Synchronized output regulation of switching networks based on synchronization observer

This paper studies the synchronized output regulation (SOR) problem of networked dynamic systems with switching topology that is uniformly connected and leader-rooted. In these networked systems, the tracked signal or the rejected disturbance is generated by the same exosystem, and however, the state of the exosystem is only available for leader nodes. First, a synchronization observer of the exosystem is proposed in this paper to overcome the difficulty caused by the unavailable state of the exosystem for follower nodes with directed switching information flow. It is shown that the observer state will synchronize to the state of the exosystem. Then, two feedback controllers based on decentralized dynamic error and state are presented to solve this SOR problem. Furthermore, the main idea in this paper will provide a promising way for realizing the multirobot systems’ tracking and formation requirement. Numerical simulation results are presented to demonstrate the effectiveness of the theoretical results.     

Applying a path planner based on RRT to cooperative multirobot box-pushing

Considering robot systems in the real world, a multirobot system where multiple robots work simultaneously without colliding with each other is more practical than a single-robot system where only one robot works. Therefore, solving the path-planning problem in a multirobot system is very important. In this study, we developed a path-planner based on the rapidly exploring random tree (RRT), which is a data structure and algorithm designed for efficiently searching for multirobot box-pushing, and made experiments in real environments. A path planner must construct a plan which avoids the robot colliding with obstacles or with other robots. Moreover, in some cases, a robot must collaborate with other robots to transport the box without colliding with any obstacles. Our proposed path planner constructs a box-transportation plan and the path plans of each robot bearing the above considerations in mind. Experimental results showed that our proposed planner can construct a multirobot box-pushing plan without colliding with obstacles, and that the robots can execute tasks according to the plan in real environments. We also checked that multiple robots can perform problem tasks when only one robot could not transport the box to the goal. This work was presented in part at the 13th International Symposium on Articifial Life and Robotics, Oita, Japan, January 31–February 2, 2008     

Dynamic consensus of high-order multi-agent systems and its application in the motion control of multiple mobile robots

In this paper, the leader-following consensus problem for multi-agent linear dynamic systems is considered. All agents and leader have identical multi-input multi-output (MIMO) linear dynamics that can be of any order, and only the output information of each agent is delivered throughout the communication network. When the interaction topology is fixed, the leader-following consensus is attained by H∞ dynamic output feedback control, and the sufficient condition of robust controllers is equal to the solvability of linear matrix inequality (LMI). The whole analysis is based on spectral decomposition and an equivalent decoupled structure achieved, and the stability of the system is proved. Finally, we extended the theoretical results to the case that the interaction topology is switching. The simulation results for multiple mobile robots show the effectiveness of the devised methods.     

Rendezvous with connectivity preservation for multi-robot systems with an unknown leader

This paper studies the leader-following rendezvous problem with connectivity preservation for multi-agent systems composed of uncertain multi-robot systems subject to external disturbances and an unknown leader, both of which are generated by a so-called exosystem with parametric uncertainty. By combining internal model design, potential function technique and adaptive control, two distributed control strategies are proposed to maintain the connectivity of the communication network, to achieve the asymptotic tracking of all the followers to the output of the unknown leader system, as well as to reject unknown external disturbances. It is also worth to mention that the uncertain parameters in the multi-robot systems and exosystem are further allowed to belong to unknown and unbounded sets when applying the second fully distributed control law containing a dynamic gain inspired by high-gain adaptive control or self-tuning regulator.     

Finite-time and fixed-time leader-following consensus for multi-agent systems with discontinuous inherent dynamics

This paper is concerned with finite-time and fixed-time consensus of multi-agent systems in a leader-following framework. Different from conventional leader-following tracking approaches where inherent dynamics satisfying the Lipschitz continuous condition is required, a more generalised case is investigated: discontinuous inherent dynamics. By nonsmooth techniques, a nonlinear protocol is first proposed to achieve the finite-time leader-following consensus. Then, based on fixed-time stability strategies, the fixed-time leader-following consensus problem is solved. An upper bound of settling time is obtained by using a new protocol, and such a bound is independent of initial states, thereby providing additional options for designers in practical scenarios where initial conditions are unavailable. Finally, numerical simulations are provided to demonstrate the effectiveness of the theoretical results.     

Global disturbance rejection for nonlinear lower triangular systems with iISS inverse dynamics and uncertain exosystem

This paper concerns about the global disturbance rejection problem for uncertain nonlinear lower triangular systems with integral input‐to‐state stable (iISS) inverse dynamics and an uncertain exosystem. The main challenges addressed in this paper include uncertain exosystem, unknown control direction, iISS inverse dynamics, and complex structure of lower triangular systems. Because of the presence of both uncertain exosystem and unknown control direction, simply combining the existing techniques for each of these challenges cannot solve the proposed problem. In fact, to handle the current case, appropriate new update laws for the estimators of the uncertain parameters are required, such that the estimators can be successfully integrated with the internal model principle. Furthermore, the changing supply function technique for iISS systems is utilized to deal with the iISS inverse dynamics. With the proposed controller, the closed‐loop system is globally asymptotically stable, and the disturbance is globally rejected. Two simulation examples are finally presented to show the effectiveness of the proposed control scheme and the practical relevance of our work. Copyright © 2016 John Wiley & Sons, Ltd.     

Time-varying formation control with attitude synchronization of multiple rigid body systems

In this article, we study the leader-following formation control problem for a group of rigid body systems whose followers' motions are described by dual quaternion equations. A few features are as follows. First, we introduce an exosystem to generate the leader's trajectory as well as the formation configuration, which can produce a large class of time-varying signals so that we can achieve a variety of time-varying formations. Second, to overcome the communication constraint described by a digraph, we extend the distributed observer to estimate not only the desired attitude and angular velocity but also the leader's position and linear velocity. Third, a novel distributed control law is synthesized to furnish a rigorous performance analysis of the closed-loop system. The effectiveness of our design is illustrated by a numerical example.     

Leader-following consensus of fractional-order multi-agent systems via adaptive pinning control

In this paper, the leader-following consensus problem of fractional-order multi-agent systems is considered via adaptive pinning control. The dynamics of leader and all followers with linear and nonlinear functions are investigated, respectively. We assume that the node should be pinned if its in-degree is less than its out-degree in the paper. Under this assumption and based on the stability theory of fractional-order differential systems, some leader-following consensus criteria are derived, which are easily obtained by matrix inequalities. The control of each agent using local information is designed and detailed analysis of the leader-following consensus is presented. The design technique is based on algebraic graph theory and the Riccati inequality. Several simulation examples are presented to demonstrate the effectiveness of the proposed method.     

考虑障碍环境下的多机器人编队控制研究

编队和避障控制是机器人路径规划设计中的典型问题,文中提出了将leader—following法和人工势场法相结合的方法,来更好地完成多机器人在未知环境下的编队和避障控制。之前的研究只将leader—following算法用于多机器人的编队控制,而文中提出此方法也可以用于多机器人系统的避障控制。基于leader—following法,多机器人能自动编队并保持队形;而结合人工势场法,多机器人可以保持队形行进,在遇到障碍物的情况下变换队形避障,在避障后恢复原队形,最终到达目标。通过仿真实验证明,该算法实现了多机器人在未知环境下的自动编队和避障,从而证明了leader—following算法可以用于机器人的避障控制。     

Leader-following consensus of multi-agent systems under fixed and switching topologies

The leader-following consensus problem of higher order multi-agent systems is considered. In the system, the dynamics of each agent and the leader is a linear system. The control of each agent using local information is designed and detailed analysis of the leader-following consensus is presented for both fixed and switching interaction topologies, which describe the information exchange between the multi-agent systems. The design technique is based on algebraic graph theory, Riccati inequality and Lyapunov inequality. Simulations indicate the capabilities of the algorithms.     

Robust Discrete-Time Markovian Control for Wheeled Mobile Robot Formation: A Fault Tolerant Approach

In this paper we use a recursive robust regulator for discrete time Markovian jump linear systems to control a group of wheeled mobile robots in formation. A leader-following formation is used with directed communication topology. The robustness is checked with a communication fault in blind areas and, if the fault affects the leader, the leadership is changed and the formation continues to follow the defined trajectory. When the communication is reestablished all robots that lost communication return to their position in the formation. Results based on simulation and real implementation are presented to show the effectiveness of the formation control approach used.     

Global exponential regulation of discrete time linear systems with unknown neutrally stable exosystems

Discrete time, linear, stabilizable and detectable systems with known parameters are considered: the regulation problem is addressed when the reference output and/or the disturbances contain sinusoidal terms generated by a linear exosystem with unknown parameters. Only an upper bound on the number of unknown sinusoids is supposed to be known. A constructive algorithm is proposed to drive the regulation error exponentially to zero on the basis of its measurement only, under the same necessary and sufficient conditions which are required when the exosystem is known. The control strategy includes an online detector for the number of excited frequencies and exponentially converging global estimates of the exosystem unknown parameters. An illustrative example containing a variable number of frequencies is worked out and simulated.     

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。     

Robust formation control of electrically driven nonholonomic mobile robots via sliding mode technique

This paper proposes a sliding mode formation control method for electrically driven nonholonomic mobile robots in the presence of model uncertainties and disturbances. We use the kinematic model based on the leader-following approach for the formation control of multiple robots. Unlike many researches considering only the kinematic model, we also consider the dynamic model including actuator dynamics to obtain the voltage input because it is more realistic to use the voltage as input than the velocity. Then, the sliding mode control method is used to deal with model uncertainties and disturbances acting on the mobile robots. The stability of the proposed control system is proven using Lyapunov stability theory. Finally, we perform computer simulations to demonstrate the performance of the proposed control system.     

A hierarchical gene regulatory network for adaptive multirobot pattern formation

Most existing multirobot systems for pattern formation rely on a predefined pattern, which is impractical for dynamic environments where the pattern to be formed should be able to change as the environment changes. In addition, adaptation to environmental changes should be realized based only on local perception of the robots. In this paper, we propose a hierarchical gene regulatory network (H-GRN) for adaptive multirobot pattern generation and formation in changing environments. The proposed model is a two-layer gene regulatory network (GRN), where the first layer is responsible for adaptive pattern generation for the given environment, while the second layer is a decentralized control mechanism that drives the robots onto the pattern generated by the first layer. An evolutionary algorithm is adopted to evolve the parameters of the GRN subnetwork in layer 1 for optimizing the generated pattern. The parameters of the GRN in layer 2 are also optimized to improve the convergence performance. Simulation results demonstrate that the H-GRN is effective in forming the desired pattern in a changing environment. Robustness of the H-GRN to robot failure is also examined. A proof-of-concept experiment using e-puck robots confirms the feasibility and effectiveness of the proposed model.     

动态环境下分布式异构多机器人避障方法研究

多机器人系统在联合搜救、智慧车间、智能交通等领域得到了日益广泛的应用。目前,多个机器人之间、机器人与动态环境之间的路径规划和导航避障仍需依赖精确的环境地图,给多机器人系统在非结构环境下的协调与协作带来了挑战。针对上述问题,本文提出了不依赖精确地图的分布式异构多机器人导航避障方法,建立了基于深度强化学习的多特征策略梯度优化算法,并考虑了人机协同环境下的社会范式,使分布式机器人能够通过与环境的试错交互,学习最优的导航避障策略;并在Gazebo仿真环境下进行了最优策略的训练学习,同时将模型移植到多个异构实体机器人上,将机器人控制信号解码,进行真实环境测试。实验结果表明:本文提出的多特征策略梯度优化算法能够通过自学习获得最优的导航避障策略,为分布式异构多机器人在动态环境下的应用提供了一种技术参考。     

Path planning for permutation-invariant multirobot formations

In many multirobot applications, the specific assignment of goal configurations to robots is less important than the overall behavior of the robot formation. In such cases, it is convenient to define a permutation-invariant multirobot formation as a set of robot configurations, without assigning specific configurations to specific robots. For the case of robots that translate in the plane, we can represent such a formation by the coefficients of a complex polynomial whose roots represent the robot configurations. Since these coefficients are invariant with respect to permutation of the roots of the polynomial, they provide an effective representation for permutation-invariant formations. In this paper, we extend this idea to build a full representation of a permutation-invariant formation space. We describe the properties of the representation, and show how it can be used to construct collision-free paths for permutation-invariant formations.     

Robust cooperative output regulation under exosystem detectability constraint

ABSTRACT

This paper revisits the robust cooperative output regulation problem for a class of linear uncertain multi-agent systems. In particular, it is assumed here that the agents in the system can only access incomplete measurements of the exosystem, and the local regulated error signals are not available to the agents to be used in control. Under these assumptions, the agents in the system cannot independently reconstruct the exosystem dynamics, or rely on their own local measurements to achieve the objectives of the output regulation problem. The solution to the regulation problem proposed in this paper is a distributed dynamic control law that reconstructs the exosystem states, given a mild collective detectability assumption. Furthermore, the proposed distributed control law incorporates an internal model of the exosystem to allow for uncertain dynamics of the multi-agent system. A numerical example is offered to illustrate the effectiveness of the proposed control solution.     

Leader-following Cluster Consensus in Multi-agent Systems with Intermittence

In this paper, the cluster consensus problem of first-order nonlinear multi-agent systems with aperiodic intermittent communication is studied through pinning leader-following approach. The pinning consensus algorithm based on the relative local intermittent information is designed according to the varies linking ways of clustered network structure. New notions of leading intermittence and inter-cluster intermittence which related to the intermittent linking ways of leader-following clustered structure are developed, and several new systems with intermittence are established due to the new notions. Besides, dynamics with inherent delay are also considered to extend our results to a more general framework. The original communication graph without intermittent pattern is supposed to be directed and weakly connected. Some consensus criteria are derived to guarantee that the cluster consensus problem for the systems with intermittent communication can be solved. Finally, numerical simulations are given to illustrate the effectiveness of the theoretical results.     

Local communication of multiple mobile robots: Design of optimal communication area for cooperative tasks

This paper presents an optimal design for local communication between multiple mobile robots. In previous studies of local communication in multirobot systems, the area of communication was not designed using mathematical analysis, but only time-consuming simulations of multirobot communications. We analyzed the information transmission efficiency and created an optimal communication area that minimizes the information transmission time to multiple robots. This optimization comprises two steps. First, we derive the “information transmission probability” for various task models. Next, the derived information transmission probability is used to minimize the information transmission time. The optimal communication design is tested for various tasks, using system parameters. The analytical results are further verified by using computer simulations of multirobot communications and experiments with local communication. © 1998 John Wiley & Sons, Inc.