Coaxial Tilt Damping Coil With Additional Active Actuation Capabilities

This paper presents a tilt stabilization coil inside an exemplary high-speed bearingless disk drive. The coil is based on the passive, electrodynamic “Null-Flux” principle, where there are no coil currents and, thus, no losses when the rotor is nondeflected during rotation. The proposed conductor structure is then used as a means of active actuation on the rotor by energizing the coil actively for producing tilt torque. Modifying the structure geometrically into multiple, coaxial conductor loops which are energized with currents in the equal or opposing directions then allows producing additional axial forces and tilt torque with multiple degrees of freedom, depending on the coil design. Different connection possibilities allow the combination of active and passive characteristics. Simulation and measurement at prototype drives separately demonstrate the functioning of both, the passive stabilization and the active actuation principles.