Abstract:
An image forming apparatus includes an image carrying member, an electrostatic latent image forming portion configured to form an electrostatic latent image on the image carrying member, and a developing device configured to develop the electrostatic latent image to form a developer image and the developing device is comprised a developer case to store a developer comprising toner and a carrier, a discharge spout provided on a wall surface in the developer case to overflow and discharge the developer increased excessively, a divider member configured to divide an inside of the developer case into a plurality of spaces, and a passing hole which is formed in the dividing member opposite to the discharge spout and is formed so as to permit the developer to pass through.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2008-103166, filed on Apr. 11, 2008; the entire contents of all of which are incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to an image forming apparatus using a two-component developer composed of toner and a carrier and a developing device. 
       DESCRIPTION OF THE BACKGROUND 
       [0003]    In a dry type two-component developer composed of toner and a carrier, the toner is consumed by image formation, though the carrier remains in the developing device. And, regarding the carrier, the resin coat material on the carrier surfaces is separated and the toner component is adhered to the carrier surfaces, thus the charging capacity as a developer is lowered and the image quality is deteriorated. 
         [0004]    Therefore, separately from supply of toner consumed by image formation, a system for supplying a carrier is proposed. Here, the toner is consumed by image formation, though the carrier remains in the developer case of the developing device. Therefore, if it is intended to keep the toner density of the developer constant, the developer quantity in the developer case is increased. Therefore, the developer increased excessively in the developer case may overflow and be discharged from the developer discharge spout for discharging the developer which is installed on the wall surface of the developer case. 
         [0005]    The supply and discharge of the developer are repeated successively like this, thereby the deteriorated developer in the developer case is replaced with a developer newly supplied, thus the developer quantity is kept constant by keeping the characteristics of the developer satisfactory. 
         [0006]    In Japanese Patent Application Publication No. 07-121017, in the developing device as described above, the developer quantity discharged by overflow is influenced greatly by the shape of the discharge spout for discharging the developer and the mechanism having a characteristic discharge spout shape is disclosed. 
         [0007]    The discharge quantity of the developer discharged by overflow depends on the shape of the discharge spout, though it is greatly influenced by the physical properties of the developer. For example, in an environment of high temperature and high humidity, the physical properties of the developer are changed and the developer quantity in the developer case is increased extremely. The developer is discharged from the discharge spout, though at this time, the developer is accumulated on the upper end of the discharge dam forming the discharge spout. If the fluidity of the developer is lowered in the environment of high temperature and high humidity, the height of the developer accumulated on the upper end of the discharge dam is increased. By doing this, the practical height of the discharge dam is increased and the area of the discharge spout is reduced. Therefore, the discharge quantity of the developer is reduced and the developer quantity in the developer case is increased. Namely, even if the shape of the discharge spout is only changed, the developer is not discharged sufficiently. 
       SUMMARY OF THE INVENTION 
       [0008]    An object of the present invention is to provide an image forming apparatus and a developing device, even if the physical properties of the developer are changed due to change in the environment, for discharging stably the developer and reducing the change in the developer quantity in the developer case. 
         [0009]    An image forming apparatus is provided in an embodiment of the present invention and the image forming apparatus comprises an image carrying member; an electrostatic latent image forming portion configured to form an electrostatic latent image on the image carrying member; and a developing device configured to develop the electrostatic latent image to form a developer image, wherein the developing device includes a developer case configured to store a developer comprising toner and a carrier; a discharge spout provided on a wall surface in the developer case to overflow and discharge the developer increased excessively; a divider member configured to divide an inside of the developer case into a plurality of spaces; and a passing hole formed in the divider member opposite to the discharge spout and formed so as to permit the developer to pass through. 
         [0010]    Further, a developing device is provided in an embodiment of the present invention and the developing device comprises a developer case configured to store a developer comprising toner and a carrier; a discharge spout provided on a wall surface in the developer case to overflow and discharge the developer increased excessively; a divider member configured to divide an inside of the developer case into a plurality of spaces; and a passing hole provided in the divider member opposite to the discharge spout and formed so as to permit the developer to pass through. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is an internal block diagram showing the image forming apparatus body which is an embodiment of the present invention; 
           [0012]      FIG. 2  is an internal schematic view of the developing device viewed from above for explaining Embodiment 1; 
           [0013]      FIG. 3  is a schematic view showing the developing device of Embodiment 1; 
           [0014]      FIG. 4  is a cross sectional view of the developing device which is an embodiment of the present invention; 
           [0015]      FIG. 5  is a schematic view of the image forming portion of the image forming apparatus which is an embodiment of the present invention; 
           [0016]      FIG. 6  is a schematic view showing the developing device of Embodiment 2; and 
           [0017]      FIG. 7  is a cross sectional view of the developing device viewed in the direction of the arrow B shown in  FIG. 6 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    Hereinafter, the embodiments of the present invention will be explained with reference to the accompanying drawings. 
         [0019]    [Embodiment 1] The entire constitution of an image forming apparatus  101  relating to this embodiment is shown in  FIG. 1 . On the upper part of the image forming apparatus  101 , a transparent document table  103  for loading documents is installed. On one side of the document table  103 , an indicator  105  is installed. The step part between the indicator  105  and the document table  103  is a reference position for setting documents. On the bottom side of the document table  103 , a carriage  107  is installed and an exposure lamp is installed on the carriage  107 . By the carriage  107  and exposure lamp  109 , an exposure unit is formed. The carriage  107  moves along the bottom of the document table  103 . The carriage  107  moves back and forth along the document table  103  and the exposure lamp  109  is turned on, thus a document loaded on the document table  103  is exposed. 
         [0020]    By exposure to the document, a reflected light image from the document is obtained and the reflected light image is projected onto a CCD  119  by reflection mirrors  111 ,  113  and  115  and a lens block  117 . The CCD  119  has many photoelectric conversion devices in the light receiving area. The CCD  119  line-scans the light receiving area and repeats the line scanning, thereby outputs an image signal corresponding to the document image. The image signal outputted from the CCD  119  is amplified and is converted to a digital signal. The digital signal is image-processed properly and is supplied to a laser unit  121  which is an exposure unit. The laser unit  121  emits a laser beam according to the input signal. 
         [0021]    At the position neighboring with the indicator  105  of the document table  103 , a window  123  for reading documents is installed. The window  123  has a dimension corresponding to the length of the indicator  105  in the longitudinal direction. Above the document table  103 , indicator  105  and window  123 , an automatic document feeder  125  serving as a cover of the document table  103  is installed in openable and closable. The automatic document feeder  125  has a supply tray  127  for loading documents. The automatic document feeder  125  feeds a plurality of documents set in the tray  127  one by one to the window  123  and discharges the documents passing through the window  123  onto a discharge tray  128 . When the automatic document feeder  125  operates, the exposure lamp  109  emits light at the position corresponding to the window  123  and the light is irradiated to the window  123 . The light irradiated to the window  123  exposes a document passing on the window  123  through the window  123 . By this exposure, a reflected light image from the document is obtained and the reflected light image is projected onto the CCD  119  by the reflection mirrors  111 ,  113  and  115  and lens block  117 . 
         [0022]    On the other hand, almost at the central part in the body, a photosensitive drum  129  which is an image carrying member is installed rotatably. Around the photosensitive drum  129 , a charger  131 , a developing device  133 , a transfer device  135  and a cleaner  139  are arranged sequentially. A developer image transferred onto a sheet by the transfer device  135  is fixed by a fixing device  143 . A laser beam B emitted from the laser unit  121  is irradiated to the surface of the photosensitive drum  129  through the space between the charger  131  and the developing device  133 . 
         [0023]    Next, the developing device  133  will be explained by referring to  FIG. 3 . The developing device  133  has a developer replenishing container  301  for storing toner and a carrier composing a two-component developer. Further, the developing device  133  has a developer case  303  and in the developer case  303 , a developing roller  315  is installed rotatably. The developing roller  315  is arranged opposite to the photosensitive drum  129  and the toner and carrier are held on the surface of the developing roller  315  and the developing roller  315  is rotated, thus the toner held on the developing roller  315  is supplied onto the photosensitive drum  129 . 
         [0024]    The developer replenishing container  301  is mounted on the developer case  303 , thus the toner and carrier are supplied to the developer case  303  through a replenishing port  302 . The developer case  303  is separated into a first space  319  and a second space  321  by the divider plate  305  which is a divider member. From the developer replenishing container  301  mounted on the upper part of the second space  321 , the toner and carrier are supplied into the developer case  303 . 
         [0025]    On the side of the developer case  303  on the side of the second space  321 , a developer discharge spout  313  for discharging a surplus developer is installed. The first space  319  and second space  321  are interconnected to each other. The first space  319  and second space  321  have respectively a circulation mechanism so as to mutually circulate the developer. As a circulation mechanism, a first auger  307  is installed in the first space  319  and a second auger  309  is installed in the second space  321 . The first auger  307  and second auger  309  are rotated, thus the developer in the developer case  303  is conveyed by being stirred. The developer of the developer case  303  is circulated in the conveying direction, in the example shown in  FIG. 3 , such as in the second space  321 , in the direction from this side to the innermost side and in the first space  319 , in the direction from the innermost side to this side. 
         [0026]    In the second space  321 , a toner density detector  311  for detecting the toner density of the developer stirred and conveyed by the second auger  309  is installed. If the toner density detected by the toner density detector  311  is reduced to a predetermined value or lower, a developer is replenished from the developer replenishing container  301 . The toner is consumed by image formation, though the carrier remains in the developer case  303  of the developing device  133 . Therefore, if it is intended to keep the toner density of the developer in the developer case  303  constant, due to supply of the developer, the developer quantity in the developer case  303  is increased. Therefore, the developer increased excessively overflows and is discharged from the developer discharge spout  313  installed on the wall surface of the developer case  303 . The developer discharged due to overflow is accumulated in a receiving portion  317 . 
         [0027]    Next, the developer discharge spout  313  of this embodiment will be explained. With respect to the developer, in an environment of high temperature and high humidity (in this embodiment, for example, at a temperature of 30° C. and a humidity of 80%), the physical properties thereof are changed and the fluidity thereof gets worse. Therefore, the quantity of the developer discharged from the developer discharge spout  313  in an environment of normal temperature and normal humidity (in this embodiment, for example, at a temperature of 20° C. and a humidity of 50%) and the quantity of the developer discharged from the developer discharge spout  313  in an environment of high temperature and high humidity are different from each other. In the environment of high temperature and high humidity, the quantity of the developer discharged from the developer discharge spout  313  becomes smaller. Therefore, the position where the developer discharge spout  313  is installed in this embodiment is determined, under the condition that the developer in the environment of high temperature and high humidity is hardly discharged, so as to discharge the developer in a predetermined quantity. Further, the dimensions of the developer discharge spout  313 , in this embodiment, are set at 30 mm in length and 5 mm in width in the longitudinal direction of the developer case  303 . 
         [0028]    Next, the divider plate  305  of this embodiment will be explained in detail. As described above, by the divider plate  305 , the inside of the developer case  303  is divided into the first space  319  and the second space  321 . The divider plate  305  has a passing hole  323  at the position opposite to the developer discharge spout  313 . 
         [0029]      FIG. 4  is a cross sectional view of the developing device shown in  FIG. 2  viewed in the direction of the arrow A-A′. In  FIG. 4 , the first auger  307  and second auger  309  are omitted. As shown in the drawing, in this embodiment, a lower edge  323   a  of the passing hole  323  is provided so as to be positioned above a lower edge  313   a  of the developer discharge spout  313  by d [mm]. However, the lower edge  323   a  of the passing hole  323  may be the same position as the lower edge  313   a  of developer discharge spout  313 . 
         [0030]    Next, the operation of each device during printing of the image forming apparatus  101  using the developing device of this embodiment will be explained.  FIG. 5  is a schematic view of the image forming portion of the image forming apparatus  101  of this embodiment. 
         [0031]    If an instruction of printing is input, the surface of the photosensitive drum  129  is charged by the charger  131 . The charged photosensitive drum  129  is exposed according to a document image by the laser unit  121  and an electrostatic latent image is formed on the photosensitive drum  129 . The electrostatic latent image on the photosensitive drum  129  is developed by toner on the developing roller  315  of the developing device  133  and a toner image is formed. To the developing roller  315 , the developer is stirred and conveyed by the first auger  307  and second auger  309 . 
         [0032]    The toner image formed on the photosensitive drum  129  is transferred onto a sheet by the transfer device  135 . The toner image transferred onto the sheet is fixed by the fixing device  143 . The residual toner on the photosensitive drum  129  after the toner image is transferred onto the sheet is collected by the cleaner  139 . The developer consumed by printing is replenished in the developer case  303  by the developer replenishing container  301 . The carrier in the developer case  303  is increased by supply of the developer, though the developer is discharged from the developer discharge spout  313 . The discharged developer is accumulated in the receiving portion  317 . 
         [0033]    The toner density in the developer case  303  is detected by the toner density detector  311  and the supply quantity of the developer is controlled. 
         [0034]    Next, the flow of the developer in the developer case  303  of this embodiment will be explained by referring to  FIG. 2 . In the environment of normal temperature and normal humidity (25° C., 60%), the developer is conveyed fluidly. The developer conveyed in the neighborhood of the passing hole  323  passes through the passing hole  323  and is conveyed into the first space  319  (in the route of the arrow B). 
         [0035]    In the developing device  133  of this embodiment, the developer discharge spout  313  is installed so as to discharge a predetermined quantity of developer in the environment of high temperature and high humidity, so that in the environment of normal temperature and normal humidity, the developer is discharged more than the predetermined quantity. However, the passing hole  323  is installed, so that the developer is discharged to the developer discharge spout  313  and is simultaneously distributed to the passing hole  323 . 
         [0036]    Therefore, in the environment of normal temperature and normal humidity, the developer will not be discharged excessively by the developer discharge spout  313 . In the environment of high temperature and high humidity, the fluidity of the developer gets worse and the developer hardly passes through the passing hole  323 , so that the developer flowing toward the developer discharge spout  313  is increased in quantity and the developer is discharged easily from the developer discharge spout  313 . 
         [0037]    Therefore, in the environment of normal temperature and normal humidity, the developer will not be discharged excessively by the developer discharge spout  313 . In the environment of high temperature and high humidity, since the fluidity of the developer gets worse and the developer hardly passes through the passing hole  323 , the developer is conveyed along with the arrow A rout shown in  FIG. 2 . Therefore, the developer flowing toward the developer discharge spout  313  is increased in quantity and the developer is discharged easily from the developer discharge spout  313 . 
         [0038]    As mentioned above, the passing hole  323  is formed in the divider plate  305 , so that both in the environment of normal temperature and normal humidity and the environment of high temperature and high humidity, the developer can be discharged satisfactorily. 
         [0039]    [Embodiment 2] In Embodiment 1 aforementioned, the passing hole  323  is formed in the divider plate  305  installed in the developer case  303 . However, this embodiment uses a structure that the passing hole  323  is not formed in the divider plate  305  and a part of the divider plate  305  on the side that in the developer case  303 , the developer is conveyed from the second space  321  to the first space  319  is lowered in height. The other constitution and operation are the same as those of Embodiment 1, so that to the same components, the same numerals are assigned and the explanation thereof is omitted. 
         [0040]      FIG. 6  is a schematic block diagram of the developing device of this embodiment viewed from above.  FIG. 7  is a cross sectional view of the developing device viewed in the direction of the arrow B shown in  FIG. 6 . The hatched part shown in  FIG. 7  indicates the divider plate  305  and a cutout portion  306  is formed at the leading edge of the divider plate  305 . As shown in  FIG. 7 , the position of a lower edge  306   a  of the cutout portion  306  formed in the divider plate  305  of this embodiment is set at the position slightly higher than the position of the lower edge  313   a  of the developer discharge spout  313 . However, the lower edge  306   a  of the cutout portion  306  may be the same position as the lower edge  313   a  of the developer discharge spout  313 . 
         [0041]    The flow of the developer in the developer case  303  of this embodiment will be explained by referring to  FIG. 6 . In the environment of normal temperature and normal humidity (25° C., 60%), the developer is conveyed fluidly. The developer conveyed in the neighborhood of the lower edge  306   a  of the cutout portion  306  formed in the divider plate  305  gets over and passes the lower edge  306   a  of the cutout portion  306  and is conveyed to the first space  319  (in the route of the arrow D). In the developing device  133  of this embodiment, the developer discharge spout  313  is installed so as to discharge a predetermined quantity of developer in the environment of high temperature and high humidity, so that in the environment of normal temperature and normal humidity, the developer is discharged more than the predetermined quantity. However, the cutout portion  306  is installed in the divider plate  305 , so that the developer is discharged to the developer discharge spout  313  and is simultaneously distributed to the route D. 
         [0042]    Therefore, in the environment of normal temperature and normal humidity, the developer will not be discharged excessively by the developer discharge spout  313 . In the environment of high temperature and high humidity, the fluidity of the developer gets worse. In this state, since the developer does not pass through the route D, the developer is conveyed along with the arrow A shown in  FIG. 6 . Therefore, the developer flowing toward the developer discharge spout  313  is increased in quantity and the developer is discharged easily from the developer discharge spout  313 . 
         [0043]    Using the image forming apparatus  101  having the developing device  133  of the Embodiments 1 and 2, the lift test was conducted on 10000 sheets. Under the test condition that the developer quantity in the developer case  303  is 400 g and the test environments are the environment of normal temperature and normal humidity (25° C., 60%) and the environment of high temperature and high humidity (30° C., 80%), 10000 A4-sized sheets were printed at a print rate of 30%. As a result, as printed images, under both conditions of normal temperature and normal humidity and high temperature and high humidity, satisfactory images are obtained free of uneven density. The quantity of the developer in the developer case  303 , in both Embodiments 1 and 2, is about 410 g in the environment of normal temperature and normal humidity and about 430 g in the environment of high temperature and high humidity. In the environment of high temperature and high humidity, the increase rate of the developer is about 8%, though it is within the tolerance and image formation provides no problem. 
         [0044]    For comparison, in the developing device  133  of Embodiment 1, the passing hole  323  is closed and the similar test is conducted. As a result, as printed image quality, in the environment of normal temperature and normal humidity, satisfactory images are obtained free of uneven density, though in the environment of high temperature and high humidity, uneven density appears and no satisfactory images are obtained. Further, in the neighborhood of the developing roller  315 , a leak of the developer is observed. 
         [0045]    The quantity of the developer in the developer case  303 , in the environment of normal temperature and normal humidity, is about 410 g, though in the environment of high temperature and high humidity, it is about 530 g including the leaked developer and the increased quantity of the developer is more than 30%. By the aforementioned test, the validity of the developing device  133  of the Embodiments 1 and 2 can be confirmed.