As people get older, their walking speed reduces. While this can be problematic and frustrating at times, it is a common problem. Exoskeletons enhance walking speed and boost strength up to 20 times, but the mechanisms behind these changes and the more significant limits on performance are unknown.
Stanford University engineers have created a prototype ankle exoskeleton system that can significantly help people walk faster while burning less energy. The exoskeleton attaches around the leg and into a running shoe, allowing the wearer to select a preferred walking speed. The system is controlled via an algorithm and powered externally by motors.
The ankle exoskeleton emulator is an experimental version that serves as a testbed for trying out different designs. How does it work? The exoskeleton acts as a mechanical calf muscle, adding a bit of strength into every step as the wearer walks. The tether (along the back of the exoskeleton) pulls the wearer’s heel upward, making their toe point downward as they push off the floor. This results in the user’s walking speed increases by about 40% compared with their regular speed without the system.
In experiments, the Stanford team tested ten young participants’ walk in regular shoes without the exoskeleton, with the exoskeleton shut off and with the exoskeleton turned on with three different modes: optimized for energy use, optimized for speed, and a placebo mode adjusted to make them walk slower.
While the user walked on the treadmill, an algorithm continually adjusted the exoskeleton settings. After around 150 rounds of adjustment and two hours per person, the team found the speed-optimized mode of the operation. Participants walked up to 42% faster than in regular shoes, with torque optimized for speed. Additionally, the speed-optimized mode minimized energy use by about 2% per meter trekked.
The engineers plan to make future versions of the ankle exoskeleton emulator that consistently reduces energy use while also being more comfortable. They also plan to run tests with older people and hope that future designs could improve balance in the elderly and reduce pain caused by weight on joints.
Steve H. Collins, Assoc. Prof. of mechanical engineering at Stanford, said:
A 40% increase in speed is more than the difference between younger adults and older adults. So, it’s possible that devices like this could not only restore but enhance self-selected walking speed for older individuals, and that’s something that we’re excited to test next.
The team published the results of this study in IEEE Transactions on Neural Systems and Rehabilitation Engineering on April 20.
