Abstract:
A print medium feeding apparatus, comprising: a knockup plate on which a ream of print medium is stacked thereon; a pickup roller for picking up a sheet of print medium stacked on the knockup plate; a sheet separation member installed in a manner to form a contact nip with the pickup roller, and supplying friction force for separating the print medium sheet by sheet; and a friction pad disposed at an upper side of the sheet separation member, being in front of the contact nip. The print medium feeding apparatus of the present invention features an improved paper feeding capacity in that variable friction force is applied for separating printing medium. Moreover, since the friction pad does not come in contact with the pickup roller, the abrasion rate of the friction pad is much reduced. Furthermore, the material cost can be reduced by reducing the size of the friction pad.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of Korean Patent Application No. 2005-57906, filed on Jun. 30, 2005, 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 An aspect of the present invention relates in general to a print medium feeding apparatus and an image forming apparatus using the same, and more specifically, to a print medium feeding apparatus for preventing double feeding, and an image forming apparatus using the same.  
         [0003]     2. Description of the Related Art  
         [0004]     An image forming apparatus is used for printing or scanning data that are generated internally or externally. For example, copy machines, printers, facsimiles, scanners, etc., are image forming apparatuses now broadly used. Each of these image forming apparatuses is equipped with an automatic paper feeding apparatus feeding paper sheets to output or receive data generated internally or externally.  
         [0005]     The automatic paper feeding apparatus has a sheet separation member for feeding sheets one by one so that double feeding (i.e., more than one sheet of paper is fed at once) does not occur.  
         [0006]      FIG. 1  is an enlarged detail view of a paper feeding unit used in a related art electrophotographic image forming apparatus  1 , and  FIG. 2  is an enlarged perspective view of a sheet separation member of  FIG. 1 .  
         [0007]     Referring to  FIGS. 1 and 2 , the paper feeding unit includes a knockup plate  1  where paper sheets are stacked on, and a pickup roller  5  in contact with the upper side of the knockup plate  1  for picking up a sheet of printing paper  3  extending to the upper side of the knockup plate  1 . A friction pad  7  is disposed between the pickup roller  5  and the front end of the knockup plate  1 . The friction pad  7  comes in contact with the pickup roller  5  and supplies frictional force for separating the printing paper  3  sheet by sheet while the printing paper  3  is picked up by the pickup roller  5 .  
         [0008]      FIG. 2  is an enlarged view illustrating a state where the friction pad  7  is installed. Referring to  FIGS. 1 and 2 , there is a friction pad mount  9  supporting the friction pad  7 . Thus, the friction pad  7  is mounted on the upper side of the friction pad mount  9 . Here, a nip portion is formed between the friction pad  7  and the pickup roller  5 .  
         [0009]     Meanwhile, paper sheets of diverse sizes pass between the friction pad  7  and the pickup roller  5 . Therefore, the friction pad  7  is made from optimum materials having a proper friction coefficient adaptive to different types of paper.  
         [0010]     However, since the friction pad  7  is in contact with the pickup roller  5  at a constant pressure all the time, sometimes it fails to cope with the friction force of each of the paper sheets according to their properties. Consequently, printing papers are not separated sheet by sheet as they are supposed to, and double feeding or slipping occurs.  
         [0011]     Moreover, as the pickup roller  5  is in direct contact with the friction pad  7 , the friction pad  7  is easily worn out.  
         [0012]     Although a large friction pad may be manufactured, this only gives rise to an increase in the material cost.  
       SUMMARY OF THE INVENTION  
       [0013]     Aspects of the present invention provide a paper feeding apparatus equipped with an improved friction pad providing friction force correspondingly to different types of paper sheets, thereby preventing the occurrence of double feeding and slippage.  
         [0014]     Another aspect of the present invention is provides a paper feeding apparatus capable of reducing the abrasion rate of a friction pad.  
         [0015]     Still another aspect of the present invention provides a paper feeding apparatus capable of reducing the material cost of a friction pad.  
         [0016]     Yet another aspect of the present invention provides an image forming apparatus using the above-described paper feeding apparatus.  
         [0017]     To achieve the above and/or other aspects and advantages, there is provided a paper feeding apparatus, including: a paper feeding tray on which a ream of printing papers are stacked; a pickup roller to pick up a sheet of printing paper stacked on the paper feeding tray; a sheet separation member installed in a manner to form a contact nip with the pickup roller, and supplying friction force for separating the printing paper sheet by sheet; and a friction pad disposed at an upper side of the sheet separation member, being in front of the contact nip.  
         [0018]     The sheet separation member may, although not necessarily, be formed of a mold.  
         [0019]     The sheet separation member may, although not necessarily, comprise a contact surface coming in contact with the pickup roller, and a friction pad mount groove into which the friction pad is inserted.  
         [0020]     An interface between the contact surface and the mount groove may, although not necessarily, be inclined.  
         [0021]     A predetermined gap is provided between an upper side of the friction pad mounted at the mount groove and the contact surface.  
         [0022]     Another aspect of the present invention provides an image forming apparatus, including: a knockup plate on which a ream of printing papers are stacked; an elastic member for supporting the knockup plate in an upward direction; a pickup roller to pick up the printing papers stacked on the knockup plate; an image formation unit to form a predetermined image on a sheet of printing paper transported through the pickup roller; a sheet separation member installed in a manner to form a contact nip with the pickup roller, and supplying friction force for separating the printing papers picked up by the pickup roller sheet by sheet; and a friction pad disposed at an upper side of the sheet separation member, being in front of the contact nip.  
         [0023]     The sheet separation member may, although not necessarily, be formed of a mold.  
         [0024]     The sheet separation member comprises a contact surface coming in contact with the pickup roller, and a friction pad mount groove into which the friction pad is inserted.  
         [0025]     An interface between the contact surface and the mount groove may, although not necessarily, be inclined.  
         [0026]     A predetermined gap is provided between an upper side of the friction pad mounted at the mount groove and the contact surface.  
         [0027]     Moreover, since the friction pad does not come in contact with the pickup roller, the abrasion rate of the friction pad is much reduced.  
         [0028]     Furthermore, the material cost can be reduced by reducing the size of the friction pad.  
         [0029]     Additional aspects and/or 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  
       [0030]     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:  
         [0031]      FIG. 1  is an enlarged detail view of a paper feeding unit used in a related art electrophotographic image forming apparatus;  
         [0032]      FIG. 2  is an enlarged perspective view of a sheet separation member of  FIG. 1 ;  
         [0033]      FIG. 3  is a schematic cross-sectional view of an image forming apparatus according to an embodiment of the present invention;  
         [0034]      FIG. 4  is an enlarged perspective view illustrating the configuration of a paper feeding unit used in the image forming apparatus of  FIG. 3 ;  
         [0035]      FIGS. 5A-5C  are drawings illustrating the operational flow of a paper feeding unit of the image forming apparatus of  FIG. 3 , in which  FIG. 5A  illustrates a state where a sheet of paper is in a paper feeding-standby position,  FIG. 5B  illustrates a paper feeding state, and  FIG. 5C  illustrates a state where paper feeding is completed and a double feeding prevention member is in operation;  
         [0036]      FIG. 6  is an enlarged cross-sectional view of VI portion of  FIG. 3  in a sheet separation member of the image forming apparatus of  FIG. 3 ; and  
         [0037]      FIG. 7  is a perspective view of a sheet separation member of the image forming apparatus of  FIG. 3 . 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0038]     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.  
         [0039]      FIG. 3  is a cross-sectional view illustrating the configuration of an image forming apparatus according to an embodiment of the present invention.  
         [0040]     Referring to  FIG. 3 , a paper feeding tray  111  is provided at a lower portion inside a main body  110 , and a knockup plate  131  where a ream of printing papers  101  are stacked thereon is mounted on the top of the paper feeding tray  111 . When a pickup roller  135  rotates, the printing papers  101  stacked on the knockup plate  131  are separated due to friction force with a sheet separation member  137  and are supplied sheet by sheet into a nip portion (hereinafter it will be referred to as a transfer nip P 1 ) between a photosensitive drum  153 , which is an image formation unit, and a transfer roller  159 .  
         [0041]     At the same time, the surface of the photosensitive drum  153  is electrically charged by discharge of a charging roller  155 . The charged surface of the photosensitive drum  153  is exposed to a specific pattern by laser beams L emitted from a laser scanning unit  170 , and therefore a desired electrostatic latent image is formed thereon. Next, as a developing roller  157  adjacent to the surface of the photosensitive drum  153  rotates, a toner image is formed on a portion where the electrostatic latent image is formed. Then, the transfer roller  159  presses the photosensitive drum  153 , and while rotating it transfers the toner image formed on the photosensitive drum  153  onto the printing paper  101  that is provided from the paper feeding tray  111 .  
         [0042]     The printing paper  101  moves continuously and passes between a heating roller  181  and a pressing roller  183  of a fixing unit  180 , where the image is heated and pressed at a predetermined temperature and a predetermined pressure. As a result, a powder toner image is fixed on the printing paper.  
         [0043]     The printing paper bearing the toner image is conveyed by rotation force of a delivery roller  191  and an idle roller  193 , and is eventually discharged through a discharge opening  117  and stacked on a paper delivery tray  118 .  
         [0044]      FIG. 4  is a perspective view showing the configuration of a paper feeding unit used in the image forming apparatus shown in  FIG. 3 .  
         [0045]     As shown in  FIGS. 3 and 4 , a knockup plate  131  where printing papers  101  are stacked on is supported by an elastic member  133  in an upward direction. A pickup roller  135  for picking up the printing papers  101  is installed on the upper side of the knockup plate  131 . As shown in  FIG. 4 , a sheet separation member  210  is disposed between the front end of the knockup plate  131  and the pickup roller  135 . Additionally, one or more double feeding prevention members  230  may be installed on either or both sides of the sheet separation member  210 , respectively, as a complement to the paper separation.  
         [0046]     The pickup roller  135  rotates to a certain extent to supply the printing papers  101  sheet by sheet, and stops running for a predetermined amount of time until another sheet of paper is fed. This process is performed under the control of a control unit. The control unit comprises a pickup gear  138  and a solenoid unit  141 . The pickup gear  138  is connected to a pickup shaft  136  supporting the rotation of the pickup roller  135 , and the solenoid unit  141  selectively transfers or intercepts a driving force to the pickup gear  138  by selectively contacting or separating from the pickup gear  138 .  
         [0047]     On the other side of the pickup shaft  136  connected to the solenoid unit  141  is provided a cam  143 , and a protruded portion  131   a  coming in contact with the cam  143  is provided on the knockup plate  131 . Also, an idle roller  145  coming in contact with the cam  143  is provided at the protruded portion  131   a.    
         [0048]     Referring to  FIG. 4 , a friction member  146  contacts the pickup roller  135 , providing a friction force to pick up the printing paper.  
         [0049]      FIGS. 5A-5C  illustrate the operational flow of the paper feeding unit of the present invention, in which  FIG. 5A  illustrates a state where a sheet of paper is in a paper feeding-standby position,  FIG. 5B  illustrates a paper feeding state, and  FIG. 5C  illustrates a state where paper feeding is completed and the double feeding prevention member is in operation.  
         [0050]     As shown in  FIG. 5A , in standby mode, the knockup plate  131  is pressed against the cam  143  by the elastic member  133 . In this state, when a user stacks sheets of paper on the knockup plate  131  and inputs a print command, the solenoid unit  141  starts running and a driving force is transferred to the pickup gear  138  (refer to  FIG. 4 ). Then, the pickup roller  135  starts rotating and picks up the printing paper  101  loaded on the knockup plate  131 .  
         [0051]     In detail, the pickup roller  135  rotates in the clockwise direction, and the cam  143  that moves interlockingly with the pickup roller  135  is separated from the knockup plate  131 . Thus, the knockup plate  131  goes up by the elastic force from the elastic member  133  and the automatic paper feeding state is established as shown in  FIG. 5B .  
         [0052]     The printing paper  101  picked up by the pickup roller  135  passes between the pickup roller  135  and the sheet separation member  210 .  
         [0053]     When the paper feeding is completed, the knockup plate  131  comes in contact with the edge of the cam  143  as shown in  FIG. 5C , and descends to a lower position than the position shown in  FIG. 5B  until the sheet separation member  210  and the lower end  233  of the double feeding preventing member  230  come in contact with the lower end portion of the knockup plate  131 . The sheet separation member  210  descends through a guide rib  219 . The double feeding prevention member  230  comprises a saw tooth portion  231  provided on the upper end part of the double feeding prevention member  230 , to which the central part of the double feeding prevention member  230  is hinged. The saw tooth portion  231  rotates instantaneously towards the pickup roller  135 . Also, a rail  218  is formed on one side of the sheet separation member  210  corresponding to the guide rib  219 . Here, the sheet separation member  210  is elastically supported against the pickup roller  135  by an elastic force from a spring (not shown) similar to the elastic member  133 . Therefore, as depicted in  FIG. 5C , when the sheet separation member  210  descends, the spring remains compressed. Meanwhile, when the knockup plate  131  ascends and is separated from the lower end  215  of the sheet separation member  210 , the spring snaps back by its restoring force.  
         [0054]     The reason for descending the sheet separation member  210  as described above is to create a predetermined space from the pickup roller  135 , and therefore to minimize the friction load between the photosensitive drum  153  and the transfer roller  159  while the printing paper  101  passes a feed roller, i.e., the photosensitive drum  153  and the transfer roller  159  of  FIG. 3 , located at the next stage of the pickup roller  135 .  
         [0055]     In addition, the upper end portion of the double feeding prevention member  230  rotates instantaneously towards the pickup roller  135  in order to push a lower sheet of paper stuck to an upper sheet of paper (i.e., in case of double feeding) in an opposite direction from the feeding direction, thereby making sure that the printing papers  101  are supplied sheet by sheet all the time.  
         [0056]      FIG. 6  is an enlarged cross-sectional view of VI portion of  FIG. 3  in the sheet separation member applied to the present invention, and  FIG. 7  is a perspective view of the sheet separation member applied to the present invention.  
         [0057]     Referring to  FIGS. 5B, 6 , and  7 , a first contact nip N is provided between the sheet separation member  210  and the pickup roller  135 . Here, the sheet separation member  210  is formed of a mold. The friction pad  250  is placed on the upper side of the sheet separation member  210  disposed in front of the contact nip N. By placing the friction pad  250  on the front end portion of the sheet separation member  210 , its width is reduced by half, compared with the related art.  
         [0058]     The sheet separation member  210  comprises a contact surface  211  forming the first contact nip N with the pickup roller  135 , and a friction pad mount groove  213  into which the friction pad  250  is inserted therein. Here, the interface between the contact surface  211  and the mount groove  213  is inclined.  
         [0059]     Moreover, a predetermined gap G is provided between the upper side of the friction pad  250  disposed at the mount groove  213  and the contact surface  211 .  
         [0060]     In this manner, the printing paper  101  picked up from the knockup plate  131  through the pickup roller  135  passes through the contact nip N between the contact surface  211  of the sheet separation member  210  and the pickup roller  135 . The printing paper  101  being conveyed here hardly comes in contact with the friction pad  250 , being almost free of the friction force of the friction pad.  
         [0061]     On the other hand, in case that two sheets of printing paper  101   a  ,  101   b  are fed together (i.e., double feeding) as shown in  FIG. 6 , the printing paper  101   b  is brought into contact with the friction pad  250  and thus subjected to a friction force. As a result, the printing paper  101   b  is not conveyed and only the printing paper  101   a  on the upper side is fed along the paper transportation pathway.  
         [0062]     Although a printer was mainly explained as an example of the image forming apparatus of the present invention, the paper feeding apparatus of the present invention can also be applied to a scanner, a facsimile, etc., requiring the paper feeding. Furthermore, although printing paper was mainly explained as the object of the present invention, the paper feeding apparatus of the present invention can also be applied to any number of different print medium, such as transparencies, overheads, etc.  
         [0063]     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 this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.