Stabilization of Compressor Surge Using Gain-Scheduled Controller

Gain scheduling is a control method that is used in nonlinear systems to optimize their controlled performance and robustness over a wide range of operating conditions. It is one of the most commonly used controller design approaches for nonlinear systems. In this control technique, the controller consists of a collection of linear controllers, each of which provides satisfactory closed-loop stability and performance for a small operating region, and combined they guarantee the stability of the system along the entire operating range. The operating region of the system is determined by a scheduling signal, also known as the scheduling variable, which may be either exogenous or endogenous with respect to the plan. A good design of the gain-scheduled controller requires a suitable selection of the scheduling variables to properly reflect the dynamics of the system. In this thesis, we apply the gain scheduling control method to the control of compression systems with active magnetic bearings (AMBs). First, a gain-scheduled controller is designed and tested for the rotor levitation control of the AMB system. The levitation controller is designed to guarantee robust rotor levitation over a wide range of rotating speeds. We show through numerical simulation that the rotor vibration is contained in the presence of uncertainties introduced by speed dependent gyroscopic forces. Next, we implement the gain scheduling control method to the active stabilization of compressor surge in a compression system using the AMBs as actuators. Recently, Yoon et al. [1] showed that AMBs can be used to stabilize the surge instability in a compression system. In this thesis, we demonstrate that gain scheduling control can effectively extend the stable operating region of the compression system beyond the limits presented in [1]. For the stabilization of surge, a gain-scheduled controller was obtained by combining six linear controllers that together they cover the full operating range of the compression system. We were able to demonstrate through numerical simulation that the designed surge controller is effective in suppressing the instability down to a throttle valve opening of 12%, and in the presence of random flow disturbance and actuator saturation. An observer-based technique was implemented to achieve a bumpless and smooth transfer when switching between the linear controllers

Development of a two axis motion simulation system for thermal/vacuum satellite testing

A two-axis motion simulation system for thermal vacuum testing of large satellites in a space simulation chamber was developed. Satellites as large as 3000 kilograms with a 4-meter diameter and a 5-meter length can be tested. This motion simulator (MS) incorporates several unique features which result in a less complicated design with improved performance when compared to previous satellite motion simulators. The design of the simulator is discussed in detail

Study and Development of Mechatronic Devices and Machine Learning Schemes for Industrial Applications

Obiettivo del presente progetto di dottorato è lo studio e sviluppo di sistemi meccatronici e di modelli machine learning per macchine operatrici e celle robotizzate al fine di incrementarne le prestazioni operative e gestionali. Le pressanti esigenze del mercato hanno imposto lavorazioni con livelli di accuratezza sempre più elevati, tempi di risposta e di produzione ridotti e a costi contenuti. In questo contesto nasce il progetto di dottorato, focalizzato su applicazioni di lavorazioni meccaniche (e.g. fresatura), che includono sistemi complessi quali, ad esempio, macchine a 5 assi e, tipicamente, robot industriali, il cui utilizzo varia a seconda dell’impiego. Oltre alle specifiche problematiche delle lavorazioni, si deve anche considerare l’interazione macchina-robot per permettere un’efficiente capacità e gestione dell’intero impianto. La complessità di questo scenario può evidenziare sia specifiche problematiche inerenti alle lavorazioni (e.g. vibrazioni) sia inefficienze più generali che riguardano l’impianto produttivo (e.g. asservimento delle macchine con robot, consumo energetico). Vista la vastità della tematica, il progetto si è suddiviso in due parti, lo studio e sviluppo di due specifici dispositivi meccatronici, basati sull’impiego di attuatori piezoelettrici, che puntano principalmente alla compensazione di vibrazioni indotte dal processo di lavorazione, e l’integrazione di robot per l’asservimento di macchine utensili in celle robotizzate, impiegando modelli di machine learning per definire le traiettorie ed i punti di raggiungibilità del robot, al fine di migliorarne l’accuratezza del posizionamento del pezzo in diverse condizioni. In conclusione, la presente tesi vuole proporre soluzioni meccatroniche e di machine learning per incrementare le prestazioni di macchine e sistemi robotizzati convenzionali. I sistemi studiati possono essere integrati in celle robotizzate, focalizzandosi sia su problematiche specifiche delle lavorazioni in macchine operatrici sia su problematiche a livello di impianto robot-macchina. Le ricerche hanno riguardato un’approfondita valutazione dello stato dell’arte, la definizione dei modelli teorici, la progettazione funzionale e l’identificazione delle criticità del design dei prototipi, la realizzazione delle simulazioni e delle prove sperimentali e l’analisi dei risultati.The aim of this Ph.D. project is the study and development of mechatronic systems and machine learning models for machine tools and robotic applications to improve their performances. The industrial demands have imposed an ever-increasing accuracy and efficiency requirement whilst constraining the cost. In this context, this project focuses on machining processes (e.g. milling) that include complex systems such as 5-axes machine tool and industrial robots, employed for various applications. Beside the issues related to the machining process itself, the interaction between the machining centre and the robot must be considered for the complete industrial plant’s improvement. This scenario´s complexity depicts both specific machining problematics (e.g. vibrations) and more general issues related to the complete plant, such as machine tending with an industrial robot and energy consumption. Regarding the immensity of this area, this project is divided in two parts, the study and development of two mechatronic devices, based on piezoelectric stack actuators, for the active vibration control during the machining process, and the robot machine tending within the robotic cell, employing machine learning schemes for the trajectory definition and robot reachability to improve the corresponding positioning accuracy. In conclusion, this thesis aims to provide a set of solutions, based on mechatronic devices and machine learning schemes, to improve the conventional machining centre and the robotic systems performances. The studied systems can be integrated within a robotic cell, focusing on issues related to the specific machining process and to the interaction between robot-machining centre. This research required a thorough study of the state-of-the-art, the formulation of theoretical models, the functional design development, the identification of the critical aspects in the prototype designs, the simulation and experimental campaigns, and the analysis of the obtained results

Optimization and control of feed and transfer pumps

A new low pressure fuel system implementation for Scania’s trucks is being investigated. The main challenge consists in exchanging the mechanical pump with electrical pumps. The electrical pumps must then be controlled to supply exactly the demanded amount of fuel at the required pressure. System redundancy allows a lot of degrees of freedom influencing the final performance. This thesis studies the factors influencing system’s performance to design a controller that enhances its behavior. The physical basis of the elements in the system are investigated and stated with that purpose. The system is analyzed and the output pressure and tank level are controlled by a LQG regulator giving successful results in reference tracking. Integral action is included for disturbance rejection and the states are estimated to overcome quantifications and noise from the signals. The disturbance rejection performance is improved by extending the regulator with a Smith Predictor for time delay compensation and including information about the engine mass-flow demand. The control actions are minimized by the tuning of the controller in order to extend component’s life. The controller includes different modes for when an external action should be input e.g., when a diagnosis test must be run. The optimization of free set-points is discussed and holistic criteria from experience is set. The result is that the system endurance is enhanced by running only two pumps when one does not provide higher efficiency. Results show that different pumps should be chosen in the final design for an improvement of the global efficiency. Future work will consist in implementing the resulting controller in the real system built with actuators selected accordingly to the optimization results

Development of a hybrid thermoplastic forming process for the manufacture of multi-facet and curvilinear surgical blades from bulk metallic glass

Bulk metallic glasses (BMGs) are multi-component alloys that have formed an amorphous atomic structure. This class of materials exhibit a unique combination of high strength/hardness and high elastic limit that is ideal for the formation and retention of a sharp edge. At high temperatures above the glass transition temperature, BMG begins to exhibit softening behavior and transitions to a supercooled liquid regime. This supercooled state allows the use of economically-viable thermoplastic forming techniques that are typically not available to metals and other hard materials. BMG has therefore been identified as an alternative material for precision surgical blades with the potential of tremendous cost savings. A hybrid thermoplastic forming processing involving sequential micro-molding and micro-drawing operations is developed to manufacture the multi-facet/curvilinear geometries found on most surgical blades. This is accomplished through an oblique drawing technique, i.e. drawing with a non-zero inclination angle. By applying time-varying force profiles during the drawing operation, a wide range of complex blade geometries are possible. A manufacturing testbed has been designed, assembled, and automated based on the oblique drawing concept. To facilitate a smooth drawing operation, a supervisory control algorithm has been specifically developed to switch between force-feedback and velocity-feedback controllers. Experiments have exhibited positive results across several multi-facet and curvilinear blade geometries. Manufacturing process capabilities are quantitatively evaluated and experimental results have measured cutting edge radii to be consistently less than 15 nm, rake face surface finish Ra to be on the order of 20 nm, and edge straightness deviations to be less than 5 µm RMS. Measurements are made at several locations along blade samples as well as across various blade geometries. A high degree of repeatability of edge radius, surface finish, and straightness are found both within a single sample as well as among different blades

MOD-0A 200 kW wind turbine generator design and analysis report

The design, analysis, and initial performance of the MOD-OA 200 kW wind turbine generator at Clayton, NM is documented. The MOD-OA was designed and built to obtain operation and performance data and experience in utility environments. The project requirements, approach, system description, design requirements, design, analysis, system tests, installation, safety considerations, failure modes and effects analysis, data acquisition, and initial performance for the wind turbine are discussed. The design and analysis of the rotor, drive train, nacelle equipment, yaw drive mechanism and brake, tower, foundation, electricl system, and control systems are presented. The rotor includes the blades, hub, and pitch change mechanism. The drive train includes the low speed shaft, speed increaser, high speed shaft, and rotor brake. The electrical system includes the generator, switchgear, transformer, and utility connection. The control systems are the blade pitch, yaw, and generator control, and the safety system. Manual, automatic, and remote control are discussed. Systems analyses on dynamic loads and fatigue are presented

Research and technology

The NASA Lewis Research Center's research and technology accomplishments for fiscal year 1987 are summarized. It comprises approximately 100 short articles submitted by staff members of the technical directorates and is organized into four sections: aeronautics, aerospace technology (which includes space communications), space station systems, and computational support. A table of contents by subject was developed to assist the reader in finding articles of special interest

A fluid power application of alternative robust control strategies

This thesis presents alternative methods for designing a speed controller for a hydrostatic power transmission system. Recognising that such a system, comprising a valve controlled motor supplied by the laboratory ring main and driving a hydraulic pump as a load, contains significant non-linearities, the thesis shows that robust 'modern control' approaches may be applied to produce viable controllers without recourse to the use of a detailed model of the system. In its introduction, it considers why similar approaches to the design of fluid power systems have not been applied hitherto. It then sets out the design and test, in simulation and on a physical rig, of two alternative linear controllers using H∞ based methods and a 'self organising fuzzy logic' controller (SOFLC). In the linear approaches, differences between the characteristics of the system and the simple models of it are accommodated in the controller design route as 'perturbations' or 'uncertainties'. The H∞ based optimisation methods allow these to be recognised in the design. “Mixed sensitivity” and “Loop shaping” methods are each applied to design controllers which are tested successfully on the laboratory rig. The SOFLC in operation does not rely on a model, but instead allows fuzzy control rules to evolve. In the practical tests, the system is subjected to a range of disturbances in the form of supply pressure fluctuations and load torque changes. Also presented are test results for proportional and proportional plus integral (PI) controllers, to provide a reference. It is demonstrated qualitatively that performance using the linear controllers is superior to that using proportional and PI controllers. An increased range of stable operation is achieved by the controller designed using “loop shaping” – performance is enhanced by the use of two controllers selected automatically according to the operating speed, using a “bumpless” transfer routine. The SOFLC proved difficult to tune. However, stable operation was achieved.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

An investigation into the design and performance of an automatic shape control system for a Sendzimir cold rolling mill.

Shape (or flatness) control for rolled steel strip is becoming increasingly important as customer requirements become more stringent. Automatic shape control is now more or less mandatory on all new four-high cold mills, but no comprehensive scheme yet exists on a Sendzimir mill. This is due to the complexity of the control system design on such a mill, where many more degrees of freedom for control exist than is the case with the four-high mills.The objective of the current work is to develop, from first principles, such a system; including automatic control of the As-U-Roll and first intermediate roll actuators in response to the measured strip shape. This thesis concerns itself primarily with the As-U-Roll control system. The material presented is extremely wide-ranging. Areas covered include the development of original static and dynamic mathematical models of the mill systems, and testing of the plant by data-logging to tune these models. A basic control system philosophy proposed by other workers is modified and developed to suit the practical system requirements and the data provided by the models. The control strategy is tested by comprehensive multivariable simulation studies. Finally, details are given of the practical problems faced when installing the system on the plant. These include problems of manual control inter-action bumpless transfer and integral desaturation.At the time of presentation of the thesis, system commissioning is still in progress and production results are therefore not yet available. Nevertheless, the simulation studies predict a successful outcome, although performance is expected to be limited until the first intermediate roll actuators are eventually included in the scheme also