Patent Publication Number: US-2005133982-A1

Title: Paper conveyance apparatus for an image forming apparatus and a method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application claims the benefit under 35 U.S.C. § 119(a) of Korean Application No. 2003-93183, filed Dec. 18, 2003, in the Korean Intellectual Property Office, the entire contents of which is incorporated herein by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to an image forming apparatus. More particularly, the present invention relates to a paper feeder and method for an image forming apparatus, for reducing the malfunction caused by abrasion of a reversible roller that rotates forwards and backwards in contact with a conveyance roller so that paper sheets are picked up one by one.  
      2. Description of the Related Art  
       FIG. 1  is a diagram illustrating a conventional electrophotographic image forming apparatus  1  which feeds a paper P using a knock-up plate type of a feeding device  2 . As shown in  FIG. 1 , a paper P is picked up by a pickup roller. A conveyance apparatus  10  having a plurality of rollers is provided to prevent the simultaneous feeding of two or more paper sheets.  
      As shown in  FIG. 2 , the conveyance apparatus  10  consists of a conveyance roller  11  and a reversible roller  12 . A torque limiter  13  is mounted on the same axis of the reversible roller  12 . Also, a reversible motor (not shown) for reversely rotating the reversible roller  12  is provided independently from a driving device for rotating the conveyance roller  11 .  
      The reversible roller  12  rotates in an opposite direction to the conveyance roller  11 . When two or more paper sheets are fed at once, the reversible roller  12  separates the top paper sheet from the underlying paper sheets using a difference in the coefficient of friction between the reversible roller  12  and the conveyance roller  11 . When a single paper sheet is fed, the friction force between the conveyance roller  11  and the reversible roller  12  becomes greater than a predetermined torque of the coaxial torque limiter  13 , thereby making the reversible roller  12  rotate in the same direction of the rotation of the conveyance roller  11 . A reversible gear  14  is also mounted on the same axis of the reversible roller  12  to receive a driving force from the reversible motor. The reversible gear  14  rotates in a direction opposite to the direction of rotation of the torque limiter  13 , and operates independently from the rotation of the conveyance roller  11 .  
      The conveyance roller  11  and the reversible roller  12  comprise a rubber having a predetermined solidity, friction coefficient and durability, such as a Natural Rubber (NR), an Acrylonitrile Butadiene Rubber (NBR), an Ethylene-Proplyene-Diene (EPDM), a urethane or a silicon.  
      Since the reversible roller  12  rotates in the opposite direction to a paper feeding direction, the surface of the reversible roller  12  contacting the conveyance roller  11  is apt to be easily abraded. As the surface of the reversible roller  12  becomes abraded, a conveyance roller shaft S 1  and a reversible roller shaft S 2  are not maintained in parallel with each other but form an incline, as shown in  FIG. 2 . This problem results from the fixed position of the reversible gear  14 . When the conveyance roller shaft S 1  and the reversible roller shaft S 2  are not in parallel with each other, the conveyance roller  11  and the reversible roller  12  do not contact sufficiently to separate two or more paper sheets fed together and smoothly feed the paper sheets sequentially. Accordingly, the abrasion of the reversible roller  12  may cause errors in the operation of the image forming apparatus.  
     SUMMARY OF THE INVENTION  
      An aspect of the present invention is to solve at least the above problems and to provide at least the advantages described below. Accordingly, an aspect of the present invention is to provide a paper feeder and method for an image forming apparatus, having an improved structure to reduce the malfunction caused by abrasion of a reversible roller that rotates forwards and backwards in contact with a conveyance roller so that paper sheets are picked up sequentially.  
      In order to achieve the above-described aspects of the present invention, there is provided a paper feeder and method for an image forming apparatus. The paper feeder and method comprise a conveyance roller, a reversible roller, a driving motor and an idle gear. The conveyance roller and the reversible roller, being in contact with each other, rotate in the same direction as or the opposite direction to a direction of paper feed to convey paper sheets to an image forming section, separating paper sheets which are fed together. The reversible roller is transmitted with a driving force by the driving motor which is separate from the conveyance roller. In order to transmit the driving force, a gear train including an idle gear is used. The center of rotation of the idle gear is movable so that a contacting force between the conveyance roller and the reversible roller can be kept over a predetermined level even when the reversible roller is abraded.  
      The idle gear is preferable movable along a track which is a part of the circumference of a virtual circle having a radius corresponding to the distance between the center of the driving gear and the center of the idle gear.  
      The central shaft of the idle gear may move along a swing slot formed on one sidewall of the image forming apparatus to correspond to the swing track of the idle gear.  
      According to a first embodiment of the present invention, the swing slot has an inner periphery with a curvature corresponding to the curved swing track of the idle gear.  
      According to a second embodiment of the present invention, the swing slot is formed in a direction of a tangent to a virtual circle having a radius corresponding to the distance between the center of the driving gear and the center of the idle gear. The swing slot may include an elastic member for elastically supporting the central shaft of the idle gear. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above and other aspects, features and advantages of the present invention will become more apparent from the following detailed description taken with the accompanying drawings in which:  
       FIG. 1  is a diagram illustrating a conventional image forming apparatus;  
       FIG. 2  is a diagram illustrating a state in which a conveyance roller and a reversible roller of the conventional image forming apparatus are inclined due to abrasion of the reversible roller;  
       FIG. 3  is a diagram illustrating a state in which rotation shafts of a conveyance roller and a reversible roller according to an embodiment of the present invention move in response to the abrasion of a reversible roller;  
       FIG. 4  is a diagram illustrating a sectional view of an arrangement of gears, motors and shafts according to an embodiment of the present invention;  
       FIG. 5  is a diagram illustrating a gear train of a reversible roller according to a first embodiment of the present invention; and  
       FIG. 6  is a diagram illustrating a gear train of a reversible roller according to a second embodiment of the present invention. 
    
    
      Throughout the drawings, it should be noted that the same or similar elements are denoted by like reference numerals.  
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Hereinafter, a few embodiments of a paper conveyance apparatus and method for an image forming apparatus according to embodiments of the present invention will now be described in detail with reference to the accompanying drawings.  
       FIG. 3  is a diagram illustrating a paper feeder according to an embodiment of the present invention.  
      As shown in  FIG. 3 , the conveyance apparatus  100  includes a conveyance roller  110 , and a reversible roller  120  pressed against the conveyance roller  110  at a predetermined pressure. In order to rotate the conveyance roller  110  and the reversible roller  120 , a conveyance gear  112  and a reversible gear  122  are provided to receive a driving force from respective driving sources (not shown).  
      A load regulator having a torque limiter T coaxial to the reversible roller  120  is mounted on a reversible roller shaft  121 . The torque limiter T detects whether the friction force between the conveyance roller  110  and the reversible roller  120  is reduced by a paper sheet fed between the two rollers  110  and  120  to a level below a predetermined friction coefficient. When a single paper sheet is fed, the reversible roller  120  rotates in the same direction as the conveyance roller  110  to convey the paper. When two or more paper sheets are fed at once, the reversible roller  120  rotates in an opposite direction to the conveyance roller  110  according to a detection signal from the torque limiter T in order to separate the fed paper sheets so that only the top paper sheet is conveyed to an image forming section.  
      More specifically, a paper picked up by a pickup roller is fed between the conveyance roller  110  and the reversible roller  120 , and conveyed to the image forming section. If the friction between the conveyance roller  110  and the reversible roller  120  is greater than a predetermined coefficient of friction, the reversible roller  120  rotates in the same direction of the rotation of the conveyance roller  110 . In contrast, if the friction is smaller than the predetermined coefficient of friction, the reversible roller  120  rotates in the opposite direction. The longer the reversible roller  120  is used, the more it becomes abraded due to friction with the conveyance roller  110 . With the increase of the abrasion of the reversible roller  120 , the reversible roller shaft  121  moves parallel by a distance ‘d’ toward the conveyance roller shaft  110  as shown in  FIGS. 3 and 4 . Therefore, in order to continuously transmit a driving force to the reversible roller  120  from a driving motor  130  ( FIG. 4 ), an idle gear  140  is required, which flexibly moves to be kept in mesh with the reversible gear  122  even when the position of the reversible roller shaft  121  is changed. As shown in  FIG. 4 , the central shaft Ci of the idle gear  140  is designed to be movable.  
      The central shaft Ci of the idle gear  140  moves along a swing track A as shown in  FIG. 4  to maintain the idle gear  140  and the reversible gear  122  in mesh. The central shaft Ci of the idle gear  140  is slidably mounted on one sidewall W ( FIGS. 5 and 6 ) of the image forming apparatus. When the reversible roller shaft  121  moves parallel toward the conveyance roller shaft  111 , the central shaft Ci also moves along the swing track A to maintain the idle gear  140  and the reversible gear  120  in mesh. The swing track A may be a part of the circumference of a virtual circle having a radius corresponding to the distance between the central shaft Cm of the driving gear  131  and the central shaft Ci of the idle gear  140 .  
       FIGS. 5 and 6  are diagrams illustrating the idle gear  140  with the central shaft Ci movable along the swing track A according to first and second embodiments of the present invention.  
      In accordance with the first embodiment of the present invention, the central shaft Ci of the idle gear  140  is slidably mounted on one sidewall W of the image forming apparatus. For this, the sidewall W has a curved swing slot  141  having a curvature corresponding to the swing track A and a width corresponding to the diameter of the central shaft Ci. Accordingly, when the position of the reversible roller shaft  121  is changed due to the abrasion of the reversible roller  120 , the central shaft Ci slides along the swing slot  141  to maintain the idle gear  140  and the reversible gear  122  in mesh.  
      As shown in  FIG. 5 , the curved swing slot  141  has a width corresponding to the diameter of the central shaft Ci of the idle gear  140 . Also, the swing slot  141  has a curvature corresponding to the curved swing track A.  
      According to the second embodiment of the present invention, the central shaft Ci of the idle gear  140  is slidably mounted on one sidewall W of the image forming apparatus. In this connection, the sidewall W has a straight swing slot  142  formed in a direction of a tangent to the swing track A, and having a width corresponding to the diameter of the central shaft Ci. An elastic member  143  such as a compression spring is mounted within the swing slot  142 . The elastic member  143  exerts an elastic restoring force so that the idle gear  140  can be maintained in mesh with the reversible gear  122 .  
      In the paper conveyance apparatus  100  for an image forming apparatus according to the first and second embodiments of the present invention, when the reversible roller  120  is abraded, the reversible roller shaft  121  moves parallel toward the conveyance roller  110  by a distance corresponding the abraded thickness of the reversible roller  120 , thereby preventing a biased abrasion of the reversible roller  120  and any error of feeding plural paper sheets at once.  
      When the distance between the conveyance roller shaft  111  and the reversible roller shaft  121  is shortened due to the abrasion of the reversible roller  120 , the idle gear  140  for transmitting the driving force to the reversible roller  120  is swung to move upward as much as the shortened distance so that the reversible roller  120  can be constantly in contact with the conveyance roller  110 . Accordingly, by eliminating any causes of biased abrasion of the reversible roller  120 , reliability of the image forming apparatus is ensured.  
      While the invention has been shown and described with reference to certain embodiments thereof, it should be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.