Time-varying formation tracking analysis and design problems for second-order Multi-Agent systems with switching interaction topologies are studied, where the states of the followers form a predefined time-varying formation while tracking the state of the leader. A formation tracking protocol is constructed based on the relative information of the neighboring agents. Necessary and sufficient conditions for Multi-Agent systems with switching interaction topologies to achieve time-varying formation tracking are proposed together with the formation tracking feasibility constraint based on the graph theory. An approach to design the formation tracking protocol is proposed by solving an algebraic Riccati equation, and the stability of the proposed approach is proved using the common Lyapunov stability theory. The obtained results are applied to solve the target enclosing problem of a multiquadrotor unmanned aerial vehicle (UAV) system consisting of one leader (target) quadrotor UAV and three follower quadrotor UAVs. A numerical simulation and an outdoor experiment are presented to demonstrate the effectiveness of the theoretical results.

Time-Varying Formation Tracking for Second-Order Multi-Agent Systems Subjected to Switching Topologies With Application to Quadrotor Formation Flying

Time-varying formation control for unmanned aerial vehicles with switching interaction topologies

NASA's Strategic Plan for the Aerospace Technology Enterprise includes ambitious objectives focused on affordable air travel, reduced emissions, and expanded aviation-system capacity. NASA Dryden Flight Research Center, in cooperation with NASA Ames Research Center, the Boeing Company, and the University of California, Los Angeles, has embarked on an autonomous-formation-flight project that promises to make significant strides towards these goals. For millions of years, birds have taken advantage of the aerodynamic benefit of flying in formation. The traditional "V" formation flown by many species of birds (including gulls, pelicans, and geese) enables each of the trailing birds to fly in the upwash flow field that exists just outboard of the bird immediately ahead in the formation. The result for each trailing bird is a decrease in induced drag and thus a reduction in the energy needed to maintain a given speed. Hence, for migratory birds, formation flight extends the range of the system of birds over the range of birds flying solo. The Autonomous Formation Flight (AFF) Project is seeking to extend this symbiotic relationship to aircraft.

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Autonomous Formation Flight

A major limitation of existing battery-powered quadrotor UAVs is their reduced flight endurance. To address this issue, by leveraging the electrical model of a brushless DC motor, we explicitly determine minimum-energy paths between a predefined initial and final configuration of a quadrotor by solving an optimal control problem with respect to the angular accelerations of the four propellers. As a variation on this problem, if the total energy consumption between two boundary states is fixed, minimum-time and/or minimum-control-effort trajectories are computed for the aerial vehicle. The theory is illustrated for the DJI Phantom 2 quadrotor in three realistic scenarios.

https://hal.archives-ouvertes.fr/hal-01276199/document

Minimum-energy path generation for a quadrotor UAV

A novel onboard relative localization method, based on ultraviolet light, used for real-time control of a leader–follower formation of multirotor UAVs, is presented in this paper. A new smart sensor, UVDAR, is employed in an innovative way, which does not require communication and is extremely reliable in real-world conditions. This innovative sensing system exploits UV spectrum and provides relative position and yaw measurements independently of environment conditions such as changing illumination and the presence of undesirable light sources and their reflections. The proposed approach exploits this retrieved information to steer the follower to a given three-dimensional position and orientation relative to the leader, which may be considered as the main building block of any multi-UAV system operating with small mutual distances among team members. The proposed solution was verified in demanding outdoor conditions, validating the usage of UVDAR in real flight scenario, and paving the way for further usage of UVDAR for practical multi-UAV formation deployments.

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UVDAR System for Visual Relative Localization With Application to Leader–Follower Formations of Multirotor UAVs

In this paper it is presented a control strategy to solve the trajectory tracking and flight formation problem, in horizontal plane, of multiple unmanned aerial vehicles (UAVs) kind quadrotor, by means of a leader-follower scheme. Time scale separation of the translational and rotational quadrotor dynamics is used to achieve trajectory tracking. A sliding mode controller is proposed for the translational dynamic and provides the desired orientation for the UAV, which is controlled by a linear PD control. Finally, from the formation error dynamics, a sliding mode control is used by the follower to preserve the formation with respect to a leader. Experimental results, using a virtual leader and a follower in formation, are shown to evaluate the proposed control law.

/pdf/quadrotors-flight-formation-control-using-a-leader-follower-5adw2hjktb.pdf

D. A. Mercado

Papers

Quadrotors flight formation control using a leader-follower approach