Improving coherence scanning interferometry signal modelling and topography measurement for complex surfaces

This thesis presents work on advanced optical surface metrology methods that enable extending the range of surface slopes that can be reliably measured by optical surface topography measurement instruments, and on investigating the reliability of the current capability. Optical instruments can only capture a limited portion of light scattered from an object’s surface, determined by the instrument’s numerical aperture. As the surface measured becomes steeper, less scatter is captured until all specular scatter is lost, referred to as the specular reflection limit (SRL). While surface measurement of slopes beyond the SRL by modern instruments is possible via the capture and detection of non-specular scatter, the instrument response to these slopes is not well understood. In addition, as the non-specular scatter has a low signal-to-noise ratio, data dropout can occur. Topography measurement of steep and complex surfaces using optical methods can therefore be challenging and have an unknown reliability, and can have significant errors when multiple scattering is present. The instrument modelling and experimental work focussed on coherence scanning interferometry (CSI). Through use of an approximate linear model the instrument response of a CSI instrument to various slope angles and spatial frequencies was described by a three-dimensional (3D) surface transfer function (STF). This theory was experimentally verified by demonstrating that an experimental 3D STF obtained from measurement of microspheres can be used to generate a filter that can compensate for the effect of lens aberration at a fundamental level and consequently reduce errors in the topographies obtained, especially from surface slopes just below the SRL. Second, a rigorous two-dimensional boundary element method (BEM) model of electromagnetic surface scatter was verified through multiple comparisons including an exact analytical Mie scatter solution and through experimental comparison to measurement data from a laser scatterometer, providing evidence of the BEM model’s capability to accurately predict scatter from complex surfaces, including those that linear models cannot accurately model. A CSI model based on this BEM scattering model was then developed and verified, demonstrating the model’s capability to accurately model the CSI signal for complex surfaces which contain steep surfaces, including those that produce multiple scattering. Using this BEM-CSI model and experimental measurement, the capability of optical surface topography measurement methods for measurement of steep surfaces was investigated, illustrated for the first time with both fringe data and the resulting height estimates for a series of surfaces at slopes steeper than the SRL. At high tilt angles it was found that sharp edges with undercuts still provide strong signals which appear as plateaus in the topography data, with a width corresponding to the width of the point spread function of the instrument. While phase information was lost, part of the topography could still be obtained from the non-specular scatter. The BEM-CSI model’s results were accurate even for challenging surfaces beyond the capabilities of linear models, providing a tool for future investigation of other complex surfaces and providing progress towards evaluating the measurement uncertainty of complex surface measurements by optical instruments

Improving coherence scanning interferometry signal modelling and topography measurement for complex surfaces

This thesis presents work on advanced optical surface metrology methods that enable extending the range of surface slopes that can be reliably measured by optical surface topography measurement instruments, and on investigating the reliability of the current capability. Optical instruments can only capture a limited portion of light scattered from an object’s surface, determined by the instrument’s numerical aperture. As the surface measured becomes steeper, less scatter is captured until all specular scatter is lost, referred to as the specular reflection limit (SRL). While surface measurement of slopes beyond the SRL by modern instruments is possible via the capture and detection of non-specular scatter, the instrument response to these slopes is not well understood. In addition, as the non-specular scatter has a low signal-to-noise ratio, data dropout can occur. Topography measurement of steep and complex surfaces using optical methods can therefore be challenging and have an unknown reliability, and can have significant errors when multiple scattering is present. The instrument modelling and experimental work focussed on coherence scanning interferometry (CSI). Through use of an approximate linear model the instrument response of a CSI instrument to various slope angles and spatial frequencies was described by a three-dimensional (3D) surface transfer function (STF). This theory was experimentally verified by demonstrating that an experimental 3D STF obtained from measurement of microspheres can be used to generate a filter that can compensate for the effect of lens aberration at a fundamental level and consequently reduce errors in the topographies obtained, especially from surface slopes just below the SRL. Second, a rigorous two-dimensional boundary element method (BEM) model of electromagnetic surface scatter was verified through multiple comparisons including an exact analytical Mie scatter solution and through experimental comparison to measurement data from a laser scatterometer, providing evidence of the BEM model’s capability to accurately predict scatter from complex surfaces, including those that linear models cannot accurately model. A CSI model based on this BEM scattering model was then developed and verified, demonstrating the model’s capability to accurately model the CSI signal for complex surfaces which contain steep surfaces, including those that produce multiple scattering. Using this BEM-CSI model and experimental measurement, the capability of optical surface topography measurement methods for measurement of steep surfaces was investigated, illustrated for the first time with both fringe data and the resulting height estimates for a series of surfaces at slopes steeper than the SRL. At high tilt angles it was found that sharp edges with undercuts still provide strong signals which appear as plateaus in the topography data, with a width corresponding to the width of the point spread function of the instrument. While phase information was lost, part of the topography could still be obtained from the non-specular scatter. The BEM-CSI model’s results were accurate even for challenging surfaces beyond the capabilities of linear models, providing a tool for future investigation of other complex surfaces and providing progress towards evaluating the measurement uncertainty of complex surface measurements by optical instruments

A feature-based reverse engineering system using artificial neural networks

Reverse Engineering (RE) is the process of reconstructing CAD models from scanned data of a physical part acquired using 3D scanners. RE has attracted a great deal of research interest over the last decade. However, a review of the literature reveals that most research work have focused on creation of free form surfaces from point cloud data. Representing geometry in terms of surface patches is adequate to represent positional information, but can not capture any of the higher level structure of the part. Reconstructing solid models is of importance since the resulting solid models can be directly imported into commercial solid modellers for various manufacturing activities such as process planning, integral property computation, assembly analysis, and other applications. This research discusses the novel methodology of extracting geometric features directly from a data set of 3D scanned points, which utilises the concepts of artificial neural networks (ANNs). In order to design and develop a generic feature-based RE system for prismatic parts, the following five main tasks were investigated. (1) point data processing algorithms; (2) edge detection strategies; (3) a feature recogniser using ANNs; (4) a feature extraction module; (5) a CAD model exchanger into other CAD/CAM systems via IGES. A key feature of this research is the incorporation of ANN in feature recognition. The use of ANN approach has enabled the development of a flexible feature-based RE methodology that can be trained to deal with new features. ANNs require parallel input patterns. In this research, four geometric attributes extracted from a point set are input to the ANN module for feature recognition: chain codes, convex/concave, circular/rectangular and open/closed attribute. Recognising each feature requires the determination of these attributes. New and robust algorithms are developed for determining these attributes for each of the features. This feature-based approach currently focuses on solving the feature recognition problem based on 2.5D shapes such as block pocket, step, slot, hole, and boss, which are common and crucial in mechanical engineering products. This approach is validated using a set of industrial components. The test results show that the strategy for recognising features is reliable

Characterization of a home-built low temperature scanning probe microscopy system

The continuing advancement of technology is the driving force behind science and fundamental research. Scanning probe instruments still have a major impact in nanoscience and technology, because they provide a link between the macroscopic world and the atomic scale. The key to a reliable performance of experiments at the nanometer scale is the instrumentation, that allows probe positioning ranging from micrometers to Ångstroms with sub atomic precisions. A new type of scanning probe microscopy (SPM) system operating in ultra high vacuum (UHV) and at liquid Helium (LHe) temperature was developed. This offers the advantages that even reactive surfaces remain clean over time periods of several days, permitting long time experiments. Moreover, these experiments this low temperature scanning probe microscopy (LTSPM) system is the implementation of a focussing Fabry Perot interferometer (fFPi) that allows the following features: - Small amplitude operations and stiff cantilevers require sensors with high deflection sensitivity. With the fFPi in this low temperature SPM system, a deflection sensitivity of 4fm/ sqrt(Hz) at 1MHz can be obtained. - Wide detection bandwidth (DC-10MHz) enables the operation of higher flexural oscillation modes as well as the torsional modes of the cantilever. - A laser spot size of 3µm allows the use of ultra small cantilevers with the dimensions 1/10 of conventional cantilevers. - Photothermal excitation of cantilevers avoids undesirable mechanical vibrations near the cantilever resonance frequency. - Simultaneous flexural and torsional force detection provides quantitative studies of frictions and thus, atom manipulations by atomic force microscopy (AFM). - The combination of both types of microscopes (simultaneous AFM/STM) reveals more information than a scanning tunneling microscopy (STM) or AFM alone. A series of measurements on Si(111)7x7, herringbone superstructure of Au(111) and highly oriented pyrolytic graphite (HOPG) provides information regarding imaging performance of the system. Among these performance tests are atomically resolved scans at three different operating temperatures in STM mode. In non-contact atomic force microscopy (nc-AFM) mode, imaging was performed with the cantilever driven at the fundamental and 2nd oscillation mode. Additional measurements were performed with the fFPi in order to quantify the impact of the laser cooling effects (radiation pressure and photothermal effects) on the oscillating cantilever at three different operating temperatures. The aim of this work is the development, implementation and characterization of a new low temperature scanning probe microscope with an ultra sensitive and high bandwidth fFPi deflection sensor, suitable for nc-AFM operations with small, simultaneous flexural and torsional cantilever oscillation modes. Furthermore, expected upgrades will allow simultaneous nc-AFM/STM operations. Keywords: low temperature home-built simultaneous STM/ nc-AFM, tip-sample gap stability, PLL and self-excitation, highly oriented pyrolytic graphite (HOPG), reconstructed Si(111)7x7, herringbone superstructure, focussing Fabry-Perot interferometer, cantilever cooling, radiation pressure and photothermal effects. Der kontinuierliche, technologische Fortschritt ist die treibende Kraft hinter Wissenschaft und Grundlagenforschung. Rasterkraft und -tunnel Instrumente haben immer noch einen bedeutenden Einfluss auf die Nanotechnologie und -wissenschaft, weil sie eine Verbindung zwischen der makroskopischen Welt und den atomaren Massstäben darstellen. Der Schlüssel für eine zuverlässige Ausführung von Experimenten mit Nanometer Massstäben ist die Instrumentierung, die eine Spitzenpositionierung von Mikrometer bis Ångstroms mit subatomarer Präzision erlaubt. Ein neuartiges Rasterspitzen Mikroskop (SPM) System wurde entwickelt, das im Ultra Hoch Vakuum (UHV) und bei flüssig Helium Temperaturen arbeitet. Dies bietet Vorteile weil sogar reaktive Oberflächen über eine Dauer von einigen Tagen sauber bleiben, was eine längere Experimentierphase zulässt. Zusätzlich zeigen diese Experimente bei tiefen Temperaturen weitere Vorteile wie kleine Driftwerte und tiefe Piezo Kriechraten. Der Ansatz bei diesem Tieftemperatur Rasterspitzen Mikroskop System ist die Implementierung eines fokussierenden Fabry Perot Interferometers das die folgenden Eigenschaften vorweist: - Der Betrieb bei kleinen Amplituden und mit steifen Cantilever setzt Sensoren mit einer hohen Ablenkempfindlichkeit voraus. Mit diesem fokussierenden Fabry Perot Interferometer (fFPi) kann eine Ablenkempfindlichkeit von 4fm/ sqrt(Hz) bei 1MHz erreicht werden. - Detektion mit einer grossen Bandbreite (DC-10MHz) erlauben einen Betrieb von Cantilever mit flexuralen und torsionalen Oszillation Modi. - Ein Laser mit einem Brennpunkt von 3µm lässt einen Betrieb mit einem ultra kleinen Cantilever zu, der 1/10 so gross ist wie ein konventioneller Cantilever. - Photothermische Anregung eines Cantilevers vermeidet unerwünschte mechanische Vibrationen rund um die Resonanzfrequenz. - Gleichzeitige flexural und torsional Kraftdetektion erlauben quantitative Untersuchungen von Reibungen und daher atomare Manipulationen mit Rasterkraft Mikroskopie (AFM). - Die Kombination und simultanen Betrieb von beiden Rasterspitzen Mikroskopen (AFM/STM) zeigen mehr Information als ein Raster Tunnel Mikroskop (STM) alleine. Eine Serie von Messungen mit Si(111)7x7, Herringbone Superstrukturen auf Au(111) und Highly Oriented Pyrolytic Graphite (HOPG) geben Information bezüglich der Leistungen des Systems preis. Einige dieser Leistungstests sind atomar aufgelöste Abbildungen bei drei unterschiedlichen Betriebstemperaturen im STM Betriebsart. Im nicht-Kontakt AFM (nc-AFM) Betriebsart, Abbildungen sind ausgeführt worden auf der Grundschwingung und der zweiten Oberschwingung. Zusätzliche Messungen wurden mit dem fFPi ausgeführt um den Einfluss der Laserkühlung auf den oszillierenden Cantilever bei drei unterschiedlichen Betriebstemperaturen zu quantifizieren. Das Ziel dieser Arbeit ist die Entwicklung, Implementation und Charakterisierung eines neuen Tieftemperatur Rasterspitzen Mikroskops mit einem ultra-empfindlichen und Breitband fokussierenden Fabry Perot Interferometer Ablenk Sensor, geeignet für den nicht-Kontakt AFM Betrieb mit kleinen, simultanen flexural und torsional Cantilever Schwingungsmodi. Naheliegende Erweiterungen des Systems gewährleisten einen simultan nc-AFM/STM Betrieb. Schlüsselwörter: Tieftemperatur simultan nc-AFM/STM aus Eigenbau, Spitzen-Probe Spalt Stabilität, PLL und Eigenanregungsbetrieb, Highly Oriented Pyrolytic Graphite (HOPG), reconstrukturiertes Si(111)7x7, Herringbone Superstruktur, fokussierenden Fabry Perot Interferometer, Cantilever Kühlung, Strahlendruck und photothermische Effekte

Mechanical Engineering

The book substantially offers the latest progresses about the important topics of the "Mechanical Engineering" to readers. It includes twenty-eight excellent studies prepared using state-of-art methodologies by professional researchers from different countries. The sections in the book comprise of the following titles: power transmission system, manufacturing processes and system analysis, thermo-fluid systems, simulations and computer applications, and new approaches in mechanical engineering education and organization systems

Sensing and actuation for the design of upper limb prosthetics

The objective of this thesis has been to improve upper limb prosthetics. With this aim in mind, and based on reported user needs, we targeted two main aspects of contemporary active prosthetics: sensing and actuation. The restoration of proprioceptive capabilities through the artificial limb is vital for their intuitive and precise control. In order to capture the prosthetics position, we designed extremely soft microfluidic sensors using conductive liquids such as eutectic Gallium Indium (eGaIn) or Room Temperature Ionic Liquid (RTIL) embedded in soft elastomers. These sensors were used first to sense unidirectional strain, then normal force through Electrical Impedance Tomography (EIT) in a soft microfluidic skin, and were finally embedded in a soft artificial skin that was used to measure the human hand motion. Conventional electromagnetic actuators are poorly suited for prosthetic actuation. Grasping tasks typically require large torque at low speeds whereas conventional actuators are designed to be efficient at high rotational speeds. In consequence, we designed the "Programmable Permanent Magnet" (PPM) actuator. This unique actuator, based on the magnetization of permanent magnets by current pulses, is able to maintain a large torque at no speed and for no energetic cost. This actuator is especially suited for tasks such as grasping or walking and represents a new type of electromagnetic actuator that will enable efficient low speed high torque efficient actuation for robotic and prosthetic applications