Cooperative Moving Target Fencing Control for Two-Layer UAVs With Relative Measurements

This paper investigates a two-layer distributed control protocol for multiple unmanned aerial vehicles (UAVs) to fence a moving target cooperatively, using relative measurements. The multi-UAVs are divided into two layers: one is equipped with target detection sensors that can acquire relative bearing information; the other is equipped with relative distance sensors that can only acquire relative positions of neighbors. First, a bearing-based controller is presented for the leader layer to eliminate the singularity problem of observability of a moving target. Then, a distance-based controller is developed to fence the moving target within a convex hull at every moment for the follower layer. The relative spacing within the formation does not need to be given in advance, and the rotation and scaling of the formation can be quickly adjusted according to the design parameters. Third, we prove sufficient conditions for the design of the formation configuration, together with the selection of the fencing scale. The fencing protocol can be directly extended to 3-D space, and the form of the controller for 3-D scenarios is given as well. Finally, two numerical simulations and a hardware-in-loop (HIL) experiment verify the effectiveness of the proposed protocol.
Note to Practitioners
—This paper was motivated by the problem of cooperative moving target fencing control for multiple fixed-wing UAVs. In many practical missions, for instance, multiple UAVs protect a critical target or entrap an intruder target, it is typical that multiple fixed-wing UAVs encircle a moving target. Additionally, it may occur with communication limitations and the absence of global information in some complex environments, and the moving target may be non-cooperative. This would lead to existing fencing methods failing to be applied, which require communication to share information about the target and UAVs. A two-layer control frame is presented to address this problem. We use onboard sensors (target detection sensors for the leader layer and relative distance sensors for the follower layer) to obtain relative measurements of the moving target and other UAVs, removing communication and global information constraints. Then, a scale factor is introduced to make the proposed protocol widely applicable in narrow areas or places with obstructed views, driving the formation translating, rotating, and scaling with the movement of the target. The proposed protocol guarantees that the moving target is encircled by the convex hull formed by multiple UAVs, and it can be extended to 3-D space directly. In future research, we will perform the proposed protocol in practice.