U.S. patent application number 15/575327 was filed with the patent office on 2018-06-07 for system and methods for fabricating actuators and electrically actuated hydraulic solid materials.
The applicant listed for this patent is Cornell University. Invention is credited to Jeffrey LIPTON.
Application Number | 20180156204 15/575327 |
Document ID | / |
Family ID | 57320742 |
Filed Date | 2018-06-07 |
United States Patent
Application |
20180156204 |
Kind Code |
A1 |
LIPTON; Jeffrey |
June 7, 2018 |
SYSTEM AND METHODS FOR FABRICATING ACTUATORS AND ELECTRICALLY
ACTUATED HYDRAULIC SOLID MATERIALS
Abstract
With applications such as soft robotics being severely hindered
by the lack of strong soft actuators, the invention provides a new
soft-actuator material--Electrically Actuated Hydraulic Solid
(EAHS) material--with a stress-density that outperforms any known
electrically-actuatable material. One type of actuator is
fabricated by making a closed cell that acts as highly paralyzed
version of a standard paraffin actuator. Each cell exhibits
microscopic expansion, which is summed to produce macroscopic
motion. The closed cellular nature of the material allows the
system to be cut and punctured and still operate. It can be
produced in a lab or industrial scale, and can be formed using
molding, 3D printing or cutting.
Inventors: |
LIPTON; Jeffrey; (Medford,
MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Cornell University |
Ithaca |
NY |
US |
|
|
Family ID: |
57320742 |
Appl. No.: |
15/575327 |
Filed: |
May 18, 2016 |
PCT Filed: |
May 18, 2016 |
PCT NO: |
PCT/US2016/033080 |
371 Date: |
November 17, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62163156 |
May 18, 2015 |
|
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|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F03G 7/06 20130101; F03G
7/065 20130101; F03G 7/005 20130101 |
International
Class: |
F03G 7/06 20060101
F03G007/06 |
Claims
1. An Electrically Actuated Hydraulic Solid (EAHS) material
comprising: a phase change material (PCM); an elastomeric polymer
material; a conductive material, the phase change material and the
conductive material embedded within the elastomeric polymer
material forming a conductive elastomeric structure, wherein the
PCM undergoes a phase change as controlled by the conductive
material to vary an internal pressure and actuate the
structure.
2. The EAHS material of claim 1, wherein the phase change material
forms a plurality of closed cells encapsulated by the elastomeric
polymer material.
3. The EAHS material of claim 1, wherein the conductive material is
randomly distributed through the elastomeric polymer material.
4. The EAHS material of claim 1, wherein the phase change material
is paraffin wax.
5. The EAHS material of claim 1, wherein the elastomeric polymer
material is Polydimethylsiloxane (PDMS).
6. The EAHS material of claim 1, wherein the elastomeric polymer
material is a two part elastomer.
7. The EAHS material of claim 6, wherein the phase change material
is added to one precursor of the two part elastomer and the
conductive material is added to the other precursor of the two part
elastomer.
8. The EAHS material of claim 1, wherein the elastomeric polymer
material is a one part silicone.
9. The EAHS material of claim 1, wherein the conductive material is
carbon black.
10. A method for fabricating EAHS material comprising the steps of:
combining a phase change material, a conductive material, and an
elastomeric polymer to form a conductive elastomeric structure with
closed cells of PCM.
11. The method for fabricating EAHS of claim 10, wherein the phase
change material forms a plurality of closed cells encapsulated by
the elastomeric polymer.
12. The method for fabricating EAHS of claim 10, wherein the
conductive material is randomly distributed through the elastomeric
polymer.
13. The method for fabricating EAHS of claim 10, wherein the phase
change material is paraffin wax.
14. The method for fabricating EAHS of claim 10, wherein the
elastomeric polymer is Polydimethylsiloxane (PDMS).
15. The method for fabricating EAHS of claim 10, wherein the
elastomeric polymer is a two part elastomer.
16. The method for fabricating EAHS of claim 15, further comprising
the steps of: adding the phase change material is added to a first
precursor of the two part elastomer; adding the conductive material
to a second precursor of the two part elastomer; and combining the
first precursor and the second precursor.
17. The method for fabricating EAHS of claim 10, wherein the
elastomeric polymer is a one part silicone.
18. The method for fabricating EAHS of claim 10, wherein the
conductive material is carbon black.
19. An actuator comprising an EAHS structure including both a phase
change material (PCM) and a conductive material, the PCM having a
phase change temperature greater than a temperature of the
structure, wherein a current applied to the conductive material
causes the PCM to expand and actuate the structure.
20. The actuator according to claim 19, wherein the EAHS structure
is confined by an external casing so that EAHS expansion causes
linear expansion of the structure.
Description
[0001] This application claims the benefit of U.S. Provisional
Application No. 62/163,156 filed May 18, 2015, incorporated by
reference in its entirety.
FIELD OF THE INVENTION
[0002] The invention relates generally to actuators. More
specifically, the invention is directed to a system and methods for
fabricating actuators including wax actuators, for robotics and
automation applications. In addition, the invention is directed to
a new material including a conductive material component for use in
the fabrication of actuators.
BACKGROUND OF THE INVENTION
[0003] Electrically driven polymeric actuators are an important
basis for modern microfluidics, soft electronics, and soft
robotics, and considered one of the bottlenecks of many
applications for robotic and automation. Each one of the existing
actuator technologies available today involves a difficult tradeoff
between performance metrics. For example, dielectric actuators
allow for high frequency responses and high strains, but are unable
to generate large forces. Piezoelectric materials require high
voltage and produce very small strains. Shape memory alloys require
high currents or small cross sections to increase resistance.
Swelling polymer gels can be compliant and generate large
volumetric changes by absorption compounds from the environment,
which limits applicability. While each has found their niche in the
Pareto front of actuators, none can generate very high quasi-static
loads, have a high stress density and be driven by low voltages. In
fact, very few material actuators can generate more than one
hundred Newtons of force in a typical engineering or lab
environment.
[0004] These actuators such as a Dielectric Actuators (DEA) or an
Ionic Polymer Metal Composite (IPMC) allow for high frequency
responses and high strains but are unable to generate large forces.
These actuators often allow for planar expansion at a constant
volume, or generate a strain differential causing a bending action.
Neither is able to generate a volumetric expansion. Swelling
polymer gels, which can be compliant and generate large volumetric
changes, rely on absorption or emission of compounds from the
environment. In order for soft actuators to find further use in
robotics and automation, a soft actuator may need to generate very
high quasi-static loads and be driven by low voltages and
currents.
[0005] The production of actuatable materials is an important area
of development for Solid Freeform Fabrication (SFF). Traditionally
manufactured actuators have a diverse set of power sources and
applications. These range from hydraulic and pneumatic systems used
in heavy equipment, to electric motors and piezoelectric systems
used for small scale manipulations. Each actuator type is generally
dependent upon the needs of a particular application. For a 3D
printed actuator to be deemed useful, it must be able to compete
with its similar non-printed actuators.
[0006] Although Solid Freeform Fabrication (SFF) has been used for
printing with wax materials for many years, SFF has had limited
success in building actuator systems. Ionic Polymer Metal
Composites (IPMCs) actuators are generally used in a research
context and show promise as artificial muscles and microfluidic
valves. They often need to have high reliability, fast response
times, and low creep.
[0007] Attempts to produce complete electromechanical motors using
electrostatics and electromagnetic designs have relied on printing
the plastic components and manually adding wires and conductors.
These are considered some of the current best efforts, but not a
true 3D printed motor since the vast majority of the complexity and
materials in their designs are still produced by hand. However,
they have allowed people to rapidly prototype a design which could
be later optimized for manufacture.
[0008] The most successful electrically powered 3D printed
actuators are human muscle cells. While these have no industrial
counterpart, they have been integrated into 3D printed constructs
to make devices which respond to electrical stimuli. Such design
may use added geometric complexity enabled through 3D printing to
help the cells receive nutrients in the device while operating.
[0009] There have been successful types of 3D printed
actuators--piezoelectric and pneumatic. Piezoelectric materials are
often used for their high speed movements, small displacements and
accurate displacements. These materials have been successfully
fabricated using SFF techniques through both direct and indirect
methods. 3D printed pneumatics have been produced using SLS systems
and integrated into other complex assemblies. These actuators have
had a high level of reliability and durability. The ability to 3D
print pneumatic actuators allows for the integration of many
support components--fluid lines, mounting brackets, etc.--to be
integrated into a single printed part.
[0010] Wax actuators are used in a limited set of applications. In
general they are used for high reliability short stroke and high
power density applications. Often they are used as part of a
temperature regulation system in greenhouses, appliances, HVAC and
automotive applications. These actuators can rely on ambient heat
or heat generated by electrical resistance to actuate. Traditional
wax actuators convert thermal energy to mechanical energy as a wax
substance within the actuator expands due to increasing
temperature. Generally, such wax actuators are comprised of a
chamber and elastomeric membrane for containment of the wax, a
piston for concentrating the displacement, and a resistive heating
source. Specifically, a wax actuator traditionally uses a single
chamber of wax in a metal enclosure which is attached to a membrane
or piston. When the wax melts, it expands causing the piston to
move of the membrane to inflate. Cooling the wax causes it to
contract and return to the original configuration. The melt profile
of the wax can be customized to allow for sharp transitions at
specific temperatures, or spread out over a range of temperature to
allow for positional control between its contracted and expanded
state.
[0011] While 3D printed actuators have been an area of active
development, only weak polymer actuators, small displacement
piezoelectric actuators, and pneumatic actuators have been produced
with 3D printing. Thus, there is a need for soft electrical
actuators capable of generating higher forces and stresses than
previously achieved. In addition, there is a need for a new
material to facilitate fabricating these soft electrical actuators
including using 3D printing techniques. The invention satisfies
these needs.
SUMMARY OF THE INVENTION
[0012] The invention is directed to actuators including wax
actuators, for robotics and automation applications. In addition,
the invention is directed to a new material including a conductive
material component for use in actuators.
[0013] According to one embodiment of the invention, material
filled actuators are fabricated. A direct fabrication method uses a
multi-step process of producing completely sealed material filled
cells. This method produces an actuator similar to the more
traditional wax actuator.
[0014] According to another embodiment of the invention, actuators
are fabricated using an Electrically Actuated Hydraulic Solid
(EAHS) material. The EAHS material according to the invention
comprises or consists of a polymer matrix including a phase change
material and a conductive material, both suspended in the polymer
matrix.
[0015] According to the invention, the EAHS material may be
utilized in many different manufacturing processes, for example,
cutting, casting and extruding processes including layer-wise
fabrication. In addition, EAHS material may be used with a 3D
printing device as described below. 3D printing of actuators has
several potential advantages over traditionally manufactured
actuators. 3D printing allows for rapid prototyping, allowing a
user to iterate through design very quickly. A 3D printable
actuator also allows a user to test a design for a new actuator
without the costs associated with setting up tooling for a new
traditionally manufactured design. 3D printing also offers added
geometric complexity over traditional methods. This added geometric
complexity may allow for new efficiencies to be achieved. 3D
printing can also allow for many diverse material combinations
which may allow for complete systems to be produced on a single
device.
[0016] According to one multi-step process of the invention to
produce completely sealed material filled cells, a direct
fabrication method is used. First, a portion of a cell is 3D
printed such as from a silicone material and allowed to cure. The
cell is then filled with a material--wax, paraffin wax, EAHS
material--and allowed to cool. Additional material may be added
after cooling to fill in the depressions left in the center of the
cell, then allowed to cool again. The cooled material forms a core
that is removed from the cell and set aside. The cell is then
washed or bathed in a solution such as water. It is contemplated
that the temperature of the solution is greater than the melting
temperature of the material forming the core causing any material
that coated the cell walls to melt and float to the surface. The
cells are then removed from the solution. The core is placed back
into the cell and a top layer of the cell is printed and allowed to
cure. According to another embodiment of the invention, a
layer-wise fabrication process is contemplated such that the cell
and the core are created simultaneously.
[0017] According to another embodiment of the invention, the cell
including core are fabricated from an Electrically Actuated
Hydraulic Solid (EAHS) material. An EAHS material may combine wax
with other materials, with the combination 3D printable in the form
of an actuator. Electrically actuated hydraulic solid (EAHS)
materials are operable at relatively low voltages and currents,
allowing for easy integration into many environments where high
voltages or currents can be detrimental. The actuators can be
formed by casting, additive manufacturing and mechanical operations
allowing for the deployment of the actuators in small scale rapid
prototyped systems and large scale commercial production.
[0018] More specifically, EAHS materials comprise or consist of a
network of conductive materials suspended in an elastomeric matrix.
The conductive material may be selectively distributed through the
polymer matrix. It is also contemplate that the conductive material
may be randomly or evenly distributed through the polymer matrix.
The conductors transfer energy into cells of thermally expansive
materials embedded inside the matrix, thereby causing the entire
EAHS material to expand. Rather than design a migration of charge,
a chemical reaction, or a realignment of atomic structures, the
bulk EAHS material replicates the functionality of different
elements of a mechanical design using different functional sub
materials. The result is a functional analog that is produced in a
massively parallelized fashion.
[0019] The invention replicates the functionality and components of
a traditional paraffin piston into a scalable material framework.
Paraffin motor actuators are well known for their high force stroke
and stable actuation, making them ideal for large quasi-static
force generation. They operate at easily achievable voltages and
currents, and have a slow cycle rate, making them robust against
intermittent power disconnections. Paraffin motors have three
distinct components: A chamber with an elastomeric membrane for
containment of the wax, the wax itself, and a resistive heating
source for converting current into thermal energy. Electrically
Actuated Hydraulic Solid (EAHS) materials are a bulk material
system where the functionality of these distinct components is
replaced by the intrinsic behavior if three raw materials. This
distributed cellular structure for the actuator makes it
significantly more robust than its mono-cellular paraffin actuator
counterpart. One advantage is that it can be punctured repeatedly
and severed into section and each cell not damaged remains
operational.
[0020] According to a particular embodiment, a phase change
material (PCM) is dispersed in an elastomer matrix. The matrix is
contains a network of conductive material. This allows the
elastomeric matrix to act as a heater and membrane for the phase
changing cells. When a voltage is applied, the system heats, the
PCM expands generating an internal pressure. This pressure causes
the overall structure to expand.
[0021] The matrix is formed of a polymer that embeds the PCM and
conductive material. The polymer may be a single part or two part
elastomeric polymer, for example RTV silicone or two part
Polydimethylsiloxane (PDMS).
[0022] PCMs include any material with a high heat of fusion (high
melting point) and that change volume significantly when undergoing
a phase transition by heating and cooling. This can include a
liquid-solid change, a solid-liquid change, a solid-gas change and
a liquid-gas phase change. Particular examples of PCMs include
paraffin wax, fatty acids and water. A PCM should be selected for a
high change in volume when undergoing the phase transition. The PCM
melting or boiling point, and direction of volume change depend on
the particular application. Water has a solid unheated state as an
expanded state, with heating causing the structure to weaken and
contract. Paraffin waxes can be blended and selected for a
particular transition temperature and expand when heated, allowing
the structure to generate force when current is applied and the
structure is heated.
[0023] Conductive material is any material that has the property of
conducting electricity and can be embedded in the elastomer matrix
to form a network of the material through the elastomer. This
includes, for example, powders, strips and fibers of metals, carbon
and other materials which are conductive. Particular examples of
conductive material include carbon black, silver nanoparticles, and
copper filings.
[0024] The method for creating EAHS material includes combining the
PCM, polymer and conductive material. Any method for combining the
PCM, polymer and conductive material is contemplated as dependent
upon the form of material used. For example, a powdered PCM solid
or melted liquid PCM may be added to a single part elastomer
containing the conductive material. As another example, a powdered
PCM and conductive material may each be added into a different
precursor of a two part elastomer, which are then combined. The
powdered PCM and conductor could be added to one part of a two part
elastomer and then mixed with the other part. Liquid PCM could be
mixed in with one part of two part elastomer and then the other
part is mixed with the powered, then both parts are mixed together.
Alternatively to mixing, the PCM could be embedded inside of an
unset conductive material-elastomer blend. This can be accomplished
using a 3D printer, inkjet, or other additive process. The
conductive material-elastomer blend is cured after the PCM is
embedded to fabricate the EAHS.
[0025] Advantageously, EAHS material may be manipulated into any
form for cutting, printing, molding, and extruding. According to
one method of fabrication of EAHS, a phase change material such as
paraffin wax is melted and stirred into a first precursor material
forming a first mixture, which is cooled. A conductive material
such as carbon black is selected and mixed into a second precursor
material forming a second mixture. A precursor is a compound that
participates in a chemical reaction that produces another compound.
The first and second mixtures are combined and cured to form the
EAHS. For example, the EAHS material is a Polydimethylsiloxane
(PDMS) elastomer embedded with a paraffin wax matrix and conductive
material.
[0026] In order to address the challenges of existing actuator
technologies, the invention identifies a new kind of bulk material
actuator that offers a new performance tradeoff in stress density
that is un-dominated by existing technologies. Whereas most
compliant electroactive polymers attempt to induce a mechanical
change by means of a charge migration, or charge separation, EAHS
actuators uses a network of conductive materials suspended inside
of an insulating elastomeric matrix to generate thermal energy.
This energy is then transferred into cells of thermally expansive
materials embedded inside of the matrix. The heated cells expand
when they transition from a solid to a liquid as they are heated,
generating internal pressure. The elastomer matrix acts as a
containment system for the embedded phase change material,
preventing the liquid phase from leaching out of the system. Each
entrapped paraffin globule acts as an independent "micro-piston" as
a result. Motion is bidirectional in that it is expansive on
heating and shrinks on cooling. Large forces however are only
generated during the expansion phase for a PCM. A PCM with a
positive coefficient of thermal expansion from melting expand when
heated. A PCM with a negative coefficient of thermal expansion from
melting expand when cooled below the freezing point.
[0027] The invention and its attributes and advantages may be
further understood and appreciated with reference to the detailed
description below of one contemplated embodiment, taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] The preferred embodiments of the invention will be described
in conjunction with the appended drawing provided to illustrate and
not to the limit the invention, where like designations denote like
elements, and in which:
[0029] FIG. 1 is a flow chart of a method for fabricating material
filled cells of an actuator according to an embodiment of the
invention.
[0030] FIG. 2 is a block diagram of the method shown in FIG. 1 for
fabricating material filled cells of an actuator according to an
embodiment of the invention.
[0031] FIG. 3 is a flow chart of a method for fabricating
Electrically Actuated Hydraulic Solid (EAHS) material according to
an embodiment of the invention.
[0032] FIG. 4 illustrates a portion of an Electrically Actuated
Hydraulic Solid (EAHS) material according to an embodiment of the
invention.
[0033] FIG. 5 is a flow chart of a method for fabricating
Electrically Actuated Hydraulic Solid (EAHS) material according to
another embodiment of the invention.
[0034] FIG. 6 is a block diagram of fabricated EAHS material
according to an embodiment of the invention.
[0035] FIG. 7 is a graph illustrating expansion in length by wax
concentration according to an embodiment of the invention.
[0036] FIG. 8 is a graph illustrating force versus displacement
data on the performance of a linear actuator made from EAHS
according to an embodiment of the invention.
[0037] FIG. 9 is a graph illustrating force versus temperature data
on the performance of a linear actuator made from EAHS according to
an embodiment of the invention.
[0038] FIG. 10 illustrates a perspective view of a robot made with
EAHS actuators according to an embodiment of the invention.
[0039] FIG. 11 illustrates a side view of the robot made with EAHS
actuators according to an embodiment of the invention.
[0040] FIG. 12 illustrates an enlarged side view of a portion of
the robot made with EAHS actuators according to an embodiment of
the invention.
[0041] FIG. 13 illustrates a table of various electroactive
material actuators compared across important performance
metrics.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0042] According to one embodiment, the invention is directed to an
actuator fabricated using Solid Freeform Fabrication (SFF). More
specifically, the invention is drawn to direct fabrication methods
and new materials for fabrication including 3D fabrication. For
exemplary purposes, the invention refers to silicone/wax cell
actuators when discussing direct fabrication methods and
Electrically Actuated Hydraulic Solid (EAHS) actuators when
discussing new materials for fabrication of electrically actuated
actuators. Similar to traditional actuators, both are complexly
soft, allowing them to be integrated into the growing field of soft
robotics. Both types of actuators are completely metal free,
allowing them to operate in environments like MRIs, where
traditional wax actuators would be unable to operate due to their
metal housings and pistons. In addition, the actuators of the
invention volumetrically expand, which may prove ideal for certain
evolutionary biology work. It is also contemplated that the system
and methods of the invention may be useful in applications such as
temperature regulation systems for greenhouses, appliances, HVAC
and automotive applications, highly reliable short stroke and high
power density applications, and rapid prototyping.
[0043] According to one embodiment of the invention, a direct
fabrication method is used to fabricate completely sealed material
filled cells. Specifically, a 3D printed wax actuator is created
using a multi-step process as shown by the flow chart in FIG. 1 and
block diagram of FIG. 2.
[0044] As shown by step 102 of FIGS. 1 and 2(a) of FIG. 2, a
portion of a cell is 3D constructed such as by 3D printing device
using a Fab@home Model 3 system. The cell is constructed of a
silicone material, however any material is contemplated that allows
deformation upon heating and cooling. Once constructed, the cell
includes a cavity formed by a bottom side connected to a first
side, a second side, a third side and a fourth side. The 3D printed
cell is allowed to cure, for example overnight or at least 6 or 8
hours. The cavity of the cell is then filled with a material at
step 104 of FIGS. 1 and 2(b) of FIG. 2. The material is allowed to
cool forming a core as show in FIG. 1 at step 106 and 2(c) of FIG.
2. According to the invention, the material used may be wax such as
paraffin wax or a material with a portion made of wax such as an
EAHS material discussed more fully below. After cooling the core
may shrink or depression may have formed. Thus, steps 104 and 106
of FIG. 1 may be repeated to add material to fill in any
depressions left in the cell, also shown by 2(d) and 2(e) of FIG.
2. The cooled material forms a core that is removed from the cell
and set aside shown by step 108 of FIGS. 1 and 2(f) of FIG. 2. At
step 110 of FIGS. 1 and 2(g) of FIG. 2, the cell is washed or
bathed in a solution such as water. As an example, the cell may be
bathed in water at a temperature greater than the melting
temperature of the material of the core, for example 85 degrees
Celsius, causing any material that coated the cell walls to melt
and float to the surface. The cell is then removed from the
solution.
[0045] The core is inserted back into the cell at step 112 of FIGS.
1 and 2(h) of FIG. 2. As shown by step 114 of FIGS. 1 and 2(i) of
FIG. 2, a top layer of the cell is created by using a 3D printing
device and allowed to cure, such as overnight, to fabricate a
compliant cell structure with the cell encapsulating the core. When
the cell is heated or re-heated, it expands and when cooled or
re-cooled, it shrinks. The cell finds the lowest energy state for
the new internal volume. It should be noted that control of the
wall thickness of the cell, i.e., a thin side wall, can direct the
expansion into that a direction. As a result, these soft actuators
are thermally activated and capable of expanding, for example by up
to 6% of volume when heated above the melting temperature of a wax
core. Closed wax filled cells produced using the method described
above were measured in the X and Y directions at their thickest
points and exhibited a 5% to 9% increase dimensional length as a
result of heating.
[0046] According to another embodiment of the invention, a novel
single bulk material actuator is developed using electrically
actuated hydraulic solid (EAHS) materials to massively parallelize
and simplify this process and convert a rigid traditional wax
actuator into an elastic material. The single bulk material
actuator replicates the functionality and components of a
traditional wax actuator through the integration of conductive
elements into the material enabling actuation (i.e., expansion,
contraction) of the actuator.
[0047] Hydraulic solids can generate higher forces and stresses per
unit density, than any previously reported actuator material. EAHS
are operable at relatively low voltages and currents, allowing for
easy integration into many environments where high voltages or
currents can be detrimental. The actuators can be formed by
casting, additive manufacturing and mechanical operations allowing
for the deployment of the actuators in small scale rapid prototyped
systems and large scale commercial production. Their main drawback
is actuation speed. Since EAHS are thermally actuated, cycle time
depends on shape and insulation, and is approximately one thousand
seconds for a centimeter cubed actuator. EAHS actuators use a
network of conductive materials suspended inside of an insulating
elastomeric matrix to generate thermal energy.
[0048] According to one embodiment, an EAHS material is a two-part
Polydimethylsiloxane (PDMS) elastomer, embedded with a paraffin wax
matrix and conductive material. As shown in FIG. 3, Electrically
Actuated Hydraulic Solid (EAHS) material 158 is fabricated by
combining a polymer material 152, a phase change material 154, a
conductive material 156. All materials 152, 154, 156 may be
combined simultaneously, however any order for combining materials
152, 154, 156 is contemplated. For example, the polymer material
152 and phase change material 154 may be combined prior to
combining with the conductive material 156. As another example, the
polymer material 152 and conductive material 156 may be combined
prior to combining with the phase change material 154. Combining a
polymer material 152, a phase change material 154, and a conductive
material 156 forms a conductive elastomeric structure.
[0049] The polymer may be a single part or two part elastomeric
polymer, for example RTV silicone or two part Polydimethylsiloxane
(PDMS).
[0050] PCMs 154 are those with a high melting point and that change
volume significantly when undergoing a phase transition by heating
and cooling, i.e., a liquid-solid change, a solid-liquid change, a
solid-gas change, a liquid-gas change. Particular examples of PCMs
include paraffin wax, fatty acids and water. PCMs may have a
positive or negative coefficient of thermal expansion. More
specifically, a PCM with a positive coefficient of thermal
expansion from melting expand when heated. A PCM with a negative
coefficient of thermal expansion from melting expand when cooled
below the freezing point.
[0051] Conductive material 156 is embedded in the elastomer matrix
to form a network of the material through the elastomer and may
include powders such as carbon black, strips and fibers of metal
such as copper filings, carbon and other conductive materials.
[0052] The method for creating EAHS material includes combining the
PCM, polymer and conductive material. Any method for combining the
PCM, polymer and conductive material is contemplated as dependent
upon the form of material used. For example, a powdered PCM solid
or melted liquid PCM may be added to a single part elastomer
containing the conductive material. As another example, a powdered
PCM and conductive material may each be added into a different
precursor of a two part elastomer, which are then combined. The
powdered PCM and conductor could be added to one part of a two part
elastomer and then mixed with the other part. Liquid PCM could be
mixed in with one part of two part elastomer and then the other
part is mixed with the powered, then both parts are mixed together.
Alternatively to mixing, the PCM could be embedded inside of an
unset conductive material-elastomer blend, for example using a 3D
printing device.
[0053] A conductive elastomeric structure of an Electrically
Actuated Hydraulic Solid (EAHS) material is shown in FIG. 4. As
shown in FIG. 4, the structure 178 of an Electrically Actuated
Hydraulic Solid (EAHS) material comprises or consists of a polymer
matrix 172 including a phase change material 174 and a conductive
material 176, both embedded and suspended in the polymer matrix
172. As shown in FIG. 4, the phase change material 174 forms a
plurality of closed cells encapsulated by the polymer matrix 172.
Although the conductive material 176 is illustrated in FIG. 4 as
being randomly distributed through the polymer matrix 172, it is
contemplated that the conductive material 176 may be evenly
distributed through the polymer matrix 172 or selectively
positioned within the matrix.
[0054] When the PCM undergoes a phase change as controlled by the
conductive material, the internal pressure varies and actuates the
structure. The PCM undergoes a phase change to vary internal
pressure and actuate the structure by either expanding or
contracting. For example, PCM in the form of water is heated to
contract the EAHS material structure and frozen to expand the EAHS
material structure. In contrast, a PCM in the form of a gas may be
heated to expand the EAHS material structure and cooled to contract
the structure. The PCM can return to its unheated state, for
example, by being embedded in an environment at a temperature lower
than the temperature required for a phase change of the PCM. This
allows the PCM to revert to its cooled state when not heated by the
conductive material. It is contemplated that changing the ambient
temperature and thermal conduction of the environment can change
the rate at which the EAHS structure cools.
[0055] As shown more specifically in FIG. 5, a phase change
material is melted at step 202. According to one embodiment, the
phase change material may be paraffin wax. The paraffin wax has a
melting temperature of 60 degrees Celsius. The liquid paraffin wax
is rapidly stirred into a precursor at step 204. Precursors
according to the invention may be a silicone elastomer matrix,
Polydimethylsiloxane (PDMS). A ratio of the phase change material
to the first precursor material achieves a desired internal
pressure. At step 206, the mixture of phase change material and
first precursor material is cooled and allowed to cure. The
material phase separates entrapping the wax structures inside the
PDMS. These structures are generated by the turbulent mixing and
phase separation, randomly distributing them through the
material.
[0056] As shown by step 252, a conductive material is selected such
as carbon black. The conductive material is mixed with a second
precursor at step 254. At step 272 both mixtures are combined. When
both sets of doped precursor are combined together the material
starts to cure and the EAHS is formed as shown by step 274. It
should be noted that material without carbon black or a conducting
matrix displays the same expansion properties, but requires an
external heat source. According to this embodiment, applying a
voltage to the combined mixture causing the phase change material
to expand or contract.
[0057] As an alternative to the method described above, a two part
Polydimethylsiloxane (PDMS) of Ecoflex 0050 by Smooth-On are mixed
together at room temperature. After the Ecoflex are mixed, it is
placed in an open metal container and liquid paraffin wax is gently
added to the metal container so as to prevent material from leaving
the container. The PDMS and liquid wax are then mechanically mixed
rapidly. The wax cooled as a result of the thermal energy transfer
from the wax to the PDMS. The wax is not allowed to pool or
stagnate in the container as the entire volume of PDMS and wax is
mixed. Mixing is stopped once the entirety of the wax is cooled to
room temperature. The mixture of wax and PDMS is then optionally
placed in a vacuum chamber to de-gas the mixture. The PDMS compound
has a pot life of 18 minute, cures in 3 hours, and must cure at
temperatures above 18 degrees Celsius. After printing the parts
must be allowed to sit to fully cure.
[0058] FIG. 6 is a block diagram of fabricated EAHS material
according to an embodiment of the invention. As shown in FIG. 6,
the material includes a phase change material such as solid wax
particles 302, a conductive material such as carbon black particles
304, and a precursor material such as PDMS 306. Heating the
material causes the phase change particles to transform from solid
particles 302 to liquid particles 308. Cooling these particles 308
causes them to transform back into solid particles. With the
material transformations of EAHS, it may be formed by cutting,
printing, molding, and extruding. For example, EAHS material may be
placed into a 3D printing device based on syringe deposition, using
the Fab@Home Model 3 platform. The material could be extruded
through an 18-gauge taper plastic tip form Nordson EFD during its
pot-life. Smaller tips lead to jamming of the head from the
particles of wax. The material was self-supporting and bonded
across layers. As an alternative to 3D printing, the material could
also be placed into rigid mold and cast into a variety of shapes.
Alternatively, a piece of the cured material can be cut or carved
into shapes using a blade. Voltage 310 as applied to the EAHS
material controls the conductive material. Thus, patterning of
placing electrodes into the material for the current delivery
allows for the control the effective resistance of the material.
Inserting the electrodes as a set of interwoven wisps or strands
allows for minimal resistance and selective actuation of the
material. The insulating nature of the elastomer matrix slows the
rate of thermal conduction between sections with current flow and
sections which are dormant.
[0059] As mentioned above, by varying the relative ratio of the
elastomeric matrix to the phase change material, the internal
pressure generated for a specified temperature can be controlled.
In order to characterize the effects of the wax to PDMS
concentration, several different ratios of wax to PDMS by liquid
volume were produced and tested. In order to test the thermal
expansion of the material, molds were out of ABS on an FDM system.
The molds were 10 mm wide, 10 mm tall, and 45 mm long. The PDMS-wax
mixture was placed in the mold and allowed to cure. The molded
PDMS-wax mixture was removed once cured and placed in a bath of
water at 85 degrees Celsius, above the melting temperature of the
wax. Once all of the wax was melted, it was removed from the liquid
and measured in the longest direction using calipers with an
accuracy of 0.01 mm. As shown by FIG. 7, increasing the percentage
wax in the material increases the amount the material expands when
heated. There is an unexpected decrease in the percentage of
expansion between 40% and 50% of wax by volume. Lower internal
pressure results in a smaller expansion and lower forces generated
for the same thermal condition. Successful EAHS were fabricated
with concentrations of phase change material between 0 and 60% of
the bulk material by volume. When the concentration of phase change
material exceeded 60%, the matrix becomes too sparse to encapsulate
the cells, causing leakage between pistons that resulted in loss of
pressure.
[0060] As shown in FIG. 7, concentrations of 0%, 20%, 33% 39% 50%
and 66% by liquid wax of the material were made and tested. The
material showed a definite increase in length relative to the pure
PDMS sample. Since PDMS has a relatively high coefficient of
thermal expansion of 3.10*10.sup.-4 percent-C.sup.-1 it is expected
that the PDMS will increase in size when heated from room
temperature to 85 degrees Celsius. Since the ambient temperature
was not recorded, it is not possible to compare the results with
the value expected in literature accurately. However an estimate of
21 Celsius for room temperature would give a 1.92% increase in
length when heated to 85 degrees Celsius and a 1.7% increase was
measured. The trend in the data shows that as the concentration of
wax is increased, the material expands more.
[0061] Additionally, a purely linear actuator is demonstrated by
confining a cylinder of the material inside of a rigid tube with a
cap on the end. Since the internal pressure from the phase change
material will expand in any direction, containing the materials
expansion is necessary for generating high forces for linear
displacement. A 50 mm long, 14 mm diameter cylindrical sample is
heated to 70 degrees C. The blocked force, outward stroke and
return stroke were measured using a MTS machine with a laser
extensometer. The sample was heated in the blocked position and
then the tester would cycle through loading and unloading three
times. The system demonstrated a significant but small amount of
hysteresis most likely due to internal energy losses from straining
the elastic matrix.
[0062] FIG. 8 is a graph illustrating force versus displacement
data on the performance of a linear actuator made from EAHS
according to an embodiment of the invention. As shown by FIG. 8,
the force generated and strain generated is dependent on the
concentration of the phase change material. There is significant
hysteresis in the actuation.
[0063] FIG. 9 is a graph illustrating force versus temperature data
on the performance of a linear actuator made from EAHS according to
an embodiment of the invention. As shown by FIG. 9, the blocked
force is dependent on the temperature of the sample and
concentration of phase change material.
[0064] This actuator allowed for up to 4.5 kN of force and a
displacement on the order of 2 mm from a 50 mm long sample. This is
several orders of magnitude (.about.10.sup.5) more force than IPMC
bending actuators can generate at their tip for similar voltages
and several orders of magnitude (.about.10.sup.2) than DEA
actuators can generate at 5 kV. The high force and low density
results in a specific actuation
( .sigma. .rho. ) of 3.0 * 10 - 2 [ MPa g cm 3 ] . ##EQU00001##
Shape memory alloys have a specific actuation of
2.8 * 10 - 2 [ MPa g cm 3 ] , ##EQU00002##
twisted polymer fibers have a specific actuation of only
6.52 * 10 - 3 [ MPa g cm 3 ] ##EQU00003##
While SMA and twisted fiber actuators generate their forces by
compressing, the EAHS actuators generate their forces by expanding.
Additionally unlike twisted fiber actuators, SMA and EAHS actuators
contain an internal heating source, allowing for a completely
integrated system.
[0065] Often actuators with high stresses have engineering
limitations on their geometry which limit the total force than can
generate. SMA actuators high conductivity necessitates their
production into thin forms to increase the effective resistance.
Without such limitations, the current requirements to get a sample
to self-heat would be enormous. As a result SMA actuators are often
used in flat sheets and thin cables. EAHS actuators have higher
resistances and therefor can be heated with less current than SMA
actuators. This allows the system to be produced in larger operable
structures than SMA actuators and therefor generate more force. The
limiting engineering principles of this material are not yet know,
but it can already generate more force than comparable electrically
driven material actuators.
[0066] To probe the utility of the linear actuator, a small robotic
system was built as shown in FIG. 10, FIG. 11 and FIG. 12. Each leg
of the robot is powered by a single 14 mm diameter cylinder of the
material. The center of the cylinder contained a copper wire for
connection to power. The exterior of the casing was connected to
ground. Activating the actuator caused it to expand from 50 mm to
52 mm. This small length changed was turned into a large angle
change by allowing the actuator to pivot through the center of the
leg. One end of the actuator was affixed 20 mm from the pivot of
the leg. The other end was affixed 32 mm from the pivot point. This
allowed the triangle formed from the three points to collapse to a
line when the actuator expanded. This resulted in a rotation of 21
degrees. This motion allowed the robot to rise 38 mm, substantially
more than the 2 mm length of expansion.
[0067] The robot was produced using a Stratasys Connex printer
using Vero Grey material. The robot was assembled using metal pins
for the joints. A separate 12V power supply actuator the muscles of
the robot to expand. Using a 50 mm long muscle with a 20 mm
diameter casing, the angle change from expanding the muscle between
50 and 52 mm is given by:
cos - 1 ( - 2304 + x 2 40 x ) - cos - 1 ( - 2100 + x 2 40 x )
##EQU00004##
[0068] In one particular embodiment, the EAHS material is heated
using 12 Volts. It is then cooled, and cut into two separate
pieces. Each piece maintains an electrical contact. The voltage is
then applied again and the system heats up and expands again. In
another embodiment, a sample containing 30% wax is heated to 71
degrees Celsius inside a metal container with and open top. In
another embodiment, a sample containing 20% wax is cooled from 71
degrees Celsius to room temperature inside a metal container with
an open top. In yet another embodiment, a 30% wax concentration
sample is reconstructed at room temperature.
[0069] FIG. 13 illustrates a table of various electroactive
material actuators compared across important performance metrics.
As shown in FIG. 13, EAHS can generate orders of magnitude more
force than other electroactive materials. When compared with other
electrically driven actuatable materials, EAHS generate these
forces at lower voltages and for less mass. Several other actuators
outperform EAHS on the strain metric, but those materials generate
very small stresses. In the table, the top third of the performance
range is colored medium gray, the middle third light gray, the
lower third dark gray. It should be noted that typical force
ratings are based upon standard applications of the technology.
[0070] High force EAHS materials offer new opportunities for the
designers of soft machines, robotics and automation applications.
Soft robotics often use pneumatics for driving pneunets, but rely
on rigid mechanical valves for control. EAHS can potentially be
used for valving of high pressure sources. Although the invention
discusses a robot directed to linear actuation, it is contemplated
that the ability of the material to expand volumetrically can be
used to augment pressure in a fluid system. It can also be
constrained to force it to generate a bending motion enabling
deformable structures which are resistant to high loads.
[0071] Electrically actuated hydraulic solids are an exciting new
class of electroactive polymer actuators. The high forces which can
be generated open up new application spaces for Electroactive
Polymer (EAP) actuators. The ability to replicate the complete
systems of a traditional wax actuator is a new way to think about
the design of material actuators. Rather than design a migration of
charge, a chemical reaction, or a realignment of atomic structures,
the bulk material replicates the functionality of different
elements of a mechanical design using different functional sub
materials. The result is a functional analog that is produced in a
massively parallelized fashion. It is contemplated that the
invention may be applied to other traditional mechanically
manufactured actuators in the future to produce many other
functionally memetic analogs to traditional actuators.
[0072] The described embodiments are to be considered in all
respects only as illustrative and not restrictive, and the scope of
the invention is not limited to the foregoing description. Those of
skill in the art may recognize changes, substitutions, adaptations
and other modifications that may nonetheless come within the scope
of the invention and range of the invention.
* * * * *