Design and Control of a Series Elastic Actuator With Clutch for Hip Exoskeleton for Precise Assistive Magnitude and Timing Control and Improved Mechanical Safety

Transparency and guaranteed safety are important requirements in the design of wearable exoskeleton actuators for individuals who have lower limb deficits but still maintain a certain level of voluntary motor control. Specifically, precision in torque delivery timing and magnitude, robustness, disturbance rejection, and repeatability are desired in the actuator design and control. Motivated by these needs, this study aims to develop a series of elastic actuators with clutch (SEAC) that can precisely generate the desired assistance in terms of both timing and torque magnitude for a wearable hip exoskeleton and guarantee the wearer's safety at the same time. The proposed mechanical design improves actuator transparency and safety by a mechanical clutch that automatically disengages the transmission when needed. A new torque control for the SEAC, based on singular perturbation theory with flexible compensation techniques, is proposed to precisely control the assistive torque by rejecting the undesired human motion disturbance. The mechanical design of the proposed device and the design of a singular perturbation control algorithm are discussed, and the SEAC performance is verified by experiments. Experimental results, derived from a test with a human subject, are presented to demonstrate the precision of the assistive torque and timing control of the SEAC while interacting with a human wearer.