HAL Arts et Métiers
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Estimation des positions articulaires du membre supérieur à partir d'un exosquelette
No full textInternational audienceEstimation des positions articulaires du membre supérieur à partir d'un exosquelett
Compact docking for precise indoor drone landing
No full textInternational audienceLightweight drones (<150g) are well-suited for indoor applications such as inspection, surveillance, orrescue operations. However, their deployment is often constrained by the lack of reliable solutions forautonomous landing in GPS-denied environments. This work presents the development of a compactdocking station (15×15×15 cm) enabling precise micro-drone docking. The station integrates a positio-ning system based on the HTC Vive Lighthouse infrared sensor and uses onboard algorithms, includingExtended Kalman Filtering (EKF), to achieve localization accuracy within a few centimeters.The docking station features a vertically mounted infrared sensor to optimize visibility and motorizedlanding supports controlled by Dynamixel motors. These supports retract during the localization phaseto prevent interference with the drone’s sensors. The drone used in this study, called Proxyflie, is a120g quadrotor developed in the laboratory. It is equipped with a Bitcraze control board and sensorsfor stabilization and navigation (optical sensors and Time-of-Flight sensors). The drone can detect thestation’s infrared signal, adjust its position, and perform a precise landing.Experimental tests compared the Lighthouse system with alternative solutions, such as OptiTrack sys-tems (Duo and Trio) and Ultra Wide Band (UWB) radio positioning systems. The results indicate thatthe Lighthouse system offers a favorable trade-off between accuracy, cost, and compactness. While Op-tiTrack systems provide higher accuracy (millimeter-level), they require bulky and expensive infrastruc-ture, making them less practical for this use case.Les drones ultra-légers (<150 g) sont particulièrement adaptés aux applications en intérieur, telles quel’inspection, la surveillance ou les missions de sauvetage. Toutefois, leur déploiement reste limité parl’absence de solutions autonomes et fiables pour l’atterrissage dans des environnements sans GPS. Cetravail présente le développement d’une station d’accueil compacte (15×15×15 cm) permettant un ar-rimage précis de micro-drones. La station intègre un système de positionnement reposant sur le capteurinfrarouge HTC Vive Lighthouse et embarque des algorithmes de traitement, notamment un filtre de Kal-man étendu (EKF), permettant une localisation avec une précision de l’ordre de quelques centimètres.La station est équipée d’un capteur infrarouge monté à la verticale pour optimiser le champ de vision,ainsi que de supports d’atterrissage motorisés contrôlés par des servomoteurs Dynamixel. Ces supportsse rétractent automatiquement pendant la phase de localisation afin de ne pas interférer avec les capteursembarqués du drone. Le drone utilisé dans cette étude, appelé Proxyflie, est un quadricoptère de 120 gdéveloppé au sein du laboratoire. Il est doté d’une carte de contrôle Bitcraze et de capteurs dédiés à lastabilisation et à la navigation, incluant des capteurs optiques et des capteurs Time-of-Flight. Le droneest capable de détecter le signal infrarouge émis par la station, d’ajuster sa position en conséquence etd’effectuer un atterrissage de haute précision.Une campagne expérimentale a permis de comparer le système Lighthouse à d’autres solutions de po-sitionnement, telles que les systèmes OptiTrack (Duo et Trio) et les systèmes radio à bande ultra-large(UWB). Les résultats mettent en évidence le bon compromis offert par la solution Lighthouse entreprécision, coût et encombrement. Bien que les systèmes OptiTrack offrent une précision supérieure (àl’échelle du millimètre), leur infrastructure lourde et coûteuse les rend peu adaptés aux contraintes dece cas d’usage.</p
Development of a custom commingled flax/PLA wrapped yarn for additive manufacturing of long-fibre biocomposites
No full textInternational audiencePlant fibres are promising reinforcements for bio-composites in additive manufacturing, but their use as long fibres remains limited, often reduced to short particles that underuse their potential. This study presents a customised yarn design that not only maintains fibre alignment parallel to the yarn axis but also ensures core resin impregnation. Commingling and wrap spinning techniques were used to produce four flax/PLA yarns with varying compositions. The manufacturing process and printing of unidirectional composite specimens are detailed. Tomography revealed up to 3.3 times lower intra-yarn porosity thanks to commingling, and tensile tests showed a modulus increase by a factor of 2.1 compared to similar previous works using conventional twisted yarns. These results pave the way for broader use of long flax fibres in 3D printing
Multiplexed Bio‐detection on an Interferometric Optical Waveguide Assembly
No full textInternational audienceMultiplexed remote bio‐detection is demonstrated through an optical waveguide assembly coated with interferometric layers. Image conduits (IC)s, composed of 3012 individual cores, are coated with interferometric layers of tantalum pentoxide (Ta 2 O 5 ) and silica (SiO 2 ) to transform each core into a sensitive sensor. The spectral response of the IC as a function of refractive index (RI) changes is obtained and compared with the simulated one. The experimental sensitivities and resolutions of individual cores of the waveguide are assessed in remote detection mode by imaging through the optical assembly. For 75% of the cores, a sensitivity better than 510%. RIU −1 (RI Unit) is obtained, corresponding to a resolution better than 7 × 10 −4 RIU. Furthermore, the coated face of IC is functionalized with two localized arrays of hundred‐micrometer droplets containing two different oligonucleotide (ODN) probes using a polymeric 3D‐printed microcantilever. Hybridization of complementary ODN strands is detected for one of the probes, the second being a negative control. Interaction kinetics are monitored in functionalized areas by grouping several cores or on individual cores. Thus, multiplexed bio‐detection on the surface of an interferometric waveguide is demonstrated for the first time paving the way for applications in multiplex in situ biosensing, and, ultimately, in vivo endoscopic diagnosis
Influence of winding and positioning defects on current measurement with a Rogowski coil
No full textInternational audienceThe Rogowski coil is a well-known transducer device use for its linear or large bandwidth characteristic, but it’s quite a challenge to wind a perfect Rogowski coil to minimize the current measurement error. In this paper, we will discuss the influence of different winding and positioning defects such as coil and turn tilt, turn density, and conductor positioning on current measurement. Using Sobol’s method combined with Monte Carlo method, this study aims to highlight the manufacturing defects that have the worst influence on the actual current measurement accuracy.La bobine de Rogowski est un capteur bien connu utilisé pour ses caractéristiques linéaires ou sa large bande passante, mais il est assez difficile d'enrouler une bobine de Rogowski parfaite afin de minimiser l'erreur de mesure du courant. Dans cet article, nous aborderons l'influence de différents défauts d'enroulement et de positionnement, tels que l'inclinaison de la bobine et des spires, la densité des spires et le positionnement des conducteurs, sur la mesure du courant. À l'aide de la méthode de Sobol combinée à la méthode de Monte Carlo, cette étude vise à mettre en évidence les défauts de fabrication qui ont la plus mauvaise influence sur la précision réelle de la mesure du courant
Physics-informed neural networks as alternative to finite element solvers
No full textInternational audienceThis study investigates the application of physics-informed neural networks (PINNs) as alternative tofinite element (FE) solvers in both classical and gradient-enhanced solid mechanics. To this end, thePINN architecture is specifically designed to represent continuous solutions of boundary value problems within spatio-temporal space. The governing partial differential equations as well as the boundary conditions are incorporated via soft constraint terms in the objective function which is minimized during the training of the PINNs. As the differential and rate form of equilibrium and constitutiveequations are directly considered using the power of automatic differentiation, the need for traditionalincremental implementation is eliminated. This advantage allows the methodology to address complexproblems, such as gradient-enhanced plasticity theories, with practically no additional effort comparedto classical frameworks. The effectiveness of the proposed methodology is demonstrated via benchmarkproblems. Moreover, as neural networks are by design smooth functions, the classic PINNs cannot precisely approximate non-smooth solutions with localization or abrupt change in the slope. To address thisissue, enrichment patches based on wavelet functions are developed by the authors to enrich the smoothsolutions learned by the PINNs, allowing precise approximation of solutions presenting localization
On the importance of Ni-Au-Ga interdiffusion in the formation of a Ni-Au / p-GaN ohmic contact
No full textInternational audienceThe Ni-Au-Ga interdiffusion mechanisms taking place during rapid thermal annealing (RTA) under oxygen atmosphere of a Ni-Au/p-GaN contact are investigated by high-resolution transmission electron microscopy (HR-TEM) coupled to energy dispersive X-ray spectroscopy (EDX). It is shown that oxygen-assisted, Ni diffusion to the top surface of the metallic contact through the formation of a nickel oxide (NiOx) is accompanied by Au diffusion down to the GaN surface, and by Ga out-diffusion through the GaN/metal interface. Electrical characterizations of the contact by Transmission Line Method (TLM) show that an ohmic contact is obtained as soon as a thin, Au-Ga interfacial layer is formed, even after complete diffusion of Ni or NiOx to the top surface of the contact. Our results clarify that the presence of Ni or NiOx at the interface is not the main origin of the ohmic-like behavior in such contacts. Auto-cleaning of the interface during the interdiffusion process may play a role, but TEM-EDX analysis evidences that the creation of Ga vacancies associated to the formation of a Ga-Au interfacial layer is crucial for reducing the Schottky barrier height, and maximizing the amount of current flowing through the contact
Why move during virtual reality sketching? Experimental study to improve the quality of sketches in virtual reality
No full textInternational audienceVirtual Reality (VR) sketching is a valuable tool for conceptual understanding, creativity, and design, but quality issues can hinder its adoption. To address this, we conducted a study involving 15 novices and 15 experts who sketched three chair models in static, mobile, and control conditions. The results showed that mental rotation skills, training, model type, and movement impact sketch quality. The static condition negatively affected performance, particularly volume and proportion. Conversely, the mobile condition didn't improve sketch quality compared to the control group. 3D perception seems tied to movement, highlighting the need to adapt VR sketching software for these challenges. Enhancing the user experience and addressing these quality concerns will be pivotal in the widespread acceptance of VR sketching tools
Least-Squares Recovery of Dual Variables in ROMs for Saddle-Point Problems
No full textIn this work, we introduce a methodolgy for recovering the reduced Lagrange multiplier in Reduced Order Models (ROMs) of general saddle-point problems. Specifically, the multiplier is determined as the least-squares minimizer of the residual of the reduced primal variable in a dual norm. We prove that this procedure yields a unique solution under the condition that the full-order primal and dual spaces satisfy the inf-sup stability condition. This is an extension to general saddle-point problems of the method recently introduced in [1] to recover the reduced pressure in ROMs of incompressible flows.We further show that the proposed approach is equivalent to solving the reduced mixed problem with an enriched reduced primal basis, augmented by the supremizers of the reduced multiplier gradients. We establish optimal error estimates for the reduced multiplier applicable to general saddle-point problems.Numerical experiments for heat diffusion in composite media validate our theoretical findings and demonstrate the suitability of the method to solve engineering problems [1] Azaïez M., Chacon Rebollo, T, Oulghelou and M., I. Sanchez Munoz : Least-squares pressure recovery in Reduced Order Methods for incompressible flows. J. Comput. Phys. 519: 113397 (2024)