Robotics has been the subject of academic study from as early as 1948. For much of this time, study has focused on very specific applications in very well controlled environments. For example, the first commercial robots (1961) were introduced in order to improve the efficiency of production lines. The tasks undertaken by these robots were simple, and all that was required of a control algorithm was speed, repetitiveness and reliability in these environments. Now however, robots are being used to move around autonomously in increasingly unpredictable environments, and the need for robotic control algorithms that can successfully react to such conditions is ever increasing. In addition to this there is an ever-increasing array of robots available, the control algorithms for which are often incompatible. This can result in extensive redesign and large sections of code being re-written for use on different architectures. The thesis presented here is that a new generic approach can be created that provides robust high quality smooth paths and time-optimal path tracking to substantially increase applicability and efficiency of autonomous motion plans. The control system developed to support this thesis is capable of producing high quality smooth paths, and following these paths to a high level of accuracy in a robust and near time-optimal manner. The system can control a variety of robots in environments that contain 2D obstacles of various shapes and sizes. The system is also resilient to sensor error, spatial drift, and wheel-slip. In achieving the above, this system provides previously unavailable functionality by generically creating and tracking high quality paths so that only minor and clear adjustments are required between different robots and also be being capable of operating in environments that contain high levels of perturbation. The system is comprised of five separate novel component algorithms in order to cater for five different motion challenges facing modern robots. Each algorithm provides guaranteed functionality that has previously been unavailable in respect to its challenges. The challenges are: high quality smooth movement to reach n-dimensional goals in regions without obstacles, the navigation of 2D obstacles with guaranteed completeness, high quality smooth movement for ground robots carrying out 2D obstacle navigation, near time-optimal path tracking, and finally, effective wheel-slip detection and compensation. In meeting these challenges the algorithms have tackled adherence to non-holonomic constraints, applicability to a wide range of robots and tasks, fast real-time creation of paths and controls, sensor error compensation, and compensation for perturbation. This thesis presents each of the above algorithms individually. It is shown that existing methods are unable to produce the results provided by this thesis, before detailing the operation of each algorithm. The methodology employed is varied in accordance with each of the five core challenges. However, a common element of methodology throughout the thesis is that of gradient descent within a new type of potential field, which is dynamic and capable of the simultaneous creation of high-quality paths and the controls required to execute them. By relating global to local considerations through subgoals, this methodology (combined with other elements) is shown to be fully capable of achieving the aims of the thesis. It is concluded that the produced system represents a novel and significant contribution as there is no other system (to the author’s knowledge) that provides all of the functionality given. For each component algorithm there are many control systems that provide one or more of its features, but none that are capable of all of the features. Applications for this work are wide ranging as it is comprised of five component algorithms each applicable in their own right. For example, high quality smooth paths may be created and followed in any dimensionality of space if time optimality and obstacle avoidance are not required. Broadly speaking, and in summary, applications are to ground-based robotics in the areas of smooth path planning, time optimal travel, and compensation for unpredictable perturbation.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Technological advances in electromechanical sensor and actuators, energy storage, data processing and control methodology made possible the development of unmanned aerial vehicles (UAVs). The quadrotor has emerged as one of these research platforms due to its mechanical simplicity, high maneuverability, as well as its capability of hovering and perform vertical take-off and landing. However, such vehicle presents some challenging issues to control area, like: nonlinearity, time-varying behavior, in addition it belongs to the class of underactuated mechanical systems, and it is subject to aerodynamics disturbances and parametric uncertainties. Therefore, this dissertation has as main objective, contribute to development and control strategies implementation to solve the positioning and path tracking problems of unmanned aerial vehicles, focusing on an underactuated mechanical system. In order to obtain a dynamic model that represents the aerial vehicle properly and realistically, the motion equations were developed based on the physics laws that define the mechanical system. The model we obtained is decoupled, thus we consider the presence of two subsystems, the rotational and the translational ones. A cascade control strategy was implemented, so that, a model predictive control (MPC) was developed to the altitude and orientation control of the aerial vehicle. However, the positioning control along the xy axis was performed through a proportional integral derivative control (PID). Such strategies allowed a smooth path tracking, beyond the possibility of dealing with physical constraints of the system. In order to assess the robustness of the control structure shown, we performed flight simulations under the presence of aerodynamics disturbances and parametric uncertainties. / Avanços tecnológicos em sensores e atuadores microeletromecânicos, no armazenamento de energia, no processamento de informações e em metodologias de controle possibilitaram o desenvolvimento dos veículos aéreos não tripulados (VANT s). O quadricóptero tem emergido como uma destas plataformas de pesquisa devido a sua simplicidade mecânica, a alta manobrabilidade, bem como a capacidade de realizar pairagem e decolagens e pousos verticais. Contudo, tal veículo apresenta algumas características desafiadoras para a área de controle, como: não linearidades, comportamento variante no tempo, além de pertencer à classe dos sistemas mecânicos subatuados e estar sujeito a distúrbios aerodinâmicos e incertezas paramétricas. Desta forma, este trabalho possui como principal objetivo contribuir para o desenvolvimento e a implementação de estratégias de controle para solucionar os problemas de posicionamento e rastreamento de trajetória em veículos aéreos não tripulados, focando em um sistema mecânico subatuado. Com o intuito de obter um modelo dinâmico que represente de forma apropriada e realista o veículo aéreo, suas equações de movimento foram desenvolvidas baseando-se nas leis físicas que regem o sistema mecânico. O modelo obtido é desacoplado, portanto, consideramos a existência de dois subsistemas, o rotacional e o translacional. Uma estratégia de controle em cascata foi implementada, de modo que, um controle preditivo baseado em modelo (CPBM) foi desenvolvido para o controle da altitude e da orientação do veículo aéreo. Já o controle de posicionamento no eixo xy foi efetuado através de um controlador proporcional integral derivativo (PID). Tais estratégias permitiram um rastreamento de trajetória suave, além da possibilidade de lidar com as restrições físicas do sistema. Com o intuito de avaliar a robustez da estrutura de controle apresentada, foram realizadas simulações de voo na presença de distúrbios aerodinâmicos e incertezas paramétricas. / Mestre em Ciências

Les études menées permettent de prendre en main un système depuis l’identification jusqu’à la commande robuste des systèmes non entiers. Les principes de la platitude permettent de parvenir à la planification de trajectoire à condition de connaître le modèle du système, d’où l’intérêt de l’identification des paramètres du système. Les principaux travaux de cette thèse concernent l’identification de système par modèles non entiers, la génération et la poursuite robuste de trajectoire par l’application des principes de la platitude aux systèmes non entiers.Le chapitre 1 rappelle les définitions et propriétés de l’opérateur non entier ainsi que les diverses méthodes de représentation d’un système non entier. Le théorème de stabilité est également remémoré. Les algèbres sur les polynômes non entiers et sur les matrices polynômiales non entières sont introduites pour l’extension de la platitude aux systèmes non entiers.Le chapitre 2 porte sur l’identification par modèle non entier. Après un état de l’art sur les méthodes d’identification par modèle non entier, deux contextes sont étudiés : en présence de bruit blanc et en présence de bruit coloré. Dans chaque cas, deux estimateurs optimaux (sur la variance et le biais) sont propos´es : l’un, en supposant une structure du modèle connue et d’ordres de dérivation fixés, et l’autre en combinant des techniques de programmation non linéaire qui optimise à la fois les coefficients et les ordres de dérivation.Le chapitre 3 établit l’extension des principes de la platitude aux systèmes non entiers.La platitude des systèmes non entiers linéaires en proposant différentes approches telles que les fonctions de transfert et la pseudo-représentation d’état par matrices polynômiales est étudiée.La robustesse du suivi de trajectoire est abordée par la commande CRONE. Des exemples de simulations illustrent les développements théoriques de la platitude au travers de la diffusion thermique sur un barreau métallique.Enfin, le chapitre 4 est consacré à la validation des contributions en identification, en planification de trajectoire et en poursuite robuste sur un système non entier réel : un barreau métallique est soumis à un flux de chaleur. / The general theme of the work enables to handle a system, from identification to robust control. Flatness principles tackle path planning unless knowing the system model, hence the system parameter identification necessity. The principal contribution of this thesis deal with system identification by non integer models and with robust path tracking by the use of flatness principles for fractional models.Chapter 1 recalls the definitions and properties of a fractional operator and also the various representation methods of a fractional system. The stability theorem is also brought to mind. Fractional polynomial and fractional polynomial matrice algebras are introduced for the extension of flatness principles for fractional systems.Chapter 2 is about non integer model identification. After a state of the art on system identification by non integer model. Two contexts are considered : in presence of white noise and of colored noise. In each situation, two optimal (in variance and bias sense) estimators are put forward : one, when considering a known model structure with fixed differentiating orders, and another one by combining nonlinear programming technics for the optimization of coefficients and differentiating orders.Chapter 3 establishes the extension of flatness principles to fractional systems. Flatness of linear fractional systems are studied while considering different approaches such as transfer functions or pseudo-state-space representations with polynomial matrices. Path tracking robustness is ensured with CRONE control. Simulation examples display theoretical developments on flatness through thermal diffusion on a metallic rod. Finally, Chapter 4 is devoted to validate the contributions to system identification, to trajectory planning and to robust path tracking on a real fractional system : a metallic rod submitted to a heat flux.

The transport industry is experiencing a disruption as fully autonomous vehicles are introduced in traffic. The intelligent, driverless vehicles will reduce cost, liberate human effort and increase safety. Today, the hardware technology seems to have reached the required processing power, but the decision-making algorithm still has a long way to go until they’re proven to be road-safe. Among these is the problem of lateral path tracking control. This thesis will consider the lateral control problem with the goal to send the right signal to the steering actuators so that the vehicle follows a predetermined trajectory. The vehicle in question is a triaxial, rigid, electric truck with active steering on both front and rearmost wheels. With servo latency and large inertial parameters in mind, a highly accurate model of the lateral and yaw behavior must be identified in order to predict the vehicle dynamics for a given steering input. Then, the properties of an optimal lateral controller are iteratively improved until a sufficiently low tracking error is obtained. Lastly, the controller is tuned to guarantee robustness for a range of uncertain vehicle parameters. The derived triaxial model with servo actuation is proven to be better at predicting the vehicle dynamics compared to other models common in literature with only one active steering input. When constructing a lateral controller, the importance was shown of considering 1) state feedback control of the lateral error, 2) feedforward control operating on future road curvature, 3) integrating control which combats biases and model errors, 4) using a tailored triaxial model and 5) minimizing the control signal change. Lastly, the derived controller was shown to have a decent stability margin with respect to estimated uncertainties. / Transportbranschen är i ett skifte då helt autonoma fordon införs i trafiken. De intelligenta, förarlösa fordonen minskar kostnader, ökar säkerheten och låter oss människor syssla med annat. Idag verkar det som att hårdvarutekniken har den processorkraft som behövs men de beslutsfattande algoritmerna har fortfarande en lång väg att gå tills de har visat sig vara helt vägsäkra. Bland dessa är problemet med lateral styrningskontroll som kommer ses över i denna avhandling. Fordonet i fråga är en rigid lastbil med tre hjulaxlar och aktiv styrning på både de främre och bakersta hjulen. Med tanke på servofördröjningar och de stora tröghetsparametrarna måste en noggrann modell av dynamiken identifieras för att förutspå responsen för en viss styrvinkel. Därefter utvecklas en optimal lågnivåregulator iterativt tills ett tillräckligt lågt spårningsfel erhållits. Slutligen ställs regulatorn in för att garantera robusthet för ett set av osäkra fordonsparametrar Den härledda triaxialmodellen med servostyrning var bevisbart bättre på att förutspå fordonsdynamiken jämfört med andra modeller som återkommer frekvent i litteraturen. Vid regulatorkonstruktionen påvisades vikten av att överväga 1) återkoppling av laterala felet, 2) förhandsgranskning som tittar på den kommande vägkrökningen, 3) integrering av styrfelet som åtgärdar modellfel, 4) en skräddarsydd fordonsmodell med tre axlar och 5) minimering av ändringen utav kontrollsignalen. Slutligen visades den härledda regulatorn ha en skaplig stabilitetsmarginal gentemot uppskattade osäkerheter av parametrar.