An ultrasonic levitation journal bearing able to control spindle center position

Abstract

A novel active non-contact journal bearing based on squeeze film levitation is presented. Two qualities distinguish the proposed design from the previous ones: significantly improved load capacity and the ability of precision spindle position control. Theoretical models to calculate load carrying forces induced by squeeze film ultrasonic levitation are studied and validated by experimental results. Dynamic behavior of the ultrasonic transducer is investigated using electro-mechanical equivalent circuit model. Levitation forces generated by each transducer are individually controlled by a state feedback controller with auto-resonant (self-excited) frequency control. Active control of the spindle center position is achieved with positioning accuracy of the spindle center in the range of 100 nm. The load capacity achieved by the proposed bearing is dramatically improved compared to previously reported approaches.