High performance, accelerometer-based control of the Mini-MAST structure at Langley Research Center

Many large space system concepts will require active vibration control to satisfy critical performance requirements such as line of sight pointing accuracy and constraints on rms surface roughness. In order for these concepts to become operational, it is imperative that the benefits of active vibration control be shown to be practical in ground based experiments. The results of an experiment shows the successful application of the Maximum Entropy/Optimal Projection control design methodology to active vibration control for a flexible structure. The testbed is the Mini-Mast structure at NASA-Langley and has features dynamically traceable to future space systems. To maximize traceability to real flight systems, the controllers were designed and implemented using sensors (four accelerometers and one rate gyro) that are actually mounted to the structure. Ground mounted displacement sensors that could greatly ease the control design task were available but were used only for performance evaluation. The use of the accelerometers increased the potential of destabilizing the system due to spillover effects and motivated the use of precompensation strategy to achieve sufficient compensator roll-off

The decoupling problem : invariants, parameter variations, composite systems and time-varying linear systems

Imperial Users onl

Relaxing Fundamental Assumptions in Iterative Learning Control

Iterative learning control (ILC) is perhaps best decribed as an open loop feedforward control technique where the feedforward signal is learned through repetition of a single task. As the name suggests, given a dynamic system operating on a finite time horizon with the same desired trajectory, ILC aims to iteratively construct the inverse image (or its approximation) of the desired trajectory to improve transient tracking. In the literature, ILC is often interpreted as feedback control in the iteration domain due to the fact that learning controllers use information from past trials to drive the tracking error towards zero. However, despite the significant body of literature and powerful features, ILC is yet to reach widespread adoption by the control community, due to several assumptions that restrict its generality when compared to feedback control. In this dissertation, we relax some of these assumptions, mainly the fundamental invariance assumption, and move from the idea of learning through repetition to two dimensional systems, specifically repetitive processes, that appear in the modeling of engineering applications such as additive manufacturing, and sketch out future research directions for increased practicality: We develop an L1 adaptive feedback control based ILC architecture for increased robustness, fast convergence, and high performance under time varying uncertainties and disturbances. Simulation studies of the behavior of this combined L1-ILC scheme under iteration varying uncertainties lead us to the robust stability analysis of iteration varying systems, where we show that these systems are guaranteed to be stable when the ILC update laws are designed to be robust, which can be done using existing methods from the literature. As a next step to the signal space approach adopted in the analysis of iteration varying systems, we shift the focus of our work to repetitive processes, and show that the exponential stability of a nonlinear repetitive system is equivalent to that of its linearization, and consequently uniform stability of the corresponding state space matrix.PhDElectrical Engineering: SystemsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/133232/1/altin_1.pd

Aeronautical engineering: A continuing bibliography, supplement 122

This bibliography lists 303 reports, articles, and other documents introduced into the NASA scientific and technical information system in April 1980

Air levitated ball-pipe system: system modelling, linearization and controller design

[EN] The air levitated ball-pipe system is a pneumatic levitation system that is based on airflow. Its working principle consists of a force created with a blower with the purpose of counteracting the opposing gravitational force of the ball. A TOF sensor measures the position of the ball inside the pipe and a Raspberry Pi Zero manages the control of the system. This work performs a modelling process of the ball-pipe system, an analysis of its non-linearities and it presents a variety of controllers and observers such as a PID controller, a LQR controller and a Kalman filter

Controlling Contour Errors in CNC Machines

Ph.DDOCTOR OF PHILOSOPH

New developments in mathematical control and information for fuzzy systems

Hamid Reza Karimi, Mohammed Chadli and Peng Sh

RF Pulse Designs for Signal Recovery in T2*-Weighted Functional Magnetic Resonance Imaging.

In blood-oxygenation-level-dependent (BOLD) functional magnetic resonance imaging (fMRI) using T2* contrast, images suffer from loss of signals at brain regions close to the air-filled cavities in the human head. The artifact arises from magnetic field distortion caused by the magnetic susceptibility difference between air and brain tissues, and hampers functional studies of important brain regions such as the orbito-frontal cortex. In this research project, I investigate two methods of designing radio-frequency (RF) pulses that can recover the signal loss. In addition to slice selective excitation, both pulse designs ``precompensate'' the through-plane dephasing that occurs between excitation and data acquisition. One method, which utilizes ``three-dimensional tailored RF pulses'', achieves these goals via three-dimensional spatially selective excitation. The other method uses spectral-spatial selective excitation, and relies on the assumption that through-plane dephasing is correlated with resonance frequency offset. All these sophisticated pulses are numerically designed using the iterative conjugate gradient method. To facilitate those design methods, I also propose new techniques applicable to general pulse designs, such as frameworks for pulse computation acceleration and joint design of excitation k-space trajectory and RF pulse. With phantom and human experiments, I demonstrate that the methods are efficacious in signal recovery, but not without costs and hurdles to overcome.Ph.D.Electrical Engineering: SystemsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/57708/2/chunyuy_1.pd

Anwendung von maschinellem Lernen in der optischen Nachrichtenübertragungstechnik

Aufgrund des zunehmenden Datenverkehrs wird erwartet, dass die optischen Netze zukünftig mit höheren Systemkapazitäten betrieben werden. Dazu wird bspw. die kohärente Übertragung eingesetzt, bei der das Modulationsformat erhöht werden kann, erforder jedoch ein größeres SNR. Um dies zu erreichen, wird die optische Signalleistung erhöht, wodurch die Datenübertragung durch die nichtlinearen Beeinträchtigungen gestört wird. Der Schwerpunkt dieser Arbeit liegt auf der Entwicklung von Modellen des maschinellen Lernens, die auf diese nichtlineare Signalverschlechterung reagieren. Es wird die Support-Vector-Machine (SVM) implementiert und als klassifizierende Entscheidungsmaschine verwendet. Die Ergebnisse zeigen, dass die SVM eine verbesserte Kompensation sowohl der nichtlinearen Fasereffekte als auch der Verzerrungen der optischen Systemkomponenten ermöglicht. Das Prinzip von EONs bietet eine Technologie zur effizienten Nutzung der verfügbaren Ressourcen, die von der optischen Faser bereitgestellt werden. Ein Schlüsselelement der Technologie ist der bandbreitenvariable Transponder, der bspw. die Anpassung des Modulationsformats oder des Codierungsschemas an die aktuellen Verbindungsbedingungen ermöglicht. Um eine optimale Ressourcenauslastung zu gewährleisten wird der Einsatz von Algorithmen des Reinforcement Learnings untersucht. Die Ergebnisse zeigen, dass der RL-Algorithmus in der Lage ist, sich an unbekannte Link-Bedingungen anzupassen, während vergleichbare heuristische Ansätze wie der genetische Algorithmus für jedes Szenario neu trainiert werden müssen

Sampling, infinite zeros and decoupling of linear systems,

In order to understand more fully some of the trade-offs involved in using a sampled-data representation of a continuous-time system, the effects of time-sampling on the ability to achieve disturbance decoupling and input-output decoupling for linear systems are investigated. It is shown that disturbance decouplability is lost through sampling whereas row-by-row dynamic input-output decouplability is preserved in a very strong way. These results are obtained by analyzing the structure at infinity of a sampled-data system.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/27318/1/0000340.pd