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Claims  |
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What is claimed is:
1. An adjustable truss structure comprising:
(a) a plurality of truss elements; and
(b) hinges pivotally connecting at least three successive truss elements,
wherein not all hinges are parallel;
wherein at least one said hinge has a means for adjusting the angle between
its associated truss elements.
2. The adjustable truss structure of claim 1, wherein said hinges are in N
sets, every Nth hinge being in the same set, and all hinges in a set being
substantially parallel when the longitudinal axis of the truss structure
is a straight line.
3. The adjustable truss structure of claim 1, wherein successive hinges are
substantially orthogonal.
4. The adjustable truss structure of claim 1 wherein the truss elements are
tetrahedra.
5. The adjustable truss structure of claim 1 wherein the truss elements are
comprised of struts joined at their ends, forming a framework.
6. The adjustable truss structure of claim 1 wherein the truss elements are
comprised of solid plates joined at their edges, forming a solid-faced
body.
7. The adjustable truss structure of claim 1, wherein the truss elements
are arranged in a closed loop configuration.
8. The adjustable truss structure of claim 2, further comprising:
(a) clamping means affixed to the end of each hinge; and
(b) a pair of structural members bearing tensile loads associated with each
set of said hinges, wherein said clamping means releasably clamps said
members at intermediate points along said members.
9. The adjustable truss structure of claim 2, wherein at least one hinge
has an adjustment assembly for adjusting the angle between its associated
truss elements, and further comprising actuating means associated with
each adjustment assembly.
10. The adjustable truss structure of claim 9, wherein said adjustment
assembly comprises a mechanical linkage.
11. The adjustable truss structure of claim 9 wherein the adjustment
assembly is removable from the truss.
12. The adjustable truss structure of claim 2, wherein one end of every
hinge in one set of hinges is releasably connected to its associated truss
elements, such that the shape of the truss elements can be deformed,
allowing the truss to be compressed.
13. An adjustable truss structure comprising:
(a) a plurality of tetrahedral truss elements;
(b) two sets of hinges pivotally connecting at least two pairs of adjacent
truss elements;
(c) a pair of tension cables associated with each set of hinges;
(d) cable clamping means affixed to at least one end of each hinge, wherein
said clamping means releasably clamps said cables at intermediate points
along said cables;
(e) at least one hinge having an associated mechanical linkage for
adjusting the angle between the truss elements associated with said hinge,
said mechanical linkage being removable from the truss; and
(f) actuating means associated with each mechanical linkage.
14. A method of constructing an adjustable truss structure, comprising the
steps of:
(a) arranging a plurality of truss elements on a surface;
(b) pivotally connecting truss elements such that at least two pairs of
adjacent truss elements are connected by hinges and not all hinges are
parallel;
(c) connecting tension cables to the ends of a plurality of said hinges;
(d) selecting a hinge to be adjusted;
(e) applying a force to at least one of the associated truss elements on
either side of said selected hinge, to adjust the hinge angle defined by
the relative positions of said associated truss elements;
(f) clamping the tension cables to maintain the hinge angle selected in
step (e); and
(g) repeating the steps (d)-(f) for other hinges as necessary.
15. A method of constructing an adjustable truss structure, comprising the
steps of:
(a) arranging a plurality of truss elements on a surface;
(b) pivotally connecting truss elements such that at least two pairs of
adjacent truss elements are connected by hinges and not all hinges are
parallel;
(c) connecting tension cables to the ends of a plurality of said hinges;
(d) applying tensile forces to selected tension cables such that truss
elements lift off the surface into an erected form; and
(e) clamping the tension cables to maintain the hinge angles achieved in
step (d).
16. A method of constructing an adjustable truss structure, comprising the
steps of:
(a) arranging a plurality of truss elements on a surface;
(b) pivotally connecting truss elements such that at least two pairs of
adjacent truss elements are connected by hinges and not all hinges are
parallel;
(c) connecting tension cables to the ends of a plurality of said hinges;
(d) applying tensile forces to selected tension cables such that truss
elements lift off the surface into an erected form;
(e) selecting a hinge to be adjusted;
(f) applying a force to at least one of the associated truss elements on
either side of said selected hinge, to adjust the hinge angle defined by
the relative positions of said associated truss elements;
(g) clamping the tension cables to maintain the hinge angle selected in
step (f); and
(h) repeating the steps (e)-(g) for other hinges as necessary.
17. A method of constructing an adjustable truss structure, comprising the
steps of:
(a) arranging a plurality of truss elements on a surface;
(b) pivotally connecting truss elements such that at least two pairs of
adjacent truss elements are connected by hinges, wherein the relative
position of said adjacent truss elements define the hinge angle of the
hinges connecting them, and not all hinges are parallel;
(c) connecting tension cables to the ends of a plurality of said hinges;
(d) applying tensile forces to selected tension cables such that truss
elements lift off the surface into an erected form, and while applying
said tensile forces, controlling the amount of said tensile forces applied
to at least one of said hinges, so as to control the adjustment of the
hinge angle of said at least one of said hinges; and
(e) clamping the tension cables to maintain the hinge angles achieved in
step (d).
18. The method of constructing an adjustable truss structure of claim 17,
wherein the amount of said tensile forces applied to at least one of said
hinges is controlled by at least one mechanical linkage.
19. A method of constructing an adjustable truss structure, comprising the
steps of:
(a) arranging a plurality of truss elements on a surface;
(b) pivotally connecting truss elements such that at least two pairs of
adjacent truss elements are connected by hinges and not all hinges are
parallel, and such that a closed loop of truss elements is formed;
(c) adjusting the hinge angles defined by the relative positions of truss
elements in a first portion of the closed loop of truss elements, to
permit said first portion to conform to the shape of the surface; and
(d) adjusting the hinge angles defined by the relative positions of truss
elements in a second portion of the closed loop of truss elements.
20. The method of constructing an adjustable truss structure of claim 19
further comprising the step of connecting tension cables to the ends of a
plurality of said hinges, and wherein the step of adjusting said second
portion of the closed loop of truss elements comprises:
(a) selecting a hinge to be adjusted;
(b) applying a force to at least one of the associated truss elements on
either side of said selected hinge, to adjust the hinge angle defined by
the relative positions of said associated truss elements;
(c) clamping the tension cables to maintain the hinge angle selected in
step (b); and
(d) repeating the steps (a)-(c) for other hinges as necessary.
21. The method of constructing an adjustable truss structure of claim 19
further comprising the step of connecting tension cables to the ends of a
plurality of said hinges, and wherein the step of adjusting said second
portion of the closed loop of truss elements comprises:
(a) applying tensile forces in the portion of the tension cables associated
with said second portion of the closed loop, such that said second portion
lifts off the surface into an erected form; and
(b) clamping the tension cables to maintain the hinge angles achieved in
step (a).
22. The method of constructing an adjustable truss structure of claim 19
further comprising the step of connecting tension cables to the ends of a
plurality of said hinges, and wherein the step of adjusting said second
portion of the closed loop of truss elements comprises:
(a) applying tensile forces in the portion of the tension cables associated
with said second portion of the closed loop, such that said second portion
lifts off the surface into an erected form;
(b) selecting a hinge to be adjusted;
(c) applying a force to at least one of the associated truss elements on
either side of said selected hinge, to adjust the hinge angle defined by
the relative positions of said associated truss elements;
(d) clamping the tension cables to maintain the hinge angle selected in
step (c); and
(e) repeating the steps (b)-(d) for other hinges as necessary.
23. The method of constructing an adjustable truss structure of claim 19
further comprising the step of connecting tension cables to the ends of a
plurality of said hinges, and wherein the step of adjusting said second
portion of the closed loop of truss elements comprises:
(a) applying tensile forces in the portion of the tension cables associated
with said second portion of the closed loop, such that said second portion
lifts off the surface into an erected form, and while applying said
tensile forces, controlling the amount of said tensile forces applied to
at least one of said hinges, so as to control the adjustment the hinge
angle of said at least one of said hinges; and
(e) clamping the tension cables to maintain the hinge angles achieved in
step (d).
24. The method of constructing an adjustable truss structure of claim 23,
wherein the amount of said tensile forces applied to at least one of said
hinges is controlled by at least one mechanical linkage. |
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Claims |
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Description |
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TECHNICAL FIELD
The present invention relates generally to structural frameworks and more
particularly to adjustable truss structures.
BACKGROUND ART
It is well-known to build rigid three-dimensional truss structures (in the
form of truss beams or planar truss arrays) out of tetrahedral elements
which are joined at their common faces. Such truss structures are used in
the construction of both temporary and permanent building structures, in
display frames, exhibition and exposition environments, and space
structures.
It is useful to be able to adjust the shape of a truss structure. This
permits easy transportation of the structure in a folded state, simplifies
erection on-site, and provides the ability to adjust the shape of the
structure after it is erected. Some work in this area is concentrated in
developing folding and adjustable truss structures for space applications,
which require that the structures be able to fold into a small volume for
transportation.
It is known to permit the adjustment of the shape of a truss structure by
using telescoping members as part of the load-bearing structure of the
truss. For example, U.S. Pat. No. 5,125,206 to Motohashi et al. describes
a cubical truss element having a frame of fixed-length rods and
telescoping diagonal bracing rods. By extending and retracting the
diagonal bracing rods, the cubical truss element can be deformed into a
parallelepiped. When a plurality of cubical elements are coupled to form a
truss structure, deformation of multiple cubical elements can effect a
change in the overall shape of the structure.
Another example of a structure using telescoping members is shown in U.S.
Pat. No. 4,655,022 to Natori, which shows a tetrahedral truss element
which is deformable in shape. Some of the rods forming the edges of the
tetrahedral unit are foldable by means of a joint, and some of the other
rods are telescopic. By extending or contracting the telescopic rods, and
folding the foldable rods, the shape of the individual tetrahedral
elements can be adjusted. A plurality of such tetrahedral elements are
coupled at their common planes to form an adjustable truss beam. By
adjusting a plurality of the tetrahedral units, the shape of the overall
truss beam can be adjusted.
Trusses of this type use rigid telescoping struts (typically
electro-mechanical actuators) to effect the shape adjustment. A
disadvantage of this approach is that the telescoping elements perform a
structural function as well as a shape-adjustment function, and are
therefore directly subject to all the static and dynamic loads borne by
the truss structure. By subjecting the actuators to tensile and
compressive loads, there is a risk of loss of position accuracy if the
actuators were to "slip" in response to the loads. Alternatively, it may
be required to keep the actuators continuously powered in order to
counteract structural loads. By subjecting the actuators to bending
moments, there is a risk of loss of structural integrity, as actuators
typically are not as resistant to bending moments as are simple
fixed-length struts. In order to withstand expected structural load
conditions, it will be necessary to use a much sturdier actuator than
would be required simply to perform the shape adjustment of the truss.
This over-specification will result in a heavier structure and will be
more expensive than if the actuators were only required to perform the
shape-adjusting function. Therefore, it is desirable to design an
adjustable truss structure in which the shape-adjusting members do not
bear structural loads.
Another disadvantage to placing the shape-adjusting members directly in the
truss itself is that such configuration does not take advantage of the
principles of mechanical advantage; the actuating means in known truss
structures must directly create the full amount of force required to
adjust the shape of the truss. It is highly desirable to employ the
principles of mechanical advantage and thereby reduce the required
actuator force, as this will permit the use of smaller, lighter, and less
expensive actuating means.
It is also known to construct building trusses out of triangular elements
which are pivotally attached at their adjacent corners. These trusses can
be erected from flat to arched configuration by pushing the ends of the
truss together. For example, U.S. Pat. No. 4,890,429 to Gatzka et al.
illustrates a truss formed of upper and lower chords with the lower chord
having a plurality of lengths of tube slidably received over a tensioning
cable. By tensioning the cable, the truss is bowed upward to form an
arched truss. The erected shape of the truss is determined by the lengths
of the abutting tube segments.
An example of a truss using similar principles is shown in U.S. Pat. No.
4,169,099 to Sircovich. This truss is formed of pivotally joined
triangular structural elements with fixed lengths of wires connecting
adjacent elements. When the truss is flat, the wires are slack. As the
ends of the structure are pushed together, the truss as a whole is bowed
upward to form an arch which reaches its erected state when the wires
become taut.
Trusses of this type offer the convenience of easy erection, but do not
permit adjustment of the shape of the erected structure, as the final
erected shape is predetermined when the dimensions of the various
components are selected. Furthermore, trusses of this type can be
characterized as being "2-dimensional," in that during erection and in the
final configuration, the truss is constrained to remain in a plane defined
by the two ends of the truss.
Traditional building trusses, including those discussed above, generally
require a flat foundation as a prerequisite to begin construction. This
requirement is costly in terms of grading and site preparation, and may
often preclude erection on certain uneven or sloped sites altogether.
Therefore, there is a need for an erectable truss structure which is
adaptable to uneven and sloping sites and which reduced the cost of site
preparation.
As the discussion above illustrates, there continues to be a need in the
art for an adjustable structural truss wherein the actuator means do not
perform a structural function, which does not require great actuator force
for shape adjustment, which is adjustable in three dimensions both after
the components have been selected and after the truss is erected, which
has means for facilitating a partially erected configuration, and
furthermore, which can easily be erected on an uneven site.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a truss
structure which allows for three-dimensional adjustability both after the
components are selected and after the truss is erected.
The truss structure of the present invention is constructed from a series
of rigid truss elements, preferably equilateral tetrahedrons in shape,
which are connected at their adjacent edges. According to one embodiment
of the invention, the tetrahedral elements are composed of struts forming
an open framework. Each tetrahedron is pivotally coupled to its neighbors;
this pivotal coupling is achieved by sharing a single strut as the edge
for each adjacent tetrahedron. This shared strut represents the hinge for
the pivotal coupling between neighboring tetrahedra.
The truss structure is constructed by consecutively coupling tetrahedral
elements in this way. In the preferred embodiment of equilateral
tetrahedral truss elements, successive hinges in the truss structure are
orthogonal. This is in significant contrast to the pivoting axes in the
"two-dimensionally" adjustable trusses known in the art. The lack of
parallelism of the hinges advantageously allows the truss structure of the
current invention to be adjustable in three dimensions.
The truss structure may be laid on a flat surface, in a linear
configuration. The structure is then in its initial, or unadjusted state.
For example, the truss could be laid on a surface such that the first,
third, fifth, etc. hinges will be parallel to the surface, and the second,
fourth, sixth, etc. hinges will be perpendicular to the surface. The
hinges form two identifiable sets, all the hinges in each set being
parallel with each other, and perpendicular to the hinges in the other
set. The two sets of hinges define non-coplanar bending planes for the
overall truss structure. By a combination of adjustments in the angles of
the individual hinges in the two bending planes, full three dimensional
adjustment of the overall structure can be achieved.
For example, if the angle of any of the hinges perpendicular to the surface
is adjusted, this will only effect a change in the shape of the truss
structure in a plane parallel with the surface. However, if the angle of
any of the hinges parallel to the surface is adjusted, this will
necessarily effect a change in the shape of the truss structure out of the
plane parallel with the surface, thus erecting the truss up from the
surface.
It is a further object of the present invention to provide an adjustable
truss structure wherein the adjustment means do not perform a structural
function. In the preferred embodiment of the present invention, the truss
elements described above are of fixed shape. Adjustment of the shape of
the overall truss is not achieved by deforming the shape of the truss
elements, but by adjusting the hinge angle between the truss elements.
The adjustment of a specific individual hinge angle in the present
invention is preferably achieved by providing tension cables running the
length of the truss structure, and mechanical adjustment assemblies
associated with individual hinges. The application of tensile forces in
the tension cables provides a force tending to effect a change in the
hinge angles. As these tensile forces are being applied, the mechanical
adjustment assemblies may be used to provide a supplemental force, in
addition to the primary shaping force provided through the tension cables.
The supplemental force serves to modulate the amount of force from the
tension cables which is applied to the individual hinges. The supplemental
force is provided by an actuator, through a linkage designed to amplify
the force provided by the actuator. By employing the principles of
mechanical advantage, the actuator force required to control the shape
adjustment can be significantly reduced. In alternate embodiments of the
invention, shape adjustment can be accomplished using either the cables or
the adjustment assemblies alone.
It is a further object of the present invention to provide an adjustable
truss structure which has means for bearing the compressive loads in rigid
structural members, and the tensile loads in flexible structural members,
such as cables. This advantageously allows for a greater
strength-to-weight ratio as compared to structures known in the art.
In the preferred embodiment, the ends of each hinge slidably receive steel
tension cables. There are a pair of such cables associated with each set
of initially parallel hinges. After a specific hinge is adjusted to the
desired angle, that hinge angle position is maintained by clamping the
tension cables, thereby fixing the length of the cable segments associated
with the hinge of interest. Forces tending to change the hinge angle will
be opposed by tension in the cable segments. In this way, all of the loads
required to maintain hinge angle positions are carried by the cable
segments. The cables therefore serve to unload the adjustment assemblies
and actuators, so that these elements do not bear any structural loads in
the erected structure. In this completed configuration, all compressive
loads in the truss structure are carried by the rigid struts which form
the tetrahedral truss structure. To the extent that the cables are placed
under tension before being clamped, tensile forces in the truss structure
will be carried primarily by the cables.
The actuators and adjustment assemblies may optionally be removably
connected to the truss structure. After the position of a specific hinge
is adjusted and then fixed by clamping the associated cable segments as
described above, the actuator and adjustment assembly are no longer
required to maintain the selected hinge angle. Therefore, these components
may be disconnected from the truss structure. The actuator and adjustment
assembly may then be reconnected to the truss structure at a different
location, to adjust a different hinge. This process can be repeated as
necessary until all hinge angles are adjusted as desired, after which the
actuator and adjustment assembly may be permanently removed from the truss
structure. This advantageously allows the erection of a truss structure
using few actuators and adjustment assemblies, and reduces the number of
components in the final erected structure.
It is a further object of the present invention to provide an adjustable
truss structure which has means for facilitating a partially erected
structure. It is an aspect of the invention that the truss structure can
be quickly and easily erected merely by use of the tension cables
discussed above. A truss structure including the tension cables can be
quickly erected without the use of adjustment assemblies, by applying
tension in the tension cables. By changing the amount of tension in the
cables, as well as the relative amount of tension among the various
cables, the truss structure can be "drawn up" into a self-supporting erect
structure. This feature of the invention permits generalized control of
the overall shape of the truss by adjusting the tension in the cables;
which is sufficient for some applications. Furthermore, a truss initially
erected in this way can subsequently be "fine tuned" using the adjustment
assemblies described above.
It is a further object of the present invention to provide an adjustable
truss structure which can be easily erected on an uneven site without
extensive site preparation. This is advantageous as it permits less
expensive construction on uneven sites, and permits construction on sites
that may otherwise not be feasible.
Due to the geometric characteristics created by the non-parallelism of the
successive hinges in the truss structure of the present invention, it has
the ability to conform in three dimensions to the topology of any building
site. A truss structure of the current invention may be formed as a closed
loop of truss elements. The hinges associated with the elements forming
the foundation would be adjusted to allow the elements to conform to the
prevailing ground surface, following all irregularities and contours. The
elements not forming the foundation would be erected as described above.
Thus, the present invention easily and inexpensively accommodates uneven
building sites.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be further described with reference to the accompanying
drawings, wherein
FIG. 1 is a perspective view of a portion of the truss according to the
preferred embodiment of the invention, in its initial state;
FIG. 2 is a perspective line drawing of a portion of the truss according to
the preferred embodiment of the invention, illustrating additional
structures not shown in FIG. 1, and further illustrating the truss
adjusted from the initial state;
FIG. 3A shows a hinge node structure of the truss of FIG. 2 in the
direction of the arrow 3A--3A;
FIG. 3B shows the hinge node structure of FIG. 3A in an exploded view;
FIG. 4 shows an adjustment node structure of the truss of FIG. 2 in an
exploded view;
FIGS. 5A-5C are schematic drawings of a preferred embodiment of the truss
of the present invention in a closed loop configuration in various stages
of erection; and
FIG. 6 is a perspective view of a portion of a truss according to the
present invention, illustrating an embodiment in which the truss elements
are constructed as solid-faced bodies.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The structure of the invention will be described in conjunction with the
drawings.
FIG. 1 shows the truss 1 in an unadjusted state. The truss 1 is constructed
by sequentially coupling truss elements, here equilateral tetrahedral
elements 12, 13, 14, 15, 16, 17. Referring to tetrahedral element 14, it
is coupled at its edges 23, 24 to the adjacent tetrahedral elements 13, 15
on either side. Thus, tetrahedral element 14 has a total of two shared
edges 23, 24, and four independent edges 141, 142, 143, 144. The edges of
the tetrahedral elements are also referred to herein as tetrahedral
struts. Shared edges 23, 24 operate as hinges, allowing neighboring
tetrahedral elements 13, 15 to pivot relative to tetrahedral element 14.
The shared edges are also referred to herein as hinges.
If greater compressive strength was desired, the tetrahedral elements could
be constructed to be solid-faced bodies, by forming them out of flat
plates joined at the edges 92. In this embodiment, the pivoting could be
achieved by separate hinges affixed to the solid-faced tetrahedral
elements.
It is a significant aspect of the present invention that each individual
tetrahedral element 12, 13, 14, 15, 16, 17 is of fixed shape. Unlike the
adjustable truss structures in the prior art, three-dimensional shape
adjustment of the overall truss is achieved not by distorting the shape of
the tetrahedral elements, but merely by adjusting the pivotal angle
between successive tetrahedral elements.
It can be observed that when the truss is in the unadjusted state
illustrated in FIG. 1, the set of alternating hinges | | |
