TABLE OF CONTENTS Takahiko Ono
Abstract. The position of the magnetic head of a hard disk drive used in a computer is a critical variable. This chapter considers the design of a hard disk drive system to achieve control of this critical variable. The control system is designed as the servo system required to maintain the position of the head over the desired track with an accuracy of 10% of the track pitch in the presence of the air turbulence caused by the disk rotation and the measurement noise.
A hard disk drive (HDD) is most widely used as a memory storage for saving data in a computer system. The inside view of a typical HDD system is illustrated in Figure 14.1. The basic components are one or more disks to store data, the swing arm to support the magnetic heads for reading and writing data, the voice coil motor (VCM) to actuate the swing arm and the electronic circuits for signal processing and interface. The disk is logically divided into concentric circles called tracks and each track is divided into small segments called sectors. The data is divided into pieces according to the sector size and recorded in the sectors on the same track or sometimes different tracks. When the HDD receives a request of reading or writing data from the operating system, the VCM rotates the swing arm and keeps the magnetic head over the desired track. In this time, the required accuracy in positioning the magnetic head...
