Research On 3D Reconstruction And Measurement Of Geometric Parameters For NC Tools

The measurement accuracy and efficiency of NC tools are the important factors restricting the development of high precision and high efficiency in China's manufacturing industry.Existing tool measuring instruments have some limitations that cannot obtain the3 D model in measuring NC tools.At present,most of the 3D scanners on the market facing on the multi-scenario applications,and most of them is monopolized by foreign companies.There is no independent NC-tool 3D measurement system in China,so the research of 3D measurement system dedicated to NC tools is urgent.In this paper,three-dimensional reconstruction of the measured tool is achieved through Phase Measuring Profilometry.The research contents and results are as follows:The mathematical model of a 3D measurement system with arbitrary positions is analyzed,and the "Phase-Point Cloud" relationship of the model is obtained.Based on the mathematical model,a three-dimensional measurement system is designed.The system includes 3D measurement structure,main shaft rotation structure,visual positioning structure and servo translation structure.Then an automated 3D measurement system solution for batch measurement tasks was proposed.The calibration method of 3D measurement system with single camera and single projector is described.The collinear equations of the linear camera model and the camera distortion model are derived.Camera calibration was then performed by Zhang's calibration method.The projector can be described as a reverse camera,and its projection model conforms to the pinhole imaging model.Therefore,the Explicit Calibration Method and the Implicit Calibration Method are proposed.Then combined with RANSAC and LevenbergMarquardt iteration methods to achieve the exact solution of the Implicit Calibration Method.Experiments show that the Implicit Calibration Method has better calibration accuracy than the Explicit Calibration Method.The common raster encoding method is explained,and the three-frequency heterodyne method with one-level expansion algorithm is proposed based on the two-step verification heterodyne method,which has the advantages of high precision and small calculation.Then combined with the calibration results to achieve a single-position spatial point cloud,and the accuracy of the single-position spatial point cloud reconstruction can reach 0.041 mm.A scattered point cloud registration algorithm for NC tool measurement is proposed.This method is based on a high-precision rotating spindle that calibrated by a checkerboard calibration plate.The space circular curve fitting is transformed into a generalized plane fitting and a two-dimensional ellipse fitting to improve the calibration accuracy.The results show that the point cloud registration accuracy of the algorithm can reach 0.072 mm.Finally,three-dimensional reconstruction experiments include stepped objects,standard cylinders,end mills and turning tool were carried out.The system can realize threedimensional reconstruction of stepped objects with large depth without ignoring the topography of the surface.The reconstruction accuracy of the standard cylinder with a diameter of 31 mm can reach 0.192 mm.T·he measurement result of the maximum turning radius of the 3D model of the end mill shows that the reconstruction accuracy is ± 0.133 mm.The results of the measurement of the cutting surface of the turning tool show that the system can completely measure the information of the cutting surface,which is of great significance to the production of the turning tools.