Development of automatic surface reconstruction technique in reverse engineering

The computer-aided design model reconstruction process is generally very complex, as it requires substantial efforts in planning and editing data points, curves, and surfaces. A novel method is developed in this study for automatic surface reconstruction from a huge number of triangular meshes. The proposed method is mainly composed of the following five steps: mesh simplification, quadrilateral mesh generation, curve net construction, connectivity data preparation, and multiple surfaces fitting with G¹ continuity across the boundaries. The first three steps build the boundary curves of the surfaces. The fourth step prepares the data needed for surface fitting, which includes segmented points, continuity conditions on the boundaries, and topological relationship of the data. In the final step, all regions of points are fitted into appropriate surfaces, with the accuracy and smoothness of the surfaces controlled and G¹ continuity between the surfaces. A detailed discussion for each of the above algorithms is provided. Successful examples are also presented to demonstrate the feasibility of the proposed method.     

Improved measurement accuracy in optical scatterometry using fitting error interpolation based library search

Library search is one of the most commonly used methods for solving the inverse problem in current optical scatterometry. One issue in the conventional library search method is that its final measurement accuracy is fundamentally limited by the grid interval of each parameter in the signature library. In this paper, we propose a fitting error interpolation based library search (FEI-LS) method to improve the measurement accuracy. By comparing the interpolated fitting errors estimated in a FEI-based fine search step, the structural parameters associated with the minimum interpolated fitting error can be treated as the final measurement result. Experiments performed on a photoresist grating have demonstrated that the FEI-LS method can achieve a higher measurement accuracy for a pre-generated library without remarkable influence on the search speed. It is expected that the FEI-LS method will provide a useful and practical means for solving the inverse problem in the state-of-the-art optical scatterometry.     

Characterization of Local 3-D Rough Dielectric Surfaces Using Standoff GPR Measurements with Widebeam Antennas

In real life most ground surfaces are not flat but rough. The observation of surface roughness depends on the wavelength and angle of the incident wave. In order to be able to detect shallow subsurface objects, on one hand we need to use higher frequencies to achieve better range resolution. One the other hand we have to deal with rough surfaces relative to shorter wavelengths. In this paper a wideband ground-penetrating radar (GPR) phase measurement and processing technique for characterizing three-dimensional (3-D) rough dielectric surfaces is presented. The method is based on the measurement of phase data by a standoff GPR with wide-beam antennas at short range over 3-D rough ground surfaces. The principle of this method was verified experimentally in the measurement of a composite surface. The height of the composite surface varies from 0 to 8 cm. The antennas are open-ended waveguide antennas whose frequency range is 2.3 GHz to 4.3 GHz. They are broadband, have low gain and wide beamwidth. The experimental tests demonstrate that the 3-D rough surfaces can be characterized locally by using a monochromatic and multifrequency broadband phase processing and imaging method. The results show good agreement between the imagery of the surface height distribution obtained by this method and the actual geometry of the 3-D rough surfaces.     

Topology recovery technique for complex freeform surface model after local geometry repair

Intersections and discontinuities commonly arise in surface modeling and cause problems in downstream operations.Local geometry repair,such as cover holes or replace bad surfaces by adding new surface patches for dealing with inconsistencies among the confluent region,where multiple surfaces meet,is a common technique used in CAD model repair and reverse engineering.However,local geometry repair destroys the topology of original CAD model and increases the number of surface patches needed for freeform surface shape modeling.Consequently,a topology recovery technique dealing with complex freeform surface model after local geometry repair is proposed.Firstly,construct the curve network which determine the geometry and topology properties of recovery freeform surface model;secondly,apply freeform surface fitting method to create B-spline surface patches to recover the topology of trimmed ones.Corresponding to the two levels of enforcing boundary conditions on a B-spline surface,two solution schemes are presented respectively.In the first solution scheme,non-constrained B-spline surface fitting method is utilized to piecewise recover trimmed confluent surface patches and then employs global beautification technique to smoothly stitch the recovery surface patches.In the other solution scheme,constrained B-spline surface fitting technique based on discretization of boundary conditions is directly applied to recover topology of surface model after local geometry repair while achieving G 1 continuity simultaneously.The presented two different schemes are applied to the consistent surface model,which consists of five trimmed confluent surface patches and a local consistent surface patch,and a machine cover model,respectively.The application results show that our topology recovery technique meets shape-preserving and G 1 continuity requirements in reverse engineering.This research converts the problem of topology recovery for consistent surface model to the problem of constructing G 1 patches from a given curve network,and provides a new idea to model repairing study.     

A robust surface fitting and reconstruction algorithm for form characterization of ultra-precision freeform surfaces

Ultra-precision freeform surfaces are non-rotational symmetric surfaces possessing sub-micrometer form accuracy and nanometric surface finish. Although they can be fabricated accurately by ultra-precision machining technology, their surface quality is difficult to be characterized. Surface reconstruction is a vital task in the form characterization of ultra-precision freeform surfaces. This paper presents a robust surface fitting algorithm to reconstruct a high fidelity surface from measured discrete points while the surface smoothness can be ensured as well. A fitting threshold named confidence interval of fitting error is proposed to strike the balance between fitting accuracy and surface smoothness in the fitting process. The fitting algorithm is in two steps. In the first step, bidirectional sampling method is developed to extract a curve network from measured points cloud to construct an initial surface. In the second step, the fitting error of the initial surface is minimized to meet the prescribed fitting error threshold. A series of experimental work has been conducted and the results show that the proposed algorithm is able to provide effective means for increasing the accuracy in the form characterization of ultra-precision freeform surfaces.     

Application of the lifting wavelet to rough surfaces

This paper proposes a lifting wavelet model for enhancement of accuracy of surface roughness characterisation. In this work, the theory and fast algorithm of the lifting wavelet are briefly introduced and a lifting wavelet model for extraction of roughness of surfaces has been developed. The rough surface recovered has good refinement accuracy in contrast to the least squares polynomial fitting. Applications are conducted by using a series of typical surfaces, planes and curves, measured by contact (stylus) and non-contact (phase-shifting interferometry) instruments, to demonstrate the feasibility and applicability of using the lifting wavelet model in the analysis of these surfaces.     

粗糙表面仿真方法综述

粗糙表面在自然界普遍存在。在研究表界面现象时,粗糙表面往往是重要的输入信息。实际测量和数值仿真是获取粗糙表面的两种常用方法。与实际测量相比,数值仿真无需昂贵的测量设备和大量机时,即可根据给定的表面特征信息高效地批量生成粗糙表面。目前,表面仿真已有近五十年的发展历史,基于不同表面形貌特征形成了采用多种表面特征参数的多种仿真方法,在摩擦学研究中应用广泛。梳理和总结表面仿真方法利于方法的高效、准确应用以及进一步发展。考虑到表面仿真方法与表面形貌特征及其表征参数密切相关,为了系统全面地综述表面仿真方法,首先介绍与表面仿真相关的形貌特征表征方法及特征参数。随后,以不同特征为线索对相应的表面仿真方法的原理、算法、优缺点进行梳理,初步提出了方法选用建议,并整理了其在摩擦学研究中的典型应用,最后展望了未来粗糙表面仿真的可能研究方向。     

基于快速傅里叶变换和共轭梯度法求解干接触问题

为求解粗糙表面弹性接触问题,将其转化为一个线性补余能问题,进而简化为一个二次函数的条件极值问题,利用共轭梯度法求解。算法实现了在共轭梯度方向上修正步长的优化,有效地提高了收敛效率。而占用大量计算时间的弹性变形求解采用快速傅里叶变换(Fast Fourier transform,FFT)技术,该算法有效地克服了传统傅里叶变换所引起的周期性误差。计算实例模拟了点接触单峰表面,正弦表面和真实粗糙表面的弹性接触以及有限长滚子线接触等接触问题。计算结果显示目前所用算法有效地缩短了干接触弹性接触问题的求解时间,对于不同的粗糙表面和接触类型都表现出一致的良好收敛性,同时计算精度对网格的依赖性很小,是工程中有效的分析设计工具。     

A novel machining of multi irregular surface using improved noncircular turning method

The backplane processing is an important part of the manufacture of electronic communication equipment; the current processing of backplane surface, especially the rough machining, is still using milling; and the production efficiency is quite low. This paper presents a new method to turn with a cylinder for the rough machining of multi backplane surfaces, which is based on a conventional horizontal lathe and uses the improved method of noncircular machining. The performance requirements of fast tool servo (FTS) device and control model for the machining of noncircular surface are analyzed firstly; the position following control strategy is used instead of traditional position interpolation, according to the multi backplane surfaces machining technology and control strategy; and a novel algorithm, which is combined UG (Unigraphics NX) software surface fitting with cubic spline curve fitting of multi backplanes’ space, is proposed for computer-aided manufacturing (CAM) software design. Finally, the proposed processing method and CAM model algorithm are proved to be effective through the simulation and actual verifications, the products meet the processing requirements and the processing time of each piece is reduced from 8 to 2 min, and they also greatly improve the production automation and achieve energy saving and emission reduction.     

含非规则粗糙间隙表面铰链关节的平面柔性多连杆传动系统动态误差与运动副磨损周期行为分析

传统旋转间隙关节接触模型假定销轴和衬套接触面形状是规则的并忽略了磨损效应的影响,降低了机构动力学模型预测精度。提出了一种含非规则粗糙间隙表面铰链关节的平面柔性多连杆机构多体动力学建模、磨损预测和动态误差分析方法。为准确描述运动副元素间碰撞行为,考虑滑动轴承间隙关节的磨损效应,提出了一种非规则粗糙间隙表面铰链关节的改进接触模型。在此基础上,考虑柔性杆的影响,基于绝对节点坐标法建立了含非规则粗糙间隙表面铰链关节的平面柔性多连杆传动系统多体动力学模型。与基于传统光滑间隙模型的结果相比,基于非规则粗糙间隙改进模型的多连杆机构动态响应更接近于试验值,验证了所提出计算方法的有效性。仿真结果表明,选用CuSn10P和CuPb30作为铰链衬套材料能够有效降低多连杆机构滑块动态响应偏差和提高机构的运动精度;表面粗糙度过高会导致运动副磨损加剧,过低则会降低间隙表面微凸体对碰撞能量的吸收。此外,磨损加剧了间隙表面轮廓不规则度,导致机构动态响应的不稳定性增大,运动精度降低。     

An Approximate Lofting Approach for B-Spline Surface Fitting to Functional Surfaces

Owing to their specific functionality, surfaces are often given as bivariate functions including non-polynomial or higher-orde polynomial terms. It is necessary to represent them in standard formats such as non-uniform rational B-splines (NURBS) for approximation. As most such surfaces require fine quality of surfacing and high precision of manufacturing, accuracy should be guaranteed in their representations. As high accuracy is likely to result in bulky and redundant representations, it is also important to make them more com-pact. For NURBS surfaces, control points must be reduced without sacrificing accuracy. This paper presents an approximate lofting method for B-spline surface fitting to a functional surface within a specified accuracy. It adopts adaptive sampling and multiple B-spline curve fitting. The method is very effective when the surface shape is longish or the cross-sectional curves vary regularly in shape along a specific direction. Some experimental results demonstrate its usefulness and quality.This revised version with a corrected online cover date was published online in April 2004.     

Inverse estimation of bi-directional reflectivity in long-wave infrared region by using RPSO algorithm

The Infrared signature is used in the fields of remote sensing, military defense and auto navigation system by detecting objects against the background. Infrared signature of objects depends on many factors, including the shape of objects, surface temperature, emissivity, bidirectional reflectivity and radiation sources such as solar irradiation and sky shine. It is essential to procure radiative surface properties in predicting the infrared signature of objects. Especially the bidirectional reflectivity is difficult to obtain due to the limited data in the literature. In this study, we develop a software which estimates radiative properties of painted surfaces inversely from the measured temperature and radiance variations with time by using the Repulsive particle swarm optimization (RPSO) algorithm. In this study surface radiative reflection properties in the LWIR region are estimated for 3 different paints by using the pre-determined radiance in LWIR region and surface temperature. The results obtained from this study show fairly good agreement with the original BRDF data used to estimate the LWIR radiance and temperature as the input data.

     

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.     

复杂曲面测量数据最佳匹配问题研究

针对复杂曲面类零件加工余量分析过程中的测量数据匹配问题,提出通过初始匹配和精确匹配来实现曲面测量数据的最佳匹配。交互式的初始匹配过程决定后续算法的变量范围,精确匹配确定测量数据与曲面的最佳匹配姿态。精确匹配采用最小二乘法构造评估函数,应用边界约束BFGS方法对问题涉及的曲面匹配变换矩阵的6个未知量进行优化求解。对通过三坐标测量机获取的数据,提出了一种测头半径补偿方案。实验结果表明,该方法与遗传算法相比具有运算速度快和精度高等特点,能较好地解决复杂曲面类零件测量数据的匹配问题。     

激光扫描表面特征的点云数据处理方法

为了提高激光测量系统对工件表面特征的测量精度,减少数据处理中由于特征点云拟合选择对测量精度的影响,针对比较常见的两种表面特征提出了正确的拟合方式。从工件表面的实测数据出发,经过多次实验,结合表面测量特征的拟合原理,分析不同点云处理方法之间的差异,并给出了最适合该特征的拟合方式及其原因。实验表明,不同的点云拟合方式对特征测量的影响比较大,选择正确的拟合方式才能保证测量的准确性。     

A hybrid approach to smooth surface reconstruction from 2-D cross sections

This article presents a hybrid approach to smooth surface reconstruction from serial cross sections, where the number of contours varies from section to section. In a triangular surface-based approach taken in most reconstruction methods, a triangular surface is constructed by stitching triangular patches over a triangular net generated from the compiled contours. In the proposed approach, the resulting surface is a G¹ composite surface consisting of three kinds of surfaces: skinned, branched, and capped surfaces. Each skinned surface is first represented by a B-spline surface approximating the serial contours of the skinned region and then is transformed into a mesh of rectangular Bezier patches. On branched and capped regions, triangular G¹ surfaces are constructed such that the connections between the triangular surfaces and their neighbouring surfaces are G¹ continuous. Because each skinned region is represented by an approximated rectangular C² surface instead of an interpolated triangular G¹ surface, the proposed approach can provide more visually pleasing surfaces and realize more efficient data reduction than the triangular surface-based approach. Some experimental results demonstrate its usefulness and quality.     

基于奇异值分解的橡胶密封圈表面缺陷检测方法

为解决橡胶密封圈表面缺陷人工检测效率低,缺陷提取困难等问题,提高橡胶密封圈缺陷在线检测速度及准确率,提出一种基于机器视觉的橡胶密封圈表面缺陷检测方法。该方法采用多相机多线程图像采集模式,采集橡胶密封圈的上下表面不同位置的局部图像;对图像自适应中值滤波后进行边缘增强,并使用高斯差分算子提取轮廓粗边缘,利用Zernike 矩获取亚像素边缘位置;针对边缘存在不连续点问题,使用Ceres库多项式拟合,估计断点位置,并更新所有边缘位置;根据边缘位置寻找出整张图像中橡胶密封圈表面图像区域,并将该环形兴趣区域映射到矩形区域中;将获得的图像进行奇异值分解（SVD）,并通过连通域分析,提取出图像中的奇异区域,即存在缺陷的位置。经实验验证,基于奇异值分解的橡胶圈表面缺陷检测方法鲁棒性好、效率高,可以快速准确地寻找出橡胶密封圈表面缺陷信息。     

A numerical-analytical approach to determining the real contact area of rough surface contact

ABSTRACT

The objective of this study is to improve the accuracy of the real contact area calculated by the semi-analytical method (SAM). Two types of surface pairs are investigated: an analytically generated sinusoidal wavy surface against a rigid flat, and a pair of real rough surfaces. The results suggest that the real contact area calculated by the SAM is extremely sensitive to the resolution of input, i.e. the grid size. The SAM results of the real contact areas show poor convergence, especially in the case of the real rough surfaces. The main reason for this difference is the ‘over-covering’ effect when SAM calculates the real contact area. An exponential extrapolation technique is proposed to predict the real contact area values when further refinement of the grid resolution is unfeasible.     

数字滤波法模拟粗糙表面的误差分析

计算机模拟加工表面是数值模拟研究表面形貌特征对摩擦和润滑性能影响的前提。基于低通数字滤波技术,通过比较计算机模拟表面和实测磨削表面的粗糙度、峰度、偏度、面积支承率和自相关函数,研究了低通数字滤波法模拟加工表面高度分布特征和自相关函数的精确度,并对加工表面模拟过程中产生的高度分布误差进行了具体分析和讨论。分析结果表明:低通数字滤波法在模拟非高斯粗糙表面时模拟精确度主要受目标表面高度分布特征的影响较大,而且该方法生成非高斯表面存在一定的局限性无法生成特定高度分布的粗糙表面。