Masaaki Miyatake

Dynamic Characteristics of Aerostatic Porous Journal Bearings With a Surface-Restricted Layer

Aerostatic porous bearings have been successfully applied to various precision devices such as machine tools and measuring equipment to achieve a higher accuracy of motion. However, aerostatic porous bearings have a disadvantage in that they are prone to cause pneumatic hammer instability. Therefore, to avoid this instability, a surface-restricted layer that has permeability smaller than the bulk of the porous material is usually formed on the bearing surface. In this paper, the dynamic characteristics of aerostatic porous journal bearings that have a surface-restricted layer are investigated numerically and experimentally. The effects of permeability in bulk porous materials and of a surface-restricted layer on the bearing characteristics are discussed using two kinds of porous material: graphite and metal. It was confirmed that aerostatic porous metal bearings with relatively large permeability could achieve large values of dynamic stiffness and damping coefficients using a low permeability, surface-restricted layer.

Impulse-Load Dynamics of Squeeze Film Gas Bearings for a Linear Motion Guide

This paper deals with a noncontact moving table using squeeze-film gas bearings for a linear motion guide, and investigates the dynamic behavior of the moving table under impulse load, experimentally and numerically, to clarify the dynamic characteristics of a squeeze-film gas bearing. This squeeze bearing for a noncontact moving table uses piezoelectric actuators as an ultrasonic vibrator to make the bearing surface vibrate at the ultrasonic resonant frequency of the bearing plate. The squeeze-film pressure is generated in the gap beneath the vibrating bearing surface and can support the moving table without any contact. It was consequently found that the numerical calculation method presented in this paper could predict well the dynamic behavior of the moving table using the squeeze-film gas bearing under impulse load.

Instability of Herringbone Grooved Aerodynamic Floating Bush Bearings Flexibly Supported by Foils With Hemispherical Bumps

In this paper, a herringbone grooved aerodynamic floating bush bearing is proposed and the instability of a rigid rotor supported by the proposed bearings is investigated, numerically and experimentally. The proposed floating bush bearing is flexibly supported by three- or four-layered foils with hemispherical bumps. Accordingly, it is expected that the rigid rotor supported by the proposed bearings will be able to rotate stably at higher speeds compared with conventional herringbone grooved bearings which are rigidly mounted on housing. It was found that the proposed floating bush bearing with 6 mm in diameter can stably support a rotor at more than 0.6 million rpm.Copyright

Threshold Speed of Instability of a Herringbone-Grooved Rigid Rotor With a Bearing Bush Flexibly Supported by Straight Spring Wires

In recent years, small-size aerodynamic bearings for turbomachines such as blowers and compressors have attracted considerable attention for increasing rotational speed. These kinds of bearings require excellent stability at high speeds and durability in a high-temperature environment. Foil bearings are one of the most suitable candidates that can satisfy these requirements but their structure is very complicated, and it is difficult to control their manufacturing accuracy. It is well known that flexibly supported herringbone-grooved aerodynamic journal bearings have excellent stability at high speeds and they are relatively easy to manufacture compared with foil bearings. Moreover, their dynamic characteristics can be easily solved numerically. In this paper, a flexibly supported herringbone-grooved aerodynamic journal bearing using straight spring wires made of stainless steel is proposed to provide a simple and reliable support system for a bearing bush. Six straight spring wires were assembled into a hexagonal shape into which the bearing bush was inserted. The threshold speed of instability of the proposed aerodynamic bearing was investigated numerically and experimentally. For this investigation, the nonlinear orbit method was adopted in numerical calculations. This investigation found that straight spring wires could steadily support the bearing bush and provide a simple and reliable support system for the bearing bush and that a 6-mm-diameter rigid rotor with a mass of 4.8 g supported by the proposed aerodynamic journal bearings could stably rotate at speeds of more than 0.7 million rpm.Copyright

Static characteristics of small aerodynamic foil thrust bearings operated up to 350,000 r/min

Foil bearings have been attracting considerable attention for their application in achieving low power consumption in small-sized turbo machines, excellent stability at high speeds, and durability at high temperature. Foil bearings with bump foils are one of the most suitable candidates for these applications as indicated in recent studies. However, it was reported that current small foil thrust bearings had insufficient load capacity to support thrust forces in practical high-speed turbo machines, and were needed to improve the load capacity at high speeds. As a first step in improving the load capacity of small foil thrust bearings, the load capacity and rotational torque of this type of foil thrust bearings that operate at up to 350,000 r/min were investigated experimentally and numerically in this paper. In the numerical calculation, the Reynolds and elasticity equations for the top foil were solved simultaneously by using the finite difference and the finite element method, respectively. It was experimentally and numerically found that the foil thrust bearings treated in this paper have the load capacity coefficient of 5.36 × 10−6 N/(mm)3 kr/min, which was comparable to that of the second-generation foil thrust bearings.