We present work to transfer decentralized neuromuscular control strategies of human locomotion to powered segmented robotic legs. State-of-the-art robotic locomotion control approaches, like centralized planning and tracking in fully robotic systems and predefined motion pattern replay in prosthetic systems, do not enable the dynamism and reactiveness of able-bodied humans. Animals largely realize dexterous segmented leg performance with leg-encoded biomechanics and local feedback controls that bypass central processing. A decentralized neuromuscular controller was recently developed that enables robust locomotion for a simulated multi-segmented planar humanoid. A portion of this controller was used in an active ankle-foot prosthesis to modulate ankle torque during stance, enabling level and inclined ground walking. While these results suggest that the neuromuscular controller is a promising alternative control method for both fully robotic systems and powered prostheses, it is unclear if the controller can be transferred to multi-segmented robotic legs. The goal of this thesis is to investigate the feasibility of controlling a multi-segmented robotic leg with the proposed neuromuscular control approach, which may enable robots and powered prostheses to react to locomotion disturbances dynamically and in a human-like way. Specifically, work in this thesis investigates two hypotheses. Hypothesis one posits that the proposed decentralized swing-leg controllers enable more robust foot placements into ground targets than state-of-the-art impedance controls. Hypothesis two posits that neuromuscular swing-leg control enables more human-like motion than state-of-the-art impedance control. To transfer neuromuscular controls to powered segmented robotic legs, we use a model-based design approach. The initial transfer is focused on neuromuscular swing-leg controls, important for maintaining dynamic stability of both fully robotic systems and powered prostheses in the presence of unexpected locomotion disturbances, such as trips and pushes. We first present the design of RNL, a three segment, cable-driven, antagonistically actuated robotic leg with joint compliance. The robot’s size, weight, and actuation capabilities correspond to dynamically scaled human values. Next, a highfidelity simulation of the robot is created to investigate the feasibility of transferring neuromuscular controls, pre-tune hardware gains via optimization, and serve as a benchmark for hardware experiments. An idealized version of the swing-leg controller with mono-articular actuation, as well as the neuromuscular interpretation of this controller with multi-articular actuation is then transferred to RNL and evaluated with foot placement experiments. The results suggest that the proposed swing-leg controllers can accurately regulate foot placement of robotic legs during undisturbed and disturbed motions. Compared to impedance control, the proposed controls achieve foot placements over a range of ground targets with a single set of gains, which make them attractive candidates for regulating the motion of legged robots and prostheses in the real-world. Furthermore, the ankle trajectory traced out by the robot under neuromuscular control is more human-like than the trajectories traced out under the proposed idealized control and impedance control. In parallel to this control transfer, a synthesis method for creating compact nonlinear springs with user-defined torque-deflection profiles is presented to explore methods for improving RNL’s series elastic actuators. The springs use rubber as their elastic element, which, while enabling a compact spring design, introduce viscoelastic behavior in the spring that needs to be accounted for with additional control. To accurately estimate force developed in the rubber, an empirically characterized constitutive rubber model is developed and integrated into the series elastic actuator controller used by the RNL test platforms. Benchtop experiments show that in conjunction with an observer, the nonlinear spring prototype achieves desired behavior at actuation frequencies up to 2 Hz, after which spring behavior degrades due to rubber hysteresis. These results show that while the presented methodology is capable of realizing compact nonlinear springs, careful rubber selection that mitigates viscoelastic behavior is necessary during the spring design process.

Soil properties (shear modulus and damping) are normally determined from laboratory tests. These tests provide both values of the shear modulus in the linear elastic range for very small levels of strain, and its variation with the level of strain. It has become more common to measure the maximum shear modulus at low levels of strain directly in the field, using geophysical techniques. The values obtained in situ can differ significantly in some cases from those determined in the laboratory, and a number of reasons and correction factors have been proposed in the literature to account for this variation. As a result, when in situ properties are available, it is normal to use these values for very low levels of strain, but still assume that the variation of the ratio G/Gmax (normalized shear modulus) with shear strain is the same as determined in the laboratory. Recently, tests have been performed using large vibrators (the Thumper and Tyrannosaurus Rex of the University of Texas at Austin) to determine soil properties in situ for larger strains, and the variation of G/Gmax obtained from these tests has been compared to that reported in the literature from lab tests. Observation indicates some generally good agreement, but also some minor variations. One must take into account, however, that in the determination of the shear modulus versus strain in the field from vibration records, a number of approximations are introduced. The objective of this work is to evaluate the accuracy of some the procedures used and to assess the validity of the simplifying assumptions which are made. For this purpose, a shear cone that would reproduce correctly the horizontal stiffness of a circular mat foundation on the surface of an elastic, homogeneous half space, was considered. The cone was discretized using both a system of lumped masses and springs and a finite difference, using second-order central difference formulation, verifying that in the linear elastic range the results were accurate. A number of studies were conducted next, increasing the level of the applied force and using nonlinear springs that would reproduce a specified G/Gmax vs. γ curve. Using a similar procedure to that used in the field tests, the shear wave velocity between hypothetical receivers and the levels of strain were determined. The resulting values of G/Gmax vs. γ were then compared with the assumed curve to assess the accuracy of the estimated values.

Ce travail de recherche porte sur le développement et la mise au point d'un récupérateur d'énergie vibratoire MEMS à transduction capacitive dédié aux applications biomédicales et plus particulièrement aux stimulateurs cardiaques sans sondes autonomes. Cette application impose une miniaturisation poussée (volume inférieur à 1 cm³), une puissance de sortie dans la gamme allant de 1 à 10 µW et une compatibilité vis-à-vis des systèmes d'Imagerie à Résonance Magnétique (IRM). Ces contraintes ainsi que l'effet de la gravité ont été pris en compte sur tout le flot de conception afin d'obtenir un dispositif innovant en technologie MEMS silicium capable de fournir une puissance de sortie suffisante quelle que soit son orientation une fois implanté. Afin de convertir efficacement les battements cardiaques ayant un spectre étendu (de 1 à 50 Hz) pour une amplitude d'accélération faible (inférieure à 1 g), le système emploie des bras de suspension ayant une raideur non-linéaire ce qui permet d'étendre notablement la bande passante effective du système. Cette non-linéarité est ici induite de manière originale en faisant en sorte que la forme initiale des bras de suspension soit une combinaison linéaire des modes de déformée propre d'une poutre doublement encastrée. Un soin particulier a été apporté afin de modéliser ceci dans le but de prédire la réponse mécanique du système quels que soient les stimuli imposés. Afin de réaliser les différents dispositifs de test, une technologie MEMS de type SOG (Silicon-On-Glass) a été développée. Cette technologie permet d'obtenir des structures en silicium monocristallin avec un fort rapport d'aspect tout en limitant le budget thermique et se montre donc compatible avec une éventuelle industrialisation. Ceci a été prouvé via la réalisation de multiples véhicules de test qui se sont montrés totalement fonctionnels. Ainsi la pertinence des modèles théoriques permettant de prédire le comportement non-linéaire des ressorts employés a été prouvée de manière expérimentale. De même, les récupérateurs d'énergie réalisés ont été testés en régime harmonique mais également via des stimuli cardiaques et ont montré une large bande passante avec une puissance de sortie équivalente à celle donnée dans l'état de l'art et ce, quelle que soit leur orientation par rapport à la gravité. / Present work addresses question of MEMS capacitive vibrational energy harvesting for biomedical applications, and notably for powering an autonomous leadless pacemaker system. Such an application imposes several critical requirements upon the energy harvesting system, notably the sufficient miniaturization (<1cm³), power output in range of 1-10 µW, compatibility with Magnetic Resonant Imaging (MRI). This work addresses a problematic of MEMS energy harvester design, simulation, fabrication and characterization fulfilling such a requirement. Moreover, a gravity effect is studied and taken into account in the conception of the device to ensure the power output at various orientations of the harvester. To attain a heartbeat frequencies (1-50 Hz) and acceleration amplitudes (<1g), the use of nonlinear springs is proposed. A nonlinear stiffness is implemented in original way of introducing a natural bending mode shapes in the initial beam form. A mechanical description of bending mode coupling along with its impact on a reaction force of the suspension springs is presented. An innovative clean room technology based on silicon-on-glass (SOG) wafers is developed for the fabrication of the innovative energy harvesters with high width-to-depth aspect ratio. A straightforward and rapid low-temperature process with the possibility of future industrialization is validated by multiple experimental realizations of miniaturized MEMS energy harvesters. Fabricated microsystems are tested mechanically and electrically. Proposed theoretical model of the curved beam is validated with reactive force measurements of the MEMS springs. Energy harvesting experiments are performed for both harmonic and heartbeat mechanical excitations, which demonstrate the large bandwidth in low frequencies domain and a sufficiently large state-of-the-art power output for envisaged application under different orientations with respect to the gravity.