Disk drive estimating a sinusoidal error in a wedge time period due to eccentricity in disk rotation

1. 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 by:

(i) positioning the head over a selected one of the tracks;

(ii) 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;

(iii) detecting an actual WTP by detecting an interval between the head passing over a first and second servo wedge;

(iv) estimating a wedge time error e(k) as the difference between the estimated WTP and the detected actual WTP;

(v) adjusting the coefficients {â,{circumflex over (b)}} for generating the estimated WTP according to:

â ( k+ 1)= â ( 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

(vi) repeating steps (ii)–(v) at least once.

2. The disk drive as recited in claim 1 , wherein the disk controller repeats steps (ii)–(v) until the wedge time error e(k) falls below a predetermined threshold.

3. The disk drive as recited in claim 1 , wherein:

(a) each servo sector comprises a servo sync mark;

(b) the disk controller controls a wedge period counter in response to the coefficients {â,{circumflex over (b)}}; and

(c) the disk controller opens a sync mark detection window in response to the wedge period counter indicating the head is approaching a servo sync mark in a servo sector.

4. A method of estimating a sinusoidal error in a wedge time period (WTP) in a disk drive due to eccentricity in a disk rotating, the disk drive comprising the disk having a plurality of tracks, wherein each track comprises a plurality of data sectors and a plurality of servo sectors forming N servo wedges, wherein the WTP occurs between each servo wedge, the disk drive further comprising a head actuated over the disk, the method comprising the steps of:

(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) detecting an actual WTP by detecting an interval between the head passing over a first and second servo wedge;

(d) estimating a wedge time error e(k) as the difference between the estimated WTP and the detected actual WTP;

(e) adjusting the coefficients {â,{circumflex over (b)}} for generating the estimated WTP according to:

â ( k+ 1)= â ( 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

(g) repeating steps (b)–(e) at least once.

5. The method as recited in claim 4 , wherein steps (b)–(e) are repeated until the wedge time error e(k) falls below a predetermined threshold.

6. The method as recited in claim 4 , wherein each servo sector comprises a servo sync mark, further comprising the steps of:

(a) controlling a wedge period counter in response to the coefficients {â,{circumflex over (b)}}; and

(b) opening a sync mark detection window in response to the wedge period counter indicating the head is approaching a servo sync mark in a servo sector.