The overall purpose of this research is to develop a real-time ultrasound based system for controlling robotic weld quality by monitoring the weld pool. The concept of real-time weld quality control is quite broad, and this work focuses on weld penetration depth monitoring and control with laser ultrasonics. The weld penetration depth is one of the most important geometric parameters that define the weld quality, hence remains a key control quantity. This research focuses on the implementation and optimization of the laser phased array generation unit and the development of signal analysis algorithms to extract the weld penetration depth information from the received ultrasonic signals. The system developed is based on using the phased array technique to generate ultrasound, and an Electro-Magnetic Acoustic Transducer (EMAT) as a receiver. The generated ultrasound propagates through the weld pool and is picked up by the EMAT. A transient FE model is built to predict the temperature distribution during welding. An analytical model is developed to understand the propagation of ultrasound during real-time welding and the curved rays are numerically traced. The cross-correlation technique has been applied to estimate the Time-of-Flight (ToF) of the ultrasound. The ToF is then correlated to the measured weld penetration depth. The analytical relationship between the ToF and penetration depth, obtained by a ray-tracing algorithm and geometric analysis, matches the experimental results. The real-time weld sensing technique developed is efficient and can readily be deployed for commercial applications. The successful completion of this research will remove the major obstacle to a fully automated robotic welding process. An on-line welding monitoring and control system will facilitate mass production characterized by consistency, high quality, and low costs. Such a system will increase the precision of the welding process, resulting in quality control of the weld beads. Moreover, in-process control will relieve human operators of tedious, repetitive, and hazardous welding tasks, thus reducing welding-related injures.

For photographers to capture good pictures of their subjects, the lighting conditions must be taken into account and adjusted for accordingly. The same holds true for a satellite attempting to photograph another object in space: it must know the lighting conditions to adjust camera settings and position itself properly to take the best photograph. This thesis presents a photon mapping based algorithm to compute a physically accurate representation of the illumination of objects in orbit around the Earth, taking into account the effects that cause refraction in the atmosphere. I also discuss the assumptions that I have made to utilize the algorithm in an interactive 3D visualization tool, which I implemented to view the illumination on objects at arbitrary positions in space. Finally, I show that the photon mapping method offers improvements over simpler methods of computing illumination.

In the last decade, computational power, memory bandwidth and programmability capabilities of graphics processing units (GPU) have rapidly evolved. Therefore, many researches have been performed to use GPUs in advanced graphics rendering. Because of its high degree of parallelism, ray tracing has been one of the rst algorithms studied on GPUs. However, the rendering of large scenes with ray tracing can easily exceed the GPU&#039 / s memory capacity. The algorithm proposed in this work uses a data parallel approach where the scene is partitioned and assigned to CPU-GPU couples in a cluster to overcome this problem. Our algorithm focuses on ray casting which is a special case of ray tracing mainly used in visualization of volumetric data. CPUs are pretty ecient in ow control and branching while GPUs are very fast performing intense oating point operations. Using these facts, the GPUs in the cluster are assigned the task of performing ray casting while the CPUs are responsible for traversing the rays. In the end, we were able to visualize large scenes successfully by utilizing CPU-GPU couples eectively and observed that the performance is highly dependent on the viewing angle as a result of load imbalance.

Standardmäßig erfolgt die Datenaufbereitung der Neutronenwirkungsquerschnitte für Reaktorkernrechnungen mit 2D-Zellcodes. Ziel dieser Arbeit war es, einen 3D-Zellcode zu entwickeln, mit diesem Code 3D-Effekte zu untersuchen und die Notwendigkeit einer 3D-Datenaufbereitung der Neutronenwirkungsquerschnitte zu bewerten. Zur Berechnung des Neutronentransports wurde die Methode der Erststoßwahrscheinlichkeiten, die mit der Ray-Tracing-Methode berechnet werden, gewählt. Die mathematischen Algorithmen wurden in den 2D/3D-Zellcode TransRay umgesetzt. Für den Geometrieteil des Programms wurde das Geometriemodul eines Monte-Carlo-Codes genutzt. Das Ray-Tracing in 3D wurde auf Grund der hohen Rechenzeiten parallelisiert. Das Programm TransRay wurde an 2D-Testaufgaben verifiziert. Für einen Druckwasser-Referenzreaktor wurden folgende 3D-Probleme untersucht: Ein teilweise eingetauchter Regelstab und Void (Vakuum oder Dampf) um einen Brennstab als Modell einer Dampfblase. Alle Probleme wurden zum Vergleich auch mit den Programmen HELIOS (2D) und MCNP (3D) nachgerechnet. Die Abhängigkeit des Multiplikationsfaktors und der gemittelten Zweigruppenquerschnitte von der Eintauchtiefe des Regelstabes bzw. von der Höhe der Dampfblase wurden untersucht. Die 3D berechneten Zweigruppenquerschnitte wurden mit drei üblichen Näherungen verglichen: Lineare Interpolation, Interpolation mit Flusswichtung und Homogenisierung. Am 3D-Problem des Regelstabes zeigte sich, dass die Interpolation mit Flusswichtung eine gute Näherung ist. Demnach ist hier eine 3D-Datenaufbereitung nicht notwendig. Beim Testfall des einzelnen Brennstabs, der von Void umgeben ist, erwiesen sich die drei Näherungen für die Zweigruppenquerschnitte als unzureichend. Demnach ist eine 3D-Datenaufbereitung notwendig. Die einzelne Brennstabzelle mit Void kann als der Grenzfall eines Reaktors angesehen werden, in dem sich eine Phasengrenzfläche herausgebildet hat.

Standardmäßig erfolgt die Datenaufbereitung der Neutronenwirkungsquerschnitte für Reaktorkernrechnungen mit 2D-Zellcodes. Ziel dieser Arbeit war es, einen 3D-Zellcode zu entwickeln, mit diesem Code 3D-Effekte zu untersuchen und die Notwendigkeit einer 3D-Datenaufbereitung der Neutronenwirkungsquerschnitte zu bewerten. Zur Berechnung des Neutronentransports wurde die Methode der Erststoßwahrscheinlichkeiten, die mit der Ray-Tracing-Methode berechnet werden, gewählt. Die mathematischen Algorithmen wurden in den 2D/3D-Zellcode TransRay umgesetzt. Für den Geometrieteil des Programms wurde das Geometriemodul eines Monte-Carlo-Codes genutzt. Das Ray-Tracing wurde auf Grund der hohen Rechenzeiten parallelisiert. Das Programm TransRay wurde an 2D-Testaufgaben verifiziert. Für einen Druckwasser-Referenzreaktor wurden folgende 3D-Probleme untersucht: Ein teilweise eingetauchter Regelstab und Void (bzw. Moderator mit geringerer Dichte) um einen Brennstab als Modell einer Dampfblase. Alle Probleme wurden zum Vergleich auch mit den Programmen HELIOS (2D) und MCNP (3D) nachgerechnet. Die Abhängigkeit des Multiplikationsfaktors und der gemittelten Zweigruppenquerschnitte von der Eintauchtiefe des Regelstabes bzw. von der Höhe der Dampfblase wurden untersucht. Die 3D berechneten Zweigruppenquerschnitte wurden mit drei üblichen Näherungen verglichen: linearer Interpolation, Interpolation mit Flusswichtung und Homogenisierung. Am 3D-Problem des Regelstabes zeigte sich, dass die Interpolation mit Flusswichtung eine gute Näherung ist. Demnach ist hier eine 3D-Datenaufbereitung nicht notwendig. Beim Testfall des einzelnen Brennstabs, der von Void (bzw. Moderator geringerer Dichte) umgeben ist, erwiesen sich die drei Näherungen für die Zweigruppenquerschnitte als unzureichend. Demnach ist eine 3D-Datenaufbereitung notwendig. Die einzelne Brennstabzelle mit Void kann als der Grenzfall eines Reaktors angesehen werden, in dem sich eine Phasengrenzfläche herausgebildet hat.

The optical design of a LED illuminator and camera imaging system were studied for potential use in a small medical "robotic type" probe to be used for minimally invasive abdominal surgery. Beam shaping optical reflectors were studied to increase the intensity distribution of the LED beam directed toward a close-by target surface. A CMOS/CCD camera and lens was used to image the targeted area. In addition, extensive optical ray tracing simulations were made to predict the intensity patterns. The experimental measurements and ray tracing simulations were in good agreement, and indicated that 20 degree cone reflectors for the LED sources and appropriate micro-lens/CCD chip imaging optics should provide a useful image at a working distance of about 5 cm.

Computational stereo estimates 3D structure by analyzing visual changes between two or more passive images of a scene that are captured from different viewpoints. It is a key enabler for ubiquitous autonomous systems, large-scale surveying, virtual reality, and improved techniques for compression, tracking, and object recognition. The fact that computational stereo is an under-constrained inverse problem causes many challenges. Its computational and memory requirements are high. Typical heuristics and assumptions, used to constrain solutions or reduce computation, prevent treatment of key realities such as reflection, translucency, ambient lighting changes, or moving objects in the scene. As a result, a general solution is lacking. Stochastic models are common in computational stereo, but stochastic algorithms are severely under-represented. In this dissertation I present two stochastic algorithms and demonstrate their advantages over deterministic approaches. I first present the Quality-Efficient Stochastic Sampling (QUESS) approach. QUESS reduces the number of match quality function evaluations needed to estimate dense stereo correspondences. This facilitates the use of complex quality metrics or metrics that take unique values at non-integer disparities. QUESS is shown to outperform two competing approaches, and to have more attractive memory and scaling properties than approaches based on exhaustive sampling. I then present a second novel approach based on the Hough transform and extend it with distributed ray tracing (DRT). DRT is a stochastic anti-aliasing technique common to computer rendering but which has not been used in computational stereo. I demonstrate that the DRT-enhanced approach outperforms the unenhanced approach, a competing variation that uses re-accumulation in the Hough domain, and another baseline approach. DRT’s advantages are particularly strong for reduced image resolution and/or reduced accumulator matrix resolution. In support of this second approach, I develop two novel variations of the Hough transform that use DRT, and demonstrate that they outperform competing variations on a traditional line segment detection problem. I generalize these two examples to draw broader conclusions, suggest future work, and call for a deeper exploration by the community. Both practical and academic gaps in the state of the art can be reduced by a renewed exploration of stochastic computational stereo techniques. / text

The Scheimpflug principle was recommended as allowing distortion-free imaging; however, a detailed analysis reveals geometrical errors as well as distortions arising from absorption of light along the optical pathway. Correction formulas and factors will be presented and applied to the biometry of the eye. / Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

Basal cell carcinoma is a form of a non-melanoma skin tumour, that commonly forms over the sun exposed regions of the head and neck. Investigation of the rate of occurrence at different sites on face and neck shows considerable variation from site to site. The inner canthus has a disproportionate number when compared to more exposed sites. The eye brow ridge, cheek bone and nose limit the field of view of the inner canthus, thus it is expected to receive less radiation than other more exposed regions. To explain the disproportionate rate, it is hypothesised that a portion of radiation incident onto the eye is reflected to the inner canthus. The aim of this thesis is to investigate the contribution that the radiation reflected off the surface of the eye makes to the overall dose on the inner canthus. The inter reflections between the eye and inner canthus were studied through the use of the ray tracing program Zemax. Zemax was used to trace rays in a non sequential mode incident onto a model eye and periorbital region. To obtain the models of the eye and periorbital region, both magnetic resonance imaging and a casting process was investigated, with the later being superior for our uses. With the model obtained, it was used in a series of three dimensional ray tracing programs. On a macroscopic scale there is a small increase in the irradiance on the inner canthus (2 % over a 1 cm2 area). Peaks of high irradiance (19 % increase in irradiance above direct irradiance) were discovered over the surface when the detector was divided into 200 mm elements. It was concluded that these increases above the direct irradiance in these small regions, increases the possibility of the occurrence of a Basal cell carcinoma. Individual facial geometry, will greatly effect the location and size of these peaks and as a result an experimental method to measure the dose distribution across the inner canthus was proposed. Initially it was planned to use polysulphone film to measure the erythemal dose on the inner canthus. Results from the modelling indicated that any measurements made had to be at a high spatial resolution. Polysulphone film was found to be inadequate for this, due to its large uncertainties. An alternative method was investigated so that a population study could be performed in future studies using visible radiation and high dynamic range images gave a simple and effective clinical assessment tool. The high dynamic range images showed hot spots in the irradiance across the inner canthus agreeing with the model. The small spots of high relative irradiance may not be the only reason for the increased rate in this region. Greater skin sensitivity and absence of sun screen use at this site are other possibilities. It is believed however that the irradiance distribution across the inner canthus on a microscopic scale goes a long way to increasing the risk for certain people.

abstract: Mostly, manufacturing tolerance charts are used these days for manufacturing tolerance transfer but these have the limitation of being one dimensional only. Some research has been undertaken for the three dimensional geometric tolerances but it is too theoretical and yet to be ready for operator level usage. In this research, a new three dimensional model for tolerance transfer in manufacturing process planning is presented that is user friendly in the sense that it is built upon the Coordinate Measuring Machine (CMM) readings that are readily available in any decent manufacturing facility. This model can take care of datum reference change between non orthogonal datums (squeezed datums), non-linearly oriented datums (twisted datums) etc. Graph theoretic approach based upon ACIS, C++ and MFC is laid out to facilitate its implementation for automation of the model. A totally new approach to determining dimensions and tolerances for the manufacturing process plan is also presented. Secondly, a new statistical model for the statistical tolerance analysis based upon joint probability distribution of the trivariate normal distributed variables is presented. 4-D probability Maps have been developed in which the probability value of a point in space is represented by the size of the marker and the associated color. Points inside the part map represent the pass percentage for parts manufactured. The effect of refinement with form and orientation tolerance is highlighted by calculating the change in pass percentage with the pass percentage for size tolerance only. Delaunay triangulation and ray tracing algorithms have been used to automate the process of identifying the points inside and outside the part map. Proof of concept software has been implemented to demonstrate this model and to determine pass percentages for various cases. The model is further extended to assemblies by employing convolution algorithms on two trivariate statistical distributions to arrive at the statistical distribution of the assembly. Map generated by using Minkowski Sum techniques on the individual part maps is superimposed on the probability point cloud resulting from convolution. Delaunay triangulation and ray tracing algorithms are employed to determine the assembleability percentages for the assembly. / Dissertation/Thesis / Ph.D. Mechanical Engineering 2011