Bio-based supervisory control of a lower exoskeleton for stance phase

This paper presents a newly supervisory impedance control strategy of a wearable lower limb exoskeleton in stance phase intended to enhance human performance and support load-carrying using biomechanical analysis. In order to control the coupled human-robot system, the impedance control strategy, previously developed by the authors for swing phase, has been herein expanded up to the stance phase by regulating the desired impedance between the exoskeleton and a wearer's limb according to a specific motion speed. The effect of human behaviours on the change of impedance parameters across variable walking speeds in the stance phase is adopted to design the fuzzy rules for the control strategy. The control performance of the designed exoskeleton is evaluated on a bench-testing over different ranges of walking speeds (about 0.3 m/s to 1.2 m/s). Experimental results show that the resulting interaction torque, the human-exoskeleton tracking error, and electrical power consumption are significantly reduced as compared to a traditional impedance control, especially in the stance phase. Besides that, an average of 72.3 % of the load was transferred to the ground by the exoskeleton during the stance phase of walking. The developed control strategy on the lower exoskeleton has the potential to increase comfort and adaptation to users during daily use.