Note: Descriptions are shown in the official language in which they were submitted.
CA 02664819 2009-04-28
SNAP TOGETHER SPLIT SPROCKET
FIELD OF THE INVENTION
The present invention relates to a split sprocket that can be assembled
without
relying on fasteners or welding to hold the various components of the sprocket
together.
BACKGROUND OF THE INVENTION
Sprockets are products that are shaped to rotate on a shaft and to interface
with
an indented or a perforated material such as a chain or track. A common type
of
sprocket known in the art is a "split sprocket", which is a type of sprocket
that
typically includes four components, a two-part hub and a two-part material-
interfacing plate, all of which are held together with nuts and bolts. The
fact that
the sprocket is split allows it to be clamped on to the shaft at any point
along the
shaft, as opposed to having to receive the shaft at one end thereof and then
slid
along the shaft to a desired position. Typically, eight nuts and bolts are
used to
hold together this type of split sprocket. Consequently, assembling or
disassembling this type of split sprocket can be quite cumbersome. It can take
roughly fifteen minutes for a person to assemble or disassemble this type of
split
sprocket, and if several of these sprockets need to be assembled or
disassembled at any one time, the amount of time required can result in
substantial decreases in productivity and substantial increases in costs.
Split sprockets can also be held together using welding. However, welding is a
time consuming process and requires hiring a relatively expensive welder.
During welding, certain safety procedures also need to be followed.
Consequently, just as when fasteners are used in split sprocket assembly,
welding can also result in substantial decreases in productivity and
substantial
increases in costs.
Accordingly, there exists a need for a split sprocket that improves on at
least one
of the deficiencies of split sprockets known in the art.
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SUMMARY OF THE INVENTION
According to a first aspect of the invention, there is provided a sprocket for
interfacing with a perforated material. The sprocket has a hub that is shaped
to
fit around an axially extending shaft. The hub is made of a plurality of hub
portions each shaped to fit around a portion of the shaft. The hub also has a
retaining portion and a hub interlocking portion, each disposed on at least
one of
the hub portions. The sprocket also has a material-interfacing plate that has
a
periphery shaped to interface with the perforated material. The material-
interfacing plate is made of a plurality of plate portions each shaped to fit
around
a portion of the hub. The material-interfacing plate also has a plate
interlocking
portion shaped to interlock with the hub interlocking portion and disposed on
at
least one of the plate portions. The material-interfacing plate is in a
secured
position when the plate interlocking portion and the hub interlocking portion
are
interlocked with each other. The interlocked plate and hub interlocking
portions
prevent the material-interfacing plate from sliding radially off the hub and
the
retaining portion prevents the material-interfacing plate from sliding axially
off the
hub when the material-interfacing plate is in the secured position.
At least one of the plate portions can be sufficiently elastic such that the
plate
interlocking portion can flex and snugly fit around a portion of the hub and
interlock with the hub interlocking portion when the material-interfacing
plate is in
the secured position.
The retaining portion may be composed of a pair of retaining walls extending
radially from the hub and be shaped to retain a portion of the material-
interfacing
plate therebetween.
At least one of the plate portions may have a slot therein, the at least one
of the
plate portions being sufficiently elastic such that it can flex about the slot
to
facilitate interlocking of the hub interlocking portion and the plate
interlocking
portion.
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A first hub portion and a second hub portion may each have a hub interlocking
portion. A fist plate portion may have both a first plate interlocking portion
and a
second plate interlocking portion. When the hub interlocking portion of the
first
hub portion interlocks with the first plate interlocking portion and the hub
interlocking portion of the second hub portion interlocks with the second
plate
interlocking portion, the material-interfacing plate is in the secured
position. The
hub interlocking portion of the first hub portion and the hub interlocking
portion of
the second hub portion may each include a notch, and the first and second
plate
interlocking portions may each include a lip. The lip of the first plate
portion can
fit into the notch of the first hub portion and the lip of the second plate
portion can
fit into the notch of the second hub portion when the material-interfacing
plate is
in the secured position.
Each of the plate interlocking portions can include a shaved corner shaped to
facilitate sliding the plate interlocking portions and the hub interlocking
portions
together into the secured position.
The hub can be made of two hub portions and the material-interfacing plate can
be made of two plate portions. The two hub portions can be identical to each
other, and the two plate portions can be identical to each other. The two hub
portions can contact each other along a hub split plane and the two plate
portions
can contact each other along a plate split plane, the hub split plane and the
plate
split plane being orthogonal to each other. The hub split plane may also
intersect
the slot in the plate portion or the axis of the shaft.
The periphery of the material-interfacing plate can have teeth for interfacing
with
the material, or it can be toothless.
One benefit of the invention is that the time required to install and remove
the
sprocket from the shaft is significantly reduced relative to conventional
split
sprockets that rely on either fasteners or welding for assembly. This results
in
less downtime for any machinery that relies on the sprockets of the present
invention relative to conventional split sprockets, and also means that fewer
man-
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hours are required to install and remove the sprockets of the present
invention,
further decreasing costs.
Another benefit of the invention is that in addition to saving a sprocket user
time
and money during sprocket installation and removal, the sprocket of the
present
invention is also easier and cheaper and faster to manufacture that
conventional
split sprockets. For example, a manufacturer does not need to pay for
expensive
metal fasteners or drill holes to prepare the sprocket to receive fasteners.
The
sprocket of the present invention can consequently typically be manufactured
for
20% - 30% less than conventional split sprockets.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a perspective view of a sprocket according to a first embodiment;
Figure 2 is a front elevation view of a sprocket according to the first
embodiment;
Figure 3 is a left side elevation view of a sprocket according to the first
embodiment;
Figure 4 is a front elevation view of a plate portion according to the first
embodiment;
Figure 5 is a perspective view of a hub portion according to the first
embodiment;
Figure 6 is a sectional view of a sprocket according to the first embodiment,
taken along line 6 - 6 in Figure 3;
Figure 7(a) is a front elevation view of the plate portion according to the
first
embodiment; Figure 7(b) is a detailed view of area A of the plate portion
depicted
in Figure 7(a); Figure 7(c) is a side elevation view of a hub of the sprocket
according to the first embodiment; Figure 7(d) is a sectional view of the hub
taken along line A-A of Figure 7(c); Figure 7(e) is a front elevation view of
the
sprocket according to the first embodiment; and Figure 7(f) is a top plan view
of
the plate portion depicted in Figure 7(a). Figures 7(a) - (f) each show
exemplary
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dimensions of the sprocket according to the first embodiment and of the
various
components thereof.
Figure 8 is a perspective view of a toothless sprocket according to a second
embodiment.
DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT
Sprockets are manufactured in various shapes and sizes and for a variety of
purposes. Sprockets include drive sprockets, which are disposed on a driven
shaft for transferring energy to a perforated material such as a chain or
track;
idler sprockets, which do not impart additional energy to the perforated
material
but are used for purposes such as maintaining tension in the perforated
material;
and toothless sprockets, which are sprockets that do not use teeth to
interface
with the perforated material. The conventional "split sprocket" is a type of
sprocket that typically includes four components, a two-part hub and a two-
part
plate that interfaces with the perforated material ("material-interfacing
plate"), all
of which is held together with nuts and bolts. Advantageously, the split
sprocket
can be clamped to a shaft at any point along the shaft; disadvantageously, the
conventional split sprocket is typically held together using fasteners or
welding.
Consequently, assembly and disassembly of conventional split sprockets is time
consuming, labour intensive, and costly.
The embodiments described herein are a type of split sprocket that
advantageously can be clamped to the shaft at any point along the shaft, but
that
do not rely on fasteners or welding for assembly and disassembly.
Consequently, the embodiments described herein can be relatively quickly and
easily assembled and disassembled relative to conventional split sprockets,
and
can therefore be more easily and inexpensively manufactured, installed, and
replaced than conventional split sprockets.
Referring now to Figures 1 - 3, there is depicted a sprocket 10 for
interfacing, or
meshing, with a perforated material such as a chain (not shown). The sprocket
CA 02664819 2009-04-28
meshes with the perforated material using teeth 54 extending along the
periphery of the sprocket 10. The sprocket 10 is composed of a hub 12 and a
material-interfacing plate 26. The hub 12 is clamped around the shaft (not
shown) by the material-interfacing plate 26. Hub and plate interlocking
portions,
discussed in more detail in relation to Figures 4 to 7, below, secure the hub
12
and the plate 26 together in a secured position. The shaft on to which the
sprocket 10 is clamped extends axially lengthwise along its axis of rotation;
the
shaft also has a radial axis, which is orthogonal to its axis of rotation.
Although
the sprocket 10 is depicted as being shaped to receive a cylindrical shaft,
the
shaft may have a cross-section that is any suitable shape, such as square or
triangular.
The sprocket 10 is composed of four separate and interlockable components,
namely a first hub portion 14 and a second hub portion 16 forming the hub 12,
and a first plate portion 30 and a second plate portion 32 forming the plate
26.
The hub portions 14, 16 meet along a hub split plane 48. In the depicted
embodiments, the first and second hub portions 14, 16 are identical and the
first
and second plate portions 30, 32 are identical. The plate portions 30, 32 meet
along a plate split plane 50. In the depicted embodiment, the hub split plane
48
and the plate split plane 50 are orthogonal to each other and both intersect
the
axis of rotation of the shaft.
Referring now to Figure 4, there is depicted a front elevation view of the
first plate
portion 30. The first plate portion 30 has a generally semi-circular profile
with a
cavity extending inwards from the flat edge of the semi-circular end into
which
the first and second hub portions 14, 16 can be inserted, as discussed in more
detail in respect of Figure 6, below. In particular, the first plate portion
30 has a
first plate interlocking portion 38 and a second plate interlocking portion
40.
Each of the plate interlocking portions 38, 40 is composed of a lip 44 that is
shaped to fit into, or engage, a corresponding notch 42 (see Figures 5 and 6)
in
one of the hub portions 14, 16 and a shaved corner 52 that facilitates initial
insertion of the hub portions 14, 16 into the first plate portion 30. As
mentioned
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above, when in the secured position, the plate 26 can clamp the hub 12 into
position around the shaft. The first plate portion 30 is composed of, for
example,
an elastic material such as a polyurethane elastomer that has a "memory". By
"memory", it is meant that a material is elastically deformable such that it
can be
temporarily deformed, or flexed, from an initial position to a deformed
position
through application of a force, and when the force is removed the material
returns to the initial position. The inherent elasticity, or memory, of the
first plate
portion 30 is used to provide the clamping force. An exemplary polyurethane
elastomer that can be used is the RedcoTM 750 Polyurethane, produced by
Redwood Plastics Corporation. In this regard, a slot 46 is disposed in the
first
plate portion 30. The length of the slot 46 is selected to reduce the amount
of
material between the cavity and the semi-circular edge of the first plate
portion
30 to an amount that provides sufficient flexibility for the first plate
portion 30 to
bend and receive the hub portions 14, 16, yet maintain sufficient mechanical
strength to meet operational requirements. In particular, the hub 12 should be
able to be inserted into and removed from the first plate portion 30, yet the
first
plate portion 30 should retain sufficient elasticity to clamp down on the hub
12.
Beneficially, the size of the slot 46 can be varied directly with the size of
the first
plate portion 30 such that a sprocket user can consistently apply roughly the
same amount of force to insert or remove the hub portions 14, 16 from the
first
plate portion 30 regardless of the size of the first plate portion 30.
Referring now to Figure 5, there is depicted a perspective view of the first
hub
portion 14. The first hub portion 14 includes two hub interlocking portions
34;
when the plate 26 is in the secured position, the first and second hub
portions 14
are pushed together and one of the hub interlocking portions 34 of the first
hub
portion 14 is inserted into the first plate portion 30 and the other of the
hub
interlocking portions 34 of the first hub portion 14 is inserted into the
second plate
portion 32. The notch 42 in each of the hub interlocking portions 34 is shaped
to
receive the lip 44 of the plate interlocking portions 38, 40 when the plate 26
is in
the secured position, thereby helping to secure the plate 26 to the hub 12 by
preventing the plate 26 from radially sliding off the hub 12.
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Referring now to Figures 3 and 5, the first hub portion 14 also has a
retaining
portion that is composed of two radially extending retaining walls 22 joined
together and axially spaced by the hub interlocking portions 34. When the
plate
26 is in the secured position and engaged with the hub interlocking portions
34, a
portion of the plate 26 is contained between the retaining walls 22, thereby
preventing the plate 26 from sliding axially off the hub 12. In the depicted
embodiments, the retaining walls 22 of each of the hub portions 14, 16 are
semi-
cylindrical and the retaining walls 22 of one of the hub portions 14 contact
the
retaining walls 22 of the other of the hub portions 16 at the hub split plane
48.
Consequently, in order for the retaining walls 22 to prevent axial sliding of
the
plate 26 in the depicted embodiments, the hub split plane 48 and the plate
split
plane 50 are not coplanar. In the depicted embodiments, the hub split plane 48
and the plate split plane 50 are orthogonal. In the depicted embodiments, the
slots 46 are disposed midway along each of the plate portions 30, 32;
consequently, the hub split plane 48 also intersects the slots 46. Both the
hub
split plane 48 and the plate split plane 50 also intersect the axis of
rotation of the
shaft; this allows the first and second hub portions 14, 16 to be identical to
each
other and the first and second plate portions 30, 32 to be identical to each
other,
thereby making manufacturing of the sprocket 10 easier, and consequently
lowering manufacturing costs.
Although the sprocket 10 is depicted as having semi-cylindrical retaining
walls
22, alternative designs are possible. For example, the first hub portion 14
may
have cylindrical retaining walls, while the second hub portion 16 may have no
retaining walls at all.
Referring now to Figure 6, the manner in which the sprocket 10 can be
assembled will be discussed. The user can first place the first and second hub
portions 14, 16 on to a desired position on the shaft, thereby surrounding a
portion of the shaft with the hub 12. The first and second hub portions 14, 16
touch each other as depicted in Figure 6. Then, while holding the hub 12 with
one hand, the user can push the first plate portion 30 on to the hub 12 such
that
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the first plate interlocking portion 38 of the first plate portion 30
interlocks with the
hub interlocking portion 34 of the first hub portion 14 and the second plate
interlocking portion 40 of the first plate portion 30 interlocks with the hub
interlocking portion 34 of the second hub portion 16. In Figure 6, the notches
42
on the first and second hub portions 14, 16 are interlocked with the lips 44
on the
first plate portion 30. The shaved corners 52 on the first plate portion 30
will
facilitate the initial insertion of the hub 12 into the first plate portion
30. Following
this, the partially assembled sprocket 10 should be stable enough to remain on
the shaft without assistance from the user. The user can then take the second
plate portion 32 and push it on to the exposed first and second hub portions
14,
16 in an similar fashion. Following this, the plate 26 is in the secured
position
and the sprocket 10 is ready for use.
To remove the sprocket 10 from the shaft, a wedge or lever can be inserted
into
the plate split plane 50 and the first and second plate portions 30, 32 can be
leveraged apart. This should be sufficient to remove at least one of the plate
portions 30, 32. If the other of the plate portions 30, 32 remains, the user
can
manually remove it by, for example, grabbing either end of the plate portion
30 or
32 and pulling it off the hub 12 while flexing the plate portion 30 or 32
about the
slot 46.
Referring now to Figure 7, there are depicted various views that illustrate
exemplary dimensions of the sprocket 10 and the various components thereof,
such as the hub 12, first plate portion 30, and first interlocking portion 38,
as
designed to accommodate a 14-tooth sprocket. Unless otherwise indicated,
distance measurements are in inches. Persons skilled in the art will recognize
that different dimensions can be utilized for sprockets having, for example,
different numbers of teeth or adapted to fit shafts of different diameters.
Exemplary materials that can be used to manufacture the sprocket 10 include
polyurethane; UMHW/polyethylene; nylon; and any other suitable materials such
as metal (e.g.: aluminum). The physical and mechanical properties of a typical
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polyurethane (RedcoTM 750 Polyurethane, as mentioned above) that can be used
in manufacturing the sprocket 10 are provided in Table 1, below:
Table 1: Typical Physical and Mechanical Properties of RedcoTM 750
Polyurethane that Can Be Used in Sprocket Manufacturing
Hardness, Durometer Value ASTM 75D
D676 - 59T
Specific Gravity 1.2
Tensile Strength, PSI ASTM D412-61T 6382
Elongation at Break, % ASTM D412 - 208
61T
100% Modulus, PSI ASTM D412 - 61T 5348
Tear Strength Split, PLI ASTM D470 157
Bayshore Rebound % 45
Impact Resistance Izod Notched, FT 17
LB/IN @ 75 OF (ASTM D746 - 57T)
Bell Brittle Point Temp OF -70
Compression Set % Method B (ASTM 43
S395)
The sprocket 10 can also be manufactured from a mix of materials; for example,
plastic could be used to manufacture the hub 12 and metal could be used to
manufacture the plate 26. When the sprocket 10 is manufactured using plastic,
it
can be manufactured through molding.
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Referring now to Figure 8, there is depicted a perspective view of a toothless
sprocket 56. The toothless sprocket 56 has a smooth periphery 28 for
interfacing
with the perforated material such as a chain, but otherwise is identical to
the
sprocket 10.
While illustrative embodiments of the invention have been described, it will
be
appreciated that various changes can be made therein without departing from
the
scope and spirit of the invention. The invention is therefore to be considered
limited solely by the scope of the appended claims.
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