Note: Descriptions are shown in the official language in which they were submitted.
CA 02016428 1999-OS-25
BACKGROUND OF THE INVENTION
Structures that transform in :size or shape have numerous uses.
If one desires to have a portable shelter of some kind, it
should package down to a compact bundle (tents being a prime
example).
I have discovered a method for constructing reversibly
expandable truss-structures that provides for an extremely
wide variety of geometries. Trusses formed by this method will
collapse and expand in a controlled, smooth and synchronized
manner. Such structures require no complex joints. Connections
are limited to simple pivots. A unique characteristic of one
embodiment of the present invention is that it provides a
three-dimensional folding truss whose overall shape and
geometry is constant and unchanging during the entire folding
process. Only its size changer between a compact bundle and an
extended self-supporting structure.
There are times when, rather than desiring a portable shelter,
one wishes to have a structure that remains fixed to a site,
but that can open and close. An example is a retractable roof
over a stadium, swimming pool, theatre or pavilion.
An alternate embodiment of the present invention provides
reversibly retractable structures that open up from the center
outwards, but maintain an essentially fixed perimeter. The
kind of motion exhibited by such structures may be described
as an iris-type motion.
The structure is a truss consisting of links joined by simple
pivots. Coverings may be provided in varius ways, such as
attaching shingled plates or a flexible membrane to the truss.
In addition to retractable roofs, numerous other uses exist
for this embodiment of the invention. Novel window shades,
toys and special irises for lighting are examples.
(2)
CA 02016428 1999-OS-25
BRIEF SUMMARY OF THE INVENTION
The present invention allows for self-supporting structures
that maintain their overall curved geometry as they expand or
collapse in a synchronized manner. An alternate embodiment of
the invention allows for iris-type retractable structures,
where the center of the structure retracts towards its
perimeter. In this embodiment the perimeter maintains a nearly
constant size.
Structures of either embodiment are comprised by special
mechanisms hereinafter referred to as loop-assemblies. These
assemblies are in part comprised by angulated strut elements
that have been simply pivotally joined to other similar
elements to form scissors-pairs these scissors-pairs are in
turn simply pivotally joined to other similar pairs or to hub
elements forming a closed loop.
When this loop is folded and unfolded certain critical angles
are constant and unchanging. These unchanging angles allow for
the overall geometry of struct=ure to remain constant as it
expands or collapses.
(3)
CA 02016428 1999-OS-25
BRIEF DESCRIPTION OF THE DRAWING FIGURES
The invention will be further described with reference to
the accompanying drawings, wherein:
Fig. 1 is a plan view showing the basic angulated strut
element that largely comprises the structure;
Figs. lA-1C are plan views of alternate configurations of
the basic element, also being angulated with regards to their
pivot points, if not their outer shape;
Fig. 2 is a plan view of two angulated strut elements
pivotally joined intermediate to their ends, also called a
scissors-pair;
Fig. 2A is a perspective view of the scissors-pair;
Fig. 3 is a view of the scissors-pair in a different
position. Also illustrated is a critical angle that remains
constant for all positions of the scissors-pair;
Fig. 4 is a plan view of an illustrative polygon;
Fig. 5 is a plan view of a closed loop-assembly of
scissors-pairs that approximates the polygon of Fig. 4;
Fig. 6 is a plan view of the closed loop-assembly of Fig.
in a different position;
Fig. 7 is a perspective view of a different embodiment of
the invention, being a three-dimensional loop-assembly
comprised of three scissors-pairs and six hub elements;
Fig. 8 is a perspective view of the loop-assembly of Fig.
7 in a different position;
Figs. 9-10 are perspective views of a different
embodiment of the invention in two positions;
Figs. 11-12 are perspective views of a different
embodiment of the invention irL two positions;
Figs. 13-16 show a sequence of perspective views of a
complete spherical structure which is comprised of loop-
assemblies, as it expands;
Figs. 17-20 show a sequence of perspective views of a
complete faceted icosahedral structure which is comprised of
loop-assemblies, as it expands;
(4)
CA 02016428 1999-OS-25
Figs. 21-23 show a sequence of views of an alternate
embodiment of the invention which is a planar retractable.
structure with an iris-type motion;
Figs. 24-27 show a sequence of views of another iris-type
retractable structure that has a domed form;
Figs. 28-30 show a sequence of views of the structure
illustrated in Figs. 24-27 with a covering attached to it, to
be used as a retractable roof;
Figs. 31-33 show a sequence of views of an iris-type
retractable structure having a.n oval-shaped perimeter and a
covering attached to it.
CA 02016428 1999-OS-25
DETAILED DESCRIPTION
Referring now more particularly to the drawings, in FIG. 1
there is shown an essentially planar rigid strut element 10
which contains a central pivot point 12 and two terminal pivot
points 14 and 16 through which pass three parallel axes. The
centers of the aforesaid three pivot points do not lie in a
straight line; the element is angulated. The distance between
points 14, 12 and the distance between 16, 12 may be each be
arbitrarily chosen. The angle between the line joining points
14, 12 and the line joining points 16, 12 may be arbitrarily
chosen. Said angle will hereinafter be referred to as the
strut-angle.
In Fig. lA there is shown another configuration 17 of a basic
strut element. It is similar in all essential aspect to that
shown n Fig. 1, save that it has a triangular rather than
angulated outer shape. Figs. 1.B and 1C show respectively strut
elements 18 and 19. They are essentially similar to that shown
in Fig. 1, save for the outer shape. The strut elements shown
in Figs. lA-1C are all angulat.ed with regards to the placement
of their three pivot points.
In FIG. 2 the scissors-pair 30 is shown. It is comprised of
element 10 and an essentially identical element 20 which
contains central pivot point 22 and two terminal pivot points
26 and 24. Element 10 is pivotally joined to element 20 by
their respective central pivot: points 12 and 22. All pivot
connections described herein are simple pivot connections with
one degree of freedom.
The elements 10 and 20 of scissors-pair 30 may be rotated such
that pivot point 14 will lie directly over pivot point 24. Two
pivot points in a scissors-pair that can line up each other in
this way are hereinafter referred to as paired terminal pivot
points. Thus, points 14 and 24 are paired terminal pivot
(6)
CA 02016428 1999-OS-25
points. Likewise points 16 and. 26 are paired terminal pivot
points.
Also shown in FIG. 2 is the line 40 which is drawn through the
center of paired terminal pivot points 14,24 and line 50 which
is drawn through the center of paired terminal pivot points
16,26. Lines 40 and 50 form an angle between them. Lines
constructed in the manner of 40 and 50 will hereinafter be
referred to as normal-lines. A more precise definition of
normal-lines is developed in the following paragraph.
In FIG. 2A a perspective view of the scissors-pair 30 is
shown. Passing through pivot point 14 is the axis 15.
Similarly, axes 13,25 and 23 pass through pivot points 16,24
and 26 respectively. A normal-line 40 is constructed that
intersects axes 15 and 25, and is perpendicular to both axes.
A normal-line 50 is constructed that intersects axes 13 and
23, and is perpendicular to both axes. Thus the general
definition of a normal-line is a line that intersects and is
perpendicular to the axes of a pair of terminal pivot points.
In FIG. 3 the scissors-pair 30 is shown where the elements 10
and 20 are shown rotated relative to each other. Also shown in
FIG. 3 is the line 60 which i~~ drawn through the center of
paired terminal pivot points 1.4,24 and line 70 which is drawn
through the center of paired germinal pivot points 16,26.
Normal-lines 60 and 70 form an angle between them. This angle
is identical to the angle between normal-lines 40 and 50. It
may be mathematically demonstrated that whatever the relative
rotation between elements 10 and 20, the angle between the
line joining one pair of terminal pivot points with the line
joining the other pair of terminal pivot points will be
constant. This angle is hereinafter referred to as the normal-
angle. It may also be demonstrated that the normal-angle is
the complement of the strut-angle.
FIG. 4 shows an illustrative polygon 80 where the number of
CA 02016428 1999-OS-25
sides, their relative lengths and the angles between them have
been arbitrarily chosen.
In FIG. 5 is shown a closed loop-assembly 100 of nine
scissors-pairs 110, 120, 130, 140, 150, 160, 170, 180, 190
where each scissors-pair is pivotally joined by its two pairs
of terminal pivot points to the terminal pivot points of its
two adjacent scissors-pairs. This loop-assembly is an
approximation of the polygon 80 in the sense that the
distances between adjacent central pivot points are equal to
the corresponding lengths of the sides of the polygon 80.
Further, the angles between the lines joining adjacent central
pivot points with other similarly formed lines in the assembly
are equal to the corresponding angles in the polygon 80.
Also shown in FIG. 5 are the normal-lines 112, 122, 132 142,
152, 162, 172, 182 and 192 that pass through the paired
terminal pivot points of the nine scissors-pairs. Note that
adjacent scissors-pairs share a normal-line.
FIG. 6 shows the loop-assembly 90 folded to a different
configuration without bending or distortion of any of its
elements. It may be demonstrated that loop-assembly 90 is a
mechanism with a degree-of-freedom equal to zero. Thus
kinematics predict such a mechanism would not be free to move.
It is due to the special proportions of the links that allows
it to move.
Also shown are the normal-lines 114, 124, 134, 144, 154, 164,
174, 184 and 194. The angle between 112 and 122 is equal to
the angle between 114 and 124. Likewise the respective angle
between any two lines among 112, 122, 132, 142, 152, 162, 172,
182 and 192 is identical to the corresponding angle between
any two lines among 114, 124, 134, 144, 154, 164, 174, 184 and
194.
C8)
CA 02016428 1999-OS-25
FIG. 7 shows a loop-assembly 200 comprised of three angulated
scissors-pairs 210, 220, 230 and six hub elements 240, 245,
250, 255, 260 and 265. Scissors-pair 210 is comprised of
angulated strut elements 211 and 212. Similarly, 220 is
comprised of elements 221 and 222; 230 is comprised of
elements 231 and 232.
Scissors-pair 210 is pivotally joined to hub elements 240 and
245 by its paired terminal pivot points 213 and 214. Hub
elements 240 and 245 are in turn pivotally joined to the
paired terminal pivot points 223 and 224 of scissors-pair 220.
Scissors-pair 220 is in turn pivotally joined to hub elements
250 and 255 by paired terminal pivot points 226 and 228. Said
hub elements are connected to scissors-pair 230 which is
similarly joined to hub elements 260 and 265. These hub
elements are connected to scissors-pair 210, thereby closing
the loop.
Also shown in FIG. 7 are three normal-lines 270, 280 and 290.
Line 270 intersects and is perpendicular to the axes that pass
through paired terminal pivot points 213 and 214. Likewise,
line 270 intersects and is perpendicular to the axes that pass
through paired terminal pivot points 223 and 224. In this
manner, normal-line 270 is shared by the scissors-pairs 210
and 220. Similarly, normal-line 280 is shared by the scissors-
pairs 220 and 230, and normal-line 290 is shared by the
scissors-pairs 230 and 210.
FIG. 8 shows the loop-assembly 200 folded to a different
configuration. The angulated :strut-elements 211 and 212 have
been rotated relative to each other. Similarly rotated are the
elements 221 and 222 as well as 231 and 232. This changed
configuration of assembly 200 is accomplished without bending
or distortion of any of its elements. Also shown are three
normal-lines 300, 310 and 320. Normal-line 300 is shared by
the scissors-pairs 210 and 220 in the manner described above.
C9)
CA 02016428 1999-OS-25
In the same manner, normal-line 310 is shared by scissors-pair
220 and 230 and normal-line 320 is shared by scissors-pair 230
and 210.
The angle between normal-liner 300 and 310 is identical to the
angle between lines 270 and 280. Similarly, the angle between
normal-lines 310 and 320 is identical to the angle between
lines 280 and 290. Also, the angle between normal-lines 320
and 300 is identical to the angle between lines 290 and 270.
When the relative rotation between two strut elements of any
scissors-pair in the loop-assembly is changed, all angles
between the normal-lines in tree loop-assembly remain constant.
In FIG.9 is shown loop-assembly 400 which is comprised of two
angulated scissors-pairs 410 and 430, two straight scissors-
pairs 420 and 440, as well as eight hub elements 450, 452,
454, 456, 458, 460, 462 and 4E~4. Also shown are normal-lines
470, 480, 490 and 500. Scissors-pair 410 is pivotally joined
to hub elements 450 and 452 by paired terminal pivot 413 and
414. Said hub elements are in turn pivotally joined to paired
terminal pivot points 426 and 428 belonging to scissors-pair
420. Similarly, 420 is connected to 430 by elements 454 and
456; 430 is connected to 440 by elements 458 and 460; 440 is
connected to 410 by elements 4:62 and 464, thus closing the
loop.
Also shown in FIG. 9 is normal. line 470 which intersects and
is perpendicular to the axes passing through paired terminal
pivot points 413 and 414 as well as terminal pivot points 426
and 428. Thus, normal-line 47C is shared by scissors-pairs 410
and 420. Similarly normal-line 480 is shared by scissors-pairs
420 and 430, normal-line 490 is shared by scissors-pairs 430
and 440 and normal-line 500 is shared by scissors-pairs 440
and 410.
FIG. 10 shows the loop-assembly 400 folded to a different
(10)
CA 02016428 1999-OS-25
configuration. The strut-elements 411 and 412 have been
rotated relative to each other. Similarly rotated are the
elements 421 and 422, 431 and 432, as well as 441 and 442.
This changed configuration of assembly 400 is accomplished
without bending or distortion of any of its elements. Also
shown are four normal-lines 510, 520, 530 and 540. Normal-line
510 is shared by the scissors--pairs 410 and 420, in the sense
that has been described above. Similarly, normal-line 520 is
shared by the scissors-pairs 420 and 430, normal-line 530 is
shared by the scissors-pairs 430 and 440, and normal-line 540
is shared by the scissors-paix-s 440 and 410.
The angle between normal-liner 510 and 520 is identical to the
angle between lines 470 and 480. Similarly, the angle between
normal-lines 520 and 530 is identical to the angle between
lines 480 and 490; the angle between normal-lines 530 and 540
is identical to the angle between lines 490 and 500; the angle
between normal-lines 540 and 510 is identical to the angle
between lines 500 and 470. As above, when the relative
rotation between two strut elements of any scissors-pair in
the loop-assembly is changed, all angles between the normal-
lines in the loop-assembly remain constant.
In FIG. 11 is shown the loop-assembly 600 which is comprised
by 12 scissors-pairs and 12 hub elements. The loop is
connected as follows: scissor~~-pair 610 joined to scissors-
pair 620, by joining the paired terminal pivot points of one
directly to the paired terminal pivot points to the other.
Connections of this type are hereinafter referred to as a type
1 connection.
Scissors-pair 620 is pivotally joined to hub element 630 and
635 by its remaining paired terminal pivot points. 630 and 635
are pivotally joined to a pair of terminal pivot points
belonging to scissors-pair 640. Thus, scissors-pair 620 is
joined to 640 via hub elements 630 and 635 by what is
(11)
CA 02016428 1999-OS-25
hereinafter referred to as a type 2 connection.
Scissors-pair 640 has a type 1 connection to 650, 650 has a
type 2 connection to 670 via elements 660 and 665; 670 has a
type 1 connection to 680; 680 has a type 2 connection to 700
via elements 690 and 695; 700 has a type 1 connection to 710;
710 has a type 2 connection to 730 via elements 720 and 725;
730 has a type 1 connection to 740; 740 has a type 2
connection to 760 via elements 750 and 755; 760 has a type 1
connection to 770; 770 has a type 2 connection to 610 via
elements 780 and 785. This last connection closes the loop.
Also shown in FIG. 11 are twelve normal-lines 602, 612, 632,
642, 662, 672, 692, 702, 722, 732, 752, 762 that intersect and
are perpendicular to the axes of the joined terminal pivot
points of adjacent scissors-pairs.
In FIG. 12 the loop-assembly 600 is shown folded to a
different configuration where each of the two strut elements
belonging to every scissors-pair have been rotated relative to
each other. As above, this folding takes place without bending
or distortion of any of the elements in the assembly. Also
shown in FIG. 12 are twelve normal-lines 604, 614, 634, 644,
664, 674, 694, 704, 724, 734, 754 and 764 that intersect and
are perpendicular to the axes of the joined associated pivot
points of adjacent scissors-pairs.
The angle between 602 and 612 is identical to the angle
between 604 and 614. As above, when the relative rotation
between two strut elements of any scissors-pair in the loop-
assembly is changed, all angles between the normal-lines in
the loop-assembly remain constant.
In FIG. 13 a spherical truss structure 1000, which is
comprised of a multiplicity of loop-assemblies as described
above, is shown in an entirely folded (collapsed)
configuration. FIG. 14 and FIG. 15 each show partially folded
(12)
CA 02016428 1999-OS-25
configurations of the structure 1000. FIG. 16 shows the
structure 1000 in an entirely unfolded (open) configuration.
The folding of the structure 1000 takes place without bending
or distortion of any of its elements. As the structure is
folded and unfolded, all angles between the normal-lines in
the structure remain constant.
In FIG. 16 the centers of the central pivot points of all the
scissors-pairs in the unfolded structure 1000 lie on a common
surface, in this case a sphere. In FIG. 13 the centers of the
central pivot points of all the scissor-pairs in the structure
lie on a common surface that is also spherical, but of a
smaller scale than the surface of FIG. 16. Likewise, in FIGS.
14-15 which show partially folded configurations of the
structure 1000, the centers of the central pivot points of all
the scissors-pairs in the structure lie on a common spherical
surface for each configuration. For any configuration of the
structure, the centers of the central pivot points of all
scissors-pairs will lie on a ~~pherical surface. As the
structure is folded and unfolded, only the scale of this
surface changes, not its three-dimensional shape.
In FIG. 17 a truss structure 7_200, of icosahedral geometry,
which is comprised of a multiplicity of loop-assemblies as
described above, is shown in an entirely folded (collapsed)
configuration. FIG. 18 and FIG. 19 each show partially folded
configurations of the structure 1200. FIG. 20 shows the
structure 1200 in an entirely unfolded (open) configuration.
The folding takes place without bending or distortion of any
of its elements. As the structure is folded and unfolded, all
angles between the normal-lines in the structure remain
constant.
In FIG. 20 the centers of the central pivot points of all the
scissors-pairs in the unfolded structure 1200 lie on a common
surface, in this case an icosahedron. In FIG. 17 the centers
(13)
CA 02016428 1999-OS-25
of the central pivot points of all the scissors-pairs in the
structure lie on a common surface that is also icosahedral but
of a smaller scale than that surface of FIG. 20. Likewise, in
FIGS. 18-19 which show partially folded configurations of the
structure 1200, the centers of the central pivot points of all
the scissors-pairs in the structure lie on common icosahedral
surfaces. As the structure is folded and unfolded, only the
scale of this icosahedral surface changes, not its three-
dimensional shape.
In FIG. 21 a planar structure 1500 is shown which is an
alternate embodiment of the invention. It is comprised of four
loop-assemblies, 1510, 1520, 1530 and 1540. The inner terminal
pivot points of 1510 meet at t=he center of the structure. The
outer terminal pivot points of loop-assembly 1510 are
pivotally joined to the inner terminal pivot points of loop-
assembly 1520. Similarly the outer terminal pivot points of
1520 are joined to the inner terminal pivot points of 1530.
The outer terminal pivot points of loop-assembly 1530 are in
turn joined to the inner terminal pivot points of 1540.
In FIG. 22, the structure 1500 is shown in a partially
retracted position, where the struts of all scissors-pairs
have undergone a relative rotation. The inner terminal pivot
points of loop-assembly 1510 have moved outwards from their
position in FIG. 21. The terminal pivot points of the loop-
assembly 1540 have moved relatively little from their position
in FIG. 21. Thus the size of the outer perimeter of the
structure 1500 has changed very little between the positions
shown in FIGS. 21 and 22.
In FIG. 23 the structure 1500 is shown in a retrated position.
The inner terminal pivot points of loop-assembly 1510, lie in
and define the inner perimeter' of the structure. This inner
perimeter has changed substantially from the positions shown
in FIGS. 22 and 21. However the outer perimeter of the
(14)
CA 02016428 1999-OS-25
structure 1500, which the outer terminal pivot points of loop-
assembly 1540 lie in, has changed very little from the earlier
positions. The essential motion of the structure 1500 is that
of the inner portion of the structure moving outwards towards
the perimeter. In this sense it may be described as an iris-
type retractable structure.
In FIG. 24 the retractable structure 2000 is shown, which is
comprised of six loop-assemblies 2010, 2020, 2030, 2040, 2050
and 2060. The inner hub elements of loop-assembly 2010 meet
near the center of the structure. The outer hub elements of
loop-assembly 2010 are joined to the inner hub elements of
loop-assembly 2020. Similarly, the outer hub elements of loop-
assembly 2010 are joined to the inner hub elements of loop-
assembly 2020. In the same manner, loop-assemblies 2030, 2040
and 2050 are joined to 2040, ;050 and 2060 respectively.
In FIG. 25 the structure 2000 is shown in a partially
retracted position. The inner perimeter of the structure,
which the inner terminal pivot: points of loop-assembly 2010
lie in and define, has moved outwards from the center. The
outer perimeter of the structure, which the outer terminal
pivot points of loop-assembly 2060 lie in, has moved very
little from its position in FI:G. 24.
The structure 2000 is shown in a further retracted position in
FIG. 26. The loop-assemblies that make up the structure have
moved further outwards towards the perimeter.
In FIG. 27 the structure 2000 is shown in its fully retracted
position. This inner perimeter' has changed substantially from
the positions shown in FIGS. 24-26. However the outer
perimeter of the structure 2000, which the outer terminal
pivot points of loop-assembly 2060 lie in, has changed very
little from the earlier positions. Thus the structure has
maintained a nearly constant diameter during the unfolding
process.
;15)
CA 02016428 1999-OS-25
FIG. 28 shows the structure 2000 used as a retractable roof
over a stadium 3000. A covering is provided to give shelter
(only half the roof is shown covered to make the illustration
clear). A series of plates 2110 have been attached to
individual elements of the loop-assembly 2010. Similarly a
series of plates 2120 have ben attached to loop-assembly 2020.
In this manner plate series 2130, 2140, 2150 and 2160 are
attached to loop-assemblies 2030, 2040, 2050 and 2060
respectively. The plates over:Lap each other in a shingled
pattern to ensure protection .from the elements.
In FIG. 29 the structure 2000 is shown in a partially
retracted position, the inner perimeter of the structure
having moved outwards towards the circumference. The plates
2110 move outwards with the loop-assembly 2010 to which they
are attached. They glide over adjacent plates without
interfering with each other. Similarly plate series 2120,
2130, 2140, 2150 and 2160 move outwards, attached to their
respective loop-assemblies, without interfering with each
other.
FIG. 30 shows the structure 2000 in its fully retracted
position. The plate series 211.0, 2120, 2130, 2140, 2150 and
2160 are located in a compact configuration around the edge of
the structure, still attached to their respective loop-
assemblies. Again there is no interference between the plate
series.
In FIG. 31 the retractable structure 4000 is shown, which is
comprised of six loop-assemblies 4010, 4020, 4030, 4040, 4050
and 4060. In this embodiment of the invention, the hub
elements are of varying length to provide an oval-shaped
perimeter to the structure. The inner hub elements of loop-
assembly 4010 meet near the center of the structure. The outer
hub elements of loop-assembly 4010 are joined to the inner hub
elements of loop-assembly 4020. In this manner, the outer hub
elements of loop-assemblies 4020, 4030, 4040 and
(16)
CA 02016428 1999-OS-25
4050 are joined to the inner hub elements of 4030, 4040, 4050
and 4060 respectively.
Also shown in FIG. 31 is a covering over the structure 4000,
to provide shelter (only half the roof is shown covered to
make the illustration clear). A series of plates 4110 have
been attached to individual elements of the loop-assembly 4010
in an alternate arrangement to the covered structure shown in
FIG. 28. Similarly a series of plates 4120 have been attached
to loop-assembly 4020. In this manner plate series 4130, 4140,
4150 and 4160 are attached to loop-assemblies 4030, 4040, 4050
and 4060 respectively. The plates overlap each other in a
shingled pattern to ensure protection from the elements.
In FIG. 32 the structure 4000 is shown in a partially
retracted position. The inner perimeter of the structure,
which the inner terminal pivot points of loop-assembly 4010
lie in and define, has moved outwards from the center. The
plates 4110 move outwards with the loop-assembly 4010 to which
they are attached. They glide over adjacent plates without
interfering with each other. Similarly plate series 4120,
4130, 4140, 4150 and 4160 move outwards, each attached to
their respective loop-assemblies, without interfering with
each other. The outer perimeter of the structure, which the
outer terminal pivot points of: loop-assembly 4060 lie in, has
moved very little from its position in FIG. 31.
In FIG. 33 the structure 4000 is shown in its fully retracted
position. This inner perimeter has changed substantially from
the positions shown in FIGS. 31-32. However the outer
perimeter of the structure 4000, which the outer terminal
pivot points of loop-assembly 4060 lie in, has changed very
little from the earlier positions. Thus the structure has
maintained a nearly constant perimeter during the retracting
process. The plate series 4110, 4120, 4130, 4140, 4150 and
4160 are located in a compact configuration around the
x;17)
CA 02016428 1999-OS-25
edge of the structure, still attached to their respective
loop-assemblies. Again there is no interference between the
plate series.
It will be appreciated that the instant specification and
claims are set forth by way of: illustration and not
limitation, and that various modifications and changes may be
made without departing from the spirit and scope of the
present invention.
(17a)