The Digital Sampling Moire Method And Its Application

The sampling moire method is a new method for the micro-macro topography, displacement and strain measurement. In1984, Bell and Kolxopoulos firstly proposed to generate moire fringes using digital signal processing technology, namely, sampling moire method. The formation of digital moire doesn’t require a reference grating. In recent years, some scholars have further developed the sampling moire method. The grating is pasted onto the object surface and is recorded by a CCD camera. The grating images before and after deformation are sampled and interpolated to generate multi-frame phase-shifting moire fringe patterns, which can be used to calculate the moire phase by the phase-shifting method. Then the displacement and strain distribution of the object can be obtained from the phase by the corresponding formula. The sampling moire method is a great potential tool for strain analysis with advantages of high accuracy, fast, automation, stable and low cost.In this paper, the basic principle of sampling moire method is introduced, some error factors are analyzed, and an error compensation method is given. Then, its accuracy and sensitivity are analyzed using experiments and simulations. And then, a sampling camera experimental system is constructed, its performance index is given. In addition, the sampling moire method is applied to three applications:structural deformation distribution measurement, structure vibration parameters measurement and the analysis of high-frequency grating pitch error.Firstly, the sampling moire method is applied to the deflection measurement of an aluminum beam under the three point bending. Experimental results show that the sampling moire method can be used in the small deformation measurement of the structure.Secondly, the sampling moire method is applied to measure the vibration waveform, amplitude and frequency of a vibration stage. Experimental results show that the sampling moire method can correctly measure the vibration waveform, amplitude and frequency.Finally, the sampling moire method is applied to the analysis of high-frequency grating pitch error. On the basis of the principle of sampling moire method, the grid line distortion evaluation method is proposed. The high-frequency grating pitch error is analyzed, and the results show the sampling moire method can be used to evaluate the quality of high-frequency grating.