47 research outputs found
Towards angle and space resolved photoemission: bonding in layered misfit compounds and development of reflective photon sieves
In this thesis the electronic structure of the layered, incommensurate TMDC misfit compounds (PbS)1.13TaS2, (PbS)1.14NbS2, (PbS)1.14(NbS2)3, (SnS)1.17NbS2, and (BiS)1.11NbS2 is investigated. Consisting of alternatingly stacked slabs of hexagonally ordered transition metal dichalcogenides (TMDCs) and cubic monochalcogenides (MCs), the layered TMDC misfit compounds are heterostructures with a complex layerâtoâlayer interface due to the different symmetries of the subsystems. In spite of their incommensurability, the alternation of different layers, and the occurrence of monochalcogen bilayers, all acting against a low total energy, they show a remarkable stability. Using a combination of angleâresolved photoelectron spectroscopy (ARPES) and photoelectron microscopy (PEM), the origin of the bonding between the layers is clarified in this thesis. The ARPES investigations of the momentum resolved electronic structure show signatures of both subsystems. In particular in the TMDC dominated Fermi surface maps, umklapp shifted bands with the symmetry of both subsystems appear. However, the band dispersion seems to be only slightly affected by the different competing potentials of the layered subsystems and the interlayer interaction seems to be weak. Since band dispersion perpendicular to the layers is not ovserved, covalent bonding should only play a minor role in the bonding between the TMDC misfit layers. In contrast, the ionic contribution to the interlayer bonding seems to be significant, because the TMDCâdominated conduction bands are more than half full for all misfit compounds. The charge transfer to the TMDC subsystem could be quantified to about 0.2 to 0.4 electrons per transition metal atom. Since only completely filled MC derived bands are observable, the origin of the charge transfer cannot be attributed to the MC layers. By performing spatially resolved measurements of core level spectra from differently terminated domains on surfaces of (PbS)1.13TaS2 direct spectroscopic evidence for Ta substitution into PbS layers as well as Pb substitution into TaS2 layers could be observed, being able to explain the increased band filling. The concentrations of the substituted atoms are of the order of 5 to 20%, which leads to an effective charge transfer of about 0.1 electrons per TaS2 unit to the TaS2 layers if a changed oxidation state of these atoms is assumed. Therefore, such metal crossâsubstitution is of fundamental importance for the stability of (PbS)1.13TaS2 and similar misfit layer compounds and indicates that nonâstoichiometry may not be a necessary condition for their stability. The results of the ARPES and PEM measurements clearly indicate the need for a combination of momentum and spatial resolution in photoelectron spectroscopy experiments. However, there is currently no experimental station available, which allows the measurement of the momentum resolved electronic structure with simultaneous high spatial resolution. To achieve this goal, a novel spatially resolved spectroscopy experiment has been developed, using a reflective photon sieve â a novel type of diffraction optics for focusing synchrotron radiation with suppressed side lobes and reduced background. The setup has been successfully tested in this thesis. In the near future the instrument will be used at highly brilliant and coherent light sources such as the freeâelectron laser (FEL) in Hamburg. Therefore, we performed ARPES test experiments at the VUVâFEL and studied the influence of the highly intense FEL radiation and the resulting high photoelectron densities onto the photoemission spectra. It turned out that even if photoemission at this radiation source is different and difficult, it is in any case possible and offers to perform a variety of novel types of experiments.In dieser Arbeit wird die elekronische Struktur schichtartig aufgebauter, inkommensurabler ĂbergangsmetallâDichalkogenid Misfitverbindungen â nĂ€mlich (PbS)1.13TaS2, (PbS)1.14NbS2, (PbS)1.14(NbS2)3, (SnS)1.17NbS2 und (BiS)1.11NbS2 â untersucht. Diese Verbindungen aus hexagonal geordneten ĂbergangsmetallâDichalkogeniden (ĂMDC) und kubisch geordneten Monochalcogeniden (MC) besitzen aufgrund der unterschiedlichen Symmetrie beider Teilsysteme eine komplexe Grenzschicht. Obwohl ihre InkommensurabilitĂ€t, der periodische Schichtwechsel und das Auftreten von MC Doppelschichten die Gesamtenergie der Kristalle erhöhen sollten, zeigen diese eine bemerkenswerte StabilitĂ€t. Unter Verwendung winkelauflösender Photoelektronenspektroskopie (ARPES) und Photoelektronenmikroskopie (PEM) konnte der Ursprung dieser Bindung aufgeklĂ€rt werden. Die impulsaufgelösten photoemissionsmessungen der elektronischen Struktur zeigen Merkmale beider Teilsysteme. Insbesondere in den ĂMDC dominierten FermiflĂ€chen sind BĂ€nder zu erkennen, die durch Umklappprozesse an den Symmetrien beider Teilsysteme enstehen. Die Banddispersion hingegen wird offenbar nur leicht durch die verschiedenen Potentiale der Teilsysteme beeinfluĂt, was auf eine eher geringe Wechselwirkung zwischen den Schichten hindeutet. WĂ€hrend der kovalente Bindungsanteil eher von untergeordneter Bedeutung ist, da keine Banddispersion senkrecht zu den Schichten beobachtet werden kann, erscheint der ionische Beitrag signifikant: Wie experimentellen Daten zeigen, sind die ĂMDC dominierten LeitungsbĂ€nder in allen Misfitverbindungen mehr als halb gefĂŒllt, und zwar zu etwa 0.2 bis 0.4 Elektronen pro Ăbergangsmetallatom. Da die BĂ€nder der MC Schichten allerdings vollstĂ€ndig gefĂŒllt sind, kann der Ladungstransfer nicht von diesen ausgehen. Ortsauflösende Messungen von Rumpfniveauspektren der Teilsysteme von (PbS)1.13TaS2 konnten Ta Atome im PbS Teilsystem und Pb Atome im TaS2 Teilsysten spektroskopisch nachweisen, welche die erhöhte BandfĂŒllung erklĂ€ren können. Die Konzentration der substituierten Atome liegt in der GröĂenordnung von 5% bis 20% und fĂŒhrt zu einem effektiven LadungsĂŒbertrag von etwa 0.1 Elektron pro TaS2 Einheit, wenn ein verĂ€nderter Oxidationszustand dieser ausgetauschten Atome angenommen wird. Daher scheint ein derartiger gegenseitiger Metallatomaustausch von grundsĂ€tzlicher Bedeutung fĂŒr die StabilitĂ€t von (PbS)1.13TaS2 und Ă€hnlichen Misfitverbindungen zu sein, unabhĂ€ngig von deren Stöchiometrie. Die Ergebnisse der ARPESâ und PEMâMessungen verdeutlichen den Bedarf an einer Kombination von Impulsâ und Ortsauflösung bei der Photoelektronenspektroskopie. Zur Zeit existiert jedoch keine Apparatur zur gleichzeitigen hochauflösenden Messung beider GröĂen; daher wurde ein neues ortsauflösendes ARPESâExperiment entwickelt. Es basiert auf einem reflektiven Photonensieb â einer neuartigen Beugungsoptik zur Fokussierung von Synchrotronstrahlung mit verringerten Nebenmaxima und verringertem Untergrund â und wurde in dieser Arbeit erfolgreich getestet. Da das Experiment in naher Zukunft an hoch brillanten, stark kohĂ€renten Strahlungsquellen wie dem FreieâElektronen Laser (FEL) in Hamburg eingesetzt werden soll, wurden zur Vorbereitung ARPES TestâExperimente an diesem durchgefĂŒhrt und der EinfluĂ der hoch intensiven FELâStrahlung und der resultierenden hohen Photoelektronendichten auf die Photoemmissionsspektren untersucht. Es zeigte sich, dass Photoemissionsmessungen an dieser neuartigen Strahlungsquelle zwar anders und komplexer sind als solche an herkömmlichen Synchrotronstrahlungsquellen, sie dafĂŒr allerdings einen breiten Zugang zu neuartigen Erkenntnissen ermöglichen
Precision Surface Processing and Software Modelling Using Shear-Thickening Polishing Slurries
Mid-spatial frequency surface error is a known manufacturing defect for aspherical and freeform precision surfaces. These surface ripples decrease imaging contrast and system signal-to-noise ratio. Existing sub-aperture polishing techniques are limited in their abilities to smooth mid-spatial frequency errors. Shear-thickening slurries have been hypothesised to reduce mid-spatial frequency errors on precision optical surfaces by increasing the viscosity at the tool-part interface. Currently, controlling the generation and mitigating existing mid-spatial frequency surface errors for aspherical and freeform surfaces requires extensive setup and the experience of seasoned workers. This thesis reports on the experimental trials of shear-thickening polishing slurries on glass surfaces. By incorporating shear-thickening slurries with the precessed bonnet technology, the aim is to enhance the ability of the precessions technology in mitigating mid-spatial frequency errors. The findings could facilitate a more streamlined manufacturing chain for precision optics for the versatile precessions technology from form correction and texture improvement, to MSF mitigation, without needing to rely on other polishing technologies. Such improvement on the existing bonnet polishing would provide a vital steppingstone towards building a fully autonomous manufacturing cell in a market of continual economic growth. The experiments in this thesis analysed the capabilities of two shear-thickening slurry systems: (1) polyethylene glycol with silica nanoparticle suspension, and (2) water and cornstarch suspension. Both slurry systems demonstrated the ability at mitigating existing surface ripples. Looking at power spectral density graphs, polyethylene glycol slurries reduced the power of the mid-spatial frequencies by ~50% and cornstarch suspension slurries by 60-90%. Experiments of a novel polishing approach are also reported in this thesis to rotate a precessed bonnet at a predetermined working distance above the workpiece surface. The rapidly rotating tool draws in the shear-thickening slurry through the gap to stiffen the fluid for polishing. This technique demonstrated material removal capabilities using cornstarch suspension slurries at a working distance of 1.0-1.5mm. The volumetric removal rate from this process is ~5% of that of contact bonnet polishing, so this aligns more as a finishing process. This polishing technique was given the term rheological bonnet finishing. The rheological properties of cornstarch suspension slurries were tested using a rheometer and modelled through CFD simulation. Using the empirical rheological data, polishing simulations of the rheological bonnet finishing process were modelled in Ansys to analyse the effects of various input parameters such as working distance, tool headspeed, precess angle, and slurry viscosity
Spherical tangible user interfaces in mixed reality
The popularity of virtual reality (VR) and augmented reality (AR) has grown rapidly in recent years, both in academia and commercial applications. This is rooted in technological advances and affordable head-mounted displays (HMDs). Whether in games or professional applications, HMDs allow for immersive audio-visual experiences that transport users to compelling digital worlds or convincingly augment the real world.
However, as true to life as these experiences have become in a visual and auditory sense, the question remains how we can model interaction with these virtual environments in an equally natural way. Solutions providing intuitive tangible interaction would bear the potential to fundamentally make the mixed reality (MR) spectrum more accessible, especially for novice users. Research on tangible user interfaces (TUIs) has pursued this goal by coupling virtual to real-world objects. Tangible interaction has been shown to provide significant advantages for numerous use cases. Spherical tangible user interfaces (STUIs) present a special case of these devices, mainly due to their ability to fully embody any spherical virtual content. In general, spherical devices increasingly transition from mere technology demonstrators to usable multi-modal interfaces.
For this dissertation, we explore the application of STUIs in MR environments primarily by comparing them to state-of-the-art input techniques in four different contexts. Thus, investigating the questions of embodiment, overall user performance, and the ability of STUIs relying on their shape alone to support complex interaction techniques.
First, we examine how spherical devices can embody immersive visualizations. In an initial study, we test the practicality of a tracked sphere embodying three kinds of visualizations. We examine simulated multi-touch interaction on a spherical surface and compare two different sphere sizes to VR controllers. Results confirmed our prototype's viability and indicate improved pattern recognition and advantages for the smaller sphere.
Second, to further substantiate VR as a prototyping technology, we demonstrate how a large tangible spherical display can be simulated in VR. We show how VR can fundamentally extend the capabilities of real spherical displays by adding physical rotation to a simulated multi-touch surface. After a first study evaluating the general viability of simulating such a display in VR, our second study revealed the superiority of a rotating spherical display.
Third, we present a concept for a spherical input device for tangible AR (TAR). We show how such a device can provide basic object manipulation capabilities utilizing two different modes and compare it to controller techniques with increasing hardware complexity. Our results show that our button-less sphere-based technique is only outperformed by a mode-less controller variant that uses physical buttons and a touchpad.
Fourth, to study the intrinsic problem of VR locomotion, we explore two opposing approaches: a continuous and a discrete technique. For the first, we demonstrate a spherical locomotion device supporting two different locomotion paradigms that propel a user's first-person avatar accordingly. We found that a position control paradigm applied to a sphere performed mostly superior in comparison to button-supported controller interaction. For discrete locomotion, we evaluate the concept of a spherical world in miniature (SWIM) used for avatar teleportation in a large virtual environment. Results showed that users subjectively preferred the sphere-based technique over regular controllers and on average, achieved lower task times and higher accuracy.
To conclude the thesis, we discuss our findings, insights, and subsequent contribution to our central research questions to derive recommendations for designing techniques based on spherical input devices and an outlook on the future development of spherical devices in the mixed reality spectrum.Die PopularitĂ€t von Virtual Reality (VR) und Augmented Reality (AR) hat in den letzten Jahren rasant zugenommen, sowohl im akademischen Bereich als auch bei kommerziellen Anwendungen. Dies ist in erster Linie auf technologische Fortschritte und erschwingliche Head-Mounted Displays (HMDs) zurĂŒckzufĂŒhren. Ob in Spielen oder professionellen Anwendungen, HMDs ermöglichen immersive audiovisuelle Erfahrungen, die uns in fesselnde digitale Welten versetzen oder die reale Welt ĂŒberzeugend erweitern.
Doch so lebensecht diese Erfahrungen in visueller und auditiver Hinsicht geworden sind, so bleibt doch die Frage, wie die Interaktion mit diesen virtuellen Umgebungen auf ebenso natĂŒrliche Weise gestaltet werden kann. Lösungen, die eine intuitive, greifbare Interaktion ermöglichen, hĂ€tten das Potenzial, das Spektrum der Mixed Reality (MR) fundamental zugĂ€nglicher zu machen, insbesondere fĂŒr Unerfahrene. Die Forschung an Tangible User Interfaces (TUIs) hat dieses Ziel durch das Koppeln virtueller und realer Objekte verfolgt und so hat sich gezeigt, dass greifbare Interaktion fĂŒr zahlreiche AnwendungsfĂ€lle signifikante Vorteile bietet. Spherical Tangible User Interfaces (STUIs) stellen einen Spezialfall von greifbaren Interfaces dar, insbesondere aufgrund ihrer FĂ€higkeit, beliebige sphĂ€rische virtuelle Inhalte vollstĂ€ndig verkörpern zu können. Generell entwickeln sich sphĂ€rische GerĂ€te zunehmend von reinen Technologiedemonstratoren zu nutzbaren multimodalen Instrumenten, die auf eine breite Palette von Interaktionstechniken zurĂŒckgreifen können.
Diese Dissertation untersucht primĂ€r die Anwendung von STUIs in MR-Umgebungen durch einen Vergleich mit State-of-the-Art-Eingabetechniken in vier verschiedenen Kontexten. Dies ermöglicht die Erforschung der Bedeutung der Verkörperung virtueller Objekte, der Benutzerleistung im Allgemeinen und der FĂ€higkeit von STUIs, die sich lediglich auf ihre Form verlassen, komplexe Interaktionstechniken zu unterstĂŒtzen.
ZunĂ€chst erforschen wir, wie sphĂ€rische GerĂ€te immersive Visualisierungen verkörpern können. Eine erste Studie ergrĂŒndet die Praxistauglichkeit einer einfach konstruierten, getrackten Kugel, die drei Arten von Visualisierungen verkörpert. Wir testen simulierte Multi-Touch-Interaktion auf einer sphĂ€rischen OberflĂ€che und vergleichen zwei KugelgröĂen mit VR-Controllern. Die Ergebnisse bestĂ€tigten die Praxistauglichkeit des Prototyps und deuten auf verbesserte Mustererkennung sowie Vorteile fĂŒr die kleinere Kugel hin.
Zweitens, um die ValiditĂ€t von VR als Prototyping-Technologie zu bekrĂ€ftigen, demonstrieren wir, wie ein groĂes, anfassbares sphĂ€risches Display in VR simuliert werden kann. Es zeigt sich, wie VR die Möglichkeiten realer sphĂ€rischer Displays substantiell erweitern kann, indem eine simulierte Multi-Touch-OberflĂ€che um die FĂ€higkeit der physischen Rotation ergĂ€nzt wird. Nach einer ersten Studie, die die generelle Machbarkeit der Simulation eines solchen Displays in VR evaluiert, zeigte eine zweite Studie die Ăberlegenheit des drehbaren sphĂ€rischen Displays.
Drittens prĂ€sentiert diese Arbeit ein Konzept fĂŒr ein sphĂ€risches EingabegerĂ€t fĂŒr Tangible AR (TAR). Wir zeigen, wie ein solches Werkzeug grundlegende FĂ€higkeiten zur Objektmanipulation unter Verwendung von zwei verschiedenen Modi bereitstellen kann und vergleichen es mit Eingabetechniken deren HardwarekomplexitĂ€t zunehmend steigt. Unsere Ergebnisse zeigen, dass die kugelbasierte Technik, die ohne Knöpfe auskommt, nur von einer Controller-Variante ĂŒbertroffen wird, die physische Knöpfe und ein Touchpad verwendet und somit nicht auf unterschiedliche Modi angewiesen ist.
Viertens, um das intrinsische Problem der Fortbewegung in VR zu erforschen, untersuchen wir zwei gegensĂ€tzliche AnsĂ€tze: eine kontinuierliche und eine diskrete Technik. FĂŒr die erste prĂ€sentieren wir ein sphĂ€risches EingabegerĂ€t zur Fortbewegung, das zwei verschiedene Paradigmen unterstĂŒtzt, die einen First-Person-Avatar entsprechend bewegen. Es zeigte sich, dass das Paradigma der direkten Positionssteuerung, angewandt auf einen Kugel-Controller, im Vergleich zu regulĂ€rer Controller-Interaktion, die zusĂ€tzlich auf physische Knöpfe zurĂŒckgreifen kann, meist besser abschneidet. Im Bereich der diskreten Fortbewegung evaluieren wir das Konzept einer kugelförmingen Miniaturwelt (Spherical World in Miniature, SWIM), die fĂŒr die Avatar-Teleportation in einer groĂen virtuellen Umgebung verwendet werden kann. Die Ergebnisse zeigten eine subjektive Bevorzugung der kugelbasierten Technik im Vergleich zu regulĂ€ren Controllern und im Durchschnitt eine schnellere Lösung der Aufgaben sowie eine höhere Genauigkeit.
Zum Abschluss der Arbeit diskutieren wir unsere Ergebnisse, Erkenntnisse und die daraus resultierenden BeitrĂ€ge zu unseren zentralen Forschungsfragen, um daraus Empfehlungen fĂŒr die Gestaltung von Techniken auf Basis kugelförmiger EingabegerĂ€te und einen Ausblick auf die mögliche zukĂŒnftige Entwicklung sphĂ€rischer EingabegrĂ€te im Mixed-Reality-Bereich abzuleiten
Conception et calibration de capteurs de mouvement à film diélectrique pour robots souples multi-degrés de liberté
Les robots souples pourraient permettre une interaction homme-robot intrinsĂšquement
sĂ©curitaire car ils sont fabriquĂ©s de matĂ©riaux dĂ©formables. Les capteurs de mouvement adaptĂ©s aux robots souples doivent ĂȘtre compatibles avec les mĂ©canismes dĂ©formables comportant plusieurs degrĂ©s de libertĂ© (DDL) retrouvĂ©s sur les robots souples. Le projet de recherche propose des outils de conception pour ce nouveau genre de systĂšmes de capteurs de mouvement. Pour dĂ©montrer ces outils, un systĂšme de capteurs est conçu pour un robot souple existant servant pour des interventions chirurgicales guidĂ©es par imagerie. De plus, un algorithme de calibration utilisant des techniques dâapprentissage automatique est proposĂ© pour les capteurs Ă plusieurs DDL. Un prototype du systĂšme de capteurs conçu est fabriquĂ© et installĂ© sur le robot souple existant. Lors dâessais expĂ©rimentaux, le prototype du systĂšme de capteurs atteint une prĂ©cision moyenne de 0.3 mm et minimale de 1.2 mm
Micro- and sub-microstructuring and characterisation of technical surfaces by means of laser direct writing including a novel approach for laser beam profiling
Within recent years, numerous fields of engineering, like mechanics, optics and
electronics, have been influenced and revolutionised by the technique of microand
nano-structuring. For example, special optical elements for beam shaping,
surface structures for the reduction of friction or modern "lab on chip" devices
have been produced.
Within this thesis a universal system has been developed facilitating the
production of such structured surfaces with dimensions down to 500 nm. This
system is not only capable of structuring surfaces by means of lithographic
processes; it further allows the inspection of surfaces by scanning their
topography.
To realise such a system, two different technologies have been evaluated: Scanning
Near-field Optical Lithography (SNOL), a very sophisticated technique which uses a
thin fibre tip to expose a photo resist-covered surface, and confocal scanning
technology. Here, the confocal scanning is accomplished using an adapted optical
component, the optical pickup unit (OPU), from a gaming console, which turned
out to be the most suitable and cost-efficient solution for the realisation of this
system. Several test series have been carried out during this work, to verify the
performance of the confocal system, both to structure photo resist surfaces and to
characterise unknown surfaces.
This present work will show the ability of the developed system to produce
structures down to the sub-micron range and to characterise unknown surfaces
with sub- micron precision. Various patterns have been written into photo resistcoated
substrates to structure their surface. Beginning with diffractive optical
elements (DOE) for beam shaping, followed by Dammann gratings for twodimensional
beam shaping and optical gratings for light guidance as well as
producing technical surfaces imitating the properties of sharkskin or simple micromechanical
structures, the developed confocal system has shown itself to be
flexible and widely-applicable.
IV
During the development of the confocal system, a strong need for a beam profiling
system analysing the light beam diverging from the OPU, was recognised. Due to
the fact that no commercially available system was capable of characterising beam
sizes within the range of the diffraction limit, a novel method for beam profiling
was invented. This method makes use of the fibre tips already applied within the
SNOL system, producing tomographical scans of the beam spot
Roadmap on Label-Free Super-resolution Imaging
Label-free super-resolution (LFSR) imaging relies on light-scattering processes in nanoscale objects without a need for fluorescent (FL) staining required in super-resolved FL microscopy. The objectives of this Roadmap are to present a comprehensive vision of the developments, the state-of-the-art in this field, and to discuss the resolution boundaries and hurdles that need to be overcome to break the classical diffraction limit of the label-free imaging. The scope of this Roadmap spans from the advanced interference detection techniques, where the diffraction-limited lateral resolution is combined with unsurpassed axial and temporal resolution, to techniques with true lateral super-resolution capability that are based on understanding resolution as an information science problem, on using novel structured illumination, near-field scanning, and nonlinear optics approaches, and on designing superlenses based on nanoplasmonics, metamaterials, transformation optics, and microsphere-assisted approaches. To this end, this Roadmap brings under the same umbrella researchers from the physics and biomedical optics communities in which such studies have often been developing separately. The ultimate intent of this paper is to create a vision for the current and future developments of LFSR imaging based on its physical mechanisms and to create a great opening for the series of articles in this field.Peer reviewe
The design and implementation of a stellar gyroscope for accurate angular rate estimation on CubeSats
Thesis (MEng)--Stellenbosch University, 2015.ENGLISH ABSTRACT: Until recently, small form factor satellites (such as CubeSats) relied almost exclusively
on micro electromechanical system (MEMS) gyroscopes for attitude propagation
purposes. Unfortunately, the nature of MEMS gyros is such that they exhibit a
measure of bias drift. This drift must be compensated for, a task for which stellar
gyros have proved to be exceptionally useful.
Stellar gyros are satellite subsystems capable of inferring three-axis attitude propagation
based on the displacement of a series of stars between successive image frames.
Their design is analogous to that of star trackers, using many of the same hardware
designs and algorithms. When used in combination with MEMS solutions,
stellar gyros provide not only a means for drift compensation, but also a measure of
functional redundancy with regard to attitude propagation.
This thesis presents the design and implementation of stellar gyroscope algorithms
capable of operating alongside existing orientation algorithms on traditional star
tracker hardware. The CubeStar star tracker module is used as development platform.
The proposed stellar gyro solution retains CubeStarâs existing star extraction
algorithms, while investigating alternative methods for star centroiding in addition to
the existing centre of gravity (CoG) approach. A dynamic proximity based matching
algorithm is suggested to determine star correspondence between image frames.
Finally, various well established estimation algorithms are considered for the purpose
of rate determination, including singular value decomposition (SVD), Davenportâs
q-Method and weighted least-squares (WLS).
An initial evaluation of the proposed algorithms is made based on simulations in the
MATLAB environment. Simulation results are confirmed through means of practical
tests, performed on a simulated night sky in a controlled environment. With a focus
on low angular rates, results suggest reliable operation up to ±1 deg/s in all three
axes of rotation. As expected for stellar imaging solutions, angular rates estimated
in both cross-boresight axes are almost an order of magnitude more accurate than
the corresponding estimates in the boresight axis itself.AFRIKAANSE OPSOMMING: Mikrosatelliete, soos CubeSats, het tot onlangs byna uitsluitlik op mikro elektromeganiese
(MEMS) vibrerende struktuur giroskope staatgemaak vir die meet van
hoeksnelhede. Ongelukkig is die aard van MEMS giroskope sodanig dat hierdie
metings afsette toon wat al hoe verder van hul werklike waardes verskuif. Daar moet
gekompenseer word vir hierdie verskuiwing, ân taak waarvoor stergiroskope besonder
geskik is.
Sterrebeeld gebaseerde giroskope (of bloot gewoon stergiroskope) is satelliet substelsels
wat daartoe in staat is om ân satelliet se oriĂ«ntasie in drie dimensies te propageer deur
gebruik te maak van die verplasing van ân reeks sterre tussen twee opeenvolgende
beelde. Hulle ontwerp in terme van beide hardeware en algoritmes is soortgelyk aan
dié van stervolger kameras. Stergiroskope kan ook saam met MEMS toestelle gebruik
word. Hulle verskaf beide ân metode om te kompenseer vir verskuiwings in MEMS
metings sowel as ân funksionele alternatief met betrekking tot hoekafskatting.
Hierdie tesis beskryf die ontwerp en implementering van ster giroskoop algoritmes wat
in staat is om hand-in-hand met bestaande oriëntasie algoritmes op tradisionele ster
volger hardeware te funksioneer. Die CubeStar stervolger module is as ontwikkelings
platform gebruik. Die beoogde stergiroskoop ontwerp behou CubeStar se bestaande
ster ontginnings algoritmes. Verskeie metodes benewens die bestaande swaartepunt
benadering word wel ondersoek vir die bepaling van ster sentroĂŻedes. Die korrespondensie
tussen opeenvolgende sterbeelde word bepaal deur middel van ân dinamiese
nabyheid gebaseerde passings algoritme. Ten slotte word verskeie algoritmes oorweeg
vir die afskatting van ân satelliet se hoeksnelhede. Dit sluit in enkelvoud waarde
ontbinding (SVD), Davenport se q-metode en ân geweegte kleinste kwadraat (WLS)
benadering.
Die voorgestelde algoritmes is ge-evalueer op grond van simulasies in die MATLAB
omgewing. Praktiese toetse is uitgevoer op ân gesimuleerde sterrebeeld om simulasie
resultate te bevestig. Met ân fokus op lae hoeksnelhede dui resultate op betroubare
afskatting teen hoeksnelhede van tot ±1 grade/s rondom al drie rotasie-asse. Soos
verwag van ster kameras is die hoekafskattings rondom die transversale asse ân orde
meer akkuraat as die ooreenstemmende afskattings rondom die optiese as