NON-CONTACT MEASUREMENT SYSTEM OF FREEFORM SURFACE AND NURBS RECONSTRUCTION OF MEASUREMENT POINTS

Based on the development of the non-contact measurement system of free-form surface, NURBS reconstruction of measurement points of freeform surface is effectively realized by modifying the objective function and recursiveprocedure and calculating the optimum number of control points. The reconstruction precision is evaluated through Ja-cobi's transformation method. The feasibility of the measurement system and effectiveness of the reconstruction algorithm above are proved by experiment.     

自由曲面模型全局美化技术

利用可微流形的无穷小变形技术,实现紧公差约束下对点云逼近的多张B-样条曲面的全局美化.根据微分流形上的Beltrami-Laplace算子,定义反映曲面整体形状变化的变形能量泛函,并得到泛函的唯一极小解.给出两张单节点B-样条曲面间G1连续的充要条件以及公共边界曲线控制顶点的本征方程,并利用局部格式构造整体收敛的G1光滑拼接的边界表示模型获得变形映射族的特解.特解的构造不可避免地导致模型在缝合区域的形状产生局部瑕疵,影响反求模型的保形性.通过特解来构造能量泛函的极小解,使得这类似应力集中的效应被逐步松弛到曲面的内部,从而改善模型的整体形状.应用实例揭示自由曲面的全局美化技术在反求工程中的意义.     

CAD-DIRECTED INSPECTION PLANNING FOR FREEFORM SURFACE USING CONTACT PROBES

A methodology for CAD-directed measurement of freeform surface using a coordinate measuring machine equipped with a touch-trigger probe is presented,mainly including adaptive sampling of measurement points and registration of freeform surface.The proposed sampling method follows four steps: Freeform surface is fitted by bi-cubic B-spline; Curvedness measure of the surface is computed; Given a number of sampling points,an iterative algorithm is constructed for selecting a set of measurement points by employing the curvedness information; The measurement points is regularized for tradeoff between maximizing the measurement accuracy and minimizing the sampling time and cost.The aforesaid algorithm is demonstrated in term of a marine propeller blade.An offset surface registration method is presented to improve alignment accuracy of freeform objects,and Monte Carlo simulation is conducted to verify the effectiveness of the method.     

非接触曲面形状测量技术

详细描述了大型曲面的非接触测量原理,分析了测量过程中所遇到的计算机控制硬、软件问题,给出了测量实例及结果。     

自由曲面工件多点连续成形方法

为了实现自由曲面工件的高效率、低成本制造,分析与比较常用的柔性成形方法;从成形过程的连续性考虑,将柔性成形分为分段成形与连续成形;从变形区大小考虑,又划分为点成形、面成形与线成形等不同类型。比较不同成形方式的优点与缺点,指出自由曲面工件的高质量、高效率成形是亟待解决的技术难题。提出基于连续线成形方法的自由曲面工件高效、柔性成形思路;并提出采用多点调整式柔性辊的多点连续成形技术方案;探讨多点连续成形技术的基本原理、关键技术及主要特点。运用具有多个控制点的挠性轴设计出可弯曲、可调整的柔性辊,开发出多点卷板成形试验装置。多种三维曲面板类件的连续成形试验结果表明,多点连续成形技术能够解决自由曲面工件的高效加工难题。     

深孔内轮廓尺寸光学测量系统

针对深孔类零件对内轮廓尺寸的检测要求较高,而目前所采用的测量方法不是分辨率太低就是测量效率较低的问题,研究了一种用于深孔内轮廓尺寸的光学测量系统,该系统主要由环形激光发生器、扩束锥镜、成像锥镜和CCD相机组成。环形激光发生器发出的环形激光照射到扩束锥镜上,经反射后投影到深孔内轮廓某断面处形成一个环形光斑,该环形光斑的形状反映了深孔内轮廓某一处断面的形貌,并经过扩束锥镜反射后在CCD相机的光敏面上成像,经过处理和计算可以得到深孔内轮廓的尺寸。试验证明,该系统可以有效快速地实现对深孔内轮廓尺寸的测量,并能够保证较高的测量精度,在改善误差影响因素和采取相应的误差补偿办法后,可以进一步提高测量精度。     

NEW VISUAL METHOD FOR FREE-FORM SURFACE RECONSTRUCTION

0 INTRODUCTION(Reverse engineering has been strongly connected with modern design, and plays an important role in new product development. By now, to get a digital geometric model of an object, a coordinate measurement machine (CMM) and some sorts of CAD software are indispensable. This is a expensive and strenuous way to reverse engineering. In fact, reverse engineering is broadly used in many other fields, such as advertisement, entertainment and virtual reality (VR), etc. Looking fo…     

三角Bézier曲面建模的RE系统与RP系统集成

为解决复合三角Bezier曲面与快速原型系统接口,以便实现两者集成,提出了按给定精度从复合三角Bezier曲面模型产生STL文件数据的方法,并在原型系统上得到验证,将推动反求工程与快速原型技术的进一步应用。     

基于多目标的宽公差复杂曲面反求工程评价方法

由曲面数字化点进行曲面重构后的误差评价是反求工程需要解决的关键技术问题。随着计算机网络飞速发展以及反求工程的应用领域不断扩大,曲面拟合误差作为反求评价的单一目标已不能满足反求工程中产品设计制造的需要。在分析反求评价需求的基础上,提出了宽公差复杂曲面反求的多目标评价概念,建立了多目标评价模型,给出了模糊层次分析法的多目标评价方法,提出了网络化的反求工程多目标评价方式。     

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.     

面向并行工程的数控机床可靠性控制模型

可靠性工作贯穿产品的全寿命周期 ,它与设计、工艺、制造、销售和使用等领域的信息集成是并行工程的重要组成部分。分析了数控机床产品全寿命周期中的可靠性工作 ,提出了面向并行工程的数控机床可靠性工程的思想 ,提出并建立了面向并行工程数控机床可靠性控制模型     

PHYSICS-BASED ILLUMINATION MODEL FOR METAL SURFACE RECONSTRUCTION IN RE

Representation of roughness is introduced and the rationality of applying the physics-based model in RE is analyzed at first. Then the scattering theory of electromagnetic wave is simplified and deduced to a physics-based model according to the characteristics of the surface to be reconstructed in RE. At last, the intensity diagrams of reflected field distribution are provided to prove the feasibility of the presented model and some spheres are rendered with this model.     

机床CNC系统中任意空间曲线的可控步长插补方法

针对机床CNC系统中加工任意空间曲线的实际问题,提出了一种基于计算机技术的、用于实时控制的、符合机械加工工艺的可控步长插补方法.凡是可表示为矢量参数方程、且Frenet标架存在的正则曲线,都可以用该方法进行插补.     

大型零件型位特征分析与CAPP／CNC信息集成

在ＣＩＭＳ环境下,提出了零件“型位特征分析法”实现ＣＡＰＰ／ＣＮＣ的集成制造,论述了型位特征法的原理,并详细介绍了特征型面的分类,特征工艺单元、程序单元及计算机ＣＡＰＰ／ＣＮＣ信息集成的方法。     

REVERSE MODELING FOR CONIC BLENDING FEATURE

A novel method to extract conic blending feature in reverse engineering is presented. Different from the methods to recover constant and variable radius blends from unorganized points,it contains not only novel segmentation and feature recognition techniques,but also bias corrected technique to capture more reliable distribution of feature parameters along the spine curve.The segmentation depending on point classification separates the points in the conic blend region from the input point cloud.The available feature parameters of the cross-sectional curves are extracted with the processes of slicing point clouds with planes,conic curve fitting,and parameters estimation and compensation.The extracted parameters and its distribution laws are refined according to statistic theory such as regression analysis and hypothesis test.The proposed method can accurately capture the original design intentions and conveniently guide the reverse modeling process.Application examples are presented to verify the high precision and stability of the proposed method.     

新型的复杂曲面磁粒光整加工机床

介绍了一种复杂曲面光整加工机械--三坐标数字化磁粒光整加工机床.该机床通过对复杂曲面的数字化测量和自动编程,得到磁极与工件保持一定间隙沿工件表面运行的加工轨迹,利用吸附在工具磁极上面的磁性磨料为工具,通过磁极带动磁粒沿工件表面作高速旋转,从而实施对工件表面的光整加工.该机床的研制成功实现了复杂曲面光整加工的自动化.     

Shape measurement based on fiber-optic technique for complex internal surface

Reverse engineering based on fiber-optic technique is a very new topic in CAD/CAM fields. A novel single-mode fiber-optic sensor is presented based on the principle of beam reflection to implement the digitizing of complex surface shape. The fibers in the sensor probe are arranged like a spoke with eight symmetrically cross-arranged receiving fibers and one centered emitting fiber. Thus, the sensor can compensate for the offsets caused by fluctuations of surface reflectivity and light power and is fit for application under rough and formidable conditions with noncontact, fast shape measurement. A prototype was developed based on the simulation results to verify the feasibility. With the GRIN lens on the exit end of the single-mode emitting fiber, the lateral resolution was greatly improved compared with former multimode fiber-optic displacement sensors. Preliminary experiments indicated that the estimated uncertainty of displacement measurement was better than ±2 μm, and the uncertainty of ±5.6 μm can be obtained when measuring a MJ20×1.5 thread.