Research On Control For Coordinated Circumnavigation With Multi-robot Systems

Circumnavigation about a target means that the robot surrounds it with prescribed radius and circular velocity.The prescribed distance needs to be within the detection range of the onboard sensor and outside the target threat range.The circumnavigation allows the robot to continuously monitor and fully cover the target.Multi-robot systems can coordinated circumnavigate the target by changing the individual position and information exchange to improve the accuracy of tracking and observation.In recent years,the circumnavigate problem has attracted considerable research interest due to its wide application in target detection and environmental monitoring.The design of the controller for circumnavigation with limited information interaction need to be further discussed to make it more practical and realistic.This thesis focuses on the coordinated circumnavigation problem for different multi-robot systems and different tasks.All robots are required to circumnavigate a moving targets with prescribed formation and circular velocity.Furthermore,we consider the controller design to improve the dynamic performance of the circumnavigation system.The main contributions of this doctoral dissertation are summarized as follows:(1)The coordinated circumnavigation problem for multi-robot systems is investigated,in which the information of the target is only known to a subset of the robots and the topology of the robot network is described by a directed graph.A distributed observer-based controller is proposed to steer the robots,such that they can surround the target with prescribed formation and circular velocity under the velocity constraints.Firstly,for the case of the target information is globally available,a decentralized controller is developed with the saturation function based on nonlinear system stability and algebraic graph theory.It enables all robots to coordinated circumnavigate the target with the velocity constraints.Furthermore,for the case of a subset of robots have access to the target information dynamically,a distributed observer-based control law is designed and the global uniform stability of the entire system is analyzed using the cascaded control theory.The proposed control scheme reduces the requirements of the sensors and communication devices.It also improves the flexibility of the system.(2)In order to improve the dynamic performance of the circumnavigation system,a distributed finitetime controller is proposed,in which the information of the target is only known to a subset of the robots and the velocity constraints are considered.Firstly,for the single robot case,a finitetime controller with the saturation function is designed based on the finitetime theory.Secondly,a decentralized finitetime controller is proposed using the finitetime consensus theory under a directed topology.It enables all robots to coordinated circumnavigate the target with the velocity constraints in finite time.Furthermore,for the case of a subset of robots have access to the target information dynamically,a distributed finitetime observer-based control law is designed.The global uniform finitetime stability of the entire system is analyzed using the finitetime cascaded control theory.The proposed control scheme reduces the requirements of the sensors and communication devices.It also improves the dynamic performance and flexibility of the system.(3)The problem of coordinated circumnavigation with multiple non-holonomic robots is discussed,in which the information of the target is only known to a subset of the robots.A distributed observer-based controller is proposed to steer the non-holonomic robots to surround the target with prescribed formation and circular velocity under a directed topology.Firstly,for the case of the target information is globally available,according to the model of the circumnavigation system in polar coordinate,a controller is designed to force each robot surrounds a target with prescribed radii and circular velocity by backstepping.Secondly,we propose a decentralized controller for the coordinated circumnavigation problem based on the nonlinear system stability and algebraic graph theory.Furthermore,for the case of a subset of non-holonomic robots have access to the target information dynamically,a distributed observer-based control scheme is designed and the global uniform stability of the entire system is analyzed using the cascaded control theory.The proposed control scheme reduces the requirements of the sensors and communication devices.It also improves the flexibility of the system.(4)For a class of heterogeneous multi-robot systems that can be transformed into heterogeneous second-order models,a decentralized finitetime coordinated circumnavigation control scheme is proposed under a directed topology,in which all robots are required to surround a moving target with prescribed formation and circular velocity in finite time.Firstly,based on the kinematic model of the robots,the coordinated circumnavigation problem with heterogeneous multi-robot systems is transformed into a class of nonlinear cascade system stability problem by feedback linearization.Then,a decentralized controller is designed for the coordinated circumnavigation problem by backstepping and algebraic graph theory.Furthermore,using adding a power integrator technique and finitetime consensus theory,a finitetime controller is proposed for the finitetime coordinated circumnavigation problem with heterogeneous multi-robot systems.The proposed control scheme improves the dynamic performance and flexibility of the system.