REVERSE ENGINEERING BASED ON COMPUTER VISION FOR FREE FORM SURFACE

The key issues such as vision sensor, sampling planning are studied for reverse engineering. For the developed sensor, the low sensitivity to the incident angle and the high linearity between the output and the input are carried out. During digitizing, the adaptive sampling planning method based on the curvature of surface and the slope of tangent line of measured point is proposed. After integrating the vision sensor, CNC milling and relevant software, the reverse engineering system based on computer vision is developed. The experiment shows that this system is reliable and efficient.

METHOD TO EXTRACT BLEND SURFACE FEATURE IN REVERSE ENGINEERING

A new method of extraction of blend surface feature is presented. It contains two steps: segmentation and recovery of parametric representation of the blend. The segmentation separates the points in the blend region from the rest of the input point cloud with the processes of sampling point data, estimation of local surface curvature properties and comparison of maximum curvature values. The recovery of parametric representation generates a set of profile curves by marching throughout the blend and fitting cylinders. Compared with the existing approaches of blend surface feature extraction, the proposed method reduces the requirement of user interaction and is capable of extracting blend surface with either constant radius or variable radius. Application examples are presented to verify the proposed method.

Deformation-based freeform feature reconstruction in reverse engineering

For reconstructing a freeform feature from point cloud, a deformation-based method is proposed in this paper. The freeform feature consists of a secondary surface and a blending surface. The secondary surface plays a role in substituting a local region of a given primary surface. The blending surface acts as a bridge to smoothly connect the unchanged region of the primary surface with the secondary surface. The secondary surface is generated by surface deformation subjected to line constraints, i.e., character lines and limiting lines, not designed by conventional methods. The lines are used to represent the underlying informa-tion of the freeform feature in point cloud, where the character lines depict the feature’s shape, and the limiting lines determine its location and orientation. The configuration of the character lines and the extraction of the limiting lines are discussed in detail. The blending surface is designed by the traditional modeling method, whose intrinsic parameters are recovered from point cloud through a series of steps, namely, point cloud slicing, circle fitting and regression analysis. The proposed method is used not only to effectively and efficiently reconstruct the freeform feature, but also to modify it by manipulating the line constraints. Typical examples are given to verify our method.

A Neural Network Approach on Reverse Engineering Surface Reasoning in the Manufacturing Field

This paper applied the neural network technology to surface reasoning in reverse engineering and established the neural network computation model. One of the main advantages of reasoning solid surface using neural network is that no knowledge about surface is needed, and the limited measured points on the surface will do sufficiently. This paper listed the related reasoning cases, including the elementary analytical surfaces and freeform surfaces, discussed the various issues occurring during reasoning process and proved the feasibility and efficiency of this approach from theory and practical computing cases. The results show that a neural network is an excellent aided analysis means for surface reasoning in reversing engineering and possesses practical use for the surface that is complex, incomplete and partially worn out or damaged.

An Application Study of Transition Surface Reconstruction in Reverse Engineering

the reconstruction of transition surface is one of time consuming activities during surface modeling in reverse engineering. Yet currently available software applications suffer from shortcoming in processing the connection among free form surfaces. In this paper, a new method is put forward combining Surfacer with Unigraphics to resolve this problem: Curves and surfaces are first constructed in Surfacer, then, the finished data is imported into Unigraphics based on IGES fonnat. At last, the transition surface can be reconstructed in Unigraphics. The application of this method in transition surface reconstruction is illustrated by means of two case studies, showing the connection between free form surfaces; filleting and rounding among multiple surfaces: transition surface between two sets of surfaces.

Three-Dimensional Geometrical Modelling of Wild Boar Head by Reverse Engineering Technology

In this paper, a wild boar head was taken as the bionic research object for the development of new ridgers, a kind of plough. The reverse engineering technology was adopted to obtain the surface geometrical information of the head. Several three-dimensional （3D） point clouds of the head were captured first using a non-touch laser scanner, and an integrated point cloud was generated by aligning these point clouds using UG/Imageware. Then, the digital surface model of the head was rebuilt by means of CATIA. The characteristic curves of the surface model were analyzed. The results show that the average error between the rebuilt surface and the point cloud is -0.431 ram. The max curvature of the ridge on the neb of the head is 0.187 mm^-1, and the max and rain Gauss curvatures on the surface are 0.008 mm^-2 and -0.002 mm^-2. These geometrical information are the essential parameters for biomimetics study of the ridger.

Color 3D Reverse Engineering

This paper presents a principle and a method of col or 3D laser scanning measurement. Based on the fundamental monochrome 3D measureme nt study, color information capture, color texture mapping, coordinate computati on and other techniques are performed to achieve color 3D measurement. The syste m is designed and composed of a line laser light emitter, one color CCD camera, a motor-driven rotary filter, a circuit card and a computer. Two steps in captu ring object’s images in the measurement process: First, the color CCD camera ta kes the color picture of the object to be used for texture mapping in post proce ssing. Secondly, the monochrome data of the object is taken. The laser light emi tter is started; the light plane and the surface of the object intersect to form an undulate line, which forms an image on the CCD sensor. After the optic- electronics transformation, the electronic signals are captured and send to the computer. A new color 3D measurement model was derived, and a rapid calibra ting method to measure the system parameters was proposed--optical plane equat ion calibrating method. A calibrating drone was designed and built. 3D color sca nning system not only provides an object’s individual point information in the 3D coordinate, in the mean time, it provides the color information of each indiv idual point. This paper also advances a multi-frame auto-merging method, i.e. several frames of color 3D digital images measured are merged quickly according to their curvature characteristics and RGB information. Initial matching and fin e tune of the registration are completely performed by the computer; initial mat ching is via user interface in helping computer to find the transformation matri x. The transformation matrix is found according to the geometric characteristics chosen by hand. After the initial transformation matrix is found, fine tune of the registration is preformed to do the optimum adjustment to achieve a complete color textured 3D model. The system can be broadly used in the fields of produc t design, mold manufacture, multimedia, game development, animation, medical eng ineering, antique digitization, etc.

LEAST-SQUARES METHOD-BASED FEATURE FITTING AND EXTRACTION IN REVERSE ENGINEERING

The main purpose of reverse engineering is to convert discrete data pointsinto piecewise smooth, continuous surface models. Before carrying out model reconstruction it issignificant to extract geometric features because the quality of modeling greatly depends on therepresentation of features. Some fitting techniques of natural quadric surfaces with least-squaresmethod are described. And these techniques can be directly used to extract quadric surfaces featuresduring the process of segmentation for point cloud.

Fringe Projection Measurement System in Reverse Engineering

Acquisition of physical data with high precision is a key step in reverse engineering (RE). It is an important stimulative for the progress of reverse engineering with which various digitizing devices are invent ed, developed and made applicable. This paper introduces a three dimensional opt ical measurement method based on digital fringe projection technique in RE to im prove the technique through its application. A practical example is presented an d the result demonstrates the applicability and feasibility of the measurement s ystem as well as the reliability and validity of relevant methods and algorithms .

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 freeform surface model; secondly, apply freeform surface fitting method determine the geometry and topology properties of recovery 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~ 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 Gt continuity requirements in reverse engineering. This research converts the problem of topology recovery for consistent surface model to the problem of constructing G1 patches from a given curve network, and provides a new idea to model repairing study.

CNC NON-CONTACT MEASURING SYSTEM FOR FREEFORM SURFACE

Developing CNC measuring method on the base of coordinate machine can makethe best of the hardware resource of CNC system and realize the integration of CAD/CAM/CAT. Based onthe evenly spaced parallel planes scanning, a new adaptive digitizing approach for freeform surfacenamely arc length extrapolation is put forward. By this way, the digitizing approach can be addedto the CNC system, while the system's hardware and software are not changed.

NEW VISUAL METHOD FOR FREE-FORM SURFACE RECONSTRUCTION

A new method is put forward combining computer vision with computer aidedgeometric design (CAGD) to resolve the problem of free-form surface reconstruction. The surface isfirst subdivided into N-sided Gregory patches, and a stereo algorithm is used to reconstruct theboundary curves. Then, the cross boundary tangent vectors are computed through reflectance analysis.At last, the whole surface can be reconstructed jointing these patches with G^1 continuity(tangentcontinuity). Examples on synthetic images are given.

A Computer Vision Method for 3D Reconstruction of Curves-Marked Free-Form Surfaces

Visual method is now broadly used in reverse engineering for 3D reconstruction. The traditional computer vision methods are feature-based, i.e., they require that the objects must reveal features owing to geometry or textures. For textureless free-form surfaces, dense feature points are added artificially. In this paper, a new method is put forward combining computer vision with CAGD. The surface is subdivided into N-side Gregory patches using marked curves, and a stereo algorithm is used to reconstruct the curves. Then, the cross boundary tangent vector is computed through reflectance analysis. At last, the whole surface can be reconstructed by jointing these patches with 1Gcontinuity.

正反向排水板真空预压法在地基处理工程中的应用

目前真空预压法加固软土地基中排水板负压源通常位于顶部,由于真空度沿竖向的衰减,普通真空预压对深层土体的加固效果较差。为此提出了正反向排水板相结合的排水方式,正向排水板的负压源在排水板顶部,反向排水板的负压源在排水板的底部。将正反向排水板结合真空预压应用于温州某地基处理工程中,对地表沉降、真空度、孔隙水压力等指标的监测结果显示,平均固结度达到93.1%。相同工况下正反向排水板结合真空预压数值模拟得到的地表沉降大于正向排水板结合真空预压得到的地表沉降,增长率达到12.9%;相同工况下正反向排水板结合真空预压数值模拟得到的孔隙水压力在3~10 m范围内的消散情况明显优于正向排水板结合真空预压,地基加固效果更好。正反向排水板结合真空预压方法值得在工程中进一步推广应用。

含氟纳米乳液的制备及在储层润湿逆转中的应用

以甲基丙烯酸甲酯、丙烯酸丁酯、γ-甲基丙烯酰氧基丙基三甲氧基硅烷、全氟己基乙基丙烯酸酯(PEA)为原料,制备了一种可改变储层润湿性、防止储层水锁的含氟纳米乳液(FPA)。采用FTIR、SEM、XRD、马尔文激光粒度仪对FPA乳液进行了表征,采用表面张力、排出率、毛细管自吸、接触角测试方法考察了FPA-3(PEA质量分数为1.5%)乳液质量分数对改变岩心润湿性的影响。结果表明,PEA成功引入到聚合物链上,随着PEA质量分数的增加,乳液粒径增大,当PEA质量分数>1.5%时,乳液出现分层,FPA-3乳液稳定性最好。随着FPA-3乳液质量分数的增大,FPA-3水溶液表面张力减小,排出率增大,毛细管自吸高度减小,与水的接触角增大。当乳液质量分数均为2.0%时,与PA水溶液相比,FPA-3水溶液的表面张力由46.01 mN/m减小至22.68mN/m,降低了50.70%;排出率由19.89%增至29.47%,提高了48.16%;岩心的表面自由能由73.2 mN/m减小至8.7 mN/m;使岩心由亲水性(θ=69.8°)转变为疏水性(θ=125.1°)。质量分数为2.0%的FPA-3水溶液的毛细管自吸高度由清水的42 mm减至30 mm。

CT用于非人体目标几何体的三维重建

当被扫描物体存在镂空、遮挡和狭小空间时,需要大量图像拍摄或激光扫描工作;利用三维点云构建三角网格时,需要大量人工交互操作,且三维面绘制容易丢失特征信息。为解决上述问题,提出了采用CT对非人体目标几何体进行三维重建,再用体绘制进行显示的方法。基于医用CT对瓷器、陶器、木器和青铜器等材质的工艺品进行三维扫描,直接基于体绘制算法进行三维显示,同时提取CT图像轮廓点实现面绘制建模。结果表明,CT扫描重建精度高、体绘制效果好且人工工作量小、速度快。因此CT扫描及体绘制在非人体目标的三维重建中具有可行性,并且可以提高效率和精度。

Surfacer在车身覆盖件逆向工程中的应用

介绍了逆向工程的含义及工作流程 ,阐述了车身覆盖件的三维点数据采集的过程及原理 ,讨论了利用逆向工程CAD软件Surfacer对车身覆盖件点云数据处理并进行曲面创建及造型的过程。

Global Continuity Adjustment and Local Shape Optimization Technique for Complex Trimmed Surface Model

Smoothly stitching multiple surfaces mainly represented by B-spline or NURBS together is an extremely important issue in complex surfaces modeling and reverse engineering. In recent years, a lot of progress has been made in smooth join of non-trimmed surface patches, while there has been seldom research on smoothly stitching trimmed surface patches together. This paper studies the problem of global continuity adjustment, damaged hole repair and local shape optimization for complex trimmed surface model, and presents a uniform scheme to deal with continuity adjustment of trimmed surfaces and geometric repair of local broken region. Constrained B-spline surface refitting technique and trim calculation are first utilized to achieve global G^1 continuity, and then local shape optimization functional is adopted to reduce fitting error and improve local quality of refitted surface patch. The proposed approach is applied to a discontinuity ship hull surface model with an irregular hole, and the result demonstrates the validation of our method. Furthermore, on the premise of global continuity, the proposed locally repairing damaged surface model provides a better foundation for following research work, such as topology recovery technique for complex surface model after geometric repair.

Surfacer二次开发在逆向工程设计中的应用

使用Scoll语言对Surfacer进行二次开发,可以令重复性、互换性很强的自动化工程变得更加容易,通过修改Surfa-cer启动目录下的菜单定义文件,Surfacer的用户界面也会相应改变。示例一段可以实现自动排列义齿的Scoll语言程序,将Scoll命令语言在Surfacer二次开发中的应用做了详细的讲解,包括自定义函数的构造,菜单文件的修改等。

RESEARCH ON ADAPTIVE DATA COMPRESSION METHOD FOR TRIANGULATED SURFACES

NC code or STL file can be generated directly from measuring data in a fastreverse-engineering mode. Compressing the massive data from laser scanner is the key of the newmode. An adaptive compression method based on triangulated-surfaces model is put forward.Normal-vector angles between triangles are computed to find prime vertices for removal. Ring datastructure is adopted to save massive data effectively. It allows the efficient retrieval of allneighboring vertices and triangles of a given vertices. To avoid long and thin triangles, a newre-triangulation approach based on normalized minimum-vertex-distance is proposed, in which thevertex distance and interior angle of triangle are considered. Results indicate that the compressionmethod has high efficiency and can get reliable precision. The method can be applied in fastreverse engineering to acquire an optimal subset of the original massive data.