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BACKGROUND OF THE INVENTION
Early space structures were fully assembled on earth prior to launching
into space, and their size was limited to the cargo volume of the launch
vehicle. Subsequent structures comprised ingenious folded, compressed, or
rolled high-density assemblies that would unfurl, deploy, or expand upon
arriving in space to form structures displacing a volume many times larger
than the original stowage volume provided by the launch vehicle.
More sophisticated and complex structures for earth orbit deployment have
been developed. Some such structures are to be manufactured in space by
roll forming and welding of densely packaged spooled strip stock, usually
of aluminum, thermoplastic graphite epoxy, or other composite material.
Pulltrusion or rolltrusion forming at elevated temperature is used on the
composite materials, and cold roll forming is the usual forming method
employed on aluminum.
For structures of increased size, which requires volumes of material beyond
the capabilities of these methods to produce, a new technique is required
that will utilize the technologies and advantages of these prior assembly
and deployment methods and will additionally possess the capabilities to
produce structures vastly larger in size. Such a technique must be highly
mechanized and automated to have the performance and cost effectiveness
required of it.
SUMMARY OF THE INVENTION
The present invention is an automated assembly, operation, maintenance, and
repair system for a large space structure using programmed,
computer-controlled, man-supervised automated equipment. The space
structure comprises a plurality of trusses and truss junctions, each truss
being made up of a plurality of individual struts and nodes. The truss
assemblies are progressively built by an assembler trolley as the trolley
crawls along the constructed truss.
The trolley comprises a forward crawler and a rear crawler joined by an
articulated coupler. The crawlers are carried along the structure by belt
transports incorporating grippers that engage the truss sructure at the
nodes.
Manipulator arms for strut and node assembly are located on the forward
crawler, and the majority of control, power, and communication systems are
located in the rear crawler. Cargo canisters filled with component parts
for constructing the space structure are carried by the forward crawler.
The space structure configuration is determined by the arrangement of the
individual struts and nodes during the assembly process.
The rear crawler may also contain a man support system so that crewmen may
come aboard to assist in the construction or make necessary repairs. It
may also carry spare struts, nodes, and manipulator arms which, if
required, are removed and installed by the manipulator arms on the forward
crawler of a companion trolley.
The size of the structure to be fabricated in space is unlimited, since the
trolley is capable of accepting the resupply of structural component parts
from an orbiting cargo vehicle which may shuttle back and forth from earth
to orbit.
The space structure will provide for the mounting of solar array blankets,
solar or microwave reflector surfaces, focal point support structures and
bolt-on components as for example, attitude control system, scientific
instruments, and various electronic communication, computation, and
control devices.
It is an object of the invention to provide synergistically compatible
structures and an autonomous, self-regulating assembler device that may be
monitored, supervised, and when necessary operationally modified by remote
sensing and control.
It is an object of the invention to provide structural truss-frame
arrangements that permit the assembler trolley to both assemble the
structure and then have access to any part of the structure to deliver and
attach add-on components or to dismantle, modify, or repair the structure.
It is an object of the invention to provide a light-weight structure,
wherein reaction loads from the assembler trolley are reacted only at
specific hard points for efficient distribution into the structure.
Another object of the invention is to provide a method for assembling the
structure while the trolley is moving at a constant rate such that inertia
loads imposed on the assembled structure during the manipulation of
components are held below the design limits of the structure.
Another object of the invention is to provide autonomous and remotely
monitored/controlled sensor systems that may stop the motion of the
trolley so that corrective procedures may be instituted by pre-programmed
and/or man-in-the-loop activities.
Another object of the invention is to provide struts and strut attachment
nodes that may be efficiently stowed in and deployed from canisters
carried on the assembler trolley, said canisters being capable of
replenishment from a cargo vehicle.
Another object of the invention is to provide an assembly device which has
significantly reduced power requirements to those required for systems
utilizing in-orbit material forming, brazing, or welding.
Another object of the invention is to provide an assembly device which
requires no large jigs or fixtures for assembly operations.
It is also an object of the invention to provide struts and strut nodes
that are nestable to permit efficient high-density storage in easy to
handle canisters.
The above and other objects and advantages of the invention will appear
more fully hereinafter from a consideration of the following description
taken together with the accompanying drawings, wherein one embodiment of
the invention is shown by way of example. It should be understood however,
that the drawings are for the purposes of illustration only and are not to
be construed as defining or limiting the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings, wherein like reference characters designate like parts
throughout the various views:
FIGS. 1, 2, and 3 are perspective views of typical large structures
assembled by the disclosed method.
FIG. 4 is an enlarged view of a portion of a structure taken substantially
in the area indicated by circular section-line 4 of FIG. 1.
FIG. 5 is an enlarged view of a single structural bay taken substantially
at the area indicated by circular section-line 5 of FIG. 4.
FIG. 6 is a perspective view of an expanded strut.
FIG. 7 is a perspective view of a compressed strut.
FIG. 8 is a partial view of the open isogrid structure of a strut taken
substantially at the area indicated by circular section-line 8 in FIG. 7.
FIG. 9 is a partial view of a center portion of the strut taken
substantially at the area indicated by circular section-line 9 in FIG. 6.
FIG. 10 is a partial view of the strut oval end taken substantially at the
area indicated by circular section-line 10 in FIG. 6.
FIG. 11 is a partial view of the flat end of a strut taken substantially at
the area indicated by circular section-line 11 in FIG. 6.
FIG. 12 is a cross section of the center strut area taken substantially
from a plane indicated by line 12--12 in FIG. 9 showing the strut
partially compressed.
FIG. 13 is a cross section of the strut taken in the same area as FIG. 12
showing the strut in the fully expanded condition.
FIG. 14 is a perspective view of a fixed geometry strut having a hat cross
section.
FIG. 15 is a perspective view of a structural nodes positioned as indicated
by circular section-line 15 in FIG. 5.
FIG. 16 is a series of cross sections of the node spring legs taken
substantially from a plane indicated by line 16--16 in FIG. 15.
FIG. 17 is a view of a stack of structural nodes positioned as indicated by
circular section-line 17 in FIG. 5.
FIGS. 18 through 20 show the junctions of different numbers of truss
structures coming together to form a structural joint, and are taken
substantially at the areas indicated by circular section-lines 18, 19 and
20 respectively in FIG. 4.
FIG. 21 is a top view of the junction shown in FIG. 18.
FIG. 22 is a side view of the junction shown in FIG. 21.
FIG. 23 is a top view of the junction shown in FIG. 19.
FIG. 24 is a side view of the junction shown in FIG. 23.
FIG. 25 is a top view of the junction shown in FIG. 20.
FIG. 26 is a side view of the junction shown in FIG. 25.
FIG. 27 is a perspective view of a structural node used at truss junctions.
FIG. 28 is a perspective view of the assembler trolley.
FIG. 29 is a perspective view of the crawler coupler shaft.
FIGS. 30 through 34 are perspective views showing the maneuvering of the
forward crawler relative to the rear crawler.
FIG. 35 is a perspective view of the forward crawler.
FIGS. 36 through 39 are enlarged partial views of the transport belt and
grippers of the forward crawler showing operations of the node grippers.
FIG. 40 is a perspective view of the assembler trolley within a truss
structure.
FIG. 41 is an enlarged cross-section of the forward crawler primary
structure taken substantially from a plane indicated by line 41--41 in
FIG. 35.
FIGS. 42 and 43 are views of the struts and nodes storage canister.
FIG. 44 is a perspective view of a tubular telescoping manipulator arm.
FIG. 45 is a perspective view of the rear crawler.
FIGS. 46 through 56 indicate the series sequential steps of the forward
crawler assembling a truss structural bay.
FIG. 57 is a perspective view of a strut inspection device.
FIG. 58 is a perspective view of a telescoping triangular truss manipulator
arm.
FIGS. 59 and 60 are schematic views of the dog-disc pitch drive belt
system.
FIG. 61 is an enlarged view of the bottom surface of the manipulator arm
working end showing the dog-disc tool.
FIG. 62 is a partial side view of the manipulator arm and includes a
cross-section through the dog-disc tool.
FIG. 63 is a cross-section of the manipulator arm taken substantially from
a plane indicated by line 63--63 in FIG. 61.
FIG. 64 is a partial side view of the manipulator arm taken in the area of
the cross-section line 64--64 of FIG. 63.
FIG. 65 is a cross-section of the manipulator arm taken substantially from
a plane indicated by line 65--65 in FIG. 61.
FIG. 66 is a view of the dog-disc tool in several prime positions.
FIGS. 67 through 72 indicate the parallel sequential steps of the forward
crawler assemblying a truss structural bay.
FIGS. 73 and 74 are views of the trolley wherein the forward crawler is
assemblying a truss junction.
FIG. 75 is a view showing the assembler trolley passing through a truss
junction.
FIG. 76 is a schematic presentation of the control and monitor systems for
the assembler trolley.
FIG. 77 is an end view of an alternate embodiment of the forward crawler
located within the structural truss.
FIGS. 78 through 81 show the assembly sequence for a platform structure
comprising a plurality of side-by-side disposed triangular trusses.
FIG. 82 is a perspective view of the structural node utilized in the
structure shown in FIGS. 78 through 81.
FIGS. 83 and 84 show a method of deploying a working surface on the
completed truss structure.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to the drawings in detail, FIGS. 1, 2, and 3 illustrate
respectively a planar space-deployed structure, a cylindrical parabola
structure, and a paraboloidal dish structure. In order to appreciate the
magnitude of these structures certain basic dimensions are shown by way of
example. These structures may cover tens or hundreds of square miles in
area, having no counterpart here on earth.
FIG. 4 is an enlarged view of that portion of the planar structure of FIG.
1 shown by view line 4. Again a dimension of the structure is shown by way
of example of the magnitude of the structure.
FIG. 5 is an enlarged view of that portion of the truss structure of FIG. 4
shown by view line 5. There are again illustrated several structural
dimensions, which are only by way of example, so that by comparing FIGS.
1, 4, and 5 one may gain an appreciation and understanding of the
relationship of the basic truss to the overall structure.
Referring again to FIG. 4, it is seen that the upper and lower faces of the
structure are composed of trusses 10 forming coincident equilateral
triangular patterns. These faces are joined by triangulated web trusses 11
to in effect form a space frame isogrid structure. Because of its
configuration, and because all members perform equally well in tension and
compression, the structure has excellent structural efficiency and
stability. This is particularly true with respect to torsional loading,
about an axis parallel to the structural plane, as well as bending and
in-plane loading. Structures employing guy wire cross members are
inherently not as efficient, since the wires contribute to structural
strength or stiffness only when loaded in tension.
In FIG. 5 it is seen that the basic truss structure is of a triangular
cross section, and is constructed of a plurality of tapered struts 12,
each strut having a circular cross section which tapers to a flat section
at each end which terminates on nodes 13. Each of the three sides of a
truss bay comprises a rectangle bounded by four struts and one diagonal
strut. This produces six strut terminatives per node 13, thereby allowing
all nodes to be of the same shape and configuration.
FIG. 6 shows a tapered strut 12 in detail. The strut comprises two conic
monocoque shells joined at their bases to define a taper in both
directions from the mid section. Portions of the shell are relieved and
lightened with an open isogrid hole pattern, shown in greater detail in
FIG. 8. Each half 14 and 15 of the conic shell is attached together by
means of a longitudinal piano hinge 16, shown in greater detail in FIG. 9.
FIG. 7 shows the tapered strut 12 in the flat stowed position. Each conical
half shell 14 and 15 (see FIG. 9) is compressed flat for storage, the
movement accommodated by a combination of the spring characteristics of
the conical shell sections and the piano hinge 16. The shell halves 14 and
15 are extremely light gage material and may be constructed of any
suitable metal such as aluminum or stainless steel, or any suitable
composite material such as for example, graphite epoxy. The diametrically
opposed longitudinal piano hinges 16 and spring action due to pre-forming
of the strut material allows the strut to assume the expanded state when
released from the stowed condition.
The relatively large diameter at the center of the strut produces low
stowed-state stresses and permits a circular cross section to develop when
released from the stowed state. Near the ends of the strut the reduced
diameter causes higher stowed-state stresses and allows for only an oval
cross section in the deployed state, which is more clearly seen in FIG.
10. It is necessary that transitions take place between different cross
sections along parts of the strut length. Therefore, the hinges 16 include
some small localized end play to eliminate hinge binding during strut
expansion. Actually, because of the small departure of the hinge line from
a straight line and the available elasticity in the thin gage strut
material, the binding action is tolerable even if no end play is included.
Deployed state roundness at the ends of the strut can be achieved or
maximized by the staggered slots 17, shown in FIG. 10.
FIG. 11 shows a plurality of strut ends in their relative positions in a
stack of stowed struts. Both ends of the strut are flat and each end
includes two circular holes 18 for attachment to the nodes 13. Located
adjacent to the two node mounting holes 18 is a keyway 19. Also in FIGS. 6
and 7 it will be noted that along the strut length there are other
periodically space keyways 19. As will be explained in more detail later,
these keyways 19 are used to hold the struts in their stowed state. The
keyway in the flat part of the strut ends is used to handle the strut
during and after expansion, and it will be noted that the keyways are
alternately clocked 90 degrees on adjacent struts in the stowed position
as shown in FIG. 11.
Mounted longitudinally to the conical shell at the mid point of the strut
is a plurality of spring clips 20. These clips bridge the two transverse
slots between the bases of the two conical shells, and when the shells are
compressed these clips are disengaged, as shown more clearly in FIG. 12.
When the strut is fully expanded the clips 20 engage the strut shell, as
shown in FIG. 13, to provide structural continuity between the two conical
portions of the strut.
For stowage the struts are stacked side by side in the compressed position
to achieve high packaging density. As indicated the keyways 19 are clocked
90 degrees between successive struts in the stack. As will be subsequently
explained this is done to implement the retaining, release and engagement
of struts in the structural assembly process.
A fixed geometry strut 21 is shown in FIG. 14. It is of a generally
hat-shaped cross-section and tapers towards each end from a maximum cross
section at strut mid point. Both ends of the strut are flat and include
the two node attachment holes 18. This fixed geometry strut 21 does not
have the structural efficiency and column/beam stability of the expandable
strut 12, and while it must be heavier than the expandable strut for
comparable performance, it is simpler to fabricate, stack and deploy.
Because no prestresses exist in the stacked condition of the fixed
geometry struts 21, the number of keyways 19 for hold down purposes may be
less than those needed in the deployable strut 12. As in the deployable
strut, excess cross-section is reduced by isogrid hole patterns.
Tapered struts, of the fixed geometry 21 and expandable types 12 are
inherently more efficient than constant cross-section struts. This is
especially true of structures primarily designed for stiffness. The
expandable strut 12 is the preferred embodiment for most structural
applications and is the type shown in all figures except FIG. 14.
FIGS. 15 and 17 illustrate enlarged views of two nodes 13 taken from FIG.
5. The node in FIG. 15 has six spring leaf legs attached to a solid hub 22
containing a keyway 19. As seen in FIG. 16, each leg consists of two
spaced leaves 23 and 24, two locating pins 25 attached to leaf 23 that
engage the strut ends 12, and a lead-in flare 26 that minimizes the
necessary alignment between the strut and node at assembly. As indicated
in FIG. 16 after the strut end 12 is inserted between the spring leaves 23
and 24 it must be tilted to pass over the pins 25 to be finally assembled.
FIG. 17 shows a plurality of stacked nodes 13. As in the case of the
struts, the keyways 19 are clocked 90 degrees between successive nodes in
the stack. A shaft mounted dog 27 retains the stacked nodes when the dog
is crosswise to the keyway. When the dog 27 is rotated into alignment with
the keyway 19 the node at the top of the stack can be removed while the
node directly below it is inhibited by the dog 27. This is also the type
of release and containment system used for the struts, and its use will be
described hereinafter.
Note that the lead-in flares 26 of leaves 23 and 24 are staggered along the
node legs. This allows the space between the leaves to be occupied by the
alternately located flares 26 so that nodes may be stacked flush for
stowage.
FIGS. 18, 19 and 20 illustrate three different truss junction forms that
may be utilized in various structures of the type illustrated in FIG. 4.
Further, FIGS. 21 and 22 are plan and elevation views respectfully of the
truss junction shown in FIG. 18; FIGS. 23 and 24 are similar views of the
truss junction shown in FIG. 19; and FIGS. 25 and 26 are plan and
elevation views of the truss junction shown in FIG. 20. The arrangements
of struts forming the truss junctions provide structural continuity
between trusses terminating on the junctions, while at the same time they
provide uninhibited communication between the internal cross sections of
these trusses. This is essential for free movement throughout the entire
structure of a trolley, to be later described, and because of these unique
truss junction characteristics it is possible for an assembler trolley to
pass through the junction when crawling between the insides of two trusses
terminating on the junction. The assembler trolley assembles both the
trusses and junctions by moving along the inside of the completed truss
structures. When the assembly is completed the trolley is then capable of
crawling to any part of the assembled structure.
As was previously described, the nodes 13 in each individual truss
structure are of the same arrangement of all points along the truss.
However the strut nodes located in the truss junctions may be of a
different arrangement than the nodes 13 used in the individual trusses. A
typical truss junction node 28 is shown in FIG. 27. For specific truss
junctions the node will vary in the number of additional legs and their
orientation, however any node arrangement must be of a shape that will
allow high density stacking. The most efficient stacking results from
stacking similar or comparable nodes in common stacks. In some cases mixed
stacking of different nodes is possible without loss of stacking
efficiency.
An important feature of all nodes 13 and 28 is the solid hub 22 to which
the spring leaf legs 23 and 24 are attached. These hubs are configured to
be engaged by tong type grippers from both the inside and outside of the
truss or truss junction structure. Because of this important feature,
engagement between the assembler trolley and the structure can be
primarily limited to the node hubs 22, and the trolley can function on
either the inside or outside of the trusses and truss junctions. Since the
nodes are also the strongest, most reinforced, parts of the structure they
are the best places to apply the necessary trolley actuation loads. A
coincident common point of intersection is provided by the geometry for
all lines of force acting on the spring leaf legs and the hub of each
node.
The assembler trolley 30 is shown in a perspective view in FIG. 28. The
trolley performs three primary functions:
It stows the structural component parts in high density pre-packaged,
easy-to-handle, canisters;
It assembles the component parts into a structural arrangement, either by
means of a pre-programmed scenario or by a remote control/monitor system;
And it is used for access to any part of the structure to make repairs,
modifications, or install non-structural items such as, for example, solar
blankets, reflector surfaces, scientific instrumentation, attitude control
devices, and electronic packages.
The trolley 30 comprises a foward crawler 31 and a rear crawler 32 which
are joined together by a coupler shaft 33. The forward crawler 31 mounts
twelve manipulator arms 34 and 35, four manipulator arms disposed on each
of the three exterior side surfaces of the forward crawler 31. The three
manipulator arms 34 at the forward end and the three manipulators 34 at
the rear end of the forward crawler 31 have single stage axial extension
capability, while the six manipulator arms 35 located in the mid area of
the crawler, two per side, have two stage extension capability.
The twelve manipulator arms, 34 and 35, have rotary drives disposed at the
base end where attachment is provided to the forward crawler 31. Linear
drives are also provided to retract and extend the manipulators,
permitting up to a three to one change in reach. All manipulator arm drive
functions are preprogrammed and numerically controlled. The total number
of manipulator arms disposed on the forward crawler 31 is a function of
the desired assembly rate of the trolley 30. As few manipulator arms as
two per side, a total of six on the forward crawler, 31, may accomplish
the assembly task. However the maximum assembly rate is attained when
approximately seven manipulator arms are disposed on each side of the
crawler, a total of twenty-one manipulator arms located on the forward
crawler 31. This optimum number of manipulator arms applies to the
triangular truss described herein, and other structural forms may require
more or less manipulator arms. The functions performed by the manipulator
arms and two embodiments of these arms will be described in greater detail
later herein. It should be understood that if desired to accomplish
certain assembly functions, manipulator arms may also be located on the
rear crawler 32.
In FIG. 29 is shown a more detailed view of the coupler shaft 33, which
connects forward crawler 31 with rear crawler 32. The coupler shaft 33 is
connected to the rear crawler 32 by means of a universal joint 36, having
an azimuth pivot pin 37 and an elevation pivot pin 38. Rotation around the
azimuth pivot 37 is controlled by azimuth drive motor 39 which drives a
gear head which mates with gear teeth contained on azimuth pivot pin 37,
the gear drives not shown. In a like manner rotation about the elevation
point 38 is controlled by elevation drive motor 40.
Located near the forward crawler 31 is a second universal joint 42, having
a similar arrangement to the first universal joint 36. Rotation around the
azimuth pivot 43 is controlled by azimuth drive motor 45, and rotation
around the elevation pivot 44 is controlled by elevation drive motor 46.
The distance between universal joint 36 and universal joint 42 is variable
by means of shaft 48 telescoping within larger diameter shaft 49.
Displacement of inner shaft 48 is controlled by a linear drive 50, which
comprises a linear drive motor 51 that drives a pinion which in turn is
engaged with a gear rack mounted on the shaft 48, in a conventional rack
and pinion arrangement. For clarity of FIG. 30 none of the gear drive
arrangements are shown, since all are of a conventional arrangement well
known by those skilled in the art. The linear drive 50 also provides a
keying function so that no axial rotation of inner shaft 48 is possible
relative to outer shaft 49.
Attached to the forward universal joint 42 is a rotary drive 52, comprising
a drive motor 53 that drives a gear that is fixedly attached to the end of
a forward shaft 54 such that drive motor 53 may rotate shaft 54 around its
longitudinal axis. The forward shaft 54 is shown in FIG. 30 fully
telescoped within the forward crawler 31. The shaft 54 may be extended
from the crawler 31 by means of a linear drive 55 that is attached to the
forward crawler 31. The linear drive 55 functions in the same manner as
linear drive 50.
From the foregoing it may be seen that the distance between the forward
crawler 31 and rear crawler 32 is variable by means of linear drive 50
extending or retracting inner shaft 48 within outer shaft 49. Further, it
may be seen that the forward crawler 31 may be displaced in azimuth
relative to rear crawler 32 by actuation of azimuth drive motor 39 and/or
azimuth drive motor 45, and in a like manner displacement in elevation may
be accomplished by elevation drive motor 40 and/or elevation drive motor
46. Longitudinal rotation of forward crawler 31 relative to rear crawler
32 is accomplished by actuation of rotary drive 52. And finally, it will
be observed that the distance of the forward universal joint 42 from the
forward crawler 31 is variable by means of linear drive 55 extending and
retracting the forward shaft 54 within the foward crawler 31.
Thus, if inner shaft 48 is extended the two crawlers move apart as shown in
FIGS. 30 and 31. If azimuth drive motor 39 and elevation drive motor 40 of
rear universal joint 36 are actuated the forward crawler 31 will be
displaced in azimuth and elevation from rear crawler 32, as shown in FIG.
32. The longitudinal axis of the forward crawler 31 will be parallel with
the longitudinal axes of outer shaft 49, inner shaft 48, and forward shaft
54, and will be skewed relative to the longitudinal axis of rear crawler
32. If the azimuth drive motor 45 of the forward universal joint 42 is
driven an equal amount in the opposite direction to azimuth motor 39, and
elevation motor 46 is driven an equal amount in the opposite direction to
elevation motor 40, the forward crawler 31 will remain disposed in azimuth
and elevation relative to rear crawler 32, but the longitudinal axes of
the two crawlers will be parallel as shown in FIG. 33. The forward crawler
31 may now be moved forward from the forward universal joint 42 by
actuating the forward linear drive 55 which extends forward shaft 54, as
shown in FIG. 34. The forward crawler 31 may also be rolled about the
forward shaft 54 by actuating the rotary drive 52. In this regard, it may
be understood that the movements of the crawlers about their three major
axes may be described as ROLL (controlled by rotary drive 52) PITCH
(controlled by elevation motors 40 and 46) and YAW (controlled by aximuth
motors 39 and 45).
The FIGS. 30 through 34 illustrate only one example of the displacement
maneuvering of forward crawler 31 relative to rear crawler 32, but from
this example it should be clear what the displacement capabilities are,
and it should be understood that all necessary drives may be operated
simultaneously if desired to effect a smooth transition to the new
position of crawler 31, rather than the stepped displacements described in
the example.
FIG. 35 is a more detailed view of the forward crawler 31, wherein it may
be seen that a pair of pulleys 56 are mounted at opposite ends of each
edge formed by two intersecting side surfaces of the crawler. A total of
six pulleys 56 are so located on the crawler. A runaround, or continuous,
belt 57 is wrapped around each pair of pulleys 56, and rests in a belt
guide 58. The belt guide 58 is attached to the crawler by a plurality of
belt guide supports 59. Attached to each belt 57 are node grippers 60, one
of which is shown in more detail by the enlarged view in FIG. 36.
FIG. 36 illustrates the node gripper 60 that is located on the lower belt
57 near the forward pulley 56 of FIG. 35. It will be seen that belt 57 is
of a generally hexagon cross section and is guided on the four side
surfaces by belt guide 58. The inner surface of the belt 57 comprises a
plurality of serrations or what may generally be described as rack gear
teeth 62. These teeth 62 engage mating teeth on the pulleys 56, each of
which is driven by a motor 64, best seen in FIG. 35. These motors, 64 like
all the drive motors utilized on the assembler trolley 30 are direct
current stepping motors that are servo controlled by pre-programmed
controllers.
The node gripper 60 comprises a spreader bar 66 and a pair of gripper jaws
68, one pivotally mounted to each end of spreader bar 66. The gripper jaws
are rotated by means of the up and down stroke of jaw actuator rod 70
within the jaw actuator guide 71, down motion causing the jaws to open and
upward motion causing the jaws to close. At the top end of the jaw
actuator rod 70 is a spherical surface 72 which functions as a cam
follower, and at the bottom end of the rod 70 is a second
spherical-surfaced cam follower 73. The actuator guide 71 is fixedly
mounted within the belt 57 and carries the node gripper 60 along the belt
as the belt is driven from one pulley 56 to the other pulley 56. At points
along the inside top surface of the belt guide 58 are linear ramps which
serve as cams to force the jaw actuator rod 70 down to open the jaws 68.
As the node gripper 60 approaches a structural strut node 13, see FIGS. 5
and 15, the lower cam surface 73 of jaw actuator rod 70 is forced upward
by contact with hub 22 of strut node 13, thereby causing the gripper jaws
68 to close and grip the strut node 13. This may best be seen in FIGS. 37,
38 and 39.
In FIG. 37 is shown a node gripper 60 attached to the lower portion of belt
57. This node gripper 60 is in the opened position and is located on the
belt in the same manner as the gripper shown in FIG. 36. On the upper
portion of belt 57 is another node gripper 60 in the closed position,
since the actuator rod 70 was forced up by the ramp in belt guide 58. This
normally is the position for gripping a strut node, such as is shown in
more detail in FIG. 38. Here it is seen that the jaws 68 have closed and
locked on the hub 22 of a strut node 13. It should be noted that in this
particular instance the crawler is within the truss structure 10 and is
gripping the inside surface of node 13. As was previously stated, the
trolley may travel inside of a truss structure 10 or on the outside of a
truss, and in FIG. 39 is shown a strut node 13 being engaged on the
outside surface by a gripper on the upper portion of belt 57. The same
arrangement for a gripper 60 located on the lower portion of belt 57 is
also shown, and it should be clear that the trolley may travel externally
either above or below a truss structure.
In FIG. 40 the trolley 30 is located within the truss structure 10. It will
be noted that the rear crawler 32 has three belts 57 and six pulleys 56 of
the same general arrangement as the forward crawler 31. The three node
grippers 60 of the rear crawler 32 are gripping the three strut nodes 13
located at the truss station designated as 113, and the three node
grippers 60 of the forward crawler 31 are gripping the three strut nodes
13 located at the truss station designated as 213. The trolley may
continue through the truss structure 10 by driving in unison all the belt
drive pulleys 56, and as it passes the next set of strut nodes 13 a second
set of node grippers 60 on the belts 57 will grip the nodes while the
grippers now locked will open. Another method to move the forward crawler
31 in the truss structure is to release the node grippers at truss station
213, while the rear crawler 32 maintains a grip on nodes at truss station
113, and then extend or retract the crawler coupler shaft 33.
FIG. 41 shows a perspective view and cross-section of the primary structure
of forward crawler 31. At the approximate geometric center of the crawler
is the longitudinal guide 76, within which the forward control shaft 54
(FIG. 29) moves fore and aft. The forward crawler structure is shaped to
form six long rectangular cargo compartments 78 and six triangular
cross-section control shaft raceways 80. Disposed within each of the
control raceways 80 are a plurality of coupling drive shafts 82 which
reach approximately the full length of the raceways 80 and are journalled
for rotation therein. Spaced along the bottom surface of each cargo
compartment 78 are a plurality of drive couplings 84 which are engaged by
means of miter gears to the coupling drive shafts 82 so that rotation of
the shafts 82 will rotate the associated couplings 84.
FIGS. 42 and 43 are perspective views of a cargo canister 90 which is sized
to fit within the canister cargo compartment 78 of the forward crawler 31.
Stowed within the canister 90 are snugly stacked struts 12 and strut nodes
13. At the bottom of each stack of struts 12 and nodes 13 is located a
stack advance plate 92. A plurality of lead screws 94 pass through the
keyways 19 of struts 12 and nodes 13, through a stack advance plate 92,
and through the bottom wall of the canister 90, terminating at the bottom
end with a drive coupling 96 which is shaped for engagement with a mating
coupling 84 in the cargo compartment 78 of the forward crawler 31. At the
top end of each lead screw 94 is mounted a dog 27 which is shaped to pass
through keyway 19 when properly oriented, but to retain the struts 12 and
nodes 13 at all other rotated positions. The stack advance plate 92 is
threaded for engagement with the lead screw 94 so that rotation of the
lead screw causes the plate 92 to advance. It should be noted that no lead
screw or dog is disposed within the keyway located at either end of the
struts.
The thread pitch of lead screw 94 is a function of the thickness of an
individual strut 12 or node 13. If the keyways 19 are alternately clocked
as shown in FIG. 11, then the dogs 27 must alternately rotate 450 degrees
once to align with a keyway 19 and rotate 270 degrees the next time to
align with the next clocked keyway, thereby requiring a repeated cycling
of 270 degrees rotation followed by 450 degrees and then 270 degrees
rotation, etc. The average rotation of the lead screw is 360 degrees per
thickness of strut, but the maximum and minimum rotations must be
accounted for in the thread pitch and the compressability of the stack of
struts or nodes. Such an arrangement requires only two configurations of
struts or nodes, that is keyways at 0 degrees position and 90 degrees
position. Another arrangement requires four configurations of struts and
nodes, wherein keyways are clocked at 0 degrees, 90 degrees, 180 degrees
and 270 degrees. With this arrangement the lead screw 94 is rotated 450
degrees each cycle to align the dog 27 with the next keyway 19, thus
eliminating the variable rotation required by the two position keyway
arrangement. Either arrangement may be utilized with satisfactory results.
The function of the lead screw 94 and dog 27 is to allow only one strut 12
or node 13 at a time to be removed from the canister.
Thus it may be seen that the forward crawler 31 is capable of carrying a
large quantity of struts and strut nodes in the six canisters 90 stowed in
the six cargo compartments 78.
If one man can assemble a given structure in one-hundred hours, the task
may be described as a one-hundred manhour task. However, this does not
necessarily imply that the task could be accomplished with the arithmetic
equivalent of one-hundred men working for one hour. Analysis may reveal
however that there does exist an optimum number of men to assign to the
task to complete it in the minimum number of manhours. For example, three
men may ac | | |
