U.S. patent application number 14/667595 was filed with the patent office on 2015-12-24 for methods for digital composites.
This patent application is currently assigned to MASSACHUSETTS INSTITUTE OF TECHNOLOGY. The applicant listed for this patent is Kenneth C. Cheung, Neil Adam Gershenfeld. Invention is credited to Kenneth C. Cheung, Neil Adam Gershenfeld.
Application Number | 20150367457 14/667595 |
Document ID | / |
Family ID | 45934395 |
Filed Date | 2015-12-24 |
United States Patent
Application |
20150367457 |
Kind Code |
A1 |
Gershenfeld; Neil Adam ; et
al. |
December 24, 2015 |
Methods for Digital Composites
Abstract
In exemplary implementations of this invention, a digital
material comprising many discrete units is used to fabricate a
sparse structure. The units are reversibly joined by elastic
connections. Each unit comprises fiber-reinforced composite
material. Each unit is small compared to the sparse structure as a
whole. Likewise, in a sparse structure made from this digital
material, the number of types of units is small compared to the
total number of units. The digital material is anisotropic. This
anisotropy may be due to different fiber orientations within each
unit. Furthermore, different units in a single sparse structure may
be oriented in different directions and in different, non-parallel
planes. In some cases, the digital material is reinforced with
carbon fibers, and connections between units are stronger than the
units themselves. The small discrete units may be assembled into a
strong, lightweight sparse structure, such as an airframe.
Inventors: |
Gershenfeld; Neil Adam;
(Somerville, MA) ; Cheung; Kenneth C.; (Boston,
MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Gershenfeld; Neil Adam
Cheung; Kenneth C. |
Somerville
Boston |
MA
MA |
US
US |
|
|
Assignee: |
MASSACHUSETTS INSTITUTE OF
TECHNOLOGY
Cambridge
MA
|
Family ID: |
45934395 |
Appl. No.: |
14/667595 |
Filed: |
March 24, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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13277103 |
Oct 19, 2011 |
8986809 |
|
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14667595 |
|
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61394713 |
Oct 19, 2010 |
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Current U.S.
Class: |
29/428 |
Current CPC
Class: |
Y10T 29/49828 20150115;
B32B 5/12 20130101; Y10T 29/49826 20150115; Y10T 428/24 20150115;
B23P 11/00 20130101; B64C 3/48 20130101; Y10T 428/24008 20150115;
B32B 5/26 20130101; B64C 1/08 20130101; B64C 1/06 20130101 |
International
Class: |
B23P 11/00 20060101
B23P011/00 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] This invention was made with U.S. government support under
Grant Number W911NF-08-1-0254, awarded by the Army Research Office.
The government has certain rights in this invention.
Claims
1. The automated process of assembling a set of discrete units into
a sparse structure, wherein: each unit comprises composite
material, and the automated process comprises reversibly connecting
each of the units to at least one other of the units, by
connections that are flexural locking mechanisms, pinned locking
mechanisms, or compression clips.
2. The automated process of claim 1, wherein some of the
connections are elastic connections that are created, for each
respective connection, by pushing a unit against the sparse
structure when the sparse structure is partially assembled, the
push being given by an automated assembly device that moves with
one degree of freedom.
3. The automated process of claim 1, wherein the sparse structure
comprises pinned units, and in order to add a new pinned unit, an
assembler device removes pins, attaches the new pinned unit, and
reattaches the pins.
4. The automated process of claim 1, wherein, due to elastic
averaging, the automated process assembles a sparse structure with
a precision (with respect to variation in absolute physical
dimensions) that exceeds the precision (with respect to variation
in absolute physical dimensions) of the units that comprise the
sparse structure.
5. The automated process of claim 1, wherein the process is
controlled by a computer algorithm and the mechanical properties of
the sparse structure produced by the process may be tuned by
changing one or more of the following: (a) the ratio of different
types of the units used to assemble the sparse structure, and (b)
the geometry of the sparse structure.
6. The automated process of claim 1, wherein the composite material
is reinforced with fibers.
7. The automated process of claim 1, wherein at least some of the
units in the set are layered, and for each layered unit, the
composite material comprises multiple layers reinforced by fibers,
each fiber having an orientation, the average orientation of the
fibers in a layer defining an average fiber orientation for that
that layer, and the average fiber orientation for at least some of
the layers of that specific unit differing by more than 45 degrees
from the average fiber orientation for at least some of the other
layers of that specific unit.
8. The automated process of claim 1, wherein at least one
individual unit in the set has one or more holes through it,
includes at least one elongate subelement that has at least a first
and a second longitudinal end, includes some fibers that extend
from a first region that is at or adjacent to the first
longitudinal end to a second region that is at or adjacent to the
second longitudinal end, and includes other fibers that are
oriented in a loop around at least one of the one or more
holes.
9. The automated process of claim 1, wherein the connections
between connected units occur at certain positions on and relative
to the connected units, and wherein, in response to loading of the
sparse structure, a reversible deformation of a lattice in the
sparse structure occurs, said reversible deformation being due at
least in part to reversible change in at least some of said
positions at which said connections occur.
10. The automated process of claim 1, further comprising connecting
at least one actuator to the sparse structure, wherein the at least
one actuator is configured for elastically deforming the
structure.
11. The automated process of claim 1, wherein at least some
specific units in the set are elongate and each of these specific
units transfer, or is adapted to transfer, axial load along its
long dimension to other units that are connected to, and aligned
orthogonally to, said specific unit.
12. The automated process of claim 1, wherein some of the units in
the set comprise elongated compression units, each of the
compression units being adapted to elastically deform further, from
its unloaded state, in response to compressive loading of a
particular magnitude along its long dimension than to tension
loading of the same magnitude along its long dimension.
13. The automated process of claim 1, wherein some of the units in
the set comprise elongated tension units, each of the tension units
being adapted to elastically deform further, from its unloaded
state, in response to tension loading of a specified magnitude
along its long dimension than to compressive loading of the same
specified magnitude along its long dimension.
14. The automated process of claim 1, wherein some of the
particular units in the set are elongate and these particular units
may be elastically connected by snapping the longitudinal end of
one unit, or the longitudinal ends of multiple units, into a notch
in another unit, which notch has a chamfered edge.
15. The automated process of claim 1, wherein the sparse structure
comprises nodes and elongate components, each of the nodes is
connected, or adapted to be connected, to three of the elongate
components, in each case at a point of connection, which point of
connection for any particular one of the elongate components is at
or adjacent to a longitudinal end of that particular elongate
component, each of the elongate components has a longitudinal axis
along its long dimension, which longitudinal axis may be curved or
may be straight, and the length of the longitudinal axis of each of
elongate components is the same.
16. The automated process of claim 1, wherein at least some of
units in the set are crossbar units, which crossbar units are
reversibly connected, or adapted to be reversibly connected, by
elastic connections, each of which elastic connections is formed by
a compression clip clipping together longitudinal ends of five
crossbar units, four of the five crossbar units being aligned in a
plane that is orthogonal to the long dimension of the fifth of the
five crossbar units.
17. The automated process of claim 1, wherein the sparse structure
is adapted to disintegrate, without exceeding the elastic limits of
the units in the structure.
18. The automated process of claim 1, wherein a first subset of the
units differs, in chemical composition or material property, from a
second subset of the units.
19. The automated process of claim 1, wherein some of the units
include electrical conductors and others of the units do not
include electrical conductors.
Description
RELATED APPLICATIONS
[0001] This application is a divisional application of U.S. patent
application Ser. No. 13/277,103, filed Oct. 19, 2011, now U.S. Pat.
No. 8,986,809, issued Mar. 24, 2015, which claims the benefit of
U.S. Provisional Application Ser. No. 61/394,713, filed Oct. 19,
2010, the entire disclosures of which are herein incorporated by
reference in their entirety.
FIELD OF THE TECHNOLOGY
[0003] The present invention relates generally to composite
materials.
SUMMARY
[0004] In exemplary implementations of this invention, a digital
material comprising many discrete units is used to fabricate a
sparse structure. The units are reversibly joined by elastic
connections. The connections allow force to be transferred among
linked units. Each unit comprises fiber-reinforced composite
material. Each unit is small compared to the sparse structure as a
whole. Likewise, in a sparse structure made from this digital
material, the number of types of units is small compared to the
total number of units.
[0005] In exemplary implementations, the digital material is
anisotropic. This anisotropy may be due to different fiber
orientations within each unit. For example, at least some of the
units may be laminates. In these laminates, there may be multiple
layers, with fibers oriented in different directions in different
layers. Or, for example, fibers in a single unit may be laid out
with different orientations (e.g., in some elongate units with
holes in them, some fibers may run around a hole, and other fibers
may run the length of the unit). Furthermore, different units in a
single sparse structure may be oriented in different directions and
in different, non-parallel planes.
[0006] In some implementations, the digital material is reinforced
with carbon fibers.
[0007] The small discrete units may be assembled into a very
strong, very lightweight sparse structure, such as a structural
element for an aircraft. This approach is contrary to a current
trend in aircraft manufacture, which is to build large, monolithic
parts made of composite materials. Conventionally, monolithic parts
are preferred over parts comprised of many small discrete units,
because of assembly complexity without robotic assemblers and
existing structural analysis and simulation paradigms. Further,
conventionally the connections between the discrete units are
thought of as weaker than the units themselves, creating weak links
that can fail when loaded.
[0008] However, in exemplary implementations of the present
invention, connections between units may be stronger than the units
themselves. This allows a sparse structure made of many discrete
units to be as strong as if it were made of a single monolithic
part. A cost of this approach is extra mass density, compared to
the mass density if a single monolithic structure of the same
sparse geometry is employed. The latter is not conventionally used
because of assembly complexity. When made from many discrete units,
strengthening the connections (between the small units) requires
extra weight and extra room. These can be accommodated by a sparse
geometry, which has plenty of empty space and tends to be
lightweight. For applications with distributed loading, such as
aircraft wing structures, sparse structures can meet strength
requirements at lower mass densities than conventional
aerostructures made (conventionally) from relatively few monolithic
parts. This is because there is extra material in the conventional
constructions that is required to redistribute loads onto the few
monolithic parts. The extra mass density cost of connections in the
digital material approach can meet or be less than the extra mass
density cost of load redistribution in conventional
constructions.
[0009] In exemplary implementations, the shape (and the functional
material properties) of the sparse structure can be tuned. Tuning
may be achieved by, for example, introducing voids, varying parts
ratios and varying geometry.
[0010] In exemplary implementations, the sparse structure is
elastically deformable. For example, the sparse structure may
include many small and simple actuators that together perform
enough work to result in large elastic deformations of the
structure.
[0011] Or, for example, when the sparse structure is loaded, a
reversible deformation (or reversible dislocation) of a lattice in
the sparse structure may occur. This reversible deformation (or
reversible dislocation) may be due, at least in part, to a
reversible change in at least some of the positions at which
connections between units exist, in response to loading. For each
of these changes in position of a connection, the connection
disconnects at one location on a unit and then reconnects at
another location on that unit or another unit.
[0012] In exemplary implementations, deformation (or dislocation)
may be designed and may be anisotropic based on the pattern of
assembly of the elements.
[0013] In some implementations, a unit transfers axial load to
other units that are connected to, and aligned orthogonally to,
that unit.
[0014] In some implementations, at least some of the units are
compression units. Each of the compression units is adapted to
elastically deform further, from its unloaded state, in response to
compressive loading than to tension loading.
[0015] In some implementations, at least some of the units are
tension units. Each of the tension units is adapted to elastically
deform further, from its unloaded state, in response to tension
loading than to compressive loading.
[0016] In some implementations, a sparse structure is assembled,
unit by unit, by snapping the longitudinal end of one unit, or the
longitudinal ends of multiple units, into a notch in another unit,
which notch has a chamfered edge.
[0017] In some implementations, the sparse structure comprises
multiple substructures. Each substructure includes three units that
are of equal length and are connected by a node. For example, in a
prototype, each substructure comprises three units that are of
equal length. The long axis of each unit in the substructure may be
a straight line, or may be curved (e.g., similarly to how the seams
of a soccer ball are curved). The substructures may be pre-loaded
when attached to the sparse structure, causing the units in the
substructures to bend.
[0018] In some implementations, the sparse structure defines a
curved surface.
[0019] In some implementations, the sparse structure defines a
highly porous surface or highly porous volume.
[0020] In some implementations, an elastic connection between the
units is formed by using a compression clip to clip together
longitudinal ends of five units, four of the five units being
aligned in a plane that is orthogonal to the long dimension of the
fifth of the five units.
[0021] In some implementations, the sparse structure is frangible.
In this case, the sparse structure is adapted to disintegrate,
without exceeding the elastic limits of the units in the structure,
upon a collision with another object. For this to occur, the
elastic limits of only the connections are exceeded.
[0022] In some implementations, the assembly of the discrete units
into a sparse structure is automated. The assembly devices may be
smaller than the sparse structure being assembled. For example, the
digital units may be assembled into a sparse structure using
massively parallel robotic assembly. Or, for example, in an
automated assembly process, some of the elastic connections between
the units may be created by snapping units into place. To do so, an
assembler device pushes a unit against a partially assembled sparse
structure to snap the unit into place. The assembler device may
move with one degree of freedom when it pushes the unit.
Alternately, for a structure comprising pinned units, in order to
add a new pinned unit, an assembler device may remove pins, attach
the new pinned unit, and reattach the pins
[0023] In some cases, the automated assembly process is controlled
by a computer algorithm.
[0024] In some implementations, due to elastic averaging, assembly
of the units produces a sparse structure with tolerances, for the
entire structure, that are more precise than the tolerances of the
individual units that comprise the structure.
[0025] In exemplary implementations, the digital material has many
benefits, such as: (a) reconfigurability, (b) error correction, and
(c) scalability. A digital material may have a longer service life,
because individual units may be replaced. For example, mobile units
travel over the structure to replace damaged units or adapt the
structure to new requirements. The digital material may allow for
highly porous large scale volumetric assemblies that can still
contain components that are extrinsic to the structure, such as
aircraft structures.
[0026] An important advantage of this invention, in exemplary
implementations, is spatial structural redundancy. Industry
conventionally looks to make structures out of as few parts as
possible, but this means that a single failure (or very low number
of failures) will result in total system failure. In contrast, in
exemplary embodiments of this invention, highly repetitive
volumetric structures may be used for applications with distributed
loading (buildings, aircraft, and bridges). If subjected to
localized stress on a part of the structure (e.g., from a
neighboring building in an earthquake, from a bird strike, or from
a car/truck accident), the structure may suffer localized damage
that does not affect the overall structural integrity as much as
would be the case with a conventional design.
[0027] Currently, in the aerospace industry, it is difficult to
join composites and to repair them. In contrast, in exemplary
implementations of the present invention, the structure comprises
units made of composite material, which units are linked by
multiple redundant force pathways, and repair is facilitated by the
fact that the units are easily replaceable.
[0028] In exemplary implementations of this invention, digital
material is assembled into space-filling sparse volumes. This is in
contrast to conventional construction with spars, ribs, and skins
(In some cases, however, this invention may be implemented as a
sparse structure covered at least in part by a skin).
[0029] The above description of the present invention is just a
summary. It is intended only to give a general introduction to some
illustrative implementations of this invention. It does not
describe all of the details of this invention. This invention may
be implemented in many other ways.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1A shows a unit that comprises fiber-reinforced
composite material.
[0031] FIG. 1B shows units of this type, linked in a chain.
[0032] FIG. 1C shows units of this type, linked to form a
surface.
[0033] FIG. 1D shows units of this type, linked to form a
volumetric structure.
[0034] FIG. 2A shows a tension unit.
[0035] FIG. 2B shows a compression unit.
[0036] FIG. 3A shows fiber orientations in a compression unit.
[0037] FIG. 3B shows fiber orientations in a tension unit.
[0038] FIG. 4 shows a pultrusion that is sliced to form units.
[0039] FIG. 5 shows bonded parts of a pultrusion.
[0040] FIGS. 6A through 6D show a compression unit comprising a
laminate material.
[0041] FIGS. 6E through 6F show a detailed view of a part of the
compression unit, in which the fiber orientation varies in
different layers of the laminate.
[0042] FIG. 7A shows two tension units, before their ends (one
longitudinal end of each unit) are snapped together through a
keyhole of a third compression unit, to elastically connect the
three units.
[0043] FIG. 7B shows these two tension units, as their ends are
being snapped together through that keyhole.
[0044] FIG. 7C shows these two tension units, after their ends have
been snapped together through that keyhole.
[0045] FIGS. 8A, 8C and 8D show different normal views, and FIG. 8B
shows a perspective view, of a sparse structure that comprises
tension elements.
[0046] FIGS. 8E, 8G and 8H show different normal views, and FIG. 8F
shows a perspective view, of a sparse structure that comprises
compression elements.
[0047] FIGS. 9A, 9B and 9C show different perspective views of a
sparse structure that comprises compression elements.
[0048] FIG. 10A shows a substructure comprising a node and three
units of equal length that are connected to that node.
[0049] FIG. 10B show an example of a type of unit that can be used
for assembly that generally requires only one type of primitive.
FIG. 10C shows a different example of such a unit.
[0050] FIG. 10D shows a substructure with curved arms.
[0051] FIG. 10E shows a portion of a sparse structure, assembled
from substructures, each node being connected with struts to three
other nodes.
[0052] FIGS. 11A, 11B and 11C are interaction potential diagrams
for (a) interaction between two neutral atoms or molecules,
according to the Lennard-Jones model, (b) interaction between
digital units with orthogonally pinned connections, and (c)
interaction between digital units with pre-loaded snap-fit
connections, respectively.
[0053] FIGS. 12A, 12B, 12C and 12D illustrate tunable multi-phase
elasticity. Specifically, these Figures are stress-strain diagrams
of bulk material in different scenarios.
[0054] FIGS. 13A and 13B shows units under compressive load and
tension load, respectively. Units of the type shown in FIGS. 13A
and 13B are sometimes referred to herein as "pinned units" or
"crossbars".
[0055] FIG. 14 shows fiber orientations in a pinned unit.
[0056] FIGS. 15A-D show fiber orientations in different layers of a
laminate pinned unit.
[0057] FIGS. 16A, 16C and 16D are normal views, and FIG. 16B is a
perspective view, of pinned units after they have been pinned
together by the clip shown in FIG. 16E.
[0058] FIGS. 17A, 17C and 17D are normal views, and FIG. 17B is a
perspective view, of pinned units after they have been
assembled.
[0059] FIGS. 18A and 18B are normal views of pinned units after
they have been assembled.
[0060] FIGS. 19A, 19B and 19C are normal views of pinned units
after they have been assembled to form a volumetric structure.
[0061] FIGS. 19D, 19E, 19F and 19G are perspective views of pinned
units after they have been pinned together to form a volumetric
structure.
[0062] The above Figures illustrate some illustrative
implementations of this invention, or provide information that
relates to those implementations. However, this invention may be
implemented in many other ways. The above Figures do not show all
of the details of this invention.
DETAILED DESCRIPTION
[0063] The following is a description of some exemplary
implementations of this invention:
[0064] In exemplary implementations of this invention, digital
composites allow rapid prototyping of fiber composite parts with
high throughput robotic digital assemblers. The individual
components are small in comparison to the finished assemblies, and
may be produced through conventional means, as suited for mass
production of identical parts.
[0065] The term "digital material" or "digital composite", as used
herein, means a material comprising many discrete units, which
units comprise composite material reinforced with anisotropic
fibers.
[0066] Natural lattice features--such as the ability to dynamically
respond to loading with the formation of dislocations--can be
designed into digital material structures. For example, this
dynamic response may be implemented using secondary connection
positions or self detachment and reattachment of connections.
[0067] The use of many smaller parts to assemble a large part
allows the use of elastic averaging to reduce error in
manufacturing methods. When many parts are used to locate a single
feature, with enough elastic compliance to adjust to small
inconsistencies in the location of the feature, the effective
location of the feature will be the average of the individual
locations provided by the individual parts. When this process is
performed correctly, this average location will be more precise
than the process used to fabricate the individual parts. This
method relies on this original per-part error being within a
certain threshold for a given system. By the same rules, when
forces are effectively distributed throughout an assembly of
smaller parts, tolerances on strength requirements may be
effectively reduced as the observed bulk strength of the assembly
will be a result of this force distribution. This is allowed by the
elasticity that is common to fiber reinforced polymer composites,
whereby weaker components can be designed to display elastic
compliance that transfers load through stronger components.
[0068] Structures may be assembled by linking units that are
individually tuned through their fiber layup, so that forces are
transferred between the units, rather than having continuous fibers
span entire macro-structures. FIG. 1A shows a unit that comprises
fiber-reinforced composite material. FIG. 1B shows units of this
type, linked in a chain. FIG. 1C shows units of this type, linked
to form a surface. FIG. 1D shows units of this type, linked to form
a volumetric structure.
[0069] Precise spatial distribution of parts for a given structural
shape may be automatically accomplished through algorithmic
distribution throughout a prescribed volume, according to external
constraints provided (i.e. via finite element analytical tools).
Strategies for tuning of mechanical properties include introducing
voids, varying part ratios, and varying core geometry.
[0070] A wide range of fibers and polymers may be employed in the
fiber-reinforced composite material.
[0071] Continuous structures may be assembled from relatively
small, simple, and discrete units, with a low number of types of
units, which makes them good candidates for trivial adaptation to
various processes for various fibers and polymers at any scale.
[0072] Reversible interlocking assembly allows deconstruction and
reuse of individual components. In addition, service life of larger
assemblies can be greatly increased by the ability to selectively
replace small portions of a structure. This may be performed
without significantly impacting the strength of the overall
structure, during the replacement process.
[0073] In some cases, the structure that is being manufactured may
be employed as part of sensing and monitoring equipment. For
example, structural carbon fiber may be employed as strain gauges,
heating elements, and/or temperature detectors. Interfaces between
units may set up to couple to each other, either conductively (e.g.
through metallic connectors or carbon fiber) or
electro-magnetically.
[0074] On cases where the part material itself is integrated into
sensing devices, additional active sensing properties may be
employed. For example, uses include strain sensing, interconnect
and composite delamination failure sensing (health monitoring), and
even computational logic.
[0075] At very high resolutions for a given structure, digital
materials can form seemingly continuous shapes. Additionally,
hierarchically scaled part types allow for adjusting of resolution
as necessary. Still, interfacing parts may be added if extremely
smooth outer surfaces are desired (i.e. for aerodynamic
reasons).
Example 1
Snap-Fit Digital Composite Volume
[0076] In an exemplary embodiment of this invention, called the
Snap Fit Digital Composite Volume, a continuous structure of
discrete units fills a volume, whereby units are distributed across
a three dimensional lattice.
[0077] FIGS. 2A and 2B show compatible tension and compression
components that can be used to assemble a tuned Snap Fit Digital
Composite Volume.
[0078] The geometry of the load transfer mechanisms defines their
function as a tension or compression component. FIG. 2A shows an
example of a compression unit; FIG. 2B shows an example of a
tension unit. Tension loading is indicated by arrows 209 in FIG.
2A; compressive loading is indicated by arrows 229 in FIG. 2B.
[0079] These compression units and tension units are carbon fiber
epoxy composite parts with flexural locking mechanisms, requiring
snap-fit preload for new parts only required at the normal to the
already built structure. To add to a part, new pieces are pushed
onto the outside of the structure, which allows an automated
assembly mechanism to have a single degree of freedom for the
procedure of installing a new part. In addition, the design
transfers axial load on components to orthogonal neighboring
elements.
[0080] Each compression unit and each tension unit includes
flexural locking mechanisms and load transfer mechanisms, which are
described in further detail, below.
[0081] The flexural locking mechanisms comprise elastically
compliant flexures (208, 228) with locking notches at their
terminal ends (203, 204, 205, 206, 223, 224, 225, 226). These
notches have chamfered outside edges, allowing the end of one unit
(e.g., 201) to snap into the keyhole (e.g., 227) of another unit,
as shown in more detail in FIGS. 7A, 7B and 7C. The keyhole (207,
227) allows two units (one from either direction) to be
simultaneously locked in. For simplicity, this design allows these
two units to enter side-by-side.
[0082] The load transfer mechanisms utilize the same armatures as
the flexural locking mechanisms, loaded axially along the primary
longitudinal axis (which intersects 201, 202 in FIG. 2A and 221,
222 in FIG. 2B) (instead of transversely, as when locking or
unlocking units). Natural loading of this digital composite
structure using these components will only result in axial loading
of the individual components. The transverse forces required to
assemble and disassemble structures (indicated by arrows marked 210
in FIG. 2A and 230 in FIG. 2B) need to be provided by an external
device, such as a robotic digital assembler.
[0083] Consider the tension unit shown in FIG. 2A: When
tension-loaded along the primary longitudinal axis (which
intersects 201, 202), and subjected to normal forces on its
terminal ends (203, 204, 205, 206) (which normal forces are along
the same lines as arrows 210, respectively, but opposite in
direction to arrows 210, respectively, and are in each case
transmitted through the keyhole of an interlocked neighbor of the
tension unit), the flexural arms (208) will provide a cam-like
action, transferring load to its orthogonal interlocked
neighbors.
[0084] Similarly, consider the compression unit shown in FIG. 2B:
When compression-loaded along the primary longitudinal axis (which
intersects 221, 222), and subjected to normal forces on its
terminal ends (203, 204, 205, 206) (which normal forces are along
the same lines as arrows 210, respectively, but opposite in
direction to arrows 210, respectively, and are in each case
transmitted through the keyhole of an interlocked neighbor of the
tension unit), the flexural arms (228) will provide a cam-like
action, transferring load to its orthogonal interlocked
neighbors.
[0085] FIGS. 3A and 3B are diagrams that show examples of fiber
continuity and orientation for these parts. Note the loop of fibers
301, 311 around the keyhole feature (302, 312), and the end-to-end
continuity of fibers that extend into the flexure and load transfer
armature (such as the fiber that extends from 303 to 304, or the
fiber that extends from 313 to 314).
[0086] Production of the parts may be via conventional resin
transfer molding or pultrusion and slicing. FIG. 4 illustrates a
pultrusion 401 that is sliced into compression units 402. Given the
fiber continuity and orientation shown in FIG. 3A, the pultrusion
process may be made simpler by producing interlocking end caps
(501, 502, 503, 504), main body (508, 509) and flexure armatures
(e.g., 505, 506), and a keyhole component (507) as separate pieces
to be bonded together before slicing.
[0087] Suitable prototype parts may also be made via two
dimensional cutting of preformed laminates with appropriately
oriented fibers. FIGS. 6A, 6B, 6C and 6D illustrate the orientation
of fibers in different laminate layers in a compression unit, with
the fibers in the respective layers oriented at angles of
0.degree., 45.degree., 90.degree. and 135.degree., respectively,
from the longitudinal axis of that compression unit. FIG. 6E shows
a compression unit, and FIG. 6F shows a detailed view of a notch in
that compression unit. As shown in FIG. 6F, different layers of the
laminate have fibers oriented at angles of 0.degree., 45.degree.,
90.degree. 135.degree., 135.degree., 90.degree., 45.degree. and
0.degree. from the longitudinal axis of that compression unit. The
symmetry of this arrangement contributes to stability during
processing and under load.
[0088] FIGS. 7A, 7B and 7C show three units being connected
together, by inserting tip 701 of a first unit and tip 702 of a
second unit into keyhole 703 of a third unit. FIG. 7A shows the
configuration before the tips are inserted into the keyhole, FIG.
7B shows the configuration after tip 701 of the first unit has been
inserted, and FIG. 7C shows the configuration after the two tips
have been inserted into the keyhole.
[0089] FIGS. 8A, 8C and 8D show different normal views, and FIG. 8B
shows a perspective view, of a sparse structure that comprises
tension elements.
[0090] FIGS. 8E, 8G and 8H show different normal views, and FIG. 8F
shows a perspective view, of a sparse structure that comprises
compression elements.
[0091] FIGS. 9A to 9C show a Snap Fit Digital Composite Volume with
the parts described previously, incorporating flexural locking
mechanisms, and programmability of the tensile and compressive
strength of specific regions of a digital composite structure,
through the placement of purpose-designed parts that compose the
structure. Through the placement of these tension units and
compression units, the material can be tuned to be stiff for
particular geometric loading conditions and highly elastic in
others. Specifically, FIGS. 9A, 9B and 9C show different
perspective views of a sparse structure that comprises compression
elements.
[0092] Through mechanical property programming, as described above,
the bulk properties of the Digital Composite material can progress
from primarily compressive strength through tensegrity-like
properties to primarily tensile strength. As such, related
attributes, such as poisson ratio, can be programmed as well.
[0093] The topology of a Digital Composite Volume may be any volume
filling meshing, with arbitrary node connectivity, as necessary to
achieve desired range of configurations.
Example 2
Digital Composite Surface
[0094] In another exemplary embodiment, called the Digital
Composite Surface, a continuous structure of discrete units forms
the structure, as a space filling surface system of three-connected
nodes (with locking mechanisms that are similar to those in the
Digital Composite Volume examples). The units may be used to form
an arbitrarily large sheet of material, with arbitrary
topology.
[0095] Smooth surface topologies can be achieved due to the
elasticity of the parts. This allows the device to form non
Euclidean, non-developable surface forms, such as spherical or
hyperbolic shells with programmable porosity (as well as continuous
assemblages of geodesic and hyperbolic regions).
[0096] FIG. 10A shows elements that can be for an assembly system
that generally employs only two types of primitives. In the example
shown in FIG. 10A, there are two main types of primitives in the
system. The first is a node (e.g., 1001), and the second is a
connector (e.g. 1002, 1003, 1004). In the example shown in FIG.
10A, all nodes connect exactly three connectors, and all connectors
are of the same length.
[0097] FIG. 10B show an example of a type of unit 1010 that can be
used for an assembly system that generally employs only one type of
primitive. In FIG. 10B, there is no need for a separate node to
join connectors. Instead, each arm 1012, 1013 and 1013 of the unit
1010 is half of a connector, and the tips 1022, 1023 and 1024 of
the respective arms can each connect to up to three other
units.
[0098] FIG. 10C shows a different example of a unit 1030 that can
be used for an assembly system that generally employs only one type
of primitive. Again, there is no need for a separate node to join
connectors. Instead, there are three arms 1032, 1033, 1034. The tip
1042 of arm 1032 is adapted to connect to two other arms (of two
different units, respectively).
[0099] The primitives shown in FIG. 10A, 10B or 10C, respectively,
may be employed to create arbitrary shapes, surfaces and
volumes.
[0100] FIGS. 10A, 10B and 10C are each normal (or top) views. In
FIG. 10A, the connectors attached to a three-connected node may
either: (a) all be located in the same plane, or (b) not be located
in a single plane. Likewise, in each primitive shown in FIGS. 10B
and 10C, the arms may either: (a) all be located in the same plane,
or (b) not be located in a single plane.
[0101] FIG. 10D shows a node connected to three curved arms.
[0102] FIG. 10E shows a sparse structure, in which each node is
connected to three arms. Each arm is also connected to another
node. Thus, each node is connected to three other nodes.
[0103] The conformation of the Digital Composite Surface is
achieved through local connectivity of the individual units. Units
in the Digital Composite Surface are connected to as many other
units as are defined in the surface topology--three, in the example
shown in FIG. 10A.
[0104] The topology of a Digital Composite Surface may be any
surface meshing, with arbitrary node connectivity, as necessary to
achieve desired range of configurations.
[0105] For complex shapes, this provides a potential "tool-less"
assembly process, where the geometry of the parts being assembled
provides the dimensional constraints required to precisely achieve
complex forms. This does not rely on each part being very precise,
but instead relies on specific knowledge of the nature of the
errors that do occur. For instance, a system whose assembly
over-constrains elastic components can provide positioning with
much higher precision than that which is contained within the shape
of any single component.
[0106] The decomposition of any surface as an assemblage of planes,
geodesic, and hyperbolic surfaces that can be approximated by this
system may be automated, based on the curvature map of the form,
and the known flexibility of the material used for the
components.
[0107] The two types of components in FIG. 10A--stick and
nodes--may be cut with a two-dimensional CNC cutting system. The
system is sufficiently constrained such that the material solves
for the final shape, which is true to the generative form without
the need for any of the conventional form-work used to manufacture
these types of shapes.
[0108] FIGS. 11A, 11B, 11C are graphs of interaction potentials,
and FIGS. 12A, 12B and 12C are graphs of stress-strain curves. Each
is discussed in more detail below.
Example 3
Pinned Digital Composite Volume
[0109] In an exemplary embodiment, called the Pinned Digital
Composite Volume, a continuous structure of discrete units fills a
volume, whereby units are distributed across a three dimensional
lattice.
[0110] This design comprises two types of elements--a crossbar
(also called a "pinned unit") and a compression clip. FIGS. 16A,
16B, 16C and 16D show that, when assembled, ends of four crossbar
1601, 1602, 1603 and 1604 meet at a central location and orthogonal
to a fifth crossbar 1605, where they are secured with a clip (1606)
that is inserted orthogonally to the five crossbars. The resulting
structure can be seen as vertex connected regular octahedrons or
square-face connected cuboctahedrons.
[0111] FIGS. 13A and 13B shows a design for a crossbar that can be
used to assemble a tuned Pinned Digital Composite Volume. The
crossbar comprises a carbon fiber epoxy composite part with a
pinned locking mechanism (e.g., clip 1606 in FIGS. 16B, 16D and
16E). To add a new crossbar to a structure, first remove any pins
that are located at connections where the new part is being added
(and remove edge placeholders if used), then insert the new
crossbar, and replace the pins.
[0112] Each of the crossbars (e.g. 1601, 1602, 1603, 1604, 1605)
are identical and include pinned locking mechanisms and load
transfer mechanisms, both of which are described in further detail,
below.
[0113] As shown in FIG. 13, the pinned locking mechanisms comprise
slotted tabs (1300, 1301, 1302, 1303, 1400, 1401, 1402, 1403) that
fit into larger slots (e.g., 1304, 1404) on adjacent parts. These
tabs can include flexural snap fit tabs, but the primary fastening
mechanism in the example shown is the pin (1606). Handles (1330,
1331, 1332, 1333, 1430, 1431, 1432, 1433) facilitate automated
assembly. These handles remain out of the way of the connection,
and can be easily grasped by a machine. Each central keyhole (1304,
1404) allows four orthogonal units (two from either direction) to
be simultaneously locked in. The regularity of the spatial
arrangement of these four parallel tabs in the central keyhole (as
shown in FIGS. 17A, 17B, 17C and 17D) affects connection derived
elastic properties, depending on the aspect ratio of the parts
(thickness to strut length). The simplest solution is to use
consistent and equalized placement of tabs according to global
orientation.
[0114] In a Pinned Digital Composite Volume, axial tensile or
compressive loads on crossbars can be transferred to orthogonal
neighboring crossbars.
[0115] The load transfer mechanisms may utilize the ideal angle of
the struts in the crossbar. Loading is shown by the arrows marked
1310, 1311, 1312, 1313 in FIG. 13A and the arrows marked 1410,
1411, 1412, 1413 in FIG. 13B. Reaction deflection is shown by the
arrows marked 1320, 1321, 1322, 1323 in FIG. 13A and the arrows
marked 1420, 1421, 1422, 1423 in FIG. 13B. The forces required to
assemble these structures can be provided by an external device
that places the pins; the forces required to disassemble these
structures are either simply set by the yield capacity of the pins,
or can be provided by an external device, such as a robotic digital
assembler/disassembler. If connection based elastic properties are
to be minimized in this design, then the crossbar struts may be
made very slender relative to the connection details, in order to
provide relatively large surface areas for the connection
mechanism.
[0116] FIG. 14 is a diagram of an example of fiber continuity and
orientation for these parts. Note the loop of some fibers around
the slots feature (1441)), and the end-to-end continuity of other
fibers (1442)) that extend across the struts and around the
slots.
[0117] Production of the parts may be via conventional resin
transfer molding or pultrusion and slicing (similar to FIG. 4).
Given the fiber continuity and orientation shown in FIG. 14, the
pultrusion process may be made simpler by producing interlocking
strut pieces and slot/hole pieces (similar to FIG. 5) as separate
pieces to be bonded together before slicing. Suitable prototype
parts may also be made via two dimensional cutting of preformed
laminates with appropriately oriented fibers. FIGS. 15A, 15B, 15C
and 15D illustrate the orientation of fibers in different laminate
layers for such a part, with the fibers in the respective layers
oriented at angles of 0.degree., 45.degree., 90.degree. and
135.degree., respectively, from a reference direction, organized
with symmetry similar to the example given in FIG. 6 unless torque
response to loading is desired.
[0118] FIGS. 16A, 16C and 16D are normal views, and FIG. 16B is a
perspective view, of crossbars after they have been pinned together
by the clip shown in FIG. 16E.
[0119] FIGS. 17A, 17C and 17D are normal views, and FIG. 17B is a
perspective view, of crossbars after they have been assembled.
[0120] FIGS. 18A and 18B are normal views of crossbars after they
have been assembled.
[0121] FIGS. 19A, 19B and 19C are normal views of crossbars after
they have been assembled to form a volumetric structure.
[0122] FIGS. 19D, 19E, 19F and 19G are perspective views of
crossbars after they have been assembled to form a volumetric
structure.
[0123] Through mechanical property programming, as described above,
the bulk properties of a digital composite material can progress
from primarily compressive strength through tensegrity-like
properties to primarily tensile strength. As such, related
attributes, such as poisson ratio, can be programmed as well.
[0124] The topology of a Pinned Digital Composite Volume may be any
volume filling meshing, with arbitrary node connectivity, as
necessary to achieve desired range of configurations.
Interaction Potentials and Stress-Strain Curves
[0125] FIGS. 11A, 11B and 11C are interaction potential diagrams
for (a) interaction between two neutral atoms or molecules,
according to the Lennard-Jones model, (b) interaction between
digital units with orthogonally pinned connections, and (c)
interaction between digital units with pre-loaded snap-fit
connections, respectively.
[0126] An important attribute in any interaction potential model is
the potential well. The top-most horizontal potential limit line in
the two graphs in FIGS. 11B and 11C indicates the designed limits
of within-part ligaments. The potential level of the peak after the
potential well in 11C represents a lower secondary limit for a
snap-fit connection model, and indicates the designed disassembly
strength of an in-band connection mechanism.
[0127] FIGS. 12A, 12B, 12C and 12D illustrate tunable multi-phase
elasticity.
[0128] Specifically, these Figures are stress-strain diagrams of
bulk material in different scenarios.
[0129] Connections may be designed such that the stress-strain
(.sigma./.epsilon.) curve of the connection
(.sigma.(.epsilon.).sub.c) has a particular relationship to the
.sigma./.epsilon. curve of the most elastic within-part ligament
(.sigma.(.epsilon.).sub.p). If .sigma.(.epsilon.).sub.c is always
greater than or less than .sigma.(.epsilon.).sub.p, then the
connection either does not contribute to, or dominates,
respectively, the bulk material behavior of the digital material.
The .sigma./.epsilon. curve of the bulk material will look typical,
as in FIG. 12A. On the other hand, if .sigma.(.epsilon.).sub.c
intersects .sigma.(.epsilon.).sub.p, then the material will appear
to have two phases of elasticity, such as in FIG. 12B. The first
phase of elasticity is useful for low power distributed small
actuator or large actuator (such as a cable winch) based morphing
structures that still display high strength characteristics. Noting
that a form of digital frangibility is a possibly useful property
of digital materials, whereby the bulk structure disintegrates
without exceeding the linear elastic limits of the individual
parts, .sigma./.epsilon. curves for frangible digital materials are
shown in FIGS. 12C and 12D, with a primary feature being the cutoff
yield strength of the connections.
[0130] The use of many small parts to assemble a large part allows
for the use of elastic averaging to reduce overall error. When many
parts are used to locate a single feature, with enough elastic
compliance to adjust to small inconsistencies in the location of
the feature, the effective location of the feature will be the
average of the individual constraints provided by the surrounding
parts. This average location can be more precise than the process
used to fabricate the individual parts. The original per-part error
must be within a certain threshold for a given system. By the same
rules, when forces are effectively distributed throughout an
assembly of smaller parts, tolerances on strength requirements may
be effectively reduced as the observed bulk strength of the
assembly will be a result of this force distribution.
Benefits and Applications
[0131] In exemplary implementation of this invention, fabrication
of structures from discrete parts is performed with discrete
relative local positioning, instead of continuous variation of
composition and location of material as in an analog fabrication
system. Digital Composite units are made from anisotropic fiber
reinforced composites, to enable low density, sparse structural
systems. Advantageously, a chain of discrete fiber composite parts
can be as strong as a monolithic part, and have advantages with
manufacturing processes, serviceability, and reusability, in
addition to tunability and extensibility.
[0132] Current industry leading fiber composite manufacturing
processes require large investments in both time and
infrastructure. In contrast, in exemplary implementations of this
invention, tunable anisotropic characteristics of fiber reinforced
composite construction can be maintained with the chaining of many
discrete parts at high resolution. Since these parts may be self
similar, and the macro scale constructions can vary arbitrarily
(depending on part resolution), the benefits include vastly
reducing time and expense for prototyping.
[0133] In exemplary implementations, digital material may be used
for rapid prototyping and fabrication of any two-dimensional or
three-dimensional shape with discretized resolution, from fiber
reinforced composite material. This may be thought of as a kit of
parts whose individual fiber layups and interconnectivity allows
for tuned macro-assemblies. Therefore, the ability to engineer very
specific mechanical material properties is maintained with this
fabrication method, whereby functional material properties as well
as overall shape are tuned via the strategy for assembly of the
parts.
[0134] Many fields (e.g., architecture, aerospace, transport,
science) have applications that call for strong, lightweight,
reconfigurable and precisely shaped surfaces, ranging from many
kilometers scale elevated light railway infrastructure to meter
scale vehicle structures, to low inertia measurement devices with
micron scale features. The present invention, in some
implementations, has the ability to reconfigurably form tuned
structures, making it a particularly valuable functional
prototyping and manufacturing tool for these applications.
[0135] The commercial aerospace industry is moving towards aircraft
designs that have fewer but larger monolithic fiber composite
parts. Conventional manufacturing processes have scaled up,
accordingly, which requires tools (for defining the shape of the
part), and ovens (for polymer matrix curing) that are large enough
to influence the size of the buildings that contain them. The
present invention can solve this problem by digital assembly of
sparse volumes comprised of many smaller components, so that all of
the tooling required may be significantly smaller than the finished
part.
[0136] The field of aerospace structural engineering seeks highly
tuned and lightweight structural systems that need to meet extreme
service, monitoring, and general environmental requirements. The
expense involved with conventional manufacturing of composite
aero-structures limits prototyping capabilities. In contrast, in
exemplary implementations of this invention, a low number of types
of simple discrete components can be assembled to large structures
according to local-only rules, which makes them good candidates for
trivial adaptation to various shapes at a large scale. In the
present invention, digital material is additionally highly tunable
in terms of its shape, density, and corresponding mechanical
properties.
[0137] Commercially available in situ fiber reinforced polymer
sensing and monitoring systems are very expensive, and many rely on
custom designed schemes for embedding non structural components
within parts. In contrast, in exemplary implementations of the
present invention, custom systems can be assembled from
standardized parts. Furthermore, according to principles of this
invention, active or passive electronic circuits may be embedded in
assembled structures, allowing the structure to store information
that may be used for purposes ranging from passive monitoring to
correcting overall shape.
[0138] In exemplary implementations of this invention, the assembly
process confines the stochasticity of the material to the
production of each part, and allows for highly porous large scale
volumetric assemblies that can still contain components that are
extrinsic to the structure, such as with aircraft structures.
[0139] In exemplary implementations, structures may be fabricated
using massively parallel assembly of digital materials, including
the assembly of structures larger than the assembly machinery. In
addition, mobile units may later travel over the structure and
replace damaged units or adapt the structure to new
requirements.
[0140] Continuously shape morphing structures currently focus on
traditional kinematics with flexural components accounting for
continuous deformation and/or high density and high cost materials
such as piezoelectric ceramics, shape memory alloys, and
electroactive polymers. This has limited the size, degrees of
freedom, and manufacturability of shape morphing structures to
date.
[0141] In contrast, in exemplary implementations of this invention,
digital materials allow for the design of materials with many small
and inexpensive actuators that combine to deliver large
displacements with large forces, and/or tunable elastic phases in a
lattice geometry that allows for deformation with simple large
scale actuation without compromising the strength of the
assembly.
[0142] With progress in unmanned vehicle technology, experience has
shown that rogue or poorly piloted vehicles represent a significant
danger to people and property. This is particularly true of
unmanned aerial vehicles, which pose a ballistic hazard to manned
aircraft during normal operation. In some implementations of this
invention, digital material may be assembled into aerostructures
with precise failure modes, because of the tunability of the
connections, so that a structure that is strong and light enough
for flight can rapidly self-disassemble upon impact with another
object.
SOME DEFINITIONS
[0143] As used herein:
[0144] A structure is "sparse" if at least 40% of the volume of the
structure comprises voids, hollows or other empty space not
occupied by solid matter.
[0145] A "crossbar" (or "crossbar unit") means a unit that includes
four elongate elements.
Variants
[0146] This invention may be implemented in many different ways.
Here are some non-limiting examples:
[0147] In some cases, at least some connections between units are
not elastic. In some cases, units comprise composite materials that
are not fiber-reinforced.
[0148] This invention may be implemented as a product comprising a
set of discrete units assembled, or adapted to be assembled, into a
sparse structure, wherein: (a) each unit comprises composite
material, and (b) a majority of the units in the set are each
reversibly connected, or adapted to be reversibly connected, to at
least two other units in the set, by connections that are adapted
to transfer forces between connected units. Furthermore: (1) the
composite material may be reinforced with fibers, (2) the
connections may be elastic, (3) at least some of the units in the
set may be layered, and for each layered unit, the composite
material may comprise multiple layers reinforced by fibers, each
fiber having an orientation, the average orientation of the fibers
in a layer defining an average fiber orientation for that that
layer, and the average fiber orientation for at least some of the
layers of that specific unit differing by more than 45 degrees from
the average fiber orientation for at least some of the other layers
of that specific unit, (4) at least one individual unit in the set
may have one or more holes through it, include at least one
elongate subelement that has at least a first and a second
longitudinal end, include some fibers that extend from a first
region that is at or adjacent to the first longitudinal end to a
second region that is at or adjacent to the second longitudinal
end, and include other fibers that are oriented in a loop around at
least one of the one or more holes, (5) the connections between
connected units may occur at certain positions on and relative to
the connected units, and wherein, in response to loading of the
sparse structure, a reversible deformation of a lattice in the
sparse structure may occur, said reversible deformation being due
at least in part to reversible change in at least some of said
positions at which said connections occur, (6) the sparse structure
may further comprise at least one actuator to elastically deform
the structure, (7) at least some specific units in the set may be
elongate and each of these specific units may transfer, or may be
adapted to transfer, axial load along its long dimension to other
units that are connected to, and aligned orthogonally to, said
specific unit, (8) some of the units in the set may comprise
elongated compression units, each of the compression units being
adapted to elastically deform further, from its unloaded state, in
response to compressive loading of a particular magnitude along its
long dimension than to tension loading of the same magnitude along
its long dimension, (9) some of the units in the set may comprise
elongated tension units, each of the tension units being adapted to
elastically deform further, from its unloaded state, in response to
tension loading of a specified magnitude along its long dimension
than to compressive loading of the same specified magnitude along
its long dimension, (10) some of the particular units in the set
may be elongate and these particular units may be elastically
connected by snapping the longitudinal end of one unit, or the
longitudinal ends of multiple units, into a notch in another unit,
which notch has a chamfered edge, (11) the sparse structure may
comprise nodes and elongate components, wherein each of the nodes
is connected, or adapted to be connected, to three of the elongate
components, in each case at a point of connection, which point of
connection for any particular one of the elongate components is at
or adjacent to a longitudinal end of that particular elongate
component, each of the elongate components has a longitudinal axis
along its long dimension, which longitudinal axis may be curved or
may be straight, and the length of the longitudinal axis of each of
elongate components is the same, (12) at least some of units in the
set may be crossbar units, which crossbar units are reversibly
connected, or adapted to be reversibly connected, by elastic
connections, each of which elastic connections is formed by a
compression clip clipping together longitudinal ends of five
crossbar units, four of the five crossbar units being aligned in a
plane that is orthogonal to the long dimension of the fifth of the
five crossbar units, (13) the sparse structure may be adapted to
disintegrate, without exceeding the elastic limits of the units in
the structure, (14) a first subset of the units may differ, in
chemical composition or material property, from a second subset of
the units, (15), some of the units may include electrical
conductors and others of the units may not include electrical
conductors.
[0149] This invention may be implemented as an automated process of
assembling a set of discrete units into a sparse structure, wherein
(a) each unit comprises composite material, and (b) the automated
process comprises reversibly connecting each of the units to at
least one other of the units, by connections that are adapted to
transfer forces between connected units. Furthermore: (1) some of
the connections may be elastic connections that are created, for
each respective connection, by pushing a unit against the sparse
structure when the sparse structure is partially assembled, the
push being given by an automated assembly device that moves with
one degree of freedom, (2) the process may be controlled by a
computer algorithm and the mechanical properties of the sparse
structure produced by the process may be tuned by changing one or
more of the following: (A) the ratio of different types of the
units used to assemble the sparse structure, and (B) geometry of
the sparse structure, and (3) due to elastic averaging, the
automated process may assemble a sparse structure with a precision
(with respect to variation in absolute physical dimensions) that
exceeds the precision (with respect to variation in absolute
physical dimensions) of the units that comprise the sparse
structure.
CONCLUSION
[0150] It should be clear to a person skilled in the art that, for
each of the examples described above, many physical variants are
possible. Interconnect between units would vary appropriately.
[0151] In the preceding descriptions, numerous specific details are
set forth in order to provide a thorough understanding of the
invention. However, it will be understood by those skilled in the
art that the present invention may be practiced without these
specific details. In other instances, well known methods,
procedures, and components have not been described in detail, so as
not to obscure the present invention.
[0152] It is to be understood that the methods and apparatus which
have been described above are merely illustrative applications of
the principles of the invention. Numerous modifications may be made
by those skilled in the art without departing from the scope of the
invention. The scope of the invention is not to be limited except
by the claims that follow.
* * * * *