Novel NRRO minimization algorithm for an ultra-high-density servo track writer

Since the introduction of magnetoresistive (MR) heads, the areal density of hard disk drives (HDDs) has been increasing at a rate around 60% a year, and the track density is increasing at roughly half that rate. The servo track writer (STW), which is used to write accurate servo patterns for head positioning on the surfaces of disks in the HDD, is a key instrument in this regard. A novel algorithm for the STW of the sector-servo architecture, using an accurate air-bearing motor and rotary-positioner, and a repeatable runout (RRO) compensation method, is proposed in order to minimize the effects of nonrepeatable runout (NRRO) components, which are generated by a spindle motor and other mechanical components of the HDD, and have a dominant influence in retarding track density growth.