Laboratoire d’analyse et d’architecture des systèmes
Y.AOUSTIN, C.CHEVALLEREAU, J.P.LAUMOND
Ouvrage (contribution) : Humanoid Robotics: A Reference, Springer, N°ISBN 978-94-007-6045-5, Octobre 2018 , N° 18021
Revue Scientifique : IEEE Robotics and Automation Letters, Vol.3, N°3, pp.2277-2282, Juillet 2018, doi 10.1109/LRA.2018.2802544 , N° 18034
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.
M.TOGNON, E.CATALDI, H.TELLO CHAVEZ, G.ANTONELLI, J.CORTES, A.FRANCHI
Revue Scientifique : IEEE Robotics and Automation Letters, Vol.3, N°3, pp.2478-2484, Juillet 2018, DOI 10.1109/LRA.2018.2803206 , N° 18033
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.
A.BIT-MONNOT, R.BAILON-RUIZ, S.LACROIX
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
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.
Ouvrage (contribution) : Humanoid Robotics: A Reference, Springer, N°ISBN 978-94-007-6047-9, Juin 2018, 22p. , N° 18003
N.STAUB, D.BICEGO, Q.SABLE, V.ARELLANO, S.MISHRA, A.FRANCHI
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
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.
M.BENALLEGUE, P.GERGONDET, H.AUDREN, A.MIFSUD, M.MORISAWA, F.LAMIRAUX, A.KHEDDAR, F.KANEHIRO
AIST, JRL, Tsukuba, GEPETTO, LIRMM
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° 18090
The dynamics of a humanoid robot cannot be correctly described independently from the external forces acting on it. These forces have to be reconstructed to enable the robot to control them or to compensate for them. Force sensors are usually used to measure these forces, but because of their cost, they are often put only on the ankle/feet and possibly the wrists. This paper addresses the issue of the estimation of external forces and moments that apply at any part of a robot without direct force measurements and without torque measurements. The sensors used are the regular force sensors and the IMUs of the robot. The method relies on a model-based estimator able to make the fusion between these sensors and the whole body dynamics. The estimator reconstructs a single state vector containing the floating-base kinematics, a filtered measurement of contact force and an additional estimation external force that we evaluate in this paper. Validation is performed on HRP-2 in a multi-contact motion.
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
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.
M.FAESSLER, A.FRANCHI, D.SCARAMUZZA
Revue Scientifique : IEEE Robotics and Automation Letters, Vol.3, N°2, pp.620-626, Avril 2018, DOI 10.1109/LRA.2017.2776353 , N° 17447
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.
J.MADRIGAL DIAZ, F.LERASLE, A.MONIN
Manifestation avec acte : IEEE Winter Conference on Applications of Computer Vision ( WACV ) 2018 du 12 mars au 15 mars 2018, Lake Tahoe (USA), Mars 2018, 9p. , N° 18087
This work presents a method that incorporates 2D and 3D cues for the estimation of head pose. We propose the use of the concept of Key-Frames (KF), a set of frames where the position and orientation of the head is automatically calculated off-line, to improve the precision of pose estimation and detection rate. Each KF consists of: 2D information, encoded by SURF descriptors; 3D information from a depth image (both acquired by an RGB-D sensor); and a generic 3D model that corresponds to the head localization and orientation in the real world. Our algorithm compares a new frame against all KFs and selects the most relevant one. The 3D transformation between both, selected KF and current frame, can be estimated using the depth image and the Iterative Closest Point algorithm in an online framework. Compared to reference approaches, our system can handle partial occlusions and extreme rotations even with noisy depth data. We evaluate the proposal using two challenging datasets: (1) an dataset acquired by us where the ground-truth information is given by a commercial Motion Capture system and (2) the public benchmark Biwi Kinect Head Pose Database.