面向飞机模具的自由曲面测量规划研究

发布时间：2018-03-31 05:27

本文选题：反求工程　切入点：形心模型　出处：《中北大学》2015年硕士论文

【摘要】：随着制造业的不断发展，反求工程已逐渐被应用到很多领域，而曲面测量点采集是反求工程和曲面测量的关键步骤，因此对曲面测量的研究对于工程实践具有重要指导作用。目前用来采集曲面零件表面数据的方法主要有两类：接触式和非接触式。而三坐标测量机CMM作为接触式测量方式，其智能化高、可靠性强，能够高效、高精度地对实物进行测量，因此被广泛应用。本文以提高CMM测量效率为出发点，对曲面的测量规划方案以及重构曲面的方法进行了研究。本文对CMM的组成及操作流程进行了详细的介绍，对比了常用的测头半径补偿方法，得出了测头半径补偿的最优方法——四点共球法。提出测量曲面时，应关闭CMM的自动补偿功能，先测得测头球心的坐标，再利用四点共球法补偿，得出被测曲面的实际坐标值。此外，经研究得出了测量路径规划的原则，并合理的设置了避障点。对于数学模型已知的自由曲面，根据均质体的三维形心模型提出了曲面自适应数字化算法，此算法可以将随机网格收敛为矩形拓扑网格，通过算法的实现，可实现测量点的自适应分布，即曲面曲率大的地方采样点分布密集，曲率小的地方采样点稀疏，这样采样点就可以有效的反映曲面的拓扑信息。在此基础上对曲率测度进行了深入研究，通过对三种不同模型的对比，得出平均曲率测度模型最能表征自由曲面上一点的弯曲程度，并且结合实例验证已知曲面数字化模型的可行性。对自由曲面测量规划方法进行了研究，，合理地确定了自由曲面测量点数目和分布，提出了两次采样的方法。第一次采样即通过提取实物的边界线和特征线，构造出初始曲面。第二次采样即在初始曲面的基础上进行采样，此时初始曲面转化成数学模型已知的曲面，即可运用数学模型已知的曲面自适应数字化算法对测量点进行自适应分布。通过飞机复合材料模具对此方法进行实验仿真，验证测量点分布合理。介绍了规则点的NURBS曲面拟合方法和散乱点的NURBS曲面拟合方法，通过将第二次采样后的结果和初始曲面的模型一起导入CMM，对曲面进行测量，得到数据点后对其进行NURBS曲面拟合，验证上述测量规划方法的可行性。通过以上规划，可以用尽可能少的测量点来反映曲面的形状特征。
[Abstract]:With the continuous development of manufacturing industry, reverse engineering has been gradually applied to many fields, and the acquisition of surface measurement points is the key step of reverse engineering and surface measurement. Therefore, the research of surface measurement plays an important role in engineering practice.At present, there are two kinds of methods for collecting surface data of curved surface: contact and non-contact.As a contact measurement method, CMM CMM is widely used because of its high intelligence, high reliability, high efficiency and high precision.In order to improve the efficiency of CMM measurement, this paper studies the measurement planning scheme of surface and the method of surface reconstruction.In this paper, the composition and operation flow of CMM are introduced in detail, the commonly used compensation methods of probe radius are compared, and the optimal method of probe radius compensation is obtained, which is called four-point cosphere method.When measuring surface, the automatic compensation function of CMM should be turned off, the coordinate of head center should be measured first, and then the actual coordinate value of measured surface should be obtained by using four-point common ball method.In addition, the principle of surveying path planning is obtained, and obstacle avoidance points are reasonably set up.According to the three-dimensional centroid model of homogeneous body, an adaptive surface digitization algorithm is proposed for free-form surfaces with known mathematical models. This algorithm can converge random grids to rectangular topological meshes.The adaptive distribution of measurement points can be realized, that is, where the curvature of the surface is large, the distribution of sampling points is dense, and where the curvature is small, the sampling points are sparse, so the sampling points can effectively reflect the topological information of the surface.On the basis of this, the curvature measure is deeply studied. Through the comparison of three different models, it is concluded that the mean curvature measure model can best represent the bending degree of a point on a free-form surface.The feasibility of the known surface digitization model is verified by an example.In this paper, the free-form surface measurement planning method is studied, the number and distribution of free surface measuring points are reasonably determined, and the method of twice sampling is put forward.The first sampling is to construct the initial surface by extracting the boundary line and characteristic line of the object.The second sampling is the sampling on the basis of the initial surface, when the initial surface is transformed into the surface of the known mathematical model, and the adaptive digitization algorithm of the surface known by the mathematical model can be used to distribute the measured points adaptively.The method is simulated by the aircraft composite mould, and the distribution of the measuring points is proved to be reasonable.This paper introduces the fitting method of NURBS surface for regular points and NURBS surface fitting method for scattered points. By importing the results of the second sampling and the model of the initial surface together, the surface is measured, and the data points are obtained and then fitted with the NURBS surface.The feasibility of the above measurement planning method is verified.Through the above programming, the shape features of the surface can be reflected with as few measuring points as possible.
【学位授予单位】：中北大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：V261

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