Development of a Clutchable Series Elastic Actuator for Robotic Hip Exoskeleton

Abstract

Precision in torque delivery timing and magnitude, robustness, disturbance rejection, and repeatability are desired in the actuator design and control. The interest of series elastic actuator (SEA) for lower-limb exoskeleton has recently increased due to the unique properties compared to rigid actuators, such as high force control accuracy, low output impedance, and tolerance to shocks. In this paper, a SEA with clutch for hip exoskeleton is designed to accurate torque delivery to provide effective assistance. A mechanical clutch that controls engages and disengages the power transmission during gait cycle to ensure transparency and user safety. The precise torque control is the main challenge in the control of SEA. By adding, a clutch in the SEA this will cause a new force control challenge with the frequent release and engage the clutch will aggravate the mechanical vibration and bring the risk of unsafety to the exoskeleton wearer. A new torque control, based on the singular perturbation integrated with flexibility compensation for SEA is proposed. Experiments are conducted to verify our proposed controller can effectively control actuation timing and allow precise assistive torque control. This study serves as a stepping stone towards utilizing and designing hip exoskeleton to assist with walking.