Research On Distortion Correction And Extrinsic Calibration Method In Monocular Fringe Projection System

With the development of modern industry,the quality control of the morphology of objects requires higher accuracy.The key to morphology quality control is obtaining the data of three-dimensional point cloud,so the measurement task proposes the requirements of high accuracy and density of data and flexibility of space.In this paper,we study on the measurement method of fringe projection profilometry(FPP),the calibration method of the intrinsic and extrinsic parameters of FPP system.And the key technologies of distortion correction and extrinsic calibration of FPP system is broken through.The accuracy of the three-dimensional point cloud data is improved by compensating the distortion of FPP system based on the per-pixel distortion correction method,and the flexibility of the coordinate transformation is improved by the extrinsic calibration method based on the substitutable target sphere for vision-measurement,and the measurement range is expanded.And through the experiment,the distortion correction and external calibration accuracy were verified.The main works of the paper are listed as follows:1.Based on the analysis of the existing fringe projection profilometry principle,the monocular fringe projection system consist of a monocular camera and a projector is built.The four-step phase shift method is used to obtain the folded phase and the three-frequency unwrapped method is used to obtain the absolute phase.The matching is realized based on extreme polar line method and three-dimensional point cloud is reconstructed based on stereo vision.2.The instrinsic calibration of fringe projection system: This paper implements the intrinsic calibration of camera and projector based on a calibration plane,and the lens distortion of the camera is corrected based on the distortion polynomial.Overall considering the flexibility of the parametric model and the accuracy of the non-parametric model,a per-pixel distortion measurement is proposed to realize distortion correction of the FPP system.Through the phase matching and the aperture imaging model,the distortion map covering the corresponding ideal and real point pairs is built,and the distortion of the system is compensated.This method greatly enhance the accuracy of the fringe projection system.3.The extrinsic calibration of fringe projection system: Through the movement of monocular fringe projection system,the measurement of the overall shape is achieved.In order to achieve splicing,the relationship between the FPP coordinate and the standard coordinate under each pose is built through the extrinsic calibration of FPP system.In this paper,a method based on a substitutable target sphere for vision-measurement is proposed to calibrate the extrinsic parameters of the FPP system.The method has the flexibility and wide applicability.Based on the principle of common points data acquisition,the design of the substitutable target sphere for vision-measurement is the combination of a circle target and a sphere shell.And the principle of the extrinsic calibration of PFF system based on this target sphere is proposed.Analysis of the propagation of error is implemented,and the calibration accuracy was optimized.