Error Analysis Of Digital Image Correlation And Its Application In Microscopic Measurement

As a non-destructive,non-contact,and full-field deformation measurement method,threedimensional digital image correlation(3D-DIC)has been widely used in many measurement fields.The system calibration and image matching are the most critical technologies,which affect the measurement accuracy.And the error analysis research of calibration and matching is also becoming more and more mature.However,the research about the quantitative error evaluation of the whole measurement system is not enough.Meanwhile,with the rapid development of electronics,biology,medicine,materials and other fields,the demand for micro-scale measurement rises dramatically.Meanwhile,compared to the ordinary 3D-DIC system,the measurement error level of micro-scale3D-DIC is much higher due to the complex optical path.Therefore,it is still worthwhile to do the measurement error analysis of microscopic 3D-DIC and improve the measurement accuracy,which helps to broaden the use of DIC in the field of micro-scale deformation measurement.Based on the principle of DIC,the quantitative error analysis theory and modified calibration method for deep insight into 3D-DIC measurement technology are proposed in this paper.The theoretical model of reconstruction error for 3D-DIC system is established,and the error transmission and its relationship with the system parameters are explained.Based on the magnitude analysis of each parameter in the 3D reconstruction equation,the derived error theory model reveals the relationship between the 3D reconstruction error and the lens focal length,pixel size,object distance,solid angle,and matching error,which provides theoretical guidance on how to obtain highprecision in-plane and off-plane deformation results.With the developed model,the full-field measurement error can be directly gained without system calibration.The theoretical expression of the relative error of 3D reconstruction is given.The relationship between the relative error of 3D reconstruction and each system parameters,as well as the difference between with the 2D system are revealed.The theoretical model of microscopic error is deduced,the relationship between the theoretical error of the 3D reconstruction of the microscopic system and each parameter is described,and the problem of the measurement error of the microscopic 3D-DIC system is solved.A microscopic calibration method for accurately solving the distortion in the homography transformation stage is proposed,which improves the accuracy of the microscopic measurement.Based on the assumption that the principal point of the microscope lens does not change under different magnifications,the improved homography transformation model not only has a smaller reprojection error,but also fits the distortion surface more accurately,which greatly simplifies the calibration process.Compared with the traditional calibration method,the proposed microscopic calibration method has higher calibration accuracy,and solves the parameters abnormality problem caused by the lack of constraints in the microscopic calibration.The error theory is used to analyze the micro-scale displacement measurement errors,realizing the application of the error theory model and the micro-calibration method in the micro-scale measurement.The experimental results show that the proposed microscopic error theory can not only be used to predict the measurement error of the system,but also can be used to judge whether the calibration result is accurate.Using the proposed high-precision microscopic calibration method,the accurate measurement of the off-plane displacement field and the deformation field of the composite material bone scaffold specimen in biomedicine was realized,providing the experimental understanding of the force performance and strain distribution characteristics of the bone scaffold and guiding the structural design and strength distribution of the bone scaffold.This paper establishes a theoretical model of the 3D-DIC system,which describes the relationship between 3D reconstruction error and system parameters,and advances the research on the quantitative evaluation of measurement errors in 3D-DIC;By extending the error theory model to the microscopic 3D-DIC,the problem that the error in microscopic 3D-DIC system is difficult to estimate due to the complex optical path is solved;The proposed improved homography transformation model simplifies the cumbersome process of pre-distortion removal in the microscopic 3D-DIC calibration,realizes the high precision microscopic calibration,which lays a foundation for the application and expansion of microscopic 3D-DIC in the field of micro-scale measurement.