Abstract:
The image forming apparatus is equipped with developer containers for housing developers and a developer carrier that is arranged at the opening of the developer container that is rotatable for supplying developer to an electrostatic latent image on an image carrier. A developing device comprising a narrow portion with an inner wall of the developer container and the developer carrier arranged closely at a point near the opening of the developer container in order to prevent leakage of the developer from the developer container is provided with a developer recovery sheet. One end of the developer recovery sheet is attached to the end of the opening of the developer container and the free end is extending in the direction of the narrow portion in the developer container and is floated up from the developer carrier when the developer carrier is turned.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to developing device and developing method that are used in image forming apparatus such as printers, copying machines, etc.  
           [0003]    2. Description of the Related Art  
           [0004]    For developing devices of image forming apparatus such as printers, copying machines, etc. to obtain images according to an electro-photographic system, there is so far available an image forming apparatus provided with a narrow portion comprising developer containers and developing rollers arranged closely at a point near the opening of a developing container so as to prevent a developer in a developing container from leaking to the outside during the development or when moving a developing device and this narrow portion is blocked up by a napping of a developer formed on the surface of the developing roller. Particularly, in the case of developing devices available in recent years, that are installed to a revolver and arranged positions of them are changed by rotating them en block to supply different color developers, there is a merit to effectively prevent leakage of developers from developer containers when turning a revolver by providing the above-mentioned narrow portion.  
           [0005]    Or, a revolver is provided with a sealing member to block up a clearance between a developing container and a developing roller at the opening of the developer container in order to prevent leakage of developer caused when turning a revolver as disclosed in Japanese Patent Publication No. 2000-75592.  
           [0006]    However, the above-mentioned conventional developing devices so far available have not a function to recover toner scattered from carriers in a developer container when toner is separated from carrier and scattered as a result of rotation of developing roller during the developing operation. In a conventional developing device with the above-mentioned narrow portion provided, as the opening of the developer container is not blocked up by a sealing member, scattering toner is once directed to the inside of a developer container from the opening on the air flow caused from the rotation of the developing roller but bounced by the napping portion blocking the narrow portion and scatters again to the outside of the developing container. On the other hand, in a conventional developing device with a sealing member provided at the opening, scattering toner scatters in the periphery without solely taking in a developing container and contaminates periphery equipment or adversely affecting images.  
           [0007]    Accordingly, it is desired so far to obtain a developing device that is capable of certainly recovering scattering toner generated when turning a developing roller in a developer container, preventing toner to scatter in the periphery of developing device, obtaining clear images without contaminating peripheral equipment and images by attaching scattering toner to them and reducing frequency of maintenance.  
         SUMMARY OF THE INVENTION  
         [0008]    An object of the present invention is to provide a developing device and a developing method without generating contamination of the periphery by scattering toner by recovering scattering toner generated during the developing operation in developing containers and preventing scattering of toner in the periphery.  
           [0009]    According to an embodiment of the present invention, in the image forming devices comprising developer containers for housing developers, rotatable image carriers for supplying developers to electrostatic latent images formed on an image carrier and a narrow portion provided with an inner wall of the developer container and the developer carrier arranged closely at a point near the opening of the developer container, a developer recovery sheet that floats from the developer carrier when turning the carrier is provided, of which one end is attached to the end of the opening of the developer container and the free end is extended in the direction of the narrow portion in the developer container.  
           [0010]    Further, according to the embodiment of the present invention, in a developing method using the developing devices provided with the narrow portion comprising the inner wall of the developer container and a rotatable developer carrier closely arranged at a point near the opening of the developer container, the developer recover sheet of which one end is attached to the end of the opening of the developer container and the free end is extended in the direction of the narrow portion in the developer container floats from the developer carrier. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 is a schematic diagram showing an image forming unit of an image forming apparatus in an embodiment of the present invention;  
         [0012]    [0012]FIG. 2 is a schematic diagram showing developing devices of an embodiment of this present invention; and  
         [0013]    [0013]FIG. 3 is a construction diagram showing a urethane sheet of the developing device of an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]    An embodiment of the present invention will be described below in detail referring to attached drawings. FIG. 1 is a schematic diagram showing an image forming unit  10  of an image forming apparatus of an embodiment of the present invention. Around a photosensitive drum  11  that is an image carrier of the image forming unit  10 , there are arranged a charger  12  for uniformly charging the photosensitive drum  11  in order with the rotation of the photosensitive drum  11  in the arrow direction s, a laser beam applying position  14  to apply a laser beam  13   a  from a laser writing unit  13  from a latent image forming unit for forming a latent image on the charged photosensitive drum  11 , a revolver  19  that is provided with yellow (Y), magenta (M) and cyan (C) developing devices  16 ,  17 ,  18  and turns in the arrow direction t, an intermediate transferring unit  21  that has an intermediate transferring belt  21   a  that rotates in the arrow u direction, a cleaner  22  and a charge elimination lamp  23 .  
         [0015]    The laser writing unit  13  forms an electrostatic latent image on the photosensitive drum  11  by applying laser beams corresponding to writing signals for respective colors according to image data that are input through an external computer terminal or others. As shown in FIG. 2, the developing devices  16 ,  17  and  18  house developers  26 ,  27  and  28  comprising 3 color toners of yellow (Y), magenta (N) and cyan (C) and carrier in developer containers  20 ,  21  and  22 , respectively. The revolver  19  turns the yellow (Y), magenta (M) and cyan (C) developing devices  16  to  18  all together by its rotation and arranges desired developing devices  16  to  18  at positions opposing to the photosensitive drum  11 .  
         [0016]    The yellow (Y), magenta (M) and cyan (C) developing devices  16  to  18  have magnet rollers  160   a  to  180   a , developing rollers  160  to  180  comprising developing sleeves  160   b  to  180   b  which turn around the magnet rollers  160   a  to  180   a , and conveying augers  16   c  to  180   c  which supply yellow (Y), magenta (M) and cyan (C) toners in the developer containers  20  to  22 , respectively. The developing sleeves  160   b  to  180   b  of the developing rollers  160  to  180  turn at a speed of 340 mm/sec. in the arrow direction during the developing operation.  
         [0017]    At the mounting ends  20   a ,  21   a  and  22   a  that are the openings of the developer containers  20 ,  21  and  22  at the downstream side in the arrow direction v of the developing rollers  160  to  180 , one end of a urethane sheet  24  that is a developer recovering sheet in 0.1 mm thickness and JIS A90 hardness is mounted. The mounting ends  20   a ,  21   a  and  22   a  of the developer containers  20 ,  21  and  22  form an angle of 30° with a horizontal line passing through the center of rotation of the developing rollers  160  to  180 .  
         [0018]    The urethane sheet  24  is attached to the mounting ends  20   a ,  21   a  and  22   a  up to the point A shown in FIG. 3 and the portion from the point A is in the free state. The point A is at the position 2.8 mm in the vertical direction and 13 mm in the horizontal direction from the center of rotation of the developing rollers  160  to  180 . The free length of the free portion from the point A of the urethane sheet  24  to the free end point B is set at 8.5 mm. Further, the urethane sheet  24  is in contact with the developing rollers  160  to  180  in the somewhat bent state when the developing rollers  160  to  180  are kept stopped. The bent amount of the urethane sheet  24  is so designed that the mounting ends  20   a ,  21   a  and  22   a  thrusts by into the tangent line of the developing rollers  160  to  180  shown by one-dot chain line in FIG. 3 by about 0.2 mm.  
         [0019]    At the end portion of the opening opposing to the mounting ends  20   a ,  21   a  and  22   a , a doctor blade  30  is provided to control developers  26  to  28  on the developing rollers  160  to  180 . The magnet rollers  160   a  to  180   a  have a developing pole N 1  opposing to the photosensitive drum  11  at the developing position, a conveying pole S 1  to convey the used developers  16  to  28  into the developer containers  20  to  22 , a separation pole N 2  to separate the developers  26  to  28  from the developing rollers  160  to  280 , a grasping pole N 3  to grasp new developers  26  to  28  supplied from the conveying augers  16   c  to  18   c  at the sides of the developing rollers  160  to  180 , and a layer forming pole S 2  opposing to the doctor blade  30 .  
         [0020]    Near the mounting ends  20   a ,  21   a  and  22   a  of the developer containers  20  to  22 , a wide clearance is formed between the developing rollers  160  to  180  to make it easy to take in the developers  26  to  28  after used for development. Further, at the upper stream side of the separation pole N 2  of the developer containers  20  to  22 , narrow portions  20   b  to  22   b  having a narrow clearance from the developing rollers  160  to  180  is formed. The narrow portions  20   b  to  22   b  are blocked by the rise of developers  26  to  28  formed on the developing rollers  160  to  180  in order to prevent scattering of the developers  16  to  18  from the developer containers  20  to  22 .  
         [0021]    Next, the color image forming process by the image forming unit  10  will be explained. In this image forming unit  10 , a full-color image is formed by superposing yellow (Y), magenta (M) and cyan (C) toner images in this order. When starting the image formation, the developing roller  160  of the yellow (Y) developing device  16  mounted to the revolver  19  is arranged opposing to the developing position of the photosensitive drum  11 .  
         [0022]    When the image forming process starts, the photosensitive drum  11  turns in the arrow direction s and uniformly charged by the charger  13  with its rotation, applied with laser beam corresponding to an yellow image signal by the laser writing unit  13  at a laser beam apply position  14 . Then, an electrostatic latent image of a yellow image is formed on the photosensitive drum  11  and the drum reaches the revolver  19 . At the revolver  19 , the Developing sleeve  160   b  of the developing roller  160  of the yellow developing device  16  turns in the arrow direction v at a velocity of 340 mm/sec.  
         [0023]    With this rotation of the developing sleeve  160   b , the developing roller  160  controls the rise of the developer  26  obtained by the grasping pole N 3  by the doctor blade  30 . And a yellow (Y) toner image is formed on the photosensitive drum  11  by giving a toner to an electrostatic latent image. Thereafter, the developer on the developing roller  160  is conveyed into the developer container  20  by the conveying pole S 1  and separated from the surface of the developer sleeve  160   b  by the separation pole N 2  through the narrow portion  20   b.    
         [0024]    During the developing roller  170  in rotating, the free end point B of the urethane sheet  24  is floated from the surface of the developing roller  160  as shown by the dotted line in FIG. 3 by the wind pressure caused from the rotation of the developing roller  160 . In the clearance between the developing roller  160  and the urethane sheet  24 , the air flow is generated in the arrow direction w, and when toner  26   a  is separated from carrier and scattered when the developing roller  160  is rotating, the scattering toner  26   a  is taken in the developer container by the air flow in the arrow direction w.  
         [0025]    The scattering toner  26   a  taken into the developer container  20  is bounced by the developer  26  blocking the narrow portion  20   b  in the direction reverse to the arrow direction w. This bounced scattering toner  26   a , however, is carried to the urethane sheet side along the inner all of the developer container  20  as shown by the arrow mark x without being scattered to the outside of the developer container  20 . The scattering toner carried to the urethane sheet  24  side is bounced by the urethane sheet  24  in the developer container  20 , carried in the arrow direction y and then, carried again to the narrow portion  20   b  of the developer container together with the scattering toner  26   a  that is newly taken into the developer container on the air flow in the arrow direction w. Meanwhile, the scattering toner  26   a  is conveyed in the direction of the separation pole N 2  jointly with the toner at the narrow portion  20   b  along the rotation of the developing roller  160 .  
         [0026]    After completing the developing, the toner image on the photosensitive drum  11  reaches the contacting position with the intermediate transferring belt  21   a  that is rotating in the arrow direction u and is electrostatically transferred primarily on the intermediate transferring belt  21   a . After completing the primary transfer, the photosensitive drum  11  is cleaned to remove residual toner by the cleaner  22  and the surface charge is eliminated by the charge elimination lamp  23 . Then, the magenta and cyan toner image forming process is repeated on the photosensitive drum  11  in the same manner as the above-mentioned yellow toner image forming process, and yellow (Y), magenta (M) and cyan (C) toner images are transferred intermediately on the intermediate transferring belt  21   a  from the photosensitive drum  11 . Thus, a color toner image with 3 color toner images superposed is formed on the intermediate transferring belt  21   a.    
         [0027]    Meanwhile, the revolver  19  turns sequentially in the arrow direction t and arranges the developing rollers  160  to  180  corresponding to a color of a toner image that is formed on the photosensitive drum  11  opposing to the photosensitive drum  11 . When the revolver  19  is turning, the developing rollers  160  to  180  are kept stopped to turn. Yellow (Y), magenta (M) and cyan (C) color toner images superposed on the intermediate transferring belt  21   a  are secondarily transferred in block on a recording paper, etc. and a color image is completed.  
         [0028]    While the image forming process is thus repeated, scattering toner generated when the developing rollers  160  to  180  are turning is recovered in the developer container  20  through the clearance between the urethane sheet  24  closing the opening of the developer container and the developing rollers  160  to  180  without scattering in the periphery of the developing devices  16  to  18 .  
         [0029]    Further, as a comparison example, the image forming process was executed by changing the urethane sheet  24  in this embodiment with a 0.2 mm thick urethane sheet. As a result, the free end of the urethane sheet was not floated by the wind pressure at the time of rotation but kept in contact with the developing rollers  160  to  180 , and the opening of the developer container  20  was closed by the urethane sheet and the toner is scattered in the periphery without being recovered in the developing container.  
         [0030]    According to this embodiment, toners  26   a  to  28   a  scattered from the developing roller  160  to  180  at the time of development are taken into the developer container  20  through the clearance between the urethane sheet  24  and the developing rollers  160  to  180  and further, the scattering of toner again to the outside from the developing container  20  is prevented by the urethane sheet  24 . Accordingly, high grade images are obtained without contaminating peripheral equipment and images by the scattering toners  26   a  to  28   a  and further, frequencies of maintenance for removing scattering toner can be reduced.  
         [0031]    Further, the present invention is not restricted to the embodiment described above but can be modified variously within the spirit and scope of the present invention. For example, the developing devices are not limited to those attached to a revolver but a stationary developing device is usable provided that recovery of scattering toner is required using a developer recovery sheet. In addition, the shape of the developer container is not limited but the rotating velocity of the developer carrier is also optional. Material, thickness, shape or mounting angle, etc. of a developer recovery sheet is not limited provided that it is floated by the wind pressure generated when a developer carrier is turning.  
         [0032]    Further, when images are developed by installing plural developing devices to the revolver, using toner colors are not limited and the number of developing devices that are installed to the revolver can be four with a black toner developing device added.  
         [0033]    According to the present invention as described above, a developer recovery sheet that floats when turning the developer carriers is provided, scattering toner is taken into the developer container by the air flow when turning developer carriers and taken scattering toner is prevented to scatter again from the developer container by the developer recovery sheet. Accordingly, high grade formed images are obtained without contaminating peripheral equipment and images when developing and frequency of maintenance for removing scattered toner adhered to peripheral equipment can be reduced.