Patent Publication Number: US-8126370-B2

Title: Developing unit and image forming apparatus having the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C §119(a) from of Korean Patent Application No. 2008-0029285, filed Mar. 28, 2008, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present general inventive concept relates to a developing unit and an image forming apparatus having the same, and more particularly, to a developing unit, in which a developing agent storing part is closed by an agitating member, and an image forming apparatus having the developing unit. 
     2. Description of the Related Art 
     Conventional image forming apparatuses form an image onto printing media according to input signals, and include printers, copying machines, fax machines, and multi-functional machines combining their functions. 
     An electro-photographic image forming apparatus, which is a kind of an image forming apparatus, forms an electrostatic latent image on a surface of a photo conductor by irradiating light onto the photo conductor charged with a designated electric potential, and forms a visible image by supplying a developing agent to the electrostatic latent image. The visible image formed on the photo conductor is transferred directly to a printing medium or transferred to the printing medium through an interim transfer body, and the image transferred to the printing medium is fixed to the printing medium through an image fixing process. 
     Here, a developing unit supplies the developing agent to the surface of the photo conductor. The developing unit includes a developing agent storing part to store the developing agent, a developing part to adhere the developing agent to the surface of the photo conductor so as to form a visible image, and an agitating member to agitate the developing agent stored in the developing agent storing part and transfer the developing agent to the developing part simultaneously. 
     Such a developing unit is a consumption article having a regular life, and is detachably attached to a main body of an image forming apparatus. The developing unit may be influenced by an external force, such as impact or vibration, during a carrying process before the developing unit is installed in the image forming apparatus, and thus the developing agent stored in the developing agent storing part may leak to the outside of the developing unit or scatter. In order to solve this problem, such as the leakage or scattering of the developing agent, a shielding film was conventionally attached to an inlet of the developing agent storing part in the final stage of the manufacturing process of the developing unit. 
     Thus, the conventional developing unit requires a user to directly remove the shielding film before the developing unit is installed in the image forming apparatus, thus causing inconvenience to the user. 
     Further, the conventional developing unit increases the total manufacturing cost due to the manufacturing cost of the shielding film and also increases the manufacturing time required because of the attaching of the shielding film to the developing unit. 
     Moreover, since the developing agent storing unit cannot be sealed again after the shielding member is removed once, if the image forming apparatus is not used for a long time, the developing agent scatters. 
     SUMMARY OF THE INVENTION 
     The present general inventive concept provides a developing unit having an improved usability, in which it is unnecessary to remove a shielding film before the developing unit is used, and an image forming apparatus having the same. 
     The present general inventive concept also provides a developing unit having an improved productivity, in which a developing agent storing part is closed using an existing structure without any separate member, and an image forming apparatus having the same. 
     The present general inventive concept also provides a developing unit, in which a developing agent storing part is re-closed after the developing unit is installed in an image forming apparatus and begins to be used, and an image forming apparatus having the same. 
     The present general inventive concept also provides a developing unit of an image forming apparatus, which increases the life of a fur-type feed roller installed in the developing unit to supply a developing agent and enhances an image quality, and an image forming apparatus having the same. 
     Additional aspects and utilities of the present general inventive concept will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the general inventive concept. 
     The foregoing and/or other aspects and utilities of the present general inventive concept are achieved by providing a developing unit including a developing agent storing part to store a developing agent, a developing part connected to the developing agent storing part, and an agitating member rotatably provided in a channel between the developing agent storing part and the developing part to transfer the developing agent stored in the developing agent storing part to the developing part, wherein the channel is closed by the agitating member. 
     The agitating member may include a shaft, and at least one film extended in the radial direction of the shaft. 
     The at least one film may be prepared in plural number. 
     At least two films among the plural films may be attached to the shaft such that the at least two films can be extended in the opposite directions with respect to the shaft. 
     When the channel is closed, the front end of the at least one film may contact the inner surface of the channel. 
     The developing unit may further include support parts provided on the shaft to support the side ends of the at least one film. 
     At least one protrusion guiding the attachment position of the at least one film may be provided on the shaft. 
     The developing unit may include a developing roller to adhere the developing agent to a photo conductor, and a feed roller to supply the developing agent transferred from the developing agent storing part to the developing roller, and the surface of the feed roller may be cleaned by the at least one film, when the developing unit is operated. 
     Plate-shaped sealing members may be provided between the agitating member and the side walls of the channel. 
     The foregoing and/or other aspects and utilities of the present general inventive concept may also be achieved by providing a developing unit including a developing agent storing part to store a developing agent, a developing part connected to the developing agent storing part, and an agitating member rotatably provided in a channel between the developing agent storing part and the developing part to transfer the developing agent stored in the developing agent storing part to the developing part, wherein the agitating member includes a shaft and at least one elastic plate attached to the shaft, and the channel is closed by the shaft and the at least one elastic plate having a tangential direction with the shaft, which is orthogonal to the transfer direction of the developing agent. 
     The developing unit may include a developing roller to adhere the developing agent to a photo conductor, and a feed roller to supply the developing agent transferred from the developing agent storing part to the developing roller, and the front end of the at least one elastic plate may intermittently contact the upper and lower surfaces of the channel and the feed roller, when the agitating member rotates. 
     The developing unit may further include support parts provided on the shaft to support the side ends of the at least one elastic plate. 
     Foamed members may be respectively inserted into gaps between the agitating member and the side walls of the channel. 
     The foregoing and/or other aspects and utilities of the present general inventive concept may also be achieved by providing an image forming apparatus having a developing unit, the developing unit including a developing agent storing part to store a developing agent, a developing part connected to the developing agent storing part, and an agitating member rotatably provided in a channel between the developing agent storing part and the developing part to transfer the developing agent stored in the developing agent storing part to the developing part, wherein the channel is closed by the agitating member. 
     The agitating member may include a shaft, and at least one film extended in the radial direction of the shaft. 
     The at least one film may be prepared in plural number. 
     At least two films among the plural films may be attached to the shaft such that the at least two films can be extended in the opposite directions with respect to the shaft. 
     When the channel is closed, the front end of the at least one film may contact the inner surface of the channel. 
     The image forming apparatus may further include support parts provided on the shaft to support the side ends of the at least one film. 
     At least one protrusion guiding the attachment position of the at least one film may be provided on the shaft. 
     The developing unit may include a developing roller to adhere the developing agent to a photo conductor, and a feed roller to supply the developing agent transferred from the developing agent storing part to the developing roller, and the surface of the feed roller may be cleaned by the at least one film, when the developing unit is operated. 
     Plate-shaped sealing members may be provided between the agitating member and the side walls of the channel. 
     The foregoing and/or other aspects and utilities of the present general inventive concept may also be achieved by providing an image forming apparatus having a developing unit, the developing unit including a developing agent storing part to store a developing agent, a developing part connected to the developing agent storing part, and an agitating member rotatably provided in a channel between the developing agent storing part and the developing part to transfer the developing agent stored in the developing agent storing part to the developing part, wherein the agitating member includes a shaft and at least one elastic plate attached to the shaft, and the channel is closed by the shaft and the at least one elastic plate having a tangential direction with the shaft, which is orthogonal to the transfer direction of the developing agent. 
     The foregoing and/or other aspects and utilities of the present general inventive concept may also be achieved by providing an image forming apparatus including a developing agent storing part to store a developing agent, a developing part connected to the developing agent storing part, and an agitating member rotatably provided in a channel between the developing agent storing part and the developing part to transfer the developing agent stored in the developing agent storing part to the developing part, wherein the agitating member includes a shaft and at least one elastic plate attached to the shaft, and the channel is opened or closed by the at least one elastic plate according to the rotation of the agitating member, the length of the at least one elastic plate is larger than the height of the channel, and the at least one elastic plate is a completely solid type. 
     The foregoing and/or other aspects and utilities of the present general inventive concept may also be achieved by providing an image forming apparatus, including a developing agent storing part to store a developing agent, a developing part to transfer the developing agent onto a printing medium, and an agitating member rotatably disposed to block a channel from the developing agent storing part to the developing part in a first mode and to open the channel from the developing agent storing part to the developing part in a second mode. 
     The image forming apparatus may further include at least one elastic film member to prevent the developing agent from entering the developing part when the shaft is in a first position. 
     The developing agent may enter the developing part when the shaft is in a second position. 
     The image forming apparatus may further include a sensor to sense a rotation angle of the shaft. 
     The image forming apparatus may further include a control unit to allow a user to control a rotation of the shaft. 
     A developing unit usable with an image forming apparatus, including a developing agent storing part to store a developing agent, and an agitating member disposed in the developing agent storing part to transfer a first portion to a second portion thereof through a channel and to block the channel to prevent the developing agent from being transferred from the first portion to the second portion thereof. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects and utilities of the present general inventive concept 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 cross-sectional view of an image forming apparatus in accordance with an embodiment of the present general inventive concept; 
         FIG. 2  is a partially exploded perspective view of a developing unit in accordance with an embodiment of the present general inventive concept; 
         FIG. 3  is an enlarged cross-sectional view of the portion ‘A’ of  FIG. 1 , illustrating the developing unit in an unused state; 
         FIG. 4  is another enlarged cross-sectional view of the portion ‘A’ of  FIG. 1 , illustrating the developing unit in a used state; 
         FIG. 5  is an enlarged cross-sectional view of the portion ‘A’ of another embodiment of the present general inventive concept, illustrating a sensor; and 
         FIG. 6  is a cross-sectional view of an image forming apparatus in accordance with another embodiment of the present general inventive concept. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the embodiments of the present general inventive concept, an example of which is illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. The embodiments are described below to explain the present general inventive concept by referring to the 
       FIG. 1  is a cross-sectional view of an image forming apparatus in accordance with an embodiment of the present general inventive concept, and  FIG. 2  is a partially exploded perspective view of a developing unit in accordance with an embodiment of the present general inventive concept. 
     As illustrated in  FIG. 1 , an image forming apparatus  1  includes a main body  10 , a printing media feed device  20 , a light scanning device  30 , a photo conductor  40 , a developing device  100 , a transfer device  50 , a fixing device  60 , and a printing media discharge device  70 . 
     The main body  10  forms an external appearance of the image forming apparatus  1 , and supports various components installed therein. A main body cover  11  is rotatably installed at one side of the main body  10 . The main body cover  11  opens and closes a portion of the main body  10 . A user can access the inside of the main body  10  through the main body cover  11 , and thus may attach and detach various components, including developing units  100 K,  100 C,  100 M, and  100 Y, to and from the main body  10 . 
     The printing media feed device  20  includes a cassette  21  to store printing media (S), a pick-up roller  22  to pick up the printing media (S) stored in the cassette  21  one by one, and transfer rollers  23  to transfer the picked-up printing media (S) to the transfer device  50 . 
     The light scanning device  30  irradiates light corresponding to image data onto the photo conductor  40 , and thus forms an electrostatic latent image on the surface of the photo conductor  40 . 
     The photo conductor  40  is rotatably installed in a photo conductor housing  41  detachably mounted in the main body  10 . An electric charging roller  42  is installed in the photo conductor housing  41 . The electric charging roller  42  charges the photo conductor  40  with a designated electric potential before the light scanning device  30  irradiates light onto the photo conductor  40 . 
     The developing device  100  supplies developing agents to the photo conductor  40 , on which the electrostatic latent image is formed, and thus forms a visible image. The image forming apparatus  1  of the embodiment of  FIG. 1  is a color image forming apparatus. Thus, the developing device  100  includes four developing units  100 K,  100 C,  100 M, and  100 Y, which respectively contain developing agents having different colors, i.e., black, cyan, magenta, and yellow, respectively. Hereinafter, a structure of the developing unit  100 K storing a black developing agent will be described. The structure of the developing unit  100 K, which will be described later, may be applied to other developing units  100 C,  100 M, and  100 Y. In  FIG. 1 , reference numerals  110 ,  120 ,  130 , and  140  represent components of the developing unit  100 K, and may be applied to components of other developing units  100 C,  100 M, and  100 Y, respectively. 
     As illustrated in  FIGS. 1 and 2 , the developing unit  100 K includes a developing unit housing  110 , a developing agent storing part  120 , a developing part  130 , and an agitating member  140 . 
     The developing unit housing  110  forms the external appearance of the developing unit  100 K, and supports various components installed therein. Handles  111  are rotatably installed at both sides of a rear end of the developing unit housing  110  respectively, such that a user can easily hold the developing unit  100 K when the developing unit  100 K is attached to and detached from the image forming apparatus  1 . 
     The developing agent storing part  120  stores the developing agent. 
     The developing part  130  includes a feed roller  131  and a developing roller  132 . The developing part  130  receives the developing agent supplied from the developing agent storing part  120  and adheres the developing agent to the surface of the photo conductor  40 , and thus forms a visible image thereon. Specifically, the developing agent stored in the developing agent storing part  120  is transferred to the feed roller  131  by the agitating member  140 , which will be described later, and is supplied to the developing roller  132  by the feed roller  131 . Then, the developing roller  132 , to which a developing bias power supply is applied, adheres the developing agent on its surface to the surface of the photo conductor  40 , on which the electrostatic latent image is formed, thus forming a visible image on the surface of the photo conductor  40 . Here, a thickness of the developing agent adhered to the surface of the developing roller  132  by the feed roller  131  is regulated by a regulating member  112  provided at one side of an upper surface of the developing unit housing  110 . 
     The agitating member  140  is rotatably provided in a transfer channel  113  connecting the developing agent storing part  120  and the developing part  130 , and agitates the developing agent, stored in the developing agent storing part  120 , so as not to coagulate the developing agent, and transfers the developing agent to the feed roller  131  simultaneously. 
     For this reason, the agitating member  140  includes a shaft  141  rotatably supported by both side walls  114  and  115  of the transfer channel  113 , and films  142  attached to the shaft  141 . The agitating member  140  is rotated by the driving power transmitted from a motor (not illustrated). In the embodiment of  FIG. 2 , the films  142  are thin film plates having a designated elastic force, which is made of a material such as polyethylene terephthalate (PET), urethane, or silicon. Further, although the embodiment of  FIG. 2  illustrates two films  142  attached to the shaft  141 , one film  142  may be attached to the shaft  141  such that the film  142  can be extended in the radial direction of the shaft  141 , or at least three films  142  may be attached to the shaft  141  in a radial manner. 
       FIGS. 3 and 4  are enlarged cross-sectional views of a portion ‘A’ of  FIG. 1 , and  FIG. 3  illustrates the developing unit in an unused state and  FIG. 4  illustrates the developing unit in a used state. 
     As illustrated in  FIG. 3 , the agitating member  140  of the present general inventive concept serves to close the transfer channel  113  to seal the developing agent storing part  120  as well as to agitate the developing agent stored in the developing agent storing part  120 . 
     Specifically, a length of the films  142  protruding from the shaft  141  with respect to a length of the film  142  may be larger than a height of the transfer channel  113 , and when a tangential direction (c) between the shaft  141  and the films  142  and the transfer direction (f) of the developing agent meet at approximately right angles to each other, front ends  142   a  of the films  142  may contact the inner surface of the transfer channel  113 , and both side ends  142   b  of the films  142  and both side surfaces  141   a  of the shaft  141  are closely adhered to both side walls  114  and  115  of the transfer channel  113 . Thus, the transfer channel  113  is closed such that opposite spaces inside the developing unit housing  110  may be isolated by the agitating member  140 , and the developing agent is prevented from transferring from one opposite space to the other opposite space, and the developing agent storing part  120  is sealed. 
     The height of an upper side of the transfer channel  113  may be different from the height of a lower side of the transfer channel  113 . However, the length of the film  142  is enough to block each of the heights of the upper and lower sides of the transfer channel  113 . 
     As illustrated in  FIG. 3 , at least one end of the films  142  is bent when contacting the developing unit housing  110 . That is, the at least one end of the films  142  is in a bending state to show a first distance (height) h 1  between the both ends of the films  142  since a distance between opposite sides of the developing unit housing  100  is narrower than the first distance (height) H 1 . The first distance h 1  becomes a second distance h 2  as illustrated in  FIG. 4 , when one of the ends of the films  142  contacting a portion of the feed roller  131 . That is, the ends of the films  142  have the second distance h 2  when at least one of the ends of the films  142  does not contact the opposite sides of the developing unit housing  110 . 
     The side of the developing unit housing  110  may have a portion to guide the ends of films  142  such that the first distance h 1  is changed to the second distance h 2 . That is, a distance from a rotational center of the agitating member  141  to the side of the developing unit housing  110  may vary or increased according to a rotational direction of the agitating member such that the first distance h 1  can be gradually changed to the second distance h 2 . 
     Accordingly, the developing unit look of the present general inventive concept can seal the developing agent storing part using the existing agitating member without adding any separate component. Further, as illustrated in  FIGS. 5 and 6 , the developing unit look of the present general inventive concept may further include a sensor  200  to sense the rotating angle of the agitating member and a control unit  300  to control the rotating angle of the agitating member, such that when the developing unit  100 K is not used for a long time or a user inputs instructions to close the developing agent storing part  120 , the developing agent storing part  120  can be automatically sealed. Of course, in the case that the developing unit  100 K does not have a separate sensor  200  or control unit  300 , the user can manually rotate the shaft  141  of the agitating member when it is expected that the developing unit will not be used for a long time, and thus seal the developing agent storing part. 
     As illustrated in  FIG. 2 , the developing unit  100 K of the present general inventive concept further includes plate-shaped sealing members  150 , which are inserted between both side walls  114  and  115  of the transfer channel  113  and the agitating member  140  so as to increase airtight force. The sealing members  150  may be made of a soft material having a high restoring force so as to minimize the interference with the films  142  when the agitating member  140  is rotated and to obtain a sufficient airtight force when the agitating member  140  is stopped. For example, the sealing members  150  may be made of a sponge-type soft material including polyurethane, poron, or ethylene propylene diene monomer (EPDM), or a rubber-type soft material including epoxy, urethane, or silicon. 
     The developing unit  100 K of the present general inventive concept further includes support parts  143  respectively provided at both sides of the shaft  141 . The support parts  143  prevent both side ends  142   b  of the films  142  from being excessively folded in a direction opposite to the rotating direction of the shaft  141  due to the friction with both side walls  114  and  115  of the transfer channel  113  or the sealing members  150 , and vary an elastic force of central portions of the films  142  and the elastic force of the portions of the films  142 , at which the support parts  143  are installed. Particularly, as the elastic force of the portions of the films  142 , at which the support parts  143  are installed, increases, the developing agent feeding force at both sides of the films  142  is strengthened, thereby overcoming a difficulty in supplying the developing agent to both sides of the agitating member  140 . 
     Further, as illustrated in  FIG. 3 , one protrusion or a plurality of protrusions may be installed on the shaft  141 . The protrusion serves as a reference plane to attach the film  142  to the shaft  141 . Further, as the developing agent flows into distal ends of the films  142  according to the rotation of the agitating member  140 , the protrusions serve to prevent the films  142  from being separated from the shaft  141 . 
     As illustrated in  FIG. 4 , as the agitating member  140  rotates, the front ends  142   a  of the films  142  of the agitating member  140  intermittently contact the feed roller  131  as well as intermittently contact upper and lower surfaces of the transfer channel  113 . Thereby, the surface of the feed roller  131  is struck by or rubbed with the films  142 , thus being cleaned. 
     Generally, a sponge-type or fur-type cylindrical roller is used as the feed roller  131 . In the embodiment of  FIG. 4 , the fur-type feed roller  131  is used, and effectively removes a portion of the developing agent, which is not supplied from the feed roller  131  to the developing roller  132  and is coagulated or caught between fur. 
     In the embodiment of  FIG. 4 , the shaft  141  has an approximately rectangular cross-section, and the two films  142  are attached to the shaft  141  such that the two films  142  are respectively extended in the opposite directions with respect to the shaft  141 . Of course, the cross section of the shaft  141  may have various shapes, and the number of the films  142  attached to the surface of the shaft  141  is not limited. However, the films  142  may be installed symmetrically, and may be attached to the shaft  141  such that tangential directions of the films  142  with the shaft  141  are parallel with each other and are respectively extended in the opposite directions with respect to the shaft  141 . 
     Further, in order to effectively block of the flow of the developing agent in the sealed state of the developing agent storing part  120 , a plate-shaped thin film, which is a completely solid type without holes or spaces formed therein, may be used as the films  142 . 
     Although this embodiment defines the transfer channel  113  divided from the developing agent storing part  120  and the developing part  130 , it may be appreciated that the developing part  130  includes the transfer channel  113 . 
     As illustrated in  FIG. 1 , the transfer device  50  includes an interim transfer belt  51 , a first transfer roller  52 , and a second transfer roller  53 . 
     The interim transfer belt  51  is supported by support rollers  54  and  55 , and travels at the similar velocity to the linear velocity of the photo conductor  40 . 
     The first transfer roller  52  is opposite to the photo conductor  40  under the condition that the interim transfer belt  51  is interposed between the first transfer roller  52  and the photo conductor  40 , and causes the visible image formed on the photo conductor  40  to be transferred to the interim transfer belt  51 . 
     The second transfer roller  53  is opposite to the support roller  55  when the interim transfer belt  51  is interposed between the second transfer roller  53  and the support roller  55 . The second transfer roller  53  is separated from the interim transfer belt  51  while the image is transferred from the photo conductor  40  to the interim transfer belt  51 , and contacts the interim transfer belt  51  with a predetermined pressure when the image on the photo conductor  40  is completely transferred to the interim transfer belt  51 . When the second transfer roller  53  contacts the interim transfer belt  51 , the image on the interim transfer belt  51  is transferred to a printing medium. 
     The fixing device  60  includes a heating roller  61  having a heat source, and a pressing roller  62  installed opposite to the heating roller  61 . When the printing medium passes through a gap between the heating roller  61  and the pressing roller  62 , the image is fixed to the printing medium by heat transmitted from the heating roller  61  and pressure applied between the heating roller  61  and the pressing roller  62 . 
     The printing media discharge device  70  includes an exit roller  71  and an exit backup roller  72 , and discharges the printing medium passed through the fixing device  60  to the outside of the main body  10 . 
     Hereinafter, the operation of the above image forming apparatus  1  will be described in brief. 
     When a printing operation is started, the surface of the photo conductor  40  is uniformly charged by the electric charging roller  42 . The light scanning device  30  irradiates light of any one color, for example, light corresponding to yellow image data, onto the surface of the photo conductor  40 , and thus an electrostatic latent image corresponding to a yellow image is formed on the photo conductor  40 . 
     The agitating member  140  of the yellow developing unit  100 Y rotates, and thus agitates the developing agent stored in the developing agent storing part  120  and transfers the developing agent to the feed roller  131  of the developing part  130  simultaneously. Then, the transferred developing agent is supplied to the developing roller  132  by the feed roller  131 . Accordingly, the front ends  142   a  of the films  142  of the agitating member  140  strike or rub against the surface of the feed roller  131 , and thus sweep away off the developing agent, which is not adhered to the photo conductor  40  and remains on the surface of the feed roller  131 . 
     Thereafter, a developing bias power supply is applied to the developing roller  132 . Thereby, a yellow developing agent is adhered to the electrostatic latent image, and forms a yellow visible image. This visible image is transferred to the interim transfer belt  51  by the first transfer roller  52 . 
     When the transfer of the yellow color of the amount of one page has been completed, the light scanning device  30  irradiates light of another color, for example, light corresponding to magenta image data, onto the surface of the photo conductor  40 , and thus an electrostatic latent image corresponding to a magenta image is formed on the photo conductor  40 . The magenta developing unit  100 M supplies a magenta developing agent to the electrostatic latent image, and forms a magenta visible image. The magenta visible image formed on the photo conductor  40  is transferred to the interim transfer belt  51  by the first transfer roller  52 . Here, the magenta visible image is overlapped with the yellow visible image, which was transferred in advance from the developing unit  100 Y. 
     When the cyan developing unit  100 C and the black developing unit  100 K perform the above-described process, a color image, obtained by overlapping the yellow, magenta, cyan, and black images, is completed on the interim transfer belt  51 . The completed color image is transferred to the printing medium passing through a gap between the interim transfer belt  51  and the second transfer roller  53 , and the printing medium passes through the fixing device  60  and is discharged to the outside of the main body  10  via the printing media discharge device  70 . 
     When the printing operation is completed or stopped, the agitating members  140  of the respective developing units  100 K,  100 C,  100 M, and  100 Y return to the state illustrated in  FIG. 3  in order to close the transfer channel  113 . This operation may be automatically carried out by the sensor  200  to sense the rotating angle of the agitating member  140  and the control unit  300  to control the rotating angle of the agitating member  140 , or may be manually carried out by a user. 
     As apparent from the above description, the present general inventive concept provides a developing unit, in which a developing agent storing part is closed by an agitating member without any separate member, so as to improve a productivity of the developing unit as well as allowing the developing unit to have a simple and compact structure, and an image forming apparatus having the same. Of course, the developing unit eliminates an inconvenience of removing a shielding member therefrom before the developing unit is used. 
     Further, in the developing unit of the present general inventive concept, the developing agent storing part can be re-closed even after the developing unit begins to be used. 
     Although embodiments of the present general inventive concept have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the general inventive concept, the scope of which is defined in the claims and their equivalents.