Special focus on formation control of unmanned systems
An unmanned system is an autonomous agent with the capabilities of basic sensing, communication, data processing and actuation. One major objective is to drive multiple agents to achieve particular tasks cooperatively. Usually, appropriate reference positions or distances are required for the agents to avoid collisions. In a cooperative scheme, more complex tasks that a single agent cannot fulfill can be accomplished by a collection of agents. Formation control for unmanned systems has applications in the areas of logistics, agriculture and military systems,including surveillance, exploration, rescue, aerial photography and 3-D sensing.
In July, SCIENCE CHINA Information Sciences published a special issue focused on formation control of unmanned systems. Seven papers were accepted covering up-to-date advances in theoretical design and applications of this research topic.
"A survey on recent progress in control of swarm systems," by Bing Zhu et al., reports 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.
More information:
link.springer.com/journal/11432/60/7
Provided by Science China Press