Wire Actuators Research Articles

Characterization, modeling, and control of Ni-Ti shape memory alloy based on electrical resistance feedback

The use of shape memory alloy actuators has steadily increased within the fields of aerospace, robotics, and biomedical engineering due to their superior properties compared to other actuation systems. Position control of shape memory alloy actuators is difficult due to the highly non-linear behavior but has been well studied using numerous approaches. Electrical resistance can be used to estimate strain in shape memory alloy actuator wire due to a correlation between the two parameters. Previous models of this correlation are subject to one or more drawbacks such as being limited to a single applied load, not accounting for hysteresis effects, or applying only to a specific actuator size. This article presents a stress–strain–resistance model that accounts for varying applied load, major and minor hysteresis effects and is normalized in terms of actuator geometry. Results of simulation and a simple position control experiment are demonstrated, validating the performance of the model. Furthermore, a correlation between the model and an augmented version of the Liang and Rogers model is also presented.

Shape memory alloy wire for self-sensing servo actuation

This paper reports on the development of a straightforward approach to realise self-sensing shape memory alloy (SMA) wire actuated control. A differential electrical resistance measurement circuit (the sensorless signal conditioning (SSC) circuit) is designed; this sensing signal is directly used as the feedback for control. Antagonistic SMA wire actuators designed for servo actuation is realized in self-sensing actuation (SSA) mode for direct control with the differential electrical resistance feedback. The self-sensing scheme is established on a 1-DOF manipulator with the discrete time sliding mode controls which demonstrates good control performance, whatever be the disturbance and loading conditions. The uniqueness of this work is the design of the generic electronic SSC circuit for SMA actuated system, for measurement and control. With a concern to the implementation of self-sensing technique in SMA, this scheme retains the systematic control architecture by using the sensing signal (self-sensed, electrical resistance corresponding to the system position) for feedback, without requiring any processing as that of the methods adopted and reported previously for SSA techniques of SMA.

FE Exploratory Investigation on the Performance of SMA‐Reinforced Laminated Glass Panels

Shape‐Memory Alloys (SMAs) are a class of metal materials that exhibit two outstanding properties, the superelastic and the shape‐memory effects. Taking advantage of these properties, several SMA actuator wires and plates have been proposed over the last years in robotic, automotive, and biomedical engineering. In this paper, the feasibility of a novel design concept of SMA‐reinforced laminated glass panels is proposed, based on an adaptive embedded system built up of SMA wires. Glass panels used as cladding walls in facades have in fact typically high size‐to‐thickness ratios, hence, major restrictions in design are represented by prevention of glass failure and large deflections. It is expected, based on the current investigation, that useful design recommendations can be derived for this novel design concept.

Design and Testing of an Innovative Wire Transmission for a Quarter-Turn Actuator

The object of this work is the development of an innovative wire actuator in collaboration with Velan ABV S.p.A., which will be mainly used in applications in which high efficiency and linear behavior are desirable specifications. In this work, the main features of the proposed actuator, which is protected by a patent, are evaluated and compared with respect to a conventional solution consisting of a scotch yoke (SY) transmission system. The comparison is performed using both the simulation results and the experimental data. In order to identify the efficiency and the dynamical response of the innovative actuator, the authors have designed a hydraulic test rig, which can be configured to perform different testing procedures. In this way, it is possible to perform both static tests to identify actuator efficiency, and dynamic ones, in which an assigned load or a valve impedance function is simulated to verify the response of the tested actuator in realistic conditions. Finally, the proposed test rig has been successfully employed to perform both reliability and fatigue tests in which the actuator is subjected to realistic and repetitive loads.

Nonlinear Model Control of Shape Memory Alloy Actuator

The paper deals with modeling and control of a Shape Memory Alloy (SMA) actuator. The considered complex model is based on physical and empirical analyses of a Ni-Ti alloy straight wire actuator. Dependence on the history of the SMA actuator inputs is modeled, especially on reversing points. The SMA actuator model consists of internal hysteresis loops with memory described by nonlinear static and dynamic equations with 16 variable parameters. Finally, the model has been simplified for control purposes.

Design and Development of Hexapod using Nitinol Actuator Wire

Objectives: This research work involves the design and implementation of Hexapod robot which is a small, inexpensive, six-legged robot. Methods/Statistical Analysis: Hexapod robots from decennium have gained considerable attention in various research and development sectors. This research work involves the design and implementation of Hexapod robot which is a small, inexpensive, six-legged robot intended to replace huge and heavy robotic that are used in space applications, industries for lifting purpose containing solenoids and servo motors. Findings: Initial stage of research work involves design and construction of the structure of Hexapod. Plastic material is used for the construction of body and a Nitinol actuator wire is used to drive the Hexapod’s legs. The final stage involves Hexapod interfacing with Arduino and HBridge module for supply to achieve proper locomotion of the Hexapod. Specifically, real element like mechanical structure, legs arrangement, impelling, payload, movement condition and waking walk are considered in proposed system design. In this work, a novel robot is constructed and found that conservative, and lightweight Hexapod robot demonstrates guarantee for use in space, therapeutic, and other large scale robotic applications. Application/Improvements: Due to the unique actuating mechanism of nitinol wire the proposed and developed model has the impact significance in many application fields.

Development of an extended Kalman filter for the self-sensing application of a spring-biased shape memory alloy wire actuator

This report presents the development of an extended Kalman filter (EKF) to harness the self-sensing capability of a shape memory alloy (SMA) wire, actuating a linear spring. The stress and temperature of the SMA wire, constituting the state of the system, are estimated using the EKF, from the measured change in electrical resistance (ER) of the SMA. The estimated stress is used to compute the change in length of the spring, eliminating the need for a displacement sensor. The system model used in the EKF comprises the heat balance equation and the constitutive relation of the SMA wire coupled with the force–displacement behavior of a spring. Both explicit and implicit approaches are adopted to evaluate the system model at each time-update step of the EKF. Next, in the measurement-update step, estimated states are updated based on the measured electrical resistance. It has been observed that for the same time step, the implicit approach consumes less computational time than the explicit method. To verify the implementation, EKF estimated states of the system are compared with those of an established model for different inputs to the SMA wire. An experimental setup is developed to measure the actual spring displacement and ER of the SMA, for any time-varying voltage applied to it. The process noise covariance is decided using a heuristic approach, whereas the measurement noise covariance is obtained experimentally. Finally, the EKF is used to estimate the spring displacement for a given input and the corresponding experimentally obtained ER of the SMA. The qualitative agreement between the EKF estimated displacement with that obtained experimentally reveals the true potential of this approach to harness the self-sensing capability of the SMA.

嚥下機能評価のための筋骨格モデルの開発

Swallowing, or deglutition, is well known as a process to transport bolus of food from mouth to stomach, whereas it is difficult to understand its physiological mechanism because it involves in complex neuromuscular coordination. In order to understand swallowing mechanism in terms of muscle activity, we develop a musculoskeletal model in which muscles around the hyoid bone and the thyroid cartilage are represented as wire actuators. The changes of muscle lengths are calculated to estimate muscle activities during normal swallowing as a static analysis using the musculoskeletal model. The results of this study would contribute to provide greater insight into swallowing and to improve treatments for dysphagia.

Adaptive Robotic Systems Design in University of Applied Sciences

In the industry for highly specialized machine building (small series with high variety and high complexity) and in healthcare a demand for adaptive robotics is rapidly coming up. Technically skilled people are not always available in sufficient numbers. A lot of know how with respect to the required technologies is available but successful adaptive robotic system designs are still rare. In our research at the university of applied sciences we incorporate new available technologies in our education courses by way of research projects; in these projects students will investigate the application possibilities of new technologies together with companies and teachers. Thus we are able to transfer knowledge to the students including an innovation oriented attitude and skills. Last years we developed several industrial binpicking applications for logistics and machining-factories with different types of 3D vision. Also force feedback gripping has been developed including slip sensing. Especially for healthcare robotics we developed a so-called twisted wire actuator, which is very compact in combination with an underactuated gripper, manufactured in one piece in polyurethane. We work both on modeling and testing the functions of these designs but we work also on complete demonstrator systems. Since the amount of disciplines involved in complex product and machine design increases rapidly we pay a lot of attention with respect to systems engineering methods. Apart from the classical engineering disciplines like mechanical, electrical, software and mechatronics engineering, especially for adaptive robotics more and more disciplines like industrial product design, communication … multimedia design and of course physics and even art are to be involved depending on the specific application to be designed. Design tools like V-model, agile/scrum and design-approaches to obtain the best set of requirements are being implemented in the engineering studies from the early beginning.

Self-sensing SMA Actuator Using Extended Kalman Filter and Artificial Neural Network

In this paper, self-sensing capability of Shape Memory Alloy wire actuator has been explored using Extended Kalman Filter assisted Artificial Neural Network. The change in length of a linear spring actuated using a Shape Memory Alloy wire is first estimated from the variation of its electrical resistance using Extended Kalman Filter. Though the estimation is qualitatively in agreement with the experiment, the quantitative mismatch makes it difficult to control the stretch of the spring solely based on the Extended Kalman Filter estimation. An Artificial Neural Network has been used to bridge the gap between the Extended Kalman Filter estimation and actual stretch of the spring. To evaluate the effectiveness of the Extended Kalman Filter based Artificial Neural Network model, the responses of the same are compared with that of the another Artificial Neural Network model, trained only using the experimental data. It has been observed that for the same number of neurons and same training data, Extended Kalman Filter based Artificial Neural Network model yields better result at higher frequencies.

A Measurement System for Shape Memory Alloy Wire Actuators

In this paper, an experimental set-up for the measurement of actuation properties of shape memory alloy wire actuators is presented. A test rig is designed and developed to characterise shape memory alloy wire actuators. The test rig is equipped with force, displacement and temperature sensors. The test rig is validated by measuring the strain of bi-atomic nickel–titanium shape memory alloy actuators by supplying various actuation currents. At 420 mA, the 0.15-mm-diameter nickel–titanium actuators underwent 3.25% strain which lies within the guideline range (3%-4%) reported by the manufacturer of the actuators.

Enhancement in fatigue life of NiTi shape memory alloy thermal actuator wire

The effect of intermittent overload cycles (OLCs) on the fatigue life of NiTi wires has been investigated. The results showed that the OLCs were effective in enhancing the fatigue life of the NiTi wires undergoing thermo-mechanical cycling (TMC). Three distinct regions were identified in the No. of cycles to failure vs. over load ratio (OLR) plot. Region I (OLR ≤ 1.5) corresponded to threshold OLR, at and below which the OLCs did not have any effect on the fatigue behaviour of the NiTi wires. In region II (1.5 < OLR < 2.5) the fatigue life was found to increase monotonically with the increase in OLR. In region III (OLR ≥ 2.5), the increase in fatigue life was quite substantial. The actuator wire with OLCs of OLR 2.5 showed fatigue life of 3 times of that of the wire with OLR of 2.25 and 9 times of that without OLCs. Study revealed that the effect of OLCs towards enhancement in fatigue life was cumulative, and its withdrawal at any stage during the TMC resulted in a life lower than that of the wire subjected to OLCs till fracture. The presence of stabilized martensite phase in the microstructure was found beneficial towards enhancement in fatigue life and its restoration by healing treatment had a detrimental effect on the life of the actuator wires.

A Wearable Haptic Device Based on Twisting Wire Actuators for Feedback of Tactile Pressure Information

&lt;div class=""abs_img""&gt; &lt;img src=""[disp_template_path]/JRM/abst-image/00270004/12.jpg"" width=""300"" /&gt; A wearable haptic device&lt;/div&gt; This paper presents a novel wearable haptic device that provides the user with knowledge of a vertical force, measured at the fingertips, by applying pressure at three different locations on the user’s body. Human prehension and manipulation abilities rely on the ability to convert tactile information into controlled actions, such as the regulation of gripping force. Current upper-limb prosthetics are able to partially replicate the mechanical functions of the human hand, but most do not provide any sensory information to the user. This greatly affects amputees, as they must rely solely on their vision to perform grasping actions. Our device uses a twisted wire actuator to convert rotational motion into linear displacement, which allows the device to remain compact and light-weight. In the past, the main shortcoming of this type of actuator was its limited linear range of motion; but with a slight modification of the principle, we have extended our actuator’s linear range of motion by 40%. In this paper, we present the design of our haptic device, the kinematic and dynamic modelling of the actuator, and the results of the experiments that were used to validate the system’s functionality. &lt;/span&gt;

A large-stroke shape memory alloy spring actuator using double-coil configuration

One way to increase the range of motion of shape memory alloy (SMA) actuators is to create displacements of the SMA associated with not only the deformation from straining but also rigid-body motion from translation and rotation. Rigid-body motion allows the SMA to create larger displacements without exceeding the maximum recovery strain so that the SMA actuators can have a larger shape recovery ratio. To improve the linear actuation stroke of SMA wire actuators, a novel SMA spring actuator is proposed that employs a double-coil geometry that allows the displacement of the SMA to be mainly induced by rigid-body motion. A double-coil SMA spring actuator is fabricated by coiling an SMA wire twice so that the double coiling results in a reduction of the initial length of the double-coil SMA spring actuator. The effects of the geometric parameters on the actuation characteristic of a double-coil SMA spring actuator are verified numerically by finite element analysis and experimentally according to a parametric study of the geometric parameters. The displacement-to-force profile of the double-coil SMA spring actuator is nonlinear, and the spring stiffness changes when the actuator transforms its configuration from a double-coil shape to a single-coil shape. According to the results of the parametric study, increasing the wire diameter increases both primary and secondary coil stiffness, and increasing the primary inner coil diameter decreases both primary and secondary coil stiffness, whereas increasing the secondary inner coil diameter decreases only the secondary coil stiffness. The result shows that one of the double-coil SMA spring actuators with an initial length of 8 mm has a recovery ratio of 1250%, while the recovery ratio of the single-coil SMA spring actuator with the same geometric parameters is 432%.

Behavior of NiTi Wires for Dampers and Actuators in Extreme Conditions

Shape memory alloys are considered smart materials because of their singular thermo-mechanical properties, due to a thermoelastic martensitic transformation, enabling possible uses as actuators (because of mechanical recovery induced from temperature changes) and as dampers (because of hysteresis). NiTi wires for dampers in Civil Engineering had been characterized and tested in facilities. Guaranteed performance needs to know behavior during fatigue life and knowledge of effects in the event of extreme conditions, as eventual overstraining. In this work, we check the possibilities to absorb mechanical energy on the fatigue life depending on stress level and explore the consequences of overstraining the material during installation, the possibilities of partial healing by moderate heating, and some effects of over-stressing the wires. The mechanical energy absorbed by the unit weight of damper wire might be very high during its lifetime if maximum stresses remain relatively low allowing high fatigue life. We show also some results on NiTi wire working as an actuator. The lifetime mechanical work performed by an actuator wire can be very high if applied stresses are limited. The overstraining produces relevant “residual” deformation, which can be to some extent reversed by moderate heating at zero stress. The reason for the observed characteristics seems to be that when external high stresses are applied to an NiTi wire, it undergoes some plastic deformation, leaving a distribution of internal stresses that alter the shape and position of the macroscopic stress-strain transformation path.

Time-delayed dynamic neural network-based model for hysteresis behavior of shape-memory alloys

Shape-memory alloys (SMAs) have received considerable amount of attentions for their engineering applications in recent years. The hysteresis in SMAs is sensitive to the state-varying tendency and frequency. Utilizing past information to estimate the hysteretic behavior gets increasing attention. In this paper, a time-delayed dynamic neural network (TDDNN) is proposed for modeling hysteresis of SMAs in online applications. By introducing a time delay between the input and output response, the TDDNN considers the time delay's effect on the hysteresis. This proposed network was applied to a SMA wire actuator. Experimental results demonstrate the effectiveness of TDDNN. The identified results obtained by TDDNN are better than those obtained by dynamic neural network without considering the delay information. It demonstrates the importance of introducing the time delay. The different values of time delay item can also affect TDDNN's identified results.

Feasibility of Shape Memory Alloy Wire Actuation for an Active Steerable Cannula

Needle insertion is used in many diagnostic and therapeutic percutaneous medical procedures such as brachytherapy, thermal ablations, and breast biopsy. Insufficient accuracy using conventional surgical cannulas motivated researchers to provide actuation forces to the cannula's body for compensating the possible errors of surgeons/physicians. In this study, we present the feasibility of using shape memory alloy (SMA) wires as actuators for an active steerable surgical cannula. A three-dimensional (3D) finite element (FE) model of the active steerable cannula was developed to demonstrate the feasibility of using SMA wires as actuators to bend the surgical cannula. The material characteristics of SMAs were simulated by defining multilinear elastic isothermal stress–strain curves that were generated through a matlab code based on the Brinson model. Rigorous experiments with SMA wires were done to determine the material properties as well as to show the capability of the code to predict a stabilized SMA transformation behavior with sufficient accuracy. In the FE simulation, birth and death method was used to achieve the prestrain condition on SMA wire prior to actuation. This numerical simulation was validated with cannula deflection experiments with developed prototypes of the active cannula. Several design parameters affecting the cannula's deflection such as the cannula's Young's modulus, the SMA's prestrain, and its offset from the neutral axis of the cannula were studied using the FE model. Real-time experiments with different prototypes showed that the quickest response and the maximum deflection were achieved by the cannula with two sections of actuation compared to a single section of actuation. The numerical and experimental studies showed that a highly maneuverable active cannulas can be achieved using the actuation of multiple SMA wires in series.

Design of an Optically Controlled MR-Compatible Active Needle.

An active needle is proposed for the development of magnetic resonance imaging (MRI)-guided percutaneous procedures. The needle uses a low-transition-temperature shape memory alloy (LT SMA) wire actuator to produce bending in the distal section of the needle. Actuation is achieved with internal optical heating using laser light transported via optical fibers and side coupled to the LT SMA. A prototype, with a size equivalent to a standard 16-gauge biopsy needle, exhibits significant bending, with a tip deflection of more than 14° in air and 5° in hard tissue. A single-ended optical sensor with a gold-coated tip is developed to measure the curvature independently of temperature. The experimental results in tissue phantoms show that human tissue causes fast heat dissipation from the wire actuator; however, the active needle can compensate for typical targeting errors during prostate biopsy.

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.

Design and investigation of a shape memory alloy actuated gripper

This paper proposes a new design of shape memory alloy (SMA) wire actuated gripper for open mode operation. SMA can generate smooth muscle movements during actuation which make them potentially good contenders in designing grippers. The principle of the shape memory alloy gripper is to convert the linear displacement of the SMA wire actuator into the angular displacement of the gripping jaw. Steady state analysis is performed to design the wire diameter of the bias spring for a known SMA wire. The gripper is designed to open about an angle of 22.5 when actuated using pulsating electric current from a constant current source. The safe operating power range of the gripper is determined and verified theoretically. Experimental evaluation for the uncontrolled gripper showed a rotation of 19.97. Forced cooling techniques were employed to speed up the cooling process. The gripper is simple and robust in design (single movable jaw), easy to fabricate, low cost, and exhibits wide handling capabilities like longer object handling time and handling wide sizes of objects with minimum utilization of power since power is required only to grasp and release operations.