Model-Based Variable Impedance Control of Active-Passive Upper-Limb Exoskeleton Assistance and Vibration Attenuation

Abstract

This letter proposes a model-based vibration attenuation method for variable-impedance control of a 1-degree-of-freedom active-passive upper-limb exoskeleton. Static and dynamic human efforts are compensated separately, the variable-impedance profile follows a standard law, and the attenuator is derived from identified structural elasticity. To evaluate human adaptation, motor learning was combined with muscle torque generator models. For raising/lowering a weight under the tested conditions, adaptation simulations and a set of human-in-the-loop experiments on one subject show reduced vibration with attenuation; simulations and another set of sEMG-based human-in-the-loop experiments on ten subjects suggest that variable impedance lowers human effort, although motor and human torques are not always aligned.