Introduction to Biomimetics: The Wealth of Inventions in Nature as an Inspiration for Human Innovation - Biomimetics: Biologically Inspired Technologies - page 31

genetic procedure which can take many years to grow, a duplicate of the human without ability to
control the outcome, the robotic version can potentially be rapidly produced and be programmed to
emulate the behavior and response of the original person. Aspects of this mimicking will need to be
addressed by future generations as the potential unlawful possibilities that may become possible
could pose major concerns to law-enforcement agencies.
1.8.1 Artificial Muscles
Polymers that can be stimulated to change shape and size have been known for years. The
functional similarity of such polymers led to their being named artificial muscles. The activation
mechanism for such polymers includes electric, chemical, pneumatic, optical, and magnetic.
Electrical excitation is one of the most attractive stimulators that can produce elastic deformation
in polymers. The convenience and the practicality of electrical stimulation, as well as the improved
capabilities, make the EAP one of the most attractive among the activatable polymers (Bar-Cohen,
2001, 2004; Chapter 10).
Generally, EAP materials can be divided into two major categories based on their activation
mechanism: electronic and ionic. Most electronic polymers (electrostrictive, electrostatic, piezo-
electric, and ferroelectric) require high activation fields ( > 150 V/mm) close to the breakdown level.
However, they can be made to hold the induced displacement under activation of a DC voltage,
allowing them to be considered for robotic applications. These materials have a faster response, a
greater mechanical energy density, and they can be operated in air. In contrast, ionic EAP materials
(gels, IPMC, conductive polymers, and carbon nanotubes) require drive voltages as low as 1 to 5 V,
and produce significant bending. However, bending actuators have relatively limited applications
for mechanically demanding tasks due to the low force or torque that can be induced. Also, with
some exceptions, these materials require maintaining their wetness and when containing water they
suffer electrolysis with irreversible effects when they are subjected to voltages above 1.23 V.
Except for conductive polymers, it is difficult to sustain DC-induced displacements.
Unfortunately, EAP-based actuators are still exhibiting low force below their efficiency limits,
are not robust, and are not available as commercial materials for practical application consider-
ations. Each of the known materials requires adequate attention to the associated unique properties
and constraints. In order to be able to take these materials from the development phase to use as
effective actuators, there is a need to have an established EAP infrastructure. Effectively addressing
the requirements of the EAP infrastructure involves developing its science and engineering basis,
namely, having an adequate understanding of EAP materials' behavior, as well as processing and
characterization techniques. Enhancement of the actuation force requires understanding the basic
principles, computational chemistry models, comprehensive material science, electro-mechanical
analysis, and improved material processing techniques. Efforts are on for a better understanding
of the parameters that control the EAP electroactivation force and deformation. The processes of
synthesizing, fabricating, electroding, shaping, and handling are being established and refined to
maximize the EAP materials actuation capability and robustness. In addition, methods of reliably
characterizing the response of these materials are being developed. This effort also includes the
establishment of a database with documented material properties in order to support design
engineers who are considering the use of these materials. Various configurations of EAP actuators
and sensors are being modeled to produce an arsenal of effective, smart EAP-driven systems. The
development of the infrastructure is multidisciplinary, and requires international collaboration and
these efforts are currently underway worldwide.
In 1999, the author challenged the world's research and engineering community to develop a
robotic arm that is actuated by artificial muscles (moniker for EAP) to win a wrestling match
against a human opponent. The objectives of the match are to promote advances in making EAP
actuators that are superior in performance to the performance of human muscles. Also, it is sought
to increase the worldwide visibility and recognition of EAP materials, attract interest among