Aerostatic Pad Research Articles

An aerostatic pad compensated by a differential diaphragm valve

This paper presents a novel prototype of a passively compensated aerostatic pad which consists in the integration of a commercial pad with a custom-built differential diaphragm valve. The static performance of the system is experimentally assessed in the presence of different supply and reference pressures. Additionally, the paper describes two lumped parameter models of the system which present different level of complexity. Experimental and numerical results are in good agreement and demonstrate that the static performance of the system can be computed more quickly through the simplified version of the described models.

An Identification Method for Orifice-Type Restrictors Based on the Closed-Form Solution of Reynolds Equation

Even though the behavior of aerostatic bearings has for long been the topic of extensive research, there are still many aspects that require further investigation. Among these, the identification of the discharge coefficients is one the most crucial. This paper presents a hybrid method to identify the discharge coefficients of aerostatic bearing orifices. The method is termed as hybrid since it exploits experimental data and the equations of the analytical model of a circular and centrally fed aerostatic pad. The obtained results demonstrate the accuracy of the method. The proposed method further offers practical advantages compared to the conventional methods.

Design and Analysis of an Aerostatic Pad Controlled by a Diaphragm Valve

Because of their distinctive characteristics, aerostatic bearings are particularly suitable for high-precision applications. However, because of the compressibility of the lubricant, this kind of bearing is characterized by low relative stiffness and poor damping. Compensation methods represent a valuable solution to these limitations. This paper presents a design procedure for passively compensated bearings controlled by diaphragm valves. Given a desired air gap height at which the system should work, the procedure makes it possible to maximize the stiffness of the bearing around this value. The designed bearings exhibit a quasi-static infinite stiffness for load variation ranging from 20% to almost 50% of the maximum load capacity of the bearing. Moreover, the influence of different parameters on the performance of the compensated pad is evaluated through a sensitivity analysis.

Dynamic behaviour and stability analysis of a compensated aerostatic pad

Thanks to their low friction, aerostatic pads have important applications in precision positioning systems and linear guides. A simple and cheap solution to increase the static stiffness of aerostatic pads is to add a proper designed pneumatic valve to regulate the air flow supplied to the bearing. However, integrating aerostatic pads with additional devices can reduce its dynamic performance. This paper presents a numerical study on the dynamic behaviour and stability a commercial aerostatic pad controlled by a custom-built diaphragm valve. The bearing performance is studied by means of a lumped parameters model. Air bearing stiffness and damping are analysed in the frequency domain. Subsequently, the lumped model is linearized to investigate the stability of the system by means of Routh-Hurwitz method. The performance of the controlled air pad is compared to that of a simple commercial air pad.

Multi-Objective Optimisation of an Aerostatic Pad: Design of Position, Number and Diameter of the Supply Holes

ABSTRACTIn this paper, a rectangular aerostatic bearing with multiple supply holes is optimised with a multiobjective optimisation approach. The design variables taken into account are the supply holes position, their number and diameter, the supply pressure, while the objective functions are the load capacity, the air consumption and the stiffness and damping coefficients. A genetic algorithm is applied in order to find the Pareto set of solutions. The novelty with respect to other optimisations which can be found in literature is that number and location of the supply holes is completely free and not associated to a pre-defined scheme. A vector x associated with the supply holes location is introduced in the design parameters and given in input to the optimizer.

An aerostatic pad with an internal pressure control

Because of their almost zero friction and wear, aerostatic pads are widely used in applications where very precise positioning is required. However, this kind of bearing suffers from poor damping and low specific stiffness. This paper presents a new compensation strategy to increase air pad stiffness. This method exploits a custom-built pneumatic valve which can be easily integrated with any commercial pad. The design and the working principle of the proposed system are described and studied with the aid of a lumped parameter model. The effectiveness of the proposed compensation is numerically and experimentally evaluated. The results demonstrate that the solution represents a good and cost-effective method to enhance the static stiffness of aerostatic pads.

An infinite stiffness aerostatic pad with a diaphragm valve

Abstract This work presents a prototype of a compensated aerostatic pad which consists in the integration of a commercial pad with a custom-built regulating pneumatic valve. The performance of the system is studied both in static and transient conditions. The stability and the capacity of compensation of the protype are proved performing step force tests. Moreover, the paper describes the lumped parameter model of the compensated pad. To take into account the compensating action of the valve, a distinctive numerical procedure was developed. Experimental and numerical results are in good agreement and demonstrate that once a suitable initial set-up is defined, the integrated regulating valve allows bearings with quasi-static infinite stiffness to be obtained.

Dynamic lumped model of externally pressurized rectangular air bearings

In this paper, a lumped mathematical model is introduced to study static and dynamic performances of rectangular aerostatic pads endowed of multiple inherent orifice type restrictors. The comparison of the results both with those of distributed parameters model and experimental data are discussed. Finally, a theoretical sensitivity analysis of the geometrical parameters on the pads behavior is carried out.

Dynamic Characterisation of Rectangular Aerostatic Pads with Multiple Inherent Orifices

Aerostatic pads are successfully employed in linear systems where very accurate and precise positioning is required, e.g. machine tools and measuring equipment. Both the static and dynamic performance of many different types of aerostatic pads have been already numerically and experimentally investigated. However, literature does not present so many works that investigate the performance of rectangular aerostatic pads with multiple restrictors, especially as regards their dynamic features. This paper shows an experimental and a numerical study of the static and dynamic performance of a rectangular aerostatic pad with multiple orifices distributed on a supply rectangle. The paper investigates the effect of the orifices diameter, of their position and of the supply pressure on the pad performance.

Numerical Simulation and Experimental Verification of the Stiffness and Stability of Thrust Pad Aerostatic Bearings

Many researchers concentrate on improving the stiffness and stability of aerostatic bearings, however the contradiction between stiffness and stability is still existed. Therefore, orifice, multiple, and porous restrictors are designed to illustrate the influence of restrictor characteristics on the stability and stiffness of the aerostatic circular pad bearings. Because both the stiffness and stability of aerostatic bearings are determined by the internal pressure distribution, the full Navier-Stokes (N-S) equations are applied to solve internal pressure distribution in bearing film by using computational fluid dynamics (CFD) method. Simulation results present that the stiffness and stability of aerostatic circular pad bearings are influenced significantly by geometrical and material parameters, such as film thickness, orifice diameters, and viscous resistance coefficient. Verified by the experimental data, the micro vibration of orifice restrictor is almost the same as multiple restrictors with amplitude of 0.02 m/s2, but it is much stronger than the porous restrictors with acceleration of 0.006 m/s2. The optimal stiffness of multiple restrictors increased by 46%, compared to only 30.2 N/μm of orifice restrictor, and the porous restrictors had obvious advantage in the small film thickness less than 6 μm where the optimal stiffness increased to 38.3 N/μm. The numerical and experimental results provide guidance for improving the stiffness and stability of aerostatic bearings.

CFD Analysis of a Simple Orifice-Type Feeding System for Aerostatic Bearings

A numerical analysis on the feeding system of externally pressurised gas bearings, for the correction of the theoretical mass flow rate formula by means of a discharge coefficient, is presented. A flat aerostatic pad with a simple orifice-type feeding system was chosen as case on study, the authors having previously carried out experimental tests on such a prototype. Using the commercial CFD code ANSYS Fluent®, preliminary simulations were carried out on a pad’s geometry using three different flow models. Having selected the flow model able to give the best prediction of the pad’s behaviour in terms of pressure distribution along the air film, additional simulations were carried out on pads with two different diameters of the supply hole, varying the film thickness in a range from 9 to 14 μm. A comparison between numerical and experimental results is presented. In addition, the effect of the flow intake used to perform experimental tests and of the shape of the orifice’s external edge on pressure distribution is analysed.

J114031 多連型空気静圧軸受パッドによるθ方向超精密位置決め機構の特性評価([J114-03]次世代アクチュエータシステム(3))

J114031 多連型空気静圧軸受パッドによるθ方向超精密位置決め機構の特性評価([J114-03]次世代アクチュエータシステム(3))