Patent ID: 7457721
Filing Date: 2008-11-25
Classification: G01B,G06T

Abstract:
1. A method for measuring small displacement to measure small displacement of an object in a non-contact manner, the method comprising: a first taking image step for taking a first image of a surface of a measuring object; a first Fourier transform step for transforming the first image taken by the first take image step by using an N-dimensional Fourier transform (where N=1 or 2); a first Hilbert transform step for replacing an amplitude of frequency spectrum of half or a part of in-plane including zero first frequency of the frequency spectrum transformed by the first Fourier transform step with zero; a first frequency extraction step for extracting a first frequency component from the first frequency spectrum after the first Hilbert transform step; a first inverse Fourier transform step for transforming the first frequency component by using an N-dimension inverse Fourier transform (where N=1 or 2) and then obtaining a first complex analytic signal; a first amplitude correction step for correcting an amplitude value of the first complex analytic signal as being a constant value; a first phase-only signal recording step for recording a first phase-only analytic signal to which the amplitude is corrected; a second take image step for taking a second image of the surface of the measuring object, on the other hand, after the first taking image step; a second Fourier transform step for transforming the second image taken by the second taking image step by using the N-dimensional Fourier transform (where N=1 or 2); a second Hilbert transform step for replacing an amplitude of frequency spectrum of half or a part of in-plane including zero frequency of the second frequency spectrum transformed by the second Fourier transform step with zero; a second frequency extraction step for extracting a second frequency component from the frequency spectrum after the second Hilbert transform step; a second inverse Fourier transform step for transforming the second frequency component by using an N-dimension inverse Fourier transform (where N=1 or 2) and then obtaining a second complex analytic signal; a second amplitude correction step for correcting an amplitude value of the second complex analytic signal as being a constant value; a second phase-only signal recording step for recording a second phase-only analytic signal to which the amplitude is corrected; a phase-only correlation processing step for obtaining a phase-only cross-correlation function to entire region or a part of region of the first phase-only analytic signal and the second phase-only analytic signal; and a displacement magnitude calculation step for calculating displacement magnitude from a location of correlation peak to which the phase-only cross-correlation function shows a maximum modulus.