An Algorithm Measurement Of In-plane Displacement By Speckle Pattern Photography Based On Phase Of Fourier Transform

In the fields of engineering applications and material mechanics,Micro displacement measurement has an important meaning.The existing measuring technology can be mainly divided into optical measurement and electrical measurement.In optical measurement,speckle photography is one of the effective methods to measure the small displacement.In this paper,based on the existing speckle photography,a new algorithm using Fourier transform,is introduced to improve the accuracy of measurement and to achieve subpixel measurement.The operation mode of new algorithm is discussed in detail.The specific works include:(1)The paper elaborates a theory of speckle photography which is based on Fourier transform.And then,it is contrasted to the traditional autocorrelation speckle photography method in the measurement limits and the measurement accuracy.(2)The speckle photography data is processed using MATLAB.Meanwhile the result is compared with that from traditional additive mode algorithm,subtraction mode algorithm and phase algorithm.(3)The theory shows that the phase algorithm can improve the measureme nt limit and the accuracy of the measurement.And it is proved by experiment.Moreover,the noise problem in the subpixel experiment is solved effectively.(4)The new algorithm is successfully to experiment white light speckle tin y displacement.The theoretical and experimental results show that the minimum measurem ent detected by phase algorithm has no matter with the speckle size,and just d epends on the size of pixel spacing of the photoelectric conversion device.And the maximum value of the phase algorithm is larger than traditional speckle photography.The phase algorithm can also be used to judge the moving directi on of speckle field conveniently.In addition,the phase algorithm can achieve sub-pixel measurement.And the measuring accuracy can reach to the level of sub-micron level.The relative error is about ten percentages.The white light speckle experiment indicates that the phase algorithm is also applicable in this neighborhood.