Simultaneous use of shape memory alloys and permanent magnets in multistable smart structures for morphing aircraft applications

This Thesis considers the simultaneous use of shape memory alloys and permanent magnets for achieving multistable smart structures aiming towards morphing applications. Motivation for this approach lies in the poor energetic efficiency of shape memory alloys, which can void system-level benefits provided by morphing technologies. Multistability can therefore be adopted to prevent continuous operation of shape memory alloy actuators. Objectives of the study involve the combination of shape memory alloys and permanent magnets in new geometrical arrangements to achieve multistable behavior; the development of a numerical modeling procedure that is able to simulate the multi-physics nature of the studied systems; and the proposal of a geometric arrangement for morphing applications that is based on a repeating pattern of unit cells which incorporate the combined use of shape memory alloy wires and permanent magnets for multistability. The proposed modeling strategy considers a geometrically nonlinear beam finite element; a thermo-mechanical constitutive behavior for shapememoryalloys;theinteractionofcuboidalpermanentmagnetswitharbitraryorienta- tions; and node-to-element contact. Experiments are performed with three distinct systems, including a proof-of-concept beam, a three cell morphing beam metastructure, and a morphing airfoil prototype with six unit cells. Results show that the combination of shape memory alloys and permanent magnets indeed allows for multistable behavior. Furthermore, the dis- tributedactuationcapabilitiesofthe morphingmetastructureallowforsmoothandlocalized geometrical shape changes.CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível SuperiorCNPq - Conselho Nacional de Desenvolvimento Científico e TecnológicoTese (Doutorado)Esta Tese considera o uso simultâneo de ligas com memória de forma e ímãs permanentes para a obtenção de estruturas inteligentes multiestáveis, com vistas a sua aplicação em aeronaves de geometria variável. A motivação para tal abordagem reside na baixa eficiência energética associada às ligas com memória de forma, a qual pode eliminar benefícios oriundos de tecnologias relacionadas a geometria variável. Multiestabilidade pode, desta forma, ser adotada para prevenir operação contínua de atuadores baseados em ligas com memória de forma. Objetivos do estudo envolvem a combinação de ligas com memória de forma e ímãs permanentes em novos arranjos geométricos para a obtenção de comportamento multiestável; o desenvolvimento de um procedimento de modelagem numérica que pode simular a natureza multifísica dos sistemas estudados; e a proposição de um arranjo geométrico para aplicações que envolvem geometria variável, o qual é baseado num padrão repetitivo de células unitárias que incorporam o uso combinado de ligas com memória de forma e ímãs permanentes para mul- tiestabilidade. A estratégia de modelagem proposta considera um elemento finito de viga com não-linearidades geométricas; um modelo constitutivo termomecânico para ligas com memória de forma; a interação entre ímãs permanentes cúbicos com orientação arbitrária; e contato entre elemento-e-nó no contexto de elementos finitos. Experimentos são realizados com três sistemas distintos, incluindo uma viga para prova de conceito, uma metaestrutura do tipo viga com geometria variável composta por três células unitárias, e um protótipo de aerofólio com geometria variável composto por seis células unitárias. Resultados mostram que a combinação de ligas com memória de forma e ímãs permanentes permite a obtenção de comportamento multiestável. Além disso, a característica de atuação distribuída das metaestruturas com geometria variável permite alterações de forma suaves e localizadas

DEVELOPMENT OF A NOVEL Z-AXIS PRECISION POSITIONING STAGE WITH MILLIMETER TRAVEL RANGE BASED ON A LINEAR PIEZOELECTRIC MOTOR

Piezoelectric-based positioners are incorporated into stereotaxic devices for microsurgery, scanning tunneling microscopes for the manipulation of atomic and molecular-scale structures, nanomanipulator systems for cell microinjection and machine tools for semiconductor-based manufacturing. Although several precision positioning systems have been developed for planar motion, most are not suitable to provide long travel range with large load capacity in vertical axis because of their weights, size, design and embedded actuators. This thesis develops a novel positioner which is being developed specifically for vertical axis motion based on a piezoworm arrangement in flexure frames. An improved estimation of the stiffness for Normally Clamped (NC) clamp is presented. Analytical calculations and finite element analysis are used to optimize the design of the lifting platform as well as the piezoworm actuator to provide maximum thrust force while maintaining a compact size. To make a stage frame more compact, the actuator is integrated into the stage body. The complementary clamps and the amplified piezoelectric actuators based extenders are designed such that no power is needed to maintain a fixed vertical position, holding the payload against the force of gravity. The design is extended to a piezoworm stage prototype and validated through several tests. Experiments on the prototype stage show that it is capable of a speed of 5.4 mm/s, a force capacity of 8 N and can travel over 16 mm

MODELING, ANALYSIS AND CONTROL OF FLEXIBLE SOLID-STATE HYSTERETIC ACTUATORS

A distributed parameters modeling and control framework for flexible solid-state hysteretic actuator is presented in this work. For the simplicity of analysis, the actuator dynamic behavior is decoupled and treated separately from the hysteresis nonlinearity. To include the effects of widely-used flexural mechanisms, a mass-spring-damper boundary condition is considered for system. Moreover, the effect of electromechanical actuation is included as a concentrate force at the boundary. The problem is then divided into two parts: first part deals with free motion analysis of system in order to obtain eigenvalues and eigenfunctions using the expansion theorem and a standard eigenvalue problem procedure. The effects of different boundary mass and spring values on the natural frequencies and mode shapes are demonstrated, which indicate their significant contribution to system performance. In the second part, forced motion analysis of system and its state-space representation are presented. A frequency based control strategy utilizing widely used Lyapunov theorem is designed to obtain an accurate control over the actuator motion. A robust variable structure control is incorporated into the developed controller for compensation of ever-present plant structural uncertainties. A full order state feedback observer is designed to accurately mimic the states of an unobservable plant. An optimization algorithm is developed to compute the optimal observer gain matrix. Various frequency tracking simulations are performed using feedback controller-observer model to observe the effect of modes deficiency on the tracking frequency bandwidth of the controller. Finally, for the accurate prediction of nonlinear multi-loop hysteresis effect, a major source of inaccuracies at quasi-static frequency, a recently developed hysteresis model based on three hysteric properties of piezoelectric material namely targeting of turning points, curve alignment and the wiping-out effect is used. Initially, the hysteresis nonlinearity is decoupled from the looping effect and modeled separately using an exponential function. The obtained exponential function is then utilized in a nonlinear mapping procedure, where it is mapped between consequent turning points recorded in model memory unit. This mapping also uses four constant shaping parameters - two for the ascending and two for the descending hysteresis trajectories. A proportional integral (PI) controller is used for the compensation of hysteresis nonlinearity. Performance of PI controller is validated using several numerical simulations. Finally, the method of combining robust feedback control strategy with the feedforward hysteresis compensation technique is presented to accomplish the precise control over actuator motion

A Review of Locomotion Systems for Capsule Endoscopy

Wireless capsule endoscopy for gastrointestinal (GI) tract is a modern technology that has the potential to replace conventional endoscopy techniques. Capsule endoscopy is a pill-shaped device embedded with a camera, a coin battery, and a data transfer. Without a locomotion system, this capsule endoscopy can only passively travel inside the GI tract via natural peristalsis, thus causing several disadvantages such as inability to control and stop, and risk of capsule retention. Therefore, a locomotion system needs to be added to optimize the current capsule endoscopy. This review summarizes the state-of-the-art locomotion methods along with the desired locomotion features such as size, speed, power, and temperature and compares the properties of different methods. In addition, properties and motility mechanisms of the GI tract are described. The main purpose of this review is to understand the features of GI tract and diverse locomotion methods in order to create a future capsule endoscopy compatible with GI tract properties

DESIGN, DEVELOPMENT, AND EVALUATION OF A MRI-GUIDED NEUROSURGICAL INTRACRANIAL ROBOT

Brain tumors are among the most feared complications of cancer. Their treatment is challenging because of the lack of good imaging modality and the inability to remove the complete tumor. To overcome this limitation, we propose to develop a Magnetic Resonance Imaging (MRI)-compatible neurosurgical robot. The robot can be operated under continuous MRI, and the Magnetic Resonance (MR) images can be used to supplement physicians' visual capabilities, resulting in precise tumor removal. We have developed two prototypes of the Minimally Invasive Neurosurgical Intracranial Robot (MINIR) using MRI compatible materials and shape memory alloy (SMA) actuators. The major difference between the two robots is that one uses SMA wire actuators and the other uses SMA spring actuators combined with the tendon-sheath mechanism. Due to space limitation inside the robot body and the strong magnetic field in the MRI scanner, most sensors cannot be used inside the robot body. Hence, one possible approach is to rely on image feedback to control the motion of the robot. In this research, as a preliminary approach, we have relied on image feedback from a camera to control the motion of the robot. Since the image tracking algorithm may fail in some situations, we also developed a temperature feedback control scheme which served as a backup controller for the robot. Experimental results demonstrated that both image feedback and temperature feedback can be used reliably to control the joint motion of the robots. A series of MRI compatibility tests were performed to evaluate the MRI compatibility of the robots and to assess the degradation in image quality. The experimental results demonstrated that the robots are MRI compatible and created no significant image distortion in the MR images during actuation. The accomplishments presented in this dissertation represent a significant development of using SMA actuators to actuate MRI-compatible robots. It is anticipated that, in the future, continuous MR imaging would be used reliably to control the motion of the robot. It is aspired that the robot design and the control methods of SMA actuators developed in this research can be utilized in practical applications

Magnetic Shape Memory Alloys as smart materials for micro-positioning devices

In the field of microrobotics, actuators based on smart materials are predominant because of very good precision, integration capabilities and high compactness. This paper presents the main characteristics of Magnetic Shape Memory Alloys as new candidates for the design of micromechatronic devices. The thermo-magneto-mechanical energy conversion process is first presented followed by the adequate modeling procedure required to design actuators. Finally, some actuators prototypes realized at the Femto-ST institute are presented, including a push-pull bidirectional actuator. Some results on the control and performances of these devices conclude the paper

Linear Macro-Micro Positioning System Using a Shape Memory Alloy Actuator

The use of high-precision automated equipment is steadily increasing due in part to the progressively smaller sizes of electronic circuits. Currently, piezoelectric transducers (piezos) dominate as the actuation device for high precision machines, but shape memory alloys (SMA) may be a viable alternative to reduce monetary costs. This work explores the implementation of a low-cost linear macro-micro positioning system. The system consists of a modified printer carriage to provide long range, macro scale linear motion (approximately 200 mm range and 200 µm precision) and a micro scale system (approximately 4 mm range and 5 µm target precision) that uses an SMA actuator. A detailed description of the design and implementation of the system is given in this research. A model of the macro-stage is then generated by first identifying and inverting a simple friction model to linearize the system, thereby allowing for modified least squares (MLS) identification of a linear model. Various controllers are attempted for the macro-stage and compared with an experimentally tuned nonlinear PD controller that is implemented in the final design. A model of the micro-stage is derived through analysis of the SMA actuator. The model for the actuator is separated into two portions, an electro-thermal model, and a hysteresis model. The hysteresis model is derived using the Preisach model, and the electro-thermal model through MLS identification. To control the micro-stage, a PI controller with antiwindup is developed experimentally. The two stages are then executed together in closed loop and the resulting coupling between the two stages is briefly examined. Experimental data used for the modelling and design is presented, along with results of the final macro-micro linear positioning system

Robust control of systems with output hysteresis and input saturation using a finite time stability approach

© 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.This paper presents a robust control approach for a class of nonlinear dynamic systems consisting of a linear plant connected in series with a hysteresis operator, and affected by control input saturation. Such a class of systems commonly appears in applications concerning smart materials, in particular thermal shape memory alloys wire actuators. The goal of this paper is to design a robust controller, in the form of an output PI law, which ensures set-point regulation with a desired decay rate and, at the same time, accounts for the effects of both hysteresis and input saturation. The resulting controller appears as attractive on the implementation stand-point, since no accurate hysteresis compensator is required. In order to deal with the proposed problem, the hysteretic plant is first reformulated as a linear parameter-varying system. Subsequently, a finite time stability approach is used to impose constraints on the control input. A new set of bilinear matrix inequalities is developed, in order to perform the design with reduced conservatism by properly exploiting some structural properties of the model. The effectiveness of the method is finally validated by means of a numerical case of study. © 2018 IEEE.Peer ReviewedPostprint (author's final draft

Dynamics and Control of Smart Structures for Space Applications

Smart materials are one of the key emerging technologies for a variety of space systems ranging in their applications from instrumentation to structural design. The underlying principle of smart materials is that they are materials that can change their properties based on an input, typically a voltage or current. When these materials are incorporated into structures, they create smart structures. This work is concerned with the dynamics and control of three smart structures: a membrane structure with shape memory alloys for control of the membrane surface flatness, a flexible manipulator with a collocated piezoelectric sensor/actuator pair for active vibration control, and a piezoelectric nanopositioner for control of instrumentation. Shape memory alloys are used to control the surface flatness of a prototype membrane structure. As these actuators exhibit a hysteretic nonlinearity, they need their own controller to operate as required. The membrane structures surface flatness is then controlled by the shape memory alloys, and two techniques are developed: genetic algorithm and proportional-integral controllers. This would represent the removal of one of the main obstacles preventing the use of membrane structures in space for high precision applications, such as a C-band synthetic aperture radar antenna. Next, an adaptive positive position feedback law is developed for control of a structure with a collocated piezoelectric sensor/actuator pair, with unknown natural frequencies. This control law is then combined with the input shaping technique for slew maneuvers of a single-link flexible manipulator. As an alternative to the adaptive positive position feedback law, genetic algorithms are investigated as both system identification techniques and as a tool for optimal controller design in vibration suppression. These controllers are all verified through both simulation and experiments. The third area of investigation is on the nonlinear dynamics and control of piezoelectric actuators for nanopositioning applications. A state feedback integral plus double integral synchronization controller is designed to allow the piezoelectrics to form the basis of an ultra-precise 2-D Fabry-Perot interferometer as the gap spacing of the device could be controlled at the nanometer level. Next, an output feedback linear integral control law is examined explicitly for the piezoelectric actuators with its nonlinear behaviour modeled as an input nonlinearity to a linear system. Conditions for asymptotic stability are established and then the analysis is extended to the derivation of an output feedback integral synchronization controller that guarantees global asymptotic stability under input nonlinearities. Experiments are then performed to validate the analysis. In this work, the dynamics and control of these smart structures are addressed in the context of their three applications. The main objective of this work is to develop effective and reliable control strategies for smart structures that broaden their applicability to space systems