Leader-follower Control Research Articles

Affine formation control for multi-agent systems with prescribed convergence time

In this paper, the affine formation control problem for multi-agent systems with prescribed convergence time is investigated. Firstly, on the basis of a time-varying scaling function, a distributed continuous control algorithm is designed, under which a stationary affine formation of the nominal configuration is able to be achieved within a prescribed time. Secondly, to track a time-varying formation within the prescribed time, a distributed control protocol is proposed by employing a leader–follower control strategy. Furthermore, the boundary layer technique is adopted to avoid chattering effect. Finally, simulation examples are provided to demonstrated the effectiveness of the proposed design.

Event-Triggered/Self-Triggered Leader-Following Control of Stochastic Nonlinear Multiagent Systems Using High-Gain Method.

In this article, the event-triggered and self-triggered leader-following output-feedback control problems are investigated for a class of high-order stochastic nonlinear multiagent systems (MASs) under an undirected graph. First, using the high-gain method, the observer is designed to estimate the unmeasured state variables of the given nonlinear system. Then, by introducing an internal dynamic variable, a distributed Zeno-free dynamic event-triggered controller is constructed. Compared with the static event-triggering results, the interevent time of the proposed dynamic event-triggering mechanism is shown to be prolonged and, thus, the advantages of the event-triggered control approaches can be enhanced. Further, to avoid continuously monitoring the states, a Zeno-free self-triggering mechanism is given. It is shown that the expectations of the output tracking errors converge to an arbitrarily small set if the diffusion terms are different for all agents, and that the expectations of all state tracking errors converge to an arbitrarily small set if the diffusion terms are the same for all agents. Finally, simulation studies are given to illustrate the effectiveness of the proposed methods.

A simple two-agent system for multi-objective flexible job-shop scheduling

In this paper, a simple two-agent multi-objective scheduling system for flexible job-shop scheduling problem is proposed and corresponding framework is given. Under the framework, a broadcast communication mechanism with task mark and leader–follower control mode are designed and used to ensure orderly activities among agents. To obtain initial solution and improve it, competition and cooperation strategies are developed. To jump out of the local optimal solution and expend the search space, an adaptive iterative loop solving mechanism is designed. Three commonly used benchmark instance sets are adopted to test the performance of the proposed method. Computation results and comparison analysis with other excellent algorithms demonstrate that it is feasible and effective.

Locally operated assistant manipulators with selectable connection system for robotically assisted laparoscopic solo surgery.

By integrating locally operated surgical assistant robots in a sterilized area, a surgeon can perform safe robotically assisted laparoscopic solo surgery while controlling a laparoscope-holding robot and a forceps robot. At present, there is no leader-follower control system with switchable connection for the leader device in which each assistant follower robot can provide the manipulation intuitively and easily. In the present study, a new locally operated leader-follower selectable control system has been developed. The leader-follower system was developed to connect one leader operating device and one of two selectable follower assistant manipulator devices with different numbers of axes, kinematics models, sensors, and actuators for view stabilization and pulling organs. The system is constructed using the middleware of the ORiN-based medical robot architecture MRLink. The system is regulated by the robot integrator application with unilateral leader-follower PTP using the relative displacement between the leader device and the selected follower device through providers of device interface including the information and control commands. The execution cycle for updating the position was 50ms, and the time delay to catch up with the same position was 100ms. Two assistant manipulators controlled by the leader-follower selectable system could successfully produce the desired view and handle the target organ model for 17min in a simulated laparoscopic cholecystectomy. A locally operated leader-follower selectable control system was constructed to facilitate minimally invasive, robotically assisted laparoscopic solo surgery by a doctor working near the patient. This system could be used for such applications.

Robust Formation Control Based on Leader-Following Consensus in Multi-Agent Systems With Faults in the Information Exchange: Application in a Fleet of Unmanned Aerial Vehicles

In this paper, a robust leader-following consensus protocol for multi-agent systems (MASs) subject to faults in the information exchange and disturbance is presented. The problem under consideration is to guarantee the convergence of the agent trajectories to a leader agent when all the agent followers are under faults in the information exchange as smooth time-varying delays and disturbances. The main contribution in this paper is the design of a robust leader-following control through the Lyapunov approach and an optimal \mathscr H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> criterion such that all agents follow a virtual leader agent despite faults in the information exchange and disturbances. Linear matrix inequalities (LMIs)-based conditions are obtained whose solution allows computing the robust controller gain. In order to show the effectiveness of the proposed approach, numerical examples are carried out comparing a state-of-the-art approach and the proposed strategy in a fleet of unmanned aerial vehicles (UAVs) subject to wind turbulence which are shown to achieve the formation control.

Three-Dimensional Fixed-Time Cooperative Guidance Law With Impact Angle Constraint and Prespecified Impact Time

In this paper, by utilizing fixed-time control technique and a leader-follower control scheme, a three-dimensional (3-D) cooperative guidance law is developed to tackle impact angle constrained simultaneous arrival problem. Firstly, in the line-of-sight (LOS) direction, guidance command for the leader is put forward to make impact time error converge to zero in fixed time such that the leader is capable of reaching the target at prespecified impact time. Then, guidance command for each follower is designed based on information from adjacent interceptors to guarantee each follower’s impact time achieves consensus with that of the leader. Secondly, in the azimuth direction and elevation direction of the LOS, guidance commands are put forward to nullify the LOS angular rates within fixed time. Then, the interceptors are able to reach the target with desired impact angles. Meanwhile, the cooperative guidance law’s fixed-time convergence is rigorously proved by Lyapunov stability theory. Finally, simulations are given to illustrate the effectiveness of the theoretical results.

Resiliency in dynamic leader–follower multiagent systems

Resilient control of multiagent systems (MASs) in the presence of dynamic leaders is studied in this paper. We consider a network of agents consisting of a leader, a set of healthy agents, and a set of attacked malicious agents. The objective is developing a control strategy for the healthy agents to follow the trajectory of the leader, while they are in interaction with the unknown malicious agents. The main contribution of this paper is resilient leader–follower control of MASs when a dynamic leader determines a continuous time-varying trajectory for the MAS. By defining the concept of r-robust leader–follower graphs, we propose and analyze sufficient conditions on interaction among the agents such that the mentioned objective is achieved. Numerical examples verify the accuracy of the proposed control scheme.

Adaptive Leader–Follower Formation Control of Underactuated Surface Vehicles With Guaranteed Performance

This article studies the formation tracking control problem for a group of underactuated surface vehicles with guaranteed transient properties, including connectivity maintenance, collision avoidance, and tracking performance specifications. The formation is within the leader–follower control framework, in which every follower is controlled to track its leader and maintain a desired relative distance and bearing angle with respect to its leader such that the prescribed formation geometry is achieved based on local sensing capability. The onboard sensor systems are of limited range and angle of view, thus defining a cone of detectable region for every follower. Each follower can detect its leader, if and only if the relative distance and bearing angle keep always inside the predefined detectable region such that the connectivity between the follower and its leader is maintained over time. In addition to the consideration of connectivity maintenance, no collision between the follower and its leader is also considered. A transverse function control approach is introduced to overcome the difficulties caused by the off-diagonal system matrix and underactuation. The barrier Lyapunov function and adaptive backstepping procedure are incorporated into the formation control design to achieve the boundedness of the closed-loop systems with guaranteed transient performance. Collision avoidance and connectivity maintenance between every follower and its leader are also proven mathematically. Simulation studies are performed to show the effectiveness of the proposed control design technique.

Decentralized aggregation and leader-following control of a swarm of quadcopters with nonlinear under-actuated dynamics

This paper studies the decentralized control of a swarm of quadrotors on the basis of the nonlinear, highly-coupled, and under-actuated dynamic model of quadcopters. The swarm of quadcopters must illustrate the desired swarm behavior as fast as possible while collision avoidance is preserved during the entire evolution process. The interaction relationship among the swarm members is modeled by artificial potential functions and according to the nearest neighbor rule. The sliding mode control technique is employed to control the velocity of quadcopters in the swarm. Finally, two fundamental swarm behaviors, i.e. swarm aggregation and leader-following, are numerically simulated to demonstrate the efficacy of the proposed algorithm.

Hierarchical Decomposition-Based Distributed Full States Tracking Consensus for High-Order Nonlinear Multiagent Systems

This article studies the distributed adaptive leader-following control for high-order time-varying nonlinear multiagent systems (MASs) with uncertain parameters. The state feedback protocol and output feedback protocol are proposed, respectively, to render all states consensus errors to converge to zero asymptotically. First, the hierarchical decomposition algorithm is used to construct a refreshed communication graph to address the mutual dependence problem of controllers. Then, by introducing a local neighborhood consensus errors-based transformation, the leader-following consensus problem is converted into the stabilization problem for the consensus error system. Using the backstepping method and tuning function technique, the distributed adaptive state feedback controller is designed to render all followers' states to track the leader's ones. Further, by constructing the reduced-order dynamic gain k-filter to estimate unmeasured states, a distributed adaptive output feedback controller is designed. In both controller design methods, the traditional Lipschitz condition need not be satisfied any more for all time-varying nonlinear functions, and different from most of the existing results on the high-order nonlinear MASs, full states consensus can be obtained. Finally, a general numerical example is given to illustrate the effectiveness of the proposed methods.

Formation control of first-order multi-agents with region constraint

ABSTRACT Formation problem of multi-agents systems has been investigated studied by more and more scientists. This paper studies the formation problem of the first-order multi-agent systems with region constraint. Not only formation control but also the constraint area is considered. The state of each agent is constrained by a common convex set. A formation control protocol is proposed based on the local information of neighbourhood and region constraint. If the communication topology is connected, and the target framework is rigid, all agents would enter the target area while reaching the desired formation. The convergence of the formation control to the final formation is guaranteed as proven by Lyapunov framework. Compared with the leader follower controller, the controller does not depend on the leader and has good robustness. In addition, the controller can quickly and accurately control all agents to all agents to enter the constrained area. Finally, the results are illustrated by numerical simulations.

Multi-UAV surveillance implementation under hierarchical dynamic task scheduling architecture

In this paper, we consider a multi-UAV surveillance scenario where a team of unmanned aerial vehicles (UAVs) synchronously covers an area for monitoring the ground conditions. In this scenario, we adopt the leader-follower control mode and propose a modified Lyapunov guidance vector field (LGVF) approach for improving the precision of surveillance trajectory tracking. Then, in order to adopt to poor communication conditions, we propose a prediction-based synchronization method for keeping the formation consistently. Moreover, in order to adapt the multi-UAV system to dynamic and uncertain environment, this paper proposes a hierarchical dynamic task scheduling architecture. In this architecture, we firstly classify all the algorithms that perform tasks according to their functions, and then modularize the algorithms based on plugin technology. Afterwards, integrating the behavior model and plugin technique, this paper designs a three-layer control flow, which can efficiently achieve dynamic task scheduling. In order to verify the effectiveness of our architecture, we consider a multi-UAV traffic monitoring scenario and design several cases to demonstrate the online adjustment from three levels, respectively.

Bearing-Only Formation Control With Prespecified Convergence Time.

This article considers the bearing-only formation control problem, where the control of each agent only relies on relative bearings of their neighbors. A new control law is proposed to achieve target formations in finite time. Different from the existing results, the control law is based on a time-varying scaling gain. Hence, the convergence time can be arbitrarily chosen by users, and the derivative of the control input is continuous. Furthermore, sufficient conditions are given to guarantee almost global convergence and interagent collision avoidance. Then, a leader-follower control structure is proposed to achieve global convergence. By exploring the properties of the bearing Laplacian matrix, the collision avoidance and smooth control input are preserved. A multirobot hardware platform is designed to validate the theoretical results. Both simulation and experimental results demonstrate the effectiveness of our design.

Reduced-order observer-based robust leader-following control of heterogeneous discrete-time multi-agent systems with system uncertainties

In this paper, the leader-following control of heterogeneous discrete-time multi-agent systems (HD_MASs) in the presence of system uncertainties under directed topology is addressed. It aims to achieve reference tracking, disturbance rejection and robust control while the references and disturbances are generated by an autonomous exosystem. In practice, these agents are often different types of devices, thus they have different internal dynamics. Moreover, it is difficult to measure all states of each aircraft due to high cost or technical limitation. In this case, a novel leader-following output consensus problem is formulated and solved in this paper. Firstly, an appropriate linear transformation is proposed to divide the state information of each agent into measurable and unmeasurable parts. Then the reduced-order observer is designed only for unmeasurable parts. Based on the designed observer, the distributed feedback controller is proposed such that the outputs of all followers reach the same trajectory with the leader. In light of the internal model principle and discrete-time algebraic Riccati equation, the robust leader-following consensus of HD_MASs is achieved. Furthermore, this paper extends the results to continuous-time multi-agent systems. Finally, several simulation experiments are presented to verify the effectiveness of the theoretical results.

Decouple design of leader-following consensus control for nonlinear multi-agent systems

This paper addresses the -consensus control problem for a class of discrete-time nonlinear multi-agent systems with missing measurements. First of all, the multi-agent systems under consideration are composed of N followers and a leader, where all agents are of nonlinear characteristics and all followers need to track the leader. Next, the measurements of all agents are not reliable, which could cause the occurrence of the missing measurements. In order to mitigate the computation burden stemming from the complicated couplings among the agents, the spectral decomposition and coordinate transformation are introduced to decouple the closed-loop systems into multiple independent subsystems. Then, a sufficient condition is established for the existence of the -consensus controller ensuring that the closed-loop multi-agent system achieves the -consensus performance by means of the Lyapunov stability theory. Besides, the controller parameters are obtained by solving some linear matrix inequalities. Finally, a simulation example is utilized to illustrate the effectiveness of the proposed control algorithm.

Dynamic Self-Organizing Leader-Follower Control in a Swarm Mobile Robots System Under Limited Communication

The leader-follower model is found efficient for robot swarm exploration tasks. When a swarm of mobile robots collaboratively explore an unknown environment with limited communication, such as communication delay or even message loss, it is necessary to adaptively re-group robots according to the dynamic communication conditions and task goals. In this paper, we propose to analyze the leader-follower topology in a graph fashion and employ Ratio Cut of the proposed graph for membership re-assignment. We take each robot as a node and consider both the communication delay and the goal, i.e., exploring towards unknown area, as the edge weight. Then we use the Laplacian matrix to bipartition the graph repeatedly to optimize group partition. Simulation results validate the effectiveness of the proposed method.

Leader-Follower Mobile Robots Control Based on Light Source Detection

This paper deals with the leader-following control of multiple autonomous mobile robots based on a new sensing method. In this method, we have mounted a light source on the leader robot and installed a photovoltaic sensor at the front end of the follower robot. The photovoltaic sensor consisting of seven micro solar modules acts as a light sensor for the follower robot which helps it to move in accordance with the leader robot by detecting the light source of the leader robot. From the relative angle measurement and ultrasonic measurement of the relative distance, angle offset and distance information between leader robot and follower robot can be estimated. Then, based on an intuitive control method for angle steering proposed in this paper, the follower robot can be controlled smoothly to achieve leader following purpose. The new leader-following control method could overcome the disadvantages of other existing formation control methods. The experimental results show that the leader following based on light source tracking is a comparatively efficient, accurate, and cost-effective method.

Distributed control plane for safe cooperative vehicular cyber physical systems

Cooperative vehicular cyber physical systems build a group of entities that can accomplish a cooperative task using the distributed control approaches. To this end, such a cooperative task can be coordinated and managed by a distributed control plane that will be able to encapsulate all the required functionality in a layered architecture providing the required interoperability. Here, the authors propose such a distributed control plane that consists of the cooperative awareness layer, the communication layer and the distributed control layer. Wireless communications play an important role for the mobility provision, taking into account different constraints in order to provide high reliability and low latency. A simulation environment is considered with a leader–follower control format, where the reliability is evaluated. Further, a distributed safety monitoring approach is devised, given a control diagram and mapping of the events to the different components. The event monitoring relies on the self-triggered approach, where a use case is evaluated to highlight the impact of the input and output delays to the model predictive control component of the overall distributed control diagram including the calculation of the number of triggered events.

Leader-Following Control System Design for a Towed Vessel by Tugboat

Leader-Following Control System Design for a Towed Vessel by Tugboat

Distance-Based Cooperative Relative Localization for Leader-Following Control of MAVs

In multi-robot systems, the capability of each robot to relatively localize its neighbors is a crucial requirement, which needs to be resolved as a prerequisite for almost any distributed scheme of operation. Notably, this problem proves to be quite challenging in GPS-denied environments. In this letter, we investigate a problem of simultaneous relative localization and leader-following control of aerial robots by using only ranging and odometry sensors, waiving the need of external positioning systems. To tackle this challenge, we propose a cooperative estimation-control scheme where specialized agents called orbiters are tasked with maintaining persistently exciting trajectories to facilitate exponential convergence of both relative localization and tracking errors for itself and others. Numerical simulations and experiments on quadcopters in a GPS-denied environment are carried out to validate the theoretical findings.