Yoshiharu Morimoto

Secure optical data storage with random phase key codes by use of a configuration of a joint transform correlator

A secure optical storage based on a configuration of a joint transform correlator by use of a photorefractive material is presented. A key code designed through the use of an optimized algorithm so that its Fourier transform has a uniform amplitude distribution and a uniformly random phase distribution is introduced. Original two-dimensional data and the key code are placed side-by-side at the input plane. Both of them are stored in a photorefractive material as a joint power spectrum. The retrieval of the original data can be achieved with the same key code. We can record multiple two-dimensional data in the same crystal by angular multiplexing and/or key code multiplexing.

Shape Measurement by Whole‐space Tabulation Method Using Phase‐shifting LED Projector

In order to obtain a 3D‐shape with grating projection method, the authors previously presented whole‐space tabulation method (WSTM). The relationship between the coordinates and the phase of the grating recorded at each pixel of a camera is obtained as calibration tables in three‐dimensional space by experiment beforehand. Therefore the analysis is very fast because of looking at the calibration tables without any complex calculation. It provides fine resolution even when the phase distribution of the grating is not linear. In this paper, a grating projector with three light emitted diode (LED) light sources is proposed. It provides a low cost system. The theory and experimental results are shown.

Development of Sampling Moire Camera for Landslide Prediction by Small Displacement Measurement

The ability to measure the small displacement caused by a landslide is important. If it were possible to measure the displacement before the landslide occurs, people would be able to evacuate before the landslide occurs and reach a safe area. Therefore, we developed a detection system using the small displacement measurement of a landslide. This system uses a displacement measurement technique known as the sampling moire method. This method is capable of analyzing the phase values from one image of a grating pattern. Because of this, the detection system is very simple and compact. In addition, it analyzes displacement very accurately. The phase is calculated from several phase-shifted method fringe patterns that are obtained by changing the sampling phase. The displacement is analyzed by determining the difference in the phase before and after displacement. However, the displacement results contain errors such as stir and air turbulence, which complicate landslide prediction. The level of error can be decreased by taking the averages of displacement that contain errors. Therefore, we developed a sampling moire camera that is capable of rapidly, acquiring images and performing a high-speed analysis. The sampling moire camera uses sampling moire method to analyzing the phase. In this paper, we describe the sampling moire camera’s ability to predict landslides by measuring small displacement. We also conduct experiments that test the system.

Theory and Application of Sampling Moiré Method

Sampling moire method is a newly developed moire method using an image processor for a grating pattern to measure shape or displacement or strain distributions. A grating pattern on an object is recorded by a digital camera. Though the digitized image shows the grating, a moire fringe pattern appears by thinning-out the pixels, i.e., sampling the image with a larger pitch than the pixel pitch. If the sampling pitch is changed, the moire pattern is changed very much. If the phase of the sampling is changed, the phase of the moire pattern is changed. The phase analysis of moire pattern provides accurate result of displacement of the grating. If the number of the phase-shifted moire patterns i.e. the number of pixels for a pitch of grating is larger, the resolution of phase analysis becomes more accurate but the spatial resolution becomes worse. Since the sampling moire method is useful to analyze the phases of a moire fringe and a grating from one image of a grating pattern, it is possible to analyze dynamic deformation accurately.

Vibration Modal Analysis by High-Speed and Accurate Shape Measurement Using One-Pitch Phase Analysis Method

To protect vibration of structures, vibration modal analysis is important. Conventional experimental vibration analysis method uses accelerometers or laser displacement meters. The analysis takes much time and troublesome work. Especially, by contacting accelerometers to objects the results of frequency mode have some errors because of contact of the accelerometer weight. The authors have previously proposed a new method for shape measurement, i.e. the one-pitch phase analysis (OPPA) method using moire topography. In moire topography, the number of pixels for one pitch is constant regardless of the object height. The OPPA method analyzes the phase of each pixel in a single-shot image by using brightness data from one pitch of a projected grating. A motion capture system has been previously developed using OPPA method and measured the 3D coordinates at every pixel of the surface of a human body. In this study, the OPPA method is applied to vibration modal analysis of a cantilever plate using a high-speed camera. This method is useful for inspection of automobiles, machines, buildings, etc. without contact, in a short time.

Prediction of Landslide by Displacement Measurement using Sampling Moiré Method

In sampling moire method, a specimen grating pattern on an object is recorded by a digital camera. A moire fringe pattern appears by sampling the recorded grating pattern with a constant pixel pitch. The phase analysis of the moire patterns obtained from one grating pattern provides accurate results of displacement values of the grating. Meanwhile, it is very important to keep our life safely by predicting landslides. If the small displacement of land before the landslide is detected, it is possible to put out an alert before the disaster happens. In this paper, a measurement system for small displacement of landslide by sampling moire method is developed.

Real‐Time Shape Measurement by Grating Projection Method Applied to Electronic Packaging

In this study, a system using a Field Programmable Gate Array (FPGA) memory board is proposed to obtain the full‐size shape without any reduction of the image in real‐time. The memory of the FPGA memory board has a phase analysis table and phase‐coordinate tables. The brightness data of the recorded grating are stored in the phase analysis table to obtain the phase of the recorded grating. The calibration data using a moving reference plane are stored as a phase‐coordinate table to obtain the coordinates of the phase. An experiment to evaluate this system was performed. The analysis speed of shape measurement using the memory board did not depend on a speed of a personal computer. The accuracy of shape measurement using the memory board and using software was almost the same. The analysis speed using the memory board was faster than the one using software.

High-accuracy and real-time shape measurement using whole-space tabulation board

A whole-space tabulation method (WSTM) is a technique to relate phase of projected grating with coordinates of the corresponded point pixel by pixel. The relation data are stored in a table. Even if there is a lens distortion of the projected grating, the WSTM can measure the shape of an object with high-accuracy. Even if a grating pitch is not equal, the WSTM can measure it with high-accuracy. And the analysis speed is very high because this method performs no calculation. The WSTM is, therefore, very useful for shape measurement. But, this method needs huge memory. It is possible to use the WSTM using a personal computer if the pixel size is small. It is necessary to reduce the pixel size of the image in the case of using a general personal computer. In this paper, a memory board for WSTM was developed to analyze shape with full size of an image. An experiment to evaluate this memory board was performed. This board has two set of a field programmable gate array (FPGA). The analysis speed of shape measurement using the memory board does not depend on a speed of a personal computer. The accuracy of shape measurement using the memory board and using software was almost same. The analysis speed using the memory board was faster than using software.