While the existing thermomechanical constitutive models can predict the behavior of SMA-actuated systems in most cases, in this study, we have shown that there are certain situations in which these models are not able to predict the behavior of SMAs. To this end, a rotary SMA-actuated robotic arm is modeled using the existing constitutive models. The model is verified against the experimental results to document that under certain conditions, the model is not able to predict the behavior of the SMA-actuated manipulator. Such cases most often occur when the temperature and stress of the SMA wire change simultaneously. The constitutive model discrepancy is also studied experimentally using a dead-weight that is actuated by an SMA wire. Subsequently, an enhanced phenomenological model is developed. The enhanced model is able to predict the behavior of SMAs under complex thermomechanical loadings. For the SMA-actuated robotic arm, several control methods are designed through simulations. A position-based PID controller is designed first, and it is found that this controller cannot perform well for all the desired angular positions(set-points). A Variable Structure Control (VSC) based on the angular position and velocity is presented that has a relatively better erformance for all the set-points. To improve the erformance of the VSC, in terms of the steady state error, an Extended Kalman Filter is designed and used to modify the VSC design. The modified VSC is based on the angular position and angular velocity of the actuator and the estimated temperature of the SMA wire. Furthermore, a Sliding Mode Controller is designed based on the stress of the SMA wire. Finally, a model-based Backstepping Controller is designed for the SMA-actuated arm. This model-bsed controller allows designing the controller parameters based on the parameters of the system. Additionally, the stability of the controller is studied. Using the Lyapunov stability analysis, it is shown that the model-based Backstepping Controller is able to asymptotically stabilize the system. / Ph. D.

Mimicking facial structures for a robotic head requires integration of multiple structural and mechanical parameters, design, synthesis and control of muscle actuation, architecture of the linkages between actuation points within skin, and implementation of the deformation matrix with respect to global skull coordinates. In this dissertation, humanoid faces were designed and fabricated to investigate all the parameters mentioned above. A prototype face and neck was developed using servo motors and extensively characterized. In this prototype, a neck mechanism was designed using a four bar mechanism to achieve nodding and turning motions. The modular neck prototype simplifies the assembly and statically in equilibrium and hence demands less torque from the cost-effective RC servo motor. The mechanism was critically investigated for dynamic performance and it was found out that RC servo based robotic head requires a PD external controller to overcome inherent overshoot. The servo based robotic head was analyzed for design and control of anchor, architecture of linkages between actuation points within skin, and deformation matrix with respect to global coordinate for creating specific expressions. A functional relationship between deformation vector of facial control points and actuator parameter, skin elasticity and angular position of actuator was derived. The developed analysis method is applicable to any rotary actuator technology utilized for facial expressions and takes into account the skin stiffness. The artificial skin materials for facial expression were synthesized using platinum-cured silicone elastomeric material (Reynolds Advanced Materials Inc.) with base consisting of mainly polyorganosiloxanes, amorphous silica and platinum-siloxane complex compounds. Systematic incorporation of porosity in this material was found to lower the force required to deform the skin in the axial direction. The performance of the servo motor based face was quite realistic but it suffers from the drawback of large power consumption, bulky, heavy, and limited functionality. Thus, significant effort was made in developing a Biometal fiber and Flexinol shape memory alloy actuator (SMA) based biped mountable baby head facial structure which resembles the form and functionality of a human being. SMAs were embedded inside a skull and connected to elastomeric skin at control points. An engineered architecture of skull was fabricated that incorporates all the muscles with their 35 routine pulleys, two fire wire CMOS cameras that serve as eyes, and a battery powered microcontroller base driving circuit within the total dimensions of 140 mm x 90 mm x 110 mm. The driving circuit was designed such that it can be easily integrated with biped and processed in real-time. The humanoid face with 12DOF was mounted on the body of DARwIn (Dynamic Anthropomorphic Robot with Intelligence) robot which has 21 DOF resulting in a total of 33 DOF system. Characterization results on the face and associated design issues are described that provide pathways for developing human-like facial anatomy. Numerical simulation using Simulink was conducted to assess the performance of a prototypic robotic face mainly focusing on jaw movement. A graphical method “Graphical Facial Expression Analysis and Design (GFEAD)” was developed that can be used to allocate the sinking points on robotic head. The method assumes that the origin of the action units are known prior and the underlying criterion in the design of faces being deformation of a soft elastomeric skin through tension in anchoring wires attached on one end to the sinking point and on the other to the actuator. Experimental characterization on a prototyping humanoid face was performed to validate the model and demonstrate the applicability on a generic platform. During characterization of the SMA based face, it was found that the currently available artificial muscle technologies do not meet the entire requirement for being embedded in the skin and provide the required strain rate, maximum strain, blocking force, response time and energy density. Thus an effort was made to develop conducting polymer based artificial muscles which can meet the metrics of human muscle. Composite stripe and zigzag actuators consisting of a sandwich structure polypyrrole /poly(vinylidene difluoride) (PPy/PVDF) were synthesized using potentiodynamic film growth on gold electrodes. The synthesis was done from an aqueous solution containing tetrabutylammonium Perchlorate (TBAP) and pyrrole by polymerization at room temperature. For depositing thin PPy films and thereby minimizing the response time, an experimental optimization of the deposition conditions was performed. The number of current-potential (potentiodynamic) growth cycles and the thickness of the deposited PPy film were highly correlated in the initial stages of polymer film growth. Strip actuator of size 11 x 5 mm2 with 63μM exhibited a deflection of 3mm under 1V DC voltage and 2mm deflection under 8V AC voltage at 0.5 Hz. It was found that three-segment zigzag actuator of segment length 15x2.5mm and thickness 63μM amplifies the displacement by 1.5 times. A study was also conducted on the synthesis and characterization of thick and thin film polypyrrole (PPy) – metal composite actuators. The fabrication method consisted of three steps based upon the approach proposed by Ding et al.: (i) winding the conductive spiral structure around the platinum (Pt)-wire core, (ii) deposition of PPy film on the Pt-wire core, and (iii) removal of the Pt-wire core. This approach yielded good performance from the synthesized actuators, but was complex to implement due to the difficulty in implementing the third step. To overcome the problem of mechanical damage occurring during withdrawal of Pt-wire, the core was replaced with a dispensable gold coated polylactide fiber that could be dissolved at the end of deposition step. Experimental results indicate that thin film actuators perform better in terms of response time and blocking force. A unique muscle-like structure with smoothly varying cross-section was grown by combining layer by layer deposition with changes in position and orientation of the counter electrode in reference to the working electrode. Synthesis of polypyrrole–metal coil was conducted in aqueous solution containing 0.25 M Pyrrole, 0.10 M TBAP and 0.50 M KCl. The actuator consisted of a single layer of platinum winding on a core substrate. Electrochemical characterization for free strain and blocking stress was conducted 0.1 M TBAP solution and a 6% free strain was obtained at an applied potential of 6V DC after 80 s stimulation time. The blocking stress 18 kPa was estimated by extrapolating the strain magnitude on stress-strain diagram. For axial type actuator with coil winding, a generalized governing equation for the electrochemical stress generated from polypyrrole–metal coil which accommodates the effect of magnetic field due to winding was proposed and numerically studied. It was considered as insightful modeling. / Ph. D.

A self-sensing and self-healing bolted joint has been developed. This concept encompasses the areas of health monitoring, joint dynamics and smart materials. In order to detect looseness in a joint the impedance health monitoring method is used. A new method of making impedance measurements for health monitoring that greatly reduces the equipment cost and equipment size was developed. This facilitates implementation of the impedance technique in real-life field applications. Several proof of concept experiments are presented and compared to the traditional method of making impedance measurements. Investigations of bolted joint dynamics were conducted. A literature review of bolted joints and their diagnostics is presented. The application of the transfer impedance method is compared to standard modal tests on various bolt tensions. An investigation of damping in bolted joints was also made comparing a bolted and monolithic beam. Practical issues in adaptive bolted joints are investigated. This includes issues on activating/heating SMA actuators, connecting the actuators to the power source, size selection of SMA actuators and insulations. These issues are examined both experimentally and theoretically. / Master of Science

No description available.

A study on shape memory alloy materials as vibration dampers is reported. An important component is the strain rate-dependent and temperature-dependent constitutive behavior of shape memory alloy, which can significantly change its energy dissipation capacity under cyclic loading. The constitutive model used accounts for the thermo-mechanical strain rate-dependent behavior and phase transformation. With increasing structural flexibility, the hysteretic loop size of shape memory alloy dampers increases due to increasing strain rates, thus further decreasing the response of the structure to cyclic excitation. The structure examined is a beam, and its behavior with shape memory alloy dampers is compared to the same beam with conventional dampers. Parametric studies reveal the superior performance of the shape memory alloy over the conventional dampers even at the resonance frequency of the beam-damper system. An important behavior of the shape memory alloy dampers is discovered, in that they absorb energy from the fundamental and higher vibration modes. In contrast, the conventional dampers transfer energy to higher modes. For the same beam control, the stiffness requirement for the shape memory alloy dampers is significantly less than that of the conventional dampers. Response quantities of interest show improved performance of the shape memory alloy over the conventional dampers under varying excitation intensity, frequency, temperature, and strain rate.

Este trabalho apresenta a modelagem, identificação de parâmetros e projeto do sistema de controle de um atuador rotacional antagônico com refrigeração forçada baseado em fios de liga de memória de forma, tendo em vista a aplicação em manipuladores robóticos. O modelo é baseado na abordagem de transformação de fases por subcamadas, que leva em conta a alta não linearidade que ocorre devido à dinâmica de transformação de fases do fio de memória de forma (especialmente a alta histerese envolvida). Um algoritmo de otimização por meio de Programação Quadrática Sequencial é então usado para se estimar os parâmetros do modelo de difícil obtenção exata, como as temperaturas de transição de fase dos fios de liga de memória de forma e o coeficiente de convecção. A função objetivo adotada é o erro entre a posição medida experimentalmente e a posição obtida por meio de modelagem e simulação. Parte-se de valores de parâmetros iniciais de tabela para a aplicação do algoritmo. Os resultados são em seguida comparados e avaliados com experimentos independentes em malha aberta, com o modelo apresentando boa correlação com a planta para uma excitação de até 2,0 Hz. Por fim, um sistema de controle não linear por modos deslizantes baseado no modelo é desenvolvido e simulado utilizando o modelo estimado, tanto em modo de controle de torque como em controle de posição. Aplica-se um controlador com camada limite e linearização utilizando a realimentação dos estados e o modelo estimado. Este tipo de controlador é robusto a eventuais diferenças entre o modelo e o sistema real. O controlador é então utilizado num modelo sistema de experimental, a partir do qual são obtidos resultados de desempenho dinâmico e exatidão do atuador controlado ao mesmo tempo em que são feitas comparações com os resultados das simulações. Por fim, demonstra-se que os objetivos iniciais do trabalho são atingidos, ao se realizar satisfatoriamente o controle de posição e de torque com robustez, exatidão e desempenho dinâmico adequados à aplicação prevista. / This work presents the modeling, grey-box parameter estimation and control design of a force-cooled antagonistic shape memory alloy (SMA) rotational actuator, having in mind the application in robotic manipulators. The model is based on a sub-layer phase transformation approach, taking account the large non-linearities that rise from the phase-transformation dynamics (in special, the highly hysteretic dynamics). An optimization Quadratic Sequential Programming Algorithm is used to for estimate estimating the model parameters, which are hard to obtain accurately, like the such as phase transition temperatures of the shape memory alloy wires and the convection coefficient. The objective function adopted is the error between the experimentally measured position and the position obtained by means of modeling and simulation. Initial parameters for the algorithm application are taken from factory tables\' datasheets. The results are then compared and evaluated with independent open loop experiments. At last, a model based nonlinear shape memory alloy SMA control scheme is designed and simulated using the estimated model, in torque and position control modes. The control scheme applied uses limit layer and feedback linearization using based on the estimated model. This control scheme is robust to eventual mismatch between modeling and the real system. The controller is then used in an experimental model, from which results of dynamic behavior and accuracy of the controlled actuator are obtained and compared with the simulated results. At last, it is showed that the initial objectives of this work are achieved, by satisfactorily performing position and torque control with robustness, accuracy and dynamic performances adequate to the application targeted.

As ligas com memória de forma (Shape Memory Alloy - SMA) consistem em um grupo de materiais metálicos que possuem a habilidade de retornar a um formato ou tamanho previamente definido quando submetidas a um ciclo térmico adequado, devido a alterações em sua estrutura cristalina. Esta mudança não é um processo termodinamicamente reversível, apresentando, conseqüentemente, histerese. Portanto, a característica principal destes materiais é a habilidade de sofrer grandes deformações e, em seguida, recuperar sua forma original quando a carga é removida ou o material é aquecido. Assim, pode-se utilizar esse fenômeno para construir atuadores leves e silenciosos, como verdadeiros músculos metálicos. O desenvolvimento de atuadores com as SMAs apresenta grande atrativo para diversos campos da engenharia, principalmente na área de robótica, substituindo os atuadores convencionais de grande peso e ruidosos, como motores, válvulas solenóides, etc. Entretanto, para o bom desempenho de atuadores SMA requer-se um complexo sistema de controle e resfriamento, reduzindo-se o tempo de resposta do atuador e minimizando-se os efeitos da histerese. Neste trabalho, propõe-se um inovador sistema de resfriamento, baseado em pastilha termo-elétrica (efeito Seebeck-Peltier). Este método possui a vantagem de ser mais compacto e simples que outros métodos de resfriamento forçado. Um modelo matemático completo foi também desenvolvido, e um protótipo experimental foi construído. Diversos experimentos foram utilizados para a validação do modelo e para a identificação de todos seus parâmetros. Analisou-se então a aplicabilidade de um controle de posição baseado em algoritmo PID, utilizando-se diversos métodos de ajuste de ganhos. Verificou-se um desempenho razoável, com uma largura de banda em malha fechada de aproximadamente 0,37Hz. Em seguida, desenvolveu-se um sistema de controle de posição baseado em teoria de modos deslizantes (sliding mode control), que utiliza o modelo matemático do sistema e leva em conta as não linearidades existentes. Embora matematicamente mais complexo, obteve-se um desempenho superior ao PID, com largura de banda de 0,69Hz. Diversos experimentos confirmaram também a robustez deste controlador e seu bom desempenho na presença de distúrbios. / Shape Memory Alloys (SMA) consist of a group of metallic materials that demonstrate the ability to return to some previously defined shape when subjected to the appropriate thermal cycle, due to shift in the materials crystalline structure. The change that occurs within SMAs crystalline structure is not a thermodynamically reversible process and results in hysteresis behavior. The key feature of these materials is the ability to undergo large plastic strains and subsequently recover these strains when a load is removed or the material is heated. Such property can be used to build silent and light actuators, similar to a mechanical muscular fiber. SMA actuators have several advantages in several engineering fields, mainly in robotics, replacing the conventional actuators like motors or solenoids. However, the good performance of the SMA actuator depends on a complex control and cooling systems, reducing the time constant and minimizing the effects of hysteresis. In the present work, a novel cooling system is proposed, based on thermo-electric effect (Seebeck-Peltier effect). Such method has the advantage of reduced weight and requires a simpler control strategy compared to other forced cooling systems. A complete mathematical model of the actuator was also derived, and an experimental prototype was implemented. Several experiments were used to validate the model and to identify all parameters. A PID position control system was developed and implemented in the prototype, using several tuning methods. A good performance was obtained, with a cut-off frequency of 0.37Hz. A position controller based on sliding mode theory was then developed, using the mathematical model of the system and taking into account the non-linear effects. Although such controller presents a more complex mathematical derivation, a better performance was obtained, with a cut-off frequency of 0.69Hz. Several experiments confirmed the robustness and disturbance filtering properties of the sliding mode controller.

L’Alliage à Mémoire de Forme (AMF) est un matériau intelligent ayant de nombreuses applications dans l'industrie aérospatiale, le génie civil, ainsi que dans le domaine biomédical. Dans toutes ces applications, le matériau est soumis à un chargement cyclique ce qui le rend vulnérable vis-à-vis du phénomène de la fatigue. Une des questions importantes dans l'étude de la fatigue de l’AMF polycristallin est l'interaction entre l’endommagement local et la transformation de phase martensitique; cette transformation se déroule dans un mode homogène macroscopique ou un mode hétérogène se traduisant par la formation de bandes de Lüders en raison de la localisation de la déformation et du changement de phase. La formation et l'évolution de ces bandes influence fortement les mécanismes physiques de déformation ainsi que l’endommagement par fatigue du matériau. Dans la littérature, on ne trouve pas d’études permettant de faire le lien entre la formation et l’évolution des bandes de localisation et la fatigue du matériau. Dans cette thèse, des expériences systématiques de fatigue en traction sont réalisées sur les éprouvettes pseudo-élastiques du Nickel-Titane avec des observations optiques in-situ de l’évolution des macro-bandes. Ces observations ont permis de retracer l'histoire de la déformation locale dans les zones où la rupture se produit. Ces résultats expérimentaux permettent de mieux comprendre le comportement de fatigue ainsi que sa dépendance par rapport à la contrainte appliquée ainsi que la fréquence du chargement. En particulier, il a été prouvé que la déformation locale résiduelle représente un meilleur indicateur de l’endommagement du matériau que la déformation résiduelle nominale/globale de la structure. / Shape Memory Alloy (SMA) is a typical smart material having many applications from aerospace industry, mechanical and civil engineering, to biomedical devices, where the material’s fatigue is a big concern. One of the challenging issues in studying the fatigue behaviors of SMA polycrystals is the interaction between the material damage and the martensitic phase transformation which takes place in a macroscopic homogeneous mode or a heterogeneous mode (forming macroscopic patterns (Lüders-like bands) due to the localized deformations and localized heating/cooling). Such pattern formation and evolution imply the governing physical mechanisms in the material system such as the fatigue process, but there is still no fatigue study of SMAs by tracing the macro-band patterns and the local material responses. To bridge this gap, systematic tensile fatigue experiments are conducted on pseudoelastic NiTi polycrystalline strips by in-situ optical observation on the band-pattern evolutions and by tracing the deformation history of the cyclic phase transformation zones where fatigue failure occurs. These experimental results help to better understand the stress- and frequency-dependent fatigue behaviors. Particularly, it is found that the local residual strain rather than the structural nominal/global residual strain is a good indicator on the material’s damage leading to the fatigue failure, which is important for understanding and modeling the fatigue process in SMAs.

Previous work done at Cal Poly has shown that thin-film nickel-titanium (NiTi) can be easily sputtered onto silicon wafers and annealed to create a crystallized shape memory alloy (SMA) film. Initial work on creating devices yielded cantilevers that were highly warped due to thin-film stress created during the sputtering process. The objective of this work was to create a thin-film NiTi SMA device that could be better characterized. A membrane was selected due to the simplicity of fabrication and testing which would also oppose the thin-film stress due to the increase in attachment points to the substrate. Silicon wafers were etched through the majority of the thickness (~75%) creating square etch pits of varying sizes varying from 1294 µm to 4394 µm. The wafers were then sputtered with an approximate NiTi film of 5 µm followed by a thin chromium film. The chromium film would act as a diffusion barrier and prevent oxygen from diffusing into the NiTi and reacting with the titanium and forming titanium dioxide. These wafers were then annealed in a custom built vacuum annealing chamber at 550 °C for 1 hour with a pressure around 77 kPa. The chromium was then etched away followed by the remaining silicon. This left a thin membrane of shape memory NiTi which was packaged in order for characterization. The devices were glued to an aluminum substrate using polydimethylsiloxane (PDMS) and sealed with a small Tygon tube leading to the sealed chamber. This packaged device was then able to be pressurized using a nitrogen tank and the resulting NiTi membrane deflection was measured using a profilometer. Due to the differences in elastic moduli of the room temperature phase (martensite) and the high temperature phase (austenite) a difference of deflection was expected. The austenite finish (Af) temperature of bulk NiTi films was found to be around 60 °C so the devices were tested at both room temperature and at 60 °C. After testing seven separate devices of varying sizes, a regression model was used to analyze the final data. It was found that pressure, membrane size and theoretical versus actual deflection all affected the maximum deflection, but temperature did not. Higher pressures and larger membranes led to higher deflections as membrane deflection models from fundamental principles indicated. Some devices showed inferior performance when compared to the model due to incomplete silicon etching which caused lower deflection due to the much higher modulus of the remaining silicon. Thickness could also limit the amount of deflection measured with a thicker film leading to less deflection, but this is likely not the case due to the high uniformity of the sputtering system. Other devices showed superior performance over the model most likely due to either local delamination or lateral silicon etching. Both these would create a membrane that was larger than expected leading to a higher deflection. Unforutnaly, differential scanning calorimetry (DSC) analysis showed no shape memory behavior on a test wafer which was anneald at 550 ˚C for 1 hour. A design of experiments was conducted in order to find a heat treatment that would anneal the NiTi film and ensure that shape memory behavior could be obtained. An annealing at 650 °C for 1 hour showed a sharper and clearer Af phase transformation at around the target temperature of 60 °C. Annealing a full wafer at this temperature and time also showed that no delamination would occur which has also been linked to nonideal behavior of the NiTi membranes which has also been linked to meaningful behavior of the NiTi membranes.

The work presents investigations into the development of a fuel-powered compact SMA actuator system. For the final SMA actuator, the K-alloy SMA strip (0.9 mm x 2.5 mm), actuated by a forced convection heat transfer mechanism, was embedded in a rectangular channel. In this channel, a rectangular piston, with a slot to accommodate the SMA strip, ran along the strip and was utilized to prevent mixing between the hot and the cold fluid in order to increase the energy density of the system. The fuel, such as propane, was utilized as main energy source in order to achieve high energy and power densities of the SMA actuator system. Numerical analysis was carried out to determine optimal channel geometry and to estimate maximum available force, strain and actuation frequency. Multi-channel combustor/heat exchanger and micro-tube heat exchanger were designed and tested to achieve high heat transfer rate and high compactness. The final SMA actuator system was composed of pumps, valves, bellows, multi-channel combustor/heat exchanger, micro-tube heat exchanger and control unit. The experimental tests of the final system resulted in 250 N force with 2 mm displacement and 1.0 Hz actuation frequency in closed-loop operation, in which the hot and the cold fluid were re-circulated by pumps.