Design and Control of an Underactuated Exoskeleton for Loaded Walking

This work presents a first demonstration of a nonanthropomorphic, underactuated exoskeleton architecture that uses a single linear actuator per leg to transfer loads directly to the ground next to the wearer’s foot. This allows the exoskeleton and user to move somewhat independently, facilitating normal kinematics during walking. We also present the control system that employs inertial measurement units (IMUs) affixed to the exoskeleton and shoes to estimate gait parameters. The performance of the exoskeleton is assessed based on its ability to touch down to the ground and lift off from the ground at the start of the stance and swing phases, respectively, as a participant walks on a treadmill at five speeds (0.67–1.34 m/s). The exoskeleton exhibited a touchdown delay of 0.093±0.019 seconds and a lift-off delay of 0.007±0.018 seconds, resulting in total support percentages of 88.9±2.9% during the stance phase across all speeds and the best performance at 0.67 m/s. Other experiments showed that our gait percentage estimation during steady state walking achieved a pooled root-mean-square error (RMSE) of 2.94%, which is less than prior works. This proof-of-concept architecture highlights a promising direction for lightweight, low-complexity exoskeletons for load carriage or bodyweight support.