Research On Coordinate Unified Technologies In Large-scale Metrology Based On Artifacts

Large scale measurements mainly include laser tracker,theodolite and laser radar,which are often used for combination measuring in the field of aerospace,shipbuilding,vehicle engineering and etc.The measured data of each large scale measurement are acquired from their own coordinate system and isolated from each other,which require setting up a correspondence between these different coordinate systems.Only when the coordinate system of each instrument is handled with high precision can the effective integration of measurement data of each instrument be achieved.That is the coordinate unified.This corresponding relation is based on the common points which have invariable spatial positions that each instrument has been measured.Therefore,the accuracy of measuring the common points and the validity of the coordinate unified algorithm play a crucial role in the data fusion within the combination measurement.This paper is aimed at improving the accuracy of the unified coordinate for large-scale metrology.It researches from the following aspects:Focusing on the problem that unknown and uncontrollable error of measuring common points in coordinate unified,it puts up with replacing the traditionally randomly chosen common points with the target points in the artifact whose spatial and geometric relationship is already obtained.It proposes to develop an artifact,through which we makes use of the highly precise coordinate measuring machines(CMMs)to mark the geometrical relationship between the target points on the artifact,and obtains the measuring errors of each target points' coordinates indirectly.By setting the limit of the error,we can constrain and control the measuring errors for the coordinates of each target points,and set the target points on the artifact that satisfy the limit of error as the common point.It analyzes the setting methods to the limit errors for several large-scale measurements.The use of artifact improves the accuracy of the common points in the unified coordinates,and realizes the site traceability for the results of the common points.To utilize the known geometrical information between the target points on the artifact,it puts forwards a bundle adjustment method for the coordinate value in fieled based on the angular constraint.The information of spatial angle formed by each marked target points on the calibrated artifact as constraint condition,it constructs an angular bundle adjustment model,and adjusts the coordinate value of the target points in field,to get the corrections of the target points' coordinate value.In the process of bundle adjustment,in terms of the problem of condition number is great for normal equation,a method of solving the ill-conditioned equation by using the Ridge estimation algorithm.This bundle adjustment method bases on the angles formed by all the vectors which pass through the artifact.It modifies and compensates for the coordinate values of all target points,which it can further improve the measuring accuracy for the coordinates of the common points.To require the optimized registration parameters,the algorithm of coordinate unified is studied deeply.The 7 parameters Procrustes method is proposed to solve coordinate unified registration parameters in different large scale measurements.Considering the operation of transfer station of large scale measurements belongs to the variance identical distribution model,it is proposed to use the method of total least squares to solve coordinate unified registration parameters in transfer station process.Both of the two algorithms belong to the numerical solution,which avoids the problem of falling into the local optimum in the iterative method,and makes the most of the original information of their own measured data.Hence,it has acquired the more accurate unified coordinate registration parameters.To ensure the effective fusion of the measurement data of the large-scale measurement after the uniformity of the coordinates,it researches on the error ellipsoid distribution law of the spatial points of laser tracker,the theodolite and the laser radar.According to the size distribution of error ellipsoid when each apparatus of large scale instrument measured the same point,determines the weights in direction of the three coordinate axes through using the united precision information measured by each apparatus,to achieve the fusion data.This method can improve the accuracy of the combination measurement.Finally,this paper designs experiments to testify the method of the coordinate unification method based on the artifact,constructs experiment platforms,compiles the systematic software and studies on the assessment methods for the precision of the large scale metrology' coordinate unified.By comparing the international general measurement software,the experimental results show that the method of this paper can improve the coordinate unified precision of large scale metrology.