• Journal of the Korean Society for Railway
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• v.2 no.2
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• pp.39-45
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• 1999

This paper presents the current-fed inverter of a TGV-K traction system with thyristor switches using phase control and commutation techniques. The current-fed inverters have two modes of operation which consist of forced commutation and natural commutation. In forced commutation mode, at speed of less than 120km/h, commutation is forced by means of the commutation capacitors and the thyristors. Above 120km/h, the thyristors operate in natural commutation mode. according to the voltages between phases of the motors. In this paper. the power conversion theory of the TGV-K traction system and the control principle of the converter and current-fed inverter are discussed.

• Proceedings of the KSR Conference
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• 2004.06a
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• pp.1404-1407
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• 2004

An electric railway system is composed of high-tech subsystems, among which main electric equipments such as transformers, converter and traction motors are critical components determining the performance of rolling stock. We developed a measurement system for on-line test and evaluation of performances of Korean High Speed Train. The measurement system is composed of software part and hardware part. Perfect interface between multi-users is possible. A new method to measure temperature was applied to the measurement system. By using the system, measurement and evaluation for the performance of electric equipments in Korean High Speed Train was conducted during test running.

• Proceedings of the SAREK Conference
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• 2004.11a
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• pp.99-99
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• 2004

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.366-371
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• 2002

Because of the environmental problems, automotive companies are trying to reduce the weight of car body. Therefore, TRIP(TRansformation Induced Plasticity) steels, which have high strength and ductility have been developed. Welding process is a complex process; therefore deciding the optimal welding conditions on the basis of experimental data is an effective method. However, trial-and-error method to decide the optimal conditions requires too many experiments. To overcome these problems, response surface methodology was used. Response surface methodology is a collection of mathematical and statistical techniques that are used in the modeling and analysis of problems in which a response of interest is influenced by several variables and the objective is to optimize this response. This method was applied to the resistance spot welding process of the TRIP steel to optimize the welding parameters.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.606-611
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• 2002

Welding using lasers can be mass-produced in high speed. In the laser welding, performing real-time monitoring system of the welding quality is very important in enhancing the efficiency of welding. In this study, the plasma and molten metal which are generated during laser welding were measured using the UV sensor and IR sensors. The results of laser welding were classified into five categories such as optimal heat input, little low heat input, low heat input, partial joining due to gap mismatch, and nozzle deviation. Also, a system was formulated which uses the measured signals with a fuzzy pattern recognition method which is used to perform real-time evaluation of the welding quality and the defects which can occur in laser welding.

• Proceedings of the KWS Conference
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• 2008.05a
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• pp.8-8
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• 2008

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.05a
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• pp.66-69
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• 2004

A new concept of multi-point dieless elasto-forming method has been developed to make various shape of curved surface without conventional dies. The developed dieless elasto-forming system consists of discrete punches controlled by servo motors and various kinds of elastomers(rubber and foam). To predict optimal position of punch elements, DTF(deformation transfer function) was introduced, and FEM analysis was carried out. The optimal arrangement of elastomer was selected considering characteristics of each elastomer, and a desired concave shape was formed. The experimental results were consistent with the numerical ones.

• ETRI Journal
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• v.34 no.1
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• pp.134-137
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• 2012

Power metal-oxide semiconductor field-effect transistor (MOSFET) devices are widely used in power electronics applications, such as brushless direct current motors and power modules. For a conventional power MOSFET device such as trench double-diffused MOSFET (TDMOS), there is a tradeoff relationship between specific on-state resistance and breakdown voltage. To overcome the tradeoff relationship, a super-junction (SJ) trench MOSFET (TMOSFET) structure is studied and designed in this letter. The processing conditions are proposed, and studies on the unit cell are performed for optimal design. The structure modeling and the characteristic analyses for doping density, potential distribution, electric field, width, and depth of trench in an SJ TMOSFET are performed and simulated by using of the SILVACO TCAD 2D device simulator, Atlas. As a result, the specific on-state resistance of 1.2 $m{\Omega}-cm^2$ at the class of 100 V and 100 A is successfully optimized in the SJ TMOSFET, which has the better performance than TDMOS in design parameters.

• 제어로봇시스템학회:학술대회논문집
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• 1993.10a
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• pp.830-835
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• 1993

The errors in machining process by CNC machining center are due to many elements, such as the delay of the servo drivers, friction and the gain mismatch between x-axis and y-axis motors and so on. We made a counter circuit to measure the output of motor encoders for the motion error analysis of a CNC machining center, and have measured the errors experimentally when the CNC performs a circular interpolation. We have also used an iterative learning method to reduce the radius errors and stick motion errors generated by the CNC machining center performing a circular interpolation. The proposed learning scheme worked well and the circle obtained has smaller error.

• 제어로봇시스템학회:학술대회논문집
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• 1993.10a
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• pp.281-286
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• 1993

In this paper, a parallel link typed wrist is developed for robotic precision assembly. The developed wrist can make the corrective motion required for compensating lateral and tilting errors. The mechanism of this wrist is one example of a motion simulator generating 6 DOF motion in space by 6 actuators connected in paralle. To make the wrist more compact, miniature DC motors containing reduction gears and servo system were used. The parallel link architecture enables a high positioning accuracy and high nominal load capacity. In this study, inverse kinematic problem is solved by using a Denavet-Hartenberg method and a simulational result about workspace of the proposed parallel mechanism is obtained.