Abstract:
A developing device includes a storage portion for retaining developer; a light guide member for forming a plurality of optical paths passing through the storage unit to detect an amount of the developer in the storage portion; a plurality of window members formed in a wall of the storage portion for passing the optical paths therethrough; a blocking member disposed to be movable for blocking the window members; and a drive unit for moving the blocking member. The blocking member is disposed on each of the optical paths. When the drive unit moves the blocking member, the blocking member periodically blocks and opens each of the optical paths in a specific cycle.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to a developing device and an image forming apparatus. 
         [0002]    A conventional developing device is used in an image forming apparatus such as a printer, a copier, and the likes. In the conventional developing device, an optical detection unit is provided for detecting a remaining amount of toner stored in a storage unit as developer. In this case, a transparent window member is disposed in a wall of the storage unit retaining toner, so that a remaining amount of toner is detected using light passing through the window member (refer to Patent Reference). 
       Patent Reference Japan Patent Publication No. 2003-162138 
       [0003]    In the conventional developing device, a remaining amount of toner is detected at one point in the storage unit. Accordingly, when toner has an uneven distribution in the storage unit depending on a pattern of an image to be formed, it is difficult to accurately detect a remaining amount of toner. 
         [0004]    In order to securely prevent toner from being supplied to a developing roller even in a case of an insufficient amount of toner, it is arranged to detect a remaining amount of toner with a certain margin, considering a situation in which a remaining amount of toner is not accurately detected. Accordingly, a toner cartridge is prompted to replace at a relatively early stage. As a result, even though a toner cartridge still retains a sufficient amount of toner, the toner cartridge is replaced with new one, thereby wasting toner. 
         [0005]    In view of the problem described above, an object of the invention is to provide a developing device and an image forming device, in which it is possible to solve the problems of the conventional developing device. The developing device includes a plurality of window members disposed on a plurality of optical paths for detecting a remaining amount of toner. Further, a cleaning unit is provided for periodically cleaning the window members in cycles shifted by a specific phase. Accordingly, even when toner retained in a storage unit has an uneven distribution, it is possible to accurately detect a remaining amount of toner, thereby conserving toner. 
         [0006]    Further objects of the invention will be apparent from the following description of the invention. 
       SUMMARY OF THE INVENTION 
       [0007]    In order to attain the objects described above, according to the present invention, a developing device includes a storage portion for retaining developer; a light guide member for forming a plurality of optical paths passing through the storage unit to detect an amount of the developer in the storage portion; a plurality of window members formed in a wall of the storage portion for passing the optical paths therethrough; a blocking member disposed to be movable for blocking the window members; and a drive unit for moving the blocking member. The blocking member is disposed on each of the optical paths. When the drive unit moves the blocking member, the blocking member periodically blocks and opens each of the optical paths in a specific cycle. 
         [0008]    In the present invention, the developing device includes the window members disposed on the optical paths for detecting a remaining amount of toner. Further, the blocking member is provided for periodically blocking and opening each of the optical paths in a specific cycle. Accordingly, even when toner retained in the storage portion has an uneven distribution, it is possible to accurately detect the remaining amount of toner, thereby conserving toner. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a schematic plan view showing a developing device according to a first embodiment of the present invention; 
           [0010]      FIG. 2  is a schematic side sectional view showing the developing device according to the first embodiment of the present invention; 
           [0011]      FIG. 3  is a schematic sectional view showing an image forming apparatus according to the first embodiment of the present invention; 
           [0012]      FIG. 4  is a schematic side sectional view showing the developing device according to the first embodiment of the present invention; 
           [0013]      FIG. 5  is a schematic front sectional view showing the developing device according to the first embodiment of the present invention; 
           [0014]      FIG. 6  is a plan view showing a light guide member of the developing device according to the first embodiment of the present invention; 
           [0015]      FIG. 7  is a perspective view showing a cleaning arm of the developing device according to the first embodiment of the present invention; 
           [0016]      FIG. 8  is a schematic view showing a positional relationship between the cleaning arm and an optical path according to the first embodiment of the present invention; 
           [0017]      FIGS. 9(   a ) to  9 ( e ) are charts showing a positional relationship between the cleaning arm and a detection signal of a light-receiving element according to the first embodiment of the present invention, wherein  FIG. 9(   a ) is a chart showing a positional relationship between a first arm and a first optical path,  FIG. 9(   b ) is a chart showing a change in detection light passing through the first optical path,  FIG. 9(   c ) is a chart showing a positional relationship between a second arm and a second optical path,  FIG. 9(   d ) is a chart showing a change in detection light passing through the second optical path, and  FIG. 9(   e ) is a chart showing a change in detection light received at the light-receiving element; 
           [0018]      FIG. 10  is a schematic side view showing a toner stirring member according to a second embodiment of the present invention; 
           [0019]      FIG. 11  is a schematic plan view showing the toner stirring member according to the second embodiment of the present invention; 
           [0020]      FIGS. 12(   a ) to  12 ( e ) are schematic views showing an operation of the toner stirring member according to the second embodiment of the present invention; 
           [0021]      FIGS. 13(   a ) to  13 ( g ) are charts showing a positional relationship between a cleaning arm and a detection signal of a light-receiving element in a state that toner decreases according to the second embodiment of the present invention, wherein  FIG. 13(   a ) is a chart showing a positional relationship between a first arm and a first optical path,  FIG. 13(   b ) is a chart showing a change in detection light entering the first optical path,  FIG. 13(   c ) is a chart showing a change in detection light outgoing from the first optical path,  FIG. 13(   d ) is a chart showing a positional relationship between a second arm and a second optical path,  FIG. 13(   e ) is a chart showing a change in detection light entering the second optical path,  FIG. 13(   f ) is a chart showing a change in detection light outgoing from the second optical path, and  FIG. 13(   g ) is a chart showing a change in detection light received at the light-receiving element; 
           [0022]      FIGS. 14(   a ) to  14 ( g ) are charts showing the positional relationship between the cleaning arm and the detection signal of the light-receiving element in a state that toner further decreases according to the second embodiment of the present invention, wherein  FIG. 14(   a ) is a chart showing a positional relationship between the first arm and the first optical path,  FIG. 14(   b ) is a chart showing a change in detection light entering the first optical path,  FIG. 14(   c ) is a chart showing a change in detection light outgoing from the first optical path,  FIG. 14(   d ) is a chart showing a positional relationship between the second arm and the second optical path,  FIG. 14(   e ) is a chart showing a change in detection light entering the second optical path,  FIG. 14(   f ) is a chart showing a change in detection light outgoing from the second optical path, and  FIG. 14(   g ) is a chart showing a change in detection light received at the light-receiving element; 
           [0023]      FIGS. 15(   a ) to  15 ( g ) are charts showing the positional relationship between the cleaning arm and the detection signal of the light-receiving element in a state that toner is completely consumed according to the second embodiment of the present invention, wherein  FIG. 15(   a ) is a chart showing a positional relationship between the first arm and the first optical path,  FIG. 15(   b ) is a chart showing a change in detection light entering the first optical path,  FIG. 15(   c ) is a chart showing a change in detection light outgoing from the first optical path,  FIG. 15(   d ) is a chart showing a positional relationship between the second arm and the second optical path,  FIG. 15(   e ) is a chart showing a change in detection light entering the second optical path,  FIG. 15(   f ) is a chart showing a change in detection light outgoing from the second optical path, and  FIG. 15(   g ) is a chart showing a change in detection light received at the light-receiving element; 
           [0024]      FIG. 16  is a schematic side view showing a toner stirring member according to a third embodiment of the present invention; and 
           [0025]      FIG. 17  is a schematic plan view showing the toner stirring member according to the third embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0026]    Hereunder, embodiments of the present invention will be described in more detail with reference to the accompanying drawings. 
       First Embodiment 
       [0027]    A first embodiment of the present invention will be explained.  FIG. 2  is a schematic side sectional view showing a developing device  11  according to the first embodiment of the present invention.  FIG. 3  is a schematic sectional view showing an image forming apparatus  10  according to the first embodiment of the present invention. 
         [0028]    In the embodiment, the image forming apparatus  10  may be any type of image forming apparatus such as a printer of an electro-photography type, a facsimile, a copier, and a multi-function printer having functions of a printer, a facsimile, and a copier. In the following description, the image forming apparatus  10  is a tandem type color printer of an electro-photography type. 
         [0029]    As shown in  FIG. 3 , in the image forming apparatus  10 , the developing devices  11  corresponding to four colors, i.e., cyan (C), magenta (M), yellow (Y), and black (K), respectively, are arranged sequentially along a transportation path of a medium in a direction that the medium is transported (to the left side in  FIG. 3 ). The developing devices  11  have an identical configuration and retain toner  30  of different colors. 
         [0030]    In the embodiment, the image forming apparatus  10  includes a medium tray  55  for storing the medium as a recording sheet; a sheet supply roller  57  for separating and supplying the medium one by one from the medium tray  55 ; a transportation roller  58  for transporting the medium thus supplied; and a transfer belt  59  for transporting the medium and transferring a toner image to the medium. When the transportation roller  58  transports the medium to the transfer belt  59 , static charge is applied to the medium to be attached to the transfer belt  59 . Afterward, while the developing devices  11  form the toner image, the transfer belt  59  transports the medium. 
         [0031]    In the embodiment, the image forming apparatus  10  further includes a fixing unit  60  as a fixing device for fixing the toner image thus transferred to the medium through heat and pressure. The fixing unit  60  includes a pressing roller  61   a  and a heating roller  61   b . The image forming apparatus  10  further includes a discharge roller  62  for discharging the medium with the toner image thus fixed thereto to outside the image forming apparatus  10 ; and a stack cover  63  for holding the medium thus discharged. 
         [0032]    As shown in  FIG. 2 , the developing device  11  includes a toner storage portion  12  as a storage portion for storing the toner  30 ; a toner supply roller  13 ; a developing roller  14 ; a photosensitive drum  15  as an image supporting member; a charge roller  52 ; a cleaning blade  53 ; and an exposure head  54 . 
         [0033]    In the embodiment, the charge roller  52  functions as a charge device for uniformly and evenly charging the photosensitive drum  15  rotating. The exposure head  54  includes an LED (Light Emitting Diode) head and the likes for irradiating a surface of the photosensitive drum  15  according to an image signal, so that the surface of the photosensitive drum  15  is selectively exposed to form a static latent image thereon. 
         [0034]    In the embodiment, the developing roller  14  attaches the toner  30  to the surface of the photosensitive drum  15  with the static latent image formed thereon, thereby forming the toner image. The toner supply roller  13  supplies the toner  30  onto the developing roller  14 . 
         [0035]    In the embodiment, the transfer belt  59  transfers the toner image formed on the surface of the photosensitive drum  15  to the medium through a static force. The cleaning blade  53  has an end portion abutting against the surface of the photosensitive drum  15  for removing the toner  30  remaining on the surface of the photosensitive drum  15 . A cleaning arm  23  is disposed in the toner storage portion  12  as a rotational member rotating in an arrow direction. 
         [0036]    A configuration of the toner storage portion  12  will be explained in more detail next.  FIG. 1  is a schematic plan view showing the developing device  11  according to the first embodiment of the present invention. 
         [0037]      FIG. 4  is a schematic side sectional view showing the developing device  11  according to the first embodiment of the present invention.  FIG. 5  is a schematic front sectional view showing the developing device  11  according to the first embodiment of the present invention.  FIG. 6  is a plan view showing a light guide member  18  of the developing device  11  according to the first embodiment of the present invention. 
         [0038]    In the embodiment, a pair of optical sensors, that is, a light-emitting element  21  and a light-receiving element  22 , is provided for detecting a remaining amount of the toner  30  stored in the toner storage portion  12 . A plurality of optical paths, that is, a first optical path  19  and a second optical path  20 , is set in the toner storage portion  12 . More specifically, the first optical path  19  and the second optical path  20  are set at a lower portion of the toner storage portion  12  near both end portions of the toner storage portion  12  in a width direction thereof. 
         [0039]    In the embodiment, a pair of first window holes  16   a  and  16   b  is formed in a wall surface of the toner storage portion  12  at the lower portion of the toner storage portion  12  near the both end portions of the toner storage portion  12  in the width direction thereof for forming the first optical path  19 . Similarly, a pair of second window holes  17   a  and  17   b  is formed in the wall surface of the toner storage portion  12  at the lower portion of the toner storage portion  12  near the both end portions of the toner storage portion  12  in the width direction thereof for forming the second optical path  20 . 
         [0040]    Note that the first window holes  16   a  and  16   b  and the second window holes  17   a  and  17   b  are located at a same position in a vertical direction. At the position, when a remaining amount of the toner  30  becomes smaller than a specific amount, the toner  30  no longer block the first optical path  19  and the second optical path  20 . 
         [0041]    As shown in  FIG. 6 , the light guide member  18  has a pair of first protruding ends  18   d  and a pair of second protruding ends  18   e . The first protruding ends  18   d  are fitted in the first window holes  16   a  and  16   b , respectively. The second protruding ends  18   e  are fitted in the second window holes  17   a  and  17   b , respectively. The first protruding ends  18   d  are formed near base portions of the light guide member  18 , and the second protruding ends  18   e  are formed near distal end portions of the light guide member  18 . 
         [0042]    In the embodiment, light outgoes from one of the first protruding ends  18   d  and enters the other of the first protruding ends  18   d  along the first optical path  19 . Similarly, light outgoes from one of the second protruding ends  18   e  and enters the other of the second protruding ends  18   e  along the second optical path  20 . 
         [0043]    In the embodiment, a light incident surface  18   a  is formed on one of the base portions of the light guide member  18 , and the light-emitting element  21  is disposed to face the light incident surface  18   a . Further, a light radiation surface  18   c  is formed on the other of the base portions of the light guide member  18 , and the light-receiving element  22  is disposed to face the light radiation surface  18   c . A control unit (not shown) is connected to the light-emitting element  21  and the light-receiving element  22  for processing a signal therefrom. 
         [0044]    In the embodiment, the light guide member  18  is formed of a transparent material such as polycarbonate. In the light guide member  18 , light emitting from the light-emitting element  21  is divided into two optical axes, so that light outgoes from one of the first protruding ends  18   d  and one of the second protruding ends  18   e . Then, the light guide member  18  collects light entering the other of the first protruding ends  18   d  and the other of the second protruding ends  18   e , and guides light to the light-receiving element  22 . 
         [0045]    In the embodiment, light entering through the light incident surface  18   a  proceeds straight through the light guide member  18 , and is reflected on reflection surfaces  18   b , so that light outgoes from one of the first protruding ends  18   d  and one of the second protruding ends  18   e . Then, light entering the other of the first protruding ends  18   d  and the other of the second protruding ends  18   e  is reflected on reflection surfaces  18   b , so that light proceeds straight through the light guide member  18  and is received with the light-receiving element  22 . 
         [0046]    In the embodiment, the cleaning arm  23  is disposed in the toner storage portion  12 . The cleaning arm  23  includes a shaft  24  extending in the width direction of the toner storage portion  12  and supported on both end surfaces of the toner storage portion  12  to be rotatable; a first arm  25   a  and a second arm  25   b  as a cleaning member attached to both end portions of the shaft  24  and extending in a radial direction; and a first cleaning pad  26   a  and a second cleaning pad  26   b  respectively disposed at outer circumferential surfaces of the first arm  25   a  and the second arm  25   b  for cleaning the first protruding ends  18   d  and the second protruding ends  18   e  of the light guide member  18  fitted into the first window holes  16   a  and  16   b  and the second window holes  17   a  and  17   b.    
         [0047]    A configuration of the cleaning arm  23  will be explained in more detail next.  FIG. 7  is a perspective view showing the cleaning arm  23  of the developing device  11  according to the first embodiment of the present invention.  FIG. 8  is a schematic view showing a positional relationship between the cleaning arm  23  and the optical path according to the first embodiment of the present invention. 
         [0048]    As shown in  FIG. 7 , the first arm  25   a  and the second arm  25   b  are attached to the shaft  24  at angles shifted with each other. More specifically, the first arm  25   a  and the second arm  25   b  are attached to the shaft  24 , so that the first arm  25   a  and the second arm  25   b  have phases shifted with each other in a rotational direction. 
         [0049]    In the embodiment, when the shaft  24  rotates, the first arm  25   a  and the second arm  25   b  periodically block detection light passing through the first optical path  19  and the second optical path  20 . As described above, the first arm  25   a  and the second arm  25   b  have phases shifted with each other in the rotational direction. Accordingly, a phase of the first arm  25   a  blocking the first optical path  19  is different from a phase of the second arm  25   b  blocking the second optical path  20 . 
         [0050]    As shown in  FIG. 8 , an edge surface  125   a  of the first arm  25   a  and an edge surface  125   b  of the second arm  25   b  rotate along a rotational path P. The rotational path P crosses the first optical path  19  and the second optical path  20  at crossing points Q and R, respectively. 
         [0051]    In this case, a line La extending from the crossing point Q to a rotational axis  24   a  of the shaft  24  has an angle A 2  with respect to a line Lb extending from the crossing point R to the rotational axis  24   a  of the shaft  24 . The first arm  25   a  and the second arm  25   b  are attached to the shaft  24  with an angle A 1 . In the embodiment, it is arranged such that the angle A 1  is smaller than the angle A 2  (A 1 &lt;A 2 ). 
         [0052]    In the embodiment, the first cleaning pad  26   a  and the second cleaning pad  26   b  are disposed at the outer circumferential surfaces of the first arm  25   a  and the second arm  25   b . When the cleaning arm  23  rotates, the first cleaning pad  26   a  and the second cleaning pad  26   b  move over the first window holes  16   a  and  16   b  and the second window holes  17   a  and  17   b . At this time, the first cleaning pad  26   a  and the second cleaning pad  26   b  remove the toner  30  and clean the first protruding ends  18   d  and the second protruding ends  18   e  of the light guide member  18  fitted into the first window holes  16   a  and  16   b  and the second window holes  17   a  and  17   b.    
         [0053]    In the embodiment, the first cleaning pad  26   a  and the second cleaning pad  26   b  are preferably formed of an ester type sponge, and may be formed of a member such as a felt, a film, and the likes. 
         [0054]    An operation of the developing device  11  will be explained next. First, as shown in  FIG. 2 , when a drive gear (not shown) drives the cleaning arm  23  to rotate in the arrow direction, the toner supply roller  13  rotates, so that the toner  30  is taken with the toner supply roller  13 . After the toner  30  is coated on the surface of the developing roller  14  through the toner supply roller  13 , the toner  30  adheres to the static latent image formed in advance on the surface of the photosensitive drum  15  as the latent image, thereby developing the static latent image as the toner image. 
         [0055]    At the same time, in the toner storage portion  12 , the first cleaning pad  26   a  and the second cleaning pad  26   b  respectively attached to the first arm  25   a  and the second arm  25   b  of the cleaning arm  23  are rubbed against the first protruding ends  18   d  and the second protruding ends  18   e  of the light guide member  18  fitted into the first window holes  16   a  and  16   b  and the second window holes  17   a  and  17   b . Accordingly, the first cleaning pad  26   a  and the second cleaning pad  26   b  remove the toner  30  and clean the first protruding ends  18   d  and the second protruding ends  18   e  of the light guide member  18 . 
         [0056]    When a sufficient amount of the toner  30  remains in the toner storage portion  12 , the toner  30  is filled in the toner storage portion  12  up to a level above the first optical path  19  and the second optical path  20 . Accordingly, even when the first cleaning pad  26   a  and the second cleaning pad  26   b  remove the toner  30  and clean the first protruding ends  18   d  and the second protruding ends  18   e  of the light guide member  18 , the toner  30  covers the first protruding ends  18   d  and the second protruding ends  18   e  of the light guide member  18  fitted into the first window holes  16   a  and  16   b  and the second window holes  17   a  and  17   b . As a result, the toner  30  blocks the first optical path  19  and the second optical path  20 , so that the light-receiving element  22  does not receive light. 
         [0057]    When the image forming apparatus  10  is continued to use, a remaining amount of the toner  30  in the toner storage portion  12  decreases.  FIGS. 9(   a ) to  9 ( e ) are charts showing a positional relationship between the cleaning arm  23  and the detection signal of the light-receiving element  22  according to the first embodiment of the present invention. In  FIGS. 9(   a ) to  9 ( e ), a horizontal direction represents a period of time. 
         [0058]    More specifically,  FIG. 9(   a ) is a chart showing a positional relationship between the first arm  25   a  and the first optical path  19 ;  FIG. 9(   b ) is a chart showing a change in detection light passing through the first optical path  19 ;  FIG. 9(   c ) is a chart showing a positional relationship between the second arm  25   b  and the second optical path  20 ;  FIG. 9(   d ) is a chart showing a change in detection light passing through the second optical path  20 ; and  FIG. 9(   e ) is a chart showing a change in detection light received at the light-receiving element  22 . 
         [0059]    As shown in  FIGS. 9(   a ) and  9 ( b ), when the first arm  25   a  does not block the first optical path  19 , detecting light passing through the first optical path  19  is turned on. That is, the light-receiving element  22  detects detection light passing through the first optical path  19 . 
         [0060]    As shown in  FIGS. 9(   c ) and  9 ( d ), when the second arm  25   b  does not block the second optical path  20 , detecting light passing through the second optical path  20  is turned on. That is, the light-receiving element  22  detects detection light passing through the second optical path  20 . 
         [0061]    As shown in  FIG. 9(   e ), when the light-receiving element  22  detects detection light passing through the first optical path  19  or the second optical path  20 , that is, the light-receiving element  22  is turned on, the states that detecting light is turned on in  FIGS. 9(   a ) and  9 ( c ) are overlapped. In this state, the light-receiving element  22  detects detection light passing through either of the first optical path  19  or the second optical path  20 . 
         [0062]    In the embodiment, the first arm  25   a  and the second arm  25   b  are attached to the shaft  24  at angles shifted with each other. Further, the first arm  25   a  or the second arm  25   b  blocks one of the first optical path  19  and the second optical path  20  all the time. Accordingly, the detection signal (a detection time T 1 ) of detection light passing through the first optical path  19  has a detection wave shifted in terms of time with respect to that of the detection signal (a detection time T 2 ) of detection light passing through the second optical path  20 . That is, the detection signal (the detection time T 1 ) of detection light passing through the first optical path  19  is not overlapped with the detection signal (the detection time T 2 ) of detection light passing through the second optical path  20 . 
         [0063]    When the toner  30  stored in the toner storage portion  12  has an uneven distribution, the light-receiving element  22  first detects detection light passing through an optical path on a side where a remaining amount of the toner  30  is smaller. When an amount of detection light passing through the first optical path  19  or the second optical path  20  becomes smaller than a specific level, the control unit determines that the toner  30  is run out, and notifies a user of the image forming apparatus  10  through a display unit (not shown). 
         [0064]    In the embodiment, the first arm  25   a  and the second arm  25   b  are attached to the shaft  24  at angles shifted with each other, so that the first arm  25   a  and the second arm  25   b  block the first optical path  19  and the second optical path  20  at the same time when the blocked optical path is switched. Accordingly, there is always an OFF signal between the detection time T 1  and the detection time T 2 . That is, there is always no ON signal between the detection time T 1  and the detection time T 2 . With the OFF signal, it is possible to confirm whether the cleaning arm  23  rotates normally. 
         [0065]    As described above, in the embodiment, a remaining amount of the toner  30  is detected at a plurality of locations in the toner storage portion  12 . Accordingly, it is possible to accurately detect a remaining amount of the toner  30  even when the toner  30  stored in the toner storage portion  12  has an uneven distribution. 
         [0066]    Further, in the embodiment, when the toner  30  stored in the toner storage portion  12  has an uneven distribution, it is possible to accordingly prompt a user to replace the toner cartridge. As a result, as compared with the case in which a remaining amount of the toner  30  is detected at a single location in the toner storage portion  12 , it is not necessary to set a margin in consideration of an uneven distribution of the toner  30 , thereby not wasting the toner  30  in the toner storage portion  12 . 
         [0067]    Still further, in the embodiment, it is possible to detect a remaining amount of the toner  30  at a plurality of locations in the toner storage portion  12  with a pair of optical sensors. Accordingly, it is possible to reduce the number of parts. 
       Second Embodiment 
       [0068]    A second embodiment of the present invention will be described below. In the description below, elements in the second embodiment similar to those in the first embodiment are designated by same reference numerals, and explanations thereof are omitted. Explanations of operations and effects in the second embodiment similar to those in the first embodiment are omitted. 
         [0069]      FIG. 10  is a schematic side view showing a toner stirring member  31  according to the second embodiment of the present invention.  FIG. 11  is a schematic plan view showing the toner stirring member  31  according to the second embodiment of the present invention. 
         [0070]    In the embodiment, the toner stirring member  31  is provided as a rotational member. As shown in  FIG. 10 , the toner stirring member  31  includes a stirring shaft  34  extending in the width direction of the toner storage portion  12  and supported on the both end walls of the toner storage portion  12  to be rotatable; a first arm  33   a  and a second arm  33   b  as a cleaning member attached to the stirring shaft  34  near both end portions thereof and extending in a radial direction; a first cleaning pad  35   a  and a second cleaning pad  35   b  respectively disposed at outer circumferential surfaces of the first arm  33   a  and the second arm  33   b  for cleaning the first protruding ends  18   d  and the second protruding ends  18   e  of the light guide member  18  fitted into the first window holes  16   a  and  16   b  and the second window holes  17   a  and  17   b ; and a stirring sheet  32  with a sheet shape attached to the stirring shaft  34  and extending in the radial direction. 
         [0071]    As shown in  FIG. 10 , the first arm  33   a  and the second arm  33   b  are attached to the stirring shaft  34  with reversed phases with each other. The first arm  33   a  and the second arm  33   b  have arc portions B situated along the inner wall of the toner storage portion  12  when the toner stirring member  31  is attached to the toner storage portion  12 . 
         [0072]    In the embodiment, the arc portions B have an angle B 1 , and the first optical path  19  and the second optical path  20  have an angle B 2  with respect to the stirring shaft  34 . It is configured such that the angle B 1  is larger than the angle B 2  (B 1 &gt;B 2 ). Accordingly, when the toner stirring member  31  rotates, at least one of the first arm  33   a  and the second arm  33   b  always blocks one of the first optical path  19  and the second optical path  20 . 
         [0073]    In the embodiment, the first cleaning pad  35   a  and the second cleaning pad  35   b  are disposed at the outer circumferential surfaces of the first arm  33   a  and the second arm  33   b , respectively. When the toner stirring member  31  rotates, the first cleaning pad  35   a  and the second cleaning pad  35   b  move over the first window holes  16   a  and  16   b  and the second window holes  17   a  and  17   b , respectively. At this time, the first cleaning pad  35   a  and the second cleaning pad  35   b  remove the toner  30  and clean the first protruding ends  18   d  and the second protruding ends  18   e  of the light guide member  18  fitted into the first window holes  16   a  and  16   b  and the second window holes  17   a  and  17   b.    
         [0074]    In the embodiment, the first cleaning pad  35   a  and the second cleaning pad  35   b  have a length smaller than that of the first window holes  16   a  and  16   b  and the second window holes  17   a  and  17   b . Accordingly, when the first cleaning pad  35   a  and the second cleaning pad  35   b  slide against the inner wall of the toner storage portion  12 , it is possible to reduce a rotational load due to friction. 
         [0075]    In the embodiment, the first cleaning pad  35   a  and the second cleaning pad  35   b  are preferably formed of a urethane rubber, a polyester film, and the likes with rigidity and wear resistance. 
         [0076]    An operation of the toner stirring member  31  will be explained next.  FIGS. 12(   a ) to  12 ( e ) are schematic views showing the operation of the toner stirring member  31  according to the second embodiment of the present invention.  FIGS. 12(   a ) to  12 ( e ) show a change in a state of the toner  30  with time while the toner stirring member  31  is rotating. 
         [0077]    In the second embodiment, the operation of the toner stirring member  31  is similar to that of the cleaning arm  23  in the first embodiment. In the second embodiment, the first arm  33   a  and the second arm  33   b  have a shape different from that of the first arm  25   a  and the second arm  25   b  in the first embodiment. Further, in the second embodiment, the stirring sheet  32  is provided for stirring a whole portion of the toner  30  in the toner storage portion  12 . 
         [0078]    In general, the toner  30  tends to lose flowability thereof with time. In the embodiment, the stirring sheet  32  is provided for stirring the toner  30 , thereby preventing the toner  30  from losing flowability thereof. 
         [0079]    As shown in  FIG. 12 , when the toner stirring member  31  rotates in an arrow direction, the first arm  33   a , the second arm  33   b , and the stirring sheet  32  sequentially stir up the toner  30 . 
         [0080]    When the image forming apparatus  10  is continued to use, a remaining amount of the toner  30  in the toner storage portion  12  decreases. A positional relationship between the remaining amount of the toner  30  and the toner stirring member  31  will be explained next. Further, a relationship of the detection signal at the light-receiving element  22  will be explained. 
         [0081]      FIGS. 13(   a ) to  13 ( g ) are charts showing the positional relationship between the cleaning arm  31  and the detection signal of the light-receiving element  22  in a state that the toner  30  decreases according to the second embodiment of the present invention.  FIGS. 14(   a ) to  14 ( g ) are charts showing the positional relationship between the cleaning arm  31  and the detection signal of the light-receiving element  22  in a state that the toner  30  further decreases according to the second embodiment of the present invention.  FIGS. 15(   a ) to  15 ( g ) are charts showing the positional relationship between the cleaning arm  31  and the detection signal of the light-receiving element  22  in a state that the toner  30  is completely consumed according to the second embodiment of the present invention. 
         [0082]    More specifically, in each of the states of the toner  30 ,  FIGS. 13(   a ),  14 ( a ), and  15 ( a ) are charts showing positional relationships between the first arm  33   a  and the first optical path  19 ;  FIGS. 13(   b ),  14 ( b ), and  15 ( b ) are charts showing changes in detection light entering the first optical path  19 ,  FIGS. 13(   c ),  14 ( c ), and  15 ( c ) are charts showing changes in detection light outgoing from the first optical path  19 ;  FIGS. 13(   d ),  14 ( d ), and  15 ( d ) are charts showing positional relationships between the second arm  33   b  and the second optical path  20 ;  FIGS. 13(   e ),  14 ( e ), and  15 ( e ) are charts showing changes in detection light entering the second optical path  20 ;  FIGS. 13(   f ),  14 ( f ), and  15 ( f ) are charts showing changes in detection light outgoing from the second optical path  20 ; and  FIGS. 13(   g ),  14 ( g ), and  15 ( g ) are charts showing changes in detection light received at the light-receiving element  22 . 
         [0083]    In  FIGS. 13(   a ) to  13 ( g ),  FIGS. 14(   a ) to  14 ( g ),  FIGS. 15(   a ) to  15 ( g ), a horizontal direction represents a period of time. 
         [0084]    As shown in  FIG. 13(   g ), when the light-receiving element  22  detects detection light passing through the first optical path  19  or the second optical path  20 , that is, the light-receiving element  22  is turned on, the states that detecting light is turned on in  FIGS. 13(   c ) and  13 ( f ) are overlapped. In this state, the light-receiving element  22  detects detection light passing through either of the first optical path  19  or the second optical path  20 . 
         [0085]    In the embodiment, the first arm  33   a  and the second arm  33   b  are attached to the stirring shaft  34  at the inversed phases with each other. Accordingly, the detection signal (a detection time T 1 ) of detection light passing through the first optical path  19  is shifted from and is not overlapped with the detection signal (a detection time T 2 ) of detection light passing through the second optical path  20 . As a result, as the remaining amount of the toner  30  decreases, the detection time T 1  of the detection signal of detection light passing through the first optical path  19  and the detection time T 2  of the detection signal of detection light passing through the second optical path  20  increase. 
         [0086]      FIGS. 14(   a ) to  14 ( g ) show the state that the toner  30  further decreases from the state shown in  FIGS. 13(   a ) to  13 ( g ). In this state, when the first arm  33   a  and the second arm  33   b  scoop up the toner  30 , the toner  30  tends to fall off from the first arm  33   a  and the second arm  33   b  more easily in a larger amount of the toner  30 . Accordingly, the toner  30  blocks the first optical path  19  and the second optical path  20  more quickly. That is, when the toner  30  further decreases, a detection time T 3  and a detection time T 4  shown in  FIG. 14(   g ) increase as opposed to the detection time T 1  and the detection time T 2  shown in  FIG. 13(   g ). 
         [0087]    When the toner  30  is completely consumed and the toner storage portion  12  becomes empty as shown in  FIGS. 15(   a ) to  15 ( g ), detection signals detected at the light-receiving element  22  are not overlapped as explained above. 
         [0088]    In the embodiment, the first arm  33   a  and the second arm  33   b  always block one of the first optical path  19  and the second optical path  20 . Accordingly, there is always an OFF signal between a detection time T 5  and a detection time T 6 . When the OFF signal appears regularly, it is possible to detect the detection signal of detection light passing through the first optical path  19  or the second optical path  20  independently. Further, it is possible to confirm whether the toner stirring member  31  rotates normally. 
         [0089]    As described above, in the embodiment, the first arm  33   a  and the second arm  33   b  have the specific shape capable of stirring the toner  30 . Further, the stirring sheet  32  is arranged coaxially with the first arm  33   a  and the second arm  33   b , thereby increasing flowability of the toner  30  in the toner storage portion  12 . Accordingly, it is possible to accurately detect the toner  30  even though the toner  30  loses flowability with time. 
       Third Embodiment 
       [0090]    A third embodiment of the present invention will be described below. In the description below, elements in the third embodiment similar to those in the first and second embodiments are designated by same reference numerals, and explanations thereof are omitted. Explanations of operations and effects in the third embodiment similar to those in the first and second embodiments are omitted. 
         [0091]      FIG. 16  is a schematic side view showing a toner stirring member  40  according to the third embodiment of the present invention.  FIG. 17  is a schematic plan view showing the toner stirring member  40  according to the third embodiment of the present invention. 
         [0092]    In the embodiment, the toner stirring member  40  is provided as a rotational member. As shown in  FIG. 16 , the toner stirring member  40  includes a stirring shaft  43  extending in the width direction of the toner storage portion  12  and supported on the both end walls of the toner storage portion  12  to be rotatable; and a first stirring sheet  41  and a second stirring sheet  42  with a sheet shape attached to the stirring shaft  43  and extending in a radial direction. 
         [0093]    In the embodiment, the first stirring sheet  41  and the second stirring sheet  42  are attached to the stirring shaft  43  with reversed phases with each other. Further, the first stirring sheet  41  and the second stirring sheet  42  respectively have first end portions  41   a  and  42   a  as a cleaning member, so that the first end portions  41   a  and  42   a  contact with the inner wall of the toner storage portion  12  when the toner stirring member  40  is attached to the toner storage portion  12 . 
         [0094]    In the embodiment, the first stirring sheet  41  and the second stirring sheet  42  further include second end portions  41   b  and  42   b , respectively. The second end portions  41   b  and  42   b  have a length in the radial direction smaller than that of the first end portions  41   a  and  42   a , so that the second end portions  41   b  and  42   b  do not contact with the inner wall of the toner storage portion  12 . Accordingly, it is possible to reduce a rotational load generated upon contacting with the inner wall of the toner storage portion  12 . 
         [0095]    In the embodiment, the first stirring sheet  41  and the second stirring sheet  42  further include third end portions  41   c  and  42   c , respectively. The third end portions  41   c  and  42   c  have a length such that the third end portions  41   c  and  42   c  block the first optical path  19  and the second optical path  20 , respectively, when the toner stirring member  40  rotates. 
         [0096]    In the embodiment, the first stirring sheet  41  and the second stirring sheet  42  have portions for blocking the first optical path  19  and the second optical path  20 , respectively. The portions are indicated as hatched areas in  FIG. 17 , and are applied with color for preventing detection light from passing therethrough. 
         [0097]    In the embodiment, the first stirring sheet  41  and the second stirring sheet  42  are preferably formed of a urethane rubber, a polyester film, and the likes with rigidity and wear resistance. An operation of the toner stirring member  40  is similar to that of the toner stirring member  31  in the second embodiment, and an explanation thereof is omitted. 
         [0098]    As described above, in the third embodiment, as compared with the stirring sheet  31  of the toner stirring member  31  in the second embodiment, the third end portions  41   c  and  42   c  of the first stirring sheet  41  and the second stirring sheet  42  extend, respectively. Accordingly, when the toner stirring member  41  rotates at a speed same as that of the toner stirring member  31 , it is possible to obtain a stirring effect doubled with respect to the toner stirring member  31  in the second embodiment. 
         [0099]    Accordingly, as compared with the second embodiment, it is possible to improve flowability of the toner  30  to an extent equal to or greater that that in the second embodiment. As a result, it is possible to accurately detect a remaining amount of the toner  30 . Further, it is possible to eliminate the first arm  33   a  and the second arm  33   b  in the second embodiment, thereby reducing the number of parts. 
         [0100]    In the first to third embodiments, the first optical path  19  and the second optical path  20  are set inside the toner storage portion  12 . It is possible to increase the number of the optical paths through adjusting the phase angle of the cleaning member. 
         [0101]    Further, in the first to third embodiments, when one of the first optical path  19  and the second optical path  20  is detected first, the control unit notifies that the toner storage portion  12  is empty. Alternatively, it may be configured such that when both of the first optical path  19  and the second optical path  20  are detected, the control unit notifies that the toner storage portion  12  is empty. With the configuration, it is possible to reduce a variance generated when one of the first optical path  19  and the second optical path  20  is detected first, thereby improving accuracy. The configuration may be applicable to a developing device in which toner is not distributed unevenly. 
         [0102]    In the embodiments described above, the two optical paths, i.e., the first optical path  19  and the second optical path  20 , are provided for detecting toner. and three or more optical paths may be provided. 
         [0103]    In the embodiments described above, the two optical paths, i.e., the first optical path  19  and the second optical path  20 , are provided on the left and right side portions of the toner storage portion  12 , and may be provided at other locations, for example, one side portion and one center portion of the toner storage portion  12 . 
         [0104]    In the embodiments described above, the two optical paths, i.e., the first optical path  19  and the second optical path  20 , are provided along the longitudinal direction of the toner storage portion  12 , and may be provided along a vertical direction of the toner storage portion  12 . 
         [0105]    The disclosure of Japanese Patent Application No. 2007-129977, filed on May 16, 2007, is incorporated in the application. 
         [0106]    While the invention has been explained with reference to the specific embodiments of the invention, the explanation is illustrative and the invention is limited only by the appended claims.