• Transactions of the Korean Society of Machine Tool Engineers
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• v.13 no.4
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• pp.1-8
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• 2004

Various controllable parameters of an experiment have influence on grinding process. In order to get good products with a high quality, these parameters should be considered whether each parameter has relations to the quality. This paper describes the use of the design of experiments to minimize geometric error in surface grinding. Controllable parameters for the design of experiments were selected as spindle speed, table speed, depth of cut and grain size. From the experimental results, a degree of influence between these parameters and the geometric error was evaluated. An optimal set of grinding conditions was obtained by means of analysis of variance(ANOVA).

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.369-374
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• 2002

This paper presents theoretical analysis of the NRRO(non-repeatable run-out) for a ball bearing with geometric imperfection. The 3DOF dynamic analysis of a ball bearing using the Newton-Raphson method is performed to calculate the displacement of shaft center. Frequency and magnitude characteristics of radial and axial vibrations are investigated. The ball form errors of the ball, the inner race, and the outer race in a HDD spindle ball bearing are precisely measured. NRRO of a ball bearing is analyzed by using the measured waviness data. It is concluded that dominant components of radial vibrations are ${\Large}f_c\;and\;2{\Larg}f_b{\pm}{\Large}f_c$, and dominant component of axial vibrations is $2{\Large}f_b$. These are generated by the size error and the second waviness of the balls.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.3 no.4
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• pp.13-19
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• 2004

This paper deals with the analysis of geometric error and the optimization of process parameters in surface grinding. Taguchi method which is one of the design of experiments has been introduced in achieving the aims. The process parameters were the grain size, the wheel speed, the depth of cut and the table speed. The effect of the process parameters on the geometric error was examined and an optimal set of the parameters was selected to minimize the geometric error within the controllable range of the used grinding machine. The reliability of the results was evaluated by the ANOVA.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.15 no.3
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• pp.32-38
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• 2006

During stereolithography processes, the shape errors such as curl distortion and distortion of side face are generated due to the shrinkage of liquid resins. In this study, the effects of dimension of part and structure of supports on the shape error are examined. Cubic specimens which have different thicknesses are manufactured and their deformations are measured with CMM. Thicker part generates smaller curl distortion of top face and larger of bottom face. Also thicker part generates larger distortion of side face until part thickness increases to about 20mm. Larger stiffness of supports which is obtained by shorter spacing of the supports and line type contact instead of point type contact generates smaller shape error of the part.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.13 no.2
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• pp.9-16
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• 2004

Because a generated heat during grinding operation makes a serious deformation on a ground surface as a convex form, a real depth of cut in deformed zone has larger than an ideal depth of cut. Consequently, the ground surface has a geometric error as a concave form after cooling the workpiece. In this study, the force and the geometric error of surface grinding were examined. From evaluating magnitude and mode of the geometric error according to grinding conditions, an optimal grinding condition was proposed to minimize the geometric error. In addiction the relationship between the geometric error and the grinding force was found out. Due to least square regression it was able to predict the geometric error by using the grinding force.

• Proceedings of the KSME Conference
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• 2001.06b
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• pp.335-340
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• 2001

It is important to model the mechanical structure precisely and reasonably in predicting the dynamic characteristics, controlling the vibration, and designing the structure dynamics. In the finite element modeling, the errors can be contained from the physical parameters, the approximation of the boundary conditions, and the element modeling. From the dynamic test, more precise dynamic characteristics can be obtained. Model updating using parameter modification is appropriate when the design parameter is used to analyze the input parameter like finite element method. Finite element analysis for cantilever and simply supported beams with uniform area and shape change are carried out as model updating examples. Mass and stiffness matrices are updated by comparing test and analytical modal frequencies. The result shows that the updated frequencies become closer to the test frequencies.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.6
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• pp.43-51
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• 2004

A method for form error prediction in side wall machining with a flat end mill is suggested. Form error is predicted directly from the tool deflection without surface generation by cutting edge locus with time simulation. Developed model can predict the surface form error about three hundred times faster than the previous method. Cutting forces and tool deflection are calculated considering tool geometry, tool setting error and machine tool stiffness. The characteristics and the difference of generated surface shape in up milling and down milling are discussed. The usefulness of the presented method is verified from a set of experiments under various cutting conditions generally used in die and mold manufacturing. This study contributes to real time surface shape estimation and cutting process planning for the improvement of form accuracy.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.1
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• pp.82.3-83
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• 2015

비축 반사경의 DTM (Diamond Turning Machine) 가공을 하기 전에는 시간 및 비용의 절감을 위해 CNC(Computerized Numerically Controlled Machine Tools)를 이용하여 비축면의 곡률반경과 가장 유사한 형태의 구면으로 1차 가공 후 3축 이상을 제어할 수 있는 MC (Machining Center)를 이용하여 근사한 비축면을 먼저 가공한다. 이후 DTM으로 광학계에서 요구하는 형상 정밀도 및 표면 조도를 만족하는 비축면을 완성한다. 하지만 비축면을 가공하는 경우, 일반적인 축 대칭 광학계와 달리 가공장비에 장착된 기상계측기를 사용할 수 없기 때문에 외부 장비를 이용하여 반사경 표면을 측정해야한다. 이때 측정과 가공 단계 사이에서 정렬오차가 발생하여 반사경의 형상 정밀도 향상을 위한 보상가공에 어려움이 있다. 본 연구에서는 비축면 반사경의 가공과 측정 과정 사이에 발생하는 정렬오차를 최소화 할 수 있는 DTM 가공용 지그를 설계 및 제작하였다. 또, DTM으로 가공한 반사경의 측정값과 설계값을 비교하여 알루미늄 반사경의 광학 성능을 평가하였다. 이러한 성능 평가 결과는 비축면 반사경의 형상 보상가공을 위한 모델링 방법을 고안하는데에 있어 핵심 자료가 될 것이다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.6
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• pp.1955-1960
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• 2010

A performance of CNC 3-axis pipe profile-cutting machine we developed was evaluated by measuring and verifying a positioning accuracy of its feeding unit and a cutting shape accuracy of pipe workpiece. The positioning accuracy was verified by comparing moving distance actuated by PLC motion controller with actual one measured by a laser interferometer. The cutting shape accuracy was also verified by comparing a cutting shape obtained through scanning and 3D modeling the pipe workpiece with that through CL data.

• The Journal of the Acoustical Society of Korea
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• v.19 no.3
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• pp.72-76
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• 2000

A calibration technique is proposed to improve the performance of 2-D towed array shape estimation using the Kalman filter. In the case of using displacement sensors, 2-D hydrophone positions estimated by the Kalman filter are calculated by assuming that the adjacent hydrophones are horizontally equi-spaced so that maximum distance is equal to the array length. The assumption causes errors in estimating hydrophone positions. The proposed technique using linear model approximation or spline interpolation can reduce the errors by exploiting the fact that the whole length of array is preserved whatever the array shape is. The numerical experiments show that the proposed method is very effective.