Patent Publication Number: US-9405267-B2

Title: Developing apparatus having pushing unit and image forming apparatus having the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority under 35 U.S.C. §119(a) to Korean Patent Application No. 10-2013-0085179, filed Jul. 19, 2013, in the Korean Intellectual Property Office, the content of which is incorporated herein in its entirety by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present general inventive concept generally relates to a developing apparatus that includes a developing unit and a photosensitive unit. More particularly, the present general inventive concept relates to a developing apparatus that includes a pushing unit that can allow a developing member of a developing unit to be in contact with or to be spaced apart from an image carrier of a photosensitive unit, and an image forming apparatus having the same. 
     2. Description of the Related Art 
     Generally, since the lifetime of a photosensitive drum is shorter than the lifetime of a developing roller, if a photosensitive unit that includes a photosensitive drum and a developing unit that includes a developing roller are configured as a single unit, the developing unit, which has a longer life, may be discarded along with the photosensitive unit, which is wasteful. Also, in recent years, in order to reduce the size of an image forming apparatus, there has been a trend to use a structure in which the developing unit and the photosensitive unit can be separated from each other. 
     In a case in which the developing unit and the photosensitive unit can be separated from each other, there is a need for a structure that allows the developing roller of the developing unit to be selectively spaced apart from the photosensitive drum of the photosensitive unit. 
       FIGS. 1 and 2  illustrate a conventional developing apparatus  1 .  FIG. 1  illustrates a state in which a developing unit  2  is spaced apart from a photosensitive unit  3 , and  FIG. 2  illustrates a state in which the developing unit  2  is in contact with the photosensitive unit  3 . 
     The developing unit  2  includes a developing housing  2 - 1  and a developing roller  4  disposed in an upper portion of the developing housing  2 - 1 . The photosensitive unit  3  includes a photosensitive housing  3 - 1  and a photosensitive drum  5  disposed in an upper portion of the photosensitive housing  3 - 1 . The developing unit  2  and the photosensitive unit  3  are connected by a hinge  9 . Accordingly, the developing unit  2  and the photosensitive unit  3  can be rotated a predetermined angle on a shaft of the hinge  9 . 
     A pushing lever  6  is disposed to be rotated a predetermined angle below the photosensitive unit  3 , and a pressed portion  7 , to be pressed by a front end of the pushing lever  6 , is provided on a lower portion of the developing unit  2 . 
     Accordingly, if the front end of the pushing lever  6  of the photosensitive unit  3  is inserted into the pressed portion  7  of the developing unit  2  by rotating the pushing lever  6 , as illustrated in  FIG. 1 , a predetermined angle in a clockwise direction, the lower portion of the developing unit  2  receives a force in the left direction so that the developing unit  2  is rotated in the clockwise direction on the shaft of the hinge  9 . Then, as illustrated in  FIG. 2 , the developing roller  4  of the developing unit  2  is in contact with the photosensitive drum  5  of the photosensitive unit  3  so that the developing unit  2  and the photosensitive unit  3  are in a state in which they are in contact. When the pushing lever  6  is rotated a predetermined angle in the counterclockwise direction from this state, the front end of the pushing lever  6  is removed from the pressed portion  7  so that the developing unit  2  is rotated in the counterclockwise direction on the shaft of the hinge  9 . Then, the developing roller  4  of the developing unit  2  is spaced apart from the photosensitive drum  5  of the photosensitive unit  3  so that the developing unit  2  and the photosensitive unit  3  are in a state in which they are spaced apart. 
     As illustrated in  FIGS. 1 and 2 , the structure, in which the developing unit  2  is rotated a predetermined angle by using the pushing lever  6  so that the developing unit  2  is in contact with or spaced apart from the photosensitive unit  3 , cannot operate smoothly because the operation of the pushing lever  6  to push the developing unit  2  depends on the mechanical configuration of the pushing lever  6  and the pressed portion  7  and because the direction of the force to rotate the pushing lever  6  is not matched with the direction of the force to push the developing unit  2 . Specifically, a substantial amount of force is needed at the time when the pushing lever  6  goes over a projection  7   a  of the pressed portion  7 . 
     Accordingly, there is a need for a developing apparatus that has a pushing structure that can smoothly push a developing unit, slowly increase force, and match a pushing direction of the developing unit with a pushing direction of a pushing lever. 
     SUMMARY OF THE INVENTION 
     The present general inventive concept has been developed in order to overcome the above drawbacks and other problems associated with the conventional arrangement. The present general inventive concept provides a developing apparatus and an image forming apparatus that have a pushing structure that is formed in a slider-crank structure to convert rotational movement into linear movement, thereby gradually pushing a developing unit in a smooth operation. 
     Additional features and utilities of the present general inventive concept will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the general inventive concept. 
     The foregoing and/or other features and utilities of the present general inventive concept may be achieved by providing a developing apparatus that includes a developing unit having a developing member, a photosensitive unit hinge-connected to the developing unit and having an image carrier, and a pushing unit disposed below the photosensitive unit and configured to selectively push a lower portion of the developing unit, wherein the pushing unit may include a pushing member disposed to move linearly in a base and having an end configured to be in contact with the lower portion of the developing unit, a link member having a first end connected to the pushing member, a crank arm rotatably connected to a second end of the link member, an elastic member disposed on the link member and that elastically supports the pushing member. and a rotation shaft rotatably disposed in the base and connected to the crank arm. 
     The pushing member may include a pair of long grooves formed in a direction parallel to a moving direction of the pushing member, and the link member may include a guide projection formed at the first end of the link member, inserted in the pair of long grooves, and configured to move inside the pair of long grooves. 
     The pushing unit may further include an operating lever disposed at an end of the rotation shaft and configured to be rotated integrally with the rotation shaft and the crank arm. 
     When the operating lever is rotated in a direction, the elastic member may push the pushing member so that the developing unit is rotated by a certain angle, and when the operating lever is rotated in an opposite direction, a force with which the elastic member pushes the pushing member may be removed so that the developing unit returns to an original state. 
     An amount of compression of the elastic member may be configured to change according to an amount of rotation of the crank arm. 
     When the link member and the crank arm form a straight line, the elastic member may be compressed to a maximum. 
     The base may include a first stopper configured to limit a rotational movement of the crank arm. 
     When the crank arm is in contact with the first stopper, the pushing member may press the developing unit with an elastic force of the elastic member so that the developing member is in contact with the image carrier. 
     When the crank arm is in contact with the first stopper, a moving direction of the pushing member may be the same as a direction of the elastic force of the elastic member. 
     The base may include a pair of guide rails to guide a linear movement of the pushing member. 
     The base may further include a second stopper disposed at an end of at least one of the pair of guide rails and configured to limit the linear movement of the pushing member. 
     The lower portion of the developing unit and the pushing member may be formed to be in surface contact with each other. 
     The lower portion of the developing unit and the pushing member may be formed to be in point contact with each other. 
     When the pushing member pushes the developing unit, the developing member may be in contact with the image carrier of the photosensitive unit, and when the pushing unit does not push the developing unit, the developing member may be spaced apart from the image carrier. 
     The foregoing and/or other features and utilities of the present inventive concept also provide an image forming apparatus that may include a main body of the image forming apparatus, a paper feeding unit disposed inside the main body, an image forming unit having at least one developing apparatus and configured to transfer an image onto a print medium supplied from the paper feeding unit, and a fixing unit configured to fix the image transferred onto the print medium, wherein the at least one developing apparatus may include a developing unit having a developing member, a photosensitive unit hinge-connected to the developing unit and having an image carrier, and a pushing unit disposed below the photosensitive unit and configured to selectively push a lower portion of the developing unit, wherein the pushing unit may include a pushing member disposed to move linearly in a base and having an end configured to be in contact with the lower portion of the developing unit, a link member having a first end connected to the pushing member, a crank arm rotatably connected to a second end of the link member, an elastic member disposed on the link member and that elastically supports the pushing member, and a rotation shaft rotatably disposed in the base and connected to the crank arm. 
     The foregoing and/or other features and utilities of the present inventive concept also provide a pushing unit that includes a pushing member configured to move linearly in a first direction to cause a developing unit of a developing apparatus to rotate about a hinge to contact a photosensitive unit of the developing apparatus, a cam configured to rotate, and a link member coupled between the pushing member and the cam and configured to convert a rotation motion of the cam into a linear motion of the pushing member. 
     The pushing unit may further include an elastic member coupled between the pushing member and the cam and configured to apply a force to the pushing member to cause the linear motion of the pushing member in the first direction. 
     An amount of the force may be a function of an angle of rotation of the cam. The amount may be a maximum amount when the cam and the link member form a substantially straight line. When the amount is the maximum amount, the force applied to the pushing member may be entirely from the elastic member rather than from the cam and the link member. 
     The pushing unit may further include a first stopper configured to limit the linear motion of the pushing member in a second direction, the second direction opposite the first direction. When the pushing member is in contact with the first stopper, the developing unit may be configured to be spaced apart from the photosensitive unit, and the angle of rotation of the cam may be at an original angle. 
     The pushing unit may further include a second stopper configured to limit the rotation motion of the cam to limit the linear motion of the pushing member in the first direction. The angle of rotation of the cam, with respect to the original angle, when the cam is in contact with the second stopper may be greater than the angle of rotation of the cam, with respect to the original angle, when the cam and the link member form the substantially straight line. 
     Other objects, advantages and salient features of the present general inventive concept are apparent from the detailed description below taken in conjunction with the annexed drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other features and utilities of the present general inventive concept will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  illustrates a conventional developing apparatus in a state in which a developing roller is spaced apart from a photosensitive drum; 
         FIG. 2  illustrates the conventional developing apparatus of  FIG. 1  in a state in which the developing roller is in contact with the photosensitive drum; 
         FIG. 3  illustrates a developing apparatus that has a pushing unit according to an embodiment of the present inventive concept; 
         FIG. 4  is a partial perspective view that illustrates a state in which a pushing member of a pushing unit, according to an embodiment of the present inventive concept, does not push a developing unit; 
         FIG. 5  is a partial sectional view that illustrates a state in which a pushing member of a pushing unit, according to an embodiment of the present inventive concept, does not push a developing unit; 
         FIG. 6  is a partial perspective view that illustrates a state in which a pushing member of a pushing unit, according to an embodiment of the present inventive concept, pushes a developing unit; 
         FIG. 7  is a partial sectional view that illustrates a state in which a pushing member of a pushing unit, according to an embodiment of the present inventive concept, pushes a developing unit; 
         FIG. 8  is a partial perspective view that illustrates a state in which a pushing member is separated from a pushing unit, according to an embodiment of the present inventive concept; 
         FIG. 9  is a view that illustrates a developing apparatus when a pushing unit, according to an embodiment of the present inventive concept, pushes a developing unit; 
         FIG. 10  is a perspective view that illustrates a pushing unit according to an embodiment of the present inventive concept; and 
         FIG. 11  is a view that schematically illustrates an image forming apparatus that includes a developing apparatus according to an embodiment of the present inventive concept. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Reference will now be made in detail to the embodiments of the present general inventive concept, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present general inventive concept while referring to the figures. 
     The matters defined herein, such as a detailed construction and elements thereof, are provided to assist in a comprehensive understanding of this description. Thus, it is apparent that exemplary embodiments may be carried out without those defined matters. Also, well-known functions or constructions are omitted to provide a clear and concise description of exemplary embodiments. Further, dimensions of various elements in the accompanying drawings may be arbitrarily increased or decreased to assist in a comprehensive understanding. 
       FIG. 3  illustrates a developing apparatus that has a pushing unit according to an embodiment of the present inventive concept.  FIG. 4  is a partial perspective view that illustrates a state in which a pushing member of a pushing unit, according to an embodiment of the present inventive concept, does not push a developing unit.  FIG. 5  is a partial sectional view that illustrates a state in which a pushing member of a pushing unit, according to an embodiment of the present inventive concept, does not push a developing unit.  FIG. 6  is a partial perspective view that illustrates a state in which a pushing member of a pushing unit, according to an embodiment of the present inventive concept, pushes a developing unit.  FIG. 7  is a partial sectional view that illustrates a state in which a pushing member of a pushing unit, according to an embodiment of the present inventive concept, pushes a developing unit. 
     Referring to  FIG. 3 , a developing apparatus  10 , according to an embodiment of the present inventive concept, may include a photosensitive unit  30 , a developing unit  20 , and a pushing unit  40 . 
     The photosensitive unit  30  may include a photosensitive housing  31  and an image carrier  32 . The image carrier  32  may be rotatably disposed in the photosensitive housing  31 . An electrostatic latent image may be formed on a surface of the image carrier  32  by an exposure unit  150  (see  FIG. 11 ). A photosensitive drum, for example, may be used as the image carrier  32 . Also, the photosensitive unit  30  may be disposed to be able to be separated from the developing unit  20  and the pushing unit  40 . 
     The developing unit  20  may be disposed to rotate on a hinge shaft  25  with respect to the photosensitive unit  30 , and may include a developing housing  21  and a developing member  22 . The developing housing  21  may be disposed to rotate on the hinge shaft  25 . The developing member  22  may be rotatably disposed in an upper portion of the developing housing  21 . A pressed portion  23 , which may be subjected to a force by the pushing unit  40 , may be provided on a lower portion of the developing housing  21 . The developing member  22  may supply the image carrier  32  with developer stored in the developing unit  20  so that the electrostatic latent image may be developed into a developer image. A developing roller, for example, may be used as the developing member  22 . 
     When the developing member  22  of the developing unit  20  is spaced apart from the image carrier  32  of the photosensitive unit  30 , the photosensitive unit  30  may be separated from the developing unit  20  and the pushing unit  40 . Accordingly, in a state in which the developing member  22  is spaced apart from the image carrier  32 , the photosensitive unit  30  that contains a depleted image carrier  32  may be replaced with a new photosensitive unit  30 . 
     The pushing unit  40  may be disposed below the photosensitive unit  30 , and may be formed to push selectively a lower portion of the developing unit  20 , namely, the pressed portion  23 . If the pushing unit  40  is formed, for example, to have a slider-crank structure and to contain an elastic member, then the pushing unit  40  may gradually and stably push the developing unit  20 . 
     Referring to  FIGS. 3, 4, and 5 , the pushing unit  40  may include a base  50 , a rotation shaft  60 , a crank arm  61 , a link member  65 , a pushing member  70 , an elastic member  80 , and an operating lever  69 . 
     The base  50  may be provided below the photosensitive unit  30 . The photosensitive unit  30  may be detachably disposed in the base  50 . The base  50  may be formed to support the rotational movement of the rotation shaft  60  and the linear movement of the pushing member  70 . The base  50  may have a length that corresponds to a width of the photosensitive unit  30  (the length of the base  50  may correspond to a length of the image carrier  32 ). 
     The rotation shaft  60  may be rotatably disposed in the base  50 . The rotation shaft  60  may project from a side surface of the base  50 . The operating lever  69  to rotate the rotation shaft  60  may be disposed at a projecting end of the rotation shaft  60 . As the operating lever  69  is rotated, the rotation shaft  60  may be rotated integrally with the operating lever  69 . 
     The crank arm  61  may be disposed in the rotation shaft  60 . The crank arm  61  may be fixed to the rotation shaft  60  so that, as the rotation shaft  60  is rotated, the crank arm  61  may be rotated integrally with the rotation shaft  60 . The crank arm  61  may be rotated by the same angle as the operating lever  69  to rotate the rotation shaft  60 . Accordingly, if the operating lever  69  is rotated a certain angle, then the crank arm  61  may also be rotated by the same angle in the same direction as the operating lever  69 . 
     The crank arm  61  may be formed, for example, so that the rotation thereof is limited by an upper wall  55  of the base  50 . In an embodiment as illustrated in  FIG. 7 , when the crank arm  61  is rotated a certain angle in the clockwise direction, the upper wall  55  may interfere with one end of the crank arm  61  so that crank arm  61  may not be able to rotate further. In other words, the upper wall  55  of the base  50  may perform a function of a first stopper to limit an angle by which the crank arm  61  may be rotated in the clockwise direction. 
     Also, an angle up to which the crank arm  61  may be rotated in the counterclockwise direction may be limited in order to limit a moving distance of the pushing member  70 . For this purpose, the first stopper (not illustrated) may be disposed to limit the counterclockwise rotation of the crank arm  61 . However, the embodiment illustrated in  FIG. 7  may exclude the first stopper to directly limit the counterclockwise rotation of the crank arm  61 , but a second stopper  53  to directly limit the movement of the pushing member  70  may be disposed as is described below. 
     The link member  65  may be disposed between the crank arm  61  and the pushing member  70 . A first end of the link member  65  may be connected to the pushing member  70 , and a second end of the link member  65  may be connected to the one end of the crank arm  61 . The second end of the link member  65  may be rotatably connected to the one end of the crank arm  61 . In the embodiment illustrated in  FIG. 7 , the second end of the link member  65  and the one end of the crank arm  61  may be connected by a rotation pin  63  so that the link member  65  and the crank arm  61  may rotate freely with respect to each other. 
     A guide projection  67  that may be inserted into a long groove  71  of the pushing member  70  may be provided at the first end of the link member  65 . The guide projection  67  may be formed, for example, in a cylindrical shape. The link member  65  may serve to change the rotation of the crank arm  61  to the linear movement of the pushing member  70 . When the pushing member  70  pushes the developing unit  20 , the link member  65  may not apply force directly to the pushing member  70 , but may help the elastic member  80  to press the pushing member  70  in a predetermined direction. 
     The pushing member  70  may be in contact with the lower portion of the developing unit  20 , and then may directly push the developing unit  20  in one direction. The pushing member  70  may be disposed to move linearly in the base  50 . Accordingly, the base  50  may be provided with a pair of guide rails  51  to guide the pushing member  70 . 
     Referring to  FIG. 8 , the pushing member  70  may be formed, for example, in a substantially hollow rectangular shape, and each of opposite internal side surfaces of the pushing member  70  may be provided with the long groove  71 . The pair of long grooves  71  may be formed parallel to the moving direction of the pushing member  70  so that opposite ends of the guide projection  67  of the link member  65  may be inserted and moved in the pair of long grooves  71 . The length of the long groove  71  may be determined so that the rotational movement of the crank arm  61  may be changed to the linear movement of the pushing member  70  and the pushing member  70  may be moved a predetermined distance along the link member  65  by an elastic force of the elastic member  80 . The pushing member  70  may be moved toward the developing unit  20  by the elastic force of the elastic member  80  being applied to the pushing member  70 , and then the developing unit  20  may be rotated on the hinge shaft  25  (see  FIG. 3 ) by the movement of the pushing member  70 . 
     A pair of guide grooves  73  may be provided on opposite external side surfaces of the pushing member  70 . The pair of guide grooves  73  may be formed to be inserted in the pair of guide rails  51  provided on the base  50 . The pair of guide rails  51  provided on the base  50  may be formed, for example in a shape of rectangular bars to face each other. Accordingly, the pair of guide grooves  73  may be formed, for example, as rectangular grooves that correspond to the rectangular bars. When the pair of guide rails  51  of the base  50  is inserted in the pair of guide grooves  73  of the pushing member  70 , the pushing member  70  may be moved linearly along the pair of guide rails  51  of the base  50 . In addition, a pair of guide wings  74  may be disposed, for example, below the guide grooves  73  on the opposite side surfaces of the pushing member  70 . 
     The second stopper  53  to limit the movement of the pushing member  70  in one direction may be provided, for example, at an end of at least one of the pair of guide rails  51  of the base  50 . The second stopper  53  may limit a distance in which the pushing member  70  may be moved in a direction away from the developing unit  20 . As illustrated in  FIGS. 4 and 8 , the second stopper  53  may be provided, for example, at an end of the guide rail  51  of the base  50  in a direction perpendicular to the guide rail  51 . 
     The front end of the pushing member  70  may be in contact with the lower portion of the developing unit  20  by the elastic member  80 . In this case, the pressed portion  23  of the lower portion of the developing unit  20 , which is in contact with the pushing member  70 , may be formed, for example, in a flat surface. If the pressed portion  23  of the developing unit  20  is formed in a flat surface, the pushing member  70  may be in surface contact with the developing unit  20  since the front end of the pushing member  70 , according to the embodiment illustrated in  FIGS. 4 and 8 , may be formed in a flat surface. Alternatively, the pressed portion  23  of the developing unit  20  and the pushing member  70  may be configured to be in point contact with each other. In this case, the pressed portion  23  of the developing unit  20  or the front end of the pushing member  70  may be formed, for example, in a convex surface. 
     The elastic member  80  may be disposed with the link member  65 , and may elastically support the pushing member  70 . For example, the link member  65  may be inserted in the elastic member  80 , and may be disposed between the pushing member  70  and the crank arm  61  so that the elastic member  80  may apply a force to the pushing member  70 . In other words, a first end of the elastic member  80  may be supported by the one end of the crank arm  61 , and a second end of the elastic member  80  may be supported by a rear end of the pushing member  70 , specifically, a rear end of a long groove portion  72  in which the long groove  71  may be formed. Because the one end of the crank arm  61  and the rear end of the long groove portion  72  may be formed, for example, in a curve, when the link member  65  is rotated by the crank arm  61 , the elastic member  80  may not interfere with the link member  65 . 
     In a state in which the first end of the elastic member  80  is supported by the crank arm  61  and the elastic member  80  is guided by the link member  65 , the elastic member  80  may push the pushing member  70  toward the developing unit  20 . Accordingly, a coil spring, for example, may be used as the elastic member  80 . In this case, the elastic member  80  (e.g., coil spring) may have an elastic force to allow the pushing member  70  to push the pressed portion  23  of the developing unit  20  so that the developing unit  20  may be rotated on the hinge shaft  25 , and then the developing member  22  may be in contact with the image carrier  32  of the photosensitive unit  30 . In other words, the developing unit  20  may be able to be rotated by only the elastic force of the elastic member  80  (e.g., coil spring) so that the developing member  22  may be in contact with the image carrier  32 . 
     The force which may be applied to the pushing member  70  by the elastic member  80  may vary depending on the rotation of the crank arm  61 . As illustrated in  FIGS. 4 and 5 , when the end of the pushing member  70  is in contact with the second stopper  53 , the elastic member  80  may not receive the force. In this case, the elastic member  80  may be in an uncompressed state or in a minimally compressed state. Then, in  FIG. 5 , as the crank arm  61  is rotated in the clockwise direction, the elastic member  80  may receive the force from the crank arm  61 , thereby becoming compressed. When the link member  65  and the crank arm  61  become, for example, a straight line (namely, when the crank arm  61  is positioned at an inflection point), the elastic member  80  may be compressed to the maximum. After that, as the crank arm  61  is rotated over the inflection point, the force being applied to the elastic member  80  may be decreased. Accordingly, when a user rotates the operating lever  69 , the user may feel that the force being applied to the operating lever  69  may be increased gradually until the inflection point, and then may be reduced gradually after passing over the inflection point. 
     Also, because the pushing unit  40 , according to an embodiment of the present inventive concept as described above, may use, for example, a slider-crank mechanism, the pushing unit  40  may change the rotational movement to the linear movement in a small space and may be gradually pressed. 
     Below, operation of the developing apparatus  10 , according to an embodiment of the present inventive concept that includes the structure as described above, is described with reference to  FIGS. 3 to 9 . 
     First, a case in which the pushing unit  40  may push the developing unit  20  so that the developing member  22  of the developing unit  20  may be in contact with the image carrier  32  of the photosensitive unit  30  is described. 
     When the photosensitive unit  30  is installed in the base  50  of the pushing unit  40 , as illustrated in  FIG. 3 , the developing member  22  of the developing unit  20  may be spaced apart from the image carrier  32  of the photosensitive unit  30 . In this case, as the user rotates the operating lever  69  in one direction, the developing unit  20  may be rotated on the hinge shaft  25  so that the developing member  22  may be in contact with the image carrier  32 . In the developing apparatus  10 , as illustrated in  FIG. 3 , as the user rotates the operating lever  69  in the clockwise direction, the developing unit  20  may be rotated in the clockwise direction (arrow F) on the hinge shaft  25  so that the developing member  22  may be in contact with the image carrier  32  as illustrated in  FIG. 9 . 
     For example, as the user rotates the operating lever  69  in a direction (the direction of an arrow A in  FIG. 4 ), the crank arm  61 , integrally fixed to the rotation shaft  60 , may be rotated in the same direction (the direction of the arrow A in  FIG. 5 ). When the crank arm  61  is rotated in the direction of the arrow A, the link member  65 , connected to the one end of the crank arm  61 , may receive a force in an upward direction. Then, the guide projection  67  of the link member  65 , which may be inserted in the pair of long grooves  71  formed in the pushing member  70 , may be moved along the pair of long grooves  71  in a direction (the direction of an arrow C in  FIG. 5 ). In this case, the elastic member  80 , positioned between the pushing member  70  and the crank arm  61 , may be gradually compressed according to the rotation of the crank arm  61 . 
     When the crank arm  61  continues to be rotated in the direction of the arrow A so that the link member  65  and the crank arm  61  may form, for example, a straight line (when the link member  65  and the crank arm  61  may be matched with a straight line S as illustrated in  FIG. 5 ), namely, when the crank arm  61  comes to the inflection point, the elastic member  80 , in which the link member  65  may be inserted between pushing member  70  and the crank arm  61 , may be compressed to the maximum, thereby pressing the pushing member  70  in the direction of the arrow C. In this case, the link member  65  and the crank arm  61  may not apply force to the pushing member  70 , and only the elastic force of the elastic member  80  may press the pushing member  70 . 
     If the user continues to rotate the operating lever  69 , the upper wall  55  of the base  50  may interfere with the one end of the crank arm  61  so that the crank arm  61  may not be able to rotate further.  FIGS. 6 and 7  illustrate when the one end of the crank arm  61  is in contact with the upper wall  55  of the base  50 , namely, the first stopper (e.g., the upper wall  55 ) so that the crank arm  61  may no longer be rotated. In a state in which the crank arm  61  may be in contact with the first stopper (e.g., the upper wall  55 ), the elastic member  80  may press the pushing member  70 . Then, as the lower portion of the developing unit  20  is pushed by the pushing member  70 , the developing unit  20  may be rotated in a direction (the direction of an arrow F in  FIG. 3 ) on the hinge shaft  25  so that the developing member  22  and the image carrier  32  may be in contact with each other as illustrated in  FIG. 9 . 
     As described above, if the crank arm  61  is in contact with the first stopper (e.g., the upper wall  55 ) after passing over the inflection point, the crank arm  61  may be prevented from being rotated in the opposite direction by an external force and the developing unit  20  may be released from the compressed state. Accordingly, the elastic force of the elastic member  80  may be determined so that the pushing member  70 , which may be pressed by the elastic member  80  in the state in which the crank arm  61  is in contact with the first stopper (e.g., the upper wall  55 ), may rotate the developing unit  20 . 
     As described above, because the pushing unit  40 , according to an embodiment of the present inventive concept, may use a slider-crank mechanism that includes the crank arm  61 , the link member  65 , and the pushing member  70 , the direction in which the pushing member  70  may press the developing unit  20  may be matched with a direction in which the developing unit  20  should be compressed. Also, the pushing unit  40 , according to an embodiment of the present inventive concept, may be configured so that the force required to rotate the crank arm  61  may be gradually increased over an entire range in which the crank arm  61  may be rotated. Also, because as the operating lever  69  is rotated, the force may be gradually increased until passing over the inflection point, the user may feel a sense that the operating lever  69  may be locked without use of a separate locking member. 
     Below, a case in which the developing member  22  may be spaced apart from the image carrier  32  in a state in which the developing member  22  of the developing unit  20  may be in contact with the image carrier  32  of the photosensitive unit  30  as illustrated in  FIG. 9  is described. 
     In order to space the developing member  22  apart from the image carrier  32 , the user may rotate the operating lever  69  in the counterclockwise direction (in the direction of an arrow B in  FIG. 6 ). 
     As the operating lever  69  is rotated in the direction of the arrow B, the crank arm  61 , fixed to the rotation shaft  60 , may also be rotated in the same direction (the direction of the arrow B in  FIG. 7 ). As the crank arm  61  is rotated in the direction of the arrow B, the link member  65 , connected to the one end of the crank arm  61 , may receive a force in a downward direction. Then, the pushing member  70  may be moved in a direction (the direction of an arrow D in  FIG. 7 ) by the guide projection  67  inserted in the long groove  71  of the pushing member  70 . 
     When the crank arm  61  is rotated a predetermined angle, the rear end of the pushing member  70  may be in contact with the second stopper  53  provided on the base  50 . Then, the crank arm  61  also may not be rotated any more in the direction of the arrow B. 
     As the pushing member  70  is moved in the direction of the arrow D, the force applied to the lower portion of the developing unit  20 , namely, the force with which the elastic member  80  may press the pushing member  70 , may be removed so that the developing unit  20  may be rotated in the opposite direction (the direction of an arrow G in  FIG. 9 ), and then may return to the original state as illustrated in  FIG. 3 . As a result, the developing member  22  of the developing unit  20  may be spaced apart from the image carrier  32  of the photosensitive unit  30 . When the developing member  22  is spaced apart from the image carrier  32  as described above, the user may remove the photosensitive unit  30  from the developing unit  20 . 
     In the above description, a single crank arm  61  may be disposed in the rotation shaft  60 , and the link member  65  and the pushing member  70  may be connected to the crank arm  61  in order. However, this is only one example. As illustrated in  FIG. 10 , two crank arms  61  and  61 ′ may be disposed at a certain interval on the rotation shaft  60 . In the same way as described above, two link members  65  and  65 ′ and two pushing members  70  and  70 ′ may be connected to each of the two crank arms  61  and  61 ′ in order. Because the pushing unit  40  as illustrated in  FIG. 10  may push two points of the developing unit  20  (see  FIGS. 3 and 9 ), the pushing unit  40  illustrated in  FIG. 10  may separate the developing unit  20  more smoothly than the pushing unit  40  that has only one pushing member  70 . 
     Below, an image forming apparatus, which has a developing apparatus according to an embodiment of the present inventive concept and includes the structure as described above, is described. 
     Referring to  FIG. 11 , an image forming apparatus  100 , according to an embodiment of the present inventive concept, may include a main body  101 , a paper feeding unit  110 , an image forming unit  120 , a fixing unit  170 , a discharging roller  180 , and a controller  190 . 
     The main body  101  may form an outward appearance of the image forming apparatus  100 . The paper feeding unit  110 , the image forming unit  120 , the fixing unit  170 , the discharging roller  180 , and the controller  190  may be disposed inside the main body  101 . 
     The paper feeding unit  110  may accommodate a number of print media P, and may include a pickup roller  111  that may pick up the print media P one by one and may feed the print media P to the image forming unit  120 . A feeding roller  115  may be disposed in front of the pickup roller  111  in a direction in which the picked print media P is moved, and may feed the picked print media P to a transfer roller  175 . 
     The image forming unit  120  may form and may transfer predetermined images to the print media P. The image forming unit  120  may include the exposure unit  150 , a plurality of developing apparatuses  10 , a transfer belt unit  160 , and the transfer roller  175 . 
     The exposure unit  150  may form an electrostatic latent image on the image carrier  32  (see  FIGS. 3 and 9 ) of each of the plurality of developing apparatuses  10  by emitting light corresponding to received printing data. 
     The plurality of developing apparatuses  10  may form a developer image that corresponds to the printing data, and may include, for example, four developing apparatuses  10  to form color images. For example, the four developing apparatuses  10  may form yellow, magenta, cyan, and black developer images. 
     The transfer belt unit  160  may include an intermediate transfer belt  161 , a driving roller  162 , and a driven roller  163 . The developer images formed on the image carriers  32  (see  FIGS. 3 and 9 ) of the four developing apparatuses  10  may be transferred onto the intermediate transfer belt  161  in an overlapping manner. The intermediate transfer belt  161  may carry the transferred image to the transfer roller  175 . The driving roller  162  and the driven roller  163  may support the intermediate transfer belt  161  and may allow the intermediate transfer belt  161  to move along a caterpillar track. 
     The transfer roller  175  may be disposed at an end of the transfer belt unit  160 . The transfer roller  175  may allow the developer image formed on the intermediate transfer belt  161  to be transferred onto the print media P fed, from the paper feeding unit  110 , between the transfer roller  175  and the intermediate transfer belt  161 . 
     The fixing unit  170  may include a pressure roller  171  and a heat roller  172  that face each other and may apply pressure and heat to the print media P, thereby fixing the developer image transferred by the transfer roller  175  to the print media P. 
     The discharging roller  180  may be formed to discharge the print media P, onto which the image is fixed in the fixing unit  170 , outside the main body  101  of the image forming apparatus  100 . 
     The controller  190  may form images on the print media P that correspond to the received printing data by controlling the paper feeding unit  110 , the exposure unit  150 , the plurality of developing apparatuses  10 , the transfer belt unit  160 , the transfer roller  175 , the fixing unit  170 , the discharging roller  180 , etc. 
     Accordingly, in the image forming apparatus  100  that has the structure as described above, an image may be transferred on the print media P supplied from the paper feeding unit  110  by the transfer roller  175  of the image forming unit  120 , and the print media P with the transferred image may pass through the fixing unit  170  so that the image is fixed onto the print media P. After that, the print media P with the fixed image may be discharged to outside the main body  101  through the discharging roller  180 , thereby completing a printing operation. 
     After the user prints for a period of time by using the image forming apparatus  100  that has the structure as described above, the image carrier  32  (see  FIGS. 3 and 9 ) of the developing apparatus  10  may reach the end of its life. In this case, the user may rotate the operating lever  69  (see  FIGS. 4, 6, and 10 ) of the pushing unit  40  disposed in the main body  101  so that the developing member  22  of the developing unit  20  may be spaced apart from the image carrier  32  of the photosensitive unit  30  (see  FIGS. 3 and 9 ). After that, the user may remove the depleted photosensitive unit  30  from the main body  101 , and then may install a new photosensitive unit  30  in the main body  101 . 
     Since the developing apparatus  10 , according to an embodiment of the present inventive concept, may push the developing unit  20  by using the slider-crank mechanism and the elastic member  80  (see  FIGS. 3-9 ), when the user rotates the operating lever  69  in order to separate the developing unit  20  from the photosensitive unit  30 , force may be gradually increased while rotating the operating lever  69  so that the pushing operation is smooth and stable. 
     In the above description, the image forming apparatus  100  may include a plurality of developing apparatuses  10 . Alternatively, the image forming apparatus  100  may include only one developing apparatus  10 . The image forming apparatus  100  that has one developing apparatus  10  has a configuration similar to a conventional black-and-white image forming apparatus except for the structure and operation of the pushing unit  40 . Therefore, a detailed description thereof is omitted. 
     Although a few embodiments of the present general inventive concept have been shown and described, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the general inventive concept, the scope of which is defined in the appended claims and their equivalents.