Fuzzy-based impedance regulation for control of the coupled human-exoskeleton system

Impedance control has been widely developed in the robotic exoskeleton field for human performance assistance and enhancement. However, the determination of desired impedance parameters that dominates the characteristics of interaction force and motion control is not straightforward since these parameters depend not only on the physical properties of the wearer but also on the speed region during locomotion. This paper presents a newly developed control strategy to regulate the desired impedance between a wearable lower exoskeleton and a wearer's limb according to a specific motion speed using a rule-based fuzzy regulator. In this control strategy, the analysis of stability and performance in frequency domain is adopted for designing the fuzzy rule. We have demonstrated the feasibility of the proposed method through a single degree of freedom exoskeleton example that employed swing movements with a chosen operator. Experimental results show that the resulting interaction torque and the human-exoskeleton tracking error are significantly reduced as compared to the traditional impedance control method used for various frequency ranges of leg motion.