Disk drive selecting TPI profile by estimating head geometry

1. A disk drive comprising:

a disk;

a head actuated radially over the disk; and

control circuitry operable to:

position the head over a first radial location;

select a first data tracks per inch (TPI_ 1 ) for data tracks recorded near the first radial location;

position the head over a second radial location;

select a second data tracks per inch (TPI_ 2 ) for data tracks recorded near the second radial location;

position the head over a third radial location;

select a third data tracks per inch (TPI_ 3 ) for data tracks recorded near the third radial location; and

estimate a geometry of the head in response to TPI_ 1 , TPI_ 2 and TPI_ 3 ,

wherein:

the first radial location is near a middle diameter of the disk;

the second and third radial locations are near one of an inner diameter of the disk and an outer diameter of the disk;

the head comprises a write width WW 0 estimated according to 1/(TPI_ 1 ·cos αs 1 ), where αs 1 is a head skew angle at the first radial location;

the head further comprises a bevel angle α and a pole height H;

the bevel angle α and the pole height H are estimated according to a two variable equation:

TPI — 2=[WW 0 ·cos·(α s 2 )+ H ·sin(α s 2 −α)/cos(α)] −1

TPI — 3=[WW 0 ·cos·(α s 3 )+ H ·sin(α s 3 −α)/cos(α)] −1

where:

αs 2 is a head skew angle at the second radial location;

αs 3 is a head skew angle at the third radial location; and

α and H are computed by solving the two variable equation in response to TPI_ 2 and TPI_ 3 .

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

the head further comprises a bevel angle αod and a pole height Hod corresponding to an inner edge of the head;

the bevel angle αod and the pole height Hod are estimated according to a two variable equation:

TPI — 2=[WW 0 ·cos·(α s 2 )+ Hod ·sin(α s 2 −αod )/cos(α od )] −1

TPI — 3=[WW 0 ·cos·(α s 3 )+ Hod ·sin(α s 3 −αod )/cos(α od )] −1

where:

αs 2 is a head skew angle at the second radial location;

αs 3 is a head skew angle at the third radial location; and

αod and Hod are computed by solving the two variable equation in response to TPI_ 2 and TPI_ 3 .

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

the head further comprises a bevel angle αid and a pole height Hid corresponding to an outer edge of the head;

the bevel angle αid and the pole height Hid are estimated according to a two variable equation:

TPI — 2=[WW 0 ·cos·(α s 2 )+ Hid ·sin(α s 2 −αid )/cos(α id )] −1

TPI — 3=[WW 0 ·cos·(α s 3 )+ Hid ·sin(α s 3 −αid )/cos(α id )] −1

where:

αs 2 is a head skew angle at the second radial location;

αs 3 is a head skew angle at the third radial location; and

αid and Hid are computed by solving the two variable equation in response to TPI_ 2 and TPI_ 3 .

4. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to select a TPI profile across the radius of the disk in response to the estimated geometry of the head.

5. A disk drive comprising:

a disk;

a head actuated radially over the disk; and

control circuitry operable to:

position the head over a first radial location;

select a first data tracks per inch (TPI_ 1 ) for data tracks recorded near the first radial location;

position the head over a second radial location;

select a second data tracks per inch (TPI_ 2 ) for data tracks recorded near the second radial location;

position the head over a third radial location;

select a third data tracks per inch (TPI_ 3 ) for data tracks recorded near the third radial location;

estimate a geometry of the head in response to TPI_ 1 , TPI_ 2 , and TPI_ 3 ; and

select at least one of TPI_ 1 , TPI_ 2 and TPI_ 3 by:

writing data to a plurality of victim data tracks, wherein each victim data track is separated by at least one aggressor data track;

reading the victim data tracks and measure a first bit error rate of the victim data tracks;

writing data to the aggressor data tracks; and

reading the victim data tracks and measure a second bit error rate of the victim data tracks.

6. A method of estimating a geometry of a head in a disk drive, the disk drive comprising a disk, and the head actuated over the disk, the method comprising:

positioning the head over a first radial location;

selecting a first data tracks per inch (TPI_ 1 ) for data tracks recorded near the first radial location;

positioning the head over a second radial location;

selecting a second data tracks per inch (TPI_ 2 ) for data tracks recorded near the second radial location;

positioning the head over a third radial location;

selecting a third data tracks per inch (TPI_ 3 ) for data tracks recorded near the third radial location; and

estimating the geometry of the head in response to TPI_ 1 , TPI_ 2 and TPI_ 3 ,

wherein:

the first radial location is near a middle diameter of the disk;

the second and third radial locations are near one of an inner diameter of the disk and an outer diameter of the disk;

the head comprises a write width WW 0 estimated according to 1/(TPI_ 1 ·cos αs 1 ), where αs 1 is a head skew angle at the first radial location:

the head further comprises a bevel angle α and a pole height H;

the bevel angle α and the pole height H are estimated according to a two variable equation:

TPI — 2=[WW 0 ·cos·(α s 2 )+ H ·sin(α s 2 −a )/cos(α)] −1

TPI — 3=[WW 0 ·cos·(α s 3 )+ H ·sin(α s 3 −α)/cos(α)] −1

where:

αs 2 is a head skew angle at the second radial location;

αs 3 is a head skew angle at the third radial location; and

α and H are computed by solving the two variable equation in response to TPI_ 2 and TPI_ 3 .

7. The method as recited in claim 6 , wherein:

the head further comprises a bevel angle αod and a pole height Hod corresponding to an inner edge of the head;

the bevel angle αod and the pole height Hod are estimated according to a two variable equation:

TPI — 2=[WW 0 ·cos·(α s 2 )+ Hod ·sin(α s 2 −aod )/cos(α od )] −1

TPI — 3=[WW 0 ·cos·(α s 3 )+ Hod ·sin(α s 3 −aod )/cos(α od )] −1

where:

αs 2 is a head skew angle at the second radial location;

αs 3 is a head skew angle at the third radial location; and

αod and Hod are computed by solving the two variable equation in response to TPI_ 2 and TPI_ 3 .

8. The method as recited in claim 6 , wherein:

the head further comprises a bevel angle αid and a pole height Hid corresponding to an outer edge of the head;

the bevel angle αid and the pole height Hid are estimated according to a two variable equation:

TPI — 2=[WW 0 ·cos·(α s 2 )+ Hid ·sin(α s 2 −αid )/cos(α id )] −1

TPI — 3=[WW 0 ·cos·(α s 3 )+ Hid ·sin(α s 3 −αid )/cos(α id )] −1

where:

αs 2 is a head skew angle at the second radial location;

αs 3 is a head skew angle at the third radial location; and

αid and Hid are computed by solving the two variable equation in response to TPI_ 2 and TPI_ 3 .

9. The method as recited in claim 6 , further comprising selecting a TPI profile across the radius of the disk in response to the estimated geometry of the head.

10. A method of estimating a geometry of a head in a disk drive, the disk drive comprising a disk, and the head actuated over the disk, the method comprising:

positioning the head over a first radial location;

selecting a first data tracks per inch (TPI_ 1 ) for data tracks recorded near the first radial location;

positioning the head over a second radial location;

selecting a second data tracks per inch (TPI_ 2 ) for data tracks recorded near the second radial location;

positioning the head over a third radial location;

selecting a third data tracks per inch (TPI_ 3 ) for data tracks recorded near the third radial location; and

estimating the geometry of the head in response to TPI_ 1 , TPI_ 2 and TPI_ 3 ,

wherein:

the first radial location is near a middle diameter of the disk;

the second and third radial locations are near one of an inner diameter of the disk and an outer diameter of the disk; and

selecting at least one of TPI_ 1 , TPI_ 2 and TPI_ 3 comprises:

writing data to a plurality of victim data tracks, wherein each victim data track is separated by at least one aggressor data track;

reading the victim data tracks and measure a first bit error rate of the victim data tracks;

writing data to the aggressor data tracks; and

reading the victim data tracks and measure a second bit error rate of the victim data tracks.