Este estudo avaliou próteses implantossuportadas obtidas por 2 técnicas (cilindro cimentado ou soldado a laser) e seus comportamentos no que tange à passividade e afrouxamento de parafusos. Foram confeccionadas PPFs de 3 elementos sobre 2 implantes: G1, técnica do cilindro cimentado; G2, técnica do cilindro soldado a laser (n=10). Avaliados níveis de desajuste vertical e passividade antes e após aplicação de cerâmica prensada e após ciclagem mecânica, e a perda de torque inicial dos parafusos de retenção protética antes e após fadiga. Ciclagem mecânica simulando 1 ano de função mastigatória normal (50N, 300.000 ciclos). Análises de desajuste vertical e passividade realizadas pelo método de Sheffield. Calculada % de perda de torque de inserção. Os dados de desajuste e perda de torque foram comparados estatisticamente pelo Modelo Linear de Efeitos Mistos. De modo geral, G1 apresentou níveis de desajuste vertical estatisticamente inferiores a G2 (p<0,05) nas três condições analisadas pelo teste de Sheffield, tanto antes quanto após ciclagem mecânica, atingindo valores máximos de desajuste correspondentes a: 11,94 ± 3,17&mu;m (G1) e 48,63 ± 39,68 &mu;m (G2), antes da ciclagem, 12,42 ± 6,19&mu;m (G1) e 47,62 ± 35,16&mu;m (G2), após a ciclagem, estando os parafusos parafusados. Adicionalmente, em todas as condições experimentais, a ciclagem mecânica não influenciou no desajuste de ambos os grupos (p<0,05), com exceção do molar em G1 quando analisado apertado (p<0,0001). Quando analisado G2, verificamos aumento estatisticamente significante do desajuste vertical após prensagem cerâmica para todos os elementos (p<0,0001) nos diferentes momentos avaliados, com exceção do molar quando avaliado solto, o qual apresentou desajustes semelhantes antes e após prensagem (p=0,052). Na análise de perda de torque, valores expressos em % de perda são apresentados: Pré-molar - G1- antes ciclagem: 31,04 ± 13,22%; G2- antes ciclagem: 33,97 ± 13,41% (G1 x G2 antes ciclagem: p=0,662); G1- após ciclagem: 42,36 ± 14,99%; G2- após ciclagem: 37,92 ± 9,32% (G1 x G2 após ciclagem: p=0,461). Quando analisado o pré-molar, não foram verificadas diferenças estatísticas antes e após ciclagem mecânica para ambos os grupos (G1: p=0,067; G2: p=0,423); Molar - G1- antes ciclagem: 30,77 ± 12,37%; G2- antes ciclagem: 44,37 ± 11,14% (G1 x G2 antes ciclagem: p=0,032); G1- após ciclagem: 39,28 ± 13,96%; G2- após ciclagem: 54,40 ± 26,39% (G1 x G2 após ciclagem: p=0,189). Quando analisado o molar, diferenças estatísticas também não foram identificadas antes e após ciclagem, para ambos os grupos (G1: p=0,392; G2: p=0,233). Diante dos resultados, é possível concluir que: G1 apresentou índices de desajuste vertical e passividade menores que G2, porém para ambos os grupos os desajustes estão dentro dos padrões aceitáveis pela literatura; ciclagem mecânica não promoveu alterações nos níveis de desajuste vertical e perda de torque (%) para ambos os grupos; ambas as técnicas não foram capazes de promover passividade absoluta, tendo em vista os maiores valores de desadaptação do lado solto quando comparados ao lado parafusado. / This study evaluated implant supported prostheses obtained by two techniques (cemented cylinder or laser welded cylinder) and their behavior regarding passivity and screw loosening. Three-element FPPs were made over 2 implants: G1, cemented cylinder technique, G2, laser welded cylinder technique (n=10). The levels of vertical misfit and passivity were evaluated before and after ceramic pressing, and after mechanical cycling; while loss of initial torque of prosthetic retaining screws, before and after mechanical cycling. The mechanical cycling simulated one year of normal masticatory function (50N, 300,000 cycles). Vertical misfit and passivity were analyzed by Sheffield\'s test. The percentage of torque loss was calculated. The misfit and torque loss data were statistically compared by Mixed Linear Model . Overall, G1 showed vertical misfit statistically lower than G2 (p<0.05) in the three conditions analyzed by Sheffield\'s test, before and after mechanical cycling, reaching maximum values of misfit corresponding to: 11.94 ± 3.17&mu;m (G1) and 48.63 ± 39.68 &mu;m (G2) before cycling; 12.42 ± 6.19&mu;m (G1) and 47.62 ± 35.16&mu;m (G2), after cycling, when screws were tightened. Additionally, in all experimental conditions, the mechanical cycling did not influence the misfit in both groups (p<0.05), except for the molar G1 when analyzed in the tightened condition (p<0.0001). When was analyzed G2, statistically significant increase in the vertical misfit was found after ceramic pressing for all elements (p<0.0001) for different moments, except when the molar was not tightened, which showed similar misfit before and after pressing (p=0.052). In the analysis of torque loss, values expressed as percentage of loss are presented: Pre-molar - G1- before cycling: 31.04 ± 13.22%, G2- before cycling: 33.97 ± 13.41% (G1 x G2 before cycling: p=0.662), G1- after cycling: 42.36 ± 14.99%, G2- after cycling: 37.92 ± 9.32% (G1 x G2 after cycling: p=0.461). When the pre-molar was analyzed, statistical differences before and after cycling were not found for both groups (G1: p=0.067; G2: p=0.423); Molar - G1- before cycling: 30.77 ± 12.37%; G2- before cycling: 44.37 ± 11.14% (G1 x G2 before cycling: p=0.032); G1- after cycling: 39.28 ± 13.96%; G2- after cycling: 54.40 ± 26 , 39% (G1 x G2 after cycling: p=0.189). When the molar was analyzed, statistical differences were not found before and after cycling for both groups (G1: p=0.392; G2: p=0.233). Based on these results, it is possible to conclude that: G1 showed vertical misfit and passivity smaller than G2, but for both groups, the misfits are within acceptable standards for the literature; mechanical cycling did not change the vertical misfit and torque loss (%) for both groups; both techniques were not able to promote absolute passivity, in view of the higher values of misfit when compared to the side no tightened.

Esta dissertação estuda a otimização da capacidade de interação de manipuladores robôs com o meio externo através do controle das forças e torques envolvidas no contato. Os modelos adotados para as análises levam em consideração a interação entre a extremidade do manipulador e uma superfície. Neste trabalho, são investigadas diferentes metodologias para controle de forças, assim como as vantagens e desvantagens de cada método estudado para comparar e desenvolver um controle adequado das forças de contato. Devido às divergências encontradas na literatura, foram implementadas experimentalmente duas abordagens distintas conhecidas por controle cinestático e controle híbrido. Também, como parte do ambiente experimental, foi desenvolvido um protótipo de um micro manipulador com um grau de liberdade instalado na extremidade do robô. O micro manipulador simplifica a implementação de controle de força ativo, pois trabalha de forma independente do acionamento \"fechado\" dos robôs industriais abordados no trabalho. Assim é possível manter uma força arbitraria desejada no contato com a superfície. O controlador de força se sobrepõe ao controlador de posições convencional do manipulador para produzir o comportamento desejado na interação com o meio externo. / The optimization of a conventional industrial robot manipulator capacity to interact with the surrounding environment is analyzed in this work. The models adopted for the analysis take into account the contact between the robot and an external surface. Different force control approaches are analyzed regarding their implementation advantages and disadvantages. Due to the well known contradictions in the literature experiments were carried out using the kinestatic control and the hybrid control. A micro manipulator with one degree of freedom was developed and installed at the end effector in association with the tool tester. With this system it is possible change the contact force on the surface. The simultaneous coordinate work of the robot position control and the micro manipulator system force control are use to produce a desired behavior in the interaction with the external surface.

A madeira é um material estrutural de fonte renovável, com alta relação resistência/peso, baixo consumo energético de produção, sequestra e armazena carbono em sua produção. A aplicação da madeira como material de construção civil é fundamental, pois além de ter qualidades muito especiais como matéria prima para outros produtos industrializados na construção de residências ou em obras de grande porte como pontes e passarelas, vem sendo utilizada amplamente em coberturas para edifícios industriais/comerciais. Comercialmente, existem limitações do comprimento das peças de madeira, fruto de sua extração de troncos de árvores, requerendo assim a adoção de elementos de ligação das peças estruturais. Uma das mais recentes alternativas para as ligações com elementos estruturais de madeira é a utilização de parafusos auto-atarraxantes solicitados por esforços que podem ser laterais e axiais, de cisalhamento, tração ou compressão. Considerando que no Brasil ainda não existe, e com o mercado futuro promissor, este trabalho tem por finalidade realizar um estudo teórico, numérico e experimental das ligações com parafusos auto-atarraxantes com diâmetros de 9 mm e 11 mm e espécies de reflorestamento de Pinus Oocarpa e Lyptus®, com a finalidade de propor os critérios de dimensionamento para estas ligações. Os resultados obtidos mostram que os ângulos de 45º entre a força aplicada e a posição de penetração do parafuso conduz aos melhores valores de resistência e rigidez das ligações. Alem disto, com base na experimentação realizada, conclui-se que o critério proposto pelo EuroCode5 se mostra adequado para o dimensionamento das citadas ligações. / Wood is a renewable source of structural material with high relative strength/weight, low energy production, kidnaps and stores carbon in its production. The use of wood as a construction material is critical because besides having very special qualities as raw material for other industrialized in building homes or large works such as bridges and walkways, product has been widely used in roofing for industrial buildings and commercial buildings. Commercially there are limitations on the length of the wood, resulting from the extraction of trees, thus requiring the adoption of binding elements of the structural parts. One of the newest alternatives for connections with wooden structural elements is to use self-tapping screws requested by efforts that may be lateral and axial, shear, tensile or compressive. Whereas in Brazil does not yet exist and the promising future market, this study aims to make a theoretical, numerical and experimental study of connections with self tapping screws with diameters of 9 mm and 11 mm and two species of reforestation Pinus oocarpa and Lyptus®, in order to offer a criteria for these connections. The results obtained show that the 45° angle between the applied force and the position of the screw penetration leads to a better strength values and stiffness. Besides this, based on experiments conducted, it has concluded that the criteria proposed by Eurocode5 prove suitable for this type of connection.

Since its publication in 1898, The Turn of the Screw has been the focus of diverse critical interpretation. It has reflected shifts in critical theory that include the Freudian, psychoanalytic, mythological, structuralist, reader-response, linguistic, and new-historical schools. The majority of critical interpretations have focused on the governess's narrative and have excluded the prologue, or frame narrative, that begins the novella. The critics who did examine the prologue overlooked James's departure from the traditional use of frame narration and the importance of the structure of the frame in creating a text of insoluble ambiguity. James departed from traditional frame narration in four ways. By using only an opening frame, the reader is forced to rely on the prologue in order to determine narrative reliability. By creating a condition of reciprocal authority between the unnamed narrator and Douglas, the opening frame denies the possibility of using either character to substantiate the reliability of the other. The condition of reciprocal authority is constructed through a dialogue pattern in which the narrator and Douglas interpret each other's gestures and comments and finish each other's sentences. It is the use of the pattern in the prologue that prepares the reader to accept it in the governess's narrative. The governess repeats the dialogue pattern with Mrs. Grose and Miles. Their discussions appear to validate the governess as a reliable narrator when in fact her reliability is as impossible to determine as the reliability of Douglas or the frame narrator. The result of these departures from traditional frame narration is the construction of a text of insoluble ambiguity.

L’extrusion biocatalytique, ou bioextrusion, est une technique d’extrusion réactive utilisant des enzymes comme catalyseurs. Cette technique est considérée en temps qu’étape intermédiaire, subséquente au prétraitement physico-chimique et précédente à l’hydrolyse enzymatique enréacteur fermé. L’utilisation de l’extrusion permet un procédé continu, facilement modulable et adaptable à des conditions de hautes consistances, de nombreuses biomasses et facilement transférable à l’échelle industrielle. Néanmoins, les données bibliographiques font ressortir la complexité des entrants et leurs interactions lors de la bioextrusion de biomasses lignocellulosiques. Les conclusions des bioextrusions de biomasses amidonnées soulignent l’importance de l’étude de l’influence de la concentration en substrat et en enzymes. Les résultats obtenus à partir de la bioextrusion des biomasses lignocellulosiques valident l’existence d’une activité enzymatique en extrudeuse malgré la contrainte thermomécanique et le temps de séjour limité. Lors de cette étape, l’hydrolyse de la fraction cellulosique est favorisée pour des milieux concentrés en substrat et en enzymes. Des modifications significatives des fractions cellulosiques cristallines et amorphes en surface, des réductions des tailles de particules, une dégradation visuelle des structures de la biomasse et l’augmentation de la sensibilité à la décomposition thermique, sont aussi observées sur la fraction solide. L’hydrolyse enzymatique des bioextrudats est prolongée en réacteur fermé. La bioextrusion permet des améliorations significatives des taux et vitesses de conversion des sucres sur le long terme, jusqu’à 48 h. Les gains observés sont relativement constants pour la paille de blé et augmentent avec le temps pour les écorces de bouleau et les résidus de maïs. Post-extrusion, la concentration en substrat influence négativement la conversion des sucres. Cependant, les plus-values de conversion du glucose lié à la bioextrusion de paille de blé sont principalement observables pour des concentrations en substrat et en enzymes élevées. À partir de 4 h, des baisses significatives de la conversion du xylose sont observées après bioextrusion. Les déstructurations de la fraction solide, déjà observées au cours la bioextrusion, se poursuivent en réacteur fermé. Les meilleurs résultats hydrolytiques aux niveaux des hautes charges en enzymes et en substrat sont associables aux bonnes conditions de mélanges caractéristiques des éléments bilobes. L’ensemble enzymatique est probablement réparti de façon plus homogène (mélange distributif) pour cibler plus de sites disponibles. De plus, le mélangé dispersif limite la proximité entre enzymes de même type et les gênes associées. Le procédé d’extrusion permet une agitation efficace, un bon transfert de masse et probablement un meilleur contact entre enzymes et substrat. Les moins bons résultats de conversion du xylose sont probablement à relier à des phénomènes d’adsorption non-spécifique, ou encore de désactivation des hémicellulases, provoqués par l’intensité des contraintes thermomécaniques et les résidus ligneux. Les bons résultats de déstructuration après bioextrusionsont associables à une action synergétique des contraintes mécanique et biochimique. Les analyses d’autofluorescence montrent l’évolution de la fraction ligneuse dans le processus de déconstruction de la fraction solide. Une production progressive de particules très fines,visiblement associée à la fraction ligneuse, est observée. Des complexes lignine-carbohydratessont aussi détectés dans la fraction liquide. Etant peu, voire pas hydrolysable par voie enzymatique, ces fractions hétéropolymériques sont un frein à la déconstruction. Si la déstructuration des lignines est probablement majoritairement liée au prétraitement alcalin, le procédé de bioextrusion provoque une diminution de la teneur en hétéropolymères de plus hautes masses moléculaires. / Biocatalytic extrusion, also named bioextrusion, is a reactive extrusion technique using enzymes as catalysts. Bioextrusion is considered as a link between the previous physico-chemical pretreatment (like alkaline extrusion) and the subsequent enzymatic hydrolysis in batch conditions. The extrusion allows a continuous, flexible and versatile process for high consistency media, easily transferable to the industrial level. However, complexity of both lignocellulosic biomass and lignocellulolytic enzymes and their interactions during the extrusion process are underlined by the literature. Numerous response surface methodology experiments with starchy biomass indicate that bioextrusion efficiency is mainly influenced by substrate and enzymes loading. Enzymatic activity during the bioextrusion process of lignocellulosic biomass is confirmed by the experiments despite the mechanical constraints and the limited residence time. During bioextrusion, best holocellulosic fraction hydrolysis results were obtained with high substrate and enzymes loadings. Significant modifications of the solid fraction like particule size reduction, visual deconstruction of the biomass structure, increased sensibility to thermal decomposition and the evolution of the surface exposure of crystalline and amorphous cellulose were observed. Enzymatic hydrolysis of the bioextrdates is prolonged in batch conditions. Clear improvements of speeds and rates of sugars conversion up to 48 h indicate a long term influence of the bioextrusion. Gain observed are steady for the pretreated wheat straw whereas it increases with time for corn residues and birch barks. Post-extrusion, a negative influence of the substrate loading is measured. However, best enhancements for the glucose conversion of pretreated wheat straw are detected for high substrate and enzymes loadings. From 4 to 48 h, significant losses in xylose conversion are measured with previous bioextrusion. Indicators of the solid fraction deconstruction, observed during the bioextrusion step, indicate a stronger biomass degradation after 48 h. Improvements of glucose conversion rates can be associated with good mixing conditions of the extruder, especially due to the use of kneading elements. Enzymes are probably more homogeneously distributed (distributive mixing) and can access more catalytic sites available. Moreover, dispersive mixing limits the enzyme jamming due to the biocatalysts concentration. Extrusion process permits an better agitation efficiency, good mass transfer conditions and probably a higher contact between substrate and enzymes. Lower xylose conversion results may be attributed to non-specific adsorptions or inactivation phenomena due to mechanical constraints and lignin residues. Good deconstruction results on the solid fraction may be associable with a synergetic action between mechanical and biochemical constraints. Autofluorescent signal analysis of the lignin fraction show its evolution during the deconstruction of the solid residue. During the hydrolysis, a progressive production of very small particles, appearing to be associated with the lignin fraction is observed. Lignin-carbohydrate complexes are also detected in the liquid fraction. These heteropolymeric complexes, difficult or even impossible for the enzymes to hydrolyze, are an obstacle to the biomass valorization. If lignin deconstruction is mainly due to the alkaline pretreatment, bioextrusion process seems to reduce the proportion of these heteropylymers with high molecular weights.

Co-rotating twin-screw extruders are unique and versatile machines that are used widely in the plastics and food processing industries. Due to the large number of operating variables and design parameters available for manipulation and the complex interactions between them, it cannot be claimed that these extruders are currently being optimally utilised. The most significant improvement to the field of twin-screw extrusion would be through the provision of a generally applicable dynamic process model that is both computationally inexpensive and accurate. This would enable product design, process optimisation and process controller design to be performed cheaply and more thoroughly on a computer than can currently be achieved through experimental trials. This thesis is divided into three parts: dynamic modelling, measurement and control. The first part outlines the development of a dynamic model of the extrusion process which satisfies the above mentioned criteria. The dynamic model predicts quasi-3D spatial profiles of the degree of fill, pressure, temperature, specific mechanical energy input and concentrations of inert and reacting species in the extruder. The individual material transport models which constitute the dynamic model are examined closely for their accuracy and computational efficiency by comparing candidate models amongst themselves and against full 3D finite volume flow models. Several new modelling approaches are proposed in the course of this investigation. The dynamic model achieves a high degree of simplicity and flexibility by assuming a slight compressibility in the process material, allowing the pressure to be calculated directly from the degree of over-fill in each model element using an equation of state. Comparison of the model predictions with dynamic temperature, pressure and residence time distribution data from an extrusion cooking process indicates a good predictive capability. The model can perform dynamic step-change calculations for typical screw configurations in approximately 30 seconds on a 600 MHz Pentium 3 personal computer. The second part of this thesis relates to the measurement of product quality attributes of extruded materials. A digital image processing technique for measuring the bubble size distribution in extruded foams from cross sectional images is presented. It is recognised that this is an important product quality attribute, though difficult to measure accurately with existing techniques. The present technique is demonstrated on several different products. A simulation study of the formation mechanism of polymer foams is also performed. The measurement of product quality attributes such as bulk density and hardness in a manner suitable for automatic control is also addressed. This is achieved through the development of an acoustic sensor for inferring product attributes using the sounds emanating from the product as it leaves the extruder. This method is found to have good prediction ability on unseen data. The third and final part of this thesis relates to the automatic control of product quality attributes using multivariable model predictive controllers based on both direct and indirect control strategies. In the given case study, indirect control strategies, which seek to regulate the product quality attributes through the control of secondary process indicators such as temperature and pressure, are found to cause greater deviations in product quality than taking no corrective control action at all. Conversely, direct control strategies are shown to give tight control over the product quality attributes, provided that appropriate product quality sensors or inferential estimation techniques are available.

This research deals with the modeling and control of a plasticating twin screw extruder (TSE) that will be used to obtain consistent product quality. The TSE is a widely used process technology for compounding raw polymers. Compounding creates a polymer with improved properties that satisfy the demand of modern plastic applications. Modeling and control of a TSE is challenging because of its high nonlinearity, inherent time delay, and multiple interactive dynamic behavior. A complete methodology is proposed in this thesis to design an advanced control scheme for a TSE. This methodology was used to develop a model predictive control scheme for a laboratory scale plasticating TSE and to implement the control scheme in real-time. The TSE has a processing length of 925 mm and a length to screw diameter ratio (L/D) of 37. High density polyethylenes with different melt indices were used as processing materials. Manipulated variables and disturbance variables were selected based on knowledge of the process. Controlled variables were selected using a selection method that includes a steady state correlation between process output variables and product quality variables, and dynamic considerations. Two process output variables, melt temperature (Tm) at the die and melt pressure (Pm) at the die, were selected as controlled variables. A new modeling approach was proposed to develop grey box models based on excitation in the extruder screw speed (N), one of the manipulated variables. The extruder was excited using a predesigned random binary sequence (RBS) type excitation in N and nonlinear models relating Tm and Pm to N were developed using this approach. System identification techniques were used to obtain model parameters. The obtained models have an autoregressive moving average with exogenous (ARMAX) input structure and the models explain the physics of the extrusion process successfully. The TSE was also excited using a predesigned RBS in the feed rate (F) as a manipulated variable. Models relating Tm and Pm to F were developed using a classical system identification technique; both models have ARMAX structures. The model between Pm and F was found to give excellent prediction for data obtained from a stair type excitation, indicating that the obtained models provide a good representation of the dynamics of the twin screw extruder. Analysis of the TSE open loop process indicated two manipulated variables, N and F, and two controlled variables, Tm and Pm. Thus, a model predictive controller (MPC) was designed using the developed models for this 2X2 system and implemented in real-time. The performance of the MPC was studied by checking its set-point tracking ability. The robustness of the MPC was also examined by imposing external disturbances. Finally, a multimodel operating regime was used to model Tm and N. The operating regime was divided based on the screw speed, N. Local models were developed using system identification techniques. The global model was developed by combining local models using fuzzy logic methodology. Simulated results showed excellent response of Tm for a wide operating range. A similar approach was used to design a global nonlinear proportional-integral controller (n-PI) and a nonlinear MPC (n-MPC). Both the controllers showed good set-points tracking ability over the operating range. The multiple model-based MPC showed smooth transitions from one operating regime to another operating regime. / Process Control

Parallel manipulators have been the subject of study of much robotic research during the past three decades. A parallel manipulator typically consists of a moving platform that is connected to a fixed base by at least two kinematic chains in parallel. Parallel manipulators can provide several attractive advantages over their serial counterpart in terms of high stiffness, high accuracy, and low inertia, which enable them to become viable alternatives for wide applications. But parallel manipulators also have some disadvantages, such as complex forward kinematics, small workspace, complicated structures, and a high cost. To overcome the above shortcomings, progress on the development of parallel manipulators with less than 6-DOF has been accelerated. However, most of presented parallel manipulators have coupled motion between the position and orientation of the end-effector. Therefore, the kinematic model is complex and the manipulator is difficult to control. Only recently, research on parallel manipulators with less than six degrees of freedom has been leaning toward the decoupling of the position and orientation of the end-effector, and this has really interested scientists in the area of parallel robotics. Kinematic decoupling for a parallel manipulator is that one motion of the up-platform only corresponds to input of one leg or one group of legs. And the input cannot produce other motions. Nevertheless, to date, the number of real applications of decoupled motion actuated parallel manipulators is still quite limited. This is partially because effective development strategies of such types of closed-loop structures are not so obvious. In addition, it is very difficult to design mechanisms with complete decoupling, but it is possible for fewer DOF parallel manipulators. To realize kinematic decoupling, the parallel manipulators are needed to possess special structures; therefore, investigating a parallel manipulator with decoupling motion remains a challenging task. This thesis deals with lower mobility parallel manipulator with decoupled motions. A novel parallel manipulator is proposed in this thesis. The manipulator consists of a moving platform that is connecting to a fixed base by three legs. Each leg is made of one C (cylinder), one R (revolute) and one U (universal) joints. The mobility of the manipulator and structure of the inactive joint are analyzed. Kinematics of the manipulator including inverse and forward kinematics, velocity equation, kinematic singularities, and stiffness are studied. The workspace of the parallel manipulator is examined. A design optimization is conducted with the prescribed workspace. It has been found that due to the special arrangement of the legs and joints, this parallel manipulator performs three translational degrees of freedom with decoupled motions, and is fully isotropic. This advantage has great potential for machine tools and Coordinate Measuring Machine (CMM). / UOIT

Extrusion compounding addresses such problems as the non-homogeneity of the mixture and separation of fiber from the polymer during rotational molding, which consequently affect the mechanical and physical properties of the resulting composites. <p>Using triethoxyvinylsilane as chemical pre-treatment on flax fibers and linear low density polyethylene (LLDPE) and high density polyethylene (HDPE) as polymer matrices, this study focused on the effects of flax fiber content (0%, 12.5% or 25%) and extrusion parameters such as barrel zone temperatures (75-110-120-130-140°C or 75-120-130-140-150°C) and screw speed (110 or 150 rpm) on the extrudate and composite properties (extrudate color, extrudate density, extrudate melt flow index, extrudate morphology, composite color, composite density, composite morphology, composite tensile strength and composite water absorption). <p>A mixture of chemically pre-treated flax fibers and powdered polyethylene matrices underwent extrusion compounding using a twin-screw extruder. The extrudates were then pelletized, ground, rotationally molded and cut into test specimens (composites). The mechanical and physical properties of both the extrudates and the composites from different treatments were then measured and compared. <p>Using multiple linear regression, models were generated to show quantitatively the significant effects of the process variables on the response variables. Finally, using response surface methodology and superposition surface methodology on the preceding data, the following optimum values for fiber content and extrusion parameters were determined: for LLDPE composites, fiber content = 6.25%, temperatures = 75-117.3-127.3-137.3-147.3°C, screw speed = 117.5 rpm; for HDPE composites, fiber content = 5.02%, temperatures = 75-118.1-128.1-138.1-148.1°C, screw speed = 125.56 rpm.

Industrial demands for higher productivity rates and more stringent part tolerances require faster production machines that can produce, assemble, or manipulate parts at higher speeds and with better accuracy than ever before. In a majority of production machines, such as machine tools, ball screw drives are used as the primary motion delivery mechanism due to their reasonably high accuracy, high mechanical stiffness, and low cost. This brings the motivation for the research in this thesis, which has been to develop new control techniques that can achieve high bandwidths near the structural frequencies of ball screw drives, and also compensate for various imperfections in their motion delivery, so that better tool positioning accuracy can be achieved at high speeds. A precision ball screw drive has been designed and built for this study. Detailed dynamic modeling and identification has been performed, considering rigid body dynamics, nonlinear friction, torque ripples, axial and torsional vibrations, lead errors, and elastic deformations. Adaptive Sliding Mode Controller (ASMC) is designed based on the rigid body dynamics and notch filters are used to attenuate the effect of structural resonances. Feedforward friction compensation is also added to improve the tracking accuracy at velocity reversals. A bandwidth of 223 Hz was achieved while controlling the rotational motion of the ball screw, leading to a servo error equivalent to 1.6 um of translational motion. The motor and mechanical torque ripples were also modeled and compensated in the control law. This improved the motion smoothness and accuracy, especially at low speeds and low control bandwidths. The performance improvement was also noticeable when higher speeds and control bandwidths were used. By adding on the torque ripple compensation, the rotational tracking accuracy was improved to 0.95 um while executing feed motions with 1 m/sec velocity and 1 g acceleration. As one of the main contributions in this thesis, the dynamics of the 1st axial mode (at 132 Hz) were actively compensated using ASMC, which resulted in a command tracking bandwidth of 208 Hz. The mode compensating ASMC (MC-ASMC) was also shown to improve the dynamic stiffness of the drive system, around the axial resonance, by injecting additional damping at this mode. After compensating for the lead errors as well, a translational tracking accuracy of 2.6 um was realized while executing 1 m/sec feed motions with 0.5 g acceleration transients. In terms of bandwidth, speed, and accuracy, these results surpass the performance of most ball screw driven machine tools by 4-5 times. As the second main contribution in this thesis, the elastic deformations (ED) of the ball screw drive were modeled and compensated using a robust strategy. The robustness originates from using the real-time feedback control signal to monitor the effect of any potential perturbations on the load side, such as mass variations or cutting forces, which can lead to additional elastic deformations. In experimental results, it is shown that this compensation scheme can accurately estimate and correct for the elastic deformation, even when there is 130% variation in the translating table mass. The ED compensation strategy has resulted in 4.1 um of translational accuracy while executing at 1 m/sec feed motion with 0.5 g acceleration transients, without using a linear encoder. This result is especially significant for low-cost CNC (Computer Numerically Controlled) machine tools that have only rotary encoders on their motors. Such machines can benefit from the significant accuracy improvement provided by this compensation scheme, without the need for an additional linear encoder.