Design of a series elastic actuator for a compliant parallel wrist rehabilitation robot

This paper presents the design of a novel linear series elastic actuator purposely designed to match the requirements of robots for wrist rehabilitation: backdriveabil-ity, intrinsic compliance, and capability to be controlled as ideal force/torque sources. An existing rehabilitation robot is adapted to include intrinsic compliance in the design. A novel linear compliant element is designed to meet dimensional and force/stiffness requirements; a force sensing scheme involving a Hall-effect sensor is optimized in FEM simulations and developed. Linearity tests of the compliant sensing element show a maximum of 4.5% of FSO combined nonlinearity and hysteresis errors. Characterization experiments show that the developed system introduces physical compliance, still guaranteeing accurate force control in a frequency range largely compatible with that required for wrist assistance during rehabilitation.