This paper addresses the problem of steering a group of vehicles along given spatial paths while holding a desired time-varying geometrical formation pattern. The solution to this problem, henceforth referred to as the coordinated path-following (CPF) problem, unfolds in two basic steps. First, a path-following (PF) control law is designed to drive each vehicle to its assigned path, with a nominal speed profile that may be path dependent. This is done by making each vehicle approach a virtual target that moves along the path according to a conveniently defined dynamic law. In the second step, the speeds of the virtual targets (also called coordination states) are adjusted about their nominal values so as to synchronize their positions and achieve, indirectly, vehicle coordination. In the problem formulation, it is explicitly considered that each vehicle transmits its coordination state to a subset of the other vehicles only, as determined by the communications topology adopted. It is shown that the system that is obtained by putting together the PF and coordination subsystems can be naturally viewed as either the feedback or the cascade connection of the latter two. Using this fact and recent results from nonlinear systems and graph theory, conditions are derived under which the PF and the coordination errors are driven to a neighborhood of zero in the presence of communication losses and time delays. Two different situations are considered. The first captures the case where the communication graph is alternately connected and disconnected (brief connectivity losses). The second reflects an operational scenario where the union of the communication graphs over uniform intervals of time remains connected (uniformly connected in mean). To better root the paper in a nontrivial design example, a CPF algorithm is derived for multiple underactuated autonomous underwater vehicles (AUVs). Simulation results are presented and discussed.

This paper addresses the problem of steering a group of underactuated autonomous vehicles along given spatial paths, while holding a desired inter-vehicle formation pattern. For a general class of vehicles moving in either two or three-dimensional space, we show how Lyapunov-based techniques and graph theory can be brought together to yield a decentralized control structure where the dynamics of the cooperating vehicles and the constraints imposed by the topology of the inter-vehicle communications network are explicitly taken into account. Path-following for each vehicle amounts to reducing an appropriately defined geometric error to a small neighborhood of the origin. Vehicle coordination is achieved by adjusting the speed of each vehicle along its path according to information on the positions of a subset of the other vehicles, as determined by the communications topology adopted. The system obtained by putting together the path-following and vehicle coordination strategies adopted takes a cascade form, where the former subsystem is input-to-state stable (ISS) with the error variables of the latter as inputs. Convergence and stability of the overall system are proved formally. The results are also extended to solve the problem of temporary communication failures. Using the concept of "brief instabilities" we show that for a given maximum failure rate, the coordinated path following system is stable and the errors converge to a small neighborhood of the origin. We illustrate our design procedure for underwater vehicles moving in three-dimensional space. Simulations results are presented and discussed

This paper addresses the development of a vision-based target tracking system for a small unmanned air vehicle. The algorithm performs autonomous tracking of a moving target, while simultaneously estimating GPS coordinates of the target. A low cost off the shelf system is utilized, with a modified radio controlled aircraft airframe, gas engine and servos. Tracking is enabled using a low-cost, miniature pan-tilt gimbal. The control algorithm provides rapid and sustained target acquisition and tracking capability. A target position estimator was designed and shown to provide reasonable targeting accuracy. The impact of target loss events on the control and estimation algorithms is analyzed in detail

The paper proposes a solution to the problem of coordinated control of multiple unmanned air vehicle (UAV) to ensure collision-free maneuvers under strict spatial and temporal constraints. First, a set of feasible trajectories are generated for all UAVs using a new direct method of optimal control that takes into account rules for collision avoidance. A by-product of this step yields, for each vehicle, a spatial path to be followed together with a nominal desired speed profile. Each vehicle is then made to execute a pure path following maneuver in three-dimensional space by resorting to a novel 3D algorithm. Finally, the speed profile for each vehicle is adjusted to enforce the temporal constraints that must be met in order to coordinate the fleet of vehicles. Simulations illustrate the potential of the methodology developed