Characterization and Compensation of Disturbances Caused by Head-Disk Contact in Hard Disk Drives

Decreased head-disk spacing introduces a new set of disturbances to the servo system due to intermittent contact between the head and disk. These disturbances must be compensated to ensure proper operation of the hard disk drive. Measurements show that as the nominal head-disk separation is decreased, the first effect is an increase in the repeatable runout. This behavior is consistent with disturbance sources that are fixed to the disk. A repetitive controller is implemented that effectively compensates for the contact-induced disturbances.