| |
|
|
| |
|
|
 |
We have the technology,” TV
doctors and engineers intoned more than 30 years ago as they
turned Steve Austin into the Six Million Dollar Man. But that
was science fiction back in the seventies. The truth is that,
even today, bionic reality falls far short of that sci-fi
fantasy.
We may have the technology within the decade, however, if
everything pans out the way the Defense Advanced Research
Projects Agency intends for its new Revolutionizing Prosthetics
2009 program. No, the new artificial arm DARPA is funding won’t
be stronger than the natural human arm, but it will look, feel
and function very like the real thing, sweat included.
Vanderbilt engineers are responsible for both the strength and
the sweat.
|
|
Professor of Mechanical Engineering
Michael Goldfarb is creating the “works” of the new arm—the power,
movement and control systems. When finished, their device will be
connected directly to the wearer’s central nervous system, either
through the peripheral nerves on the shoulder or inside the brain,
itself. The arm will thus be thought-controlled and virtually
indistinguishable from a natural arm.
It is rocket science
Instead of using heavy batteries or requiring connection to a wall
outlet, the new arm will be steam-powered by rocket fuel, releasing
moisture comparable to the perspiration a normal arm would release.
This power system is much lighter than the state-of-the-art
artificial arms available currently, and because it is a pneumatic
system it will also provide smoother, more fluid control of the
apparatus.
Goldfarb and his team were selected to design the crucial elements
of the hand and arm because of their prior work developing a
strap-on lower-extremity exoskeleton that they designed to help
soldiers carry heavy loads over long distances and difficult
terrain. They are coupling the innovations from this prior research
with a complex new system of servo valves and sensors to achieve
precision control of the arm and to deliver feedback to the wearer
much like the neural feedback experienced from a natural arm.
Developing a thought-controlled, lifelike arm is a highly ambitious
goal, and DARPA has pulled together top experts in prosthetics and
robotics throughout the nation to achieve it. But from the
perspective of those who have lost limbs in Afghanistan and Iraq,
it’s a long overdue invention. Despite great efforts in research and
development to create artificial arms that are functional and
practical, even the best of these devices are too heavy and too
cumbersome, or they must be plugged into an electrical outlet.
Today many amputees simply make do with their remaining natural arm,
or resort to using World War II technology-based artificial arms
with hooks.
“Even the state-of-the-art artificial arm doesn’t allow a user to
drink a glass of water,” Goldfarb says. “We need a paradigm shift.” |
Goldfarb and his team are indeed shifting the paradigm by harnessing
fluid power to give the arm needed strength without excess weight.
Their new power and control systems eliminate the need for batteries
and motors, give smoother and more precise control, and enable 21
degrees of freedom for the arm as a whole, including 17 degrees of
freedom for the hand. That’s a big improvement over the 3 degrees of
freedom the state-of-the-art myoelectric (controlled by electrical
signals from the
body) arm allows. |
|
“We will leverage the actuation
technology we have already developed with the exoskeleton project to
design the artificial arm,” Goldfarb says. “Our goal is to develop a
biomimetic prosthesis that has the strength and power approaching an
intact human arm.”
Sweat included
Not to mention a decent appearance. The arm will look as lifelike as
possible, with breathable, sweat-able “skin.”
Working under the skin will be 9 pneumatic actuators, 13 sensors,
support structure, and a computer to help monitor and control the
motions. To achieve the desired fidelity between thought and action,
Goldfarb and his team have developed a system of sensors that sense
the position and direction of movement of the arm that work with
pneumatically driven valves that produce precise movements in
response to control signals from the wearer’s central nervous
system.
Energy-dense rocket propellant is released into a thermometer-size
reaction chamber filled with iridium pellets, which serve as a
catalyst separating the fuel into steam and oxygen. The flow is
controlled by the servovalves, which control the flow of fuel in
relation to the signal from the nervous system. The exhaust from the
system of steam and oxygen will be vented through the porous “skin.”
Goldfarb and his team have already achieved some of their goals for
dexterity and control of the arm, using a nitrogen-powered cool gas
system for power. The next phase of development will involve
strengthening the design of the AA battery-size servo valves so that
they can function accurately and efficiently under the pressures and
heat produced by catalyzed rocket fuel. The valves will need to work
at 500 degrees Fahrenheit.
“The heat will be mostly contained within the system, and you can
put your hand over the exhaust,” Goldfarb says.
DARPA expects the technology to be ready for clinical trials in only
four years. Johns Hopkins University Applied Physics Laboratory is
the lead institution of the $30.4 million project, $2.7 of which
will go to Vanderbilt.
|
|