Robotic exoskeleton helps regain limb function
26 February 2007
A robotic exoskeleton controlled by nerve signals
could help people with partial nervous system impairment to regain limb
University of Michigan researchers developed an ankle
exoskeleton and tested it on healthy subjects to measure how the device
affected ankle function. The results suggest promising applications
for rehabilitation and physical therapy, and a similar approach could be
used by other groups who develop such technology.
"This could benefit
stroke patients or patients with incomplete injuries of the spinal cord,"
said Daniel Ferris, associate professor in movement science at the
University of Michigan (UM). "For patients that can walk slowly, a brace
like this may help them walk faster and more effectively."
former UM doctoral student Keith Gordon, who is now a post-doctoral fellow
at the Rehabilitation Institute of Chicago, showed that the wearer of the UM
ankle exoskeleton could learn how to walk with the exoskeleton in about 30
minutes. Additionally, the wearer's nervous system retained the ability to
control the exoskeleton three days later.
In people with spinal injuries
or some neurological disorders, electrical signals sent by the brain to
control muscles don't arrive at full strength and are uncoordinated. In
addition, patients are less able to keep track of exactly where and how
their muscles move, which makes re-learning movement difficult.
robotic rehabilitative devices are worn by patients so that the limb is
moved by the brace, which receives its instructions from a computer. Such
devices use repetition to help force a movement pattern.
The University of
Michigan robotic exoskeleton works the opposite of these rehabilitation
aids. In the UM device, electrodes were attached to the wearer's leg and
those electrical signals received from the brain were translated into
movement by the exoskeleton.
"The (artificial) muscles are pneumatic. When
the computer gets the electrical signal from the (wearer's) muscle, it
increases the air pressure into the artificial muscle on the brace," Ferris
said. "Essentially the artificial muscle contracts with the person's
Initially the wearer's gait was disrupted because the mechanical power added
by the exoskeleton made the muscle stronger. However, in a relatively short
time, the wearers adapted to the new strength and used their muscles less
because the exoskeleton was doing more of the work. Their gait normalized
after about 30 minutes.
The next step is to test the device on patients
with impaired muscle function, Ferris said.
The complete paper, "Learning to Walk with a Robotic Ankle Exoskeleton"
is available online at the Journal of Biomechanics:
http://www.sciencedirect.com/science (link direct to article is too long