Research Of S-transform Profilometry Based On The Telecentric Scheimpflug Lens

Due to the advantage about high resolution,non-contact and fast calculation,an active optical three-dimensional measuring base on the structure light projection is widely used in reverse engineering,rapid prototype manufacturing and three-dimensional detection.With the development of technology,we need the higher accuracy requirement of the active optical threedimensional measuring.Because of the unique imaging path and the characteristics of orthogonal projection,telecentric camera have the obvious advantage of big depth of field and low distortion.The telecentric camera can eliminate the perspective errors limitation of conventional lens because the magnification of object and image in certain distance in the telecentric lens will not change.However,the field of view and the depth of field are limited.In active optical three-dimensional measuring,S-transform combines the advantage of windowed Fourier transform and wavelet transform.It can obtain the two-dimensional timefrequency spectrum with one picture,have the characteristic of multiresolution liked wavelet transform and relates to Fourier frequency of the signal.In recent years,S-transform is gradually used in the three-dimension sensing methods with structured illumination.In this paper,the grating projection telecentric Scheimpflug measuring system and Stransform Profilometry been deeply studied.The main research contents and achievements include the following aspects:1.Research the imaging principle of telecentric lens on Scheimpflug condition and the calibration model of telecentric Scheimpflug camera.On this basis,we propose three type calibration method based on nonlinear optimization,radial alignment constraint and projective transformation matrix constraint.The experiment can show the method's validity and we compare and analyze the advantages,disadvantages and application scenarios of calibration method.2.Research S transform Profilometry,we accomplish S transform filtering method and S transform ridge method and compare the advantages and disadvantages of these two method.The S transform Profilometry have higher accuracy by comparing the S transform filtering method with other Profilometry.For the problem of phase wrapping in S transform Profilometry,we propose Weighted Least-Squares Phase Unwrapping base on S-transform Ridge Value.The experiment shows the method can reduce the interference of noise and shadow and increase the speed and accuracy of phase unwrapping of S transform Profilometry.3.We built the 3D measurement system of telecentric Scheimpflug grating projection and use the calibration method of telecentric Scheimpflug camera and S-transform Profilometry and phase unwrapping proposed in this paper achieve the 3D reconstruction based on single stripe pattern and measure the one yuan coin.The experiment shows the three-dimensional precision imaging of the measured object in the telecentric Scheimpflug measurement system can be realized,and illustrates the correctness of the proposed calibrations of Scheimpflug telecentric lens and weighted least square phase unwrapping based on S-transform ridge value.