scholarly journals Fixed-Time Observer Based Prescribed-Time Containment Control of Unmanned Underwater Vehicles with Faults and Uncertainties

Sensors ◽  
2019 ◽  
Vol 19 (20) ◽  
pp. 4515 ◽  
Author(s):  
Tingting Yang ◽  
Shuanghe Yu
Keyword(s):  
Control Strategy ◽  
Fixed Time ◽  
Underwater Vehicles ◽  
Convergence Time ◽  
Control Input ◽  
Containment Control ◽  
Unmanned Underwater Vehicles ◽  
Time Control ◽  
Intermediate Variables ◽  
Uniformly Bounded

The problem of prescribed-time containment control of unmanned underwater vehicles (UUVs) with faults and uncertainties is considered. Different from both regular finite-time control and fixed-time control, the proposed prescribed-time control strategy is built upon a novel coordinate transformation function and the block decomposition technique, resulting in the followers being able to move into the convex hull spanned by the leaders in prespecifiable convergence time. Moreover, intermediate variables and the control input terms are also shown to remain uniformly bounded at the prescribed-time. To reduce the magnitude of the bounds, a novel fixed-time observer for the fault is proposed. Two numerical examples are provided to verify the effectiveness of the proposed prescribed-time control strategy.

Event-triggered integral sliding mode fixed time control for trajectory tracking of autonomous underwater vehicle

2021 ◽  
pp. 014233122199438
Author(s):  
Bo Su ◽  
Hongbin Wang ◽  
Ning Li
Keyword(s):  
Trajectory Tracking ◽  
Control Strategy ◽  
Autonomous Underwater Vehicle ◽  
Sliding Mode ◽  
Fixed Time ◽  
Underwater Vehicle ◽  
Reference Trajectory ◽  
Integral Sliding Mode ◽  
Time Control ◽  
Event Triggered

In this paper, an event-triggered integral sliding mode fixed-time control method for trajectory tracking problem of autonomous underwater vehicle (AUV) with disturbance is investigated. Initially, the global fixed time stability is ensured with conventional periodic sampling method for reference trajectory tracking. By introducing fixed time integral sliding mode manifold, fixed time control strategy is expressed for the AUV, which can effectively eliminate the singularity. Correspondingly, in order to reduce the damage caused by chattering phenomenon, an adaptive fixed-time method is proposed based on the designed continuous integral terminal sliding mode (ITSM) to ensure that the trajectory tracking for AUV is achieved in fixed-time with external disturbance. In order to reduce resource consumption in the process of transmission network, the event-triggered sliding mode control strategy is designed which condition is triggered by an event. Also, Zeno behavior is avoided by proof of theoretical. It is shown that the upper bounds of settling time are only dependent on the parameters of controller. Theoretical analysis and simulation experiment results show that the presented methods can realize the control object.

scholarly journals Model-Based Optimisation and Control Strategy for the Primary Drying Phase of a Lyophilisation Process

Pharmaceutics ◽  
2020 ◽  
Vol 12 (2) ◽  
pp. 181 ◽  
Author(s):  
Brecht Vanbillemont ◽  
Niels Nicolaï ◽  
Laurens Leys ◽  
Thomas De Beer
Keyword(s):  
Real Time ◽  
Control Strategy ◽  
Freeze Drying ◽  
Fixed Time ◽  
Chamber Pressure ◽  
Interface Temperature ◽  
Real Time Control ◽  
Choked Flow ◽  
Model Based ◽  
Time Control

The standard operation of a batch freeze-dryer is protocol driven. All freeze-drying phases (i.e., freezing, primary and secondary drying) are programmed sequentially at fixed time points and within each phase critical process parameters (CPPs) are typically kept constant or linearly interpolated between two setpoints. This way of operating batch freeze-dryers is shown to be time consuming and inefficient. A model-based optimisation and real-time control strategy that includes model output uncertainty could help in accelerating the primary drying phase while controlling the risk of failure of the critical quality attributes (CQAs). In each iteration of the real-time control strategy, a design space is computed to select an optimal set of CPPs. The aim of the control strategy is to avoid product structure loss, which occurs when the sublimation interface temperature ( T i ) exceeds the the collapse temperature ( T c ) common during unexpected disturbances, while preventing the choked flow conditions leading to a loss of pressure control. The proposed methodology was experimentally verified when the chamber pressure and shelf fluid system were intentionally subjected to moderate process disturbances. Moreover, the end of the primary drying phase was predicted using both uncertainty analysis and a comparative pressure measurement technique. Both the prediction of T i and end of primary drying were in agreement with the experimental data. Hence, it was confirmed that the proposed real-time control strategy is capable of mitigating the effect of moderate disturbances during batch freeze-drying.

scholarly journals Distributed Adaptive Fixed-Time Tracking Consensus Control for Multiple Uncertain Nonlinear Strict-Feedback Systems under a Directed Graph

Complexity ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-21
Author(s):  
Pinwei Li ◽  
Jiyang Dai ◽  
Jin Ying ◽  
Zhe Zhang ◽  
Cheng He
Keyword(s):  
Directed Graph ◽  
Control Strategy ◽  
Design Procedure ◽  
Fixed Time ◽  
Convergence Time ◽  
Approximation Technique ◽  
Feedback Systems ◽  
Consensus Control ◽  
Consensus Tracking ◽  
Strict Feedback

In this brief, we study the distributed adaptive fixed-time tracking consensus control problem for multiple strict-feedback systems with uncertain nonlinearities under a directed graph topology. It is assumed that the leader’s output is time varying and has been accessed by only a small fraction of followers in a group. The distributed fixed-time tracking consensus control is proposed to design local consensus controllers in order to guarantee the consensus tracking between the followers and the leader and ensure the error convergence time is independent of the systems’ initial state. The function approximation technique using radial basis function neural networks (RBFNNs) is employed to compensate for unknown nonlinear terms induced from the controller design procedure. From the Lyapunov stability theorem and graph theory, it is shown that, by using the proposed fixed-time control strategy, all signals in the closed-loop system and the consensus tracking errors are cooperatively semiglobally uniformly bounded and the errors converge to a neighborhood of the origin within a fixed time. Finally, the effectiveness of the proposed control strategy has been proved by rigorous stability analysis and two simulation examples.

scholarly journals Event-Triggered Fixed-Time Control for Steer-by-Wire Systems With Prespecified Tracking Performance

2021 ◽  
Author(s):  
Bingxin Ma ◽  
Gang Luo ◽  
Yongfu Wang
Keyword(s):  
Tracking Error ◽  
Output Feedback Control ◽  
Lyapunov Stability Theory ◽  
Fixed Time ◽  
Area Network ◽  
Control Input ◽  
Tracking Accuracy ◽  
Time Control ◽  
Steer By Wire ◽  
Event Triggered

Abstract This paper addresses the event-triggered output feedback control problem for (steer-by-wire) SbW systems with uncertain nonlinearity and time-varying disturbance. First, a new framework of event-triggered control systems is proposed to eliminate the jumping phenomenon of event-based control input, and the trade-off between saving communication resources and attenuating jumping phenomenon can be removed. Then, the adaptive disturbance observer and fuzzy-based state observer are developed to estimate the external disturbanceand unavailable state of augmented SbW systems, respectively. Third, an event-triggered fixed-time control is developed for SbW systems to achieve prespecified tracking accuracy while saving communication resources of the controller area network (CAN). Furthermore, theoretical analysis based on Lyapunov stability theory is provided to verify the tracking error of SbW systems can converge to the prespecified neighborhood of the origin in fixed time regardless of the initial tracking error. Finally, simulations and experiments are given to evaluate the effectiveness and superiority of the proposed methods.

Fixed-Time Inverse Dynamics Control for Robot Manipulators

2019 ◽  
Vol 141 (6) ◽  
Author(s):  
Yuxin Su ◽  
Chunhong Zheng
Keyword(s):  
Inverse Dynamics ◽  
Robot Manipulators ◽  
A Priori ◽  
Lyapunov Stability Theory ◽  
Fixed Time ◽  
Convergence Time ◽  
Tracking Errors ◽  
Inverse Dynamics Control ◽  
Improved Performance ◽  
Uniformly Bounded

This paper concerns with global fixed-time trajectory tracking of robot manipulators. A simple nonlinear inverse dynamics control (IDC) is proposed by using bi-limit homogeneity technique. Lyapunov stability theory and geometric bi-limit homogeneity technique are employed to prove global fixed-time tracking stability. It is proved that there exists a convergence time that is uniformly bounded a priori and such a bound is independent of the initial states such that the tracking errors converge to zero globally. The appealing advantages of the proposed control are that it is fairly easy to construct and has the global fixed-time tracking stability featuring faster transient and higher steady-state precision. Numerical simulation comparisons are provided to demonstrate the improved performance of the proposed approach.

Smooth adaptive fixed time convergent controller design for BTT missiles with uncertainties

2019 ◽  
Vol 124 (1273) ◽  
pp. 323-345
Author(s):  
Y. Yun ◽  
S. Tang ◽  
J. Guo ◽  
Y. Yun
Keyword(s):  
Control Algorithm ◽  
Performance Metrics ◽  
Controller Design ◽  
Sliding Mode ◽  
Fixed Time ◽  
Convergence Time ◽  
Control Input ◽  
Time Stability ◽  
Terminal Sliding Mode ◽  
Satisfactory Performance

ABSTRACTA smooth adaptive sliding-mode-based controller is developed for BTT missiles considering nonlinear couplings and aerodynamic uncertainties, wherein fixed-time stability theory is synthesised into sliding-mode control algorithm, such that control variables follow the desired command within fixed-bounded convergence time. Unlike other terminal sliding-mode-related works, the bound of settling time is independent of initial states, indicating that performance metrics, for instance the convergence rate, can be evaluated in advance. The control input is designed to be intrinsically smooth, based on adaptive estimations, and therefore the problem of singularity and chattering is effectively eliminated. Simulation results demonstrate the satisfactory performance and validate the effectiveness of the designed approach.

scholarly journals Adaptive Fixed-Time Control of Strict-Feedback High-Order Nonlinear Systems

Entropy ◽  
2021 ◽  
Vol 23 (8) ◽  
pp. 963
Author(s):  
Yang Li ◽  
Jianhua Zhang ◽  
Xiaoyun Ye ◽  
Cheng Siong Chin
Keyword(s):  
Nonlinear Systems ◽  
Fixed Time ◽  
High Order ◽  
Convergence Time ◽  
Feedback Form ◽  
Time Control ◽  
Control Scheme ◽  
Lyapunov Stability Criterion ◽  
The Stability ◽  
Strict Feedback

This paper examines the adaptive control of high-order nonlinear systems with strict-feedback form. An adaptive fixed-time control scheme is designed for nonlinear systems with unknown uncertainties. In the design process of a backstepping controller, the Lyapunov function, an effective controller, and adaptive law are constructed. Combined with the fixed-time Lyapunov stability criterion, it is proved that the proposed control scheme can ensure the stability of the error system in finite time, and the convergence time is independent of the initial condition. Finally, simulation results verify the effectiveness of the proposed control strategy.

scholarly journals A Novel Decentralized Fixed-Time Tracking Control for Modular Robot Manipulators: Theoretical and Experimental Verification

2021 ◽  
Author(s):  
Zengpeng Lu ◽  
Yuanchun Li ◽  
Yan Li
Keyword(s):  
Tracking Control ◽  
Control Method ◽  
Robot Manipulators ◽  
Fixed Time ◽  
Convergence Time ◽  
Modular Robot ◽  
Total Uncertainty ◽  
Control Approach ◽  
Time Control ◽  
Tracking Ability

Abstract This paper presents a novel decentralized fixed-time tracking control approach, which realizes the advantages of modular robot manipulators (MRMs) with fixed-time convergence, strong robustness, and high tracking performance. First, to estimate the total uncertainty of MRMs, the fixed-time observer based on the extended state is developed. Then, combined with the disturbance observer, a novel decentralized control method based on a fixed-time control strategy was devised to accomplish global fixed-time convergence of MRMs. And, stability analysis based on Lyapunov is utilized to obtain the fixed-time stability as well as convergence time of MRMs. Finally, numerical analysis and experiment respectively verify the excellent tracking ability of the presented decentralized fixed-time tracking control.

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