Sliding Mode Formation Control Research Articles

Formation tracking control for an air–ground system under position deviations and wind disturbances

AbstractIn this paper, a formation tracking control strategy based on a leader–follower structure is investigated under position deviations and wind disturbances for an air–ground system. A backstepping controller is designed to achieve the expected trajectory‐tracking performance for the leader which is a car‐like vehicle. A robust nonsingular integral terminal sliding mode formation controller based on leader–follower formation errors is presented to provide desired positions under the influence of position deviation for the follower which is a quadrotor. A backstepping‐based adaptive recursive sliding mode position controller is proposed for the follower to ensure tracking accuracy under wind disturbances. Comparison experiments with existing studies show superior performances and effectiveness of the proposed control method for the air–ground system.

Finite-time robust formation control of multiple aerial robotic vehicles with uncertainties and time-varying complex perturbations

Formation control of aerial robotic vehicles (ARVs) has a wide range of applications in the battlefield reconnaissance, medical rescue and load transportation, etc. System parameter variations and complex disturbances are inevitable in the formation control of ARVs, and the effects of them on the formation stability control of ARVs are unnegligible. This paper addresses the robust formation control problem of finite-time leader–follower for multiple ARVs suffering from parameter uncertainties and time-varying perturbations. To ensure the states (e.g. position and velocity) of all followers to converge to leader in finite time, a novel finite-time high-order sliding mode consensus control (HOSMCC) scheme is designed. To better cope with the parameter uncertainties and time-varying disturbances, improve formation control accuracy and achieve the robust formation control of finite-time leader–follower in multiple ARV systems, a new finite time high-order sliding mode formation control (HOSMFC) scheme on the basis of finite-time HOSMCC is proposed. The finite-time stability of multi-ARV formation control system is guaranteed, and the desired formation pattern of multi-ARV systems is achieved using Lyapunov stability theorem. Performance comparisons with proportional differential formation controller (PDFC) and sliding mode formation controller (SMFC) are studied on a four-ARV formation control system. The results validate the designed formation control scheme.

Leader-Follower UAV formation flight control based on feature modelling

To solve the problems of backstepping error and poor dynamic tracking approach rate in traditional PID neural network control in UAV formation flight control, a Leader-Follower UAV formation flight control method based on feature modelling is proposed,and the pose relationship model between virtual follower and pilot is established by trajectory tracking and pose dynamic fitting. The pose distribution of thefollower is analyzed in the ground coordinate system, and the parameter information of linear velocity and angular velocity control of UAV is obtained, and the backstepping sliding mode formation controller is formed. The variable structure PID neural network controller is used to design the flight control law of UAV formation, and the fast piecewise power approaching factor is introduced into the PID controller to eliminate the chattering of sliding mode control. The simulation results show that this method can ensure the rapidity of UAV formation flight control also show strong anti-jamming ability. Due to the fast piecewise power approach rate, the UAVs can complete the UAV formation reorganization under disturbance and buffeting in a short time, and the trajectory tracking error approaches zero, and it has good anti-buffeting ability.

Neuroadaptive Distributed Sliding Mode Formation Control of UAVs: A More Simple Approach

Neuroadaptive Distributed Sliding Mode Formation Control of UAVs: A More Simple Approach

Leader–follower sliding mode formation control of fractional-order multi-agent systems: A dynamic event-triggered mechanism

This paper examines the concept of the leader–follower formation for fractional-order multi-agent systems (FO-MASs) by utilizing dynamic event-triggered sliding mode control (SMC) method. Firstly, a dynamic event-triggered mechanism (DETM) is designed relying on the combined measurement vector, in which an auxiliary variable is introduced to dynamically adjust the threshold for each fractional-order agent system. Unlike most existing event-triggered communication mechanisms, whose threshold parameters are always fixed, the threshold parameters in our designed event-triggered conditions can be dynamically adjusted according to the fractional-order dynamic rule. Numerical results show that the proposed DETM can achieve a better system performance in reducing the sampling frequency and the expected formation performance. Secondly, the leader–follower formation control problem is transformed into checking the asymptotic stability problem of the closed-loop system. In addition, due to the memorability of fractional calculus operators, a distinctive condition is established to avoid the occurrence of Zeno behaviors reported in existing dynamic event-triggered schemes. Finally, a simulation example is presented to illustrate the effectiveness and feasibility of the dynamic event-triggered SMC method proposed in this paper.

Distributed prescribed‐time leader‐following formation control for second‐order multi‐agent systems with mismatched disturbances

AbstractThis article investigates the distributed prescribed‐time formation control problem for the second‐order multi‐agent systems (MASs) subject to matched and mismatched disturbances in time‐varying formation case. As a stepping stone, novel distributed estimators are first proposed to accurately estimate the position and velocity information of the leader within prescribed time. Subsequently, the nominal control protocol is presented for the MAS in the absence of the disturbances to deal with the time‐varying formation control problem, and the prescribed‐time stability of the system is guaranteed. For system subject to matched and mismatched disturbances, the observer‐based integral sliding mode formation control protocol is then presented such that the desired trajectories can be tracked and the desired patterns can be achieved within the prescribed settling time. By adopting the sinusoidal function to the control scheme, the singularity‐like problem is solved if there exist measurement errors in the agents. Finally, a numerical simulation example utilizing unmanned aerial vehicles modeled by Simscape and Solidworks is presented to show the efficiency of the proposed scheme.

Observer-based adaptive integral terminal sliding mode formation control for a vessel train with obstacle avoidance

This paper proposes a novel adaptive integral terminal sliding mode (AITSM) control for a vessel train with obstacle avoidance . A vessel train comprises several autonomous surface vehicles (ASVs). First, a finite-time lumped uncertainty observer is used to estimate the lumped uncertainties and compensate them for the controller, which enhances the robustness of the motion system. Second, based on graph theory and a novel obstacle avoidance mechanism, the desired trajectory of ASVs is obtained for formation control and obstacle avoidance. Finally, a novel AITSM formation controller for ASVs is designed. It improves the accuracy of the system by introducing an adaptive law to follow the control gain of the sliding mode variable in real-time. Moreover, the presence of the equivalent input causes the closed-loop error of the system to quickly slide onto the sliding mode surface, whereas the switching input compensates for the remaining uncertainty, thereby increasing the robustness of the system. In conclusion, the proposed method can enhance stability and accuracy and improve the robustness of the system. Additionally, it can cause the tracking error of the system to converge to the origin in finite time. The superiority of the proposed control method is verified via using a simulation.

Robust Finite-Time Control of a Multi-AUV Formation Based on Prescribed Performance

This paper focuses on the finite-time formation-control problem of a multi-AUV formation under unknown perturbations with prescribed performance. First, the nonlinear AUV model is transformed into a second-order integral model using feedback linearization. Suitable prescribed performance functions are selected to constrain the control errors of AUVs within a preset range and convert AUV tracking errors into unconstrained tracking errors using an error-conversion function to facilitate controller design. Finite-time sliding-mode disturbance observers are designed for unknown disturbances in the ocean so that they can accurately estimate the unknown disturbances in finite time. Based on the unconstrained tracking error and the unknown disturbance observer, the fast terminal sliding-mode formation controller is designed so that the multi-AUV formation can converge in finite time. Finally, the simulation experimental results show that the finite-time formation-control method with prescribed performance proposed in this paper can better cancel the unknown disturbance in the ocean in finite time and improve the robustness of the multi-AUV formation control.

Distributed anti-windup NN-sliding mode formation control of multi-ships with minimum cost

Due to the harsh marine environment, the communication cost of multi-ship formation is expensive, but it is often ignored in the existing research. On this basis, this paper proposes a novel distributed anti-windup neural network (NN)-sliding mode formation controller of multi-ships with minimum cost. Firstly, distributed control is applied to devise the formation controller of multi-ships because it is a promising solution for the problem of single point failure. Secondly, the Dijkstra algorithm is introduced to optimize the communication topology, and then an optimized communication topology with minimum cost is used in the distributed formation controller design. Thirdly, to alleviate the influence of input saturation, an anti-windup mechanism is devised by combining an auxiliary design system with sliding mode control and radial basis function neural network method; and then a novel distributed anti-windup neural network-sliding mode formation controller of multi-ships is obtained, which can also handle the problem of nonlinearity, model uncertainty, and time-varying disturbances of ship motion. On the strength of Lyapunov theory, the closed-loop signals are proved to be stable. Multiple comparative simulations are carried out to validate the effectiveness and advantage of the proposed distributed formation controller.

Adaptive fractional‐order nonsingular fast terminal sliding mode formation control of multiple quadrotor UAVs‐based distributed estimator

AbstractThis paper mainly solves two major problems that are unavoidable in leader–follower formation process of quadrotor UAV group: the existence of external uncertainty disturbance and communication limited between quadrotor unmanned aerial vehicle (UAV) group. To solve the problem that only one of the followers in the leader–follower formation can obtain the leader's information, an improved distributed estimator is proposed in this paper, which can accurately estimate the leader's information for each follower. In addition, in order to eliminate the influence of uncertain external disturbance on the performance of quadrotor UAV, an adaptive estimation law is designed based only on velocity and position variables. For the attitude and position subsystem of the quadrotor UAV, a sliding surface with fractional‐order term is designed. Which makes the quadrotor UAV tracking error system obtain good robustness at the stage of reaching the sliding surface and fast convergence and accurate tracking performance in the sliding stage. Based on Lyapunov stability theory, the convergence results are analyzed strictly. The results show that the algorithm can make the position distance between leader and followers converge to the desired offset. Simulation results verify the effectiveness and superiority of the control algorithm.

Fast fixed-time nonsingular terminal sliding-mode formation control for autonomous underwater vehicles based on a disturbance observer

In this paper, a novel disturbance observer-based fixed-time formation control method is proposed for autonomous underwater vehicles with actuator faults, model uncertainties and unknown disturbances. Firstly, a fast fixed-time stable system is improved, which has a faster convergence rate than existing stable system. Then, the leader-follower formation control strategy is combined with the path planning strategy based on the artificial potential field to obtain a collision-free formation configuration. Besides, a fast fixed-time disturbance observer is designed to compensate for unknown composite disturbances, which enhances the robustness of the system. Further, based on the disturbance estimation information and the improved nonsingular fast fixed-time terminal sliding-mode surface, a robust fast fixed-time formation control method is presented, which achieves the desired formation configuration. Finally, simulation and comparison results show the effectiveness of the proposed control strategy.

Cerebellar Model Articulation Neural Network-Based Distributed Fault Tolerant Tracking Control with Obstacle Avoidance for Fixed-Wing UAVs

In this paper, the distributed fault-tolerant tracking control (FTTC) and obstacle avoidance problem is investigated for multiple unmanned aerial vehicles (UAVs) considering lumped disturbances and communication link faults. Firstly, a cerebellar model articulation neural network (CMANN) is introduced to esti-mate the lumped disturbances. Meanwhile, the distributed virtual leader state observers are used to address unknown communication faults. Then, a distributed nonsingular fast terminal sliding mode formation controller is implemented to track desired trajectory, and an virtual-agent artificial potential function (VAAPF) is designed to accomplish obstacle avoidance. Furthermore, the stability of the closed loop formation control systems with obstacle avoidance is proved using graph theory and Lyapunov theory. Finally, simulation results of three fixed-wing UAVs are given to show the effectiveness and good performance of the proposed scheme.

Distributed Cooperative Control of Multiple UAVs in the Presence of Actuator Faults and Input Constraints

A distributed cooperative control algorithm of multiple unmanned aerial vehicles (UAVs) with directed topology is investigated in this brief. To overcome the actuator faults and external disturbance, incremental sliding mode formation controller is developed to realize the distributed coordination of the UAVs system, where an adaptive mechanism is utilized to deal with the chattering problem. Moreover, to reduce the adverse influence of input saturation, an auxiliary system is introduced to regulate the control signals. It is shown by Lyapunov method that the stability of the proposed algorithm can be guaranteed. A numerical example is given to illustrate that all follower UAVs can track the leader UAV.

Event-based distributed sliding mode formation control of multi-agent systems and its applications to robot manipulators

This article deals with the event-based distributed sliding mode formation control issue of leader-following multi-agent systems subject to uncertain perturbations. Firstly, a distributed linear sliding manifold that ensures the asymptotic convergence of the states of multi-agent systems is constructed. Secondly, based on the controller output signal, an event-triggered mechanism is put forward to weaken the demand of continuous monitoring. In spite of external disturbances, the distributed robust sliding mode formation protocol relied on an event-triggered condition can guarantee the closed-loop system to reach the preestablished sliding manifold in finite time and keep a desired formation pattern while eliminating the Zeno behavior. Thirdly, sufficient conditions are derived for the distributed formation control of multi-agent systems. Finally, a numerical example is given and a simulation is performed on the robotic manipulators systems to verify the effectiveness of the proposed strategy.

Event-triggered integral sliding mode formation control for multiple quadrotor UAVs with unknown disturbances

Taking the external disturbances with unknown boundaries into consideration, this paper deals with the time-varying formation control problem of multiple quadrotors system based on static/dynamic event-triggered integral sliding mode control (ISMC) and adaptive sliding mode disturbance estimator (ASMDE). At first, two different position controllers, static event-triggered and dynamic event-triggered controllers, are proposed to deal with the time-varying formation problem of the multiple quadrotors system based on ISMC. The stability conditions are obtained through the Lyapunov theory. By the reverse proving method, it is also proved that there is no Zeno behavior in both static event-triggered position controller and dynamic event-triggered position controller. Then, the external disturbances are considered where the bounds of the perturbations are unknown. The ASMDE is applied to estimate the external disturbances, which increases the robustness of the multiple quadrotors system when applying the proposed methods. Next, the chattering free terminal sliding mode attitude controller for individual quadrotor is designed. Finally, the theoretical results are validated through numerical simulations.

Robust adaptive super-twisting sliding mode formation controller for homing of multi-underactuated AUV recovery system with uncertainties

This paper is concerned with the homing process in which a multi-underactuated AUV recovery system tracks the moving mother submarine in finite time in the presence of uncertain hydrodynamic parameters and unknown environmental disturbances. In the homing stage, underactuated AUVs and the moving mother submarine are treated as followers and the leader, respectively. The multi-underactuated AUV system finite time homing problem is converted to the leader-following finite-time formation control problem. The proposed leader-following formation strategy requires only the position information of the leader. The velocity of the leader can be designed as an additional degrees of freedom to stabilize position errors of the formation. A novel robust adaptive super-twisting sliding mode formation controller (ASTASMC) is proposed, specifically the super-twisting algorithm (STA) with adaptive uncertainty estimation. Wherein, the robust adaptive law can compensate for uncertainty with unknown upper bound in real time. Therefore, the proposed controller can not only enhance the tracking accuracy but also reduce the chattering. In addition, the finite-time convergence of estimation errors and tracking errors is rigorously proved. Finally, simulation results demonstrate the effectiveness of theoretical results.

A Unified Approach for Finite-Time Global Stabilization of Affine, Rigid, and Translational Formation

This article studies the multiagent control problem for affine, rigid, and translational formation, with the aim of developing a unified distributed control strategy for global and finite-time convergence. Global stabilization of rigid formation in arbitrary dimensional spaces still remains open and challenging. This article provides a general solution to this open problem based on the sliding mode control idea. The control law design consists of two parts: the main control force regulates the trajectories of all agents to reach a sliding surface defined by an affine formation space in finite time and remain in it thereafter; the extra control force governs certain chosen leader agents towards the desired formation in the sliding surface. The article then presents in detail two approaches for designing the extra control force, one based on distance constraints and the other based on relative position constraints. For the first time, the proposed sliding mode formation control laws solve the open problem of (almost) global and finite-time stabilization of affine, rigid, and translational formations in any dimensional space. Simulation results are provided to illustrate the effectiveness of the proposed control schemes.

Decentralized adaptive formation control based on sliding mode strategy for a class of second‐order nonlinear unknown dynamic multi‐agent systems

AbstractThis article investigates a decentralized adaptive sliding mode formation control (SMFC) based on the leader–follower formation strategy for a class of second‐order nonlinear unknown dynamic multi‐agent systems. Unlike the first‐order multi‐agent formation, the second‐order formation needs to control not only the position but also the velocity, therefore it is more challenging and interesting. In order to handle the unknown dynamic problem, the adaptive neural network (NN) is employed to approximate the unknown dynamic function. Since every agent is required to directly communicate with leader agent, the adaptive NN law can be trained more sufficient. Moreover, in the control design, because a continuous proportional function is introduced to replace the discontinuous switching signal of the traditional sliding mode method, the chattering phenomenon that is a stubborn shortcoming of sliding strategy is effectively suppressed. According to Lyapunov stability analysis, it is proven that the proposed method can fulfill the control task. Finally, a numerical simulation example is executed to demonstrate the performance of the proposed controller.

Sliding mode formation control of leaderless unmanned surface vehicles with environmental disturbances

This paper, in light of the sliding mode control (SMC) approach, concerns the formation regulation for a network of unmanned surface vehicles (USVs) with environmental disturbances. The formation pattern is configured within the consensus-based leaderless framework. Undirected connected graphs are exploited to portray the network communication in a switching manner. To begin with, thanks to the definition on relative formation error, one mathematically formulates the concerned formation control problem into the leaderless consensus design for resultant formation error systems. Then an integral-type sliding surface is constructed by a collection of neighboring USVs’ position and velocity information. Based on a characterized orthogonal transformation, the regulation of the formation performance upon the sliding surface is cast into the asymptotic stability analysis of the reduce-order sliding mode system. By partitioning the state space into agreement and disagreement subspaces, a formation reference function (FRF) with determined initial condition is derived as a disturbance-free autonomous system, whose dynamical behavior explicitly symbolizes the global movement of the leaderless USV formation system. Finally, to ensure the finite-time reachability of the sliding surface, a distributed sliding mode controller is designed by utilizing the tool from finite-time stabilization technique. As a byproduct, the theoretical analysis is extended to the case of fixed topology. The derived results are validated by some numerical examples.

Predictor-based practical fixed-time adaptive sliding mode formation control of a time-varying delayed uncertain fully-actuated surface vessel using RBFNN

This paper focuses on fixed-time formation control (FTFC) of a fully-actuated surface vessel (FASV) considering complex unknowns, including fully unknown dynamics and disturbances, input saturation and time-varying delays. First, using prediction idea to address time delay, a novel state predictor (SP) strategy combining with state transformation (ST) technique is devised for each FASV to predict the evolution of system states such that fixed-time stability can be ensured while solving the delay problem. Besides, the uncertainties in the transformed system are attentively considered. In addition, aiming to distinctly identify complex unknowns, predictor-based neural network is injected into the foregoing delay processing method. Finally, using time base generator (TBG), a new adaptive terminal sliding mode (ATSM) is incorporated into FTFC strategy which in turn contributes to decreasing control inputs and acquiring smooth convergence process. Simulation results and comparisons are thoroughly provided to testify the effectiveness and superiority of the designed FTFC scheme.