Research On Model Registration In Digital Inspection For Aircraft Sheet Metal Part

With the continuous improvement of the aircraft performance, the shape accuracy requirements of sheet metal parts become more and more strict. The traditional sheet metal parts inspection method become more and more difficult to meet the requirements of high efficiency, fast and high precision of sheet metal parts because of the low inspection accuracy and high cost of inspection mould. The digital inspection method of sheet metal parts is designed to realize parts rapid measurement and align the measurement point cloud data with theoretical CAD model, and then the detailed error information of the part can be obtained, thus realize the fast and non-mould quality inspection. Model registration is of great importance in the process of digital inspection, its accuracy directly affect the result of the inspection. In this paper, we studied the model registration of sheet metal parts in digital inspection, mainly focus on the registration data sampling and the registration of sheet metal parts with positioning holes. The main research contents are summarized as follows:1. A registration data sampling method for balancing registration constraint force is proposed.Based on the analysis of constraint state of different degree of freedom by using the registration constraint theory in the process of model registration, a measurement point cloud data sampling method is presented, after sampling by this method, the registration constraint force of six degree of freedom will be more balanced, thus the convergence speed and stability of the model registration can be effectively improved.2. To the registration problem of sheet metal parts with positioning holes, a model registration method is proposed which based on the least square registration and three datum registration, the key of this method is that the degree of freedom can be adjusted within the preset relaxation range, it keeps the already constrained direction of degree of freedom unchanged and adjusts other degree of freedom effectively, thus the registration result of all six degree of freedom can be optimal.3. Based on the research of registration algorithm and the existing laboratory software platform,the registration module is developed to realize the whole registration process of sheet metal parts, and the validity of the registration function module is verified by the concrete examples. The error calculation function is developed to inspect and analysis the whole or the section, bendings and subsidence of sheet metal parts.