Research On 3D Digital Image Correlation Method Based On Modulation Measuring Profilometry

Digital image correlation method is a full-field,non-destructive,non-contact modern optical mechanics method,which has simple measuring equipment,convenient implementation and strong adaptability to the environment.This method has become an important direction in the field of image measurement,and has played a great role in medicine,materials and mechanics.The traditional 3D digital image correlation method is based on the principle of binocular stereo vision,which is restricted by occlusion and other problems when measuring objects with complex topography such as sudden changes.To study the method to overcome this problem is of great theoretical and practical significance for further developing digital image correlation method and broadening its applications.The modulation measuring profilometry based on coaxial measurement principle is not affected by occlusion.According to the principle of digital image correlation method and modulation measuring profilometry,the advantages of modulation measuring profilometry to solve the occlusion and other problems existing in 3D digital image correlation method are analyzed.This paper studies the 3D topography and displacement measurement technology combining modulation measuring profilometry and digital image correlation method.The main research contents are as follows.(1)Aiming at the problem that a large error may occur when the optical axis is not perpendicular to the calibration plane during the calibration process of modulation measuring profilometry based on modulation ratio,a calibration method based on pose estimation was proposed.In the calibration process,monocular pose estimation algorithm was used to calculate the relative pose of the calibration plane and the camera,and the mapping relationship between the modulation ratio and the depth in the camera coordinate system was established.The improved calibration method can overcome the problem that the calibration plane is not perpendicular to the optical axis in the calibration process,and this method can directly obtain the coordinates in the camera coordinate system by modulation ratio,which is convenient for the subsequent displacement measurement using 3D digital image correlation.The experimental results show that the proposed method is more accurate than the traditional method when the calibration plane and measuring optical axis are not vertical.(2)Aiming at the problems of occlusion,a 3D digital image correlation method based on modulation measuring profilometry was proposed.The modulation measuring profilometry based on coaxial measurement principle is combined with digital image correlation method,and the 3D morphology of the points to be measured on the surface of the measured object is measured by the modulation ratio,and the 2D displacement is obtained by matching the homonymous points of the images before and after deformation through the 2D digital image correlation method.The displacement of the measured point before and after deformation was obtained by combining the 3D topography and digital image correlation matching results.Based on the principle of coaxial measurement,this method can effectively overcome the problem of occlusion existing in the traditional binocular stereo vision principle,and is competent for the deformation measurement of complex morphologic objects which is difficult to be measured by traditional methods.The experimental results show that this method has a good effect on the measurement of sudden change objects.