Search Results (86)

With the rapid advancement of maritime sports, the integration of auxiliary unmanned surface vehicles (USVs) has emerged as a promising solution to enhance the efficiency and safety of maritime education, particularly in tasks such as buoy deployment and escort operations. This paper presents a novel high-precision trajectory tracking control algorithm designed to ensure stable navigation of the USVs along predefined competition boundaries, thereby facilitating the reliable execution of buoy placement and escort missions. First, the paper proposes an improved adaptive fractional-order nonsingular fast terminal sliding mode control (AFONFTSMC) algorithm to achieve precise trajectory tracking of the reference path. To address the challenges posed by unknown environmental disturbances and unmodeled dynamics in marine environments, a nonlinear lumped disturbance observer (NLDO) with exponential convergence properties is proposed, ensuring robust and continuous navigation performance. Additionally, an artificial potential field (APF) method is integrated to dynamically mitigate collision risks from both static and dynamic obstacles during trajectory tracking. The efficacy and practical applicability of the proposed control framework are rigorously validated through comprehensive numerical simulations. Experimental results demonstrate that the developed algorithm achieves superior trajectory tracking accuracy under complex sea conditions, thereby offering a reliable and efficient solution for maritime sports education and related applications. Full article

Rehabilitation devices such as actuated lower-limb exoskeletons can provide essential mobility assistance for pediatric patients with gait impairments. Enhancing their control systems under conditions of user variability and dynamic disturbances remains a significant challenge, particularly in active-assist modes. This study presents a human-in-the-loop control architecture for a pediatric lower-limb exoskeleton, combining outer-loop admittance control with robust inner-loop trajectory tracking via a non-singular terminal sliding-mode (NSTSM) controller. Designed for active-assist gait rehabilitation in children aged 8–12 years, the exoskeleton dynamically responds to user interaction forces while ensuring finite-time convergence under system uncertainties. To enhance adaptability, we augment the inner-loop control with a twin delayed deep deterministic policy gradient (TD3) reinforcement learning framework. The actor–critic RL agent tunes NSTSM gains in real-time, enabling personalized model-free adaptation to subject-specific gait dynamics and external disturbances. The numerical simulations show improved trajectory tracking, with RMSE reductions of 27.82% (hip) and 5.43% (knee), and IAE improvements of 40.85% and 10.20%, respectively, over the baseline NSTSM controller. The proposed approach also reduced the peak interaction torques across all the joints, suggesting more compliant and comfortable assistance for users. While minor degradation is observed at the ankle joint, the TD3-NSTSM controller demonstrates improved responsiveness and stability, particularly in high-load joints. This research contributes to advancing pediatric gait rehabilitation using RL-enhanced control, offering improved mobility support and adaptive rehabilitation outcomes. Full article

This paper focuses on the integrated modeling and disturbance rejection of the aerial work quadrotor with a robotic arm. First, to address the issues of model incompleteness and parameter uncertainty commonly encountered in traditional Newton–Euler-based modeling approaches for such a system, the Lagrangian energy conservation principle is adopted. By treating the quadrotor and robotic arm as a unified system, an integrated dynamic model is developed, which accurately captures the coupled dynamics between the aerial platform and the manipulator. The innovative approach fills the gap in existing research where model expressions are incomplete and parameters are ambiguous. Next, to reduce the adverse effects of the robotic arm’s motion on the entire system stability, a finite-time disturbance observer and a fast non-singular terminal sliding mode controller (FNTSMC) are designed. Lyapunov theory is used to prove the finite-time stability of the closed-loop system. It breaks through the limitations of the traditional Lipschitz framework and, for the first time at both the theoretical and methodological levels, achieves finite-time convergence control for the aerial work quadrotor with a robotic arm system. Finally, comparative simulations with the integral sliding mode controller (ISMC), sliding mode controller (SMC), and PID controller demonstrate that the proposed algorithm reduces the regulation time by more than 45% compared to ISMC and SMC, and decreases the overshoot by at least 68% compared to the PID controller, which improves the convergence performance and disturbance rejection capability of the closed-loop system. Full article

This paper focused on the motion control of an underwater vehicle installed on a linear guide system, which is driven by two electric winches with wire ropes. The vehicle is subject to complex nonlinear time-varying disturbances and actuator input saturation effects during motion. A coupled dynamic model, incorporating an underwater vehicle, winches, and wire ropes, was established. Particular attention was paid to the nonlinear time-varying hydrodynamic disturbances acting on the underwater vehicle. The Kelvin–Voigt model was introduced to characterize the nonlinear dynamic behavior of the wire ropes, enabling the model to capture the dynamic response characteristics of traction forces. To tackle cross-coupling within the towing system, a differential tension coordination control method was proposed that simultaneously regulates system tension during motion control. For the vehicle dynamics model, a nonsingular fast-terminal sliding-mode (NFTSM) controller was designed to achieve high-precision position tracking control. An auxiliary dynamic compensator was incorporated to mitigate the impact of actuator input saturation. To handle time-varying disturbances, a fuzzy adaptive nonlinear disturbance observer (FANDO) is developed to perform feedforward compensation. Stability proof of the proposed algorithms was provided. Extensive numerical simulations demonstrate the effectiveness of the control strategies. Compared to the NFTSM without the disturbance observer the absolute mean value of the tracking error decreased by 76%, the absolute maximum value of the tracking error decreased by 67%, and the mean square error decreased by 93.5%. Full article

Regarding the high susceptibility problem of the Permanent Magnet Synchronous Motor (PMSM) to various uncertain factors, including load variations, parameter perturbations, and external interferences in the ship’s electric propulsion system, this paper presents a non-singular fast terminal composite sliding mode control (NFTCSMC) strategy based on the improved exponential reaching law. This strategy integrates the system’s state variables and the power function of the sliding mode surface into the traditional exponential reaching law, not only enhancing the sliding mode reaching rate but also effectively mitigating system chattering. Additionally, a sliding mode disturbance observer is developed to compensate for both internal and external disturbances in real time, further enhancing the system’s robustness. Finally, the proposed control strategy is experimentally validated using the rapid control prototyping (RCP) technology applied on a semi-physical experimental platform for ship electric propulsion. Experimental results indicate that, compared to traditional proportional–integral (PI), sliding mode control (SMC), and fast terminal sliding mode control (FTSMC) strategies, the NFTCSMC strategy enhances the propulsion and anti-interference capabilities of the propulsion motor, thereby improving the dynamic performance of the ship’s electric propulsion system. Full article

This study proposes a novel fuzzy disturbance observer (FDO)-augmented adaptive nonsingular terminal sliding mode control (NTSMC) framework for multi-joint robotic manipulators, addressing critical challenges in trajectory tracking precision and disturbance rejection. Unlike conventional disturbance observers requiring prior knowledge of disturbance bounds, the proposed FDO leverages fuzzy logic principles to dynamically estimate composite disturbances—including unmodeled dynamics, parameter perturbations, and external torque variations—without restrictive assumptions about disturbance derivatives. The control architecture achieves rapid finite-time convergence by integrating the FDO with a singularity-free terminal sliding manifold and an adaptive exponential reaching law while significantly suppressing chattering effects. Rigorous Lyapunov stability analysis confirms the uniform ultimate boundedness of tracking errors and disturbance estimation residuals. Comparative simulations on a 2-DOF robotic arm demonstrate a 97.28% reduction in root mean square tracking errors compared to PD-based alternatives and a 73.73% improvement over a nonlinear disturbance observer-enhanced NTSMC. Experimental validation on a physical three-joint manipulator platform reveals that the proposed method reduces torque oscillations by 58% under step-type disturbances while maintaining sub-millimeter tracking accuracy. The framework eliminates reliance on exact system models, offering a generalized solution for industrial manipulators operating under complex dynamic uncertainties. Full article

To reduce weight and improve dexterity performance, dexterous robot fingers usually use tendons for transmission, which may lead to complex nonlinear control problems. In order to improve tracking performance in joint space, this paper proposes an anti-interference controller, which synthesizes the nonsingular fast terminal sliding mode technique. A flexible joint dynamic model is established considering the flexibility of the cable-driven mechanism. A nonlinear disturbance observer is adopted to estimate and compensate the system uncertainties and various disturbances, and global fast terminal sliding mode is used to ensure good control performance in both the reaching phase and the sliding mode phase. Furthermore, symmetry is used to simplify dynamic modeling and control design, and the stability of the controller is proven with Lyapunov theory. Finally, the effectiveness of the controller is verified through simulation experiments. The simulation results demonstrate that the proposed controller achieves a steady state in 0.3 s, higher tracking accuracy than the other controllers through quantitative analysis of MAE and MSE metrics, and stronger anti-interference capability, which can satisfy the requirements of finger dexterity operation. Full article

Piezo-driven fast steering mirrors (PFSMs) are widely employed in high-precision beam steering and accurate tracking applications. However, the inherent hysteresis nonlinearity of piezoelectric actuators significantly degrades tracking accuracy. To address the challenges posed by dynamic hysteresis nonlinearity, this study proposes an improved non-singular fast terminal sliding mode control strategy. The proposed method integrates a non-singular fast terminal sliding surface and introduces an adaptive function in the reaching law to enhance response speed and improve control robustness. Additionally, the strategy incorporates an extended state observer (ESO) and an inverse model-based feedforward compensation mechanism. Specifically, the feedforward compensation based on the inverse model aims to offset hysteresis effects, while the ESO provides a real-time estimation of the total system disturbance to mitigate the impact of external disturbances and unmodeled hysteresis. Experimental results demonstrate that the proposed method effectively compensates for the hysteresis nonlinearity of PFSMs, improves disturbance rejection performance, and enhances position control accuracy. Full article

The hybrid unmanned aerial vehicle combines the vertical take-off and landing and hover abilities of rotary-wing UAVs with the high-speed cruise and long-endurance capabilities of fixed-wing UAVs, expanding the flight envelope and application areas. The designed controller must handle the highly nonlinear dynamics and variable actuators resulting from this combination. Furthermore, the performance of the controller is also influenced by uncertainties in model parameters and external disturbances. To address these issues, a unified robust disturbance rejection control based on fixed-time stability theory is proposed for attitude control. A fixed-time disturbance observer is utilized to estimate composite disturbances without some strict assumptions. Based on this observer, a nonsingular chattering-free fixed-time integral sliding mode control law is introduced to ensure that tracking errors converge to the origin within a fixed time. In addition, an optimized control allocator based on the weighted least squares method is designed to handle the overactuation of a dual-system hybrid UAV. Finally, numerical simulations and hardware-in-the-loop experiments under different flight modes and disturbance conditions are carried out, and compared with nonlinear dynamic inverse and the nonsingular terminal sliding mode control based on a finite-time observer, the developed controller enhances attitude angle tracking accuracy and disturbance rejection performance. Full article

This study presents an advanced second-order sliding-mode guidance law with a terminal impact angle constraint, which ingeniously combines reinforcement learning algorithms with the nonsingular terminal sliding-mode control (NTSM) theory. This hybrid approach effectively mitigates the inherent chattering issue commonly associated with sliding-mode control while maintaining high levels of control system precision. We introduce a parameter to the super-twisting algorithm and subsequently improve an intelligent parameter-adaptive algorithm grounded in the Twin-Delayed Deep Deterministic Policy Gradient (TD3) framework. During the guidance phase, a pre-trained reinforcement learning model is employed to directly map the missile’s state variables to the optimal adaptive parameters, thereby significantly enhancing the guidance performance. Additionally, a generalized super-twisting extended state observer (GSTESO) is introduced for estimating and compensating the lumped uncertainty within the missile guidance system. This method obviates the necessity for prior information about the target’s maneuvers, enabling the proposed guidance law to intercept maneuvering targets with unknown acceleration. The finite-time stability of the closed-loop guidance system is confirmed using the Lyapunov stability criterion. Simulations demonstrate that our proposed guidance law not only meets a wide range of impact angle constraints but also attains higher interception accuracy and faster convergence rate and better overall performance compared to traditional NTSM and the super-twisting NTSM (ST-NTSM) guidance laws, The interception accuracy is less than 0.1 m, and the impact angle error is less than 0.01°. Full article

This paper proposes a dual-loop control strategy to address the trajectory tracking problem of differential wheeled mobile robots (WMRs). First, the kinematic model of the WMR is established, and the dynamic model including the actuators is derived. To tackle the issue of y-axis direction divergence in existing methods, a predefined-time velocity control law based on intermediate variables is proposed. By introducing the y-axis error term into the angular velocity control, the ability to rapidly track the target trajectory is enhanced, providing a reliable velocity tracking target for the dynamic controller. Furthermore, a predefined-time nonsingular fast terminal sliding mode controller is designed, which combines a nonsingular fast terminal sliding surface with predefined-time stability theory to overcome the singularity problem in existing approaches, achieving fast and accurate tracking of velocity errors. Additionally, to improve the system’s disturbance rejection capability, a nonlinear extended state observer (NESO) is proposed to estimate external disturbances and provide feedforward compensation to the dynamic controller. Experimental results demonstrate that the proposed strategy outperforms existing methods in terms of trajectory tracking accuracy and robustness, providing an effective solution for the high-performance control of WMRs. Full article

In manufacturing, the position tracking accuracy and stability of Permanent Magnet Synchronous Motors are often challenged by uncertainties, especially in complex environments. Existing control methods struggle to balance fast response with high-precision tracking. To address this, we propose a Prescribed Performance Global Non-Singular Fast Terminal Sliding Mode Control (PPGNFTSMC) method using a linear extended state observer (LESO). A smooth and bounded prescribed performance function is designed to ensure finite-time convergence while satisfying performance requirements such as overshoot and settling time. Based on this function, the system error is reconstructed to align the system response with predefined specifications. The reconstructed error is then used to design a global non-singular fast terminal sliding mode surface. A LESO is employed for real-time disturbance estimation, and the disturbance estimates, along with the sliding mode surface, are used to derive the control law for the position–speed integrated controller. Experimental results show that the proposed method outperforms the comparison methods in transient response, tracking accuracy, and robustness across various signal types. Full article

This paper presents a cross-coupling control strategy that enhances sliding mode control by incorporating active disturbance rejection control. This approach effectively addresses the issue of inadequate synchronous control accuracy in a dual-motor servo system subjected to high load disturbances. Firstly, a mathematical model of a single motor is established, and a discrete sliding mode controller (DSMC) is designed to enhance the motor’s response speed and dynamic performance. Secondly, the approach rate is optimized to improve the control smoothness of the single-motor controller, and the system’s stability is demonstrated using the Lyapunov theorem. In addition, to enhance the precision and stability of synchronous control when the load is unevenly distributed on both sides of the motor, a discrete nonlinear tracking differentiator (DNLTD) and a discrete nonlinear extended state observer (DNLESO) based on active disturbance rejection control (ADRC) theory are proposed, which are, in turn, combined with nonsingular fast terminal sliding mode control (NFTSMC), utilizing an optimized approach rate to form the ADRC-NFTSMC control strategy, and the cross-coupled control structure is used to achieve synchronous closed-loop control. Finally, the experimental results demonstrate that, compared to the NFTSMC strategy, the proposed control strategy improves response speed by 18.9% and synchronous control accuracy by 46.7%, which significantly enhances the quality of dual-motor servo control. Full article

This paper presents an intelligent proportional-derivative adaptive global nonsingular fast-terminal sliding-mode control (IPDAGNFTSMC) for tracking temperature trajectories of a hypersonic missile in thermal structural tests. Firstly, the numerical analyses on a hypersonic missile’s aerodynamic heating are based on three different external flow fields via the finite element calculation, which provides the data basis for the thermal structural test of hypersonic vehicles; secondly, due to temperature trajectory differences of a hypersonic missile and the thermal inertia and nonlinear characteristics of quartz lamps in thermal structural test, IPDAGNFTSMC is proposed, consisting of three components: (i) the mathematical model of the thermal structural test is established and further replaced via an intelligent proportional-derivative with a nonlinear extended state observer (NESO) for online unknown disturbances observation; (ii) compared with the traditional sliding-mode control method, the AGNFTSMC method eliminates the reaching phase and the initial control state is trapped on the sliding-mode surface. Therefore, it can alleviate chattering phenomenon, accelerate the convergence rate of the sliding mode, and ensure that there is no singular problem in the entire control process; (iii) the adaptive law is designed to effectively solve problems of convergence stagnation and chattering phenomenon. The Lyapunov stability theory is used to prove the stability of the proposed IPDAGNFTSMC-NESO. Finally, the advantages of the designed control method are verified by experimental simulation and comparison. Full article

We address the problems in the trajectory tracking control of a multi-joint robotic arm, including uncertainty in the internal modeling of its significant external unknown time-varying disturbances. With the control objective of tracking the desired trajectories of each joint stably and accurately, this paper proposes an adaptive non-singular terminal sliding mode control method based on a nonlinear disturbance observer (NDO). In order to speed up the convergence of the tracking error and avoid the singular value problem existing in the traditional terminal sliding mode (TSM), a non-singular terminal sliding mode (NTSM) surface is proposed in this paper. Given the system modeling uncertainty and external unknown time-varying disturbances, a nonlinear disturbance observer is used to observe the total set disturbance for feed-forward compensation. Secondly, the switching gain adaptive law is used to estimate the observation error of the total set disturbance and allow for the online adjustment of the switching gain weights. A robust gain adaptive law is also designed to reconverge quickly to the non-singular sliding mode surface when transient significant disturbances shock the system’s state variables out of the sliding phase. A simulation analysis of the spatial two-link robotic arm is carried out in Simulink. The results show that the adaptive non-singular terminal sliding mode control strategy based on the nonlinear disturbance observer proposed (PNDOANTSM) in this paper can reduce the average steady-state errors of robotic arm joints 1 and 2 by 36.58%, 38.40%, 44.68%, and 42.86%, compared with those observed in switching term adaptive law non-singular terminal sliding mode control based on a nonlinear disturbance observer (NDOANTSM) and non-singular terminal sliding mode control based on a nonlinear disturbance observer (NDONTSM). This paper provides a practical and feasible trajectory tracking control method for multi-joint robotic arms. Full article