Camera Calibration Technology And Its Application In Digital Image Correlation

3D digital image correlation(3D-DIC)is an important optical measurement method in the field of experimental mechanics.This method has become a hot research field in recent years because of its advantages such as easy to use,non-contact and full-field measurement.With the rapid development of technology,aerospace,precision machining,high-end manufacturing puts forward higher requirements on high precision and high flexibility measurement.To further play its role in the production and construction,digital image correlation method,as a kind of high precision image measurement method,requires the knowledge of camera 3D reconstruction to improve the precision and extend application scenario.Based on the theory of machine vision and aiming at engineering application,this thesis studies camera calibration technology from two aspects:1)A marking point detection method is proposed in the case of poor light and the calibration plate occupies a small field of view.This thesis points out the problem that the global and local image binarization methods fail in the complex environment,and proposes an adaptive binarization method to improve the recognition rate of the calibration plate.2)A calibration method of fixed scale is proposed.This thesis analyzes the problem of scale information loss in nonlinear optimization of camera calibration,points out the influence of this problem on the measurement results,and proposes a fixed scale iterative optimization algorithm to improve the calibration accuracy and retain the scale information.This thesis studies the measurement difficulties in two application scenarios,proposes a reasonable solution,and verifies its feasibility by experiments:1)A high-precision optical extensometer based on coordinate transformation theory and 2D-DIC is proposed.The effect of out-of-plane motion on the correlation of 2D-DIC in loading is analyzed,and a compensation method based on coordinate transformation is proposed to realize the high-precision measurement of single camera extensometer.The advantages and disadvantages of the existing method and the new method are compared by means of simulation and experiment.The results show that the proposed method can effectively improve the measurement accuracy and achieve the expected effect.2)A 3D measurement method for large space deployable antennas combining laser ranging and digital image correlation algorithm is proposed.This thesis analyzes the measurement requirements and technical difficulties of large space deployable antennas.Considering the characteristics of large scale,high depth of field and complex measurement environment,a 3D measurement method combining laser ranging and digital image correlation is proposed,and the feasibility of this method is verified by experiments.