Coordinated 3D path following control for a team of UAVs with reference velocity recovery

In this paper we develop new type of control law to steer a group of multiple unmanned air vehicles (UAVs) along given spacial paths (path-following), while ensuring that they reach and maintain a desired formation pattern. The methodology utilized to derive the cooperative path following controller unfolds in two basic steps. First, a path-following control law is derived based on the use of the 3D Serret-Frenet formulation to represent the UAV kinematics in terms of path parameters, which allows for convenient definition of cross, along and vertical-track error, to steer each vehicle to its assigned path regardless of the speed profile adopted. In second step, the speeds of the UAVs are adjusted so as to synchronize, the position of the corresponding UAVs. Unlike previews research work designs that assume availability of the reference velocity to each UAVs, we consider the situation where this information is only available to a leader of this formation. The control scheme relies on an adaptive design to estimate the reference velocity which the other UAVs need to reconstruct to recover the desired formation.