 |
Description  |
|
|
BACKGROUND OF THE INVENTION
This invention relates to jointed extendible truss beams which form an
elongated truss structure when unfolded and occupy little space when
folded.
Structures which are similar to this kind of truss beam are very widely
used. The requirements for this kind of structure, particularly for use in
space, is that it be light, rigid and fold into a small space for
transportation.
Examples of prior art extendible truss structures are the so-called simplex
mast disclosed in U.S. Pat. No. 3,486,279 and the STACBEAM disclosed in
IECEC-829260, "An Efficient Low-Mass, Sequentially Deployable Structure"
Adams, Intersociety Energy Conversion Eng. Conf. 1982, Vol. 3, 1578-1583.
The simplex mast is a nearly perfect, extremely simplified, extendible
truss beam. One part of the structural elements of this beam includes a
tensile cable. This is different in concept from the jointed extendible
truss beam of this invention, and is not suitable for large structures
requiring strength and rigidity.
The STACBEAM is a jointed extendible truss beam formed entirely of beam
elements. A joint is provided in the central portion of these beams for
folding and the beams parallel to the lengthwise truss beams, which are
the main load bearing members, are also foldable in the center section.
The total number of beams that bend in the middle represents 2/3 of the
total number of beams. Also, the number of joints is up to three times the
minimum number required to construct the truss structure. Including the
mechanism for locking the joints themselves, complicated devices
sufficiently capable of bearing the load are required.
Truss beams, which are a basic structural element of space structures, must
be carried into space by transportation vehicles such as rockets or the
space shuttle. The first consideration in setting up large structures in
space is the efficient use of storage and the greatest possible reduction
in weight.
The beams making up the truss beam can be made light using composite
materials, for example, but it is difficult to reduce the weight of the
joints and locking mechanisms. Also, when the truss beam is folded, these
joints and locking mechanisms interfere with each other and represent a
major difficulty in designing stage for making the most efficient use of
storage space.
In consideration of these points, the structural concept of present day
jointed extendible truss beams having many joints and locking members is
being restudied with a view to major reductions in weight and
simplification of design by reducing the number of these joints and
locking members. These truss beams are structures as well as a kind of
mechanism, which, including the joints and locking members, have very many
parts. Structures which have very many parts, particularly when they are
to be used in space, require adjustment and checks in order to guarantee
high reliability, which results in greatly inflated costs. Proposals for
solving these problems are greatly sought, and the object of this
invention is to respond to this need.
SUMMARY OF THE INVENTION
The object of the invention is to provide a jointed extendible truss beam,
in which a tetrahedron having six beams, or two triangular plates and one
beam, and at least four joints are rotatably coupled with the beams, forms
one unit, one triangular plane of this tetrahedron is commonly coupled
with the next tetrahedron to form a truss beam, and the length of each
beam of the tetrahedral unit, which has at least one locking mechanism, is
telescopic for varying the length to form a jointed extendible truss beam
in which the tetrahedrons fold sequentially in a plane.
Another object of the invention is to provide a jointed extendible truss
beam, in which a tetrahedron having six beams and at least four joints
rotatably coupled with the beams, forms one unit, one triangular plane of
this tetrahedron is commonly coupled with the next tetrahedron to form a
truss beam, and at least one of the five beams that are not in the
longitudinal direction of the truss beam and that has a locking mechanism,
has a joint in the middle of the beam for folding the beam, and depending
on the shape of the tetrahedron, one beam is telescopic such that by
contracting, the tetrahedron sequentially folds up.
BRIEF DESCRIPTION OF THE DRAWINGS
This invention may be better understood with reference to the drawings in
which:
FIG. 1 shows the structure of the truss beam according to the first
embodiment of the invention;
FIG. 2 is a perspective view of a minimum unit of the structure shown in
FIG. 1;
FIGS. 2A, 2B, 2C, 2D and 2E are perspective line drawings showing the
folding order of the minimum units;
FIG. 3 is a perspective view of a vertical minimum unit of the second
embodiment of the invention;
FIGS. 3A, 3B, 3C, 3D and 3E are perspective line drawings showing the
folding order of the vertical minimum units;
FIG. 4 is a perspective view of the truss beam structure assembled of the
vertical minimum units;
FIG. 5 is a perspective view of another minimum unit in which the
longitudinal member has been shortened;
FIGS. 5A, 5B, 5C, and 5D are perspective line drawings showing the folding
order of the vertical minimum units of FIG. 4;
FIGS. 5E, 5F, 5G and 5H are perspective line drawings showing another
folding order of the vertical minimum units of FIG. 4;
FIG. 6 is a perspective view of the truss beam structure assembled of the
vertical minimum units;
FIG. 7 shows the hinge structure of the frame of FIG. 6 in the direction of
the arrow 7--7;
FIG. 7A is a view of FIG. 7 along the arrow 7A--7A;
FIG. 7B is a view of FIG. 7 along the arrow 7B--7B;
FIG. 8 is a perspective view of an embodiment in which part of one plane of
the tetrahedron is missing;
FIGS. 8A, 8B, 8C, 8D, 8E are perspective views showing the folding order;
FIG. 9 is a perspective view of an embodiment in which midway joints are
provided;
FIGS. 9A, 9B, 9C, 9D show the folding order of the embodiment shown in FIG.
9;
FIG. 10 is a perspective view of another embodiment in which midway joints
are provided; and
FIGS. 11 and 12 are perspective views of the truss beams assembled of the
minimum units of FIGS. 9 and 10.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The structure of the invention will be described in conjunction with the
drawings.
FIG. 1 shows the truss beam constructed by sequentially coupling regular
tetrahedrons formed of six beams. In the drawing, reference numerals 1, 2,
. . . , 12 denote joints. When viewed overall, this truss beam appears to
be constructed of a number of helical lines. There are three kinds of
helices: three large-pitch helices (members constituting these helices are
called longitudinal members and are arranged along the length of the truss
beam) are formed by lines connecting joints 1, 4, 7, 10, . . . , joints 2,
5, 8, 11, . . . , and joints 3, 6, 9, 12, . . . , in the order named; one
small-pitch helix (members constituting this helix are called helical
members) is formed by a line connecting joints 1, 2, 3, 4, 5, 6, . . . ,
in the order named; and two medium-pitch helices (members constituting
these helices are called angle members) are formed by lines connecting
joints 1, 3, 5, 7, 9, 11, . . . , and joints 2, 4, 6, 8, 10, 12, . . . One
tetrahedron (formed, for example, by joints 1, 2, 3 and 4 as the apexes)
is constructed of one longitudinal member 21, three helical members 24,
25, 26, and two angle members 29, 30. A minimum unit of the truss beam can
be considered to be three tetrahedrons which include three longitudinal
members (namely, the part formed by joints 1, 2, 3, 4, 5 and 6). The lower
plane of the truss beam, i.e., the triangle formed by apexes 1, 2, 3, is
generally not perpendicular to the length of the truss beam.
To understand the extension or folding mechanism of the entire truss beam
it is sufficient to describe the folding mechanism of the minimum unit.
FIG. 2 shows a part constructed of joints 1, 2, 3, 4, 5 and 6, i.e., a
minimum unit. FIG. 2A shows the state in which the tetrahedron formed by
joints 3, 4, 5 and 6 is partially folded by the simultaneous extension of
angle members 31 and 32, and FIG. 2B shows the tetrahedron fully folded.
In FIG. 2B, joint 6 is on the same plane as the triangular plane having
its apexes formed by joints 3, 4 and 5. FIG. 2C shows the minimum unit
being further folded by the extension of angle members 29 and 30. FIG. 2D
shows angle members 29 and 30 extended still further and FIG. 2E shows the
minimum unit almost fully folded. As is clear from FIG. 2E, joint 5 is
folded on top of joint 1 and joint 6 is folded on top of joint 2. By
extending four angle members, it is possible to fold the minimum unit
flat, and when viewed at an angle from above, the tetrahedron has become a
square with the sides of the tetrahedron forming the sides of the square.
This minimum unit has suitable locking mechanisms for when it is extended
such as mechanism 200 depicted schematically only in FIG. 2 but equally
usable with the other embodiments.
FIG. 3 shows the tetrahedron of FIG. 2 in which angle members 29, 30, 31
and 32 have been lengthened simultaneously by 1.155, resulting in the
helical pitch of the three longitudinal members becoming infinite and the
direction of the longitudinal members coming exactly into line with the
lengthwise direction of the truss beam. This kind of minimum unit is
called a vertical minimum unit.
By coupling there vertical minimum units it is possible to form a truss
beam in which the longitudinal members are completely straight. The end
planes of the minimum unit, i.e., the triangles formed by joints 1, 2, 3
and joints 4, 5, 6 as the apexes, are inclined at a fixed angle in the
lengthwise direction of the truss beam. There is essentially no difference
in the folding of the vertical minimum unit and the tetrahedral minimum
unit of FIG. 2.
In the series of FIGS. 2 to 2E the folding states obtained by the extension
of four longitudinal members of the minimum unit are shown. Next will be
shown the folding states of the vertical minimum unit of FIG. 3 by the
extension of only two angle members. It is of course possible to also fold
the minimum unit shown in FIG. 2 by the extension of the two angle
members, and to fold the minimum unit shown in FIG. 3 by the extension of
four angle members.
FIG. 3A shows exactly the same two bottom tetrahedrons shown in FIG. 3
formed by joints 1, 2, 3, 4, 5 with only angle member 32 extended. FIG. 3B
shows the topmost tetrahedron folded in with joint 6 on the same plane as
the triangle formed with joints 3, 4 and 5 as the apexes. FIG. 3C shows
only the angle member 30 slightly extended with the bottom two
tetrahedrons folded simultaneously. When angle member 30 is extended
further, the tetrahedron folds further (FIG. 3D) until it is almost flat
(FIG. 3E).
In this case, only the lengths of angle members 30 and 32 have varied from
that in the extended state shown in FIG. 3, and the folded form is diamond
shaped. With the method of folding the minimum unit by extending only two
of the angle members, the planes of the extended minimum unit are
maintained as compared to when four angle members are extended. Namely, as
can be seen in FIG. 3E, the five triangles whose apexes are formed by
joints 1, 2 and 3, joints 2, 4 and 1, joints 3, 4 and 5, joints 3, 5, and
2, and joints 3, 5 and 6, do not vary at all. It is therefore possible to
form these portions of plates. The operation of the joints is also very
straightforward and designing the joints is very easy.
FIG. 4 shows the truss beam, which is formed by successively coupling the
vertical minimum units shown in FIG. 3, as it looks when extended from a
flat diamond shape by the extension of two telescopic angle members of the
minimum units. Reference numerals 51a and 51b denote the two telescopic
extendible angle members that have locking mechanisms. These are the only
beam members which have mechanisms for folding. The minimum unit is
comprised of twelve beams of which three are common to the next minimum
unit, so the total number of beam members which have mechanisms for
folding is approximately 2/9 of the total number of beams, which is a
great reduction over prior art jointed extendible truss beams.
Reference numeral 52 denotes one kind of joint. These joints are arranged
at the minimum number of connections required to construct the truss
structures. The folding movement of the beams is also comparatively simple
so the joints are easy to design. Also, what should be noted is that both
ends of the truss beam, when extended, are perpendicular to the lengthwise
direction of the truss beam.
The embodiment of FIG. 3, in which the four angle members of the minimum
unit of FIG. 3 are telescopically extended and the minimum unit is folded
into a flat square shape, has the same shape as that shown in FIG. 4 when
extended. In this case, the number of beam members having folding
mechanisms is twice that of the embodiment shown in FIG. 4, which, in turn
makes it possible to obtain a wide variety of extension directions and
speeds simply by suitably controlling the length of the beam member when
extending.
FIG. 5 shows the vertical minimum unit of FIG. 3 with the three
longitudinal members simultaneously shortened. The angle members have a
length 1.718 that of the longitudinal members. A mast that is constructed
of successively coupled minimum units having shortened longitudinal
members close together is very resistant to flexion and deflection loads.
The following is a description of the folding of such a vertical minimum
unit by contracting the angle members. First, contraction of the four
angle members is shown. FIG. 5A shows the angle members 31 and 32
simultaneously contracted, and FIG. 5B shows the topmost tetrahedron
folded in with joint 6 on the same plane as the triangle which has joints
3, 4 and 5 as its apexes. FIG. 5C next shows the angle members 29 and 30
simultaneously contracted, and FIG. 5D shows joint 6 on top of joint 1,
forming a minimum unit that is folded flat.
The following drawings show the case where only two angle members of the
minimum unit are contracted. FIG. 5F shows the minimum unit of FIG. 5 with
only angle member 32 contracted. In this case the bottom two tetrahedrons
do not vary. FIG. 5F shows the top tetrahedron folded in with joints 6 on
the same plane as the triangle which has joints 3, 4 and 5 as its apexes.
FIG. 5G next shows angle member 30 contracted and the bottom two
tetrahedrons folded in. In this case the bottom plane of the triangle
whose apexes are formed by joints 1, 2 and 3 does not vary. FIG. 5H shows
the minimum unit folded flat.
With a truss beam that is constructed by successively coupling these
vertical minimum units, the odd numbered joints come on top of the circle
circumscribing the triangle whose apexes are formed by joints 1, 3 and 5,
and the even numbered joints come on top of the circle circumscribing the
triangle whose apexes are formed by joints 2, 4 and 6. With this kind of
method in which the minimum unit is folded by contracting only two angle
members, it is possible to use plates for the five triangles, which remain
the same, as was similarly described in reference to FIG. 3E, and the
design of the joints is simplified. These drawings show the telescopic
contraction of the angle members. However, it is also possible to obtain
the same effect by providing joints in the middle of the angle members so
that they can bend.
FIG. 6 shows an extended truss beam of this embodiment in which the
vertical minimum units shown in FIG. 5 are successively coupled. The
helical and angle members are arranged close together so this truss beam
is resistant to flexion and deflection. When the folding in is carried out
by telescopically extending or contracting two or four angle members of
the minimum unit, or when it is carried out by bending the joints provided
in the middle of the angle members, load bearing capacity, storage
efficiency and cost can be selected as required to meet various design
requirements. With this embodiment it is also possible to lengthen the
longitudinal members to form vertical minimum members which are narrower
and longer than that shown in FIG. 3 but which fold in the same way.
FIGS. 7 to 7B show the structure of hinge 52, which is used in this truss
beam. Hinge 52 has a hinge body 61 to which forks 62 are rotatably
attached. Shafts 68, which have a circular cross section, are formed on
the base section of the forks 62. Shafts 68 are rotatably fitted into
hinge body 61. Forks 62 are fixed by bolt 67 and pin 70 which pass through
the forks. Longitudinal members 51c are rotatably connected to rod ends 63
which are connected to forks 62. Rotating member 64 is rotatably fitted
into shaft 69, which protrudes from hinge body 61, to which member 64 is
fixed by bolt 66. Angle members 51a, 51b are rotatably connected to forked
rod ends 65 which are connected to rotating member 64.
FIG. 8 shows an embodiment in which part of each plane of the tetrahedron
of FIG. 5 has been replaced with a plate. In this embodiment, the planes
of the triangles formed by hinges 1, 2 and 3, hinges 1,3 and 4, hinges 2,
3 and 5, hinges 3, 4 and 5, and hinges 3, 5 and 6 have been replaced with
plate material 40. Reference numerals 30, 32 denote beam members. FIGS. 8A
to 8E show the folding sequence of the embodiment of the FIG. 8. The
extending sequence is the opposite of the folding sequence.
The following is a description of an embodiment in which beam members
having joints in the middle are used for bending. FIG. 9 shows the same
minimum unit shown in FIG. 3 except that joints are provided in the middle
of the angle members for bending. These joints are fastened to the angle
members with suitable fastening mechanisms. In FIG. 9, reference numerals
39, 40a and 41 denote these midway joints. With this vertical minimum
unit, the length of the eight members other than the angle members is the
same. In this embodiment, the folding order is sequentially shown in FIGS.
9A to 9D. When angle member 32 bends at midway joint 42, joint 6 folds
onto joint 4, and the tetrahedron whose apexes are formed by joints 3, 4,
5 and 6 is folded up. In other words, longitudinal member 23 stacks onto
helical member 26 and helical member 28 stacks onto helical member 27. As
the members, of course, have a certain thickness, the joints are
correspondingly offset. No members are stacked on to angle member 31 so if
this angle member is next bent at midway joint 41, joint 5 will be stacked
on joint 3, and the tetrahedron whose apexes are formed by joints 2, 3 and
4 is folded.
In this way, when angle member 30 and finally angle member 29 are folded,
the minimum unit is folded into a bar shape at the location of helical
member 24. In actual practice, by taking the offset required into
consideration when designing the joints, it is possible to form the
members, which are closely packed when folded and stored, of plates such
that members extend at right angles, or to form the members of tubes such
that they expand at right angles. When folded in this way, the storage
efficiency is extremely high and it is possible to fold the tetrahedrons
sequentially from the top, making both extension and storage very simple.
Furthermore, it is possible to fold the unit with no joints being provided
in the middle of the longitudinal members or the main load bearing
members, which are features that are greatly desirable in future large
spacecraft structures.
FIG. 10 shows a variation in the vertical minimum unit in which both end
planes of the triangle are right triangles and are perpendicular to the
lengthwise direction of the truss beam. The reference numbers of the
joints and members are the same as that used up to now. The difference
between this variant minimum unit and those considered up to now lies in
helical member 26 being longer than the other four members, which have
equal lengths, and angle members 30, 31 being equal in length but longer
than equal-length angle members 29 and 32.
In the folding process of this kind of minimum unit, helical member 26
becomes equal in length to the other four helical members, and the length
of the angle members of different length varies suitably or the midway
joints bend suitably so that the minimum unit folds up in the same way as
the previously described minimum units do. In this case, as well, it is
not necessary to provide joints in the middle of the longitudinal members.
Consider, for example, the minimum unit shown in FIG. 10 being folded into
the bar shape described earlier. In this case, joints are provided in the
middle of the four angle members so that the bending of these members is
exactly the same as was described earlier, i.e., the longitudinal members
and the equal-length helical members become equal in length. First, the
tetrahedron whose apexes are formed by joints 3, 4, 5 and 6 contracts
simultaneously with the bending in the middle of angle member 32 such that
helical member 26 expands telescopically to become equal in length to the
other helical members. In this way, it is possible for joint 6 to stack
onto joint 1, and the angle members to bend in the middle in the sequence
31, 30 and then 29.
FIG. 11 shows an extended truss beam constructed of vertical minimum units,
which have midway joints and are successively coupled together. Midway
joint 53 provided in the angle member is one such joint. As was described
in detail earlier, when the angle members bend sequentially at these
joints, all the members fold into a bar shape at the helical member. In
actual practice, because design consideration must be given to the offset
of the joints, it is possible to make the beam members of plates or tubes
which are tightly packed together, and to store the device in a suitable
case for transportation into space.
FIG. 12 shows an extended truss beam constructed of the variant minimum
units. In this case, both end planes of the truss beam and the triangles
corresponding to both end planes of the minimum unit are all perpendicular
to the lengthwise direction of the truss beam. In this embodiment, when
beam members 54a, 54b and 54c, etc., which are angled and which constitute
one side plane of a triangular truss beam, are folded, they must
telescopically contract to the same length as the beams which form the
right triangle of the end plane. Simulate with the contraction movement of
the beams, the length of the angle members is telescopically varied as was
described with reference to FIG. 10, or midway joints are provided and the
angle members bend, so that the truss beam according to this embodiment
folds up.
The truss beam of these embodiments is divided into constant length
sections which constitute one unit. The design of the coupling of a
plurality of these units is also vary effective from the viewpoint of
manufacturing and the restrictions imposed on the storage capacity for
transportation.
With a truss beam constructed of tetrahedrons successively coupled
together, and in which the length of the angle members is varied
telescopically or the angle members are bent at the joints in the middle
to perform the folding operation, very many advantages effects can be
obtained.
First, compared to a prior art jointed extendible truss beam in which all
the members except those in plane perpendicular to the lengthwise
direction of the truss beam bend, with a truss beam of these embodiments
the number of beams which have telescopic mechanisms or midway joints is
greatly reduced. In the embodiment in which two angle members of the
minimum unit are provided with a folding mechanism, the number of such
mechanism-equipped beams is approximately 2/9 of the total number of
beams. Also, the design of such joints is extremely simple. These features
mean that the weight of the device is, of course, reduced, and the cost of
the parts, the adjustment and inspection can be greatly reduced. Also,
because the amount of adjustment required is reduced, it is possible to
manufacture a product having high reliablity.
Secondly, storage efficiency is high. Of course, when the truss beam is
folded into a bar shape, and when the truss beam is folded into a flat
shape as well, the base area of the planar shape is at most double the
cross-sectional area of the extended truss beam. The rigidity of the
extended truss beam is proportional the diameter of the beam to a power of
4.
Truss beams having a large diameter are essential structural elements of
large spacecraft and so the suitable truss beams have been desired. The
truss beam of this invention is in response to this demand and the truss
beam of this invention which folds into a bar shape, in particular, has a
very large diameter when extended. If full use is made in the lengthwise
direction of the cargo bay of the space shuttle, it is possible to make a
large truss beam having a diameter of 19 meters using helical members that
are 15 meters long. This kind of a large truss beam has long been desired,
but up to the present time, only assembled truss beams of that size have
been built. The assembly of this kind of truss beam outside the spacecraft
by astronauts has involved many difficult engineering problems. Therefore,
an extendible truss beam that has good storage efficiency has a great
advantage as a structural part of a large spacecraft.
According to this invention, no more elements are added to the prior art
device, rather the number of elements are reduced, making the structure
simple, the requirements mentioned earlier are met sufficiently, resulting
in a truss beam that is superior to the prior art device in many points.
* * * * *
|
|
 |
|
 |
Description |
|
