Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
35()
FIELD OF INVENTION
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This invention relates to apparatus for wrapping pallet
loads with a membrane adapted to contain the load during
shipping and transport, and more particularly relates to a
method and apparatus for wrapping pallet loads including a
planetary gear assembly responsive to variations in the
force drawing the membrane from the said apparatus so as
to maintain said drawing force at a preselected level.
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Background to the Invention
Various methods and apparatus for packaging and shipping
goods have heretofore been proposed and implemented. For
example, multiple unit products can be stacked in boxes
for shipment. Furthermore various boxes or articles may
be unltized in a pallet load having a rectangular, square
or irregular cross section for shipment by wrapping
20 various boxes or articles with a web of stretched plastic
film.
Such arrangements generally include a mechanism which
dispenses a web of plastic film as it rotates about the
pallet load, Such plastic film may be prestretched
between rollers prior to being wrapped around the pallet
load~
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Generally speaking, the p1astic film which is dispensed
about said pallet load encounters different load demands
or tension as it rotates about the pallet load edges.
More particularly, as the plastic film rounds the corner
or edge of a pallet load the plastic film must be supplied
at a faster speed in order to maintain a constant tension
in the plastic film. Various apparatus and method have
heretofore been proposed to attempt to maintain a
relativiely constant tension in the plastic film.
1 0
For example, United States Patent No. 4,676,048 is
directed towards apparatus and process for applying
stretchable plastic film to loads using a prestretch
mechanism which is driven and controlled lndependently of
the web tension to minimize the variation in the force
exerted on the film web at load edges by varying the film
web supply speed.
1: ~
; ~ Moreover, United States Patent No. 4,628,667 discloses a
20 wrapplng machine for wrapping a load in a unitary
packaging, said wrapping machine including a mechanism
. .
;~ controlling the operation of a variable speed DC driving
motor so as to rotate a support at a first speed during a
- first portion of the rotatable movement of the support and
~-~then at a second slower speed during a subsequent portion
of the rotatable movement of the support so as to
gradually stop the rotation of the support and avoid
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damage to either the load or stretchable material being
used for wrapping the load.
Moreover, United States Patent No. 4,524,568 teaches a
rotatable film wrapping apparatus for wrapping a load on a
conveyor with an overwrap of stretched plastic film web
having a film web prestretching mechanism which is
provlded with a constant torque by a power assistance
mechanism so that the force on the film to the load can be
substantially reduced while allowing the prestretch drive
to speed up and slow down according to the film demand
from corner or changing load.
Furthermore United States Patent No. 4,497,159 discloses
apparatus for applying stretchable plastic fil~ to loads
using two frictionally connected rollers which are held
together and driven by the film web at different speeds to
,
elongate plastic film beyond its yield point.
:
20~Aiso United States Patent No. 4,590,746 discloses a
tension maintaining device which applies a biasing force
against a tension roller over which stretchable material
passes so as to maintain a constant tension on the
stretchable material.
Each of th~e prior art devlces generally disclose
complicated struciure. Moreover, such prior art devices
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have a relatively slow response time wherein there is a
lag between the time when a greater supply of plastic web
is required and the time that it is actually supplied so
that in many cases the plastic film breaks due to the
increased tension imparted thereon.
It is an object of this invetion to provide apparatus and
a method for dispensing plastic film which is simple to
construct and capable of maintaining a preselected tension
10 in the film web as it rotates about the pallet load.
:Summary Of The Invention
The broadest aspect of this invention relates to apparatus
for dispensing a web of material including; at least one
roller means adapted to engage said web; structure for
rotationally driving said roller means when said web is
drawn from said roller means at a preselected force; and
20 planetary gear assembly including a rotatable ring gear
: and outpu~t gear, said output gear engageable with said
driving structure; a motor for rotating said ring gear and
said~ output gear of sald planetary gear; and a brake
adapted to variably bear against: said ring gear in
response to variations in said force drawing said web from
:~said roller means so as to vary the relative rotation of
:
~ : said ring gear and said output gear to vary the rate of
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rotatably driving said roller means in response to
variations in said force drawing said web from said roller
means and maintain said drawing force at said preselected
level.
It is another aspect of this invention wherein said roller
means comprises a first and second roller adapted to
stretch said material a predetermined amount.
~ .
It is another aspect o~ this invention to provide a
carriage adapted for rotational movement about a pallet
load for dispensing a web of stretchable film about said
pallet load comprising; at least one roller means adapted
to dispense said web of stretchable film; structure for
rotationally driving said roller means when said
stretchable film is pulled from said roller means at a
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: preselected tension during rotatlon of said carriage about
said pallet load so as to wrap said stretchable film about
said load; and planetary gear means including a rotatable
20 ring gear and a driving sprocket, said driving- sprocket
engageable: with said drlving structure; a motor for
rotating sai~d ring gear and said driving sprocket of said
planetary gear means; a brake adapted to variably bear
against said~ ring gear in response to variations in said
tension when said fllm is pulled from said roller means so
~:: as to vary the relative rotation of said ring gear and
~ said driving sprocket to vary the rate of rotatably
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driving said roller means in response to variations in
said tension and maintain said tension of said film at
said preselected level.
It is another aspect of this invention wherein said roller
means comprises first and second roller means adapted to
stretch said stretchable film a predetermined amount
during rotation of said carriage about said pallet load so
: : as to wrap said stretchable~film around said pallet load.
Yet another aspect of this invention relates to a pallet
wrapping machine for wrapping pallet loads with a
.
stretchable p1astic film comprising; a support beam
adapted for genera11y horizontal securement to a vertical
:
structure above said pallet load; an arm one end of which
:~ ~ is rota~tab1y connected; to said beam; carriage means
depending from said other end of said arm for dispensing
said stretchable plast;ic film, structure adapted to rotate
: said arm about said load; said carriage means including,
20~flrst and: second rollers, structure for rotatably driving
said first and second rollers so as to stretch said
plastic film~a:predetermined amount between said first and
: second rollers when said stretched film is drawn from said
rollers at a preselected tension as said arm rotates about
said pallet load so as to wrap said pallet load with such
stretched film, and planetary gear assembly including a
rotatable ring gear and an output gear, said output gear
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engageable with said driving structure; a motor for
rotating said ring gear and said output gear of said
planetary gear means; and a brake adapted to bear against
said ring gear in response to variations in said tension
when said film is drawn from said roller means so as to
vary the relative rotation of said ring gear and said
output gear to vary the rate of rotatably driving said
roller in response to variations in said tension and
maintain said tension of said film at said preselected
level.
A further aspect of this invention relates to a method of
wrapp1ng a pallet load wlth a web of material dispensed
from a carriage comprising the steps of: rotating said
carriage about said pallet load, dispensing said web o~
material from at least one roller when said web is pulled
from said roller at a preselected tension during rotation
, ~
; of said carriage about said pallet so as to wrap said web
about said pallet; and varying the rate of rotatably
:: :
20 driving said roller by a planetary gear assembly having a
rotatable ring gear and output gear by variably braking
: said ring gear in response to variations in the tension of
said web during rotation of said carriage about said
~: pallet load so as to vary the relative rotation of said
: ring gear and said output gear to vary the rate of
rotatably driving said first and second roller in response
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to variations in said tension and maintain the tension of
said web drawn from said roller at a preselected level.
Another aspect of this invention relates to a method of
: wrapping a pallet load with a film of stretchable material
dispensed from a carriage comprising the steps: rotating
said carriage about said pallet load,. stretching said
stretchable material a preselected amount between a first
and second roller when said stretched material is pulled
10 from said rollers at a preselected tension during rotation
of said carriage about said pallet so as to wrap said
stretched plastic film about said pallet load; and varying
the rate of rotat3bly driving said rollers by planetary
gear assembly adding a rotatable ring gear and output gear
by variably braking said ring gear in response to
; variations in the tension of said stretched material
: : during rotation of such carriage about said pallet load so
as to vary the relative rotation of said ring gear and
: said output gear to vary the rate of rotatably driving
20 said first and second roller in response to variations in
said tension and maintdin said tension of said stretched
material drawn from said rollers at said preselected
~ :: level.
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Description of the Drawin~s
These and other objects and features are illustrated and
described in the following specification to be read in
conjunction with the sheets o~ drawings in which:
Figure 1 is a cross sectional view of the pallet wrapping
apparatus.
10 Figure 2 is an exploded perspective view of the carriage
for dispensing the prestretched film.
Figure 3 is an exploded perspective view of the planetary
gear assembly.
,
Figure 4 is a top view of said pallet wrapping apparatus.
Figure 5 is an exploded view of the tension control.
?O Description of the Invention
In the Figures like numerals represent like elements.
:
A pallet wrapping machine is generally disclosed as
numeral 10 in Figure 1. The pallet wrapping machine
includes a support beam 12 adapted for generally
horizontal securement to a vertical structurè 14 above a
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pallet load 16 supported on a pallet 18. An arm 20 is
rotatably connected to the beam 12 at one end thereof.
A carriage or dispensing apparatus 22 depends from the
other end arm 20. More par$icularly, the carriage 22
depends along the leg 24 located at the other end of the
arm 20.
The support beam 12 houses a motor 26 and a gear box
10 arrangement 28. The motor 26 and gear box 28 each present
a pulley and shaft assembly 30 and 32 respectively which
are connected together by means of an endless belt 34.
':
The arm 20 presents a shaft 36. One end of the shaft 36
is fixedly secured to the arm 20 and the other end of the
; ~ shaft 36 is rotatably connected to the support bar 12.
" ~ : The gear box 28 includes an aperture 38 which fixedly
releaseably secures the other end of the shaft 36.
~,~
20 Energization of the motor 26 causes the endless belt 34 to
: act1vate gears (not shown) within the gear box 28 thereby
rotating a shaft 36 fixedly secured to the arm 20 which
:: :
causes the arm 20 to rotate about the pallet load 16.
: ;: :
The other end of the arm 20 rotates about pallet load 16
in the direction R, and a web of stretchable material or
plastic film 40 is drawn from the carriage 22 in a manner
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to be more fully particularized herein so as to wrap the
pallet load 16 with the web of stretchable material 40.
.
Furthermore the carriage or dispensing apparatus 22 is
adapted to be displaced or moved along leg 24 between
- upper and lower limits A and B respectively so as to
helically wind the stretchable material 40 about pallet
load 16 in a manner which is more fully particularized in
Canadian Patent Application filed by applicant on November
10 14th, 1986 as Application No. 523,014-4.
The apparatus 22 for dispensing a web of plastic film 40
is more fully particularized in Figure 2.
~; The apparatus or carriage 22 comprises a carriage housing
generally depicted as 42 which includes a top and bottom
portion 44 and 46, respectively. The housing 42 includes
projections 48 which are adapted to rotatably secure a
roll or web of plastic film 40.
Carriage 22 also includes a first roller 50 and a second
roller 52 which are adapted to be rotatably secured
between top and bottom portions 44 and 46 respéctively of
carraige 22. The upper ends of first and second rollers
- 50~ and 52 include a shaft 54 and 56 respectively fixedly
secured thereto. Shaft 54 and 56 are adapted to engage
first and second sprockets 58 and 60.
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Electromagnetic clutch means 62 is adapted to be
co-axially disposed between first sprocket 58 and first
roller 50, and electromagnetic clutch means 64 is adapted
to be co-axially disposed between second sprocket 60 and
second roller 52. Each electromagnPtic clutch means 62
and 64 is electrically connected (not shown) to a power
source which is adapted to activate and deactivate the
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electromagnetic clutch means 62 and 64 so as to engage and
disengage the rollers 50 and 52 from the sprockets 58 and
10 60, respectively.
More particularly when the electromagnetic clutch means 62
:
and 64 are deactivated, the web of plastic film 40 may be
easily pulled or drawn through the first and second
rollers 50 and 52 without movement or engagement with the
first:and second sprocket 58 and 60. In other words the
web of plastic material 40 may be easily drawn from the
roll of film 40 around the first roller 54 and around the
second~ roller 52 as illustrated in Figure 2; as the
20 rollers 50 and 54 freely rotate when the electromagnetic
~:: clutch means 62 and 64 are in the deactivated stage.
:
When electromagnetic clutch means 62 and 64 are
electrically activated the first and second rollers are
engaged with the first and second sprockets 58 and 60
~: ~ respectively and are adapted to be driven by drive means
:
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which include motor 62, planetary gear assembly 64, and
endless chain 66.
:
the endless chain 66 is adapted to be endlessly rotatably
driven by drive sprocket 68. As the endless chain 66 is
rotatably driven by drive sprockekt 68, the endless chain
66 is rotatably connected to first and second sprocket 58
and 60 and idler sprocket 70 causing the first and second
sprockets 58 and 60 to be rotated in the direction of
arrows F and S, respectively.
Because second sprocket 60 has a smaller diameter and
fewer teeth than first sprocket 58, second sprocket 60 and
second roller 52 has a greater revolutions per minute
(RPM) than first sprocket 58 and first roller 50.
Furthermore the cylindrical surface of first and second
rollers 50 and 52 are adapted to frictionally engage the
web~plastic film 40. As first roller S0 rotates in the
dlrection of arrow C, :the web of film 40 is fed around
first roller 50. Since second roller 52 rotates at a
higher RPM then the first roller 50, the web of plastic
film is stretched between roller 50 and 52.
As the stretched web 40 is dispensed from first and second
rollers S0 a~nd 52 the carr1age 22 is rotated around pallet
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load 16 in the direction of arrow R as best seen in Figure
4 to wrap the pallet load 16.
When the stretched web 40 rounds corner 72 of pallet 16
there is a tension build-up in the stretched web since the
arm 20 generally rotates about pallet load 16 at a
constant RPM.
, .
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: In order to maintain a relatively constant tension in the
10 stretched web 40 rotation of first and second rollers 50
and 52 must be either increased or decreased so that the
. supply of stretched film 40 is increased or decreased as
required.
:~ :
A planetary gear assembly 64 is utilized herein in order
to maintain a constant tension in the stretched film 40.
.
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An electric motor 62 is located in the region between the
top and bottom portions 44 and 46 respectively of carriage
~: ~ : 20 housing 42, and particularly in the region adjacent to top
::: portion 44.
.',~:: ~:
The top portion 44 includes an opening 74 which is
adapated to receive the driving shaft 76 of motor 62. The
motor 62 is fixedly secured to top portion 44 of carriage
42 by means~ of fasteners 78, lock washer 80 and washer 82.
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The motor 62 is adap~ed to drive roller 50 and 52 in a
manner to be more fully particularized herein.
A planetary gear assembly 64 is associated with the
driving means, namely motor 76, endless chain 66, and
sprockets 58, 60, 68 and 70.
, .
The planetary gear assembly 64 is more fully
particularized in Figure 3 and includes ring gear 74,
10 spaced first and second discs 76 and 78 which are
concentrically disposed interiorally of the ring gear 74.
One of the discs, namely disc 76, includes a driving shaft
80 which is fixedly secured to the disc 76. The driving
; ~ shaft 80 is also removably fixedly secured to driving
sprocket 68 by means of key ways 82 and key 84 (not
shown)~. The other disc 78 includes an aperture (not
shown~.
A plurallty of planetary geirs 84, 86 and 87 (not shown)
20 are symetrically disposed between disc 76 and 78 and
;~ ~ rotatably engagable with the ri~ng gear 74. The planetary
gears 849 86 and 87 are rotatably secured between disc 76
,
~ and 78 by means of bots 88.
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A sun gear 90 is rotatably driven by shaft 76 of motor 62.
The sun gear 90 is adapted to be received by the aperture
(not shown) of disc 78 and is rotatably engagable with the
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planetary gears 84, 86 and 87 so as to variably rotatably
drive the ring gear 74 and the drive sprooket 88 secured
to the disc 76 as shall be more fully particularized.
: ;
Since motor 62 is adapted to rotate at a relatively
. constant speed RPM, sun gear 90 also rotates at a
relatively constant speed or RPM. Since sun gear 90 is
rotatably engaged with planetary gears 84, 86 and 87, such
planetary gears will be driven by sun gear 90. The
:10 rotational motion.of planetary gears 84, 86 and 87 will be
transferred either to ring gear 74 or drive gear 68.
Since drive gear 68 is adapted to be engaged with endless
chain 66 which in turn is engagable with sprockets 58, 60,
70 and first and second rollers 50 and 52, there will be
; a~n inherent resistance or inertia to the rotation of drive
~ :gear 68.: Accordingly the rotational motion of planetary
" ~ gears 8~, 86 and 87 :will be transferred to the path of
least resistance namely ring gear 74. When the ring gear
20 74 is subjected to a resistance or drag force the
:rotational motion of planetary gears 84, 86 and 87 will be
differentially transferred to rotate disc 76 which is
~fixedly secured to dr~ve gear:68.
The more drag or friction that ring gear 74 is subjected
., , .~ ,.
: : ~ to,~'the' more rotational motion is transferred to drive
~gear 68. Accordingly the more drag imparted on ring gear
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74, the faster the endless chain 66 rotates which in turn
rotates first and second rollers 50 and 52 to supply the
stretched film 40 at a greater demand rate.
.
A brake or band 92 is utilized to perform the variable
rotational means of the planetary gear assembly 64.
The band 92 is adapted to substantially encircle ring gear
74. One end of band 92 is fixedly secured to the top
10 portion 44 by means of fasteners 94. The other end of the
band 92 1s displaceably connected to pivot mounting 96 by
meaos of screw 126 and threaded portion 128. The pivot
mounting 86 is also connected to a dancer bar assembly 98.
The dancer bar assembly 98 comprises top and bottom plates
100 and 102 respectively, ~and bar 104 which is adapted to
be received within aperture 106 and 108 of top and bottom
.: :.
~ ~ plates 100 and 102 respectively. The upper portion of bar
.~
~ 104 lS adapted to be received by aperture 114 of pivot
,
mounting 96. Set screws 110 fixedly secure the bar 104 to
20 the top and bottom plates 100 and 102.
The bottom plate 102 ls pivotly secured about set screw
112 which is fixedly secured to bottom portion 46 of
- ~ carriage 22 within threaded hole 114. The top plate 100
is piv`otly secured to the top portion 44 of carriage 22 by
screw ll3.
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The dancer bar assembly 98 also includes a dancer roller
116 which is adap~ed to idle or freely rotate about shaft
118 which is fixedly secured to top and bottom plates 100
and 102.
;
. Since the idle roller 120 is provided between top and
bottom portions 44 and 46 respectively, the idler roller
120 is secured to be freely rotatable between top and
bottom portions 44 and 46 by means of screws 122 and set
10 screw 124.
The web of film 40 is adapted to be inserted between
dancer roller 116 and bar 104 and to rotatably engag,e the
~-:: cylindrical surface of dancer roller 116 as best
illustrated in Figure 2.
The web 40 is also adapted to rotatably engage the
cylindrical surface of; idler roller 120. The operation of
:; the dispensing apparatus 22 shall now be described by
~ 20 reference to Figure 2.
:': :
~ When the stretched material 40 is pulled from the carriage
': ~ :22 at a ~preselected tension as shall be more fully
' ~ : particularized herein, the dancer roller 116 is pulled by
: the web 40 in a dir~ection illustrated by arrow P which
:~ :
: ~ ~auses the pivot mount1ng and top and bottom plates to
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pivot about screws 112 and 113 in the direction of
arrow Q.
When the pivot mouoting 96 pivots about screws 113 in the
; direction of arrow Q the diameter of brake 92 becomes
smaller and adapted to frictional1y engage ring gear 74.
.,,
Accordingly as the web of plastic material 40 is pulled at
a tension greater than a preselected tension sufficient to
10 cause the brake 92 to frictionally engage the ring gear 74
so as to differentially transfer rotational energy or
motion to drive gear 68 and thereby drive first and and
second roller 50 and 52 so that the web of plastic
~ material will be stretched between the rollers 50 and 52
-~ and dispensed in the stretched mode. The greater the
~':
~ force that stretched film 40 is pulled from the
:~; carriage 22, the more;rotational energy is transferred to
drive sprocket 68, and the faster that endless chain 66 is
driven, and the faster that first and second rollers 50
: 20 and 52 wi11 be driven so as to stretch the film 40 between
: the rollers 50 and 52 and thereby dispense stretched
~ ~ : : film 40 a~ a faster speed and thereby relieving the
-~ tension in the film 40 drawn from the carriage 22.
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:; It should be noted that the amount of stretching of the
web of plastic 40 between first and second rollers 50
. `and~52 is dictated by the difference in the rotation of
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rollers 50 and 52 which depends upon such factors as the
diameter of the rollers and the gear ratios of the
sprockets 58 and 60. The amount of stretch is
predetermined for any set of diameter of rollers and gear
ratios of sprockets 58 and 60 and is not depended on the
rate of rotation of the endless chain 66, since rollers 50
and 52 are interconnected and the amount of stretch of the
f1lm will be the same whether the rollers 50 and 52 speed
up or slow down, and only the speed or supply/dernand of
the stretched film will vary as required.
Although the preferred web material utilized herein
comprises of stretchable plastic film 40 and particularly
,:
linear low density polyethylene (LLD) a web of paper or
the like could also be used.
:
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Furthermore it has been found that most plastic films when
stretched above their yield point gain significantly in
ultimate strength. For example, when 50 guage LLD film 40
20 is stretched 260% the resultant stretched film has a guage
of approximate 13.8 guage having increased strength
characteristics. Furthermore since the first and second
rollers 50 and 52 are located relatively close to one
another there is very little necking or shrinkage of the
web along the axis of the rollers 50 and 52.
:
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Moreover it has been found that the 50 guage LLD film
subjected to a 230% stretching has a 10% memory. In other
words when the stretched material 40 is dispensed from the
carriage 22, the web 40 will shrink 10% of the stretched
length. Such memory assists in the holding of palletized
art;cles wrapped with stretched film as the memory or
tendency to shrink will assist in holding the articles
together under compression. If the 50 gauge LLD film is
stretched 260% the stretched film has a 2% memory. It has
10 been found that LLD film having a stretch of 400% can be
consistently produced without tearing under working
conditions by utilizing the carriage 22 as described
herein. Film which has been stretched up to 400% has
substantially no memory.
,: ~
Furthermore 50 guage of stretched film may be controlled
or selected by increasing or decreasing the amount of
stretch such as for example selecting the diameter of
rollers 50 and 52 or gear ratios of sprockets 589 and 60.
;,
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Figure 5 illustrates the means for selecting the tension
at which the stretched web may be wrapped around pallet
load 16. Prior to describing such structure it should be
noted that the memory of the stretched film 40 will also
add a component of tension within the film due to the
tendency of the film to shrink.
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The structure of Figure 5 is adapted to select the tension
at which the tension of the web will be drawn from the
carriage 22.
The tension selecti ng means 130 includes a ratchet wheel
130, pawl 134 and tension adjusting gear 136. The tension
adjusting gear 136 is rotatably secured to the bottom
portion 46 by means of screw 138 which is thereby screwed
to threaded hole 140 of bottom portion 46.
;~ 10
The ratchet wheel 132 is rotatably secured to the bottom
portion 46 by means of screw 142 secured to threaded hole
144 of bottom portion 46.
The ratchet wheel 132 also included a tension spring 146
one end of which is fixedly secured to ratchet wheel 132
:and the other end of which is adapted to engage bar 104.
The pawl 134 is biased against ratchet wheel 32 by means
20~o~ ~bias1ng spring 148, one end of which is secured to pawl
132 by means of screw 150 an:d the other end of which is
secured: to~ a ~threaded hole 154 in bottom portion 46 by
:means of screw 152.
.
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Pawl 134 is adapted to pivot about screw lS6 which is
threaded~ly secured to threaded hole 158 of bottom portion
46.~
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As the tension gear 136 is rotated in the direction of
arrow T the ratchet wheel is rotated in the direction of
arrow S as the pawl 134 allows rotation of ratchet wheel
132. By rotating ratchet wheel 132 in the direction of
arrow S, the tension in tensioning spring 146 is increased
thereby increasing the tension force that must be applied
to the bar 104 of dancer assembly 98. This in turn
increases the tension force which must be applied to the
stretched film 40 in order to pivot or activate pivot
10 mounting 96 and band 92.
It should be noted that a fine tune tensioning means is
also provided by means of screw 126, spring 160 and
threaded post 128 located at the other end o~ brake 92.
The threaded screw 126 may be turned to increase or
decrease the diameter of brake 92.
The operation of the pallet wrapping machine incorporating
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~ the invention herein shall now be described. As arm 20
, ~ .
20 rotates about pallet load 16 the carriage 22 reciprocates
along leg 24 between upper and lower limits A and B
respectlvely. A web of plastic material 40 is
~ rotationally wrapped around load 16 as best illustrated in
; Figure 1. As the film 40 is wrapped around load 16 the
web of material 40 is stretched between rollers 50 and 52
an~d ~accordingly the pallet load 16 is wrapped with
~ stretched,film. The amount of stretching is selected in a
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manner as described above. Futhermore the tension at
which the stretched web 40 is wrapped around pallet load
16 is selected by means of adjusting the tension selecting
means 130 or the fine tune tensioning means as described
above. Accordingly when the carriage 22 is rotated about
load 16 the planetary gear structure 64 will vary the rate
of rotatably driving the rollers 50 and 52 in response to
variations of tension of the web 40 pulled from the
rollers 50 and 52 during rotation of the carriage 22 about
10 the pallet 16 so as to maintain the tension of the web at
the preselected level as more fully particularized above.
Although Figure 1 illustrates the use of the carriage 22
being rotated about a vertical axis to wrap a pallet 16;
the carriage 22 may also be utilized in a wrapping machine
10 when the carriage 22 is adapted to be rotated about a
horizontal axis.
The invention described herein is more sensitive and has a
20 faster response time than the time prior art devices used
; ; heretoforeO More particularly the prior art devices which
utilize a motor having a variable RPM to increase the
supply of film exhibit a time delay or inertia to build up
speed, in order to supply more film as required. Such
delay results in increased tension in the film wrapping
the pallet and contributes to the tearing of the film.
The invention described herein has available kinetic
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- 24 -
energy which i5 substantially immediately available to be
transferred to the driving mechanism as required to
dispense the film. Accordingly the tension of the web 40
is more accurately controlled by the carriage 22 and there
is less film tearing as the web of material rounds
corners 72 due to the improved tension maintaining
characteristics of the carriage 220 With less tearing
there is less down time of the machine.
10 More particularly the tensioning means 130 may be
accurately and finally controlled so that it is now
possible for empty plastic bottles to be wrapped with
,~ stretched film without knocking or dislodging such bottles
from the pallet load 18.
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It should also be noted that the carriage 22 described
; herein may be adapted so that only one roller means is
provided to dispense a web of material without stretching
the web 40 but still providing the substantially
20 simultaneous increase or decrease or the speed of film 40
required in order to maintain the tension of the web of
material 40 at the preselected level.
A
Although the preferred embodiment as well as the operation
and use has been specifically described in relation to the
.
drawings, it should be understood that variations in the
preferred embodiment could be easily achieved by a skilled
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man in the traAe without departing from the spirit of the
nvention. Accordingly the invention should not be
understood as being limited to the exact form revealed in
the drawings.
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