Abstract
This paper proposes a novel controller, fast fractional-order terminal sliding mode control (FFOTSMC), for a seven-degree-of-freedom (7-DOF) robot manipulator with tracking control. The new controller applies the fractional-order derivative on both the sliding surface design and the sliding control/reaching law. Compared to previous research, which only applies the fractional-order derivative on the sliding surface design, the proposed controller has a faster convergence for reaching the sliding surface and maintaining stay on it because of the new fractional-order control law, which helps the tracking accuracy. To implement the controller on the robot with less chattering, a sliding perturbation observer (SPO) is used to estimate the disturbance and uncertainties. Stability analysis is analyzed using Lyapunov functions for fractional-order systems. The controller performance is evaluated by a simulation of a single-input and single-output (SISO) system in MATLAB Simulink and experiments on the robot manipulator.
Highlights
Sliding mode control (SMC) has been widely studied and applied to robot manipulators because of its simplicity of implementation, fast global convergence, high robustness to external variations, and insensitivity to modeling error and system parameter variations [1]
The control/reaching law in TSM control (TSMC) contains a nonlinear term, which allows the sliding surface to be reached in finite time with fast convergence
In order to implement the fractional-order derivative, the Grünwald–Letnikov fractional derivative is applied in this research
Summary
Sliding mode control (SMC) has been widely studied and applied to robot manipulators because of its simplicity of implementation, fast global convergence, high robustness to external variations, and insensitivity to modeling error and system parameter variations [1]. SMC includes a conventional linear sliding mode (LSM) control, which is asymptotically stable, and a terminal sliding mode (TSM). It includes two steps to design an SMC: the choice of sliding surface and the control/reaching law to reach the sliding surface and maintain stay on it. TSM control (TSMC) utilizes a nonlinear sliding surface instead of a linear sliding surface in sliding surface design. It generates faster convergence, less tracking errors than LSM control (LSMC), and finite stability for reaching the equilibrium point. The control/reaching law in TSMC contains a nonlinear term, which allows the sliding surface to be reached in finite time with fast convergence. Many researchers have focused on solving the singularity [4,5]
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