Triangular formation control using range measurements: an application to marine robotic vehicles

This paper addresses the problem of maintaining an autonomous robotic vehicle in a moving triangular formation by regulating its position with respect to two leader vehicles. The robotic vehicle has no a priori knowledge of the path described by the leaders and its goal is to follow them by constantly regulating the inter-vehicle distances to a desired fixed value, using range-only measurements. To solve this station keeping problem, we propose a control strategy that estimates the formation speed and heading from the ranges obtained to the two leading vehicles, and uses simple feedback laws for speed and heading commands to drive suitably defined common and differential errors to zero. For straight-line motion, we provide guaranteed conditions under which the proposed control strategy achieves local convergence of the distance errors to zero. We also indicate how our design procedure can be extended to full dynamic models of marine robotic vehicles equipped with inner loops for yaw and speed control. Simulation results using realistic models are described and discussed

A Packet Loss Compliant Logic-Based Communication Algorithm for Cooperative Path-Following Control

We introduce an event driven communication logic for decentralized control of a network of robotic vehicles (agents). The strategy proposed is robust to packet losses and drives the vehicles to predefined paths while holding a desired geometric formation pattern. To this effect, the paper extends an existing cooperative path following framework to consider the practical case where communications among the vehicles occur at discrete instants, instead of continuously. The introduced communication logic takes into account the topology of the communication network, the fact that communications are discrete, and the cost of exchanging information. We also address explicitly communication losses and bounded delays. Conditions are derived under which the overall closed loop system is input-to-state practically stable. The communication logic is applied to a cooperative path-following control system of multiple underactuated autonomous marine robots. Simulation results are presented and discussed

FTIR-chemometric analytical methodology as a tool for clustering oils from centenarian olive trees grown in the Côa Valley region

The centenarian olive trees are part of the historical and cultural heritage of the Côa Valley region where a significant number of these specimens can be found. They have high importance in olive grove heritage; however, their genetic and phenotypic diversity is still poorly studied. Recently, Fourier Transform Infrared (FTIR) spectroscopy start to be widely used in several studies in the food field, becoming a powerful analytical tool for the analysis of edible oils and fats. This technique has numerous advantages, allowing a fast and non-destructive analysis, and requiring minimal sample preparation. In this context, FTIR has been applied to classify and identify different fats, detection of virgin olive oils adulteration, determination of trans fatty acids and evaluation of oil mixtures' composition in foods, all this based on the spectral profiles. Considering that there is a great diversity of centenarian olive trees in which the varieties are unknown, the objective of this work was to use the FTIR technique to identify groups of olive oils with similar chemical characteristics, thus reducing the time and required amount of samples for analysis.The authors are grateful to the Foundation for Science and Technology (FCT, Portugal) for financial support by national funds FCT/MCTES to CIMO (UIDB/00690/2020) and to Associate Laboratory for Green Chemistry-LAQV (UIDB/50006/2020). Nuno Rodrigues and Aran Santamaria-Echar thanks to National funding by FCT- Foundation for Science and Technology, P.I., through the institutional scientific employment program-contract. This work was financially supported by the project “COA/BRB/0035/2019” OLIVECOA - Centenarian olive trees of Côa Valley region: rediscovering the past to valorise the future funded by the Foundation for Science and Technology (FCT, Portugal).info:eu-repo/semantics/publishedVersio

A Graph-Based Formation Algorithm for Odor Plume Tracing

Odor plume tracing is a challenging robotics application, made difficult by the combination of the patchy characteristics of odor distribution and the slow response of the available sensors. This work proposes a graph-based formation control algorithm to coordinate a group of small robots equipped with odor sensors, with the goal of tracing an odor plume to its source. This approach makes it possible to organize the robots in arbitrary and evolving formation shapes, with the aim of improving tracking performance. The algorithm was evaluated in a high-fidelity submicroscopic simulator, using different formations and achieving quick convergence and negligible distance overhead in laminar wind flows

Detection of mooring line failures using Dynamic Hypothesis Testing

This article proposes a novel methodology for the detection of mooring line breakage in thruster assisted position mooring (PM) systems, when no measurements of the tensions on the mooring lines are available. For dynamic positioning (DP) of marine vessels moored to the seabed via a turret-based spread mooring system, thrusters provide only complementary assistance to the mooring system, which is responsible for generating a large part of the forces and moments required for station keeping. However, in extreme weather conditions thruster assistance is essential to avoid mooring line failure. Once a mooring line is parted, the remaining lines must withstand an increase in the tension forces required to compensate for the lost tension in the ruptured line. This in turn may lead to a cascade breakage of the mooring lines. Hence, it is of paramount importance to detect any line breakage as soon as it occurs to compensate for the lost tension by proper use of DP thruster assistance. As a contribution to solving this problem, in this paper we propose a methodology that builds on Dynamic Hypothesis Testing (DHT) whereby a set of hypotheses are assessed, at each sampling time, using the measured inputs and outputs of the thruster assisted position mooring system. While the first hypothesis corresponds to the assumption that all mooring lines are intact, the remaining hypotheses are built assuming that a single, or multiple line breakage events have taken place. At each sampling time, the inputs and outputs to the system are used to generate the conditional probability of each hypothesis being true. The conditional probabilities are then used to evaluate which hypothesis is more probable to be compatible with the collected measurements. In addition, we find conditions for any pair of hypothesis to be distinguishable. Numerical simulations, carried out using a high fidelity nonlinear PM simulator, illustrate the efficiency of the proposed methodology.Detection of mooring line failures using Dynamic Hypothesis TestingThis work was supported in part by FCT [UID/EEA/50009/2013] and the European Commission under the H2020-ICT-2014 WiMUST Project (Grant Agreement No. 645141) and was the result of a collaborative effort between ISR/IST and AMOS; the Norwegian Research Council is acknowledged as the main sponsor of AMOS.acceptedVersio

Linear Parametrically Varying Systems with Brief Instabilities: An Application to Vision/Inertial Navigation

This paper addresses the problem of nonlinear filter design to estimate the relative position and velocity of an unmanned air vehicle (UAV) with respect to a point on a ship using infrared (IR) vision, inertial, and air data sensors. Sufficient conditions are derived for the existence of a particular type of complementary filters with guaranteed stability and performance in the presence of so-called out-of-frame events that arise when the vision system loses its target temporarily. The results obtained build upon new developments in the theory of linear parametrically varying systems (LPVs) with brief instabilities–also reported in the paper–and provide the proper framework to deal with out-of-frame events. Field tests with a prototype UAV illustrate the performance of the filter and the scope of applications of the new theory developed.Office of Naval Research under Contract N0001497AF00002National Science Foundation under Grants CCR-0311084 and ECS-0093762Portugese FCT POSI program under framework QCA II