Establishment And Optimization Of Iarge-volume Measuring Field In Aircraft Assembly

In aircraft assembly sytem, the accuracy of large-volume merology system is one of the most important factors that determine the final assembly quality of the aircraft. During aircraft assembly process, single laser tracker cannot measure all the target points, due to the obstacle of aircraft components and assembly toolings, so multiple laser trakcers are needed to work cooperatively to construct a measurement nerwork to cover the entire assembly volume. As the measurements from different laser trackers are independent, a unified large-volume measuring field should be established to fuse all the measurements. In this thesis, the establishement method of the large-volume measuring field, as well as the uncertainty evaluation method and configuration optimization method, are discussed. The research results provide reliable precision guarantee for modern aircraft assembly.The present state of the large-volume metrology system in aircraft assembly is introduced. The establishment principle of large-volume measuring field based on rigid-body registration method is expatiated. The most used three solutions of rigid-body registration:Singular value decomposition (SVD) method, orthogonal matrix method and quaternion method are expounded in details.According to the principle of registration, the error propagation model of the transformation parameter errors and measurement error estimation model of measureing field are established theoretically, which reveal the influences of the layout of the ERS points and the measurement errors of the ERS points from the laser tracker that affect on the registration errors. Based on the error propagation model, the uncertainty evaluations of transformation parameter and measurement error are fulfilled. The uncertainty evaluation method is verified with the Monte Carlo simulation method.Detailed analysis of the configuration of large-volume metrology system is expatiated. The sensitivity coefficients of the transformation parameter errors are proposed as criterias to evaluate the configuration quality of the ERS points. With the sensitivity coefficients, the influence of ERS points with varied layouts, varied volume sizes that the ERS points envelop, varied point numbers, and varied position and orientation of the ERS layout relative to assembly coordinate system are analyzed. Then, general guidance is summarized for deploying the ERS points in the design stage, and a selection optimization method of the ERS points is proposed in assembly stage. Besides, a location optimization method of the laser tracker with location constraints is proposed, which aims to minimize the uncertainties of the transformation parameter errors. The experiment implemented in factory floor validates the location optimization method.The influence of displacements of the ERS points resulted from the thermal deformation is analyzed. An anisotropy thermal-deformation compensation method of the ERS points is developed, in which the displacements of the ERS points in the length, width and height directions of the assembly platform are corrected meanwhile in an iteration way. The performance of the new compensation method is proved to be superior to the tranditional conpenation method by assembly cases.