39  rotates, not only do the wiping sheet  39   a  and auxiliary wiping sheet  39   b  of the cleaning member  39  clean the light exit surface  40   a  and light entrance surface  41   a , but also, block the detection light L while they are wiping the light exit surface  40   a  and light entrance surface  41   a.    
         [0140]      FIG. 16  is a cross-sectional view of the process cartridge  7  immediately after the cleaning of the light exit surface  40   a  and light entrance surface  41   a , respectively, by the cleaning member  39 . When the process cartridge  7  is in the state shown in  FIG. 16 , the detection light L transmits through the recess  42 , and is detected by the light receiving portion in the main assembly of the image forming apparatus, through the light exit surface  41   a.    
         [0141]    On the other hand,  FIG. 17  is a cross-sectional view of the process cartridge  7  immediately before the light exit surface  40   a  and light entrance surface  41   a , respectively, are cleaned by the cleaning member  39 . When the process cartridge  7  is in the state shown in  FIG. 17 , the detection light L is blocked in the recess  42  by the body of toner T, which is being conveyed by the toner stirring member  36 , and therefore, it does not reach the light exit surface  41   a . Thus, it is not received by the light receiving portion in the main assembly of the image forming apparatus. 
         [0142]    With the employment of the above described structural arrangement, the amount of the toner remaining in the toner chamber  29   a  can be estimated based on the length of time the detection light L transmits through the toner chamber  29   a  (that is, recessed portion  42 ), that is, the length of time the detection light L is received by the light receiving portion of the image forming apparatus, per rotation of the toner stirring member  36 . 
       [Position and Shape of Light Exit Surface and Light Entrance Surface] 
       [0143]    At this time, referring to  FIGS. 14 and 18 , the position and shape of the light exit surface  40   a  and light entrance surface  41   a  of the pair of transparent members  40  and  41 , respectively, will be described in more detail. 
         [0144]    In this embodiment, the amount of the toner remainder is detected by the pair of transparent members  40  and  41 , based on the light transmission through the transparent members  40  and  41 . 
         [0145]    That is, referring to  FIG. 18 , as described above, according to the toner remainder amount detecting means in this embodiment, the detection light L in  emitted from the light emitting portion (unshown), such as a LED, attached to the main assembly of the image forming apparatus is guided to the transparent member  40 . Entering the transparent member  40 , the detection light L in  is deflected by 90°, by the reflective surface  40   r  of the transparent member  40 , being thereby guided toward the light exit surface  40   a  of the transparent member  40 , and exits from the transparent member  40  through the light exit surface  40   a . Exiting through the light exit surface  40   a , the detection light L travels through the process cartridge, and is guided into the light entrance surface  41   a  of the transparent member  41 , that is, the other transparent member, which opposes the transparent member  40 . Entering the transparent member  41 , the detection light L is deflected by 90° by the reflective surface  41   r  of the transparent member  41 . Then, the detection light L travels through the transparent member  41 , and exits from the transparent member  41 , that is, exits from the process cartridge. Exiting from the process cartridge, the detection light L out  is guided to the light receiving portion, such as a phototransistor, attached to the main assembly of the image forming apparatus. 
         [0146]    Referring also to  FIG. 18 , in this embodiment, the transparent members  40  and  41  are structured and positioned (attached to development unit  4 ) so that the distance W 2  between the inward edges of the mutually opposing light exit surface  40   a  and light entrance surface  41   a  is greater than the outward edges of the mutually opposing light exit surface  40   a  and light entrance surface  41   a  (that is, W 2 &gt;W 1 ). 
         [0147]    Therefore, in order to ensure that the tilted light exit surface  40   a  and light entrance surface  41   a , which oppose each other, are satisfactorily cleaned by the wiping sheet  39   a  of the cleaning member  39 , the wiping sheet  39   a  is rendered trapezoidal, as described above. Also in order to ensure that the wiping sheet  39   a  of the cleaning member  39  cleans the light exit surface  40   a  and light entrance surface  41   a  by elastically contacting the surfaces  40   a  and  41   a , the wiping sheet  39   a  is rendered slightly larger than the trapezoidal area which the mutually opposing light exit surface  40   a  and light entrance surface  41   a  form as shown in  FIG. 18(   a ). 
         [0148]    Depending on the positional relationship among the light exit surface  40   a , light entrance surface  41   a , and toner stirring member  36 , the toner on the toner stirring member  36  and the toner on the cleaning member  39  sometimes fall from the toner stirring member  36  and/or cleaning member  39 , respectively, and adheres to the light exit surface  40   a  and light entrance surface  41   a , immediately after the cleaning of the surfaces  40   a  and  41   a  by the cleaning member  39 . Therefore, the detection light L is sometimes blocked by the toner fell from the stirring member  36  and/or cleaning member  39  immediately after the cleaning. Further, the detection light L is sometimes blocked because the toner particles floating in the toner chamber  29   a  adhere to the light exit surface  40   a  and light entrance surface  41   a.    
         [0149]    Thus, in this embodiment, in order to prevent the problem that the toner, which fell from the toner stirring member  36  and/or cleaning member  39 , adhere to the light exit surface  40   a  and light entrance surface  41   a , the following structural arrangement is employed. 
         [0150]    That is, referring to  FIG. 14 , the transparent members  40  and  41  are attached to the portion Wa of the toner chamber wall, which will be above the horizontal plane H which coincides with the rotational axis O of the stirring member  36  when the process cartridge is in its image forming position in an image forming apparatus. Further, the portion Wa of the wall of the toner chamber  29   a  is tilted so that a straight line Va drawn perpendicularly and inwardly from the portion Wa is on the bottom side of the horizontal plane which coincides with the point of the portion Wa, from which the straight line Va is drawn. Further, referring to  FIG. 18 , the development unit  4  is structured so that a straight line Vb drawn inward of the toner chamber  29   a  from the light exit surface  40   a  ( 41   a ), and perpendicularly to the light exit surface  40   a  ( 41   a ), is under the horizontal plane which coincides with the point of the light exit surface  40   a , from which the straight line Vb is drawn. 
         [0151]    Incidentally, the angle of the top surface of the body of developer in the toner chamber  29   a  is affected by the angle of the axial line of the stirring member during the mounting of the process cartridge. Therefore, in order to reduce the effect of the inclination of the surface of the body of developer in the toner chamber  29   a , the light exit surface  40   a  and light entrance surface  41   a  are desired to be positioned roughly at the middle of the toner chamber  29   a  in terms of the direction parallel to the axial line of the stirring member  36 . 
       [Improvement in Blocking of Detection Light by Toner] 
       [0152]    In this embodiment, the toner chamber  29   a  is provided with the recess  42 , which is recessed outward from the toner chamber  29   a  in the radius direction of the sweeping area of the stirring member  36 . More specifically, the portion Wa of the wall W of the toner chamber  29   a , which is between the portions Wb and Wc of the wall W of the toner chamber  29   a , is provided with the recess  42 . As will be evident from  FIG. 18 , the recess  42  is a boxy space which opens to the toner chamber  29   a , and the opening of which has a size of w 1  (length of edge perpendicular to axial line of toner stirring member)×w 3  (length of edge parallel to axial line of toner stirring member). 
         [0153]    That is, the recess  42  has lateral walls  42   a   1  and  42   a   2  which oppose each other in terms of the direction parallel to the rotational axis of the toner stirring member  36 , and walls  42   b   1  and  42   b   2  which oppose each other in terms of the rotational direction of the toner stirring member  36 . Further, the recess  42  has the bottom wall which holds a distance h from the plane of the opening  42 A of the recess  42 , that is, the border between the recess  42  and toner chamber  29   a , and has a size of w 2 ×w 3 . In this embodiment, the transparent members  40  and  41  are attached to the bottom wall  42   c  of the recess  42 . 
         [0154]    Also referring to  FIG. 18 , in this embodiment, the wall of the recess  42  is an integral part of the portion Wa (tilted portion) of the wall W of the toner chamber  29   a  (that is, development means frame  29 ). However, the wall of the recess  42 , and the pair of transparent members  40  and  41  may be integrally formed as a single piece, which is attachable to the portion Wa of the wall W of the toner chamber  29   a  (that is, developing means frame  29 ). 
         [0155]    The development unit  4  (recess  42 ) is structured so that there is a gap g between the most inward edge of the surface  40   a  ( 41   a ) of the transparent member  40  ( 41 ) and the plane of the opening  42 A of the recess  42  ( FIGS. 18(   b ) and  21 ). The value of the gap g has only to be such that the transparent members  40  and  41  is prevented from protruding beyond the plane coinciding the inward surface of the portion Wa of the toner chamber wall. That is, the gap g is to be provided to prevent the problem that the toner stirring member  36  deform by hanging up on the transparent members  40  and  41 . Also in this embodiment, the development unit  4  (recess  42 ) is structured so that there is a certain amount of distance between the light exit surface  40   a  (and light entrance surface  41   a ) and the bottom wall  42   c . This structural arrangement is made to prevent the problem that sometimes, the amount of the toner remainder cannot be accurately detected because toner sometimes fails to reach the adjacencies of the bottom wall  42   c.    
         [0156]    Thus, in this embodiment, the above described structural arrangement is employed to ensure that the detection light L remains satisfactorily blocked until the sweeping edge  36   b A of the stirring sheet  36   b  begins to move through the adjacencies of the light exit surface  40   a  and light entrance surface  41   a , and also, to better control the toner in its behavior while the sweeping edge  36   b A of the stirring sheet  36   b  moves through the adjacencies of the light exit surface  40   a  and light entrance surface  41   a.    
         [0157]    However, regarding the blocking of the detection light L while the sweeping edge  36   b A of the stirring sheet  36   b  moves through the adjacencies of the light exit surface  40   a  and light entrance surface  41   a , because toner slips through the gap between the sweeping edge  36   b A of the stirring sheet  36   b  and the portion Wa of the toner chamber wall, which has the recess  42 , it is still difficult to keep the detection light L satisfactorily blocked while the sweeping edge  36   b A of the stirring sheet  36   b  is moving through the abovementioned area. 
         [0158]    More specifically, referring to  FIG. 21 , while the sweeping edge  36   b A of the stirring sheet  36   b  moves through the adjacencies of the light exit surface  40   a  and light entrance surface  41   a , the wiping sheet  39   a , which is on the downstream side of the stirring sheet  36   b  in terms of the rotational direction of the toner stirring member  36 , enters the space between the light exit surface  40   a  and light entrance surface  41   a . Further, the development unit  4  (toner chamber  29   a ) is structured so that the wiping sheet  39   a  for cleaning the light exit surface  40   a  and light entrance surface  41   a  comes into contact with the sweeping edge  36   b A of the stirring sheet  36   b  when the wiping sheet  39   a  enters the space between the light exit surface  40   a  and light entrance surface  41   a . Therefore, while the stirring sheet  36   b  moves through the space between the light exit surface  40   a  and light entrance surface  41   a , the gap g between the sweeping edge  36   b A of the stirring sheet  36   b , and the portion Wa of the wall W of the toner chamber  29   a , which corresponds to the recess  42 , is covered by the wiping sheet  39   a . Therefore, this embodiment is superior to the first embodiment in terms of keeping the detection light L satisfactorily blocked while the sweeping edge  36   b A of the stirring sheet  36   b  move through the adjacencies of the light exit surface  40   a  and light entrance surface  41   a.    
         [0159]    Further, because the development unit  4  (toner chamber  29   a ) is structured so that the wiping sheet  39   a  for cleaning the light exit surface  40   a  and light entrance surface  41   a  comes into contact with the sweeping edge  36   b A of the stirring sheet  36   b  when the wiping sheet  39   a  enters the space between the light exit surface  40   a  and light entrance surface  41   a , and also, so that the wiping sheet  39   a  begins to clean the light exit surface  40   a  and light entrance surface  41   a  the moment the body of toner T, which is being conveyed by the stirring sheet  36   b , finishes moving through the space between the light exit surface  40   a  and light entrance surface  41   a . Therefore, it is possible to reduce the problem that because the blockage of the detection light and the transmission of the detection light through the toner chamber (recess) are affected by the variation in the amount by which toner adheres or remains adhered to the light exit surface  40   a  and light exit surface  41   a , the amount of the toner remaining in the toner chamber cannot be accurately detected. 
       [Improvement of Wiping Performance of Cleaning Member] 
       [0160]    Referring to  FIGS. 15 ,  18 , and  21 , the pair of light exit surface  40   a  and light entrance surface  41   a , transparent members  40  and  41 , recess  42 , and cleaning member  39  will be described in more detail regarding their shape. 
         [0161]    The cleaning member  39  cleans the light exit surface  40   a  and light entrance surface  41   a  by being moved through the space between the light exit surface  40   a  and light entrance surface  41   a , which are aligned in the direction parallel to the rotational axis of the toner stirring member  36 . 
         [0162]    The shape of the sheet stirring member  36  and cleaning member  39 , and the recess  42 , are as described above with reference to  FIGS. 15 and 18 . 
         [0163]    In order for the wiping sheet  39   a  to satisfactorily wipe clean the light exit surface  40   a  and light entrance surface  41   a , the rigidity of the wiping sheet  39   a  in terms of the vertical direction needs to greater than a certain value. However, if the piping sheet  39   a  is excessively increased in rigidity, the wiping sheet  39   a  cannot be moved into the space between the light exit surface  40   a  and light entrance surface  41   a . Thus, in order to allow the wiping sheet  39   a  to enter the space between the light exit surface  40   a  and light entrance surface  41   a , the rigidity of the wiping sheet  39   a  in terms of the direction parallel to the circumferential direction of the sweeping area of the toner stirring member  36  needs to be greater than the rigidity of the wiping member  39   a  in terms of the direction perpendicular to the light exit surface  40   a  and light entrance surface  41   a.    
         [0164]    Therefore, in this embodiment, in order to add to the rigidity of the wiping sheet  39   a  in terms of the circumferential direction of the sweeping area of the toner stirring member  36 , the cleaning member  39  is provided with the auxiliary wiping sheet  39   b , which is positioned on the downstream side of the wiping sheet  39   a  in terms of the rotational direction of the stirring member. 
         [0165]    The width W 3  of the edge of the auxiliary wiping sheet  39   b  on the wiping sheet side is less than the width W 1   a  of the wiping edge  39   a B of the wiping sheet  39   a , which is perpendicular to the light exit surface  40   a  and light entrance surface  41   a  (W 3 &lt;W 1   a ). Further, the auxiliary wiping sheet  39   b  is shaped so that the width W 3  is less than the shortest distance W 1  between the light exit surface  40   a  and light entrance surface  41   a  (W 3 &lt;W 1 ). 
         [0166]    Further, referring to  FIG. 18 , the light exit surface  40   a  and light entrance surface  41   a  are tilted so that their inward edges in terms of the radius direction of the sweeping area of the toner stirring member  36 , is longer than their outward edges (W 1 &lt;W 2 ). Therefore, the wiping sheet  39   a  is shaped so that the its inward edge  39   a C, in terms of the radius direction of the stirring member  36 , is longer than its outward edge  39   a B (W 2   a &gt;W 1   a ). 
         [0167]    The wiping sheet  39   a  is shaped and sized to ensure that even if the wiping sheet  39   a  deforms and/or creeps, or the like problems occur, it can still wipe clean the light exit surface  40   a  and light entrance surface  41   a  across their entire range in terms of the circumferential direction of the sweeping area of the toner stirring member  36 . That is, the wiping sheet  39   a  is rendered long enough, in terms of the radius direction of the sweeping area of the toner stirring member  36 , to enter the portion of the recess  42 , which is between the light exit surface  40   a  and light entrance surface  41   a , deep enough to reach the bottom wall  42   c  of the recess  42 . 
         [0168]    Further, in order to ensure that the wiping sheet  39   a  wipes the light exit surface  40   a  and light entrance surface  41   a  across their entire range in terms of the rotational direction of the toner stirring member  36 , a gap g 1 , which is the gap between the transparent member  40  ( 41 ) and the lateral wall  42   b   1 , which is the downstream wall of the recess  42  in terms of the rotational direction of the toner stirring member  36 , and a gap g 2 , which is the gap between the transparent member  40  ( 41 ) and the lateral wall  42   b   2 , which is the upstream wall of the recess  42  in terms of the rotational direction of the toner stirring member  36 , are rendered large enough for the wiping sheet  39   a  to satisfactorily wipe the light exit surface  40   a  and light entrance surface  41   a  across their entire ranges in terms of the rotational direction of the toner stirring member  36 . 
       [Prevention of Toner Adhesion After Wiping of Light Exit Surface and Light Entrance Surface by Cleaning Member] 
       [0169]    Referring to  FIG. 22 , while the wiping sheet  39   a  moves between the light exit surface  40   a  and light entrance surface  41   a , it is kept deformed by the light exit surface  40   a  and light entrance surface  41   a , and there is toner T on the wiping sheet  39   a.    
         [0170]    As soon as the wiping sheet  39   a  moves past the space between the light exit surface  40   a  and light entrance surface  41   a , the wiping sheet  39   a  is freed from the restriction placed on the wiping sheet  39   a  by the light exit surface  40   a  and light entrance surface  41   a , and therefore, it springs back into its normal shape because of its resiliency. As a result, the toner T on the wiping sheet  39   a  is catapulted downward in terms of the rotational direction of the toner stirring member  36 , in the recess  42 . 
         [0171]    If there is no space between the lateral wall  42   a   1  and transparent member  40 , and between the lateral wall  42   a   2  and transparent member  41  ( FIG. 27 ), the toner T on the wiping sheet  39   a  falls through the space between the light exit surface  40   a  and light entrance surface  41   a  after the cleaning of the light exit surface  40   a  and light entrance surface  41   a . As the toner T falls, it sometimes adheres again to the light exit surface  40   a  and light entrance surface  41   a.    
         [0172]    Thus, in this embodiment, in order to prevent the problem that after the toner T is wiped away from the light exit surface  40   a  and light entrance surface  41   a , it adheres again to the light exit surface  40   a  and light entrance surface  41   a , a space S is provided between the transparent members  40  and  41 , and lateral walls  42   a   1  and  42   a   2 , respectively, of the recess  42 , as shown in  FIG. 22 . With the provision of the space S between the transparent members  40  and  41 , and lateral walls  42   a   1  and  42   a   2 , respectively, of the recess  42 , the toner borne on the wiping sheet  39   a  while the wiping sheet  39   a  moves between the light exit surface  40   a  and light entrance surface  41   a  falls through the gaps S between the transparent members  40  and  41 , and lateral walls  42   a   1  and  42   a   2 , respectively, of the recess  42 . Therefore, when the wiping sheet  39   a  moves out of the space between the light exit surface  40   a  and light entrance surface  41   a , there remains only a small amount of toner on the wiping sheet  39   a.    
         [0173]    The problem that the amount of the toner remainder in the toner chamber  29   a  is inaccurately detected because of the variation in the amount of the toner which adheres again to the light exit surface  40   a  and light entrance surface  41   a  after the light exit surface  40   a  and  41   a  are cleaned, can be reduced by reducing the amount by which toner T remains on the wiping sheet  39   a  when the wiping sheet  39   a  moves out of the space between the light exit surface  40   a  and light entrance surface  41   a , that is, when the wiping sheet  39   a  kept deformed while moving between the light exit surface  40   a  and light entrance surface  41   a  is allowed to spring back into its normal shape. 
         [0174]    Further, if the body of toner T, which entered the recess  42  during the period in which the detection light L was blocked, remains in the recess  42  even after the passage of the cleaning member  39  through the space between the light exit surface  40   a  and light entrance surface  41   a , the toner sometimes adheres to the light exit surface  40   a  and light entrance surface  41   a , and therefore, blocks the detection light L, after the cleaning of the light exit surface  40   a  and light entrance surface  41   a.    
         [0175]    The lateral wall  42   b   2  of the recess  42 , that is, the lateral wall of the recess  42 , which is on the bottom side, and on the upstream side in terms of the rotational direction of the toner stirring member  36  ( FIG. 18 ), is tilted by the angle of θ, the value of which is large enough to cause the toner T to fall into the toner chamber  29   a . This structural arrangement is for preventing the toner T from remaining in the recess  42  after the cleaning member  39  moves between the light exit surface  40   a  and light entrance surface  41   a.    
         [0176]    As described above, not only can this embodiment offer the same effects as the first embodiment, but also, can prevent the problem that during the period in which the detection light L is to be allowed to transmit through the space between the light exit surface  40   a  and light entrance surface  41   a , the toner adheres to the light exit surface  40   a  and light entrance surface  41   a  immediately after the cleaning of the light exit surface  40   a  and light entrance surface  41   a . On the other hand, the toner in the toner chamber  29   a  is moved into the light passage L by the stirring member  36  to block the detection light L. Therefore, the length of time the detection light L remains blocked is not affected by the change in the fluidity of the toner. Further, the light exit surface  40   a  and light entrance surface  41   a  are more efficiently wiped clean by the cleaning member  39 . 
         [0177]    In the foregoing examples, the use has been made with a toner remainder amount detecting means of the light transmission type, but the present invention is no limited to the toner remainder amount detecting means of this type, and those utilizing electrostatic capacity is usable. 
         [0178]    According to the present invention, the developer detecting member is attached to the portion of the developer storage chamber wall, along which the developer stirring member conveys upward the developer in the developer storage chamber into the development chamber located on top of the developer storage chamber. Therefore, the amount of the developer remaining in the developer storage chamber can be detected while the body of developer is stable. Therefore, the amount of the developer remainder can be more precisely detected. Further, the developer remainder amount detecting method based on the amount of light transmission is employed. Therefore, the amount of the developer remainder can be detected with the use a small number of components which are inexpensive. Therefore, it is possible to provide a developing apparatus, a process cartridge, and an electrophotographic image forming apparatus, which are significantly lower in cost than those in accordance with the prior art. 
         [0179]    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. 
         [0180]    This application claims priority from Japanese Patent Applications Nos. 022466/2007 and 291356/2007 filed Jan. 31, 2007 and Nov. 8, 2007, respectively which are hereby incorporated by reference.