Airfoil morphing based on SMA actuation technology

We have developed a discretely actuated steerable probe for percutaneous procedures. We propose use of shape memory alloy (SMA) actuators in our design due to their small size and high power density. SMAs are attractive actuators when large forces or displacements are required and limited spaces are available. SMA actuators are shape-setted to an arc shape and mounted on the outer surface of the probe to generate bending action upon thermal actuation. SMA can recover large deformation on thermal activation and recovery strain of SMA is related to its temperature. Hence, we propose controlling the temperature of the SMA actuators for position control of the probe by heating up the SMA wires at each joint. Pulse width modulation (PWM) based control scheme is used to be able to control all SMA wires simultaneously. PWM is implemented via use of a switching circuit. Proposed controller is validated through an experiment to heat up the SMA wires to a desired temperature. Another experiment is carried out inside gelatin to mimic the motion of the probe inside soft tissue. PWM control was successfully implemented and we were able to demonstrate local actuation of the steerable probe.

The use of Shape Memory Alloy (SMA) materials for actuation represents a technological opportunity for the development of innovative applications. The issue of using the SMA actuators is an enticing solution that has attracted the interest of specialists in recent years, due to their numerous advantages (i.e. reliability, compactness and flexibility, reduced cost, linear or angular movement etc.). In addition, their unmatched energy density, easy integration into various structures and the simplicity in terms of design, have all motivated the authors to develop a barrier structure model, actuated by three SMA helical springs. The actuator used in this structure works as a linear actuator, contracting with great strength and speed, thus exerting the necessary force to lift the barrier arm in the SMA springs heat-activated, austenitic state. The first part of this paper provides a description of the accomplished model and of its functioning principle. The second part of the study presented in this paper focuses on the authors' investigation on how the performances of the actuator inserted in the barrier structure—namely the actuator's heating time, cooling time, actuation time and stroke—are affected by the SMA spring activating direct current values. The tests were conducted while keeping the geometrical parameters of SMA springs and the weight of the barrier arm constant.

We present here our progress towards the development of a type of biomimetic active hydrofoil that utilizes Shape Memory Alloy (SMA) actuator technology. The actuation is presently applied to the control of hydrodynamic forces and moments, including thrust generation, on a 2D hydrofoil. The SMA actuation elements are two sets of thin wires (0.015' to 0.027') on either side of an elastomer element that provides the main structural support. Controlled heating and cooling of the two wire sets generates bi-directional bending of the elastomer, which in turn deflects (for quasi-static control) or oscillates (for thrust generation) the trailing edge of the hydrofoil. The aquatic environment of the hydrofoil lends itself to cooling schemes that utilize the excellent heat transfer properties of water. The SMA actuator was able to deflect the trailing edge by +/- 5 degree(s) at rates as high as 2 Hz. FEM modeling of hydrofoil response to thermoelectric heating has been carried out using a thermomechanical constitutive model for SMAs. FEM predictions are compared with experimental measurements.

Wind turbine rotor upscaling has entered a range of rotor diameters where the blade structure cannot sustain the increased aerodynamic loads without novel load alleviation concepts. Research on load alleviation using morphing blade sections is presented. Antagonistic shape memory alloy (SMA) actuators are implemented to deflect the section trailing edge (TE) to target shapes and target time-series relating TE movement with changes in lift coefficient. Challenges encountered by the complex thermomechanical response of morphing section and the enhancement of SMA transient response to achieve frequencies meaningful for aerodynamic load alleviation are addressed. Using a recently developed finite element for SMA actuators [1], actuator configurations are considered for fast cooling and heating cycles. Numerical results quantify the attained ranges of TE angle movement, the moving time period and the developed stresses. Estimations of the attained variations of lift coefficient vs. time are also presented to assess the performance of the morphing section.

Shape memory alloy (SMA) actuators’ unique features like compact design and high force to weight ratio attracts numerous position control applications. Due to the nonlinear behaviour and control difficulties SMA actuators are not widely employed in position control applications. In this work, a simple and easy to construct closing mode SMA wire actuated gripper is presented. The mechanical structure of the gripper includes a pair of jaws - one movable and other fixed, an SMA wire employed to close the jaw upon actuation and a torsion spring bias for the strain recovery in SMA wire. An experimental setup of the SMA gripper is established to perform the study. The SMA actuator is heated by an electric current. A non-contact laser displacement sensor is engaged to measure the position of the movable jaw. In order to control the position of the devised gripper, a model of the gripper is estimated from open loop experimental data using system identification technique. Experimental evaluation of manually tuned PI controller for SMA actuated closing mode gripper is compiled to track various stationary and variable (dynamic) trajectories to suit applications that can manipulate objects of varied dimensions. Control results demonstrate that the gripper is able to track the position rapidly and precisely.

There are two different ways of using shape memory alloy (SMA) wire as an actuator for shape control of flexible structures: it can be either embedded within the composite laminate or externally attached to the structure. As the actuator can be placed at different offset distances from the beam, external actuators produce more bending moment and, consequently, considerabnle shape changes with the same magnitude of actuation force compared with the embedded type. Such a configuration also provides faster heat transfer rate owing to convection, which is very important in shape control applications that require a highfrequency response of SMA actuators. Although combination and physics-based modeling of externally attached SMA actuator wires and strips have been considered by many researchers, these studies have some drawbacks, which, if neglected, result in a number of errors in the theoretical results compared with experimental results. These shortcomings are considering the linear Euler-Bernoulli beam theory, not deriving the actuation force of the SMA from the constitutive equations, and taking into account the effect of only one SMA wire actuation force on, for example, the structure. These assumptions may lead to erroneous theoretical modeling results compared with experimental results. In this study, the aforementioned difficulties of attaching SMA actuators to the smart structures have been addressed. In other words, instead of linear beam theory, nonlinear beam theory is used in system modeling and, therefore, the proposed method and results are valid in large deflection and rotation behavior of beam. Also, in comparison to many other analyses that the effect of only one SMA wire is investigated, in the present research the effect of all active and inactive SMA wires is considered. Accordingly, the result of this paper can easily be generalized to the structure with several SMA wire actuations. Moreover, with the purpose of having practical applications in modeling and control, the heat transfer equations of all SMA wires are considered in the analysis and, as a result, the control inputs of the presented model are SMA wire electric currents rather than SMA temperatures. First, a flexible beam actuated by two active SMA actuators is modeled. Then, the Brinson constitutive equations and thermoelectric equations for SMA materials are coupled with the nonlinear beam behavior, and the coupled system of equations is numerically solved for some particular practical cases. Finally, the numerical results of the model simulation are verified against the experimental results using a test setup to validate the proposed model prediction. The implemented method used in this paper can be easily extended to the more complex smart structure with numerous externally attached SMA wires.

Shape memory alloy (SMA) actuators have recently been developed in the form of torsional tubes that can undergo large twisting deformations. Wing twisting has been investigated as a means to reduce induced drag in cruise conditions in small aircraft, but the actuation hardware required to generate wing twist at larger scales is prohibitively cumbersome. Replacing conventional actuators with SMA torque tubes provides a way to minimize weight of the twisting system but wing structural design then becomes more challenging. This analysis-driven design study examines an SMA torque tube as applied to the twisting wing design problem. A composite skin is considered to maximize wing performance under combined twist and aerodynamic loads. The SMA has been analyzed using a 3-D thermo-mechanical constitutive model while a preliminary study was performed to determine a composite lamina with appropriate unidirectional properties. An optimization was then completed to find an ideal composite layup. This optimization also included the design of a passive torque tube used to properly balance the twist generated by the SMA against that required in the wing. Localized buckling in the twisted wing was also considered and avoided. The product of this optimization was a composite wing that twisted while considering constraints of stress on the SMA. To validate the controllable use of SMA actuators, testing was completed on a scaled wing model fitted with a rapid prototype shell.

This paper describes the development of fuzzy systems for modeling the hysteresis behavior of shape memory alloy (SMA) actuators. Due to their simplicity and ease of actuation, SMA actuators are very attractive for applications such as miniature robots for micro manufacturing. However, SMAs have not been widely used for motion control applications due to their nonlinear behavior and control difficulties. One approach to design a position controller for SMA systems is to employ an inverse-model of the system in the control loop to compensate the hysteresis properties of the material. Fuzzy systems, due to their nonlinear learning and adaptation abilities, are good candidates for obtaining inverse-models. In this paper two fuzzy modeling approaches are employed and compared to develop a model for a SMA wire actuator. A set of experiments are conducted to generate the training data. The test stand includes a Nickel-Titanium (TiNi) SMA wire, a position sensor, a bias spring and a current amplifier. By comparing the performance of the two employed fuzzy modeling techniques, it is revealed that the approach based on fuzzy Gustafson-Kessel (GK) clustering shows a better performance in the modeling of the hysteresis in the SMA wire. Thus, GK clustering algorithm is employed to develop the inverse-model for the SMA. The reported results demonstrate the ability of the employed fuzzy algorithm for modeling the hysteresis in the system, and the merits of the introduced inverse-model in the control of the position of the SMA.

Shape Memory Alloys (SMAs) are unique materials capable of recovering predefined shapes through reversible phase transformations between austenite and martensite phases. This behavior enables SMAs to exhibit the shape memory effect and pseudoelasticity, allowing for the recovery of large strains and the generation of significant forces. These properties make SMAs highly desirable for applications in actuation, sensing, and other engineering domains. Conventional SMA actuator designs, while effective, often face limitations such as slow response times, non-uniform stress distribution, and reduced fatigue life under cyclic loading.
Integrating Kirigami-inspired techniques into SMA actuator design addresses these challenges by introducing precise cut patterns that transform 2D SMA materials into complex 3D structures. Kirigami-based SMA structures offer enhanced stroke lengths, improved heat dissipation, and uniform load distribution, reducing stress concentrations and extending actuator lifespan. This approach enables the creation of versatile and efficient actuators with tailored mechanical properties, overcoming traditional design constraints.
This paper presents a constitutive model for Kirigami-based SMA structures, coupling mechanical deformation and thermal response modeling to capture in-plane and out-of-plane deformations. The proposed framework provides a detailed understanding of the unique thermomechanical behavior of Kirigami-inspired SMA actuators, offering insights into their performance under varying operational conditions. The findings highlight the potential of Kirigami-based SMA structures for advancing actuator technologies across a range of applications.

This article proposes a numerical model to predict actuation frequencies (strain-cycling frequencies) for 1-D shape memory alloy (SMA) actuators. The numerical model is designed by comprehensively considering the factors that significantly affect an SMA actuator's strain-cycling frequency, i.e., heat convection methods, constant or nonconstant bias loads, and Joule heating methods. For computing strain cycles of SMA actuators, we develop a computation framework that effectively integrates an SMA constitutive model, a phase transformation kinetic model, stress-strain models for different types of bias stress, and a heat transfer model of SMA wires. The strain and temperature rates are formulated by nonlinear ordinary differential equations. The strain and temperature cycles can be accurately approximated by numerical iterative methods. Experimental verification was conducted to investigate the effectiveness of the proposed model. By initially identifying the SMA characteristic parameters, we employed Latin hypercube sampling method to generate 30 sets of design parameters for comparing the predicted and measured actuation frequencies. In addition, we investigated how the uncertainty of premeasured SMA characteristic parameters affect the numerical prediction of actuation frequency by conducting sensitivity analysis. The experiments demonstrate 0.7%-9.03% and 2.65%-17.57% differences between predicted and measured actuation frequencies for constant bias loads and spring bias loads, respectively.

Improving hydrodynamic efficiency of composite marine propellers in off-design conditions using shape memory alloy composite actuators

This paper describes the development of a neural network control for shape memory alloy (SMA) actuators as well as the control tests. Precise control of SMA actuators that are integrated in the composite structure is difficult because of the hysteretic behaviour of SMA and time delays in the control system. The weakness of the static model of SMA is that it does not take into account the actuator dynamics. The NARMA-L2 neural network model enables us to solve the inverse dynamic model of the nonlinear discrete-time dynamical system. In this study the NARMA-L2 model of the airfoil (a cross section of wind turbine blade) was created using Matlab Simulink software and neural networks. Data for network training was measured from the specimen. The performance of the constituted NARMA-L2 controller was tested in control tests. According to the control tests the NARMA-L2 controller is well suited for controlling embedded SMA actuators. The constituted controller enabled fast and stable actuation in step responses and it was also able to compensate for changes in cooling conditions.

The use of shape memory alloys (SMAs) in engineering applications has increased the interest of the accuracy analysis of their thermomechanical description. This work presents an uncertainty analysis related to experimental tensile tests conducted with shape memory alloy wires. Experimental data are compared with numerical simulations obtained from a constitutive model with internal constraints employed to describe the thermomechanical behavior of SMAs. The idea is to evaluate if the numerical simulations are within the uncertainty range of the experimental data. Parametric analysis is also developed showing the most sensitive constitutive parameters that contribute to the uncertainty. This analysis provides the contribution of each parameter establishing the accuracy of the constitutive equations.

A new approach of designing and controlling a multi-axis actuator system using segmented binary control (SBC) is presented. In SBC, Shape Memory Alloy (SMA) actuator wire is divided into multiple segments and their thermal states are controlled in a binary manner using thermoelectric modules. Two-dimensional array architecture for multi-axis SMA actuators is created using SBC. Similar to the biological muscle network, multi-axis SMA actuator wires can be combined flexibly with a two-dimensional segmentation method in order to activate multiple links of a skeletal robot structure in a coordinated manner. Ten-axis actuator is built using this method. Thermoelectric modules are laid on a substrate made of PCB board and SMA actuators are placed in between two substrate layers with a gap to allow the movement of the actuators. The actuator creates coordinated gross motion as well as independent fine movements with reduced number of control loops. The new actuator architecture will provide a novel actuator system forming a network of array actuators connected to a vast number of bone-like linkages.

This paper presents a novel compliant differential (CD) Shape Memory Alloy (SMA) actuator with improved performance compared to traditional SMA actuators. This actuator is composed of two antagonistic SMA wires and a mechanical joint coupled with a torsion spring. The torsion spring is employed to reduce the total stiffness of SMA actuator and improve the range of motion. The antagonistic wires increase the response time as one wire can be heated up while the other wire is still in the cooling process. Dynamic model of this actuator was established for control design. Experimental results proved that this new actuator can provide larger output range of motion and faster response speed than traditional SMA actuators under the same conditions. Sine wave tracking with 0.05 Hz, 0.08 Hz and 0.1 Hz were performed and our results demonstrated that this compliant actuator has good tracking performance under simple PID control.