• 한국정밀공학회지
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• 제23권1호
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• pp.193-200
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• 2006

To perform the finish grinding process of ferrules which are widely used as fiber optic connectors, a high-precision centerless grinding machine is necessary. The high-precision centerless grinding machine is consisted of the hydrostatic GW and RW spindle systems, hydrostatic RW feeding mechanism, RW swivel mechanism, on-machine GW and RW dressers, and concrete-filled steel bed. In this study, the thermal characteristics of the high-precision centerless grinding machine such as the temperature distribution, temperature rise and thermal deformation, are estimated based on the virtual prototype of the grinding machine and the heat generation rates of heat sources related to the machine operation conditions. The reliability of the predicted results is demonstrated by the temperature characteristics measured from the physical prototype. Especially, the predicted and measured results show the fact that the high-precision centerless grinding machine has very stable thermal characteristics.

• International Journal of Precision Engineering and Manufacturing
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• 제8권1호
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• pp.32-37
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• 2007

The outer diameter finishing grinding process required for ferrules, which are widely used as fiber optic connectors, is carried out by high-precision centerless grinding machines. In this study, the thermal characteristics of such a machine, for example, the temperature distribution, temperature rise, and thermal deformation, were estimated based on a virtual prototype and the heat generation rates of heat sources related to normal operating conditions. The prototype consisted of a concrete-filled bed. hydrostatic grinding wheel (GW) and regulating wheel (RW) spindle systems, a hydrostatic RW feed mechanism, a RW swivel mechanism, and on-machine GW and RW dressers. The reliability of the predicted results was demonstrated using temperature characteristics measured from a physical prototype. The predicted and measured results indicated that this particular high-precision centerless grinding machine had very stable thermal characteristics.

• 대한기계학회논문집A
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• 제36권11호
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• pp.1441-1446
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• 2012

유압피스톤모터는 정압베어링부분의 마찰손실과 용적손실, 기구적 운동부분의 마찰손실, 오일의 관로저항에 의한 압력저하, 압축성에 의한 체적손실 그리고 하우징 오일 처닝(churning) 손실 등이 있다. 이러한 손실 중에서 일정한 틈새의 유막(oil film, $8{\sim}15{\mu}m$)으로 고속 회전하는 피스톤 슈(piston shoe)와 슈 플레이트(shoe plate) 사이 정압베어링 부분의 마찰 및 용적손실이 유압모터의 전체효율을 좌우 한다. 본 연구에서는 최고압력 35MPa, 최고회전수 2500rpm, 배재용적 320cc/rev급 2속(2-speed) 초대형 굴삭기의 주행모터용 유압피스톤모터를 대상으로 정압베어링비가 유압모터의 전 효율에 미치는 영향을 실험적으로 분석하였다.

• Tribology and Lubricants
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• 제38권2호
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• pp.33-40
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• 2022

In this study, we present rotor dynamic analysis and operation test of a turbo expander for a hydrogen liquefaction plant. The turbo expander consists of a turbine and compressor wheel connected to a shaft supported by two hydrostatic radial and thrust bearings. In rotor dynamic analysis, the shaft is modeled as a rigid body, and the equations of motion for the shaft are solved using the unsteady Reynolds equation. Additionally, the operating test of the turbo expander has been performed in the test rig. Pressurized helium is supplied to the bearings at 8.5 bar. Furthermore, we monitor the shaft vibration and flow rate of the helium supplied to the bearings. The rotor dynamic analysis result shows that there are two critical speeds related with the rigid body mode under 40,000 rpm. At the first critical speed of 36,000 rpm, the vibration at the compressor side is maximum, whereas that of the turbine is maximum at the second critical speed of 40,000 rpm. The predicted maximum shaft vibration is 3 ㎛, whereas sub-synchronous vibration is not presented. The operation test results show that there are two critical speeds under the rated speed, and the measured vibration value agrees well with predicted value. The measured flow rate of the helium supplied to the bearing is 2.0 g/s, which also agrees well with the predicted data.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2000년도 제32회 추계학술대회 정기총회
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• pp.177-185
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• 2000

The characteristics of multi-leaf feil bearing are investigated. The Foil bearing is preloaded and has several leaf foils modeled by curved beams. An analysis of the air foil bearing was performed, considering effects of foil deflection and compressible lubrication equation simultaneously. A parametric study shows that the number of foils significantly affect the static characteristics of air foil bearings and describes what the minimum film thickness means. The results include pressure profile, load capacity, dimensionless torque and minimum film thickness in the foil bearing.

• International Journal of Precision Engineering and Manufacturing
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• 제5권2호
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• pp.60-67
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• 2004

For improving the motion accuracy of hydrostatic tables, a corrective machining algorithm is proposed in this paper. The algorithm consists of three main processes. The reverse analysis is performed firstly to estimate the rail profile from the measured linear and angular motion error, in the algorithm. For the next step, the corrective machining information is obtained based upon the estimated rail pronto. Finally, the motion errors on the correctively machined rail are analyzed by using the motion error analysis method. These processes are iterated until the analyzed motion errors are satisfactory within the target accuracy. In order to verify the validity of the algorithm theoretically, the motion errors calculated by the estimated rail after the corrective machining process, are compared with those by the true rail which is previously assumed as the initially measured value. The motion errors calculated using the estimated rail show good agreement with the assumed values, and it is shown that the algorithm is effective in acquiring the corrective machining information to improve the accuracy of hydrostatic tables.

• 드라이브 ㆍ 컨트롤
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• 제12권2호
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• pp.21-26
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• 2015

In order to design a swash plate type pump for electro-hydrostatic actuators the performance of the hydrostatic piston shoe bearings in the low speed range needs to be examined, since the pump operates frequently at low speeds, compensating for position control errors as a control element. As a common practice, piston shoes are equipped with inner rings as an auxiliary element to enhance their tribological performance. In this paper, the effects of the inner rings of the piston shoes on the frictional loss and leakage flow rate were investigated, where three piston shoe models, with different inner ring shapes and different inlet orifice sizes, were integrated. The test results showed that a large inner ring and small inlet orifice were advantageous for reducing both the frictional loss and leakage flow rate; this could also be confirmed by computational analyses.

• 드라이브 ㆍ 컨트롤
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• 제11권4호
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• pp.25-31
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• 2014

This paper details application of a DLC(Diamond Like Carbon)-coating to the swash plate and the ball joint of pistons that make sliding contact with the piston shoes of an axial piston pump. This process, aimed to reduce the frictional and leakage power losses of the hydrostatic piston shoe bearings at the low speed range. At lower speeds than 100rpm, the positive effects of the DLC-coating on the power loss reduction of the hydrostatic piston shoe bearings could be confirmed. These effects resulted in little improvement in volumetric efficiency of the test pump, but the mechanical efficiency could be raised by up to 5% at 100rpm; here, the DLC-coated swash plate played a more dominant role than the DLC-coated ball joint.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2011년 춘계학술대회논문집
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• pp.387-391
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• 2011

Since MEMS based micro actuators or generating devices have high efficiency per volume, plenty of research are ongoing. Among them, MEMS based millimeter-scale micro gas' turbine is one of the most powerful issue for replacing chemical batteries. However, since limiting of MEMS manufacturing technique, it is very difficult that makes wide turbine bearing area. It causes low DN number, so sufficient bearing force is hard to achieve. Thus, the most important issue on micro gas turbine is proper bearing design which can keep rotor stable during operation. In order to that, micro-scale gas-lubricated bearing is generally used. In this paper, basic feasibility study and design of journal bearing for 10mm diameter micro gas turbine is described Journal bearing is hydrostatic gas-lubricated type. Numerical simulation is performed with ANSYS CFX 11.0 which is commercial numerical tool. Repulsive force when there is radial displacement in bearing and returning time is calculated using steady and unsteady cases. Auto re-meshing technic is used for moving mesh unsteady cases which simulate displacement of axis and its movement. The simulation results are used for further design of micro gas turbine, and experiment will be done later.

• Tribology and Lubricants
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• 제24권6호
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• pp.343-348
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• 2008

In this paper, a CFD (Computational fluid dynamics) code, FLUENT is adopted to investigate accurate flow characteristics for a slipper bearing which is used swash plate type hydraulic axial piston pump. Static pressure and velocity distributions, and velocity vectors are plotted for different film thickness and slipper rotational velocity. In recess region, there exists a doughnut shaped vortex ring. The static pressure distributions are non-uniform and the flow fields are highly asymmetrical under bearing rotation. Therefore the numerical method adopted in this paper can be use in design of hydrostatic components and further studies are required.