Papers by Keyword: Aerostatic Bearing

Abstract: The pocketed orifice structure for the air-nozzles of an aerostatic bearing is usually a particular pocketed orifice. This structure can not help the shaft to reach high stiffness in working process, so the applicability of the aerostatic bearing in machines with large centrifugal or horizontal force is not focused. A common pocketed orifice structure for the air-nozzles of the aerostatic bearing to meet the demand of high stiffness of the journal shaft has been developed.. Experimental results show that the stiffness of the aerostatic bearing increases, the eccentricity is only about 0.03 mm at a pressure of 2 to 2.5 bar compared to the structure of particular pocketed orifice. Besides operating at high pressure, a common pocketed orifice structure does not suffer from air congestion (blockage) as in a particular pocketed orifice structure. This results in reducing vibration and avoiding damage inside the aerostatic bearing.

Abstract: In this paper, Computational Fluid Dynamics (CFD) is used to analyze the micro self-vibration of aerostatic bearing with pocketed orifice type restrictor as the bearings performance is stable and it is widely used ultra-precision equipments. By using Large Eddy Simulation (LES), time-variation flow field inside the bearing is obtained. Then the pressure fluctuation characteristics is discussed because it influences the micro self-vibration of the bearing directly. Moreover, the relationship between bearing diameter, orifice diameter, air chamber diameter, air chamber depth and the micro self-vibration is researched. The results can be considered for the designing of ultra-precision aerostatic bearing with pocketed orifice type restrictor.

Abstract: In this paper, the transient turbulent flow field in ultra-precision aerostatic bearings is numerically investigated, with the focus on vortex structures and pressure distribution in the bearing clearance. In order to capture details of transient turbulent flow, large eddy simulation (LES) is employed. It is found that with the increase of air supply pressure, the flow in the recess becomes turbulent and vortex shedding occurs near the orifice outlet. It is also demonstrated that this unsteady vortex shedding results in pressure fluctuation in the bearing clearance, which is related to the experimentally observed small vibration of the bearing on the order of nanometers.

Abstract: This paper discusses about how to optimize design of an aerostatic bearing. In order to achieve the objective, there are four necessary qualifications: high load capacity, high stiffness, low flow rate and uniformly pressure distribution, those make an aerostatic bearing optimized. The finite difference method is employed to obtain the numerical solution of the pressure distribution between the surface of aerostatic bearing and worktable. The performance is determined by the pressure distribution of aerostatic bearing. Furthermore, this study proposed an integrated optimal approach that is HTGA/Gray. Comparing with many kinds of optimal theories finds out the most suitable parameters of an aerostatic bearing. Finally, the experimental results for the load capacities and flow rates clearly indicate that the proposed aerostatic bearing can enhance ability effectively.

Abstract: The aerostatic bearings used in guide ways in ultra precision motion stages can provide both normal stiffness and roll stiffness, which are critical to the dynamic characteristics and control of systems. The normal stiffness has been widely investigated so far, but the roll one has seldom been studied. A new method for analyzing the roll stiffness is proposed, in which the aerostatic bearing is modeled as a set of distributed springs. The stiffness distribution is obtained by using the derivate of the pressure distribution with respect to the air gap. All the distributed springs are then integrated by using the presented transformation and it leads to an equivalent spatial spring which contains both the normal stiffness and the roll stiffness. A planar aerostatic bearing is taken as an example to illustrate the procedure of the calculation. The proposed method can be used to predict the vibration characteristics of various kinds of aerostatic bearings under working conditions.

Abstract: Micro-vibration of aerostatic bearings has been the bottleneck in the improvement of the moving and positioning accuracy of ultra-precision fabrication and metrology equipments. In this study, a new type of aerostatic bearing restrictor has been proposed. The prototype of arrayed microhole restrictor, instead of the conventional single hole restrictor was developed with the aim of reducing the harmful micro-vibration of aerostatic bearings. Computational fluid dynamics (CFD) was employed to numerically calculate the air flow field. It is found that the employment of arrayed microhole restrictors can reduce the amount of micro-vibration while maintain the load carrying capacity and stiffness of the aerostatic bearing. Experimental measurement of the micro-vibration confirms the effectiveness of this new type of restrictor.

Abstract: A vacuum preloaded circular aerostatic bearing was designed and its static characteristics were investigated experimentally. The load carrying capacity and air film thickness of the bearing were measured for different air supply pressure and vacuum pressure values. An orthogonal table was constructed to optimize the experimental measurement. Regression analysis was performed on the experimental results to obtain an analytical model of the bearing stiffness as a function of the load carrying capacity, air supply pressure and vacuum pressure. Accuracy of this analytical model in predicting static characteristics of the aerostatic bearing was validated by comparison with experimental data, and influences of the functioning parameters were also discussed.

Abstract: 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.

Abstract: The static performance of an aerostatic bearing with angled surface self-slot-compensation is analyzed. The consistent condition was applied to unitize the Reynolds equation of different forms and the finite element method (FEM) was used to solve the equation. The load carrying capacity (LCC) and the stiffness of the bearing was obtained and the influence of the geometric parameters was discussed. It is concluded that this self-compensating aerostatic bearing can achieve a good performance; the geometric parameters of the gap are interactive, and should be rationally matched.

Abstract: Air Spindles have been used in ultra precision machines for several years due to their advantages such as high speed rotation, low friction, and low vibration, [1]. Air spindles are widely used in these machines for producing precise work pieces. Although, spindles function on a very complicated theoretical basis, [2, 3], their structure is very simple and consists of mainly a rotor and a stator. The rotor/stator could be made of different shapes. A cylindrical shape is the one commonly in use. The spindle designed in this work has a spherical configuration. It has been designed so that it could be moved without application of electric motor and only by a wind turbine system, [4]. The spindle studied in this research uses compressed air for rotor suspension, and has an air turbine for rotating its shaft. A thin air film acts as bearing layer between rotor and stator. In design procedure, operation parameters such as air inlet pressure for turbine, air inlet pressure for bearing, diameter of turbine nuzzles, diameter of bearing nuzzles, clearance between rotor and stator and etc. have been considered, [5]. A prototype spindle has been manufactured using design criteria. The influence of above mentioned parameters have been recognized through experiments.