Note: Descriptions are shown in the official language in which they were submitted.
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Ti : METHOD AND APPARATUS FO:R RECYCLING STRAPPING
FIELD OF THE INVENTION
This invention relates generally to a method and apparatus
for recycling used plastic strapping or other material in strip form
(hereinafter called "strapping")
BACKGROUND OF THE INVENTION
Plastic strapping is widely used to bundle together stacks or
other groupings of articles for shipping. For example, stacks of corrugated
cardboard stock are bundled together using flat section polypropylene or
polyethylene strapping. The strapping may be applied by a paper stock
supplier prior to shipping the stock. to a corrugated container
manufacturer; the manufacturer will then cut, print and otherwise form
the stock into blanks or finished containers. When the stock is to be used,
the strapping is simply cut with a knife at random locations, pulled away
from the stack and discarded.
Typically, the strapping comprises lengths of polypropylene
or polyethylene strapping, each of which is looped around a stack of
cardboard stock and secured in place by heat sealing together overlapping
end portions of the length of strapping, forming a double-thickness lap
joint. A single stack may be encircled by t~n~o loops of strapping in a
crossed
configuration. When the strapping is cut, i:he cut is almost always made at
a location remote from the heat seal. As such, each discarded length of
strapping usually includes a heat seal that may be at almost any location
along the length of the strapping.
These used lengths of strapping not only are difficult to
handle locally, but represent a significant disposal cost. Often, the
discarded lengths of strapping are simply loaded into waste disposal
containers and shipped to a landfill site. Sometimes, the strapping will
first be chopped up into small fragments. This tends to make handling
and disposal somewhat easier but involves cost in terms of equipment and
an operator to feed in the discarded length:> of strapping.
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At the very least, the container manufacturer is forced to
incur significant costs in dealing with the v~~aste strapping. Not only that,
but finished container blanks that have been made from the cardboard
stock usually must later be rebundled for shipping to the end user. A
container manufacturer must accordingly purchase new strapping for that
purpose.
In summary, significant costs are involved in disposing of the
old strapping and buying new strapping. There is also a negative
environmental impact that results from dumping of plastic strapping into
landfill sites.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method
and apparatus that addresses this problem by providing for recycling or
reuse of discarded lengths of strapping, some or all of which may include
heat-sealed lap joints.
In a method aspect of the invention, successive lengths of
strapping, at least some of which include lap joints, are advanced along a
defined path from an input station to a tak;e-up station, and a number of
steps are performed on the lengths of strapping as they are advanced along
the path. First, at a cutter station downstream from the input station,
leading and trailing end portions of each successive length of strapping are
cut off to provide "clean" leading and trailing ends. Any lap joints are cut
out of the lengths of strapping, thereby forming respective upstream and
downstream strapping sections having "clean" leading and trailing ends.
A first one of the strapping sections is advanced to a position in which a
trailing end portion thereof is located at a joining station. A leading end
portion of the next succeeding strapping section is then advanced into
overlapping relationship with the trailing end portion of the first section .
and the two overlapping portions are sealed together to join the two
sections end-to-end. The joined sections are wound or otherwise taken up
at the take-up station downstream of thE~ joining station as continuous
strapping. This process is continued with successive strapping sections.
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In other words, the old discarded lengths of strapping are in
effect "cleaned up" by making fresh clean cuts at the leading and trailing
end of each section and cutting out any old lap joints. The resulting
strapping sections are then joined together .end-to-end by forming new lap
joints and the resulting continuous strapping is taken up, for example, by a
winding unit or mandrel. The recycled strapping can then be used in the
same manner as new strapping in a binding machine or other equipment.
Preferably, the cutter station includes a cutter head having
upstream and downstream cutters that are spaced a predetermined
distance along the path in which the strapping is advanced. The spacing
between the cutters is selected as appropriate to cut out a portion of the
strapping that includes a heat seal. The upstream cutter of the cutter head
can also be used to trim a leading end portion from the length of strapping
and the downstream cutter can be used to trim a trailing end portion of a
length of strapping.
In this embodiment, the method also includes the step of
detecting a leading end of a strapping length at a detection station
upstream from the cutter station, and advancing the strapping length to
the cutter station and into a predetermined to position with the leading
end of the strapping between the upstream and downstream cutters.
Similarly, the trailing end of a length of strapping can be detected at the
detection station and the strapping advanced through essentially the same
distance to position the trailing end of the length of strapping between the
upstream and downstream cutters of the cutter head.
A lap joint in a length of strapping provides a double-
thickness of strapping that can be detected at the detection station. The
strapping can then be advanced through am amount selected to position
the lap joint between the upstream and dovmstream cutters so that the lap
joint will be cut out when the cutter head is operated.
In another aspect, the invention also provides an apparatus
for recycling strapping that includes an input station, a take-up station and
a strapping guide extending from the inpuit station to the take-up station,
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and along which can be advanced successive lengths of strapping at least
some of which include lap joints. The .apparatus also includes drive
means for advancing the strapping along the guide, and a cutter station for
cutting off leading and trailing end portions of each successive length of
strapping to provide "clean" leading and trailing ends, and for cutting out
any lap joints, thereby forming respective upstream and downstream
strapping sections having "clean" leading and trailing ends.
The apparatus also includes a joining station downstream of
the cutter station, to which a first one of the strapping sections can be
advanced so that a trailing end portion of that section is at the joining
station. A leading end portion of the next succeeding strapping section is
then advanced into overlapping relationship with the trailing end portion
of the first strapping section and the overlapping portions of strapping are
sealed together to join the sections end-to-end. The sequence is repeated
with successive strapping sections while the take-up station accumulates
the continuous strapping that is formed Erom the individual strapping
sections.
Typically, the joining station mill be designed to heat-seal the
strapping sections together, although other joining methods may be used,
such as gluing or crimping. Typically, heat sealing will be used for plastic
strappings, gluing might be more appropriate for other strapping
materials. Crimping may be used where the strapping is metal.
BRIEF DESCRIPTION OF THE DRAWINGS
In order that the invention may be more clearly understood,
reference will now be made to the accompanying drawings which
illustrate a particular preferred embodiment of the invention by way of
example, and in which:
Fig. 1 comprises six sequential views denoted (a) to (f) which
illustrate successive steps in the method of the invention;
Fig. 2 is a front perspective view showing the overall
apparatus for performing the method;
Fig. 3 is a front elevational view illustrating the principal
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components of the apparatus of Fig. 2;
Fig. 4 is a perspective view of part of the input station that is
visible at the left hand end of Fig. 3;
Fig. 5 is a perspective view of a further downstream part of
the input station;
Fig. 6 is a perspective view of a lap joint detection station of
the apparatus;
Fig. 7 is a perspective view of a strapping guide that is
immediately downstream of the station shown in Fig. 6;
Fig. 8 is a perspective view of a cutter head of the apparatus;
Fig. 9 is an elevational view from the left in Fig. 8;
Fig. 10 is a perspective vie~n~ of a strapping joining (heat-
sealing) station of the apparatus;
Fig. 11 is a perspective view of a strapping take-up station;
Fig. 12 comprises views denoted (a), (b) and (c) that illustrate
removal of a lap joint from a length of strapping;
Fig. 13 comprises views denoted (a) to (f) that illustrates heat-
sealing of two sections of strapping;
Fig. 14 comprises views denoted (a) to (f) that illustrate a
sequence of operation that follows on from the sequence of Fig. 12;
Fig. 15 comprises views denoted (a) to (d) that illustrate a
subsequent heat-sealing step; and,
Fig. 16 comprises views denoted (a) to (c) that illustrate
trimming of a trailing end portion of a length of strapping.
DESCRIPTION OF PREFERRED EMBODINfENT
The drawings illustrate a method and an apparatus that was
devised primarily in the context of recycling polypropylene or
polyethylene strapping that had been used for bundling corrugated
cardboard stock. Typically, a length of strapping is looped around a stack of
cardboard and the ends of the length of strapping are joined together by
heat sealing to form a lap joint. When the stock is to be used, the strap-
ping is simply cut at a random location, usually remote from the heat seal.
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Fig. 1(a) shows a cut length of strapping such as might have
been used for bundling a stack of cardboard stock. In the drawing, the
strapping is denoted by reference numeral 20 and is shown laid flap and as
having opposite end portions 22 and 24 that were formed by cutting a loop
of strapping. An "old" lap joint is indicated at 26. In order to be able to
recycle the strapping in accordance with tree method of the invention, it is
necessary to cut out the lap joint 26 and "clean up" each end of the length
of strapping by cutting off an end portion o:E the strapping.
As will be described in detail later, the method of the
invention involves feeding successive lengths of strapping lengthwise
into a machine that cuts the strapping in this fashion and then forms a
new lap joint between the cut sections of strapping.
It is irrelevant which end of the length of strapping is fed first
into the machine, but if it is end portion 22 (the leading end portion) the
first step in the method is to cut off the leading end portion of the length
of strapping, sufficiently far back from the old cut that any frayed area is
removed. A typical cut line is indicated at 28.
The next step is to cut out the lap joint 26 by making a pair of
cuts 30 and 32 that are spaced in the direction of travel of the length of
strapping sufficient to ensure that the lap joint is completely removed.
This forms upstream and downstream strapping sections 20a and 20b
which are then joined by advancing the upstream section 20b to bring its
leading end portion into overlapping relationship with the trailing end
portion of the downstream section 20a (Fig. 1(d)) and then heat-sealing the
overlapping portions together to form a new lap joint 34 as shown in Fig.
1(e).
Finally, the trailing end portion of the length of strapping is
removed, for example, by making a cut along the line indicated at 36 in
Fig. 1(e). Fig. 1(f) shows the completed "new" length of strapping.
Additional strapping sections can then be added to the "trailing" end
portion of the new length of strapping by repeating the step shown in Fig.
1(a), heat-sealing the leading end portion of that length of strapping to the
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trailing end portion of the length shown in Fig. 1(f) and then repeating the
steps shown in Fig. 1(b) to 1(e).
Referring now to Figs. 2 and ;3, an apparatus for carrying out
the method of the invention is generally iindicated by reference numeral
38 and includes the cabinet 40 which houses the components shown in
Fig. 3. The apparatus includes the input atation (not visible in Fig. 2) at
which successive lengths of strapping are fed into the housing, as indicated
by the arrow 42 and a take-up station generally indicated at 44 at which a
continuous "new" strapping is wound onto a mandrel 46. An
accumulator 48 is provided upstream of the mandrel so that rotation of
the mandrel does not have to be timed to travel of strapping through the
apparatus. A strapping guide is shown at 50 for directing strapping from
cabinet 40 to accumulator 48.
For safety reasons, doors 52 a.re provided on cabinet 40. The
doors may be transparent so that operation of the components within the
cabinet can be visually monitored. however, for convenience of
illustration, the components within the cabinet have not been shown in
Fig. 2.
Referring now to Fig. 3, the input station referred to
previously is generally denoted 60 and receives strapping fed into the
apparatus (by hand) in the direction of arrow 42. The apparatus also
includes, in sequence from the input station 60 to the take-up station 44, a
detection station 64, a cutter station 66, a joining (heat-sealing) station 68
and a downstream detection station 70. 'These stations together define a
path for strapping from the input station Ei0 to the take-up station 44. The
two detection stations 64 and 70 include respective pairs of rollers 74, 76
and 78, 80. Each pair of rollers defines a nip for receiving strapping and the
rollers are driven to convey the strapping through the apparatus.
Cutter station 66 includes a cutter head 82 that has upstream
and downstream cutters 84 and 86 spaced in the direction of travel of
strapping through the apparatus by an amount corresponding to the
spacing between the two cut lines 30 and 32 indicated in Fig. 1(b) for cutting
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an old lap joint out of a length of strapping. The two cutters 84 and 86
move up and down together when the cutaer head is actuated (as will be
described). In addition to cutting out old lap joints, the upstream cutter 84
is used to trim off a leading end portion of a length of strapping, while the
downstream cutter 86 is used to cut a trailing end portion from a length of
strapping.
The heat-sealing station 86 includes a heated blade 88 that can
be advanced and retracted horizontally beitween overlapping end portions
of sections of strapping to be sealed together as shown in Fig. 1(d), and a
pair of anvils or jaws 90 and 92 that can be moved vertically towards and
away from one another to respectively clamp the strapping against knife 88
and release the strapping.
Briefly, the leading end portion of an in-coming length of
strapping is advanced to a position approximately mid-way between the
twvo cutters 84 and 86 and the cutter head is actuated to cut off the leading
end portion of the strapping (Fig. 1(a)). Strapping advance is then
continued until the detector station 64 detects a lap joint. The strapping is
then advanced to bring the lap joint to a position mid-way between the
two cutters 84 and 86 and the cutter head is operated to cut out the lap
joint. Next, the section of strapping do~n~nstream of the cut is advanced
until its trailing end portion is at the heat-sealing station 68. The section
of the strapping upstream of the cut is advanced to bring its leading end
portion into overlapping relationship with the trailing end of the
downstream portion, and the two portions are sealed together. Strapping
advance then continues. The sequence of operation is essentially repeated
on successive lengths of strapping that are fed into the apparatus forming
continuous "new" strapping.
In more detail, Fig. 4 shows an input guide or "horn" 94 that
opens to the exterior of the cabinet at the input station, as best seen in
Fig.
3. The horn presents a relatively large "ta.rget" opening 94a to an operator
feeding lengths of strapping into the apparatus and in effect guides the in-
coming strapping to a relatively narrow slot 94b that is sized to relatively
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closely match the size of the strapping. Thus, the operator does not have
to be overly careful about precisely feeding the strapping into the
apparatus, and can work quite rapidly. A photo-electric cell set 96 is
incorporated in the horn to provide a si~mal indicating the presence of
strapping at the input station.
Immediately downstream of t:he horn opening 96 is a device
98 that is designed to precisely locate thE~ strapping both vertically and
laterally as the strapping begins to travel through the apparatus. The
strapping locating device 98 includes a base plate 100 which carries on its
upper face a fixed guide element 102. Element 102 is of inverted L-shape
and defines with the base plate 100 an. opening 104 that is sized to
relatively closely match the thickness of the strapping. Element 102
defines at the left hand side of opening 104 as drawn, a fixed guide face
102a for the left hand edge of strapping 20.
A corresponding opposite edge of opening 104 is defined by
an edge of a guide element 106 which can move laterally with respect to
opening 104 within limits defined by a pair of parallel links 108 that are
pivotally coupled between element 106 and base plate 100. One of those
links has an extension 108a to which is coupled one end of a tension
spring 110 that extends to a fixed pin 112 on base plate 100. Spring 110
biasses guide element 106 inwardly with respect to opening 104. This has
the effect of urging the strapping 20 against the left hand guide surface 102a
of guide 102, positively locating the strapping in the lateral direction.
Immediately downstream of the locating device 98 is the first
detection station 64; this is shown in detail in Fig. 6. Device 98 has been
omitted for clarity of illustration. For they same reason, also omitted from
Fig. 6 is a fixed guide 114 shown in Fig. 7. Like device 98, guide 114 has an
opening 116 through which the strapping 20 passes; however, in this case,
the opening 116 is of fixed dimensions selected to allow smooth passage of
strapping 20 through the guide, while laterally and vertically constraining
the strapping fairly precisely. Fig. 3 shows the locations of device 98 and
guide 114 relative to the roller pair 74 and 76.
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Reverting to Fig. 6, a length o:E strapping 20 having a lap joint
26 is shown positioned immediately before it enters the nip between the
two rollers 74 and 76. It will be seen that the rollers have respective
smooth surface portions 76a and 78a, on which the strapping 20 rides as it
passes through the detection station 64. Inwardly of the smooth surface
portions 76a and 78a, the two rollers have respective sets of teeth 76b and
78b that mesh with one another as the rollers turn. The teeth 76b, 78b are
relatively deep so that the rollers can move apart slightly while remaining
in driving engagement (see later). In fact, roller 76 is mounted on a rotary
shaft 118 that is fixed, while roller 74 is mounted on a corresponding shaft
120 carried by a lever arm 122 that can pivot about a pivot pin 124. Arm
122 is part of a double arm lever, the second arm 126 of which is generally
horizontal. This arrangement allows roller 74 to move away from roller
76 in response to entry of a length of strapping 20 into the nip between the
two rollers. The distal end 126a of arrn 126 then moves upwardly as
indicated in ghost outline in Fig. 6. Roller 74 is biassed downwardly
towards roller 76 by a spring 127.
Since a lap joint 26 in strapping 20 represents a double
strapping thickness, the distal end 26a of arm 126 will in fact move to one
of two elevated positions depending on whether only a single or a double
thickness of strapping is present in the nip between the two rollers 74 and
76. A pair of proximity detectors 128 are provided adjacent arm end 126a
for detecting the respective positions. In .other words, the lower one of the
two detectors 128 will respond when only a single thickness of strapping is
present between the rollers, while the upper detector will respond to the
presence of a lap joint 26.
Fig. 6 also shows part of a generally vertically disposed base
plate 130, on which are mounted all of the components of the apparatus
that can be seen in Fig. 3. In Fig. 6, it can be seen that shaft 118 carrying
roller 76 is in fact a drive shaft that extends through base plate 130 and is
provided, at the rear side of base plate 130, with a toothed pulley 132 by
which roller 76, and hence roller 74 are driven. A drive motor for the
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rollers is also mounted at the rear side of base plate 130 and is indicated at
134. A drive shaft 136 from motor 134 drives a further toothed pulley 138
that in turn drives pulley 132 by way of a toothed belt 140.
Motor 134 is an electric servo-motor that is capable of very
precise control so that the rotational distance through which rollers 74 and
76 are turned can be determined with some precision. This means that a
length of strapping 28 in the nip between the rollers can be advanced
through a very precise distance to accurately position the leading end of
the strapping, for example, in relation to the two cutters 84 and 86 (Fig. 3).
Sophisticated control circuitry is provided for the entire apparatus and
includes a programmable logic controller (I'LC) that can be set to precisely
control all of the various components of the apparatus and their sequence
of operation. The control circuitry is desi~med in accordance with known
programmable control principles and does not form part of the invention.
Accordingly, details of the control circuitry have not been given.
Immediately downstream of detection station 64 is the cutter
station 66; this is shown in detail in Fig. 8. As indicated previously, the
cutter station includes a cutter head 82 that: is provided with upstream and
downstream cutters (knives) 84 and 86 respectively. Cutter head 82 is
mounted for vertical sliding movement on a T-section slide 142 that is
received in a complementary slide-away (n.ot visible) in head 82. Slide 142
is fixed with respect to the base plate 130 (Fig. 3). At its lower end, slide
142
carries an inverted channel member 144 treat overlies a plate 146 to define
a passageway 148 for guiding strapping through the cutter station. This
passageway precisely positions the strapping with respect to the cutters at
opposite ends of the cutter station. A aimilar, but fixed guide 150 is
provided immediately downstream of cutter 84 for conveying the
strapping to the sealing station 68 (Fig. 3).
In the case of guide 148, however, the bottom plate 146 is
retractable as indicated by the arrow 152 in Fig. 8, and as best seen in Fig.
9.
Plate 146 normally occupies the advanced position in which it shown in
Fig. 8. However, immediately after the cutter head has been operated,
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plate 146 is retracted so that a cut off' section of strapping within
passageway 148 can fall away as indicated by the arrow 154 in Fig. 9. It will
be recalled that this piece of strapping will either be a waste leading or
trailing end portion of strapping, or a piece of strapping that includes an
old lap joint 26 (Fig. 1(a)).
Reverting to Fig. 9, it will be ~;een that plate 146 is retractable
through a slot 156 in the base plate 130. .A pneumatic cylinder and ram
unit 158 is mounted by a bracket 160 to the rear face of base plate 130 for
advancing and retracting plate 146. Cylinder and ram unit 158 is also
shown in Fig. 8. A further, but vertically mounted cylinder and ram unit
162 is carried by a bracket 164 on the front face of base plate 130 and is
coupled to the cutter head 82 for vertically displacing the cutter head
between the inoperative upper position in 'which it is shown in Fig. 8, and
a lower position, for cutting the strapping in passageway 148. The stroke of
movement of the cutter head between these two positions is relatively
small.
Downstream of the cutter station 66 is the heat-sealing station
68, and that is shown in detail in Fig. 10. Again, a length of strapping 20 is
shown approaching the heat-sealing station 68 but the guide 150 through
which the strapping travels is not shown. The principal components of
the heat sealing station are upper and lower jaws 90 and 92 respectively,
and heated blade 88 (see also Fig. 3). The various arrows that appear in Fig.
10 indicate that the two jaws 90 and 92 are vertically movable towards and
away from one another and that the heated blade 88 can be extended or
retracted in a generally horizontal plane through an opening (not shown)
in base plate 130. In Fig. 10, the blade 88 is shown in its advanced position
and the two jaws are shown in their retracted positions clear of the blade.
In order to form a heat seal between the leading end of one
section of strapping and the trailing end of another section of strapping,
the end portions of the two strapping sections are initially positioned
respectively above and below blade 88 with the blade and the jaws 90 and
92 in the positions in which they are shown in Fig. 10. The two jaws are
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then closed onto the strapping sections and press the strapping sections
against the blade 88. The strapping sections are held in this position for a
pre-determined period of time sufficient to partially melt the surfaces of
the strapping sections that are in contact with blade 88. The jaws 90 92 are
then opened, and blade 88 is retracted. The jaws are then closed again to
press the two strapping sections directly against one another for a period of
time sufficient to finalize formation of the heat seal. The jaws are then
retracted again and the strapping can nov~~ be advanced and continue on
through the apparatus.
Fig. 10 shows a cylinder and ram device 172 that is mounted
horizontally behind base plate 130 and connected to blade 88 so that the
blade can be advanced and retracted by actuating the device 172 in the
appropriate direction. Support structure for cylinder and ram unit 172 is
indicated at 174. Wires for supplying power to the blade 88 for heating are
indicated at 176.
On the front face of base plate 130 a second cylinder and ram
unit 178 is mounted in a vertical position .and coupled to a slide block 180
that carries the upper jaw 90. Block 180 slides on a fixed slideway 182 so
that the upper jaw 90 can be advanced and retracted in the vertical
direction by appropriate operation of cylinder and ram unit 178.
A similar slide block 184 carries the lower jaw 92 and is
mounted on a slide 186. Immediately below slide 186 a rocker 188 is
pivoted to base plate 130 about a pivot pin 190. Vertical links 192 and 194
at respectively opposite ends of rocker 1.88 extend vertically, one to the
upper slide block 180 and the other to i:he lower slide block 184. This
arrangement causes movement of jaw 92 that is equal and opposite to the
movement of the upper jaw 90 that takes place when cylinder and ram
unit 178 is actuated.
Immediately downstream of blade 88 as seen in Fig. 10 is a
strapping guide 196 comprising respective upper and lower plates 198 and
200, of which the upper plate 198 has a recess (not visible) forming a
passageway for the strapping similar to the passageway 148 shown in Fig. 8.
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At its end adjacent the upper jaw 90, the upper plate 198 is angled
upwardly as indicated at 198a and fitted with an air nozzle 202 that,
accordingly, is angled downwardly somewhat obliquely with respect to the
heated blade 88, as best seen in Fig. 3. Fig. 3 also shows that a second,
similar nozzle 204 is angled upwardly andl oppositely to nozzle 202 from
the strapping guide 150 at the upstream side of the heat sealing station. As
best shown in Fig. 13(a) (to be described), air jets that issue from the
respective nozzles 202 and 204 serve to separate the two portions of
strapping that are to be sealed together at the heat-sealing station, and
ensure that one is positioned above and one below the heated blade 88.
Reverting again to Fig. 3, it will be seen that the second pair of
rollers (78, 80) are positioned immediately downstream of the strapping
guide 196. Strapping travels from the heat-sealing station towards the
take-up station 44 through the nip between these rollers. The rollers and
the take-up station 44 are illustrated in Fig. 11.
Rollers 78, 80 are essentially the same as the rollers 74, 76
described previously in connection with Fig. 6, and are driven in the same
way, from their own electric servo-motor 206 through a belt drive
generally indicated at 208. Again, roller 80 drives roller 78 and roller 78 is
carried by a two armed lever generally indicated at 210 and pivotally
mounted on a pin 211. In this case, only a single proximity detector (212) is
provided adjacent the distal end of the upper arm of lever 210. This
responds to the presence of lever 210 as indlicating that strapping is passing
between the two rollers 78, 80. When the strapping leaves the nip between
the rollers, arm 210 is no longer detected and a signal is given indicating
that the strapping has run out.
A curved strapping guide 50 (Fig. 2) extends outwardly and
then downwardly from a location adjacent the nip between the two rollers
78 and 80 and delivers the strapping into a~n accumulator 48, which is best
seen in Fig. 2; Fig. 11 merely shows the path of the strapping through the
accumulator. Referring to Fig. 2, it will be seen that the accumulator is
essentially a thin and flat receptacle or box: having a transparent front face
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216 so that the strapping can be visually observed within the accumulator.
Strapping enters through guide 50 at the top right corner of the
accumulator as shown in Fig. 2 and is allowed to adopt a random looped
configuration within the accumulator. The strapping is then led out of the
accumulator adjacent guide 50 through t:he nip between a pair of idler
spools 220, and forward towards the take-up mandrel 46.
A photo-electric detector set 222 detects when the loop or
loops of strapping within the accumulator reach the bottom of the
enclosure and provide a signal to indicate that the mandrel should be
actuated to wind up strapping from the accumulator. In other words, the
mandrel is operated only intermittently when the photo-electric detector
set 222 determines that the accumulator is filling up with strapping.
Reverting to Fig. 11, strapping mandrel 46 carries a strapping
spool 224 which is keyed to the mandrel 4Ei (key not shown) but removable
so that a full spool of strapping can be removed as a unit and transported
elsewhere for reuse or storage.
From the idler spools 220, ~:he strapping passes through a
strapping guide 226 which is designed to traverse laterally parallel to
mandrel 46 to guide the strapping axially of the spool 224 so that the
strapping is wound uniformly onto the spool. Thus, guide 226 has an
internally screw-threaded lower portion that receives a screw-threaded
shaft 228 driven by a belt 230 from the mandrel 46. A main mandrel drive
motor 232 drives mandrel 46 through a gear box 234 and a further belt
drive 236.
To summarize, when the photo-electric detector set 222
detects that the accumulator is filling up, a signal is sent to motor 232 to
start the mandrel: As the mandrel rotates, the strapping guide 226
progressively traverse in the axial direcaion of the mandrel to lay the
strapping in a consistent spiral onto the spool 224. After a predetermined
time interval, motor 232 stops until another signal is received from the
photo-electric detector set. When the spool 224 is full, strapping can be
allowed to accumulate in accumulator 48 while the spool is changed.
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Figs. 12 to 16 are schematic sequence drawings illustrating
operation of the apparatus.
Referring first to Fig. 12(a), a first length of strapping 20' is
assumed to have been advanced to a position in which its trailing end
portion is at the heat-sealing station 68. An in-coming length of "old"
strapping 20" is detected by upward movement of roller 74 at the detection
station 64. This provides a timing signal to the programmable logic
controller (PLC) of the control circuitry. T'he PLC then "directs" the rollers
74, 76 to advance the strapping by a rotational amount that is sufficient to
bring the leading end of the strapping to approximately mid-way between
the two cutters 84, 86 of the cutter station 66. Cylinder and ram unit 162 is
then actuated to cut off the leading end portion of strapping length 20", as
shown in Fig. 12(b). As soon as the cut h;as been made, the bottom plate
146 of the strapping guide 144, 146 is retracted so that the cut off piece of
strapping can fall down and be discarded as shown in Fig. 12(c). The PLC
then "directs" the rollers 74 and 76 to advance the strapping section 20" to
bring the leading end portion thereof to the heat-sealing station.
Fig. 13 shows the heat-sealin~; operation in principle. Jets of
air from the nozzles 202, 204 separate they end portions of the respective
sections of strapping and allow the heated blade 88 to be advanced between
the jaws 90 and 92. The jaws then close as shown in Fig. 13(b) and remain
closed for a time sufficient to allow the hE~ated blade to partially melt the
opposing faces of the strapping sections.
The two jaws 90, 92 are then retracted as shown in Fig. 13(c),
blade 88 is withdrawn, and the jaws are again closed, pressing the two
overlapping portions of strapping against one another. The jaws remain
closed for a time sufficient to ensure bonding (Fig. 13(d)).
The jaws then open and the strapping is advanced by
operation of the rollers 78 and 80 under tile control of the PLC, as shown
in Figs. 13(e) and (f).
The strapping continues along its path driven by the two sets
of drive rollers 74, 76 and 78, 80 as shown in Fig. 14(a). When an "old"
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heat seal approaches the rollers 74, 76, roller 74 is lifted to a greater
extent
that before, triggering the upper one of the two proximity detectors and
providing a specific indicator signal to the P'LC (Fig. 14(b)).
The PLC then directs the rollers 74, 76 to advance the
strapping to bring the "old" heat seal 26 to a position mid-way between the
two cutters 84, 86 of the station 66. Thiis is shown in Fig. 14(c). The
following two views show the cutter head 82 being actuated to cut out the
portion of the strapping that includes the old heat seal, and the lower
strapping guide plate 146 being retracted as the cutter head returns
upwardly, so that the portion of strapping containing the old heat seal can
fall away.
The strapping is then advanced by the rollers 74, 76 to bring
the "new" leading end portion of the strapping to the heat-sealing station
68 as shown in Fig. 14(f).
Figs. 15(a) to (d) show formation of a heat seal in generally the
same fashion as in Fig. 13.
Finally, Figs. 16(a) to (c) shove that, when the trailing end of
the last length of strapping leaves the nip between the two drive rollers 74,
76, neither of the two proximity detectors 128 is actuated. The PLC then
"knows" that there is no strapping between the rollers. The rollers 78, 80
upstream of the heat-sealing station 68 are "directed" to advance the
strapping through a sufficient distance to bring the trailing end of the
strapping section to a position between the two cutters 84, 86 of the cutter
station. The cutter head is then operated and the trailing end portion of
the strapping discarded as described previously. The rollers 78, 80 are then
directed to advance the strapping to brim; the trailing end portion to the
heat-sealing station 68, and then stop, until a new incoming length of
strapping is detected at station 64.
In summary, the method and apparatus provided by the
invention allows strapping such as plastic strapping that would otherwise
be discarded and represent a disposal cost and possible environmental
hazard to be reused simply by feeding lengths of strapping successively
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into the apparatus. The ends of the lengths of strapping are automatically
trimmed, old heat seals cut out and the resulting sections heat-sealed
together to form new, continuous strapping.
It will of course be appreciated that the preceding description
relates to a particular preferred embodinnent of the invention and that
many modifications are possible. Some of those have been indicated
previously and others will be apparent to a person skilled in the art.
In particular, it is to be noted that, while reference has been
made specifically to plastic strapping, the invention is not limited in this
respect, and may be applied to other material in strip form, e.g. strips of
metal, irrespective of whether or not the strips are intended to be used for
bundling articles. Also, while heat sealing has been referred to as a
particular example of a joining method, the invention is not limited to
heat sealing and could be practised using; other sealing techniques, such,
for example, as gluing or crimping. For example, crimping might be
appropriate for metal strips.
Alternative forms of cutter station may include co-operating
vertically movable and stationary cutters at each end of the cutter station;
and a separate cutter (e.g. at the input station) for trimming leading and
trailing end portions of a length of strapping. In the former case it may be
possible to omit the strapping guide (144, 7.46) between the cutters.
The heat-sealing station 68 as shown, for example, in Fig. 10
may be simplified by making the lower heat-sealing jaw 92 stationary and
moving the upper jaw 90 only, towards and away from the lower jaw. In
that event, the lower jaw 92 would be positioned somewhat higher than
shown in Fig. 10. It might also be desirable to allow for some flexibility in
the position of the blade 88, for example, by pivoting the blade at its inner
end about a horizontal axis parallel to tree path of strapping through the
heat-sealing station.
A further modification in the area of the heat-sealing station
may be to replace one or both of the air nozzles 202, 204 with a mechanical
lever arranged to physically engage and mechanically displace the
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strapping to ensure that the respective portions of the strapping are
disposed above and below the blade 88. For example, a lever may be used
in place of the upstream nozzle 204 and the downstream nozzle 202 may
be retained. The lever may be pivotally mounted adjacent blade 88 so that
an operative end of the lever can be movE~d between an elevated position
in engagement with the strapping, and a depressed position clear of the
strapping. The lever may be spring-biassed to its depressed position and
movable under the control of an air cylinder to its strapping deflecting
position.
