逆向工程中自由曲面重构的算法探讨

介绍常用的自由曲面反求的几种算法和特点及归类 ,探讨目前曲面重构过程中的难点、热点问题。     

An integrated reverse engineering approach to reconstructing free-form surfaces

An integrated reverse engineering approach to generating free-form surfaces has been developed to create CAD-compatible free-form surface models with a coordinate measurement machine and a touch trigger probe. The approach integrates data digitization and surface modelling to obtain an efficient and accurate digitization process with a collisionfree exploration path, and to reconstruct least-squares bi-cubic B-spline surface models for rapid product prototyping. The whole approach is divided into two stages: the planning of boundary digitization; and the adaptive model-based digitizing process (AMDP). The planning of boundary digitization defines the exploration surface region. The AMDP then automatically explores the whole measured surface region with a collision-free exploration path, continuing until a satisfactory surface model corresponding to the user's specified digitizing accuracy is obtained. This approach significantly reduces the product development lead time and obtains a surface model with controlled digitizing accuracy. The validity and applicability of this approach are demonstrated by three practical industrial examples.     

逆向工程中自由曲面拟合方法的分类与比较

阐述了逆向工程中自由曲面拟合的曲面重构和多个曲面整合两方面内容。曲面重构可分为插值和逼近两种方法,其中插值的方法有样条插值、基于散乱点数据的三角曲面插值;而逼近的方法有最小二乘逼近、基于能量原理的曲面逼近、偏微分方程逼近和小波理论的逼近方法等。则多个曲面整合包括几何连续性和参数连续性。本文对他们分别进行了介绍归类和比较,并且得出了有关的结论。     

基于实物的一种自由曲面逆向工程方法

提出一种基于实物的自由曲面逆向工程方法,利用投影栅相位法和ObjectARX开发工具,可在AutoCAD环境下自动建立三维曲面模型,方便地实现自由曲面的反求,并可直接实现与其他CAD软件的数据交换.     

Parameterization of prismatic shapes and reconstruction of free-form shapes in reverse engineering

This article proposes an adaptive loss function (AL) control chart for statistical process control (SPC). This chart is able to monitor process shifts in the mean and variance simultaneously. It is appealing for its effectiveness in detecting process shifts and simplicity in operation under a computerized SPC environment. By using a fixed sample size and a fixed sampling interval, the AL chart can be operated as easily as the conventional ${\bar X}$ and S charts from the stand of the operators. Nevertheless, via the computer-aided adaption of some charting parameters, the AL chart is not only significantly more effective than the ${\bar X}$ and S charts, but it also outperforms the cumulative sum (CUSUM) charts for most of the combinations of mean and increasing variance shifts.     

利用AutoCAD图形数据库技术的自由曲面反求软件系统设计

以AutoCAD为平台,研究开发自由曲面反求软件系统,阐述AutoCAD图形数据库技术在系统中的应用,提出了创建反求曲面实体及绘制曲面特征线的具体实现方法,最后给出了系统应用实例。     

反求工程中的数字化方法及其集成化研究

表面数字化是反求工程中的基础和关键技术之一，而多种数字化方法的集成化研究已成为一种重要的研究趋势。首先对反求工程中常用的表面数字化方法原理、特点和应用范围进行了分析，并对被动视觉、主动视觉及三坐标测量机等多种数字化方法的集成化研究现状进行了综述。最后对反求工程中的数字化方法进行了总结并指出了进一步研究的方向。     

In-field performance of an optical digitizer for the reverse engineering of free-form surfaces

The use of OPL-3D, a robust, flexible and easy-to-use optical digitizer, in conjunction with reverse engineering procedures is presented. The optical digitizer is used as a stand-alone (i.e., not in tandem with popular CMM’s) system, whose output point clouds can be manipulated, by means of both specifically-designed software and high-performance commercial software, to produce mesh surfaces and NURBS of the acquired shape. The digitizer-process combination yields accurate digital replicas of the target object, the accuracy of the whole combination being on the order of 1/1500 of the measurement range. The speed of acquisition, combined with the above high accuracy, the ease of use and the fact that recalibration is seldom required makes the digitizer ideal for reverse engineering in an enormous number of applications ranging from automotive to biomedical.     

Rapid and accurate reverse engineering of geometry based on a multi-sensor system

The reduction of the lead time in measurement and reverse engineering, and the increased requirements in terms of accuracy and flexibility, have resulted in a great deal of research effort aimed at developing and implementing multi-sensor systems. This paper describes an effective competitive approach for using a tactile probe to compensate the data from a laser line scanner to perform accurate reverse engineering of geometric features. With the data acquired using laser scanning, intelligent feature recognition and segmentation algorithms can be exploited to extract the global surface information of the object. The tactile probe is used to re-measure the geometric features with a small number of sampling points and the obtained information can be subsequently used to compensate the point data patches which are measured by laser scanning system. Then, the compensated point data can be exploited for accurate reverse engineering of a CAD model. The limitations of each measurement system are compensated by the other. Experimental results on three parts validate the rapidity and accuracy of this multi-sensor data fusion approach.     

NURBS curve and surface fitting for reverse engineering

Reverse engineering is an approach for constructing a computer-aided design (CAD) model from a physical part through dimensional measurement and surface modelling. This paper presents alternatives for reverse engineering of free-form parts using Non-Uniform Rational B-Spline (NURBS) surfaces. A two-step linear approach is employed for fitting NURBS curves and surfaces using the measured points. During the first step, the weights of the control points are identified from a homogeneous system using symmetric eigenvalue decomposition. The control points are further processed in a way similar to B-spline curve and surface fitting. Some examples are presented to illustrate both the steps of reverse engineering and the process of NURBS curve and surface fitting.     

涡流喷嘴反求技术研究

涡流喷嘴是涡流管的核心部件,其结构特征直接决定涡流管能量分离效果的好坏。基于逆向工程技术,以快速模具制造技术(RT)实现快速实物特征复制,获取完整的原型表面点云信息;以逆向工程(RE)技术完成喷嘴流道高精度重建;以正向再设计完成喷嘴的改进,找到优化喷嘴结构的设计方案。     

An algorithm of NURBS surface fitting for reverse engineering

Reverse engineering is an approach for constructing a CAD model from a physical part through dimensional measurement and a surface model. Different from conventional methods, this paper develops a new algorithm by which a desired fitted surface is obtained with less computation. Let selected m×n measured points be control points to construct B-spline or NURBS surface, then modify this constructed surface by using all the measured points and least squares minimization. A new algorithm for parameterization for measured points is also presented in this paper. The effectiveness and efficiency of these proposed algorithms are demonstrated.     

A rapid and intelligent approach to design forming shape model for precise manufacturing of flanged part

Adjusting the part shape with complex flanges to compensate springback deformation is key to forming shape design for manufacturing rapidly and precisely. Classical forming shape design by displacement adjustment (DA) method using finite element (FE) simulation is usually time-consuming and not accurate enough for complex surface part in industrial application. In this paper, the forming shape is modeled by changing the relations of geometric features of part model with the new flange control surfaces directly. Control surface processing (CSP) method is presented including control surface trimming, cross section division, springback compensation, and extending to design forming shape model of doubly curved flange part with joggles rapidly. The algorithms of cross section curves division of control surfaces and subsequent subdivision of each curve with circular arc and line segments are proposed. A case-based reasoning (CBR) technique and gray relation analysis (GRA) are used to support the intelligent springback prediction of each bending segment of the cross section curve. The geometric data of control surface is expressed in XML format to realize the integration of the CAD-based tools of control surface division and compensation with the Web-based springback prediction system. The approach is demonstrated on an industrial aircraft wing rib part. The forming shape model could be designed rapidly by comparison with DA method. The part shape deviations of flange angle (?0.465° ~ 0.528°) and surface position (?0.3 mm ~ 0.3 mm) were detected by comparing the desired geometry with the actual digital formed part shape, and the results indicate that the approach can achieve the industrial part manufacturing rapidly and precisely.     

Improved intermediate point curve model for integrating reverse engineering and rapid prototyping

Direct integration of reverse engineering and rapid prototyping removes two intermediate steps of surface fitting from point cloud data and STL file generation from CAD models. Therefore errors introduced due to surface fitting and triangulations are eliminated and also the process of STL data validation and repair is avoided. Intermediate point based curve model (IPCM) method is one of the promising approaches for direct integration of reverse engineering and rapid prototyping however this approach has the limitation that it cannot handle objects, which result in multiple contoured slices. Moreover, IPCM based method is implemented with layers of constant thickness slices, and adaptive slicing with this method is not attempted. The present work is an attempt towards improving the capabilities of IPCM based method by overcoming the above-mentioned two limitations. The new system developed here has been tested on many parts, which demonstrates the capability of the proposed system. An erratum to this article can be found at     

逆向工程中三角Bezier曲面建模方法的研究

针对目前逆向工程三角Bezier曲面建模中存在的缺点,介绍两种解决方法:基于三角Bezier曲面模型的逆向工程CAD建模方法和基于局部三角Bezier曲面片逼近的点插补算法.通过这两种方法解决了所构造的曲面模型与现有的CAD/CAM软件系统接口难等问题,使得三角Bezier曲面建模变得切实可行.     

A reverse engineering approach to generate a virtual plant model for PLC simulation

A reverse engineering approach to generate a virtual plant model is proposed. The model can be used for programmable logical controller (PLC) simulation. The virtual plant model for the PLC simulation consists of virtual device models and must interact with the input and output signals of a PLC. The behavior of a virtual device model should be the same as that of real device. Conventionally, the discrete event system specifications (DEVS) formalism has been used to represent the behavior of a virtual device model. Modeling using DEVS formalism, however, requires in-depth knowledge of the simulation area, as well as a significant amount of time and effort. One of the key ideas of the proposed methodology is to provide a method to generate a virtual plant model using both log data (time-stamped signal history) and a PLC I/O signal table extracted from the existing production system. The proposed reverse engineering approach provides two major benefits: (1) significant reduction in the time and effort for the construction of a reliable virtual plant model of a current production system, which can be referenced for newly planned production systems, and (2) reduction in the stabilization time of a production system through PLC simulation. The proposed approach was implemented and applied to an automated production line.     

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.     

基于实物的复杂曲面产品反求工程中的CAD建模技术

基于零件实物样件的几何模型的反求已成为ＣＡＤ／ＣＡＭ领域中的一个研究热点,对目前国内外在复杂曲面产品反求工程中ＣＡＤ建模方面的研究现状做一较为简要的归纳。     

复杂曲面实物的逆向工程及其关键技术

系统研究和分析了逆向工程主要实施阶段中的关键问题。将整个逆向工程分为数据获取、数据处理和曲面重构相互衔接的 3部分 ,针对各部分不同的特点和解决方案加以论述和分析 ,着重论述曲面重构中的一些关键步骤并归纳总结出解决方案 ,最后提出逆向工程的整体框架模型