Patent Publication Number: US-8112017-B2

Title: Developing unit and developer stirring and transporting method

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a Continuation of application Ser. No. 11/479,827 filed on Jun. 30, 2006, the entire contents of both of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a developing unit and a developer stirring and transporting method. 
     2. Description of the Related Art 
     Heretofore, as something to discharge a developer in a developing unit from the developing unit, there is one to discharge a developer by overflow from a developer discharge port formed in a side wall of the developer. In this structure as stated above, there is known a technique in which in order to cause the overflow more easily, in a second stirring and transporting member to stir and transport a developer, a rotary wing in the vicinity of the developer discharge port is changed to a rotary wing with a transporting force lower than normal, so that the developer top surface height in the vicinity of the developer discharge port becomes locally higher than that in another area (see, for example, JP-A-2000-81787). 
     However, since the fluidity of the developer is changed according to the use environment, according to what is disclosed in the related art, for example, when used in a high humidity environment such as a temperature of 30° C. and a humidity of 80%, the developer contains water, the fluidity becomes poor, and it becomes hard to discharge. Thus, there arises a disadvantage that the developer is accumulated more than necessary, and it is not discharged unless the volume is much increased. Besides, since the amount of surplus developer discharged becomes smaller than the amount of developer supplied into the developing unit, the amount of developer contained in the developing unit is significantly increased, and the developer can leak from the developing unit. Thus, it becomes necessary to enlarge the developing unit more than necessary in expectation of the amount of developer increased in the developing unit. Besides, with the increase of the developer, the stirring performance is lowered, and therefore, an insufficiency of density is caused, and it becomes difficult to keep high picture quality. 
     SUMMARY OF THE INVENTION 
     The invention has an object to provide a developing unit and a developer stirring and transporting method in which the amount of developer in the developing unit can always be kept at a specified amount without being influenced by a use environment. 
     In order to solve the problem, a developing unit according to an aspect of the invention has a following structure and includes a developer supply member configured to supply a developer to an image bearing body, a containing unit configured to contain the developer supplied to the developer supply member and having a discharge port to discharge the overflown developer in a side wall, a stirring and transporting member configured to stir and transport the developer along a passage formed in the containing unit, and a guide unit provided in the passage correspondingly to the discharge port and configured to guide the developer transported in the passage by the stirring and transporting member to the discharge port side. 
     Besides, a developing unit according to an aspect of the invention has a following structure and includes developer supply means for supplying a developer to image bearing means, developer containing means for containing the developer supplied to the developer supply member and having a discharge port to discharge the overflown developer in a side wall, stirring and transporting means for stirring and transporting the developer along a passage formed in the developer containing means, and guide means provided in the passage correspondingly to the discharge port of the developer containing means and for guiding the developer transported in the passage by the stirring and transporting means to the discharge port side. 
     Further, a developer stirring and transporting method according to an aspect of the invention has a following structure and includes stirring and transporting a developer in a container to contain the developer, guiding the developer flowing in a transport passage to a discharge port, and discharging the overflown developer through the discharge port. 
     According to the structure as described above, even in the case where the fluidity of the developer is poor in a high humidity environment or the like, since the flow of the developer to the discharge port direction is guided and formed, the surplus developer is positively discharged through the discharge port. Accordingly, the amount of developer in the developing unit can always be kept at a specified amount without being influenced by a use environment. 
     Accordingly, in the case where the use environment is a high humidity state, although the leakage of a developer from a developing unit conventionally occurs due to the increase of the developer in the developing unit, and the developing unit is enlarged more than necessary in order to prevent this, such disadvantage can be eliminated. Besides, it is possible to solve such problems that the stirring performance is lowered by the increase of the developer in the developing unit, the uneven density is caused, and a high picture quality can not be kept. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view in which a developing unit of embodiment 1 is cut in the horizontal direction at the center of a discharge port in the vertical direction. 
         FIG. 2(   a ) is a side view of the developing unit at the discharge port side. 
         FIG. 2(   b ) is a C-C sectional view of  FIG. 2(   a ). 
         FIG. 3  is a perspective view showing only a containing unit of  FIG. 2(   b ). 
         FIG. 4  is a plan view in which a developing unit of embodiment 2 is cut in the horizontal direction at the center of a discharge port in the vertical direction. 
         FIG. 5(   a ) is a side view of the developing unit at the discharge port side. 
         FIG. 5(   b ) is a C-C sectional view of  FIG. 5(   a ). 
         FIG. 6  is a perspective view showing only a containing unit of  FIG. 5(   b ). 
         FIG. 7  is a plan view in which a developing unit of embodiment 3 is cut in the horizontal direction at the center of a discharge port in the vertical direction. 
         FIG. 8(   a ) is a side view of the developing unit at the discharge port side. 
         FIG. 8(   b ) is a C-C sectional view of  FIG. 8(   a ). 
         FIG. 9  is a perspective view showing only a containing unit of  FIG. 8(   b ). 
         FIG. 10  is a perspective view of a containing unit showing a guide unit of embodiment 4. 
         FIG. 11  is a perspective view of a containing unit showing a guide unit of embodiment 5. 
         FIG. 12  is a perspective view of a containing unit showing a guide unit of embodiment 6. 
         FIG. 13  is a perspective view of a containing unit showing a guide unit of embodiment 7. 
         FIG. 14  is a perspective view of a containing unit showing a guide unit of embodiment 8. 
         FIG. 15  is a perspective view of a containing unit showing a guide unit of embodiment 9. 
         FIG. 16  is a plan view in which a developing unit of embodiment 10 is cut in the horizontal direction at the center of a discharge port in the vertical direction. 
         FIG. 17(   a ) is a side view of the developing unit at the discharge port side. 
         FIG. 17(   b ) is a C-C sectional view of  FIG. 17(   a ). 
         FIG. 18  is a perspective view showing only a containing unit of  FIG. 17(   b ). 
         FIG. 19  is a structural view showing a copying machine as an image forming apparatus in which the developing unit of the embodiment is mounted. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     In embodiments of the invention, a description will be given to a developing system in which a new carrier is supplied into a developing unit little by little at the same time as the supply of toner consumed, and a surplus developer is made to overflow through a discharge port in a wall surface of the developing unit. By this, the deteriorated developer is replaced by the new toner and carrier, the developing performance is kept, and a reduction in picture quality can be suppressed. Besides, in this system, since it is not necessary to replace the developer collectively, excellent maintenance can be kept. 
     Hereinafter, embodiments of the invention will be described with reference to the drawings. 
     Embodiment 1 
       FIG. 1 ,  FIG. 2  and  FIG. 3  are structural views of a developing unit of embodiment 1.  FIG. 1  is a plan view in which the developing unit of embodiment 1 is cut in the horizontal direction at the center of a discharge port in the vertical direction,  FIG. 2(   a ) is a side view of the developing unit at the discharge port side,  FIG. 2(   b ) is a C-C sectional view of  FIG. 2(   a ), and  FIG. 3  is a perspective view showing only a containing unit of  FIG. 2(   b ). 
     The developing unit  10  includes a developing roller (developer supply member, developer supply means)  12 , a containing unit (developer containing means)  16  to contain a developer and having a discharge port  14  for discharging the overflown developer in its side wall, a stirring and transporting member (stirring and transporting means)  20  to stir and transport the developer along a passage  18  formed in the containing unit  16 , and a guide unit (guide means)  22  to guide the developer transported by the stirring and transporting member  20  in the passage  18  to the discharge port  14  side. 
     The discharge port  14  is provided at a position where the surplus developer is discharged to the outside of the developing unit  10  by overflow so that the amount of developer contained in the developing unit  10  can always be kept at a specified amount correspondingly to the amount of developer supplied into the developing unit  10 . 
     The guide unit  22  is provided in the passage  18  correspondingly to the height position of the discharge port  14 , and the sectional shape is rectangular when viewed in the passage  18  direction (that is, the developer transport direction, that is, the rotation axis direction of the stirring and transporting member  20 ). Besides, a bottom (bottom surface)  22   a  of the guide unit  22  is formed at a position higher than the lower end of the discharge port  14  in the containing unit  16 , specifically, at a height position of 0 to 3 mm from the lower end of the discharge port  14 . The height position of the bottom  22   a  is almost the same position as the height position of a developer surface at the time when the amount of the developer contained in the developing unit  10  is the specified amount. In the guide unit  22 , a guide surface  22   b  to guide the developer is formed above the bottom  22   a , and the guide surface  22   b  is positioned to be in parallel to the discharge port  14 . The guide unit  22  is formed such that an upper wall surface in the passage  18  at a wall surface  24  side opposite to the discharge port  14  is partially lowered, and an upper wall part of the wall surface  24  opposite to the discharge port  14  in the passage  18  overhangs in the discharge port  14  direction by a specified amount. The overhang width of the guide unit  22  is set to be narrower than the passage  18  width of from the end of the overhang to the discharge port  14 , and the length of the guide unit  22  in the passage  18  direction is set to be equal to or larger than at least the length of the discharge port  14  in the passage  18  direction. 
     The plural stirring and transporting members  20  are arranged in parallel to each other in the containing unit  16 , and a partition unit (partition means)  26  is provided between the plural stirring and transporting members  20 . Besides, the passage  18  is formed of the inner wall of the containing unit  16  and the side surface of the partition unit  26 , and one side surface of the partition unit  26  constitutes the wall surface  24 . A spiral  20   a  is provided in each of the stirring and transporting members  20 , and the spiral  20   a  is rotated so that the developer is stirred and transported. The developer circulates in the containing unit  16  in the counterclockwise direction when viewed from above and the developer is supplied to the developing roller  12 . The stirring and transporting member  20  at the discharge port  14  side is not provided with the spiral  20   a  in the vicinity of the discharge port  14 , and since a force to stir and transport the developer is not generated in the portion where the spiral  20   a  is not provided, the developer is accumulated in this portion and is placed in a swelled state. 
     Besides, a toner density sensor  28  to control the density of the toner is disposed in the developing unit  10 , and the toner density sensor  28  is located at a position indicated by a broken line circle of  FIG. 1  on the bottom surface of the containing unit  16 . 
     Further, in the developing unit  10 , a supply port  30  to supply the developer from a hopper  32  shown in  FIG. 19  is disposed at a position indicated by a broken line circle of  FIG. 1  in the upper part of the containing unit  16 . 
     Next, the operation of embodiment 1 will be described. 
     The developer supplied from the hopper  32  through the supply port  30  into the containing unit  16  is stirred and transported along the passage  18  in the counterclockwise direction by the stirring and transporting member  20 . In the case where the use environment of the developer at this time is a normal environment state, that is, in the case of room temperature and normal humidity, a developer surface A is located at a position of a solid line in  FIG. 2 . Incidentally, the state of room temperature and normal humidity is the state in which the temperature is about 23° C., and the humidity is about 50%. In a portion where stirring and transporting are performed by the spiral  20   a  of the stirring and transporting member  20 , the upper surface of the developer is located at a position lower than the discharge port  14 , and in the vicinity of the discharge port  14  in which the spiral  20   a  does not exist, the developer is accumulated and is swelled up to the position almost equal to the bottom  22   a  of the guide unit  22 , and is excellently discharged through the discharge port  14 . 
     Next, in the case where the use environment of the developer is a high humidity state, that is, in the case of the state where the humidity is 80% or more, the fluidity of the developer becomes poor, and it becomes hard to discharge through the discharge port  14 . Thus, when the developer in the developing unit  10  is not increased more than that in the normal environment, it is not discharged, and therefore, the amount of developer in the developing unit  10  becomes slightly larger than that in the normal environment, and rises up to a position of a developer surface B indicated by a broken line in  FIG. 2 . By this, in the vicinity of the discharge port  14 , the developer is swelled up to a position higher than the bottom  22   a  of the guide unit  22 , however, the space of the passage  18  in the height direction is narrowed by the bottom  22   a , and the straight movement is blocked. Thus, the developer flows in the passage  18  toward the side where the guide unit  22  is not provided, and the developer is discharged through the discharge port  14  as indicated by an arrow of  FIG. 1 . By this, the developer is further swelled in the portion of the discharge port  14  as compared with the structure where the guide unit  22  is not provided in the passage  18 , and since the swelling effect of the developer is increased, the developer becomes easy to be discharged through the discharge port  14 . 
     Incidentally, although the fluidity of the developer mainly relates to the humidity, even if the humidity is the same value, the fluidity becomes slightly poor in the case where the temperature is high as compared with the case where it is low. 
     Incidentally, with respect to embodiment 2 to embodiment 9 described below, in the case where the use state is the normal environment, the operation is the same as that of embodiment 1, and therefore, the description of the operation in the case of the normal environment will be omitted in embodiment 2 to embodiment 9. Besides, also in the case where the use environment is a high humidity, only the flow state of the developer in the vicinity of the guide unit  22  varies, and the others are the same, and therefore, only the flow state of the developer in the vicinity of the guide unit  22  will be described. 
     Embodiment 2 
       FIG. 4 ,  FIG. 5  and  FIG. 6  are structural views of a developing unit of embodiment 2.  FIG. 4  is a plan view in which the developing unit of embodiment 2 is cut in the horizontal direction at the center of a discharge port in the vertical direction,  FIG. 5(   a ) is a side view of the developing unit at the discharge port side,  FIG. 5(   b ) is a C-C sectional view of  FIG. 5(   a ), and  FIG. 6  is a perspective view showing only a containing unit of  FIG. 5(   b ). Incidentally, since a structure other than the shape of a guide unit  22  is the same as that of embodiment 1, the description of redundant portions will be omitted. 
     The guide unit  22  has a sectional shape which is a triangular shape when viewed from above, and is formed to overhang the whole length of a passage  18  in a width direction. A guide surface  22   b  forms an inclined surface such that an end at a wall surface  24  side is positioned at an upstream side when viewed in the passage  18  direction, and an end at a side wall side of a containing unit  16  is positioned at a downstream side. 
     Since other structure is the same as that of embodiment 1, the description will be omitted. 
     Next, the operation of embodiment 2 will be described. 
     In the case where the use environment is a high humidity state, the developer flowing to the vicinity of the guide unit  22  is prevented from going straight ahead since the space of the passage  18  in the height direction is narrowed by a bottom  22   a  of the guide unit  22 , and flows in the passage  18  direction between the guide surface  22   b  and the containing unit  16 . In addition, since the guide surface  22   b  is inclined to a discharge port  14  side, the developer flowing to the passage  18  between the guide surface  22   b  and the containing unit  16  is guided to the discharge port  14  direction by the guide surface  22   b . By this, as indicated by a broken line of  FIG. 4 , although the developer in the vicinity of the side wall of the containing unit  16  goes straight ahead, the developer flowing in a portion other than that flows to the discharge port  14  direction along the guide surface  22   b . Finally, the developer going straight ahead is also pushed out by the guided developer and flows to the discharge port  14  direction. 
     As stated above, in addition to the effect of the guide unit of embodiment 1, since the guide unit  22   b  of embodiment 2 has the structure to cause the flow of the developer toward the discharge port  14  side, the developer becomes easy to be discharged, and as compared with the guide unit  22  of embodiment 1, the increase of the developer in the developing unit  10  can be further suppressed. 
     Embodiment 3 
       FIG. 7 ,  FIG. 8  and  FIG. 9  are structural views of a developing unit of embodiment 3.  FIG. 7  is a plan view in which the developing unit of embodiment 3 is cut in the horizontal direction at the center of a discharge port in the vertical direction,  FIG. 8(   a ) is a side view of the developing unit at the discharge port side,  FIG. 8(   b ) is a C-C sectional view of  FIG. 8(   a ), and  FIG. 9  is a perspective view showing only a containing unit of  FIG. 8(   b ). Incidentally, since a structure other than the shape of a guide unit  22  is the same as that of embodiment 1, the description of redundant portions will be omitted. 
     The guide unit  22  is formed to overhang the whole length of a passage  18  in a width direction so that a bottom (bottom surface)  22   a  is inclined upward to a discharge port  14  side when viewed in the passage  18  direction. An inclined surface is formed such that a height direction position of the bottom  22   a  is lowest at an end on a wall surface  24  side and is highest at an end on a side wall side of a containing unit  16 , and the height position of the bottom  22   a  at the end on the side wall side of the containing unit  16  is the same position as the upper end of the discharge port  14 . In this case, the bottom  22   a  of the guide unit  22  functions as the guide surface. 
     Since other structure is the same as that of embodiment 1, the description will be omitted. 
     Next, the operation of embodiment 3 will be described. 
     In the case where the use environment is a high humidity state, in a portion where the height position of the bottom  22   a  is low, the space of the passage  18  in the height direction is narrowed by the bottom  22   a , and the developer flowing to the vicinity of the guide unit  22  is prevented from going straight ahead, and is pushed toward a part where the height position of the bottom  22   a  is high. Since the height position of the bottom  22   a  of the guide unit  22  is high at the discharge port  14  side and is low at the wall surface  24  side, the developer is pushed toward the discharge port  14  side, and the swelling effect at the discharge port  14  side is increased. By this, the developer becomes easy to be discharged through the discharge port  14 . 
     Embodiment 4 
       FIG. 10  is a perspective view of a containing unit showing a guide unit of embodiment 4. Incidentally, since a structure other than the shape of a guide unit  22  is the same as that of embodiment 1, the description of redundant portions will be omitted. 
     The guide unit  22  has a semicylindrical shape in which a sectional shape is a semicircular shape when viewed from above, and is formed such that a wall surface  24  opposite to a discharge port  14  in a passage  18  overhangs by a specified amount in the discharge port  14  direction. 
     Since other structure is the same as embodiment 1, the description will be omitted. 
     Next, the operation of embodiment 4 will be described. 
     The overhang of the guide unit  22  of embodiment 4 is up to a halfway position of the passage  18  in the width direction similarly to embodiment 1, and a bottom  22   a  is horizontal similarly to embodiment 1 and embodiment 2. Besides, since a guide surface  22   b  is constructed of a semicircular circumference, similarly to the guide surface  22   b  of the guide unit  22  of embodiment 2, it has a structure inclined in the discharge port  14  direction, and therefore, the same operation and effect as those of embodiment 1 and embodiment 2 can be obtained. 
     Embodiment 5 
       FIG. 11  is a perspective view of a containing unit showing a guide unit of embodiment 5. Incidentally, since a structure other than the shape of a guide unit  22  is the same as that of embodiment 1, the description of redundant portions will be omitted. 
     The guide unit  22  has a sectional shape which is a trapezoidal shape when viewed from above, and is shaped such that a wall surface  24  opposite to a discharge port  14  in a passage  18  overhangs by a specified amount in the discharge port  14  direction. A bottom  22   a  is horizontal similarly to embodiment 1 and embodiment 2. 
     Since other structure is the same as that of embodiment 1, the description will be omitted. 
     Next, the operation of embodiment 5 will be described. 
     The overhang of the guide unit  22  of embodiment 5 is up to a halfway position in the width direction of a passage  18  similarly to embodiment 1, and the bottom  22   a  is horizontal similarly to embodiment 1 and embodiment 2. Besides, since a guide surface  22   b  is structured to have an inclined surface similar to that of embodiment 2, the same operation and effect as those of embodiment 1 and embodiment 2 can be obtained. 
     Embodiment 6 
       FIG. 12  is a perspective view of a containing unit showing a guide unit of embodiment 6. Incidentally, since a structure other than the shape of a guide unit  22  is the same as that of embodiment 1, the description of redundant portions will be omitted. 
     The guide unit  22  has a sectional shape which is an inverted trapezoidal shape when viewed in a passage  18  direction, and is formed to overhang the whole length of the passage  18  in the width direction. The guide unit  22  has the same structure as that of embodiment 1 from a wall surface  24  to a halfway position of the passage  18  in the width direction, and has the same structure as that of embodiment 3 from the halfway position of the passage  18  in the width direction to a side wall of a containing unit  16 . Accordingly, a bottom  22   a  of the guide unit  22  is horizontal from the wall surface  24  to the halfway position of the passage  18  in the width direction and is an inclined surface which rises from the halfway position of the passage  18  in the width direction to the side wall direction of the containing unit  16 . 
     Since other structure is the same as that of embodiment 1, the description will be omitted. 
     Next, the operation of embodiment 6 will be described. 
     As described above, since the guide unit  22  of embodiment 6 has the same structure as that of embodiment 1 from the wall surface  24  to the halfway position of the passage  18  in the width direction, and has the same structure as that of embodiment 3 from the halfway position of the passage  18  in the width direction to the side wall of the containing unit  16 , the same operation and effect as those of embodiment 1 and embodiment 3 can be obtained. 
     Embodiment 7 
       FIG. 13  is a perspective view of a containing unit showing a guide unit of embodiment 7. Incidentally, since a structure other than the shape of a guide unit  22  is the same as that of embodiment 1, the description of redundant portions will be omitted. 
     The guide unit  22  is formed such that a wall surface  24  opposite to a discharge port  14  in a passage  18  overhangs by a specified amount in the discharge port  14  direction, has the same structure as that of embodiment 1 from the wall surface  24  to a halfway position of the passage  18  in the width direction, and has the same structure as that of embodiment 4 from the halfway position of the passage  18  in the width direction. 
     Since other structure is the same as that of embodiment 1, the description will be omitted. 
     Next, the operation of embodiment 7 will be described. 
     As described above, since the guide unit  22  of embodiment 7 has the same structure as that of embodiment 1 from the wall surface  24  to the halfway position of the passage  18  in the width direction, and has the same structure as that of embodiment 4 from the halfway position of the passage  18  in the width direction, the same operation and effect as those of embodiment 1 and embodiment 4 can be obtained. 
     Embodiment 8 
       FIG. 14  is a perspective view of a containing unit showing a guide unit of embodiment 8. Incidentally, since a structure other than the shape of a guide unit  22  is the same as that of embodiment 1, the description of redundant portions will be omitted. 
     The guide unit  22  is formed to overhang the whole length of a passage  18  in the width direction, a bottom  22   a  has the same structure as that of embodiment 3, and a guide surface  22   b  has the same structure as that of embodiment 2. 
     Since other structure is the same as embodiment 1, the description will be omitted. 
     Next, the operation of embodiment 8 will be described. 
     In the guide unit  22  of embodiment 8, as described above, since the bottom  22   a  has the same structure as that of embodiment 3 and the guide surface  22   b  has the same structure as that of embodiment 2, the same operation and effect as those of embodiment 3 and embodiment 2 can be obtained. 
     Embodiment 9 
       FIG. 15  is a perspective view of a containing unit  16  showing a guide unit  22  of embodiment 9. Incidentally, since a structure other than the shape of a guide unit  22  is the same as embodiment 1, the description of redundant portions will be omitted. 
     The guide unit  22  is formed to overhang the whole length of a passage  18  in the width direction, and has a fan-like shape in a sectional view when viewed from above. 
     Since other structure is the same as embodiment 1, the description will be omitted. 
     Next, the operation of embodiment 9 will be described. 
     As described above, the guide unit  22  of embodiment 9 has the fan-like shape in the sectional view when viewed from above, and this is the structure in which the width of the passage  18  is gradually narrowed in a discharge port  14  direction from the upstream side to the downstream side when viewed in the passage  18  direction, and is almost the same structure as that of embodiment 2 though there is a difference between an arc shape and a straight-line shape. Besides, a guide surface  22   b  is arc-shaped similarly to embodiment 4, and by this, the same operation and effect as those of embodiment 2 and embodiment 4 can be obtained. 
     Incidentally, although the guide unit  22  of from embodiment 1 to embodiment 9 is formed such that the upper wall surface in the passage  18  at the wall surface  24  side opposite to the discharge port  14  is partially lowered, no limitation is made to this shape. For example, the shape may be such that the wall surface  24  projects in the discharge port  14  direction, and a gap is formed between the upper surface of the guide unit  22  and the upper wall surface. 
     Embodiment 10 
       FIG. 16 ,  FIG. 17  and  FIG. 18  are structural views of a developing unit of embodiment 10.  FIG. 16  is a plan view in which a developing unit of embodiment 10 is cut in the horizontal direction at the center of a discharge port in the vertical direction,  FIG. 17(   a ) is a side view of the developing unit at the discharge port side,  FIG. 17(   b ) is a C-C sectional view of  FIG. 17(   a ), and  FIG. 18  is a perspective view showing only a containing unit of  FIG. 17(   b ). Incidentally, since a structure other than the shape of the guide unit  22  is the same as that of embodiment 1, the description of redundant portions will be omitted. 
     The guide unit  22  is formed of a projection projecting from an upper wall surface of a passage  18 , and is formed to have a specified length in a passage direction so that an upper part of the passage  18  is divided by the guide unit  22  into a part at a discharge port  14  side and a part at a wall surface  24  side opposite to the discharge port  14 . The length of the guide unit  22  is set to be longer than at least the length of the discharge port  14  in the passage direction similarly to embodiment 1. Besides, the guide unit  22  is provided so that the width of a passage L 2  at the wall surface  24  side in the passage  18  is narrower than the width of a passage L 1  at the discharge port  14  side. 
     Since other structure is the same as that of embodiment 1, the description will be omitted. 
     Next, the operation of embodiment 10 will be described. 
     In embodiment 10, only the flow state of a developer in the vicinity of the guide unit  22  is different from that of embodiment 1, and the others are same, and accordingly, only the flow state of the developer in the vicinity of the guide unit  22  will be described. 
     In the case where the use environment of the developer is the normal environmental state, the developer flowing to the vicinity of the guide unit  22  is divided by the guide unit  22 , however, since the fluidity of the developer is excellent, the developer smoothly flows in the passage L 1  and the passage L 2 , and the developer is excellently discharged through the discharge port  14 . 
     Next, in the case where the use environment of the developer is a high humidity state, since the fluidity of the developer is poor, as indicated by an arrow in  FIG. 16 , the developer flowing to the vicinity of the guide unit  22  flows more to the passage L 1  which has the wide passage width and facilitates the flow as compared with the passage L 2 . By this, a developer surface B ( FIG. 17 ) at the discharge port  14  side rises, and the flow of the developer toward the discharge port  14  occurs by the split flow by the guide unit  22 . By this, since the developer becomes easy to be discharged through the discharge port  14 , even in the state where the use environment is the high humidity and the fluidity of the developer is poor, it can be excellently discharged. 
     Next, based on  FIG. 19 , a copying machine as an image forming apparatus in which the developing unit  10  of the embodiment is mounted will be described. 
     A copying machine  34  includes a combination panel  42  provided with a copy button  36  for copying, a copy number button  38  to input the number of copies, a display  40  to display information of the copying machine  34 , and the like. In addition, there are provided a CPU  44  to control copying, a memory  46  to store data necessary for performing the control, a photoconductive body (image bearing body, image bearing means)  48 , a charging device (charging unit, charging means)  50  to charge the photoconductive body  48 , an exposure device (electrostatic latent image forming unit, electrostatic latent image forming means)  52  to form an electrostatic latent image on the photoconductive body  48 , the developing unit  10  to supply a developer to the electrostatic latent image by a developing roller  12  and to develop the electrostatic latent image, an electricity removal device  54  to remove electricity on the surface of the photoconductive body  48 , a transfer device (transfer unit, transfer means)  56  to transfer a toner image from the photoconductive body  48  to a sheet (transfer member)  62 , a cleaner device (cleaning unit)  58  to remove residual toner on the photoconductive body  48  by a blade, and a fixing device (fixing unit, fixing means)  60  to fix the toner to the sheet  62 . 
     A process cartridge is constructed of at least one of the developing unit  10 , the charging device  50  and the cleaner device  58  and the photoconductive body  48 , and the process cartridge is detachably mounted to a main body of the copying machine  34 . 
     Next, the operation at the time of recording will be described. 
     When the number of copies is inputted by the copy number button  38  of the combination panel  42 , and the copy button  36  is pressed, the operation of image formation starts based on image information from a not-shown scanner. 
     The surface of the photoconductive body  48  is charged by the charging device  50  under the control of the CPU  44 , exposure according to an image is performed by the exposure device  52 , and an electrostatic latent image is formed on the photoconductive body  48 . The electrostatic latent image on the photoconductive body  48  is developed by the developer on the developing roller  12  of the developing unit  10 , and a developer image is formed on the photoconductive body  48 . The developer always well stirred by the stirring and transporting member  20  is transported to the developing roller  12 . 
     The developer image formed on the photoconductive body  48  is electrostatically transferred by the transfer device  56  onto the transported sheet  62 , and next, it is fixed to the sheet  62  by heat and press in the fixing device  60 . By this, a specified image is formed. 
     Besides, with respect to the photoconductive body  48  after the transfer to the sheet  62 , the residual toner is removed by the cleaner device  58  having a blade, and electricity is removed by light irradiation from the electricity removal device  54 . 
     The operation is repeated by the inputted number of copies and the copying is ended. 
     Toner of an amount equivalent to the consumption by the development is supplied from the hopper  32  into the developing unit  10 . Thus, although a trace amount of carrier is supplied at the same time as the toner, the increase is discharged through the discharge port  14  by overflow, and is stored in a not-shown waste developer container. As stated above, the deteriorated developer is replaced by a new developer, so that the developing performance is kept and a reduction in picture quality can be suppressed. 
     Besides, in this embodiment, the toner density in the developing unit  10  is detected by a toner density sensor  28  to perform magnetic detection, the supply amount of toner is determined according to the output of the toner density sensor  28 , and the supply amount of developer is controlled. 
     The respective operations are repeated, and the copying is performed. 
     Although the invention has been described with the specific aspect, it would be obvious for one skilled in the art that various modifications and improvements can be made insofar as they do not depart from the spirit and scope of the invention. 
     As described above in detail, according to the invention, it is possible to provide the developing unit and the developer stirring and transporting method in which the amount of developer in the developing unit can always be kept at a specified amount without being influenced by the use environment.