17 research outputs found
Modeling and Control of a Flexible Space Robot to Capture a Tumbling Debris
RĂSUMĂ La conquĂȘte spatiale des 60 derniĂšres annĂ©es a gĂ©nĂ©rĂ© une grande quantitĂ© dâobjets Ă la dĂ©rive
sur les orbites terrestres. Leur nombre grandissant constitue un danger omniprĂ©sent pour lâexploitation des satellites, et requiert aujourdâhui une intervention humaine pour rĂ©duire les risques de collision. En effet, lâestimation de leur croissance sur un horizon de 200 ans,
connue sous le nom de âsyndrĂŽme de Kesslerâ, montre que lâaccĂšs Ă lâEspace sera grandement menacĂ© si aucune mesure nâest prise pour endiguer cette prolifĂ©ration. Le scientifique J.-C. Liou de la National Aeronautics and Space Administration (NASA) a montrĂ© que la tendance
actuelle pourrait ĂȘtre stabilisĂ©e, voire inversĂ©e, si au moins cinq dĂ©bris massifs Ă©taient dĂ©sorbitĂ©s par an, tels que des satellites en fin de vie ou des Ă©tages supĂ©rieurs de lanceur. Parmi les nombreux concepts proposĂ©s pour cette mission, la robotique sâest imposĂ©e comme une des
solutions les plus prometteuses grĂące aux retours dâexpĂ©rience des 30 derniĂšres annĂ©es. La Station Spatiale Internationale (ISS) possĂšde dĂ©jĂ plusieurs bras robotiques opĂ©rationnels, et de nombreuses missions ont dĂ©montrĂ© le potentiel dâun tel systĂšme embarquĂ© sur un satellite.
Pour deux dâentre elles, des Ă©tapes fondamentales ont Ă©tĂ© validĂ©es pour le service en orbite,et sâavĂšrent ĂȘtre similaires aux problĂ©matiques de la dĂ©sorbitation des dĂ©bris. Cette thĂšse se concentre sur lâĂ©tape de capture dâun dĂ©bris en rotation par un bras robotique
ayant des segments flexibles. Cette phase comprend la planification de trajectoire et le contrĂŽle du robot spatial, afin de saisir le point cible du dĂ©bris de la façon la plus dĂ©licate possible. La validation des technologies nĂ©cessaires Ă un tel projet est quasiment impossible sur Terre, et requiert des moyens dĂ©mesurĂ©s pour effectuer des essais en orbite. Par consĂ©quent, la modĂ©lisation et la simulation de systĂšmes multi-corps flexibles est traitĂ©e en dĂ©tails, et constitue une forte contribution de la thĂšse. Ă lâaide de ces modĂšles, une validation mixte est proposĂ©e par des essais expĂ©rimentaux, en reproduisant la cinĂ©matique en orbite par des
manipulateurs industriels contrĂŽlĂ©s par une simulation en temps rĂ©el. En rĂ©sumĂ©, cette thĂšse est construite autour des trois domaines suivants : la modĂ©lisation des robots spatiaux, le design de lois de contrĂŽle, et leur validation sur un cas test. Dans un premier temps, la modĂ©lisation de robots spatiaux en condition dâapesanteur est
dĂ©veloppĂ©e pour une forme âen Ă©toileâ.----------ABSTRACT
After 60 years of intensive satellite launches, the number of drifting objects in Earth orbits is reaching a shifting point, where human intervention is becoming necessary to reduce the threat of collision. Indeed, a 200 year forecast, known as the âKessler syndromeâ, states that
space access will be greatly compromised if nothing is done to address the proliferation of these debris. Scientist J.-C. Liou from the National Aeronautics and Space Administration (NASA) has shown that the current trend could be reversed if at least five massive objects,
such as dead satellites or rocket upper stages, were de-orbited each year. Among the various technical concepts considered for debris removal, robotics has emerged, over the last 30 years, as one of the most promising solutions. The International Space Station (ISS) already
possesses fully operational robotic arms, and other missions have explored the potential of a manipulator embedded onto a satellite. During two of the latter, key capabilities have been demonstrated for on-orbit servicing, and prove to be equally useful for the purpose of debris
removal. This thesis focuses on the close range capture of a tumbling debris by a robotic arm with light-weight flexible segments. This phase includes the motion planning and the control of a space robot, in order to smoothly catch a target point on the debris. The validation of such
technologies is almost impossible on Earth and leads to prohibitive costs when performed on orbit. Therefore, the modeling and simulation of flexible multi-body systems has been investigated thoroughly, and is likewise a strong contribution of the thesis. Based on these models, an experimental validation is proposed by reproducing the on-orbit kinematics on a test bench made up of two industrial manipulators and driven by a real-time dynamic simulation.
In a nutshell, the thesis is built around three main parts: the modeling of a space robot, the design of control laws, and their validation on a test case. The first part is dedicated to the flexible modeling of a space robot in conditions of weightlessness. A âstar-shapedâ multi-body system is considered, meaning that the rigid base carries
various flexible appendages and robotic arms, assumed to be open mechanical chains only. The classic Newton-Euler and Lagrangian algorithms are brought together to account for the flexibility and to compute the dynamics in a numerically efficient way. The modeling step starts with the rigid fixed-base manipulators in order to introduce the notations, then, détails the flexible ones, and ends with the moving-base system to represent the space robots
Control of a launcher in atmospheric ascent with guardian maps
This paper describes the synthesis of a SISO scheduled controller for a launcher vehicle. The problem consists
in designing a control law which will be valid on the atmospheric ascent trajectory from time 25 s to time 60 s,
while ensuring robustness and performance requirements. Moreover a flexible model with two bending modes is
considered, making the problem more challenging. An algorithm based upon guardian maps has been retained in
order to find an a priori fixed architecture controller. The algorithm yields a sequence of controllers that ensures
that pole confinement constraints are fulfilled for any time between 25 s and 60 s. The user can then interpolate
those controllers to find a scheduled controller with respect to time
ContrÎle d'attitude d'un lanceur en phase atmosphérique approche par applications gardiennes
RĂSUMĂ:
Dans un premier temps, la modĂ©lisation dâun lanceur spatial met en avant lâimportance
des variations des paramĂštres au cours de lâascension. Ils sont en effet fortement dĂ©pendants
de la variation de la masse avec la consommation des ergols. Le modÚle utilisé prend ainsi
en compte cette évolution en linéarisant les équations autour de 6 points de vol principaux,
pour obtenir des modÚles linéaires invariants dans le temps. Chacun de ces modÚles devra
ĂȘtre stabilisĂ© par une unique loi de commande, tout en respectant les performances dĂ©sirĂ©es.
La considération des modes de flexion du lanceur rend alors la synthÚse plus complexe.
Une autre consĂ©quence de lâĂ©volution temporelle est le sĂ©quencement des gains des contrËo-
leurs obtenus. Il est en effet montrĂ© dans le mĂ©moire quâaucun rĂ©glage constant du correcteur
adopté ne permet de respecter le cahier des charges sur toute la trajectoire.
Ensuite, la complexité de modélisation du lanceur complet amÚne à considérer les erreurs
et les incertitudes de modĂšle. Elles sont lĂ encore un enjeu majeur du projet puisquâil faut
pouvoir assurer les performances nominales précédentes de façon robuste. Les applications
gardiennes, de par leur propriétés, se sont révélées les plus adaptées pour traiter un tel pro-
blÚme de séquencement avec respect de performances robustes.
Dans cette optique, un aspect essentiel de la Maßtrise porte sur le développement de
méthodes de synthÚse basées sur les applications gardiennes. Il est en effet apparu que les
quelques travaux portant sur ce sujet développaient essentiellement la théorie, et que la mise
en Ćuvre de ces mĂ©thodes pouvait ĂȘtre amĂ©liorĂ©e.
Deux approches sont ainsi dĂ©veloppĂ©es Ă travers le projet. La premiĂšre sâappuie sur une vi-
sualisation graphique des lieux dâannulation des applications gardiennes. Un programme basĂ©
sur lâanalyse dâimage permet de vĂ©rifier automatiquement les rĂ©glages des gains qui satisfont
les contraintes. La seconde mĂ©thode sâappuie sur une optimisation portant sur les applications
gardiennes dans des zones dâintĂ©rĂȘt. Par itĂ©rations successives, il est alors possible de partir
du systÚme en boucle ouverte pour aboutir à un réglage des gains acceptable en boucle fermée.
Les méthodes élaborées ont été testées et éprouvées sur le cas du lanceur, avec le cahier des
charges fourni par ASTRIUM-ST. Cette application pratique a été motivée par la complexité
du systĂšme, les contraintes variĂ©es Ă considĂ©rer et lâimportance de la robustesse pour ce type
de commande. Autant de contraintes qui ont permis de valider lâintĂ©rĂȘt et lâefficacitĂ© des
applications gardiennes sur ce type de problĂšme.----------
ABSTRACT:
In a first phase, the modelling process underlines the presence of highly time varying
parameters during the ascent, due to a fast mass variation along with propellant consumption.
Linearizing the dynamical equations at six main flight instants yields linear time invariant
models to be considered during control design. Each of them is to be stabilized by one control
law, while respecting given specifications. The synthesis becomes even more complex when
the bending modes are taken into account.
Moreover, scheduling appears necessary to deal with the time variations. Indeed it is
shown that no single gain setting is able to respect all the specifications along the trajectory.
Furthermore, increasing complexity when modelling a whole launch vehicle pushes one
to consider the modelâs errors and uncertainties. They represent a major issue in this study
since it is asked to ensure the nominal performances in a robust fashion. Owing to their
properties, guardian maps appear to be the most suitable tool to deal with such a problem
of scheduling with robust performances.
In light of this, the development of synthesis methods based on guardian maps is the main
contribution of the project. It appears that actual state of the art in this field is focused on
theoretical issues, whereas practical ones could be improved.
Two approches are presented in the memoire. The first one is based on a graphical ap-
proach consisting in drawing the vanishing locus of guardian maps. A program using image
analysis techniques is devised to check automatically which gain settings satisfy the con-
straints. The second one is based on an optimisation procedure involving guardian maps.
Starting with the open loop system, the iterative process proposed ends up with a satisfactory
gain setting for the closed-loop.
These methods are tried and tested for the launch vehicle, with specifications from
ASTRIUM-ST. Their practical application is motivated by the system complexity, the differ-
ent kinds of constraints and the essential need for robustness. Many restrictions that finally
bring about the interest and the efficiency of guardian maps for such a problem
Linear dynamics of flexible multibody systems : a system-based approach
A new methodology to derive the linear model of flexible multibody system dynamics is presented in this paper. This approach is based on the twoport model of each body allowing the model of the whole system to be built just connecting the inputs/outputs of each body model. Boundary conditions of each body can be taken into account through inversion of some input-output channels of its two-port model. This approach is extended here to treat the case of closed-loop kinematic mechanisms. Lagrange multipliers are commonly used in an augmented differential-algebraic equation to solve loop-closure constraints. Instead, they are considered here as a model output, which is connected to the adjoining body model through a feedback. After a summary of main results in the general case, the case of planar mechanisms with multiple uniform beams is considered and the two-port model of the Euler-Bernouilli beam is derived. The choice of the assumed modes is then discussed regarding the accuracy of the first natural frequencies for various boundary conditions. The overall modeling approach is then applied to the well-known four bar mechanism
Incorporating delayed and multi-rate measurements in navigation filter for autonomous space rendezvous
In the scope of space missions involving rendezvous between a chaser and a target, vision based navigation relies on the use of optical sensors coupled with image processing and computer vision algorithms to obtain a measurement of the target relative pose. These algorithms usually have high latency time, implying that the chaser navigation filter has to fuse delayed and multi-rate measurements. This article has two main contributions: it provides a detailed modelization of the relative dynamics within the estimation filter, and it proposes a comparison of two delay management techniques suitable for this application. The selected methods are the Filter Recalculation method -which always provides an optimal estimation at the expense of a high computational load- and the Larsenâs method -which provides a faster solution whose optimality lies on stronger requirements. The application of these techniques to the space rendezvous problem is discussed and formalized. Finally, the current article proposes a comparison of the methods based on a Monte-Carlo campaign, aimed at demonstrating whether the loss of performance of Larsenâs method due to its sub-optimality still enables target state robust tracking
Modeling & control of a space robot for active debris removal
Space access and satellites lifespan are increasingly threatened by the great amount of debris in Low Earth Orbits (LEO). Among the many solutions proposed in the literature so far, the emphasis is put here on a robotic arm mounted on a satellite to capture massive debris, such as dead satellites or launch vehicle upper stages. The modeling and control of such systems are investigated throughout the paper. Dynamic models rely on an adapted Newton-Euler algorithm, and control algorithms are based on the recent structured H infinity method. The main goal is to efficiently track a target point on the debris while using simple PD-like controllers to reduce computational burden. The structured H infinity framework proves to be a suitable tool to design a reduced-order robust controller that catches up with external disturbances and is simultaneously compatible with current space processors capacities
Vision-based navigation for autonomous space rendezvous with non-cooperative targets
This study addresses the issue of vision-based navigation
for space rendezvous with non-cooperative targets. After
a brief description of the scenario and its peculiarities, the theory underlying monocular edges-based tracking for pose estimation is recalled and an innovative tracking algorithm is formally developed and implemented. This algorithm is coupled with a dynamic Kalman Filter propagating the dynamics which underlies a space rendezvous. The navigation filter increases the robustness of target position and attitude estimation, and allows the estimation of target translational velocity and rotation rate using only pose measurements. Moreover, the filter implements
a computationally efficient delay management technique that
allows merging the delayed and infrequent measurements typical of vision-based navigation. The performance of the algorithm is tested in different scenarios with high fidelity synthetic images
Addressing mental health problems among persons without stable housing in the context of the COVID-19 pandemic: study protocol for a randomised trial. RESPOND â France
Background The COVID-19 pandemic has had an impact on population-wide mental health and well-being. Although people experiencing socioeconomic disadvantage may be especially vulnerable, they experience barriers in accessing mental health care. To overcome these barriers, the World Health Organization (WHO) designed two scalable psychosocial interventions, namely the web-based Doing What Matters in Times of Stress (DWM) and the face-to-face Problem Management Plus (PM+), to help people manage stressful situations. Our study aims to test the effectiveness of a stepped-care program using DWM and PMâ+âamong individuals experiencing unstable housing in France â a majority of whom are migrant or have sought asylum. Methods This is a randomised controlled trial to evaluate the effectiveness and cost effectiveness of a stepped-care program using DWM and PMâ+âamong persons with psychological distress and experiencing unstable housing, in comparison to enhanced care as usual (eCAU). Participants (Nâ=â210) will be randomised to two parallel groups: eCAU or eCAU plus the stepped-care program. The main study outcomes are symptoms of depression and anxiety measured using the Patient Health Questionnaire Anxiety and Depression Scale (PHQ-ADS). Discussion This randomised controlled trial will contribute to a better understanding of effective community-based scalable strategies that can help address the mental health needs of persons experiencing socioeconomic disadvantage, whose needs are high yet who frequently have limited access to mental health care services
Modeling and Control of a Flexible Space Robot to Capture a Tumbling Debris
Les dĂ©bris en orbite sont actuellement une source de prĂ©occupation majeure pour les acteurs du spatial et pour le reste de la population, comme en tĂ©moignent les articles de presse et les Ćuvres cinĂ©matographiques sur le sujet. En effet, la prĂ©sence de ces objets menace directement les astronautes en mission et les satellites en opĂ©ration. Parmi les nombreuses options dĂ©jĂ envisagĂ©es pour les traiter, cette thĂšse se concentre sur lâapproche robotique, en proposant des outils et des mĂ©thodes de modĂ©lisation et de contrĂŽle pour un satellite chasseur Ă©quipĂ© dâun bras manipulateur. Des modĂšles dynamiques et des schĂ©mas de simulation optimisĂ©s sont ainsi dĂ©veloppĂ©s pour tout systĂšme multi-corps constituĂ© dâune base mobile supportant un nombre quelconque dâappendices rigides ou flexibles. Par la suite, les trajectoires de capture sont gĂ©nĂ©rĂ©es en conservant la continuitĂ© en accĂ©lĂ©ration avec le mouvement naturel du point cible, dans le but de saisir aussi dĂ©licatement que possible le dĂ©bris en rotation. Le suivi de cette trajectoire par lâeffecteur du robot chasseur est alors assurĂ© par une loi de contrĂŽle Ă deux niveaux, dont le rĂ©glage repose sur la synthĂšse H1 structurĂ©e. Une Ă©tude de robustesse est Ă©galement mise en place pour assurer la stabilitĂ© et les performances du systĂšme en boucle fermĂ©e, malgrĂ© les changements de configuration du bras. Enfin, la validation des travaux de thĂšse est rĂ©alisĂ©e par voie numĂ©rique avec un simulateur haute-fidĂ©litĂ©, et par voie pratique avec un banc dâessais robotique incluant des composants physiques en temps rĂ©el.On-orbit debris are currently causing deep concern for space agencies, related companies, and also among the population. Âżis is evidenced by the numerous scientific articles and recent movies on the matter. Indeed, these objects pose a serious threat for the astronauts on mission and for operational satellites. Among the various technical concepts already designed to address these threats, this thesis focuses on space robotics. Tools and methods are thus introduced for the modeling and control of a chaser satellite equipped with a manipulator. Dynamic models and optimized simulation schemes are developed to handle any multi-body system made up of amoving base embedding various appendages, either rigid or flexible. Âżen, a trajectory planner is designed to ensure acceleration continuity with the natural motion of the debris in order to perform a soft capture. Âżis reference trajectory is tracked by the end-effector of the chaser using a two-level control law, which is tuned by the structured H1 synthesis. A robustness analysis is also presented to assess the stability and the performances of the closed-loop system with respect to the motion of the robotic arm. Finally, the outcome of the thesis is validated by a twofold approach: by numerical means with a highfidelity simulator, and by practical ones with a robotic test bench including physical components in real time
Advanced GNC for In-Orbit Autonomous Assembly of Flexible Vehicles â IOA-GNC
International audienc