Real-time Video Extensometer Based on FPGA

In the uniaxial tensile test of sheet metal, the use of contact type electronic extensometers may cause slipping or installation difficulties due to sample size issues. The use of video extensometers can effectively solve potential problems. While traditional video extensometers use computers as the computing platform, this paper proposes a video extensometer with Xilinx FPGA as the computing core. Researches on the calibration method of video extensometer based on single perspective are carried out. Using the calibration calculation results for interpolation to generate the frontal projection image of the sample reduces the position calculation error caused by the polarization axis angle. A lookup table compression method for image interpolation is also proposed. Real time interpolation of 8 pixels per clock is achieved through pre reading and caching methods. Implement a marker point positioning method based on the center of gravity on FPGA. The positioning accuracy of the video extensometer proposed in this paper is about 1pm when the camera is well calibrated. And it can achieve real-time calculation and output exceeding 150Hz. The reliability and accuracy of the real-time video extensometer were verified through tension-free displacement tests and uniaxial tensile tests.