Robust sliding mode impedance control of manipulators for complex force-controlled operations

The multi-source uncertainties in complex force control operation scenarios will seriously affect the force control accuracy and operation quality of industrial manipulators. The complex force control method of manipulators considering multi-source uncertainties (environmental position uncertainty, environmental stiffness uncertainty and other uncertainties, etc.) is investigated in this paper. Firstly, the parametric representation of environmental position uncertainty and the impedance model parameter uncertainty is introduced under the traditional impedance control framework. A new impedance control model is proposed by considering the environmental position uncertainty and the implicit dynamic adjustment terms of impedance model parameters as the lumped disturbance. Then, a finite-time disturbance observer is designed for real-time estimation of the lumped disturbance, and a new robust sliding-mode impedance control method is proposed to compensate for the lumped disturbance combined with the sliding-mode variable structure theory, so as to construct a novel composite control framework for uncertain and complex force control operation scenarios. Finally, based on the Lyapunov stability theory, the stability of the control method and the observer is guaranteed. Simulations and experiments are carried out to verify the proposed method, and a comprehensive comparison is made with existing state-of-the-art methods such as traditional impedance control, variable stiffness impedance control and indirect adaptive impedance control. The results show that the proposed sliding-mode impedance control method can realize the fast and stable adjustment of the contact force of the end-effector in different operation scenarios and can achieve the effect of the relative contact force error within 4.73%, which proves the effectiveness and feasibility of the proposed method.