In the last decades, the quadrotor has been used in many areas, and deigning an effective flight control algorithm for the quadrotor has attracted great interests in both control and robotics communities. This thesis focuses on the flight control of the quadrotor by using different methods: The extend Kalman filter (EKF) based linear quadratic regulator (LQR) method and learning-based model predictive control (LBMPC) method. Chapter 4 investigates the flight control of a quadrotor subject to the model uncertainties and external disturbances. We propose a LQR based tracking algorithm. However, the designed LQR controller is hard to be implemented because of the existing noises in the measured states. A modified EKF is then designed for the online estimation of the position, velocity and motor dynamics by using the measured outputs. From the experimental testing results, it is shown that the proposed EKF-based LQR control method solves the tracking problem of the quadrotor with less tracking errors than only using the LQR method. In Chapter 5, the tracking control problem of the quadrotor subject to external disturbances and physical constraints is studied. A model predictive control (MPC) based algorithm is proposed. To reduce the computational load, a modified prior barrier interior-point method is used to solve the quadratic programming (QP) problem. Nevertheless, the achievable flight performance by using the standard MPC algorithm is affected by external disturbances. A LBMPC algorithm is proposed for the disturbance rejection. From the simulation results, it is shown that using the proposed LBMPC algorithm have less tracking errors than applying the standard MPC algorithm. / Graduate

Motion planning is the field of computer science that aims at developing algorithmic techniques allowing the automatic computation of trajecto- ries for a mechanical system. The nature of such a system vary according to the fields of application. In computer animation it could be a humanoid avatar. In molecular biology it could be a protein. The field of application of this work being aerial robotics, the system is here a four-rotor UAV (Unmanned Aerial Vehicle) called quadrotor. The motion planning problem consists in computing a series of motions that brings the system from a given initial configuration to a desired final configuration without generating collisions with its environment, most of the time known in advance. Usual methods explore the system’s configuration space regardless of its dynamics. By construction the thrust force that allows a quadrotor to fly is tangential to its attitude which implies that not every motion can be performed. Furthermore, the magnitude of this thrust force and hence the linear acceleration of the center of mass are limited by the physical capabilities of the robot. For all these reasons, not only position and orientation must be planned, higher derivatives must be planned also if the motion is to be executed. When this is the case we talk of kinodynamic motion planning. A distinction is made between the local planner and the global planner. The former is in charge of producing a valid trajectory between two states of the system without necessarily taking collisions into account. The later is the overall algorithmic process that is in charge of solving the motion planning problem by exploring the state space of the system. It relies on multiple calls to the local planner. We present a local planner that interpolates two states consisting of an arbitrary number of degrees of freedom (dof) and their first and second derivatives. Given a set of bounds on the dof derivatives up to the fourth order (snap), it quickly produces a near-optimal minimum time trajectory that respects those bounds. In most of modern global motion planning algorithms, the exploration is guided by a distance function (or metric). The best choice is the cost-to-go, i.e. the cost associated to the local method. In the context of kinodynamic motion planning, it is the duration of the minimal-time trajectory. The problem in this case is that computing the cost-to-go is as hard (and thus as costly) as computing the optimal trajectory itself. We present a metric that is a good approximation of the cost-to-go but which computation is far less time consuming. The dominant paradigm nowadays is sampling-based motion planning. This class of algorithms relies on random sampling of the state space in order to quickly explore it. A common strategy is uniform sampling. It however appears that, in our context, it is a rather poor choice. Indeed, a great majority of uniformly sampled states cannot be interpolated. We present an incremental sampling strategy that significantly decreases the probability of this happening.

This dissertation aims to apply non-zero attitude and position setpoint tracking to a quadrotor aircraft, achieved by solving the problem of a quadrotor’s inherent underactuation. The introduction of extra actuation aims to mechanically accommodate for stable tracking of non-zero state trajectories. The requirement of the project is to design, model, simulate and control a novel quadrotor platform which can articulate all six degrees of rotational and translational freedom (6-DOF) by redirecting and vectoring each propeller’s individually produced thrust. Considering the extended articulation, the proposal is to add an additional two axes (degrees) of actuation to each propeller on a traditional quadrotor frame. Each lift propeller can be independently pitched or rolled relative to the body frame. Such an adaptation, to what is an otherwise well understood aircraft, produces an over-actuated control problem. Being first and foremost a control engineering project, the focus of this work is plant model identification and control solution of the proposed aircraft design. A higher-level setpoint tracking control loop designs a generalized plant input (net forces and torques) to act on the vehicle. An allocation rule then distributes that virtual input in solving for explicit actuator servo positions and rotational propeller speeds. The dissertation is structured as follows: First a schedule of relevant existing works is reviewed in Ch:1 following an introduction to the project. Thereafter the prototype’s design is detailed in Ch:2, however only the final outcome of the design stage is presented. Following that, kinematics associated with generalized rigid body motion are derived in Ch:3 and subsequently expanded to incorporate any aerodynamic and multibody nonlinearities which may arise as a result of the aircraft’s configuration (changes). Higher-level state tracking control design is applied in Ch:4 whilst lower-level control allocation rules are then proposed in Ch:5. Next, a comprehensive simulation is constructed in Ch:6, based on the plant dynamics derived in order to test and compare the proposed controller techniques. Finally a conclusion on the design(s) proposed and results achieved is presented in Ch:7. Throughout the research, physical tests and simulations are used to corroborate proposed models or theorems. It was decided to omit flight tests of the platform due to time constraints, those aspects of the project remain open to further investigation. The subsequent embedded systems design stemming from the proposed control plant is outlined in the latter of Ch:2, Sec:2.4. Such implementations are not investigated here but design proposals are suggested. The primary outcome of the investigation is ascertaining the practicality and feasibility of such a design, most importantly whether or not the complexity of the mechanical design is an acceptable compromise for the additional degrees of control actuation introduced. Control derivations and the prototype design presented here are by no means optimal nor the most exhaustive solutions, focus is placed on the whole system and not just a single aspect of it.

A quadrotor is a type of small unmanned aerial vehicle (UAV) with four rotors. Various control techniques have been successfully applied to the quadrotor. In this thesis, two control methods, including linear quadratic regulator (LQR) and H2-optimal control, are applied to the autonomous navigation and control of a quadorotor named QBall-X4 that is developed by Quanser. The continuous-time dynamic model is established using the Euler-Lagrange approach. Due to the nonlinearities in the quadrotor dynamics, we propose a simplified linear model, which is further used for the controller design in this thesis. According to the simplified quadrotor dynamics, we design an LQR controller to regulate the quadrotor system from its initial position to the desired position. The effectiveness of the controller is verified by simulation studies. However, the LQR control system is operated in the nominal model, and it can not present guaranteed performance when system uncertainties exist. The main emphasis is placed on designing an H2-optimal controller that minimizes the H2-norm of the transfer function. The solution is obtained by using the state-space approach and linear matrix inequality (LMI) method, respectively. In contrast to LQR control method, which is normally applied to a system with no disturbance, the H2-optimal controller takes the form of an observer together with a state feedback control gain to deal with the system uncertainties and disturbances. The simulation results and experimental study verify that the proposed H2-optimal controller is an effective option for the quadrotor with the attendance of uncertainties and disturbances. / Graduate

Αντικείμενο της εργασίας είναι ο έλεγχος του προσανατολισμού ελικοπτέρου Quadrotor με χρήση ελεγκτή PID. Το ελικόπτερο Quadrotor είναι ένα μη γραμμικό, ασταθές, υποενεργοποιούμενο σύστημα. Για αυτούς τους λόγους, ο έλεγχός του παρουσιάζει σοβαρά προβλήματα. Ο ελεγκτής PID αρχικά εφαρμόζεται στο γραμμικοποιημένο μοντέλο του συστήματος, και εν συνεχεία διακριτοποιείται και εξετάζεται στο πλήρες μη γραμμικό μοντέλο του Quadrotor. Ιδιαίτερο βάρος δίνεται στη ρύθμιση του ελεγκτή PID. Αφού παρουσιαστούν οι κυριότερες μέθοδοι ρύθμισης ενός τέτοιου ελεγκτή, επιλέγεται η μέθοδος Extremum Seeking, μία επαναληπτική μέθοδος που βελτιστοποιεί τον PID ώστε να ελαχιστοποιείται τοπικά μια συνάρτηση κόστους. Σημαντικό πλεονέκτημα αυτής της μεθόδου αποτελεί το γεγονός ότι μπορεί να εφαρμοστεί κατ' ευθείαν στο μη γραμμικό μοντέλο του συστήματος βελτιστοποιώντας περαιτέρω τον ελεγκτή. Στη συνέχεια ο ελεγκτής PID εξετάζεται σε ένα πραγματικό ελικόπτερο που κατασκευάστηκε στο εργαστήριο. Στο πειραματικό αυτό σύστημα, η υλοποίηση του PID γίνεται σε έναν ηλεκτρονικό υπολογιστή, με τη βοήθεια του προγράμματος Labview ενώ η επικοινωνία ανάμεσα στον υπολογιστή και στο ελικόπτερο επιτυγχάνεται με τη βοήθεια σειριακής θύρας RS232. Μετά τη διεξαγωγή των πειραμάτων και την αξιολόγηση της απόδοσης του ελεγκτή PID, αναφέρονται τα γενικότερα συμπεράσματα της εργασίας, καθώς και προτάσεις για περαιτέρω έρευνα. / This thesis focuses on attitude control of a quadrotor helicopter with PID technique. Quadrotor is a non linear, unstable, underactuated system, so the controller design is a very challenging task. Initially the PID controller is applied to the linearized model of the helicopter, and then to the discretized one, because the controller is later implemented on a personal computer. Then we describe some PID tuning techniques that are often used in practice. In this thesis we use Extemum Seeking which is an iterative, optimization method for the PID tuning that can be used in either linear or non linear models. So Extremum Seeking can be applied to the full non linear model of the quadrotor to further improve the PID parameters. Finally the PID controller is applied to a real Quadrotor helicopter. The controller is implemented on Labview while the communication between the PC and the helicopter is achieved with two RS232 links.

La manipulation aérienne a été un domaine de recherche actif ces dernières années, principalement parce que les applications actives des véhicules aériens autonomes (UAV en anglais), augmente l'employabilité de ces véhicules pour diverses applications.Le développement récent de la manipulation aérienne a trouvé des applications potentielles dans les deux domaines, militaires et civils. Les applications militaires incluent le patrouilleur des frontières, la détection des mines, la reconnaissance, etc., tandis que les applications civiles sont en matière de gestion des catastrophes, d'inspection des ponts, de construction, de livraison de matériel, de recherche et de sauvetage, etc.La recherche sur la robotique aérienne implique principalement des hélicoptères et des architectures de décollage et d'atterrissage verticales (VTOL). Le principal avantage de ces plates-formes est leur maniabilité et la capacité d'effectuer des vols stationnaires, ce qui est essentiel pour les applications. Cette thèse porte sur les avions VTOL, où l'hélicoptère à quatre rotors ou quadrirotor est principalement étudié.En ce qui concerne le problème de la manipulation aérienne, la quantité d'applications augmente, mais en même temps, la complexité de la modélisation et du contrôle d'un tel système est également plus grande. L'un des plus grands défis réside dans leur charge utile limitée. Certaines approches ont essayé de résoudre le problème en utilisant plusieurs robots pour transporter des charges utiles avec des pinces ou des câbles, où leurs effecteurs et pinces doivent être légers eux-mêmes et capables de saisir des formes complexes. Un autre défi est que la dynamique du robot est considérablement modifiée par l'ajout de charges utiles. Cependant, pour le transport de la charge utile, il est nécessaire que les robots puissent estimer l'inertie de la charge utile et s'y adapter pour améliorer les performances de suivi.Selon les antécédents et les défis sur les véhicules VTOL portant des charges utiles ou des manipulateurs, la contribution du présent travail est centrée sur la modélisation et la conception d'une loi de commande non linéaire et une analyse de stabilité formelle pour la stabilisation asymptotique d'un véhicule VTOL portant un bras manipulateur. Pour cela, un modèle général d'un quadrirotor portant un bras manipulateur est proposé. Après cela, une loi de commande presque globalement asymptotique lisse pour la stabilisation de l'attitude qui prend en compte les effets de mouvement du bras est conçue. Une fois que le problème d'attitude est résolu, il est possible de concevoir un contrôleur non linéaire globalement asymptotique pour la dynamique de position basée sur l'utilisation de somme des fonctions saturés afin de prendre en compte les limitations des actionneurs. Enfin, certaines expériences pour valider les lois de commande proposées sont effectuées. / Aerial manipulation has been an active area of research in recent years, mainly because the active tasking of Unmanned Aerial Vehicles (UAV) increases the employability of these vehicles for various applications.The recent development of the aerial manipulation has found potential applications in both, military and civilian domains. Military applications include border patrolling, mine detection, reconnaissance, etc., while civilian applications are in disaster management, bridge inspection, construction, material delivery, search and rescue, etc.The research on aerial robotics has mainly involved helicopters and Vertical Take-off and Landing (VTOL) architectures. The main advantage of these platforms is theirmaneuverability and the capacity to perform hovers, which is essential for the applications. This thesis deals with VTOL aircrafts, where the four rotor helicopter, quadcopter or quadrotor is mainly studied.Regarding the problem of aerial manipulation, the amount of applications are increased, but at the same time the complexity of modeling and control of such a system are equally bigger. One of the biggest challenges arise from their limited payload. Some approaches have tried to solve the problem using multiple robots to carry payloads with grippers or with cables, where their end effectors and grippers have to be lightweight themselves and capable of grasping complex shapes. Another challenge is that the dynamics of the robot are significantly altered by the addition of payloads. However, for payload transport, it is necessary that the robots are able to estimate the inertia of the payload and adapt to it to improve tracking performance.According to the background and challenges on VTOL vehicles carrying payloads or manipulators, the contribution of the present work is centered on the modelling and the design of a nonlinear control and a formal stability analysis for the asymptotical stabilization of a VTOL vehicle carrying a manipulator arm. For this a general model of a quadcopter carrying a manipulator arm is proposed. After that, a smooth almost globally asymptotically control law for attitude stabilization which takes into account the arm motion effects is designed. Once the attitude problem is solved, it is possible to design a a globally asymptotically nonlinear controller for the translational dynamics based in the usage of nested and sum of saturation functions in order to take into account the actuators limitations. Finally, some experiments in order to validate the proposed control laws are carried out.

Insects posses an incredible ability to navigate their environment at high speed, despite having small brains and limited visual acuity. Through selective pressure they have evolved computationally efficient means for simultaneously performing navigation tasks and instantaneous control responses. The insect’s main source of information is visual, and through a hierarchy of processes this information is used for perception; at the lowest level are local neurons for detecting image motion and edges, at the higher level are interneurons to spatially integrate the output of previous stages. These higher level processes could be considered as models of the insect's environment, reducing the amount of information to only that which evolution has determined relevant. The scope of this thesis is experimenting with biologically inspired visual control of flying robots through information processing, models of the environment, and flight behaviour. In order to test these ideas I developed a custom quadrotor robot and experimental platform; the 'wasp' system. All algorithms ran on the robot, in real-time or better, and hypotheses were always verified with flight experiments. I developed a new optical flow algorithm that is computationally efficient, and able to be applied in a regular pattern to the image. This technique is used later in my work when considering patterns in the image motion field. Using optical flow in the log-polar coordinate system I developed attitude estimation and time-to-contact algorithms. I find that the log-polar domain is useful for analysing global image motion; and in many ways equivalent to the retinotopic arrange- ment of neurons in the optic lobe of insects, used for the same task. I investigated the role of depth in insect flight using two experiments. In the first experiment, to study how concurrent visual control processes might be combined, I developed a control system using the combined output of two algorithms. The first algorithm was a wide-field optical flow balance strategy and the second an obstacle avoidance strategy which used inertial information to estimate the depth to objects in the environment - objects whose depth was significantly different to their surround- ings. In the second experiment I created an altitude control system which used a model of the environment in the Hough space, and a biologically inspired sampling strategy, to efficiently detect the ground. Both control systems were used to control the flight of a quadrotor in an indoor environment. The methods that insects use to perceive edges and control their flight in response had not been applied to artificial systems before. I developed a quadrotor control system that used the distribution of edges in the environment to regulate the robot height and avoid obstacles. I also developed a model that predicted the distribution of edges in a static scene, and using this prediction was able to estimate the quadrotor altitude.

Recent miniaturization of computer hardware, MEMs sensors, and high energy density batteries have enabled highly capable mobile robots to become available at low cost. This has driven the rapid expansion of interest in multi-rotor unmanned aerial vehicles. Another area which has expanded simultaneously is small powerful computers, in the form of smartphones, which nearly always have a camera attached, many of which now contain a OpenCL compatible graphics processing units. By combining the results of those two developments a low-cost multi-rotor UAV can be produced with a low-power onboard computer capable of real-time computer vision. The system should also use general purpose computer vision software to facilitate a variety of experiments. To demonstrate this I have built a quadrotor UAV based on control hardware from the Pixhawk project, and paired it with an ARM based single board computer, similar those in high-end smartphones. The quadrotor weights 980 g and has a flight time of 10 minutes. The onboard computer capable of running a pose estimation algorithm above the 10 Hz requirement for stable visual control of a quadrotor. A feature tracking algorithm was developed for efficient pose estimation, which relaxed the requirement for outlier rejection during matching. Compared with a RANSAC- only algorithm the pose estimates were less variable with a Z-axis standard deviation 0.2 cm compared with 2.4 cm for RANSAC. Processing time per frame was also faster with tracking, with 95 % confidence that tracking would process the frame within 50 ms, while for RANSAC the 95 % confidence time was 73 ms. The onboard computer ran the algorithm with a total system load of less than 25 %. All computer vision software uses the OpenCV library for common computer vision algorithms, fulfilling the requirement for running general purpose software. The tracking algorithm was used to demonstrate the capability of the system by per- forming visual servoing of the quadrotor (after manual takeoff). Response to external perturbations was poor however, requiring manual intervention to avoid crashing. This was due to poor visual controller tuning, and to variations in image acquisition and attitude estimate timing due to using free running image acquisition. The system, and the tracking algorithm, serve as proof of concept that visual control of a quadrotor is possible using small low-power computers and general purpose computer vision software.

The performance of a quadrotor can be significantly disturbed in presence of wind. In this paper, a simple-to-implement attitude controller is proposed to render a robust and accurate trajectory tracking in presence of disturbance and model uncertainties. The attitude controller design is based on Quantitative Feedback Theory (QFT). A fuzzy logic controller is further employed to provide satisfactory position trajectory tracking for the quadrotor. The performances of the controllers, in terms of disturbance rejection and trajectory tracking are experimentally studied. Finally, a flight scenario is performed to compare the performances of the designed QFT-Fuzzy control scheme with the ArduCopter controller. / May 2016

Diagnostic et tolérance aux défauts sont des enjeux importants pour les systèmes de contrôle, particulièrement dans les systèmes de sécurité fondamentaux. La théorie et l'application des approches classiques de diagnostic et tolérance aux défauts doivent être revisités lorsqu'il s'agit de SCR. L'objectif de cette thèse est de proposer de nouvelles approches de diagnostic pour les systèmes contrôlés en réseau en considérant la perte de paquets et la contrainte de communication. De plus, les algorithmes de l'ordonnancement et de diagnostic proposés sont implémentés dans un mini hélicoptère / Fault diagnosis and fault-tolerant control are important issues for practical control systems, especially in safety-critical systems. The theory and application of classical approaches of fault diagnosis and fault tolerant control should be revised when dealing with NCSs. Objective of this thesis is proposing new approaches to design a fault detection and isolation (FDI) system with considering network-induced effects such as packet dropout and medium access constraints. In addition, proposed algorithms of scheduling and fault diagnosis are implemented in a mini helicopter