Note: Descriptions are shown in the official language in which they were submitted.
lZ~1~588
BACKGRO~' OF THY INVENTION
The present invention generally relates to
packaging and more particularly is directed to a
rotating stretch wrapping apparatus for making unitary
packages which hold a plurality of components, each
package containing a load wrapped in a web of stretched
film.
Case packing or boxing is a common way of
shipping multiple unit products. Multiple unit
products are generally stacked in a corrugated box or
are wrapped with kraft paper with the ends of the kraft
paper being glued or taped.
Some manufacturers use strapping of vertical
steel or plastic binding to unitize the product. The
problems incurred in the use of strappins are the
requirement of costly corner protectors, dcnger of
bending or snapping and injuring the operator while
applying this high tension material to the loads, the
ever present settling due to moisture wetting the
cartons, and the sides bulging or normal vibrations
causing the straps to loosen and the load to come
apart.
Glue is an alternative method used in some
areas, but customers are dissatisfied with gluing
because removal of glued cartons or bags from the
unitized loads tends to tear outside layers of the
cartons. Glue, although an inexpensive material,
... . .
- ~LZ~1588
demands interleaving for product orientation and thus
requires more durable and expensive packaging material.
Because of the lack of alternatives of
packaging, tape is currently beins used to horizontally
bind the top layer of the load. However, tape is
expensive and allows relatively free movement of all
products surrounded.
Another way of shipping products is by
putting a sleeve or covering of heat shrinkable
material around the products and shrinking the sleeve
to form a unitized package. The use of heat shrinkable
film is described in '~.S. Patent Nos. 3,793,798;
3,626,645; 3,590,549 and 3,514,920. A discussion of
this art us set forth in U.S. Patent No. 3,867,806.
; on economical w2y of packaging products is by
wrapping the product load with a web of stretched
plastic film.
The elasticity of the stretched plastic film
holds the products o, the load under more tension than
either shrink wrap or kraft wrap, particularly with
products which settle when packaged. The effectiveness
of stretched plastic film in holding a load together is
a functior. of the containment or stretch force being
placed on the load and the ultimate strength of the
total layered film wrap. These two functions are
determined by the modulus or hardness of the film after
stretch has occurred and the ultimate strength of the
12~1S~38
film afte. application. Containment force is currently
achieved by maximizino elongation until just below a
critical point where breaking of the film occurs.
he use of wrapping machinery to wrap
stretched film around a load is well known in the art.
Four types of stretch wrapping apparatus are commonly
used in the packaging industry and these types are
generally described us spiral rotary machines, full web
rotary machines, passthrough machines, and circular
rotating machines.
A typical spiral machine is shown in U.S.
Patent No. 3,863,425 in which film is guided from a
roll and wrapped around a load in a spiral
configuration. A carriage drives the film roll
adjacent the cur_ace of the load to deposit a spiral
wrap arour.c the loac and returns in the opposite
direction to deposit another spiral wrap around the
load.
Spiral wrapping machines which are currently
commercially available are manufactured by Lantech,
Inc. uncer yodel as SVS-80, SVSM-80, STVS-80,
STVSM-80 and SAHS-80.
full web type of apparatus which wraps
stretched film around a rotating load is disclosed in
U.S. Patent Jo. 3,867,806 assigned to Lantech, Inc. A
similar fu1l web apparatus using a tensioned cling film
wrapped around a rotating toad is shown by U.S. Patent
lZg~588 '
NG. 3,986, 611 while another apparatus using a tacky PVC
film is disclosed in U.S Patent NO. 3,795,086.
Full web wrapping machines typical of those
presently commercially available are Model NOS. S_65,
T-65 and SAH-70 manufactured by Lantech, Inc.
Anther type of machine for wrapping a pallet
load commonly called a passthrough machine is disclosed
in U.S. Patent No. 3,596,434. In this reference a
pallet load is transported along a conveyor and the
leading face of the pallet load contacts a vertical
curtain of film formed by the sealed leading edges of
film webs dispensed by two rolls of film on opposite
sides o. the path of the pallet load. The pallet load
cor.tinues to move along the conveyor, carrying with it
the se~1ec film curtain until the two side faces of the
pzllet iOad as well as the front face are covered by
film web. A pair of clamping jaws then close behind
the pallet ioad, bringing the two film web portions
trailing from the side faces of the pallet load into
contact with one another behind the pallet. The jaws
then seal the film web portions together along two
vertical lines, and cut the web portions between those
two seals. Thus, the film web portions are cornected
to cover the trailing face of the pallet load, and the
film curtain across the conveyor is re-established to
receive the next pallet load. The pallet load may
subsequently be exposed to heat in order to shrink the
~2~11588
filn web thus applying unitizing tension to the load,
as is aisclosed in U.S. Patent No. 3,662,512.
Commercial passthrough machines are currently
manufactured by Weldotron, Arenco, and SAT of France.
Various apparatus and processes have been
developed to rotatably wrap stacked components to form
a load.
Stationary loads which are brought to a
loading area and are wrapped by a rotating member
dispensing stretched film are disclosed in U.S. Patent
Nos. 4,079,565 and 4,109,445. U.S. Patent No.
4,079,565 discloses a full web vertical wrap of the
load while U.S. Patent No. 4,109,445 discloses the
horizontal spiral wrap of a load. U.S. Patent No.
4,050,220 discloses a wrapping device or multiple unit
loadc, pa ch load is conveyed to a wrapping area in
which a load is supported on one or more stationary
planar surfaces. The leading edge of a roll of
stretchable plastic wrapping material is held adjacent
to the load, and the roll of material is rotated about
the load and the supporting planar surfaces beneath the
load, wrapping the load and the supporting surfaces
together. Plastic wrapping r,aterial is stretched
during the wrapping operation so that the material is
under tension when applied to the load. After the
wrapping cycle is complete, the load is pushed past the
ends of the supporting surf aces, and the wrapping
~Z41588
material which covered the supporting surfaces
collapses against the supported sides of the load.
Further developments of this wrapping system are
disclosed in U.S. Patent Nos. 4,110,957 and 4,178,734.
U.S. Patent No. 603,585 discloses a spiral
wrapping device for enclosing individual newspapers in
pape'r wrap for mailing purposes.
Each newspaper is placed on a cylindrical
core with a circumference-approximately twice that of a
newspaper, and each newspaper advances along the length
of the core as the core is rotated. Wrapping paper is
applied to the core at an angle and the wrapping paper
between nehspapers is severed as each newspaper reaches
the end cf the cylinder and is placed on a flat
horizontai surface, thereby collapsing the wrapping
paper aa2inst the underside of the newspaper previously
pressed to the cylinder.
U.S. Patent No. 1,417,591 discloses a
wrapping machine for individual items such as boxes in
which each such item is conveyed along the surface of a
horizontal sheet of wrapping material. The edges of
wrapping material on each side of an item are curled
upward to meet one another atop the item to be wrapped
thereby iorming a tube around the item. The leading
end of the tube is sealed and the trailing end of the
tube is severed and then sealed to enclose the item.
Another device which utilizes this system of wrapping
is disclosed in U.S. Patent No. 3,473,288.
124~5~8
In U.S. Patent No. 2,575,467, a wrapper of
cylindrical packages for material such as sausage is
disclosed in which the package is rotated about its
cylindrical axis as wrapping tape is applied at an
angle to form a cylindrical wrap.
In U.S. Patent No. 2,863,270, two cylindrical
items of approximately equal diameter are abutted at
their planar ends, and placed by hand in a cradle which
exposes the complete circumference of the abutting
e;lds. A roll of wrapping material is then driven by a
hand crank mechanism to circulate around the
circumference of the abutting ends, applying wrapping
material thereto. When sealed together, the pair of
cylindrical items are removed from the cradle by hand.
spiral wrapping machine for long bundles of
i.er, such as filaments is disclosed in U.S. Patent No.
3,000,167. As the bundle of filaments moves along its
axis through the wrapping area, a ring circulates about
the bundle carrying a roll of wrapping material which
is applied to the bundle to form a spiral wrap pattern.
Because the normal load of filaments or similar items
is much longer than the wrapping area, it is not
necessary to provide support for the bundle in the
wrapping area, and therefore no support structure is
wrapped with the bundle.
All of these prior art apparatuses suffer
from a severe limitation which relates to cost per unit
~241588
load for film unitization. Friction brake devices do
not maintain a consistent stretch force on the film.
These brake devices are subject to variation due to
their physical construction, sensitivity to speed
change caused by passage of load corners, and the
resultant sudden acceleration and deceleration of film
payaut. A typical load will incur a surface speed
change of more than 40~ with each quarter turn, and
each quarter turn occurs in about second under
current practice. Moreover, it can be appreciated that
these speed changes are substantially discontinuous as
film dispensed by relative rotation of the film roll
around the load is intercepted by successive edges of
the load. Higher rotation speeds produce additional
resonatina forces which change during payout and the
resultant weight decrease of the film roll. Additional
limitatior.s on maximum elongation are caused by film
roll imperfections and gauge variations which
accentuate the force variations described above to
produce film ruptures.
Commercial circular rotating wrapping
machines are presently manufactured by Lantech, Inc.
under the trademark LANRINGER, and are provided with
wrapping ring inner diameters of 36 inches, 54 inches,
72 inches, and 84 inches. In differentiating between
the various circular rotating wrapping machines
manufactured by Lantech, Inc., the manual model has the
lZ41588
designatio-, SR; the full web models have the
designations SVR and SAVR; the multiple banding models
have the aesianation SvsR and SAVBR; the spiral models
have the cesignation SVSR and SAVSR, and the continuous
wrap or bundler models have the model designations SVCR
and SAVCR.
United States Patent Nos. 4,302,920 and
4,317,322, assigned to Lantech, Inc., disclose a
pre-stretch film elongation system mounted adjacent a
film roll and rotated about a stationary load. The
pre-stretch system which is mounted on the rotating
ring includes an upstream roller and a downstream
roller across which the film web successively passes.
The two rollerc are coupled by gears, belts, or the
like, which force a constant ratio of velocity between
the roller--. Film is drawn from the film roll and
across each of the rollers by relative rotation of the
ring arounc the load. The fixed speed ratio between
the upstream anc downstream rollers, in which the
downstream roller moves more quickly than the upstream
roller, causes substantial and constant stretching
between the rollers of the web. In this device the
substantial changes in demand speed are transmitted
directly fror the load back through the web to the
pre-stretch device, so that the supply speed of the
film moving across the downstream roller to the load
changes accordingly. However, it can be appreciated
lZ4:1588
that the entire force exerted between the rollers is
applied to the rollers by film being wrapped about the
load, and that pre-stretch device inertia and the
elasticity of film web between the downstream roller
and the load causes a phase delay or lag in supply
speed changes. It has also become clear that any hole
in the web, such as those which commonly occur at web
imperfections or guage variations, causes a weakening
between the load and the pre-stretch mechanism, thus
slowing or stopping the pre-stretch mechanism. The
hole is then elongated and enlarged by the growing
difference between supply and demand speeds, finally
breaking the film web and interrupting the wrapping
procedure.
Purthermore, it has been discovered that two
characteristics of the film wrapping systems described
above combine after wrapping is completed to reduce the
containment force exerted on the load. One such
characteristic is that a film web segment applied to
any one side of the load exhibits elongation and
containment force independent of contiguous film web
applied to either of the sides immediately prior to or
after the given side. This is because load edges
isolate each film web segment applied to a side from
connecting film web segments applied to adjacent sides,
so that slippage across edges does not occur. Film web
characteristics are thus effectively "locked in" on
lZ41S88
each side as the film web encounters the edge at the
end of-the side.
The second characteristic is that, in prior
art wrapping systems, locking in at load edges occurred
precisely at the point where the film web experienced a
minimum of force and elongation, having partly
retracted and recovered from a prior maximum
force/elongation point, thereby locking in the same
minimum characteristics. Since a maximum force was
also experienced during the wrapping of each load side,
an attempt to raise overall force in order to raise the
minimum point will also raise the maximum point and
increase the risk of exceeding the failure point for
the fil. web. An attempt to lower overall force for
aelicate loads will reduce the minimum print and risk:
zero cont2inment of the loaa. Hence, the prior ar-
wrapping systems are compelled to wrap stretchable filr
web to a load at containment force levels well below-
those levels theoretically possible, which, in turn,
reduces the final post-unitizing force to the load
after film web recovery and after shifting and settling
has reducec the load circumference.
It therefore remains clear that there exists
a need and use for a circular rotating wrapping
apparatus and process which incorporates a pre-stretch
system and avoids the force pattern which reaches a
minimum as each load edge is encountered, preferably
- - - _ . . .. ..
; .~; .: . ; , . , . - .
- 1241588
introducing a pattern which minimizes changes in force
and elongation at each edge to lock in desirable web
characteristics. Moreover, the apparatus and process
should avoid control of the pre-stretch system through
the film web itself, so that the pre-stretch system
will not decelerate when holes develop in the film web.
Thus the risk of hole expansion and film failure wlll
be minimized.
SUMMARY OF THE INVENTION
The present invention is directed toward an
apparatus and process for applying stretchable plastic
film to loads using a pre-stretch mechanism which is
driven anc controlled independently of the web tension
to minimize variations in the force exerted on the film
web at load edges by varying the film web supply speed.
Film web is drawn to the load at a demand speed which
varies during rotation of a film roll about a load.
The supply speed changes required to minimize web
elongation and containment force changes at load edges
are transmitted to the pre-stretch mechanism by a
supply speed control mechanism using a predetermined
model of the load, which permits higher levels of
stretch, faster payout speeds, and use of less uniform
film than were previously thought possible. The
present invention reduces the likelihood of unexpected
web breakage during wrapping, increases throughput and
-- 1241588
conserves film by establishing load containment with
fewer web layers.
In the apparatus a series of loads are fed
into a rotating wrapping apparatus having a film web
pre-stretch mechanism and elongation drive mechanism.
Each load is covered by a plurality of layers of
stre'tched film to form a unitary package. The
pre-stretch mechanism is mounted on a rotating ring
through which a load travels for encirclement by
stretched film web. The supply speed control mechanism
is mounted adjacent the rotating ring. Energy is
delivered to the pre-stretch mechanism during rotation
of the rotating ring by way of a power pulley, cam
follower or the like mounted to the pre-stretch
mechanism. The power pulley engages the supply speed
control mechanism and revolves at a varying rate due to
friction thereon. The power pulley then transfers its
energy and speed to the film pre-stretch mechanism.
The pre-stretch mechanism is thus operated at a varying
speed and supplied with the force required to stretch
the film by the supply speed control mechanism.
Thus, it can be seen that the structure
provides a novel and useful improvement over the prior
art rotating wrapping machines, both those utilizing
braze stretching systems and those utilizing coupled
roller stretching systems. This is advantageously
accomplished without the need to transfer electrical
14
124~51~8
power or control signals from a stationary source to
devices such as brakes or motors on the rotating ring.
Most plastic films when stretched above their
yield point gain significantly in modulus and ultimate
strength. The typical polyethylene will multiply three
times the ultimate strength in pounds per square inch
of cross sectional area after being elongated
approximately 300 percent. This significant increase
in strength begins approximately when the yield point
is exceeded in the elongation phase. The term "yield
point" designates a range or region on the
stress-strain curve, rather than a dimensionless point.
Limitations of friction-based constant force devices
prevent current stretch wrap applications from
achievina the higher levels of containment force and
ultimate strength available in the foremost plastic
films. Achieving the higher elongation levels with the
invention allows wrapping with fewer revolutions of
film yet maintains equivalent holding power. These
higher levels of stretch not only allow fewer
revolutions of film but also permit wrapping with less
film by weight for each revolution.
Thus, the present structure allows at least
double the practical level of elongation currently
experienced with prior art "brake" systems. This gives
higher containment forces and/or lower film costs to
the end user.
~2~1588
Furthermore, the,structure allows for more
precise control of web speeds and forces thereby
achieving greater cost efficiency from high yield
films, along with higher film strength or modulus
achieved at higher levels of elongation.
The novel construction of the invention
provides for isolation of the pre-stretch mechanism
from stretch forces which eliminates premature film
failure from development and elongation of holes at web
imperfections. This construction eliminates friction
brakes and the problems of those brakes such as speed
variation, break away from stop position, temperature
variation, wear and operator control meddling.
It can thus be seen that the present
invention provides a unique apparatus and process with
an elongation mechanism driven to apply uniform film
web containment across every side of the load. The
film is preferably stretched beyond its yield point a
it is accelerated. The acceleration force is providec
by the supply speed control mechanism, which also
precisely varies the web supply speed to lock in
predetermined elongation and containment force on the
load. my limiting the stretching action to a minimum
distance within the elongation mechanism and avoiding
secondary stretch between the elongation mechanism and
the load, web neck down is significantly reduced.
Although the invention is set forth in the
claims, the invention itself and the method by which it
16
~Z41S~8
is made and used may be better understood by referring
to the following description taken in connection with
the accompanying drawings forming a part hereof, in
which like reference numerals refer to like parts
throughout the several views and in which:
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a perspective view of the
invention partly broken away disclosing a preferred
embodiment of the inventive apparatus;
Figure 2 is an enlarged reversed side
elevational view of the apparatus shown in Figure l;
Figure 3 is an enlarged front elevational
vie of the apparatus shown in Figure 1;
Figure 4 is a side elevational view of a
continuous spiral bundling system with a seouence of
consecutive packages wrapped by the present invention;
Figure 5 is a graph of force versus time as
exhibited by prior art wrapping apparatus;
Figure 6 is a generalized graph of force
versus elongation for film web utilized in the present
invention;
Figure 7 is a schematic representation of
film web demand during relative rotation of a load;
Figure 8 is a schematic representation of
film web demand at a wrapping stage on the load
subsequent to that of Figure 7;
''
17
1;Z4'1S88
Figure 9 is a schematic representation of film
web demand at a wrapping stage on the load subsequent to
that of Figure 8;
Figure 10 (shown on Sheet 3 of the drawings) is
a graph of force versus time for the preferred embodiment
of the present inventive apparatus;
' Figure 11 is a front elevational view of the
web cutting mechanism shown in various positions during
cutting of the film web;
Figure 12 (shown on Sheet 4 of the drawings)
is an enlarged front elevational view of an alternate
embodiment of the present invention;
Figure 13 is an enlarged rear elevational view
of the apparatus of Figure 12;
Figure 14 is an enlarged reversed side
elevational view of the apparatus of Figure 12;
Figure 15 (shown on Sheet 6 of the drawings)
is a side elevational view of the cutting apparatus of
Figure 11;
Figure 16 shown on Sheet 4 of the drawings)
is a side elevational view of a full web wrap mode
accomplished by the present invention;
Figure 17 (shown on Sheet 4 of the drawings) is
a side elevational view of a banding wrap mode accomplished
by the present invention; and
Figure 18 (shown on Sheet 4 of the drawings) is
a side elevational view of a spiral wrap mode accomplished
by the present invention.
18
~Z41588
DETAILED DESCRIPTION OF THE DRAWINGS
The best mode and preferred embodiment of the
present invention is disclosed in Figures 1 through 3,
and comprises a ring wrapping apparatus 30 comprising a
feed conveyor 32, a wrap and load conveyor assembly 34,
a film dispensing mechanism 36 with a take-off conveyor
20.,
As shown in Figure 1, a plurality of units 22
forming a load 24 have been loaded in a stacked
relationship on an infeed conveyor assembly 32 by
either manual or mechanical means. It should be noted
that the load, depending on if S nature and composition,
may or may not require spacing. The loading device 31
is schematically shown and may be one of a number of
types of stacking or placing devices which are well
known in the art to place a stack of cartons or
materials into designated areas.
Throughout this specification, containment
force refers to force applied to a load by film web
surrounding the load when wrapping is completed, while
wrapping force refers to force applied by film web
extending from the wrapping system to the load during
wrapping. Wrapping force is, of course, applied
equally and oppositely to the film web and to the load
simultaneously.
In the preferred embodiment, the load 24 is
placed on an infeed conveyor 32 which is comprised of
19
~Z415~8
an endless belt 26 mounted on frame support 28.
An alternate embodiment of the infeed
conveyor could take the form of a hydraulic or
pneumatic pushing device (not shown) which can be used
to engage each load 24 with a platen to push the load
into the wrapping area. However, the conveyor
embddiment is preferred and the belts of the conveyor
of the present invention are preferably textured so
that they have a high coefficient of friction.
. The particular arrangement of the conveyors
set forth in Figures 1 and 2 lends itself to random
variation of total load size in all three dimensions.
It is apparent however that other configurations could
be cor,structed which would be advantageous for specific
products. Thus, the conveyance of twelve-packs or
six-packs of cans or bottles could be handled by a
horizontal conveyor with guide conveyors on each side.
The conveyor belt 26 as seen in Figure 1 is
mounted on rollers 29 which are rotatably journalled by
suitable bearing means in brackets which are secured to
the frame support 28. The infeed conveyor 32 carries
the loads 24 onto a wrapping station 41 comprising film
dispensin apparatus 36, and wrapping conveyor assembly
34.
The preferred embodiment and best mode of the
invention comprises a frame 42 on which a steel "donut"
or ring-shaped film support member 44 is rotatably
;
. 20
' 124151~38
mounted and supported on three planes by yuide rollers
46. If desired, the film support member can be
constructed of aluminum. A plurality of guide rollers
46 project inward from the frame 42 on arms 47 and
mounting plates 48 to engage the ring-shaped member so
that it can be driven in a predetermined path. A
friction drive wheel 49 is positioned adjacent the ring
member 44 at its base and engages the member 44 to
rotate the member 44 within the guide wheel rolling
area. The friction drive wheel 49 is driven by a motor
50 having a shaft which is suitably connected with a
drive reducer 52. A material roll dispensing shaft 54
is rotatably secured to the ring member 44 for rotation
on its axis and is adapted to receive and hold a roll
of film raterial 56.
! ~.n important aspect of film wrapping
apparatus performance is that the elongation and
containme-t force exerted by any one layer of film
applied across any given side of a load is not
influenced by the characteristics of the same layer of
film wrapped to either a prior side or a subsequent
side of the load. Load edges are barriers preventing
film slippage which would otherwise alter film
elongation and containment force. In other words, film
elongation and containment force are locked in for a
given load side when the film encounters the edge at
the end of the side. thus, it is advantageous to
I;:
21
.. ...
12a~1588
increase the containment force and elongation just
before the corner is encountered, in order to minimize
wrapping force fluctuation and minimize the risX of
film destruction due to excessive force at any other
point in the wrap cycle.
It has been found that the prior art supply
systems lock in elongation and containment force at a
minimum value when each load edge is encountered. A
schematio representation of film demand rate at load
edges is shown in Figures 7 through 9 in which a
pre-stretch mechanism 70 is rotated in the direction
indicated by the arrow D around a center point Y at a
constant angular velocity to wrap a representative
rectangular load 2~. In Figure 7, the film web 5B has
just completed wrapping a long side of the load and has
encountered corner X. At this print the film web 58
passes on a straight line from pre-stretch mechanism 70
across the long face of the load. The line of film web
58 therefore forms a right angle with the line segment
A extending from the rotation center Y to the tangent
point T. At this instant, the rate of demand for film
web by the load 24 during wrapping can be computed by
treating the line segment A as the effective wrapping
radius of a circle J to which film 58 is tangent at
point T. It can readily be appreciated that the rate
of demand for film will increase as the effective
wrapping radius increases, under constant angular
22
1241~38 i
rotation of the pre-stretch mechanism 70.
Turning to Figure 8, subsequent rotation of
the pre-stretch mechanism 70 has reached the point of
maximum demand rate. The tangent point T is now
equivalent to the corner X, and the line segment B from
the corner X to the rotation center Y defines the
effective wrapping radius of a circle X. It can
readily be appreciated that the radius B is much longer
than the radius A, so that the film demand rate in
Figure 8 is much greater than the film demand rate in
Figure 7.
Turning to Figure 9, further rotation of the
pre-stretch mechanism 70 about the load has completed
the wrapping of the short side and encountered the
corner X1 subsequent to the corner X. The film web 58
no lies along the short side of the load, and the line
segment C from the rotation center Y to the tangent
point T defines the effective wrapping radius of a
circle L. It can clearly be seen that the radius C is
shorter than the prior radius B, so that the linear
film demand rate at this stage in wrapping the load is
less than that in Figure 8.
To summarize, it can be appreciated that film
web is demanded by the lOâd at a rate which varies but
is always at a minimum when a side is completely
wrapped and a corner is encountered. This swing from
minimum to maximum and back occurs once for each load
1241588
side, or four times per revolution for a load of
rectangular cross-section. If film web 58 is dispensed
from pre-stretch mechanism 70 at a constant rate, the
net film web acceleration and force will follow the
same pattern of vaxiation as the demand rate. This is
illustrated in Figure 5, in which a curve 190 shows the
varying wrapping force experienced by the load as well
as the film web between the load and the downstream
roller of a typical prior art pre-stretch system. Each
minimum point 196 of the curve 190 occurs precisely
when a corner is wrapped at the completion of wrapping
a side of a load. Each maximum point 198 of curve 190
occurs after the minimum point 196 occurs and before
the film web characteristics are locked in for the side
when a subsequent corner is encountered. Thus, it can
be appreciated that the final level of force 196 is
significantly less than the maximum force level 198,
during the prior art wrapping of any side of the load.
Turning now to Figure 6, a general
stress-strain curve 140 is shown which illustrates the
relationship between elongation and force for a
generalized film web composition. The curve region
indicated at 141 is generally known as the elastic
limit or yield point for the material. If, starting
with no elongation, the material is stretched by a
force which is sufficient to elongate the material no
further than the region indicated at 141, then when the
24
l2a~1 S88
force is removed the material will return along the
same curve 140 back to zero elongation at zero force.
However, if force is exerted to carry the elongation of
the film Deb beyond the region indicated at 141, such
as to the point indicated at 148, then the film web has
exceeded its elastic limit and reaches elongation point
248. It will remain permanently elongated to some
extent depending upon the subsequent pattern of force
applied. If the subsequent force is reduced, then
elongation will recover along a curve such as that
shown at 150, reaching finally a point 160 where
permanent elongation is exhibited without any force
whatsoever. It can be appreciated that the point 160
is to be avoiaed in film wrapping because this
represents zero containment force experienced by the
load. At such a point, then, the wrap sits loosely on
the load and subsequent vibration or motion can cause
contained units to spill out of the wrap.
The point 148 in Figure 6 is reached at each
maximum point 198 of the curve of Figure 5. At these
points, the force experienced by the load and the web
is at a level indicated at point 194 and film
elongation is at point 248. When the wrap of the side
is completed, however, the force is reduced to the
minimum level 192, which corresponds to the point 162
on curve 150 of Figure 6 and elongation level 262.
Thus, in the prior art constant-speed pre-stretch
:~5
lZ~lS88
systems, maximum containment force to the load is
forfeited. Any reduction in load circumference after
wrapping, such as is commonly experienced due to
settling, allows further reduction from elongation
level 262 ultimately to the point 160, where no
containment force is exerted. This point can be
reached with a relatively modest circumference
reduction from point 262, typically on the order of ten
percent.
In contrast, the preferred embodiment of the
present invention advantageously exerts a wrapping
force to a load as well as on the film web between the
load anc the pre-stretch mechanism which approaches
curve 300 illustrated in Figure lO, which is a flat
line. Thus, there is reduced swing between minimum and
maximum points in the force curve; and the force curve
can easily be elevated to lock in elongation and force
to the load at a point 148 on curve 140 of Figure 6
above the elastic limit region 141. It can be
appreciated that, for a load wrapped with the present
invention, extreme load circumference reduction would
have to occur before containment force were relaxed to
the point 160 illustrated in Figure 6. If the force of
the prior art mechanism as illustrated in Figure 5 were
merely raised so that both the maxima 198 and the
minima 196 were higher, there is a substantial risk
that the maxima 198 will exceed the force point at
26
12a~1588
which film destruction occurs. However, the
performance of the present invention elevates and
flattens the load force curve so that the force to the
load closely approaches the film destruction point
without any risk of exceeding it.
Toe force curve can also be easily depressed
to wrap delicate loads at low wrapping force without
risk of a variation eliminating containment force
completely.
Typical films which can be used in the
stretch wrapping apparatus are EVA copolymer films with
a high EVA content such as the films manufactured by
Consolidated Thermoplastics "RS-50", Bemis
"Super-Tough~, and PPD "Stay-Tight" films. PVC films
such as Borden Resinite "PS-26" can be used in the
invention along with premium films such as Mobil-X,
Presto premium and St. Regis which utilize a low
pressure polymerization process resin manufactured by
Union Carbide and Dow Chemical Company. This resin,
called linear low density polyethylene, has
significantly different stretch characteristics than
previous stretch films. These characteristics allow
the film to withstand the high stress of extreme
elongation without tearing during wrapping of the load.
It should be noted that film, film material
and film web are used interchangeably throughout the
specification.
.
; 27
lZ415B8
Turning to Figures 1 through 3, supply speed
control mechanism 90 comprises a pulley frame 39
parallel to ring member 44 fixed to frame 42, and a
plurality of double-sheave pulleys 62 rotably mounted
on shafts 63 journalled to frame 39. The frame 39
comprises horizontal members 172 defining lengthwise
slots 173, and vertical members 174 defining lengthwise
slots 175. Bolts 176 are placed through slots 173 and
175 to adjustably retain members 172 and 174 in a
particular orientation as will be set forth more fully
below. Shafts 63 may be threaded at a frame end and
locked with threaded nuts into a particular spacing in
slots 174. The shafts 63 are placed so that they
define corners of a polvgon having an aspect ratio
equal to that of a load cross-section. The term
"aspect ratio eaual" here means idéntical length ratios
of adjacent sides and identical edge angles
therebetween. Two polygons having equal side ratios
and equal edge angles are said to have identical aspect
ratios even though one may enclose greater area than
another. It will be appreciated that the illustrated
form of frame 39 permits easy adjustment to accomodate
variation in load cross-section. Although four pulleys
62 and a rectangular frame 39 are shown in the
drawings, this number is exemplary only and any
appropriate number of pulleys and sides may be
utilized. A power belt 64 passes around an outer
~8
lZ~S88
sheave 65 of each pulley 62, and a drive belt 66 passes
around an inner sheave 67 of each pulley 62. selts 64
and 66 may comprise chains, belts or other well-known
equivalents. If chains are utilized then the sheaves
are replaced by coaxial gears.
A power pulley 68 mounted on power axle 61
across ring member 44 engages belt 64 so that rotation
of ring member 44 relative to belt 64 causes pulley 68
and axle 61 to rotate in an opposite direction at a
speed which varies in each revolution of ring member 44
due to passage of belt 64 around pulleys 62. Drive
belt 66 also engages drive pulley 78 mounted to a
rotating output shaft of drive motor 81, so that belt
64 is driven by motor 81 and the speed of motor 81 may
be adjusted to increase or decrease the rate of
relative rotation between belt 6,4 and rins member 44
without affecting the rotation rate of ring member 44
relative to the load.
The film web is drawn from roll 56 through a
pre-stretching or elongation mechanism 70 and is tucked
or fastened underneath or held adjacent the load. The
pre-stretching mechanism 70 which is best seen in
Figure 2, comprises connected roller members 72 and 74
which are rotatably mounted respectively on shafts 73
and 75 which are in turn journalled to a housing 76.
The housing 76 is mounted to and across the plane of
the ring. member 44. Gears 77 and 79 are mounted
29
~241588
respectively to shafts 73 and 75, and mesh together and
are driven by the supply speed control mechanism 90 as
the film web engages the rubber roller surfaces. The
film web passes first across the upstream roller 72 and
then across the downstream roller 74 as it is pulled
from film roll 56 to the load 24, and the gears 77 and
79 operate as an elongation control to rotate
downstream roller 74 faster than the upstream roller
72, causing the film to be accelerated and stretched in
a narrow space 80 between the two rollers. The ratio
of the gear 77 to the gear 79 preferably ranges from
3:2 to 4:1, so that downstream roller 74 rotates faster
than upstream roller 72 by a ratio ranging from 3:2 to
4:1. While a two-roller elongation system is
preferred, it is an obvious modification to utilize any
number of rollers therein, including a single roller
pulling against a restrained film roll.
Film roll 56 can be urged against upstream
roller 72 in any well-known conventional manner such as
by a coil spring (not shown), which maintains friction
of upstream roller 72 and film roll 56 as film payout
reduces the diameter of film roll 56. Contact of
roller 72 and roll 56 prevents uncontrolled payout of
film Deb due to momentum of film roll 56 upon
deceleration of roller 72 during normal operation.
Alternatively a pivoting collar 83 may be
placed around upstream roller shaft 73, and a
~Z4~5~38
counterweight 85 and contact frame 84 may be mounted at
angles to the collar 83. At an end of frame 84
opposite the collar 83, a contact roller shaft 51 is
rotatably journalled to frame 84. Contact roller 57 is
mounted to an end of shaft 51 adjacent roll 56 for
engagement with roll 56. Contact roller pulley 53 is
mounted to an end of shaft 51 opposite roller 57. An
upstream pulley 55 is mounted to shaft 73. Pulleys 53
and 55 are engaged by pulley belt 59, and the ratio of
pulley sizes and the circumference of roller 57 are
chosen such that the linear surface speed of roller 57
is slightly less than the linear speed of upstream
roller 72. A coil spring 86 is coupled to frame 84 and
housing 76 so as to constan.ly urge contact roller 57
against the surface of film roll 56 which decreases in
radius ac film web 5& is paid out during wrapping.
Spring 86 forces roller 57 to maintain contact with the
surface of roller 56 during rotation of ring member 44.
Counterweight 85 exerts leverage on frame 84 to
compensate for the effect of the force of gravity on
roller 57 as ring member 44 rotates. Therefore,
friction between roller 57 and film roll 56 will be
maintained, and pay out speed of film web 58 from roll
56 will accelerate and decelerate precisely to match
speed changes of the elongation system.
Shaft 61 extends through housing 76 a
distance at least equal to the distance between rotary
12415~3
ring 44 and pulleys 62 for interaction with supply
speed control means 90. A power pulley 68 is mounted
on the end of shaft 61 so as to engage belt 64 as ring
member 44 rotates. Contact of pulley 68 and belt 64
is maintained throughout the revolution of ring member
44, Rand tension on belt 64 is maintained by pressure of
tensioner roller 69, which is spring-loaded in any
wellknown conventional manner. Belts 64 and 66 are
preferably made of rubber or another material with
resilience and a high coefficient of friction against
the material of pulleys 62 and 68, which is preferably
metal.
An end of shaft 61 opposite that to which
pulley 68 is mounted extends beyond the housing 76, and
transfer pulley 21 is mounted thereto. An end of
downstream roller shaft 75 likewise extends beyond the
side of housing 76 where pulley 21 is mounted, and
downstream roller pulley 25 is mounted to it. Transfer
belt 23 engages pulleys 21 and 25, so that downstream
roller 74 is driven to rotate at a speed proportional
to that of pulley 68 via shaft 61, pulley 21, belt 23
and pulley 25.
Reduced variation in force to the load is
achieved because the film supply rate from the
pre-stretch mechanism 70 varies precisely as the film
demand rate to the load varies, so that the net
acceleration difference between the rates is constant.
32
1 2~1S88
The film supply rate is controlled by the rate of
passage of belt 64 across pulley 68, which varies as
belt 64 encounters each pulley corresponding to a load
corner. Because the load 24 and the pulleys 62 share a
common aspect ratio, the speed of belt 64 varies
precisely as shown in Figure 5 for the same reasons,
illustrated in figures 7 through 9, that the film
demand rate varies along the curve show,n in Figure 5.
That is, the portion of belt 64 trailing from pulley 68
is demanded or pulled away by pulleys 62 at a rate
which varies according to the changing effective
wrapping radius around pulleys 62, just as the film is
pulled away from pre-stretch mechanism 70 to the load
24 at a rate which varies according to the changing
effective wrapping radius around the load. As
illustrated, the film supply Nate changes from a
minimum to a maximum and back four times per dispenser
revolution about a load of rectangular cross-section,
but other configurations of pulleys 62 can be used with
equal effectiveness for loads of other cross-sectional
shapes. Thus the pulleys 62 and belt 64 of supply
speed control means 90 serve as a predetermined model
of the load' 24 which controls the output rate of
pre-stretch mechanism 70 without reliance on feedback
through film web between roller 74 and the load. So
long as the angles and ratios of side lengths remain
equal for the pulley 62 area and the load
~241S81~
cross-section, the demand rate for belt 64 will follow
the load demand rate for film 58.
An alternate embodiment of the supply speed
control mechanism designated 95 is illustrated in
figures 12 through 14. The belt 65, motor 81, pulley
78, pulley 68, pulley 63, frame 39, pulleys 6~, and
tension idler 69 are omitted. In this embodiment ring
or track 60 is configured as a solid surface having a
series of consecutive areas of greater or lesser
radius, which may be considered as cam bumps or
depressions respectively. The number and spacing of
depressions 97 corresponds to the number and spacings
of load vertices for purposes which will become
apparent below.
In the alternate embodiment a power column
182 is mounted to power axle collar 181. The column
182 extends beyond the housing 76, and a second collar
183 is mounted at an end of column 182 remote from
collar 181. An axle 184 passes through collar 183 and
extends to the plane of ring 60. At the end of axle
184 adjacent ring 60, a contact roller 185 is mounted
to axle 184. A tensioned coil spring 189 extends from
housing 76 to collar 183 in order to urge roller 185
against the surface of ring 60 during rotation of ring
44. At an end of axle 184 opposite the contact roller
185, pulley 186 is mounted to the axle 184. A second
pulley 187 is mounted to power axle 61, and a belt 188
engages pulleys 186 and 187.
34
lZ41588
As ring 44 rotates at a constant speed,
contact roller 185 is driven to rotate by friction
against ring 60. The rotation of contact roller 185 in
turn rotates axle 184, pulley 186, belt 188, pulley 187
and power axle 61. Power axle 61 acts to drive
elongation and dispensation of film web 58 as described
abov;e or the preferred embodiment. However, the rate
of rotation of contact roller 185 increases across each
raised portion of ring 60 and decreases in each
depression of ring 60, with the column 182 acting as a
cam follower by pivoting about power axle 61 to
maintain contact between ring 60 and contact roller
185.
Each depression 97 of ring 60 is positioned
so as to reduce contact roller 185 speed and thereby
minimize the supply speed V1 of film web across the
downstream roller 74 precisely when a corresponding
edge 89 of the load is approached by the film web 58.
The depth of each depression 97 is sufficient to
maintain the difference between the takeup speed V2 and
the supply speed Vl to minimize the force and
elongation variations as each load edge is encountered
by film web 58. Following the edge, the roller 185
encounters a plateau on ring 60, with a corresponding
greater linear circumferential distance per unit of
angular rotation of ring 44. The linear speed of
roller 185 will increase, correspondingly increasing
12~15S8
the supply speed Vl of film web 58 leaving the downstream
roller 74. Thus the alternate embodiment achieves the desired
effect of uniform acceleration, elongation and force at each
load edge to lock in containment on each side of the load. As
5 illustrated, the alternate embodiment decelerates and
accelerates the speed Vl of film web 58 four times per
revolution of the system about a load of rectangular
cross-section, but other patterns of depressions 97 could be
used with equal effectiveness for loads of other
cross-sections. Thus the ring 60 comprises a predetermined
model of the load which controls the output rate of pre-stretch
mechanism 70 without reliance on feedback through film web
between roller 74 and the load.
The wrapping conveyor assembly 34 as best seen in
Figure 14 comprises two stacked conveyors 92 and 94. As more
fully described in U.S. Patent No. 4,317,322, assigned to
Lantech, Inc., these conveyors comprise driven endless belts 96
and 98 mounted on a plurality of rollers 100. The rollers are
supported by plates 102 secured in turn to a frame member (not
shown) which holds the rollers in a rotatable position. The
upper surface of endless belt 96 is rotated in a direction shown
by the arrow A and the lower surface of belt 96 frictionally
engages the top surface of endless belt 98
-36-
lo
1241588
to drive it at the same speed. Belt 96 is driven by a
motor assembly 104 which is connected by linkage 106 in
the form of chains or belts to drive the conveyors.
The upper belt segment of conveyor 92 travels
downstream with the lower segment travelling upstream.
The upper belt segment of conveyor 94 travels upstream
whilé the lower segment travels downr-tream. The upper
and/or lower conveyor can comprise multiple belts.
This construction allows a web of film to be
wrapped around a load 24 which was carried from the
infeed conveyor 32 onto the wrapping station 41. The
stretched wrap of web is wrapped around the conveyor
assembly 34 and the load with both the load and wrap
being carried by the conveyor assembly in the same
direction. In the full web, spiral and banding modes,
the convevor assembly and wrapping ring is stopped, the
clamp apparatus 88 clamps the film web and the cutter
mechanism 110 severs the film web. The conveyor
assembly 34 is activated carrying the load and the wrap
downstream to a take-off conveyor 20. When the load
encounters the take-off conveyor 20 as shown in Figure
14, the elongated stretched web coming off of the end
of the conveyor assembly assumes its memory position M
against the load in the space between the conveyor
assembly 34 and take-off conveyor 20, allowing the
contained load covered by stretched wrap to be carried
away.
37
1241S3~8 `
As shown in Figures 11 and 15, the cutting
mechanism 110 used in the preferred embodiment of the
invention comprises a driven pivoted standard which is
adapted to project upward to engage the film web
between clamping apparatus 88 and the load 24. The
cutting mechanism 110 comprises a support standard 112
which is pivotally mounted at 114 to a base member 116.
The base member 116 can either be a part of frame 42 or
be secured to frame 42. A pneumatic lifting cylinder
118 has one end mounted by a suitable ear or bracket
attachment to the base member 116 with the end of its
piston rod 119 attached to the support standard 112 by
suitable means such as a yoke member 121. Upon
activation of the pneumatic cylinder, the upright
standard 112 is transported in an arcuate path into the
film web 58. Mounted to the s,upport standard is a
cutting assembly 120 comprising a support plate 113, a
pneumatic cylinder 122 mounted to the support plate
113, and a cutting blade assembly 123 mounted to the
piston rod 126 of cylinder 122. A brush 128 is
vertically mounted on the support plate to brush down
the trailing edge of the web against the conveyor
assembly. A bumper member 130 is positioned in front
of brush 128 to protect the brush base from initial
contact with the film web and conveyor assembly. Upon
appropriate activation, as for example a predetermined
number of revolutions of the ring member, which is
38
12~1588
sensed by an appropriate sensor device, the cutting
mechanism 110 is propelled upward so that the cutting
assembly 120 engages the film web. The blade assembly
123 subsequently severs the film web from the load. If
desired, the cylinder 118 can be activated after
cutting to propel the standard 112 forward a
predetermined distance causing the brush 128 to engage
the remainder of the trailing edge of the film web and
wipe it against an underlying film layer.
The conveyor assembly 34 leads from the
infeed conveyor 32 to a take-off conveyor 20 which is
constructed like the infeed conveyor and runs at the
same speed as the infeed conveyor. In order to control
both conveyors at the same rate of speed, a suitable
mechanical means (not shown) is set up to make the
drive of both the infeed conveyor and the take-off
conveyor equal to the reduction gearing assembly of the
drive motor. Thus, if the motor slows down or speeds
up to drive the wrapping mechanism at different speeds,
the infeed and take-off conveyors are simultaneously
speeded up or slowed down so that the load is moved to
conveyor assembly 34 and taken away from the conveyor
assembly 34 at consistent relative speed.
In an alternate mode of wrapping,
continuously wrapped loads are taken off of the
apparatus and are severed into separate loads away from
the apparatus. In this embodiment, the take-off
39
1~415~38
conveyor 220 carries the continuously spiral wrapped
loads as shown in Figure 9 connected together by the
film overwrap from the wrapping station. The take-off
conveyor assembly 220 carries the spirally wrapped
bundle onto cutting conveyor 222.
The wrapped spiral bundle 224 as seen in
Figure 4 is severed into individual packages by a
guillotine-like cutting apparatus 225 comprising a
frame 227 and a cutter mechanism 22~ slideably mounted
to the frame. The cutter mechanism 229 consists of a
bow frame 230 strung with nichrome wire 232 which is
electrically connected to a source of energy. The
resistance of the wire causes sufficient heat so that
when the wire is reciprocated between the encapsulated
loads 224 to cut them apart, the film material is
simultaneously bonded to the edges so that the film
will not unravel in shipment. As the continuously-
wrapped bundle 224 enters the cutting area, a sensor
131 projects a light source through the transparent
film in a space S between the individual loads against
a reflector 133 to generate an electrical signal
commanding the cutter blade drive circuitry to activate
a pneumatic cylinder 236. Upon activation, the hot
cutter wire 232 is driven through the film to sever the
load 124 from the wrapped spiral bundle 224. Such
sensing apparatus are well known in the art, and any
standard circuit can be used to cause the pneumatic
lZ4~58~3
cylinder 236 to be activated when the sensor senses a
space between loads 124. Likewise, a limit switch,
contact switch, pressure sensitive switch or other
suitable means can be used to activate the cylinder
236.
The wire is heated by connection to a current
source of about nine volts which heats the wire
sufficiently so that the edges of the film are bonded
to form a holding edge. The severed edge stretches
back to its original memory shape to form the holding
shape. The spiral bundle advances and the next spacing
S between the loads 124 is sensed by the light sensor
131.
Other cutting apparatus can be used in place
of the heating cutting wire, namely a knife blade with
sawtooth edges secured to the frame in place of the
cutter wire. When the blade is driven against the
film, the cutting edge strikes the wrapping material
substantially causing the wrapping material to shear.
The cutting is done while the wrapped bundle is being
transported by the conveyors.
In the operation of the preferred embodiment
of the inventive wrapping apparatus, the predetermined
load model is first configured by positioning
horizontal members 172, vertical members 174 and
pulleys 62 to define a polygon having an aspect ratio
equal to that of a cross-section of the load. In the
~Z41588
alternative embodiment, a ring 60 is configured with
depressions positioned to decelerate downstream roller
74 as the film web approaches each edge of the load.
The full web, spiral web, and banding modes of
operation are operated in a substantially identical
manner. In these modes, feed conveyor 32 brings the
load 24 onto the wrapping conveyor assembly 34 which
then carries the load to a predetermined wrap position
within the film dispensing path and the conveyor
assembly stops, leaving the load in a stationary
position. The leading edge 57 of the film web 58 is
held in clamping assembly 88 located beneath the
conveyor assembly 34 as is best seen in Figure 3.
Rotation of ring 44 about the load is then begun.
As ring 44 rotates, the contact of belt 64
with pulley 68 forces pulleys 68 and 59 to rotate at a
speed which varies as belt 64 changes position with
respect to pulleys 62. Pulley 59 rotates belt 55,
which in turn drives pulley 57 and downstream roller 74
on shaft 75. Film is drawn from film roll 56 across
the surface of roller 74 to encircle the load. Thus,
the rotation speed of roller 74 is independent of
changes in the linear speed of the film web being
wrapped on the load. Through gears 79 and 77, the
rotation speed of upstream roller 72 is held to a
constant ratio of that of downstream roller 74, so that
when upstream roller 72 contacts film roll 56 and
42
lZ4151~8
engages the film web, the film web is stretched during
passage between the rollers due to the speed
differential therebetween. Thus, the wrapping force
changes experienced by the load in its effort to draw
film across upstream roller 72 and downstream roller 74
are reduced, and the variations in speed of the film
web due to edge passage on the load do not change
wrapping force on the film.
After at least one wrap has been made around
the load and the clamp assembly, the film edge which is
held by the film web wrap may be released. If the wrap
is for a full web load as shown in Figure 16 or a
banded load as shown in Figure 17, a plurality of
overlying layers of film are wrapped around the load
and the conveyor assembly 14. In the spiral wrap mode
as shown in Figure 18, a plural, number of wraps are
wrapped around the downstream end of the load as shown
in phantom in Figure 18 in the same manner as the
banding in Figure 17 and the conveyor assembly is
activated carrying the load downstream to a take-off
conveyor so that a spiral wrap is formed around the
load. When the load reaches a station where the end is
sensed by a feeler gauge, light sensing means, pressure
sensitive switch or other suitable sensing mechanism,
both the take-off conveyor and wrapping conveyor
assembly stop and a second band is placed around the
upstream end of the load in the same manner as if a
.
43
lZ~L588
band or full web wrap were being wrapped around the
load. It should be noted that there is a space between
the conveyor assembly 34 and the take-off conveyor 20
allowing the stretched film web to be discharged from
the conveyor assembly and assume its memory position M
around the load.
The end of the wrap cycle is determined in
the present invention by a proximity switch 99 located
a short distance away from ring 44 which senses a bent
metal plate 45 secured to the ring. The proximity
switch is electrically connected to a counter which is
activated to determine each revolution of wrap. The
particular counter which is utilized is an Eagle
counter, Model D2100-AG, which is an off-the-shelf
standard apparatus. When the counter has indicated a
predetermined number of revolutiohs determined by the
type of wrap and the load desired to be wrapped, the
counter activates a switch which stops the take-off
conveyor and wrapping conveyor assembly for cutting of
the film web. The activation of the fluid cylinders to
fire in a predetermined order and extend a
predetermined distance is well known in the art and can
be accomplished by common fluid circuitry. When the
cutter mechanism is activated, the cutter standard and
head is directed upward and abuts the film carryinq the
film to the middle of the load. It should be noted
that the dispensiny roll 56 on ring 44 in the stop
44
1241588
position is located underneath the load and is
substantially perpendicular to the axis ox the load.
When the film roll has been positioned in this manner,
the web itself has engaged either the load edge or
conveyor assembly edge and is angled from the edge down
towards the roll positioned on the ring. The cutter
mechanism 110 when driven upward by the pneumatic
cylinder 118 engages the angled film web and carries it
into substantial conformance with a perpendicular line
drawn from the center axis of the conveyor assembly
with the brush 128 brushing the film down over an
underlying film layer wrapped around the conveyor
assembly as is shown in Figure 11. The clamping
mechanism 82 is then rotated to clamp and hold the film
web between the cutter head 120 and the dispensing roll
56. The pr.eumatic cylinder 122 of the cutting head is
then fired, driving a sawtooth cutter blade 221 into
the film web 58 to sever the film web. When the film
web is severed, a small portion of the trailing edge is
left hanging free from the wrap. If desired, this film
edge may be wiped onto the load by firing the cutter
standard cvlinder 118 a second time so that the
standard moves a short distance further on carrying the
rush on to wipe the remnant edge against the wrap.
The cutter standard is then withdrawn away from the
load into a rest position as shown in phantom in Figure
11 for the next cutting operation and the conveyors are
12415~
activated to carry the wrapped load away from the
wrapping station and a new load into the wrapping
station.
In the continuous wrapping operation, the
previously described cutter mechanism is not used and
the loads are continuously carried along the wrapping
conveyor assembly onto a take-off conveyor which spaces
the loads for severing downstream. The loads are then
severed between the spaced film areas as previously
discussed and taken away to another transport area.
It can readily be appreciated that the
present inventive system provides the capability to
wrap loads with minimal variation in wrapping force and
levels of elongation despite substantial variation in
load demand for film. As a result, the user can elect
to apply maximum force for high containment without
risk of film failure, or to apply minimum force for
delicate loads without risk of load failure or wrap
loosening. Also, the system continues to operate at
normal speed when film web holes develop, so that web
tension changes do not cause holes to enlarge. All of
these characteristics contribute to the high
reliability, throughput and economy of the present
inventive system.
In the foregoing description, the invention
has been described with reference to a particular
preferred embodiment, although it is to ye understood
46
1241S88
that the specific details shown are merely
illustrative, and the invention may be carried out in
other ways without departing from the true spirit and
scopé of the following claims.
47
