Abstract:
A paper pick-up unit of an image forming apparatus includes an elliptical pick-up rubber having a first arcuate part and a second arcuate part. The first and second arcuate parts are symmetrical to each other and contact a paper. A pick-up housing supports the pick-up rubber, which are attached around the circumference thereof. A first shaft opening and a second shaft opening are formed opposite to each other in the pick-up housing and are eccentrically disposed with respect to a center of the pick-up housing. A pick-up shaft is engaged with one of the first shaft opening and the second shaft opening of the pick-up housing, and is capable of rotating. The pick-up shaft is engaged with the first shaft opening of the pick-up housing for the first arcuate part of the pick-up rubber to pick up a paper. The pick-up shaft is engaged with the second shaft opening of the pick-up housing for the second arcuate part of the pick-up rubber to pick up a paper.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit under 35 U.S.C. § 119(a) of Korean Patent Application No. 2004-70962 filed on Sep. 6, 2004, the entire disclosure of which is hereby incorporated by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an image forming apparatus, such as a printer, a multi-function peripheral device, and a facsimile. More particularly, the present relates to an improved paper pick-up unit and an image forming apparatus having the same. 
   2. Description of the Related Art 
   As is well known, a paper pick-up unit of an image forming apparatus picks up the uppermost sheet of paper from a plurality of papers stacked in a feeding cassette to feed it on a paper transmission path.  FIG. 1  is a view of an example of a typical paper pick-up unit. 
   In  FIG. 1 , the reference numerals  100  and  110  denote a feeding cassette and a paper pick-up unit, respectively. Referring to  FIG. 1 , the paper pick-up unit  110  includes a pick-up rubber  111  contacting a paper P, and a pick-up housing  113  supporting the pick-up rubber  111 . A pick-up shaft  115  penetrates through the pick-up housing  113  and is rotated by a driving device (not shown). A pick-up idler  117  engages the pick-up shaft  115  and is located at both ends of the pick-up housing  113 . 
   In the above paper pick-up unit, an arc portion  111   a  of the pick-up rubber  111  frictionally contacts the paper P to pick up the paper P. Because the diameter of the pick-up idler  117  is smaller than the diameter of the arc portion  111   a  of the pick-up rubber  111 , only the arc portion  111   a  of the pick-up rubber  111  contacts the paper P during rotation of the pick-up rubber  111 . The pick-up idler  117  operates to regularly keep contact between the paper P and the pick-up rubber  111 . 
   As described above, because only the arc portion  111   a  of the pick-up rubber  111  frictionally contacts the paper P, the arc portion  111   a  is abraded by the paper P or damaged by paper powders. As such, the coefficient of friction decreases with the passage of time, and the pick-up rubber may not function properly. 
   The pick-up rubber  111  has a predetermined life span, and can be averagely used for approximately fifty thousand to sixty thousand sheets of paper P. The image forming apparatus can be averagely used for more than approximately one hundred thousand sheets of paper P. In other words, the average life span of the image forming apparatus is relatively longer than that of the pick-up rubber  111 . As such, if the arc portion  111   a  of the pick-up rubber  111  is abraded and the life span is terminated, the pick-up rubber  111  or the whole paper pick-up unit  110  needs to be replaced. To replace the conventional paper pick-up unit, a user needs the help of a specialist due to the complex construction of the paper pick-up unit. In other words, the conventional paper pick-up unit burdens the user in time and economy. 
   Accordingly, a need exists for an image forming apparatus having an improved paper pick-up unit with a longer lifespan. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide a paper pick-up unit of which life span may be doubled by changing the position of one pick-up rubber to reuse, and in which the position of the pick-up rubber may be easily changed by a user of an image forming apparatus, and an image forming apparatus having the same. 
   A paper pick-up unit of an image forming apparatus includes an elliptical pick-up rubber having a first arcuate part and a second arcuate part. The first and second arcuate parts are symmetrical to each other and are adapted to contact a paper. A pick-up housing supports the pick-up rubber attached around a circumference thereof. A first shaft opening and a second shaft opening are formed opposite to each other and eccentrically with respect to a center of the pick-up housing. A pick-up shaft engages one of the first shaft opening and the second shaft opening of the pick-up housing, and is capable of rotating. 
   The pick-up shaft may be engaged with the first shaft opening of the pick-up housing for the first arcuate part of the pick-up rubber to pick up a paper, and the pick-up shaft is engaged with the second shaft opening of the pick-up housing for the second arcuate part of the pick-up rubber to pick up a paper. 
   If one arcuate part is used up, the other arcuate part may be used, and as such, the life span of the pick-up rubber may be doubled. 
   The paper pick-up unit may further include a pick-up idler engaged with the pick-up shaft for maintaining regular contact between the first arcuate part or the second arcuate part and the paper. 
   Two idlers may be used to engage the pick-up shaft and to distance from the opposite sides of the pick-up housing. 
   The pick-up housing may include a connecting opening to connect the first shaft opening and the second shaft opening and to easily change the position of the pick-up shaft. A lock means locks the pick-up shaft when the pick-up shaft changes the position from the first shaft opening to the second shaft opening or vice versa. 
   The pick-up shaft locking means may include locking protrusions each protruding inward from both ends of a mouth part of the first shaft opening and the second shaft opening, respectively. 
   The pick-up shaft locking means may include key grooves formed at the mouth part of the first shaft opening and the second shaft opening and a key engaged with the key grooves. 
   The first shaft opening and the second shaft opening may be quadrangle, and the pick-up shaft may have a flattened U shape cross section. 
   An image forming apparatus includes an image forming unit having a photoconductive medium for forming an electrostatic latent image, and a development unit for developing the electrostatic latent image of the photoconductive medium. A transmission unit having a paper transmission path connects the image forming unit with a paper feeding cassette stacking a plurality of papers therein. A paper pick-up unit picks up a sheet of paper stacked in the paper feeding cassette to enter the paper to the paper transmission path. The paper pick-up unit includes an elliptical pick-up rubber having a first arcuate part and a second arcuate part. The first and second arcuate parts are symmetrical to each other and contact a paper. A pick-up housing supports the pick-up rubber attached around the circumference thereof, and has a first shaft opening and a second shaft opening that are formed oppositely to each other and eccentrically with respect to a center of the pick-up housing. A pick-up shaft engages with one of the first shaft opening and the second shaft opening of the pick-up housing, and is capable of rotating. 
   According to the present invention, the life span of the pick-up rubber may be doubled, and the arcuate parts of the pick-up rubber may be easily replaced by a user. As such, the cost may be decreased and the convenience for use may be increased. 
   Accordingly, a need exists for an image forming apparatus having an automatic document feeder that controls the speed of a document passing therethrough to improved the quality of copied and scanned images. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other aspects, features and advantages of the present invention will be more apparent from the following detailed description taken with reference to the accompanying drawings, in which: 
       FIG. 1  is a schematic view of a conventional paper pick-up unit of an image photographing apparatus; 
       FIG. 2  is a schematic view of an image photographing apparatus applying a paper pick-up unit according to an exemplary embodiment of the present invention; 
       FIG. 3  is a perspective view of the paper pick-up unit of  FIG. 2 ; 
       FIG. 4A ,  FIG. 4B  and  FIG. 4C  are elevational views showing each step of replacing a pick-up rubber of the paper pick-up unit of  FIG. 3 ; 
       FIG. 5  is a perspective view of a paper pick-up unit according to another exemplary embodiment of the present invention; and 
       FIG. 6A ,  FIG. 6B  and  FIG. 6C  are views showing each step of replacing a pick-up rubber of the paper pick-up unit of  FIG. 5 . 
   

   Throughout the drawings, like reference numerals will be understood to refer to like parts, components and structures. 
   DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
   Certain embodiments of the present invention will be described in greater detail with reference to the accompanying drawings. 
   The matters defined in the description, such as a detailed construction and elements thereof, are provided to assist in a comprehensive understanding of the invention. Thus, it is apparent that the present invention may be carried out without those defined matters. Also, descriptions of well-known functions and constructions are omitted to provide a clear and concise description. 
     FIG. 2  is a schematic view of an image photographing apparatus  200  applying a paper pick-up unit  300  according to an exemplary embodiment of the present invention.  FIG. 3  is a perspective view of the paper pick-up unit according to an exemplary embodiment of the present invention. 
   Referring to  FIGS. 2 and 3 , an image forming unit  210  includes a photoconductive medium  211  and a development part  213 . A laser scan unit  220  emits a laser beam to the photoconductive medium  211  to form an electrostatic latent image. The electrostatic latent image of the photoconductive medium  211  is developed to a visible image with a toner by the development part  213 , and the visible image is transferred to a paper P that passes between the photoconductive medium  211  and a transfer roller  230  rotating in contact with the photoconductive medium  211 . The paper P is then fed through a fuse unit  240 . 
   The paper P stacked in a paper feeding cassette  250  is picked up sheet-by-sheet by a paper pick-up unit  300  according to an exemplary embodiment of the present invention. The picked-up paper is fed along a paper transmission path  260 , and transferred to the image forming unit  210  by a transmission unit having a plurality of transmission rollers  271  and  272 . 
   The paper pick-up unit  300  includes a pick-up rubber  310 , a pick-up housing  320 , a pick-up shaft  330  and pick-up idlers  340  and  340 ′, as shown in  FIGS. 3 and 4A . 
   The pick-up rubber  310  is wrapped around the pick-up housing  320 , and directly contacts the paper P. The pick-up rubber  310  is preferably made from Ethylene Propylene Diene Monomer (EPDM) in view of friction with the paper P. The pick-up rubber  310  may be averagely used for approximately fifty thousand to sixty thousand sheets of paper P. 
   The pick-up housing  320  takes on an elliptical configuration and has a first shaft opening  321  and a second shaft opening  323  to be selectively engaged with the pick-up shaft  330 . 
   The elliptical pick-up housing  320  may be manufactured as follows. First, two circles of substantially the same diameter are partially overlapped with each other, with the center of each circle positioned in the partially overlapped portion. The other portions except for the overlapped portion are removed, and the first shaft opening  321  and the second shaft opening  323  are formed at the center of each circle. 
   Due to the presence of the pick-up housing  320 , only the first arcuate part  310   a  of the pick-up rubber  310  contacts the paper P when the pick-up shaft  330  is rotated in engagement with the first shaft opening  321 . The first shaft opening  321  is a center of the first arcuate part  310   a  of the pick-up rubber  310 . Alternatively, only the second arcuate part  310   b  of the pick-up rubber  310  contacts the paper P when the pick-up shaft  330  is rotated in engagement with the second shaft opening  323 . The second shaft opening  323  is a center of the second arcuate part  310   b  of the pick-up rubber  310 . 
   If the aforementioned structure is applied, the life span of the pick-up rubber  310  becomes twice as long as a pick-up rubber  111  (refer to  FIG. 1 ) of a conventional pick-up unit. This is because the first arcuate part  310   a  and the second arcuate part  310   b  of the pick-up rubber  310  may be used in turn. 
   Each of the first shaft opening  321  and the second shaft opening  323  is open at one side and connected with each other by a connection opening  327  extended therebetween. Accordingly, a user may more easily use the first arcuate part  310   a  and the second arcuate part  310   b  of the pick-up rubber  310  in turn. A user does not need to separate the pick-up shaft  330  from the pick-up housing  320 , but simply moves the pick-up shaft  330  from the first shaft opening  321  of the pick-up housing  320  to the second shaft opening  323 , or vice versa along the connection opening  327 . 
   The connecting opening  327  takes on the configuration of a quadrangular opening and is sized for the pick-up shaft  330  to be rotated by an angle of 180 degrees. The pick-up shaft should be rotated by an angle of 180 degrees in the connecting opening  327  to use the first arcuate part  310   a  and the second arcuate part  310   b  of the pick-up rubber  310  in turn, and the detailed description thereof will follow below. 
   Lock protrusions  326  protrude inwardly from both ends of open side of the first shaft opening  321  and the second shaft opening  323 , respectively, to lock the pick-up shaft  330  in its respective opening. When the pick-up shaft  330  is engaged with the first shaft opening  321  or the second shaft opening  323 , movement of the pick-up shaft  330  is prevented due to the lock protrusions  326 . 
   The lock protrusions  326  are preferably elastic such that the pick-up shaft  330  may move from the first shaft opening  321  to the second shaft opening  323 , or from the second shaft opening  323  to the first shaft opening  321 . 
   For example, if the pick-up shaft  330  engaged with the first shaft opening  321  moves to the connecting opening  327 , the pick-up shaft  330  moves over the lock protrusions  326 . The lock protrusions  326  are elastic and resilient enough to bend and then recover after the pick-up shaft  330  moves over the lock protrusions  326 . As such, the thickness of the lock protrusions  326  is set in view of proper elasticity. Additionally, hollow spaces  325  may be formed on an upper portion and a lower portion of the pick-up housing  320  having the lock protrusions  326 , to provide the lock protrusions  326  with more elasticity. 
   The pick-up shaft  330  is a rotation shaft having a substantially flattened U-shape cross section that receives a driving force from a driving device (not shown) and provides the pick-up rubber  310  with a rotation force to transfer the paper P to the image forming unit  210 . 
   The driving device may include a gear, a clutch and a solenoid. Normally, the pick-up rubber  310  and the pick-up housing  320  do not rotate due to the clutch, and then are rotated once by the operation of the solenoid to pick up the paper P. 
   The pick-up idlers  340  and  340 ′ are engaged with the pick-up shaft  330  and regulate contact between the pick-up rubber  310  and the paper P. For example, if the pick-up shaft  330  is engaged with the first shaft opening  321  of the pick-up housing  320 , only the first arcuate part  310   a  of the pick-up rubber  310  contacts the paper P. Although the pick-up idler  340  and  340 ′ are rotated, the second arcuate part  310   b , which is the opposite side of the first arcuate part  310   a , of the pick-up rubber  310  does not contact the paper P because the diameter of the rotation orbit of the second arcuate part  310   b  is smaller than that of the pick-up idlers  340  and  340 ′. As such, contact between the pick-up rubber  310  and the paper P is regulated. 
   Referring to  FIGS. 2 and 3 , as the driving device (not shown) rotates the pick-up shaft  330  in a direction indicated by arrow R, the pick-up housing  320  and the pick-up idlers  340  and  340 ′ engaged with the pick-up shaft  330  are rotated by the rotating of the pick-up shaft  330 . At this time, the pick-up rubber  310  wrapped around the pick-up housing  320  contacts the paper P to transfer the paper P to the development unit  240 . 
   If the pick-up shaft  330  is engaged with the first shaft opening  321 , only the first arcuate part  310   a  of the pick-up rubber  310  contacts the paper P. The second arcuate part  310   b  of the pick-up rubber  310  does not contact the paper P because the diameter of the rotation orbit of the second arcuate part  310   b  is smaller than that of the pick-up idlers  340  and  340 ′. As such, only the first arcuate part  310   a  of the pick-up rubber  310  is stained and abraded by paper powder, and finally used up. Meanwhile, the second arcuate part  310   b  of the pick-up rubber  310  maintains the initial status (that is, abrasion of the second arcuate part  310   b  is substantially prevented since the second arcuate part is not being used to pick up paper). As such, when the life span of the first arcuate part  310   a  of the pick-up rubber  310  is ended, the paper pick-up unit  300  is set for the second arcuate part  310   b  of the pick-up rubber  310  to contact the paper P. 
   Referring to  FIG. 4A , when the life span of the first arcuate part  310   a  contacting the paper P of the pick-up rubber  310  is ended by abrasion and stain, a user moves the pick-up housing  320  in a direction indicated by arrow A with a certain force to unlock the pick-up shaft  330  engaged with the first shaft opening  321  from the first shaft opening  321 . At this time, the pick-up shaft  330  engaged with the first shaft opening  321  moves past the lock protrusions  326 . The elasticity and resiliency of the lock protrusions  326  causes the lock protrusions to return to their original position after the pick-up shaft  330  moves over the lock protrusions  326 . 
   Referring to  FIG. 4B , when the pick-up shaft  330  moves to the connecting opening  327 , a user rotates the pick-up housing  320  by an angle of approximately 180 degrees in a direction indicated by arrow B for the second arcuate part  310   b  of the pick-up rubber to contact the paper P. As such, the position of the abraded first arcuate part  310   a  of the pick-up rubber  310  and the non-used second aruatec part  310   b  of the pick-up rubber  310  are changed to opposite positions with regard to the paper P. 
   Referring to  FIG. 4C , when the position of the second arcuate part  310   b  and the first arcuate part  310   a  of the pick-up rubber  310  is changed with respect to the paper P, a user moves the pick-up housing  320  in a direction indicated by arrow C to lock the pick-up shaft  330  to the second shaft opening  323 . 
   In the above process, the pick-up shaft  330  moves over the lock protrusions  326 . The lock protrusions  326  return to their original position due to their elasticity and resiliency after the pick-up shaft  330  moves over the lock protrusions  326 . By the above method, the first arcuate part  310   a  is replaced with the second arcuate part  310   b  to contact and pick up the paper P. 
   Referring to  FIG. 5 , a key  460  may be used instead of the lock protrusions  326  (refer to  FIG. 3 ), to lock or unlock a pick-up shaft  430  in a first shaft opening  421  and a second shaft opening  423  of a pick-up housing  420 . Key grooves  429  are formed at a mouth part of the first shaft opening  421  and the second shaft opening  423  to mount the key  460  locking or unlocking the pick-up shaft  430 . 
   Referring to  FIG. 6A , when the life span of the first arcuate part  410   a  of the pick-up rubber  410  is ended, a user removes the key  460  from the key grooves  429  in a direction indicated by arrow E and then moves the pick-up shaft  430  in a direction indicated by arrow F into the connecting opening  427  to unlock the pick-up shaft  430  from the first shaft opening  421 . 
   Referring to  FIG. 6B , when the pick-up shaft  430  moves to the connecting opening  427 , a user rotates the pick-up housing  420  in a direction indicated by arrow G by an angle of approximately 180 degrees for the second arcuate part  410   b  of the pick-up rubber  410  to contact the paper P. As such, the position of the abraded first arcuate part  410   a  and the second arcuate part  410   b  to maintain the initial status of the pick-up rubber  410  is changed in the opposite direction with regard to the paper P. 
   Referring to  FIG. 6C , when the first arcuate part  410   a  is replaced with the second arcuate part  410   b , a user moves the pick-up housing  420  in a direction indicated by arrow H and then inserts the key  460  into the key grooves  429  in a direction of arrow I to lock the pick-up shaft  430  into the second shaft opening  423 . Accordingly, the second arcuate part  410   b  of the pick-up rubber  410  replacing the first arcuate part  410   a  now contacts the paper P to pick up the paper P. 
   As described above, both of the first arcuate part and the second arcuate part of an elliptical pick-up rubber may be used according to exemplary embodiments of the present invention. Therefore, the life span may be extended and the material costs may be reduced. Additionally, a user may easily replace the first arcuate part and the second arcuate part of the pick-up rubber such that the use convenience of an image forming apparatus may be highly improved. 
   The foregoing exemplary embodiments and advantages are merely exemplary and are not to be construed as limiting the present invention. The present teaching may be readily applied to other types of apparatuses. Also, the description of the exemplary embodiments of the present invention is intended to be illustrative, and not to limit the scope of the claims, and many alternatives, modifications, and variations will be apparent to those skilled in the art.