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

CFD based investigation on influence of orifice chamber shapes for the design of aerostatic thrust bearings at ultra-high speed spindles

Axis orientation stability of aerostatic bearing spindles has great influence on machining precision of ultra-precision fly cutting machines used for processing ultra-precision optical components of large diameter. Mid-spatial frequency errors (amplitude

Modeling of dynamic characteristic of the aerostatic bearing spindle in an ultra-precision fly cutting machine

Aerostatic bearings design and analysis with the application to precision engineering: State-of-the-art and future perspectives

Improvement on load performance of externally pressurized gas journal bearings by opening pressure-equalizing grooves

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.

Comparison between grooved and plane aerostatic thrust bearings: static performance

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

A test bench for rotors supported by air bearings floating on O-rings is designed in order to study the whirl phenomenon and characterize the stability threshold with damping elements mounted on bearings. The work includes a description of the test bench and some preliminary experimental results. A rotor of 1 kg mass and 37 mm diameter is rotated up to 75,000 rpm by an air turbine machined on the rotor. Capacitance probes, placed in two radial planes, allow orbit scanning of both the rotor and the bushing at different rotating speeds and suitable load devices permit measurement of the static and dynamic stiffness of the rotor-bearing system. Curves of rotational response using rubber O-rings of three different materials are shown and compared. Also presented are the Fourier spectra of the signals for rotor displacement. The phenomenon of whirl instability is shown in terms of whirl frequency and orbit amplitudes of the rotor and bearings. The effects of both supply pressure and angular velocity on the stability threshold are shown.

High-Speed Rotor With Air Bearings Mounted on Flexible Supports : Test Bench and Experimental Results

Externally pressurized grooved gas thrust bearings for shaft systems were studied both numerically and experimentally. Three thrust bearings composed of a symmetric pair of rings facing a shaft collar were tested. The rings, with inner and outer diameters of 52 and 110 mm, respectively, are equipped with a polar array of eight holes, with a 0.35-mm diameter, distributed on a 65-mm-diameter circumference. The influence of a circumferential groove situated in correspondence with the supply holes is discussed. In particular, two thrust bearings have a rectangular cross-sectional groove of 0.7-mm width and 10- and 20-μm depth. A numerical model based on Reynolds' equation is used to study thrust-bearing performance in relation to geometry (diameter of supply holes, clearance, and groove dimensions). A test rig is used to monitor thrust-bearing axial load capacity and stiffness, and evaluate damping and stability at different supply pressure rates. Experimental and numerical results are compared and discussed.

Federico Colombo

Papers

Comparison between grooved and plane aerostatic thrust bearings: static performance

Aerostatic thrust bearings active compensation: Critical review

High-Speed Rotor With Air Bearings Mounted on Flexible Supports : Test Bench and Experimental Results

Performance of Externally Pressurized Grooved Thrust Bearings

Externally pressurized gas bearings: A comparison between two supply holes configurations