Accuracy Analysis And Application Of Digital Image Correlation Method Based On Four-Camera Bidirectional Combination System

Three-dimensional Digital Image Correlation(3D-DIC)method has been widely utilized in industry and scientific reserach,with requirements for the accuracy of full-field measuremen.higher than before.How to use limited hardware devices to achieve high-precision measurement and achieve consistency of the whole field measurement accuracy is meaningful.For a certain 3D-DIC setup,parameters such as lens focal length,pixel size,stereo angle and working distance can be easily obtained.The range of matching error is generally 0.01~0.02 pixels.If the measurement error of the system can be estimated based on the parameters above before the deformation measurement of the 3D-DIC system is carried out,it will bring convenience to practical application and has guiding significance.In this paper,two commonly used dual-camera 3D-DIC measurement systems,namely horizontal and vertical dual-camera 3D-DIC,are studied.It is found that the measurement accuracy of the two systems is not consistent in X direction and Y direction,and the measurement accuracy in one direction is lower;the measurement accuracy of the central area and the edge area is inconsistent,and the accuracy of the edge area is lower than that of the central area.In order to achieve high precision measurement and ensure the consistency of the whole field measurement accuracy,this paper systematically analyzed the measurement accuracy of with four-camera bidirectional combination and orthogonal arrangement 3D-DIC.The results of numerical simulation show that the three-dimensional reconstruction accuracy of the dual-camera 3D-DIC measurement method is closely related to the stereo angle,while the three-dimensional reconstruction accuracy of the four-camera bidirectional combination layout measurement method changes gently with the increase of the stereo angle.The 3D reconstruction accuracy of the whole field of dual-camera 3D-DIC measurement method is inconsistent in plane direction and consistent in out-plane direction,while the 3D reconstruction accuracy of the whole field of four-camera is consistent in plane direction and out-plane direction.The accuracy of 3D reconstruction of horizontally arranged dual-camera 3D-DIC in Y direction is slightly higher than that in X direction;that of vertical arranged dualcamera 3D-DIC in X direction is slightly higher than that in Y direction;and that of four-camera bidirectional combination measurement method in X direction and Y direction has good consistency.Through comparison,it is found that the measurement accuracy of the four-camera bidirectional combination measurement method is higher than that of the dual-camera 3D-DIC method,and the accuracy of both in-plane and out-plane directions can be guaranteed.Based on the above research,a simple four-camera bidirectional combination measurement system is developed,and the specific expressions describing the threedimensional reconstruction errors of the center point of two dual-camera systems and fourcamera bidirectional combination system are derived respectively.The theoretical error formula reveals the relationship between three-dimensional reconstruction error and system parameters.It also reveals the reason why the measurement accuracy of the four-camera system has been improved under the combined action of increasing constraints and introducing errors.The correctness of the theoretical formula of three-dimensional reconstruction error is verified by a series of static experiments at different stereo angles.By comparison,it is found that the fourcamera bidirectional combination system can provide about 1 times higher measurement accuracy than that with dual-camera system.Finally,four-camera bidirectional combination measurement system is applied to practical measurement,and high-precision measurement results are obtained.The theoretical formula of three-dimensional reconstruction error plays a guiding and error estimation role.