• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.04a
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• pp.466-471
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• 1996

This work is concerned with the development of digital contouring controller formulti-axial servosystems. Digital optimal contouring controller is proposed to coordinate each of the controllers of multiple feed drives and specifically improve the controuring performance. The optimal control formulation includes the contour error explicity in the performance index to be minimized. The contouring control is exercised for straight line and circular contours. Substantial improvement in contouring perfomance is obtained for a range of contouring conditions. Both steady state and transient error measures have been considered. The simulation study presented has estiblished the potential of the proposed controller to improve contourning perfomance.

• 한국신재생에너지학회:학술대회논문집
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• 2005.06a
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• pp.701-704
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• 2005

Aquifer Thermal Energy Storage (ATES) can be a cost-effective and renewable geothermal energy source, depending on site-specific and thermohydraulic conditions. To design an effective ATES system having influenced by groundwater movement, understanding of thermo hydraulic processes is necessary. The heat transfer phenomena for an aquifer heat storage are simulated using FEFLOW with the scenario of heat pump operation with pumping and waste water reinjection in a two layered confined aquifer model. Temperature distribution of the aquifer model is generated, and hydraulic heads and temperature variations are monitored at the both wells during 365 days. The average groundwater velocities are determined with two hydraulic gradient sets according to boundary conditions, and the effect of groundwater flow are shown at the generated thermal distributions of three different depth slices. The generated temperature contour lines at the hydraulic gradient of 0.00 1 are shaped circular, and the center is moved less than 5m to the groundwater flow direction in 365 days simulation period. However at the hydraulic gradient of 0.01, the contour center of the temperature are moved to the end of boundary at each slice and the largest movement is at bottom slice. By the analysis of thermal interference data between two wells the efficiency of the heat pump system model is validated, and the variation of heads is monitored at injection, pumping and no operation mode.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.20 no.5
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• pp.589-597
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• 2011

In this paper, optimal tuning of a cross-coupled controller linked with the feedforward controller and the disturbance observer is studied to improve contouring and tracking accuracy as well as robustness against disturbance. Previously developed integrated design and optimal tuning methods are applied for developing the robust tuning method. Strict mathematical modeling of the multivariable system is formulated as a state-space equation. Identification processes of the servomechanism are conducted for mechanical servo models. An optimal tuning problem to minimize both the contour error and settling time is formulated as a nonlinear constrained optimization problem including the relevant controller parameters of the servo control system. Constraints such as relative stability, robust stability and overshoot, etc. are considered for the optimization. To verify the effectiveness of the proposed optimal tuning procedure, linear and circular motion experiments are performed on the xy-table. Experimental results confirm the control performance and robustness despite the variation of parameters of the mechanical subsystems.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.8
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• pp.1685-1691
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• 2004

The objective of this study is aimed at reducing the contour error of AC Servo derives by improving the interpolation error of each axis through variable structure control system. The errors in machining process by AC Servo motor 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. Sliding mode control system is applied to a AC servo drive as a numerical example in this paper. The experiment results which are compared with those of typical PI scheme show the validity of improvement in circular interpolation error of the system.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.05a
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• pp.31-34
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• 2004

A new extrusion process of the circular section product with helical fins could be developed by using rotating extrusion dies. The twisting of extruded product is caused by the twisted conical die surface connecting the die entrance section and the die exit section linearly. But, until now, because the process has used fixed extrusion dies, it needs high pressure in order to twist billet and form fin shape on the surface of billet. So, during extruding billet, in order not to twist billet, the extrusion dies is needed to rotate itself instead of twisting billet. And in order to rotate dies, the shape of inside contour of extrusion dies must have conical type with twisted Inclined die surface connecting the die entrance section and the die exit section linearly. The results of experiments show that, in spite of using twisted extrusion dies, twisting of the billet should not happen because of rotating dies in the opposite direction of twisting direction of billet during extruding billet, and, from the results, it shows that it can decrease the power of extrusion pressure and could prevent crack of teeth for fin forming.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.3
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• pp.357-366
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• 2003

An experimental study is performed to investigate characteristics of near of wakes of circular cylinders with serrated fins using a hot-wire anemometer for various freestream velocities. The main focus of this paper is to investigate a reason why a vortex formation length is increased suddenly. Velocity of the fluid which flow through fins decreases as fin's height and freestream velocity increases and fin pitch decreases, and a thickness of boundary layer increases. The finned tube has a lower velocity gradient when the higher boundary layer grows. This velocity gradient on finned tube makes a weak shear force in the wake and moves to downstream in a state of lower momentum transfer between the freestream and the wake. The phenomenon makes a vortex formation length increased suddenly. The fluctuations of the velocity distributions on the finned tube and (equation omitted) = 1.0 contour line in the vortex formation region decreases when the fin height increases and the pitch decreases.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.10
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• pp.1420-1426
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• 2003

The stability of turbulent nonpremixed interacting flames is investigated in terms of nozzle configuration shapes and kind of fuels. Four nozzle arrangements - cross 5, matrix 8, matrix 9 and circle 8 nozzles - are used in the experiment. There are many parameters affecting flame stability in multi-nozzle flames such as nozzle separation distance, fuel flowrates and nozzle configuration etc. Key factors to enhance blowout limit are the nozzle configuration and the existence of center nozzle. Even nozzle exit velocity equal 204 m/s, flame is not extinguished when there is not a center nozzle and s/d=15.3∼27.6 in matrix-8 and circular-8 configurations. At these conditions, recirculation of burnt gas is related with stability augmentation. Fuel mole fraction measurements using laser induced fluorescence reveal lifted flame base is not located at the stoichiometric contour.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.10a
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• pp.1033-1038
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• 1995

NC 공작기계의 contour 운동 오차를 측정하기 위하여 사용되는 Ball-Bar에 의한 원호 보간 시험 데이터를 이용하여 NC controller의 성능을 평가 할 수 있는 S/W에 의한 방법을 제시한다. 본 논문에서 지금까지는 분석이 어려웠던 Masrer-Slave Changeover의 분석을 가능하게 하였으며, Ball-Bar로 부터 얻어지는 데이터를 Weighted Residual Method에 의한 종합적인 분석을 하였으며, 오차 원인별 비교를 위해 Eztra Sum of Squares Method를 도입하였다. 본 연구의 실제 적용을 위한 측정 및 분석 S/W를 개발하였으며, 결과적으로 NC controller의 성능평가에 유용함을 알 수 있었다. 무부하 조건에서의 Ball-Bar에 의한 분석 데이터와의 비교를 위하여 원형 시편을 가공하고, 진원도 측정 및 분석을 통하여 유사한 오차 pattern을 가짐을 알 수 있었다.

• 제어로봇시스템학회:학술대회논문집
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• 1996.10b
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• pp.656-659
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• 1996

An universal NURBS interpolation for an open architectured CNC controller is proposed in order to unify internal data structure and algorithm of different interpolations such as linear, circular and spline, and to intelligently interface CAD database of the various workpiece contour. Furthermore, NURBS interpolation may result in better surface roughness and high speed machining due to the continuous generation of cutter movement. The mathematical manipulation of NURBS is presented and the practical implementation on the CNC controller of a lathe is discussed for real machining. The comparison between a computer design and workpieces machined on a lathe shows the feasibility of the NURBS interpolation format as an universal interpolation scheme.

• Journal of the Korean Society for Precision Engineering
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• v.7 no.1
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• pp.63-73
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• 1990

Low cost automatic welding machine is developed for the purpose of welding process automation of automobile parts with two dimensional welding joints. Developed gantry type machine is equipped with X, Y and roll axis stepping motors, and dirive units units are designed by two phase on drive scheme using shift registers. Control system is constructed by single board microcomputer of Z80A CPU, and also it is equipped with parallel input output ports and counter-timer chips. Linear and circular interpolation of welding head movement is accomplished by employing software digital differential analyzers. It has been shown that contour error of develped system is withi ${\pm}1.0mm$, meaning that the machine is suitable for CO2 arc welding process of automoble parts and is expected it's application to industry.