Papers by Author: Yoshiharu Morimoto

Abstract: Sampling moiré method is useful to measure shape, displacement and strain distributions of multi-functional materials and structures. When a specimen grating pattern on an object is recorded by a digital camera, a moiré fringe pattern is obtained by sampling the digitized grating image with a constant pixel pitch. The method can analyze phase values from one image of a grating pattern. By using this sampling moiré method, the displacement measurement of land is analyzed to develop a landslide prediction system. The theory and the application for measuring the displacement of land are shown in this paper.

Abstract: In order to measure 3D displacement components and surface strain distributions of objects, three systems for digital holographic interferometry were developed. In this study, these three systems are introduced and the applications to measurement of 3D displacement components and surface strain distributions of cantilevers are shown.

Abstract: We previously proposed a real-time shape measurement method using two-component synthesis grating projection. In the method, phase unwrapping of the projected grating is performed by using aliasing of the Fourier spectrum of the grating images. It requires only 5 images obtained for one-cycle phase-shifting. Each phase in the two-component can be extracted from only 5 phase-shifted grating images. In this paper, we propose a real-time shape measurement system. The theory, the algorithm for the analysis and the experimental results are shown.

Abstract: Phase-shifting digital holography can be used for displacement measurement instead of strain gauge. Our research group is developing the measurement equipment for phase-shifting digital holography. Generally, in the measurement equipment, piezo stages are used as phaseshifting devices. But the piezo stage is expensive. Cheaper and smaller phase-shifting device is required in order to put the measurement equipment into practical use. In this paper, we, therefore, propose a phase-shifting device using the deflection of a cantilever and we verify whether this phase-shifting device can be used
for digital holography.

Abstract: The authors have been developing some novel methods to measure shape, deformation, stress and strain of structures using optical methods and image processing as follows: (1) Phase analysis methods using Fourier, wavelet or Gabor transforms, etc., (2) Real-time 2-D strain measurement using moiré interferometry, (3) Scanning moiré method using thinning-out of scanning lines and a DMD camera (4) Strain rate distribution measurement by a high-speed video camera, (5) Real-time integrated phase-shifting method, (6) Shape measurement methods using multi-reference planes, a linear image sensor, or a frequency modulated grating, and (7) Windowed phase-shifting digital holographic interferometry (WPSDHI). Theories of these methods and some applications are introduced. The most accurate result is 88 picometer standard deviation of errors using the WPSDHI.

Abstract: In this paper, we apply phase-shifting digital holographic interferometry to simultaneous measurement for out-of-plane and in-plane displacements by employing two beam illuminations for an object. Phase-shifted holograms before and after displacements of the object using each of two beams are recorded by a CCD camera, separately. The complex amplitude at each pixel of the CCD plane is analyzed from the holograms taken with phase-shifting. The complex amplitude of he object is reconstructed from the complex amplitude distribution on the CCD plane using the Fresnel diffraction integral. Each directional phase difference distribution is obtained by calculating the phases before and after deformation for each directional beam. The phase distribution for out-of-plane displacements is obtained by calculating the sum of the two phase difference distributions. The phase distribution for in-plane displacements is obtained by calculating the difference of the two phase difference distributions. The phase values provide accurate displacement distribution information. Actually, when the object deforms in both out-of-plane and in-plane directions, it is possible to analyze the displacement distribution in each direction. The theory and an experiment are shown.

Abstract: Displacement measurement can be performed with high accuracy using phase-shifting method. In phase-shifting method, it is often used four steps of phase-shifting for one cycle. In conventional method, to measure the displacement of an object by an interferometer, the phase of a reference beam should be shifted by every π/2 in the four-step phase-shifting. In this paper, a phase-shifting method with unknown intervals is proposed. This method does not need to shift a phase by every π/2. It can detect an intensity distribution and a phase distribution from five fringe images with equal intervals even if the phase-shift amount is unknown. Using this method, we propose a displacement measurement of phase-shifting digital holographic interferometry using spherical wave as reference wave.