Development of Variable Transmission Series Elastic Actuator for Hip Exoskeletons

Series Elastic Actuator-based exoskeleton can offer precise torque control and transparency when interacting with human wearers. Accurate control of SEA-produced torques ensures the wearer's voluntary motion and supports the implementation of multiple assistive paradigms. In this paper, a novel variable transmission series elastic actuator (VTSEA) is developed to meet torque-speed requirements in different exoskeleton-assisted locomotion modes, such as running, walking, sit-to-stand, and stand-to-sit. The VTSEA features a SEA-coupled variable transmission ratio adjusting mechanism and works between three discrete levels of transmission ratio depending on the user's initiative. The proposed prototype can also improve transparency in human-robot interaction. Also, an accurate torque controller with inertial compensation is developed for the VTSEA via the singular perturbation theory, and its stability is proved. The feasibility of the proposed VTSEA prototype and the precise output torque performance of VTSEA are verified by experiments.