Friction Stir Welding (FSW) is a solid-state joining process that is of special interest in joining aluminum and other alloys that are traditionally difficult to fusion weld. The energy required for this joining process is transmitted to the work-pieces through a rotating FSW tool. Modeling attempts, aimed at perfecting the process, rely on assumptions of the contact conditions present between the work-pieces and the FSW tool. Various studies have attempted to define these contact conditions. Both theoretical and experimental studies indicate the contact conditions between the work-piece and weld tool are unknown and may vary during the FSW process. To provide insight into the contact conditions, the objective of this study is to characterize the FSW nugget in terms of swept volume as indicated by the cross-sectional area and symmetry of the FSW nugget over a range of processing conditions.

The kinematic analysis of an articulated twin body, four-wheel, robotic vehicle is presented. Polaris, a research platform and contending robotic vehicle in the Intelligent Ground Vehicle Competition (IGVC) at Virginia Tech, was redesigned in 2006 to improve the mobility of the vehicle by incorporating an innovative four-bar linkage that connects the two bodies. The new linkage design minimizes vehicle off-tracking by allowing the rear wheels to closely track the path of the front wheels. This thesis will outline the theoretical kinematic model of the four-bar linkage as applied to a twin-bodied, differentially driven vehicle. The kinematic model is validated through computer simulation as well as experimentation on a fully operational robotic vehicle. The kinematic model presented here outlines the foundations for an autonomous, four-wheel drive, multi-body control system and opens avenues for dynamically controlling the tracking of the vehicle's rear body with an actuated linkage configuration. / Master of Science

A multi-unit tracked vehicle such as a continuous haulage system is widely used in underground mining applications due to its high mobility and payload capacity on rugged and soft terrain. To automate such a system, a high fidelity model of a tracked vehicle is essential in designing a controller for each tracked vehicle in the system, and a system model is required to simulate its response to input commands. This thesis presents the 2-D mathematical models of a tracked vehicle and a multi-unit tracked vehicle. All existing track-terrain interaction models are investigated and modified. By employing the modified track-terrain interaction model and applying Newton's second law of motion, the equations of motion of both single and multi-unit tracked vehicles can be derived. Computer programs for simulating the motions of these tracked vehicles on level ground have been implemented on a digital computer based on the derived system of differential equations. The fourth-order Runge-Kutta and Keun's methods are adopted to numerically integrate these differential equations. The simulation results clearly show that the programs can accurately predict the motion of a tracked vehicle maneuvered on horizontal plane, and closely predict the response of a multi-unit tracked vehicle operated on level ground its command inputs. / Master of Science

Kinematics based guidance laws like the proportional navigation (PN) and many other linear optimal guidance laws perform well in near-collision course conditions. These have been studied thoroughly in the literature from all aspects, ranging from optimality to capturability, for planar or two dimensional interceptor-target engagements, and to a lesser extent, for three dimensional engagements. But guidance in widely off-collision course conditions like high initial heading errors has been relatively less studied. This is probably due to the inherently high nonlinearity of the problem, which makes it a far more difficult problem to solve. However, with increasing speed and agility of interceptors and targets, solutions of such problems have acquired an increased urgency, as has been reflected in the recent literature. This thesis proposes a guidance law based on differential evolution (DE), a member of the evolutionary algorithms (EA) family. While EAs have been applied extensively to static optimization problems, they have been considered unsuitable for solving dynamic optimization or optimal control problems, due to their computationally intensive nature, and their consequent inability to produce solutions online in real-time, except for systems with very slow dynamics. This thesis proposes an online-implementable optimal control for interceptor guidance, a problem with inherently fast dynamics. The proposed law is applicable to all initial geometries including those that involve high to very high heading errors. While interception by itself is a challenging task in the presence of high heading errors, an additional requirement of optimality is also imposed. The first part of the thesis considers only the 2-D kinematic model with high heading errors. In the second part, a 3-D realistic dynamic model, which includes a time-varying interceptor speed, thrust, drag and mass, besides gravity in the vertical plane of motion, and upper bound on the lateral acceleration, is considered, in addition to high heading errors. It is shown that the same structure of the law that is proposed for the 2-D kinematic model can also be used for the 3-D realistic model, if the rest of the complexities of moving from 2-D space to 3-D space, and from kinematics to dynamics is duly addressed. The guidance law proposed does not require time-to-go, the estimation of which can be a difficult problem in high heading error scenarios in which the closing velocity can be negative. Easy to compute and simple to implement in practice, the proposed law does not need any of the techniques or methods from classical optimal control theory, which are complicated and suffer from several limitations. The empirical pure PN (PPN) law is augmented with a term that is a polynomial function of the heading error. The values of the coefficients of the polynomial are found by using the DE. The computational effort required for this low dimensional polynomial optimization problem is shown to be low enough to enable online implementation in real-time. The performance of the proposed law in nominal and off-nominal conditions is validated through several simulations for the 2-D kinematic model, and the 3-D realistic dynamic model. The results are compared with the PPN, augmented PPN and the all-aspect proportional navigation (AAPN) laws in the literature, as per several criteria like optimality, peak latax required and robustness to off-nominal conditions. A successful online implementation of the proposed law for application in practice is also demonstrated. An obvious limitation of optimization by soft computation methods like differential evolution is that no rigorous proof of either convergence or optimality exists for such methods. A fallback option in the form of a conventional guidance law is included in the scheme in case of failure of convergence, and an indirect proof of optimality is provided in the third and final part of the thesis. The same guidance problem is solved by direct multiple shooting method, and it is shown that the numerical results of the two methods compare favourably. The solution by the shooting method is optimal, but computationally far more intensive and takes a computation time of an order of magnitude that is at least one or two times that of the simulation time of the plant. It also needs a good initial guess solution that lies within the region of convergence, which can be a difficult task by itself. Moreover, the shooting method solution is only open loop, and hence applicable for the given model and initial conditions only. Whereas, the simplicity of the method proposed in the thesis makes the solution or guidance law computable in a fraction of the flight time of the engagement, thereby making it online implementable. Equally important, is the fact that it is closed loop, and hence robust to off-nominal conditions like variations in the plant model and parameters assumed in its design.

The thesis deals with modelling and control of wheeled mobile robots. The thesis introduces the mathematical models of diferentially driven mobile robot, robot with Ackerman steering and a skid steered robot. The thesis describes open-loop and feedback control. Feedback control is divided into point-to-point control, path following and trajectory tracking.

In autonomous racing there is a need to accurately localize the vehicle while simultaneously creating a map of the track. This information can be delivered to planning and control layers in order to achieve fully autonomous racing. The kinematic model is a commonly used motion model in feature-based SLAM. However, it is a poor representation of the vehicle when considering high lateral accelerations since the model is only based on trigonometric relationships. This Master’s Thesis investigates the consequence of using the kinematic model when undertaking demanding maneuvers; and if by switching to a dynamic model, which takes the tire forces into account, can improve the localization performance. An EKF-SLAM algorithm comprising the kinematic and dynamic model was implemented on a development platform. The pose estimation accuracy was compared using either model when subject to typical maneuvers in racing-scenarios. The results showed that the pose estimation accuracy was in general similar when using either of the vehicle models. When exposed to large slip angles, the implications of switching from a kinematic model to a dynamic model resulted in a significantly better pose estimation accuracy when driving in an unknown environment. However, switching to a dynamic model had little effect when driving in a known environment. The implications of the study suggest that, during the first lap of a racing track, the kinematic model should be switched to a dynamic model when subject to high lateral accelerations. For the consecutive laps, the choice of vehicle model has less impact. Keywords: SLAM, EKF-SLAM, Localization, Estimation, Vehicle Dynamics, Kinematic Model, Dynamic Model, Autonomous Racing / I autonom racing är det viktigt att kunna lokalisera fordonet med hög noggrannhet samtidigt som en karta över banan skapas. Den här informationen kan vidare bli hanterad av planerings- och reglersystem för att uppfylla autonom racing fullt ut. Den kinematiska modellen är en vanligt förekommande rörelsemodell i SLAM. Den är däremot en bristande representation av fordonet vid höga laterala accelerationer eftersom modellen enbart är baserad på trigonometriska samband. Det här masterarbetet undersöker den kinematiska modellens påverkan vid olika manövrar och huruvida den dynamiska modellen, som modellerar däckkrafterna, kan förbättra prestandan. En EKF-SLAM algorithm innehållande den kinematiska- och dynamiska modellen implementerades på en utvecklingsplattform. Estimeringsnoggrannheten av positionen och orienteringen jämfördes vid typiska manövrar för racingscenarier. Resultatet visade att estimeringsnoggrannheten av positionen och orienteringen var generellt sett lika vid användandet av antingen den kinematiska eller den dynamiska modellen. Implikationerna av att byta från den kinematiska modellen till den dynamiska modellen vid höga glidvinklar, resulterade i en signifikant bättre estimeringsnoggrannhet av positionen och orienteringen vid körning i en okänd miljö. Emellertid så var effekterna av att byta till en dynamisk modell insignifikanta vid körning i en känd miljö. Implikationerna av denna studie föreslår att under det första varvet av racingbanan byta från den kinematiska modellen till den dynamiska vid höga laterala accelerationer. Under kommande varv har valet av fordonsmodell mindre effekt. Nyckelord: SLAM, EKF-SLAM, lokalisering, estimering, fordonsmodellering, kinematisk modell, dynamisk modell, autonom racing.

La simulation du geste humain est une thématique de recherche importante et trouve notamment une application dans l'analyse ergonomique pour l'aide à la conception de postes de travail. Le sujet de cette thèse concerne la génération automatique de tâches d'atteinte dans le plan horizontal pour un humanoïde. Ces dernières, à partir d'un objectif exprimé dans l'espace de la tâche, requièrent une coordination de l'ensemble des liaisons. L'une des principales difficultés rencontrées lors de la simulation de gestes réalistes est liée à la redondance naturelle de l'humain. Notre démarche est focalisée principalement sur deux aspects : - le mouvement de la main dans l'espace opérationnel (trajectoire spatiale et profil temporel), - la coordination des différentes sous-chaînes cinématiques. Afin de caractériser le mouvement humain, nous avons mené une campagne de capture de mouvements pour des gestes d'atteinte contraignant la position et l'orientation de la main dans le plan horizontal. Ces acquisitions nous ont permis de connaître l'évolution spatiale et temporelle de la main dans l'espace de la tâche, en translation et en rotation. Ces données acquises couplées à une méthode de rejeu ont également permis d'analyser les relations intrinsèques qui lient l'espace de la tâche à l'espace articulaire du mannequin. Le schéma de génération automatique de mouvements réalistes est basé sur une pile de tâche avec une approche cinématique. L'hypothèse retenue pour simuler le geste est de suivre le chemin le plus court dans l'espace de la tâche tout en bornant le coût dans l'espace articulaire. Un ensemble de paramètres permet de régler le schéma. Il en résulte une cartographie de réglages qui permet de simuler une classe de mouvements réalistes. Enfin, ce schéma de génération automatique de mouvements réalistes est validé par une comparaison quantitative et qualitative entre la simulation et le geste humain. / The simulation of human movement is an active theme of research, particularly in ergonomic analysis to aid in the design of workstations. The aim of this thesis concerns the automatic generation of reaching tasks in the horizontal plane for a virtual humanoid. An objective expressed in the task space, requires coordination of all joints of the mannequin. The main difficulties encountered in the simulation of realistic movements is related to the natural redundancy of the human. Our approach is focused mainly on two aspects: - Motion of the hand's operator in the task space (spatial and temporal aspect), - Coordination of all kinematic chains. To characterize human movement, we conducted a set of motion capture with position and orientation constraints of the hand in the horizontal plane. These acquisitions allowed to know the spatial and temporal evolution of the hand in the task space, for translation and rotation aspects. These acquired data were coupled with a playback method to analyze the intrinsic relations that link the task space to joint space of the model. The automatic generation scheme of realistic motion is based on a stack of task with a kinematic approach. The assumption used to simulate the action is to follow the shortest path in the task space while limiting the cost in the joint space. The scheme is characterized by a set of parameters. A global map of parameter adjustment enables the simulation of a class of realistic movements. Finally, this scheme is validated quantitatively and qualitatively with comparison between the simulation and the human gesture.

This thesis is focused on the issue of computational modeling of soil harvesting while using the compact excavator from the company DOOSAN BOBCAT EMEA s.r.o.. The solution consists in creating two computational models in Rocky DEM and Ansys Mechanical. Rocky DEM software is used to solve the disconnection of soil by excavator components using the discrete element method. The outcome includes courses of forces and moments during the particular time of the individual joints of the model that was used. The obtained courses are then applied as an external load to the joint of a selected structural part of the analyzed model using a kinematic model in ANSYS Mechanical. The kinematic model consists of simplified geometry models of individual parts of the excavator arm, and a more detailed geometry model of the analyzed part of the arm. All the parts are connected to each other by rotational bonds representing joints. A static structural analysis of the mechanical stress is performed in ANSYS Mechanical for the prepared model during the simulated process. Finally, the selected structural part is assessed with respect to the elastic limit and fatigue strength.

This thesis focuses on different methods to analyze power transmission systems with computer software to aid in detection of faulty or damaged systems. It is split into three sections. The first section involves utilizing finite element software to analyze gear stiffness and stresses. A quasi-static and dynamic analysis are done on two sets of fixed axis spur gears and a planetary gear system using ABAQUS to analyze the stress, strain and gear mesh stiffness variation. In the second section, the vibrational patterns produced by a simple bevel gear system are investigated by an experiment and by dynamic modeling in ADAMS. Using a Fast Fourier Transform (FFT) on the dynamic contact forces, a comprehensive frequency-domain analysis will reveal unique vibration spectra at distinct frequencies around the gear mesh frequencies, their super- and sub- harmonics, and their side-band modulations. ADAMS simulation results are then compared with the experimental results. Constraints, bearing resistant torques, and other key parameters are applied as closely as possible to real operating conditions. The third section looks closely at the dynamic contact forces of a practical two-stage planetary gear. Using the same FFT approach in the second section, a frequency-domain analysis will reveal distinct frequencies around both the first-stage and the second-stage gear mesh frequencies, and their harmonics. In addition, joint time-frequency analysis (JTFA) will be applied to damaged and undamaged planetary gear systems with transient start-up conditions to observe how the frequency contents of the contact force evolve over time.

L'agriculture est un secteur d'activité qui est confronté aujourd'hui à des objectifs d'accroissement de productivité pour subvenir aux besoins alimentaires de la population mondiale en pleine explosion démographique. Cependant, cette activité sollicite fortement les biens environnementaux tels que l'eau et le sol, et des solutions sont aujourd'hui recherchées pour limiter l'incidence des pratiques agricoles sur l'environnement. Les systèmes de guidage des véhicules agricoles font partie de ces nouvelles technologies qui contribuent à cet objectif, en offrant la possibilité d'assurer la précision du suivi des trajectoires dans les parcelles, et de favoriser ainsi l'efficacité et la qualité du travail agronomique réalisé. Des fonctionnalités essentielles font néanmoins aujourd'hui défaut à ces systèmes. Citons la capacité à compenser la marche en crabe du véhicule sur les terrains glissants en pente, la capacité à contrôler les trajectoires des outils agricoles traînés, et la capacité à effectuer certaines manoeuvres en zone de fourrière. Ce travail de thèse aborde l'ensemble de ces problématiques au travers l'étude de la commande en milieu naturel de robot mobile poly-articulé à roues (RMPA), composé d'un véhicule " tracteur " à deux trains directeurs associé à n remorques passives à attache déportée. Une modélisation cinématique étendue est d'abord adoptée pour tenir compte des effets induits par les faibles conditions d'adhérence sur le comportement global du RMPA. Les variables de glissement introduites sur chacun des trains directeurs et roulants sont estimées à l'aide d'un observateur bâti à la manière d'une loi de commande. La trajectoire de référence à suivre gamma est quant à elle préalablement apprise ou construite à l'aide de primitives élémentaires et d'arcs de clothoïdes pour générer les manoeuvres de demi-tour. En premier lieu, les deux trains directeurs du RMPA sont exploités pour contrôler avec précision non seulement l'écart latéral mais également l'écart angulaire du véhicule " tracteur " par rapport à gamma : la commande du train directeur avant est basée sur la transformation du modèle en un système chaîné, conduisant à un découplage exact des performances latérales et longitudinales, puis sur des techniques de linéarisation exacte pour assurer la régulation latérale. La commande du train directeur arrière se base sur la dynamique de l'écart angulaire pour compenser les glissements et asservir cet écart sur le point de fonctionnement choisi. En second lieu, ces commandes sont étendues pour asservir latéralement la ieme remorque du RMPA le long de gamma : une approche en cascade est utilisée pour traduire une commande virtuelle de la ieme remorque en terme de commande du train directeur avant du véhicule " tracteur ". La commande longitudinale du RMPA est quant à elle basée sur une stratégie de commande prédictive à modèle interne, afin de suivre avec précision le profil de vitesse associé à gamma. De nombreuses expérimentations en conditions réelles, effectuées sur un RMPA composé d'un véhicule " tracteur " à deux trains directeurs et d'une remorque passive à attache déportée, viennent valider les différentes approches présentées dans ce mémoire et permettent d'apprécier les performances des lois de commande proposées. / Agriculture has today the challenge to increase its productivity in order to supply enough food for the growing needs of the world population. However, this activity strongly damages environmental ressources as water and soil, and new solutions are today required to reduce the impact of agricultural practices on environment. Automatic guidance systems for farm vehicles are some new technologies that contribute to this objective, allowing accurate path following in the fields and therefore improving efficiency and quality of the agricultural work carried out. Essential functionalities are however absent in these systems, as the capacities to compensate for the crabway motion of the vehicle on sliding sloping fields, to control the trajectories of the towed implement,and to perform U-turn maneuvers in headland. This thesis studies these problems through the control in presence of sliding of a poly-articulated wheeled mobile robot called RMPA, composed of a four-wheel-steering vehicle and n passive trailers hooked up at some distance from the rear axle of the previous one. An extended kinematic model of the RMPA is first used in order to take into account for the sliding effects on the overall behaviour of the robot. The sliding parameters, introduced on each rolling and steering axle of the RMPA, are estimated using a state observer built as a control law. The reference path [gamma] to be followed is either previously learned or specially planned using elementary primitives connected together with pieces of clothoid to produce the U-turn maneuvers. In a first step, both front and rear steering actuations of the robot are used to accurately control both lateral and angular deviations of the RMPA's four-wheel-steering vehicle with respect to [gamma] : the control of the front steering wheels is based on the transformation of the extended kinematic model into a chained system, allowing to dissociate the lateral and longitudinal commands, and on exact linearization techniques in order to servo lateral deviation. The control of the rear steering wheels is built from the angular deviation dynamic and ensures the convergence of the vehicle deviation to the desired set point. In a second step, these control laws are extended to control the lateral deviation of the ith trailer of the RMPA with respect to [gamma] : a backstepping approach is proposed to calculate the control law for the RMPA's front steering wheels from the study of a virtual control law for the ith trailer. Finally, the longitudinal control law of the RMPA is based on model predictive control, in order to accurately follow the velocity references linked to [gamma]. Numerous experiments relying on an actual RMPA, composed of a passive trailer hooked up at some distance from the rear axle of a four-wheel-steering vehicle, permit to validate the various approaches presented in this thesis and to appreciate the capabilities of the proposed control laws.