A PC-based system integrating CMM and CAD for automated inspection and reverse engineering

A personal computer (PC)-based system integrating a manual CMM and a CAD system has been developed for on-line capture of 3D point data, resulting in the automation of the inspection process. The sequence of steps taken to measure a master component using the CMM is stored in a measurement program in teach mode and replayed for repetitive measurement of a batch of identical components in the replay mode. The measurement program guides the CMM operator regarding the geometric entity to be measured, the number of points to be input and the direction to be followed for taking the points on the CMM. The operator has simply to follow the sequence displayed on the computer screen. The program automatically computes the dimensions and the deviations from the corresponding dimensions of the master component. The 3D measurement data from the CMM are transferred to a CAD system in real time. Programs have been developed to create 3D cubic splines and surfaces from the 3D point data taken on the CMM. The full features of the CAD software can be used to manipulate the 3D point data for CAD applications.     

Measuring external profiles of porous objects using CMM

Coordinate measuring machine (CMM) has been extensively used in surface measurement and inspection. CMM produces more accurate and reliable results compared with non-contact measurement devices, since CMM measures target surfaces in a tactile way and is not affected by surface reflection quality. However, when there is porosity on the outside surfaces, CMM measurement will have errors because part of the probing stylus will come into the porosity spaces. This paper presents a method of using CMM to measure external profiles of objects with external porosity spaces. The center of a CMM probing stylus will be compensated to avoid porosity spaces and located above external surface areas along surface normal directions. Such a probing strategy can be implemented in both computer-aided design (CAD)-guided mode and non-CAD-guided mode. When the CAD model is available, the probing styli are guided to approach the surface along its normal directions successively to identify and avoid porosity spaces. When the CAD model is unavailable, surface normal directions will be estimated first and then adjusted. The presented method is able to avoid porosity spaces in CMM measurement regardless of the availability of CAD models.     

基才Geomagic软件的汽车保险杠逆向工程设计

介绍了逆向工程的含义、基本工作流程及Geomagic软件的功能特点。针对汽车保险杠的特点,利用三维坐标测量仪,测出汽车保险杠的点云数据,然后将测量的点云数据用Geomagic软件进行各项优化处理,包括减少噪声点、点云数据的采样和在点对象上创建多边形网格及NURBS曲面,然后利用UG软件的曲面造型功能,做出汽车保险杠的CAD模型。实现了汽车保险杠由实物到点云、再由点云到三维模型的快速逆向设计。     

Combination of a Vision System and a Coordinate Measuring Machine for the Reverse Engineering of Freeform Surfaces

This paper describes a novel methodology for the reverse engineering of complex, free form surfaces, based on the integration of the measurement information from a 3D vision sensor and a coordinate measuring machine (CMM). The aim is to reconstruct the CAD model of objects of complex geometry with high accuracy and at the same time, rapidly exploiting the advantages deriving from the use of both the optical and the mechanical sensors, with a minimum of human intervention. The combination is performed at the level of measurement information, within a module for the intelligent aggregation of the information from optical and mechanical sensors. Tools are developed for digitising, filtering, grouping and surface-fitting the 3D images of the vision sensor and the point clouds from digitisation of the CMM. In the paper, the combined system is described, and two industrial applications are presented.     

基于点云数据的复杂型面数字化检测技术研究

针对设计制造流程中复杂型面检测难的问题,建立了由数据获取、点云与计算机辅助设计模型匹配及偏差分析组成的数字化测量系统。采用格雷码加相移技术的三维非接触式光学测量技术,获取了待测零件的表面数据。为满足光学三角法要求,在测量机构中采用了定制光栅,提出了具有小扰动的改进最邻近点迭代算法进行点云与计算机辅助设计模型的准确匹配。在偏差分析中采用多分辨率层次分析法对测量点云与计算机辅助设计模型进行比较,为设计人员及时提供了精度分析数据,使设计制造检测成为一个反馈系统。以某型号轿车车灯配光镜为例,验证了该系统的可行性。     

MEASURING INFORMATION INTEGR—ATION MODEL FOR CAD／CMM

A CAD/CMM workpiece modeling system based on IGES file is proposed. The modeling system is implemented by using a new method for labelling the tolerance items of 3D workpiece. The concept-"feature face" is used in the method. First the CAD data of workpiece are extracted and recognized automatically. Then a workpiece model is generated, which is the integration of pure 3D geometry form with its corresponding inspection items. The principle of workpiece modeling is also presented. At last, the experiment results are shown and correctness of the model is certified.     

基于多传感器集成的三坐标测量机自动检测规划系统研究

为了充分发挥多传感器集成的优势，提高检测自动化水平，提出了该环境下三坐标测量机自动检测规划系统的体系结构。构建了专家规则库来制定检测策略，选择检测设备。重点分析了接触式测量检测规划的流程，提供了零件定位、测点自动生成等模块的解决方案。讨论了光学自动检测规划的要点。通过中性文件的使用和映射，实现了CAD与三坐标测量系统的集成，从而为产品的自动检测和质量控制提供了保障。     

基于CAD数模的零件自动检测

三坐标测量机能够实现基于CAD数模的零件自动检测,该技术具有测量精度高、效率高、测量结果直接反映零件加工实际值与设计理论值的误差等特点,是坐标测量技术的一个新的发展方向。本文结合ARCOCAD测量软件,对基于CAD数模的零件自动检测的关键技术进行了分析。     

基于逆向工程的个性化人工膝关节CAD建模

采用接触式的CMM测量设备对人工膝关节自由曲面进行了数字化测量，用Surfacer反求软件分析了测量数据由点到面的处理方法，重构了人工膝关节的CAD三维模型并经CAM模块处理后由数控加工生成应用于临床的产品。个性化膝关节CAD模型的建立对定制人工关节构成了基本自由曲面数据库，不同患者所使用的不同类型关节只需对模型进行局部改动，满足了个性化假体设计需要并缩短产品的开发周期和开发费用。     

Investigation on sampling size optimisation in gear tooth surface measurement using a CMM

Coordinate measuring machines (CMMs) are widely used in the gear manufacturing industry. One of the main issues for contact inspection using a CMM is the sampling technique. In this paper the gear tooth surfaces are expressed by series of parameters and inspection error compensation and initial value optimisation method are presented. The minimum number of measurement points for 3D tooth surfaces are derived. If high precision is required, more points need to be inspected. The sampling size optimisation is obtained from the criterion equation. The surface form deviation and initial values are optimised using the minimum zone method and genetic algorithms. A feature-based inspection system for spur/helical gears is developed and trials and simulations demonstrate that the method developed is suitable and very effective. This revised version was published online in October 2004 with a correction to the issue number.     

三坐标测量机检测数据与CAD系统之间的接口技术研究

提出一种需要人工适当干预的曲面处理方法。该方法通过对大量的点位数据进行处理，生成相应的曲线，然后由设计人员对曲线进行修整，生成相应的曲面。并采用ObjectARX为开发工具，在MDT环境下开发了三坐标测量机与CAD系统之间的接口程序。     

Integrated precision inspection system for manufacturing of moulds having CAD defined features

An integrated precision inspection system has been developed for manufacturing moulds having CAD defined features. The techniques of precision measurement are implemented for CAD/CAI integration for moulds having sculptured surfaces with some basic features, such as, holes, slots and bosses. Features to be inspected are chosen in the CAD environment, and inspection planning is performed for each feature. The sampling-point strategies are: uniform distribution, curvature dependent distribution, or hybrid distribution of the two depending on the complexity of the sculptured surface. Line and plane features are divided into subintervals, and the measurement points are distributed at random positions in the subinterval. Prime number subintervals are considered for a circle feature, in order to avoid possible periodic distortion of the measurement features. The measurement path planning is performed considering collision avoidance and coordinate matching between the coordinates. The output of the planning is the machine code for a specific CMM having CNC capability. The machine code is downloaded to a specific CMM, and the measurement results are fed back to the computer. A new algorithm, called MINIMAXSURF, is developed to evaluate the form error precisely for sculptured surfaces. The algorithm considers the radius of the touch probe and evaluates the profile tolerance successfully by removing the unavoidable setup errors. The developed measurement system has been applied to real moulds, demonstrating high performance and accuracy.     

On-machine measurement using a noncontact sensor based on a CAD model

Once a machining process is finished, an inspection process is carried out to check whether the part is within dimensional tolerances. A coordinate measuring machine (CMM) is a general metrological device for assessment of dimensions on the shop floor. It cannot be ignored, however, that CMM measurements require significant resources in operating time and cost, which has led to many studies into on-machine measurement (OMM) systems. This study aims to develop an OMM system with a noncontacting laser displacement sensing apparatus and a computer-aided design (CAD) model for ease of operation, improved operating speed, and free form profiling. The system is composed of two software modules, one for sensor alignment with the machine tool and the other for measurement based on CAD/CAM (computer-aided machining). Consequently, the system was verified on the shop floor at a numerical control (NC) machining center.     

复杂曲面特征线自动提取技术研究

复杂曲面零件的几何模型重构是逆向工程的研究重点之一,由零件表面的数字化数据提取特征线是构造几何模型的重要步骤。针对由CMM获取的三维数据“点云”,提出了基于扫描线的三维分层式方法实现特征线的自动提取,提出了基于局部增量网格扩张的三维散乱数据三角剖分算法,实现任意曲面尖锐棱线的自动提取。实践说明,通过该算法得到的复杂曲面的边界线能够满足模型重建的工程需求。     

Investigation of a measurement scheme based on IGES

The integration research of measuring machine and CAD information, just CMM/CAD integration technology, is far behind the information integration of mechanical processing and CAD. With the rapid development of information integration industry and in the manufacturing process of the parts with complex curve surface, it is crucial to integrate the measurement and machining procedures based on IGES as that IGES is a general ANSI standard of information exchange for CAD/CAM among different computer systems. The measuring path planning determines the realization of measuring each sampling point and the completion of all sampling points safely and effectively by using measuring equipment. Based on IGES in this paper, the calculation method of normal direction at the location of sample point is studied for different surfaces, so as to improve the measuring precision. Then the calculation strategy for the positioning points and the measuring range is established, and the identification method for the topological relation between surfaces is also researched for improving the measuring efficiency and security. At last, the measuring sequence of the sampling points to be planned reasonably based on TSP is given. It is believed that the research results can provide some useful contributions towards the development of automated inspection task planning and systems, especially for coordinate measuring machines.     

Robust generalized numerical inspection fixture for the metrology of compliant mechanical parts

Free-form non-rigid parts form the essence of today’s automotive and aerospace industries. These parts have different shapes in free state due to their dimensional and geometric variations, gravity and residual strains. For the geometric inspection of such compliant parts, special inspection fixtures are used in combination with coordinate measuring systems (CMM) and/or optical data acquisition devices (scanners). In our previous work, a general procedure was developed to eliminate the use of inspection fixtures. We measured the similarities between CAD model and scanned data by taking the advantage of the geodesic distance metric. Then, using finite element non-rigid registration, we deformed the CAD model into range data to find the geometric deviations. Here, we apply a new method to robustify the generalized numerical inspection fixture. We filter out points causing incoherent geodesic distances and demonstrate that our approach has several significant advantages, one being the ability to handle parts with missing range data. The other advantage of the method presented is its capacity to inspect parts with large deformations.     

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。     

面向三坐标测量机应用的检测特征自动提取和识别

为了解决三坐标测量机(CMM)中手工输入检测信息的问题,提出了自动提取和识别检测特征的方案。应用特征技术,实现了基于CAD模型公差特征的自动提取。利用CAD模型中几何要素标识唯一的特点,建立了STEP和QDAS中性文件的匹配,解决了几何信息和检测信息在CAD和CMM之间的传递和识别问题。在Unigraphics上进行了二次开发,使其能自动输出匹配好的STEP和QDAS文件,并能被CMM软件识别和应用。     

基于Geomagic Qualify软件的冲压件回弹检测

快速准确获得回弹量是实现冲压件回弹控制的关键因素。针对冲压件的回弹检测,提出了基于Geomagic Qualify的检测方法。利用Geomagic Qualify的强大比较分析功能,对冲压件的点云数据和CAD模型进行3D比较、2D比较和边界比较,分别检测了冲压件的整体、重要截面以及边界的回弹情况,并将检测的结果以图文方式直观显示出来。该研究为冲压件的回弹检测提供了方便、快捷的方法。