Adaptive Time-Varying Barrier Lyapunov Function-Based Model-Free Hybrid Position/Force Control for Series Elastic Actuator-Based Manipulator

In this brief, an adaptive time-varying barrier Lyapunov function-based model-free hybrid position/force controller (ABLF-MFC) is designed for a series elastic actuator (SEA)-based 2-link manipulator. The proposed ABLF-MFC is designed based on impedance control and has a dual-loop structure, which is an outer force control loop and an inner position control loop. The outer force control loop converts the desired interaction force into a reference trajectory through the impedance model, which is later tracked by the inner position control loop to achieve hybrid position and force control. In order to simplify the inner position control loop design, an ultra-local model (ULM) is introduced to approximate the original system, and all the dynamic characteristics and uncertainties are lumped into an unknown term. And the time-delay estimator (TDE) is used to estimate the unknown term in ULM. Then, a time-varying barrier Lyapunov function is introduced in the inner position control loop, which can effectively improve the transient and steady responses. In addition, an adaptive term is added to compensate for the estimation error of TDE. The effectiveness of the proposed ABLF-MFC is verified by rigorous mathematical proofs and simulation results.