Magnetically levitated planar actuator with moving magnets

Mechanical systems with multiple degrees of freedom typically consist of several one degree-of-freedom electromechanical actuators. Most of these electromechanical actuators have a standard, often integrated, commutation (i.e. linearization and decoupling) algorithm deriving the actuator inputs which result in convenient control properties and relatively simple actuator constraints. Instead of using several one degree-of-freedom actuators, it is sometimes advantageous to combine multiple degrees of freedom in one actuator to meet the ever more demanding performance specifications. Due to the integration of the degrees of freedom, the resulting commutation and control algorithms are more complex. Therefore, the involvement of control engineering during an early stage of the design phase of this class of actuators is of paramount importance. One of the main contributions of this thesis is a novel commutation algorithm for multiple degree-of-freedom actuators and the analysis of its design implications. A magnetically levitated planar actuator is an example of a multiple degree of freedom electromechanical actuator. This is an alternative to xy-drives, which are constructed of stacked linear motors, in high-precision industrial applications. The translator of these planar actuators is suspended above the stator with no support other than magnetic fields. Because of the active magnetic bearing the translator needs to be controlled in all six mechanical degrees of freedom. This thesis presents the dynamics, commutation and control design of a contactless, magnetically levitated, planar actuator with moving magnets. The planar actuator consists of a stationary coil array, above which a translator consisting of an array of permanent magnets is levitated. The main advantage of this actuator is that no cables from the stator to the translator are required. Only coils below the surface of the magnet array effectively contribute to its levitation and propulsion. Therefore, the set of active coils is switched depending on the position of the translator in the xy-plane. The switching in combination with the contactless translator, in principle, allows for infinite stroke in the xy-plane. A model-based commutation and control approach is used throughout this thesis using a real-time analytical model of the ironless planar actuator. The realtime model is based on the analytical solutions to the Lorentz force and torque integrals. Due to the integration of propulsion in the xy-plane with an active magnetic bearing, standard decoupling schemes for synchronous machines cannot be applied to the planar actuator to linearize and decouple the force and the torque components. Therefore, a novel commutation algorithm has been derived which inverts the fully analytical mapping of the force and torque exerted by the set of active coils as a function of the coil currents and the position and orientation of the translator. Additionally, the developed commutation algorithm presents an optimal solution in the sense that it guarantees minimal dissipation of energy. Another important contribution of this thesis is the introduction of smooth position dependent weighing functions in the commutation algorithm. These functions enable smooth switching between different active coil sets, enabling, in principle, an unlimited stroke in the xy-plane. The resulting current waveform through each individually excited active coil is non-sinusoidal. The model-based approach, in combination with the novel commutation algorithm, resulted in a method to evaluate/design controllable topologies. Using this method several stator coil topologies are discussed in this thesis. Due to the changing amount of active coils when switching between active coil sets, the actuator constraints (i.e. performance) depend on the xy-position of the translator. An analysis of the achievable acceleration as a function of the position of the translator and the current amplifier constraints is given. Moreover, the dynamical behavior of the decoupled system is analyzed for small errors and a stabilizing control structure has been derived. One of the derived coil topologies called the Herringbone Pattern Planar Actuator (HPPA) has been analyzed into more detail and it has been manufactured. The stator of the actuator consists of a total of 84 coils, of which between 15 and 24 coils are simultaneously used for the propulsion and levitation of the translator. The real-time model, the dynamic behavior and the commutation algorithm have been experimentally verified using this fully-operational actuator. The 6-DOF contactless, magnetically levitated, planar actuator with moving magnets (HPPA) has been designed and tested and is now operating successfully according to all initial design and performance specifications

Verdrongen kwetsbaarheid. Een theoretisch afstudeeronderzoek naar de duiding van grenservaringen

In dit literatuuronderzoek staat de volgende vraag centraal: ‘Hoe worden binnen verschillende wetenschappelijke disciplines grenservaringen geduid, welke visie op transitie wordt zichtbaar en wat betekent dit voor de oriëntatie op kwetsbaarheid?’ In een sociologische analyse van de hedendaagse oriëntatie op kwetsbaarheid, wordt een tendens tot verdringing en beheersing zichtbaar, ten aanzien van ervaringen ‘waarin de vanzelfsprekende geborgenheid van het bestaan wegvalt’ - grenservaringen. Dit zijn vaak ervaringen van verlies: van een baan, gezondheid, geliefde of het eigen bestaan. De tendens om deze ervaringen te verdringen en te beheersen maakt de hedendaagse oriëntatie op kwetsbaarheid problematisch, doordat de mogelijkheid tot betekenisgeving uit beeld verdwijnt. Dit vraagt om een heroriëntatie. Vanuit een interdisciplinaire benadering wordt gekeken wat denkers uit de ontwikkelingspsychologie, het existentialisme, de theologie, de gendertheorie en het zenboeddhisme ten aanzien van deze heroriëntatie te bieden hebben. Zij wijzen erop de kwetsbaarheid niet toe te dekken, maar aan te gaan (Epstein, 2000; Yalom, 2008), te erkennen (Butler, 2004) en erover in gesprek te treden (Anbeek, 2013). Afsluitend volgt een kritische dialoog waarin een aantal noties worden uitgelicht die in een heroriëntatie op kwetsbaarheid van belang zijn: de betekenis van de ander, de ontoereikendheid van de taal en de tweezijdigheid van de grenservaring

A utility framework for interaction models for spatial processes

In the post-war period human settlement and mobility patterns have shown rapid and significant changes. Urbanization and spatial agglomera-tion were a first major trend, foliowed by a large-scale suburbanizaticn movement and an urban decay in a broader sense. At present a more diffus

Stereotypical behaviours in the striped mouse Rhabdomys pumilio: evaluating the coping hypothesis

Student Number : 9905625D - MSc dissertation - School of Animal, Plant and Environment Science - Faculty of ScienceStereotypic behaviours are repetitive invariant behaviours that serve no obvious purpose and are common in both domestic and non-domestic captive animals. Stereotypies are regarded as indicators of poor welfare although the growing body of work pertaining to these behaviours has challenged many previously held notions of stereotypy. The most widely accepted, although frequently contested, hypothesis used to explain stereotypies is the coping hypothesis, which states that animals perform stereotypies to cope with the stress of adverse environments. The aim of my study was to investigate the fitness effects of stereotypy, and whether or not environmental enrichment protocols were effective in reducing or eliminating stereotypy in the adult striped mouse Rhabdomys pumilio. Both of these experiments were designed to evaluate the coping hypothesis. I intentionally used wild caught and F1 individuals to eliminate any potential captive selection bias that may exist in extant captive populations that could affect interpretation of fitness. For the first aim, 40 breeding pairs were assigned to one of four treatments: 1) stereotypic female and stereotypic male (S-S); 2) stereotypic female and non-stereotypic male (S-NS); 3) non-stereotypic female and stereotypic male (NS-S); and 4) non-stereotypic female and non-stereotypic male (NS-NS). Compared to non-stereotypic females, stereotypic striped mice females had better reproductive output, including larger litter size, higher growth rate, higher litter survival, shorter interlitter interval and shorter time to first litter. Reproductive success was higher in S-S and S-NS pairs, indicating that genetic and maternal effects jointly determined fitness in striped mice. Unlike other published research, maternal mass was not a predictor of fitness. For the second aim, I housed 20 non-stereotypic and 20 stereotypic striped mice (equal sex ratio) in barren cages for 60 days, and transferred them to enriched cages, and repeated this experiment with striped mice housed initially in enriched cages and transferred to barren cages. While there was a measurable reduction in stereotypy in individuals transferred from barren to enriched environment cages, no increase in stereotypy was noted in striped mice transferred from enriched to barren cages. These findings appear to concur with the coping hypothesis, that stereotypies become perseverative (e.g. bad habits) and difficult to disrupt. Non-stereotypic striped mice were not influenced by the swap. I conclude that the expression of stereotypy is a potential sign of positive welfare and that it may be worthwhile to specifically elicit stereotypic behaviours in order to improve the welfare, and in certain cases, breeding success, of captive animals. Moreover, I maintain that where necessary, effort should be applied to combating stereotypies before they arise, rather than attempting to eliminate them once they have actually developed

"Oumense het blotvoet gebruik": Nederlandse taalresten in de variëteiten van het Afrikaans

English Title: "Oumense het blotvoet gebruik": Dutch relics in the regional varieties of AfrikaansEnglish AbstractThe Bureau of the WAT has developed a survey of all varieties of Afrikaans. One part thereof is the survey of Dutch language relics in the Afrikaans regional varieties which is discussed here. From earlier surveys it has been shown that many Dutch relics are present; the Dutch language and in particular the dialect from Holland from the 16th and 17th centuries have had a strong influence on (the origin of) Afrikaans. Questionnaires were used to check with 183 informants from the Northern and the Western Cape whether Dutch relics are still present in the varieties they use, on the phonetic as well as the lexical level.The survey has shown that Dutch relics are found on both levels. In the pronunciation especially there is still [ø] where standard Afrikaans has [e], and less often [y] is found instead of [œy]. It is noticeable that the [«i]/[i] variation is present less frequently, while in Dutch a parallel development in the diphtongisation of [y] and [i] has occurred. Afrikaans has seemingly undergone an independent development in this regard. Most phonetic relics were found in Namaqualand, particularly among informants with little schooling, and somewhat more among women than among men.On a lexical level the results were quite different. There are still many Dutch relics present in word meaning as well as in knowledge of idioms. The Muslim community of Cape Town scores particularly high in this regard, while phonetic relics were scarcely found. Informants with higher education levels score more highly in this regard than those with lower schooling or less, and among men more lexical relics are recorded than among women.Lastly, both on a lexical level and on a phonetic level, a number of indirect results were gathered from the survey which also point to the presence of Dutch language relics.Keywords: woordeboek van die afrikaanse taal; inventorying of relics; use of language description; questionnaire; influence of dutch on afrikaans; phonetic language relics; sound variation; lexical language relics; word meaning; idioms; correlations with sex; schooling and age; indirect result

Should I be eating that? eating, drinking and environmental ethics.

What each individual eats and drinks can, and does, have a varying degree of impact on the environment in which they live. This impact can be on a local, regional or global scale and can range from affecting the viability of species’ populations, to contributing to global warming. This thesis sets out to explore what moral implications might exist with regard to the choices that individuals make within the context of environmental ethics. This paper discusses environmental considerations (as opposed to animal welfare or social implications for instance) and utilises various examples to illustrate different types of impacts and what this might mean. Conclusions indicating that moral obligations do exist are presented and argued for, but it is clear that there is certainly a complex matrix of factors that would (and should) affect the choices that each individual makes with regards to the food that they consume