Design and experimental study on an ultrasonic bearing with bidirectional carrying capacity

Based on near-field acoustic levitation effect and piezoelectric drive theory, an ultrasonic bearing prototype with bidirectional carrying capability is designed and fabricated which is actuated by piezoelectric transducers. The ultrasonic bearing is able to support radial and axial loads simultaneously. Its axial load-carrying capacity relies on acoustic levitation force generated by the bearing lateral surfaces’ vibration. Its radial load capacity is derived from two parts: the acoustic levitation force excited by the bearing inner ring's vibration and the hydrodynamic pressure caused by high-speed rotation of the rotor. The axial and radial levitation force models are established to predict the bearing's load-carrying capacity. The starting friction torque of the bearing is about 1.76 μNm, and the running friction torque is less than 120 μNm when the bearing runs at a speed of 20,000 r/min. In the running performance experiments, the bearing shows good stability in rising and reduction stage within its limiting speed.