Abstract:
Provided is a waste developer container to be fixed to an image forming device including a developing device and a waste developer amount detection unit for obtaining information on an amount of accumulated waste developer discharged from the developing device, wherein the developing device uses toner image carrier holding a toner image and two-component developer to form a toner image, the waste developer amount detection unit obtains the information on the accumulated amount by emission and reception of light, and the waste developer container includes: a container space for containing waste developer discharged; a detection window for passing light that is emitted from the waste developer amount detection unit, passes the container space, and is incident again to the waste developer amount detection unit; and a magnet provided to a position where a magnetic force is applied to the detection window and light passing the detection window is not shut.

Description:
[0001]    The present invention claims priority under 35 U.S.C §119 to Japanese Patent Application No. 2016-094843 filed May 10, 2016 including description, claims, drawings, and abstract are incorporated herein by reference in its entirety. 
       BACKGROUND OF THE INVENTION 
     Field of the Invention 
       [0002]    The present invention relates to an image forming device for forming a toner image with two-component developer and its waste developer container. In more detail, the present invention relates to a waste developer container that can detect the amount of contained waste developer and an image forming device including the same. 
       Description of the Related Art 
       [0003]    In an image forming device that uses toner, waste toner is produced in connection with forming an image. Therefore, there is an image forming device including a waste toner container for containing produced waste toner. An example is the image forming device described in JP 2012-155279 A. That is, the collection container  101  disclosed in JP 2012-155279 A (see paragraph [0053] and FIGS. 2 and 3 of JP 2012-155279 A) corresponds to waste toner container. 
         [0004]    However, in the technique described above, there has been the following problems. Of course, such a waste toner container will be full by forming an image. Therefore, it is necessary to detect that the waste toner container is full or almost full by some methods. This is to notify a user of necessity of maintenance such as change of the waste toner container. One method is optical detection. In optical detection, light passes in the waste toner container and full of the waste toner container is detected when light is shielded with the increase of waste toner. 
         [0005]    In addition, recently, an image is developed by a trickle developing method in some image forming devices that use two-component developer (toner+carrier). In a trickle developing method, carrier is also supplied when toner is supplied to a developing device. The amount of the carrier in the developing device is kept at appropriate range by discharging developer including deteriorated carrier from the developing device. The trickle developing method is advantageous in keeping electric charging amount of the toner against durable use constant and keeping image quality high. 
         [0006]    In such an image forming device, not only waste toner but also waste developer is produced. Therefore, a waste developer container is necessary and detection of full of the waste developer container is also necessary. Then, although the use of optical detection is considered as described above, it is not as successful for waste developer as in the case of waste toner. The reason is that the waste developer contained in the waste developer container is floating and adheres to an inner wall surface of the container. Therefore, since light for detecting full is shielded, full is detected much earlier than actual full. Although it does not mean that there is no such a phenomenon for waste toner, this problem is apparent for waste developer due to difference in charging characteristic and light shielding property between toner and carrier. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention has been developed to solve the problems described above. That is, an object of the present invention is to provide an image forming device that successfully detects the amount contained in a waste developer container while developing an image by a trickle developing method with two-component developer. In addition, another object of the present invention is to provide a waste developer container suitable for such an image forming device. 
         [0008]    To achieve at least one of the abovementioned objects, according to an aspect, a waste developer container reflecting one aspect of the present invention is to be fixed to an image forming device including a developing device and a waste developer amount detection unit for obtaining information on an amount of accumulated waste developer discharged from the developing device, wherein the developing device is a developing device that uses toner image carrier holding a toner image and two-component developer including toner and carrier to form a toner image held on the toner image carrier by a trickle developing method, the waste developer amount detection unit obtains the information on the accumulated amount by emission and reception of light, and the waste developer container comprises: a container space for containing waste developer discharged from the developing device; a detection window for passing light that is emitted from the waste developer amount detection unit, passes the container space, and is incident again to the waste developer amount detection unit; and a magnet provided to a position where a magnetic force is applied to the detection window and light passing the detection window is not shut. 
         [0009]    In the waste developer container according to the aspect, light emitted from a waste developer amount detection unit of an image forming device is incident to a waste developer amount detection unit again without being shielded by waste developer in a container space when the amount of waste developer contained in the container space is little. However, as the amount of contained waste developer increases, light emitted from the waste developer amount detection unit is shielded by waste developer in the container space. Accordingly, the light is not incident again in the waste developer amount detection unit. Such a change in existence of re-incidence can be treated as information regarding the amount of accumulation of waste developer discharged from the developing device in the image forming device. Here, in the aspect described above, magnetic force of magnet is applied to a detection window. Therefore, even if part of waste developer is floating in the container space, carrier in the floating developer is attracted by the magnet near the detection window. Therefore, carrier in the waste developer is prevented from adhering to an inner surface of the detection window. Accordingly, the amount of accumulation of waste developer is successfully detected by the waste developer amount detection unit without being affected by adherence of the carrier to the detection window. 
         [0010]    In the waste developer container according to the aspect, the magnet preferably faces the container space. This is because that floating carrier can be attracted by the magnet more certainly. 
         [0011]    In the waste developer container according to the aspect, the magnet is preferably provided at a position that is upper in a direction of a gravitational force than the location where light that is incident from the waste developer amount detection unit in the detection window and light emitted to the waste developer amount detection unit pass. With the configuration described above, the magnet will not be covered by waste developer until the light is shielded by contained but not floating waste developer. Therefore, absorption characteristic of floating carrier by magnet can be maintained until the actual amount of accumulation of waste developer is detected. 
         [0012]    In the waste developer container according to the aspect, the waste developer container preferably further comprises a carrying member for carrying waste developer contained in the container space in the container space, wherein the magnet is preferably provided to a position that is upper than the carrying member in a direction of a gravitational force. This carrying member prevents waste developer from concentrating on the specific area in the container space and is useful for effectively using the capacity of the container space. In contrast, waste developer can be scattered to float. By arranging the magnet in such a way, it is possible to effectively attract the carrier scattered by the carrying member. 
         [0013]    In the waste developer container according to the aspect, the waste developer container preferably further comprises a partition wall for dividing the container space into a waste developer container space for containing waste developer discharged from the developing device and a waste toner container space for containing waste toner collected from the toner image carrier, wherein the carrying member is preferably provided in the waste developer container space, and the detection window is preferably a part of an outer wall that separates the waste developer container space from outside. Generally, in an image forming device using two-component developer, waste toner is produced as well as waste developer. With the configuration described above, the amount of accumulation of waste developer including carrier can be successfully detected as described above while waste toner and waste developer are contained in different container spaces. 
         [0014]    In the waste developer container according to the aspect, the detection window is preferably made of polystyrene or synthetic resin that is on a minus charging side on a triboelectric series with respect to polystyrene. With such a configuration, charging of the carrier and static electricity of the detection window are likely to be reverse polarity. Therefore, floating carrier easily adheres to the detection window. Accordingly, the significance of removing floating carrier by magnet is large. 
         [0015]    To achieve at least one of the abovementioned objects, according to an aspect, an image forming device reflecting one aspect of the present invention comprises: a toner image carrier for holding a toner image; a developing device that uses two-component developer including toner and carrier to forma toner image held on the toner image carrier by a trickle developing method; a waste developer container including a container space for containing waste developer discharged from the developing device; a waste developer amount detection unit provided outside the waste developer container for obtaining information on an amount of waste developer contained in the waste developer container by receiving light that is emitted to the waste developer container, passes the container space, and is emitted from the waste developer container; a detection window provided as a part of the waste developer container for passing the light between the waste developer amount detection unit and the container space; and a magnet provided to a position where a magnetic force is applied to the detection window and light passing the detection window is not shut. 
         [0016]    In the image forming device according to the aspect, the developing device preferably develops an image with an amount of charging of the carrier being a range between 40 and 60 μC/g. The large amount of charging of carrier in a developing device means that the amount of charging of carrier discharged as waste developer is also large. Since this means that floating carrier easily adheres to the detection window, the significance of removing floating carrier by magnet is large. 
         [0017]    In the image forming device according to the aspect, the magnet preferably faces the container space. 
         [0018]    In the image forming device according to the aspect, the magnet is preferably provided at a position that is upper in a direction of a gravitational force than the location where light that is incident from the waste developer amount detection unit in the detection window and light emitted to the waste developer amount detection unit pass. 
         [0019]    In the image forming device according to the aspect, the image forming device preferably further comprises a carrying member for carrying waste developer contained in the container space in the container space, wherein the magnet is preferably provided to a position that is upper than the carrying member in a direction of a gravitational force. 
         [0020]    In the image forming device according to the aspect, the image forming device preferably further comprises a partition wall for dividing the container space into a waste developer container space for containing waste developer discharged from the developing device and a waste toner container space for containing waste toner collected from the toner image carrier, wherein the carrying member is preferably provided in the waste developer container space, and the detection window is preferably a part of an outer wall that separates the waste developer container space from outside. 
         [0021]    In the image forming device according to the aspect, the detection window is preferably made of polystyrene or synthetic resin that is on a minus charging side on a triboelectric series with respect to polystyrene. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    The above and other objects, advantages and features of the present invention will become more fully understood from the detailed description given hereinbelow and the appended drawings which are given byway of illustration only, and thus are not intended as a definition of the limits of the present invention, and wherein: 
           [0023]      FIG. 1  is a cross-sectional view illustrating a schematic configuration of an image forming device according to an embodiment; 
           [0024]      FIG. 2  is a perspective view illustrating a chassis inside the image forming device according to the embodiment together with a waste developer container; 
           [0025]      FIG. 3  is a perspective view illustrating the waste developer container according to the embodiment viewer from the rear side; 
           [0026]      FIG. 4  is a first sectional perspective view illustrating an inner structure of the waste developer container according to the embodiment; 
           [0027]      FIG. 5  is a side cross-sectional view illustrating the inner structure of the waste developer container according to the embodiment; 
           [0028]      FIG. 6  is a plan cross-sectional view illustrating relationship of arrangement of a projection part of the waste developer container and a waste developer amount detection unit of a main unit; 
           [0029]      FIG. 7  is a rear view illustrating the waste developer container according to the embodiment; 
           [0030]      FIG. 8  is a second sectional perspective view illustrating the inner structure of the waste developer container according to the embodiment; 
           [0031]      FIG. 9  is a perspective view illustrating relationship of the waste developer container and an image forming unit according to the embodiment; and 
           [0032]      FIG. 10  is a perspective view illustrating relationship of the waste developer container and an intermediate transfer belt according to the embodiment. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0033]    Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. However, the scope of the invention is not limited to the illustrated examples. In the embodiment of the present invention, the present invention is applied to an image forming device  1  illustrated in  FIG. 1 . The image forming device  1  illustrated in  FIG. 1  includes an intermediate transfer belt  2  and four image forming units  3 Y to  3 K provided under the intermediate transfer belt  2 . Hereinafter, the image forming units  3 Y to  3 K are simply referred to as image forming unit  3  in some cases without distinguishing by the color symbols Y to K. 
         [0034]    Each image forming unit  3  has a photoreceptor  4  in the center thereof. A charging unit  5 , an exposure head  6 , a developing device  7 , a primary transfer roller  8 , and a photoreceptor cleaner  9  are provided around the photoreceptor  4 . The primary transfer roller  8  is provided opposite to the photoreceptor  4  with the intermediate transfer belt  2  provided therebetween. Accordingly, a toner image is formed on the photoreceptor  4  by the developing device  7  and the toner image is transferred to the intermediate transfer belt  2 . 
         [0035]    The image forming device  1  further includes a paper feeding unit  10 , a secondary transfer roller  11 , and a fixing device  12 . The toner image is transferred from the intermediate transfer belt  2  to paper P supplied from the paper feeding unit  10  and the toner image is fixed on the paper. Moreover, a belt cleaner  13  is provided in contact with the intermediate transfer belt  2 . Furthermore, supplement developer bottles  14 Y to  14 K (hereinafter, simply referred to as “supplement developer bottle  14 ” in some cases) are detachably provided to the image forming device  1 . 
         [0036]    The developing device  7  according to the embodiment of the present invention develops an image with two-component developer including toner and carrier. Moreover, the developing device  7  according to the embodiment of the present invention develops an image by a trickle developing method. That is, not only the amount of toner in the developing device  7  is reduced by development but also the developing device  7  discharges the developer contained therein to some extent in order to prevent deterioration. Therefore, not only toner but also carrier is supplied from the supplement developer bottle  14  to the developing device  7 . Since trickle developing method itself is a known method, detailed description thereof will be omitted. In addition, the developing device  7  according to the embodiment of the present invention develops an image with carrier charged at the charging amount ranging from 40 to 60 μC/g. This charging amount is bit higher than the charging amount in a known and popular two-component developing device. 
         [0037]      FIG. 2  is a perspective view illustrating a chassis (frame)  15  inside the image forming device  1  according to the embodiment of the present invention. Various inner devices of the image forming device  1  illustrated in  FIG. 1  are fixed to various parts in the chassis  15 . For example, the fixing device  12  is located near the axis shown by an arrow A, and the secondary transfer roller  11  is located near the axis shown by an arrow B. In addition, the paper feeding unit  10  is located near the symbol D that is the lower part in the chassis  15 . The intermediate transfer belt  2  is contained under an upper plate  16  of the chassis  15 . The supplement developer bottles  14 Y to  14 K are located in a space at the upper side of the upper plate  16 . 
         [0038]    Then, the image forming device  1  according to the embodiment of the present invention includes a waste developer container  17  illustrated in  FIG. 2 . The waste developer container  17  is a container for containing waste developer and waste toner produced by execution of image forming by the image forming device  1 . In the image forming device  1  that is operating, the waste developer container  17  is fixed to the front of a front plate  18  of the chassis  15 . The waste developer container  17  can be attached and detached, and is exchanged when it is full of waste developer or waste toner. 
         [0039]      FIG. 3  is a perspective view illustrating the waste developer container  17 . In  FIG. 3 , the waste developer container  17  is viewed from the rear side unlike  FIG. 2 . That is, the front side of the waste developer container  17  in  FIG. 3  is the side that faces the front plate  18  of the chassis  15  when it is fixed to the image forming device  1 . Cross-cut parts  19  are provided at both ends at the upper part of the waste developer container  17  in  FIG. 3 . This part is made of a flexible rubber film, and is a waste toner acceptance inlet for accepting the waste toner from the image forming device  1  in the waste developer container  17 . 
         [0040]    In addition, a waste developer acceptance inlet  20  is provided at the slightly left side with respect to the center in the right and left direction and the lower side with respect to the cross-cut part  19 . The waste developer acceptance inlet  20  is an opening that opens upward for accepting the waste developer from the image forming device  1  in the waste developer container  17 . The waste developer acceptance inlet  20  in  FIG. 3  opens obliquely upward. In addition, a projection part  21  is provided at the slightly right side with respect to the center in the right and left direction and the lower side with respect to the waste developer acceptance inlet  20 . As described later, the projection part  21  functions as a detection window for detecting the amount of contained waste developer on the main unit side of the image forming device  1 . 
         [0041]    Referring back to  FIG. 2 , a waste developer discharge unit  22  and a waste developer amount detection unit  23  are provided in the front of the chassis  15 . The waste developer discharge unit  22  is a part that discharges waste developer produced by execution of image forming by the image forming device  1 . That is, waste developer discharged from the developing devices  7  of each of image forming units  3 Y to  3 K is collected and discharged from the waste developer discharge unit  22 . The waste developer amount detection unit  23  is a part that optically acquires information on the amount of waste developer contained in the waste developer container  17 . Therefore, when the waste developer container  17  is fixed to the front face of the chassis  15 , the waste developer discharge unit  22  faces the waste developer acceptance inlet  20  and the waste developer amount detection unit  23  faces the projection part  21 . 
         [0042]    Next, the inner structure of the waste developer container  17  will be described.  FIG. 4  is a perspective view illustrating an inner surface of a cut piece on the chassis  15  side when the waste developer container  17  is cut on the plane parallel to the front plate  18  of the chassis  15 . That is, it is understood that  FIG. 4  illustrates the shape of the back face of the front face of the waste developer container  17  in  FIG. 3 . Therefore, the cross-cut part  19  illustrated in  FIG. 4  is the cross-cut part  19  of  FIG. 3  viewed from the inner surface side. This is also true for the waste developer acceptance inlet  20  in  FIG. 4 . This is also true for the projection part  21 , but the projection part  21  in  FIG. 4  has of course concave shape. Note that,  FIG. 4  is a drawing for explanation and the waste developer container  17  is not cut as illustrated in this drawing when it is actually used. 
         [0043]    As illustrated in  FIG. 4 , a partition wall  24  is provided in the waste developer container  17 . Accordingly, the inner space of the waste developer container  17  is divided into an upper chamber  25  and a lower chamber  26 . The upper chamber  25  is connected to the cross-cut part  19 . That is, the upper chamber  25  is a waste toner container space for containing waste toner. On the other hand, the lower chamber  26  is connected to the waste developer acceptance inlet  20 . That is, the lower chamber  26  is a waste developer container space for containing waste developer. As described, waste toner and waste developer are contained in separate chambers in the waste developer container  17 . However, a cylindrical part  27  projecting upward is provided to a part of the partition wall  24 . The upper chamber  25  and the lower chamber  26  are connected in the cylindrical part  27 . Therefore, when the depth of accumulation of the waste toner in the upper chamber  25  exceeds the projecting height of the cylindrical part  27 , part of the waste toner in the upper chamber  25  spills down to the lower chamber  26 . Note that, the projection part  21  described above is a part of an outer wall of the lower chamber  26  that projects outward. 
         [0044]    A delivery screw  28  is provided in the lower chamber  26  of the waste developer container  17 . The delivery screw  28  illustrated in  FIG. 4  is obtained by forming a wire member in spiral shape. The delivery screw  28  is provided in the horizontal direction in the lower chamber  26 . That is, the delivery screw  28  rotates to move the waste developer in the horizontal direction in the lower chamber  26 . The reason why the delivery screw  28  is provided is that the lower chamber  26  is long and thin in the horizontal direction. The delivery screw  28  is provided so that the waste developer contained in the lower chamber  26  spreads over the lower chamber  26  without being kept at a location immediately under the waste developer acceptance inlet  20 . Note that, the delivery screw  28  is rotationally driven by operation from the main unit side of the image forming device  1 . In addition, of course, the delivery screw  28  is located lower than the partition wall  24 . 
         [0045]      FIG. 5  is a side cross-sectional view illustrating the waste developer container  17 .  FIG. 5  is a cross-sectional view illustrating the waste developer container  17  that is cut on the vertical plane orthogonal to the front plate  18  of the chassis  15  at the position of the cylindrical part  27 , and is a drawing viewing the right side from the left side in  FIG. 2 . The cut position in the sectional perspective view of  FIG. 4  is the position of an arrow E in  FIG. 5 . Note that, the cross-cut part  19  and the waste developer acceptance inlet  20  described above are not shown on the cross-section of  FIG. 5 . 
         [0046]    Here, the projection part  21  of the waste developer container  17  and the waste developer amount detection unit  23  on the main unit side of the image forming device  1  will be described. For that purpose,  FIG. 6  is a plan cross-sectional view illustrating the projection part  21 . In  FIG. 6 , the projection part  21  is illustrated with the waste developer container  17  fixed to the chassis  15  (hereinafter referred to as “fixed state”). Therefore, in  FIG. 6 , the projection part  21  faces the waste developer amount detection unit  23 . Note that, an inner space of the projection part  21  is connected to the lower chamber  26 . Therefore, when the amount of waste developer contained in the lower chamber  26  increases, the waste developer enters the inner space of the projection part  21  as well. 
         [0047]    As illustrated in  FIG. 6 , detection windows  29  are provided on both side faces of the projection part  21 . The detection window  29  is a part of the wall surface of the projection part  21  and made from a transparent member. It is not opened. That is, the detection window  29  is a part of an outer wall that divides the lower chamber  26  from outside. On the other hand, a light emitting part  30  and a light receiving part  31  are provided to the waste developer amount detection unit  23 . In the fixed state illustrated in  FIG. 6 , the detection windows  29  on the both side faces of the projection part  21  are between the light emitting part  30  and the light receiving part  31 . 
         [0048]    Therefore, when light L is emitted from the light emitting part  30 , the light L penetrates the detection window  29 , enters the inner space of the projection part  21 , penetrates the detection window  29  again, and reaches the light receiving part  31 . That is, the light L once penetrates the inner space of the projection part  21 . The light L can be detected by the light receiving part  31  without problems when the amount of waste developer contained in the lower chamber  26  is little. However, as the amount of contained waste developer increases, the inner space of the projection part  21  will also be full of waste developer. In such a situation, the light L is shielded by the waste developer and cannot be detected by the light receiving part  31 . The image forming device  1  can treat this situation as information that indicates that the lower chamber  26  is full of or almost full of waste developer. Accordingly, the image forming device  1  can display a notice to persuade the user to exchange the waste developer container  17  and take a measure for forcibly stopping image forming operation. 
         [0049]    Here,  FIG. 7  is a rear view illustrating the waste developer container  17 . In  FIG. 7 , the light emitting part  30  and the light receiving part  31  described above, which are parts on the main unit side, are also illustrated in addition to the waste developer container  17 . From  FIG. 7 , it is understood that the light emitting part  30  and the light receiving part  31  are provided to relatively upper position in the height direction where the projection part  21  exists. This means that the height of the position of detection of the waste developer by the light emitting part  30  and the light receiving part  31  is very close to the lower face of the partition wall  24 . That is, in the embodiment of the present invention, the waste developer amount detection unit  23  detects that the lower chamber  26  is almost full of the waste developer. Hereinafter, this is simply referred to as “full detection.” 
         [0050]    Here, the waste developer container  17  includes magnet near the detection window  29  of the projection part  21 . This will be described with reference to  FIG. 8 .  FIG. 8  is almost the same perspective view as  FIG. 4 , but viewing direction is slightly different. That is, in  FIG. 8 , the cut piece of the waste developer container  17  illustrated in  FIG. 4  is illustrated as viewed obliquely upward from slightly lower position. As illustrated in  FIG. 8 , magnet  32  is fixed to the lower face of the partition wall  24 . The magnet  32  is provided at both sides very close to the position where the projection part  21  is provided. Therefore, the magnet  32  is located near as viewed from the detection window  29  of the projection part  21 . Therefore, magnetic force by the magnet  32  is applied to the position of the detection window  29 . Note that, although the magnet  32  is illustrated also in  FIG. 5 , the side face, not the cross-section, of the magnet  32  is illustrated in  FIG. 5 . Therefore, the magnet  32  does not close the inner side of the cylindrical part  27 . In addition, in  FIG. 8 , the magnet  32  is fixed near the cylindrical part  27 . However, this is not mandatory. 
         [0051]    The reason why the magnet  32  is provided is to prevent interruption of full detection of the lower chamber  26  by floating waste developer. This is because the waste developer contained in the lower chamber  26  tends to be charged by friction. Therefore, part of the waste developer may float in dust and fume form by electrostatic repulsion. The floating developer particle adheres to the wall surface of the lower chamber  26  by static electricity force in some cases. If such adhesion occurs to the inner surface of the detection window  29 , full detection by the waste developer amount detection unit  23  is interrupted. Of course, the developer adhering to the inner surface of the detection window  29  shields the light L emitted from the light emitting part  30 . Therefore, the light receiving part  31  cannot detect the light L even if the inner space of the projection part  21  is yet not full of developer, depending on the density of adhesion of the developer on the inner surface of the detection window  29 . That is, full is detected much earlier than it is actually full. Therefore, the actual amount of content of the waste developer container  17  may not be fully used. This is a phenomenon of interruption of full detection by floating developer. 
         [0052]    In the embodiment of the present invention, such interruption of full detection is prevented because of the magnet  32 . This is because magnetic force by the magnet  32  is applied to the location of the detection window  29  and it vicinity as described above. On the other hand, carrier of the developer is iron powder. Therefore, carrier of the floating waste developer is attracted by the magnetic force of the magnet  32  and adheres to the surface of the magnet  32  near the detection window  29 . The carrier adhering to the surface of the magnet  32  once hardly becomes floating state again. Therefore, near the detection window  29 , even if floating developer exists, what is floating is toner and floating carrier is very few. Therefore, because there is no adhesion of floating carrier to the inner surface of the detection window  29 , there is no interruption of full detection as described above. Therefore, it is possible to fully use the actual content of the waste developer container  17 . 
         [0053]    Note that, as is understood from the above description, what is attracted by the magnet  32  is only carrier that is iron powder. Resin toner is not attracted by the magnet  32 . Therefore, theoretically, adhesion of floating toner to the detection window  29  occurs even if the magnet  32  is provided. However, this is not a big practical problem. This is because light shielding property of resin toner is lower than that of carrier that is iron powder. In addition, since toner is lighter than carrier, it tends to be largely affected by repulsion by charging of the same polarity of toner than carrier. Therefore, even if toner adheres to the inner surface of the detection window  29 , the adhesion density is not so much increased than carrier. There is another reason, which will be described later. 
         [0054]    Here, the position of the magnet  32  will be described. In the embodiment of the present invention, the position described above where the magnet  32  is provided is the position near the almost upper end of the lower chamber  26  that contains waste developer. That is, the position of the magnet  32  in the embodiment of the present invention is higher than the position of incidence/emission of the light L at the detection window  29 . In addition, it is higher than the delivery screw  28 . 
         [0055]    The configuration described above provides following advantages. First, even if the amount of the waste developer contained in the lower chamber  26  is increased, absorption characteristic of the floating carrier by the magnet  32  is not lost. This is because the magnet  32  is not covered by the waste developer accumulated on the bottom of the lower chamber  26 . That is, it is preferable that the magnet  32  be at a high position rather than at a low position. This is because it is less likely to be covered by the accumulated waste developer. 
         [0056]    Specifically, the position of the magnet  32  higher than the position of incidence/emission of the light L has a following meaning. That is, absorption characteristic of the magnet  32  is maintained until full is actually detected. The absorption characteristic of the magnet  32  is required until the position of incidence/emission is covered by the accumulated waste developer. Once the position of incidence/emission is covered by the waste developer, full is actually detected and it has nothing to do thereafter. 
         [0057]    In addition, the position of the magnet  32  higher than the position of the delivery screw  28  has a following meaning. That is, delivery of the waste developer in the lower chamber  26  by the delivery screw  28  causes part of the accumulated waste developer to fly and may become a cause of production of floating waste developer. Of course, such floating waste developer floats above the delivery screw  28 . Therefore, with the magnet  32  being higher than the delivery screw  28 , produced floating carrier can be efficiently attracted. Note that, the position of the magnet  32  higher than the position of the delivery screw  28  means that, the position of the magnet  32  needs to be at least higher than the lowest position in the delivery screw  28 . It is more preferable that the position of the magnet  32  be higher than the center of the delivery screw  28 . Moreover, it is much more preferable that the position of the magnet  32  be much higher than the highest position in the delivery screw  28 . 
         [0058]    In addition, according to the embodiment of the present invention, the magnet  32  is provided to face the container space of the lower chamber  26 . Therefore, of course, it is advantageous in terms of absorption characteristic of the magnet  32 . This is because the magnetic force of the magnet  32  is directly applied to the container space without a wall member of the waste developer container  17 . However, even if the magnet  32  is located outside via the wall member of the waste developer container  17  as viewed from the lower chamber  26 , it is acceptable as long as sufficient magnetic force can be applied to the space near the detection window  29 . Note that, it is needless to say that the magnet  32  should not be provided at the position where it interrupts the light path of the light L. 
         [0059]    Next, material of the detection window  29  will be described. Before that, as to material of the entire waste developer container  17 , synthetic resin is often used in terms of requirement of reduction in weight. Type of synthetic resin is not particularly limited in the present invention. Then, as for material of the detection window  29 , any material is acceptable as long as it is transparent. It may be glass. However, transparent synthetic resin is often practically used together with the material of the entire waste developer container  17 . A typical example is polystyrene. 
         [0060]    However, since polystyrene has rather minus characteristic on triboelectric series of various substances, it tends to be charged with minus static electricity. Then, since the surface resistance is as high as 10 17 Ω, it hardly discharges once charged. On the other hand, two-component developer used for a two-component developing device such as developing device  7  in the embodiment of the present invention is generally used with the carrier being frictionally charged in plus and toner being frictionally charged in minus. 
         [0061]    The charging state of the developer in the developing device  7  is almost kept even when it becomes waste developer and is contained in the lower chamber  26 . Therefore, it is likely that the floating carrier in the lower chamber  26  is also charged in plus. Floating carrier easily adheres to the detection window  29  if there is no magnet  32 . In that respect, the significance of the magnet  32  is large. In addition, as described above, in the embodiment of the present invention, the extent of charging of the carrier in the developing device  7  is set stronger than normal. This means that plus charging of the floating carrier in the lower chamber  26  is also stronger than normal devices. In addition, in that respect, the significance of attraction of the floating carrier by the magnet  32  is large. Note that, from the above description, it is likely that floating toner is charged in minus in contrast. This is also a reason that adhesion of floating toner to the detection window  29  is not a big problem. 
         [0062]    The above description is true for not only a case in which polystyrene is used as a material of the detection window  29  but also a case in which other kind of transparent resin on the minus side with respect to polystyrene on triboelectric series is used. However, “transparent” used herein means transparent against the light L used in the waste developer amount detection unit  23 . It is not necessarily transparent against visible light if light other than visible light is used as the light L. 
         [0063]    Next, relationship between the waste developer container  17  and other members in fixed state will be described.  FIG. 9  illustrates relationship between the waste developer container  17  and the image forming unit  3 K. In the fixed state illustrated in  FIG. 9 , the photoreceptor  4  is located little lower than the upper end of the waste developer container  17 .  FIG. 9  is a perspective view illustrating the waste developer container  17  and the image forming unit  3 K viewed from the rear side of the image forming device  1 . Therefore, the image forming units  3 Y to  3 C located to the left of the image forming unit  3 K in  FIG. 1  are arranged in series to the right of the image forming unit  3 K if illustrated in  FIG. 9 . However, in  FIG. 9 , the image forming units  3 Y to  3 C are omitted. In addition, although the rotation direction of the photoreceptor  4  is clockwise in  FIG. 1 , it is anticlockwise in  FIG. 9 . Therefore, in  FIG. 9 , the photoreceptor cleaner  9  is located to the left of the photoreceptor  4  and the developing device  7  is located to the right of the photoreceptor  4 . 
         [0064]    As illustrated in  FIG. 9 , a waste toner nozzle  33  is provided to the image forming unit  3 K. The waste toner nozzle  33  projects toward the waste developer container  17 , and its end enters inside of the waste developer container  17  through the left cross-cut part  19  in  FIG. 9 . Accordingly, the waste toner collected by the photoreceptor cleaner  9  of the image forming unit  3 K is contained in the upper chamber  25  of the waste developer container  17  via the waste toner nozzle  33 . 
         [0065]    Note that, the waste developer produced in the developing device  7  of the image forming unit  3 K is contained in the lower chamber  26  of the waste developer container  17  as described with reference to  FIG. 2 . However, the locations of the waste developer discharge unit  22  and the waste developer acceptance inlet  20  are not shown in  FIG. 9  because they are behind the image forming unit  3 K. Note that, in  FIG. 9 , the surrounding of the waste developer amount detection unit  23  that forms the main unit of the image forming device  1  is illustrated on the location of the projection part  21  of the waste developer container  17 . Therefore, the projection part  21  is not shown in  FIG. 9 . 
         [0066]    Next,  FIG. 10  illustrates relationship between the waste developer container  17  and the intermediate transfer belt  2 . In the fixed state as illustrated in  FIG. 10 , the intermediate transfer belt  2  is located to protrude a bit from the upper end of the waste developer container  17 .  FIG. 10  is the same as  FIG. 9  in that it is a perspective view illustrating the object viewed from the rear side of the image forming device  1 . However, they are different in that the line of sight in  FIG. 9  is from right rear while that in  FIG. 10  is from left rear (right-left is right-left in  FIG. 2 ). Note that, although the image forming unit  3 K is illustrated also in  FIG. 10 , most parts of it are behind the intermediate transfer belt  2  and only a few parts is shown. 
         [0067]    As illustrated in  FIG. 10 , the end of the intermediate transfer belt  2  in the front middle of  FIG. 10  is covered by a cover member  34 . What is covered by the cover member  34  is the left end of the intermediate transfer belt  2  in  FIG. 1 . Therefore, the belt cleaner  13  is hidden behind the cover member  34 . The cover member  34  itself is one of components that form the chassis  15 . As illustrated in  FIG. 10 , a waste toner nozzle  35  is provided to project forward with respect to the front end of the cover member  34  (right end in  FIG. 10 ). The end of the waste toner nozzle  35  enters inside of the waste developer container  17  through the right cross-cut part  19  in  FIG. 10 . Accordingly, the waste toner collected by the belt cleaner  13  from the intermediate transfer belt  2  is contained in the upper chamber  25  of the waste developer container  17  via the waste toner nozzle  35 . 
         [0068]    Note that, although the image forming units  3 Y to  3 C are omitted also in  FIGS. 9 and 10 , handling of waste toner and waste developer produced therefrom will be as follows. First, the waste toner collected by the photoreceptor cleaner  9  of the image forming units  3 Y to  3 C goes to one of the waste toner nozzles  33  and  35  described above to be contained in the upper chamber  25  of the waste developer container  17 . The waste developer produced in the developing device  7  of the image forming units  3 Y to  3 C is also thrown into the waste developer acceptance inlet  20  of the waste developer discharge unit  22  as with the waste developer produced in the developing device  7  of the image forming unit  3 K. 
         [0069]    As described above in detail, according to the present embodiment, the magnet  32  is provided near the detection window  29  of the lower chamber  26  of the waste developer container  17 . Accordingly, waste carrier floating near the detection window  29  of the inner space of the lower chamber  26  is attracted to the magnet  32  so that adhesion to the detection window  29  is prevented. By this means, interruption of detection of full of the lower chamber  26  by adhesion of floating waste carrier is prevented and correct full detection is secured. Accordingly, the waste developer container  17  that effectively uses the capacity of the lower chamber  26  and the image forming device  1  with such waste developer container are realized. Specifically, waste carrier is appropriately attracted by the magnet  32  by locating the magnet  32  near the upper end of the lower chamber  26 . 
         [0070]    Note that, the present embodiment is merely an example and does not limit the present invention in any way. Therefore, various improvements and modifications are possible without departing from the spirit of the present invention. For example, the magnet  32  may be provided outside the lower chamber  26  as described above and the magnet  32  may be provided to the main unit side of the image forming device  1 . In addition, a reflecting mirror may be provided inside the projection part  21  and the light L from the light emitting part  30  may be reflected by the reflecting mirror and received by the light receiving part  31 . In this case, there may be only one detection window  29 . 
         [0071]    In addition, the present invention may be applied to a waste developer container in which the upper chamber  25  and the lower chamber  26  are not divided by the partition wall  24  and waste developer and waste toner are contained in container space together. Alternatively, the present invention may be applied to a container of waste developer in which a container of waste developer and a container of waste toner are completely separate. In addition, any of such containers is not necessarily detachable from the main unit of the image forming device  1 . It may be fixed type. Moreover, configuration of the image forming device  1  is not limited to tandem color type described above but may be multi-cycle color type or monochromic type. Moreover, it may be a copying machine with a scanner function or may be one that can communicate with an external line. 
         [0072]    According to an embodiment of the present invention, with this configuration, an image forming device that develops an image by a trickle developing method with two-component developer and successfully detects the amount contained in a waste developer container is provided. In addition, a waste developer container suitable for such an image forming device is provided. 
         [0073]    Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustrated and example only and is not to be taken by way of limitation, the scope of the present invention being interpreted by terms of the appended claims.