Patent Publication Number: US-9405268-B2

Title: Image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the priority benefit of Korean Patent Application No. 10-2014-0117002, filed on Sep. 3, 2014 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND 
     1. Field 
     Embodiments of the disclosure relate to an image forming apparatus, and more particularly, to an image forming apparatus having an improved structure capable of easily installing a developing unit. 
     2. Description of the Related Art 
     An image forming apparatus generally refers to an apparatus which forms an image on a print medium according to an input signal, and may be a printer, a copy machine, a fax, and an official replicator in which these functions are integrated. 
     An electro-photographic image forming apparatus which is one type of image forming apparatus may include a photoreceptor unit having a photoreceptor therein, a charging unit disposed around the photoreceptor unit to charge the photoreceptor with a predetermined electric potential, a developing unit having a developing roller, and an optical scanning unit. The optical scanning unit serves to radiate light to the photoreceptor charged with the predetermined electric potential by the charging unit, and thus to form an electrostatic latent image on a surface of the photoreceptor, and the developing unit serves to supply a photosensitizer to the photoreceptor on which the electrostatic latent image is formed and thus to form a visible image. 
     In the case of the image forming apparatus having a structure in which the developing roller comes into contact with the photoreceptor so as to supply the photosensitizer, when a printing operation is performed, the developing roller and the photoreceptor should come into contact with each other, and also when the developing unit is replaced, the developing roller and the photoreceptor should be separated from each other to prevent interference between the developing roller and the photoreceptor. 
     However, the developing unit may be replaced while the developing roller and the photoreceptor come into contact with each other, and thus the developing unit or the photoreceptor may be damaged, or the image forming apparatus may be operated while the developing roller and the photoreceptor are separated from each other, and thus a defective image may be formed. 
     SUMMARY 
     Therefore, it is an aspect of the disclosure to provide an image forming apparatus in which a fixing structure of a developing device is improved. 
     Additional aspects of the disclosure 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 disclosure. 
     In accordance with an aspect of the disclosure, an image forming apparatus may include a main body, a developing device formed in a first direction, and including a photoreceptor unit having a photoreceptor, and a developing unit provided adjacent to the photoreceptor and having a developing roller provided to come into contact with or be separated from the photoreceptor, and a pressing assembly provided adjacent to the developing device and configured to restrict a movement of the developing device. The pressing assembly may include a rotating shaft formed to extend in the first direction to be rotatable, and an operating unit provided at an end of the rotating shaft to be rotated along with the rotating shaft and configured to restrict the movement of the developing device in the first direction. 
     The operating unit may be provided to be rotated between a stand-by position and an operating position in which the operating unit is rotated from the stand-by position and supports an end of the developing device to restrict a movement of the developing device in the first direction. 
     The operating unit may include an operating body rotatably provided at an end of the rotating shaft, and a pressing member provided at one side of the operating body to press the developing device. 
     The pressing member may be formed to be more convex than the adjacent operating body. 
     The first direction may include an installing direction in which the photoreceptor unit is installed at the developing device seating part, and a separating direction which is opposite to the installing direction and in which the photoreceptor unit is separated from the developing device seating part, and the pressing member may include a first pressing part in which the operating unit comes into contact with the developing device while moved from the stand-by position to the operating position, and a second pressing part which extends from the first pressing part so as to more protrude in the installing direction than the first pressing part, the operating unit coming in contact with the developing device at the operating position. 
     The first direction may include an installing direction in which the photoreceptor unit is installed at the developing device seating part, and a separating direction which is opposite to the installing direction and in which the photoreceptor unit is separated from the developing device seating part, and the photoreceptor unit may include a to-be-pressed surface formed to be inclined, such that the photoreceptor unit is pressed in the installing direction by the operating unit while the operating unit is moved from the stand-by position to the operating position. 
     A movement of the rotating shaft in the first direction may be restricted by the developing device seating part. 
     The first direction may include an installing direction in which the photoreceptor unit is installed at the developing device seating part, and a separating direction which is opposite to the installing direction and in which the photoreceptor unit is separated from the developing device seating part, and the operating unit may further include an operation elastic part configured to press the operating body in the installing direction. 
     The operation elastic part may include a fastening member provided at one end of the rotating shaft to have a component vertical to a rotating axis of the rotating shaft, and an installation elastic member of which one end is supported by the fastening member, and the other end presses the operating unit in the installing direction. 
     The operating unit may be pressed in the installing direction by the installation elastic member, and a movement of the operating unit in the separating direction may be restricted by the fastening member. 
     The operating unit may further include an installing space formed at an inner side of the operating body so that the operation elastic part is installed therein, and the installing space may include a first installing space in which the installation elastic member is installed to extend or be compressed, and a second installing space which is formed using a movement restricting surface configured to restrict a movement of the operating unit in the separating direction as a boundary line and in which the fastening member is installed. 
     The pressing assembly may further include at least one pressing unit configured to press the developing unit so that the developing roller and the photoreceptor come into close contact with each other, and provided to be interlocked with the operating unit. 
     The operating unit may press the photoreceptor unit in the first direction while moved from the stand-by position to the operating position, and the at least one pressing unit may be interlocked with the movement of the operating unit from the stand-by position to the operating position, and presses the developing unit in a second direction vertical to the first direction. 
     The at least one pressing unit may include a link unit configured to convert rotating motion of the rotating shaft due to rotation of the operating unit into linear reciprocating motion, and a pressing part connected with the link unit so as to press the developing device. 
     The link unit may include a first link member rotated along with the rotating shaft, and a second link member of which one end is connected with an end of the first link and the other end linearly reciprocates. 
     The at least one pressing unit may include a plurality of pressing units disposed at the rotating shaft to be spaced apart from each other. 
     The link unit may include a pressing elastic member provided at the second link member to generate a pressing force of the pressing unit. 
     The second link member may include a stopper insertion part of which at least a part is inserted into the pressing part depending on a position of the pressing unit, and a variable seating part which is disposed adjacent to the stopper insertion part, and in which the pressing elastic member is seated thereon, and with which a length of the pressing elastic member is interlocked and varied so that the pressing force of the pressing elastic member is varied. 
     One end of the pressing elastic member may be supported by an end of the second link member, and the other end thereof may be supported by the pressing part. 
     The pressing elastic member may be compressed to a maximally compressed length ML, when the operating unit is disposed between the operating position and the stand-by position. 
     In accordance with an aspect of the disclosure, an image forming apparatus may include a main body, a developing device including a photoreceptor unit having a photoreceptor, and a developing unit provided adjacent to the photoreceptor and having a developing roller provided to come into contact with or be separated from the photoreceptor, and a pressing assembly provided adjacent to the developing device, wherein the pressing assembly may include a pressing unit configured to press the developing unit so that the developing roller and the photoreceptor come into contact with each other, and an operating unit provided to be moved between an operating position in which a pressing force is generated from the pressing unit and a stand-by position in which the pressing force is released, and also to restrict a movement of the developing device. 
     A first direction may be a lengthwise direction of the developing device, and the operating unit may press the developing device in the first direction, and the pressing unit may press the developing unit in a second direction vertical to the first direction. 
     A pressing operation of the operating unit in the first direction with respect to the developing device, and a pressing operation of the pressing unit in the second direction with respect to the developing unit may be performed simultaneously. 
     The operating unit may include an operating body rotatably provided at an end of a rotating shaft, and a pressing member provided at one side of the operating body to press the developing device. 
     The pressing member may be formed to be more convex than the adjacent operating body. 
     The first direction may include an installing direction in which the photoreceptor unit is installed at the developing device seating part, and a separating direction which is opposite to the installing direction and in which the photoreceptor unit is separated from the developing device seating part, and the pressing member may include a first pressing part in which the operating unit comes into contact with the developing device while moved from the stand-by position to the operating position, and a second pressing part which extends from the first pressing part so as to more protrude in the installing direction than the first pressing part, the operating unit coming in contact with the developing device at the operating position. 
     The first direction may include an installing direction in which the photoreceptor unit is installed at the developing device seating part, and a separating direction which is opposite to the installing direction and in which the photoreceptor unit is separated from the developing device seating part, and the photoreceptor unit may include a to-be-pressed surface formed to be inclined, such that the photoreceptor unit is pressed in the installing direction by the operating unit while the operating unit is moved from the stand-by position to the operating position. 
     The pressing assembly may further include a rotating shaft configured to extend in the first direction so as to transmit an operation of the operating unit to the pressing unit. 
     A movement of the rotating shaft in the first direction may be restricted by the developing device seating part. 
     The first direction may include an installing direction in which the photoreceptor unit is installed at the developing device seating part, and a separating direction which is opposite to the installing direction and in which the photoreceptor unit is separated from the developing device seating part, and the operation unit may further include an operating elastic part configured to press the operating body in the installing direction. 
     The operation elastic part may include a fastening member provided at one end of the rotating shaft to have a component vertical to a rotating axis of the rotating shaft, and an installation elastic member of which one end is supported by the fastening member, and the other end presses the operating unit in the installing direction. 
     The operating unit may be pressed in the installing direction by the installation elastic member, and a movement of the operating unit in the separating direction may be restricted by the fastening member. 
     The operating unit may further include an installing space formed at an inner side of the operating body so that the operation elastic part is installed therein, and the installing space may include a first installing space in which the installation elastic member is installed to extend or be compressed, and a second installing space which is formed using a movement restricting surface configured to restrict a movement of the operating unit in the separating direction as a boundary line and in which the fastening member is installed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects of the disclosure will become apparent and more readily appreciated from the following description of embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  is a cross-sectional view of an image forming apparatus in accordance with an embodiment of the disclosure; 
         FIG. 2  is a view illustrating a developing device and a cover unit of the image forming apparatus in accordance with an embodiment of the disclosure; 
         FIG. 3  is a view illustrating a coupling of the developing device and the cover unit of the image forming apparatus in accordance with an embodiment of the disclosure; 
         FIGS. 4A and 4B  are views respectively illustrating an operation of a pressing assembly and a developing unit in accordance with an embodiment of the disclosure; 
         FIGS. 5A, 5B, and 5C  are views illustrating the operation of the pressing assembly in accordance with an embodiment of the disclosure; 
         FIGS. 6A and 6B  are views illustrating the pressing assembly in accordance with an embodiment of the disclosure; 
         FIGS. 7A, 7B, and 7C  are cross-sectional views of a pressing unit depending on the operation of the pressing assembly in accordance with an embodiment of the disclosure; 
         FIG. 8A  is a view illustrating the cover unit in accordance with an embodiment of the disclosure; 
         FIG. 8B  is an enlarged view of a portion A of  FIG. 8A ; 
         FIG. 9  is a cross-sectional view of an image forming apparatus in accordance with an embodiment of the disclosure; 
         FIG. 10  is a view illustrating an arrangement of a developing device and an optical scanning unit of the image forming apparatus in accordance with an embodiment of the disclosure; 
         FIGS. 11A and 11B  are views illustrating an operation of a pressing assembly and the developing device in accordance with an embodiment of the disclosure; 
         FIGS. 12A and 12B  are perspective views illustrating the operation of the pressing assembly in accordance with an embodiment of the disclosure; 
         FIGS. 13A and 13B  are cross-sectional views illustrating a pressing unit depending on the operation of the pressing assembly in accordance with an embodiment of the disclosure; 
         FIGS. 14A and 14B  are cross-sectional views illustrating a shutter unit and the developing device depending on the operation of the pressing assembly in accordance with an embodiment of the disclosure; 
         FIG. 15  is a perspective view illustrating an arrangement of an operating unit in accordance with an embodiment of the disclosure; 
         FIG. 16  is a side view illustrating a pressing state of the operating unit in accordance with an embodiment of the disclosure; 
         FIG. 17  is an exploded perspective view of the operating unit in the pressing assembly in accordance with an embodiment of the disclosure; 
         FIG. 18  is a cross-sectional perspective view illustrating the operating unit in accordance with an embodiment of the disclosure; 
         FIG. 19  is a view illustrating an arrangement of a developing device and a cover unit of an image forming apparatus in accordance with an embodiment of the disclosure; 
         FIG. 20  is a front view illustrating a pressing unit in accordance with an embodiment of the disclosure; 
         FIG. 21  is a perspective view illustrating the pressing unit and a shutter unit in accordance with an embodiment of the disclosure; 
         FIGS. 22A and 22B  are views illustrating an interlocking operation of the pressing unit, the shutter unit and the cover unit in accordance with an embodiment of the disclosure; 
         FIG. 23  is a view illustrating a developing device and a cover unit in accordance with an embodiment of the disclosure; 
         FIGS. 24A and 24B  are views illustrating an operation of a pressing assembly and the developing device in accordance with an embodiment of the disclosure; 
         FIGS. 25A and 25B  are cross-sectional views illustrating a pressing unit depending on the operation of the pressing assembly in accordance with an embodiment of the disclosure; 
         FIG. 26  is an exploded perspective view of the pressing assembly in accordance with an embodiment of the disclosure; and 
         FIGS. 27A and 27B  are views illustrating the developing device of the cover unit depending on the operation of the pressing assembly in accordance with an embodiment of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to embodiments of the disclosure, examples of which are illustrated in the accompanying drawings. Embodiments are described below to explain the disclosure by referring to the figures. 
     An image forming apparatus in accordance with an embodiment of the disclosure will be described. 
       FIG. 1  is a cross-sectional view of the image forming apparatus in accordance with an embodiment of the disclosure. 
     As illustrated in  FIG. 1 , the image forming apparatus  1  may include a main body  10 , a print medium supplying device  20  which stores and feeds a print medium S, a developing device  30  which forms an image on the print medium S supplied through the print medium supplying device  20 , a toner device  40  which supplies toner to the developing device  30 , an optical scanning device  50  which forms an electrostatic latent image on a photoreceptor  32  of the developing device  30 , a fixing device  60  which fixes a toner image transferred on the print medium S to the print medium S, and a discharging device  70  which discharges the print medium S on which an image forming is completed. 
     The print medium supplying device  20  which stores and feeds the print medium S is provided at a lower portion of the main body  10  to supply the print medium S toward the developing device  30 . 
     The print medium supplying device  20  may include a print medium cassette  21  which is coupled to the main body  10  to be opened and closed and thus to store the print medium S, and a transporting member  25  which picks up each sheet of the print medium S stored in the print medium cassette  21  and transports it toward the developing device  30 . 
     One end of the print medium cassette  21  may be rotatably coupled so as to guide the print medium S stored therein toward the transporting member  25 , and the other end thereof may have a knock-up plate  23  supported by a pressing spring  22 . 
     The transporting member  25  may include a pick-up roller  27  which picks up each sheet of the print medium S loaded on the knock-up plate  23 , and a feed roller  28  which transports the print medium S picked up by the pick-up roller  27  toward the developing device  30 . 
     The developing device  30  may include a housing  31  which defines an exterior thereof, the photoreceptor  32  which is rotatably coupled in the housing  31  to form the electrostatic latent image, stirring screws  33   a  and  33   b  which stir the toner supplied from the toner device  40 , a developing roller  34  which supplies the toner stirred by the stirring screws  33   a  and  33   b  to the photoreceptor  32 , and a charging member  35  which charges the photoreceptor  32 . 
     The toner supplied from the toner device  40  is introduced into the housing  31 , and then stirred and transported to one side of the housing  31  by the stirring screws  33   a  and  33   b . The stirred and transported toner may be supplied to the photoreceptor  32  by the developing roller  34  so as to form the visible image. 
     The photoreceptor  32  comes into contact with a transfer roller  14  so as to form a transfer nip N 1 , such that the toner supplied to the photoreceptor  32  and forming the visible image is transferred on the print medium S. The transfer roller  14  may be rotatably disposed in the main body  10 . 
     The toner device  40  may be coupled with the developing device  30  so as to receive and store the toner which forms an image on the print medium S and also to supply the toner to the developing device  30  when the image forming operation is performed. 
     The optical scanning device  50  radiates light including image information onto the photoreceptor  32  so as to form the electrostatic latent image on the photoreceptor  32 . 
     The fixing device  60  may include a housing  62 , a heating member  64 , and a pressing member  66  which are rotatably disposed in the housing  62 . 
     The print medium S on which the toner image is transferred passes between the heating member  64  and the pressing member  66 . At this time, the toner image is fixed to the print medium S by heat and pressure. 
     The heating member  64  is rotated while engaged with the pressing member  66 , forms a fixing nip N 2  with the pressing member  66 , and heated by a heating source  68  so as to transfer heat to the print medium S passing through the fixing nip N 2 . The heating member  64  may be a heating roller which receives power from a driving source (not shown) so as to be rotated. The heating source  68  which applies the heat to the print medium S on which the toner is transferred may be disposed at an inner side of the heating member  64 . A halogen lamp may be used as the heating source  68 . However, an electro-thermal wire, an induction heater, or the like may be also used as the heating source  68 . 
     The pressing member  66  may be disposed to come into contact with an outer circumferential surface of the heating member  64 , such that the fixing nip N 2  is formed between the pressing member  66  and the heating member  64 . The heating member  64  may be a pressing roller which receives power from a driving source (not shown) to be rotated. 
     The discharging device  70  may include a first discharging roller  71  and a second discharging roller  72  which are engaged with each other so as to discharge the print medium S passing through the fixing device  60  to an outside of the main body  10 . 
       FIG. 2  is a view illustrating the developing device and a cover unit of the image forming apparatus in accordance with an embodiment of the disclosure, and  FIG. 3  is a view illustrating a coupling of the developing device and the cover unit of the image forming apparatus in accordance with an embodiment of the disclosure. 
     The developing device  30  may be provided to be seated on a developing device seating part  5 . A waste toner storing unit in which waste toner generated from the developing device  30  is stored may be provided at one side of the developing device  30 . The toner used in the developing device  30  may be moved to the waste toner storing unit and then stored in the waste toner storing unit. In an embodiment of the disclosure, the waste toner storing unit may be referred to as a cover unit  170 . 
     A pressing assembly  100  (see  FIGS. 6A to 7C ) may be provided at one side of the developing device  30  so that a developing unit  30   a  and a photoreceptor unit  30   b  come into close contact with each other. Specifically, the developing roller  34  of the developing unit  30   a  and the photoreceptor  32  of the photoreceptor unit  30   b  may be provided to come into close contact with or separated from each other by an operation of the pressing assembly  100 . 
     A guide rib  174  which guides the operation of the pressing assembly  100  may be provided at the cover unit  170 . 
     The relationship between the pressing assembly  100  and the guide rib  174  and the structures thereof will be described below. 
       FIGS. 4A and 4B  are views respectively illustrating the operation of the pressing assembly and the developing unit in accordance with an embodiment of the disclosure,  FIGS. 5A, 5B, and 5C  are views illustrating the operation of the pressing assembly in accordance with an embodiment of the disclosure,  FIGS. 6A and 6B  are views illustrating the pressing assembly in accordance with an embodiment of the disclosure, and  FIGS. 7A, 7B, and 7C  are cross-sectional views of the pressing unit depending on the operation of the pressing assembly in accordance with an embodiment of the disclosure. 
     The pressing assembly  100  is disposed adjacent to the developing device  30 , such that the developing unit  30   a  and the photoreceptor unit  30   b  come into close contact with or are separated from each other. Specifically, the pressing assembly  100  is provided so that the developing roller  34  of the developing unit  30   a  and the photoreceptor  32  of the photoreceptor unit  30   b  come into close contact with or are separated from each other. An arrangement of the pressing assembly  100  is not limited. However, in the embodiment of the disclosure, the pressing assembly  100  is disposed at the developing device seating part  5 . 
     The pressing assembly  100  may include a rotating shaft  110 , a pressing unit  120 , and an operating unit  150 . 
     The rotating shaft  110  may be rotatably provided so that an operation of the operating unit  150  is transmitted to the pressing unit  120 . Assuming that a lengthwise direction of the developing device  30 , the developing unit  30   a , and the photoreceptor unit  30   b  is a first direction W 1 , the rotating shaft  110  may be formed to be elongated in the first direction W 1 . The first direction W 1  may be defined as a direction vertical or perpendicular (substantially vertical or perpendicular) to a moving direction of the print medium. The rotating shaft  110  may serve as a rotating center of the operating unit  150  to be described below. 
     The rotating shaft  110  may be disposed in the first direction W 1 , and may be provided so that a movement thereof in the first direction W 1  is restricted. The rotating shaft  110  may be provided to be rotatable about a rotating axis. At least one shaft stopper  111  may be provided at an outer circumferential surface of the rotating shaft  110  so that the movement of the rotating shaft  110  in the first direction W 1  is restricted. 
     The pressing unit  120  is provided so that the developing roller  34  and the photoreceptor  32  come into close contact with each other. Specifically, the pressing unit  120  is provided so as to press the developing unit  30   a , such that the developing roller  34  and the photoreceptor  32  come into close contact with or are separated from each other. The pressing unit  120  may be disposed on the rotating shaft  110 , and may be provided to receive the operation of the operating unit  150  through the rotating shaft  110  and thus to be operated. 
     The pressing unit  120  may be provided to be interlocked with the operating unit  150 . At least one pressing unit  120  may be provided. By such a structure, at least one pressing unit  120  may be provided to be interlocked with the operating unit  150 . In the case in which a plurality of pressing units  120  are provided, the plurality of pressing units  120  may be disposed on the rotating shaft  110  to be spaced apart from each other. As an example, the plurality of pressing units  120  may be disposed on the rotating shaft  110  to be spaced apart at regular intervals from each other, such that the same pressing force is distributed in the first direction W 1 , and thus the developing unit  30   a  is pressed by an uniform pressing force, regardless of a position in a lengthwise direction thereof. 
     The pressing unit  120  may be provided to be moved between a pressing position P 1  (see, e.g.,  FIG. 4A  and  FIG. 7A ) in which the developing roller  34  and the photoreceptor  32  come into contact with each other, and a releasing position P 2  (see, e.g.,  FIG. 4B  and  FIG. 7B ) which is moved back from the pressing position P 1  so that the developing roller  34  and the photoreceptor  32  are separated from each other. Specifically, when the pressing unit  120  is located at the pressing position P 1 , the developing unit  30   a  is pressed by the pressing unit  120 , and thus the developing roller  34  and the photoreceptor  32  come into contact with each other. Also, when the pressing unit  120  is located at the releasing position P 2 , the pressing of the pressing unit  120  with respect to the developing unit  30   a  is released, and thus the developing roller  34  and the photoreceptor  32  are separated from each other. 
     The operating unit  150  may be rotatably provided so that the pressing unit  120  is operated by the operation of the operating unit  150 . That is, at least one pressing unit  120  is provided to be interlocked with the operating unit  150 . 
     The operating unit  150  may include an operating body  152  which is connected with the rotating shaft  110  so as to be rotated about the rotating shaft  110 . 
     The operating unit  150  may be provided to be movable between an operating position  01  in which a pressing force is generated from the pressing unit  120  and a stand-by position  02  in which the pressing force is released. 
     When the operating unit  150  is located at the operating position  01 , the pressing unit  120  presses the developing unit, and when the operating unit  150  is located at the stand-by position  02 , the pressing of the pressing unit  120  with respect to the developing unit  30   a  is released. 
     The operating position  01  of the operating unit  150  may include a fixed operating position  01   a  and a movable operating position  01   b.    
     In the fixed operating position  01   a , the pressing unit  120  may be continuously located at the pressing position P 1 , and in the movable operating position  01   b , the pressing unit  120  may be movably located at the pressing position P 1 . In the fixed operating position  01   a , the operating unit  150  may be moved to the movable operating position  01   b  or the stand-by position  02 , only when an external force is applied. In the movable operating position  01   b , the operating unit  150  may be moved to the stand-by position  02  without the external force. 
     When the operating unit  150  is located at the fixed operating position  01   a  and the movable operating position  01   b , the pressing force generated at the pressing unit  120  interlocked with the operating unit  150  may be the same. 
     The pressing unit  120  may include a link unit  130  and a pressing part  140 . 
     The link unit  130  serves to convert rotating motion of the rotating shaft  110  generated by the operation of the operating unit  150  into linear motion. 
     The link unit  130  may include a first link member  131  and a second link member  132 . 
     One end of the first link member  131  is coupled to the rotating shaft  110  so as to be rotated along with rotation of the rotating shaft  110 . Due to such a structure, a rotating center of the first link member  131  is provided to coincide with that of the rotating shaft  110 . 
     At least a part of the link unit  130  is disposed at an inner side of the developing device seating part  5  so that rotation of the first link member  131  is partly limited by an inner wall of the developing device seating part  5 . This will be described below in detail. 
     One end of the second link member  132  is connected with an end of the first link member  131 , and the other end thereof is provided to linearly reciprocate. 
     The pressing part  140  is provided at the other end of the second link member  132  so as to reciprocate depending on the linear reciprocating motion of the other end of the second link member  132 . 
     Rotation of the operating unit  150  is transmitted to the first link member  131  by the rotating shaft  110 , and the rotation of the first link member  131  is converted into the linear reciprocating motion of the other end of the second link member  132 . The pressing part  140  presses the developing unit  30   a , while reciprocating linearly through the motion of the other end of the second link member  132 , and thus the developing roller  34  and the photoreceptor  32  may come into contact with each other. 
     The link unit  130  may include a pressing elastic member  134 . 
     The pressing elastic member  134  may be provided to generate an elastic force depending on the motion of the pressing unit  120 . That is, the pressing elastic member  134  may be provided to extend or be compressed depending on the motion of the pressing unit  120 , and thus to provide the elastic force to the pressing unit  120 . 
     The pressing elastic member  134  may be disposed to have a component in a direction opposite to a rotating direction of the rotating shaft  110 . That is, the pressing elastic member  134  may be provided to apply an elastic force that has a component of direction opposite to a moving direction of one end of the first link member  131  when the first link member  131  is rotated by the rotation of the rotating shaft  110 . 
     The pressing part  140  may include a pressing body  142  and a pressing movement rail  146 . 
     A pressing surface  142   a  may be provided at a front portion of the pressing body  142 . The pressing surface  142   a  may be provided to come into direct contact with the developing unit  30   a  and thus to press the developing unit  30   a.    
     The pressing body  142  may be provided at an end of the second link member  132  so as to be interlocked with an operation of the second link member  132 . 
     Specifically, a stopper pin  133  which is formed perpendicular to a lengthwise direction of the second link member  132  may be provided at the end of the second link member  132 . A stopper moving part  143  through which the stopper pin  133  is moved may be formed at the pressing body  142 . 
     The pressing part  140  may include a stopper rib  144  which is provided to limit a movement of the stopper pin  133  in the stopper moving part  143 . The stopper rib  144  may be provided on the pressing body  142 . The stopper rib  144  may be provided to catch the stopper pin  133 , when the pressing unit  120  is moved back from the pressing position P 1  to the stand-by position  02 . Due to such a structure, when the pressing unit  120  is moved from the stand-by position  02  to the pressing position P 1 , the second link member  132  does not affect the pressing part  140 , but when the pressing unit  120  is moved back from the pressing position P 1  to the stand-by position  02 , the stopper pin  133  of the second link member  132  is caught by the stopper rib  144 , and thus the pressing part  140  is moved back. 
     The second link member  132  may include a stopper insertion part  132   a  and a variable seating part  132   b.    
     The stopper insertion part  132   a  of the second link member  132  is a part which is inserted into the stopper moving part  143  of the pressing part  140  by the operation of the pressing unit  120 . 
     The variable seating part  132   b  of the second link member  132  is provided so that the pressing elastic member  134  is seated thereon. The variable seating part  132   b  refers to the remaining parts of the second link member  132 , except the stopper insertion part  132   a . That is, the variable seating part  132   b  may be the parts of the second link member  132 , which are formed between one surface of the stopper rib  144  and the end of the second link member  132 . 
     A length of the second link member  132  may be formed to be the same as a sum of a length of the variable seating part  132   b  and a length of the stopper insertion part  132   a . The lengths of the variable seating part  132   b  and the stopper insertion part  132   a  may be changed depending on the operation of the pressing unit  120 , and may be provided so that the sum of the lengths of the variable seating part  132   b  and the stopper insertion part  132   a  is the same as the length of the second link member  132 . 
     Since the length of the variable seating part  132   b  is changed depending on the operation of the pressing unit  120 , a length of the pressing elastic member  134  provided at the variable seating part  132   b  is also changed. That is, since the length of the variable seating part  132   b  is changed depending on the operation of the pressing unit  120 , the length of the pressing elastic member  134  is also changed depending on the operation of the pressing unit  120 . Since a change in the length of the pressing elastic member  134  means a change in the elastic force, the elastic force of the pressing elastic member  134  is changed depending on the operation of the pressing unit  120 . 
     Due to such a structure, when the pressing unit  120  is moved from the stand-by position  02  to the pressing position P 1 , the length of the variable seating part  132   b  is reduced, and thus the elastic force of the pressing elastic member  134  provided at the variable seating part  132   b  is applied to one surface of the stopper rib  144  of the pressing body  142 , and the pressing part  140  is moved in a direction in which the pressing part  140  presses the developing unit  30   a . Contrarily, when the pressing unit  120  is moved from the pressing position P 1  to the stand-by position  02 , the length of the variable seating part  132   b  is increased, and thus the elastic force of the pressing elastic member  134  provided at the variable seating part  132   b  is also reduced, and the pressing part  140  is moved back in a direction opposite to the direction in which the pressing part  140  presses the developing unit  30   a , while the stopper pin  133  of the second link member  132  is caught by the stopper rib  144 . 
     The pressing movement rail  146  is provided at the pressing body  142  so that the pressing part  140  reciprocates linearly. Specifically, a moving protrusion  147  is provided at the developing device seating part  5  to correspond to the pressing movement rail  146 , and the pressing movement rail  146  is provided to be moved along the moving protrusion  147 . 
     One pair of pressing movement rails  146  is provided up and down at both side surfaces of the pressing body  142 , respectively, such that the moving protrusion  147  is inserted therebetween. A protrusion insertion part  146   a  may be formed between one pair of pressing movement rails  146  so that the moving protrusion  147  is inserted therein. 
     The rotating motions of the operating unit  150  and the rotating shaft  110  are transmitted to the pressing part  140  by the first and second link members  131  and  132 , and converted into the linear reciprocating motion at the pressing part  140  by the pressing movement rail  146  and the moving protrusion  147 . 
     The pressing elastic member  134  may be provided so that a compressed length thereof differs according to a state of the operating unit  150 . As described above, this is because the length of the variable seating part  132   b  is changed depending on the operation of the pressing unit  120 , and thus the length of the pressing elastic member  134  provided at the variable seating part  132   b  differs. 
     Specifically, when the operating unit  150  may be at the stand-by position  02 , the length of the pressing elastic member  134  is a first length L 1 , and when the operating unit  150  is at the fixed operating position  01   a , the length of the pressing elastic member  134  may be a second length L 2 , and when the operating unit  150  is at the movable operating position  01   b , the length of the pressing elastic member  134  may be a third length L 3 . 
     When the pressing elastic member  134  has the first length L 1 , the pressing elastic member  134  may be in a state which does not extend or is not compressed. When the pressing elastic member  134  has the second length L 2  and the third length L 3 , the pressing elastic member  134  may be in a state which is compressed so that the elastic force is applied to the pressing elastic member  134 . That is, the second length L 2  and the third length L 3  are provided to be shorter than the first length L 1 . 
     The second length L 2  and the third length L 3  may be the same so that a pressing force generated when the operating unit  150  is at the fixed operating position  01   a  is the same as that generated when the operating unit  150  is at the movable operating position  01   b.    
     The pressing elastic member  134  may be provided to be maximally compressed, when the operating unit  150  is located between the fixed operating position  01   a  and the movable operating position  01   b . That is, the pressing elastic member  134  is compressed to have a maximum compressed length ML, when the operating unit  150  is moved between the fixed operating position  01   a  and the movable operating position  01   b.    
     Therefore, in order to move the operating unit  150  from the fixed operating position  01   a  to the movable operating position  01   b  or the stand-by position  02 , an external force by which the pressing elastic member  134  is compressed from the second length L 2  to a maximally compressed length ML should be applied. Also, the movement of the operating unit  150  from the movable operating position  01   b  to the stand-by position  02  may be performed without the external force by which the pressing elastic member  134  is compressed to the maximally compressed length ML, while the pressing elastic member  134  is elastically returned from the third length L 3  to the first length L 1 . 
     An operation restricting surface  6   a  may be provided above the link unit  130  so as to restrict an operation of the link unit  130 . The operation restricting surface  6   a  may be provided at the developing device seating part  5  to face an upper portion of the link unit  130 . Specifically, the developing device seating part  5  may include an assembly cover  6  which covers at least a part of the pressing assembly  100 . The rotating shaft  110  and at least a part of the pressing unit  120  may be disposed at an inner side of the assembly cover  6 . The operation restricting surface  6   a  which faces the link unit  130  may be provided at the inner side of the assembly cover  6 , and the operation of the link unit  130  is partly restricted by the operation restricting surface  6   a.    
     This will be described with the operating unit  150 . 
     When the operating unit  150  is at the fixed operating position  01   a , the end of the first link member  131  of the link unit  130  is in a state in which rotation thereof in one direction is restricted by the operation restricting surface  6   a . At this time, since a compressed elastic force of the pressing elastic member  134  provided at the second link member  132  is applied in the other direction, the operating unit  150  may be fixed at the fixed operating position  01   a.    
       FIG. 8A  is a view illustrating the cover unit in accordance with an embodiment of the disclosure, and  FIG. 8B  is an enlarged view of a portion A of  FIG. 8A . 
     The cover unit  170  may be detachably provided at one side of the developing device  30 . The cover unit  170  may be provided so that the operation of the operating unit  150  is interlocked with an attachment and detachment thereof. Specifically, while the cover unit  170  is installed at the one side of the developing device  30 , the cover unit  170  may guide the operating unit  150  located at the stand-by position  02  or the fixed operating position  01   a  to the movable operating position  01   b.    
     The cover unit  170  may include a cover body  172  and a guide rib  174 . 
     The cover body  172  may be provided to cover one side of the developing device  30 , and may be connected with the developing device  30  so that the waste toner generated from the developing device  30  is stored therein. 
     The guide rib  174  may be provided at one surface of the cover body  172 , which faces the developing device  30 , so as to guide the rotation of the operating unit  150 . 
     The guide rib  174  may include a first guide rib  175  and a second guide rib  176 . The first guide rib  175  serves to guide the operating unit  150  which is moved from the fixed operating position  01   a  to the movable operating position  01   b , and the second guide rib  176  serves to guide the operating unit  150  which is moved from the stand-by position  02  to the movable operating position  01   b.    
     The cover unit  170  may include an operating unit seating part  178 . The operating unit seating part  178  may be provided at an end of the guide rib  174  so as to locate the operating unit  150  at the movable operating position  01   b  when the cover unit  170  is installed at the one side of the developing device  30 . In an embodiment, the operating unit seating part  178  may be provided between the first guide rib  175  and the second guide rib  176 , and the operating unit  150  may be guided from the fixed operating position  01   a  or the stand-by position  02  by the guide rib  174  so as to be located at the movable operating position  01   b  corresponding to the operating unit seating part  178 . 
     The guide rib  174  may be formed so that an end thereof is inclined toward the operating unit seating part  178 . Due to such a structure, when the cover unit  170  is coupled to the one side of the developing device  30 , the operating unit  150  may be rotated and seated on the operating unit seating part  178  corresponding to the movable operating position  01   b.    
     Specifically, the guide rib  174  may include a first rib contact part  174   a , and a second rib contact part  174   b  which is spaced apart a predetermined angle from the first rib contact part  174   a  with respect to the rotating center of the operating unit  150  and extends from the first rib contact part  174   a  so as to have a slope inclined toward the cover body  172 . 
     The operating unit  150  may include an operating body  152 , and a first guide surface  152   a  and a second guide surface  152   b  which are provided at the operating body  152 . 
     The first guide surface  152   a  may be provided to be guided by the first guide rib  175 , and may be provided at an upper portion of the operating body  152 . Specifically, the first guide surface  152   a  may be provided at an upper edge of the operating body  152  so as to be guided from the first rib contact part  174   a  of the first guide rib  175  to the second rib contact part  174   b  thereof. 
     The second guide surface  152   b  may be provided to be guided by the second guide rib  176 , and may be provided at a lower portion of the operating body  152 . Specifically, the second guide surface  152   b  may be provided at a lower edge of the operating body  152  so as to be guided from the first rib contact part  174   a  of the second guide rib  176  to the second rib contact part  174   b  thereof. 
     Hereinafter, an operation of the image forming apparatus in accordance with an embodiment of the disclosure will be described. 
     To perform a printing operation after the developing device  30  is seated on the developing device seating part  5 , the developing unit  30   a  and the photoreceptor unit  30   b  should come into close contact with each other so that the developing roller  34  and the photoreceptor  32  come into contact with each other. 
     The pressing assembly  100  is operated so that the developing unit  30   a  and the photoreceptor unit  30   b  should come into close contact with each other. 
     In the initial stage, the operating unit  150  is at the stand-by position  02 , and when the developing device  30  is seated on the developing device seating part  5 , the operating unit  150  is rotated so that the pressing unit  120  presses the developing unit  30   a.    
     When the operating unit  150  is rotated from the stand-by position  02  to the fixed operating position  01   a  or the movable operating position  01   b , the link unit  130  of the pressing unit  120  is operated, and the pressing part  140  presses the developing unit  30   a . The pressed developing unit  30   a  comes into close contact with the photoreceptor unit  30   b , and the developing roller  34  and the photoreceptor  32  come into contact with each other. 
     As described above, the operating unit  150  may be arbitrarily moved from the stand-by position  02  to the fixed operating position  01   a  or the movable operating position  01   b  so that the developing unit  30   a  and the photoreceptor unit  30   b  should come into close contact with each other. By installing the cover unit  170  at the one side of the developing device  30 , the operating unit  150  may be provided to be moved to the operating position  01 . 
     When the cover unit  170  is installed at the one side of the developing device  30 , the operating unit  150  is moved to the movable operating position  01   b , regardless of the position of the operating unit  150 . 
     Specifically, in the case in which the operating unit  150  is at the fixed operating position  01   a , when the cover unit  170  is installed at the one side of the developing device  30 , the operating unit  150  is guided by the first guide rib  175  of the cover unit  170 , and moved to the movable operating position  01   b . Also, in the case in which the operating unit  150  is at the stand-by position  02 , when the cover unit  170  is installed at the one side of the developing device  30 , the operating unit  150  is guided by the second guide rib  176  of the cover unit  170 , and moved to the movable operating position  01   b . The operating unit guided by the first guide rib  175  or the second guide rib  176  is seated on the operating unit seating part  178 , and maintained at the movable operating position  01   b.    
     Of course, in the case in which the operating unit  150  is at the movable operating position  01   b , when the cover unit  170  is installed at the one side of the developing device  30 , the operating unit  150  is seated on the operating unit seating part  178 , and maintained at the movable operating position  01   b.    
     When the cover unit  170  is separated from the developing device  30  to replace the developing device  30 , the operating unit  150  located at the movable operating position  01   b  is rotated to the stand-by position  02  by an elastic returning force of the pressing elastic member  134 . As the operating unit  150  is rotated to the stand-by position  02 , the pressing force of the pressing unit  120  applied to the developing unit  30   a  is released, and the developing roller  34  and the photoreceptor  32  are separated from each other. 
     Hereinafter, an image forming apparatus in accordance with an embodiment of the disclosure will be described. 
     Repeated description of the same structure as that previously described above will be omitted. 
       FIG. 9  is a cross-sectional view of the image forming apparatus in accordance with an embodiment of the disclosure. 
     As illustrated in  FIG. 9 , the image forming apparatus  1001  may include a main body  1010 , a print medium supplying unit  1020 , an optical scanning unit  1030 , a developing device  1040 , a transfer unit  1060 , a fixing unit  1070 , and a print medium discharging unit  1080 . 
     The main body  1010  defines an exterior of the image forming apparatus  1001 , and also supports various components installed therein. Further, a cover  1011  may be rotatably installed at one side of the main body  1010 . The cover  1011  serves to open and close a part of the main body  1010 . A user may open the cover  1011 , may have access to an inner side of the main body  1010 , and may remove paper jammed in a printing path. 
     The print medium supplying unit  1020  may include a cassette  1021  in which a print medium S is stored, a pick-up roller  1022  which picks up each sheet of the print medium S stored in the cassette  1021 , and a transporting roller  1023  which transports the picked-up print medium toward the transfer unit  1060 . 
     The optical scanning unit  1030  may be disposed under a developing device  1040  to radiate light corresponding to image information onto a photoreceptor  1052  and thus to form an electrostatic latent image on a surface of the photoreceptor  1052 . The optical scanning unit  1030  may include a light source  1032  which generates the light, a plurality of reflection mirrors  1034  which change a route of the light generated from the light source  1032 , and a plurality of optical windows  1036  through which the light reflected by the plurality of reflection mirrors  1034  is transmitted. 
     The developing device  1040  may include a developing unit  1041  and a photoreceptor unit  1050 . 
     Developing units  1041 Y,  1041 M,  1041 C and  1041 K which receive yellow (Y), magenta (M), cyan (C) and black (K) developers, respectively, have a developing roller  1042  and supplying rollers  1044  and  1046 , respectively. The supplying rollers  1044  and  1046  serve to supply the developers to the developing roller  1042 , and the developing roller  1042  serves to attach the developers on the surface of the photoreceptor on which the electrostatic latent image is formed and thus to form a visible image. 
     Each photoreceptor unit  1050 Y,  1050 M,  1050 C, or  1050 K corresponding to each developing unit  1041 Y,  1041 M,  1041 C, or  1041 K has a photoreceptor  1052  and a charger  1054 . The charger  1054  serves to charge the photoreceptor  1052  with a predetermined electric potential, and the electrostatic latent image is formed on the surface of the charged photoreceptor  1052 . 
     The transfer unit  1060  may include a transfer belt  1061  which is in contact with the photoreceptor  1052  of each photoreceptor unit  1050 Y,  1050 M,  1050 C, or  1050 K while being circulated, a driving roller  1063  which drives the transfer belt  1061 , a tension roller  1065  which provides a predetermined tensile force to the transfer belt  1061 , and four rollers  1067  which transfer the visible image developed on the photoreceptor  1052  of each photoreceptor unit  1050 Y,  1050 M,  1050 C, or  1050 K to the print medium P. 
     The fixing unit  1070  may include a heating roller  1071  which has a heating source, and a pressing roller  1072  which is installed so as to face the heating roller  1071 . When the print medium passes between the heating roller  1071  and the pressing roller  1072 , the image is fixed on the print medium by heat transmitted from the heating roller  1071  and pressure acting between the heating roller  1071  and the pressing roller  1072 . 
     The print medium discharging unit  1080  has a plurality of discharging rollers  1081  so as to discharge the print medium passing through the fixing unit  1070  to an outside of the main body  1010 . 
     Each photoreceptor unit  1050 Y,  1050 M,  1050 C, or  1050 K may be fixed to an inner side of the main body  1010 , and each developing unit  1041 Y,  1041 M,  1041 C, or  1041 K may be provided to be attached or detached through one side of the main body  1010 . When each developing unit  1041 Y,  1041 M,  1041 C, or  1041 K is installed at the main body  1010 , each developing unit  1041 Y,  1041 M,  1041 C, or  1041 K is coupled to each photoreceptor unit  1050 Y,  1050 M,  1050 C, or  1050 K so as to be rotated about each rotating center CY, CM, CC, or CK. The developing rollers  1042  included in each developing unit  1041 Y,  1041 M,  1041 C, or  1041 K and the photoreceptors  1052  included in each photoreceptor unit  1050 Y,  1050 M,  1050 C, or  1050 K come into contact with each other, when the image forming apparatus  1001  performs the printing operation, and then are separated from each other, when each developing unit  1041 Y,  1041 M,  1041 C, or  1041 K is detached and replaced. Hereinafter, a structure in which the developing rollers  1042  and the photoreceptors  1052  are in contact with or separated from each other will be described in detail. 
       FIG. 10  is a view illustrating an arrangement of the developing device and the optical scanning unit of the image forming apparatus in accordance with a second embodiment of the disclosure. 
     The developing device  1040  may be provided to be seated on a developing device seating part  1005 . A waste toner storing unit (not shown) which stores waste toner generated from the developing device  1040  may be provided at one side of the developing device  1040 . Toner used in the developing device  1040  may be provided to be moved to the waste toner storing unit and then stored therein. In an embodiment of the disclosure, the waste toner storing unit may be referred to as a cover unit. The cover unit may be provided to guide an operation of an operating unit  250 , as described previously. The description of this structure will be omitted below for the sake of brevity. 
     A pressing assembly  200  may be provided at one side of the developing device  1040  so that the developing unit  1041  and the photoreceptor unit  1050  come into close contact with each other. Specifically, the developing roller  1042  of the developing unit  1041  and the photoreceptor  1052  of the photoreceptor unit  1050  may come into close contact with or be separated from each other through an operation of the pressing assembly  200 . 
       FIGS. 11A and 11B  are views illustrating the operation of the pressing assembly and the developing device in accordance with an embodiment of the disclosure,  FIGS. 12A and 12B  are perspective views illustrating the operation of the pressing assembly in accordance with an embodiment of the disclosure,  FIGS. 13A and 13B  are cross-sectional views illustrating a pressing unit depending on the operation of the pressing assembly in accordance with an embodiment of the disclosure, and  FIGS. 14A and 14B  are cross-sectional views illustrating a shutter unit and the developing unit depending on the operation of the pressing assembly in accordance with an embodiment of the disclosure. 
     The pressing assembly  200  may be disposed adjacent to the developing device  1040  so that the developing unit  1041  and the photoreceptor unit  1050  come into contact with or are separated from each other. Specifically, the pressing assembly  200  may be provided so that the developing roller  1042  of the developing unit  1041  and the photoreceptor  1052  of the photoreceptor unit  1050  come into contact with or are separated from each other. An arrangement of the pressing assembly  200  is not limited. However, in an embodiment, the pressing assembly  200  may be disposed at the developing device seating part  1005 . 
     The pressing assembly  200  may include a rotating shaft  210 , a pressing unit  220 , and an operating unit  250 . 
     The rotating shaft  210  may be rotatably provided so that an operation of the operating unit  250  is transmitted to the pressing unit  220 . At least one shaft stopper  211  may be provided at an outer circumferential surface of the rotating shaft  210  so that a movement of the rotating shaft  210  in a first direction W 1  is restricted. 
     The pressing unit  220  may be provided so that the developing roller  1042  and the photoreceptor  1052  come into close contact with each other. The pressing unit  220  may be provided to be interlocked with the operating unit  250 . The pressing unit  220  may be provided to be moved between a pressing position P 1  in which the developing roller  1042  and the photoreceptor  1052  come into contact with each other, and a releasing position P 2  which is moved backed from the pressing position P 1  so that the developing roller  1042  and the photoreceptor  1052  are separated from each other. 
     The operating unit  250  may be provided to be rotatable, such that the pressing unit  220  is operated by the operation of the operating unit  250 . That is, at least one pressing unit  220  may be provided to be interlocked with the operating unit  250 . 
     The operating unit  250  may include an operating body  252  which is connected with the rotating shaft  210  so as to be rotated about the rotating shaft  210 . 
     The operating unit  250  may be provided to be movable between an operating position  01  in which a pressing force is generated from the pressing unit  220  and a stand-by position  02  in which the pressing force is released. 
     The pressing unit  220  may include a link unit  230  and a pressing part  240 . 
     The link unit  230  may include a first link member  231 , a second link member  232 , and a pressing elastic member  234 . The second link member  232  may include a stopper insertion part  232   a  and a variable seating part  232   b . A stopper pin  233  which is formed perpendicular to a lengthwise direction of the second link member  232  may be provided at an end of the second link member  232 . 
     The pressing elastic member  234  may be provided to be maximally compressed, when the operating unit  250  is located between the operating position  01  and the stand-by position  02 . That is, the pressing elastic member  234  may be compressed to a maximum compressed length ML, when the operating unit  250  is moved between the operating position  01  and the stand-by position  02 . 
     An operation restricting surface  1006   a  may be provided above the link unit  230  so as to restrict an operation of the link unit  230 . The operation restricting surface  1006   a  may be provided at an assembly cover  1006  of the developing device seating part  1005  to face an upper portion of the link unit  230 . 
     The pressing part  240  may include a pressing body  242  and a pressing movement rail  246 . A pressing surface  242   a  is provided at a front portion of the pressing body  242 . The pressing surface  242   a  may be provided to come into direct contact with the developing unit  1041  and thus to press the developing unit  1041 . A stopper moving part  243  through which the stopper pin  233  is moved is formed at the pressing body  242 . The pressing part  240  may include a stopper rib  244  which is provided to limit a movement of the stopper pin  233  in the stopper moving part  243 . The stopper rib  244  may be provided on the pressing body  242 . 
     The pressing movement rail  246  is provided at the pressing body  242  so that the pressing part  240  reciprocates linearly. Specifically, a moving protrusion (not shown) is provided at the developing device seating part  1005  to correspond to the pressing movement rail  246 , and the pressing movement rail  246  is provided to be moved along the moving protrusion. 
     One pair of pressing movement rails  246  may be provided up and down at both side surfaces of the pressing body  242 , respectively, such that the moving protrusion is inserted therebetween. A protrusion insertion part  246   a  may be formed between one pair of pressing movement rails  246  so that the moving protrusion is inserted therein. 
     The pressing part  240  may include a shutter guide member  248 . 
     The shutter guide member  248  may be provided to guide an operation of a shutter unit  280  and also to open and close an optical window  1036 . In an embodiment, one pair of pressing units  220  may be provided to guide both sides of the shutter unit  280 , such that the shutter unit  280  is operated. However, the disclosure is not limited thereto, and at least one pressing unit  220  may be provided so as to guide the operation of the shutter unit  280 . 
     The shutter guide member  248  may be provided to protrude from one side surface of the pressing body  242  of the pressing part  240 . That is, the shutter guide member  248  may be provided to have a protrusion shape which extends from the pressing body  242 . 
     Specifically, the shutter guide member  248  may be formed to protrude from the pressing body  242 , and may be formed to protrude perpendicular to a forward and backward moving direction of the pressing part  240 . Due to such a structure, the shutter guide member  248  may guide the shutter unit  280  and a forward and backward movement of the pressing part  240 . 
     The shutter unit  280  is provided to open and close the optical window  1036 . Light generated from the optical scanning unit is radiated through the optical window  1036 , and the radiated light passes through the optical window  1036  and is radiated onto the photoreceptor  1052 . The shutter unit  280  is provided to open and close the optical window  1036 , such that the light is selectively radiated onto the photoreceptor  1052 . 
     The shutter unit  280  may include a shutter body  282  and a shutter rotating part  284  provided at the shutter body  282 . 
     The shutter body  282  may be provided to correspond to the optical window  1036 . The shutter body  282  may be formed in a lengthwise direction of the optical window  1036  or the photoreceptor  1052  so as to correspond to the optical window  1036  and the photoreceptor  1052 . The shutter body  282  may be provided to be moved between an opening position S 1  in which the optical window  1036  is opened and a closing position S 2  in which the optical window  1036  is closed. The shutter body  282  may be rotated about the shutter rotating part  284  and thus may be moved between the opening position S 1  and the closing position S 2 . 
     A shutter protrusion  283  which corresponds to the shutter guide member  248  of the pressing part  240  may be provided at the shutter body  282 . The shutter protrusion  283  may be formed to protrude from the shutter body  282 , and may be provided at an end of the shutter body  282 . In an embodiment of the disclosure, since one pair of pressing units  220  is provided at both ends of the shutter unit  280 , one pair of shutter protrusions  220  may be provided at both ends of the shutter body  282 . 
     Due to such a structure, while the pressing unit  220  is moved from the releasing position P 2  to the pressing position P 1 , the shutter guide member  248  of the pressing part  240  presses the shutter protrusion  283  of the shutter unit  280 . Therefore, when the pressing unit  220  is at the pressing position P 1 , the developing unit  1041  is pressed, and at the same time, the shutter unit  280  is at the opening position S 1 . 
     A movement of the shutter unit  280  from the closing position S 2  to the opening position S 1  may be performed so that the shutter protrusion  283  is pressed by the shutter guide member  248 , and a movement of the shutter unit  280  from the opening position S 1  to the closing position S 2  may be performed so that the shutter falls down due to its own weight. Of course, the movement of the shutter unit  280  from the opening position S 1  to the closing position S 2  may be interlocked with a movement of the pressing unit  220  from the pressing position P 1  to the releasing position P 2 . However, in the embodiment, for example, the shutter unit  280  is provided to be operated by its own weight. 
     The shutter body  282  may be rotated about the shutter rotating part  284 , and is provided so that an angle between the shutter body  282  when the shutter unit  280  is at the closing position S 2  and the shutter body  282  when the shutter unit  280  is at the opening position S 1  forms an acute angle. That is, a rotating angle of the shutter unit  280  between the opening position S 1  and the closing position S 2  forms the acute angle. 
     At the closing position S 2 , the shutter body  282  may be provided in parallel with the optical window  1036 , and at the opening position S 1 , the shutter body  282  forms the acute angle with respect to the optical window  1036 . 
     Due to such a structure, when the shutter unit  280  is moved from the opening position S 1  to the closing position S 2 , the shutter body  282  may be moved by its own weight. 
       FIG. 15  is a perspective view illustrating an arrangement of the operating unit in accordance with an embodiment of the disclosure,  FIG. 16  is a side view illustrating a pressing state of the operating unit in accordance with an embodiment of the disclosure,  FIG. 17  is an exploded perspective view of the operating unit in the pressing assembly in accordance with an embodiment of the disclosure, and  FIG. 18  is a cross-sectional perspective view illustrating the operating unit in accordance with an embodiment of the disclosure. 
     The operating unit  250  may be provided to be rotatable, such that the pressing unit  220  is operated by the operation of the operating unit  250 . That is, the at least one pressing unit  220  is provided to be interlocked with the operating unit  250 . 
     The operating unit  250  may include an operating body  252  which is connected with the rotating shaft  210  so as to be rotated about the rotating shaft  210 . 
     The operating unit  250  is provided to be movable between an operating position  01  in which a pressing force is generated from the pressing unit  220  and a stand-by position  02  in which the pressing force is released. 
     When the operating unit  250  is located at the operating position  01 , the pressing unit  220  presses the developing unit  1041 , and when the operating unit  250  is located at the stand-by position  02 , the pressing of the pressing unit  220  with respect to the developing unit  1041  is released. 
     The operating unit  250  may include the operating body  252  and a pressing member  260 . 
     The operating body  252  may be provided to be rotated about the rotating shaft  210 . 
     The pressing member  260  may be provided at the operating body  252  so as to press the developing device  1040  in a direction in which the developing device  1040  is installed at the developing device seating part  1005 . The first direction W 1  may include an installing direction W 1   a  in which the developing device  1040  is installed at the developing device seating part  1005 , and a separating direction W 1   b  which is opposite to the installing direction W 1   a  and in which the developing device  1040  is separated from the developing device seating part  1005 . The pressing member  260  may be provided to press the developing device  1040  in the installing direction W 1   a . Specifically, the pressing member  260  may be provided to press the photoreceptor unit  1050  of the developing device  1040 . 
     The operating unit  250  may include a rotating part  254 . The rotating part  254  may be provided at the operating body  252  to be rotatably supported by the rotating shaft  210 . The rotating part  254  has a hollow portion through which the rotating shaft  210  passes, and the operating body  252  extends from the rotating part  254  in a direction perpendicular to a rotating axis. One end of the rotating part  254  may be formed to be supported by the developing device seating part  1005 . 
     An operation elastic part  264  may be provided at the rotating part  254 , and the operating unit  250  may be provided to press the developing device  1040  in the installing direction W 1   a . The operation elastic part  264  will be described below in detail. 
     The pressing member  260  may include a pressing surface  262  which is formed toward the developing device  1040  so as to come into contact with the developing device  1040 . The pressing surface  262  may be provided to come into direct contact with the developing device  1040 . The pressing surface  262  may be provided to press the developing device  1040 , while the operating unit  250  is moved from the stand-by position  02  to the operating position  01 . 
     The pressing surface  262  may include a first pressing part  262   a  and a second pressing part  262   b . The first pressing part  262   a  may be disposed in front of the second pressing part  262   b  in a direction in which the operating unit  250  is rotated from the stand-by position  02  to the operating position  01 . 
     The first pressing part  262   a  may be provided to be more concave in the separating direction W 1   b  than the second pressing part  262   b.    
     Contrarily, the second pressing part  262   b  may be provided to be more convex in the installing direction W 1   a  than the first pressing part  262   a.    
     When the operating unit  250  is moved from the stand-by position  02  to the operating position  01 , the developing device  1040  first comes into contact with the first pressing part  262   a , and then into contact with the second pressing part  262   b . That is, the second pressing part  262   b  which extends from the first pressing part  262   a  is formed to be more spaced apart in the installing direction W 1   a  than the first pressing part  262   a , and thus the second pressing part  262   b  comes into contact with the developing device  1040  after the operating unit  250  is moved to the operating position  01 . 
     At least a part of the pressing surface  262  may be provided to form a curved surface. Thus, the second pressing part  262   b  may extend from the first pressing part  262   a  in the form of the curved surface. Due to such a structure, when the operating unit  250  is moved from the stand-by position  02  to the operating position  01 , the developing device  1040  may be pressed smoothly. 
     A to-be-pressed surface  1056  is provided at the developing device  1040  to correspond to the pressing surface  262 . The to-be-pressed surface  1056  is provided to be pressed by the pressing surface  262  of the operating unit  250 . Specifically, the to-be-pressed surface  1056  may be provided at the photoreceptor unit  1050  of the developing device  1040 . 
     The to-be-pressed surface  1056  may be inclined so as to correspond to the pressing surface  262 . That is, the to-be-pressed surface  1056  may include a first to-be-pressed part  1056   a  with which the first pressing part  262   a  comes into contact, and a second to-be-pressed part  1056   b  with which the second pressing part  262   b  comes into contact and which is formed to extend from the first to-be-pressed part  1056   a  and to have a slope inclined in the separating direction W 1   b.    
     The operating unit  250  may include the operation elastic part  264 . 
     The operation elastic part  264  may be provided at the rotating part  254  to provide the elastic force to the operating unit  250 . That is, the operation elastic part  264  may be provided so as to provide the elastic force to the operating unit  250  in the installing direction W 1   a , such that the operating unit  250  presses the developing device  1040  in the installing direction W 1   a . The rotating part  254  may be formed in a cylindrical shape with a hollow internal space. An installing space  256  may be formed at an inner side of the rotating part  254  so that the operation elastic part  264  is located therein. The installing space  256  may include a first installing space  256   a  in which an installation elastic member  265  to be described below is installed, and a second installing space  256   b  in which a fastening member  266  is installed. 
     The operation elastic part  264  may include the installation elastic member  265  and the fastening member  266 . 
     The fastening member  266  may be provided at the rotating shaft  210  to support one end of the installation elastic member  265 . That is, since the movement of the rotating shaft  210  in the first direction W 1  is restricted, and the fastening member  266  is disposed perpendicular to the axial direction, the installation elastic member  265  may be provided not to be separated from the fastening member  266 . A shape of the fastening member  266  provided at the rotating shaft  210  is not limited specifically. In an embodiment of the disclosure, the fastening member  266  is formed in a pin shape, and provided to pass through the rotating shaft  210  perpendicular to the axial direction of the rotating shaft  210 . 
     The operating unit  250  may include a movement restricting surface  257  which is provided to come into contact with the fastening member  266  and thus to restrict the movement of the operating unit  250  in the separating direction W 1   b . The second installing space  256   b  may be formed in the rotating part  254  using the movement restricting surface  257  as a boundary line. When the operating unit  250  is moved in the separating direction W 1   b , the fastening member  266  comes into contact with the movement restricting surface  257  of the operating unit  250 , and thus the movement of the operating unit  250  in the separating direction W 1   b  is restricted. 
     Since the fastening member  266  supports one end of the installation elastic member  265 , a diameter of the second installing space  256   b  in which the fastening member  266  is installed is greater than that of the first installing space  256   a  in which the installation elastic member  265  is installed, and thus the movement restricting surface  257  may be formed from a circumference of the first installing space  256   a  to a circumference of the second installing space  256   b.    
     The installation elastic member  265  may be disposed in the installing space  256 . One end of the installation elastic member  265  may be supported by the fastening member  266 , and the other end thereof is supported by an axial inner side surface of the rotating part  254 . The installation elastic member  265  is provided to surround an outer circumferential surface of the rotating shaft  210 , such that the elastic force generated from the installation elastic member  265  is axially transmitted to the operating unit  250 . Specifically, the installation elastic member  265  generates the elastic force so as to press the operating unit  250  in the installing direction W 1   a.    
     Hereinafter, an operation of the image forming apparatus in accordance with an embodiment of the disclosure will be described. 
     After the developing device  1040  is seated on the developing device seating part  1005 , the developing unit  1041  and the photoreceptor unit  1050  should come into close contact with each other so that the developing roller  1042  and the photoreceptor  1052  come into contact with each other, and thus the printing operation may be performed. 
     The pressing assembly  200  is operated so that the developing unit  1041  and the photoreceptor unit  1050  come into close contact with each other. 
     In the initial stage, the operating unit  250  may be located at the stand-by position  02 , and when the developing device  1040  is seated on the developing device seating part  1005 , the operating unit  250  is rotated so that pressing unit  220  presses the developing unit  1041 . 
     When the operating unit  250  is rotated from the stand-by position  02  to the operating position  01 , the link unit  230  of the pressing unit  220  is operated so that the pressing part  240  presses the developing unit  1041 . The pressed developing unit  1041  comes into close contact with the photoreceptor unit  1050 , and the developing roller  1042  and the photoreceptor  1052  come into contact with each other. 
     While the operating unit  250  is rotated from the stand-by position  02  to the operating position  01 , the pressing unit  220  is moved from the releasing position P 2  to the pressing position P 1 . While the pressing unit  220  is moved from the releasing position P 2  to the pressing position P 1 , the pressing part  240  presses the developing unit  1041  and also opens the shutter unit  280  at the same time. 
     Specifically, the pressing surface  242   a  of the pressing part  240  presses the developing unit  1041 , and the shutter guide member  248  of the pressing part  240  guides the rotation of the shutter unit  280 . The shutter guide member  248  presses the shutter protrusion  283  of the shutter unit  280 , and the shutter unit  280  is rotated about the shutter rotating part  284  and moved from the closing position S 2  to the opening position S 1 . 
     When the operating unit  250  is rotated from the stand-by position  02  to the operating position  01 , the developing device  1040  is in a state capable of forming an image, and at the same time, the light generated from the optical scanning unit is radiated onto the photoreceptor  1052 . 
     When the operating unit  250  is at the operating position  01 , the pressing unit  220  presses the developing unit  1041 , and the operating unit  250  presses the photoreceptor unit  1050  of the developing device  1040  in the installing direction W 1   a . The pressing member  260  of the operating unit  250  presses the developing device  1040  in the installing direction W 1   a.    
     When the operating unit  250  is rotated from the stand-by position  02  to the operating position  01 , the first pressing part  262   a  of the pressing member  260  first comes into contact with the first to-be-pressed part  1056   a  of the to-be-pressed surface  1056  of the developing device  1040 . When the operating unit  250  is rotated to the operating position  01 , the second pressing part  262   b  of the pressing member  260  comes into contact with the second to-be-pressed part  1056   b  of the to-be-pressed surface  1056  of the developing device  1040 . 
     In this process, the operating unit  250  presses the photoreceptor unit  1050  of the developing device  1040  in the installing direction W 1   a  by the elastic force generated by the operation elastic part  264 . 
     When the operating unit  250  is rotated from the pressing position P 1  to the stand-by position  02 , a reverse process is performed. 
     Hereinafter, an image forming apparatus in accordance with an embodiment of the disclosure will be described. 
     Repeated description of the same structure as that described previously will be omitted. 
       FIG. 19  is a view illustrating an arrangement of a developing device and a cover unit of the image forming apparatus in accordance with an embodiment of the disclosure,  FIG. 20  is a front view illustrating a pressing unit in accordance with an embodiment of the disclosure, and  FIG. 21  is a perspective view illustrating the pressing unit and a shutter unit in accordance with an embodiment of the disclosure. 
     The developing device  1040  may be provided to be seated on the developing device seating part  1005 . The waste toner storing unit in which the waste toner generated from the developing device  1040  is stored may be provided at one side of the developing device  1040 . The toner used in the developing device  1040  may be moved to the waste toner storing unit and stored therein. In an embodiment of the disclosure, the waste toner storing unit may be referred to as a cover unit  370 . 
     A shutter unit  380  may be provided to open and close the optical window  1036 . Light generated from the optical scanning unit is radiated through the optical window  1036 , and the radiated light passes through the optical window  1036  and is radiated onto the photoreceptor  1052 . The shutter unit  380  may be provided to open and close the optical window  1036 , such that the light is selectively radiated onto the photoreceptor  1052 . 
     The shutter unit  380  may include a shutter body  382 , and a shutter to-be-pressed part  386  which is provided at the shutter body  382 . 
     The shutter body  382  may be provided to correspond to the optical window  1036 . The shutter body  382  may be elongated in a lengthwise direction of the optical window  1036  or a lengthwise direction of the photoreceptor  1052  so as to correspond to the optical window  1036  and the photoreceptor  1052 . The shutter body  382  may be provided to be moved between the opening position S 1  in which the optical window is opened, and the closing position S 2  in which the optical window is closed. In an embodiment of the disclosure, since the image forming apparatus having a plurality of developing devices  1040  is applied, the shutter body  382  is also provided to correspond to the plurality of developing devices  1040 . However, the image forming apparatus having a single developing device  1040 , instead of the plurality of developing devices  1040 , may also be applied. 
     The shutter body  382  may include a shutter hole  382   a  corresponding to the optical window  1036 . The shutter hole  382   a  is elongated so as to correspond to the optical window  1036 , and provided so that the light radiated to the optical window  1036  may pass through the photoreceptor  1052 . 
     When the shutter unit  380  is at the opening position S 1 , the light radiated to the optical window  1036  may pass through the shutter hole  382   a , and when the shutter unit  380  is at the closing position S 2 , the light radiated to the optical window  1036  may be blocked by the shutter body  382 . 
     The light which is selectively radiated to the optical window  1036  through the movement of the shutter unit  380  between the opening position S 1  and the closing position S 2  may be transmitted to the photoreceptor  1052 . 
     Assuming that the lengthwise direction of the optical window  1036  or the lengthwise direction of the photoreceptor unit  1050  is a first direction W 1 , the shutter unit  380  is provided to reciprocate in a second direction W 2  vertical to the first direction W 1 . 
     The shutter unit  380  may include a returning elastic member  387 . The returning elastic member  387  may be provided at one side of the shutter body  382  so that the shutter unit  380  is returned from the opening position S 1  to the closing position S 2 . One end of the returning elastic member  387  is supported by the shutter body  382 , and the other end thereof is supported by the developing device seating part  1005 . Due to such a structure, when the pressing of the pressing unit  320  is released, the shutter unit  380  may be elastically returned from the opening position S 1  to the closing position S 2 . An arrangement of the returning elastic member  387  is not limited. However, in the embodiment of the disclosure, the returning elastic member  387  is disposed on a moving route of the shutter unit  380 . Specifically, the returning elastic member  387  is disposed at a rear side of a moving route of the shutter body  382  so that the shutter body  382  is elastically returned. 
     The pressing unit  320  is provided to be interlocked with the shutter unit  380 . The pressing unit  320  is provided to be moved between a pressing position P 1  in which the shutter unit  380  is pressed, and a releasing position P 2  in which the pressing applied to the shutter unit  380  is released. 
     The pressing unit  320  may include a pressing body  342  and a pressing elastic member  348  which provides an elastic force to the pressing body  342 . 
     The pressing body  342  may be provided to reciprocate by an external force. The pressing body  342  may be formed to be elongated in the first direction W 1 . One end of the pressing body  342  receives the external force in the first direction W 1 , and the other end thereof transmits the external force to the shutter unit  380 . 
     The pressing body  342  may be formed to be elongated in the first direction W 1  and to reciprocate in the first direction W 1 . Specifically, the pressing body  342  may be moved in an installing direction W 1   a  of the first direction W 1  by the external force, and returned in a separating direction W 1   b  when the external force is released. That is, the pressing body  342  is moved from the releasing position P 2  to the pressing position P 1  by the external force, and returned from the pressing position P 1  to the releasing position P 2  when the external force is released. 
     The pressing elastic member  348  may be provided so that the pressing unit  320  moved in the installing direction W 1   a  is returned in the separating direction W 1   b . The pressing body  342  may include an elastic catching protrusion  344  which protrudes from the pressing body  342  so that one end of the pressing elastic member  348  is supported thereby. One end of the pressing elastic member  348  may be supported by the elastic catching protrusion  344  which protrudes from the pressing body  342 , and the other end thereof may be supported by the main body. When the external force is applied to the pressing body  342 , and thus the pressing body  342  is moved in the installing direction W 1   a , the pressing elastic member  348  generates the elastic force by which the pressing body  342  is moved in the separating direction W 1   b , and when the external force is released, the pressing body  342  is returned to its original position by the elastic force. 
     The other end of the pressing body  342  is provided so as to press the shutter unit  380 . Specifically, the pressing body  342  may include a pressing part  346  which presses the shutter unit  380 . The pressing part  346  presses the shutter to-be-pressed part  386  of the shutter unit  380 . Since the pressing unit  320  reciprocates in the first direction W 1 , and the shutter unit  380  reciprocates in the second direction W 2  perpendicular to the first direction W 1 , the shutter to-be-pressed part  386  of the shutter unit  380  has an inclined surface which is inclined in the first and second directions W 1  and W 2 . 
     That is, the shutter to-be-pressed part  386  may include a pressing inclined surface  386   a  having a component of the first direction W 1  and a component of the second direction W 2  so that the shutter unit  380  is operated in the second direction W 2  perpendicular to the first direction W 1 . The pressing part  346  of the pressing body  342  comes into contact with the pressing inclined surface  386   a  and then presses the pressing inclined surface  386   a , and thus the shutter unit  380  may be moved in the second direction W 2 . 
     The cover unit  370  may be detachably provided at one side of the developing device  1040 . The cover unit  370  may be provided so that the operation of the pressing unit  320  is interlocked with an attachment and detachment of the cover unit  370 . Specifically, the cover unit  370  moves the pressing unit from the releasing position P 2  to the pressing position P 1 , while installed at one side of the developing device  1040 . Contrarily, when the cover unit  370  is separated from the one side of the developing device  1040 , the pressing unit  320  is moved from the pressing position P 1  to the releasing position P 2 . 
     Hereinafter, an operation of the image forming apparatus in accordance with an embodiment of the disclosure will be described. 
       FIGS. 22A and 22B  are views illustrating an interlocking operation of the pressing unit, the shutter unit and the cover unit in accordance with an embodiment of the disclosure. 
     First, an operation in which the shutter unit  380  is opened will be described. 
     When the pressing unit  320  is moved from the releasing position P 2  to the pressing position P 1 , the pressing part  346  of the pressing unit  320  presses the shutter unit  380 , and moves the shutter unit  380  from the closing position S 2  to the opening position S 1 . 
     Specifically, while the pressing unit  320  is moved from the releasing position P 2  to the pressing position P 1 , the pressing part  346  is moved in the first direction W 1  so as to press the shutter to-be-pressed part  386  of the shutter unit  380 . The pressing inclined surface  386   a  of the shutter to-be-pressed part  386  converts the movement of the pressing part  346  in the first direction W 1  into the movement of the shutter unit  380  in the second direction W 2 . 
     While the shutter unit  380  is moved from the closing position S 2  to the opening position S 1 , the light radiated to the optical window  1036  is transmitted to the photoreceptor  1052 , and thus the electrostatic latent image may be formed. 
     The pressing unit  320  may be directly moved from the releasing position P 2  to the pressing position P 1 , or the pressing unit  320  may be operated by the cover unit  370 , similar to the embodiment of the disclosure. 
     When the cover unit  370  is installed at one side of the developing device  1040 , the cover body of the cover unit  370  presses the pressing unit  320  so that the pressing unit  320  is moved from the releasing position P 2  to the pressing position P 1 . Through such a structure, the cover unit  370  is installed at the developing device  1040  so that the developing device  1040  is in an available state, and also the optical window  1036  is opened so that the light may be radiated. 
     Then, an operation in which the shutter unit  380  is closed will be described. 
     When the pressing unit  320  is moved from the pressing position P 1  to the releasing position P 2 , the pressing of the pressing part  346  of the pressing unit  320  with respect to the shutter unit  380  is released. When the pressing of the pressing unit  320  is released, the returning elastic member  387  of the shutter unit  380  returns the shutter unit  380  from the opening position S 1  to the closing position S 2 . 
     In the case in which the pressing unit  320  is directly moved from the releasing position P 2  to the pressing position P 1 , when the pressing with respect to the pressing unit  320  is released, the pressing unit  320  is moved from the pressing position P 1  to the releasing position P 2  by the elastic force of the pressing elastic member  348 . 
     Similar to an embodiment of the disclosure, in the case in which the pressing unit  320  is pressed by the cover unit  370 , when the cover unit  370  is separated from the developing device  1040 , the restriction on the pressing unit  320  by the cover unit  370  is released, and the pressing unit  320  is moved from the pressing position P 1  to the releasing position P 2  by the elastic force of the pressing elastic member  348 . 
     Hereinafter, an image forming apparatus in accordance with an embodiment of the disclosure will be described. 
       FIG. 23  is a view illustrating a developing device and a cover unit in accordance with an embodiment of the disclosure,  FIGS. 24A and 24B  are views illustrating an operation of a pressing assembly and the developing device in accordance with an embodiment of the disclosure,  FIGS. 25A and 25B  are cross-sectional views illustrating a pressing unit depending on the operation of the pressing assembly in accordance with an embodiment of the disclosure, and  FIG. 26  is an exploded perspective view of the pressing assembly in accordance with an embodiment of the disclosure. 
     A pressing assembly  100  may be disposed adjacent to the developing device  1040 , such that the developing unit  1041  and the photoreceptor unit  1050  come into contact with or are separated from each other. Specifically, the pressing assembly  100  is provided so that the developing roller  1042  of the developing unit  1041  and the photoreceptor  1052  of the photoreceptor unit  1050  come into contact with or are separated from each other. An arrangement of the pressing assembly  100  is not limited. However, in an embodiment, the pressing assembly  100  is disposed at the developing device seating part  1005 . 
     The pressing assembly  400  may include a rotating shaft  410 , a pressing unit  420 , and an operating unit  450 . 
     The rotating shaft  410  may be rotatably provided so that an operation of the operating unit  450  is transmitted to the pressing unit  420 . Assuming that a lengthwise direction of the developing device  1040 , the developing unit  1041  and the photoreceptor unit  1050  is a first direction W 1 , the rotating shaft  410  may be formed to be elongated in the first direction W 1 . The first direction W 1  may be defined as a direction vertical to a moving direction of the print medium. The rotating shaft  410  may serve as a rotating center of the operating unit  450 , which will be described below. 
     The rotating shaft  410  may be disposed in the first direction W 1  and may be provided so that a movement thereof in the first direction W 1  is restricted. The rotating shaft  410  may be provided to be rotated about a rotating axis. At least one shaft stopper may be provided at an outer circumferential surface of the rotating shaft  410  (in a manner similar to shaft stopper  211 ) so that a movement of the rotating shaft  410  in the first direction W 1  is restricted. 
     The pressing unit  420  is provided so that the developing roller  1042  and the photoreceptor  1052  come into close contact with each other. Specifically, the pressing unit  420  is provided to press the developing unit  1041 , such that the developing roller  1042  and the photoreceptor  1052  come into contact with or in close contact with each other. The pressing unit  420  may be disposed on the rotating shaft  410 , and may be provided so as to receive an operation of the operating unit  450  through the rotating shaft  410  and thus to be operated thereby. 
     The pressing unit  420  may be provided to be interlocked with the operating unit  450 . At least one pressing unit  420  may be provided. Through such a structure, at least one pressing unit  420  is provided to be interlocked with operating unit  450  and thus to be operated. In the case in which a plurality of pressing units  420  are provided, the plurality of pressing units  420  may be disposed on the rotating shaft  410  to be spaced from each other. As an example, the plurality of pressing units  420  may be disposed on the rotating shaft  410  to be spaced at regular intervals from each other, such that the same pressing force is distributed in the first direction W 1 , and thus the developing unit  1041  is pressed by an uniform pressing force, regardless of a position in a lengthwise direction thereof. 
     The pressing unit  420  may be provided to be moved between a pressing position P 1  in which the developing roller  1042  and the photoreceptor  1052  come into contact with each other, and a releasing position P 2  which is moved backed from the pressing position P 1  so that the developing roller  1042  and the photoreceptor  1052  are separated from each other. Specifically, when the pressing unit  420  is at the pressing position P 1 , the developing unit  1041  is pressed by the pressing unit  420 , and thus the developing roller  1042  and the photoreceptor  1052  come into contact with each other. Also, when the pressing unit  420  is at the releasing position P 2 , the pressing of the pressing unit  420  with respect to the developing unit  1041  is released, and thus the developing roller  1042  and the photoreceptor  1052  are separated from each other. 
     The operating unit  450  may be rotatably provided so that the pressing unit  420  is operated by the operation of the operating unit  450 . That is, at least one pressing unit  420  may be provided to be interlocked with the operating unit  450 . 
     The operating unit  450  may include an operating body  453  which is connected with the rotating shaft  410  so as to be rotated about the rotating shaft  410 . 
     The operating unit  450  may be provided to be movable between an operating position  01  in which a pressing force is generated from the pressing unit  420  and a stand-by position  02  in which the pressing force is released. 
     When the operating unit  450  is at the operating position  01 , the pressing unit  420  presses the developing unit  1041 , and when the operating unit  450  is at the stand-by position  02 , the pressing of the pressing unit  420  with respect to the developing unit  1041  is released. 
     The pressing unit  420  may include a pressing part  440  and a direction control part  430 . 
     The pressing part  440  may be provided to generate a pressing force, and the direction control part  430  may be provided to change a direction of the pressing force of the pressing part  440 . 
     The pressing part  440  may include a pressing body  442  and a pressing elastic member  446 . 
     The pressing body  442  may be provided to press the developing unit  1041 . The pressing body  442  may be disposed perpendicular to a lengthwise direction of the rotating shaft  410 . A pressing surface  442   a  is provided at a front portion of the pressing body  442 . The pressing surface  442   a  may be provided to come into direct contact with the developing unit  1041  and thus to press the developing unit  1041 . 
     The pressing body  442  may be provided so that the rotating shaft  410  passes through one side thereof. Specifically, the pressing body  442  has a through-hole  442   b  through which the rotating shaft  410  passes, and is provided to be rotated separately from the rotating shaft  410 . 
     The pressing elastic member  446  is provided to provide an elastic force to the pressing body  442  and thus to press the developing unit  1041 . One end of the pressing elastic member  446  supports an inner side surface of the pressing body  442 , and the other end thereof supports the rotating shaft  410  in a direction perpendicular to the lengthwise direction of the rotating shaft  410 . 
     Both side surfaces of the pressing body  442  are opened, and the pressing body  442  is provided to be moved in the direction perpendicular to the lengthwise direction of the rotating shaft  410 . Specifically, a pressing space  443  in which the pressing elastic member  446  is disposed and an available space  444  which is varied according to an extension and compression of the pressing elastic member  446  are formed at an inner side of the pressing body  442 . That is, when the pressing elastic member  446  is compressed, the pressing space  443  is reduced, and the available space  444  is increased, and when the pressing elastic member  446  is restored, the pressing space  443  is increased, and the available space  444  is reduced. 
     The direction control part  430  is provided to control a direction of the pressing part  440  depending on a rotation of the rotating shaft  410 . 
     The direction control part  430  is formed to extend perpendicular to an axial direction from the rotating shaft  410  and also to be rotated along with the rotation of the rotating shaft  410 . The direction control part  430  may be integrally formed with the rotating shaft  410 , or may be formed to be vertically inserted into the rotating shaft  410 . 
     The direction control part  430  may include a direction guide part  448  guiding a direction of the pressing part  440 . 
     The direction guide part  448  serves as a medium between the pressing body  442  and the direction control part  430 . A change of a position of the direction control part  430  is transmitted to the pressing body  442  so as to change the direction of the pressing force of the pressing body  442 . 
     The direction guide part  448  is provided to cover at least a part of the pressing body  442 . The direction guide part  448  may include a direction guide surface  448   a  of which a direction is guided by the direction control part  430 . One pair of direction guide surfaces  448   a  may be provided in a circumferential direction of the rotating shaft  410  with respect to the direction control part  430 . An insertion space  448   b  in which the direction control part  430  is inserted is formed between the one pair of direction guide surfaces  448   a . Through such a structure, when the direction control part  430  is rotated by the rotation of the rotating shaft  410 , one of the pair of direction guide surfaces  448   a  is guided, and the pressing part  440  may be rotated also. 
     The operating unit  450  may include a rotating body  451 , and an operating member  452  which operates the rotating body  451 . 
     The rotating body  451  is provided to be rotated along with the rotating shaft  410 , and the operating member  452  is provided to be rotatable with respect to the rotating shaft  410  and thus to rotate the rotating body  451 . 
     The rotating body  451  may be provided at an end of the rotating shaft  410  to be rotated along with the rotating shaft  410 . The rotating body  451  may be provided to protrude perpendicular to the axial direction of the rotating shaft  410 . A fastening member  451   a  may be provided at the rotating body  451  so that the rotating body  451  and the rotating shaft  410  are rotated together. 
     The operating member  452  may be provided to rotate the rotating body  451 . 
     The operating member  452  may include the operating body  453 , a unit pressing part  454 , and a rotation guide part  456 . 
     The operating body  453  is disposed perpendicular to the rotating shaft  410  and adjacent to the rotating body  451 . The operating body  453  may be integrally formed with the rotating shaft  410  to be rotated along with the rotation of the rotating shaft  410 . However, in an embodiment, the operating body  453  may be provided to guide the rotation of the rotating body  451 , such that the rotating shaft  410  integrally formed with the rotating body  451  is also rotated together. That is, the operating body  453  may be rotated separately from the rotating shaft  410 , and may have a hole through which the rotating shaft  410  passes. 
     In regard to a cover unit  470  which will be described below, the operating body  453  may be provided so that whether or not the cover unit  470  may be installed is determined according to a pressed state of the developing unit  1041 . 
     The unit pressing part  454  may be provided on the operating body  453  so as to press the photoreceptor unit  1050 . Specifically, the unit pressing part  454  may be disposed at an end of the operating body  453 , and when the operating unit  450  is at the operating position  01 , the unit pressing part  454  presses the photoreceptor unit  1050 . The unit pressing part  454  may be is formed to protrude more than the adjacent operating body  453 , and a unit to-be-pressed part  1058  which is formed to be concave corresponding to the pressing part  440  is disposed at the photoreceptor unit  1050 . By seating the unit pressing part  454  on the unit to-be-pressed part  1058 , the photoreceptor unit  1050  is prevented from being separated in the separating direction W 1   b.    
     The rotation guide part  456  may be disposed at the operating body  453  in a direction of the rotating center thereof so as to guide the rotation of the rotating body  451 . The rotation guide part  456  and the rotating body  451  are spaced apart a predetermined distance, and when the operating body  453  is rotated at a predetermined angle, the rotation guide part  456  and the rotating body  451  come into contact with each other, and thus the rotating force is transmitted. Therefore, an actual rotating angle of the rotating body  451  is greater than a rotating angle of the operating body  453 . As the rotating angle of the operating body  453  is increased, a risk of malfunction in a structure which is interlocked with whether or not the cover unit  470  may be installed is reduced. The distance between the rotation guide part  456  and the rotating body  451  is not limited, and may be varied according to various factors such as a size of the image forming apparatus and an arrangement of the developing device  1040 . 
     The rotation guide part  456  may include an operating rotation guide part  456   a  and a stand-by rotation guide part  456   b.    
     When the operating unit  450  is moved from the stand-by position  02  to the operating position  01 , the operating rotation guide part  456   a  presses the rotating body  451 , and thus the pressing unit  420  is moved to the pressing position P 1 . Contrarily, when the operating unit  450  is moved from the operating position  01  to the stand-by position  02 , the stand-by rotation guide part  456   b  presses reversely the rotating body  451 , and thus the pressing unit  420  is moved to the releasing position P 2 . One pair of the operating rotation guide part  456   a  and the stand-by rotation guide part  456   b  may be provided within a rotational radius of the rotating body  451  on the operating body  453 . 
     The cover unit  470  may be detachably provided at one side of the developing device  1040 . Whether or not the cover unit  470  may be installed may be determined according to a position of the operating unit  450 . Specifically, the cover unit  470  may be installed only when the operating unit  450  is at the operating position  01 . 
     The cover unit  470  may include a cover body  472  and an operating insertion part  474 . 
     The cover body  472  may be provided to cover one side of the developing device  1040 , and may be provided to be connected with the developing device  1040  and thus to store waste toner generated from the developing device  1040 . 
     The operating insertion part  474  may be formed to be concave from the cover body  372  so that the operating body  453  of the operating unit  450  is inserted therein. The operating body  453  may be inserted into the operating insertion part  474 , only when the operating unit  450  is at the operating position  01 . That is, only when the operating unit  450  is at the operating position  01 , and the pressing unit  420  is at the pressing position P 1 , the operating body  453  may be inserted into the operating insertion part  474 . The operating insertion part  474  is provided to correspond to the operating body  453 , such that the operating body  453  is inserted therein, only when the operating unit  450  is at the operating position  01 . 
     The operating insertion part  474  may be more concave than the adjacent cover body  472 . When the operating unit  450  is at another position other than the operating position  01 , the cover body  372  interferes with the operating body  453 , and the cover unit  470  may not be installed at the developing device  1040 . 
     Hereinafter, an operation of the image forming apparatus in accordance with an embodiment of the disclosure will be described. 
       FIGS. 27A and 27B  are views illustrating the developing device of the cover unit depending on the operation of the pressing assembly in accordance with an embodiment of the disclosure. 
     To perform a printing operation after the developing device  1040  is seated on the developing device seating part  1005 , the developing unit  1041  and the photoreceptor unit  1050  should come into close contact with each other so that the developing roller  1042  and the photoreceptor  1053  come into contact with each other. 
     The pressing assembly  400  is operated so that the developing unit  1041  and the photoreceptor unit  1050  should come into close contact with each other. 
     In the initial stage, the operating unit  450  is at the stand-by position  02 , and when the developing device  1040  is seated on the developing device seating part  1005 , the operating unit  450  is rotated so that the pressing unit  420  presses the developing unit  1041 . 
     The operating body  453  is rotated so as to rotate the operating unit  450  from the stand-by position  02  to the operating position  01 . Due to the rotation of the operating body  453 , the operating rotation guide part  456   a  of the rotation guide part  456  of the operating body  453  presses the rotating body  451 , and thus the rotating body  451  and the rotating shaft  410  are rotated. The rotating shaft  410  is rotated along with the direction control part  430  of the pressing unit  420 . Through such an operation, the direction of the pressing force generated from the pressing part  440  is controlled, and the developing unit  1041  is pressed. That is, the pressing unit  420  is moved to the pressing position P 1 . 
     When the operating unit  450  is at the operating position  01 , the unit pressing part  454  of the operating body  453  is seated on the unit to-be-pressed part  1058  of the photoreceptor unit  1050  to prevent the photoreceptor unit  1050  from being separated. When the operating unit  450  is at the operating position  01 , the operating body  453  may be inserted into the operating insertion part  474  of the cover unit  470 , and thus the cover unit  470  may be installed at the developing device  1040 . 
     To rotate the operating unit  450  from the operating position  01  to the stand-by position  02 , the operating body  453  is rotated reversely. Due to the rotation of the operating body  453 , the stand-by rotation guide part  456   b  of the rotation guide part  456  of the operating body  453  presses reversely the rotating body  451 , and thus the rotating body  451  and the rotating shaft  410  are rotated. The rotating shaft  410  is rotated along with the direction control part  430  of the pressing unit  420 . Through such an operation, the direction of the pressing force generated from the pressing part  440  is controlled, and the pressing to the developing unit  1041  is released. That is, the pressing unit  420  is moved to the releasing position P 2 . 
     When the operating unit is at the stand-by position  02 , the unit pressing part  454  of the operating body  453  is separated from the to-be-pressed surface  1056  of the photoreceptor unit  1050 , and the developing device  1040  is in a state to be separable from the developing device seating part  1005 . When the operating unit is at the stand-by position  02 , the cover body  472  interferes with the operating body  453 , and thus the cover unit  470  may not be installed at the developing device  1040 . Therefore, the image forming apparatus is operated, even though the developing roller  1042  and the photoreceptor  1052  are separated, and thus the malfunction or damage of the image forming apparatus may be prevented. That is, whether the image forming apparatus may be operated may be determined by whether or not the cover unit  470  may be installed, and thus the malfunction or the damage may be prevented beforehand. 
     According to the image forming apparatus of the disclosure, the fixing structure of the developing unit is improved, and thus the developing unit may be effectively installed in the main body. 
     Also, the pressing structure of the developing unit is improved, and thus a defective image may be prevented from being formed even when the external impact is applied. 
     Although example embodiments of the disclosure have been shown and described, it would be appreciated by those skilled in the art that changes may be made to these embodiments without departing from the principles and spirit of the disclosure, the scope of which is defined in the claims and their equivalents. 
     Also, each embodiment may be applied complementarily. For example, the operating unit of the image forming apparatus in accordance with any embodiment of the disclosure may be applied to that in accordance with any other embodiment of the disclosure, and the shutter unit of the image forming apparatus in accordance with any embodiment of the disclosure may be applied to that in accordance with any other embodiment of the disclosure.