Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND APPARATUS FOR STACKING AND ACCUMULATING BAGS
FIELD OF THE INVENTION
The present invention relates generally to the art
of bag making equipment. More specifically, it relates to
equipment for stacking and accumulating folded bags.
BACKGROUND OF THE INVENTION
Plastic or poly bags are currently made using high
speed equipment that can form, perforate, separate, fold
stack and wrap bags. The present invention is directed to
stacking and temporarily accumulating the bags after they
have been folded.
After bags have been folded (typically single,
double or triple folded) they are often stacked and then
packaged. The stack ranges from five to twenty-five bags.
The bags should be uniformly folded and stacked to work well
with downstream automated wrapping equipment.
One prior art stacker operates in conjunction with
a triple folder, such as CMD Corporation's model 3013 triple
folder. The bags are discharged from the triple folder with
corrugating rolls. The corrugating rolls have upper discs
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that mesh with lower discs. As each bag passes through the
rolls, the bag is given a corrugated shape. Bags with such
a corrugated shape travel farther without support than do
un-corrugated bags.
The bags are expelled from the folder and land on
a stacker "hand" in the prior art stacker. A stacker hand
is comprised of a number of fingers that catch the bags.
After a few bags are caught, the hand retracts, dumping the
bags on a conveyor where the remainder of the stack is
formed. The hand then returns to a resting position, until
it moves to begin catching the first few bags of the next
stack. All bags after the first few are dropped from the
folder to the stack on the conveyor. Diverters (vertical
separators) on the conveyors separate adjacent stacks.
Only the first few bags are caught by the hand
because the hand needs time to return to the position to
catch the first bag of the subsequent stack.
When bags travel without support they are more
likely to get out of alignment, and result in an improper
stack. Thus, the bags travel a foot or two feet to form a
stack, and increase the likelihood improper stacking.
Because it is difficult to use automated packaging equipment
~located downstream of the stacker) with improperly stacked
bags, the long drop is undesirable.
Another prior art stacker is described in U.S.
Patent 5,388,746. This stacker uses two sets of fingers
(i.e. two hands) that follow a single rectangular path.
When the first hand is full, the second hand replaces it.
However, because the hands follow a single path, one hand
does not move into position to catch the bags until after
the other hand has left the catching position.
Accordingly, a stacker that reduces the distance
bags travel unsupported is desired. The stacker should be
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able to operate at a high rate of speed, preferably using
pneumatics (rather than servo motors) to reduce the cost.
The design will preferably have hands that catch the bags
and travel different paths, so that a second hand can
quickly move into position to catch bags after another hand
has left that position. It is also desirable to have the
hands that support the folded bags be capable of moving at
multiple speeds so that they can travel as slow as possible,
given the time constraints of the process.
The stacker would preferably include an inspection
device to reject improperly folded bags before the stack is
made. The inspection should be adjustable for various
widths and lengths of bags.
In addition to a stacker, it is desirable to have
a machine which can take stacks of folded bags from the
stacker and accumulate the stacks to create a buffer for
downstream equipment (such as a wrapper or automatic
packager). The accumulator will preferably sense the number
of stacks present and control the speed of the downstream
equipment.
Such a stacker and accumulator should preferably
be capable of creating neat, proper stacks that are conveyed
to downstream equipment such as an automatic packager. The
stacks should be of a selectable count, and the bags should
be allowed to be a variety of heights, lengths, and widths,
film types, gauges, colors, fold configurations, and styles.
Preferably, such a stacker will be modular, so different
downstream equipment can be used with it.
SUMMARY OF THE PRESENT INVENTION
An apparatus for stacking objects is comprised of
a first and second set of fingers in one embodiment of the
invention. The fingers each have their own paths of travel,
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and move into and out of resting and stacking positions. In
one alternative the stacking position is formed by guides on
4 sides of the position.
According to a second aspect of the invention a
pneumatic mover (such as an air cylinder) is coupled to the
first set and/or second set of fingers.
According to a third aspect of the invention the
first and second sets of fingers approach the stacking
position from different directions.
According to a fourth aspect of the invention a
conveyor is provided to transport the objects to the
stacking position. A sensor is provided along the conveyor
to detect objects that should be rejected.
According to another aspect of the invention a
height sensor is placed near the stacking station and senses
when the stack of objects reaches a predetermined height.
One set of fingers are then moved in response to the stack
reaching the predetermined height.
According to another aspect of the invention a
third set of fingers having a third path of travel are
provided. The third path of travel is the same as the first
path of travel. The first, second and third sets of fingers
may be moved independently. The third set of fingers may be
pneumatically moved.
According to yet another aspect of the invention
the second set of fingers are prestacking fingers, and the
second path of travel is shorter than the other path of
travel. Means for moving the first set of fingers into the
stacking station after a stack has been started and for
removing the second set of fingers from the stacking station
before the stack is completed are provided. The first set
of fingers may be moved at a plurality of speeds by a
pneumatic mover.
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According to a different aspect of the invention a
method for stacking objects includes moving a first set of
fingers into and out of a stacking position from a first
direction. Also, a second set of fingers are moved into and
out of a stacking position from a second direction. In one
embodiment the steps of moving include the step of directing
air into and out of an air cylinder.
Another aspect of the invention includes the step
of conveying the objects to the stacking position and
detecting objects to be rejected. Also, in an alternative
the height of the stack is sensed and one set of fingers is
lowered when the stack reaches a predetermined height.
In another aspect of the invention a third set of
fingers are moved into and out of the stacking position.
The first and third sets fingers are moved along the same
path. The first, second and third sets of fingers may be
moved independently, and at a number of speeds.
In another embodiment the second set of fingers
are prestacking fingers and they are moved into the stacking
position when a stack is to be started. They are then moved
out before the stack is completed. The first or third sets
of fingers are moved into the stacking position after the
new stack is to be started. The movements may be
accomplished pneumatically.
Other principal features and advantages of the
invention will become apparent to those skilled in the art
upon review of the following drawings, the detailed
description and the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a perspective view of a stacker and
accumulator constructed in accordance with the present
invention;
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Figure 2 is a side view of a stacker constructed
in accordance with the present invention;
Figure 3 is a side view of stacking fingers and
prestacking fingers used in the present invention;
Figure 4 is a top view of a set of fingers used in
the present invention;
Figure 5 is a top view of stacking fingers and
prestacking fingers used in the present invention;
Figure 6 is a side view of an accumulator
constructed in accordance with the present invention;
Figure 7 is a top view of an accumulator
constructed in accordance with the present invention; and
Figure 8 is a schematic of the piping for the
pneumatics used to control the movement of a stacker
constructed in accordance with the present invention.
Before explaining at least one embodiment of the
invention in detail it is to be understood that the
invention is not limited in its application to the details
of construction and the arrangement of the components set
forth in the following description or illustrated in the
drawings. The invention is capable of other embodiments or
of being practiced or carried out in various ways. Also, it
is to be understood that the phraseology and terminology
employed herein is for the purpose of description and should
not be regarded as limiting. Like reference numerals are
used to indicate like components.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will be illustrated with
reference to the stacker and accumulator shown in the
Figures, and described as being used with plastic bags. It
should be understood at the outset that the Figures and
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description are merely exemplary, and that products other
than bags could be stacked and/or accumulated.
Figures 1 and 2 show a stacker 101 and an
accumulator 102 from a perspective view and side view,
respectively. Generally, stacker 101 receives bags from a
folding device 201 (Figure 2) such as CMD Corporation's
model 3013 triple folder. Stacker 101 stacks the bags, and
when the stack reaches a predetermined number, the stacker
is transferred to accumulator 102. The stack is held in
accumulator 102 and then transferred to a downstream device,
such as a Hayssen~ wrapper. The bags may be folded in any
style, and be comprised of a wide variety of materials.
Also, a wide variety of dimensions of bags may be used.
The operation of stacker 102 will be described in
detail below with respect to Figures 1 and 2. It should be
noted that the views are from opposite sides of the machine.
Thus, in Figure 1 the bags to be stacked travel from right
to left, while in Figure 2 the bags to be stacked travel
from left to right.
Stacker 101 includes a frame 105 (Figure 1) that
allows for adjusting the height of a pair of infeed rolls
106 and 107 (preferably from 43 to 48 inches from the
floor). The adjustability allows infeed rolls 106 and 107
to be aligned with a pair of outfeed rolls 203 and 204 of
folder 201. Ropes or belts 205 and 206 are guided by
discharge rolls 203 and 204, respectively. Additionally,
corrugating rolls may be used to put a corrugation into each
bag. This will help the bag travel in a straight line when
unsupported.
Infeed rolls 106 and 107 form a nip to receive an
incoming bag 231 from folder 201. As shown on Figure 2 roll
106 may be slightly offset from roll 107. The position of
roll 106 may be adjusted to open or close the nip, to allow
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for flexibility for variations in different bags. The nip
will allow a bag 1/4 inch thick to pass through, in the
preferred embodiment.
Infeed rolls 106 and 107 each drive a set of ropes
108 and 109, respectively. Ropes 108 and 109 are preferably
poly-urethane hollow tubes. The ends are spliced together
with a steel barb for easy replacement. Ropes 108 are
returned by a roll 112, and ropes 109 are returned by rolls
216 and 217.
During operation a folded bag 231 is discharged by
folder 201 and caught in the nip between rolls 106 and 107
and transferred by ropes 108 and 109, past sensors 207 - 209
(Figure 2). The preferred embodiment uses Sick brand,
retro-reflective, photo eyes. The eyes emit a signal that
is reflected back and sensed. When an object is between the
eye and the reflector it will block that light and a signal
is sent to a controller (such as a microprocessor). The
eyes used have a lens that allows the detection of clear
plastic material. The controller is not shown, but would
include the necessary input and output connections in a
manner well known in the art.
Sensors 207-209 are used to detect improperly
folded bags. When a bag is improperly folded it is too long
in either the direction of travel, or two wide
(perpendicular to but in the same horizontal plane as the
direction of travel). Sensors 207 and 209 cooperate to
detect bags that are too long. If the folded bag covers
both sensors 207 and 209, then it is too long, and the
controller causes the bag to be rejected. Sensors 207 and
209 are preferably located in the center of the bag.
Sensor 208 cooperates with another sensor directly
behind it (not shown). The sensors are offset from the
center of the bag by equal amounts determined by the
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tolerance of the width. If sensor 208 or the other sensor
detects the bag, then the bag is too wide, and subsequently
rejected. The locations of the sensors are adjustable, so
that bags of different lengths and widths may be
accommodated.
Rejected bags are disposed of along a path shown
by arrow 213 (Figure 2). Ropes 109 make a downward turn at
roll 216, and cooperate with a set of ropes 114 to form the
rejection path. Both ropes 114 and 109 have a downward
direction along the rejection path. The rejected bags are
directed into the rejection path by a blast of air from an
air pipe 214. Air pipe 214 can be located either upstream
or downstream of roll 112, and need only be positioned to
insure that rejected bags will follow the rejection path.
The rejection of bags can be continuous (if the
user so desires~ or automatic as described above. Also, if
the downstream equipment (such as a Hayssen~ wrapper) cannot
keep up with the incoming bags, then even good bags can be
rejected. Because the rejected bags are discharged toward
the floor, access is preferably provided between framing 105
to allow access to the rejected bags.
Bags that are not rejected are carried between two
sets of ropes 116 and 218. Ropes 116 travel around roll 112
and a roll 117, and ropes 218 travel around roll 212 and a
roll 219. Ropes 114 and 218 share a common roll 212, even
though they travel in opposite directions. Roll or shaft
212 has some pulleys that are driven (and cooperate with
ropes 218) and others that are idlers (and cooperate with
ropes 114) to allow for the opposite directions of travel.
Roll 112 is shown to be driven by a gear reducer
222 and motor 223. All the rolls that are driven, are done
so by motor 223, although the connections are not shown for
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clarity. Of course, other arrangements of rolls, ropes,
belts, motors, gear reducers and pulleys could be used.
As the folded bags are carried by ropes 218 and
116 they pass under another sensor 221. Sensor 221 is also
a photo eye and is used to count bags. The number of bags
that are not rejected, and thus stacked, is kept track of.
The user can select the number of bags in each stack (from 5
to 25 in the preferred embodiment, although other ranges may
be used). When the selected number of bags are counted by
sensor 221 the trailing edge of the last bag is sensed, and
based on that the stacking operations (described later) are
initiated. Sensor ?21 is located close to rolls 117 and 219
to allow accurate initiation of the stacking operations. In
alternative embodiments one of sensors 207-209 is used to
count the bags and sense the trailing edge.
When the bags reach the end of ropes 117 and 219,
they fall onto fingers. The preferred embodiment uses three
sets of fingers, 226, 227 and 229. Fingers 226 and 227 are
used for stacking and fingers 229 are used for prestacking.
Stacking fingers 226 and 227 follow a single clockwise
rectangular path, as shown by arrows 230A-230D. In an
alternative embodiment fingers 226 and 227 follow different
paths. Stacking fingers 226 are shown in a stacking
position and fingers 227 are shown in a resting position.
Other positions 235 and 236 for stacking fingers 226 and 227
are shown with dashed lines.
Fingers 22g are shown in a resting position.
Prestacking fingers 229 follow a counter-clockwise
rectangular path, (different from that of stacking fingers
226 and 227) as shown by arrows. The arrows indicate that,
in the preferred embodiment, not only do fingers 229 follow
a different path than fingers 226 and 227, they approach the
stacking position from different directions, and thus
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fingers 226 and 227 do not interfere with the movements of
fingers 229.
The three sets of fingers interact to insure that
bags are always supported, and that the incoming bags can
operate at high speeds. When in the position shown,
stacking fingers 226 catch the bags (shown as 231) as they
leave ropes 116 and 218. The fingers are in the positions
shown in figure 2 in the middle of a cycle, i.e. after a
stack has been started, but before it is completed. The
bags 231 are guided into a proper position by a set of
vertical bars 233 at the downstream end of stacking fingers
226. A set of vertical bars 234 contain the upstream end of
the bags. A pair of side plates prevent the bags from being
displaced in the cross direction. Thus, the bags being
stacked are contained and guided on all sides by the bars
and plates which form a stacking station. Bars 233 and 234
are used rather than plates to allow the fingers to travel
through them.
Another sensor ~not shown) is positioned to sense
bags 231 stacked on fingers 226, at a height near
(preferably less than two inches below) that of roll 219 and
detects the top of the stack of bags. When the stack get
high enough the photo eye is blocked, and the controller
causes fingers 231 to be lowered. The controller requires
that the eye be blocked for greater than a predetermined
time to distinguish bags falling past the sensor. In the
preferred embodiment fingers 226 are lowered until the eye
stops detecting a bag. This arrangement reduces the
distance the bags fall before being stacked on fingers 226
and keeps the top of the stack at about the same height to
give consistent stacking. In the preferred embodiment the
stack typically increments by about one half inch to one
inch, and the distance each bag has to fall to the stack is
2 ~ 2 1
preferably 2 inches or less. In an alternative embodiment
the stack is incremented down a predetermined amount for
each bag (or some number of bags). The process continues
until the user-set number of bags have been stacked (as
counted with sensor 221).
When the count is complete, prestacking fingers
229 move directly down from the resting position to catch
bags to be stacked (the prestacking position). The
prestacking position is at or near the position in which
fingers 226 are shown in Figure 2. The distance prestacking
fingers 229 move is relatively little (about two inches in
the preferred embodiment). Because they travel such a short
distance fingers 229 can be in position to catch bags before
the first bag in each stack arrives. The short distance
also allows use of pneumatics to move the fingers, rather
than a costly and complex servo motor. In an alternative
embodiment an air pipe is provided to direct a blast of air
straight down on the last bag of a stack, to insure the tail
of the bag is onto the stack before the prestacking fingers
move into position.
When prestacking fingers 229 reach the prestacking
position, stacking fingers 227 (in the resting position)
begin to move to the stacking position. After a slight
delay prestacking fingers 229 are retracted to the right,
leaving stacking fingers 227 holding the bag(s). The slight
delay is provided so that the bags are always supported.
Prestacking fingers 229 then complete the travel to the
right, clearing the bags, and move up, and then return to
the resting position (shown in Figure 2).
Thus, as may be seen, prestacking fingers 229 move
quickly and catch the first bags of each stack while the
stacking fingers are moving into position. This reduces the
need for servo motors to move the fingers. However, in one
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embodiment servo motors are used to move one or more sets of
fingers. Another alternative is to use only two sets of
fingers that either follow different paths or they follow
the same path and one set always acts as a prestacker and
catches the first few bags in each stack. In the preferred
embodiment the prestacking fingers cooperate with the
stacking fingers and because they follow a different path,
they do not interfere with each others movements. Stacking
fingers 226 and 227 follow a clockwise path, while
prestacking fingers 229 follow a counter-clockwise path.
Meanwhile, after the last bag in the stack is
counted, fingers 226 move to position 236, which places the
stack of bags on a set of ropes 240, which are guided by a
pair of rolls 241 and 242. Fingers 226 then retract to
position 235, and then travel to the resting position,
assuming it has been cleared by the other stacking fingers.
Thus, a complete cycle for one set of stacking
fingers would be to begin at rest in the position occupied
by fingers 227 in Figure 2, and then move to the stacking
position when the previous stack is completed. The stacking
fingers travel about 12 inches to reach the stacking
position (much more than the two inches the prestacker has
to travel). The fingers increment down as bags are added to
the stack. When the stack is completed the bags are
deposited on ropes 240, and the fingers return to the rest
position. ~uring this time prestacking fingers 229 have
made two complete cycles, one for each set of stacking
fingers.
Referring now to Figures 3-5 the interaction of
the stacking and prestacking fingers can be seen. Figure 3
is a side view of the fingers mounted on frame 105.
Stacking fingers 226 are shown in a position below
prestacking fingers 229. Vertical bars 233 and 234 are
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shown, and one side plate 301, that form the space within
which the bags are stacked. The distances between the side
plates and vertical bars may be adjustable, to accommodate a
wide range of bag sizes. Figure 4 shows that fingers 229
are comprised of a plurality of bars having spaces
therebetween.
Figure 5 shows a top view of fingers 226 and 229
mounted on frame 105. Fingers 229 and 226 follow different
paths and, as shown, do not interfere with the other's
movements.
In the preferred embodiment the fingers are
controlled with an XY pneumatic positioner. This avoids
using a costly and complex servo motor. The speed of each
motion is controlled by flow control. The piping and flow
control for the stacking fingers is such that they can move
up or down, and the down motion can be in increments or at
three different speeds.
Three speeds are obtained by using a 4-way, double
solenoid 3 position, 5 port valve, such as model H243
available from Humphrey. The valve has a holding position
in the center so that when its unactuated, it will hold a
mid-stroke position (for incrementing). The exhaust port of
that valve is diverted to three additional parallel valves.
Each of the three additional valves have a flow control
associated with its exhaust. The valve selected (and
associated flow control) determines the speed of the
movement. In alternative embodiments 2 or 3-way valves or
valves that control the flow themselves may be used.
The valves are operated such that when a stack of
bags is incrementing down towards position 236 the fingers
move slowly. When the stack is complete the fingers move at
one of three speeds: low, medium or high, to set that stack
down onto ropes 240. The speed is determined by the number
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of bags the user selected to place in each stack. For
larger stacks (and lesser distances) the speed is slower.
Alternatively, the speed of the downstroke may be directly
selected by the user. After depositing the stack the
fingers move at high speed back to the rest position.
Referring now to Figure 8, the piping for the
pneumatics is shown. A 4-way valve 801 has output ports
connected to an air cylinder 802 through hoses 804 and 805.
Air cylinder 802 is linked to and moves one set of stacking
fingers. Valve 801 has an exhaust port with a muffler 806
when the speed at which fingers travel does not need to be
limited ~for example when the fingers return to the resting
position from position 235). An input port is connected to
an air supply through a hose 807.
An exhaust port is connected to hose 808, for
controlling the speed of the fingers when they are carrying
a stack of bags. A hose 809 is connected to hose 808 and
leads to a valve 810. Valve 810 has a flow control 811 on
its exhaust, and a muffler 812 is attached to flow control
811. Flow control 811 is set to provide a slow speed, thus
valve 810 is opened when a slow speed is desired.
Similarly, a hose 814 is connected to hose 808 and
leads to a valve 815. Valve 815 has a flow control 816 on
its exhaust, and a muffler 817 is attached to flow control
816. However, flow control 816 is set to provide a medium
speed, thus valve 815 is opened when a medium speed is
desired. A hose 819, valve 820, flow control 821 and
muffler 822 are similarly arranged. However flow control
821 is selected for high speed operation.
Referring again to Figure 2, ropes 240 are
intermittently moved, in cooperation with a set of ropes 243
which are guided by a pair of rolls 244 and 245. After a
stack of bags have been deposited on ropes 240, ropes 240
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and 243 begin moving and the stack of bags is advanced to
position 250. If a stack had been at position 250 it is
advanced to accumulator 102.
When the bags are at position 250 they are
directly beneath a pneumatic squasher 251. Pneumatic
squasher 251 moves downward and applies pressure to the top
of the stack. A plate 252 underneath the ropes supports the
stack so squasher 251 creases the bags, thus creating a
cradle which is perpendicular to the direction of travel.
The cradle makes the stack more stable so that as it is
intermittently moved it has less tendency to tip over or so
the bags have less tendency to slide and create a sloppy
stack. In an alternative embodiment the squasher includes
fingers which shape the cradle. For example, the fingers
may be curved to control the arc of the cradle, or the
fingers may be flat to flatten the stack.
Referring now to Figures 6 and 7, accumulator 102
is shown. Accumulator 102 includes rolls 602-611 mounted on
framing 601. Rolls 602-611 each have a motor shown
therewith, and each drive ropes which form a conveyor
leading from squasher 251 to a packager 615. In the
preferred embodiment packager 615 ls a Hayssen~ IL-llP
wrapper.
The motion of accumulator 102 is intermittent, but
is controlled separately from rolls 241, 242, 244 and 245.
In one embodiment a single roll replaces rolls 242 and 244.
In the preferred embodiment, each section of accumulator 102
may be operated independently of the other sections. The
accumulator includes ten sections as shown, although there
could be more or less than ten. Each section acts
cooperatively with the other sections to transfer the
stacked bags from squasher 251 to the end of accumulator
102. The use of numerous sections gives the ability to back
2 ~
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up stacks of bags or purge them out, depending on the in-
feeding rate and the out-feeding rate. Preferably, each
motor provides a smooth acceleration and deceleration so the
stacks are not disturbed. The speed may be selectable from
a number of preset speeds (five e.g.). Each section
includes one of sensors 622-631, so the number of stacks
located within the accumulator may be determined.
One advantage of the accumulator is it creates a
buffer between the intermittent motion stacker and the
downstream continuous motion wrapper or packager. This is
advantageous since many types of continuous motion wrappers
need to be held at close to a constant speed.
The ten sections in accumulator 102 use feedback
with sensors to detect how many stacks have accumulated. If
there are only a few stacks (two or three, e.g.) the
downstream wrapper would be operated at a slow speed (ten
percent under normal e.g.). Conversely, if the accumulator
gets close to being full, the downstream equipment can be
run at a higher speed (ten percent over normal e.g.). If
the accumulator remains full even at the higher speed, the
controller can cause good bags to be rejected using airpipe
214, thereby slowing down the stacking speed. If the number
of stacks falls to one or two the downstream wrapper could
be stopped, rather than have it wrap poorly. After stacks
begin to back up in the accumulator the wrapper can be
restarted.
As one skilled in the art should recognize, the
stacker and accumulator described above are of a modular
design and thus may be used with any downstream equipment.
The stacker may be used without any downstream equipment.
Numerous modifications may be made to the present
invention which still fall within the intended scope hereof.
Thus, it should be apparent that there has been provided in
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accordance with the present invention a method and apparatus
for stacking bags and accumulating stacks of bags that fully
satisfies the objectives and advantages set forth above.
Although the invention has been described in conjunction
with specific embodiments thereof, it is evident that many
alternatives, modifications and variations will be apparent
to those skilled in the art. Accordingly, it is intended to
embrace all such alternatives, modifications and variations
that fall within the spirit and broad scope of the appended
clalms .
