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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.

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17220
01/07/2018

Aerial Co-Manipulation with Cables: The Role of Internal Force for Equilibria, Stability, and Passivity

M.TOGNON, C.GABELLIERI, L.PALLOTTINO, A.FRANCHI

RIS, Pise

Revue Scientifique : IEEE Robotics and Automation Letters, Vol.3, N°3, pp.2577-2583, Juillet 2018 , N° 17220

Lien : https://hal.laas.fr/hal-01551105

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This paper considers the study of cooperative transportation of a cable-suspended load with two aerial robots and without explicit communication. The role of the internal force for the asymptotic stability of the beam-position/beam-attitude equilibria is analyzed in depth and explained thoroughly. Using a nonlinear Lyapunov-based approach, we prove that that if a non-zero internal force is chosen then asymptotic stabilization of any desired beam-position/beam-attitude configuration can be achieved by using a decentralized and communication-less master-slave admittance controller. If, conversely , a zero internal force is chosen, as done in the majority of the state-of-the-art algorithms, the attitude of the beam is not controllable without communication. Non-zero internal force can be interpreted then as a fundamental factor that enables the use of cables as implicit communication means between the two aerial vehicles in replacement of the explicit ones. The theoretical findings are validated through numerical simulations with added noise and realistic uncertainty.

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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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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.

142619
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
17370
12/06/2018

Fundamental actuation properties of multi-rotors: force-moment decoupling and fail-safe robustness

G.MICHIELETTO, M.RYLL, A.FRANCHI

RIS

Revue Scientifique : IEEE Transactions on Robotics, Vol.34, N°3, pp.702-715, Juin 2018 , N° 17370

Lien : https://hal.laas.fr/hal-01612602

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Abstract

In this paper we shed light on the fundamental actuation capabilities of multi-rotors, such as force-moment decoupling and ability to robustly fly still in place after the loss of propellers. These two actuation properties are formalized through the definition of some necessary algebraic conditions on the control force and control moment input matrices of generically tilted multi-rotors. Standard quadrotors are not able to robustly fly still at a constant spot after the loss of a propeller. The increased number of actuators of a hexarotor does not always help to overcome this limitation. To deeply understand this counterintuitive result, we apply the developed theory on the analysis of fail-safe robustness of hexarotor platforms, and clarify the role of the tilt angles and locations of the propellers in the vehicle. We show that standard star-shaped hexarotors are unable of robust static hovering after a propeller failure, while both the tilted star-shaped hexarotor and the Y-shaped hexarotor possess this important property. The analysis is validated with both simulation and experimental results testing the control of six-rotor vehicles subject to rotor loss.

143752
18113
02/06/2018

Formal Verification of Complex Robotic Systems on Resource-Constrained Platforms

M.FOUGHALI, B.BERTHOMIEU, S.DAL ZILIO, P.E.HLADIK, F.INGRAND, A.MALLET

RIS, VERTICS, IDEA

Manifestation avec acte : International Conference on Formal Methods in Software Engineering ( FormaliSE ) 2018 du 02 juin au 02 juin 2018, Gothenburg (Suède), Juin 2018, 8p. , N° 18113

Lien : https://hal.laas.fr/hal-01778960

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Abstract

Software constitutes a major part of the development of robotic and autonomous systems and is critical to their successful deployment in our everyday life. Robotic software must thus run and perform as specified. Since most of these systems are used in a hard real-time context, the schedulability of their tasks is a crucial property. In this work, we propose to use formal methods to check whether the tasks of a robotic application are schedulable with respect to a given hardware platform. For this, we automatically translate functional components specified in GenoM into FIACRE, a formal language for timed systems. The generated models integrate realistic real-time schedulers based on the FCFS and the SJF cooperative policies. We use then the model-checker TINA to assert schedulability properties. We carry out experiments on a real robotic system, namely a quadcopter flight controller. We demonstrate that, on its actual hardware, schedulability properties can be formally expressed and verified. We give examples on how we can check other important behavioral and timed properties on the same synthesized models.

143433
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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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
18063
25/05/2018

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

Manifestation avec acte : IEEE International Conference on Robotics and Automation ( ICRA ) 2018 du 21 mai au 25 mai 2018, Brisbane (Australie), Mai 2018, 7p. , N° 18063

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.

143612
16073
01/05/2018

Prediction and clarification of structures of (bio)molecules on surfaces-a review

J.C.SCHON, C.OLIGSCHLEGER, J.CORTES

Max Planck, BRS, RIS

Revue Scientifique : Zeitschrift fuer Naturforschung B (Chemical Sciences), Vol.71, N°5, Mai 2018, doi 10.1515/znb-2015-0222 , N° 16073

Lien : https://hal.archives-ouvertes.fr/hal-01295377

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Abstract

The design of future materials for biotechnological applications via deposition of molecules on surfaces will require not only exquisite control of the deposition procedure. Of equal importance will be our ability to predict the shapes and stability of individual molecules on various surfaces. Furthermore, one will need to be able to predict the structure patterns generated during the self-organization of whole layers of (bio)molecules on the surface. In this review, we present an overview over the current state of the art regarding the prediction and clarification of structures of biomolecules on surfaces using theoretical and computational methods.

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