Recent control technologies for fast and precise servo system of hard disk drives

Areal density increases are required to satisfy the demand for larger capacity hard disk drives. Furthermore, the increase of the track density is expected to be larger than that of bit density due to several reasons of magnetic recording and data transfer problems. By 2001, it is expected that track pitch will have reduced to 0.4 /spl mu/m. To accomplish this, a head-positioning accuracy of 35-40 nm must be achieved during track-following, which is 8-10% of the track pitch. In the paper, several servo methods including multirate feedforward control methods, and the use of servo systems for dual stage actuators, are reviewed. Then our latest research results on a mode-switching control servo are shown.