Abstract:
The present invention relates to a developing apparatus for developing an electrostatic image formed on an image carrier, comprising a developing container, a first developing member formed at the first chamber for conveying developer to a first developing portion, a second developing member provided with the second chamber for conveying the developer to a second developing portion and a magnetic field generating means for generating magnetic field for transferring the developer between the first developing member and the second developing member. The diaphragm is disposed in a non-contacting manner to the first developing member and the second developing member and has a restricting member for restricting entry of the developer out of an interior of the developing container to a space between the first developing member and the second developing member.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to a developing apparatus for developing electrostatic images formed on an image carrier using, e.g., an electrophotographic method, an electrostatic recording method and, more particularly, to an apparatus used for photocopiers, printers, and facsimile machines. 
   2. Description of Related Art 
   Conventionally, color image forming apparatuses have been well known in which having plural developing apparatuses containing respectively developers of different colors and obtaining multicolor images using electrophotographic methods. 
   Referring to  FIG. 3 , described is a main cross-sectional structure of a conventional multicolor image forming apparatus. Exemplified herein as a conventional multicolor image forming apparatus is that four-color developing apparatuses are contained in a rotary body, which rotates by a prescribed angle at developing operation of respective colors to develop properly the images of respective colors. 
   In this prior art, the developing apparatus has a feature equipped with two developing rollers for respective colors, and the developer contains a two-component made of a so-called carrier serving as a magnetic agent and a toner for actually developing the latent image. 
   In this color image forming apparatus, an image processing means is constituted of a photosensitive drum  1  serving as an image carrier, a primary charger  2  as a charging means, a laser scanner  3  providing image information, a rotary type developing apparatus  5  supporting developing devices  4   a ,  4   b ,  4   c ,  4   d  as four developing means, an intermediate transfer body  6 , and a cleaning apparatus  7  collecting remaining transfer toner. 
   The image processing means ensures a size in the longitudinal direction corresponding to a prescribed length in the longitudinal direction of the photosensitive drum  1  required for image formation of a prescribed width. 
   The rotary type developing apparatus  5  is of a type settling one of four developing devices  4   a  to  4   d  to a developing position according to the rotation of a supporting body  9 . The rotary type developing apparatus  5  has development opening surfaces for the respective developing devices  4   a  to  4   d  on a circumference of a circle whose center is at a support body rotary shaft  8 . 
   The developing devices  4   a  to  4   d  have first developing rollers  10   a ,  10   b ,  10   c ,  10   d  and second developing rollers  11   a ,  11   b ,  11   c ,  11   d  serving as rotary developer carriers for conveying the toner to a portion contacting to the photosensitive drum  1 . 
   The rotary type developing apparatus  5  has a structure that only during the developing operation the first developing rollers  10   a ,  10   b ,  10   c ,  10   d  and the second developing rollers  11   a ,  11   b ,  11   c ,  11   d  in the developing devices  4   a  to  4   d  are made closer to the photosensitive drum  1  within a prescribed amount by moving the developing devices  4   a  to  4   d  with positioning apparatuses  12   a ,  12   b ,  12   c ,  12   d  and that during the rotation of the rotary type developing apparatus  5  as well as during non-development operation the first developing rollers  10   a ,  10   b ,  10   c ,  10   d  and the second developing rollers  11   a ,  11   b ,  11   c ,  11   d  in the developing devices  4   a  to  4   d  are isolated from the photosensitive drum  1  by releasing the contacting operation of the positioning apparatuses  12   a ,  12   b ,  12   c ,  12   d.    
   Referring to  FIG. 4  and  FIG. 5 , the developing device positioning apparatus for the rotary type developing apparatus in  FIG. 3  is described. Numeral  20  denotes a photosensitive drum; numeral  21  denotes a supporting body of a rotary type developing apparatus  22 ; numeral  23  denotes a developing device. The developing device  23  has mounted therein a first developing roller  24  and a second developing roller  25 . The developing device  23  is installed movably on a developing guide  26 . The developing guide  26  is set so that the first developing roller  24  and the second developing roller  25  are movable parallel with the surface of the photosensitive drum  20  up to coming closer in a prescribed amount. Numeral  27  is a positioning cam and moves pivotally around a pivotal shaft  28 . A roller  29  is disposed rotatably at a tip thereof. 
   The rotary type developing apparatus  22  rotates the developing device  23  by a rotary driving means, not shown, to a prescribed position on the photosensitive drum  20  at which the electrostatic latent image can be developed. The positioning cam is rotated in arrow B direction in the drawing with a drive apparatus, not shown, around the pivotal shaft  28 . According to this rotation, the developing device  23  moves in arrow C direction in the drawing and reaches the state shown in  FIG. 5 . 
   In  FIG. 5 , a part of a container  30  hits a hitting member, not shown, of the supporting body  21  to cease the developing device  23 , so that the developing device  23  is held as it is according to a holding force of the positioning cam  27 . In this state, the first developing roller  24  and the second developing roller  25  of the developing device  23  can come closer to the prescribed amount such that the electrostatic latent images on the photosensitive drum  20  can be properly developed. The prior art has a structure that this prescribed amount is in a range from 200 microns to 400 microns. 
   Next, a process for forming color images on a transfer material using this color image forming apparatus is described. 
   The photosensitive drum  1  is rotated in arrow A direction, and the primary charger  2  charges the photosensitive drum  1  uniformly. Exposure  13  by the laser scanner  3  then forms electrostatic latent images on the photosensitive drum  1 . These latent images are corresponding to color developing agent developers in the developing devices  4   a  to  4   d , or namely respective colors such as yellow (Y), magenta (M), cyan (Y), and black (Bk). 
   Regarding to the first color, the electrostatic latent image corresponding to, e.g., the yellow developer is formed on the photosensitive drum  1 , and the image, after being visualized with the known process among the developer rollers  10   a ,  11   a  of the developing device  4   a  in which the yellow developer is contained, and the photosensitive drum  1 , is transferred with a first transfer roller  14  to the intermediate transfer body  6 . 
   Subsequently, after the remaining toner on the photosensitive drum  1  is cleaned up with the cleaning apparatus  7  such as a blade or the like, the electrostatic latent image corresponding to, e.g., the developer, as the second color, is formed on the photosensitive drum  1 , and the image, after being visualized with the known process among the developer rollers  10   b ,  11   b  of the developing device  4   b  in which the magenta developer is contained, and the photosensitive drum  1 , is transferred in an overlapping manner with the first transfer roller  14  to the intermediate transfer body  6  to which the yellow visualized image of the first color is transferred. 
   After the above operations are done in a plural number, the toner overlapped as plural layers on the intermediate transfer body  6  is transferred onto a transfer material  102  as described below. 
   Hereinafter, the step that the toner of the plural layers on the intermediate transfer body  6  is transferred onto the transfer material  102  is described. 
   A transfer material  102  stacked on a cassette  101  in  FIG. 3  is fed out with a pickup roller  103 , and the topmost transfer material P 2  is solely transferred on a downstream side by a feeding roller  104  and a reverse separation roller  105  rotating in the reverse direction to the feeding direction. The transfer material P 2  is then conveyed along a conveyance path by plural conveyance roller pairs  106 , and is bent upon the front end&#39;s engagement with a nipping portion of a stopped registration roller pair  107 , thereby being corrected from obliquely feeding. 
   The registration roller pair  107  begins rotating at a timing synchronized with a toner image formed on the intermediate transfer body  6 , thereby feeding out the transfer material  102 . The fed transfer material  102  enters in the nipping portion formed with the intermediate transfer body  6  and a second transfer roller  108 , and the toner image on the intermediate transfer body  6  is transferred to the transfer material (P 1  in  FIG. 3 ). 
   The transfer material P 1  is then conveyed with a conveyance belt  109  to a fixing apparatus  110  made of two rollers, located on upper and lower sides. The toner image on the transfer material P 1  at the fixing apparatus  110  is fixed to the transfer material P 1 , and is delivered to a delivery tray  112  via delivery rollers  111 . 
   Such a color image forming apparatus has been proposed as an example of a color image forming apparatus particularly for higher image quality than the usual image quality. Such an apparatus has a feature that each of the four-color developing devices contained in the rotary body has two developing rollers. Described herein as an example of such an apparatus feature is that the four-color developing devices contained in the rotary body have the same shape and the same mass and are disposed equally with 90 degrees spaced with respect to a rotary center of the rotary body. 
   Next, the developing device in the rotary body is described. 
     FIG. 6  and  FIG. 7  show two states taken by the developing device in a rotary body  40 . In  FIG. 7 , numeral  41  shows a photosensitive drum, and  FIG. 7  shows a situation that the electrostatic latent image on the photosensitive drum  41  is developed by an developer of a developing device  42 . The rotary body  40  has a structure to rotate by each of 90 degrees in the counterclockwise direction (arrow D in the drawing).  FIG. 6  shows the state that the rotary body  40  is located at a position of −90 degrees in the rotational direction of the rotary body  40  (rotational direction of the rotary body  40  is defined as “+”) with respect to the developing position shown in  FIG. 7 . 
   With reference to  FIG. 6 , an internal structure of the developing device  42  is described. The developing device  42  has a first developing roller  44  and a second developing roller  45 , and each of the developing rollers  44 ,  45  has a first developing sleeve  46  and a second developing sleeve  47 , which are in a rotatable state with a drive mechanism, not shown, and a first magnet roller  48  and a second magnet roller  49  stationally formed at respective centers of the developing rollers  44 ,  45 . 
   As shown in  FIG. 6 , the magnetic polarity arrangement of the first magnet roller  48  and the second magnet roller  49  is such that the north polarity and the south polarity are set entirely reverse to each other. 
   In the developing device  42 , a first screw  50  and a second screw  51  are disposed. A diaphragm  53  structured by a part of a container  52  is projected between the first screw  50  and the second screw  51 , thereby forming a developing chamber  54  enclosed with the first developing roller  44  and a stirring chamber  55  enclosed with the second developing roller  45 , respectively. The opposite ends in the longitudinal direction of the first screw  50  and the second screw  51  are supported with bearings, not shown. 
   For the purpose of the explanation, the space between the first developing roller  44  and the second developing roller  45  is defined as an SS space  56 . 
   A situation shown in  FIG. 6  is described. As described above,  FIG. 6  shows the state of −90 degrees with respect to the developing position, and in this state, the first developing roller  44  and the second developing roller  45  are positioned on a substantially lower side, and therefore, a developer  57  existing in the developing device  42  is deposited as to overlap the first developing roller  44  and the second developing roller  45  by operation of the gravity force as shown with “circle patterns” in  FIG. 6 . From another viewpoint, the developing  57  developer is attracted by magnetic force of the first magnet roller  48  and the second magnet roller  49  in the first developing roller  44  and the second developing roller  45 , and a space including the SS space  56 , other than an empty space at an upper portion of the developing chamber  54  and the stirring chamber  55 , is filled with the developer  57  by a synergy effect with the above gravity force. 
   Next, the state shown in  FIG. 7  is described below. As described above,  FIG. 7  shows a state for developing position, and in this state, the first developing roller  44  and the second developing roller  45  are in a drive state, while the first developing sleeve  46  and the second developing sleeve  47  rotate in directions of arrows E, F. 
   Regarding the first screw  50  and the second screw  51 , as shown in the drawing in respect with the developer  57  in the developing device  42 , the lead and rotational direction of the first screw  50  is set so that the developer  57  is conveyed in a direction toward the front side of the drawing, and similarly, the lead and rotational direction of the second screw  51  is set so that the developer  57  is conveyed in a direction toward the rear side of the drawing. The developing chamber  54  containing the first screw  50  and the stirring chamber  55  containing the second screw  51  are structured to communicate with each other at the opposite ends in the longitudinal direction. 
   Referring to  FIG. 8 , the flow of the developer  57  existing in the developing device  42  is described.  FIG. 8  is a schematic view showing a cross section along an axial line extending in the longitudinal direction of a developing device  60 . Numeral  61  denotes a first screw described in  FIGS. 6 ,  7 ; numeral  62  denotes a second screw; numeral  63  denotes a developing chamber containing the first screw  61 ; numeral  64  denotes a stirring chamber containing the second screw  62 . Numeral  65  denotes a toner hopper for supplying a toner  66  to the developing device  60 . 
   One flow is for equalizing the toner density of the developer in the developing device  60 . The toner  66  supplied from the toner hopper  65  is supplied to the developing device  60  from extension  641  of the stirring chamber  64  and conveyed in the stirring chamber  64  in arrow direction of arrows G, H as stirred with the carrier in the stirring chamber  64  and as maintaining the state of the developer. The toner  66  at that time receives further triboelectric charges from adequate stirring with the carrier. 
   The developer is overly filled at an end  642  of the stirring chamber  64  because the developer is sent to the second screw  62 . The end  642  of the stirring chamber  64  is structured with a communication path  67  in communication with the end  632  of the developing chamber  63 , so that overly filled developer enters toward a side of the end  632  of the developing chamber or first chamber  63 . 
   The first screw  61  of the developing chamber  63  conveys the developer in the developing chamber or first chamber  63  in a direction of arrow I in the drawing. The developer conveyed in the developing chamber  63  reaches the other end  631  of the developing chamber  63 . Another communication path  68  in communication with the stirring chamber or second chamber  64  is formed even at the other end  631  of the developing chamber  63 , so that the developer is circulated into a merging portion  643  of the stirring chamber  64  again. 
   Other flows of the developer are used for a process developing the electrostatic latent image on the photosensitive drum  41  with the developer in the developing device  42 . This flow is described with reference to  FIG. 7 . 
   As shown in  FIG. 7 , the developer  571  in the developing chamber  54  faces to the first developing roller  44 , and a part of the developer  571  conveyed thereto is fed around the surface of the first developing sleeve  46  by magnetic attracting force of the first magnet roller  48  of the first developing sleeve  46 , and is carried as a thin layer with a restricting blade  58 . The developer  57  develops the electrostatic latent image on the surface of the photosensitive drum  41  according to the rotation of the first developing sleeve  46  and is further conveyed to the second developing roller  45 . 
   As a feature of the magnetic polarity arrangement of the first magnet roller  48  and the second magnet roller  49 , the magnetic flux density is made higher at a space between the N 1  polarity  481  of the first magnet roller  48  and the S 2  polarity  491  of the second magnet roller  49  because the N 1  polarity  481  of the first magnet roller  48  and the S 2  polarity  491  of the second magnet roller  49  are arranged as opposed to each other, so that transfer of the developer  571  can be done surely from the first developing sleeve  46  to the second developing sleeve  47 , and so that the toner and the carrier can be prevented from scattered between the sleeves  46 ,  47 . 
   The second developing roller  45  carries the developer  571  to the surface of the second developing sleeve  47  in substantially the same manner by the magnetic attracting force of the second magnet roller  49 . The developer  571  on the surface of the second developing sleeve  47  performs the second development of the electrostatic latent image on the photosensitive drum  41 . Accordingly the two developments with the first developing roller  44  and the second developing roller  45  render the developer  571  entering into the stirring chamber  55  in the developing device  42  again in a state that the toner density of the developer  571  is lowered. In the stirring chamber  55 , the developer  572  is stirred and conveyed by the second screw  51 , exists and merges with the developer  571 . 
   In a meantime, as described above, almost all of the space including the SS space  56  is filled with the developer  57  by the synergy effect of the gravity force and the magnetic force of the two magnet rollers  48 ,  49 . 
   If the rotary body  40  is rotated to a developing position shown in  FIG. 7  from this state, the developer  57  in the developing device  42  is located in a range shown with “circle patterns” and “dot patterns” in the drawing. 
   Regarding the developer  571  of “circle patterns” in  FIG. 7 , as shown as the prior art, while the agent is circulated by the two developing screws  50 ,  51  in the developing device  42 , a part of the agent is carried with two developing rollers  44 ,  45  to contribute the development of the electrostatic latent image on the photosensitive drum  41 . 
   On the other hand, the portion shown with “dot patterns” in  FIG. 7  is a portion defined as the SS space  56  in  FIG. 6  and is a portion at which the developer  573  is carried by magnetic force of the two magnet rollers  48 ,  49 . In this SS space  56 , the S 2  polarity  482  of the first magnet roller  48  and the N 1  polarity  492  of the second magnet roller  49  are arranged as to be opposed to each other, so that the magnetic flux density is made higher between the polarities, and so that the SS space  56  is subject to higher constraint force against the developer  573  by the magnetic force. 
   The developer  573  is a agent that is circulated into the stirring chamber  55  after the developing operation of the previous time and that is contained in the stirring chamber  55 . That is, the developer  573  is a developer with a reduced toner density, which is entirely different from the developer passing through the restricting blade  58  under the regular process. In the state shown in  FIG. 6 , the developer enters into the SS space  56 . 
   The developer  573  carried in the SS space  56  is conveyed to the second developing sleeve  47  again as shown in arrow K in  FIG. 7 , and the coating amount of the developer of the second developing sleeve  47  greatly excesses the coating amount of the first developing sleeve  47  normalized with the restricting blade  58 . 
   With such a state that the developer is mixed, not only defective image such as reduced density after duration may be formed, but also the coating amount of the second developing sleeve  46  itself becomes greatly larger than the proper amount, in the developing process of the electrostatic latent image on the photosensitive drum  41 , thereby raising various problems such that blurs and overflows from the container  52  simply occur to scatter the toner in the device. 
   This invention is made in consideration of the above problems. It is an object to provide a developing apparatus avoiding a developer to be coated more than the necessary amount on a developing roller to prevent blurs and overflows out of a container form occurring and to obtain developed images with high quality. 
   SUMMARY OF THE INVENTION 
   It is an object of the invention to provide a developing apparatus capable of restricting entry of a developer into a space between a first developer carrier and a second developer carrier. 
   It is another object of the invention to provide a developing apparatus, without reducing the duration of the first developer carrier and the second developer carrier, capable of restricting entry of a developer into a space between a first developer carrier and a second developer carrier. 
   It is yet another object of the invention to provide a developing apparatus for developing an electrostatic image formed on an image carrier, comprising: a developing container containing a magnetic developer; a diaphragm substantially dividing the developing container into a first chamber and a second chamber constituting a circulation path of the developer, the first chamber being disposed on an upper side of the second chamber; a developing container for containing a magnetic developer, the developing container being divided into a first chamber and a second chamber constituting a circulation path of the developer, the first chamber being disposed on an upper side of the second chamber; 
   a first developing member, provided within the first chamber, for supplying the developer to the electrostatic image on the image carrier; 
   a second developing member, provided within the second chamber, for supplying the developer to the electrostatic image on the image carrier; and 
   a magnetic field generating means for generating a magnetic field for transferring the developer from the first developing member to the second developing member on the image carrier side, and 
   a restricting member for restricting entry of the developer in the developing container to a space between the first developing member and the second developing member, the restricting member being disposed in the developer container in a non-contacting manner with the first developing member and the second developing member. 
   Further objects of the invention will be apparent from reading the following detailed description in reference to the attached drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a diagram showing a state that a developing device is isolated from a photosensitive drum according to the invention; 
       FIG. 2  is a diagram illustrating a flow of a developer in the developing device according to the invention; 
       FIG. 3  is an illustration showing a color image forming apparatus mounting a rotary type developing apparatus; 
       FIG. 4  is a diagram showing a pre-operation state of a development positioning apparatus at a developing position; 
       FIG. 5  is a diagram showing a post-operation state of the development positioning apparatus at the developing position; 
       FIG. 6  is a diagram showing a state in which a conventional developing device is isolated from a photosensitive drum; 
       FIG. 7  is a diagram showing a flow of a developer in the conventional developing device; 
       FIG. 8  is a diagram showing a flow of a developer in a cross section along a longitudinal direction of the conventional developing device; 
       FIG. 9  is an illustration showing another embodiment of the color image forming apparatus mounting a developing device according to the invention; and 
       FIG. 10  is a detailed diagram showing the interior of the developing device in  FIG. 9 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Hereinafter, referring to the drawings, the preferred embodiments of the invention are described in detail in an exemplifying manner. Size, material, and shape of structural parts as set forth in the embodiments below, and correlated arrangement of those parts can be modified properly according to the constitution of the apparatus to which this invention applies and various conditions, and as far as no special description is made, it is not intended that the scope of the invention is limited to those embodiments only. 
   [First Embodiment] 
   An embodiment of the invention is shown in  FIG. 1  and  FIG. 2 . It is to be noted that the schematic structure of the image forming apparatus having the developing apparatus or developing device according to this embodiment is substantially the same as that of the prior art, and therefore, a detailed description is omitted. With respect to the members commonly used in the prior art, reference numbers used in the prior art are used as they are, and a detailed description is omitted. 
     FIG. 1 ,  FIG. 2  are for showing two states taken by a developing device  42  in a rotary body  40 .  FIG. 1  is for a state that the developing device  42  is located at a position of −90 degrees with respect to a rotational direction of the rotary body  40  prior to the developing position;  FIG. 2  shows the developing position. 
   The state shown in  FIG. 1  is described. With this situation, a first developing roller  44  serving as a first developer carrier (first developing member) and a second developing roller  45  serving as a second developer carrier (second developing member) are located on a lower side, so that a developer  57  existing in the developing device  42  is deposited according to operation of gravity force as to overlap the first developing roller  44  and the second developing roller  45  as shown with “circle patterns” in  FIG. 1 . 
   In this embodiment, a diaphragm  53  constituted of a part of a developing container  52  in the developing device  42  is protruded to form a developing chamber  54  enclosed with the first developing roller  44  and a stirring chamber  55  enclosed with the second developing roller  45 , respectively. 
   A restricting member  70  for restricting entry of the developing agent into an SS space  56  as a region between the first developing roller  44  and the second developing roller  45  is arranged as to continue to the diaphragm  53  where the front end of the diaphragm  53  is widened. 
   With this structure, in this embodiment, the developer  57  in the SS space  56  can be avoided from attracted by the magnetic force of a first magnet roller  48  and a second magnet roller  49  in the first developing roller  44  and the second developing roller  45  from operation of the restricting member  70 . 
   Flow of the developer at the developing position is described next. In this embodiment, the cross-sectional structure of the developing device  42  along the longitudinal direction is equal to what is shown in the prior art (see  FIG. 8 ), duplicated description is omitted. The flow of the developer  57  is basically the same as that of the prior art, which is for unifying the toner density of the developer  57  in the developing device  42  and for use in a process developing electrostatic latent images on a photosensitive drum  41  with the developer  57  in the developing device  42 . 
   Herein, particularly, flow of the developer  57  with respect to the developing process is described. As shown in  FIG. 2 , the developer  571  in the developing chamber  54  reaches the surface of the first developing sleeve  46  in the same way as in the prior art and is carried as in a thin layer shape by means of the restricting blade  58 . The developer  571  is then transferred to the second developing sleeve  47  as developing the electrostatic latent images on the surface of the photosensitive drum  41 . 
   The developer carried on the surface of the second developing sleeve  47  performs the second development on the electrostatic latent images on the photosensitive drum  41 , and enters in the stirring chamber  55  in the developing device  42  as in a state that the toner density is lowered to merge with the developer  572 , which is stirred and conveyed by a second screw  51 . 
   As described with reference to  FIG. 1 , because the front end of the diaphragm  53  is widened and because the restricting member  70  for restricting the entry of the developer into the SS space  56  located between the first developing roller  44  and the second developing roller  45  is disposed, the entry of the developer into the SS space  56  is prevented. It is to be noted that the diaphragm  53  is not formed as to completely partition between the developing chamber  54  and the stirring chamber  55 , and the developing chamber  54  and the stirring chamber  55  are formed with a communication path permitting passage of the developer  57  around the vicinity of the opposite ends in the longitudinal direction as to constitute a circulation path of the developer  57 . 
   The shape of the restricting member  70  is described in detail. As other features of the magnetic arrangement of the first magnet roller  48  and the second magnet roller  49  as described above, the S 2  magnetic polarity  482  and S 1  magnetic polarity  483 , which are magnetic polarities of the same polarity adjacent to each other, are disposed at the first magnet roller  48 . This is a known technology that the magnet polarities of the same polarity are disposed in parallel so that the developer  57  does not come around from the S 2  magnetic polarity side on the upstream side in the rotational direction of the first developing sleeve  46  to the S 1  magnetic polarity side to separate the developer  57  from the surface of the first developing sleeve  46  at a so-called “magnetic flux zero point”  484  (shown with a single dotted line) at which no magnetic flux exists between both of the polarities. 
   In substantially the same way, the N 2  magnetic polarity  493  and the N 1  magnetic polarity  492 , magnetic polarities adjacent to each other, are arranged at the second magnet roller  49 , thereby rendering the magnetic flux null at the “magnetic flux zero point”  494  (shown with a single dotted line) located between the magnetic polarities to separate the developer from the surface of the second developing sleeve  47 . 
   The restricting member  70  is desirably positioned most closely to the first developing sleeve  46  and the second developing sleeve  47  at the “magnetic flux zero point”  484 ,  494  described above. In this embodiment, a part of the restricting member  70  is extending to a position  71  with respect to the “magnetic flux zero point”  484 , whereas extending to a position  72  with respect to the “magnetic flux zero point”  494 , thereby realizing the structure described above. 
   This structure can form a structure that the developer  57  little enters into the space between the restricting member  70  and sleeve surface at a position of the least magnetic flux amount on the developing roller  44 ,  45 , so that with the synergy effect, the entering amount of the toner can be suppressed to the minimum amount to the SS space  56 . 
   The restricting member  70 , at least, may be desirably formed to have the narrowest space to the sleeve  46 ,  47  around the “magnetic flux zero point”  484 ,  494  even where not reaching the positions  71 ,  72  as in this embodiment. 
   According to an experiment, by setting the space at the closest position between the restricting member  70  described above and the sleeve to 2 mm or lower, an advantage was obtained for prevention of entry of the developer  57  to the SS space  56 . 
   With the structure described above, even where the developing device  42  moves to the developing position in  FIG. 2 , the developer  57  still does not enter into the SS space  56 . That is, the developer  57  deteriorated may not be re-coated on the second developing roller  45 . 
   As described above, according to the embodiment, since the restricting member  70  is disposed for restricting the entry of the developer  57  to the region (the SS space  56 ) sandwiched between the first developing roller  44  and the second developing roller  45  extending adjacent to each other as well as the region of the interior of the developing container  52 , the developer  57  may not enter into the SS space  56  serving as the above region, so that the developer  57  is avoided to be coated more than the necessary amount on the second developing roller  45 , and so that blurs and overflows from the developing container  52  are prevented to bring developing images with higher quality. 
   [Second Embodiment] 
   This invention is not limited to the rotary type image forming apparatus described above, and is applicable to an inline type image forming apparatus in which four developing devices are arranged. It is to be noted that because the image forming apparatus shown in  FIG. 9  has substantially the same structure as that of the first embodiment except the developing devices are arranged in parallel, members and apparatuses having the same functions are assigned with the same reference numbers, and a detailed description is omitted. 
     FIG. 10  shows a detailed structure of the developing apparatus shown in  FIG. 9 . The outline of the developing apparatus is as follows: the developing container is partitioned to, as upper and lower, a developing chamber  63  and a stirring chamber  64  with the diaphragm  53  (the stirring chamber is located on a lower side of the developing chamber  63  in the gravity force direction), and a magnetic developer having a non-magnetic toner and a magnetic carrier is sent to a developing chamber  63  upon pushed up by a second screw  51  at a path  67  on an end side in the longitudinal direction of the stirring chamber  64 . It is to be noted that the drawing depicted as to overlap the developing chamber  63  with the stirring chamber  64  shows a first developing roller  44  and a second developing roller  45 . 
   Therefore, the powder surface of the developer around the path  67  of the stirring chamber  64  is lifted up as to reach the diaphragm  53  as shown with a double-dotted chain line in the drawing. 
   If the agent surface of the developer is lifted up, the developer may enter into a gap between the first developing roller  44  and the second developing roller  45 , in substantially the same manner as in the first embodiment, or namely the SS space  56 , so that consequently, the coating amount of the developer on the second developing roller  45  is raised, thereby possibly rendering defective the image density. 
   A restricting member  70  is formed to restrict the entry of the developer by protruding the shape of the diaphragm  53  in substantially the same manner as in the first embodiment, thereby preventing the developer from entering into the SS space  56 . 
   It is to be noted that the restricting member  70  is provided across substantially the entire region along the longitudinal direction of the first and second developing rollers  44 ,  45  because the entry of the developer into the SS space  56  is done at the entire region in the longitudinal direction at the developing apparatus mounted on the developing rotary described above, but in this embodiment, the restricting member  70  is preferably formed at least around the path  67  because the developing apparatus is stationally arranged. 
   [Other Embodiments] 
   According to the first and second embodiments, exemplified as the restricting member is the restricting member, unitedly formed with the container, in which the front end of the diaphragm formed by protruding the part of the container is widened, but the member is not limited to this, and can be a separate member. The shape of the restricting member is not limited to the shape shown in  FIG. 1  and  FIG. 2 , and other shapes can be possible as far as the shape restricts the entry of the developer into the SS space as the above region. It is to be noted that as described in the first and second embodiments, it is desirable to set the restricting member as extending along the circumferential surfaces of the first developing roller and the second developing roller. 
   In the above embodiments, exemplified as a developing apparatus having plural developer carriers is a developing apparatus having two developer carriers (first developer carrier and second developer carrier), but the number of the developer carriers is not limited to this. 
   In the above embodiments, exemplified is an image forming apparatus having the four developing devices, but the used number is not limited and can be set properly according to the necessity. Exemplified also is the image forming apparatus capable of forming color images, but this invention is not limited to this, and this invention is applicable to a developing apparatus used in an image forming apparatus capable of forming monochrome images. 
   Although in the above embodiments the printer is exemplified as the image forming apparatus, this invention is not limited to this, and this invention applicable to image forming apparatuses such as, e.g., photocopiers, facsimile machines, other image forming apparatuses such as combined machines combining those functions, and image forming apparatuses using a transfer carrier and multiply transferring toners of respective colors to a transfer material carried on a transfer material carrier in a sequentially overlapping manner, so that substantially the same advantages can be obtained in applying this invention to such image forming apparatuses. 
   As described above, according to the above embodiments, coating of the developer more than the necessary amount on the developer carrier can be avoided, so that blurs of the developer and overflows from the developing container can be prevented, thereby producing developing images with high quality.