Fractional-order Sliding Mode Constraint Control for Manipulator Systems Using Grey Wolf and Whale Optimization Algorith
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ISSN:1598-6446 eISSN:2005-4092 http://www.springer.com/12555
Fractional-order Sliding Mode Constraint Control for Manipulator Systems Using Grey Wolf and Whale Optimization Algorithms Seong-Ik Han Abstract: This study investigates a new fractional-order nonsingular terminal sliding mode control (FTSMC) leveraging a finite-time extended state observer, a simpler prescribed control, and hybrid grey wolf optimization (GWO) combined with whale optimization algorithm (WOA) for manipulator systems. The new FTSMC system is based on an improved fractional-order terminal sliding surface. Initially, the study experimentally optimizes the dynamic parameters and gains of the controller and the observer with the help of the newly developed GWO-WOA technique. As the next step, the uncertainties including optimization error and external disturbances are estimated by the finite-time extended state observer designed using the sliding mode dynamics. Experimental results of GWOWOA optimization and joint position tracking for a self-designed articulated manipulator prove the efficacy of the proposed control scheme. Keywords: Experiemental grey-wolf and whale optimization, finite-time extended state observer, fractional-order nonsingular terminal sliding mode control, manipulator systems, sliding mode constraint control.
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INTRODUCTION
The sliding mode control (SMC) approach [1] has been widely used owing to its attractive features of low sensitivity to uncertainties, fast response, and easy realization. To further improve the transient time performance and to ensure finite-time convergence, the terminal sliding mode control (TSMC) [2, 3] was developed to add a nonlinear sliding surface to the first-order sliding surface, which improve the robustness and tracking control properties. However, the singularity issue that occurs in achieving equivalent control via derivation of the terminal sliding surface limits the applicability of the TSMC approach. Thus, nonsingular terminal sliding mode controllers (NTSMCs) were designed [4, 5] to overcome the singularity issue and sustain the finite-time convergence performance. Fractional-order TSMC (FTSMC) methods [6–12] have recently been proposed owing to their advantages of fractional-order calculus over integer-order based TSMC methods. Successful results have been obtained by applying FTSMC methods to several systems. This study proposes a new fractional-order nonsingular sliding surface that offers faster convergence compared to the previous FTSMC systems. The proposed FTSMC surface helps in avoiding the singularity issue while improving the con-
vergence control performance, comparing to the previous methods. Additionally, the extended state observer provides feedforward compensation for modeling errors and external disturbances, by utilizing finite-time secondorder sliding mode observer, thereby improving robustness to uncertainties and reducing the conservativeness of selecting switching control gains [13]. In most control systems, gains of the controller and the observer are tuned u
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