SMA-Based Muscle-Like Actuation in Biologically Inspired Robots: A State of the Art Review

New actuation technology in functional or "smart" materials has opened new horizons in robotics actuation systems. Materials such as piezo-electric fiber composites, electro-active polymers and shape memory alloys (SMA) are being investigated as promising alternatives to standard servomotor technology [52]. This paper focuses on the use of SMAs for building muscle-like actuators. SMAs are extremely cheap, easily available commercially and have the advantage of working at low voltages. The use of SMA provides a very interesting alternative to the mechanisms used by conventional actuators. SMAs allow to drastically reduce the size, weight and complexity of robotic systems. In fact, their large force-weight ratio, large life cycles, negligible volume, sensing capability and noise-free operation make possible the use of this technology for building a new class of actuation devices. Nonetheless, high power consumption and low bandwidth limit this technology for certain kind of applications. This presents a challenge that must be addressed from both materials and control perspectives in order to overcome these drawbacks. Here, the latter is tackled. It has been demonstrated that suitable control strategies and proper mechanical arrangements can dramatically improve on SMA performance, mostly in terms of actuation speed and limit cycles

Biomechanics of smart wings in a bat robot: morphing wings using SMA actuators

This paper presents the design of a bat-like micro aerial vehicle with actuated morphing wings. NiTi shape memory alloys (SMAs) acting as artificial biceps and triceps muscles are used for mimicking the morphing wing mechanism of the bat flight apparatus. Our objective is twofold. Firstly, we have implemented a control architecture that allows an accurate and fast SMA actuation. This control makes use of the electrical resistance measurements of SMAs to adjust morphing wing motions. Secondly, the feasibility of using SMA actuation technology is evaluated for the application at hand. To this purpose, experiments are conducted to analyze the control performance in terms of nominal and overloaded operation modes of the SMAs. This analysis includes: (i) inertial forces regarding the stretchable wing membrane and aerodynamic loads, and (ii) uncertainties due to impact of airflow conditions over the resistance–motion relationship of SMAs. With the proposed control, morphing actuation speed can be increased up to 2.5 Hz, being sufficient to generate lift forces at a cruising speed of 5ms−1

Smart Material Wing Morphing for Unmanned Aerial Vehicles.

Morphing, or geometric adaptation to off-design conditions, has been considered in aircraft design since the Wright Brothers’ first powered flight. Decades later, smooth, bio-mimetic shape variation for control over aerodynamic forces still remains elusive. Unmanned Aerial Vehicles are prime targets for morphing implementation as they must adapt to large changes in flight conditions associated with locally varying wind or large changes in mass associated with payload delivery. The Spanwise Morphing Trailing Edge (SMTE) concept is developed to locally vary the trailing edge camber of a wing or control surface, functioning as a modular replacement for conventional ailerons without altering the wing’s spar box. The SMTE design was realized utilizing alternating active sections of Macro Fiber Composites (MFCs) driving internal elastomeric compliant mechanisms and passive sections of anisotropic, elastomeric skin with tailorable stiffness, produced by additive manufacturing. Experimental investigations of the modular design via a new scaling methodology for reduced-span test articles revealed that increased use of more MFCs within the active section did not increase aerodynamic performance due to asymmetric voltage constraints. The comparative mass and aerodynamic gains for the SMTE concept are evaluated for a representative finite wing as compared with a conventional, articulated flap wing. Informed by a simplistic system model and measured control derivatives, experimental investigations identified a reduction in the adaptive drag penalty up to 20% at off-design conditions. To investigate the potential for augmented aeroelastic performance and actuation range, a hybrid multiple-smart material morphing concept, the Synergistic Smart Morphing Aileron (SSMA), is introduced. The SSMA leverages the properties of two different smart material actuators to achieve performance exceeding that of the constituent materials. Utilizing the relatively higher work density and phase transformation of Shape-Memory Alloys combined with the larger bandwidth and conformal bending of MFCs, the resultant design is demonstrated to achieve the desired goals while providing additional control authority at stall and for unsteady conditions through synergistic use of reflex actuation. These advances highlight and motivate new morphing structures for the growing field of UAVs in which adaptation involves advanced compliance tailoring of complex geometry with synergistic actuation of embedded, smart materials.PhDAerospace EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/111533/1/alexmp_1.pd

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

A general method for the design and fabrication of shape memory alloy active spring actuators

Shape memory alloys have been widely proposed as actuators, in fields such as robotics, biomimetics and microsystems: in particular spring actuators are the most widely used, due to their simplicity of fabrication. The aim of this paper is to provide a general model and the techniques for fabricating SMA spring actuators. All the steps of the design process are described: a mechanical model to optimize the mechanical characteristic for a given requirement of force and available space, and a thermal model for the estimation of the electrical power needed for activation. The parameters of both models are obtained by experimental measurements, which are described in the paper. The models are then validated on springs manufactured manually, showing also the fabrication process. The design method is valid for the dimensioning of SMA springs, independently from the external ambient conditions. The influence on the actuator bandwidth was investigated for different working environments, providing numerical indications for the utilization in underwater applications. The spring characteristics can be calculated by the mechanical model with an accuracy of 5%. The thermal model allows one to calculate the current needed for activation under different ambient conditions, in order to guarantee activation in the specific loading conditions. Moreover, two solutions were found to reduce the power consumption by more than 40% without a dramatic reduction of bandwidth

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

Modeling a shape memory alloy based actuator for aerodynamic load control on aircraft wings

Este Proyecto Fin de Carrera está basado en la investigación de un futuro tipo de alas de avión que son capaces de adaptarse a diferentes condiciones de vuelo: condiciones medioambientales y condiciones de maniobra. En concreto, las alas adaptativas mostradas en este Proyecto se centran en el estudio en el borde de salida del ala. Con ello se pretende modificar su geometría y, por consiguiente, su aerodinámica. Para modificar la geometría del ala, se introducen los materiales inteligentes denominados Aleaciones con Memoria de Forma (Shape Memory Alloys o SMA) en modo de hilos en actuadores poliméricos, que durante su uso inducen la de exión en el actuador. El objetivo de este Proyecto es describir el comportamiento de estas aleaciones y desarrollar un modelo de simulación que represente su comportamiento. Además se estudia el rendimiento de este material y se compara con los resultados del modelo implementado. Todos estos ensayos confirman que el proceso de enfriamiento del material es el factor meterminante en el proceso. El primer punto de este Proyecto ha sido desarrollar un modelo de simulación de SMA (single model). Este modelo ha sido implementado en COMSOL siguiendo el modelo desarrollado por Muller Achenbach Seelecke. Este modelo requiere algunos parámetros iniciales referentes al material para su solución, que se obtienen mediante dos ensayos isotermos a diferentes temperaturas y un ensayo isobárico. Los ensayos isotermos proporcionan algunos parámetros geométricos referentes a su comportamiento, mientras que el isobárico hace referencia al coeficiente de transferencia de calor. Con todos estos parámetros, se consiguió que el modelo convergiera correctamente con soluciones satisfactorias y comparables con los ensayos de laboratorio. Así, se aprobó la validación del modelo, empleándolo para analizar el comportamiento en diferentes simulaciones y usarlo como base para el modelo antagonista (antagonistic model). Validado el modelo para un único hilo SMA, se realizaron y compararon diferentes ensayos isobáricos con los resultados obtenidos del modelo. Se analizó así la respuesta del hilo frente a los procesos de calentamiento y enfriamiento para diferentes masas y caudales de aire. Con estos ensayos, se obtuvieron los tiempos de respuesta del hilo SMA (calentamiento y enfriamiento) y, con su combinación, los tiempos de proceso en diferentes situaciones. El máximo ratio de trabajo está limitado por la potencia eléctrica de entrada y el flujo de aire, como se ha observado en los ensayos de laboratorio y de simulación. Comparando ambos resultados, se observaron algunas diferencias. Éstas son debidas principalmente al modelo de simulación implementado, ya que éste es un modelo monocristalino mientras que el hilo real es policristalino. Por ello, el modelo implementado tiene respuestas más rápidas y deformaciones más grandes. Como se ha comentado anteriormente, el modelo para un único hilo SMA se siguió desarrollando hasta implementar el modelo antagonista (actuador con hilos SMA en su interior desplazados de la fibra neutra con el objetivo de conseguir una de exión bidireccional). Como en el primer modelo, algunos parámetros fueron necesarios para su simulación. Alguno de éstos fueron importados del primero modelo, mientras que otros fuera calculados, como por ejemplo la in uencia del actuador. Además, para que el modelo convergiera, fue necesario un parámetro extra de ajuste, que disminuyera la in uencia del actuador. Siendo este parámetro una de las futuras vías de investigación del modelo. Es importante destacar la importancia del enfriamiento forzado mediante caudal de aire en el comportamiento del SMA en ambos modelos. Ya que la in uencia del ujo convectivo en el sistema es hasta 8,5 veces mayor que la convección natural, lo que hace que se consigan importantes ratios de trabajo de hasta 0,12 Hz en ensayos experimentales o 0,45 Hz en simulación. La diferencia en los resultados se debe principalmente al modelo de simulación implementado, como se ha comentado anteriormente. Por último, el modelo antagonista también muestra resultados satisfactorios comparando los resultados experimentales y de simulación. Este modelo es una futura vía de investigación con el objetivo de entender mejor la in uencia del actuador en el sistema, así como su interacción con el resto de parámetros.This Thesis studies a kind of wings that are able to adapt them to di erent ight conditions: aircraft manoeuvre and environment conditions. The adaptive wings shown here are focused on the trailing edge of the wing. Thus, the aerodynamics of the wing and its surface can be changed. In order to modify its geometry, Shape Memory Alloys are embedded in an actuator, so that a de ection of the actuator can be induced. The goal of this Thesis was to describe the Shape Memory Alloy behaviour and develop a model that was able to provide its behaviour. In addition, the performance of the material was studied and compared with the model results. Those tests confirm that the active cooling is the main actuation factor. The first point of this Thesis has been the development of a model for a SMA. This model has been implemented in COMSOL, following the the M uller - Achenbach - Seelecke SMA model. In order to run the model, some parameters were required in a SMA wire. Those parameters were obtained by two isothermal tests at different temperatures and isobaric tests. The isothermal tests provided some geometrical parameters about its behaviour, whereas the isobaric tests yielded the heat transfer coeficient. Therefore, the model was run successfully and validated, because the model shows a good agreement with the results obtained by experiments. This model was used to analyse the SMA behaviour at different simulations and implement the antagonistic model. Once the single model was validated, different isobaric tests were done and compared with the model results. For weights from 1kg to 6kg, the wire was tested analysing the heating and cooling responses. The time that takes for the wire to be contracted and elongated is calculated. Combining them, the maximum working rate was obtained. This rate is limited by the power and air ow, as has been shown in the experimental and simulation results. Some inaccuracies could be appreciated in both results, due to the model implemented. This model is monocrystalline, whereas the real wire is polycrystalline. Therefore, the model has faster responses and higher strains. Moreover, the best strain-area was determined around the midpoint of the strain, where the highest responses were obtained. Following to the single model, the antagonistic model has been implemented and validated. Some parameters were required to run the model properly. Some of them were imported from the single wire model, and other were calculated, as such the beam in uence. In order to get comparable results, a tuning parameter was necessary. This parameter affects to the actuator in uence, reducing its in uence. This parameter is one of the future work in order to improve the model. ModelingIngeniería Industria

The Effect of Thin Film Adhesives on Mode I Interlaminar Fracture Toughness in Carbon Fiber Composites with Shape Memory Alloy Inserts

Shape Memory Alloy (SMA) was placed within Polymer Matrix Composite (PMC) panels alongside film adhesives to examine bonding. Double cantilever beam (DCB) testing was performed using ASTM D5528. C-scanning was performed before testing, modal acoustic emissions (MAE) were monitored during testing, and microscopy performed post-test. Data was analyzed using modified beam theory (MBT), compliance calibration (CC) and modified compliance calibration (MCC) methods. Fracture toughness for control specimens was higher than previously reported due to fiber-bridging. Specimens with SMAs and adhesives stabilized crack propagation. Results revealed SMA-bridging; a phenomenon mimicking fiber-bridging which increased the load and fracture toughness of SMA specimens

Thermo-Mechanical System Identification of a Shape Memory Alloy Actuated Mechanism

Shape memory alloy (SMA) actuators paired in an antagonistic arrangement can be used to produce mechanisms that replicate human biomechanics. To investigate this proposal, the biomechanical articulation of the elbow by means of the biceps brachii muscle is compared with that of a SMA actuated arm. This is accomplished by parametric analysis of a crank-slider kinematic mechanism actuated, first, with an experimentally characterized SMA wire and then an idealized musculotendon actuator based on actuation properties of muscles published in the literature. Next, equations of motion for the system dynamics of the SMA actuated mechanism are derived and phase portrait analysis is conducted varying system parameters around different operating points. The eigenvalues of the differential equation are examined around equilibrium points and a stiffness ratio metric is proposed to characterize dynamic stability based on system parameters. Next, a heat transfer model is proposed and energy analysis is conducted on each stage of phase transformation for the SMA wire. The unknown parameters in the heat transfer model are theoretically derived and an experimental system identification is conducted. A proof of concept antagonistic SMA actuated mechanism is designed and kinematic analysis is conducted on an experimental prototype