• Tribology and Lubricants
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• 제38권2호
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• pp.53-62
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• 2022

This study presents experimental measurements of the rotordynamic performance of a motor-driven small turbocompressor supported by gas beam foil journal bearings (GBFJBs) and compares the test results with the predictions of a computational model. The experiments confirmed that the rotational synchronous frequency component dominates the behavior of the overall rotor vibrations, whereas the nonsynchronous components are insignificant, indicating the rotor-bearing system remains stable up to 100 krpm. The undamped natural frequency and imbalanced response of the rotor-bearing system are predicted when integrating the finite element model of the rotor-bearing system with the predictions of the bearing dynamic coefficients. The results are in good agreement with the experimental results. In addition, base excitation test results show that the small turbocompressor can endure large external forces and demonstrate limited rotor amplitudes. A simple single degreeof-freedom rotor model using the nonlinear stiffness of the GBFJBs can effectively predict the test results.

• Tribology and Lubricants
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• 제30권3호
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• pp.131-138
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• 2014

This study investigates the effects of the slopes of the rotational axis and bearing preloads on the natural frequencies and onset speeds of the instability of a rotor supported on gas foil bearings (GFBs). The predictive model for the rotating system consists of a rigid rotor supported on two gas foil journal bearings (GFJBs) and a pair of gas foil thrust bearings (GFTBs). Each GFJB supports approximately half the rotor weight. As the slope of the rotational axis increases from $0^{\circ}$(horizontal rotor operation) to $90^{\circ}$(vertical rotor operation), the applied load on the GFJB owing to the rotor weight decreases. The predictions show that the natural frequency and onset speed of instability decrease significantly with an increase in the slope of the rotational axis. In a parametric study, the nominal radial clearance and preload for the GFJB were changed. In general, a decrease in the nominal radial clearance lead to an increase in the natural frequency and onset speed of instability. For constant assembly clearance, the decrease in the preload changed the natural frequency and onset speed of instability with insignificant improvements in the rotordynamic stability. The present predictions can be used as design guidelines for GFBs for oil-free high-speed rotating machinery with improved rotordynamic performance.

• Tribology and Lubricants
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• 제30권1호
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• pp.9-14
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• 2014

In this Part II study, rotordynamic stability analyses were carried out to confirm improvements to the stability of a process high-speed lightweight centrifugal compressor, depending on the effects of tilting pad journal bearing designs. The bearing design variables considered were the clearances, LBPs, LOPs, and preloads. The results showed that the rotordynamic stability of the subject compressor rotor-bearing system improves exactly in accordance with the effects of the bearing design variables, which were determined in the preceding Part I study, owing to reduced bearing stiffnesses. Specifically, it was confirmed that the stability of the rotor system can be greatly improved by increasing both the machined and assembled bearing clearances, but there were no stability improvements by simply changing from an LBP to an LOP design. In addition, it was confirmed that for given fixed machined bearing clearances, the stability can be additionally improved by decreasing the preloads, i.e., by increasing the assembled clearances. In conclusion, it may be necessary to improve the designs of the original tilting pad bearings to obtain a sufficient margin of rotordynamic stability against a possible aerodynamic cross-coupled stiffness in a process high-speed centrifugal compressor. Thus, increasing the machined and assembled bearing clearances and decreasing the preload could be effective solutions.

• 소음진동
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• 제9권5호
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• pp.1042-1049
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• 1999

In the Part I has been reported a rotordynamic analysis of the driving motor-bull gear rotor-bearing system of a turbo-chiller. In this study, Part II, a rotordynamic analysis is performed with the turbo-chiller compressor pinion-impeller rotor system supported on two fluid film bearings. The pinion-impeller rotor system is driven to a rated speed of 14,600 rpm through a speed-increasing pinion-bull gear. It is modeled utilizing the finite element method for analysis. As loadings on the bearings due to the gear action are significant in the system considered, each resultant bearing load is calculated statically by considering the generalized forces of the gear action as well as the rotor itself. The two support bearings, the generalized forces of the gear action as well as the rotor itself. The two support bearings, partial and 3-axial groove bearings, are designed to take their varying loads along with their varying load angles, and they are also analyzed to give their rotordynamic coefficients. Then, a complex rotordynamic analysis of the compressor pinion-impeller rotor-bearing system is carried out to evaluate its stability, whirl natural frequencies and mode shapes, and unbalance responses under various loading conditions. Results show that the bearings and entire rotor system are well designed regardless of operating conditions, i.e., loads and operating speeds.

• 대한기계학회논문집A
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• 제38권9호
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• pp.925-932
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• 2014

회전체의 자이로스코픽 모멘트가 크거나 회전속도가 고속인 경우 회전속도에 따라 회전체의 동역학적 특성이 변화하는 정도가 커지게 되며, 자기베어링을 이용하여 회전축을 지지하는 경우 자기베어링의 제어기는 회전속도의 영향을 고려하여야 한다. 각 축의 부상력이 해당 축의 센서 출력에 의해서만 결정되는 독립축 제어기는 회전속도에 따른 변화에 대응하기 어려운 구조이나, 혼합축 제어기는 센서출력을 변환하여 진동 모드와 일치하도록 하고 각각의 진동 모드에 대해 독립적으로 제어기가 작동하는 구조로서, 진동 모드에 직접적으로 대응할 수 있는 장점이 있다. 본 논문에서는 회전체의 유연 모드를 포함하는 자기베어링 시스템의 수학적 모델을 기반으로 혼합축 제어기를 설계하고 제어기의 성능을 ISO 민감도 기준 및 불평형질량 응답 측면에서 평가하였다. 제어기 성능 평가 시 회전속도에 따른 시스템의 동특성 변화를 고려하여, 운전 속도 범위에서 성능 지표를 만족함을 확인하였다.

• 대한기계학회논문집
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• 제17권2호
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• pp.351-358
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• 1993

Recently a high speed spindle system for machine tools has attracted considerable attention to reduce the machining time, to improve the machining accuracy, to perform the machining of light metals and hard materials and to unite the cutting and grinding processes. In this study, a high speed spindle system is developed by applying the oil-air lubrication method, angular contact ball bearings, injection nozzles with dual orifices and so on. And a lubrication experiment for evaluating the performance of the spindle system is carried out. Especially, in order to establish the lubrication conditions related to the development of a high speed spindle system, the effects of oil supply rate, rotational spindle speed and so on are studied and discussed on the bearing temperature rise, bearing temperature distribution and frictional torque. And the effect of spindle system structure on the bearing temperature distribution is investigated.

• 한국생산제조학회지
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• 제20권1호
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• pp.96-100
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• 2011

The hydrostatic bearings have a relatively small run-out comparing to its shape error by fluid film effect in hydrostatic state as like pneumatic bearing and have a high stiffness, load capacity and damping characteristics. As there is no maintenance and semipermanent in these bearing type, it has been usually adopted as main spindle bearing for grinding machine. In this thesis, to develop hydrostatic bearing for high speed spindle, the cooler setting temperature, bearing clearance and nozzle pressure of belt-driven hydrostatic bearing are investigated. The bearing temperature is decreased, as the cooler setting temperature is lower, nozzle pressure is higher and bearing clearance is wider. The front temperature of bearing is nearly $8^{\circ}C$ higher than the rear one up to 13,000 rpm of spindle revolution. The thermal deflection of X-axis is ${\pm}16\;{\mu}m$ in range of 12,000 rpm-13,000 rpm. Therefore, it is conformed that the built-in motor hydrostatic bearing can be used to high speed spindle.

• 한국정밀공학회지
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• 제29권6호
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• pp.671-679
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• 2012

This paper presents an estimation procedure for axial displacement in spindle equipped with angular contact ball bearings due to rotational speed. High-speed spindle-bearing system experiences axial displacement due to thermal expansion and rotational speed-dependent characteristics of angular contact ball bearings. This paper deals with the axial displacement caused by the rotational speed-dependent effects such as centrifugal force and gyroscopic moments. To this end, a bearing dynamic model is established that includes all the static and dynamic properties of angular contact ball bearing. An analytical formula to calculate the axial displacement based on contact angles between ball and races is derived to discuss the physics regarding the axial displacement in spindle. The proposed dynamic model is compared with a reference and a commercial program. Numerical examples are presented to show the effects of centrifugal force and gyroscopic moment on the axial displacement. The proposed model is also validated with an experimental result.

• 한국정밀공학회지
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• 제11권1호
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• pp.123-128
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• 1994

A high speed spindle system for machine tools can be used to reduce the machining time, to improve the machining accuracy, to perform the machining of light metals and hard materials, and to unite the cutting and grinding processes. In this study, a high speed spindle system is developed by applying the oil-air lubrication method, angular contact ball bearings, injection nozzles with dual orifices, cooling jacket and so on. And an air cooling experiment for evaluating the performance of the spindle system is carried out. Especially, in ofder to establish the air cooling conditions related to the development of a high speed spindle system, the effects of cooling air pressure, oil supply rate, air supply rate and rotational spindle speed are studied and discussed on the bearing temperature rise and frictional torque. Also the effects of cooling air pressure, rotational spindle speed and spindle system structure is investigated on the bearing temperature distribution. The experiment on the test model reveals the usefulness of the air cooling method.

• 한국항공우주학회지
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• 제50권6호
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• pp.413-422
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• 2022

본 논문에서는 중대형 위성용 '제어모멘트자이로'의 고속회전체인 모멘텀 휠의 고장 분석에 대해 기술하였다. 고장 분석을 위해 변조된 신호에서 주기적으로 발생되는 충격신호를 찾기 위해 힐베르트 변환 기법과 신호 복조 기법을 사용한 포락선 스펙트럼 분석을 하였다. 이를 통해 높은 신호의 크기를 가지는 특정 주파수 밴드에서 회전주파수의 조화 성분과 베어링 결함 주파수가 있는지 분석하여 모멘텀 휠의 고장을 진단하였다.