Contactless Measurement Method for Hard Disk Drive Spindle Motor Impedance

The conventional method of measuring inductance involves using an RLC meter. Such a measurement method has limited accuracy due to the interference of back-electromotive force 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 the inductance profile of a spindle motor without the need for mechanical locking. The implementation involves using a dc electrical locking signal superpositioned with a pulse-measuring signal to perform the measurement. The dc locking signal is then made sweep to allow microstepping of the motor so that the inductance profile could be captured at all rotor positions. The proposed method is shown to be effective, supported by derivations and experimental results.