Research On 3D Measurement Method Of Grating Projection For Highly Reflective Surface

Compared with the traditional contact measurement method,the grating projection 3D measurement can obtain the height information of the measured object more efficiently and conveniently in a non-contact way.However,due to its high requirements on the environment and the measurement effect is largely dependent on the reflection characteristics of the object surface,it is easy to form brightness saturation(overexposure)when the camera takes pictures of objects with a high surface reflectivity.As a result,phase error is generated,resulting in inaccurate 3D measurement results.Therefore,in order to improve the measurement accuracy and efficiency of the strongly reflected surface structured light method,the following work is done in this paper:Firstly,the principle and techniques of traditional grating projection measurement,such as equipment calibration,phase unwrapping and image processing,are discussed in detail.Among them,the time phase unwrapping method based on multi-frequency heterodyne is suitable for phase unwrapping of highly reflective surface because its phase unwrapping is undisturbed by each other in a single store and is not affected by the object morphology,and the number of projected stripes is relatively small.However,when multiple frequencies are used as heterodyne,it is easy to cause jumping errors after phase unwrapping.Based on this,this paper analyzes the phase error of the third frequency heterodyne unwrapping,determines the error source,and proposes an improved phase unwrapping method.Based on the third frequency heterodyne,this method uses the formula to correct the expansion result,and lists the conditional formula that can accurately solve the phase.By contrast experiments,it is verified that the method can obtain smooth unwrapping phase without jump.Secondly,when grating projection 3D measurement is carried out on the surface of highly reflected objects,local brightness saturation is easily formed in camera shooting,which leads to information distortion or loss,so that accurate 3D reconstruction cannot be carried out.The method realizes the analysis and detection of saturated pixels through the projection of binarization processed phase shift grating fringe patterns,so as to accurately locate the saturated region and repair it.Then the images collected under multiple exposure times are used for image fusion and stripe image sequence reconstruction.The traditional method and the improved method were used for 3D reconstruction of the stainless steel vessels respectively,which verified that the method proposed in this paper can effectivelyovercome the problem of image pixel saturation caused by the large fluctuation range of reflectance of the object surface.In this way,the 3D morphologies of the strongly reflected surface can be measured with high accuracy.Finally,the 3D morphologies of the structural light are measured.According to the 3D measurement model and principle of grating projection,the simulation program is written.Firstly,establish the world coordinate system and calibrate the parameters of camera and projector.Then the calibration parameters and the improved measurement method are combined to carry out the actual measurement for the object with strong reflective surface.The feasibility and applicability of the proposed method for 3D measurement of strongly reflective surfaces are verified by comparing and analyzing the 3D reconstruction effects obtained from different materials.