• 한국정밀공학회지
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• 제32권5호
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• pp.423-429
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• 2015

Linear motion (LM) ball guides have good accuracy and high efficiency. They are widely applied for precision machinery such as machine tools, semiconductor fabrication machines and robots. However, friction force incurs heat between the balls and grooves. Thermal expansion due to the heat deteriorates stiffness and accuracy of the LM ball guides. For accurate estimation of stiffness and accuracy during the linear motion, friction models of LM ball guides are required. To formulate accurate frictional models of LM ball guides according to load and preload conditions, rolling and viscous frictional analyses have been performed in this paper. Contact loads between balls and grooves are derived from Hertzian contact analysis. Contact angle variation is incorporated for the precision modeling. Viscous friction model is formulated from the shear stress of lubricant and the contact area between balls and grooves. Experiments confirm validity of the developed friction model for various external load and feedrate conditions.

• Structural Engineering and Mechanics
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• 제43권5호
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• pp.679-690
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• 2012

A new concept sea-floating port called mobile harbor has been introduced, in order to resolve the limitation of current above-ground port facilities against the continuous growth of worldwide marine transportation. One of important subjects in the design of a mobile harbor is to secure the dynamic stability against wave-induced excitation, because a relatively large-scale heavy crane system installed at the top of mobile harbor should load/unload containers at sea under the sea state up to level 3. In this context, this paper addresses a two-step sequential analytical-numerical method for analyzing the structural dynamic response of the mobile harbor crane system to the wave-induced rolling excitation. The rigid ship motion of mobile harbor by wave is analytically solved, and the flexible dynamic response of the crane system by the rigid ship motion is analyzed by the finite element method. The hydrodynamic effect between sea water and mobile harbor is reflected by means of the added moment of inertia.

• 한국정밀공학회지
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• 제22권8호
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• pp.57-63
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• 2005

Development of a locomotive mechanism fer the capsule type endoscopes will largely enhance the ability to diagnose disease of digestive organs. In connection with it, most of researches have focused on an installable locomotive mechanism in the capsule. In this paper, it is introduced that the movement of a capsule type endoscope in digestive organ can be manipulated by magnetic force produced outside human body. Since the magnetic force is provided by permanent magnets, no additional power supply to the capsule is required. Using a robotic manipulator for locating the external magnet, the capsule motion control system can cover the whole human digestive organs. This study is particularly concentrated on dither motion effect to improve the mobility of capsule type endoscope. It was experimentally found out that the friction coefficient between the capsule and digestive organ can be remarkably reduced by superposing yawing or rolling dither motion on the translatory motion. In this paper, the experimental results obtained with the direction, amplitude and frequency of sinusoidal dither motion changed is reported.

• 수산해양기술연구
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• 제38권3호
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• pp.226-233
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• 2002

불규칙 해면에 있어서 선미식 트롤선의 추파중의 선체 응답의 특성을 얻기 위하여 3척의 실선운동을 해상에서 계측하고, 이것을 통계적 방법과 이론적인 방법을 이용하여 분석하였으며, 그 결과를 요약하면 다음과 같다. 1. 각 선박의 종동요의 응답의 에너지분포는 추파와 추사파에서 모두 대체로 낮으며, 특히 선박의 크기가 클수록 매우 낮았다 응답스펙트럼의 대역폭은 모두 넓은 편이며, 응답 peak의 주기는 분명하지 않으며, 한 개 이상 나타나는 때도 있다. 2. 각 선박의 횡동요 응답의 에너지 분포는 추파와 추사파에서 모두 크며, 특히 소형선에서는 매우 크다. 응답스펙트럼의 대역폭은 종동요의 응답에 비해 비교적 좁은 편이며, 응답의 peak 주기는 분명하고 한개만 나타난다. 3. 실선실험과 이론계산에 의한 세 선박의 추파와 추사파 중의 종동요와 횡동요응답의 크기와 peak주기는 대체로 양자가 잘 일치하고 있는 것으로 나타나고 있다. 따라서 이론추정치로부터 어선의 응답특성을 평가하는데 큰 문제는 없는 것으로 생각된다. 4. 소형선의 경우 종동요 응답만 고려하면 선미쪽으로 파를 받는 것이 유리하나, 횡동요의 경우에는 오히려 불리하게 되므로 선미쪽으로 파를 받는 경우에는 유의파고와 평균파주기에 따른 자선의 복원성을 고려하는 등 안전에 보다 세심한 주의가 필요하다. 이상과 같이 추파와 추사파 중 선박 크기에 따른 종동요와 횡동요의 응답 특성을 고찰해 보았으나, 이 결과는 제한된 해상의 조건에서 얻어진 것이므로 어선의 일반적인 응답 특성을 도출해내기 위해서는 보다 다양한 해상 조건과 선박을 이용하여 더 많은 연구가 이루어져야 할 것으로 사료된다.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1999년도 제29회 춘계학술대회
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• pp.182-188
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• 1999

A theoretical study of elastohydrodynamic lubrication of elliptical contacts with both rolling and spin has been carried out. A finite difference method and the Newton-Raphson method are applied to solve the problem. The velocity vectors resulting from combined spin and rolling/sliding motion lead to asymmetric pressure distributions and film shapes. Film contours and variations of the minimum and central film thicknesses are compared with various spin-roll ratios. At high spin-roll ratios the minimum film thickness is considerably reduced, whereas the central film thickness decreases less dramatically, The present numerical scheme can be used in the analysis of general elliptical contact problems.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2003년도 ICCAS
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• pp.1994-1999
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• 2003

This paper discusses dynamic characteristics of motion of a pair of multi-degrees of freedom robot fingers executing grasp of a rigid object and controlling its orientation with the aid of rolling contacts. In particular, the discussions are focused on a problem of gain-tuning of sensory feedback signals proposed from the viewpoint of sensorymotor coordination, which consist of a feedforward term, a feedback term for controlling rotational moment of the object, and another term for controlling its rotational angle. It is found through computer simulations of the overall fingersobject dynamics subject to rolling contact constraints that some dynamic characteristics of torque-angular velocity relation may play an important role likely as reported by experimental results in muscle physiology and therefore selection of damping gains in angular velocity feedback depending on the guess of object mass is crucial. Finally, a guidance of gain-tuning in each feedback term is suggested and its validity is discussed by various computer simulations.

• 소음진동
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• 제6권6호
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• pp.819-825
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• 1996

Nonlinear dynamic characteristics of rubbing phenomenon in rotor dynamics are investigated experimentally and numerically. Rubbing phenomenon occurs when rotor contacts with stator during whirling and causes the large amplitude of vibration, high whirl frequencies, and possibly catastrophic failure. Rubbing has various types of forward whirl, backward rolling, backward slipping, and partial rub depending on the system parameters of rotating machinery and running speed. Experiments are performed for forward whirl and backward whirl. And numerical analysis are conducted to explain the changes between backward rolling and backward slipping. Experimental and numerical results show that the types of whirling motion depends on the friction coefficient between rotor and stator and the eccentricity of rotor.

• 정보저장시스템학회논문집
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• 제9권2호
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• pp.36-41
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• 2013

Frictional behavior of a single carbon nanotube(CNT) was investigated using molecular dynamics simulation. A single CNT aligned horizontally on silver or graphene substrate was modeled to evaluate its frictional behavior such as frictional force and rolling/sliding motion with respect to potential parameter and lattice structure of the substrate. As a result, it was found that friction and rolling was affected by adhesion between two surfaces and period of the rolling depended on lattice distance of the substrate.

• 한국기계기술학회지
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• 제13권2호
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• pp.71-78
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• 2011

A kart is a vehicle without the suspension system and the differential gear. The kart frame as an elastic body plays the role of a spring. By the cornering of a kart, rolling, pitching and twisting motions are induced in the kart frame. Also the slip or noncontact of the wheel and a permanent deformation of the kart frame can be induced. In order to examine closely this phenomenon, measurement on height-displacements with various sensors and tracking system and analysis on the kart frame twisting characteristics with the rolling and pitching angle are needed. According to the measurement result, while driving in a curve at high speed the kart frame is quite twisted. Analysis on the measurement results shows that a kart used primarily in high speed requires a frame with low torsional stiffness and a frame material with high tensile strength and large elongation.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집A
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• pp.262-267
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• 2000

This paper describes a weight in motion(WIM) sensor to measure the weight of a vehicle in motion. The main sensing element of the WIM sensor is the PVDF(Polyvinylidene fluoride) film that shows rapid response to an external excitation. Due to the property of rapid response, it is possible to measure the weight of a vehicle in motion with high speed. In the development of the WIM sensor, the dominant target value was the uniformity of the sensor. To increase the uniformity, We employed shrinkable tube made of rubber to enhance the uniformity, and performed the rolling of the brass tube repeatedly. The uniformity of the sensor was examined experimentally. It was comparable to that of a WIM sensor of the MSI which was the benchmark of this development. This paper also describes the mechanical modeling of the sensor and the suitable charge amplifier for the sensor.