ABSTRACT

This chapter discusses functions and principle of operations of different components of the hard disk drive (HDD) servomechanism, explains sources of noise and disturbances, and presents the basic guidelines for design of controller. Accurate and precise control of radial position of the head slider is done by the head positioning servomechanism. This servomechanism is a feedback system consisting of a sensing element that measures the displacement of the head, a servo motor and actuator, an amplifier, and a controller controlling the movement of the actuator. The HDD servomechanism is a unique example of practical applications that demonstrate the degree of precision achieved in a mechatronics system. The head positioning servomechanism moves the read/write head as fast as possible from one track to another when asked by the host system. In the head positioning servomechanism of HDD, position feedback is obtained from the readback signal produced by sensing special magnetic patterns written on the disks.