• Transactions of the Korean Society of Mechanical Engineers
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• v.3 no.1
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• pp.35-41
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• 1979

In order to improve the load capacity of externally pressurized air-lubeicatedjournal bearings, a new type(doubly-stepped type) bearing was revised and experimented. Through the results of experiment, the load capacity of doubly-stepped bearings was discussed and compared with equivalent conventional circular journal bearings. Results were obtained for speed up to 18000rpm and for supply pressure ratio(Ps/Pa) 4.8,6,7. Compared with equivalent conventional bearings, doubly-stepped bearings resultd a high gain in load capacity. It is also shown that the increasing rate of load capacith increases with decreasing the eccentricity ratio. Furthermore, the increasing rate is higher in the case of great clearanceratio than small dleatance ratio of doubly-stepped bearings. Such an increase in load capacity is confirmed by pressure distributions in the bearings.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2000.10a
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• pp.466-470
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• 2000

Externally pressurized air journal bearing has been widely used in high-speed spindle system and precision machinery because of its characteristics such as substantially low frictional loss, low heat generation and averaging effect leading better running accuracy. But air journal bearing have a disadvantage of the low load capacity due to the low viscosity. In this paper, The air journal bearing design to overcome the defects of air bearing such as low stiffness and dimping coefficients was investigated theoretically.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2000.11a
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• pp.353-362
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• 2000

Herringbone groove journal bearing (HGJB) is developed to improve the static and dynamic performances of hydrodynamic journal bearing. In this study, static and dynamic compressible isothermal lubrication problems are analyzed by the finite element method together with the Newton-Raphson iterative procedure. This analysis is introduced for prediction of the static and dynamic characteristics of air lubricated HGJB for various bearing configurations. The bearing load characteristics and dynamic characteristics are dependent on geometric parameters such as asymmetric ratio, groove depth ratio, groove width ratio and groove angle.

• Proceedings of the KIPE Conference
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• 2010.11a
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• pp.218-219
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• 2010

유도 전동기의 편심 고장은 베어링 손상 등으로 발생되며, 심해질 경우 고정자와 회전자간의 접촉으로 전동기 파괴를 일으킨다. 이를 진단하는 대표적인 방법으로 온라인 전류 스펙트럼 분석법(Motor Current Signature Analysis, MCSA)이 있으나 전동기 정보의 필요, 부하에 영향을 받는 등의 문제점이 있다. 본 논문에서는 유도 전동기의 편심을 오프라인으로 진단하는 새로운 방법을 제안한다. 유도 전동기의 회전자의 위치를 변경하며 고정자 권선으로부터 관측된 임피던스 값으로 편심을 진단한다. 제안된 방법은 온라인 진단 후 정확한 편심 고장 여부를 확인하는데 사용될 수 있으며, 7.5마력 유도전동기의 정적, 동적, 복합 편심에 대한 실험을 통해 증명되었다.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.2 s.95
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• pp.23-30
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• 1999

This paper investigates the radial performance of self-acting spiral-grooved air bearing, used to support small high-speed rotating bodies. Repeatable runout, nonrepeatable runout, stiffness and supporting load are selected as the performance. The clearance between rotor and stator, the stator groove depth, and the rotating speed are chosen as three main parameters affecting the performances. Force application and displacement measurement are done in a noncontact manner, in order not to disturb operation: electromagnetic force is applied to the rotor and gap sensors are used to measure the displacement of the rotor. Experimental results show that repeatable runout decreases as speed, groove depth and clearance decrease. Nonrepeatable runout decreases as clearance decreases, and it has a minimum value at $5.5{\mu}m$ of grove depth and a maximum value at speed of 18.000rpm. Stiffness increases as speed increases and clearance decreases, and has a maximum value around $5.5{\mu}m$ of groove depth. The relationship between force and displacement is linear for small displacement, but becomes nonlinear for large displacement. Supporting load is linearly proportional to the stiffness, and it is a maximum value around $4.75{\mu}m$ of clearance.

• Tribology and Lubricants
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• v.25 no.2
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• pp.108-113
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• 2009

This paper presents a experimental results for the performance evaluation of a double-bumped air foil bearing. The test results of a double-bumped AFB is compared with a single-bumped AFB at a heavily-loaded condition. The diameter of the test bearing is 50 mm, and the axial length is 50 mm. Nominal clearance of the single-bumped AFB is evaluated as $105{\mu}m$, and that of the double-bumped AFB is as $95{\mu}m$. The test of the AFBs are demonstrated at 3 test mode; the load variation mode, the speed variation mode, and start-stop mode. The single-bumped AFB demonstrated a upward load-carrying capacity of 95 N and a downward load-carrying capacity of 130 N at 20,000 rpm. The double-bumped AFB demonstrated a upward load-carrying capacity of 170 N and a downward load-carrying capacity of 170 N at 20,000 rpm. The single-bumped AFB demonstrated a downward lift-off speed of 16,300 rpm at 105 N. The double-bumped AFB demonstrated a downward lift-off speed of 15,400 rpm at 105 N. The start-stop test of the AFBs assure 5,000 cycle endurance life. The test results are compared with the theoretical calculation results. The test and theorectical results show thata double-bump air foil bearing provides a higher load-carrying capacity, stiffness and damping than a single-bump air foil bearing in a heavily-loaded condition.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.4
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• pp.255-262
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• 2016

There has been intense research on self-diagnosis systems in railway applications, since stability and reliability have become more and more significant issues. Wired sensors have been widely used in the railway vehicles, but because of the difficulty in their maintenance and accessibility, they ar not considered for self-diagnosis systems. To have a self-monitoring system, wireless data transmission and self-powered sensors are required. For this purpose, a thermoelectric energy harvesting module that can generate electricity from temperature gradient between the bogie axle box and ambient environment was introduced in this work. The temperature gradient was measured under actual operation conditions, and the behavior of the thermoelectric module with an external load resistance and booster circuits was studied. The proposed energy harvesting system can be applied for wireless sensor nodes in railroad vehicles with optimization of thermal management.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.12 no.4
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• pp.349-358
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• 2019

This paper aimed at collecting sensor signals to extract characteristic parameter of the rotor. A vibration test rig has been developed to perform model tests. Signal characteristics were analyzed when driving normally. Envelope FFT Analysis is used to extract vibration components caused by periodic impacts from other vibration factors. Signal analysis was performed when load changes were given to speed sensors and vibration test rigs that show low frequency characteristics of the rotor and signal analysis according to rotational speed. The acceleration signal measured in the bearing housing has a small amplitude and produces only the rotational frequency component and harmonic component of the motor. As the number of rotations increases, the amplitude of acceleration can be seen. As the rotational speed increases, it can be seen that there is a difference in the shape of the original data and compared with the acceleration FFT graph, it can be seen that the noise is strong at low frequencies and the corresponding rotational frequency components are clearly represented. It can be seen that changing the load does not increase the main rotational frequency component.

• Tribology and Lubricants
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• v.1 no.1
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• pp.46-58
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• 1985

The basic mechanism of lubrication between the piston ring and the cylinder wall is developed theoretically under the assumption of a reciprocating and dynamically loaded slider-bearing pair of parabolic form and smooth plane. A numerical computation for the prediction in cyclic variations of film thickness, net lubricant flow and frictional behaviour is attempted, and the influenec on the performance characteristics due to the ring height, ring face radius of curvature and the degree of offset, is also examined. The computational procedures develeped for a single ring system are extended and applied further to the complex problem of a ring pack system. It is well known that the ring pressure which is the total load on a ring, can be obtained from either an experimental measurement or a gas flow analysis. In this work, the latter of a gas low analysis method was used to calculate the pressures. It is remarked that the work done was focused on the role of flow continuity and lubricant starvation within the ring pack lubrication.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.6 no.2
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• pp.294-299
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• 2002

This paper presents a faults diagnosis technique of induction motors based on a neural network. Only stator current is measured, transformed by using FFT and normalized for the training. Healthy, bearing fault, stator fault and rotor end-ring fault motors are prepared to obtain the learning data and diagnose the several faults. For more effective diagnosis, the load rate is changed by 100%, 60%, 30% of full load and the obtained are applied to the teaming process. The experimental results show the proposed method is very detectable and applicable to the real diagnosis system.