It is believed that structures and actuation systems should be tightly integrated together in the future to create fast moving, efficient, lightweight dynamic machines. Such actuated structures could be used for morphing aircraft wings, lightweight actuated space structures, or in robotics. This requires actuators to be distributed through the structure. A tensegrity structure is a very promising candidate for this future integration due to its potentially excellent stiffness and strength-to-weight ratio, and the inherent advantage of being a multi-element structure into which actuators can be embedded. Development of these machines will utilise expertise in several fields, involving kinematics, dynamics, actuation and multi-axis motion control. The research presented in this thesis concerns the study of multi-axis actuated tensegrity structures. A form-finding method has been developed to find stable geometries and determine stiffness properties of the type of tensegrity structure proposed. It has been shown that a tensegrity structure, with practical nodes of finite size, can be designed with actuated members to give shape-changing properties while potentially allowing a good stiffness to mass ratio. An antagonistic multi-axis control scheme has been developed for the tensegrity structure. The describing function technique has been used to analyse the dead band controller in the control scheme, giving a stability criterion. An experimental actuated tensegrity system has been designed and built incorporating pneumatic muscles controlled by switching valves. Mathematical models for the experimental actuated tensegrity system have been developed in detail, including the pneumatic actuation system and the structure geometry. The dynamic behaviour of the tensegrity system has been investigated via several simulation studies, using the developed models and the proposed control scheme. Experimental validation has been successfully conducted. The multi-axis control scheme can accurately control the tensegrity structure to achieve shape changes while maintaining a desired level of internal pre-load. The mathematical models can be used as a basis for further development.

Propõe-se, com este trabalho, estudar numericamente se a redundância cinemática e a redundância de atuação podem ser boas alternativas para que manipuladores planares de cinemática paralela atinjam altas acelerações. Sabe-se que estes tipos de redundância promovem uma redução de singularidades do sistema robótico entre outros benefícios. No entanto, a avaliação comparativa do desempenho dinâmico de manipuladores redundantes ainda é pouco estudada. Este estudo não é trivial pois a redundância significa não somente o aumento do torque disponível, mas também que a inércia do sistema foi aumentada. A avaliação numérica deste trabalho se dará por meio do desenvolvimento de modelos cinemáticos e dinâmicos das possíveis configurações de manipuladores paralelos planares com redundância cinemática e redundância de atuação. Esta avaliação pode ser feita pela comparação entre os manipuladores redundantes e o não-redundante para desenvolver uma mesma trajetória do end-effector. Entretanto, esta avaliação é dependente da trajetória, logo esse trabalho também propõe uma avaliação através de um índice dinâmico em toda a área de trabalho dos manipuladores. / The aim of this work is to study numerically if the kinematic redundancy and the actuation redundancy can be good alternatives for parallel planar manipulators to achieve high accelerations. It is known that types of redundancy promote, among other benefits, a significant reduction in the singularities. However, the evaluation of the redundancy as a good solution to increase the dynamic performance was not studied. This study is not trivial because the redundancy means not only that there is more torque available, but also that the inertia of the system has been considerably increased. Different configurations of the redundant manipulator will be evaluated numerically through kinematic and dynamic models. This evaluation can be performed by the comparison among the non redundant manipulator and the redundant manipulators to execute the same task. This evaluation is task dependent, so this work proposes a dynamic index to desing dynamic maps over the workspace.

There is an urgent and unmet clinical need to improve accuracy and safety during needle-based interventional procedures including regional anaesthesia and cancer biopsy. In ultrasound guided percutaneous needle procedures, there is a universal problem of imaging the needle, particularly the tip, especially in dense tissues and steep insertion angles. Poor visualization of the needle tip can have serious consequences for the patients including nerve damage and internal bleeding in regional anaesthesia and, in the case of biopsy, mis-sampling, resulting in misdiagnosis or the need for repeat biopsy. The aim of the work was to design and develop an ergonomic ultrasound device to actuate standard, unmodified needles such that the visibility of needle can be enhanced when observed under colour Doppler mode of ultrasound imaging. This will make the needle procedures efficient through accurate needle placement while reducing the overall procedure duration. The research reported in this thesis provides an insight into the new breed of piezoelectric materials. A methodology is proposed and implemented to characterize the new piezocrystals under ambient and extreme practical conditions. For the first time, the IEEE standard method (1987) was applied to an investigation of this type with binary (PMN-PT) and ternary (PIN-PMN-PT) compositions of piezocrystals. Using the existing data and the data obtained through characterization, finite element analysis (FEA) were carried to adequately design the ultrasound device. Various configurations of the device were modelled and fabricated, using both piezoceramic and piezocrystal materials, in order to assess the dependency of device’s performance on the configuration and type of piezoelectric material used. In order to prove the design concept and to measure the benefits of the device, pre-clinical trials were carried out on a range of specimens including the soft embalmed Thiel cadavers. Furthermore, an ultrasound planar cutting tool with various configurations was also designed and developed as an alternative to the existing cumbersome ultrasonic scalpels. These configurations were based on new piezocrystals including the Mn-doped ternary (Mn:PIN-PMN-PT) material. It is concluded that the needle actuating device can significantly enhance the visibility of standard needles and additionally benefits in reducing the penetration force. However, in order to make it clinically viable, further work is required to make it compliant with the medical environment. The piezocrystals tested under practical conditions although offer extraordinary piezoelectric properties, are vulnerable to extreme temperature and drive conditions. However, it is observed that newer piezocrystals, especially Mn:PIN-PMN-PT have shown the potential to replace the conventional piezoceramics in high power and actuator applications. Moreover, the d31-mode based planar cutting tool contrasts with the cumbersome design of mass-spring transducer structure and has the potential to be used in surgical procedures.

Soft robotic platforms are becoming increasingly popular as they are generally safer, lighter, and easier to manufacture than their more rigid, heavy, traditional counterparts. These soft platforms, while inherently safer, come with significant drawbacks. Their compliant components are more difficult to model, and their underdamped nature makes them difficult to control. Additionally, they are so lightweight that a payload of just a few pounds has a significant impact on the manipulator dynamics. This thesis presents novel methods for addressing these issues. In previous research, Model Predictive Control has been demonstrably useful for joint angle control for these soft robots, using a rigid inverted pendulum model for each link. A model describing the dynamics of the entire arm would be more desirable, but with high Degrees of Freedom it is computationally expensive to optimize over such a complex model. This thesis presents a method for simplifying and linearizing the full-arm model (the Coupling-Torque method), and compares control performance when using this method of linearization against control performance for other linearization methods. The comparison shows the Coupling-Torque method yields good control performance for manipulators with seven or more Degrees of Freedom. The decoupled nature of the Coupling-Torque method also makes adaptive control, of the form described in this thesis, easier to implement. The Coupling-Torque method improves performance when the dynamics are known, but when a payload of unknown mass is attached to the end effector it has a significant impact on the dynamics. Adaptive Control is needed at this point to compensate for the model's poor approximation of the system. This thesis presents a method of layering Model Reference Adaptive Control in concert with Model Predictive Control that improves control performance in this scenario. The adaptive controller modifies dynamic parameters, which are then delivered to the optimizer, which then returns inputs for the system that take all of this information into account. This method has been shown to reduce step input tracking error by 50% when implemented on the soft robot.

<p>Microrobots have a promising prospect to be used in healthcare and bioengineering applications due to their capability to gently access small and delicate body sites. Unfortunately, traditional materials used for the fabrication of microrobots are rigid, hindering safe operation due to the transfer of high stresses to the surrounding tissue. Additionally, traditional microrobots are often not biocompatible, which threatens the health of the patient if not properly retrieved. This dissertation describes the fabrication and actuation of small-scale (several micrometers in all dimensions) magnetic robots that are soft, biocompatible, and capable of moving over smooth and corrugated surface. <u>S</u>oft <u>M</u>agnetic <u>M</u>icro <u>R</u>obots (SMµRs) can carry payloads in their porous interior and release them using external magnetic inputs. SMµRs has therefore the potential to be used in a wide range of applications—including targeted drug release and remote biosensing and bio sampling—and access a number of difficult-to-reach sites in the human body, such as intestines or blood vessels. The structure of SMµRs consist of three thin layers: Two layers of polymer with embedded magnetic particles aligned along a preferential direction. One porous layer, in between the magnetic layers, where the SMµRs can accumulate and release payloads. SMµRs are small, light in weight, and fast and inexpensive to fabricate. Moreover, the manufacturing of SMµRs is compatible with large-scale production processes, facilitating their future commercial exploitation. Using external rotating magnetic fields, the position of the SMµRs can be controlled wirelessly <i>via</i> tumbling locomotion. We demonstrate two types of tumbling locomotion (length-wise and side-wise) as well as the possibility to release the internal payload of the SMµRs in a discrete or continuous manner using only changes in the intensity of the external magnetic field. We studied the performance of SMµRs under a variety of environmental conditions as well as their capability of overcoming obstacles.</p>

A series of tests were performed on nickel-titanium alloy wire, also known as nitinol, to determine the plausibility of designing an actuator using this wire as the method of actuation. These tests have been designed to fully characterize how the wire behaves under steady state and transient conditions allowing for a specific wire selection to be made given known actuator specifications which will result in an efficient design. The wire transient data can be used to design a controller which reduces the actuation time. The research done for the overall project covers a wide scope including wire hysteresis, nitinol transition temperature, variable wire resistance, wire actuation as a function of current and pull force, cable fabrication, and wire actuation control to optimize performance. Using these test results, a prototype actuator has been designed using nitinol wire. It has been determined that an actuator can be efficiently designed using this material.

L’intérêt des ultrasons pour la caractérisation de milieux ou pour l’actionnement à plus forte puissance n’est plus à démontrer. L’intégration de fonctions acoustiques substrats de silicium soulève en revanche de nombreux problèmes technologiques. Le travail de thèse présenté fait suite aux premiers développements technologiques qui ont permis la validation du concept de caractérisation acoustique haute fréquence en canal microfluidique. Les principales avancées de ce travail concernent l’optimisation du transfert de l’énergie acoustique dans le canal microfluidique dans une bande de fréquence allant de 500 à 1000 MHz. Des dépôts de couches minces sur les miroirs et le développement de transducteurs en couches épaisses constituent les principales avancées. Une première évaluation de l’actionnement de fluides ou de particules en canal microfluidique est également présentée ainsi qu’une application du système à la mesure de température en canal microfluidique par ultrasons. / The interest of ultrasounds for media characterization or for actuation when using more power is well known. Nevertheless, the integration of these acoustic functions in silicon based Lab-on-chips requires specific technological developments. The possibility to use high frequency bulk acoustic waves in this kind of systems for characterization or detection has been presented previously in another PhD work. The main objective of this work was to optimize acoustic energy transfer to a microfluidic channel in a frequency range between 500 MHz and 1000 MHz. To do that, the main technological developments achieved among others concern the coating of the guiding mirrors to avoid acoustic mode conversion and ZnO thick films sputtering for the fabrication of piezoelectric transducers. The developed system has been used for particles detection or concentration evaluation. Moreover, a first evaluation of fluids/particles actuation was demonstrated, along with temperature evaluation using ultrasound were achieved in microfluidic channels.

In this work, a multi dimensional RF MEMS variable capacitor that utilizes electrostatic actuation is designed and fabricated on a 425um thick silicon substrate. Electrostatic actuation is preferred over other actuation mechanisms due to low power consumption. The RF MEMS variable capacitor is designed in a CPW topology, with multiple beams supported (1 - 7 beams) on a single pedestal. The varactors are fabricated using surface micromachining techniques. A 1um thick silicon monoxide (Er - 6) is used as a dielectric layer for the varactor. The movable membrane is suspended on a 2.5um thick electroplated gold pedestal. The capacitance between the membrane and the bottom electrode increases as the bias voltage between the membrane and the bottom electrode is increased, eventually causing the membrane to snap down at the actuation voltage. For the varactors designed herein, the actuation voltage is approximately 30 - 90V. Full-wave electromagnetic simulations are performed from 1 - 25GHz to accurately predict the frequency response of the varactors. The EM simulations and the measurement results compare favorably. A series RLC equivalent circuit is used to model the varactor and used to extract the parasitics associated with the capacitor by optimizing the model with the measurement results. The measured capacitance ratio is approximately 12:1 with a tuning range from 0.5 - 6pF. Furthermore, the measured S-parameter data is used to extract the unloaded Q of the varactor (at 1GHz) and is found to be 234 in the up state and 27 in the down state. An improved anodic bonding technique to bond high resistivity Si substrate and low alkali borax glass substrate that finds potential application towards packaging of MEMS varactors is investigated. To facilitate the packaging of the varactors the temperature is maintained at 400°C. The bonding time is approximately 7min at an applied voltage of 1KV.

Résumé. Ce mémoire concerne la modélisation analytique et l'optimisation d'actionneurs électrostatique basés sur une membrane. Le modèle analytique de fléchissement de la membrane mince de silicium, parfaitement encastrée, décrit par l'équation Lagrange/Newton pour les petites déflexions est présentée en prenant sur compte des phénomènes comme les contraintes résiduelles et les déflexions initiales de la membrane. Les réponses pour la pression uniforme sont obtenues grâce à la méthode de Galerkin et sont étudiées pour décrire le comportement de la membrane avec un modèle réduit. Les deux modèles sont analysés pour l'actionnement électrostatique et sont comparés sur le plan de la précision, le gamme d'usage, le temps des calculs et le facilité d'usage en phase d'optimisation. Puis, le modèle réduit est corrigé pour être complètement applicable pour un actionnement hydrostatique et électrostatique sans perte de précision et est comparé avec la simulation FEM réalisée dans l'ANSYS®. Les résultats obtenus permettent de déterminer les avantages et les inconvénients du modèle. En suite, le modèle analytique est utilisé pour développer un outil d'optimisation et de statistique sous MATLAB®. Ce dernier permet d'estimer l'influence de la dispersion des paramètres technologiques sur le comportement des actionneurs. Finalement la fabrication et la caractérisation de structures de tests ont été réalisées au LAAS-CNRS et ont permis la validation du modèle analytique.

In this paper, the problem of dual actuation in the atomic force microscope (AFM) is analyzed. The use of two actuators to balance the trade-off between bandwidth, range, and precision has been recently extended to nano-positioning systems. Despite existing demands, this concept undergoes fundamental limitations towards its extension to AFMs. This is attributed to the non-conventional requirement imposed on the control signal response, as it used to create the image of the characterized surface. / Singapore-MIT Alliance (SMA)