• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.2 s.233
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• pp.188-200
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• 2005

Control of a multi-fingered robotic hand is usually based on the theoretical analysis for kinematics and dynamics of fingers and of object. However, the implementation of such analyses to robotic hands is difficult because of errors and uncertainties in the real situations. This article presents the control method for estimating the kinematic constraint of an unknown object by active sensing. The experimental system has a two-fingered robotic hand suspended vertically for manipulation in the vertical plane. The fingers with three degrees-of-freedom are driven by wires directly connected to voice-coil motors without reduction gears. The fingers are equipped with three-axis force sensors and with dynamic tactile sensors that detect slippage between the fingertip surfaces and the object. In order to make an accurate estimation for the kinematic constraint of the unknown object, i.e. the constraint direction and the constraint center, four kinds of the active sensing and feedback control algorithm were developed: two position-based algorithms and two force-based algorithms. Furthermore, the compound and effective algorithm was also developed by combining two algorithms. Force sensors are mainly used to adapt errors and uncertainties encountered during the constraint estimation. Several experimental results involving the motion of lifting a finger off an unknown object are presented.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.820_821
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• 2009

전력기기는 일반적으로 상용주파수인 60 Hz의 교류 전원하에서 운용된다. 따라서 고온초전도체를 전력기기에 응용하는데 있어 교류전류나 교류자장에 의한 교류손실 발생 문제는 전력기기의 경제적 운용과 관련하여 중요하게 부각되어 왔다. 또한 고온초전도체에서 발생하는 교류손실은 에너지의 열적 변환으로 인한 냉동부하 문제와도 관련되어 있기 때문에 전력기기의 안정적인 운용을 위해서도 반드시 연구되어야 할 부분이다. 특히 변압기와 같이 유도형 권선이 필요한 전력기기의 경우에는 무유도 권선 형태가 적용되는 다른 전력기기에 비해 교류 손실의 크기가 매우 크기 때문에 이를 줄이기 위한 방안에 대한 연구가 다각도로 이루어지고 있다. 본 연구에서는 임계전류와 인덕턴스의 크기는 동일하지만 권선 형태를 다르게 할 수 있는 유도형 솔레노이드 코일을 제작하였다. 그리고 제작된 솔레노이드 코일의 병렬연결 구조를 달리하여 각각의 구조에 대한 교류손실의 차이를 측정하고 분석하였다. 그리하여 측정된 결과를 토대로 고온초전도 선재를 이용한 솔레노이드 코일에서 교류손실을 줄이기 위한 구조적 방안을 제시하고자 한다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.3
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• pp.232-239
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• 2008

The position sensors used in a magnetic bearing system are desirable to provide some degree of fault-tolerance as the rotor position is necessary for the feedback control to overcome the open-loop instability. In this paper, we propose an inductive position sensor that can cope with a partial fault in the sensor. The sensor has multiple poles which can be combined to sense the in-plane motion of the rotor. When a high-frequency voltage signal drives each pole of the sensor, the resulting current in the sensor coil contains information regarding the rotor position. The signal processing circuit of the sensor extracts this position information. In this paper, we used the magnetic circuit model of the sensor that shows the analytical relationship between the sensor output and the rotor motion. The multi-polar structure of the sensor makes it possible to introduce redundancy which can be exploited for fault-tolerant operation. The proposed sensor is applied to a magnetically levitated turbo-molecular vacuum pump. Experimental results validate the fault-tolerance algorithm.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.25 no.1
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• pp.93-100
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• 2011

This paper presents a technical study for the first short stroke lightning current generator using a crowbar device. The so-called crowbar-technology is most common to make 10/350[${\mu}s$] impulse currents with high amplitude, and the lightning current generator with crowbar device has an economic advantage than the nominal RLC current generator. But both the operating efficiency and the operating reliability of crowbar spark gap are very important to design the current generator. So, the peaking circuit which consists of small capacitors and a spark gap is applied. And the multi-step coil for controlling the circuit constant at the different test conditions is used. The presented test facility is designed to perform impulse tests with amplitudes up to 50[kA] of 10/350[${\mu}s$].

• Progress in Superconductivity
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• v.5 no.2
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• pp.94-97
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• 2004

Step-edge Josephson junctions (SEJ) have been fabricated on sapphire substrates with in situ deposited films of CeO$_2$ buffer layer and YBa$_2$Cu$_3$O$_{7}$ films on the low angle steps. Direct coupled SQUID magnetometers with the SEJ were formed on 1 cm X 1 cm R-plane sapphire substrates. Typical 5-${\mu}{\textrm}{m}$-wide Josephson junctions have R$_{N}$ of 3 Ω and I$_{c}$ of 50 $mutextrm{A}$ at 77 K. The direct coupled SQUID magnetometers were designed to have pickup coils of 50-${\mu}{\textrm}{m}$-wide 16 parallel loops on the 1 cm X 1 cm substrates with outer dimension of 8.8 mm X 8.8 mm. The SEJ SQUID magnetometers exhibit relatively low 1/f noise even with dc bias control, and could be stably controlled by flux-locked loops in the magnetically disturbed environment. Field noise of the do SQUID was measured to be 200∼300 fT/Hz$^{1}$2/in the white noise region and about 2 pT/Hz$^{1}$2/ at 1 Hz when measured with dc bias method.hod.d.

• Proceedings of the Korean Institute of Intelligent Systems Conference
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• 2008.04a
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• pp.205-208
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• 2008

This paper propose a advanced technique for exciting and receiving the guided torsional wave to detect flaws in pipe systems. There are some difficulties in selecting and exciting of modes by using the nickel strip attached on pipe systems, such as qualification of residual magnetic field and multi-exciting of the unwanted modes etc. In order to there difficulties we propose the new sensor, so called Crossed-coils sensor. We will prove that it is possible to select the modes to be excited and to find a optimal excitation condition for torsional mode by using the proposed sensor.

• Solar Energy
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• v.18 no.3
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• pp.95-105
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• 1998

In this study, basic design data which were required for development of highly efficient ice storage system with low temperature latent heat were experimentally obtained. The ice storage system considered in this study was the one that has been widly used in the developed country and called the ice-on-coil type. Using the system, the ice storage performance for various design parameters which were the flow direction and the inlet temperature of the secondary fluid was tested. In addition, the timewise variation of the interface profiles between the solid and the liquid were visualized, and the heat transfer characteristics of the Phase Change Material(PCM) in the ice storage tank were Investigated. During the freezing processes in the ice storage tank with several vertical tubes, decrease of the heat transfer area and the heat resistance of the ice layer made the increasing rate of ice packing factor(IPF) less. The total freezing energy for the upward flow of the secondary fluid was higher than that for the downward flow. The average ice storage efficiency for the upward flow of the secondary fluid was higher than that for the downward flow.

• Journal of the Society of Naval Architects of Korea
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• v.42 no.3
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• pp.241-248
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• 2005

The induction heating is more efficient for a plate bending because of its easy operation and control of working parameters compared with the heating by torch. In this study, a more efficient method was proposed for the prediction of plate bending. The existing analysis method using the axi-symmetric coil model could not handle the varying temperature during the heating and the forming process for curved plates like a saddle or a concave type curvature. The proposed method using some discrete steps in this study could overcome these difficulties and show more accurate, reasonable results in temperatures and deflections of fiat or curved plates. This method is composed of multi-disciplinary analyses such as an electro-magnetic analysis, a heat transfer analysis and a deformation analysis based on inherent strain approach.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.47 no.8
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• pp.36-46
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• 2010

In multi-GHz RF ICs and high-speed digital interfaces, ESD protection devices introduce considerable parasitic capacitance and resistance to inputs and outputs, thereby degrading the RF performance, such as input/output matching, gain, and noise figure. In this paper, the impact of ESD protection devices on the performance of RF ICs is investigated and design methodologies to minimize this impact are discussed. With RF and ESD test results, the 'RF/ESD co-design' method is discussed and compared to the conventional RF ESD protection method which focuses on minimizing the device size.

• Journal of the Korean Institute of Intelligent Systems
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• v.18 no.6
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• pp.856-862
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• 2008

This paper propose a advanced technique for exciting and receiving the guided torsional wave to detect flaws in pipe systems. There are some difficulties in selecting and exciting of modes by using the nickel strip attached on pipe systems, such as qualification of residual magnetic field and multi-exciting of the unwanted modes etc. In order to there difficulties we propose the new sensor, so called Crossed-coils sensor. We will prove that it is possible to select the modes to be excited and to find a optimal excitation condition for torsional mode by using the proposed sensor.