Vibration monitoring is widely used to determine the condition of various mechanical systems. Traditionally a transducer is attached to the structure under investigation and the vibration signal recorded. This signal is then processed and the required information extracted from the signal. With epicyclic gearboxes this traditional approach is not advisable. This is in part due to the fact that the planet gears rotate internally on a planet carrier. Special techniques are therefore required to extract a viable data signal from the measured vibration signal. These techniques require an additional post-processing step in which a compiled data signal is extracted from the measured data signal. This work investigates the possibility of mounting transducers internally on the rotating planet carrier. Mounting transducers at this location removes the relative motion seen in traditional measurement techniques. An epicyclic gearbox is modified to facilitate the internal mounting of the accelerometers. A number of implementation problems are highlighted and solutions to these problems are discussed. A large portion of the work is dedicated to implementing and qualifying the epicyclic time synchronous averaging technique which is traditionally used to evaluate epicyclic gearboxes. As this technique forms the basis to evaluate the data obtained from internal measurements, it is of fundamental importance that the technique is implemented correctly. It is shown that vibration data can be reliably measured internally, by means of accelerometers mounted on the planet carrier. The internally measured data is compared to data obtained by traditional techniques and shown to be equally adept in detecting deterioration of a planet gear tooth. Simple condition indicators were used to compare the vibration data of the two techniques. It was seen that the data obtained from the internally mounted accelerometers was equally, and in certain cases, slightly more sensitive to planet gear damage. This implies that the technique can be used successfully to evaluate epicyclic gearbox damage. There are a number of practical implementation problems that will limit the use of this technique. As the technology becomes available to transmit measured vibration signals wirelessly, the application of the internal measurement technique will become more viable. A preliminary investigation was also launched into the relationship between a planetary gearbox with a single planet gear and one with multiple planet gears. It is illustrated that vibration data, measured from a gearbox containing a single planet gear, shows an increased sensitivity to planet gear damage. Although a special test rig might be required, the increased sensitivity to damage can provide a method to test planet gears in critical applications such as aircraft gearboxes. Copyright / Dissertation (MEng)--University of Pretoria, 2010. / Mechanical and Aeronautical Engineering / unrestricted

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La réalité augmentée consiste à superposer à l’environnement réel des informations virtuelles générées numériquement. Parmi les systèmes qui permettent de réaliser un tel mélange, nous nous intéressons dans ce travail aux systèmes de visualisation en réalité augmentée liés à la tête de l’utilisateur, généralement appelés HMD (Head-Mounted Display). Dans un tel système, la superposition des informations virtuelles à l’environnement réel peut être réalisée par un élément optique (optique mélangeuse) positionné devant l’oeil de l’utilisateur. La conception d’un système HMD est cependant une tâche complexe. En effet, la proximité de la tête introduit des contraintes géométriques importantes et provoque des déformations (aberrations) des images virtuelles. Généralement, ces aberrations sont minimisées de façon simultanée sur l’ensemble du champ de vision de l’utilisateur. Cette optimisation du système se fait néanmoins soit au détriment de la compacité ce qui s’avère problématique pour le confort d’utilisation du HMD, soit au détriment de la qualité de l’image au centre du champ de vision. Nous proposons dans ce travail ce qui nous semble être une nouvelle approche de conception en associant un modulateur spatial de lumière (SLM) et une optique mélangeuse diffractive statique. L’image virtuelle est créée séquentiellement point par point en modifiant l’incidence sous laquelle on éclaire l’optique mélangeuse. Le SLM permet d’adapter dynamiquement la correction des aberrations associées à chaque point virtuel. Nous avons dans un premier temps défini la fonction optique de l’optique mélangeuse diffractive et le champ de vision maximal (18° x 18°) qu’il est possible d’atteindre en respectant les contraintes géométriques d’utilisation. Nous avons pu alors montrer théoriquement que l’approche proposée permet d’atteindre une qualité d’image optimale sur l’ensemble du champ de vision. Les fonctions de correction sont réalisables avec les technologies actuelles. La validation expérimentale de ces résultats a été réalisée. / Augmented reality (AR) supplements the real world with computer-generated objects that appear to coexist in the same space as the real world. Among the systems that achieve such a mixture, we focus in this work on augmented reality head mounted displays (HMD). In such a system, the superimposition of virtual information to the real environment can be achieved by a combiner. This combiner is an optical element positioned in front of the eye of the user. It is a complex challenge to design an HMD. They generally have off-axis configurations because of the proximity of the head of the user. The optical system therefore suffers for high geometrical aberrations as Gauss conditions are not respected. Usually, these aberrations are minimized simultaneously on the entire field of vision of the user. However, such a simultaneous approach implies either a loss of compactness or a loss of the quality of the image. We propose in this work a novel design for an augmented reality HMD. We studied an optical system associating a dynamic element (spatial light modulator) and a static diffractive combiner. The virtual image is created sequentially point by point by illuminating the diffractive combiner with different incidences. The SLM allows to adapt, in a dynamical way, the correction of the aberrations associated to each position of the virtual point. We initially defined the phase transfer function of the diffractive combiner. We showed that it is possible to reach a 18° by 18° field of view considering the geometrical constraints. Then, we proved theoretically that the proposed approach can achieve an optimal image quality over the entire field of view. We demonstrated that it is possible to realize the correction functions with current technologies. The experimental validation of the results was performed.

It is widely considered that in-store shopping is a repetitive yet vital activity in human life. People are accustomed to making shopping lists on a piece of paper or on their mobile phones, or more commonly, memorizing the list in their minds. However, people tend to forget the items they want to buy if they cannot write them down immediately when they have the shopping demand, let alone keeping the list in their minds. Some work has started to help people resolve this problem, yet most of them are based on smartphones and are focused on riching add-on functions of the shopping list applications instead of allowing real-time recording. Namely, these existing shopping-list systems cannot let people record items and satisfy their information needs while minimizing the intervention to their ongoing activities. In this study, a new Augmented Reality (AR) solution named AR Shopping List was proposed. It is a smart-glasses application that allows users to add items at any time and place and with arbitrary input formats (photos, videos, and voice to text). We conducted semi-structured interviews with twelve participants aged from 20 to 30 by letting them experience the AR Shopping List app themselves on Microsoft HoloLens (1st gen). Our interviews reveal that the AR Shopping List realizes real-time recording, and therefore releases people’s hands from touching a physical device when making a list. It also shows the app’s potential in helping people reduce the opportunity of forgetting something to buy, as well as shopping more targeted. Furthermore, this research sheds light on future designs on smart-glasses applications for assisting people in recording and remembering items, building a new memorizing habit, and further functioning as people’s working memory expansion. / Trots att det är repetitivt att handla i butik så anses det allmänt vara en vital del av vardagen. Det är vanligt förekommande att inköpslistor skrivs ner på ett paper eller på en mobiltelefon, men även att memorera inköpslistor är vanligt förekommande. Att memorera en inköpslista är dock svårt, och det är ofta viktigt att skriva ner varor som behöver införskaffas, så fort behovet att köpa varorna uppstår. Några metoder har tagits fram för att lösa detta problem, men de flesta av dessa metoder är till för att användas på mobiltelefoner och fokuserar främst på att lägga till funktioner för att skapa avancerade inköpslistor, istället för att tillåta skapandet av listor i realtid. Framförallt så kan de existerande systemen för att skapa inköpslistor inte registrera varor och tillfredsställa användarens andra behov, utan att användarens pågående aktiviteter påverkas. I denna studie presenteras en ny lösning kallad AR Shopping List baserad på Augmented Reality (AR). Det är en applikation för smarta glasögon som tillåter användare att lägga till varor när som helst och var som helst, med godtyckligt format (bilder, videor och text genererad med rösten). Vi genomförde semistrukturerade intervjuer där tolv deltagare i åldrarna 20 till 30 år, fick prova på att använda AR Shopping List applikationen på en Microsoft HoloLens (första generationen). Våra intervjuer visar att AR Shopping List kan skapa inköpslistor i realtid, utan att användarna behöver använda en fysisk enhet. De visar även potentialen som applikationen har för att minska antalet tillfällen där varor som behöver köpas in glöms bort, samt potentialen för mer riktade inköp. Dessutom belyser denna rapport designen för framtida applikationer till smarta glasögon för att underlätta skapandet av inköpslistor, bygga upp nya minnesvanor, och för att utöka det aktiva minnet.

Die Simulation von Prozessen ist schon immer ein zentraler Bestandteil bei der Entwicklung von Produkten. Durch sie können Aussagen über das Produkt gewonnen und Vorgänge verändert, erneuert oder auch verbessert werden. Virtual Reality spielt in diesem Zusammenhang eine immer größere Rolle.

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The process of capturing solid geometry as 3 dimensional data requires the use of laser based reverse engineering hardware, known as a digitizer. Many digitizers exist as articulated coordinate measuring machines augmented with a laser, which forces the operator into many postures that are not ergonomically sound, particularly in the operator's upper body. This study analyzes the traditional method of laser digitizing using modern methods and technologies. An alternative user interface using a head-mounted monocular display is hypothesized and evaluated.

Nowadays mid-range smartphones have enough computational power to run simultaneous location and mapping (SLAM) algorithms that, together with their onboard inertial sensors makes them capable of position and rotation tracking. Based on this, Google and Apple have released their own respective software development kits (SDKs) that allow smartphones to run augmented reality applications using six degrees of freedom tracking. However, this same approach could be implemented to virtual reality head-mounted-display (HMD) based on smartphones, but current virtual reality SDKs only offer rotational tracking. In this study the positional tracking technology used for augmented reality mobile applications has been implemented in a virtual reality head-mounted-display only powered by a smartphone by combining virtual and augmented reality SDKs. Compatibility issues between SDKs have been faced to develop a working prototype. An objective and controlled measurement study has been conducted that included 34.200 measurements, to test the accuracy, precision and jitter tracking of the protype against the Oculus Rift, a dedicated virtual reality system. Results show that the developed prototype offers a decent tracking precision and accuracy in optimal conditions. It was concluded to be highly dependent on the camera view. Although, jitter presented the opposite behavior, being dependent to the device used but independent on the camera view. In its optimal conditions, user studies demonstrated that the prototype was capable of offering the same tracking performance feeling as the Oculus Rift although jitter was quite noticeable, and a common user complain. Further studies are proposed that can improve the tracking performance of the prototype by filtering jitter and using two or more cameras with a different angular to correlate feature points and obtain a wider view of the environment were the prototype is used. / Idag har mellanklass-smartphones tillräckligt med beräkningskapacitet för att simultant köra lokalisering och kartläggnings(SLAM) algoritmer tillsammans med deras tröghetssensorer ombord, vilket gör att de kan positionera och rotera spårning. Baserat på det här så har Google och Apple släppt sina egna respektive programvaror (SDK) som gör att smartphones kan köra ökade realitetsapplikationer med sex graders frihetsspårning. Emellertid kan samma tillvägagångssätt implementeras till virtuell verklighet på en huvudmonterad display (HMD) baserat på smartphones, men nuvarande VR SDK erbjuder endast rotationsspårning. I denna studie så har positionell spårningsteknik som används för AR i mobila applikationer implementerats i ett VRheadset som endast drivs av en smartphone genom att kombinera VR och ARSDKs. Kompatibilitetsproblem mellan SDKs har resulterat i att utveckla en fungerande prototyp. En objektiv och kontrollerad mätstudie har genomförts som inkluderade 34.200 mätningar, för att testa noggrannheten, precision och jitterspårning av protyp mot Oculus Rift, ett dedikerat virtuellt verklighetssystem. Resultat visar att den utvecklade prototypen ger en anständig spårningsprecision och noggrannhet i optimala betingelser. Denna slutsats var mycket beroende av kameravy. Även om jitter presenterade det motsatta beteendet, beroende på vilken enhet som används men oberoende av kamerans vy. I sina optimala förhållanden visade användarstudier att prototypen kunde erbjuda samma spårningsförmåga som Oculus Rift, även om jitter var ganska märkbar, och en vanlig användares klagomål. Ytterligare studier föreslås som kan förbättra prototypens spårningsprestanda genom att filtrera jitter och använder två eller flera kameror med en annan vinkling till att korrelera funktionspunkter och få en bredare bild av miljön var prototypen används.

Die Rehabilitation von Gangstörungen bei Patienten mit MS und Schlaganfall erfolgt häufig mithilfe eines konventionellen Laufbandtrainings. Einige Studien haben bereits gezeigt, dass durch eine Erweiterung dieses Trainings um eine virtuelle Realität die Motivation der Patienten gesteigert und die Therapieergebnisse verbessert werden können. In der vorliegenden Studie wurde eine immersive VR-Anwendung (unter Verwendung eines HMD) für die Gangrehabilitation von Patienten evaluiert. Hierbei wurden ihre Anwendbarkeit und Akzeptanz geprüft sowie ihre Kurzzeiteffekte mit einer semi-immersiven Präsentation (unter Verwendung eines Monitors) und mit einem konventionellen Laufbandtraining ohne VR verglichen. Der Fokus lag insbesondere auf der Untersuchung der Anwendbarkeit beider Systeme und der Auswirkungen auf die Laufgeschwindigkeit und Motivation der Benutzer. Im Rahmen einer Studie mit Innersubjekt-Design nahmen zunächst 36 gesunde Teilnehmer und anschließend 14 Patienten mit MS oder Schlaganfall an drei experimentellen Bedingungen (VR über HMD, VR über Monitor, Laufbandtraining ohne VR) teil. Sowohl in der Studie mit gesunden Teilnehmern als auch in der Patientenstudie zeigte sich in der HMD-Bedingung eine höhere Laufgeschwindigkeit als beim Laufbandtraining ohne VR und in der Monitor-Bedingung. Die gesunden Studienteilnehmer berichteten über eine höhere Motivation nach der HMD-Bedingung als nach den anderen Bedingungen. Es traten in beiden Gruppen keine Nebenwirkungen im Sinne einer Simulator Sickness auf und es wurden auch keine Erhöhungen der Herzfrequenzen nach den VR-Bedingungen detektiert. Die Bewertungen des Präsenzerlebens waren in beiden Gruppen in der HMD-Bedingung höher als in der Monitor-Bedingung. Beide VR-Bedingungen erhielten hohe Bewertungen für die Benutzerfreundlichkeit. Die meisten der gesunden Teilnehmer (89 %) und Patienten (71 %) präferierten das HMD-basierte Laufbandtraining unter den drei Trainingsformen und die meisten Patienten könnten sich vorstellen, es häufiger zu nutzen. Mit der vorliegenden Studie wurde eine strukturierte Evaluation der Anwendbarkeit eines immersiven VR-Systems für die Gangrehabilitation geprüft und dieses erstmals in den direkten Vergleich zu einem semi-immersiven System und einem konventionellen Training ohne VR gesetzt. Die Studie bestätigte die Praktikabilität der Kombination eines Laufbandtrainings mit immersiver VR. Aufgrund ihrer hohen Benutzerfreundlichkeit und der geringen Nebenwirkungen scheint diese Trainingsform besonders für Patienten geeignet zu sein, um deren Trainingsmotivation und Trainingserfolge, wie z. B. die Laufgeschwindigkeit, zu steigern. Da immersive VR-Systeme allerdings nach wie vor spezifische technische Installationsprozeduren erfordern, sollte für die spezifische klinische Anwendung eine Kosten-Nutzen-Bewertung erfolgen. / Rehabilitation of gait disorders in patients with MS and stroke is often done with the help of conventional treadmill training. Some studies have already shown that extending this training with virtual reality can increase patient motivation and improve therapy outcomes. In the present study, an immersive VR application (using an HMD) was evaluated for gait rehabilitation of patients. Here, its applicability and acceptability were tested, and its short-term effects were compared with a semi-immersive presentation (using a monitor) and with conventional treadmill training without VR. In particular, the focus was on investigating the applicability of both systems and the effects on user walking speed and motivation. In a study using a within-subjects design, first 36 healthy participants and then 14 patients with MS or stroke participated in three experimental conditions (VR via HMD, VR via monitor, treadmill training without VR). In both the healthy participant study and the patient study, the HMD condition showed a higher walking speed than the treadmill training without VR and the monitor condition. The healthy study participants reported higher motivation after the HMD condition than after the other conditions. No side effects in terms of simulator sickness occurred in either group, and no increases in heart rates were detected after the VR conditions. Presence experience ratings were higher in both groups in the HMD condition than in the monitor condition. Both VR conditions received high ratings for usability. Most of the healthy participants (89%) and patients (71%) preferred the HMD-based treadmill training among the three training modalities, and most patients could imagine using it more often. The present study tested a structured evaluation of the applicability of an immersive VR system for gait rehabilitation and, for the first time, compared it directly with a semi-immersive system and conventional training without VR. The study confirmed the practicability of combining treadmill training with immersive VR. Due to its high usability and low side effects, this form of training seems to be particularly suitable for patients to increase their training motivation and training success, such as walking speed. However, immersive VR systems still require specific technical installation procedures, so a cost-benefit assessment should be performed for the specific clinical application.

Interacting with a Virtual Environment (VE) generally requires the user to correctly perceive the relative position and orientation of virtual objects. For applications requiring interaction in personal space, the user may also need to accurately judge the position of the virtual object relative to that of a real object, for example, a virtual button and the user's real hand. This is difficult since VEs generally only provide a subset of the cues experienced in the real world. Complicating matters further, VEs presented by currently available visual displays may be inaccurate or distorted due to technological limitations. Fundamental physiological and psychological aspects of vision as they pertain to the task of object manipulation were thoroughly reviewed. Other sensory modalities--proprioception, haptics, and audition--and their cross-interactions with each other and with vision are briefly discussed. Visual display technologies, the primary component of any VE, were canvassed and compared. Current applications and research were gathered and categorized by different VE types and object interaction techniques. While object interaction research abounds in the literature, pockets of research gaps remain. Direct, dexterous, manual interaction with virtual objects in Mixed Reality (MR), where the real, seen hand accurately and effectively interacts with virtual objects, has not yet been fully quantified. An experimental test bed was designed to provide the highest accuracy attainable for salient visual cues in personal space. Optical alignment and user calibration were carefully performed. The test bed accommodated the full continuum of VE types and sensory modalities for comprehensive comparison studies. Experimental designs included two sets, each measuring depth perception and object interaction. The first set addressed the extreme end points of the Reality-Virtuality (R-V) continuum--Immersive Virtual Environment (IVE) and Reality Environment (RE). This validated, linked, and extended several previous research findings, using one common test bed and participant pool. The results provided a proven method and solid reference points for further research. The second set of experiments leveraged the first to explore the full R-V spectrum and included additional, relevant sensory modalities. It consisted of two full-factorial experiments providing for rich data and key insights into the effect of each type of environment and each modality on accuracy and timeliness of virtual object interaction. The empirical results clearly showed that mean depth perception error in personal space was less than four millimeters whether the stimuli presented were real, virtual, or mixed. Likewise, mean error for the simple task of pushing a button was less than four millimeters whether the button was real or virtual. Mean task completion time was less than one second. Key to the high accuracy and quick task performance time observed was the correct presentation of the visual cues, including occlusion, stereoscopy, accommodation, and convergence. With performance results already near optimal level with accurate visual cues presented, adding proprioception, audio, and haptic cues did not significantly improve performance. Recommendations for future research include enhancement of the visual display and further experiments with more complex tasks and additional control variables.