Research On Key Algorithms Of Visual Dynamic Measurement Of Extensometer

Extensometer plays an important role in the tensile test,and is one of the most critical equipment to measure the properties of the material.Although the traditional extensometer is quite mature in technology,its disadvantages are also obvious.During the material testing,traditional extensometer produce errors due to the friction between the blade and the material and it cannot be used in the special environment such as high temperature and high pressure,which limits its practical application in the production practice.In this paper,the machine vision technology is used to carry out the dynamic real-time monitoring of the material stretching process.The operation is simple and convenient,and the results are stable.The main research contents of this topic include the following aspects:(1)According to the measurement requirements of visual extensometer,and the difficulties in the measurement process of the visual extensometer are analyzed,based on the general flow of machine vision measurement,the general idea of the measurement algorithm of visual extensometer is designed.(2)A camera calibration method based on circular calibration plate is designed.By extracting the characteristic point data of the calibration plate in the calibration picture,the inner and outer parameters of the camera are calculated by Zhang’s calibration method,and then the camera distortion is corrected to reduce the measurement error of the extensometer.(3)An image deformation tracking algorithm based on normalized cross correlation matching was designed for the deformation of materials during tensile test.During the stretching of the material,the image of the stretched material is collected in real time,and the position of the deformed material is tracked in real time based on the feature of image gray value.In order to verify the feasibility of visual dynamic key measurement algorithm of extensometer in this paper,an experimental testing platform was built.Implement camera calibration algorithm and target tracking algorithm under Visual Studio 2015 platform,develop the functions and interface of Visual extensometer system.Tensile tests were carried out on rebar to measure its deformation and to compare the results with those of the Mercury RT test system.The experimental results show that the method can be applied to the extensometer tension monitoring.