Vibration assisted machining: Modelling, simulation, optimization, control and applications

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University, 30/11/2010.Increasing demand for precision components made of hard and brittle materials such as glasses, steel alloys and advanced ceramics, is such that conventional grinding and polishing techniques can no longer meet the requirements of today's precision manufacturing engineering. Particularly, in order to undertake micro-milling of optical glasses or other hard-machining materials, vibration assisted machining techniques have been adopted. However, it is essential and much needed to undertake such processes based on a scientific approach, i.e. the process to be quantitatively controlled and optimized rather than carried out with a trial-and-error manner. In this research, theoretical modelling and instrumental implementation issues for vibration assisted micro-milling are presented and explored in depth. The modelling is focused on establishing the scientific relationship between the process variables such as vibration frequency, vibration amplitude, feedrate and spindle speed while taking into account machine dynamics effect and the outcomes such as surface roughness generated, tool wear and material removal rate in the process. The machine dynamics has been investigated including a static analysis, machine tool-loop stiffness, modal analysis, frequency response function, etc, carried out for both the machine structure and the piezo-actuator device. The instrumentation implementation mainly includes the design of the desktop vibration assisted machining system and its control system. The machining system consists of a piezo-driven XY stage, air bearing spindle, jig, workpiece holder, PI slideway, manual slideway and solid metal table to improve the system stability. The control system is developed using LabVIEW 7.1 programming. The control algorithms are developed based on theoretical models developed by the author. The process optimisation of vibration assisted micro-milling has been studied by using design and analysis of experiment (DOE) approach. Regression analysis, analysis of variance (ANOVA), Taguchi method and Response Surface Methodology (RSM) have been chosen to perform this study. The effects of cutting parameters are evaluated and the optimal cutting conditions are determined. The interaction of cutting parameters is established to illustrate the intrinsic relationship between cutting parameters and surface roughness, tool wear and material removal rate. The predicted results are confirmed by validation experimental cutting trials. This research project has led to the following contribution to knowledge: (1) Development of a prototype desktop vibration assisted micro-milling machine. (2) Development of theoretical models that can predict the surface finish, tool wear and material removal rate quantitatively. (3) Establishing in depth knowledge on the use of vibration assisted machining principles. (4) Optimisation of cutting process parameters and conditions through simulations and machining trials for through investigation of vibration assisted machining.Financial support was obtained from Brunel University

Yb ion trap experimental set-up and two-dimensional ion trap surface array design towards analogue quantum simulations

Ions trapped in Paul traps provide a system which has been shown to exhibit most of the properties required to implement quantum information processing. In particular, a two-dimensional array of ions has been shown to be a candidate for the implementation of quantum simulations. Microfabricated surface geometries provide a widely used technology with which to create structures capable of trapping the required two-dimensional array of ions. To provide a system which can utilise the properties of trapped ions a greater understanding of the surface geometries which can trap ions in two-dimensional arrays would be advantageous, and allow quantum simulators to be fabricated and tested. In this thesis I will present the design, set-up and implementation of an experimental apparatus which can be used to trap ions in a variety of different traps. Particular focus will be put on the ability to apply radio-frequency voltages to these traps via helical resonators with high quality factors. A detailed design guide will be presented for the construction and operation of such a device at a desired resonant frequency whilst maximising the quality factor for a set of experimental constraints. Devices of this nature will provide greater filtering of noise on the rf voltages used to create the electric field which traps the ions which could lead to reduced heating in trapped ions. The ability to apply higher voltages with these devices could also provide deeper traps, longer ion lifetimes and more efficient cooling of trapped ions. In order to efficiently cool trapped ions certain transitions must be known to a required accuracy. In this thesis the 2S1/2 → 2P1/2 Doppler cooling and 2D3/2 → 2D[3/2]1/2 repumping transition wavelengths are presented with a greater accuracy then previous work. These transitions are given for the 170, 171, 172, 174 and 176 isotopes of Yb+. Two-dimensional arrays of ions trapped above a microfabricated surface geometry provide a technology which could enable quantum simulations to be performed allowing solutions to problems currently unobtainable with classical simulation. However, the spin-spin interactions used in the simulations between neighbouring ions are required to occur on a faster time-scale than any decoherence in the system. The time-scales of both the ion-ion interactions and decoherence are determined by the properties of the electric field formed by the surface geometry. This thesis will show how geometry variables can be used to optimise the ratio between the decoherence time and the interaction time whilst simultaneously maximising the homogeneity of the array properties. In particular, it will be shown how the edges of the geometry can be varied to provide the maximum homogeneity in the array and how the radii and separation of polygons comprising the surface geometry vary as a function of array size for optimised arrays. Estimates of the power dissipation in these geometries will be given based on a simple microfabrication

A scanning cavity microscope

Nano ist überall! Nanoskalige Systeme sind allgegenwärtig, wie in farbigen Gläsern, neuartigen Solarzellen oder in Lebewesen. Für ein umfassendes Verständnis des Nanokosmos ist es unabdingbar, Nanoteilchen einzeln zu untersuchen, um einen tiefen und faszinierenden Einblick in eine Welt, die dem Betrachter auf dem ersten Blick verborgen ist, zu erlangen. Optische Spektroskopie von einzelnen Nanosystemen liefert grundlegende Erkenntnisse von deren physikalischen und chemischen Eigenschaften. Quantitative Messungen von Extinktion und Dispersion an einzelnen Teilchen sind sehr schwierig, gleichzeitig sind solche Messungen sehr wünschenswert, da sich die Teilchen in Form, Größe oder Zusammensetzung unterscheiden können. Diese Arbeit zeigt eine Methode zur gleichzeitigen Messung von Extinktion und Dispersion einzelner Nanopartikel mit Ortsauflösung. Tausende Umläufe von Licht in einem optischen Resonator verstärken dieWechselwirkung von Licht mit Materie und ermöglichen sehr sensitive Messungen an einzelnen Teilchen. Die Mode eines Fabry-Pérot Resonators mit einer Finesse von bis zu 85 000 wird als Rastersonde verwendet, um die Extinktion von Nanoteilchen im Resonator zu bestimmen. Der Resonator ist aus einer mikrobearbeiteten und hochreflektiv beschichteten Glasfaser und einem makroskopischen Planspiegel, der gleichzeitig als Probenhalter dient, aufgebaut. Transversales Verschieben von Faser und Planspiegel zueinander liefert Ortsauflösung. Zur Messung der Verschiebung der Resonanzfrequenz aufgrund eines Teilchens im Resonator werden Transversalmoden höherer Ordnung genutzt. Die Kombination beider Messungen erlaubt es, die komplexe Polarisierbarkeit, die die optischen Eigenschaften eines Nanoteilchens im Rayleigh-Grenzfall vollständig beschreibt, zu bestimmen. In dieser Arbeit werden Extinktions-, Dispersions- und Polarisierbarkeitsmessungen an Goldnanoteilchen verschiedener Form und Größe gezeigt. Verglichen mit beugungsbegrenzter Mikrokopie liefert die Rasterresonatormikroskopie um mehr als 3200fach stärkere Messsignale, die zu einer Sensitivität für Extinktionsmessungen von 1.7 nm² und zu Frequenzverschiebungen aufgrund von Dispersion von weniger als 200 MHz, was der Verschiebung durch eine Glaskugel mit einem Durchmesser von 31.6 nm entspricht, führen. Darüber hinaus werden höhere Transversalmoden dazu verwendet, um die Ortsauflösung zu erhöhen. Durch die Kombination von Extinktionskarten, die mit der Grundmode und den darauf folgenden, höheren Transversalmoden aufgenommen wurden, ist eine signifikante Erhöhung der Ortsauflösung, gegebenenfalls sogar jenseits der Beugungsgrenze, möglich. Das Rasterresonatormikroskop ist zunächst für die Untersuchung von Nanoteilchen in einer trockenen Umgebung konzipiert worden. Viele Nanosysteme, darunter biologische Proben, zeigen ihre einzigartigen Eigenschaften jedoch erst in einer wässrigen Umgebung. Um den Untersuchungsbereich dorthin auszuweiten, wurde ein faserbasierter Resonator hoher Finesse mit einer mikrofluidischen Zelle kombiniert. Mit diesem System können nicht nur die Extinktion oder Dispersion von Teilchen gemessen, sondern auch Teilchen gefangen werden, um beispielsweise deren Reaktionsdynamik zu beobachten. In dieser Arbeit wird demonstriert, dass es möglich ist, einen Fabry-Pérot Resonator hoher Finesse in einer wässrigen Umgebung zu betreiben und es werden erste Messsignale von Teilchen, die den Resonator passieren, als auch vom Resonator gefangen werden, gezeigt. Dieses System, das optische Detektion mit einem kontrollierten Flüssigkeitsstrom vereint, öffnet Möglichkeiten für neuartige Experimente mit einzelnen, unmarkierten Nanosystemen.Nano is everywhere! All around us, there are nanoscaled systems such as in coloured glass, novel solar cells or in living beings. For a detailed understanding of the nanocosmos, studying it at a single particle level is indispensable, leading to deep and intriguing insights into a world that is at a first glance hidden to the eye. Optical spectroscopy of nanosystems at the single particle level provides profound insight into their physical and chemical properties. Retrieving quantitative signals for extinction as well as dispersion at this level is very challenging. At the same time it is desirable to investigate individual particles as they may vary in size, shape or composition. This work presents a spatially resolved method for simultaneous extinction and dispersion measurements of single nanoparticles. Harnessing thousands of round trips of light within an optical microresonator, the interaction of light with the particle gets enhanced and very sensitive quantitative measurements become possible. The cavity mode of a Fabry-Pérot cavity with a finesse up to 85 000 is used as a scanning probe to assess the extinction of nanoobjects placed into the cavity. The resonator consists of a micro-machined and high-reflectively coated end-facet of an optical fibre and a macroscopic plane mirror that serves as a sampleholder and that can be scanned transversally with respect to the fibre, allowing for spatially resolved measurements. Higher order transverse cavity modes are exploited to retrieve the cavity’s resonance frequency shift due to a particle inside. Combining both measurements allows to quantify the complex polarizability, which fully determines the particle’s optical properties at the Rayleigh limit. Extinction, dispersion and polarizability measurements of gold nanoparticles of various size and shape are presented in this work. Compared to diffraction limited microscopy, scanning cavity microscopy reaches a signal enhancement by a factor of more than 3200 resulting in a sensitivity for extinction of 1.7 nm² and for frequency shifts due to dispersion below 200 MHz which corresponds to the shift due to a glass sphere with a diameter of 31.6 nm. Furthermore, the higher order cavity modes are used to increase the spatial resolution of the scanning cavity microscope. By combining extinction maps taken with the fundamental and subsequent higher order modes, a significant increase in resolution potentially beyond the diffraction limit is demonstrated. The scanning cavity microscope is dedicated to investigate nanoparticles in a dry environment. Many nanosystems, especially biological samples, show their unique properties only in an aqueous environment. To extend the field of investigation to these nanosystems a fibre-based high-finesse microcavity has been combined with a microfluidic cell. This system would not only allow to measure the extinction or dispersion of a particle, but also to trap it to monitor e.g. reaction dynamics. In this work, the feasibility of bringing a high-finesse Fabry-Pérot cavity to an aqueous environment is demonstrated and first signals of trapping glass nanoparticles with the cavity mode as well as of particle transitions through the mode are shown. This combined system of optical detection and fluid control opens the perspective for novel experiments with label-free individual nanosystems

Ytterbium ion trapping and microfabrication of ion trap arrays

Over the past 15 years ion traps have demonstrated all the building blocks required of a quantum computer. Despite this success, trapping ions remains a challenging task, with the requirement for extensive laser systems and vacuum systems to perform operations on only a handful of qubits. To scale these proof of principle experiments into something that can outperform a classical computer requires an advancement in the trap technologies that will allow multiple trapping zones, junctions and utilize scalable fabrication technologies. I will discuss the construction of an ion trapping experiment, focussing on my work towards the laser stabilization and ion trap design but also covering the experimental setup as a whole. The vacuum system that I designed allows the mounting and testing of a variety of ion trap chips, with versatile optical access and a fast turn around time. I will also present the design and fabrication of a microfabricated Y junction and a 2- dimensional ion trap lattice. I achieve a suppression of barrier height and small variation of secular frequency through the Y junction, aiding to the junctions applicability to adiabatic shuttling operations. I also report the design and fabrication of a 2-D ion trap lattice. Such structures have been proposed as a means to implement quantum simulators and to my knowledge is the first microfabricated lattice trap. Electrical testing of the trap structures was undertaken to investigate the breakdown voltage of microfabricated structures with both static and radio frequency voltages. The results from these tests negate the concern over reduced rf voltage breakdown and in fact demonstrates breakdown voltages significantly above that typically required for ion trapping. This may allow ion traps to be designed to operate with higher voltages and greater ion-electrode separations, reducing anomalous heating. Lastly I present my work towards the implementation of magnetic fields gradients and microwaves on chip. This may allow coupling of the ions internal state to its motion using microwaves, thus reducing the requirements for the use of laser systems

Ultra conformable and multimodal tactile sensors based on organic field-effect transistors

Cognitive psychology is the branch of psychology related to all the processes by which sensory input is transformed, processed and used. Academic and industrial research has always invested time and resources to develop devices capable to simulate the behavior of the organs where the perceptions are located. In recent years, in fact, there have been numerous discoveries related to new materials, and new devices, capable of reproducing, in a reliable manner, the sensory behavior of humans. Particular interest in scientific research has been aimed at understanding and reproducing of man's tactile sensations. It is known that, through the receptors of the skin, it is possible to detect sensations such as pain, changes in pressure and/or temperature. The development of tactile sensor technology had a significant increase in the last years of 1970s, thanks to the important surveys of Stojiljkovic, Harmon and Lumelsky who presented the firsts prototype of sensors for artificial skin applications, and summarized the main characteristics and requirements of tactile sensors. Recently, organic electronics has been deeply investigated as technology for the fabrication of tactile sensors using biocompatible materials, which can be deposited and processed on ultra flexible and ultra conformable substrates. In general, the most attractive property of these materials is mainly related to their high mechanical flexibility, which is mandatory for artificial skin applications. The main object of this PhD research activity was the development and optimization of an innovative technology for the realization of physical sensors able to detect pressure and temperature variations, which can be applied in the field of biomedical engineering and biorobotics. By exploiting the particular characteristics of the employed materials, such as mechanical flexibility, the proposed sensors are very suitable to be integrated with flexible structures (for example plastics) as a pressure and temperature sensor, and therefore, ideal for the realization of an artificial skin like. In Chapter 1, the basics of humans somatosensory system will be introduced: after a brief description of tactile thermoreceptors, mechanoreceptors and nociceptors, a definition of electronic skin and its characteristics will be provided. In Chapter 2, a wide analysis of the state of the art will be reported. Several and different examples of tactile sensor (in inorganic and organic technology) will be presented, underlining advantages and disadvantages for each approach. In Chapter 3, the firsts experimental results, obtained in the first part of my PhD program, will be presented. All the steps of the fabrication process of the devices will be described, as well as the measurement setup used for the electrical characterization of the sensors. In Chapter 4, the sensor structure optimization will be presented. It will be demonstrated how the presented devices are able to sense simultaneously thermal and mechanical stimuli. Moreover, it will be demonstrated that, thanks to an alternative and innovative fabrication process, the sensors can be transferred directly on skin, thus proving the suitability of the proposed sensor architecture for tactile applications

Measurement and prediction of in-cylinder friction in internal combustion engines

Currently, nearly 75% of worldwide transport is powered by internal combustion engines, with the worldwide transport sector accounting for 14% of the world’s greenhouse gas emissions. With the current trend of downsizing and reducing vehicle cost, expensive solutions such as hybrids are often not viable. One solution is to reduce engine parasitic losses, thereby indirectly improving fuel efficiency, hence emissions. In terms of frictional losses, the piston-cylinder system accounts for 50% of all such losses, which altogether contribute to 20% of all engine losses. The thesis describes an efficient analytical-numerical model in terms of computation times and CPU requirements. The model is a one dimensional analytical solution of Reynolds equation using Elrods cavitation algorithm. The model also includes determination of viscous friction as well as boundary/asperity friction based on the work of Greenwood and Tripp. Lubrication rheology is adjusted for generated hydrodynamic pressures and measured conjunctional temperature based on the cylinder liner. Model predictions are supported by a range of experimental work, from basic science measurements using an instrumented precision slider bearing rig for direct measurement of friction to the development and use of a floating liner on a motored and fired high speed, high performance internal combustion engine at the real situation practical level. The thesis highlights the development of the experimental rigs/engines as well application of state of the art instrumentation and data processing. The combined numerical and experimental analysis show that a significant proportion of friction takes place at the top-dead-center reversal in the transition from the compression to the power stroke. Under motored conditions with low in-cylinder pressures this appears to follow Poiseuille friction, whereas under fired conditions with higher in-cylinder pressures causing increased compression ring sealing a mixed and/or boundary regime of lubrication is observed and predicted. Other than at the TDC reversal in both motored and fired conditions the frictional characteristics follow in direct proportion to the piston sliding velocity, therefore showing the dominance of viscous friction. One outcome of the thesis is a validated analytical model which due to its computational efficiency can now be used in industry to provide timely predictions for the compression ring contact zone. Most significantly, the thesis has established an experimental procedure, infrastructure and data processing methods which enable the determination of the regime of lubrication and the underlying mechanisms of friction generation from basic science sliding surfaces to in situ direct measurements from a fired engine at high loads and sliding speeds