Abstract:
A method and apparatus for reducing burden in retrieving sheets of material from the bottom of a substantially vertical stack of sheets in a sheet feeder. The apparatus comprises a first convex surface at the bottom half of the stack protruding into one side of the stack for pushing the sheets toward the other side, and a second convex surface on the second side below the first convex surface for pushing the sheets toward the first side. The first and second convex surfaces each provide a counteracting force resisting the downward movement of the stack, and these countering forces have upward vertical components partially countering the downward vertical force due to the weight of the stack.

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to a sheet feeder, which can be used in an envelope inserting machine or the like, and, more particularly, to a sheet feeder for feeding sheets from a vertical stack. 
     BACKGROUND OF THE INVENTION 
     In an inserting machine for mass mailing, there is a gathering section where enclosure material is gathered before it is inserted into an envelope at an envelope insertion area. The gathering section is sometimes referred to as a chassis subsystem, which includes a gathering transport with pusher fingers rigidly attached to a conveyor belt and a plurality of enclosure feeders mounted above the transport. If the enclosure material contains many documents, these documents must be separately fed from different enclosure feeders. 
     Inserting machines are well-known. For example, U.S. Pat. No. 4,501,417 (Foster et al.) discloses an inserter feeder assembly for feeding enclosures; U.S. Pat. No. 4,753,429 (Irvine et al.) discloses a collating station; and U.S. Pat. No. 5,660,030 (Auerbach et al.) discloses an envelope inserter station, wherein envelopes are separately provided to an envelope supporting deck where envelopes are spread open so as to allow enclosure materials to be stuffed into the envelopes. 
     An exemplar inserting machine is shown in FIG.  1 . As shown, an inserting machine  10  typically includes an envelope feeder/inserter station  12  and a plurality of enclosure feeders  20 . The envelope feeder/inserter station  12  includes an envelope feeder  14  above an envelope insertion area  16 . Documents  22  are separately released from the enclosure feeders  20  onto a long deck  30  and collated as the released documents (not shown) are pushed by a plurality of pusher fingers  32  driven by one or more endless belts or chains  34  toward the envelope feeder/inserter station  12 . At the same time, a stack of envelopes  18  are placed on the envelope feeder  14  so that one envelope at a time is released from the envelope feeder  14  into the envelope insertion area  16  where the envelope is spread open to allow the collated documents to be stuffed into the envelope. Typically the enclosure feeders are fixedly mounted to inserting machine  10  above the deck  30 . As shown, the enclosure feeder  20  has a slant tray  24  for supporting the documents  22  to be released. This type of slant tray design has a very limited capacity for stacking the documents  22 , partly due to the fixed distance between adjacent enclosure feeders  20 . Slant trays are widely used in envelope inserting machines, as can be seen in earlier mentioned U.S. Pat. Nos. 4,501,417 (Foster et al.), 4,753,429 (Irvine et al.) and 5,660,030 (Auerbach et al.). U.S. Pat. No. 5,120,043 (Mazullo) also discloses an enclosure feeder with a slant tray for supporting the documents. U.S. Pat. No. 4,817,368 (DePasquale et al.) discloses a mailing inserting and collating apparatus, wherein a plurality of envelope hoppers each containing a vertical stack of mailing inserts for releasing the inserts into a plurality of opened envelopes. Under each envelope hopper, a rubber kicker roller having an arcuate outer surface, along with a vacuum port, is used to retrieve the lowermost insert from the stack. The major advantage of the vertical stack is that it can support more inserts or documents to be released. The major disadvantage is that the weight of the vertical stack imposes a burden to the retrieving mechanism. The weight may cause an incomplete retrieval of inserts or a torn sheet. 
     Thus, it is advantageous and desirable to provide a method and apparatus for reducing the burden in retrieving a lowermost sheet from a vertical stack of sheets due to the weight of the stack. 
     SUMMARY OF THE INVENTION 
     It is the primary object of the present invention to reduce the burden in retrieving a lowermost sheet from a vertical stack of sheets in a sheet feeder or the like. In particular, the burden is mostly due to the weight of the stack. 
     Accordingly, the first aspect of the present invention is a method of reducing the burden in retrieving sheets from the bottom of a stack of sheets of material in a sheet feeder, wherein the stack has a downward vertical force associated with gravity and the burden is related to the downward vertical force, and wherein the stack has a first side and an opposing second side, and the stack is caused to move downward toward the bottom due to the retrieving. The method comprises the steps of providing a first counteracting surface in the lower portion of the stack protruding into the first side of the stack for pushing the sheets in a first portion of the stack toward the second side, and providing a second counteracting surface on the second side below the first counteracting surface for pushing the sheets in a second portion of the stack below the first portion of the stack toward the first side, wherein the first counteracting surface provides a first counteracting force resisting the downward movement of the stack on the first side and the second counteracting surface provides a second counteracting force resisting the downward movement of the stack on the second side, and wherein the first reaction force and the second reaction force comprise upward vertical components for partially countering the downward vertical force. 
     Preferably, the first counteracting surface comprises a convex surface. 
     Preferably, the convex surface is part of a circumference of a roller, which is caused to turn by the downward movement of the stack on the first side. 
     Preferably, the second counteracting surface comprises a further convex surface. 
     It is possible that the further convex surface is part of a circumference of another roller. 
     It is also possible that the further convex surface is part of a large surface, which includes a concave section. 
     The second aspect of the present invention is an apparatus for reducing burden in retrieving sheets from bottom of a stack of sheets in a sheet feeder, wherein the stack has a downward vertical force associated with gravity and the burden is related to the downward vertical force, and wherein the stack has a first side and an opposing second side, and the stack is caused to move downward toward the bottom due to the retrieving. The apparatus comprises a first counteracting surface in the lower portion of the stack protruding into the first side of the stack for pushing the sheets in a first portion of the stack toward the second side, and a second counteracting surface on the second side below the first counteracting surface for pushing the sheets in a second portion of the stack below the first portion of the stack toward the first side, wherein the first counteracting surface provides a first counteracting force resisting the downward movement of the stack on the first side and the second counteracting surface provides a second counteracting force resisting the downward movement of the stack on the second side, and wherein the first reaction force and the second reaction force comprise upward vertical components for partially countering the downward vertical force. 
     The third aspect of the present invention is a sheet feeder for feeding a substantially vertical stack of sheets, wherein the stack has a bottom, a first side and an opposing second side. The sheet feeder comprises a retrieving mechanism for retrieving sheets from the bottom of the stack; a first counteracting surface in the lower portion of the stack protruding into the first side of the stack for pushing the sheets in a first portion of the stack toward the second side; and a second counteracting surface on the second side below the first counteracting surface for pushing the sheets in a second portion of the stack below the first portion of the stack toward the first side, wherein the stack is caused to move downward toward the bottom due to the retrieving, and the first counteracting surface provides a first countering acting force resisting the downward movement of the stack on the first side and the second counteracting surface provides a second countering action force resisting the downward movement of the stack on the second side results in a second reaction force from the second counteracting surface, and wherein the first counteracting force and the second counteracting force comprise upward vertical components for partially countering a downward vertical force associated with the weight of the stack. 
     The present invention will become apparent upon reading the description taken in conjunction with FIGS. 2 to  5   b.   
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagrammatic representation illustrating a prior art envelope inserting machine for mass mailing. 
     FIG. 2 is a diagrammatic representation of a sheet feeder, illustrating the burden reduction principle, according to the present invention. 
     FIG. 3 a  is a vector diagram illustrating the force and counteracting forces in the sheet feeder, according to the present invention. 
     FIG. 3 b  is a vector diagram illustrating the net force acting on the sheet retrieving mechanism in the sheet feeder, according to the present invention. 
     FIG. 4 a  is a diagrammatic representation illustrating the preferred embodiment of the present invention. 
     FIG. 4 b  is a diagrammatic representation illustrating an alternative embodiment of the present invention. 
     FIG. 4 c  is a diagrammatic representation illustrating yet another embodiment of the present invention. 
     FIG. 5 a  is a diagrammatic representation illustrating the protrusion of the first countering surface into the first side of the stack. 
     FIG. 5 b  is a vector diagram illustrating various forces acting on the first counteracting surface. 
    
    
     DETAILED DESCRIPTION 
     It has been observed that it is usually not possible to support a single thin sheet of paper at its edges when the beam strength of the sheet is insufficient to support the weight of the paper. Similarly, it is usually not possible to support a thin stack of thin paper because the stack would sag, causing the sheets to slip off their support. However, when a sufficient quantity of paper is supported by two edges, the stack will be supported as a beam. A plausible explanation for this observed fact is that the internal friction of the stack, generated by the sheet-to-sheet friction, propagates gradually across the sheet to support the uppermost sheets of the stack with even pressure. This demonstrates that a small point support of a stack of sheets at two sides thereof can be used to support a full stack. Therefore, it is plausible to introduce a plurality of small-point supporting members into the path of a downward moving stack of sheets in a sheet feeder to reduce the burden of a sheet retriever that is used to retrieve sheets from the bottom of the stack. 
     When attempting to impede the flow of a stack moving by the force of gravity, the supporting members must simultaneously hinder and allow movement of the fed material. Because of this requirement, the supporting members can be provided at different portion of the stack and allow the sheets to move by. This requirement can be met by the sheet feeder, as shown in FIGS. 2,  4   a  to  5   b.    
     Referring to FIG. 2, a sheet feeder  100  has a first wall  102  and an opposing second wall  104  to contain a stack of sheets  200  having a first side  210  and a second side  220 . A retrieving mechanism  300 , together with a separation mechanism  350  (such as a fixed roller, an idler roller, a nip, a wedge and the like), is used to retrieve a sheet  202  from the bottom section  250  of the stack  200 . Because the sheets  202  are constantly retrieved from the bottom section  250 , there is a downward movement, as denoted by arrow  260 , of the stack  200  related to the retrieving. The weight of the stack  200  imposes a burden, as denoted by a downward force F g , to the retrieving mechanism  300 . In order to reduce the burden on the retrieving mechanism  300  due to this gravity-related force, small-point supporting members are provided on the first side  210  and the second side  220  of the stack  200  for hindering the downward movement of the stack  200 . As shown in FIG. 2, a first convex surface  110  is provided on the first side  210  of the stack  200  and a second convex surface  120  is provided on the second side  220 . In order to allow the downward movement of the stack  200 , a concave surface  140  conforms to the shape of the first convex surface  110  so that the first convex surface  110  can push the sheets in a first portion  230  of the stack  200  toward the second side  220 . The hindrance to the downward movement of the stack  200  on the first side  210  by the first convex surface  110  results in a first counteracting force F 1 , as shown in FIG.  2 . Likewise, the hindrance to the downward movement of the stack  200  on the second side  220  by the second convex surface  120  results in a second counteracting force F 2 . In order to allow the downward movement of the stack  200  below the first portion  230 , the section  150  of the wall  102  conforming to the shape of the convex surface  120  is provided so that the sheets in the second portion  240  below the first portion  230  can be pushed back toward the first side  102 . 
     The first counteracting force F 1  has an upward, vertical component F 1V , and the second counteracting force F 2  has an upward, vertical component F 2V , as shown in FIG. 3 a . Together, these vertical components counter a part of the downward force F g , as shown in FIG. 3 b , thereby reducing the torque required to retrieve a sheet  202  from the bottom of the stack  200  by the retrieving mechanism  300  (FIG.  2 ). 
     It should be noted that the reduction in the downward force F g  by the counteracting surfaces  110  and  120  depends on the location of these surfaces. It is preferable to locate both the first and second surfaces in the lower portion  224  of the stack  200 , as shown in FIG.  2 . As shown in FIG. 2, the upper portion of the stack  200  is denoted by reference numeral  222 . 
     In the preferred embodiment of the present invention, as shown in FIG. 4 a , the first counteracting surface  110  (FIG. 2) can be a part of the circumference  112  of a wheel, cylindrical element or roller  114 . The downward movement of the stack  200 , as noted by arrow  260 , causes the roller  114  to turn in a clockwise direction, as denoted by arrow  116 . This clockwise motion helps to prevent the sheets in the first portion  230  of the stack  200  from being stuck by the first counteracting surface. 
     The second counteracting surface  120  (FIG. 2) can also be a part of the circumference  122  of another wheel, cylindrical element or roller  124 , as shown in FIG. 4 b . The downward movement of the stack  200 , as noted by arrow  260 , causes the roller  124  to turn in a clockwise direction, as denoted by arrow  126 . This clockwise motion helps to prevent the sheets in the second portion  240  of the stack  200  from being stuck by the second counteracting surface. It is also possible to install another wheel or roller  130  above the concave surface  140  on the second side  202  of the stack  200  to help the downward movement of the stack  200 . Alternatively, the rollers  130  and  124  are used on the second side  220  of the stack  200 , but the roller  114  is not used on the first side wall  210 , as shown in FIG. 4 c.    
     It has been found that the protrusion of the first counteracting surface  110  or the circumference  112  of the roller  114  into the first side  210  of the stack  200  depends upon many factors. For example, it depends on the stiffness of the sheets, the size of the sheets, the stack height and the friction between sheets. However, the protrusion distance of the first convex surface  110  into the first side  210  of the stack  200  can be estimated as follows. As shown in FIG. 5 a , the roller  114  has a radius R and protrudes into the first side  210  by a distance equal to R(1-cosα). Because the stack  200  is supported by both the first counteracting surface  110  on the first side  210  and the second counteracting surface  120  on the second side  220  (FIG.  2 ), it can be assumed that the roller  114  is responsible for roughly half the reduction in the downward force F g  (FIG. 3 b ). The actual reduction is a function of angle and friction. For simplicity, however, it can be assumed that the roller  114  roughly carries half of the stack weight, or W s /2, where W s  is the weight of the stack above the counteracting surfaces  110  and  120 . Accordingly, the weight of the stack below the counteracting surfaces  110  and  120  is not carried by these counteracting surfaces. Thus, it would be advantageous to position the first and second counteracting surfaces in the lower portion of the stack  200 . As shown in FIG. 5 a , the force acting on the roller  114  is assumed to be located along the first wall  102  of the feeder  100 . In addition to the stack weight, the frictional force acting on the roller  114  is assumed to be W s μ where μ is the frictional force coefficient. The vector diagram of the forces acting on the roller  114  are shown in FIG. 5 b . Summing the moments around the center O of the roller  114  at point X, we obtain: 
     
       
           W   s μ sin α−( W   s /2)cos α=0  
       
     
     or 
     
       
         tan β=(½μ)  
       
     
     Assuming that μ=0.52, we have α=43.88 degrees. For a stack of sheets 17 inches (43.2 cm) high and each sheet measures 3.81″×8.5″×0.004″ (9.68 cm×21.6 cm×0.01 cm) and a roller with a radius of 47 mm is used, the protrusion distance d is given by              d   =                R   -     R                 cos                 α                   =                47        (     1   -   0.721     )                   =                13.1                   mm   .                                    
     The present invention has been described in conjunction with FIG. 2 to FIG. 4 c , wherein the stack is illustrated as a vertical stack. It should be noted that the stack can be tilted away from the vertical position. As shown in the FIG. 2 to FIG. 4 c , there is only one supporting surface (i.e. counteracting surface) on each side of the stack. However, it is possible to implement two or more supporting surfaces on each side of the stack. Also, it is possible to use supporting surfaces on the third and fourth sides of the stack. Furthermore, the same principle can be applied to an envelope feeder. Therefore, the word “sheet”, as used herein, is used in a broader context to include any flat item, such as an envelope, or a folded piece. 
     The first and second counteracting surfaces have been described hereinabove as convex surfaces. It should be understood that these surfaces can be of many different shapes and forms. They can be flat, partly convex and partly concave or flat, or partly flat and partly concave. They can be oriented in different directions, relative to the downward force. 
     Thus, although the invention has been described with respect to a preferred embodiment thereof, it will be understood by those skilled in the art that the foregoing and various other changes, omissions and deviations in the form and detail thereof may be made without departing from the spirit and scope of this invention.