• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.6 s.177
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• pp.1520-1528
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• 2000

This study presents a method for determining bearing stiffness and damping coefficients of air-lubricated slider bearing, and shows influences of air-bearing surface geometry(recess depth, crown an d pivot location) on flying attitude and dynamic characteristics. To derive the dynamic lubrication equation, the perturbation method is applied to the generalized lubrication equation which based on linearized Boltzmann equation. The generalized lubrication equation and the dynamic lubrication equation are converted to a control volume formulation, and then, the static and dynamic pressure distributions are calculated by finite difference method. The recess depth and crown of the slider show significantly influence on flying attitude and dynamic characteristics comparing with those of pivot location.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.6
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• pp.1039-1046
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• 2007

This paper presents the analysis for power consumption, mechanical vibration and acoustic noise characteristics of the Coreless and Slotless Brushless DC motor in Digital Lightening Processor(DLP) Motor with the Air-Dynamic Bearing. The Coreless BLDC motor has not the stator yoke as well as the stator slot to remove the unbalance force by the interaction between the stator yoke and Air-Dynamic Bearing clearance. The assembling tolerance and the processing error make the air-gap difference between the magnet and the stator yoke .which occurs the unbalanced electro-magnetic force in the Slotless BLDC motor. It imposes the air-dynamic bearing on the disturbance force and makes the Air-Dynamic Bearing vibrated and noised. Also, The attractive force between the magnet and the silicon steel stator yoke increases the power consumption. In this paper, the power consumption, mechanical vibration and acoustic noise of the Coreless BLDC motor and the Slotless BLDC motor with the silicon steel stator yoke are simulated, analyzed, and tested using the manufactured proto-type motors with Air-Dynamic bearing. The simulated and tested results present that the Coreless BLDC motor without the silicon steel stator yoke has the lower mechanical vibration and noise ,and lower power consumption than the Slotless BLDC motor with the silicon steel stator yoke in Digital Lightening Processor Motor with Air-Dynamic Bearing.

• KSTLE International Journal
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• v.9 no.1_2
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• pp.1-6
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• 2008

In this study is performed a complex lubrication analysis of a herringbone groove air journal bearing, which shows a big potential as an oilless bearing for a color wheel used as an original color source for a large DLP projection television and rotating at a rated-speed of 10,800 rpm. The Galerkin FE and perturbation methods are used for a lubrication analysis of the bearing. The effects of groove number, angle and depth and bearing clearance on the dynamic stability of the bearing are investigated in terms of the critical mass, and its equilibrium positions, stiffness and damping coefficients are calculated at various rotating speeds. Results have shown that the designed herringbone groove air journal bearing is quite suitable as a support bearing for the considered high-speed color wheel in terms of the complex lubrication performances of the bearing itself.

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

• Tribology and Lubricants
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• v.33 no.6
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• pp.309-314
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• 2017

This paper presents a theoretical investigation of the dynamic characteristics of externally pressurized air pad bearings with closed loop grooves. These grooves are made on the surface of bearings to reduce the number of supply holes so that manufacturing costs can be reduced. The semi-implicit method is applied to calculate the time varying pressure profile on the air bearing surface owing to the advantages of numerical stability and fast time tracing characteristics. The static pressure of the groove bearings is much higher than that without grooves, so the groove bearings can provide high load carrying capacity. The equation of motion considering vertical motion and tilting motion are also solved using the Runge-Kutta 4th order method. By combining the semi-implicit method and the Runge-Kutta method, fast calculations of the dynamic behavior of the air bearing can be achieved. The variations of bearing reaction force, air film reaction moment, height, and tilting angle are investigated for the step force input, which is 20% higher than the bearing reaction, when the nominal clearance is 6 mm. The effect of the groove width and the groove depth are investigated by calculating the dynamic behavior. The possibility of the air hammering with the depth of the groove is found and discussed.

• KSTLE International Journal
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• v.2 no.1
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• pp.46-54
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• 2001

The herringbone groove journal bearing (HGJB) has chevron type grooves on stationary or rotating member of the bearing so that they pump the lubricant inward the grooves when journal rotates. As a result, the pressure is generated around the journal so that the radial stiffness and dynamic stability are improved comparing to the plain journal bearing (PJB) when the bearing operates near the concentric condition. The narrow groove theory, conventionally adopted to simulate the concentric operation of HGJB, is limited to the infinite number of grooves. A numerical study of air-lubricated HGJB is presented for the finite number of grooves. The compressible isothermal Reynolds equation is solved by using Finite Element Method together with the Newton-Raphson iterative procedure and perturbation method. The solutions render the static and dynamic performances of HGJB. Comparison of present results with a PJB validates previously published finite difference solution. The HGJB's geometric parameters influence its static and dynamic characteristics. The optimum geometric parameters are presented for the air-lubricated HGJB in particular conditions.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2001.04a
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• pp.429-434
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• 2001

This paper has been presented the dynamic effect by the journal speed, eccentricity and source positions in order to overcome the defects of air bearing such as low stiffness and damping coefficient. Choosing two row sources position of air bearing is different from previous investigations in the side of pressure distribution of air film by the wedge effects. An experimental study was performed to compare theoretical analysis. The dynamic stiffness was measured in actual cutting. It helps predicting of air spindle s characteristic in machining of die more precisely. The results of investigated characteristics was applied to air spindle for high speed milling.

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

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1999.06a
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• pp.325-330
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• 1999

The dynamic behavior analysis of air-lubricated tilting pad journal bearing which considers start-up, running and shutdown Process were performed. By carrying out the experiment of shaft vibration, measurement of the vibration amplitudes supported by air lubricated tilting pad bearing and analysis of the result, we found more accurate dynamic behavior of the system. There were many investigations in these bearings, but dynamic behavior of startup, shutdown and running process were lacked. By using the experimental data we found the accurate dynamic behavior of the system.

• 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.