Ministry of Education and Science of the Russian Federation
State Educational Institution of Higher Professional Training
National Research Tomsk Polytechnic University
Artificial Muscles:
Present-Day Technologies and Future Prospects
Student
M.N. Rud
Group
8Е00
Scientific supervisor
T.V. Alexandrova
Language supervisor
T.I. Butakova
Tomsk 2012
Contents
1. Introduction………………………………………………………………….3
2. Methodology of creating artificial muscles………….………………………4
2.1. Artificial muscles based on carbon nanotubes………………………….5
2.2. Artificial muscles based on electro active polymers…………………....6
2.3. Electro muscular armor…………………………………………………8
3. Conclusion………………………………………………………………..…9
4. References……………………………………………………………….....10
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1. Introduction
The truth of the matter is that in modern engineering industries, two
effective methods of mechanical work performance are used: thermodynamic and
electromagnetic. The first one is based on the use of compressed gas energy (for
example, in pneumatic motors), whereas the second one converts the energy of
electromagnetic field into mechanical energy (for example, electrical motors).
At the same time, we admit that having been developing motion
technologies for many millions of years, the natural world has a completely
different method to get a mechanical movement, that is to say, a controlled
deformation of an object (by objects we imply muscles). Muscles of humans or
other creatures work in accordance with this principle. Admission of a nerve
impulse causes chemical reactions, which in their turn, lead to contraction or
expansion of muscle fibers. Advantages of such a “muscular actuator” (an
actuator is a
motor that translates control signals into mechanical ones) are
connected with the fact that the tissues deform as a whole unit, with no separate
parts, that move relatively to each other and deteriorate over time, as that happens
in electric and pneumatic machines. Movement appears on a molecular level, thus
relieving muscles from inertia. The latter is known to be the resistance of any
physical object to a change in its state of motion or rest, or the tendency of an
object to resist any change in its motion.
The preceding natural phenomenon has encouraged thorough research to
design a new type of actuators which can use the above type of mechanical work
performance. Such actuators can be made up of artificial muscles (AM). However,
there exists a problem nowadays, how to create such AM and how to provide or
guarantee their performance.
If we consider muscles of a living being, it is essential to ensure a
continuous inflow of chemical components, which are vital for cells. The muscles
represent constituent parts of a complex living organism. In addition, there is
gradual aging of any tissue material. In living organisms cells are constantly
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changed and “updated”, however, it is impossible at present to enable such selfupdating in a monolith technical device.
What is more, when researching AM that can be used in robotics, medicine,
aeronautics, and other fields, scientists and engineers try to keep the advantages for
the muscle actuator to possess, and, at the same time, find the most efficient way to
provide AM performance. Artificial muscles enable a great power compared to the
power of an electrical or pneumatic motor, but at the same time, the price,
durability and measurements of an AM actuator is significantly less. That is the
reason why artificial muscles technology is very important for us to study.
The goals of this study paper are as follows:
- Firstly, to give coverage of the most effective means and principles of
work when creating AM, although a number of different technological
approaches dealing with AM is also available in engineering at present;
- Secondly, to find out what countries and engineering branches are at the
cutting edge of technology to create AM at present, and analyze the
reasons explaining that;
- Lastly, to predict the future of AM technology: prospects and tendencies.
In the next section we will describe the most significant two methods of
creating AM, and introduce the latest military invention based on these methods as
well.
2. Methodology of creating artificial muscles
Completely different methods of creating AM are based on application of
carbon nanotubes and electroactive polymers materials. Moreover, they differ in
the type of impact, which activates muscles, in other words, electrical, optical and
pneumatic. These methods have their own advantages, and we are going to
introduce them.
2.1. Artificial muscles based on carbon nanotubes
It is a well-known fact, that carbon nanotubes have fantastic mechanical and
physical properties, and enable creating light and strong chemical compounds.
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Taking into consideration the interests of robotics, the most interesting application
of nanotubes is their ability to help in creating AM, which can provide the
opportunity of making such a structure which is stronger than steel, lightweight,
and, what is the most important, as elastic as rubber. The latest achievement of
scientists [4] is obtaining a muscular structure made of a vertically oriented
nanotubes sheaf (Figure 1).
Fig.1. Carbon nanotubes
Such muscles are controlled with the help of electric signals – exactly as a real
living muscle performs. Surprisingly, carbon muscles show very high strength.
Natural muscle can contract by 10 % per second. An artificial one can contract by
10000% per second. The operating temperatures range is impressive too: from
liquid nitrogen temperature to the melting point of iron. This fact allows using such
muscles in the most extreme conditions, including the open space.
Let us describe the work principles of carbon nanotubes artificial muscles.
These artificial muscles are sheets of carbon nanotube aerogel, the latter was
created with a new technology, developed by researchers of Texas University,
Dallas, USA. Sometimes called “frozen smoke”, aerogel is a solid low-density
material derived from a gel, in which the liquid component has been replaced with
gas. Aerogel is composed mostly of air. The basic material is an array of vertically
oriented carbon nanotubes, manufactured by cracking of hydrocarbons. Carbon
nanotubes can be formed into sheets because of their view (nanotubes look like a
bamboo forest). Such low density sheets, that one ounce can cover an acre. (1
ounce ≈ 30 grams (28.3), 1 acre ≈ 4 thousand meters ²). When voltage is applied to
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sheets of aerogel, the nanotubes repel each other. These transparent sheets have
very unusual properties that are important for muscle work. For all that, they have
a density similar to the density of air, and, in one direction, they have higher
strength than a steel template. In another direction, they provide extensibility of
rubber.
On the contrary, in addition to their advantages, now carbon nanotubes have
one big disadvantage: after a powerful impact is applied, a tube slightly expands.
That is a serious problem; and according to scientists it is going to be a great work
to improve the material [8].
While carrying out the research on nanotubes, scientists and engineers are
simultaneously developing new methods and materials. Thus, one more AM
material, having great prospects in this field has been discovered. We will describe
it in the section below.
2.2. Artificial muscles based on electro active polymers (EAP)
For many years, electro active polymers (EAP) have received relatively
little attention due to the small number of available materials and their
limited actuation capability. The recent emergence of EAP materials with large
displacement response has enabled great potentials for such materials. EAP have
been studied for years by scientists from 15 countries. The most significant
laboratories and researchers are from USA, Japan, France, and Sweden. Since 1996
all scientific work in this field has been managed by Dr. Yoseph Bar-Cohen (Jet
Propulsion Laboratory, in National Aeronautics and Space Administration
(NASA).
In 2001 NASA had two types of artificial muscles, based on EAP. The first was
a polymer tape which consisted of carbon, fluorine and oxygen molecules. When
electric impulse went through the tape, molecules of the polymer shrank or
expanded lengthwise, depending on polarity. Having applied the technology,
scientists created a device for collecting stones which consisted of four polymer
tapes. The second variant of EAP technology represented a thin layer of dielectric
polymer film sandwiched between compliant electrodes. When some voltage was
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applied across the electrodes, the electrodes attracted each other; as a result, the
film contracted in thickness, and expanded in area. This basic operation can be
shown in Figure 2:
Fig. 2. Electro active polymers
An EAP film can be transformed into an actuator with mechanisms that convert
the film’s expansion into motion in the desired directions, allowing EAP to achieve
significant motion with less power as compared to other technologies.
In addition to fast response time, the actuators’ performance has nearly silent
operation volume. And having a fraction of a millimeter thick, this EAP
technology is remarkably customizable, allow developers to create any design they
imagine. To produce artificial muscles, which can be executed in the open space,
silicon plastics, which work even in vacuum at a very low temperature, can be
used. To achieve bigger output power, we can increase the volume of polymer or
connect some elementary actuators sequentially or in parallel. High voltage, from 1
to 5 kV, is essential for activating the polymers. But these actuators work under
low current, and so they get warm slightly. The higher the voltage, the greater is
the tension. The only limitation is how well material resists the voltage (it can be
an electrical breakdown, if too high voltage is applied).
We have described two methods of creating muscular actuators, which can be
used for obtaining a mechanical movement. The next section will introduce a
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cutting-edge invention, which serves quite a different purpose, being applied no to
the civil engineering branch.
2.3. Electro muscular armor
Scientific interests of specialists who deal with AM creation are incomparable
with volumes of financing and technical opportunities of laboratories that work for
military corporations, for instance BAE Systems, UK. This company fills orders
for almost all technically developed countries in the world, and due to this fact, the
information about its research and development activity appears quite often in
media, in spite of secrecy. According to British laws, information about military
and medical companies’ activities cannot be hidden behind the security of patents,
so in their reports information about the state-of-the-art designs in military sphere
can be found.
As a result, some information has been recently published in mass-media by a
small-sized British company H.P. White Laboratory, which is concerned, in
general, with strength tests of protective systems of armor, bulletproof glass and
vests. The company researchers suggest to use EAP principle for creating an
«armor with multiple tension», which is a multilayer structure that comprises a
huge amount of polymer tapes, interspersed with micro particles of strong armor
ceramics and definitely oriented magnetized particles. A bullet that hits the armor
causes a starting deformation and a sharp displacement of magnetized particles.
That causes, due to electrical induction, a short electrical impulse that forces
polymer tapes to contract, in this way sharply increasing strength of the armor,
because particles of armor ceramics have a certain silhouette that allows them,
when contracting lengthwise, to interlock to continuous coating.
The main advantage of the above system is the fact, that maximum strength of
armor is formed exactly in the place of a bullet hit, gradually decreasing around.
As a consequence, bullet kinetic energy is evenly distributed throughout the area of
the vest. Though this armor has much more volume than other modern types of
armor, it has far less weight. Earlier if a weapon fire did not kill a soldier, it
guarantied putting him/her out of action at least for some hours, and on the
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contrary, according to preliminary calculations, this new innovative protective
system based on AM technology will not leave even hematomas on the soldier’s
body.
3. Conclusion
Having studied the latest research concerned with AM, we have drawn the
following inferences:
So far AM have been designed and used, as a general rule, only in specific
engineering branches, traditionally supported financially by powerful states. At
present research on AM in civil and even medical engineering branches lag far
behind the military field. All designers carefully protect secrets of R&D and
production of AM. For example, Artificial Muscles Inc., a company which
produces EAP muscles, does not sale their primary artificial polymer tapes, they
sell only the end product, a final actuator, based on AM technology. Once the
situation was so outrageous, that Bar-Cohen group published some basic principles
of producing EAP, to make other independent scientists, technologists and
engineers contribute into the AM research.
Elastic carbon nanotubes and electro active polymers are promising artificial
muscle technologies in early-stage experimental development. The research results,
obtained by these two methods and described in this paper, could lead to numerous
applications of AM in many areas in the near future, the most possible are:
I) Creating new efficient and durable materials which can be applied in
different branches of industry.
II) In Robotics the first public devices, using AM, will inevitably be released
already in the next decade, and will have all chances to become
revolutionary innovations, which will open a way for the creation of
inexpensive multifunctional and self-moved domestic robots.
III)
Since the absence of defects in carbon nanotubes and EAP enables
these filaments to deform elastically by several percent, with energy storage
levels of perhaps 10 J/cm3 for metal nanotubes, human biceps could be
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easily replaced with an 8 mm diameter wire of this material. Such compact
"muscle" might allow future robots to outrun and outjump humans.
Therefore, AM application will ultimately benefit our progress in the quest
of creating an intelligent artificial being.
According to Dr. Bar-Cohen, the development of AM technology reminds the
inventive boom of the end of 19 and beginning of 20 centuries: materials, made up
of AM are easy-got, each person can carry out his/her own experiment, where the
loss of money is minimal [2]. No doubt, in forthcoming years we will be disclosing
new techniques to create and use artificial muscles. This branch of technology is
rapidly developing at the moment, and, needless to say, the more researchers will
be interested in it, the more groundbreaking inventions will appear in this field.
4. References
1. Y. Bar-Cohen and S. Leary “Electro active polymers as artificial muscles
changing robotics paradigms”, Jet Propulsion Laboratory (JPL)/Caltech,
Pasadena, California, USA.
2. Y. Bar-Cohen “EAP Actuators as Artificial Muscles: Reality, Potential and
Challenges”, 2004, USA.
3. Y. Bar-Cohen “Bionic Humans Using EAP as Artificial Muscles: Reality and
Challenges”, USA
4. R. Baughman, John D.W. Madden “Polymer Artificial Muscles”, Texas
University, USA
5. Artificial Muscles Inc. http://www.artificialmuscle.com/technology.php
6. Worldwide EAP Actuators http://eap.jpl.nasa.gov/
7. Artificial muscles research institute http://artificialmuscles.org/
8. Strong nanotube muscles were created http://www.membrana.ru/particle/10954
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