Acoustic journal bearing – Performance under various load and speed conditions

Abstract

Traditional non-contact bearings, such as air bearings (aerostatic and aerodynamic) and magnetic bearings are commonly used in a number of practical specialist applications. However, magnetic bearings are unacceptable where a strong magnetic flux is harmful to the surrounding environment while a continuous supply of a large volume of clean air, never sufficiently clean for food and medical applications, from external auxiliary devices is required for air bearings (for example batteries of drilling spindles used in mass scale manufacturing), which increases the cost of their use. Also, aerodynamic air bearings are known to become unstable when lightly loaded and operating at high speeds. Therefore, alternative and radically new concepts, such as acoustic bearings, offer an exciting solution. Acoustic levitation, being at the heart of an acoustic bearing concept, uses an acoustic wave to exert a force on objects immersed in the wave field. These forces are normally weak but can become quite large when using high frequency and high intensity waves, large enough to suspend substances against gravity force. Ultrasonic levitation (frequencies higher than 20 kHz) has been used initially for levitating small objects using a standing wave field between a sound radiator and a reflector. In standing wave acoustic levitation, the size of the levitated object is limited to less than a wavelength. Standing wave type ultrasonic levitators have been *Manuscript Click here to view linked References designed for applications in various scientific disciplines such as material processing and space engineering [1]. Kundt's in his tube experiment [2] in 1866, in which small dust particles moved towards the pressure nodes of a standing wave created in a horizontal tube, was the first to observe standing wave levitation. The first detailed theoretical description of standing wave levitation was given by King [3] in 1934, which was extended by Hasegawa [4] to include the effects of compressibility. Embleton [5] adopted King's approach to fit to the case of a rigid sphere in a progressive spherical or cylindrical wave field. Westervelt [6,7,8] derived a general expression for the force owing to radiation pressure acting on an object of arbitrary shape and normal boundary impedance to show that a boundary layer with a high internal loss can lead to forces that are several orders of magnitude greater than those predicted by the classical theory. Another type of levitation is the squeeze-film (or near field acoustic) levitation in which an object (not limited by wavelength) is brought very close to a radiation surface vibrating at high frequency. The gap is smaller than the wavelength of the generated sound, which means that the standing wave is replaced by a gas film with pressure that varies according to the motion of the radiation surface. Squeeze film levitation can carry higher loads than standing wave levitation and has been widely investigated for building non-contact linear and rotational bearings [9-13]. A contribution to the analys...

Experimental Verification of the CFD Model of the Squeeze Film Lifting Effect

“…The deforming part was a deformable bush allowing for frictionless rotation of the shaft. Later, operational conditions of such and a new configuration were studied [8,9].…”

Prediction of Load-Carrying Capacity in the Radial Direction for Piezoelectric-Driven Ultrasonic Bearings

“…The equation set that consists of Eq. (19) and Eq. 20is solved, and the pressure difference p is obtained.…”

“…A good surface finishing and form accuracy are also important for a squeeze film levitation system to achieve higher levitation capacity [15], [16]. Stolarski et al [17], [19] and Stolarski [18] established a modified three-dimensional Reynolds equation for an aerodynamic bearing to investigate its suspended rotor's trajectory changing rule under the perturbation and validated the suspending force's influence on the bearing's running stability. For bearings with complex structures such as ball-shaped bearing used in the gyroscope, the finite element softwares (ANSYS or COMSOL) are generally used to study the ultrasonic bearing's levitation characteristics [20].…”

Suspending force modeling based on nonlinear acoustics and high-speed running experiments for an ultrasonic journal bearing

“…The running performance at high speeds can reflect the bearing's dynamic suspending characteristics. Stolarski and colleagues [25][26][27] established a modified three-dimensional Reynolds equation for an aerodynamic bearing to investigate its suspended rotor's trajectory changing rule under the perturbation and validate the suspending force's influence on the bearing's running stability. For bearings with complex structures such as ball-shaped bearing used in the gyroscope, the finite element software (ANSYS or COMSOL) is generally used to study the ultrasonic bearing's suspending characteristics.…”