no abstract available / Dissertation (LLM)--University of Pretoria, 2013. / Public Law / unrestricted

The purpose of this thesis is to design, develop, implement and test a novel soft-switching inverter topology suitable for switched reluctance motor drives. Present research being done in the field of switched reluctance motor drive inverters, including soft-switching inverters, is discussed. The novel topology is presented and the principle of operation is described in detail. The validity of the topology is verified through simulation. The various components of the system are designed and the hardware implementation is presented. Experiments carried out to verify the operation of this inverter are explained. Results are presented and comparison is made between hard switching and soft switching inverter topologies. Conclusions are drawn regarding the effectiveness of the proposed topology. / Master of Science

INTRODUCTION: Cephalometric soft tissue findings have shown correlation with pharyngeal width. Facial photographic analysis of patients with Obstructive Sleep Apnea (OSA) shows an increase in width and flatness of the midface. However, three-dimensional facial soft tissue morphology of children with OSA has not been studied. OBJECTIVE: The objective of the current study was to evaluate the association between facial morphology, upper airway volume, Polysomnography (PSG), and Pediatric Sleep Questionnaire (PSQ) findings in children with OSA versus controls. MATERIAL AND METHODS: The sample included de-identified pre-treatment Cone-beam Computed Tomography images, PSG and PSQ results of 36 children (mean age 6.8 ± 2.8) from one pediatric dental practice. Three-dimensional facial soft tissue landmarks were digitized using Mimics v.20 software. Upper airway volume was segmented into right nasal cavity (RNC), left nasal cavity (LNC), nasopharynx (NP), oropharynx (OP), and hypopharynx (HP). Apnea Hypopnea Index (AHI), Respiratory Disturbance Index (RDI) scores and Pediatric sleep questionnaire (PSQ) values were correlated with soft tissue measurements (a modified Farkas anthropometric analysis) and upper airway volumes using Pearson’s correlation. Student’s T-test was used to evaluate the difference between facial soft tissue measurements of children with obstructive sleep apnea (OSA) versus the control group. RESULTS: Experimental versus control: Polysomnography findings: Apnea/Hipopnea Index and Respiratory Disturbance Index were statistically higher in obstructive sleep apnea children compared to controls (p=<.0001, 0.0001), and lowest oxygen percentage SpO2 was significantly lower (p=0.006). Airway volume findings: Right nasal cavity was statistically larger in obstructive sleep apnea children compared to controls (p=0.04). Soft tissue findings: Exocanthus right to midsagittal plane, Exocanthus right and Exocanthus left, and Soft tissue orbitale right to midsagittal plane were smaller in obstructive sleep apnea children compared to controls (p=0.01, 0.02, 0.03). Experimental group results: Transverse. Nose: Bialar distance was positively correlated to right nasal cavity and nasopharynx, and negatively correlated to hypopharynx, Apnea/Hipopnea Index, and Respiratory Disturbance Index. Lips: Chelion Right and Left, and Crista Philtri Right and Left were positively correlated to NasoPharynx. Anteroposterior. Most of nose and lips measurements were positively correlated to Right Nasal Cavity and negatively correlated to Respiratory Disturbance Index and low oxygen percentage SpO2. Vertical. Nose measurements were positively correlated to NasoPharynx. Lips measurements were positively correlated to NasoPharynx and OroPharynx and negatively correlated to low oxygen percentage SpO2. Control group result: Transverse. Nose: Nostril Base Right to midsagittal was positively correlated to NasoPharynx and average oxygen percentage SpO2 and negatively correlated to Respiratory Disturbance Index. ProNasale to Nostril Base Right and Nostril Base Left was negatively correlate to Pediatric Sleep Questionnaire. Lips: Crista Philtri Right to midsagittal and Chelion Right to midsagittal plane were positively correlated to NasoPharynx and average oxygen percentage SpO2. Anteroposterior. Nose measurements were positively correlated to Right Nasal Cavity, NasoPharynx, OroPharynx, and HypoPharynx and negatively correlated to Pediatric Sleep Questionnaire. Lips measurements were positively correlated to Right Nasal Cavity, NasoPharynx. And OroPharynx. Vertical. Most nose and lips measurements were positively correlated to Right Nasal Cavity, NasoPharynx, OroPharynx, and HypoPharynx, and negatively correlated to Apnea/Hypopnea Index and Respiratory Disturbance Index. CONCLUSION: It can be concluded that for the experimental group wider faces at the level of the eyes, nose and lips indicated increased upper airway volumes, decreased Polysomnography, and Pediatric Sleep Questionnaire values. Moreover, more forward position of the nose and lips in relation to the coronal plane were linked to increased nasal airway volume and decreased Polysomnography values. Finally, long-faced individuals displayed higher volume of the upper airway and decreased oxygen saturation levels. In regards to the control group, anteroposterior measurements positively correlated to all airway compartments and negatively correlated to Pediatric Sleep Questionnaire values. Vertically, longer faces exhibit larger airway compartments and decreased Polysomnography values.

This thesis describes the concept of programmable materials with tunable physical properties applicable to soft robots. We present these materials for three major applications in soft robotics: sensing, actuation, and robotic manipulation. The strain sensors recognize the internal stimuli in a soft robot, whereas the conductors collect the sensors’ signals to the control part. In the first part, we want to develop both stretchable strain sensors and conductors from a single material by programming a nanowire network’s electrical property, which we achieve through Electrical Welding (e-welding). We demonstrate the transformation of a Silver Nanowire (AgNW)-polymer sponge from a strain sensor to a stretchable conductor through e-welding. Using this method, we produced a soft hybrid e-skin having both a sensor and conductor from a single material. In the second part, we propose new active actuation solutions by obtaining quick, tunable pressure inside a soft material that we achieve through a liquid-gas phase transition of a stored liquid using an efficient electrode. We discuss the significant design variables to improve the performance and propose a new design for the electrodes, for enhancing actuation speed. We propose using low voltage equipment to trigger the phase transition to produce compact actuation technology for portable applications. Using this method, we produced a portable soft gripper. In the third and last part, we want to develop a simple robotic manipulation technology using a single-chambered soft body instead of a multi-chambered system. We propose using on-demand stiffness change in soft material to control the shape change of a single-chambered soft body. For this, we introduce a new concept of a stiffness tunable hybrid fiber: a fiber with stiff and soft parts connected in a series. We demonstrate a substantial change in membrane stiffness in the fiber through locking/unlocking of the soft part of the fiber. We integrated these fibers into a pneumatically operated single-chambered soft body to control its stiffness for on-demand shape change. If applied together, these three concepts could result in a fully printable, cheap, light, and easily controllable new generation soft robots with augmented functionalities.

Lwethulwa ukufeza izidingo zeziqu zo-buDokotela kunzululwazi emnyangweni weZilimi zabomdabu eNyunivesithi yakwaZulu. = Submitted in fulfilment of the requirements of the Doctor of Philosophy in the Department of African Languages, at the University of Zululand, South Africa, 2009. / Ekudukeni kokukhuluma okuqanjwa ngabantu kutholakala imilozi idwanguza idinga ongayeqela ukuze ithole umthamo wayo ongalandelwa. Njengoba iqanjwe ngabantu kumele igcinwe futhi ithole ukunonophaliswa ngoba ayipheli olimini lwabantu kuphela nje ukuthi banokungayinaki abantu kepha bayayenza. Le milozi eqanjwa ngokuzwakala endlebeni njengesitho esingagcwali kulokho esikulalelayo senza iqambeke futhi ibe nobumtoti obuhamba nolimi lwesiZulu. Isahluko sokuqala sidingida, sihlahle indlela ebalulekile emsebenzini ozoqhutshwa ngayo. Umehluko kuso isahluko uveziwe wokuthi inhloboni yemilozi okubhalwa ngayo. Umklamo uqoqile uveza amanoni ngemilozi azothintwa kwashiywa amanangananga angadingekile ukuze indlela icace. Isahluko sikubeka kucace ukuthi ngobani labo abazohlomula behlomula uma benzenjani. Ongcweti nochwepheshe badaluliwe kuso isahluko ngenhloso yokunonophalisa umsebenzi ukuze umsebenzi ufakaziseke. Isahluko sesibili siveza imilozi ngokwahlukana kwayo njengoba itholakala yenzeka kuyo imvelo ezungeze abantu. Kulesi sahluko kutholakala imilozi eyenziwa izinyoni kuphela. Kwazona zehlukanisiwe ngokwehlukana kwazo njengoba zivela kubantu zibakhombisa izimo ezingefani. Lezo zimo kuyinhlanhla, amashwa nokubika imvula. Kuso isahluko kutholakala nokuthuthukisa ulimi ngalokho imilozi ekuqukethe nokuyinkulumobuthule edalulwa ukwenza kwezinyoni okufundwa ngezikwenzayo. Isahluko sesithathu siqukethe imilozi eyenziwa izilwane ezingafuyiwe zasendle. Lezo kube indlovu, ibhubesi, ubhejane nezinye. Zehlukaniswe ngenhloso yokuthi zona zinokuthile okudinga kutholakale kuzo kucoshelelwe ukuthi zinokubaluleka okungakanani esintwini esingamaZulu. Siqhubekile isahluko sethula imibuzo engazo nanenkulumobuthule eyethulwa yizo izilwane lezi. Ukubaluleka kwazo kuthinte nobumqoka bazo ekuqambekeni kwezibongo zaMakhosi nokuzimbandakanya kwazo ngobungozi bazo kwabangaMakhosi oselwa. Isahluko sesine sethula imilozi eqondene nemikhando yabantu. Siqalisa ngokuchaza okudinga kwazeke ngendlela imilozi engahlaziywa ngayo. Isahluko sethule ukuhlaziya ngoba imilozi ifuna ukukhanyisa kafuphi okutholakala kuyo okunobunkondlo. Ukubumbeka kwayo ngaphandle nangaphakathi nokunye. Isahluko sisaqhubeka nokuveza ongoti abasibona isidingo sokuthola ubunkondlo ngayo. Asigcini isahluko ngokuthola lokho kepha siqhubeka naleyo milozi eqondene nemikhando yabantu nalokho ekwenza kubo. Imilozi eqondene nemikhando kungasatshalalwa nakho konke okukhandwe ngabantu, kwakhethwa leyo enobumqoka kubo. Isahluko sesihlanu sidalula okuhlaziywa ngemilozi ukuthi ubumqoka bayo esintwini esingamaZulu ithini. Amaphuzu alandelene aveza ubumqoka nokubaluleka kwemilozi nabonakale ngokucwaningwa kwayo ngenkathi izihloko zicutshungulwa. Siqhubekile isahluko sesihlanu saveza izincomo ezithamundwe zalandelana ngenhloso yokugqamisa okutholakala kulahleka olimini lwesiZulu. Isiphetho sisonge konke okwethuliwe sabuye sanenezela ngokuphosa inselelo kulabo abangabukela phansi ubumtoti obutholakala ngemilozi.

Soft pneumatic actuators produce more energy output per unit mass than conventional rigid pneumatic actuators and are safer for applications involving physical contact with users or fragile objects. The design, modelling, fabrication, and optimization of origami-inspired soft pneumatic actuators (OSPA) are investigated in this thesis. A novel fabrication method employing heat shrinkable polymers conforming to reusable 3D printed molds is proposed. It is rapid, cost-effective, and more systematic than prior OSPA fabrication methods. A nonlinear finite-element analysis (FEA) model for an OSPA based on the accordion crease pattern is developed for predicting the actuator's folding behavior and blocked force. The model includes a nonlinear hyperelastic model of the heat shrink material’s behaviour (obtained empirically) and nonlinear frictional contacts. It is validated with experimental results and is shown to predict the blocked force with a 5.7% maximum error. Prototypes of two OSPA designs (accordion and Yoshimura patterns) are fabricated. Isometric, isobaric, isotonic, and cyclic fatigue tests are performed on the accordion pattern OSPA. The tests demonstrate that it can lift more than 124 times its own weight, and had no decrease in performance after 150,000 contraction/extension cycles with a payload of 2 kg. This durability is superior to existing OSPA. Lastly, a FEA model-based design optimization approach is proposed. A multi-objective genetic algorithm (MOGA) is used to find the origami design parameters that maximize the accordion pattern OSPA's work output. The optimized design is validated experimentally. Although this research focuses on the accordion pattern OSPA, the proposed fabrication, modelling and optimization approaches can be easily adapted to other OSPA designs. In addition to linear force and motion, these actuators can be combined to produce different motions, e.g., a pair of actuators can be connected by a cable to a pulley in an agonist-antagonist arrangement to produce a bidirectional rotary actuator. / Thesis / Doctor of Philosophy (PhD) / Soft pneumatic actuators are lighter than conventional rigid pneumatic actuators and are safer for applications involving physical contact with users or fragile objects. The design, modelling, fabrication, and optimization of origami-inspired soft pneumatic actuators (OSPA) are investigated. A novel fabrication method that is rapid, cost-effective, and more systematic than prior OSPA fabrication methods is proposed. A nonlinear model is developed and shown to predict the OSPA’s output force with a 5.7% maximum error. An extensive series of tests are performed on OSPA prototypes. The accordion pattern OSPA can lift more than 124 times its own weight, and had no decrease in performance after 150,000 contraction/extension cycles with a payload of 2 kg. This durability is superior to existing OSPA. Lastly, a model-based approach for optimizing the OSPA design is presented and validated experimentally. The proposed fabrication, modelling and optimization approaches can be easily adapted to other OSPA designs.

Stable Frank-Kasper spherical packing phases have been observed in a wide variety of soft-condensed matter systems, but the universality of these phases is not well understood. Recently, it was shown that the Frank-Kasper $\sigma$ and A15 phases are stable in the well-known Landau-Brazovskii (LB) model. In this work we consider the $\sigma$ and A15 phases, as well as the Laves C14 and C15 phases, and show that none of these is stable in the Ohta-Kawasaki (OK) model, which is another widely studied Ginzburg-Landau theory. The LB and OK models differ only in their quadratic coefficients. We conduct a thorough investigation of the role that this coefficient plays in stabilizing the complex phases. We uncover generic principles linking the functional form of the coefficient in reciprocal space with the stability of the complex phases. A Ginzburg-Landau theory for a for diblock copolymer system with a conformational asymmetry parameter is derived, but the complex phases are not found to be stable in this model. We also consider a Ginzburg-Landau theory for a system of hard spheres interacting via a pairwise short-range attractive, long-range repulsive (SALR) potential, and use our framework to demonstrate how the parameters in the potential influence the stability of the Frank-Kasper phases. Taken together, these results provide insight into the universal mechanisms that underlie the formation of the complex spherical packing phases in soft condensed matter. / Thesis / Doctor of Philosophy (PhD) / Soft condensed matter physics is the study of soft, deformable materials, such as soap bubbles, foams, and plastics. Many different soft matter systems undergo a fascinating phenomenon known as self-assembly, wherein the constituent particles spontaneously arrange themselves to form various ordered structures. In particular, the spherical packing phases appear when the particles first cluster into spherical aggregates, which then pack into larger arrangements. This sort of self-assembly is interesting because many different spherical arrangements are observed, including the complex spherical packing phases (also known as the Frank-Kasper phases). The fact that these complex phases appear in many different types of materials is not well understood. In this thesis we use a model known as the Ginzburg-Landau theory to ask which of these arrangements will form in a given system, and why. We uncover generic features of the Ginzburg-Landau theory that control which spherical packing phases appear, and we connect these features to several specific systems. These results provide insight into the mechanisms behind the formation of the complex spherical packing phases in a diverse range of systems.

Recently, a number of spherical packing phases belonging to the class of Frank-Kasper (F-K) phases have been observed in a wide range of soft matter systems, including block copolymers, ionic surfactants, liquid crystalline dendrimers, and giant surfactants. Although their emergence in such systems has been conjectured to be due to a competition between mesodomain sphericity and incompressibility, we lack a description of a precise and general mechanism underlying the formation of F-K phases in soft matter systems. In this work, we consider the two most common F-K phases found in soft matter systems, the σ and A15 phases, and study their stability in the context of a well-known Landau model known as the Landau-Brazovskii model. This model has been applied to systems ranging from block copolymers to liquid crystals. We find that the phase behavior of the Landau-Brazovskii model is controlled only by two parameters, rather than by three parameters, as was suggested by previous works. We also find that the Landau-Brazovksii phase diagram contains regions in which the σ or A15 phase is the most stable among a set of candidate phases. The fact that such a simple model can predict these complex phases provides some insight into the question of why the occurrence of the Frank-Kasper phases in soft matter is so widespread. / Thesis / Master of Science (MSc) / Soft condensed matter physics studies the properties of materials that easily deform, such as soap, gel and plastic. Many of these materials can self-assemble into various fascinating ordered structures. One particularly complex class of structures, found in a wide range of soft materials, is the class of Frank-Kasper phases. Frank-Kasper phases in soft materials have potential applications in fields such as photonics, so their formation in these materials is particularly interesting. However, it is not well understood why the Frank-Kasper structures occur in so many soft materials. We investigate this problem, and show that the occurrence of these structures might be described by a very simple mathematical model known as the Landau-Brazovskii model. The fact that such a simple model can predict the complex Frank-Kasper phases provides insight into the origin of the widespread nature of the occurrence of Frank-Kasper phases in soft materials.

The work presented in this thesis focuses on the study of viscous and elastic polymer thin films in initially unstable configurations. The systems are driven to flow viscously or deform elastically to minimize their free energy. Since these experiments take place on length scales at which gravity does not play a role, the physics is governed purely by surface tension and viscosity in the case of fluid films, or elasticity in the case of rigid films. It is also possible to combine hydrodynamics and elasticity, for example, a viscous film that flows in response to the bending energy of an elastic perturbation, or an elastic film deformed by the capillarity or flow of a fluid. Viscous flow in thin polymer films is studied in a system which is free-standing in air, meaning it has two fluid-air interfaces. Cylindrical holes are formed part way through a nano-scale polymer film, creating an unstable geometry with dissimilar surface areas at the two interfaces. When heated above its glass transition temperature, surface tension drives the film to flow to minimize its total excess surface area. The evolution is first dominated by fast vertical flow, which equilibrates Laplace pressure through the film by forming symmetric holes at each interface. Slow horizontal flow then becomes dominant, which continually reduces excess surface area by filling in the holes. A novel atomic force microscopy method is developed to monitor the two interfaces of a film as they flow, allowing the total free energy evolution of the system to be measured. The results agree with a hydrodynamic model developed to describe both stages of flow. Elastic instabilities, where a rigid film deforms in response to geometrical confinement, are studied in a free-standing bilayer system consisting of a thin film on a pre-strained elastic substrate. These instabilities include sinusoidal wrinkling of the capping film, or, since the entire bilayer is free-standing, global buckling, where the entire system deforms out-of-plane. The transition between wrinkling and buckling is found to depend on the thickness and moduli ratios of the films, as well as the pre-strain in the substrate. A simple model shows good agreement with experiments. Finally, the interaction between elasticity and viscosity is studied by measuring the flow of a viscous fluid perturbation driven by the bending energy of a rigid capping film. The experimental scaling of the perturbation size is in agreement with the theoretical prediction in the large perturbation limit. / Thesis / Doctor of Science (PhD)

Soft robotic systems have recently been considered as a new approach that is in principle better suited for tasks where safety and adaptability are important. That is because soft materials are inherently compliant and resilient in the event of collisions. They are also lightweight and can be low-cost; in general, soft robots have the potential to achieve many tasks that were not previously possible with traditional robotic systems. In this paper, we propose a new manufacturing process for creating multi-chambered pneumatic actuators and robots. We focus on using fabric as the primary structural material, but plastic films can be used instead of textiles as well. We introduce two different methods to create layered bellows actuators, which can be made with a heat press machine or in an oven. We also describe origami-like actuators with possible corner structures. Moreover, the fabrication process permits the creation of soft and soft/rigid hybrid robotic systems, and enables the easy integration of sensors into these robots. We analyze various textiles that are possibly used with this method, and model bellows actuators including operating force, restoring force, and estimated geometry with multiple bellows. We then demonstrate the process by showing a bellows actuator with an embedded sensor and other fabricated structures and robots. We next present a new design of a multi-DOF soft/rigid hybrid robotic manipulator. It contains a revolute actuator and several roll-pitch actuators which are arranged in series. To control the manipulator, we use a new variant of the piece-wise constant curvature (PCC) model. The robot can be controlled using forward and inverse kinematics with embedded inertial measurement units (IMUs). A bellows actuator, which is a subcomponent of the manipulator, is modeled with a variable-stiffness spring, and we use the model to predict the behavior of the actuator. With the model, the roll-pitch actuator stiffnesses are measured in all directions through applying forces and torques. The stiffness is used to predict the behavior of the end effector. The robotic system introduced achieved errors of less than 5% when compared to the models, and positioning accuracies of better than 1cm. / Doctor of Philosophy / Future robotic systems are expected to deal with many tasks in real-world environments. The natural environment is highly unpredictable and unstructured, making manipulation and locomotion challenging for robots. Robots need to rely on adaptability, reconfigurability, and safety. Soft robotic systems have recently been considered as a new approach that is in principle better suited for tasks where safety and adaptability are important. That is because soft materials are inherently compliant and resilient in the event of collisions. They are also lightweight and can be low-cost; in general, soft robots have the potential to achieve many tasks that were not previously possible with traditional robotic systems. In this paper, we propose a new manufacturing process for creating multi-chambered pneumatic actuators and robots. We focus on using fabric as the primary structural material, but plastic films can be used instead of textiles as well. We introduce two different methods to create layered bellows actuators, which can be made with a heat press machine or household iron, or in an oven. We also describe origami-like actuators with possible corner structures. Moreover, the fabrication process permits the creation of soft and soft/rigid hybrid robotic systems, and enables the easy integration of sensors into these robots. We analyze various textiles that can be used with this method, and make models of bellows actuators including their operating force, restoring force, and estimated geometry with multiple bellows. We then demonstrate the process by showing a bellows actuator with an embedded sensor and other fabricated structures and robots. We next present a new design of a multi-DOF soft/rigid hybrid robotic manipulator. It contains a revolute actuator and several roll-pitch actuators which are arranged in series. To control the manipulator, we use a new variant of the piece-wise constant curvature (PCC) model. The robot can be controlled using forward and inverse kinematics with embedded inertial measurement units (IMUs). A bellows actuator, which is a subcomponent of the manipulator, is modeled with a variable-stiffness spring, and we use the model to predict the behavior of the actuator. With the model, the roll-pitch actuator stiffnesses are measured in all directions through applying forces and torques. The stiffness is used to predict the behavior of the end effector.