In this paper, a novel accurate deformation distribution measurement technique by using sampling moiré method is proposed. The basic principle and an experimental result of a steel beam in symmetric three-point bending are reported. In this method, the measurement area of a target is attached with an adhesive tape of a known pitch grating firstly. An ordinary CCD camera is installed on a fixed point to record the image during deformation. The captured image is analyzed by performing easy image processing, i.e., thinning-out and linear interpolation, to obtain the multiple phase-shifted moiré patterns. Then, the phase distribution of the moiré pattern can be calculated using phase-shifting method. Finally, the deformation distribution is calculated by the grating pitch times the phase difference of before deformation and after deformation. The experimental results in symmetric three-point bending test show that the displacement of the steel beam at loading point agree well with those obtained by an accurate displacement sensor. The average error of displacement measurement is less than 4 μm when 2 mm grating pitch is used, and it corresponds to 1/500 of the grating pitch accuracy. This indicates that noncontact deformation distribution measurement is possible by simple and easy procedure with high accuracy, high speed, and low cost for the structural evaluation of infrastructures.

We measured the surface flatness of both sides for refractive media using the transmitted digital holography method. To enhance the accuracy of the result, phase-shifting system was used. With two different phase modulation of reference beam, the phase profile of object can be easily obtained. Thus, we proposed the surface measurement method which can measure large area fast, compared with conventional methods. To guarantee the reliability of obtained result, we compared with Zygo measurement system. With the proposed method, the surface flatness of 3.45 μm resolution could be obtained. 1. 서 론 홀로그래피 저장 장치[1-2]는 고밀도의 정보를 광학적으로 저장하기 위한 기술로써, 기존의 2 차 원적인 광학 정보 저장장치에 비해 저장매체에 3 차원적으로 정보를 기록하는 방식이다. 매체에 저 장된 데이터는 기록시 사용된 동일한 참조광을 입 사함으로써 얻어진다. 이렇게 얻어진 정보는 센서 로 획득되고 인코딩 과정을 거쳐 원래의 정보를 복원한다. 디지털 홀로그래피는 일반적인 광학 홀 로그래피와는 다르게 저장 매체로써 CCD 등의 이미지 센서를 사용한다. 디지털 홀로그래피는 저 장 매체에 아날로그적으로 정보를 기록하는 홀로 그래피 저장 장치에 비해 저장된 데이터도 디지털 형태를 띠므로, 데이터에 여러가지 후처리가 가능 하다. 이러한 장점으로 인해 디지털 홀로그래피는 많은 분야에 응용할 수 있으며, 역으로 이 과정에 서 개발된 기술을 저장 장치 기술에 접목시키는 것도 가능하다. 디지털 홀로그래피[3]는 3 차원 이미징 분야에서 활발히 연구가 이루어지고 있는 기술 중 하나이다. 디지털 홀로그래피는 일반적인 광학계를 약간의 수정만으로 이용할 수 있음에도 불구하고 높은 해 상도를 기대할 수 있으며, 깊이 방향 정보의 경우 피사체의 위상 정보를 이용해 획득하므로 광학계 의 Diffraction Limit 을 크게 뛰어넘는 높은 해상도 를 취득할 수 있다. 이러한 장점으로 인해 디지털 홀로그래피는 3 차원 디스플레이, 현미경을 통한 미소물체의 측정, 유체의 3 차원 유동 기록 등의 다양한 응용분야에 활발한 연구가 이루어지고 있 다. 특히 디지털 홀로그래피 현미경의 경우, 기존 의 3 차원 이미징 방식에 비해 간소한 광학계 설 계와 빠른 촬영속도, 높은 해상도를 확보할 수 있 는 장점을 가지고 있다. 디지털 홀로그래피 현미경을 응용할 수 있는 분야 중 하나는 물체의 표면 평면도를 측정하는 것이다. 팁이나 스타일러스를 이용한 기존의 기계적인 측 †School of Mechanical Engineering, Yonsei Univ.

A camera based on the digital micromirror device (DMD) technology has been previously developed. In this optical system, the correspondence of each mirror of the DMD to each pixel of the CCD cannot readily be done since the pixel sizes of the DMD and the CCD are very small. An accurate pixel-to-pixel correspondence adjustment in the DMD camera by means of the phase-shifting moiré method is proposed. To perform high accurate adjustment of the optical system, the phase distribution of a moiré fringe pattern is analyzed when the CCD pixels and the DMD mirrors have a mismatch and/or misalignment with each other. This technique does not need a complicated setting or complex image processing to generate the moiré fringe pattern, and it needs only one captured image. In the adjustment experiment, the proposed method provided very accurate adjustment whose error was less than 1/25 pixel. An experiment of phase analysis to demonstrate the usefulness was performed.

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High-speed height measurement is required in industrial fields for analyzing the behavior of a breaking object, a vibrating object or a rotating object. A shape measurement performed using a phase-shifting method can measure the shape with high spatial resolution because the coordinates can be obtained pixel by pixel. A light-source-stepping method (LSSM) that uses a linear LED array by means of a whole-space tabulation method (WSTM) has been proposed. Accurate shape measurement can be performed using this method. The response speed of the LED array is greater than 12 kHz. In this paper, height measurement is performed using WSTM and LSSM with a linear LED array and a high-speed camera. It was verified that the response speed of the linear LED is greater than 200 kHz. The phase shifting was performed at 12 kHz, and the height measurement of the vibrating woofer was performed at 4 kHz using a 3-step phase-shifting method.