Advances in dielectric elastomer actuation technology

Dielectric elastomer actuators (DEAs) have attracted much interest over the past decades due to the inherent flexibility, large strain, high efficiency, high energy density, and fast response of the material, which are known as one of the most promising candidates for artificial muscle. In this paper, we first introduce the actuation principle and electromechanical modeling approaches of dielectric elastomers (DEs). Then, the performance of different DEs material and existing compliant electrodes that are widely utilized for DEAs are presented. We also highlight the compatibility of DEs, which is suitable for a variety of actuator designs and applications. Lastly, we summarize the challenges and future development in terms of electromechanical modeling, improvement of materials including compliant electrodes and dielectric elastomer, designs and applications of novel dielectric elastomer actuators.     

介电弹性材料驱动器在机器人中的应用进展

简要介绍介电弹性材料驱动器的基本原理、结构组成及其在机器人中的应用现状,重点分析介电弹性材料性能的理论研究进展,包括材料特性、本构理论、失效模式及稳定性等.总结介电弹性材料驱动器对柔性电极性能的要求,并对柔性电极工艺特性进行具体分析,深入探讨介电弹性驱动器目前所面临的挑战,对介电弹性材料驱动器在机器人系统中的应用前景进行了展望.     

电场活化聚合物材料特性的数学建模研究与分析

电场活化聚合物在直流电场作用下会产生大幅度的应变.在定量试验研究的基础上,采用Monney-Rivlin理论建立了电场活化聚合物变形特性的数学模型,有效地验证了电场活化聚合物的变形特性,分析了材料在不同状态下的力学特性.     

电场活化聚合物的破坏机理分析

以电场活化聚合物试验为基础,对它在电场中发生破坏的机理进行分析,提出用单位厚度上的极限电压表征电场活化聚合物抗电击穿破坏的强度,并揭示了预拉伸不仅能加快电场活化聚合物在电场力作用下的响应速度,提高变形率,降低工作电压,而且能大幅度提高其抗电击穿破坏的强度.     

Analysis of progressive failure of pillar and instability criterion based on gradient-dependent plasticity

A mechanical model for strain softening pillar is proposed considering the characteristics of progressive shear failure and strain localization. The pillar undergoes elastic, strain softening and slabbing stages. In the elastic stage, vertical compressive stress and deformation at upper end of pillar are uniform, while in the strain softening stage there appears nonuniform due to occurrence of shear bands, leading to the decrease of load-carrying capacity.In addition, the size of failure zone increases in the strain softening stage and reaches its maximum value when slabbing begins. In the latter two stages, the size of elastic core always decreases. In the slabbing stage, the size of failure zone remains a constant and the pillar becomes thinner. Total deformation of the pillar is derived by linearly elastic Hooke‘s law and gradient-dependent plasticity where thickness of localization band is determined according to the characteristic length. Post-peak stiffness is proposed according to analytical solution of averaged compressive stressaverage deformation curve. Instability criterion of the pillar and roof strata system is proposed analytically using instability condition given by Salamon. It is found that the constitutive parameters of material of pillar, the geometrical size of pillar and the number of shear bands influence the stability of the system; stress gradient controls the starting time of slabbing, however it has no influence on the post-peak stiffness of the pillar.     

Adjustable stiffness elastic composite soft actuator for fast-moving robots

The application of soft pneumatic actuators is typically hindered by the low strength and slow response speed caused by their intrinsic material limitation and unstressed stable form. In this work, we present a design strategy for improving the performance and response speed for Pneu-Nets actuators by incorporating adjustable elastic components to form the elastic composite pneumatic actuator(ECPA). The elastic energy storage of the elastic component is implemented to enhance the capability and speed up the response of ECPA and pre-bend the actuator. Due to the design principle, the fully-flexible ECPA is easy to manufacture and regulate. Theoretical modeling and experiments are implemented to reveal the fast response characteristics and adjustable mechanical characteristics of ECPA. Experimental results show that the deflation response speed of ECPA is increased by at least 3.1 times with the action of elastic components, what is more, the stiffness of ECPA is increased by 22 times. Based on the ECPA, two kinds of locomotion robots including a running robot(runs at an average locomotion speed of 6.3 BL/s(body lengths, BL)) and an underwater swimming robot(achieves an average speed of 1.1 BL/s) are designed. The fast-moving robots both demonstrate high-speed mobility because of the rapid response and high strength of ECPA.     

A soft gripper of fast speed and low energy consumption

Grasping of complicated objects is an active research area which is developing fast throughout the years. Soft grippers can be an effective solution, since they are capable of holding workpieces of various shapes and interacting with unstructured environments effectively. Soft grippers generally consist of soft, flexible and compliant materials, which are able to conform to the shape of the object so that the gripper will not deform or bruise the soft object. Fast grasping of objects with various sizes and shapes remains a challenging task for soft grippers. In the present article, a soft gripper based on bi-stable dielectric elastomer actuator(DEA) inspired by the insect-catching ability of the Venus flytrap, is designed. This soft gripper can achieve good performances in grasping various objects by a simple actuation system. The gripper can switch from one stable state to another when subject to an impulse voltage of 0.04 s. The time duration for each grasping action is 0.17 s, and no continuous voltage is required for holding the gripped object. Thus, energy consumption can be achieved as low as 0.1386 J per grasping action. The mechanism of achieving bi-stable states is related to the duration of impulse voltage applied and the resonant frequency of the structure. The present study demonstrates that bi-stable dielectric elastomer actuators are capable of achieving fast speed for grasping with very low energy consumption, which is significant in the applications to soft grippers and biomimetic robots.     

非均匀电介质边缘效应的研究

论述了非均匀电介质中电极边缘电场强度的理论和计算方法,表明如果材料介电常数随着接近电极边缘而增大,非均匀电介质电场强度增益系数会大大低于均匀电介质电场强度的增益系数.非均匀电介质材料影响空间测量特性和电场对称性,以致在非均匀电介质中采用平面电极设计得到电场强度的分布规律类似于均匀电介质非对称装置中电场强度的分布.     

基于电磁模型的大气压表面波等离子体数值模拟

针对表面波等离子体模拟复杂程度高和计算工作量大的问题,提出基于电磁模型来开展大气压等离子体的数值模拟.根据表面波等离子体的放电特性,合理建立和简化电磁模型.通过对比实验诊断与数值计算结果,验证了模型的可靠性及其参数适用范围,拟合得到的电子有效碰撞频率((1.5±0.25)×1011 s?1)与实验测量值吻合.在此基础上...     

Method towards optimal design of dielectric elastomer actuated soft machines

Soft machines are combinations of hard and soft active materials, thus the coupling and interaction between soft and hard components dictate the performance of soft machines. Structural optimization has been intensively used for design of conventional hard machines, while, to our best knowledge, few attempts have been made towards optimal design of soft machines. Here, we describe the sizing optimization problem of a dielectric elastomer (DE) actuated mechanical amplifier, and achieve the optimal design through combination of a commercial finite element method (FEM) software and an optimization automation software. We then design, fabricate and demonstrate a locomotive soft machine driven by DE actuator with amplified displacement output. The methodology and results present here open the door towards optimal designs of active materials based soft machines.     

横场长度伸缩压电陶瓷振子

本文对典型的横场长度伸缩压电陶瓷振子的振动状态进行了分析并得到其等效电路。推导了振子的谐振频率、反谐振频率、等效电路参数与振子材料的介电常数、压电常数、弹性常数之间的关系式。最后讨论了振子的某些特性。     

Control of endwall secondary flow in a compressor cascade with dielectric barrier discharge plasma actuation

Three dielectric barrier discharge plasma actuators were mounted at the positions of 20%, 40% and 60% of chord length on the endwall in a compressor cascade. The downstream flow field of the cascade has been measured with a mini five-hole pressure probe with and without the plasma actuation. The measured results show that the plasma actuation most effectively reduces total pressure loss and flow blockage when the actuators are operated simultaneously. As each of the actuators is operated independently, the actuator at the position of 20% of chord length most effectively reduces flow blockage, and the actuator at the position of 60% of chord length fairly reduces total pressure loss. However, negative pressure loss reduction occurs with the plasma actuator at the position of 40% of chord length. In brief, the plasma actuation placed on the endwall in the cascade apparently influences the endwall secondary flow, and the optimal locations and strength of actuation are critical for the control of endwall secondary flow in a compressor cascade with the plasma actuators.     

高压电场下凝结液膜的不稳定性分析

在自行设计、制作的强化凝结换热模型基础上,以R11为工质,对高压电场下的凝结液膜进行了实验分析,得出了表面微扰的增长行为取决于表面能,弹性势能,电能的交互作用关系,电场既可以加强也可以抑制表面微扰引发的表面不稳定性.所以在适当的电场强度下,可以促使液膜凝结成珠状或假珠状,明显提高强化换热系数.     

CNFs/EVA复合材料的介电性能

将表面金属化的纳米碳纤维(CNFs)与乙烯-醋酸乙烯酯(EVA)在平行磁场作用下进行复合,压片制得厚度为0.4 mm的薄膜样品。所得产品利用扫描电镜(SEM)进行表征,观察到薄膜的脆断面上存在大量的纳米碳纤维末端,证明CNFs在EVA中取向分布。对薄膜样品进行介电谱性能测试,结果表明,CNFs/EVA取向复合材料在高频电场环境中的介质损耗因数降低,且取向复合材料的介质损耗因数与掺杂CNFs质量分数有关,在较高掺杂量时,高频电场环境下的介质损耗因数降低。     

壁电荷电场对介质阻挡放电时空特性的影响

通过对介质阻挡放电中壁电荷电场强度、电势以及静电能的分析,说明了实验获得的正方结构斑图的稳定性。     

交变电磁场对电容的影响

在静电场中电容器的电容决定于电容器的结构、几何状态、尺寸以及两极板之间材料的介电常数。但是在交变电磁场中,电容器的电容和多种因素有关。本文运用叠加原理,从麦克斯韦方程的积分形式出发推导出在交变电磁场中储藏在电容器中的电场能量,并且指出了决定电容器电容数值的因素。     

液晶单分子膜光电效应的研究

采用LB膜技术制备了液晶／花生酸混合膜，利用表面等离极化激元（SPP）技术对液晶单分子膜电光效应进行了研究，其结果表明：在电场作用下液晶／花生酸混合膜的SPP谱的共振峰变窄，共振角的位置也发生变化，即电场作用使得单分子膜的介电常数发生变化，单分子膜的这种电光效应与电场的频率无关。     

A comparative analysis of dielectric properties of oil-paper insulation and polymer materials before and after thermal aging

The shortcomings of oil-immersed transformer solid insulation like low high-temperature resistance of the insulation paper and the uneven distribution of electric field caused by the large difference of dielectric constants between insulation paper and transformer oil,restricted the development of transformer with smaller size and larger capacity.In view of this situation and the transformer’s demand for the dielectric physicochemical and mechanical property of insulation material,polycarbonate,polyester film and polyphenylene sulfide with high high-temperature resistance were chosen for the comparison analysis in this paper We did the 300-day thermal aging experiment on four samples in transformer oil under different aging temperatures of90°C,110°C and 130°C,then analyzed the changes of their dielectric properties.The experiment results are as follows;the permittivity and dielectric dissipation factor of the three polymer materials are apparently smaller than those of the paper both before and after 300-day aging;the volume resistivity and partial discharge inception voltage of the three materials are higher than those of the paper both before and after aging;and the breakdown field strength of polycarbonate is higher than that of the paper both before and after aging,while that of polyester film and polyphenylene sulfide are slightly lower than that of the paper.     

压电致动式圆片驱动装置结构分析与设计

根据压电致动的工作原理,建立了圆片微驱动装置的压电复合层薄板的机电耦合力学模型;应用弹性薄板的小挠度弯曲理论,推导出圆形压电复合层薄板的弹性曲面微分方程,提出由逆压电效应引起的平面应变可以等效为作用在压电复合层薄板上的横向荷载的设计方法;指出等效横向荷载取决于平行板电容器的边缘电场分布.推导了压电复合层薄板中性面的表达式.在求电场的超越方程数值解的基础上,建立了微驱动装置的有限元结构模型,并对某微泵驱动装置进行了计算仿真,得到令人满意的结果.     

微型超磁致伸缩高速阀致动器的优化设计

通过优化设计驱动线圈和Terfenol-D的形状尺寸,改善以超磁致伸缩材料Terfenol-D为主动材料的高速开关阀的性能.选择合适的漆包线线径以降低线圈电阻;优化线圈形状函数以提高线圈的磁场生成能力;改善Terfenol-D的尺寸来降低磁通路径的磁阻,减小涡流损耗,提高致动器的磁场利用率;兼顾提高致动器的能量转换效率,提出优化设计超磁致伸缩致动器的规律.两个致动器的实验对比验证了该设计方法的可行性.