Research On Key Technology In Reconstruction Of Aircraft Structural Parts

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.