EMD相关度去噪及其在轧机信号处理中的应用

基于经验模式分解(EMD)时间尺度滤波特性,在引入相关度分析的基础上提出了EMD相关度去噪方法.首先对含噪信号进行EMD分解得到信号各个本征模函数(IMF)分量,再根据所建立的相关度阈值函数计算各个分量的相关度值,在与预定阈值比较得到满足阈值要求的IMF分量,然后对这些分量进行信号重构得到去噪信号.该方法消除了EMD时间尺度滤波不适用于噪声和信号在IMF成分混叠情况下的限制.通过对平稳含噪信号和非平稳含噪信号进行的去噪仿真研究,表明了该方法的有效性.通过轧机在轧钢时实测信号分析验证了该方法的可靠性.     

两种莫尔条纹信号对光栅系统测量精度的影响

对两种莫尔条纹（光闸条纹和横向条纹）信号的谐波含量以及它们对光栅系统测量精度的影响进行了分析，并用实测数据加以比较，指出在光栅系统中，取横向莫尔条纹信号的谐波量小，正弦性好，细分误差小，在其它参数相同的情况下，可提高系统的测量精度2倍左右。     

基于增量式光电编码器细分的自适应滤波技术研究

利用光栅副调制原理,在建立了光栅副调制几何光学模型与物理光学模型的基础上,提出了一种针对增量式编码器细分的自适应滤波方法。分析莫尔条纹光电信号输出波形不确定的原因,通过自适应滤波方法将高频信号滤除保留基频信号。自适应滤波效果等价于一个中心频率为基频的窄带带通滤波器,当基频随机变化时其通带也会随之改变。实验证明采用这种自适应滤波技术可以较好地滤除计数信号中除基频外所有高频分量,使莫尔条纹光电信号输出波形趋近于标准正弦波,将信号失真量减小了约7/8。     

基于EMD的振动信号去噪方法研究

煤矿机械在重载情况下运行,其振动信号往往具有非线性、不平稳等特性,其不仅带有大量设备运动状态的信息,同时也夹杂着大量的环境噪声,无法直接对其进行分析。而经验模式分解(EMD)在处理非线性、非平稳信号时具有一定优势,是一种自适应的信号处理方法。针对煤矿机械振动信号的特性,提出基于EMD的去噪方法,首先将振动信号进行EMD分解,得到各固有模态函数(IMF),然后计算各IMF与原始信号的相关系数,并将相关系统按照从小到大进行排序,通过相邻两个相关系数的差值最大,找到敏感IMF分量重构,实现非平稳信号的滤波,为机械设备后期故障诊断奠定了良好基础。并通过实验数据分析,验证了EMD方法对振动信号进行去噪的有效性及可行性。     

提高莫尔条纹正切法细分精度的改进算法

为提高莫尔条纹信号正切法细分的精度和倍数,应用改进算法对原始信号进行数据预处理.通过神经网络自适应算法在莫尔条纹信号降噪方面的移植,结合滤波步长的实时调整,有效滤除了信号的宽频段有色噪声干扰;采用了基于滞后相位补偿思想的相位调整算法,通过分段处理,提高了原始正余弦信号的相位正交性.对算法处理后的莫尔条纹信号进行正切法细分验证,实验结果表明当细分倍数为1 024时,可确保细分误差小于1个细分当量,即0.618″,若不考虑信号的非正弦性影响,细分精度提高了10倍以上.     

光栅莫尔条纹细分及辨向方法研究

提出了一些新的基于数字处理技术的莫尔信号细分及辨向方法.单光栅副莫尔条纹采用差值细分方法;双光栅副莫尔条纹采用乘积细分法.将信号进行区间划来实现辨向.实验采用DSP器件内置的高速A/D模块实现数/模转换,利用DSP专用指令实现信号的滤波、细分和辨向.实验结果表明,单光栅副和多光栅副的细分精度分别为3"和0.3".     

光栅莫尔条纹信号正交误差的补偿

为了补偿在作用微处理器对光栅莫尔条纹信号进行相位细分时，由于两路莫尔条纹信号不正交所引起的误差，推导了正交误差方程并给出了求解方法和相应软件。实验证明，引入相应补偿程序之后，细粉数明显提高。     

光栅信号质量检测及电路实现

对光栅信号的质量指标，主要是对光栅到莫尔条纹信号质量指标进行了分析，并通过采用谐波分析法，对光栅信号质量进行动态综合检测的电路进行了实现。这对计量光栅的发展和长光栅的检测，具有一定的现实意义。     

一种改进的集合平均经验模态分解去噪方法

针对现有非平稳信号去噪处理中的难点,提出一种改进的基于集合平均经验模态分解（EEMD）去噪方法,该方法根据本征模态函数（IMF）能量从被测信号中估计出噪声,使用估计的噪声代替EEMD方法中添加的噪声,最后将集合平均IMF分量累加得到去噪信号。使用相关性判据剔除了EMD分解产生的伪IMF分量,改进了噪声估计方法。仿真表明,改进的方法能够对调幅调频含噪信号进行有效的去噪处理。     

采用软件细分技术的光栅测角仪

本文叙述的光栅数显测角仪,采用计算机软件对光栅莫尔条纹信号实现了400细分,与用硬件细分莫尔条纹信号方法相比,该整机具有成本低廉、准确度高、显视直观、并可根据需要进行实时控制、操作简单等特点。     

Sub-20-nm alignment in nanoimprint lithography using Moiré fringe

Accurate multi-level overlay capability for nanoimprint lithography (NIL) is essential to integrated circuit manufacturing and other multilayer imprint applications. Using the "beat" grating image (Moiré fringe) generated by overlaying two sets of gratings that have slightly different periods, we obtained an alignment signal with a sensitivity better than 10 nm in nanoimprint lithography. The alignment signal is, as expected, independent of the size of the gap between the wafer and the imprint mold. We achieved a single-point overlay accuracy (error distribution) of sub-20 nm between the first and second imprinted layers by using two sets of Moiré fringes. With higher precision nanopositioning stages, better single-point alignment accuracy is expected. Furthermore, we achieved sub-150 nm alignment over an area of 1 sq in and sub-250 nm over the entire area of a 4 in wafer using simple low-resolution stages without temperature control or wafer-mold mismatch compensation. With better stages, precision temperature control, and wafer-mold mismatch compensation, we believe that much higher overlay alignment accuracy over large areas (either in a 1 sq in die or a full wafer) is feasible.     

基于计算全息的无衍射光莫尔条纹三自由度测量方法研究

针对工作台运动误差,提出了一种基于计算全息的无衍射光莫尔条纹三自由度测量方法。通过液晶空间光调制器(SLM)生成无衍射光,利用两束无衍射光干涉生成莫尔条纹。设计了无衍射光莫尔条纹三自由度测量光路,建立了三自由度运动误差数学模型,并用几何分析法将三种运动误差(偏摆角、滚转角和俯仰角)进行分离。利用旋转台模拟不同大小的三自由度运动误差,带有误差信息的无衍射光和莫尔条纹图案分别由CCD1和CCD2接收。实验结果表明,通过光斑中心偏移量计算出的实际运动误差值接近理论值,测量误差不超过0.0104°,验证了无衍射光莫尔条纹三自由度测量系统的可行性与正确性。     

计量光栅信号质量综合评价系统

光电轴角编码器中的莫尔条纹信号质量决定了整个系统的细分精度。计量光栅信号质量综合评价系统由编码器、数据采集卡和相应的软件组成，采用一种以莫尔信号离散采集和数据处理为主的数字化检测方法，实现了莫尔条纹信号质量各项指标的评价，对提高测量精度以及光栅系统的设计具有一定意义。     

Application of "parallel" moiré deflectometry and the single beam Z-scan technique in the measurement of the nonlinear refractive index

In this paper, the application of "parallel" moiré deflectometry in measuring the nonlinear refractive index of materials is reported. In "parallel" moiré deflectometry the grating vectors are parallel, and the resulting moiré fringes are also parallel to the grating lines. Compared to "rotational" moiré deflectometry and the Z-scan technique, which cannot easily determine the moiré fringe's angle of rotation and is sensitive to power fluctuations, respectively, "parallel" moiré deflectometry is more reliable, which allows one to measure the radius of curvature of the light beam by measuring the moiré fringe spacing. The nonlinear refractive index of the sample, including the sense of the change, is obtained from the moiré fringe spacing curve. The method is applied for measuring the nonlinear refractive index of ferrofluids.     

Noise-free normalized fringe patterns and local pixel transforms for strain extraction

Noise reduction is one of the most exciting problems in automatic fringe processing. We propose a two-dimensional (2-D) envelope transform for normalization of fringe patterns, coupled with spin filtering, to construct so-called noise-free normalized fringe patterns. The 2-D envelope transform uses correct fringe intensity envelopes for normalization of fringe patterns, i.e., for making the fringe background and amplitude constant over the whole field. Spin filtering is applied to fringe patterns for removal of random noise taking into account fringe flow. With spin filtering and the 2-D envelope transform, a noise-free normalized fringe pattern is constructed for postprocessing. Based on this improved fringe pattern, two local pixel transforms for strain extraction from a single moiré pattern are developed, in which the digital pure secondary moiré method is improved and the strain-field image method with division is developed.     

Phase-shifting shadow moiré based on iterative self-tuning algorithm

We proposed a general algorithm for phase-shifting shadow moiré by an iterative self-tuning algorithm. In our proposed system, the grating is translated in equal distance to introduce phase shifts across the field of view. The proposed algorithm produces accurate phase information with five interferograms and can calibrate the precise phase step during the process of the height demodulation. Compared with the traditional method, the proposed algorithm is insensitive to the height dependent effects, which is the main systematic source of error in phase-shift shadow moiré when reconstructing surfaces from fringe patterns. Numerical simulations and optical experiments show that the proposed method can eliminate the nonuniform phase-shift error and possesses a superior performance to existing typical phase-shifting algorithms.