Terminal Sliding Mode Control Scheme Research Articles

Decoupled adaptive terminal sliding mode control strategy for a 6-DOF electro-hydraulic suspension test rig with RBF coupling force compensator

Aiming at the problems of poor tracking accuracy, low convergence speed, weak robustness of a 6-DOF electro-hydraulic suspension test system under system uncertainties and external disturbance, this article proposes double closed-loop control scheme. In the outer loop controller, this article designs a new decoupled adaptive fast nonsingular terminal sliding mode (DAFNTSM) control to achieve fast convergence rate, high accurate and adaptive disturbances estimation during trajectory tracking. Additionally, a coupling force compensator based on RBF neural network is employed, which can reduce online calculation quantity and guarantee accuracy. For six inner loop controllers, each hydraulic actuator can precisely follow the required force solved by outer loop controller. The hard-in-loop experiment results reveal that the control approach we proposed in this paper realize superior trajectory tracking characteristics in comparison with the conventional nonsingular terminal sliding mode (CNTSM) method.

Design and implementation of fast terminal sliding mode control with synchronization error for cable-driven parallel robots

Since the cable structure generally leads to lower stiffness, cable-driven parallel robots (CDPRs) currently face some graver control challenges, where the inevitable system uncertainty will have more significant impacts on the control accuracy of CDPRs. To improve this situation, a novel sliding mode surface and the corresponding novel approaching law are defined by investigating the multi-cable synchronization, and then a new fast terminal sliding mode control strategy with synchronization error (FTSMC-SE) is proposed in this paper. Referring to the parallel structure of CDPRs, the synchronous motion of adjacent cables is ensured to obviously improve the control accuracy. Meanwhile, by deeply analyzing the finite-time convergence characteristic of the fast terminal sliding mode control, the defined synchronization error is skillfully integrated with the sliding mode surface and its novel approaching law to achieve further improvement. The Lyapunov theory is then used to analyze the finite-time stability with the error convergence guarantee of the control system. Simulation and experimental results indicate that the more synchronized cable motion and the faster error convergence can be achieved by the proposed FTSMC-SE, which together promotes the final higher precision trajectory tracking.

TDE-Based Adaptive Super-Twisting Multivariable Fast Terminal Slide Mode Control for Cable-Driven Manipulators With Safety Constraint of Error

An adaptive super-twisting multivariable fast terminal sliding mode control scheme based on time delay estimation (TDE) and asymmetric error constraints are proposed to guarantee high-precision trajectory tracking control of cable-driven manipulators under complicated unknown uncertainties. The control system is constrained by joint position errors, which are asymmetric and time-varying. First, the error range of the joints is designed to ensure that the deviation of the joint position from the desired profile is not too large while ensuring the safety performance of the manipulator, and the remaining set-total system dynamics are estimated and compensated using time-delay estimation. Secondly, the design analysis of the angular false expectation using safety constraint functions allows the constraints of different cross sections to be handled in a unified system architecture; the problem of robotic arm motion trajectories with output constraints and uncertainties is addressed through rigorous analysis. The super-twisting adaptive control effectively ensures fast, accurate and robust convergence of the algorithm in satisfying all constraints in operation, and the stability of the closed-loop control system is analyzed using the Lyapunov method. Finally, the effectiveness and superiority of the proposed adaptive hyper-torsional non-singular terminal sliding mode control scheme are verified by simulations and experiments in 2-DOF.

Improved Super-Twisting Non-Singular Fast Terminal Sliding Mode Control of Interior Permanent Magnet Synchronous Motor Considering Time-Varying Disturbance of the System

To solve the problems that control performance of high torque traction interior permanent magnet synchronous motor (IPMSM) is degraded by parameter perturbation and unknown disturbance, this paper proposes a novel Improved Super-Twisting non-singular fast terminal sliding mode control strategy (IST-NFTSMC) for IPMSM based on Extended Nonsingular Fast Terminal Sliding Mode Disturbance Observer (ENFTSMDO). Firstly, the mathematical model of IPMSM under parameter perturbation is established; Then, an improved Super-Twisting nonsingular fast terminal sliding mode speed controller (IST-NFTSMC) based on extended nonsingular fast terminal sliding mode disturbance observer (ENFTSMDO) is designed, in which the improved Super-Twisting control law designed can effectively weaken the chattering of traditional NFTSMC, and ENFTSMDO can more accurately observe the unknown disturbance part of the system in real-time than ESMDO; Finally, compared with PI control and traditional NFTSMC control by simulations and experiments, the method proposed has merits of accelerating convergence, improving steady-state accuracy and minimizing the current and torque pulsation.

Non-Negative Adaptive Mechanism-Based Sliding Mode Control for Parallel Manipulators with Uncertainties

In this paper, a non-negative adaptive mechanism based on an adaptive nonsingular fast terminal sliding mode control strategy is proposed to have finite time and high-speed trajectory tracking for parallel manipulators with the existence of unknown bounded complex uncertainties and external disturbances. The proposed approach is a hybrid scheme of the online non-negative adaptive mechanism, tracking differentiator, and nonsingular fast terminal sliding mode control (NFTSMC). Based on the online non-negative adaptive mechanism, the proposed control can remove the assumption that the uncertainties and disturbances must be bounded for the NFTSMC controllers. The proposed controller has several advantages such as simple structure, easy implementation, rapid response, chattering-free, high precision, robustness, singularity avoidance, and finite-time convergence. Since all control parameters are online updated via tracking differentiator and non-negative adaptive law, the tracking control performance at high-speed motions can be better in real-time requirement and disturbance rejection ability. Finally, simulation results validate the effectiveness of the proposed method.

Fuzzy adaptive recursive terminal sliding mode control for an agricultural omnidirectional mobile robot

Nowadays, agricultural robots play a vital role in the development of agriculture. This paper proposes a fuzzy adaptive recursive terminal sliding mode control strategy for a Mecanum-wheeled omnidirectional mobile robot to fulfill trajectory-tracking tasks in transporting agricultural products. First, a kinematic-and-dynamic model with four control inputs and three states is established for the mobile robot. Then, a fuzzy adaptive recursive terminal sliding mode controller is designed, and the control system’s stability is assured via detailed mathematical proof. Subsequently, a dead-reckoning scheme based on the Runge–Kutta formula is presented to reckon the robot’s position-and-posture information online. A conventional sliding mode controller and a nonsingular terminal sliding mode controller are designed for comparison. Lastly, experiments in two scenarios of circular and figure-eight trajectories with different loads are carried out. The experimental results reveal the superiority of the proposed control strategy compared with the benchmark controllers.

Adaptive integral‐type terminal sliding mode control: Application to trajectory tracking for mobile robot

SummaryThis paper presents an Adaptive Terminal Integral Sliding Mode Control (ATISMC) scheme for trajectory tracking problems applied to a differential Wheeled Mobile Robot (WMR). First, a terminal integral sliding variable is designed. Based on the finite‐time concept, an adaptive control law has been developed in which a switching gain is adjusted adaptively by using a novel strategy. This control method aims to deal with unknown bounded disturbances and uncertainties. Moreover, it allows fast convergence of the system states to an equilibrium point. The main features of the proposed ATISMC are its robustness, fast convergence rate, and chattering avoidance. To realize trajectory tracking for WMR, the ATISMC is incorporated into a double closed loop scheme. Stability analysis is performed using the Lyapunov stability theory. Numerical simulations and real‐time experiments demonstrate the feasibility of the proposed controller scheme. A comparison study with the classical ISMC was performed to show the superiority of the developed method.

Adaptive Terminal Sliding Mode Control of Picking Manipulator Based on Uncertainty Estimation

In this paper, a robust nonsingular fast terminal sliding mode control scheme for the picking manipulator under the condition of load change and nonlinear friction disturbance is presented. Firstly, the dynamic equation of the picking manipulator under the condition of load change and nonlinear friction disturbance is established. Then, in order to avoid the singularity problem existing in the terminal sliding mode and improve the convergence time, a new nonsingular fast terminal sliding mode control strategy is adopted to design the control law of the picking manipulator, which can guarantee the finite time convergence. The adaptive law is used to estimate the uncertainties of the system, and the finite time convergence of the system state is proved by the Lyapunov criterion. In addition, the genetic algorithm is used to identify the friction parameters to realize the nonlinear friction compensation control of the system. Finally, the simulation results of the picking manipulator under different load conditions show that the controller designed in this paper realizes the fast and accurate positioning of the picking manipulator under load change and nonlinear friction, and the control strategy is reasonable and effective.

Adaptive Non-Singular Fast Terminal Sliding Mode Trajectory Tracking Control for Robot Manipulators

In order to improve the efficiency of human–robot interaction (HRI), it is necessary to carry out research on precise control of the manipulator. In this paper, an adaptive non-singular fast terminal sliding mode control scheme is proposed for robot manipulators to solve the trajectory tracking problem with model uncertainty and external disturbances. At first, a novel non-singular fast terminal sliding mode surface is proposed, and by introducing an auxiliary function, the singularity problem caused by the inverse of the error-related matrix could be avoided in the controller design process. Then, the controller is developed by using Lyapunov synthesis. A robust adaptive strategy is used to deal with lumped uncertainty, with an adaptive update law designed to compensate for the upper bound of lumped uncertainty whose upper bound is prior unknown. Finally, a two-link robot manipulators as a simulation example is given to illustrate the effectiveness of the proposed scheme. Compared with other similar algorithms, the proposed adaptive non-singular fast terminal sliding mode control scheme has higher efficiency and smaller computational complexity for the reason that no piecewise continuous function is needed to be constructed during the controller design.

Non-singular terminal extended sliding mode control of permanent magnet synchronous motor based on variable exponential reaching law

A non-singular terminal extended sliding mode control method based on variable exponential reaching law is presented because the permanent magnet synchronous motor speed control system is subject to parameter disturbance, external disturbance, and end effect. In order to accomplish global rapid convergence and get rid of singularity, a non-singular terminal extended sliding mode surface is first created. After the system reaches the sliding mode surface, a new extended state variable is constructed in accordance with the first-order angular velocity model, and a new better exponential reaching law is utilized to eliminate chattering. Finally, a disturbance observer is designed to detect the disturbance during motor operation in real-time and add it to the speed control loop as a compensation. The simulation findings demonstrate that, in comparison to the conventional sliding mode control strategy, the suggested variable-parameter non-singular terminal sliding mode control strategy lowers the effect of disturbance on the motor’s real operation and has the benefits of rapid convergence speed, good resilience, minimal speed overshoot, and high control precision.

Neural network based recursive terminal sliding mode control and its application to active power filters

SummaryIn recent times, research interests for the control design of uncertain nonlinear systems are observed in neuroscience‐inspired intelligent controllers. In this article, a recursive terminal sliding mode control scheme based on continuous radial basis emotional neural network (CRBENN) is proposed. First, a recursive terminal sliding mode controller is constructed. The sliding mode surface is composed of a fast non‐singular terminal sliding mode surface and a recursive integral terminal sliding mode surface, which not only ensures that the tracking error converges to zero in a finite time, but also can eliminate the reaching phase and achieve global robustness by setting the surface parameters with appropriate initial values. In addition, in order to effectively deal with the uncertainty, an adaptive CRBENN controller with online parameter adjustment capability is established, and its stability and convergence are analyzed using the Lyapunov method. The designed CRBENN, inspired by neuroscience, is simple in structure and fast in response. Simulation and experimental results on active power filter show that the control scheme has good current tracking ability and anti‐interference ability.

Finite time fault tolerant tracking control for multiple unmanned aerial vehicles with actuator faults

SummaryAn adaptive fast nonsingular integral terminal sliding mode control scheme is proposed for the distributed formation control problem of multiple unmanned aerial vehicles (UAVs) affected by actuator faults and external disturbances. In order to achieve a good cooperative tracking performance of UAVs during mission execution, the adverse effect of the lumped disturbances composed of actuator failures, wind and vortex disturbances is estimated by the cerebellar model articulation neural network, meanwhile the tangent function is introduced to eliminate the chattering of the sliding mode. Then the analysis of superior convergence performance of the fast nonsingular integral terminal sliding manifold is implemented, and the finite time stability of the closed‐loop formation flight control system is proved. Finally, the simulation experiments verify that the proposed approach is superior to the nonsingular integral terminal sliding mode control for the formation control system of faulty multiple UAVs.

Two-stage isolated AC/DC converter and its compound control strategy.

With the continued development of the new energy vehicle industry, two-stage isolated AC/DC converters are widely used because of their simple topology and easy control characteristics. In this study, we investigate the front-stage Buck power factor correction (PFC) converter and rear-stage full-bridge converter. The main circuit design and component selection were completed through a detailed analysis of the circuit characteristics. In terms of the control strategy, the front-stage adopting PI control and parameter adaptive terminal sliding mode control strategy were proposed for the rear-stage full-bridge converter. This new compound control strategy ensures an optimal regulation of the system under different operating conditions. Simulation analysis verified the correctness of the system topology and control strategy. Based on an analysis of the main parameters of the system, a low-power experimental prototype was trial-produced. The experimental results show that under the same load switching conditions, the parameter-adaptive terminal sliding mode control enhanced faster dynamic regulation and stronger robustness than the conventional PI control. The study is also a good reference in terms of engineering work.

Finite-Time Synchronization of Uncertain Fractional-Order Delayed Memristive Neural Networks via Adaptive Sliding Mode Control and Its Application

Finite-time synchronization (FTS) of uncertain fractional-order memristive neural networks (FMNNs) with leakage and discrete delays is studied in this paper, in which the impacts of uncertain parameters as well as external disturbances are considered. First, the fractional-order adaptive terminal sliding mode control scheme (FATSMC) is designed, which can effectively estimate the upper bounds of unknown external disturbances. Second, the FTS of the master–slave FMNNs is realized and the corresponding synchronization criteria and the explicit expression of the settling time (ST) are obtained. Finally, a numerical example and a secure communication application are provided to demonstrate the validity of the obtained results.

Wavelet neural network sliding mode control of two rigid joint robot manipulator

To solve the problems of low accuracy and poor stability due to uncertainties, external disturbances and unknown load, which exist in the position control of rigid joint robot manipulator, this article is to propose Non-Singular Fast Terminal Sliding Mode Control strategy with Wavelet neural networks observer (NSFTSMCW). The wavelet observer is designed using the online approximation capability of the neural network, which is used to online estimate the modeling error, external disturbances and uncertainties generated by the dynamic surface control of the joint robot online. Combining the above strategies, the robot manipulators position controller is designed. The stability of this control strategy is demonstrated by stability analysis using the Lyapunov criterion. Simulations on the 2-Link Rigid Joint (2LRJ) robot show that the control strategy can overcome the chattering phenomena ensures the accuracy and stability of the joint robot position control.

Steady-State Error Band Improvement Using Dead-Beat Terminal Sliding Mode Control

This brief presents the development of a dead-beat terminal sliding mode control strategy, based on the smooth terminal sliding function and the dead-beat reaching law (RL). By means of the dead-beat RL, the sliding mode occurrence is always guaranteed and the desired tracking error dynamics can be achieved by the chosen smooth terminal sliding function. A finite-order backward-difference uncertainty compensator is incorporated into the controller design to improve the uncertainty rejection capability. The steady-state error band is analyzed in detail, for characterizing the attractivity and steady-state tracking performance with respect to control parameters. Effectiveness of the proposed control strategy is illustrated by simulation results on a DC-DC buck converter.

Fractional-order nonsingular terminal sliding mode controller for a quadrotor with disturbances

This paper proposes a finite-time controller for an unmanned aerial vehicle in the presence of Figures/uncertainties using fractional-order terminal sliding mode. First, contrary to existing fractional-order backstepping sliding mode controllers, this paper introduces a new control approach for quadrotor position control, which is based on fractional-order fast terminal backstepping sliding mode control. Using an appropriate sliding surface, the position tracking error converges to zero in finite time while providing good robustness properties in different complex path scenarios under unknown disturbances. Then, a novel fractional-order fast terminal sliding mode control scheme is developed for quadrotor attitude control, which provides good properties in terms of robustness against unknown disturbances, and in terms of convergence time, etc. Finally, simulation results are presented to discuss the advantages of the hybrid control approach proposed in this work for quadrotors under unknown disturbances compared to other existing controllers.

A sliding mode control algorithm based on improved super-twisting and its application to quadrotors

This paper presents a fast terminal sliding mode control strategy based on improved super-twisting algorithm (IST-FTSMC) for quadrotors with external disturbances. First, the dynamic model of quadrotors is described. Then, a control strategy based on fast terminal sliding mode with improved super-twisting algorithm is proposed for attitude subsystem and position subsystem. Finally, some comparative results show superior tracking performance of the proposed method in this paper under external disturbances.

An Adaptive Terminal Sliding Mode Control Scheme via Neural Network Approach for Path-following Control of Uncertain Nonlinear Systems

An Adaptive Terminal Sliding Mode Control Scheme via Neural Network Approach for Path-following Control of Uncertain Nonlinear Systems

High-Order Fast Nonsingular Terminal Sliding Mode Control of Permanent Magnet Linear Motor Based on Double Disturbance Observer

In order to realize the high-speed and high-precision movement of the direct drive system, it is important to study the strong robust control strategy of permanent magnet linear synchronous motor (PMLSM) servo system. This article proposes a high-order fast nonsingular terminal sliding mode control strategy for PMLSM based on double disturbance observer. The double disturbance observer is used to observe the mismatched/matched disturbances to reduce the conservativeness of the system to multiple disturbances. In addition, a high-order fast nonsingular terminal sliding mode controller is designed to enhance the robustness of the system. By adding feedback current into the controller, the overall control of current, speed, and position is realized. In addition, the steady-state performance and dynamic performance of position tracking system are improved. The stability and convergence of the closed loop system are proved by the Lyapunov stability theory. Experimental results show that the proposed strategy can effectively improve position tracking accuracy of the system and robustness to uncertain disturbances.