Determination of the static characteristics of air bearings constitutes the necessary first phase in a design problem, which determines general feasibility. In order to realize a successful application, a good knowledge and assessment of the dynamic behaviour is needed to complement the previous step. In a conventional, passive bearing application, dynamically stable behaviour should be ensured by overcoming the occurrence of self-excited vibrations; the so-called “pneumatic hammering”. In active bearing applications, on the other hand, the dynamic bearing force, induced by actuation of the gap geometry or supply pressure, provides for a means of enhancing bearing static and dynamic performance, when integrated in a mechatronics system context. This paper presents on the one hand an overview of the methods used to model the dynamic characteristics of aerostatic films, deducing that the method of harmonic perturbation is often sufficient in providing a good estimate of the dynamic stiffness. This is confirmed by comparing theoretical results with dynamic response experiments. On the other hand, the general problem of active dynamic compensation is outlined and an application example is provided to show the high levels of performance achievable by employing this method.

/pdf/on-the-modelling-of-the-dynamic-characteristics-of-314iwh6sg8.pdf

On the modelling of the dynamic characteristics of aerostatic bearing films: From stability analysis to active compensation

Research and applications of active bearings: A state-of-the-art review

\n This paper offers an extensive review of publications dealing with the modeling, the design, and the experimental investigation of grooved dynamic gas-lubricated bearings. Recent years have witnessed a rise in small-scale and high-speed turbomachinery applications. Besides the well-known gas foil bearings, grooved bearings offer attractive advantages, which unveil their potential in particular at small scale due to the structural simplicity as well as satisfying predictability. This paper starts with a general background of the application of gas-lubricated bearings and introduces and compares the different gas bearing topologies. Further, the state-of-the-art modeling of grooved gas-lubricated bearings is introduced, systematically assessing the advantages and inconveniences of two major approaches, i.e., the narrow groove theory (NGT) and direct discretization method. Since the NGT method is an elegant and efficient approach to model the complex effects of periodic grooves, a critical section is dedicated to the NGT. In a second phase, different models to include additional physical phenomena such as real gas lubrication, rarefaction, or turbulence effects are reviewed. The paper concludes with a critical assessment of the state-of-the-art and indicates potential fields of research that would allow to shed more light into the understanding of these bearings, as well as with some thoughts on the integrated design methodologies of gas bearing supported rotors.

/pdf/a-review-of-grooved-dynamic-gas-bearings-4fby4om92v.pdf

A Review of Grooved Dynamic Gas Bearings

An active control method for aerostatic bearings is proposed in this paper. The proposed method employs an active inherent restrictor AIR, (which was invented by the authors) to control pneumatic pressure on the bearing surface. The AIR consists of a piezoelectric actuator with a through hole, one end of which is small enough to function as an orifice when the actuator is embedded in the bearing to be controlled. Nine AIRS are incorporated into the aerostatic radial and thrust bearings of an air bearing spindle. According to the radial and/or thrust displacements of the spindle detected by sensors, a microcomputer changes the length of the piezoelectric actuators for controlling the orifice area of the AIRs and for compensating the displacements. Thus, the stiffness and the rotational accuracy in both radial and thrust directions can be improved without the occurrence of pneumatic hammer. Instead of ordinary passive inherent restrictors, the AIR can be incorporated into most conventional aerostatic bearings. An example of retrofit of the AIR to a commercially available air bearing spindle is also shown.

Active inherent restrictor for air-bearing spindles

Aero-static thrust bearings are widely used in high precision conventional applications, e.g., in machine tools, measuring instruments, precise positioning systems, manufacturing and medical equipment. Their appeal is due to the absence of contact between moving and stationary parts, which ensures their low friction, limited heat generation and long life. Moreover, the use of air bearings usually does not contribute to the environmental contamination. However, aerostatic thrust bearings have usually lower stiffness and load capacity than rolling or oil bearings. For this reason, active and passive compensation are currently used to enhance these properties, thus extending the bearing's operating range. Recently, active compensation methods have become more popular thanks to improvements in mechatronics technology, and because they can provide the very high accuracy required by current high precision applications. This paper reviews the state of the art of the active compensation method and provides general classification criteria, outlining dissimilarities and the pros and cons of the available solutions. The paper concludes with several considerations and comments regarding the main performance features of each solution.

Aerostatic thrust bearings active compensation: Critical review

The optimum geometries of disk and cylindrical sprial groove viscous pumps to provide the maximum pressure or flow rate are investigated theoretically. The geometrical design parameters, such as the groove angle, groove to ridge clearance ratio, groove width ratio and ridge clearance ratio, are considered as functions of meridional coordinate. Results are obtained from the solution of a differential equation for the smoothed overall pressure distribution of a spiral groove viscous pump. It is found that outflow rate increases with the increase of groove to ridge clearance ratio λ, and that for each value of λ there exist “optimum” values of groove angle and groove width ratio, which give a maximum outflow rate. However, the increase of λ decreases the ridge clearance.

The Optimum Groove Geometry for Spiral Groove Viscous Pumps

Caracteristiques dynamiques d'un palier de butee aerostatique avec des restrictions de section reglable

Dynamic Characteristics of Hydrostatic Thrust Air Bearing With Actively Controlled Restrictor

Stability Characteristics of a Journal Bearing Mounted in an Uncentralized Squeeze Film Damper

Fluid Inertia Effects on the Load Capacity of Spherical Spiral Groove Bearings

Etude theorique d'une pompe a disques avec des patins de Rayleigh en tenant compte de la compressibilite du fluide

Analysis of Viscous Pumps With Shrouded Rayleigh-Steps Using Compressible Fluid

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