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이후상,Lee, Hu-Sang 한국과학기술단체총연합회 2000 과학과 기술 Vol.33 No.5
현대의 대표적인 정밀가공기술의 하나는 반도체 가공기술이다. IMB메모리 반도체를 만드는 최소의 선폭은 1985년에는 I마이크로미터(㎛)였으나 현재의 256MB의 메모리 반도체에는 0.2㎛의 미세선폭이 사용되고 있다. 21세기에는 나노테크놀로지 기술이 정밀가공기술의 최선단을 이룰 것으로 예견되고 있는데 현재 국내의 미세가공기술은 메모리 반도체의 제조기술에 관한 한 세계의 선두를 달리고 있으며 0.18마이크론 선폭의 가공기술을 개발하여 1GB의 메모리 반도체 개발에 활용하고 있다.
박천홍,이후상,Park, Cheon-Hong,Lee, Hu-Sang 한국기계연구원 1993 硏究論文集 Vol.23 No.-
The present work deals with the theoretical prediction of static & dynamic characteristic of annular type externally pressurized thrust air bearings with metal-sintered porous media. For the evaluation of surface loading effect by machining, it is assumed that the flow at the porous surface is dominant and which is equivalent to the flow through orifice. Finite different method with over-relaxation method is used to solve the numerical problems. The influences of radius ratio, supply pressure and squeeze number on performances are investigated, as the results. The results of this study can be used to predict the optimal running condition and stable realm of porous bearings.
박천홍,이후상,Park, Cheon-Hong,Lee, Hu-Sang 한국기계연구원 2004 硏究論文集 Vol.34 No.-
In order to analyze the motion errors of the aerostatic stage, it is necessary to consider the influence of the moment variation occurredinside the pads. In this paper, a motion error anaysis method utilizing the transfer functions on the reaction force and moment is proposed, and general characteristics of the transfer functions are discussed. Calculated motion errors by the proposed method show good agreement with the ones calculated by Multi Pad Method, which is considered the entire table as an analysis object. Also, by the introduction of the transfer function of motion errors, which represent the relationship between the spatial frequency components of the rail form error and motion errors, motional characteristics of the porous aerostatic stage can be generalized. In detail, the influence of the spatial frequencies is analyzed quantatively, and the patterns of the insensitive frequencies which almost do not affect the linear motion error or angular motion error according to the rail length ratio and the number of the pad are verified. The relationship between the moment variation occurred inside the pads and the motion errors is also verified together.
공작기계 이송계의 Stick-Slip 특성에 관한 연구
박종권,이후상,Park, Jong-Gwon,Lee, Hu-Sang 한국기계연구원 1988 기계연구원소보 Vol.18 No.-
When low sliding velocities in the boundary lubrication range are operating, irregular movements frequently occur which are a result of the stick-slip phenomenon. Such slide motions are undesirable in precision machine tools, particularly with feed back systems used in numerical and adaptive control machine tools. Accordingly, this paper reports analytical and experimental studies in the stick-slip characteristic of machine tool feeding system. The main conclusions of this study are as follows; The tendency towards stick-slip effects may be reduced by; 1). Reducing the drop in friction coefficient in the Stribeck curve(on the rising part of the friction characteristic at higher sliding speeds, the system is stable all the time) 2). Reducing the transition velocity by the use of a higher viscosity lubricating oil. 3). Increasing the stiffness(Damping)and reducing normal load(Sliding mass) Therefore, the Critical velocity is decided from the above conclusions and in designing of machine tool, feed rates(sliding velocity)must be design the more than critical velocity.
박천홍,김석일,이후상,Park, Cheon-Hong,Kim, Seok-Il,Lee, Hu-Sang 한국기계연구원 1988 기계연구원소보 Vol.18 No.-
In this study, a series of experiments and analyses are performed to estimate the static characteristics of hydrostatic journal bearing such as load capacity, pressure change in each recess, eccentricity of spindle, etc. The experiments are carried out for a multi-recess type journal bearing with capillary restrictor. The Finite Element Method(FEM) is used for the analyses. The predicted load capacity under the condition of stationary or eccentric ratio of bellow 0.2 of the spindle shows excellent agreement with the measured. But, with an increase of the eccentric ratio when the spindle is rotating, the predicted load capacity is largely estimated than the measured. It seems that the difference is mainly caused among others from the fact that the effect of oil-viscosity variation due to the temperature change in the bearing is not introduced into the analyses. The analysis method proposed to estimate the static characteristics of hydrostatic journal bearing is considered to be very reliable since the predicted results are overall in good agreement with the measured.