Walking exoskeletons hold the potential to let people walk longer, faster, or walk while carrying more weight.

 

Autonomous powered leg exoskeleton

For over a century, technologists have strived to develop autonomous leg exoskeletons that reduce the metabolic energy consumed when humans walk and run, but such technologies have traditionally remained unachievable. An autonomous powered ankle exoskeleton was designed and developed to augment human walking. A lightweight electric actuator mounted on the lower-leg provides mechanical assistance to the ankle during powered plantar flexion. Use of the exoskeleton significantly reduced the metabolic cost of walking by 11 ± 4% (p = 0.019) compared to walking without the device. In a separate study, use of the exoskeleton reduced the metabolic cost of walking with a 23 kg weighted vest by 8 ± 3% (p = 0.012). A biomechanical study revealed that the powered ankle exoskeleton does not simply replace ankle function, but augments the biological ankle while assisting the knee and hip. Use of the powered ankle exoskeleton was shown to significantly reduced the mean positive power of the biological ankle by 0.033 ± 0.006 W/kg (p<0.01), the knee by 0.042 ± 0.015 W/kg (p = 0.02), and the hip by 0.034 ± 0.009 W/kg (p<0.01). In the design of leg exoskeletons, this project underscores the importance of minimizing exoskeletal power dissipation and added limb mass, while providing substantial positive power to a walking human. These design requirements were used to develop the first autonomous exoskeleton to reduce the metabolic cost of walking.

L. M. Mooney and H. M. Herr.
Biomechanical walking mechanisms underlying the metabolic reduction caused by an autonomous exoskeleton,
Journal of NeuroEngineering and Rehabilitation, vol. 11, January. 2016.
L. M. Mooney, E. J. Rouse and H. M. Herr.
Autonomous exoskeleton reduces metabolic cost of human walking,
Journal of NeuroEngineering and Rehabilitation, vol. 11, pp. 151, November. 2014.
L. M. Mooney, E. J. Rouse and H. M. Herr.
Autonomous exoskeleton reduces metabolic cost of walking,
International Conference of the IEEE Engineering in Medicine and Biology Society, August. 2014.
L. M. Mooney, E. J. Rouse and H. M. Herr.
Autonomous exoskeleton reduces metabolic cost of human walking during load carriage,
Journal of NeuroEngineering and Rehabilitation, vol. 6, pp. 80, May. 2014.
 

A quasi-passive leg exoskeleton for load-carrying augmentation

A quasi-passive leg exoskeleton is presented for load-carrying augmentation during walking. The exoskeleton has no actuators, only ankle and hip springs and a knee variable-damper. Without a payload, the exoskeleton weighs 11.7 kg and requires only 2 Watts of electrical power during loaded walking. For a 36 kg payload, we demonstrate that the quasi-passive exoskeleton transfers on average 80% of the load to the ground during the single support phase of walking. By measuring the rate of oxygen consumption on a study participant walking at a self-selected speed, we find that the exoskeleton slightly increases the walking metabolic cost of transport (COT) as compared to a standard loaded backpack (10% increase). However, a similar exoskeleton without joint springs or damping control (zero-impedance exoskeleton) is found to increase COT by 23% compared to the loaded backpack, highlighting the benefits of passive and quasi-passive joint mechanisms in the design of efficient, low-mass leg exoskeletons.

C. Walsh, K. Endo, and H.M. Herr.
A quasi-passive leg exoskeleton for load-carrying augmentation,
Intl. J. Humanoid Robotics, 2007.