Patent Publication Number: US-2018046129-A1

Title: Development cartridge and electrophotographic image forming apparatus adopting the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of Korean Patent Application No. 10-2016-0101223, filed on Aug. 9, 2016, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND 
     1. Field 
     The present disclosure is related to an electrophotographic image forming apparatus for forming an image on a recording medium in an electrophotographic manner, and a development cartridge capable of being detachably attached to the electrophotographic image forming apparatus. 
     2. Description of the Related Art 
     An electrophotographic image forming apparatus operating in an electrophotographic manner prints an image onto a recording medium by forming a visible toner image on a photosensitive body by supplying a toner to an electrostatic latent image formed on the photosensitive body, transferring the toner image to the recording medium, and fixing the transferred toner image onto the recording medium. A development cartridge contains a toner (developer) and includes a developing roller that supplies the toner to the electrostatic latent image formed on the photosensitive body. 
     During an image forming operation, the photosensitive body and the developing roller rotate in a specific direction (a forward direction), and a power connection structure with a driving source is implemented by taking into account a rotation direction of the photosensitive body and the developing roller. If required, the photosensitive body may be driven in a direction (a reverse direction) opposite to the rotation direction during the image forming operation. If a rotation direction of the driving source is changed to drive the photosensitive body in the reverse direction, the developing roller is also driven in the reverse direction. When the developing roller is repeatedly driven in the forward direction and the reverse direction, the toner in the development cartridge may be leaked externally. 
     SUMMARY 
     Provided are a development cartridge capable of regulating rotation of a developing roller, and an electrophotographic image forming apparatus employing the development cartridge. 
     Additional aspects will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the presented embodiments. 
     According to an aspect of an embodiment, a development cartridge capable of being detachably attached to a main body of an image forming apparatus includes a developing roller; a driving power receiving member configured to rotate in a first direction or a second direction by receiving a driving power from the main body; and a power delivery member configured to connect the driving power receiving member to the developing roller and to deliver only torque of the driving power receiving member in the first direction to the developing roller. 
     The power delivery member may include a rotational member including a first latch, and configured to be rotated by the driving power receiving member and to axially reciprocate between a first position and a second position when the driving power receiving member rotates in the first direction and the second direction, respectively; and a delivery member including a second latch having a form that is complementary with a form of the first latch, and configured to deliver the torque of the driving power receiving member in the first direction to the developing roller in such a manner that the first and second latches are connected to each other when the rotational member is positioned at the first position. 
     The first latch may include a female screw, the second latch may include a male screw corresponding to the female screw, and when the driving power receiving member rotates in the first direction, the female screw and the male screw may be coupled to each other so that the developing roller rotates, and when the driving power receiving member rotates in the second direction, the female screw and the male screw may be decoupled from each other so that the developing roller does not rotate. 
     The delivery member may be combined with a rotation axis of the developing roller. 
     The delivery member may include a rotation axis of the developing roller, wherein the male screw is formed at a side of the rotation axis. 
     The driving power receiving member may include a first gear, the rotational member may include a second gear coupled to the first gear, and the first and second gears may be helical gears that generate thrust in a direction toward where the rotational member is moved to the first position when the driving power receiving member rotates in the first direction. 
     The delivery member may be combined with a rotation axis of the developing roller, the first and second latches may have concavo-convex shapes that are complementary in the axial direction, so that the first and second latches are engaged with each other when the rotational member is positioned at the first position, and the first and second latches may be spaced apart from each other when the rotational member is positioned at the second position, the driving power receiving member may include a first gear, the rotational member may include a second gear coupled to the first gear, and the first and second gears may be helical gears that generate thrust in a direction toward where the rotational member is moved to the first position when the driving power receiving member rotates in the first direction. 
     The power delivery member may include a first rotational member configured to be combined with the developing roller, and including a guiding portion and a latch; a second rotational member configured to be mounted on a same axis as the first rotational member and to rotate by being coupled to the driving power receiving member, and including an inner gear; and a latch gear configured to be mounted at the guiding portion while being engaged with the inner gear, so that, when the driving power receiving member rotates in the first direction, the latch gear moves along the guiding portion to an engaged position where the latch gear is to be engaged with the latch so as to allow the first rotational member and the second rotational member to rotate together, and when the driving power receiving member rotates in the second direction, the latch gear moves along the guiding portion to a disengaged position where the latch gear is spaced apart from the latch. 
     The development cartridge may further include a photosensitive drum configured to form a development nip by contacting the developing roller; and a development nip releasing member configured to move the developing roller to be spaced apart from the photosensitive drum to release the development nip when the driving power receiving member rotates in the second direction. 
     When the driving power receiving member rotates in the first direction, the development nip releasing member may move the developing roller to contact the photosensitive drum to form the development nip. 
     The development cartridge may further include a stirring chamber containing developer; and a stirrer provided in the stirring chamber so as to stir the developer, wherein the stirrer is driven by being connected to the driving power receiving member. 
     The stirring chamber may include first and second stirring chambers that extend in a longitudinal direction of the developing roller and have interconnected ends to form a circulation path, and the stirrer may include first and second stirrers that are respectively provided in the first and second stirring chambers so as to deliver the developer in opposite directions to each other. 
     According to an aspect of another embodiment, an electrophotographic image forming apparatus includes a main body; and the development cartridge, the development cartridge being capable of being detachably attached to the main body. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a schematic configuration diagram illustrating an electrophotographic image forming apparatus, according to an embodiment; 
         FIG. 2  is a side view of one of development cartridges, according to an embodiment; 
         FIG. 3  is an exploded perspective view of a power delivery member, according to an embodiment; 
         FIGS. 4A through 4D  illustrate operations of the power delivery member shown in  FIG. 3 ; 
         FIG. 5  is an exploded perspective view of a power delivery member, according to another embodiment; 
         FIGS. 6A through 6D  illustrate operations of the power delivery member shown in  FIG. 5 ; 
         FIG. 7  is an exploded perspective view of a power delivery member, according to another embodiment; 
         FIG. 8  is an exploded perspective view of a power delivery member, according to another embodiment; 
         FIG. 9  illustrates a coupler that rotates in a first direction in the embodiment of the power delivery member of  FIG. 8 ; 
         FIG. 10  illustrates the coupler that rotates in a second direction in the embodiment of the power delivery member of  FIG. 8 ; 
         FIGS. 11 and 12  are side views of the development cartridge, according to an embodiment, in which  FIG. 11  illustrates a state in which a photosensitive drum and a developing roller contact each other so that a development nip is formed, and  FIG. 12  illustrates a state in which the photosensitive drum and the developing roller are spaced apart from each other so that the development nip is released; 
         FIGS. 13 and 14  are side views of the development cartridge, according to an embodiment, in which  FIG. 13  illustrates a state in which a developing unit is positioned at a development position, and  FIG. 14  illustrates a state in which the developing unit is positioned at a release position; 
         FIG. 15  is a schematic configuration diagram illustrating an electrophotographic image forming apparatus, according to another embodiment; 
         FIG. 16  illustrates a partial cross-sectional view of a development cartridge, according to an embodiment; and 
         FIG. 17  illustrates a partial perspective view of the development cartridge, according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure will be described in detail by explaining embodiments of an electrophotographic image forming apparatus and a development cartridge with reference to the attached drawings. Throughout the specification and drawings, those elements performing substantially the same function are rendered the same reference numeral, and redundant explanations thereof are omitted. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
       FIG. 1  is a schematic configuration diagram illustrating an electrophotographic image forming apparatus, according to an embodiment. The electrophotographic image forming apparatus (also referred to as the image forming apparatus) according to the present embodiment prints a color image to a recording medium P, according to an electrophotographic manner. Referring to  FIG. 1 , the image forming apparatus may include a main body  1  and a plurality of development cartridges  2 . The plurality of development cartridges  2  are detachably attached to the main body  1 . An exposure device  13 , a transfer device, and a fixing device  15  are arranged at the main body  1 . In addition, a recording medium transport unit for loading and transporting the recording medium P to which an image is to be formed is arranged at the main body  1 . 
     For color printing, the plurality of development cartridges  2  may include four development cartridges  2  for developing images with cyan color, magenta color, yellow color, and black color. Developers, e.g., toners, with cyan (C) color, magenta (M) color, yellow (Y) color, and black (K) color may be contained in the four development cartridges  2 , respectively. Although not illustrated, the toners with cyan color, magenta color, yellow color, and black color may be respectively contained in four toner supply containers, and may be respectively supplied from the four toner supply containers to the four development cartridges  2 . The image forming apparatus may further include development cartridges  2  for containing and developing toners of other various colors such as a light magenta color, a white color, or the like. Hereinafter, the image forming apparatus including the four development cartridges  2  will now be described, and unless there is a particular description contrary thereto, items with reference numerals C, M, Y, and K indicate elements for developing images with cyan color, magenta color, yellow color, and black color. 
     In the present embodiment, each of the four development cartridges  2  is an integrated development cartridge. Each development cartridge  2  may include a photosensitive unit  100  and a developing unit  200 . 
     The photosensitive unit  100  includes a photosensitive drum  21 . The photosensitive drum  21 , as a photosensitive body on which an electrostatic latent image is formed, may include a conductive metal pipe and a photosensitive layer formed at an outer circumference of the conductive metal pipe. A charging roller  23  is an example of a charger that charges a surface of the photosensitive drum  21  to have a uniform surface potential. Instead of the charging roller  23 , a charging brush, a corona charger, or the like may be used. The photosensitive unit  100  may further include a cleaning roller (not shown) for removing foreign substances attached to a surface of the charging roller  23 . A cleaning blade  25  is an example of a cleaning member that removes residual toners and foreign substances attached to the surface of the photosensitive drum  21  after a transfer process to be described below. Instead of the cleaning blade  25 , a cleaning device in another form, such as a rotating brush, may be used. 
     The developing unit  200  includes a toner container  209 . The developing unit  200  supplies a toner in the toner container  209  to an electrostatic latent image formed on the photosensitive drum  21 , thereby developing the electrostatic latent image to a visible toner image. A developing method may include a one-component developing method using a toner and a two-component developing method using a toner and a carrier. In the present embodiment, the developing unit  200  adopts the one-component developing method. A developing roller  22  supplies a toner to the photosensitive drum  21 . A developing bias voltage may be applied to the developing roller  22  to supply the toner to the photosensitive drum  21 . 
     In the present embodiment, a contact development technique in which the developing roller  22  and the photosensitive drum  21  contact each other and thus form a development nip is used. A supply roller  27  supplies the toner in the toner container  209  to a surface of the developing roller  22 . To do so, a supply bias voltage may be applied to the supply roller  27 . The developing unit  200  may further include a regulation member  28  for regulating an amount of toner to be supplied to a development nip N where the photosensitive drum  21  and the developing roller  22  contact each other due to the developing roller  22 . For example, the regulation member  28  may be a doctor blade that elastically contacts the surface of the developing roller  22 . The developing unit  200  may further include a bottom sealing member  29  that contacts the developing roller  22  in an opposite side of the regulation member  28  so as to prevent a toner leakage. The bottom sealing member  29  may be a film that contacts the developing roller  22 . 
     An exposure device  13  forms the electrostatic latent image on the photosensitive drum  21  by irradiating light to the photosensitive drum  21 , the light being modulated according to image information. Examples of the exposure device  13  may include a laser scanning unit (LSU) using a laser diode as a light source, a light emitting diode (LED) exposure device using an LED as a light source, or the like. 
     A transfer device may include an intermediate transfer belt  31 , a first transfer roller  32 , and a second transfer roller  33 . The intermediate transfer belt  31  temporarily receives a toner image developed on the photosensitive drum  21  of each of the development cartridges  2 C,  2 M,  2 Y, and  2 K. The intermediate transfer belt  31  is circularly driven while being supported by supporting rollers  34 ,  35 , and  36 . Four first transfer rollers  32  are positioned to face the photosensitive drums  21  of the development cartridges  2 C,  2 M,  2 Y, and  2 K by interposing the intermediate transfer belt  31  therebetween. A first transfer bias voltage is applied to the four first transfer rollers  32  so as to firstly transfer toner images, which are developed on the photosensitive drums  21 , to the intermediate transfer belt  31 . Instead of the first transfer rollers  32 , a corona transfer device or a pin scorotron-type transfer device may be used. A second transfer roller  33  is positioned to face the intermediate transfer belt  31 . A second transfer bias voltage is applied to the second transfer roller  33  so as to transfer, to the recording medium P, the toner images that are firstly-transferred to the intermediate transfer belt  31 . 
     When a print command is transmitted from a host (not shown) or the like, a controller (not shown) charges, by using the charging roller  23 , the surface of the photosensitive drum  21  to have a uniform surface potential. 
     The exposure device  13  forms electrostatic latent images on the photosensitive drums  21  by scanning four light-beams to the photosensitive drums  21  of the development cartridges  2 C,  2 M,  2 Y, and  2 K, the four light-beams being modulated according to image information corresponding to cyan, magenta, yellow, and black colors, respectively. The developing rollers  22  of the development cartridges  2 C,  2 M,  2 Y, and  2 K supply C, M, Y, and K toners to the photosensitive drums  21 , respectively, thereby developing the electrostatic latent images to visible toner images. The developed toner images are firstly transferred to the intermediate transfer belt  31 . The recording mediums P loaded on a loading plate  17  are output one by one by a pick-up roller  16 , and are transported to a transfer nip by a feed roller  18 , the transfer nip being formed by the second transfer roller  33  and the intermediate transfer belt  31 . The toner images that are firstly-transferred to the intermediate transfer belt  31  are secondly transferred to the recording medium P due to the second transfer bias voltage applied to the second transfer roller  33 . When the recording medium P passes through the fixing device  15 , the toner images are fixed on the recording medium P due to heat and a pressure. The recording medium P for which fixing is completed is externally discharged by a discharging roller  19 . 
     The development cartridges  2 C,  2 M,  2 Y, and  2 K may be detachably attached to the main body  1  through a door (not shown). 
       FIG. 2  is a side view of one of the development cartridges  2 , according to an embodiment. Referring to  FIG. 2 , when the development cartridge  2  is mounted to the main body  1 , rotational members of the development cartridge  2 , e.g., the photosensitive drum  21  and the developing roller  22 , may be driven by being connected to a driving motor  40  arranged at the main body  1 . The driving motor  40  may be arranged at the main body  1  so as to drive the four development cartridges  2 , or four driving motors  40  may be arranged with respect to the four development cartridges  2 . 
     A coupler (a driving power receiving member)  310  may be arranged at the development cartridge  2  so as to be connected to the driving motor  40  at the main body  1  when the development cartridge  2  is mounted to the main body  1 . The rotational members may be connected to the coupler  310  by using a power connecting member (not shown), e.g., gears. A coupler  320  may be further arranged at the development cartridge  2  so as to be connected to the driving motor  40  at the main body  1  when the development cartridge  2  is mounted to the main body  1 . In this case, the developing roller  22  and the supply roller  27  may rotate by being coupled to the coupler  310 , and the photosensitive drum  21  may rotate by being coupled to the coupler  320 . The coupler  320  may be positioned on a same axis as a rotation axis of the photosensitive drum  21  or may be positioned on the rotation axis of the photosensitive drum  21 . 
     During an image forming operation, the photosensitive drum  21  and the developing roller  22  rotate in a forward direction D 1 . When the driving motor  40  is forwardly driven, the coupler  310  rotates in a first direction C 1 , the developing roller  22  rotates in the forward direction D 1 , and the photosensitive drum  21  also rotates in the forward direction D 1  by using the coupler  320 . If required, the photosensitive drum  21  may rotate in a reverse direction D 2 . For example, when a reusable paper is often used as the recording medium P, paper dusts from the reusable paper are attached onto the photosensitive drum  21  and the cleaning blade  25  so that a printing error with a shape of a line in a longitudinal direction (a rotation direction of the photosensitive drum  21 ) may occur on a printed image. In order to remove the paper dusts, the driving motor  40  may be reversely driven to allow the photosensitive drum  21  to rotate in the reverse direction D 2 . In this regard, when the coupler  310  rotates in a second direction C 2 , the developing roller  22  may also rotate in the reverse direction D 2 . As described above, when the developing roller  22  rotates in the reverse direction D 2 , a toner is leaked between the bottom sealing member  29  and the developing roller  22  that have a relatively low contact pressure. The leaked toner is transported to an area of the regulation member  28  due to rotation of the developing roller  22 , and since a contact pressure of the regulation member  28  with respect to the developing roller  22  is higher than the contact pressure of the bottom sealing member  29  with respect to the developing roller  22 , the toner does not pass through a gap between the regulation member  28  and the developing roller  22 . Therefore, the toner may be collected in the vicinity of the regulation member  28  and then may fall to the inside of the image forming apparatus, thereby contaminating the image forming apparatus. When the developing roller  22  rotates again in the forward direction D 1 , the toner collected in the vicinity of the regulation member  28  may leave the developing roller  22  and thus may contaminate the image forming apparatus. 
     A side sealing member (not shown) is disposed between longitudinal-direction ends of the developing roller  22  and ends of the toner container  209 . When the developing roller  22  repeatedly rotates in the forward direction D 1  and the reverse direction D 2 , the developing roller  22  may repeatedly move in a longitudinal direction due to thrust and then may repeatedly interfere with the side sealing member, so that a sealing function of the side sealing member may deteriorate, resulting a toner leakage to the outside of the toner container  209  and damage to the developing roller  22 . In addition, when the developing roller  22  rotates in the reverse direction D 2 , the regulation member  28  installed in a counter manner may be deformed so that its regulation function may deteriorate or the regulation member  28  may be damaged. 
     In order to solve these problems, torque of the driving motor  40  may not be delivered to the developing roller  22  when the driving motor  40  is reversely driven. Referring to  FIG. 2 , the development cartridge  2  includes a power delivery member  50 . The power delivery member  50  connects the coupler  310  to the developing roller  22 , and delivers only torque of the coupler  310  in the first direction C 1  to the developing roller  22 . 
       FIG. 3  is an exploded perspective view of the power delivery member  50 , according to an embodiment. Referring to  FIGS. 2 and 3 , the power delivery member  50  includes a rotational member  51  and a delivery member  52 . The rotational member  51  is coupled to the coupler  310  and rotates. The coupler  310  includes a first gear  311  (refer to  FIG. 4A ), and the rotational member  51  includes a second gear  51 - 1  coupled to the first gear  311 . When the coupler  310  rotates in the first direction C 1  and the second direction C 2 , the rotational member  51  may reciprocate in axial directions X 1  and X 2 . The delivery member  52  selectively delivers torque of the rotational member  51  to the developing roller  22  according to a rotation direction of the coupler  310 . To do so, the rotational member  51  includes a first latch, and the delivery member  52  includes a second latch. The first and second latches have forms that are complementary with each other so as to deliver the torque of the rotational member  51  to the delivery member  52  only when the coupler  310  rotates in the first direction C 1 , and not to deliver the torque of the rotational member  51  to the delivery member  52  when the coupler  310  rotates in the second direction C 2 . When the coupler  310  rotates in the first direction C 1 , the rotational member  51  is moved to a first position where the first and second latches are connected to each other, and when the coupler  310  rotates in the second direction C 2 , the rotational member  51  is moved to a second position where the first and second latches are disconnected from each other. 
     Referring to  FIG. 3 , the delivery member  52  is combined with a rotation axis  22 - 1  of the developing roller  22 . For example, a D-cut portion  22 - 2  is arranged at an end of the rotation axis  22 - 1 , and an insertion hole  52 - 2  having a complementary shape with the D-cut portion  22 - 2  is arranged at the delivery member  52 . The delivery member  52  has a male screw  52 - 2  and a cylindrical-shape first support part  52 - 3  on its outer circumferential surface. The rotational member  51  has a female screw  51 - 2  and a cylindrical-shape second support part  51 - 3  to be rotatably supported by the cylindrical-shape first support part  52 - 3 . A diameter of the female screw  51 - 2  is greater than an external diameter of the rotation axis  22 - 1 . When the rotational member  51  is mounted on the rotation axis  22 - 1 , and the delivery member  52  is combined with the rotation axis  22 - 1 , the first support part  52 - 3  is inserted into the second support part  51 - 3 . The female screw  51 - 2  and the male screw  52 - 2  are respective examples of the first latch and the second latch. When the coupler  310  rotates in the first direction C 1 , the female screw  51 - 2  and the male screw  52 - 2  are coupled to each other, and when the coupler  310  rotates in the second direction C 2 , the female screw  51 - 2  and the male screw  52 - 2  are decoupled from each other. 
       FIGS. 4A through 4D  illustrate operations of the power delivery member  50  shown in  FIG. 3 . Referring to  FIG. 4A , the rotational member  51  is positioned at a second position. In this state, when the coupler  310  rotates in the first direction C 1 , the female screw  51 - 2  and the male screw  52 - 2  are coupled to each other and the rotational member  51  is moved in the axial direction X 1 . While the rotational member  51  is moved in the axial direction X 1 , the delivery member  52  and the developing roller  22  do not rotate. 
     As illustrated in  FIG. 4B , when the rotational member  51  reaches a first position, the female screw  51 - 2  and the male screw  52 - 2  are completely coupled to each other. In this state, when the coupler  310  rotates in the first direction C 1 , the torque of the rotational member  51  is delivered to the developing roller  22  via the delivery member  52 , and the developing roller  22  rotates in the forward direction D 1 . 
     In the state shown in  FIG. 4B , when the coupler  310  rotates in the second direction C 2 , the female screw  51 - 2  is decoupled from the male screw  52 - 2  as shown in  FIG. 4C , and the rotational member  51  is moved in the axial direction X 2  and the delivery member  52  does not rotate. Therefore, the developing roller  22  does not rotate, either. 
     As shown in  FIG. 4D , when the rotational member  51  reaches the second position, the rotational member  51  rotates while the second support part  51 - 3  of the rotational member  51  is supported by the first support part  52 - 3  of the delivery member  52 . In this state, even if the coupler  310  keeps rotating in the second direction C 2 , the rotational member  51  rotates while being supported by the delivery member  52  so that the delivery member  52  and the developing roller  22  do not rotate. 
     According to the aforementioned structure, the developing roller  22  does not rotate while the photosensitive drum  21  rotates in the reverse direction D 2 , so that durability of the developing roller  22  may be maintained, and contamination of the image forming apparatus due to the toner leakage may be prevented. 
       FIG. 5  is an exploded perspective view of a power delivery member  50   a , according to another embodiment. Referring to  FIG. 5 , the power delivery member  50   a  according to the present embodiment is different from the embodiment of  FIG. 3  in that the male screw  52 - 2  is directly arranged on the rotation axis  22 - 1  of the developing roller  22 . That is, the rotation axis  22 - 1  of the developing roller  22  functions as the delivery member  52 . A male screw  52 - 2   a  is formed at a side of the rotation axis  22 - 1 , and a first support part  52 - 3   a  is arranged at an outer side of the male screw  52 - 2   a . A diameter of the first support part  52 - 3   a  is smaller than a root diameter of the male screw  52 - 2   a . A rotational member  51   a  includes a female screw  51 - 2   a , and a second support part  51 - 3   a  to be rotatably supported by the first support part  52 - 3   a.    
       FIGS. 6A through 6D  illustrate operations of the power delivery member  50   a  shown in  FIG. 5 . Referring to  FIG. 6A , the rotational member  51   a  is positioned at the second position. In this state, when the coupler  310  rotates in the first direction C 1 , the female screw  51 - 2   a  and the male screw  52 - 2   a  are coupled to each other, and the rotational member  51   a  is moved in the axial direction X 2 . While the rotational member  51   a  is moved in the axial direction X 2 , the developing roller  22  does not rotate. 
     As illustrated in  FIG. 6B , when the rotational member  51   a  reaches the first position, the female screw  51 - 2   a  and the male screw  52 - 2   a  are completely coupled to each other. In this state, when the coupler  310  rotates in the first direction C 1 , torque of the rotational member  51   a  is delivered to the rotation axis  22 - 1  of the developing roller  22 , and the developing roller  22  rotates in the forward direction D 1 . 
     In the state shown in  FIG. 6B , when the coupler  310  rotates in the second direction C 2 , the female screw  51 - 2   a  is decoupled from the male screw  52 - 2   a  as shown in  FIG. 6C , and the rotational member  51   a  is moved in the axial direction X 1 , and the developing roller  22  does not rotate. 
     As shown in  FIG. 6D , when the rotational member  51   a  reaches the second position, the rotational member  51   a  rotates while the second support part  51 - 3   a  thereof is supported by the first support part  52 - 3   a . In this state, even if the coupler  310  keeps rotating in the second direction C 2 , the rotational member  51   a  rotates while being supported by the first support part  52 - 3   a  so that the developing roller  22  does not rotate. 
     In the embodiments of  FIGS. 3 through 5 , the first gear  311  and the second gear  51 - 1  may be helical gears. In this case, helical directions of the first gear  311  and the second gear  51 - 1  may be determined to generate thrust in a direction toward where the rotational members  51  and  51   a  are moved to the first position, i.e., in a direction where the female screws  51 - 2  and  51 - 2   a  are coupled to the male screws  52 - 2  and  52 - 2   a  when the coupler  310  rotates in the first direction C 1 . By doing so, the rotational members  51  and  51   a  may be easily moved from the second position to the first position. In addition, even when the female screws  51 - 2  and  51 - 2   a  are spaced apart from the male screws  52 - 2  and  52 - 2   a , the female screws  51 - 2  and  51 - 2   a  and the male screws  52 - 2  and  52 - 2   a  may be easily coupled to each other when the coupler  310  rotates in the first direction C 1 . On the other hand, when the coupler  310  rotates in the second direction C 2 , due to the thrust of the first gear  311  and the second gear  51 - 1  that are the helical gears, a thrust to move the rotational members  51  and  51   a  toward the second position is applied to the rotational members  51  and  51   a , so that the female screws  51 - 2  and  51 - 2   a  may be easily decoupled from the male screws  52 - 2  and  52 - 2   a.    
       FIG. 7  is an exploded perspective view of a power delivery member  50   b , according to another embodiment.  FIG. 7  illustrates only a portion of the coupler  310  to rotate the developing roller  22 . Referring to  FIG. 7 , the power delivery member  50   b  includes a rotational member  51   b  and a delivery member  52   b , wherein the rotational member  51   b  is coupled to the coupler  310  and rotates, and the delivery member  52   b  is combined with the rotation axis  22 - 1  of the developing roller  22 . The combined structure of the delivery member  52   b  and the rotation axis  22 - 1  may be the same as the combined structure of the delivery member  52  and the rotation axis  22 - 1  shown in  FIG. 3 . 
     The coupler  310  includes the first gear  311  in the form of a helical gear. The rotational member  51   b  includes a second gear  51 - 1   b  in the form of a helical gear to be engaged with the first gear  311 . Helical directions of the first and second gears  311  and  51 - 1   b  are determined to generate thrust in a direction toward where the delivery member  52   b  is moved to the first position, i.e., in the axial direction X 1 , when the coupler  310  rotates in the first direction C 1 , and in a direction in which the delivery member  52   b  is moved to the second position, i.e., in the axial direction X 2 , when the coupler  310  rotates in the second direction C 2 . Due to this configuration, the rotational member  51   b  may rotate about a common axis with the delivery member  52   b , and may be moved in the axial directions X 1  and X 2 . 
     In the present embodiment, first and second latches  51 - 2   b  and  52 - 2   b  of the power delivery member  50   b  have concavo-convex shapes that are complementary in the axial directions X 1  and X 2 , so that the first and second latches  51 - 2   b  and  52 - 2   b  are engaged with each other when the rotational member  51   b  is positioned at the first position, and the first and second latches  51 - 2   b  and  52 - 2   b  are spaced apart from each other when the rotational member  51   b  is positioned at the second position. The first latch  51 - 2   b  is arranged at the rotational member  51   b , and the second latch  52 - 2   b  is arranged at the delivery member  52   b . The first and second latches  51 - 2   b  and  52 - 2   b  may deliver only torque in one direction. That is, the first and second latches  51 - 2   b  and  52 - 2   b  may have shapes that are engaged with each other to deliver torque to each other when they rotate in one direction, and that are spaced apart from each other when they rotate in another direction. For example, as illustrated in  FIG. 7 , the second latch  52 - 2   b  may have a slope  52 - 2   b - 1  and a facing surface  52 - 2   b - 2 , wherein the slope  52 - 2   b - 1  extends in a circular direction and is slanted in an axial direction and the facing surface  52 - 2   b - 2  extends in the axial direction from the slope  52 - 2   b - 1 . The first latch  51 - 2   b  and the second latch  52 - 2   b  may have shapes that are complementary with each other. The rotational member  51   b  may have an inner diameter portion  51 - 4   b , and the first latch  51 - 2   b  may be formed at an inner wall of the inner diameter portion  51 - 4   b . The delivery member  52   b  may have an outer diameter portion  52 - 4   b , and the second latch  52 - 2   b  may be formed at an outer surface of the outer diameter portion  52 - 4   b . The second latch  52 - 2   b  is inserted into the inner diameter portion  51 - 4   b . By doing so, while the first latch  51 - 2   b  and the second latch  52 - 2   b  are engaged with each other, torque of the rotational member  51   b  may be delivered to the delivery member  52   b , and when the first latch  51 - 2   b  and the second latch  52 - 2   b  are spaced apart from each other, the torque of the rotational member  51   b  is not delivered to the delivery member  52   b.    
     When the coupler  310  rotates in the first direction C 1 , the rotational member  51   b  is moved in the axial direction X 1  and thus reaches the first position, and the first and second latches  51 - 2   b  and  52 - 2   b  are engaged with each other. Torque of the coupler  310  in the first direction C 1  is delivered to the developing roller  22  via the delivery member  52 b. Therefore, the developing roller  22  rotates in the forward direction D 1 . 
     When the coupler  310  rotates in the second direction C 2 , thrust in the axial direction X 2  that is opposite to the axial direction X 1  is generated in the rotational member  51   b . Therefore, the rotational member  51   b  is moved in the axial direction X 2  and thus reaches the second position, and the first and second latches  51 - 2   b  and  52 - 2   b  are spaced apart from each other. In a rotation direction of the rotational member  51   b  when the coupler  310  rotates in the second direction C 2 , the first and second latches  51 - 2   b  and  52 - 2   b  are pushed away from each other, thus, the rotational member  51   b  is easily moved in the axial direction X 2 . Therefore, torque of the coupler  310  in the second direction C 2  is not delivered to the delivery member  52   b  and the developing roller  22 , and the developing roller  22  does not rotate. 
       FIG. 8  is an exploded perspective view of a power delivery member  50   c , according to another embodiment.  FIG. 9  illustrates the coupler  310  that rotates in the first direction C 1  in the embodiment of the power delivery member  50   c  of  FIG. 8 .  FIG. 10  illustrates the coupler  310  that rotates in the second direction C 2  in the embodiment of the power delivery member  50   c  of  FIG. 8 . In  FIGS. 8 through 10 , only a portion of the coupler  310  to rotate the developing roller  22  is illustrated. 
     Referring to  FIG. 8 , the power delivery member  50   c  includes a first rotational member  53 , a second rotational member  54 , and a latch gear  55 . The first rotational member  53  is combined with the rotation axis  22 - 1  of the developing roller  22 . The combined structure of the first rotational member  53  and the rotation axis  22 - 1  may be the same as the combined structure of the delivery member  52  and the rotation axis  22 - 1  shown in  FIG. 3 . The first rotational member  53  includes a latch  53 - 1  and a guiding portion  53 - 2 . The guiding portion  53 - 2  is provided to enable a swing and rotation of the latch gear  55 . The second rotational member  54  is coupled to the coupler  310  and rotates. The second rotational member  54  includes a second gear  54 - 1  to be engaged with the first gear  311  of the coupler  310 , and an inner gear  54 - 2 . The inner gear  54 - 2  is engaged with the latch gear  55 . According to rotation directions of the second rotational member  54 , the latch gear  55  moves (swings) to an engaged position (refer to  FIG. 9 ) so as to be engaged with the latch  53 - 1 , and to a disengaged position (refer to  FIG. 10 ) spaced apart from the latch  53 - 1 . 
     When the coupler  310  rotates in the first direction C 1 , the latch gear  55  swings along the guiding portion  53 - 2  in a rotation direction of the second rotational member  54  as shown in  FIG. 9 , and is engaged with the latch  53 - 1 . In this state, the latch  53 - 1  does not rotate, and the first rotational member  53  rotates along with the second rotational member  54 . Therefore, the developing roller  22  rotates in the forward direction D 1 . 
     When the coupler  310  rotates in the second direction C 2 , the latch gear  55  swings along the guiding portion  53 - 2  in a rotation direction of the second rotational member  54  as shown in  FIG. 10  and is spaced apart from the latch  53 - 1 . The latch gear  55  rotates in the guiding portion  53 - 2 . Therefore, torque of the coupler  310  in the second direction C 2  is not delivered to the first rotational member  53 , and the developing roller  22  does not rotate. 
     In the embodiments of  FIGS. 2 through 7 , the rotational members  51 ,  51   a ,  51   b , and  54  may be combined with the coupler  310  via a direct gear coupling structure, or a plurality of gears may be arranged between the rotational members  51 ,  51   a ,  51   b , and  54  and the coupler  310 . 
     During an image forming operation, the photosensitive drum  21  and the developing roller  22  contact each other to form the development nip N. However, if the photosensitive drum  21  and the developing roller  22  maintain their contact even if the image forming operation is not performed, the developing roller  22  may be deformed, and the photosensitive body may be damaged. In addition, when a plurality of images are continuously printed, if the photosensitive drum  21  and the developing roller  22  maintain their contact during an image non-forming period between image forming periods, a toner on the developing roller  22  is delivered to the photosensitive drum  21  during the image non-forming period so that an amount of toner consumption may be increased and waste toner may be increased, and since the photosensitive drum  21  and the developing roller  22  rotate while contacting each other, a stress is applied to the developing roller  22  so that a life of the developing roller  22  may be decreased. 
       FIGS. 11 and 12  are side views of the development cartridge  2 , according to an embodiment.  FIG. 11  illustrates a state in which the photosensitive drum  21  and the developing roller  22  contact each other so that the development nip N is formed, and  FIG. 12  illustrates a state in which the photosensitive drum  21  and the developing roller  22  are spaced apart from each other so that the development nip N is released. 
     Referring to  FIGS. 11 and 12 , the development cartridge  2  includes the photosensitive unit  100  and the developing unit  200 . The photosensitive unit  100  may include a first frame  101  and the photosensitive drum  21  supported by the first frame  101 . The developing unit  200  may include a second frame  201  and the developing roller  22  supported by the second frame  201 . The photosensitive unit  100  and the developing unit  200  are connected to each other so as to rotate to a development position (refer to  FIG. 11 ) where the photosensitive drum  21  and the developing roller  22  contact each other to form the development nip N and a release position (refer to  FIG. 12 ) where the photosensitive drum  21  and the developing roller  22  are spaced apart from each other to release the development nip N. For example, the photosensitive unit  100  and the developing unit  200  are connected to rotate to the development position and the release position with respect to a hinge axis  301 . In the image forming apparatus, the photosensitive drum  21  is related to a location of the first transfer roller  32 , or the like, thus, when the development cartridge  2  is mounted to the main body  1 , a position of the photosensitive drum  21  is fixed. The developing unit  200  is coupled to the photosensitive unit  100  so as to be rotatable with respect to the hinge axis  301 . 
     Rotational members of the development cartridge  2 , e.g., the photosensitive drum  21 , the developing roller  22 , the supply roller  27 , or the like may be driven by being connected to the driving motor  40  when the development cartridge  2  is mounted to the main body  1 . The driving motor  40  may drive all of the four development cartridges  2 , or four driving motors  40  may be arranged with respect to the four development cartridges  2 . 
     For example, the coupler (the driving power receiving member)  310  may be arranged at the development cartridge  2  so as to be connected to the driving motor  40  at the main body  1  when the development cartridge  2  is mounted to the main body  1 . The rotational members may be connected to the coupler  310  by using the power connecting member (not shown), e.g., the gears. The coupler  320  may be further arranged at the development cartridge  2  so as to be connected to the driving motor  40  at the main body  1  when the development cartridge  2  is mounted to the main body  1 . In this case, the rotational members of the developing unit  200 , e.g., the developing roller  22  and the supply roller  27 , may rotate by being coupled to the coupler  310 , and the rotational member of the photosensitive unit  100 , e.g., the photosensitive drum  21 , may rotate by being coupled to the coupler  320 . The coupler  320  may be positioned on a same axis as a rotation axis of the photosensitive drum  21  or may be positioned on the rotation axis of the photosensitive drum  21 . The hinge axis  301  may be a same axis as the rotation axis of the coupler  310 . 
     An elastic member  330  provides an elastic force to generate the development nip N. The elastic member  330  provides the elastic force to the developing unit  200  to rotate in a direction where the development nip N is to be formed. Due to the elastic force of the elastic member  330 , the developing unit  200  rotates with respect to the hinge axis  301 , so that the developing roller  22  contacts the photosensitive drum  21  and thus the development nip N is formed as shown in  FIG. 11 .  FIGS. 11 and 12  illustrate, as an example of the elastic member  330 , a tension coil spring of which ends are supported by the developing unit  200  and the photosensitive unit  100 , respectively, but the example of the elastic member  330  is not limited thereto. For example, a member having one of various types including a torsion coil spring, a plate spring, or the like may be used as the elastic member  330 . 
     The development cartridge  2  of the present embodiment may include a development nip releasing member to move the developing unit  200  to the development position where the development nip N is formed and to the release position where the development nip N is released. The development nip releasing member locates the developing unit  200  at the development position during a printing operation (an image forming operation and an image forming period), and locates the developing unit  200  at the release position during a non-printing operation (while the image forming operation is not performed, and an image non-forming period). The development nip releasing member shifts the developing unit  200  between the development position and the release position, according to a rotation direction of the coupler  310 . For example, when the coupler  310  rotates in the first direction C 1 , the developing roller  22  rotates in the forward direction D 1 . When the coupler  310  rotates in the second direction C 2 , the development nip releasing member shifts the developing unit  200  from the development position to the release position. When the coupler  310  rotates in the first direction C 1  again, the development nip releasing member shifts the developing unit  200  from the release position to the development position. 
       FIGS. 13 and 14  are side views of the development cartridge  2 , according to an embodiment.  FIG. 13  illustrates a state in which the developing unit  200  is positioned at the development position, and  FIG. 14  illustrates a state in which the developing unit  200  is positioned at the release position. Referring to  FIGS. 13 and 14 , the development cartridge  2  may include a driving gear  410 . The driving gear  410  may rotate by being coupled to the coupler  310 . In the present embodiment, the coupler  310  includes the first gear  311 , and in this regard, the first gear  311  is engaged with the second gear  51 - 1  in the power delivery member  50 . Instead of the power delivery member  50 , the power delivery members  50   a ,  50   b , and  50   c  respectively shown in  FIGS. 5, 7, and 8  may be used. The driving gear  410  is engaged with the second gear  51 - 1 . When the coupler  310  rotates in the first direction C 1  and the second direction C 2 , the driving gear  410  rotates in a direction A 1  and a direction A 2 . The coupler  310  rotates in the first direction C 1  during a printing operation, and rotates in the second direction C 2  during a non-printing operation. 
     A moving member  430  is included in the developing unit  200 . The moving member  430  shifts the developing unit  200  between the development position and the release position by rotating the developing unit  200  with respect to the hinge axis  301 . To do so, the moving member  430  is mounted in the developing unit  200 , e.g., the second frame  201 , so as to be movable to a third position and a fourth position corresponding to the release position and the development position, respectively. The moving member  430  includes a gear  431 . In the present embodiment, the moving member  430  slides to the third and fourth positions and the gear  431  is a rack gear. The moving member  430  is moved to the third and fourth positions, according to a rotation direction of the driving gear  410 . For example, the driving gear  410  rotates in the direction A 2  during a non-printing operation, and rotates in the direction A 1  during a printing operation. Hereinafter, the rotation direction of the driving gear  410  is marked, A 2  indicates a rotation direction during a non-printing operation, and A 1  indicates a rotation direction during a printing operation. 
     The moving member  430  includes a second connection part  432  to be connected to a first connection part  102  placed at the first frame  101 . For example, the first connection part  102  may have a projected shape, and the second connection part  432  may have a loop shape to which the first connection part  102  is inserted. Shapes of the first and second connection parts  102  and  432  are not limited to those shown in  FIG. 13 . 
     A switching member is interposed between the moving member  430  and the driving gear  410 . The switching member rotates by being coupled to the driving gear  410 . The switching member is switched between a first switching position and a second switching position when the driving gear  410  rotates in the directions A 1  and A 2 , wherein, at the first switching position, the switching member is spaced apart from the gear  431  and allows the moving member  430  to switch from the third position to the fourth position, and at the second switching position, the switching member is coupled to the gear  431  and allows the moving member  430  to switch from the fourth position to the third position. 
     In the present embodiment, a swing gear  420  is used as the switching member. The swing gear  420  is engaged with the driving gear  410  and swings between the first switching position ( FIG. 13 ) and the second switching position ( FIG. 14 ), according to rotation directions of the driving gear  410 . When the driving gear  410  rotates in the direction A 2 , as illustrated in  FIG. 14 , the swing gear  420  is positioned at the second switching position and is engaged with the gear  431 . When the driving gear  410  rotates in the direction A 1 , as illustrated in  FIG. 13 , the swing gear  420  is positioned at the first switching position, and is spaced apart from the gear  431 . A guiding portion  202  may be arranged in the developing unit  200 , e.g., the second frame  201 , so as to allow the swing gear  420  to swing between the first switching position and the second switching position. The guiding portion  202  may have a long-hole shape. 
     A spring  440  provides the moving member  430  with an elastic force to maintain the moving member  430  at the fourth position. 
     With reference to  FIGS. 13 and 14 , a process of forming and releasing the development nip N will now be described. 
     Referring to  FIG. 13 , the developing unit  200  is positioned at the development position, the moving member  430  is positioned at the fourth position, and the swing gear  420  is positioned at the second switching position. For printing, the driving motor  40  arranged at the main body  1  rotates in a forward direction, and the coupler  310  rotates in the first direction C 1 . In this regard, torque of the coupler  310  in the first direction C 1  is delivered to the developing roller  22  by the power delivery member  50 , and the developing roller  22  rotates in the forward direction D 1 . The driving gear  410  rotates in the direction A 1  by being coupled to the second gear  51 - 1 . Then, as illustrated in  FIG. 13 , the swing gear  420  is positioned at the second switching position, and remains spaced apart from the gear  431 . Therefore, the moving member  430  remains at the fourth position, and the developing roller  22  rotates in the forward direction D 1  by being coupled to the coupler  310  via the power delivery member  50 . Therefore, a printing operation may be performed while the development nip N is formed. 
     During a non-printing operation, when the driving motor  40  rotates in a reverse direction, the coupler  310  rotates in the second direction C 2 . In this regard, due to the power delivery member  50 , torque of the coupler  310  in the second direction C 2  is not delivered to the developing roller  22 , so that the developing roller  22  does not rotate. The driving gear  410  coupled to the second gear  51 - 1  rotates in the direction A 2 . Then, as illustrated in  FIG. 14 , the swing gear  420  swings to the first switching position and is engaged with the gear  431 . When the driving gear  410  continuously rotates in the direction A 2 , the swing gear  420  rotates while being engaged with the gear  431 . The moving member  430  slides from the fourth position to the third position, and the second connection part  432  pulls the first connection part  102 . Since a position of the photosensitive unit  100  is fixed, the developing unit  200  rotates in an arrow direction B 2  with respect to the hinge axis  301 . As illustrated in  FIGS. 12 and 14 , when the moving member  430  reaches the third position, the developing unit  200  reaches the release position, and the developing roller  22  is spaced apart from the photosensitive drum  21 , so that the development nip N is released. 
     When the driving motor  40  is stopped, the developing unit  200  may remain at the release position. Due to the elastic force of the elastic member  330 , the developing unit  200  tends to return to the development position. However, since the driving motor  40 , the coupler  310 , the driving gear  410 , the swing gear  420 , and the gear  431  are coupled to each other, the developing unit  200  may remain at the release position. 
     When the driving motor  40  rotates in a forward direction for printing, in a state shown in  FIG. 14 , torque of the driving motor  40  is delivered to the driving gear  410  via the coupler  310 , so that the driving motor  40  rotates in the direction A 1 . In this regard, since torque of the coupler  310  in the first direction C 1  is delivered to the developing roller  22 , the developing roller  22  rotates in the forward direction D 1 . As illustrated in  FIG. 13 , the swing gear  420  swings to the second switching position, and due to the elastic force of the elastic member  330  of the developing unit  200 , the developing unit  200  rotates in an arrow direction B 1 . Since the first connection part  102  and the second connection part  432  are connected to each other, the moving member  430  slides from the third position to the fourth position. When the moving member  430  reaches the fourth position, the swing gear  420  remains at the second switching position, the moving member  430  remains at the fourth position, and a printing operation may be performed while the development nip N is formed. 
     According to the embodiments of the development cartridge  2 , the development nip N may be formed or released by rotating the driving gear  410  by rotating the coupler  310  in the first direction C 1  or the second direction C 2 , so that a device structure for forming and releasing the development nip N in the main body  1  is not necessary, therefore, the number of parts of the main body  1  may be decreased and the manufacturing costs and a size of the image forming apparatus may be reduced due to the decrease. In addition, the development nip N may be separated by a structure provided in the development cartridge  2 , so that a particular separating member for maintaining a separation state of the development nip N may not be mounted to the development cartridge  2 . Accordingly, it is possible to resolve inconvenience of a user who has to remove a separating member when initially mounting the development cartridge  2  to the main body  1 . In addition, since the power delivery member  50  is used, when the coupler  310  rotates in the second direction C 2 , the developing roller  22  does not rotate due to the power delivery member  50 . Therefore, damage to parts or a leakage of a toner due to rotation of the developing roller  22  in the reverse direction D 2  may be prevented. 
       FIG. 15  is a schematic configuration diagram illustrating an electrophotographic image forming apparatus, according to another embodiment. Referring to  FIG. 15 , the electrophotographic image forming apparatus (also referred to as the image forming apparatus) according to the present embodiment prints a color image medium in an electrophotographic manner. The image forming apparatus includes a plurality of development cartridges  510  and a plurality of developer cartridges  520  accommodating developers. The developer cartridges  520  are respectively connected to the development cartridges  510 , and the developers contained in the developer cartridges  520  are respectively supplied to the development cartridges  510 . The developer cartridges  520  and the development cartridges  510  may be individually replaced. 
     The development cartridges  510  include four development cartridges  510 C,  510 M,  510 Y, and  510 K for developing developers with cyan color (C), magenta color (M), yellow color (Y), and black color (K). The developer cartridges  520  contain the developers with cyan color, magenta color, yellow color, and black color, respectively. Unless there is a particular description contrary thereto, items with reference numerals C, M, Y, and K indicate elements for developing the developers with cyan color, magenta color, yellow color, and black color. 
     Each of the development cartridges  510  may include the photosensitive drum  21  on which an electrostatic latent image is formed, and the developing roller  22  for developing the electrostatic latent image to a visible toner image by supplying the developer from the developer cartridge  520  to the electrostatic latent image. The photosensitive drum  21  is an example of a photosensitive body on which the electrostatic latent image is formed, and may include a conductive metal pipe and a photosensitive layer formed at an outer circumference of the conductive metal pipe. The charging roller  23  is an example of a charger that charges a surface of the photosensitive drum  21  to have a uniform surface potential. Instead of the charging roller  23 , a charging brush, a corona charger, or the like may be used. 
     Although not illustrated, the development cartridges  510  may further a charging roller cleaner for removing foreign substances or dusts attached to a surface of the charging roller  23 , a cleaning member for removing residual developers attached to the surface of the photosensitive drum  21  after a transfer process to be described below, and a regulation member for regulating an amount of developer to be supplied to a development area where the photosensitive drum  21  and the developing roller  22  face each other. 
     In the present embodiment, a two-component developing method is used. In this case, developer contained in the developer cartridge  520  may be a toner, or a toner and a carrier. 
     When the two-component developing method is used, developer contained in the developer cartridge  520  may be the toner and the carrier. The carrier may be contained in the development cartridge  510 . In this case, in order to constantly maintain a ratio of the toner to the carrier in the development cartridge  510 , surplus carriers are discharged to the outside of the development cartridge  510  and are contained in a waste developer container (not shown). The developing roller  22  is spaced apart from the photosensitive drum  21  by a distance of several tens to several hundreds of micron. Although not illustrated, the developing roller  22  may include a development sleeve and a magnetic roller that is disposed in the development sleeve. The toner and the carrier are mixed with each other in the development cartridge  510 , and the toner is attached onto a surface of a magnetic carrier. The magnetic carrier is attached onto a surface of the developing roller  22  and is delivered to a development area where the photosensitive drum  21  and the developing roller  22  face each other. Due to a developing bias voltage applied to a gap between the developing roller  22  and the photosensitive drum  21 , only the toner is supplied to the photosensitive drum  21  so that the electrostatic latent image formed on a surface of the photosensitive drum  21  is developed to a visible image. 
     An exposure device  550  forms the electrostatic latent image on the photosensitive drum  21  by irradiating light to the photosensitive drum  21 , the light being modulated according to image information. Examples of the exposure device  550  may include an LSU using a laser diode as a light source, an LED exposure device using an LED as a light source, or the like. 
     An intermediate transfer belt  560  temporarily receives a toner image developed on the photosensitive drum  21  of each of the development cartridges  510 C,  510 M,  510 Y, and  510 K. A plurality of intermediate transfer rollers  561  are positioned to face the photosensitive drums  21  of the development cartridges  510 C,  510 M,  510 Y, and  510 K by interposing the intermediate transfer belt  560  therebetween. An intermediate transfer bias voltage is applied to the intermediate transfer rollers  561  so as to intermediately transfer images, which are developed on the photosensitive drums  21 , to the intermediate transfer belt  560 . Instead of the intermediate transfer rollers  561 , a corona transfer device or a pin scorotron-type transfer device may be used. 
     A transfer roller  570  is positioned to face the intermediate transfer belt  560 . A transfer bias voltage is applied to the transfer roller  570  so as to transfer, to a recording medium P, the toner images that are transferred to the intermediate transfer belt  560 . 
     A fixing device  580  fixes the toner image on the recording medium P by applying heat and/or pressure to the toner image that has been transferred onto the recording medium P. A form of the fixing device  580  is not limited to an example shown in  FIG. 15 . 
     According to the aforementioned structure, the exposure device  550  scans a plurality of lights, each of which being modulated according to image information of each color, to the photosensitive drums  21  of the development cartridges  510 C,  510 M,  510 Y, and  510 K, and forms electrostatic latent images on the photosensitive drums  21 . Due to C, M, Y, and K developers supplied from the developer cartridges  520 C,  520 M,  520 Y, and  520 K to the development cartridges  510 C,  510 M,  510 Y, and  510 K, the electrostatic latent images on the photosensitive drums  21  of the development cartridges  510 C,  510 M,  510 Y, and  510 K are developed to visible toner images. The developed toner images are intermediately transferred to the intermediate transfer belt  560  in a sequential order. The recording medium P loaded in a paper-feeding member  590  is transported along a paper-feeding path  591  to a portion between the transfer roller  570  and the intermediate transfer belt  560 . Due to a transfer bias voltage applied to the transfer roller  570 , the toner images that have been intermediately transferred onto the intermediate transfer belt  560  are transferred onto the recording medium P. When the recording medium P passes through the fixing device  580 , the toner images are fixed on the recording medium P due to heat and a pressure. The recording medium P for which fixing is completed is externally discharged by a discharging roller  592 . 
     The development cartridge  510  and the developer cartridge  520  are detachably attached to a main body  500 . Developer contained in the developer cartridge  520  is supplied to the development cartridge  510 . When the developer contained in the developer cartridge  520  is completely used, the developer cartridge  520  may be replaced with a new developer cartridge, or a new developer may be filled in the developer cartridge  520 . In order to stably supply the developer to the development cartridge  510 , a developer supply unit  530  may be arranged between the developer cartridge  520  and the development cartridge  510 . The developer supply unit  530  receives developer from the developer cartridge  520 , contains a predetermined amount of the developer, and delivers the contained developer to the development cartridge  510 . A supply pipe line  540  connects the developer supply unit  530  to the development cartridge  510 . 
     The developer that is supplied to the inside of the development cartridge  510  via the supply pipe line  540  is sufficiently stirred and is supplied to the developing roller  22 .  FIG. 16  illustrates a cross-sectional view of a portion of the development cartridge  510 , according to an embodiment. Referring to  FIG. 16 , a toner and a carrier are mixed with each other while they are delivered in an axial direction of the developing roller  22  in an internal space of the development cartridge  510 , i.e., a stirring chamber  511 . In this process, the toner is charged by friction with the carrier. In the stirring chamber  511 , at least one stirrer  512  is arranged to mix and stir the developer and to transport the developer in a direction parallel to the axial direction of the developing roller  22 . 
     The stirring chamber  511  may include first and second stirring chambers  511 - 1  and  511 - 2  that extend in the axial direction of the developing roller  22  and are parallel to each other. The stirrer  512  may include a first stirrer  512 - 1  installed in the first stirring chamber  511 - 1 , and a second stirrer  512 - 2  installed in the second stirring chamber  511 - 2 . The first and second stirring chambers  511 - 1  and  511 - 2  are separated from each other by a partition  513  extending in the axial direction of the developing roller  22 . First and second openings (not shown) are respectively formed in both longitudinal-direction ends of the partition  513 , i.e., the ends being in the axial direction of the developing roller  22 . The first and second stirring chambers  511 - 1  and  511 - 2  are connected to each other via the first and second openings. For example, the first and second stirrers  512 - 1  and  512 - 2  may each be an auger having an axis extending in the axial direction of the developing roller  22  and spiral wings formed at an outer circumference of the axis. 
     When the first stirrer  512 - 1  rotates, developer in the first stirring chamber  511 - 1  is delivered in the axial direction by the first stirrer  512 - 1 , and then is delivered to the second stirring chamber  511 - 2  via the first opening formed near one end of the partition  513 . Developer in the second stirring chamber  511 - 2  is delivered by the second stirrer  512 - 2  in an opposite direction to the delivery direction by the first stirrer  512 - 1 , and is delivered to the first stirring chamber  511 - 1  via the second opening formed near the other end of the partition  513 . By doing so, the developer is circulated throughout the first and second stirring chambers  511 - 1  and  511 - 2 , and in the circulation process, the developer is supplied to the developing roller  22  in the second stirring chamber  511 - 2 . 
     In the image forming apparatus using the two-component developing method, a toner is sufficiently charged while circulating in the stirring chamber  511  and then is transferred as an electrostatic latent image on the photosensitive drum  21 . When the image forming apparatus is initially driven or a long time elapses after printing, charge of the toner may be reduced. When printing is performed in this state, the toner with low charge may not be developed to an electrostatic latent image on the photosensitive drum  21  and may be scattered to the outside of the development cartridge  510 . Therefore, it is necessary to sufficiently charge the toner by circulating the toner with a carrier in the stirring chamber  511  by driving the stirrer  512 . In this regard, when the developing roller  22  rotates along with the stirrer  512 , the toner may be scattered. Thus, when the stirrer  512  is driven to charge the toner, it is required to ban the developing roller  22  from rotating, and to do so, the power delivery members  50 ,  50   a ,  50   b , and  50   c  shown in  FIGS. 3 through 10  may be used. 
       FIG. 17  illustrates a perspective view of a portion of the development cartridge  510 , according to an embodiment.  FIG. 17  particularly illustrates only the developing roller  22  and the stirrer  512  in detail. Referring to  FIG. 17 , the coupler (the driving power receiving member)  310  is arranged at the development cartridge  510 . When the development cartridge  510  is mounted to the main body  500 , the coupler  310  is connected to the driving motor  40  and rotates in the first direction C 1  and the second direction C 2  when the driving motor  40  is driven in a forward direction and a reverse direction, respectively. 
     The power delivery member  50  is arranged between the developing roller  22  and the coupler  310 . In the present embodiment, the power delivery member  50  is used, but the power delivery member  50   a ,  50   b , or  50   c  may be used. The first gear  311  of the coupler  310  is engaged with the second gear  51 - 1  of the power delivery member  50 . The second gear  51 - 1  is connected to a gear  515  via an idle gear  514 , the gear  515  being coupled to a rotation axis of the first stirrer  512 - 1 . The first stirrer  512 - 1  and the second stirrer  512 - 2  are connected to each other by using a timing belt  516 . 
     During a printing operation, the driving motor  40  is driven in a forward direction, and the coupler  310  rotates in the first direction C 1 . Then, the developing roller  22  rotates in the forward direction D 1  by the power delivery member  50 , and the first and second stirrers  512 - 1  and  512 - 2  also rotate in the forward direction D 1 . A toner and a carrier are circulated together throughout the first and second stirring chambers  511 - 1  and  511 - 2 , and a charged toner passes through the developing roller  22  and then is developed to an electrostatic latent image formed on the photosensitive drum  21 . 
     When the image forming apparatus is initially driven or a long time elapses after printing, the driving motor  40  is driven and in a reverse direction and the coupler  310  rotates in the second direction C 2  so as to charge a toner. Then, torque of the coupler  310  in the second direction C 2  is blocked by the power delivery member  50 , and the developing roller  22  does not rotate. The second gear  51 - 1  rotates in the reverse direction D 2 , and the first and second stirrers  512 - 1  and  512 - 2  connected to the second gear  51 - 1  also rotate in the reverse direction D 2 . A toner and a carrier are circulated together throughout the first and second stirring chambers  511 - 1  and  511 - 2  in a direction opposite to a circulation direction when the first and second stirrers  512 - 1  and  512 - 2  rotate in the forward direction D 1 , and the toner is charged. 
     When the toner is sufficiently charged, the driving motor  40  is forwardly driven to perform a printing operation. The coupler  310  rotates in the first direction C 1 , and the developing roller  22  and the first and second stirrers  512 - 1  and  512 - 2  also rotate in the forward direction D 1 . 
     As described above, by using the power delivery members  50 ,  50   a ,  50   b , and  50   c , the developing roller  22  is banned from rotating while a toner is charged, so that it is possible to prevent the toner from being scattered. 
     According to the embodiments of the development cartridge and the electrophotographic image forming apparatus, a driving power to be delivered to a developing roller may be blocked to ban the developing roller from rotating while the image forming apparatus is driven in a reverse direction. Accordingly, damage to parts and a leakage of a toner which are caused by the reverse-direction rotation of the developing roller, and deterioration of a printing quality due to the damage and the leakage may be prevented. 
     While this disclosure has been particularly shown and described with reference to the embodiments thereof, it will be understood by one of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the disclosure as defined by the appended claims. The embodiments should be considered in a descriptive sense only and not for purposes of limitation. Therefore, the scope of the disclosure is defined not by the detailed description of the disclosure but by the appended claims, and all differences within the scope will be construed as being included in the present disclosure.