A review of current variable-stiffness actuators reveals a need for more simple, cost effective, and lightweight designs that can be easily incorporated into a variety of human-interactive robot platforms. This thesis considers the potential use of compliant mechanisms to improve the performance of variable-stiffness actuators. The advantages and disadvantages of various concepts using compliant mechanisms are outlined, along with ideas for further exploration. A new variable-stiffness actuator that uses a compliant flexure as the elastic element has been modeled, built, and tested. This new design involves a variable stiffness joint that makes use of a novel variable transmission. A prototype has been built and tested to verify agreement with the model which shows a reasonable range of stiffness and good repeatability. Ideas for further exploration are identified.

There is an increasing need for compact mechanical systems that can accomplish sophisticated tasks. Technologies like ortho-planar and lamina emergent mechanisms (LEMs) have been developed to satisfy needs like these by stowing in planar sheets from which they emerge to perform their function. They can be compact, lightweight, monolithic, scalable, and can withstand harsh environments. They are limited, however, by their base element---planar surfaces. Applications requiring these advantages often include curved surfaces, like aircraft wings, needles, and automotive bodies. In this research, developable mechanisms are presented as a solution to satisfy the need for mechanisms that can conform to or emerge from curved surfaces. Foundational principles which enable designers to leverage the advantages of developable mechanisms are described herein.Developable mechanisms result from the union of mechanisms and developable surfaces. Developable (flattenable) surfaces act as a fitting medium because of their particular advantages in manufacturability and how well they accompany four-link, revolute joint (4R) mechanisms. The definition, including specific qualifying criteria, for developable mechanisms is given. Certain types of mechanisms and classes of developable surfaces can be combined to satisy that criteria. Developable mechanism sub-classes are defined as planar, cylindrical, conical and tangent developable mechanisms. It is shown that planar and spherical mechanisms can be used to create cylindrical and conical developable mechanisms, respectively. The Bennett and other 7R mechanisms can be used for tangent developable mechanisms. Steps for developable mechanism creation are presented, and several physical prototypes are provided to demonstrate feasibility.The cylindrically curved Lamina Emergent Torsional (LET) joint is offered as an enabling technology for producing compliant developable mechanisms. A mathematical model predicting force-deflection and stress behavior is provided and verified. The relationship between stiffness and strain energy storage for curved sheet materials with incorporated LET joints is explored. Material shape factors are used to derive an effective modulus of elasticity and an effective modulus of resilience, which are compared with original values on an Ashby plot. While there is a decrease in the modulus of resilience, there is a much more significant decrease in the modulus of elasticity. A material performance index is provided as an example for determining suitable materials for a given stiffness-reduction application. It is shown that the cylindrically curved LET joint makes it possible to create highly flexible joints that maintain much of their energy storage capability in curved sheet materials.

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This research presents methods for modeling and optimizing an origami design using compliant mechanisms, improving origami design processes, modeling and analyzing rolling behavior of compliant designs, and an antenna design for SmallSats. A framework for the optimization of the origami Flasher pattern to mitigate issues with rigid-foldability is shown, and several optimization solutions are presented to overcome these issues. An alternative design method is presented which allows designers to more accurately predict the characteristics of a design in the deployed state, and configurations are shown for an example use case. A model for rolled gossamer structures is presented which predicts the relative slippage that adjacent panels will experience, and slippage trends are correlated with key pattern parameters. Finally, a SmallSat antenna design is presented, which stows compactly, incorporates a unique hinge design, utilizes magnets for stabilization in the deployed state, and self-deploys using compliant mechanisms.

La radiologie interventionnelle percutanée permet le diagnostic ou le traitement de tissus cancéreux grâce à l'utilisation d'aiguilles et d'un guidage par imageur. Bénéfique pour le patient, ce type de procédure clinique est en revanche complexe pour le radiologue. Afin de lui apporter une assistance et de contrôler l'aiguille de manière déportée, nous proposons dans ces travaux de réaliser des dispositifs robotisés compliants, donc monoblocs, et multi-matériaux en exploitant la fabrication additive multi-matériaux. Pour y parvenir, nous proposons plusieurs solutions pour réaliser les fonctions cinématique, d'actionnement et de perception. En particulier, nous proposons une nouvelle liaison compliante, la liaison HSC, ainsi qu'un nouvel actionneur pneumatique pour l'insertion d'aiguille. Nous démontrons finalement les apports de la fabrication additive pour la robotique médicale en combinant l'ensemble de ces solutions dans un dispositif assurant un contrôle à distance de l'aiguille. / Percutaneous interventional radiology permits the diagnosis or the treatment of cancer tissues thanks to the use of needles and imaging devices. Being minimally invasive, such procedures are beneficial for the patient, but for the radiologist, they are highly complex. In order to assist the physician and remotely control the needle, we propose in this work the design and the manufacturing of multi-material compliant devices by taking advantage of multi-material additive manufacturing. To perform the design of such device, we propose several solutions in terms of kinematics, actuation and sensing. In particular, we developed a new compliant joint, the HSC joint, as well as a new pneumatic actuator for needle insertion. In the end, we demonstrate in the thesis the contributions of multi-material additive manufacturing for medical robotics, by combining all those solutions into a single device that remotely controls both the orientation and the insertion of the needle

This thesis adds to the knowledge base of constant-force mechanisms (CFMs). It begins by reviewing past work done in the area of CFMs and then develops new nondimensionalized parameters that are used to simplify the calculations required to design a CFM. Comparison techniques are then developed that utilize these non-dimensionalized parameters to compare mechanisms based on stiffnesses, percent constant-force, actual lengths, normal displacements, and feasible design orientations. These comparison techniques are then combined with optimization to define new mechanisms with improved performance and range of capabilities. This thesis also outlines a design process, methods to identify mechanisms that are suitable for a given design problem, and relationships and trends between variables. The thesis concludes by discussing the adaptation of CFMs for use in electrical contacts and presenting the results of a design case study which successfully developed a constant-force electrical contact (CFEC).

Microactuators are needed to convert energy into mechanical work at the microscale. Thermal microactuators can be used to produce this needed mechanical work. The purpose of this research was to design, fabricate, and test thermal microactuators for use at the microscale in microelectromechanical systems (MEMS). The microactuators developed were tested to determine the magnitude of their deflection and estimate their force. Five groups of thermal microactuators were designed and tested. All of the groups used the geometrically constrained expansion of various segments to produce their deflection. The first group, Thermal Expansion Devices (TEDs), produced a rotational displacement and had deflections up to 20 µm. The second group, Bi-directional Thermal Expansion Devices (Bi-TEDs) were similar to the TEDs. The difference, as the name implies, was that the Bi-TEDs deflected up to 6 µm in two directions. Thermomechanical In-plane Micromechanisms (TIMs) were the third group tested. They produced a linear motion up to 20 µm. The fourth group was the Rapid Expansion Bi-directional Actuators (REBAs). These microactuators were bi-directional and produced up to 12 µm deflection in each direction. The final group of thermal microactuators was the Joint Actuating Micro-mechanical Expansion Systems (JAMESs). These thermal microactuators rotated pin joints up to 8 degrees. The thermal microactuators studied can be used in a wide variety of applications. They can move ratchets, position valves, move switches, change devices, or make connections. The thermal microactuator groups have their own unique advantages. The TIMS can be tailored for the amount of deflection and output force they produce. This will allow them to replace some microactuator arrays and decrease the space used for actuation. The Bi-TEDs and REBAs are bi-directional and can possibly replace two single direction micro-actuators. The JAMESs can be attached directly to a pin joint of an existing mechanism. These advantages allow these thermal microactuator groups to be used for a wide variety of applications.

In this research a variable-stiffness compliant mechanism was developed to generate variable force-displacement profiles at the mechanisms coupler point. The mechanism is based on a compliant Roberts straight-line mechanism, and the stiffness is varied by changing the effective length of the compliant links with an actuated slider. The variable-stiffness mechanism was used in a one-degree-of-freedom haptic interface to demonstrate the effectiveness of varying the stiffness of a compliant mechanism. Unlike traditional haptic interfaces, in which the force is controlled using motors and rigid links, the haptic interface developed in this work displays haptic stiffness via the variable-stiffness compliant mechanism. The force-deflection behavior of the mechanismwas analyzed using the Pseudo-Rigid Body Model (PRBM), and two key parameters, KQ and g,were optimized using finite element analysis (FEA) to match the model with the behavior of the device. One of the key features of the mechanism is that the inherent return-to-zero behavior of the compliant mechanism was used to provide the stiffness feedback felt by the user. A prototype haptic interface was developed capable of simulating the force-displacement profile of Lachmans Test performed on an injured ACL knee. The compliant haptic interface was capable of displaying stiffnesses between 4200 N/m and 7200 N/m.

La robotique chirurgicale vise à rendre les gestes du chirurgien plus précis et moins invasifs. La complexité d’une salle d’opération conduit à rechercher des dispositifs robotiques aussi compacts que possible et pouvant être facilement stérilisés. Une conception robotique basée sur l’emploi de mécanismes compliants à structures monolithiques et d’actionneurs piézoélectriques est particulièrement intéressante sur ce point. Des travaux précédents conduits au laboratoire ont permis de proposer un dispositif robotique pour le pontage coronarien qui facilite la réalisation des gestes minimalement invasifs sur cœur battant. Ce dispositif répond au besoin médical mais manque aujourd’hui de la compacité souhaitée pour une intégration optimale. À partir du cas d’application où nous cherchons à réduire la taille du dispositif de compensation, nous nous intéressons, dans cette thèse, aux problématiques de conception de mécanismes compliants à fortes contraintes d’intégration. Nous étudions d’abord la possibilité d’intégrer le dispositif de compensation directement dans la tige du stabilisateur cardiaque passif. Puis, nous étudions la possibilité de réduire la taille du dispositif de compensation en amont, en explorant les possibilités de réaliser des mécanismes dans un plan. Nous avons notamment proposé une méthode originale de conception de mécanismes compliants plans à partir de l‘analyse des singularités de mécanismes à architectures parallèles en configuration plane. Afin d’optimiser les différents mécanismes très contraints par les volumes imposés, une méthode originale d’optimisation à base d’un algorithme de colonie de fourmis est employée. / Surgical robotics helps to increase the surgeon’s accuracy and limits the invasiveness of the surgery. The complexity of an operation room implies to design surgical devices that are as compact as possible and that can be easily sterilized. One interesting design approach is to combine compliant mechanisms, which have a monolithic structure, and piezoelectric actuators. Based on this approach, a robotic device for minimally invasive coronary artery bypass grafting has been proposed previously in our laboratory. This device successfully helps to increase the stabilization of the heart surface during the surgery but its compactness needs to be increased for an optimal integration in the operation room. Based on the need to reduce the compensation mechanism of this device, the problem of the design of compliant mechanisms with strong integration constrains is studied in this PhD thesis. First, the possibility to integrate the compensation mechanism directly in the shaft is considered. Then, the possibility to reduce the compensation mechanism at the end of the shaft by considering an assembly of planar manufactured structures is considered. Among the contributions, we propose an original design method based on the analysis of singularities of parallel manipulators in planar configuration. We also propose an original optimization method based on ant colony optimization in order to optimize the compliant architectures proposed in this work.