Continuous fuzzy nonsingular terminal sliding mode control of flexible joints robot manipulators based on nonlinear finite time observer in the presence of matched and mismatched uncertainties

Abstract

In the present study, a continuous fuzzy nonsingular terminal sliding mode control (CFNTSMC) was proposed based on the nonlinear finite-time observer (NFTO), in a voltage-based manner, to control the position of a serial-chain n-link flexible-joint electrically-driven robot manipulator in presence of matched and mismatched uncertainties with the electrical and mechanical equations. In order to design the controller sliding surface, a continuous function was proposed, which could make the concerned sliding surface zero at the beginning of the control process so that the proposed control had only the sliding phase. Afterward, an NFTO was adopted to facilitate access to the information of the state variables and matched and mismatched uncertainties. According to the Lyapunov stability theorems, the closed-loop control system had finite-time global asymptotically stability in presence of NFTO and existing uncertainties. Finally, a fuzzy-based control law was proposed to avoid chattering phenomena in the control input, whose computational complexity was extremely low. In order to evaluate the efficiency of the proposed control, multi-stage simulations were conducted for a 2-link flexible-joint serial robot manipulator. The mathematical evidence and simulation results confirmed the desired performance of the proposed CFNTSMC.