A bilateral wrist robotic system with compliant actuation for rehabilitation training

In this article, we present a bilateral wrist robotic system for rehabilitation training that extracts subject-adaptive reference movements from the unaffected limb using a passive module while safely assisting the affected limb using an active module. The system features a parallel mechanism for both modules, supporting three degrees of freedom (DoF) in wrist motion with reduced inertia. The active module employs three linear series elastic actuators (SEAs) to ensure low mechanical impedance and safe interaction. Force and motion tracking controls are implemented in the robot's end-effector space to enable various bilateral training exercises. Additionally, we introduce a dynamic model for the multi-DoF SEA-driven parallel robot, with a feedforward design compensating for unmodeled nonlinearities. Experimental results validate the system's performance in transparency, force tracking, and motion tracking. Finally, the bilateral training framework's effectiveness is demonstrated through two case studies involving healthy subjects with simulated impairments.