Abstract:
A medium pickup unit including a pickup roller, having a circumferential section and a non-circumferential section, to rotate and to pick up a medium due to friction between the circumferential section and the medium, idle rollers respectively disposed at opposite ends of the pickup roller to maintain an orientation of the medium once the non-circumferential section of the pickup roller faces the medium during the rotation of the pickup roller, and a connecting unit coupled to the pickup roller to cause the idle rollers to rotate together.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of Korean Application No. 2006-92953, filed Sep. 25, 2006 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    An aspect of the present invention relates to an image forming apparatus. More particularly, aspects of the present invention relate to a medium pickup unit capable of preventing a medium that is being picked up and conveyed from being twisted, and an image forming apparatus having the same installed therein. 
         [0004]    2. Description of the Related Art 
         [0005]    Generally, an image forming apparatus includes a medium pickup unit and a medium conveying unit. The medium pickup unit picks up media (i.e., printing paper, transparencies, etc.) accommodated in a medium supplying cassette in a one by one sequence. The medium conveying unit conveys the picked up medium toward a developing unit. 
         [0006]      FIG. 1  is a perspective view exemplifying a medium supplying cassette and a medium pickup unit of a general image forming apparatus,  FIG. 2  is a perspective view exemplifying the medium pickup unit selected from  FIG. 1 , and  FIG. 3  is a side elevation view of  FIG. 1 . As is illustrated in the drawings, media are accommodated in the medium supplying cassette  10 , and are urged and supported upward by a knockup plate  11 . As illustrated in  FIG. 3 , the knockup plate  11  is lifted to a position where the accommodated media contacts a medium pickup unit  20 . 
         [0007]    The medium pickup unit  20  is operated according to a printing signal inputted thereto. When a pickup command is issued, the medium pickup unit  20  picks up the accommodated media in a one by one sequence and conveys the picked-up medium toward a medium conveying unit  30 . 
         [0008]    The medium pickup unit  20  includes a pickup roller  21 , and idle rollers  22  disposed at both sides of the pickup roller  21 . As illustrated in  FIG. 2 , the pickup roller  21  is not formed in an exact circular shape, but, rather, in a semicircular shape having a circumferential section and a non-circumferential section. Since the circumferential section contacts the medium, the circumferential section conveys the medium by a friction therewith toward the medium conveying unit  30 . The circumferential section has a diameter slightly larger than that of the idle rollers  22 . Accordingly, when the pickup roller  21  picks up the medium with the circumferential section thereof, the idle rollers  22  are spaced apart from the medium and, thus, are not rotated. 
         [0009]    Then, as the pickup roller  21  continues to rotate, the non-circumferential section of the pickup roller  21  separates from the medium, and the idle rollers  22  contact the medium. At this time, since the medium, having been separated from the pickup roller  21 , is continuously conveyed by a conveying roller  31  and a conveying idle roller  32  of the conveying unit  30 , the idle rollers  22  are idled due to friction with the medium. 
         [0010]    On the other hand, since the idle rollers  22  disposed at both sides of the pickup roller  21  are configured to be independently idle with respect to each other, they cannot restrain the medium from twisting left and right. Accordingly, to prevent the medium from twisting until a rear end of the medium is completely released from the medium supplying cassette  10 , a medium aligning device  12  is formed and disposed in a size corresponding to that of the medium at left and right sides of the medium supplying cassette  10 . 
         [0011]    However, because of the construction of the medium supplying cassette  10 , the medium aligning device  12  cannot be formed to be long enough long to sufficiently extend in a longitudinal direction of a medium. Accordingly, when media, such as letter-sized papers, A4-sized papers, legal-sized papers, or the like, which are elongated in the longitudinal direction, move in a direction of arrow A in  FIG. 1 , a rear end of the medium is not guided by the medium aligning device  12 . As a result, a particular elongated medium may twist, with the rear end thereof being shaken, in a direction of arrow B in  FIG. 1 . While being conveyed, the twisted medium is likely to be increasingly twisted, so that it is difficult for a desired image to be printed on the medium. In the worst case, a medium supplying error may occur, in which a medium is jammed in the apparatus. 
       SUMMARY OF THE INVENTION 
       [0012]    Aspects of the present invention have been developed in order to solve the above and/or other problems. Accordingly, the present invention provides a medium pickup unit having an improved structure to prevent a medium from twisting during pickup and conveyance operations of the medium, and an image forming apparatus having the same installed therein. 
         [0013]    The foregoing and/or other aspects and utilities of the present invention may be achieved by providing a medium pickup unit including a pickup roller, having a circumferential section and a non-circumferential section, to rotate and to pick up a medium due to friction between the circumferential section and the medium, idle rollers respectively disposed at opposite ends of the pickup roller to maintain an orientation of the medium once the non-circumferential section of the pickup roller faces the medium during the rotation of the pickup roller, and a connecting unit coupled to the pickup roller to cause the idle rollers to rotate together. 
         [0014]    According to an exemplary embodiment of the present invention, the connecting unit includes an idle pin to penetrate the pickup roller, planet gears disposed on both ends of the idle pin, respectively, and sun gears disposed on the idle rollers to engage with the planet gears, respectively. 
         [0015]    The planet gears rotate and simultaneously revolve around the sun gears when the pickup roller rotates to pick up a medium, and rotate in connection with rotations of the sun gears when the idle rollers are rotated by the picked-up medium. 
         [0016]    According to another exemplary embodiment of the present invention, the connecting unit includes an idle pin to penetrate the pickup roller, planet gears disposed on both ends of the idle pin, respectively, and ring gears disposed on inner circumferential surfaces of the idle rollers to engage with the planet gears, respectively. 
         [0017]    The planet gears rotate and simultaneously revolve along the ring gears when the pickup roller rotates to pick up a medium, and rotate in connection with rotations of the ring gears when the idle rollers are rotated by the picked-up medium. 
         [0018]    The foregoing and/or other aspects and utilities of the present invention may also be achieved by providing an image forming apparatus including a medium supplying cassette, and the medium pickup unit as described above to pick up a medium accommodated in the medium supplying cassette. 
         [0019]    Additional and/or other aspects and advantages of the invention 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 invention. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
           [0021]      FIG. 1  is a perspective view exemplifying a medium supplying cassette and a medium pickup unit of a general image forming apparatus; 
           [0022]      FIG. 2  is a perspective view exemplifying the medium pickup unit of  FIG. 1 ; 
           [0023]      FIG. 3  is a side elevation view exemplifying an operation of the medium pickup unit of  FIG. 1 ; 
           [0024]      FIG. 4  is a top plan view exemplifying a medium supplying cassette and a medium pickup unit of an image forming apparatus according to an embodiment of the present invention; 
           [0025]      FIG. 5  is a top plan view exemplifying the medium pickup unit according to the embodiment of  FIG. 4 ; 
           [0026]      FIG. 6  is an exploded perspective view exemplifying the medium pickup unit of  FIG. 5 ; 
           [0027]      FIGS. 7 and 8  are partial perspective views exemplifying a connection relation of an connecting unit interposed between a pickup roller and idle rollers in the medium pickup unit of  FIG. 5 ; 
           [0028]      FIGS. 9 and 10  are schematic views exemplifying an operation principle of the medium pickup unit of  FIG. 5 ; 
           [0029]      FIGS. 11 and 12  are partial perspective views exemplifying a connection relation of an connecting unit interposed between a pickup roller and idle rollers in a medium pickup unit according to another exemplary embodiment of the present invention; 
           [0030]      FIG. 13  is a schematic view exemplifying an operation principle of the medium pickup unit of  FIG. 11 ; and 
           [0031]      FIG. 14  is a side view of an image forming apparatus according an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0032]    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 the like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures. 
         [0033]    As illustrated in  FIGS. 4 ,  5  and  6 , a medium pickup unit  100 , according to an embodiment of the present invention, includes a pickup roller  110 , idle rollers  120 , and a connecting unit  130 . The pickup roller  110  has a circumferential section and a non-circumferential section, and the idle rollers  120  are disposed at both sides of the pickup roller  110 . The connecting unit  130  connects the idle rollers  120  to one another so that the idle rollers  120  rotate together and at the same speed. 
         [0034]    As illustrated in  FIG. 6 , the connecting unit  130  includes an idle pin  131   a , planet gears  131 , and sun gears  132 . The idle pin  131   a  penetrates the pickup roller  110  and in coupled to the pickup roller  110 . As illustrated in  FIGS. 6 and 7 , the idle pin  131   a  is rotatably disposed in a pinhole  111   a  formed in a pickup housing  111 . The planet gears  131  are disposed on both ends of the idle pin  131   a  to be respectively rotatable therewith. According to an embodiment of the invention, the idle pin  131   a  is cut into a D-lettered shape at the both ends thereof, so that the idle pin  131   a  rotates along with the planet gears  131  when the idle pin  131   a  is combined with the planet gears  131 . 
         [0035]    The sun gears  132  are integrally formed to inner idle housings  121  which are respectively disposed in outer idle housings  122  on both sides of the idle roller  120 . As illustrated in  FIGS. 6 ,  7  and  8 , the sun gears  132  are coaxial with an axis of rotation  101  on which the idle rollers  120  are mounted. As such, the sun gears  132  engage with the planet gears  131 . Accordingly, as illustrated in  FIGS. 9 and 10 , when the pickup roller  110  rotates during a medium (such as a piece of paper) pickup operation, the planet gears  131  rotate and simultaneously revolve around the sun gears  132 . Further, when the idle rollers  120  are idled due to friction with the medium, the planet gears  131  rotate in connection with rotations of the sun gears  132  but do not revolve around the sun gears  132 . 
         [0036]    According to another embodiment of the present invention, as illustrated in  FIGS. 11 through 13 , a connecting unit  130  includes an idle pin  131   a , planet gears  131  and ring gears  133 . Since constructions of the idle pin  131   a  and planet gears  131  are similar to those in the preceding exemplary embodiment as described with reference to  FIGS. 5 through 10  above, a detailed description thereof will be omitted for clarity and conciseness. 
         [0037]    As illustrated in  FIGS. 11 and 12 , ring gears  133  are formed on inner circumferential surfaces of the idle rollers  120 , respectively. The ring gears  133  engage with the planet gears  131 . Accordingly, the idle rollers  120  rotate together. As illustrated in  FIGS. 11 and 13 , when the pickup roller  110  rotates to pick up a medium at the circumferential section thereof, the planet gears  131  also rotate and simultaneously revolve around the ring gears  133 . When the pickup roller  110  stops rotating and the idle rollers  120  rotate, the planet gears  131  rotate in connection with rotations of the ring gears  133 . 
         [0038]    Hereinafter, an operation of the medium pickup unit according to the exemplary embodiment of the present invention will now be described with reference to the drawing figures. 
         [0039]      FIGS. 9 and 10  are schematic views exemplifying an operation of the medium pickup unit  100 . Particularly,  FIG. 9  illustrates a state in which the pickup roller  110  picks up a medium at a circumferential section thereof, and  FIG. 10  illustrates a state in which idle rollers  120  prevent the medium from twisting when the medium is admitted to a medium conveying unit  200 . 
         [0040]    As illustrated in  FIG. 9 , when picking up a medium, the pickup roller  110  rotates and, thus, contacts the medium at the circumferential section thereof. Here, only the pickup roller  110  rotates with the idle rollers  120  being stopped. This is due to the fact that the circumferential section of the pickup roller  110  at the circumferential section thereof has a diameter that is slightly larger than that of the idle rollers  120 . At this time, since the planet gears  131  are mounted to the pickup roller  110  to be idled by the idle pin  131   a , they rotate and revolve around the sun gears  132  formed on the idle rollers  120 . With this construction, when the pickup roller  110  picks up the medium, the idle rollers  120  are stopped. 
         [0041]    As illustrated in  FIG. 10 , when the medium is admitted to the medium conveying unit  200 , the pickup roller  110  rotates to allow the non-circumferential section thereof to face the medium in conveyance. Thus, the pickup roller  110  separates itself from the medium. At this time, the medium, which is conveyed by the medium conveying unit  200 , causes the idle rollers  120  to rotate. Here, the sun gears  132  that are integrally formed with the idle rollers  120  also rotate along with the idle rollers  120  and, as such, run through the same number of rotations as the idle rollers  120 . However, since the planet gears  131  are connected together through the idle pin  131   a , the idle rollers  120  mounted on the both sides of the pickup roller  110  are restricted to run through the same number of rotations. 
         [0042]    As the idle rollers  120  run through the same number of rotations, the medium in conveyance moves straight in a medium proceeding direction. That is, a likelihood of a medium supplying error, such as a twisting of the medium twist or a jamming of the medium, is prevented from occurring even though a separate medium guide is not installed. 
         [0043]      FIGS. 11 and 12  illustrate the medium pickup unit according to another exemplary embodiment. Here, the idle rollers  120  mounted on the both sides of the pickup roller  110  are connected together to run through the same number of rotations. That is, as illustrated in  FIG. 13 , when the idle rollers  120  are idled by the medium in conveyance, the ring gears  133 , formed in the idle rollers  120 , run through the same number of rotations as the idle rollers  120 . Since the planet gears  131  that are engaged with the ring gears  133  are connected together through the idle pin  131   a , they run through the same number of rotations. Accordingly, the idle rollers  120  run through the same number of rotations as each other. 
         [0044]    As illustrated in  FIG. 14 , an image forming apparatus according to aspects of the present invention includes a medium supplying cassette  90 , and a medium pickup unit  100 . Media accommodated in the medium supplying cassette  90  are picked up in a one by one sequence by the medium pickup unit  100  without being twisted. The picked-up medium is then conveyed to a developing unit  300  to have a desired image formed thereon. Then; the image formed on the medium is heated and compressed by a fixing unit  400  so that the image is fixed on the medium. The medium is then discharged outside the image forming apparatus through a medium discharging unit  500 . 
         [0045]    As is apparent from the foregoing description, according to aspects of the exemplary embodiments of the present invention, the medium pickup unit and the image forming apparatus having the same installed therein are configured so that the idle rollers mounted at the both sides of the pickup roller rotate at the same speed. Accordingly, the rear end of the medium is prevented from twisting while the medium picked up from the medium supplying cassette is conveyed by the medium conveying unit. Thus, the medium is conveyed in as straight a line as possible, thereby allowing quality in conveyance to improve. 
         [0046]    Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.