U.S. patent application number 12/082033 was filed with the patent office on 2009-02-26 for roll-up inflatable beam structure.
Invention is credited to Steven D. Potter.
Application Number | 20090049757 12/082033 |
Document ID | / |
Family ID | 40380854 |
Filed Date | 2009-02-26 |
United States Patent
Application |
20090049757 |
Kind Code |
A1 |
Potter; Steven D. |
February 26, 2009 |
Roll-up inflatable beam structure
Abstract
A sandwich beam including in one example first and second spaced
walls, a core configured to maintain a predetermined spacing
between the walls when the core is filled with pressurized gas and
to resist shear when the beam is loaded in bending and a port for
filling the core with gas biasing both walls in tension. The
tension tends to increase in the second wall and decrease and cause
a compression load in the first wall in response to a sufficiently
large applied bending load. A compression element is fixed only
with respect to the first wall and is configured (a) to support the
compression load so that the beam is stronger at a given gas
pressure and (b) to flex sufficiently to allow the beam to be
rolled up when the gas is emptied from the core via the port.
Inventors: |
Potter; Steven D.; (Bedford,
MA) |
Correspondence
Address: |
Iandiorio Teska & Coleman
260 Bear Hill Road
Waltham
MA
02451-1018
US
|
Family ID: |
40380854 |
Appl. No.: |
12/082033 |
Filed: |
April 8, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60965670 |
Aug 21, 2007 |
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Current U.S.
Class: |
52/2.23 ; 441/74;
52/2.22 |
Current CPC
Class: |
B63B 32/51 20200201;
B64C 3/30 20130101 |
Class at
Publication: |
52/2.23 ;
52/2.22; 441/74 |
International
Class: |
E04B 1/343 20060101
E04B001/343; B63B 35/79 20060101 B63B035/79 |
Claims
1. A sandwich beam comprising: first and second spaced walls; a
core configured to maintain a predetermined spacing between the
walls when the core is filled with gas and to resist shear when the
beam is loaded in bending; a port for filling the core with gas,
said gas biasing both walls in tension, said tension tending to
increase in the second wall and decrease and cause a compression
load in the first wall in response to a sufficiently large applied
bending load; and a compression element fixed only with respect to
the first wall and configured (a) to support the compression load
so that the beam is stronger at a given gas pressure and (b) to
flex sufficiently to allow the beam to be rolled up when the gas is
emptied from the core via the port.
2. The sandwich beam of claim 1 in which the beam has a load
capacity X without the compression element and a load capacity of N
times X when the compression element is added to the beam.
3. The sandwich beam of claim 2 in which N is greater than 1.5.
4. The sandwich beam of claim 1 in which the beam is at least
1.5.times. weaker when loaded in the reverse direction.
5. The sandwich beam of claim 1 in which the compression element is
a sheet of material secured to the outer surface of the first
wall.
6. The sandwich beam of claim 1 in which the first and second walls
are fabric.
7. The sandwich beam of claim 1 in which the core includes a
plurality of drop-stitches between the first and second walls.
8. The sandwich beam of claim 6 in which the drop-stitches are
angled.
9. The sandwich beam of claim 1 in which the compression element is
between 1/64 and 1/16 inches thick.
10. The sandwich beam of claim 1 in which the compression element
is selected from materials including fiber reinforced polymers,
polymer films, polymer sheets, metals, wood, and wood-based
products.
11. The sandwich beam of claim 1 in which the compression element
is flat.
12. The sandwich beam of claim 1 in which the compression element
is curved concave.
13. The sandwich beam of claim 1 in which the compression element
is curved convex.
14. The sandwich beam of claim 1 in which the core includes
baffles.
15. The sandwich beam of claim 14 in which the baffles are
angled.
16. The sandwich beam of claim 14 in which the baffles are angled
and intersecting.
17. The sandwich beam of claim 14 in which the baffles are tube
shaped.
18. The sandwich beam of claim 1 in which the core includes
foam.
19. The sandwich beam of claim 1 in which there are a plurality of
compression elements.
20. The sandwich beam of claim 19 in which each compression element
is a flat strip.
21. The sandwich beam of claim 19 in which the compression elements
are rods.
22. The sandwich beam of claim 19 in which the compression elements
are tape springs.
23. The sandwich beam of claim 1 further including a skin over the
compression element.
24. The sandwich beam of claim 1 in which the core includes baffles
and there is a compression element associated with select baffles
each including a top leaf hinged to a side leaf.
25. The sandwich beam of claim 1 in which there is a vacuum pocket
about the compression element.
26. The sandwich beam of claim 1 in which the compression element
includes multiple plies that are clamped together by pressure or
vacuum force, but are allowed to slide when the beam is deflated,
thus allowing the beam to be rolled up more easily.
27. A waterboard comprising: upper and lower walls; a core
configured to maintain a predetermined spacing between the walls
when the core is filled with gas and to resist shear when the
waterboard is loaded in bending; a port for filling the core with
gas, said gas biasing both walls in tension, said tension tending
to increase in the lower wall and decrease and cause a compression
load in the upper wall in response to a sufficiently large applied
bending load; and a compression sheet secured about the upper wall
and configured to support the compression load on the upper wall
and to flex sufficiently to allow the waterboard to be rolled up
when the gas is emptied from the core via the port.
28. A method of making a sandwich beam, the method comprising:
securing a first wall to a second wall via a core configured to
maintain a predetermined spacing between the walls when the core is
filled with a gas and to resist shear when the beam is loaded in
bending; and applying a compression element only to and fixed with
respect to the first wall, the compression element configured to
support the compression load on the first wall resulting from
bending so that the beam is stronger at a given gas pressure and
configured to flex sufficiently to allow the beam to be rolled up
when the gas is emptied from the core via the port.
29. The sandwich beam of claim 1 having one or more second
compression elements received by one or more sleeve pockets
attached to the second wall.
30. The sandwich beam of claim 1 in which the compression element
is pre-curled such that the beam rolls up when deflated and unrolls
when inflated.
31. A sandwich beam comprising: first and second spaced walls; a
core configured to maintain a predetermined spacing between the
walls when the core is filled with pressurized gas and to resist
shear when the beam is loaded in bending; a port for filling the
core with gas; and narrow compression elements fixed to both walls
and configured (a) to support compression loads in the first and
second walls due to bending loads applied to the beam in either
direction (b) to flex sufficiently to allow the beam to be rolled
up when the gas is emptied from the core via the port, and (c) to
nest when deflated to allow each compression element to bend about
its neutral axis.
Description
RELATED APPLICATIONS
[0001] This application claims the benefit of and priority to U.S.
Provisional Application Ser. No. 60/965,670, filed Aug. 21, 2007,
which is incorporated herein by reference.
FIELD OF THE INVENTION
[0002] This subject invention relates to inflatable structures.
BACKGROUND OF THE INVENTION
[0003] Inflatable structures such as the surfboard discussed in
U.S. Published Patent Application No. 2003/0153221 (incorporated
herein by this reference) are becoming increasingly popular. U.S.
Pat. No. 2,743,510 (incorporated herein by this reference)
discloses an inflatable structure with top and bottom walls made of
fabric and drop stitches securing the top and bottom walls together
to hold them in a desired shape when the structure is inflated. See
also U.S. Pat. No. 6,066,016 also incorporated herein by this
reference.
[0004] Such inflatable structures are generally weak in buckling
owing to the fact that the top and bottom walls must be
sufficiently flexible so that the structure can be rolled up when
deflated for transport and storage.
[0005] For example, an inflatable surf board in accordance with
U.S. Published Patent Application No. 2003/0153221, when inflated
to 15 psi and placed across two saw horses, could not support 170
lbs. Adding additional air pressure so the surfboard can sustain
greater loads is both difficult in the field and can be dangerous
and/or result in severe stress on the components of the inflated
surfboard.
[0006] U.S. Pat. No. 2,743,510 discloses a coating on the top and
bottom fabric plies but solely for gas imperviousness. U.S.
Published Patent Application No. 2003/0153321 also discusses
overlays of "flexible material" to increase "strength or
durability" of the board, however, "flexible material" is defined
as being an elastomer or elastomer-coated fabric as are typically
used for inflatable boats. These overlays add puncture resistance
and tensile stiffness, but have minimal resistance to buckling.
[0007] While it is common knowledge that an inflatable beam can be
stiffened by adding batons (e.g., shock-corded aluminum tubes used
on the Feathercraft Gemini kayak), this method is time consuming to
assemble and provides only a small increase in strength and
stiffness.
BRIEF SUMMARY OF THE INVENTION
[0008] It is therefore an object of this invention to provide a
stronger inflatable structure.
[0009] It is a further object of this invention to provide such an
inflatable structure which better withstands buckling loads.
[0010] It is a further object of this invention to provide such an
inflatable structure which better withstands buckling loads without
the need to increase the inflation pressure.
[0011] It is a further object of this invention to provide such an
inflatable structure which can still be easily deflated and rolled
up for transport and/or storage.
[0012] It is a further object of this invention to provide such an
inflatable structure which is easily manufactured.
[0013] The subject invention results from the realization that the
problem of an inflated sandwich structure buckling upon the
application of a bending load is solved by understanding that
buckling occurs when one wall of the sandwich structure is no
longer in tension and the solution is to add a compression element
which can withstand the in-plane compressive load and which, at the
same time, is sufficiently compliant so that the sandwich structure
can still be rolled up for transport and/or storage. A further
realization is that for most beam-like applications, the
compression element is needed on only one side, and that by
allowing buckling of the other side, the deflated beam can be
rolled up easily.
[0014] The subject invention features a sandwich beam comprising
first and second walls and a core configured to maintain a
predetermined spacing between the walls when the core is filled
with pressurized gas and to resist shear when the beam is loaded in
bending. A port is provided for filling the core with gas which
biases both walls in tension. In response to a bending load, the
tension increases in the second wall and decreases in the first
wall. If the load is sufficiently large, the first wall goes into
compression. A compression element is fixed only with respect to
the first wall and is configured (a) to support the compression
load so that the beam is stronger at a given gas pressure and (b)
to flex sufficiently to allow the beam to be rolled up when the gas
is emptied from the core via the port.
[0015] The typical beam has a load capacity X without the
compression element and a load capacity of N times X when the
compression element is added to the beam. In one example, N is
greater than 1.5. The typical beam is also approximately N times X
stronger when loaded in the intended direction than when loaded in
the reverse direction; the intended direction being that which
tends to cause in-plane compression of the first wall.
[0016] The compression element may be a sheet of material secured
to the outer surface of the first wall. Typically, the first and
second walls include fabric. One core construction includes a
plurality of drop-stitches between the first and second walls. The
drop-stitches may be angled. In one variation, the compression
element is between 1/64 and 1/16 inches thick. The compression
element may include fiber reinforced polymers, polymer films,
polymer sheets, metals, wood, and wood-based products. In one
example, the compression element is flat. But, the compression
element may also be curved concave or curved convex. The core may
include baffles. The baffles may be angled and/or intersecting. The
baffles may be tube shaped. Another core includes foam.
[0017] In some embodiments, there are a plurality of compression
elements. Each compression element may be a flat strip. The
compression elements may be rods. In other embodiments, the
compression elements are tape springs. There may be a skin over the
compression element.
[0018] In one particular example, the core includes baffles and
there is a compression element associated with select baffles each
including a top leaf hinged to a side leaf. There may be a vacuum
pocket about the compression element. In one example, the
compression element includes multiple plies that are clamped
together by pressure or vacuum force, but are allowed to slide when
the beam is deflated, thus allowing the beam to be rolled up more
easily.
[0019] One waterboard in accordance with the subject invention
features upper and lower walls, a core configured to maintain a
predetermined spacing between the walls when the core is filled
with gas and to resist shear when the waterboard is loaded in
bending, a port for filling the core with gas, thus biasing both
walls in tension until the upper wall experiences compression due
to a sufficiently large bending load, and a compression sheet
secured about the upper wall and configured to support the
compression on the upper wall and to flex sufficiently to allow the
waterboard to be rolled up when the gas is emptied from the core
via the port.
[0020] One method of making a sandwich beam in accordance with the
subject invention includes securing a first wall to a second wall
via a core configured to maintain a predetermined spacing between
the walls when the core is filled with a gas and to resist shear
when the beam is loaded in bending. A compression element is
applied only to and fixed with respect to the first wall. The
compression element is configured to support the compression load
on the first wall so that the beam is stronger at a given gas
pressure and configured to flex sufficiently to allow the beam to
be rolled up when the gas is emptied from the core via the
port.
[0021] One sandwich beam in accordance with the subject invention
includes first and second spaced walls, a core configured to
maintain predetermined spacing between the walls when the core is
filled with pressurized gas and to resist shear when the beam is
loaded in bending, a port for filling the core with gas, and narrow
compression elements fixed to both walls and configured (a) to
support compression loads in the first or second walls due to
bending loads applied to the beam in either direction (b) to flex
sufficiently to allow the beam to be rolled up when the gas is
emptied from the core via the port, and (c) to nest when deflated
to allow each compression element to bend about its neutral
axis.
[0022] The subject invention, however, in other embodiments, need
not achieve all these objectives and the claims hereof should not
be limited to structures or methods capable of achieving these
objectives.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0023] Other objects, features and advantages will occur to those
skilled in the art from the following description of a preferred
embodiment and the accompanying drawings, in which:
[0024] FIG. 1 is a schematic three-dimensional top view showing an
inflatable surfboard in accordance with the prior art;
[0025] FIG. 2 is a cross-sectional view showing the surfboard of
FIG. 1 under a load;
[0026] FIG. 3 is a highly schematic three-dimensional top view of
an inflatable surfboard in accordance with the subject
invention;
[0027] FIG. 4 is a schematic cross-sectional view showing the
inflatable surfboard of FIG. 3 in its partially rolled up
configuration;
[0028] FIG. 5 is a cross-sectional end view showing an example of
an inflatable beam in accordance with the subject invention with a
concave compression element;
[0029] FIG. 6 is a schematic cross-sectional end view of an
inflatable beam in accordance with the subject invention with a
convex compression element;
[0030] FIG. 7 is a schematic cross-sectional end view of an
inflatable beam in accordance with the subject invention with a
corrugated compression element;
[0031] FIG. 8 is a schematic cross-sectional end view of a
drop-stitched inflatable beam in accordance with the subject
invention including a compression element;
[0032] FIG. 9 is a schematic cross-sectional side view showing a
portion of a drop-stitched reinforced inflatable beam in accordance
with the subject invention;
[0033] FIG. 10 is a schematic cross-sectional side view showing a
portion of a reinforced inflatable beam with angled threads in
accordance with the subjection invention;
[0034] FIG. 11 is a load diagram for an unreinforced inflatable
beam in accordance with the prior art;
[0035] FIG. 12 is a cross-sectional end view of a reinforced
inflatable beam with angled threads in accordance with the subject
invention;
[0036] FIG. 13 is a cross-sectional end view of an inflated beam
with stitched baffles in accordance with the subject invention;
[0037] FIG. 14A is a highly schematic view showing baffles being
pre-sewn to the top surface of an inflatable beam in accordance
with the subject invention;
[0038] FIG. 14B is a highly schematic depiction showing baffles
being sewn to the bottom surface of an inflatable beam in
accordance with the subject invention;
[0039] FIG. 15A is a schematic front view showing a fabric strip
including biased fibers;
[0040] FIG. 15B is a schematic front view showing a fabric strip
including zero and ninety degree fibers;
[0041] FIG. 15C is a schematic front view showing a two-ply baffle
strip including biased fibers and fibers at zero and ninety
degrees;
[0042] FIG. 16 is a schematic cross-sectional end view showing a
reinforced inflated beam with angled baffles in accordance with the
subject invention;
[0043] FIG. 17 is a schematic cross-sectional end view showing a
reinforced inflated beam in accordance with the subject invention
including angled/intersecting baffles;
[0044] FIG. 18 is a schematic cross-sectional end view showing a
reinforced inflated beam having tubular baffles in accordance with
the subject invention;
[0045] FIG. 19 is a schematic cross-sectional end view showing a
portion of a reinforced inflated beam with mated/joined tubular
baffles in accordance with the subject invention;
[0046] FIG. 20 is a schematic cross-sectional end view showing a
portion of a sheet reinforced beam with mated/joined tubular
baffles and tensile reinforcement of the bottom surface;
[0047] FIG. 21 is a schematic cross-sectional end view of an
inflatable airfoil with a foam core including a compression element
on the top surface of the airfoil in accordance with the subject
invention;
[0048] FIG. 22 is a schematic cross-sectional side view of a
portion of a reinforced beam with a random fibrous core in
accordance with the subject invention;
[0049] FIG. 23 is a schematic cross-sectional end view of an
inflated beam reinforced with flat compression elements strips in
accordance with the subject invention;
[0050] FIG. 24 is a schematic cross-sectional end view showing an
example of an inflated beam reinforced with compression element
rods in accordance with the subject invention;
[0051] FIG. 25 is a schematic cross-sectional end view showing an
inflated beam with compression elements in the form of tape
springs;
[0052] FIG. 26 is a schematic cross-sectional end view of an
inflated beam with top and bottom skins in accordance with the
subject invention;
[0053] FIG. 27 is a schematic cross-sectional end view showing a
portion of an inflated beam in accordance with the subject
invention with hinged-strip compression elements;
[0054] FIG. 28 is a schematic cross-sectional end view of an
inflated beam in accordance with the subject invention with narrow
compression elements on both sides;
[0055] FIG. 29 is a schematic cross-sectional end view showing an
example of a beam with a two layer structural sheet in accordance
with the subject invention;
[0056] FIG. 30 is a schematic cross-sectional end view showing an
example of a beam with a two layer structural sheet and edge seals
in accordance with the subject invention;
[0057] FIG. 31 is a schematic cross-sectional end view showing a
portion of a beam with tape spring compression elements residing in
sleeves in accordance with the subject invention; and
[0058] FIG. 32 is a schematic cross-sectional end view showing a
portion of a beam with multi-layer tape springs residing in sleeves
in accordance with the subject invention.
DETAILED DESCRIPTION OF THE INVENTION
[0059] Aside from the preferred embodiment or embodiments disclosed
below, this invention is capable of other embodiments and of being
practiced or being carried out in various ways. Thus, it is to be
understood that the invention is not limited in its application to
the details of construction and the arrangements of components set
forth in the following description or illustrated in the drawings.
If only one embodiment is described herein, the claims hereof are
not to be limited to that embodiment. Moreover, the claims hereof
are not to be read restrictively unless there is clear and
convincing evidence manifesting a certain exclusion, restriction,
or disclaimer.
[0060] FIG. 1 shows a prior art inflatable surfboard 10 with top
wall 12, bottom wall 14, and side wall 16. Inflation port 18 is for
filling the interior core of the surfboard with compressed air.
FIG. 2, also prior art, shows core 20 including drop-stitches 22
extending between top wall 12 and bottom wall 14 to maintain a
predetermined spacing between walls 12 and 14.
[0061] Inflation pressure causes tension in the drop-stitches 22,
as well as planar (X and Y) tension in the top wall 12 and bottom
wall 14. The planar tension results from the pressure acting on the
sidewalls 16. When surfboard 10 is loaded in bending as shown by
the surfer's weight at 24 and buoyant force 25 in FIG. 2, this
results in a decrease in the X-axis tension in the top wall 12
(shown at 26), and an increase in tension in the bottom wall (shown
at 27). The changes in X-axis tension cause the surfboard to bend
concave up, as does the tendency of the beam to "rack" as in a
parallelogram. The "racking" effect causes horizontal shear, i.e.
the tendency of the bottom wall 14 to move inward relative to the
top wall 12, as shown at 28. Shear is resisted by the sidewalls,
and by a small component of the tension in the drop-stitches 22
acting in-line with the top and bottom walls.
[0062] In the prior art, the walls of the surfboard are typically
made of elastomer-coated polyester or nylon fabric. These materials
are very flexible in bending and thus buckle easily when the top
wall tension 26 goes to zero. The typical way to increase the load
capacity is to increase the inflation pressure, but this increases
the inflation time and effort, requires more expensive pump and
valving, makes the surfboard more likely to leak, requires heavier
materials, and creates an explosion hazard.
[0063] FIG. 3 shows reinforced surfboard 10' having compression
element 40 fixed on top wall 12. When loaded as in FIG. 2, the load
capacity of the reinforced surfboard 10' is not limited by the
tension 26 in the top wall going to zero, in fact, the compression
element 40 can sustain significant in-plane compressive force
without buckling. Compression element 40 is preferably stiff and
strong in tension and compression, but can still be flexible in
bending, for example, it may be a very thin (e.g., 0.031 inches
thick) layer of G10 fiberglass-epoxy laminate (a common circuit
board material). The buckling strength of compression element 40 is
greatly enhanced by the stabilizing effect of the inflated
structure. When the surfboard 10' is deflated, it can be rolled up
for storage and/or transport as shown in FIG. 4. Preferably, the
surfboard is turned upside down before rolling.
[0064] In testing, at 2.7 times increase of load carrying capacity
was realized as was a 2.3 times increase in bending stiffness
holding pressure constant at 15 psi. Alternatively, the reinforced
surfboard could support more load at an inflation pressure of 5 psi
than the unreinforced surfboard at 15 psi. In this way, the problem
of an inflated sandwich structure of any type buckling upon the
application of a large load is solved by understanding that
buckling occurs when one wall of the sandwich structure is no
longer in tension and cannot withstand the resulting compressive
load. The solution is to include a compression element which can
withstand the compressive load and which at the same time is
sufficiently compliant so that the inflated sandwich structure can
be rolled up for transport and/or storage. The result is an
inflated beam with increased bending strength and stiffness and the
ability to reduce the inflation pressure, the size, or the overall
weight of the beam. The advantage is more compact storage and fast
deployment or repacking. Reduction of the inflation pressure is
advantageous since it reduces the inflation time, the leak rate,
and the risk of an explosion and/or damage to the surfboard.
[0065] The method of the subject invention can be applied to all
inflatable beams and plates, but is especially applicable to beams
that are relatively long or wide compared to their thickness and
have a simple curvature on their compression side. Example
applications include the surfboard example discussed above, as well
as the following: other waterboards such as paddleboards, rescue
boards, sailboards, boogie-boards and sit-on-top kayaks; floor
panels for kayaks and Zodiak boats, watercraft such as car ferries,
barges and the like; floating devices such as docks, bridges and
runways; airfoils, e.g. for aircraft, kites, sails or wind power
generation; ramps and bridges; and other beam structures such as
tables, stretchers, floor panels, walls, roofs, tent supports,
masts, towers, helipads, and the like.
[0066] FIG. 4 shows a cross-section of a partially rolled-up beam
similar to that of FIG. 3. The bottom wall has no compression
elements and is therefore able to compress, buckle, and wrinkle in
order to absorb the difference in arc/length between the outside
and inside of the roll.
[0067] In general, when a sandwich structure is rolled, the outer
wall (of the roll) goes into tension, the inner wall into
compression, and the core and sidewalls go into shear. To
facilitate rolling, the possibilities are to allow stretch of the
outer surface, allow compression or buckling of the inner wall,
and/or allow shear of the core and sidewalls. However, in an
inflated structure, e.g., a drop-stitched surfboard, the sidewalls
tend to have significant resistance to shear, and the top and
bottom walls are preferably stiff, at least in tension. One aspect
of the subject invention is that the compression element (e.g.
sheet) is fixed only on the top side. By allowing compression or
buckling of the bottom side, the surfboard (or other beam) can be
easily rolled up. This solution also allows the use of high-tensile
fibers in the bottom wall and sidewalls. When inflated, the
surfboard has high bending stiffness which improves controllability
and reduces hydrodynamic drag.
[0068] In this specification, the terms "top" and "bottom" of the
beam are illustrative, and should not be considered limiting. The
term "top" or "top wall" is used to describe the side of the beam
or plate that goes into compression in response to the predominant
bending moment. This terminology is literally correct for a
surfboard, ramp, bridge, or wing (while flying). However, there are
other applications where the compression side is on the bottom
(e.g., a see-saw).
[0069] The compression element is preferably made of a low-density,
high strength, high-modulus material in sheet form. The sheet
should be as stiff as possible without being too difficult to roll
up to the desired stowed size. For best results, the sheet should
have a minimum bend diameter significantly smaller than the desired
rolled-up diameter. In the 0.031 inch G10 example, the minimum bend
diameter is about 1.4 inches but the rolled up diameter is about 12
inches. A small minimum bend radius can also allow the inflated
beam to be overloaded (i.e., buckled) without causing permanent
damage.
[0070] Other candidate materials for the compression element
include, but are not limited to, the following: fiber reinforced
polymers (FRP) such as fiberglass, Kevlar, Spectra, Vectran, carbon
fiber in a matrix of epoxy, polyester, or PEEK; polymer films such
as Vectran, PBO, Mylar, Ultem, Kapton; polymer sheets such as ABS,
nylon, acetal, PEEK; alloys of aluminum, iron, copper, titanium;
and woods such as bamboo, hickory, etc. The structural sheet can
also be thin sandwich, e.g., two layers of FRP or film bonded to a
thin core of foam, balsa wood, or honeycomb material.
[0071] The structural sheet can also be formed by laying up
high-modulus fibers (e.g., cloth or roving) directly on an air-beam
structure (e.g., a drop-stitched beam). Conventional methods such
as squeegees and/or vacuum bagging can be used to impregnate the
fibers with a polymer resin such as epoxy or polyester.
[0072] Increased bending capacity can be achieved by making the
compression element curved or wavy in the direction transverse to
the direction of maximum compression. FIGS. 5-7 show cross-sections
of inflatable beams having a concave, convex and corrugated sheet
respectively. In all cases, the compression element 40 is attached
to the compression-side of the beam (e.g., the top of a surfboard).
The curvature increases the bending stiffness of the compression
element, thus increasing buckling resistance. When the beam is
deflated and rolled, the curvature tends to flatten out and has
only a small effect on the resistance to rolling and diameter of
the roll.
[0073] FIGS. 5-7 show an approximately constant beam thickness but
this should not be considered limiting: the beam can have variable
thickness transversely or along its length as determined by the
sidewalls, baffles and/or threads connecting the top and bottom
walls.
[0074] In the surfboard example, and other beams having
non-circular cross-sections, a collapsible core is needed to
control the spacing between the top and bottom walls. The
collapsible core can include fibers, threads, fabric, foam, or any
combination thereof. An especially convenient construction is shown
in FIGS. 8 and 9. FIG. 8 is an end-view cross-section of a
drop-stitched inflatable beam with a structural sheet attached on
the top side. FIG. 9 is a partial side-view cross-section of the
same beam. This construction is consistent with the reinforced
surfboard 10' of FIG. 3.
[0075] Drop-stitching is a manufacturing process in which two
layers of fabric are stitched together leaving slack threads
between the two layers. The fabric layers are typically impregnated
and/or coated with an airtight elastomer such as PVC, urethane or
Hypalon. To make an inflatable panel or beam, the drop-stitched
material is cut and the edges are sealed around the perimeter using
one or more strips of coated fabric. The edge strips are typically
bonded with contact adhesive or welded using heat, ultrasound, RF,
or a solvent.
[0076] When inflated, the beam assumes the shape as shown in FIGS.
8 and 9. Typically, drop-stitch material is made with
constant-length threads oriented substantially parallel to each
other. The density of stitches is typically on the order of 10 per
square inch.
[0077] Having the fibers oriented in the thickness, or Z direction,
is simpler to achieve, but results in lower beam stiffness since
the core provides little resistance to horizontal shear until there
is significant deflection. In FIG. 2 note the angle of the threads
relative to the top and bottom surfaces. Only a small component of
the thread tension resists shear between the top and bottom
layers.
[0078] For greater shear stiffness, the threads may be angled,
e.g., as in FIG. 10. Angled drop-stitched material is commercially
available, however, the angle with respect to the Z-axis is
typically much smaller than would be optimal for the present
invention. There are two reasons for this. Firstly, the existing
techniques for angled drop-stitching limit the angle to +/-half the
arctangent of the stitch spacing divided by the thread length. For
example, a 3'' thick drop-stitched panel with 0.3 inch thread
spacing would have thread angles of +/-2.9.degree.. The second
reason is that the optimal thread angle for an un-reinforced
inflatable drop-stitched beam is, in fact, very small.
[0079] FIG. 11 shows a load diagram for a cantilever un-reinforced
inflatable beam having length L, thickness T, inflation pressure P,
thread angle +/-.theta., and applied load F. There are two main
"failure" modes: buckling of the top surface at the fixed end
(left), and slack in the left-leaning threads. The latter does not
actually cause failure, but leads to larger deflections. The
"optimal" thread angle .theta. is that which avoids slack threads
up to the point where the top wall buckles. Resolving the various
forces and stresses, and neglecting strain in the top and bottom
surfaces, results in the following equation:
.theta. = tan - 1 ( T 2 L + T ) ( 1 ) ##EQU00001##
[0080] For example, a 3 inch thick un-reinforced drop-stitched
surfboard spanning a 6 foot gap between two waves will have an
"optimal" drop-stitch angle of +/-2.3.degree.. The pressure P
required to support load F is given by the following equation
(where W is the width of the beam):
P = F 2 L + T W T 2 ( 2 ) ##EQU00002##
[0081] In the surfboard example, assuming a width of 20'', a
pressure of approximately 41.7 psi would be needed to support a 200
lb rider, assuming a 6 foot span.
[0082] With a structural sheet attached to the top wall of an
angled drop-stitched inflatable beam, the resulting "reinforced"
beam can support many times greater load. Whereas the improvement
in load capacity was 2.7.times. adding a 0.031 inch G10 sheet to a
straight drop-stitched surfboard, the improvement would be
approximately 4-5.times. using the same sheet to reinforce an
angled drop-stitched surfboard. The angled drop-stitch reduces
deflection of the beam which reduces the curvature of the top wall
near the point of maximum compressive stress. With less curvature,
the top wall has a higher buckling load.
[0083] The preferred drop-stitch angle for a reinforced inflatable
beam is described by the following equation:
.theta. = tan - 1 [ F P W T ] ( 3 ) ##EQU00003##
[0084] In the surfboard example above, the pressure requirement can
be reduced to about 10 psi, and the preferred thread angle is about
+/-10.degree.. This angle provides just enough shear resistance to
avoid "racking" up to the load capacity of the beam. Larger thread
angles are typically undesirable since a component of the thread
angle tends to reduce the pre-tension in the bottom wall, thus
reducing beam strength in the non-dominant direction of loading. In
the surfboard application, a reversal of the typical direction of
loading can occur for example when a wave momentarily supports the
middle of a surfboard while the rider has one foot forward and one
aft.
[0085] In the surfboard example, the beam is relatively long
compared to its width and it is most important to angle the threads
as viewed from the side (see FIG. 10). For better bi-axial (i.e.,
plate-like) stiffness, the threads can also be angled as viewed
from the end, e.g., as in FIG. 12. This will reduce deflection due
to shear in the Y/Z plane.
[0086] Another source of compliance in a drop-stitched beam is the
stretch of the fabric. If, in accordance with the present
invention, the top wall is reinforced with a structural sheet, the
resulting beam will be much stiffer. Further stiffness improvement
is possible by adding tensile material to the bottom wall of the
beam. The tensile material is preferably made of a high-strength,
high-modulus material which can sustain repeated buckling and
wrinkling as is likely to occur when the beam is rolled up. Example
materials include fabrics, sailcloth, elastomer-coated fabric, mat,
unidirectional ribbons, flat braid or cord made of polyester,
Nylon, Kevlar, Vectran, fiberglass, Spectra or PBO fiber. At least
some of the fibers should be aligned substantially in the direction
of greatest tension (typically the long, or X-direction). To allow
for buckling and wrinkling, the fibers should be embedded in a
low-modulus matrix (e.g., an elastomer), or have voids where the
fibers are not impregnated and are therefore allowed to shear. The
tension element(s) can be bonded or welded to the bottom wall of
the drop-stitch panel over the full mating surface area, or can be
attached at more localized areas. The latter method is less likely
to kink and damage the fibers, but also creates pockets between the
tensile element(s) and the bottom surface which may be undesirable
in some applications.
[0087] The tensile material can also be a polymer film. Desired
properties are high-modulus, high strength, low creep, high
elongation to failure, and good fatigue and tear resistance.
Example film materials are Mylar, PEEK, Ultem, and Vectran. Metal
films such as stainless steel or aluminum could also be used.
[0088] In accordance with the invention, the variations described
above relating to fiber angles in the core and tensile
reinforcement of the bottom wall also apply to other core
constructions. For instance, the drop-stitch threads could instead
be small wires or filaments and could be attached directly to a top
structural sheet and bottom tensile film. The threads can also be
replaced by baffles made of fabric or a collapsible film.
[0089] FIGS. 5-7 showed three examples of a core construction using
baffles. FIG. 13 shows a more detailed view. In this variation, the
top and bottom walls, sidewalls and baffles are made of fabric and
are joined by sewing. An example of a sewing method is shown in
FIGS. 14A and 14B. The last sewing operation (not shown) would be
to sew the edges of the top and bottom walls together, thus forming
the sidewalls.
[0090] Outer walls can be sealed by coating with an air-tight
elastomer to form an inflatable sealed volume. Alternately, each
compartment can be inflated with a separate bladder. Additional
layers of bias fabric (e.g., having fiber angles +/-45.degree. when
viewed in the Y/Z plane) can be bonded to the top and/or bottom
walls to better transfer horizontal shear from the baffles to the
top and bottom walls, and to improve the torsional stiffness of the
beam.
[0091] To stiffen the beam against shear loads in the X/Z plane,
the baffles preferably have fibers that are angled when viewed from
the side. Since most fabric is produced with angles 0 and
90.degree., one solution would be cut fabric on the bias to make
strips having fiber angles +/-45.degree., however, when inflated,
the tension in the fibers needed to resist the outward pressure
force produces an equal force tending to contract the beam
lengthwise. In effect, the pressure forces in X and Z cancel,
resulting in essentially zero pre-tension in the top and bottom
surface assemblies. This has little effect on the bending capacity
in the preferred direction (i.e., the structural sheet in
compression), but it greatly reduces bending capacity in the
opposite direction. Applications such as surfboards, kayaks, wings
etc, tend to have much greater bending load in one direction, but
the some strength in the opposite direction is still needed.
[0092] In accordance with the invention, one solution when using
fabric baffles is to bond or sew strips of 0/90.degree. fabric 50,
FIG. 15B, to bias-cut strips 52, FIG. 15A, thus producing
0/90/-45/+45.degree. two-ply baffle material 54, FIG. 15C. Outward
pressure is directly resisted by the Z-oriented fibers, thus
minimizing the contractile force in the X-direction.
[0093] Alternately, the baffles, sidewalls, bottom wall and/or top
wall can be made from a film material such as Mylar, PEEK, Ultem or
Vectran. The parts could be bonded or welded. If the latter, a
method can be used similar to that shown in FIGS. 14A and 14B, but
replacing the sewing assembly with a device that pinches the layers
together and uses heat, ultrasound, RF or other method to weld the
layers together.
[0094] For improved bi-axial shear stiffness, the baffles can be
angled in the Y/Z plane as shown in FIG. 16. An intersecting
pattern of baffles can also be achieved e.g., by sewing, bonding or
welding the intersection points shown in FIG. 17. This allows for
smoother top and bottom surfaces (i.e., more closely spaced
baffles) and/or greater baffle angle .PHI..
[0095] In another variation, the baffles are made from fabric or
film tubes, e.g., as shown in FIG. 18. The tubes can be spaced
apart, or mated and joined together as in FIG. 19. If joined, the
bottom of the tubes can form the bottom wall of the beam, or to
reduce peel forces in the corners of the tubes, an additional
tensile film or fabric can be added to the bottom wall as in FIG.
20. The latter approach is advantageous in that the tubes need not
be airtight or as abrasion/puncture resistant. This allows the use
of thinner/lighter tubes to make the baffles. Note that in
accordance with the invention, the bottom surface assembly is
sufficiently thin and flexible to allow it to buckle and/or wrinkle
when the beam is deflated and rolled-up.
[0096] In accordance with the invention, the core of the beam can
also be made from open-cell foam, e.g., the airfoil of FIG. 21. The
foam is preferably made from a high-tensile strength, high-modulus
polymer having relatively large cells and thin connecting strands
or webs. The foam should be easily collapsible, but have high
tensile stiffness and strength when the beam is inflated. The foam
may be blown into a female mold in which the top and bottom walls,
front "sidewall" and/or structural sheet are held in place, e.g.,
by vacuum. Alternately, the foam can be cut or molded, and then
bonded to the structural sheet and bottom tensile film.
[0097] In another variation of the invention, the core is made from
randomly oriented fibers as shown in FIG. 22. This type of
construction can be achieved for example by bonding the top and
bottom walls to fibrous batting, as taught by U.S. Pat. No.
5,552,205 incorporate herein by this reference.
[0098] In another variation, the inflatable beam or panel is placed
inside a female mold and inflated while subjected to heating, e.g.,
by the introduction of hot air internally or externally.
Thermoplastic elements of the top and bottom walls, structural
sheet, sidewalls and/or core are allowed to stretch or creep as the
beam assumes the shape of the mold. This process allows for complex
curvature of the beam surfaces, avoids wrinkles, and is a cost
effective way to provide varying core thickness with high accuracy.
If the core includes random fibers or foam, stretching the core
will tend to orient the fibers or foam interconnections in the
Z-direction. This tends to improve the load capacity of the beam
since the structural sheet (or other compression element(s)) is
better stabilized against buckling.
[0099] In additional variations, the compression elements attached
to or integral with the top wall can include structural strips,
tape-springs, hinged strips, rods, bars, tubes or other elongate
structural elements. In accordance with the invention, the
compression elements can be rolled up without damage and without
disassembling them from the inflatable structure.
[0100] FIG. 23 shows a cross-sectional view of a beam with flat
strips 40' attached to the top surface. The flat strips are
preferably aligned in the direction of maximum compression
(typically the long direction -X) due to the principal bending
moment. Bending strength in this direction will be similar to that
of a sheet-reinforced beam (of similar local bending resistance).
Lateral bending strength will be lower since the gaps between
strips do not support compression in the Y direction. Candidate
materials for the strips are the same as for the structural sheet,
as described above.
[0101] FIG. 24 shows a cross-sectional view of a beam reinforced
with rods 40''. The rods are best stabilized against buckling if
they are attached at the intersection of baffles and the top
wall.
[0102] Curved strips 40''', FIG. 25 also known as "tape-springs",
are especially advantageous since they have high bending stiffness
when curved, but are easy to roll up as they flatten out. Combined
with a baffle-type beam construction, the inflation pressure helps
maintain the curvature and further stabilize the tape-springs
against buckling. In this case, coarser baffle spacing tends to
improve the strength of the beam since it increases the Z-height of
the tape springs. Preferred materials for making the tape springs
are the same as for the structural sheet described above.
[0103] In many applications it will be desirable for the top and/or
bottom surfaces to be smooth. This is especially important for
airfoils where the accuracy of the surfaces has a major effect on
the lift/drag ratio. For flat beams, such as that shown in FIG. 26,
smooth surfaces can be achieved using a skin 60 to bridge between
the convex ridges. In this case, the skin(s) can be thin, flexible
membranes. The voids between the skins and the rest of the beam
assembly are preferably held at or near the ambient pressure and/or
filled with open-cell foam.
[0104] For airfoil applications, flat spots between the convex
ridges may reduce lift or add drag. Possible solutions are to fill
the voids with open-cell foam in a molding operation, or use skins
with bending resistance in the lateral direction. To allow the beam
to be rolled up, the skins can be made of a directional material
such as FRP with most of the fibers oriented close to the
Y-direction. This is especially important for the bottom skin
since, in accordance with the invention it must compress and/or
buckle as the beam is rolled up.
[0105] When rolled, the top skin will experience tension in the
X-direction. For ease of rolling, it should be allowed to stretch
in this direction, but to smooth between the convex ridges, lateral
bending stiffness is desirable. As with the bottom skin, orienting
the fibers close to the Y-direction is one way to achieve the
desired effect. Use of a top-skin with bi-axial stiffness (e.g.,
G10, polymer or metal sheet, etc) is also possible, but will
increase the bending resistance and/or require thinner tape
springs.
[0106] Another way to provide high compression strength but
preserve the ability to be rolled-up, is to use hinged strips
40.sup.iv as shown in FIG. 27. Each hinged strip includes a top
leaf 70 attached to the top wall 12 of the beam, a side leaf 72
attached to a baffle, and a hinge. The hinge can be a pinned hinge
(e.g., piano hinge), a thinned part (e.g., flexure or "plastic
hinge"), or can be achieved by bonding the hinge to a flexible
element such as thin metal, Nitinol superelastic material, polymer,
elastomer, or fabric. The hinge can also be achieved by having the
material (e.g., fabric or film) of the top wall and baffles act as
the hinge.
[0107] When inflated, the leaves of the hinge form an L shape which
provides a high moment of inertia. When deflated, the hinged strips
lay flat and can be rolled-up. For easiest rolling, the width of
each pair of hinged strips is less than width between baffles. This
allows the strips to all lie in-plane, and avoids a build-up of
horizontal shear.
[0108] FIG. 28 presents an embodiment of the invention wherein
narrow compression elements 40.sup.v (e.g., rods, strips, etc) are
attached to the top and bottom walls, thus providing bi-directional
bending strength. When deflated, the compression elements are
allowed to lie in-plane for easy rolling. The "compression
elements" in fact provide tensile strength and stiffness (as well
as compressive) depending on the direction of the bending load.
This reduces the need for high tensile stiffness in the film or
fabric of the top and bottom walls, and can result in higher beam
stiffness and lower overall weight.
[0109] To clarify the terminology used in this specification, the
primary function of the "top wall" and "bottom wall" is to resist
the Z-axis inflation force, and transfer this force to the baffles,
threads or other core material. The two walls may or may not have
an airtight coating, since internal bladders can also be used. The
two walls also may or may not provide the primary tensile elements
resisting bending of the beam, since this function can be provided
by adding tensile elements (such as braided high-modulus cord) or
"compression elements" such as rods.
[0110] In this specification, when compression elements or tension
elements are said to be "attached" to the top or bottom wall, this
includes the case where the compression or tension elements are
attached to the baffles, threads or other shear-resistant core
material in close proximity to the top or bottom walls. For
example, the rods of FIG. 28 can be "attached" to the top and
bottom walls, by bonding them to baffles near the connection of the
baffles and the top or bottom wall.
[0111] In one embodiment, compression elements are shear-locked to
one or both of the top and bottom walls core, or sidewalls of the
inflatable structure by friction, using pressure or vacuum to
supply the normal force. In the deflated state, one or more of the
compression elements are allowed to slide, which allows the beam to
be rolled-up much more easily. The compression elements can also be
made of multiple thin layers. When clamped together by pressure
forces, the compression elements have effectively greater
thickness. This increases the local bending resistance and results
in greater beam strength and greater tolerance of contact forces
(i.e., local Z-axis pressure by a surfer's foot).
[0112] An example of this embodiment is shown in FIG. 29. In this
case, the top wall is reinforced by two structural sheets 40a and
40b which are "attached" to the top wall by pulling a vacuum on the
vacuum port. The two sheets are constrained in a vacuum pocket 80
by sleeve material 82. When the vacuum is applied, the sleeve
material 82 collapses on the sheets 40a and 40b and applies a
normal force up to atmospheric pressure (e.g. 14.7 psi). Friction
clamps the two sheets together and clamps the inner sheet to the
"top wall" of the beam.
[0113] The vacuum pressure required to prevent slippage between the
inner compression element and the top surface is given by the
following equation (where V is the vertical shear force, W is the
beam width, T is the thickness and f is the friction
coefficient):
P = V W T f ( 4 ) ##EQU00004##
[0114] In the surfing example, the vertical shear is half the
rider's weight (.about.100 lb), and the beam dimensions (W.times.T)
were 20''.times.3''. Assuming a friction coefficient of 0.5, the
required vacuum pressure is 3.3 psi. For greater load capacity or
safety factor, the vacuum can be increased and/or the friction
coefficient can be enhanced, e.g., using coatings, films,
particles, surface texture, or mating features such as bumps and
pockets or ridges engaging troughs.
[0115] Multi-layer compression elements are advantageous since
bending stiffness (when shear-locked) scales with thickness cubed,
but when shear is allowed (i.e., when rolling-up the beam), the
bending stiffness scales linearly with thickness (i.e., the number
of layers). For a given stowed diameter and bending moment (i.e.,
resistance to rolling), the multi-layer type of compression element
will provide greater local bending stiffness, greater resistance to
buckling, higher beam load capacity and greater tolerance of
contact forces.
[0116] FIG. 30 shows another variation of this embodiment which
avoids the need for a sleeve. Instead, outer sheet 40b is sealed to
the top wall 12 or sidewalls of the beam by an edge seal around the
perimeter of the sheet. One or more inner sheets 40a are allowed to
"float" inside the vacuum pocket 80, but when vacuum is applied to
the vacuum port, the sheets are all clamped to each other and to
the top wall of the beam.
[0117] To make sure the vacuum pocket gets fully evacuated, the
surfaces of the sheets can be textured or roughened or additional
porous "breather" material can be used between the layers and/or
around the perimeter of the sheet(s). The breather material
preferably should have should have high shear stiffness and a high
coefficient of friction.
[0118] In another variation of this embodiment, the beam inflation
pressure is used to preload the compression elements against the
bottom and/or top walls. In FIG. 31, the compression elements are
tape springs 40'''. As shown, the top tape springs are bonded to
the top wall, but those on the bottom are constrained in sleeves
96. The beam is inflated using inflation bladders, and the
inflation force presses the bottom tape springs against the bottom
wall. As in the previous example, shear is inhibited by
friction.
[0119] As shown, the sleeve material is needed primarily to keep
the bottom tape springs in place when the beam is deflated and
rolled up. For best results, the sleeve should have excess lateral
(Y-direction) slack so that the full pressure force is applied to
the bottom tape springs, and the bottom wall bears the Y-axis
tension resulting from the inflation pressure. The sleeves can also
be formed by using a series of threads or bands to hold the
compression elements in position.
[0120] As shown, the sleeve material, baffles, and top and bottom
walls are preferably air-permeable, however, it is also possible to
avoid the need for the inflation bladders if the sleeve material
and top, bottom and side walls are impermeable.
[0121] In another variation, both the sleeve material and the
bottom wall are impermeable, and the sleeve pockets are plumbed to
a port. If the port is blocked during inflation of the beam, the
air trapped in the sleeve pockets will prevent shear-locking of the
bottom tape springs. Once full pressure is reached, the port can be
vented to the atmosphere (e.g., by opening a valve). The air
trapped in the sleeves will be driven out and the tape springs with
be shear-locked. This procedure can result in a more accurate final
shape of the beam than if shear-locking occurs during partial
inflation. A passive version of this process is also possible if
the sleeve and/or bottom wall are very slightly permeable. During
inflation the air in the sleeves will take some time to leak out,
thus delaying the clamping and shear-locking of the bottom tape
springs. This variation does not require a port or valve.
[0122] As shown in FIG. 32, the principle of using internal
pressure and friction to cause shear-locking can also be applied to
multi-layer compression elements, in this case tape springs. This
example also avoids the use of bladders by using impermeable
material for the sleeves and sidewalls.
[0123] In both FIGS. 31 and 32, the topmost tape spring was bonded
to the top surface. This is beneficial to avoid wrinkles in the top
wall as the beam is inflated, but wrinkles can also be avoided by
delaying the expulsion of air from the sleeves. In accordance with
the invention, is it also acceptable for the topmost tape spring,
or other compression element to be slidingly accepted by the
sleeve.
[0124] The above examples are not to be considered limiting. The
tape springs or sheet may be replaced by any other rollable
compression element such as rods, strips, bars, etc. The
compression elements may be single layer or multi-layer and may be
disposed on the top wall or bottom wall of the beam, and any
combination of pressure or vacuum may be used to clamp and
shear-lock the compression elements to the top and bottom walls or
to the baffles.
[0125] In one embodiment, the compression elements are pre-stressed
so as to make the beam roll-up automatically or with reduced effort
when the beam is deflated. The pre-stress can be imparted either
prior to after attaching to the air-beam structure. If the
compression elements are sufficiently ductile (e.g., metal)
pre-stress can be achieved by rolling the material or the final
assembly through a sheet metal roll, or wrapping it around a
mandrel that is significantly smaller than the desired stowed
diameter. If the compression elements are made of FRP, pre-stress
can be achieved, for example by wrapping on a mandrel prior to
final curing (e.g., using time, elevated temperature or UV). FRP
can also be wrapped on a mandrel and stress-relieved, by raising
the temperature above the stress-deflection temperature. This is
most effective if the polymer is a thermoplastic.
[0126] For best results, the tendency of the compression elements
to roll-up, i.e., the bending moment, should be greatest at the end
of the beam farthest from the inflation port. This will tend to
cause the beam to roll-up more neatly. The rolled-up beam can be
further compacted by twisting the inside of the roll while holding
the outside. When inflated, the beam will un-roll like a party
favor.
[0127] Although specific features of the invention are shown in
some drawings and not in others, this is for convenience only as
each feature may be combined with any or all of the other features
in accordance with the invention. The words "including",
"comprising", "having", and "with" as used herein are to be
interpreted broadly and comprehensively and are not limited to any
physical interconnection. Moreover, any embodiments disclosed in
the subject application are not to be taken as the only possible
embodiments. Other embodiments will occur to those skilled in the
art and are within the following claims.
[0128] In addition, any amendment presented during the prosecution
of the patent application for this patent is not a disclaimer of
any claim element presented in the application as filed: those
skilled in the art cannot reasonably be expected to draft a claim
that would literally encompass all possible equivalents, many
equivalents will be unforeseeable at the time of the amendment and
are beyond a fair interpretation of what is to be surrendered (if
anything), the rationale underlying the amendment may bear no more
than a tangential relation to many equivalents, and/or there are
many other reasons the applicant can not be expected to describe
certain insubstantial substitutes for any claim element
amended.
* * * * *