• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.869-872
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• 2001

A new in-pipe locomotive mechanism is developed using piezoelectric bimorphs. Two bimorphs are linked serially and produce an ellipsoidal motion at the end of bimorph. The device moves by the friction force between the rubber attached at the bimorph end and the inner surface of the pipe. The developed mechanism is very simple and need relatively small power compared to a conventional multi-layer piezoelectric motor.

• 한국지구물리탐사학회:학술대회논문집
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• 2005.05a
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• pp.233-236
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• 2005

Polarization filtering based on the multicomponent complex trace analysis method is performed to reject Rayleigh waves and to enhance S waves. To test the polarization filter, synthetic seismic data were constructed for a simple two-layer model based on the finite difference method. Rayleigh waves with elliptic motion are eliminated effectively and P and S waves with linear motions are well separated each other.

• Journal of the Korean Geophysical Society
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• v.8 no.1
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• pp.35-38
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• 2005

Polarization filtering based on the multicomponent complex trace analysis method is performed to reject Rayleigh waves and to enhance S waves. To test the polarization filter, synthetic seismic data were constructed for a simple two-layer model based on the finite difference method. Rayleigh waves with elliptic motion are eliminated effectively and P and S waves with linear motions are well separated each other.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.12 s.177
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• pp.198-204
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• 2005

For precise micro V-grooving, ultrasonic elliptical vibration cutting (UEVC) is proposed using two parallel piezoelectric actuators, which are energized by sinusoidal voltages with a phase difference of 90 degrees. Experimental setup is composed of stacked PZT actuators, a single crystal diamond cutting tool, and a precision motorized xyz stage. It is found that the chip formed in the process of UEVC is discontinuous because of the periodic contacts and non-contacts occurring between the tool and workpiece. It is experimentally observed that the cutting force in the process of UEVC significantly reduces compared to the ordinary non-vibration cutting. In addition, the creation of burr during UEVC is significantly suppressed, which is attributable to the decrease in the specific cutting energy.

• Bulletin of the Korean Space Science Society
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• 2010.04a
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• pp.28.1-28.1
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• 2010

이 연구에서는 기존 선형 상대운동방정식에 차등중력, 주위성의 이심율, J2 섭동 등의 비선형항을 추가하여 보다 정확한 상대운동방정식을 만든 후 섭동이론을 적용하여 위성편대 연료최적화 재배치 문제에 대한 근사 해석해를 구하고자 한다. 먼저, 비선형 섭동항을 테일러 급수를 이용하여 2차항까지 전개한 후, 이를 기존 선형상대운동방정식에 추가하여 새로운 비선형 상대운동방정식을 만든다. 이 때 사용된 선형상대운동방정식은 힐스 방정식으로 주위성의 궤도가 일반적인 타원이고 위성 간 상대거리가 충분히 가깝다고 가정한다. 최적화 조건으로부터 상태벡터와 라그랑지 곱수로 이루어진 연립 미분방정식이 만들어 지는데, 이 식은 힐스 방정식에 기인한 선형부분과 2차 비선형항에 기인한 섭동부분으로 나뉜다. 이 때, 이 연립미분방정식의 해는 선형부분의 해와 섭동으로 인한 변화량의 합으로 근사할 수 있으며 그 변화량은 섭동이론을 적용하여 얻을 수 있다. 이와 같이 얻어진 해는 여러 섭동의 비선형항을 2차까지 포함한 상대운동방정식을 사용했기 때문에, 기존 선형상대운동방정식을 사용하여 구한 최적해 보다 더 정확한 결과를 얻을 것이라 예상한다.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.3
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• pp.11-17
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• 1998

The mecanum wheel was originaly developed in sweden to realize the omni-directional motion of the cart. The circumference of each wheel is lined with rollers set at 45 degrees relative to the main wheel. This paper proves that the roller of the mecanum wheel shapes the ellipsoid, derives the kinematic relationships between the parameters of the wheel and rollers, and proposes the procedure to determine the parameters of the wheel. The result was implemented into the computer program for the design of the mecanum wheel.

• Journal of the Korean Geophysical Society
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• v.3 no.1
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• pp.37-48
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• 2000

In order to investigate in-line ground motions caused by earthquakes, we examine the multicomponent complex trace analysis method (MCTAM) for the synthetic data and apply it to real earthquake data. An experimental result for synthetic data gives correct information on the arrival times, duration of individual phases, and approaching angles for body waves. Rayleigh waves are also easily identified with the MCTAM. A deep earthquake with magnitude of 7.3 was chosen to test various polarization attributes of ground motions. For P waves, instantaneous phase difference between the vertical and the in-line horizontal components ${\phi}(t)$, instantaneous reciprocal ellipticity ${\rho}(t)$, and approaching angle ${\tau}(t)$ are computed to be ${\pm}180^{\circ},\;0{\sim}0.25,\;and\;-30^{\circ}{\sim}-45^{\circ}$, respectively. For S waves, ${\phi}(t)$ tends to vary while ${\rho}(t)$ have values of $0{\sim}0.3\;and\;{\tau}(t)$ remains near vertical, respectively. A relatively low frequency signal registered just prior to the S wave event is interpreted as a P-wave phase based on its polarization characteristics. Velocities of P and S waves are computed to be 8.633 km/s and 4.762 km/s, and their raypath parameters 0.074 s/km and 0.197 s/km. Dynamic Poisson's ratio is obtained as 0.281 from the velocities of P and S waves.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2007.06a
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• pp.147-148
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• 2007

• The Journal of Korean Academy of Sensory Integration
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• v.19 no.2
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• pp.36-45
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• 2021

Purpose : This study aims to identify changes in the visuomotor coordination and fine motor coordination functions caused by the use of a task-oriented intervention in a child with developmental delay. Methods : The participant, who was a 6-year-old girl, was not diagnosed but showed a developmental delay in overall function. The study period was February 5, 2021, to June 4, 2021, and a single-subject A-B study design was used. The baseline (A) was initially evaluated in the first three sessions to identify the child's functions. In the intervention period, 12 session (B), task-oriented intervention was applied; the child engaged in many of the activities in kindergarten, such as painting, writing, making, and cutting with scissors. Visuomotor coordination and fine motor coordination were equally measured during the baseline and intervention periods. Visuomotor coordination was measured via drawing of an oval according to the Korean Developmental Test of Visual Perception 3 (K-DTVP-3), and fine motor coordination was assessed using the finger-nose touching item of the Clinical Observation of Motor and Postural Skills (COMPS). Results : The mean of the baseline of the K-DTVP-3 oval drawing was 23, and the mean of the intervention period was 39.66. The mean of the baseline of the COMPS finger-nose touching was 0, and the mean of the intervention period was 5.08. Conclusion : Task-oriented intervention seems to have a positive effect on the visuomotor coordination and fine motor coordination abilities of children with developmental delay.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.2
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• pp.137-143
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• 2011

The pitch motion of a gravity-gradient satellite can be chaotic, depending on the ratio of mass moments of inertia and the eccentricity of the satellite orbit. For a precise prediction of motion, chaotic pitch motion has to be changed to non-chaotic motion. Feedback control can be used to obtain nonchaotic pitch motion. For chaos control and stabilization of the pitch motion of a gravity-gradient satellite, a feedback control system is designed, based on the linear nonautonomous system obtained by linearizing the nonlinear pitch motion. The control law obtained has two parameters and is applied to chaotic nonlinear pitch motion. The nonlinear control system satisfies the proposed control objectives in the range of the nonchaotic parameter space.