Study On Dynamic Deformation Measurement Based On Stereoscopic Vision

With the advantages of simple experimental setup,low environmental requirements,and non-contact full-field measurement,the deformation measurement technology based on stereoscopic vision clearly stands out among the technologies of modern photo-mechanics.This technology is widely applied in industry and engineering field.However,with the deepening of the study on dynamic mechanical properties and failure behavior of structures,it is necessary to test and analyze the whole process of dynamic destruction using experimental methods.In dynamic tests,optical systems do not only put forward higher requirements on the light source illumination,the synchronizing and frame rates of cameras to the system,but also bring great challenges to the measurement precision and the test range of the dynamic deformation.In the multi-camera dynamic deformation measurement,the change of the pose between cameras is an important factor to affect the measurement accuracy.To correct the cameras' real-time attitude,it is proposed a real-time extrinsic parameter of camera calibration method.This method may be used to eliminate the influence of motion between cameras on the measurement accuracy due to environmental or artificial factors.By constructing the coplanar equation,the extrinsic parameters are optimized with the matching points of images captured by two synchronous cameras.The world coordinate system is established according to the stationary benchmarks during the test.Both the numerical simulation and the real experiments verified that the method is effective to improve the displacement accuracy.It is further analyzed the influencing factors on the precision.The camera calibration error and the image matching error are pointed out to be the main sources of the measurement errors.The measurement errors are divided into three types:in-plane error,out-of-plane error,and total error.Numerical simulation experiments are conducted to compare the errors produced by the different arrangement of the system.The intuitive explanation is given with the graphic interpretation.This conclusion is of great significance to the system layout.Multi-camera joint measurement is an effective way to achieve a wide range of deformation measurements.Using the independent designed eight-camera full-circle dynamic deformation measurement system,the full circle deformation measurement of basalt fiber reinforced polymer(BFRP)wrapped concrete columns was carried out.The arrangement scheme of the eight camera system is analyzed in detail,and the strain measurement accuracy of the system is verified by comparing with the measurement results of the strain gauge.Simultaneously,in order to reduce the complexity of the system and improve its ease of use,it is proposed a multi-camera two-dimensional full-field digital image correlation method based on stereoscopic vision.Without reducing the measurement accuracy under the premise of improving the test range,it is applied to measure large-scale in-plane deformation of planar specimen.The influencing factors of strain precision in two-dimensional digital image correlation method are deduced theoretically.With the displacement precision unchanged,when the strain is uniform,the bigger the window is,the higher the strain accuracy is.Therefore,based on the improved image stitching method,multi-camera deformation measurement method is proposed to improve the spatial resolution of digital images.The test accuracy of this method is verified by the experiment of pure translation and three-point bending of rubber beam.In particular,to achieve the goal of large-scale structural full surface deformation measurement,a dynamic measurement method based on the camera array is proposed,and the corresponding test system is developed.They are applied to solve the high-definiton large field of view(FOV)structure surface imaging problem in the turbid medium.In conclusion,for high-precision full surface deformation measurement under dynamic test environments,a series of problems are deeply studied.Through the independent development of computer software,real-time correction of the camera's attitude in dynamic tests and real-time correction and stitching of array camera images are realized.The above methods provide reliable means for the dynamic deformation test of the actual engineering components,and have a good application prospect.