• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2004년도 학술대회지
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• pp.66-74
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• 2004

The sliding wear behavior of $ZrO_2-22wt\%MgO\;(MZ)\;and\;ZrO_2-8wt\%Y_2O_3\;(YZ)$ deposited on a casting aluminum alloy with bond layer (NiCrCoAlY) by plasma spray against an SiC ball was investigated under dry test conditions at room temperature. At all load conditions, the wear mechanisms of the MZ and the YZ coatings were almost the same. The wear mechanisms involved the forming of a smooth film by material transferred on the sliding surface and pullout. The wear rate of the MZ coating was less than that of the YZ coating. With an increase normal load the wear rate of the studied coatings increased. The SEM was used to examine the sliding surfaces and elucidate likely wear mechanisms. The EDX analysis of the worn surface indicated that material transfer was occurred from the SiC ball to the disk. It was suggested that the material transfer played an important role in the wear performance.

• 대한수학회지
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• 제32권3호
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• pp.447-459
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• 1995

A fundamental problem is to construct linear systems with given transfer functions. This problem has a well known solution for unitary linear systems whose state spaces and coefficient spaces are Hilbert spaces. The solution is due independently to B. Sz.-Nagy and C. Foias [15] and to L. de Branges and J. Ball and N. Cohen [4]. Such a linear system is essentially uniquely determined by its transfer function. The de Branges-Rovnyak construction makes use of the theory of square summable power series with coefficients in a Hilbert space. The construction also applies when the coefficient space is a Krein space [7].

• 대한기계학회논문집
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• 제14권1호
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• pp.241-250
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• 1990

본 연구에서는 낙구식 점도계를 이용하여 낮은 농도의 용액을 실험할 때 종말 속도측정의 어려움을 해결하기 위하여 레이저와 특수 타이머를 설치하였으며 정확한 특성시간을 결정하기 위하여 실린더 내부의 시험유체를 교란시키지 않고, 떨어뜨린 구 를 회수하는 장치를 제작하였다. 또한 주로 rheogoniometer에 의존하던 영 전단률 점성계수를 측정하기 위하여 속이 빈 알루미늄 구(hollow aluminium ball)의 밀도를 시험 유체와 거의 같은 정도까지 변화시켜가며 종말 속도를 측정하였으며 점탄성 유체 로써 Separan AP-273의 낮은 농도인 300에서 2000wppm까지의 저농도 용액에 대한 특성 시간을 여러모델에 의하여 실험적으로 결정하고 저농도 폴리머 용액에서 퇴화로 인한 점탄성유체의 특성 변화를 분석하였다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1997년도 춘계학술대회 논문집
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• pp.312-317
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• 1997

This paper present an optimum design for the rotor-bearing system of a high-speed (80000RPM) ultra-centrifuge supported by ball bearings with nonlinear stiffness characteristics. To obtain the nonlinear bearing stiffnesses, a ball bearing is modelled in five degrees of freedom and is analyzed quasi-statically. The dynamic behaviors of the nonlinear rotor-bearing system are analyed by using a transfer-matrix method iteratively. For optimum design, minimizing the weight of a rotor is used as a cost function and the Augmented Lagrange Multiplier (ALM) method is employed. The result shows that the rotor-bearing system is optimized to obtain 8% weight reduction.

• 한국HCI학회:학술대회논문집
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• 한국HCI학회 2009년도 학술대회
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• pp.122-128
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• 2009

이 논문에서는 모바일 환경에서 촉각적 사용자 체험 (User Experience)을 향상 시킬 수 있도록 디자인된 새로운 방식의 핸드헬드 볼 기반의 햅틱 인터페이스 "TouchBall" 을 소개하고 그 성능을 평가한다. 작은 모바일 디바이스(모바일 폰, PDA, PMP 등)에 적당하도록 볼 기반의 기계적 메커니즘을 사용하여 작은 회전력으로도 높은 감도의 다양한 촉감을 손에 전달할 수 있도록 구성되어 있다. 제안하는 인터페이스를 적용한 프로토타입 버전을 구현하였고, 정신물리학적 실험을 통해 사람의 감각 인식의 가장 기본적인 척도가 되는 감지 역치를 측정하였다. 그리고 구현 가능한 다양한 촉각 패턴들의 인식강도를 절대적 강도추정 방법으로 측정하여 정확도와 인식강도를 알아보고 그 응용 가능성을 찾아보았다.

• 동력기계공학회지
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• 제17권1호
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• pp.91-96
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• 2013

The present paper focuses on the fabrication of materials with higher thermal conductivity. Nanofluid is a novel transfer prepared by dispersing nanometer-sized solid particles in traditional heat transfer fluid to increase thermal conductivity and heat transfer performance. The purpose of this study is making the nano-size particle. The experiment of MWCNT and $Al_2O_3$ was carried out using a planetary ball mill at several rotation speeds: 200 ~ 400 rpm. The results were examined using scanning electron microscope(SEM). In the case of the MWCNT, it could be more grinding into the small particle in the dry condition and it confirm in the case of the $Al_2O_3$ to be more grinding into the small particle contrary to the MWCNT in the wet condition. In the mixture grinding result of MWCNT and $Al_2O_3$, the dry condition showed the good result in low rotation speed than the wet condition.

• 한국정밀공학회지
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• 제12권8호
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• pp.86-91
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• 1995

Recently, motor integrated spindle is often used in a high speed spindle system of machine tools in order to increase machining speed. The important problem in high speed motor integrated spindle is to reduce thermal effect occured by motor and ball bearings. In this study, the effect of heat transfer from motor is investigated. The experimental equipment is composed with oil-air lubrication method, air cooling system and angular contact ball bearings. The results show that the thermal effect in motor is larger than in ball bearing until DmN 8000,000 with air cooling.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2000년도 춘계학술대회논문집 - 한국공작기계학회
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• pp.635-640
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• 2000

Thermal deformation of machine tools can be evaluated from the analysis of the whole temperature field. However, it is extremely inefficient and impossible to acquire the whole temperature field by measuring temperatures of every point. So, a temperature estimator, which can estimate the whole temperature field from the temperatures of just a few points, is required. In this paper, 1-dimensional heat transfer problem is modeled with modal analysis and state space equations. and then state observer is designed to estimate the intensity of heat source and the whole temperature field in real-time. The reliability of this estimator is verified by making a comparison between solutions by the proposed method and the exact solutions of examples. The proposed method is applied to the estimation of temperature distribution in a ball screw system.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1997년도 추계학술대회논문집
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• pp.168-171
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• 1997

With the development of computers, CAD(Computer-Aided-Design)/CAM (Computer-Aided-Manufacturing) has been increasingly applied to manufacturing processes to increase productivity, and recently studies of expert systems, a field of Al(Artificial Intelligence), are being carried out to assist process designs. In this study, an expert system for the process design of ball stud was developed. The adequacy of the developed system was examined through comparisons with actual blueprints and verification by experts. The designed process data was saved in dxf file format for transfer to AutoCAD, from which prototype process blueprints were obtained.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 1997년도 춘계학술대회논문집; 경주코오롱호텔; 22-23 May 1997
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• pp.160-166
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• 1997

The spindle motor in a computer hard disk drive can be modeled as a rotor-bearing system supported by the base plate. Ball bearing is the crucial element to determine the stiffness of the spindle motor, and its design parameters and operating conditions determine the dynamic characteristics of the spindle motor. In the analysis of a rotor-bearing system with a short shaft like a spindle motor, the stiffness of the base plate as well as ball bearings must be considered accurately to analyze the dynamic charateristics of a spindle motor. In this paper, the lateral and the axial vibration of the spindle motor were analyzed by the transfer matrix method for the dual-shaft rotor-bearing model and by d.o.f lumped parameter model, respectively. The simulation results had good agreements with the experimental modal testing. The dynamic characteristics were fully investigated for the change of the major design parameters of the spindle motor, i.e. the preload of ball bearings and the rotational speed.