An earthworm-like micro robot using shape memory alloy actuator

A novel bio-mimetic micro robot with wireless control and wireless power supply using shape memory alloy (SMA) actuator is developed. There have been many kinds of mobile micro robot using the micro actuators such as ionic polymer metal composite (IPMC), micro motors and piezo actuators. These actuators generally require electric cable for power supply, which might highly influence the mobility of the micro robot. Therefore, a perfect wireless micro robot comprising telemetry and batteries is realized using only one SMA spring actuator and one silicone bellow. The SMA actuator and bellow play a role in contraction and extension of an earthworm muscle respectively. Based on theoretical analysis, specifications of a SMA actuator and a bellow are properly selected. For temporal stopping, setae of earthworm mimicked claws are employed. On the issue of control, the proposed robot is controlled according to On/Off signal via wireless communication. The operation is customized through tuning of on-/off-time of an actuator and using different type batteries such as a lithium, silver oxide and alkaline battery. After the design and experiment, we find out that the earthworm-like micro robot without wired power supply and control can move freely without limitation of working space and be fabricated easily.     

形状记忆合金驱动器的自适应滑模反步控制

形状记忆合金(SMA)作为一种智能材料,相对于传统的驱动器具有功率重量比大、驱动电压低、质量轻、干净、无噪音等特性,被广泛应用在各领域.然而,非线性、迟滞、时变等因素影响了形状记忆合金的控制精度,限制了它的应用.为此,本文提出了自适应滑模反步控制方法,用于解决精确控制问题.文中首先搭建了实验装置,建立了形状记忆合金的机理模型;然后,采用最小二乘算法辨识了模型参数;最后,基于机理模型设计了自适应滑模反步控制器.实验结果表明,本文提出的方法具有动态响应快、跟踪精度高和抗干扰能力强的特性.     

Design and characterization of a multi-stable magnetic shape memory alloy hybrid actuator

This paper describes the design and the characterization of a multi-stable hybrid actuator composed of a single magnetic shape memory alloy element and an electromagnetic actuator. The series arrangement of the active material and the electromagnetic actuator allows a new shape of hysteresis curve and a precise positioning can be obtained. The design of the different magnetic circuits has been done by analytic and numeric simulations in MatLab and FEMM 4.2. This study gives results of the elongation, the blocking force, and the holding force that can be obtained with such an actuator. Strokes up to 0.35 mm and a blocking force of 2.6 N have been measured for the hybrid actuator using a magnetic shape memory alloy with a cross section of 2.5 mm². Such an actuator can find application in precise positioning and medium frequency actuation systems. Nevertheless, there is much design space for improvements in terms of energy consumption, heat transfer, and overall cost of the device.     

Robust design of a shape memory actuator with slider and slot layout and passive cooling control

Microsystem Technologies - This work proposes a new shape memory actuator based on a slider and slot mechanism. The device is composed by two couples of opposed SMA coil elements. The SMA elements...     

Nitinol one-way shape memory springs: Thermomechanical characterization and actuator design

One-way shape memory effect (OWSME) in NiTi springs has been investigated in this work. The main goal is the definition of a guide-line for the design of a linear actuator for high cycles duty. Some SMA and steel springs with various geometrical features have been produced from wires with different diameters. SMA spring's behavior has been analyzed measuring the maximum length (austenitic condition, T > A_F – austenite finish) under different applied loads. The measurement of this length has been performed at successive thermomechanical complete working cycles (150, 5350, 43,000 and 600,000) under a constant applied load necessary to full recovery in the martensitic phase. It has been found that the higher the thermomechanical cycles the lower the reached maximum length. In particular the length loss is negligible at higher cycles. Starting from these considerations and the knowledge of the mechanical characteristics of the springs, a linear actuator (SMA spring–harmonic steel spring) for high-cycle duty can be designed. The right working conditions have been verified too.     

Modeling of shape memory alloy shells for design optimization

A three-dimensional phenomenological constitutive model for the analysis and design optimization of shape memory alloy (SMA) structures is presented. This model specifically targets the pseudoelastic behavior due to the R-phase transformation in NiTi alloys, but also applies to similar SMA materials with low hysteresis. A history-independent formulation is presented, which allows cost-effective sensitivity analysis. The possibility to efficiently compute design sensitivities is essential for enabling the use of gradient-based optimization algorithms, which will allow design optimization of complex SMA structures. The use of the constitutive model in a problem of realistic complexity is illustrated by the analysis of a SMA miniature gripper, modeled using shell elements. The sensitivity analysis of SMA structures using the presented model is addressed in an accompanying paper.     

On thermodynamic active control of shape memory alloy wires

We propose a model for the control of high-frequency oscillations in shape memory alloy wires. We introduce a notion of generalized solution for a generalized control and in this context prove a local exact controllability result effectively corresponding to an approximate controllability result for the nonconvex pseudoelastic material system.     

Modeling and time delay control of shape memory alloy actuators

Shape memory alloy (SMA) actuators possess hard nonlinearities including backlash-like hysteresis and saturation. These nonlinearities result in steady-state error and limit-cycle problems when conventional controllers such as the proportional integral derivative (PID) are used for trajectory control. In this study, a dynamics for an SMA actuator was newly derived using the modified Liang's model. The derived dynamics showed continuity at the change of the phase transformation process, but the original model could not. SMA actuator characteristics could be well described using this dynamics. The derived dynamics could be also used effectively for the prediction of control performance and gain tuning of the time delay control (TDC). The dynamics consisted of first-order linear and second-order nonlinear equations. Accordingly, a control strategy was established for the TDC to regulate only the second-order nonlinear part for simplicity and for the internal closed loop to regulate the rest. The control strategy was examined from the point of view of influence of an antiwindup scheme and high gain tuning on control performance. An anti-windup scheme was essential to protect windup phenomenon and high gain tuning was effective when a temperature disturbance existed. In the robustness test, the TDC with high gains showed robustness to inertia variation and temperature disturbance in comparison with the TDC with low gains.     

SMA在星载天线上的热变形控制研究

为了保证星载大型可展开桁架天线在轨运行时能可靠的工作,就必须对其进行在轨热变形控制.通过使用ANSYS软件对可展开天线加入NiNi形状记忆合金丝且在轨道的不同位置点的情况进行了计算,得出了天线反射面的均方根误差.通过研究可以发现,在周边桁架天线中嵌入SMA后减小了天线反射面的均方根误差,从而达到了保证天线型面精度的目的.     

Design of membrane actuator based on ferromagnetic shape memory alloy composite for synthetic jet applications

The active flow control (AFC) technology has been studied and shown that it can help aircraft improve aerodynamic performance and jet noise reduction. AFC can be achieved by a synthetic jet actuator injecting high momentum air into the airflow at the appropriate locations on aircraft wings. To produce strong synthetic jet flow at high frequency, a new membrane actuator based on ferromagnetic shape memory alloy (FSMA) composite and hybrid mechanism was designed and constructed. The hybrid mechanism is the stress-induced martensitic phase transformation caused by large force due to large magnetic field gradient, thus enhancing the displacement, as the stiffness of shape memory alloy reduces due to the martensitic transformation. This sequential event can take place within milliseconds. The high momentum airflow will be produced by the oscillation of the circular FSMA composite diaphragm close to its resonance frequency driven by electromagnets. Due to large force and martensitic transformation on the FSMA composite diaphragm, the membrane actuator that we designed can produce 190 m/s synthetic jets at 220 Hz.     

Normally closed plunger-membrane microvalve self-actuated electrically using a shape memory alloy wire

Various microfluidic architectures designed for in vivo and point-of-care diagnostic applications require larger channels, autonomous actuation, and portability. In this paper, we present a normally closed microvalve design capable of fully autonomous actuation for wide diameter microchannels (tens to hundreds of µm). We fabricated the multilayer plunger-membrane valve architecture using the silicone elastomer, poly-dimethylsiloxane (PDMS) and optimized it to reduce the force required to open the valve. A 50-µm Nitinol (NiTi) shape memory alloy wire is incorporated into the device and can operate the valve when actuated with 100-mA current delivered from a 3-V supply. We characterized the valve for its actuation kinetics using an electrochemical assay and tested its reliability at 1.5-s cycle duration for 1 million cycles during which we observed no operational degradation.     

A neural differential evolution identification approach to nonlinear systems and modelling of shape memory alloy actuator

This paper proposes a hybrid modified differential evolution plus back‐propagation (MDE‐BP) algorithm to optimize the weights of the neural network model. In implementing the proposed training algorithm, the mutation phase of the differential evolution (DE) is modified by combining two mutation strategies rand/1 and best/1 to create trial vectors instead of only using one mutation operator or rand/1 or best/1 as the standard DE. The modification aims to balance the global exploration and local exploitation capacities of the algorithm in order to find potential global optimum solutions. Then the local searching ability of the back‐propagation (BP) algorithm is applied in that region so as to swiftly converge to the optimum solution. The performance and efficiency of the proposed method is tested by identifying some benchmark nonlinear systems and modeling the shape memory alloy actuator. The proposed training algorithm is compared with the other algorithms, such as the traditional DE and BP algorithm. As a result, the proposed method can improve the accuracy of the identification process.     

形状记忆合金手指系统的输出力自适应控制

形状记忆合金(SMA)是智能材料中的一种,具有功率重量比大、质量轻、无噪音等特性.作为驱动器有利于结构的小型化和轻型化.然而SMA的非线性、多映射的迟滞特性严重影响了输出力的精确控制.为此,本文提出了基于扰动补偿策略的自适应控制方法用于SMA输出力的精确控制.首先,搭建了SMA驱动的手指实验装置,建立了机理模型;其次,...     

Bio-inspired Actuating System for Swimming Using Shape Memory Alloy Composites

The paper addresses the designs of a caudal peduncle actuator, which is able to furnish a thrust for swimming of a robotic fish. The caudal peduncle actuator is based on concepts of ferromagnetic shape memory alloy (FSMA) composite and hybrid mechanism that can provide a fast response and a strong thrust. The caudal peduncle actuator was inspired by Scomber Scombrus which utilises thunniform mode swimming, which is the most efficient locomotion mode evolved in the aquatic environment, where the thrust is generated by the lift-based method, allowing high cruising speeds to be maintained for a long period of time. The morphology of an average size Scomber Scombrus (length in 310 mm) was investigated, and a 1:1 scale caudal peduncle actuator prototype was modelled and fabricated. The propulsive wave characteristics of the fish at steady speeds were employed as initial design objectives. Some key design parameters are investigated, i.e. aspect ratio (AR) (AR = 3.49), Reynolds number (Re = 429649), reduced frequency (σ= 1.03), Strouhal number (St = 0.306) and the maximum strain of the bent tail was estimated atε= 1.11% which is in the range of superelasticity. The experimental test of the actuator was carried out in a water tank. By applying 7 V and 2.5 A, the actuator can reach the tip-to-tip rotational angle of 85°at 4 Hz.     

Uncertainty of shape memory alloy micro-actuator using generalized polynomial chaos method

Microsystem Technologies - In last decades, there has been an increasing interest in the use of micromachining technology. Intelligent materials such as shape memory alloy are considered for the...     

Modeling and control of a finger-like mechanism using bending shape memory alloys

Microsystem Technologies - In this research a biologically inspired finger-like mechanism similar to human musculoskeletal system is developed based on Shape Memory Alloys (SMAs). SMA actuators are...     

Path optimization and control of a shape memory alloy actuated catheter for endocardial radiofrequency ablation

This paper introduces a real-time path optimization and control strategy for shape memory alloy (SMA) actuated cardiac ablation catheters, potentially enabling the creation of more precise lesions with reduced procedure times and improved patient outcomes. Catheter tip locations and orientations are optimized using parallel genetic algorithms to produce continuous ablation paths with near normal tissue contact through physician-specified points. A nonlinear multivariable control strategy is presented to compensate for SMA hysteresis, bandwidth limitations, and coupling between system inputs. Simulated and experimental results demonstrate efficient generation of ablation paths and optimal reference trajectories. Closed-loop control of the SMA-actuated catheter along optimized ablation paths is validated experimentally.     

Experimental comparison of classical PID and model-free control: Position control of a shape memory alloy active spring

Shape memory alloys (SMA) are being more frequently integrated into engineering applications. These materials with their shape memory effect enable the simplification of mechanisms and the reduction in size of actuators. SMA parts can easily be activated by Joule effect but their modeling and consequently their control remains difficult. It is principally due to their non-linear hysteretic thermomechanical behavior. Most of successful control strategies applied to SMA actuators are not often suitable for industrial applications: they are particularly heavy and use the Preisach model or neural networks to model the hysteretic behavior of these materials; this kind of model is difficult to identify and to use in real time. This paper deals with an application of the new framework of model-free control (MFC) of an SMA-spring based actuator. This control strategy relies on new results for fast derivative estimation of noisy signals. Their main advantages are: its simplicity and its robustness. Experimental results and comparisons with PI control are presented that demonstrate the efficiency of this new control strategy.     

Sensitivity analysis of shape memory alloy shells

This paper presents procedures for efficient design sensitivity analysis for shape memory alloy (SMA) structures modeled with shell elements. Availability of sensitivity information at low computational cost can dramatically improve the efficiency of the optimization process, as it enables use of efficient gradient-based optimization algorithms. The formulation and computation of design sensitivities of SMA shell structures using the direct differentiation method is considered, in a steady state electro-thermo-mechanical finite element context. Finite difference, semi-analytical and refined semi-analytical sensitivity analysis approaches are considered and compared in terms of efficiency, accuracy and implementation effort, based on a representative finite element model of a miniature SMA gripper.