Patent Publication Number: US-7899368-B2

Title: Development device, and image forming apparatus and process cartridge using the development device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This patent application is based on Japanese patent application, No. 2006-135217 filed on May 15, 2006 in the Japan Patent Office, the entire contents of which are incorporated by reference herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Exemplary aspects of the present invention relate to a development device, and more particularly to a development device using a two-component developer. In addition, the exemplary aspects of the present invention also relate to an image forming apparatus and a process cartridge using a development device. 
     2. Description of the Related Art 
     A related art development device, which employs a two-component developer including a toner and a magnetic carrier, for use in an image forming apparatus includes a supply conveyance path and an agitation conveyance path to circulate the developer. The supply conveyance path supplies the developer to a developer carrying member while conveying the developer to a direction parallel to the axis of an image carrying member. The agitation conveyance path conveys the developer in a direction opposite to the supply conveyance path while agitating the developer. 
     In a such development device, the developer thus supplied to the developer carrying member passes a development region, and is collected in the supply conveyance path. The toner in the developer is consumed in the development region and, the developer is mixed with the developer within the supply conveyance path. The more developer located on the downstream portion of the supply conveyance path, the greater the amount of developer particles passing through the development region. Consequently, the more developer located downstream of the supply conveyance path in a developer conveyance direction, the lower the toner density the developer has. When the toner density decreases, the image density of an image developed by the developer decreases. In other words, the image density of an image varies at the upstream side and downstream side in the developer conveyance direction of the conveyance path in which the developer is supplied to the developer carrying member, resulting in generation of an uneven density image. 
     In addition, the developer used for development is collected through the agitation conveyance path. The developer reaching the end of the downstream side of the agitation conveyance path in the developer conveyance direction is transferred to the end of the upstream side of the supply conveyance path in the developer conveyance direction. The developer collected at a position closer to the downstream side of the agitation path in the developer conveyance direction is agitated for a shorter time period. Accordingly, the developer collected at the downstream side of the developer conveyance direction of the agitation conveyance path is immediately supplied to the supply conveyance path. This immediate supply of the collected developer causes inadequate agitation of the developer, resulting in non-uniform charging of the toner, thereby decreasing of the image density even if the toner density is maintained at an appropriate level. 
     One example attempts to reduce the deterioration of the toner density and image density by providing an additional conveyance path serving as a collection conveyance path in a development device. Specifically, the development device as well as the collection conveyance path include a supply conveyance path and an agitation conveyance path. The supply conveyance path is disposed at substantially the same level as that of the developer carrying member to convey and supply the developer to the developer carrying member. The collection conveyance path is disposed below the developer carrying member to collect and convey the collected developer. The agitation conveyance path is disposed at substantially the same level as that of the collection conveyance path and below the supply conveyance path. The agitation conveyance path agitates excess developer reaching the end of the downstream side of the supply conveyance path relative to the developer conveyance direction, and the collected developer reaching the end of the downstream side of the collection conveyance path relative to the developer conveyance direction. The supply conveyance path, collection conveyance path and agitation conveyance path are disposed to be parallel to the developer carrying member. The conveyance paths are separated from one another by separation members. One separation member is disposed between the end of the downstream side of the agitation conveyance path and the supply conveyance path, and includes an opening so that the agitated developer is transferred to the supply conveyance path through the opening. Another separation member is disposed between the end of the downstream side of the supply conveyance path and the agitation conveyance path, and includes an opening so that the excess developer is transferred to the agitation conveyance path through the opening. Still another separation member is disposed between the end of the downstream side of the collection conveyance path and the agitation path, and includes an opening so that the collected developer is transferred to the agitation conveyance path through the opening. By providing an additional collection conveyance path, the developer can be supplied and collected independently. 
     The collection conveyance path is disposed below the developer carrying member in such a manner that the collected developer in the collection conveyance path is adhered to the developer carrying member when the volume of the collected developer in the collection conveyance path reaches a certain level. The collection conveyance path conveys the collected developer from the upstream side to the downstream side thereof, and transfers the developer from the downstream side thereof to the agitation conveyance path. In the course of the transfer from the downstream side of the collection conveyance path to the agitation conveyance path, the developer conveyance direction of the collected developer shifts significantly. Consequently, the collected developer can be accumulated at the downstream side of the collection conveyance path, and the height of the collected developer can reach higher than a certain level. In this case, the collected developer in the collection conveyance path is re-supplied to the developer carrying member, resulting in an occurrence of a problem in that the collected developer having an inappropriate toner density (i.e., the toner is consumed) is mixed with the developer having an appropriate toner density. Thereby, the toner density can be decreased, and uneven images can be generated. 
     SUMMARY OF THE INVENTION 
     According to an aspect of the invention, a development device includes a developer carrying member, a developer supply conveyance path, a developer collection conveyance path, a developer agitation conveyance path, at least one partition member, at least one transfer opening, and a communication opening. The developer carrying member rotates while bearing thereon a two-component developer including a magnetic carrier and a toner. This developer carrying member supplies the toner to a latent image on a surface of a latent image carrier in a development region in which the developer carrying member faces the latent image carrier so as to develop the latent image. The developer supply conveyance path includes a developer supply conveyance member supplying the two-component developer to the developer carrying member so as to convey the two-component developer in a first direction of the developer carrying member. The developer collection conveyance path includes a developer collection conveyance member collecting a developer collected from the developer carrying member passed the opposing position so as to convey the collected developer in the first direction. The developer agitation conveyance path includes a developer agitation conveyance member receiving an excess developer unused for development and the collected developer. The developer agitation conveyance path conveys the excess developer and the collected developer in a second direction opposite to the first direction while agitating the developers, and supplies the agitated developers to the developer supply conveyance path. The at least one partition member separates the developer collection conveyance path, the developer supply conveyance path, and the developer agitation conveyance path from each other. The at least one transfer opening is disposed in the partition member to transfer the collected developer from an end of the developer collection conveyance path at a downstream side relative to the first direction to an upstream side of the developer agitation conveyance path relative to the second direction. The communication opening communicates the developer collection conveyance path with the developer agitation conveyance path. The communication opening is disposed at a further upstream side of the developer collection conveyance path than the at least one transfer opening relative to the first direction and at a higher position than a predetermined height of the developer collection conveyance path. 
     A process cartridge detachably installed in an image forming apparatus as a unit including a development device and at least one of a latent image carrying member, a charging device, and a cleaning device. The development device develops a latent image on the latent image carrying member. A charging device charges the latent image carrying member. The cleaning device cleans a surface of the latent image carrying member. 
     An image forming apparatus includes a latent image carrying member and a development device. The latent image carrying member carries a latent image, and the development device develops the latent image. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the exemplary aspects of the invention and many of the attendant advantage thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
         FIG. 1  is a schematic diagram illustrating an image forming apparatus according to an exemplary embodiment of the present invention; 
         FIG. 2  is a schematic diagram illustrating a development device and a photoconductor of the image forming apparatus of  FIG. 1 ; 
         FIG. 3  is a schematic perspective view illustrating the development device of  FIG. 2  with an opening through which a developer is transferred; 
         FIG. 4  is a schematic perspective view illustrating flow of a developer in the development device of  FIG. 2 ; 
         FIG. 5  is a schematic diagram illustrating the flow of the developer in the development device of  FIG. 2 ; 
         FIG. 6  is a schematic view illustrating the development device of  FIG. 2 ; 
         FIG. 7  is a schematic diagram illustrating flow of a developer in a background development device; and 
         FIG. 8  is a perspective view illustrating a toner supply opening of the development device of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In describing exemplary embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner. 
     Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, an image forming apparatus according to an exemplary embodiment of the present invention is described. 
     Referring to  FIG. 1 , a tandem image forming apparatus  500  having four photoconductor drums  1 Y,  1 M,  1 C and  1 K for four colors is illustrated. The image forming apparatus  500  includes a printing unit  100 , a sheet feeder  200 , a scanner  300  and an automatic document feeder  400 . 
     The printing unit  100  includes an optical writing unit  21 , an image forming unit  20 , an intermediate transfer unit  17 , a secondary transfer device  22 , a pair of registration rollers  49  and a fixing device  25 . 
     The optical writing unit  21  includes an optical source (not shown), a polygon mirror (not shown), a fθ lens (not shown) and a reflection mirror (not shown). The optical writing unit  21  writes an electrostatic latent image, for example, on the photoconductor drum  1 Y, with a laser beam that is formed based on image data. The description of the optical writing unit  21  will be explained later. 
     The image forming unit  20  includes four process cartridges  18 Y,  18 M,  18 C and  18 K for the four colors, yellow, magenta, cyan and black which are abbreviated as Y, M, C and K, respectively. The abbreviations may be omitted as necessary. The process cartridge  18 Y is treated as representative of the process cartridges  18 Y,  18 M,  18 C and  18 K, and includes the photoconductor drum  1 Y, a charging device (not shown), a development device  4 Y, a drum cleaning device (not shown) and a discharger (not shown). As the process cartridges  18 Y,  18 M,  18 C and  18 K are substantially similar to one another except for the color of the toner, only the process cartridge  18 Y will be explained. 
     The charging device of the process cartridge  18 Y uniformly charges a surface of the photoconductor drum  1 Y. The optical writing unit  21  modulates and deflects the laser beam to irradiate the surface of the photoconductor drum  1 Y so that the potential of an irradiated area of the photoconductor drum  1 Y decays, resulting in formation of an electrostatic latent image on the surface of the photoconductor drum  1 Y. The development device  4 Y develops the electrostatic latent image on the photoconductor drum  1 Y with a developer including a yellow toner to form a yellow toner image Y. 
     The toner image Y on the photoconductor drum  1 Y is primarily transferred onto an intermediate transfer belt  110  which will be described later. The drum cleaning device removes a remaining toner from the surface of the photoconductor drum  1 Y. The discharger discharges the photoconductor drum  1 Y. Thus, the photoconductor drum  1 Y is initialized, and the charging device uniformly charges the photoconductor drum  1 Y to form the next image. Similarly, the processes cartridges  18 M,  18 C and  18 K execute the series of the image forming process such as charging, writing, developing, transferring, cleaning and discharging. 
     The intermediate transfer unit  17  includes the intermediate transfer belt  110 , a belt cleaning device  99 , a tension roller  14 , a drive roller  15 , a secondary backup roller  16  and primary transfer bias rollers  62 Y,  62 M,  62 C and  62 K. 
     The intermediate transfer belt  110  is tightly stretched by a plurality of rollers including the tension roller  14 , and rotates clockwise with an endless movement. The drive roller  15  is driven by a belt driving motor (not shown) so as to drive the intermediate transfer belt  110  to rotate. 
     The primary transfer bias rollers  62 Y,  62 M,  62 C and  62 K are disposed in such a manner to contact an inner circumference side of the intermediate transfer belt  110  so as to receive a primary transfer bias applied thereto from a power source (not shown). The primary transfer bias rollers  62 Y,  62 M,  62 C and  62 K press the inner circumference side of the intermediate transfer belt  110  towards the photoconductor drums  1 Y,  1 M,  1 C and  1 K to form primary transfer nips. In each of the primary transfer nips, a primary transfer electric field generated by the primary transfer bias is generated. Specifically, the primary transfer electric field is formed between the photoconductors  1  and the respective primary transfer bias rollers  62 . 
     The toner image Y formed on the photoconductor drum  1 Y is primarily transferred onto the intermediate transfer belt  110  by the primary transfer electric field and nip pressure. Similarly, toner images M, C and K formed on respective photoconductors drums  1 M,  1 C and  1 K are primarily transferred onto the intermediate transfer belt  110 . In other words, a four-color image is formed on the intermediate transfer belt  110  while overlaid. 
     The four-color image on the intermediate transfer belt  110  is secondarily transferred onto a transfer sheet as a recording sheet (not shown) at a secondary transfer nip which will be described later. After the intermediate transfer belt  110  passes the secondary nip, the belt cleaning device  99  removes the remaining toner from the surface of the intermediate transfer belt  110 . 
     The secondary transfer device  22  is disposed below the intermediate transfer unit  17 , and includes a sheet conveyance belt  24  and secondary transfer tension rollers  23 . The sheet conveyance belt  24  is tightly stretched by the secondary transfer tension rollers  23 , and rotates counterclockwise with rotation of at least one of the secondary transfer tension rollers  23 . One of the secondary transfer rotation rollers  23  disposed at a right hand side of  FIG. 1  and the secondary transfer backup roller  16  sandwich the intermediate transfer belt  110  and the sheet conveyance belt  24  therebetween. In other words, the intermediate transfer belt  110  and the sheet conveyance belt  24  contact each other at the secondary transfer nip. The power source applies a secondary transfer bias having a polarity opposite to that of the charge of the toner to one of the secondary transfer tension rollers  23  disposed at the right hand side. Application of the secondary transfer bias forms a secondary transfer electric field in the secondary transfer nip. The secondary transfer electric field electrostatically transfers the four-color image on the intermediate transfer belt  110  towards the secondary transfer tension roller  23  at the right hand side of  FIG. 1 . The pair of registration rollers  49  register the transfer sheet to feed into the secondary transfer nip in such a manner to be synchronized with the four-color image on the intermediate transfer belt  110 . The four-color image is secondary transferred onto the transfer sheet by the secondarily transfer electric field and nip pressure. The exemplary embodiment of the present invention employs the secondary transfer system to apply the secondary transfer bias to one of the secondary transfer tension rollers  23 . However, a charger can be employed to charge the transfer sheet in a non-contact manner, substituting for the secondary transfer system. 
     The image forming apparatus  500  includes the sheet feeder  200  at a lower portion thereof as shown in  FIG. 1 . The sheet feeder  200  includes sheet cassettes  44 , sheet feeding rollers  42 , a feeding path  46 , a sheet bank  43  and sheet separation rollers  45 . Each of the sheet cassettes  44  stores a plurality of transfer sheets therein. The sheet cassettes  44  are disposed one above another in a vertical direction. Each of the sheet cassettes  44  presses an uppermost sheet against the corresponding sheet feeding roller  42 , and the uppermost sheet is fed towards the feeding path  46  by rotation of the sheet feeding roller  42 . 
     The feeding path  46  is a path in which the recording sheet is conveyed towards the registration rollers  49 . The feeding path  46  includes a plurality of conveyance rollers  47  and the registration rollers  49  in a vicinity of the end portion thereof. When the four-color image on the intermediate transfer belt  110  is entered into the secondary transfer nip with an endless movement of the intermediate transfer belt  110 , the pair of registration rollers  49  sandwich the transfer sheet therebetween and feed the transfer sheet at a desired timing to the four-color image on the intermediate transfer belt  110 . The four-color image is adhered to the transfer sheet at the secondary transfer nip to be secondarily transferred, resulting in formation of a full color image on the transfer sheet. The transfer sheet with the full color image is fed out from the secondary transfer nip with rotation of the sheet conveyance belt  24 , and is conveyed to the fixing device  25 . 
     The fixing device  25  of the printing unit  100  includes a belt unit and a pressure roller  27 . The belt unit includes a fixing belt  26  and two rollers. The fixing belt  26  is tightly stretched by the two rollers and rotates with endless movement. The pressure roller  27  presses one of the rollers. The fixing belt  26  and the pressure roller  27  contact each other so as to form a fixing nip in which the transfer sheet conveyed from the sheet conveyance belt  24  is nipped. One of the rollers pressed by the pressure roller  27  includes a heat source (not shown) therein to heat the fixing belt  26 . The heated fixing belt  26  heats the transfer sheet nipped at the fixing nip. Therefore, the full color image is fixed onto the transfer sheet by the heat and nip pressure. 
     The fixing device  25  fixes the full color toner image on the transfer sheet, and the transfer sheet is stacked on a stacking area  57  disposed at a left hand side of the image forming apparatus  500 . When a toner image is formed on another side of the transfer sheet, the transfer sheet is returned to the secondary transfer nip. 
     The image forming apparatus  500  includes the automatic document feeder  400  disposed above the scanner  300  as shown in  FIG. 1 . The automatic document feeder  400  includes an original table  30 . When the image forming apparatus  500  is used to make a copy, for example, an original bunch is placed on the original table  30 . However, when one side of an original is bound like a book, the automatic document feeder  400  is opened with respect to the image forming apparatus  500 , and the original is placed on a contact glass  32  that is included in the scanner  300 . This opening of the automatic document feeder  400  exposes the contact glass  32 . The original on the contact glass  32  is held by closing the automatic document feeder  400 . 
     The scanner  300  includes the contact glass  32 , a first traveling body  33 , a second traveling body  34 , an imaging lens  35  and a reading sensor  36 . The first traveling body  33  includes a light source (not shown), and the second traveling body includes a mirror (not shown). 
     The scanner  300  reads the original on the contact glass  32  by pressing a start switch (referring to as an original reading operation). When the original is placed on the original table  30 , the original is automatically transferred to the contact glass  32  so as to be read by the scanner  300 . During the original reading operation, the first and second traveling bodies  33  and  34  begin to travel, and the light source in the first traveling body  33  emits the light that is reflected from a surface of the original. The mirror in the second traveling body  34  reflects the light. The reflected light passes through the imaging lens  35  and enters into the reading sensor  36 . The reading sensor  36  constructs image information based on the entered light. 
     In parallel with the original reading operation, each element in the process cartridges  18 Y,  18 M,  18 C and  18 K, the intermediate transfer unit  17 , the secondary transfer device  22  and the fixing device  25  begin to drive. The optical writing unit  21  is controlled based on the image information constructed by the reading sensor  36 , and the toner images Y, M, C and K are formed on the respective photoconductors  1 Y,  1 M,  1 C and  1 K. The toner images Y, M, C and K are superimposed and transferred onto the intermediate transfer belt  110  to form the four color toner image. 
     The sheet feeder  200  begins a feeding operation therewithin at substantially the same timing as the beginning of the original reading operation. In the feeding operation, one of the sheet feeding rollers is selected and rotated, and the transfer sheets are fed from one of the sheet cassettes  44  installed in the sheet bank  43 . The sheet separation roller  45  separates the transfer sheets one by one so that each transfer sheet is entered into the feeding path  46  and is conveyed towards the secondary transfer nip by the conveyance rollers  47 . The transfer sheets can be fed from a manual feeding tray  51  as well as the sheet cassettes  44 . For example, a manual feeding roller  50  is selected and rotated to feed the transfer sheets on the manual feeding tray  51  into a separation roller  52 . The separation roller  52  separates the transfer sheets one by one, and each separated transfer sheet is fed into a manual feeding path  53 . 
     When the image forming apparatus  500  forms a multi-color image with at least two different toner colors, the intermediate transfer belt  110  is tightly stretched in such a manner that the upper stretch surface thereof becomes horizontal. In this regard, the photoconductors  1 Y,  1 M,  1 C and  1 K contact the stretched upper surface of the intermediate transfer belt  110 . In contrast, when the image forming apparatus  500  forms a monochrome image with the black toner, the intermediate transfer belt  110  is positioned in such a manner as to incline towards lower left of  FIG. 1  by using a mechanism (not shown). Thereby, the stretched upper surface of the intermediate transfer belt  110  is separated from the photoconductors  1 Y,  1 M and  1 C. The photoconductor  1 K rotates counterclockwise while contacting the stretched upper surface of the intermediate transfer belt  110  so that the toner image K is formed thereon. During the monochrome image formation, the photoconductors  1 Y,  1 M and  1 C and the development devices  4 Y,  4 M and  4 C halt, thereby reducing an occurrence of unnecessary consumption of the toner and wearing of the photoconductors. 
     The image forming apparatus  500  includes a control unit (not shown) and an operation display unit (not shown). The control unit includes a CPU, and the operation display unit includes a liquid crystal display and key buttons. For example, when a user keys in an input to the operation display unit, a command is sent to the control unit so that the user can select one of three one-sided print modes. The toner image is formed on one side of the transfer sheet by selecting one of the three one-sided print modes such as a direct ejection mode, a reverse ejection mode, and a reverse decor ejection mode. 
     Referring to  FIG. 2 , one of the photoconductors  1 Y,  1 M,  1 C and  1 K and one of the development devices  4 Y,  4 M,  4 C and  4 K included in one of the process cartridges  18 Y,  18 M,  18 C and  18 K of  FIG. 1  are enlarged, as representatives of the photoconductors  1  and the development devices  4 . The color abbreviations are omitted as necessary. 
     The photoconductor  1  rotates in a direction G, represented by an arrow shown in  FIG. 2 , to charge a surface thereof with the charging device (not shown). The surface of the photoconductor  1  is irradiated by the laser beam from the optical writing unit  21  of  FIG. 1  so as to form the electrostatic latent image thereon. The development device  4  develops the electrostatic latent image with the toner to form the toner image. 
     The development device  4  includes a development roller  5 , a supply screw  8 , a development doctor  12 , a collection screw  6 , a supply conveyance path  9 , a collection conveyance path  7 , an agitation conveyance path  10 , a first partition wall  133  and a second partition wall  134 . 
     The development roller  5  serving as a developer carrying member supplies the toner to the electrostatic latent image on the surface of the photoconductor  1  while moving a surface thereof in a direction I, represented by an arrow shown in  FIG. 2 . The supply screw  8  serving as a developer supply conveyance member conveys the developer to a rear direction of  FIG. 2  while supplying the developer to the development roller  5 . 
     The development doctor  12  serving as a developer regulation member regulates a thickness of the developer supplied to the development roller  5  to be an appropriate level. The development doctor  12 , made of for example, stainless steel, is located at a downstream side in a surface movement direction of the development roller  5  from a position substantially opposite to the supply screw  8  as shown in  FIG. 2 . 
     The collection screw  6  serving as a developer collection conveyance member collects the developer passed a development region and conveys the collected developer to a direction substantially the same as the supply screw  8 . The collection screw  6  is located at the downstream side in the surface movement direction of the development roller  5  from a position of the development region substantially opposite to the photoconductor  1  as shown in  FIG. 2 . The supply conveyance path  9  serving as a developer supply conveyance path conveying the developer includes the supply screw  8 , and is disposed at substantially the same elevation as the development roller  5 . The collection conveyance path  7  serving as a developer collection conveyance path collecting the developer includes the collection screw  6 , and is disposed below the development roller  5 . 
     The agitation conveyance path  10  serving as a developer agitation conveyance path is disposed below the supply conveyance path  9  and side by side with the collection conveyance path  7 . The agitation conveyance path  10  includes an agitation screw  11  that conveys the developer in an opposite direction to the supply screw  8  (towards a front side of  FIG. 2 ) while agitating the developer as a developer agitation conveyance member. 
     The first partition wall  133  serving as a first partition member separates the supply conveyance path  9  from the agitation conveyance path  10  while including openings at a front side and a rear side thereof of  FIG. 2 . Thereby, the supply conveyance path  9  and the agitation conveyance path  10  are in communication with each other. 
     The first partition wall  133  also separates the supply conveyance path  9  from the collection conveyance path  7 . However, the first partition wall  133  has substantially no opening between the supply conveyance path  9  and the collection conveyance path  7 . 
     The second partition wall  134  serving as a second partition member separates the agitation conveyance path  10  from the collection conveyance path  7 . The second partition wall  134  includes an opening in a front side thereof of  FIG. 2  so that the agitation conveyance path  10  and the collection conveyance path  7  are in communication with each other. The second partition wall  134  includes a communication opening  94  (shown in  FIG. 3 ). 
     Each of the supply screw  8 , collection screw  6  and agitation screw  11  includes resin with a diameter of 18 mm, a screw pitch of 25 mm, and an approximate rotation speed of 600 rpm. 
     The development roller  5  includes the developer regulated by the development doctor  12  to be a thin layer thereon. The thin layer developer is conveyed to the development region positioned opposite to the photoconductor  1  for the development. The surface of the development roller  5  can include a V-groove or can be sandblasted. The development roller  5  includes an aluminum tube with a diameter of 25 mm. The developer roller  5  and the developer doctor  12  include a gap therebetween, and the developer roller  5  and the photoconductor  1  include another gap therebetween. Each of the gaps can be approximately 0.3 mm. 
     After the development, the collection conveyance path  7  collects the developer and conveys to the front side of  FIG. 2 . The developer is transferred to the agitation conveyance path  10  at the opening of the first partition wall  133 . The opening is disposed in a non-image area. The agitation conveyance path  10  includes a toner supply opening (not shown) thereabove in a vicinity of the opening of the first partition wall  133  at the upstream side in the developer conveyance direction thereof. Accordingly, the toner is supplied to the agitation conveyance path  10  from the toner supply opening. 
     Referring to  FIG. 3 , the communication opening  94  of the second partition wall  134  is illustrated. As stated above in the description of  FIG. 2 , the second partition wall  134  includes the opening in the front side thereof. The communication opening  94  is disposed at a further upstream side than the opening in the developer conveyance direction of the collection conveyance path  7 , and is positioned higher than a predetermined height (i.e., volume) of the collected developer conveyed by the collection conveyance path  7 . Therefore, the collected developer conveyed by the collection conveyance path  7  can reduce the increase in volume, and reduce an occurrence of higher volume than the predetermined volume. By using the communication opening  94 , the collection conveyance path  7  and the agitation conveyance path  10  are in communication with each other. 
       FIG. 4  is a schematic perspective view illustrating flow of the developer in the development device  4 . Each arrow in  FIG. 4  represents a movement direction of the developer. 
       FIG. 5  is a schematic diagram illustrating the flow of the developer in the development device  4 . Each arrow in  FIG. 5  represents the movement direction of the developer. 
     The agitation conveyance path  10  supplies the developer to the supply conveyance  9 . The supply conveyance path  9  conveys the developer to the downstream side of the supply screw  8  relative to the developer conveyance direction while supplying the developer to the development roller  5 . The first partition wall  133  includes an excess developer opening  92  through which an excess developer is supplied to the agitation conveyance path  10 . The excess developer may represent a developer that is supplied to the development roller  5 , but unused for the development. The excess developer is conveyed to the downstream end of the supply conveyance path  9  relative to the developer conveyance direction, and is supplied through the excess developer opening  92  to the agitation conveyance path  10 , represented by an arrow E in  FIG. 5 . 
     The second partition wall  134  includes a collection developer opening  93 . The collected developer is transferred from the developer  5  to the collection conveyance path  7 , and is conveyed to the downstream end of the collection conveyance path  7  relative to the developer conveyance direction by the collection screw  6 . The collected developer is supplied to the agitation conveyance path  10  through the collection developer opening  93 , indicated by an arrow F in  FIG. 5 . When the collected developer is supplied from the downstream side of the collection conveyance path  7  to the agitation conveyance path  10 , the collected developer can be accumulated at the downstream side in the collection conveyance path  7  due to a formation of the developer conveyance direction that is shifted at a substantially right angle. For example, when the collection conveyance path  7  collects a large volume of the collected developer, the volume of the collected developer can be higher than the predetermined volume at the downstream side of the collection conveyance path  7 . A volume of the collected developer that is higher than the predetermined level (e.g., an excess volume) is supplied to the agitation conveyance path  10  from the collection conveyance path  7  through the communication opening  94 , indicated by an arrow G in  FIG. 5 . Therefore, the collected developer can reduce the increase in volume, and reduce an occurrence of a higher volume than the predetermined volume. By using the communication opening  94 , the volume of the collected developer of the collection conveyance path  7  is regulated, thereby reducing the movement of the collected developer of the collection conveyance path  7  to the developer carrying member. In an exemplary embodiment, the communication opening  94  is disposed at the downstream side of the collection conveyance path  7  so as to deal with the volume of the accumulated collected developer. However, the communication opening  94  can be disposed at another position in the partition wall as long as the likelihood of the collected developer movement to the development roller  5  can be reduced. The communication opening  94  can be disposed in an upstream side of the collection conveyance path  7 , for example, when the development device  4  has a likelihood of including the excess volume of the collected developer at the upstream side of the collection conveyance path  7 . Consequently, the likelihood of the collected developer movement to the development roller  5  can be reduced at the upstream side. Therefore, the communication opening  94  can be disposed at an appropriate position according to the configuration of the development device  4  to reduce an occurrence of the collected developer movement of the collection conveyance path  7  to the developer roller  5 . The communication opening  94  can include a plurality of openings in a plurality of locations as illustrated in  FIG. 5 . However, the communication opening  94  can include an opening in a location. 
     The first separation wall  133  includes a supply opening  91 . The agitation conveyance path  10  agitates the excess developer and the collected developer to convey towards the downstream side of the agitation screw  11  in the developer conveyance direction and the upstream side of the supply screw  8  in the developer conveyance direction. Accordingly, the agitated developer is supplied to the supply conveyance path  9  through the supply opening  91 , represented by an arrow D in  FIG. 5 . 
     In the agitation conveyance path  10 , the agitation screw  11  agitates the collected developer, the excess developer and a supply toner, and conveys in a direction opposite to the developer of the collection conveyance path  7  and the supply conveyance path  9 . The supply toner is toner that is supplied at a transfer area as may be necessary. The agitation screw  11  transfers the agitated developer to the upstream side of the supply conveyance path  9  relative to the developer conveyance direction of which the downstream side relative to the developer conveyance direction is communicated. The agitation conveyance path  10  includes a toner density sensor (not shown) therebelow. The toner density sensor outputs a sensor to operate a toner supply control unit (not shown) to supply the toner from a toner container (not shown). 
     As shown in  FIG. 5 , the development device  4  includes the supply conveyance path  9  and the collection conveyance path  7  so that the developer is supplied and collected separately. In this way, the developer used for the development (i.e., the developer after the development) cannot be mixed in the supply conveyance path  9 . The toner density of the developer supplied to the development roller  5  can reduce a deterioration occurrence as closer to the downstream side of the supply conveyance path  9  relative to the developer conveyance direction. Therefore, the toner density of the developer in the supply conveyance path  9  can reduce the deterioration occurrence, and an image density during the development can remain substantially constant. 
     As shown in  FIG. 5 , the arrow D represents a movement of the developer from a lower portion to an upper portion of the development device  4 . When the agitation screw  11  rotates, the developer from the lower portion is forced to be lifted and supplied to the supply conveyance path  9 . 
     However, such movements can place stress on the developer, and the lifespan of the developer can be shortened. 
     For example, when stress is placed on the developer due to the developer moving from the lower portion to the upper portion of the development device  4 , a cover layer of the carrier in the development can be abraded, or the carrier can deteriorate chargeability thereof due to adhesion of the toner thereto in a stress area, causing deterioration of the image quality. 
     In other words, the developer can extend the lifespan thereof by reducing the stress placed by the movement of the developer indicated by the arrow D. The reduction of stress will be described later. Extending the lifespan of the developer can reduce deterioration of the developer. Thereby, the development device  4  can provide a quality image while reducing unevenness in image density. 
     In the development device  4  of the exemplary embodiment as shown in  FIG. 2 , the supply conveyance path  9  is disposed in such a manner to be obliquely above the agitation conveyance path  10  compared to a situation in which the conveyance path  9  is disposed above the agitation conveyance path  10 . Therefore, the stress placed on the developer indicated by the arrow D in  FIG. 5  can be reduced. 
     As the supply conveyance path  9  is disposed obliquely above the agitation conveyance path  10 , an upper wall surface of the agitation conveyance path  10  is positioned higher than a lower wall surface of the supply conveyance path  9  as shown in  FIG. 2 . 
     For example, when the developer in the agitation conveyance path  10  is vertically lifted to the supply conveyance path  9 , the agitation screw  11  applies pressure to lift the developer. In other words, the agitation screw  11  works against gravity, resulting in placing stress on the developer. In contrast, when the upper wall surface of the agitation conveyance path  10  is positioned higher than the lower wall surface of the supply conveyance path  9 , the developer in substantially the highest point of the agitation conveyance path  10  is transferred to substantially the lowest point of the supply conveyance path  9  by using gravity. Therefore, stress placed on the developer can be reduced. 
     The agitation screw  11  at the downstream side of the developer conveyance path of the agitation conveyance path  10  at which the agitation conveyance path  10  and the supply conveyance path  9  communicate with each other and can include a fin in an axis thereof. The fin can be a plate member, and can include a side parallel to an axis direction of the agitation screw  11  and another side perpendicular to the axis direction of the agitation screw  11 . The fin can scoop up developer so as to increase the transfer efficiency of developer from the agitation conveyance path  10  to the supply conveyance path  9 . 
     As shown in  FIG. 2 , the development device  4  has a center-to-center distance A between the development roller  5  and the supply conveyance path  9 , and a center-to-center distance B between the development roller  5  and the agitation conveyance path  10 . The supply conveyance path  9  and the agitation conveyance path  10  are disposed such that the center-to-center distance A is shorter than the center-to-center distance B. Thereby, the development device  4  can supply developer from the supply conveyance path  9  to the developer roller  5  reasonably, and the development device  4  can be downsized. 
     The agitation screw  11  of  FIG. 2  rotates counterclockwise as indicated by an arrow C to lift the developer along the shape thereof and transfer the developer to the supply conveyance path  9 . Accordingly, the agitation screw  11  can efficiently lift the developer and reduce the amount of stress placed on the developer. 
       FIG. 6  is a cross section illustrating a rotational center of the supply screw  8  of the development device  4  when observed as seen from an arrow J of  FIG. 4 . A development region H is a region in which the development roller  5  supplies toner to the photoconductor  1 . The development region H includes a development region α that is a width in an axis line direction of the rotational axis of the development roller  5 . 
     As shown in  FIG. 6 , the development device  4  includes the supply opening  91  through which developer is lifted to the supply conveyance path  9  from the agitation conveyance path  10 , and the excess developer opening  92  through which developer is supplied to the agitation conveyance path  10  from the supply conveyance path  9  within the development region α. 
     Referring to  FIG. 7 , a background development device  40  illustrates the flow of developer. The development device  40  includes a supply opening  910  and an excess developer opening  920  located outside a development region α′. As the supply opening  910  is disposed outside the development region α′, a supply conveyance path  90  at an upstream side in a developer conveyance direction is longer than a development roller  50  by an amount β′. As the excess developer opening  920  is disposed outside the development region α′, the supply conveyance path  90 , at a downstream side in the developer conveyance direction, is longer than the development roller  50  by an amount γ′. β′ and γ′ are respectively referred to as a supply conveyance path upstream side region and a supply conveyance path downstream side region. 
     The development device  40  includes a plurality of development elements such as an agitation conveyance path  1000 , a collection opening  930 , and a collection conveyance path  70 . These elements may be similar to the agitation conveyance path  10 , the collection opening  93 , and the collection conveyance path  7  of  FIG. 5 , respectively. In  FIG. 7 , arrows D′, E′ and F′ represent the movement of developer, and these arrows may be similar to arrows D, E and F in  FIG. 5 . 
     Compared to development device  40  of  FIG. 7 , the supply opening  91  of development device  4  of the exemplary embodiment in  FIG. 5  is disposed within the development region α, and the supply conveyance path  9  at the upstream side in the developer conveyance direction can be shorter than the development device  40  of  FIG. 7  in an amount of β′. As the excess developer opening  92  is disposed within the development region α in  FIG. 5 , the supply conveyance path  9  at the downstream side in the developer conveyance direction can be shorter than the development device  40  of  FIG. 7  in an amount of γ′. 
     Therefore, the development device  4  of the exemplary embodiment having the supply opening  91  and the excess developer opening  92  within development region α can downsize an upper portion thereof. 
     As shown in  FIG. 5 , the communication opening  94  is disposed in the collection conveyance path  7  within the development region α. In this way, the volume of developer can be reduced within the development region α, thereby reducing the possibility of a higher volume than the predetermined volume. Accordingly, the collected developer of the collection conveyance path  7  supplied to the development region H can be reduced. In other words, the developer supplied to the development region H cannot mix with the developer having low toner density, thereby reducing uneven image density during development. 
     Referring to  FIG. 8 , a toner supply opening  95  of the development device  4  of an exemplary embodiment is illustrated in a schematic perspective view. 
     The toner supply opening  95  is disposed above an end of the upstream side of the agitation conveyance path  10  relative to the developer conveyance direction, and supplies toner therethrough. The toner supply opening  95  is disposed outside an end of the development roller  5 , along the axial direction of the development roller  5 , thereby positioning the toner supply opening  95  outside the development region α of  FIG. 5 . 
     The toner supply opening  95  is positioned on an extended line in the developer conveyance direction of the supply conveyance path  9 . The space where the toner supply opening  95  is positioned substantially corresponds to the supply conveyance path downstream side region γ′ of  FIG. 7 . The excess developer opening  92  is disposed within the development region so that the space is generated to dispose the toner supply opening  95  therein, and thereby, the development device  4  can be downsized. 
     The toner supply opening  95  is disposed above the end of the upstream side of the agitation conveyance path  10  relative to the developer conveyance direction. However, the toner supply opening  95  can be disposed above an end of the downstream side of the collection conveyance path  7 . 
     The toner supply opening  95  can also be disposed over the collection developer opening  93  through which the developer is supplied from the collection conveyance path  7  to the agitation conveyance path  10 . As the excess developer opening  92  is disposed within the development region α, a space is generated over the collection developer opening  93 . The toner supply opening  95  can be disposed in the space so that the development device  4  can be downsized. The collection developer opening  93  is an opening member at which the developer can be mixed more easily. Therefore, developer is supplied to the collection developer opening  93  to be agitated efficiently. 
     According to the development device  4  of an exemplary embodiment, the supply conveyance path  9  is disposed above the agitation conveyance path  10  and the collection conveyance path  7 . However, the development device  4  of an exemplary embodiment is not limited to the description above, and can be applied to a development device having a supply conveyance path, agitation conveyance path and a collection conveyance path disposed at substantially the same elevation. When the collection conveyance path  7  and the agitation conveyance  10  are arranged so as to not be in contact with each other, a developer transfer path can be disposed to communicate the communication opening  94  at a side of the collection conveyance path  7  and the communication opening  94  at a side of the agitation conveyance path  10 . Thereby, the excess volume of the collected developer can be conveyed to the agitation conveyance path  10  from the collection conveyance path  7 . 
     According to an exemplary embodiment of the invention, the image forming apparatus  500  includes the process cartridge  18  detachable thereto. The process cartridge  18  includes the development device  4  including the development roller  5 , supply conveyance path  9 , collection conveyance path  7 , and the agitation conveyance path  10 . The development roller  5  rotates with the two-component developer having the magnetic carrier and the toner on a surface thereof, and supplies the toner to the electrostatic latent image on the surface of the photoconductor  1  at a position opposite to the photoconductor  1  so as to develop the image. The supply conveyance path  9  includes the supply screw  8  supplying the two-component developer to the development roller  5  so as to convey the two-component developer along the axis line direction of the development roller  5 . The collection conveyance path  7  includes the collection screw  6  collecting developer passed to a position opposite to the photoconductor  1  from the development roller  5 . The collection screw  6  conveys the collected developer along the axis line direction of the development roller  5 . The agitation conveyance path  10  includes the agitation screw  11 , and supplies the agitated developer to the supply conveyance path  9 . The agitation screw  11  conveys the excess developer and collected developer along the axis line direction of the development roller  5  while agitating these developers. Each of the collection conveyance path  7 , supply conveyance path  9  and agitation conveyance path  10  is separated from one another by a partition wall. The second partition wall  134  separates the collection conveyance path  7  from the agitation conveyance path  10 , and includes the collection developer opening  93 . The second partition wall  134  includes the communication opening  94  at the upstream side of the collection conveyance path  7  relative to the developer conveyance direction and at a position higher than the predetermined height of the collection conveyance path  7 . 
     Therefore, when the volume of the collected developer becomes excessive at the collection conveyance path  7 , the excess volume is transferred to the agitation conveyance path  10  from the collection conveyance path  7 . Thereby, the collected developer within the collection conveyance path  7  can reduce the increase in volume so as to reduce the frequency in which the volume is higher than the predetermined volume. The collected developer of the collection conveyance path  7  can reduce the movement thereof to the development roller  5 . Thereby, the collected developer in which the unused toner and the developer to be supplied to the developer roller  5  are not mixed. Consequently, uneven image density during development can be reduced. 
     According to an exemplary embodiment, the second partition wall  134  is disposed within the development region α in the axis line direction of the development roller  5  of the development region H, and the communication opening  94  is disposed in the second partition wall  134 . 
     Accordingly, the volume of the collected developer at the collection conveyance path  7  within the development region α can reduce the frequency in which there is an increase in amount higher than the predetermined volume. The collected developer of the collection conveyance path  7  can reduce the movement thereof to the development region H of the development roller  5 . The developer having a low toner density can not mix with the developer to be supplied to the developer region H. Thereby, the uneven image density during the development can be reduced. 
     According to an exemplary embodiment, the supply conveyance path  9  and the agitation conveyance path  10  communicate with each other through the excess developer opening  92  supplying the excess developer from the downstream side of the supply conveyance path  9  relative to the developer conveyance direction to the upstream side of the agitation conveyance path  10  relative to the developer conveyance direction. The agitation conveyance path  10  and the supply conveyance path  9  communicate with each other through the supply opening  91  supplying the agitated developer from the downstream side the agitation conveyance path  10  relative to the developer conveyance direction to the upstream side of the supply conveyance path  9  relative to the developer conveyance direction. At least one of the excess developer opening  92  and the supply opening  91  is disposed in the first partition wall  133  within the development region α. Thereby, space for the supply conveyance path  9  can be saved, and the development device  4  can be downsized. Downsizing the development device  4  can save space within the process cartridge  18 . In other words, the process cartridge  18  can also be downsized. The image forming apparatus  500  can include the development device  4  of an exemplary embodiment and the process cartridge  18  so as to save a space therewithin. 
     Numerous additional modifications and variations are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the disclosure of this patent specification may be practiced otherwise than as specifically described herein.