• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.573-576
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• 2005

A compact linear and angular displacement measurement device was developed by combining a Michelson interferometer and an autocollimator to characterize the movement of a precision stage. A Michelson interferometer and an autocollimator are typical devices for measuring linear and angular displacement, respectively. By controlling the polarization of reflected beam from the target mirror of the interferometer, some part of light was retro-reflected to the light source and the reflected beam was used for angle measurement. The interferometer and the autocollimator use the same optic axis and the target mirror can be easily and precisely aligned orthogonal to the optic axis by monitoring the autocollimator s signal. The autocollimator was designed for angular resolution of 0.1 arcsec and dynamic range of 60 arcsec. The nonlinearity error of interferometer was minimized by trimming the gain and offset of the photodiode signals. Through the experiments, we evaluate the performance of measurement device and discuss its applications.

• Journal of the Semiconductor & Display Technology
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• v.3 no.2
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• pp.41-46
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• 2004

This paper proposes a robust discrete time Kalman filter (RDKF) for the dynamic compensation of nonlinearity in a homodyne laser interferometer for high-precision displacement measurement and in real-time. The interferometer system is modeled to reduce the calculation of the estimator. A regulator is applied to improve the robustness of the system. An estimator based on dynamic modeling and a zero regulator of the system was designed by the authors of this study. For real measurement, the experimental results show that the proposed interferometer system can be applied to high precision displacement measurement in real-time.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1994.10a
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• pp.515-518
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• 1994

Holographic interferometry is a useful whole-field nondestructive testing for measuring deformations and vibrations of engineering structure. A diverging beam is used as a light source int the most of holographic interferometer practically. For a relatively small object the optical arrangement using a collimated light source has no difficulty in use technically, but for a large object it is difficult to use a collimated beam. In this study we calculate the error of measured displacement from the sensitivity vector dominated by the geometry of optical arrangement for holographic interferometer and show the result obtained with 2-D plots. A Plane surface and a cylindrical surface were chosen as objects to be calculated and computer analysis was carried out for the cases of a diverging beam and a collimated one.

• Journal of the Korean Society for Precision Engineering
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• v.14 no.6
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• pp.128-134
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• 1997

Holographic interferometry is a useful whole-field nondestructive tesing method for measuring deformations and vibrations of engineering structure. In practical way most holographic interferometer uses a diverging beam, a point light source. When an oject is relatively small, the optical arrangement using a collimated light source has no difficulty technically but for a large object the collimated beam connot be applied anymore practically. In this paper we calculate the error of measured displacement from the sensi- tivity vector dominated by the geometry of optical arrangement for holographic interferometer and show the result with 2-D plots. A plane surface and a cylindrical surface were chosen as objects to be measured and the results from the cases of a diverging and a collimated beams were compared and analyzed.

• International Journal of Aeronautical and Space Sciences
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• v.13 no.2
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• pp.221-228
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• 2012

An active compensation method for the deformation of composite structures using additional controllable metal parts is proposed, and its feasibility is experimentally investigated in a simulated space environment. Composite specimens are tested in a vacuum chamber, which is able to maintain pressure on the order of 10-3 torr and interior temperature in the range of ${\pm}30^{\circ}C$. The displacement-measuring interferometer system, which consists of a heterodyne HeNe laser and an interferometer, is used to measure the displacement of the whole structure. Meanwhile, the strain of the composite part and temperature of both parts are measured by fiber Bragg grating sensors and thermistors, respectively. The displacement of the composite structure is maintained within a tolerance of ${\pm}1{\mu}m$ by controlling the elongation of the metal part, which is bonded to the end of the composite part. Also, the possibility of fiber Bragg grating sensors as control input sensors is successfully demonstrated using a proper corrective factor based on the specimen temperature gradient data.

• Proceedings of the KIEE Conference
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• 1993.11a
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• pp.353-355
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• 1993

A single-mode fiber-optic interferometer for measuring small vibrations was constructed. The interferometer is based on the Fabry-Perot configuration that uses a single mode bidirectional fiber coupler as a beam splitter and employs peak detection scheme in the signal processing. The instrument was used to measure the displacement of the translator clamped to a piezo crystal.

• Journal of the Korean Society for Precision Engineering
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• v.33 no.4
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• pp.295-301
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• 2016

The out-of-squareness is one of the error sources that affect the positioning accuracy of machine tools and coordinate measuring machines. Laser interferometer is widely used to measure the position and angular errors, and can measure the squareness using an optical square. However, the squareness measurement using the laser interferometer is difficult, as compared to other errors due to complicated optics setup and Abbe's error occurrence. The effect of out-of-squareness mainly appears at the face-diagonal of the movable plane. The diagonal displacements are also affected by the position dependent geometric errors. In this study, the squareness estimation techniques via diagonal displacement measurement using the laser interferometer without an optical square were proposed. For accurate estimation and measurement time reduction, the errors selected from proposed discriminant were measured. Discrepancy between the proposed technique with the laser interferometer (with an optical square) result was $0.6{\mu}rad$.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.6
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• pp.80-86
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• 2001

This paper proposes a precision displacement measuring method of detecting fringe movement of interferograms with a nanometric resolution. It is well known that the laser interferometer plays a useful and essential role in scientific and industrial application, but they have such error sources as an unequal gain of detectors, imbalanced beams, and lack of quadrature. These error sources degrade the accuracy of the interferometer. However, the fringe movement of interferograms has little relation with these error sources. In order to investigate performance of the proposed method. analysis and simulation were executed over random noise and wavefront distorion. Results of the simulation show that the proposed method is robust against these errors. Experiment was implemented to verify this method.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.9
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• pp.167-173
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• 2004

The heterodyne He-Ne laser interferometer is the most widely used sensing unit to measure the position error. It measures the positioning error from the displacement of a moving reflector in terms of the wave length. But, the wave length is affected by the variation of atmospheric temperature. Temperature variation of 1$^\circ C$ results in the measuring error of 1ppm. In this paper, for measuring more accurately the position error of the ultra precision stage, the refractive index compensation method is introduced. The wave length of the laser interferometer is compensated using the simultaneously measured room temperature variations in the method. In order to investigate the limit of compensation, the stationary test against two fixed reflectors mounted on the zerodur$\circledR$ plate is performed firstly. From the experiment, it is confirmed that the measuring error of the laser interferometer can be improved from 0.34${\mu}m$ to 0.11${\mu}m$ by the application of the method. Secondly, for the verification of the compensating effect, it is applied to estimate the positioning accuracy of an ultra precision aerostatic stage. Two times of the refractive index compensation are performed to acquire the positioning error of the stage from the initially measured data, that is, to the initially measured positioning error and to the measured positioning error profile after the NC compensation. Although the positioning error of an aerostatic stage cannot be clarified perfectly, it is known that by the compensation method, the measuring error by the laser interferometer can be improved to within 0.1${\mu}m$.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.11
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• pp.1646-1655
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• 2004

A description of the basic principles of moire interferometry leads to the design of a eight-mirror four-beam interferometer for obtaining fringe patterns representing contour-maps of in-Plane displacements. The technique is implemented by the optical system using an environmental chamber for submicro-displacement mesurement. In order to estimate the reliability and applicabili쇼 of the system developed, the measurement of coefficient of thermal expansion (CTE) for a aluminium block is performed. Consequently, the system is applied to the measurement of thermal deformation of a WB-PBGA package assembly. Temperature dependent analyses of global and local deformations are presented to study the effect of the mismatch of CTE between materials composed of the package assemblies. Bending displacements of the packages and average strains of solder balls are documented. Thermal induced displacements calculated by FEM agree quantitatively with experimental results.