Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02894909 2015-06-18
METHOD AND APPARATUS FOR FABRICATING STRETCH FILM ROLLS
Field of the Invention
[0001] The present invention relates generally to stretch film and in
particular,
to a method and apparatus for fabricating stretch film rolls.
Background of the Invention
[0002] Stretch film is widely used for wrapping and securing pallet loads
for
shipping. This is due to the fact that stretch film exhibits a "memory", or a
tendency
to shrink, upon stretching. For example, stretch film that is stretched by an
amount of
10% will shrink nearly 10% of its stretched length. This "memory" assists in
securing
wrapped palletized articles together under compression.
[0003] Stretch film is fabricated in the form of stretch film rolls. Each
stretch
film roll may be used to manually wrap a pallet load, or may be loaded into an
automated wrapping machine.
[0004] An issue with conventional stretch film rolls is that the stretch
film
wound within the roll can become damaged if the stretch film roll is dropped
or
otherwise mishandled. For example, dropping the stretch film roll on its edge
can
result in tearing of the stretch film during wrapping of a pallet load.
[0005] One approach to avoiding such tearing involves folding the
longitudinal edges of the stretch film prior to winding, so as to provide a
stretch film
having reinforced longitudinal edges within the stretch film roll. Methods of
folding
the longitudinal edges of stretch film prior to winding have been described.
For
example, U.S. Patent No. 5,520,872 to Scherer discloses a strip of stretch-
wrap
material having flat, double thickness hems at opposite margins thereof. The
hemmed
strip is formed on an apparatus including a first roller having a width less
than the
width of stock material, whereby opposite margins of the stock material
project
beyond opposite ends of the roller, and a second roller for guiding the strip
at an acute
angle from the first roller for causing opposite marginal portions to fold.
The strip is
maintained under tension by a take-up roller or other means, and guide bars
are
provided for further folding the marginal portions past 90 degree angles so
that they
continue to be folded inwardly against the main body of the strip.
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[0006] Another approach to avoiding tearing involves oscillating the
stretch
film during winding, so as to prevent formation of hard edges within the
stretch film
roll. Methods of oscillating stretch film during winding have been described.
For
example, U.S. Patent No. 5,967,437 to Martin-Cocher et al. discloses a method
of
manufacturing rolls of pre-stretched film that comprises importing oscillation
to the
film with a component perpendicular to the film axis. During pre-stretching
and
winding of the film on a take-up roll, a feed roll, namely a spool from which
the
stretchable film for stretching is taken, is caused to oscillate, and/or the
take-up core is
caused to oscillate.
[0007] Improvements are generally desired. It is therefore an object at
least to
provide a novel method and apparatus for fabricating stretch film rolls.
Summary of the Invention
[0008] In one aspect, there is provided an apparatus for fabricating
stretch film
rolls, comprising: a first plurality of cutting blades configured to be
oscillated; a
second plurality of cutting blades configured to be oscillated independently
of the first
plurality of cutting blades, the first and second pluralities of cutting
blades being
configured for cutting a stretch film web into one or more stretch film web
sections
each having at least one non-linear longitudinal edge; and a driven winding
shaft for
winding the one or more stretch film web sections.
[0009] Each stretch film web section may have a variable width. The first
and
second pluralities of cutting blades may be configured to be oscillated in an
asymmetric manner. Each stretch film web section may have a constant width.
The
first and second pluralities of cutting blades may be configured to be
oscillated in a
symmetric manner.
[00010] The first plurality of cutting blades may be configured to be
oscillated
by a first linear oscillating device, and the second plurality of cutting
blades may be
configured to be oscillated by a second linear oscillating device. One or both
of the
first linear oscillating device and the second linear oscillating device may
be selected
from the group consisting of: a servomotor; an electric motor; and a
conventional
electric motor configured to drive an eccentric cam.
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[00011] Each plurality of cutting blades may be configured to be
oscillated
along an axis that is generally orthogonal to a direction of travel of the
stretch film
web. The first and second pluralities of cutting blades may be configured to
be
oscillated along the same axis.
[00012] At least one plurality of cutting blades may be configured to be
oscillated over a fixed distance. At least one plurality of cutting blades may
be
configured to be oscillated over a variable distance. At least one plurality
of cutting
blades may be configured to be oscillated at a fixed frequency. At least one
plurality
of cutting blades may be configured to be oscillated at a variable frequency.
[00013] The apparatus may further comprise a roller positioned adjacent
the
winding shaft, a wound surface of the one or more stretch film web sections
being in
contact with a surface of the roller. The roller may be configured as a driven
roller.
The roller may be configured as an idler roller.
[00014] In another aspect, there is provided a method for fabricating
stretch
film rolls, comprising: providing a stretch film web; cutting the stretch film
web into
one or more stretch film web sections using a first plurality of cutting
blades
configured to be oscillated and a second plurality of cutting blades
configured to be
oscillated independently of the first plurality of cutting blades, the one or
more stretch
film web sections each having at least one non-linear longitudinal edge; and
winding
the one or more stretch film web sections.
[00015] The winding may further comprise winding each stretch film web
section onto a core.
[00016] In another aspect, there is provided a method for cutting stretch
film
during fabrication of stretch film rolls, comprising: cutting a stretch film
web using a
first plurality of cutting blades and a second plurality of cutting blades
into one or
more stretch film web sections each having at least one non-linear
longitudinal edge,
the cutting blades being oscillated during said cutting, the second plurality
of cutting
blades being configured to be oscillated independently of the first plurality
of cutting
blades.
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Brief Description of the Drawings
[00017] Embodiments will now be described more fully with reference to the
accompanying drawings in which:
[00018] Figure 1 is a schematic side view of a portion of an apparatus for
fabricating stretch film rolls, during use;
[00019] Figure 2 is a schematic front view of a cutting station forming
part of
the apparatus of Figure 1, during use;
[00020] Figure 3 is a side view of a stretch film roll fabricated using
the
apparatus of Figure 1; and
[00021] Figure 4 is a schematic front view of another embodiment of a
cutting
station forming part of the apparatus of Figure 1, during use.
Detailed Description of the Embodiments
[00022] Turning now to Figures 1 and 2, a portion of an apparatus for
fabricating stretch film rolls is shown, and is generally indicated by
reference numeral
20. Apparatus 20 comprises an extruder (not shown) that is configured to
dispense a
continuous sheet of plastic film onto a surface of a rotating cast roller (not
shown) so
as to form a stretch film web 22. Apparatus 20 also comprises a set of rollers
(not
shown) configured to receive the stretch film web 22 from the cast roller.
[00023] Apparatus 20 further comprises a cutting station 30 that is
positioned
downstream from the set of rollers. The cutting station 30 comprises a first
plurality
of cutting blades 32 coupled to a first linear oscillating device 34, and a
second
plurality of cutting blades 36 coupled to a second linear oscillating device
38. The
first linear oscillating device 34 is configured to oscillate the first
plurality of cutting
blades 32 along an oscillation axis that is generally orthogonal to the
direction of
travel of the stretch film web 22. Similarly, the second linear oscillating
device 38 is
configured to oscillate the second plurality of cutting blades 36 along an
oscillation
axis that is generally orthogonal to the direction of travel of the stretch
film web 22.
In turn, the cutting blades 32 and 36 are configured to cut, or "slit", the
moving
stretch film web 22 into a plurality of stretch film web sections 40, with
each section
40 having a variable width. In the embodiment shown, both pluralities of
cutting
blades 32 and 36 are oscillated along a common oscillation axis 41.
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[00024] In this embodiment, each cutting blade 32 is mechanically coupled
to
the first linear oscillating device 34 via a linkage arm 42 connected to a
first push rod
44 that is configured to be extended from and retracted toward the first
linear
oscillating device 34 in an oscillating manner; similarly, each cutting blade
36 is
mechanically coupled to the second linear oscillating device 38 via a linkage
arm 46
connected to a second push rod 48 that is configured to be extended from and
retracted toward the second linear oscillating device 38 in an oscillating
manner.
[00025] Each of the first and second linear oscillating devices 34 and 38
is
configured to be independently operated via suitable control structure (not
shown).
The control structure may comprise any of analog controls and digital
processing
structure, for example, and may be a single control structure configured to
operate
both linear oscillating devices 34 and 38 independently, or may be two
separate
control structure units in communication with each other and each
independently
operating a respective linear oscillating device 34 and 38. In this
embodiment, each
of the first and second linear oscillating devices 34 and 38 is a servomotor
or an
electric motor.
[00026] In the embodiment shown, the first and second linear oscillating
devices 34 and 38 are configured to oscillate the first and second pluralities
of cutting
blades 32 and 36, respectively, such that each of the first and second
pluralities of
cutting blades 32 and 36 is oscillated at the same fixed frequency and over
the same
fixed distance along the oscillation axis. In this embodiment, the fixed
frequency is a
frequency in the range from 0 cycles per minute to about 200 cycles per
minute, and
the fixed distance, and namely the distance travelled during one cycle, is a
distance in
the range from 0 inches to about 4 inches, and preferably is a distance in the
range
from about 0.5 inches to about 1.5 inches.
[00027] Apparatus 20 also comprises a first intermediate roller 52 that is
configured to receive the stretch film web sections 40 downstream from the
cutting
station 30, and a second intermediate roller 54 that is configured to receive
the stretch
film web sections 40 from the first intermediate roller 52. In this
embodiment, the
first inteiniediate roller 52 and the second intermediate roller 54 are idler
rollers.
[00028] Apparatus 20 further comprises a roller 62 that is configured to
receive
the stretch film web sections 40 from the second intermediate roller 54.
Apparatus 20
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further comprises a winding shaft 64 positioned adjacent the roller 62 and
supporting
a plurality of cores 68. The winding shaft 64, with the cores 68 supported
thereon, is
configured to receive the stretch film web sections 40 from the roller 62 for
winding
each stretch film web section 40 onto a respective core 68, so as to form a
plurality of
stretch film rolls. An assembly (not shown) is provided for rotatably driving
the
winding shaft 64. The surface of the stretch film wound onto the cores 68 is
in
contact with the surface of the roller 62, so as to prevent entrapment of air
between
layers of the stretch film during winding. In this embodiment, the roller 62
is
configured as an idler roller.
[00029] During operation, the extruder dispenses a continuous sheet of
plastic
film onto the surface of the rotating cast roller to form the stretch film web
22, which
is then received by the set of rollers. From the set of rollers, the stretch
film web 22
travels downstream to the cutting station 30, where it is engaged by the
plurality of
cutting blades 32 and 36 and cut into a plurality of stretch film web sections
40. The
cutting blades 32 and 36 are being oscillated along the oscillation axis. As a
result of
this oscillation, each stretch film web section 40 has a variable width, and
has
longitudinal edges 70 that are defined by cutting lines which are generally
non-linear
along the length of the stretch film web section 40, as shown schematically in
Figure
2.
[00030] Downstream from the cutting station 30, the stretch film web
sections
40 are received by the first intermediate roller 52, and in turn by the second
intermediate roller 54. From the intermediate roller 54, the stretch film web
sections
40 are received by the roller 62, and in turn by the winding shaft 64
supporting the
plurality of cores 68, at which each stretch film web section 40 is wound onto
a
respective core 68 so as to form a plurality of stretch film rolls.
[00031] A stretch film roll fabricated by the apparatus 20 is shown in
Figure 3,
and is generally indicated by reference numeral 80. Stretch film roll 80
comprises a
body 82 of stretch film wound onto core 68. The body 82 of stretch film has a
generally cylindrical central portion 84 and tapered end portions 86, with the
end
portions 86 being generally softer than the central portion 84. The
configuration of
the stretch film roll 80, and in particular the softness and the tapered shape
of the end
portions 86, results from the oscillation of the cutting blades 32 and 36
during
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winding onto the core 68. As will be understood, this oscillation causes the
formation
of longitudinal edges 70 that are generally non-linear, which prevents direct
overlap
of the longitudinal edges 70 during winding, and thereby eliminates the
formation of
hard, right-angled corners within the wound film at ends of the roll that
would
otherwise form in absence of oscillation. As will be appreciated, the softness
and the
tapered shape of the end portions 86 advantageously increases the tolerance of
the
stretch film roll 80 to handling errors, such as dropping, which in turn
renders the
stretch film within the stretch film roll 80 less prone to tearing during use.
[00032] Additionally, and as will be appreciated, oscillating the first
plurality
of cutting blades 32 separately from the second plurality of cutting blades 36
advantageously provides greater control of the final shape of the stretch film
roll,
which permits greater manufacturing flexibility as compared to what might
otherwise
be possible by oscillating all of the cutting blades in unison in the same
direction and
over the same distance. For example, oscillating the first plurality of
cutting blades
32 separately from the second plurality of cutting blades 36 advantageously
permits
the first plurality of cutting blades 32 to be oscillated in a different
manner (e.g. over a
different distance, and/or at a different frequency) than the second plurality
of cutting
blades 36, for allowing the end portions of the stretch film roll to be
tailored to
desired shapes. For example, although in the example shown in Figure 3, the
shapes
of the end portions 86 are the same and the stretch film roll 40 has a
symmetric shape,
the first and second pluralities of cutting blades 32 and 36 may alternatively
be
oscillated such that the shape of each end portion is different from the other
and such
that the resulting stretch film roll has an asymmetric shape. As another
example,
oscillating the first plurality of cutting blades 32 separately from the
second plurality
of cutting blades 36 advantageously permits the oscillation of only one
plurality of
cutting blades to be adjusted, as desired, as the diameter of the stretch film
roll
increases during winding.
1000331 Other configurations of the apparatus are possible. For example,
although in the embodiment described above, each of the first and second
linear
oscillating devices is a servomotor or an electric motor, in other
embodiments, one or
both of the first and second linear oscillating devices may alternatively be a
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conventional electric motor configured to drive an eccentric cam for
generating the
oscillation.
[00034] Although in the embodiment described above, both pluralities of
cutting blades are oscillated along a common oscillation axis, in other
embodiments,
the oscillation axis of the first plurality of cutting blades may
alternatively be offset
from the oscillation axis of the second plurality of cutting blades such that
the
oscillation axes do not coincide. In one such embodiment, the non-coincident
oscillation axes may be offset in the direction of travel of the stretch film
web.
[00035] In other embodiments, the cutting blades may alternatively be
coupled
to the linear oscillating devices in a different manner than that of the
embodiment
described above. For example, although in the embodiment described above, each
cutting blade is mechanically coupled to its respective linear oscillating
device via the
linkage arm connected to the respective push rod, in other embodiments, some
or all
of the cutting blades may alternatively be mounted on the push rod directly,
such as
via a mounting bracket, without any linkage arm. Those skilled in the art will
appreciate that still other configurations may be used for coupling the
cutting blades
to the linear oscillating devices.
[00036] Although in the embodiment described above, the first and second
linear oscillating devices are configured to oscillate the first and second
pluralities of
cutting blades, respectively, such that each of the first and second
pluralities of cutting
blades is oscillated at the same fixed frequency and over the same fixed
distance
along the oscillation axis, in other embodiments, the first and second
pluralities of
cutting blades may alternatively be oscillated at different frequencies,
and/or over
different distances along the oscillation axis.
[00037] Although in the embodiment described above, each of the first and
second pluralities of cutting blades is oscillated at a fixed frequency, in
other
embodiments, one or both of the first and second pluralities of cutting blades
may
alternatively be oscillated at a variable frequency, such as a periodically
variable
frequency or a random frequency, for example.
[00038] Although in the embodiment described above, each of the first and
second pluralities of cutting blades is oscillated over a fixed distance along
the
oscillation axis, in other embodiments, one or both of the first and second
pluralities
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of cutting blades may alternatively be oscillated over a variable distance
along the
oscillation axis, such as a periodically variable distance or a random
distance, for
example.
[00039] Although in the embodiment described above, the fixed frequency is
a
frequency in the range from 0 cycles per minute to about 200 cycles per
minute, in
other embodiments, the fixed frequency may alternatively be a frequency that
is
greater than 200 cycles per minute.
[00040] Although in the embodiment described above, the fixed distance is
a
distance in the range from 0 inches to about 4 inches, in other embodiments,
the fixed
distance may alternatively be a distance that is greater than 4 inches.
[00041] Although in the embodiment described above, the oscillation axis
of
each of the pluralities of cutting blades is generally orthogonal to the
direction of
travel of the stretch film web, in other embodiments, the oscillation axis of
one or
both pluralities of cutting blades may alternatively be non-orthogonal to the
direction
of travel of the stretch film web, provided that each stretch film web section
has
longitudinal edges defined by cutting lines that are generally non-linear
along the
length of the stretch film web section.
[00042] In the embodiment described above, the first and second linear
oscillating devices are configured to oscillate the first and second
pluralities of cutting
blades, respectively, such that the cutting blades cut the moving stretch film
web into
a plurality of stretch film web sections, with each section having a variable
width. As
will be understood, operating the first and second linear oscillating devices
in this
manner results in "asymmetric" oscillation of the first and second pluralities
of cutting
blades. In other embodiments, the first and second linear oscillating devices
may
alternatively be configured to oscillate the first and second pluralities of
cutting
blades, respectively, such that the cutting blades cut the moving stretch film
web into
a plurality of stretch film web sections, with each section having a constant
width and
having longitudinal edges defined by cutting lines that are generally non-
linear along
the length of the stretch film web. As will be understood, operating the first
and
second linear oscillating devices in such a manner would result in "symmetric"
oscillation of the first and second pluralities of cutting blades.
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[00043] For example, Figure 4 shows another embodiment of a cutting
station
forming part of apparatus 20, and which is generally indicated by reference
numeral
130. Cutting station 130 is generally similar to cutting station 30 described
above,
and comprises the first plurality of cutting blades 32 coupled to a first
linear
oscillating device 134, and the second plurality of cutting blades 36 coupled
to a
second linear oscillating device 138. The first linear oscillating device 134
is
configured to oscillate the first plurality of cutting blades 32 along an
oscillation axis
that is generally orthogonal to the direction of travel of the stretch film
web 22.
Similarly, the second linear oscillating device 138 is configured to oscillate
the
second plurality of cutting blades 36 along an oscillation axis that is
generally
orthogonal to the direction of travel of the stretch film web 22. In turn, the
cutting
blades 32 and 36 are configured to be oscillated in a "symmetric" manner so as
to cut,
or "slit", the moving stretch film web 22 into a plurality of stretch film web
sections
40, with each section 40 having a constant width. In the embodiment shown,
both
pluralities of cutting blades 32 and 36 are oscillated along a common
oscillation axis
41. More specifically, in this embodiment, the first and second linear
oscillating
devices 134 and 138 are configured to oscillate the first and second
pluralities of
cutting blades 32 and 36, respectively, such that each of the first and second
pluralities of cutting blades 32 and 36 is oscillated at the same fixed
frequency and
over the same fixed distance along the oscillation axis in a symmetric,
synchronous
manner.
[00044] Although in the embodiment described above, the first intermediate
roller and the second intermediate roller are configured as idler rollers, in
other
embodiments, one (1) or both of the first intermediate roller and the second
intermediate roller may alternatively be configured as a driven roller.
[00045] Although in the embodiment described above, the apparatus
comprises
a first intermediate roller and a second intermediate roller, in other
embodiments, the
apparatus may alternatively comprise fewer or more intermediate rollers. In
one
embodiment, the apparatus may alternatively comprise no intermediate rollers.
[00046] Although in the embodiment described above, the cutting station
comprises a plurality of cutting blades that are configured to cut the stretch
film web
into a plurality of stretch film web sections, in other embodiments, the
cutting station
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may alternatively comprise two (2) cutting blades that are configured to cut
the stretch
film web into one (1) stretch film web section, with each cutting blade being
oscillated independently of the other in the manner described above.
[00047] Although in the embodiment described above, the winding shaft
supports a plurality of cores, in other embodiments, the winding shaft may
alternatively support one (1) core.
[00048] Although in the embodiment described above, the roller adjacent
the
winding shaft is configured as an idler roller, in other embodiments, the
roller
adjacent the winding shaft may alternatively be configured as a driven roller.
In one
such embodiment, the surface speed of the driven roller may be matched to the
surface speed of the wound film on the winding shaft using automated or
computer-
controlled speed matching. In another such embodiment, there may be no
assembly
provided for rotatably driving the winding shaft, and the winding shaft may
alternatively be driven through contact with the surface of the driven roller.
[00049] Although in the embodiment described above, the surface of the
stretch
film wound onto the cores is in contact with the surface of the roller
adjacent the
winding shaft so as to prevent entrapment of air between layers of the stretch
film
during winding, in other embodiments, the winding shaft and any roller
adjacent
thereto may alternatively be configured to enable entrapment of air between
layers of
the stretch film during winding.
[00050] Still other apparatus configurations are possible. For example,
although in the embodiment described above, the apparatus comprises an
extruder and
a rotating cast roller for forming the stretch film web, in other embodiments,
the
apparatus may alternatively not comprise an extruder and a cast roller for
forming the
stretch film web, but may alternatively comprise a supply (e.g. a spool, a
roll, etc.) of
previously-fabricated stretch film web, and provisions for feeding the stretch
film web
from the supply to the set of rollers, or from the supply to the cutting
station if no set
of rollers is provided. It will be understood that such a configuration would
provide
an "off-line" or "secondary" apparatus for fabricating the stretch film roll.
Those
skilled in the art will recognize that such previously-fabricated stretch film
webs may
otherwise typically be used for other "off-line" or "secondary" processes such
as, for
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example, one or more of: conventional rewinding, slitting, pre-stretching, and
edge
folding/rolling.
[00051] Although embodiments have been described above with reference to
the accompanying drawings, those of skill in the art will appreciate that
variations and
modifications may be made without departing from the scope thereof as defined
by
the appended claims.
