Aerostatic Thrust Bearings Research Articles

Static Characteristics of Aerostatic Thrust Bearings With Multiple Porous Inlet Ports

Aerostatic porous bearings have been applied successfully to various precision devices, such as precision machine tools and precision measuring equipment, to achieve higher accuracy of motion. Recently, large aerostatic porous thrust bearings have been used as essential components in a lithography machine for large liquid crystal display (LCD) glasses. Conventional aerostatic porous bearings are made of porous material that covers the whole of the bearing surface area, requiring a large piece of such material for large bearings. However, making large pieces of porous material requires the use of a large electric furnace, which is a very expensive part of the bearing's manufacturing cost. To overcome this problem, this paper proposes an aerostatic thrust bearing with multiple porous inlet ports. The proposed bearing has a number of small porous inlet ports on the bearing surface, thereby avoiding the need for large electric furnaces. The static characteristics of the proposed bearings are investigated numerically and experimentally. The results show that the proposed aerostatic thrust bearing is potentially very useful for the manufacture of large aerostatic thrust bearings, where it would have advantages over conventional aerostatic porous thrust bearings.

The Effect of Rotational Speed on Fluid Compressibility and Gap Pressure of a Partially Porous Aerostatic Thrust Bearing

This study investigated the effect of the spindle speed on pressure distribution in the air gap and the load carrying capacity of a porous aerostatic annular thrust bearing. Based on the finite volume method and the pressure-velocity coupling scheme of the SIMPLE algorithm with the standard k-ε turbulent model, a CFD software was used to solve the Navier-Stokes equations to calculate pressure and velocity of the air flow. The results revealed there were positive pressure zones and vacuum pressure zones in the air gap between the thrust disk and the bearing. Under the same spindle speed, the pressure difference between the positive peak and the negative peak in the case of incompressible air was greater than that in the case of compressible air. The averaged pressure on the surface of the thrust disk with compressible air flow was higher than that with incompressible air flow. So was the load carrying capacity of the bearing, which increased when the spindle rotated faster.

Numerical Study on the Static Characteristics of Novel Aerostatic Thrust Bearings Possessing Elastomer Capillary Restrictor and Bearing Surface

Numerical Study on the Static Characteristics of Novel Aerostatic Thrust Bearings Possessing Elastomer Capillary Restrictor and Bearing Surface

Research on the Gas Pressure Fluctuation Characteristics inside an Aerostatic Thrust Bearing with a Pocketed Orifice-Type Restrictor

In this article, large eddy simulation (LES) is used to analyze the time variation flow field inside an aerostatic thrust bearing with a pocketed orifice-type restrictor. The results indicate that there is a complicated turbulent flow region inside the bearing and many vortices exist in the region. In the vortices, gas pressure increases gradually from the center to the edge. It is the rapid repetition of the formation and disappearance of the vortices that causes the gas pressure to fluctuate quickly and it is directly related to the micro self-vibration of the bearing. Furthermore, the influence of the bearing structure and film thickness on the pressure fluctuation is discussed. Compared to the experiments of other researches, it is concluded that LES predicts the gas pressure fluctuation characteristics inside an aerostatic bearing very well and it is useful for designing bearings with low vibration.

On the analysis of aerostatic thrust bearings with the differential quadrature method

This paper presents a numerical approach to analyze the performance of aerostatic thrust bearings based on the differential quadrature method. The Reynolds equation of aerostatic thrust bearings is firstly discretized as a series of algebraic equations by the differential quadrature method and the pressure distribution is calculated with the discretized equations invoking the boundary conditions. Analytical approximation of Heaviside step function and a multi-domain technique are then introduced to resolve the discontinuous problem of grooved aerostatic bearings. Numerical solutions are obtained for two types of aerostatic thrust bearings. The mass flow rate, load capacity, and stiffness predicted by these solutions are further compared with corresponding analytical, finite difference method and computational fluid dynamics solutions. It is demonstrated that the differential quadrature method has high efficiency and accuracy for the solution of aerostatic thrust bearings.

Analysis of the Micro Self-vibration of Aerostatic Thrust Bearing Based on Large Eddy Simulation

In order to find out the mechanism of the micro self-vibration of aerostatic thrust bearing,large eddy simulation(LES) is used to analyze the flow field of the bearing with pocketed orifice-type restrictor.The results show that there are complicated vortexes near orifice outlet.Gas pressure and velocity change gradually from the centre to the edge of the vortexes.It is the repetition of the generation and crack of vortexes causes gas pressure to fluctuate with gas flow inside the bearing and induces the bearing to be micro self-vibration.By comparing to the calculation results of standard k-e model,the correctness of LES is validated.Moreover,the mechanism of vortexes induce the micro self-vibration of aerostatic thrust bearing is validated by comparing to the flow field of aerostatic thrust bearing with inherently orifice-type restrictor.The results also indicate that there exists a maximum value of the magnitude of pressure fluctuation with the increases of film thickness.Therefore,the film thickness of the maximum pressure fluctuation should not be close to that of the maximum stiffness in order to make the bearings with better stiffness and less self-vibration simultaneously.

Study on Tilt Properties of Orifice-Compensated Aerostatic Thrust Bearings

Under different throttle type, the bearing lateral force is calculated with the heeling angle changed by using the finite volume method. Also, cavity diameter and depth are selected, which can get influence on bearing lateral force in the same heeling angle. By attributing the error between experiment results and compensational ones to measurement error and instrument error itself, the results are verificated.

Numerical and Compared Study on The Aerostatic Thrust Bearing with Annular Gap Throttling Structure

An aerostatic thrust bearing (ATB) with annular gap throttling structure was investatged using Computational fluid dynamic (CFD) method in this paper. The CFD software FLUENT was used for solveing NS equations. SST k-ω was used to serve as a turbulent flow model for the two dimensional axis fluid field. A traditional orifice thrust bearing was also calculated. The numerical results agree well with experiement dates. The load capacity, air flow rate at different bearing clearance were obtained by numerical simulation. The flow details such as pressure and mach number at different bearing clearance were discussed. The results shows that, the new ATB has a better load capacity, there is stable a high pressure zone of new aero thrust bearing. The mass flow rate of new ATB is higher than traditional one and the pressure drop is lower than tradional one at the same conditions.

3D Numerical Study on The Aerostatic Thrust Bearing with Annular Gap Throttling Structure

An aerostatic thrust bearing (ATB) with annular gap throttling structure and trapezoid air chamber was investatged using Computational fluid dynamic (CFD) method. The CFD software FLUENT was used for solveing NS equations. SST k-ω was used to serve as a turbulent flow model for the three dimensional periodic fluid field. The numerical results agree well with experiement dates. The ATB flow field was subsonec and the load capacity, air flow rate at different bearing clearance were obtained by numerical simulation. The flow details such as pressure and velocity at different bearing clearance were discussed. The results shows that CFD is a useful tool in the design of aerostatic thrust bearing.

CFD Investigation of an Aerostatic Thrust Bearing Flow Field with New Type of Throttling Structure

A new aerostatic thrust bearing was investatged using Computational fluid dynamic (CFD) method in this paper. The throttling structure of the aerostatic thrust bearing in this paper is an annular gap type. The CFD software FLUENT was used for solveing NS equations. SST k-ω was used to serve as a turbulent flow model for the two dimensional axis fluid field. The load capacity, air flow rate at different bearing clearance and supply pressure were obtained by numerical simulation. The flow details such as pressure and mach number at different bearing clearance were disccused. The results shows that, there is stable a high pressure zone of new aero thrust bearing. If the supply pressure or bearing clearance is high enough, the supursonic flow will occur in the throttle annular gap, and an oblique shock wave is produced around the end of gap.

Design of an Aerostatic Thrust Bearing with Pressure-equalizing Grooves

To solve the problem in the space robot's microgravity simulation experiment that lateral interference force/moment exists and the workbench is uneven,a high load capacity,high stiffness round aerostatic thrust bearing with circumferential and radial pressure-equalizing grooves is designed and manufactured,and its load capacity is modeled and numerically analyzed using deformational Reynolds equation.In order to validate the theoretical calculation results,simulation analysis using Fluent is carried out to get the load capacity characteristics,and the influence of the impact created by the high pressure gas on the load capacity is analyzed.Finally,an experiment about the bearing's load capacity characteristics is performed on the standard test platform,and the result is compared with the data of bearing without grooves.It turns out that the structure design and theoretical analysis are correct.

Research on Flow Characteristics of Aerostatic Circular Thrust Bearing with a Cone Cavity

The aerostatic circular thrust bearing was taken as a study subject. The numerical simulation method was used to calculate the flow passage. Meanwhile, the single-point testing method was used to test the pressure distribution. The simulation and experiment measurement results were compared and analyzed. The results show that: The single-point testing method is effective to capture the change of flow characteristics. The overall results of simulation and testing coincide with each other well. In the range of cone cavity, the flow pattern for the gas is turbulent flow, and the flow field should be divided into different zones for simulation.

Numerical calculation and experimental verification of static and dynamic characteristics of aerostatic thrust bearings with small feedholes

In this work, aerostatic annular thrust bearings with feedholes of less than 0.05 mm in diameter are considered, and the static and dynamic characteristics of these bearings are investigated experimentally and numerically. In numerical calculations using the finite difference method (FDM), the discharge coefficients of a small feedhole were determined based on computational fluid dynamics (CFD) software and verified experimentally. In addition, the effect of the bearing surface roughness on the bearing characteristics was analyzed experimentally and numerically. It was confirmed that aerostatic thrust bearings with small feedholes could have larger stiffness and damping coefficient than bearings with compound restrictors.

Finite Element Analysis and Calculation of Load Capacity on Aerostatic Thrust Bearing

For the design and application of ultra-high speed aerostatic spindle, it is often difficult to determine the load capacity of bearing gas film because of nonlinear problem, especially when the gas film is very thin. As ultra-high speed aerostatic spindle is working, rotational velocity of spindle ranges up to 300,000 rpm, while Reynolds number of air flow also increases in aerostatic bearing, so we need to consider the impact of gas inertia on the load capacity. In order to improve design accuracy of ultra-high speed aerostatic spindle, it is vitally necessary to consider hydrodynamic effect of aerostatic bearings. By using finite element analysis software ANSYS software as analysis platform, through finite element the analysis of the internal flow field of aerostatic thrust bearing, this paper obtains the relationship of rotation speed and load capacity of aerostatic thrust bearing.

Comparison between grooved and plane aerostatic thrust bearings: static performance

The demand of air bearings is increasing for those applications that require precision linear movements or high-speed rotations. In particular in this paper air pads for air motion technology are studied. The paper analyses the effect of a circumferential groove machined on the pad surface on pressure distribution, air flow consumption and stiffness. Two geometries are investigated and compared: one with three supply orifices and the other with a circumferential groove as well. The static characteristics of the pads are experimentally determined with also the pressure distributions under the pads along the radial and circumferential directions. The experimental pressure distributions are compared with the simulated ones, obtained with a numerical program at the purpose developed. The numerical model considers a general formulation of the supply holes discharge coefficient that can be used also in presence of a circumferential groove.

Numerical investigation of static and dynamic characteristics of aerostatic thrust bearings with small feed holes

Recently, laser beam machining and micro drills have made it easier to manufacture small feed holes of less than 0.1 mm diameter. Accordingly, aerostatic bearings with these small feed holes have become commercially available for improving bearing performance. In this work, an aerostatic annular thrust bearing with small feed holes of less than 0.05 mm diameter was treated and the static and the dynamic characteristics of this type of bearing were investigated numerically. In numerical calculations, computational fluid dynamics (CFD) was used to determine discharge coefficients for a small feed hole and the finite difference method (FDM) was used to obtain the bearing characteristics. In addition, the characteristics of this type of bearing were compared with those of aerostatic thrust bearings with typical compound restrictors to show clearly the features of this type of bearing.

A multiphysics model for optimizing the design of active aerostatic thrust bearings

Abstract Aerostatic bearing solutions avoid problems related to friction and enable high precision linear guiding. However, their relatively low stiffness hinders the accuracy when disturbance forces, such as inertial effects or machining forces, are present. An active compensation strategy based on air gap shape control with piezoelectric actuators has been proposed, which can achieve nanometre position control and high bandwidth disturbance compensation. Suitable design strategies and tools still need to be developed to optimize the performance and enforce the industrial application of these systems. This paper proposes a new multiphysics finite element model which considers the interaction between the air flow dynamics, the structural flexibility of the bearing, the piezoelectricity for the actuators and the control with strongly coupled formulation. A setup for high bandwidth and resolution experiments has been built and used to test the prototypes. The experimental results prove the validity of the model and the relevance of the fluid–structure interaction, and thus the need for such a coupled multiphysics model for optimizing the design of active air bearings.

1104 空気圧サーボ軸受アクチュエータを用いた超精密位置決めXYステージの開発(潤滑剤・機械要素,一般講演)

With the development in 1C technology, ultraprecise positioning on the nanometer order has been strongly required in semiconductor stepper equipment. To meet such demands, our laboratory developed 'pneumatic servo bearing actuator' as a new actuator for ultraprecise positioning. This actuator mainly consists of a pneumatic servo valve and an aerostatic thrust bearing. In this paper, we developed an ultraprecise positioning XY stage composed of six pneumatic servo bearing actuators. First, we investigated the basic performance of the actuator with a spherical bearing before assembling it to the XY stage. Second, we checked the specification of the developed XY stage, especially focusing on its minimum resolution.

Entrance Effect on Load Capacity of Orifice Compensated Aerostatic Bearing with Feeding Pocket

The current research of the aerostatic thrust bearing mainly focuses on the porous material bearing and inherent compensated air bearing, which aims at obtaining small physical dimension and large load capacity. Although porous material bearing appears larger load capacity, materials anisotropy itself and void content distortion caused in heat-treating, and machining processes add greater complexity to internal flow transfer process. Inherent compensated air bearing has the advantages of simple structure and good stability, but its load capacity and static stiffness is not worth somewhat. In this paper, based on hydrostatic lubrication theory, finite volume method is presented for taking entrance effects into account in computing pressure distribution, load capacity and mass flow rates of circular aerostatic thrust bearings. Technical analysis, numerical simulations and laboratory demonstration tests of influence of pocket diameter and pocket depth on loading capacity of aerostatic thrust bearing are carried out on simple orifice compensated air bearings with feeding pockets. The static parameters, such as air consumption and pressure distributions, are measured as a function of supply pressure and air gap height for several different orifices and pockets size. Entrance effects are described in term of typical throttling types, and the effect of pocket diameter and pocket depth on load capacity is systematically described respectively. The proposed research results uncover the causation of throttling action of the orifice compensated air bearing with feed pocket and further develop and improve the design theory of air bearing.

Analysis of Dynamic Stiffness and Damping of Partial Porous Aerostatic Thrust Bearings

Porous materials have been successfully used in an aerostatic bearing. In this paper, the dynamic stiffness and damping of partial porous aerostatic thrust bearings are analyzed by numerical calculation method. Firstly, the pressure distribution function of the bearing is divided into the static and dynamic pressure distribution functions through minor perturbation method. Then, the static and dynamic pressure distribution functions are calculated by FEM. Finally, the dynamic stiffness and damping coefficients of the bearing are solved. The result indicates that the dynamic stiffness increases obviously with the increment of supply pressure and first increases then decreases with the increment of frequency, and that there is negative damping in the low frequency band and the supply pressure has a great impact on the stability of the bearing.