Abstract:
An image forming apparatus includes a charger to charge an image carrying member, an optical device to irradiate a light onto the image carrying member to form an electrostatic latent image, a developing device to develop the electrostatic latent image on the image carrying member to form a developed image and a transfer device to transfer the developed image on a sheet. The developing device includes a developer container to store a developer including toner and a carrier, a developer supply device to supply the developer to the developer container, a driver device to drive the developer supply device, a developer collection device installed in the developer container to interlock with the driver device and collect a surplus developer left over due to supply of the developer from the developer supply device to the developer container, and a collected developer container to contain the developer collected by the developer collection device.

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, 103168, 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, a process cartridge and a developing device, and more particularly to an image forming apparatus, in a developing device of a system of supplying a developer to the developing device and furthermore discharging the developer in the developing device, for supplying and discharging the developer in link motion, a process cartridge and the developing device. 
       DESCRIPTION OF THE BACKGROUND 
       [0003]    Conventionally, a developing device using a two-component developer composed of toner and a carrier is used. In such a developing device, the toner is consumed by the developing operation, though the carrier remains in the developing device without being consumed. The carrier stirred together with the toner in the developing device, as the stirring frequency increases, causes a situation that the resin coat layer on the surface is separated or the toner is adhered onto the surface, thereby causes deterioration. As a result, the charging characteristic of the developer is lowered slowly. 
         [0004]    Therefore, there is a developing device available, separately from feed of toner consumed by development, for feeding a carrier little by little into the developing device, thereby suppressing a lowering of the charging characteristic. 
         [0005]    This developing device permits the developer becoming excessive due to feed of a carrier to overflow and discharge from the developer discharging port for developer discharge installed at a predetermined position on the wall of the developer bath. By successive repetition of such feed and discharge, the deteriorated developer in the developing tank is replaced with toner and a carrier which are fed newly. 
         [0006]    By doing this, the developer quantity in the developing tank is kept constant and the charging characteristic of the developer is maintained and the copied image quality is prevented from lowering, thus the image formation can be performed satisfactorily. 
         [0007]    However, in this overflow system, the supply of the developer to the developing device and the discharge of the developer from the developing device are not interlocked with each other. Therefore, the quantity of the developer in the developing device depends on an environmental change. For example, when the developer is increased in quantity, the drive torque of the developing device becomes high and there are possibilities of damage of the gears of the developing device. When the developer is decreased in quantity, in correspondence to the conveying screw pitch of the developing device, image irregularities are caused easily. 
         [0008]    To solve the aforementioned problems, in Japanese Patent Application Publication No. 10-90991, an art of detecting accurately the supply quantity and discharge quantity of a developer, controlling the developer supply and discharge highly precisely, thereby maintaining the developer quantity constant is disclosed. 
         [0009]    In the apparatus disclosed in Japanese Patent Application Publication No. 10-90991, a problem arises that in order to detect accurately the toner feed quantity and toner discharge quantity, the toner consumption quantity detecting means and exhausting developer quantity detecting means are used, thus the necessary parts of the apparatus are increased in number and the structure is complicated in correspondence to it and the cost thereof is increased. 
       SUMMARY OF THE INVENTION 
       [0010]    An object of the present invention is to provide an image forming apparatus capable of keeping the developer quantity constant in the developing device in an inexpensive mechanism, a process cartridge and the developing device. 
         [0011]    An image forming apparatus is provided in an embodiment of the present invention and the image forming apparatus comprises a charger to charge an image carrying member; an optical device to irradiate a light onto the image carrying member to form an electrostatic latent image; a developing device to develop the electrostatic latent image on the image carrying member to form a developed image; and a transfer device to transfer the developed image on a sheet, wherein the developing device includes a developer container to store a developer including toner and a carrier; a developer supply device to supply the developer to the developer container; a driver device to drive the developer supply device; a developer collection device installed in the developer container to interlock with the driver device and collect a surplus developer left over due to supply of the developer from the developer supply device to the developer container; and a collected developer container to contain the developer collected by the developer collection device. 
         [0012]    Further, a process cartridge is provided in an embodiment of the present invention and the process cartridge comprises an image carrying member whereon an electrostatic latent image is formed; a developer container to store a developer including toner and a carrier; a developer supply device to supply the developer to the developer container; a driver device to drive the developer supply device; a developer collection device installed in the developer container to interlock with the driver device and collect a surplus developer left over due to supply of the developer from the developer supply device to the developer container; and a collected developer container to contain the developer collected by the developer collection device. 
         [0013]    Furthermore, a developing device is provided in an embodiment of the present invention and the developing device comprises a developer container to store a developer including toner and a carrier; a developer supply device to supply the developer to the developer container; a driver device to drive the developer supply device; a developer collection device installed in the developer container to interlock with the driver device and collect a surplus developer left over due to supply of the developer from the developer supply device to the developer container; and a collected developer container to contain the developer collected by the developer collection device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is an internal block diagram showing the developing device relating to the first embodiment of the present invention; 
           [0015]      FIG. 2  is an internal block diagram showing the process cartridge relating to the first embodiment of the present invention; 
           [0016]      FIG. 3  is an internal block diagram showing the color image forming apparatus relating to the first embodiment of the present invention; 
           [0017]      FIG. 4  is an illustration for the conveying auger used in the developing device relating to the first embodiment of the present invention; 
           [0018]      FIG. 5  is a drawing of the inside of the developing device relating to the first embodiment of the present invention which is viewed from the side of the photoreceptor drum; 
           [0019]      FIG. 6  is a drawing of the inside of the developing device relating to the first embodiment of the present invention which is viewed from the side of the exhaust sleeve; 
           [0020]      FIG. 7  is an internal block diagram showing the toner cartridge for supplying a developer to the developing device relating to the first embodiment of the present invention; 
           [0021]      FIG. 8  is a drawing showing the toner cartridge mounted in the developing device relating to the first embodiment of the present invention; 
           [0022]      FIG. 9  is a schematic view of the toner cartridge; 
           [0023]      FIG. 10  is a schematic view of the interlocking mechanism of the toner cartridge and exhaust sleeve which is viewed from the exhaust sleeve side; 
           [0024]      FIG. 11  is a schematic view of the interlocking mechanism of the toner cartridge and exhaust sleeve which is viewed from the front side; and 
           [0025]      FIG. 12  is a schematic view of the interlocking mechanism of the toner cartridge and exhaust sleeve which is viewed from the toner cartridge. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]    Hereinafter, the embodiment of the present invention will be explained with reference to the accompanying drawings. 
         [0027]      FIG. 3  shows schematically the internal constitution of the color image forming apparatus of a four-each tandem type. A color image forming apparatus  301  is equipped with a scanner portion A for exposing a document and an image forming portion B. 
         [0028]    On one side of the color image forming apparatus  301 , a paper feeding device  303  with sheets P stacked is installed and by a paper feeding roller  305  installed in the paper feeding device  303 , the sheets P are fed one by one into the color image forming apparatus  301 . 
         [0029]    The sheets P fed from the paper feeding device  303  into the color image forming apparatus  301  are aligned by a pair of aligning rollers  307  and are conveyed onto a transfer belt  309 . 
         [0030]    The transfer belt  309 , as a material which is stable thermally and in respect of wear resistance, is made of, for example, semi-conducting polyimide. The transfer belt  309  is stretched between a drive roller  311  and a driven roller  313 . The driven roller  313  is given tension and the transfer belt moves free of sagging. 
         [0031]    Above the transfer belt  309  (in the direction of the scanner portion A), process cartridges  201 Y,  201 M,  201 C and  201 K composing the image forming portion B are installed. The respective process cartridges  201 Y,  201 M,  201 C and  201 K include toner of yellow (Y), magenta (M), cyan (C) and black (K) colors. 
         [0032]    The respective process cartridges  201 Y,  201 M,  201 C and  201 K include furthermore photoreceptor drums  203 Y,  203 M,  203 C and  203 K which are image carrying members. Around each of the process cartridges  201 Y,  201 M,  201 C and  201 K, in the rotational direction, a charger for charging uniformly the surface of each photoreceptor drum, a developing device for developing a latent image formed on each photoreceptor drum and a cleaning device for removing residual toner remaining on each photoreceptor drum after transfer are arranged. 
         [0033]    The process cartridges  201 Y,  201 M,  201 C and  201 K are respectively converted to a cartridge and are installed removably on the color image forming apparatus  301 . 
         [0034]    Further, between the respective process cartridges  201 Y,  201 M,  201 C and  201 K and the scanner portion A, a laser beam optical device  315  is installed. A laser beam emitted from the laser beam optical device  315  is led to the photoreceptor drums  203 Y,  203 M,  203 C and  203 K. 
         [0035]    Furthermore, inside the transfer belt  309 , opposite to the photoreceptor drums  203 Y,  203 M,  203 C and  203 K, transfer devices  317 Y,  317 M,  317 C and  317 K are installed. On the conveyance end side of the transfer belt  309 , a fixing device  319  is installed. The fixing device  319  is composed of a fixing roller  323  having a built-in fixing roller lamp  321  and a pressing roller  327  which has a built-in pressing roller lamp  325  and is arranged opposite to the fixing roller  323 . 
         [0036]    On the conveyance end side of the fixing device  319 , a pair of discharge rollers  329  are arranged. By the discharge rollers  329 , the sheets P are discharged to a receiving tray  331  attached to the side of the color image forming apparatus  301 . 
         [0037]    Next, each of developing devices  101  installed in the respective process cartridges  201 Y,  201 M,  201 C and  201 K will be explained in detail by referring to  FIGS. 1 and 2 . 
         [0038]    The developing device  101  has a developer container  103 . In the developer container  103 , opposite to the photoreceptor drum  203 , a developing roller  105  which is a cylindrical rotator is installed. The developer container  103  is internally partitioned by a divider  113  so as to form an upper chamber  115   a  and a lower chamber  115   b . In the upper chamber  115   a , an upper conveying auger  107  is installed and in the lower chamber  115   b , a lower conveying auger  109  is installed. In the upper chamber  115   a  and lower chamber  115   b , a two-component developer composed of non-magnetic toner and a magnetic carrier is stored. 
         [0039]    Furthermore, in the developer container  103 , a doctor blade  111  for forming a toner layer with a fixed thickness on the developing roller  105  is installed. 
         [0040]    The developing roller  105  is composed of a metallic cylindrical sleeve  105   a  driven to rotate and a plurality of magnets  105   b  fixed and arranged in the sleeve  105   a . The magnetic permeability of the magnets  105   b  in the developing roller  105  is, for example, 800 G. 
         [0041]    In the developer container  103 , an exhaust roller  119  which is a developer collection device is installed at the position opposite to the upper conveying auger  107 . The exhaust roller  119 , similarly to the developing roller  105 , is composed of a metallic cylindrical sleeve  119   a  driven to rotate and a plurality of magnets  119   b  fixed and arranged in the sleeve  119   a . On the divider  113 , on the side where the exhaust roller  119  is installed, a doctor blade  123  for forming a developer layer with a fixed thickness on the exhaust roller  119  is installed. 
         [0042]    Under the exhaust roller  119  (on the side where the lower chamber  115   b  is installed), an exhausting developer storage case  121  as a collected developer container for storing an exhausting developer collected by the exhaust roller  119  is installed. On the upper part of the exhausting developer storage case  121 , an exhaust blade  125  for rubbing off a developer remaining on the exhaust roller  119  is installed. The magnetic permeability of the magnets in the exhaust roller  119  is lower than the magnetic permeability of the magnets in the developing roller  105  such as 200 G. Here, in this embodiment, the length of the exhaust roller  119  is set to the same as that of the upper conveying auger  107 . 
         [0043]      FIG. 5  is a drawing of the developing device  101  shown in  FIG. 2  which is viewed from the side of the photoreceptor drum  203 .  FIG. 5  shows the status that the developing roller  105  is removed. The actual developing roller  105  is arranged at the position indicated by the arrow B. 
         [0044]      FIG. 6  is a drawing of the developing device  101  shown in  FIG. 2  which is viewed from the side of the exhaust roller  119 .  FIG. 6  shows the status that the exhaust roller  119  is removed. The actual exhaust roller  119  is arranged at the position indicated by the arrow D. 
         [0045]    When the developing device  101  is mounted in the color image forming apparatus  301 , the front side of the color image forming apparatus  310  is referred to as the F side and the rear side thereof is referred to as the R side. 
         [0046]    At both ends of the divider  113  for partitioning the developer container  103  into the upper chamber  115   a  and lower chamber  115   b , a first opening  505  and a second opening  507  are installed. The first opening  505  is installed at the end on the F side so as to let a developer conveyed by the upper conveying auger  107  pass through the lower chamber  115   b . The second opening  507  is installed at the end on the R side so as to let a developer conveyed by the lower conveying auger  109  pass through the upper chamber  115   a.    
         [0047]    Furthermore, in the upper chamber  115   a , a developer replenishing port  503  through which a developer is supplied by a toner cartridge  701 , which will be described later, is installed between the end on the F side of the developing roller  105  and the first opening  505 . 
         [0048]    Next, by referring to  FIGS. 4 and 5 , the upper conveying auger  107  and lower conveying auger  109  will be explained. 
         [0049]    The upper conveying auger  107  and lower conveying auger  109  are structured so that a window spline  403  is wound spirally round a spindle  401 . The diameter of the window spline  403  is, for example, 18 mm and the spiral pitch is, for example, 27 mm. Particularly in the lower conveying auger  109 , a return blade  501  for supplying upward the developer at the end on the R side is installed. 
         [0050]    If the upper conveying auger  107  is rotated in the arrow direction shown in  FIG. 2 , the developer in the upper chamber  115   a  is stirred ad conveyed by the upper conveying auger  107 . If the lower conveying auger  109  is rotated in the arrow direction shown in  FIG. 2 , the developer in the lower chamber  115   b  is stirred ad conveyed by the lower conveying auger  109 . Here, the developer in the developing device  101  flows in the directions indicated by the arrows a, b, e and f. 
         [0051]    Next, the entire constitution of the toner cartridge  701  for supplying a developer to the developing device  101  will be explained by referring to  FIGS. 7 to 10 . As shown in  FIG. 7 , the toner cartridge  701  is composed of a cartridge main body  705 , a developer supply groove  707 , a driven coupling  709  and a developer conveying auger  711 . The cartridge main body  705  stores a developer D and has a developer supply port  703  interlocking with the developer supply port  503  of the developer device  101 . The developer supply groove  707  is formed on the bottom of the cartridge main body  705 . The driven coupling  709  is installed at the end of the developer supply groove  707  and receives drive force. The developer conveying auger  711  is installed in the developer supply groove  707  and receives the drive force from the driven coupling  709 , thereby rotates. By the rotation of the developer conveying auger  711 , the developer D is conveyed to the developer supply port  703 . 
         [0052]    Furthermore, a developer stirring paddle  713  for rotating in link motion with the rotation of the developer conveying auger  711 , thereby stirring the developer D in the cartridge main body  705  and leading the developer D to the developer supply groove  707  is installed. 
         [0053]    The toner cartridge  701  is inserted into the color image forming apparatus  301  in the direction of the arrow E shown in  FIG. 9  and as shown in  FIG. 8 , is mounted on the upper part of the developer container  103  of the developing device  101 . At this time, the toner cartridge  701  is mounted at the position where the developer replenishing port  503  of the developer container  103  and the developer supply port  703  of the toner cartridge  701  are fit to each other. 
         [0054]    As shown in  FIG. 10 , the color image forming apparatus  310  is equipped with a drive motor  1001  which is a drive device. At the end of the drive shaft of the drive motor  1001  on the F side, a drive coupling  1009  is installed. If the toner cartridge  701  is mounted in the color image forming apparatus  301 , the driven coupling  709  of the toner cartridge  701  is connected to the drive coupling  1009  and receives drive force from the drive motor  1001 . 
         [0055]    Next, the interlocking mechanism of the developer conveying auger  711  of the toner cartridge  701  and the exhaust roller  119  will be explained by referring to  FIGS. 10 to 12 . 
         [0056]    As shown in  FIG. 12 , at the end of the drive shaft of the drive motor  1001 , the drive coupling  1009  is installed. Between the drive motor  1001  and the drive coupling  1009 , a drive pulley  1103  is installed. In the color image forming apparatus  301 , a driven pulley  1003  is installed and between the drive pulley  1103  and the driven pulley  1003 , a timing pulley  1101  is stretched. 
         [0057]    On the rotary shaft of the driven pulley  1003 , a first gear  1005  for following the rotation of the driven pulley  1003  is installed. The driven pulley  1103  and first gear  1005  are installed in the color image forming apparatus  301 . 
         [0058]    On the other hand, on the F side of the rotary shaft of the exhaust roller  119 , a second gear  1007  is installed. The exhaust roller  119  is installed at the position where the second gear  1007  is connected to the first gear  1005  installed in the color image forming apparatus  310  by the rotation of the second gear  1007 . 
         [0059]    By the mechanism aforementioned, the drive force of the drive motor  1001  is transferred to the developer conveying auger  711  of the toner cartridge  701  and the exhaust roller  119  and the developer conveying auger  711  and exhaust roller  119  are interlocked with each other. 
         [0060]    Next, the operation of each device during image formation will be explained. During image formation, the photoreceptor drum  203 Y is uniformly charged, for example, at −700 V on the surface thereof by the charger. Next, according to an image signal, a laser beam is irradiated to the photoreceptor drum  203 Y from the laser beam optical device  315 . 
         [0061]    The photoreceptor drum  203 Y is reduced in the resistance only of the portion where the laser beam is exposed, so that the negative charge of the portion where the laser beam is exposed is deleted, thus an electrostatic latent image is formed. 
         [0062]    The formed electrostatic latent image is developed by the developing device  101 . Namely, onto the portion of the photoreceptor drum  203 Y where the negative charge of the electrostatic latent image is deleted, toner charged negatively is adhered by being given a development bias voltage of −500 V, thus the electrostatic latent image is converted to a developed image. 
         [0063]    The sheet P is conveyed between the photoreceptor drum  203 Y and the transfer belt  309  and the developed image is transferred onto the sheet P by the transfer device  317 Y. The transfer device  317 Y, for example, is given a positive charge of 1000 V via the transfer belt  309 , thereby attracts and transfers the developed image developed by the toner charged negatively on the photoreceptor drum  203 Y onto the sheet P. 
         [0064]    Similarly, developed images of magenta, cyan and black are sequentially superimposed and formed on the sheet P by the process cartridges  201 M,  201 C and  201 K, the laser beam optical device  315  and the transfer devices  317 Y,  317 M,  317 C and  317 K. 
         [0065]    The sheet P is conveyed between the fixing roller  323  heated by the fixing roller lamp  321  and the pressing roller  327  heated by the pressing roller lamp  325 . The developed images on the sheet P are heated and pressed by the fixing roller  323  and pressing roller  327 , thereby are fixed onto the sheet P. 
         [0066]    Hereafter, the sheet P is discharged onto the receiving tray  331  by the pair of exhaust rollers  329 . Further, on each of the photoreceptor drums  203 Y,  203 M,  203 C and  203 K, there is toner remaining without being transferred. The residual toner is rubbed off by the cleaner, thus the photoreceptor drums  203 Y,  203 M,  203 C and  203 K are cleaned. 
         [0067]    As shown in  FIG. 2 , in the developing device  101  during image formation, a part of the developer under conveyance in the upper chamber  115   a  is supplied to the neighborhood of the developing roller  105 , is attracted to the developing roller  105  by a magnetic pole N 1  installed in the developing roller  105  and is stacked on the developing roller  105 , thus a developer layer is formed. 
         [0068]    The developer layer formed on the developing roller  105  is conveyed according to rotation of the developing roller  105 , is controlled to a fixed height by the doctor blade  111  and is sent between the photoreceptor drum  203  and the developing roller  105  which is a developing section. The developer sent into the developing section is adhered to the photoreceptor  203 . The developer after development passes through a developer attraction receiver  117 , separates and falls from the developing roller  105  between the magnets S 2  and S 3  in the developing roller  105 , returns to the lower chamber  115   b  and is conveyed again by the lower conveying auger  109 . 
         [0069]    Next, the developer supply and discharge operation of the present invention will be explained. 
         [0070]    If the toner is consumed by image formation, the developer is supplied to the developing device  101  from the toner cartridge  701 . During developer supply, by rotation of the drive motor  1001  shown in  FIG. 10 , the developer conveying auger  711  in the toner cartridge  701  is rotated. If the developer conveying auger  711  rotates, the developer D in the toner cartridge  701  is conveyed toward the developer supply port  703 . The developer D conveyed to the developer supply port  703  is supplied from the developer replenishing port  503  installed in the developing device  101  to the developing  101 . 
         [0071]    As shown in  FIG. 2 , a part of the developer under conveyance in the upper chamber  115   a  in the developing device  101  is supplied to the neighborhood of the exhaust roller  119  and is attracted to the exhaust roller  119  by a magnetic pole N 3  installed in the exhaust roller  119 . 
         [0072]    The exhaust roller  119  is rotated, thus the developer D is conveyed. The conveyed developer D is controlled to a fixed height by the doctor blade  123  and then separates and falls from the exhaust roller  119  between the magnets S 4  and S 5  in the exhaust roller  119 . The fallen developer D is stored in the exhausting developer storage case  121 . The developer D remaining on the exhaust roller  119  without falling is rubbed down in the exhausting developer storage case  121  by the exhaust blade  125 . 
         [0073]    The exhaust roller  119  of the developing device  101  and the developer conveying auger  711  in the toner cartridge  701  interlock with each other and when a developer is supplied from the toner cartridge  701 , the developer is discharged by the exhaust roller  119 . Here, the developer discharge quantity by the exhaust roller  119  depends upon the magnetic permeability of the magnets in the exhaust roller  119  and the rotational angle of the exhaust roller  119 . Therefore, by changing the magnetic permeability of the magnets in the exhaust roller  119  and the rotational angle of the exhaust roller  119 , the developer quantity in the developing device  101  can be kept constant. 
         [0074]    If the developer supply and discharge are interlocked with each other in this way, the developer quantity in the developing device  101  can be kept constant.