A digital sampling moire method for two-dimensional displacement measurement

摘要

Measuring static and dynamic displacements for in-service structures is an important issue for the purpose of design validation, performance monitoring and safety assessment of structures. Currently available techniques can be classified into indirect measurement and direct measurement. These methods however have their own problems and limitations Digital sampling moire method is a newly developed vision-based technique for direct displacement measurement. It uses one camera to capture digital images containing a grating pattern. The images are subsampled and interpolated to generate moire patterns whose phase information can then be used to calculate displacements of the grating pattern. As the moire patterns can magnify the pattern's movement, this technique is expected to provide more accurate displacement measurement than the other vision based approaches. In this study, a digital sampling moire technique is proposed for measuring two-dimensional structural displacements using a designed grating pattern. The pattern contains two orthogonally inclined gratings and does not have to be perfectly aligned with the image plane. A series of simulation and laboratory tests are conducted to validate the accuracy of the proposed technique. Results show that the technique can achieve accuracy in the order of 10 micrometers in the laboratory. Also, the technique does not seem to suffer from the issue of misalignment between the camera and the pattern and exhibits a potential for accurate measurement of displacement for civil engineering structures.