Antagonistic Shape Memory Alloy Research Articles

Model based design of antagonistic shape memory alloy spring devices

Shape memory alloy actuated devices employing a network of antagonistic components can reach an equilibrium of the internal forces by multiple sets of individual force magnitudes. In networks of star topologies particularly, the actuators are placed radially with one end connected at a common node. The ability to produce multiple sets of force equilibria suggests then that similar motions of the common node correspond to different thermomechanical paths. Two factors linked to this behavior are examined in this work, namely the initial design of the antagonistic system and the operational profile used during actuation. A shape memory alloy model is initially constructed based on an elementary hysteresis operator to produce a direct representation of the shape memory alloy behavior in the force–deformation plane. This description enables the identification of the operating point for the actuator by the geometric relationship of these models. In the second part, the placement of the antagonists is guided by the model based on specifications on the range of the workspace and the internal forces. The antagonistic operation is finally compared, in terms of time, work produced, and energy consumption, for a bang-bang (minimum time controller for the actuator) and a bang-off-bang (minimum internal forces for the system) actuation scheme.

Zero-electric-power position retaining utilizing hysteresis on an antagonistic shape memory alloy system

Zero-electric-power position retaining utilizing hysteresis on an antagonistic shape memory alloy system

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.

Development of a Meso-Scale SMA-Based Torsion Actuator for Image-Guided Procedures.

This paper presents the design, modeling, and control of a meso-scale torsion actuator based on shape memory alloy (SMA) for image-guided surgical procedures. Developing a miniature torsion actuator is challenging, but it opens the possibility of significantly enhancing the robot agility and maneuverability. The proposed torsion actuator is bi-directionally actuated by a pair of antagonistic SMA torsion springs through alternate Joule heating and natural cooling. The torsion actuator is integrated into a surgical robot prototype to demonstrate its working performance in the humid environment under C-Arm CT image guidance.

Shape memory alloy with bi-functionality in the master system to control a slave

Application of a shape memory alloy (SMA) with bi-functionality, acting as a force sensor and as an actuator (sensor+haptics=‘sensaptics’) is proposed for the master side of a master – slave system. A 1-DOF master is instrumented with SMA wires to servo a 2-DOF slave. Antagonistic shape memory alloy wires employed in master system performs shared sensing and actuation; the operator's command to control the slave system is sensed by the variation in the differential electrical resistance of SMA and it functions as a haptic device to display the interactive force fed back from the slave to the master. From the haptic information the operator can make decisions and take appropriate action/correction in co-ordination with the requirement of the slave environment. The laboratory model of SMA based master – slave system is designed, developed and evaluated for its performance. The validity of the results proves the concept of shared bi-functionality.

Independent Control of Force & Displacement Using Shape Memory Alloy Tactile Display

This paper proposes one of the possible techniques for interacting for shape memory alloy (SMA) actuator based tactile display, which can act as demonstrator devices. This work is focused on developing a model of a pair of antagonistic high strain SMA tension actuators with independent control of force and displacement. The technology employed utilizes two Flexinol 100 micron heat actuated wires of Titanium-Nickel (NiTi) shape-memory alloy which contract when heated under pre-stress and produces up to 5% strain recovery. This phenomenon, which provides a unique mechanism for actuation, is associated with the unique interaction between the martensite and austenite crystal structures of the SMA. Physical measurements of the behaviour of the actuator elements were performed using a laser displacement sensor to verify the fidelity of response to software commands, and to measure step response to pulse-width modulated (PWM) current control at different frequencies and duty cycles. Results yielded high accuracy across a wide range of frequencies and duty cycles, proving the SMA actuation technique has potential to present and convey useful tactile information of surface deformation for virtual environment applications.

Design, modeling and characterization of a novel meso-scale SMA-actuated torsion actuator

This paper presents our work on design, modeling, and characterization of a novel shape memory alloy (SMA)-actuated torsion actuator for meso-scale robots. Development of a miniature torsion actuator is challenging, but it can enhance the agility and enlarge the workspace of meso-scale robots. This torsion actuator comprises a pair of antagonistic SMA torsion springs, which bi-directionally actuate the actuator by Joule heating and natural cooling. First, the mechanical design of the torsion actuator is presented, followed by the fabrication of SMA torsion springs. Then, we present the constitutive model of the SMA torsion spring with an analysis of its strain change, and derive a quasi-static model with the Coulomb friction torque for this torsion actuator. Finally, a series of characterization experiments are conducted on the SMA torsion spring and the torsion actuator prototype to determine the values of all model parameters. This work shows that the properties of the SMA-actuated torsion actuator can be appropriately characterized by experiments and the actuator is feasible for robotics applications.

Design and Fabrication of a Soft Robotic Hand With Embedded Actuators and Sensors

This paper details the design and fabrication process of a fully integrated soft humanoid robotic hand with five finger that integrate an embedded shape memory alloy (SMA) actuator and a piezoelectric transducer (PZT) flexure sensor. Several challenges including precise control of the SMA actuator, improving power efficiency, and reducing actuation current and response time have been addressed. First, a Ni-Ti SMA strip is pretrained to a circular shape. Second, it is wrapped with a Ni-Cr resistance wire that is coated with thermally conductive and electrically isolating material. This design significantly reduces actuation current, improves circuit efficiency, and hence reduces response time and increases power efficiency. Third, an antagonistic SMA strip is used to improve the shape recovery rate. Fourth, the SMA actuator, the recovery SMA strip, and a flexure sensor are inserted into a 3D printed mold which is filled with silicon rubber materials. The flexure sensor feeds back the finger shape for precise control. Fifth, a demolding process yields a fully integrated multifunctional soft robotic finger. We also fabricated a hand assembled with five fingers and a palm. We measured its performance and specifications with experiments. We demonstrated its capability of grasping various kinds of regular or irregular objects. The soft robotic hand is very robust and has a large compliance, which makes it ideal for use in an unstructured environment. It is inherently safe to human operators as it can withstand large impacts and unintended contacts without causing any injury to human operators or damage to the environment.

Fuzzy based sliding surface for shape memory alloy wire actuated classical super-articulated control system

This paper presents the experimental study on a system which is an interesting crossover between a standard benchmark control problem and a smart material. The study represents the effect of stress, strain and temperature over bandwidth of antagonistic shape memory alloy (SMA) and its relative performance in influencing the stability of the system. The experiment is implicated on an underactuated open loop unstable ball and beam system, designed and developed to be driven by SMA. A proportional derivative controller cascaded with sliding mode controller (SMC) based on simplified fuzzy adaptive sliding surface is considered to study the dynamics of the system. The designed simplified fuzzy based sliding surface controller is able to balance the ball and beam system around its equilibrium state, which as a control perspective shows that performance of this controller is better than the conventional SMC. Furthermore from smart material perspective decisive results are arrived to handle the issues like stability, speed of operation and performance of antagonistic SMA.

Design and control of a novel compliant differential shape memory alloy actuator

This paper presents the design and control of a novel compliant differential shape memory alloy (SMA) actuator with significantly improved performance compared to traditional bias and differential type SMA actuators. This actuator is composed of two antagonistic SMA wires and a mechanical joint coupled with a torsion spring. The differential SMA wires are utilized to increase the response speed, and the torsion spring is employed to reduce the total stiffness of SMA actuator and improve the output range. Theoretical models that include the stiffness equations of the SMA wire as well as the dynamics of three different SMA actuation systems are introduced and compared. Simulation and experimental results have proved that this new actuator can provide larger output angle compared to conventional SMA actuators under the same conditions. Moreover, regulation and tracking control experiments have demonstrated that this compliant differential SMA actuator achieves higher response speed compared to the bias SMA actuator using compatible PI controller. The tracking performance is further improved by the saturated PI controller.

OS0201-393 拮抗SMAシステムを用いた省エネルギ位置保持制御

To keep a position using Shape Memory Alloy (SMA) actuators, the SMA actuators must be continued to be heated. To save the energy, a control method utilizing hysteresis in deformation was proposed for an antagonistic SMA system. To show feasibility of the control method, a fundamental experiment was performed. When a pulsed current was applied to the two SMA wires alternately, the equilibrium position changed between two positions alternately. To confirm the behavior, numerical simulation was also performed. The one-dimensional phase transformation model [Ikeda, Proc. SPIE 5757 (2005), 344-352] was applied to predict the deformation behavior of the antagonistic SMA system. The simulated result agreed with the experiment qualitatively. The feasibility of the proposed control method could be indicated both experimentally and numerically and the validity of the mathematical model also could be proved.

Effect of stress on bandwidth of antagonistic shape memory alloy actuators

This article presents the experimental study on the influence of stress generated between the antagonistically connected shape memory alloy wire actuators over its bandwidth of operation. It is a well-known fact that behaviour of shape memory alloy is strongly coupled with temperature, stress and strain. An attempt is made to understand the effect of these factors on its bandwidth from control perspective through frequency response analysis. A phenomenological correlation is presented between the frequency response of antagonistic shape memory alloy and stress acting between the wires under different strains and temperatures. A clear demarcation between influence of temperature and stress over the operating frequency is discussed. Experimental result shows that apart from temperature, operating frequency of antagonistically connected shape memory alloy is also highly influenced by stress acting between the wires at higher temperatures. Also, the effect becomes much more significant under partial transformation strain. The result of the study is extended and demonstrated through tracking control of antagonistic shape memory alloy at a frequency of about 2 Hz.

Performance analyses of antagonistic shape memory alloy actuators based on recovered strain

In comparison with conventional shape memory actuated structures, antagonistic shape memory alloy (SMA) actuators permits a fully reversible two-way response and higher response frequency. However, excessive internal stress could adversely reduce the stroke of the actuators under repeated use. The two-way shape memory effect might further decrease the range of the recovered strain under actuation of an antagonistic SMA actuator unless additional components (e.g., spring and stopper) are added to regain the overall actuation capability. In this paper, the performance of all four possible types of SMA actuation schemes is investigated in detail with emphasis on five key properties: recovered strain, cyclic degradation, response frequency, self-sensing control accuracy, and controllable maximum output. The testing parameters are chosen based on the maximization of recovered strain. Three types of these actuators are antagonistic SMA actuators, which drive with two active SMA wires in two directions. The antagonistic SMA actuator with an additional pair of springs exhibits wider displacement range, more stable performance under reuse, and faster response, although accurate control cannot be maintained under force interference. With two additional stoppers to prevent the over stretch of the spring, the results showed that the proposed structure could achieve significant improvement on all five properties. It can be concluded that, the last type actuator scheme with additional spring and stopper provide much better applicability than the other three in most conditions. The results of the performance analysis of all four SMA actuators could provide a solid basis for the practical design of SMA actuators.

Servo control of an under actuated system using antagonistic shape memory alloy

This paper presents the design, modelling and, simulation and experimental results of a shape memory alloy (SMA) actuator based critical motion control application. Dynamic performance of SMA and its ability in replacing servo motor is studied for which the famous open loop unstable balancing ball and beam system direct driven by antagonistic SMA is designed and developed. Simulation uses the mathematical model of ball and beam structure derived from the first principles and model estimated for the SMA actuator by system identification. A PID based cascade control system consisting of two loops is designed and control of ball trajectory for various target positions with settling time as control parameter is verified experimentally. The results demonstrate the performance of SMA for a complicated i.e., under actuated, highly nonlinear unstable system, and thereby it\'s dynamic behaviour. Control strategies bring out the effectiveness of the actuator and its possible application to much more complex applications such as in aerospace control and robotics.

Indirect Intelligent Sliding Mode Control of Antagonistic Shape Memory Alloy Actuators Using Hysteretic Recurrent Neural Networks

This paper presents the development of an indirect intelligent sliding mode control (IISMC) system for use with antagonistic shape memory alloy (SMA) actuators. The controller manipulates input voltages to a pair of offset antagonistic SMA tendons, resulting in heat-induced bending of a flexible beam. Hysteresis compensation is achieved using a pair of hysteretic recurrent neural networks, which map the nonlinear, hysteretic relationships between SMA temperatures and bending angle for each tendon. The sliding mode control law regulates tendon temperatures based on reference and measured bending angle. Additionally, the IISMC incorporates an antislack component to increase tendon responsiveness. Experimental results demonstrate precise tracking of periodic reference trajectories. The controller is robust to model uncertainty, disturbances, and parameter variations, with bending angle tracking results superior to those of an optimized proportional + integral controller.

Model of a NiTi shape memory alloy actuator

A model of motion of an agonistic–antagonistic shape memory alloy actuator is developed in this article. The model shows that the dynamics of the actuator can be well described by a nonlinear motion model of human muscle with nonlinear damping. To complete the model, a method for the determination of the damping properties of the actuator system is suggested. To this end, an analytical expression for the damping coefficient of the system was developed. The experimental verification of the proposed model of motion was conducted through a comparison of the experimentally measured and numerically simulated step responses. The simulated step responses were in close agreement with their experimentally measured counterparts on the shape memory alloy actuator prototype.

A fuzzy PID-controlled SMA actuator for a two-DOF joint

Shape memory alloy (SMA) actuator is a potential advanced component for servo-systems of aerospace vehicles and aircraft. This paper presents a joint with two degrees of freedom (DOF) and a mobility range close to ±60° when driven by SMA triple wires. The fuzzy proportional-integral-derivative (PID)-controlled actuator drive was designed using antagonistic SMA triple wires, and the resistance feedback signal made a closed loop. Experiments showed that, with the driving responding frequency increasing, the overstress became harder to be avoided at the position under the maximum friction force. Furthermore, the hysteresis gap between the heating and cooling paths of the strain-to-resistance curve expanded under this condition. A fuzzy logic control was considered as a solution, and the curves of the wires were then modeled by fitting polynomials so that the measured resistance was used directly to determine the control signal. Accurate control was demonstrated through the step response, and the experimental results showed that under the fuzzy PID-control program, the mean absolute error (MAE) of the rotation angle was about 3.147°. In addition, the investigation of the external interference to the system proved the controllable maximum output.

Dynamic stabilization and rapid motion control system driven by antagonistic shape memory alloy actuators

The frequency response analysis of antagonistic shape memory alloy actuators and the influence of temperature, stress and strain on its speed of operation are studied and presented. Based on the decisive results an interesting servo control application is designed and tested such that the operating angle utilizes only partial strain of shape memory alloy (SMA) wire. The application developed is an open loop unstable, under actuated, a renowned highly dynamic ball balancing beam system driven by antagonistic SMA wires. The control scheme of proportional derivative controller cascaded with sliding mode controller is designed in order to demonstrate the tracking control capability of SMA wires under partial transformation. Experimental results show the motion control with significantly faster response of SMA under partial transformation. The robustness of the control system for disturbance rejection is also tested. The implication is that this design scheme can be extended to all other dynamic applications including robotics, automotive, aerospace, etc.

IntraVAD, An Intra-Ventricular Assistive Device for Heart Failure Patients: Design and Proof of Concept Simulations

Ventricular assistive devices are approved by Food and Drug Administration as an alternative to heart transplant for congestive heart failure patients. Unlike other devices requiring open-heart surgery, thin active flexible membrane of IntraVAD, made of ionic polymer-metal composites and shape memory alloys (SMA), enables transcatheter implantation and eliminates thoracotomy. Actuation mechanism of the device mimics the natural motion of the heart, applies almost no shear stress on blood cells, and leaves no stagnant points. Hence, it reduces hemolysis and thrombosis risks. The first step in designing the device is defining the objectives based on hemodynamics of eligible patients. A 3-dimensional model is extracted from magnetic resonance images of a subject to provide a precise representation of the inner shape of the ventricle. Numerical solution to the mathematical model of the behavior of ionic polymer-metal composites is then used to check their compliancy with the objectives. Different actuator designs are evaluated to perform the desired motions and address the cardiac insufficiency. Using an iterative design and simulation process, various geometric and material parameters affecting the performance of the device are optimized, including those of the antagonistic two-way SMA actuators. Although methods and results provided here are for the left ventricle, the same are also applicable to the right ventricle.