Robust formation control without velocity measurement of the leader robot

In this paper a control problem of leader–follower motion coordination of multiple nonholonomic mobile robots is addressed and subsequently in the proposed scheme, a reference trajectory generated based on the information from the leader is tracked by the follower robots. To alleviate demanded information on the leader, specifically to eliminate the measurement requirement or estimation of the leader's velocity and dynamics, a virtual vehicle is constructed whereby its trajectory converges to the reference trajectory of the follower. Trajectory tracking controller is then designed to allow the follower robot to track the virtual vehicle using neural network approximation, in combination with the backstepping and Lyapunov direct design technique and finally the performance and effectiveness of the controller is verified throughout the experiments.     

基于领航位置信息的AUV三维编队控制方法

研究了自治水下机器人（Autonomous Underwater Vehicle,AUV）三维环境中编队控制问题,应用领航一跟随式队形控制方法,仅利用领航者的位置信息及期望编队队形得到虚拟机器人的航行轨迹及速度信息,作为跟随者的航行参考量,应用反步及滑模控制方法为跟随者设计自适应控制律,使其轨迹收敛于虚拟机器人的轨迹,从而与领航者保持期望位姿关系。随后,在具体AUV动力学模型上,利用MATLAB／SIMULINK平台进行了编队控制的仿真研究,实现了预期的控制效果,验证了算法的有效性及实用性。     

考虑车辆跟驰作用和通信时延的网联车辆队列轨迹跟踪控制

针对智能网联车辆轨迹跟踪问题, 本文通过考虑车辆跟驰作用和车车通信过程中存在的通信时延, 提出了一种分布式非线性轨迹跟踪控制器. 具体来讲, 首先, 提出一种双向领导跟随通信拓扑来描述智能网联环境下车辆间的通信连接. 其次, 考虑车辆跟驰作用和通信时延, 设计一种分布式非线性轨迹跟踪控制器. 然后, 使用Lyapunov方法证明了所设计控制器的稳定性. 最后, 考虑速度干扰作用于领导者车辆, 针对无时延、同质时延和异质时延等三种场景进行数值仿真实验. 仿真结果表明: 本文所设计的控制器不仅保证了车辆位置跟踪误差收敛到原点, 而且车辆运动规律符合交通流理论, 即无负位置跟踪误差和负速度现象.     

Adaptive neural control for multiagent systems with asymmetric time‐varying state constraints and input saturation

This article investigates the leader‐follower consensus problem of a class of non‐strict‐feedback nonlinear multiagent systems with asymmetric time‐varying state constraints (ATVSC) and input saturation, and an adaptive neural control scheme is developed. By introducing the distributed sliding‐mode estimator, each follower can obtain the estimation of leader's trajectory and track it directly. Then, with the help of time‐varying asymmetric barrier Lyapunov function and radial basis function neural networks, the controller is designed based on backstepping technique. Furthermore, the mean‐value theorem and Nussbaum function are utilized to address the problems of input saturation and unknown control direction. Moreover, the number of adaptive laws is equal to that of the followers, which reduces the computational complexity. It is proved that the leader‐follower consensus tracking control is achieved without violating the ATVSC, and all closed‐loop signals are semiglobally uniformly ultimately bounded. Finally, the simulation results are provided to verify the effectiveness of the control scheme.     

T-CPS下考虑人驾车行为影响的混行车辆协同控制

由于传统人驾车(traditional human-driven vehicles,HVs)驾驶行为会受到驾驶员的心理和生理活动的不确定性影响,可能使得车辆频繁地加减速,进而导致混合交通条件下网联自动车(connected and automated vehicles,CAVs)很难快速跟踪此行为.针对这一问题,首先提出一种提前预测传统人驾车行为的组合神经网络.在此基础上,考虑通信时延和车辆运动学特性,设计一种基于交通信息物理系统(transportation-cyber physical system,T-CPS)的混行车群内车辆协同控制策略,使其能够快速跟踪上传统人驾车行为,并对混行车群内网联自动车之间的串稳定性进行分析.最后,在混合交通条件下设置由1辆传统人驾车、1辆领头网联自动车和4辆跟随网联自动车形成的混行车群,利用下一代交通仿真(next generation simulation,NGSIM)车辆轨迹数据选出高质量传统人驾车状态,并通过仿真实验验证所提协同控制策略的有效性和可行性.由仿真实验结果可知,所提协同控制策略可以保证所有的网联自动车能够快速跟踪上传统人驾车行为,为解决新型混合交通带来的新问题提供一定的理论指导和借鉴.     

Synchronization of leader‐follower networks with coupling delays via variable structure control

This paper investigates synchronization in leader‐follower networks with varying time‐delay interconnections. In such a network, the leader has its own dynamics and is followed by all the other nodes. Specifically, a variable structure control strategy is developed for the synchronization of the leader‐follower networks based on the Lyapunov stability theory. Copyright © 2009 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society     

Finite‐time formation control of multiple nonholonomic mobile robots

This paper considers finite‐time formation control problem for a group of nonholonomic mobile robots. The desired formation trajectory is represented by a virtual dynamic leader whose states are available to only a subset of the followers and the followers have only local interaction. First of all, a continuous distributed finite‐time observer is proposed for each follower to estimate the leader's states in a finite time. Then, a continuous distributed cooperative finite‐time tracking control law is designed for each mobile robot. Rigorous proof shows that the group of mobile robots converge to the desired geometric formation pattern in finite time. At the same time, all the robots can track the desired formation trajectory in finite time. Simulation example illustrates the effectiveness of our method. Copyright © 2012 John Wiley & Sons, Ltd.     

Fixed-time Sliding Mode Formation Control of AUVs Based on a Disturbance Observer

In this paper,we investigate formation tracking control of autonomous underwater vehicles(AUVs)with model parameter uncertainties and external disturbances.The external disturbances due to the wind,waves,and ocean currents are combined with the model parameter uncertainties as a compound disturbance.Then a disturbance observer(DO)is introduced to estimate the compound disturbance,which can be achieved within a finite time independent of the initial estimation error.Based on a DO,a novel fixed-time sliding control scheme is developed,by which the follower vehicle can track the leader vehicle with all the states globally stabilized within a given settling time.The effectiveness and performance of the method are demonstrated by numerical simulations.     

一种双无人机协同跟踪地面移动目标方法

针对通信延时情况下双无人机协同跟踪地面移动目标问题进行研究, 构建了基于分布式遗传算法和滚动时域优化结合的目标跟踪航迹规划算法模型。考虑到通信延时会增加目标状态信息数据融合时的误差, 导致无人机跟踪任务效果变差, 结合递推最小二乘滤波和加权最小二乘估计设计了融合方法, 来融合处理目标状态信息; 考虑到无人机对目标的观测效果与未来时刻的目标状态信息密切相关, 采用递推最小二乘滤波预测目标的状态信息, 结合分布式遗传算法和滚动时域优化设计了双无人机目标跟踪航迹规划算法。适应度函数考虑了无人机和目标之间的距离、无人机之间的通信距离、无人机之间的通信角度。仿真结果表明：该协同跟踪方法能够较好地完成跟踪任务; 与一架无人机跟踪相比误差明显减小, 并且可以减小通信延时带来的跟踪误差。     

反馈控制策略的自适应群集运动

针对有领航者的多智能体群集运动中可能出现的跟踪误差大或跟随者掉队的现象,提出了一种基于信息反馈的自适应的群集运动跟踪方法.采用邻近规则在领航者与周围邻近的跟随者之间引入双向信息流,使得领航者按事先确定的轨迹运行的同时,能根据邻近的跟随者的状态信息自适应地调节自身的运行状态.并采用李亚普诺夫方法分析了系统的稳定性,证明了...     

An MPC-based manoeuvre stability controller for full drive-by-wire vehicles

Aiming at the actuator time delay caused by the drive-by-wire technology, a novel manoeuvre stability controller based on model predictive control is proposed for full drive-by-wire vehicles. Firstly, the future vehicle dynamics are predicted by a two-degree-of-freedom vehicle model with input delay. Secondly, in order to prevent the vehicle from destabilizing due to excessive side slip angles, the determined ideal yaw rate and side slip angle are tracked simultaneously by optimizing the front wheel angle and additional yaw moment. Moreover, in order to improve the trajectory tracking ability, a side slip angle constraint determined by phase plane stability boundaries is added to the cost function. The results of Matlab and veDYNA co-simulation show that the regulated yaw rate can track the reference value well and the side slip angle decreases. Meanwhile, the trajectory tracking ability is improved obviously by compensating the time delay.     

An internal model approach to autonomous leader/follower trailing for non‐holonomic vehicles

The focus of this paper is on the design of a control architecture of decentralized type for controlling a leader/follower pair of autonomous non‐holonomic vehicles. A fundamental constraint in this trailing control requires that each agent employs local sensor information to process data on the relative position and velocity between its neighbouring vehicles, without relying on global communication with mission control. This constraint poses a challenge in the design of the control system because the reference trajectory to be tracked, which in the case considered in this paper is related to the motion of the leader, is not known a priori. It is shown in the paper that this specific control problem can be approached from the point of view of the internal model paradigm. In particular, once models of the autonomous dynamics of the leader are embedded in a decentralized dynamic controller, the design of the controller can be completed with a robust stabilizer, obtained by using ISS‐gain‐assignment techniques. It is shown that asymptotic convergence of the follower to an arbitrarily small neighbourhood of the desired steady‐state configuration is achieved, despite the presence of possibly large parameter uncertainties, while the motion of each agent remains confined into specified ‘sectors’ to avoid possible collision between neighbouring vehicles during transients. Simulation results are presented to illustrate the design methodology. Copyright © 2006 John Wiley & Sons, Ltd.     

Finite‐time formation tracking control for multiple vehicles: A motion planning approach

This paper addresses the finite‐time formation tracking problem for multiple vehicles with dynamics model on SE(3) (the specific Euclidean group of rigid body motions), under the condition that the tracking time is preassigned according to the task requirements. By using Pontryagin's maximum principle on Lie groups, a class of finite‐time optimal tracking control laws are designed for vehicles to track a desired trajectory within a given finite time. Meanwhile, the corresponding cost function is minimized. Furthermore, a tracking‐time lower bound is derived for multi‐vehicle systems with control constraints. Finally, an illustrative example is provided to demonstrate the effectiveness of the proposed control laws. Copyright © 2015 John Wiley & Sons, Ltd.     

On input‐to‐state stability‐based design for leader/follower formation control with measurement delays

This paper addresses the design of low‐level controllers for leader–follower formations of nonholonomic vehicles in the presence of bounded measurement delays. The concept of input‐to‐state stability is extended to encompass the effect of bounded delays and restrictions on the input. A method is proposed to integrate a Smith predictor in a backstepping design on the basis of nested saturations and nonlinear small‐gain assignment, which allows for time delays in the feedback loop. Robustness analysis under uncertain bounded time delays is provided, and design tradeoffs resulting from the use of bounded controls are discussed. Illustrative simulations are shown to validate the design and robustness analysis in the context of a simple leader–follower trailing control problem. Copyright © 2012 John Wiley & Sons, Ltd.     

An Active Disturbance Rejection Approach to Leader‐Follower Controlled Formation

This article describes the design of a linearizing, observer‐based, robust dynamic feedback control scheme for output reference trajectory tracking tasks in a leader‐follower non‐holonomic car formation problem. The approach is based on the cars' kinematic models. A radical simplification in the form of a global ultra‐model is proposed on the follower's exact open loop position tracking error dynamics obtained via flatness considerations. This results in a system described by an additively disturbed set of two, second order integrators with non‐linear velocity dependent control input gain matrix. The unknown additive disturbances are modeled as absolutely uniformly bounded time signals which may be locally approximated by arbitrary elements of a sufficiently high degree family of Taylor polynomials. Linear high‐gain Luenberger observers of the generalized proportional integral (GPI) type may be readily designed. These observers include the self updating internal model of the unknown disturbance input vector components in the form of generic, instantaneous, time‐polynomial models. The proposed (GPI) observers, which are the dual counterpart of GPI controllers [17], achieve a simultaneous disturbance estimation and tracking error phase variables estimation. This on‐line gathered information is used to advantage on the follower's feedback controller thus allowing for a simple, yet efficient, disturbance and control input gain cancelation effort. The results are applied to have the follower track a time‐delayed version of the actual leader's trajectory. Experimental results are presented which illustrate the robustness and viability of the proposed approach.     

Semi‐global output consensus of a group of linear systems in the presence of external disturbances and actuator saturation: An output regulation approach

This paper studies the problem of semi‐global leader‐following output consensus of a multi‐agent system. The output of each follower agent in the system, described by a same general linear system subject to external disturbances and actuator saturation, is to track the output of the leader, described by a linear system, which also generates disturbances as the exosystem does in the classical output regulation problem. Conditions on the agent dynamics are identified, under which a low‐gain feedback‐based linear state‐control algorithm is constructed for each follower agent such that the output consensus is achieved when the communication topology among the agents is a digraph containing no loop, and the leader is reachable from any follower agent. We also extend the results to the non‐identical disturbance case. In this case, conditions based on both the agent dynamics and the communication topology are identified, under which a low‐gain feedback‐based linear state‐control algorithm is constructed for each follower agent such that the leader‐following output consensus is achieved when the communication topology among the follower agents is a strongly connected and detailed balanced digraph, and the leader is a neighbor of at least one follower. In addition, under some further conditions on the agent dynamics, the control algorithm is adapted so as to achieve semi‐global leader‐following output consensus for a jointly connected undirected graph and the leader reachable from at least one follower. Copyright © 2015 John Wiley & Sons, Ltd.     

Coordinated transportation of a single object by two nonholonomic mobile robots

We propose a decentralized control algorithm for transporting a single object by two nonholonomic mobile robots. One of the robots acts as a leader, whose trajectory is planned by itself or defined previously, whereas the other robot, referred to as a follower, follows the leader by keeping a constant distance from the leader. The follower can also avoid obstacles while following the leader without any absolute information about their position. Furthermore, the two mobile robots can realize an omnidirectional motion of the object when the leader broadcasts some simple information to the follower. Some simulation results show a good performance by the proposed decentralized control algorithm. This work was presented, in part, at the Seventh International Symposium on Artificial Life and Robotics, Oita, Japan, January 16–18, 2002.     

Tracking Control of Leader-follower Multi-agent Systems Subject to Actuator Saturation

This paper addresses the tracking problem of leaderfollower multi-agent systems subject to actuator saturation. A leader node or command generator is considered, which generates the desired tracking trajectory. To track such a leader, a new family of scheduled low-and-high-gain feedback controllers is designed for each follower, provided that the linear dynamic mode is asymptotically null controllable with bounded controls, and such control laws rely on the asymptotic property of a class of parametric algebraic Ricatti equations. We show that if the associated undirected graph of the system is connected, with the proposed control law, all the followers can track the leader eventually. A simulation example is finally given to illustrate the performance of the proposed control scheme.      

Leader–follower formation control of nonholonomic mobile robots based on a bioinspired neurodynamic based approach

This paper investigates the leader–follower formation control problem for nonholonomic mobile robots based on a bioinspired neurodynamics based approach. The trajectory tracking control for a single nonholonomic mobile robot is extended to the formation control for multiple nonholonomic mobile robots based on the backstepping technique, in which the follower can track its real-time leader by the proposed kinematic controller. An auxiliary angular velocity control law is proposed to guarantee the global asymptotic stability of the followers and to further guarantee the local asymptotic stability of the entire formation. Also a bioinspired neurodynamics based approach is further developed to solve the impractical velocity jumps problem. The rigorous proofs are given by using Lyapunov theory. Simulations are also given to verify the effectiveness of the theoretical results.