Research On Geometric Element Fitting Of The Virtual Coordinate Measuring Machine And Evalution Method

Coordinate Measuring Machine(CMM)is a task-oriented measuring device.The diversity of measurement tasks and complexity errors makes it difficult to assess the uncertainty of the measurement results.Using virtual coordinate measuring machine(VCMM)assess measurement uncertainty is an effective and fast method.VCMM has all the characteristics of the coordinate measuring machine in actual operation.Full error modeling,geometric standard element calculation software,uncertainty calculation model,random number generator with specific distribution and Monte Carlo simulation are the main components of VCMM.This paper based on the principle of virtual coordinate measuring machine realizes offline task-oriented measurement uncertainty evaluation.The research contents are as follows:Firstly,a geometric standard element fitting software is designed.The common geometric standard elements such as straight lines,circles,planes,spheres,cylinders and cones are analyzed and the GUI interface is designed.The measured coordinate data input into geometry standard element fitting software can directly obtain the measurement result.Secondly,the fitting result is compared with the standard data set of geometric elements provided by NIST.The difference between the direction cosine of the line and the plane is less than 1E-14,and the difference between the diameter of the circle,the diameter of the cylinder and the diameter of the sphere is less than 1E-11 mm,difference of the cone angle is less than 1E-11 rad.Thirdly,the measurement model and uncertainty evaluation model of the virtual coordinate measuring machine are established according to the specific tasks.Finally,the measurement uncertainty of the ball-beam spacing is evaluated by measuring the standard ball diameter and the spacing of the standard ball-beam.Ball coordinates are input into the software to obtain the spherical coordinates and diameter of each ball.The calculation results are compared with the commercial coordinate measuring machine and show that the results are consistent.Then use the distance calculation function of the fitting software calculate the distance of each ball.The influencing factors affecting the uncertainty of the measured ball-beam spacing are analyzed,and the measurement uncertainty calculation model is established.Lastly,measurement uncertainty obtained by the virtual coordinate machine is compared with the uncertainty obtained by the GUM method,showing that the results are consistent.