本文選題：反求工程　切入點：形心模型　出處：《中北大學》2015年碩士論文

【摘要】：隨著制造業(yè)的不斷發(fā)展，反求工程已逐漸被應用到很多領(lǐng)域，而曲面測量點采集是反求工程和曲面測量的關(guān)鍵步驟，因此對曲面測量的研究對于工程實踐具有重要指導作用。目前用來采集曲面零件表面數(shù)據(jù)的方法主要有兩類：接觸式和非接觸式。而三坐標測量機CMM作為接觸式測量方式，其智能化高、可靠性強，能夠高效、高精度地對實物進行測量，因此被廣泛應用。本文以提高CMM測量效率為出發(fā)點，對曲面的測量規(guī)劃方案以及重構(gòu)曲面的方法進行了研究。 本文對CMM的組成及操作流程進行了詳細的介紹，對比了常用的測頭半徑補償方法，得出了測頭半徑補償?shù)淖顑?yōu)方法——四點共球法。提出測量曲面時，應關(guān)閉CMM的自動補償功能，先測得測頭球心的坐標，再利用四點共球法補償，得出被測曲面的實際坐標值。此外，經(jīng)研究得出了測量路徑規(guī)劃的原則，并合理的設(shè)置了避障點。 對于數(shù)學模型已知的自由曲面，根據(jù)均質(zhì)體的三維形心模型提出了曲面自適應數(shù)字化算法，此算法可以將隨機網(wǎng)格收斂為矩形拓撲網(wǎng)格，通過算法的實現(xiàn)，可實現(xiàn)測量點的自適應分布，即曲面曲率大的地方采樣點分布密集，曲率小的地方采樣點稀疏，這樣采樣點就可以有效的反映曲面的拓撲信息。在此基礎(chǔ)上對曲率測度進行了深入研究，通過對三種不同模型的對比，得出平均曲率測度模型最能表征自由曲面上一點的彎曲程度，并且結(jié)合實例驗證已知曲面數(shù)字化模型的可行性。 對自由曲面測量規(guī)劃方法進行了研究，，合理地確定了自由曲面測量點數(shù)目和分布，提出了兩次采樣的方法。第一次采樣即通過提取實物的邊界線和特征線，構(gòu)造出初始曲面。第二次采樣即在初始曲面的基礎(chǔ)上進行采樣，此時初始曲面轉(zhuǎn)化成數(shù)學模型已知的曲面，即可運用數(shù)學模型已知的曲面自適應數(shù)字化算法對測量點進行自適應分布。通過飛機復合材料模具對此方法進行實驗仿真，驗證測量點分布合理。 介紹了規(guī)則點的NURBS曲面擬合方法和散亂點的NURBS曲面擬合方法，通過將第二次采樣后的結(jié)果和初始曲面的模型一起導入CMM，對曲面進行測量，得到數(shù)據(jù)點后對其進行NURBS曲面擬合，驗證上述測量規(guī)劃方法的可行性。通過以上規(guī)劃，可以用盡可能少的測量點來反映曲面的形狀特征。
[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.
【學位授予單位】：中北大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：V261

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