Dynamic Modeling and Control System Design for Shape Memory Alloy Actuators

Shape memory alloy (SMA) is a type of smart material which remembers its original state. It is light weight and small, and known to provide high contraction force with low noise. Its application has wide range from robotics to medical science. One of its potential applications in space is a supporting system of membrane structure that can be used as synthetic aperture radar (SAR) antenna to achieve high flatness. It exhibits nonlinear phenomena called hysteresis when it's electrically heated. Hysteresis is a nonlinear phenomenon that refers to the dependence of a physical system on the environment. Hysteresis in SMA causes a major difficulty in control system design. Un-modeled or poorly modeled hysteresis introduces inaccuracy in tracking and the performance of the system. Experimental test bench is constructed for one set of SMA actuators that resembles the membrane structure's supporting system. Hysteresis is obtained by running open loop test with the test bench. Dynamic model of the SMA wires is developed using classical Preisach model and modified Maxwell model. Then the inverse model is implemented in feed-forward loop to compensate for nonlinear hysteresis. Simple feedback controllers are added to correct the modeling errors. Experimental results reveal that the error is significantly reduced when comparing feedback controller with hybrid feedback and feed-forward controller

Modeling and simulation of magnetic components in electric circuits

This thesis demonstrates how by using a variety of model constructions and parameter extraction techniques, a range of magnetic component models can be developed for a wide range of application areas, with different levels of accuracy appropriate for the simulation required. Novel parameter extraction and model optimization methods are developed, including the innovative use of Genetic Algorithms and Metrics, to ensure the accuracy of the material models used. Multiple domain modeling, including the magnetic, thermal and magnetic aspects are applied in integrated simulations to ensure correct and complete dynamic behaviour under a range of environmental conditions. Improvements to the original Jiles-Atherton theory to more accurately model loop closure and dynamic thermal behaviour are proposed, developed and tested against measured results. Magnetic Component modeling techniques are reviewed and applied in practical examples to evaluate the effectiveness of lumped models, 1D and 2D Finite Element Analysis models and coupling Finite Element Analysis with Circuit Simulation. An original approach, linking SPICE with a Finite Element Analysis solver is presented and evaluated. Practical test cases illustrate the effectiveness of the models used in a variety of contexts. A Passive Fault Current Limiter (FCL) was investigated using a saturable inductor with a magnet offset, and the comparison between measured and simulated results allows accurate prediction of the behaviour of the device. A series of broadband hybrid transformers for ADSL were built, tested, modeled and simulated. Results show clearly how the Total Harmonic Distortion (THD), Inter Modulation Distortion (IMD) and Insertion Loss (IL) can be accurately predicted using simulation.A new implementation of ADSL transformers using a planar magnetic structure is presented, with results presented that compare favourably with current wire wound techniques. The inclusion of transformer models in complete ADSL hybrid simulations demonstrate the effectiveness of the models in the context of a complete electrical system in predicting the overall circuit performance

Identification of loss models from measurements of the magnetic properties of electrical steel sheets

Numerical simulations of electrical machines require good knowledge of the magnetic properties of the materials they are made of. The magnetic cores of these machines are made of electrical steel sheets, the magnetic properties of which are nonlinear and hysteretic. Moreover, the behavior of the magnetic flux density and the magnetic field strength of such materials depends on the form of the supply. In the Laboratory of Electromechanics, there are several projects which aim to model correctly the behavior of the electrical steel sheet (hysteresis, stress-dependency, losses, etc.) when used in electrical machines. For this purpose, numerical models are developed and built in an in-house finite element program package. However, knowledge of the material properties and the parameters of loss models are necessary and needs to be measured. This work is proposed to measure the magnetization curves and specific losses of an electrical steel sheet. The measurements were carried out using a device specially designed for this purpose and adequate programs for field control. The measurements were conducted under rotating and alternating magnetic fields at different fundamental frequencies and amplitudes. The results of the measurements consisted of a large amount of data that has been analyzed, processed and presented in an appropriate manner. Moreover, the parameters of the loss models were estimated from the measurements through identification procedures that have been written and constructed in MATLAB software. The conclusions of this work provide the basis for a better understanding of the parameters needed to improve loss models

Design, analysis, and modeling of giant magnetostrictuve transducers

The increased use of giant magnetostrictive, Terfenol-D transducers in a wide variety of applications has led to a need for greater understanding of the materials performance. This dissertation attempts to add to the Terfenol-D transducer body of knowledge by providing an in-depth analysis and modeling of an experimental transducer. A description of the magnetostriction process related to Terfenol-D includes a discussion of material properties, production methods, and the effect of mechanical stress, magnetization, and temperature on the material performance. The understanding of the Terfenol-D material performance provides the basis for an analysis of the performance of a Terfenol-D transducer. Issues related to the design and utilization of the Terfenol-D material in the transducers are considered, including the magnetic circuit, application of mechanical prestress, and tuning of the mechanical resonance. Experimental results from two broadband, Tonpilz design transducers show the effects of operating conditions (prestress, magnetic bias, AC magnetization amplitude, and frequency) on performance. In an effort to understand and utlilize the rich performance space described by the experimental results a variety of models are considered. An overview of models applicable to Terfenol-D and Terfenol-D transducers is provided, including a discussion of modeling criteria. The Jiles-Atherton model of ferromagnetic hysteresis is employed to describe the quasi-static transducer performance. This model requires the estimation of only six physically-based parameters to accurately simulate performance. The model is shown to be robust with respect to model parameters over a range of mechanical prestress, magnetic biases, and AC magnetic field amplitudes, allowing predictive capability within these ranges. An additional model, based on electroacoustics theory, explains trends in the frequency domain and facilitates an analysis of efficiency based on impedance and admittance analysis. Results and discussion explain the importance of the resonance of the electromechanical system, as distinct from the mechanical resonance. Conclusions are drawn based on the experimental work, transducer analysis, and modeling approaches

Preisachův model a jeho použití přimodelování hystereze v elektrotechnice

Tato práce je zaměřena na měření a modelování hysterezních jevů u feromagnetik při použití Preisachova modelu. Největší díl práce je věnován nastavování parametrů Preisachova modelu z experimentálního měření, jakož i detailní rozbor komplikací v podobě nedostatečné saturace materiálu a magnetické viskozity, které výrazným způsobem komplikují určení váhové funkce Preisachova modelu experimentálním měřením. V práci je popsána možnost snížení výpočetní náročnosti Preisachova modelu různými způsoby, jejich přednosti a komplikace, které může přinést redukce výpočetní náročnosti. V práci je řešeno použití Preisachova modelu, který je upraven do podoby, kdy není využita, pro feromagnetické materiály na bázi oceli, obtížně získatelná váhová funkce. Praktické použití modelu je demonstrováno na simulaci ferorezonance na vysokonapěťovém transformátoru. Pro demonstraci univerzálnosti Preisachova modelu, je tento původně magnetický model nasazen i na modelování nabíjecích a vybíjecích cyklů lithium-iontových akumulátorů.This work is focused on measuring and modeling hysteresis phenomena in ferromagnets using the Preisach model. The largest part of the work is devoted to setting the parameters of the Preisach model from experimental measurements, as well as a detailed analysis of complications in the form of insufficient material saturation and magnetic viscosity, which significantly complicate determining the weight function of the Preisach model by experimental measurements. The paper describes the possibility of reducing the computational complexity of the Preisach model in various ways, their advantages and complications, which can bring a reduction in computational complexity. The work deals with the use of the Preisach model, which is modified to a form where it is not used, for ferromagnetic materials based on steel, difficult to obtain weight function. The practical use of the model is demonstrated on the simulation of ferroresonance on a high voltage transformer. To demonstrate the versatility of the Preisach model, this originally magnetic model is also used to model the charging and discharging cycles of lithium-ion batteries.

Modeling of Force and Motion Transmission in Tendon-Driven Surgical Robots

Tendon-based transmission is a common approach for transferring motion and forces in surgical robots. In spite of design simplicity and compactness that comes with the tendon drives, there exists a number of issues associated with the tendon-based transmission. In particular, the elasticity of the tendons and the frictional interaction between the tendon and the routing result in substantially nonlinear behavior. Also, in surgical applications, the distal joints of the robot and instruments cannot be sensorized in most cases due to technical limitations. Therefore, direct measurement of forces and use of feedback motion/force control for compensation of uncertainties in tendon-based motion and force transmission are not possible. However, force/motion estimation and control in tendon-based robots are important in view of the need for haptic feedback in robotic surgery and growing interest in automatizing common surgical tasks. One possible solution to the above-described problem is the development of mathematical models for tendon-based force and motion transmission that can be used for estimation and control purposes. This thesis provides analysis of force and motion transmission in tendon-pulley based surgical robots and addresses various aspects of the transmission modeling problem. Due to similarities between the quasi-static hysteretic behavior of a tendon-pulley based da Vinci® instrument and that of a typical tendon-sheath mechanism, a distributed friction approach for modeling the force transmission in the instrument is developed. The approach is extended to derive a formula for the apparent stiffness of the instrument. Consequently, a method is developed that uses the formula for apparent stiffness of the instrument to determine the stiffness distribution of the tissue palpated. The force transmission hysteresis is further investigated from a phenomenological point of view. It is shown that a classic Preisach hysteresis model can accurately describe the quasi-static input-output force transmission behavior of the da Vinci® instrument. Also, in order to describe the distributed friction effect in tendon-pulley mechanisms, the creep theory from belt mechanics is adopted for the robotic applications. As a result, a novel motion transmission model is suggested for tendon-pulley mechanisms. The developed model is of pseudo-kinematic type as it relates the output displacement to both the input displacement and the input force. The model is subsequently used for position control of the tip of the instrument. Furthermore, the proposed pseudo-kinematic model is extended to compensate for the coupled-hysteresis effect in a multi-DOF motion. A dynamic transmission model is also suggested that describes system’s response to high frequency inputs. Finally, the proposed motion transmission model was used for modeling of the backlash-like hysteresis in RAVEN II surgical robot

What Can Scattered Light Tell You About Your Favorite Magnetic Material?: A Magneto Optical Investigation of the Magnetic Properties of Aligned Janus Fiber Agglomerates.Influence of Dynamic Multiaxial Transverse Loading on Ultrahigh Molecular Weight Polyethylene Single Fiber Failure

Here we seek to take a traditional Magneto Optic Kerr Effect (MOKE) experimental design, useful for local magnetization measurements, and apply it to measuring aligned multiferroic Janus nano fiber agglomerates. In order to achieve this we modify the traditional MOKE geometry by measuring our Kerr rotation from collimated scattered light, rather than the conventional specular reflection. Using various techniques to improve signal to noise ratio (SNR), we extend the application of this scattered MOKE geometry to build families of First Order Reversal Curves (FORC). Using an alternative analysis technique, FORC curves are processed and become a FORC diagram, which is shown to look very similar to FORC diagrams created with literature suggested methods. From the FORC diagram we gain insights into how the coercivities are distributed within the aligned agglomerates and how their magnetization evolves as a function of applied field

An investigation of space suit mobility with applications to EVA operations

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2001.Includes bibliographical references (p. 193-196).The primary aim of this thesis is to advance the current understanding of astronauts' capabilities and limitations in space-suited extravehicular activity (EVA) by compiling a detailed database of the torques needed to bend the joints of a space suit, developing models of the mechanics of space suit joints based on experimental data, and utilizing these models to estimate a human factors performance metric, the work envelope for space suited EVA work. A detailed space suit joint torque-angle database is compiled in a novel experimental approach that uses space-suited human test subjects to generate realistic, multi-joint motions, which are used to drive an instrumented robot to measure the torques required to accomplish the motions in a pressurized space suit. Based on the experimental data, a mathematical model using the Preisach hysteresis modeling technique is developed to predict joint torque from the joint angle history. Two physics-based models describing the bending load-deflection characteristics of pressurized fabric cylinders were compared to the experimental space suit data. The beam model assumes that bending deflections are completely attributable to elongation of the fabric cylinder wall, while the membrane model assumes that the fabric never stretches.(cont.) The experimental data corresponds closely with the membrane model, implying that space suit joint stiffness is primarily determined by volume changes as the joint bends and the resulting compression of the gas inside the space suit. The space suit models were applied in a computational work envelope analysis to determine the volume in which a space-suited astronaut can comfortably work. A new method that uses inverse kinematics and the space suit model to calculate a work envelope based on visibility constraints and human strength limits is developed. Sensitivity analysis of the work envelope indicates that improving shoulder mobility and upward and downward visibility enlarge the space-suited work envelope.by Patricia Barrett Schmidt.Ph.D