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QC 20100901

One of the biggest challenges of putting a robot on an extraterrestrial surface is the entry, descent and landing. By making the robot impact resistant, the need for landing thrusters and parachutes is reduced, lowering the weight and cost of an interplanetary robotic mission. The Dynamic Tensegrity Research Lab at the NASA Ames Research Center in Mountain View, California, is currently doing research in tensegrity robots, consisting of bars and cables creating a complex dynamic system. With motors on the cables, the system can shift its center of mass to create a ”rolling” locomotion and explore remote and dangerous areas. For octahedron tensegrities with 12 bars, intuitive locomotion patterns have been explored previously. The findings included difficulties in keeping the momentum, resulting in the robot getting stuck. In this thesis, over 7.000 configurations of a central pattern generator were tested. The parameters were generated with the Monte Carlo method, with the aim to allow the robot of keeping its momentum in the motion. The resulting locomotion behavior was simulated in NASA Tensegrity Robotic Toolkit. With the method described above, a central pattern generator for a 0.5 m in diameter 12 bar tensegrity of octahedron shape was found, capable of moving 10 m during the course of a 60 s simulation. This is about four times faster than traditional rovers such as NASA’s Curiosity, indicating the need of smaller, faster robots in addition to traditional types. This, together with the impact resistance resulting in a capability of moving in difficult terrain, makes this type of robot an integral part in any future space exploration mission.

Le contexte de cette thèse est la conception d'assistants robotiques aux gestes chirurgicaux guidés par IRM. Cette conception est rendue délicate par l’environnement qui impose des contraintes de compacité, de légèreté et de compatibilité. La présence du patient dans cet environnement impose également des impératifs de sécurité qui limitent les architectures robotiques viables. Cette thèse vise à évaluer le potentiel applicatif des mécanismes de tenségrité, et plus généralement des systèmes précontraints, qui présentent de nombreuses propriétés intéressantes qui justifient d’envisager leur emploi dans ce contexte, notamment pour leur capacité de raideur variable bénéfique à la sécurité du patient. Afin de juger de la pertinence de leur utilisation, nous nous concentrons sur l’analyse, la conception et la commande de ces systèmes peu connus des roboticiens, étapes nécessaires à leur évaluation. Nos contributions incluent le développement d’outils numériques pour permettre leur analyse, de méthodes de synthèse pour générer des architectures à raideur variable adéquates, et de stratégies de commande pour piloter leur configuration et leur raideur. / This thesis is focused on the design of robotic assistants for MRI-guided surgeries. This design is submitted to several constraints due to the MR-environment, such as compactness, lightness, or compatibility. Safety issues related to the patient within the scanner also restrict the choice of suitable robotic solutions. This thesis thus aims at evaluating the applicative potential of tensegrity mechanisms, and more generally prestressed systems, that exhibit numerous interesting properties for this context. In particular, their stiffness can be adjusted, which is opportune for the patient safety. The relevance of our approach is assessed through the analysis, the design and the control of these systems that are required to fulfil their evaluation. Our contributions include the development of numerical tools for their analysis, synthesis methods for the generation of suitable variable stiffness designs, and control strategies for the simultaneous control of their configuration and their stiffness.

The master’s thesis deals with computational modelling of mechanical testing of isolated cells, particularly of single-axle tensile test. The aim is to imitate the real deformed shape known from experiments. At first, the structure of each cell component is described and analyzed according to their significance for mechanical behavior. The outline of basic mechanical tests used for cell testing is discussed next. A structural computational model comprising all components significant for mechanical purposes is created for the modelling. Those components are nucleus, cytoplasm, cell membrane and cytoskeleton. Due to the problems with convergence the model was divided into two parts. The first one treats separately the shape of cytoskeleton and the second one treats the shape of communicating components (nucleus, cytoplasm and cell membrane). Both of those partial models succeed in reaching the deformations according to the experiments.

Indiana University-Purdue University Indianapolis (IUPUI) / Endothelial cells form the lining of the walls of blood vessels and are continuously subjected to mechanical stimuli from the blood flow. Microtubule-organizing center (MTOC), also known as centrosome is a structure found in eukaryotic cells close to the nucleus. MTOC relocates relative to the nucleus when endothelial cells are exposed to shear stress which determines their polarization, thus it plays a critical role in cell migration and wound healing. The nuclear lamina, a mesh-like network that lies underneath the nuclear membrane, is composed of lamins, type V intermediate filament proteins. Mutations in LMNA gene that encodes A-type lamins cause the production of a mutant form of lamin A called progerin and leads to a rare premature aging disease known as Hutchinson-Gilford Progeria Syndrome (HGPS). The goal of this study is to investigate how fluid flow affects the cytoskeleton of endothelial cells. This thesis consists of two main sections; computational mechanical modeling and laboratory experimental work. The mechanical model was implemented using Ansys Workbench software as a tensegrity-based cellular model in order to simulate the state of an endothelial cell under the effects of induced shear stress from the blood fluid flow. This tensegrity-based cellular model - composed of a plasma membrane, cytoplasm, nucleus, microtubules, and actin filaments - aims to understand the effects of the fluid flow on the mechanics of the cytoskeleton. In addition, the laboratory experiments conducted in this study examined the MTOC-nuclear orientation of endothelial cells under shear stress with the presence of wound healing. Wild-type lamin A and progerin-expressing BAECs were studied under static and sheared conditions. Moreover, a custom MATLAB code was utilized to measure the MTOC-nuclear orientation angle and classification. Results demonstrate that shear stress leads to different responses of the MTOC orientation between the wild-type and progerin-expressing cells around the vertical wound edge. Future directions for this study involve additional experimental work together with the improved simulation results to confirm the MTOC orientation relative to the nucleus under shear stress.

Tensegrity-membrane systems are a class of new bar-tendon-membrane systems. Such novel systems can be treated as extensions of tensegrity structures and are generally lightweight and deployable. These two major advantages enable tensegrity-membrane systems to become one of the most promising candidates for lightweight space structures and gossamer spacecraft. In this dissertation, modeling and control of tensegrity-membrane systems is studied. A systematic method is developed to determine the equilibrium conditions of general tensegrity-membrane systems. Equilibrium conditions can be simplified when the systems are in symmetric configurations. For one-stage symmetric systems, analytical equilibrium conditions can be determined. Three mathematical models are developed to study the dynamics of tensegrity-membrane systems. Two mathematical models are developed based on the nonlinear finite element method. The other model is a control-oriented model, which is suitable for control design. Numerical analysis is conducted using these three models to study the mechanical properties of tensegrity-membrane systems. Two control strategies are developed to regulate the deployment process of tensegrity-membrane systems. The first control strategy is to deploy the system by a nonlinear adaptive controller and use a linear H∞ controller for rapid system stabilization. The second control strategy is to regulate the dynamics of tensegrity-membrane systems using a linear parameter-varying (LPV) controller during system deployment. A gridding method is employed to discretize the system operational region in order to carry out the LPV control synthesis. / Ph. D.

[pt] No contexto das pesquisas que se desenvolvem no LILD, DAD, PUC-Rio, sobre o encapsulamento de colmos de bambu, este trabalho explora uma nova modalidade de proteção do material, que se desdobra em benefício estético. Em síntese, propõe-se aqui a pintura ou impregnação de pigmentos e corantes sobre superfícies de colmos de bambu com resinas transparentes e translúcidas. A proposição que origina esta tese deriva da premissa de que a geometria do bambu extraído é a característica mais relevante de sua forma, e não a cor natural, que perde seu viço após a extração do solo. Nesse sentido, desde os primeiros experimentos com pintura, percebemos que a cor artificial poderia substituir a cor natural, realçando a curvatura da fibras longitudinais e outros aspectos da geometria única do bambu, dando origem, em verdade, a uma outra dimensão possível do material, na qual a perda da naturalidade crômica seria compensada por ganhos em representação geométrica – para além dos benefícios em relação à proteção do material e em coerência com a integração forma/função que marca a essência do design. Considerando a cor, nessa e noutras funções, a pesquisa compreende quatro produções inter-relacionadas no tempo: a) Experimentos iniciais de pintura, impregnação de cores e encapsulamento; b) Manejo de algumas espécies de bambu, pintura e encapsulamento de bambus abertos e construção de objetos tensegrity para testes de resistência às tensões e à ação do tempo; c) Produção dos objetos demonstrativos das aplicações de uso; d) Instalações. Constituindo-se na espinha dorsal do trabalho, as quatro produções são expostas em linha de tempo no capítulo 3, demonstrando desencobrimentos e técnicas aplicadas. Os capítulos precedentes de introdução e contextualização abordam aspectos relacionados a esse eixo principal, com foco na cor como função na natureza, no design e na arquitetura. / [en] In the scope of the researches developed at LILD, DAD, PUC-Rio about the encapsulating of bamboo stems, this work explores a new way to protect this material, which also creates esthetic benefits. We propose the painting or impregnation of pigments and dyes on surfaces of bamboo stems with transparent and translucent resins. This thesis proposition is that the most relevant characteristic of the shape of the extracted bamboo is its geometry, rather than its natural color, which loses its freshness after the extraction. Since our first painting experiments, we realized that artificial color could replace the natural one, highlighting the longitudinal fiber s curves and other aspects of the unique geometry of the bamboo, originating a new possible dimension of the material, where the loss of natural color would be compensated by gains in geometric representation – in addition to benefits regarding material protection and in keeping with the integration of form and function that is the essence of design. Regarding color, in this and other functions, the research comprehends four interrelated productions: a) initial experiments of painting, color impregnation and encapsulating; b) handling of some bamboo species, painting and encapsulating open bamboos and construction of tensegrity objects used in stress tests for tension and the effects of time; c) production of objects to demonstrate possible uses; d) installations. Being the backbone of this work, these four productions are displayed on the timeline in Chapter 3, showing the uncovering and the techniques applied. The preceding chapters (Introduction and Contextualization) approach aspects related to this main axis, with a focus on color as a function in nature, as well as in design and architecture.

The master’s thesis deals with the computational modelling of the mechanical testing of isolated smooth muscle cells. The main aims are to create computational model of a cell, to simulate single-axis tensile test and to modify the model so that the model reflects real mechanical response. The model of the cell includes cytoplasm, nucleus, cell membrane and cytoskeleton which is modelled as a tensegrite structure. On this model the tensile test was simulated in case of the cell with cytoskeleton and the cell with distributed the cytoskeleton. Force-elongation curves, which were obtained from this simulation, were compared with experimental data which were taken from literature. Tensile properties were measured on freshly isolated cells from rat thoracic aorta, cultured cells, and cells treated with cytochalasin D to disrupt their actin filaments. It was found that the cytoskeleton influence on the cell load in computational model was smaller than in the real cell. Therefore the model was modified by changing material propreties and geometry so that the model of the cell corresponded with the different types of experimentally measured cells.

[pt] Esta pesquisa está inserida no universo dos portadores de necessidades especiais e pretende desenvolver uma nova tecnologia para projetar a estrutura de cadeira de rodas. Tal estrutura será composta por um módulo tensegrity composto de varas de bambu e cabos tensionados e adota todos os padrões antropométricos com a observância aos estudos ergonômicos e necessidades individuais de uso dos cadeirantes. Esse novo conceito de design de estrutura, por ser inédito, resulta num produto inovador e permite novas interpretações e desdobramentos. Essa pesquisa também inicia uma nova interpretação do tensegrity por sua aplicação a órteses para reabilitação que atualmente é amplamente difundido nas artes plásticas, arquitetura e no design de produto. O seu emprego pode suprir algumas necessidades como adaptação corporal favorável pela maleabilidade da estrutura que absorve os movimentos mais bruscos que possam causar incômodos, lesões e má acomodação do usuário à cadeira de rodas. / [en] This research is part of the universe of people with special needs and aims to develop a new technology to design the wheelchair frame. This structure will consist of a compound tensegrity module bamboo poles and tensioned cables and adopts all anthropometric standards with respect to ergonomic studies and individual needs of use of the wheelchair. This new concept of structure design, to be unheard of, resulting in an innovative product and allows new interpretations and developments. This research also initiates a new interpretation of tensegrity by its application to orthoses for rehabilitation that is currently widespread in art, architecture and product design. Your job can fill some needs as body adaptation favor the flexibility of the structure that absorbs the most sudden movements that may cause nuisance, injuries and poor user accommodation to the wheelchair.