Automatic Gain Tuning of a Momentum Based Balancing Controller for Humanoid Robots

This paper proposes a technique for automatic gain tuning of a momentum based balancing controller for humanoid robots. The controller ensures the stabilization of the centroidal dynamics and the associated zero dynamics. Then, the closed-loop, constrained joint space dynamics is linearized and the controller's gains are chosen so as to obtain desired properties of the linearized system. Symmetry and positive definiteness constraints of gain matrices are enforced by proposing a tracker for symmetric positive definite matrices. Simulation results are carried out on the humanoid robot iCub.Comment: Accepted at IEEE-RAS International Conference on Humanoid Robots (HUMANOIDS). 201

Design, implementation, control, and user evaluations of assiston-arm self-aligning upper-extremity exoskeleton

Physical rehabilitation therapy is indispensable for treating neurological disabilities. The use of robotic devices for rehabilitation holds high promise, since these devices can bear the physical burden of rehabilitation exercises during intense therapy sessions, while therapists are employed as decision makers. Robot-assisted rehabilitation devices are advantageous as they can be applied to patients with all levels of impairment, allow for easy tuning of the duration and intensity of therapies and enable customized, interactive treatment protocols. Moreover, since robotic devices are particularly good at repetitive tasks, rehabilitation robots can decrease the physical burden on therapists and enable a single therapist to supervise multiple patients simultaneously; hence, help to lower cost of therapies. While the intensity and quality of manually delivered therapies depend on the skill and fatigue level of therapists, high-intensity robotic therapies can always be delivered with high accuracy. Thanks to their integrated sensors, robotic devices can gather measurements throughout therapies, enable quantitative tracking of patient progress and development of evidence-based personalized rehabilitation programs. In this dissertation, we present the design, control, characterization and user evaluations of AssistOn-Arm, a powered, self-aligning exoskeleton for robotassisted upper-extremity rehabilitation. AssistOn-Arm is designed as a passive back-driveable impedance-type robot such that patients/therapists can move the device transparently, without much interference of the device dynamics on natural movements. Thanks to its novel kinematics and mechanically transparent design, AssistOn-Arm can passively self-align its joint axes to provide an ideal match between human joint axes and the exoskeleton axes, guaranteeing ergonomic movements and comfort throughout physical therapies. The self-aligning property of AssistOn-Arm not only increases the usable range of motion for robot-assisted upper-extremity exercises to cover almost the whole human arm workspace, but also enables the delivery of glenohumeral mobilization (scapular elevation/depression and protraction/retraction) and scapular stabilization exercises, extending the type of therapies that can be administered using upper-extremity exoskeletons. Furthermore, the self-alignment property of AssistOn-Arm signi cantly shortens the setup time required to attach a patient to the exoskeleton. As an impedance-type device with high passive back-driveability, AssistOn- Arm can be force controlled without the need of force sensors; hence, high delity interaction control performance can be achieved with open-loop impedance control. This control architecture not only simpli es implementation, but also enhances safety (coupled stability robustness), since open-loop force control does not su er from the fundamental bandwidth and stability limitations of force-feedback. Experimental characterizations and user studies with healthy volunteers con- rm the transparency, range of motion, and control performance of AssistOn- Ar

Design And Development of A Powered Pediatric Lower-limb Orthosis

Gait impairments from disorders such as cerebral palsy are important to address early in life. A powered lower-limb orthosis can offer therapists a rehabilitation option using robot-assisted gait training. Although there are many devices already available for the adult population, there are few powered orthoses for the pediatric population. The aim of this dissertation is to embark on the first stages of development of a powered lower-limb orthosis for gait rehabilitation and assistance of children ages 6 to 11 years with walking impairments from cerebral palsy. This dissertation presents the design requirements of the orthosis, the design and fabrication of the joint actuators, and the design and manufacturing of a provisional version of the pediatric orthosis. Preliminary results demonstrate the capabilities of the joint actuators, confirm gait tracking capabilities of the actuators in the provisional orthosis, and evaluate a standing balance control strategy on the under-actuated provisional orthosis in simulation and experiment. In addition, this dissertation presents the design methodology for an anthropometrically parametrized orthosis, the fabrication of the prototype powered orthosis using this design methodology, and experimental application of orthosis hardware in providing walking assistance with a healthy adult. The presented results suggest the developed orthosis hardware is satisfactorily capable of operation and functional with a human subject. The first stages of development in this dissertation show encouraging results and will act as a foundation for further iv development of the device for rehabilitation and assistance of children with walking impairments

Design, implementation and control of self-aligning, bowden cable-driven, series elastic exoskeletons for lower extremity rehabilitation

We present AssistOn-Leg, a modular, self-aligning exoskeleton for robotassisted rehabilitation of lower extremities. AssistOn-Leg consists of three selfaligning, powered exoskeletons targeting ankle, knee and hip joints, respectively. Each module can be used in a stand-alone manner to provide therapy to its corresponding joint or the modules can be connected together to deliver natural gait training to patients. In particular, AssistOn-Ankle targets dorsiflexion/ plantarflexion and supination/pronation of human ankle and can be configured to deliver balance/proprioception or range of motion/strengthening exercises; AssistOn-Knee targets flexion/extension movements of the knee joint, while also accommodating its translational movements in the sagittal plane; and AssistOn- Hip targets flexion/extension movements hip joint, while allowing for translations of hip-pelvis complex in the sagittal plane. Automatically aligning their joint axes, modules of AssistOn-Leg ensure an ideal match between human joint axes and the exoskeleton axes. Self-alignment of the modules not only guarantees ergonomy and comfort throughout the therapy, but also significantly shortens the setup time required to attach a patient to the exoskeleton. Bowden cable-driven series elastic actuation is utilized in the modules located at the distal (knee and ankle) joints of AssistOn-Leg to keep the apparent inertia of the system low, while simultaneously providing large actuation torques required to support human gait. Series elasticity also provides good force tracking characteristics, active back-driveability within the control bandwidth and passive compliance as well as impact resistance for excitations above this bandwidth. AssistOn-Hip is designed to be passively back-driveable with a capstan-based multi-level transmission. Thanks to passive compliance of the distal modules and passive backdriveability of the hip module, the overall design ensures safety even under power losses and robustness throughout the whole frequency spectrum

Conception de systèmes mécaniques auto-adaptatifs pour la locomotion

RÉSUMÉ Les mécanismes auto-adaptatifs (ou sous-actionnés) permettent d’accomplir des tâches complexes en utilisant un nombre minimal d’actionneurs. Leur caractéristique principale est la division de l’actionnement, à l’aide de mécanismes souvent différentiels, entre plusieurs mouvements de sortie dont la séquence de déclenchement peut être contrôlée à l’aide d’éléments passifs. Actuellement, ils sont majoritairement employés pour fabriquer des doigts ou de mains robotiques capables de s’adapter mécaniquement à la forme de l’objet à saisir, sans utiliser de contrôle en boucle fermée. Il est ainsi possible d’effectuer des économies substantielles en générant de manière purement mécanique un comportement qui nécessiterait autrement un grand nombre de moteurs et de capteurs. Dans ce projet, deux thèmes distincts, liés à l’application de cette philosophie de conception au domaine de la locomotion, sont explorés avec comme but principal de transférer l’expertise développée avec les doigts auto-adaptatifs vers de nouveaux cas d’utilisation. En premier lieu, un mécanisme de patte mécanique à deux degrés de liberté, actionné par un seul moteur, a été développé. En cas de collision avec un obstacle durant la phase de vol, le ratio de transmission de l’actionnement est altéré, combinant ainsi les deux degrés de liberté pour permettre à la patte de glisser le long de l’obstacle à la recherche d’un nouveau point d’appui. Ce mécanisme a été analysé en profondeur, notamment par le biais de la théorie des visseurs, afin de quantifier sa capacité d’adaptation. Il a ensuite été possible de procéder à une optimisation multi-objectifs visant à mettre en évidence le compromis entre les capacités d’adaptation de la patte et la qualité de la trajectoire générée. La validation expérimentale de ce mécanisme est également présentée. Le second thème relève du domaine de la réadaptation. Le mécanisme développé correspond à celui d’une orthèse entièrement passive, capable de générer des couples correcteurs sur les articulations de la hanche et du genou. Pour ce faire, un système de poulies non-circulaires et de câbles relie les rotations de ces deux articulations à l’allongement de deux ressorts. La synthèse des profils des poulies, par le biais d’une méthode graphique innovante, est décrite, de même que les résultats expérimentaux obtenus à l’aide du prototype réalisé. Les travaux réalisés dans le cadre du présent projet ont par ailleurs mené à d’autres contributions dans le domaine des poulies non-circulaires, soit un mécanisme d’équilibrage statique et un autre permettant de guider une plateforme suspendue le long d’une trajectoire de type « pick-and-place ».----------ABSTRACT Self-adaptive mechanisms (also referred to as underactuated) allow to perform complex tasks using only a minimal number of actuators. Their main characteristic is their ability to distribute actuation, often using differential mechanisms, between several output motions which can be triggered sequentially through the use of passive elements. As of now, they are mostly used in fingers and hands able to mechanically adapt to the shape of the grasped object, without relying on closed-loop control. Indeed, they allow for significant cost savings by generating purely mechanically a behavior which would otherwise require several motors and sensors. In this project, two separate themes, both linked to the application of this design philosophy to the field of locomotion, are explored. The main goal is to transfer existent expertise developed for self-adaptive fingers to new use cases. First, a two degree of freedom mechanical leg, driven by a single motor, has been developed. In case of an unexpected collision with an obstacle during the swing phase, the actuation transmission ratios are altered, thus combining both degrees of freedom to generate a sliding motion along the obstacle in search of the next foothold. This mechanism is here analyzed in depth through the application of screw theory, in order to quantify this adaptation capability. A multi-objective optimization was subsequently performed to highlight the trade-off between the mechanism’s adaptation to obstacles and the quality of the generated leg endpoint trajectory. Experimental results validating the increased reachable ground clearance for the proposed linkage are provided. The second theme belongs to the field of rehabilitation. The developed mechanism is a fully passive orthosis able to generate correcting torques to the hip and knee joints of the leg. This behavior is obtained by relating the elongations of two springs to these articular rotations by the means of cables and non-circular pulleys. The synthesis of the pulley profiles, through an innovative graphical method, as well as initial experimental results are presented. This project has also yielded relevant contributions to the field of non-circular pulleys, with one mechanism developed to achieve static balancing of a pendulum, and another guiding a suspended platform through a pick-and-place trajectory

Instantaneous Momentum-Based Control of Floating Base Systems

In the last two decades a growing number of robotic applications such as autonomous drones, wheeled robots and industrial manipulators started to be employed in several human environments. However, these machines often possess limited locomotion and/or manipulation capabilities, thus reducing the number of achievable tasks and increasing the complexity of robot-environment interaction. Augmenting robots locomotion and manipulation abilities is a fundamental research topic, with a view to enhance robots participation in complex tasks involving safe interaction and cooperation with humans. To this purpose, humanoid robots, aerial manipulators and the novel design of flying humanoid robots are among the most promising platforms researchers are studying in the attempt to remove the existing technological barriers. These robots are often modeled as floating base systems, and have lost the assumption -- typical of fixed base robots -- of having one link always attached to the ground. From the robot control side, contact forces regulation revealed to be fundamental for the execution of interaction tasks. Contact forces can be influenced by directly controlling the robot's momentum rate of change, and this fact gives rise to several momentum-based control strategies. Nevertheless, effective design of force and torque controllers still remains a complex challenge. The variability of sensor load during interaction, the inaccuracy of the force/torque sensing technology and the inherent nonlinearities of robot models are only a few complexities impairing efficient robot force control. This research project focuses on the design of balancing and flight controllers for floating base robots interacting with the surrounding environment. More specifically, the research is built upon the state-of-the-art of momentum-based controllers and applied to three robotic platforms: the humanoid robot iCub, the aerial manipulator OTHex and the jet-powered humanoid robot iRonCub. The project enforces the existing literature with both theoretical and experimental results, aimed at achieving high robot performances and improved stability and robustness, in presence of different physical robot-environment interactions

Neuroecology of social organization in the Australasian weaver ant, Oecophylla smaragdina

The social brain hypothesis predicts that larger group size and greater social complexity select for increased brain size. In ants, social complexity is associated with large colony size, emergent collective action, and division of labor among workers. The great diversity of social organization in ants offers numerous systems to test social brain theory and examine the neurobiology of social behavior. My studies focused on the Australasian weaver ant, Oecophylla smaragdina, a polymorphic species, as a model of advanced social organization. I critically analyzed how biogenic amines modulate social behavior in ants and examined their role in worker subcaste-related territorial aggression. Major workers that naturally engage in territorial defense showed higher levels of brain octopamine in comparison to more docile, smaller minor workers, whose social role is nursing. Through pharmacological manipulations of octopaminergic action in both subcastes, octopamine was found to be both necessary and sufficient for aggression, suggesting subcaste-related task specialization results from neuromodulation. Additionally, I tested social brain theory by contrasting the neurobiological correlates of social organization in a phylogenetically closely related ant species, Formica subsericea, which is more basic in social structure. Specifically, I compared brain neuroanatomy and neurometabolism in respect to the neuroecology and degree of social complexity of O. smaragdina major and minor workers and F. subsericea monomorphic workers. Increased brain production costs were found in both O. smaragdina subcastes, and the collective action of O. smaragdina majors appeared to compensate for these elevated costs through decreased ATP usage, measured from cytochrome oxidase activity, an endogenous marker of neurometabolism. Macroscopic and cellular neuroanatomical analyses of brain development showed that higher-order sensory processing regions in workers of O. smaragdina, but not F. subsericea, had age-related synaptic reorganization and increased volume. Supporting the social brain hypothesis, ecological and social challenges associated with large colony size were found to contribute to increased brain size. I conclude that division of labor and collective action, among other components of social complexity, may drive the evolution of brain structure and function in compensatory ways by generating anatomically and metabolically plastic mosaic brains that adaptively reflect cognitive demands of worker task specialization and colony-level social organization