【作者】 汪俊；

【导师】 周来水；

【作者基本信息】 南京航空航天大学 ， 航空宇航制造工程， 2007， 博士

【摘要】 反求建模技术在我国新型飞机研制及已有飞机的改进改型设计制造中具有广阔的应用前景。然而,飞机产品的反求建模比一般机械产品的反求建模要求高、难度大:首先,飞机测量数据量大,外形品质要求高;其次,飞机结构复杂,结构间协调要求高;同时,通过反求建立的模型只能作为飞机进一步设计的初始模型,不可能直接作为飞机设计的最终模型,因此,反求重建的飞机产品模型必须符合飞机设计表达,易于设计修改。本文针对飞机产品反求建模必须符合飞机设计表达、易于设计修改的要求,对飞机结构件反求建模关键技术进行了系统深入的研究,主要研究内容与成果如下:提出了基于特征的飞机结构件模型重建思路:将样件测量数据(三角网格模型)进行特征分解;提取各基本特征参数及约束,并重建基本特征;根据各特征之间的依赖关系,通过布尔运算及曲面裁剪等特征操作,获得结构件的参数化特征模型。重建模型反映原始设计意图,符合飞机设计表达,为后续的飞机详细设计或改进改型设计奠定了基础。针对基本特征重建需要,提出了基于特征的数据自动分割算法。依次采用法矢准则、曲率准则和曲面拟合误差准则对测量获得的三角网格模型进行数据粗分割、再分割以及细分割,并采用后置优化处理方法调整分割结果中“不合格”数据块,实现了网格模型的特征精确分解,为后续的特征重建作好了准备。针对与外形无关飞机结构件特征的特点,将其模型重建归结为参与布尔运算的基本实体特征重建和实施曲面裁剪操作的曲面特征重建。针对基本实体特征,给出了拉伸特征、旋转特征、扫掠特征、放样特征、圆角特征以及对称特征的重建方法。针对曲面特征,提出了基于SDM策略的单个规则曲面重建方法、基于约束的多个规则曲面整体重建方法以及基于误差控制的B样条自由曲面重建方法。两者结合,实现了与外形无关飞机结构件特征模型重建。针对与外形相关飞机结构件特征的特点,提出了基于外形曲面等距的结构件表面特征重建方法和可近似为直纹面的结构件表面特征重建方法。对飞机结构件中与飞机外形贴合的表面较宽、面积较大的表面特征,采用基于外形曲面等距的方法重建表面特征,该方法遵循了原结构件的设计要求。对飞机结构件中与飞机外形贴合的表面较窄、面积较小的表面特征,由于其表面轮廓外形线比较平坦,接近于直线(通常采用四、五坐标机床的铣刀摆角功能以线接触方式加工得到),该类特征可近似为可展直纹面特征,采用直纹面来重建该类表面特征,反映了该类零件加工制造的实际。本文研究成果已集成到南京航空航天大学CAD/CAM工程研究中心开发的逆向工程软件系统FBRES中,并成功应用于某型号飞机结构件的反求建模,大量的应用实例验证了本文方法的正确性和有效性。更多还原

【Abstract】 Model reconstruction has wide applications in the national defense because it plays an important role in the improvement and redesign of the aircrafts which are under research or in service. However, The aircraft products are more difficult to be reconstructed than those mechanical parts for the following reasons: Firstly the measured data of aircraft products are huge, and the airplane contour requires higher quality; Secondly the aircraft structures are complicated, and the high synchronization between them is required; Moreover, the reconstructed model of aircraft product just serves as a initial model for further design, not the final model. Therefore, the reconstructed model of aircraft product must accord with the design expression of aircraft and be facile to improve and redesign. Based on those requirements, the model reconstruction of aircraft structural parts is studied systematically and deeply. The main subjects and achievements of this paper are summarized as follows:A novel thought for feature-based model reconstruction of aircraft structural parts is proposed: the features within triangle-mesh model of structural part are disassembled firstly; then the basic features are reconstructed on basis of the parameters and the constraints extracted from original features; finally the parameterized feature model of aircraft is reconstructed by performing operations, including Boolean operation, trim operation and so on, among basic features based on dependency relationships of basic features. The reconstructed model reflects original design intent, accords with design expression, which lays a foundation for further detailed design and redesign.The feature-based segmentation algorithm is put forward for the further reconstruction of basic features. Firstly based on the normal rule, the raw segmentation is achieved, secondly the further segmentation is performed according to the curvature rule, and then the precise segmentation is realized in accordance with the surface fitting error rule, finally the segmented model could be refined by some methods such as eliminating impure triangle meshes, combining small segments and smoothing jagged boundary. With a result, the basic features are disassembled accurately, which makes preparations for the model reconstruction.According to the characteristics of these aircraft structural parts, which are not conjoint with aircraft contour directly, their model reconstruction could be divided by two parts: the solid feature reconstruction and the surface feature reconstruction. As for the former, the methods for reconstruction of extrude feature, revolute feature, sweep feature, lofting feature, blend feature, symmetry feature are presented; for the latter, the fitting method based on SDM is proposed for the reconstruction of sole regular surface firstly, then the method for simultaneous fitting of several regular surfaces with constraints is put forward, finally the error-based fitting method of B-spline surface is proposed to reconstruct freedom surface. With the above-mentioned methods, those aircraft structural parts, connected with aircraft contour directly, could be reconstructed facilely.According to the characteristics of these aircraft structural parts, which are conjoint with aircraft contour directly, the reconstruction method of the surface feature generated by offsetting aircraft contour and the reconstruction algorithm for the surface feature, approximated by ruled surface, are proposed. The former method is applicable to the surface feature within aircraft structural parts, which conjoins aircraft contour with wide area, while the latter algorithm is suitable for the surface feature within aircraft structural parts, which conjoins aircraft contour with narrow area. The former method follows the design acquirement of original feature, while the latter algorithm reflects the manufacture fact of original feature.The research achievements above have been integrated into the FBRES (Feature-Based Reverse Engineering System), developed by Research Center of CAD/CAM Engineering, Nanjing University of Aeronautics and Astronautics, and also applied for the model reconstruction of some aircraft structural parts. Experimental results demonstrate the accurateness and effectiveness the proposed methods.更多还原