曲面模型重构方法比较及误差分析

三维CAD模型重建是逆向工程中的关键环节,在逆向设计中起到至关重要的作用。在运用Geomagic Studio软件进行点云处理、错误修复和曲面生成的基础上,重点讨论了曲面阶段的精确曲面重构和参数化曲面重构两种不同的曲面重构方法,并对同一种模型进行重构和误差分析。精确曲面重构方法可保证模型数据的完整性与精确性,从而生成高质量的模型;参数化曲面重构方法通过参数转换功能将初始曲面导入Solid Works软件中进行编辑,最后得到参数化模型。实际应用中可结合这两种方法各自特点及优势,高效优质地构建CAD曲面模型。     

大型管道快速测量与建模技术研究及应用

为了提高大尺寸管道测量效率和测量精度,搭建了一套具有快速、高精度、密集点云采集、实时数据处理等功能的扫描测量系统。基于坐标系变换理论,提出了一种数字摄影测量技术、双目结构光扫描技术和逆向工程重构建模技术的组合式测量方案,快速便捷地获得大范围高密度的物体表面点云,并利用三维重构软件对物体表面测量数据进行曲面重构,利用误差合成理论对测量及曲面重构过程中的误差进行了分析,论证了该方法在理论精度上满足工业生产对逆向工程的要求。将该组合式测量系统应用于大型锻造管道的测量重构,在效率和精度等各方面都取得了良好的效果。     

基于Imageware的卡扣模型曲面重构技术

曲面重构技术是逆向工程的重要组成部分,在工业制造、医疗、军事等应用领域意义重大。对曲面重构技术理论和imageware软件进行了介绍,并举例阐述了针对不同类型曲面应用imagaware软件进行曲面重构的典型方法。     

基于逆向工程的柴油机气道造型技术研究

本文采用逆向工程技术对某型船用柴油机气道模型进行了数据采集和逆向建模,研究了其建模关键技术,经过曲面重构和误差检验建立气道三维模型,模型取得了良好的精度和效果,为后续的产品分析和机械加工奠定了基础,为产品的开发和再设计提供了原始依据.     

犁臂三维几何模型逆向工程研究

介绍了逆向工程的基本概念,基于RE技术上的三维建模方法:数据采集、点云数据处理、三维模型重建。并以犁臂的三维重构过程为实例———利用ATOS光学扫描仪对犁臂表面进行扫描,获取三维点云数据。将测量的点云数据用Imageware软件进行处理后,再利用UGNX软件的曲面造型功能,实现犁臂的三维模型重构,最后对三维模型的精度进行了检测。说明在产品设计中利用数字化逆向工程技术,可大大缩短产品的开发周期,对快速响应市场产生显著效果。     

基于UG的汽车倒车镜的逆向设计

逆向工程技术作为一种实用、快速的产品设计开发方法,近几年来得到了广泛地应用.本文采用CMM对汽车后车镜进行数据测量,并在UG平台上对倒车镜的点云数据进行预处理、曲面重构、验证分析等,采用逆向工程技术对倒车镜进行设计开发.结果表明了UG软件在逆向曲面造型以及绘图效率等方面,有明显的优越性与实用性.     

偏转线圈逆向工程的解决方案

在对原偏转线圈逆向工程技术分析的基础上,提出了偏转线圈逆向工程新的解决方案。对其逆向过程中实物数字化和曲面重构等关键问题进行了论述,指出了使用新的方法可以大大提高偏转线圈反求的效率和精度。     

基于结构光视觉系统的三维曲面反求的研究

本文主要通过对结构光视觉系统的研究,描述了逆向工程中三维表面重构技术的基本原理和关键技术,通过MAT-LAB软件实现了曲面的重构;此研究对逆向工程很有意义。     

基于逆向工程的注塑模具快速设计

采用逆向工程技术可显著提高模具设计效率。在重构零件模型的过程中,先对零件的曲面特性进行分析,然后划分若干曲面片,对每一个曲面片分别进行重构,再进行重新组合,产生过渡曲面,从而完成整个曲面的重构。利用重构好的曲面模型,进行零件的CAD实体模型的造型。最后利用该CAD实体模型,设计出注塑模具。结果表明,重构模型的精度可以满足零件的注塑模具的设计要求。采用该方法,可以实现模具的快速设计,缩短新产品的开发设计周期。     

逆向工程关键技术及应用实例

介绍了逆向工程技术的定义及其工作流程,整个流程分为数据采集、数据处理和曲面重构三个部分。根据理论学习和自身实践经验对逆向工程的关键技术做了一些探讨。并以摩托车装饰板模型的曲面重建为例,用激光扫描仪获取三维点云数据,在CATIA中对点云进行数据处理,实现曲面重构,说明了逆向工程的整个设计应用流程.     

Accurate evaluation of free-form surface profile error based on quasi particle swarm optimization algorithm and surface subdivision

Although significant progress has been made in precision machining of free-form surfaces recently, inspection of such surfaces remains a difficult problem. In order to solve the problem that no specific standards for the verification of free-form surface profile are available, the profile parameters of free-form surface are proposed by referring to ISO standards regarding form tolerances and considering its complexity and non-rotational symmetry. Non-uniform rational basis spline(NURBS) for describing free-form surface is formulated. Crucial issues in surface inspection and profile error verification are localization between the design coordinate system(DCS) and measurement coordinate system(MCS) for searching the closest points on the design model corresponding to measured points. A quasi particle swarm optimization(QPSO) is proposed to search the transformation parameters to implement localization between DCS and MCS. Surface subdivide method which does the searching in a recursively reduced range of the parameters u and v of the NURBS design model is developed to find the closest points. In order to verify the effectiveness of the proposed methods, the design model is generated by NURBS and the measurement data of simulation example are generated by transforming the design model to arbitrary position and orientation, and the parts are machined based on the design model and are measured on CMM. The profile errors of simulation example and actual parts are calculated by the proposed method. The results verify that the evaluation precision of freeform surface profile error by the proposed method is higher 10%-22% than that by CMM software. The proposed method deals with the hard problem that it has a lower precision in profile error evaluation of free-form surface.     

基于参数曲面建模的车身表面逆向设计研究

针对在汽车车身设计逆向工程过程中,由于雕塑模型的精度有限以及三坐标测量的机测误差,所得的散乱点不能真实反映曲面形状而建立了一种曲面拟合方法,能够减小误差较大点的影响,保证据散乱点求得的曲面最接近于"理想"曲面.并简述了车身曲面逆向设计拟合方法的数学模型和CATIA软件创成式曲面设计模块的主要功能.将车身曲面的逆向设计分为2D图纸和3D实物逆向设计2类,给出设计流程和应用开发实例,解决了设计中容易出现的问题.     

复杂曲面机器人三维测量的误配准筛除算法

航空叶片属于复杂异形曲面,作为航天发动机的重要零件之一,其形状结构的高精度检测必不可少。复杂异形曲面由于其边缘曲率复杂,使得目前的点云配准技术尚无法满足其高精度配准需求,针对航空发动机叶片复杂异形曲面高精度配准的要求,提出了基于多尺度描述子的空间角度差分阈值筛除误配准对的配准算法,创新性的通过多尺度特征与空间角度差分阈值筛除算法相结合的方法实现高精度的异形曲面配准。该方法可以有效降低误匹配点和噪声点对配准效果的影响。实验表明,本算法对于航空叶片复杂异形曲面具有很好的配准效果,配准精度高,且具有良好的鲁棒性。     

基于表面贴合的不同视点传感器点云拼合方法研究

针对视觉传感器对物体表面点云数据采集的离散性,提出基于表面贴合的点云精确拼合方法。先对不同视点传感器获得的点云进行初始配准拼合,再以包容球方法选取点云重合表面区域的三处局部表面,用三维二次曲面方程拟合;旋转变换采用四元数法,经非线性最小二乘优化得到精确拼合的平移和旋转参数。该方法具有较快的收敛速度和较高的拼合精度,实例验证了所提方法的可行性。       

装配误差传递建模及其精度可靠性评估

研究了刚体零件的装配误差建模以及装配精度可靠性评估方法。将零件误差分成位置误差和方向误差,并采用误差矢量加以描述。综合考虑尺寸误差和形位误差,将装配过程误差分成零件内误差和配合面误差,给出主动配合面和被动配合面的定义。针对典型配合面类型,分析误差组成及其计算方法。采用位姿变换矩阵法建立装配误差模型,分析误差在零件内部以及配合面间的传递过程,计算装配总误差并据此确定装配误差的概率分布。给出装配精度可靠度的定义,通过仿真获得装配精度的可靠度指标。以某测量平台的装配过程为例,完成装配过程误差分析和装配精度可靠度评估,验证模型的有效性。     

An Automated Inspection System

An automated inspection system for manufactured parts is proposed using a cloud of 3D measured points of a part provided by a range sensor, and its CAD model. In spite of the high precision attained by coordinate measuring machines (CMM), range sensors offer significant advantages for dimensional inspection: a high speed of digitisation and the capacity to take 3D measurements on the whole surfaces of a part without physical contact. The system first registers a cloud of 3D points with a CAD model of the part, then segments the 3D points in different surfaces by using the CAD model, and finally measures the control of the specified tolerances on the part. Results of the inspection are displayed in two ways: visually, using a colour map to display the level of discrepancy between the measured points and the CAD model, and a hardcopy report of the evaluation results of the tolerance specifications. Two range sensor technologies have been tested and inspection results are compared with the results obtained with a CMM.     

给定精度条件下的Catmull-Clark细分曲面求交研究

细分曲面由于没有整体解析表达式,与参数、隐式曲面相比求交更加困难。针对基于平面四边形网格的Catmull-Clark细分曲面,在给定精度条件下,把对细分曲面的求交转化为对一定细分层次控制网格的求交:首先构造两张控制网格上相交四边形网格带及其1-邻域网格带,然后不断细分相交四边形网格带及其1-邻域网格带,提高求交精度,其次求解出相交四边形网格的交点,并根据拓扑关系将其顺序连接起来既得到两细分曲面之间的相交曲线,实现了细分曲面的求交。     

Prediction of surface reconstruction uncertainties for freeform surface inspection

A method is introduced to predict uncertainties of the B-spline freeform surfaces that are reconstructed from the measurement points for inspection of freeform surfaces. The uncertainties of a reconstructed B-spline surface are modeled by variances of coordinates of points on this freeform surface. Prediction of the uncertainty at any location on the reconstructed B-spline surface is carried out in two steps: (1) estimation of variances of the B-spline surface’s control points introduced by the surface reconstruction process, and (2) propagation of the variances from the control points to the points on the B-spline freeform surface. In this research, the variances of the control points of the reconstructed B-spline surface in all three directions are considered to improve the accuracy of uncertainty prediction in the regions with significant changes of geometric shapes. Both the errors and uncertainties at different locations on the reconstructed surface are considered in freeform surface inspection to compare the manufactured surface against the design surface and its tolerance. The developed method has been applied to two case studies to demonstrate its effectiveness.     

Modeling outlier formation in scanning reflective surfaces using a laser stripe scanner

Scanning reflective surfaces using 3D laser scanners is a challenging task since reflective surfaces of complex geometry promote the formation of unwanted data outliers. These outliers are characterized with large measurement errors, which significantly deteriorate the quality of the scanned point cloud data. This paper experimentally investigates the formation of outliers in relation to scanning reflective surfaces using a commercial laser stripe scanner. Two outlier formation models are developed: mixed reflection and multi-path reflection. The undesirable specular reflections in both mixed reflection and multi-path reflection scanning situations cause multiple peaks in the image sensing arrays. The false image peaks are recorded and will eventually be observed as outliers because they are not part of the scanned object surface geometry. A series of scanning experiments have been conducted and the results confirm the validity of the developed outlier formation models. Potential applications of the developed models such as scan path evaluation and outlier filter design are also discussed.     

基于三坐标测量机双参数向自适应测量自由曲面

提出一种基于三坐标测量机的双参数向自适应测量自由曲面方法。CMM手动测量被测曲面边界点后,连接点生成可测区域,由可测区域自动拓扑生成几条均布初始扫描线以及每条扫描线的均匀初始点,对于U向的各条扫描线,CMM在自动测完初始点后,不断拟合已测点为B样条曲线,由曲线末端曲率自适应预测下一测点并指导CMM自动测量。测完初始扫描线后拟合已测点云为B样条曲面,由曲面V向边界最大曲率自适应确定下一扫描线位置,并进行该条扫描线U向自适应测量,重复这一过程直至曲面测量完毕。测点可随被测曲面自身曲率变化特性而疏密分布,曲率变化大的重要特征区域分布密集,曲率变化小的非重要区域分布稀疏,既保证了重要特征点不会遗漏又避免了数据冗余。理论曲线曲面自适应测量实验结果表明该方法测量精度可达微米级,实例零件应用验证了该方法的可行性。