Wire Actuators Research Articles

A Soft Five-Fingered Hand Actuated by Shape Memory Alloy Wires: Design, Manufacturing, and Evaluation.

This work presents a novel five-fingered soft hand prototype actuated by Shape Memory Alloy (SMA) wires. The use of thin (100 μm diameter) SMA wire actuators, in conjunction with an entirely 3D printed hand skeleton, guarantees an overall lightweight and flexible structure capable of silent motion. To enable high forces with sufficiently high actuation speed at each fingertip, bundles of welded actuated SMA wires are used. In order to increase the compliance of each finger, flexible joints from superelastic SMA wires are inserted between each phalanx. The resulting system is a versatile hand prototype having intrinsically elastic fingers, which is capable to grasp several types of objects with a considerable force. The paper starts with the description of the finger hand design, along with practical considerations for the optimal placement of the superelastic SMA in the soft joint. The maximum achievable displacement of each finger phalanx is measured together with the phalanxes dynamic responsiveness at different power stimuli. Several force measurement are also realized at each finger phalanx. The versatility of the prototype is finally demonstrated by presenting several possible hand configurations while handling objects with different sizes and shapes.

Morphing Origami Block for Lightweight Reconfigurable System

Origami provides a unique tool for the design of robotic frames owing to its simple shaping principle by “folding.” However, achieving the fast and reversible activeness of a highly reconfigurable structure remains challenging owing to the limitations of accessible actuators. In particular, it is difficult to find an actuator that can realize a simultaneously large, rapid, reversible, and stable movement while leading to a favorable form factor for the origami. To overcome this, in this article, we propose a 3-D shape-shifting system consisting of a morphing origami block that complements the stability problem of shape memory alloy wire actuators by tuning its structural characteristics. This cooperative scheme improves the reversibility and stability of the shape-shifting system, which enables the rapid transformation with high degrees of freedom unlike in existing programmable origami. As a stand-alone unit of transformation, morphing block equipped with deployable mechanism and actuators weighs 6 g and has a volume change factor of ten. Furthermore, the transformation time in both directions is less than 5 s, and the block can carry more than 120 g of payload in the deployed state. The proposed system composed of multiple origami blocks can reconfigure itself into diverse 3-D target shapes.

Development of Wire Actuation 2 Stage Extension Mechanism Considering to Use for Spacecraft

Extension mechanism is attracting attention to use for capturing mechanism of the active debris removal spacecraft. Authors developed the debris capturing end effector consist of multiple wire action 2 stage extension mechanism. This mechanism is selected because of its high extension ratio, fast extending speed, high stiffness and retry capability using single motor. This end effector and mechanism's experimental results showed that it satisfies the requirements. However, this mechanism is not yet evaluated to use in space environment. In this study, wire actuation 2 stage extension mecha- nism's movement is discussed, and equation of motion is proposed to discuss which data to be acquired to evaluate the mechanism to use in space. The device to obtain the data is introduced, and experimental results shows that the introduced device can well acquire the data. Experiment inside the vacuum chamber is also conducted, and the results showed that this mechanism can be used in space environment.

Effect of Environmentally Friendly Oil on Ni-Ti Stent Wire Using Ultraprecision Magnetic Abrasive Finishing

Nickel-titanium (Ni-Ti) has been widely used to make shape-memory actuator wire for numerous medical industrial applications, with the result that it frequently comes into contact with the human body. High-quality and nontoxic surfaces of this material are therefore in high demand. We used a rotating magnetic field for an ultraprecision finishing of Ni-Ti stent wire biomaterials and evaluated the finishing technique’s efficacy with different processing oils. To create nontoxic Ni-Ti stent wire, the industrial processing oils that are generally used in the surface improvement process were exchanged for oils with low environmental impacts, and processed under rotating magnetic fields at different speeds and processing times. The processing performance of the different oils was compared and verified. The results show that ultraprecision magnetic abrasive finishing that uses olive and castor oil improves surface roughness by 66.67%, and 45.83%, respectively. SEM and energy-dispersive X-ray spectroscopy (EDX) analyses of the finished components (before and after processing) showed that the material composition of the Ni-Ti stent wire was not changed. Additionally, the magnetic abrasive tool composition was not found on the surface of the finished Ni-Ti stent wire. In conclusion, the environmentally friendly oil effectively improved the diameter of the Ni-Ti stent wire, demonstrating the utility of olive and castor oil in ultraprecision finishing of Ni-Ti stent wire biomaterials.

Shape memory alloy actuator with active cooling device and deflectable winglet application

Heating and cooling time directly influence the response speed of a shape memory alloy (SMA) wire actuator. An SMA wire is heated quickly by electric current, however quickly cooling it to a given temperature is difficult. In this study, we proposed a pipeline-type active air convection cooling scheme, which uses compressed air as cooling airflow to achieve rapid active cooling of SMA wire actuators. We designed an SMA wire linear actuator consisting of SMA wires, a compressed air tank, an air valve, an Outlet Pipeline, an SMA Cooling Pipeline, and some other additional accessories. We established theoretical models of heat transfer under natural cooling and active convection cooling of an SMA wire. In addition, we carried out theoretical simulation and experiments on a NiTi alloy SMA wire with a diameter of 1 mm and compared the accuracy of simulation with test results. The SMA wire actuators are used for deflectable morphing winglets of aircraft wing. We designed three-dimensional numerical models of the morphing winglets that can be deflected within ±20° and the experimental models are machined and assembled. Final test results show that active cooling time is reduced by more than 70% compared with natural cooling and the response speed is improved significantly.

An experimental investigation on time response characteristics of SMA wire actuators under electric heating for engineering design

Shape memory alloys (SMAs) are proved to have high energy-to-volume ratio and large displacement. However, they have the defect of longer recovery time. In practice, designing SMA wire actuators is a very complex and exhausted thing because of extensive and various needs. In this study, a special setup was designed, which can test many characteristics of a SMA wire heated by electric current, including temperature, deformation, response time, recovery time, wind speed (for cooling), and load. Besides, an empirical model of the wires temperature was presented for avoiding overheating the wires. By fitting experiment data, unknown parameters in this model are determined. Next, main design parameters are investigated on how they exert effects on the characteristics of the SMA wires, including wire radius, convection type, load, and voltage. At last, the time response characteristics were also analyzed. Through this study, one can make clear how each design parameter plays its part in SMA wire actuators.

Concept and design of the caging-based debris gripper for PAF capturing

This paper presents the concept and design of a gripper intended to capture an un-cooperative object, such as a rocket body that became a debris object. The Payload Attach Fitting (PAF) is selected as the grasping point of the debris. The caging technique is used for the capturing method, and form closure is chosen as the holding method of the gripper. Wire actuation is selected for the gripper's actuation mechanism. This paper also introduces the extending mechanism and wire routing design, and the gripper is developed. The performance of the developed gripper's mechanisms are experimentally verified, and PAF capturing was demonstrated to show that the developed gripper satisfies the conceptual design.

Modeling of integrated shape memory alloy and Macro-Fiber Composite actuated trailing edge

Owing to their high energy densities, smart materials like shape memory alloys (SMAs), Macro-Fiber Composites (MFCs) and, electroactive polymers (EAPs) have massive potential as actuators in wing morphing applications. In this article, a detailed numerical model is developed for the shape prediction of an elastic base that is actuated by a combination of a shape memory alloy (SMA) wire and a Macro-Fiber Composite (MFC) bimorph. It has been demonstrated using the model that it is possible to achieve large deflections at low frequencies by virtue of the phase transformations in the SMA wire and rapid actuation with small deflections due to the MFC bimorph. In the developed scheme, the elastic base is modeled using non-linear Euler-Bernoulli beam theory. The influence of the non-linear hysteresis in the SMA wire and the linear actuation characteristics of the MFC is studied by incorporating thermo-mechanical and electro-mechanical constitutive behavior into the non-linear beam theory. The system of coupled equations hence obtained, is solved iteratively to obtain the deflected shape of the elastic base. The results from the developed numerical scheme are validated against the previously available studies in the literature and experiments. Additionally, the synergistic advantage of using the two actuators together has been shown through experiments. As an illustration, a smart trailing edge camber morphing concept is developed by integrating the flexible elastic structure along with the two smart actuators to a NACA 0012 airfoil as the trailing edge.

A novel smart assistive knee brace incorporated with shape memory alloy wire actuator

The knee plays a significant role in locomotion and stability of the entire body through supporting the body weight and assisting the lower body kinematics during walking. However, the knee is at constant risk of becoming weakened due to disease, age, and accidents. One approach to treating weakened knee is wearing an assistive knee brace. To design a clinical knee brace, many factors such as weight and compliant mechanism should be considered. In this study, a novel smart assistive knee brace mechanism incorporated with wire actuators made of shape memory alloys is proposed to ameliorate the issues associated with weight and flexibility of existing brace designs. Unlike earlier studies, the proposed orthosis includes pressure sensor, shape memory actuator, and smart linkage. Furthermore, two distinct shape memory alloy actuator design concepts with improved stiffness are developed, and the best option is chosen systematically and prototyped. The novel mechanism proposed in this research overcomes the weight of the lower limb during swing phase using the combined shape memory alloy actuation and feed-forward controller design. As such, it can be used as a potential replacement to its conventional counterparts when the higher weight reduction as well as a flexible and controllable mechanism are simultaneously sought.

Influence of Heat Treatment Parameters on the Functional Behavior and Corrosion Performance of a Shape Memory Wire Actuator

In the present study, the effect of heat treatment parameters on the functional response, corrosion behavior and microstructural evolution of NiTi shape memory alloys were investigated. Various heat treatment regimes were utilized to study the impact of temperature and duration on the actuation behavior of wire samples under bending. Results clarified that austenite transformation temperatures As and Af increased at higher treatment temperatures. Cyclic response in the range of 0 to 15 degrees indicated that the actuation force exhibits an inverse relation with the treatment temperature. Higher treatment durations below 500°C elevated both the hardness and the sustained load. Bending force levels above 1500gf were achieved after a 90 min treatment at 400°C, whereas that over 500°C brought about a noticeable drop in strength. Investigations on the corrosion behavior of NiTi alloy was utilized in the simulated body fluid revealing that the sample heat treated at 400°C for 90 min showed the highest corrosion resistance.

Shape memory alloy actuator-embedded smart clothes for ankle assistance

This study presents the design of a lower limb-worn, soft wearable robot that assists ankle plantar flexion using soft textiles and a shape memory alloy (SMA) wire actuator. Textile-based clothing-type soft wearable robots, the smart clothes in short, are proposed to build a soft exoskeleton that is inherently lightweight and comfortable for the wearer. SMA wire actuators are embedded in the smart clothes to provide assistive forces to the wearer. The SMA wire actuator is a low-profile wire-type artificial muscle actuator, which can be embedded on the textile without any extruded parts on the clothing. We have built an SMA wire actuator-embedded smart clothing that is able to provide ankle assistive force without rigid kinematic mechanisms. The smart clothing has a mass of 428.5 g without a power battery, and it can generate an ankle moment of 100 N cm in each ankle during walking.

Development of form-fit connection for NiTi shape memory wire actuators using laser processing

Shape memory alloy actuators (SMAA) are attractive for lightweight construction applications such as in the fields of e-mobility and aerospace due to their properties (high actuator performance, low weight, silent operation). Used force-fit and firmly bonded connections (crimping, casting) can only be released again non-destructively to a limited extent. Combined with the complex material behavior of NiTi-SMAA, the development of standardized SMAA is limited. In this paper, a novel approach based on a form-fit connection is presented.

Experimental Study on a Power Exoskeleton driven by a wire actuation system for waist twisting motion

Experimental Study on a Power Exoskeleton driven by a wire actuation system for waist twisting motion

Hysteresis Modeling, Identification and Fuzzy PID Control of SMA Wire Actuators Using Generalized Prandtl-Ishlinskii Model with Experimental Validation

In this paper, hysteretic behavior modeling, system identification and control of a mechanism that is actuated by shape memory alloy (SMA) wires are presented. The mechanism consists of two airfoil plates and the rotation angle between these plates can be changed by SMA wire actuators. This mechanism is used to identify the unknown parameters of a hysteresis model. Prandtl–Ishlinskii method is employed to model the hysteresis behavior of SMA actuators, and then, a self-tuning fuzzy-PID controller is designed based on the obtained model and implemented experimentally on the mechanism. The process of designing the controller has been implemented based on the model which results in compensating time and price. Self-tuning fuzzy-PID controller is applied to the closed control loop in order to control the position of the morphing wing. The performance of the controller has been investigated under different input signals including square and sinusoidal waves, and the results show the proper effectiveness of the method.

Characterization and Lubrication of Tube-Guided Shape-Memory Alloy Actuators for Smart Textiles

Smart textiles are flexible materials with interactive capabilities such as sensing, actuation, and computing, and in recent years have garnered considerable interest. Shape-memory alloy (SMA) wire is a well-suited for smart textiles due to its high strength, small size, and low mass. However, the contraction of SMA wire is low, limiting its usefulness. One solution to increasing net contraction is to use a long SMA wire and guide it inside a tube that is wound back and forth or coiled inside a smart textile. In this article, we characterize the performance of tube-guided SMA wire actuators. We investigate the effect of turn radius and number of loops, showing that the stroke of an SMA-based system can be improved by up to 69.81% using the tube-guided SMA wire actuator concept. Finally, we investigate how tube-guided SMA wire actuators can be lubricated to improve their performance. Coarse graphite powder and tungsten disulfide lubricant both delivered improvements in stroke compared with an unlubricated system.

Enhancing the actuation frequency of shape memory alloy wire by vibration-enhanced cooling

Shape memory alloy wire actuators are lightweight, compact, and have high actuation stress, but their actuation frequency is limited by the rate they can be thermally cycled. Heating time can be reduced with high current, but rapidly cooling the material without introducing disadvantages is a challenge. This study establishes the feasibility of a novel approach to more rapidly cool shape memory alloy wires based on inducing their first mode of vibration. To achieve this, a steel spring pin placed on the wire was driven by an electromagnet as the shape memory alloy cooled. Experiments were conducted with a shape memory alloy wire (250 mm length, 0.381 mm diameter, 70°C austenite finish temperature) that was thermally cycled against constant forces and against an extension spring. The heating and cooling times were measured for the vibrating and non-vibrating trials to determine the factor of actuation frequency increase, which ranged from 1.55 to 2.10. A model of cooling time was developed and compared with the experimental results, with percent errors ranging from 5.3% to 32.8%. The approach was demonstrated in an application: a shape memory alloy–driven rotary ratcheting mechanism, with which factors of actuation frequency increase greater than 1.80 were measured due to vibration-enhanced cooling.

An active compression sleeve with variable pressure levels using a wire-fabric mechanism and a soft sensor

Compression garments are frequently used in daily life activities as well as in specialized fields, such as medical and sports sciences, to enhance bodily functions. However, conventional compression garments provide a fixed compression force to the body and can thus cause several side effects including discomfort, skin irritation, and loss of circulation when worn incorrectly. Development of a new type of compression garment that can control the compression force is required. This paper proposes a new sleeve-type compression garment that alters its compression force by employing a wire-fabric based mechanism. The proposed sleeve has several benefits compared with conventional methods. It not only is lightweight compared with those with pneumatic actuation but also can generate variable compression force by bidirectional driving of the tendons, which is not possible with other wire driving mechanism, such as shape memory alloy actuation. The proposed garment was manufactured by integrating two-layered fabrics with a soft pressure sensor, a wire actuation system, and a feedback controller. The performance was evaluated using three different experiments that tested the ability of varying and maintaining the compression force. This design can be employed in the field of compression garments and assistive devices to provide a means of applying an accurate and customized compression force to the body.

Influence of thermal insulation and wind velocity on the SMA actuator for morphing applications

This paper presents the modeling and simulation of shape memory alloy (SMA) wire actuators for morphing micro air vehicles (MAVs) when exposed to high-velocity wind during flight. The specific operating conditions include thermal insulation, varying convective heat-transfer coefficients due to wind velocity, aerodynamic loads, and operation from MAV battery. Application-oriented modeling parameters were determined from a flyable morphing MAV. The simulation could dynamically generate the morphing angle as a function of the electrical input pulse duty cycle. The model showed that compared with 10 % duty cycle, a 25 % duty cycle achieves an energy saving of 33 % and an increase in actuation speed of 3.7 times. Further, increasing the duty cycle has a negligible improvement in energy saving, but the actuation rate is increased by 15.8 times. The SIMULINK® model, which was validated through the ground test, would help in the design of SMA actuators and controllers for aerospace vehicles and automobiles.

Morphodynamic Tissues via Integrated Programmable Shape Memory Actuators

AbstractManipulating the shape of preformed living tissues can present a novel fabrication route toward complex biological architectures. However, external manipulation of tissues can be challenging to implement robustly at multiple length scales and with high degrees of freedom, particularly in soft fibrous tissue constructs. Here, a versatile platform is developed to drive soft tissue morphodynamics using embeddable shape memory actuators that generate multiscale, repetitive, and highly customized tissue deformation on demand. To achieve this, a thermally isolating coating technique is designed and developed for programmable shape memory wires, which protects surrounding biological materials from cytotoxic heating effects during wire actuation. The coated tissue actuators (CTAs) can then be embedded in engineered tissues and activated to produce both large‐ and small‐scale tissue deformations in a highly customized and reproducible manner. Using this strategy, tissues can be forced to adopt specified shapes, with precise control over cell elongation and orientation within an encapsulating matrix. Furthermore, the system can produce predictable, highly localized, and customizable strains within fibrous matrices, capable of elongating cells and biasing their orientation within degrees of a desired direction. This strategy may hence have broad applicability in both applied tissue biofabrication and for fundamental studies of cell–matrix interactions.

Design and testing of a microgripper with SMA actuator for manipulation of micro components

The extremely high work-to-volume ratios of the SMA actuators make them suitable to be used as a powerful actuator in micro-scale manipulation. In this study, an easily manufacturable micro-gripper with shape memory alloy (SMA) wire actuator was designed and manufactured. The concept of the designed micro-gripper was based on flexible hinge structures to increase the deflection efficiency and strength. The size of microgripper was a significant criterion in our design. Also, innovative layout in locating of SMA wire caused the microgripper to gripe and manipulate a boarder range of objects. The finite element method was used to analyze and calculate the stress distribution and jaw’s deflection in the gripper. In order to verify the modeling results, an experimental analysis by building a set-up for micro-gripper and running tests were implemented and it showed a good agreement with the modeling results. The approximate size of the micro-gripper is about 12 × 10 mm and its maximum achievable deflection is 200 μm which is perceptibly higher than SMA actuated micro-grippers with the same size.