Patent Publication Number: US-7715763-B2

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

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application is based on and claims priority from Japanese Patent Application No. 2006-273096 filed on Oct. 4, 2006 in the Japan Patent Office, the entire contents of which are incorporated by reference herein. 
   BACKGROUND 
   Field of the Invention 
   Exemplary aspects of the present invention relate to a development device. More particularly, the present invention relates to a development device developing an electrostatic image with a developer having toner and carrier to form a toner image, and a process cartridge and an image forming apparatus including the development device. 
   Description of the Related Art 
   Image forming apparatuses of recent years are expected to reliably produce high quality images with uniform image density even when images with high image area ratios are successively printed succession. In attempting to fulfill this requirement, an image forming apparatus including a development device having a developer conveyance mechanism is proposed that feeds a developer vertically, unlike conventional development devices that feed a developer horizontally. An example of such image forming apparatus is shown in  FIG. 1 . 
   Referring to  FIG. 1 , a related-art development device  71  includes a development casing  72 , a doctor  73 , a developer carrying member  74 , a developer supply mechanism  75 , a developer agitation conveyance mechanism  76 , and a developer collection mechanism  77 . A photoconductor drum  78  is disposed in the vicinity of the development device  71 . 
   The doctor  73  controls the thickness of a developer carried on the developer carrying member  74  in order to supply a suitable amount of the developer to the photoconductor drum  78  for developing an electrostatic latent image thereon. After development of the electrostatic latent image, the developer, which has been used for a development process at least once, is collected by the developer collection mechanism  77  and is conveyed in a direction of from rear to front in  FIG. 1 . Thus, the collected developer is supplied to the developer agitation conveyance mechanism  76  through a first opening, not shown, that is disposed within a development region HH shown in  FIG. 2 . A toner supply mechanism, not shown, disposed above the developer agitation conveyance mechanism  76  and in the vicinity of the first opening properly supplies additional toner to the developer agitation conveyance mechanism  76  so as to increase the toner density to a desirable level. The developer agitation conveyance mechanism  76  conveys the collected developer and the additional toner to the rear side of  FIG. 1  while mixing the two together. 
   The developer agitation conveyance mechanism  76  has a second opening A at a downmost stream side thereof relative to the developer conveyance direction to communicate with the developer supply mechanism  75  as shown in  FIG. 2 . Specifically, the developer agitation conveyance mechanism  76  supplies the developer to the developer supply mechanism  75  though the second opening A located within the development region HH. Subsequently, the developer supply mechanism  75  supplies the developer to the developer carrying member  74  from an upstream side to the downstream side thereof. As shown in  FIG. 2 , the developer supply mechanism  75  has a third opening B at a downmost stream side thereof relative to the developer conveyance direction to communicate with the developer agitation conveyance mechanism  76 . Therefore, the developer supply mechanism  75  can supply the developer to the developer agitation conveyance mechanism  76  through the third opening B located within the development region HH. 
   However, the related-art development device  71  can frequently cause developer accumulation in the vicinity of the first opening through which the developer collection mechanism  77  communicates with the developer agitation conveyance mechanism  76 . Consequently, as shown in  FIG. 3 , the developer mechanism  77  can frequently cause excess supply of the developer at the downstream side thereof relative to the developer conveyance direction. In this case, the developer is supplied within the development region HH and the collected developer having a low density is fed into the developer carrying member  74 , resulting in formation of an image of uneven density. 
   One example attempts to arrange an opening outside a development region of a development device to supply developer to each developer conveyance mechanism. Such a disposition of the opening can reduce the risk of low density developer being supplied to a developer carrying member. However, such a development device needs to increase the length of each of the developer conveyance mechanisms in a developer conveyance direction by the length of the opening, which increases the size of the developer carrying member, resulting in a larger size of the development device and in an image forming apparatus as a whole, which is undesirable. 
   SUMMARY 
   According to one aspect of the invention, a development device includes a developer carrying member, developer collection conveyance path, and a developer supply conveyance path. The developer carrying member rotates while bearing thereon developer including toner and carrier to carry the developer to a development region, in which the developer carrying member faces a latent image carrier, to develop a latent image on the latent image carrier. The developer collection conveyance path includes a developer collection conveyance member collecting the developer from the developer carrying member after the developer on the developer carrying member passes through the development region. The developer collection conveyance path is disposed obliquely above the developer carrying member and conveys the collected developer in a first direction parallel to an axis of the developer carrying member. In addition, the developer collection conveyance path has first and second openings within the development region. The developer supply conveyance path includes a developer supply conveyance member supplying the developer to the developer carrying member. The developer supply conveyance path is disposed below the developer collection conveyance path and conveys the developer in a second direction opposite to the first direction. The developer supply conveyance path has third and fourth openings within the development region. The developer on a downstream side of the developer collection conveyance path conveyed by the developer collection conveyance path is transferred to an upstream side of the developer supply conveyance path through the first and third openings. The developer on a downstream side of the developer supply conveyance path conveyed by the developer supply conveyance path is transferred to an upstream side of the developer collection conveyance path through the fourth and second openings. 
   According to another aspect of the present invention, a process cartridge is detachably installed in an image forming apparatus. The process cartridge includes at least one member selected from a latent image carrier carrying a latent image thereon, a charging member charging the latent image carrier, and a cleaning member cleaning a surface of the latent image carrier, and a development device configured to develop the latent image on the latent image carrier with developer including toner and carrier. 
   According to yet another aspect of the present invention, an image forming apparatus includes a latent image carrier carrying a latent image thereon and a development device developing the latent image on the latent image carrier with developer including toner and carrier. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete appreciation of the exemplary aspects of the invention and many of the attendant advantages 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 a related-art development device; 
       FIG. 2  is a cross-sectional view illustrating the related-art development device of  FIG. 1 ; 
       FIG. 3  is a schematic perspective view illustrating a flow of developer in the related-art development device of  FIG. 2   
       FIG. 4  is a schematic diagram illustrating an image forming apparatus according to an exemplary embodiment of the present invention; 
       FIG. 5  is a schematic diagram illustrating a development device of the image forming apparatus of  FIG. 4 ; 
       FIG. 6  is a schematic diagram illustrating a flow of developer in the development device of  FIG. 5 ; and 
       FIG. 7  is a schematic diagram illustrating a flow of developer in another related-art development device. 
   

   DETAILED DESCRIPTION OF EXEMPLARY 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 thereof, an image forming apparatus according to an exemplary embodiment of the present invention is described. 
   Referring to  FIG. 4 , 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 serving as a latent image carrier, with a laser beam that is formed based on image data. The optical writing unit  21  will be described in detail 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 color abbreviations may be omitted as necessary. 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, the one process cartridge  18 Y is described as representative of all the process cartridges  18 Y,  18 M,  18 C and  18 K. 
   The process cartridge  18 Y 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. 
   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, thereby forming the 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  that 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, thereby initializing the photoconductor drum  1 Y. 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 a series of operations in 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  90 , a tension roller  14 , a drive roller  15 , a secondary transfer 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. 
   Each of the primary transfer bias rollers  62 Y,  62 M,  62 C and  62 K is disposed in such a manner as to contact an inner circumference side of the intermediate transfer belt  110 , thereby applying a primary transfer bias 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  toward the photoconductor drums  1 Y,  1 M,  1 C and  1 K to form primary transfer nips. The application of the primary transfer bias generates a primary transfer electrical field in each of the primary transfer nips. For example, the photoconductor drum  1 Y and the primary transfer bias roller  62 Y have the primary transfer electrical field therebetween. 
   The toner image Y formed on the photoconductor drum  1 Y is primarily transferred onto the intermediate transfer belt  110  by the primary transfer electrical 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  by superimposition of each color image. 
   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 described later. After the intermediate transfer belt  110  passes the secondary nip, the belt cleaning device  90  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. 4  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 that of a charge of the toner to the secondary transfer tension roller  23  disposed at the right-hand side. The application of the secondary transfer bias forms a secondary transfer electrical field in the secondary transfer nip. The four-color image on the intermediate transfer belt  110  is transferred by the secondary transfer electrical field toward the secondary transfer tension roller  23  disposed at the right-hand side of  FIG. 4 . The pair of registration rollers  49  registers the transfer sheet to feed into the secondary transfer nip in such a manner as to be in sync with the four-color image on the intermediate transfer belt  110 . The four-color image is secondary transferred onto the transfer sheet by the secondary transfer electrical field and the nip pressure. 
   It should be noted that, although 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 , alternatively a charger may 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. 4 . The sheet feeder  200  includes a plurality of sheet cassettes  44 , sheet feed rollers  42 , a feed 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 plurality of 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 feed roller  42  so that the uppermost sheet is fed toward the feed path  46  by rotation of the sheet feed roller  42 . 
   Subsequently, the transfer sheet is conveyed toward the registration rollers  49  through the feed path  46  including a plurality of conveyance rollers  47 . The registration rollers  49  are disposed near one end of the feed path  46 . For example, when the four-color image on the intermediate transfer belt  110  is put into the secondary transfer nip by an endless movement of the intermediate transfer belt  110 , the pair of registration rollers  49  sandwich the transfer sheet therebetween and feed it in sync with the four-color image on the intermediate transfer belt  110 . The four-color image is affixed to the transfer sheet at the secondary transfer nip and is secondarily transferred, thereby forming 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 endlessly. The pressure roller  27  presses one of the two 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 two 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 affixed to the transfer sheet by the heat and the 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. 4 . 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  of 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 in place 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  34  includes a mirror, not shown. 
   The scanner  300  reads the original on the contact glass  32  by pressing a start switch, referred 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 the reading sensor  36 . The reading sensor  36  then 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 photoconductor drums  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 time as the beginning of the original reading operation. In the feeding operation, one of the sheet feed 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 put into the feed path  46  and is conveyed toward the secondary transfer nip by the conveyance rollers  47 . The transfer sheets can be fed from a manual feeding tray  51 , substituting for the sheet cassettes  44 . For example, when the transfer sheet is fed from the manual feeding tray  51 , a manual feed 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 feed 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 photoconductor drums  1 Y,  1 M,  1 C and  1 K contact the stretched upper surface of the intermediate transfer belt  110 . By 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 toward the lower left of  FIG. 4  using a mechanism, not shown. Therefore, the stretched upper surface of the intermediate transfer belt  110  is separated from the photoconductor drums  1 Y,  1 M and  1 C. The photoconductor drum  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 photoconductor drums  1 Y,  1 M and  1 C and the development devices  4 Y,  4 M and  4 C halt, thereby reducing unnecessary consumption of toner and unnecessary abrasion of the photoconductor drums. A description of the development devices  4 Y,  4 M,  4 C and  4 K is given below with reference to  FIG. 5  by using a development device  4  as representative of the development devices  4 Y,  4 M,  4 C and  4 K. 
   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 inputs a key 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, such as a direct ejection mode, a reverse ejection mode, and a reverse decor ejection mode, to form the toner image on one side of the transfer sheet. 
     FIG. 5  illustrates the development device  4  of the image forming apparatus  500 . The process cartridges  18 Y,  18 M,  18 C and  18 K shown in  FIG. 4  include the development devices  4 Y,  4 M,  4 C and  4 K and the photoconductor drums  1 Y,  1 M,  1 C and  1 K, respectively. In  FIG. 5 , since each of the development devices  4 Y,  4 M,  4 C and  4 K is similar to every other except for the color of the toner, and each of the photoconductor drums  1 Y,  1 M,  1 C and  1 K is also similar to every other except for the color of the toner, the color abbreviations are omitted for the sake of simplicity. 
   The photoconductor drum  1  rotates in a direction indicated by an arrow G shown in  FIG. 5  to charge a surface thereof with the charging device. The surface of the photoconductor drum  1  is irradiated by the laser beam from the optical writing unit  21  shown in  FIG. 4  so as to form the electrostatic latent image thereon. The development device  4  develops the electrostatic latent image on the photoconductor drum  1  with the developer including the toner, thereby forming 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 , and a collection conveyance path  7 . 
   The development roller  5  serving as a developer carrying member supplies the toner to the electrostatic latent image on the surface of the photoconductor drum  1  while moving a surface thereof in a direction indicated by an arrow I shown in  FIG. 5 . The supply screw  8  serving as a developer supply conveyance member conveys the developer to a rear side of  FIG. 5  while supplying it to the development roller  5 . 
   The development doctor  12  serving as a developer regulation member adjusts a thickness of the developer supplied to the development roller  5  to a suitable level for development. The development doctor  12 , which is made of stainless steel, is located at a downstream side from a facing position, in which the development roller  5  faces the supply screw  8 , relative to a surface movement direction of the development roller  5  as shown in  FIG. 5 . The development doctor  12  regulates the developer so as to deposit a thin layer of developer on the development roller  5 . The thin layer of developer is conveyed to a development region H in which the development roller  5  faces the photoconductor drum  1  for the development. A description of the development region H is given below with reference to  FIG. 6 . 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  have a gap therebetween, and the developer roller  5  and the photoconductor drum  1  have another gap therebetween. Each of the gaps is approximately 0.3 mm. 
   The collection screw  6  serving as a developer collection conveyance member collects collection developer that has passed the development region H and conveys it in a direction opposite the supply screw  8 . The collection screw  6  is located at the downstream side from the development region H relative to the surface movement direction of the development roller  5 . Each of the supply screw  8  and the collection screw  6  is comprised of resin, and each screw has a diameter of 18 mm, a screw pitch of 25 mm, and an approximate rotation speed of 600 rpm (rotations per minute). 
   As shown in  FIG. 5 , the supply conveyance path  9  includes the supply screw  8  and is disposed obliquely below the development roller  5 . The collection conveyance path  7  includes the collection screw  6  and is disposed above the supply conveyance path  9 . The collection conveyance path  7  and the supply conveyance path  9  communicate with each other through supply openings  91  and  91 ′ and excess developer openings  92  and  92 ′, described with reference to  FIG. 6 . 
     FIG. 6  schematically illustrates a flow of the developer within the development device  4  of  FIG. 5 . Each arrow in  FIG. 6  represents a direction of movement of the developer. 
   In the development device  4 , the collection conveyance path  7  includes the supply opening  91  and the supply conveyance path  9  includes the supply opening  91 ′, so that the developer is supplied from the downstream side of the collection conveyance path  7  to the upstream side of the supply conveyance path  9 . The supply conveyance path  9  includes an excess developer opening  92  and the collection conveyance path  7  includes the excess supply opening  92 ′, so that the developer including any excess developer is supplied from the downstream side of the supply conveyance path  9  to the upstream side of the collection conveyance path  7 . Excess developer refers to developer conveyed to the downstream of the supply conveyance path  9  without being supplied to the development roller  5 . The development roller  5  supplies the developer to the photoconductor drum  1  in the development region H. As shown in  FIG. 6 , the development region H includes a development region width a that is a width in an axial direction of the rotation axis of the development roller  5 . The supply openings  91  and  91 ′ and the excess developer openings  92  and  92 ′ are positioned within the width α. 
   The supply conveyance path  9  conveys the developer to the downstream side thereof relative to the developer conveyance direction while supplying the developer to the development roller  5  with the supply screw  8 . Since the supply screw  8  rotates, the excess developer is lifted and supplied to the downstream side of the supply conveyance path  9  relative to the developer conveyance direction and to the collection conveyance path  7  through the excess developer openings  92  and  92 ′. Such a movement of the excess developer through the excess developer openings  92  and  92 ′ is indicated by an arrow D shown in  FIG. 6 . The development doctor  12  of  FIG. 5  regulates the thickness of the developer supplied to the development roller  5  from the supply conveyance path  9  even when the developer at the downstream side of the supply conveyance path  9  is lifted, thereby reducing the occurrence of images of uneven density. 
   The collection conveyance path  7  conveys the excess developer supplied from the supply conveyance path  9  and the developer collected from the developer roller  5  while agitating them with the collection screw  6 . The agitated developer is then conveyed to the downstream end of the collection conveyance path  7  relative to the developer conveyance direction. Subsequently, the agitated developer is supplied to the supply conveyance path  9  through the supply openings  91  and  91 ′ indicated by an arrow E shown in  FIG. 6 . In other words, the agitated developer falls to the supply conveyance path  9  from the collection conveyance path  7  through the supply openings  91  and  91 ′. The collection conveyance path  7  has the supply opening  91  at the downstream side thereof relative to the developer conveyance direction, thereby reducing a frequency of the excess supply of the developer therewithin. Consequently, the supply conveyance path  9  is unlikely to supply low-density developer to the development roller  5 . In addition, the collection conveyance path  7  conveys the collection developer, the excess developer, and any additional toner described later while agitating them with the collection screw  6 . 
   The development device  4  includes a toner density sensor, not shown, disposed below the collection conveyance path  7 . The toner density sensor outputs a sensor to activate a toner supply controller, not shown, that controls a supply of the additional toner from a toner container, not shown, having a toner supply opening, not shown. The toner supply opening will be described later. 
     FIG. 7  illustrates the flow of developer within a related-art development device  40 . 
   The related-art development device  40  includes supply openings  910  and  910 ′ and excess developer openings  920  and  920 ′ disposed outside a development region width αα. Since the supply openings  910  and  910 ′ are disposed outside the width αα, a supply conveyance path  900  at an upstream side thereof relative to a developer conveyance direction is longer than a development roller  55  by an amount β. Since the excess developer openings  920  and  920 ′ are also disposed outside the width αα, the supply conveyance path  900  at a downstream side thereof relative to the developer conveyance direction is longer than the development roller  55  by an amount γ. The β and γ are respectively referred to as a supply conveyance path upstream side region and a supply conveyance path downstream side region. 
   Compared to the development device  40  of  FIG. 7 , the development device  4  of the exemplary embodiment shown in  FIG. 6  includes the supply openings  91  and  91 ′ and the excess developer openings  92  and  92 ′ disposed within the width α. In this regard, the supply conveyance path  9  at the upstream side thereof relative to the developer conveyance direction can be shorter than the supply conveyance path  900  of the related-art development device  40  by an amount β. Similarly, the supply conveyance path  9  at the downstream side thereof relative to the developer conveyance direction can be shorter than the supply conveyance path  900  of the related-art development device  40  by an amount γ. 
   Therefore, the development device  4  of the exemplary embodiment can be made more compact than the related-art development device  40 . 
   A description is now given of the toner supply opening of the development device  4  of the exemplary embodiment of the present invention. 
   The toner supply opening supplies the additional toner to a developer conveyance path including the supply conveyance path  9  and the collection conveyance path  7  of the development device  4 . The toner supply opening is disposed at the upstream side of the collection conveyance path  7  relative to the developer conveyance direction within the width a so that the development device  4  and the image forming apparatus  500  can reduce the size thereof. Moreover, the development device  4  can secure an agitation conveyance distance to disperse the additional toner into the developer within the collection conveyance path  7 . 
   The toner supply opening can be disposed at the upstream side from the excess developer opening  92 ′ of the collection conveyance path  7  relative to the developer conveyance direction. For example, the toner supply opening can be disposed in a space generated by disposing the excess developer opening  92 ′ within the width α. The development device  4  with such a disposition of the toner supply opening can be smaller than the related-art development device  40 . In addition, since the toner supply opening is disposed outside the width of each conveyance path, the additional toner can not only be supplied easily but also the agitation conveyance distance can be increased, thereby mixing the additional toner and the developer sufficiently. 
   According to the above-described embodiment, the development device  4  includes the development roller  5 , the supply conveyance path  9 , the collection conveyance path  7 , the supply openings  91  and  91 ′, and the excess developer openings  92  and  92 ′. 
   The development roller  5  serving as the developer carrying member rotates while carrying thereon the developer having the toner and the carrier, and supplies the toner to the electrostatic latent image on the surface of the photoconductor drum  1  at the opposing position, in which the development roller  5  faces the photoconductor drum  1 , to develop the electrostatic latent image. 
   The supply conveyance path  9  includes the supply screw  8  supplying the developer to the development roller  5 , and conveys the developer in an axial direction of the development roller  5 . 
   The collection conveyance path  7  includes the collection screw  6  collecting the collection developer from the development roller  5  having passed the position opposite the photoconductor drum  1 , and conveys the collection developer in the axial direction of the development roller  5  in an opposite direction relative to the supply screw  8 . 
   The supply openings  91  and  91 ′ serving as first and third openings communicate with the downstream side of the collection conveyance path  7  relative to the developer conveyance direction with the upstream side of the supply conveyance path  9  relative to the developer conveyance direction. In the exemplary embodiment as shown in  FIG. 6 , the supply openings  91  and  91 ′ are separately disposed in the respective paths. However, the supply openings  91  and  91 ′ can be integrated when a lower portion of the collection conveyance path  7  and an upper portion of the supply conveyance path  9  are adjacent to each other or contact each other. The excess developer openings  92  and  92 ′ serving as fourth and second openings communicate with the downstream side of the supply conveyance path  9  relative to the developer conveyance direction with the upstream side of the collection conveyance path  7  relative to the developer conveyance direction. In the exemplary embodiment as shown in  FIG. 6 , the excess developer openings  92  and  92 ′ are separately disposed in the respective paths. However, the excess developer openings  92  and  92 ′ can be integrated when a lower portion of the collection conveyance path  7  and an upper portion of the supply conveyance path  9  are adjacent to each other or contacted with each other. 
   The collection conveyance path  7  is disposed obliquely above the development roller  5 . The supply conveyance path  9  is disposed below the collection conveyance path  7 . The supply openings  91  and  91 ′ and the excess developer openings  92  and  92  are disposed within the width α which is the width in the axial direction of the rotation axis of the development roller  5  of the development region H in which the toner is supplied to the photoconductor drum  1 . Since the supply openings  91  and  91 ′ and the excess developer openings  92  and  92 ′ are disposed within the width α, the development device  4  can be smaller than a related-art development device such as the related-art development device  40  having the openings  910 ,  910 ′,  920  and  920 ′ outside the width αα. In addition, the developer falls from the supply opening  91  at the downstream side of the collection conveyance path  7  relative to the developer conveyance direction to the supply conveyance path  9  so that the collection conveyance path  7  can reduce the developer accumulation at the downstream thereof relative to the developer conveyance direction. Therefore, the collection conveyance path  7  can reduce the excess supply of the developer therewithin. Consequently, the development roller  5  can reduce the supply of the low-density collection developer thereto from the collection conveyance path  7  through the supply conveyance path  9 . Therefore, the development device  4  of the exemplary embodiment of the present invention can not only reduce the size thereof but can also reduce a frequency of the uneven density image caused by the low-density collection developer being supplied to the development roller  5 . 
   According to the above-described embodiment, the development device  4  includes the development doctor  12  serving as the developer regulation member which regulates the thickness of the developer supplied to the development roller  5  to be the appropriate level. The development doctor  12  is disposed below the development roller  5 . Therefore, the development doctor  12  can regulate the thickness of the developer supplied to the development roller  5  from the supply conveyance path  9  at the appropriate level even when an excess amount of the developer is supplied from the supply conveyance path  9  to the development roller  5  caused by the excess supply of the developer within the supply conveyance path  9 , thereby reducing a frequency of the uneven density image. 
   According to the above-described embodiment, the toner supply opening, which supplies the additional toner to the collection conveyance path  7 , is disposed at the upstream side of the collection conveyance path  7  relative to the developer conveyance direction. Therefore, the development device  4  can save the space thereof and can secure the agitation conveyance distance to disperse the additional toner into the developer within the collection conveyance path  7 . 
   According to the above-described embodiment, the toner supply opening is disposed at the upstream side from the excess developer opening  92 ′ of the collection conveyance path  7  relative to the developer conveyance direction. Since the toner supply opening is disposed outside the width of each conveyance path, the additional toner can not only be supplied easily but also the agitation conveyance distance can be increased, thereby mixing the additional toner and the developer sufficiently. 
   According to the above-described embodiment, the development device  4  and at least one of the development elements selected from the photoconductor drum  1 , the charging device and the drum cleaning device are integrally supported to form the process cartridge  18 , which is detachably installed in the image forming apparatus  500 . The employment of the process cartridge  18  provides the same effects as described above and can enhance maintainability. 
   According to the above-described embodiment, the image forming apparatus  500  includes the development device  4  so as to permit the same effects provided by the development device  4 , thereby providing good image forming. 
   According to the above-described embodiment, the image forming apparatus  500  includes the process cartridge  18  including the development device  4 , thereby permitting the same effects provided by the development device  4 . Therefore, the image forming apparatus  500  can provide good image formation and can enhance maintainability by employing the process cartridge  18 . 
   As can be appreciated by those skilled in the art, numerous additional modifications and variation of the present invention are possible in light of the above-described 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.