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18176
01/09/2018

Hybrid parallelization of a multi-tree path search algorithm: Application to highly-flexible biomolecules

A.ESTANA, K.MOLLOY, M.VAISSET, N.SIBILLE, T.SIMEON, P.BERNADO, J.CORTES

CBS, RIS, IDEA

Revue Scientifique : Parallel Computing, Vol.77, pp.84-100, Septembre 2018, DOI 10.1016/j.parco.2018.06.005 , N° 18176

Lien : https://hal.laas.fr/hal-01823694

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Abstract

The study of the conformational energy landscape of a molecule is essential for the understanding of its physicochemical properties. This requires the exploration of a continuous, high-dimensional space to identify the most probable conformations and the transition paths between them. The problem is computationally difficult, in particular for highly-flexible biomolecules such as Intrinsically Disordered Proteins (IDPs). In recent years, a robotics-inspired algorithm called Transition-based Rapidly-exploring Random Tree (TRRT) has been proposed to solve this problem, and has been shown to provide good results with small and middle-sized biomolecules. Aiming to treat larger systems, we propose a hybrid strategy for the efficient parallelization of a multi-tree variant of TRRT, called Multi-TRRT, enabling an efficient execution in (possibly large) computer clusters. The parallel algorithm uses OpenMP multi-threading for computation inside each multi-core processor and MPI to perform the communication between processors. Results show a near-linear speedup for a wide range of cluster configurations. Although the paper mainly deals with the application of the proposed parallel algorithm to the investigation of biomolecules, the explanations concerning the methods are general, aiming to inspire future work on the parallelization of related algorithms.

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18165
24/08/2018

Mutual Localization of UAVs based on Blinking Ultraviolet Markers and 3D Time-Position Hough Transform

V.WALTER, N.STAUB, M.SASKA, A.FRANCHI

CTU, RIS

Manifestation avec acte : IEEE International Conference on Automation Science and Engineering ( CASE ) 2018 du 20 août au 24 août 2018, Munich (Allemagne), Août 2018, 6p. , N° 18165

Lien : https://hal.laas.fr/hal-01814840

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Abstract

A novel vision-based approach for indoor/outdoor mutual localization on Unmanned Aerial Vehicles (UAVs) with low computational requirements and without external infrastructure is proposed in this paper. The proposed solution exploits the low natural emissions in the near-UltraViolet (UV) spectrum to avoid major drawbacks of the visible spectrum .Such approach provides much better reliability while being less computationally intensive. Working in near-UV requires active markers, which can be leveraged by enriching the information content through blinking patterns encoded marker-ID. In order to track the markers motion and identify their blinking frequency, we propose an innovative use of three dimensional Hough Transform, applied to stored position-time points. The proposed method was intensively tested onboard multi-UAV systems in real-world scenarios that are very challenging for visible-spectrum methods.The results of our methods in terms of robustness, reliability and precision, as well as the low requirement on the system deployment, predestine this method to be an enabling technology for using swarms of UAVs.

143881
18175
01/08/2018

Conformational changes in antibody Fab fragments upon binding and their consequences on the performance of docking algorithms

A.BAROZET, M.BIANCIOTTO, T.SIMEON, H.MINOUX, J.CORTES

RIS, Sanofi-Aventis R&D

Revue Scientifique : Immunology Letters, Vol.200, pp.5-15, Août 2018 , N° 18175

Lien : https://hal.laas.fr/hal-01823695

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Abstract

Background: The existence of conformational changes in antibodies upon binding has been previously established. However, existing analyses focus on individual cases and no quantitative study provides a more global view of potential moves and repacking, especially on recent data. The present study focuses on analyzing the conformational changes in various antibodies upon binding, providing quantitative observations to be exploited for antibody-related modeling. Methods: Cartesian and dihedral Root-Mean-Squared Deviations were calculated for different subparts of 27 different antibodies, for which X-ray structures in the bound and unbound states are available. Elbow angle variations were also calculated. Previously reported results of four docking algorithms were condensed into one score giving overall docking success for each of 16 antibody-antigen cases. Results: Very diverse movements are observed upon binding. While many loops stay very rigid, several others display side-chain repacking or backbone rearrangements, or both, at many different levels. Large conformational changes restricted to one or more antibody hypervariable loops were found to be a better indicator of docking difficulty than overall conformational variation at the antibody-antigen interface. However, the failure of docking algorithms on some almost-rigid cases shows that scoring is still a major bottleneck in docking pose prediction. Conclusions: This study is aimed to help scientists working on antibody analysis and design by giving insights into the nature and the extent of conformational changes at different levels upon antigen binding.

143925
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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Abstract

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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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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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.

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
18169
15/06/2018

Fast Mutual Relative Localization of UAVs Using Ultraviolet LED Markers

V.WALTER, M.SASKA, A.FRANCHI

CTU, RIS

Manifestation avec acte : International Conference on Unmanned Aircraft Systems ( ICUAS ) 2018 du 12 juin au 15 juin 2018, Dallas (USA), Juin 2018, 10p. , N° 18169

Lien : https://hal.laas.fr/hal-01814828

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Abstract

This paper proposes a new methodology for outdoor mutual relative localization of UAVs equipped with active ultraviolet markers and a suitable camera with specialized bandpass filters. Mutual relative localization is a crucial tool for formation preservation, swarming and cooperative task completion in scenarios in which UAVs share working space in small relative distances. In most current systems of compact UAV swarms the localization of particular UAVs is based on the data obtained from motion capture systems for indoor experiments or on precise RTK-GNSS data outdoor. Such an external infrastructure is unavailable in most of real multi-UAV applications and often cannot be pre-installed. To account for such situations, as well as to make the system more autonomous, reliance on onboard sensors only is desirable. In the proposed approach, we rely on ultraviolet LED markers, that emit light in frequencies that are less common in nature than the visible light or infrared radiation, especially in high intensities. Additionally, common camera sensors are sensitive to ultraviolet light, making the addition of a filter the only necessary modification, keeping the platform low-cost, which is one of the key requirements on swarm systems. This also allows for a smaller size of the markers to be sufficient, without burdening the processing resources. Thus the proposed system aspires to be an enabling technology for deployment of large swarms of possibly micro-scale aerial vehicles in real world conditions and without any dependency on an external infrastructure.

143913
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.

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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.

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