During the past two decades, many researchers have developed methods for the detection of structural defects at the early stages to operate the aerospace vehicles safely and to reduce the operating costs. The Surface Response to Excitation (SuRE) method is one of these approaches developed at FIU to reduce the cost and size of the equipment. The SuRE method excites the surface at a series of frequencies and monitors the propagation characteristics of the generated waves. The amplitude of the waves reaching to any point on the surface varies with frequency; however, it remains consistent as long as the integrity and strain distribution on the part is consistent. These spectral characteristics change when cracks develop or the strain distribution changes. The SHM methods may be used for many applications, from the detection of loose screws to the monitoring of manufacturing operations. A scanning laser vibrometer was used in this study to investigate the characteristics of the spectral changes at different points on the parts. The study started with detecting a load on a plate and estimating its location. The modifications on the part with manufacturing operations were detected and the Part-Based Manufacturing Process Performance Monitoring (PbPPM) method was developed. Hardware was prepared to demonstrate the feasibility of the proposed methods in real time. Using low-cost piezoelectric elements and the non-contact scanning laser vibrometer successfully, the data was collected for the SuRE and PbPPM methods. Locational force, loose bolts and material loss could be easily detected by comparing the spectral characteristics of the arriving waves. On-line methods used fast computational methods for estimating the spectrum and detecting the changing operational conditions from sum of the squares of the variations. Neural networks classified the spectrums when the desktop – DSP combination was used. The results demonstrated the feasibility of the SuRE and PbPPM methods.

Orientador: Luiz Carlos Kretly / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-14T12:34:11Z (GMT). No. of bitstreams: 1 Silva_MauricioWeberBenjoda_M.pdf: 7910629 bytes, checksum: ba689f61e380994adce43b3aad0b347c (MD5) Previous issue date: 2009 / Resumo: O desenvolvimento de chaves MEMS (Micro Electro Mechanical System) de RF, usando os conceitos e a tecnologia de placa de circuito impresso (PCB) é objeto desta pesquisa. Foram fabricadas micro-chaves na configuração paralela, sobre guias de onda coplanares (CPW). Recentemente, suas aplicações vêm sendo direcionadas a circuitos mais sofisticados, onde são monoliticamente integrados com outros componentes de RF, como antenas e deslocadores de fase. As chaves desenvolvidas são projetadas para operar com baixa tensão de ativação, e fabricadas usando a técnica surface micromachining, que consiste em construir as estruturas em camadas de filmes finos, e removendo as camadas sacrificiais até a liberação da parte flexível do dispositivo. Neste trabalho é apresentada toda a metodologia do projeto, incluindo as simulações eletromecânicas e eletromagnéticas das chaves MEMS em PCB, bem como s caracterizações. As chaves mostraram desempenho compatível com dispositivos equivalentes comerciais de RF, apresentando larga banda de operação de 1,8 - 18 GHz. Tendo em vista o desempenho físico e operacional dos dispositivos fabricados, essa tecnologia mostra-se viável com tecnologias dominadas localmente e se aplica tanto para Rádio Freqüência como para micro-ondas. / Abstract: The development of RF MEMS (Micro Electro Mechanical System) switches, using the concepts and technology of Printed Circuited Board (PCB) is the object of this research. Micro switches in the shunt configuration through the Coplanar Waveguide (CPW) were manufactured. Recently, its applications have been directed to more sophisticated circuits, which are monolithic integrated with other RF components such as antennas and phase shifters. The developed switches are designed to operate with low actuation voltage and manufactured using the surface micromachining technique, which consists to build the structures in thin film layers, and removing the sacrificial layers to the release of the flexible device part. In this work is presented all the methodology of the project, including the electromechanical and electromagnetic simulations of the MEMS switches on PCB, as well as the characterizations. The switches had shown compatible performance when compared with equivalent RF devices available in the market, showing broadband operation from 1,8 - 18 GHz. Due the physical and operational performance of the manufactured devices, this technology shows viable with locally known technologies and feasible for applications in both Radio Frequency and microwave. / Mestrado / Eletrônica, Microeletrônica e Optoeletrônica / Mestre em Engenharia Elétrica

With wind turbines growing in size, operation and maintenance has become a more important area of research with the goal of making wind energy more profitable. Wind turbine blades are subjected to intense fluctuating loads that can cause significant damage over time. The need for advanced methods of alleviating blade loads to extend the lifespan of wind turbines has become more important as worldwide initiatives have called for a push in renewable energy. An area of research whose goal is to reduce the fatigue damage is smart rotor control. Smart bladed wind turbines have the ability to sense aerodynamic loads and compute an actuator response to manipulate the aerodynamics of the wind turbine. The wind turbine model for this research is equipped with two different smart rotor devices. Independent pitch actuators for each blade and trailing edge flaps (TEFs) on the outer 70 to 90% of the blade span are used to modify aerodynamic loads. Individual Pitch Control (IPC) and Individual Flap Control (IFC) are designed to control these devices and are implemented on the NREL 5 MW wind turbine. The consequences of smart rotor control lie in the wind turbine’s power capture in below rated conditions. Manipulating aerodynamic loads on the blades cause the rotor to decelerate, which effectively decreases the rotor speed and power output by 1.5%. Standard Region 2 generator torque control laws do not take into consideration variations in rotor dynamics which occur from the smart rotor controllers. Additionally, this research explores new generator torque control algorithms that optimize power capture in below rated conditions. FAST, an aeroelastic code for the simulation of wind turbines, is utilized to test the capability and efficacy of the controllers. Simulation results for the smart rotor controllers prove that they are successful in decreasing the standard deviation of blade loads by 26.3% in above rated conditions and 12.1% in below rated conditions. As expected, the average power capture decreases by 1.5%. The advanced generator torque controllers for Region 2 power capture have a maximum average power increase of 1.07% while still maintaining load reduction capabilities when coupled with smart rotor controllers. The results of this research show promise for optimizing wind turbine operation and increasing profitability.

This thesis presents the design, construction, and control of a two-wheeled inverted pendulum (TWIP) robotic walker prototype for assisting mobility-impaired users with balance and fall prevention. A conceptual model of the robotic walker is developed and used to illustrate the purpose of this study. A linearized mathematical model of the two-wheeled system is derived using Newtonian mechanics. A control strategy consisting of a decoupled LQR controller and three state variable controllers is developed to stabilize the platform and regulate its behavior with robust disturbance rejection performance. Simulation results reveal that the LQR controller is capable of stabilizing the platform and rejecting external disturbances while the state variable controllers simultaneously regulate the system’s position with smooth and minimum jerk control. A prototype for the two-wheeled system is fabricated and assembled followed by the implementation and tuning of the control algorithms responsible for stabilizing the prototype and regulating its position with optimal performance. Several experiments are conducted, confirming the ability of the decoupled LQR controller to robustly balance the platform while the state variable controllers regulate the platform’s position with smooth and minimum jerk control.

This thesis presents the design for a novel haptic interface for large-format touchscreens. Techniques such as electrovibration, ultrasonic vibration, and external braked devices have been developed by other researchers to deliver haptic feedback to touchscreen users. However, these methods do not address the need for spatial constraints that only restrict user motion in the direction of the constraint. This technology gap contributes to the lack of haptic technology available for touchscreen-based upper-limb rehabilitation, despite the prevalent use of haptics in other forms of robotic rehabilitation. The goal of this thesis is to display kinesthetic haptic constraints to the touchscreen user in the form of boundaries and paths, which assist or challenge the user in interacting with the touchscreen. The presented prototype accomplishes this by steering a single wheel in contact with the display while remaining driven by the user. It employs a novel embedded force sensor, which it uses to measure the interaction force between the user and the touchscreen. The haptic response of the device is controlled using this force data to characterize user intent. The prototype can operate in a simulated free mode as well as simulate rigid and compliant obstacles and path constraints. A data architecture has been created to allow the prototype to be used as a peripheral add-on device which reacts to haptic environments created and modified on the touchscreen. The long-term goal of this work is to create a haptic system that enables a touchscreen-based rehabilitation platform for people with upper limb impairments.

The dissertation thesis is focused on research and development of modern emission MEMS sensors. The emission sensor based on the field emission from nanostructured materials represents innovative approach to pressure sensing. The nanostructures serve as electron emitter in an electric field between the cathode and anode in the pressure sensor. This electric field is constant and the change in ambient pressure causes the change of distance between electrodes, thereby the electric field is increasing. This intensity is proportional to the emission from the cathode made of nanostructured material. Changing the distance between the electrodes is caused by the deflection of the deformation element - the membrane, which operates the measured pressure. In the current state of the art an extensive research is carried out to find new nanostructured materials with good emission properties. Four nanostructured materials have been chosen and then experimentally prepared and characterized inside the vacuum chamber. For the simulation of diaphragm bending, the chamber is equipped with linear nano-motion drive SmarAct that enables precise changes of the distance between two electrodes inside the vacuum chamber. The computer model to predict the deformation of diaphragm was prepared in the simulation program CoventorWare. The behavior of diaphragm in a wide range of dimensions of the membrane, its thickness and the applied pressure are possible to predict. The dependencies of the current density on the electric field are plotted from the measured emission characteristics of nanostructured materials and thus characterized nanostructured materials can be compared. The dependencies are further converted by Fowler-Nordheimovy theory on the curve (ln(J/E2) vs. 1/E), whose advantage is linear shape. Basic parameters describing the emission properties of characterized nanostructured materials are deducted. Two methods for vacuum packaging of the sensor electrodes are designed. Anodic bonding technology and encapsulating using glass frit bonding are tested. To evaluate the bonding strength, the bonded substrates are tested for tensile strength.

Modern lower limb prostheses are devices that replace missing limbs, making it possible for lower limb amputees to walk again. Most commercially available prosthetic limbs lack intelligence and passive adaptive capabilities, and none available can adapt on a step by step basis. Often, amputees experience a loss of terrain adaptability as well as stability, leaving the amputee with a severely altered gait. This work is focused on the development of a semi-active damping system for use in intelligent terrain adaptive ankle prostheses. The system designed consists of an optimized hydraulic cylinder with an electronic servo valve which throttles the hydraulic fluid flowing between the cylinder’s chambers, acting on the prosthesis joint with a moment arm in series with a carbon spring foot. This provides the capability to absorb energy during the amputees gait cycle in a controlled manner, effectively allowing the passive dynamic response to be greatly altered continuously by leveraging a small energy source. A virtual simulation of an amputee gait cycle with the adaptive semi-active ankle design revealed the potential to replicate adaptive abilities of the human ankle. The results showed very similarly that irregularities in amputee biomechanics can be greatly compensated for using semi-active damping.

This thesis presents an activity mode intent recognition approach for safe, robust and reliable control of powered backbone exoskeleton. The thesis presents the background and a concept for a powered backbone exoskeleton that would work in parallel with a user. The necessary prerequisites for the thesis are presented, including the collection and processing of surface electromyography signals and inertial sensor data to recognize the user’s activity. The development of activity mode intent recognizer was described based on decision tree classification in order to leverage its computational efficiency. The intent recognizer is a high-level supervisory controller that belongs to a three-level control structure for a powered backbone exoskeleton. The recognizer uses surface electromyography and inertial signals as the input and CART (classification and regression tree) as the classifier. The experimental results indicate that the recognizer can extract the user’s intent with minimal delay. The approach achieves a low recognition error rate and a user-unperceived latency by using sliding overlapped analysis window. The approach shows great potential for future implementation on a prototype backbone exoskeleton.

Small electric uninhabited aerial vehicles (UAV) represent a rapidly expanding market requiring optimization in both efficiency and weight; efficiency is critical during cruise or loiter where the vehicle operates at part power for up to 99% of the mission time. Of the four components (battery, motor, propeller, and electronic speed controller (ESC)) of the electric propulsion system used in small UAVs, the ESC has no accepted performance model and almost no published performance data. To collect performance data, instrumentation was developed to measure electrical power in and out of the ESC using the two wattmeter method and current sense resistors; data was collected with a differential simultaneous data acquisition system. Performance of the ESC was measured under different load, commanded throttle, bus voltage, and switching frequency, and it was found that ESC efficiency decreases with increasing torque and decreasing bus voltage and does not vary much with speed and switching frequency. The final instrumentation was limited to low-voltage systems and error propagation calculations indicate a great deal of error at low power measurements; despite these limitations, an understanding of ESC performance appropriate for conceptual design of these systems was obtained. MODELING AND TEST OF THE EFFICIENCY OF ELECTRONIC SPEED CONTROLLERS FOR BRUSHLESS DC MOTORS

ABSTRACT Fabrication and Characterization of Torsional Micro-Hinge Structures Mike Marrujo There are many electronic devices that operate on the micrometer-scale such as Digital Micro-Mirror Devices (DMD). Micro actuators are a common type of DMD that employ a diaphragm supported by torsional hinges, which deform during actuation and are critical for the devices to have high stability and reliability. The stress developed within the hinge during actuation controls how the actuator will respond to the actuating force. Electrostatically driven micro actuators observe to have a fully recoverable non-linear viscoelastic response. The device consists of a micro-hinge which is suspended by two hinges that sits inside a micro machined well. To achieve a specific angle of rotation when actuated, the mechanical forces need to be characterized with a range of different forces applied to the edge of the micro-hinge. This research investigates the mechanical properties and the amount of force needed to rotate to specific angles by comparing theoretical performance to experimentally measured values. Characterizing the mechanical forces on the micro-hinge will further the understanding of how the device operates under a specific applied force. The material response to the amount of stress within the hinges will control the amount of actuation that is achieved by that force. The test devices were fabricated using common semiconductor fabrication techniques. The micro-hinge device was created on a 500µm, double-sided polished, single crystal (100) silicon wafer. In order to create this device, both wet etching and dry etching techniques were employed to produce an 8µm thick plate structure. The bulk etching of 480µm was achieved by wet etching down into the silicon (Si) to create the wells. Dry etching was used for its high precision to release the micro-hinge structure. Once fabricated, the micro-hinge actuators were tested using a Technics turntable arm with a built in micrometer that applied a constant force while measuring the displacement of the actuator. The rotation of the hinge was measured by reflecting a Helium-Neon (HeNe) laser beam off a mirror, which is attached to the pivot of the arm that’s applying the force, and any type of displacement was recorded with a Photo Sensitive Device (PSD). The test stand applied a small force which replicated the amount of electrostatic forces needed to achieve a specific degree of rotation. Results indicate that the micro-hinge achieved a repeatable amount of rotation when forces were applied to it. The micro-hinge would endure deformation when too much force would be applied and yield a maximum amount of force allowed.