Fabrice Le Bars

Brief paper: Set-membership state estimation with fleeting data

This paper deals with offline nonlinear state estimation where measurements are available only when some given equality conditions are satisfied. For this type of problems, which are often met in robot localization when sonar or radar are involved, the data are qualified as fleeting because the measurements are available only at some given unknown dates. In this paper, the first approach able to deal with nonlinear estimation with fleeting data is presented. An illustration related to offline robot localization with a laser rangefinder will be given.

An Experimental Validation of a Robust Controller with the VAIMOS Autonomous Sailboat

A sailboat is a strongly non-linear system that has, however, been proven to be easily controllable. Indeed, its mechanical design has been evolved over thousands of years with two main concerns: having a fast, reliable and efficient vehicle which can be easily controlled by humans. This article describes the functionality, the validation process and the performance of a simple controller, inspired by what navigators do, through tests made on the sailboat robot VAIMOS built by IFREMER for oceanography. This controller requires tweaking a few parameters with real physical meaning while ensuring accurate trajectory following, needed to make oceanographic measurements in a specific area.

A Simple Controller for Line Following of Sailboats

This paper proposes a simple controller for sailboat robots. The resulting controller is simple to implement and its parameters are easy to tune. Its complexity is low enough to be applicable for sailing robots with very limited computation power. The presentation contains all the necessary details to allow a fast and reliable implementation of a sailboat robot controller which follows a line. The paper also presents a simple collision avoidance strategy based on interval analysis.

Using interval methods in the context of robust localization of underwater robots

In this paper we will apply interval methods to solve the problem of robust localization of an underwater robot. The localization problem is cast into a constraint satisfaction problem (CSP) where constraint propagation algorithms are particularly efficient. The method is designed to work in real environments with numerous outliers. Besides, we used a new approach to represent the map by a binary image. This allow us to represent even unstructured maps. We tested the algorithm on a real data set gathered by an underwater robot in a marina located in Costa Brava.

Sailboat as a Windmill

This paper proposes to transform a sailboat robot into a big wind turbine (or windmill) corresponding to the boat itself. The main idea is to make the sailboat rotating as fast as possible. When the wind open the sail, the mainsheet is able to pull a generator in order to produce electric energy. The resulting controller is simple to implement and its parameters are easy to tune. A simulated test-case shows that the proposed technique could generate an average power of approximatively 100W.

Guaranteed computation of robot trajectories

This paper proposes a new method for guaranteed integration of state equations. Within this framework, the variables of interest are trajectories submitted to both arithmetic and differential equations. The approach consists in formalizing a problem thanks to a constraint network and then apply these constraints to sets of trajectories. The contribution of the paper is to provide a reliable framework to enclose the solutions of these differential equations. Its use is shown to be simple, more general and more competitive than existing approaches dealing with guaranteed integration, especially when applied to mobile robotics. The flexibility of the developed framework allows to deal with non-linear differential equations or even differential inclusions built from datasets, while considering observations of the states of interest. An illustration of this method is given over several examples with mobile robots. A contractor-based approach is proposed for guaranteed integration of state equations.The framework is based on the use of tubes as envelopes of feasible trajectories.A dedicated differential contractor is provided to deal with dynamical systems.The use of tubes is well suited for multi-differential and non-linear equations.An illustration of this approach is given over several mobile robotics examples.

Obstacle Avoidance for an Autonomous Marine Robot—A Vector Field Approach

A marine robot, especially a sailing boat robot, is exposed to a dynamic environment. This paper presents a simple and efficient obstacle avoidance control algorithm. The presented control method uses vector fields to regulate the marine robot.

Estimating the Trajectory of Low-Cost Autonomous Robots Using Interval Analysis: Application to the euRathlon Competition

In this paper, we describe a method based on interval arithmetic and contractors to compute an envelope containing the trajectory of a robot from usual proprioceptive and exteroceptive data, using a simple state equation model. To illustrate the applicability of the method, data from the euRathlon 2015, a multi-domain robotics competition, will be processed to build an estimation of the trajectory of a low-cost AUV (Autonomous Underwater Vehicle), navigating with the help of acoustic communication and ranging with an ASV (Autonomous Surface Vehicle).

Reliable non-linear state estimation involving time uncertainties

Abstract This paper presents a new approach to bounded-error state estimation involving time uncertainties. For a given bounded observation of a continuous-time non-linear system, it is assumed that neither the values of the observed data nor their acquisition instants are known exactly. For systems described by state-space equations, we prove theoretically and demonstrate by simulations that the proposed constraint propagation approach enables the computation of bounding sets for the systems’ state vectors that are consistent with the uncertain measurements. The bounding property of the method is guaranteed even if the system is strongly non-linear. Compared with other existing constraint propagation approaches, the originality of the method stems from our definition and use of bounding tubes which enable to enclose the set of all feasible trajectories inside sets. This method makes it possible to build specific operators for the propagation of time uncertainties through the whole trajectory. The efficiency of the approach is illustrated on two examples: the dynamic localization of a mobile robot and the correction of a drifting clock.

Complex Robot Behavior Creation Using Vector Fields

In term of motion planning for robots, several solutions are possible: grid-based search [1], interval-based search [2], geometric algorithms and potential fields [3]. However, potential fields offer a computational efficient way to generate a desired behavior for robots. However, a principal limit of potential fields is that they deal only with repulsion and attraction. To extend it to perpendicular, tangential and uniform fields, we base our paper on the works of S. Schmitt [4] and R. Arkin [3]. Our contribution consist in developing a method to construct complex vector fields, which are a linear combination of primitive fields. It also explains how to implement this method on a robot using the middleware ROS (Robot Operating System) with any controller.