TDI imaging-a tool for profilometry and automated visual inspection

TDI imaging is introduced as a solution to industrial web inspection under low-light illumination. In addition to the original purpose of recording clear blur-free images of the objects moving over industrial platforms, it can also be used as a tool for profilometry and automated visual inspection when coupled with proper structured light illumination modules. This paper illustrates a system employing a pulsed laser diode, uniform intensity line generating optics and a high-speed TDI imager for recording structured light patterns from rotating cylindrical objects. Defect or shape information is coded as distortions in a regular grating pattern recorded by the TDI imager. The shape or defect profile is retrieved by employing Fourier transform and scanning spatial phase detection techniques.     

A transputer-based automated visual inspection system for electronic devices and PCBs

Computer vision has been gaining popularity for industrial applications, and the transputer offers a cost-effective vision hardware platform for an automated vision system. In this paper, component level inspection was carried out on the integrated circuit (IC), diode, resistor and capacitor. Board level inspection was also implemented for inspection of multiple ICs and missing components on assembled PCBs. The algorithms used were implemented for parallel processing using transputers. Through experiments, it was found that inspection of a component takes less than l.5 s, with an accuracy of above 85%. The transputer has also proven to out-perform sequential processing. The implementation of transputers for real-time image processing was successfully achieved.     

Optical preprocessing for texture classification using specialized binary black and white pseudocoloring masks

Image texture is a neighborhood information which is time consuming to analyze by computer. Optical processing can be used as a preprocessor to reveal some of the texture information in parallel on the whole image before classification of the preprocessed image by computer. Pseudocoloring allows an easy discrimination of texture information. A specialized binary black and white mask is introduced which selects at one particular wavelength one peak of the diffracted power spectrum of each texture considered. The method is applicable to textures showing some periodicity. The resolution, selectivity and difficulties of the method are described qualitatively and an experimental example including a problem of partial cross talk between different textures is presented.     

Optical inspection by internal reflection and spatial filtering

Some optical techniques for surface inspection applications are described. Paper texture is analyzed by a frustrated-total-internal-reflection method followed by spatial filtering of the diffracted pattern. Fibre-optics and micro-lenses are used to obtain a rugged and flexible sensor. Similar sensors are used for defect monitoring of roughly-polished surfaces. The practical aspects of sensor manufacture, speckle and vignetting considerations are discussed.     

Signal preprocessing for digital correlators

The input format of fast digital correlators, such as used in photon correlation or recurrence rate correlation, is often exceeded by input signals, if high count rates coincide with sample times of the order of several hundred nanoseconds or more. Clipping, random clipping, and scaling are well known methods to reduce such signals appropriately. We discuss these procedures with special attention to noise performance possible errors introduced into the correlogram. Generalizations from single to multi-bit correlators are presented with a thorough discussion of random preset scaling, a new process suitable for multi-bit correlation of signals with arbitrary statistics. Furthermore we describe a new additional preprocessor which offers significant decrease of quantization noise, if constant background contributions are present in the signal. Though demonstrated on optical measurements, the methods treated in this paper generally apply, whenever the format of digital data has to be reduced prior to correlation.     

Industrial resin inspection for display production using automated fluid-inspection based on multimodal optical detection techniques

The large-scale liquid-crystal display (LCD) industry requires an accurate inspection system for identifying defects, as the LCD quality can be drastically degraded because of defects. In particular, the refractive index of LCD panels can be changed by internal micrometer-range substances, which form as a result of defectiveness and the insufficient solidification of industrial liquid resins. Intrinsically, the defect inspection of the raw materials must be performed prior to the LCD manufacturing process. Thus, optical coherence tomography (OCT) based automated fluid-inspection (AFI) methodology was introduced to demarcate and enumerate the defects in industrial liquid resins and the final product (LCD smartphone). The accuracy of the method was enhanced by implementing an intensity-detection algorithm. Subsequently, the optimal solidification rates of liquid resins were investigated using a fluorescence sensor-based ultraviolet hardening method to prevent the formation of defects between the internal layers of the LCD panel. Therefore, AFI can be implemented as an effective and cost-saving method in the smartphone industry for improving the quality of the final product.     

Optical inspection and characterization of microoptics using confocal microscopy

With the growing demand for microoptics in different areas the importance of the characterization increases. Methods for a fast defect detection in microlens arrays are developed. We present a technique where the confocal principle is applied for determining the variation and the absolute value of the focal length. Additionally, using a self–filtering method the deviation of the periodic structure of microlens arrays is investigated theoretically and experimentally. Point-like defects as well as aberrations have been detected. The introduced methods allow the fast, parallel characterization of microlens arrays.     

Optical coherence tomography as a method of quality inspection for printed electronics products

Application of time domain, ultra high resolution optical coherence tomography (UHR-OCT) in printed electronics products’ quality inspection is demonstrated. Presented study was done using experimental UHR-OCT device based on a Kerr-lens mode locked Ti:sapphire femtosecond laser, photonic crystal fibre and modified, free-space Michelson interferometer. Possibilities of the technique are demonstrated by analysis of an RF antenna—example of printed electronics products. Measurements were done with submicron axial resolution, offered by UHR-OCT system developed in our laboratory. Such high resolution is necessary due to the thickness of material layers used in printed electronics. In addition to tomography imaging, numerical results were compared with data provided by two commercially available measurement devices: Wyko NT3300 optical profiler and Dektak 8 stylus profiler (both Veeco). Comparison of profile heights and their spatial correlation is presented. Ability for full volumetric reconstruction and accuracy justified with reference measurements prove OCT to be a reliable tool in printed electronics product testing.     

Optical inspection system with tunable exposure unit for micro-crack detection in solar wafers

Micro-cracks are a major cause of wafer breakage in the solar wafer manufacturing process. Furthermore, the existence of micro-cracks may lead to electrical failure in the post-fabrication inspection of solar cells and solar modules. Thus, the reliable detection of micro-cracks is an important concern in the photovoltaic industry. Accordingly, the present study proposes a novel micro-crack inspection system comprising a near infrared light source, a CCD camera and a tunable exposure unit. In the proposed system, the intensity of the light transmitted through the wafer is sensed by a photodetector and the exposure time of the CCD camera is tuned accordingly in order to maximize the contrast of the CCD image; thereby improving the performance of the crack detection process. The experimental results show that the proposed system enables the reliable detection of micro-cracks in solar wafers with a thickness of up to 240 μm within 1 s. In other words, the system provides an ideal solution for on-line micro-crack inspection applications in the photovoltaic industry.     

On preprocessing techniques for bandlimited parametric loudspeakers

The self-demodulation property of finite-amplitude ultrasonic waves can be applied with parametric loudspeaker to produce audible sound. A special characteristic of the reproduced sound waves using parametric loudspeaker is its high directivity. However, the demodulated signal from parametric loudspeaker suffers from high distortion. To reduce the distortion in the demodulated signal, preprocessing of the modulating signal is usually employed. To determine the effectiveness of the preprocessing technique, an important practical constraint on the bandwidth of the ultrasonic transducer of the parametric loudspeaker should be accounted. In this paper, we shall discuss a class of preprocessing techniques that is based on quadrature amplitude modulation. As compared to the conventional preprocessing methods used with bandlimited ultrasonic transducer, the demodulated signal from our proposed preprocessing techniques exhibits lower distortion.     

基于CCD的乳腺X线摄影图像预处理方法的研究

为提高由闪烁屏到CCD的光耦合效率,减小大相对孔径和近距离成像造成CCD图像严重失真,提出一种有效补偿图像失真的预处理方法。该方法根据物像共轭关系将物面划分为与图像传感器像素相对应的许多微小物元,应用蒙特卡罗方法模拟从每一物元发出的光在像面上形成的光分布,即点扩散函数。由所有物元的点扩散函数构成一个点扩散数组,数组的每一行对应一个物元的点扩散函数。基于该点扩散数组建立描述像元与物元关系的线性方程组,解线性方程组可得到接近实物的图像。用实际光学系统的计算结果验证了该方法的有效性。     

人脸图像光照预处理的一种新方法

人脸识别是图像分析和理解领域中最成功的应用之一,近年来得到了迅速的发展,但是阻碍人脸识别技术应用到实际中的瓶颈之一——光照问题,一直没能得到很好的解决。局部二值模式是最近发展起来的一种理论简单但功能强大的纹理分析算法,在计算机视觉等领域表现出良好的性能。将该纹理提取算法应用到图像预处理中并并利用大规模中国人脸图像数据库CAS-PEAL-R1来检验这种方法的有效性。实验结果表明:加入LBP纹理后,该方法能较好解决光照变化问题,提高识别性能。     

Optical coherence tomography as an accurate inspection and quality evaluation technique in paper industry

Optical coherence tomography (OCT), a technique for the noninvasive imaging of turbid media, based on low-coherence interferometry, was originally developed for the imaging of biological tissues. Since the development of the technique, most of its applications have been related to the area of biomedicine. However, from early stages, the vertical resolution of the technique has already been improved to a submicron scale. This enables new possibilities and applications. This article presents the possible applications of OCT in paper industry, where submicron or at least a resolution close to one micron is required. This requirement comes from the layered structure of paper products, where layer thickness may vary from single microns to tens of micrometers. This is especially similar to the case with high-quality paper products, where several different coating layers are used to obtain a smooth surface structure and a high gloss. In this study, we demonstrate that optical coherence tomography can be used to measure and evaluate the quality of the coating layer of a premium glossy photopaper. In addition, we show that for some paper products, it is possible to measure across the entire thickness range of a paper sheet. Furthermore, we suggest that in addition to topography and tomography images of objects, it is possible to obtain information similar to gloss by tracking the magnitude of individual interference signals in optical coherence tomography.     

Optical Filters Using Optical Multi-Layer Structures for Optical Communication Systems

Abstract

In this article, light reflection spectrums for different one-dimensional multi-layer structures are obtained. Optical reflectivities for periodic, superperiodic, and quasiperiodic structures have been calculated using the transfer matrix method. PBGs of each structure have been obtained using the optical reflectivity pattern. From a comparison of reflectivity and standard dense wavelength division multiplexing grids, it is demonstrated that narrow and dense band filters can be built from generalized Fibonacci quasiperiodic structures. Reflectivity of these structures contains bands that meet the ITU-T dense wavelength division multiplexing standard. Reflectivity of other multi-layer structures has poor or less potential to be used in dense wavelength division multiplexing systems.     

无线光通信系统中的光接收机设计

介绍了无线光通信的特点，比较了光电检测器、光纤接收模块、自聚焦透镜和多模光纤接收机耦合三种设计方案，提出了自聚焦透镜和多模光纤之间的耦合设计是最优方案。详细讨论了自聚焦透镜和多模光纤之间的耦合设计和电信号处理过程。试验证明，采用该方案后系统输出信号的信噪比显著提高，完全可以满足通信系统的要求。     

Phase diversity with undersampled systems via superresolution preprocessing

Phase diversity algorithms allow a wavefront to be reconstructed from through-focus measurements of a point source or extended scene. These algorithms have traditionally been limited to systems that are Nyquist sampled. Many optical systems for remote sensing applications are designed to be undersampled, however. One approach to phase diversity with undersampled systems is to employ superresolution techniques to first create properly sampled scenes. This is demonstrated experimentally for a point object, but is applicable to extended scenes as well.     

Diffractive Optical Elements for Dynamic Optical Coupling

Diffractive optical elements such as the complementary Dammann gratings are incorporated for dynamic optical fiber splitting and combining. Experimental results of 1′8 dynamic optical couplings are presented.     

一种眼镜镜片缺陷自动化检测系统的研究

根据光散射原理和视觉检测的方法,研究开发了一种基于机器视觉的眼镜镜片缺陷自动化检测系统,对眼镜镜片进行图像获取、简单的图像处理与分级、分拣,实现对镜片的分类。系统采用并行机构运行,利用低角度前向照明方式获得了镜片表面和内部的斑、杂质、羽毛等缺陷图像;利用归一算法进行图像处理与分级,得到不同缺陷的识别信息。实验结果表明,系统能够检测出镜片中含有的所有缺陷,每个镜片的平均检测时间控制在2 s以内,检测精度为0.038 mm。