Shape Memory Alloy Actuators Research Articles

An Inchworm Robot with Self-Healing Ability Using SMA Actuators

In this paper, we propose an inchworm-type soft robot using a self-healing gel as its body and shape-memory alloy (SMA) wires as its actuators. To realize inchworm-like locomotion, two coiled SMA wires are placed in parallel in the gel-fabricated body. The bottom-side wire and the upper-side wire reciprocally bend by applying electric current to the actuators. To realize the self-restoration automatically, the robot consists of a self-healing body equipped with magnets. The paper introduces the structure of the inchworm-shaped robot with its inchworm-like locomotion performance, together with the self-healing function.

An Inchworm-Snake Inspired Flexible Robotic Manipulator With Multisection SMA Actuators for Object Grasping

Aiming at achieving the object grasping task, an inchworm-snake inspired Flexible Robotic Manipulator (FRM) is presented in this paper. By using both flexible and rigid materials in the robot structure, the FRM has the stability and control accuracy of a rigid robot as well as the compliant behavior of a soft robot. The piecewise-linear driving characteristic of the Shape Memory Alloy (SMA) actuator enables the accurate establishment of the FRM's kinematic model and model-based control method. Deep learning-based eye-in-hand binocular visual perception is designed to obtain the state feedback without relying on external sensors, making it suitable to perform tasks in confined and unstructured environment. A model-based controller with the deformation planning is introduced with the aim of achieving accurate control in object grasping. The experiments demonstrate that the FRM possesses the capability of performing the object grasping with the proposed methods.

Mathematical modelling and experimental study of a novel planar micro-positioning stage using shape memory alloy actuators

The application of smart materials as actuators in precise positioning systems has witnessed significant growth in recent years. However, the use of shape memory alloy (SMA) materials in this context is hindered by their slow response and complex nonlinear behaviour. To overcome these limitations, this paper introduces a novel approach that incorporates two opposite SMA actuators into a flexure hinge type micro-positioning stage, aiming to enhance the system speed. A semi-analytical modelling approach is employed to model the nonlinear behaviour of the SMA actuator. Using the available material models for SMA materials and the nonlinear curved beam theory, the governing equations of the proposed SMA actuator are derived and the resulted partial differential equations are reduced to an algebraic equation based on the Galerkin method. The resulting equations are then solved using the return map method. To validate the accuracy and effectiveness of the proposed model, an experimental setup is constructed. The experimental results demonstrate the model ability to accurately predict the behaviour of the system. Additionally, the developed model allows for the extraction of stress and strain profiles of the SMA actuators for designing the actuator. The study highlights the potential of integrating the proposed model with robust control methods for future works, aiming to effectively control micro-positioning systems and further enhance their performance.

Development and Dynamic State Estimation for Robotic Knee–Ankle Orthosis With Shape Memory Alloy Actuators

Abstract The development of rehabilitation robots has long been an issue of increasing interest in a wide range of fields. An important aspect of the ongoing research field is applying flexible components to rehabilitation equipment to enhance human−machine interaction. Another major challenge is to accurately estimate the individual’s intention to achieve safe operation and efficient training. In this article, a robotic knee−ankle orthosis (KAO) with shape memory alloy (SMA) actuators is developed, and the estimation method is proposed to determine the joint torque. First, based on the analysis of human lower limb structure and walking patterns, the mechanical design of the KAO that can achieve various rehabilitation training modes is detailed. Next, the dynamic model of the hybrid-driven KAO is established using the thermodynamic constitutive equation and Lagrange formalism. In addition, the joint torque estimation is realized by the nonlinear Kalman filter method. Finally, the prototype and human subject experiments are conducted, and the experimental results demonstrate that the KAO can assist lower limb movements. In the three experimental scenarios, reductions of 59.1%, 16.5%, and 73% of the torque estimation error during the knee joint movement are observed, respectively.

New phase diagram for low hysteresis response of a coiled shape memory alloy actuator

We demonstrate a new phase diagram describing the responses of shape memory alloy (SMA) spring actuators. The SMA spring actuator has a wide range of temperatures for phase transitions and responses with low hysteresis. To describe these specific responses of the SMA spring actuator, a new phase diagram with an overlapping layer is proposed. In the overlapping layer, even if it changes from a heating phase to a cooling phase or vice versa, a phase transition occurs whenever the temperature of the SMA changes. Because there is no region in which only the temperature changes without a force changes, the hysteresis is reduced. The overlapping layer is formed by changing the properties of the SMA when fabricating the spring actuator. One of the properties that change in the SMA is the amount of latent heat when the phase transition occurs. The latent heat of the SMA spring is significantly low compared to that of the SMA wire due to the plasticity produced by the stress applied to form the spring shape. Therefore, there will be a tradeoff between the amount of the phase transition and the hysteresis of the SMA actuator.

A Physics-Based Hybrid Dynamical Model of Hysteresis in Polycrystalline Shape Memory Alloy Wire Transducers

Shape memory alloys (SMAs) are a class of smart materials that exhibit a macroscopic contraction of up to 5% when heated via an electric current. This effect can be exploited for the development of novel unconventional actuators. Despite having many features such as compactness, lightweight, and high energy density, commercial SMA wires are characterized by a highly nonlinear behavior, which manifests itself as a load-, temperature-, and rate-dependent hysteresis exhibiting a complex shape and minor loops. Accurate modeling and compensation of such hysteresis are fundamental for the development of high-performance SMA applications. In this work, we propose a new dynamical model to describe the complex hysteresis of polycrystalline SMA wires. The approach is based on a reformulation of the Müller–Achenbach–Seelecke model for uniaxial SMA wires within a hybrid dynamical framework. In this way, we can significantly reduce the numerical complexity and computation time without losing accuracy and physical interpretability. After describing the model, an extensive experimental validation campaign is carried out on a 75- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> m diameter SMA wire specimen. The new hybrid model will pave the development of hybrid controllers and observers for SMA actuators.

Ankle Foot Orthosis for Patients with Drop Foot Using Shape-Memory-Alloy Actuators

AbstractGait disorders can lower the quality of life of patients. Drop foot, a causative factor of deviated gait patterns, renders patients unable to lift their forefoot towards the body. Hence, a light and compact ankle–foot orthosis (AFO), which is the most common treatment for drop foot, must be designed, especially for patients with impaired lower limb muscles as oxygen consumption increases by 30% per 1.96 N load on their foot. Furthermore, the limited range of ankle angles in the first 10% of the gait cycle (GC) is a major drawback for patients with drop foot compared to healthy individuals. This limited range of ankle angles can be improved by gaining support from an AFO composed of shape memory alloy (SMA) actuators (SMA-AFO). Therefore, in this study, an SMA was used to fabricate a soft actuator to reduce the weight of the AFO. An adaptive frequency oscillator (AO) was implemented in real time for continuous gait phase detection. Walk tests were performed on a treadmill with the SMA-AFO attached to the participants (N = 3). The experimental results showed that the participants could lift their forefoot in the dorsiflexion direction with an ankle angle of 8.75° in the first 10% of the GC. Furthermore, the current required to operate the SMA actuator can be supplied to only 45.3% of the GC, reducing the power consumption. Therefore, the proposed SMA-AFO can be used in patients with drop foot.

Scaling Effects on Morphing Structures: Preliminary Guidelines for Managing the Effects on a Case Study

The technique of morphing in aerospace engineering is a relatively new discipline targeting the improvement of aircraft performance, even through dramatic changes to some critical geometrical and mechanical features, to adapt aircrafts’ configurations to evolving operation conditions. The development path of morphing systems is complex and shall pass through articulated gates to prove its readiness level due to the concurrence of different disciplines and approaches. The characterization and demonstration of the concepts in a representative environment, such as wind tunnel test facilities, are some of the most relevant steps needed for the maturation of the engineering technique. The practical size limitations of test facilities usually impose the use of scaled models. In the case of morphing systems, whose architecture is strictly dependent on the available room, and whose performance is tightly correlated with the general structural stiffness, changes in dimensions may affect the overall behaviour significantly. Therefore, the adaptive design may change a lot until it arrives to the formation of completely different products. Transportability issues of certain architectural forms, as well as the different classes of vehicles, are also related to that aspect. The scope of this paper is to investigate the impact of some effects of scaling processes on certain features of a morphing system, particularly focusing on the stiffness parameters, for their impact on several features such as the load bearing capability and structural stability in both steady and dynamic conditions. As a case study, a rotorcraft blade segment integrated with torsional shape memory alloy (SMA) actuators was considered. Relevant numerical models were exploited to highlight the different evolution laws of the characteristic structural parameters vs. the referred scale factors. In this investigation, the axial, flap, lag bending, and torsion stiffnesses, as well as normal modes and stress levels, are considered. The achieved results confirm the complexity of attaining an effective reproduction of the targeted morphing architecture, as scaled configurations are considered. In spite of the unavoidable specificity of the analysis herein reported, it is believed that such attainments can have a general validity at least to some extent, and the outcomes may be exported to other morphing systems, at least as guidelines. This study took place within the European project SABRE (Shape Adaptive Blades for Rotorcraft Efficiency, H2020).

A wearable assistive system for the visually impaired using object detection, distance measurement and tactile presentation

With the current development of society, ensuring traffic and walking safety for the visually impaired is becoming increasingly important. We propose a wearable system based on a system previously developed by us that uses object recognition, a distance measurement function, and the corresponding vibration pattern presentation to support the mobility of the visually impaired. The system recognizes obstacles in front of a user in real time, measures their distances, processes the information, and then presents safety actions through vibration patterns from a tactile glove woven with shape memory alloy (SMA) actuators. The deep learning model is compressed to achieve real-time recognition using a microcomputer while maintaining recognition accuracy. Measurements of the distances to multiple objects are realized using a stereo camera, and vibration patterns are presented through a tactile glove in response to these distances. Experiments are conducted to verify the system performance to provide safe navigation depending on the positions and the distances of multiple obstacles in front of the user.

Improving the Response Time of a Soft Robotic Gripper Using a Heat Sink with Shape Memory Alloy Actuators

Improving the Response Time of a Soft Robotic Gripper Using a Heat Sink with Shape Memory Alloy Actuators

A Self–Tuning Intelligent Controller for a Smart Actuation Mechanism of a Morphing Wing Based on Shape Memory Alloys

The paper exposes some of the results obtained in a major research project related to the design, development, and experimental testing of a morphing wing demonstrator, with the main focus on the development of the automatic control of the actuation system, on its integration into the experimental developed morphing wing system, and on the gain related to the extension of the laminar flow over the wing upper surface when it was morphed based on this control system. The project was a multidisciplinary one, being realized in collaboration between several Canadian research teams coming from universities, research institutes, and industrial entities. The project’s general aim was to reduce the operating costs for the new generation of aircraft via fuel economy in flight and also to improve aircraft performance, expand its flight envelope, replace conventional control surfaces, reduce drag to improve range, and reduce vibrations and flutter. In this regard, the research team realized theoretical studies, accompanied by the development and wind tunnel experimental testing of a rectangular wing model equipped with a morphing skin, electrical smart actuators, and pressure sensors. The wing model was designed to be actively controlled so as to change its shape and produce the expansion of laminar flow on its upper surface. The actuation mechanism used to change the wing shape by morphing its flexible upper surface (manufactured from composite materials) is based on Shape Memory Alloys (SMA) actuators. Shown here are the smart mechanism used to actuate the wing’s upper surface, the design of the intelligent actuation control concept, which uses a self–tuning fuzzy logic Proportional–Integral–Derivative plus conventional On–Off controller, and some of the results provided by the wind tunnel experimental testing of the model equipped with the intelligent controlled actuation system. The control mechanism uses two fuzzy logic controllers, one used as the main controller and the other one as the tuning controller, having the role of adjusting (to tune) the coefficients involved in the operation of the main controller. The control system also took into account the physical limitations of the SMA actuators, including a software protection section for the SMA wires, implemented by using a temperature limiter and by saturating the electrical current powering the actuators. The On–Off component of the integrated controller deactivates or activates the heating phase of the SMA wires, a situation when the actuator passes into the cooling phase or is controlled by the Self–Tuning Fuzzy Logic Controller.

Modeling and Application of an SMA-Actuated Lightweight Human-Inspired Gripper for Aerial Manipulation

The increasing usage of multi-rotor aerial platforms and the reliability of flights enabled researchers to add equipment and devices to them for application. The addition of lightweight manipulators, grippers, and mechanisms to fulfill specific tasks has been reported frequently recently. This work pushes the idea one step ahead and uses an Artificial Human Hand (AHH) in an uncrewed aerial vehicle for aerial manipulation, device delivery, and co-operation with human workers. This application requires an effective end-effector capable of grasping and holding objects of different shapes. The AHH is a lightweight custom-made human-inspired design actuated using Shape Memory Alloy (SMA) materials. The SMA actuators offer significantly high forces with respect to their light weights though the control of these new actuators is a challenge that has been successfully demonstrated in this paper. The control of the SMA actuators could be achieved via heat exchange on the actuator, indirectly carried out by changing the current. The benefit of using this new actuator is removing the motors and mechanical mechanisms and simplifying the design. A soft cover is developed for the AHH to add friction and make it closer to a human hand. The modeling of the structured actuators on the system through tendons is presented, and a series of experiments for handling and manipulating different objects have been conducted. The objects were chosen with different weights and shapes to show the effectiveness of the design. An analysis of a generated torque of the manipulator for different cylindrical objects has been carried out. An analysis and comparison for grasping a series of items, pressure and temperature analysis, and the weight-to-volume ratio have been presented.

The Design of a NI-TI Based Shape Memory Alloy Actuator

A simpffied procedure for the design of SMA(Shape Memory Alloy) actuators is presented. The inter-relationship between the mechanical properties and the electrical properties that are relevant for the design of SMA actualors working under a conEtant load are clearly brought out. The dilferent conditions that arise while using an SMA actuator against o constant load has been considered. The locus of SMA acluators in relation to conventional actuators has been clartfied. The joule heating efects and power developed by the SMA actuator in relation to its weight has been also dealt with.

Neural Network Adaptive Control of Magnetic Shape Memory Alloy Actuator With Time Delay Based on Composite NARMAX Model

Magnetic shape memory alloy (MSMA) based actuator plays an important role in the field of micro and nano-fabrication due to its large stroke. However, the inherent hysteresis of MSMA seriously affects the application prospects of MSMA-based actuator in the field of precision positioning. In this study, a composite model is proposed for hysteresis in the MSMA-based actuator by coupling an improved fractional-order Bouc-Wen model to a nonlinear auto-regressive moving average with exogenous inputs (NARMAX) model. Based on the proposed model, a neural network adaptive control method is then used to control the MSMA-based actuator, and the controller design takes into account the effect of time delay on the system performance to improve the positioning accuracy of the MSMA-based actuator. First, we fuse the composite NARMAX model with the canonical form of the nonlinear system to describe the MSMA-based actuator. Then, a control strategy is developed to address the impact of the unknown time delay for controller design and achieve the satisfactory positioning accuracy of the MSMA-based actuator. By using Lyapunov theory, the tracking error is proven to be asymptotic convergence. Experimental studies are provided to validate the effectiveness of the proposed modeling and control schemes.

Integral sliding mode control (ISMC) with an extended state observer (ESO) for an arc-shaped shape memory alloy actuator

Integral sliding mode control (ISMC) with an extended state observer (ESO) for an arc-shaped shape memory alloy actuator

Feasibility Investigation of Attitude Control with Shape Memory Alloy Actuator on a Tethered Wing

This study is aimed at assessing the feasibility of employing an innovative, smart-material-based control effector for an inflatable wing. A shape memory alloy (SMA) actuator is primarily investigated as a control effector in this work for its advantages of a simple actuation mechanism and a high force-to-weight ratio. This paper presents the design, control strategy and simulation results of the SMA actuator used as a stability augmentation system for a small-scale prototype kite. Stable flight of the kite is achieved during open wind tunnel tests using the SMA actuator. Based on experimental and simulation analyses, it is evident that the current SMA actuator is better for low-frequency actuations rather than stability augmentation purposes, as its performance is sensitive to practical conditions. The study also discusses potential improvements and applications of the SMA actuator.

Design and evaluation of shape memory alloy-actuated active needle using finite element analysis and deflection tracking control in soft tissues.

Conventional needles lack active mechanisms for large tip deflection to bypass obstacles or guide through a desired trajectory in needle-based procedures, compromising accuracy and effectiveness. An active needle with a shape memory alloy (SMA) actuator was designed and evaluated by demonstrating deflections in tissue-mimicking gels. Finite element simulation and real-time needle tip deflection tracking in tissue-mimicking gels were performed. The active needle deflected 50 and 39mm at 150mm insertion depth in the liver and prostate mimicking gels, respectively. Reasonable simulation errors of 16.42% and 12.62% in needle deflections and small root mean squared errors of 1.42 and 1.47mm in deflection tracking were obtained. The proposed needle produced desirable large tip deflections capable of bypassing obstacles in the insertion path and tracked a preplanned trajectory with minor errors. The finite element study would help optimise needle designs and predict deflections in soft tissues.

Fabrication and Characterization of the Kirigami-Inspired SMA-Powered Actuator

This paper presents an innovative approach to creating Shape Memory Alloys (SMA)-based actuators that are lightweight, compact, and capable of providing large strokes. Inspired by the Kirigami structure, an SMA actuator is designed using the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\Omega$</tex-math></inline-formula> -pattern, which utilizes out-of-plane flexion to produce a flexible metamaterial. The study focuses on providing a unique method for fabricating these actuators utilizing different cutting methods and 3D printing. The stability behavior of the SMA-based Kirigami pattern is analyzed, and two cutting strategies and their effects are discussed. The paper concludes with the successful validation of the proposed design technique through the creation of a lightweight linear actuator using the SMA active element inspired by Kirigami and a biasing element based on a flexure design. This study offers valuable insights into the development of SMA-based actuators and their potential to address the pressing need for high-stroke and high-force output in a wide range of fields, from medical devices to industrial automation, and from aerospace to robotics.

Shape Memory Alloy (SMA) Actuators: The Role of Material, Form, and Scaling Effects.

Shape memory alloys (SMAs) are smart materials that are widely used to create intelligent devices because of their high energy density, actuation strain, and biocompatibility characteristics. Given their unique properties, SMAs have been found to have significant potential for implementation in many emerging applications in mobile robots, robotic hands, wearable devices, aerospace/automotive components, and biomedical devices. In this review, we summarize the state-of-the-art of thermal and magnetic SMA actuators in terms of their constituent materials, form, and scaling effects, including their surface treatments and functionalities. We also analyze the motion performance of various SMA architectures (wires, springs, smart soft composites, and knitted/woven actuators). Based on our assessment, we emphasize current challenges of SMAs that need to be addressed for their practical application. Finally, we suggest how to advance SMAs by synergistically considering the effects of material, form, and scale. This article is protected by copyright. All rights reserved.

Explorations of knitted shape memory alloy actuation behavior under high loads via finite element analyses and experimental studies

The properties of shape memory alloy (SMA) wires have long been leveraged across a variety of industries. While the response of such SMA forms implemented as straight axial actuators is well understood, curved and complex configurations such as knits have received far less attention. Considering 2D configurations, it is well known that knits exhibit more in-plane compliance than weaves and meshes, the curved wires comprising the former being much more flexible than the straight wire segments in the latter. In addition, knitted structures are uniquely highly tailorable. Knitting techniques and patterns developed in the textile industry allow for variable materials and geometries in the same structure, allowing for a large range of tailored macro-structure responses. Existing efforts to model the behavior of knitted SMA structures are lacking; though finite element analysis (FEA) models have been presented for knit SMAs, these models either only consider superelastic SMA behavior, or, in those that account for actuation behavior, the applied load conditions studied are insufficient to fully leverage the thermally induced strain recoverability of SMAs. This work seeks to develop and validate a finite element model for the actuation of SMA knitted structures where individual SMA wire components are axially stressed to more than 100 MPa. A representative volume element is developed for a common knit pattern, and macro-structure responses are explored and compared with experiments. This research provides a foundation for better understanding fundamental capabilities and responses of knitted SMA structures, allowing for better design, functionality, and customizability of the applications into which they are incorporated, enabling development of unique soft actuators. A shape-set sample examined herein generated 13% extension (analogous to strain) and recovered more that 6% under a load associated with 100 MPa stress in a straight wire, and a sample knit off-the-spool generated over 20% extension and recovered 9% for the same load.