Abstract:
A pickup roller increasing a force adhering a top sheet contacting the pickup roller, an image forming apparatus with the same, and a method. A plurality of holes are formed on a surface of the pickup roller contacting the paper, and an internal diameter of part of the holes is expanded by compression between the paper and the pickup roller.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit from Korean Patent Application No. 10-2004-0063760, filed on Aug. 13, 2004, in the Korean Intellectual Property Office, the disclosure of which is hereby incorporated by reference  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to an image forming apparatus, and more particularly, to an improved pickup roller for increasing a force adhering to a top sheet contacting the pickup roller, and an image forming apparatus with the same.  
         [0004]     2. Description of the Related Art  
         [0005]     In general, image forming apparatuses, such as printers or copiers, include a paper pickup unit accommodating plural sheets of paper and picking up an uppermost paper sheet of a paper pile to feed it into a main body of the image forming apparatus.  FIG. 1  shows one example of a conventional paper pickup unit  10 .  
         [0006]     Referring to  FIG. 1 , a paper pickup unit  10  includes a knock-up plate  12  connected to a paper cassette (not shown) and detachably mounted to a body (not shown) of an image pickup apparatus. Sheetsets of paper P are stacked on a knock-up plate  12 . A spring  18  elastically biases in an upward direction a knock-up plate  12 . A pickup roller  20  is provided in the body of the image pickup apparatus and positioned on the knock-up plate  12 .  
         [0007]     The pickup roller  20  is rotatably engaged with a shaft  28  transferring a rotational force, and has a surface generally made of rubber to pick up the paper P. The pickup roller  20  may be constructed such that an inside portion coupled to the shaft  28  is detachably coupleable and with a surface portion contacting the paper P, or such that the inside portion and the surface portion are integrally formed of a rubber material.  
         [0008]     The shaft  28  has a pair of cams  30  with the pickup roller  20  interposed therebetween. The cams  30  press down both sides of the knock-up plate  12  in a printing standby state to cause a front end of the paper P to be separated from the pickup roller  20 .  
         [0009]     If a printing command is inputted into the image forming apparatus (not shown), the pickup roller  20  and the cams  30  are rotated, in direction shown by the arrow, by rotation of the shaft  28 . The cam  30  pressing down the knock-up plate  12  is lifted, and the knock-up plate  12  is rotated around a hinge  14  by a biasing force of the spring  18 , so that a front end of the knock-up plate  12 , spaced apart from the hinge  14 , moves in an upward direction. The front end of the paper P stacked on the knock-up plate  12  contacts the rotating pickup roller  20 , and is picked up by a frictional force between the paper and the outer portion of the pickup roller  20  so as to feed the paper into the body (not shown) of the image forming apparatus.  
         [0010]     The surface portion of the pickup roller  20  is surface-treated by various techniques so as to increase the frictional force between the paper and the surface portion of the pickup roller.  FIGS. 2 through 4  show examples of a surface pattern of a conventional pickup roller that is formed by a surface treatment.  
         [0011]      FIG. 2  shows a wave-type surface pattern formed by polishing a surface of a pickup roller. The wave-type surface pattern is easily abraded, and a foreign substance (e.g., dust) is likely to adhere to the wave pattern. Therefore, a problem exists in that since a frictional force of the surface will rapidly decrease, paper pickup performance is rapidly deteriorated.  
         [0012]      FIG. 3  shows another wave-type surface pattern in which a wave is inclined with respect to a traveling direction of the paper. The wave pattern shown in  FIG. 3  can reduce abrasion of a surface relative to that of the wave pattern shown in  FIG. 2 , but foreign substances are still likely to adhere to the surface. Therefore, the wave pattern also has a problem in that a frictional force still rapidly decreases.  
       SUMMARY OF THE INVENTION  
       [0013]     Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the invention.  
         [0014]     The present invention provides a pickup roller in which paper pickup performance is maintained for a long time relative to that of a conventional pickup roller, and an image forming apparatus including the pickup roller.  
         [0015]     According to one aspect of the present invention, a pickup roller that rotates and contacts a sheet of paper to pick up the paper is provided including a plurality of holes on a surface of the pickup roller that contacts the paper, and an internal diameter of a hole is expanded by a compressive force between the paper and the pickup roller.  
         [0016]     According to another aspect of the present invention, an image forming apparatus is provided including a print unit printing an image on a sheet of paper and a paper pickup unit picking up the paper to be transferred to the print unit, in which the paper pickup unit rotates and contacts the paper so as to pick up the paper. A plurality of holes are on a surface of the pickup roller contacting the paper, and an internal diameter of a hole is expanded by compression between the paper and the pickup roller. According to an aspect of the present invention, a topology of holes for a pickup roller include a pattern of holes extending from a surface of the pickup roller.  
         [0017]     According to an aspect of the present invention, the hole may be extend toward a rotating center of the pickup roller.  
         [0018]     According to an aspect of the present invention, a surface of the pickup roller contacting the paper may be made of material having Poisson&#39;s ratio of 0.1 to 0.49.  
         [0019]     According to an aspect of the present invention, a surface of the pickup roller contacting the paper may be made of EPDM material.  
         [0020]     According to an aspect of the present invention, a plurality of holes may be distributed in a regular pattern on the surface contacting the paper. According to an aspect of the present invention, a printing medium moving member includes a surface including a plurality of holes a part of which are expandable. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]     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:  
         [0022]      FIG. 1  is a perspective view of a conventional paper pickup unit;  
         [0023]      FIGS. 2 through 4  are plan views depicting examples of surface patterns of a conventional pickup roller;  
         [0024]      FIG. 5  is a cross-sectional view of an image forming apparatus according to an example embodiment of the present invention;  
         [0025]      FIGS. 6 and 7  are plan views depicting embodiments of surface patterns of a pickup roller in the  FIG. 5 ; and  
         [0026]      FIGS. 8 and 9  are partially enlarged cross-sectional views of a pickup roller in  FIG. 5 , in which  FIG. 8  shows a state before the pickup roller contacts a paper, and  FIG. 9  shows a state where the pickup roller contacted the paper. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]     Reference will now be made in detail to the 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 to explain the present invention by referring to the figures.  
         [0028]     Reference will now be made in detail to a pickup roller according to an embodiment of the present invention, and an image forming apparatus including the pickup roller.  
         [0029]      FIG. 5  is a cross-sectional view of an image forming apparatus  100  according to an example embodiment of the present invention.  
         [0030]     Referring to  FIG. 5 , the image forming apparatus  100  is a electrophotograph-type that supplies a toner as a developer onto an electrostatic latent image formed on an outer surface of a photosensitive medium by light emission to develop the electrostatic latent image into a visible image and transfers and fuses the image onto a sheet of paper to print a desired image. The image forming apparatus  100  includes a case  101 , a developing unit  110 , a transferring unit  125 , a light scanning unit  127 , and a fixing unit  130  Units  110 ,  125 ,  127  and  130  are a print unit. The image forming apparatus further includes a paper pickup unit  150  picking up a sheet of paper P to be printed.  
         [0031]     The developing unit  110  includes a housing  111  accommodating a toner as a developer, and a photosensitive medium  115  forming an electrostatic latent image therein by a light scanning. The developing unit also includes charging roller  113  charging the photosensitive medium  115 , a wasted toner cleaner  114  removing a wasted toner remained on the photosensitive medium  115 , and a developing roller  117  supplying a toner onto the electrostatic latent image formed on the outer surface of the photosensitive medium  115  to develop the image onto the outer surface. The developing unit also includes a doctor blade  118  regulating a thickness of the toner adhered to the surface of the developing roller  117 , and a supply roller  119  supplying the toner to the developing roller  117 . Also, the developing unit  110  includes an agitator  121  agitating the toner in the housing  111  to prevent solidification of the toner. The developing unit  110  a cartridge-type, and thus is replaceable with a new cartridge if the developer is completely exhausted.  
         [0032]     The transferring roller  125  is located opposite to the photosensitive medium  115 , and in contact with the photosensitive medium  115 . The transferring roller  125  presses the paper P against the photosensitive medium  115  so that the visible image developed on the outer surface of the photosensitive medium  115  is transferred onto the paper P passing through the transferring roller  125  and the photosensitive medium  115 .  
         [0033]     The fixing unit  130  includes a heat roller  131  and a pressing roller  133  opposite the heat roller. When the paper P with the visible image transferred thereon passes between the heat roller  131  and the pressing roller  133 , the visible image is fixed onto the paper P by thermal compression.  
         [0034]     The paper pickup unit  150  includes a knock-up plate  153  that is hingedly coupled to a paper feeding cassette  151  and on which paper to be printed on is stacked. A shaft  165  is positioned above a front end of the knock-up plate  153  when the paper feeding cassette  151  is mounted on the image forming apparatus  100  and rotated by a rotation of a drive motor (not shown). A pickup roller  170  is rotatably coupled to the shaft  165 . The paper pickup unit  150  includes a lifting means for lifting the knock-up plate  153  in connection with the rotation of the pickup roller  170  so that a front end of paper P stacked on the knock-up plate  153  selectively contacts the pickup roller  170 .  
         [0035]     The lifting means has a spring  157  for elastically biasing the knock-up plate  153  in an upward direction, and a cam (not shown) coupled to the shaft  165  and rotated with the pickup roller  170 . The cam is rotated together with the pickup roller  170 , and periodically pushes a front-end of the knock-up plate  170  in a downward direction. Accordingly, paper P stacked on the knock-up plate  153  is periodically spaced apart from the pickup roller  170  so that the paper P does not contact the pickup roller  170 . A friction pad  160  is provided in a front portion of the front end of the knock-up plate  153 . Even though plural sheets of the paper P are picked up by the pickup roller  170 , a movement of other sheets of paper is impeded by the friction pad  160 , and only an uppermost sheet of paper P stacked on the knock-up plate  153  is advanced toward the print unit  110 .  
         [0036]     The image forming apparatus  100  also includes a paper arranging unit  140  providing a transferring force to the paper P picked up by the paper pickup unit  150  and arranging the paper P to transfer the visible image onto a desired part of the paper P before the paper P reaches the photosensitive medium  115 . In addition, the image forming apparatus  100  includes a delivery roller  135  delivering the paper P with a desired image printed thereon to a delivery tray  102  disposed at an external position of the case  101 .  
         [0037]     An example operation of the image forming apparatus  100  will now be described. The photosensitive medium  115  is charged at a certain potential by the charging roller  113 , and an electrostatic latent image corresponding to the image to be printed is formed on the outer surface of the photosensitive medium  115  by a light L scanned from the light scanning unit  127 . The toner in the housing  111  is supplied through the supply roller  119  and the developing roller  117  to the photosensitive medium  115 , with the electrostatic latent image formed thereon, to develop the visible image on the outer surface of the photosensitive medium  115 . The paper P is picked up by the paper feeding unit  150 , and passes between the photosensitive medium  115  and the transferring roller  125 , being fed and arranged by the paper arranging unit  140 . At this time, the visible image developed on the outer surface of the photosensitive medium  115  is transferred to a surface of the paper P that is opposite to the photosensitive medium  115 . When the paper P passes through the fixing unit  130 , the image transferred to the paper P is fixed onto the paper P by thermal compression. The paper P is delivered to the delivery tray  102  by the delivery roller  135 .  
         [0038]     An example pickup roller  170  is formed of EPDM material so as to increase a frictional force between the paper P and the pickup roller  170 . The pickup roller  170  may be made of natural rubber (NR), nitrile rubber (NBR), urethane base rubber, or silicon base rubber.  
         [0039]     The pickup roller  170  contacts the paper P with a plurality of holes  172  for improving paper pickup performance. The respective holes  172  extend in a direction toward the shaft  165  which is a rotating center of the pickup roller  170 . The holes  172  may be regularly distributed over the surface of the pickup roller  170  as shown in  FIGS. 6 and 7 . More specifically,  FIG. 6  shows rows of holes  172  arranged parallel with a feeding direction of the paper P indicated by an arrow.  FIG. 7  shows rows of holes  172  arranged in a zigzag pattern with respect to the feeding direction of the paper P indicated by an arrow. Alternatively, the holes  165  may be irregularly distributed over the surface of the pickup roller  170 . The pickup roller  170  may also include a wave-type surface pattern so as to improve the frictional force between the pickup roller and the paper.  
         [0040]     As shown in  FIG. 8 , where the paper P stacked on the knock-up plate  153  (see  FIG. 5 ) is not in contact with the pickup roller  170 , the pickup roller  170  and the holes  172  on the surface of the pickup roller are maintained in original shapes. An internal pressure P in  of the hole  172  is maintained so as to be equal to an external pressure P atm  of the hole  172 . As a printing process starts, the knock-up plate  153  is lifted and the paper P contacts a lower end of the pickup roller  170 . A lower end of the pickup roller is pressed by the paper P and deformed, as shown in  FIG. 9 , so that an internal diameter of a part of the hole  172  closer to an opening of the hole is expanded from D 1  to D 2 .  
         [0041]     Assuming the variation is an adiabatic process, since the variation of the internal diameter instantaneously occurs, the expansion of the internal diameter of part of the hole  172  results in a cubic expansion inside the hole  172 . Accordingly, as understood in thermodynamic law, the internal pressure P in  of the hole  172  will be less than the external pressure P atm  of the hole  172 . Thus, it would be understood that paper P adheres to the lower end of the pickup roller  170  due to the pressure difference.  
         [0042]     According to an aspect of the present invention, the pickup roller  170  is made of material having a Poisson&#39;s ratio of 0.1 to 0.49. The Poisson&#39;s ratio is defined as a ratio of transverse contraction strain to longitudinal extension strain of a material when a stress is applied to the material. If the Poisson&#39;s ratio is less then 0.1, the pickup roller  170  is rigid so that the variation of the internal diameter of the hole  172  is slight. If the Poisson&#39;s ratio is greater than 0.49, the pickup roller  170  is so soft that the pickup roller  170  may be deformed in a direction other hat an internal diameter of the hole  172 .  
         [0043]     The pickup roller according to aspects of the present invention and the image forming apparatus with the pickup roller include the following advantages.  
         [0044]     Since the pickup roller pulls the paper by use of the suction force resulting from the deformation of the holes, in addition to the frictional force, the paper pickup performance is improved compared to that of a conventional pickup roller.  
         [0045]     The paper pickup performance is not affected by reducing the frictional force due to the increased suction force resulting from the deformation of the holes. Therefore, abrasion of the pickup roller is reduced by adjusting the frictional strength between the paper and the pickup roller, thereby improving the durability of the pickup roller.  
         [0046]     A frictional force between the sheets of paper is capable of being reduced by adjusting the frictional force between the pickup roller and the paper, thus preventing overlapping delivery of paper.  
         [0047]     Foreign adhered to the surface of the pickup roller are easily detached from the surface of the pickup roller in a process where an inner diameter of the hole is repeatedly expanded and restored.  
         [0048]     According to another aspect of the present invention, a pickup roller may include a plastic bracket coupled to the shaft and a rubber band wound around the bracket, and the holes may be formed in the rubber band.  
         [0049]     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.