【作者】 唐克伦；

【导师】 张湘伟；

【作者基本信息】 重庆大学 ， 一般力学与力学基础， 2008， 博士

【摘要】 在逆向工程中,自由曲线曲面的测量一直以来是逆向工程的重要组成部分,受到众多学者的关注。计算机视觉与三坐标机是反求工程中不同的两种测量手段的代表,他们各具有自己的优缺点。作为非接触式测量的代表,计算机立体视觉测量具有速度快、灵活、采样范围广、有利于整体形状信息的获取等优点,可以方便地提取物体的边界轮廓与特征信息,其缺点是测量精度较差;三坐标机作为接触测量的设备之一,其优点是测量精度高,适应性强,鲁棒性能优越,但作为逐点测量的设备,是在人为制定的测量规则指导下,对产品原型进行测量获取三维坐标数据,实现产品表面的数字化,其测量效率低,测量过程过分依赖于测量者的经验,特别是在未知产品几何数值模型的前提下,难以保证测点分布的合理性。基于线结构光-立体视觉与三坐标机信息集成技术的集成式测量以其测量精度高、速度快、智能化程度高而成为一种很有前途的测量方法,特别是如能实现二者信息的融合,将势必大大提高集成系统的测量速度和精度。本文就线结构光-立体视觉与三坐标机系统集成与信息融合的一些关键性技术展开了研究,其主要内容包括:1)主动轮廓提取技术。主动轮廓(又称为蛇形轮廓)为计算机立体视觉提供了获取线激光器扫描曲线在摄像机图像中曲线轮廓的方法。线结构光测量数据在每条扫描线内测量点排列密集、杂乱,且测量点之间没有明显的拓扑关系,无法直接应用于CAD系统中建模。主动轮廓提取的曲线则为测量点之间建立了拓扑关系。2) B样条最佳逼近。以差分法提取的主动轮廓包含了大量的曲线数据,不利于数据的保存与结果后处理。利用B样条曲线去逼近轮廓曲线,大大减少了轮廓曲线的数据存储量,且使得曲线变得更为光滑,也给曲线的后处理带来了方便。3) B样条曲线变形(修改)技术。基于物理模型的B样条曲线变形是在尽量维持曲线整体轮廓特征的基础上产生的。它不像其它局部变形技术那样会产生局部的“肿块”,从而影响了曲线的整体轮廓特征。基于物理模型的B样条曲线变形在力学上类似于一根曲杆在外力作用下产生整体变形,其数学模型上就好像在原有曲线的基础上,加上了一条光滑的误差拟合曲线。本文将此技术应用于线结构光-立体视觉与三坐标机信息的融合,实现利用三标机测量的精确数据去修正立体视觉测量的曲线,从而提高视觉测量的精度,减少利用三坐标测量机测量的数据量,提高了测量效率与测量精度。4)摄像机的标定。摄像机的标定建立了三维数据点与摄像机像点之间的对应关系,是实现立体视觉系统最为重要的一环。利用三坐标机的测头实现摄像机的标定为立体视觉测量系统和三坐标机的集成建立了数据点坐标间的关系,实现了立体视觉测量的世界坐标系与三坐标机的世界坐标系相统一。5)测头半径补偿。测头半径补偿问题是三坐标机测量中的一个关键问题,影响着三坐标机的测量精度。在已知截面轮廓线的情况下,可以计算出测头接触工件的法线方向,并由此可以计算出测头接触工件的位置,解决了测头的半径补偿问题,并同时实现了测头半径向一个平面内补偿问题。更多还原

【Abstract】 Measuring a free curve or surface is an important component in the reverse engineering. Many researchers and scholars have fixed their eyes upon it. Computer stereo vision and coordinate measuring machine(CMM) belong to two kind of measuring equipment respectively. They have their respective merits and drawbacks. As a representative of non-touching measuring equipment, computer stereo vision has many merits, such as fast measuring speed, agility, broad sampling scope and convenience of extracting the boundary contours and characters. However, the drawback is its lower measuring precision. As a touching equipment, CMM has many advantages such as higher measuring precision, strong adaptability and robusticity. However, being a point-by-point touching measuring equipment, its obtaining the three dimensional measuring data of prototype is directed by the man-made measuring rules. It is much lower efficiency, and is excessively depended on the experience of manipulator to digitize the product. When there is no digital geometric prototype of product, it is difficult to properly distribute the measuring points.An integrated measuring equipment is suggested which is composed of seam-laser stereo vision equipment and CMM. It is a promising measuring equipment due to its high efficiency, high precision and high intelligentizing. The efficiency and the precision will become much higher if we can fuse the information obtained by these two different types of equipments.This paper will devote to investigate some key techniques of information fusion between the seam-laser stereo vision equipment and CMM. The contents include the following:1) Active contour models. Active contour models (or snake models) provide a method of obtaining the curve contour in the image produced by seam-laser stereo vision. The measuring data are dense, unorderly, and there is no topology relationship between them. They can not be applied to erect CAD models directly. Active contour models establish a topology relationship among these measuring data.2) B-spline approaching. The solution to active contour models is traditionally through the difference method, which includes large amount of curve data. It is not convenient to save them and to manipulate in the following procedure. Approaching the curve by B-spline will largely cut down the amount of curve data to be stored. It also makes the curve smoother and is easier to manipulate in the following procedures.3) Deformation of B-spline curve. The Physical model based deformation of B-spline curve keeps the contour character of the whole curve well. It will not produce local bump like the local curve deformation to hurt the contour character of the whole curve. The deformation is just like a crooked stick to produce a deformation under the external forces in mechanics, or like a smooth error curve fitted by given conditions adding up to original curve in mathematics. This paper will apply this deformation technique of B-spline curve to realize the information fusion between the seam-laser stereo vision equipment and CMM, in order to revise the curve measured by seam-laser stereo vision through the accurate data measured by CMM. This will increase the measuring precision measured by seam-laser stereo vision, and cut down the amount of data measured by CMM, so the efficiency and the precision will be promoted.4) Calibration of camera. The calibration of camera erects a corresponding relationship between the space points and the points in the camera images. It is a very important step to realize stereo vision. The tip center of the CMM touch probe is regarded as the space points to calibrate the camera, which set up a relationship of coordinate systems between two measuring equipments, and the two coordinate systems are unified into unitary CMM coordinate systems.5) Compensating of tip radius of CMM. Compensating of tip radius is a key problem in CMM. It has a great influence to its measuring accuracy. According to the contour curves which have been figured out,the normals of touching points can be computed, and the postions of touching points also can be decided. Hence, the proplem of compensating of tip radius of CMMM is solved, and at the same time the compensating of tip radius in a plane is also realized.更多还原