Shape Memory Alloy Spring Research Articles

A novel model-based approach for resistance estimation using rise time and sensorless position control of sub-millimetre shape memory alloy helical spring actuator

Shape memory alloy shows considerable strain during heating and cooling. This effect is due to its phase transformation with temperature. Due to this property, shape memory alloys can be deployed for physical actuation in place of conventional actuators in bio-medical and bio-mimicking robots. Sub-millimetre diameter shape memory alloy wires wound as helical springs are also used for this purpose. Due to their small size, it is difficult to use sensors for temperature or displacement measurements of shape memory alloy springs. This article attempts to demonstrate that the rise time of the current through a sub-millimetre diameter shape memory alloy helical spring is directly proportional to its displacement. To characterize the rise time–displacement hysteresis, a constant current drive with overcurrent protection is developed. The data generated are utilized to implement an open-loop sensorless control. A method to estimate the resistance from the rise time is proposed with which the temperature of the shape memory alloy during actuation can be obtained. The design avoids using an analogue-to-digital converter for the direct measurement of voltage and current for measuring the resistance variation in the shape memory alloy under actuation. This helps in the development of a new sensorless control using only the digital Input/Output pins of a microcontroller/microprocessor.

Midface Distraction Osteogenesis Using a Modified External Device With Elastic Distraction for Crouzon Syndrome.

Midface distraction osteogenesis has been popularized for the correction of midface hypoplasia associated with exophthalmos and obstructive sleep apnea in patients with Crouzon syndrome. The purpose of this study was to present the method of utilizing the modified external device with elastic distraction for the midface advancement in Crouzon syndrome, and the clinical outcomes and skeletal changes were analyzed. Five consecutive patients with Crouzon syndrome underwent Le Fort III osteotomy with midface advancement using a modified external device with elastic distraction. The distraction system consists of a rigid external distractor, nickel-titanium shape memory alloy spring, and bone-borne traction hooks. The midface advancement was initiated with the bony anchorage around the nasomaxillary buttress at the level between occlusal plane and infraorbital margin. The device was activated at a rate of 1 to 1.5 mm per day by the length of spring. The skeletal changes were analyzed by cephalometric and computed tomographic measurement. All the patients achieved improvements in midface appearance, obstructive sleep apnea, exophthalmos, and occlusion. No complications occurred during this procedure. After the distraction, 1 patient developed an open bite that was corrected by a definitive orthognathic surgery. Cephalometric and computed tomographic measurement analysis showed a differential advancement of midface with more at the occlusal level than the orbital level. In addition, midface suture and bone remodeling was also observed in growing patient. Our modified external device with elastic distraction offers an alternative method to achieve midface advancement in patients with Crouzon syndrome.

A hybrid dynamic model of shape memory alloy spring actuators

This paper presents the development of a hybrid model that describes the temperature, elongation and inner force relationships in a spring Shape Memory Alloy (SMA) actuator. The temperature-inner force relationship obeys a hybrid structure in which a sigmoid function correlates the variation of temperature for the SMA and the force executed by the spring actuator. The hybrid nature of the model describes the regular hysteresis behavior of the SMA. The switching law of the hybrid model depends on the time derivative of the temperature. A multivariable model depending on temperature, and inner and external forces was developed in order to characterize the Shape Memory Effect (SME). A set of experiments was carried out to obtain the parameters used to characterize the model. The application of the Levenberg-Marquardt method resulted in the parametric estimation procedure. An averaged correlation factor of 0.95 between the model response and experimental results justifies the proposed modeling approach.

Aeroelastic behavior of a typical section with shape memory alloy springs: Modeling nonhomogeneous distribution of state variables

In this paper, a two-degree-of-freedom (namely, plunge and pitch) aeroelastic typical section with shape memory alloy helical springs in the pitch degree-of-freedom is modeled. A linear aerodynamic model is employed to predict the unsteady loads. The shape memory springs model is based on classical models modified by the von Mises pure shear assumption. Nonhomogeneous distributions of shear strain, shear stress and martensitic fraction in the wire cross-section are represented by axi-symmetric annular regions. The numerical predictions of the effects of pseudoelastic hysteresis of shape memory alloy springs on the aeroelastic behavior of the typical section when both the homogeneous and nonhomogeneous cross-sectional distributions are considered in the simulations are compared with experimental data obtained in wind tunnel tests. The nonhomogeneous assumption results in good agreement between numerical predictions and experiments. Both the numerical and experimental results show that the pseudoelastic hysteresis of SMAs can be employed as a passive alternative to modify the behavior of aeroelastic systems.

Experimental study on the aeroelastic behavior of a typical airfoil section with superelastic shape memory alloy springs

An experimental study on the aeroelastic behavior of a 2-degree-of-freedom typical airfoil section with superelastic shape memory alloy springs is reported. Shape memory alloy helical springs are included in the pitch degree-of-freedom of the typical section so that the effects of pseudoelastic hysteresis on the aeroelastic behavior of the system can be investigated. The experimental identification of the aeroelastic parameters is described. Wind tunnel tests are conducted for different shape memory alloy springs’ preload levels, airflow speeds, and initial conditions. It is shown that the linear unstable post-flutter behavior is transformed into stable limit cycle oscillations of acceptable amplitudes over a range of airflow speeds due to pseudoelastic hysteresis. Therefore, shape memory alloy springs can be effectively exploited to passively enhance the aeroelastic behavior of a typical section.

Toward the Development of a Flexible Mesoscale MRI-compatible Neurosurgical Continuum Robot.

Brain tumor, be it primary or metastatic, is usually life threatening for a person of any age. Primary surgical resection which is one of the most effective ways of treating brain tumors can have tremendously increased success rate if the appropriate imaging modality is used for complete tumor resection. Magnetic resonance imaging (MRI) is the imaging modality of choice for brain tumor imaging because of its excellent soft-tissue contrast. MRI combined with continuum soft robotics has immense potential to be the next major technological breakthrough in the field of brain cancer diagnosis and therapy. In this work, we present the design, kinematic, and force analysis of a flexible spring-based minimally invasive neurosurgical intracranial robot (MINIR-II). It is comprised of an inter-connected inner spring and an outer spring and is connected to actively cooled shape memory alloy spring actuators via tendon driven mechanism. Our robot has three serially connected 2-DoF segments which can be independently controlled due to the central tendon routing configuration. The kinematic and force analysis of the robot and the independent segment control were verified by experiments. Robot motion under forced cooling of SMA springs was evaluated as well as the MRI compatibility of the robot and its motion capability in brainlike gelatin environment.

Aeroelastic flutter enhancement by exploiting the combined use of shape memory alloys and nonlinear piezoelectric circuits

In this paper, the combined effects of semi-passive control using shunted piezoelectric material and passive pseudoelastic hysteresis of shape memory springs on the aerolastic behavior of a typical section is investigated. An aeroelastic model that accounts for the presence of both smart materials employed as mechanical energy dissipation devices is presented. The Brinson model is used to simulate the shape memory material. New expressions for the modeling of the synchronized switch damping on inductor technique (developed for enhanced piezoelectric damping) are presented, resulting in better agreement with experimental data. The individual effects of each nonlinear mechanism on the aeroelastic behavior of the typical section are first verified. Later, the combined effects of semi-passive piezoelectric control and passive shape memory alloy springs on the post-critical behavior of the system are discussed in details. The range of post-flutter airflow speeds with stable limit cycle oscillations is significantly increased due to the combined effects of both sources of energy dissipation, providing an effective and autonomous way to modify the behavior of aeroelastic systems using smart materials.

Design and analysis of a microfluidic colour-changing glasses controlled by shape memory alloy (SMA) actuators

In this work, a microfluidic colour-changing glasses controlled by shape memory alloy (SMA) actuators is designed and presented by circulating colour liquids in the microfluidic channels on the lens. For liquids controlling, a unidirectional NiTi SMA spring is employed to design and fabricate a simple microfluidic actuator, which can provide the maximum restoring force of 5.27 N and the fastest recovering rate of 2.71 mm/s. After the responding characteristics of the SMA controller are tested and calculated under different conditions, the pressure changes at the channel inlet are investigated in liquids circulation process for different channel designs. This liquid colour-changing glasses show fast response, rapid prototyping and high controllability compared with the traditional solid colour-changing way. Meantime, the impacts of different channel designs on response performances are validated, which can provide foundations for further optimization of the channel designs. Soft lithography technology is applied for the fabrication of the colour-changing layer made of transparent silicone PDMS (polydimethylsiloxane) instead of conventional mechanical machining. Organosilicon coating based on methyltrimethoxysilane and phenyltrimethoxysilane (PTMS) is firstly fabricated for modification of PDMS surface to increase the wear resistance of the colour-changing lens.

Pattern Reconfigurable Antenna Based on Morphing Bistable Composite Laminates

In this paper, a novel pattern reconfigurable antenna based on morphing bistable composite laminates is presented. The bistable asymmetric glass-fiber reinforced polymer (GFRP) composite laminates have two stable configurations with curvatures of opposite signs. The antenna pattern is reconfigured by transforming the configuration of the bistable GFRP laminate which acts as the substrate of the antenna. The coplanar waveguide transmission lines feeding technique is used for the microstrip quasi-Yagi antenna. A prototype of the proposed antenna is fabricated using a semi-automatic screen printer and an autoclave. The transformation between the two stable states of the proposed antenna using Ni/Ti shape memory alloy springs is investigated experimentally. The out-of-plane displacements, reflection coefficients and radiation patterns for the two stable configurations of the antenna are measured, which agree well with the simulated results. The main beam direction is 89° and 59° for the two stable configurations, respectively. In addition, the influences of various bending radii on the radiation patterns are investigated to gain a thorough understanding of the reconfigurable mechanism of the proposed antenna. Finally, a two-element array of such an antenna is presented and measured. The proposed antenna provides a potential application in multifunctional, conformal, morphing, and integrated structures.

Thermally modulated shape memory alloy friction pendulum (tmSMA-FP) for substantial near-fault earthquake structure protection

Vibration control of structures under near-fault earthquakes by employing a friction pendulum supplemented with thermally modulated shape memory alloy (SMA) springs as damper system is studied. Temperature modulation of the SMA spring during the earthquake effectively alters its hysteretic energy dissipation capacity and thereby the control efficiency of the isolation system. The response of a structure with the isolation system is evaluated through nonlinear dynamic time-history analysis under a set of recorded near-fault ground motions. Through temperature modulation that effectively yields a large SMA hysteretic energy dissipation, the hybrid friction pendulum system with SMA temperature modulation shows enormous control efficiency. A parametric study reveals that under a wide range of conditions, the thermally modulated SMA friction pendulum isolation system shows improved control efficiency over conventional friction pendulum and SMA friction pendulum isolation systems. Further, the temperature-tuned SMA hysteresis loops substantially suppress the high frequency components of earthquake motions, thus reducing the possibility of damage to the structure.

New Actuation Mechanism for Actively Cooled SMA Springs in a Neurosurgical Robot.

The paper presents the use of shape memory alloy (SMA) spring actuators with real-time cooling to control the motion of the MINIR-II robot. A new actuation mechanism involving the passage of water as the cooling medium and air as the medium to drive out the water has been developed to facilitate real-time control of the springs. Control parameters, such as current, water flow rates, SMA pre-displacement, and gauge pressure of the compressed air, are identified from the SMA thermal model and from the actuation mechanism. In depth modeling and characterization have been performed regarding these parameters to optimize the robot motion speed. Forced water cooling has also been compared with forced air cooling and proved to be the superior method to achieve higher robot speed. An improved robot design and an MRI-compatible experimental platform have been developed for the implementation of the actuation mechanism.

An Overview of Shape Memory Alloy-Coupled Actuators and Robots.

The one-dimensional deformation of shape memory alloy (SMA) wires and springs can be implemented into different types of functional structures with three-dimensional deformations. These structures can be classified based on the type of structure and how the SMA element has been implemented into the following categories: rigid mechanical joints, semi-rigid flexural hinges, SMA elements externally attached to a soft structure, and embedded into the soft structure. These structures have a wide range of properties and implementation requirements, and they have been used to produce a variety of robots with rigid and soft motions. The different research efforts to develop actuators and robots related to each type of structure are presented along with their respective strengths and weaknesses. A model is then developed to discuss the performance and applicability of SMA wires versus SMA springs for actuators with a polymeric matrix to see the effect of each type of SMA on the selection of design parameters. A comparison of the different types of structures and the applicability of different types of SMA elements for different types of structures is then presented.

Modeling and Motion Control of a Soft Robot

A soft robot with locomotive abilities controlled by body deformations is modeled, analyzed, and then constructed in this study. The robot is composed of a thin steel shell, four sensors, and four shape memory alloy (SMA) springs. Due to the force exerted by the SMAs, the thin steel shell deforms and causes the robot to roll and move forward continuously. The study is conducted in four tiers. Initially, after producing a model of the soft robot, the constraint conditions of rolling actions from deformations are analyzed. Then, the relationship between the deformation and the heating time of SMAs is studied. A dynamic analysis on the rolling motion is presented based on the deformation of SMAs and the change in the robot's center of gravity. A dynamic simulation is also conducted to test the feasibility of the theory. The third tier consists of designing a closed-loop controller based on feedback data from the four deformable sensors, a feature that has never been applied to soft robots in previous studies. Finally, a prototype of the soft robot is built, and an experiment is conducted and compared to prove the validity of the theory.

Modeling and characterization of shape memory alloy springs with water cooling strategy in a neurosurgical robot.

Since shape memory alloy (SMA) has high power density and is magnetic resonance imaging (MRI) compatible, it has been chosen as the actuator for the meso-scale minimally invasive neurosurgical intracranial robot (MINIR-II) that is envisioned to be operated under continuous MRI guidance. We have devised a water cooling strategy to improve its actuation frequency by threading a silicone tube through the spring coils to form a compact cooling module-integrated actuator. To create active bi-directional motion in each robot joint, we configured the SMA springs in an antagonistic way. We modeled the antagonistic SMA spring behavior and provided the detailed steps to simulate its motion for a complete cycle. We investigated heat transfer during the resistive heating and water cooling processes. Characterization experiments were performed to determine the parameters used in both models, which were then verified by comparing the experimental and simulated data. The actuation frequency of the antagonistic SMAs was evaluated for several motion amplitudes and we could achieve a maximum actuation frequency of 0.143 Hz for a sinusoidal trajectory with 2 mm amplitude. Lastly, we developed a robotic system to implement the actuators on the MINIR-II to move its end segment back and forth for approximately ±25°.

SMA-Based System for Environmental Sensors Released from an Unmanned Aerial Vehicle

In the work at hand, a shape memory alloy (SMA)-based system is presented. The system, conceived for releasing environmental sensors from ground or small unmanned aerial vehicles, UAV (often named UAS, unmanned aerial system), is made of a door, integrated into the bottom of the fuselage, a device distributor, operated by a couple of antagonistic SMA springs, and a kinematic chain, to synchronize the deployment operation with the system movement. On the basis of the specifications (weight, available space, energy supply, sensors size, etc.), the system design was addressed. After having identified the main system characteristics, a representative mock-up was manufactured, featuring the bottom part of the reference fuselage. Functionality tests were performed to prove the system capability to release the sensors; a detailed characterization was finally carried out, mainly finalized at correlating the kinematic chain displacement with the SMA spring temperature and the supplied electrical power. A comparison between theoretical predictions and experimental outcomes showed good agreement.

Experimental Design Validation of Tilting Calibration Mechanism by Using Shape Memory Alloy Spring Actuator

A tilting calibration mechanism is periodically deployed to view the reference temperature target during on-board calibration of a spaceborne imaging sensor and stowed after calibration. In the present work, we have proposed a new design strategy using a shape memory alloy (SMA) spring as an actuator that provides a fail-safe function to prevent the blocking of the main optical path when the mechanical driving part of the mechanism is stopped at a certain position during on-board calibration. Although a launch locking device was not considered in the design, this approach makes it possible to impose mechanical constraints on the driving part of the mechanism in severe launch vibration environments. The effectiveness of the proposed design was experimentally validated by a deploying and stowing function test and launch vibration environment tests such as a sine burst test, a random vibration test, and a pyroshock simulating impulse shock test. The test results demonstrated that the mechanism fulfills all the required functions for on-board calibration. The use of an SMA spring actuator was proved effective for implementing the dual function of a fail-safe in an emergency phase and a mechanical constraint on the driving part of the mechanism in severe launch vibration environment.

Comparative analysis of electrical and hot water actuation of shape memory alloy spring using thermo-mechanical cycle test bench

<p>The optimal design and analysis of hot water actuated shape memory alloy spring is presented. Smart materials exhibit special properties that make them a preferred choice for industrial applications in many branches of engineering. The serviceable properties of a Ni-Ti piece can be improved by altering the energy source. With hot water actuation, as the temperature reaches 70 °C - 90 °C, spring gets fully compressed for the first few cycles followed by loss in actuation. The actuation loss is then studied with different characterisation methods such as thermo gravimetric analysis (TGA) and scanning electron microscopy (SEM). With SEM results, it can be strongly recommended that the energy source is sufficient for actuation (not affecting too much the structure). Results observed from TGA shows high oxygen content at lower temperature, suggest the need of conducting experiments in inert atmosphere. For the validation of hot water actuation, comparative analysis between electrical and hot water actuation is done. Graph shows that, there is a good agreement between both the methods. In addition to this, the application of hot water actuation is some micro-devices like micro-valve, drug delivery, directional control valve, also in engine in place of thermostat valve etc.</p>

Analysis of Mechanical Properties of Shape Memory Alloy

In this study, a particular mechanism is designed to obtain the mechanical properties of shape memory alloys (SMA). Mechanical behavior occurring due to the super elastic properties is investigated by applying current to shape memory alloys via designed mechanism. Displacement, velocity, time, force physical effects of SMA springs is obtained for different current values, and active operating range of springs is determined. This acquired data are of importance in determining the area of use of shape-memory alloys. This paper presents the structure of the designed mechanism and data of mechanical properties of shape memory alloys which are obtained by using this designed mechanism.

Influence of a hysteretic damper on the flutter instability

The influence of a hysteretic damper on the airfoil flutter instability is investigated. In particular, its effect on the post-critical limit cycle oscillations (LCOs) is emphasized. For that purpose, an aeroelastic model including large amplitude motions and dynamic stall phenomenon, is considered for a rigid flat plate having two degrees of freedom in pitch and plunge motions. The hysteretic behaviour is modeled thanks to a generalized Bouc-Wen formulation. A parametric study of aeroelastic as well as hysteresis model parameters, allows one to draw a complete picture of the bifurcation scenario, highlighting the capacity of the hysteretic damper in precluding the occurrence of stall. The special case of shape memory alloy (SMA) springs is then used numerically and experimentally for controlling the flutter oscillations of a flat plate. The study reveals the ability of the SMA springs to drastically reduce the amplitudes of the LCOs caused by the flutter instability.

Experimental and numerical study on hysteretic performance of SMA spring-friction bearings

This paper presents an experimental and numerical study to investigate the hysteretic performance of a new type of isolator consisting of shape memory alloy springs and friction bearing called an SMA spring-friction bearing (SFB). The SFB is a sliding-type isolator with SMA devices used for the seismic protection of engineering structures. The principle of operation of the isolation bearing is introduced. In order to explore the possibility of applying SMA elements in passive seismic control devices, large diameter superelastic tension/compression NiTi SMA helical springs used in the SFB isolator were developed. Mechanical experiments of the SMA helical spring were carried out to understand its superelastic characteristics. After that, a series of quasi-static tests on a single SFB isolator prototype were conducted to measure its force-displacement relationships for different loading conditions and study the corresponding variation law of its mechanical performance. The experimental results demonstrate that the SFB exhibits full hysteretic curves, excellent energy dissipation capacity, and moderate recentering ability. Finally, a theoretical model capable of emulating the hysteretic behavior of the SMA-based isolator was then established and implemented in MATLAB software. The comparison of the numerical results with the experimental results shows the efficacy of the proposed model for simulating the response of the SFB.