A Novel Funnel-Based L1 Adaptive Fuzzy Approach for the Control Of An Actuated Ankle Foot Orthosis

This paper introduces a novel funnel-based adaptive ${{\mathcal{L}}_1}$ fuzzy control strategy for assisting ankle joint movement during walking with the use of an actuated ankle foot orthosis (AAFO). A projection-based adaptation mechanism employing a fuzzy system is used to estimate the unknown time-varying parameters of the ${{\mathcal{L}}_1}$ control law, ensuring precise tracking of the AAFO-wearer system by the state estimator. The projection operator guarantees the convergence of the parameters while offering a limited amount of assistance torque. Funnel-based feedback control is used to mitigate the typical time lag seen when using ${{\mathcal{L}}_1}$-based approaches due to the presence of a low-pass filter commonly used in this type of approach. The effectiveness of the proposed control strategy is demonstrated through real-time experiments involving five healthy subjects.