Uncertainty Analysis And Optimization Of Large Scale Measurement Field

With the application of Measurement Aided Assembly technology,the accuracy of aircraft digital assembly measurement field has become one of the important assurances for the quality of aircraft assembly.The use of the concept of uncertainty to evaluate the accuracy of a measurement field is more accurate and reliable.Based on the reference position,instrument position and covariance propagation rate,a mathematical model of the uncertainty of the measurement field can be established to evaluate the accuracy of the measurement field.The mathematical model can also be used to optimize the reference layout and station layout to improve the accuracy of the measurement field.In the case of the completion of the measurement field,the accuracy of coordinate conversion can be further improved by repeating the weighted adjustment according to the actual fitting error.The main contents of this paper are as follows:(1)Aiming at the special situation of symmetry distribution of reference point,the relationship between the reference points position and its uncertainty and the uncertainty of the three translation parameters was obtained by theoretical derivation.Considering the complexity of matrix operations,the Monte Carlo method was used to study the uncertainty of the three rotation parameters.The formulas of coordinate transformation uncertainty are given by analyzing the multiple sets of data obtained by simulation.(2)The measurement uncertainty model of the instrument is established based on the coordinate of the point to be measured and the position parameters of the measuring instrument.Then,considering the problem of covariance propagation caused by coordinate transformation,a model of uncertainty of measurement field is established.Based on this model,a 3D visualization software is developed to analyze the uncertainty.(3)An algorithm for data fusion of multiple measurement systems is proposed,and the uncertainty of the fusion measurement is obtained.Based on the fused measurement uncertainty model,the optimization of measurement stations is carried out with the help of MATLAB tool library.(4)Aiming at the possible big error of some reference coordinates,an improved Iterative Reweighed Least Squares algorithm is proposed to optimize the accuracy of coordinate transformation.