小型自感应原子力显微镜测头及其标定

设计了一种小型轻敲式自感应原子力显微镜(AFM)测头以实现微/纳尺度下的几何量测量.轻敲式测头采用石英音叉式自感应探针,通过自身的电信号输出检测悬臂梁的振幅变化,无需额外的光学传感器.设计了测头的微弱自感应信号放大电路,并补偿音叉寄生电容对测量的干扰.机械结构紧凑便于将测头固定于光学显微镜下观察测量情况,同时屏蔽外界的干扰.利用显微激光多普勒测振系统,标定了测头机电耦合系数为145 nm/V,由此可以计算测头工作频率下悬臂梁的振幅.搭建了以纳米测量机(NMM)为高精度定位平台的测试系统,利用该系统对测头进行进/退针实验,标定测头的灵敏度为0.47 nm/mV,NMM内置的干涉仪保证标定直接溯源至"米"定义.实验表明测头的非线性误差小于1%,测量范围在百纳米级.     

基于卡尔曼滤波和高频信号注入法的永磁同步电机转子位置自检测

永磁同步电机的运动控制是一个强耦合的非线性动态控制系统,而且在控制过程中测量数据带有噪声,采用传统的线性控制理论很难达到系统要求.提出一种非线性系统的随机观测器——卡尔曼位置观测器,它用于高频信号注入法下的转子位置检测.利用脉动高频信号注入法进行永磁同步电机转子位置自检测,将产生的高频载波电流解调后,送入设计的卡尔曼位置观测器,可有效去除干扰噪声,准确观测出转子位置.仿真实验结果表明,在有系统噪声和测量噪声的情况下,基于卡尔曼位置观测器的脉动高频信号注入法能够精确地跟踪转子位置.     

无轴承同步磁阻电机最小二乘法转子位移自检测策略

位移传感器是无轴承同步磁阻电机悬浮运行时转子位置闭环可控的关键部件,但装配多个位移传感器阻碍了无轴承同步磁阻电机的低成本实用化和结构简单化,由此提出最小二乘法转子位移自检测（无传感器）策略。基于电机悬浮绕组和转矩绕组的磁链、电压和电流状态方程,重构最小二乘法转子位移检测模型,通过采样两套绕组电压和电流,应用最小二乘递推算法对转子位移进行在线辨识。仿真实验表明,该方法能准确实现无传感器工况下转子位移自检测,检测系统有较强的负载扰动适应性。     

Strain self-sensing of a piezoelectric material using phase delay compensation

This paper deals with analytical modeling and experimental verification of strain self-sensing. Three strain self-sensing methods are investigated, including a conventional method with a capacitance bridge, an adaptive filter, and phase delay compensation to minimize the effect of the phase delay from a piezoelectric material. The piezoelectric beam consists of two laminated lead zirconium titanates (PZT) on a metal shim and generates bi-directional movement. A mathematical model of the beam dynamics is derived by Hamilton's principle, and the accuracy of the modeling is verified by comparison with experimental results. The efficacy of these methods is investigated by comparison of the experimental results with a prediction from the derived analytical model. It turns out that the method using the newly proposed phase delay compensation gives more accurate results for strain self-sensing performance than each of the other two methods.     

压电纤维复合材料在结构减振中的应用

介绍了压电纤维复合材料,并利用该材料设计了自传感驱动器,并将其应用于梁的频响辨识。将该材料用于飞机垂尾的减振系统,目的是为了抑制在飞行过程中产生的振动和测试压电纤维复合材料在尾翼振动主动控制方面的性能表现。试验结果表明,该材料具有良好的传感和驱动性能,并且减振效果优于压电陶瓷。     

Self-Sensing Cementitious Composites with Hierarchical Carbon Fiber-Carbon Nanotube Composite Fillers for Crack Development Monitoring of a Maglev Girder

In view of high-performance, multifunctional, and low-carbon development of infrastructures, there is a growing demand for smart engineering materials, making infrastructures intelligent. This paper reports a new-generation self-sensing cementitious composite (SSCC) incorporated with a hierarchically structured carbon fiber (CF)-carbon nanotube (CNT) composite filler (CF-CNT), which is in situ synthesized by directly growing CNT on CF. Various important factors including catalyst, temperature, and gas composition are considered to investigate their kinetic and thermodynamic influence on CF-CNT synthesis. The reciprocal architecture of CF-CNT not only alleviates the CNT aggregation, but also significantly improves the interfacial bonding between CF-CNT and matrix. Due to the synergic and spatially morphological effects of CF-CNT, that is, the formation of widely distributed multiscale reinforcement networks, SSCCs with CF-CNTs exhibit high mechanical properties and electrical conductivity as well as excellent self-sensing performances, particularly enhanced sensing repeatability. Moreover, the SSCCs with CF-CNTs are integrated into a full-scale maglev girder to devise a smart system for crack development monitoring. The system demonstrates high sensitivity and fidelity to capture the initiation of cracks/damage, as well as progressive and sudden damage events until the complete failure of the maglev girder, indicating its considerable potential for structural health monitoring of infrastructures.     

DC electric polarization of cured cement paste being unexpectedly hindered by free water

Electric polarization is basic to the dielectric behavior, which is pertinent to the science and applications of cement-based materials. This work reports the dynamics of the DC-current-induced electric polarization/depolarization of cured cement paste and their dependence on the water/cement ratio. This dependence has not been previously reported for any cement-based material. The extent of the polarization is unexpectedly found in this work to decrease as the water/cement ratio increases, indicating that the free water hinders the polarization. This hindrance is due to (i) the dominance of ions behind the polarization (as supported by the previously reported increase in permittivity with increasing temperature), and (ii) the polar water molecules partly shielding the ions from the applied electric field. The fraction of ions in the pore solution that participates in the polarization increases with the polarization time and is 4.5 × 10^-14 for 570 s of polarization at a current of 1 μA for water/cement ratio 0.35. Upon increasing the water/cement ratio (0.3–0.4), the polarization rate decreases, the polarization extent at a given polarization time decreases, and the time to reach polarization saturation decreases. The polarization/depolarization rate decreases as the current application progresses because the polarization/depolarization hinders further polarization/depolarization. The degree of this hindrance increases with increasing water/cement ratio. Thus, a higher water/cement ratio is preferred if less polarization is desired as in resistance-based self-sensing, whereas a lower water/cement ratio is preferred if more polarization is desired as in capacitance-based self-sensing.     

基于自感知执行器原理的调谐滤波器

根据自感知执行器的工作原理,利用一只变压器完成谐波检测和抑制两种功能,处于正常工作状态时可实现谐波抑制,处于非正常工作状态时不致放大谐波。首先对工频信号进行数字采样,再利用自相关函数法结合递推最小二乘估计工频信号的频率,再根据该频率产生反向抑制谐波,来抑制当前谐波。为实时调整各次反向抑制谐波的权重,根据当前时刻的谐波抑制的结果,采取最小均方自适应算法来更新权重。模拟试验表明,该调谐滤波器具有良好的控制特性。     

智能结构中压电驱动器产生的局部应变场分析

为研究压电驱动元件产生局部应变的机理,设计了一两端固支梁模型,通过ANSYS有限元分析软件,比较了结构不同位置压电传感元件的感应电压,同时对局部应变值进行了数值分析,探讨了其产生因素,最后通过试验验证了局部应变的存在.     

磁悬浮开关磁阻电机径向位移自检测

针对传统位移传感器灵敏度容易受温度和电磁噪声干扰,增大电机体积和结构复杂度等问题,在研究磁悬浮开关磁阻电机转矩绕组和悬浮力绕组之间互感与转子径向位移非线性关系的基础上,研究了一种实用的转子径向位移自检测方法。具体做法是:将一高频测试电流注入转矩绕组,然后在悬浮绕组端电压中滤出由该测试电流引起的互感电压,解调后提取出直流部分,再经简单数学处理后即可得到转子的径向位移。该方法无需专用的位移传感器,简单易行,可以减小电机尺寸,并提高系统的可靠性。仿真及dSPACE平台的实验结果验证了该方法的正确性和有效性。