• Structural Engineering and Mechanics
• /
• v.57 no.1
• /
• pp.141-159
• /
• 2016

Bearing joint dynamic parameter identification is crucial in modeling the high speed spindles for machining centers used to predict the stability and natural frequencies of high speed spindles. In this paper, a hybrid method is proposed to identify the dynamic stiffness of bearing joint for the high speed spindles. The hybrid method refers to the analytical approach and experimental method. The support stiffness of spindle shaft can be obtained by adopting receptance coupling substructure analysis method, which consists of series connected bearing and joint stiffness. The bearing stiffness is calculated based on the Hertz contact theory. According to the proposed series stiffness equation, the stiffness of bearing joint can be separated from the composite stiffness. Then, one can obtain the bearing joint stiffness fitting formulas and its variation law under different preload. An experimental set-up with variable preload spindle is developed and the experiment is provided for the validation of presented bearing joint stiffness identification method. The results show that the bearing joint significantly cuts down the support stiffness of the spindles, which can seriously affects the dynamic characteristic of the high speed spindles.

• The KSFM Journal of Fluid Machinery
• /
• v.2 no.2 s.3
• /
• pp.32-38
• /
• 1999

An experimental study is performed to investigate the frequency effects of the excitation force on the linear stiffness and damping coefficients of a LOP (load on pad) type five-pad tilting pad journal bearing with the diameter of 300.91 mm and the length of 149.80 mm. The main parameter of interest in the present work is excitation frequency to shake the test bearing. The excitation frequency is controlled independently, using orthogonally mounted hydraulic exciters. The relative movement between the bearing and shaft, and the acceleration of the bearing casing are measured as a function of excitation frequency using the different values of bearing load and shaft speed. Measurements show that the variation of excitation frequency has quite a little effect on both stiffness and damping coefficients. Both direct stiffness and damping coefficients in the direction of bearing load decrease by the increase of shaft speed, but increase with the bearing load.

• 유체기계공업학회:학술대회논문집
• /
• 1998.12a
• /
• pp.173-179
• /
• 1998

An experimental study is performed to investigate the frequency effects of the excitation force on the linear stiffness and damping coefficients of a LOP (load on pad) type five-pad tilting pad journal bearing with the diameter of 300.91 mm and the length of 149.80 mm. The main parameter of interest in the present work is excitation frequency to shake the test bearing. The excitation frequency is controlled independently, using orthogonally mounted hydraulic exciters. The relative movement between the bearing and shaft, and the acceleration of the bearing casing are measured as a function of excitation frequency using the different values of bearing load and shaft speed. Measurements show that the variation of excitation frequency has quite a little effect on both stiffness and damping coefficients. Both direct stiffness and damping coefficients in the direction of bearing load decrease by the increase of shaft speed, but increase with the bearing load.

• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.19 no.6
• /
• pp.717-723
• /
• 2010

Radial stiffness of angular contact ball bearings are decreased remarkably at high speed revolution, because the inner and outer ball contact angle with races arc changed under the ball centrifugal forces at high speed. In the past, the optimizations of spindle units were done under the assumption of unchanged bearing stiffness for the whole speed range. But the bearing stiffness is changed and the dimension of optimum spindle is also changed with speed. In the design phase, only one model of many optimum spindle models with speed should be selected. As optimization criterion, the area of transfer function at spindle nose is proposed to estimate simply and accurately improvement of dynamic characteristics in spindle units. Finally, according to many analyses of diverse spindle models with decreased bearing stiffness, the spindle with shorter bearing span is better than longer bearing span from the viewpoint of dynamic characteristics.

• Tribology and Lubricants
• /
• v.29 no.6
• /
• pp.386-391
• /
• 2013

Part I of this study analyzed the effects of tilting pad bearing designs to reduce the stiffness of the bearings used in a process high-speed lightweight centrifugal compressor intended for a domestic refinery use. This was done in an attempt to enhance the robustness of its rotordynamic stability against possible aerodynamic cross-coupled stiffness. The bearing design variables reviewed were the clearances, LBPs, LOPs, and preloads. The results showed that there was practically no difference between the LBP and LOP designs in terms of the bearing stiffness, because the compressor rotor was lightweight and the bearings had relatively high preloads. Increasing both the machined and assembled clearances in bearing designs has resulted in the bearing stiffness being greatly reduced. In addition, it has been confirmed that an additional reduction in the bearing stiffness can be obtained for given fixed machined clearances by decreasing the preloads, i.e., by increasing the assembled clearances.

• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.24 no.3
• /
• pp.278-286
• /
• 2015

The effects of the main bearing stiffness combined with vertical non-torque force on the input load and shaft deflection of a gearbox were investigated for the three-point suspension drive train of a wind turbine. A finite element analysis model for the drive train was studied experimentally, and its applicability to the present study was verified. The results show that, as the main bearing stiffness is increased, the input load of the gearbox decreases, whereas the input shaft deflection increases. The stiffness component for the pitch moment has the largest influence on the gearbox input load. Although the gearbox life increases at a higher main bearing stiffness, the economic efficiency and durability of the entire drive train system should also be considered in the selection of the main bearing stiffness.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2005.11a
• /
• pp.75-78
• /
• 2005

In this paper, an experimental study on porous air bearing stiffness for ultra precision positioning system was performed. In general manufacturer provide bearing stiffness under specific air pressure, but the air pressure used in the field is different. Therefore it is necessary to know the stiffness of air bearing under the pressure used in the field. In order to know that, experimental device which can realize actual operating conditions was made. Using this device, static and dynamic stiffness of air bearing can be obtained. As a result, displacement error occurred around 1 $\mu$m at recommended load.

• Tribology and Lubricants
• /
• v.14 no.1
• /
• pp.14-22
• /
• 1998

This paper describes the effects of exciting frequency on the stiffness and damping coefticients of a 5-pad tilting pad journal bearing, LOP (load on pad) type. The stiffness and damping coefficients are investigated experimentally under the different values of exciting frequency, bearing load and shaft speed. These coefficients are estimated by measuring the response of the relative displacement between the bearing and the shaft and acceleration of the bearing due to the known exciting loads acting on the bearing. In order to analysis the response of exciting load, displacement and acceleration, a FFT analyzer is used. It is shown that the variation of exciting frequency has a little effect on both the stiffness and damping coefficients. Both the stiffness and damping coefficients in the loading direction are decreased by the increase of shaft speed but increased by the increase of bearing load.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
• /
• 2005.05a
• /
• pp.468-472
• /
• 2005

In this paper, the static and dynamic stiffness of the air bearing stage for micro-micro machine tool are examined experimentally. For stiffness and precision concerns, air bearing stages are adapted for 3-axis micro-milling machine which is size of $200x200\;mm^2$. The air bearings in the stage are preloaded by permanent magnets to achieve desired bearing clearance and stiffness for vertical direction. As the stiffness of the air bearing is primary interests, static stiffness test were performed on XY stage in Z direction and Z column in Y direction. Dynamic test were performed on XY stage and Z column, respectively. Both static and dynamic tests were performed in different air pressure conditions. The vertical stiffness of XY stage is about 9 N/ pm where Y stiffness of Z column is much smaller as $1\;N/{\mu}m$ because of the large moment generated by Y force on the column.

• Journal of the Korean Society for Precision Engineering
• /
• v.17 no.3
• /
• pp.129-135
• /
• 2000

Air-dynamic bearings are increasingly used in supporting small high-speed rotating bodies. This study investigates the effects of design parameters on the axial stiffness of spiral-grooved air bearings of various curvatures. Design parameters are fundamental clearance, groove depth, and bearing number. The pressure distribution at the clearance between the stator and rotor of the bearing is obtained by solving the Reynolds equation, and the supporting load and the axial linear stiffness are calculated from the pressure distribution. It is found that a larger curvature increases the axial linear stiffness more and that there exist an optimal groove depth for the linear stiffness of the air bearing. It is also found that the linear stiffness has a linear relationship with the bearing number.