Patent Publication Number: US-6698748-B1

Title: System and method for singulating a stack of sheet-like materials

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims the benefit of U.S. Provisional Patent Application Serial No. 60/235,125, which was filed on Sep. 25, 2000, by H. W. Crowley entitled SINGULATING A STACK OF ITEMS and is hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to feed mechanisms and methods for feeding sheets and envelopes from a stack into a utilization device. 
     2. Background Information 
     Current estimates place the number of envelopes used annually in the United States at over 100 billion. A significant percentage of these envelopes are used in connection with bulk mailings, and are accordingly filled, addressed and processed by a variety of automated machines. A lynchpin of all automated processes is the automatic envelope inserter. Automatic inserters are large, complex machines that are loaded with contents to be inserted (e.g., individual letter sheets and/or fillers) and envelopes in which these contents are to be inserted. Other machines such as binders, that bind inserts together (into a books, catalogs, newspapers or magazines), presses that apply logos and decoration, addressing machines, collating and a variety of other machines are also used selectively to process individual sheet-like materials in bulk mailing and other processes. These various devices can be termed generally “utilization devices” as they utilize sheet-like materials that are typically dispensed in stacks. 
     FIG. 1 shows a high-volume envelope inserter in current use by industry. The exemplary inserter  100  is a large, modular unit that combines various contents stored in hoppers (not shown) in the rear  102  of the machine and that directs (arrows  104  and  106 ) contents  105  onto a raceway  108  downstream (arrow  110 ) toward a stack of envelopes  112 . At each point along the raceway, additional insert sheets are added to the contents. These contents may be folded, or otherwise compacted, to fit within the selected envelope by mechanism within the inserter. Envelopes are drawn from the stack  112 , and directed downstream (arrow  114 ) to a inserting station  116  at which the closed-but-unsealed envelope flaps  118  are opened so that the final contents  120  can be inserted thereinto. The filled envelopes  122  are then transferred further downstream (arrow  124 ) to a stacking position or further-processing module (not shown). 
     Industrial inserters, referred to generically as swing-arm inserters, are available from a variety of well-known companies including Bell &amp; Howell (Phillipsburg), as well as by Mailcrafter (Inserco model), Pitney Bowes (AMOS model), EMC Document System (Conquest Lsi model) and H M Surchin (Cornish model). A rotary variation is made by Buhrs (BB300 and BB 500) series. One more-specific example is the Bell &amp; Howell Imperial™. 
     Most inserters cycle at least 10,000 per hour without any material. However, once the various hopper materials are inserted into the envelopes, the net production is significantly slower. Due to paper handling problems, swing-arm inserters often net less than one third of their capabilities. A typical swing-arm machine in production may net less than 3000 completed envelopes per hour. After careful study, it is now recognized that the primary cause is the unreliable feeding of materials from the hoppers onto the collating raceway. The hopper is subject to jams, double feeds and no feeds. The design of these hoppers has not changed significantly in 30 years. And for that matter, they have changed little since their invention 60 years ago, as exemplified by U.S. Pat. No. 2,325,455. 
     With reference to FIG. 1, the envelope stack  112 , the stacking location or “feed station”  130  consists of a series of upright guide rails  132 ,  134  that, respectively, contain the four opposing sides of each envelope in the stack. 
     As also shown in FIG. 1, the contents  105  entering the raceway originate from separate feed hoppers  150 ,  152 , and  154 . The hoppers include separate stacks of folded or unfolded sheet material  158 . Each stack  158  represents a piece of the total inserted package  120  to be provided to the downstream envelope  118 . The number of hoppers used varies based upon the number of content sheets to be inserted. For the purposes of illustration, further reference will be made to the hopper  154 , which is the first hopper along the raceway  108 . The hopper includes a rear backing guide  160  and a pair of front corner guides  162 . The guides  160  and  162  essentially contain the stack of materials  158  so that bottom sheets can be stripped and directed (arrow  104 ) one at a time into the raceway  108 . 
     With further reference to FIGS. 2-6, a content feed hopper and associated feeding and singulating assembly is shown in further detail, according to a prior art implementation. The stack of sheet-like materials (envelope inserts)  158  is confronted by a front stop  170  that retains the stack against forward movement into the raceway area. The stack is suspended at its rear (adjacent to the rear guide  160 ) by a partial floor  172 . An opening  174  is defined between the front edge of the floor  172  and the front stop  170 . This opening defines the region through which bottom sheets  176  are allowed to pass out of the stack and into the raceway, as will be described. At the bottom of the front stop  170  is located an adjustable pin  180  that is implemented as a threaded thumb screw with a projecting conical point  182 . As shown in the plan view of FIG. 6, there are two pins  180  located at a horizontal spacing along the front stop  170 . These pins are used to retain the front end of the stack of materials  158  from entering the opening  174 . The pins are adjusted fairly finely because the points, if overly retracted, will not support the stack, while if overly projecting, will tear or prevent the bottom sheet  176  from passing over the pin  182  and into the opening when needed. 
     More particularly, FIGS. 3-5 show the general sequence by which a conventional vacuum sucker assembly  190  is used to draw bottom sheets  176  from the stack of materials  158 . The sucker assembly  190  consists of a moving bracket arm  192  mounted on a common rotating shaft  194 . In the illustrated example, the shaft moves an associated sucker assembly on each feed hopper simultaneously. The operative element of the sucker assembly  190  is a vacuum lead tube  196  that is adjustable upwardly and downwardly (double arrow  198  in FIG. 2) and rotationally (double curved arrow  200  in FIG. 2) using associated turn screws  202  and  204 , respectively. These adjustments bring a suction cup  210  at the end of the feed tube  196  into a desired alignment with respect to the bottom of the stack. As will be described, these adjustments are problematic, and must be attended to regularly. 
     Referring to the feed operation in FIG. 3, the suction cup  210  engages the bottom sheet  176  and then draws it downwardly in a rotational motion as shown beneath the bottom edge of the front stop  170 , having overcome the holding force of the pin point  182 —in a generally downward-peeling motion away from the overlying stack. A moving hold-down finger  212  retracts to allow the rotational downward movement of the sheet  176 , and then returns to the position shown in FIG. 3, in which it interferes with any return upward movement of the sheet  176 . In accordance with FIG. 4, once the finger  212  is brought back into interfering contact with the sheet  176 , the suction cup drops its vacuum and continues on its rotational path away from interference with the sheet  176 . Just prior to the disengagement, a jawed gripper or “plucker” assembly  220  moves into engagement with the forward edge of the sheet  176 . The forward edge has been restrained by the finger  212  to enable an accurate grip upon the sheet  176 . Once grip is achieved, the mechanism causes the upper jaw  222  to close against the lower jaw  224 , and thereby firmly grasp the sheet. The gripper assembly  220  then rotates as shown in FIG. 5 (double arrow  226 ). When the gripper assembly  220  has swung sufficiently, the upper jaw and lower jaw,  222  and  224 , pass between a set of stripper guides  230  that, in this example are a pair of upright, angled plates. The stripped guides engage the front edge of the sheet  176  at approximately the same time that the upper jaw  222  of the assembly  220  opens with respect to the lower jaw  224 . The sheet, hence, is unable to move past stripper guides and is forced to fall away from the gripper assembly  220  and into the raceway  108 . It becomes captured by opposing edge guides  232  and  234  and is moved along the raceway by a set of chain lugs  240  that push the upstream edge in a downstream direction (arrow  244  in FIG.  6 ). 
     As described generally above, the removal of sheets from the hopper stack involves accurate and complex sequential phasing of the individual mechanism elements. If any element is out of time or not accurately aligned, the fed sheets may become jammed or otherwise fail to feed properly. For example, the pins  182 , while supporting the stack  158 , and allowing singulation of the bottom sheet  176 , often do so at the expense of producing a tear in the sheet as it is peeled past the pin&#39;s sharp points. These two screw-adjusted pins are independently operator adjustable and since they are tapered, interact with the chosen sucker height adjustment—the sucker itself being subject to several adjustments that further contemplate the delicate balance. 
     Specifically, the sucker requires two difficult, interrelated operator adjustments, one to tilt the sucker in-and-out and the other to raise it up-and-down. Due to the interrelationship, the in/out adjustment also raises and lowers the sucker, but in a non-linear, not-easily predictable way. For example, the operator may desire to screw in the pins to attain a more-aggressive singulation. Screwing the pins in raises the stack. They are then faced with two possible sucker adjustments to raise the sucker to follow the stack. They may inadvertently choose the incorrect tilt adjustment (which both raises and tilts the sucker, and unbalances the feeding) rather than the correct up/down adjustment. 
     In the prior art, to help with the reduction of feeding multiple sheets, the inserter manufactures provide an adjustable hopper floor plate, referred to as a T-plate. That is movable to increase or decrease the opening  174  size, depending upon how stiff or flexible the sheets are. Its purpose is to increase the stiffness of the sheet being peeled down by the sucker. This increases the deflecting force and helps prevent the sucker from dragging more than one sheet down at a time. 
     There are also several significant disadvantages to the above-described T-plate arrangement. It is difficult for an operator to know how to adjust the location of the plate forwardly or rearwardly, and it is highly dependent on the particular characteristics of a type (or even batch) of sheet material. The base of the “T” also provides a frictional component that impedes subsequent plucking of the sheet. Notably, the base of the “T” contains a ridge  173  on the trailing side next to the back guide  160  that, due to the weight of the stack on the lowest sheet, can emboss (e.g. indent) the sheets in the stack. The recent use of non-stick coating has not effectively alleviated the friction problem. It has been recognized that the friction is chiefly caused by the embossing on the T-plate ridge. The resulting embossed edge can make it very hard to pluck the sheet from under the weight of the sheets in the hopper. This embossing produces frictional sliding forces far greater than would be predicted by hopper weight and coefficient of friction calculations. 
     Excessive plucker sliding forces can scratch or scuff the sheets. Excessive sliding forces can also cause a sheet misfeed as the plucker tears the sheet&#39;s edge off, rather than drawing the sheet fully from the stack. 
     The sucker peels the sheet down towards two metal lips or shelves  250  (FIG.  6 ). When the sucker peels the sheet down, a finger  212  withdraws and returns to hold the edge of the sheet in the singulated state against the shelves. The shelves are provided for registering the sheets, and their angle is adjustable by plastically deforming (bending) the metal. This angular bending compensates for several other misadjustments, and the shelves, hence, assist in singulating the sheets as the sucker pulls each of the sheets between the shelves. 
     There is a particular disadvantage to the prior art shelves. Since the edges of the shelves are parallel, sheets of a certain stiffness can become lodged or wedged within the shelves&#39; parallel gape—effectively bowed and pinched between the two inner edges of the shelves. This is particularly troublesome because the gripping throat of the plucker&#39;s jaws is limited, and therefore the position in which the sheets are held becomes critical. The throat of the jaws is less than one-quarter inch when opened, and it will not pluck successfully unless the material is held within that tolerance. 
     Finally, it has been recognized that, when the plucker attempts to pull the singulated sheets from the hopper, it has many forces to overcome. First, it must overpower the sliding friction forces produced by the coefficient of friction of the bottom sheet against the floor plate. Then the gripper must tug against forces caused by (a) fiber-lock between uncoated paper sheets, (b) static electricity forces that bind the sheets together, (c) adhesion due to surface tension, and (d) ink or adhesive between adjacent sheets that has oozed and/or dried. Sheets may also contain secondary sheets such as refrigerator magnets, medallions or small parts that must be slid from under the weight of a hopper full of these sheets. There is no present method for reducing or overcoming these various resistance forces between the bottom sheet and the adjacent sheet(s) in the stack. 
     There have been various prior attempts to address inserter feed hopper and feed mechanism unreliability problem. There are several Bell &amp; Howell patents suggesting solutions, such as U.S. Pat. Nos. 3,844,551, 3,965,644, 4,411,416, 4,013,283. However, at this date, Bell &amp; Howell and their competitors still offer a hopper design that has remained essentially unchanged for decades. 
     SUMMARY OF THE INVENTION 
     This invention overcomes various disadvantages of the prior art by providing an improved hopper and singulating/feed assembly for a utilization device, such as an inserter, that feeds sheet-like materials from a hopper feed stack that reduces the various geometrical and physical problems that lead to jams, misfeeds and failures to properly singulate the stack. Notably, a hopper that reduces the pressure on the bottom sheets of the stack by providing a parallel wedge structure at the stack base is provided. This wedge structure also helps to drive bottom sheets successively forward toward a front face so as to further break frictional and adhesive contact between sheets at the bottom of the stack. Hopper side guides are provided with integral angled shelves that engage front side edges of the stack and allow easier singulation of respective bottom sheets. Likewise a fixed sucker block assembly is provided, which seats a suction cup in a rotating base with a surrounding planar block face and an integral fulcrum edge for improving the separation of the bottom sheet from the overlying stack. The block face is adjusted to lift the stack upon engagement for further aid in singulation. This block is also fixed in rotation and vertical position with respect to the stack, requiring no continual adjustment. There are also lower shelves upon which the sheet is driven as the sucker rotates away from the stack that have non-parallel sides to avoid binding, and more accurately locate the sheets for subsequent draw into a raceway by a gripper/plucker assembly. A central roller is provided between the front face of the hopper bottom and the rear guide so as to reduce friction during draw of a sheet forwardly. The parallel wedge, structure, likewise, can include a rear angled edge with short (forward-extension) base for supporting the rear of the bottom sheet of the stack that reduces friction. Overall, the of support area for the bottom of the stack (front shelves, rear shelf and roller) is minimized while still maintaining sheets in a positively supported orientation until drawn by the sucker. 
     According to further embodiments, the sucker block can includes a valve for varying the vacuum flow passing through the suction cup. The block can include a front edge that supplies a variable airflow to the stack to balance the suction force and assist in breaking up the sheets for better singulation. The block can be centered or offset with respect to the stack. Alternatively, a plurality of side-by-side blocks can be used on the stack. The blocks can be arranged to engage the stack at time-separated intervals by for example, varying their length and/or rotational positioning on a common rotating shaft. The shaft can be driven at a variable rotational rate so that respective bottom sheets are initially drawn from the stack at a slower rate by the sucker than the subsequent rate of rotation/draw into a final position to be pulled away by a plucker assembly (at a point resting on the non-parallel shelves). The hopper can be provided with anti-static bars to reduce attraction between sheets. Likewise, a variety of air sources/air knives can be used to selectively direct break-up air at the stack at various times. The hopper&#39;s angled rear edge can be the lower part of an adjustable rear guide that is sized shorter than the length of the sheets to induce a small trough-shape (via gravitational droop) to further stiffen the respective bottom sheets as they are drawn from the stack. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other objects and advantages of this invention will become clear with reference to the following detailed description as illustrated by the drawings, in which: 
     FIG. 1, already described, is a perspective view of an exemplary inserter including an envelope feed station and a series of contents feed hoppers according to the prior art; 
     FIG. 2, already described, is a partial side cross section of an exemplary contents feed hopper for the inserter of FIG. 1 shown prior to withdrawal of a bottom sheet from the feed stack; 
     FIG. 3, already described, is a partial side cross section of an exemplary contents feed hopper for the inserter of FIG. 1 shown during withdrawal of a bottom sheet from the feed stack; 
     FIG. 4, already described, is a partial side cross section of an exemplary contents feed hopper for the inserter of FIG. 1 showing the gripper assembly withdrawing the sheet from the feed stack; 
     FIG. 5, already described, is a partial side cross section of an exemplary contents feed hopper for the inserter of FIG. 1 showing the deposition of the sheet by the gripper assembly onto the inserter raceway; 
     FIG. 6, already described, is a partial plan view of the inserter of FIG. 1 detailing the hopper and raceway; 
     FIG. 7 is a cutaway perspective view of an improved hopper and contents feed mechanism according to an illustrative embodiment of this invention; 
     FIG. 8 is a cutaway perspective view of the improved hopper and contents feed mechanism of FIG. 7 showing a stack of contents sheets loaded thereinto; 
     FIGS. 9-12 are respective plan, front, side and perspective views of a sucker block according to an illustrative embodiment of this invention; 
     FIG. 13 is a partial side cross section of the improved hopper and sucker block shown about to withdraw a bottom sheet from the stack; 
     FIG. 14 is a somewhat schematic perspective view of the draw effect on a bottom sheet with respect to the stack; 
     FIG. 15 is a partial side cross section of the improved hopper and sucker block shown about to withdraw a bottom sheet from the stack; 
     FIG. 16 is a side cross section of the hopper according to an alternate embodiment detailing various feed improvements; 
     FIG. 17 is a schematic side view of a sucker block assembly mounted on a conventional pivot point and lever arm arrangement according to an embodiment of this invention; 
     FIG. 18 is a schematic side view of a sucker block assembly mounted on an improved pivot point and lever arm arrangement according to an alternate embodiment; 
     FIG. 19 is front cross section of an offset sucker block arrangement according to an alternate embodiment; 
     FIG. 20 is a front cross section of a multiple sucker block arrangement according to an alternate embodiment; 
     FIG. 21 is a schematic partial cross section of a rotational sucker block suction cup according to an embodiment of this invention; 
     FIG. 22 is a block diagram of an airflow volume control arrangement according to an embodiment of this invention; 
     FIG. 23 is a top view of a sucker block having multiple hold-down fingers according to an alternate embodiment; 
     FIGS. 24 and 25 are respective top and side views, of an improved hopper detailing airflow and anti-static mechanisms according to an alternate embodiment; 
     FIG. 26 is a side cross section of the sucker assembly and a hold-down finger in motion featuring a timing sequence according to an embodiment of this invention; and 
     FIG. 27 is a graph of sucker position versus an actuating cam position according to an embodiment of this invention. 
    
    
     DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT 
     FIGS. 7 and 8 show a contents feed hopper according to an illustrative embodiment of this invention. The feed hopper includes a pair of upright side guides  300  and  302  that engage the widthwise edges of the sheets in the stack  304  (see particularly FIG.  8 ). The side guides are adjustable along preexisting inserter rails  306  and  308  and can be locked in position using set screws or other locking devices as shown. The side guides  300  and  302  include integral shelves  310  and  312 , respectively, at their lower ends. The shelves  310 ,  312  are angles, being narrowed towards the backstop so that the opposing shelf edges are not parallel. This prevents a stiff sheet from becoming undesirably wedged between the shelves  310 ,  312 , and hence jammed. 
     More particularly, the shelves  310 ,  312  advantageously enable sheets to be supported firmly in the stack, but easily drawn away based upon the mechanical advantage that is derived from the catenary action of a flexible member. This catenary action is attained based upon the normal forces applied by the sucker that become translated into inwardly directed lateral forces at the shelves. This is shown for example in the draw of the bottom sheet  346  in FIG. 8 wherein a catenary is created adjacent the sucker assembly  350  causing the side edges to draw away from the outer edges of the stack  304 . The geometry of the side lips is such that the edges of the bottom sheet are slipped as well as peeled. Both forces act solely on the lowest sheet. The next sheet has only sheet-to-sheet sliding forces, but in equal force amounts to the stationary third sheet above it and to the singulating first sheet below it. The combination of these forces help to produce reliable sheet singulation on the lowest sheet. When the lowest sheet  346  is drawn from the stack, it has to move only a short distance to clear the ledge and it is then further relieved of frictional forces. 
     The shelves  310 ,  312  are shown attached integrally to the side guides  300 ,  302  as a preferred attachment point. Advantageously, this automatically locates them at a fixed point with respect to the side guide, and hence the overall hopper geometry, thereby alleviating the necessity for a separate operator adjustment of the height of the shelves. 
     In an illustrative embodiment, the side guides  300 ,  302  have a depth DS of approximately ½ inch to 3 inches. The shelves  310 ,  312 , at their frontmost ends, project inwardly in a range of between ⅛ inch to ½ inch. However, these ranges may be varied for different size, stiffness and types of materials according to alternate embodiments. 
     The hopper further includes a moveable back guide/backstop  320 . In one embodiment, the back guide engages slots (not shown) in the base plate  322  of the inserter. It can be locked into a lateral position within the slots using an appropriate lock screw or other locking mechanism. Notably, the bottom edge of the base or back plate includes an angled bottom edge  324  (See FIG.  10 ). The bottom edge  324  is angled to direct the lower sheets in the stack forwardly toward the raceway  108  Pulling the sheets forward, while singulating, substantially eliminates the need for the sheets to be stacked evenly (e.g. edge-justified) in the hopper. 
     There is also provided an improved front wall  330  that forms the front stop for the stack closest to the raceway. The lower edge  332  of the front wall  330  is first straight, and then angled so that it is approximately parallel to only part of the angle surface defined in the lower edge  324  of the back guide  320 . In this manner, the top group of sheets are supported by the wedge and the bottom group of sheets in the stack  304  are directed forwardly as they drop downwardly toward the bottom. The bottom edge of the back guide  320  also includes a horizontal shoulder or ledge  340 . This raised shoulder supports the rear edge of the forwardly directed stack bottom. Approximately midway between the front wall  330  and the base plate  322  is a central support roller  342 . The bottom sheet  346  of the stack directly engages this roller. In one embodiment, the roller  342  can rotate freely and includes a somewhat continuous surface constructed from an drawn from the stack  304 . 
     Hopper floor components, such as the ramp  324 , ledge  340  and rollers  342  are centrally located, do not span the entire width of the sheets and may leave the outside edges unsupported. This provides relief for fragile sheet edges to prevent snags in that area. Centrally located components also provide slight troughing of the sheets with the center being slightly higher than the edges. This increases beam strength to the sheets and helps overcome other bending or curl distortion in the sheets. This slight troughing or corrugation thus provides stiffness to aid the sheet to be slide out of the hopper. This physical concept is discussed further in U.S. Pat. No. 5,213,216 (RE 35,844), entitled PAPER GUIDING METHOD AND APPARATUS, by H. W. Crowley. 
     FIGS. 9-12 show an improved sucker assembly  350  according to an illustrative embodiment of this invention. The sucker assembly will be described further below. Briefly, it comprises a base block  352  defining a cavity  354  into which is seated a sucker suction-cup  356  constructed from an appropriate elastomeric material. In one embodiment, the depth of the suction cup cavity  354  is in a range of between ¼ to ½ inch. The block is fixedly mounted to, and rotates with the common shaft  194  described above along a radially spaced swing-arm movement path (see generally the swing arm  371  of FIG.  17 ). It is interconnected with a vacuum force as shown in FIG. 13, and thereby provides draw force for removing the bottom sheet  346  from the stack adjacent to the front wall  330 . Before describing further the sucker block assembly  350 , the geometry of the hopper as it relates particularly to the operation of the sucker is now described in further detail. 
     The angled rear edge  324  of the back guide  320  causes the sheet material to be subject to deflecting forces. Thus, if the sheet material is warped or curled, then the effect of these deflecting forces causes all the material to conform to a known geometry. This counteracts most unpredictable sheet geometry, since bending material in one axis generally removes the bend in any other possible axis. Accordingly, the resulting, predictable sheet geometry overcomes many sources of poor singulating performance. 
     Significantly, the angled rear edge  324  extends upwardly higher than the angled front edge  332  of the front wall  330 . A plane  360  taken through the corner of the angled front edge  332  passes beneath the apex of the angled rear edge. The difference  362  defines a region in which the stack becomes constricted above the region in which the front and rear edges  332 ,  324  are essentially parallel. This constriction, in essence, creates a support beam within a certain number of sheets residing in the constricted region that relieves pressure on the lower sheets (which are unconstricted due to the parallel front and rear edges). According to the geometry produced, the lowest sheets are relatively small in number and are not largely effected by the weight of the overlying stack. Rather, this weight is supported by the constricted sheets. As sheets exit the lower portion of the stack through action of the sucker and plucker (shown, for example in FIGS.  2 - 5 ), further constricted sheets pass below the plane  360  and become part of the free stack. It should be noted that prior attempts to increase stack size have heretofore only served to increase weight on the lowest sheets in the stack. The present technique alleviates the effects of increased stack weight on the bottom sheets by providing, in essence, a secondary base above the lowest sheets in the stack. As such, the size of the stack (and its associated weight) can be increased substantially without negative effects. 
     In addition, the use of a pair of forwardly angled parallel edges, combined with a reduction in pressure on the lower portion of the stack, allows gravity to urge each successively lower sheet further forward to aide in justifying the sheets against the desired front edge location. Clearly, the reduction in force between sheets in the lower portion of the stack reduces a variety of negative influences on the sheets such as fiber lock, frictional engagement, electrostatic attraction and adhesive effects of glues and inks. In fact, the urging of successive sheets more forwardly by the angled surfaces aides in breaking adhesive and other effects—where they might otherwise remain unbroken before singulation according to prior art techniques. 
     The ledge or shoulder  340  also provides a region that is relatively small and, that when the sheet is withdrawn by the plucker, causes it to reside in an open cavity free of any influence from the next adjacent sheet in the stack. Additionally, the roller  342  acts to substantially reduce friction applied to the bottom sheet  346 , while providing a contact point that enables the sheet to apply a measured frictional force to the adjacent sheet the reabove so as to assist in drawing that next sheet forwardly as desired. Note that this force acts in a relatively small region of the next sheet, thereby avoiding several of the negative influences brought about by fiber lock and other influences involving large areas of confronting contact between adjacent sheets. 
     With reference to exemplary FIG. 16, according to alternate embodiments, the rear ledge or shoulder  349  can define a partial or complete moving surface to further reduce friction on the bottom sheet. Additionally, the angled rear edge  351  and front edge  353  can be passive or active revolving rollers or belts as shown. There can also be brushes  355 ,  357  and  359  provided at various locations to aid in reducing friction by enabling increased sliding of sheets. Likewise air-bearings  361  and/or belts  363  (driven by a motor  365  as shown or undriven, freewheeling units) can be provided to further reduce local friction and aid singulation. The motors can be driven on a timed cycle based upon draw of sheets, or can be provided with slip clutches (not shown) that maintain a constant forward an/or downward force on the sheets that is maintained at a non-damaging level, but that generally urges the sheets in the desired direction. Other actuators, flat belts, brushes or circular surfaces that provide local reduction in friction and scuffing while still maintaining desired components of force directed generally forwardly can be provided alone or in combination according to these various embodiments. 
     In one illustrative embodiment the ledge or shoulder  340  extends outwardly between approximately ¼ and ⅛ inch. The height of the angled edge  324  from the shoulder to its apex is in a range of between ¼ to 1 inch. The height of the front edge  332  is approximately ¼ to ⅛ inch less than the height of the rear edge  324 . 
     With further reference to the sucker assembly  350 , the top face  370  defines generally a plane that, when the sucker is in its upmost position, is located above the upper faces of the side guide shelves  310  and  312 . In this manner, the top face  370  periodically protrudes into the bottom of the stack, thereby compressing the front portion of the stack together. In one embodiment, the protrusion above the shelves  310 ,  312  can be in a range of approximately ⅛ inch to ¼ inch. Notably, the protrusion of the top face  370 , to thereby cause compression of the front portion of the stack, creates an effect that homogenizes the sheet-to-sheet compression to make for a more predictable draw (peel-away) of the bottom sheet  346  from the remaining sheets. Similarly, the compression of sheets in the lower portion of the stack by the protrusion of the surface  370  assists in removing all air pockets between sheets. This reduces aerodynamic effects when one sheet is pulled rapidly away from another, thereby further ensuring that only the bottom sheet will be drawn by the sucker assembly. Explained differently, there is a lower breakaway force between the bottom sheet and the next (second) sheet than is generated between the second sheet and a third adjacent sheet further upwardly in the stack. The breakaway force between the second and the third sheets results, in part, from a vacuum along a large portion of the surface area therebetween. 
     Referring to FIGS. 17 and 18, the conventional spacing LB 1  (approximately 1½ inch) and positioning of the lever arm  371  for ration of the sucker block  352  is shown. The lever arm moves the common shaft  194  within an arc of a radius equivalent to the spacing between the shaft ( 194 ) center and the pivot point  393 . The pivot point  393  is aligned approximately with the bottom of the stack  304  (dashed line  397 ). This position, while effective, can be further optimized in an illustrative embodiment as detailed in FIG.  18 . The local sheet-to-sheet vacuum peeling forces are proportional to the amount of overlapping sheet-to-sheet area. Thus, by decreasing the peeling radius the sheet-to-sheet vacuum forces that tend to prevent singulation are reduced. Accordingly, the pivot point  395  (FIG. 18) is moved below the line  397  to a new line  398  by a distance DO of approximately ¼ inch. Similarly, the lever arm  399  is shortened to LB 2  (approximately ¾ inch). 
     It has been recognized that, when a sheet is not peeled from the center, the peeling is over a smaller area than a centrally located sucker, thus reducing the vacuum forces which tend to peel more than one sheet at a time. Referring briefly to FIG. 19 the central axis  369  sucker block  352  has been offset by a distance OS on the shaft  194  from the centerline  373 . 
     Similarly, as detailed in FIG. 20, a plurality of sucker blocks  352  (or other blocks without suction cups per se) can be mounted at one or more positions around the bottom the sheet perimeter. In this embodiment, the blocks are mounted s that their faces are at differing heights with respect to the sheet bottom. This is accomplished by using like-sized blocks  352  on a doglegged shaft  375 . Conversely the sizes or configurations of the blocks themselves can be varied to locate the faces  370  at differing desired heights. The result of this configuration is that the faces  370  engage the bottom sheet at different times in the cycle, and in differing degrees of protrusion. Hence, a further sheet separating/singulating component is introduced. This arrangement advantageously enables the overall vacuum force to be reduced, which serves to reduce the chances of sheet damage and draw of adjacent sheets in the overlying stack. 
     Referring to FIGS. 7 and 8, another pair of shelves  380  and  382  are provided in-board of the side guide shelves  310  and  312 , respectively. These shelves are mounted with respect to the lower surface of the base plate  322 . They extend, generally beyond the front wall  330  into the region of the raceway. The bottom sheet from the sucker force and also to provide a backstop at which location the plucker (described in FIGS. 2-5) can reliably expect the front edge to reside. As shown in FIG. 7, the shelves  380  and  382  include front edges  390  and  392  that face eachother but are non-parallel. In other words, in this embodiment they angle outwardly in a forward direction with respect to eachother forming a widening opening in this direction. The use of directly opposing, parallel shelves may tend to bind the sheets in a wedged orientation so that it does not spring back after sucker pressure is removed. By using non-parallel opposing edges a directly opposing force along the full length of the sheet is not generated, thereby preventing the undesirable binding effect. 
     The geometry of the sucker assembly  350  is now described in further detail, with reference to FIGS. 9-12. As described generally above, the top surface  370  of the block includes a cavity  354  into which is mounted a suction cup  356 . The suction cup is of somewhat conventional design, appearing as a flexible bellows-style cup in this arrangement. However, it can also be defined as another acceptable shape like the continuously curved dome shape shown in alternate embodiments herein. The cup is mounted on a tubular stem  400  that is interconnected with the vacuum source (not shown). The vacuum source in the exemplary inserter is a switched-constant vacuum force source generated by a vacuum pump (not shown). 
     The suction cup  356  is mounted so its top edge is slightly above the plane of the top surface  370  (for, example {fraction (1/16)}-⅛ inch above). This assures that it will always come into contact with the bottom sheet when the top surface flexibly engages the stack. As such, no particular adjustments of the height of the vacuum block or its suction cup are needed. 
     Without controlling the mount location on the vacuum stem  401 , the height of the suction cup  407  within the sucker block may difficult to regulate, and may tend to slip. According to an illustrative embodiment detailed further in FIG. 21, the vacuum stem  401  has a lip  403  that flexibly snaps over a conforming internal ridge or shoulder  405  within the base area of the suction cup. The lip  403  gives the operator a positive indication that the suction cup  407  has been seated to a repeatable, known height with respect to the sucker block and its associated movement path. The stem lip  403  also prevents the suction cup  407  from slowly sliding off its tube  401  due to the continuous pulling forces of singulation. 
     In addition, the suction cup  407  can be mounted so as to rotate slowly (curved arrow  409 ) to provide a more-even wear pattern to the lip of the cup, thus extending cup life significantly over prior implementations. In this example, the stem  401  is mounted within the sucker block on a bearing  411 . The stem  401  is connected to a rotary union  413  that enable a vacuum lead to remain stationary and sealed, but allows the communicating stem to rotate by way of a drive belt  415 . The belt is indexed for a predetermined rotational distance by an indexer mechanism  417 . Any acceptable mechanical or electromechanical indexing mechanism (using gears, pawls ratchets, stepper motors, etc.) can be employed. In one embodiment, the indexing occurs each time a cycle of the sucker assembly completes 
     The sucker block&#39;s top face  370  has an overall surface area that is sufficient to enable the stack to become compressed as described above. In one embodiment, the top surface defines ¼-1 inch walls (broken in places) around the central cavity  354 . However, this geometry is highly variable. The sucker block&#39;s peeling motion produces an oscillation to bring only one sheet at a time into the plucker position. This up-down oscillation motion serves to lift and retract the stack in the forward area of the stack. This action breaks several types of sheet-to-sheet adhesion forces. For example, the up-down, oscillating peeling action of the sucker block vibrates the stack and loosens the sheets with respect to one another. Further, the rapid draw of the lower sheet, and the simultaneous lowering of the stack, creates a brief but important weight reduced interaction between the stack and the sheet undergoing singulation. 
     The rear edge  402  of the block&#39;s top face  370  acts as a fixed fulcrum when the bottom sheet is pulled off the stack. This is detailed generally in FIG. 15. A fulcrum provides desired rotational moment to the sheet, which further aides in singulation. According to the prior art inserter, the above-described T-shaped  172  floor plate is used, to provide such a fulcrum (generally along its forward edge). However, as noted above, adjustment of this plate forwardly and rearwardly is problematic. Porous and/or flimsy sheets are particularly troublesome in the prior art. Significantly, free-energy peel forces of thin/flimsy materials are not strong enough to resist the separation forces. Therefore, as one sheet is peeled down, others in the overlying stack often follow. 
     The rear edge  402  of the top face  370  can be coated with a high-friction surface to further assist pulling the sheet forward out of the stack. This edge  402  is preferably made of high-friction material, vacuum ports or knurled surface. Thus, when the sucker peels the edge of the sheet  346  down, this rear edge  402  offers a force multiplier, to give the sucker greater gripping strength, as a function of the amount of wrap angle around the rear edge. This is the appropriate action since the amount of force needed by the suction increases the more the sheet bends. In this invention, the force available to peel a sheet is the sucker force (f-sucker) times the effects of the coefficient of friction of the sucker ridge (f-ridge). The friction force of the sucker ridge increases as e (2.718) raised to the power of μ, the coefficient of friction, times θ, the wrap angle in radians. i.e. 
     
       
           f -ridge= f -sucker* e   {circumflex over ( )}(μ*θ) . 
       
     
     In one embodiment, the forward edge  404  of the block&#39;s top face  370  can comprise a source of compressed air having appropriate feed conduits ( 406  shown in phantom) interconnected with an optional air source (not shown). In an illustrative embodiment, the timing and amount of air pressure is controlled to be just appropriate volume for filling the vacuum created by the separating sheets. It has been recognized that using air to fill a vacuum caused by rapidly separating components (sheets) requires a carefully controlled volume to be introduced to the space created by the separation of the two or more sheets. By providing an air source at the front edge, this force is able to counterbalance the generated vacuum force, and thereby, fills the cavity to replace the vacuum force when needed with air atmospheric pressure to aide in the release of the sheet. Peeling of one sheet from another can only be accomplished when the vacuum between the sheets is dissipated. As further detailed in FIG. 22, the air source can be regulated on a time basis to match the needed air volume in a separation/singulation cycle. Accordingly, a timer  430  and pressure regulator  432  are provided in series with the air source so that a regulated amount of air volume is delivered depending upon the stage of the cycle. A cycle stage monitor/indicator  434  communicates with the timer. This can be an electromechanical monitor or a mechanical linkage operatively connected to the shaft  194  or its is associated drive components. For example, a geared valve can be connected to the shaft or an interconnected component. This air may also act a “air knife” to flutter and peel two sheets apart during initial singulation. This would be useful anywhere there is access to the edges of the stack. As discussed further below, this air source could also be mounted for example on the finger  212 , surface  324 , shoulder  340 , edge  310  and/or the front angled lip  332 . 
     The block&#39;s suction cup cavity  354  defines a broken shape along its front edge that creates a recess  408  enabling the finger  212  (described above with reference to FIGS. 2-5) to project thereinto. The depth of the cavity  354  should be sufficient for an appropriately sized finger to pass without interference. This recess  408  allows the sucker block  352  to pivot up within the overlapping edges of the finger. This further ensures the block cannot snag the material in the stack as it rotates. In an illustrative embodiment, the recess  408  for the finger  212  provides an additional source of wrinkles and peel separation forces. The finger remains stationary for the first few degrees of the sucker blocks  350  rotating peeling. This cause bending in the material, increasing the same wrinkling actions started by the sides of the sucker cavity  354 . 
     In one embodiment, detailed in FIG. 23, additional fingers (finger  440 ) are added with respect to the sucker block  352  to hold the sheet down symmetrically about each of the shelves. Additional fingers have been used in the prior art in specialized applications involving large sheets (typically 8½ inch by 11½ inch sheets or greater). Two or more fingers used on smaller sheets (generally 6 inch by 9 inch), according to this embodiment, ensures a flat, well-located placement of the sheet for the subsequent plucking action. 
     It is anticipated that the various functions of the sucker block could be accomplished with individual elements, and not necessarily combined into one block. Accordingly, more than one block could be used. 
     Again, sucker block force and peeling components  402 ,  404 ,  356 ,  354 ,  420  in additional embodiments could be composed of, or constructed with, elements such as various types of passive or active belts, rollers, air-bearings, geometry or brushes. These elements in conjunction with actuators or vibrators can be made to break the adhesion and peel the sheet away from the stack that is otherwise contained. One or more sucker force and peeling components could be place on the outside edges in concert with the side-guides. 
     The existence of the forward lip  404 , extending from the suction cup  356  in connection with at least two other sides, provides an additional surface area that, in essence, attempts to create a wrinkling in the sheet  346  as shown generally by the wrinkled area  410 . Wrinkling is produced in stiff sheets that are bent in two different angles in intersecting areas. The wrinkled sheet further enhances singulation and enables release of the bottom sheet from the remaining stack. This is most beneficial on very flexible or thin, permeable sheets, which are often the most problematic sheets to singulate. 
     In particularly, it has been recognized that thin sheets tend to feed in groups because they tend to easily closely conform to each other. Adjacent surfaces create a vacuum force when they are rapidly separated. The closer the surfaces reside, the more vacuum forces are created, tending to pull several sheets as one. It should be appreciated that in different embodiments, the foregoing vacuum dissipation may be likewise produced with any geometry that creates a gap or space between successive sheets. 
     Thin material is also often more permeable and thus the vacuum can attach together several adjacent sheets. The wrinkling  410  aids in solving both of these problems. The stresses caused by the wrinkles induce small bends that force the sheets apart. The bends also provide a channel that allows in atmospheric air to prevent a sheet-to-sheet vacuum from forming during singulation. 
     In one embodiment (particularly useful for porous sheets like cloth), the sucker block has a variable vacuum restrictor. The portion of the vacuum stem tube  400  passing through the sucker block  352  receives the distal end of a volume restrictor  420  that can be constructed in a variety of ways. In general, this embodiment employs a threaded turn screw  422  with a knurled knob that extends and retracts the distal (regulating) end  424  of the restrictor  420  with respect to the tube  400 . This enables the airflow of the vacuum to be varied without changing the overall vacuum force (e.g. the prevailing vacuum level). As such, the flow of suction air acting upon the bottom sheet can be carefully controlled. This serves to prevent excessive vacuum airflow from passing undesirably through adjacent sheets via the bottom sheet&#39;s pores. Prior art designs reduce the vacuum for all hoppers at a central point. In some custom modifications, this approach has been replicated at each hopper individually. But it is not desirable to reduce the vacuum. Porous material can require even higher vacuum since it can be just as stiff, but some of the vacuum force is lost due to the sheets porosity. According to this invention, by restricting, rather than reducing the vacuum, the force can remain high, but the volume of vacuum flow is constrained so that it cannot effect subsequent sheets in the hopper. 
     As described briefly above, air sources can be used to aid singulation with respect to any hopper components that are adjacent to the edges of the lower portion of the stack. 
     Referring to FIGS. 24 and 25, the hopper assembly  450  includes a number of air sources (AS) that distribute air via ports or other channels. These ports or channels are (in this example) located on some or all of the following components: the back guide  452 ; side guides  454  and  456 ; front guide  458 ; hold-down fingers  460  and lower shelves  462  and  464 . In this example, the ports are a series of appropriately sized and placed pinholes on each component where it confronts the stack  304  or bottom sheet  346 . 
     Another force that causes the sheets in the hopper to adhere together, and not singulate, is static electricity. It is well-known, that rubbing and/or sliding components together causes a triboelectric effect that introduces opposite charges on each sheet, and thus develops an attraction force therebetween. Ionization of the hopper material solves static problems by increasing the conduction and dissipates any attempt to build up charge. As shown for example in FIG. 25, the hopper area  450  is uniquely provided with an anti-static bar or ionizer  470  consisting of an electrode  472  interconnected to a high-voltage power supply (HVPS)  474 . An optional air supply and distributor  476  enhances flow of ionized particles towards the bottom sheet  346  and associated stack  304 . 
     With general reference to the hold-down finger  212 , it recedes as the sucker block rotates down. It is recognized that with correct timing of the receding finger, it can flick the edge of the sheets upwardly to further aid in inducing sheet separation. Referring to an embodiment detailed in FIG. 26, the finger  212  is brought inward (arrow  480 ) at a time at which it can intercept the bottom sheet  346  as shown during the sucker&#39;s downward singulation movement. Such timing can be accomplished using an appropriate cam or other linkage (not shown) that is properly sized and timed to the general rotation of inserter components (such as the shaft  194  about its associated pivot point). 
     Finally, it has been recognized that the amount of local sheet-to-sheet vacuum force (not to be confused with sucker vacuum) between the peeling sheets is generally proportional to the acceleration of the sheets away from each other. To minimize this phenomenon, in an illustrative embodiment, the sucker&#39;s peeling motion is slower in the first few degrees of rotational motion. This reduces the local sheet-to-sheet vacuum force between the sheets, gives more time for air to flow between the sheets, and reduces the sheet-to-sheet vacuum forces. If this sheet-to-sheet vacuum is not adequately dissipated, it is likely that additional sheets will follow the bottom sheet as it is peeled down by the sucker. FIG. 27 shows a graph  490  of rotation of the sucker block according to an illustrative embodiment. A constant-rotating-speed eccentric cam (not shown) is used to rotate the sucker assembly with respect to other inserter drive components. According to the graph, during the first 20 degrees of cam rotation (Degree of Rotation  491 ), the sucker block is only moved approximately ⅛ inch (Gap  492 ). This allows air to enter the space created between the bottom sheet and the second, adjacent sheet. During the next 25 degrees of rotation, the gap separates an additional ⅞ of an inch. This is possible because the interaction of the sheets is greatly reduced by the pervious introduction of atmospheric air into the sheet-to-sheet vacuum area. 
     The foregoing has been a detailed description of illustrative embodiments of this invention. Various modifications and additions can be made without departing from the spirit and the scope of this invention. For example, the exemplary inserter shown and described can be substituted with another inserter. The general mechanisms can be substituted. Significantly, the sheets shown and described herein can be a variety of stackable materials constructed of paper, cloth, metal or any other acceptable material. The term “sheet” or “sheet-like material” is used broadly herein to refer to any such material. Having now described several methods and several embodiments of the present invention along with certain variations thereof, it should be apparent to those skilled in the art that various modifications and additions and other embodiments will also fall within the spirit and scope of, without departing from, the present invention as defined by the following claims. Different arrangements of sheet singulating devices may be used. Plucker locating components ( 380 ,  382  and  212 ) in alternate embodiments could be composed of; or constructed with, one or more elements such as various types of belts, rollers, air-bearings, geometry or brushes. These elements in conjunction with actuators or vibrators can be made to position, locate and hold the singulated sheet in a known location that is otherwise not in the proper location for the plucker (elements  220 ,  222 , and  224 ). Accordingly, this description is meant only to be taken by way of example and not to otherwise limit the scope of the invention.