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Description  |
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The present invention relates to inflatable structures. By inflatable
structures is meant an assembly of parts, of which at least some are
inflatable, joined one to another in such a fashion that the assembly
assumes a specific rigid form after inflation of the inflatable parts.
Inflatable structures in the sense of the foregoing definition have been
known for a long time. Thus, U.S. Pat. No. 511,472 dating from 1893
describes such structures; since then many improved inflatable structures
have been proposed and described, but, in fact, none has enjoyed the
success anticipated. This is attributable to the fact that, up to now, all
have suffered from the same major drawback of lack of rigidity.
FIGS. 1, 2 and 3 show in schematic sectional representation the inflatable
structures known at the moment.
One kind of known inflatable structure was made up of an assembly of
inflatable cells coupled together.
Another type of structure was formed of two layers of woven material linked
together by partition walls, also of woven material, which thus defined
chambers into which were inserted inflatable bladders which were not fixed
to the said layers of woven material and whose purpose was simply to
maintain these latter in spaced relationship.
Another form of prior art structure was made up of two layers of a
flexible, gas-tight, woven material or sheet, linked together by partition
walls also of a gas-tight material so as to define chambers which were
subsequently inflated.
In all the above described prior art structures, the same principle was
employed, namely to use the pressure of the inflating medium simply to
hold two walls apart.
All these structures lack rigidity; in order that they may retain their
shape, braces or rigid attachment members had to be used, or certain
portions had to be inflated with a lighter-than-air gas such as helium. In
this connection, U.S. Pat. No. 511,472 shows structures in which the means
used do not allow the desired rigidity to be achieved. It can thus be said
that, since 1893 at least, efforts have been made to produce inflatable
structures which should be extremely rigid after inflation, but, up to
now, no simple expedient has been found which enables this rigidity to be
conferred on them.
One object of the invention is an inflatable structure whose rigidity,
after inflation of the inflatable parts, may be of any desired magnitude.
Another object of the invention is an inflatable structure which does not
exert on its supports any strains other than those due to its weight. A
further object of the invention is an inflatable structure which may be
made in a large variety of sizes.
Yet another object of the invention is an inflatable structure which may be
used to form shelters or parts of shelters, which may or may not be
collapsible, or to form objects intended to carry loads, such as bridges
and, in a general way, inflatable constructions and articles of many
different kinds.
Inflatable structures according to the invention comprise two rectilinear
flexible sheets, separated one from the other, and inflatable enclosures
situated in the space separating the two sheets, the said inflatable
enclosures being fixed to each sheet and being joined together so that, on
inflation, they mutually support one another and apply tension to the
members forming the two sheets.
The inflatable enclosures are enclosures formed from a flexible sheet or
woven material, impervious to the inflating medium. As will be seen below,
enclosures can be used which are cellular in nature and may be rectilinear
or curvilinear: their section may be constant or vary along their length.
Enclosures may also be used which are spheres or cylinders with spherical
dome-like ends.
The rectilinear members forming the sheets between which the enclosures are
positioned and to which they are fixed must have sufficient mechanical
strength to bear the strain imposed by the inflation of the enclosures.
This may be incorporated by a layer or strip of woven material or by wires
or cords.
The attachment of the rectilinear members forming the two sheets to the
enclosures may be effected by conventional means not per se forming part
of the invention, for example by bonding.
In order that the invention may be more clearly understood, reference will
now be made to the accompanying drawings which, firstly, show some
examples of prior art structures and then certain embodiments of the
invention by way of example, and in which:
FIGS. 1, 2 and 3 show schematically sections through various prior art
inflatable structures,
FIG. 4 shows schematically a cross-section through a part of a first
embodiment of inflatable structure according to the invention,
FIG. 5 shows schematically a cross-section through part of another
embodiment of structure;
FIG. 6 shows schematically a cross-section through a third embodiment of
structure,
FIG. 7 shows a cross-section of the structure of FIG. 6 during erection,
FIG. 8 shows schematically a cross-section of another structure according
to the invention, used as the collapsible part of a shelter,
FIG. 9 shows a section of the structure of FIG. 8 in a partly open state,
FIG. 10 shows a perspective view of a structure of the invention,
FIG. 11 shows a perspective view of another embodiment of structure
according to the invention,
FIG. 12 shows a view from above of another embodiment,
FIG. 13 shows a cross-section of the structure of FIG. 12 along the line
XIII--XIII thereof,
FIG. 14 shows a view from above of another embodiment,
FIG. 15 shows a view from above of another embodiment, and
FIG. 16 shows a view from above of a part of a further embodiment of the
invention.
Referring now to the drawings, FIG. 1 shows a first example of an
inflatable structure of the prior art, which comprises a plurality of
inflatable cells 1 that are coupled together.
FIG. 2 shows another example of a prior art construction which is formed of
two layers 2 and 3 of a woven material which are linked together by
partition walls 4 which also are of woven material, and these walls thus
define chambers 5 serving as location means for inflatable bladders 6
inserted therein. These bladders 6 are not fixed to the layers 2 and 3 and
their purpose is simply to maintain the layers 2 and 3 in spaced
relationship.
FIGS. 4 and 5 show a flat, inflatable structure; it may, for example, be
used as a cover by being placed on the exterior walls of a building.
This structure is made up as shown of rectilinear, inflatable cells, 10a,
10b, 10c . . . which are attached to the sheet 11 at A.sub.1, B.sub.1,
C.sub.1 and to sheet 12 at A.sub.2, B.sub.2, C.sub.2.
In this embodiment, the inflatable cells are made of a gas-tight rubberised
material and sheets 11 and 12 are of a woven material of which the warp
runs perpendicularly to the axis of the cells. Instead of being made up of
a woven material, the sheets 11 and 12 could also be formed by cables,
mutually parallel and perpendicular to the axis of the cells; in this
case, a light and water-proof sheet, made, for example, of a plastics
material, could be attached to the upper sheet 11 for water-proofing
purposes.
Sheets 11 and 12 are attached to the cells 10 by bonding but they could
also be attached by some other conventional means, not forming part of the
invention. Since the structure is flat, the lengths d' at A' B', B' C', C'
. . . and the lengths d.sub.2 at A.sub.2 B.sub.2, B.sub.2 C.sub.2, C.sub.2
. . . are all of equal size.
The circumference of the cell walls is sufficiently great, taking into
account the size of lengths d.sub.1 or d.sub.2 that, after inflation,
cells 10 bear on and support one another. (This condition is fulfilled as
soon as the circumference of the boundary walls exceeds the value .mu. x
d.sub.1). The cells are inflated to the same or to a very similar pressure
so that their meeting faces, which are formed by lines a.sub.1 a.sub.2,
b.sub.1 b.sub.2, c.sub.1 c.sub.2, of FIG. 4 are plane.
When they are deflated, cells 10 are collapsed and the sheets 11 and 12, no
longer being under tension, are in close proximity. When the cells are
inflated, sheets 11 and 12 move apart and each cell 10, taking a purchase
on the adjoining cell, places the portion of the sheet situated between
the attachment of the cell to the sheet and the attachment of the
adjoining cell to the sheet, under tension.
Thus, successive portions A.sub.1 B.sub.1, B.sub.1 C.sub.1, C.sub.1 . . .
A.sub.2 B.sub.2, B.sub.2 C.sub.2, C.sub.2 . . . of the two sheets 11, 12,
mutually separated by cells 10, are all placed under tension.
The inflatable structures according to the invention, by reason of having
two sheets under tension, separated from each other, are extremely rigid
and little subject to deformation as a result of external stresses such as
those due to gravity or the action of the wind. This rigidity increases as
sheets 11 and 12 are more strongly tensioned. The tension of the sheets
varies both as a function of the pressure inside the cells and of the
length of the portions a.sub.1 a.sub.2, b.sub.1 b.sub.2, c.sub.1 c.sub.2 .
. . it may thus be set to the desired amount by varying the pressure
inside the cells by giving to the cells a circumference such that the
length of said portions is greater or smaller.
The tension of each section of sheet, such as A.sub.1 B.sub.1 or A.sub.2
B.sub.2 being in each transverse section exactly balanced, cells 10 can be
as long as desired which means that the range of sizes of the inflatable
structures in the invention is theoretically unlimited.
Not only are the inflatable structures self-stabilising (i.e. they do not
distort of themselves in the absence of external stresses), once inflation
is completed, but also, during inflation, the parts already inflated are
themselves self-stabilising (and similarly during deflation). This has the
result that, to erect or collapse the structures, it is not necessary to
use additional means to support or guide them and that, with advantage,
they may be used to produce constructions which are wholly or partly
collapsible. This self-stabilising property has the additional result that
any bases or foundations used, which have only to bear the strains due to
the weight of the structures, which are extremely light, are of minor
importance.
The structure shown in FIG. 6 is formed similarly to those in FIGS. 4 and 5
but lengths d.sub.1 and d.sub.2, instead of being equal, are different,
which gives the structure a curvilinear shape. The lines a.sub.1 a.sub.2,
b.sub.1 b.sub.2, c.sub.1 c.sub.2, shown in FIGS. 4 and 5 are decreased to
zero in the arrangement of FIG. 6 meeting at a point which is the centre
of the circle of curvature of which the radius depends both on the ratio
d.sub.1 /d.sub.2 and on the distance separating the two sheets 11 and 12
which itself depends on the circumference of the inflatable cells.
FIG. 6 shows in fact a cross-section through a shelter such as a shed,
having the shape of a segment of a cylinder.
This shelter is formed by an inflatable structure similar to that in FIG.
5; cells 10 place the portions of the sheets 11 and 12 extending between
two adjoining cells under tension; lengths d.sub.1 and d.sub.2 are
unequal.
This construction may be of very large dimensions and, on account of its
small weight and of the absence of stresses not vertical to the ground, it
may be erected on surfaces of loose consistency without the need for
considerable foundation work.
FIG. 7 shows the ease of erection of such a construction, which is, and
remains, self-stabilising during inflation of the cells. The central cells
are inflated first; due to this inflation, the central portion of the
structure takes up the curve described by a radius R equal to that in the
construction in FIG. 6 and the central portion, inflated, being
self-stabilising, there is no need to use additional means of support or
guidance; the process is continued by inflating the cells immediately
adjacent to the portion already inflated and so on; when the two end cells
are inflated, the whole of the structure has been formed and is ready for
use. From this example, it can be seen that the erection of structures
according to the invention is extremely simple. Similarly, to collapse
such a structure, it is merely necessary to deflate the end cell then the
immediately adjacent cells and so on.
The inflatable structure in FIGS. 8 and 9 constitute the collapsible
portion of a shelter.
Cells 10 form an arc and their cross-section decreases from the centre
towards the ends; in addition, the distances d.sub.1 and d.sub.2 between
the attachments of two adjacent cells to the sheets 11 and 12 are unequal
as in the case of FIG. 6; thus, a dome-shaped structure is obtained.
In the embodiment, this inflatable dome rests on another part 13 of the
shelter; this part 13 is built of masonry and includes a projecting
portion 13a against the face 13b of which the inflatable dome bears.
The inflatable dome may be totally or partially collapsed by deflating the
lower cells as at 10a in FIG. 9 which Figure shows the shelter of FIG. 8
with the dome partially collapsed.
When the lower cells 10a are deflated, the corresponding portions of the
dome weaken and fold up and the upper cell 10b moves away from part 13a;
each cell, still inflated, moves around an axis passing through the centre
0 of the circle of curvature each time one of the lower cells is deflated,
which brings about the opening of the dome. As has been explained above,
the portion of the dome still inflated is self-stabilising which allows
the dome to be left partially open, if desired.
In the structure in FIG. 10, which is a segment of cylinder, the cells are
straight-sided and arranged parallel to the axis of the cylinder, i.e.,
parallel to the faces on which it rests. Here the curvature results from
the fact that the distances between the attachments of two adjacent cells
to the upper and lower sheet (i.e. portions d.sub.1 and d.sub.2 of FIG. 4)
are unequal.
The structure in FIG. 11 has the same shape as that of FIG. 10 but the
arch-shaped cells are perpendicular to the axis of the cylinder. Here the
equivalent to distances d.sub.1 and d.sub.2 are equal, the curvature of
the structure resulting from the shape of the cells.
In the inflatable structures described up to this point, the enclosures are
formed by laterally flattened tubular cells, i.e. cylindrical formations.
However, as referred to above, the enclosures may also be spheres or
cylinders whose ends terminate in spherical domes; inflatable enclosures
of this latter kind will hereinafter be called "spherical
enclosures.revreaction. or "inflatable spherical enclosures".
The application of the invention to the use of inflatable spherical
enclosures, will be explained by FIGS. 12, 13 in the case of inflatable
structures assumed to comprise only seven inflatable enclosures.
In the case of FIGS. 12 and 13 the inflatable enclosures are spheres linked
together. Two adjacent spheres are attached to two straight and flexible
members 14 and 16, situated diametrically oppositely of the spheres,
tangential to one another and parallel to the plane of the centres of the
spheres. There are thus twelve flexible members 14 and twelve flexible
members 16, each of these members being attached to two adjacent spheres;
the attachment points of the flexible members 14 and 16 to the spheres
carry respectively references A'.sub.1, B'.sub.1, C'.sub.1 . . . A'.sub.2,
B'.sub.2, C'.sub.2 . . . if the structure is to be flat, the lengths
A'.sub.1 B'.sub.1, B'.sub.1 C'.sub.1, C'.sub.1 A'.sub.1 . . . are equal to
lengths A'.sub.2 B'.sub.2, B'.sub.2 C'.sub.2, C'.sub.2 A'.sub.2 . . . and,
so that, after inflation, the spheres may press against one another, the
flexible members 14 and 16 are of a length at least slightly smaller than
the radius of the spheres.
As above where the inflatable enclosures were laterally flattened tubes,
after inflation, the spheres press against one another and tense members
14 and 16.
If the structure is to take up a curve, lengths such as A'.sub.1 B'.sub.1
and A'.sub.2 B'.sub.2 are unequal, the shorter ones being placed, with
regard to the spheres, on the same side as the centre of curvature, as in
the case where the inflatable enclosures are laterally flattened tubes.
After inflation of the spheres, the members 14 and 16 form two layers, each
of which is a trellis or a mesh configuration, the members of which are
under tension.
Members 14 and 16 may be formed by an assembly of parallel wires or cords;
they may also be made up by strips either of woven material or of a
material having sufficient mechanical strength.
In most cases, it is necessary to render the structures impervious, for
example to rain; it is then sufficient to attach to members 14 or 16 a
continuous, impervious sheet.
Finally, instead of attaching members in the form of strips to the spheres,
a sheet or a woven material having no discontinuities, may be attached
thereto, provided that it possesses sufficient mechanical strength in the
direction in which it will be under tension due to the effect of the
inflation of the spheres.
Instead of spheres, inflated enclosures in the form of a cylinder, the ends
of which are formed by spherical domes, may be used; these enclosures,
which behave in all respects as spheres, are easier to construct than
spheres when the distance separating members 14 and 16 is relatively
large, for example more than 50 cm.
FIG. 12 shows the mesh of a trellis, the members of which meet at an angle
of 60.degree..
FIG. 14 shows another possible method of laying out the spheres; in this
case sphere centres are placed at the corners of squares, which brings
about the formation of a trellis, the members of which meet at an angle
90.degree..
They may also be laid out in the manner shown in FIGS. 15, 16 or in any
other way provided that the members 14 and 16 form a mesh pattern, which
meshes need not be identical to one another.
FIGS. 12 to 16 show the possible variations of trellis pattern which can be
produced; to form structures extending over a greater area, it is merely
necessary to join up several patterns, identical or different, by laying
out the spheres in the appropriate positions.
If a member 14 (or 16) is not in alignment with two other adjacent members
14 (or l6), due to the trellis pattern selected, or because the spheres
are those on the edge of the structure, the tensions in members 14 (or 16)
are not balanced by any other tension. To avoid this, which may be a
drawback, it is possible, as shown in FIG. 13, to link members 14 and 16,
lying one above the other, by a member 15 lying in the plane of members 14
and 16 and surrounding the hemisphere which, in relation to members 14 and
16, points outwards; this member 15 may be identical to members 14 or 16.
By using spherical enclosures, inflatable structures according to the
invention may be produced having the shape of a dome or exhibiting
multiple and various curvatures, more easily than by using laterally
flattened tubes; in fact, it is sufficient to vary the length of members
14 and 16 if spherical enclosures are being used, while arch-shaped cells
must be made if it is desired to produce structures, which like the domes,
are not in the form of a segment of a cylinder or a succession of segments
of cylinder.
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