Special focus on formation control of unmanned systems

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An Unmanned System refers to the autonomous agent possessing the capability of basic sensing, communication, data processing and actuation. Formation control of unmanned systems has become one of the most active topics in the past decade. The objective is to drive multiple agents to achieve particular tasks cooperatively. Usually, appropriate reference positions or distances are required to be maintained for the agents to avoid collisions. Based on the cooperative scheme, more complex tasks that a single agent cannot fulfilled can be accomplished by a collection of agents. Up until now, quite a lot of applications of formation control for unmanned systems are witnessed in the areas of logistics, agriculture, military systems, etc., including surveillance, exploration, rescuing, aerial photography and 3D sensing.

2017 No.7 issue of SCIENCE CHINA Information Sciences published a special issue focus on formation control of unmanned Systems. This special focus is expected to present readers with some recent significant achievements on formation control of unmanned systems. Seven excellent papers have been accepted in this special focus to cover up-to-date advances in theoretical design and applications of this research topic.

The survey paper "A survey on recent progress in control of swarm systems" by Bing Zhu et al. introduces some up-to-date progress in the areas of consensus, formation control, flocking, containment, optimal coverage/mission planning, and sensor networks for unmanned systems. Based on the current progress in this area, some new research topics are also suggested.

The research paper "Formation control with disturbance rejection for a class of Lipschitz nonlinear systems" by Chunyan Wang et al. proposes a leader-follower formation control for general multi-agent systems with Lipschitz nonlinearity and unknown disturbances. The time-varying formation control is proposed with the disturbance observer for each follower to address disturbances. The proposed strategy guarantees that all signals in the closed-loop dynamics are uniformly ultimately bounded and the formation errors converge to an arbitrarily small residual set.

In the research paper "Saturated coordinated control of multiple underactuated unmanned surface vehicles over a closed curve" by Lu Liu et al., the proposed formation control is composed by a kinematic control that is designed based on a reduced-order extended state observer to compensate for the effort of the sideslip, and a kinetic control that is developed with the saturated function, the projection operator, and the dynamic surface control. The parameter cyclic pursuit approach is proposed to guarantee that the vehicles are evenly spaced over the closed curve. The input-to-state stability of the closed-loop system is analyzed via cascade theory.

The research paper "Fault-tolerant cooperative control for multiple UAVs based on sliding mode techniques" proposes a fault-tolerant cooperative control for multiple unmanned aerial vehicles, where the outer-loop control and the inner-loop fault accommodation are explicitly considered. In this paper, the reference signals for the inner-loop of the follower UAV is directly produced by resorting to a proportional control. The estimation of the fault information is completed within finite time in presence of actuator faults. The inner-loop control is reconfigured the the fault information adaptation and sliding mode techniques, such that the deleterious effects due to failed actuators can be compensated within finite time.

In the research paper "Simultaneous attack of a stationary target using multiple missiles: a consensus-based approach" by Jialing Zhou et al., a consensus-based approach is proposed to design the cooperative guidance law for simultaneously attacking the stationary target. Time-varying navigation ratios are presented for the missiles to exchange the time-to-go estimates among neighboring missiles via a communication network. It is shown that the cooperative guidance law can solve the simultaneous attack problem where the communication topology is undirected or the navigation ratio cannot be tuned in the leader-follower structure.

The formation control of networked nonholonomic vehicles is considered in the research paper "Leader-follower formation of vehicles with velocity constraints and local coordinate frames" by Xiao Yu and Lu Liu. Two dynamic control laws satisfying the velocity constraints are developed respectively, such that the leader-follower formation defined in local coordinate frames can be achieved in two cases. The proposed control laws only require each vehicle use the information of its neighbors in the network via local measurements and communication.

In the highlight "Tight formation control of multiple unmanned aerial vehicles through an adaptive control method" by Yin Wang and Daobo Wang, a hybrid particle swarm optimization with genetic algorithm is proposed to solve the multi-UAV formation reconfiguration problem, which is modeled as a parameter optimization problem. This new approach combines the advantages of particle swarm optimization and genetic algorithm to determine time-optimal solutions simultaneously.

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All the articles can be found under https://link.springer.com/journal/11432/60/7 and http://engine.scichina.com/doi/10.1007/s11432-016-9008-0 on the official website of SCIENCE CHINA Information Sciences.

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