Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: This thesis gives a cost model for the manufacture of bipolar plates in South Africa. The methods for the manufacture considered are machining, using a micro-milling machine, and compression moulding. The focus of this thesis is on compression moulding. Details of the work done towards developing and validating the models are described, and then the cost models are discussed in detail. The results of the analysis done using the cost model is given with attention paid to the effect of changing design parameters, such as channel size and flow field area, and of the cost of production for both methods over various production volumes. The thesis concludes that compression moulding becomes the better option for production volumes greater than 324 bipolar plates, with a cost that eventually reaches close to R140 per plate for high enough production volumes (over 5000). The cost to produce 1000 plates using compression moulding is estimated at R294 per plate. An increase of the channel size gives a small reduction in the total cost, while the increase in cost with an increase in flow field area is large. / AFRIKAANSE OPSOMMING: Hierdie tesis gee 'n koste-model vir die vervaardiging van bipolêre plate in Suid- Afrika. Die vervaardigingsmetodes wat oorweeg word, is masjinering deur 'n mikro-freesmasjien en persvorming. Die fokus van hierdie tesis is op persvorming. Die besonderhede van die ontwikkeling en validering van die modelle word beskryf, en daarna word die modelle in besonderhede beskryf. Die resultate van 'n analise wat met die koste-model gedoen is, word daarna gegee, met die oorweging van die verandering van ontwerp-parameters soos die vloeikanaalgrootte en vloeiveld-area, en van die koste van vervaardiging vir beide metodes vir verskeie produksievolumes. Die tesis kom tot die slotsom dat persvorming die voorkeurproses is vir produksievolumes groter as 324 bipolêre plate, met 'n koste wat tot naastenby R140 per plaat daal vir hoë produksievolumes (meer as 5000). Die koste om 1000 plate met persvorming te maak, word op R294 per plaat beraam. 'n Toename in kanaalgrootte gee 'n klein vermindering in die totale koste, terwyl die toename in koste groot is wanneer die vloeiveld-area toeneem.

Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: This thesis describes the process of developing a user interface for a seven degree of freedom (DOF), minimally invasive surgical robot. For the first two main stages of the overall project, completed by previous students, a primary slave manipulator (PSM) and a secondary slave manipulator (SSM) were developed. The stage in this thesis concentrates on creating a joystick that can control the combined movement of the PSM and SSM. Background information on the field of robotic surgery, with specific reference to current systems’ user interfaces, is given and the technical aspects of the PSM and SSM are determined. This is followed by the motivation and main objectives of the thesis. Objectives were divided into the main categories of mechanical design, electronic design, control system design and testing. The mechanical design of the joystick progresses through a concept development stage, before a final seven DOF articulated arm design is presented and evaluated based on engineering specifications. Aluminium is used as the construction material; electromagnetic brakes are specified for each joint, leading to the final assembly, which is a constructed joystick fulfilling all requirements. The electronic design implements magnetic rotary encoders for the joystick’s position and orientation tracking as well as designs of the necessary power and control circuitry to enable correct joystick functioning. The interfacing of the PSM and SSM had to enable successful communication capabilities between the master and the slave. Several necessary adjustments were therefore made to the slave system, after which the joystick and robot were electronically interfaced to provide a direct serial communication line. For control system design, the joystick and robot were modelled according to the Denavit-Hartenberg principle, which allows direct relation between the position and orientation of the respective end effectors on the joystick and robot sides. Forward kinematic equations were then applied to the joystick; the desired position and orientation of the robot end effector were determined, and inverse kinematic equations were applied to these data to establish the robot’s joint variables. This stage ended with the development of two operational modes: one where only the SSM motors are controlled in order for the slave to follow the master’s movements, and the other where the PSM’s motors are controlled separately. The simultaneous control of all robot motors could not be demonstrated due to fundamental mechanical flaws in the PSM and SSM designs. Finally, testing was undertaken to demonstrate movement control of the robot by the joystick. The intuitiveness of the product was also tested successfully. The study ends with the presentation of the conclusions, the main conclusions being the successful development and testing of a joystick that controls the movement of a surgical robot, as well as the achievement of all main thesis objectives. / AFRIKAANSE OPSOMMING: Hierdie tesis beskryf die proses vir die ontwikkeling van ’n gebruikerskoppelvlak vir ’n sewevryheidsgraad-, minimaal indringende chirurgiese robot. In die eerste twee hoofstadia van die algehele projek, voltooi deur ander studente, is ’n primêre slaafmanipuleerder (PSM) en ’n sekondêre slaafmanipuleerder (SSM) ontwikkel. Die stadium in hierdie tesis konsentreer op die skep van ’n stuurstok waarmee die gekombineerde beweging van die PSM en SSM beheer kan word. Agtergrondinligting oor die gebied van robotiese chirurgie word verskaf, met spesifieke verwysing na die gebruikerskoppelvlakke van huidige stelsels, en die spesifikasies van die PSM en SSM word vasgestel. Daarna volg die beweegrede sowel as die belangrikste oogmerke van die projek. Die oogmerke is in die hoofafdelings van meganiese ontwerp, elektroniese ontwerp, beheerstelselontwerp en toetsing verdeel. Die meganiese ontwerp van die stuurstok behels ’n konsepontwikkelingstadium, wat uitloop op ’n finale sewevryheidsgraad-ontwerp, wat dan op grond van ingenieurspesifikasies aangebied en beoordeel word. Aluminium word as boumateriaal gebruik; elektromagnetiese remme word vir elke koppeling gespesifiseer, en die finale samestel is ’n gekonstrueerde stuurstok wat aan alle vereistes voldoen. Die elektroniese ontwerp behels die gebruik van magnetiese draaikodeerders om die stuurstok se posisie en oriëntasie te bepaal, sowel as meganismes met die nodige krag- en beheerstroombaanwerk om die stuurstok reg te laat funksioneer. ’n Koppelvlak tussen die PSM en die SSM moes suksesvolle kommunikasie tussen die meester en die slaaf bewerkstellig. Verskeie nodige aanpassings is dus aan die slaafstelsel aangebring, waarna die stuurstok en robot elektronies gekoppel is om ’n direkte reekskommunikasielyn te skep. Vir beheerstelselontwerp is die stuurstok en robot volgens die Denavit- Hartenberg-beginsel gemodelleer, wat ’n direkte verhouding tussen die posisie en oriëntasie van die onderskeie eindpunt-effektors aan die stuurstok- en robotkant daarstel. Voorwaartse kinematiese vergelykings is daarna op die stuurstok toegepas; die gewenste posisie en oriëntasie van die robotiese eindpunt-effektor is bepaal, waarna terugwaartse kinematiese vergelykings op hierdie data toegepas is om die robot se koppelingveranderlikes te bepaal. Hierdie afdeling word afgesluit met die ontwikkeling van twee bedryfsmodusse: een waar slegs die SSM-motore beheer word sodat die slaaf die meester se bewegings kan navolg, en die ander waar die PSM se motore afsonderlik beheer word. Die gelyktydige beheer van al die robotmotore kon nie getoon word nie weens fundamentele meganiese tekortkominge in die PSM- en SSM-ontwerp. Laastens is ’n toets uitgevoer om die bewegingsbeheer van die robot deur die stuurstok te toon. Die intuïtiwiteit van die produk is ook suksesvol getoets. Die studie sluit af met die projekgevolgtrekkings, waarvan die belangrikste die suksesvolle ontwikkeling en toetsing van ’n stuurstok is wat daarin slaag om die beweging van ’n chirurgiese robot te beheer, sowel as die verwesenliking van alle hoofprojekoogmerke.

Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Orthodontics is the eld of dentistry concerned with the treatment of maloc- clusion and anomalies of the dento-facial complex. This thesis is concerned with studying the underlying biomechanical principles of orthodontic tooth movement. It aims to develop a novel treatment approach and an orthodontic appliance to facilitate said approach by employing advanced technologies. A thorough review of the literature is used to form a comprehensive knowledge base pertaining to the factors a ecting orthodontic tooth movement. It is hypothesised that an electromechanical orthodontic appliance could improve treatment by characterising orthodontic cases based on the relationship be- tween the applied mechanical stimulus and the resulting changes to the af- fected structures, which can then be sensed by the appliance. A prototype is built using electronically controllable linear actuators and a custom built force transducer system for measuring orthodontic forces. Electronic circuits are de- veloped to connect the appliance to a USB port and allow it to be controlled from a graphical user interface (GUI). This further facilitates real-time viewing of important orthodontic parameters. Experiments are carried out to evaluate the appliance functionality with regard to the proposed hypothesis. To con- clude, the relevance of the results to the orthodontic eld is highlighted and recommendations for further development of an electromechanical orthodontic appliance are provided. / AFRIKAANSE OPSOMMING: Ortodonsie is die vakgebied in tandheelkunde gemoeid met die behandeling van wanpassing en abnormaliteit van die tand- en gesig-area. Hierdie tesis bestudeer die onderliggende biomeganiese beginsels van ortodontiese tandbeweging om sodoende 'n nuwe benadering sowel as 'n ortodontiese apparaat te ontwikkel om die genoemde benadering te fasiliteer deur gebruik te maak van gevorderde tegnologie. 'n Deeglike oorsig van die literatuur word gebruik om 'n omvattende kennisbasis op te bou rondom die faktore wat ortodontiese tandbeweging a ekteer. Die hipotese word gestel dat 'n elektromeganiese ortodontiese apparaat behandeling kan verbeter deur ortodontiese gevalle te identi seer/- karakteriseer gebaseer op die verhouding tussen die toegepaste meganiese stimulus en die gevolglike veranderinge aan die gea ekteerde strukture wat deur die apparaat aangevoel word. Elektronies-beheerbare lineêre aandrywers en 'n pasgemaakte krag-oordraerstelsel vir die meet van ortodontiese kragte word gebruik om 'n prototipe te vervaardig. Elektroniese stroombane word ontwikkel om die apparaat te koppel aan 'n USB poort sodat dit beheer kan word d.m.v. 'n gra ese gebruikerskoppelvlak. Eksperimente poog om die apparaat funksioneel te evalueer volgens die voorgestelde hipotese. Ter afsluiting: die toepaslikheid van die verwerfde resultate in die ortodontiese vakgebied word beklemtoon en aanbevelings word gemaak vir toekomstige/verdere ontwikkelings m.b.t. 'n elektromeganiese ortodontiese apparaat.

Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: This thesis entails the stages of the development of an arterial catheter capable of being guided by the impedance of human tissue. Such a device would be desired in cases where it is not possible to locate the artery of a patient using anatomical landmarks. This design thus aims to improve the accuracy of first time placement of arterial catheters. The thesis entails the literature study done in order to initiate the development of said device, followed by preliminary concept design and evaluation. The thesis also contains a description of all experimental phases, done on in vitro tissue samples, in vivo samples in living porcine subjects and in vivo samples in living human patients. Experiments were performed to determine if any repeatable noticeable difference in tissue impedance could be identified and utilized in the hope of guiding this device using acquired differences in tissue impedance. The different stages of development for the prototype used in these tests are also described in detail. In addition, the results of the different tests are presented, which prove that there is a significant difference between blood tissue impedance and the surrounding tissue types encountered, allowing for guidance of the proximal tip of the arterial catheter, based on the tissue impedance measured. Finally, the thesis entails a description of further work which could be performed if this concept were to be considered as a marketable product. / AFRIKAANSE OPSOMMING: Hierdie tesis behels die verskillende stappe in die ontwerp van 'n kateter wat deur middel van die verskillende impedansie vlakke van biologiese weefsel gelei kan word in die menslikke liggaam. Sò ‘n toestel sal behulpsaam wees in gevalle waar plasing nie gedoen kan word met die behulp van anatomiese landmerke nie. Hierdie ontwerp mik dus om die akkuraatheid van die plasing van kateters te verbeter. Die tesis behels die literatuur studies benodig om sò 'n toestel te ontwerp, gevolg deur voorlopige konsep ontwerpe en die evaluasie van hierdie konsepte. Die tesis behels ook die verskillende eksperimentele fases van die projek; eksperimente op in vitro weefsel monsters, in vivo diere toetse en in vivo kliniese toetse op menslike weefsel. Al hierdie eksperimente is gedoen om te bepaal of enige herhaalbare, waarneembare verskil in weefsel impedansie geidentifiseer kan word en dus gebruik word met die hoop om diè teoretiese kateter te lei met behulp van diè verskil in weefsel impedansie. Die verskillende stappe van die ontwerp van die prototipes gebruik in hierdie eksperimente word ook in detail beskryf. Die resultate van die verskillende eksperimente word ook aangebied, wat bewys dat daar 'n beduidende verskil is tussen die impedansie van bloed weefsel en die impedansie van die aanliggende weefsel tipes, wat dus impliseer dat die proksimale punt van die kateter gelei kan word deur die gemete impedansie by die punt van die toestel, gebaseer op die resultate wat gevind is. Laastens behels die tesis ook 'n beskrywing van toekomstige werk wat gedoen kan word indien die konsep ontwikkel word tot 'n bemarkbare produk.

Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Pleural effusion is a common respiratory condition that is characterized by an abnormal collection of fluid in the lung cavity. In this study, an innovation using the transmission of sound into the respiratory system as a novel tool to detect fluid in the lung was developed. First, the method was evaluated on a phantom model of a lung. Based on the results of this test model, the appropriate technique was used in a clinical study. This method has several advantages, such as that is non-invasive, low cost, and easy for clinical review. Two techniques, including analysis of the frequency response of the model and the transient time of transmitted sound in the lung, were evaluated in the phantom models of the human lung. Two phantom models with similar geometry to the human lung, including a healthy model (without fluid in the model) and a pleural effusion model (with bulk of fluid in the model) were developed. These models have acoustical properties similar to the lung parenchyma. To obtain the frequency responses of the model, a sine sweep signal was transmitted into the model and the frequency response of the model was then calculated using the fast Fourier transform. The transient time of the transmitted sound was calculated using a cross correlation method. The results show that the locations of fluid in the model were detectable using both techniques. However, the transient time technique is better than the frequency response technique because it is simple, fast, and has potential for use in a clinical enviorment. Based on the results obtained from the phantoms, the transient time method was performed on both 22 healthy participants and four patients diagnosed with pleural effusion. To perform this technique on human subjects, a data acquisition system was developed. Two types of sound, including a complex chirp sound and a polyphonic sound, were transmitted into the respiratory systems of the participants. The time delay between a reference microphone, located on the trachea of the subject, and eight microphones attached to the chest was computed using a cross correlation method, and the effect of inhalation and lung size on the transient time of transmitted sound on the healthy subject was evaluated. The results show that using transmission of sound in the lung is a promising technique in the diagnosis of pleural effusion. / AFRIKAANSE OPSOMMING: Pleurale effusie is 'n algemene respiratoriese toestand wat gekenmerk word deur 'n abnormale versameling van vloeistof in die longholte. In hierdie studie is 'n innoverende manier ontwikkel om vloeistof in die long met behulp van die transmissie van klank te bespeur. Die metode is eers op 'n fantoommodel van 'n long geëvalueer. Op grond van die resultate van hierdie toetsmodel is die geskikte tegniek in 'n kliniese studie gebruik. Hierdie metode het verskeie voordele, soos dat dit ingreepsvry is, nie duur is nie en kliniese evaluering moontlik maak. Twee tegnieke, naamlik ontleding van die frekwensierespons van die model en die oorgangstyd van versende klank in die long, is in die fantoommodel van die menselong geëvalueer. Twee fantoommodelle met soortgelyke geometrie aan die menselong, met inbegrip van 'n gesonde model (sonder vloeistof in die model) en 'n pleurale-effusie-model (met 'n massa vloeistof in die model), is ontwikkel. Hierdie modelle het akoestiese eienskappe soortgelyk aan die longparenchiem. Om die frekwensieresponse van die model te verkry, is 'n sinuskrommesein tot in die model versend. Die frekwensierespons van die model is met behulp van die vinnige Fourier-transformasie bereken. Die oorgangstyd van die versende klank is deur 'n kruiskorrelasie-metode bereken. Die resultate toon dat die ligging van die vloeistof in die model met albei tegnieke bespeur kan word. Die oorgangstyd-tegniek is egter beter as die frekwensierespons-tegniek, aangesien dit eenvoudig en vinnig is en maklik in 'n kliniese omgewing gebruik kan word. Op grond van die resultate wat van die fantome verkry is, is die oorgangstyd-metode op 22 gesonde deelnemers en vier pasiënte wat met pleurale effusie gediagnoseer is, uitgevoer. 'n Dataverkrygingstelsel is ontwikkel ten einde hierdie tegniek op proefpersone uit te voer. Twee soorte klank, naamlik 'n komplekse tjirpgeluid en 'n polifoniese klank, is na die respiratoriese stelsels van die deelnemers versend. Die tydvertraging tussen 'n verwysingsmikrofoon in die tragea van die proefpersoon en agt mikrofone wat aan die bors vasgeheg is, is met 'n kruiskorrelasie-metode bereken, en die uitwerking van inaseming en longgrootte op die oorgangstyd van versende klank op die gesonde proefpersone is geëvalueer. Die resultate toon dat die gebruik van transmissie van klank in die long 'n belowende tegniek vir die diagnose van pleurale effusie is.

Σκοπός της διπλωματικής εργασίας, είναι η κατασκευή ενός κυκλώματος με ανάδραση για τον έλεγχο ενός ηλεκτρομαγνήτη με στόχο την αιώρηση ενός σταθερού μαγνητικού αντικειμένου. / The purpose of the thesis is to build a circuit with feedback in order to control a solenoid to levitate a constant magnetic object.

Analyse et conception de la fiabilité sont indispensables pour le processus de développement des systèmes mécatroniques. Toutefois, des outils puissants sont nécessaires en raison de la complexité croissante et de la cherté d'essai des systèmes mécatroniques. Cette complexité nous amène des difficultés de l'incertitude de modélisation et de la dépendance inconnus, tels que la dépendance fonctionnelle et temporelle. Pour faire face à une telle complexité, la fiabilité des outils d'analyse doivent être mathématiquement puissant, facile à utiliser et efficace de calcul.Les outils classiques ont une certaine quantité d'inconvénients lors de l'évaluation de la fiabilité au niveau du système. Par exemple, les méthodes basées sur la chaîne de Markov ont un problème infime d'explosion combinatoire et le formalisme de l'arbre de défaillance ne fonctionne que quand les composants sont indépendants les uns des autres. Bien que certaines extensions, comme les arbres de défaillance dynamiques, aient été faites pour pallier les lacunes, tous ne peuvent être traitées dans un cadre unique. Le formalisme des réseaux Bayésiens a été récemment considéré comme un outil prometteur de l'inférence statistique pour l'évaluation de fiabilité du système grâce à de nombreux avantages, tels que la capacité de modélisation de la dépendance incertaine, l'intégration de données provenant de diverses sources et les outils de raisonnement bien étudiés. D'autre part, la plus grande valeur ajoutée en mécatronique est en sous-système du contrôle et du traitement de l'information. Les ingénieurs se rendent compte que la conception de contrôleur d'un système dynamique ne peut pas négliger l'exigence de la fiabilité dynamique. Diverses incertitudes influencent non seulement les performances des contrôleurs, mais aussi la fiabilité. Cependant, peu de recherches ont examiné la fiabilité dynamique des contrôleurs.Dans cette recherche, nous avons étudié le formalisme des réseaux bayésiens et développé une méthode de l'évaluation de la fiabilité des systèmes mécatroniques complexes. Cette méthode étend l'analyse bayésienne sur les composants à celle sur les systèmes complexes et permet de considérer des incertitudes des paramètres des modèles asymétriques de temps à l'échec dans les systèmes complexes. Pour effectuer l'inférence dans notre modèle de réseau bayésien, nous avons développé un algorithme modifié de la propagation de croyances non-paramétrique qui est plus efficace dans le cas complexe par rapport à d'autres outils de raisonnement. Nous avons montré également comment effectuer l'analyse de sensibilité dans notre modèle de réseau bayésien qui a une structure non-déterministe.Un contrôleur linéaire dynamique-fiable a été conu pour le module de contrôle des systèmes mécatroniques. Nous avons établi un nouveau lien entre le probabilité de la défaillance du premier passage et les gains de rétroaction des contrôleurs, et obtenu une nouvelle contrainte dynamique de fiabilité pour les objectifs classiques. Le contrôleur linéaire dynamique-fiable est également étendu au formalisme de multiple-modèle pour que la réalisation d'un contrôleur dynamique-fiable soit applicable dans le cas nonlinéaire/non-gaussien. La performance du système peut encore être améliorée dans ce cadre en utilisant les méthodes de multiple-modèle plus avancées.Une grande quantité de résultats de simulation ont démontré que les méthodes développées ont été appliquées avec succès pour analyser et concevoir des systèmes de suspension active du véhicule et peuvent être appliquée à d'autres applications, telles que d'autres systèmes mécatroniques et systèmes de contrôle actif de construction. / Reliability analysis and design become indispensable for the development process of mechatronic systems. However, versatile tools are called for because of the increas•ing complexity and the testing expensiveness of mechatronic systems. Such complexity brings the difficulties of modeling uncertainty and unknown dependency, such as functional and temporal dependency. To deal with such complexity, reliability analysis tools need to be mathematically powerful, be easy to use and be computationally efficient.Conventional tools have a number of drawbacks when evaluating the reliability at system level. For instance, Markov chain based methods have a problem of infamous combinatorial explosion and fault trees formalism works under the assumption of component independency. Although sorne extensions, such as dynamic fault trees, have been made to make up for shortcomings, not all of them can be handled in one framework. Bayesian networks formalism is recently believed to be a promising statistical inference tool for system reliability assessment thanks to many advantages, such as the ability of modeling uncertain dependency, integrating data from diverse sources and the well-studied reasoning tools. On the other hand, the biggest value-added in mechatronics is in control/information processing subsystem. Engineers realize that the controller design of a dynamic system cannot neglect the dynamic reliability requirement. Various uncertainties influence not only the controller performance but also the reliability. However, little research has considered the dynamic reliability of controllers.In this research, we have investigated the Bayesian networks formalism and developed a new system reliability assessment method for complex mechatronic systems. This method extends Bayesian analysis on components to that on complex systems and allows to consider parameter uncertainties of various skewed time-to-failure models in complex systems. To perform the inference in our Bayesian network model, we developed a modified nonparametric beHef propagation which is more efficient in the complex case compared with other reasoning tools. We showed also how to perform the sensitivity analysis in our Bayesian network model that has a non-deterministic structure. A dynamic-reliable linear controller has been designed for the control module of mechatronic systems. We established a new link between the first-passage failure probability and controllers' feedback gains, and obtained a new dynamic-reliability constraint for classical objectives. The dynamic-reliable linear controller is also extended to the multiple model formalism for achieving a dynamic-reliable controller applicable to nonlinearjnon-Gaussian cases. The system performance can be further improved in this framework by using more advanced multiple model methods.A number of simulation results demonstrated that the developed methods have been successfully applied to analyze and design active vehicle suspension systems and can be applied to other applications, such as other mechatronic systems and active building control systems.

A LIDAR that measures distance to an object in motion must be directed with precision. This is something that can be done automatically. In this project, a construction where two LIDAR sensors are attached to each step motors is built. One LIDAR scans the environment in 2D and a second LIDAR is directed based on the information from the scanning sensor. In order to get rid of incorrect values and to find a central position on an object, different variants of moving average filters are used and tested. The result shows that a filter with fewer values included in the average analysis of the filter, resulting in a more stable result, especially when the object being tracked is located far away from the sensor. The results show that the concept can be used for tracking a moving object. / En LIDAR-sensor som mäter avstånd till ett objekt i rörelse måste riktas med bra precision. Detta är något som kan göras automatiskt. I detta projekt byggs en konstruktionen där två stycken LIDAR-sensorer fästs vid var sin stegmotor. En sensor skannar omgivningen i 2D och en andra sensor riktas sedan utifrån informationen från den skannande sensorn. För att får bort felaktiga värden samt för att hitta en position mer centralt på ett sökt objekt används och testas olika varianter av glidande medelvärdesfilter. Resultatet visar att ett filter där färre värden tas med i filtrets medelvärdesberäkningar ger ett stabilare resultat, framförallt då objektet som följs befinner sig på längre avstånd. Resultaten visar att principen går att använda för att rikta en sensor mot ett objekt i rörelse.

Since the 1960s, research into the medical applications of wearable robots has been fueled by a growing need for assistive technologies that can help individuals impacted by musculoskeletal disorders such as sarcopenia independently manage common activities of daily living while maintaining their natural physical capacities. While contemporary research has demonstrated promising developments, the usefulness of exoskeletons in everyday settings remains limited due to design factors that include the limited practicality of existing battery technologies, the need for actuators exhibiting a high output torque-to-weight ratio, a need for modular designs that are minimally disruptive to wearers, and the need for control systems that can actively work in sync with a user. To explore potential solutions to some of these limiting factors, a novel ankle exoskeleton prototype supporting ankle plantarflexion during gait was developed under a design approach that seeks to optimize actuator performance. The actuation system featured in this prototype consists of a custom dual-action linear actuator that can provide mechanical assistance to both ankles via a single BLDC motor and an underlying Bowden cable system. The metric ball screw and BLDC motor implemented in the linear actuator were selectively chosen to minimize the motor torque and current required to assist wearers impacted by a degree of muscle weakness under an assistance-as-needed design paradigm. The prototype additionally features an array of force sensing resistors for tracking gait progression and exploring potential user-based control strategies for synchronizing the exoskeleton actuator with a wearer's gait. Performance analysis for this prototype was conducted with the goal of quantifying the exoskeleton's force output, actuator settling time, and the control system's ability to track gait and identify key events in the gait cycle. The preliminary findings of this experimental analysis support the viability of the actuator's dual-action concept and gait progression tracking system as a starting ground for future developments that build on a similar design optimization approach. / Master of Science / Healthy aging and good physical health are characterized in part by one's ability to self-manage a core set of daily living tasks, one of the most prominent of which is gait. Relative to existing assistive technologies such as wheelchairs, exoskeletons provide the unique benefit of providing active mechanical support while encouraging users to rely on their natural physical capabilities. While recent technological developments in the field of wearable robots show promise, the viability of exoskeletons in an everyday setting remains constrained in part by three underlying design factors: the limited practicality of existing battery technologies, a need for actuators that can satisfactorily balance a high force output with weight, and a need for control strategies that can properly synchronize wearable robots with users. The ankle exoskeleton prototype introduced in this thesis is a portable, energetically autonomous wearable device that supports ankle plantarflexion during the push-off stages of the gait cycle. The design for this prototype seeks to optimize actuator performance and features a novel dual-action linear actuator that provides walking support to both ankles using a single DC motor. The exoskeleton additionally features an array of contact sensors that track the user's progression throughout the gait cycle and allow for the examination of potential control strategies for synchronizing the actuator with the wearer's gait. Performance analysis conducted for this prototype quantifies the exoskeleton's force output, approximates the actuator's settling time between steps, and assesses the control system's ability to track gait and synchronize with a wearer. The findings from these performance evaluation experiments support the viability of the actuator's dual-action concept and gait progression tracker as a foundation for future developments that build on a similar design optimization approach.

MScEng / Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2009. / In this project the shape and attachment method of tissue leaflets for a percutaneous aortic valve is designed and tested as a first prototype. Bovine and kangaroo pericardium was tested and compared with natural human valve tissue by using the Fung elastic constitutive model for skin. Biaxial tests were conducted to determine the material parameters for each material. The constitutive model was implemented using finite element analysis (FEA) by applying a user-specified subroutine. The FEA implementation was validated by simulating the biaxial tests and comparing it with the experimental data. Concepts for different valve geometries were developed by incorporating valve design and performance parameters, along with stent constraints. Attachment techniques and tools were developed for valve manufacturing. FEA was used to evaluate two concepts. The influence of effects such as different leaflet material, material orientation and abnormal valve dilation on the valve function was investigated. The stress distribution across the valve leaflet was examined to determine the appropriate fibre direction for the leaflet. The simulated attachment forces were compared with suture tearing tests performed on the pericardium to evaluate suture density. In vitro tests were conducted to evaluate the valve function. Satisfactory testing results for the prototype valves were found which indicates the possibility for further development and refinement.