A Survey of path following control strategies for UAVs focused on quadrotors

The trajectory control problem, defined as making a vehicle follow a pre-established path in space, can be solved by means of trajectory tracking or path following. In the trajectory tracking problem a timed reference position is tracked. The path following approach removes any time dependence of the problem, resulting in many advantages on the control performance and design. An exhaustive review of path following algorithms applied to quadrotor vehicles has been carried out, the most relevant are studied in this paper. Then, four of these algorithms have been implemented and compared in a quadrotor simulation platform: Backstepping and Feedback Linearisation control-oriented algorithms and NLGL and Carrot-Chasing geometric algorithms.Peer ReviewedPostprint (author's final draft

Cooperative Path-Following of Multiple Multirotors over Time-Varying Networks

The article of record as published may be found at https://doi.org/10.1109/TASE.2015.2406758This paper addresses the problem of time-coordina- tion of a team of cooperating multirotor unmanned aerial vehicles that exchange information over a supporting time-varying net- work. A distributed control law is developed to ensure that the vehicles meet the desired temporal assignments of the mission, while flying along predefined collision-free paths, even in the pres- ence of faulty communication networks, temporary link losses, and switching topologies. In this paper, the coordination task is solved by reaching consensus on a suitably defined coordination state. Conditions are derived under which the coordination errors converge to a neighborhood of zero. Simulation and flight test results are presented to validate the theoretical findings

Cooperative autonomous systems: Motion planning and coordinated tracking control for multi-vehicle missions

In this dissertation a framework for planning and control of cooperative autonomous systems is presented, which allows a group of Unmanned Vehicle Systems (UxSs) to generate and follow desired trajectories, while coordinating along them in order to satisfy relative temporal constraints. The described methodology is based on two key results. First, a centralized optimal motion planning algorithm produces a set of feasible and flyable trajectories, which guarantee inter-vehicle safety, while satisfying specific temporal mission requirements, as well as dynamic constraints of the vehicles. Then, a distributed coordinated tracking controller ensures that the vehicles follow the trajectories while coordinating along them in order to arrive at the final destination at the same time, or with a predefined temporal separation, according to the mission requirements. The optimal motion planning problem is formulated as a continuous-time optimal control problem, which is then approximated by a discrete-time formulation using Bernstein polynomials. Using the convergence properties of Bernstein polynomial approximation, the thesis provides a rigorous analysis that shows that the solution to the discrete-time approximation converges to the solution to the continuous-time problem. The motivation behind this approach lies in the fact that Bernstein polynomials possess favorable geometric properties that allow for efficient computation of various constraints along the entire trajectory, and are particularly convenient for generating trajectories for safe operation of multiple vehicles in complex environments. The coordinated tracking algorithm relies on the presence of a virtual target tracking controller which guarantees that the distance between each vehicle and its assigned virtual target running along the desired trajectory remains bounded throughout the mission. Then, the speed of the virtual target is adjusted in order to satisfy the temporal constraints and achieve coordination. The coordination problem is formulated as a consensus problem, with the objective of regulating a suitably defined set of coordination variables to zero. Conditions are derived under which the consensus algorithm proposed solves the coordination problem in the presence of faulty communications and switching topologies