Evaluation of surface roughness based on monochromatic speckle correlation using image processing

The measurement of roughness on machined surfaces is of great importance for manufacturing industries as the roughness of a surface has a considerable influence on its quality and function of products. In this paper, an experimental approach for surface roughness measurement based on the coherent speckle scattering pattern caused by a laser beam on the machined surfaces (grinding and milling) is presented. Speckle is the random pattern of bright and dark regions that is observed when a surface is illuminated with a highly or partially coherent light beam. When the illuminating beam is reflected from a surface, the optical path difference between various wavelets with different wavelength would result in interference showing up as a granular pattern of intensity termed as speckle. The properties of this speckle pattern are used for estimation/quantification of roughness parameters. For measurement of surface roughness, initially the speckle patterns formed are filtered in the spatial frequency domain. The optical technique, namely spectral speckle correlation (autocorrelation) is utilized in this work for the measurement of roughness on machined surfaces. It has been observed that the pattern formed is dependent on the roughness of the illuminated surface. For example, a rough surface (milled) shows a small central bright region with a rapid decrease in intensity towards the edges, while a smooth surface (ground) shows a large central bright region with gradually decreasing intensity towards the edges. The complete methodology and analysis for quantification/estimation of surface finish of milled and ground surfaces based on speckle images that could be implemented in practice, is presented in this paper.     

Measurement of surface roughness of metals using binary speckle image analysis

In this paper, results from an optical technique for measuring surface roughness using image analysis of speckle pattern images are presented. The technique coined as statistical properties of binary images (SPBI) utilizes the combined effects of speckle and scattering phenomena. The speckle patterns obtained with a He–Ne laser were binarized and examined. The parameters such as bright and dark regions and their ratios obtained from this model to evaluate the surface roughness were compared with the surface roughness parameter R_a obtained from a profilometer. It was found that there is a strong relationship between these parameters and R_a, especially in the range of λ<R_a<2λ where λ is He–Ne laser wavelength. Although, it is a relative method, it has great potential to be used for in-process measurement and automation due to the simplicity of optical system used. The proposed method for the surface roughness combined with a non-contact optical measuring system is applied to samples from 0.5825 to 1.9 μm of steel (CK 45) through CNC face-milling process.     

3-D measurement and evaluation of surface texture produced by scraping process

The scraping process involves traditional manual work and is an important technique for producing flat bearing surfaces with lubricating grooves on a sliding surface. In order to meet the requirements of precision engineering, the scraped surface should have an equally distributed pattern with a required number of high points per unit area while retaining good flatness. In the machine tool manufacturer’s workshop, however, the quality inspection of scraped surfaces still depends on human eyes. In this study, a 2-D evaluation system is first developed using image processing so that the peak points per area of square inch (PPI) and the percentage of points (POP) can be quantified as parameters. A vision-assisted laser focus probe system is then developed to measure the 3-D form of the scraped profiles. The laser probe is made of a DVD pickup head based on the astigmatic principle. Driven by an XY stage, the entire scraped profile can rapidly be scanned. The quality of the scraped surface can thus be interpreted in a more scientific manner. Based on the measured 3-D data, new evaluation methods are proposed for five parameters, namely the PPI, POP, height of points (HOP) or depth of surroundings (DOS), flatness, and oil retention volume. Experiments show that the 3-D system is consistent with the 2-D system. It not only reveals more surface quality parameters but also uncovers more characteristic surface phenomena than the 2-D image system.     

基于小波包变换和奇异值分解的机加工表面纹理特征提取

为提取机加工表面的纹理特征,提出利用小波包变换和奇异值分解提取灰度图像特征的新方法,给出了小波包变换算法及奇异值分解算法,依据矩阵奇异值特征向量的均值和方差分别定义了灰度图像的特征参数k1和k2,并探讨了特征参数与表面纹理之间的关系。结果表明:特征参数能够敏感地反映机加工表面的纹理特征。k1表征了机加工表面的支撑面积,其值越大,支撑面积越大;k2表征了机加工表面纹理的粗糙度,其值越大,纹理越粗糙。因此,机加工表面的纹理特征可通过灰度图像特征参数k1和k2评定。     

复合工艺制备的表面微凹坑织构的摩擦性能研究

在构建的激光电化学复合微加工系统上,采用皮秒脉冲激光辐照与电解刻蚀复合加工方法在7075铝合金表面制备出不同尺寸的阵列凹坑微织构。采用共聚焦显微镜观测复合加工织构试样表面形貌,采用MFT-5000型RTEC摩擦磨损试验机研究润滑条件下凹坑织构的摩擦学性能,并探讨直径、深度、面积密度对减摩性能的影响。结果表明:复合加工工艺制备的表面微织构具有良好的表面形貌;润滑条件下材料表面的凹坑型织构能显著改善其摩擦学性能,相比光滑表面最高可降低摩擦因数30%;在实验参数范围内,凹坑的直径与面积密度对材料表面摩擦性能影响较大,凹坑深度对摩擦性能影响较小。     

Rapid measurement of surface roughness for face-milling aluminum using laser scattering and the Taguchi method

In this paper, an experimental model for the rapid measurement of surface roughness (R_rms) in CNC face-milling specimens using the laser speckle method and digital image processing is established. The specimens used in this study were made of 6061-aluminum alloys through the high-speed face-milling process. In order to evaluate the effect of machining conditions, such as the feed rate, the spindle speed, the depth of cut, and the material of the cutting tool on the roughness of the specimens, the Taguchi method was used to determine the optimal parameters for machining. The laser radiation results in the speckle structure formed in the space when coherent light is scattered through an optically rough surface. The features of the speckles depend on the characteristics of the rough surfaces. Hence, the experimental work for the roughness measurement is based on the speckle effect. The experimental setup in this study consisted of a He-Ne laser, a ground glass, a CCD camera, and a digital image processing system developed using the Virtual Basic language. Computer evaluation of the speckle images revealed the values of R_rms rapidly. This study proposed a precise and non-contact optical method for evaluating the surface roughness from 0.20 to 0.60 μm.     

Measurement of surface roughness on rough machined surfaces using spectral speckle correlation and image analysis

A speckle pattern is formed when a rough surface is illuminated with coherent light. The properties of this pattern can be used in the calculation of roughness parameters. Spectral speckle correlation (SSC) is a technique applicable to the measurement of roughness on rough machined surfaces. This paper presents the SSC obtained from measurements on specimens with a surface roughness in range R_a = 0.5–5 μm. The measurement results correspond to reference measurements made using a stylus instrument, Form Talysurf.     

高强钢薄板高温焊接变形的视觉测量

为了实现高强钢薄板高温焊接条件下屈曲变形的准确测量,基于数字图像处理技术、立体视觉原理及数字图像相关法,提出一种高强钢薄板全场动态焊接变形的视觉测量技术,并以规则散斑图像的高精度匹配方法研究为基础,将其应用到焊接图像中。针对焊接高温导致的散斑纹理的变色或脱落,采用高温漆与高温胶混合涂布的方式,获得了低成本、高稳定性的散斑纹理。选择薄板背侧进行测量以及在相机镜头前加装滤光片组的方法,抑制焊接过程中的强光、火花及烟雾的干扰。采用高斯平滑的数字图像处理技术,寻找最佳滤波参数并应用到焊接图像中,在保证测量精度的前提下提高了图像匹配的成功率及精度。实验结果表明,该方法能够有效地降低焊接图像匹配的均值误差、均方根误差及Z向静态均值误差,均值误差最大降幅为78.6%,均方误差最大降幅为47.7%,Z向静态均值误差降幅为37.9%。本文的方法和系统可以满足焊接高温条件下薄板屈曲变形的全场应变测量要求,散斑纹理稳定,散斑图像匹配成功率高、稳定性好,是薄板全场动态焊接变形检测的有效途径。     

光针轮廓扫描技术测量内螺纹曲面

分析了激光光针扫描在测量内螺纹曲面时的特性及影响精度的因素。根据光斑在被测面的噪声分布特点,采用中值滤波与小波阈值去噪相结合的综合滤波算法对光斑图像进行了去噪处理,其中中值滤波可以有效地消除光斑图像中的脉冲噪声,而基于小波变换的阈值去噪算法可以消除图像中的高斯噪声。通过综合滤波算法对光斑图像进行处理,可以有效消除激光光斑噪声,消除图像噪声对测量精度的影响,同时保持了光斑图像的细部特征。根据激光光斑图像在倾斜被测物体表面光强分布特点,设计了近似圆拟合算法来确定光斑中心,该算法相对传统算法具有计算量小、计算效率高,适合在线检测的特点,可以克服测量面倾斜对激光光斑中心的影响。利用采用上述方法的坐标机激光光针扫描系统,对标准内螺纹量规进行测量,对比应用前后的测量结果,螺距精度提高了0.48 mm,中径测量精度提高了0.44 mm,牙型角精度提高0.57°。     

Continuous scanning laser Doppler vibrometry and speckle noise occurrence

Continous scanning laser Doppler vibrometry (CSLDV) is a type of “spatial field” non-contact technique for measuring structural vibrations by employing a laser Doppler vibrometer whose laser beam is moving continuously on the structure surface. When an LDV is scanned continuously along an arbitrarily line, the LDV output is an amplitude-modulated sine wave according to the structure operational deflection shape. Smooth mode shapes, which can be defined by polynomial functions across the scanned area, may be recovered as a set of polynomial coefficients derived from the LDV output analysed in the frequency domain, which spectrum comprises sidebands centred on the excitation frequency and spaced at multiples of the scan frequency(ies).This paper concentrates its attention to the influence of the speckle noise on the measured data quality, the speckle being an unavoidable phenomenon occurring when a coherent light beam is scattered back from an optically rough surface.     

一种新的表面形貌检测方法

共焦激光扫描显微镜是近年来发展起来的一种新型显微镜。本文介绍了日本奥林巴斯公司研制OLS1100型共焦激光扫描显微镜性能特点，并着重介绍了利用其独有的纵向分辨能力和高的平面分辨率，在对微动磨损、显微划痕以及进行表面形貌观察和参数检测的应用。     

磨粒类型识别研究

提出了一种有效的磨粒类型识别方法,该方法除了选用传统的磨粒形态特征参数,将表面粗糙度和表面纹理指数也作为重要的磨粒识别参数,选用面积、长度、圆度、纤维比率、体态比、边界分形维数、表面粗糙度．Sa．Sq,和表面纹理指数（Stdi）等9个参数,采用人工神经网络来识别磨粒类型,应用示例表明效果良好,提高了磨粒类型识别的精确度。     

激光显示中散斑的减弱

为减弱激光显示中散斑的影响,在对散斑对比度进行理论分析的基础上,提出了一种利用位相光学元件减弱散斑的方法。实验以绿光为光源,让激光束通过位相光学元件,再经过CCD相机和图像处理系统处理,得到屏幕上散斑对比度和光强的变化。实验结果表明:散斑的对比度降低到3.7%,可满足激光显示中对散斑减弱的要求。该方法具有简单易行、成本低、适合批量化生产等优点。     

METHODOLOGY TO COMPARE 3-D AND 2-D PARAMETERS FOR THE OPTIMIZATION OF HARD TURNED SURFACES

Hard Turning provides an alternative to grinding in some finishing applications. Average Surface Roughness R_a has been widely used in industry to establish surface texture needed for a given application. It is known that the single parameter R_a is inadequate to define the functionality of a surface texture. The quality of a surface can be determined by the nature of its interaction with another surface. Thus a surface with significant peaks will not make as good a bearing surface as a surface with deep valleys and low peaks. Two different surfaces with similar values of R_a can behave differently under fatigue loading conditions. 3-D visualization of expected surface texture will facilitate optimization of machining parameters to produce function-specific surfaces. The advantages and shortcomings of some current surface texture prediction models are discussed. A new method based on neuro-fuzzy techniques is proposed. Optimization using some 3-D surface parameters was carried out and compared with the results of those obtained using 2-D parameters.     

Effect of geometrical parameters in micro-grooved crosshatch pattern under lubricated sliding friction

Tribological test was carried out using a pin-on-disc geometry with textured SKD11 pin on bearing steel disc, under sliding in paraffin oil. Micro-grooved crosshatch pattern has been fabricated with various angles and widths. The effects of geometrical parameters on friction were mainly examined in mixed and elastohydrodynamic lubrication. The results show that friction control can be achieved by fabricating the micro-grooved crosshatch pattern on a contact surface. It is observed that each geometrical parameter of texture influence on friction, especially decrease of groove aspect ratio and increases of groove sliding length show friction reduction performance. Crucial parameter G_l was proposed for micro-grooved crosshatch texture. The friction mechanism is explained by micro fluid flow with limited theoretical approach.     

An active manufacturing method of surface micro structure based on ordered grinding wheel and ultrasonic-assisted grinding

At present, many studies have shown that crosshatch micro structures can effectively improve surface performance. This paper presents a method for manufacturing micro structure based on ultrasonic-assisted grinding (UAG) and ordered grinding wheel. Firstly, the parameters of ordered grinding wheel and the surface characteristic parameters in relation to working performance are proposed. According to the kinematics of grinding, the governing equation between the surface characteristic parameters and the machining parameters is established. Based on the proposed characteristic parameters, the pattern parameters and machining parameters are inversely solved by the governing equation. The crosshatch micro structure manufacturing based on ordered grinding wheel and ultrasonic-assisted grinding is achieved, and because the fabrication technology of the grinding wheel is not mature, its correctness and feasibility are preliminary verified by the numerical simulation method and grinding experiment. The paper method is original for the active manufacturing of the crosshatch micro structure and is of reference value for the micro structure active manufacturing.     

ISSUES IN MODELING MACHINED SURFACE TEXTURES

This paper discusses the issues involved in modeling surface textures generated during machining and presents the potential of scale-sensitive fractal analysis in addressing these issues. Modeling surface texture creation supports the design machining processes for producing product surface textures with desired properties. The current understanding of how surface textures behave is largely incomplete. In order to understand how surface textures influence surface behavior, it is necessary to a) develop surface texture characterization methods with enough sophistication to capture the essence of the information inherent in the surface texture, and b) convey it so that the discovery of functionality, or behavior, of the texture is enabled. For a model of texture formation to be useful, the parameters that it calculates must be the same as the parameters that explain the texture behavior.     

激光器在数字散斑干涉系统中的应用

介绍了在数字散斑干涉系统中经常使用的激光器 :He- Ne激光器、半导体激光器和 LD泵浦的固体激光器 ,总结了这几种激光器在数字散斑干涉系统中的应用原理 ,对比了各自的优缺点 ,并提出了一种新的应用领域——在采用数字散斑干涉技术的机器人口型识别系统中 ,应用微片激光器作为光源 ,对该激光器作了分析介绍 ,讨论了它的特点。     

基于图像识别的激光切割质量分析

为了准确量化激光切割过程中出现的烧蚀缺陷,提出了基于改进的形态学缺陷提取算法与基于霍夫变换的缺陷测量相结合的方法。改进的形态学提取算法用于缺陷位置的检测和提取,霍夫变换用于缺陷尺寸计算,该方法可以准确提取并测量出切割缺陷尺寸和面积特征。以不同工艺参数下切割产品烧蚀区域宽度和面积为激光切割质量评价指标,研究了切割速度和氧气压力对切割质量的影响。当氧气压力在1.0 MPa范围内,顺时针切割时烧蚀区域宽度和面积呈现出相同的变化规律,逆时针切割时烧蚀区域宽度和面积呈现相反的变化规律。顺时针切割时,切割质量最佳,最小烧蚀宽度为9 px,最小烧蚀区域面积为34 px²。实验结果表明,所提出的方法能够快速识别出激光切割产品缺陷特征,准确评价激光切割质量。     

电子散斑干涉法测量金属表面受热变形及系统优化分析

为准确测量金属表面的受热形变,基于激光电子散斑干涉测量原理搭建了实验平台,实现了对金属受热形变的测量,经过数字图像处理,得到了金属表面形变的三维图形。为了优化测量效果,依托现有条件对所用激光光源进行了处理,并比对了不同粗糙度的物体测量效果。结果表明,使用经小孔滤波处理后的激光光源,可以得到效果更好的散斑图,而且粗糙的物体散斑对比度较高,可以有更高的测量准确度。所做工作可为测量金属表面形变提供实验方法,同时为提高散斑测量精度提供参考依据。