• Journal of the Korean Society for Precision Engineering
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• v.22 no.9 s.174
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• pp.115-122
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• 2005

Errors resulting from magnification variations of a optical system are largely generated in three-dimensional shape measurements based on depth-from-focus. In the case of measuring the surface morphology of tiny objects based on DFF, images are acquired with a very small interval so that magnification changes can be minimized. However, the magnification variations are actually existed in the acquired images and so focus measures are wrongly or ambiguously extracted. In this paper, a methodology with linear magnification calibrations, based on DFF, is proposed to make more accurate measurement in surface morphology with high depth discontinuity, compared with previous ones. Several experiments show that the proposed method outperforms existing ones without magnification calibrations.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.3 s.96
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• pp.198-207
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• 1999

This paper presents an accurate algorithm for geometric calibration of X-ray imaging system. Calibration is a very important process for improving an imaging system performance. There has been a lot of previous works using linear camera modeling technique, where lens distortion is neglected and/or center of distortion is assumed to be known. Geometrical distortion of image intensifier, however, is very large and its center of distortion should be calculated. This paper presents a new calibration method to estimate the intensifier position and orientation, scale factor, distortion coefficient, magnification factor, and center of distortion using the least square method. We investigate the properties of the algorithm by computer simulation. Simulation results show that the parameters can be estimated accurately using the proposed algorithm.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.13 no.1
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• pp.16-22
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• 2014

Resonance refers to the magnification of a structural response which occurs when a linear lightly damped system is driven with a sinusoidal input at its natural frequency. An exploratory vibration test (a natural frequency measurement test) is very important for the vibration testing of machine parts, as the value measured in an actual laboratory affects test results. For this reason, it is necessary to estimate the measurement uncertainty to verify the reliability of this type of test. In this study, measurement uncertainty is estimated based on three uncertainty factors. The uncertain factors are the measured points in the machine parts, the resolution of the vibration equipment, and uncertainty of the calibration certificate.

• Journal of the Korean Society for Precision Engineering
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• v.26 no.8
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• pp.72-78
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• 2009

We developed a line standards measurement system using an optical microscope and measured two kinds of line standards. It consists of three main parts: an optical microscope module including a CCD camera, a stage system with a linear encoder, and a measurement program for a microscopic image processing. The magnification of microscope part was calibrated using one-dimensional gratings and the angular motion of stage was measured to estimate the Abbe error. The threshold level in line width measurement was determined by comparing with certified values of a line width reference specimen, and its validity was proved through the measurement of another line width specimen. The expanded uncertainty (k=2) was about 100 nm in the measurements of $1{\mu}m{\sim}10{\mu}m$ line width. In the comparison results of line spacing measurement, two kinds of values were coincide within the expanded uncertainty, which were obtained by the one-dimensional measuring machine in KRISS and the line standards measurement system. The expanded uncertainty (k=2) in the line spacing measurement was estimated as $\sqrt{(0.098{\mu}m)^2+(1.8{\times}10^{-4}{\times}L)^2}$. Therefore, it will be applied effectively to the calibration of line standards, such as line width and line spacing, with the expanded uncertainty of several hundreds nanometer.