State Of Leader Research Articles

Robust decentralised mean field control in leader following multi‐agent systems

This study addresses a robust counterpart of the deterministic mean field control in a multi-agent system. A decentralised mean field algorithm is proposed to solve a min–max control problem for a large population of heterogeneous agents. In the proposed leader following scheme, the leader tracks a reference signal which is unknown to the followers and each follower tracks a convex combination of the population state average and the leader's state. The leader plays a robust min–max game against disturbance and the followers play a mean field e N -Nash game against each other and at the same time, each follower plays a robust min–max game against the disturbance. For all the players, finite horizon quadratic cost is considered. In the proposed decentralised algorithm, followers do not need the knowledge about each of leader's and other followers' states and they only use an estimate of the population state average. In this way, propose a policy iteration method which guarantees the convergence to the saddle point mean field e N -Nash solution. The proposed method is applied to a large population of agents and compared with centralised algorithm to demonstrate the results.

Fixed‐Time Synchronization of a Class of Second‐Order Nonlinear Leader‐Following Multi‐Agent Systems

AbstractThe fixed‐time synchronization problem for a class of second‐order nonlinear multi‐agent systems with a leader‐follower architecture is investigated in this paper. To achieve the fixed‐time tracking task, the design procedure is divided into two steps. At the first step, a distributed fixed‐time observer is designed for each agent to estimate the leader's state in a fixed time. Then, at the second step, based on the technique of adding a power integrator, a fixed‐time tracking controller for each agent is proposed such that the estimate leader's state can be tracked in a fixed time. Finally, an observer‐based fixed‐time controller is developed such that the leader can be tracked by all the followers in a fixed time, which can be predetermined. Simulations are presented to verify the effectiveness of the proposed approach.

Event-Based Set-Membership Leader-Following Consensus of Networked Multi-Agent Systems Subject to Limited Communication Resources and Unknown-But-Bounded Noise

This paper addresses the problem of leader-following consensus for networked multi-agent systems subject to limited communication resources and unknown-but-bounded process and measurement noise. First, a new distributed event-based communication mechanism on the basis of a time-varying threshold parameter is developed to schedule transmission of each sensor's measurement through a communication network so as to alleviate consecutive occupancy of communication resources. Second, a novel concept of set-membership leader-following consensus is put forward, through which the true states of all followers are guaranteed to always reside in a bounding ellipsoidal set of the leader's state. Third, in the case that full information of followers’ states are not measurable, a distributed observer-based consensus protocol is presented to provide a set-membership estimation of each follower's state. Then, based on a recursive computation of confidence state estimation ellipsoids and leader state ellipsoid, a delicate convex optimization algorithm in terms of recursive linear matrix inequalities is proposed to design desired consensus protocol and event-based mechanism. Finally, an illustrative example is given to show the effectiveness and advantage of the developed approach.

Distributed attitude and translation consensus for networked rigid bodies based on unit dual quaternion

SummaryThis paper provides unified solutions for distributed attitude and translation consensus problems for networked fully actuated rigid bodies under the fixed and undirected communication topology with the tool of unit dual quaternion. We investigate two kinds of consensus, that is, leaderless consensus and leader‐following consensus with a static leader. Firstly, the dynamics of rigid bodies are presented by unit dual quaternion. The control inputs of rigid bodies are also obtained from unit dual quaternion. Secondly, we propose a distributed consensus law in the form of dual quaternion to guarantee that the attitudes and translations of all rigid bodies reach consensus, respectively, without a leader. Thirdly, the leader‐following consensus problem with a static leader is studied. With the proposed leader‐following consensus law, the states of all rigid bodies converge to the corresponding states of the static leader, including the attitude and the translation. Finally, numerical examples are provided to validate the effectiveness of the theoretical results. Copyright © 2017 John Wiley & Sons, Ltd.

Adaptive finite‐time consensus tracking for multiple uncertain mechanical systems with input saturation

SummaryThis paper investigates the problem of finite‐time consensus tracking for a class of multiple uncertain mechanical systems under switching topologies. In the presence of uncertainties and input saturations, a distributed observer‐based adaptive finite‐time tracking protocol is proposed. At the first step, a distributed observer is proposed for each mechanical system to observe the leader's state in finite time; then, an adaptive finite‐time tracking protocol is designed to track the estimated state via recursive design method. Neural networks are used to approximate the unknown continuous functions. It is proved that under the designed protocol, the consensus tracking of position and velocity can be achieved in finite time. Finally, an example is given to demonstrate the effectiveness of the proposed method. Copyright © 2017 John Wiley & Sons, Ltd.

Second-Order Containment Control of Multiagent Systems in the Presence of Uncertain Topologies with Time-Varying Delays

This paper considers the containment control problem of second-order multiagent systems in the presence of time-varying delays and uncertainties with dynamically switching communication topologies. Moreover, the control algorithm is proposed for containment control, and the stability of the proposed containment control algorithm is studied with the aid of Lyapunov-Krasovskii function when the communication topology is jointly connected. Some sufficient conditions in terms of linear matrix inequalities (LMIs) are provided for second-order containment control with multiple stationary leaders. Finally, simulations are given to verify the effectiveness of the obtained theoretical results.

On Convergence Rate of Leader-Following Consensus of Linear Multi-Agent Systems With Communication Noises

This note further studies the previously proposed consensus protocol for linear multi-agent systems with communication noises in [15], [16]. Each agent is allowed to have its own time-varying gain to attenuate the effect of communication noises. Therefore, the common assumption in most references that all agents have the same noise-attenuation gain is not necessary. It has been proved that if all noise-attenuation gains are infinitesimal of the same order, then the mean square leader-following consensus can be reached. Furthermore, the convergence rate of the multi-agent system has been investigated. If the noise-attenuation gains belong to a class of functions which are bounded above and below by $t^{-\beta}$ $(\beta\in(0,1))$ asymptotically, then the states of all follower agents are convergent in mean square to the leader's state with the rate characterized by a function bounded above by $t^{-\beta}$ asymptotically.

Quaternion-based attitude synchronisation for multiple rigid bodies in the presence of actuator saturation

ABSTRACTThis paper concentrates on the quaternion-based attitude synchronisation problems of networked rigid bodies under fixed and undirected communication topology without relative angular measurements in the presence of actuator saturation. We first consider the leaderless attitude synchronisation problem with zero final angular velocity. In this case, we not only discuss the performance under the acyclic communication topology with the proposed bounded control algorithm, but also analyse that if there exist cycles in the topology, the proposed bounded algorithm guarantees that all equilibrium points are unstable except that the attitudes of networked rigid bodies achieve synchronisation. We also expand the result to the case of attitude tracking synchronisation with a static leader in the presence of actuator saturation. Next, the tracking synchronisation problem with the desired time-varying attitude is addressed in the presence of actuator saturation. Numerical examples are provided to validate the effectiveness of the proposed bounded schemes and illustrate the performances of multiple rigid bodies.

Finite‐time attitude synchronisation for multiple spacecraft

This study investigates the finite-time attitude synchronisation problem for multiple spacecraft under a directed communication topology. Attitude synchronisation problem for a leaderless formation system without specified reference attitude is studied, and finite-time control laws are proposed and analysed without using neighbours' angular velocity measurements. By applying the graph theory, homogeneous method and Lyapunov stability theory, it is proved that the system is globally finite-time stable and attitude synchronisation can be achieved. Then the obtained control results are extended in the scenario with a stationary leader. Numerical simulations are finally given to demonstrate the effectiveness and feasibility of the obtained results.

Cooperative Control of Heterogeneous Uncertain Dynamical Networks: An Adaptive Explicit Synchronization Framework.

This paper proposes an adaptive explicit synchronization framework to address the cooperative control for heterogeneous uncertain dynamical networks under switching communication topologies. The main contribution is to develop an adaptive explicit synchronization algorithm, in which the synchronization state can be completely tracked by each agent in real time rather than only be measured after the synchronization process of all agents is over. By introducing appropriate assumptions, a class of adaptive explicit synchronization protocols is designed by using a combination of the virtual leader's states, the neighboring agents' relative information, distributed feedback gain, and distributed average weighted parameters. It is proved in the sense of Lyapunov that, if the dwell time is larger than a positive threshold, the cooperative control problem for the closed-loop heterogeneous uncertain dynamical networks under switching of strongly-connected communication topologies can be solved by the proposed adaptive explicit synchronization algorithm. Furthermore, by assuming that the topology is frequently strongly-connected, it shows that intermittent adaptive explicit synchronization can be achieved with well-designed control parameters. Two examples are presented to demonstrate the effectiveness of the proposed theory.

Neural-network-based containment control of nonlinear multi-agent systems under communication constraints

Purpose The purpose of this paper is to investigate the neural-network-based containment control of multi-agent systems with unknown nonlinear dynamics. Moreover, communication constraints are taken into account to reflect more realistic communication networks. Design/methodology/approach Based on the approximation property of the radial basis function neural networks, the control protocol for each agent is designed, where all the information is exchanged in the form of sampled data instead of ideal continuous-time communications. Findings By utilizing the Lyapunov stability theory and the Lyapunov–Krasovskii functional approach, sufficient conditions are developed to guarantee that all the followers can converge to the convex hull spanned by the stationary leaders. Originality/value As ideal continuous-time communications of the multi-agent systems are very difficult or even unavailable to achieve, the neural-network-based containment control of nonlinear multi-agent systems is solved under communication constraints. More precisely, sampled-data information is exchanged, which is more applicable and practical in the real-world applications.

Distributed Attitude Consensus for Multiple Rigid Spacecraft under Jointly Connected Switching Topologies

We study the distributed leader-following attitude consensus problem for multiple rigid spacecraft with a single leader under jointly connected switching topologies. Two cases are considered, where the first case is with a static leader and the second case is with a dynamic leader. By constructing an auxiliary vector and a distributed observer for each follower spacecraft, the controllers are designed to drive all the attitudes of the follower spacecraft to the leader’s, respectively, for both of the two cases, though there are some time intervals in which the communication topology is not connected. The whole system is proved to be stable by using common Lyapunov function method. Finally, the theoretical result is illustrated by numerical simulations.

Coordination of Marine Robots Under Tracking Errors and Communication Constraints

This paper presents the development and the experimental validation of a centralized coordination control scheme that is robust to communication constraints and individual tracking errors for a team of possibly heterogeneous marine vehicles. By assuming the existence of a lower level target tracking control layer, a centralized potential-field-based coordination scheme is proposed to drive a team of robots along a path that does not necessarily need to be defined a priori. Furthermore, the formation is allowed to hold its position (the vehicles hold their positions with regard to a static virtual leader), which is particularly appreciated in several marine applications. As it is important to guarantee stability and mission completion in adverse environments with limited communications, the centralized control scheme for coordination is constructed in a way that makes it robust to tracking errors and intermittent communication links. The study and developments presented in this paper are complemented with field experiments in which vehicles have coordinated their operation to keep in formation over a dynamic path and static points. This work considers two types of communication technologies. Firstly, standard high rate radio communications are used to drive the formation and, secondly, acoustic communications are employed to assess the performance and the robustness of the proposed approach to degraded and highly variable conditions.

Distributed control of a network of single integrators with limited angular fields of view

The consensus and containment problems in a multi-agent system consisting of single integrators with angular field of view (FOV) constraints in their sensing capabilities are investigated in this paper. First, it is assumed that all FOVs are half-planes and an impulsive switching strategy is developed such that the underlying sensing graph of the network remains uniformly quasi-strongly connected (UQSC) throughout the system evolution. The control schemes are designed in the framework of switched interconnected systems in such a way that the objectives of consensus and containment are achieved over the entire network. Then, the problem is extended to address a network of single-integrator agents with limited heterogeneous angular FOVs. The FOV of all sensing devices are assumed to rotate with sufficiently large angular velocities, which are controlled independently along with the translational motion of all agents. The velocity vector and the lower bound on the magnitude of the angular velocity of the FOVs are designed such that the agents converge to an arbitrarily small ball, and reach consensus. The convergence of the moving followers to the convex hull of static leaders is addressed for the containment problem as well. Simulation results verify the effectiveness of the proposed control strategies.

Distributed adaptive consensus control of heterogeneous multi‐agent chaotic systems with unknown time delays

In this study, the distributed consensus tracking problem for heterogeneous multi-agent chaotic delayed non-linear systems is addressed. Each follower is modelled as a chaotic system with non-identical and unknown time delays, non-linear dynamics, and disturbances. The general case of directed communication graphs is considered and the graph structure is taken into account in the control protocol design. Distributed controllers with an adaptive learning feature based on neural network approximations are designed to guarantee that all agents synchronise to the leader's state with bounded synchronisation error. A graph-dependent Lyapunov proof provides error bounds that depend on the maximum time delays, the graph topology, and the agent dynamics properties. Special cases of the dynamics considered here cover many examples in the literature, including master–slave synchronisation of two chaotic delayed systems. A simulation with multiple non-identical chaotic agents is given to verify the effectiveness of the proposed method.

Task complexity and transformational leadership: The mediating role of leaders' state core self-evaluations

While substantial scholarly attention has been paid to the beneficial consequences of transformational leadership and the conditions in which this leadership style is most effective, there is a remarkable shortage of research on the contextual antecedents of transformational leadership behavior itself. To address this gap, a laboratory experiment was conducted in which we tested the relationship between task complexity and the emergence of transformational leadership behavior. In this experiment, 111 participants were divided in groups of three (comprising one leader and two subordinates), and were instructed to solve three decision-making tasks with varying levels of task complexity. Results indicated that task complexity was negatively related to transformational leadership behavior, and that this relationship was partially mediated by the leader's state core self-evaluations. In other words, when leaders encounter tasks that are overwhelmingly complex, they act in less transformational ways because they momentarily lack the psychological resources to do so. Limitations and future research directions are discussed.

Consensus of a heterogeneous multi-agent system with input saturation

In this paper, the consensus problem for a class of heterogeneous multi-agent systems with input saturation is investigated. The heterogeneous multi-agent system is composed of first-order agents and second-order agents. We consider that only a few first-order agents are restrained and their control input must be bounded. Firstly, a consensus control protocol under leaderless network is proposed. By applying the graph theory and LaSalle invariance principle, the protocol is proved feasible. Secondly, the consensus problem of heterogeneous multi-agent systems is discussed with a static leader and an active leader, respectively. Particularly, when the velocity of the active leader cannot be obtained in real time, a new neighbour-based consensus control protocol based on distributed observers and auxiliary systems is developed. Some sufficient conditions for consensus are established under fixed undirected connected topology. Finally, some examples were presented to illustrate the theoretical results.

Distributed containment control and state observer design for multi-agent robotic system

Aiming at the distributed containment control problem for multi-agent robotic system with stationary leaders, a position-sensorless control strategy is proposed based on binocular visual servo and feedback dissipative Hamilton theory. Firstly, the topological relationship among the robots is built by using directed graph, which makes each follower determine its neighbour robots. Secondly, a binocular visual servo model is established, so as to describe the dynamic information of the tracking target point for each follower through the neighbour robots' image information. Thirdly, the distributed containment controllers are designed based on the pre-feedback control strategy and feedback dissipative Hamilton theory; furthermore, in the case that each follower is not equipped with internal position sensor, the full-order state observers are developed by using the 'expansion + feedback' method, and then realise the position-sensorless control. Finally, a simulation is carried out on multiple two degrees-of-freedom (DOF) robots, and results show the validity of the proposed control strategy.

Distributed Consensus for Multiple Rigid-Bodies Based on Unit Dual Quaternion

This paper addresses the distributed consensus problem for multiple rigid-bodies under directed communication topology having a spanning tree with the tool of unit dual quaternion. The dynamics of rigid-bodies in 3-D are represented by unit dual quaternion with notion concision and nonsingularity. A distritbuted consensus algorithm is proposed to control attitudes and positions of all rigidbodies to the same values. We also expand the leaderless distributed algorithm to tracking consensus case with a static leader. Finally, the proposed control algorithms are simulated to illustrate the theoretical results.

Distributed control design for leader escort of multi-agent systems

In this paper, we consider two-group leader escort control for multi-agent systems, where the agents are separated into two groups to escort an active leader with the same distance. To escort the moving leader, we propose different distributed controls for different cases: the bounded-leader case and the schedule-based general leader case (under either known or unknown time-varying parameter rotation-schedule). Because some agents may not get access to the leader directly, we construct the distributed controllers to escort the leader by moving symmetrically around the leader under either fixed or switching topologies, based on a distributed observer for each agent to estimate the leader's state. With the help of graph theory and Lyapunov function technique, we prove that the leader escort can be achieved asymptotically by theoretical analysis. Finally, simulation results demonstrate good performance of the proposed protocols.