U.S. patent application number 11/709872 was filed with the patent office on 2007-09-06 for method and apparatus for metered pre-stretch film delivery.
Invention is credited to David E. Eldridge, Willie Martin Hall, Richard L. Johnson, Patrick R. III Lancaster, Curtis W. Martin, Philip R. Moore, Joseph Donald Norris.
Application Number | 20070204565 11/709872 |
Document ID | / |
Family ID | 38293113 |
Filed Date | 2007-09-06 |
United States Patent
Application |
20070204565 |
Kind Code |
A1 |
Lancaster; Patrick R. III ;
et al. |
September 6, 2007 |
Method and apparatus for metered pre-stretch film delivery
Abstract
The present invention provides a method and apparatus for
dispensing a predetermined substantially constant length of
pre-stretched packaging material based upon load girth. Based upon
the girth of the load to be wrapped, an amount of pre-stretched
packaging material to be dispensed for each revolution of relative
rotation between a packaging material dispenser and the load is
determined. A rotational drive system used to provide the relative
rotation is linked to a pre-stretch assembly portion of the
packaging material dispenser. The linkage may be mechanical or
electrical. The linkage controls a ratio of the rotational speed to
the pre-stretch assembly dispensing speed, such that the
predetermined substantially constant length of pre-stretched
packaging material is dispensed for each revolution of the
packaging material dispenser relative to the load regardless of the
speed of the rotational drive. In the case of a mechanical linkage,
the linkage also connects the rotational drive to the pre-stretch
assembly portion such that the rotational drive also drives the
pre-stretch assembly portion.
Inventors: |
Lancaster; Patrick R. III;
(Louisville, KY) ; Eldridge; David E.; (Fem Creek,
KY) ; Hall; Willie Martin; (Taylorsville, KY)
; Johnson; Richard L.; (LaGrange, KY) ; Martin;
Curtis W.; (Georgetown, KY) ; Moore; Philip R.;
(Mount Washington, KY) ; Norris; Joseph Donald;
(Pleasureville, KY) |
Correspondence
Address: |
FINNEGAN, HENDERSON, FARABOW, GARRETT & DUNNER;LLP
901 NEW YORK AVENUE, NW
WASHINGTON
DC
20001-4413
US
|
Family ID: |
38293113 |
Appl. No.: |
11/709872 |
Filed: |
February 23, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60775779 |
Feb 23, 2006 |
|
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|
Current U.S.
Class: |
53/399 ;
53/588 |
Current CPC
Class: |
B65B 11/025 20130101;
B65B 2210/18 20130101; B65B 2210/20 20130101; B65B 2011/002
20130101; B65B 11/006 20130101; B65B 11/045 20130101; B65B 2210/16
20130101; B65B 57/04 20130101; B65B 2210/14 20130101 |
Class at
Publication: |
053/399 ;
053/588 |
International
Class: |
B65B 13/04 20060101
B65B013/04 |
Claims
1. An apparatus for stretch wrapping a load, comprising: a
packaging material dispenser for dispensing a film web, the
packaging material dispenser including an upstream pre-stretch
roller and a downstream pre-stretch roller within a pre-stretch
assembly; a rotational drive system for providing relative rotation
between the load and the dispenser during the wrapping cycle; and a
mechanical input/output ratio control configured to set a ratio of
relative rotation speed to pre-stretch speed, an output of the
mechanical input/output ratio control driving the pre-stretch
assembly to dispense a predetermined substantially constant length
of pre-stretched packaging material for each revolution of the
relative rotation between the load and the packaging material
dispenser.
2. The apparatus of claim 1, wherein the mechanical input/output
ratio control includes a mechanical transmission.
3. The apparatus of claim 2, further comprising a film break
sensing roller operatively connected to the mechanical
transmission.
4. The apparatus of claim 3, wherein the film break sensing roller
is configured to shift the mechanical transmission into neutral
upon sensing a film break.
5. The apparatus of claim 2, wherein the mechanical transmission is
a hydrostatic transmission.
6. The apparatus of claim 1, wherein the rotational drive system
includes one of a turntable and a rotatable arm.
7. The apparatus of claim 1, further comprising a final roller
positioned a predetermined distance from the downstream pre-stretch
roller, the predetermined distance being such that at least a
portion of a length of film extending between the downstream
pre-stretch roller and the final roller acts to dampen variations
in forces acting on the predetermined substantially constant length
of pre-stretched packaging material as it travels from the
dispenser to the load.
8. The apparatus of claim 1, wherein the rotational drive system
includes a rotatable ring.
9. The apparatus of claim 1, further comprising a film drive down
roller positioned to continuously engage at least a portion of a
width of the film web in a film path from the dispenser to the
load, the film drive down roller being selectively moveable between
a vertical position and a tilted film drive down position.
10. The apparatus of claim 9, further comprising at least one
roping element.
11. The apparatus of claim 1, further comprising a film cutting and
sealing assembly.
12. An apparatus for stretch wrapping a load, comprising: a
packaging material dispenser for dispensing a film web, the
packaging material dispenser including a pre-stretch assembly; a
rotational drive system for providing relative rotation between the
load and the dispenser during the wrapping cycle; a mechanical
input/output ratio control configured to set a ratio of relative
rotation speed to pre-stretch speed, an output of the mechanical
input/output ratio control driving the pre-stretch assembly to
dispense a predetermined substantially constant length of
pre-stretched packaging material for each revolution of the
relative rotation between the load and the packaging material
dispenser; and a virtual film accumulator configured to accommodate
variations in film demand as the film is dispensed at the
predetermined substantially constant length for each
revolution.
13. The apparatus of claim 12, wherein the mechanical input/output
ratio control includes a mechanical transmission.
14. The apparatus of claim 12, wherein the mechanical input/output
ratio control includes a hydrostatic transmission.
15. The apparatus of claim 12, further comprising a film break
sensing roller.
16. The apparatus of claim 15, wherein the film break sensing
roller is operatively coupled to the mechanical input/output ratio
control.
17. The apparatus of claim 16, wherein a connection between the
film break sensing roller and the mechanical input/output ratio
control prevents output of the mechanical input/output ratio
control when a film break is sensed.
18. The apparatus of claim 12, wherein the rotational drive system
includes one of a turntable, a rotatable ring, and a rotatable
arm.
19. The apparatus of claim 12, wherein the virtual film accumulator
includes an arrangement of rollers configured to provide at least
thirteen additional inches of film to a film path extending between
the dispenser and the load.
20. The apparatus of claim 12, further comprising a film drive down
roller positioned to continuously engage at least a portion of a
width of the film web in a film path from the dispenser to the
load, the film drive down roller being selectively moveable between
a vertical position and a tilted film drive down position.
21. The apparatus of claim 20, further comprising at least one
roping element.
22. The apparatus of claim 12, further comprising a film cutting
and sealing assembly.
23. The apparatus of claim 12, wherein the mechanical input/output
ratio control includes an input shaft, and further comprising a
mechanical connector connecting the rotational drive system to the
input shaft.
24. The apparatus of claim 12, wherein the mechanical input/output
ratio control includes a rotatable input shaft and a rotatable
output shaft, wherein the rotatable output shaft drives a
downstream roller of the pre-stretch assembly.
25. An apparatus for stretch wrapping a load, comprising: a
packaging material dispenser for dispensing a film web, the
packaging material dispenser including an upstream pre-stretch
roller and a downstream pre-stretch roller within a pre-stretch
assembly; a rotational drive system for providing relative rotation
between the load and the dispenser during the wrapping cycle; a
mechanical input/output ratio control configured to set a ratio of
relative rotation speed to pre-stretch speed, an output of the
mechanical input/output ratio control driving the pre-stretch
assembly to dispense a predetermined substantially constant length
of pre-stretched packaging material for each revolution of the
relative rotation between the load and the packaging material
dispenser; and a final roller positioned a predetermined distance
from the downstream pre-stretch roller, wherein a film length
extending between the downstream pre-stretch roller and the final
roller is at least thirteen inches.
26. An apparatus for stretch wrapping a load, the load having a
shortest wrap radius and a longest wrap radius, the apparatus
comprising: a packaging material dispenser for dispensing a film
web, the packaging material dispenser including an upstream
pre-stretch roller and a downstream pre-stretch roller within a
pre-stretch assembly; a rotational drive system for providing
relative rotation between the load and the dispenser during the
wrapping cycle; a mechanical input/output ratio control configured
to set a ratio of relative rotation speed to pre-stretch speed, an
output of the mechanical input/output ratio control driving the
pre-stretch assembly to dispense a predetermined substantially
constant length of pre-stretched packaging material for each
revolution of the relative rotation between the load and the
packaging material dispenser; and a final roller positioned a
predetermined distance from the downstream pre-stretch roller,
wherein a length of film extending from the second pre-stretch
roller to the final roller has a length greater than a difference
between the shortest wrap radius and the longest wrap radius of the
load.
27. A method for stretch wrapping a load, comprising: determining a
girth of a load to be wrapped; determining a substantially constant
length of pre-stretched packaging material to be dispensed for each
revolution of a packaging material dispenser around the load;
dispensing the predetermined substantially constant length of
pre-stretched packaging material during each revolution of the
packaging material dispenser around the load; and rotating the
packaging material dispenser around the load at a speed sufficient
to wrap the predetermined substantially constant length of
pre-stretched packaging material around the load before the
pre-stretched packaging material recovers from pre-stretching.
28. The method of claim 27, wherein determining a substantially
constant length of pre-stretched packaging material to be dispensed
includes determining a substantially constant length of
pre-stretched packaging material to be dispensed for each
revolution of a packaging material dispenser around the load based
on the girth of the load.
29. The method of claim 27, further comprising setting a ratio of
relative rotation speed to pre-stretch speed.
30. The method of claim 29, further comprising maintaining the set
ratio of rotational speed to pre-stretch speed through a mechanical
input/output ratio control.
31. The method of claim 30, further comprising driving the
pre-stretch assembly to dispense the predetermined substantially
constant length of pre-stretched packaging material with an output
of the mechanical input/output ratio control.
32. The method of claim 31, wherein the driving the pre-stretch
assembly includes providing an input to the mechanical input/output
ratio control from a rotational drive rotating the dispenser.
33. The method of claim 32, wherein driving the pre-stretch
assembly further includes providing an input to a pre-stretch
roller of the pre-stretch assembly from an output of the mechanical
input/output ratio control.
34. The method of claim 29, further comprising maintaining the set
ratio of relative rotation speed to pre-stretch speed during a
primary portion of a wrap cycle through an electronic control.
35. The method of claim 27, further comprising sensing a break in
the film during a wrapping cycle.
36. The method of claim 35, further comprising stopping dispensing
the predetermined substantially constant length of pre-stretched
packaging material upon sensing the film break.
37. A method for stretch wrapping a load, comprising: determining a
girth of a load to be wrapped; determining a substantially constant
length of pre-stretched packaging material to be dispensed for each
revolution of a packaging material dispenser around the load;
dispensing the predetermined substantially constant length of
pre-stretched packaging material during each revolution of the
packaging material dispenser around the load; and rotating the
packaging material dispenser around the load at a speed sufficient
to permit the predetermined substantially constant length of
pre-stretched packaging material of a revolution to conform to at
least two successive corners of the load substantially
simultaneously.
38. The method of claim 37, further comprising setting a ratio of
relative rotation speed to pre-stretch speed.
39. The method of claim 38, further comprising maintaining the set
ratio of relative rotation speed to pre-stretch speed through a
mechanical input/output ratio control.
40. The method of claim 38, further comprising maintaining the set
ratio of relative rotation speed to pre-stretch speed during a
primary portion of the wrap cycle through an electronic
control.
41. The method of claim 39, further comprising driving the
pre-stretch assembly to dispense the predetermined substantially
constant length of pre-stretched packaging material with an output
of the mechanical input/output ratio control.
42. The method of claim 41, wherein driving the pre-stretch
assembly includes providing an input to the mechanical input/output
ratio control from a rotational drive rotating the packaging
material dispenser.
43. The method of claim 42, wherein driving the pre-stretch
assembly further includes providing an input to a pre-stretch
roller of the pre-stretch assembly from an output of the mechanical
input/output ratio control.
44. The method of claim 40, further comprising varying the set
ratio of relative rotation speed to pre-stretch speed during one of
an initial acceleration and a final deceleration portion of the
wrap cycle through an electronic control.
45. A method for stretch wrapping a load, comprising: providing a
packaging material including a pre-stretch portion; providing
relative rotation between the packaging material dispenser and the
load; setting a ratio of relative rotational speed to pre-stretch
speed with a mechanical input/output ratio control; driving the
pre-stretch assembly through an output of the mechanical
input/output ratio control to dispense a predetermined
substantially constant length of pre-stretched packaging material
during each revolution of the relative rotation between the load
and the packaging material dispenser; and compensating for
variations in film demand during each revolution of the relative
rotation as the dispensed predetermined substantially constant
length of pre-stretched packaging material travels from the
dispenser to the load.
46. The method of claim 45, further comprising continuously
engaging the film web in a film path between the dispenser and the
load with at least one film drive down roller; and selectively
driving down a portion of the film web in the film path with the at
least one film drive down roller.
47. The method of claim 46, further comprising roping a portion of
the film web into a cable.
48. The method of claim 47, further comprising wrapping the roped
portion of the film web spirally around the load.
49. The method of claim 45, further comprising sealing a final tail
of packaging material to the load.
50. The method of claim 49, further comprising severing the final
tail of film.
51. A method for stretch wrapping a load, comprising: determining a
substantially constant length of pre-stretched packaging material
to be dispensed for each revolution of a packaging material
dispenser relative to the load; using a rotational drive to provide
relative rotation between the packaging material dispenser and the
load; setting a ratio of relative rotational speed to pre-stretch
speed; driving the pre-stretch portion at the set ratio through a
mechanical connection to the rotational drive to dispense the
predetermined substantially constant length of pre-stretched
packaging material during each revolution of the relative rotation
between the load and the packaging material dispenser; and damping
variations in forces acting on the dispensed predetermined
substantially constant length of pre-stretched packaging material
as the pre-stretched packaging material travels from the dispenser
to the load.
52. An apparatus for stretch wrapping a load, comprising: a
packaging material dispenser for dispensing a film web, the
packaging material dispenser including a powered pre-stretch
portion; a rotational drive system for providing relative rotation
between the load and the dispenser during the wrapping cycle; and
an electronic control configured to maintain a predetermined ratio
between a drive powering the pre-stretch portion and the rotational
drive system during a primary portion of a wrap cycle.
53. The apparatus of claim 52, wherein the predetermined ratio is
set such that the pre-stretch portion dispenses a predetermined
substantially constant length of pre-stretched packaging material
for each revolution of the relative rotation between the load and
the packaging material dispenser.
54. The apparatus of claim 52, wherein the electronic control is
configured to vary the predetermined ratio during at least one of
initial acceleration and final deceleration of the wrap cycle.
55. The apparatus of claim 52, wherein the electronic control is
configured to stop the relative rotation upon sensing a film
break.
56. The apparatus of claim 52, further comprising a virtual film
accumulator configured, to accommodate variations in film demand as
the film is dispensed.
57. The apparatus of claim 56, wherein the virtual film accumulator
includes an arrangement of rollers configured to provide at least
thirteen additional inches of film to a film path extending between
the dispenser and the load.
58. The apparatus of claim 52, wherein the rotational drive system
includes one of a turntable, a rotatable ring, and a rotatable
arm.
59. The apparatus of claim 52, further comprising a film drive down
roller positioned to continuously engage at least a portion of a
width of the film web in a film path from the dispenser to the
load, the film drive down roller being selectively moveable between
a vertical position and a tilted film drive down position; and at
least one roping element.
60. The apparatus of claim 52, further comprising a film cutting
and sealing assembly.
61. An apparatus for stretch wrapping a load, comprising: a
packaging material dispenser for dispensing a film web, the
packaging material dispenser including an upstream pre-stretch
roller and a downstream pre-stretch roller within a powered
pre-stretch assembly; a rotational drive system providing relative
rotation between the load and the dispenser during the wrapping
cycle; an electronic control configured to maintain a predetermined
ratio between a drive powering the pre-stretch portion and the
rotational drive system during a primary portion of a wrap cycle;
and a final roller positioned a predetermined distance from the
downstream pre-stretch roller, wherein a film length extending
between the downstream pre-stretch roller and the final roller is
at least thirteen inches.
62. The apparatus of claim 61, wherein the predetermined ratio is
set such that the pre-stretch portion dispenses a predetermined
substantially constant length of pre-stretched packaging material
for each revolution of the relative rotation between the load and
the packaging material dispenser.
63. The apparatus of claim 61, wherein the electronic control is
configured to vary the predetermined ratio during at least one of
initial acceleration and final deceleration of the wrap cycle.
64. The apparatus of claim 61, further comprising a film break
sensing roller.
65. The apparatus of claim 64, wherein the electronic control is
configured to stop the relative rotation upon sensing a film
break.
66. The apparatus of claim 61, wherein the rotational drive system
includes one of a turntable, a rotatable ring, and a rotatable
arm.
67. The apparatus of claim 61, further comprising a film drive down
roller positioned to continuously engage at least a portion of a
width of the film web in a film path from the dispenser to the
load, the film drive down roller being selectively moveable between
a vertical position and a tilted film drive down position; and at
least one roping element.
68. The apparatus of claim 61, further comprising a film cutting
and sealing assembly.
69. An apparatus for stretch wrapping a load, comprising: a
packaging material dispenser for dispensing a film web, the
packaging material dispenser including a powered pre-stretch
portion; a rotational drive system providing relative rotation
between the load and the dispenser during the wrapping cycle; an
electronic control configured to maintain a predetermined ratio
between a drive powering the pre-stretch portion and the rotational
drive system during a primary portion of a wrap cycle, wherein the
electronic control is configured to vary the predetermined ratio
during at least one of initial acceleration and final deceleration
of the wrap cycle; and a virtual film accumulator configured to
accommodate variations in film demand as the film is dispensed.
70. The apparatus of claim 69, wherein the virtual film accumulator
includes an arrangement of rollers configured to provide at least
thirteen additional inches of film to a film path extending between
the dispenser and the load.
71. The apparatus of claim 69, wherein the predetermined ratio is
set such that the pre-stretch portion dispenses a predetermined
substantially constant length of pre-stretched packaging material
for each revolution of the relative rotation between the load and
the packaging material dispenser.
72. The apparatus of claim 69, further comprising a film break
sensing roller.
73. The apparatus of claim 72, wherein the electronic control is
configured to stop the relative rotation upon sensing a film
break.
74. The apparatus of claim 69, wherein the rotational drive system
includes one of a turntable, a rotatable ring, and a rotatable
arm.
75. The apparatus of claim 69, further comprising a film drive down
roller positioned to continuously engage at least a portion of a
width of the film web in a film path from the dispenser to the
load, the film drive down roller being selectively moveable between
a vertical position and a tilted film drive down position; and at
least one roping element.
76. The apparatus of claim 69, further comprising a film cutting
and sealing assembly.
77. An apparatus for stretch wrapping a load, comprising: a
packaging material dispenser for dispensing a film web, the
packaging material dispenser including an upstream pre-stretch
roller and a downstream pre-stretch roller within a powered
pre-stretch assembly; a rotational drive system providing relative
rotation between the load and the dispenser during the wrapping
cycle; an electronic control configured to maintain a predetermined
ratio between a drive powering the pre-stretch portion and the
rotational drive system during a primary portion of a wrap cycle,
wherein the electronic control is configured to vary the
predetermined ratio during at least one of initial acceleration and
final deceleration of the wrap cycle; and a final roller positioned
a predetermined distance from the downstream pre-stretch roller,
the predetermined distance being such that at least a portion of a
length of film extending between the downstream pre-stretch roller
and the final roller acts to dampen variations in forces acting on
the pre-stretched packaging material as the pre-stretched packaging
material travels from the dispenser to the load.
78. A method for stretch wrapping a load, comprising: providing a
packaging material including a powered pre-stretch portion;
providing relative rotation between the packaging material
dispenser and the load; setting a ratio of relative rotational
speed to pre-stretch speed; electronically maintaining the set
ratio during a primary portion of the wrap cycle to dispense
pre-stretched packaging material; and electronically varying the
set ratio during at least one of an initial acceleration and a
final deceleration of the packaging material dispenser relative to
the load.
79. The method of claim 78, further comprising damping variations
in forces acting on the dispensed pre-stretched packaging material
as it travels from the dispenser to the load.
80. The method of claim 78, further comprising continuously
engaging the film web in a film path between the dispenser and the
load with at least one film drive down roller; and selectively
driving down a portion of the film web in the film path with the at
least one film drive down roller.
81. The method of claim 80, further comprising roping a portion of
the film web into a cable.
82. The method of claim 78, further comprising sealing a final tail
of packaging material to the load.
83. The method of claim 82, further comprising severing the final
tail of film.
84. The method of claim 78, further comprising using a film break
sensing roller to sense a break in the film during the wrap
cycle.
85. The method of claim 84, further comprising discontinuing
dispensing pre-stretched packaging material upon sensing a film
break.
86. The method of claim 78, wherein electronically maintaining the
set ratio during a primary portion of the wrap cycle to dispense
pre-stretched packaging material includes dispensing a
predetermined substantially constant length of pre-stretched
packaging material per revolution of the dispenser relative to the
load.
87. A method for stretch wrapping a load, comprising: providing
relative rotation between the packaging material dispenser and the
load; setting a ratio of relative rotational speed to pre-stretch
speed; electronically maintaining the set ratio during a primary
portion of the wrap cycle to dispense the predetermined
substantially constant length of pre-stretched packaging material
during each revolution of the packaging material dispenser relative
to the load during the primary portion of the wrap cycle;
electronically varying the set ratio upon sensing at least one of a
film break and slack film; and and damping variations in forces
acting on the dispensed predetermined constant length of
pre-stretched packaging material as the pre-stretched packaging
material travels from the dispenser to the load.
Description
[0001] This application claims priority under 35 U.S.C. .sctn.119
based on U.S. Provisional Application No. 60/775,779, filed Feb.
23, 2006, the complete disclosure of which is incorporated herein
by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to an apparatus and a method
for wrapping a load with packaging material, and more particularly,
stretch wrapping.
BACKGROUND OF THE INVENTION
[0003] Various packaging techniques have been used to build a load
of unit products and subsequently wrap them for transportation,
storage, containment and stabilization, protection and
waterproofing. One system uses stretch wrapping machines to
stretch, dispense and wrap stretch packaging material around a
load. Stretch wrapping can be performed as an inline, automated
packaging technique that dispenses and wraps packaging material in
a stretch condition around a load on a pallet to cover and contain
the load. Pallet stretch wrapping, whether accomplished by a
turntable, rotating arm, vertical rotating ring, or horizontal
rotating ring, typically covers the four vertical sides of the load
with a stretchable packaging material such as polyethylene
packaging material. In each of these arrangements, relative
rotation is provided between the load and the packaging material
dispenser to wrap packaging material about the sides of the
load.
[0004] Stretch wrapping machines provide relative rotation between
a stretch wrap packaging dispenser and a load either by driving the
stretch wrap packaging dispenser around a stationary load or
rotating the load on a turntable. Upon relative rotation, packaging
material is wrapped on the load. Rotating ring style stretch
wrappers generally include a roll of packaging material mounted in
a dispenser, which rotates about the load on a rotating ring.
Wrapping rotating rings are categorized as vertical rotating rings
or horizontal rotating rings. Vertical rotating rings move
vertically between an upper and lower position to wrap packaging
material around a load. In a vertical rotating ring, as in
turntable and rotating wrap arm apparatuses, the four vertical
sides of the load are wrapped, along the height of the load.
Horizontal rotating rings are stationary and the load moves through
the rotating ring, usually on a conveyor, as the packaging material
dispenser rotates around the load to wrap packaging material around
the load. In the horizontal rotating ring, the length of the load
is wrapped. As the load moves through the rotating ring and off the
conveyor, the packaging material slides off the conveyor (surface
supporting the load) and into contact with the load.
[0005] Historically, rotating ring style wrappers have suffered
from excessive packaging material breaks and limitations on the
amount of containment force applied to the load (as determined in
part by the amount of pre-stretch used) due to erratic speed
changes required to wrap "non-square" loads, such as narrow, tall
loads, short, wide loads, and short, narrow loads. The non-square
shape of such loads often results in the supply of excess packaging
material during the wrapping cycle, during time periods in which
the demand rate for packaging material by the load is exceeded by
the supply rate of the packaging material by the packaging material
dispenser. This leads to loosely wrapped loads. In addition, when
the demand rate for packaging material by the load is greater than
the supply rate of the packaging material by the packaging material
dispenser, breakage of the packaging material may occur.
[0006] When stretch wrapping a typical rectangular load, the demand
for packaging material varies, decreasing as the packaging material
approaches contact with a corner of the load and increasing after
contact with the corner of the load. When wrapping a tall, narrow
load or a short load, the variation in the demand rate is even
greater than in a typical rectangular load. In vertical rotating
rings, high speed rotating arms, and turntable apparatuses, the
variation is caused by a difference between the length and the
width of the load. In a horizontal rotating ring apparatus, the
variation is caused by a difference between the height of the load
(distance above the conveyor) and the width of the load.
[0007] The amount of force, or pull, that the packaging material
exhibits on the load determines how tightly and securely the load
is wrapped. Conventionally, this force is controlled by controlling
the feed or supply rate of the packaging material dispensed by the
packaging material dispenser with respect to the demand rate of
packaging material required by the load. Efforts have been made to
supply the packaging material at a constant tension or at a supply
rate that increases as the demand rate increases and decreases as
the demand rate decreases. However, when variations in the demand
rate are large, fluctuations between the feed and demand rates
result in loose packaging of the load or breakage of the packaging
material during wrapping.
[0008] The wrap force of many known commercially available pallet
stretch wrapping machines is controlled by sensing changes in
demand and attempting to alter supply of packaging material such
that relative constant packaging material wrap force is maintained.
With the invention of powered pre-stretching devices, sensing force
and speed changes was immediately recognized to be critically
important. This has been accomplished using feedback mechanisms
typically linked to or spring loaded dancer bars and electronic
load cells. The changing force on the packaging material caused by
rotating a rectangular shaped load is transmitted back through the
packaging material to some type of sensing device which attempts to
vary the speed of the motor driven pre-stretch dispenser to
minimize the force change on the packaging material incurred by the
changing packaging material demand. The passage of the corner
causes the force on the packaging material to increase. This
increase force is typically transmitted back to an electronic load
cell, spring-loaded dancer interconnected with a sensing means, or
by speed change to a torque control device. After the corner is
passed the force on the packaging material reduces as the packaging
material demand decreases. This force or speed is transmitted back
to some device that in turn reduces the packaging material supply
to attempt to maintain a relatively constant wrap force.
[0009] With the ever faster wrapping rates demanded by the
industry, the rotation speeds have increased significantly to a
point where the concept of sensing demand change and altering
supply speed is no longer effective. The delay of response has been
observed to begin to move out of phase with rotation at
approximately 20 RPM. The actual response time for the rotating
mass of packaging material roll and rollers approximating 100 lbs
must shift from accelerate to decelerate eight times per revolution
that at 20 RPM is a shift more than every 1/2 sec.
[0010] Even more significant is the need to minimize the
acceleration and deceleration times for these faster cycles.
Initial acceleration must pull against the clamped packaging
material, which typically cannot stand a high force especially the
high force of rapid acceleration that cannot be maintained by the
feedback mechanisms described above. Use of high speed wrapping has
therefore been limited to relatively lower wrap forces and
pre-stretch levels where the loss of control at high speeds does
not produce undesirable packaging material breaks.
[0011] Packaging material dispensers mounted on horizontally
rotating rings present additional special issues concerning
effectively wrapping at high speeds. Many commercially available
rotating ring wrappers that are in use depend upon electrically
powered motors to drive the pre-stretch packaging material
dispensers. The power for these motors must be transmitted to the
rotating ring. This is typically done through electric slip
rotating rings mounted to the rotating ring with an electrical pick
up fingers mounted to the fixed frame. Alternately others have
attempted to charge a battery or run a generator during rotation.
All of these devices suffer complexity, cost and maintenance
issues. But even more importantly they add significant weight to
the rotating ring which impacts its ability to accelerate and/or
decelerate rapidly.
[0012] Packaging material dispensers mounted on vertically rotating
rings have the additional problem of gravity forces added to
centrifugal forces of high-speed rotation. High-speed wrappers have
therefore required expensive and very heavy two part bearings to
support the packaging material dispensers. The presence of the
outer race on these bearings has made it possible to provide a belt
drive to the pre-stretch dispenser. This drive is taken through a
clutch type torque device to deliver the variable demand rate
required for wrap force desired.
[0013] Accordingly, it is an object of the present invention to
provide a method and apparatus for regulating the feed of packaging
material to produce a secure load for shipment without distorting
the top layers of a load, crushing product, or breaking film.
[0014] It is another object of the present invention to provide a
method and apparatus capable of regulating the packaging material
supply rate to maintain a wrapping force below the force that will
incur film breaks.
[0015] It is an additional object of the present invention to
provide a method and apparatus for wrapping loads at faster
wrapping rates.
[0016] It is an additional object of the present invention to
provide a method and apparatus capable of minimizing packaging
material dispenser acceleration and deceleration times, in order to
obtain faster wrapping cycles.
[0017] It is an additional object of the present invention to
provide a method and apparatus that reduces the amount of
complexity, cost, weight, and maintenance associated with known
rotating ring apparatuses.
SUMMARY OF THE INVENTION
[0018] In accordance with the invention, a method and apparatus for
dispensing a predetermined substantially constant length of
pre-stretched packaging material relative to load girth is
provided. The method and apparatus include a linkage between a
rotational drive system for providing relative rotation between a
load and a packaging material dispenser and a pre-stretch assembly
portion of the packaging material dispenser. The linkage may be
mechanical or electrical. The linkage controls a ratio of the
rotational speed to the pre-stretch assembly dispensing speed, such
that the predetermined substantially constant length of
pre-stretched packaging material is dispensed for each revolution
of the packaging material dispenser relative to the load regardless
of the speed of the rotational drive. In the case of a mechanical
linkage, the linkage also connects the rotational drive to the
pre-stretch assembly portion such that the rotational drive also
drives the pre-stretch assembly portion.
[0019] According to one aspect of the present invention, an
apparatus for stretch wrapping a load is provided. The apparatus
includes a packaging material dispenser for dispensing a film web,
the packaging material dispenser including an upstream pre-stretch
roller and a downstream pre-stretch roller within a pre-stretch
assembly, a rotational drive system for providing relative rotation
between the load and the dispenser during the wrapping cycle, and a
mechanical input/output ratio control configured to set a ratio of
relative rotation speed to pre-stretch speed, an output of the
mechanical input/output ratio control driving the pre-stretch
assembly to dispense a predetermined substantially constant length
of pre-stretched packaging material for each revolution of the
relative rotation between the load and the packaging material
dispenser.
[0020] According to another aspect of the present, an apparatus for
stretch wrapping a load comprises a packaging material dispenser
for dispensing a film web, the packaging material dispenser
including a pre-stretch assembly, a rotational drive system for
providing relative rotation between the load and the dispenser
during the wrapping cycle, a mechanical input/output ratio control
configured to set a ratio of relative rotation speed to pre-stretch
speed, an output of the mechanical input/output ratio control
driving the pre-stretch assembly to dispense a predetermined
substantially constant length of pre-stretched packaging material
for each revolution of the relative rotation between the load and
the packaging material dispenser, and a virtual film accumulator
configured to accommodate variations in film demand as the film is
dispensed at the predetermined substantially constant length for
each revolution.
[0021] According to a further aspect of the present invention, an
apparatus for stretch wrapping a load comprises a packaging
material dispenser for dispensing a film web, the packaging
material dispenser including an upstream pre-stretch roller and a
downstream pre-stretch roller within a pre-stretch assembly, a
rotational drive system for providing relative rotation between the
load and the dispenser during the wrapping cycle, a mechanical
input/output ratio control configured to set a ratio of relative
rotation speed to pre-stretch speed, an output of the mechanical
input/output ratio control driving the pre-stretch assembly to
dispense a predetermined substantially constant length of
pre-stretched packaging material for each revolution of the
relative rotation between the load and the packaging material
dispenser, and a final roller positioned a predetermined distance
from the downstream pre-stretch roller, wherein a film length
extending between the downstream pre-stretch roller and the final
roller is at least thirteen inches.
[0022] According to yet another aspect of the present invention, an
apparatus for stretch wrapping a load, the load having a shortest
wrap radius and a longest wrap radius, includes a packaging
material dispenser for dispensing a film web, the packaging
material dispenser including an upstream pre-stretch roller and a
downstream pre-stretch roller within a pre-stretch assembly, a
rotational drive system for providing relative rotation between the
load and the dispenser during the wrapping cycle, a mechanical
input/output ratio control configured to set a ratio of relative
rotation speed to pre-stretch speed, an output of the mechanical
input/output ratio control driving the pre-stretch assembly to
dispense a predetermined substantially constant length of
pre-stretched packaging material for each revolution of the
relative rotation between the load and the packaging material
dispenser, and a final roller positioned a predetermined distance
from the downstream pre-stretch roller, wherein a length of film
extending from the second pre-stretch roller to the final roller
has a length greater than a difference between the shortest wrap
radius and the longest wrap radius of the load.
[0023] According to one aspect of the present invention, a method
for stretch wrapping a load is provided. The method comprises
determining a girth of a load to be wrapped, determining a
substantially constant length of pre-stretched packaging material
to be dispensed for each revolution of a packaging material
dispenser around the load, dispensing the predetermined
substantially constant length of pre-stretched packaging material
during each revolution of the packaging material dispenser around
the load, and rotating the packaging material dispenser around the
load at a speed sufficient to wrap the predetermined substantially
constant length of pre-stretched packaging material around the load
before the pre-stretched packaging material recovers from
pre-stretching.
[0024] According to another aspect of the present invention, a
method for stretch wrapping a load comprises determining a girth of
a load to be wrapped, determining a substantially constant length
of pre-stretched packaging material to be dispensed for each
revolution of a packaging material dispenser around the load,
dispensing the predetermined substantially constant length of
pre-stretched packaging material during each revolution of the
packaging material dispenser around the load, and rotating the
packaging material dispenser around the load at a speed sufficient
to permit the predetermined substantially constant length of
pre-stretched packaging material of a revolution to conform to at
least two successive corners of the load substantially
simultaneously.
[0025] According to a further aspect of the present invention, a
method for stretch wrapping a load includes providing a packaging
material including a pre-stretch portion, providing relative
rotation between the packaging material dispenser and the load,
setting a ratio of relative rotational speed to pre-stretch speed
with a mechanical input/output ratio control, driving the
pre-stretch assembly through an output of the mechanical
input/output ratio control to dispense a predetermined
substantially constant length of pre-stretched packaging material
during each revolution of the relative rotation between the load
and the packaging material dispenser, and compensating for
variations in film demand during each revolution of the relative
rotation as the dispensed predetermined substantially constant
length of pre-stretched packaging material travels from the
dispenser to the load.
[0026] According to yet another aspect of the present invention, a
method for stretch wrapping a load comprises determining a
substantially constant length of pre-stretched packaging material
to be dispensed for each revolution of a packaging material
dispenser relative to the load, using a rotational drive to provide
relative rotation between the packaging material dispenser and the
load, setting a ratio of relative rotational speed to pre-stretch
speed, driving the pre-stretch portion at the set ratio through a
mechanical connection to the rotational drive to dispense the
predetermined substantially constant length of pre-stretched
packaging material during each revolution of the relative rotation
between the load and the packaging material dispenser, and damping
variations in forces acting on the dispensed predetermined
substantially constant length of pre-stretched packaging material
as it travels from the dispenser to the load.
[0027] According to one aspect of the present invention, an
apparatus for stretch wrapping a load comprises a packaging
material dispenser for dispensing a film web, the packaging
material dispenser including a powered pre-stretch portion, a
rotational drive system for providing relative rotation between the
load and the dispenser during the wrapping cycle, and an electronic
control configured to maintain a predetermined ratio between a
drive powering the pre-stretch portion and the rotational drive
system during a primary portion of a wrap cycle.
[0028] According to another aspect of the present invention, an
apparatus for stretch wrapping a load includes a packaging material
dispenser for dispensing a film web, the packaging material
dispenser including an upstream pre-stretch roller and a downstream
pre-stretch roller within a powered pre-stretch assembly, a
rotational drive system providing relative rotation between the
load and the dispenser during the wrapping cycle, an electronic
control configured to maintain a predetermined ratio between a
drive powering the pre-stretch portion and the rotational drive
system during a primary portion of a wrap cycle, and a final roller
positioned a predetermined distance from the downstream pre-stretch
roller, wherein a film length extending between the downstream
pre-stretch roller and the final roller is at least thirteen
inches.
[0029] According to a further aspect of the present invention, an
apparatus for stretch wrapping a load comprises a packaging
material dispenser for dispensing a film web, the packaging
material dispenser including a powered pre-stretch portion, a
rotational drive system providing relative rotation between the
load and the dispenser during the wrapping cycle, an electronic
control configured to maintain a predetermined ratio between a
drive powering the pre-stretch portion and the rotational drive
system during a primary portion of a wrap cycle, wherein the
electronic control is configured to vary the predetermined ratio
during at least one of initial acceleration and final deceleration
of the wrap cycle, and a virtual film accumulator configured to
accommodate variations in film demand as the film is dispensed.
[0030] According to yet another aspect of the present invention, an
apparatus for stretch wrapping a load includes a packaging material
dispenser for dispensing a film web, the packaging material
dispenser including an upstream pre-stretch roller and a downstream
pre-stretch roller within a powered pre-stretch assembly, a
rotational drive system providing relative rotation between the
load and the dispenser during the wrapping cycle, an electronic
control configured to maintain a predetermined ratio between a
drive powering the pre-stretch portion and the rotational drive
system during a primary portion of a wrap cycle, wherein the
electronic control is configured to vary the predetermined ratio
during at least one of initial acceleration and final deceleration
of the wrap cycle, and a final roller positioned a predetermined
distance from the downstream pre-stretch roller, the predetermined
distance being such that at least a portion of a length of film
extending between the downstream pre-stretch roller and the final
roller acts to dampen variations in forces acting on the
pre-stretched packaging material as it travels from the dispenser
to the load.
[0031] According to one aspect of the present invention, a method
for stretch wrapping a load comprises providing a packaging
material including a powered pre-stretch portion, providing
relative rotation between the packaging material dispenser and the
load, setting a ratio of relative rotational speed to pre-stretch
speed, electronically maintaining the set ratio during a primary
portion of the wrap cycle to dispense pre-stretched packaging
material, and electronically varying the set ratio during at least
one of an initial acceleration and a final deceleration of the
packaging material dispenser relative to the load.
[0032] According to another aspect of the present invention, a
method for stretch wrapping a load includes providing relative
rotation between the packaging material dispenser and the load,
setting a ratio of relative rotational speed to pre-stretch speed,
electronically maintaining the set ratio during a primary portion
of the wrap cycle to dispense the predetermined substantially
constant length of pre-stretched packaging material during each
revolution of the packaging material dispenser relative to the load
during the primary portion of the wrap cycle, electronically
varying the set ratio upon sensing at least one of a film break and
slack film, and damping variations in forces acting on the
dispensed predetermined constant length of pre-stretched packaging
material as it travels from the dispenser to the load.
[0033] Additional objects and advantages of the invention will be
set forth in part in the description which follows, and in part
will be obvious from the description, or may be learned by practice
of the invention. The objects and advantages of the invention will
be realized and attained by means of the elements and combinations
particularly pointed out in the appended claims.
[0034] It is to be understood that both the foregoing general
description and the following detailed description are exemplary
and explanatory only and are not restrictive of the invention, as
claimed.
[0035] The accompanying drawings, which are incorporated in and
constitute a part of this specification, illustrate one embodiment
of the invention and together with the description, serve to
explain the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] FIG. 1 is an isometric view of a stretch wrapping apparatus
for wrapping a load according to one aspect of the present
invention;
[0037] FIG. 2 is an isometric view of a roll carriage of the
stretch wrapping apparatus of FIG. 1, the roll carriage including a
packaging material dispenser with a pre-stretch portion, a film
drive down portion, a virtual accumulator, and a film metering
portion, according to one aspect of the present invention;
[0038] FIG. 3A is an isometric view of a roll carriage of the roll
carriage including a packaging material dispenser with a
pre-stretch portion, a film drive down portion, a virtual
accumulator, and a film metering portion of FIG. 2, with certain
elements in different positions, according to one aspect of the
present invention;
[0039] FIG. 3B is an enlarged portion of the isometric view of the
roll carriage of FIG. 3A;
[0040] FIG. 4 is an isometric view of a lower film roll support on
a roll carriage according to one aspect of the present
invention;
[0041] FIG. 5 is an isometric view of an upper film roll support on
a roll carriage according to one aspect of the present
invention;
[0042] FIG. 6 is an isometric view of a support structure for the
rotating ring of a stretch wrapping apparatus according to one
aspect of the present invention;
[0043] FIG. 7 is a top view of a load being wrapped and
illustrating the shortest wrap radius and the longest wrap radius
according to one aspect of the present invention;
[0044] FIG. 8 is a side view of a rolled portion of packaging
material formed into a cable according to one aspect of the present
invention;
[0045] FIG. 9 is an isometric view of an alternative embodiment of
a stretch wrapping apparatus according to one aspect of the present
invention;
[0046] FIG. 10 is a front cross-sectional view of the stretch
wrapping apparatus of FIG. 9;
[0047] FIG. 11 is a side view of another alternative embodiment of
a stretch wrapping apparatus according to the present
invention;
[0048] FIG. 12 is a side view of an alternative drive system of the
stretch wrapping apparatus of FIG. 11; and
[0049] FIG. 13 is a side view of yet another alternative embodiment
of a stretch wrapping apparatus according to the present
invention.
DESCRIPTION OF THE EMBODIMENTS
[0050] Reference will now be made in detail to the present
embodiment of the invention, an example of which is illustrated in
the accompanying drawings. Examples and descriptions of the
invention are also set forth in the Invention Disclosure that is
included as part of the provisional application and incorporated
herein by reference. In addition, the disclosures of each of U.S.
Pat. No. 4,418,510, U.S. Pat. No. 4,953,336, U.S. Pat. No.
4,503,658, U.S. Pat. No. 4,676,048, U.S. Pat. No. 4,514,995, and
U.S. Pat. No. 6,748,718 are incorporated herein by reference in
their entirety. In addition, U.S. patent application Ser. No.
11/398,760, filed Apr. 6, 2006, and entitled "Method and Apparatus
for Dispensing a Predetermined substantially constant length of
Pre-stretched Film Relative to Load Girth," and U.S. patent
application Ser. No. 10/767,863, filed Jan. 30, 2004, and entitled
"Method and Apparatus for Rolling a Portion of a Film Web into a
Cable" are incorporated by herein by reference in their entirety.
Wherever possible, the same reference numbers will be used
throughout the drawings to refer to the same or like parts.
[0051] The present invention is related to a method and apparatus
for dispensing a predetermined substantially constant length of
pre-stretched packaging material per revolution of a packaging
material dispenser around a load during a wrapping cycle. The
packaging material dispenser may include a pre-stretch portion and
a pre-stretch metering assembly. The packaging material dispenser
may be rotated about the load to be wrapped, or the load may be
rotated relative to the packaging material dispenser. In each case,
a rotational drive system is used to provide the relative rotation.
The rotational drive system may include a rotating ring (vertical
or horizontal), a turntable, or a rotatable arm. A mechanical
linkage may be used to connect the rotational drive system to the
pre-stretch portion of the packaging material dispenser to drive
the pre-stretch portion. Thus, rotation of the downstream roller of
the pre-stretch portion of the packaging material assembly is
mechanically linked to the rotational drive, ensuring that a ratio
of relative rotational speed to pre-stretch speed may be set such
that the pre-stretch portion dispenses a substantially constant
length of pre-stretched packaging material during each
revolution.
[0052] The substantially constant length of pre-stretched packaging
material dispensed per revolution of the packaging material
dispenser is predetermined based upon the girth of the load to be
wrapped. The girth (G) of a load is defined as the length (L) of
the load plus the width (W) of the load times two (2) or
G=[2.times.(L+W)]. Test results have shown that good wrapping
performance in terms of load containment (wrap force) and optimum
packaging material use (efficiency) is obtained by dispensing a
length of pre-stretched packaging material that is between
approximately 90% and approximately 130% of load girth, and
preferably between approximately 95% and approximately 115% of load
girth. The amount of film dispensed divided by the girth of the
load is referred to in this application as the payout percentage.
For example, a 40 inch.times.48 inch load has a girth of
(2.times.(40+48) or 176 inches. To provide a payout percentage of
between approximately 95% and approximately 115%, it would be
necessary to dispense a length of pre-stretched packaging material
that has a length of between approximately 167 inches and
approximately 202 inches. Additional testing has shown that a
payout percentage equal to approximately 107% of load girth gives
best containment and efficiency results. Thus, for the example
above, the predetermined amount of pre-stretched packaging material
to be dispensed for each revolution of the packaging material
dispenser would be approximately 188 inches. However, the optimum
payout percentage will vary according to the type of stretch wrap
packaging material used, the level of pre-stretch used (i.e.,
percentage of elongation), and different load containment (i.e.,
wrap force) required.
[0053] Because a ratio of the relative rotational speed to
pre-stretch speed is set and maintained during the wrap cycle, the
same amount of pre-stretched packaging material will be dispensed
during each revolution of the dispenser relative to the load,
regardless of the speed of relative rotation. For example, if
approximately 190 inches of packaging material are needed per
revolution of the rotating ring/dispenser, one can measure the
circumference of the downstream pre-stretch roller, for example 10
inches, and know that each rotation of the downstream pre-stretch
roller will dispense 10 inches of pre-stretched packaging material.
Therefore, in order to dispense 190 inches of packaging material
during one revolution of the rotating ring and dispenser, the
downstream pre-stretch roller may rotate 19 times (190 inches/10
inches). Once the necessary number of revolutions of the downstream
pre-stretch roller is known, it is possible to set the sprocket to,
for example, 19 pre-stretch roller revolutions per one rotating
ring rotation. Thus, the length of the pre-stretched packaging
material that is dispensed may be between approximately 90% and
approximately 120% of girth per rotating ring revolution and the
dispensing is mechanically controlled and precisely selectable by
establishing a mechanical ratio of a rotational drive (e.g., drive
to rotate a rotatable ring, a turntable, or a rotating arm) to
pre-stretch roller surface speed (e.g., number of pre-stretch
roller revolutions per rotating ring rotation).
[0054] Drive components can be arranged for easy change of the
amount of pre-stretch of the packaging material or the payout
percentage dispensed per revolution of the rotatable ring. For
example, in one exemplary embodiment, the packaging material
dispenser is mounted on the rotatable ring, and a motor rotates a
belt that rotatably drives the rotatable ring. A first portion of a
mechanical connection can translate the drive of the motor and
rotating belt to drive pre-stretch rollers in the pre-stretch
assembly of the packaging material dispenser. A second portion of
the mechanical connection controls an input to output ratio so as
to set a ratio of the speed of the rotation of the rotatable ring
to the speed of the rotation of the pre-stretch rollers in order to
obtain the predetermined substantially constant length of film per
revolution of the rotatable ring. No electrical slip rings, motor,
control box, or force controls are required because the rotation of
the rotatable ring drives the pre-stretch rollers through the
mechanical connection.
[0055] The dispensing of the predetermined substantially constant
length of pre-stretched packaging material per revolution of the
packaging material dispenser relative to the load may be
independent of the speed of the relative rotation. It is
independent of the speed of the relative rotation because a ratio
of the relative rotational speed to pre-stretch speed is set and
mechanically maintained during the wrap cycle. Thus, regardless of
the speed of the relative rotation, the ratio is maintained and
thus the pre-stretch speed changes accordingly with the relative
rotation speed. The dispensing of the predetermined substantially
constant length of pre-stretched packaging material per revolution
of the packaging material dispenser relative to the load may also
be independent of load girth shape or placement of the load. That
is, for each revolution of the packaging material dispenser
relative to the load, regardless of the speed of the relative
rotation, the pre-stretch roller may complete a fixed number of
revolutions. If the speed of the relative rotation increases, the
amount of time it takes for the pre-stretch roller to complete the
fixed number of revolutions may decrease, but the same fixed number
of revolutions will be complete during one revolution of the
packaging material dispenser relative to the load. Similarly, if
the speed of the relative rotation decreases, the amount of time
required for the downstream pre-stretch roller to complete the
fixed number of revolutions may increase, but the same fixed number
of revolutions may be complete during one revolution of the
packaging material dispenser relative to the load. Because the
speed of the relative rotation is tied to the speed of the
pre-stretch through the mechanical link, the proportion or ratio of
the speeds is constant, regardless of what those speeds may be.
Thus, during acceleration and deceleration of the relative
rotation, the pre-stretch assembly accelerates and decelerates with
the rotational drive system.
[0056] The ability of the rotational drive system and the
pre-stretch assembly to accelerate and decelerate together is a
particular advantage when a rotatable ring is the means of
providing relative rotation. The rotatable ring may be powered for
very rapid acceleration to over 60 rpm with an acceleration period
of one second and a deceleration period of one second. Since the
packaging material feed (via the pre-stretch assembly) may be
independent of the relative rotational speed as described above,
there is no extra force on the packaging material during
acceleration or excess packaging material during deceleration.
[0057] If a reduced force below optimum wrapping force is required
during initial startup, the rotating ring can be reversed to create
slack packaging material at the end of the previous cycle. A
one-way clutch may be included to prevent any backlash from
packaging material feed while the rotating ring is reversed. The
slack packaging material may remain well around the first corner of
the load until the elasticity of the dispensed packaging material
can take it up. [058] According to one aspect of the invention, a
film break sensing roller is provided. The primary purpose of the
film break sensing roller is to completely stop film feed as
quickly as possible when the film breaks so that the film does not
backlash and wind up on the rollers. The film break sensing roller
is connected to the mechanical connection which controls the
input/output ratio of the speed of the rotational drive to the
surface speed of the pre-stretch roller. The film break sensing
roller has the ability to shift this ratio such that even though an
input is received, the output is zero, effectively stopping the
dispensing of film. A secondary purpose of the film break sensing
roller is that it senses slack film. As the film break sensing
roller moves toward a neutral position, the input/output ratio
decreases, slowing the film feed. As the film feed slows and the
rotatable ring continues to rotate, the slack is taken up and a new
film feed position and input/output ratio are established.
[0058] According to one aspect of the present invention, a stretch
wrapping apparatus 100 for wrapping a load may include a
non-rotating frame, a moveable frame, a rotatable ring, a fixed
ring, a rotational drive system, and a packaging material dispenser
with a pre-stretch assembly.
[0059] As embodied herein and shown in FIG. 1, the apparatus 100
may include the non-rotating frame 1 10. The non-rotating frame 110
may include four vertical legs, 112a, 112b, 112c, and 112d. The
legs 112a, 112b, 112c, and 112d of the non-rotating frame 110 may
or may not be positioned over a conveyor (not shown) such that a
load 138 to be wrapped may be conveyed into a wrapping space
(defined in part by the non-rotating frame 110), wrapped, and then
conveyed away from the wrapping space. Thenon-rotating frame 110
may also include a plurality of horizontal supports 116a, 116b,
116c, 116d, that connect the vertical legs 112a, 112b, 112c, and
112d, to each other, forming a square or rectangular shape (see
FIG. 1). Additional supports may be placed across the square or
rectangle formed by the horizontal supports 116a, 116b, 116c, 116d
(see FIG. 1). In one exemplary embodiment, the non-rotating frame
110 may have a footprint of 88 inches by 100 inches. The benefit of
this particular footprint is that it may allow the stretch wrapping
apparatus 100 to fit into an enclosed truck for shipment. Prior art
devices may generally have a much larger footprint. Due to their
large size, disassembly may be required to transport the prior art
devices. Otherwise, shipment on a flatbed may be required. Either
of those two scenarios could significantly increase shipping
costs.
[0060] A vertically movable frame portion 118 may be connected to
and movable on the non-rotating frame 110. As embodied herein and
shown in FIGS. 1, 2, 3A, and 3B, the vertically movable frame
portion 118 may include a support portion 120, a rotatable ring
122, and a fixed (i.e., non-rotatable) ring 124. A plurality of
rotatable ring supports 126 (see FIG. 6) may extend downwardly from
the support portion 120. Each rotatable ring support 126 may have
an L-shape and may comprise one or more pieces of material, such as
steel, to form the L-shape. It is possible that the rotatable ring
supports 126 may have a shape other than an L-shape. Connected to
each rotatable ring support 126 may be a roller or wheel 128.
Rotatable ring 122 may rest on top of the rollers 128, such that
rotatable ring 122 may ride on the rollers 128. Preferably,
rotatable ring 122 may be constructed of a very lightweight
material. The lightweight nature of the rotatable ring 122 may
allow for faster movement of the rotatable ring 122, and thus,
faster wrapping cycles. In one exemplary embodiment, the rotatable
ring 122 may have an inner diameter of 80 inches, an outer diameter
of 88 inches, and may be made of a lightweight composite material.
Use of a composite material may reduce the weight of the rotatable
ring by approximately 75% when compared to conventional steel or
aluminum rotatable rings.
[0061] Independent of the rotatable ring 122, the fixed ring 124
may be positioned below and outside of the rotatable ring 122.
Fixed ring 124 may be supported by the support portion 120. A first
drive belt 130, driven by a motor 132, may be positioned around an
outer circumference of the rotatable ring 122. The motor 132
rotates the first drive belt 130 which in turn rotates the
rotatable ring 122. Thus, the motor 132 and the first drive belt
130 form a rotational drive system. A second drive belt 134 may be
positioned around the outer circumference of the fixed ring 124.
The second drive belt is a fixed belt that does not rotate. This
second drive belt 134 may be used as part of a mechanical
connection between the rotational drive system of the rotatable
ring 122 and a pre-stretch assembly of a packaging material
dispenser, as will be discussed below. It is also contemplated that
a second motor 136 may be provided to raise and/or lower the
movable frame portion 118 on non-rotating frame 110. Alternatively,
the rotatable ring 122 can be frictionally driven by suitably
surfaced wheel(s) pressed against the outer surface of the
rotatable ring 122.
[0062] As embodied herein and shown in FIGS. 1-3B, the stretch
wrapping apparatus 100 may include a packaging material dispenser
140. As shown in FIGS. 2, 3A, and 3B, the packaging material
dispenser 140 may dispense a sheet of packaging material 142 in a
web form. The packaging material dispenser 140 may include a roll
carriage 144. As embodied herein and shown in FIGS. 2-4, the roll
carriage 144 may include a structure for supporting a roll 152 of
packaging material 142. A lower support plate 146 includes a lower
roll support 148 mounted thereon. It is contemplated that the lower
roll support 148 may be configured to engage a core 150 of the roll
152 of packaging material 142, and may rotate as roll 152 rotates.
Alternatively, roll 152 may rotate relative to the lower roll
support 148. The roll carriage 144 may also include an upper
support plate 154. The upper support plate 154 may include a
rotatable plate 155 hingedly connected to the upper support plate
154 of the roll carriage 144 and include an upper roll support 156.
The upper roll support 156 may be similar to the lower roll support
148 in structure and operation. The upper roll support 156 may be
mounted on the rotatable plate 155. When removal of the roll 152 of
packaging material 142 is desired, the rotatable plate 155 may be
lifted, causing the rotatable plate 155 to rotate about a hinge,
moving the upper roll support 156 out of engagement with the top of
the core 150 of roll 152 of packaging material. This allows the
remainder of the roll 152 to be easily removed from the lower roll
support 148 and from the roll carriage 144. Insertion of a new roll
152 of packaging material 142 into the roll carriage 144 may be
accomplished by reversing the steps, e.g., placing the bottom of
the core 150 over the lower roll support 148, lifting the rotatable
plate 155 to raise the upper roll support 156, sliding the roll 152
into position in the roll carriage 144, and then returning the
rotatable plate 155 to its lowered position to allow the upper roll
support 156 to engage the top of the core 150.
[0063] Preferably, the packaging material dispenser 140 is
lightweight, which in combination with the lightweight rotatable
ring 122 may allow for faster movement of the rotatable ring 122,
and thus, shorter (faster) wrapping cycles. By using the second
drive belt 134 to drive a pre-stretch assembly off of the
rotational drive system, it is possible to eliminate the
conventional motor that drives the packaging material dispenser 140
as well the conventional control box, greatly reducing the weight
of the packaging material dispenser 140. By providing an entirely
mechanical connection between the rotational drive system and the
pre-stretch assembly, the need for placing electrical power sources
or connections on the rotatable ring 122 for electrically powering
the pre-stretch assembly may be eliminated.
[0064] In an exemplary embodiment, the packaging material 142 is
stretch wrap packaging material. However, it should be understood
that various other packaging materials such as netting, strapping,
banding, or tape may be used as well. As used herein, the terms
"packaging material," "film," "film web," "web," and "packaging
material web" are interchangeable.
[0065] The packaging material dispenser 140 and rotatable ring 122
may rotate about a vertical axis 158 (FIG. 1) as the moveable frame
118 moves up and down the non-rotating frame 110 to spirally wrap
packaging material 142 about a load 138. The load 138 can be
manually placed in the wrapping area or conveyed into the wrapping
area by the conveyor 114. As shown in FIGS. 1-3B, the packaging
material dispenser 140 may be mounted underneath and outboard of
the rotatable ring 122, thus maximizing wrapping space.
[0066] The packaging material dispenser 140 may include a
pre-stretch assembly 160. Pre-stretch assembly 160 may include an
upstream pre-stretch roller 162 and a downstream pre-stretch roller
164. "Upstream" and "downstream," as used in this application, are
intended to define the direction of movement relative to the flow
of packaging material 142 from the packaging material dispenser
140. Thus, since the packaging material 142 flows from the
packaging material dispenser 140, movement toward the packaging
material dispenser 140 and against the flow of packaging material
142 from the packaging material dispenser 140 may be defined as
"upstream" and movement away from the packaging material dispenser
140 and with the flow of packaging material 142 from the packaging
material dispenser 140 may be defined as "downstream."
[0067] The surfaces of the upstream and downstream pre-stretch
rollers 162 and 164 may either be coated or uncoated depending on
the type of application in which the stretch wrapping apparatus 100
is being used. The upstream and downstream pre-stretch rollers 162
and 164 may be mounted on roller shafts 166 and 168, respectively.
Sprockets 170 and 172 may be located on the ends of the roller
shafts 166 and 168, respectively, and may be configured to provide
control over the rotation of the roller shafts 166 and 168 and the
upstream and downstream pre-stretch rollers 162 and 164. It is
contemplated that the upstream pre-stretch roller 162 and the
downstream pre-stretch roller 164 may have different sized
sprockets 170 and 172 so that the surface movement of the upstream
pre-stretch roller 162 may be at least approximately 40% slower
than that of the downstream pre-stretch roller 164. The sprockets
170, 172 may be sized depending on the amount of packaging material
elongation desired. Thus, the surface movement of the upstream
pre-stretch roller 162 can be about 40%, 75%, 200% or 300% slower
than the surface movement of the downstream pre-stretch roller 164
to obtain pre-stretching of 40%, 75%, 200% or 300%. While
pre-stretching normally ranges from 40% to 300%, excellent results
have been obtained when narrower ranges of pre-stretching are used,
such as pre-stretching the material 40% to 75%, 75% to 200%, 200%
to 300%, and at least 100%. In certain instances, pre-stretching
has been successful at over 300% of pre-stretch. The upstream and
downstream pre-stretch rollers 162 and 164 may be operatively
connected by a drive chain or belt 174.
[0068] Rapid elongation of the packaging material 142 by the
pre-stretch rollers 162 and 164, followed by rapid strain relief of
the packaging material 142, may cause a "memorization" effect. Due
to this "memorization" effect, the packaging material 142 may
actually continue to shrink for some time after being wrapped onto
the load 138. Over time, the packaging material 142 may
significantly increase holding force and conformation to the load
138. This characteristic of the packaging material 142 may allow it
to be used for wrapping loads at very close to zero stretch
wrapping force, using the memory to build holding force and load
conformity. As previously noted, some embodiments of the present
invention permit relative rotation between the load and dispenser
at approximately 60 rpm. At this speed, the dispensed pre-stretched
film has a tendency to billow around the load before
contracting/shrinking onto the load such that the film contacts all
sides/corners of the load substantially simultaneously. This is
particularly beneficial when dealing with light, crushable, or
twistable loads.
[0069] In one exemplary embodiment, each of the upstream and
downstream pre-stretch rollers 162 and 164 may preferably be the
same size, and each may have, for example, an outer diameter of
approximately 2.5 inches. The upstream and downstream pre-stretch
rollers 162 and 164 should have a sufficient length to carry a
twenty (20) inch wide web of packaging material 142 along their
working lengths, and they may be mounted on the roller shafts 166
and 168, which may include, for example, hex shafts. The upstream
and downstream pre-stretch rollers 162 and 164, may be connected to
each other through chains to a sprocket idle shaft with the
sprockets 170 and 172 selected for the desired pre-stretch level.
It is contemplated that, in one exemplary embodiment, rollers used
for conventional conveyors may be used to form the upstream and
downstream pre-stretch rollers 162 and 164.
[0070] As embodied herein and shown in FIGS. 2, 3A, and 3B, the
pre-stretch assembly 160 may include a midstream idle roller 176
positionable between the upstream and downstream pre-stretch
rollers 162 and 164. The midstream idle roller 176 may be the same
diameter as or smaller in diameter than the upstream and downstream
pre-stretch rollers 162 and 164. Preferably, midstream idle roller
176 is uncoated. In one exemplary embodiment, midstream idle roller
176 may include an idle roller operatively connected to an upper
frame portion 178 of the packaging material dispenser 140. The
midstream idle roller 176 may also be a cantilevered roller that is
not connected to any additional structure and is unsupported at its
base. Although not physically connected at its base or to a base
support, the midway idle roller 176 may nest in a U-shaped guard
(not shown) that connects the upstream and downstream pre-stretch
rollers 162 and 164 as disclosed in U.S. patent application Ser.
No. 11/371,254, filed Mar. 9, 2006, and entitled "Stretch Wrapping
Apparatus Having Film Dispenser with Pre-Stretch Assembly," the
entire disclosure of which is incorporated herein by reference.
Preferably the midstream idle roller 176 may be aligned to provide
a pinching action on the upstream pre-stretch roller 162, as
disclosed in U.S. Pat. No. 5,414,979, the entire disclosure of
which is incorporated herein by reference. Additional idle rollers
may be provided adjacent the upstream and downstream pre-stretch
rollers 162 and 164 as necessary to direct the film path.
[0071] According to another aspect of the present invention, the
packaging material dispenser 140 may include a final idle roller
180 positioned downstream of the second downstream pre-stretch
roller 164. Spacing the final idle roller 180 downstream of the
last pre-stretch roller 164 may provide an extra length 182 of
packaging material 142 between the downstream pre-stretch roller
164 and the final idle roller 180 mounted on the packaging material
dispenser 140. See FIG. 7. The extra length 182 of packaging
material 142 may provide the additional elasticity in the
pre-stretched packaging material 142 to accommodate the passage of
a corner of the load 138 or to accommodate offset and/or off-center
loads. The extra length 182 of packaging material 142 provides the
same benefits as a film accumulator or a dancer bar without require
the usual structure and connections required by such. For this
reason, the extra length 182 of packaging material 142 may also be
referred to as a "virtual accumulator" 182.
[0072] The virtual accumulator 182 may also permit the length of
packaging material 142 to the load 138 to always be longer than at
least one side of the load 138. Preferably, the final idle roller
180 is positioned to provide an extra length 182 of packaging
material 142 that is equal to a length greater than a difference
between the shortest wrap radius of a load and the longest wrap
radius of a load 138. FIG. 7 illustrates the wrap radii with regard
to a rectangular load 138 and shows that the shortest wrap radius
186 can be found along the middle of the side of the load and the
longest wrap radius 188 can be found at a corner of the load 138.
By providing an extra length 182 of film 142 that is greater than
the difference between these two radii, there is sufficient extra
film 142 to accommodate movement from the shortest wrapping radius
186 to the longest wrapping radius 188.
[0073] Experimentation, and observation of the geometry of the wrap
process revealed that the virtual accumulator 182 produces
significant dampening of the force variation when the load is
relatively centered. A 40.times.48 rectangular load would add
approximately 13 inches to the film length. Although less than this
will be required where the load does not "fill the ring wrap space"
since the film from the final idle roller to the load will be more,
testing has shown that a minimum length of 13 inches should be
used. Depending on the positioning of the load, a maximum of length
of up to about 88 inches of extra film may be used. The optimum
length, considering threading and film roll change, has been found
to be approximately 29 inches between the downstream pre-stretch
roller 164 and the final idle roller 180 mounted to the roll
carriage 144. It should be noted that the distance from the final
idle roller 180 to the load 138 constantly varies as the corners of
the load 138 pass. If the ring is "filled," the passage of a corner
of the load 138 may permit only inches of film to the final idle
roller 180.
[0074] As shown in FIGS. 2, 3A, and 3B, the packaging material
dispenser 140 may also include a pre-stretch packaging material
metering assembly 190. The pre-stretch packaging material metering
assembly 190 may include a mechanical input/output ratio control
192, a film break sensing roller 194, and a metering adjustment
control 196.
[0075] As embodied herein, the second drive belt 134 forms a first
part of a mechanical connection between the rotational drive system
and the pre-stretch assembly 160. The mechanical input/output ratio
control 192 forms the second part of the mechanical connection
between the rotational drive system and the pre-stretch assembly
160. As shown in FIGS. 2, 3A, and 3B, the mechanical input/output
ratio control 192 may be a variable transmission such as, for
example, a hydrostatic transmission 200. One exemplary such
hydrostatic transmission is made by Hydrogear, model number
BDR-311. The hydrostatic transmission 200 may include a first
rotatable input shaft 202 and a second rotatable output shaft 204.
A series of hydraulic pumps and valves control the ratio between
the input and the output of the hydrostatic transmission 200. This
ratio may be set as desired.1 -3B, the second drive belt 134 may
engage the rotatable input shaft 202 of the hydrostatic
transmission 200 on the roll carriage 144 of the packaging material
dispenser 140. During operation of the apparatus 100, the motor 132
drives the first drive belt 130, which in turn rotates the
rotatable ring 122 and the packaging material dispenser roll
carriage 144 mounted on the rotatable ring 122. As the roll
carriage 144 rotates with the ring 122, the second drive belt 134
on fixed ring 124 engages the rotatable input shaft 202 of the
hydrostatic transmission 200, causing the input shaft 202 to
rotate. Thus, the second drive belt 134 translates the rotational
drive from the rotatable ring 122 to the hydrostatic transmission
200. The output of the hydrostatic transmission 200, via the
rotatable output shaft 204, drives the downstream roller 164 of the
pre-stretch assembly 160, and through the connection 174 between
the pre-stretch rollers 162, 164, the upstream pre-stretch roller
164. As the pre-stretch rollers 162, 164 rotate, the packaging
material 142 flows downstream from the packaging material roll 152
through the pre-stretch assembly 160, through the pre-stretch
packaging material metering assembly 190 and to the load 138, as
will be discussed in greater detail below.
[0076] As embodied herein, the hydrostatic transmission 200 may
include a rotatable input shaft 202 that engages the fixed second
drive belt 134 through gear teeth or any other suitable mode of
engagement. Accordingly, when the rotatable ring 122 and the roll
carriage 144 are rotatably driven by the first drive belt 130 via
the motor 132, the movement of the roll carriage 144, including the
rotatable input shaft 202, relative to the fixed second drive belt
134 causes rotation of the rotatable input shaft 202. The
hydrostatic transmission 200 may be set to control a ratio of the
relative rotational speed to pre-stretch speed by controlling a
ratio of drive input to drive output. The speed at which the
rotatable input shaft 202 rotates, based on the speed at which the
rotatable ring 122 and the roll carriage 144 rotate, may be
considered the input. The series of pumps and valves contained
within the hydrostatic transmission 200 transmit the input from the
input shaft 202 to the output shaft 204, adjusting the rotational
speed of the output shaft 204 based on the input/output ratio of
the hydrostatic drive 200.
[0077] The rotation of the rotatable output shaft 204 drives the
downstream pre-stretch roller 164. The connection 174 between the
upstream and downstream pre-stretch rollers 162, 164 causes the
upstream pre-stretch roller 162 to rotate as the downstream
pre-stretch roller 164 rotates, thus dispensing film 142.
Engagement between the rotatable output shaft 204 and the
downstream pre-stretch roller 164 may include, for example, drive
belts, gears, chains, and/or any other suitable devices configured
to convert rotation of the rotatable output shaft 204 into rotation
of the upstream and downstream pre-stretch rollers 162, 164. In the
exemplary embodiment, the hydrostatic transmission 200 may have a
ninety degree angle between its rotatable input shaft 202 and its
rotatable output shaft 204. Although a hydrostatic drive is used in
the exemplary embodiment, any other appropriate mechanical power
transmissions may be used to control the input/output ratio.
Further, other suitable mechanical controls such as, for example, a
split sheave, variable pitch belt sheaves, fixed center and
adjustable center sheaves, wider range variable pitch belt drives,
cone and ring variable speed drives, rolling ring variable speed
drives, and ball and ring variable speed drives may be used to
control the input/output ratio. Alternatively, methods such as a
moving second ring with the differential between the rings
generating the output, using a differential and controlling one
output to adjust another output, and an electric motor without load
cell feedback.
[0078] The input/output ratio of the hydrostatic transmission 200
may be selectively and variably adjusted. As the input/output ratio
increases, the relative speed of the output shaft 204 increases,
and the rotational speed of the upstream and downstream pre-stretch
rollers 162 and 164 increases proportionally. The increased
rotational speed of the upstream and downstream pre-stretch rollers
162 and 164 causes an increase in the supply rate of the packaging
material 142. If, on the other hand, the input/output ratio
decreases, then the speed of the rotational output shaft 204
decreases, and the relative rotational speed of the upstream and
downstream pre-stretch rollers 162 and 164 decreases
proportionally, resulting in a decrease in the supply rate of the
packaging material 142. Thus, it should be apparent that while the
rotatable ring 122 and the rotatable input shaft may rotate at
substantially the same speed, the rotational speed of the rotatable
output shaft 204, and consequently the rotational speed of the
upstream and downstream pre-stretch rollers 162 and 164 may vary
depending on the input/output ratio setting of the hydrostatic
transmission 200.
[0079] A transmission lever 206 may be operatively coupled to the
hydrostatic transmission such that the orientation of the
transmission lever 206 may affect the input/output ratio of the
hydrostatic transmission 200. For example, the transmission lever
206 may be adjusted to a first position, where the transmission
lever 206 may set a minimal input/output ratio such that the speed
of the rotatable input shaft 202 is much greater than the speed of
the rotatable output shaft 204 and thus the downstream pre-stretch
roller 164. It is contemplated that in the first position, the
transmission lever 206 may prevent input at the rotatable input
shaft 202 from being transmitted/translated to the rotatable output
shaft 204. This may be accomplished, for example, by controlling a
valve positioned between an input pump and an output pump in the
hydrostatic transmission. With the transmission lever 206 in such a
position, the hydrostatic drive is essentially in neutral. It can
accept an input from the rotatable input shaft 202 but does not
produce an output through the rotatable output shaft 204. The
transmission lever 206 may also be adjusted to a second position,
where the transmission lever 206 may allow for a maximum
input/output ratio. The transmission lever 206 may be adjusted to
virtually any position between the first and second positions,
causing changes in the input/output ratio and thus ratio of
relative rotational speed to pre-stretch speed. Changes in the
input/output ratio and the ratio of relative rotational speed to
pre-stretch speed result in changes to the relative speed of the
rotatable output shaft 204. Accordingly, the input/output ratio may
vary between a maximum ratio and a minimum ratio, depending on the
angular orientation of the transmission lever 206 relative to the
hydrostatic transmission 200, and the output of the hydrostatic
transmission 200. The speed of downstream pre-stretch roller 164,
and thus the amount of film dispensed by the pre-stretch assembly
160, varies based on the input/output ratio.
[0080] According to one aspect of the present invention, a metering
adjustment control 196 may be provided. The metering adjustment
control 196 may include, for example, a sliding plate 220 having a
slot 222 therein extending through a first surface 224. The sliding
plate 220 may also include a second surface 226 extending
substantially perpendicularly to the first surface 224. The first
surface 224 of the sliding plate 220 may rest on the lower frame
portion 216 of the packaging material dispenser 140, and may be
configured to slide thereon. The slot 222 in the sliding plate 220
may be arranged such that it at least partially overlaps a slot
(not shown) in the lower frame portion 216 of the packaging
material dispenser 140. The metering adjustment control 196 may
include an adjustment knob 232 and a bolt assembly, including a
bolt 234 and a nut 236. The bolt 234 may be inserted through an
aperture 238 in the second surface 226 of the sliding plate 220,
and may also extend through an aligned aperture 240 in a side frame
portion 242 of the packaging material dispenser 140. Rotation of
the adjustment knob 232 in a first direction may draw the bolt 234
towards the adjustment knob 232, causing the sliding plate 220 to
slide in a first direction. Rotation of the adjustment knob 232 in
a second direction (opposite the first direction) may cause the
sliding plate 220 to slide away from the adjustment knob 232.
Accordingly, an operator may selectively determine the input/output
ratio of the hydrostatic transmission 200 by adjusting the
adjustment knob 232. The position of the sliding plate 220, through
a series of linkages, adjusts the input/output ratio of the
hydrostatic transmission 200, and thus, the supply rate of
packaging material 142. Thus, by using the adjustment knob 232 to
position the sliding plate 220 in a predetermined position, an
operator can set the input/output ratio of the hydrostatic
transmission 200, thereby setting the rotational speed of the
pre-stretch rollers relative to the speed of the rotatable ring
122. This in turn "sets" the pre-stretch rollers 162, 164 to
dispense a predetermined substantially constant length of film per
revolution of the rotatable ring 122.
[0081] In situations when the packaging material apparatus is to be
used for loads having different girths, the adjustment knob 232 of
the metering adjustment control 196 should be positioned to adjust
the payout percentage for the girth of the load and wrap force
desired. Setting the payout percentage with knob 232 will set the
input/output ratio of the hydrostatic transmission 200, ultimately
determining the amount of packaging material 142 that will be
distributed per revolution of the upstream and downstream
pre-stretch rollers 162 and 164. Thus, to wrap larger girth loads,
more packaging material will be required per revolution and thus
the ratio of relative rotational speed to pre-stretch speed should
be higher to permit a higher predetermined substantially constant
length of packaging material to be distributed for each revolution.
On the other hand, if the load has a small girth, less packaging
material will be required per revolution and thus the ratio of
relative rotational speed to pre-stretch speed should be lower to
permit a smaller predetermined substantially constant length of
packaging material to be dispensed per revolution of the rotatable
ring 122. Thus, adjustment of the metering adjustment control 196
may allow an operator to selectively adjust the input/output ratio
of the transmission 200 and thus the rotational speed of the
pre-stretch rollers 162 and 164, and the supply rate of the
packaging material 142, such that the stretch wrapping apparatus
100 may be used to wrap loads have varying shapes and sizes.
Therefore, by adjusting the input/output ratio, an operator is
adjusting the speed of the pre-stretch rollers proportional to the
rotational ring speed.
[0082] According to another aspect of the present invention, a film
break sensing roller 194 may be provided. The film break sensing
roller 194 may be operatively coupled to the transmission lever 206
through a series of linkages. The film break sensing roller 194 may
be mounted to the roll carriage 144 on a shaft 212. The film break
sensing roller 194 may have an outer diameter of approximately 2.5
inches, and may have a sufficient length to carry a twenty (20)
inch wide web of packaging material 142 along its working length.
In one embodiment, bearings for supporting the shaft 212 may be
press-fit or welded into each end of the film break sensing roller
194, and the shaft 212 may be placed therethrough, such that the
shaft 212 may be centrally and axially mounted through the length
of the film break sensing roller 194.
[0083] The primary purpose of the film break sensing roller 194 is
to completely stop film feed as quickly as possible when the film
142 breaks so that the film 142 does not backlash and wind up on
the rollers. During normal operation of the stretch wrap apparatus
100, tension in the packaging material 142 holds the film break
sensing roller 194 in a "full forward" position (i.e., retracted
toward pre-stretch assembly 160). When the film break sensing
roller 194 moves from the "full forward" position to a "neutral"
position due to tension release in the packaging material 142, the
film break sensing roller 194 extends away from the pre-stretch
assembly 160. The hydrostatic transmission moves to a neutral
position, i.e., to a position where the output of the hydrostatic
transmission 200 goes to zero even with continued input into the
hydrostatic transmission due to the continued rotation of the
rotatable ring 122 and the packaging material dispenser 140. A
secondary purpose of the film break sensing roller 194 is that it
may sense slack film. For example, if the girth of the load 138 is
radically reduced (as in a few boxes on the only top layer of the
load) the film break sensing roller 194 senses slack film (which
feels the same as a film break) and begins to move towards the
"neutral" position. As the film break sensing roller 194 moves
toward the neutral position, the input/output ratio of the
hydrostatic drive decreases, slowing the film feed. As the film
feed slows and the rotatable ring continues to rotate, the slack is
taken up as the smaller top layer is wrapped and the film break
sensing roller 194 remains in the position at which it no longer
senses the slack, establishing a new film feed position and
input/output ratio where less film/revolution is dispensed.
[0084] As embodied herein and shown in FIGS. 3A and 3B, the film
break sensing roller 194 may be mounted on a shaft 212. A first end
of the shaft may extend through a slot 214 in a lower frame portion
216 of the packaging material dispenser 140, and may be pivotally
attached to an upper support plate 218 of the packaging material
dispenser 140. Additionally, the shaft 212 may be cantilevered,
such that a second end of the shaft may hang freely. Consequently,
the film break sensing roller 194 may swing back and forth between
extended (neutral) and retracted (full forward) positions. The
swinging movement of the film break sensing roller 194 may be
linked to the rotation of the transmission lever 206 as the film
break sensing roller 194 may be coupled to rotate with the
transmission lever 206 through a series of linkages.
[0085] According to another aspect of the present invention, the
stretch wrapping apparatus 100 may be provided with a belted
packaging material clamping and cutting apparatus as disclosed in
U.S. Pat. No. 4,761,934, the entire disclosure of which is
incorporated herein by reference.
[0086] The packaging material 142 may be sealed to the layers of
wrap on the load 138 by any conventional means such as by heat
sealing and by the use of wipe down mechanisms. Further, heated
cutting and sealing elements as known in the art may be used. Also,
the sealing systems may be automatic, semi-automatic, or manually
operated.
[0087] According to another aspect of the present invention, the
stretch wrapping apparatus 100 may be provided with a film drive
down and roping system as disclosed in U.S. patent application Ser.
No. 10/767,863, filed Jan. 30, 2004, and entitled "Method and
Apparatus for Rolling a Portion of a Film Web into a Cable" and in
U.S. patent application Ser. No. ______, filed Feb. 23, 2007, and
entitled "Method and Apparatus for Securing a Load to a Pallet with
a Roped Film Web," the entire disclosures of which are incorporated
herein by reference.
[0088] As shown in FIGS. 2, 3A, and 3B, the stretch wrap apparatus
100 may include a film drive down assembly 38. The film drive down
assembly 38 may include a film drive down roller 40, a film drive
down roller support 42, an actuation mechanism 46, a roping
apparatus 48, and a latching assembly 50. The film drive down
roller support 42 may include a shaft 52, a leg 54 extending
substantially alongside the shaft 52, and a lever 56. The lever 56
may extend at an angle from a bottom end of the leg 54. The shaft
52 may rotatably support the film drive down roller 40. The film
drive down roller support 42 may be rotatably mounted by a pivot
connection 58 on its bottom end either directly or indirectly to
the packaging material dispenser 140. The top end of the film drive
down roller support 42 may move freely, and thus, the entire film
drive down roller support 42 may rotate about an axis extending
through the pivot connection 58, allowing the film drive down
roller support 42 to move between a relatively vertical position
and a tilted film drive down position, shown in FIGS. 2 and 3A,
respectively. When the film drive down roller 40 is in the tilted
film drive down position (FIG. 3A), the film web 142 will enter
onto the surface of the film drive down roller 40 at a first
height. Due to the tilted orientation of the film drive down roller
40, the film web 142 will be forced downward as it travels around
the film drive down roller 40, coming off of the film drive down
roller 40 at a lower height than when film web 142 entered.
[0089] Rotation of the film drive down roller support 42 about the
pivot connection 58 may be achieved using the actuation mechanism
46 shown in FIG. 3A. The actuation mechanism 46 may selectively
engage the lever 56 during certain times in a wrap cycle. The
actuation mechanism 46 may include, for example, an air cylinder
activated pad, and/or any other suitable mechanical, electrical, or
hydraulically powered device configured to project outwardly to
abut and drive the lever 56 upwardly, thus causing clockwise
rotation of the film drive down roller support 42 and the film
drive down roller 40 from the relatively vertical position of FIG.
2 to the tilted film drive down position of FIG. 3A. The film drive
down roller 40 may remain in contact with the film web 142
throughout the wrap cycle, whether the film drive down roller 40 is
in the relatively vertical position or in the tilted film drive
down position.
[0090] In one embodiment, the actuation mechanism 46 may cause
tilting of the film drive down roller 40 at the start of the wrap
cycle, when the packaging material dispenser 140 is in the initial
position. After abutting the lever 56, the air cylinder activated
pad may retract inwardly out of the path of travel of the packaging
material dispenser 140 as relative rotation is provided between the
packaging material dispenser 140 and the load 138. Additionally or
alternatively, the actuation mechanism 46 may include an abutment,
wherein the packaging material dispenser 140 may be lowered while
not rotating to bring the abutment into contact with the lever 56
and cause rotation of the film drive down roller support 42. Prior
to providing relative rotation between the packaging material
dispenser 140 and the load 138, the packaging material dispenser
140 may be moved so as not to be obstructed by the abutment.
[0091] The roping apparatus 48 may be configured to engage a least
a portion of a bottom edge of the film web 142. The roping
apparatus 48 may include, for example, a cable rolling roper
element 60, a pulley 62, and a linking cable 64. The cable rolling
roping element 60 may be slidably or otherwise moveably mounted
either directly or indirectly to the packaging material dispenser
140, such that the cable rolling roping element 60 may move upward
and downward relative to the packaging material dispenser 140. In
FIGS. 2 and 3A, the cable rolling roping element 60 is shown in
lowered and raised positions, respectively. The cable rolling
roping element 60 may move in between the lowered and raised
positions due to movement of the film drive down roller support 42,
which may be operatively connected to the cable rolling roping
element 60 by the linking cable 64. In one embodiment, the linking
cable 64 may include a first end looped or otherwise attached to
the cable rolling roping element 60, and a second end looped or
otherwise attached to an upper portion of the film drive down
roller support 42. When the film drive down roller support 42 is in
the relatively vertical position of FIG. 2, the cable rolling
roping element 60 may be in the lowered position. When the film
drive down roller support 42 rotates towards the tilted film drive
down configuration, it may pull on the linking cable 64. The
pulling force may be translated by the pulley 62 into an upward
movement of the first end of the linking cable 64, causing the
cable rolling roping element 60 to move towards the raised
position. As long as film drive down roller support 42 remains in
the tilted film drive down configuration, the roping element 60 may
remain in the raised position. When the film drive down roller
support 42 is released from the tilted film drive down
configuration, and moves back to the relatively vertical position,
the cable rolling roping element 60 may move back to the lowered
position. The cable rolling roping element 60 may be positioned
downstream of and adjacent to an upstream idle roller 34.
[0092] Preferably, the cable rolling roping element 60 may include
low friction materials, for example unpainted steel bars or
elements coated with zinc chromate. The cable rolling roping
element 60 may have a v-shaped circumferential groove for engaging
the film web 142. The cable rolling roping element 60 works with
the film drive down roller 40 to create a rolled rope 49 of film
that is capable of maintaining its structural integrity as a rope
structure during and after wrapping of a load. The cable rolling
roping element 60 and film drive down roller 40 may form a "cable
rolling means" for rolling a portion of the film web into a cable
of film. The cable rolling means rolls an outer edge of the film
web inward upon itself and toward the center of the film web. The
film is rolled upon itself to form a tightly rolled cable of film,
or a high tensile cable of film along an edge of the film web 142.
As used herein, a "cable of film" or a "rolled cable" or a "rolled
rope" are intended to denote a specific type of "roped" packaging
material, where the film web has been rolled upon itself to create
the rolled cable structure. An example is shown in FIG. 8.
[0093] Once the film drive down roller support 42 rotates into the
position shown in FIG. 3A, it may engage the latching mechanism 50.
The latching mechanism 50 may include a catch, configured to
receive and hold a bolt member 66 mounted to the top end of the
film drive down roller support 42. As long as the bolt member 66 is
held in the catch, the film drive down roller support 42 and the
film drive down roller 40 may be locked in the tilted film drive
down position, and thus, the roping element 60 may be held in the
raised position. In order to release the bolt member 66, the
latching mechanism 50 may include a release device 68. Actuation of
the release device 68 may serve to unlock (release) the catch to
allow the bolt member 66 to escape, thus allowing the film drive
down roller support 42 and film drive down roller 40 to return to
the relatively vertical position of FIG. 2. The release device 68
may include, for example, a spring steel release pad. The spring
steel release pad 68 may be configured to engage an abutment 69
mounted on a non-rotating frame 71, such as, for example, a roller
or wheel. At a pre-determined point in the wrap cycle, the spring
steel release pad 68, may be brought into contact with the abutment
69, causing the spring steel release pad 68 to bend inwardly in the
direction of the load. That inward movement of the spring steel
release pad 68 may actuate the catch into an unlocking position,
allowing the bolt member 66 to escape. Continued movement of the
packaging material dispenser 10 may disengage the abutment 69 from
the spring steel release pad 68, which may bend back outwardly due
to its inherent resiliency. The catch may be returned to the
locking position by the outward movement of the spring steel
release pad 68 and/or by the force generated by a return spring or
other suitable biasing device. The next time in the wrap cycle that
the film drive down roller support 42 moves to the tilted film
drive down position, the bolt member 66 may once again be received
and held by the catch.
[0094] According to another aspect of the invention, a method of
using the stretch wrapping apparatus 100 will now be described. In
operation, the load 138 may be manually placed in the wrapping area
or may be conveyed into the wrapping area by the conveyor 114. The
girth of the load 138 may be determined, and a substantially
constant length of packaging material 142 to be dispensed for each
revolution of the packaging material dispenser 140 and rotatable
ring 122 may be subsequently determined based on that girth. The
substantially constant length of packaging material 142 to be
dispensed per revolution may be between approximately 90% and
approximately 130% of the load girth, and preferably may be between
approximately 95% and approximately 115% of load girth, and most
preferably may be approximately 107% of load girth. Once the
substantially constant length of packaging material 142 to be
dispensed per revolution of the rotatable ring 122 is known, the
mechanical input/output ratio control 192 of the pre-stretch
packaging material metering assembly 190 may be set through use of
the metering adjustment control 196. The setting of the
input/output ratio of the variable transmission (hydrostatic
transmission 200) sets the ratio of the relative rotational speed
(i.e., speed of the rotatable ring) to the pre-stretch speed (i.e.,
pre-stretch roller surface speed).
[0095] A leading end of the packaging material 142 may be threaded
through the upstream and downstream pre-stretch rollers 162 and
164, and around any middle idle rollers 176 of pre-stretch assembly
160. Then, the leading end of the packaging material 142 may be
wrapped around the film break sensing roller 194 and a final idle
roller 180, and then may be attached to the load 138 using a film
clamp, or by tucking the leading end of the packaging material 142
into the load 138. It is noted that if the spacing between the
pre-stretch rollers 162, 164 and the film break sensing roller 194
is sufficient to provide the extra length 182 of film 142, a final
idle roller 180 may not be used. Additionally, the final idle
roller 180 may be located anywhere within the film path between the
downstream pre-stretch roller 164 and the load 138 that will
provide the desired extra length 182 of film 142.
[0096] The first motor 132 may operate to rotate the first drive
belt 130 and thus the rotatable ring 122 and the packaging material
dispenser 140 around the load 138. As the packaging material
dispenser 140 rotates relative to the fixed ring 124, the fixed
second drive belt 134 may be picked up by a pulley system 250
mounted to the rotatable ring 122 and move relative to the
rotatable input shaft 202 of the hydrostatic transmission 200,
causing the rotatable input shaft 202 to rotate. As the rotatable
ring 122 rotates, a tensile force may be created in the length of
the packaging material 142 extending between the load 138 and the
film break sensing roller 194. That tensile force may tend to pull
the film break sensing roller 194 toward its retracted (full
forward) position.
[0097] Rotation of the input shaft 202 is translated to output
shaft 204 according to the set input/output ratio, and the rotation
of the output shaft 204 in turn causes rotation of the downstream
pre-stretch roller 164 and thus, via the connector and sprockets,
the upstream pre-stretch roller 162. As the upstream and downstream
pre-stretch rollers 162 and 164 rotate, they may elongate the
packaging material 142 and dispense a predetermined substantially
constant length of pre-stretched packaging material 142 during each
revolution of the rotatable ring 122. The packaging material
dispenser 140 may rotate about a vertical axis 158 as the moveable
frame 118 moves up and down the non-rotating frame 110 to spirally
wrap packaging material 142 about the load 138.
[0098] During the wrapping cycle, the film break sensing roller 194
may sense the occurrence of packaging material breaks. For example,
if a break occurs in the length of packaging material 142 extending
between the load 138 and the film break sensing roller 194, the
tensile force holding the film break sensing roller 194 in the full
forward position will cease to exist. The film break sensing roller
194 will then rapidly move toward its extended (neutral) position,
thus causing the rotational speed of the pre-stretch rollers 162
and 164 and the supply rate of packaging material 142 to rapidly
decrease to zero. This rapid decrease coincides with the shifting
of the hydrostatic transmission to neutral. Thus, the ring 122 may
still be rotating and providing input to the hydrostatic
transmission 200, but the hydrostatic transmission 200 provides no
output. This ensures that the pre-stretch assembly 160 will not
continue to dispense packaging material 142 after a break occurs
and thus prevents back lash and winding of the film on the
rollers.
[0099] It is also contemplated that a sensor device, such as for
example, a photo-cell sensor, may be placed on the packaging
material dispenser 140 to detect the orientation of the film break
sensing roller 194. The sensor device may be configured to send a
signal to a controller to bring the apparatus 100 back to a home
position and stop. It may additionally signal an operator that
there has been a failure.
[0100] According to another aspect of the present invention, the
means for providing relative rotation between the dispenser and the
load may be a horizontal rotatable ring as shown in FIGS. 9 and 10.
For example, the horizontal ring stretch wrapping apparatus 300 may
include substantially the same elements as the vertical rotatable
ring apparatus described above. The horizontal ring stretch
wrapping apparatus may function in substantially the same manner as
the vertical rotatable ring apparatus 100 described above, with the
exception that the horizontal ring structure is rotated 90 degrees
relative to the vertical ring structure.
[0101] As embodied herein and shown in FIGS. 9 and 10, a housing
302 of a horizontal ring apparatus 300 may include a central
aperture 304 through which a conveyor 306 passes. A load 338 to be
wrapped may be conveyed into a wrapping space defined by the
central aperture 304, wrapped, and then conveyed away from the
wrapping space.
[0102] The horizontal ring apparatus may have a structure similar
to that of conventional horizontal ring apparatus as described in
U.S. Pat. No. 6,748,718, issued on June 15, 2004, and entitled
"Method and Apparatus for Wrapping a Load," the entire disclosure
of which is incorporated herein by reference. The horizontal ring
apparatus may include a packaging material dispenser 340. The
packaging material dispenser 340 may include the same or
substantially similar components as the packaging material
dispenser 140 mounted on the rotatable ring 122 of stretch wrapping
apparatus 100. Thus, the descriptions of the packaging material
dispenser 140 provided above may be applicable to the packaging
material dispenser 340. A mechanical link between the rotation of
the roll carriage and the pre-stretch rollers may be provided. The
mechanical link may include a hydrostatic transmission carried by
the roll carriage. As discussed above, the hydrostatic transmission
may provide an input/output ratio control for controlling a
relative speed of the rotation of horizontal ring relative to the
speed of the pre-stretch rollers to thus ensure that a
predetermined substantially constant length of packaging material
is dispensed for each revolution of the packaging material
dispenser 340 relative to the load 338. The setting of the
input/output ratio may be accomplished in the same manner as
described above with respect to the stretch wrapping apparatus
100.
[0103] According to another aspect of the invention, the means for
providing relative rotation between the dispenser and the load may
be a rotatable turntable as shown in FIG. 11. A stretch wrapping
apparatus 400 including a rotatable turntable 422, as shown in FIG.
11, may also be configured to dispense a predetermined
substantially constant length of pre-stretched packaging material
442 per revolution of a load 438 during a wrapping cycle. The
rotating turntable apparatus 400 may include a turntable assembly
420 including a rotatable turntable 422, a mechanical connection
492 between a rotational drive of the turntable assembly 420 and
the pre-stretch rollers 462, 464 of a pre-stretch assembly 460, and
a packaging material dispenser 440. Embodiments of the rotatable
turntable apparatus 400 are shown in FIGS. 11 and 12.
[0104] The rotatable turntable assembly 420 may include a load
support surface 405 for supporting the load 438. The load support
surface 405 may include a flat surface, non-powered conveyor
surface with one or more non-powered rollers, or powered conveyor
surface with one or more powered rollers. The load support surface
405 may be operatively coupled to a rotational drive system of the
turntable assembly 420. The rotational drive system may include,
for example, a turntable drive motor 432 and a turntable drive belt
or chain 430 configured to convert rotational power generated by
the turntable drive motor 432 into rotation of the load support
surface 405. The drive belt 430 may engage sprockets or pulleys 434
and 436 mounted on both the load support surface 405 and a first
output of the turntable drive motor 432.
[0105] The turntable drive motor 432 may also be operatively
coupled at a second output to the power transfer assembly 438 by a
drive belt or chain 439. The drive belt 430 may engage sprockets or
pulleys 442, 444 mounted on both the turntable drive motor 432 and
a rotatable shaft 446 housing in a column 448. Also, a split shive
or stacked pulley system 450 may also be provided at or near the
turntable drive motor 432 to help control the feed rate of the
packaging material. The rotational power generated by the turntable
drive motor 432 may drive the drive belt 439, which may in turn
cause rotation of the rotatable shaft 446. Rotation of the
rotatable shaft 446 may be used to power the packaging material
dispenser 440, as will be described in greater detail below.
[0106] A spring clutch 452 may be operatively coupled between the
turntable drive motor 432 and the shaft 446. When a break in the
packaging material is detected by a switch or sensor, the spring
clutch 452 may at least partially disengage the turntable drive
motor 432 from the shaft 446 to slow or stop the shaft 446 and the
packaging material dispenser 440. This may prevent malfunctions by
slowing or stopping the supply rate of packaging material from the
packaging material dispenser 440 when breakages occur.
[0107] The power transfer assembly 438 may also include a sprocket
drive 454 used to turn rotation of the shaft 446 into power for
operating the packaging material dispenser 440. In particular, the
sprocket drive 454 may be used to rotate an upstream pre-stretch
roller 464 and a downstream pre-stretch roller 464 of a pre-stretch
assembly 460 of the packaging material dispenser 440. In one
embodiment, the sprocket drive 454 may include two drive chains or
belts 456 and 458 operatively coupling the upstream and downstream
pre-stretch rollers 462 and 464 to the shaft 446.
[0108] The upstream and downstream pre-stretch rollers 462 and 464
may include packaging material engaging surfaces that may either be
coated or uncoated depending on the application in which the
stretch wrapping apparatus 400 is being used. The upstream and
downstream pre-stretch rollers 462 and 464 may be mounted on roller
shafts (not shown). Sprockets 466 and 468 may be located on the
ends of the roller shafts, and may be configured to provide control
over the rotation of the roller shafts and the upstream and
downstream pre-stretch rollers 462 and 464. It is contemplated that
the upstream pre-stretch roller 462 and the downstream pre-stretch
roller 464 may have different sized sprockets 466 and 468 so that
the surface movement of the upstream pre-stretch roller 462 may be
at least 40% slower than that of the downstream pre-stretch roller
464. In these and in other ways, the upstream and downstream
pre-stretch rollers 466 and 468 may be structurally and operatively
similar to the upstream and downstream pre-stretch rollers 162 and
164 of the stretch wrapping apparatus 100.
[0109] The packaging material dispenser 440 may also include a roll
carriage 470 and one or more idle rollers, similar to those
previously described with respect to the stretch wrapping apparatus
100. The packaging material dispenser 440 may also be driven up and
down the column 448 by a vertical drive mechanism (not shown)
during a wrapping cycle to spirally wrap packaging material about
the load 438.
[0110] According to one aspect of the invention, a corner lock
mechanism may be provided. The corner lock mechanism of the
rotating turntable apparatus 400 may include a set of programmable
controls (not shown), a corner target 472 on the load support
surface 405 positioned just before each corner of the load 438 and
a corner target sensor 474. Each time that a corner of the load 438
approaches the corner target sensor 474, the corner target sensor
474 senses the corner target 472 associated with that corner of the
load 438. The programmable controls may momentarily reduce or stop
the feed of pre-stretched film to increase the force on the film as
it engages the corner of the load. This could be accomplished
mechanically by clutch-brake means. This corner lock mechanism or a
similar mechanism may be used with any of the stretch wrapping
apparatus embodiments disclosed herein.
[0111] Additionally or alternatively, a spring clutch 552 and/or a
split shive or stacked pulley system 550 may be separated from a
turntable drive motor 532 as shown in the embodiment of FIG. 12. In
this embodiment, a shaft 556 may include two welded rotational fins
457, fixed at locations opposite each other on the surface of the
shaft 556. As the shaft 556 is rotated by the turntable drive motor
532, two cam followers 576 on a disc 578 may ride on the rotational
fins 457, causing the disc 578 to rotate with the shaft 556.
Rotation of the disc 578 may cause rotation of the upstream and
downstream pre-stretch rollers 562 and 564 through the engagement
of drive belts or chains 556 and 668 to sprockets or pulleys 554
and 555 on the upstream and downstream pre-stretch rollers 562 and
564 and the disc 578.
[0112] According to another aspect of the invention, the means for
providing relative rotation between the dispenser and the load may
be a rotatable arm as shown in FIG. 13. A rotating arm apparatus
600, shown in FIG. 13, may also be configured to dispense a
predetermined fixed amount of pre-stretched packaging material per
revolution of a load during a wrapping cycle. The rotating arm
apparatus 600 may include a rotating arm assembly 602, packaging
material dispenser 604 mounted on the rotating arm assembly 602,
and a power transfer assembly 606. An exemplary embodiment of the
rotating arm apparatus 600 is shown in FIG. 13.
[0113] The rotating arm assembly 602 may include a horizontal arm
608 cantilevered from a pivot point 610. A column 611 may be
cantilevered from the free end of the horizontal arm 608. The
packaging material dispenser 604 may be mounted on the column 611,
and may be driven by a vertical drive device (not shown),
vertically along the length of the column 611. The rotating arm
assembly 602 may be rotated by an arm motor 612. Rotation of the
rotating arm assembly 602, when coupled with vertical movement of
the packaging material dispenser 604, may serve to wrap packaging
material spirally about the load.
[0114] The power transfer assembly 606 may include a fixed (i.e.,
non-rotating) sprocket or pulley wheel 614. The fixed sprocket 614
may be operatively coupled by a drive belt or chain 616 to a split
shive or stacked pulley system 618 mounted in the rotating arm
assembly 601. The split shive or stacked pulley system 618 may be
operatively coupled by a drive belt or chain 620 to a rotatable
shaft 622 in the column 611. As the arm motor 612 rotates the
rotating arm assembly 602, the engagement of the fixed sprocket 614
to the split shive or stacked pulley system 618 through the drive
belt 620 causes the split shive or stacked pulley system 618 to
rotate. As the split shive or stacked pulley system 618 rotates,
the drive belt 620 is also driven, causing the shaft 622 to rotate.
The shaft 622 may include two welded rotational fins 624, fixed at
locations opposite each other on the surface of the shaft 622. As
the shaft 622 is rotated, two cam followers 626 on a disc 628 may
ride on the rotational fins 624, causing the disc 628 to rotate
with the shaft 622. Rotation of the disc 628 may power a
pre-stretch assembly 630 of the packaging material dispenser. In
particular, rotation of the disc 628 may cause rotation of upstream
and downstream pre-stretch rollers 632 and 634 through the
engagement of drive belts or chains 636 and 638 to sprockets or
pulleys 614 and 618 on the upstream and downstream pre-stretch
rollers 632 and 634 and the disc 628.
[0115] The split shive or stacked pulley system 618 may also
include a spring clutch device 640. When a packaging material break
is detected by, for example, a break sensor or switch, the spring
clutch device 640 may at least partially disengage the fixed
sprocket 614 from the shaft 622 to slow or stop the shaft 622 and
the packaging material dispenser. This may prevent malfunctions by
slowing or stopping the supply rate of packaging material from the
packaging material dispenser when breakages occur.
[0116] According to yet another aspect of the invention, the
mechanical connection between the rotational drive system and the
pre-stretch assembly may be replaced by an electrical connection.
This use of an electrical connection may be used in any of the
embodiments of the stretch wrap apparatuses discussed herein. In
such embodiments, two separate drives may be provided, a first
rotational drive for providing relative rotation between the load
and the packaging material dispenser, and a second rotational drive
for rotating the pre-stretch rollers of the pre-stretch assembly.
The two rotational drives may be electronically linked such that a
ratio of the drive speeds remains constant throughout a primary
portion of the wrap cycle in order to permit the pre-stretch
assembly to dispense a predetermined substantially constant length
of film for each revolution of the dispenser relative to the load.
A means for providing relative rotation between the load and the
dispenser may include any of the systems previously discussed,
e.g., vertical or horizontal rings, rotatable arms, and
turntables.
[0117] An electrical connection, such follower circuits, for
example a tachometer follower, or encoders may be used to link the
first rotational drive and the second rotational drive such that a
ratio of the drive speeds remains constant throughout a primary
portion of the wrap cycle. In this manner, the electronic
connection mimics the mechanical connection previously
described
[0118] Unlike the mechanical connection, there may be times when it
is undesirable for the two drives to be proportionally controlled
at the same ratio for the entire wrap cycle. There may be times
when it is instead desirable to vary the ratio while continuing to
proportionally control the drives. Such times include start of the
wrap cycle to accommodate prior art clamping systems and at the end
of a wrap cycle to accommodate limitations of prior art film
cutting and wiping systems or when one of the rotational drives may
be moving in an opposite direction from the other (e.g., backing up
the dispenser to provide slack in the film). Additionally there may
be other reasons to vary the ratio for special applications such as
corner board insertion, securing slip sheet flaps, etc. In
addition, should the film break or become slack, it would be
undesirable to have the pre-stretch assembly continue to dispense
film that wind up the rollers.
[0119] According to an exemplary embodiment of the invention, two
AC variable frequency drives, such as Allen-Bradley Power Flex 40
drives, may be used to drive the relative rotation between the load
and the dispenser and to drive the pre-stretch rollers. A Control
Logix processor may be used to electronically control the speed of
the drives relative to one another so as to permit the pre-stretch
assembly to dispense a predetermined substantially constant length
of film for each revolution of the dispenser relative to the load.
Preferably, an interface will be provided that permits the operator
to select the payout percentage.
[0120] A corner lock mechanism, such as discussed with regard to
the turntable stretch wrap apparatus 400, may be easily
incorporated into any of the stretch wrap apparatuses using an
electronic control to maintain the ratio of the rotational drive to
the pre-stretch drive. The use of a corner lock mechanism is
another instance when it may be desirable to vary the ratio while
continuing to proportionally control the drives. In such an
embodiment, proximity switches would be used to "pulse" the
pre-stretch drive off for a precise rotation angle as a flag passes
the proximity switches. For example, on a turntable embodiment
flags could be positioned immediately prior to each corner of a
load and be required to pass two proximity switches adjacent the
mast upon which the packaging material dispenser is mounted, a
first to pulse the pre-stretch drive off and a second to pulse the
pre-stretch drive on again. This would be done four times during a
revolution of the packaging material dispenser relative to a square
or rectangular load, each time immediately prior to the passage of
a corner of the load, in order to lock in a higher wrap force at
the corners of the load. Appropriate alternative positioning of the
flags and proximity switches for other types of means for providing
relative rotation may be used. In addition, for other shapes of
loads, the corner lock mechanism may be adapted accordingly.
[0121] Other embodiments of the invention will be apparent to those
skilled in the art from consideration of the specification and
practice of the invention disclosed herein. It is intended that the
specification and examples be considered as exemplary only, with a
true scope and spirit of the invention being indicated by the
following claims.
* * * * *