2017 年 15 巻 APISAT-2016 号 p. a37-a44
A noncontact method of measuring the strain on a wire-mesh surface using a digital image correlation technique was developed and its feasibility was investigated. In this method, the mesh feature is utilized; thus, target markers, painting, and strain gauges on the mesh surface are not required. The strain on the mesh surface is estimated based on changes in the spatial frequencies of the mesh grating (mesh regularity), and the digital image correlation technique is used to clar-ify the regularity of the mesh by calculating the distribution of the similarities. The spatial frequency of the mesh grating is evaluated using fast Fourier transform (FFT) analysis of the similarities.
In this study, Welch's method is employed to reduce the influence of noise caused by imperfect and finite data. Then, a quadratically interpolated FFT (QIFFT) method is used to find the spectral peak. The spatial frequency of the mesh grating in the digital image captured is affected by the mesh's angle of tilt and distance from the camera. Therefore, a method to correct the effects of the mesh's angle of tilt and distance of the mesh from the camera on the estimated spa-tial frequency was also developed based on the shape measurement results obtained using a stereoscopic vision system. Experiments were conducted to investigate the feasibility of these methods. The camera captured the images of the mesh. The spatial frequencies of the mesh grating were analyzed using FFT and corrected using digital image correla-tion with the shape measurement results obtained using the stereoscopic vision system. The results of the experiments were in good agreement with the test conditions we set, thus clearly indicating the efficiency of the method developed.
