ABSTRACT
This chapter introduces the Hard Disk Drive (HDD) servo system and presents the components of a typical HDD that constitute the HDD servo system. It presents the modeling of the components and mechanical dynamics of the head-positioning control system in HDDs. Since a magnetic head in HDD is always affected by disturbances such as air flow or windage which causes Flow-Induced Vibration, modeling of disturbance is as important as modeling of the plant dynamics. In general, the modeling of mechanical resonant modes is performed based on matching both the gain and phase of the frequency response data measured from the Voice Coil Motor (VCM) current to the head position. In reality, the driver voltage is limited and the dynamics of the VCM are too complicated to be cancelled out by a zero of the compensator. Down-sampling the measurements and pre-filtering for identification of the low frequency modes are also other effective techniques from an engineering point of view.
