References of "Lens, Stéphane"
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See detailEfficient and Precise Trajectory Planning for Nonholonomic Mobile Robots
Lens, Stéphane ULiege

Doctoral thesis (2015)

Trajectory planning is one of the fundamental problems in mobile robotics. A wide variety of approaches have been proposed over the years to deal with the various issues of this problem. This thesis ... [more ▼]

Trajectory planning is one of the fundamental problems in mobile robotics. A wide variety of approaches have been proposed over the years to deal with the various issues of this problem. This thesis presents an original and complete solution to tackle the motion planning problem for nonholonomic mobile robots in two-dimensional space. Given a set of obstacles, an initial and a goal configuration, the problem consists in computing efficiently a physically feasible trajectory that reaches the specified target as fast as possible. One of the original aspects of this work lies in the decomposition of the general problem into several simpler subproblems, for which very efficient solutions are developed. Their combination provides a complete trajectory planning approach that is one of the most computationally effective method suited for the motion of cylindrically shaped wheeled mobile robots in the presence of polygonal obstacles. This complete solution consists of three main steps. The first one is aimed at finding a short path that avoids obstacles and manages to reach the destination, without taking into account nonholonomic constraints of the robot. Our path planning method relies on an original refinement procedure of a constrained Delaunay triangulation of the obstacles, that outperforms other existing planning techniques. The second step consists in interpolating paths into smooth curves that can be followed by a real robot without slowing down excessively. By joining only two arcs of clothoids for moving from one curvature to another, our approach is simpler and also computationally cheaper than other interpolation methods. Finally, thanks to the introduction of an original discretization scheme, an efficient algorithm for computing a time-optimal speed profile for arbitrary paths is presented. The speed profile that results from this procedure not only allows the robot to follow the synthesized path as fast as possible while taking into account a broad class of velocity and accelerations constraints, but also provides the accurate advance information necessary to implementing coordinated actions during the displacement of the robot (e.g., between the locomotion system and other actuators). [less ▲]

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See detailFrom Constrained Delaunay Triangulations to Roadmap Graphs with Arbitrary Clearance
Lens, Stéphane ULiege; Boigelot, Bernard ULiege

E-print/Working paper (2015)

This work studies path planning in two-dimensional space, in the presence of polygonal obstacles. We specifically address the problem of building a roadmap graph, that is, an abstract representation of ... [more ▼]

This work studies path planning in two-dimensional space, in the presence of polygonal obstacles. We specifically address the problem of building a roadmap graph, that is, an abstract representation of all the paths that can potentially be followed around a given set of obstacles. Our solution consists in an original refinement algorithm for constrained Delaunay triangulations, aimed at generating a roadmap graph suited for planning paths with arbitrary clearance. In other words, a minimum distance to the obstacles can be specified, and the graph does not have to be recomputed if this distance is modified. Compared to other solutions, our approach has the advantage of being simpler, as well as significantly more efficient. [less ▲]

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See detailEfficient Path Interpolation and Speed Profile Computation for Nonholonomic Mobile Robots
Lens, Stéphane ULiege; Boigelot, Bernard ULiege

E-print/Working paper (2015)

This paper studies path synthesis for nonholonomic mobile robots moving in two-dimensional space. We first address the problem of interpolating paths expressed as sequences of straight line segments, such ... [more ▼]

This paper studies path synthesis for nonholonomic mobile robots moving in two-dimensional space. We first address the problem of interpolating paths expressed as sequences of straight line segments, such as those produced by some planning algorithms, into smooth curves that can be followed without stopping. Our solution has the advantage of being simpler than other existing approaches, and has a low computational cost that allows a real-time implementation. It produces discretized paths on which curvature and variation of curvature are bounded at all points, and preserves obstacle clearance. Then, we consider the problem of computing a time-optimal speed profile for such paths. We introduce an algorithm that solves this problem in linear time, and that is able to take into account a broader class of physical constraints than other solutions. Our contributions have been implemented and evaluated in the framework of the Eurobot contest. [less ▲]

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See detailEfficient Path Planning for Nonholonomic Mobile Robots
Lens, Stéphane ULiege; Boigelot, Bernard ULiege

Report (2014)

This work addresses path planning for nonholonomic robots moving in two-dimensional space. The problem consists in computing a sequence of line segments that leads from the current configuration of the ... [more ▼]

This work addresses path planning for nonholonomic robots moving in two-dimensional space. The problem consists in computing a sequence of line segments that leads from the current configuration of the robot to a target location, while avoiding a given set of obstacles. We describe a planning algorithm that has the advantage of being very efficient, requiring less of one millisecond of CPU time for the case studies that we have considered, and produces short paths. Our method relies on a search in a Voronoi graph that characterizes the possible ways of moving around obstacles, followed by a string-pulling procedure aimed at improving the resulting path. [less ▲]

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See detailLocomotion d'un robot mobile
Lens, Stéphane ULiege

Master's dissertation (2008)

Dans le domaine de la robotique mobile, l’étude de la locomotion possède une place prépondérante. De nombreuses approches et solutions peuvent être envisagées et il convient d’apporter un soin particulier ... [more ▼]

Dans le domaine de la robotique mobile, l’étude de la locomotion possède une place prépondérante. De nombreuses approches et solutions peuvent être envisagées et il convient d’apporter un soin particulier quant à leur sélection afin de garantir les performances du système final. Ce travail de fin d’études a pour objectif la conception complète du système de locomotion d’un robot mobile participant à un concours de robotique. La réalisation des cartes électroniques de commande pour les moteurs, ainsi que la synthèse des lois de contrôle sont étudiées en détails. Ces lois seront principalement divisées en deux phases : d’une part, la génération d’une trajectoire réalisable, et d’autre part, une régulation sur cette trajectoire grâce, entre autres, à un contrôle local de la vitesse des roues motrices. Ce travail se termine, enfin, par une implémentation pratique du système étudié et par une évaluation de ses performances. [less ▲]

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