对队形控制的思考

首先指出多机器人队形控制研究要解决的主要问题,并较为完整地阐述了当前国内外相关研究的状况．然后总结了队形控制的各种研究方法,并指出当前队形控制研究中存在的一些问题以及在实际设计队形控制系统时应考虑的问题．最后指出了今后的研究方向．     

异质多移动机器人协同技术研究的进展

随着移动机器人应用的领域和范围的不断扩展，多移动机器人由于其单个机器人无法比拟的优越性已经越来越受到重视．从体系结构、协作与协调、协作环境感知与定位、重构及机器学习几个重要课题对多移动机器人协同技术进行了综述，尤其侧重于各种技术如何处理和包容团队中的异质性，并分析了本领域中的研究难点问题，最后展望了异质多移动机器人研究的前景与发展趋势．     

多移动机器人的领航-跟随编队避障控制

针对多移动机器人的编队控制问题,提出了一种结合Polar Histogram避障法的领航-跟随协调编队控制算法。该算法在领航-跟随l-φ编队控制结构的基础上引入虚拟跟随机器人,将编队控制转化为跟随机器人对虚拟跟随机器人的轨迹跟踪控制。结合移动机器人自身传感器技术,在简单甚至复杂的环境下为机器人提供相应的路径运动策略,实现实时导航的目的。以两轮差动Qbot移动机器人为研究对象,搭建半实物仿真平台,进行仿真实验。仿真结果表明:该方法可以有效地实现多移动机器人协调编队和避障控制。     

Active visual localization for multiple inspection robots

In the routine inspection of industrial or other areas, teams of robots with various sensors could operate together to great effect, but require reliable, accurate and flexible localization capabilities to be able to move around safely. We demonstrate accurate localization for an inspection team consisting of a robot with stereo active vision and its blind companion with an active lighting system, and show that in this case a single sensor can be used for measuring the position of known or unknown scene features, measuring the relative location of the two robots and actually carrying out an inspection task.     

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。     

Marching control based on the leader-followers scheme and formation graphs

This paper analyzes the case of marching control, where a leader robot follows a desired trajectory, while the whole group reaches a formation pattern established by a formation graph. To guarantee that the group preserves the desired formation and follows the marching path simultaneously, two approaches are given, based on the feedback of the velocity of the desired trajectory or the velocity of some robots. The main result establishes that for both approaches and any well-defined formation graph, there is convergence to the formation and the marching path. The analysis addresses the cases of omnidirectional robots and the extension to unicycle-type robots. The performance of the control strategies is shown some numerical simulations and real-time experiments.     

Distributed consensus-based formation control for multiple nonholonomic mobile robots with a specified reference trajectory

In this paper, the distributed formation control problem for multiple nonholonomic mobile robots using consensus-based approach is considered. A transformation is given to convert the formation control problem for multiple nonholonomic mobile robots into a state consensus problem. Distributed control laws are developed for achieving the formation control objectives: a group of nonholonomic mobile robots at least exponentially converge to a desired geometric pattern with its centroid moving along the specified reference trajectory. Rigorous proofs are provided by using graph, matrix , and Lyapunov theories. Simulations are also given to verify the effectiveness of the theoretical results.     

Symmetry position/force hybrid control for cooperative object transportation using multiple humanoid robots

A symmetry position/force hybrid control framework for cooperative object transportation tasks with multiple humanoid robots is proposed in this paper. In a leader-follower type cooperation, follower robots plan their biped gaits based on the forces generated at their hands after a leader robot moves. Therefore, if the leader robot moves fast (rapidly pulls or pushes the carried object), some of the follower humanoid robots may lose their balance and fall down. The symmetry type cooperation discussed in this paper solves this problem because it enables all humanoid robots to move synchronously. The proposed framework is verified by dynamic simulations.     

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.     

A finite-time approach to formation control of multiple mobile robots with terminal sliding mode

In this study, a new finite-time synchronised approach is developed for multiple mobile robots formation control based on terminal sliding mode control principle and system synchronisation theory. Associated stability analysis is presented to lay a foundation for analytical understanding in generic theoretical aspects and safe operation for real systems. An illustrative example of multiple mobile robots formation control is bench tested to validate the effectiveness of the proposed approach.     

一种引入通信的多移动机器人编队方法*

提出以视觉跟踪为基础并引入通信进行多机器人的编队控制方法,根据需要编写了一种新的通信协议,采用闭环l-Φ实现编队算法.这种多机器人编队控制避免了视觉系统的局限,能够更好地在复杂未知环境中协作完成任务,解决了编队控制的无反馈和实时性不高的问题,使得机器人能够准确迅速地进行跟踪和通信编队,一起顺利达到目标点.试验结果证明了该方法的有效性.     

多动态目标的多机器人协同环航控制

主要研究了多个非完整机器人对多个动态目标的协同环航控制问题;首先,针对多目标护航任务,建立目标扩展圆形构型,以期完成紧密目标保卫任务;其次,针对护航机器人,通过利用自身及相邻节点的位置与方位信息及所包围的动态目标的中心位置及扩展半径设计分布式时变圆形编队控制协议,实现预定几何分布下的机器人环航编队设计;其中,通过引入虚拟信号变量设计期望的速度及角速度控制律,利用反步技术提出了一种新的考虑时变护航半径的分布式控制策略;在对目标节点速度的温和假设下,所提出的编队控制器可以驱动多护航机器人渐近收敛到以多目标中心的圆上,同时维持一个预定的几何编队配置;Lyapunov分析证明了所有的误差都可以渐进稳定到原点,数值仿真核实了所构建的控制方案的可行性。     

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。     

Robust formation tracking control of mobile robots via one-to-one time-varying communication

We solve the formation tracking control problem for mobile robots via linear control, under the assumption that each agent communicates only with one ‘leader’ robot and with one follower, hence forming a spanning-tree topology. We assume that the communication may be interrupted on intervals of time. As in the classical tracking control problem for non-holonomic systems, the swarm is driven by a fictitious robot which moves about freely and which is a leader to one robot only. Our control approach is decentralised and the control laws are linear with time-varying gains; in particular, this accounts for the case when position measurements may be lost over intervals of time. For both velocity-controlled and force-controlled systems, we establish uniform global exponential stability, hence consensus formation tracking, for the error system under a condition of persistency of excitation on the reference angular velocity of the virtual leader and on the control gains.     

基于虚拟力的群机器人队形控制

提出了一种基于虚拟力的群机器人队形形成原理,提出了一种使用拟合法构建虚拟力模型的方法及其应用。实验结果表明该方法可以快速、有效地完成队形分布,并指出了今后的研究方向。     

Nonlinear formation control strategies for agents without relative measurements under heterogeneous networks

This paper proposes cooperative control protocols for a group of unmanned vehicles to make a stable formation around a maneuvering target. The control protocols are proposed on the basis of heterogeneous communication networks, which represents more challenging and generalized situations. Two different scenarios are considered. Separate control protocols are developed for each case. In both scenarios, agents do not have relative position, velocity, and acceleration measurements as feedback. In the first scenario, each agent uses its own position and velocity measurement in a consensus algorithm. In the second scenario, each agent needs only its own position information for the consensus algorithm. For both protocols, agents compute virtual estimates of a target's position and velocity and exchange these among the neighbors. Three different communication networks are used for exchanging two virtual estimates calculated by each agent and a time derivative of one virtual estimate. Each interagent communication network is represented by a fixed, undirected, and connected graph. Furthermore, it is considered that at least one agent receives the position, velocity, and acceleration information of the maneuvering target. It is not necessary that the agent receiving the target's position and the agent receiving the velocity and/or the acceleration information of the target be the same. However, the target does not receive any information about any agent. Stability of the formation is analyzed by using Barbalat's lemma. It is also shown that, despite the large difference in received information, the acceleration of the agents remains bounded for all time. The performance of the proposed formation control protocols is illustrated through numerical simulations.     

Moving formation convergence of a group of mobile robots via decentralised information feedback

In this article, a decentralised information feedback mechanism is introduced to a group of mobile robots such that the robots asymptotically converge to a given moving formation. It is assumed that the robots can exchange only position information according to a pre-specified communication graph. Each node represents a robot. Two robots are neighbours of each other if there is an edge between the two nodes. A feedback controller is performed for each robot by only using its own velocity information and the position information from its neighbours. It is proven that if the graph is connected, then the convergence to the moving formation of the closed-loop system is guaranteed. Several numerical simulations are presented to illustrate the results.     

Propagation of Uncertainty in Cooperative Multirobot Localization: Analysis and Experimental Results

This paper examines the problem of cooperative localization for the case of large groups of mobile robots. A Kalman filter estimator is implemented and tested for this purpose. The focus of this paper is to examine the effect on localization accuracy of the number N of participating robots and the accuracy of the sensors employed. More specifically, we investigate the improvement in localization accuracy per additional robot as the size of the team increases. Furthermore, we provide an analytical expression for the upper bound on the positioning uncertainty increase rate for a team of N robots as a function of N, the odometric and orientation uncertainty for the robots, and the accuracy of a robot tracker measuring relative positions between pairs of robots. The analytical results derived in this paper are validated both in simulation and experimentally for different test cases.     

微小型群机器人室外组合定位系统与方法

传统群机器人的室外定位主要依靠单一的GPS定位,精度较低,且在城市及野外复杂环境下容易受到障碍物的影响,导致其无法获得准确位置。利用差分GPS定位技术和RSSI无线定位技术组建了一种基于AVR单片机的控制平台,XBee为通讯网络的组合定位系统,显著提高了定位精度,消除了定位盲点,在复杂环境下也能得到较为准确的位置,且具有低功耗,低成本,高稳定性的特点,并在实验和仿真中得到了验证。     

双参考点切换的多移动机器人队形运动控制方法

为描述机器人队列的运动过程,从相对位姿的角度定义了多移动机器人的队形模型.在传统leader-following队形控制的基础上,引入切换控制思想,每对领路机器人与跟随机器人之间设计3个控制器,对应跟随机器人中轴线上两参考点分别设计两个运动子控制器,控制领路机器人与跟随机器人之间的相对位姿;切换控制器根据系统处于平衡状态时,跟随机器人线速度的符号切换运动控制器,从而保证队列收敛到目标队形.仿真实验结果表明,机器人队列表现出良好的整体一致性,队列运动更加平稳.