Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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1 LOW TENSION PLASTIC CONVEYOR BELT SYSTEM
2 S P E C I F I C A T I O N
4 Background of the Invention
The invention relates to conveyor belt systems, and more
6 particularly to a low tension system wherein a plastic
7 conveyor belt is used, in such a way as to eliminate most
8 wear problems.
9 Plastic conveyor belts have been in increasing use,
particularly in the food industry where dwell time in an
11 oven, a freezer or other food treating environment is needed,
12 for a maximum amount of product and with minimum space
13 requirement. These belts are also used in the electronics
14 and computer industries. See, for example, U.S. Patent
No. 4,742,907 directed to a plastic conveyor belt formed of a
16 series of modules, assigned to the same assignee as the
17 present invention. Such a plastic conveyor belt is designed
18 to travel in straight paths and around curves, and may make
19 both left and right curves. The belt collapses on the inside
of curves, having rods connecting adjacent belt seg~ents
21 through slotted holes.
22 Some plastic conveyor belts have had end members or end
23 plates which are thickened and have recesses at their outer
24 surfaces, for recessing the head of a rod SQ that the rod
head does not protrude out from the end member or end plate.
26 This prevents snagging of the heads on components of the belt
27 driving or guidance system.
28 In low tension spiral conveyor belt systems (such as
29 Ashworth Low Tension Spiral System) a belt, generally of
metal, travels in a helical path around a rotating driving
31 tower or cage or drum. The belt passes over a driven
32 sprocket at a take-up drive location separate from the
33 driving tower. In passing around and in contact with the
34 driving tower, the belt is friction driven, assisted in its
movement generally throughout the length of the belt's path
36 on the tower, greatly reducing tension in the belt as
37 compared to tension which would occur if the belt were only
38 driven from one point. The belt is actually driven at a
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great number of points of conkact with the cage or drum.
In sueh low tension systems, ~he edges of the belts have
been engaged generally by bars or vertical members or rods of the
driving cage or tower. The edges of the belts have generally been
irregular, with end structure of the component belt modules
exposed and irregular and not smooth. This is often due to
exposed and protruding heads of transverse module connecting rods,
and results in snagging of the rod heads against the driving cage
and in excessive wear of the rod heads or other protruding
components or surfaces of the belt as well as of the cage members.
The problem is particularly accentuated by the fact that the tower
or cage must be driven at a speed somewhat ~aster than that of the
belt in an overdrive condition, inasmuch as the belt is moving
both horizontally and vertically along the cage. A slipping
condition therefore exists between the edge surfaces of the belt
and the external surfaces of the driving tower or caye. This
condition must exist whether the belt starts from the bottom and
ends up at the top or starts from the top and ends up at the
bottom in relation to the moving cage. (The cage is actually
driving the belt supported by spiral support strips around the
drum or the cage, up or down, as shown in the drawings and
discussed further below).
Previous to the present invention, there has been no
suggestion for solving this problem by eliminating snagging,
tearing and catching and thereby improving the performance,
wearability and life of a low tension conveyor belt system
utilizing a plastic conveyor belt, as in the present invention
described below.
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Summarv of the Invention
In accordance with the present invention there is
provided a low tension conveyor belt system with a plastic
conveyor belt, comprising,
a driving tower or drum on a substantially vertical axis,
with a wearstrip belt support platform arranged in a helical path
around the driving tower,
an endless plastic conveyor belt positioned on a wearstrip
belt support and extending tangentially off the wearstrip belt
support and away from the driving tower, with means separate from
the driving tower for engaging the driving belt and feeding it in
a return path back to the driving tower and onto the wearstrip
belt support at an opposite axia]. end of the dxiving tower from
the position at which the belt exited the driving tower, and
said plastic conveyor belt being assembled from a series of
plastic belt modules each having end members at its ends, and the
adjacent belt modules heing interconnected by rods passing through
openings in the modules in interdigited projections of the
adjacent modules, said end members having a substantially smooth
æurface which engages against the exterior surfaces of the driving
: tower,
whereby the plastic conveyor belt operates smoothly around
the driving tower, without snagging and without excessive wear of
exposed co~ponents on the edge o~ the belt engaged by the drivlng
tower.
In accordance with the present .invention ~here is
provided, a low tension spiral conveyor belt system includes an
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endless conveyor belt of all plastic or substantially all plastic
components. The belt is made up of a series of elongated plastic
modules with interdigited projections held together by plas~ic
rods passing transversely through bores in the overlapping
projections. At the ends of the plastic rods are heads or
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1 other end members holding the rods in the plastic modules,
2 and these heads are recessed into end members of the plastic
3 modules, each of which has, at least on one side of the belt,
4 a recessed or enlarged outer bore portion in the end m~mber,
for receiving the rod head.
6 In this way, the plastic conveyor belt of the low
7 tension system of the invention presents relatively smooth
8 surfaces to the driving cage or drum which engages the edge
9 of the belt at the inside of its curvature. The belt is more
efficiently driven by the drum, wear to the edges of the belt
11 and to the driving drum or cage is minimized, and the
12 overdriving or higher speed of rotation of the drum in order
13 to move the belt both horizontally and vertically is more
14 readily accomplished.
The plastic conveyor belt system of the invention
16 efficiently travels around the curves in a way not possible
17 with previously available belts. It is therefore efficiently
18 used in the described low tension system, spiraling around
19 the driving cage.
In a speci~ic embodiment, the end plates or members at
21 the ends of the belt modules, which form the exposed surfaces
22 of the inside edge of the belt, are slightly curved to match
23 the curvature of the driving drum. This further reduces wear
24 and adds to the frictional engagement of the driving drum
against the belt edges, tending to further reduce tension in
26 the conveyor belt by evenly applying driving power to the
27 belt as it rides on wear strip surfaces in its helical path
28 around the drum.
29 In another specific embodiment, the belt segments or
modules include side plates at the inside of the curve which
31 may be of a different material than the rest of the belt~ In
32 this way a plastic material of higher friction coefficient
33 can be used for the side plates, where friction with the
34 driving tower should be relatively high. This is different
from the belt's horizontal surface engagement with the
36 helical wear strip on which it rides, where friction must be
37 minimized. Friction with the driving tower, however, should
38 not be so high that the lifting of the belt along the tower,
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1 which requires vertical sliding along the tower's bars, is
2 interfered with significantly.
3 Another embodiment of the invention, which can be
4 combined with either or both of the above embodiments,
includes raised outer plates on one or preferably both sides
6 of the belt. The raised plates ~eep products from falling
7 off the belt or running into the cage.
8 It is therefore among the objects of the present
9 invention to improve over prior low tension spiral conveyor
belt systems with driving towers or drums, by incorporating
11 in such a system a substantially all plastic conveyor which
12 is free of rod heads or other protrusions on the belt's edge
13 at the inside of the curve where the belt progresses
14 helically around the drum. These and other objects,
advantages and features of the invention will be apparent
16 from the following description of a preferred embodiment,
17 considered along with the accompanying drawings.
18
19 Description of the Drawings
Figure 1 is a perspective view generally illustrating a
21 low tension spiral conveyor belt system in accordance with
22 the invention.
23 Figure lA is a schematic elevational view of the system
24 shown in Figure 1.
Figure 2 is a plan view showing details of construction
26 of a plastic conveyor belt incorporated in the system
27 illustrated in Figure 1.
28 Figure 3 is a plan view showing another embodiment
29 wherein each belt module has attached to it a separate,
non-integral end plate.
31 Figure 4 is a partial plan view showing the belt curving
32 around a driving tower or drum of the low tension system,
33 illustrating the contact between the driving tower and the
34 edges of the conveyor belt, and including a variation of the
construction shown in Figure 3.
36 Figure 5 and 6 are plan and side elevation views showing
37 another modification of the plastic conveyor belt.
38
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1 Description_of Preferred Embodiments
2 In the drawings, Figures 1 and lA show a low tension
3 conveyor belt system 10 in accordance with the principles of
4 the invention. The system 10 includes a plastic conveyor
belt 12, preferably with all plastic or substantially a~l
6 plastic components~ a take-up belt drive or sprocket drive
7 which may be at a sprocket 14 driven by a motor (not
8 specifically shown), additional feed sprockets 15, 16 and 17,
9 a take-up sprocket 18, and additional sprockets 20 and 22,
all defining a path through which the conveyor belt 12 is
11 fed. The system includes a helical wearstrip belt support or
12 ramp 24 and a driving tower or cage or drum 26 about which
13 the wearstrip ramp is positioned and against which the belt
14 12 engages at its inside edge as it travels helically around
the drum 26.
16 As is known in the prior art, the driving cage 26 is
17 intended to drive the conveyor belt (which has generally been
18 a steel conveyor in the prior art) by engaging against the
19 inner edge of the belt with vertical bars or spindles 28 or
other exterior drum structure, thereby providing driving
21 force to tha belt at many points (or substantially
22 continuously) along its movement and accordingly greatly
23 reducing tension in the belt as compared to a belt driven
24 from a single location.
The driving cage, as in prior systems, is rotated at a
26 speed slightly higher than that of the moving belt 12,
27 providing a positive driving assistance to the belt, and a
28 constant slipping of the driving cage over the edge surfaces
29 of the belt occurs. This is an "overdrive" condition. There
must be sufficient overdrive to lift the belt and load along
31 the inclined ramp 24 while also moving it generally
32 horizontally. The take-up drive 14 acts as an assist and
33 tension drive, and moves the belt only horizontally in
34 relation to the cage.
However, in prior systems having a driving cage or drum
36 for belt driving and lowering of tension, there has been
37 present a series of protrusions at the edge surfaces of the
38 belt enga~ing the driving drum. Primarily these have
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1 comprised heads or ends on connecting rods which secure
2 successive belt modules together. Although such systems have
3 functioned satisfactorily, they have produced excessive wear
4 on the protrusions, such as the rod head, and distortion of
the belt as well as the sur4ace of the driving drum itself
6 (occasionally the vertical bars of the driving cage have been
7 of plastic to reduce this wear problem). The protrusions
8 have also interfered with the smooth engagement of the belt
9 by the driving drum, reducing the effective frictional
engagement between the belt edges and the surfaces of ~he
11 driving drum. This has resulted in reduced efficiency of the
12 low tension system and in relatively severe variations in the
13 degree of tension of the belt and surges of the belt as it
14 passed around the drum.
In the system of the present invention, these problems
16 are eliminated by the use of the plastic conveyor belt 12 in
17 the structure as illustrated particularly in Figures 2, 3 and
18 4. As shown, plastic connecting rods 32 which serve to
19 connect adjacent belt modules 34 have heads 36 on each end
which are protected from interference or engagement with
21 driving surfaces of the driving drum 26. The rods 32 connect
22 interdigited projections 38 of each belt module as depicted
23 in the drawing. Their heads 36 lie in recesses 40 formed in
24 end members 42 of the belt modules. The recesses 40 comprise
enlarged bores on the axis of smaller bores 44 which extend
26 through the end members and all pro~ections of the
27 interdigited structure.
28 As illustrated in Figure 2, the rod heads 36 do not
29 protrude beyond the outer surface of the end members 42 of
the belt modules. As discussed above, this avoids excessive
31 wear of the belt module, of the rod and of the driving cage
32 as the belt is "overdriven" by the cage.
33 Figure 3 shows a portion of the belt 12, i.e. several
34 modules 34 connected by rods 32 which are also preferably of
plastic. In this embodiment, the end members of the modules
36 34 comprise separate plates 46, non-integral with the body of
37 the module 34. The cage engaging plates 46 have bores 48 and
38 recesses 50, as in the end members 42 discussed above and
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1 shown in Figure 2. The use of separate plates enables the
2 cage-engaging members to be of a higher-friction material
3 than the body of the module 34. This is important in
4 controlling the friction between the driving drum or cage and
the belt in rela~ion ~o the force required to lift the belt,
6 and it enables minimizing friction (with a different plastic
7 material) between the belt's lower surface and the wearstrip
8 24 on which it slides.
9 Figure 4 shows a portion of a belt 12a which is
traveling in an arcuate path around the driving cage 26. In
11 the belt 12a, end plates 46a are slightly modified, arcuately
12 (concavely) shaped for a more complementary engagement
13 against the driving drum. An outer cage-engaging surface 52
14 of each end plate 46a is concave, with a radius generally
matched to that of the driving drum or cage 26. This can
16 help promote still smoother frictional driving of the belt by
17 the drum.
18 Figures 5 and 6 show a further variation which can be
19 used in combination with what is shown in Figures 3 and 4.
In this embodiment the separate plates 46a are raised,
21 extending substantially higher than the top surface of the
22 belt 12a, to provide barriers at both left and right for
23 retention of product on the belt. In many uses of such
24 belts, products are loaded quite densely on the belt, and
there often is low friction between the belt and the bottom
26 of the product. Thus, items can tend to slide o~f the belt
27 or into the driving cage, on a belt without edge barriers.
28 In the present invention the barriers are integral with the
29 separate end member plates 46a of each belt module, thus
enabling the plate to cooperate in providing a higher
31 friction driving surface (as discussed above) while also
32 functioning to hold product on the belt.
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34 I CLAIM:
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