Reducing Safety Interventions in Provably Safe Reinforcement Learning

Deep Reinforcement Learning (RL) has shown promise in addressing complex robotic challenges. In real-world applications, RL is often accompanied by failsafe controllers as a last resort to avoid catastrophic events. While necessary for safety, these interventions can result in undesirable behaviors, such as abrupt braking or aggressive steering. This paper proposes two safety intervention reduction methods: proactive replacement and proactive projection, which change the action of the agent if it leads to a potential failsafe intervention. These approaches are compared to state-of-the-art constrained RL on the OpenAI safety gym benchmark and a human-robot collaboration task. Our study demonstrates that the combination of our method with provably safe RL leads to high-performing policies with zero safety violations and a low number of failsafe interventions. Our versatile method can be applied to a wide range of real-world robotic tasks, while effectively improving safety without sacrificing task performance.Comment: 8 pages, 6 figure

Recommendations on using VPN over SATCOM

VPN are a secured tunnel that help service providers to exchange data over non-secured networks. There is a large variety of VPN solutions that have variable deployment impacts on the target architecture as well as performance limitations or opportunities. This technical report compares Wireguard and OpenVPN for various SATCOM deployment scenarios and topologies

Zero reflections by a 1D Acoustic Black Hole termination using thermally controlled damping

International audienceThe design of lightweight and stiff structures with attractive vibration damping properties is a major issue in mechanical engineering. The insertion of Acoustic Black Holes (ABH) in a beam is a technique that consists in locally reducing its thickness at the end and coating it with a visco-elastic film. The reflection coefficient of the resulting system decreases with frequency and displays typical arches which can exactely reach zero when the amount of losses is well adjusted, reaching the critical coupling condition. However, the precise amount of added damping is very difficult to tune by using classical visco-elastic layers. It is here proposed to control it by using a thermal active system acting in a shape memory polymer (SMP). In this manner, the damping and stiffness profiles become tunable via a given thermal gradient which leads to create an enhanced ABH (eABH) that can be tuned in real time, so that the critical coupling can be reached. The objective of the paper is to demonstrate numerically and experimentally the capability of an eABH to achieve exact zero reflections using precise control of temperature gradients

Enhanced acoustic black holes (EABH) based on tuned damping properties obtained by thermal control

International audienceThe design of lightweight and stiff structures with attractive vibration damping properties is a major issue in mechanical engineering. The insertion of Acoustic Black Holes (ABH) is an innovative technique that consists in locally reducing the thickness of the stucture<br&gtand coating it with a viscoelastic film. In the particular case where the damping layer provides a perfect adjustment of the losses, the reflection coefficient R of the resulting system is zero at the resonance of a trapped mode localized in the ABH profile. This phenonemon is<br&gtreached when the critical coupling conditions are fulfilled. However, the precise amount of losses is particularly difficult to tune by using only classical viscoelastic layers. It is here proposed to control it by using a thermal active system acting in a shape memory polymer (SMP).<br&gtThe goal of the paper is to investigate several enhanced ABH (eABH) in beams for which the damping and the stiffness are controlled by a thermal profile. For each eABH configuration, the trajectory of the zeros of R is studied in order to approach the critical coupling conditions

Reflection coefficients of Enhanced Acoustic Black Holes at a beam termination

International audienceThe design of lightweight and stiff structures with high vibration damping properties is an important issue in mechanical engineering. The insertion of Acoustic Black Holes (ABH) in a flat panel or in a beam termination is an innovative technique for passive structural vibration damping without added mass. ABH consist in local heterogeneities of the stiffness and the damping and are known as efficient absorbers forflexural waves above their cut-on frequency. The goal of the paper is to identify and to push the current limitations of this existing strategy by developing ”enhanced acoustic black holes” (eABH) absorbers based on the integration of thermal adaptive systems. The capability of such techniques to enhance the control of the flexural rigidity and the local damping is investigated numerically. The reflection coefficients, R, of several architectures of ABH beam termination are computed using the Impedance Matrix method. Such a method is adapted to the accurate computation of R of a structural wave guide with varying properties. Comparing R of several architectures allows us to discuss the potentialities of such eABH

Mesure et modèle du coefficient de réflexion d’un Trou Noir Acoustique bidimensionnel intégré à une plaque

Les Trous Noirs Acoustiques (TNA) intégrés en bout de poutres, sujettes à des vibrations de flexion, sont des variations locales d'épaisseur, associées à des mécanismes dissipatifs locaux réalisés par des revêtements appropriés. Un TNA est une terminaison anéchoïque, que l'on peut caractériser de façon intrinsèque par son coefficient de réflexion. Dans ce travail, on propose d’étendre cette caractérisation au cas de TNA circulaires, intégrés à des plaques. Ces TNA sont constitués par des cuvettes axisymétriques dont le profil d'épaisseur est parabolique et revêtues d'un matériau absorbant. Ils constituent des diffuseurs pénétrables, résonants et absorbants, que l'on peut caractériser au moyen d'une matrice de diffusion. En considérant uniquement les ondes axisymétriques convergentes et divergentes centrées sur le TNA, l'absorption réalisée est décrite par le premier terme R0 de cette matrice de diffusion. Ce coefficient R0 est calculé au moyen d'un modèle semi-analytique basé sur une approche ondulatoire, dont les résultats sont confirmés par un modèle numérique basé sur la méthode des éléments finis. Une technique de mesure, utilisant une cartographie du champ de vitesse vibratoire sur une couronne entourant le TNA obtenue par vibrométrie, est développée et simulée. On montre qu'un filtrage par décomposition en séries de Fourier permet de séparer les contributions des différents ordres circonférentiels et en particulier d'extraire l'ordre 0, ce qui permet une estimation de R0. La possibilité pratique de mesurer R0 par cette méthodologie expérimentale est discutée. Les résultats expérimentaux confirment la structure de R0 prédite par les modèles développés et l'intérêt de ce descripteur pour caractériser les effets intrinsèques des TNA 2D

Contrôle de la réflexion d’une poutre en flexion par des résonateurs sub-longueur d'onde accordables thermiquement

Dans ce travail, l'absorption parfaite d'une onde de flexion par un absorbeur sub-longueur d'onde accordable thermiquement est démontrée analytiquement et expérimentalement pour un problème de réflexion dans des poutres. Ces absorbeurs sont des résonateurs locaux situés à l'extrémité d'une poutre semi-infinie et sont constitués de lames minces recouvertes d'une couche de Polymère à Mémoire de Forme (PMF), dont la rigidité et l'amortissement dépendent fortement de la température. Les résonateurs présentent donc à la fois des fuites d'énergie des absorbeurs vers la poutre et des pertes inhérentes à la présence du PMF. En particulier, la situation dans laquelle les pertes inhérentes équilibrent la fuite d'énergie est connue sous le nom de conditions de couplage critique et conduit à l'absorption parfaite de l'onde incidente. Il est démontré que ces conditions peuvent être remplies simultanément pour différentes lames du système en ajustant la température du PMF et la géométrie des lames. Les résultats analytiques sont basés sur la méthode de la matrice impédance. La validation expérimentale met en évidence la possibilité de réaliser une absorption sub-longueur d'onde multi-fréquences dans le cas de configurations multi-lames

Control of bending wave reflection at beam terminations by thermally tunable subwavelength resonators

International audienceThe perfect absorption of bending waves by thermally tunablesubwavelength absorbers is analytically and experimentallydemonstrated in this work for a reflection problem in beams. Theseabsorbers are local resonators located at the end of asemi-infinite beam and consist of<br /&gtthin blades covered with a layer of Shape Memory Polymer (SMP), thestiffness and damping of which strongly depend on the temperature.The resonators therefore present both energy leakage from theabsorbers to the beam and inherent losses thanks to the presence ofthe SMP. In particular, the situation in which the inherent lossesbalances the energy leakage is known as the critical couplingconditions and leads to the perfect absorption of the incident wavein the reflection problem. It is shown that these conditions can besimultaneously fulfilled for the different blades of the resonatingsystem by tuning the temperature of the SMP and the geometry of theblades. The analytical results are based on the Impedance MatrixMethod. The experimental validation highlights the possibility ofachieving multi-frequency subwavelength absorption in the case ofmulti-blades configurations

Latest VO developments at Paris VO Data Center

International audienceParis VO Data Center aims at providing VO access to its databases ressources, at participating to international standards developments, at implementing VO compliant simulation codes and data visuali- sation and analysis softwares. We will present some of the latest VO developments involving ressources from Paris VO Data Center, i.e, the first simple spectra access for data of the Nanay radiotelescope observatory, a validator for Simple Spectra Access protocols and its implementation tools, a Cone-search access to the exoplanet catalog, a pipeline for images processing to make them ”science-ready” in vo-format, implemen- tation of Simple Image Access using Geographic Information System in databases. Developments involving other ressources may be found in their own contributions to this meeting

Latest VO developments at Paris VO Data Center

International audienceParis VO Data Center aims at providing VO access to its databases ressources, at participating to international standards developments, at implementing VO compliant simulation codes and data visuali- sation and analysis softwares. We will present some of the latest VO developments involving ressources from Paris VO Data Center, i.e, the first simple spectra access for data of the Nanay radiotelescope observatory, a validator for Simple Spectra Access protocols and its implementation tools, a Cone-search access to the exoplanet catalog, a pipeline for images processing to make them ”science-ready” in vo-format, implemen- tation of Simple Image Access using Geographic Information System in databases. Developments involving other ressources may be found in their own contributions to this meeting