Non-Singular Terminal Sliding Mode Controller with Nonlinear Disturbance Observer for Robotic Manipulator

Abstract

Aiming at the problems of model uncertainties and other external interference in trajectory tracking control of n-degree of freedom manipulators, a non-singular terminal sliding mode controller with nonlinear disturbance observer (NDO–NTSMC) trajectory tracking method is proposed. A nonlinear disturbance observer (NDO) is designed to forecast and compensate the system external interference, and a nonlinear gain is designed to make the observer error achieve the expected exponential convergence rate so that the feedforward compensation control is realized. Then, a non-singular terminal sliding mode controller (NTSMC) built on nonlinear sliding surface is designed to surmount the singularity fault of classic terminal sliding mode controller (TSMC). Therefore, the time required from any initial state to reach the equilibrium point is finite. In addition, the redesign of the sliding surface ensures the tracking accuracy rate of uncertain systems. Then, based on Lyapunov principle, we complete the stability analysis. Finally, the method is applied to a 2-DOF robotic manipulator model compared with other methods. In the simulation, the manipulator needs to track a continuous trajectory under the condition of joint friction disturbance. The simulation result shows that the torque output of the designed method is chattering-free and smooth, and the tracking effect is precise. Simulation results indicate that the proposed controller has the advantages of excellent tracking performance, strong robustness, and a fast response.

Critic-Only Learning Based Tracking Control for Uncertain Nonlinear Systems with Prescribed Performance

“…To deal with the impact induced by uncertainties during controller design, there emerge a large amount of tools to approximate uncertainties and combined with other controllers, e.g., neural networks (NNs) [4,5], fuzzy logic systems [6][7][8], and disturbance observers [9][10][11]. For example, by integrating with a backstepping control, an adaptive tracking controller is designed in [5] for uncertain nonlinear systems, where an NN is utilized to estimate the uncertain term of the model.…”

“…Taking the disturbance ability of an observer-based controller into consideration, the tracking performance can be guaranteed. For manipulators, a sliding-mode controller is investigated for tracking problems, where a nonlinear disturbance observer is implemented to predict and remove the effect of disturbance [10]. However, manually tunned parameters limit above controllers applied in practical applications.…”

“…(1) Compared with the existing observer-based controllers [9][10][11], where the disturbance is estimated with observers by adjusting manually multiple parameters, the USDE was employed to approximate the lumped disturbance of nonlinear uncertain systems with an invariant manifold principle. Moreover, differing from previous function approximatorbased control schemes [12][13][14], by combining the RL technique into the optimal control design, the precise tracking performance and the low control cost can be achieved.…”

Enhanced Trajectory Tracking via Disturbance-Observer-Based Modified Sliding Mode Control

“…Researchers have proposed a disturbance observer (DO)-based SMC for accurate position tracking [30][31][32][33]. The DO estimates system states and perturbations/disturbances.…”