A Methodology Towards Comprehensive Evaluation of Shape Memory Alloy Actuators for Prosthetic Finger Design

Presently, DC motors are the actuator of choice within intelligent upper limb prostheses. However, the weight and dimensions associated with suitable DC motors are not always compatible with the geometric restrictions of a prosthetic hand; reducing available degrees of freedom and ultimately rendering the prosthesis uncomfortable for the end-user. As a result, the search is on-going to find a more appropriate actuation solution that is lightweight, noiseless, strong and cheap. Shape memory alloy (SMA) actuators offer the potential to meet these requirements. To date, no viable upper limb prosthesis using SMA actuators has been developed. The primary reasons lie in low force generation as a result of unsuitable actuator designs, and significant difficulties in control owing to the highly nonlinear response of SMAs when subjected to joule heating. This work presents a novel and comprehensive methodology to facilitate evaluation of SMA bundle actuators for prosthetic finger design. SMA bundle actuators feature multiple SMA wires in parallel. This allows for increased force generation without compromising on dynamic performance. The SMA bundle actuator is tasked with reproducing the typical forces and contractions associated with the human finger in a prosthetic finger design, whilst maintaining a high degree of energy efficiency. A novel approach to SMA control is employed, whereby an adaptive controller is developed and tuned using the underlying thermo-mechanical principles of operation of SMA wires. A mathematical simulation of the kinematics and dynamics of motion provides a platform for designing, optimizing and evaluating suitable SMA bundle actuators offline. This significantly reduces the time and cost involved in implementing an appropriate actuation solution. Experimental results show iii that the performance of SMA bundle actuators is favourable for prosthesis applications. Phalangeal tip forces are shown to improve significantly through bundling of SMA wire actuators, while dynamic performance is maintained owing to the design and implementation of the selected control strategy. The work is intended to serve as a roadmap for fellow researchers seeking to design, implement and control SMA bundle actuators in a prosthesis design. Furthermore, the methodology can also be adopted to serve as a guide in the evaluation of other non-conventional actuation technologies in alternative applications

형태적응형 이력현상 모형을 이용한 유연구동 메커니즘의 모델링

학위논문 (박사) -- 서울대학교 대학원 : 공과대학 기계항공공학부, 2020. 8. 김종원.Flexible surgical robots and instruments are slowly paving its way into the modern surgical arena. Compared to conventional laparoscopic surgical systems, flexible systems have some distinct advantages in that it can approach surgical targets that were unreachable before, leaves less scar and therefore reducing recovery time for patients. In order to drive the articulated surgical instruments joints, flexible instruments require a tendon-sheath mechanism (TSM). Utilization of TSM brings about a different attribute in a position control standpoint, compared to the rather simple cable-pulley system found in conventional robotic surgical instruments. In this research, a tendon-sheath mechanism was configured, taking into account the actual size constraint of a robotic surgical instrument and the material characteristics of the components. An experiment hardware was designed to measure the input signal and the corresponding output response while varying the shape configuration parameters of TSM. Twenty four distinct experiments with different shape configuration parameters were carried out to identify how the shape affects the performance and the hysteresis curve of the TSM. For modeling the hysteretic behavior of the TSM, a composite model consisting of elementary hysteresis operators is proposed. Such a composite models parameters are empirically identified with least-squares optimization, for every shape configurations defined. The model processes the input to produce an estimated output for a certain shape, and this was verified with various types of input signals. Lastly, for compensating TSMs hysteretic behavior, a recursive algorithm producing inverse control signal from the empirical model is proposed, with a guaranteed real-time performance. The inverse algorithms position control effectiveness was verified under various shape configurations and input signal types.본 연구에서는 유연한 로봇 수술도구를 구현하기 위해 사용되는 Tendon-Sheath Mechanism (TSM)이 형상에 따른 이력현상의 변화가 발생하는 것을 실험적으로 확인하였으며, 이러한 이력현상을 표현하기 위한 모형을 제안하고 이를 이용하여 이력현상을 보상할 수 있는 알고리즘을 제안하였다. 첫 단계로 TSM을 구성하는 부품인 Tendon과 Sheath를 선정하는데 있어, 이력현상에 일조 하는 비선형적 특성을 최소화하는 재료와 공정 및 후처리 방법을 고려하여 적용하였다. 다음으로 TSM의 형상 변수를 정의하고 이를 다양한 형상하에서 이력현상의 변화를 관찰하는 실험장치를 설계하여 실험 데이터를 수집하였다. 이를 토대로 입력에 대한 출력의 관계를 Preisach type 연산자를 이용하여 표현하였고 실험 데이터에 기반한 연산자의 변수들을 최소자승 최적화를 통해 탐색하였으며, 모델의 적합성을 다양한 형상하에서, 각기 다른 종류의 입력 신호에 대한 출력을 모델을 통해 생성되는 출력 추정치와의 오차 분석으로 검증하였다. 이러한 모델로 이력현상을 보상하기 위해서 Set-Point 출력에 대한 Inverse Control 신호를 생성하는 재귀적 알고리즘을 제안하였으며, 이러한 알고리즘이 다양한 Set-point 출력의 형태에 대해서 실시간성이 보장되는 빠른 연산이 가능하다는 점을 보였다. 이력현상이 보상된 실험데이터와 기존의 보상전 실험데이터의 비교를 통해 보상전략이 효과적이라는 것을 보였으며, 다양한 형태에서도 적용이 가능함을 검증하였다.Table of Contents Chapter 1. Introduction 1 1.1 Background 1 1.1.1 Evolution of surgical robots 1 1.1.2 Flexible robotic systems 3 1.2 Tendon-sheath mechanism 6 1.2.1 Application of TSM in flexible surgical instruments 6 1.2.2 Effects on motion transfer characteristics 8 1.3 Previous studies 10 1.4 Research objectives 12 Chapter 2. Configuration and fabrication of TSM 14 2.1 Sheath 17 2.2 Tendon 19 2.2.1 Cable 19 2.2.2 Fitting 23 Chapter 3. Hysteretic behavior of TSM 25 3.1 Experiment setup 26 3.1.1 Experiment design 26 3.1.2 Hardware design 28 3.2 Experiment results 34 3.2.1 Effect of curve angle variation 34 3.2.2 Effect of radius of curvature variation 39 3.2.3 Summary of results of hysteretic behavior 46 Chapter 4. Modeling Hysteresis of TSM 49 4.1 Preisach model and Hysterons 50 4.2 Mechanical play operator 53 4.3 Complex hysteresis operator: 56 4.4 Parameter identification for complex hysteresis operator 59 4.5 Result of experimental verification of complex hysteresis operator 60 4.5.1 Result of reference input profile sinusoidal excitation 63 4.5.2 Result of validation input profile triangular excitation 65 4.5.3 Result of reference input profile trapezoidal excitation 67 4.5.4 Obtained weights for all shape configurations and summary 69 4.6 Inverse operator formulation 60 4.7 Experimental verification of hysteresis compensation with the inverse operator: 77 4.7.1 Experiment setup 77 4.7.2 Result of hysteresis compensation for shape =90,r=30mm 79 4.7.3 Result of hysteresis compensation for shape =60,r=60mm 82 4.7.4 Error statistic and result analysis 85 Chapter 6. Conclusion 87 Bibliography 88 Abstract in Korean 92Docto

Development of Modeling and Simulation for Magnetic Particle Inspection Using Finite Elements

Magnetic particle inspection (MPI) is a widely used nondestructive inspection method for aerospace applications essentially limited to experiment-based approaches. The analysis of MPI characteristics that affect sensitivity and reliability contributes not only reductions in inspection design cost and time but also improvement of analysis of experimental data. Magnetic particles are easily attracted toward a high magnetic field gradient. Selection of a magnetic field source, which produces a magnetic field gradient large enough to detect a defect in a test sample or component, is an important factor in magnetic particle inspection. In this work a finite element method (FEM) has been employed for numerical calculation of the MPI simulation technique. The FEM method is known to be suitable for complicated geometries such as defects in samples. This thesis describes the research that is aimed at providing a quantitative scientific basis for magnetic particle inspection. A new FEM solver for MPI simulation has been developed in this research for not only nonlinear reversible permeability materials but also irreversible hysteresis materials that are described by the Jiles-Atherton model. The material is assumed to have isotropic ferromagnetic properties in this research (i.e., the magnetic properties of the material are identical in all directions in a single crystal). In the research, with a direct current field mode, an MPI situation has been simulated to measure the estimated volume of magnetic particles around defect sites before and after removing any external current fields. Currently, this new MPI simulation package is limited to solving problems with the single current source from either a solenoid or an axial directional current rod

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

A dynamic model of the extravehicular mobility unit (EMU) : human performance issues during EVA

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1997.Includes bibliographical references (leaves 97-99).by David B. Rahn.M.S

Magnetodynamic vector hysteresis models for steel laminations of rotating electrical machines

This thesis focuses on the modeling and prediction of iron losses in rotating electrical machines. The aim is to develop core loss models that are reasonably accurate and efficient for the numerical electromagnetic field analysis. The iron loss components, including hysteresis, classical eddy-current, and excess losses, are determined by modeling the dynamic hysteresis loops, whereby the incorporation of the core losses into the field solution is feasible and thus the influence of the core losses on the performance of the machine is investigated. The thesis presents a magnetodynamic vector hysteresis model that produces not only an accurate, overall prediction of the iron losses, but also explicitly models the magnetization behavior and the loop shapes. The model is found to be efficient, stable, and adequate for providing accurate predictions of the magnetization curves, and hence iron losses, under alternating and rotating flux excitations. It is demonstrated that the model satisfies the rotational loss property and reproduces the shapes of the experimental loops. In addition, a more simplified, efficient, and robust version of the magnetodynamic vector hysteresis model is introduced. The thesis also aims to analyze the convergence of the fixed-point method, examine the barriers behind the slow convergence, and show how to overcome them. The analysis has proved useful and provided sound techniques for speeding up the convergence of the fixed-point method. The magnetodynamic lamination models have been integrated into a two-dimensional finite-element analysis of rotating electrical machines. The core losses of two induction motors have been analyzed and the impact of core losses on the motor characteristics has been investigated. The simulations conducted reveal that the models are relatively efficient, accurate, and suitable for the design purposes of electrical machines.reviewe

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