• Journal of the Korean Society for Precision Engineering
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• v.19 no.5
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• pp.118-125
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• 2002

The previous kinematic analysis of wheeled mobile robots(WMRs) is performed in an ad-hoc manner, while those of the robot manipulators are done in a consistent way using the coordinate system assignment and the homogeneous transformation matrix. This paper shows why the method for the robot manipulators cannot be used directly to the WMRs and proposes the method for the WMRs, which contains modeling the wheel with the Sheth-Uicker notation and the homogeneous transformation. The proposed method enable us to model the velocity kinematics of the WMRs in a consistent way. As an implementation of the proposed method, the Jacobian matrices were obtained for conventional steered wheel and non-steered wheel respectively and the forward and inverse velocity kinematic solutions were calculated fur a tricycle typed WMR. We hope that our proposed method comes to hold an equivalent roles for WMRs, as that of the manipulators does for the robot manipulators.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.10a
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• pp.1017-1021
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• 1995

Geometric and thermal errors are responsible for major components of the errors of a computer numerically controlled turning center. The planar error of a CNC turning center are comprised of 11 geometric and thermal error components. The error synthesis model is formulated by homogeneous coordinate transformation method and expresses the effect of such error components on the planar error of a CNC turning center. In this paper, the sensitivity analysis of the model on the noises through sensing and the change of temperature is addressed. The sensitivity analysis show that the error systhesis model is robust on the noses and z planar error is much affected by the change of temperatures.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.11
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• pp.67-75
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• 1998

Geometric and thermal errors are key contributors to the errors of a computer numerically controlled turning center. A planar error synthesis model is obtained by synthesizing 11 geometric and thermal error components of a turning center with homogeneous coordinate transformation method. This paper shows the sensitivity analysis on the temperature change, the confidence evaluation on the uncertainty Of measurement systems, and the error contribution analysis from the planar error synthesis model. Planar error in the z direction was very sensitive to the temperature change. and planar errors in the x and z directions were not affected by the uncertainty of measurement systems. The error contribution analysis ,which is applicable to designing a new turning center, was helpful to find the large error components which affect planar errors of the turning center.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.658-663
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• 2003

A process of 3-D stereo particle image velocimetry(PIV)was developed for the measurement of an illuminated sliced section field of 3-D complex flows. The present method includes modeling of camera by a calibrator based on the homogeneous coordinate system, transformation of the oblique-angled image to the right-angled image, identification of 2-D velocity vectors by 2-D cross-correlation equation, stereo matching of 2-D velocity vectors of two cameras, accurate calculation of 3-D velocity vectors by homogeneous coordinate system, removal of error vectors by a statistical method followed by a continuity equation criteria, and finally 3-D display as the post processing. An experimental system was also used for the application of the proposed method. Two high speed digital CCD cameras and an Argon-Ion Laser for the illumination were adopted to clarify the time-dependent characteristics of the leading edge extension(LEX) in a highly swept shape applied to a delta wing found in modern air-fighters.

• Smart Structures and Systems
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• v.31 no.4
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• pp.409-419
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• 2023

Structural integrity can be accessed from dynamic deformations of structures. Moreover, dynamic deformations can be acquired from non-contact sensors such as video cameras. Kanade-Lucas-Tomasi (KLT) algorithm is one of the commonly used methods for motion tracking. However, averaging throughout the extracted features would induce bias in the measurement. In addition, pixel-wise measurements can be converted to physical units through camera intrinsic. Still, the depth information is unreachable without prior knowledge of the space information. The assigned homogeneous coordinates would then mismatch manually selected feature points, resulting in measurement errors during coordinate transformation. In this study, a two-stage optimization method for video-based measurements is proposed. The manually selected feature points are first optimized by minimizing the errors compared with the homogeneous coordinate. Then, the optimized points are utilized for the KLT algorithm to extract displacements through inverse projection. Two additional criteria are employed to eliminate outliers from KLT, resulting in more reliable displacement responses. The second-stage optimization subsequently fine-tunes the geometry of the selected coordinates. The optimization process also considers the number of interpolation points at different depths of an image to reduce the effect of out-of-plane motions. As a result, the proposed method is numerically investigated by using a truss bridge as a physics-based graphic model (PBGM) to extract high-accuracy displacements from recorded videos under various capturing angles and structural conditions.

• Atmosphere
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• v.26 no.3
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• pp.473-482
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• 2016

An accurate determination of turbulent fluxes over an urban area is a challenging task due to its morphological diversity and associated flow complexity. In this study, an eddy covariance (EC) method is applied over a highly heterogeneous urban area in a small city (Gongju), South Korea to investigate the quantitative influence of 'coordinate tilt' in determining the turbulent fluxes of sensible heat, latent heat, momentum, and carbon dioxide mass. Two widely-used coordinate transform methods are adopted and applied to eight directional sections centered on the site to analyze a 1-year period EC measurement obtained from the urban site: double rotation (DR) and planar fit (PF) transform. The results show that mean streamline planes determined by the PF method are distinguished from the sections, representing morphological heterogeneity of the site. The sectional pitch angles determined by the DR method also compare well with those in the PF method. Both the PF and DR methods show large variabilities in the determined streamline planes at each directional section, implying that flow patterns may form in a complicate way due to the surface heterogeneity. Resulting relative differences of the turbulent fluxes, defined by $(F_{DR}-F_{PF})/F_{DR}$, are found on average +13% in sensible heat flux, +21% in latent heat flux, +37% in momentum flux, and +26% in carbon dioxide mass flux, which are larger values than those reported previously for fairly homogeneous natural sites. The fractional differences depend significantly on wind direction, showing larger differences in northerly winds at the measurement site. It is also found that the relative fractional differences are negatively correlated with the mean wind speed at both stable/unstable atmospheric conditions. These results imply that EC turbulent fluxes determined over heterogeneous urban areas should be carefully interpreted with considering the uncertainty due to 'coordinate tilt' effect in their applications.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.389-390
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• 2006

The cycloidal reducer is one of the velocity controlling equipments in machinery. It has advantages of the higher reduction ratio, the higher accuracy, the easier adjustment of the transmission ratio and the smaller workspace than any other kinds of the reducers. This paper proposes a simple and exact approach for the lobe profile design of the two teeth difference cycloidal plate gear, which is different from the standard cycloidal reducer, by means of the principle of the instant velocity center in the general contact mechanism and the homogeneous coordinate transformation.