A Rotation-Invariant and Non-Referential Approach for Ball Grid Array (BGA) Substrate Conducting Path Inspection

The aim of this paper is to locate and classify boundary defects such as open and short circuits, mousebites, and spurs on ball grid array (BGA) substrate conducting paths using machine vision. Boundary defects are detected by a boundary-based corner detection method using covariance matrix eigen-values. Detected defects are then classified by discrimination rules derived from variation patterns of eigenvalues and the geometrical shape of each defect type. Real BGA substrates with both synthetic and real boundary defects are used as test samples to evaluate the performance of the proposed method. Experimental results show that the proposed method achieves 100% correct identification for BGA substrate boundary defects under a sufficient image resolution. The proposed method is invariant with respect to the orientation of the BGA substrates, and it does not require prestored templates for matching. This method is suitable for various types of BGA substrate in small-batch production because precise positioning of BGA substrates and the prestored templates are not necessary.     

基于小波和灰度共生矩阵的带钢表面缺陷识别

提出了一种基于小波变换和灰度共生矩阵的带钢表面缺陷识别方法。采用小波变换分解缺陷图像并提取其低频子带信息。通过在低频子带上构造0°、45°、90°和135°四个方向的灰度共生矩阵,分别计算角二阶矩、熵、对比度和逆差矩4个特征值,共获得16个特征值,并将其输入支持向量机,完成对6类共1800张带钢表面缺陷图像的识别,总体识别精度大于96%。实验结果表明,小波变换与灰度共生矩阵结合能有效描述带钢表面缺陷纹理特征,具有较好的识别效果。     

基于协方差矩阵的点云孔洞边界检测

逆向工程中点云模型孔洞边界的检测是孔洞修补的前提,完美的孔洞轮廓线有利于提高孔洞修补的质量.参照二维图像中边界的定义,给出了三维模型中点云孔洞边界的定义,并且提出了一种简单的孔洞轮廓线生成算法.首先,通过分析邻域点协方差矩阵特征值之间的关系,提出了一种边界点检测算子,用于初步提取孔洞特征点;然后,综合考虑邻域点最大特征...     

Directional textures auto-inspection using principal component analysis

This paper describes a global image restoration scheme using a principal component analysis that can be used to inspect defects in directional textured surfaces automatically. Decomposing the gray level of image pixels into an ensemble of row vectors, the input spatial domain image is transformed into principal component space so that the directional textures are well approximated by first k major components and their corresponding weight vectors, named truncated component solution (TCS). Then the local defects will be revealed by applying image subtraction between the original image and the TCS. This procedure blurs all directional textures and preserves only the local defects that were initially embedded in the input image. These defects, if any, are finally extracted by thresholding. Experiments on a variety of product surfaces with directional textures such as straight, slanted, orthogonal, slanted orthogonal, and oblique linear primitives were conducted to demonstrate the effectiveness and robustness of the proposed method. Furthermore, some preliminary experiments were also conducted to demonstrate the proposed scheme was insensitive to horizontal and vertical shifting, changes in illumination, and image rotation.     

Automatic surface inspection for directional textures using nonnegative matrix factorization

A global image restoration scheme using nonnegative matrix factorization (NMF) is proposed in this paper. This NMF-based image restoration scheme can be used for inspecting the defects in directional texture surfaces automatically. Decomposing the gray level of image pixels into an ensemble of row vectors, we first reduce the data set from original data space into a lower-dimensional NMF space. The repetitive and periodical primitives are well reconstructed by two lower-dimensional basis and weight matrices with nonnegative elements, named nonnegative matrix approximation (NMA). Then the local defects will be revealed by applying image subtraction between the original image and the NMA. As a consequence, the directional textures are eliminated, and only local defects are preserved if they initially are embedded in the surface. A supervised heuristic, elbow of residual curve rule, is devised which helps users to determine a proper basis space size of a specific image. Experiments on a variety of directional texture surfaces are given to demonstrate the effectiveness and robustness of the proposed method.     

基于应力边界条件的超声散射数值模拟

为了更好地反映超声波检测过程中各种缺陷产生的复杂散射波场特性,从无限固体介质的线弹性本构关系出发,用势函数表示波动方程,引入势函数和位移的关系,推导出适用于各种波形的人工截断边界应力的计算公式。采用应力边界条件对固体中超声波的传播进行数值模拟时,介质边界单元体表面的应力大小与分布需满足介质的本构关系和穿过人工边界向外辐射的波动方程,边界节点与内部节点的反应采用相同的积分格式计算。数值算例和实验结果表明,采用应力边界条件的数值模拟结果误差很小,能够很好地反映超声波检测过程中各类缺陷产生的复杂散射波场特性。     

Automatic optical inspection for detecting defects on printed circuit board inner layers

This paper studies automatic optical inspection for detecting defects on the printed circuit board inner layer. The development of this study can be divided into five stages, they are reference image rebuilding, inspection image normalization, image subtraction, defects separation and defect classification. In the image subtraction stage, the difference between the reference image from the printed circuit board design and the inspected image is checked for defects. Each defect region is separated using a defect outer boundary tracing method. A boundary state transition method is proposed to classify the defect types. This system can recognize eight defect types, open, mouse bite, pinhole, missing conductor, short, spur, excess copper and missing hole. In addition, a comparison with the methods described in the literature is made, proving that the proposed method produces better results .     

Left eigenstructure assignment via Sylvester equation

An effective and disturbance suppressible controller can be designed by assigning a left eigenstructure (eigenvalues/left eigenvectors) of a system. In this note, a novel left eigenstructure assignment scheme via Sylvester equation is proposed. The biorthogonality property between the right and left modal matrices of a system is utilized to develop the scheme.     

A symmetry preserving alternating projection method for matrix model updating

The matrix model updating problem (MMUP), considered in this paper, concerns updating a symmetric second-order finite element model so that the updated model reproduces a given set of desired eigenvalues and eigenvectors by replacing the corresponding ones from the original model, and preserves the symmetry of the original model. In an optimization setting, this is a constrained nonlinear optimization problem. Taking advantage of the special structure of the constraint sets, it is first shown that the MMUP can be formulated as an optimization problem over the intersection of some special subspaces and linear varieties on the space of matrices. Using this formulation, an alternating projection method (APM) is then proposed and analyzed. The projections onto the involved subspaces and linear varieties are characterized. To the best of our knowledge, an alternating projection method for MMUP has not been proposed in the literature earlier. A distinct practical feature of the proposed method is that it is implementable using only a few measured eigenvalues and eigenvectors. No knowledge of the eigenvalues and eigenvectors of the associated quadratic matrix pencil is required. The results of our numerical experiments on both illustrative and benchmark problems show that the algorithm works well. The paper concludes with some future research problems.     

轴承套圈端面缺陷在线视觉检测的研究与实现

针对轴承生产企业套圈生产过程中普遍存在端面缺陷的问题与人工目检的现状,提出了基于机器视觉的轴承套圈端面缺陷在线检测方法.首先,对套圈图像预处理后进行边缘检测,采用四连通域定位套圈端面区域;其次,采用最小二乘法拟合端面轮廓以判别外形缺陷,采用极坐标变换将套圈环形端面拉伸成矩形,采用Sauvola局部二值化算法对矩形图进行...     

Robust cooperation of connected vehicle systems with eigenvalue-bounded interaction topologies in the presence of uncertain dynamics

This study presents a distributed H-infinity control method for uncertain platoons with dimensionally and structurally unknown interaction topologies provided that the associated topological eigenvalues are bounded by a predesigned range.With an inverse model to compensate for nonlinear powertrain dynamics, vehicles in a platoon are modeled by third-order uncertain systems with bounded disturbances. On the basis of the eigenvalue decomposition of topological matrices, we convert the platoon system to a norm-bounded uncertain part and a diagonally structured certain part by applying linear transformation. We then use a common Lyapunov method to design a distributed H-infinity controller. Numerically, two linear matrix inequalities corresponding to the minimum and maximum eigenvalues should be solved. The resulting controller can tolerate interaction topologies with eigenvalues located in a certain range. The proposed method can also ensure robustness performance and disturbance attenuation ability for the closed-loop platoon system. Hardware-in-the-loop tests are performed to validate the effectiveness of our method.     

炭素制品缺陷的X射线自动检测技术研究

针对炭素制品X光图像的特点,对其缺陷的提取与识别技术进行了研究,给出了目标边界提取算法和基于小波变换的图像增强算法,实现了图像的背景去除及增强处理。在此基础上,为排除噪声干扰的影响,采用数学形态学和迭代阈值分割相结合的方法从背景去除后的图像中提取出缺陷区域,取得了良好的效果。对缺陷特征选择及识别方法进行了研究,设计了基于遗传策略的特征选择和基于BP神经网络的缺陷识别算法,计算表明:缺陷正确识别率可达95%以上。采用上述技术开发完成了一套炭素制品缺陷X射线自动检测系统。     

Study on Complete Analysis of LRE Test Samples Based on PCA

Incomplete data samples have a serious impact on the effectiveness of data mining.Aiming at the LRE historical test samples,based an correlation analysis of condition parameter,this paper introduced principle component analysis (PCA)and proposed a complete analysis method based on PCA for incomplete samples.At first,the covariance matrix of complete data set was calculated; Then,according to corresponding eigenvalues which were in descending,a principle matrix composed of eigen- vectors of covariance matrix was made; Finally,the vacant data was estimated based on the principle matrix and the known data.Compared with traditional method validated the method proposed in this paper has a better effect on complete test samples.An application example shows that the method suggested in this paper can update the value in use of historical test data.     

Improving electrical discharging machining efficiency by using a Kalman filter for estimating gap voltages

Gap voltage can be used as an indicator on the direction of the electrode movement along a desired tool path in electrical discharging machining (EDM) processes. However, due to the noise induced by electrical discharges, the estimation of gap voltages is difficult due to the lack of an appropriate state space model. In this paper, gap voltage signals are considered to be generated as a summation of colored noise through a linear filter and measurement noise. Obtained by the Yule–Walker auto-covariance method, the transfer function of the linear filter can be converted into a state space model. The composite process noise and the composite measurement noise are defined to derive the composite noise covariance matrices. A Kalman filter can thus be designed based on the state space model and the noise covariance matrices. Experimental results showed that, as compared with the traditional 10-point moving average filter, the Kalman filter can decrease the average machining time as well as improve the discharging gap status.     

Automated Surface Inspection Using Gabor Filters

In this paper we present a machine vision system for the automatic inspection of defects in textured surfaces found in industry. The defects to be inspected are those that appear as local anomalies embedded in a homogeneous texture. The proposed method is based on a Gabor filtering scheme that computes the output response of energy from the convolution of a textured image with a specific Gabor filter. The best parameters of a Gabor filter are selected so that the energy of the homogeneous texture is zero, and any unpredictable defeats will generate significantly large energy values. A simple thresholding scheme then follows to discriminate between homogeneous regions and defective regions in the filtered image. This transforms texture differences into detectable filter output. The experiments on structural textures such as leather and sandpaper have shown the effectiveness of the proposed method.     

凸轮轴凸轮表面缺陷检测与诊断方法的研究

凸轮轴是高速运转的复杂轴类零件,是发动机五大核心部件之一.由于凸轮异形,在智能制造中采用视觉检测技术时,其磨削后凸轮面反光,对检测系统的设计带来挑战.本研究提出一种凸轮视觉检测方法,利用拍摄凸轮图片进行阈值二值化,提取凸轮轮廓,得到凸轮表面选定区域,再进行缺陷轮廓提取,得到缺陷轮廓,对表面缺陷的大小和周长进行筛选后实现...     

SYMMETRIC INVERSE EIGENVALUE VIBRATION PROBLEM AND ITS APPLICATION

This paper summarises the authors' previous effort on inverse eigenvalue problem for linear vibrating systems described by a vector differential equation with constant coefficient matrices and non-proportional damping. The inverse problem of interest here is that of determining real symmetric coefficient matrices assumed to represent mass normalised velocity and position coefficient matrices, given a set of specified complex eigenvalues and eigenvectors. There are given two solutions of a symmetric inverse eigenvalue problem presented by Starek and Inman [1, 2].The theory of inverse eigenvalue problem is applied to the model updating problem. The goal of this paper is to recognise that the model updating problem is a subset of the inverse eigenvalue problem. The approach proposed here is to use the results of inverse eigenvalue problem to develop methods for model updating.Comments are made on how their procedure may be used to solve the damage detection problem.     

A case study: passive component inspection using a 1D wavelet transform

This paper exploits a wavelet-based scheme to inspect the surface defects and basic dimensions of 0805 Multi-layer Ceramic Chip capacitors (MLCC) using machine vision. The image of a passive component is initially processed to show only two solder plates (terminations). Then, the covariance matrix eigenvector for each boundary point generates the 1D θ-p representation to describe the angle variations at the boundaries of each termination. The 1D θ-p representation is further decomposed directly by a one-dimensional wavelet transform (1D WT). Since a single corner (an intersection of two boundary edges) and the jag corners (the surface defects) are local deviations on termination boundaries, their locations are represented as intensive and have a highly fluctuated wavelet energy at the 1st detail scale. Concerning a 0805 MLCC type of passive component, the surface defects and single corners on termination boundaries can be captured by appropriate thresholds (e.g., in wavelet energy). The basic dimensions of a passive component are simply the direct distance between located single corners. Real 0805 MLCCs are testing samples to evaluate the performance of the proposed approach. Experimental results show that the proposed method achieves a precise identification of the surface defects and measurements for basic dimensions. The proposed approach is invariant with respect to the orientation, easy to implement and free from a primitive-matching process. Therefore, it is especially suitable for various types of passive components that are similar to the 0805 MLCC in small-batch production.     

光学薄膜表面微细缺陷在线检测方法研究

为了对光学薄膜进行精密光学检测,需要采用数个具有高解析度的线阵CCD相机进行光学薄膜缺陷图像的同步采集。基于计算机视觉的理论,提出了一种有效的自动质量监测方案,实现对光学薄膜表面微细缺陷项目的检测,并根据检测结果驱动打标机对光学薄膜缺陷进行自动标识和定位,该方法具有高精度、实时、在线和非接触的显著优势。探索性实验结果表明,采用该方法可获得光学薄膜表面缺陷的清晰图像,缺陷的细节能够得到很好的展现,并且能够完成缺陷特征的提取与识别。     

采用自适应一致性UKF的分布式目标跟踪

由于传统分布式跟踪方法在先验噪声协方差与其实际值不相匹配时跟踪误差较大,提出了一种采用自适应一致性无迹卡尔曼滤波的分布式目标跟踪方法,该方法首先执行分布式UKF算法得到对当前移动目标状态的估计值,然后通过一个系统错误检测机制,确定是否需要对噪声协方差值进行更新。如需要,则根据当前获得的测量信息去估计当前噪声协方差,并联合该估计值和先前的噪声协方差值获得一个新的先验噪声协方差值。最后根据新获得的噪声协方差值对获得的目标状态估计值进行修正。实验结果表明该方法具有较好的准确性和鲁棒性：在噪声未知环境下,基于ACUKF的分布式跟踪方法相比于基于容积信息滤波和基于分布式无迹卡尔曼滤波的跟踪方法,最大跟踪误差值分别减少了49.93%和 51.46%;在目标过程噪声发生动态变化的情况下,提出的方法相比于上述两种传统跟踪方法,跟踪误差值分别减少了40.67%和40.06%。