Développement d'une unité de valves motorisées et algorithme de transition pour actionnement hydrostatique bimodal d'une jambe robotique

Les robots mobiles, tels que les exosquelettes et les robots marcheurs, utilisent des actionneurs qui doivent satisfaire à une large plage de requis de force et de vitesse. Par exemple, pour le cycle de marche d’une jambe robotique, la phase d’appui nécessite une force élevée tandis que la phase de balancement requiert une grande vitesse. Pour satisfaire ces requis opposés, le dimensionnement d’un système d’actionnement traditionnel à rapport de réduction unique conduit généralement à un moteur électrique lourd, surdimensionné et à une faible efficacité énergétique. Ainsi, l’alternative explorée est une architecture hydrostatique à deux vitesses où des valves motorisées sont utilisées pour reconfigurer dynamiquement le système entre deux modes de fonctionnement : fort ou rapide. La complexité réside dans le choix d’une technologie de valve légère ainsi que dans le développement d’un algorithme de contrôle permettant de réaliser les transitions de manière rapide et fluide. Un prototype d’une unité de valves motorisées est conçu et intégré dans l’architecture hydrostatique complète de l’actionneur et un banc d’essai d’une jambe robotique est fabriqué. Trois stratégies de contrôle des moteurs sont comparées lors du changement de mode : une vitesse constante, une diminution de vitesse et une réduction du courant. La méthode choisie, le contrôle en courant, est ensuite utilisée pour la démonstration des phases d’appui et de balancement de la jambe robotique. Par cette méthode, il est possible d’effectuer des transitions rapides, de maintenir une force suffisante et de minimiser les oscillations qui surviennent lors du contact avec le sol. Ces travaux offrent donc un premier point de comparaison au niveau du choix de valves, de la masse, de la vitesse d’actionnement et de la stratégie de contrôle

Conception et évaluation d'actionneurs à embrayages magnétorhéologiques pour la robotique collaborative

La robotique collaborative se démarque de la robotique industrielle par sa sécurité dans le but de travailler en collaboration avec les humains. Toutefois, la majorité des robots collaboratifs sériels reposent sur un actionnement à haut ratio de réduction, ce qui augmente considérablement la masse reflétée à l’effecteur du robot, et donc, nuit à la sécurité. Pour pallier cette masse reflétée et maintenir un seuil minimal de sécurité, les vitesses d’opération sont abaissées, nuisant ainsi directement à la productivité des entreprises. Afin de minimiser la masse reflétée à l’effecteur, les masses des actionneurs ainsi que leur inertie reflétée doivent être minimisés. Les embrayages à fluide magnétorhéologique (MR) maintenus en glissement continus découplent l’inertie provenant de la source de puissance, souvent un moteur et un réducteur, offrant ainsi un actionneur possédant un haut rapport couple-inertie. Toutefois, les embrayages MR, utilisés de façon antagoniste, ajoutent des composantes à l’actionneur ce qui réduit la densité de couple, et donc, augmente la masse reflétée à l’effecteur du robot. Certains actionneurs MR [1–3] ont été développés, mais leur basse densité de couple contrebalance leur faible inertie lorsqu’utilisés comme actionneurs aux articulations de robots collaboratifs sériels. Cette constatation a mené à ma question de recherche : Comment profiter de la faible inertie des actionneurs MR pour maximiser les performances dynamiques des robots collaboratifs sériels? L’objectif de ce projet de recherche vise donc à étudier le potentiel des embrayages MR en robotique collaborative. Pour ce faire, deux architectures MR sont développées et testées expérimentalement. La première architecture consiste en une articulation robotisée modulaire comportant des embrayages MR en glissement continu et possédant un rapport couple/masse et une taille équivalente à l’actionneur d’Universal Robots (UR) de couple égal, mais possédant un rapport couple/inertie 150 fois supérieur. À l’intérieur de l’articulation, deux chaines de puissance (2 moteurs et 2 embrayages MR) indépendantes se rejoignent à la sortie du joint offrant ainsi une redondance et augmentant la densité de couple comparativement à une architecture standard (1 moteur pour 2 embrayages MR). La deuxième architecture étudiée consiste en un actionnement délocalisé du robot où les embrayages MR sont situés à la base du robot et une transmission hydrostatique à membranes déroulantes achemine la puissance aux articulations. Cette architecture a été testée expérimentalement dans un contexte de bras robotisé surnuméraire. Contrairement à l’articulation MR, cette architecture n’offre pas une modularité habituellement recherchée en robotique sérielle, mais offre la possibilité de réduire l’inertie de la structure avec la délocalisation de l’actionnement. Finalement, les deux architectures développées ont été comparées à une architecture standard (haut ratio avec réducteur harmonique) afin de situer le potentiel du MR en robotique collaborative. Cette analyse théorique a démontré que pour un robot collaboratif sériel à 6 degrés de liberté, les architectures MR ont le potentiel d’accélérer 6 et 3 fois plus (respectivement) que le robot standard d’UR, composé d’actionneurs à hauts ratios

An autonomous self-reconfigurable modular robotic system with optimised docking connectors

Includes bibliographical references.Self-Reconfigurable Modular Robots are robotic systems consisting of a number of self-contained modules that can autonomously interconnect in different positions and orientations thereby varying the shape and size of the overall modular robot. This ground breaking capability is what in theory, makes self-reconfigurable modular robots more suitable for use in the navigation of unknown or unstructured environments. Here, they are required to reconfigure into different forms so as to optimise their navigation capabilities, a feat that is rendered impossible in conventional specialised robots that lack reconfiguration capabilities. However, the frequent development and use of self-reconfigurable modular robots in everyday robotic navigation applications is significantly hampered by the increased difficulty and overall cost of production of constituent robotic modules. One major contributor to this is the difficulty of designing suitably robust and reliable docking mechanisms between individual robotic modules. Such mechanisms are required to be mechanically stable involving a robust coupling mechanism, and to facilitate reliable inter-module power sharing and communication. This dissertation therefore proposes that the design and development of a functional low cost self-reconfigurable modular robot is indeed achievable by optimising and simplifying the design of a robust and reliable autonomous docking mechanism. In this study, we design and develop such a modular robot, whose constituent robotic modules are fitted with specialised docking connectors that utilise an optimised docking mechanism. This modular robot, its robotic modules and their connectors are then thoroughly tested for accuracy in mobility, electrical and structural stability, inter-module communication and power transfer, self-assembly, self-reconfiguration and self-healing, among others. The outcome of these testing procedures proved that it is indeed possible to optimise the docking mechanisms of self-reconfigurable modular robots, thereby enabling the modular robot to more easily exhibit efficient self-reconfiguration, self-assembly and self-healing behaviours. This study however showed that the type, shape, functionality and structure of electrical contacts used within the docking connectors for inter-module signal transfer and communication play a major role in enabling efficient self-assembly, self-reconfiguration and self-healing behaviours. Smooth spring loaded metallic electrical contacts incorporated into the docking connector design are recommended. This study also highlights the importance of closed loop control in the locomotion of constituent robotic modules, especially prior to docking. The open loop controlled locomotion optimisations used in this project were not as accurate as was initially expected, making self-assembly rather inaccurate and inconsistent. It is hoped that the outcomes of this research will serve to improve the docking mechanisms of self-reconfigurable modular robots thereby improving their functionality and pave the way for future large scale use of these robots in real world applications

DISTRIBUTED ELECTRO-MECHANICAL ACTUATION AND SENSING SYSTEM DESIGN FOR MORPHING STRUCTURES

Smart structures, able to sense changes of their own state or variations of the environment they’re in, and capable of intervening in order to improve their performance, find themselves in an ever-increasing use among numerous technology fields, opening new frontiers within advanced structural engineering and materials science. Smart structures represent of course a current challenge for the application on the aircrafts. A morphing structure can be considered as the result of the synergic integration of three main systems: the structural system, based on reliable kinematic mechanisms or on compliant elements enabling the shape modification, the actuation and control systems, characterized by embedded actuators and robust control strategies, and the sensing system, usually involving a network of sensors distributed along the structure to monitor its state parameters. Technologies with ever increasing maturity level are adopted to assure the consolidation of products in line with the aeronautical industry standards and fully compliant with the applicable airworthiness requirements. Until few years ago, morphing wing technology appeared an utopic solution. In the aeronautical field, airworthiness authorities demand a huge process of qualification, standardization, and verification. Essential components of an intelligent structure are sensors and actuators. The actual technological challenge, envisaged in the industrial scenario of “more electric aircraft”, will be to replace the heavy conventional hydraulic actuators with a distributed strategy comprising smaller electro-mechanical actuators. This will bring several benefit at the aircraft level: firstly, fuel savings. Additionally, a full electrical system reduces classical drawbacks of hydraulic systems and overall complexity, yielding also weight and maintenance benefits. At the same time, a morphing structure needs a real-time strain monitoring system: a nano-engineered polymer capable of densely distributed strain sensing can be a suitable solution for this kind of flying systems. Piezoresistive carbon nanotubes can be integrated as thin films coated and integrated with composite to form deformable self-sensing materials. The materials actually become sensors themselves without using external devices, embedded or attached. This doctoral thesis proposes a multi-disciplinary investigation of the most modern actuation and sensing technologies for variable-shaped devices mainly intended for large commercial aircraft. The personal involvement in several research projects with numerous international partners - during the last three years - allowed for exploiting engineering outcomes in view of potential certification and industrialization of the studied solutions. Moving from a conceptual survey of the smart systems that introduces the idea of adaptive aerodynamic surfaces and main research challenges, the thesis presents (Chapter 1) the current worldwide status of morphing technologies as well as industrial development expectations. The Ph.D. programme falls within the design of some of the most promising and potentially flyable solutions for performance improvement of green regional aircrafts. A camber-morphing aileron and a multi-modal flap are herein analysed and assessed as subcomponents involved for the realization of a morphing wing. An innovative camber-morphing aileron was proposed in CRIAQ MD0-505, a joint Canadian and Italian research project. Relying upon the experimental evidence within the present research, the issue appeared concerns the critical importance of considering the dynamic modelling of the actuators in the design phase of a smart device. The higher number of actuators involved makes de facto the morphing structure much more complex. In this context (Chapter 2), the action of the actuators has been modelled within the numerical model of the aileron: the comparison between the modal characteristics of numerical predictions and testing activities has shown a high level of correlation. Morphing structures are characterized by many more degrees of freedom and increased modal density, introducing new paradigms about modelling strategies and aeroelastic approaches. These aspects affect and modify many aspects of the traditional aeronautical engineering process, like simulation activity, design criteria assessment, and interpretation of the dynamic response (Chapter 3). With respect the aforementioned aileron, sensitivity studies were carried out in compliance with EASA airworthiness requirements to evaluate the aero-servo-elastic stability of global system with respect to single and combined failures of the actuators enabling morphing. Moreover, the jamming event, which is one of the main drawbacks associated with the use of electro-mechanical actuators, has been duly analyzed to observe any dynamic criticalities. Fault & Hazard Analysis (FHA) have been therefore performed as the basis for application of these devices to real aircraft. Nevertheless, the implementation of an electro-mechanical system implies several challenges related to the integration at aircraft system level: the practical need for real-time monitoring of morphing devices, power absorption levels and dynamic performance under aircraft operating conditions, suggest the use of a ground-based engineering tool, i.e. “iron bird”, for the physical integration of systems. Looking in this perspective, the Chapter 4 deals with the description of an innovative multi-modal flap idealized in the Clean Sky - Joint Technology Initiative research scenario. A distributed gear-drive electro-mechanical actuation has been fully studied and validated by an experimental campaign. Relying upon the experience gained, the encouraging outcomes led to the second stage of the project, Clean Sky 2 - Airgreen 2, encompassing the development of a more robotized flap for next regional aircraft. Numerical and experimental activities have been carried out to support the health management process in order to check the EMAs compatibility with other electrical systems too. A smart structure as a morphing wing needs an embedded sensing system in order to measure the actual deformation state as well as to “monitor” the structural conditions. A new possible approach in order to have a distributed light-weight system consists in the development of polymer-based materials filled with conductive smart fillers such as carbon nanotubes (CNTs). The thesis ends with a feasibility study about the incorporation of carbon nanomaterials into flexible coatings for composite structures (Chapter 5). Coupons made of MWCNTs embedded in typical aeronautic epoxy formulation were prepared and tested under different conditions in order to better characterize their sensing performance. Strain sensing properties were compared to commercially available strain gages and fiber optics. The results were obtained in the last training year following the involvement of the author in research activities at the University of Salerno and Materials and Structures Centre - University of Bath. One of the issues for the next developments is to consolidate these novel technologies in the current and future European projects where the smart structures topic is considered as one of the priorities for the new generation aircrafts. It is remarkable that scientists and aeronautical engineers community does not stop trying to create an intelligent machine that is increasingly inspired by nature. The spirit of research, the desire to overcome limits and a little bit of imagination are surely the elements that can guide in achieving such an ambitious goal

Aerial-aquatic robots capable of crossing the air-water boundary and hitchhiking on surfaces.

Many real-world applications for robots-such as long-term aerial and underwater observation, cross-medium operations, and marine life surveys-require robots with the ability to move between the air-water boundary. Here, we describe an aerial-aquatic hitchhiking robot that is self-contained for flying, swimming, and attaching to surfaces in both air and water and that can seamlessly move between the two. We describe this robot's redundant, hydrostatically enhanced hitchhiking device, inspired by the morphology of a remora (Echeneis naucrates) disc, which works in both air and water. As with the biological remora disc, this device has separate lamellar compartments for redundant sealing, which enables the robot to achieve adhesion and hitchhike with only partial disc attachment. The self-contained, rotor-based aerial-aquatic robot, which has passively morphing propellers that unfold in the air and fold underwater, can cross the air-water boundary in 0.35 second. The robot can perform rapid attachment and detachment on challenging surfaces both in air and under water, including curved, rough, incomplete, and biofouling surfaces, and achieve long-duration adhesion with minimal oscillation. We also show that the robot can attach to and hitchhike on moving surfaces. In field tests, we show that the robot can record video in both media and move objects across the air/water boundary in a mountain stream and the ocean. We envision that this study can pave the way for future robots with autonomous biological detection, monitoring, and tracking capabilities in a wide variety of aerial-aquatic environments

A novel approach to gait synchronization and transition for reconfigurable walking platforms

Legged robots based on one degree-of-freedom reconfigurable planar leg mechanisms, that are capable of generating multiple useful gaits, are highly desired due to the possibility of handling environments and tasks of high complexity while maintaining simple control schemes. An essential consideration in these reconfigurable legged robots is to attain stability in motion, at rest as well as while transforming from one configuration to another with the minimum number of legs as long as the full range of their walking patterns, resulting from the different gait cycles of their legs, is achieved. To this end, in this paper, we present a method for the generation of input joint trajectories to properly synchronize the movement of quadruped robots with reconfigurable legs. The approach is exemplified in a four-legged robot with reconfigurable Jansen legs capable of generating up to six useful different gait cycles. The proposed technique is validated through simulated results that show the platform׳s stability across its six feasible walking patterns and during gait transition phases, thus considerably extending the capabilities of the non-reconfigurable design

An Energy Efficient Electro-Hydraulic Control System For A Collaborative Humanoid Robot

DissertationThis study presents the design of an energy efficient electro-hydraulic control system for a collaborative humanoid robot. Robots can be found in almost every aspect of our lives with different applications such as manufacturing, construction, agriculture, surgery, and transportation. The need for robots is on the rise as they perform certain tasks much faster and with more precision than humans. The lack of them having cognitive ability limits them in certain tasks as human interaction is often needed. Humans are currently better than robots in performing some tasks such as decision making and problem solving. In collaborative robotics, humans and robots are required to work together to achieve a common goal. In most cases, this is achieved by confining both entities in the same space. This allows for better accuracy for these robots with the flexibility and cognition of humans. Furthermore, research lately shows an increase in robots that use hydraulics with most showing that these hydraulics have energy saving abilities in robotic actuation. It is known that hydraulics have a high power to weight ratio thus allowing for more powerful yet compact robots to be built. An electro-hydraulic control system is thus described in this research in which the system allows the human user to manipulate the robot by having it mimic the user’s moves. This approach allows the user to not do any strenuous activities while the robot does the heavy lifting. Furthermore, the system does not need to be reprogrammed for a new task therefore reducing the reconfiguration time of the system. The proposed approach further allows the robot to work in hazardous situations while the user is in a safe environment. The system uses a proportional-integral-derivative (PID) algorithm to control a hydraulic cylinder allowing it to move with the user. Experiments performed to validate the study shows the reaction time as well as energy saving abilities of the system. Additionally, the results show that hydraulic systems have the ability to save energy during stall as well as increasing power density of the robot. Furthermore, an improved response time was recorded for the hydraulic system when being controlled by a remote operator