Patent Publication Number: US-6987940-B2

Title: Developing apparatus

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to a developing apparatus for use in a copying machine, a printer, a facsimile apparatus or the like using an electrophotographic process or an electrostatic recording process. 
   2. Description of Related Art 
   Heretofore, in multi-color image forming, use has been made of a technique of forming a plurality of colors of toner images successively, for example, on an electrophotographic photosensitive member (photosensitive member) which is an image bearing member, and successively or collectively superimposing the plurality of colors of toner images onto a transfer medium such as recording paper. 
   In such a multi-color image forming apparatus, there has heretofore been proposed and put into practical use a so-called rotary developing process of mounting developing devices for black, yellow, magenta and cyan, for example, on a rotary type developing member, and rotating this rotary type developing member to thereby successively move the necessary developing devices to a developing position opposed to the photosensitive member which is the image bearing member and perform a developing operation. 
   On the other hand, in image forming apparatuses of a conventional electrophotographic type or electrostatic recording type, above all, particularly in a multi-color image forming apparatus for effecting colored image forming, use has widely been made of a two-component developing process using chiefly a mixture of a nonmagnetic toner and a magnetic carrier as a developer. The two-component developing process, as compared with other developing processes being proposed at present, has merits such as the stability of image quality and the durability of the apparatus. On the other hand, in the two-component developing process, the deterioration of the developer due to a long period of endurance, particularly the deterioration of the carrier, has been unavoidable and therefore, with the long period of use of the apparatus, the work of interchanging the developer has become necessary, and this has brought about an increase in service cost and running cost. 
   Several methods of solving such a problem have heretofore been proposed. For example, there is a developing device loaded with an interchangeable developer supplying cartridge to thereby effect the supply of a developer including a toner and a carrier, and the collection of the developer (see Japanese Patent Application Laid-Open No. 6-308829). 
   In this developing device, however, there is adopted structure using a plurality of screws to collect the developer overflowing from the developing device into the developer supplying cartridge and therefore, the apparatus becomes large-scaled, and a control mechanism also becomes complicated. Also, when the developing device of such a construction and the developer supplying cartridge are carried on a rotary type developing member, the diameter of the rotary type developing member becomes large and the apparatus becomes bulky. Further, a developer conveying route is complicated, and when the rotary type developing member is rotated, the developer may leak. 
   So, particularly in the rotary developing process, there has been put into practical use a developer discharging process of utilizing a change in the acting direction of gravity resulting from the rotational motion of the rotary type developing member to supply a two-component developer to the developing device, and discharge the two-component developer from the developing device. 
   For example, Japanese Patent Application Laid-Open No. 9-218575 discloses a rotary developing process designed such that as shown in  FIG. 6  of the accompanying drawings, a developer including an amount of toner consumed by a developing operation at a developing position P 1  opposed to a photosensitive drum  201  is supplied to a developing device  210 , and any excessive developer in the developing device  210  is discharged to a developer cartridge  220  through a discharge port  221 , a transport tube  222  and a collection port  223  by the utilization of a change in the acting direction of gravity by the rotation of a rotary type developing member  204 . That is, this process is simple in structure because movement peculiar to the rotary type developing member  204  is utilized to effect the supply and collection of the developer, and a reduction in charging capability for a carrier is prevented without causing the bulkiness and a rise in the cost of the apparatus. 
   On the other hand, Japanese Patent Application Laid-Open No. 10-142888 discloses a rotary developing process designed such that as shown in  FIG. 7  of the accompanying drawings, a developer discharged from a developing device  310  through a discharge port  321  at a developing position P 1  whereat the developing device  310  is opposed to a photosensitive drum  301  is temporarily stored in a storing portion  322 , and by the utilization of a change in the acting direction of gravity by the rotation of a rotary type developing member  304 , the developer in the storing portion  322  is transported to a cylindrical shaft  323  at the center of the rotary type developing member  304  through a collection port  323   a , and is finally collected into a developer collecting container (not shown) at an end portion of the cylindrical shaft  323  by a developer transporting member  323   b  in the cylindrical shaft  323 . That is, as in an image forming apparatus proposed in Japanese Patent Application Laid-Open No. 9-218575, movement peculiar to the rotary type developing member  304  is utilized to effect the discharge of the developer. Therefore, a reduction in charging capability for a carrier is prevented without causing the bulkiness of the apparatus. In addition, design is made such that even when single-color image forming is continued, the developing operation is not stopped, but at the developing position, the excessive developer in the developing device  310  is discharged to the storing portion  322  outside the developing device  310  and therefore, the lowering of image productivity is suppressed to a certain extent, and the amount of developer in the developing device  310  is maintained within an allowable value. 
   The above-described examples of the conventional art, however, have suffered from the following problems. 
   In the midst of recent years when the market of full-color copying machines/printers has been enlarged and various functions are required, there have been commercialized many image forming apparatuses having been downsized and reduced in cost, and yet seeking for high image productivity, and this seems to become one of the mainstreams of the market in the future, too. 
   In the image forming apparatus described in the above-mentioned Japanese Patent Application Laid-Open No. 9-218575, the rotational motion of the rotary type developing member  204  is utilized to discharge the deteriorated developer to the developer cartridge and therefore, structure is simple and the bulkiness and high cost of the apparatus are not caused and the deteriorated developer is gradually replaced with a fresh developer, to thereby stabilize the characteristic as the whole of the developer. Therefore, the interchange of the developer becomes unnecessary and maintenance property is improved. However, at the developing position P 1 , the excessive developer in the developing device  210  is not discharged to the outside of the developing device  210  and therefore, particularly when single-color high density images are continuously formed, in order to prevent any increase in the amount of developer in the developing device  210 , the developing operation must be stopped in spite of images being formed and the operation of discharging the developer, i.e., the operation of rotating the rotary type developing member  204 , must be performed, and a great reduction in image productivity could not be avoided. 
   On the other hand, in an image forming apparatus described in the above-mentioned Japanese Patent Application Laid-Open No. 10-142888, the deteriorated developer is discharged into the collecting container provided at an end portion of the cylindrical shaft  323  of the rotary type developing member  304  and is gradually replaced with a fresh developer to thereby stabilize the characteristic as the whole of the developer. Thus, the interchange of the developer becomes unnecessary and maintenance property is improved and in addition, design is made such that at the developing position P 1 , the excessive developer in the developing device  310  is discharged to the storing portion  322  outside the developing device  310  and therefore, during continuous single-color image forming, the developer can be stably discharged without the rotary type developing member  304  being rotated up to a certain degree of amount of excessive developer discharge. Accordingly, within the allowable range thereof, image productivity is not lowered due to the developer discharging operation. 
   Again in this image forming apparatus, however, as in the image forming apparatus described in the above-mentioned Japanese Patent Application Laid-Open No. 9-218575, basically a change in the direction of gravity by the rotative movement of the rotary type developing member  304  is utilized to discharge the developer to the collection port  323   a , and make the developer fall and therefore, when the discharged developer is too much stored in the storing portion  322  (exceeds the aforementioned allowable range), the discharging operation cannot be performed any further. 
   Therefore, particularly when single-color high-density images are continuously formed, in order to prevent any increase in the amount of developer in the storing portion  322 , the developing operation must be stopped in spite of images being formed, and the operation of discharging the developer, i.e., the operation of rotating the rotary type developing member  304 , must be performed. Thus, a great reduction in image productivity could not be avoided. 
   Also, the storing portion  322  must be discretely provided in the developing device  310  and therefore, a plurality of members unnecessary for ordinary image forming must be provided, and the complication and a rise in the cost of the apparatus could not be avoided. 
   Now, heretofore, in image forming apparatuses of an electrophotographic type having a rotary type developing member, there has often been seen a construction in which a developer bearing member provided in a developing device is made to wait at a phase position (so-called home position) in which it is not opposed to a photosensitive member so that when an image forming operation is not being performed, the photosensitive member may not be adversely affected by the strong magnetic force of the developer bearing member provided in the developing device. 
   Also, when there is adopted a construction in which a developer cartridge comprising a toner bottle is detachably mounted on the rotary type developing member, there is a case where the phase position at which the developer bearing member is stopped and waits in order to interchange the developer cartridge is provided at a phase position discrete from the above-described developing position or home position stop and waiting position. 
   When such a construction is adopted, besides a “development stopping position” which is the stop position of the rotary type developing member when a developing device for each color is disposed at the developing position, the stop and waiting positions of a plurality of rotary type developing members become necessary. For example, the stop positions of developing device provided in a rotary type developing member holding developing devices for four colors are not restricted to four locations of 90 degrees, 180 degrees, 270 degrees and 360 degrees from the developing position which is at 0 degree, but cannot help having a plurality of stop positions besides them. 
   However, both of the image forming apparatuses described in the above-mentioned Japanese Patent Application Laid-Open No. 9-218575 and Japanese Patent Application Laid-Open No. 10-142888 are of a construction in which a change in the direction of gravity by the rotative movement of the rotary type developing member is utilized to make the excessive developer fall to the destination of discharge and therefore, as the rotation stopping positions are increased, a discharging mechanism becomes more unstable, whereby there are cases where unexpected discharge is effected, and it becomes difficult to maintain a high quality of image. 
   Particularly, in the image forming apparatuses having a rotary type developing member, the shortening of a changeover time for this rotary type developing member has been advanced in order to cope with the high productivity in recent years. In this case, the shock force when the rotation of the rotary type developing member is started and stopped tends to become great, but in other rotation modes than a continuous image forming operation, it is often the case that an acceleration and deceleration curve is set to a slow one in order to make the shock force small. When as described above, the image forming apparatus has a rotation mode for a plurality of rotary type developing members, the instability of a discharging mechanism resulting from the above-described increase in the rotation stopping positions tends to be further promoted. 
   This is because during a continuous image forming operation, the aforedescribed development stopping position visits periodically and stably, whereas the “home position waiting position” is for stopping and waiting only after the termination of a job and the “developer cartridge interchange stopping and waiting position” is for stopping and waiting only when the toner in the cartridge has become little. If an attempt is made to include all these conditions and obtain a stable discharge characteristic of the developer, it has required much difficulty in setting the conditions. 
   That is, in the conventional art, the work of interchanging the developer becomes unnecessary and maintenance property is improved, but it is difficult to obtain a stable high image quality maintaining characteristic, and particularly taking into account a case where single-color high-density images continue or the like, it has been very difficult to realize all of the simplification and reduced cost of the apparatus and high image productivity at a time. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a developing apparatus, which can realize a high maintenance property and high image productivity by a simple construction. 
   Further objects of the present invention will become apparent from the following detailed description when read with reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic cross-sectional front view of an image forming apparatus according to Embodiment 1. 
       FIG. 2  is a schematic cross-sectional front view of a rotary developing device provided in the image forming apparatus of FIG.  1 . 
       FIG. 3  is a schematic cross-sectional front view of a developing device provided in the rotary developing device of FIG.  2 . 
       FIG. 4  is a top developed view illustrating the developing device of FIG.  3 . 
       FIGS. 5A ,  5 B,  5 C and  5 D are illustrations for illustrating a developer discharging operation. 
       FIG. 6  is a schematic cross-sectional front view of an example of a conventional rotary type developing member. 
       FIG. 7  is a schematic cross-sectional front view of another example of the conventional rotary type developing member. 
       FIG. 8  is a schematic cross-sectional front view of an image forming apparatus according to Embodiment 2. 
       FIG. 9  is a schematic cross-sectional front view of a rotary developing device provided in the image forming apparatus. 
       FIG. 10  is a schematic cross-sectional front view of a developing device provided in the rotary developing device of FIG.  9 . 
       FIG. 11  is a top developed view illustrating the developing device of FIG.  10 . 
       FIG. 12  is a schematic perspective view illustrating the discharge port and shutter member of the developing device of FIG.  10 . 
       FIGS. 13A ,  13 B and  13 C are illustrations for illustrating an example of the rotated state of a rotary developing device according to the present invention. 
       FIGS. 14A ,  14 B and  14 C are illustrations for illustrating another example of the rotated state of the rotary developing device according to the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   A rotary type developing member and an image forming apparatus according to the present invention will hereinafter be described in detail with reference to the drawings. 
   Embodiment 1 
     FIG. 1  shows a schematic cross-sectional view of an embodiment of the image forming apparatus according to the present invention. The image forming apparatus  100  of the present embodiment is a multi-color image forming apparatus (color copying machine) provided with a rotary type developing member. 
   The image forming apparatus  100  of the present embodiment has a rotary developing device  104  which is a rotary type developing member most characteristic in the present embodiment. Also, an image forming apparatus main body (apparatus main body) A is provided with a reader portion R provided with an original supporting stand  110 , a light source  111 , a mirror system  112 , a lens system  113  and a CCD unit  114 , a paper feeding portion V, an image forming portion I, etc. The paper feeding portion V has cassettes  115  and a manually feeding cassette  116  containing transfer materials S such as recording sheets or OHP sheets therein and detachably mountable on the apparatus main body A, and the transfer materials S are supplied from these cassettes  115  and the manually feeding cassette  116 . 
   In the image forming portion I, there are disposed a cylindrical electrophotographic photosensitive member, i.e., a photosensitive drum  101  as an image bearing member, a primary charging device  102  as charging means for charging the photosensitive drum  101 , a rotary developing device  104  ( FIG. 2 ) containing therein a plurality of developing devices (developing means)  11  made integral with one another by a developer cartridge  6  being mounted thereon, a post-charging device  117  for adjusting the quality of an image after being developed, an endless ring-shaped transfer belt  105  which is an intermediate transfer member for superimposing and transfer-forming, for example, toner images of four colors, and thereafter transferring a multi-color image to the transfer material S, a drum cleaner  108  for removing any toners (untransferred toners) residual on the photosensitive drum  101  after the transfer, a secondary transfer roller  107  as secondary transferring means for transferring the toner images from the transfer belt  105  to the transfer material S in a secondary transferring portion N 2 , a belt cleaner  118  for removing any untransferred toners on the transfer belt  105 , etc. The transfer belt  105  is passed over a plurality of rollers and is endlessly moved. At a position opposed to the photosensitive drum  105  with the transfer belt  105  interposed therebetween, there is disposed a primary transfer roller  106  which is primary transferring means for transferring the toner images from the photosensitive drum  101  to the transfer belt  105 , and it forms a primary transferring portion N 1 . 
   As shown in  FIG. 2 , in the present embodiment, the rotary developing device  104  has, in a rotary  104   a  which is a rotatable developing device supporting member, developing devices for four developing colors, i.e., a developing device  11 K for black, a developing device  11 Y for yellow, a developing device  11 M for magenta, and a developing device  11 C for cyan. The rotary developing device  104  is rotated in the counter-clockwise direction of arrow “a” around a cylindrical rotary shaft (cylinder shaft)  104   b , and when necessary, moves a developing device for a desired color to a developing position P 1  opposed to the photosensitive drum  101 . 
   Upstream of the image forming portion I in the transport route of the transfer material S, there are provided registration rollers  122  for enhancing the posture and position accuracy of the transfer material S supplied from the cassette  115  or the manually feeding cassette  116  in the paper feeding portion V through a pickup roller  119 , transport rollers  120  and a transport path  121 , and feeding out the transfer material S in timed relationship with the toner images on the transfer belt  105 . Also, downstream of the image forming portion I, there are disposed a transporting apparatus  123  for transporting the transfer material S to which the toner images have been transferred, a fixing apparatus  124  for fixing an unfixed image on the transfer material S, delivery rollers  124  for delivering the transfer material on which the image has been fixed out of the apparatus main body A, etc. 
   While in the present embodiment, the construction of a four-color rotary is shown as an example of the rotary developing device  104 , the number of the developing devices carried on the rotary is of course not restricted thereto from the gist of the present invention. 
   The operation of the image forming apparatus  100  of the present embodiment will now be described. When a paper feed signal is outputted from a control apparatus (not shown provided in the apparatus main body A for generally controlling the operation of the image forming apparatus  100 , a transfer material S is supplied from the cassette  115  or the manually feeding cassette  116 . On the other hand, light applied from the light source  111  in the reader portion R to an original D placed on the original supporting stand  110  is once read by the CCD unit  114 , and thereafter is converted into an electrical signal. This signal is replaced with a laser beam L from a laser scanner unit  103  as exposure means provided in the image forming portion I, and is applied onto the photosensitive drum  101  rotated in the counter-clockwise direction of arrow R 1 . The photosensitive drum  101  is charged in advance by the primary charging device  102 , and an electrostatic latent image is formed thereon by the light being applied thereto. Thereafter, a toner image of a selected color is formed by the plurality of developing devices  11  disposed in the rotary developing device  104 . 
   The toner image formed on the photosensitive drum  101  has its potential adjusted by the post-charging device  117 , and is soon transferred onto the transfer belt  105  by the action of a primary transferring bias voltage applied to the primary transfer roller  106  in the primary transferring portion N 1 . The toner image transferred onto the transfer belt  105 , in the case of a color mode, goes toward the primary transferring portion N 1  by the transfer belt  105  making one more rotation so that the next toner image may be formed and transferred. In the meantime, the rotary developing device  104  is rotated in the counter-clockwise direction of arrow “a” so that the developing device for the next designated color may be opposed to the photosensitive drum  101 , and is prepared to develop the next electrostatic latent image. 
   Thus, in a full-color mode, the steps of forming and developing an electrostatic latent image and transferring a toner image are repeated until a predetermined image (color) number of toner images have been successively transferred to the transfer belt  105 . 
   On the other hand, the transfer material S fed from the paper feeding portion V has its skew feed corrected by the registration rollers  122 , and is further adjusted in timing and is fed to the image forming portion I. Then, by the action of a secondary transferring bias voltage applied to the secondary transfer roller  107 , the toner images are transferred from the transfer belt  105  to the transfer material S. 
   Thereafter, the transfer material S separated from the transfer belt  105  is transported to the fixing apparatus  109  by the transporting apparatus  123 , and the unfixed transferred image is permanently fixed on the transfer material S by heat and pressure. The transfer material S on which the image has been fixed is delivered out of the apparatus main body A by the delivery rollers  124 . 
   In this manner, an image is formed on the transfer material S fed from the paper feeding portion V and the transfer material is delivered. Also, any untransferred toners, etc. residual on the photosensitive drum  101  after the toner images have been transferred are removed by the drum cleaner  108 , and any untransferred toners, etc. residual on the transfer belt  105  are removed by the belt cleaner  118 , and the photosensitive drum  101  and the transfer belt  105  are repetitively used for image forming. 
   The rotary developing device (rotary type developing member) of the present embodiment will now be further described. 
   As shown in  FIG. 2 , in the present embodiment, the rotary developing device  104  has the developing device  11 K for black, the developing device  11 Y for yellow, the developing device  11 M for magenta and the developing device  11 C for cyan in the rotary  104   a  which is a rotatable developing device supporting member. The rotary developing device  104  is freely rotatable about the rotary shaft (cylinder shaft)  104   b  by a motor (not shown) as driving means provided in the apparatus main body A. 
   When for example, a black toner image is first to be formed on the photosensitive drum  101 , development is effected by the developing device  11 K for black at the developing position P 1  proximate to the photosensitive drum  101 , and when next, a yellow toner image is to be formed, the rotary developing device  104  is rotated by about 90° in the counter-clockwise direction of arrow “a” in  FIG. 2  to thereby dispose the developing device  11 Y for yellow at the developing position P 1 , thus effecting development. When a magenta toner image and a cyan toner image are also to be formed, the rotary developing device  104  is further rotated by about 90° each in a similar manner to thereby dispose the corresponding developing device at the developing position P 1 , thus effecting development. 
   When single-color image forming is to be effected, a toner image formed on the photosensitive drum  101  by a developing device containing a desired toner therein is primary-transferred onto the transfer belt  105 , and thereafter is immediately secondary transferred onto the recording paper S. Thereafter, the recording paper S stripped off from the transfer belt  105  is transported by the transporting apparatus  123 , and is pressurized/heated by the fixing apparatus  124 , whereby a permanent image is formed on the surface of the recording paper S. The single-color image forming by this process is higher by four times or so in image productivity than full-color image forming. 
   Here, the developing devices  11  provided in the rotary developing device  104  will be further described with reference to  FIGS. 3 and 4 . In the present embodiment, the developing device  11 K for black, the developing device  11 Y for yellow, the developing device  11 M for magenta and the developing device  11 C for cyan are substantially of the same construction except for the colors of the developers. Accordingly, in the following description, when the developing devices for the respective colors need not be particularly distinguished from one another, the suffixes K, Y, M and C given to show that they are elements belonging to the developing devices for the respective colors will be omitted. 
   The developing device  11  contains therein a two-component developer (developer) chiefly provided with a nonmagnetic toner (toner) and a magnetic carrier (carrier), and in the present embodiment, the density of the toner in the developer in its initial state is of the order of 8% in terms of weight ratio. This value is one which should be properly adjusted in accordance with the charging amount of the toner, the particle diameter of the carrier, the construction of the multi-color image forming apparatus, etc., and is not always restrictive. 
   The developing device  11  opens at a developing area opposed to the photosensitive drum  101 , and a developing sleeve  8  as a developer bearing member is rotatably disposed in such a manner as to be partly exposed in this opening portion. The developing sleeve  8  containing therein a stationary magnet which is magnetic field generating means is formed of a nonmagnetic material, and during the developing operation, it is rotated in the counter-clockwise direction of arrow “b” in  FIG. 3 , retains thereon the developer in the developing device  11  in the form of a layer and bears and transports it, and supplies the developer to the developing area opposed to the photosensitive drum  101  to thereby develop the electrostatic latent image on the photosensitive drum  101 . The developer on the developing sleeve  8  after it has developed the electrostatic latent image is transported in accordance with the rotation of the developing sleeve  8  and is collected into the developing device  11 . 
   The developer in the developing device  11  is circulated in a developing device  11  by a first developer circulating screw  7   a  (a side near to the developing sleeve  8 ) and a second developer circulating screw  7   b  (a side far from the developing sleeve  8 ) which are developer agitating and transporting members, and is mixed and agitated. The first developer circulating screw  7   a  and the second developer circulating screw  7   b  are disposed substantially in parallel to the developing sleeve  8 , and the direction of circulation of the developer is a direction from this side toward the inner side in  FIG. 3  (the direction of arrow “c” in  FIG. 4 ) on the first developer circulating screw  7   a  side, and is a direction from the inner side toward this side in  FIG. 3  (the direction of arrow “d” in  FIG. 4 ) on the second developer circulating screw  7   b  side. In the developing device  11 , a partition wall  14  is provided so as to partition the space between the first developer circulating screw  7   a  and the second developer circulating screw  7   b  substantially in parallel to the respective developer circulating screws  7   a  and  7   b . The lengthwise end portions of the partition wall  14  do not reach the inner side wall of the developing device  11 , but communicating portions  13   a  and  13   b  are formed there. Through these communicating portions  13   a  and  13   b , the developer is delivered between the first developer circulating screw  7   a  and the second developer circulating screw  7   b.    
   When the developing device  11  performs the developing operation at the developing position P 1 , the two-component developer (developer) including a toner corresponding to the amount of toner consumed by image forming is supplied from a developer cartridge  6  as a developer supplying container connected to the developing device  11 , and at that time, the carrier of the order of 10% in terms of weight ratio is also supplied. That is, each time image forming is terminated, the carrier is supplied to the developing device  11 , and particularly when a high-density image is to be formed, a great deal of carrier amounting to the order of several tens of mg is supplied depending on the construction of the apparatus. Therefore, the amount of developer in the developing device  11  is increased and the surface (upper surface) of the developer becomes high. When the surface of the developer becomes higher by an allowable value or greater than the second developer circulating screw  7   b , the second developer circulating screw  7   b  cannot sufficiently agitate the developer and therefore, the toner immediately after supplied is not sufficiently charged and is transported to the first developer circulating screw  7   a , and is used for the developing operation. Therefore, toner fog occurs to the white ground portion of the image, and when the amount of developer is further increased, the developer overflows from the developing device  11  and the interior of the apparatus is contaminated. 
   In the present embodiment, the developing device  11  is provided with a developer supplying port (supplying port)  9  on one end side of the upper wall of the developing device  11  near the second developer circulating screw  7   b . Also, as will be described later in detail, the developing device  11  is provided with a developer discharging port (discharging port)  1  having a shutter member  3 , on the other end side of the upper wall thereof, and this discharging port communicates with one end portion of a developer discharging path (discharging path)  4 . The other end of the discharging path  4  communicates with a developer collecting port (collecting port)  2 . 
   When the developing device  11  is disposed at the developing position P 1 , the discharging port  1  is disposed substantially at the same height as the upper portion of the second developer circulating screw  7   b  and opens upwardly and therefore, it never happens that with an increase in the amount of the two-component developer in the developing device  11 , the surface (upper surface) of the developer becomes higher by the allowable value or greater than the second developer circulating screw  7   b.    
   As shown in  FIG. 4 , the discharging port  1  is disposed near the second developer circulating screw  7   b  and upstream of the supplying port  9  with respect to the direction of circulation of the developer. Therefore, the circulation of the developer near the developing sleeve  8  is not disturbed, and it never happens that the developer supplied just before is discharged. 
   The two-component developer containing a toner corresponding to the amount of toner consumed by image forming is supplied into the developing device  11  through the supplying port  9  by the rotational force of a supplying screw  10   a  which is developer supplying means provided in a developer supplying portion  10  and gravity. The developer to be supplied is supplied from a developer cartridge  6  as a developer supplying container to the developer supplying portion  10  through a developer supplying port (supplying port)  6   b . The supplying screw  10   a  transports the developer supplied from the supplying port  6   b  toward the supplying port  9  in accordance with the rotation thereof, and makes the developer fall into the developing device  11  by gravity. 
   The developer cartridge  6  is provided with a rotatable developer transporting member  6   a , and transports the developer therein toward the supplying port  6   b . The developer cartridge  6  is detachably mounted with respect to the developing device  11  and the rotary developing device  104 . By the developer cartridge  6  being mounted with respect to the developing device  11 , the supplying port  6   b  is adapted to communicate with the developer supplying portion  10  of the developing device  11 . In the present embodiment, the developer cartridge is of a substantially cylindrical shape. 
   The mixing ratio of the toner and the carrier in this supplied developer is of the order of 9:1 in terms of weight ratio in the present embodiment, but is not particularly restricted to this numerical value. That is, as compared with the ratio between the toner and the carrier in the developer in the developing device  11 , the amount of the toner is overwhelmingly great in the developer to be supplied, and considering the volume ratio, it can be considered that a slight amount of carrier is mixed with the toner. That is, when the toner consumed by image forming is to be made up for, a slight amount of carrier is gradually supplied. If the rate of the carrier in the developer to be supplied becomes great, the amount of replacement of the carrier becomes great by the same amount of toner supply and the two-component developer in the developing device  11  approximates to a fresh state, but correspondingly the consumed amount of carrier becomes great, and this leads to an increase in running cost. Therefore, it is preferable to discretely determine a suitable mixing ratio in each apparatus. 
   The supplied amount of the developer is roughly determined by the number of revolutions of the supplying screw  10   a , and this number of revolutions is determined by toner supply amount controlling means, not shown. As the toner supply amount controlling means, use can be made of one for calculating an amount of toner corresponding to the amount consumed by image forming as by counting, for example, the number of pixels of a formed image, and converting it into the number of revolutions of the supplying screw  10   a . Such toner supply amount controlling means itself is well known to those skilled in the art and therefore need not be described any further. 
   A description will now be made of a method of discharging any excess developer from the developing device  11  which is most characteristic in the present embodiment. 
   As shown in  FIG. 2 , the rotary developing device  104  in the present embodiment has the developer discharging port (discharging port)  1  disposed in the developing device  11  for discharging the excess developer, and the developer collecting port (collecting port)  2  disposed in the rotary  104   a  for collecting the excess developer. These are mentioned as the most characteristic portions in the present embodiment. 
   Also, in the present embodiment, the shutter member  3  for controlling the discharging position of the excess developer is provided near the discharging port  1  provided in the developing device  11 , and the developer discharging path (discharging path)  4  which is a communicating portion for communicating the discharging port  1  and the collecting port  2  with each other is also provided. 
   Provision is further made of a collected developer transporting portion (transporting portion)  5  for transporting the excess developer collected from the collecting port  2  to the outside of the rotary developing device  104 . In the present embodiment, the transporting portion  5  is formed in the interior of a cylinder shaft  104   b  which is the rotary shaft of the rotary developing device  104  (hereinafter referred to as the “collected developer transporting pipe (transporting pipe)”). As described above, the transporting portion  5  is formed in the interior of the rotary shaft  104   b  and is thereby provided near the central shaft of rotation of the rotary developing device  104 , whereby when the developer is to be collected and transported from the plurality of developing devices  11 , the rotary developing device  104  is made maximally compact and the disposition relationship between the developer discharging port  1  and the developer collecting port  2  which will be described later can be optimized. The present invention, however, is not restricted to a construction in which the rotary shaft functions as a collected developer transporting path. In the present embodiment, the collecting port  2  is an opening portion provided in the transporting pipe  5 . In the present embodiment, the collecting portion  2  is provided on one end portion side of the transporting pipe  5 . 
   In the interior of the transporting pipe  5 , a transporting member (not shown) which is a screw in the present embodiment is rotatably disposed to transport the collected developer, and design is made such that the collected developer can be transported to the outside of the rotary developing device  104  at any timing by drive transmitting means (not shown) provided in the apparatus main body A. The developer transported to the outside of the rotary developing device  104  through the transporting pipe  5  can be collected into a developer collecting container (not shown) or the like connected, for example, to lengthwise one end portion of the transporting pipe  5  and provided in the apparatus main body A. 
   The discharging path  4  is formed integrally with the rotary developing device  104 , and is disposed at a position corresponding to the developing device  11  for each color, and is rotated with the developing device  11  with the rotation of the rotary developing device  104 . On the other hand, the transporting pipe  5  is constructed discretely from the rotary developing device  104  (rotary  104   a ) and therefore, the collecting port  2  is an opening at only one location corresponding to the developing position P 1 . That is, only the discharging path  4  communicating with the developing device  11  disposed at the developing position P 1  by the rotation of the rotary developing device  104  is connected to the collecting port  2  provided in the transporting pipe  5 . 
   In the present embodiment, the shutter member has a shutter main body  3   a  which is a sealing portion of larger dimensions than the discharging port  1 . The shutter main body  3   a  has its one end portion fixed to a shutter rotary shaft  3   b , and is rotated about this shutter rotary shaft  3   b  by gravity to thereby open and close the discharging port. The shutter rotary shaft  3   b  is fixed for rotation relative to the inner wall of the developing device  11  near the discharging port  1  by a bearing member (not shown). That is, the shutter member  3 , as will be described later in detail, is rotated about the shutter rotary shaft  3   b  to thereby open and close the discharging port  1  from the inside of the developing device  11 . 
   The method of discharging the excessive developer will hereinafter be described in greater detail with reference also to  FIGS. 5A ,  5 B,  5 C and  5 D, with the developing device  11 K for black taken as an example. Such a discharging method also holds true of the developing devices for the other colors, namely, in the present embodiment, the developing device  11 Y for yellow, the developing device  11 M for magenta and the developing device  11 C for cyan. 
   As shown in  FIG. 5A , the discharging port  1 K is disposed substantially at the same height as the upper end of the second developer circulating screw  7   b , and when the developing device  11 K for black is at the developing position P 1 , the shutter member  3 K for opening and closing the discharging port  1 K, in the present embodiment, is in its opened state by gravity. Accordingly, when the surface of the developer becomes higher than the second developer circulating screw  7   b , the excessive developer overflows and is discharged from the discharging port  1 K, and the surface of the developer in the developing device  11 K for black is maintained substantially at the height of the second developer circulating screw  7   b . Therefore, it never happens that the toner fog to the white ground portion of the image and the overflow of the developer from the developing device  11 K for black as noted above occur. 
   Here, in the present embodiment, the positional relationship between the discharging port  1  and the collecting port  2  when the developing device  11  is at the developing position P 1  is characteristic. 
   That is, in accordance with the present invention, when the developing device  11  is at the developing position P 1 , the discharging port  1  is located above the collecting port  2 . Thus, the developer discharged from the discharging port  1  falls to the collecting port  2  along the discharging path  4  by gravity. Thus, at the developing position P 1 , the excess developer in the developing device  11  can be continuously discharged out of the developing device  11  at any time and therefore, particularly even in a case where the single-color image forming of high-density images is continued, the rotating operation of the rotary developing device  104  for discharging the developer is not required, and the amount of developer in the developing device  11  can be maintained within an allowable range. Therefore, it never happens that image productivity is lowered. 
   When the developing operation of the developing device  11 K for black is terminated, the rotary developing device  104  is rotated by about 90° in preparation for the developing operation by the developing device  11 Y for yellow which is the next color, and the developing device  11 K for black which has so far been at the developing position P 1  is moved to a position P 2  (FIG.  5 B). At this time, in the present embodiment, as shown in  FIG. 5B , the shutter member  3 K is rotatively moved by gravity and the discharging port  1 K becomes closed and therefore, it never happens that the developer in the developing device  11 K for black leaks out from the discharging port  1 K to the discharging path  4 K. This can also be mentioned as a very characteristic point in the present embodiment. 
   When the developing operation of the developing device  11 Y for yellow is terminated, the rotary developing device  104  is again rotated by about 90° in preparation for the developing operation by the developing device  11 M for magenta which is the next color, and the developing device  11 K for black is moved to a position P 3  (FIG.  5 C). At this time, as shown in  FIG. 5C , the shutter member  3 K still closes the discharging port  1 K by gravity and therefore, it never happens that the developer in the developing device  11 K for black leaks out from the discharging port  1 K to the discharging path  4 K. 
   When the developing operation of the developing device  11 M for magenta is terminated, the rotary developing device  104  is again rotated by about 90° in preparation for the developing operation by the developing device  11 C for cyan which is the next color, and the developing device  11 K for black is moved to a position P 3  (FIG.  5 D). At this time, as shown in  FIG. 5D , the shutter member  3 K still closes the discharging port  1 K by the pressure of the developer in the developing device  11 K for black and therefore, it never happens that the developer in the developing device  11 K for black leaks out from the discharging port  1 K to the discharging path  4 K. Even if the developer should leak out, it never happens owing to the action in the direction of gravity that the developer flows to the discharging path  4 K. 
   Owing to such a construction and method, not only at the rotation stop position of 90° each of the developing device  11 , but also when the rotary developing device  104  is stopped at other various stop positions such as the home position and the developer cartridge interchanging position as described with respect to the conventional art, the excess developer is always discharged only from the developing device  11  in a stable posture which is at the developing position P 1 , and is not discharged at any other phase position and therefore, there is realized an always stable discharging characteristic of the excess developer, and this contributes to the stability of a high quality of image. 
   Also, even when single-color continuous image forming using a developing device  11  is effected, it becomes possible to continue to collect the developer including the deteriorated carrier into the collecting port  2  by the utilization of the direction of gravity without rotatively moving the developing device  11  from the developing position P 1 , and excellent image quality maintaining stability can be realized without image productivity being lowered. 
   Further, there is not required such a complicated constituent member as a storing chamber for storing therein the excess developer discharged at the developing position P 1  until the rotation of the rotary developing device  104  is effected, and this means an inexpensive and stable construction. The work of interchanging the developer also becomes unnecessary and therefore, an improvement in maintenance property and a decrease in running cost can be realized. 
   Further describing, according to my studies, the deterioration of the developer due to its long-term use originates from two great causes, i.e., so-called toner-spent in which the toner is secured to the surface of the carrier, and so-called extraneous additive adherence in which an extraneous additive having drifted away from the toner adheres to the surface of the carrier. When the toner-spent and extraneous additive adherence to the surface of the carrier occur, a carrier surface area capable of charging the toner decreases and therefore, the charging amount of the toner is lowered. Therefore, there occur image defects such as an increase in image density and toner fog to a white portion, and the contamination of the image forming apparatus by the scattering of the toner. 
   According to the present embodiment, however, the developer including the deteriorated carrier is discharged out of the developing device  11  and is gradually replaced with a developer including a fresh carrier, whereby it becomes possible to stop the apparent progress of the deterioration of the carrier and stabilize the characteristic as the whole of the developer, and the stability of a high quality of image heightens. 
   On the other hand, in a rotation developing process as well, it is often the case that single-color continuous image forming is required. According to the present embodiment, at the developing position P 1  whereat the developing device  11  becomes proximate to the photosensitive drum  101 , the excessive developer in the developing device  11  is contained from the discharging port  1  into the collecting port  2  by gravity. Therefore, even during the single-color continuous image forming, it is possible to maintain the amount of developer in the developing device  11  within an allowable value without stopping the developing operation and therefore, the operation of rotating the rotary developing device  104  to discharge the developer in the developing device  11  becomes unnecessary, and image productivity is not lowered. In addition, use is not made of such a member and an apparatus unnecessary for ordinary image forming as a mechanism member for once storing the excessive developer therein and therefore, the complication and higher cost of the apparatus are not caused, and such an improvement in maintenance property as the interchange of the developer during service maintenance becoming unnecessary can be realized. 
   Also, according to the present embodiment, the discharging and collecting of the excessive developer can be done only at the developing position P 1 , and at the other phase positions of the developing device  11 , the shutter member  3  can suppress the discharging of the excessive developer. Thus, even in the case that the rotary developing device  104  has a plurality of rotation stop positions as in a construction wherein the developing sleeve  8  is stopped and waits at a home position whereat it is not opposed to the photosensitive drum  101  or a construction in which it is stopped and waits at a developer cartridge interchanging position, as has heretofore often been seen in an image forming apparatus having a rotary type developing member, the discharging and collecting of the developer can be done only at the developing position P 1 , and at the other phase positions of the developing device, the shutter member  3  can suppress the discharging of the developer. Consequently, even if the rotation stop positions are further increased, it never happens that the discharging mechanism becomes unstable and it becomes difficult to maintain a high quality of image. Accordingly, even in the case that the developing device exhibits, besides a development stop position visiting periodically and stably during a continuous image forming operation, such unstable stop position behavior as a home position waiting position visiting after the termination of a job, or a developer cartridge interchange stop waiting position at which the developing device is stopped and waits only when the toner in the developer cartridge  6  has become little, a stable developer discharging characteristic can be obtained and no trouble is required in the setting of a condition therefor. 
   As described above, according to the present embodiment, the high maintenance property that the interchange of the developer is unnecessary, and the high image productivity particularly when single-color image forming is continued can be realized by a simple construction. 
   It should be understood that the construction of the multi-color image forming apparatus described in the present embodiment is exemplification for describing the present invention, and the present invention is not restricted thereto, but various changes are possible within the scope of the present invention. For example, while in the above-described embodiment, the image forming apparatus adopts an intermediate transferring process, the present invention restricts the transferring process in no way, but may adopt the process of successively superimposing and transferring toner images on a recording material borne on a transfer material bearing member which is well known to those skilled in the art, or like process. 
   As described above, according to the above-described Embodiment 1, the high maintenance property that the interchange of the developer is unnecessary and high image productivity can be realized by a simple construction. Also, even in a case where a rotary type developing member having a plurality of developing devices is stopped at a plurality of phase positions, it becomes possible to maintain images of high quality always stably. 
   Embodiment 2 
     FIG. 8  is a schematic cross-sectional view of an image forming apparatus according to Embodiment 2. The image forming apparatus of the present embodiment is the same as that of the above-described embodiment except for some constructions, and the same members as those in the above-described embodiment are given the same reference characters, but a detailed description thereof will hereinafter be made again. 
   The image forming apparatus  100  of the present embodiment has a rotary developing device  104  which is a rotary type developing member most characteristic in the present embodiment. Also, an image forming apparatus main body (apparatus main body) A is provided with a reader portion R provided with an original supporting stand  110 , a light source  111 , a mirror system  112 , a lens system  113  and a CCD unit  114 , a paper feeding portion V, an image forming portion I, etc. The paper feeding portion V has cassettes  115  and a manually feeding cassette  116  containing transfer materials S such as recording paper or OHP sheets therein and detachably mountable with respect to the apparatus main body A, and the transfer materials S are supplied from these cassettes  115  and the manually feeding cassette  116 . 
   In the image forming portion I, there are disposed a cylindrical electrophotographic photosensitive member, i.e., a photosensitive drum  101 , as an image bearing member, a primary charging device  102  as charging means for charging the photosensitive drum  101 , a singly constructed developing device (developing means)  12  for black, a rotary developing device  104  ( FIG. 9 ) containing therein color developing devices (developing means)  11  for other three colors on which developer cartridges  6  are integrally mounted, a post-charging device  117  for adjusting the quality of an image after being developed, an endless ring-shaped transfer belt  105  which is an intermediate transfer member for superimposing, for example, toner images of four colors and transfer-forming a multi-color image thereon, and thereafter transferring the multi-color image to the transfer material S, a drum cleaner  108  for removing any toners (untransferred toners), etc. residual on the photosensitive drum  101  after the transfer, a secondary transfer roller  107  as secondary transferring means for transferring the toner image from the transfer belt  105  to the transfer material S at a secondary transferring portion N 2 , a belt cleaner  118  for removing any untransferred toners on the transfer belt  105 , etc. The transfer belt  105  is passed over a plurality of rollers and is endlessly moved. At a position opposed to the photosensitive drum  101  with the transfer belt  105  interposed therebetween, there is disposed a primary transfer roller  106  which is primary transferring means for transferring the toner images from the photosensitive drum  101  to the transfer belt  105 , whereby a primary transferring portion N 1  is formed. 
   As shown in  FIG. 8 , in the present embodiment, the developing device  12  for black and the rotary developing device  104  are disposed in the image forming portion I, and this rotary developing device  104  has the color developing devices for three colors, i.e., the developing device  11 Y for yellow, the developing device  11 M for magenta and the developing device  11 C for cyan. In the present embodiment, the construction of a three-color rotary is shown as an example of the rotary developing device  104 , but from the gist of the present invention, of course, the number of the developing devices carried on the rotary is not restricted thereto. 
   In the transport route of the transfer material S, on the upstream side of the image forming portion I, there are provided registration rollers  122  for enhancing the posture position accuracy of the transfer material S supplied from the cassette  115  or the manually feeding cassette  116  in the paper feeding portion V through the intermediary of a pickup roller  119 , transport rollers  120  and a transport path  121 , and feeding out the transfer material S in timed relationship with the toner images on the transfer belt  105 . Also, on the downstream side of the image forming portion I, there are disposed a transporting apparatus  123  for transporting the transfer material S to which the toner images have been transferred, a fixing apparatus  109  for fixing an unfixed image on the transfer material S, delivery rollers  124  for delivering the transfer material S on which the image has been fixed to the outside of the apparatus main body A. 
   A description will now be made of the operation of the image forming apparatus  100  of the present embodiment. When a paper feeding signal is outputted from a control apparatus (not shown) provided in the apparatus main body A for generally controlling the operation of the image forming apparatus  100 , a transfer material S is supplied from the cassette  115  or the manually feeding cassette  116 . On the other hand, light applied from the light source  111  in the reader portion R to an original D placed on the original supporting stand  110  and reflected by the original D is once read by the CCD unit  114 , and thereafter is converted into an electrical signal. This signal is replaced with a laser beam L from a laser scanner unit  103  as exposure means provided in the image forming portion I, and the laser beam L is applied onto the photosensitive drum  101  rotated in the counter-clockwise direction of arrow R 1  in FIG.  8 . The photosensitive drum  101  is charged in advance by the primary charging device  102 , and by the light being applied thereto, an electrostatic latent image is formed thereon. Then, for example, a black toner image is first formed by the developing device  11 K for black. 
   The black toner image formed on the photosensitive drum  101  has its potential adjusted by the post-charging device  117 , and is soon transferred onto the transfer belt  105  by the action of a primary transferring bias voltage applied to the primary transfer roller  106  at the primary transferring portion N 1 . In the case of the color mode, the toner image transferred to the transfer belt  105  goes toward the primary transferring portion N 1  by the transfer belt  105  being caused to make one more rotation so that the next toner image may be formed and transferred. In the meantime, the rotary developing device  104  rotates the developing device  11  for the next designated color of the color developing-devices contained therein in the counter-clockwise direction of arrow “a” in  FIG. 9  so as to be opposed to the photosensitive drum  101  in order to begin to be prepared for forming the first toner image, and is prepared to develop the next electrostatic latent image. 
   Thus, in a full-color mode, the steps of forming and developing the electrostatic latent image, and transferring the developed image are repeated until a predetermined image (color) number of toner images have been successively transferred to the transfer belt  105 . 
   On the other hand, the transfer material S fed from the paper feeding portion V has its skew feed corrected by the registration rollers  122 , and is further adjusted in timing and is sent to the image forming portion I. Then, by the action of a secondary transferring bias voltage applied to the secondary transfer roller  107 , the toner images are transferred from the transfer belt  105  to the transfer material S. 
   Thereafter, the transfer material S separated from the transfer belt  105  is transported to the fixing apparatus  109  by the transporting apparatus  123 , and the unfixed transferred image is permanently fixed on the transfer material S by heat and pressure. The transfer material S on which the image has been fixed is delivered out of the apparatus main body A by the delivery rollers  124 . 
   In this manner, an image is formed on the transfer material S fed from the paper feeding portion V and the transfer material S is delivered. Also, any untransferred toners, etc. residual on the photosensitive drum  101  after the toner images have been transferred are removed by the drum cleaner  108 , and any untransferred toners, etc. residual on the transfer belt  105  are removed by the belt cleaner  118 , and the photosensitive drum  101  and the transfer belt  105  are repetitively used for image forming. 
   The rotary developing device (rotary type developing member)  104  in the present embodiment will now be further described. 
   In the present embodiment, the rotary developing device  104  has the developing device  11 Y for yellow, the developing device  11 M for magenta and the developing device  11 C for cyan in a rotary  104   a  which is a rotatable developing device supporting member, and the rotary developing device  104  is freely rotatable about a rotary shaft (cylinder shaft)  104   b  by a motor (not shown) as driving means provided in the apparatus main body A. 
   As will be described later in detail, the rotary developing device  104  is stopped at a rotated position 60° short of a developing position P 1  at which the photosensitive drum  101  and the developing device  11 Y for yellow are in proximity to each other as an initial state ( FIGS. 14A ,  14 B and  14 C). This is for causing a developing sleeve  8  provided in the developing device  11  for each color to be stopped and wait at a phase position farthest from the photosensitive drum  101  so that the photosensitive drum  101  may not be adversely affected by the strong magnetic force of the developing sleeve  8  as a developer bearing member. 
   When for example, a full-color toner image is to be formed on the photosensitive drum  101 , the rotary developing device  104  is first rotatively moved by 60° in the counter-clockwise direction of arrow “a” in  FIG. 9  after the termination of the developing by the developing device  12  for black to thereby dispose the developing device  11 Y for yellow at the developing position P 1  whereat it is proximate to the photosensitive drum  101 , and effect developing. Next, in order to form a toner image of other color, the rotary developing device  104  is rotated by 120° to thereby dispose the developing device  11 M for magenta at the developing position P 1 , and likewise effect developing. Further, in order to form a cyan toner image, the rotary developing device  104  is further rotated by 120° to thereby effect developing in the same manner as described above. When the developing operations in the respective colors are terminated, the rotary developing device  104  is rotated by 60° to wait again at the home position, and comes to wait for the start of the next job. 
   When the forming of a black image (black-and-white image) is to be effected, a toner image formed on the photosensitive drum  101  by the developing device  12  for black containing a black toner therein is primary-transferred onto the transfer belt  105 , and thereafter is immediately secondary-transferred onto the recording paper S. Thereafter, the recording paper S stripped off from the transfer belt  105  is transported by the transporting apparatus  123 , and is pressurized heated by the fixing apparatus  109 , whereby a permanent image is formed on the surface thereof. The single-color image forming by this process is higher in image productivity by the order of four times than full-color image forming. 
   The construction of the color developing devices carried in the rotary developing device  104  will be further described here with reference also to  FIGS. 10 and 11 . In the present embodiment, the color developing devices  11 , i.e., the developing device  11 Y for yellow, the developing device  11 M for magenta and the developing device  11 C for cyan are substantially of the same construction except for the colors of the developers. Accordingly, in the following description, when it is unnecessary to particularly distinguish the developing devices for the respective colors from one another, the suffixes Y, M and C given to show that they are elements belonging to the developing devices for the respective colors are omitted. 
   The developing device  11  contains therein a two-component developer (developer) chiefly provided with a nonmagnetic toner (toner) and a magnetic carrier (carrier), and in the present embodiment, the density of the toner in the developer in its initial state is of the order of 8% in terms of weight ratio. This value should be properly adjusted depending on the charging amount of the toner, the particle diameter of the carrier, the construction of the multi-color image forming apparatus etc., and is not always restrictive. 
   The developing device  11  opens in a developing area opposed to the photosensitive drum  101 , and the developing sleeve  8  as a developer bearing member is rotatably disposed in such a manner as to be partly exposed in this opening portion. The developing sleeve  8  containing therein a stationary magnet which is magnetic field generating means is formed of a nonmagnetic material, and during the developing operation, it is rotated in the counter-clockwise direction of arrow “b” in  FIG. 10 , and retains thereon the two-component developer in the developing device  11  in a layer shape and bears and transports the developer thereon to thereby supply the developer to the developing area opposed to the photosensitive drum  101  and develop an electrostatic latent image on the photosensitive drum  101 . The developer on the developing sleeve  8  after the electrostatic latent image has been developed is transported in accordance with the rotation of the developing sleeve  8 , and is collected into the developing device  11 . 
   The developer in the developing device  11  is circulated in the developing device  11  by a first developer circulating screw  7   a  (a side near to the developing sleeve  8 ) and a second developer circulating screw  7   b  (a side far from the developing sleeve  8 ) which are developer agitating and transporting members, and is mixed and agitated. The first developer circulating screw  7   a  and the second developer circulating screw  7   b  are disposed substantially in parallel to the developing sleeve  8 , and the direction of circulation of the developer is a direction from this side toward the inner side of  FIG. 10  (the direction of arrow “c” in  FIG. 11 ) on the first developer circulating screw  7   a  side, and is a direction from the inner side toward this side of  FIG. 10  (the direction of arrow “d” in  FIG. 11 ) on the second developer circulating screw  7   b  side. In the developing device  11 , a partition wall  14  is provided so as to partition the space between the first developer circulating screw  7   a  and the second developer circulating screw  7   b  substantially in parallel to the developer circulating screws  7   a  and  7   b . The lengthwise end portions of the partition wall  14  do not reach the inner side wall of the developing device  11 , and communicating portions  13   a  and  13   b  are formed there. Through these communicating portions  13   a  and  13   b , the developer is delivered between the first developer circulating screw  7   a  and the second developer circulating screw  7   b.    
   When the developing device  11  performs a developing operation at the developing position P 1 , a two-component developer (developer) including a toner corresponding to an amount of toner consumed by image forming is supplied from a developer cartridge  6  as a developer supplying container connected to the developing device  11 , and at that time, a carrier of the order of 10% in terms of weight ratio is also supplied. That is, each time image forming is terminated, the carrier is supplied to the developing device  11 , and particularly when a high-density image is to be formed, a great deal of carrier amounting to the order of several tens of mg is supplied depending on the construction of the apparatus. Therefore, the amount of developer in the developing device  11  is increased and the surface (upper surface) of the developer becomes high. When the surface of the developer becomes higher by an allowable value or greater than the second developer circulating screw  7   b , the second developer circulating screw  7   b  cannot sufficiently agitate the developer and therefore, the toner immediately after supplied is transported to the first developer circulating screw  7   a  while remaining not sufficiently charged, and is used for the developing operation. Therefore, toner fog occurs to the white ground portion of an image, and when the amount of developer is further increased, the developer overflows from the developing device  11 , and the interior of the apparatus is contaminated. 
   In the present embodiment, the developing device  11  is provided with a developer supplying port (supplying port)  9  on one end side of the upper wall of the developing device  11  which is near the second developer circulating screw  7   b . Also, as will be described later in detail, a developer discharging port (discharging port)  1  having a shutter member  3  is provided on the other end side of the upper wall, and communicated with one end portion of a developer discharging path (discharging path)  4 . Also, as will be described later, in the present embodiment, at a predetermined rotation stop position of the rotary developing device  104 , the other end of the discharging path  4  communicates with a developer collecting port (collecting port)  2 . 
   When the developing device  11  is disposed at the developing position P 1 , the discharging port  1  is disposed substantially at the same height as the upper portion of the second developer circulating screw  7   b  and opens upwardly and therefore, it never happens that with an increase in the amount of the two-component developer in the developing device  11 , the surface (upper surface) of the developer becomes higher by the allowable value or greater than the second developer circulating screw  7   b.    
   The discharging port  1  is disposed near the second developer circulating screw  7   b  and upstream of the supplying port  9  with respect to the direction of circulation of the developer. Therefore, the circulation of the developer near the developing sleeve  8  is not disturbed, and it never happens that the developer supplied just before is discharged. 
   The two-component developer containing a toner corresponding to an amount of toner consumed by image forming is supplied into the developing device  11  through the supplying port  9  by the rotational force of a supplying screw  10   a  which is developer supplying means provided in a developer supplying portion  10  and gravity. The developer to be supplied is supplied to the developer supplying portion  10  from a developer cartridge  6  as a developer supplying container through a developer supplying port (supplying port)  6   b . The supplying screw  10   a  transports the developer supplied through the supplying port  6   b  toward the supplying port  9  in accordance with the rotation thereof, and makes the developer fall to the developing device  11  by gravity. 
   The developer cartridge  6  is provided with a rotatable developer transporting member  6   a , and transports the developer therein toward the supplying port  6   b . The developer cartridge  6  is detachably mounted with respect to the developing device  11  and the rotary developing device  104 . By the developer cartridge  6  being mounted with respect to the developing device  11 , the supplying port  6   b  is adapted to communicate with the developer supplying portion  10  of the developing device  11 . In the present embodiment, the developer cartridge  6  is of a substantially cylindrical shape. 
   The mixing ratio of the toner and the carrier in this supplied developer is of the order of 9:1 in terms of weight ratio in the present embodiment, but is not particularly restricted to this numerical value. That is, as compared with the ratio between the toner and the carrier in the developer in the developing device  11 , the amount of toner is overwhelmingly great in the developer to be supplied, and considering a volume ratio, it can also be considered that a slight amount of carrier is mixed with the toner. That is, when the toner consumed by image forming is to be made up for, a slight amount of carrier is gradually supplied. If the rate of the carrier in the developer to be supplied becomes great, the amount of replacement of the carrier becomes great by the supply of the same amount of toner and the two-component developer in the developing device  11  approximates to a fresh state, but correspondingly the amount of consumed carrier becomes great, and this leads to an increase in running cost. Therefore, it is preferable to discretely determine a suitable mixing ratio in each apparatus. 
   The supply amount of the developer is roughly determined by the number of revolutions of the supplying screw  10   a , and this number of revolutions in turn is determined by toner supply amount controlling means, not shown. As the toner supply amount controlling means, use can be made of one for calculating an amount of toner corresponding to an amount of toner consumed by image forming as by counting, for example, the number of pixels of a formed image, and converting it into the number of revolutions of the supplying screw  10   a , or the like. Such toner supply amount controlling means itself is well known to those skilled in the art and therefore need not be described any further. 
   As regards also the developing device  12  for black, the construction of the developing device itself can be made similar to that of the color developing device  11 . The developer is supplied from a discretely provided developer supplying container (not shown) to the developing device  12  for black. 
   Reference is now had also to  FIG. 12  to describe a method of discharging any excessive two-component developer (excessive developer from the color developing device  11  which is characteristic in the present embodiment. Such a discharging method is similar with respect to the respective color developing devices  11 , i.e., the developing device  11 Y for yellow, the developing device  11 M for magenta and the developing device  11 C for cyan. 
   As shown in  FIG. 9 , the rotary developing device  104  in the present embodiment has a developer discharging port (discharging port)  1  disposed in the developing device  11  for discharging the excess developer therethrough, and a developer collecting port (collecting port)  2  disposed in the rotary  104   a  for collecting the excess developer therethrough. 
   Also, in the present embodiment, a shutter member  3  for controlling the discharging position of the excessive developer is disposed near the discharging port  1  provided in the developing device  11 . The shutter member  3 , as shown in  FIG. 12 , has a shutter main body  3   a  which is a sealing portion larger in dimensions than the discharging port  1 . The shutter main body  3   a  has its one end portion fixed to a shutter pivot shaft  3   b , and is pivotally moved about this shutter pivot shaft  3   b  by gravity to thereby open and close the discharging port  1 . The shutter pivot shaft  3   b  is pivotally fixed to the inner wall of the developing device  11  near the discharging port  1  by bearing members  3   c . That is, the shutter member  3 , as will be described later in detail, is pivotally moved about the shutter pivot shaft  3   b  to thereby open and close the discharging port  1  from the inside of the developing device  11 . 
   Here, that surface (discharging port surface) E of the discharging port  1  which is adjacent to the developing device  11  when the shutter member  3  renders the discharging port  1  closed is set so as to be inclined by an angle (α) of 30° from a horizontal plane “h” at the developing position P 1  (FIG.  10 ). This is mentioned as the most characteristic portion in the present embodiment. 
   From the gist of the present invention, however, this angle α is not restricted to 30°, but may of course be other angle. This angle α, as will be described later in detail, can be set to the most preferable angle for rendering the discharging port  1  opened when the discharging port  1  is at a higher level than the surface of the developer in the developing device  11 , and rendering the discharging port  1  closed when the discharging port  1  is at a lower level than the surface of the developer. 
   The discharging port  1  of the developing device  11  is disposed substantially at the same height as the upper end of the second developer circulating screw  7   b , and when the developing device  11  is at the developing position P 1 , in the present embodiment, the shutter member  3  for opening and closing the discharging port  1  is rendered opened by gravity. Accordingly, when the surface of the developer becomes higher than the second developer circulating screw  7   b , the excessive developer overflows and is discharged from the discharging port  1 Y, and the surface of the developer in the developing device  11 Y for yellow is maintained substantially at the height of the second developer circulating screw  7   b . Therefore, it never happens that the toner fog onto the white ground portion of the image and the overflow of the developer from the developing device  11 Y for yellow as noted above occur. 
   Also, there is provided a developer discharging path (discharging path)  4  which is a communicating portion for communicating the discharging port  1  and the collecting port  2  with each other. The developer discharged through the discharging port  1  goes down along the discharging path  4  by gravity. The discharging path  4  once stores therein the excess two-component developer discharged from the developing device  11 , and thereafter discharges the developer into the collecting port  2 . 
   There is further provided a collected developer transporting portion (transporting portion)  5  for transporting the excess developer collected through the collecting port  2  to the outside of the rotary developing device  104 . In the present embodiment, the transporting portion  5  is formed in the interior of a cylinder shaft  104   b  which is the rotary shaft of the rotary developing device  104  (the transporting portion  5  will hereinafter be referred to as the “collected developer transporting pipe (transporting pipe)”). As described above, the transporting portion  5  is formed in the interior of the rotary shaft  104   b  and is thereby provided near the center axis of rotation of the rotary developing device  104 , whereby when the developers are to be collected and transported from the plurality of developing devices  11 , the rotary developing device  104  can be made maximally compact, and the disposition relationship between the developer discharging port  1  and the developer collecting port  2  which will be described later can be optimized. The present invention, however, is not restricted to a construction in which the rotary shaft functions as the collected developer transporting path. In the present embodiment, the collecting port  2  is an opening portion provided in the transporting pipe  5 . In the present embodiment, the collecting portion  2  is provided on one end portion side of the transporting pipe  5 . 
   In the present embodiment, in the interior of the transporting pipe  5 , there is rotatably disposed a transporting member (not shown) which, in the present embodiment, is a screw in order to transport the collected developer so that the collected developer can be transported to the outside of the rotary developing device  104  at any timing by drive transmitting means (not shown) provided in the apparatus main body A. The developer transported to the outside of the rotary developing device  104  through the transporting pipe  5  can be collected, for example, into a developer collecting container (not shown) connected to a lengthwise end portion of the transporting pipe  5  and provided in the apparatus main body A, or the like. 
   In the present embodiment, a system in which there is disposed a storing portion (in the present embodiment, provided by the discharging path  4 ) for once storing therein the once discharged excess developer will be described as an example. That is, in the present embodiment, the discharging path  4  is formed integrally with the rotary developing device  104 , and is disposed at a location corresponding to the developing device  11  for each color, and is rotated with the developing device  11  with the rotation of the rotary developing device  104 . On the other hand, the transporting pipe  5  is constructed discretely from the rotary developing device  104 , i.e., the rotary  104   a  which is a developing device supporting member corresponding to the main body thereof, and therefore the collecting port  2  is an opening only at one location corresponding to a position P 2 , i.e., a position at which the developing device  11  being at the developing position P 1  has been moved by 120° in the direction of rotation of the rotary developing device  104  and stopped. That is, only the discharging path  4  communicating with the developing device  11  disposed at the developing position P 1  by the rotation of the rotary developing device  104  is connected to the collecting port  2  provided in the transporting pipe  5 . 
   From the gist of the present invention, however, the presence or absence of the storing portion is not particularly restricted. For example, there can be adopted a construction in which the transporting pipe  5  is constructed discretely from the rotary developing device  104  and the collecting port  2  opens only at one location corresponding to the developing position P 1 . Only the discharging path  4  communicating with the developing device  11  disposed at the developing position by the rotation of the rotary developing device  104  is connected to the collecting port  2  provided in the transporting pipe  5 . Thus, when the developing device  11  is at the developing position P 1 , the discharging port  1  is located above the collecting port  2 . Thereby, the developer discharged through the discharging port  1  falls to the collecting port  2  along the discharging path  4  by gravity. Thus, at the developing position P 1 , the excess developer in the developing device  11  can always be continuously discharged to the outside of the developing device  11  and therefore, particularly even when single-color image forming of high-density image is continued, the rotary operation of the rotary developing device  104  for discharging the developer is not required, and the amount of developer in the developing device  11  can be maintained within an allowable range. Thereby, the image productivity particularly during single-color continuous image forming can be obtained. 
   Reference is now had to  FIGS. 13A ,  13 B and  13 C and  FIGS. 14A ,  14 B and  14 C to describe in detail the operating mechanism of the shutter member  3  when the rotary developing device  104  is rotated which is most characteristic in the present embodiment.  FIGS. 13A ,  13 B and  13 C show the operating state of the shutter member  3  when during a continuous image forming operation, the rotary developing device  104  is at a development stop position. Also,  FIGS. 14A ,  14 B and  14 C show the operating state of the shutter member  3  when the rotary developing device  104  is at a home position waiting position as an example of a case where the rotary developing device  104  is at other rotation stop position (phase position) than the development stop position. 
   With reference to  FIGS. 13A ,  13 B and  13 C, the operating situation of the shutter member  3  during an ordinary continuous image forming operation will first be described with the developing device  11 Y for yellow taken as an example. This operating situation is also similar with respect to the other developing devices, i.e., the developing device  11 M for magenta and the developing device  11 C for cyan. 
   When in  FIGS. 13A ,  13 B and  13 C, the developing device  11 Y for yellow is at the developing position P 1  (FIG.  13 A), the positional relationship between the discharging port  1 Y and the surface (upper surface) U of the developer in the developing device  11 Y for yellow is such that the discharging port  1 Y is located above (at a higher level than) the surface U of the developer. That is, at the developing position P 1 , the shutter member  3 Y is pivotally moved by gravity and the discharging port  1 Y is in its opened state. Thus, at the developing position P 1 , the two-component developer (developer) including a toner corresponding to an amount of toner consumed by image forming is supplied from the developer cartridge  6 Y, whereby the amount of developer in the developing device  11 Y for yellow is increased and the surface U of the developer becomes higher than the second developer circulating screw  7   b , whereupon the excessive developer overflows from the discharging port  1 Y and is discharged, and is once stored in the discharging path  4 Y. Therefore, the surface U of the developer is maintained at the height of the second developer circulating screw  7   b.    
   When the developing operation of the developing device  11 Y for yellow is terminated, the rotary developing device  104  is rotated by about 120° in preparation for the developing operation by the developing device  11 M for magenta which is the next color, and the developing device  11 Y for yellow is moved to a position P 2  (FIG.  13 B). At this time, as shown, the shutter member  3 Y is rotatively moved by gravity and the discharging port  1 Y becomes closed. Also, in this state, the discharging port  1 Y is below (at a lower level than) the surface U of the developer in the developing device  11 Y for yellow, and the shutter member  3 Y is pushed by the pressure of the developer in the developing device  11 Y for yellow so as to bring the discharging port  1 Y into its closed state. Therefore, it never happens that the developer in the developing device  11 Y for yellow leaks out from the discharging port  1 Y to the discharging path  4 Y. The excess developer once collected in the discharging path  4 Y falls into the collecting port  2  at this time, and is discharged to the outside of the rotary developing device  104  by the transporting pipe  5 . 
   When the developing operation of the developing device  11 M for magenta is terminated, the rotary developing device  104  is again rotated by about 120° in preparation for the developing operation by the developing device  11 C for cyan which is the next color, and the developing device  11 Y for yellow is moved to a position P 3  (FIG.  13 C). At this time, as shown, the discharging port  1 Y is below (at a lower level than) the surface U of the developer in the developing device  11 Y for yellow, and the shutter member  3 Y still renders the discharging port  1 Y closed by the pressure of the developer in the developing device  11 Y for yellow and therefore, it never happens that the developer in the developing device  11 Y for yellow leaks out from the discharging port  1 Y to the storing discharging path  4 Y. Even if the developer should leak out, it never happens owing to the action in the direction of gravity that the developer flows to the discharging path  4 Y side. 
   Reference is now had to  FIGS. 14A ,  14 B and  14 C to describe the operating situation of the shutter member  3  of the developing device for each color at a home position waiting position, as an example of other stopping operation than the periodical and equal rotation stopping operation during continuous image forming, i.e., a case where the rotary developing device  104  is stopped at other position than the development stop position. This is a portion mentioned as the most characteristic point in the present embodiment. 
     FIG. 14A  shows a stopped state at a waiting position whereat the developing device  11 Y for yellow is located 60° on this side of the developing position P 1 . At this time, as shown in  FIG. 14A , the discharging port  1 Y of the developing device  11 Y for yellow is below (at a lower level than) the surface U of the developer in the developing device  11 Y for yellow, and the shutter member  3 Y is operating so that the discharging port  1 Y may be rendered closed by the pressure of the developer in the developing device  11 Y for yellow. Therefore, it never happens that the developer in the developing device  11 Y for yellow leaks out from the discharging port  1 Y to the discharging path  4 Y. Actually, it is conceivable that the discharging port  1 Y is rendered opened by the shock of rotation, but even if the developer should leak out, it never happens owing to the action in the direction of gravity that the developer flows to the discharging path  4 Y side. 
   Also, in the developing device  11   c  for cyan corresponding to a position rotated by 120° from the developing device  11 Y for yellow, the shutter member  3 C is operating so that the discharging port  1 C may be rendered closed by gravity ( FIG. 14B ) Also, in this state, the discharging port  1 C of the developing device  11 C for cyan is below (at a lower level than) the surface U of the developer in the developing device  11 C for cyan, and by the pressure of the developer in the developing device  11 C for cyan, the shutter member  3 C is pushed so as to render the discharging port  1 C closed. Therefore, it never happens that the developer in the developing device  11 C for cyan leaks out from the discharging port  1 C to the discharging path  4 C. Here, consider a case where the angle α of the surface E of the discharging port  1  at the developing position P 1  which is adjacent to the developing device  11  is set so as to be 0°, that is, so that the surface E of the discharging port may be horizontal. In this case, the shutter member  3 C tends to be closed by the pressure of the developer, but when this becomes unstable by the shock of rotation, the excess developer flows down to the discharging path  4 C side. 
   The shutter member  3 M of the developing device  11 M for magenta corresponding to a position further rotated by 120° from the developing device  11 C for cyan is operating so that the discharging port  1 M may be rendered closed by gravity (FIG.  14 C). Also, in this state, the discharging port  1 M of the developing device  11 M for magenta is below (at a lower level than) the surface U of the developer in the developing device  11 M for magenta, and by the pressure of the developer in the developing device  11 M for magenta, the shutter member  3 M is pushed so as to render the discharging port  1 M closed. Therefore, it never happens that the developer in the developing device  11 M for magenta leaks out from the discharging port  1 M to the discharging path  4 M. 
   In  FIGS. 14A ,  14 B and  14 C, description has been made of the operating situation of the shutter member  3  at the home position waiting position, but even if besides, there is, for example, another stop position for the interchange of the toner cartridge, a similar effect can be displayed. Also, in the present embodiment, the developing devices  11  for the respective colors are substantially of the same construction. Accordingly, not only when as shown in  FIGS. 14A ,  14 B and  14 C, the developing devices  11  for the respective colors are disposed and stopped, but also even if any developing device  11  is stopped at any position, it is obvious that the shutter member  3  can likewise act. 
   As described above, only at the developing position P 1 , the shutter member  3  becomes opened and it never happens that the excess developer in the developing device  11  is unexpectedly discharged outwardly and therefore, even in a case where in order to discharge the developer, a rotating operation having a plurality of non-uniform stop positions (phase positions) including the development stopping position of the rotary developing device  104  is performed, the amount of developer in the developing device  11  can be stably maintained within an allowable range and therefore, a high image quality maintaining property is not lowered. 
   Also, in the present embodiment, the rotary developing device  104  adopts a three-color rotary construction using 120° rotation as the basis. Therefore, the surface (discharging port surface) E of the discharging port  1  which is adjacent to the shutter member  3  is inclined by 30° from a horizontal direction at the developing position P 1 , whereby there is suitably realized a construction which can easily cope with various rotation stop positions, and excellent high image quality maintaining stability is realized. In the present embodiment, by this excellent developer leakage preventing operation of the shutter member  3 , the construction of the discharging path  4  for once storing the discharged developer therein can be made very simple, and this greatly contributes to a reduction in the costs of the rotary developing device  104 , and further the image forming apparatus  100 . 
   Besides, according to the present invention in which the surface E of the discharging port  1  which is adjacent to the shutter member  3  is inclined, not only in a three-color rotary having 120° rotation as the basis, but also in a construction having a plurality of rotation stop positions, an optimum angle of inclination based on the respective rotation stop position conditions thereof is selected, whereby it can be made easy to suitably cope with various rotation stop positions, and a developer discharge preventing characteristic can be stabilized. 
   As described above, even in a case where for example, besides such a development stopping position that the rotation stop position is at 120° each, there are other various stop positions such as a non-uniform developer cartridge interchange position, design is made such that the developer is always discharged only from a developing device  11  of stable posture which is at the developing position P 1 , and is not discharged at any other phase position and therefore, there is realized a developer discharging characteristic which is wide and very stable in coping width, and this contributes to the stability of a high quality of image. 
   Also, the rotation stop positions of the rotary developing device  104  are increased by a simple construction, whereby unexpected discharging of the developer can be prevented from being effected, and the storing chamber does not require any complicated constituent member and therefore, the necessity of the work of interchanging the developer can be eliminated by an inexpensive and stable construction, and an improvement in a maintenance property and a reduction in running cost can be realized. 
   Further describing, according to my studies, the deterioration of the developer by the long-term use thereof is due to two great causes, i.e., so-called toner-spent in which the toner adheres to the surface of the carrier, and the adherence of an extraneous additive in which the extraneous additive having drifted away from the toner adheres to the surface of the carrier. When the toner-spent and the adherence of the extraneous additive to the surface of the carrier occur, the surface area of the carrier which can charge the toner is decreased and therefore, the charging amount of the toner is reduced. Therefore, such image defects as an increase in image density and toner fog to the white portion, and the contamination of the image forming apparatus by the scattering of the toner occur. 
   According to the present embodiment, however, the developer including the deteriorated carrier is discharged out of the developing device  11  and is gradually replaced with a developer including a fresh carrier, whereby it becomes possible to stop the progress of the apparent deterioration of the carrier and stabilize the characteristic as the whole of the developer, and the stability of a high quality of image heightens. 
   On the other hand, as previously described, in recent years, a demand is heightening for increasing the stop positions of the rotary developing device  104 , such as providing the home position waiting position and the developer cartridge interchange stop waiting position. According to the present embodiment, the developing device  11  disposed in the rotary developing device  104  is designed to have therein the discharging port  1  for discharging the excess developer therethrough, and the shutter member  3  near this discharging port  1 , and design is made such that at the developing position P 1  whereat the developing device  11  is opposed to the photosensitive drum  101 , the surface E of the discharging port of the developing device  11  which is adjacent to the developing device  11  becomes an inclined surface. Thus, even if the rotation stop position of the rotary developing device  104  assumes any angle, an allowable value corresponding thereto becomes great, and a more reliable shutter operation becomes possible. 
   Therefore, even in a case where the rotary developing device  104  has a plurality of rotation stop positions as in a construction wherein the rotary developing device is stopped and made to wait at a home position whereat the developing sleeve  8  is not opposed to the photosensitive drum  101 , or a construction wherein the rotary developing device is stopped and made to wait at a developer cartridge interchanging position, as is often seen in an image forming apparatus having a rotary type developing member, the shutter mechanism can be reliably operated and the shutter member  3  can suppress discharging. Consequently, even if the rotation stop positions are further increased, it will never happen that the discharging mechanism becomes unstable and it becomes difficult to maintain a high quality of image. Accordingly, even in a case where besides the development stop position visiting periodically and stably during a continuous image forming operation, unstable stop position behavior is exhibited like a home position waiting position visiting after the termination of a job, and a developer cartridge interchange stop waiting position in which the rotary developing device is stopped and waits only when the toner in the developer cartridge  6  has become little, a stable developer discharging characteristic can be obtained, and the setting of a condition therefore becomes easy, and this can be expected to greatly contribute to the shortening of a development period. 
   According to the present embodiment, even in a case where as described above, the rotary developing device  104  is stopped at a plurality of non-uniform stop positions, the reliably stable discharging and non-discharging characteristic of the developer is obtained irrespective of the rotation stop position, and it is possible to stably maintain the amount of developer in the developing device  11  within an allowable value and therefore, it never happens that a high image quality maintaining characteristic is lowered. In addition, even in a case where a mechanism member for once storing the excess developer therein is required, the complication and bulkiness of the mechanism member and the apparatus can be prevented and thus, without the complication and higher cost of the apparatus itself being caused, the maintenance property is improved such as the interchange of the developers during service maintenance becoming unnecessary. 
   As described above, according to the present embodiment, it is possible to obtain the high maintenance property that the interchange of the developers is unnecessary, and a high image quality maintaining characteristic excellent when the rotary developing device  104  is stopped at a plurality of non-uniform stop positions. 
   It should be understood that the construction of the multi-color image forming apparatus described in the present embodiment is exemplification for illustrating the present invention, and that the present invention is not restricted thereto, but various changes are possible within the scope of the present invention. For example, while in each of the above-described embodiments, the image forming apparatus adopts the intermediate transferring process, the present invention restricts the transferring process in no way, but may also adopt the process of successively superimposing and transferring toner images on a recording material borne on a transfer material bearing member, as is well known to those skilled in the art, or like process. 
   As described above, according to the above-described Embodiment 2, the high maintenance property that the interchange of the developers is unnecessary and high image productivity can be realized by a simple construction. Also, according to the present invention, even in a case where a rotary type developing member provided with a plurality of developing devices is stopped at a plurality of phase positions, it becomes possible to always stably maintain a high quality of image.