Iceland
based Össur makes some of the slickest bionic limb attachments you can buy. The
company’s lower leg prosthetics have the ability to sense the phase of
the gait and smoothly power the artificial ankle joint to the appropriate angle
for different points in the stride. While that’s pretty handy for making
predictable movements on predictable terrain, what would be even better is if
the prosthetic could be automatically positioned at any time in response to
residual muscle commands still naturally generated by the wearer.
On Wednesday, the
Össur team announced that they have in fact already achieved just that
with the willing cooperation of two amputees. The team is calling their results
nothing less than “subconscious thought control,” and nobody seems to be
contesting that claim. At the the heart of the new prosthetic is their standard
Proprio foot, only now instead of taking commands from a suite of inertial or
other position sensors, it smoothly responds to myoelectric sensors embedded in
the wearers intact calf muscle.
The 3mm x 5mm sensors were
not directly developed by Össur — instead, they were supplied by the US-based
Alfred Mann Foundation. They are inductively energized by a power system embedded
in the overlying socket that receives the ankle prosthetic. After a 15-minute
surgery to implant the sensors, and a few minutes to play around with moving
the joint, the users found they could precisely position the joint as if it
were their own natural foot.
To say that they are doing
this just by thinking is in a strict sense true, but it is not quite the same
principle as a direct brain-controlled interface (BCI). For one thing, it is
much more accurate and reliable. The device is so fast that it reads natural
commands sent from the motorneurons to the muscle and initiates actuation of
the foot faster, and then the commands actually contract the user’s own calf
muscle. However, although the process is fairly described as automatic, the
user still has to make the actual motive effort. That is a little different
than just making the purely mental effort of imagining a moving foot, or
whispering an intention of movement in one’s inner voice.
One bonus of the concept
is that the user’s own muscle, while not bearing true loads in any practical
sense, is still exercised toward a productive end. Not only does that help
maintain the muscle, but we might presume that the ‘feels’ accompanying the
movement would be convincing and satisfying. In perusing the Össur build-a-body
website, it looks like they have many other kinds of amenities an amputee might
want to add to their shopping cart. Nothing yet as far as true
osseointegrated limbs
are available, but there are fancy vacuum systems which compensate for
fluctuations in limb volume to maintain a snug fit. Depending on how and where
the vacuum is applied, it might also serve to keep the limb engorged with blood
to maintain it dimension.
Össur also has
various joint locks, clutches, and attachment sockets which can even add
functionality lacking in the real thing. There still doesn’t seem to be much
info out there as far as how capable the actuators in the joints are. In other
words, how much power might potentially be available in the basic design to do
more than just passive positioning. It looks like they have hydraulic
capability in some of their ankles, but we might have to wait a bit to learn
everything they have in store.
Source : http://www.extremetech.com/
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