Dissertationen zum Thema „Freeformer“

Les procédés de fabrication additive (FA) permettent de répondre, aujourd’hui, à des problématiques industrielles majeures. Ces technologies offrent la possibilité de réaliser, pour un temps et un coup raisonnables, des pièces avec des géométriques complexes difficiles, voire impossibles, à réaliser avec des procédés traditionnaux. Parmi les différents procédés de FA, le procédé APF (Arburg Plastic Freeforming) permet la fabrication de pièces 3D à partir de granulés de polymères identiques à ceux employés en injection. Ces granulés peu onéreux constituent une matière première de choix puisque, théoriquement, n’importe quel thermoplastique peut être utilisé. La technologie Freeformer s’appuie sur deux unités d’injection qui permettent de fondre et de plastifier les granulés de polymère et ainsi d’alimenter la tête d’impression. L'unité de décharge dotée d’un système piézo-électrique d’ouverture/fermeture génère, en tête de buse, des gouttelettes de polymère fondu (jusqu'à 200 μm) déposées sur une plaque de fabrication spécifique au matériau employé. Ces gouttes sont déposées selon un fichier CAO défini en amont afin de constituer des pièces 3D, couche par couche, dans une chambre thermorégulée. Même si la réalisation de pièces à partir de matériaux standards (ABS, TPU, …) est relativement simple, il est nécessaire d’optimiser les paramètres de fabrication de l’APF pour obtenir des pièces de bonne qualité avec d’autres matériaux. De la même manière que dans le cas d’un procédé de transformation de matière polymère classique, le choix de grades appropriés et l’optimisation des paramètres de fabrication associés est nécessaire. Ainsi, les différents phénomènes physico-chimiques impliqués dans la réalisation d’une pièce doivent être étudiés pour la réalisation de pièces avec un polymère peu employé en FA : le polypropylène. Une approche classique d’optimisation des paramètres de fabrication consisterait en la réalisation d’une étude paramétrique faisant intervenir, par exemple, un plan d’expérience. Cette méthode chronophage et demandeuse en matière ne permet pas la compréhension fine du procédé et n’est finalement applicable qu’à un polymère donné. L’objectif de ces travaux, cofinancés par la région Hauts de France, est donc de comprendre les corrélations existantes entre les paramètres du procédé et les propriétés du polymère pour comprendre comment le procédé influence la matière
Additive Manufacturing (AM) concerns are growing the last years due to the capabilities brought by the technology. Indeed, the AM processes offer the possibility to simply and rapidly create 3D parts with specific geometries, difficult or impossible to obtain with conventional processes. A new technology called Freeformer supplied by ARBURG (Germany) allows to manufacture high quality 3D parts using standard-commercial pellets. Contrary to the standard FDM processes, feedstock materials are cheap and any thermoplastic polymer can be theoretically employed. The Freeformer technology is based on two injection molding units that enables to melt the standard pellets and to feed the printing head. The discharge unit featuring a pulsed nozzle closure generates small (down to 200 μm) molten polymer droplets to build, layer-by-layer, three-dimensional parts in a thermoregulated chamber. Even if 3D parts are easily fabricated by using standard materials (ABS, TPU, …), the process parameters have to be optimized before getting good-quality parts with all other polymers, which consumes times and materials. In the same way than for a conventional polymer processing technology the choice of appropriate grades and the optimization of the associated processing parameters are needed. Hence, the different phenomenon which occur during a part realisation have to be examined in the case of a non-standard material in AM: polypropylene (PP). To optimize the structure and the mechanical properties of the parts, a common approach is to practice a parametric study. This time-consuming approach is not always efficient. Thus, the aim of this work, cofounded by the Région Hauts de France, is to understand the correlations between materials properties and process parameters

Notwithstanding several years of robust growth, solar energy still only accounts for<1% of total electrical generation in the US. Before solar energy can substantially replace fossil fuels subsidy-free at utility scale, further cost reductions and efficiency improvements are needed in complete generating systems. Flat panel silicon PV modules are by far the most dominant solar technology today, but have little room for improvement in efficiency and are limited by balance of system costs. Concentrated PV (CPV) is an alternate approach with long-term potential for much higher efficiency in sunny climates. In CPV modules, large area optics collect and concentrate direct sunlight onto small multi-junction cells with>40% conversion efficiency. Concentrated Solar Power (CSP) uses mirrors to concentrate sunlight onto thermally absorbing receivers, which generate electricity with convention thermal cycles. In this dissertation, four new optical approaches to CPV and CSP with potential for lower cost are analyzed. Common to each approach is the use of large square glass reflectors, which have very low areal cost (~$35/m^2) and field-proven reliability in the CSP industry. Chapter 2 describes a freeform toroidal lens array used to intercept the low concentration line focus of a parabolic trough to produce multiple high concentration foci (>800X) for multi-junction cells. In Chapter 3, three embodiments of dish mirrors and freeform lenslet arrays are explored, including an off-axis system. In each case, a dish mirror illuminates a freeform lenslet array, which divides sunlight equally to a sparse matrix of multi-junction cells. The off-axis optical system achieves +/-0.45° acceptance angle and averages 1215X geometric concentration over 400 multi-junction cells. Chapter 4 proposes a new architecture for CSP central receivers that achieves extremely high collection efficiency (>70%) with unconventional heliostat field tracking. In Chapter 5, the design and preliminary testing of a spectrum-splitting hybrid PV/thermal generator is discussed. This system has the advantage of 'drop-in' capability in existing CSP trough plants and allows for thermal storage, an important mitigation to the intermittency of the solar resource.

This thesis provides a review of the state-of-the-art in vision systems and methodologies and an introduction of important surface attributes and representations. Then three novel methods for the dynamic inspection of specular freeform surfaces are presented. These comprise two novel machine vision systems as well as a novel high-speed, multi-scale line tracing algorithm. Both of the novel systems employ a reciprocal deflectometric arrangement. The reflection of a laser line from a surface is monitored on a translucent screen. Here, a complex curve, known as the 'specular signature', is formed that contains all the information on the surface. Methods for extracting and interpreting this information are presented and incorporated into the two vision systems. Prototype demonstrators were designed and assembled to verify the presented methodologies. Extensive experimental validations of all three contributions are shown and the results are compared to ground truth data. Statistical validations of the systems are also presented. Also, the optical and angular resolutions as well as the limitations and the allowable ranges of surface characteristics for both systems, were calculated and presented. It is shown that they are applicable to a range of surface geometries and roughnesses that is comparable to those of existing techniques. The first of the two novel systems is designed for the robust and qualitative detection, classification and localisation of surface defects. It was validated using various real defects on specular freeform surfaces. It is shown that any discontinuity on a surface will be detected and can be classified as long as one criterion regarding the smallest radius of concave curvature on the surface is fulfilled. It is known that this criterion will be fulfilled for a very wide range of common surfaces. The second proposed vision system serves the purpose of a complete, quantitative reconstruction and digitalisation of moving, specular freeform surfaces. While the first system only requires the information from the specular signature, the second system also uses traditional and highly inaccurate surface height data, gathered through laser triangulation. These two data sets, computed from the diffuse as well as the specular reflection, are fused together to generate highly accurate surface bump (gradient) maps. Through the reverse engineering of several real specular specimens and the comparison to ground truth, it is shown that the standard deviation of the error of the height map reaches micrometer levels while that of the angular accuracy reaches levels below one degree. As a third original contribution to knowledge, a novel, high speed, multi-scale line extraction algorithm was developed. Intended for the rapid extraction of the specular signature from the screen images, it combines the processing speed of crude edge detectors with the versatility and accuracy of complex differential geometrical line extractors. It is also multi- scale, with best match scale space being chosen fully automatically. By combining the formerly separated steps of line point detection and line point linkage, the new algorithm is able to increase the processing speed of existing line extractors by up to 50 times. The time requirement is of the same order of magnitude as for crude edge detection algorithms such as Canny. The novel algorithm can also be implemented without the need for any global thresholds as it defines itself a variable local threshold, thereby increasing the sensitivity drastically.

Reflector design stemmed from the need to shape the light emitted by candles or lamps. Over 2,000 years ago people realized that a mirror shaped as a parabola can concentrate light, and thus significantly boosts its intensity, to the point where objects can be set afire. Nowadays many applications require an accurate control of light, such as automotive headlights, streetlights, projection displays, and medical illuminators. In all cases light emitted from a light source can be shaped into a desired target distribution with a reflective surface. Design methods for systems with rotational and translational symmetry were devised in the 1930s. However, the freeform reflector shapes required to illuminate targets with no such symmetries proved to be much more challenging to design. Even when the source is assumed to be a point, the reflector shape is governed by a set of second-order partial non-linear differential equations that cannot be solved with standard numerical integration techniques. An iterative approach to solve the problem for a discrete target, known as the method of supporting ellipsoids, was recently proposed by Oliker. In this research we report several efficient implementations of the method of supporting ellipsoids, based on the point source approximation, and we propose new reflector design techniques that take into account the extent of the source. More specifically, this work has led to three major achievements. First, a thorough analysis of the method of supporting ellipsoids was performed that resulted in two alternative implementations of the algorithm, which enable a fast generation of freeform reflector shapes within the point source approximation. We tailored the algorithm in order to provide control over the parameters of interest to the designers, such as the reflector scale and geometry. Second, the shape generation algorithm was used to analyze how source flux can be mapped onto the target. We derived the condition under which a given source-target mapping can be achieved with a smooth continuous surface, referred as the integrability condition. We proposed a method to derive mappings that satisfy the integrability condition. We then use these mappings to quickly generate reflector shapes that create continuous target distributions as opposed to reflectors generated with the method of supporting ellipsoids that create discrete sets of points on the target. We also show how mappings that do not satisfy the integrability condition can be achieved by introducing step discontinuities in the reflector surface. Third, we investigated two methods to design reflectors with extended sources. The first method uses a compensation approach where the prescribed target distribution is adjusted iteratively. This method is effective for compact sources and systems with rotational or translational symmetry. The second method tiles the source images created by a reflector designed with the method of supporting ellipsoids and then blends the source images together using scattering in order to obtain a continuous target distribution. This latter method is effective for freeform reflectors and target distributions with no sharp variations. Finally, several case studies illustrate how these methods can be successfully applied to design reflectors for general illumination applications such as street lighting or luminaires. We show that the proposed design methods can ease the design of freeform reflectors and provide efficient, cost-effective solutions that avoid unnecessary energy consumption and light pollution.
Ph.D.
Optics and Photonics
Optics and Photonics
Optics PhD

Personal computing is continuously moving away from traditional input using mouse and keyboard, as new input technologies emerge. Recently, natural user interfaces (NUI) have led to interactive systems that are inspired by our physical interactions in the real-world, and focus on enabling dexterous freehand input in 2D or 3D. Another recent trend is Augmented Reality (AR), which follows a similar goal to further reduce the gap between the real and the virtual, but predominately focuses on output, by overlaying virtual information onto a tracked real-world 3D scene. Whilst AR and NUI technologies have been developed for both immersive 3D output as well as seamless 3D input, these have mostly been looked at separately. NUI focuses on sensing the user and enabling new forms of input; AR traditionally focuses on capturing the environment around us and enabling new forms of output that are registered to the real world. The output of NUI systems is mainly presented on a 2D display, while the input technologies for AR experiences, such as data gloves and body-worn motion trackers are often uncomfortable and restricting when interacting in the real world. NUI and AR can be seen as very complimentary, and bringing these two fields together can lead to new user experiences that radically change the way we interact with our everyday environments. The aim of this thesis is to enable real-time, low latency, dexterous input and immersive output without heavily instrumenting the user. The main challenge is to retain and to meaningfully combine the positive qualities that are attributed to both NUI and AR systems. I review work in the intersecting research fields of AR and NUI, and explore freehand 3D interactions with varying degrees of expressiveness, directness and mobility in various physical settings. There a number of technical challenges that arise when designing a mixed NUI/AR system, which I will address is this work: What can we capture, and how? How do we represent the real in the virtual? And how do we physically couple input and output? This is achieved by designing new systems, algorithms, and user experiences that explore the combination of AR and NUI.

Over the past two decades, a major part of the manufacturing and assembly market has been driven by its customer requirements. Increasing customer demand for personalised products create the demand for smaller batch sizes, shorter production times, lower costs, and the flexibility to produce families of products - or different parts - with the same sets of equipment. Consequently, manufacturing companies have deployed various automation systems and production strategies to improve their resource efficiency and move towards right-first-time production. However, many of these automated systems, which are involved with robot-based, repeatable assembly automation, require component- specific fixtures for accurate positioning and extensive robot programming, to achieve flexibility in their production. Threaded fastening operations are widely used in assembly. In high-volume production, the fastening processes are commonly automated using jigs, fixtures, and semi-automated tools. This form of automation delivers reliable assembly results at the expense of flexibility and requires component variability to be adequately controlled. On the other hand, in low- volume, high- value manufacturing, fastening processes are typically carried out manually by skilled workers. This research is aimed at addressing the aforementioned issues by developing a freeform automated threaded fastener assembly system that uses 3D visual guidance. The proof-of-concept system developed focuses on picking up fasteners from clutter, identifying a hole feature in an imprecisely positioned target component and carry out torque-controlled fastening. This approach has achieved flexibility and adaptability without the use of dedicated fixtures and robot programming. This research also investigates and evaluates different 3D imaging technology to identify the suitable technology required for fastener assembly in a non-structured industrial environment. The proposed solution utilises the commercially available technologies to enhance the precision and speed of identification of components for assembly processes, thereby improving and validating the possibility of reliably implementing this solution for industrial applications. As a part of this research, a number of novel algorithms are developed to robustly identify assembly components located in a random environment by enhancing the existing methods and technologies within the domain of the fastening processes. A bolt identification algorithm was developed to identify bolts located in a random clutter by enhancing the existing surface-based matching algorithm. A novel hole feature identification algorithm was developed to detect threaded holes and identify its size and location in 3D. The developed bolt and feature identification algorithms are robust and has sub-millimetre accuracy required to perform successful fastener assembly in industrial conditions. In addition, the processing time required for these identification algorithms - to identify and localise bolts and hole features - is less than a second, thereby increasing the speed of fastener assembly.

The Functional Freeform Fitting (F4) method is utilized to design a freeform optic for oblique illumination of Mark Rothko's Green on Blue (1956). Shown are preliminary results from an iterative freeform design process; from problem definition and specification development to surface fit, ray tracing results, and optimization. This method is applicable to both point and extended sources of various geometries.

Computer-controlled additive manufacturing (AM) processes, also known as three-dimensional (3D) printing, create 3D objects by the successive adding of a material or materials. While there have been tremendous developments in AM, the 3D printing of optics is lagging due to the limits in materials and tight requirements for optical applicaitons. We propose a new precision additive freeform optics manufacturing (AFOM) method using an pulsed infrared (IR) laser. Compared to ultraviolet (UV) curable materials, thermally curable optical silicones have a number of advantages, such as strong UV stability, non-yellowing, and high transmission, making it particularly suitable for optical applications. Pulsed IR laser radiation offers a distinct advantage in processing optical silicones, as the high peak intensity achieved in the focal region allows for curing the material quickly, while the brief duration of the lasermaterial interaction creates a negligible heat-affected zone.

This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Thesis: M. Eng., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2019
Cataloged from student-submitted PDF version of thesis. "June 2019."
Includes bibliographical references (pages 53-55).
CurveBoards are 3D breadboards integrated into the surface of physical prototypes. CurveBoards offer both the flexibility of breadboards, i.e., the ability to add or remove components, while also integrating well with the shape of the prototype. Thus, designers can use CurveBoards to test function directly in context of the actual physical form. We demonstrate our method for fabricating the CurveBoard in which designers only have to 3D print the housing and then fill the wire channels with conductive silicone. We also discuss limitations to this approach and alternative fabrication methods. We display a range of different application scenarios and report on a user study with six participants that showed that prototypes created as CurveBoards looked and felt closer to the final design.
by LottaGili Blumberg.
M. Eng.
M.Eng. Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science

We present a miniature camera lens design method that uses a freeform surface based on the pedal curve to the ellipse in polynomial form. Two designs are presented and their benefits of optical performance and tolerance sensitivity are compared to designs with conventional aspheric surfaces. We also reverse a freeform design using even aspherical surfaces to show that the optimization solution of a freeform design cannot be reproduced by even aspherical surfaces.

Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 79-88).
Additive manufacturing by photopolymerization (e.g., stereolithography) is attractive due to its high resolution and its compatibility with soft and hard polymers, composites, and biomaterials. While traditional stereolithography machines are designed to build on planar substrates, patterning of non-planar surfaces would enable integration of new functionality onto existing objects for applications such as structurally integrated sensors, conformal electronics, and customized medical implants. This thesis presents the design, construction, and initial performance evaluation of a robotic system capable of maskless photopatterning on objects having complex curvature and dimensions ranging from centimeters to meters. The system incorporates a six-axis serial robot arm, a high-precision rotary stage, a custom-built DLPbased end effector, and custom software that coordinates and controls the system. The workpiece is patterned by first digitally triangulating the surface with a 3D scanner and associating the location of each triangle in the digital space with the corresponding location on the workpiece surface in real space. Subsequently, the area enclosed by each triangle is associated with a user-specified texture photomask. The large-area photopattern is then fabricated by sequentially exposing each individual textured triangle in the photomask as the robot steps to each corresponding location on the workpiece surface, which is coated with a photocurable polymer. By measuring patterning results on a test object, the system was determined to have a positioning accuracy over a subsection of the working volume of 330tm and a repeatability of 20pm was measured by a motion test. The system positioning accuracy is limited by performance of the actuators and the kinematics of the manipulator. System patterning rate is limited by the power output of the light source. The system's performance is demonstrated by patterning a 21cm diameter sphere with a map of the Earth and performing a preliminary test on the patellar surface of an anatomical femur model. Future work will focus on improving the system accuracy by mapping the workspace using a coordinate measuring machine and increasing throughput by a combination of increased optical power and more efficient use of the projection field of view. The system will also be investigated as an enabling technology for deterministically patterning cartilage cells onto joint surfaces or three-dimensional anatomical models.
by Adam G. Stevens.
S.M.

Several next generation astronomical telescopes or large optical systems utilize aspheric/freeform optics for creating a segmented optical system. Multiple mirrors can be combined to form a larger optical surface or used as a single surface to avoid obscurations. In this paper, we demonstrate a specific case of the Daniel K. Inouye Solar Telescope (DKIST). This optic is a 4.2 m in diameter off-axis primary mirror using ZERODUR thin substrate, and has been successfully completed in the Optical Engineering and Fabrication Facility (OEFF) at the University of Arizona, in 2016. As the telescope looks at the brightest object in the sky, our own Sun, the primary mirror surface quality meets extreme specifications covering a wide range of spatial frequency errors. In manufacturing the DKIST mirror, metrology systems have been studied, developed and applied to measure low-to-mid-to-high spatial frequency surface shape information in the 4.2 m super-polished optical surface. In this paper, measurements from these systems are converted to Power Spectral Density (PSD) plots and combined in the spatial frequency domain. Results cover 5 orders of magnitude in spatial frequencies and meet or exceed specifications for this large aspheric mirror. Precision manufacturing of the super-polished DKIST mirror enables a new level of solar science.

Metal layers within a laminar ceramic can improve damage tolerance of ceramics by arresting large cracks either by ductile bridging or by crack deflection at the ceramic/metal interface, which will allow engineers to design reliable ceramics for structural applications. At low volume fractions of the metal ductile bridging is not very effective, mainly owing to decreased distance between the crack tip and next ceramic layer. Significant increase in the energy absorption during fracture can come from delamination, but depends on the interfacial fracture resistance. A two-fold increase in energy absorption is realized in the case of glass-ceramic/silver laminates prepared by extrusion freeform fabrication. Interfacial fracture energy for glass-ceramic/silver is found to be 100 J/m² in comparison to 15 J/m² for glass-ceramic/SiC, which should explain the sporadic crack deflection in notched four-point bend. For a short beam flexural test shear failure is more favorable in four-point than in three-point bending. In four-point tests, the shear stresses between the outer and inner loading pins can precipitate shear delamination prior to tensile cracking of the layers. Damage modes under low velocity impact tests are similar to four-point bend showing delamination as primary energy dissipation mechanism.

Composites are known for their unique blend of modulus, strength, and toughness. This study focuses on two types of composites; organic-inorganic hybrids and the mineralization of highly swollen polymer gels. Both of these composite systems mimic the biological process of composite formation, known as biomineralization. Biomineralization allows for the control of the precipitating phase through an interaction with the organic matrix. This allows higher volume fractions of inorganic material than can be achieved by many traditional processing techniques. Solid freeform fabrication is a processing method that builds materials by the sequential addition of thin layers. As long as the material can easily be converted from a liquid to a solid, it should be amenable for this processing technique. Freeform fabrication has three distinctions from traditional processing techniques that may enable the formation of composite materials with improved mechanical properties. These are the sequential addition of layers, which allows a layer by layer influence of chemistry, the ability to form complex geometries, and finally, extrusion freeform fabrication has been shown to align fibers due to the extrusion of the slurry through a needle. Cracking and shrinkage still play a major role in forming solid parts. The use of an open mesh structure in combination with proper materials selection allowed the formation of highly loaded composite materials without cracking. The modulus values of these materials ranged from 0.1 GPa to 6.0 GPa. The mechanical properties of these materials were modeled.

Modern industries operate under high cost pressure coupled with ever increasing demands on their processes and products. Production processes are e.g. increasingly complex while the permitted tolerances, batch sizes and time-to-market times decrease. These partly contradictory trends require sophisticated production processes with advanced strategies for quality assurance and process control. The aim of this work is to analyse such a complex, multi-stage production process, the production of turbine blades, in terms of quality, process adjustment for small batch sizes and cost. In the considered process, turbine blades are manufactured by forging and are cooled down in calm air to ambient temperature for subsequent machining. This significantly impedes quality control during the process due to the prevailing elevated temperature of workpieces and the consequential need for several hours of cooling before measurements can be performed. Due to small batch sizes, forging of one batch is completed within hours, possibly before quality control at the first produced workpiece takes place. This results in late verification of tolerances when all workpieces are already produced and potentially violate their tolerance limits. After forging, the focus is on verification of dimensional forging tolerances. These asymmetric tolerances allow only for additional material that is to be subsequently removed by machining. Equivalent asymmetry is encountered in the incurred cost, positive deviations increase machining cost while negative deviations cause high cost due to classification as defective. Analysis of the production process indicated substantial process optimisation opportunities by quality control during the process. However, not only measurements at elevated workpiece temperature have to be performed, also the cooling influence on the workpiece must be predicted to make early conformance statements. This is especially crucial for the thin freeform aerofoil of turbine blades that is subject to complex geometrical distortions during cooling. Additionally, if the process parameters shall be adjusted according to measurement results, appropriate methods to account for asymmetric tolerances and cost are necessary. Adjusting process parameters during the ramp-up of a batch is necessary to setup the process for the specific product. Such adjustments slow down the production, can be costly and may require a considerable period of the production time, especially for small batches. Therefore, a method shall be developed to determine when to stop initial adjustments. In this work, a multisensor light sectioning coordinate measuring system for dimensional measurements at elevated temperature is presented and discussed. For visualisation and measurand evaluation, an existing heuristic surface reconstruction method is adapted for enhanced surface quality on partly concave freeform workpieces as turbine blades. Its low time complexity enables realtime visualisation during measuring, allowing operators to monitor and qualitatively verify measurement results quickly. Main uncertainty contributors on the system are identified, quantified and, where necessary, corrected. In particular for freeform workpieces, the requirement for improved sensor adjustment is demonstrated. A novel method for sensor adjustment and multisensor registration is proposed, yielding a five times improvement in experiments compared to manual methods. By the discussed corrections, process adjustment for small batch turbine blade manufacturing becomes feasible. A method to obtain the optimal number of adjustments is available from literature for a specific combination of symmetric cost model and process variation by analytic evaluation of expected cost. A novel formulation and appropriate numerical methods are proposed to evaluate expected cost with arbitrary, possibly asymmetric, cost models and process variation models. Based on this formulation, two generalised criteria when to stop adjustments optimally are presented, each exhibiting distinct advantages for specific application cases. Their performance is compared to a state-of-the-art deadband model for process adjustment, yielding down to 90% lower cost for the evaluated cases if measurements are performed during the adjustment phase only. Eventually, a novel comprehensive framework for process adjustment, incorporating the proposed methods, is discussed.
Le moderne industrie manifatturiere si trovano ad operare in una condizione di forte stress economico, ma allo stesso tempo con richieste dal mercato sempre più complesse. Ad esempio, se da un lato i processi produttivi aumentano la proprio complessità, dall’altro, le tolleranze richieste, le dimensioni dei lotti e il “time-to-market” si riducono sempre più. Questo andamento, per certi versi contradditorio, richiede l’adozione di processi produttivi sempre più sofisticati e tecniche avanzate per il controllo della qualità e del processo. L’obbiettivo di questo lavoro è di analizzare, in un processo produttivo complesso come quello delle palette per turbina, il controllo qualità e l’ottimizzazione di processo per lotti ridotti col fine di abbassare i costi legati alla produzione. Nel processo in analisi, le palette per turbina vengono forgiate a caldo e poi raffreddate in aria calma fino al raggiungimento della temperatura ambiente in modo da poter essere successivamente lavorate tramite macchine a controllo numerico. Le attuali tecnologie di misura rendono possibile il primo controllo dimensionale solo a valle del completo raffreddamento, che può richiedere fino a diverse ore. Date le dimensioni dei lotti tipicamente ridotte, spesso, la forgiatura di un intero lotto viene completata prima che sia stato possibile verificare la geometria del primo pezzo; ciò implica che potenzialmente può essere prodotto un intero lotto fuori tolleranza. Dopo la fase di forgiatura, il controllo dimensionale viene focalizzato alla ricerca dei sovrametalli, che, nel caso siano superiori al valore imposto in fase di progetto comporteranno un aumento dei costi di lavorazione a macchina, diversamente, qualora siano inferiori, porteranno a scartare il pezzo appena prodotto. A seguito di queste considerazioni si comprende l’importanza di anticipare la fase di controllo qualità, ma per fare ciò, non solo è importante essere in grado di misura ad elevate temperature occorre anche sviluppare dei modelli per la comprensione degli effetti distorsivi indotti dal raffreddamento così da prevedere la geometria finale. Ciò diventa un punto cruciale per le geometrie sottili e "freeform" che caratterizzano la foglia di una paletta per turbina. Inoltre, per ottimizzare il processo in base ai risultati delle misurazioni, è necessario comprendere le tolleranze e i costi legati all’ottimizzazione. Infatti, l’ottimizzazione dei parametri di processo durante le fasi iniziali di produzione di un lotto, essenziali per la corretta lavorazione di un componente, comportano rallentamenti e conseguenti costi. Lotti di ridotte dimensioni ne vengono maggiormente penalizzati. Di conseguenza è necessario sviluppare una procedura per determinare quando valga la pena fermare il processo di ottimizzazione. In questo lavoro, un sistema di misura basato sulla triangolazione laser per misura dimensionale di pezzi ad elevata temperatura viene presentato e discusso. Per ragioni di visualizzazione e misurazione, un algoritmo euristico, per la ricostruzione di superfici a partire da nuvole di punti, è stato adattato per superfici libere e concave come quelle che caratterizzano le palette per turbina. Data la rapidità dell’algoritmo è possibile visualizzare la geometria in contemporanea alla misura, permettendo all’operatore di monitorare qualitativamente l’andamento della misura. Le cause di incertezza principali del sistema di misura sono state identificate, quantificate e, se necessario, corrette. In particolare, nel caso di geometrie tipo "freeform", è stata dimostrata l’importanza di una miglior procedura di settaggio dei sensori. Un nuovo metodo per la taratura di sistemi multisensore è stato sviluppato ed è in grado di garantire tempi di settaggio cinque volte inferiori rispetto ai metodi manuali. Grazie alle correzioni proposte, l’ottimizzazione di processo per piccoli lotti di palette per turbina diventa possibile. Un metodo per la valutazione del numero ottimale di iterazioni durante il processo di ottimizzazione è disponibile in letteratura per una specifica combinazione di cosi asimmetrici e variabilità del processo tramite la valutazione del costo atteso ("expected cost"). Una nuova formulazione e un appropriato approccio numerico sono proposti per valutare i costi attesi con variabilità di processo e modello di costo arbitrari. A partire da queste considerazioni, due criteri generalizzati per decidere quando fermare l’ottimizzazione sono proposti, ognuno con particolari vantaggi in specifiche applicazioni. Le prestazioni di queste procedure sono comparate ad un esistente modello allo stato dell’arte, portando una riduzione dei costi pari al 90% quando le misurazioni vengono effettuate solamente durante la fase di ottimizzazione. Infine, una procedura complessiva per l’ottimizzazione di processo, incorporando i metodi proposti, verrà discussa.

Thesis (Ph.D.)--University of Missouri-Columbia, 2005.
The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (November 15, 2006) Vita. Includes bibliographical references.

Slow-servo single-point diamond turning as well as advances in computer controlled small lap polishing enable the fabrication of freeform optics, specifically, optical surfaces for imaging applications that are not rotationally symmetric. Freeform optical elements will have a profound importance in the future of optical technology. Orthogonal polynomials added onto conic sections have been extensively used to describe optical surface shapes. The optical testing industry has chosen to represent the departure of a wavefront under test from a reference sphere in terms of orthogonal ?-polynomials, specifically Zernike polynomials. Various forms of polynomials for describing freeform optical surfaces may be considered, however, both in optical design and in support of fabrication. More recently, radial basis functions were also investigated for optical shape description. In the application of orthogonal ?-polynomials to optical freeform shape description, there are important limitations, such as the number of terms required as well as edge-ringing and ill-conditioning in representing the surface with the accuracy demanded by most stringent optics applications. The first part of this dissertation focuses upon describing freeform optical surfaces with ? polynomials and shows their limitations when including higher orders together with possible remedies. We show that a possible remedy is to use edge clustered-fitting grids. Provided different grid types, we furthermore compared the efficacy of using different types of ? polynomials, namely Zernike and gradient orthogonal Q polynomials. In the second part of this thesis, a local, efficient and accurate hybrid method is developed in order to greatly reduce the order of polynomial terms required to achieve higher level of accuracy in freeform shape description that were shown to require thousands of terms including many higher order terms under prior art. This comes at the expense of multiple sub-apertures, and as such computational methods may leverage parallel processing. This new method combines the assets of both radial basis functions and orthogonal phi-polynomials for freeform shape description and is uniquely applicable across any aperture shape due to its locality and stitching principles. Finally in this thesis, in order to comprehend the possible advantages of parallel computing for optical surface descriptions, the benefits of making an effective use of impressive computational power offered by multi-core platforms for the computation of ?-polynomials are investigated. The ?-polynomials, specifically Zernike and gradient orthogonal Q-polynomials, are implemented with a set of recurrence based parallel algorithms on Graphics Processing Units (GPUs). The results show that more than an order of magnitude speedup is possible in the computation of ?-polynomials over a sequential implementation if the recurrence based parallel algorithms are adopted.
Ph.D.
Doctorate
Electrical Engineering and Computing
Engineering and Computer Science
Computer Engineering

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Architecture, February 2001.
Includes bibliographical references (p. 151-160).
Statement: If computational tools are to be employed in the aesthetic design of freeform surfaces, these tools must better reflect the ways in which creative designers conceive of and develop such shapes. In this thesis, I studied the design of aesthetically constrained freeform surfaces in architecture and industrial design, formulated a requirements list for a computational system that would aid in the creative design of such surfaces, and implemented a subset of the tools that would comprise such a system. This work documents the clay modeling process at BMW AG., Munich. The study of that process has led to a list of tools that would make freeform surface modeling possible in a computer environment. And finally, three tools from this system specification have been developed into a proof-of-concept system. Two of these tools are sweep modification tools and the third allows a user to modify a surface by sketching a shading pattern desired for the surface. The proof-of-concept tools were necessary in order to test the validity of the tools being presented and they have been used to create a number of example objects. The underlying surface representation is a variational expression which is minimized using the finite element method over an irregular triangulated mesh.
by Evan P. Smyth.
Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1997.
Includes bibliographical references (leaves 83-84).
Solid Freeform Fabrication, SFF, is a set of manufacturing processes that fabricates parts as a bonded stack of individual layers. The Three Dimensional Printing process, 3DPTM process, is an SFF technology developed at MIT. It builds layers by ink jet printing binder onto the surface of a bed of powder. The bed of powder is lowered and fresh powder is spread onto the bed. As subsequent cross sections of the part are printed, the part exists, submerged in the powder bed. Access to the individual layers as they are fabricated gives access to the interior structure of the part. This approach allows the part to have high geometric complexity. In this work a designer centric Computer Aided Design system is proposed to allow the interactive creation of functional surface texture on mechanical parts. This system is structured to behave like a VLSI CAD system, which offers substantial process capabilities. The requirements for a Mechanical CAD, MCAD, system to behave like VLSI CAD are determined to be: 1. That the informational model of the unit cell of texture be separable into distinct logical subsets.2. That manipulations on either subset not violate the logical consistency of the other subset. This thesis shows that geometric dimensions and tolerances carry the essential information of the model of a unit cell of functional texture. A variety of Unit Cell editors are evaluated according to their ability to meet the desired system criteria. A tool, Swiss Solid Geometry, SSG, for the design of unit cells of functional texture is developed, that fulfills requirement #1. SSG is an approach to MCAD modeling that combines geometric primitives in the manner of Constructive Solid Geometry, however the primitives of SSG, are different. They consist of simple objects such as lines, but includes the spatial envelope around them of a fixed offset. Also, they are used to represent both positive and negative regions of space. The placement of the individual replications is established by a mesh, that covers the intended 3D surface region. A meshing algorithm is developed that regularizes the mesh by directly utilizing the dimensional tolerances specified in the process of Unit Cell design. The geometric dimensions are instantiated as standalone geometric entities that push and pull on the nodes of the mesh in order to bring their length into dimensional tolerance. This method fulfills requirement #2, and it is implemented into a CAM software called Vari 4. The modularity of the CAM software, Vari 4, is described in detail.
by John G. Nace.
S.M.

Optical character recognition (OCR) software has advanced greatly in recent years. Machine-printed text can be scanned and converted to searchable text with word accuracy rates around 98%. Reasonably neat hand-printed text can be recognized with about 85% word accuracy. However, cursive handwriting still remains a challenge, with state-of-the-art performance still around 75%. Algorithms based on hidden Markov models have been only moderately successful, while recurrent neural networks have delivered the best results to date. This thesis explored the feasibility of using a special type of feedforward neural network to convert freeform cursive handwriting to searchable text. The hidden nodes in this network were grouped into clusters, with each cluster being trained to recognize a unique character bigram. The network was trained on writing samples that were pre-segmented and annotated. Post-processing was facilitated in part by using the network to identify overlapping bigrams that were then linked together to form words and sentences. With dictionary assisted post-processing, the network achieved word accuracy of 66.5% on a small, proprietary corpus. The contributions in this thesis are threefold: 1) the novel clustered architecture of the feed-forward neural network, 2) the development of an expanded set of observers combining image masks, modifiers, and feature characterizations, and 3) the use of overlapping bigrams as the textual working unit to assist in context analysis and reconstruction.

A novel approach to incorporate surface information into the ray mapping method is proposed. This method calculates irradiance at the physical optical surface and target plane instead of the usually flat or hemispherical dummy surface, resulting in a mapping relationship which reflects the true geometry of the system. The robustness of the method is demonstrated in an extreme example (60 degrees off axis) where the uniformity is as high as 82%. (C) 2017 Optical Society of America

Rapid prototyping (RP) is a set of fabrication technologies that are used to produce accurate parts directly from computer aided drawing (CAD) data. These technologies are unique in a way that they use an additive fabrication approach in which a three dimensional (3D) object is directly produced. In this thesis study, a RP application with a modular architecture is designed and implemented to satisfy the possible requirements of future rapid prototyping studies. After a functional classification, the developed RP software is divided into View, RP and Slice Modules. In the RP module, the process parameter selection and optimal build orientation determination steps are carried out. In the Slice Module, slicing and tool path generation steps are performed. View Module is used to visualize the inputs and outputs of the RP software. To provide 3D visualization support for View Module, a fully independent, open for development, high level 3D modeling environment and graphics library called Graphics Framework is developed. The resulting RP application is benchmarked with the RP software packages in the market according to their memory usage and process time. As a result of this benchmark, it is observed that the developed RP software has presented an equivalent performance with the other commercial RP applications and has proved its success.

Freeform curve design has existed in various forms for at least two millennia, and is important throughout computer-aided design and manufacture. With the increasing importance of animation and robotics, coupled with the increasing power of computers, there is now interest in freeform motion design, which, in part, extends techniques from curve design, as well as introducing some entirely distinct challenges. There are several approaches to freeform motion construction, and the first step in designing freeform motions is to choose a representation. Unlike for curves, there is no "standard" way of representing freeform motions, and the different tools available each have different properties. A motion can be viewed as a continuously-varying pose, where a pose is a position and an orientation. This immediately presents a problem; the dimensions of rotations and translations are different, and it is not clear how the two can be compared, such as to define distance along a motion. One solution is to treat the rotational and translational components of a motion separately, but this is inelegant and clumsy. The philosophy of this thesis is that a motion is not defined purely by rotations and translations, but that the body following a motion is a part of that motion. Specifically, the part of the body that is accounted for is its inertia tensor. The significance of the inertia tensor is that it allows the rotational and translational parts of a motion to be, in some sense, compared in a dimensionally- consistent way. Using the inertia tensor, this thesis finds the form of kinetic energy in <;1'4, and also discusses extensions of the concepts of arc length and curvature to the space of motions, allowing techniques from curve fairing to be applied to motion fairing. Two measures of motion fairness are constructed, and motion fairing is the process of minimizing the measure of a motion by adjusting degrees of freedom present in the motion's construction. This thesis uses the geometric algebra <;1'4 in the generation offreeform motions, and the fairing of such motions. <;1'4 is chosen for its particular elegance in representing rigid-body transforms, coupled with an equivalence relation between elements representing transforms more general than for ordinary homogeneous coordinates. The properties of the algebra germane to freeform motion design and improvement are given, and two distinct frameworks for freeform motion construction and modification are studied in detail.

Shape computations are a formal representation that specify particular aspects of the design process with reference to form. They are defined according to shape grammars, where manipulations of pictorial representations of designs are formalised by shapes and rules applied to those shapes. They have frequently been applied in architecture in order to formalise the stylistic properties of a given corpus of designs, and also to generate new designs within those styles. However, applications in more general design fields have been limited. This is largely due to the initial definitions of the shape grammar formalism which are restricted to rectilinear shapes composed of lines, planes or solids. In architecture such shapes are common but in many design fields, for example industrial design, shapes of a more freeform nature are prevalent. Accordingly, the research described in this thesis is concerned with extending the applicability of the shape grammar formalism such that it enables computation with freeform shapes. Shape computations utilise rules in order to manipulate subshapes of a design within formal algebras. These algebras are specified according to embedding properties and have previously been defined for rectilinear shapes. In this thesis the embedding properties of freeform shapes are explored and the algebras are extended in order to formalise computations with such shapes. Based on these algebras, shape operations are specified and algorithms are introduced that enable the application of rules to shapes composed of freeform B´ezier curves. Implementation of the algorithms enables the application of shape grammars to shapes of a more freeform nature than was previously possible. Within this thesis shape grammar implementations are introduced in order to explore both theoretical issues that arise when considering computation with freeform shapes and practical issues concerning the application of shape computation as a model for design and as a mode for generating freeform shapes.

Thesis (Ph. D.)--Hong Kong University of Science and Technology, 2002.
Includes bibliographical references (leaves 143-152). Also available in electronic version. Access restricted to campus users.

One of the challenges in tissue engineering is to fabricate scaffolds which can mimic the natural microenvironments of cells. In a cell niche, biophysical and mechanical cues are crucial factors influencing cell functions. Given the complexity of natural extracellular matrix (ECM) engineered ECMs providing controllable biophysical and mechanical cues are appealing both in enhancing the understanding of cell-matrix interaction and in controlling cell fates in vitro. The ultimate goal of our study is to establish a platform as an engineered ECM by fabricating customized solid protein microstructures from solution using two-photon photochemical crosslinking, a novel laser-based freeform fabrication technique. In this study, protein structures varying from submicron lines, 2D micropatterns and microporous matrices, to 3D micropillars were successfully fabricated, demonstrating freeform fabrication capability with two-photon photochemical crosslinking. Two-photon fluorescent imaging and scanning electron microscope (SEM)-based microstructural characterization revealed that power, scan speed, total exposure time and concentrations of protein (bovine serum albumin) and photosensitizer (rose Bengal) in the solution were crucial processing parameters in this fabrication technique. Quantitative imaging analysis showed that porosity of protein matrices was highly dependent on processing parameters including power, scan speed, number of cycles in time series scan and protein concentrations in the solution. An atomic force microscopy (AFM)-based step change nano-compression test was used to measure the reduced elastic modulus of 3D viscoelastic protein micro-pillars fabricated, as a pilot study. Microporous protein matrices and 3D micropillar arrays fabricated with two-photon photochemical crosslinking can be used as engineered ECM for future study in cell-ECM interactions.
published_or_final_version
Mechanical Engineering
Master
Master of Philosophy

Freeform optics provide excellent performance for a wide variety of applications. However, obtaining an accurate freeform surface measurement is highly challenging due to its large aspheric/freeform departure. It has been proven that SCOTS (Software Configurable Optical Test System), an advanced deflectometry system developed at the University of Arizona, can measure the departure of a freeform surface from the desired shape with nanometer accuracy. Here, a new data processing technique was used to measure a freeform surface without any prior knowledge of the shape of the surface. Knowing only the geometry of one point on the test surface, this method can take a blind measurement of a freeform surface and arrive at the true surface through iterative construction.

Two optical design scenarios—imaging and illumination—were investigated for their use of Cartesian- and polar-based functions to generate freeform optical surfaces. The imaging scenario investigated a single-element, refracting freeform surface that converts an on-axis object field to an off-axis image point. XY polynomials (Cartesian but not orthogonal) and Zernike polynomials (Polar and orthogonal) were the two different function sets used to manipulate the surfaces to achieve the freeform imaging scenarios. The investigation discovered that the results between both function sets did not differ enough to single out a more effective surface type. However, the results did indicate that the Zernike function set typically required fewer coefficients to converge on an optimal imaging solution. The illumination scenario utilized an architectural lighting situation surrounding the Rothko exhibit for Green on Blue at the University of Arizona Museum of Art. The source location was fixed to the light track in the exhibit space and pointed in many different orientations towards the painting. For each orientation, a point cloud of a freeform optical surface was generated such that the painting surface was illuminated with uniform and low-level light. For each of these generated point clouds, a Legendre (Cartesian and orthogonal) and a Zernike (polar and orthogonal) fitting function was applied, and the convergence results were compared. In general, it was found that, after the 20th included fit term, the Legendre function resulted in a smaller RMS fit error than the Zernike function. However, if the light source was pointed near the center of the painting, the Zernike function converged on a solution with fewer fit terms than Legendre. Amidst the imaging scenario, a definition for the extent to which a surface was freeform, or the "freeformity", was given. This definition proved to be an effective solution when the image size was compared for an F/3.33, F/4, F/5, and F/6.67 system for a range of different image focusing heights: the image size trends for each F-number overlapped, indicating a universal freeform term. In addition, a recursive formula for Cartesian Zernike polynomials was defined, which was used to generate an infinite number of Zernike terms using one single recursive expression.

The aim of this paper is to develop a new composite structure of catadioptric optical system containing both freeform refractive surface and freeform total internal reflective (TIR) surface for LED road illumination applications. The role of freeform refractive part is to generate the shifted general rectangular illumination pattern to optimally match the shape of the road surface. The application of TIR mechanism is aimed to control the stray light in the sidewalk direction of the road luminaire and maximize the efficient energy efficiency. In this paper, we use the "double pole" ray mapping technique to design the refractive optical surface and the theta-phi coordinate ray mapping technique to derive the freeform TIR surface. The simulation shows that the novel catadioptric design has relatively high collection efficiency, thus high average illuminance level inside the effective illumination area. This lens also has good control of stray light on the backside of the road luminaire. (c) 2017 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

A systematic method for the design of unsymmetrical optical systems is described. Freeform optical surfaces are constructed by superposition of a conic segment and a polynomial, and successfully applied to design relatively fast wide field-of-view optical systems.

The solidification behavior of an Aluminum-Lithium-Copper (Al-Li-Cu) alloy, AA2199, and the microstructural morphology and solute distributions resulting from three rapid solidification processing techniques were investigated. Controlled-Short-Circuiting Metal-Inert-Gas (CSC-MIG) welding, Laser Re-melting (LRM), and Electrospark Deposition (ESD) were investigated. The morphology of the rapidly solidified material was then compared with the Kurz-Giovanola-Trivedi (KGT) model for microstructural development during rapid solidification, to allow for the estimation of the solidification front velocity (SFV) realized during processing. This SFV was then compared with that required for non-equilibrium solute partitioning as predicted by the Continuous Growth Model (CGM) of Aziz. The solute distributions where then measured and compared with that expected for equilibrium and non-equilibrium partitioning, to determine if the solute trapping phenomenon had been induced during solidification. The CSC-MIG deposited material displayed a fine (4.3 ±1 μm) cellular structure, comparable to that reported for electron beam welding. The SFV was estimated to be ~2-4.5x10-4m/s, a value below that required to impart any deviation from equilibrium partitioning. Chemical analysis via Energy Dispersive Spectroscopy (EDS) and Time-Of-Flight Secondary-Ion-Mass-Spectroscopy (TOF-SIMS) revealed lateral segregation of copper to the cell walls, and a similar segregation profile to that predicted by the Clyne-Kurz model. TOF-SIMS also revealed a homogeneous lateral lithium distribution, while depth profiling displayed some lithium enrichment at the surface.Within the LRM material it was determined that laser pulse energies on the order of 0.25 – 0.5 Joules resulted in a fine cellular solidification structure. The SFV was estimated to be between 3 and 25cm/s were realized during solidification. Furthermore, a pulse energy of 0.125J resulted in a featureless solidification structure. The SFV for the samples produced with a pulse energy of 0.125J was estimated to be >1m/s. The CGM predicted a deviation from equilibrium partitioning all pulse energy levels employed. This was supported by the chemical profiling of lithium within the re-melted samples measured via X-ray photoelectron spectroscopy (XPS). Measurement of the lattice parameter via X-ray diffraction (XRD) revealed that the solute trapping phenomenon resulted in the formation of a super saturated solid solution, evident through a reduction of the lattice parameter from 4.0485 Å for the starting material to 4.0399 Å in the LRM material produced with a pulse energy of 0.125 Joules. The analysis of the ESD solidified material revealed the breakdown of a planar solid-liquid interface into a cellular morphology, resulting in fine copper rich cells within the microstructure (~30-60nm in width). The KGT model predicted this occurred at a SFV of ~1m/s. The CGM predicted significant trapping of Li at a SFV of 1m/s, which was supported by the TOF-SIMS data, which revealed a homogeneous distribution of lithium within the solidified material. Finally Atom-Probe-Tomography revealed the presence of Al3Li upon the cell walls. It was then determined that the Al3Li was not formed during the solidification process, as predicted by a time dependent nucleation model for phase suppression during rapid solidification, and the result of subsequent aging. It was also revealed that the T1 hardness of the LRM material is similar to that of the T3 BM. It was therefore concluded that the LRM process is capable of producing SFF components of AA2199, which can achieve adequate hardness via a natural aging process, without requiring cold-working prior to aging. Finally the LRM solidified material in the T5 condition was determined to be capable of aging to 81% of the hardness (~122HV) of the BM in the T8' condition, without the application of a cold working process prior to aging.
Le comportement de solidification d'un alliage aluminium-lithium (Al-Li), AA2199, et la morphologie microstructurale des distributions de soluté de trois techniques rapides de traitement de solidification ont été étudiés. Contrôle de court-circuit métallique de gaz inerte (CSC-MIG), Re-fondrement au Laser (LRM), et dépôt d'électro-érosion (ESD), ont été étudiés. La morphologie microstructurale du matériel solidifié rapidement a ensuite été comparée au modèle Kurz-Giovanola-Trivedi (KGT) qui décrit le développement microstructurale lors de la solidification rapide afin de permettre l'estimation de la vitesse du front de solidification (SFV) apparaissant au cours du traitement. Cet SFV a ensuite été comparé à celui des partitions de soluté non-équilibrés prédit par le modèle de croissance continue d'Aziz. Les distributions de soluté ont ensuite été mesurées et comparées à celles prédites pour l'éffet de partage à l'équilibre et hors d'équilibre afin de déterminer si le phénomène de piégeage de soluté a été incité au cours du solidification.Le matériel déposé par CSC-MIG affiche une structure cellulaire très fine(4,3 ± 1 micron) et comparable à celle rapportée antérieurement pour le soudage par faisceau d'électrons. L'estimation de l'SFD est d'environ 2-4.5x10-4m / s. Ceci est inférieure à celle requise pour causer une déviation de partition à l'équilibre comme prévu par le CGM. L'analyse chimique par EDS et TOF-SIMS a révélé une ségrégation latérale de cuivre sur les parois cellulaires et un profil de ségrégation semblable à celui prédit par le modèle Clyne-Kurz. Time-Of-Flight-secondary-Ion Mass Spectroscopy-(TOF-SIMS) a révélé une distribution latérale homogène de lithium. Cependant, le profile en profondeur affiche une certaine quantité d'enrichissement de lithium à la surface du matériel déposé.Au sein du matériel LRM, il a été déterminé que les énergies de pulsation au laser à l'ordre de 0,125 à 0,5 Joules causent une structure cellulaire de solidification fine. Il a ensuite été estimé que des vitesses de front de solidification (SFV) entre 3 et 25 cm / s ont été atteints au cours de la solidification. Le CGM pour le piégeage des solutés a prédit une déviation des partitions à l'équilibre lors de la solidification pour tous niveaux d'énergie de pulsation employés. Ce phénomène a été appuyé par le profile chimique de lithium dans les échantillons refondus et mesurés à l'aide du spectroscopie de photoélectrons au rayons X (XPS). Les mesures du paramètre du réseau crystalline par diffraction de rayons X (XRD) ont révélé que le phénomène de piégeage de soluté donne lieu à la formation d'une solution saturée super-solide, ce qui est démontré par une réduction du paramètre du réseau de 4,0485 Å pour le matériel de départ comparé à 4,0399 Å pour le matériel refondu avec une énergie de pulsation de 0,125 joule.L'analyse de la matière solidifiée par ESD a révélé la désintégration de l'interface planaire solide-liquide en une morphologie cellulaire qui entraîne la présence de cellules fines riches en cuivre à l'intérieure de la microstructure (~ 30-60nm de largeur). Le modèle déduit par KGT prédit que ceci se produit à un SFV d'environ 1m / s. Le CGM prédit une piégeage significatif de lithium à une SFV de 1 m / s, ce qui a été soutenu par les données TOF-SIMS qui ont révélé une distribution homogène de lithium dans le matériel solidifié. Ensuite, la tomographie par sonde d'atoms a révélé la présence de la phase Al3Li sur les parois des cellules riches en cuivre. De plus, il a été déterminé que le Al3Li n'a pas été formé lors de la solidification. Ceci est prédit par un modèle temporel de nucléation qui sert à la prédiction de la suppression de phases au cours de la solidification rapide, et donc le résultat est un processus de vieillissement antérieur.

Surface metrology has been widely used in manufacturing for many years. There has been a wide range of techniques applied for measuring surface topography. A photometric stereo technique is one of the best ways for the analysis of three-dimensional (3D) surface textural patterns. Many published works are concerned the developed approach for recovering the 3D profiles from surface normal. This research not only presents a methodology used to retrieve the profiles of surface roughness standards but also investigates the uncertainty estimation of textural measurement determined by the photometric stereo method. Various input quantities have been studied such as pixel error from recovered 3D surface textural patterns, the power of light source which involved with surface roughness average (Ra) value and the effect of room temperature. The surface roughness standards were utilized as the reference value. In term of increasing accuracy of the reference value, a contact method (stylus instrument) was used to calibrate them. Illumination angles of light source had some influence on the measurement results. A coordinate measuring machine (CMM) was used for holding the light source in order to study the effects of tilt and slant angles. The effect of tilt and slant angles were investigated. The results of these experiments successfully indicated that the angle used in photometric stereo method played an important role to the accuracy level of the roughness measurement results. The surface roughness specimen manufactured by a Computer Numerical Control (CNC) was applied to validate the capability of the photometric stereo system.

The emergence of freeform architecture provides interesting geometric challenges with regards to the design and manufacturing of large-scale structures. To design these architectural structures, we have to consider two types of constraints. First, aesthetic constraints are important because the buildings have to be visually impressive. Sec- ond, functional constraints are important for the performance of a building and its e cient construction. This thesis contributes to the area of architectural geometry. Specifically, we are interested in the geometric rationalization of freeform architec- ture with the goal of combining aesthetic and functional constraints and construction requirements. Aesthetic requirements typically come from designers and architects. To obtain visually pleasing structures, they favor smoothness of the building shape, but also smoothness of the visible patterns on the surface. Functional requirements typically come from the engineers involved in the construction process. For exam- ple, covering freeform structures using planar panels is much cheaper than using non-planar ones. Further, constructed buildings have to be stable and should not collapse. In this thesis, we explore the geometric rationalization of freeform archi- tecture using four specific example problems inspired by real life applications. We achieve our results by developing optimization algorithms and a theoretical study of the underlying geometrical structure of the problems. The four example problems are the following: (1) The design of shading and lighting systems which are torsion-free structures with planar beams based on quad meshes. They satisfy the functionality requirements of preventing light from going inside a building as shad- ing systems or reflecting light into a building as lighting systems. (2) The Design of freeform honeycomb structures that are constructed based on hex-dominant meshes with a planar beam mounted along each edge. The beams intersect without torsion at each node and create identical angles between any two neighbors. (3) The design of polyhedral patterns on freeform surfaces, which are aesthetic designs created by planar panels. (4) The design of space frame structures that are statically-sound and material-e cient structures constructed by connected beams. Rationalization of cross sections of beams aims at minimizing production cost and ensuring force equilibrium as a functional constraint.

碩士
臺灣大學
光電工程學研究所
98
Optical systems are composed by various of optical elements, such as lenses and mirrors. In order to achieve different purpose, positions, materials, and surface shapes of the optical elements can be regulated. Among these specifications, regulating surface shapes of the optical elements is an issue that is worth researching. In early age, the surface shapes of lens or mirrors are spherical. For the sake of decreasing optical aberrations or other purpose, aspherical or freeform surfaces may be adapted. Although it is more difficult to design or manufacture, progress of computer power and manufacture technology have made the applications of aspherical and freeform elements more and more various. In order to achieve better performance of optical systems, designing aspherical and freeform surfaces are worth more concerns. In the thesis, freeform surfaces are applied to progressive Addition lenses (PAL), A PAL can combine different requirements of diopter on one lens, avoiding the necessity of a presbyopic changing different pairs of spetacles while viewing far side and near side. B-spline surfaces are used to describe the freeform surfaces applied on PALs in the thesis. The designs are achieved by optimization. Sample PALs are also produced and measured to show the feasibility. The simulation and measurement result shows that the performance of view zone area and cylinder are equal or even better to modern products.

Lai Yuen-hoo.
Thesis submitted in: November 2004.
Thesis (M.Phil.)--Chinese University of Hong Kong, 2005.
Includes bibliographical references (leaves 100-102).
Abstracts in English and Chinese.
Abstract --- p.i
摘要 --- p.ii
Acknowledgment --- p.iii
List of Figures --- p.iv
Table of Content --- p.vii
Chapter 1. --- Introduction --- p.1
Chapter 1.1. --- Problem Definition --- p.1
Chapter 1.2. --- Proposed Solution --- p.2
Chapter 1.3. --- Thesis Contributions --- p.2
Chapter 2. --- Modeling Approaches --- p.4
Chapter 2.1. --- Polygon Modeling --- p.4
Chapter 2.2. --- Patch Modeling --- p.6
Chapter 2.3. --- Freehand Sketch-based Modeling --- p.7
Chapter 2.4. --- Template Based Modeling --- p.8
Chapter 2.5. --- Curve Interpolation Method --- p.9
Chapter 3. --- Surface Operations --- p.11
Chapter 3.1. --- Surface Blending --- p.11
Chapter 3.2. --- Surface Trimming --- p.13
Chapter 3.3. --- Boolean Operations --- p.14
Chapter 4. --- Subdivision Surface --- p.16
Chapter 4.1. --- Basic Principle --- p.16
Chapter 4.2. --- Catmull-Clark Surface --- p.17
Chapter 5. --- Modeling Algorithm Overview --- p.21
Chapter 6. --- Subdivision Surface Generation --- p.23
Chapter 6.1. --- Input Curves --- p.23
Chapter 6.2. --- Surface Sweeping --- p.24
Chapter 6.3. --- Subdivision Surface Fitting --- p.29
Chapter 7. --- Surface Blending --- p.32
Chapter 7.1. --- Introduction --- p.32
Chapter 7.2. --- Problem Definition --- p.32
Chapter 7.3. --- Algorithm Overview --- p.36
Chapter 7.4. --- Blend Region Detection --- p.39
Chapter 7.4.1. --- Collision Detection --- p.40
Chapter 7.4.2. --- Result and Analysis --- p.42
Chapter 7.5. --- "Mesh Refinement, Surface Fitting and Region Removal" --- p.46
Chapter 7.5.1. --- Mesh Refinement --- p.46
Chapter 7.5.1.1. --- Adaptive Subdivision --- p.46
Chapter 7.5.1.2. --- Additional Subdivision Constraint --- p.47
Chapter 7.5.2. --- Surface Fitting --- p.49
Chapter 7.5.2.1. --- General Approach --- p.49
Chapter 7.5.2.2. --- Surface Point Correspondence --- p.50
Chapter 7.5.2.3. --- Numerical Fitting Method --- p.51
Chapter 7.5.3. --- Unwanted Region Removal --- p.55
Chapter 7.5.4. --- Result and Analysis --- p.56
Chapter 7.6. --- Boundary Smoothing --- p.58
Chapter 7.6.1. --- General Approach --- p.59
Chapter 7.6.2. --- Constraint on Deformation Direction of Vertex --- p.61
Chapter 7.6.3. --- Result and Analysis --- p.63
Chapter 7.7. --- Blend Curves --- p.65
Chapter 7.7.1. --- Problem Definition --- p.65
Chapter 7.7.2. --- Proposed Solution Overview --- p.66
Chapter 7.7.3. --- Maintenance of Regular Vertex Valence along Blend Curve --- p.67
Chapter 7.7.3.1. --- Pairing Up Blend Boundary Vertices --- p.70
Chapter 7.7.4. --- Minimization of Distortion Caused by Extraordinary Vertices --- p.72
Chapter 7.7.5. --- Blend Vertex Position Optimization Function --- p.74
Chapter 7.7.5.1. --- Face Normal Expression --- p.74
Chapter 7.7.5.2. --- Face Normal Difference Energy Function --- p.77
Chapter 7.7.5.3. --- Midpoint Distance Energy Function --- p.78
Chapter 7.7.5.4. --- Weighted Least Square Energy Minimization --- p.78
Chapter 8. --- Implementation --- p.81
Chapter 8.1. --- Data Structure --- p.81
Chapter 8.2. --- User Interface --- p.82
Chapter 9. --- Results --- p.83
Chapter 9.1. --- Surface Generation --- p.83
Chapter 9.2. --- Surface Blending --- p.86
Chapter 9.2.1. --- Ideal Case --- p.86
Chapter 9.2.2. --- Angle of Insertion --- p.87
Chapter 9.2.3. --- Surface Feature Near Intersection --- p.88
Chapter 9.2.4. --- Comparison --- p.89
Chapter 9.2.5. --- Other Examples --- p.92
Chapter 9.3. --- Overall Performance --- p.94
Chapter 9.4. --- Limitations --- p.97
Chapter 9.4.1. --- Limitation on Generated Shape --- p.97
Chapter 9.4.2. --- Limitation on Input Surfaces --- p.98
Chapter 10. --- Conclusion and Future Work --- p.99
References --- p.100

博士
國立交通大學
光電工程研究所
104
In this thesis, we propose freeform design model for constructing a single refractor (or reflector) surface under a predefined geometry. The freeform model based on energy conservation and ray propagation law can be characterized by a nonlinear partial differential equation (PDE) under the small planar approximation. The nonlinear PDE can be solved by finite element method with high order element to satisfy the condition of continuity (1st -order) and smoothness (2nd - order). To validate the proposed methodology, we use commercial software LightTools® , to evaluate the illumaninance performance via designed freeform engine in realization of uniform and non-uniform illuminance distribution on the planar.