Abstract:
The present invention provides for a developing device comprising a developing roller configured to supply developer to a developing portion, a first conveying path configured to guide a moving of the developer and from which the developer is supplied by the developing roller to the developing portion, a first mixer configured to mix the developer while the developer is moving along the first conveying path, a second conveying path configured to guide the moving of the developer, wherein a residual developer left on the developing roller is recovered to the second conveying path and conveyed to the first conveying path, a second mixer configured to mix the developer while the developer is moving along the second conveying path, and a partition member arranged between the developing roller and the first conveying path to prevent leakage of the developer from between the developing roller and the first conveying path to the second conveying path directly, wherein one end of the partition member is brought in contact with the developing roller.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a developing device that is applicable to, for instance, electrophotographic copying machines. 
     2. Description of the Related Art 
     A developing device of this type, equipped with a developing magnet roller and upper and lower mixers, circulates developer along upper and lower conveying paths by rotating the upper and lower mixers and develops images by supplying developer to the developing magnet roller from a developer accumulating portion via the upper conveying path. 
     Further, after developing images, residual developer remaining on the developing magnet roller is recovered and conveyed along the lower conveying path. 
     By the way, the developer accumulating portion and the lower conveying path are communicated with each other and developer tends to leak from the developer accumulating portion to the lower conveying path. Leakage (flow) of developer to the lower conveying path is prevented because developer is retained by the magnetic force of a conveying pole located close to the developer accumulating portion of the developing magnet roller. 
     However, in conventional developing devices, developer is retained by the magnetic force of the conveying pole and if the magnetic force of the conveying pole drops, the developer leaks (flows) from the developer accumulating portion to the lower conveying path and the circulation of developer is unbalanced. That is, there was such a defect that developer in the upper conveying path decreases, amount of developer supplied to the developing magnet roller via the developer accumulating portion drops and in the worst case, developer may not be supplied. 
     Further, when the magnetic force of the conveying pole is too high, used developer is drawn in the developer accumulating portion from the lower conveying path and an image density is apt to drop. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a developing device that is capable of preventing leakage (flow) of developer from a developer accumulating portion to a lower conveying path without relying on the magnetic force of a conveying pole and drawing-up of used developer from a lower conveying path. 
     According to the present invention, a developing device is provided. The developing device comprises a developing roller configured to supply developer to a developing portion, a first conveying path configured to guide a moving of the developer and from which the developer is supplied by the developing roller to the developing portion, a first mixer configured to mix the developer while the developer is moving along the first conveying path, a second conveying path configured to guide the moving of the developer, wherein a residual developer left on the developing roller is recovered to the second conveying path and conveyed to the first conveying path, a second mixer configured to mix the developer while the developer is moving along the second conveying path, and a partition member arranged between the developing roller and the first conveying path to prevent leakage of the developer from between the developing roller and the first conveying path to the second conveying path directly, wherein one end of the partition member is brought in contact with the developing roller. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an internal block diagram showing an image forming apparatus to which a developing device of the present invention is applicable; 
     FIG. 2 is a vertical sectional view showing a first embodiment of the developing device of the present invention; 
     FIG. 3 is a schematic diagram showing an enlarged partition member that is used in the developing device shown in FIG. 3; 
     FIG. 4 is a vertical sectional view showing a second embodiment of the developing device of the present invention; 
     FIG. 5 is a schematic diagram showing the enlarged partition member that is used in the developing device shown in FIG. 4; 
     FIG. 6 is a graph showing thickness of the partition member and partition performance corresponding to change in amount of thrust to a developing roller; 
     FIG. 7 is a schematic diagram showing amount of projection of the contacting edge of the partition member; 
     FIG. 8 is a graph showing the relationship between the magnetic force of a conveying pole and a conveying amount of developer. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will be described below with reference to embodiments shown in the drawings. 
     FIG. 1 is an internal block diagram showing an image forming apparatus. There is a paper feeder  2  equipped with a paper feed roller  3  provided on one side of a main body ( 1 ). 
     In the main body ( 1 ), there are an aligning roller pair  4  to align paper P, a conveyer belt  5  to convey paper P, a fixing device  6  to fix an image on paper P, and an exit roller pair  7  to exit paper P having a fixed image are provided in order along the conveying direction of paper P. 
     The conveyor belt  5  is manufactured by, for instance, semiconductive polyimide and has a characteristic stabilized from the viewpoint of thermal as well as abrasion resistance. The conveyor belt  5  is put between a driving roller  8  and a driven roller  9 . The driven roller  9  is given with a tension so that the conveyor belt  5  travels without being loosened. 
     Above the conveyor belt  5 , there are process units  10 Y,  10 M,  10 C and  10 B provided in the conveying direction of paper P. Yellow, magenta, cyan and black toners are used in the process units  10 Y,  10 M,  10 C and  10 B, respectively. 
     Each of the process units  10 Y,  10 M,  10 C and  10 B is provided with a photosensitive drum  15  and around this photosensitive drum  15 , there are a main charger  16 , a optical laser beam unit  17 , a developing device  18  and a cleaning device  19  arranged in order along the rotating direction of the photosensitive drum. 
     At the inside of the conveyor belt  5 , transfer devices  20 Y,  20 M,  20 C and  20 B are arranged. These transfer devices are facing the photosensitive drums  15  in the process units  10 Y,  10 M,  10 C and  10 B via the conveyor belt  5 . 
     The fixing device  6  comprises a fixing roller  24  that is heated by a heat lamp  23  and a pressure roller  26  that is provided under the fixing roller  24 , press fitted and heated by a heat lamp  25 . 
     Next, the image forming operation will be described. 
     The surfaces of the photosensitive drums  15  of the process units  10 Y,  10 M,  10 C and  10 B are uniformly charged to, for instance, about −700V by the main charger  16 . Then, the laser beam is applied to each of the photosensitive drums  15  by an optical laser beam unit  17  corresponding to an image signal. On each of the photosensitive drums  15 , resistance on a portion applied with the laser beam decreases, the minus charge is discharged and an electrostatic latent image is formed. Further, a semiconductive laser is normally used as a laser and laser beam modulated according to an image is scanned by a rotary polygonal mirror (not shown). An electrostatic latent image thus formed is developed by a developing device  18 . That is, a toner that is fine color particles minus charged by the reversal development is given with developing bias of about −500V and adhered to the portion where the minus charge of the electrostatic latent image was discharged on each photosensitive drum  15 . By this adhered toner, an electrostatic latent image is visualized and magenta, cyan or black color image is formed. 
     On the other hand, at this time, a sheet of paper P is fed from the paper feeder  2  and this sheet of paper P is taken in by the rotation of the paper feed roller  3 . This sheet of paper P taken in is aligned by the aligning roller pair  4 , placed on the conveyor belt  5  at a proper timing and conveyed by the traveling conveyor belt  5 . This sheet of paper P is fed between the photosensitive drums  15  and the transfer devices  20 Y- 20 B, respectively and yellow, magenta, cyan and black color images are transferred on the sheet of paper P by the transfer devices  20 Y- 20 B, respectively. 
     On the transfer devices  20 Y- 20 B, a charge of about +1000 V is given to a sheet of paper P from its back via the conveyor belt  5 . Thus, the yellow, magenta, cyan and black color images developed by the minus charged toners on the photosensitive drums  15  are attracted to and transferred on the sheet of paper P. A sheet of paper P on which a color image transferred is conveyed between the fixing roller  24  heated by the heat lamp  23  and the pressure roller  26  heated by the heat lamp  25 , and heated and pressed by the fixing roller  24  and the pressure roller  26 , the color image is fixed on the sheet of paper P, and the printing operation is completed. Thus, the printed paper P is ejected to the outside of the machine by the exit roller pair  7 . 
     Further, the residual toner left on each of the photosensitive drums  15  without being transferred on a sheet of paper P during the development is scraped and removed by a cleaning blade  19   a  of each of the cleaning device  19 . 
     FIG. 2 is a vertical sectional view showing the above-mentioned developing device  18 . This developing device  18  has a casing  31  and a developing roller  32  as a developing means to feed developer is provided in the casing  31 . The developing roller  32  comprises a rotary sleeve  33  that rotates in the arrow direction and a magnet roller  34  that is fixed in the rotary sleeve  33 . The developing roller  32  is facing the photosensitive drum  15 . Above the developing roller  32 , a doctor blade  39  is provided to form a thin layer of developer on the developing roller  32 . 
     Further, in the casing  31 , an upper mixer  36  is provided rotatably as a first stirring/conveying means to feed developer to the developing roller  32  via a developer accumulating portion  41  by mixing/conveying developer along an upper conveying path  35  as a first conveying path. Below the upper mixer  36 , there is a lower mixer  38  as a second stirring/conveying means to circulate developer between it and the upper mixer  36  by mixing/conveying developer along the lower conveying path  37  as a second conveying path. The upper conveying path  35  and the lower conveying path  37  are partitioned with a guide  40 . 
     Further, the developer accumulating portion  41  and the lower conveying path  37  are partitioned by a block material  43  that is used as a partition member as a partition means. The block material  43  is formed with, for instance, polyurethane foam. One end of the block material  43  is fixed to the guide  40  and the other end is kept in contact with the rotary sleeve  33  of the developing roller  32 . 
     Next, the developing operation will be described. 
     During the development, the upper and lower mixers  36  and  38  are rotated and developer is mixed/conveyed and circulated upward and downward by the rotation of the mixers and at the same time, supplied to the developing roller  32  via the developer accumulating portion  41  by the rotation of the upper mixer  36  as shown by an arrow a (as shown in FIG.  2 ). This developer is supplied onto the photosensitive drum  15  by the rotation of the rotary sleeve  33  and an electrostatic latent image is developed. Then, the developer left on the rotary sleeve  33  after the development is sent to the lower mixer  38  and recovered as shown by an arrow b (as shown in FIG.  2 ). 
     By the way, there was so far no partition member between the developer accumulating portion  41  and the lower conveying path  37 , developer is held by magnetic force of a magnetic pole N 2  of the magnet roller  34  so as to prevent leakage of developer from the developer accumulating portion  41  to the lower conveying path  37 . 
     However, according to this method, the quantity of used developer drawn up from the lower conveying path  37  increases if the magnetic force of the magnetic pole N 2  is too high and the image density tends to drop as shown in FIG.  8 . 
     Further, if the magnetic force is decreased in order to suppress the draw-up quantity from the lower conveying path  37 , developer may possibly leak from the developer accumulating portion  41  to the lower conveying path  37  due to fluctuation of magnetic force of the magnetic pole N 2  between solid matters. 
     In this embodiment, because the developer accumulating portion  41  and the lower conveying path  37  are partitioned with the block material  43  as mentioned above, developer in the developer accumulating portion  41  is kept therein by the block material  43  so that leakage of developer from the developer accumulating portion  41  to the lower conveying path  37  can be certainly prevented. At the same time, used developer flowing to the developer accumulating portion  41  from the lower conveying path  37  can be cut off by the block material  43  and is not drawn up. 
     FIG. 4 shows the second embodiment of the present invention. 
     Further, the same component elements shown in the first embodiment will be assigned with the same reference numerals and the explanation thereof will be omitted. 
     In this second embodiment, a soft plate material  51  is used as a partition means to partition the developer accumulating portion  41  and the lower conveying path  37 . As the soft plate material  51 , a thin sheet material such as urethane rubber or Mylar rubber may be used. 
     The lower end of the plate material  51  is a fixed end that is fixed to the guide  40  by a both-sided tape and the upper end is a contact end to contact the rotary sleeve  33  of the developing roller  32  as shown in FIG.  5 . The plate material  51  has been mounted so that the direction from its fixed end to the contact end is the same direction as the rotary direction of the rotary sleeve  33  of the developing roller  32 . 
     Accordingly, when receiving a force from above, the contact end of the plate material  51  is pressed against the developing roller  32  to maintain the developer accumulating portion  41  and the lower conveying path  37  in the partitioned state. When receiving a force from below, the plate material  51  is elastically deformed to separate its contact end from the developing roller  32  and the partitioned state between the developer accumulating portion  41  and the lower conveying path  37  is cancelled. 
     By the way, if the developing device was mounted in the tilted state or developer toner density increased and the developer filling in the casing  31  became partially dense or fluidity of developer became worse, developer pressure in the lower conveying path  37  will increase. In this case, developer tends to overflow from a gap G (shown in FIG. 4) between the developing roller  32  and the inner bottom surface of the casing  31 . 
     At this time, however, the plate material  51  is pushed up by developer to separate its contact end from the developing roller  32  and draw up developer to the developer accumulating portion  41 . 
     Accordingly, even if the developer pressure in the lower conveying path  37  increased, developer does not overflow from the gap G between the developing roller  32  and the inner bottom surface of the casing  31 . 
     Further, in the first embodiment, as the block material  43  is provided simply by pushing it against the developing roller  32 , developer cannot be drawn up to the developer accumulating portion  41  even when the developer pressure in the lower conveying path  37  increased. Accordingly, developer may possibly overflow from the gap G between the developing roller  32  and the inner bottom surface of the casing  31 . 
     FIG. 6 is a graph showing the performance of the partition member (urethane rubber, polyurethane foam) shown in the first and second embodiment corresponding to the thickness and changes in amount of thrust to the developing roller  32 . 
     From this graph, it is seen that a plate material is advantageous to prevent the overflow of developer; however, if it is thicker and harder, its scraping force will increase and the filming and overflow tend to occur and further, in the case of a block material, overflow of developer also tends to occur. 
     Further, A shown in FIG. 6 means the polyurethane foam hardness of  10  degree and B means the polyurethane foam hardness of 35 degree. For measuring this hardness, Asker-C hardness meter (Kobunshi Keiki Co. made) that is generally called a durometer was used. 
     So, in the second embodiment a urethane rubber sheet in the thickness below 0.1 mm or a Mylar sheet in the thickness below 0.05 mm is used as the plate material. 
     
       
         
               
               
               
             
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                                  Contact Projecting 
                 Filming on Rotary Sleeve of 
               
               
                   
                 Length (mm) 
                 Developing Roller 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 0 
                 0 
               
               
                   
                 1 
                 0 
               
               
                   
                 2 
                 0 
               
               
                   
                 3 
                 0 
               
               
                   
                 4 
                 X 
               
               
                   
                 5 
                 X 
               
               
                   
                 6 
                 X 
               
               
                   
                 8 
                 X 
               
               
                   
                 10 
                 X 
               
               
                   
                   
               
               
                   
                 0: None, X: Yes  
               
             
          
         
       
     
     Table 1 shows the relationship between the contact end projecting amount to the developing roller  32  of the plate material  51  and generation of the filming on the rotary sleeve  33 . 
     As shown in Table 1, even when the material of the plate material  51  and amount of thrust a (shown in FIG. 5) are proper, the flow of developer in the developer accumulating portion  41  becomes downward as shown by the arrow if the projecting length b (shown in FIG. 7) of the plate material  51  is made longer than 4 mm. In this case, the pressure around the plate material  51  rises and the filming (adherence of toner) to the rotary sleeve  33  is generated. 
     As this invention provides a partition means to partition between the developer accumulating portion and the lower conveying path as described above, the leakage (flow) of developer from the developer accumulating portion to the lower conveying path can be prevented. Therefore, it is possible to certainly prevent defective supply and lack of conveying of developer to a portion to be developed. 
     Further, used developer flowing to the developer accumulating portion from the lower conveying path can be shut off, and without drawing up used developer, developer in proper density can be supplied to a portion to be developed. 
     Further, a partition means uses a soft plate material, where one end of this plate material is a contact end to contact the developing means and the other end is a fixed end, and the direction toward the contact end from the fixed end is the same as the rotating direction of the developing means. So, when pressure of developer in the lower conveying path rises, the contact end of the plate material is separated from the developing means and developer can be drawn up. 
     Accordingly, even when pressure of developer rises in the lower conveying path, developer is not over flown to the outside. 
     Further, as the amount of projection of the contact end is set within the predetermined size, contact pressure of the contact end of the plate material to the developing means can be made small and the developer filming can be prevented.