Patent Publication Number: US-8109500-B2

Title: Medium supply unit and image forming apparatus having the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from Korean Patent Application No. 10-2009-0114345, filed on Nov. 25, 2009 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND 
     1. Field of the Invention 
     Apparatuses and methods consistent with the exemplary embodiments relate to a medium supply unit to supply a printing-target medium to an image forming unit of forming an image; and an image forming apparatus having the same, and more particularly, to a medium supply unit in which the assembly structure of a pickup roller assembly to pick up and supply loaded printing-target media is improved and; and an image forming apparatus having the same. 
     2. Description of the Related Art 
     An image forming apparatus can form a visual image by a developing solution or an ink on a printing-target medium based on image data supplied from an external host apparatus. To that end, the image forming apparatus includes an image forming unit and a medium supply unit which supplies a printing-target medium to the image forming unit. 
     In the medium supply unit of the image forming apparatus, a plurality of printing-target media are loaded in a loading cassette that is attachable to a housing of a main body thereof or in a loading tray that is pivotable with respect to the housing. The loaded printing-target media are picked up by a pickup roller to be supplied to the image forming unit. 
     Such a pickup roller is made of a material having a high frictional coefficient, such as a synthetic rubber, and rotatable while being brought into contact with the printing-target media with a predetermined pressure to pick up the printing-target media by a frictional force therebetween. Accordingly, if the pickup roller is used for a long period of time, a surface of the pickup roller is worn out by such friction, thereby lowering the picking-up performance thereof. Therefore, there is a requirement to replace the old pickup roller with a new one in adequate intervals. 
     In the meantime, the old pickup roller is required to be separated from an activating shaft, used to rotate the pickup roller, to be replaced with a new one. Since, however, the activating shaft penetrates through the pickup roller in such a conventional medium supply unit, the activating shaft and the pickup roller are required to be separated together from a main body of the image forming apparatus in order to replace the pickup roller. In this case, the time that it takes to replace the pickup roller is increased because the assembly structure of the pickup roller in the main body thereof is complex. 
     SUMMARY 
     Exemplary embodiments of the present general inventive concept provide a medium supply unit and an image forming apparatus having the same, in which an assembly structure of a pickup roller to pick up loaded printing-target media is simply embodied. 
     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. 
     Embodiments of the present general inventive concept may be achieved by providing a medium supply unit of an image forming apparatus, the medium supply unit including: a main body housing; a tray connected to the main body housing and loading a printing-target medium therein; an activating shaft connected to the main body housing and being rotated in a predetermined direction by an activating force of an activating source; an intermediate member supported by one end of the activating shaft to deliver a rotating force of the activating shaft; a first elastic member having one end connected to the intermediate member and the other end supported by the activating shaft; and elastically biasing the intermediate member in a direction facing the printing-target medium according to a rotation of the activating shaft; and a roller unit having a roller unit housing that is attachable to the intermediate member and at least one roller that is supported by the roller unit housing and picks up and supplies printing-target media loaded in the tray; and configured to deliver to the roller(s) an elastic force of the first elastic member and a rotating force of the activating shaft when the activating shaft is rotated. 
     The first elastic member may include a torsion spring that is wound around the activating shaft, and when the activating shaft is rotated, a wound diameter of the torsion spring may be reduced, thereby increasing a friction between the torsion spring and the activating shaft. 
     The reduced diameter of the torsion spring may be recovered to an original state when the activating shaft is stopped to be rotated. 
     The medium supply unit may include a second elastic member configured to elastically bias the intermediate member in a direction in which the roller unit is separated from the printing-target medium when the activating shaft is stopped to be rotated. 
     The rollers may include a first roller arranged at a same axis line as that of the activating shaft; and a second roller arranged at an axis line that is separated in parallel from that of the first roller. 
     The second roller may be pivotable, with respect to the first roller, from a supply position, where the printing-target medium loaded in the tray is supplied, to a separated position, where the second roller is separated from the supply position. 
     The second roller may be pivoted to the supply position by the first elastic member, when the activating shaft is rotated, and to the separated position by the second elastic member, when the activating shaft is stopped to be rotated. 
     The activating shaft may include an activating shaft coupling part which is formed at one end thereof extending through a through hole formed in the intermediate member and is coupling-connected with the roller unit to deliver the rotating force of the activating shaft. 
     The roller unit may include a first clutch unit which is coupling-connected with the activating shaft coupling part and selectively engaged with the first roller according to whether or not the activating shaft is rotated. 
     The first clutch unit may be engaged with the first roller to deliver the rotating force of the activating shaft, when the activating shaft is rotated, and disengaged therewith to enable the first roller to be idle-rotated, when the activating shaft is stopped to be rotated. 
     The roller unit may include a second clutch unit which receives the rotating force of the activating shaft from the first clutch unit and is selectively engaged or disengaged with the second roller to selectively deliver the delivered rotating force according to whether or not the first clutch unit is engaged with the first roller. 
     Embodiments of the present general inventive concept may also be achieved by providing an image forming apparatus including: a medium supply unit configured to supply a printing-target medium; and an image forming unit configured to form an image on the printing-target medium supplied from the medium supply unit, wherein the medium supply unit includes: a main body housing; a tray connected to the main body housing and loading a printing-target medium therein; an activating shaft connected to the main body housing and being rotated in a predetermined direction by an activating force of an activating source; an intermediate member supported by one end of the activating shaft to deliver a rotating force of the activating shaft; a first elastic member having one end connected to the intermediate member and the other end supported by the activating shaft; and elastically biasing the intermediate member in a direction facing the printing-target medium according to a rotation of the activating shaft; and a roller unit having a roller unit housing that is attachable to the intermediate member and at least one roller that is supported by the roller unit housing and picks up and supplies printing-target media loaded in the tray; and configured to deliver to the roller(s) an elastic force of the first elastic member and a rotating force of the activating shaft when the activating shaft is rotated. 
     Embodiments of the present general inventive concept may be achieved by providing a medium supply unit, including: an activating shaft to supply a rotating force; an intermediate member to receive and transfer the rotating force of the activating shaft when the activating shaft is in contact therewith; and a roller unit in contact with the intermediate member and including at least one roller to engage with and disengage with printing media based on whether the activating shaft is supplying a rotating force. 
     The intermediate member may include an elastic device connected to the activating shaft and the intermediate member such that when the activating shaft is rotated, the elastic device applies a force to the intermediate member to move the intermediate member toward the printing media such that the roller unit is brought into contact with the printing media. 
     The elastic device may include: a first elastic member surrounding the activating shaft and connected thereto at one end and connected to the intermediate member an opposite end such that when the activating member is rotated, the first elastic member receives a force to be compressed closer to the activating member; and a second elastic member connected at one end to the intermediate member to bias the intermediate member away from the printing media, wherein when the activating shaft rotates by a certain predetermined amount, the force to compress the first elastic member becomes greater that an elastic force of the second elastic member to elastically bias the intermediate member toward the printing media, and when the activating shaft is stopped from rotating, the first elastic member becomes uncompressed such that the elastic force of the second elastic member overcomes the elastic force of the first elastic member to elastically bias the intermediate member away from the printing media. 
     The roller unit may include a clutching device to engage the at least one roller to rotate when the activating shaft is rotated, and to disengage the at least one roller such that the at least one roller is idle when the activating shaft is not rotated. 
     The at least one roller may include a first roller to engage with the clutching device when the activating shaft is rotated and a second roller to engage with the clutching device when the activating shaft is rotated. 
     The clutching device may include: a first clutching unit to engage with the first roller; a second clutching unit to engage with the second roller; and an intermediate gear to engage the first and second clutching units to rotate together when the activating shaft rotates. 
     Embodiments of the present general inventive concept may be achieved by providing a medium supply unit, including: an activating shaft to supply a rotating force; a roller unit in contact with the activating shaft and including at least one roller to engage with and disengage with printing media based on whether the activating shaft is supplying a rotating force; and an elastic support system connected between the activating shaft and the roller unit to supply an elastic force to the roller unit to bias the roller unit toward the printing media when the activating shaft supplies a predetermined amount of rotating force. 
     The roller unit may include a clutching system in contact with an end of the activating shaft to engage the at least one roller to rotate when the activating shaft is rotated such that a frictional force is applied to the printing media when the activating shaft rotates, and to disengage the at least one roller to be idle when the activating shaft is stopped from being rotated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above 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 exemplary embodiments, taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a side cross sectional view showing an image forming apparatus in accordance with an exemplary embodiment; 
         FIG. 2  is a perspective view showing main parts of a second pickup roller assembly in the image forming apparatus shown in  FIG. 1 ; 
         FIG. 3  is a perspective view showing main parts of an activating shaft and an intermediate member in the second pickup roller shown in  FIG. 2 ; 
         FIG. 4  is a perspective view showing main parts of a roller unit in the second pickup roller assembly; 
         FIG. 5  is a plan view showing the second pickup roller assembly in the image forming apparatus shown in  FIG. 1 ; 
         FIG. 6  is a plan view showing how a first and a second clutch unit are engaged with a first and a second roller main body, respectively, in the second pickup roller assembly shown in  FIG. 5 ; 
         FIG. 7  is a plan view showing how the first and the second clutch unit are disengaged with the first and the second roller main body, respectively, in the second pickup roller assembly shown in  FIG. 5 ; and 
         FIG. 8  is a side view showing a pivoting structure of the roller unit in the second pickup roller assembly shown in  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Below, exemplary embodiments will be described in detail with reference to accompanying drawings so as to be easily realized by a person having ordinary knowledge in the art. The exemplary embodiments may be embodied in various forms without being limited to the exemplary embodiments set forth herein. Descriptions of well-known parts are omitted for clarity, and like reference numerals refer to like elements throughout. Throughout the description of the present embodiments, only elements directly relative to the sprit and scope of the exemplary embodiments are described, while the description of other elements may be omitted. This, however, does not mean that the omitted elements are not essential to embody an image forming apparatus of the exemplary embodiments. 
       FIG. 1  is a side cross sectional view showing an image forming apparatus  1  in accordance with an exemplary embodiment. The image forming apparatus  1  of the present embodiment may transfer a visual image by a developing solution on a printing-target medium by using an intermediate transfer method. However, the sprit and scope of the present embodiment is not limited thereto. Alternatively, the sprit and scope of the exemplary embodiment is applicable to the image forming apparatus  1  by using various methods regardless of whether a color image or a white-and-black image is formed, transfer method, whether an image is formed by a developing solution or an ink, and the like. 
     As shown in  FIG. 1 , the image forming apparatus  1  of the present embodiment may include a main body housing  3  which constitutes an outer appearance thereof; a medium supply unit  10  which loads a printing-target medium therein and supplies the loaded printing-target medium  10 ; and an image forming unit  20  which forms an image on the printing-target medium supplied from the medium supply unit  10 . 
     The medium supply unit  10  may include a loading cassette  11  which is attachable to the main body housing  3 ; a first pickup roller assembly  12  which picks up a printing-target medium M from the loading cassette  11 ; a registration roller  13  which supplies the picked printing-target medium M to the image forming unit  20  with an adequate timing; a duplex roller  14  which inversely sends to the registration roller  13  the printed medium M on which an image has been transferred; a loading tray  15  which is pivotable with respect to the main body housing  3 ; and a second pickup roller assembly  17  which picks up a printing-target medium M from the loading tray  15 . 
     The loading cassette  11  may be separated from the main body housing  3  to load printing-target media M therein. Then, the loading cassette  11  may be re-connected to the main body housing  3 . If a printing process is started, the first pickup roller assembly  12  may pick up a top printing-target medium M of the printing-target media M loaded in the loading cassette  11  and supply it to the registration roller  13 . 
     The registration roller  13  can align a leading end of the sent printing-target medium M and supply the printing-target medium M to the image forming unit  20  with a predetermined timing such that a visual image formed by the image forming unit  20  is transferred on the printing-target medium M. 
     When there is a request for a duplex printing, the duplex roller  14  can inversely send to the registration roller  13  the printed medium M, one surface of which the image has already been transferred. The printed medium M inversely sent by the duplex roller  14  can be re-supplied to the image forming unit  20  by the registration unit  13  such that another image is transferred on the other surface of the printed medium M on which no image has been transferred. 
     To perform the printing process, the printing-target medium M may be loaded in the loading tray  15  instead of the loading cassette  11  before being supplied from the medium supply unit  10  to the image forming unit  20 . 
     The loading tray  15  may be connected to the main body housing  3  to be pivotable thereto. The printing-target media M may be loaded in the loading tray  15  when the loading tray  15  is pivoted to be separated from the main body housing  3 . The printing-target media M loaded in the loading tray  15  can be picked up by the second pickup roller assembly  17  and guided along a guide frame  16  to be supplied to the registration roller  13 . Here, a path through which the printing-target media M picked up by the second pickup roller assembly  17  is supplied may be partially overlapped with a path through which the printed media M are inversely sent by the duplex roller  14 . 
     The image forming unit  20  may include image receptors  21 Y,  21 M,  21 C, and  21 K (or collectively referred to as “ 21 ”) which forms a latent electrostatic image and a visual image on a surface; an exposure unit  22  which exposes the image receptors  21  to form the latent electrostatic image; developing cartridges  23 Y,  23 M,  23 C, and  23 K (or collectively referred to as “ 23 ”) which apply developing solutions to latent electrostatic image of the image receptors  21  to form the visual image; a transfer unit  30  which transfers the visual image of the image receptors  21  on a printing-target medium M according to an intermediate transfer method; and a fixing unit  40  which fixes the image on the printing-target medium M by a heat and a pressure. 
     The image receptors  21  may be installed for various colors to form a latent electrostatic image on a surface thereof based on image data for various colors by the exposure unit  22 . If developing solutions are applied to the image receptors  21 , the developing solutions may selectively be attached on the image receptors  21  by an electric potential. As a result, the image receptors  21  may form a visual image by the developing solutions. 
     The exposure unit  22  may scan a beam of light to the respective image receptors  21 Y,  21 M,  21 C, and  21 K, which are uniformly charged, based on the image data for various colors to form a latent electrostatic image. The exposure unit  22  may be embodied as a light scanning unit including a light source (not shown), a polygon lens (not shown), and various optical lenses (not shown). 
     The developing cartridges  23  may be installed corresponding to the image receptors  21 . The developing cartridges  23 Y,  23 M,  23 C, and  23 K may contain therein the developing solutions for various colors to apply the contained developing solutions to the respective image receptors  21 Y,  21 M,  21 C, and  21 K, respectively. For example, the developing cartridges  23 Y,  23 M,  23 C, and  23 K may be installed corresponding to four colors: yellow, magenta, cyan, and black. Moreover, the corresponding developing cartridges  23 Y,  23 M,  23 C, and  23 K may be respectively attached to and detached from the main body housing  3  for the replacement. 
     The transfer unit  30  may include an intermediate transfer belt  31  which is moved in a caterpillar method, the intermediate belt  31  being in contact with the respective image receptors  21 Y,  21 M,  21 C, and  21 K; a plurality of intermediate transfer rollers  32 Y,  32 M,  32 C, and  32 K (or collectively referred to as “ 32 ”) which are installed corresponding to the respective image receptors  21 Y,  21 M,  21 C, and  21 K, the intermediate transfer belt  31  being placed between the intermediate transfer rollers  32  and the image receptors  21 ; an activating roller  33  which is rotated to move the intermediate transfer belt  31 ; a final transfer roller  34  which is provided at a contact portion between the intermediate transfer belt  31  and the path through which the printing-target media M are supplied from the registration roller  13 ; a transfer backup roller  35  which backs up the intermediate transfer belt  31  with respect to the final transfer roller  34 ; and a tension roller  36  which applies a tension to the intermediate belt  31 . 
     As shown in  FIG. 1 , when the activating roller  33  is rotated in a counterclockwise direction, the intermediate transfer rollers  32 Y,  32 M,  32 C, and  32 K may successively transfer on the intermediate transfer belt  31  the visual image of the image receptors  21 Y,  21 M,  21 C, and  21 K, respectively. At this time, portions of the visual image corresponding to yellow, magenta, cyan, and black can successively be transferred, and the four-color portions of the visual image can be overlapped with each other, thereby forming a final color image. 
     If the final color image is formed, a printing-target medium M is supplied from the registration roller  13  with an adequate timing. The final transfer roller  34  can transfer the final color image of the intermediate transfer belt  31  on the printing-target medium M. 
     The fixing unit  40  can perform a fixing operation by applying a heat and a pressure to the printed medium M on which the final color image has been transferred. The printed medium M on which the fixing has been completed may be output external to the image forming apparatus  1 . 
     A configuration of the second pickup roller assembly  17  will be described with reference to  FIG. 2 , the second pickup roller assembly  17  being configured to pick up a printing-target medium M from the loading tray  15  to supply it to the registration roller  13  in the above-described image forming apparatus  1 .  FIG. 2  is a perspective view showing main parts of the second pickup roller assembly  17  in the image forming apparatus shown in  FIG. 1 . 
     First, each direction shown in  FIG. 2  will be described. An X, Y and Z-axis may basically indicate each of the three-dimensional directions. Reverse directions of the X, Y, and Z-axis direction are referred to as −X, −Y, and −Z-axis direction, respectively. In the X-axis direction, the printing-target media M is supplied to the registration roller  13 . The Y-axis direction is a direction perpendicular to the X-axis direction. The Z-axis direction is an upper and a lower direction perpendicular to the X-axis direction and the Y-axis direction, respectively. Here, the X-Y plane is a plane formed by the X and the Y-axis. 
     As shown in  FIG. 2 , the second pickup roller assembly  17  of the present embodiment may include an activating shaft  100  which is rotatable in a predetermined direction by an activating force of an activating source (not shown); a roller unit  200  which is arranged at one end side of the activating shaft  100  to pick up a printing-target medium M; and an intermediate member  300  which is arranged between the activating shaft  100  and the roller unit  200  to deliver a rotating force of the activating shaft  100  to the roller unit  200 . 
     The activating shaft  100  may extend in the Y-axis direction on the guide frame  16 . One of opposite ends of the activating shaft  100  which is located at a central portion of the guide frame  16  may be coupling-connected to the roller unit  200 , and the other end thereof which is located at an edge portion of the guide frame  16  may be connected to a clutch  110  which controls the activating force of the activating source (not shown). 
     When the activating force is permitted to be delivered by the clutch  110 , the activating shaft  100  may be rotated in a direction in which the printing-target media M are supplied in the X-axis direction. Since one end of the activating shaft  100  is coupling-connected to the roller unit  200 , a rotating force of the activating shaft  100  may be delivered to the roller unit  200 . Accordingly, the roller unit  200  may supply the printing-target media M. 
     Hereinafter, configurations of the activating shaft  100  and the intermediate member  300  will be described with reference to  FIG. 3 .  FIG. 3  is a perspective view showing main parts of the activating shaft  100  and the intermediate member  300 . 
     As shown in  FIG. 3 , the activating shaft  100  may extend through the intermediate member  300 . The activating shaft  100  may include an activating shaft coupling part  120  which is formed at one end thereof extending through the intermediate member  300  and coupling-connected to the roller unit  200 . 
     One side of the intermediate member  300  where the activating shaft coupling part  120  protrudes may be connected to the roller unit  200 . In other words, one side of the roller unit  200  which is coupling-connected to the activating shaft coupling part  120  may be connected to the intermediate member  300 . The connecting method of the roller unit  200  and the intermediate member  300  is not limited thereto. Alternatively, easy connection may be made therebetween by applying an engaging structure such as a hook structure, a protrusion and protrusion receiving structure, and a prominence and depression structure. 
     In the meantime, the second pickup roller assembly  17  may include a first elastic member  400  having one end which is supported by the activating shaft  100  and the other end which is connected to the intermediate member  300 ; and a second elastic member  500  which is connected to one side of the intermediate member  300 . 
     The first elastic member  400  may be embodied as a torsion spring or an elastic body, one end of which is wound around the activating shaft  100 . The other end of the first elastic member  400 , which is not wound around the activating shaft  100 , may be connected to the intermediate member  300 . 
     The second elastic member  500  may have one end which is connected to the intermediate member  300  and the other end which is connected to a support member (not shown) provided at an upper side of the intermediate member  300 . The second elastic member  500  may be embodied as one of various members such as a coil spring and a plate spring. 
     When a portion of the intermediate member  300  where the activating coupling part  120  extends therethrough corresponds to that of a first roller main body  210  of the roller unit to be described later, a portion of the intermediate member  300  where the second elastic member  500  is connected therewith may correspond to that of a second roller main body  220  of the roller unit. Moreover, a portion of the intermediate member  300  where the first elastic member  400  is connected therewith may be positioned at a side of the second elastic member  500  with reference to the activating shaft  100 . Accordingly, the second roller main body  220  may be pivoted with respect to the first roller main body  210 . This will be described in more detail later. 
     The second elastic member  500  may elastically bias the intermediate member  300  in a direction in which the intermediate member  300  is separated from the printing-target media M. 
     In the above-mentioned configuration, when the activating shaft  100  is rotated, the diameter of the first elastic member  400  that is wound around the activating member  100  may be reduced because the first elastic member  400  is connected to the intermediate member  300 . In other words, the first elastic member  400  becomes wound tighter such that the diameter decreases and approaches the activating member  100 . Accordingly, the friction between the first elastic member  400  and the activating shaft  100  may be increased, and the intermediate member  300  may be downwardly pivoted with respect to the activating shaft  100 . At this time, an elastic force of the second elastic member  500  may be overcome. 
     When the activating shaft  100  is stopped from rotating, the wound diameter of the first elastic member  400 , which is in the reduced state, may be recovered to an original state. Accordingly, the friction between the first elastic member  400  and the activating shaft  100  may be decreased, and the intermediate member  300  may be upwardly pivoted with respect to the activating shaft  100  by the second elastic member  500 . 
     Here, the detailed structure of the first elastic member  400  is as follows. 
     The first elastic member  400  has two end parts, e.g., a first end part and a second end part. The first end part is fixed to the intermediate member  300 . On the other hand, the second end part opposite to the first end part is not fixed to but wound on the outer circumference of the activating shaft  100  while pressing and contacting the outer circumference with predetermined pressure. 
     With this structure, if the activating shaft  100  rotates, the contact between the second end part of the first elastic member  400  and the outer circumference of the activating shaft  100  may cause the wound diameter of the first elastic member  400  to be decreased depending on a winding direction. When the wound diameter of the first elastic member  400  is decreased, the friction between the first elastic member  400  and the activating shaft  100  increases. Also, the increased friction makes the intermediate member  300  to which the first end part of the first elastic member  400  is fixed be elastically biased. 
     Then, if the activating shaft  100  stops rotating, the wound diameter of the first elastic member  400  is put back and the friction returns to its original level. Accordingly, the intermediate member  300  is free from the elastic bias. 
     Hereinafter, a configuration of the roller unit  200  will be described with reference to  FIG. 4 .  FIG. 4  is a perspective view showing main parts of the roller unit  200 . 
     As shown in  FIG. 4 , the roller unit  200  may include a roller unit housing  201 ; the first and the second roller main body  210  and  220  which are arranged in parallel with each other in the roller unit housing  201 ; a first clutch unit  230  which delivers a rotating force of the activating shaft  100  to the first roller main body  210 ; a second clutch unit  240  which receives the rotating force of the activating shaft  100  from the first clutch unit  230  and delivers this force to the first roller main body  220 ; and an intermediate gear  250  which is provided between the first and the second clutch unit  230  and  240  to deliver the rotating force from the first clutch unit  230  to the second clutch unit  240 . 
     The roller unit housing  201  may accommodate therein various components of the roller unit  200  and have an open lower surface facing the printing-target media M, the open lower surface through which the first and the second roller main body  210  and  220  can be brought into contact with the printing-target media M. A roller unit coupling part  237  which is to be coupling-connected with the activating shaft coupling part  120  may be formed on one surface of the roller unit housing  201  which is connected to the intermediate member  300 . 
     The first and the second roller main body  210  and  220  may be rotated along with the activating shaft  100  by being connected thereto to pick up and deliver the printing-target media M. The first and the second roller main body  210  and  220  may be made of a material having a relatively high frictional coefficient, such as a synthetic rubber, to pick up the printing-target media M by a frictional force therebetween. 
     The first roller main body  210  may be arranged in a same axis line as that of the activating shaft  100 , and the second roller main body  220  may be arranged and separated from the first roller main body  210  in a direction perpendicular to the axis line. 
     The first clutch unit  230  may be provided between the activating shaft  100  and the first roller main body  210  in the roller unit housing  102 . The roller unit coupling part  237  may be formed at one side of the first clutch unit  230  facing the activating shaft  100  and selectively engaged or disengaged with the first roller main body  210  according to whether or not the activating shaft  100  is rotated. 
     While the activating shaft  100  is rotated, the first clutch unit  230  may be engaged with the first roller main body  210  to rotate the first roller main body  210 . On the other hand, when the activating shaft  100  is stopped from rotating, the first clutch unit  230  may be disengaged from the first roller main body  210  such that the first roller main body  210  is idle-rotated. A configuration of the first clutch unit  230  will be described in detail later. 
     The second clutch unit  240  may be provided between the intermediate gear  250  and the second roller main body  220  to deliver to the second roller main body  220  the rotating force of the activating shaft  100  supplied through the intermediate gear  250 . Similar to the first clutch unit  230 , the second clutch unit  240  may be selectively engaged or disengaged with the second roller main body  220  according to whether or not the activating shaft  100  is rotated. 
     Similarly, while the activating shaft  100  is rotated, the second clutch unit  240  may be engaged with the second roller main body  220  to rotate the second roller main body  220 . On the other hand, when the activating shaft  100  is stopped to be rotated, the second clutch unit  240  may be disengaged from the second roller main body  220  such that the second roller main body  220  is idle-rotated. 
     In other words, while the activating shaft  100  is rotated, the first and the second clutch unit  230  and  240  may enable the first and the second roller main body  210  and  220 , respectively, to be rotated in order to pick up and supply the printing-target media M. 
     On the other hand, when the activating shaft  100  is stopped from rotating, the first and second clutch unit  230  and  240  may enable the first and the second roller main body  210  and  220 , respectively, to be idle-rotated. Accordingly, it is possible to reduce the friction between the printing-target media M and the first and the second roller main body  210  and  220 , respectively, to thereby supply the printing-target media M easily. 
     The second clutch unit  240  may include a second clutch main body  241 ; a second gear  242  which is formed on an outer peripheral surface of the second clutch main body  241  to be engaged with the intermediate gear  250 ; a second protrusion  243  which protrudes in the second clutch main body  241  between the second gear  242  and the second roller main body  220 ; a third engaging part  244  which surrounds an outer periphery of the second clutch main body  241  and is installed to be freely rotatable; an inclined part  245  which is formed in the third engaging part  244  along the outer periphery of the second clutch main body  241  and guided by the second protrusion  243 ; and a fourth engaging part  246  which is connected to the second roller main body  220  to be selectively engaged with the third engaging part  244 . 
     The first clutch unit  230  may have the same configuration as that of the above-mentioned second clutch unit  240 . The first and the second clutch unit  230  and  240  will be described in detail later. 
     Hereinafter, a configuration of the second pickup roller assembly  17  of the present embodiment will be described with reference to  FIG. 5 .  FIG. 5  is a plan view showing the second pickup roller assembly  17 . 
     As shown in  FIG. 5 , the intermediate member  300  may be connected to a right surface of the roller unit  200 , and an activating shaft through hole  310  may be formed at a portion corresponding to the roller unit coupling part  237 . The activating shaft  100  may extend through the activating shaft through hole  310 . Accordingly, the activating shaft coupling part  120  may be coupling-connected with the roller unit coupling part  237 . 
     The first elastic member  400  may have one end which is wound around the activating shaft  100  and the other end which is connected to the intermediate member  300 . One end of the second elastic member  500  may be connected to the intermediate member  300 . 
     The first roller main body  210  may extend along the axis line of the activating shaft  100 , and a first roller shaft  211  may extend from the first roller main body  210  in the reverse direction to which the activating shaft  100  is provided. A bushing  60  may be arranged at a left side of the roller unit  200 , the bushing  60  being supported by a supporting frame  50  and elastically pressed by a spring  70  in the direction of the activating shaft  100 . The first roller shaft  211  may be rotatably supported by the bushing  60 . 
     In the disassembling of the roller unit  200 , the activating shaft  100  and the intermediate member  300  may be separated from the roller unit  200  and, then, the first roller shaft  211  may be separated from the bushing  60 . Accordingly, it is possible to easily disassemble the roller unit  200 . Reversely, in the assembling of the components of the roller unit  200 , the first roller shaft  211  may be supported by the bushing  60 . Then, the roller unit coupling part  237  may be coupling-connected to the activating shaft coupling part  120 , and the intermediate member  300  may be connected to the roller unit  200 . Accordingly, it is possible to easily assemble the components of the roller unit  200 . 
     Since each of the first and the second elastic member  400  and  500  is connected to the intermediate member  300  instead of the roller unit  200 , it is not necessary to consider the relationship of a connection between the roller unit  200  and each of the first and the second elastic member  400  and  500 , especially during a replacement of the roller unit  200 . Accordingly, it is possible to easily separate and replace the roller unit  200 . 
     The first clutch unit  230  may include a first clutch main body  231 ; a first gear  232  which is formed on an outer peripheral surface of the first clutch main body  231  to be engaged with the intermediate gear  250 ; a first protrusion  233  which protrudes in the first clutch main body  231  between the first gear  232  and the first roller main body  210 ; a first engaging part  234  which surrounds an outer periphery of the first clutch main body  231  and is installed to be freely rotatable; an inclined part  235  which is formed in the first engaging part  234  along the outer periphery of the first clutch main body  231  and guided by the first protrusion  233 ; and a second engaging part  236  which is connected to the first roller main body  210  to be selectively engaged with the first engaging part  234 . The roller unit coupling part  237  may be formed at a side of the first clutch main body  231  or embodied as an additional member to be connected to the first clutch main body  231 . 
     The first engaging part  234  may have a ring shape of a predetermined width which surrounds the outer periphery of the first clutch main body  231 . One side of the first engaging part  234  may have a saw-toothed shape to face the second engaging part  236  such that the first engaging part  234  can engage with the second engaging part  236 . The inclined part  235  may be formed in a spiral shape at a predetermined portion along an axis line of the first clutch main body  231  in the reverse direction to the first engaging part  234 , i.e., in the direction facing the activating shaft  100 . The first protrusion  233  may be hooked onto opposite ends of the inclined part  235  to control the pivoting of the first engaging part  234 . 
     The second engaging part  236  may annularly protrude from an end portion of the first roller main body  210 . The second engaging part  236  may accommodate the end portion of the first clutch main body  231  at a central portion thereof and have a shape to engage with the saw-toothed shape of the first engaging part  234 . 
     Once the activating shaft  100  is rotated, the first clutch main body  231  may also be rotated because of the coupling-connection between the activating shaft coupling part  120  and the roller unit coupling part  237 . The rotating force of the first clutch main body  231  may be delivered to the second clutch main body  241  through the first gear  232 , the intermediate gear  250 , and the second gear  242 . The second clutch main body  241  may be rotated in the same direction as that of the first clutch main body  231 . 
     As the first and the second clutch main body  231  and  241  are rotated, the first and the third engaging part  234  and  244  may be engaged with the second and the third engaging part  236  and  246 , respectively. Accordingly, the rotating forces of the first and the second clutch main body  231  and  241  may be delivered to the first and the second roller main body  210  and  220 , respectively. 
     Therefore, the first and the second roller main body  210  and  220  may be rotated to pick up and supply the printing-target media M. 
     In the meantime, when the activating shaft  100  is stopped from being rotated, the printing-target media M may be supplied by being brought into contact with each of the first and the second main body  210  and  220 . In this case, if the first and the second roller main body  210  and  220  are stopped from being rotated, it may become difficult to supply the printing-target media M due to the friction between the printing-target media M and the first and the second roller main body  210  and  220 . Accordingly, the first and the second main body  210  and  220  can be configured to be idle-rotated when the activating shaft  100  is stopped from being rotated. 
     Hereinafter, a configuration where the first clutch unit  230  is selectively engaged with the first roller unit  210  according to whether or not the activating shaft  100  is rotated will be described with reference to  FIGS. 6 and 7 . Since the configuration of the first clutch unit  230  is applicable to the second clutch unit  240 , the corresponding description will be omitted. 
       FIG. 6  is a plan view showing how the first and the second clutch unit  230  and  240  are engaged with the first and the second roller main body  210  and  220 , respectively, while the activating shaft  100  is rotated. 
     As shown in  FIG. 6 , the inclined part  235  may be formed on the first engaging part  234  in the direction facing the first protrusion  233 . The inclined part  235  may have opposite ends, i.e., one (first) end S 1  and the (second) other end S 2  which are controlled by the first protrusion  233 . The inclined part  235  may be inclined extending from the second end S 2  toward the first end S 1  in the direction of the activating shaft  100 , i.e., the −Y-axis direction. 
     The first protrusion  233  may be provided between the first end S 1  and the second end S 2  and brought into contact with the first end S 1  or the second end S 2  according to the rotation of the first clutch main body  231 . 
     When the activating shaft  100  is rotated, the first clutch main body  231  may also be rotated by interlocking therewith. Here, the activating shaft  100  may be rotated in a predetermined direction to supply the printing-target media M. 
     As the first clutch main body  231  is rotated, the first protrusion  233  may press the first end S 1  by moving thereto. Accordingly, the first engaging part  234  may be moved to an engaged position E to be engaged with the second engaging part  236 . 
     While the activating shaft  100  is rotated, the first protrusion  233  may continuously press the first end S 1  and, thus, the state where the first engaging part  234  is engaged with the second engaging part  236  may be maintained. Accordingly, the first roller main body  210  may be rotated by interlocking with the activating shaft  100 . 
       FIG. 7  is a plan view showing how the first and the second clutch unit  230  and  240  become disengage with the first and the second roller main body  210  and  220 , respectively. 
     As shown in  FIG. 7 , when the printing-target media M is supplied by being brought into contact with the roller main body  210  in the state where the activating shaft  100  is stopped from being rotated by the activating shaft  100 , the first roller main body  210  may also be rotated by the friction with the printing-target media M. At this time, the rotating direction of the first roller main body  210  may be the same as that of the above-described activating shaft  100 . 
     As the first roller main body  210  is rotated, the second engaging part  236  and, furthermore, the first engaging part  234  engaged with the second engaging part  236  may also be rotated. Since, however, the activating shaft  100  is stopped, the first clutch main body  231  may not be rotated. As the first engaging part  234  is rotated, the first protrusion  233  may press the second end S 2 . 
     When the first protrusion part  233  presses the second end S 2 , if the first roller main body  210  is rotated, the first engaging part  234  may be disengaged from the second engaging part  236  and moved back to a disengaged position D. Accordingly, since the first and the second engaging part  234  and  236  are disengaged with each other, the first roller main body  210  may be idle-rotated by being brought into contact with the printing-target media M. 
     As such, the first and the second clutch unit  230  and  240  may be selectively engaged with the first and the second roller main body  210  and  220 , respectively, according to whether or not the activating shaft  100  is rotated. 
     Hereinafter, a pivoting structure of the roller unit  200  according to the rotation of the activating shaft  100  will be described with reference to  FIG. 8 .  FIG. 8  is a side view showing the second pickup roller assembly  17 . 
     As shown in  FIG. 8 , when the activating shaft  100  and the first roller main body  210  are located at the same axis line, the second roller main body  220  may be pivoted from a supply position B to a separated position A with respect to the first roller main body  210 . 
     The second roller main body  220  may be upwardly pivoted and separated from the printing-target media M in the loading tray  15  to the separated position A such that the printing-target media M are easily loaded in the loading tray  15 . 
     The second roller main body  220  may be downwardly pivoted to the supply position B such that the second roller main body  220  supplies the printing-target media M by being brought into contact therewith. When the activating shaft  100  is stopped from being rotated, the second roller main body  220  may be located at the supply position B. 
     The first elastic member  400  that has been wound around the activating shaft  100  may be connected to the intermediate member  300 , and the second elastic member  500  may elastically bias the intermediate member  300  such that the intermediate member  300  is pivotable to the separated position A. 
     Hereinafter, a pivoting structure of the second roller main body  220  according to the rotation of the activating shaft  100  will be described. 
     When the activating shaft  100  is rotated, the diameter of the first elastic member  400  that has been wound around the activating shaft  100  may be reduced. Accordingly, the friction between the first elastic member  400  and the activating shaft  100  may be increased, and the first elastic member  400  may elastically bias the intermediate member  300  in the direction of the supply position B. At this time, the elastic force of the first elastic member  400  may overcome that of the second elastic member  500 . 
     As the intermediate member  300  is pivoted, the second roller main body  200  may also be pivoted to the supply position B. The second roller main body  200  that has been pivoted to the supply position B may be interfered with by the printing-target media M. Such interference may cause the first elastic member  400  to be compressed toward the activating shaft  100 . 
     Such an elastic force of the first elastic member  400  may press the second roller main body  220  toward the printing-target media M, thereby increasing the friction between the second roller main body  220  and the printing-target media M such that the printing-target media M are easily picked up. 
     On the other hand, when the activating shaft  100  is stopped from being rotated, the wound diameter of the first elastic member  400 , reduced when the activating shaft  100  has been rotated, may be recovered to an original state. Accordingly, the friction between the first elastic member  400  and the activating shaft  100  may be decreased, and the second roller main body  220  may be pivoted to the separated position A by the elastic force of the second elastic member  500 . 
     In the above-described configurations of the first and the second elastic member  400  and  500 , it is possible to selectively pivot the second roller main body  220  from the supply position B to the separated position A. 
     In accordance with the exemplary embodiment, it is possible to replace a roller unit only without separating an activating shaft and an intermediate member by installing the intermediate member that is supported by an end portion of the activating shaft and is connected to a first elastic member; and connecting the roller unit to the intermediate member. As such, by simply embodying an assembly structure of the roller unit, a user can easily replace the abraded roller unit and reduce the time that it takes to replace it. 
     In addition, it is possible to apply a pressing force for picking up printing-target media to the pickup roller by employing a torsion spring that is wound around the activating shaft and reducing such wound diameter thereof. 
     Moreover, it is possible to scale down the roller unit by employing a plurality of pickup rollers rather than the case of employing one pickup roller. 
     Further, while the activating shaft is rotated, the first elastic member may cause a second pickup roller to be brought into contact with the printing-target media; on the other hand, when the activating shaft is stopped from being rotated, a second elastic member may cause the second pickup roller to be separated from the printing-target media. Accordingly, the printing-target media may be easily picked up and loaded in a loading tray when such pickup is not performed. 
     Finally, although the activating shaft is stopped from being rotated, the printing-target media may be easily supplied by employing a first and a second clutch unit where the first and second pickup roller, respectively, are idle-rotated when activating shaft is stopped. 
     Although a few exemplary 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 exemplary 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.