Detection And Evaluation Of Line Profile Error Based On Laser Scanning

The line profile reflects the variation of the actual profile relative to the theoretical profile,and is one of the indicators for evaluating the part profile.How to accurately and quickly measure the contour of a certain contour line of a part has always been an important research direction in the field of geometric metrology.The commonly used detection methods for line profile are template method,profiling method,projection method and coordinate method.The first three methods can only do qualitative analysis.The principle of the coordinate method is to measure the coordinate values of a series of points on the measured contour,and then mathematically fit the curve equation of the measured contour,and compare the fitted contour curve with the theoretical contour curve to obtain the measured The line profile of the outline.The non-contact measurement method can effectively avoid errors caused by equipment contact during measurement.With the development of related technologies in recent years,machine vision has become an important way to achieve non-contact measurement.In this paper,starting from the needs of non-contact measurement,combined with the commonly used methods of machine vision,in accordance with the shape characteristics and accuracy requirements of the measured object,the construction plan of the monitoring platform is determined.Infrared laser is used to scan the outer surface of the tested part,the image is collected by a high-resolution camera,the data about the surface contour of the measured object in the image is extracted and analyzed to find the corresponding point of the measured contour in the image.The measured data is processed to finally obtain the line profile error value of the profile.The research work of this thesis can be divided into the following four aspects:(1)The basic theory of line profile is analyzed,and the advantages and disadvantages of existing line profile detection methods are compared;based on direct laser triangulation,an integrated camera and high-precision rotating platform are designed and built,Computer and raster line profile error detection platform.(2)The source of error of the testing platform is studied,the reason for the error in the testing process is described,and the compensation scheme is determined through the analysis of the geometric structure.The gross error and random error in the detection process are discriminated and eliminated.(3)The evaluation method of line profile error is studied,and the Hausdoff distance is applied to the evaluation of line profile error.When the definition of line profile is met,a plane curve line profile evaluation based on the minimum unidirectional Hausdoff distance is proposed Methods,the mathematical model of evaluation was established,and the model was linearized.At the same time,the reconstruction of the theoretical contour curve is studied,and several methods of fitting discrete points are analyzed.Finally,the NURBS method is used to reconstruct the theoretical contour curve of the part.(4)Experiments were carried out on the detection platform.The detection steps of line profile error are determined.The system describes the preparations before starting the measurement,and focuses on the camera and its calibration.In-depth research on the preprocessing of measurement data,that is,image processing methods,focuses on the identification and extraction of feature points.The experiment was conducted by changing the number of sampling points,and compared with the experimental results of the coordinate measuring machine to verify the effectiveness of the detection platform.