Contactless measurement method for HDD spindle motor parameters

Conventional method of measuring inductance involves using a R-L-C meter. Such measurement method has limitation on accuracy due to the interference of back EMF during rotation. Profiling of the inductance at various motor positions thus requires cumbersome mechanical locking of the rotor. In this paper, an elegant method is introduced to capture inductance profile of spindle motor without the need for mechanical locking. The method involves using a DC electrical locking signal super-positioned with a pulse measuring signal to perform the measurement. The DC locking signal is then made sweep to allow micro-stepping of the motor so that inductance profile could be captured at all rotor position. The proposed method is shown to be effective, supported by derivations and experimental results.