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18033
01/07/2018

Control-Aware Motion Planning for Task-Constrained Aerial Manipulation

M.TOGNON, E.CATALDI, H.TELLO CHAVEZ, G.ANTONELLI, J.CORTES, A.FRANCHI

RIS, UNICAS

Revue Scientifique : IEEE Robotics and Automation Letters, Vol.3, N°3, pp.2478-2484, Juillet 2018, DOI 10.1109/LRA.2018.2803206 , N° 18033

Lien : https://hal.laas.fr/hal-01704127

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Abstract

This paper presents a new method to address the problem of task-constrained motion planning for aerial manipulators. We propose a control-aware planner based on the paradigm of tight coupling between planning and control. Such paradigm is especially useful in aerial manipulation, where the separation between planning and control is not advisable. The proposed sampling based motion planner uses a controller composed of a second-order inverse kinematics algorithm and a dynamic tracker, as a local planner, thus allowing a more natural consideration of the closed-loop system dynamics. For task constrained motions, this method lets to i) sample directly in the reduced and more relevant task space, ii) predict the behavior of the controller avoiding motions that bring to singularities or large tracking errors, and iii) guarantee the correct execution of the maneuver. The method is tested in simulation for a multidirectional-thrust vehicle endowed with a two-DoF manipulator. The proposed approach is very general, and could be applied to ground and underwater robotic systems to perform manipulation or inspection tasks.

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18034
01/07/2018

Omnidirectional Aerial Vehicles with Unidirectional Thrusters: Analysis, Optimal Design, and Motion Control

M.TOGNON, A.FRANCHI

RIS

Revue Scientifique : IEEE Robotics and Automation Letters, Vol.3, N°3, pp.2277-2282, Juillet 2018, doi 10.1109/LRA.2018.2802544 , N° 18034

Lien : https://hal.laas.fr/hal-01704054

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Abstract

This paper presents a theoretical study on omni-directional aerial vehicles with body-frame fixed unidirectional thrusters. Omniplus multi-rotor designs are defined as the ones that allow to exert a total wrench in any direction using positive-only lift force and drag moment (i.e., positive rotational speed) for each rotor blade. Algebraic conditions for a design to be omniplus are derived, a simple necessary condition being the fact that at least seven propellers have to be used. An energy optimal design strategy is then defined as the one minimizing the maximum norm of the input set needed to span a certain wrench ellipsoid for the adopted input allocation strategy. Two corresponding major design criteria are then introduced: firstly, a minimum allocation-matrix condition number aims at an equal sharing of the effort needed to generate wrenches in any direction; secondly, imposing a balanced design guarantees an equal sharing of the extra effort needed to keep the input in the non-negative orthant. We propose a numerical algorithm to solve such optimal design problem and a control algorithm to control any omnidirectional platform. The work is concluded with informative simulation results in non-ideal conditions.

142621
18084
29/06/2018

A Local Search Approach to Observation Planning with Multiple UAVs

A.BIT-MONNOT, R.BAILON-RUIZ, S.LACROIX

RIS

Manifestation avec acte : International Conference on Automated Planning and Scheduling ( ICAPS ) 2018 du 24 juin au 29 juin 2018, Delft (Pays-Bas), Juin 2018, 9p. , N° 18084

Lien : https://hal.archives-ouvertes.fr/hal-01730655

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Abstract

Observation planning for Unmanned Aerial Vehicles (UAVs) is a challenging task as it requires planning trajectories over a large continuous space and with motion models that can not be directly encoded into current planners. Furthermore, realistic problems often require complex objective functions that complicate problem decomposition. In this paper, we propose a local search approach to plan the trajectories of a fleet of UAVs on an observation mission. The strength of the approach lies in its loose coupling with domain specific requirements such as the UAV model or the objective function that are both used as black boxes. Furthermore, the Variable Neighborhood Search (VNS) procedure considered facilitates the adaptation of the algorithm to specific requirements through the addition of new neighborhoods. We demonstrate the feasibility and convenience of the method on a large joint observation task in which a fleet of fixed-wing UAVs maps wildfires over areas of a hundred square kilometers. The approach allows generating plans over tens of minutes for a handful of UAVs in matter of seconds, even when considering very short primitive maneuvers.

143097
18055
25/05/2018

Trajectory Generation for Minimum Closed-Loop State Sensitivity

P.ROBUFFO-GIORDANO, Q.DELAMARE, A.FRANCHI

INRIA Rennes, IRISA, RIS

Manifestation avec acte : IEEE International Conference on Robotics and Automation ( ICRA ) 2018 du 21 mai au 25 mai 2018, Brisbane (Australie), Mai 2018, 8p. , N° 18055

Lien : https://hal.laas.fr/hal-01716843

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In this paper we propose a novel general method to let a dynamical system fulfil at best a control task when the nominal parameters are not perfectly known. The approach is based on the introduction of the novel concept of closed-loop sensitivity, a quantity that relates parameter variations to deviations of the closed-loop trajectory of the system/controller pair. This new definition takes into account the dependency of the control inputs from the system states and nominal parameters as well as from the controller dynamics. The reference trajectory to be tracked is taken as optimization variable, and the dynamics of both the sensitivity and of its gradient are computed analytically along the system trajectories. We then show how this computation can be effectively exploited for solving trajectory optimization problems aimed at generating a reference trajectory that minimizes a norm of the closed-loop sensitivity. The theoretical results are validated via an extensive campaign of Monte Carlo simulations for two relevant robotic systems: a unicycle and a quadrotor UAV.

142793
18054
25/05/2018

Towards a Flying Assistant Paradigm: the OTHex

N.STAUB, D.BICEGO, Q.SABLE, V.ARELLANO, S.MISHRA, A.FRANCHI

RIS

Manifestation avec acte : IEEE International Conference on Robotics and Automation ( ICRA ) 2018 du 21 mai au 25 mai 2018, Brisbane (Australie), Mai 2018, 6p. , N° 18054

Lien : https://hal.laas.fr/hal-01716845

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Abstract

This paper presents the OTHex platform for aerial manipulation developed at LAAS–CNRS. The OTHex is probably the first multi-directional thrust platform designed to act as Flying Assistant which can aid human operators and/or Ground Manipulators to move long bars for assembly and maintenance tasks. The work emphasis is on task-driven custom design and experimental validations. The proposed control framework is built around a low-level geometric controller, and includes an external wrench estimator, an admittance filter, and a trajectory generator. This tool gives the system the necessary compliance to resist external force disturbances arising from contact with the surrounding environment or to parameter uncertainties in the load. A set of experiments validates the real-world applicability and robustness of the overall system.

142791
17447
01/04/2018

Differential flatness of quadrotor dynamics subject to rotor drag for accurate tracking of high-speed trajectories

M.FAESSLER, A.FRANCHI, D.SCARAMUZZA

Zurich, RIS

Revue Scientifique : IEEE Robotics and Automation Letters, Vol.3, N°2, pp.620-626, Avril 2018, DOI 10.1109/LRA.2017.2776353 , N° 17447

Lien : https://hal.laas.fr/hal-01658577

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Abstract

In this paper, we prove that the dynamical model of a quadrotor subject to linear rotor drag effects is differentially flat in its position and heading. We use this property to compute feed-forward control terms directly from a reference trajectory to be tracked. The obtained feed-forward terms are then used in a cascaded, nonlinear feedback control law that enables accurate agile flight with quadrotors. Compared to state-of-the-art control methods, which treat the rotor drag as an unknown disturbance, our method reduces the trajectory tracking error significantly. Finally, we present a method based on a gradient-free optimization to identify the rotor drag coefficients, which are required to compute the feed-forward control terms. The new theoretical results are thoroughly validated trough extensive comparative experiments.

141721
18063
14/03/2018

Integrating planning and execution for a team of heterogeneous robots with time and communication constraints

P.BECHON, M.BARBIER, C.GRAND, S.LACROIX, C.LESIRE-CABANIOLS, C.PRALET

ONERA, RIS, ONERA

Rapport LAAS N°18063, Mars 2018, 7p.

Lien : https://hal.laas.fr/hal-01706146

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Abstract

Field multi-robot missions face numerous unavoidable disturbances, such as delays in executing tasks and intermittent communications. Coping with such disturbances requires to endow the robots with high-level decision skills. We present a distributed decision architecture based first on a hybrid planner that can manage decentralized repairs with partial communication, and secondly on a distributed execution algorithm that efficiently propagates delays. This architecture has been successfully experimented on the field for the achievement of surveillance missions involving eight (8) real autonomous aerial and ground robots.

142832
18042
09/03/2018

Full-Pose Tracking Control for Aerial Robotic Systems With Laterally Bounded Input Force

A.FRANCHI, R.CARLI, D.BICEGO, M.RYLL

RIS, University of Padova

Revue Scientifique : IEEE Transactions on Robotics, 10p., Mars 2018, doi 10.1109/TRO.2017.2786734 , N° 18042

Lien : https://hal.laas.fr/hal-01710770

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A class of abstract aerial robotic systems is introduced , the Laterally Bounded Force (LBF) vehicles, in which most of the control authority is expressed along a principal thrust direction, while along the lateral directions a (smaller and possibly null) force may be exploited to achieve full-pose tracking. This class approximates platforms endowed with non-collinear rotors that can modify the orientation of the total thrust in body frame. The proposed SE(3)-based control strategy achieves, if made possible by the force constraints, the independent tracking of position-plus-orientation trajectories. The method, which is proven using a Lyapunov technique, deals seamlessly with both under-and fully-actuated platforms, and guarantees at least the position tracking in the case of an unfeasible full-pose reference trajectory. Several experimental tests are presented, that clearly show the approach practicability and the sharp improvement with respect to state of-the-art.

142675
18035
07/03/2018

Towards Aerial Physical Locomotion: the Contact-Fly-Contact Problem

Q.DELAMARE, P.R.GIORDANO, A.FRANCHI

IRISA, INRIA Rennes, RIS

Revue Scientifique : IEEE Robotics and Automation Letters, Vol.3, N°3, pp.1514-1521, Mars 2018, doi 10.1109/LRA.2018.2800798 , N° 18035

Lien : https://hal.laas.fr/hal-01704043

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Abstract

In this paper we consider the problem of letting an aerial robot exploiting its contact with the environment in order to enhance its motion possibilities, in a way reminiscent of legged robots exploiting contact forces for locomotion purposes. As a representative and initial case study, we consider a quadrotor equipped with a 1-DOF arm able to hook at some pivot points, and needing to perform a maneuver from an initial hooked configuration to a final hooked configuration while passing though a free-flight phase between the two anchor points. To this end, we propose a dynamical modeling able to capture the various phases (hooked, free-flying) together with an optimization framework for generating optimal motion plans compatible with actuation constraints. Simulation results illustrate the effectiveness of the approach and the promising potential in terms of more advanced maneuvers.

142653
17175
01/02/2018

Adaptive sampling of cumulus clouds with UAVs

C.REYMANN, A.RENZAGLIA, F.LAMRAOUI, M.BRONZ, S.LACROIX

RIS, CNRM-GAME, ENAC

Revue Scientifique : Autonomous Robots, Vol.42, N°2, pp.491-512, Février 2018, 10.1007/s10514-017-9625-1 , N° 17175

Lien : https://hal.archives-ouvertes.fr/hal-01522250

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Abstract

This paper presents an approach to guide a fleet of Unmanned Aerial Vehicles to actively gather data in low-altitude cumulus clouds with the aim of mapping atmospheric variables. Building on-line maps based on very sparse local measurements is the first challenge to overcome, for which an approach based on Gaussian Processes is proposed. A particular attention is given to the on-line hyperparameters optimization , since atmospheric phenomena are strongly dynamical processes. The obtained local map is then exploited by a trajectory planner based on a stochastic optimization algorithm. The goal is to generate feasible trajectories which exploit air flows to perform energy-efficient flights, while maximizing the information collected along the mission. The system is then tested in simulations carried out using realistic models of cumu-lus clouds and of the UAVs flight dynamics. Results on mapping achieved by multiple UAVs and an extensive analysis on the evolution of Gaussian Processes hyper-parameters is proposed.

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