Shape Memory Alloy Spring Research Articles

Environmentally Responsive Intelligent Dynamic Water Collector.

Collecting water from fog flow is emerging as a promising solution to the water shortage problem. This work demonstrated a novel environmentally responsive water collector made from a self-prepared Janus polyvinyl alcohol sponge in combination with a two-way shape memory alloy spring, which transforms the traditional manner of static water collection into a dynamic one. The unidirectional water transport of the Janus structure together with the dynamic collection approach correspond to a 30.8% increase in the water-collection rate (WCR). The resultant WCR is up to 5.1 g/h, which ranks relatively high compared to similar studies. The light- and thermal-response capability, easy fabrication, and good cycling performance indicate that our devices could be utilized in a variety of applications. In this work, an efficient, intelligent adaptive, simple-preparation, precision-guided, and economical fog-collecting devices are recommended. Our work provides new insights on the design of high-efficient water collectors with practicability.

Force Control of a Shape Memory Alloy Spring Actuator Based on Internal Electric Resistance Feedback and Artificial Neural Networks

ABSTRACT This paper presents a study of the resistive behavior of a Shape Memory Alloy spring, with a focus on the application of electrical resistance feedback in control systems. Artificial Neural Networks of different topologies were designed to learn the relation between spring electrical resistance and the force exerted. The feedback between layers in Neural Networks is demonstrated to be a key parameter in learning the non-linear and hysteretic behavior of Shape Memory Alloys. Experiments with closed-loop systems showed that shape memory alloy springs generated forces that converged satisfactorily to the desired reference values. The scientific contribution of this work is the use of electrical resistance variation as feedback for controlling the spring force, eliminating the use of an external force sensor. Neural networks were used for both, the sensing process and the system control; in that way the nonlinear and hysterical behavior of the shape memory alloy actuator was well considered.

Manipulation of wave motion in smart nonlinear phononic crystals made of shape memory alloys

Thanks to the functional role of shape memory alloys (SMAs) in controlling the mechanical behavior of structures, researchers have started investigating the possibility of manipulating wave motion in phononic crystals using SMAs. While SMAs were used before to tune the wave propagation in linear phononic crystals, in this work, we aim to extend their utilization to nonlinear lattices. For this purpose, SMA helical springs are used to manipulate the dispersion curves and the location of stop-bands in weakly nonlinear monoatomic and diatomic lattice chains. Using Brinson’s formulation to describe the thermo-mechanical behavior of SMA wires and Lindstedt-Poincaré method to solve the derived governing equations, closed-form nonlinear dispersion relations in monoatomic and diatomic lattice chains are obtained and the effects of temperature-induced phase transformation and stiffness nonlinearity on the wave propagation are investigated. The results reveal that the dispersion curves of a weakly nonlinear monoatomic chain are formed at lower frequencies through the austenite-to-martensite phase transformation. Similarly, both the acoustic and optical branches of a diatomic lattice are moved to lower frequencies during the phase transformation in the cooling process. Therefore, the generated stop-bands in nonlinear diatomic lattices are also moved to lower frequencies. In addition, using auxiliary SMA ground springs, new classes of nonlinear monoatomic and diatomic chains exhibiting additional low-frequency attenuation zones are introduced. These low-frequency stop-bands are tunable and their frequency range can be modulated by exploiting the temperature-induced phase transformation in the SMA springs. The results obtained from analytic formulations are verified by numerical calculations and an excellent agreement is observed. Such tunability and the potential for adding stop-bands in low frequencies reveal that SMAs can be very helpful in designing nonlinear phononic and acoustic devices, such as vibration mitigators and wave filters with pre-defined attenuation zones.

Phase transformation-driven artificial muscle mimics the multifunctionality of avian wing muscle.

Skeletal muscle provides a compact solution for performing multiple tasks under diverse operational conditions, a capability lacking in many current engineered systems. Here, we evaluate if shape memory alloy (SMA) components can serve as artificial muscles with tunable mechanical performance. We experimentally impose cyclic stimuli, electric and mechanical, to an SMA wire and demonstrate that this material can mimic the response of the avian humerotriceps, a skeletal muscle that acts in the dynamic control of wing shapes. We next numerically evaluate the feasibility of using SMA springs as artificial leg muscles for a bipedal walking robot. Altering the phase offset between mechanical and electrical stimuli was sufficient for both synthetic and natural muscle to shift between actuation, braking and spring-like behaviour.

Modelling of SMA Vibration Systems in an AVA Example.

Vibration suppression, as well as its generation, is a common subject of scientific investigations. More and more often, but still rarely, shape memory alloys (SMAs) are used in vibrating systems, despite the fact that SMA springs have many advantages. This is due to the difficulty of the mathematical description and the considerable effortfulness of analysing and synthesising vibrating systems. The article shows the analysis of vibrating systems in which spring elements made of SMAs are used. The modelling and analysis method of vibrating systems is shown in the example of a vibrating system with a dynamic vibration absorber (DVA), which uses springs made of a shape memory alloy. The formulated mathematical model of a 2-DOF system with a controlled spring, mounted in DVA suspension, uses the viscoelastic model of the SMA spring. For the object, a control system was synthesised. Finally, model tests with and without a controller were carried out. The characteristics of the vibrations’ transmissibility functions for both systems were determined. It was shown that the developed DVA can tune to frequency excitation changes of up to ±10%.

Angular control of differential shape-memory alloy spring actuator for underactuated dynamic system

This article dwells on two technical aspects, the design and implementation of an upgraded version of the differential shape-memory alloy–based revolute actuator/rotary actuating mechanism for stabilization and position control of a two-degree-of-freedom centrally hinged ball on beam system. The actuator is configured with differential and inclined placement of shape-memory alloy springs to provide bidirectional angular shift. The shape-memory alloy spring actuator occupies a smaller space and provides more extensive reformation with justifiable actuation force than an equally able shape-memory alloy wire. The cross or diagonal architecture of shape-memory alloy springs provides force amplification and reduces the actuator’s control effort. The shape-memory alloy spring–embodied actuator’s function is exemplified by the highly dynamic underactuated custom-designed ball balancing system. The ball position control is experimentally demonstrated by cascade control using the control laws that have been unattempted for shape-memory alloy actuated systems; the ball is positioned with linear (integer-order and fractional-order) proportional–integral–derivative controllers optimized with genetic algorithm and particle swarm optimization at the outer/primary loop. Angular control of the shape-memory alloy actuated beam is obtained with nonlinear (integer-order and fractional-order sliding mode control) control algorithms in the inner/secondary loop.

Design and experiment of a SMA-based continuous-stiffness-adjustment torsional elastic component for variable stiffness actuators

The variable stiffness actuator (VSA) is widely applied in robotics and human-robot interactions, generating controllable torque with sufficient compliance to ensure safety and robustness. At present, typical VSA design usually adopted pure mechanical structures that integrated an additional motor for stiffness adjustment, making it hard to meet the demand of lightweight joint actuation due to large actuator size and weight. As a new functional material, shape memory alloy (SMA) shows the prospect of lightweight actuation due to its high power-to-weight ratio. In this paper, a compact SMA-based torsional elastic component (SMA-TE) for the VSA is proposed. The SMA-TE with torsional stiffness is implemented by the confrontational arrangement of paired spiral SMA springs. The ceramic heating plate and semiconductor refrigeration plate are installed in the elastic component shell, and the thermally conductive medium is filled between the internal gap. The torsional stiffness of the SMA-TE can be continuously adjusted via a feed-forward cascade controller. Repeated experimental results show that the SMA-TE can precisely maintain constant stiffness and continuously adjust its stiffness between 2.6 Nm rad−1 and 6.8 Nm rad−1 when performing precise square wave stiffness tracking under variable frequencies.

Development of XY Micro-Position Stage Based on a Shape Memory Alloy

This paper reports a novel monolithic two DoF micro-positioning stage using shape-memory-alloy (SMA) actuator. The design was fabricated in a one fabrication step and it comprises all actuation functions in a single piece of SMA. The square shaped actuator has dimensions of 10 mm × 10 mm × 0.25 mm. The device includes a moving stage in the center which is connected to four SMA springs to generate large displacement in two directions, x- and y- axes. The four SMA actuators underwent annealing process using internal joule heating by flowing electrical current through the springs. Each of SMA springs has been actuated individually by internal joule heating generated using an electrical current. The developed design has been simulated to verify thermal response and heat distribution. In addition, the micro-positioning stage was experimentally tested. The maximum displacement results of the stage are 1.1 mm and 1.1 mm along the directions of x- and y- axes, respectively. The developed micro-positioning stage has been successfully demonstrated to control the position of a small object for microscopic imaging applications.

Modified PID like fuzzy servo control applied to smart actuator based miniature Parallel Robot

Miniature flexible parallel robots, popularly used for micro positioning application demands the use of non conventional actuators. Shape memory alloys (SMA) are popular smart actuators because of its light weight, integration compatibility, ease of actuation and high power density. Inclusion of shape memory alloy actuators to the parallel robot brings in control challenges due to its nonlinearity, coupling effects and cocontraction of antagonistic pair of actuators in the mechanism in order to achieve bi directional motion. In this paper, a PID like fuzzy controller is designed and applied to a nonlinear SMA spring actuator connected to a symmetric 2 DOF miniature parallel robot. The fuzzy rules are designed from the general response plot and modified to be applied to a parallel mechanism which involves cocontraction of antagonistic actuators. The paper has also presented the control and electrical circuit design used in the experimental set up. The fuzzy control is implemented in the hardware controller with model based position feedback and tested for the trajectory tracking characteristics of the end effector with disturbances. Experimental results are presented with quantitative analysis to show the effectiveness of the proposed controller in handling nonlinearities and disturbances compared to the conventional PID control and nonlinear Sliding mode control (NSMC). The test results has demonstrated the superior nature of proposed control over other controllers in the trajectory tracking with disturbances and also linearizing the hysteresis of controlled system.

An Extended Three-Dimensional Finite Strain Constitutive Model for Shape Memory Alloys

AbstractA 3D finite-strain constitutive model for shape memory alloys (SMAs) is proposed. The model can efficiently describe reversible phase transformation from austenite to self-accommodated and/or oriented martensite, (re)orientation of martensite variants, minor loops, latent heat effects, and tension–compression asymmetry based on the Eulerian logarithmic strain and the corotational logarithmic objective rate. It further accounts for smooth thermomechanical response; temperature dependence of the critical force required for (re)orientation, temperature, and load dependence of the hysteresis width; and asymmetry between forward and reverse phase transformation, and it is flexible enough to address the deformation response in the concurrent presence of several phases, i.e., when austenite, self-accommodated, and oriented martensite co-exist in the microstructure. The ability of the proposed model to describe the aforementioned deformation response characteristics of SMAs under multiaxial, thermomechanical, and nonproportional loading relies on the set of three independent internal variables, i.e., the average volume fraction of martensite variants, their preferred direction, and the magnitude of the induced inelastic strain, which further allow for an implicit description of a fourth internal variable, the volume fraction of oriented as opposed to self-accommodated martensite. The calibration of the model and its numerical implementation in an efficient scheme are presented. The model is validated against experimental results associated with complex thermomechanical paths, including tension/compression/torsion experiments, and the efficiency of its numerical implementation is verified with simulations of the response of a biomedical superelastic SMA stent and an SMA spring actuator.

A Soft Haptic Glove Actuated with Shape Memory Alloy and Flexible Stretch Sensors.

Haptic technology allows us to experience tactile and force sensations without the need to expose ourselves to specific environments. It also allows a more immersive experience with virtual reality devices. This paper presents the development of a soft haptic glove for kinesthetic perception. It is lightweight and soft to allow for a more natural hand movement. This prototype actuates two fingers with two shape memory alloy (SMA) springs. Finite element (FE) simulations of the spring have been carried out to set the dimensions of the actuators. Flexible stretch sensors provide feedback to the system to calculate the tension of the cables attached to the fingers. The control can generate several recognizable levels of force for any hand position since the objects to be picked up can vary in weight and dimension. The glove can generate three levels of force (100, 200 and 300 g) to evaluate more easily the proper functioning. We realized tests on 15 volunteers simulating forces in various order after a quick training. We also asked volunteers about the experience for comfort, global experience and simplicity). Results were satisfactory in both aspects: the glove fulfilled its function, and the users were comfortable with it.

Mechatronics Design and Kinematic Analysis of SMA Spring Actuated Parallel Manipulator

Flexible parallel manipulators can be used as an orienting device because of their precise positioning ability and better stiffness. The flexibility to the manipulator induces challenges in the selection of actuator, sensors and control. The paper presents a novel mechatronics design of a flexible symmetric parallel manipulator with minimum number of actuators used as an orienting device. Shape memory alloy springs (SMA) are used as an actuator because of ease of integration and higher deflection. In order to avoid any contact type sensor which could affect the compliance of the manipulator, the position of SMA spring is calculated indirectly from the kinematic model with the end effector orientation data measured from IMU sensor. The complete experimental set up design including electrical and control circuitry is explained in detail in the work. Preliminary open loop test is conducted on the prototype to understand the SMA response to various current input and to verify the effectiveness of the kinematic model in the actuator length measurement. Closed loop control based on ON/OFF control is implemented in the controller and is tested for step input.

Simultaneous measurements for the interlink of electro-thermo-mechano-electro characteristics in shape memory springs

This experimental study aimed to obtain the actuation properties of Shape Memory Alloy (SMA) spring actuators available under the commercial names of Biometal® NiTiCu and KRL® NiTi NiTiCu, NiTiFe. An objective is to characterize the electro-thermo-mechano-electro behavior of shape memory spring through experimentation via simultaneous measurement techniques. These measurements are synchronized by embedding an impedance analyzer and data acquisition module through a unique program. Moreover, to obtain the mathematical model by parts of the SMA spring and equivalent circuit analysis of active spring through their electro-thermo-mechano-electro characteristics exhibited during shape memory effect. Based on the experimental results, the SMA spring’s equivalent circuit is considered a series resistance – inductance circuit. It was found from the experimental results that the Biometal® actuator produced more resistance, inductance variation and offered more displacement as compared to KRL® actuators.

Ocean Thermal Energy Harvester using shape memory alloy spring

ABSTRACT A prototype Ocean Thermal Energy Harvester (OTEH) is designed and constructed using Nitinol shape memory alloys (SMAs) spring as a driving element. Thermal to mechanical energy conversion is produced by the Nitinol SMA spring shape memory effect. Assumed seawater temperature (70 °C) difference between hot ocean surface water and depth bottom cold water (100 m) causes the martensitic phase transformation. And this temperature is achieved using a solar water heater incorporated into the system floating at the seawater surface. Engine behavior is modeled and simulated. A comparison between experimental and simulated data is carried out, and it gives a good fitting between them. The methodology used is by developing the new conceptual design and theory of the engine, then followed by construction and testing of the engine. The experiment conducted involved the measurement of the output torque as well as the performance of the engine. The maximum driving force, rotational speed, moment, output power, and efficiency are measured and calculated as 21.4 N, 13rpm, 2.18 Nm, 1.7 watt, and 3.5%, respectively. The efficiency of the engine is also observed to be decreasing as speed increases. The mechanical power generated by the engine will be further converted to electrical power through the coupling of a DC generator on the engine output shaft on pulley 2.

Performance prediction of biomimetic adaptive building skins: Integrating multifunctionality through a novel simulation framework

Biomimetic adaptive building skins (Bio-ABS), being adaptable to changing environmental conditions, can foster improved comfort and reduced energy demand. Bio-ABS are climate-adaptable façades, and biological functions inspire their design. Buildings often require multiple functions for improved environmental performance. Multifunctionality refers to hosting multiple triggered by diverse stimuli interdependently. The realisation of multifunctional Bio-ABS may be challenging due to difficult construction processes, expensive materials, and the complexity in their application. Thus, digital modelling and simulation of multifunctional Bio-ABS are important to predict their performance. This paper reviews the studies on simulating Bio-ABS, proposes a novel simulation framework for multifunctional Bio-ABS and demonstrates it through a parametric case study. Performance comparisons among twenty base-case scenarios and 600 iterations of shading and ventilating multifunctional Bio-ABS provides shading through photovoltachromic (PVC) glazing and ventilation through Shape Memory Alloy (SMA) springs triggered openings. It is multifunctional by changing its morphology and physiology due to photovoltachromic glazing triggered by solar irradiance and Shape Memory Alloys being triggered by temperature. The results show that Bio-ABS improves building performance when compared against non-adaptable façades, reaching 37.1% for 90% acceptability limits and 18% for 80% acceptability limits for adaptive thermal comfort in an educational building in the humid subtropical climate of Sydney. Australia. The main outcome and contribution of this study is a novel simulation framework to predict the performance of morphology and physiology changing multifunctional Bio-ABS. Future work may focus on prototyping and validated experiments to close the gap between theory and the real world.

Effect of biasing conditions on the performance of a SMA spring actuator under thermo-mechanical loading

This paper presents an extension of the existing phase kinetics model of shape memory alloy (SMA) wire on a SMA spring actuator. The phenomenological modeling of an SMA spring under two different bias conditions – SMA spring with (A) normal spring (B) SMA wire along with the computing algorithm is addressed. The results of Case A are found in close agreement with the published literature. Whereas, the results of Case B are reported for the first time and outperform the results of Case A in terms of equal deflection, more controllability, and degrees of freedom as compared with Case A.

Fine resolution smart force sensor based on lever arm mechanism using shape memory alloy spring

SummaryA novel force measurement technique using the variable resistance property of shape memory alloy (SMA) spring is presented. The unique abilities of SMA, a smart material make it a potential candidate to construct actuators and dampers and of late is added to the domain of sensing technology in the design of creative sensing systems. The sensing mechanism is realized using a lever arm made of less stiff acrylic material; one of the links of the lever arm is integrated with an SMA spring actuator that is connected perpendicular to the stationary base, and the unknown load is placed at the other link; the force due to the measurand and the transmitted force act on the arms of the lever. The displacement due to the application of force on one of the flexible arms causes a variation in the strain that leads to resistance variation of the Joule‐heated SMA spring attached at the other arm. The active sensor possesses static and dynamic sensing capabilities and can detect force in the range of a few millinewtons, and the sensor design is validated from the experimental measurements and analytical results. The performance of the sensor is evaluated from its static and dynamic characteristics and depicts promising results. The design methodology of the sensor mechanism and selection of material suitable to offer flexible transformation of force leads to the development of a force sensor with fine resolution.

Studies on the damping mechanism of shape memory alloy-spring tuned vibration absorber attached to a multi-degree-of-freedom structure

To mitigate the adverse structural responses, an improved version of the traditional tuned vibration absorber has been proposed based on the shape memory alloy spring, referred as the shape memory alloy-spring tuned vibration absorber. The finite element numerical models of the multi-degree-of-freedom structure (e.g., transmission tower) and shape memory alloy-spring tuned vibration absorber are developed by using the commercial software ANSYS, and the nonlinear behavior of the shape memory alloy spring is validated based on a previous experimental study. The damping mechanism of the shape memory alloy-spring tuned vibration absorber attached to a multi-degree-of-freedom structure under seismic excitations is investigated, and the nonlinear hysteretic behavior of the shape memory alloy spring is also discussed. The results show that the proposed damper has a two-stage damping mechanism, and its control performance is remarkable. Because the coupled system response is sensitive to the amplitude level, the optimal configuration of the shape memory alloy-spring tuned vibration absorber can be obtained by parametric analysis. Particularly, because of the nonlinear target energy transfer and transient resonance capture mechanism, the shape memory alloy-spring tuned vibration absorber exhibits stable control ability under different seismic waves, indicating a good stability in vibration control of a multi-degree-of-freedom system.

Shaking table test of a frame structure retrofitted by externally-hung rocking wall with SMA and disc spring self-centering devices

An innovative externally-hung rocking wall (ERW) with shape memory alloy (SMA) and disc spring self-centering devices for retrofitting existing structures was proposed in this paper. By arranging steel corbels on the columns of an existing structure, the rocking walls were connected to the corbel using H-shaped connectors. Two types of self-centering devices, using disc spring and SMA separately, were installed between rocking wall and foundation to prevent collision damage, and can provide self-centering capability for the structure. The seismic performance characteristic of the ERW structure was studied via a shaking table test. For comparison, an unretrofit control (UC) structure was also tested. The UC structure was severely damaged and nearly collapsed after PGA = 1.2 g test cases: some steel bars at the bottom of the beam were fractured, and concrete at the beam end and column foot were crushed. For the ERW structure, the damage was significantly reduced after PGA = 1.5 g test cases: there were some cracks appeared in the structure, and concrete at the column foot were slightly crushed. However, no obvious damage was observed in the self-centering devices. The maximum story drift and residual deformation of the ERW structure are reduced 86.7% and 91.2%, respectively, relative to the UC structure.

DYANMIC ANALYSIS OF SHAPE MEMORY ALLOY OSCILLATORS IN ACTIVE SUSPENSION SYSTEM

Smart materials have a growing technological importance due to their unique thermomechanical characteristics. Shape memory alloys belong to this class of materials being easy to manufacture, relatively lightweight, and able to produce high forces or displacements with low power consumption. These aspects could be exploited in different applications including vibration control. A dynamic vibration absorber (DVA) can be used as an effective vibration control device. It is essentially a secondary mass, attached to an original system via a spring and damper. The natural frequency of the DVA is tuned such that it coincides with the frequency of unwanted vibration in the original system. This work aims to develop a dynamic vibration absorber with the help of shape memory alloy (SMA) springs in order to attenuate the vibration for a range of excitation frequencies. The experimental apparatus consisted of low-friction cars free to move in a rail. A shaker that provides harmonic forcing excites the system. Special attention is dedicated to the analysis of vibration reduction that can be achieved by considering different approaches exploiting temperature variations promoted either by electric current changes or by vibration absorber techniques. The results established that adaptability due to temperature variations is defined by modulus of stiffness