Research On Key Technologies Of 3D Measurement Based On Digital Fringe Projection

Because the structured light three-dimensional reconstruction technology has the advantages of non-contact,large field of view,high measurement accuracy,etc.,it has been paid more and more attention in the field of industrial automation,especially in the aspects of defect detection of industrial parts,dimension measurement and vision guidance.This paper focuses on the key technologies of 3D measurement based on digital fringe projection such as structured light coding,error analysis,camera and projector calibration.The specific research work has the following aspects:(1)The mathematical theory model is established based on the principle and geometric model of the structured light 3D measurement system,including the mapping relationship between height and phase.Besides,an experimental dedicated complementary Gray code pattern is produced based on the Gray code principle.With respect to the problem of wrapped phase,the three frequencies for phase-unwrapping are calculated based on the multi-frequency heterodyne method.(2)The source of the projected fringe error is analyzed.The mathematical analysis of the non-sinusoidal error of the fringe pattern and the spectrum analysis experiment is carried out.The influence of different light intensities on the gray value distribution of the fringe pattern are analyzed through experiments.A method based on the gradient gray map to determine the input and output response curves of the system is proposed.As a result,the phase error is reduced by 33%.(3)Based on the camera calibration and projector calibration principle of DFP system,the imaging process of the camera and the three types of distortion models of the lens are analyzed.Zhang's method is selected as the calibration method of the experiment.The comparative experiment of calibration of the camera is carried out by HALCON and MATLAB.(4)An improved experiment of stereo calibration of the measurement was implemented,which reduced the failure rate of corner extraction.The calibration error of the projector was 47.8%higher than that of the original author.In the three-dimensional measurement test of the four-step gauge block,the measurement error was about 0.33?0.42mm,based on this,the three-dimensional reconstruction of the wheel hub of electric vehicle is realized,and the three-dimensional shape of the surface of the electric wheel hub has a good measurement accuracy.