Patent Publication Number: US-8977165-B2

Title: Multi-pass type image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Korean Patent Application No. 2011-0121792, filed on Nov. 21, 2011 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Embodiments of the present inventive concept relate to a multi-pass type image forming apparatus having an assembly to transmit power to an image-carrier and a developing unit through a coupling. 
     2. Description of the Related Art 
     Generally, image forming apparatuses are devised to form an image on a printing medium according to input signals. Examples of image forming apparatuses include printers, copiers, fax machines, and devices combining functions thereof. 
     One type of image forming apparatus is an electro-photographic image forming apparatus that includes an image-carrier, a light scanning unit, and a developing unit. The light scanning unit forms an electrostatic latent image on a surface of the image-carrier by irradiating light to the image-carrier that has been charged with a predetermined electric potential. The developing unit forms a visible image by supplying developer to the image-carrier on which the electrostatic latent image has been formed. 
     Commonly, yellow, magenta, cyan and black toners are used in the image forming apparatus, and thus four developing units may be necessary to attach the four colors of toners to the electrostatic latent image. 
     Image forming methods include a single-pass method in which each of four developing units includes an image-carrier, and a multi-pass method in which four developing units share a single image-carrier. 
     In the case of the multi-pass method, the four developing units are concentrically arranged about the image-carrier to share a single image-carrier. 
     A conventional multi-pass type image forming apparatus includes driving couplers to drive an image-carrier and four developing units, which are movable independently of one another and are adapted to be coupled to or separated from the image-carrier and the developing units. 
     The above-described configuration, however, may require devices to couple or separate the driving couplers to or from the image-carrier and developing units equal in number to the number of driving couplers. Therefore, the number of constituent elements is increased, causing higher manufacturing costs. Moreover, an expanded installation space may prevent reduction in the size of the image forming apparatus. 
     SUMMARY OF THE INVENTION 
     Therefore, the present inventive concept provides a multi-pass type image forming apparatus having an improved assembly to allow driving-couplings to be coupled to and separated from an image-carrier and developing units simultaneously. 
     The present inventive concept also provides a multi-pass type image forming apparatus having an improved configuration to reduce the size of the image forming apparatus. 
     Additional features and utilities of the present 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 inventive concept. 
     Exemplary embodiments of the present inventive concept provide an image forming apparatus including a main body, a cover to open or close one side of the main body, an image-carrier unit placed in the main body and including an image-carrier on which an image is formed and a first driven-coupling connected to a rotating shaft of the image-carrier, a plurality of developing units mounted in the main body to slidably move through one side of the main body opened by the cover, each of which includes a developing roller to feed developer to the image-carrier and a second driven-coupling connected to a rotating shaft of the developing roller, a first driving-coupling and a second driving-coupling located in a side region of the main body to transmit drive power generated from a drive source to the first driven-coupling and the second driven-coupling, a link unit to move in a first direction in linkage with opening/closing operations of the cover, and a guide unit to be rotatable about a rotating shaft of the first driving-coupling in linkage with the link unit, the guide unit being adapted to move in a second direction perpendicular to the first direction when rotated about the rotating shaft of the first driving-coupling so as to couple or separate the first driving-coupling and the second driving-coupling to or from the first driven-coupling and the second driven-coupling. 
     The second driven-coupling may be concentrically arranged about the first driven-coupling in a state in which the plurality of developing units is mounted in the main body. 
     The second driving-coupling may be concentrically arranged about the first driving-coupling. 
     The first driving-coupling and the second driving-coupling may be pressed by the guide unit and connected respectively to the first driven-coupling and the second driven-coupling as the cover closes one side of the main body, and may be no longer pressed by the guide unit and separated from the first driven-coupling and the second driven-coupling as the cover opens one side of the main body. 
     The guide unit may include a first through-hole formed in a rotation center thereof, and a second through-hole formed in a circumferential direction of a concentric circle defined by the second driving-coupling. 
     The first driving-coupling may be connected to the first driven-coupling via the first through-hole, and the second driving-coupling may be connected to the second driven-coupling via the second through-hole. 
     The guide unit may include a first support portion and a second support portion formed at one surface thereof, the first support portion being formed along the first through-hole to support the first driving-coupling, and the second support portion being formed along the second through-hole to support the second driving-coupling. 
     The first driving-coupling may include a first flange having a greater diameter than a diameter of the first through-hole so as to be supported by the first support portion. 
     The second driving-coupling may include a second flange having a greater diameter than a radial width of the second through-hole so as to be supported by the second support portion. 
     The image forming apparatus may further include a plurality of elastic members to press the first driving-coupling and the second driving-coupling toward the first driven-coupling and the second driven-coupling, so as to maintain contact between the first and second flanges and the first and second support portions. 
     The second direction may be an axial direction of the rotating shaft of the first driving-coupling. 
     The image forming apparatus may further include a guide cover provided at one side of the main body to receive the guide unit, and the guide cover may include at least one first guide protrusion to come into contact with one surface of the guide unit so as to guide movement of the guide unit in the second direction as the guide unit rotates about the rotating shaft of the first driving-coupling. 
     The guide unit may include at least one second protrusion to come into contact with the first guide protrusion so as to guide movement of the guide unit in the second direction. 
     The first guide protrusion may include a slope to guide movement of the second guide protrusion as the guide unit rotates about the rotating shaft of the first driving-coupling. 
     The slope may be inclined in a rotating direction of the guide unit. 
     The at least one first guide protrusion and the at least one second guide protrusion may be arranged in the rotating direction of the guide unit. 
     Exemplary embodiments of the present general inventive concept also provide an image forming apparatus including a main body, a cover to open or close one side of the main body, a plurality of rotators placed in the main body, a plurality of driven-couplings connected to rotating shafts of the rotators, a plurality of driving-couplings placed in a side region of the main body to transmit drive power generated from a drive source to the driven-couplings, a link unit to move in linkage with opening/closing operations of the cover, and a guide unit to be rotatable about one rotating shaft of the plurality of driving-couplings in linkage with the link unit, the guide unit being adapted to move toward the driven-couplings when rotated so as to cause the driving-couplings to be engaged with the driven-couplings, and to move away from the driven-couplings when rotated so as to cause the driving-couplings to be separated from the driven-couplings. 
     The guide unit may include a plurality of through-holes perforated therein to enable connection between the plurality of driving-couplings and the plurality of driven-couplings, and a plurality of support portions formed on peripheries of the through-holes to support the plurality of driving-couplings. 
     The image forming apparatus may further include a plurality of elastic members to press the driving-couplings toward the driven-couplings, so as to allow the driving-couplings to be supported by the support portions and be moved in a rotating shaft direction of the driving-couplings along with the guide unit. 
     The plurality of driven-couplings may include a first driven-coupling connected to a rotating shaft of an image-carrier on which an image is formed, and a plurality of second driven-couplings connected to a rotating shaft of a developing roller that feeds developer to the image-carrier, and the plurality of second driven-couplings may be concentrically arranged about the first driven-coupling. 
     The plurality of driving-couplings may include a first driving-coupling positioned to correspond to the first driven-coupling so as to be engaged with the first driven-coupling, and a plurality of second driving-couplings positioned to correspond to the second driven-couplings so as to be engaged with the second driven-couplings. 
     The guide unit may be movable in the rotating shaft direction of the first driving-coupling when rotated about the rotating shaft of the first driving-coupling. 
     The image forming apparatus may further include a guide cover provided at one side of the main body to receive the guide unit. 
     The guide cover may include a first guide portion formed at an inner surface thereof facing one surface of the guide unit, and the first guide portion may include a first guide protrusion having a first slope that is inclined in a rotating direction of the guide unit. 
     At least one second guide portion may be placed at one surface of the guide unit in the rotating direction of the guide unit to guide movement of the guide unit along with the first guide portion, and the second guide portion may include a second guide protrusion having a second slope that moves relative to the first slope in contact with the first slope as the guide unit is rotated. 
     The first guide portion may include a first receiving recess in which the second guide protrusion is received in a state in which the cover closes the main body, and the second guide portion may include a second receiving recess in which the first guide protrusion is received in a state in which the cover closes the main body. 
     One end of the first guide protrusion and one end of the second guide protrusion may come into contact with each other in a state in which the cover opens the main body. 
     The guide unit may move toward the driven-couplings as the cover closes the main body, so as to allow the driving-couplings to be engaged with the driven-couplings, and may move away from the driven-couplings as the cover opens the main body, so as to allow the driving-couplings to be separated from the driven-couplings. 
     Exemplary embodiments of the present general inventive concept also provide an image forming apparatus comprising: a main body; a cover to open and close one side of the main body; a first driven-coupling and second driven-couplings to drive an image carrier and developing rollers, respectively; a first driving-coupling and second driving-couplings to transmit a drive power generated from a drive source to the first driven-coupling and second driven-couplings, respectively; and a guide unit to be rotatable about a rotating shaft of the first driving-coupling and configured to move toward the driven-couplings when rotated in a first direction so as to cause the driving-couplings to be engaged with the driven-couplings, and to move away from the driven-couplings when rotated in a second direction so as to cause the driving-couplings to be separated from the driven-couplings. 
     In an exemplary embodiment, the image forming apparatus also includes a link unit to move in linkage with opening/closing operations of an access cover of the main body such that the guide unit rotates with the movement of the link unit. 
     In an exemplary embodiment, the guide unit moves about the rotating shaft of the first driving-coupling and in a direction perpendicular to the movement of the link unit to perform the coupling and decoupling of the driving-couplings and driven-couplings. 
     In another exemplary embodiment, the second driven-couplings are disposed concentric with respect to the first driven-coupling and the second driving-couplings are disposed concentric with respect to the second driven-couplings. 
     In another exemplary embodiment, the first driving-coupling and second driving-couplings simultaneously move toward the first driven-coupling and second driven-couplings when the access cover is being closed, and move away from the first driven-coupling and second driven-couplings when the access cover is being opened. 
     In another exemplary embodiment, the first driving-coupling and second driving-couplings simultaneously move toward the first driven-coupling and second driven-couplings when the access cover is being closed, and move away from the first driven-coupling and second driven-couplings when the access cover is being opened. 
     In yet another exemplary embodiment, the guide unit includes a first through-hole formed in the rotation center thereof, a second through-hole formed in a circumferential direction of a concentric circle defined by the second driving-couplings, a first support portion to support the first driving-coupling, a second support portion to support the second driving-couplings, and a guide portion to guide axial movement of the guide unit during rotation of the guide unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other features and utilities of the present 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  is a view schematically illustrating a configuration of an image forming apparatus according to an embodiment of the present inventive concept; 
         FIG. 2  is a perspective view illustrating a state in which developing units are mounted in a main body of the image forming apparatus; 
         FIG. 3  is a perspective view illustrating a state in which the developing units are separated from the main body of the image forming apparatus; 
         FIG. 4  is a perspective view illustrating a positional relationship between an image-carrier and the developing units; 
         FIG. 5  is an exploded perspective view illustrating an assembly to drive the image-carrier and the developing units; 
         FIG. 6  is an exploded perspective view of the assembly of  FIG. 5  viewed at a different angle; 
         FIG. 7  is a view illustrating a positional relationship between a link unit and a guide unit in a state in which a cover closes the main body of the image forming apparatus; 
         FIG. 8  is a view illustrating a positional relationship between the link unit and the guide unit in a state in which the cover opens the main body of the image forming apparatus; 
         FIG. 9  is a sectional view taken along line I-I of  FIG. 7  illustrating a positional relationship between a first guide protrusion and a second guide protrusion in a state in which the cover closes the main body of the image forming apparatus; 
         FIG. 10  is a sectional view taken along line II-II of  FIG. 8  illustrating a positional relationship between the first guide protrusion and the second guide protrusion in a state in which the cover opens the main body of the image forming apparatus; 
         FIG. 11  is a sectional view taken along line III-III of  FIG. 7  illustrating a connection relationship between a driving-coupling and a driven-coupling in a state in which the cover closes the main body of the image forming apparatus; and 
         FIG. 12  is a sectional view taken along line IV-IV of  FIG. 8  illustrating a positional relationship between the driving-coupling and the driven-coupling in a state in which the cover opens the main body of the image forming apparatus. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED 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. 
       FIG. 1  is a view schematically illustrating a configuration of an image forming apparatus according to an embodiment of the present inventive concept,  FIG. 2  is a perspective view illustrating a state in which developing units are mounted in a main body of the image forming apparatus,  FIG. 3  is a perspective view illustrating a state in which the developing units are separated from the main body of the image forming apparatus, and  FIG. 4  is a perspective view illustrating a positional relationship between an image-carrier and the developing units. 
     As illustrated in  FIGS. 1 to 4 , the image forming apparatus  1  includes a main body  10 , a printing media feeding unit  20 , a light scanning unit  30 , an image-carrier unit  100 , a developing unit  40 , a transfer unit  50 , a fixing unit  60 , and a printing media discharge unit  70 . 
     The main body  10  defines an external appearance of the image forming apparatus  1  and supports a variety of elements received therein. A main body cover  11  is pivotally rotatably coupled to one side of the main body  10 . The main body cover  11  is configured to open or close a partial region of the main body  10 . As such, a user may access the interior of the main body  10  to attach or detach internal elements, such as an image-carrier unit  100  and the developing units  40 . 
     The printing media feeding unit  20  includes a cassette  21  in which printing media S is stored, a pickup roller  22  to pick up the printing media S stored in the cassette  21  one by one, and a delivery roller  23  to deliver each picked printing medium toward the transfer unit  50 . 
     The light scanning unit  30  is placed below the image-carrier unit  100  and serves to form an electrostatic latent image on a surface of an image-carrier  120  by irradiating light corresponding to image information to the image-carrier  120 . 
     The image-carrier unit  100  includes an image-carrier housing  110 , the image-carrier  120  rotatably installed to the image-carrier housing  110  to carry the electrostatic latent image formed by the light scanning unit  30  as well as a visible image formed by the developing unit  40 , a first driven-coupling  130  connected to a rotating shaft of the image-carrier  120 , and a charging roller  140  to charge the image-carrier  120  with a predetermined electric potential before the light scanning unit  30  irradiates light to the image-carrier  120 . 
     The developing unit  40  serves to form a visible image on the image-carrier  120  by feeding developer to the image-carrier  120  on which the electrostatic latent image has been formed. The developing unit  40  may include four developing devices  40 Y,  40 M,  40 C and  40 K, in which different colors of developers, for example, yellow (Y), magenta (M), cyan (C), and black (K) color developers are received respectively. 
     Each of the developing devices  40 Y,  40 M,  40 C and  40 K includes a developer receptacle  41 , a feed roller  42 , a developing roller  43 , and second driven-couplings  48  connected to a rotating shaft of the developing roller  43 . Each developer receptacle  41  stores developer to be fed to the image-carrier  120 , and each feed roller  42  feeds the developer stored in the respective developer receptacle  41  to the respective developing roller  43 . Each developing roller  43  attaches the developer to the surface of the image-carrier  120  on which the electrostatic latent image has been formed, so as to form a visible image. 
     The respective developing devices  40 Y,  40 M,  40 C and  40 K are separably mounted to the main body  10  via guide rails  15 . 
     The transfer unit  50  includes an intermediate transfer belt  51 , a first transfer roller  52 , and a second transfer roller  53 . 
     The intermediate transfer belt  51  is supported by support rollers  54  and  55 , and is moved at the same velocity as a linear velocity of the image-carrier  120 . The first transfer roller  52  opposites the image-carrier  120  with the intermediate transfer belt  51  interposed therebetween, and transfers the visible image formed on the image-carrier  120  to the intermediate transfer belt  51 . 
     The second transfer roller  53  opposites the support roller  55  with the intermediate transfer belt  51  interposed therebetween. The second transfer roller  53  is spaced apart from the intermediate transfer belt  51  while the image is transferred from the image-carrier  120  to the intermediate transfer belt  51 . After the image of the image-carrier  120  is completely transferred to the intermediate transfer belt  51 , the second transfer roller  53  is brought into contact with the intermediate transfer belt  51  at a predetermined pressure. Once the second transfer roller  53  has come into contact with the intermediate transfer belt  51 , the image of the intermediate transfer belt  51  is transferred to the printing medium. 
     The fixing unit  60  includes a heating roller  61  containing a heat source, and a pressure roller  62  installed to face the heating roller  61 . When the printing medium passes between the heating roller  61  and the pressure roller  62 , the image is fixed to the printing medium by heat transmitted from the heating roller  61  and pressure applied between the heating roller  61  and the pressure roller  62 . 
     The printing media discharge unit  70  may include a discharge roller  71  and a backup roller  72  to discharge the printing medium having passed through the fixing unit  60  to the outside of the main body  10 . 
     Now, operation of the image forming apparatus having the above-described configuration will be described in brief. Once a printing operation has begun, the surface of the image-carrier  120  is evenly charged by the charging roller  140 . The light scanning unit  30  irradiates light corresponding to information on any one color image, for example, a yellow image to the evenly charged surface of the image-carrier  120 . As such, an electrostatic latent image corresponding to the yellow image is formed on the image-carrier  120 . 
     Subsequently, as a developing bias is applied to the developing roller  43  of the yellow developing device  40 Y, yellow developer is attached to the electrostatic latent image, causing a yellow visible image to be formed on the image-carrier  120 . The visible image is transferred to the intermediate transfer belt  51  via the first transfer roller  52 . 
     After transfer of the single-page yellow image is completed, the light scanning unit  30  irradiates light corresponding to information on another color image, for example, a magenta image to the image-carrier  120 , forming an electrostatic latent image corresponding to the magenta image. The magenta developing device  40 M feeds magenta developer to the electrostatic latent image to form a visible image. The magenta visible image formed on the image-carrier  120  is transferred to the intermediate transfer belt  51  via the first transfer roller  52 . In this case, the magenta visible image overlaps with the visible yellow image that has previously been transferred. 
     When performing the above-described procedure with respect to cyan and black images, a color image in which the yellow, magenta, cyan and black images overlap with one another is formed on the intermediate transfer belt  51 . The resulting color image is transferred to the printing medium passing between the intermediate transfer belt  51  and the second transfer roller  53 , and the printing medium is discharged outward of the main body  10  via the printing media discharge unit  70 . 
     An assembly to drive the image-carrier  120  and the developing unit  40  is provided in a side region of the main body  10 . 
       FIG. 5  is an exploded perspective view illustrating an assembly to drive the image-carrier and the developing units, and  FIG. 6  is an exploded perspective view when viewed at a different angle from  FIG. 5 . 
     As illustrated in  FIGS. 5 and 6 , the assembly to drive the image-carrier  120  and the developing unit  40  includes a first driving-coupling  210  and second driving-couplings  220  which engage with the first driven-coupling  130  and the second driven-couplings  48 , respectively, to transmit a drive power generated by a drive source, such as a drive motor (not shown), to the image-carrier  120  and developing rollers  43 , a link unit  230  which is moved according to opening/closing operations of the cover  11 , a guide unit  240  which is operated in linkage with the link unit  230  to couple or separate the first driving-coupling  210  and second driving-couplings  220  to or from the first driven-coupling  130  and second driven-couplings  48 , and a guide cover  250  which is configured to receive the first driving-coupling  210 , second driving-couplings  220  and guide unit  240 . 
     The first driving-coupling  210  includes a plurality of bosses  212  to engage with the first driven-coupling  130 , and a first flange  214  which comes into contact with one surface of the guide unit  240 . Each second driving-coupling  220  includes a plurality of bosses  222  to engage with the second driven-coupling  48 , and a second flange  224  which comes into contact with one surface of the guide unit  240 . 
     Elastic members  228  are provided to press the first flange  214  and second flange  224  toward the first driven-coupling  130  and second driven-coupling  48 , respectively, which ensures that the first and second flanges  214  and  224  continuously come into contact with one surface of the guide unit  240 . 
     The first driving-coupling  210  is positioned to correspond to the first driven-coupling  130 , and the second driving-couplings  220  are positioned to correspond to the respective second driven-couplings  48 . As such, the second driving-couplings  220  are concentrically arranged about the first driving-coupling  210 . 
     The guide unit  240  takes the form of a partially incised disc and is rotatable about the first driving-coupling  210 . The guide unit  240  includes a first through-hole  242  formed in the rotation center thereof, a second through-hole  244  formed in a circumferential direction of a concentric circle defined by the second driving-couplings  220 , a first support portion  247  to support the first driving-coupling  210 , a second support portion  248  to support the second driving-couplings  220 , and a second guide portion  246  to guide axial movement of the guide unit  240  during rotation of the guide unit  240 . 
     The first driving-coupling  210  is connected to the first driven-coupling  130  via the through-hole  242 , and the second driving-couplings  220  are connected to the second driven-couplings  48  via the second through-hole  244 . 
     The first support portion  247  is formed along the first through-hole  242  to support the first flange  214  of the first driving-coupling  210 . The second support portion  248  is formed along the second through-hole  244  to support the second flanges  224  of the second driving-couplings  220 . The first flange  214  has a greater diameter than a diameter of the first through-hole  242 , and the second flange  224  has a greater diameter than a radial width of the second through-hole  244 . 
     At least one second guide portion  246  is placed in the circumferential direction or rotating direction of the guide unit  240 . The second guide portion  246  includes a second guide protrusion  246   a , which comes into contact with a first guide protrusion  252   a  of a first guide portion  252  or is received in a first receiving recess  252   b  provided at the guide cover  250  that will be described hereinafter, and a second receiving recess  246   b  in which the first guide protrusion  252   a  is received. 
     The second guide protrusion  246   a  has a second slope  246   c  coming into contact with a first slope  252   c  of the first guide protrusion  252   a  to enable relative movement thereof. As the guide unit  240  is rotated, the second guide protrusion  246   a  may come into contact with the first guide protrusion  252   a  or may be received in the first receiving recess  252   b  to enable axial movement of the guide unit  240 . 
     The guide cover  250  includes through-holes  251  to enable connection between the first and second driving-couplings  210  and  220  and the first and second driven-couplings  130  and  48 , and the first guide portion  252  to guide axial movement of the guide unit  240  according to rotation of the guide unit  240 . 
     The first guide portion  252  is provided to correspond to the second guide protrusion  246   a . The first guide portion  252  includes the first guide protrusion  252   a  which protrudes from an inner surface of the guide cover  250  facing the guide unit  240  and has a first slope  252   c  that is inclined in the rotating direction of the guide unit  240 , and a first receiving recess  252   b  in which the second guide protrusion  246   a  is received. 
     As the guide unit  240  is rotated, the first guide protrusion  252   a  may come into contact with the second guide protrusion  246   a  or may be received in the second receiving recess  246   b  to enable axial movement of the guide unit  240 . 
     The link unit  230  includes a first connecting portion  232  connected to the cover  11  and a second connecting portion  234  connected to the guide unit  240 . The first connecting portion  232  has a guide groove  232   a  to guide pivotal rotation of the cover  11  as the cover  11  opens or closes the main body  10 . The second connecting portion  234  has a fastening boss  234   a  fitted into a fastening hole  249  of the guide unit  240  to guide pivotal rotation of the guide unit  240 . 
     The link unit  230  is moved in a direction A or in a direction opposite to the direction A (see  FIG. 8 ) in linkage with pivotal rotation of the cover  11  to open or close a portion of the main body  10 . The guide unit  240  rotates in a direction B and in a direction opposite to the direction B (see  FIG. 8 ) in linkage with the link unit  230 . 
     Hereinafter, the procedure and principle in which the first and second driving-couplings  210  and  220  are coupled to or separated from the first and second driven-couplings  130  and  48  according to opening/closing operations of the cover  11  will be described. 
       FIG. 7  is a view illustrating a positional relationship between the link unit  230  and the guide unit  240  in a state in which the cover  11  closes the main body,  FIG. 8  is a view illustrating a positional relationship between the link unit  230  and the guide unit  240  in a state in which the cover  11  opens the main body,  FIG. 9  is a sectional view taken along line I-I of  FIG. 7  illustrating a positional relationship between the first guide protrusion  252   a  and the second guide protrusion  246   a  in a state in which the cover  11  closes the main body,  FIG. 10  is a sectional view taken along line II-II of  FIG. 8  illustrating a positional relationship between the first guide protrusion  252   a  and the second guide protrusion  246   a  in a state in which the cover  11  opens the main body,  FIG. 11  is a sectional view taken along line III-III of  FIG. 7  illustrating a connection relationship between the driving-couplings and the driven-couplings in a state in which the cover closes the main body, and  FIG. 12  is a sectional view taken along line IV-IV of  FIG. 8  illustrating a positional relationship between the driving-couplings and the driven-couplings in a state in which the cover opens the main body. 
     As illustrated in  FIG. 8 , if the cover  11  is pivotally rotated to open the main body  10 , the link unit  230 , connected to the cover  11 , is moved in the direction A in linkage with the cover  11 , and the guide unit  240 , connected to the link unit  230 , is pivotally rotated in the direction B about the first driving-coupling  210 . 
     If the guide unit  240  is pivotally rotated in the direction B, as illustrated in  FIG. 10 , the second guide protrusion  246   a , which was previously received in the first receiving recess  252   b , is then moved along the first slope  252   c  of the first guide protrusion  252   a  formed at the guide cover  250 , thereby being engaged with the first guide protrusion  252   a.    
     As the second guide protrusion  246   a  engages with the first guide protrusion  252   a , the first and second support portions  247  and  248  of the guide unit  240  and the elastic members  228  cause the guide unit  240  to press the first and second driving-couplings  210  and  220  coming into contact with one surface of the guide unit  240 . Thereby, the first and second driving-couplings  210  and  220  as well as the guide unit  240  are moved away from the first and second driven-couplings  130  and  48 , thereby being separated from the first and second driven-couplings  130  and  48 . 
     After the first and second driving-couplings  210  and  220  are separated from the first and second driven-couplings  130  and  48 , replacement of the developing unit  40  may be possible through one side of the main body  10  that is opened by the cover  11 . 
     As illustrated in  FIG. 7 , if the cover  11  is pivotally rotated to close the main body  10  in a state in which the developing unit  40  is mounted in the main body  10 , the link unit  230  connected to the cover  11  is moved in the direction opposite to the direction A in linkage with the cover  11 , and the guide unit  240  connected to the link unit  230  is pivotally rotated in the direction opposite to the direction B about the first driving-coupling  210 . 
     Once the guide unit  240  has been pivotally rotated in the direction opposite to the direction B, as illustrated in  FIG. 9 , the second guide protrusion  246   a , previously engaged with the first guide protrusion  252   a , is moved along the first slope  252   c  of the first guide protrusion  252   a  formed at the guide cover  250 , thereby being received in the first receiving recess  252   b.    
     As the second guide protrusion  246   a  is received in the first receiving recess  252   b , the first and second support portions  247  and  248  of the guide unit  240  and the elastic members  228  cause the guide unit  240  and the first and second driving-couplings  210  and  220  to come into contact with one surface of the guide unit  240  to be moved toward the first and second driven-couplings  130  and  48 , thereby engaging with the first and second driven-couplings  130  and  48 . 
     After the first and second driving-couplings  210  and  220  are engaged with the first and second driven-couplings  130  and  48 , respectively, a printing operation may be performed as the first and second driving-couplings  210  and  220  are driven to rotate the image-carrier  120  and the developing roller  43 . 
     As described above, through the link unit  230  being moved in linkage with the cover  11 , the guide unit  240  being moved in linkage with the link unit  230  and the guide cover  250  to guide axial movement of the guide unit  240 , the first driving-coupling  210  to drive the image-carrier  120  and the second driving-couplings  220  to drive the respective developing rollers  43  may be engaged with or separated from the first driven-coupling  130  and the second driven-couplings  48 . In this way, a simplified assembly to drive the image-carrier  140  and the developing rollers  43  is accomplished. 
     As is apparent from the above description, according to the embodiments of the present inventive concept, an assembly to couple or separate driving-couplings to or from an image-carrier and a developing unit is simplified, resulting in reduced material costs and enhanced productivity. 
     Further, the simplified assembly to couple or separate the driving-couplings to or from the image-carrier and developing unit occupies a smaller space, which enables reduction in the size of an image forming apparatus. 
     Although a few embodiments of the present inventive concept have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the inventive concept, the scope of which is defined in the claims and their equivalents.