Research On The Method Of Three-dimensional Measurement By Binary Fringe Defocus Projection

The fringe projection 3D measurement technology has been widely used in many fields such as intelligent manufacturing,machine vision,industrial detection,biomedicine,cultural relic protection and so on because of its advantages of high speed,low cost,non-contact and full-field measurement.The traditional fringe projection 3D measurement technology uses the sine fringe pattern as the projection pattern to measure the 3D shape of the object to be measured.However,due to the gamma effect of projector,the fringe patterns projected onto the surface of the object to be measured are no longer sinusoidal,resulting in nonlinear errors in three-dimensional shape measurement.In order to avoid the gamma effect of projectors,binary defocusing technology has been proposed.This technology not only solves the above problems,but also accelerates the projection frame rate of the projector.It provides the possibility to realize high-precision and high-speed three-dimensional shape measurement,and has become a research hotspot in recent years.The main research contents of this paper can be summarized as follows:(1)The basic theory of fringe projection 3D measurement technology is analyzed.This article mainly introduces the wrap phase solution algorithm and phase unwrapping algorithm.And compare different wrap phase solving algorithms and different phase unwrapping algorithms to illustrate their advantages,disadvantages,and applicable scenarios.(2)The binary defocus technology is studied.Through the mathematical modeling of the process of projecting binary fringe patterns from the defocus of the projector,it is proved theoretically that the binary defocus technology can generate sinusoidal fringe patterns.Use MATLAB to simulate the fringe patterns with different defocusing degrees collected by industrial cameras,and carry out discrete Fourier transform on them,draw their spectrum diagrams,and explain that the defocusing amount of the projector affects the sine of the fringe patterns in the frequency domain.(3)The introduction of digital correlation provides a theoretical basis for the proposed quantitative evaluation method of binary defocus based on digital correlation.This article mainly introduces the basic principle of digital correlation method and various correlation coefficients,and selects a correlation coefficient with strong reliability and high computational efficiency as the correlation coefficient used in this article through comparison.(4)A reliable solution is proposed to solve the problem that the defocusing amount is difficult to determine in binary defocusing technology.The correlation coefficient between the binary defocus fringe pattern and its second-order differential is used as the evaluation value of the defocus degree to determine the best defocus degree.Compared with other methods to determine the best defocusing degree,the advantages of this method are proved.(5)Based on the method proposed in this paper,a three-dimensional shape measurement of a cylindrical surface is carried out.First,eight sets of deformed fringe patterns with different defocusing degrees were collected by a camera,and then the method proposed in this article was used to select a set of deformed fringe patterns with the best sinusoidal property.Finally,based on this set of deformed fringe patterns,the three-dimensional reconstruction of a cylindrical surface was completed using a four step phase shift algorithm and a point by point phase unwrapping algorithm.