Patent Publication Number: US-7591461-B2

Title: Automatic document feeder having a sheet-lifting mechanism

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The invention relates to an automatic document feeder having a sheet-lifting mechanism, and more particularly to an automatic document feeder which can lift up a leading edge of a sheet elastically to facilitate a pick-up roller in picking up the sheet and a sheet feeding roller in feeding the sheet subsequently. 
     2. Related Art 
     Automatic document feeders are widely used in the apparatuses such as scanners, printers, copiers and multi-function peripherals. An automatic document feeder using a pick-up roller to pick up a sheet is commonly used in conjunction with a paper tray having a larger capacity. 
     Due to the mechanical design of the pick-up roller and for collocating the pick-up roller and the large paper tray, the large paper tray is usually provided with a stopper for stopping the leading edges of a stack of sheets disposed in the paper tray. So, the sheet, which is picked up by the pick-up roller, has to pass over the top of the stopper so as to reach a separating roller installed in the automatic document feeder smoothly. The stopper may be designed to have a steep or vertical surface for restricting the position of the leading edge of the sheet. In this case, when there are many sheets stacked in the paper tray, the topmost sheet of the stack is very close to the top of the stopper, and the topmost sheet can pass over the stopper without any difficulty. However, when few sheets are left in the paper tray, the topmost sheet is farther from the top of the stopper, and it is difficult for the sheet to pass over the stopper, thereby causing some disruption in the sheet feeding process. 
     In order to solve this problem, the stopper may be designed to have a slightly inclined surface such that the slope of the stopper is smaller. In this case, the user may unintentionally insert the sheets into the clearance between the separating roller and the sheet separating pad, and the sheet-separating function may be disabled. In addition, when there are few sheets in the paper tray, the topmost sheet still can pass over the top of the stopper easily because the slope of the stopper is gradual, despite that the topmost sheet is farther from the top of the stopper. When many sheets are disposed in the paper tray, some upper sheets are very near the top of the stopper. So, multiple sheets may easily pass over the stopper such that the stopper cannot function to stop the sheet and the sheet cannot be easily fed. In addition, the gradually sloped stopper occupies larger space because it has the inclined surface with the smaller slope. Thus, the prior art cannot solve the problems presented when the sheets in the paper tray are many or few. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the invention to provide an automatic document feeder having a sheet-lifting mechanism for partially lifting a sheet to help the sheet pass over a stopper of a paper tray such that the sheet may be fed smoothly. 
     To achieve the above-identified object, the invention provides an automatic document feeder including a paper tray, a pick-up roller and a sheet-lifting mechanism. The paper tray stores a plurality of sheets including a bottommost first sheet and a second sheet above the first sheet. The paper tray includes a bottom plate in contact with the first sheet and a stopper for stopping leading edges of the first sheet and the second sheet. The pick-up roller, which is movable and rotatable, picks up the second sheet and enables the leading edge of the second sheet to pass over the stopper. The sheet-lifting mechanism disposed on the paper tray lifts the leading edges of the second sheet and the first sheet from the bottom plate. 
     Further scope of the applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while the indicating preferred embodiment of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein: 
         FIG. 1  is a schematic illustration showing an automatic document feeder having a sheet-lifting mechanism according to a preferred embodiment of the invention; 
         FIG. 2  is a top view of  FIG. 1 ; 
         FIG. 3  is a schematic illustration showing a first modified example of  FIG. 1 ; 
         FIG. 4  is a schematic illustration showing a second modified example of  FIG. 1 ; 
         FIG. 5  is a schematic illustration showing a third modified example of  FIG. 1 ; 
         FIG. 6  is a partial top view of  FIG. 5 ; 
         FIG. 7  is a schematic illustration showing a fourth modified example of  FIG. 1 ; and 
         FIG. 8  is a schematic illustration showing a fifth modified example of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will be apparent from the following detailed description, which proceeds with reference to the accompanying drawings, wherein the same references relate to the same elements. 
       FIG. 1  is a schematic illustration showing an automatic document feeder having a sheet-lifting mechanism according to a preferred embodiment of the invention.  FIG. 2  is a top view of  FIG. 1 . Referring to  FIGS. 1 and 2 , the automatic document feeder according to this embodiment includes a paper tray  10 , a pick-up roller  20 , a sheet-lifting mechanism  30 , a sheet separating mechanism  40  and a rocker arm  50 . 
     The paper tray  10  stores a plurality of sheets including, for example, a bottommost first sheet S 1  and a second sheet S 2  above the first sheet S 1 . Although two sheets are described, one of ordinary skill in the art may easily understand that the invention is also suitable for the application of more than two sheets or a single sheet. However, the conditions of feeding two sheets and one sheet occur at the end of the overall feeding processes no matter how many pages of sheets are originally placed in the paper tray. The main function of the invention is to solve the problem in the prior art, which occurs when there are few sheets, such as two or one. The sheet-lifting mechanism of the invention mainly functions to lift the sheets when there are few sheets. When many sheets are stacked, the sheets cannot be lifted because the sheet-lifting force provided by the sheet-lifting mechanism cannot overcome the weight of all the sheets. In fact, when there are many sheets in the paper tray, the topmost sheet is very near the top of a stopper. Thus, the sheet feeding operation cannot be interrupted even if the sheets are not lifted. The paper tray  10  includes a bottom plate  12  in contact with the first sheet S 1  and a stopper  14  for stopping leading edges L 1  and L 2  of the first sheet S 1  and the second sheet S 2 . 
     The pick-up roller  20 , which may be moved in a direction indicated by the arrow by the rocker arm  50  connected to a separating roller  42  and the pick-up roller  20 , can rotate and pick up the second sheet S 2  and enables the leading edge L 2  of the second sheet S 2  to pass over the stopper  14 . 
     The sheet-lifting mechanism  30 , which may be fixed to or disposed on the bottom plate  12  and/or the stopper  14  of the paper tray  10 , can apply an upward lifting force to the first sheet S 1  and the second sheet S 2 , lifting the leading edge L 2  of the second sheet S 2  and the leading edge L 1  of the first sheet S 1  from the bottom plate  12 . When the leading edge L 1  of the first sheet S 1  is lifted from the bottom plate  12 , only a portion of the first sheet S 1  is in contact with the bottom plate  12 . That is, if the sheet-lifting mechanism  30  is removed, the leading edge L 1  lies on the bottom plate  12  and the entirety of the first sheet S 1  is in contact with the bottom plate  12 . The bottom plate  12  of  FIG. 1  is connected with the stopper  14 . 
     When only the first sheet S 1  is left in the paper tray  10 , the bottom plate  12  of the paper tray  10  is in partial surface contact with the first sheet S 1 . The sheet-lifting mechanism  30  lifts the leading edge L 1  of the first sheet S 1  from the bottom plate  12  and the stopper  14  stops the leading edge L 1  of the sheet S 1 . The pick-up roller  20 , which is movable and rototable, picks up the first sheet S 1  and enables the leading edge L 1  of the first sheet S 1  to pass over the stopper  14 . 
     The sheet separating mechanism  40 , which includes the separating roller  42  and a sheet separating pad  44  in contact with the separating roller  42 , receives and feeds the second sheet S 2 , which passes over the stopper  14 , and feeds the second sheet S 2  and blocks the first sheet S 1  in case that both of the first sheet S 1  and the second sheet S 2  pass over the stopper  14 . 
     The sheet-lifting mechanism  30  may have various variations. For example, the sheet-lifting mechanism  30  may only include one upper elastic piece  33  or a lower elastic piece  31 . Alternatively, the sheet-lifting mechanism  30  may include an upper elastic piece  33  and a lower elastic piece  31 , or include one lower elastic piece  31  and two upper elastic pieces  33  respectively disposed on two sides of the lower elastic piece  31 . Thus, the number of the upper elastic pieces  33  and the lower elastic pieces  31  can be adjusted according to the design requirements such that various combinations may be carried out. 
     As shown in  FIGS. 2 and 4 , each of the upper elastic pieces  33  for lifting the first sheet S 1  and the second sheet S 2  has a first end  33 A disposed on the stopper  14  and a second end  33 B in sliding contact with or movably lying on the bottom plate  12 . 
     As shown in  FIGS. 2 and 3 , the lower elastic piece  31  for lifting the first sheet S 1  and the second sheet S 2  has a first end  31 A disposed on the bottom plate  12  and a free second end  31 B. Two contact points P 2  of the upper elastic pieces  33  and the first sheet S 1  are located on two sides of one contact point P 1  of the lower elastic piece  31  and the first sheet S 1 , such that the leading edges L 1  and L 2  of the first sheet S 1  and the second sheet S 2  may be kept leveled, and the situation that the middle of the sheet can pass over the stopper but the two sides of the sheet cannot pass over the stopper can be avoided. When only the first sheet S 1  is left in the paper tray  10 , the two contact points of the upper elastic pieces  33  and the first sheet S 1  are located on two sides of the contact point of the lower elastic piece  31  and the first sheet S 1 . As shown in  FIG. 3 , the lower elastic piece  31  further has a middle portion  31 C for connecting the first end  31 A to the second end  31 B. The middle portion  31 C is bendable towards the first end  31 A and supports the sheet The second end  31 B is bendable towards the middle portion  31 C and movable within a first recess  12 A of the bottom plate  12 . The middle portion  31 C contacts the sheet S 1  to lift the sheets S 1  and S 2 . When only the first sheet S 1  is left in the tray  10 , the middle portion  31 C pushes the sheet S 1  upwards. Alternately, the lower elastic piece  31  may have no middle portion  31 C. In this case, the lower elastic piece  31  may have the first end  31 A disposed on the bottom plate  12  and the second end  31 B in sliding contact with the stopper  14  so as to lift the sheets. 
     As shown in  FIGS. 2 and 5 , the upper elastic piece  33  has the first end  33 A disposed on the stopper  14  and the second end  33 B movably accommodated within a second recess  12 B of the bottom plate  12 . Thus, it is possible to prevent the second end  33 B of the upper elastic piece  33  from warping and thus blocking the sheets inserted into the paper tray. The second recess  12 B may also have a flange  13  for restricting the upper elastic piece  33  within the second recess  12 B. 
     As shown in  FIGS. 6 and 5 , no matter whether the flange  13  exists or not, a width W 1  of the second end  33 B of the upper elastic piece  33  is greater than a width W 2  of the second recess  12 B in order to prevent the second end  33 B of the upper elastic piece  33  from leaving the second recess  12 B. During installation, the second end  33 B of the upper elastic piece  33  may be inserted into the second recess  12 B by slightly twisting the upper elastic piece  33 . 
     As shown in  FIG. 7 , the sheet-lifting mechanism  30  is an elastic piece  34  disposed on the stopper  14 . The elastic piece  34  has a free first end  34 A and a free second end  34 B. The sheet separating pad  44  is disposed on the elastic piece  34  and near the first end  34 A but far from the second end  34 B. 
     Referring to  FIG. 8 , the sheet-lifting mechanism  30  includes a flat plate  35  and a spring  36 . One end of the flat plate  35  is pivoted on the stopper  14 . The spring  36  disposed between the flat plate  35  and the stopper  14  applies a resilient force to the flat plate  35  when the flat plate  35  is pressed down by the first sheet S 1  and the second sheet S 2 . When only the first sheet S 1  is left in the paper tray  10 , the spring  36  applies a resilient force to the flat plate  35  pressed down by the sheet S 1 . Thus, the leading edges of the sheets may be lifted under the cooperation of the spring  36  and the pivotal flat plate  35 . 
     In summary, the effect provided by this invention can block a stack of sheets using the stopper and then lift the sheets using the sheet-lifting mechanism. According to the structure of the invention, the leading edge of the sheet can be effectively lifted to facilitate the operation of picking up the sheet. 
     According to the action of the elasticity of the elastic piece or the spring, the elastic piece or the flat plate is pressed down by a larger distance when more sheets are placed in the paper tray. Thus, the topmost sheet is positioned near the top of the stopper. When the sheets are fewer, the elastic piece or the flat plate is pressed down by a smaller distance. Thus, the topmost sheet is still positioned near the top of the stopper. Consequently, the user does not have to stack the sheets to a minimum level to solve the problem of the unsmooth sheet feeding operation. In addition, the sheets do not slide backward and out of the paper tray to cause the unsmooth sheet-feeding operation because the sheets are only partially lifted. 
     While the invention has been described by way of examples and in terms of a preferred embodiment it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications. Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications.