Patent Publication Number: US-6671476-B1

Title: Process cartridge and image forming apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is related to an electro-photographic type image forming apparatus and a process cartridge used in this image forming apparatus. 
     2. Description of the Related Art 
     As a conventional image forming apparatus, such an image forming apparatus is well known in this technical field in which a process cartridge is detachably mounted on a main body of the image forming apparatus. As one of conventional process cartridges, such a process cartridge is known in which both a cleaning apparatus and a developing apparatus are relatively arranged in an upper/lower positional relationship, while sandwiching therebetween an optical scanning path. 
     In the image forming apparatus employing such a process cartridge, in such a mode that transferring/fixing operations are carried out while recording mediums are transported along a substantially vertical direction, the developing apparatus is arranged under the optical scanning path. As a result, in order to reduce the height of this image forming apparatus, since the developing apparatus is located on the lower side of the optical scanning path, the height of the developing apparatus is required to be decreased. Since the developing apparatus contains a developer storage unit for storing thereinto developer, the size of this developer storage unit must be reduced. However, while the developer storage capacity is maintained, it is practically difficult to make the developing apparatus compact. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a process cartridge and an image forming apparatus using the process cartridge, which can be made compact, while a sufficiently large developer storage capacity is maintained. 
     To achieve the above-described object, a first feature of the present invention is realized by a process cartridge detachably mounted on a main body of an image forming apparatus, comprising: an image carrier; and a developing apparatus having a developer storage space, for developing a latent image formed on the image carrier to produce a visible image; in which the developer storage space is segmented into a first developer storage portion and a second developer storage portion along upper/lower directions, while sandwiching therebetween a latent image writing position of the image carrier into which the latent image is written; and also the first developer storage portion is communicated to the second developer storage portion via a developer path. Since the developer storage space is segmented into upper/lower portions while sandwiching therebetween the developer path, even when the developer storage capacity of the second developer storage portion located under the latent image writing position is reduced, the necessary amount of the developer can be replenished with the developer stored in the second developer storage portion. 
     In the case that, for instance, a scanning type laser exposing apparatus is employed as a means for forming a latent image, in order to secure an optical scanning path outputted from this scanning type laser exposing apparatus, a window portion which constitutes the optical scanning path is formed between the first developer storage portion and the second developer storage portion, and also, both the first developer storage portion and the second developer storage portion are separated from each other along the upper/lower direction while sandwiching therebetween this window portion. Also, developer paths may be preferably provided on the both sides of this window portion. 
     Preferably, the first developer storage portion is provided with a first stirring/transporting member which stirs/transports the developer from a center of the first stirring/transporting member to both sides thereof. This first stirring/transporting member may be constituted by, for example, a wire line material. Although the first stirring/transporting member may be formed in a crank shape, this first stirring/transporting member may be formed in a helical shape in such a manner that the wire line materials are wound from a center portion thereof (viewed from axial line direction) toward both edge portions thereof along different winding direction. 
     Preferably, the second developer storage portion is provided with a second stirring/transporting member which stirs/transports the developer from both side portions of the second stirring/transporting member to a center portion thereof. As a result, the amounts of the developer can be made equal to each other along the axial direction. It should be understood that when the developer owns good fluidity, this second stirring/transporting member need not employ a specific structure, but may be formed in, for instance, a crank shape. 
     Also, the present invention may cover an image forming apparatus having the process cartridge with employment of the above-explained construction. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view for indicating an image forming apparatus according to an embodiment mode of the present invention. 
     FIG. 2 is a sectional view for representing a process cartridge according to an embodiment mode of the present invention. 
     FIG. 3 is a side view for showing a supply path of developer in the process cartridge according to the embodiment mode of the present invention. 
     FIG. 4 is a perspective view for indicating the process cartridge according to the embodiment mode of the present invention. 
     FIG. 5 is an exploded perspective view for indicating an image carrier unit of the process cartridge according to the embodiment mode of the present invention. 
     FIG. 6 is an exploded perspective view for representing a developing appliance unit of the process cartridge according to the embodiment mode of the present invention. 
     FIG. 7 is a perspective view for showing the developing appliance unit of the process cartridge according to the embodiment mode of the present invention. 
     FIG. 8 is an exploded perspective view of the developing appliance unit of the process cartridge according to the embodiment mode of the present invention, as viewed from a rear surface of the developing appliance unit. 
     FIGS. 9A to  9 E are side views for indicating modifications of second stirring/transporting members employed in the process cartridge according to the embodiment mode of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to drawings, embodiment modes of the present invention will be described. 
     FIG. 1 schematically shows an image forming apparatus  10  according to an embodiment mode of the present invention. The image forming apparatus  10  contains a main body  12  of the image forming apparatus. An image forming section  14  is mounted on this image forming apparatus main body  12 . An ejection unit  16  (will be explained later) is provided at an upper portion of this image forming apparatus main body  12 , and also, for instance, two stages of paper supply units  18   a  and  18   b  are arranged at a lower portion of this image forming apparatus main body  12 . Furthermore, two stages of paper supply units  18   c  and  18   d  are arranged below the image forming apparatus main body  12 , while these paper supply units  18   c  and  18   d  are detachably mounted thereon as an optional paper supply unit. 
     Each of the paper supply units  18   a  to  18   d  owns a paper supply unit main body  20  and a paper supply cassette  22  into which paper is stored. The paper supply cassette  22  is slidably mounted with respect to the paper supply unit main body  20 , and is drawn out from this paper supply unit main body  20  along a front plane direction (namely, right direction of FIG.  1 ). Also, a nudger roller  24  is arranged at an upper portion near an inner end of the paper supply cassette  22 , and both a retard roller  26  and a feed roller  28  are arranged in front of this paper supply roller  24 . Furthermore, feed rollers  30  are provided with the optionally-provided paper supply units  18   c  and  18   d , and these feed rollers  30  may constitute a pair of feed rollers. 
     A transport path  32  corresponds to a paper path defined from the nudger roller  24  of the lowermost paper supply unit  18   d  up to an ejection port  34 . While this transport path  32  is located in the vicinity of a rear surface (namely, left side surface viewed in FIG. 1) of the image forming apparatus main body  12 , this transport path  32  owns such a portion which is formed along the substantially vertical direction from the feed roller  30  of the lowermost paper supply unit  18   d  up to a fixing apparatus  36  (will be discussed later). Both a transferring apparatus  42  (will be explained later) and an image carrier  44  (will be explained later) are arranged on an upper stream side of the fixing apparatus  36  of this transport path  32 . Furthermore, a register roller  38  is arranged on an upper stream side of both the transferring apparatus  42  and the image carrier  44 . In addition, an ejection roller  40  is arranged in the vicinity of an ejection port  34  of the transport path  32 . 
     As a result, the recording mediums which are fed out by the nudger roller  24  from the paper supply cassettes  22  of the paper supply units  18   a  to  18   d  are smoothly separated by the retard roller  26  and the feed roller  28  to be conducted to the transport path  32 , and then, are temporarily stopped by the register roller  38 . After proper timing is controlled, a developer image is transferred to the recording medium while the recording medium is penetrated between the transferring apparatus  42  and the image carrier  44  (will be explained later), and this transferred developer image is fixed on the fixing apparatus  36 , and then, the recording medium on which the fixed image has been formed is ejected from the ejection port  34  to the ejection unit  16  by the ejection roller It should be noted that when a double-surface printing mode is carried out, this recording medium is returned to an inversion path  48 . In other words, a front path portion of the transport path  30  as to the ejection roller  40  is separated into two paths, a switching craw  46  is provided at this separated path portion, and the inversion path  48  is formed from this separated path portion up to the register roller  38 . While transport rollers  50   a  to  50   c  are provided in this inversion path  48 , in the case of the double-surface printing mode, the switching claw  46  is switched to such a side that the inversion path  48  is opened. Then, the ejection roller  40  is inverted at a time instant when a front edge portion of a recording medium is engaged with the ejection roller  40 , so that this recording medium is conducted to the inversion path  48 , and then, is penetrated through the register roller  38 , the transfer apparatus  42 , the image carrier  44 , and the fixing apparatus  36  so as to be ejected from the ejection port  34  to the ejection unit  16 . 
     The ejection unit  16  owns an inclination unit  52  which is freely pivotable with respect to the image forming apparatus main body  12 . This inclination unit  52  is inclined in such a manner that an ejection port portion thereof is low and is gradually heightened toward a front surface direction (namely, right direction viewed in FIG.  1 ). This ejection port portion is used as a lower end of the inclination unit  52  and a tip portion which is heightened is used as an upper end thereof. This inclination unit  52  is supported with respect to the image forming apparatus main body  12  in such a manner that this inclination unit  52  is freely pivotable, while the lower end thereof is located at a center. As indicated by a two-dot/dash line in FIG. 1, when this inclination unit  52  is rotated toward the upper direction so as to be opened, an opening unit  54  is formed, and a process cartridge (will be explained later)  64  can be detachably mounted via this opening unit  54 . 
     The image forming section  14  is made of, for instance, an electro-photographic type image forming unit. This image forming section  14  is arranged by the image carrier  44  constructed of a photosensitive material, a charging apparatus  56 , an optical writing apparatus  58 , a developing appliance  60 , a transferring apparatus  42 , a cleaning apparatus  62 , and a fixing apparatus  36 . The charging apparatus  56  is constituted by, for example, a charge roller capable of uniformly charging the image carrier  44 . The optical writing apparatus  58  writes a latent image in an optical manner on the image carrier  44  charged by the charging apparatus  56 . The developing appliance  60  develops the latent image of the image carrier  44 , which has been formed by the optical writing apparatus  58 , by way of developer so as to produce a visible image. The transferring apparatus  42  is constituted by, for example, a transfer roller which transfers the developer image by the developing appliance  60  to paper. The cleaning apparatus  62  is constituted by, for instance, a blade which cleans the developer left on the image carrier  44 . The fixing apparatus  36  is arranged by both a pressure-applying roller and a heating roller, by which the developer image which has been transferred onto the paper by the transferring apparatus  42  is fixed on this paper. The optical writing apparatus  58  is constructed of, for example, a scanning type laser exposing apparatus, and is arranged in parallel to the above-described paper supply units  18   a  to  18   d , and is located in the vicinity of a front surface of the image forming apparatus main body  12 . As will be explained later, the optical writing apparatus  58  exposes the image carrier  44  by scanning light beams across the inner space of the developing appliance  60 . This exposing position of the image carrier  44  may constitute a latent image writing position “P”. It should be noted that in this embodiment mode, the scanning type laser exposing apparatus has been employed as the optical writing apparatus  58 . Alternatively, an LED (Light Emitting Diode), a surface emitting laser, and the like may be employed. 
     The process cartridge  64  is arranged by employing the image carrier  44 , the charging apparatus  54 , the developing appliance  60 , and the cleaning apparatus  62  in an integral body. This process cartridge  64  is arranged just under the inclination unit  52  of the ejection unit  16 , and as previously explained, is detachably mounted via the open portion  54  which is formed when the inclination unit  52  is opened. 
     This process cartridge  64  is detachably separated into an image carrier unit  66  and a developing appliance unit  68 . In the image carrier unit  66 , the image carrier  44 , the charging apparatus  54 , and the cleaning apparatus  60  are arranged. In the developing appliance unit  68 , the developing appliance  60  is arranged. The developing appliance unit  68  owns a developer storage space  70  which stores there into, for example, developer. An upper portion of this developer storage unit  70  belongs to such an area “A” which is surrounded by the inclination unit  52 , a horizontal plane extended from the lower end of the inclination unit  52 , and also, a vertical plane extended from the upper end of this inclination unit  52  as indicated by a two-dot/dash line in FIG.  1 . Also, an upper wall plane  72  which constitutes the developer storage space  70  is formed in such a manner that this upper wall plane  72  is located in parallel to the inclination unit  52  and along this inclination unit  52 . Also, a plurality of ribs  74  are formed on a lower surface of the inclination unit  52  in such a way that these plural ribs  74  are positioned in parallel to each other along the inclination direction of the inclination unit  52 . Since these ribs  74  are formed, a flow path  76  is formed between the inclination unit  52  and the process cartridge  64 . This flow path  76  is employed so as to penetrate air therethrough, and this flow path  76  may disperse heat produced from the fixing apparatus  36 . Furthermore, a grip unit  78  is formed on the upper portion of the developer storage space  70 . This grip unit  78  is formed in such a manner that wall surfaces of both sides of the upper portion of the developer storage space  70  are entered into the inside thereof. When the process cartridge  64  is detachably mounted, this process cartridge  64  can be readily detachably mounted by gripping this grip unit  78 . 
     In FIG. 2 to FIG. 8, a detailed construction of the above-described process cartridge  64  is indicated. As explained above, the process cartridge  64  is arranged by the image carrier unit  66  and the developing appliance unit  68 , and this image carrier unit  66  is coupled to the developing apparatus unit  68  via coupling pins  80   a  and  80   b  in such a manner that this image carrier unit  66  is freely pivotable with respect to the developing apparatus unit  68 . Also, both the image carrier unit  66  and the developing apparatus  68  are energized with each other by a tension spring  82  and a depression spring  84 , and a developing roller  86  is depressed against the image carrier  44 . 
     It should also be understood that a memory  88  for storing thereinto a total print number and the like is provided on a side surface of the process cartridge  64  (namely, side surface of one, or both image carrier unit  66  and developing appliance unit  68 ). 
     The image carrier unit  66  owns a main body  90  of the image carrier unit  66 , and both the image carrier  44  and the charging apparatus  56  are supported by this image carrier unit main body  90  in such a manner that both the image carrier  44  and the charging apparatus  56  are rotatably supported by this image carrier unit main body  90  via bearing  92   a  and  93   b  used for the image carrier  44 , and bearings  94   a  and  94   b  used for the charging apparatus  56 , respectively. An one of the above-described bearing  94   a  and bearing  94   b  for the charging apparatus  56  own another function of a power supply portion. Also, for example, two fingers  96   a  and  96   b  are supported by the image carrier unit main body  90  in such a manner that these fingers  96   a  and  96   b  are freely pivotable with respect to this image carrier unit main body  90 . Since tip portions of these fingers  96   a  and  96   b  are depressed by a spring for the fingers  96   a  and  96   b  on the surface of the image carrier  44 , a recording medium which will wrap the image carrier  44  is stripped by these tip portions. Also, a developer collecting space  98  is formed above the cleaning apparatus (cleaning blade)  62  within the image carrier unit main body  90 , and thus, developer which has been scratched/dropped by the cleaning apparatus  62  is collected into this developer collecting space  98 . A paddle  100  is rotatably provided in this developer collecting space  98 . This paddle  100  is supported via a gear  102  for the paddle  100  by the image carrier unit main body  98 , and transports the developer which has been collected by being rotated to an inner side of the developer collecting space  98 . Also, a shutter  104  is provided at the upper portion of the image carrier unit main body  90  in such a manner that this shutter  104  can be freely opened/closed. This shutter  104  is supported via a shaft  106  for the shutter  104  with respect to the image carrier unit main body  90  in a freely movable manner. This shutter  104  closes an opening portion of the image carrier  44  before the process cartridge  64  is mounted, and is opened in order that the image carrier  44  is come out to the front in the case that the process cartridge  64  is mounted. 
     The developing appliance unit  68  contains a main body  112  of the developing appliance unit  68  which is constituted by jointing a front housing  108  to a rear housing  110 . An inner space of this developing appliance unit main body  112  is segmented into the above-described developer collecting space  70  and a developing unit  114  in which the developing roller  86  is arranged. The developer collecting space  70  is separated into a first developer storage portion  116   a  and a second developer storage portion  116   b  via a partition wall  118 , while a horizontal line extended from the latent image writing position “P” is defined as a boundary. This horizontal line corresponds to a scanning optical path originated from the optical writing apparatus  58 . The first developer collecting portion  116   a  is located at an upper portion of the developer collecting space  70 , whereas the second developer storage portion  116   b  is located at a lower portion thereof. A developer storage capacity of the first developer storage unit  116   a  is made larger than a developer storage capacity of the second developer storage unit  116   b.    
     As shown in FIG. 3, the partition wall  118  constitutes a window portion  120  having, for example, a rectangular shape, which forms the optical scanning path defined from the optical writing apparatus  58 . Also, this partition wall  118  constitutes developer paths  122   a  and  122   b  in connection with the developing appliance unit main body  112  on both sides of this window portion  120 . Both the developer paths  122   a  and  122   b  cause the first developer storage portion  116   a  to be communicated with the second developer storage portion  116   b . In the first developer storage portion  116   a , as previously explained, a first stirring/transporting member  124  is rotatably arranged, and also an upper portion of this first developer storage portion  116   b  is arranged within the area “A.” 
     As indicated in FIG.  3  and FIG. 6, the first stirring/transporting member  124  contains a shaft portion  126 , and winding portions  128   a  and  128   b  which are formed in helical shapes along different winding directions which are directed from a center portion (viewed along axial line direction) of this shaft portion  126  to both edge portions thereof. This shaft portion  126  and the winding portions  128   a ,  128   b  are constituted by a single wire material. As a consequence, when this first stirring/transporting member  124  is rotated, the developer stored in the first developer storage portion  116   a  can be supplied to the developer paths  122   a  and  122   b  provided on both sides along the axial line direction, and thus, the developer maybe supplied via these developer paths  122   a  and  122   b  to the second developer storage portion  116   b.    
     A second stirring/transporting member  130  is rotatably arranged at a lower position of the first stirring/transporting member  124  within the second developer storage unit  116   b . As shown in FIG.  3  and FIG. 6, this second stirring/transporting member  130  is constituted as a screw shaft which is constituted by a shaft portion  132 , and also screw portions  134   a  and  134   b . These screw portions  134   a  and  134   b  are formed from edge portions (viewed along axial direction) of this shaft portion  132  to a center portion thereof along different directions. As a consequence, when this second stirring/transporting member  130  is rotated, larger amounts of the developer are transported from the both-sided developer paths  122   a  and  122   b  toward the center direction, and then the developer is uniformly dispersed to be supplied to a subsequent third stirring/transporting member  136 . 
     Furthermore, both a third stirring/transporting member  136  and a fourth stirring/transporting member  138  are arranged in the second developer storage portion  116   b . The third stirring/transporting member  136  transports the developer to the fourth stirring/transporting member  138 , while this third stirring/transporting member  136  owns a shaft portion  140 , and a plate-shaped portion  142 , one edge of which is fixed on this shaft portion  140 , and also which is extended along a circumferential direction. The fourth stirring/transporting member  138  transports the developer which has been transported by the third stirring/transporting member  142  to the developing roller  86 , and also, mixes this new developer with the developer which has been scratched/dropped from the developing roller  86 . 
     As is well known in the field, the developing roller  86  is constructed in such a manner that a sleeve is wound on a magnet roller, and tracking caps  144   a  and  144   b  are provided on both sides of the magnet roller. These tracking caps  144   a  and  144   b  are made in contact to the image carrier  44 , and as explained in the above description, a developing gap may be secured by depressing these tracking caps  144   a  and  144   b  against the image carrier  44  by both the tension spring  82  and the depression spring  84 . A layer thickness restricting member  146  made of, for instance, a resin is made in contact with the developing roller  86 . A thickness of a developer layer adhered on the surface of the developing roller  86  is restricted by this layer thickness restricting member  146 . Also, a side surface of this developing roller  86  is sealed by a developing portion sealing member  148 . 
     It should also be noted that reference numerals  150   a  and  150   b  indicate developer caps which are detachably mounted on the developing appliance unit main body  112 . Since these developer caps  150   a  and  150   b  are pulled out, the developer is supplied to either the first developer storage unit  116   a , or the second developer storage unit  116   b.    
     In the drive system of the process cartridge  64 , drive force is transferred from the side of the image carrier  44 , and then, is transferred via a developing roller gear  152 , a gear  154  for the respective first to fourth stirring/transporting members, and an idle gear  156  to the developing roller  86  and also to the respective first to fourth stirring/transporting members  124 ,  130 ,  136 , and  138 . A stirring/transporting member sealing member  158  is inserted into a bearing portion of the stirring/transporting member gear  154 . Furthermore, a gear cover  159  is provided on the side surface of the developing appliance unit main body  112 , while this gear cover  159  covers the gear  154  for the respective stirring/transporting members and the idle gear  156 . 
     Next, operations of the image forming apparatus according to the above-described embodiment mode will now be described. 
     While the image carrier  44  is uniformly charged by the charging apparatus  56 , light emitted from the optical writing apparatus  58  is irradiated onto this charged image carrier  44  in response to an image signal, and then, a latent image is formed at the latent image forming position “P” thereof. The light emitted from the optical writing apparatus  58  passes through the process cartridge  64  via the window portion  120  of the process cartridge  64 . The latent image which has been formed on the image carrier  44  by this optical writing apparatus  58  is developed by the developer of the developing appliance  60  so as to produce a visible image. 
     While the developer has been stored in both the first developer storage portion  116   a  and the second developer storage portion  116   b , the developer stored in the first developer storage portion  116   a  is transported to both sides by rotating the first stirring/transporting member  124 , and then both the developer located on the both sides is transported via the two developer paths  122   a  and  122   b  to the second developer storage unit  116   b . Furthermore, the developer of the second developer storage portion  116   b  is uniformly dispersed by rotating the second stirring/transporting member  130 , and then, the uniformly dispersed developer is transported to the developing unit  114  by the third stirring/transporting member  136  and the fourth stirring/transporting member  138 . In this developing unit  114 , the transported developer is adhered onto the developing roller  86 , the layer thickness of the adhered developer is restricted by the layer thickness restricting member  146 , the thickness restricted developer is transported up to a developing position located opposite to the image carrier  44 , and then, an image made of the developer is formed in correspondence with the latent image of the image carrier  44 . 
     On the other hand, one of the paper supply units  18   a  to  18   d  is selected in response to a size signal and the like, recording mediums stored in one of these paper supply cassettes  22  are fed out by the nudger roller  24 , and these recording mediums are smoothly separated by the retard roller  26  and the feed roller  28  so as to conduct a recording medium to the transport path  32 . Then, this conducted recording medium is temporarily stopped by the register roller  38 , and thereafter, this recording medium is conducted between the transferring apparatus  42  and the image carrier  44  at proper timing. 
     When the recording medium is conducted between the transferring apparatus  42  and the image carrier  44  in this manner, the developer on the image carrier  44  is transferred to the recording medium by the transferring apparatus  42 . This recording medium to which the developer has been transferred is penetrated through the fixing apparatus  36 , and then is ejected from the ejection port  34  to the ejection unit  16 . 
     The recording medium is penetrated through the transport path  32 , and then is ejected to the ejection unit  16 , and thus a so-called “C-path” is constituted, while this transport path  32  is formed along the substantially vertical direction from the paper supply units  18   a  to  18   d  arranged along the horizontal direction. In this embodiment mode, since the process cartridge  64  is stored within the C-path, the layout of this image forming apparatus can be made compact. However, if the developer storage space connected to the developing unit  114  is arranged lower than the latent image writing position “P” in the normal design manner, such a dead space is produced under the ejection portion  16 . More specifically, in the case that a storage capacity of the developer is increased, since the space located lower than the latent image writing position “P” must be increased, a larger dead space is produced. 
     However, in this embodiment mode, the window portion  120  which constitutes the scanning optical path from the optical writing apparatus  58  is formed in the process cartridge  64 , and also, the developer paths  122   a  and  123   b  are formed on both sides of this window portion  120 , so that the first developer storage portion  116   a  can be arranged above the scanning optical path. As a result, the image forming apparatus can be made compact, while the sufficiently large developer storage capacity can be maintained. 
     In FIGS. 9A to  9 E, various sorts of modifications are illustrated with respect to the above-described second stirring/transporting member  130 . Similar to the above-described embodiment mode, a second stirring/transporting member  130  shown in FIG. 9A is similarly constituted by employing a shaft portion  132 , and two screw portions  134   a  and  134   b  which are formed from edge portions of this shaft portion  132  (as viewed in axial line direction thereof) toward a center portion thereof along mutually different directions. However, this second stirring/transporting member  130  owns such a different structural point that a pitch of each screw part of the screw portions  134   a  and  134   b  is continuously changed. The pitches of the screw portions  134   a  and  134   b  are gradually increased from the both edge portions thereof to the center portions thereof in order that the developer may be easily collected to the center parts thereof, and thus, the transport amounts of the developer along the axial direction can be made equal to each other. 
     As to a second stirring/transporting member  130  indicated in FIG. 9B, pitches of respective screw portions are changed in a stepwise manner in contrast to the above-explained second stirring/transporting member  130  of FIG. 9A in which the pitches of the respective screw portions are changed in the continuous manner. As to a third stirring/transporting member  130  shown in FIG. 9C, while flat plate portions  160   a  and  160   b  are employed instead of the screw portions, pitches of these flat plate portions  160   a  and  160   b  are changed in a continuous manner. As to a second stirring/transporting member  130  represented in FIG. 9D, the pitches of the flat plate portions  160   a  and  160   b  are changed in a stepwise manner. 
     A second stirring/transporting member  130  indicated in FIG. 9E is constituted by a wire line material formed in a crank shape. In the case that developer owns good fluidity, the developer may be uniformly transported due to the good fluidity of this developer by merely forming the wire line material in the crank shape and by merely stirring the developer. 
     It should be noted that the second stirring/transporting members  130  with employment of the above-described constructions may be driven in an intermittent manner so as to control the transport amount thereof. In order to intermittently drive these second stirring/transporting members  130 , for instance, a pulse motor may be employed irrespective of motors which are employed in other drive systems. 
     In the above-described embodiment modes, the one-component developing system is employed. The present invention is not limited to this one-component developing system, but may be applied to a two-component developing system. Also, in the above-explained embodiment mode, the developer image is directly transferred from the image carrier to the recording medium. However, the present invention is not limited to this transfer operation, but may be applied to another embodiment in which an intermediate transfer member may be interposed between the image carrier and the recording medium. Furthermore, in the above-described embodiment modes, the black/white image forming apparatus has been described. Apparently, the present invention may be applied to a color image forming apparatus. 
     As previously explained, in accordance with the present invention, since the developer storage portions are provided along the upper/lower portions by sandwiching therebetween the latent image writing position of the image carrier, the image forming apparatus can be made compact while the sufficiently large developer storage capacity can be maintained.