Shape Memory Alloy Coil Spring Research Articles

Highly Inductive Coil Spring Strain/Compress Sensors Integrated with Shape Memory Alloy and Shape Memory Polymers-CNTs.

Future wearable electronic gadgets offer greatpotential for using stretchable, strain-sensitive materials to instantly detect human motion and record physiological information. This paper presens a strain/compress sensor made from a Shape memory alloy (SMA) coil spring covered with silver pastes and the composite of carbon nanotubes and Shape memory polymer (SMP). The combination of the shape memory materials that expand or contract automatically by temperature improved the mechanics of the sensor. First, the proposed sensors showed an excellent ability to broad-range strain of 250% and compress of 50% with a relative inductance (∆L/L0 ) range from -35% to 50%, respectively. Durability during 1000 loading and unloading cycles at 200% strain is included. Secondly, by monitoring changes in resistance, inductance, and time, it is determined how many silver layers appropriate for transformation should be in order to improve the recovery time of the SMA coil spring. Moreover, the presence of CNTs in the composite-covered outer of sensors helps to reduce the influence of the relation between resistance and temperature in the range from 30 °C to 110 °C. Finally, a device is suggested for monitoring arm and triceps brachii muscle movements based on the stretchable area as a key parameter.

Thermomechanical Characterization and Modeling of NiTi Shape Memory Alloy Coil Spring.

Today, shape memory alloys (SMAs) have important applications in several fields of science and engineering. This work reports the thermomechanical behavior of NiTi SMA coil springs. The thermomechanical characterization is approached starting from mechanical loading-unloading tests under different electric current intensities, from 0 to 2.5 A. In addition, the material is studied using dynamic mechanical analysis (DMA), which is used to evaluate the complex elastic modulus E* = E' - iE″, obtaining a viscoelastic response under isochronal conditions. This work further evaluates the damping capacity of NiTi SMA using tan δ, showing a maximum around 70 °C. These results are interpreted under the framework of fractional calculus, using the Fractional Zener Model (FZM). The fractional orders, between 0 and 1, reflect the atomic mobility of the NiTi SMA in the martensite (low-temperature) and austenite (high-temperature) phases. The present work compares the results obtained from using the FZM with a proposed phenomenological model, which requires few parameters for the description of the temperature-dependent storage modulus E'.

Soft Wearable Robot With Shape Memory Alloy (SMA)-Based Artificial Muscle for Assisting With Elbow Flexion and Forearm Supination/Pronation

This letter proposes a soft wearable robot with shape memory alloy (SMA)-based artificial muscle to assist with upper limb motion. The SMA-based artificial muscle was designed by embedding a bundle of SMA coil springs into a stretchable coolant vessel, which allows active cooling of the SMA bundles through coolant circulation. By attaching SMA-based artificial muscles to a soft wearable brace, a soft wearable robot was designed to assist elbow flexion and forearm supination/pronation. To support the activities of daily living (ADLs), the proposed robot can produce more than 3 Nm torque in the direction of elbow flexion. In addition, the proposed robot can increase the forearm supination/pronation ROM by an average of 15.7° for impaired users. Finally, to evaluate the effect of the assistance provided by the proposed system, experiments and system usability scale (SUS) assessments were conducted on a group of patients with stroke and spinal cord injuries (SCI). The results indicate that the robot improves not only the range of motion (ROM) but also the torque produced by the users. In addition, from the results of the user experiment, we found certain design issues that require further development for better performance of the robot.

Wrist Assisting Soft Wearable Robot With Stretchable Coolant Vessel Integrated SMA Muscle

This article proposes a shape memory alloy (SMA)-based artificial muscle that has an active cooling system. An SMA coil spring is embedded into a stretchable coolant vessel, which allows active cooling of SMA through coolant circulation. The coolant effect has been investigated by measuring actuation speed. Integrating a thermomechanical model and heat transfer model between coolant and SMA, actuation times have been estimated. Based on these results, actuation performances that use four different coolants have been found out, and the mineral oil cooling case shows both contraction and extension times of less than 1 s to contract to over 35% of its initial length with 1 kg load. A soft wearable robot for assisting wrist motion has been designed by integrating multiple SMA muscles with a glove, wristband, and elbow anchor. Thanks to the advantages of the SMA coil spring actuator, the proposed robot is compliant and weight-balanced structure. The robot shows ranges of motion of 38°, 50°, 34°, and 35°, for flexion, extension, radial deviation, and ulnar deviation, respectively. In addition, the robot shows improved cyclic performance compared to a natural air-cooling system. Finally, its torque assistance and theamount of time needed to wear it have been analyzed with user tests.

Thermomechanical performance analysis and experiment of electrothermal shape memory alloy helical spring actuator

In this paper, an electrothermal shape memory alloy helical spring actuator constructed from shape memory alloy with copper-cored enameled wire is presented and fabricated. Based on the shear constitutive model of a shape memory alloy, the Thermo equilibrium equation and the geometrical equation of helical spring establish the thermomechanical theoretical model of helical spring actuator with electrothermal shape memory alloys under different scenarios. The thermomechanical behaviors of the actuator were verified by numerical simulation with experimental tests, and the actuator thermomechanical properties were derived from the analysis with current, temperature, response time, restoring force, and axial displacement as parameters. The experimental results show that the actuator produces a maximum recovery force of 70.2 N and a maximum output displacement of 7.7 mm at 100°C. The actuator response time is 26 s at a current of 3A. It is also demonstrated that the theoretical model can effectively characterize the complex thermo-mechanical properties of the actuator due to the strong nonlinearity of the shape memory alloy. The experimental temperature-force response and temperature-displacement response, as well as the force-displacement response at different temperatures, provide references for the design and fabrication of electrothermal shape-memory alloy coil spring actuators.

Automatic Actuation of the Anti-Freezing System Using SMA Coil Springs

Studies have been actively conducted on systems that prevent the breakage of water pipes from freezing in winter. Shape memory alloy (SMA) coil springs have been used as the key components of actuators that can operate automatically by detecting the real-time outside temperature changes, but research on its use as an actuator that can operate at sub-zero temperatures is insufficient. This study proposes the anti-freezing system using Ni-44.08Ti-1.46Co (wt.%) SMA coil springs that operate near sub-zero temperatures to prevent the freezing accident of water pipes. After fabricating the SMA coil springs, the test for performance evaluation of the springs applied static load conditions was conducted on the specific outside temperature. To examine the operation of anti-freezing systems applied the SMA coil spring as an actuator, the water discharge test (WDT) was also conducted along with the computational fluid simulation. The results of water discharge measurement obtained by WDT, simulations, and theoretical equations applied to the fluid resupply system constructed were compared with each other to verify the reliability. Consequently, it was confirmed that water discharge can be automatically controlled in real time according to temperature changes of SMA coil springs in the anti-freezing system.

Experimental and numerical studies on a novel shape-memory alloy wire–woven trusses capable of undergoing large deformation

Currently, most wire-woven trusses are fabricated with traditional metals such as steel and aluminum, thus the deformation ability is constrained due to the low yield strain of common metals. Shape-memory alloy is a kind of smart material which can bear large recoverable strain while producing hysteresis. Due to the unique capacity of large deformation and remarkable damping property of the shape-memory alloy, a novel lattice trusses assembled by superelastic shape-memory alloy coil springs was proposed. Furthermore, the treatment processes to prepare the shape-memory alloy coil springs and the assembly method to fabricate the shape-memory alloy wire–woven trusses were also introduced. The quasi-static compression under different maximum deformation and temperatures was performed to investigate the mechanical and thermal responses of the proposed shape-memory alloy wire–woven trusses. Cyclic compression tests were also performed to study the functional fatigue of the shape-memory alloy wire–woven trusses. The proposed wire-woven trusses can undergo up to 80% deformation by compression and recover without evident residual deformation after unloading. Finite element analysis simulation of representative volume element under different deformation was presented. Analytical modeling of the stiffness of shape-memory alloy wire–woven trusses was also carried out. Both the numerical and analytical methods can predict the stiffness within a small deviation.

Design of Shape Memory Alloy Coil Spring Actuator for Improving Performance in Cyclic Actuation

Performance of the shape memory alloy (SMA) coil spring actuator in cyclic actuation as an artificial muscle is strongly related to the mechanical design of the coil geometry. This paper proposes a practical design method for improving the frequency and efficiency of the SMA coil spring actuator; by designing the SMA coil spring to have large index (coil diameter/wire diameter) and pitch angle (LIP), cooling characteristics can be improved (increasing the actuation frequency) and large deformation can be obtained. The LIP design process is based on the two-state static model that describes the displacement-force relationship of the SMA coil spring in two states—a fully austenite phase and a fully martensite phase. The design process gives accurate design parameters of the SMA coil spring actuator that satisfy the required stroke and force. The model of the fully martensite phase of the SMA coil that includes the stress-induced detwinning enables the use of maximum shear strain of the SMA. The design method reduces the mass of an SMA without changing the stroke and increase the power density and efficiency. The cyclic actuation experiments demonstrate that the LIP design doubles the maximum frequency of SMA coil actuator with one-sixth the mass of the non-LIP design.

Airfoil-based piezoelectric energy harvesting by exploiting the pseudoelastic hysteresis of shape memory alloy springs

The modeling and analysis of an electromechanically coupled typical aeroelastic section with shape memory alloy springs for wind energy harvesting is addressed in this paper. An airfoil with two-degrees-of-freedom, namely pitch and plunge, is considered and piezoelectric coupling is added to the plunge degree-of-freedom. A load resistance is assumed in the electrical domain of the problem in order to estimate the electrical power output. Shape memory alloy coil springs are modeled in the pitch degree-of-freedom of the typical section. A nickel–titanium alloy that exhibits pseudoelasticity at room temperature is assumed. The constitutive model for the shape memory alloy is based on classical phenomenological models. The unsteady aerodynamic loads are obtained by Jones’ approximation to Wagner’s indicial function. The resulting nonlinear electroaeroelastic model is cast into a state-space representation and solved with a Runge–Kutta method. The effects of preload values of the shape memory springs and resistive power generation on the aeroelastic behavior of the wind energy harvester are investigated at the flutter boundary and in a post-flutter regime. The nonlinear kinetics of the austenite-to-martensite phase transformation changes the typical linear flutter behavior to stable limit-cycle oscillations over a range of airflow speeds. Such nonlinear aeroelastic behavior introduced by the hysteretic behavior of the SMA springs provides an important source of persistent electrical power.

Helical Kirigami-Enabled Centimeter-Scale Worm Robot With Shape-Memory-Alloy Linear Actuators

The wormlike robots are capable of imitating amazing locomotion of slim creatures. This paper presents a novel centimeter-scale worm robot inspired by a kirigami parallel structure with helical motion. The motion characteristics of the kirigami structure are unravelled by analyzing the equivalent kinematic model in terms of screw theory. This reveals that the kirigami parallel structure with three degrees-of-freedom (DOF) motion is capable of implementing both peristalsis and inchworm-type motion. In light of the revealed motion characteristics, a segmented worm robot which is able to imitate contracting motion, bending motion of omega shape and twisting motion in nature is proposed by integrating kirigami parallel structures successively. Following the kinematic and static characteristics of the kirigami structure, actuation models are explored by employing the linear shape-memory-alloy (SMA) coil springs and the complete procedure for determining the geometrical parameters of the SMA coil springs. Actuation phases for the actuation model with two SMA springs are enumerated and with four SMA springs are calculated based on the Burnside's lemma. In this paper, a prototype of the worm robot with three segments is presented together with a paper-made body structure and integrated SMA coil springs. This centimeter-scale prototype of the worm robot is lightweight and can be used in confined environments for detection and inspection. The study presents an interesting approach of integrating SMA actuators in kirigami-enabled parallel structures for the development of compliant and miniaturized robots.

Sensorless displacement estimation of a shape memory alloy coil spring actuator using inductance

To measure the displacement of a shape memory alloy (SMA) coil spring actuator for feedback control, displacement sensors larger than the actuator are normally required. In this study, a novel method for estimating the displacement of an SMA coil spring actuator without a sensor is proposed. Instead of a sensor, coil inductance is used for estimating the displacement. Coil inductance is estimated by measuring the voltage and the transient response of the current. It has a one-to-one relationship with the displacement of the coil and is not affected by load. Previous methods for estimating displacement using resistance measurements are heavily affected by load variations. The experimental results herein show that displacement is estimated with reasonable accuracy under varying loads using coil inductance. This sensorless method of estimating the displacement of an SMA coil spring actuator can be used to build a compact feedback controller because there is no need for a bulky displacement sensor.

Engineering design framework for a shape memory alloy coil spring actuator using a static two-state model

A shape memory alloy (SMA) coil spring actuator is fabricated by annealing an SMA wire wound on a rod. Four design parameters are required for the winding: the wire diameter, the rod diameter, the pitch angle and the number of active coils. These parameters determine the force and stroke produced by the actuator. In this paper, we present an engineering design framework to select these parameters on the basis of the desired force and stoke. The behavior of the SMA coil spring actuator is described in detail to provide information about the inner workings of the actuator and to aid in selecting the design parameters. A new static two-state model, which represents a force–deflection relation of the actuator at the fully martensitic state (M100%) and fully austenitic state (A100%), is derived for use in the design. Two nonlinear effects are considered in the model: the nonlinear detwinning effect of the SMA and the nonlinear geometric effect of the coil spring for large deformations. The design process is organized into six steps and is presented with a flowchart and design equations. By following this systematic approach, an SMA coil spring actuator can be designed for various applications. Experimental results verified the static two-state model for the SMA coil spring actuator and a case study showed that an actuator designed using this framework met the design requirements. The proposed design framework was developed to assist application engineers such as robotics researchers in designing SMA coil spring actuators without the need for full thermomechanical models.

318 形状記憶合金コイルばねを用いた熱エンジンの開発(機械材料・材料加工III)

318 形状記憶合金コイルばねを用いた熱エンジンの開発(機械材料・材料加工III)

Proposal of Minimal Invasive Shape Memory Alloy Double-Transducer Unit for Blood Analysis or Drug Delivery

The purpose of this research is to develop minimally invasive medical devices by applying heated actuations of Shape Memory Alloy (SMA) transducers using a medical Ti-Ni alloy in order to enable minimal hypodermic invasive microvolume for either blood suction or drug delivery through the use of a nontoxic and minimal edged microneedle to be created in the author's laboratory. The author has focused on lymphocytes for immunotoxin and erythrocytes for the glucose level in blood. This paper reports the double-action mechanisms of the compact unit during its development and its actions by low DC inputs. Joule's heating of an SMA coil spring transducer might be useful for indenting blood vessels whose diameter is larger than the microneedle as a result of generating an indentation stroke of 2.0 mm and recovery force of 0.25 N 0.23 s following the start of moving when applied to DC 2.0 V and 0.5 A. An octagonal-pyramidal foil transducer for blood suction recovered its plane condition as before octagonal-pyramidal forming 8.3 s following the start of moving when applied to DC 1.5 V and 2.0 A.

Experimental Study and Modeling of a Differential SMA Spring Actuator

A theoretical model of the displacement-heating response of the differential shape memory alloy (SMA) actuator was developed. The model was constructed by using the constitutive equation and considering the force equilibrium and the energy balance on the SMA. The output displacement was predicted as a function of the heating power by the model and the simulations of the output displacement and temperature of the SMA actuator were also obtained. To evaluate the model, a prototype actuator which was made up of two SMA coil springs placed opposite each other was briefly described and an experimental setup of the SMA actuator was developed to study the relations among the heating power, the temperature and the output displacement of the SMA actuator. The similarity between the simulated and experimental results verified the proposed model, which indicated that the proposed model could express the thermo-mechanical behavior of the differential Ni-Ti SMA actuators.

K-0403 定温負荷・除荷サイクルにおけるTi-Ni形状記憶合金コイルの機能特性(S08-1 機能特性・変態)(S08 形状記憶合金の製造・加工技術と機能発現)

The deformation behavior of Ti-Ni shape memory alloy coil spring was investigated using loading-unloading cycling tests under fixed temperatures. And the effect of Ni content and shape memory treatment temperature on superelastic function was investi gated. The deformation behavior within elastic region of parent phase did not almost change during tensile cyclic loading. However, when the martensite phase was induced by stress, the deformation behavior changed largely. The critical shear stress for inducing martensites and the dissipated strain energy per unit volume decreased with increasing number of cyclic loading. The functional degradation depended on the Ni content and the shape memory treatment temperature, and increased with decreasing Ni content and increasing shape memory treatment temperature.

Environmental recognition devices

When a micromachine works inside a narrow space inside tubes and equipment such as a microfactory, a microdevice that has a visual function is indispensable. To monitor the minute shapes of microfabrication and microassembly process that are impossible to observe, fiberscope types of environmental recognition devices have been developed. The devices are designed to allow stereoscopic and microscopic observation and to measure the dimensions of microparts. To achieve these goals and to realize minute structures and functions, we developed a microstereoscope, a microscope with a fiber-optic tactile sensor, and shape memory alloy (SMA) actuators that can bend the tip in any direction with high precision. A microstereoscope that is 2 mm in outer diameter with the parallax mechanism using an optically driven balloon actuator can vary the binocular parallax. To obtain the microscopic image, a contact scope is used. The contact scope obtains the near field image and can observe structures that are even smaller than the outer diameter of the contact scope. The tip articulation mechanism can bend approximately 60° and returned to the straight position when a current is applied to each of the SMA coil springs. The results show that easy and safe environmental recognition is possible in the narrow spaces of a microfactory.

Fatigue Properties of Ti-Ni Shape Memory Alloy Springs

Fatigue properties of a Ti-Ni shape memory alloy coil spring are studied as a function of the amount of the B19’ martensite generating in thermal cycles The recovery force decays more with the number of cycles with an increasing amount of the martensite The temperature ranges of the R-phase and R→B19’ martensitic transformations also widen with the increasing martensite. The shape memory characteristic change of the coil spring results from the reduction in its free length. It is deduced from the change in the transformation temperatures that the free length reduction is caused by the introduction of dislocations during the thermal cycles.

Load-Elongation Characteristics of Ti-Ni Shape Memory Alloy Coil Spring.

The strain and stress behavior in a coil spring of a Ti-Ni SMA were investigated over a wide range of elongation, for the case of zero axial twist because of the simple calculation of shear and normal strain with the geometrical condition only. The basic σ-e and τ-γ relations of the SMA material were obtained from the results of a tensile test and torsional test carried out under several constant temperatures, using a φ1 wire specimen. The strain criteria for start and finish of transformation under the combined strain were expressed by a strain circle and a modified strain circle, respectively, in each temperature. The simulation for load-elongation behavior of the SMA coil spring based on the basic stress-strain curves and the strain criteria under the combined strain showed a good correlation with experimental results.