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 Metal exoskeleton suits worn outside the body, delivering energy for
limb movement, are becoming more widespread, helping survivors of
strokes, spinal cord injuries, and other lower extremity weaknesses
to walk again. But one of the main limitations of current
exoskeletons is restricted joint mechanisms that make anything other
than walking in a straight line difficult.
The VariLeg team in Zurich believes they have hit upon the novel
idea of adjustable softness in the knee that could make their
exoskeleton the first model that does not struggle on uneven
terrain. It mimics the natural behavior of knee movement during gait
more accurately thanks to built in variable impedance actuators that
continuously change the knee stiffness so it can adapt to irregular
surfaces or obstacles.
"With the Varileg we implemented the mechanical variable impedance,
which is something special that no other exoskeleton has implemented
at the moment. And the advantage of this is that we can mimic the
human-like stiffness adaptation of the human knee and this also
allows us to adapt to unexpected obstacles because we can say how
stiff the knee should behave," mechanical engineering student
Patrick Pfreundschuh told Reuters.
He added: "This will give people the ability to adapt to unexpected
obstacles which will also make them more flexible to walk and it's
also possible to adapt this stiffness, and that's also what the
human body does during the natural human gait cycle."
The first prototype VariLeg exoskeleton that uses the mechanical
variable impedance is, admittedly, very bulky. However, the team has
been working with paraplegics to work out how the design can be
improved. Pfreundschuh explained that they are currently building
the much more streamline VariLeg 2 exoskeleton. He added that the
wearer would still need to use crutches with the VariLeg, but that
these will act as a control to adjust the device for different
situations.
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"On the crutches we will have several buttons and with these buttons
he (the wearer) can decide where he's going and also to change the
modes; so we will have straight-walking mode, and stairs mode and
sit-down mode. So he can change between the modes and then tell the
device what it should do," said Pfreundschuh.
The VariLeg developers will be one of a number of teams
participating in the first annual Cybathlon - a championship for
physically disabled athletes who will use new assistive devices to
compete to finish a variety of everyday tasks that are particularly
difficult for their individual handicap. For instance, patients with
prosthetic upper limbs will perform tasks such as carrying shopping
bags or preparing a meal, while those with lower limb paralysis will
be asked to undertake activities such as climbing stairs, using a
robotic exoskeleton for assistance.
According to the ETH Zurich website, "through the organization of
the Cybathlon we want to help removing barriers between the public,
people with disabilities and science."
The event takes place in October 2016.
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