Abstract
In recent years, underactuated nonlinear dynamic systems trajectory tracking, such as space robots and manipulators with structural flexibility, has become a major field of interest due to the complexity and high computational load of these systems. Hierarchical sliding mode control has been investigated recently for these systems; however, the instability phenomena will possibly occur, especially for long-term operations. In this paper, a new design approach of an adaptive fuzzy hierarchical terminal sliding-mode controller (AFHTSMC) is proposed. The sliding surfaces of the subsystems construct the hierarchical structure of the proposed method; in which the top layer includes all of the subsystems’ sliding surfaces. Moreover, terminal sliding mode has been implemented in each layer to ensure the error convergence to zero in finite time besides chattering reduction. In addition, online fuzzy models are employed to approximate the two nonlinear dynamic system’s functions. Finally, a simulation example of an inverted pendulum is proposed to confirm the effectiveness and robustness of the proposed controller.
Highlights
IntroductionInterests toward developing under-actuated systems have been increased
In the recent years, interests toward developing under-actuated systems have been increased
The main features of the proposed adaptive fuzzy hierarchical terminal sliding-mode controller (AFHTSMC) are as follows: 1) The implementation of the terminal sliding mode (TSM) control, which guarantees the fast finite time convergence and reduces the chattering and steady state errors. This superior property becomes admirable in the applications requiring high precision; 2) The unknown nonlinear system functions are approximated by the adaptive fuzzy systems with adaptive learning laws; 3) The hierarchical structure of the proposed method is a very effective tool to guarantee the stability, especially for complex and high nonlinear dynamic systems
Summary
Interests toward developing under-actuated systems have been increased. As can be clearly seen in the aforementioned studies, the implementation of the adaptive fuzzy system besides the sliding mode and hierarchical structure could not solve the chattering and fast time convergence problems; in this study, our main objective is to propose a novel control method, named as the adaptive fuzzy hierarchical terminal sliding mode control (AFHTSMC), which enables us to use the advantages of terminal sliding mode control besides the adaptive fuzzy hierarchical structure for uncertain under-actuated nonlinear dynamic systems control. The main features of the proposed AFHTSMC are as follows: 1) The implementation of the TSM control, which guarantees the fast finite time convergence and reduces the chattering and steady state errors This superior property becomes admirable in the applications requiring high precision; 2) The unknown nonlinear system functions are approximated by the adaptive fuzzy systems with adaptive learning laws; 3) The hierarchical structure of the proposed method is a very effective tool to guarantee the stability, especially for complex and high nonlinear dynamic systems.
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