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The purpose of this project was to construct a holonomic mobile robot driven with omni wheels. That would enable movement in all degrees of freedom. The finished product was a robot platform within a spherical shell body controlled by input commands defining speed and direction from a wireless communication medium. The platform was iteratively designed and constructed with parts made out of laser cut acrylic plastic. By using omni wheels powered by Direct Current (DC) motors, which will be described further, the holonomic drive could be realized as the wheel hubs were placed on the platform with calculated angles. / Syftet med detta projekt var att konstruera en holonomisk robot, vilket kan uppfyllas med hjälp av omnihjul som kan drivas i samtliga riktningar i planet. Den färdiga produkten blev en robot som placerats i en sfärisk kropp som tar in hastighet- och riktningssignaler från en trådlös kommunikationsmodul. Plattformen, som iterativt designades, laserskärdes ur akrylplast. På den placerades omni-hjul drivna av DC-motorer, vilka möjliggjorde den holonomiska rörelsen

Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The RoboCup offers a research platform to advance robotics and multi-robot cooperation in dynamic environments. This project builds on work previously done to develop a research platform for multi-robot cooperation at Stellenbosch University. This thesis describes the development of an active ball handling system for a robot in the RoboCup Small Size League (SSL). This was achieved by building on the work done in the previous projects. The hardware for the kicker and dribbler mechanisms on the robot were implemented and tested to characterise their capabilities. The kicker was characterised to control the speed at which a ball is kicked and the dribbler for optimal control over a ball. More accurate movement was required and the Proportional Integral and Derivative (PID) controllers for translational and rotational movement on the robot were improved. The test results show an improvement in straight line trajectory tracking when compared to those of the previous controllers. Dribble control sensors were implemented on the robot for successful dribbling by the robot. This resulted in a significant improvement to the dribbling ability of the robot when these sensors are used. This dribbling ability was compared to the dribbling ability of the robot when no feedback was received from the sensors. Lastly a proposed curved trajectory tracking algorithm was tested by combining translational and rotational movement of the robot. This algorithm showed the capabilities of the robot to follow a curved trajectory with the improved translational and rotational controllers. / AFRIKAANSE OPSOMMING: Die RoboCup bied ’n navorsingsplatvorm om robotika en multi-robot samewerking in ’n dinamiese omgewing te bevorder. Hierdie projek bou voort op werk wat reeds gedoen is om ’n navorsingsplatvorm vir multi-robot samewerking aan die Universiteit van Stellenbosch te ontwikkel. Hierdie tesis beskryf die ontwikkeling van ’n aktiewe balhanteringsstelsel vir ’n robot in die RoboCup Klein Liga (KL). Dit is bereik deur voort te bou op die werk wat in vorige projekte gedoen is. Die hardeware vir die skopper- en dribbelmeganismes is geïmplementeer en getoets om hulle vermoëns te karakteriseer. Die skopper is gekenmerk deur die spoed waarteen ’n bal geskop word en die dribbler vir optimale beheer oor ’n bal. Meer akkurate beweging was nodig en die PID-beheerders vir translasie- en rotasiebeweging in die robot is verbeter. Die resultate van die toetse toon ’n verbetering in reguitlynbeweging in vergelyking met dié van die vorige beheerders. Dribbelbeheersensors is in die robot geïmplementeer vir suksesvolle dribbelbeweging deur die robot. Gevolglik is daar ’n aansienlike verbetering in die dribbelvermoë van die robot wanneer hierdie sensors gebruik word. Hierdie dribbelvermoë is vergelyk met die dribbelvermoë wanneer die robot geen terugvoer van die sensors ontvang nie. Laastens is ’n voorgestelde algoritme vir die robot om ’n geboë trajek te volg, getoets. Dit is bereik deur die translasie- en die rotasiebeweging van die robot te kombineer. Hierdie algoritme het die vermoë van die robot om ’n geboë baan te laat volg deur gebruik te maak van die verbeterde translasie- en rotasiebeheerders.

This thesis addresses a number of problems in computer vision, image processing, and geometry processing, and presents novel solutions to these problems. The overarching theme of the techniques presented here is a multi-scale approach, leveraging mathematical tools to represent images and surfaces at different scales, and methods that can be adapted from one type of domain (eg., the plane) to another (eg., the sphere). The main problem addressed in this thesis is known as stereo reconstruction: reconstructing the geometry of a scene or object from two or more images of that scene. We develop novel algorithms to do this, which work for both planar and spherical images. By developing a novel way to formulate the notion of disparity for spherical images, we are able effectively adapt our algorithms from planar to spherical images. Our stereo reconstruction algorithm is based on a novel application of distance transforms to multi-scale matching. We use matching information aggregated over multiple scales, and enforce consistency between these scales using distance transforms. We then show how multiple spherical disparity maps can be efficiently and robustly fused using visibility and other geometric constraints. We then show how the reconstructed point clouds can be used to synthesize a realistic sequence of novel views, images from points of view not captured in the input images, in real-time. Along the way to this result, we address some related problems. For example, multi-scale features can be detected in spherical images by convolving those images with a filterbank, generating an overcomplete spherical wavelet representation of the image from which the multiscale features can be extracted. Convolution of spherical images is much more efficient in the spherical harmonic domain than in the spatial domain. Thus, we develop a GPU implementation for fast spherical harmonic transforms and frequency domain convolutions of spherical images. This tool can also be used to detect multi-scale features on geometric surfaces. When we have a point cloud of a surface of a particular class of object, whether generated by stereo reconstruction or by some other modality, we can use statistics and machine learning to more robustly estimate the surface. If we have at our disposal a database of surfaces of a particular type of object, such as the human face, we can compute statistics over this database to constrain the possible shape a new surface of this type can take. We show how a statistical spherical wavelet shape prior can be used to efficiently and robustly reconstruct a face shape from noisy point cloud data, including stereo data.

[pt] Este trabalho aborda o projeto de antenas omnidirecionais de duplorefletores, onde o refletor principal é obtido a partir de uma geratriz circular. A antena é composta de refletores circularmente simétricos e concêntricos que são alimentados por uma corneta cônica coaxial excitada pelo modo TEM para a produção de polarização vertical. Para realizar este estudo são utilizadas técnicas de síntese e de análise eletromagnética rigorosa. A técnica de análise eletromagnética rigorosa é baseada na associação do Método de Casamento de Modos para representar os campos no interior do alimentador e do Método dos Momentos para solucionar as equações integrais para o campo elétrico e para o campo magnético e determinar a corrente elétrica induzidas sobre as paredes metálicas externas e a amplitude dos modos sobre a abertura da corneta. A técnica de síntese destas antenas é baseada na aplicação dos princípios da Ótica Geométrica para modelar o subrefletor que irá produzir uma distribuição de fase uniforme em uma abertura cônica colocada em frente ao refletor principal com geratriz circular. O estudo exploratório sobre o desempenho destas antenas é dividido em três partes. Na primeira, as soluções fornecidas pela síntese ótica e aproximações para os campos na abertura são utilizadas para identificar configurações de antenas compactas ou que maximizem o ganho ao longo do plano horizontal. Entretanto, pode-se obter uma melhor iluminação da área de cobertura através da inclinação do lobo principal (down tilt). Para reduzir o custo de fabricação de um conjunto de antenas que atendam diferentes áreas de cobertura, pode-se utilizar o mesmo refletor principal e modelar os subrefletores para deslocar a direção de máximo do diagrama. Assim, em uma segunda etapa do estudo paramétrico, são considerados alguns refletores principais, e, para cada um deles, é obtida uma família de subrefletores modelados para deslocar o máximo do diagrama no plano vertical. Esta estratégia se torna efetiva na medida em que o custo de fabricação do subrefletor é menor do que o do refletor principal. Na terceira parte, utilizando o método híbrido composto pelo Método do Casamento de Modos e pelo Método dos Momentos, é feito o modelamento da corneta coaxial TEM com o objetivo de reduzir sua perda de retorno e estender sua banda de operação. Por fim, ainda utilizando este método híbrido, é feita uma análise rigorosa das antenas duplo-refletoras propostas neste trabalho, procurando otimizar o desempenho destas antenas em termos do diagrama de radiação e da perda de retorno. / [en] This work presents a design study of omnidirectional dual-reflector antennas, where the main reflector is obtained from a circular generatrix. The antenna is composed of two concentric circularly symmetric reflectors and it is fed by a coaxial conical horn excited by TEM mode to produce vertical polarization. To obtain the subreflector surface, the study employs a GO synthesis technique to shape the subreflector in order to produce a uniform phase distribution in a conical aperture placed in front of the main reflector. To validate the results, it is employed a rigorous electromagnetic analysis technique based on the association of Mode Matching Technique to represent the fields inside the horn and Method of Moments to solve the integral equations of electric and magnetic fields. The solution of Method of Moments yields the induced electric current on the outer surface of the horn and the amplitude of the modes on the aperture of the horn. The exploratory study is divided in three parts. First, by using the GO approximations for the aperture fields, the geometry parameters are explored to identify compact antenna configurations that maximize the gain along the horizontal plane. However, a more uniform coverage of the ground can be obtained by tilting the main lobe. Thus, in a second step of the parametric study, it is considered a family of designs with the same main reflector and a set of subreflectors that are designed for different tilt angle of main lobe. This strategy is effective to reduce the manufacturing costs of a family of antennas designed to provide different coverage. Third, by using the hybrid method, the TEM coaxial horn is shaped to reduce the return loss and extend its operating band, and, finally, the overall antennas performance is optimized by controlling radiation pattern and return loss.

This thesis addresses a number of problems in computer vision, image processing, and geometry processing, and presents novel solutions to these problems. The overarching theme of the techniques presented here is a multi-scale approach, leveraging mathematical tools to represent images and surfaces at different scales, and methods that can be adapted from one type of domain (eg., the plane) to another (eg., the sphere). The main problem addressed in this thesis is known as stereo reconstruction: reconstructing the geometry of a scene or object from two or more images of that scene. We develop novel algorithms to do this, which work for both planar and spherical images. By developing a novel way to formulate the notion of disparity for spherical images, we are able effectively adapt our algorithms from planar to spherical images. Our stereo reconstruction algorithm is based on a novel application of distance transforms to multi-scale matching. We use matching information aggregated over multiple scales, and enforce consistency between these scales using distance transforms. We then show how multiple spherical disparity maps can be efficiently and robustly fused using visibility and other geometric constraints. We then show how the reconstructed point clouds can be used to synthesize a realistic sequence of novel views, images from points of view not captured in the input images, in real-time. Along the way to this result, we address some related problems. For example, multi-scale features can be detected in spherical images by convolving those images with a filterbank, generating an overcomplete spherical wavelet representation of the image from which the multiscale features can be extracted. Convolution of spherical images is much more efficient in the spherical harmonic domain than in the spatial domain. Thus, we develop a GPU implementation for fast spherical harmonic transforms and frequency domain convolutions of spherical images. This tool can also be used to detect multi-scale features on geometric surfaces. When we have a point cloud of a surface of a particular class of object, whether generated by stereo reconstruction or by some other modality, we can use statistics and machine learning to more robustly estimate the surface. If we have at our disposal a database of surfaces of a particular type of object, such as the human face, we can compute statistics over this database to constrain the possible shape a new surface of this type can take. We show how a statistical spherical wavelet shape prior can be used to efficiently and robustly reconstruct a face shape from noisy point cloud data, including stereo data.

In this thesis, a pipeline for structure-from-motion with mixed camera types is described and methods for the steps of this pipeline to make it effective and automatic are proposed. These steps can be summarized as calibration, feature point matching, epipolar geometry and pose estimation, triangulation and bundle adjustment. We worked with catadioptric omnidirectional and perspective cameras and employed the sphere camera model, which encompasses single-viewpoint catadioptric systems as well as perspective cameras. For calibration of the sphere camera model, a new technique that has the advantage of linear and automatic parameter initialization is proposed. The projection of 3D points on a catadioptric image is represented linearly with a 6x10 projection matrix using lifted coordinates. This projection matrix is computed with an adequate number of 3D-2D correspondences and decomposed to obtain intrinsic and extrinsic parameters. Then, a non-linear optimization is performed to refine the parameters. For feature point matching between hybrid camera images, scale invariant feature transform (SIFT) is employed and a method is proposed to improve the SIFT matching output. With the proposed approach, omnidirectional-perspective matching performance significantly increases to enable automatic point matching. In addition, the use of virtual camera plane (VCP) images is evaluated, which are perspective images produced by unwarping the corresponding region in the omnidirectional image. The hybrid epipolar geometry is estimated using random sample consensus (RANSAC) and alternatives of pose estimation methods are evaluated. A weighting strategy for iterative linear triangulation which improves the structure estimation accuracy is proposed. Finally, multi-view structure-from-motion (SfM) is performed by employing the approach of adding views to the structure one by one. To refine the structure estimated with multiple views, sparse bundle adjustment method is employed with a modification to use the sphere camera model. Experiments on simulated and real images for the proposed approaches are conducted. Also, the results of hybrid multi-view SfM with real images are demonstrated, emphasizing the cases where it is advantageous to use omnidirectional cameras with perspective cameras.

Robots have growing potential to enter the daily lives of people at home, at work, and in cities, for a variety of service, care, and entertainment tasks. However, several challenges currently prevent widespread production and use of such human-centered robots. The goal of this thesis was first to help overcome one of these broad challenges: the lack of basic safety in human-robot physical interactions. Whole-body compliant control algorithms had been previously simulated that could allow safer movement of complex robots, such as humanoids, but no such robots had yet been documented to actually implement these algorithms. Therefore a wheeled humanoid robot "Dreamer" was developed to implement the algorithms and explore additional concepts in human-safe robotics. The lower mobile base part of Dreamer, dubbed "Trikey," is the focus of this work. Trikey was iteratively developed, undergoing cycles of concept generation, design, modeling, fabrication, integration, testing, and refinement. Test results showed that Trikey and Dreamer safely performed movements under whole-body compliant control, which is a novel achievement. Dreamer will be a platform for future research and education in new human-friendly traits and behaviors. Finally, this thesis attempts to address a second broad challenge to advancing the field: the lack of standard design methodology for human-centered robots. Based on the experience of building Trikey and Dreamer, a set of consistent design guidelines and metrics for the field are suggested. They account for the complex nature of such systems, which must address safety, performance, user-friendliness, and the capability for intelligent behavior. / text

The primary goal of this thesis is to develop generic motion and structure algorithms for images taken from constructed scenes by various types of central imaging systems including perspective, fish-eye and catadioptric systems. As-suming that the mapping between the image pixels and their 3D rays in space is known, instead of image planes, we work on image spheres (projection of the images on a unit sphere) which enable us to present points over the entire viewsphere suitable for presenting omnidirectional images. In the first part of this thesis, we develop a generic and simple line matching approach for images taken from constructed scenes under a short baseline motion as well as a fast and original geometric constraint for matching lines in planar constructed scenes insensible to the motion of the camera for all types of centralimages including omnidirectional images.Next, we introduce a unique and efficient way of computing overlap between two segments on perspective images which considerably decreases the over all computational time of a segment-based motion estimation and reconstruction algorithm. Finally in last part of this thesis, we develop a simple motion estima-tion and surface reconstruction algorithm for piecewise planar scenes applicable to all kinds of central images which uses only two images and is based on mini-mum line correspondences.To demonstrate the performance of these algorithms we experiment withvarious real images taken by a simple perspective camera, a fish-eye lens, and two different kinds of paracatadioptric sensors, the first one is a folded catadioptric camera and the second one is a classic paracatadioptric system composed of a parabolic mirror in front of a telecentric lens.

This thesis addresses the pose stabilization of a car-like vehicle using omnidirectional visual feedback. The presented method allows a vehicle to servo to a pre-learnt target pose based on feature bearing angle and range discrepancies between the vehicle's current view of the environment and that seen at the learnt location. The best example of such a task is the use of visual feedback for autonomous parallel-parking of an automobile. Much of the existing work in pose stabilization is highly theoretical in nature with few examples of implementations on 'real' vehicles, let alone vehicles representative of those found in industry. The work in this thesis develops a suitable test platform and implements vision-based pose stabilization techniques. Many of the existing techniques were found to fail due to vehicle steering and velocity loop dynamics, and more significantly, with steering input saturation. A technique which does cope with the characteristics of 'real' vehicles is to divide the task into predefined stages, essentially dividing the state space into sub-manifolds. For a car-like vehicle, the strategy used is to stabilize the vehicle to the line which has the correct orientation and contains the target location. Once on the line, the vehicle then servos to the desired pose. This strategy can accommodate velocity and steering loop dynamics, and input saturation. It can also allow the use of linear control techniques for system analysis and tuning of control gains. To perform pose stabilization, good estimates of vehicle pose are required. A simple, yet robust, method derived from the visual homing literature is to sum the range vectors to all the landmarks in the workspace and divide by the total number of landmarks--the Improved Average Landmark Vector. By subtracting the IALV at the target location from the currently calculated IALV, an estimate of vehicle pose is obtained. In this work, views of the world are provided by an omnidirectional camera, while a magnetic compass provides a reference direction. The landmarks used are red road cones which are segmented from the omnidirectional colour images using a pre-learnt, two-dimensional lookup table of their colour profile. Range to each landmark is estimated using a model of the optics of the system, based on a flat-Earth assumption. A linked-list based method is used to filter the landmarks over time. Complementary filtering techniques, which combine the vision data with vehicle odometry, are used to improve the quality of the measurements.