If you’ve been glued to the Paralympics coverage, you’ll have seen some of the remarkable feats of athletes who have lost one or more limbs. Equally, we are familiar with the sight of people wearing high-tech limbs on the high street as well as setting world records in athletics on high spec blades.
Now, work by the MIT Media Lab’s Biomechatronics group in the USA reveals the next step in the evolution of prosthetics as powered, robotic limbs that interact with the wearer’s own body. Or, as MIT PhD student Matthew Carney describes it:
“The TF8 actuator … an untethered, lower-extremity powered-prostheses designed to replicate biological kinetic and kinematic function of ankles.”
The TF8 heralds the next generation of power protheses that seek to replicate both function and feel for those who have had lower leg amputations. These “neurally-controlled “ powered limbs use sensors that allow the wearer to control the bionic foot’s movement using their own remaining muscle system after amputation.
Load cells in robotic limbs
At the heart (or should that be sole) of the TF8 system is a load cell that measures force measurement. This sits at the rear of the limb in a position akin to the section of fibula above the ankle joint (talus). The load cell continually measures the force exerted on the foot. This data can be used to adjust the ‘stiffness’ in the software, and to tailor the foot action to the user’s preferences.
While the mechanical and electrical systems foot replicate the natural movement of the human foot, the sensors on the remaining limb allow 2-way connection between the body and the robot prosthetic.
The next generation
In the excellent Bloomberg Quicktake video below, engineer and MIT faculty member Everett Lawson explains how his leg was amputated using a new surgical technique. This preserved his muscular and nervous system in his remaining limb, allowing him to control the bionic leg using his own muscles.
He also explains how he went on to reverse engineer that capability, and map which muscles correlate to positions on his ‘original’ foot. Using sensors stick to his skin and specific pressure points on the robotic foot plate, he can now ‘feel’ his toes and particular parts of his foot as sensations. The scene in the video where his young son “tickles” his Papa’s robot foot is absolutely priceless!
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