U.S. patent application number 09/909548 was filed with the patent office on 2002-03-07 for novel metal hydride artificial muscles.
Invention is credited to Kim, Kwang J., Shahinpoor, Mohsen.
Application Number | 20020026794 09/909548 |
Document ID | / |
Family ID | 26914480 |
Filed Date | 2002-03-07 |
United States Patent
Application |
20020026794 |
Kind Code |
A1 |
Shahinpoor, Mohsen ; et
al. |
March 7, 2002 |
Novel metal hydride artificial muscles
Abstract
New artificial muscles and actuators, that are operated by
hydrogen gas as working fluid stored interstitially in metal
hydrides as a hydrogen sponge. These artificial muscles and
actuators are operated both electrically and thermally. The
artificial muscles and actuators have fast response, are
compact/light-weight, are noiseless, and produce high-power
density. They can be used for biomedical, space, defense,
micro-machines, and industrial applications.
Inventors: |
Shahinpoor, Mohsen;
(Albuquerque, NM) ; Kim, Kwang J.; (Albuquerque,
NM) |
Correspondence
Address: |
Dennis F. Armijo, Esq.
Dennis F. Armijo, P.C.
Suite 200
5300 Sequoia Rd. NW
Albuquerque
NM
87120
US
|
Family ID: |
26914480 |
Appl. No.: |
09/909548 |
Filed: |
July 19, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60220006 |
Jul 21, 2000 |
|
|
|
Current U.S.
Class: |
60/508 ; 2/2.11;
623/14.13; 623/24; 901/22 |
Current CPC
Class: |
B25J 9/0006 20130101;
A61F 2/08 20130101; B64G 6/00 20130101; B25J 9/1095 20130101; A61F
2/50 20130101; A61F 2002/501 20130101; A61F 2002/0894 20130101;
A61F 2002/5066 20130101 |
Class at
Publication: |
60/508 ;
623/14.13; 623/24; 2/2.11; 901/22 |
International
Class: |
A61F 002/08; A61F
002/54; A61F 002/74; B25J 011/00; B64G 006/00 |
Claims
What is claimed is:
1. A metal hydride artificial muscle comprising: an expandable
bladder; at least one metal hydride specimen encased within said
expandable bladder; and a means to heat said at least one metal
hydride.
2. The invention of claim 1 wherein said expandable bladder
comprises a collapsible bladder.
3. The invention of claim 1 wherein said bladder comprises a
hermetically sealed bladder.
4. The invention of claim 1 wherein said expandable bladder further
comprises at least one actuator arm affixed to at least one part of
said expandable bladder.
5. The invention of claim 4 further comprising spring loading said
at least one actuator arm.
6. The invention of claim 1 wherein said at least one metal hydride
specimen comprises encapsulated particles within said at least one
metal hydride specimen.
7. The invention of claim 6 wherein said encapsulated particles
comprise an encapsulated material comprising a thermally conductive
medium.
8. The invention of claim 1 wherein said means to heat said at
least one metal hydride comprises a controller.
9. The invention of claim 8 wherein said controller comprises a
temperature sensor feedback loop.
10. The invention of claim 8 wherein said controller comprises a
microprocessor.
11. The invention of claim 1 wherein said means to heat said at
least one metal hydride specimen comprises an electric Joule
heater.
12. The invention of claim 1 wherein said means to heat said at
least one metal hydride specimen comprises a heater to heat said at
least one metal hydride specimen above at least one critical
temperature.
13. The invention of claim 1 wherein said means to heat said at
least one metal hydride specimen further comprises a means to cool
said at least one metal hydride specimen.
14. The invention of claim 13 wherein said means to cool said at
least one metal hydride specimen comprises an apparatus to cool
said at least one metal hydride specimen to below at least one
critical temperature.
15. A method for actuating an object with a metal hydride
artificial muscle, the method comprising the steps of: a) providing
at least one metal hydride specimen in an expandable bladder; b)
affixing at least one part of the expandable bladder to an actuator
arm; and c) heating the at least one metal hydride specimen.
16. The method of claim 15 wherein the step of heating comprises
heating the at least one metal hydride specimen above at least one
critical temperature.
17. The method of claims 15 further comprising the step of cooling
the at least one metal hydride specimen.
18. The method of claim 17 wherein the step of cooling comprises
cooling the at least one metal hydride specimen below at least one
critical temperature.
19. The method of claim 15 wherein the step of heating comprises
controlling a heater.
20. The method of claim 19 wherein the step of controlling
comprises sensing a temperature of the at least one metal hydride
and feeding the sensed temperature to the controller.
21. The method of claim 15 further comprising the step of spring
loading the at least one actuating arm.
22. The method of claim 15 wherein the step of providing at least
one metal hydride specimen comprises encapsulating particles within
the at least one metal hydride specimen with a thermally conductive
medium.
23. A metal hydride artificial muscle for a biomedical and robotic
applications comprising: an expandable bladder with a first end
affixed to a first portion of a body and a second end affixed to a
second portion of a body; at least one metal hydride specimen
encased by said expandable bladder; and a means for heating and
cooling said at least one metal hydride specimen.
24. A metal hydride artificial muscle for hydrogen gas aided take
off, flying and landing of an object comprising: a bladder; at
least one metal hydride specimen encased by said bladder; and a
means for heating and cooling said at least one metal hydride
specimen.
25. A metal hydride artificial muscle joint power augmentation
system for external assistance of a person comprising: an
expandable and collapsible bladder with a first end affixed to a
first portion of the area to be augmented and a second end affixed
to a second portion of the area to be augmented; at least one metal
hydride specimen encased by said expandable and collapsible
bladder; and a means for heating and cooling said at least one
metal hydride specimen.
26. The invention of claim 25 wherein said joint power augmentation
system comprises a joint power augmentation system for astronaut
space suits.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based on U.S. Provisional Application
Ser. No. 60/220,006 entitled "Novel Metal Hydride Artificial
Muscles", filed on Jul. 21, 2000, the teachings of which are
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention (Technical Field)
[0003] The invention relates to artificial muscles and more
particularly to artificial muscles actuated by a hydrogen gas as a
working fluid and metal hydrides as a hydrogen sponge and can be
operated both electrically and thermally.
[0004] 2. Background Art
[0005] Materials and devices that can mimic biological muscles and
thus be considered as artificial muscles have been discussed in the
pertinent literature. There are prior art artificial muscles using
ionic polymers as disclosed in M. Shahinpoor, Y. Bar-Cohen, J.
Simpson, and J. Smith, "Ionic Polymer-Metal Composites (IPMC's) As
Biomimetic Sensors, Actuators and Artificial Muscles-A Review",
Smart Materials & Structures Journal, Vol. 7, pp. R15-R30,
(1998); M. Shahinpoor, "Ionic Polymer Metal Composite As Biomimetic
Sensors and Actuators", in Polymer Sensors and Actuators, edited by
Y. Osada and D. DeRossi, Springer-Verlag Publishing, Springer,
Berlin-Heidelberg, pp. 325-360, (1999).
[0006] In addition, shape memory alloy artificial muscles have been
disclosed in M. Shahinpoor, "Fibrous, Parallel Spring-Loaded
Shape-Memory Alloy (SMA) Robotic Linear Actuators", U.S. Pat. No.
5,821,664, issued Oct. 13th, 1998; G. Wang and M. Shahinpoor,
"Design, Prototyping and Computer Simulation of A Novel Large
Bending Actuator Made with A Shape Memory Alloy Contractile Wire",
Smart Materials and Structures Journal, Vol. 6, No. 2, pp. 214-221,
(1997); G. Wang and M. Shahinpoor, "Design for Shape Memory Alloy
Rotatory Joint Actuators Using Shape Memory Effect and
Pseudoelastic Effect", Smart Materials Technology, Edited by W.
Simmons, Ilhan Aksay and D. R. Huston, SPIE Publication Vol. 3040,
pp. 23-30, (1997); and G. Wang and M. Shahinpoor, "A New Design for
A Rotatory Joint Actuator Made with Shape Memory Alloy Contractile
Wire", J. Intelligent Materials Systems & Structures, Vol. 8,
no. 3, pp. 215-219, March (1997).
[0007] Liquid crystal elastomer artificial muscles are discussed in
M. Shahinpoor, "Electrically-activated artificial muscles made with
liquid crystal elastomers", paper no. 3987-27, SPIE Smart Materials
& Structures Conference, New Port Beach, Calif., Mar. 5-9,
(2000).
[0008] Other types of artificial muscles are discussed in U.S. Pat.
No. 5,250,167 entitled Electrically Controlled Polymeric Gel
Actuators; and U.S. Pat. No. 5,389,222 entitled Spring-Loaded Ionic
Polymeric Gel Linear Actuator.
[0009] However, none of the prior art discloses metal hydride
artificial muscles.
SUMMARY OF THE INVENTION (DISCLOSURE OF THE INVENTION)
[0010] In accordance with the present invention there is provided a
method and apparatus for using metal hydrides for an artificial
muscle system. The preferred metal hydride artificial muscle
comprises an expandable bladder, at least one metal hydride
specimen encased within the expandable bladder and an apparatus to
heat the at least one metal hydride. The preferred expandable
bladder also comprises a collapsible bladder. The preferred
expandable bladder comprises a hermetically sealed bladder. The
expandable bladder can further comprise at least one actuator arm
affixed to at least one part of said expandable bladder and can
also comprise spring loading the at least one actuator arm. The
preferred at least one metal hydride specimen comprises
encapsulated particles within the at least one metal hydride
specimen. The preferred encapsulated particles comprise an
encapsulated material comprising a thermally conductive medium. The
preferred apparatus to heat the at least one metal hydride
comprises a controller. The preferred controller comprises a
temperature sensor feedback loop. The controller can also comprise
a microprocessor. The apparatus to heat the at least one metal
hydride specimen can comprise an electric Joule heater. The
preferred apparatus to heat the at least one metal hydride specimen
comprises a heater to heat the at least one metal hydride specimen
above at least one critical temperature. The apparatus to heat the
at least one metal hydride specimen can further comprise an
apparatus to cool the at least one metal hydride specimen. The
preferred apparatus to cool the at least one metal hydride specimen
comprises an apparatus to cool the at least one metal hydride
specimen to below at least one critical temperature.
[0011] The preferred method for actuating an object with a metal
hydride artificial muscle comprising the steps of providing at
least one metal hydride specimen in an expandable bladder, affixing
at least one part of the expandable bladder to an actuator arm and
heating the at least one metal hydride specimen. The step of
heating comprises heating the at least one metal hydride specimen
above at least one critical temperature. The preferred method
further comprises the step of cooling the at least one metal
hydride specimen. The preferred step of cooling comprises cooling
the at least one metal hydride specimen below at least one critical
temperature. The step of heating preferably comprises controlling a
heater. The step of controlling comprises sensing a temperature of
the at least one metal hydride and feeding the sensed temperature
to the controller. The method can also comprise the step of spring
loading the at least one actuating arm. The preferred step of
providing at least one metal hydride specimen comprises
encapsulating particles within the at least one metal hydride
specimen with a thermally conductive medium.
[0012] The preferred metal hydride artificial muscle for biomedical
and robotic applications comprises an expandable bladder with a
first end affixed to a first portion of a body and a second end
affixed to a second portion of a body, at least one metal hydride
specimen encased by the expandable bladder and an apparatus for
heating and cooling the at least one metal hydride specimen.
[0013] The preferred metal hydride artificial muscle for hydrogen
gas aided take off, flying and landing of an object, comprises a
bladder, at least one metal hydride specimen encased by the
bladder, and an apparatus for heating and cooling the at least one
metal hydride specimen.
[0014] The preferred metal hydride artificial muscle joint power
augmentation system for external assistance of a person comprises
an expandable and collapsible bladder with a first end affixed to a
first portion of the area to be augmented and a second end affixed
to a second portion of the area to be augmented, at least one metal
hydride specimen encased by the expandable and collapsible bladder
and an apparatus for heating and cooling the at least one metal
hydride specimen. The joint power augmentation system can comprise
a joint power augmentation system for astronaut space suits.
[0015] A primary object of the present invention is to provide a
new family of artificial muscles capable of actuating with a broad
range of applications.
[0016] Yet another object of the present invention is to provide
electrical and thermal robotic control capabilities.
[0017] Yet another object of the present invention is to mimic
biological situations that require high force, power, and velocity
responses.
[0018] A primary advantage of the present invention is that it
provides biological-like smooth operation capability with long
stroke capabilities of actuation along with large forces.
[0019] Another advantage of the present invention is that it is
noiseless and vibrationless.
[0020] Yet another advantage of the present invention is that the
functioning mechanism is the simultaneous hydrogen
absorption/desorption and can lead to a buffering effect preventing
sharp power surge or shock loads.
[0021] Another advantage of the present invention is that in
selecting an appropriate hydride, the desired operating pressure
can be easily obtained.
[0022] Another advantage of the present invention is that it can
also provide a large actuation-displacement.
[0023] Other objects, advantages and novel features, and further
scope of applicability of the present invention will be set forth
in part in the detailed description to follow, taken in conjunction
with the accompanying drawings, and in part will become apparent to
those skilled in the art upon examination of the following, or may
be learned by practice of the invention. The objects and advantages
of the invention may be realized and attained by means of the
instrumentalities and combinations particularly pointed out in the
appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] The accompanying drawings, which are incorporated into and
form a part of the specification, illustrate several embodiments of
the present invention and, together with the description, serve to
explain the principles of the invention. The drawings are only for
the purpose of illustrating a preferred embodiment of the invention
and are not to be construed as limiting the invention. In the
drawings:
[0025] FIG. 1A illustrates the chemisorption by a metal hydride
onto the surface.
[0026] FIG. 1B illustrates the hydriding reaction of a metal
hydride.
[0027] FIG. 2A is a van't Hoff plot of LaNi.sub.5 showing pressure
vs. atom ratio.
[0028] FIG. 2B is a van't Hoff plot of LaNi.sub.5 showing pressure
vs. negative inverse temperature.
[0029] FIG. 3A shows a configuration of the preferred embodiment of
the invention.
[0030] FIG. 3B is an expanded view of the metal hydride of FIG.
3A.
[0031] FIG. 4A shows a LaNi.sub.5 particle (D.sub.p.about.40
micron) encapsulated by a thin copper shell.
[0032] FIG. 4B is depicts the manufactured porous metal hydride
compact.
[0033] FIG. 5 shows a biorobotic arm.
[0034] FIG. 6 is a schematic of the flying high-power metal hydride
system.
[0035] FIG. 7 depicts the actuator configuration of the metal
hydride artificial muscle.
[0036] FIGS. 8A, 8B, 8C, and 8D show deployable structures using
metal hydride artificial muscles.
[0037] FIG. 9 is a joint power augmentation of astronauts using
metal hydride artificial muscles.
DESCRIPTION OF THE PREFERRED EMBODIMENTS (BEST MODES FOR CARRYING
OUT THE INVENTION)
[0038] A new artificial muscle is disclosed that is biorobotic,
noiseless, compact/light-weight, fast actuation, high-powered,
biocompatible, and environmentally clean. The new metal hydride
artificial muscles (MHAM's) are actuated by hydrogen gas as a
working fluid and metal hydrides as hydrogen sponge and can be
operated both electrically and thermally. These MHAM's have
immediate applications for biomedical, space, micro-machines and
other industries. Therefore, they can be used as micro-to-macro
scale applications.
[0039] The large uptake/discharge capacity of hydrogen in metal
hydrides, for example, the volume of hydrogen gas equal to
approximately 1,000 times metal hydride, and their rapid kinetics
provide MHAM's applications as being noiseless, having fast
response, being compact/light-weight, and having high-power. Metal
hydrides can absorb or store and desorb or release a large amount
of hydrogen gas to obtain significantly high mechanical energy. A
MHAM's application unit can be highly compact and ultra light as
opposed to current state-of-the-art actuators. Fast actuation time
can be obtained, such as 1 Hz for heating/cooling switching.
[0040] Metal hydrides are the binary combination of hydrogen and a
metal or metal alloy. They can absorb large amounts of hydrogen via
surface chemisorption and subsequent hydriding reactions as
illustrated in FIGS. 1A and 1B. At a given temperature metal
hydrides form condensed phases with hydrogen upon the partial
pressure of hydrogen present. The useful characteristics of metal
hydrides are the large uptake/discharge capacity of hydrogen, safe
operation because hydrogen desorption is an endothermic process,
rapid kinetics, and they are environmentally clean. They have been
used for a long time for hydrogen storage and for thermal
devices.
[0041] The equilibrium composition of metal hydrides is of
interest. In most metal hydrides, there are two distinct phases,
.alpha. and .beta. phases, as shown in FIGS. 2A and 2B. An isotherm
gives the absolute equilibrium absorption or desorption pressure as
a function of the hydrogen concentration, H/M (M=metal atom).
Initially, hydrogen dissolves within the solid lattice of the metal
hydride. Continued addition of hydrogen results in a sample
consisting of the chemisorbed phase. All interstitial hydrogen is
chemically combined in the solid lattice. The endpoints,
H/M.sub..alpha. and H/M.sub..beta. are called the phase limits of
the plateau region. They are generally not sharply defined. In a
dehydriding or desorption process frequently hysteresis is
observed, with the dehydriding isotherm lying slightly below the
hydriding isotherm.
[0042] A typical metal hydride is the rare-earth intermetallic
LaNi.sub.5 (lanthanium-pentanickel). The hydriding/dehydriding
reaction can be written as, 1 LaNi 5 + x 2 H 2 LaHi 5 H x + H a ( 1
)
[0043] where x and .DELTA.H.sub.a are non-stoichiometric constant
which is about 6-6.7 for this particular compound and the heat of
absorption giving off (-3.1.times.10.sup.4 kJ/kgmole of H.sub.2,
for LaNi.sub.5), respectively. It is usually close to the heat of
desorption, .DELTA.H.sub.d). The equilibrium behavior of metal
hydrides in the plateau region can be described by van't Hoff plots
as shown in FIGS. 2A and 2B, according to the following relation, 2
1 n P H2 ( atm ) = H a RT - S R ( 2 )
[0044] where R is the molar gas constant, equal to 8.314
kJ/kgmole-K, T is the absolute temperature in K, .DELTA.H.sub.a is
the heat of absorption in kJ/kgmole of H.sub.2, and .DELTA.S is the
standard entropy of formation in kJ/kgmole of H.sub.2-K. The van't
Hoff plots and the static p-H/M-T data available for particular
metal hydrides are the usual basis for thermo-mechanical design.
FIGS. 2A and 2B also shows the van't Hoff plots for LaNi.sub.5.
Depending upon pressure/temperature requirements and available
temperature desired hydrides could be selected for a use in various
artificial muscle systems.
[0045] The principle of the metal hydride artificial muscles
(MHAM's) is shown in FIGS. 3A and 3B. The MHAM functions using
hydrogen gas pressure from the metal hydride by manipulating
thermoelectric input. The thermoelectric elements 30 are located
near the metal hydride unit 31 to provide appropriate heat sources,
either heating or cooling, by simply changing the direction of
electric current to the element 30. The expandable inner bladder
polymeric material 32, such as Manosil.TM. silicon rubber, that
contains the hydrogen gas 33 constructs the functioning part. The
key parameter of the expandable material 32 is the capability to
sustain repeated strains of over 300%. A rubber material is used
since it can manage large strains with nearly no plastic strain and
creep. When heat is applied to the metal hydride unit 31, hydrogen
gas 33 is immediately desorbed from the metal hydride unit 31.
Then, the functioning part or the shell 34 contracts while the
polymeric material 32 expands under constant pressure, causing
pulling force between the endpoints 35 as designated as .DELTA.L.
The maximum force at a given pressure is obtained when the shell 34
is pulled out as far as possible. The relationship between pressure
and force is nearly linear at constant extensions. In fact, this
allows the movement distance .DELTA.L to be set by regulating the
H.sub.2 pressure in the system by controlling heat input to the
metal hydride unit 31. When metal hydride unit 31 is cooled, the
hydrogen gas 33 moves back to the metal hydride unit 31 being
absorbed. Therefore, internal pressure decreases and the shell 34
goes back to the starting position. A computer controller 36, such
as a microprocessor or the like, of the metal hydride system can
accelerate its performance. The computer controller 36 preferably
has a current control with temperature sensing with feedback.
Therefore, the amount of H.sub.2 discharged and the internal
pressure can be automatically controlled. In Table 1, the
properties of the metal hydride artificial muscles are briefly
compared with shape memory alloys and electrostrictive or
magnetostrictive ceramic actuators.
1TABLE 1 Properties of Interest for a Number of Different Types of
Actuators Typical Electrostrictive or Metal Hydride Shape Memory
Magnetostrictive Property Artificial Muscles Alloys (SMA) Ceramics
Actuation >1000% <8% short 0.1-0.3% Displacement fatigue life
Stress (MPa) 0.1-100 About 700 30-40 Reaction speed msec to sec sec
to min .mu.sec to msec Density 3-8 g/cc 5-6 g/cc 6-8 g/cc Drive
voltage N/A N/A 50-800 V
[0046] The manufacturing process for the preferred metal hydrides
is essential. In most metal hydrides undergoing
absorption/desorption cycles, high volumetric strain lead to
decrepitation of metal hydrides into a powdered bed of micron-sized
particles. Although metal hydrides themselves have rapid intrinsic
kinetics, the poor thermal conductivity of such powder beds
(k.sub.eff.about.0.1 W/m-k) limits the heat transfer communication
with the beds, therefore, retards the apparent kinetics. To obtain
reasonably rapid kinetics, actuator fabrication must improve the
thermal conductance of the unit.
[0047] Typically, metal hydride particles are sieved to a diameter
of 25-45 micrometer and then micro-encapsulated with a thin copper
using an electroless plating technique. In general, electroless
plating technique refers to chemical processes in which a metal as
an ion in aqueous solution is reduced to the metallic state by
means of a chemical reducing agent. The favorable electron transfer
reaction would be, 3 3 2 Cu 2 + + La 3 2 Cu + La ; G = - 830 kJ ( 3
)
[0048] Then, the standard reaction indicates a transfer of 3 moles
of electrons per unit mole of LaNi.sub.5. The process that has been
developed uses a simple/inexpensive solution prepared with
H.sub.2SO.sub.4 and CuSO.sub.4 and shows a homogeneous ion exchange
occurred that reduces the Cu.sup.+2 anion. Since the Gibb's free
energy is negative, the process is thermodynamically feasible.
[0049] In FIG. 4A, a LaNi.sub.5 particle (D.sub.p.about.40 micron)
encapsulated by a thin copper shell is shown. LaNi.sub.5 particles
were initially manufacturer-sieved, cleaned, and then copper plated
by using an electroless method described above in a batch reactor.
The condition for compaction is 5 kpsi. A photograph of
manufactured porous metal hydride compact is also provided in FIG.
4B.
[0050] The new metal hydride artificial muscle invention can be
used as a biorobotic arm as shown in FIG. 5. In this configuration,
initially, the metal hydride artificial muscle 50 is resting. The
biorobotic arm 51 is bent when the metal hydride biorobotic
actuator is in action for contraction. The sequence is reversed for
stretching.
[0051] The present invention can also be used as a taking-off and
landing metal hydride actuator. A schematic of the flying
high-power metal hydride system is given in FIG. 6. A typical
miniaturized balloon 60 has a set fully inflated diameter, for
example 2 ft. It consists of an inflatable balloon 60 equipped with
a metal hydride actuation unit 61 that releases hydrogen gas 62
upon being activated by any means of heating, such as solar
irradiation, laser or Joule heating. Once the balloon 60 starts to
inflate, the balloon 60 takes off. One feature of such a flying
system is that, as the balloon 60 raises its flying height level,
it senses the ambient temperature that typically gets cooled. As a
consequence, a portion of hydrogen gas 62 moves back to the metal
hydride unit 61. Then, the buoyancy force is reduced to lower its
flying altitude. Implementing this feature creates a potential for
a flying machine for uses in both defense and commercial
applications. Hydrogen gas 62 out of metal hydride actuator 61 can
also be used for the propulsion unit 63.
[0052] The present invention can also be used as a cylindrical
actuator. The cylindrical actuator configuration of the metal
hydride artificial muscle is schematically shown in FIG. 7. This
embodiment functions using hydrogen gas 70 pressure from the metal
hydride 71 by manipulating thermoelectric input 72. The
thermoelectric input can be any kind of heating/cooling elements
such as heat radiation panels and direct/indirect heat exchangers.
The heat input device or thermoelectric elements 72 with controller
75 are located near the metal hydride 71 to provide appropriate
heat or cooling sources by simply changing the direction of
electric current to the element 72. Metal bellows 73 or a soft
inflation material that contains the hydrogen gas 70 comprises the
functioning part. When heat is applied to the metal hydride 71,
hydrogen gas 70 is immediately desorbed from the metal hydride 71
and piston 74 is pushed up or H.sub.2 inflated. When metal hydride
71 is cooled, the hydrogen gas 70 is absorbed into metal hydride
71. Therefore, internal pressure decreases and piston 74 moves
down. The piston can also be spring-loaded to quicken the action
(not shown).
[0053] This metal hydride artificial muscle is driven by heat
input, so the efficiency of the metal hydride actuator is
important. The overall efficiency of the metal hydride actuator,
.eta..sub.MH, can be defined as, 4 MH = P out P in , ( 4 )
[0054] where P.sub.out and P.sub.in are power output generated and
consumed electric power input, respectively. The power output
generated, P.sub.out, will be, 5 P out = W out t op , ( 5 )
[0055] where W.sub.out is the output work generated during the
period of actuation, t.sub.op. The output work generated,
W.sub.out, is,
W.sub.out=.eta..sub.0Q.sub.in-.DELTA.U.sub.MH+H2 (6),
[0056] where .eta..sub.o, Q.sub.in, and .DELTA.U.sub.MH+H2 are the
overall efficiency associated with the thermo-electric device
including heat transfer effects, or other types of heat input
devices, the heat input, and the change of internal energy for both
metal hydride and hydrogen, respectively. From Equations (4), (5),
and (6), the efficiency of metal hydride actuators can be written
as, 6 MH = 0 Q in - U MH + H 2 t op P in . ( 7 )
[0057] The estimated typical efficiency of the metal hydride
actuator, .eta..sub.MH, is approximately 60% when the actuation
temperature is set at 30.degree. C. with LaNi.sub.5 selected as the
metal hydride. If an appropriate hydride can be selected, the
actuation temperature can be lowered, for example, Calcium-based
metal hydride actuates at approximately -50.degree. C. Note that
one goal is to find .eta..sub.MH by building a device and measuring
.eta..sub.MH. The equilibrium pressure will be approximately
200-300 kPa (.about.2-3 atm). Then, the expected overall hydrogen
volume generated, .DELTA.v.sub.g, will be approximately 37-55
cm.sup.3/g LaNi.sub.5. Although the metal hydride actuator
efficiency itself appears less than that of an electric actuator
that uses electric power directly, and accounting for the necessary
auxiliary components for the electric actuator, the power output
per weight of the proposed metal hydride actuator is significantly
large. Furthermore, the metal hydride artificial muscles can
operate by waste heat. Hence, the metal hydride actuator is
suitable for use as a space actuator with necessary features of
having high specific-power and being lubricationless, noiseless,
fast and smooth.
[0058] The present invention can also be used for deployable
structures. FIGS. 8A, 8B, 8C, and 8D show deployable structures
using metal hydride artificial muscles. When heat is applied to the
metal hydride 80, hydrogen gas 81 is immediately desorbed from the
metal hydride 80 and hydrogen inflates deployable structure 82.
When metal hydride 80 is cooled, hydrogen gas 81 is absorbed
quickly by the metal hydride actuator body 83 with controller
84.
[0059] Effective soldier metal hydride systems meet the criteria of
battlefield capabilities of "lethality, command/control,
survivability, sustainment, and mobility." The metal hydride system
provides large weight reduction capabilities to perform enhanced
mission capabilities upon being burdened with advanced equipment.
Also, it can function as a weight reduction system and actuator
using hydrogen gas pressure from the metal hydride by any heat
input, such as cigarette lighters, Joule-heating by electric input,
and heat radiation panels. Specially designed deployable structures
that contain the hydrogen gas can construct the functioning part.
When heat is applied to the metal hydride, hydrogen gas is
immediately desorbed from the metal hydride and hydrogen is
inflated. When metal hydride is cooled by the ambient surroundings,
the hydrogen gas is absorbed quickly by the metal hydride actuator
body. For a soldier system application, as shown in FIGS. 8C and
8D, when hydrogen is acting, the deployed structure can provide a
net lift force that is governed by the buoyancy. In this case, the
deployed structure can function as an enhanced surface to improve
the mobility of the soldier system.
[0060] A joint power augmentation of astronauts using metal hydride
artificial muscles is shown in FIG. 9. As can be seen, thermally
driven metal hydride systems 91 can augment an astronauts' regular
and extra vehicular activities. The space cold environment is
favorable for metal hydrides, therefore, the cooling is natural,
resulting in an increased cycling time. The heating can be done by
any means, as discussed above.
[0061] Although the invention has been described in detail with
particular reference to these preferred embodiments, other
embodiments can achieve the same results. Variations and
modifications of the present invention will be obvious to those
skilled in the art and it is intended to cover in the appended
claims all such modifications and equivalents. The entire
disclosures of all references, applications, patents, and
publications cited above, are hereby incorporated by reference.
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