Spindle Motor With Active Electromagnetic Damping

摘要

In general, a spindle motor can be characterised as a rotational inertia mounted on a pair of flexible bearing support. For the case of ball bearings, the mechanical damping of the supports is very small. This leads to a resonant mechanical system: the spin axis of the rotational inertia is subject to some resonant movement. In disc drive application, the gyroscopic modes are the resonant motion with magnitude high enough to cause head positioning errors. This paper shows that the magnitude of these oscillations can be reduced by adding an active system in parallel to the standard mounting. This paper first describe the principle of active damping through a theoretical example. An impact applied on the disc is simulated with and without additional damping. Finally a practical set-up of an active damping system is described in a disc drive application. The spindle motor itself is used as an actuator to generate the damping forces. The measured response to an impact applied on the disc is compared with and without active damping. The results show consequent improvement. The measured resonant oscillation following the impact last more than 8 revolutions for the standard mounting of the spindle motor. With the developed active damping, the resonant oscillation lasts less than 1 revolution.