Patent Publication Number: US-7903997-B2

Title: Coupling apparatus and image forming apparatus employing the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims all benefits accruing under 35 U.S.C. §119 from Korean Patent Applications Nos. 10-2006-122948, 10-2006-129578 and 10-2007-0096135, filed on Dec. 6 and 18, 2006, and Sep. 20, 2007, respectively, in the Korean Intellectual Property Office the disclosures of which are incorporated herein by reference in their entireties. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Aspects of the present invention relate to a coupling apparatus that performs a coupling function in cooperation with a rotation of a knob and an image forming apparatus employing the same and, more particularly, to a coupling apparatus installed in a small space to be automatically decoupled when a force applied to a knob is released and an image forming apparatus employing the same. 
     2. Related Art 
     Generally, an image forming apparatus driven by a motor is provided with a coupling apparatus between a power supply unit and a driving unit so that power can be automatically discontinued when a cover is opened while the power is on.  FIGS. 1A and 1B  are schematic views illustrating a coupling apparatus for a conventional image forming apparatus. In the coupling apparatus for a conventional image forming apparatus, a driving gear  25  and a driving power transmitting gear  35  are mutually engaged or disengaged in cooperation with an opening and closing operation of a front cover (not shown) of an image forming apparatus. The driving gear  25  is provided on a shaft  27  of a driving roller (not shown) that rotatably drives a transfer belt (not shown) to be driven lengthwise of the shaft  27  by an operation of a coupling lever  21  to be described later. 
     In order to perform the above-described coupling function, the conventional coupling apparatus includes a locking lever  15  rotatably provided in a frame  10 , a coupling lever  21  rotated in cooperation with the locking lever  15 , and a tensile spring  17  provided between the frame  10  and the locking lever  15 . The locking lever  15  is rotated by an opening and closing operation of the front cover. If the front cover is closed, the locking lever  15  rotates from a position shown in  FIG. 1A  to a position shown in  FIG. 1B . The tensile spring  17  pulls the locking lever  15  so as to locate the locking lever  15  in the position shown in  FIG. 1A  while the front cover is open. When the locking lever  15  rotates, the tensile spring  17  pulls the locking lever  15  to a direction to accelerate the rotation of the locking lever  15  at the moment when the rotating angle exceeds an elastic bias critical point. The locking lever  15  snaps to the position shown in  FIG. 1B  by the elastic force. 
     The coupling lever  21  is rotatably installed and centered around on the shaft  27  of the driving roller (not shown). The coupling level  21  rotates in cooperation with the rotation of the locking lever  15 . A long hole  21   a  is formed in the coupling lever  21 , and a guide projection  15   a  coupled to the long hole  21   a  is formed in the locking lever  15 . When the locking lever  15  rotates, the guide projection  15   a  slides along the long hole  21   a  and guides the rotation of the coupling lever  21 . 
     However, the coupling apparatus according to the above described configuration has several problems. First, an error by the user or an external impact while the front cover is open may cause the position of a driving gear and a power transmitting gear to change to the position shown in  FIG. 1B  (where the driving and power transmitting gears  25  and  35  are engaged with each other) by rotation of the locking lever  15  and an elastic force of the tensile spring. As such, the coupling structure may be damaged. If the user wants to close the front cover while in a coupled state by the snap operation of the locking lever  15 , the front cover is not closed normally, and the front cover or the coupling structure may be damaged by an abnormal contact between the front cover and the coupling apparatus. 
     Second, since the locking lever  15  and the coupling lever  21  have a different center of rotation, the configuration can be complicated and takes up a large amount of space. Third, since the locking lever  15  and the coupling lever  21  are engaged in a sliding system, durability of the system is reduced. Since the front cover of the image forming apparatus is repeatedly opened and closed, and accordingly, a strong coupling structure is related to a color registration quality of the image forming apparatus, the sliding system wears out quickly and will need to be replaced often. 
     SUMMARY OF THE INVENTION 
     Aspects of the present invention provide a coupling apparatus that can be automatically decoupled if an external force does not adequately perform a coupling function by converting a rotational movement into an axial direction rectilinear movement, and at the same time, can make an entire configuration more compact and more durable by disposing the components on one axis. According to additional aspects of the present invention, an image forming apparatus employing the system described above is provided. 
     According to an aspect of the present invention, an image forming apparatus includes: a main body unit which has an image forming unit; a door unit which couples with the main body unit to open and close the main body unit, and has a projection at one side thereof; a mid-transfer unit which couples with the door unit; a coupling knob which is provided in the main body unit and rotates in cooperation with pressure of the projection when the door unit is closed; and a coupling apparatus which is provided in the main body and transmits a driving force from the main body unit to the mid-transfer unit in cooperation with the rotation of the coupling knob. 
     According to another aspect of the present invention, the coupling apparatus includes: a frame; and a shaft installed in the frame and arranged to rotate and move in an axial direction, wherein the shaft interlocks with the rotation of the coupling knob and moves to the mid-transfer unit in the axial direction. 
     According to another aspect of the present invention, the coupling apparatus includes: a coupling link coupled to the frame movably in the axial direction of the shaft and arranged to move in the axial direction in cooperation with the rotation of the coupling knob; and a coupling unit coupled to the shaft, and arranged to rotate along with the shaft and to move between a coupling position and a decoupling position in the axial direction of the shaft according to the movement of the coupling link. 
     According to another aspect of the present invention, the image forming apparatus further includes an elastic member to elastically bias the coupling unit to the decoupling position. 
     According to another aspect of the present invention, the coupling unit includes: a coupling member coupled to the shaft, rotatably installed independently of the coupling link, and coupled to the mid-transfer unit; and a relay member coupled to the shaft to transmit a driving force from a driving source to the shaft. 
     According to another aspect of the present invention, the elastic member is provided between the relay member and the coupling knob. 
     According to another aspect of the present invention, the shaft includes a first stopping part in which the coupling member is installed, the mid-transfer unit includes a mid-transfer belt and a driving roller to drive the mid-transfer belt, and the coupling member includes a first hook member hooked to the first stopping part and a spline formed on an inside circumference of the coupling member and engaged with a rotational shaft of the driving roller. 
     According to another aspect of the present invention, the frame includes: a frame main body having an installing hole in which the shaft, the coupling knob, and the coupling link are installed; a first installing part formed in the frame main body, and in which the coupling knob is rotatably installed; and a first guide part formed in the frame main body to guide the coupling link to move in the axial direction. 
     According to another aspect of the present invention, the coupling knob includes: a knob main body having a first through hole through which the shaft is installed; a first movement changing part formed on one side of the knob main body to change the rotational movement of the knob main body into the axial direction movement; a second installing part formed in a position of the knob main body so as to face the first installing part; and a knob member formed in the knob main body to rotate the knob main body. 
     According to another aspect of the present invention, the first installing part is provided as a guide hole formed around the installing part to guide the rotation of the coupling knob; and the second installing part is provided as a coupling protrusion projected in the knob main body and rotatably installed in the guide hole, to regulate the rotation of the knob main body. 
     According to another aspect of the present invention, the coupling link includes: a link main body having an accommodating part that accommodates the coupling member, and a second through hole through which the shaft is installed; a second movement changing part formed on one side of the link main body to face the first movement changing part to change the rotation of the first movement changing part into the axial direction movement; and a second guide part formed in a position of the link main body corresponding to the first guide part to guide the link main body to move in the axial direction. 
     According to another aspect of the present invention, the first guide part is provided as a guide projection protruding from one side of the frame main body, and the second guide part is provided as a guide groove in the link main body in a shape corresponding to a shape of the guide projection. 
     According to another aspect of the present invention, the image forming apparatus further includes a coupling lever coupled to the coupling knob and arranged to rotate along with the coupling knob, wherein the elastic member is coupled to the coupling lever to elastically bias the coupling lever in a direction of moving the coupling knob to the decoupling position when the coupling knob is released from the pressure of the projection. 
     According to another aspect of the present invention, the coupling link includes: a link main body having a through hole through which the shaft is installed; and a third movement changing part protruding from an external circumference of the link main body to change rotation of the coupling knob into an axial direction movement. 
     According to another aspect of the present invention, the coupling knob includes: a knob main body arranged to move in the axial direction of the shaft; a knob member extended from the knob main body outwardly and coupled to the coupling lever; and a second guide part that formed on one side of the knob main body and accommodating and releasing the third movement changing part in cooperation with rotation of the knob main body to guide the knob main body to move in the axial direction. 
     According to another aspect of the present invention, the coupling member includes: a gear part coupled to the shaft and transmitting a rotational force from a driving source to the shaft; and a coupling unit coupled to the mid-transfer unit at the coupling position and transmitting the rotational force from the gear part to the mid-transfer unit. 
     According to an aspect of the present invention, a coupling apparatus is provided. The coupling apparatus comprises a frame; a shaft installed in the frame and arranged to rotate in an axial direction; a coupling knob rotatably coupled to the frame and arranged to rotate coaxially with and independently of the shaft by an external force; a coupling link coupled to the frame movably in the axial direction of the shaft, and arranged to move in the axial direction according to the rotation of the coupling knob; a coupling unit coupled to the shaft arranged to rotate along with the shaft and to move between a coupling position and a decoupling position in the axial direction of the shaft according to the movement of the coupling link, to couple a component to a driving unit; and an elastic member installed around the shaft to elastically bias the coupling unit to the decoupling position. 
     In addition to the example embodiments and aspects as described above, further aspects and embodiments will be apparent by reference to the drawings and by study of the following descriptions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A better understanding of the present invention will become apparent from the following detailed description of example embodiments and the claims when read in connection with the accompanying drawings, all forming a part of the disclosure of this invention. While the following written and illustrated disclosure focuses on disclosing example embodiments of the invention, it should be clearly understood that the same is by way of illustration and example only and that the invention is not limited thereto. The spirit and scope of the present invention are limited only by the terms of the appended claims. The following represents brief descriptions of the drawings, wherein: 
         FIGS. 1A and 1B  are schematic views illustrating a coupling apparatus for an image forming apparatus that has a configuration for transmitting power in cooperation with a conventional front cover; 
         FIG. 2  is a separate perspective view illustrating a coupling apparatus according to a first example embodiment of the present invention; 
         FIGS. 3A to 3C  are schematic views illustrating an operating principle of the coupling apparatus according to the first example embodiment of the present invention when coupling is released; 
         FIGS. 4A to 4C  are schematic views illustrating an operating principle of the coupling apparatus according to the first example embodiment of the present invention when coupling is performed; 
         FIG. 5  is a schematically sectional view illustrating an image forming apparatus according to the first example embodiment of the present invention; 
         FIG. 6  is a schematically sectional view illustrating a transfer unit and the coupling apparatus of the image forming apparatus according to the first example embodiment of the present invention; 
         FIG. 7  is a schematically perspective view illustrating a main part of the transfer unit and the coupling apparatus of the image forming apparatus according to the first example embodiment of the present invention; 
         FIG. 8  is an exploded perspective view of a coupling apparatus according to a second example embodiment of the present invention; 
         FIGS. 9A and 9B  are schematic views illustrating the coupling apparatus according to the second example embodiment of the present invention at coupling and decoupling positions, respectively; 
         FIG. 10  is a schematic perspective view of a coupling member according to the second example embodiment of the present invention when coupling is released; and 
         FIGS. 11A and 11B  are sectional views illustrating the coupling apparatus according to the second example embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Reference will now be made in detail to the present embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures. 
       FIG. 2  is a separate perspective view illustrating a coupling apparatus  10  according to a first example embodiment of the present invention. The coupling apparatus  10  includes a frame  100 , a shaft  110  installed in the frame  100  to rotate and move in an axial direction, a coupling knob  120  rotatably coupled to the frame  100 , a coupling link  130  coupled to the shaft  110  to move in the axial direction of the shaft  110 , coupling units  141 ,  145  coupled to the shaft  110 , and an elastic member  150 . 
     The frame  100  includes a frame main body  101 , a first installing part  103 , and a first guide part  105 . The first installing part  103  and the first guide part  105  are formed in the frame main body  101 . The frame main body  101  includes an installing hole  101   a  through which the shaft  110 , the coupling knob  120 , and the coupling link  130  are at least partially installed. The first installing part  103  is formed around the first installing hole  101   a . The coupling knob  120  is installed inside the first installing part  103  so as to rotate independently with respect to the rotation of the shaft  110 . 
     The first guide part  105  guides a movement direction of the coupling link  130 . If the coupling link  130  moves in cooperation with the rotation of the coupling knob  120 , the first guide part  105  guides the coupling link  130  to move in the axial direction of the shaft  110 . The first guide part  105  also regulates the rotation of the coupling link  130 . 
     The coupling knob  120  is rotatably coupled to the first installing part  103  of the frame  100 , and rotates independently from the shaft  110  by an external force. The coupling knob  120  has the same rotating center as that of the shaft  110 . The shaft  110  and the coupling knob  120  rotate on the same shaft. As described above, if the coupling knob  120  and the shaft  110  are disposed on the same shaft, the frame  100  takes up a smaller volume, and the configuration of the coupling apparatus  10  is more compact. 
     The coupling knob  120  includes a knob main body  121  having a first through hole  121   a  through which the shaft  110  is formed, a first movement changing part  123  formed on one side of the knob main body  121 , and a second installing part  125 . The coupling knob  120  further includes a knob member  127  projected from the knob main body  121 . The knob member  127 , which comes into contact with a user&#39;s hand or a separate component, enables the knob main body  121  to rotate. 
     The first movement changing part  123  changes the rotational movement of the knob main body  121  into the axial movement. The first movement changing part  123  protrudes from a side of the knob main body  121  facing the coupling link  130 , and has a slide cam configuration of a predetermined profile. 
     The second installing part  125  is formed in a predetermined position of the knob main body  121  facing the first installing part  103 . The first and the second installing part  103  and  125  have complementary shapes. The second installing part  125  is rotatably coupled to the first installing part  103 . The coupling knob  120  is rotatably coupled to the frame  100 . 
       FIG. 2  shows an example of the first and the second installing parts  103  and  125 . The first installing part  103  is provided as a guide long hole perforated around the installing hole  101   a . The second installing part  125  may be provided as a coupling protrusion protruding from the knob main body  121  and rotatably coupled to the guide long hole. The coupling protrusion is provided as a hook to prevent the coupling knob  120  and the frame  100  from separating and to regulate the rotation of the knob main body  121  if the coupling protrusion is coupled to the guide long hole. However, the first and the second installing part  103  and  125  are not limited to the configuration shown in  FIG. 2 , but may be configured in various shapes. For example, the first installing part  103  may be formed as a coupling protrusion, the second installing part  103  may be formed as a guide long hole, etc. 
     The knob member  127  is formed in the knob main body  121  to rotate the knob main body  121 . The knob member  127  is rotated by the user or by a pressing member  310  (shown in  FIG. 3A ) formed in a cover  300  (shown in  FIG. 3A ) to be described later. 
     The coupling link  130  is coupled to the frame  100  in the axial direction of the shaft  110 . The coupling link  130  moves in the axial direction in cooperation with the rotation of the coupling knob  120 . The coupling link  130  includes a link main body  131 , a second movement changing part  133  formed on one side of the link main body  131 , and a second guide part  135 . An accommodating part  131   a  and a second through hole  131   b  are formed in the link main body  131 . 
     The second movement changing part  133  changes the rotational movement of the first movement changing part  123  into movement in the axial direction. The second movement changing part  133  is formed on one side of the link main body  131  facing the first movement changing part  123 . The second movement changing part  133  has a slide cam structure of a predetermined profile corresponding to the first movement changing part  123 . The second guide part  135  is formed in a position of the link main body  131  corresponding to the first guide part  105 , and guides the link main body  131  to move in the axial direction of the shaft  110 . 
       FIG. 2  also shows an example of the first and the second guide parts  105  and  135 . The first guide part  105  may be provided as a guide protrusion protruding from the frame main body  101 . The second guide part  135  is provided as a shape corresponding to a shape of the guide protrusion and may be provided as a guide groove in the link main body  131 . However, the first and the second guide parts  105  and  135  are not limited to the configuration shown in  FIG. 2 , but may be formed in various shapes. For example, the first installing part  103  may be formed as a coupling protrusion, the second installing part  103  may be formed as a guide long hole, etc. 
     The coupling unit  141 ,  145  is coupled to the shaft  110  so as to rotate with the shaft  110 . The coupling unit  141 ,  145  also moves between a decoupling position (shown in  FIGS. 3A and 3B ) and a coupling position in an axial direction of the shaft  110  in cooperation with the movement of the coupling link  130 . For this purpose, the coupling unit  141 ,  145  includes a coupling member  141  and a relay member  145 . 
     The coupling member  141  is installed in the accommodating part  131   a  to rotate independently, and is coupled to the first counterpart (see  210  in  FIG. 3B ). The coupling member  141  is grooved, and includes a coupling part  142  and a first coupling hole  143  coupled to the shaft  110 . A spline is formed on the inside circumference  142   a  of the coupling part  142 . An end part of the first counterpart  210  is formed with a spline on the external circumference  211  to selectively engage the first counterpart  210  with the coupling part  142  according to an operating mode. The first coupling hole  143  and the shaft  110  are provided in the shape of “D” to mutually correspond so as to rotate the coupling member  141  with the shaft  110 . If the shaft  110  rotates, the coupling member  141  rotates in cooperation with the rotation of the shaft  110 . 
     The coupling member  141  grooved in the shaft  110  may be arranged so as not to be separated from the shaft  110 . For this purpose, a first stopping part  111  is formed in the shaft  110  and a first hook member  144  is provided in a predetermined position of the coupling member  141 . The first hook member  144  is hooked to the first stopping part  111  to prevent the coupling member  141  and the shaft  110  from separating. 
     The relay member  145  is coupled to the shaft  110  and transmits a rotational force between the shaft  110  and a second counterpart  220  (shown in  FIG. 3B ). The second counterpart  220  may be provided as a driving gear rotatably driven in engagement with a driving part (P). 
     The relay member  145  rotates along with the shaft  110 , and at the same time, moves in the axial direction of the shaft  110 . A coupling relation between the relay member  145  and the second counterpart  220  is maintained. A gear part  148  formed on the external circumference of the relay member  145  engages with the second counterpart  220 . The engaged state is maintained even if the relay member  145  has moved in the axial direction of the shaft  110  with respect to the second counterpart  220 . 
     A second coupling hole  146  is formed in the relay member  145  and the shaft  110  has in a “D” shape corresponding to each other so that the relay member  145  can rotate with the shaft  110 . When the relay member  145  rotates, the shaft  110  rotates in cooperation with the rotation of the relay member  145 . The relay member  145  grooved in the shaft  110  may be provided so as not to be separated from the shaft  110 . For this purpose, a second stopping part  113  is formed in the shaft  110 . A second hook member  147  is provided in a corresponding predetermined position of the relay member  145 . The second hook member  147  is hooked to the second stopping part  113  to prevent the relay member  145  and the shaft  110  from separating. 
     The elastic member  150  elastically biases the coupling unit  141 ,  145  toward the decoupling position if the external force applied to the coupling knob  120  is released. The elastic member  150  automatically releases the coupling if the external force does not successfully convert the rotation of the coupling knob  120  into the axial direction movement to perform the coupling function. The elastic member  150  is provided between the coupling knob  120  and the relay member  145 . The elastic member  150  may be provided as a compressed spring that elastically biases the coupling unit  141 ,  145  in a decoupling direction. However, the elastic member  150  is not limited to the above-described compressed spring, but may be provided as a spring, such as a tensile spring or a torsion spring, or may be provided as an elastic material such as rubber. 
     An operation of the coupling apparatus  10  according to the first example embodiment of the present invention will be described with reference to  FIGS. 3A to 4C .  FIGS. 3A to 3C  are schematic views illustrating an operating principle of the coupling apparatus  10  according to the first example embodiment of the present invention in a decoupled state.  FIGS. 4A to 4C  are schematic views illustrating an operating principle of the coupling apparatus  10  according to the first example embodiment of the present invention in a coupled state. 
     Referring to  FIG. 3A , when the coupling apparatus  10  is in a decoupled state, the knob member  127  is in a free state. While in the free state, the knob member  127  is not in contact with the pressing member  310  formed in the cover  300  or with the user&#39;s hand. As shown in  FIGS. 3B and 3C , the relay member  145  is elastically biased in a direction receding from the coupling knob  120  (an arrow A) by elasticity of the elastic member  150 . The coupling link  130  and the coupling member  141  are positioned so as to correspond to the cam profile between the first and the second movement changing parts  123  and  133 . Accordingly, the spline engagement is released between the first counterpart  210  and the coupling member  141 . As a result, the coupling member  141  rotates with the shaft  110  by the rotational movement of the second counterpart  220  rotatably driven by the driving part M, but the rotational force is not transmitted to the first counterpart  210 . The coupling is automatically released by the elastic bias of the elastic member  150  when the knob member  127  is restored to a state without the external force. 
     As shown in  FIG. 4A , the coupling knob  120  rotates by the external force applied to the knob member  127  in the coupled state. The knob member  127  may rotate by contacting with the projection member  310  formed in the cover  300 . The cam profile provided between the first movement changing part  123  and the second movement changing part  133  is mismatched, and accordingly, the rotational movement of the coupling knob  120  changes to a rectilinear movement of the coupling link  130 . The coupling link  130  moves linearly. The rotational state of the coupling link  130  is regulated by the first guide part  105 . 
     The coupling member  141  accommodated in the accommodating part  131   a  of the coupling link  130  and the shaft  110  and the relay member  145  move in the axial direction (an arrow B direction) in which the elasticity of the elastic member  150  increases. While in the coupled state, the spline of the coupling member  141  and the spline of the first counterpart  210  are engaged, and the rotational force supplied from the driving part M is transmitted to the first counterpart  210  through the second counterpart  220 , the relay member  145 , the shaft  110  and the coupling member  141 . The first counterpart  210  is rotatably driven by the transmitted rotational force. 
     If the force to the knob member  127  is released, for example, if the cover  300  is opened, the components are repositioned by the elastic bias of the elastic member  150  to the position shown in  FIGS. 3A to 3C . Accordingly, the spline-engagement between the first counterpart  210  and the coupling member  141  is released. 
       FIG. 5  is a schematic sectional view illustrating the image forming apparatus employing the coupling apparatus according to the first example embodiment of the present invention.  FIG. 6  is a schematic sectional view illustrating a transfer unit and a coupling apparatus of the image forming apparatus according to the first example embodiment of the present invention.  FIG. 7  is a schematic perspective view illustrating a main part of a transfer unit and a coupling apparatus of an image forming apparatus according to the first example embodiment of the present invention. 
     Referring to  FIGS. 5 to 7 , the image forming apparatus according to the first example embodiment of the present invention includes a cabinet  410 , the cover  300 , an image forming unit  430 ,  440 , a transfer unit  450 , a fusing unit  470 , a driving unit P, and the coupling apparatus  10 . The cover  300  is coupled to the cabinet  410  to be opened or closed. The image forming unit  430 ,  440  is provided inside the cabinet  410  and develops a toner to form an image. The transfer unit  450  transfers the image formed in the image forming unit  430 ,  440  onto a printable medium M. The driving unit P and the coupling apparatus  10  are provided inside the cabinet  410 . The fusing unit  470  fuses the image transferred onto the printable medium M through the transfer unit  450 . 
     The cabinet  410  forms an external appearance of the image forming apparatus. A supplying unit  480  is detachably provided in the cabinet  410  to store a printable medium M to be supplied to the image forming apparatus. The printable medium M supplied through the supplying unit  480  is fed between the image forming unit  430 ,  440  and the transfer unit  450  through a feeding path. 
     The cover  300  is coupled to the cabinet  410  by a hinge  423  and is rotatably installed with respect to the hinge  423 . The transfer unit  450  can be replaced with the image forming unit  430 ,  440  by opening and closing the cover  300 . The cover  300  includes the pressing member  321  that is selectively contacted to the coupling apparatus  10  to perform the coupling function. The pressing member  310  is protruded in the inside of the cabinet  410  and is selectively contacted to the coupling knob  120  of the coupling apparatus  10 . 
     The coupling apparatus  10  transmits the power supplied from the driving unit P to the transfer unit  450  by the external force applied to the pressing member  310  when the cover  300  is closed. When the cover  300  opens, the coupling apparatus  10  blocks power transmission by separating the pressing member  310  from the coupling apparatus  10 . 
     The image forming unit  430 ,  440  includes a developing unit  431  and a light scanning unit  435 . The developing unit  431  includes a photosensitive body  433  that responds to a light beam scanned from the light scanning unit  440  to form an electrostatic latent image. The developing unit  431  develops the toner onto the photosensitive body  435 , to form a toner image on the photosensitive body  435 . The developing unit  431  may be provided in plural numbers according to each of colors so as to form full color image in a single-pass type.  FIG. 5  illustrates an example made of four units so as to realize yellow (Y), magenta (M), cyan (C), and black (B). 
     The light scanning unit  435  scans the light beam onto each of the plural photosensitive bodies  433  to form an electrostatic latent image thereon. For this purpose, the light scanning unit  440  has a multi-beam light scanning configuration to scan the light beam onto the plural photosensitive bodies  433  at the same time. The light scanning unit  435  includes a light part (not shown), a beam deflecting unit  437  that deflects the beam emitted from the light part, and an f-θ lens  439 . The light part may be configured to have a plurality of radiating points or may be configured to provide a semi-conductive element having a single radiating point for each of the colors. 
     The transfer unit  450  is disposed to face the photosensitive bodies  435  across the printable medium M fed through the feeding path. The transfer unit  450  transfers the toner image formed in the photosensitive bodies  435  onto the supplied printable medium M. To perform the transfer function, the transfer unit  450  includes a transfer belt  451 , a transfer roller  455 , and a belt driving unit  460  (shown in  FIG. 6 ). The transfer belt  451  and the transfer roller  455  are disposed to face the plurality of photosensitive bodies  435 . The belt driving unit  460  rotatably drives the transfer belt  451 . 
     The belt driving unit  460  includes a plurality of rollers  461 ,  463 , and  465  that rotatably support the transfer belt  451  and a belt tension applying unit  467  that applies tension to the transfer belt  451  when the belt is normally driven and releases the tension applied to the transfer belt  451  in an initial stage. The plurality of rollers include a driving roller  461  that rotatably drives the transfer belt  451  and a tension roller  463  that applies tension to the transfer belt  451 . The transfer belt  451  is driven by the rotational driving of the driving roller  461 . The rotational force transmitted to the driving roller  461  is supplied from the driving unit  500  through the coupling apparatus  10 . 
     The driving roller  461  corresponds to the above-described first counterpart  210 . A spline part  462  (shown in  FIG. 7 ) selectively coupled to the coupling apparatus  10  is installed in the end part of the driving roller  461 . The driving roller  461  is selectively coupled to the coupling member  141  of the coupling apparatus  10  in engagement with the opening and closing operation of the cover  300  to be rotatably driven or not to be rotatably driven. 
     Turning to  FIG. 7 , a rotational shaft  461  a of the driving roller  461  may be installed coaxially with the shaft  110  of the coupling apparatus  10 . In this way, the driving roller  461  and the coupling apparatus  10  are disposed on the same axis, the rotational components that constitute the coupling apparatus  10  can rotate centering on the shaft  523 , and power transmitting components can be disposed in a small space, thereby improving space efficiency and enhancing durability. 
       FIG. 8  is an exploded perspective view of a coupling apparatus  600  according to a second example embodiment of the present invention. The coupling apparatus  600  includes a coupling link  610  fastened to a frame P; a shaft  640  installed in the coupling link  610  and to rotate and move in an axial direction; a coupling lever  650  provided to be rotated by an external force; a coupling member  630  coupled to the shaft  640 , transmitting a rotational force from a second counterpart  220  (see  FIG. 3B ) to the shaft  640 , and coupled to a first counterpart  211  (see  FIG. 3B ); a coupling knob  620  moving in cooperation with the rotation of the coupling lever  650  between a coupling position where the coupling member  630  is coupled to the first counterpart  211  and a decoupling position where the coupling member  630  moves from the coupling position in the axial direction of the shaft  640 ; and an elastic member  660  elastically biasing the coupling lever  650  in a direction of moving the coupling knob  620  toward the decoupling position. 
     The coupling link  610  is coupled to the frame P as shown in  FIG. 8 , and guides the coupling knob  620  to move in the axial direction according to the rotation of the coupling lever  650 . The coupling link  610  includes a link main body  611  coupled to the frame P, and a third movement changing part  613  protruding from an external circumferential surface of the link main body  611  and guiding a second guide part  625  of the coupling lever  650 . 
     The coupling knob  620  is coupled to the coupling lever  650  and moves along the axial direction of the shaft  640  in cooperation with the rotation of the coupling lever  650 . The coupling knob  620  includes a knob main body  621  formed with a through hole to accommodate the link main body  611  of the coupling link  610 , a knob member  623  extended from the knob main body  621  and accommodated in a knob coupling rib  655  of the coupling lever  650 , and the second guide part  625  accommodating the third movement changing part  613  when the knob main body  621  rotates and guiding the knob main body  621  to the coupling position. 
     The knob main body  621  is larger than an outer diameter of the link main body  611  by a predetermined gap, and rotates across the knob main body  621  when the coupling lever  650  rotates. As shown in  FIG. 11A , when the coupling lever  650  is not rotated, the second guide part  625  and the coupling lever  650  are positioned alternately with each other, so that the second guide part  625  does not accommodate the third movement changing part  613 . On the other hand, as shown in  FIG. 11B , when the coupling lever  650  is rotated, the second guide part  625  accommodates the third movement changing part  613  as the knob main body  621  rotates. Accordingly, the knob main body  621  moves to the coupling position in the axial direction along the third movement changing part  613 . 
     The coupling member  630  moves together with the coupling knob  620  when the coupling knob  620  moves in the axial direction, and transmits the rotation of the second counterpart  410  to the first counterpart  211 . In other words, the coupling member  630  is coupled to the first counterpart  211  when the coupling knob  620  is placed in the coupling position, and transmits the rotational force of the second counterpart  410  (refer to  FIG. 7 ) to the first counter part  211 . 
     The coupling member  630  includes a coupling member main body  631  rotatably coupled to the shaft  640 , a gear part  633  formed on an external circumference of the coupling member main body  631  and receiving the rotational force from the second counterpart  410 , and a coupling part  635  accommodating the shaft  640  and engaged with the first counterpart  211 . Here, the coupling part  635  may be threaded on an inner surface thereof to be engaged with the first counterpart  211 . 
     The shaft  640  is coupled with the coupling link  610 , the coupling knob  620  and the coupling member  630 , and transmits the rotational force of the second counterpart  410  to the first counterpart  211 . The shaft  640  may have a cutting portion or a D-shaped cross-section so that the shaft  640  and the coupling member  630  are not separated while rotating. 
     Meanwhile, an additional elastic member  643  may be provided for elastically biasing the shaft  640  and the coupling member  630  toward the coupling position. 
     The coupling lever  650  is rotatably coupled to the frame P and rotates by an external force (refer to ‘ 310 ’ in  FIG. 9A ), thereby moving the coupling knob  620  to the coupling position. The coupling lever  650  includes a lever main body  651  to be pressed by the external force, the knob coupling rib  655  extended from the lever main body  651  and coupling with the coupling knob  620 , and a hinge  653  coupled to the frame P. 
     The knob coupling rib  655  is accommodated in the knob member  623  and guides the coupling member  630  when the knob main body  621  moves between the coupling position and the decoupling position. 
     The elastic member  660  elastically urges the coupling lever  650  in such a manner that the coupling knob  620  and the coupling member  630  moves toward the decoupling position. The elastic member  660  has a first end coupled to the hinge  653  of the coupling lever  650  and a second end coupled to the knob coupling rib  655 , thereby applying elasticity in the decoupling direction as shown in  FIG. 9B . 
     With this configuration, operations of the coupling apparatus  600  according to the second example embodiment of the present invention will be described with reference to  FIGS. 9A through 11B . 
     First, if the external force  310  is not applied to the coupling lever  650  as shown in  FIG. 9A , the second guide part  625  of the coupling knob  620  and the third movement changing part  613  of the coupling link  610  are disposed alternately with each other as shown in  FIG. 11A . At this time, due to difference in size between an outer diameter of the coupling link  610  and an inner diameter of the knob main body  621 , the coupling link  610  cannot move toward the coupling knob  620 . Accordingly, the first counter part  211  and the coupling part  635  are not connected to each other, and thus the rotational force is not transmitted from the second counter part  410  to the first counter part  111 . 
     On the other hand, if the external force  310  is applied as shown in  FIG. 9B , the coupling lever  650  rotates along with the coupling knob  620 . At this time, the second guide part  625  of the knob main body  621  is rotated to fit to the third movement changing part  613 , so that the knob main body  621  can move in the axial direction. Accordingly, the coupling member  630  is coupled to the first counterpart  211  and transmits the rotational force from the second counterpart  410  to the first counterpart  211  as the gear part  633  rotates. 
     Meanwhile, the elastic member  660  elastically biases the coupling lever  650  in such a manner that the first counterpart  211  and the coupling part  635  are decoupled from each other. Accordingly, at a moment when the coupling lever  650  is released from pressure, the elastic member  660  elastically biases the coupling lever  650  to an initial position, so that the coupling knob  620  and the coupling member  630  directly move to the decoupling position. 
     According to the second example embodiment of the present invention, the coupling apparatus additionally includes the coupling lever and the elastic member and is thus more quickly changed from the coupling position to the decoupling position as compared with that of the first example embodiment. Further, in the second example embodiment, the total number of components is reduced as compared with that of the first example embodiment, so that an assembling process can be simplified. 
     In the example embodiments described above, the coupling apparatus is described as transmitting power to the belt driving unit  460  that drives the transfer belt  451  forming the transfer unit  450 , but aspects of the present invention are not limited thereto. The belt driving unit according to aspects of the present invention is not limited to the transfer unit, and may be used for other image forming apparatuses, such as a monochrome printer, a facsimile machine, a digital photocopier, and multifunction devices. In addition, the belt driving unit may be used for a printable medium feeding unit that feeds an outputted printable medium, a photosensitive belt unit that forms an electrostatic latent image to form a toner image, and a mid-transfer unit that transfers and maintains the toner image. Also, aspects of the present invention may be used in a belt feeding unit such as a belt conveyor. 
     As described above, the coupling apparatus according to aspects of the present invention is provided to be automatically restored to a decoupling position by an elastic member when the external force is released from the coupling knob, to thereby be prevented from being coupled by opening of the cover or an external impact. Accordingly, the image forming apparatus employing the coupling apparatus can be prevented from being damaged when the cabinet is opened or closed by malfunction of the coupling apparatus. 
     Rotational components among the components forming the coupling apparatus according to aspects of the present invention are disposed to be rotatably driven centering on the shaft, thereby obtaining a compact configuration to enhance durability, and reducing an installing space. Since the rotational center of the coupling apparatus is disposed on a rotational axis of the driving roller driving the transfer unit in the image forming apparatus employing the coupling apparatus, coupling components can be disposed in a small space. The compact configuration of the coupling apparatus improves intensity, thereby enhancing durability. 
     While there have been illustrated and described what are considered to be example embodiments of the present invention, it will be understood by those skilled in the art and as technology develops that various changes and modifications, may be made, and equivalents may be substituted for elements thereof without departing from the true scope of the present invention. Many modifications, permutations, additions and sub-combinations may be made to adapt the teachings of the present invention to a particular situation without departing from the scope thereof. For example, aspects of the present invention may include a method of coupling or decoupling a component of an image forming apparatus from a driving unit when a cover of the image forming apparatus is closed or opened so as to reduce damage to components of the apparatus. The method may include applying a force to a coupling knob attached to a coupling apparatus that selectively couples a driving unit to a component of an image forming apparatus while the coupling apparatus is in a decoupled state wherein the component of the image forming apparatus is not coupled to the driving unit; automatically rotating the coupling knob in response to the application of the force; converting the rotation of the coupling knob into an axial movement of a shaft; switching the state of the coupling apparatus from the decoupled state to a coupled state in which the coupling apparatus couples the component of the image forming apparatus to the driving unit, in response to the axial movement of the shaft; maintaining the coupling apparatus in the coupling state while the force is applied to the coupling knob; and automatically switching the state of the coupling apparatus from the coupled state to the decoupled state when the force is no longer applied to the coupling knob. Accordingly, it is intended, therefore, that the present invention not be limited to the various example embodiments disclosed, but that the present invention includes all embodiments falling within the scope of the appended claims.