Apparatus for feeding sheet material from the bottom of a stack
United States Patent 1191 Bilbrey 1 APPARATUS FOR FEEDING SHEET MATERIAL FROM THE BOTTOM OF A STACK [75] Inventor: Robert A. Bilbrey, Orinda, Calif.  
 [73] Assignee: Decision Consultants, Oakland,  
 Calif.  
  22 Filed: May 8,1972  
  2: Appl. No.: 251,187  
 [ 1 Apr. 1, 1975 3,499,710 3/1970 Sahley 271/4 UX 3,566,083 2/1971 McMillin 250/227 X 3,618.933 11/1971 Roggenstein et a1. 271/126 3,660,639 5/1972 Cassel 235/6111 .1 3,761,688 9/1973 Cassel 235/61.11 E  
 Primary Examiner-Evan C. Blunk Assistant Examiner-Bruce H. Stoner, Jr. Attorney, Agent, or Firm-Limbach, Limbach &amp; Sutton [57] ABSTRACT The end of a movable belt adjoins a supporting surface for removing a bottom sheet from a stack of sheets sitting on the supporting surface. A wall structure over the conveyor belt prevents those sheets other than the bottom sheet from being removed from the stack. The sheet supporting surface may be a transparent plate with a document reader located thereunder, thus allowing sheets containing information thereon to be placed face down on the glass plate and optically read automatically before removal by the movable belt.  
 18 Claims, 8 Drawing Figures sum 1 0r 4 v BK HHH PAIENTEDIPR 1 I915 SHEET &#39;4 Bf 4 :21 93/39 -o o .iv M  
 FIG -7- |./5TARTIN6 PULSE BY SWITCH I23 I CAM SUSTAINER SWITCH H9 CLOSED TIMING MOTOR I09 ENERGIZED [:j BELT START SWITCH IZI cwseo I BELT SUSTAINER SWITCH 97 cwseo J I BELT MOTOR 55 ENEKGIZED J I LOADEK BAR 45 LII-TED TIME ANGULAR POSITION OF CAM III APPARATUS FOR FEEDING SHEET MATERIAL FROM THE BOTTOM OF A STACK BACKGROUND OF THE INVENTION This invention relates generally to sheet feeding mechanisms. and more particularly to sheet feeding mechanisms that extract sheets from the bottom of a stack.  
  There are many existing types of document reading machines. such as those of the Xerox process and various character recognition systems. For each of these types of devices, it is necessary to accurately position one document at a time for optical reading ofthe information thereon. For automatic handling ofdocuments. existing mechanisms employ three stations, the first station where the documents are placed face up in a stack. a second station to which the docutncnts are moved one at a time to he optically viewed. and thirdly a station where the optically read documents are collected and stacked. Existing document feeders for this and additional applications are bulky and complicated.  
  Therefore, it is a primary object of the present invention to provide a document feeder for use with an optical reading device that is simple in operation. compact and reliable.  
  It is another object of the present invention to provide an improved technique and apparatus for moving sheet material generally.  
 SUMMARY OF THF. lNVENTlON Briefly. these and additional objects are realized according to the techniques of the present invention wherein a stack of sheets to be moved one at a time is set on a fixed surface with one edge of the stack sitting on a movable surface, such as the end of a conveyor belt. located adjacent the fixed surface. Operation of the conveyor belt or other movable surface removes the bottom sheet of the stack by frictional engagement therebetween. A wall structure is situated generally vertically above the conveyor belt to stop all sheets of the stack other than the bottom sheet from moving with the conveyor belt. A loader bar is situated adjacent the wall and over the end of the conveyor belt for pushing downward along one edge of a stack of sheets, thus increasing the frictional engagement of the conveyor belt with the bottom sheet. A control mechanism is provided to relieve the downward force of the loader bar after the conveyor belt has operated to remove a bottom sheet of the stack under the wall and into engagement with some other mechanism, such as a resiliently held roller, which holds the sheet to the conveyor belt at a position beyond the wall structure. This prevents the next to the bottom sheet from following on the conveyor immediately behind the bottom sheet just removed. The loader bar is later allowed to exert a downward force on the stack of sheets after the bottom sheet just removed has been conveyed a distance away from the wall.  
  Although the techniques and apparatus of the present invention have a wide variety of applications for sheet feeding generally, the techniques of the present invention have a particular advantage when used in conjunction witlt an optical reading device of some type. In this case. the stationary stack supporting surface may be made transparent and an optical reading det ice positioned underneath the transparent plate for iewing the bottom surface of the bottom document of a stack of documents placed thereon. Certain types of optical readers require the documents to be accurately positioned with respect thereto. and this technique allows careful positioning by an operator who manually stacks documents face down on the glass sheet with their leading edge sitting on the end of the adjacent conveyor belt and against the wall structure. A disadvantage of present machines wherein automatic positioning of a document with respect to an optical reader is subject to error is eliminated. Furthermore, a separate feeding mechanism to the optical reader is unnecessary. The documents may be scanned and read by the optical reader after which the bottom document is removed by the feeding mechanism. This sequence of events is continued until an entire stack of documents has been reviewed. The document feeding mechanism stacks the documents at its output in the same order in which they were presented to the optical reader. By eliminating one station in an optical reading and document feeding combination. the entire operation may he done with a much more compact apparatus than that presently used.  
  The wall structure adjacent the stack of documents is preferably tilted in a manner to form an angle with the flat document support surface that is a few degrees less than 90. such as 8587 therewith. This prevents the sheets in a stack of sheets from binding against the wall as they drop down onto the supporting surface. The gap between the wall and the top of the conveyor belt is preferably accurately controlled to a magnitude that is slightly larger than the thickness of the sheets being moved thereby. Since the thickness of sheets may vary, it is preferable to provide a mechanism for adjusting the height of this gap such as by providing individually adjustable gates on the wall structure which may be moved up and down with respect thereto and secured in place when the desired gap has been set. These gates can then be made as precision elements. Each gate preferably is relieved at its bottom edge on the surface adjacent the stack of sheets in a manner to form a notch that receives the next to the bottom sheet as the bottom sheet is withdrawn by the conveyor belt underneath the wall structure. The use of such a notch prevents curling of the sheet next in line to be removed from the stack and thus prevents the leading edge of the bottom sheet from snagging on the bottom edge of the gate as the conveyor draws it thereunder. A conveyor belt is preferably supported by a rigid member. such as a Teflon coated metal plate, in order to further accurately define the size of this gap.  
  There are many ways to adjust the gap between the conveyor belt and the gate. but for persons not intimately familiar with the sheet feeding device, it has been found that a particular technique is highly useful. This technique involves the use of a sample sheet of the thickness that is to be fed by the machine. A gauging material of a certain thickness, such as Mylar having a thickness of().()()l inch, is folded over one edge of the document sheet. This three layer composite sheet is then positioned between the conveyor belt and the gate and the gate is dropped down to engage this composite sheet and is fastened in such a position. Since the Mylar is slippery, the docutnent sheet in the middle thereof may be easily pulled front underneath the gate after adjustment even though there may be some compressive force thereagainst. Once this document sheet has been removed. the Mylar can be pulled from underneath the gate.  
  Additional objects and advantages of the various techniques and forms of apparatus according to the present invention are described in the following detailed description which is to be taken in conjunction with the accompanying drawings.  
 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 7 is a schematic diagram of an electrical system for use in the embodiment of FIG. I; and  
 FIG. 8 is illustrates in bar graph form the sequential operation of the various components of the cmbodiment shown in FIGS. I7 during one cycle of operation thereof.  
 DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring primarily to FIGS. I and 3. the structure of the preferred embodiment of the present invention in the form of a document feeder is generally described. A stationary planar stack supporting surface element II has one end thereof positioned adjacent an end of a conveyor plate I3. A wall structure is positioned above the conveyor support plate I3 and across its width. The wall structure l5 preferably forms an angle of something less than 90 with atop surface of the planar support plate II and the conveyor plate I3 on the side of the wall IS which is contacted by a stack I7 (FIG. I I of documents to be moved one at a time. Side walls I9 and 2| define. along with the wall structure [5. a surface for supporting a stack of documents. The stack supporting surface includes adjoining portions of the support plate II and the conveyor plate I3.  
  When the document feeder of the present invention is used in conjunction with an optical reader. the stack supporting plate II is preferably transparent and made of a material such as glass that may be carefully optically controlled. A document reader 23 is positioned immediately below the glass plate II in a manner to be able to read any information carried by the bottom sur&#39; face of the bottom document of the stack I7 through the glass plate I I. The optical reader 23 may be. for instance. of a type described in a co-pending patent application of Lester J. Lloyd. filed June 28, l97l. Ser. No. 57.348. and entitled Document scanner. now US. Pat. No. 3.752.558 issued Aug. l4. I973.&#34; The optical reader 23 can be synchronized with the document feeder so that as soon as the information on the face down document at the bottom of the stack II has been read. the mechanical feeder mechanism will operate to remove that document in order to present the information on the face of the next to the bottom document for recognition or reading by the optical reader 23.  
  The bottom sheet of the stack 17 is moved underneath the wall structure I5 by frictional engagement with four conveyor belt strips 25. 27. 29 and 3|. All four of the belts are driven together. the belts 25 and 27 being driven by a belt drive roll 33 and the belts 29 and 3I being driven by a belt drive roll 35. the two belt drive rolls being connected to a common drive shaft 37. The shaft 37 is rotated by an appropriate chain connection by a motor 39. Tensions on the belts is controlled by an idler tension roller 4] that is positioned under the rigid conveyor plate I3. The motor 39 drives the belts in a direction away from the glass plate II for removal of the bottom document from the stack I7. As is cxplained more fully hereinafter, the motor 39 is operated intermittently in synchronism with other components of the sheet feeding mechanism. The top surface of the rigid belt support plate I3 is treated so that the belts and sheets will slide easily thereovcr. For instance. the top surface of the plate 13 may be coated with a Teflon material. Each of the belts is held at the end of the plate I3 adjacent the glass plate II by an appropriate hearing. such as the bearing 43 for the belt 29 as shown in FIGS. I and 2.  
  With reference primarily to FIGS. I and 3. a loader plate 45 is held adjacent the wall structure IS on its side contacted by a stack of documents or other sheets 17. The loader bar 45 extends across all four of the moving belt sections and is held by the frame in a manner to be movable up and down in a direction parallel with the orientation of the wall structure IS. The purpose of the loader bar 45 is to press the leading edge of the stack of documents I7 down against the conveyor belts for improved frictional engagement of the bottom sheet therewith. The loader bar 45 is not heavy enough to provide the required force itself, so the downward force is aided by a torsion spring 47 which is connected between the side wall I9 ofthe frame and a torque bar 49 that extends across the width of the ma chine. The torque bar 49 pushes downward at opposite ends thereof against loader arms SI and 53 which extend in a direction parallel to the conveyor belts. The loader arms SI and 53 pass through individual vertical slots (not shown in FIGS. I and 3) in the wall structure I5 and terminate in receptacles of the loader bar 45 in a manner to be able to push down on the loader bar 45 no matter how high the stack of sheets I7 on which it rests. The opposite ends of the loader arms SI and 53 are held by a torque shaft 55 for rotation with respect thereto. The torque shaft 55 is journaled between the side walls 19 and 2] of the document feeder frame. As is explained hereinafter. a mechanism is provided for rotating the torque shaft 55 to overcome the effect of the torsion spring 47 on the loader bar 45 to substantially reduce the downward force applied thereby to the leading edge of the document stack I7. The downward force of the loader bar 45 is removed during those portions of the feeder operation when frictional engagement between the conveyor belts and the bottom sheet is desired to be very low.  
  Referring primarily to FIG. 3. a pair of follower wheels are provided over each of the conveyor belts to hold a sheet against the conveyor belt after it has been moved under the wall structure I5. Follower wheels 57 and S9. for instance. are positioned at opposite ends of the conveyor belt 25. Similarly. follower wheels 6I and 63 press down against the conveyor belt 27. Follower wheels 65 and 67 press down against the conveyor belt 29. and follower wheels 69 and 7| press against the conveyor belt 3]. The follower wheels 59 and 63 are held in a rotatable manner by a roller arm 73 that is loosely held by the torque shaft 55 in a manner that it is free to rotate with respect thereto. Similarly. the follower wheels 67 and 7| are held by a roller arm 75 which is in turn supported in a nonrotatable manner by the torque shaft 55. A roller shaft 75 extending between the side walls I) and 2] of the machine similarly hold the forward four follower wheels. 57. 61. 65 and 69. Springs 77 and 79 are normally held in tension in a manner to force the follower wheels against their respective conveyor belts.  
  With reference primarily to FIGS. 3 and 4. the mechanism for adjusting the gap between the top surface of the conveyor belts and the underside of the wall struc ture I5 is illustrated. Vertically adjustable gates 8]. 83, RS. and 87 are held by the wall structure I5 by thumb screws 89, 9|, 93 and 95. respectively. Provision is made for one gate over each conveyor belt. However.  
 in order to prevent the change of a bottom sheet being removed from a stack being snagged by the gates, only two gates are generally used. The two gates that are selccted for use in any given circumstance depends on the width of the sheet material being used. The structure and adjustment of the gates is described hereinaf- ILT.  
  With reference primarily to FIG. 3. an electrical micro-switch 97 is provided immediately above the conveyor plate [3 in a manner to close an electrical circuit when sheet material is positioned thereunder. As is deseribed more fully hereinafter. the switch 97 is one of the control devices for controlling the conveyor belt drive motor 39. The primary function of the switch 97 is to turn off that motor once a sheet has been moved past the switch 97.  
  Referring primarily to FIGS. I and 3. it will be seen that the conveyed sheets are discharged into a tray 99 at the output end of the feeder. The sheets are stacked in the tray 99 in the same order as they were presented in the stack I7 at the output of the document feeder machine. Thus, no reorganization of the sheets is required after being passed through the document feeder illustrated in the drawings. Of course. a more elaborate receivingmechanism than the tray 99 may be provided depending on the particular application. For instance. a deflector could be used that is controlled by the optical reader 23 so that certain documents are segregated from others depcnding upon the informational content thereof that is detected by the optical reader 23.  
  Referring primarily to FIG. 2. the operation of the gates. as represented by gate 85 shown therein. permitting only a bottom sheet l0I from the stack I7 to pass thereunder under the influence of the belt 29 may be observed. The gate 85 is adjusted so that its lowest most surface I03 is separated from the top of the conveyor belt 29 by a distance equal to the thickness of one sheet from the stack l7 plus an extra distance such as 0.002 inch. The thickness of normal paper which is likely to be used in conjunction with the document reader and feeder is about 0.005 inch thick. Thus. the gap between the bottom 103 of the gate 85 and the top of the conveyor belt 29 is slightly greater than the thickness of the sheet to be conveyed but less than twice the thickness of the sheets in order to permit only the bottom sheet to pass thereunder. The gate 85 is adjusted to produce this preferable gap dimension by the use of a sample sheet and a folded Mylar piece. as described hereinabove. When the gap is set, the thumbscrcw 93 associated with the gate is tightened to hold the gate 85 rigidly to the wall member I5.  
  Each of the gates is relieved on its leading edge by a notch adjacent its lowest most edge I03. Referring to FIG. 2. the gate 85 includes such a notch I05. The notch I05 preferably has a height that is about equal to the thickness of sheets to be conveyed thereunder so that a sheet I07 that is next to the bottom of the stack I7 will have its leading edge moved into the notch I05 as the bottom sheet I0] is moved under the gate 85. This positions the sheet I07 in a manner to be passed under the gate 85 after the bottom sheet IOI is completely moved thereunder. Without the notch I05. it is likely that the leading edge of the next to the bottom sheet [07 could occasionally curl upwards along the leading surface of the gate 85 and thus would snag on the gate 85 when it is attempted to move the sheet I07 under the gate. Such a snag would require human intervention in order to continue the sheet feeder&#39;s operation. This undesirable curling would be especially likely when the stack I7 is extremely high and thus causing downward forces ofthe loader bar 45 to be very diffuse at the bottom of the stack. The notch I05 is preferably about as deep as it is high and thus for paper of a dimension of 0.005 inch thick. the notch I05 would be about 0.005 inch square. The notch extends completely across each of the gates that are utilized. Each of the gates SI. 83. 85 and 87 is treated at its lower edge to reduce friction with the sheets passing thereunder.  
  It will be noticed from FIG. 2 that once the lower sheet I0l has been moved by the belt 29 far enough to be engaged by the follower wheel 65. the sheet I01 is then pressed against the moving belt 29 independent of the force applied by the loader bar 45. Thus. the downward force of the loader bar 45 is unnecessary and it may be removed by counteracting the downward force applied thereto by the torsion spring 47 (FIG. 3). Removing the downward force of the loader bar 45 has the advantage that as the bottom sheet I0l is removed from under the lower edge I03 of the gate 85. that the next to the bottom sheet 107 does not follow immediately therebehind but rather will remain behind the gate 85 until the loader bar 45 is again pressed down on the stack I7. The frictional engagement of the bottom sheet of the stack 17 with the conveyor belt is insufficient without the added force provided to the loader bar 45 to move the bottom sheet under the gate 85.  
  Referring primarily to FIGS. 5 and 6. the control mechanism for removing the downward force on the loader arms SI and 53 is shown. A timing electrical motor I09 is held by one side of the document feeder frame below the conveyor plate 13. The timing motor I09 is independent of the belt drive motor 39 but each is preferably of an alternating current synchronous type. The timing motor I09 drives a cam wheel 1]] whose outside cam surface is followed by a cam follower roller 113 that is rotatably attached to a cam follower arm 114. The cam follower arm 114 is pinned to the torque shaft 55 by a pin I I5. At least one block I I6 forms a rigid attachment between the torque shaft 55 and the torque bar 49. Therefore. as the cam wheel I I I is rotated by the timing motor I09. a single cycle occurs whereby the loader bar 45 has initially been pressed down on the stack I7 by the torsion spring 47 and subsequently has had the downward force removed therefrom by action of the cam arm H4. The loader bar 45 preferably maintains contact with a stack of sheets 17 at all times with only an added downward force being controllably applied by the torsion spring 47 during a portion of each single sheet feeding cycle. The cam wheel H] is shown in FIG. 6 in its normal position at the beginning of a cycle. During one cycle of operation. a single sheet from the bottom of the stack 17 is passed under the wall structure [5 and onto the conveyor plate 13. The gear ratio between the motor [09 and the cam wheel [11 is appropriately selected so that one revolution of the cam wheel I H is coincident with the desired cycle period.  
  Besides the outside cam surface of the cam wheel Ill upon which the cam follower wheel H3 rides. the cam wheel 11] includes a switch actuating cam surface 117 which mechanically actuates a cam sustainer switch H9 and a belt starting switch 121. The cam sustainer switch [19 is held electrically open when eontacted by the cam surface 117 while the belt starting switch 12] is held electrically closed when contacted by the cam surface 117.  
  Referring primarily to FIGS. 7 and 8. the sequence of operation and timing ot&#39;cvents for one cycle may be observed. One cycle (one revolution of the cam wheel lll results in the removal of the bottom sheet from a stack of sheets. At time zero, the cam III is in a rest position shown in FIG. 6. A starting switch 123 initiates a cycle of operation by being closed momentarily. This connects the timing motor 109 to power supply terminals I26 and I27. It will be noted from FIG. 6 that at this first instant the cam sustainer switch 119 is held open by contact with the cam surface &#34;7. As the trailing edge of the cam surface 117 disengagcs the cam sustainer switch 119. the cam sustainer switch H9 is closed until the cam wheel ll l makes a complete revolution and again opens the switch H9. The timing motor I09 is then de-energized until a new starting pulse is applied at the switch I23. This pulse may come from a manual pushbutton switch or. alternatively. may come from some external source such as the document reader 23 after its reading operation has been completed. For continuous operation of the document feeder. the switch 123 is kept closed at all times.  
  The conveyor belt drive motor 39 is first energized when the belt starting switch I2] is closed. This occurs a very short instant after the cycle is initiated and the cam wheel Ill first starts to rotate. The belt starting switch [2! remains electrically closed. however, only so long as the switch cam surface 117 is in contact therewith, a short portion of the cycle as can best be seen from FIG. 8. The belt motor sustainer switch )7 will be closed. however, to continue electrical energization of the belt drive motor 39, as soon as the leading edge of the bottom sheet of the stack l7 physically contacts the switch 97. If no sheet is fed to the area of the switch 97 before the switch 12] is opened. the motor 39 is stopped. lfa sheet is delivered to the switch 97. the belt motor 39 continues to operate in one cycle until the trailing edge of the sheet passes beyond the switch 97. The belt sustainer switch 97 is then caused to be electrically open and disconnect power from the belt drive motor 39. A manual switch I25 is provided in parallel with the switches 97 and l2l for actuation by an operator to remove the last sheet of a stack from the conveyor belts.  
  Although the various techniques and apparatus of the present invention have been described with respect to a single preferred embodiment of a sheet feeding device, it will be understood that protection of the invention is to be granted within the full scope of the appended claims.  
 I claim:  
 I. A sheet feeding mechanism. comprising:  
 a flat surface including a stationary portion for sup porting a stack of sheets and another portion adjacent thereto that is movable away from the stationary portion,  
 means for moving said movable surface portion in a direction away from said stationary surface portion,  
 a wall structure extending upward above the movable portion of said supporting surface adjacent the stationary portion to define one edge of a supporting surface fora stack of sheets and to hold the sheets of a stack placed thereon against lateral movement off the stationary surface. said wall surface being positioned with a lower edge held a distance above the movable portion of said supporting surface to form a controlled gap thcrebctween. whereby the gap may be made large enough to allow only a single sheet to pass thereunder.  
 means adjacent said wall on its side toward the stationary surface portion and positioned over the movable portion of said supporting surface for providing a downward force on a stack of sheets carried by the supporting surface. thereby to increase the frictional engagement between the bottom sheet of a stack with the movable portion of the supporting surface.  
 means removed laterally a distance from the support ing surface for engaging with the movable surface portion a bottom sheet of said stack that has been partially removed from the stack. and  
 control means for sequentially effecting the following actions for a single cycle of operation to remove a bottom sheet from a stack of sheets positioned on said supporting surface:  
 1. causing said downward force means to push downward on a stack of sheets positioned thereunder while the moving means maintains the movable surface portion stationary,  
 2. causing said moving means to move the movable surface portion laterally away from the stationary supporting surface and to deliver the bottom sheet to said engaging means while the downward force means urges the bottom sheet against the movable surface portion, and  
 3. causing said downward force means to stop pushing downward on a stack of sheets positioned thereunder after a bottom sheet has been moved by the movable surface portion under the wall structure to said engaging means.  
  2. A sheet feeding mechanism according to claim I wherein said means for applying a downward force to the top of the stack includes a loader bar normally resiliently pressed downward. and wherein said control means includes a rotating cam surface with an associated cam follower assembly operably connected to said loader bar for counteracting the resilient downward resilient forces against the loader bar in synchronism with the bottom sheet being removed from a stack of sheets to said engaging means.  
  3. A sheet feeding mechanism according to claim 2 wherein the movable portion of said flat surface is a movable belt. and further wherein said engaging means is a downwardly forced roller positioned above said belt to hold a bottom sheet that is partially removed from said stack firmly against said belt for continued movement after said downward force means has been caused to stop pushing downward on the stack of sheets.  
  4. A sheet feeding mechanism according to claim 1 wherein said stationary portion of the flat surface includes an optically transparent plate.  
  5. A sheet feeding mechanism according to claim 4 which additionally comprises an optical character reader positioned underneath said optically transparent plate for viewing information on said sheets therethrough.  
  6. A sheet feeding mechanism according to claim I wherein the lower edge of said wall structure which controls said gap is set by at least one gate that is adjustable in a generally vertical direction with respect to a main supporting portion of said wall structure.  
  7. A sheet feeding mechanism according to claim I wherein said wall structure includes at least one gate member whose lower edge position defines said gap distance. said gate having a notch along its bottom edge and on its side adjacent said supporting surface for receiving the leading edge of a sheet of a stack that is next to the bottom sheet.  
  8. A sheet feeding mechanism according to claim 7 wherein said wall structure forms an angle of at least a few degrees less than 90 with said supporting surface.  
  9. A sheet feeding mechanism according to claim 1 wherein said movable portion of said flat surface includes an endless flexible belt arranged with its top sur face held to travel in a plane including said stationary portion of the Hat surface.  
 It). A sheet feeding mechanism, comprising;  
 a planar supporting surface.  
 a conveyor belt supported by a rigid conveyor plate and positioned adjacent said planar supporting surface in a manner that said belt may be operated with its top surface moving away from said planar supporting surface.  
 motor means for driving said belt.  
 a wall structure extending upward from said con- \eyor belt near its end adjacent said planar stipporting surface. the bottom edge of said wall being suspended at distance above said belt.  
 at least one vertically adjustable gate held as part of said wall structure for precisely setting a gap between the bottom edge of said gate and the top surface of said conveyor belt.  
 a loader bar over said conveyor belt at its end near said planar supporting surface and adjacent said wall structure on its side closest to the planar supporting surface.  
 means for urging said loader bar downward toward said conveyor belt.  
 a follower wheel pressing downward against said conveyor belt a distance from said wall in its opposite side to that of said planar supporting surface.  
 a timing motor.  
 a cam surface rotatably attached to said timing motor.  
 a cam follower assembly associated with said cam wheel and operably connected to said loader bar to relieve the downward force thereagainst during a portion of the revolution of said cam surface beginning after said conveyor belt has advanced a bottom sheet of a stack ofsheets into engagement with said follower wheel. and  
 electrical switch means for controlled energization of said belt drive motor and mechanically associated with said cam wheel for starting said belt drive motor when said loader bar is being downwardly pressed toward said conveyor. whereby said conveyor belt will advance the bottom sheet of a stack of sheets stacked against said wall.  
  I]. Fora sheet material feeding device having a moving means for engaging the bottom sheet of a stack of sheets for moving it away from the stack and a wall structure adjacent one edge of the stack to hold back all the sheets the stack except for the bottom. the method of optimally adjusting the gap between the lower edge of said wall structure and said sheet moving means. comprising the steps of:  
 selecting a sheet of the type to be fed by said device.  
 folding a sheet of gauge material over one edge of said document sheet.  
 placing the composite thickness of said document sheet and two layers of said gauge sheet material in said gap.  
 adjusting said wall structure until its lower edge engages and holds the composite thickness of said document sheet and two layers of gauge sheet material.  
 withdrawing said document sheet from between the folded gauge sheets. and  
 removing said folded gauge sheet material from said gap.  
 12. A sheet feeding mechanism. comprising:  
 a stationary surface having a defined edge.  
 at least one flexible belt member held to travel over a predetermined surface path having an edge thereof that is positioned adjacent said stationary surface defined edge.  
 means for controllably moving said belt across said predetermined surface path in a direction away from said stationary surface.  
 wall means positioned over said belt member adjacent its said edge and generally parallel thereto. said wall means forming a gap between a lower surface thereof and said belt in its predetermined surface that remains substantially constant as a sheet is drawn through the gap. said predetermined belt surface between its said edge and said gap being positioned with respect to said stationary surface to maintain a flexible sheet in contact with said stationary surface along its said defined edge when said sheet straddles said surfaces.  
 means adjacent said wall on its side toward said stationary surface and positioned over the belt for providing a downward force on a stack of sheets carried by said belt and said stationary surface when the edges of the sheets of said stack are abutted up against said wall means.  
 means operably connected with said downward force means for controllably applying either a large downward force or a small downward force. and  
 control means for time sequentially operating said belt moving means and said downward force controlling means,  
  13. The sheet feeding mechanism according to claim 12 wherein said downward force applying means includes a resilient clement normally urging said downward force means with its said larger downward force and means for counteracting said resilient element when said small downward force thereof is desired.  
  14. The sheet feeding mechanism according to claim [2 which additionally comprises a rigid planar stationary plate positioned under said belt to maintain said belt in said predetermined moving surfacev 15. The sheet feeding mechanism according to claim 12 wherein said gap distance lies between about (L005 inch and less than (UH!) inch.  
  [6. The sheet feeding mechanism according to claim 12 wherein said stationary surface is substantially optically transparent and further wherein optical reading means are positioned beneath said surface for optically scanning a bottom surface of a document optical pattern thereon.  
  17. The sheet feeding mechanism according to claim 12 wherein said control means includes:  
  12 means for operating said downward force applying means so that the downward force means exerts its said large force while said belt moving means maintains the belt stationary. means for subsequently initiating said belt moving means to move said belt a distance while its said large downward force is applied to said downward force means. and  
 means operating said applying means for subsequently providing said small downward force of said downward force means simultaneously with the continued movement of said belt. whereby a single bottom sheet is removed from a stack of sheets positioned under said downward force means against said wall means.  
  18. The sheet feeding mechanism according to claim [2 wherein said stationary surface is substantially planar and said predetermined belt path includes a portion in the same plane between the belt edge and said wall means.