Design and Control of a Multifunctional Ankle Exoskeleton Powered by Magnetorheological Actuators to Assist Walking, Jumping, and Landing

Abstract

Lower-limb exoskeletons have shown increasing potential to augment human performance in many locomotion tasks. However, most lower-limb exoskeletons use highly geared, non-back-drivable actuators with limited power and force bandwidth in order to be light enough to be carried without metabolic penalty. Moreover, they rely on controllers that depend on past motion history to assist the user, which limits the multifunctional capabilities of exoskeletons. Here, we study the potential of delocalized magnetorheological (MR) clutches to provide transparent but yet powerful multifunctional exoskeleton assistance. A single high-speed, lightweight motor is coupled with two MR clutches that modulate the plantar-flexion torque at each ankle. The exoskeleton is controlled by a state map controller that can assist users in real time while walking, jumping, and landing. Results confirm the potential of the MR actuation approach by demonstrating instantaneous adaptation to transient walking and by producing a maximal torque of 90 N $\cdot$ m per ankle with a total power of 1.4 kW when jumping. The system also actively braked landing impact and achieved multifunctional assistance in a sequence of walking, jumping, and landing. With a total mass of 6.2 kg including 0.9 kg on each leg, the system reduces metabolic cost of walking by 5.6% on average with tethered electronics and power supply.