Head Pad Positioning Control System for Hard Disk Drives

High track densities and short access times have been achieved using an H¿ controller with a sector servo system. The authors studied the difference in control performance for a system designed using the weighted mixed-sensitivity problem and one designed using the four block problem. By designing a two-degrees-of-freedom controller using H2 optimal theory, fast seeking was realized. On applying these servo systems to a hard disk drive, ±0.2¿m head positioning accuracy and a 2.5 ms one-track seek time were achieved.