Естимација крутости и адаптивно управљање код попустљивих робота

Although there has been an astonishing increase in the development of nature- inspired robots equipped with compliant features,i.e.soft robots, their full potential has not been exploited yet. One aspect is that the soft robotics research has mainly focused on their position control only, whilest iffness is managed in open loop. Moreover, due to the difficulties of achieving consistent production of the actuation systems for soft articulated robots and the time-varyingnatureoftheirinternalflexibleelements,whicharesubjecttoplasticdeformation overtime,itiscurrentlyachallengetopreciselydeterminethejointstiffness. . In this regard, the thesis puts an emphasis on stiffness estimation and adaptive control for soft articulated robots driven by antagonistic Variable Stiffness Actuators (VSAs) with the aim to impose the desired dynamics of both position and stiffness, which would finally contribute to the overall safety and improved performance of a soft robot. By building upon Unknown Input Observer (UIO) theory, invasive and non-invasive solutions for estimation of stiffness in pneumatic and electro-mechanical actuators are proposed and in the latter case also experimentally validated. Beyond the linearity and scalability advantage, the approaches have an appealing feature that torque and velocity sensors are not needed. Once the stiffness is determined, innovative control approaches are introduced for soft articulated robots comprising an adaptive compensator and a dynamic decoupler. The solutions are able to cope with uncertainties of the robot dynamic model and, when the desired stiffness is constant or slowly-varying, also of the pneumatic actuator. Their verification is performed via simulations and then the pneumatic one is successfully tested on an experimental setup. Finally, the thesis shows via extensive simulations the effectiveness of adaptive technique ap- plied to soft-bodied robots, previously deriving the sufficient and necessary conditions for the controller convergence.Iako se danas izuzetno intenzivno radi na razvoju robota inspirisanih prirodom koje odlikuje elastična struktura, njihov puni potencijal jox uvek nije iskorišćen. Sa jedne strane, istraživanja u oblasti popustljivih robota su uglavnom fokusirana samo na upravljanje njihovom pozicijom, dok se krutost reguliše u otvorenoj sprezi. Pored toga, zbog poteškoća u postiznju konzistentne proizvodnje aktuatora i promenljive prirode njihovih elastičnih elemenata, koji su vremenom podlo_ni plastičnoj deformaciji, trenutno je izazov precizno odrediti krutost zglobova robota. U cilju doprinosa poboljšanja_u performansi i bezbednosti rada popustivih robota, teza prikazuje doprinos proceni krutosti i adaptivnog simultanog upravljanja pozicijom i krutosti antagonističkih aktuatora promenljive krutosti (VSA). Oslanjajući se na teoriju opservera nepoznatih ulaza (UIO), predložena su invazivna i neinvazivna rešenja za procenu krutosti u pneumatskim i elektromehaničkim aktuatorima i eksperimentalno verifikovana u slučaju druge grupe aktuatora. Pored linearnosti i skalabilnosti, ovi pristupi imaju privlaqnu osobinu da senzori momenta i brzine nisu potrebni. Teza predla_e inovativne sisteme upravljanja koji poseduju adaptivni kompenzator i dinamički dekupler. Predložene metode upravljanja demonstriraju mogućnost da kompenzuju nesigurnosti dinamičkog modela robota bez obzira da li je on pogođen električnim ili pneumatskim aktuatorima. Nakon simulacija, razvijeno upravljanje je verifikovano i na pneumatskom robotu. Na kraju teze, obimne simulacije pokazuju efikasnost adaptivne tehnike kada se primeni na robote sa fleksibilnim linkovima, prethodno izvodeći dovoljne i potrebne uslove za konvergenciju kontrolera

Compliant Actuation Based on Dielectric Elastomers for a Force-Feedback Device: Modeling and Experimental Evaluation

Thanks to their large power densities, low costs and shock-insensitivity, Dielectric Elastomers (DE) seem to be a promising technology for the implementation of light and compact force-feedback devices such as, for instance, haptic interfaces. Nonetheless, the development of these kinds of DE-based systems is not trivial owing to the relevant dissipative phenomena that affect the DE when subjected to rapidly changing deformations. In this context, the present paper addresses the development of a force feedback controller for an agonist-antagonist linear actuator composed of a couple of conically-shaped DE films and a compliant mechanism behaving as a negative-rate bias spring. The actuator is firstly modeled accounting for the visco-hyperelastic nature of the DE material. The model is then linearized and employed for the design of a force controller. The controller employs a position sensor, which determines the actuator configuration, and a force sensor, which measures the interaction force that the actuator exchanges with the environment. In addition, an optimum full-state observer is also implemented, which enables both accurate estimation of the time-dependent behavior of the elastomeric material and adequate suppression of the sensor measurement noise. Preliminary experimental results are provided to validate the proposed actuator-controller architecture

Compliant actuation based on dielectric elastomers for a force-feedback device: modeling and experimental evaluation

Thanks to their large power densities, low costs and shock-insensitivity, Dielectric Elastomers (DE)seem to be a promising technology for the implementation of light and compact force-feedback devices such as,for instance, haptic interfaces. Nonetheless, the development of these kinds of DE-based systems is not trivialowing to the relevant dissipative phenomena that affect the DE when subjected to rapidly changingdeformations. In this context, the present paper addresses the development of a force feedback controller foran agonist-antagonist linear actuator composed of a couple of conically-shaped DE films and a compliantmechanism behaving as a negative-rate bias spring. The actuator is firstly modeled accounting for the viscohyperelasticnature of the DE material. The model is then linearized and employed for the design of a forcecontroller. The controller employs a position sensor, which determines the actuator configuration, and a forcesensor, which measures the interaction force that the actuator exchanges with the environment. In addition, anoptimum full-state observer is also implemented, which enables both accurate estimation of the time-dependentbehavior of the elastomeric material and adequate suppression of the sensor measurement noise. Preliminaryexperimental results are provided to validate the proposed actuator-controller architectur

Compliant actuation based on dielectric elastomers for a force-feedback device: modeling and experimental evaluation

Thanks to their large power densities, low costs and shock-insensitivity, Dielectric Elastomers (DE) seem to be a promising technology for the implementation of light and compact force-feedback devices such as, for instance, haptic interfaces. Nonetheless, the development of these kinds of DE-based systems is not trivial owing to the relevant dissipative phenomena that affect the DE when subjected to rapidly changing deformations. In this context, the present paper addresses the development of a force feedback controller for an agonist-antagonist linear actuator composed of a couple of conically-shaped DE films and a compliant mechanism behaving as a negative-rate bias spring. The actuator is firstly modeled accounting for the viscohyperelastic nature of the DE material. The model is then linearized and employed for the design of a force controller. The controller employs a position sensor, which determines the actuator configuration, and a force sensor, which measures the interaction force that the actuator exchanges with the environment. In addition, an optimum full-state observer is also implemented, which enables both accurate estimation of the time-dependent behavior of the elastomeric material and adequate suppression of the sensor measurement noise. Preliminary experimental results are provided to validate the proposed actuator-controller architecture&nbsp

Non Invasive Measurement of Variable Mechanical Stiffness of Robots and Humans: an Exact Linearized Observer Approach.

The present thesis focused on the problem of observing the stiffness of Variable Stiffness Mechanical Stiffness, whose measure is impossible. Stiffness is in fact a derived quantity and no sensors exist for its direct measure. The main idea for solving such a problem, is designing a non linear observer with linear error dynamics. In the present we tackle the problem of extending such class of observer to locally unobsrvable systems, since our target systems succumb to unobservability conditions. We prove the strength of the method both through numerical and experimental analysis, the former on a simple single spring-damping-mass mechanical system, the latter on a Variable Stiffness Actuator (VSA)

Optimal workloop energetics of muscle-actuated systems

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.Includes bibliographical references (p. 117-122).Skeletal muscles are the primary actuators that power, stabilize and control locomotive and functional motor tasks in biological systems. It is well known that coordinated action and co-activation of multiple muscles give rise to desirable effects such as enhanced postural and dynamic stability. In this thesis, we study the role of muscle co-activation from an energetics perspective: Are there situations in which antagonist co-activation leads to enhanced power generation, and if so, what is the underlying mechanism? The mechanical energetics of muscles are traditionally characterized in terms of workloop measures where muscles are activated against oscillating, zero-admittance motion sources. We extend these measures to more natural, "mid-range" admittance loads, actuated by multiple muscles. Specifically, we set up the problem of a second-order mechanical system driven by a pair of antagonist muscles. This is the simplest problem where the influences of load dynamics and muscle co-activation on the output energetics may be investigated. To enable experimentation, a muscle testing apparatus capable of real-time servo emulation of the load is developed and utilized for identification and workloop measurements.(cont.) Using this apparatus, an experimentally identified model predicting muscle contractile force is proposed. Experimental data shows that with a simple Weiner structure, the model accounts for 74% (sigma = 5.6%) of the variance in muscle force, that force dependence on contraction velocity is minimal, and that a bilinear approximation of the output nonlinearity is warranted. Based on this model we investigate what electrical stimulation input gives rise to maximal power transfer for a particular load. This question is cast in an optimal control framework. Necessary conditions for optimality are derived and methods for computing solutions are presented. Solutions demonstrate that the optimal stimulation frequencies must include the effects of muscle impedances, and that optimal co-activation levels are indeed modulated to enable a pair of muscles to produce more work synergistically rather than individually. Pilot experimental data supporting these notions is presented. Finally, we interpret these results in the context of the familiar engineering notion of impedance matching. These results shed new light on the role of antagonist co-activation from an energetics perspective.by Walled A. Farahat.Ph.D

Robot Manipulators

Robot manipulators are developing more in the direction of industrial robots than of human workers. Recently, the applications of robot manipulators are spreading their focus, for example Da Vinci as a medical robot, ASIMO as a humanoid robot and so on. There are many research topics within the field of robot manipulators, e.g. motion planning, cooperation with a human, and fusion with external sensors like vision, haptic and force, etc. Moreover, these include both technical problems in the industry and theoretical problems in the academic fields. This book is a collection of papers presenting the latest research issues from around the world

Models, algorithms and architectures for cooperative manipulation with aerial and ground robots

Les dernières années ont vu le développement de recherches portant sur l'interaction physique entre les robots aériens et leur environnement, accompagné de l'apparition de nombreux nouveaux systèmes mécaniques et approches de régulation. La communauté centrée autour de la robotique aérienne observe actuellement un déplacement de paradigmes des approches classiques de guidage, de navigation et de régulation vers des tâches moins triviales, telle le développement de l'interaction physique entre robots aériens et leur environnement. Ceci correspond à une extension des tâches dites de manipulation, du sol vers les airs. Cette thèse contribue au domaine de la manipulation aérienne en proposant un nouveau concept appelé MAGMaS, pour " Multiple Aerial Ground Manipulator System ". Les motivations qui ont conduites à l'association de manipulateurs terrestres et aériens pour effectuer des tâches de manipulation coopérative, résident dans une volonté d'exploiter leurs particularités respectives. Les manipulateurs terrestres apportant leur importante force et les manipulateurs aériens apportant leur vaste espace de travail. La première contribution de cette thèse présente une modélisation rigoureuse des MAGMaS. Les propriétés du système ainsi que ses possibles extensions sont discutées. Les méthodes de planning, d'estimation et de régulation nécessaire à l'exploitation des MAGMaS pour des tâches de manipulation collaborative sont dérivées. Ce travail propose d'exploiter les redondances des MAGMaS grâce à un algorithme optimal d'allocation de forces entre les manipulateurs. De plus, une méthode générale d'estimation de forces pour robots aériens est introduite. Toutes les techniques et les algorithmes présentés dans cette thèse sont intégrés dans une architecture globale, utilisée à la fois pour la simulation et la validation expérimentale. Cette architecture est en outre augmentée par l'addition d'une structure de télé-présence, afin de permettre l'opération à distances des MAGMaS. L'architecture générale est validée par une démonstration de levage de barre, qui est une application représentative des potentiels usages des MAGMaS. Une autre contribution relative au développement des MAGMaS consiste en une étude exploratoire de la flexibilité dans les objets manipulés par un MAGMaS. Un modèle du phénomène vibratoire est dérivé afin de mettre en exergue ses propriétés en termes de contrôle. La dernière contribution de cette thèse consiste en une étude exploratoire sur l'usage des actionneurs à raideur variable dans les robots aériens, dotant ces systèmes d'une compliance mécanique intrinsèque et de capacité de stockage d'énergie. Les fondements théoriques sont associés à la synthèse d'un contrôleur non-linéaire. L'approche proposée est validée par le biais d'expériences reposant sur l'intégration d'un actionneur à raideur variable léger sur un robot aérien.In recent years, the subject of physical interaction for aerial robots has been a popular research area with many new mechanical designs and control approaches being proposed. The aerial robotics community is currently observing a paradigm shift from classic guidance, navigation, and control tasks towards more unusual tasks, for example requesting aerial robots to physically interact with the environment, thus extending the manipulation task from the ground into the air. This thesis contributes to the field of aerial manipulation by proposing a novel concept known has Multiple Aerial-Ground Manipulator System or MAGMaS, including what appears to be the first experimental demonstration of a MAGMaS and opening a new route of research. The motivation behind associating ground and aerial robots for cooperative manipulation is to leverage their respective particularities, ground robots bring strength while aerial robots widen the workspace of the system. The first contribution of this work introduces a meticulous system model for MAGMaS. The system model's properties and potential extensions are discussed in this work. The planning, estimation and control methods which are necessary to exploit MAGMaS in a cooperative manipulation tasks are derived. This works proposes an optimal control allocation scheme to exploit the MAGMaS redundancies and a general model-based force estimation method is presented. All of the proposed techniques reported in this thesis are integrated in a global architecture used for simulations and experimental validation. This architecture is extended by the addition of a tele-presence framework to allow remote operations of MAGMaS. The global architecture is validated by robust demonstrations of bar lifting, an application that gives an outlook of the prospective use of the proposed concept of MAGMaS. Another contribution in the development of MAGMaS consists of an exploratory study on the flexibility of manipulated loads. A vibration model is derived and exploited to showcase vibration properties in terms of control. The last contribution of this thesis consists of an exploratory study on the use of elastic joints in aerial robots, endowing these systems with mechanical compliance and energy storage capabilities. Theoretical groundings are associated with a nonlinear controller synthesis. The proposed approach is validated by experimental work which relies on the integration of a lightweight variable stiffness actuator on an aerial robot

A Stiffness Estimator for Agonistic-Antagonistic Variable-Stiffness-Actuator Devices

International audienceSafe Physical Human Robot Interaction, conservation of energy and adaptability are just the main robotic applications that prompted the development of a number of Variable Stiffness Actuators (VSA). Implemented in a variety of ways, they use various technologies, and feature the most diverse mechanical solutions, all of which share a fundamentally unavoidable nonlinear behavior. The control schemes proposed for these actuators typically aim at independent control of the position of the link, and its stiffness. Although effective feedback control schemes using position and force sensors are commonplace in robotics, control of stiffness is at present completely open-loop: the stiffness is inferred from the mathematical model of the actuator. We consider here the problem of estimating the nonlinear stiffness of Variable Stiffness Actuator in Agonistic-Antagonistic configuration. We propose an algorithm based on modulating functions which allow to avoid the need of numerical derivative and for which the tunning is then very simple. An analysis of the error demonstrates the convergence. Simulations are provided and the algorithm is validated on experimental data