SMA Actuators Research Articles

Mechanical properties and damage mechanism of SMAHC laminates

Abstract The combination of smart materials and composite materials to achieve lightweight and intelligent structures has been an important research direction in recent years. In this paper, a three-dimensional woven hybrid shape memory alloy (SMA actuator) is modularly implanted into a composite laminate to prepare a SMA hybrid composite (SMAHC) laminate. The orthogonal test was designed with the three variables of SMA actuator modular implantation position, SMA pre-strain and SMA number. According to the orthogonal test results and finite element results, the influence of the three variables on the stiffness before heating, the stiffness change rate after heating and the strength of SMAHC laminates was studied. According to the test index, the influence of the three variables on the results was further evaluated. The results show that the implantation position has the greatest influence on the mechanical properties of SMAHC laminates, followed by SMA pre-strain, and the number of SMA has the least influence. The location and form of damage of SMAHC laminates are further summarized, and the bending damage mechanism of SMAHC laminates is analyzed.

A Novel Design of a Torsional Shape Memory Alloy Actuator for Active Rudder.

SMA actuators are a group of lightweight actuators that offer advantages over conventional technology and allow for simple and compact solutions to the increasing demand for electrical actuation. In particular, an increasing number of SMA torsional actuator applications have been published recently due to their ability to supply rotational motion under load, resulting in advantages such as module simplification and the reduction of overall product weight. This paper presents the conceptual design, operating principle, experimental characterization and working performance of torsional actuators applicable in active rudder in aeronautics. The proposed application comprises a pair of SMA torsion springs, which bi-directionally actuate the actuator by Joule heating and natural cooling. The experimental results confirm the functionality of the torsion springs actuated device and show the rotation angle of the developed active rudder was about 30° at a heating current of 5 A. After the design and experiment, one of their chief drawbacks is their relatively slow operating speed in rudder positioning, but this can be improved by control strategy and small modifications to the actuator mechanism described in this work.

Temperature gradient for improving the output non-linearity in shape memory alloy actuators

The non-linearity of shape memory alloy’s (SMA) input vs. output relationship has been a significant barrier to their broader application for actuators. In this article, we introduce a novel activation approach with the objective of improving the output nonlinearity in SMA actuators by using a liquid temperature gradient for activation. This gradient, with a narrow inflection point, selectively activates and deactivates different portions of the SMA, allowing control of the overall actuator’s output by adjusting the inflection point’s position. Two prototypes with the proposed concept were constructed and tested for force and displacement output. Their inner shape design facilitates the creation of a temperature gradient, whose inflection point is adjusted by varying the mix ratio of the inlet of hot and cold water. The performance of the prototypes was evaluated, including their ability to generate a temperature gradient, output linearity, activation dead time and time constant, and compatibility with a linear controller. The output linearity, activation dead time, and time constant were also compared with traditional wet activation. Our findings suggest that this technique significantly enhances the performance and predictability of SMA-based actuators and is compatible with PID controllers without additional feedforward or modeling techniques, offering a practical solution to a long-standing challenge in the field.

A bio-inspired shape memory alloy-based smart fin system for adaptive thermal management

Thermal management systems utilizing fixed-area extended surfaces for thermal enhancement have been extensively investigated. Unlike these systems, in nature, few creatures display the ability to control heat dissipation in adaptation to changes in environmental conditions by controlling their exposed surface area of the body. Motivated by this, the primary objective of this research is the design, development, numerical and experimental evaluation of an adaptive variable area smart fin system for intelligent thermal management using a high-strain SMA spring actuator. Unlike most thermal management devices and techniques that involve a fixed surface area, a smart fin controlled by Pennate structure-based SMA (PeSMA) actuator is proposed for large actuation and compact arrangement. The capabilities of the smart fin to adaptively enhance heat transfer are experimentally demonstrated and numerically modeled. The proposed fin design can deliver improved thermal performance in terms of reduced operating temperature and pressure drop, which is an indicator of operational cost when the application involves variable and uncertain thermal load conditions. We envisage one of the future applications of this technology in the battery thermal management of Electric Vehicles (EVs) where deployable compact heat transfer system is highly desirable.

Mapping actuating performance of knitted shape memory alloys and proposing design guidelines for assistive wearable applications

The purpose of this study was to map the actuating performance of knitted SMA modules, and propose design guidelines for developing optimal SMA actuators, to be used in wearable assistive devices, suitable to be worn on the human body. To validate the findings of this study in the real world, we adopted an assistive rehabilitation glove for hemiplegic patients as a particular design case. To characterize the bending and contractile properties of knitted SMA modules, we conducted actuating performance tests with 720 knitted SMA samples under various conditions in actuation force, bending angle, contraction, electric power, and surface temperature. Based on the results, we proposed design guidelines by aligning the actuating performance of knitted SMA modules with joint mobility of hemiplegic patients for a smart rehabilitation glove. We anticipate that the outcomes of this study will serve as a practical yardstick for researchers in determining the desired actuating performance of a knitted SMA module that can support and assist the joint motion of the human body, when designing a wearable assistive device.

An SMA Transducer for Sensing Tactile Sensation Focusing on Stroking Motion.

The authors have developed a micro-vibration actuator using filiform SMA wire electrically driven by periodic electric current. While applying the SMA actuators to tactile displays, we discovered a phenomenon that the deformation caused by a given stress to an SMA wire generated a change in the electrical resistance. With this characteristic, the SMA wire works as a micro-force sensor with high sensitivity, while generating micro-vibration. In this paper, the micro-force sensing ability of an SMA transducer is described and discussed. Experiments are conducted by sliding the SMA sensor on the surface of different objects with different speeds, and the sensing ability is evaluated to be related with human tactile sensation.

Numerical simulation and experimental comparison of antagonistic shape memory alloy linear actuator for automotive applications

This paper introduces several commonly used constitutive models of SMA materials, expounds the relationship between material temperature, stress and strain from the perspective of one-dimensional model, and establishes the simulation model of reciprocating motion of SMA actuator based on the material parameters obtained from quasi-static mechanical property experiments in the previous paper. A double wire pull SMA actuator is designed and a prototype is made. The output displacement data obtained from the experiment is compared with the established simulation model to prove the accuracy of the simulation process.

A High-Performance Modular SMA Actuator With Fast Heating and Active Cooling for Medical Robotics

Shape memory alloy (SMA) has been adopted in medical robotics due to its high power density, compactness, and medical imager compatibility. However, its use in clinical applications remains limited due to its low actuation bandwidth and the lack of proper system integration approaches, leading to poor control accuracy and repeatability. In this article, we report the design, modeling, and characterization of a high-performance SMA actuator for real-time medical robotics application. It uses nichrome wire for fast heating and forced air convection for active cooling to improve the actuation bandwidth, with the SMA spring predisplacements tunable with a simple mechanism. All structures are packaged in a compact module to facilitate practical integration in a robotic system, and enable consistent performance and convenient use. We have also developed an intuitive constitutive model and heat transfer model of the actuator to facilitate selection of its critical parameters, such as SMA predisplacement, heating current, and air pressure, based on the performance requirements. During characterization, the actuator achieved a stroke of 147.2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathrm{^{\circ }}$</tex-math></inline-formula> , stall torque of 172.5 Nmm and actuation bandwidth of 0.43 Hz at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula> 5 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathrm{^{\circ }}$</tex-math></inline-formula> rotation amplitude. It also demonstrated high control accuracy (error <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$&lt; $</tex-math></inline-formula> 1 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathrm{^{\circ }}$</tex-math></inline-formula> ) and high repeatability (standard deviation <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$&lt; $</tex-math></inline-formula> 0.16 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathrm{^{\circ }}$</tex-math></inline-formula> ) under closed-loop control. Torque–speed relationship was experimentally determined to show its performance under external loading. Finally, the actuator was used to build a steerable endoscope manipulator as a demonstration for real-time application in surgical robotics.

Using inverse learning for controlling bionic robotic fish with SMA actuators

Using inverse learning for controlling bionic robotic fish with SMA actuators

Intelligent controller for robust orientation control of smart actuator based parallel manipulator

Flexible parallel manipulators can be used as an orienting device due to its precise positioning ability. The flexibility demands the use of non-conventional actuators and noncontact type/flexible sensors for feedback measurement. This study proposes a novel 2 Degree of Freedom (DoF) parallel manipulator actuated by shape memory alloy springs (SMA) which could be used as an orienting device for a table top Cartesian robot. To mitigate the use of contact type sensor, model based feedback is proposed to obtain SMA length for the feedback control. The inclusion of SMA actuators to parallel mechanism imposes control challenges due to nonlinearities, coupling effects, and disturbances. This work also proposes a novel control scheme based on concept of partition control law to control the SMA spring position without the use of any complex mathematical model. The proposed controller is a combination of two parts Fuzzy PID servo control and the time delay estimation (TDE) based auxiliary control. The fuzzy PID control handles the error tracking and the auxiliary control tries to cancel the nonlinearities and disturbances, thus enhancing the robustness. The performance of the proposed controller is tested for a complex trajectory under disturbances and the results are compared with existing nonlinear controllers which proves superior nature of the proposed controller.

Bio-Inspired Control System for Fingers Actuated by Multiple SMA Actuators

Spiking neural networks are able to control with high precision the rotation and force of single-joint robotic arms when shape memory alloy wires are used for actuation. Bio-inspired robotic arms such as anthropomorphic fingers include more junctions that are actuated simultaneously. Starting from the hypothesis that the motor cortex groups the control of multiple muscles into neural synergies, this work presents for the first time an SNN structure that is able to control a series of finger motions by activation of groups of neurons that drive the corresponding actuators in sequence. The initial motion starts when a command signal is received, while the subsequent ones are initiated based on the sensors’ output. In order to increase the biological plausibility of the control system, the finger is flexed and extended by four SMA wires connected to the phalanges as the main tendons. The results show that the artificial finger that is controlled by the SNN is able to smoothly perform several motions of the human index finger while the command signal is active. To evaluate the advantages of using SNN, we compared the finger behaviours when the SMA actuators are driven by SNN, and by a microcontroller, respectively. In addition, we designed an electronic circuit that models the sensor’s output in concordance with the SNN output.

Backstepping control of novel arc-shaped SMA actuator

Backstepping control of novel arc-shaped SMA actuator

Design, Modeling and Evaluation of a Hybrid Driven Knee-Ankle Orthosis with Sma Actuators

Design, Modeling and Evaluation of a Hybrid Driven Knee-Ankle Orthosis with Sma Actuators

Structural considerations of sound radiator driven by SMA actuator

Structural considerations of sound radiator driven by SMA actuator

Response characteristics of SMA actuator in audio frequency range

Response characteristics of SMA actuator in audio frequency range

Application of shape memory alloys in engineering – A review

Shape Memory Alloy is a smart alloy which retains their original shape under thermomechanical or magnetic variation. Shape Memory Alloy are widely used in different engineering field because of its superior properties and variety of application. Recent research of SMA has been applied in the field of Aerospace, Automotive, Biomedical, and Robotics. This memory effect is due to the presence of austenite and martensite crystalline structures. These alloys are bio-compatible, lightweight, and also possess a high force-to-weight ratio. Due to this SMA actuators are very much suitable for soft robotic applications. However, due to high cooling times during phase change, SMA has small bandwidth and low operating frequencies. This alloy can replace a sensor as it performs the same work done by sensors or transducer. An extensive review of history, material characterization, and opportunities of SMA in the engineering field.

Development of a Combined Micro-Macro Mechanics Analytical Approach to Design Shape Memory Alloy Spring-Based Actuators and Its Experimental Validation.

In this work, an analytical procedure for the preliminary design of shape memory alloy spring-based actuators is investigated. Two static analytical models are considered and interconnected in the frame of the proposed procedure. The first model, based on the works from An, is able to determine the material properties of the SMA components by means of experimental test data and is able to size the SMA component based on the requirements of the system. The second model, based on a work from Spaggiari, helps to design and size an antagonist spring system that allows one to obtain the geometric characteristics of springs (SMA and bias) and the mechanical characteristics of the entire actuator. The combined use of these models allows one to define and size a complex SMA actuator based on the actuation load requirements. To validate the design procedure, static experimental tests have been performed with the entire SMA actuator.

SHAPE MEMORY ALLOY ACTUATORS ARE USED TO CREATE A VARIABLE AREA JET NOZZLE FOR NOISE REDUCTION: A REVIEW

The real study details the design and implementation of Shape memory alloy actuators to produce a noise-reducing variable area jet nozzle. A subscale design specification of a changeable area jet nozzle was created using SMA actuators in an asymmetrical design. Commercial transportation planes must be quieter, cleaner, and more efficient, according to the international community. The aviation industry is reacting by developing new technology in order to achieve those objectives. Changing the area of a commercial jet engine's fan nozzle can result in substantial noise reduction and reduced fuel economy. At takeoff and approach, a bigger diameter reduces jet velocity, which reduces noise. In cruise, adjusting the diameter to account for variable Mach numbers, altitude, and other factors helps optimise fan loading and minimise fuel consumption and emissions. Boeing has tested a 20 percent area change scaled variable area jet nozzle. At the nozzle exit, Shape Memory Alloy actuators were utilised to place 12 interlocking panels. To maintain a range of consistent diameters with variable flow circumstances and to alter the diameter under constant flow conditions, a closed loop control system was utilised. At each condition, acoustic data was gathered using side line microphones, and flow field measurements were taken using PIV at various crosssections. The design of a variable area nozzle is explained in this work. The diameter of the nozzle and its influence on acoustic performance are discussed. The effects of the joints between the interlocking panels are seen in the flow field data.

Force Control for Anthropomorphic Fingers Actuated by Shape Memory Alloy Wires

High accuracy in modelling the behavior of human hand and fingers is obtained using control devices of high biological plausibility. Such devices are typically based on neural networks and are able to control in parallel multiple artificial muscles. This paper presents the structure of an electronic spiking neural network that was implemented to control the force of two opposing fingers of an anthropomorphic hand. In order to increase the level of bio-inspiration, the artificial muscles are implemented using shape memory alloy wires which actuates by contraction as the natural muscles. Moreover, the contraction force of the SMA actuators is directly related to the spiking frequency that is generated by the artificial neurons. The results show that using few excitatory and inhibitory neurons the neural network is able to set and regulate the contraction force of the SMA actuators.

Fuzzy Time Delay Algorithms for Position Control of Soft Robot Actuated by Shape Memory Alloy

Due to the nonlinear saturated hysteretic behavior of SMA during the phase transformation, it is not easy to achieve accurate position tracking control by establishing an effective controller for the SMA actuator system. In this paper, an accurate position control method based on fuzzy time delay algorithms for a soft robot is proposed. The error of TDE is unavoidable because the smallest value for the time delay is the sampling time of the microcontroller, a rule-based fuzzy logic controller for online gain tuning combined with TDC is proposed to eliminate the position control errors. Three different sets of experiments are conducted, using step, sine and ramp signals as reference inputs. The experimental results demonstrate that the proposed method has the smallest steady state error and the least overshoot than TDE and PI controller. In conclusion, the proposed method should be a viable alternative for position control of SMA actuator.