• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.05a
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• pp.174-174
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• 2004

본 논문에서는 4변이 고정된 정사각형 알루미늄 평판의 진동 진폭을 측정하기 위하여, 기존의 위상 이동 ESP떼 스트로보스코프식 조사를 적용한 스트로보스코픽 ESPI 기법을 이용하였다. 일반적으로 시간평균 ESPI를 이용하면 진동하고 있는 대상체의 정성적인 진동 패턴을 측정할 수 있다. 그러나 시간평균 ESPI로는 진동하고 있는 대상체의 두께방향으로의 진폭량을 측정하기는 어렵다. 또한 일반적인 위상이동법을 적용시킬 경우, 대상체가 진동을 하게 됨으로써 정확한 진동 진폭을 측정하기 어렵다.(중략)

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.12
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• pp.2535-2540
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• 2002

ESPI is a noncontact, nondestructive and relatively fast inspection method. For these reasons ESPI is being applied as a valuable tool in the nondestructive evaluation of structural components. Phase shifting ESPI is used more effectively than the traditional ESPI because spatial resolution of small object displacements are improved and numerical phase values are obtained for all pixels in the image. Consequently the quantitative measurement of deformation is possible. ESPI fringe patterns are contaminated with high levels of speckle noise. Therefore the phase image is to be smoothed to remove the noise and obtain a better signal-to-noise ratio. In this study, smoothing is done by phase shifting convolution to avoid smoothing errors close to the 2$\pi$ phase ambiguities in the deformation phase image, and median filter is used as a smoothing filter.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.443-446
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• 2003

The vibration mode shape changed by the phase angle that can be controlled by phase-shifting ESPI system is discussed. For the phase-shifting ESPI experiment the stroboscopic illumination by using AOM(Acousto-Optic Modulator) is needed, and the initial phase angle can be adjusted by the program. The vibration mode shape is changed when the initial phase angle is changed. We examined the vibration mode shape change due to the initial phase angle change at each resonance frequency. Through this study, we found that in the vibration testing using phase-shilling ESPI the vibration mode shape is improved in the quality by adjusting exact phase angle and the error of the quantitative vibration analysis can be reduced.

• Journal of KSNVE
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• v.9 no.3
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• pp.509-516
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• 1999

The ESPI (Electronic Speckle Pattern Interferometry) algorithm has been simulated to calculate vibrational modes of a thin right-angled STS304 plate. The phase transformation of the reference wave of the ESPI is carried out only one time during vibration in order to clarify ESPI speckle patterns. Two dimensional vibrational modes are calculated from one ESPI pattern before vibration onset and two ESPI patterns during vibrations but with and without the phase transformation. The ESPI harmonic results are compared with those derived from the finite element method (FEM), and they agree very well. Additionally a phase unwrapping algorithm has been newly developed to derive a displacement map from an ESPI phase map.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.226-230
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• 2001

Electronic Speckle Pattern Interferometry (ESPI) has been recently developed and widely used because it has advantage to be able to measure surface deformations of engineering components and materials in industrial areas with non-contact. The spekle patterns to be formed with interference phenomena of scattering phenomena measure the out-of-plane deformations, together with the use of digital image equipment to process the informations included in the speckle patterns and the display consequent interferogram on a computer monitor. In this study, the experimental results of a canti-levered plate using ESPI were compared with those obtained from the simple beam theory. The ESPI results of the canti-levered plate analyzed by 4-step phase shifting method are close to the theoretical expectation. Also, out-0of-plane displacements of a spot welded canti-levered plate were measured by ESPI with 4-step phase shifting technique. The phase map of the spot welded canti-levered plate is quite different from that of the canti-levered plate without spot welding.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.911-914
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• 2003

The non-contact laser measurement system what can be used for the vibration analysis of structures is discussed. There are few systems using laser speckle interferometer for vibration analysis. One of these systems is the Electronic Speckle Pattern Interferometer (ESPI). With ESPI system, one can obtain the vibration mode shape qualitatively and the maximum vibration amplitude quantitatively of the structure at each resonance frequency. In this paper, the phase-shifting ESPI system with stroboscopic illumination for measuring vibration mode shapes is constructed and the operating software is programmed. The results are compared with that of commercial ESPI system.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.11
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• pp.121-129
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• 1998

In-plane ESPI(Electronic Speckle Pattern Interferometry) was devised to measure in-plane deformations and rotation of a specimen with laser in this study. ESPI is a optical measuring method to be able to measure the deformations of engineering components and materials in industrial fields. The conventional measuring methods of surface deformations such as the strain gauge have many demerits because they are contact and point-to-point measuring ones. But that ESPI is noncontact, nondestructive and whole field measuring method can overcome previous disadvantages. We used ESPI which is sensitive to in-plane displacement for measuring in-plane deformations of a disk. And the 4-frame phase shifting method was used for the quantitative analysis. First of all, the system calibration was done due to an in-plane rotation before getting deformations of a disk. Finally we showed good agreement between the experiment results and those of the FEA(Finite Element Analysis).

• Proceedings of the Optical Society of Korea Conference
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• 1996.09a
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• pp.102-102
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• 1996

• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.5
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• pp.423-428
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• 2010

In this paper, we analyzed the characteristics of thermal deformation of the TPS which is a core part of engine in vehicle by measuring out-of-plane deformation using ESP!. Inspection area of a test piece was minimized to 5 cm by 5 cm by using a high resolution CCD and a zoom lens. 4-step phase shifting method was used along with phase unwrapping algorithm to get a continuous phase map, configurations and deformations were displayed as 3D images. When heating the test pieces while maintaining the temperature at about $70^{\circ}C$, the out-of-plane deformations were measured. The results showed that a test piece with longer distance traveled tends to show larger thermal deformation, we could observes a convex shaped deformation on the surface. The inner defect sample, we could monitor discontinuous pattern phase map, and a concave shaped deformation on the surface.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.3
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• pp.66-72
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• 2002

Electronic Speckle Pattern Interferometry (ESPI) has been recently developed and widely used because it has advantage to be able to measure surface deformations of engineering components and materials in industrial areas with non-contact. The speckle patterns to be formed with interference and scattering phenomena can measure not only out-of-plane but also in-plane deformations, together with the use of digital image equipment to process the informations included in the speckle patterns and to display consequent interferogram on a computer monitor. In this study, the experimental results of a canti-levered plate using ESPI were compared with those obtained from the simple beam theory. The ESPI results of the canti-levered plate analyzed by 4-step phase shifting method are close to the theoretical expectation. Also, out-of-plane displacements of a spot welded cacti-levered plate were measured by ESPI with 4-step phase shifting technique. The phase map of the spot welded cacti-levered plate is quite different from that of the canti-levered plate without spot welding.