Finite-Time Tracking Control of AUV with Model Uncertainty

In this paper, an adaptive fast terminal sliding mode control technique combined with a global sliding mode control scheme is investigated for the tracking problem of uncertain nonlinear third-order systems. The proposed robust tracking 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. Under the uncertainty and nonlinearity effects, the reaching phase is removed and the chattering phenomenon is eliminated. This scheme guarantees robustness against nonlinear functions, parameter uncertainties and external disturbances. The derivative of the state variable is replaced by a delay term in the form of an Euler approximation of the derivative function. Furthermore, the knowledge of upper bounds of the system uncertainties is not required, which is more flexible in the real implementations. Simulation results are presented to show the effectiveness of the suggested method.

In this paper, an active fault tolerant controller is proposed for the unmanned aerial vehicle (UAV) attitude control system using nonsingular fast terminal sliding mode control technique. Firstly, the nonlinear attitude dynamics model of UAV with actuator faults and external disturbance is described. Next, a neural network-based fault estimation observer is designed to obtain the estimated value of unknown actuator faults and external disturbance, and the stability of the designed observer is also proved. Then, an active fault tolerant controller is designed based on the fault estimation observer and nonsingular fast terminal sliding mode control technique. The Lyapunov stability analysis shows that the proposed fault tolerant controller can guarantee the finite time asymptotic stability for nonlinear closed-loop attitude control systems of UAV with actuator faults and external disturbances. Finally, numerical simulation results are presented to illustrate the benefit of the proposed scheme.

In this paper, a nonsingular, essentially continuous and finite-time convergent impact angle constrained guidance law for intercepting stationary, constant speed, and maneuvering targets is developed using advanced terminal sliding mode control schemes and extended state observer. In order to achieve the specified intercept angle in finite time without singularity, the nonsingular fast terminal sliding mode control algorithm is employed to construct sliding surface. The fast terminal sliding mode control technique is used to establish the reaching law, so the system trajectory converges quickly from initial state to the switching surface in the whole reaching phase and the proposed guidance law is essentially continuous. Noticing the interception of a maneuvering target, the unknown target acceleration is estimated and compensated using extended state observer. Due to its inherent attribute of singularity-free, continuity, and faster convergence rate, no approximation is necessary in the implementation of the proposed guidance law, so better tracking accuracy of the desired intercept angle in a shorter time with a smoother guidance command can be guaranteed compared with conventional terminal sliding mode guidance law. A large number of numerical simulations are implemented to justify the effectiveness of the proposed guidance law.

This paper proposes a nonsingular fast terminal sliding mode approach integrated with finite-time disturbance observer (DO-NFTSMC) for a magnetic levitation system exposed to uncertainties and external disturbances. A finite-time disturbance observer is first proposed to handle disturbances and modeling uncertainties. Then a nonsingular fast terminal sliding mode control (NFTSMC) approach is formulated relying on a newly constructed sliding surface to ensure fast transient convergence to the equilibrium. Overall stability and finite-time estimation were verified using the Lyapunov stability theory. Computer experiments using a highly nonlinear magnetic levitation (maglev) system showed promising results in terms of finite-time attainability, disturbance rejection and effective continuous control with reduced chattering. Additionally, performance comparison to that of a dynamic sliding mode control (DSMC) design was carried over and showed that the proposed controller outperformed the DSMC in all aspects.

This paper investigates trajectory tracking control of a dielectric electro-active polymers (DEAP) actuator with hysteresis nonlinearity by using second-order adaptive discrete-time fast terminal sliding mode control (2-ADFTSMC) scheme. Taking into account that the hysteresis behaviour is asymmetric rate-dependent, a Hammerstein model is established to represent the DEAP actuator. Then, based on a novel 2-ADFTSM function and a terminal-sliding-mode-type switching control law, a 2-ADFTSMC scheme is proposed to improve the trajectory tracking performance. Furthermore, the stability of the closed-loop system is proved. Compared with discrete-time sliding mode control (DSMC) and discrete-time fast terminal sliding mode control (DFTSMC) schemes, the proposed control scheme can provide higher tracking accuracy, faster convergence speed, and stronger robustness in presence of model uncertainties and external disturbances. The effectiveness and practicality of the proposed control scheme are validated through the experiments on the DEAP actuator.

A Global Fast Terminal Sliding Mode Controller (GFTSMC) is proposed for n-link robotic manipulators by employing the Fast Terminal Sliding Mode (FTSM) control concept in both the reaching phase and the sliding phase. Under the control, the system states will reach FTSM in desired finite time and then converge to the origin along the FTSM in specified finite time, resulting in a reduced steady tracking error in comparison with the conventional sliding mode controller. The proposed controller is continuous and therefore chattering-free. An example is presented to demonstrate its effectiveness.

For fully actuated marine surface vessels (MSVs) with model uncertainties, unknown external disturbance, and unmeasurable velocity, this paper proposes an adaptive non-singular fast terminal sliding mode (NFTSM) finite-time trajectory tracking control scheme based on an improved nonlinear disturbance observer (INDO) and radial basis function neural networks (RBFNN). Firstly, this paper proposes a novel form of second-order nonlinear tracking differentiator (NTD) to generate more accurate virtual position and velocity signals. Then, this paper designs an INDO for more accurate estimation and compensation of unknown external disturbance problems. By combining the NTD-based virtual signals with desired signals, an NFTSM surface is constructed to accelerate system convergence and improve tracking accuracy. In addition, this paper designs RBFNN to approximate model uncertainties with added estimation velocity error. Furthermore, an improved adaptive law is used to estimate the upper bound of neural networks approximation error and INDO error to enhance the system’s adaptability to complex uncertainties and improve the robustness of the system. Lyapunov stability analysis shows that all system signals remain globally bounded in finite time. Finally, the comparative simulation verifies the accuracy and superiority of the proposed scheme (INDO-RBFNN-ANFTSMC).

In this paper, a finite-time trajectory tracking control approach is proposed for an unmanned surface vehicle (USV) with unknown dead-zones and unknown disturbances. External disturbances can be observed exactly by a robust homogeneous differentiator with finite-time convergence. Based on the information of the bounds of the dead-zone slopes as well as treating the time-varying inputs coefficients as system uncertainties, a finite-time controller for trajectory tracking of an USV is eventually addressed via the non-singular terminal sliding mode control technique. Moreover, the boundary layer method with a novel saturation function is employed to reduce the chattering and to ensure that tracking errors can be rendered to zero in a finite time. Simulation results demonstrate the effectiveness of the proposed approach.

RBFNN-based nonsingular fast terminal sliding mode control for robotic manipulators including actuator dynamics

This article proposes an adaptive nonsingular fast terminal sliding mode control scheme with piecewise fast multi-power reaching law for tracking control of underactuated autonomous underwater vehicles under model uncertainties, ocean disturbances, and measurement noise. This control approach enhances the robustness and guarantees faster convergence of state error to zero in finite time while reducing the chattering effect. Utilizing the benefit of adaption law prevents overestimating control parameters, and it eliminates the need for the upper bound value of disturbances. The overall stability of the system is analyzed using the Lyapunov criterion. The results of the proposed approach are compared with adaptive nonsingular terminal sliding mode control and adaptive sliding mode control. The performance of the proposed control approach is evaluated by using the performance indices root mean square error and chattering indicator. The simulation results confirm the efficiency of the proposed approach.

Adaptive finite-time sliding mode control design for finite-time fault-tolerant trajectory tracking of marine vehicles with input saturation

For a hybrid mechanism for automobile electro-coating conveying which is self-developed, a dynamic model is established based on screw theory and the principle of virtual work to simplify the process of modeling. Then, to solve the chattering problem and the slow rate of convergence problem of the existing sliding mode control methods for the hybrid mechanism, a super-twisting algorithm based second-order nonsingular fast terminal sliding mode control method is proposed. The stability of the proposed control method is proved by Lyapunov stability theorem. Finally, compared with the reaching law based sliding mode control method and the super-twisting algorithm based second-order sliding mode control method, it is indicated from the simulation and experiment results that the proposed control method not only has high steady-state accuracy, better dynamic performance and strong robustness, but also reduces the chattering and improves the rate of convergence of the system. And it lays foundation for realizing the high performance control of the hybrid mechanism for automobile electro-coating conveying.

This brief is devoted to the predesigned motion trajectory-based finite time dynamic positioning (DP) control for a marine surface vehicle (MSV) with unknown external disturbances. Firstly, a preset motion trajectory is presented through establishing the relationship function among position tracking errors and heading tracking error, facilitating the MSV to arrive in the equilibrium point along the pre-designed trajectory. Furthermore, a novel nonsingular and fast terminal sliding mode control (NTSMC) approach is investigated, which ensures faster convergence rate and better stability performance of the close-loop system than the conventional backstepping control approach. What’s more, by incorporating the adaptive technique with the NTSMC approach, an adaptive nonsingular and fast terminal sliding mode control (ANTSMC) strategy is addressed. Compared to the NTSMC approach, it strengthens robustness to disturbances and guarantees system states to converge to a closer neighborhood of the equilibrium point. Finally, simulation results illustrate the remarkable effectiveness of proposed control schemes.

The paper presents a method of synthesizing the Variable Structure Controller (VSC) based on the Fast Terminal Sliding Mode (FTSM) control for an optoelectronic observatory to eliminate the effects of the vibration and the change of vehicle’s direction. An improved fast terminal sliding surface and a fuzzy saturation function have been proposed to develop the improved fast terminal sliding mode variable structure controller (IFTSM-VSC). Based on the theory of Lyapunov stability, the article has proved that the IFTSM-VSC controller ensures the Line of Sight (LOS) stabilization of the observation devices and ensures the tracking errors converge to zero in finite time. The simulation uses data about the vibration and navigation of the vehicle recorded on some streets and roads. Simulation results in Matlab/Simulink show the effectiveness of the IFTSM-VSC controller.

For accurate trajectory tracking of robotic manipulators with actuators, a novel nonsingular fast terminal sliding mode control (NFTSMC) strategy based on radial basis function neural network (RBFNN) is put forward and investigated in this paper. Because of the existence of nonsingular fast terminal sliding mode (NFTSM) manifold, the controller possesses high precision and fast convergence. Considering that it is difficult to obtain accurate model parameters owing to modeling errors or external disturbances, RBFNN is used to approximate the nonlinear uncertainties due to its simple structure and great generalization ability. A new adaptive law is designed to adjust RBFNN. In order to compensate the estimation errors and suppress other unstable factors, a robust term is introduced. A new adaptive law is developed to flexibly adjust the robust term. Then, Lyapunov theory is applied to prove the system stability and finite-time convergence. Finally, a small-sized industrial robotic manipulator Epson LS3-401S with its first two joints is taken as the simulation plant, and several simulations between the proposed controller and the other two controllers are performed. External disturbances and other two conditions are considered to simulate the real environment, and the corresponding results verify the effectiveness and superiority of the proposed controller.