• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.751-755
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• 2005

We propose a sound source localization method using the Head-Related-Transfer-Function (HRTF) to be implemented in a robot platform. In conventional localization methods, the location of a sound source is estimated from the time delays of wave fronts arriving in each microphone standing in an array formation in free-field. In case of a human head this corresponds to Interaural-Time-Delay (ITD) which is simply the time delay of incoming sound waves between the two ears. Although ITD is an excellent sound cue in stimulating a lateral perception on the horizontal plane, confusion is often raised when tracking the sound location from ITD alone because each sound source and its mirror image about the interaural axis share the same ITD. On the other hand, HRTFs associated with a dummy head microphone system or a robot platform with several microphones contain not only the information regarding proper time delays but also phase and magnitude distortions due to diffraction and scattering by the shading object such as the head and body of the platform. As a result, a set of HRTFs for any given platform provides a substantial amount of information as to the whereabouts of the source once proper analysis can be performed. In this study, we introduce new phase and magnitude criteria to be satisfied by a set of output signals from the microphones in order to find the sound source location in accordance with the HRTF database empirically obtained in an anechoic chamber with the given platform. The suggested method is verified through an experiment in a household environment and compared against the conventional method in performance.

• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.296-301
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• 2005

This paper describes the kinematics, dynamics and control of a 6-DOF shaking table with a bell crank structure, which converts the direction of reciprocating movements. In this shaking table, the bell crank mechanism is used to reduce the amount of space needed to install the shaking table and create horizontal displacement of the platform. In kinematics, joint design is performed using $Gr{\ddot{u}}bler's$ formula. The inverse kinematics of the shaking table is discussed. The derivation of the Jacobian matrix is presented to evaluate singularity conditions. Considering the maximum stroke of the hydraulic actuator, collision between links and singularity, workspace is computed. In dynamics, computations are based on the Newton-Euler formulation. To derive parallel algorithms, each of the contact forces is decomposed into one acting in the direction of the leg and the other acting in the plane orthogonal to the direction of the leg. Applying the Newton-Euler approach, the solution of inverse dynamics is almost completely parallel. Only one of the steps-the application of the Newton-Euler equations to the platform-must be performed on one single processor. Finally, the efficient control scheme is proposed for the tracking control of the motion platform.

• The Journal of the Acoustical Society of Korea
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• v.25 no.3E
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• pp.101-109
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• 2006

Besides dorsal-aspect target strength (TS) of the fish, side-aspect TS information is also acoustically important parameter in fisheries acoustics. In this study, the side-aspect TS of 11 black sea bream (Acanthopagurus schlegeli) were measured using a split beam echosounder of 120, 200, and 420 kHz; total length of the fish ranged from 12.4 to 23.7 cm, and wet weight from 27.5 to 229.8g. For the precise TS measurement with side-aspect angle, we used anesthetized and tethered specimens of known size while being rotated through $360^{\circ}C$ by means of a carousel structure. The side-aspect TS measurements of the fish were conducted by rotating the fish in the horizontal plane at 50 interval. The ping interval was 0.2 second and elapsed time at each angle was 30-60 second. As a result, the measured side-aspect TS data were fitted by sinusoidal function. The relationships between fish length and near full side-aspect TS were as follows: $TS_{120kHz}= 21.46 log (TL)-67.5 (r = 0.70), \;TS_{200 kHz}= 31.03 log (TL)-76.9 (r=0.83),\;TS_{420 kHz}= 30.79 log (TL)-72.2 (r = 0.77)$. For comparison, theoretically estimated side-aspect TS from the Kirchhoff ray mode (KRM) model, which based on swimbladder and body morphology, were compared with the measured TS.

• Journal of IKEEE
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• v.22 no.2
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• pp.432-439
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• 2018

In this paper, an omnidirectional visible light detector was developed by making the detecting surface of a flexible solar cell in a cylindrical form, which has a uniform receiving pattern in the horizontal plane. This solar cell detector receives simultaneously multiple signal lights incident from different directions and provides electrical power to the ASK demodulator in the receiver. In experiments, time division transmission method was used to receive three signal lights incident from different directions to the solar cell detector. Each signal light was ASK modulated using a carrier of 40 kHz, and the synchronizing pulses required for time division transmission were generated by detecting the 120 Hz AC signal included in the indoor illumination lamp with Cds cells. This receiving structure is useful in constructing an $N{\times}1$ optical link in visible light communication.

• Journal of The Korean Astronomical Society
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• v.17 no.2
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• pp.69-103
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• 1984

Five different calibrations of metal abundances of globular clusters are examined and these are compared with metallicity ranking parameters such as $(Sp)_c$, . Q39 and IR-indices. Except for the calibration $[Fe/H]_H$ by the high dispersion echelle analysis. the other calibration scales are correlated with the morphological parameters of red giant branch. In the $[Fe/H]_H$-scale. the clusters later than ${\sim}F8$ have nearly a constant metal abundance. $[Fe/H]_H{\simeq}-1.05$, regradless of morphological characteristics of horizontal branch and red giant branch. By the two fundamental calibration scales of $[Fe/H]_L$ (derived by the low dispersion analysis) and $[Fe/H]_{{\Delta}s}$ (derived by the spectral analysis of RR Lyrae stars). the globular clusters are divided into the halo clusters with [Fe/H]<-1.0 and the disk clusters confined within the galactocentric distance ${\tau}_G=10\;kpc$ and galactic plane distance |z|=3 kpc. In this case the abundance gradient is given by d[Fe/H]/$dr_G{\approx}-0.05\;kpc^{-1}$ and d[Fe/H]/$d|z|{\simeq}-0.08\;kpc^{-1}$ within ${\tau}_G=20\;kpc$ and |z|=10 kpc, respectively. According to these characteristics of the spatial distribution of globular clusters. the chemical evolution of the galactic globular clusters can be accounted for by the two-zone (disk-halo) slow collapse model when the $[Fe/H]_L$-or $[Fe/H]_{{\Delta}s}$-scale is applied. In the case of $[Fe/H]_H$-scale, the one-zone fast collapse model is preferred for the evolution of globular clusters.