Patent Publication Number: US-2011069993-A1

Title: Developing unit for electrophotography system image forming apparatus and process cartridge, and electrophotography system image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2009-218766 filed on Sep. 24, 2009. 
     BACKGROUND 
     1. Technical Field 
     The present invention relates to a developing unit for an electrophotography system image forming apparatus and a process cartridge, and an electrophotography system image forming apparatus. 
     2. Related Art 
     It is an object of the present invention to provide a developing unit that contributes to increase charge amount of the toner, and a process cartridge and an electrophotography system image forming apparatus containing the same. 
     SUMMARY 
     [1] According to an aspect of the invention, a developing unit includes a developing roller and a carrying member. The carrying member includes a main helical blade and a sub helical blade. The carrying member stirs developers containing a toner by using the main helical blade and carries in an axial direction the developers being fed to the developing roller. The sub helical blade is helically screwed in an opposite direction to the main helical blade in at least a part of the axial direction. Each of the main helical blade and the sub helical blade has carrying power of the developers. The carrying power of the sub helical blade is smaller than the carrying power of the main helical blade. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein: 
         FIG. 1  is a schematic sectional view showing a developing unit in the present embodiment; 
         FIG. 2  is a schematic view showing an internal configuration of the developing unit; 
         FIG. 3  is a view explaining a function of a trimmer; and 
         FIG. 4  is a view showing a change in charge amount of the toner in time. 
     
    
    
     DETAILED DESCRIPTION 
     Exemplary, an embodiment of the present invention will be explained in accordance with the drawings hereinafter.  FIG. 1  is a sectional view showing a schematic configuration of a developing unit  10  of an electrophotography system image forming apparatus of the present embodiment. The electrophotography system image forming apparatus has the developing unit  10  to supply the toner onto the photosensitive member on which the electrostatic latent image and development the latent image. The developing unit  10  includes a developing roller  14  opposing to a photosensitive drum  12 , and two carrying members  16 ,  18  with blades for supplying the developers to a surface of the developing roller  14 . One carrying member with blade located on the developing roller  14  is referred to as the carrying member  16  with front blade, and the other carrying member with blade is referred to as the carrying member  18  with rear blade. The developing roller  14  and the carrying member  16  with front blade and the carrying member  18  with rear blade are installed in a housing  20 . A developer container  22  for containing the developers is provided integrally with the housing  20 . The developer container may be constructed separately from the housing  20 , i.e., independently with the developing unit  10 . An interior of the housing  20  is partitioned into a front space  26  in which the carrying member  16  with front blade is contained, and a rear space  28  in which the carrying member  18  with rear blade is contained, by a partition wall  24 . 
       FIG. 2  is a schematic view showing a schematic configuration of the interior of the housing  20  of the developing unit when viewed from the direction that intersects orthogonally with shafts of the developing roller  14  and two carrying members  16 ,  18  with blade. The developing roller  14  and two carrying members  16 ,  18  with blade are arranged in parallel. The carrying member  16  with front blade contains a shaft  30 , and a main helical blade  32  provided to wind helically around this shaft. According to the rotation of the carrying member  16  with front blade around its own shaft, the developers in the front space  26  are fed in the axial direction indicated with an arrow A while being stirred. Also, the developers are fed to the developing roller  14 . The carrying member  18  with rear blade contains a shaft  34 , and a main helical blade  36  and a sub helical blade  38  both provided to wind helically around this shaft. According to the rotation of the carrying member  16  with front blade around its own shaft, the developers in the rear space  28  is fed in the axial direction indicated with an arrow B by the main helical blade  36  while being stirred. The sub helical blade  38  is helically screwed in the opposite direction to the main helical blade  36 , and its height is set lower. In this present embodiment, respective helical pitches of the main helical blade  36  and the sub helical blade  38  are set equal to each other. But another helical pitch may be employed. Also, a height of the blade of the sub helical blade  38  is set to 0.5 of the height of the main helical blade  36  in this present embodiment. In this case, another height may be employed if the developers can be fed in the direction indicated with an arrow B as a whole. In another case, the height of the sub helical blade may be set to range 0.01 to 0.8 of the height of the main helical blade. In further another case, the height of the sub helical blade may be set to range 0.1 to 0.7 of the height of the main helical blade. In further another case, the height of the sub helical blade may be set to range 0.2 to 0.5 of the height of the main helical blade. Accordingly, carrying power of the sub helical blade  38  is smaller than the carrying power of the main helical blade  36 . 
     Openings  40 ,  42  are provided in vicinity of both ends of the partition wall  24  respectively. The developers can move between the front space  26  and the rear space  28  through the openings  40 ,  42 . As described above, the developers contained in the front space  26  and fed by the carrying member  16  with front blade in the direction indicated with an arrow A reaches the bottom end portion in  FIG. 2 , and then enters into the rear space  28  through the opening  42 . In the rear space  28 , the developers are fed by the carrying member  18  with rear blade in the direction indicated with an arrow B, then reach the top end portion in  FIG. 2 , and then enter into the front space  26  through the opening  40 . In this manner, the developers are circulated throughout the housing  20 , and the toner in the developers is charged due to the stirring performed at that time. 
     The helically screwing direction of the sub helical blade  38  is opposite to the main helical blade  36 . Therefore, the developers are fed by the sub helical blade  38  oppositely to the feeding direction of the main helical blade  36 , i.e., oppositely to the direction indicated with an arrow B. As a result, when the carrying member  18  with rear blade is rotated, the developers located in vicinity of the shaft  34  are fed in the opposite direction to the direction indicated with an arrow B and the developers located on the outer side are fed in the direction indicated with an arrow B. On account of the feeding actions made in the opposing directions, friction is produced between respective developers and the charging is promoted. 
     A driving unit  44  for rotating/driving the developing roller  14  and the carrying member  16  with front blade and the carrying member  18  with rear blade is arranged on the side (at the bottom in  FIG. 2 ) of the housing  20  of the developing unit. The driving unit  44  includes a motor  46 , and a gear train  48  that transfers the rotation of the motor to the developing roller  14  and the carrying member  16  with front blade and the carrying member  18  with rear blade. The gear train  48  is illustrated schematically in  FIG. 2 . 
       FIG. 3  is a view explaining a function of a trimmer  50  that causes a predetermined amount of the developers to attach to the developing roller  14 . The developing roller  14  has a sleeve  52  that is formed of nonmagnetic material and is formed into a cylinder shape. Plural permanent magnets are provided on the inner side of the sleeve. In  FIG. 3 , only permanent magnets  56  arranged in positions opposing to the trimmer  50  are illustrated. The trimmers  50  are arranged at a predetermined clearance to oppose to the outer side surface of the sleeve  52 . A clearance  54  between the trimmer  50  and the sleeve  52  is depicted largely in an exaggerated manner in  FIG. 3 . At least a part of the trimmer  50  is formed of magnetic material, and lines of magnetic force are extended between the magnetic material portions and the permanent magnets  56 . Developers  58  contain the magnetic carriers and the nonmagnetic toners, and the magnetic carriers are held in the clearance  54  by the magnetic force of the permanent magnet  56 . The developers  58  being held in the clearance  54  block the developer that is fed by the rotation of the sleeve  52 . A part of the blocked developers  58  is fed to the position opposing to the photosensitive drum  12  according to the rotation of the sleeve  52 . Here, only the toner transfers from the surface of the carrier to the photosensitive drum  12 . 
     Also, friction is produced between the developers  58  being held in the clearance  54  and the developers that are moved along with the rotation of the sleeve  52 , and thus these developers  58  are also charged. When an amount of blocked developers  58  is large, such developers are a burden on the rotation of the sleeve  52 . In contrast, an amount of blocked developers  58  is small, the charging in this portion is decreased, and in some cases it is impossible to give a required charge amount to the toner. From an aspect of overcoming a shortage of charge amount, the sub helical blade  38  provided to the carrying member  18  with rear blade in the present embodiment functions effectively. 
       FIG. 4  is a view showing a change in charge amount of the toner in time. The carrying member with blade, an outer diameter of a shaft of which is 6 mm and an outer diameter of the main helical blade of which is 14 mm, are employed respectively, and a rotation speed is 325 rpm. An outer diameter of the developing roller is 18 mm, and a rotation speed is 325 rpm. A solid line C shows a graph of charge amount when two carrying members  16 ,  18  with blade in the present embodiment are rotated/driven in a state that the developing roller  14  is stopped. In contrast, a dot-dash line D shows a graph of charge amount when the developing roller  14  and two carrying members with blade and without sub helical blade are rotated/driven, and a broken line E shows a graph of charge amount when two carrying members with blade and without sub helical blade are rotated/driven. In all cases, the toner is added to the developer in the housing at time t 1  by a weight ratio of 5%. A difference between the dot-dash line D and the broken line E is caused depending on whether or not the developing roller  14  is rotated. It is appreciated that, when the developing roller  14  is not rotated, charge amount of the toner is lowered. Also, a difference between the solid line C and the broken line E is caused depending on whether or not the carrying member with rear blade has the sub helical blade  38 . It is appreciated that, when the sub helical blade  38  is provided, charge amount of the toner is improved. Also, it is confirmed separately that, even after the toner is added at a time t 1 , the additional toner is charged quickly by the carrying member  18  with rear blade, to which the sub helical blade  38  is provided. With the above, it is appreciated that the provision of the sub helical blade  38  to the carrying member  18  with rear blade can serve as one means for recovering a reduction in charge amount of the toner caused due to a reduction of amount of the developer that is blocked by the trimmer  50 . 
     In the present embodiment, the height of the sub helical blade  38  is lower than the height of the main helical blade  36 . In this case, the sub helical blade  38  may be perforated to lessen the carrying power of the sub helical blade  38 . Also, the slope of the sub helical blade  38  may be changed to lessen the carrying power of the sub helical blade  38 . 
     In the present embodiment, the sub helical blade  38  is provided only to the carrying member  18  with rear blade. In this case, the sub helical blade  38  may be provided to the carrying member  16  with front blade. Also the sub helical blade  38  may be provided to a part of the carrying member with blade in the axial direction. 
     In the present embodiment, the height of the sub helical blade  38  is set only to 0.5 of the height of the main helical blade  36 . Also, the height of the sub helical blade  38  may be set to range 0.01 to 0.8 of the height of the main helical blade  36 . The height of the sub helical blade  38  may be set to range 0.1 to 0.7 of the height of the main helical blade  36 . Preferably, the height of the sub helical blade  38  may be set to range 0.2 to 0.5 of the height of the main helical blade  36 . The Inventor of this application confirms that all of ranges above are effective for increasing charge amount of the toner. 
     The developing unit  10  in the present embodiment may be provided as a part of the so-called process cartridge that is integrated together with the photosensitive drum  12  and the developer container  22  and is detachably attached integrally to the image forming apparatus. 
     The foregoing description of the exemplary embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understood the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.