Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2009. / This thesis details the development and comparison of two linear control systems that performhover control for a vertical take-off and landing unmanned aerial vehicle. A non-linear mathematical model of the aircraft dynamics is developed. A classical successive loop closure control approach is presented, which applies static gains to the decoupled model around hover. A variable gain approach is presented using optimal control, which linearises the aircraftmodel around its state at fixed time steps. Simulation performance and robustness results are examined for both systems. Different aspects of both controller design processes and results are compared, including navigational performance, robustness and ease of use.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: This thesis presents the development and implementation of a position based kinematic guidance system, the derivation and testing of a Dynamic Pursuit Navigation algorithm and a thorough analysis of an aircraft’s runway interactions, which is used to implement automated take-off of a fixed wing UAV. The analysis of the runway is focussed on the aircraft’s lateral modes. Undercarriage and aerodynamic effects are first analysed individually, after which the combined system is analysed. The various types of feedback control are investigated and the best solution suggested. Supporting controllers are designed and combined to successfully implement autonomous take-off, with acceleration based guidance. A computationally efficient position based kinematic guidance architecture is designed and implemented that allows a large percentage of the flight envelope to be utilised. An airspeed controller that allows for aggressive flight is designed and implemented by applying Feedback Linearisation techniques. A Dynamic Pursuit Navigation algorithm is derived that allows following of a moving ground based object at a constant distance (radius). This algorithm is implemented and verified through non-linear simulation. / AFRIKAANSE OPSOMMING: Hierdie tesis handel oor die ontwikkeling en toepassing van posisie-afhanklike, kinematiese leidings-algoritmes, die ontwikkeling van ’n Dinamiese Volgings-navigasie-algoritme en ’n deeglike analise van die interaksie van ’n lugraam met ’n aanloopbaan sodat outonome opstygprosedure van ’n vastevlerk vliegtuig bewerkstellig kan word. Die bogenoemde analise het gefokus op die laterale modus van ’n vastevlerk vliegtuig en is tweeledig behartig. Die eerste gedeelte het gefokus op die analise van die onderstel, terwyl die lugraam en die aerodinamiese effekte in die tweede gedeelte ondersoek is. Verskillende tipes terugvoerbeheer vir die outonome opstygprosedure is ondersoek om die mees geskikte tegniek te bepaal. Addisionele beheerders, wat deur die versnellingsbeheer gebaseerde opstygprosedure benodig word, is ontwerp. ’n Posisie gebaseerde kinematiese leidingsbeheerstruktuur om ’n groot persentasie van die vlugvermoë te benut, is ontwikkel. Terugvoer linearisering is toegepas om ’n lugspoedbeheerder , wat in staat is tot aggressiewe vlug, te ontwerp. ’n Dinamiese Volgingsnavigasie-algoritme wat in staat is om ’n bewegende grondvoorwerp te volg, is ontwikkel. Hierdie algoritme is geïmplementeer en bevestig deur nie-lineêre simulasie.

M.Ing. / Linear control system theory is well developed and has lead to a number of control system types with well-defined design methods that can be applied to any linear system. Unfortunately, no system in nature is truly linear. As a result, such non-linear systems must be represented by a linear model that is accurate over some region of the operating states of the system. The success of linear control theory in commercial applications is testament to the fact that some types of systems can be adequately represented by a linear model. However, systems with time-varying dynamics or non-linearities such as input or operating state saturation cannot always be adequately controlled by linear control systems. For that reason, non-linear control techniques must be investigated. This project aims to investigate Non-linear Model Predictive Control theory and practical implementation in the context of developing an autopilot for an Unmanned Aerial Vehicle based on a miniature helicopter. A non-linear model of the dynamics of an X-Cell Spectra G radio-controlled helicopter was developed based on the existing literature. A number of experiments were performed to determine the parameters of this model. Significant future work exists in designing additional ground experiments since certain parameters are difficult to measure safely in the laboratory. Additional work to improve the accuracy of the model at high airspeeds, as well as incorporating a more accurate yaw dynamics model, is also required. Following this, a Non-linear Model Predictive Control autopilot was simulated using MATLAB®. The simulation tested the effects of control system parameters such as control horizon and sampling period, as well as the sensor noise susceptibility and its ability to handle wind as a random disturbance. The results determined adequate control system parameters for level flight as well as landing the helicopter under ideal conditions. Simulations in which sensor noise and wind were added showed that the control system is significantly affected by sensor noise and that it cannot hover in the presence of wind. A real-time implementation was not achieved during this work; however, several directions for future research have been discussed.

The advantages of UAVs in the aviation arena have led to extensive research activities on autonomous technology of UAVs to achieve specific mission objectives. This thesis mainly focuses on the development of a mission-based guidance system. Among various missions expected of UAVs for future needs, autonomous formation flight (AFF) and obstacle avoidance within safe operation limits are investigated. In the design of an adaptive guidance system for AFF, the leader information except position is assumed to be unknown to a follower. Thus, the only measured information related to the leader is the line-of-sight range and angle. Adding an adaptive element with neural networks into the guidance system provides a capability to effectively handle leader's velocity changes. Therefore, this method can be applied to the AFF control systems that use passive sensing methods. The simulation and flight test results clearly show that the adaptive guidance control system is a promising solution for autonomous formation flight of UAVs. The successful flight evaluations using the GTMax rotary wing UAV also demonstrate unique maneuvering aspects associated with rotary wing UAVs in formation flight. In the design of an autonomous obstacle avoidance system, an integrated approach is proposed to resolve the conflict between aggressive maneuvering needed for obstacle avoidance and the constrained maneuvering needed for envelope protection. A time-optimal problem with obstacle and envelope constraints is used for an integrated approach for obstacle avoidance and envelope protection. The Nonlinear trajectory generator (NTG) is used as a real-time optimization solver. The computational complexity arising from the obstacle constraints is reduced by converting the obstacle constraints into a safe waypoint constraint along with an implicit requirement that the horizontal velocity during the avoidance maneuver must be non-negative. The issue of when to initiate a time-optimal avoidance maneuver is addressed by including a requirement that the vehicle must maintain its original flight path to the maximum extent possible. The simulation results using a rotary wing UAV demonstrate the feasibility of the proposed approach for obstacle avoidance with envelope protection.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: This thesis presents the design and implementation of all the subsystems required to perform precision autonomous helicopter landings within a low-cost framework. To obtain high-accuracy state estimates during the landing phase a vision-based approach, with a downwards facing camera on the helicopter and a known landing target, was used. An e cient monocular-view pose estimation algorithm was developed to determine the helicopter's relative position and attitude during the landing phase. This algorithm was analysed and compared to existing algorithms in terms of sensitivity, robustness and runtime. An augmented kinematic state estimator was developed to combine measurements from low-cost GPS and inertial measurement units with the high accuracy measurements from the camera system. High-level guidance algorithms, capable of performing waypoint navigation and autonomous landings, were developed. A visual position and attitude measurement (VPAM) node was designed and built to perform the pose estimation and execute the associated algorithms. To increase the node's throughput, a compression scheme is used between the image sensor and the processor to reduce the amount of data that needs to be processed. This reduces processing requirements and allows the entire system to remain on-board with no reliance on radio links. The functionality of the VPAM node was con rmed through a number of practical tests. The node is able to provide measurements of su cient accuracy for the subsequent systems in the autonomous landing system. The functionality of the full system was con rmed in a software environment, as well as through testing using a visually augmented hardware-in-the-loop environment. / AFRIKAANSE OPSOMMING: Hierdie tesis beskryf die ontwikkeling van die substelsels wat vir akkurate outonome helikopter landings benodig word. 'n Onderliggende doel was om al die ontwikkeling binne 'n lae-koste raamwerk te voltooi. Hoe-akkuraatheid toestande word benodig om akkurate landings te verseker. Hierdie metings is verkry deur middel van 'n optiese stelsel, bestaande uit 'n kamera gemonteer op die helikopter en 'n bekende landingsteiken, te ontwikkel. 'n Doeltreffende mono-visie posisie-en-orientasie algoritme is ontwikkel om die helikopter se posisie en orientasie, relatief tot die landingsteiken, te bepaal. Hierdie algoritme is deeglik ondersoek en vergelyk met bestaande algoritmes in terme van sensitiwiteit, robuustheid en uitvoertyd. 'n Optimale kinematiese toestandswaarnemer, wat metings van GPS en inersiele sensore kombineer met die metings van die optiese stelsel, is ontwikkel en deur simulasie bevestig. Hoe-vlak leidingsalgoritmes is ontwikkel wat die helikopter in staat stel om punt-tot-punt navigasie en die landingsprosedure uit te voer. 'n Visuele posisie-en-orientasie meetnodus is ontwikkel om die mono-visie posisie-en orientasie algoritmes uit te voer. Om die deurset te verhoog is 'n saampersingsalgoritme gebruik wat die hoeveelheid data wat verwerk moet word, te verminder. Dit het die benodigde verwerkingskrag verminder, wat verseker het dat alle verwerking op aanboord stelsels kan geskied. Die meetnodus en mono-visie algoritmes is deur middel van praktiese toetse bevestig en is in staat om metings van voldoende akkuraatheid aan die outonome landingstelsel te verskaf. Die werking van die volledige stelsel is, deur simulasies in 'n sagteware en hardeware-indie- lus omgewing, bevestig.

Thesis (MScEng)-- Stellenbosch University, 2013. / ENGLISH ABSTRACT: In this thesis the design, analysis, implementation, and verification of a fault-tolerant unmanned aerial vehicle (UAV) flight control system which is robust to structural damage causing the natural flight dynamics of the vehicle to become asymmetric, is presented. The main purpose of the robust control architecture is to maintain flight stability after damage has occurred. The control system must be able to handle an abrupt change from an undamaged to a damaged state, and must also not depend on explicit knowledge of the damage. A robust control approach is therefore preferred above an adaptive control approach. As a secondary objective, the system must provide robust flight performance to ensure adequate response times and acceptable transients’ behaviour, both in normal flight, and after damage has occurred. An asymmetric six degrees of freedom equations of motion model is derived. The model accounts for the changes in the aerodynamic model of the aircraft as well as changes in the centre of gravity location. Vortex lattice techniques are used to determine the aerodynamic coefficients of the aircraft for damage to the main wing resulting in 0% to 40% spanwise lifting surface loss. A sequential quadratic programming optimisation algorithm is applied to the force and moment equations to find the trim flight state and actuator deflections of the asymmetric aircraft for constant airspeed and altitude. The trim flight state can be further constrained to force zero bank angle, zero sideslip angle or a desired relative weighting of nonzero bank angle and nonzero sideslip angle. The calculated trim actuator deflections are compared to the physical deflection limits to determine the feasibility of maintaining trim flight for different percentages of wing loss. Assuming that a valid trim condition exists, the relative stability of the aircraft’s natural modes is analysed as a function of percentage wing loss by tracing the locus of the open-loop poles. An acceleration-based flight control architecture is designed and implemented, and the robustness of the flight control stability and performance is analysed as a function of percentage wing loss. The robustness and performance of the flight control system is verified with a nonlinear simulation for spanwise wing loss from 0 to 40%. Practical flight tests are performed to verify the robustness and performance of the flight control systems to in-flight damage. A detachable wing with release mechanism is designed and manufactured to simulate 20% wing loss. The flight control system is implemented on a practical UAV and a successful flight test shows that it performs fully autonomous flight control, and is able to accommodate an in-flight partial wing loss. / AFRIKAANSE OPSOMMING: In hierdie tesis word die ontwerp, analise, implementasie en verifikasie van ’n fout-verdraende onbemande vliegtuig beheerstelsel wat robuust is tot strukturele skade wat die natuurlike vlug dinamika van die voertuig asimmetries maak, voorgestel. Die hoofdoel van hierdie robuuste beheer argitektuur is om stabiliteit te verseker na die skade aangerig is. Die beheerstelsel moet die skielike verandering van normale na beskadigde vlug hanteer sonder enige eksplisiete kennis daarvan. Dus word ’n robuuste beheer aanslag verkies bo ’n aanpassende beheer struktuur. Tweedens moet die vlugbeheerstelsel robuust genoeg wees om steeds die gewenste reaksietyd en aanvaarbare oorgangsverskynsels te kan hanteer, tydens beide normale en beskadigde vlug. ’n Asimmetriese ses grade van vryheid beweginsvergelykings model word afgelei. Die model het die vermoë om veranderinge in die aerodinamiese model van die vliegtuig, sowel as massamiddelpunt verskuiwing, voor te stel. “Vortex Lattice” metodes is gebruik om die aerodinamiese koëffisiënte van die beskadigde vlerk voor te stel tussen 0% en 40% verlies. ’n Sekwensiële kwadratiese programmering optimiserings algorithme is aangewend op die krag en moment vergelykings om die ekwilibrium vlug toestand en aktueerder defleksies te vind vir ’n asimmetriese vliegtuig met konstante lugspoed en hoogte. Die ekwilibrium vlug toestand word verder beperk deur ’n nul rolhoek, ’n nul sygliphoek of ’n relatiewe weging van die twee. Die bepaalde ekwilibrium defleksies word dan vergelyk met die fisiese limiete om hulle geldigheid te bepaal vir ekwilibrium vlug. As ’n geldige ekwilibrium toestand bestaan, kan die relatiewe stabiliteit van die vliegtuig se natuurlike modusse ontleed word as ’n persentasie van vlerkverlies deur die wortellokusse van die ooplus pole na te gaan. ’n Versnellings-gebaseerde vlug beheerstelsel argitektuur is ontwerp en geïmplementeer. Daarna is die robuustheid ontleed as ’n funksie van die persentasie vlerkverlies. Die robuustheid en gedrag van hierdie vlugbeheerstelsel is geverifieer met ’n nie-linêre simulasie vir 0 tot 40% vlerkverlies. Praktiese vlugtoetse is onderneem om die robuustheid en gedrag tydens/na skade gedurende ’n vlug, te verifeer. ’n Vlerkverlies meganisme is ontwerp en vervaardig om 20% vlerkverlies te simuleer. Die vlugbeheerstelsel is geïmplementeer op ’n onbemande vliegtuig en die daaropvolgende suksesvolle vlug lewer bewys dat die vlugbeheerstelsel wel skade, in die vorm van gedeeltelike vlerkverlies, tydens vlug kan hanteer.

No description available.

La surveillance des systèmes industriels et/ou embarqués constitue une préoccupation majeure en raison de l’accroissement de leur complexité et des exigences sur le respect des profilsde mission. La détection d’anomalies tient une place centrale dans ce contexte. Fondamentalement,les procédures de détection à base de modèles consistent à comparer le fonctionnement réel dusystème avec un fonctionnement de référence établi à l’aide d’un modèle sans défaut. Cependant,les systèmes à surveiller présentent souvent des dynamiques non linéaires et difficiles à caractériserde manière exacte. L’approche retenue dans cette thèse consiste à englober leur influencepar des incertitudes bornées. La propagation de ces incertitudes permet l’évaluation de seuils dedécision visant à assurer le meilleur compromis possible entre sensibilité aux défauts et robustesseaux perturbations tout en préservant une complexité algorithmique raisonnable. Pour cela, unepart importante du travail porte sur l’extension des classes de modèles dynamiques à incertitudesbornées pour lesquels des observateurs intervalles peuvent être obtenus avec les preuves d’inclusionet de stabilité associées. En s’appuyant sur des changements de coordonnées variant dans letemps, des dynamiques LTI, LPV et LTV sont considérées graduellement pour déboucher sur desclasses de dynamiques Non Linéaires à Incertitudes Bornées continues (NL-IB). Une transformationdes modèles NL-IB en modèles LPV-IB a été utilisée. Une première étude sur les non-linéaritésd’une dynamique de vol longitudinal est présentée. Un axe de travail complémentaire porte surune caractérisation explicite de la variabilité (comportement aléatoire) du bruit de mesure dansun contexte à erreurs bornées. En combinant cette approche à base de données avec celle à basede modèle utilisant un prédicteur intervalle, une méthode prometteuse permettant la détection dedéfauts relatifs à la position d’une surface de contrôle d’un avion est proposée. Une étude portenotamment sur la détection du blocage et de l’embarquement d’une gouverne de profondeur. / The monitoring of industrial and/or embedded systems is a major concern accordingto their increasing complexity and requirements to respect the mission profiles. Detection of anomaliesplays a key role in this context. Fundamentally, model-based detection procedures consist incomparing the true operation of the system with a reference established using a fault-free model.However, the monitored systems often feature nonlinear dynamics which are difficult to be exactlycharacterized. The approach considered in this thesis is to enclose their influence through boundeduncertainties. The propagation of these uncertainties allows the evaluation of thresholds aimingat ensuring a good trade-off between sensitivity to faults and robustness with respect to disturbanceswhile maintaining a reasonable computational complexity. To that purpose, an importantpart of the work adresses the extension of classes of dynamic models with bounded uncertaintiesso that interval observers can be obtained with the related inclusion and stability proofs. Based ona time-varying change of coordinates, LTI, LPV and LTV dynamics are gradually considered tofinally deal with some classes classes of nonlinear continuous dynamics with bounded uncertainties.A transformation of such nonlinear models into LPV models with bounded uncertainties has beenused. A first study on nonlinearities involved in longitudinal flight dynamics is presented. A complementarywork deals with an explicit characterization of measurement noise variability (randombehavior of noise within measurement) in a bounded error context. Combining this data-drivenapproach with a model-driven one using an interval predictor, a promising method for the detectionof faults related to the position of aircraft control surfaces is proposed. In this context, specialattention has been paid to the detection of runaway and jamming of an elevator.

LPV approaches are being published in the Czech Republic nowadays. Their usage is enabled by the EGNOS European satellite augmentation system. However, published decision heights do not allow equivalence with the ILS CAT I precision approach yet. This work presents the model of automated control of aircraft precision approach. Verification of its functionality shows that applicable airspace requirements can be fulfilled for lower values of decision heights than values already published. The model is developed using contemporary methods of model-based development in the tool supporting common processing of both continuous and discrete signals. Although model architecture follows the structure of commonly used ILS system in definition of coordinate system and in establishing control in two separate directions it allows curved approach. Usage of digital navigation data provided by satellite system opens further opportunities in its usage, expansion and improvements. Model functionality in control of flight course, position and height control is verified in the scenarios covering detailed thesis goals. The goals were defined based on definition of precision approach process and include navigation signal drop-out, impact of wind, various flight path angles and curved approach. Analysis of behavior of controlled aircraft dynamics was a stimulator for research of specific system modules up to the application level, i.e. specific simulations of successful precision approaches.

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