An improved robot manipulator decentralized non-linear adaptive controller that performs well in the presence of disturbances with unknown parameters and non-linearities is presented in this work. The proposed decentralized adaptive structure is a modification of the controller developed by Seraji [13-17] and is characterized by an auxiliary signal that compensates for the unmodeled dynamics and improves the tracking performance, by a feedforward component based on the inverse system to ensure high performance over a wide range and by a PD feedback component of constant gain to improve the speed of response of the system. As a result, a very accurate and fast path tracking is achieved despite the non-linearities. The scheme requires only the measurement of angular speed and displacement of each joint, and it does not require any knowledge about the mathematical model of the manipulator. Due to its decentralized structure, it can be implemented on parallel processors to speed up the operation. The main advantages of the proposed control scheme over similar controllers are that the control activity is smoother, it is less sensitive to sampling size and to the time period elapsed when the whole trajectory is traversed, as verified by simulations of several test conditions of-two of the joints of the PUMA 560 robot arm. / Graduation date: 1991

The objective of this investigation is the development of improved techniques for the estimation of robustness for dynamic systems with structured uncertainties, a problem which was approached by application of the Lyapunov direct method. This thesis considers the sign properties of the Lyapunov function derivative integrated along finite intervals of time, in place of the traditional method of the sign properties of the derivative itself. This proposed approach relaxes the sufficient conditions of stability, and is used to generate techniques for the robust design of control systems with structured perturbations. The need for such techniques has been demonstrated by recent research interest in the area of robust control design. The system considered is assumed to be nominally linear, with time-variant, nonlinear bounded perturbations. Application of the proposed technique warrants that estimates of robustness will either match or constitute an improvement upon those obtained by application of the traditional Lyapunov approach. The application of numerical procedures are used to demonstrate improvements in estimations of robustness for two-, three- and four-dimensional dynamic systems with one or more structured perturbations. The proposed numerical approaches obtain improved bounds, which are considered in the sense of their engineering aspects. To increase the accuracy of the numerical procedures, symbolic algebraic calculations are utilized. / Graduation date: 1991

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A complete method for calculating the largest Lyapunov exponent is developed in this thesis. For phase space reconstruction, a time delay estimator based on the average mutual information is discussed first. Then, embedding dimension is evaluated according to the False Nearest Neighbors algorithm. To obtain the parameters of all of the sub-functions and their derivatives, a multilayer feedforward neural network is applied to the time series data, after the time delay and embedding dimension are fixed. The Lyapunov exponents can be estimated using the Jacobian matrix and the QR decomposition. The possible applications of this method are then explored for various chaotic systems. Finally, the method is applied to some real world data to demonstrate the general relationship between the onset and progression of faults and changes in the largest Lyapunov exponent of a nonlinear system.

The last decade has seen significant advances in the development of Vertical takeoff and landing (VTOL) unmanned aerial vehicles (UAVs). The emergence of enabling technologies, in addition to the practical usefulness of such systems has driven their development to a point where numerous technology demonstrators and commercial products are now in existence. Of particular interest has been the development of small scale, VTOL UAVs commonly referred to as mini and micro-VTOL UAVs. The versatility and agility of such vehicles offers great potential for the use in clustered, urban environments. Despite recent advancements, the autonomous navigation of VTOL UAVs remains a very challenging research area. The dynamics of VTOL UAVs are heavily nonlinear, underactuated and non-minimum phase. This, coupled with the aggressive maneuvers that such vehicles are expected to execute provides a stimulating problem in dynamic control. This is particularly true in the case of micro-VTOL UAVs. The fast, nonlinear nature of these systems render classical, linear control approaches inadequate. The past twenty years has seen great interest in the development of nonlinear control strategies. This has led to the emergence of a number of standard design tools, most notably feedback linearisation and Lyapunov-based, backstepping approaches. Such design techniques offer a framework for the derivation of model based control laws capable of achieving global stabilisation and trajectory tracking control for heavily nonlinear systems. Recently, there has been significant interest in the application of such nonlinear control paradigms for the stabilisation and control of VTOL UAVs. The aim of this thesis is to further the application and analysis of nonlinear control design techniques for the control of VTOL UAVs. In particular, focus is placed on Lyapunov-based, backstepping-type control approaches. The first half of this thesis investigates Lyapunov-based control strategies that cast the closed-loop VTOL dynamics into a globally stable, cascade structure. This work was directly inspired by, and builds on, a variety of previously published works. Firstly, an alternative design approach to that previously published is presented, resulting in an improved closed-loop dynamic structure. Although inspired by the VTOL system, this idea may be generalised for the control of a broad class of systems, and is presented as such. A singularity issue arising in the cascade control of VTOL vehicles is then investigated, and a novel approach to overcome this issue is formulated. The second half of this thesis is dedicated to the trajectory tracking control of VTOL UAVs at velocities where the influence of aerodynamics is significant. In general, the aerodynamic models of VTOL UAVs are heavily nonlinear and poorly known. The use of such models in a backstepping framework that uses explicit differentiation of these models for dynamic inversion is questioned, due to the potential sensitivity of such nonlinear models. Consequently, an alternative approach utilising coupled filters to avoid such sensitivity issues is proposed. All control designs formulated in this thesis are accompanied by proofs guaranteeing their global stability, and numerical simulations demonstrating their time domain response characteristics. / http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1298413 / Thesis (Ph.D.) -- University of Adelaide, School of Mechanical Engineering, 2007

Thesis (M.S.) -- Worcester Polytechnic Institute. / Keywords: model predictive control; discrete-time model; continuous-time model; nonlinear systems; Lyapunov design. Includes bibliographical references (p. 99-102).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1968. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record.

Thesis (Ph. D.)--Oregon State University, 2007. / Printout. Includes bibliographical references (leaves 151-157). Also available on the World Wide Web.