Patent ID: 7251098

Claim:
A disk drive comprising: (a) a disk comprising a plurality of tracks, wherein: each track comprises a plurality of data sectors and a plurality of servo sectors forming N servo wedges; and a wedge time period (WTP) occurs between each servo wedge; (b) a head actuated over the disk; and (c) a disk controller for: estimating a sinusoidal error in the WTP due to eccentricity in the disk rotating to generate an eccentricity compensation value associated with a target track and a target servo wedge; positioning the head over a target data sector within the target track, the target data sector being in proximity to the target servo wedge; setting a write clock frequency for the target data sector in response to the eccentricity compensation value; and writing data to the target data sector using the write clock frequency; wherein the disk controller estimates the sinusoidal error in the WTP by: (A) positioning the head over a selected one of the tracks; (B) calculating an estimated WTP according to: EST — WTP=RTP+â *cos(2 πk/N )+{circumflex over ( b )}*sin(2 πk/N ) wherein RTP is a reference time period corresponding to a nominal WTP, k is an index representing one of the servo wedges, and {â,{circumflex over (b)}} are adjustable coefficients; (C) estimating a wedge time error e(k) as the difference between the estimated WTP and the detected actual WTP; (D) adjusting the coefficients {â,{circumflex over (b)}} for generating the estimated WTP according to: â ( k+ 1)={circumflex over ( a )}( k )− G*e ( k )*cos(2 πk/N ) {circumflex over (b)} ( k+ 1)={circumflex over ( b )}( k )− G*e ( k )*sin(2 πk/N ) wherein G is a predetermined gain; and (E) repeating steps (B)–(D) at least once.