Research On The Data Registration And Precision Machining Technologies Towards Complex Surfaces

Complex surfaces have been widely applied into the products development, such as automobile precise panels, propeller of naval vessel and blade of aero-engine. The research on data registration and precision machining technologies towards complex surfaces is a key point to improve the machining accuracy and efficiency of such products. Based on ingoing analysis and summary of previous works, this thesis has investigated the key technologies of data processing, such as data registration, tool path generation and surface localization et al. The major research works and contributions of the thesis are introduced as follows:Study the coarse and fine registration algorithms of measured data. (1) For the problem that most coarse registration algorithms have difficulty in defining similarity index and handling non-overlapping data, the thesis has proposed a new algorithm based on Dimensionality-Reduction Shape Descriptions, where Harmoinic Mapping and Angle Based Flattening are used to represent mesh surfaces in both local and global manners. Therefore, searching for closest point, calculating transformation parameters, verifying overlapping regions and evaluating error can be carried out in low-dimensional space. The experimental results indicate that DRSD algorithm is efficient and robust to Gaussian noise, resolution, fixed point and occlusion. (2) For the pros and cons of current fine registration algorithms, the thesis has proposed a new algorithm based on adaptive distance function (ADF), which is used to describe the point-surface distance error. The main difference between adaptive distance function and traditional distance functions is that the curvature feature is considered to quatify point-surface shortest distance. Non-linear optimization model is established to calculate the rigid transformation. The experimental result indicates that ADF algorithm has evident superiority in balancing convergent speed and stability, especially when the initial value is poor and the surfaces have high-curvature features.Study the tool path generation algorithm of 3-axis machining in low dimensional space. For the problem that most of current tool path generation methods are only suitable for parametric surfaces, the thesis has presented a 3-axis tool path generation method with dimensionality-reduction strategy, by applying Angle Based Flattening to strech the overall surface on parametric plane. For one hand, iso-planar tool path is generated by employing Principal Component Analysis to obtain a maximal length of machining path. Hence, redundant tool paths of traditional iso-planar methods are relieved. For the other hand, contour-translation tool path is generated by extracting a boundary drive curve on meshes. This avoids complex calculations in 3D space such as slicing, offsetting, intersection, and projection, which increases the computational efficiency.Study the surface localization and accuracy evaluation method between point cloud data and parametric family of surfaces. The thesis has proposed an ADF localization algorithm between point and parametric family of surfaces, established the non-linear optimization model for quality inspection, curve fitting and surface localization with symmetrical features. In addition, the thesis focuses on analyzing the differential relationship between localization error and geometric error, and deriving the linear mapping relationship from the geometric error, in order to construct a mathematical statistics with Cartesian frame-independence property. With the constructed statistics, the localization result can be determined by a criminative accuracy model based on t distribution, from which the uppers of translation and rotation errors are also derived.Set up a reverse engineering-based digital manufacture platform by applying the proposed algorithms. Based on the existing software and hardware platforms in State Key Laboratory of Digital Manufacturing Equipment and Technology, we have developed the algorithms and basically set up a digital manufacture platform which integrates surface measurement, data processing, machining and quality inspection. To verify its feasibility, a typical complex surface has been employed to implement data acquirement, point cloud registration, tool path generation, milling, surface localization and quality inspection, from which a new product with specified accuracy is produced.