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DDMC 2016: Proceedings of the 3rd Fraunhofer Direct Digital Manufacturing Conference, ISBN:978-3-8396-1001-5, ISBN:3-8396-1001-X

Solid Freeform Fabrication 2016: proceedings of the 27th Annual International Solid Freeform Fabrication Symposium

The first objective of the PhD thesis is to develop a new type of positioning sensor to align components at micrometre level over 200 m with respect to a laser beam as straight line reference. The second objective is to estimate the measurement accuracy of the total alignment system over 200 m. The context of the PhD thesis is the Compact Linear Collider project, which is a study for a future particle accelerator. The proposed positioning sensor is made of a camera and an open/close shutter. The sensor can measure the position of the laser beam with respect to its own coordinate system. To do a measurement, the shutter closes, a laser spot appears on it, the camera captures a picture of the laser spot and the coordinates of the laser spot centre are reconstructed in the sensor coordinate system with image processing. Such a measurement requires reference targets on the positioning sensor. To reach the rst objective of the PhD thesis, we used laser theory and cam- era model to de ne an accurate image processing and we performed experiments to validate a prototype of a positioning sensor. For the second objective, we could not obtain results regarding measurement accuracy because we could not develop a full alignment system under vacuum over 200 m. However, we could estimate laser pointing stability over 200 m by extrapolating results obtained over 12 m. As a result, we present in this report a sensor design, a calibration protocol and estimations regarding measurement uncertainty. In case of a separate cali- bration with theodolites, we estimated the measurement uncertainty of the po- sitioning sensor to be 4 μ m for all coordinates. In case of a full auto-calibration, we estimated the measurement uncertainty of the positioning sensor to be 10 μ m for the radial and the vertical coordinates and 20 μ m for the depth coordinate. Concerning the extrapolation over long distance, we estimated laser pointing stability to be 10 μ m for a laser beam propagation distance of 200 m. Our work does not provide a complete laser beam alignment system at mi- crometre level over 200 m but it is the rst necessary step towards it.

Proceedings of the 27th Annual International Solid Freeform Fabrication

Essentials, ISBN:3-658-12288-9, ISBN:978-3-658-12288-1

Proceedings of the 26th Annual International Solid Freeform Fabrication Symposium

Selective laser sintering (SLS) is a manufacturing technology whereby parts are built through layerwise application and selective consolidation of a polymer powder by a laser. With this additive manufacturing technology, polymer parts can be built with nearly no limits to complexity and nearly without geometrical constraints. Recently, a handful of polypropylene (PP) materials has been added to the rather limited portfolio of laser sintering powders. In conventional extrusion, the use of nucleating agents to increase clarity and impact resistance of PP is widespread. The current investigation focusses on the use of a nucleating agent in the SLS process to improve the mechanical properties of PP parts. Using a nucleating agent is not without challenges. It must be assured that addition of the agent does not change the thermal properties of the polymer in such a way, that the requirements of the SLS process cannot be met. On the other hand, it must be assured that the nucleating agent becomes effective, eve...

Polymer processing using Additive Manufacturing Technologies (AM) has experienced a remarkable growth during the last years. The application range has been expanding rapidly, particularly driven by the so-called consumer 3D printing sector. However, for applications demanding higher requirements in terms of thermo-mechanical properties and dimensional accuracy the long established AM technologies such as Selective Laser Sintering (SLS) do not depict a comparable development. The higher process complexity hinders the number of materials that can be currently processed and the interactions between the different physics involved have not been fully investigated. In case of thermoplastic materials the crystallization kinetics coupled to the shrinkage strain development strongly influences the stability of the process. Thus, the current investigation presents a transient Finite Element simulation of the warpage effect during the SLS process of a new developed polyolefin (co-polypropylene) coupling the thermal, mechanical and phase change equations that control the process. A thermal characterization of the material was performed by means of DSC, integrating the Nakamura model with the classical Hoffmann-Lauritzen theory. The viscoelastic behavior was measured using a plate-plate rheometer at different degrees of undercooling and a phase change-temperature superposition principle was implemented. Additionally, for validation porpoises the warpage development of the first sintered layers was captured employing an optical device. The simulation results depict a good agreement with experimental measurements of deformation, describing the high sensitivity of the geometrical accuracy of the sintered parts related to the processing conditions.

Proceedings of the 14th international conference of the European Society for Precision Engineering and Nanotechnology : Vol. 2, ISBN:978-0-9566790-3-1

International Journal of Modelling, Identification and Control, 20 (3), ISSN:1746-6172, ISSN:1746-6180

Physik, ISBN:978-3-89963-781-6

2007 IEEE/RSJ International Conference on Intelligent Robots and Systems : San Diego, CA, 29 October - 2 November 2007, ISBN:978-1-424-40912-9

In dieser Arbeit werden Experimente vorgestellt, in denen es gelungen ist, die Quantenphysik eindimensionaler Systeme mit ultrakalten atomaren Gasen zu untersuchen. Mithilfe von optischen Gittern wird die Bewegungsfreiheit der Atome auf eine Dimension beschränkt, während in den transversalen Richtungen nur quantenmechanische Grundzustandsbewegungen erlaubt sind. Zusätzlich zur Dimensionalität kann auch die Stärke und das Vorzeichen der Wechselwirkung zwischen den Atomen verändert werden. Diese einzigartige Flexibilität erlaubt die präzise Untersuchung grundlegender Fragen der Festkörper- und Quantenphysik. Der Zustand eines kinematisch eindimensionalen Bose Gases wurde durch die Messung der kollektiven Moden charakterisiert. Diese geben Auskunft über den Quantenzustand des Vielteilchensystems und belegen, daß ein eindimensionales Bose-Einstein Kondensat erzeugt wurde. Indem wir ein zusätzliches periodisches Potential entlang der Bewegungsrichtung anlegten, konnten wir in das Regime stark korrelierter Systeme vordringen: wir beobachteten den Übergang von einer eindimensionalen Supraflüssigkeit in den Mott-Isolator Zustand und charakterisierten ihn durch Messungen des Anregungsspektrums sowie der Kohärenzeigenschaften. Dabei fanden wir Anzeichen für verstärkt auftretende Quanten-Fluktuationen, die in eindimensionalen Systemen eine besondere Rolle spielen. Die Verwendung von Feshbach-Resonanzen eröffnet die Möglichkeit, die Molekülbildung und die Streueigenschaften der Atome in einer Dimension zu untersuchen. In einer Dimension wurden schwach gebundene Dimere sowohl für positive als auch für negative Streulänge erzeugt und charakterisiert, während im dreidimensionalen Fall gebundene Zustände grundsätzlich nur für positive Streulänge existieren. Die gebundenen Zustände bei negativer Streulänge sind Besonderheiten des niederdimensionalen Systems und werden durch den starken radialen Einschluss im optischen Gitter stabilisiert. Neben der Molekülbildung ändern sich auch die Streueigenschaften drastisch. In diesem Zusammenhang wurde die p-Wellenstreuung untersucht, die aufgrund ihrer anisotropen Wechselwirkung besonders interessant ist. Durch die Spinausrichtung und Dimensionalität konnten gezielt einzelne Streukanäle unterdrückt werden. Die Experimente zu den Streueigenschaften und der Molekülbildung zeigen, daß sich die Zweikörperphysik in einer Dimension in grundlegenderWeise von der in höheren Dimensionen unterscheidet. Eindimensionale System nehmen einen besonderen Platz in der Vielteilchenphysik ein, da Wechselwirkung und Quantenfluktuationen eine dominierende Rolle spielen. Mit der Untersuchung des bosonischen Mott-Isolator Übergangs haben wir dieses faszinierende Gebiet betreten. Die in dieser Arbeit entwickelte Apparatur eignet sich in idealer Weise dazu, auch stark korrelierte fermionische Systeme zu erforschen. Eine besonders spannende Herausforderung stellt in diesem Zusammenhang die Beobachtung des BEC-BCS Übergangs in einer Dimension dar, der dort durch ein exakt lösbares Modell beschrieben wird. In this thesis I present experiments which enabled us to explore the quantum physics of one dimensional systems with ultracold atomic gases. Using optical lattices the motion of the atoms was restricted to one dimension, permitting only ground state oscillations in the transverse directions. In addition to the dimensionality, the strength and the sign of the interaction are adjustable. This unique tunability facilitates the investigation of fundamental issues of solid state and quantum theory. A one-dimensional Bose gas was realised and characterised by measuring its lowest lying collective oscillations. The collective oscillations are a very sensitive probe of the state of the gas, proving that a one-dimensional Bose condensate was created. By applying a periodic potential in the direction of motion the regime of strongly correlated systems was entered: we observed the transition from a one-dimensional superfluid to a Mott insulator and characterised it by studying its excitation spectrum as well at the coherence properties. We detected signatures for increased fluctuations which are characteristic for one-dimensional systems. Feshbach resonances offer the possibility to explore the effects of reduced dimensionality on the formation of molecules and the scattering properties of the atoms. We created and studied weakly bound dimers in one dimension which exist irrespective of the sign of the scattering length, contrary to the situation in free space. These confinement induced molecules are peculiar to the low dimensional system and are stabilised by the confining potential. The reduced dimensionality has also a profound influence on the scattering properties. We investigated the p-wave scattering, which is especially intriguing due to its anisotropic character. By controlling the symmetry and the dimensionality of the system a selective suppression of individual p-wave scattering channels was achieved. One-dimensional systems occupy a special place in many-body physics because interactions and quantum fluctuations play a dominant role. With our studies of the bosonic Mott insulator transition we have entered this fascinating regime. The apparatus that was constructed in the course of this thesis is ideally suited to study also strongly correlated fermionic systems. A particularly exciting challenge in this context is the observation of the BCS-BEC crossover for which exactly solvable models exist in one dimension.