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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 of the information thereon. For
automatic handling of documents, existing mechanisms employ three
stations, the first station where the documents are placed face up in a
stack, a second station to which the documents are moved one at a time to
be 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 THE INVENTION
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
with an optical reading device of some type. In this case, the stationary
stack supporting surface may be made transparent and an optical reading
device positioned underneath the transparent plate for viewing 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 be 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.degree., such as 85.degree.-87.degree. 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
preferably 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 0.001 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 document sheet in the middle thereof may be easily
pulled from 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. 1 is a cross-sectional view taken along a vertical plane through a
preferred embodiment of the present invention;
FIG. 2 is an enlarged view of a portion of the embodiment of FIG. 1;
FIG. 3 is a top view of the embodiment of FIG. 1;
FIG. 4 is a sectional view of the embodiment of FIG. 1 taken across section
4--4 thereof;
FIG. 5 is a sectional view of the embodiment of FIG. 1 taken across section
5--5 thereof;
FIG. 6 is an outside side view of the embodiment of FIG. 1 showing the
control mechanism therefor;
FIG. 7 is a schematic diagram of an electrical system for use in the
embodiment of FIG. 1; and
FIG. 8 illustrates in bar graph form the sequential operation of the
various components of the embodiment shown in FIGS 1-7 during one cycle of
operation thereof.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring primarily to FIGS. 1 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
11 has one end thereof positioned adjacent an end of a conveyor plate 13.
A wall structure 15 is positioned above the conveyor support plate 13 and
across its width. The wall structure 15 preferably forms an angle of
something less than 90.degree. with a top surface of the planar support
plate 11 and the conveyor plate 13 on the side of the wall 15 which is
contacted by a stack 17 (FIG. 1) of documents to be moved one at a time.
Side walls 19 and 21 define, along with the wall structure 15, a surface
for supporting a stack of documents. The stack supporting surface includes
adjoining portions of the support plate 11 and the conveyor plate 13.
When the document feeder of the present invention is used in conjunction
with an optical reader, the stack supporting plate 11 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 11 in a manner to be able to read any information carried
by the bottom surface of the bottom document of the stack 17 through the
glass plate 11. 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, 1971, Ser. No. 157,348, and entitled "Document Scanner." 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 11 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 15
by frictional engagement with four conveyor belt strips 25, 27, 29 and 31.
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 31 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 41 that is positioned under the rigid conveyor plate 13. The motor
39 drives the belts in a direction away from the glass plate 11 for
removal of the bottom document from the stack 17. As is explained 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 13 is treated so that the belts and sheets
will slide easily thereover. 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 13 adjacent the glass plate 11 by an appropriate bearing,
such as the bearing 43 for the belt 29 as shown in FIGS. 1 and 2.
With reference primarily to FIGS. 1 and 3, a loader plate 45 is held
adjacent the wall structure 15 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 15. The purpose of the loader bar 45 is to press the
leading edge of the stack of documents 17 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 19 of the frame and a torque bar 49 that extends
across the width of the machine. The torque bar 49 pushes downward at
opposite ends thereof against loader arms 51 and 53 which extend in a
direction parallel to the conveyor belts. The loader arms 51 and 53 pass
through individual vertical slots (not shown in FIGS. 1 and 3) in the wall
structure 15 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 17 on which it rests. The opposite ends of the loader arms 51
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 21 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
17. The downward force on 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 15. Follower wheels 57 and 59,
for instance, are positioned at opposite ends of the conveyor belt 25.
Similarly, follower wheels 61 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 71 press against the conveyor belt 31. 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 71 are held by
a roller arm 75 which is in turn supported in a non-rotatable manner by
the torque shaft 55. A roller shaft 75 extending between the side walls 19
and 21 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 structure 15 is illustrated. Vertically adjustable gates 81, 83, 85,
and 87 are held by the wall structure 15 by thumb screws 89, 91, 93 and
95, respectively. Provision is made for one gate over each conveyor belt.
However, in order to prevent the chance 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 selected 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 hereinafter.
With reference primarily to FIG. 3, an electrical micro-switch 97 is
provided immediately above the conveyor plate 13 in a manner to close an
electrical circuit when sheet material is positioned thereunder. As is
described 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. 1 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 17 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
receiving mechanism 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 depending 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 101 from the
stack 17 to pass thereunder under the influence of the belt 29 may be
observed. The gate 85 is adjusted so that its lowest most surface 103 is
separated from the top of the conveyor belt 29 by a distance equal to the
thickness of one sheet from the stack 17 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
thumbscrew 93 associated with the gate 85 is tightened to hold the gate 85
rigidly to the wall member 15.
Each of the gates is relieved on its leading edge by a notch adjacent its
lowest most edge 113. Referring to FIG. 2, the gate 85 includes such a
notch 105. The notch 105 preferably has a height that is about equal to
the thickness of sheets to be conveyed thereunder so that a sheet 107 that
is next to the bottom of the stack 17 will have its leading edge moved
into the notch 105 as the bottom sheet 101 is moved under the gate 85.
This positions the sheet 107 in a manner to be passed under the gate 85
after the bottom sheet 101 is completely moved thereunder. Without the
notch 105, it is likely that the leading edge of the next to the bottom
sheet 107 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 107 under the gate. Such a snag would require human intervention
in order to continue the sheet feeder's operation. This undesirable
curling would be especially likely when the stack 17 is extremely high and
thus causing downward forces of the loader bar 45 to be very diffuse at
the bottom of the stack. The notch 105 is preferably about as deep as it
is high and thus for paper of a dimension of 0.005 inch thick, the notch
105 would be about 0.005 inch square. The notch extends completely across
each of the gates that are utilized. Each of the gates 81, 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 101 has been moved
by the belt 29 far enough to be engaged by the follower wheel 65, the
sheet 101 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 101 is removed from under the lower edge 103 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 17. 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 51 and 53 is shown. A timing
electrical motor 109 is held by one side of the document feeder frame
below the conveyor plate 13. The timing motor 109 is independent of the
belt drive motor 39 but each is preferably of an alternating current
synchronous type. The timing motor 109 drives a cam wheel 111 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 115. At least one block 116 forms a
rigid attachment between the torque shaft 55 and the torque bar 49.
Therefore, as the cam wheel 111 is rotated by the timing motor 109, a
single cycle occurs whereby the loader bar 45 has initially been pressed
down on the stack 17 by the torsion spring 47 and subsequently has had the
downward force removed therefrom by action of the cam arm 114. 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 111 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 15 and onto the
conveyor plate 13. The gear ratio between the motor 109 and the cam wheel
111 is appropriately selected so that one revolution of the cam wheel 111
is coincident with the desired cycle period.
Besides the outside cam surface of the cam wheel 111 upon which the cam
follower wheel 113 rides, the cam wheel 111 includes a switch actuating
cam surface 117 which mechanically actuates a cam sustainer switch 119 and
a belt starting switch 121. The cam sustainer switch 119 is held
electrically open when contacted by the cam surface 117 while the belt
starting switch 121 is held electrically closed when contacted by the cam
surface 117.
Referring primarily to FIGS. 7 and 8, the sequence of operation and timing
of events for one cycle may be observed. One cycle (one revolution of the
cam wheel 111) results in the removal of the bottom sheet from a stack of
sheets. At time zero, the cam 111 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
125 and 127. 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 117.
As the trailing edge of the cam surface 117 disengages the cam sustainer
switch 119, the cam sustainer switch 119 is closed until the cam wheel 111
makes a complete revolution and again opens the switch 119. The timing
motor 109 is then de-energized until a new starting pulse is applied at
the switch 123. 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 121 is closed. This occurs a very short instant after the cycle is
initiated and the cam wheel 111 first starts to rotate. The belt starting
switch 121 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 97
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 17 physically contacts the switch 97. If no sheet is fed to the area
of the switch 97 before the switch 121 is opened, the motor 39 is stopped.
If a 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 125 is provided in parallel with the switches 97 and 121 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.
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