异构多机器人编队相互通信时延精确控制

编队控制是多机器人协同控制领域研究的重点问题。考虑实际复杂环境,对异构多机器人系统的编队控制研究更具工程意义。再者,当异构多机器人编队系统存在通信时延时,同时对系统中不同阶机器人进行一致性分析的难度增大。针对以上问题,提出一种基于一致性理论的异构系统编队控制算法。考虑零时延与固定时延两种情况,首先,利用一致性思想将领航跟随者模式下的异构多机器人系统编队控制问题转换为稳定性问题。然后,根据矩阵分析与Routh-Hurwitz定理,推导出零时延系统实现编队控制的充要条件。进一步构造Lyapunov-Razumikhin函数,利用Newton-Leibniz公式与Lyapunov定理,推导出固定时延系统实现编队控制的充分条件。仿真结果表明：基于一致性算法的异构多机器人系统能够实现相互通信时延条件下的编队精确控制。     

基于改进人工势场法的多机器人编队避障

为解决多机器人系统在编队过程中的避障以及成员之间避碰问题,提出了基于改进人工势场(IAPF)的避障以及基于一致性的编队控制方法。为分析机器人的运动学,建立了数学模型,构造了运动态势感知图(MSAM),使机器人能够更好地感知周围环境信息以做出最佳决策;为解决人工势场法中的局部最小值与目标不可达(GNRON)问题,建立了旋转势场;为避免机器人之间的碰撞,设定了排斥势函数与机器人优先级模型。使用基于一致性的编队原理,设计稳定的拓扑结构,对多机器人进行编队控制。为证明所提算法的有效性,设计了一系列的仿真实验,最终证得该方法可有效解决多机器人系统在编队过程中的避障以及避碰问题。     

具有通信延迟的多无人机编队飞行控制

针对固定通信拓扑下的具有时变通信延迟的多无人机(multi-UAVs)系统,在一致性协议的基础上提出了分布式的编队控制算法.利用Lyapunov-Krasovskii函数分析了时延多无人机系统的稳定性,并以线性不等式(LMI)的形式给出了系统稳定的条件.当满足稳定性条件时,编队控制算法将使系统中无人机的速度和编队队形分别渐近地收敛至期望速度和期望队形.仿真实例验证了控制算法的有效性.     

基于预测控制的时滞多机器人编队脉冲控制

针对多机器人编队控制的时滞问题, 提出一种基于预测控制的脉冲控制方法. 首先, 利用一致性思想将多机器人编队控制转换为系统稳定性问题; 然后构建预测模型, 采用脉冲控制协议, 利用Schur 稳定性定理推导实现多机器人编队控制的充分条件; 最后, 在数值仿真中随机设置一种包含生成树的通信拓扑关系, 并比较了不同采样时间间隔下时滞系统的控制效果. 仿真结果验证了所提出方法的有效性.

     

一种多非完整移动机器人分布式编队控制方法

本文研究了多非完整移动机器人编队控制算法。在该算法中,参考轨迹被视为虚拟领导者,只有部分机器人可以接收到领导者信息,机器人之间只能进行局部信息交互。利用坐标变换将机器人系统的编队问题转化为变换后系统的一致性问题,在持续激励的条件下,设计了一种分布式控制算法,通过图论与Lyapunov 理论证明了该分布式控制算法可以使移动机器人队伍指数收敛于期望队形,并使队形的几何中心指数收敛到参考轨迹。最后,数值仿真验证了该控制算法的有效性。     

非完整性约束的平面多智能体位置时变一致性控制

多智能体的通用一致性协议被广泛用于智能体的编队控制问题中.在实际工程中,多智能体系统为了完成期望的协作控制,智能体之间的位置关系通常是时变的.目前,在多智能体编队控制问题中,尽管已有研究成果能够解决多智能体某些特殊类型的时变编队控制,但对一般性的时变编队还没有成熟的研究成果.本文以受非完整性约束的平面多智能体为研究对象,提出了平面非完整性多智能体的位置时变一致性协议.实验结果表明:本文提出的位置时变一致性协议能够有效解决平面非完整性多智能体系统一般性的时变编队问题.     

基于一致性Unsented卡尔曼滤波的多机器人定位

主要研究了多机器人编队过程中机器人的定位问题.在编队过程中机器人仅利用通过场地上方的摄像头捕获的图像得到自身的位置容易受干扰导致定位不准.利用队列中某个机器人观测到另外一个或几个机器人时,用相对观测信息和自身的位置以及附近被观测机器人的位置估计来更新一致性Unsented卡尔曼滤波算法中的状态估计.最后通过实验来对比未滤波前定位精度和分别采用Unsented卡尔曼滤波算法和一致性Unsented卡尔曼滤波算法定位精度,实验结果表明一致性Unsented卡尔曼滤波算法能够有效地提高定位的精度.     

多移动机器人避障编队控制

研究多移动机器人避障优化设计,针对多移动机器人在障碍物环境下的编队控制问题,为了保持整体合理避障和控制系统的稳定性和安全性,提出一种多机器人避障编队控制策略.首先获得多移动机器人编队的队形结构模型,结合多机器人完成避障编队任务的问题描述;在此基础上引入导航函数采用一种避障编队控制算法,使移动机器人能以设定的队形运动到目标点,可保证编队运动过程中未与障碍物发生碰撞.进行仿真的结果证明,所提算法解决了多机器人编队与避障问题,并保证了闭环系统的稳定性与安全性,验证了设计方法的有效性.     

分数阶多机器人的领航–跟随型环形编队控制

针对多机器人系统的环形编队控制复杂问题,提出一种基于分数阶多机器人的环形编队控制方法,应用领航–跟随编队方法来控制多机器人系统的环形编队和目标包围,通过设计状态估测器,实现对多机器人的状态估计.由领航者获取系统中目标状态的信息,跟随者监测到领航者的状态信息并完成包围环绕编队控制,使多机器人系统形成对动态目标的目标跟踪....     

基于网络通信的多机器人系统的稳定性分析

研究多机器人系统的协同一致性问题. 在考虑了系统中存在采样、保持以及时延的情况下, 对多机器人系统进行稳定性分析. 提出了一种简便的图形的稳定性判据, 以保证多机器人协同控制系统的一致性收敛. 在此基础上, 推导出了时延为一个采样周期时系统的稳定域. 最后, 利用Matlab进行车辆编队控制系统的仿真, 结果证明了提出的稳定性判据的可行性.     

A switched-system approach to formation control and heading consensus for multi-robot systems

This paper proposes a novel, hybrid and decentralized, switched-system approach for formation and heading consensus control of mobile robots under switching communication topology, including collision avoidance capability. The set of robots consists of nonholonomic wheeled mobile robots and can include a teleoperated UAV. The key feature of this approach is a virtual graph, which is derived by adding a set of relative translation vectors to the real graph of the multiple robots. Our approach results in the robots in the real graph moving to the desired formation and achieving heading consensus while the virtual robots on the virtual graph reach pose consensus. If any robot detects a nearby obstacle or other robot, the robot will temporarily move along an avoidance vector, which is perpendicular and positively projected onto the attractive vector, such that collision is avoided while minimally deviating from its formation control path. Experimental results are provided by two different research groups to demonstrate the effectiveness of our approach. These experiments extend the theoretical development by introducing a teleoperated quadrotor as a leader robot of the multi-robot systems. The same control law works for the extended system, with no modifications.     

Robot Formations Using a Single Camera and Entropy-based Segmentation

This work presents a new problem along with our new algorithm for a multi-robot formation with minimally controlled conditions. For multi-robot cooperation, there have traditionally been prevailing assumptions in order to collect the necessary information. These assumptions include the existence of communication systems among the robots or the use of specialized sensors such as laser scanners or omnidirectional cameras. However, they are not always valid, especially in emergency situations or with miniature robots. We, therefore, need to deal with the conditions that have received less attention in research regarding a multi-robot formation. There are several challenges: (1) less information is available than the well-known formation algorithms assume, (2) following strategies for deformable shapes in a formation with only local information available are needed, and (3) target segmentation without any markers is required. This work presents a formation algorithm based on a visual tracking algorithm, including how to process the image measurements provided by a single monocular camera. Through several experiments with real robots (developed at the University of Minnesota), we show that the proposed algorithms work well with minimal sensing information.     

Decentralised consensus-based formation tracking of multiple differential drive robots

This article investigates the control problem for formation tracking of multiple nonholonomic robots under distributed manner which means each robot only needs local information exchange. A class of general state and input transform is introduced to convert the formation-tracking issue of multi-robot systems into the consensus-like problem with time-varying reference. The distributed observer-based protocol with nonlinear dynamics is developed for each robot to achieve the consensus tracking of the new system, which namely means a group of nonholonomic mobile robots can form the desired formation configuration with its centroid moving along the predefined reference trajectory. The finite-time stability of observer and control law is analysed rigorously by using the Lyapunov direct method, algebraic graph theory and matrix analysis. Numerical examples are finally provided to illustrate the effectiveness of the theory results proposed in this paper.     

基于部分三阶邻居信息的一致性算法

针对多智能体一致性算法中的通信问题, 提出了一种近邻原则, 即利用部分二阶和部分三阶邻居信息, 在固定无向连通拓扑图的基础上, 应用于三阶多智能体系统.通过MATLAB仿真, 将所提出的算法与经典的三阶一致性算法进行比较, 仿真结果表明该算法能够使系统达到一致, 并且提高了系统的收敛速度, 减少了系统通讯量.     

一种基于离散时间一致性理论的多机器人分布式巡逻算法

在多机器人巡逻任务中,由于通信距离的限制,单个机器人很难获得全局信息。然而,现有的大多数多机器人分布式巡逻算法都要求每个机器人获得其巡逻区域的全局信息进行决策。因此,考虑到通信半径约束和局部信息约束,为了通过相邻机器人之间的交互完成巡逻任务,基于离散时间一致性理论提出了两种巡逻算法。算法1使用全局信息进行决策,算法2基于离散时间一致性理论实现局部信息对全局信息的预测进行决策。通过模拟器Stage对所提算法与对比算法在不同机器人数量、通信半径、地图环境下进行了对比。实验验证了所提出的基于局部信息的分布式多机器人巡逻算法具有与原算法类似的特性和性能,能够使机器人在没有全局信息的情况下判断全局状态,并基于邻居之间的协商完成巡逻任务。     

Altruistic coordination for multi-robot cooperative pathfinding

When multiple robots perform tasks in a shared workspace, they might be confronted with the risk of blocking each other’s ways, which will lead to conflicts or interference among them. Planning collision-free paths for all the robots is a challenge for a multi-robot system, which is also known as the multi-robot cooperative pathfinding problem in which each robot has to navigate from its starting location to the destination while keeping avoiding stationary obstacles as well as the other robots. In this paper, we present a novel fully decentralized approach to this problem. Our approach allows robots to make real-time responses to dynamic environments and can resolve a set of benchmark deadlock situations subject to complex spatial constraints in a shared workspace by means of altruistic coordination. Specifically, when confronted with congested situations, each robot can employ waiting, moving-forwards, dodging, retreating and turning-head strategies to make local adjustments. Most importantly, each robot only needs to coordinate and communicate with the others that are located within its coordinated network in our approach, which can reduce communication overhead in fully decentralized multi-robot systems. In addition, experimental results also show that our proposed approach provides an efficient and competitive solution to this problem.     

Adaptive Distributed Fault-tolerant Formation Control for Multi-robot Systems under Partial Loss of Actuator Effectiveness

This paper presents an adaptive distributed fault-tolerant formation control for multi-robot systems. Both the kinematics and dynamics of differential wheeled mobile robots are considered. In particular, the problem caused by actuator faults is investigated. Based on dynamic surface control techniques, adaptive formation controllers can be obtained under a directed communication network. The closed-loop stability is guaranteed by using Lyapunov stability analysis such that all followers can exponentially converge to a leader-follower formation pattern. Simulation and experimental results illustrate that the desired formation pattern can be preserved for a group of wheeled robots subject to unknown uncertainties and actuator faults.     

Distributed adaptive control for consensus tracking with application to formation control of nonholonomic mobile robots

In this paper, we investigate the output consensus problem of tracking a desired trajectory for a class of systems consisting of multiple nonlinear subsystems with intrinsic mismatched unknown parameters. The subsystems are allowed to have non-identical dynamics, whereas with similar structures and the same yet arbitrary system order. And the communication status among the subsystems can be represented by a directed graph. Different from the traditional centralized tracking control problem, only a subset of the subsystems can obtain the desired trajectory information directly. A distributed adaptive control approach based on backstepping technique is proposed. By introducing the estimates to account for the parametric uncertainties of the desired trajectory and its neighbors’ dynamics into the local controller of each subsystem, information exchanges of online parameter estimates and local synchronization errors among linked subsystems can be avoided. It is proved that the boundedness of all closed-loop signals and the asymptotically consensus tracking for all the subsystems’ outputs are ensured. A numerical example is illustrated to show the effectiveness of the proposed control scheme. Moreover, the design strategy is successfully applied to solve a formation control problem for multiple nonholonomic mobile robots.     

Trajectory design and control for aggressive formation flight with quadrotors

In this work we consider the problem of controlling a team of micro-aerial vehicles moving quickly through a three-dimensional environment while maintaining a tight formation. The formation is specified by shape vectors which prescribe the relative separations and bearings between the robots. To maintain the desired shape, each robot plans its trajectory independently based on its local information of other robot plans and estimates of states of other robots in the team. We explore the interaction between nonlinear decentralized controllers, the fourth-order dynamics of the individual robots, time delays in the network, and the effects of communication failures on system performance. Simulations as well as an experimental evaluation of our approach on a team of quadrotors suggests that suitable performance is maintained as the formation motions become increasingly aggressive and as communication degrades.