London, A double amputee MIT biophysicist has designed a robotic ankle that allows wearers to exert 20 percent less effort compared to a conventional prosthetic leg.
The robotic ankle puts a motorised spring in the step of amputees and lets them to walk using less energy and with a more natural gait, according to its inventor, Hugh Herr.
Herr, who also tested it, said: "It feels amazing. It feels like I'm attached to robotic legs and they're moving me - I can walk very fast with little effort. Also my gait is normalised and how I look when I walk is greatly improved".
Herr demonstrated the ankle at the Veterans Affairs Medical Center in Providence, Rhode Island, US, which also partly funded the research.
The combination foot and ankle is designed for amputees who have lost their legs below the knee. Herr said the key is to give the artificial limb a compacted partly-motorised component.
"The problem is, from an engineering perspective, the human ankle puts out very, very high power. If one were to build an ankle and try to produce all that power with a motor, the motor and the battery would be far too large," said Herr.
So Herr built an ankle that stores energy from the impact of the foot strike in a spring, but also uses a battery-operated motor to add additional power as the artificial foot pushes off. This is roughly analogous with the way a biological foot and ankle work. Some energy from the impact of the foot striking the ground is stored in tendons, while extra force is generated by muscles for pushing off again.
The robotic ankle also uses a microprocessor and various sensors to regulate the position of the foot and ankle sections, to control its stiffness, and to determine how much power should be produced by the motor.
For instance, when the wearer strolls uphill, the motor has to generate extra power, but going downhill the ankle has to use a brake-like device to dissipate some energy.
The robotic ankle is powered by a rechargeable battery about the size of three large flashlight batteries, which store enough electricity to power the ankle for a walk of several miles, reports New Scientist.