Research On Flatness Error Evaluation Method Of Discontinuous Plane

High precision measurement technology is a necessary condition for modern advanced manufacturing industry and all kinds of precision engineering.High precision measurement of plane elements is required in various equipment,structure and parts.With the continuous updating of various measuring equipment and software,the types of measurement data are also diversified.As a common digital description data,point cloud is often used to solve various measurement problems.At present,the flatness error evaluation theory of continuous plane is relatively perfect,but it is not absolutely applicable to the discontinuous measured surface.Therefore,how to effectively use the huge point cloud data to evaluate the flatness error of discontinuity plane is worth studying.The main contents of this paper are as follows:Through the research of flatness error evaluation fundamentals and measurement model stipulated by national standard,it is found that the traditional evaluation method has some limitations when the measured surface is discontinuous.In view of the limitations of the traditional algorithm and the characteristics of the discontinuous measured surface,this paper proposes an evaluation method to establish the minimum area by replacing the inclusion plane with two parallel inclusive lines in the space.In order to realize the flatness error evaluation of inclusive line method,a set of processing flow based on point cloud data is proposed in this paper.The main steps are: principal component analysis method to eliminate noise,least square plane fitting,multi threshold extraction algorithm to extract the point set of fitting inclusive line,line fitting with constraints and outputting flatness error value.This paper studies the evaluation method of measurement uncertainty,constructs the mathematical model of measurement uncertainty of flatness,and determines the uncertainty component of measurement experiment.The three-dimensional point cloud obtained by high-precision three-dimensional scanning instrument is used as experimental data.Convex hull algorithm,genetic algorithm and inclusive line method proposed in this paper are used to evaluate the flatness error at the same time,and the evaluation results are compared and analyzed.At the same time,the uncertainty of flatness measurement is calculated by MCM and GUM method to verify the accuracy of the evaluation model.The experimental results show that this method is more robust than the traditional convex hull algorithm.The flatness error is reduced by 0.011 mm compared with the genetic algorithm,and the flatness error is reduced by 1.959 mm after adjusting the plane according to the output offset information.The uncertainty of MCM and GUM method are 4.46 ? m and 4.79 ? m respectively,which is close to each other.It is proved that the flatness error evaluation of the inclusion line method has certain stability,and can effectively evaluate the flatness error of discontinuity plane and guide the plane adjustment.