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A multi‐motor coordinated tracking control strategy based on a disturbance sliding‐mode observer and an anti‐saturation non‐singular fast‐terminal sliding mode is proposed to address the issues of slow convergence and controller output saturation in multi‐motor coordinated control systems. Firstly, a mathematical model of a multi‐motor traction system considering uncertain parameter perturbations, external disturbances, and dead zones was established. Secondly, a disturbance sliding‐mode observer was designed based on the mathematical model to eliminate motor disturbances and estimate the torque. The observer's forward compensation was added to design a total‐consensus‐based fast non‐singular terminal sliding‐mode controller. Then, a fast anti‐saturation auxiliary system with fast finite‐time convergence was constructed. Finally, a comparative experiment was conducted with traditional anti‐saturation sliding‐mode control to demonstrate that the proposed method had faster convergence, stronger disturbance rejection, and better tracking performance in the presence of multi‐motor parameter perturbations, unknown disturbances, and input saturation.

This paper investigates the trajectory tracking problem of the quadrotor unmanned aerial vehicles (UAV) with consideration of both attitude and position dynamics. First of all, the trajectory tracking problem is divided into the commands tracking in position and attitude loops by introducing the virtual attitude angle commands. Secondly, the high-order sliding mode observers (HSMOs) are introduced to estimate the lumped disturbances in position loop and the derivatives of the attitude angle tracking errors, the lumped disturbances in the attitude loop. And then the composite nonlinear dynamical inversion controller in position loop and the composite nonsingular terminal sliding mode controller in attitude loop are constructed by introducing the estimation information of HSMOs into controller design process. Finally, the simulations based on the data of a practical UAV are carried out to verify the effectiveness of the proposed method.

This paper proposes a new fixed-time sliding mode (FSM) control, where the settling time for reaching the system origin is bounded to a constant independent of the initial condition; this is in contrast to the initial condition-dependent constants used in the traditional linear sliding mode (LSM) and terminal sliding mode (TSM) controls. First, a new sliding mode control with a single power term is discussed, where the power term can have any nonnegative value. Except for the traditional LSM and TSM controls, a new sliding mode control called power sliding mode (PSM) is proposed, whose power term is larger than 1. Then, a new FSM control with two power terms is investigated, whose design is based on the combination of TSM and PSM. In particular, the two power terms on the plane in the first quadrant are carefully discussed, and a detailed classification is provided. Here, the first quadrant can be classified into six categories, including LSM, generalized LSM, TSM, fast TSM (FTSM), PSM, and FSM. Furthermore, the analytical settling time is calculated, and three different estimation bounds of the settling time are given for reaching the origin under any initial condition. It is also interesting to derive the lowest bound for the settling time. Finally, FSM control design for general nonlinear dynamical systems with the relative degree from the control input to the output is also discussed.

The dead-zone nonlinearity and uncertain dynamics inevitably weaken the tracking performance of the displacement system for a hydraulic roofbolter. To solve the above problem, a global sliding-mode controller based on a reduced-order proportional-derivative-type (PD-type) extended state observer (GSMC-PDESO) is proposed. Firstly, the displacement system model of a hydraulic roofbolter is built by using a compensation technique to suppress the effect of dead-zone nonlinearity on control performance. Following that, a novel extended state observer that has less dimensions and few gains than standard one, called reduced-order PD-type extended state observer, is designed, with the purpose of improving the estimation performance and suppressing noise amplification. Moreover, a global sliding-mode unit mainly composed of a novel global integral sliding-mode surface and a novel global sliding-mode control law is developed, which aims to improve global robustness, eliminate the chattering and adverse impact on estimation error of disturbances, as well as provide an effective and continuous control law. By comparing the proposed GSMC-PDESO with ten control methods, the comparative experimental results verify the effectiveness of the proposed GSMC-PDESO and strategies.

This paper proposes a new dynamic PID sliding mode control technique for a class of uncertain nonlinear systems. The offered controller is formulated based on the Lyapunov stability theory and guarantees the existence of the sliding mode around the sliding surface in a finite time. Furthermore, this approach can eliminate the chattering phenomenon caused by the switching control action and can realize high-precision performance. Moreover, an adaptive parameter tuning method is proposed to estimate the unknown upper bounds of the disturbances. Simulation results for an inverted pendulum system demonstrate the efficiency and feasibility of the suggested technique.

Sliding dynamics is a peculiar phenomenon to discontinuous dynamical systems, while homoclinic orbits play a role in studying the global dynamics of dynamical systems. This paper provides a method to ensure the existence of sliding homoclinic orbits of three-dimensional piecewise affine systems. In addition, sliding cycles are obtained by bifurcations of the systems with sliding homoclinic orbits to saddles. Two examples with simulations of sliding homoclinic orbits and sliding cycles are provided to illustrate the effectiveness of the results.

Near the 100th anniversary of the discovery of ferroelectricity, so-called sliding ferroelectricity has been proposed and confirmed recently in a series of experiments that have stimulated remarkable interest. Such ferroelectricity exists widely and exists only in two-dimensional (2D) van der Waals stacked layers, where the vertical electric polarization is switched by in-plane interlayer sliding. Reciprocally, interlayer sliding and the “ripplocation” domain wall can be driven by an external vertical electric field. The unique combination of intralayer stiffness and interlayer slipperiness of 2D van der Waals layers greatly facilitates such switching while still maintaining environmental and mechanical robustness at ambient conditions. In this perspective, we discuss the progress and future opportunities in this behavior. The origin of such ferroelectricity as well as a general rule for judging its existence are summarized, where the vertical stacking sequence is crucial for its formation. This discovery broadens 2D ferroelectrics from very few material candidates to most of the known 2D materials. Their low switching barriers enable high-speed data writing with low energy cost. Related physics like Moiré ferroelectricity, the ferroelectric nonlinear anomalous Hall effect, and multiferroic coupling are discussed. For 2D valleytronics, nontrivial band topology and superconductivity, their possible couplings with sliding ferroelectricity via certain stacking or Moiré ferroelectricity also deserve interest. We provide critical reviews on the current challenges in this emerging area.

This paper proposes a novel nonlinear speed control method for permanent magnet synchronous motors that enhances their robustness and tracking performance. This technique integrates a sliding-mode disturbance observer and variable-gain fractional-order super-twisting sliding-mode control within a vector-control framework. The proposed control scheme employs a sliding-mode control method to mitigate chattering and improve dynamics by implementing fractional-order theory with a variable-gain super-twisting sliding manifold design while regulating the speed of the considered motor system. The aforementioned observer is suggested to enhance the control accuracy by estimating and compensating for the lumped disturbances. The proposed methodology demonstrates its superiority over other control schemes such as traditional sliding-mode control, super-twisting sliding-mode control, and the proposed technique. MATLAB/Simulink simulations and real-time implementation validate its performance, showing its potential as a reliable and efficient control approach for the system under study in practical applications.

•An improved delay-dependent stability criterion is derived for linear time-delay systems with two constant delays with overlapping ranges.•This overlapping feature of the delays is exploited in the delay-dependent analysis using Lyapunov–Krasovskii approach to reduce conservatism compared to the approaches treating the delays individually.•The proposed approach is less conservative than existing approaches. In this paper, an adaptive super twisting sliding mode controller (ASTSMC) is proposed for a class of nonlinear systems to counteract mismatched uncertainties. To estimate the unknown external disturbance efficiently, an adaptive terminal sliding mode disturbance observer (ATSMDO) is proposed. The stability of the over all closed loop system is proved by Lyapunov stability theory. To validate the proposed ATSMDO based ASTSMC, a case study of a nonlinear liquid level regulation problem is considered. Both simulation and real-time results are presented to show the effectiveness of the proposed controller than the traditional adaptive sliding mode controller (ASMC) and reported controllers in literature. From the analysis, it is observed that the proposed controller alleviates the chattering problem effectively.

This paper describes the design of a robust composite high-order super-twisting sliding mode controller (HOSTSMC) for robot manipulators. Robot manipulators are extensively used in industrial manufacturing for many complex and specialized applications. These applications require robots with nonlinear mechanical architectures, resulting in multiple control challenges in various applications. To address this issue, this paper focuses on designing a robust composite high-order super-twisting sliding mode controller by combining a higher-order super-twisting sliding mode controller as the main controller with a super-twisting higher-order sliding mode observer as unknown state measurement and uncertainty estimator in the presence of uncertainty. The proposed method adaptively improves the traditional sliding mode controller (TSMC) and the estimated state sliding mode controller (ESMC) to attenuate the chattering. The effectiveness of a HOSTSMC is tested over six degrees of freedom (DOF) using a Programmable Universal Manipulation Arm (PUMA) robot manipulator. The proposed method outperforms the TSMC and ESMC, yielding 4.9% and 2% average performance improvements in the output position root-mean-square (RMS) error and average error, respectively.