Made available in DSpace on 2016-12-12T20:25:11Z (GMT). No. of bitstreams: 1 Luis Reanto Meneghelli.pdf: 5980064 bytes, checksum: 65a0002e42f206e56e3875504a6f0660 (MD5) Previous issue date: 2013-03-07 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Compliant mechanisms are mechanical devices that transform or transfer motion, force or energy through a single part. These mechanisms have important applications in micro electromechanical systems (MEMS) as well as systems that require large accuracy in motion and micro scale. In this work the compliant mechanisms design is performed by means of the Topology Optimization Method, and the optimization problem is formulated in order to maximize the strain energy stored inside the mechanism, eliminating the appearance of hinges. The kinematic behavior of the mechanism is imposed through a set of constraints on displacements of a few degrees of freedom of interest. The elastic behavior is imposed by means of a global stress constraint and some issues associated to the stress parametrization in topology optimization are addressed in the context of mechanisms design. The numerical examples shown that the proposed formulation is able to generate clean topologies of feasible compliant mechanisms. Based on the results, it is clear that the stress constraint has a deep impact on the design of compliant mechanisms, since it can constraint the amount of energy used to enforce the displacement constraints. / Mecanismos flexíveis são dispositivos mecânicos que transformam ou transferem movimento, força ou energia, através de uma única peça. Este tipo de mecanismo encontra aplicações importantes em sistemas micro eletromecânicos (MEMS, micro electromechanical systems) e demais sistemas que exijam grandes precisões nos movimentos e escala microscópica. O projeto de mecanismos flexíveis é realizado através do Método de Otimização Topológica e o problema de otimização será formulado tendo em vista a maximização de energia de deformação elástica armazenada pelo mecanismo, eliminando assim a ocorrência de rótulas (hinges). O comportamento cinemático do mecanismo é imposto através de restrições sobre o campo de deslocamentos em alguns graus de liberdade de interesse. O comportamento elástico dos mecanismos flexíveis é imposto usando um critério global de restrição de tensão e algumas questões importantes associadas a parametrização das tensões são discutidas no contexto de projeto de mecanismos. Os exemplos numéricos mostram que é possível obter topologias bem definidas e que satisfaçam as restrições do projeto. Com base nestes exemplos, verifica-se que a restrição de tensão exerce forte influência no resultado, podendo limitar a quantidade de energia necessária para atender às restrições do mecanismo.

Mecanismos flexíveis, nos quais a deformação elástica é aproveitada na atuação cinemática, têm grande empregabilidade em dispositivos de mecânica de precisão, engenharia biomédica, e mais recentemente em microeletromecanismos (MEMS). Entre as diversas técnicas empregadas para o seu projeto, a otimização topológica tem se mostrado a mais genérica e sistemática. A grande dificuldade destes projetos é conciliar os requisitos cinemáticos com a resistência mecânica da estrutura. Neste trabalho, é implementado um critério de resistência dentro da formulação do problema de otimização, com o intuito de gerar mecanismos que cumpram a tarefa cinemática desejada mas ao mesmo tempo não ultrapassem limites de tensão predeterminados. Esta restrição adicional também visa aliviar o problema bastante conhecido do aparecimento de articulações. Não linearidade geométrica e de material (hiperelasticida de compressível) são implementadas na solução das equações através do método dos elementos finitos para levar em conta os grandes deslocamentos do mecanismo. O método das assíntotas móveis é usado para a atualização das variáveis de projeto. As derivadas do problema de otimização são calculadas analiticamente, pelo método adjunto. Técnicas de projeção são aplicadas para a garantia de topologias livres de instabilidades numéricas comuns em otimização topológica, e projetos otimizados mais próximos de um espaço 0/1 para as densidades físicas. / Compliant me hanisms, in whi h the elasti strain is the basis for kinemati a tua- tion are widely used in pre ision me hani s devi es, biomedi al engineering, and re ently in mi roele trome hani al systems (MEMS). Among several te hniques applied in ompliant me hanisms design, topology optimization has been one of the most general and systemati . The great hallenge in these designs is to ouple both the kinemati s and the me hani al strength riteria requirements. In this work, a strength riteria for the optimization problem is applied, with the aim of generating ompliant me hanisms that ful ll the desired kine- mati tasks while omplying with a stress threshold. The addition of a stress onstraint to the formulation for ompliant me hanisms in topology optimization also aims to allevi- ate the appearan e of hinges in the optimized topology, a well known issue in the design of ompliant me hanisms. Geometri al and material ( ompressible hyperelasti ity) nonlin- earities are applied to the nite element equilibrium equations, to take into a ount large displa ements. The method of moving asymptotes is applied for design variables updating. The derivatives are al ulated analyti ally, by the adjoint method. Proje tion ltering te h- niques are applied, in order to guarantee topologies free of ommon numeri al instabilities in topology optimization, and optimized designs near the 0/1 solution for the physi al densities.

Mecanismos flexíveis, nos quais a deformação elástica é aproveitada na atuação cinemática, têm grande empregabilidade em dispositivos de mecânica de precisão, engenharia biomédica, e mais recentemente em microeletromecanismos (MEMS). Entre as diversas técnicas empregadas para o seu projeto, a otimização topológica tem se mostrado a mais genérica e sistemática. A grande dificuldade destes projetos é conciliar os requisitos cinemáticos com a resistência mecânica da estrutura. Neste trabalho, é implementado um critério de resistência dentro da formulação do problema de otimização, com o intuito de gerar mecanismos que cumpram a tarefa cinemática desejada mas ao mesmo tempo não ultrapassem limites de tensão predeterminados. Esta restrição adicional também visa aliviar o problema bastante conhecido do aparecimento de articulações. Não linearidade geométrica e de material (hiperelasticida de compressível) são implementadas na solução das equações através do método dos elementos finitos para levar em conta os grandes deslocamentos do mecanismo. O método das assíntotas móveis é usado para a atualização das variáveis de projeto. As derivadas do problema de otimização são calculadas analiticamente, pelo método adjunto. Técnicas de projeção são aplicadas para a garantia de topologias livres de instabilidades numéricas comuns em otimização topológica, e projetos otimizados mais próximos de um espaço 0/1 para as densidades físicas. / Compliant me hanisms, in whi h the elasti strain is the basis for kinemati a tua- tion are widely used in pre ision me hani s devi es, biomedi al engineering, and re ently in mi roele trome hani al systems (MEMS). Among several te hniques applied in ompliant me hanisms design, topology optimization has been one of the most general and systemati . The great hallenge in these designs is to ouple both the kinemati s and the me hani al strength riteria requirements. In this work, a strength riteria for the optimization problem is applied, with the aim of generating ompliant me hanisms that ful ll the desired kine- mati tasks while omplying with a stress threshold. The addition of a stress onstraint to the formulation for ompliant me hanisms in topology optimization also aims to allevi- ate the appearan e of hinges in the optimized topology, a well known issue in the design of ompliant me hanisms. Geometri al and material ( ompressible hyperelasti ity) nonlin- earities are applied to the nite element equilibrium equations, to take into a ount large displa ements. The method of moving asymptotes is applied for design variables updating. The derivatives are al ulated analyti ally, by the adjoint method. Proje tion ltering te h- niques are applied, in order to guarantee topologies free of ommon numeri al instabilities in topology optimization, and optimized designs near the 0/1 solution for the physi al densities.

Mecanismos flexíveis, nos quais a deformação elástica é aproveitada na atuação cinemática, têm grande empregabilidade em dispositivos de mecânica de precisão, engenharia biomédica, e mais recentemente em microeletromecanismos (MEMS). Entre as diversas técnicas empregadas para o seu projeto, a otimização topológica tem se mostrado a mais genérica e sistemática. A grande dificuldade destes projetos é conciliar os requisitos cinemáticos com a resistência mecânica da estrutura. Neste trabalho, é implementado um critério de resistência dentro da formulação do problema de otimização, com o intuito de gerar mecanismos que cumpram a tarefa cinemática desejada mas ao mesmo tempo não ultrapassem limites de tensão predeterminados. Esta restrição adicional também visa aliviar o problema bastante conhecido do aparecimento de articulações. Não linearidade geométrica e de material (hiperelasticida de compressível) são implementadas na solução das equações através do método dos elementos finitos para levar em conta os grandes deslocamentos do mecanismo. O método das assíntotas móveis é usado para a atualização das variáveis de projeto. As derivadas do problema de otimização são calculadas analiticamente, pelo método adjunto. Técnicas de projeção são aplicadas para a garantia de topologias livres de instabilidades numéricas comuns em otimização topológica, e projetos otimizados mais próximos de um espaço 0/1 para as densidades físicas. / Compliant me hanisms, in whi h the elasti strain is the basis for kinemati a tua- tion are widely used in pre ision me hani s devi es, biomedi al engineering, and re ently in mi roele trome hani al systems (MEMS). Among several te hniques applied in ompliant me hanisms design, topology optimization has been one of the most general and systemati . The great hallenge in these designs is to ouple both the kinemati s and the me hani al strength riteria requirements. In this work, a strength riteria for the optimization problem is applied, with the aim of generating ompliant me hanisms that ful ll the desired kine- mati tasks while omplying with a stress threshold. The addition of a stress onstraint to the formulation for ompliant me hanisms in topology optimization also aims to allevi- ate the appearan e of hinges in the optimized topology, a well known issue in the design of ompliant me hanisms. Geometri al and material ( ompressible hyperelasti ity) nonlin- earities are applied to the nite element equilibrium equations, to take into a ount large displa ements. The method of moving asymptotes is applied for design variables updating. The derivatives are al ulated analyti ally, by the adjoint method. Proje tion ltering te h- niques are applied, in order to guarantee topologies free of ommon numeri al instabilities in topology optimization, and optimized designs near the 0/1 solution for the physi al densities.

My work has been focused on compliant mechanisms, origami engineering, and rapid prototyping. Two of the projects that I worked on were focused on compliant mechanisms and origami engineering. The similar goal of both of those projects was to create an origami membrane whose kinematics mimic that of an existing mechanism. The first project created an origami membrane to mimic the kinematics of a planar shape-changing mechanism. This mechanism was a square shaped unit-cell which could shear, compress, and expand in its own plane. In addition to waterproofing the mechanism, the first project also sought to optimize the dimensions of the mechanism in order to reduce internal stresses during actuation. The results of the optimization portion of this project were a reduction of internal stresses by more than 22%. The results of the origami synthesis portion of the project was the creation of a membrane with an origami pattern whose kinematics mimic that of the shape-shifting surface. The origami membrane is capable of being folded into each of the various positions that the shape-shifting surface is able to fold into. The second project sought to create a similar type of origami fold pattern, but for a Shape Morphing Space Frame (SMSF). This project created an origami membrane designed to mimic the kinematics of a mechanism that had been developed in a different previous project. The mechanism consisted of a series of Linear Bistable Elements (LBEs) which were assembled to form a cylinder. When the LBEs were actuated the cylinder would deform to a hyperboloid. This project created an origami membrane whose kinematics mimic that of the shape-morphing space frame and was able to change side length by more than 30%. The origami membrane was able to fold to each of the SMSF’s states. This project also developed a method for synthesizing an origami fold pattern with shape-morphing triangles. Both of the first two projects that comprise this dissertation sought to develop an origami fold pattern whose kinematics mimic that of an existing mechanism. In each of these projects one of the future goals for the project was to create a prototype where the mechanism and the origami are fabricated together as one integrated prototype. Possible methods of accomplishing this goal include rapid prototyping. Thus, the mechanics of rapid prototyping are of concern for future work on these projects. The third project developed a part which could be printed from a Fused Deposition Modeling (FDM) machine to test certain material properties (yield strength and elastic modulus) after it had been processed through the FDM. This would allow the material properties to be tested without the use of expensive test equipment. This project developed eight parts which could be used to bracket certain material properties of rapid prototyped parts after processing. The parts developed in this project were capable of bracketing the material properties of the materials in question, and were able to do so when tested across multiple FDM machines. The results of this work were stress-strain data which indicates the behavior of the part under load, and a method for inexpensively testing the material properties of rapid prototyped parts after processing.

A compliant force/torque sensor for robot force control has been developed. This thesis presents methods of designing, testing, and implementing the sensor on a robotic system. The sensor uses an orthoplanar spring equipped with Hall-effect sensors to measure one component of force and two moment components. Its unique design allows for simple and cost effective manufacturing, high reliability, and compactness. The device may be used in applications where a robot must control contact forces with its environment, such as in surface cleaning tasks, manipulating doors, and removing threaded fasteners. The compliant design of the sensor improves force control performance and reduces impact forces. Sensor design considerations are discussed, followed by a discussion of the proposed design concept. Theoretical compliance and stress analysis of the orthoplanar spring is presented that allows for rapid design calculations; these calculations are validated via finite element analysis. A mechanical design method is given which uses the results of the compliance and stress analysis. Transducer design is then addressed by developing a model of the sensor. The design methods are used to design a prototype sensor which is tested to determine its instrument uncertainty. Finally, the sensor is implemented on a robotic platform to test its performance in force control.

Flexible electronics have demonstrated potential in a wide range of applications including wearable sensors, photovoltaics, medical devices and more, due to their properties of extreme adaptability while also being lightweight and highly robust. The main challenge standing in the way of progress in this field is the difficulty of large-scale manufacturing of these flexible electronics compared to their rigid counterparts. Microcontact printing is a form of soft lithography in which an elastomeric stamp is used to transfer sub-micron scale surface patterns onto a flexible substrate via ink monolayers. The integration of microcontact printing into a roll-to-roll (R2R) system will enable continuous printing of flexible electronics and scale it up for massive manufacturing. The proposed thesis outlines a novel mechanical design for a microcontact printer which utilizes flexural motion stages with integrated position and force sensors to control the print process on a R2R system. The printhead is designed to fit the available space on the pre-installed UMass Amherst Intelligent Sensing Laboratory test table and breadboard. The R2R system includes motorized rollers for winding/unwinding the PET (polyethylene terephthalate) web substrate, and idler rollers for guiding a web through the print system. As the central element to this design, two matching plate flexures are designed on the two ends of the printer roller to control the tilting and positioning of the print roller. Flexure mechanisms rely on bending and torsion of flexible elements: this allows them to achieve much higher precision in positioning compared to conventional mechanisms which rely on surface interaction between multiple moving parts. The print resolution target for this design is 500 nm (linewidth), based on current state-of-the-art designs [1, 2]. In the initial version of the printhead design, a total of 33 parts are custom fabricated for assembly and installation in the R2R system lab setup. These include everything from the components of the print roller, specially adapted air-bearing mounts, support structures, and connectors. The design and 4 fabrication process for every component is outlined here along with the functionality, as every component was designed with the system objectives and constraints in mind. Using SolidWorks simulation, FEA (finite element analysis) is performed for every part of the assembly that is subjected to stress in the real system, so that predictions can be made about the displacement of the motion stages and the frequency of vibration. These predictions are evaluated by comparation with the experimental results from tests conducted on the real system hardware and used to assess the quality of the fabricated assembly. The work performed in this thesis enables advancements in the assembly of an updated, optimized R2R system and has led to an experimentally functioning lab setup that is ripe for further improvements. Completion and calibration of this augmented R2R system will, in future, enable UMass Amherst in-house production of large-area flexible electronics which may be used in a wide range of applications, including medical sensors, solar cells, displays, and more. In addition to microcontact printing, this R2R system may also be applied to nanoimprint lithography, another contact-based print method, or integrated with inkjet printing, a non-contact method.

The purpose of this thesis is to prove that the use of compliant mechanisms in gearbox applications is viable. Compliant mechanisms are developed for their implementation in Scania’s hybrid asynchronous gearboxes. These mechanisms are presented as a replacement for the latch assembly currently in use to hold the position of the gear-shifting elements. The objective is to implement a compliant mechanism in order to avoid wear and increase the life cycle within the given constraints, as well as to have a better understanding of this kind of mechanisms. The presented literature study shows that bistable and tristable compliant mechanisms are the most suitable ones for this application. Titanium alloys, tool steels, and bulk metallic glasses are discussed as the best material options for compliant mechanism manufacturing. A mechanism idea generation and selection process is conducted. Finite Element Analysis (FEA) is developed with the chosen bistable and tristable compliant mechanism ideas. The tristable concept results on being inappropriate for this application, as it does not fulfil the volume and positioning constraints. The bistable device is proven to be suitable, and further analysis is carried out to study its fatigue resistance and show that it fulfils all the requirements, solving the weaknesses of the latch and absorbing the impact in the shaft. Additive manufacturing methods and injection moulding are found to be incompatible with the designed mechanisms. That is why the chosen bistable mechanism is designed to be made out of different parts. Future work is presented to strengthen the weaker points of this project.

Origami has been extensively studied by engineers for its unique motions and ability to collapse to small volumes. Techniques have been studied for replicating origami-like folding motion in thick materials, but limited practical applications of these techniques have been demonstrated. Developable mechanisms are a new mechanism type that has a similar ability to collapse to a low profile. The cylindrical developable mechanism has the ability to emerge from and conform to a cylindrical surface. In this work, a few practical applications of devices with novel expanding motions are presented. The design and testing of an origami-inspired deployable ballistic barrier, which was designed by combining and modifying existing thickness accommodation techniques, is discussed. The properties of cylindrical developable mechanisms are examined and two devices designed for use with minimally invasive surgical tooling are presented. Various hinge options for small-scale cylindrical developable mechanisms are then reviewed and discussed. A planar modeling assumption for curved lamina emergent torsional joints in thin-walled cylinders is then analytically and empirically validated. Conclusions are drawn and recommendations for future work are given.

This work develops models and tools to help designers address the challenges associated with designing origami-based and developable mechanisms. These models utilize strain energy, kinematics, compliant mechanisms, and graphical techniques to make the design of origami-based and developable mechanisms approachable and intuitive. Origami-based design tools are expanded through two methods. First presented is a generalized approach for identifying single-output mechanical advantage for a multiple-input compliant mechanism, such as many origami-based mechanisms. The model is used to predict the force-deflection behavior of an origami-based mechanism (Oriceps) and is verified with experimental data from magnetic actuation of the mechanism. Second is a folding technique for thick-origami, called the regional-sandwiching of compliant sheets (ReCS), which creates flat-foldable, rigid-foldable, and self-deploying thick origami-based mechanisms. The technique is used to create mountain/valley assignments for each fold about a vertex, constraining motion to a single branch of folding. Strain energy in deflected flexible members is used to enable self-deployment. Three physical models, a simple single-fold mechanism, a degree-four vertex mechanism, and a full tessellation, are presented to demonstrate the ReCS technique. Developable mechanism design is further enabled through an exploration of their feasible design space. Terminology is introduced to define the motion of developable mechanisms while interior and exterior to a developable surface. The limits of this motion are identified using defined conditions. It is shown that the more difficult of these conditions may be treated as a non-factor during the design of cylindrical developable mechanisms given certain assumptions. These limits are then applied to create a resource for designing bistable developable mechanisms (BDMs) that reach their second stable positions while exterior or interior to a cylindrical surface. A novel graphical method for identifying stable positions of linkages using a single dominant torsional spring, called the Principle of Reflection, is introduced and implemented. The results are compared with a numerical simulation of 30,000+ mechanisms to identify possible incongruencies. Two tables summarize the results as the guide for designing extramobile and intramobile BDMs. In fulfilling the research objectives, this dissertation contributes to the scientific community of origami-based and developable mechanism design approaches. As a result of this work, practitioners will be better able to approach and design complex origami-based and developable mechanisms.