Magnetic-Aerostatic Hybrid Bearing for Mini-Type High-Speed Air Turbine Cartridge

Under the development trend of high speed and high efficiency, mini-type air turbines have been widely applied to high-speed dental handpieces for decades. Bearing is the key component deciding efficiency of mini-type air turbine. Friction, collision and wear are the main causes to let the traditional ball and roller bearing not be able to reach higher efficiency. Although aerostatic bearing can realize very small sliding friction, but its weak bearing characteristic limits its application. In our research, we combined a magnetic levitation bearing with an aerostatic bearing to create a novel magnetic-aerostatic hybrid bearing, which can significantly promote the mini-type air turbine in a dental handpiece to achieve a better high-speed performance. The aerostatic bearing undertakes the function of radial bearing, and the magnetic levitation is responsible for the thrust bearing. The aerostatic bearing utilizes a composite orifice form with a large depth to width aspect ratio that can be realized by simple machining process. Its radial arranged orifices provide the spindle a sufficient and uniform radial support with high pressured air film. In consideration of operational safety and size constraint of the dental handpiece, the passive magnetic levitation method with repulsive NdFeB magnet rings is adopted for the thrust bearing. For comprehending their characteristics of the aerostatic and the magnetic levitation bearings, the finite element analytical method is employed to investigate the relationship between system parameters and performance and also to deduce the optimal construction for the prototype development. Our developed magnetic-aerostatic hybrid bearing is also experimentally approved to be able to provide stable and sustainable bearing capacity under low air pressure condition.Copyright © 2011 by ASME