FIELD OF THE INVENTION
The device of invention relates to containing unwarranted warping and deforming
of light weight and soft polyolefin woven fabric pieces (over their desired
rectangular shape) as the fabric pieces advance past the pinch roll feeding
mechanism and then over the feeding conveyor belts beneath in an automatic bag
conversion machine/line.
BACKGROUND INFORMATION
In automatic cutting and sewing machines for polyolefin woven fabrics, the fabric
is conveyed through various sections of the machine as it is converted into bags in
stages. In the entry section the fabric is drawn from the fabric roll by a web puller,
after which it passes successively through a web aligner and a fabric accumulator,
and leads to a feeding pinch roll line. The fabric is next cut into pieces of desired
lengths.
The fabric, up to the cutting point, remains in continuous length and in stretched
condition while being in the machine, and maintains without difficulty its flat
shape.
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After leaving the pinch roll line, the fabric pieces are no longer in a taut condition
and thus likely to lose their flatness. At feeding rates of 25 bags per minute or
higher, the fabric pieces, particularly light weight and soft ones, easily get
deflected by atmospheric air and become warped or deformed from its normal
rectangular shape. The fabric pieces are next transported over a transverse
conveyor to the main conveyor where the open ends of the fabric pieces are folded
and stitched to form a seam. Deformed fabric pieces disturb the folding/stitching
process resulting in distorted folds and seams. The bags produced with deformed
fabric pieces poor in quality with irregular shapes and weak seams. The device of
the invention helps overcome this problem in the case of soft and light weight
fabric and it also improves transportation of heavier bag lengths as well.
Existing machines (prior art) are typically fitted with a flat belt which runs over
the underlying conveyor belt, with a gap provided between the flat belt and the
conveyor belt; fabric pieces would pass through the gap. This approach reduces
the warping of fabric to some extent. However, in absence of a positive grip,
especially at high speeds, light weight fabric still gets deformed due to air’s
dynamic effects.
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Therefore there is a need to provide machines that prevent deformation of light
weight and soft fabric at high speeds.
In the present invention this advancing fabric remains in grip between the
gripping face of a gripping device and the lower feeding conveyor. The gripping
device may be in the form of a simple Teflon strip or a strip made from any
similar low friction coefficient material. Also as because the feeding conveyor is
made to run slightly at higher speed than the pinch roll feeding speed of the fabric,
the advancing length of fabric remains in a state of tension and so is able to
maintains it square shape better. The dynamics of air cannot now disturb the
fabric shape even at higher speeds as the griping force on the fabric of the
proposed invention is higher than that exerted by air dynamics.
After the feeding is over and the fabric is cut to desired length, the gripping device
above is lifted slightly to relieve the grip of the strip over the fabric so that the
transverse conveyor may now pull the cut fabric length without resistance. The
gripping device is again released over the conveyor before next feeding of fabric
commences. This lifting and releasing of the fabric is done by a suitable air
cylinder and controlling solenoid valve that controls its timings using appropriate
PLC programming.
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This device may also be put over the main conveyor belt with advantage. Here too
it helps in smooth transport of the cut bags over the main conveyor. But here since
there is no transverse conveyor the lifting mechanism for the gripping device is
not needed.
The cost of the device of the invention is much lower over its prior art described
earlier. This mechanism is simpler in construction, easy in maintenance with
added feature of maintaining better quality production above 25 bags per minute
even for light weight fabric grade measured in terms of grams per square meter
(gsm) below 50 gsm or so.
SUMMARY OF THE INVENTION
Accordingly, one object of the present invention is to provide machines that
prevent deformation of light weight and soft fabric at high speeds.
Another object of the present invention is to provide a mechanism incorporating a
gripping device whereby a positive grip is provided to the advancing fabric.
The invention ensures smooth flow of the fabric pieces without distortion caused
by fabric flight and various other forces encountered, as it travels through
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different conveyors while being converted to a bag in an automatic bag
conversion machine/line of polyolefin woven fabrics.
The following embodiments are described with strips, termed as first strips made
from low friction material being used as gripping device. Therefore, according to
the invention, the woven fabric – as it moves past the pinch roll feeding device –
is positively gripped as it enters a gap between a stationary thick first strips and a
running belt conveyor provided beneath the first strips. The running belt conveyor
has a high frictional grip and pulls the fabric along while the first strips, made of
very low frictional coefficient, cannot resist the belt’s frictional pull on the fabric.
The fabric thus remains in a mildly stretched condition and maintains its
rectangular form. The air surrounding the belt is turbulent due to the belt’s high
speed. In existing machines, the fabric, once in contact with the turbulent air, is
lifted off the conveyor belt and deforms in an uncontrolled manner. In the present
invention, the first strips prevent the fabric lift off and subsequent deformation.
Teflon is a suitable material for making first strips.
After the desired length feeding of the bag is over the pinch roll stops feeding and
subsequently when the cutting of the fabric is done the first strips are lifted up.
Thereafter the transverse conveyor pulls the cut fabric in the transverse direction.
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Lifting of the first strips relieves the fabric off the former’s grip and the fabric
now can move freely along with the transverse conveyor.
This enables the cut fabric to maintain its deserved (rectangular) shape as it passes
through the various conveyors and is thus converted into finished bags of
improved quality even at the rates of 25 bags per minute or much higher for broad
range of fabric gsm.
This device is very simple in construction with few components and much lower
in cost as well over its prior arts while more effective.
BRIEF DESCRIPTION OF THE FIGURES
To clearly describe the invention it will now be described in details with reference
to the accompanying drawings, wherein
Fig. 1 shows a partial top view of the area of automatic bag conversion
machine/line representing the preferred embodiment of the invention.
Fig. 2 is a simplified schematic diagram of the preferred embodiment as a
sectional view alongside the feeding direction 'b' of the fabric after the cutting
point.
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Fig. 3 is a simplified schematic diagram of the preferred embodiment as a cross
sectional view across the feeding direction 'b' of the fabric after the cutting point.
Figure 4 shows the stabilizers provided along the movement direction 'c' of the
fabric.
Figure 5 shows a general arrangement of the main conveyor.
LIST OF PARTS:
Pinch roller (1)
Fabric cutting zone (2)
First web conveyor (3a)
Belt for first web conveyor belt (3)
Woven fabric (4)
Main web conveyor (5)
Belts for main web conveyor (5a)
Transverse conveyor (6)
Mounter for first strips (7)
First strip (8)
Lifting ribbon (9)
Air cylinder and lifting ribbon link (10)
Air cylinder (11)
Weight stabilizers (12)
Flexible second strip (13)
Fixed Support (14)
Suspension mechanism (14a)
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DETAILED DESCRIPTION OF THE INVENTION
In Fig-1 a part of a standard bag conversion machine/line (BCM) is depicted
where the present invention is in operation. The lettered arrows show direction of
fabric flow in various zones of the machine. Arrow ‘a’ represents flow of fabric
through a line of pinch rolls (which through its frictional properties exerts
sufficient pull over the fabric to pull it in the direction of arrow ‘b’, therefore the
pinch roll line is also referred to as a pinch poll puller) and the fabric cutting zone.
Arrow ‘b’ represents the flow of fabric over a first web conveyor (3a) which
carries the advancing and cut fabric as it is fed by the pinch roll puller and where
the present embodiment of the invention is installed. Arrow ‘c’ represents flow of
fabric in transverse direction using a transverse conveyor (6), while the arrow ‘d’
represents flow of fabric over the main web conveyor where further downstream
the bag is folded and stitched to produce the finished bags.
In a typical BCM, the fabric is unwound from the fabric roll and is made to flow
down the machine through its various zones. The fabric, till it reaches up to the
pinch roll line (1), remains an uncut continuous fabric fed under tension; the taut
fabric easily maintains its flat shape. As the fabric crosses the line of pinch rolls
(1), it is cut and thus no more under tension. The piece of fabric cut to the desired
length is free of any tension or grip as it’s released by the pinch roller.
Conventionally the cut piece of fabric flows over the first moving belts (3) of the
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first web conveyor (3a) which in their turn move at a speed slightly higher than
the fabric-feed speed.
At high fabric-feed speeds, pieces made from light and soft fabric tend to fly, in
an uncontrolled manner, off the first moving belts (3) due to air dynamics. This
causes warping and deformation of the fabric shape from its desired flat
rectangular state. Therefore after cutting of the fabric at cutting line (2) and as the
transverse conveyor (6) transfers it to another web conveyor (which is the main
web conveyor (5)), a deformed and misaligned bag often reaches the main web
conveyor (5) which upon folding and stitching produces a correspondingly
defective bag. The main web conveyor (5) typically comprises a number of
second moving belts (5a).
In the present invention, first strips (8) that are made from materials that have low
friction coefficient, are provided in the cut-web conveyor region. The first strips
(8), which stretch over the first web conveyor region, are mounted over a mounter
for first strips (7). An operating mechanism is provided for the operation of the
first strips – that is to enable their lifting and lowering.
Fig-2 shows a sectional view of the invention along the line A-A marked on
Figure 1. The fabric cut piece, when fed through the pinch roll drive, enters the
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space between a typical first strip (8) and the first moving belt (3). The belt (3)
moves forward at a speed slightly higher than the fabric-feed speed. The first
strips (8), under their own weight, and aided by the positive frictional
characteristics of the first moving belt (3), grip the fabric between itself (the strip)
and the running belt (3). Due to the frictional drag exerted by the first moving belt
(3), the fabric is pulled along the belt (3). The frictional drag exerted by the first
strips (8) on the fabric is negligible and doesn’t offer much resistance to the
fabric’s forward movement.
The positive pull-forward (in the direction of fabric feed) and provision that the
speed of the belt (3) is slightly higher over fabric feed speed, allows the fabric to
remain in a stretched, flat and undistorted condition. The weight of the first strips
(8) is sufficient to hold the fabric down over a flat surface, thus preventing the
fabric from flying off from the first moving belt (3). The first strips (8) are bent
upwards (see Figure 2) to facilitate easy entry of the fabric cut piece into the gap
between the typical first strip (8) and the belt (3). Till the fabric is under grip of
the first strips (8) from above, the feeding of fabric is done at a speed slower than
the full processing speed of the machine in order to avoid unwanted fabric
warping. Thereafter the fabric is fed at full speed & no warping or deformation of
fabric would occur.
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Thus the invention keeps the forward moving fabric, after it moves past the pinch
roll feeders, in a stretched and flat condition reducing the possibilities of its
warping up and distortion of shape.
After the feeding is over and the fabric is cut at the edge of the fabric cutting zone
(2), the air cylinder (11) lifts the first strips (8) to relieve griping force on the
fabric (see Fig-3). The pinch roller (1) feeds the fabric to cutting zone (2). The
fabric, after having been cut, gets pressed by the first strips (8). The first strips (8),
under their positive grip action, keep the fabric aligned along direction ‘b’. As full
length of fabric comes under the grip of the first strips (8), a sensor senses
presence of fabric and triggers pulling action of transverse conveyor (6) to allow
the fabric movement along direction 'c' in the region of the second (or main) web
conveyor (5). The cut fabric piece (which is distortion-free and flat and
rectangular in shape) thus moves in direction ‘c’ and transfers over to the main
conveyor (5). Here it is converted into a bag.
The first strips are released back on the first web conveyor belts (3) after the cut
bag transfer by the transverse conveyor is over and the BCM is ready for feeding
of the next bag length. The cycle thus continues.
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The lifting ribbon (9) for the typical first strip (8) (Fig-2 & Fig-3) is made from
flexible strips. This allows lifting up of first strips (8) by the air cylinder (11)
while advantageously not transferring the thrust generated by the cylinder to the
first strips (8) when they are lowered.
As seen in Figures 4 and 5, it has also been observed that the cut and stitched
fabric, when moving along the direction 'c' over the main web conveyor (5) which
has second moving belts (5a) may also experience destabilizing forces, even
though these forces are not as powerful as those experienced during the fabric's
movement in direction 'b'. In an embodiment of the invention, therefore, weight
stabilizers (12) are provided along the movement direction 'c'. These stabilizers
are in the form of objects that provide downward force (due to their weight) that
helps to hold down the fabric firmly during its movement along the direction 'c'.
In one embodiment the stabilizers are supported on at least one flexible second
strip (13), said strip being suspended using a suspension mechanism (14a) from a
fixed support (14). The flexible second strip (13) is shaped in an upward curve at
its upstream end in order to facilitate easy entry of the fabric into the gap between
said flexible strip and the second moving belts (5a).
The present invention thus helps to make a bag of better quality and form even
when the fabric material is of light weight and soft and the feeding speed is high.
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It is evident from the foregoing discussion that the present invention has a number
of embodiments as disclosed here.
1. A fabric guide device characterised in that it comprises gripping device
provided in the region of at least one web conveyor of a standard bag
conversion machine/line, said gripping device incorporating a gripping
surface made from a low-friction material and being capable of exerting a
positive grip or control on the advancing cut woven fabric during its
transportation over the conveying mechanism.
2. A fabric guide device as disclosed in embodiment 1, characterised in that
said gripping device provided in the region of any of said web conveyor
regions is in the form of strips termed as first strips (8), which spread over
said web conveyor region, are mounted over a mounter of first strips (7),
and an operating mechanism for the operation of said strips to enable their
lifting and lowering, said operating mechanism being positively controlled
by pneumatic or electro-pneumatic or mechanical means.
3. A fabric guide device as disclosed in embodiment 2, characterised in that
the fabric cut piece, when fed through the pinch roll drive of said bag
conversion machine/line, enters the space between said first strips (8) and
the first moving belts (3) of said bag conversion machine/line, wherein
said belts (3) move forward at a speed slightly higher than the fabric-feed
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speed, and wherein said first strips (8), under own weight, and aided by the
positive frictional characteristics of said first moving belts (3), grip the
fabric between themselves (the strips) and the running belt, thereby
making said first moving belts (3) exert a frictional drag over said fabric
causing it to pull along said conveyer belt..
4. A fabric guide device as disclosed in embodiments 1-3, characterised in
that the weight of said first strips (8) is sufficient to hold said fabric down
over a flat surface, thus preventing the fabric from flying off from said
first moving belts (3).
5. A fabric guide device as disclosed in embodiments 1-4, characterised in
that said first strips (8) are bent upwards to facilitate easy entry of said
fabric cut piece into said gap between said first strips (8) and said first
moving belts (3).
6. A fabric guide device as disclosed in embodiments 1-5, characterised in
that till the fabric is under grip of said first strip (8) from above, the
feeding of fabric is done at a speed slower than the full processing speed
of said bag conversion machine/line in order to avoid unwanted fabric
warping, whereafter said fabric is fed at full speed.
7. A fabric guide as disclosed in embodiments 1-6, characterised in that after
the feeding of fabric is over and the fabric is cut at the edge of a fabric
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cutting zone (2), an air cylinder (11) lifts said first strips (8) using a lifting
ribbon (9) to relieve griping force on said fabric, whereafter a transverse
conveyor (6) pulls the cut fabric piece in direction ‘c’ and transfers it over
to the main conveyor (5) where it is converted into a bag and transferred to
the next stage of operation, further whereafter, said first strips (8) are
released back onto said first moving belts (3).
8. A fabric guide device as disclosed in embodiments 1-7, characterised in
that said lifting ribbon (9) is made from flexible strips.
9. A fabric guide device as disclosed in embodiment 8, characterised in that
said gripping surface has lower frictional co-efficient than that for the
surface of the said cut-web conveyor.
10. A fabric guide device as disclosed in embodiments 1-9, further
characterised in that weight stabilizers (12) are provided in the region of a
second web conveyor (5) along the movement direction 'c', wherein said
second web conveyor incorporates second moving belts (5a) as conveying
means.
11. A fabric guide as disclosed in embodiments 1-10, characterised in that said
stabilizers (12) are supported on at least one flexible second strip (13), said
second strip (13) being suspended from a fixed support (14) using a
suspension mechanism (14a).
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12. A fabric guide as disclosed in embodiments 1-11, characterised in that said
flexible second strip (13) is shaped in an upward curve at its upstream end
in order to facilitate easy entry of the fabric into the gap between said
flexible second strips (13) and said second moving belts (5a).
13. A fabric guide device as disclosed in embodiments 1-12 wherein the
material of said first strips (8) is Teflon.
14. A fabric guide device as disclosed in embodiments 1-13 wherein the
material of said second strips (13) is Teflon.
While the above description contains much specificity, these should not be
construed as limitation in the scope of the invention, but rather as an
exemplification of the preferred embodiments thereof. It must be realized that
modifications and variations are possible based on the disclosure given above
without departing from the spirit and scope of the invention. Accordingly, the
scope of the invention should be determined not by the embodiments illustrated,
but by the appended claims and their legal equivalents.

We claim:
1. A fabric guide device characterised in that it comprises gripping device
provided in the region of at least one web conveyor of a standard bag
conversion machine/line, said gripping device incorporating a gripping
surface made from a low-friction material and being capable of exerting a
positive grip or control on the advancing cut woven fabric during its
transportation over the conveying mechanism.
2. A fabric guide device as claimed in claim 1, characterised in that said
gripping device provided in the region of any of said web conveyor
regions is in the form of strips termed as first strips (8), which spread over
said web conveyor region, are mounted over a mounter of first strips (7),
and an operating mechanism for the operation of said strips to enable their
lifting and lowering, said operating mechanism being positively controlled
by pneumatic or electro-pneumatic or mechanical means.
3. A fabric guide device as claimed in claims 1-2, characterised in that the
fabric cut piece, when fed through the pinch roll drive of said bag
conversion machine/line, enters the space between said first strips (8) and
the first moving belts (3) of said bag conversion machine/line, wherein
said belts (3) move forward at a speed slightly higher than the fabric-feed
speed, and wherein said first strips (8), under own weight, and aided by the
positive frictional characteristics of said first moving belts (3), grip the
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fabric between themselves (the strips) and the running belts (3), thereby
making said first moving belts (3) exert a frictional drag over said fabric
causing it to pull along said conveyer belt.
4. A fabric guide device as claimed in claims 1-3, characterised in that the
weight of said first strips (8) is sufficient to hold said fabric down over a
flat surface, thus preventing the fabric from flying off from said first
moving belts (3).
5. A fabric guide device as claimed in claims 1-4, characterised in that said
first strips (8) are bent upwards to facilitate easy entry of said fabric cut
piece into said gap between said first strips (8) and said first moving belts
(3).
6. A fabric guide device as claimed in claims 1-5, characterised in that till the
fabric is under grip of said first strips (8) from above, the feeding of fabric
is done at a speed slower than the full processing speed of said bag
conversion machine/line in order to avoid unwanted fabric warping,
whereafter said fabric is fed at full speed.
7. A fabric guide device as claimed in claims 1-6, characterised in that after
the feeding of fabric is over and the fabric is cut at the edge of a fabric
cutting zone (2), an air cylinder (11) lifts said first strips (8) using a lifting
ribbon (9) to relieve griping force on said fabric, whereafter a transverse
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conveyor (6) pulls the cut fabric piece in direction ‘c’ and transfers it over
to a main conveyor (5) where it is converted into a bag and transferred to
the next stage of operation, further whereafter, said first strips (8) are
released back onto said first moving belts (3).
8. A fabric guide device as claimed in claims 1-7, characterised in that said
lifting ribbon (9) is in the form of flexible strips.
9. A fabric guide device as claimed in claims 1-8, characterised in that said
gripping surface has lower frictional co-efficient than that for the surface
of the said first moving belt (3).
10. A fabric guide device as claimed in claims 1-9, further characterised in
that weight stabilizers (12) are provided in the region of a second web
conveyor (5) along the movement direction 'c', wherein said second web
conveyor incorporates second moving belts (5a) as conveying means.
11. A fabric guide as claimed in claims 1-10 characterised in that said
stabilizers (12) are supported on at least one flexible second strip (13), said
second strip (13) being suspended from a fixed support (14) using a
suspension mechanism (14a).
12. A fabric guide as claimed in claims 1-11 characterised in that said flexible
second strip (13) is shaped in an upward curve at its upstream end in order
to facilitate easy entry of the fabric into the gap between said flexible
second strip (13) and said second moving belts (5a).
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13. A fabric guide device as claimed in claims 1-12 wherein the material of
said first strips (8) is Teflon.
14. A fabric guide device as claimed in claims 1-13 wherein the material of
said second strips (13) is Teflon.