An Assistive Wrist-Elbow Exoskeleton (WE-Exo) Driven by Variable Stiffness Actuators

Exoskeletons have been developed to assist the rehabilitation of stroke patients in the recent years. However, the safety of the physical human-robot interaction (pHRI) of the exoskeleton still need to be further improved. In this study, a 2-degree-of-freedom (2-DoF) rehabilitation exoskeleton is designed for the assistance of elbow flexion/extension (FE) and wrist supination/pronation (SP). The joints are powered by two independent variable stiffness actuators (VSAs), which ensures the intrinsic safety of pHRI of the exoskeleton, and enhances its adaptability to environmental changes, e.g., collisions. Each VSA has two independent DC motors to adjust the output torque and stiffness, respectively. To reduce the moment inertia of the exoskeleton, the wrist actuator is coupled with its main drive motor through a cable-driven system. A feedback linearization controller of the exoskeleton is developed to achieve position tracking of the joints. A prototype of the exoskeleton is developed to evaluate its performance. The result finds that the proposed exoskeleton can assist the movement of users sufficiently with the controller.