Disk drive employing repeatable disturbance compensation for fly height control
View Patent ↗A disk drive is disclosed comprising a disk, a head actuated over the disk, and control circuitry operable to generate a fly height control signal. A fly height of the head is measured, and the measured fly height is combined with a target fly height and a feedforward signal, wherein the feedforward signal is generated according to: a 1 ·cos(2πn 1 k/N)+b 1 ·sin(2πn 1 k/N) where a 1 and b 1 are coefficients and 2πn 1 k/N represents a frequency of a repeatable disturbance in the fly height of the head.
1. A disk drive comprising:
a disk;
a head actuated over the disk; and
control circuitry operable to generate a fly height control signal by:
measuring a fly height of the head; and
combining the measured fly height with a target fly height and a first feedforward signal, wherein the first feedforward signal is generated according to:
a 1 ·cos(2πn 1 k/N)+b 1 ·sin(2πn 1 k/N)
where a 1 and b 1 are coefficients and 2πn 1 k/N represents a frequency of a first repeatable disturbance in the fly height of the head.
2. The disk drive as recited in claim 1 , wherein:
N represents a number of discrete time intervals over a rotation of the disk;
the first feedforward signal is updated at each time interval; and
k represents the current time interval.
3. The disk drive as recited in claim 2 , wherein:
the disk comprises a plurality of tracks;
each track comprises N servo sectors; and
the first feedforward signal is updated at each servo sector.
4. The disk drive as recited in claim 1 , wherein n 1 is a multiple of a once around frequency of the disk.
5. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to adapt the coefficients according to:
a 1 ( k+ 1)= a 1 ( k )− g 1 ·e ( k )·cos(2π n 1 k/N )
b 1 ( k+ 1)= b 1 ( k )− g 1 ·e ( k )·sin(2π n 1 k/N )
where g 1 is a gain and e(k) comprises a difference between the measured fly height and the target fly height.
6. The disk drive as recited in claim 5 , wherein the control circuitry is further operable to adapt the coefficients according to:
a 1 ( k+ 1)= a 1 ( k )− g 1 ·e ( k )·cos(2π n 1 k/N+φ 1 )
b 1 ( k+ 1)= b 1 ( k )− g 1 ·e ( k )·sin(2π n 1 k/N+φ 1 )
where φ 1 represents a phase of the first repeatable disturbance.
7. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to generate a fly height control signal by:
combining the measured fly height with the target fly height, the first feedforward signal, and a second feedforward signal, wherein the second feedforward signal is generated according to:
a 2 ·cos(2πn 2 k/N)+b 2 ·sin(2πn 2 k/N)
where a 2 and b 2 are coefficients and 2πn 2 k/N represents a frequency of a second repeatable disturbance in the fly height of the head.
8. The disk drive as recited in claim 7 , wherein the control circuitry is further operable to adapt the coefficients according to:
a 2 ( k+ 1)= a 2 ( k )− g 2 ·e ( k )·cos(2π n 2 k/N )
b 2 ( k+ 1)= b 2 ( k )− g 2 ·e ( k )·sin(2π n 2 k/N )
where g 2 is a gain and e(k) comprises a difference between the measured fly height and the target fly height.
9. The disk drive as recited in claim 8 , wherein the control circuitry is further operable to adapt the coefficients according to:
a 2 ( k+ 1)= a 2 ( k )− g 2 ·e ( k )·cos(2π n 2 k/N+φ 2 )
b 2 ( k+ 1)= b 2 ( k )− g 2 ·e ( k )·sin(2π n 2 k/N+φ 2 )
where φ 2 represents a phase of the first repeatable disturbance.
10. The disk drive as recited in claim 7 , wherein:
n 1 is a first multiple of a once around frequency of the disk;
n 2 is a second multiple of the once around frequency of the disk; and
n 2 is greater than n 1 .
11. A method of generating a fly height control signal in a disk drive, the disk drive comprising a disk, and a head actuated over the disk, the method comprising:
measuring a fly height of the head; and
combining the measured fly height with a target fly height and a first feedforward signal, wherein the first feedforward signal is generated according to:
a 1 ·cos(2πn 1 k/N)+b 1 ·sin(2πn 1 k/N)
where a 1 and b 1 are coefficients and 2πn 1 k/N represents a frequency of a first repeatable disturbance in the fly height of the head.
12. The method as recited in claim 11 , wherein:
N represents a number of discrete time intervals over a rotation of the disk;
the first feedforward signal is updated at each time interval; and
k represents the current time interval.
13. The method as recited in claim 12 , wherein:
the disk comprises a plurality of tracks;
each track comprises N servo sectors; and
the first feedforward signal is updated at each servo sector.
14. The method as recited in claim 11 , wherein n 1 is a multiple of a once around frequency of the disk.
15. The method as recited in claim 11 , further comprising adapting the coefficients according to:
a 1 ( k+ 1)= a 1 ( k )− g 1 ·( k )·cos(2 πn 1 k/N )
b 1 ( k+ 1)= b 1 ( k )− g 1 ·e ( k )·sin(2 πn 1 k/N )
where g 1 is a gain and e(k) comprises a difference between the measured fly height and the target fly height.
16. The method as recited in claim 15 , further comprising adapting the coefficients according to:
a 1 ( k+ 1)= a 1 ( k )− g 1 ·e ( k )·cos(2 πn 1 k/N+φ 1 )
b 1 ( k+ 1)= b 1 ( k )− g 1 ·e ( k )·sin(2 πn 1 k/N+φ 1 )
where φ 1 represents a phase of the first repeatable disturbance.
17. The method as recited in claim 11 , further comprising:
combining the measured fly height with the target fly height, the first feedforward signal, and a second feedforward signal, wherein the second feedforward signal is generated according to:
a 2 ·cos(2πn 2 k/N)+b 2 ·sin(2πn 2 k/N)
where a 2 and b 2 are coefficients and 2πn 2 k/N represents a frequency of a second repeatable disturbance in the fly height of the head.
18. The method as recited in claim 17 , further comprising adapting the coefficients according to:
a 2 ( k+ 1)= a 2 ( k )− g 2 ·e ( k )·cos(2 πn 2 k/N )
b 2 ( k+ 1)= b 2 ( k )− g 2 ·e ( k )·sin(2 πn 2 k/N )
where g 2 is a gain and e(k) comprises a difference between the measured fly height and the target fly height.
19. The method as recited in claim 18 , further comprising adapting the coefficients according to:
a 2 ( k+ 1)= a 2 ( k )− g 2 ·e ( k )·cos(2π n 2 k/N+φ 2 )
b 2 ( k+ 1)= b 2 ( k )− g 2 ·e ( k )·sin(2 πn 2 k/N+φ 2 )
where φ 2 represents a phase of the first repeatable disturbance.
20. The method as recited in claim 17 , wherein:
n 1 is a first multiple of a once around frequency of the disk;
n 2 is a second multiple of the once around frequency of the disk; and
n 2 is greater than n 1 .