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The main focus of this study is on the active and semi-active control of civil engineering structures subjected to seismic excitations. Among different candidate control strategies, the sliding mode control approach emerges as a convenient alternative, because of its superb robustness under parametric and input uncertainties. The analytical developments and numerical results presented in this dissertation are directed to investigate the feasibility of application of the sliding mode control approach to civil structures. In the first part of this study, a unified treatment of active and semi-active sliding mode controllers for civil structures is presented. A systematic procedure, based on a special state transformation, is also presented to obtain the regular form of the state equations which facilitates the design of the control system. The conditions under which this can be achieved in the general case of control redundancy are also defined. The importance of the regular form resides in the fact that it allows to separate the design process in two basic steps: (a) selection of a target sliding surface and (b) determination of the corresponding control actions. Several controllers are proposed and extensive numerical results are presented to investigate the performance of both active and semi-active schemes, examining in particular the feasibility of application to real size civil structures. These numerical studies show that the selection of the sliding surface constitutes a crucial step in the implementation of an efficient control design. To improve this design process, a generalized sliding surface definition is used which is based on the incorporation of two auxiliary dynamical systems. Numerical simulations show that this definition renders a controller design which is more flexible, facilitating its tuning to meet different performance specifications. This study also considers the situation in which not all the state information is available for control purposes. In practical situations, only a subset of the physical variables, such as displacements and velocities, can be directly measured. A general approach is formulated to eliminate the explicit effect of the unmeasured states on the design of the sliding surface and the associated controller. This approach, based on a modified regular form transformation, permits the utilization of arbitrary combinations of measured and unmeasured states. The resulting sliding surface design problem is discussed within the framework of the classical optimal output feedback theory, and an efficient algorithm is proposed to solve the corresponding matrix nonlinear equations. A continuous active controller is proposed based only on bounding values of the unmeasured states and the input ground motion. Both active and semi-active schemes are evaluated by numerical simulations, which show the applicability and performance of the proposed approach. / Ph. D.

The contact patch of the tire is responsible for all of the transmission of a vehicle's motion to the road surface. This small area is responsible for the acceleration, stopping and steering control of the vehicle. Throughout the development of vehicle safety and stability control systems, it is desirable to possess the exact forces and moments at the tire contact patch. The tire is a passive element in the system, supplying no explicit information to vehicle control systems. Current safety and stability algorithms use estimated forces at the tire contact patch to develop these control strategies. An "intelligent" tire that is capable of measuring and transmitting the instantaneous forces and moments at the contact patch to the control algorithms in real-time holds promise to improve vehicle safety and performance. Using the force and friction information measured at the contact patch, an anti-lock braking control strategy is developed using sliding mode control. This strategy is compared to the performance of a current commercial anti-lock braking system that has been optimized by performing a threshold sensitivity analysis. The results show a definite improvement in control system strategy having known information at the tire contact patch. / Master of Science

This thesis presents the use of sliding mode control applied to a 1/10th scale robotic car to operate at a desired slip. Controlling the robot car at any desired slip has a direct relation to the amount of force that is applied to the driving wheels based on road surface conditions. For this model, the desired traction/slip is maintained for a specific surface which happens to be a Lego treadmill platform. How the platform evolved and the robot car was designed are also covered. To parameterize the system dynamics, simulated annealing is used to find the minimal error between mathematical simulations and physical test results. Also discussed is how the robot car and microprocessor can be modeled as a hybrid system. The results from testing the robot car at various desired percent slip show that it is possible to control the slip dynamics of a 1/10th scale automated robotic car and thus pave the way for further studies using scaled model cars to test an automated highway system. / Master of Science

Robustness of the closed-loop system has repercussions on both stability and performance, making the study of robustness very important. Fundamentally, the performance and stability of closed-loop systems utilizing state-feedback are tied to that of the observers. The primary goal of this thesis is to develop a robust nonlinear observer and closely examine the usefulness of the observer in the presence of non-collocation and parametric uncertainty and as an integral component in closed-loop control. The usefulness of the observer being investigated depends on robustness, accuracy, computational burden, tunability, ease of design, and ease of implementation on an actual flexible motion system. The design and subsequent integration of the Kalman filter, an optimal observer, into a closed-loop system is well known and systematic. However, there are shortcomings of the Kalman filter in the presence of model uncertainty which are highlighted in this work. Simulation studies are conducted using the Simulation Module in National Instruments LabVIEW 8.5 and experiments are conducted on a physical system consisting of a single flexible link with non-collocation of actuators and sensors using LabVIEW Real Time 8.5. Simulations serve as a means to analyze the performance of the optimal observer and the robust observer by analyzing their dynamic behavior as well as that of the closed-loop system with each observer in place. The focus of experiments is on investigating implementation of the robust observer, including initialization and tuning of observer design parameters off-line and on-line. Simulations verify the robustness properties of the sliding mode observer while experiments show that the robust observer can be implemented at fast control rates and that replacing the Kalman filter with a robust observer has direct ramifications on closed-loop performance.

Ein Haupteinsatzgebiet der Großraummanipulatoren stellen Betonverteilermasten dar. Aufgrund der langen schmalen Armkonstruktionen fällt bei diesen Maschinen der Trend zum Leichtbau bezüglich der Dynamik besonders ins Gewicht. Um die Vorteile leichter Konstruktionen wie geringere Achslasten, geringerer Kraftstoffverbrauch und kleinere Antriebe nutzen zu können, werden Regelungen benötigt, die die Struktur stabilisieren und ein Schwingen der Mastspitze verhindern. Zur Systemanalyse und Regelungsauslegung wurde ein Mehrkörpermodell aus starren und elastischen Körpern sowie den notwendigen Hydraulikzylindern erstellt und durch Messungen validiert. Am Modell konnte gezeigt werden, dass die Regelung im letzten Gelenk die Schwingung an der Mastspitze maßgeblich beeinflusst und zur Schwingungstilgung eingesetzt werden kann. Hierfür wird die Bewegung des Verteilermastes durch eine Ausgleichsbewegung im letzten Gelenk kompensiert, sodass die Mastspitze keine starken Schwingungen ausführt. Die Schwingungen werden über Beschleunigungsmessung detektiert und nach entsprechender Filterung kann die Bewegung bestimmt werden. Mittels Sliding Mode Control erfolgt die Berechnung der schwingungsmindernden Zylinderkraft und garantiert somit Robustheit gegenüber Modellierungsungenauigkeiten und äußeren Störungen. Die Kraftregelung des Hydraulikzylinders wird anschließend über eine Integrator-Backstepping Regelung realisiert. Die resultierende Schwingungsminimierung beträgt in unterschiedlichsten Maststellungen bis zu 95%. / A special case of multi-link manipulators are truck mounted concrete pumps. Due to the lightweight design of the long and slender boom, it is vulnerable to vibrations. The advantages are smaller masses and therefore less actuation power which results in smaller actuators with less fuel consumption. In order to retain the advantages of lightweight design, special controllers are needed to stabilize the overall system and result in a vibration free motion of the boom tip. A multibody system with flexible bodies has been built in order to analyse the system's behaviour and to test and design appropriate control strategies. It could be demonstrated, that controlling only the last joint of the boom decisively effects the motion of the boom tip and is therefore suitable to suppress vibrations. The idea is to compensate the boom's motion by adjusting the last joint angle in a way, so that the boom tip stays at its initial position. In order to implement these findings and obtain a robust control three steps are necessary: the boom's motion must be measured and a vibration reducing force defined which has to be applied by the hydraulic actuator. The vibrations are detected by acceleration measurement and after appropriate filtering a joint angle trajectory can be determined. The cylinder force is found using Sliding Mode Control which guarantees robustness against modeling inaccuracies and external disturbances. A mathematical description of the last segment is necessary for the design of this nonlinear control strategy. The force control of the hydraulic cylinder is then implemented via backstepping control. The resulting vibration is minimized by this control by up to 95% at different boom positions.