Abstract:
A paper cassette for an image forming apparatus includes a cassette body, a pair of aligning plates, paper separating fingers, and a biasing member. The cassette body has a knock-up plate on which paper is stackable. The pair of aligning plates are disposed on the paper cassette body and moving in a widthwise direction for aligning paper stacked on the knock-up plate in the widthwise direction. The paper separating fingers are disposed on the aligning plates and are vertically movable to a predetermined distance above the aligning plates, for pressing against two corners of a leading edge of an uppermost sheet of paper stacked on the knock-up plate. The biasing member is connected to at least a side of one of the paper separating fingers, for increasing a relative downward pressure exerted by the paper separating finger on the uppermost sheet of paper stacked on the knock up plate.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    This application claims the benefit of Korean Application No. 2003-11199, filed Feb. 22, 2003, 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]    The present invention relates to an image forming apparatus, and more particularly, to a paper cassette for an image forming apparatus.  
           [0004]    2. Description of the Related Art  
           [0005]    An image forming apparatus, which may be used in an office or a home, for outputting a desired image by fusing ink or toner onto paper, has a paper cassette for in seriatim supplying the paper sheets to a printing engine for printing.  
           [0006]    [0006]FIG. 1 shows a conventional paper cassette  100  for a conventional image forming apparatus (not shown). As shown in FIG. 1, the paper cassette  100  is mountable in a body (not shown) of the image forming apparatus with a plurality of sheets of paper being stacked on a knock-up plate  110 . The topmost sheet of the paper stacked on the knock-up plate  110  is in contact with a pick-up roller  10 , and both corners of a leading edge of the topmost sheet are in contact with a paper separating finger  120 .  
           [0007]    As shown in FIG. 2, when the pick-up roller  10  is driven in a clockwise direction, force is exerted to the topmost sheet in the direction of A. In this condition, the leading end of the topmost sheet is hindered from advancing due to the presence of the separating finger  120  and thus a part of the leading end of the topmost sheet is curved away from the sheet underneath it, so that the paper is fed to a printing engine by a feeding roller (not shown).  
           [0008]    This conventional arrangement is not without drawbacks. For example, if the distance between the pick-up roller  10  and the paper separating finger  120  is extended to accommodate the use of a large-sized paper, multiple sheets of paper may be picked up. Accordingly, in order to prevent the picking-up of multiple sheets of paper, the pick-up roller  10  has to be positioned within a predetermined distance from the paper separating finger  120 .  
           [0009]    However, it is impractical for the conventional paper cassette  100  of the conventional image forming apparatus to have the pick-up roller  10  which is always positioned at an optimal distance from the paper separating finger  120  because various-sized papers are used. And, when the paper in use is large-sized, the occurrence of multiple sheet pick-up increases.  
           [0010]    It is known to employ two spaced pick up rollers to remedy this multiple sheet pickup problem for A4 size paper. When using two spaced apart pick up rollers, the distance between the two pick-up rollers can be extended in order to prevent the pick up of multiple sheets of A4 paper. In this case, however, there is a disadvantage in that paper of a narrow width such as A5 size paper cannot be used.  
         SUMMARY OF THE INVENTION  
         [0011]    The present invention has been developed in order to solve the above and/or other problems in the related art. Accordingly, an aspect of the present invention is to provide a paper cassette for an image forming apparatus which is capable of using various-sized paper and preventing multiple picking-up.  
           [0012]    The above and/or other aspects are achieved by providing, in one aspect of the present invention, a paper cassette for an image forming apparatus comprising a cassette body having a knock-up plate on which paper is stackable, a pair of aligning plates disposed on the paper cassette body and movable in a widthwise direction for aligning in the widthwise direction paper stacked on the knock-up plate, paper separating fingers disposed on the aligning plates and vertically movable through a predetermined distance above the aligning plates, for pressing against two corners of a leading edge of an uppermost sheet of paper stacked on the knock-up plate, and a biasing member connected to at least a side of one of the paper separating fingers, for increasing a relative downward pressure exerted by the paper separating finger on the uppermost sheet of paper stacked on the knock up plate.  
           [0013]    The pressing member may be a spring having one end connected with the aligning plate and the other end connected to one side of the paper separating finger or a weight connected to one side of the paper separating finger.  
           [0014]    At least one paper separating finger can be provided with a friction pad formed thereon.  
           [0015]    The paper cassette for the image forming apparatus may include an aligning lever disposed on the knock-up plate and moving in a length direction, for aligning the paper stacked on the knock-up plate in length direction.  
           [0016]    According to another aspect of the present invention, there is provided a paper separator for use in a paper cassette. The paper separator includes a body pivotably connected to a side of an alignment plate of the paper cassette and pivotable between a first position and a second position about a pivot point located substantially at a pivot end of the body; a pressing portion connected to the body at a pressing end opposite the pivot end; a travel limiter disposed between the pivot end and the pressing end which limits the pivotable travel of the body to between the first position and the second position; and a biasing unit disposed between the travel limiter and the pivot end which urges the body. At least a portion of a base plate which supports paper in the paper cassette is urged substantially upwardly and the biasing unit urges the body substantially downwardly.  
           [0017]    According to still another aspect of the present invention, there is provided a paper cassette having a cassette body. The paper cassette includes: a support plate movably disposed within the cassette body and on which paper is stackable; a pair of aligning plates disposed on opposing sides of the cassette body and movable in a widthwise direction to align paper stacked on the support plate in the widthwise direction; paper separating fingers pivotably disposed on the aligning plates, an end of each of the paper separating fingers movable through a range of travel and pressable against a corner of a leading edge of an uppermost sheet of paper stacked on the support plate; and a biasing unit connected to at least a side of one of the paper separating fingers, for increasing a relative downward pressure exerted by the paper separating finger on the uppermost sheet of paper stacked on the knock up plate.  
           [0018]    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  
       [0019]    These and/or other aspects and advantages of the invention will be apparent and more readily appreciated from the following description of the preferred embodiments of the present invention with reference to the accompanying drawings, in which:  
         [0020]    [0020]FIG. 1 is a schematic side section view showing a conventional paper cassette for an image forming apparatus;  
         [0021]    [0021]FIG. 2 is a side section view showing the paper cassette of FIG. 1 to explain the paper separating operation;  
         [0022]    [0022]FIGS. 3 and 4 are schematic perspective views showing a paper cassette for an image forming apparatus according to an embodiment of the present invention; and  
         [0023]    [0023]FIG. 5 is a side section view showing various parts of the paper cassette for the image forming apparatus according to the embodiment of the present invention illustrated in FIGS. 3 and 4. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]    Reference will now be made in detail to the present preferred 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.  
         [0025]    As shown in FIG. 3, a paper cassette  200  for an image forming apparatus according to an embodiment of the present invention includes a cassette body  210 , aligning plates  221 ,  222 , and paper separating fingers  230 ,  240 .  
         [0026]    The cassette body  210  has a storage space formed therein for storing paper, and the storage space is provided with a knock-up plate  211  on which sheets of paper are stacked. The knock-up plate  211  is supported by a spring  111  (an example of which is shown in FIG. 2) so as to be biased or urged upwardly so that the topmost sheet stacked on the knock-up plate  211  comes into contact with pick-up rollers  11 ,  12  disposed in a body of the image forming apparatus. Also, one side of the knock up plate  211  is provided with an aligning lever  212  for aligning the sheets in the length direction. The aligning lever  212  slides along a guide slit  211   a  formed in the knock-up plate  211  in a lengthwise direction to thereby align the sheets of paper stacked on the knock-up plate  211 .  
         [0027]    The aligning plates  221 ,  222  are disposed at both sides of the knock-up plate  211 , for aligning the sheets of the paper in the width direction. The aligning plates  221 ,  222  slide along guide slits (not shown) formed in the cassette body  210  in a widthwise direction, to thereby align the sheets of the paper stacked on the knock-up plate  211 .  
         [0028]    The paper separating fingers  230 ,  240  prevent the pick up of multiple sheets of paper stacked on the knock-up plate  211 , and are respectively disposed on the aligning plates  221 ,  222  to press both corners of a leading end of the paper. The paper separating finger  230 , as shown in FIG. 5, includes a supporting portion  231  pivotably connected with the aligning plate  221  and a pressing portion  232  for pressing the corner of the leading end of the paper stacked on the knock-up plate  211 .  
         [0029]    The supporting portion  231  has one end pivotably connected with an outer surface of the aligning plate  211  on a pivoting point  223 . The other end of the supporting portion  231  has a hole  231   a  of a predetermined size formed therein, for receiving a stopper pin  224  protruding from the outer surface of the aligning plate  221 . Accordingly, the paper separating finger  230  is limited in its movement within a predetermined range because the stopper pin  224  moves within the hole  231   a . Also, the pressing portion  232  is disposed at the other end of the supporting portion  231  and extended toward an end of the knock-up plate  211 . The end of the pressing portion  232  is bent toward the knock-up plate  211  so that it comes into contact with the corner of the leading end of the paper. The pressing portion  232  is provided with a friction pad  233  formed thereon. The paper picked up from the knock-up plate  211  moves with a backside surface thereof in contact with the friction pad  233 , thereby causing a friction. When multiple sheets are picked up, the sheets can be separated from each other due to the presence of the friction pad  233 .  
         [0030]    There is a spring  225  connected with one end to the supporting portion  231  of the paper separating finger  230 . The other end of the spring  225  is connected with the outer surface of the aligning plate  221  so that the paper separating finger  230  is subject to the downward recovery force of the spring  225 . Accordingly, the paper separating finger  230  presses the sheets of paper stacked on the knock-up plate  211  with a combined pressure of a self-weight of the paper separating finger  230  and the recovery force of the spring  225 .  
         [0031]    Hereinafter, the operations of the paper cassette  200  for the image forming apparatus according to the present invention will be described in greater detail.  
         [0032]    When using small-sized paper such as, for example, A5 size paper having a width of 105 mm, the aligning lever  212  and the aligning plates  221 ,  222  are adjusted to be narrower in length and width according to the A5 size paper as shown in FIG. 3. Next, when the A5 size paper is stacked on the knock-up plate  211 , both corners of a leading end of the A5 size paper are subjected to a predetermined pressure by the pressing portions  232 ,  242  of the paper separating fingers  230 ,  240 . When the paper cassette  200  with the paper stacked therein is mounted in the body of the image forming apparatus, the pick-up rollers  11 ,  12  provided in pair in the body come into contact with top surfaces at both corner portions of the paper stacked on the knock-up plate  211 .  
         [0033]    When the pick-up rollers  11 ,  12  are driven, a friction occurs between the pick-up rollers  11 ,  12  and the A5 size paper, and the friction is exerted on the A5 size paper in the direction toward the separating fingers  230 ,  240 . At this point, the leading end of the A5 size paper is hindered from advancing by a resistance of the paper separating fingers  230 ,  240 , and thus a part of the leading end gets bent and starts separating from the underneath sheet. When the force generated at the bent portion of each corner of the A5 size paper becomes greater than the resistance of the paper separating fingers  230 ,  240 , the leading end of the A5 size paper lifts the paper separating fingers  230 ,  240  and pops out of the paper separating fingers  230 ,  240 . Then, the A5 size paper is fed to a printing engine by a feeding roller (not shown) provided in the body of the image forming apparatus.  
         [0034]    Meanwhile, when using large-sized paper, for example, a letter size paper having a width of 216 mm, the aligning lever  212  and the aligning plates  221 ,  222  are adjusted to be wider in length and width according to the letter size paper as shown in FIG. 4. When the letter size paper is stacked on the knock-up plate  211 , both corners of leading end of the letter size paper are subjected to a predetermined pressure due to the pressing portions  232 ,  242  of the paper separating fingers  230 ,  240 . When the paper cassette  200  with the paper stacked therein is mounted in the body of the image forming apparatus, the pair of pick-up rollers  11 ,  12  provided in the body come into contact with the top surface of the letter size paper stacked on the knock-up plate  211 . And, since there is no variation in a position of installing the pick-up rollers  11 ,  12 , the distance from a contacting portion between each pick-up roller  11 ,  12  and the letter size paper to the corner of the leading end of the letter size paper is greater than that of the A5 size paper.  
         [0035]    When the pick-up rollers  11 ,  12  are driven, a force is exerted on the letter size paper toward the paper separating fingers  230 ,  240 . The leading end of the letter size paper is hindered from advancing due to a resistance of the paper separating fingers  230 ,  242 , and thus a part of the letter size paper gets bent and is separated from the lower sheet of the letter size paper. When the force generated by the bent portion of the letter size paper becomes greater than the resistance of the paper separating fingers  230 ,  240 , the leading end of the letter size paper lifts the paper separating fingers  230 ,  240 , pops out therefrom, and then is picked-up. The letter size paper takes much more time to pop out from the paper separating fingers  230 ,  240  than the A5 size letter, and the bent portion of the letter size paper is larger than that of the A5 size paper. However, since the resistance of the paper separating fingers  230 ,  240  against the movement of the letter size paper is greater than in the case of the A5 size paper, there is no paper slip. Accordingly, the picking-up of multiple sheets of paper is prevented, and, if multiple sheets of paper are picked up, the paper can be separated sheet by sheet by the contact with the friction pads provided on the paper separating fingers  230 ,  240 .  
         [0036]    Table 1 shows data obtained from various tests with respect to the frequency of multiple sheet pick up according to the level of resilient recovery force of the spring  225  exerted on the paper separating fingers  230 ,  240  and according to thickness of the friction pads  233 ,  243  used. As shown in Table 1, the occurrence of multiple sheet pick up occurs less frequently when the resistance of the paper separating fingers  230 ,  240  is combined with the resilient recovery force of the spring  225  than when the resistance of the paper separating fingers  230 ,  240  occurs by self-weight of the paper separating fingers  230 ,  240 . Also, the presence of the friction pads  233 ,  243  makes the occurrence of multiple sheet pick up less frequent than in absence of the friction pads  233 ,  243 .  
                                           TABLE 1                                               Add   Add                               resilient   resilient       Paper       Add   Add   Add   Add   force 40 g   force 60 g       separating   Initial   resilient   resilient   friction   friction   and friction   and friction       fingers   State   force 40 g   force 60 g   pad 1t   pad 3t   pad 3t   pad 3t                   Occurrence of   62/500   24/500   5/500   60/500   53/500   0/500   2/500       multiple sheet                       4/500   1/500       pick up                       6/500   2/500                  
 
         [0037]    The embodiment illustrated in FIGS. 3 and 4 uses a construction in which the spring  225  acting as a pressing member presses the paper separating fingers  230 ,  240  downwardly in order to increase the resistance of the paper separating fingers  230 ,  240  against the movement of the paper. However, it is to be understood that other pressing or biasing arrangements may be used to increase the resistance of the paper separating fingers  230 ,  240  against the movement of the paper. By way of a non-limiting example, instead of the spring  225 , a weight may be connected to each paper separating finger  230 ,  240  so as to increase the resistance of the paper separating fingers  230 ,  240  against the movement of the paper.  
         [0038]    By increasing the resistance generated by the paper separating fingers  230 ,  240 , which press both corners of the leading end of the paper, against the movement of the paper, the frequency of multiple sheet pick up is lessened, even when the distance between the corners of the paper and the pickup-rollers  11 ,  12  increases. Accordingly, the paper cassette capable of using various types of paper differing in width can be realized.  
         [0039]    Although a few embodiments of the present invention have been shown and described, the present invention is not limited to the disclosed embodiment. Rather, it would be appreciated by those skilled in the art that changes and modifications may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.