Design and Implementation of a Range-Based Formation Controller for Marine Robots

There is considerable worldwide interest in the use of groups of autonomous marine vehicles to carry our challenging mission scenarios, of which marine habitat mapping of complex, non-structured environments is a representative example. Relative positioning and formation control becomes mandatory in many of the missions envisioned, which require the concerted operation of multiple marine vehicles carrying distinct, yet complementary sensor suites. However, the constraints placed by the underwater medium make it hard to both communicate and localise the vehicles, even in relation to each other, let alone maintain them in a formation. As a contribution to overcoming some of these problems, this paper deals with the problem of keeping an autonomous marine vehicle in a moving triangular formation with respect to two leader vehicles. Simple feedback laws are derived to drive a controlled vehicle to its intended position in the formation using acoustic ranges obtained to the leading vehicles with no knowledge of the formation path. The paper discusses the implementation of this solution in the MEDUSA class of autonomous marine vehicles operated by IST and describes the results of trials with these vehicles exchanging information and ranges over an acoustic network

Nonlinear Coordinated Path Following Control of Multiple Wheeled Robots with Bidirectional Communication Constraints

The paper presents a solution to the problem of steering a group of wheeled robots along given spatial paths, while holding a desired inter-vehicle formation pattern. This problem arises for example when multiple robots are required to search a given area in cooperation. The solution proposed addresses explicitly the dynamics of the cooperating robots and the constraints imposed by the topology of the inter-vehicle communications network. Lyapunov-based techniques and graph theory are brought together to yield a decentralized control structure where the information exchanged among the robots is kept at a minimum. With the set-up proposed, path following (in space) and inter-vehicle coordination (in time) are essentially decoupled. Path following for each vehicle amounts to reducing a conveniently defined error variable to zero. Vehicle coordination is achieved by adjusting the speed of each of the vehicles along its path according to information on the positions and speeds of a subset of the other vehicles, as determined by the communications topology adopted. Simulations illustrate the efficacy of the solution proposed.Portuguese FCT POSI programme under framework QCA IIIproject MAYA-Sub of the AdIPortuguese FCT POSI programme under framework QCA IIIproject MAYA-Sub of the Ad

Coordinated Path Following in the Presence of Communication Losses and Time Delays

SIAM Journal of Control Optimization, Vol 48, No 1, pp 234-26

Coordinated Path Following in the Presence of Commmunication Losses and Time Delays

SIAM Journal of Control Optimization, Vol 48, No 1, pp 234-265This paper addresses the problem of steering a group of vehicles along given spa- tial 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 ad- justed 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, con- ditions 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 con- sidered. 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

Coordinated Path Following of Multiple UAVs for Time-Critical Missions in the Presence of Time-Varying Communication Topologies

We address the problem of steering multiple unmanned air vehicles (UAVs) along given paths (path-following) under strict temporal coordination constraints requiring, for example, that the vehicles arrive at their final destinations at exactly the same time. Pathfollowing relies on a nonlinear Lyapunov based control strategy derived at the kinematic level with the augmentation of existing autopilots with L1 adaptive output feedback control laws to obtain inner-outer loop control structures with guaranteed performance. Multiple vehicle timecritical coordination is achieved by enforcing temporal constraints on the speed profiles of the vehicles along their paths in response to information exchanged over a dynamic communication network. We consider that each vehicle transmits its coordination state to only a subset of the other vehicles, as determined by the communications topology adopted. We address explicitly the case where the communication graph that captures the underlying communication network topology may be disconnected during some interval of time (or may even fail to be connected at any instant of time) and provide conditions under which the closed-loop system is stable. Flight test results obtained at Camp Roberts, CA in 2008 and hardware-in-the-loop (HITL) simulations demonstrate the benefits of the algorithms developed

Time-Critical Cooperative Path Following of Multiple UAVs over Time-Varying Networks

submitted to AIAA Journal of Guidance, Control and Dynamic

Reactive Safe Path Following for Differential Drive Mobile Robots Using Control Barrier Functions : 2022 10th International Conference on Control, Mechatronics and Automation (ICCMA)

acceptedVersionPeer reviewe

Time-Critical Cooperative Path Following of Multiple UAVs: Case Studies

This paper describes a multi-vehicle motion control framework for time-critical cooperative missions and evaluates its performance by considering two case stud- ies: a simultaneous arrival mission scenario and a sequential auto-landing of a fleet of UAVs. In the adopted setup, the UAVs are assigned nominal spatial paths and speed profiles along those, and the vehicles are then tasked to execute co- operative path following, rather than “open-loop” trajectory-tracking maneuvers. This cooperative strategy yields robust behavior against external disturbances by allowing the UAVs to negotiate their speeds along the paths in response to coordi- nation information exchanged over the supporting communications network. The approach applies to teams of heterogeneous vehicles and does not necessarily lead to swarming behavior