Fixed‐time asymmetric barrier Lyapunov function‐based model‐free hybrid position/force control for 3‐DOF SEA‐based manipulator with output constraints

Abstract

In this work, a fixed‐time asymmetric barrier Lyapunov function (BLF)‐based model‐free hybrid position/force controller (FBMHC) is proposed for 3‐DOF SEA‐based manipulator for large surface machining with asymmetric time‐varying output constraints. The proposed FBMHC has a dual‐loop structure, which consists of a force sub‐control loop and a position sub‐control loop. The force sub‐control loop converts the control of the interaction force into position control through the idea of impedance control. The position sub‐control loop is designed under the model‐free control framework, which includes asymmetric time‐varying BLF, time‐delay estimator (TDE), and adaptive compensation term, so as to reduce the complexity of controller design and keep the joint angles within the asymmetric time‐varying output constraints. Strict mathematical derivation proves that the proposed method can achieve fixed‐time convergence, so the influence of the initial value on the control effect is reduced. Finally, the effectiveness of FBMHC is verified by comparison simulation with TDE‐intelligent PD and finite time BLF‐based model‐free control.