Initial levitation of an electrostatic bearing system without bias

The force analysis of a three-axis electrostatic bearing supporting a spherical rotor shows that classical linear control using linearization by a fixed bias necessitates the supporting lands due to highly nonlinear and coupled nature of electrostatic bearings. This paper proposes a suspension control without voltage bias to achieve a steady levitation of the rotor over the entire housing orientations for a class of electrostatic bearings without supports. A nonlinear controller which minimizes the cross-axis coupling is designed using a nonlinear model and feedback linearization techniques. A linear controller is then utilized for this linearized plant to stabilize the closed-loop system. The performance of the proposed nonlinear suspension control system is experimentally investigated on a three-degree freedom electrostatic bearing in the absence of supporting lands. The experimental results demonstrate that the rotor lift in an arbitrary orientation is realized with desired dynamic performance and global stability.