[show abstract][hide abstract] ABSTRACT: We present a control-based approach for visual navigation of humanoid robots in office-like environments. In particular, the objective of the humanoid is to follow a maze of corridors, walking as close as possible to their center to maximize motion safety. Our control algorithm is inspired by a technique originally designed for unicycle robots and extended here to cope with the presence of turns and junctions. The feedback signals computed for the unicycle are transformed to inputs that are suited for the locomotion system of the humanoid, producing a natural, human-like behavior. Exper-imental results for the humanoid robot NAO are presented to show the validity of the approach, and in particular the successful extension of the controller to turns and junctions.
[show abstract][hide abstract] ABSTRACT: We consider the problem of planning collision-free motions for general (i.e., possibly nonholonomic) redundant robots subject to task space constraints. Previous approaches to the solution are based on the idea of sampling and inverting the task constraint to build a roadmap of task-constrained configurations which are then connected by simple local paths; hence, task tracking is not enforced during the motion between samples. Here, we present a control-based randomized approach relying on a motion generation scheme that guarantees continued satisfaction of such constraint. The resulting planner allows to achieve accurate execution of the desired task without increasing the size of the roadmap. Numerical results on a fixed-base manipulator and a free-fying mobile manipulator are presented to illustrate the performance improvement obtained with the proposed technique.
Intelligent Robots and Systems, 2009. IROS 2009. IEEE/RSJ International Conference on; 11/2009
[show abstract][hide abstract] ABSTRACT: In this paper, we characterize the time-optimal trajectories leading a Dubins car in collision with the obstacles in its workspace. Due to the constant velocity constraint characterizing the Dubins car model, these trajectories form a sufficient set of shortest paths between any robot configuration and the obstacles in the environment. Based on these paths, we define and give the algorithm for computing a distance function that takes into account the nonholonomic constraints and captures the nonsymmetric nature of the system. The developments presented here assume that the obstacles and the robot are polygons although the methodology can be applied to different shapes.
IEEE Transactions on Robotics 11/2009; · 2.57 Impact Factor
[show abstract][hide abstract] ABSTRACT: We present a decentralized cooperative exploration strategy for a team of mobile robots equipped with range finders. A roadmap of the explored area, with the associate safe region, is built in the form of a sensor-based random graph (SRG). This is expanded by the robots by using a randomized local planner that automatically realizes a tradeoff between information gain and navigation cost. The nodes of the SRG represent view configurations that have been visited by at least one robot, and are connected by arcs that represent safe paths. These paths have been actually traveled by the robots or added to the SRG to improve its connectivity. Decentralized cooperation and coordination mechanisms are used so as to guarantee exploration efficiency and avoid conflicts. Simulations and experiments are presented to show the performance of the proposed technique.
IEEE/ASME Transactions on Mechatronics 05/2009; · 3.14 Impact Factor
[show abstract][hide abstract] ABSTRACT: In this paper we present implementation and experiments of a decen-tralized cooperative exploration strategy developed by our research group. The ex-ploration strategy is based on the construction of a roadmap of the explored area, with the associate safe region. No task decomposition/allocation is performed. The roadmap is incrementally built through a simple and efficient decentralized coop-eration mechanism: each robot biases its exploration towards its local frontier, i.e., local areas which appear to be unexplored by the whole robot team on the basis of the exchanged information. A detailed description of the software architecture used to implement the strategy is given. Experiments with a team of Khepera III robots are presented to show the performance of the proposed technique.
[show abstract][hide abstract] ABSTRACT: We present a cooperative exploration strategy for mobile robots. The method is based on the randomized incremental generation of a collection of data structures called sensor-based random trees, each representing a roadmap of an explored area with an associated safe region. Decentralized cooperation and coordination mechanisms are introduced so as to improve the exploration efficiency and to avoid conflicts. Simulations in various environments are presented to show the performance of the proposed technique.
Robotics and Automation, 2007 IEEE International Conference on; 05/2007
[show abstract][hide abstract] ABSTRACT: We present a decentralized cooperative exploration strategy for mobile robots. A roadmap of the explored area, with the associate safe region, is built in the form of a compact data structure, called Sensor-based Random Graph. This is incremen- tally expanded by the robots by using a randomized local planner which automatically realizes a trade-off between information gain and navigation cost. Connecting structures, called bridges, are incrementally added to the graph to create shortcuts and improve the connectivity of the roadmap. Decentralized cooperation and coordination mechanisms are used so as to guarantee exploration efficiency and avoid conflicts. Simulations are presented to show the performance of the proposed technique.
Proceedings of the 1st International Conference on Robot Communication and Coordination, ROBOCOMM 2007, Athens, Greece, October 15-17, 2007; 01/2007
[show abstract][hide abstract] ABSTRACT: This paper shows how to compute the nonholonomic distance between a polygonal car-like robot and polygonal obstacles. The solution extends previous work of Reeds and Shepp by finding the shortest path to a manifold (rather than to a point) in configuration space. Based on optimal control theory, the proposed approach yields an analytic solution to the problem
IEEE Transactions on Robotics 11/2006; · 2.57 Impact Factor
[show abstract][hide abstract] ABSTRACT: We present a steering algorithm for regular – i.e., without singularities – nonholonomic systems which are not required to possess special properties such as flatness or exact nilpotentizability. The method makes use of local steering laws, with suitable contraction properties, designed on the basis of a continuous approximation of the system. The algorithm is amenable to extension to systems with singularities.
Decision and Control, 2005 and 2005 European Control Conference. CDC-ECC '05. 44th IEEE Conference on; 01/2006
[show abstract][hide abstract] ABSTRACT: We present a framework for the stabilization of nonholonomic systems that do not possess special properties such as flatness or exact nilpotentizability. Our approach makes use of two tools: an iterative control scheme and a nilpotent approximation of the system dynamics. The latter is used to compute an approximate steering control which, repeatedly applied to the system, guarantees asymptotic stability with exponential convergence to any desired set point, under appropriate conditions. For illustration, we apply the proposed strategy to design a stabilizing controller for the plate-ball manipulation system, a canonical example of nonflat nonholonomic mechanism. The theoretical performance and robustness of the controller are confirmed by simulations, both in the nominal case and in the presence of a perturbation on the ball radius.
IEEE Transactions on Robotics 05/2005; · 2.57 Impact Factor
[show abstract][hide abstract] ABSTRACT: We consider the problem of planning point-to-point motion for general robotic systems subject to non-integrable differential constraints. The constraints may be of first order (on velocities) or of second order (on accelerations). Various nonlinear control techniques, including nilpotent approximations, iterative steering, and dynamic feedback linearization, are illustrated with the aid of four case studies: the plate-ball manipulation system, the general two-trailer mobile robot, a two-link robot with flexible forearm, and a planar robot with two passive joints. The first two case studies are non-flat nonholonomic kinematic systems, while the last two are flat underactuated dynamic systems.
[show abstract][hide abstract] ABSTRACT: To evaluate whether fuzzy operators can be usefully applied to the interpretation of genotypic HIV-1 drug resistance by experts, and to improve the prediction of salvage therapy outcome by adapting interpretation rules of genotypic resistance on the basis of their association with virological response data.
We used a clinical dataset of 231 patients failing highly active antiretroviral therapy (HAART) and starting salvage therapy with baseline resistance genotyping and virological outcomes after 3 and 6 months. A set of rules predicting genotypic resistance was initially derived from an expert (ADL). Rules were implemented using a fuzzy logic approach and the virological outcomes dataset used for the training phase. The resulting algorithm was validated using a separate set of 184 selected patients by correlating the resulting predicted activity with observed virological response at 3 months. For comparison, the expert systems from the drug resistance group of the Agence Nationale de Recherches sur le SIDA (ANRS-AC11) and the algorithm from the Stanford's HIV drug resistance database (Stanford HIVdb) were evaluated on the same set.
The starting algorithm had a correlation with virological outcomes of R2=0.06 (P=0.0001). After the training phase the correlation with virological outcomes increased to R2=0.19 (P<0.000001). In the validation set of patients, the activity of the salvage regimen predicted by the fuzzy algorithm was the only variable independently predictive of the 3-month viral load change even after adjusting by the activity predicted by the two expert systems and baseline viral load (for each 10% salvage regimen's activity increase, mean HIV RNA change from baseline: -0.27 log10 copies/ml; 95% CI -0.39, -0.15).
Using fuzzy operators in a virological outcomes training database to implement a rules-based algorithm for genotypic resistance interpretation, significant improvements of outcomes prediction were obtained. The resulting algorithm showed an independent predictive capability of virological outcomes over that of two rules-based interpretation algorithms made by experts. Although the system was trained and validated on a limited number of cases, the approach deserves further evaluation.
[show abstract][hide abstract] ABSTRACT: Nilpotent approximations are a useful tool for analyzing and controlling systems whose tangent linearization does not preserve controllability, such as nonholonomic mechanisms. However, conventional homogeneous approximations exhibit a drawback: in the neighborhood of singular points (where the system growth vector is not constant) the vector fields of the approximate dynamics do not vary continuously with the approximation point. The geometric counterpart of this situation is that the sub-Riemannian distance estimate provided by the classical Ball-Box Theorem is not uniform at singular points. With reference to a specific family of driftless systems, we show how to build a nonhomogeneous nilpotent approximation whose vector fields vary continuously around singular points. It is also proven that the privileged coordinates associated to such an approximation provide a uniform estimate of the distance.
IEEE Transactions on Automatic Control 03/2004; · 2.72 Impact Factor
[show abstract][hide abstract] ABSTRACT: We present a method for sensor-based exploration of unknown environments by a mobile robot. The method is based on the randomized incremental generation of a data structure called sensor-based random tree (SRT), which represents a roadmap of the explored area with an associated safe region. Different exploration strategies may be obtained by instantiating the general method with different perception techniques. Two such techniques are discussed: the first, conservative and particularly suited to noisy sensors, results in an exploration strategy called SRT-Ball. The second perception technique is more confident, and the corresponding strategy is called SRT-Star. The two strategies are critically compared by simulations as well as by experiments on the MagellanPro robot.
Robotics and Automation, 2004. Proceedings. ICRA '04. 2004 IEEE International Conference on; 01/2004
[show abstract][hide abstract] ABSTRACT: We discuss a strategy for sensor-based exploration of unknown environments by a mobile robot. The strategy, called SRT-Ball, is an instance of a general paradigm based on the randomized generation of a sensor-based random tree (SRT), which represents a roadmap of the explored area with an associated safe region. In SRT-Ball, the safe region is conservatively estimated as the maximum collision-free circle surrounding the robot in the workspace. We also present FB-SRT-Ball, a frontier-based version of SRT-Ball aimed at increasing the efficiency of exploration. The two strategies are critically compared by simulations
World Automation Congress, 2004. Proceedings; 01/2004
[show abstract][hide abstract] ABSTRACT: Robotic manipulation by rolling contacts is an appealing method for achieving dexterity with relatively simple hardware. While there exist techniques for planning motions of rigid bodies in rolling contact under nominal conditions, an inescapable challenge is the design of robust controllers of provable performance in the presence of model perturbations. As a preliminary step in this direction, we present in this paper an iterative robust planner of arbitrary accuracy for the plate-ball manipulation system subject to perturbations on the sphere radius. The basic tool is an exact geometric planner for the nominal system, whose repeated application guarantees the desired robustness property on the basis of the iterative steering paradigm. Simulation results under perturbed conditions show the effectiveness of the method.
Proceedings of the 2003 IEEE International Conference on Robotics and Automation, ICRA 2003, September 14-19, 2003, Taipei, Taiwan; 01/2003
[show abstract][hide abstract] ABSTRACT: The subject of the paper is the motion control problem of wheeled mobile robots (WMRs) in environments without obstacles. With reference to the popular unicycle kinematics, it is shown that dynamic feedback linearization is an efficient design tool leading to a solution simultaneously valid for both trajectory tracking and setpoint regulation problems. The implementation of this approach on the laboratory prototype SuperMARIO, a two-wheel differentially driven mobile robot, is described in detail. To assess the quality of the proposed controller, we compare its performance with that of several existing control techniques in a number of experiments. The obtained results provide useful guidelines for WMR control designers.
IEEE Transactions on Control Systems Technology 12/2002; · 2.00 Impact Factor
[show abstract][hide abstract] ABSTRACT: We consider the problem of planning collision-free motions for a redundant robot whose end-effector must travel along a given path. Although collision avoidance is one of the main reasons for introducing kinematic redundancy in manipulators, the planning methods so far proposed for this particular problem are neither efficient nor complete. In this paper, we introduce some algorithms that may be considered as an extension of probabilistic planning techniques to the problem at hand. All the algorithms are based on the same simple mechanism for generating random samples of the configuration space that are compatible with the end-effector path constraint. Experimental results illustrate the performance of the planners.
Intelligent Robots and Systems, 2002. IEEE/RSJ International Conference on; 02/2002