Method and apparatus for determining modulated, amplitude ramping RRO harmonics in multi-screw clamped HDD disk/spind assembly

1. A method for determining harmonics of repeatable runout error during disk drive operation, such that correction of the error by feed forward techniques is facilitated, comprising:

using at least one algorithm to determine at least one RRO error harmonic based on a number of disk fasteners.

2. The method of claim 1 , further comprising using an output of the algorithm to establish a feed forward signal to a head positioning assembly to correct repeatable errors.

3. The method of claim 2 , wherein the algorithm is established at least in part by n+m=NS, 2NS, 3NS, . . . , wherein NS is the number of periodically-spaced fasteners, n is a wave number of disk deformation, and m is a harmonic number induced by the NS fasteners to cause the disk to deform with wave number equal to n.

4. The method of claim 2 , wherein the algorithm is established at least in part by the magnitude of |n−m|=NS, 2NS, 3NS, . . . , wherein NS is the number of periodically-spaced fasteners; n is a wave number of disk deformation, and m is a harmonic number induced by the NS fasteners to cause the disk to deform with wave number equal to n.

5. A hard disk drive, comprising:

at least one disk susceptible to RRO error;

at least one error correction circuit to cancel RRO error; and

at least one input representing algorithmically determined RRO error harmonics based on a number of fasteners used to hold the disk.

6. The disk drive of claim 5 , wherein the fasteners hold the disk to a spindle.

7. The disk drive of claim 5 , wherein the RRO error is determined by an algorithm established at least in part by n+m=NS, 2NS, 3NS, . . . , wherein n is a wave number, m is a harmonic number, and NS is the number of fasteners.

8. The disk drive of claim 5 , wherein the RRO error is determined by an algorithm established at least in part by the magnitude of |n−m|=NS, 2NS, 3NS, . . . , wherein n is a wave number, m is a harmonic number, and NS is the number of fasteners.

9. A system, comprising:

at least one disk;

an integer number of screws holding the disk to a rotating component;

at least one head positioning assembly positioning a head over a disk;

at least one error correction circuit controlling the head positioning assembly in response to an error signal; and

at least one error signal generation component generating the error signal at least in part based on the number of screws.

10. The system of claim 9 , wherein the error signal generation component uses at least one algorithm to generate the error signal, the error signal being an RRO error signal.

11. The system of claim 10 , wherein the RRO error signal is determined by an algorithm established at least in part by n+m=NS, 2NS, 3NS, . . . , wherein n is a wave number, m is a harmonic number, and NS is the number of fasteners.

12. The system of claim 10 , wherein the RRO error signal is determined by an algorithm established at least in part by the magnitude of |n−m|=NS, 2NS, 3NS, . . . , wherein n is a wave number, m is a harmonic number, and NS is the number of fasteners.

13. A data storage system, comprising:

means for determining harmonics of repeatable runout (RRO) error during disk drive operation to generate an error signal based on a number of disk fasteners; and

means for feeding forward the error signal to cancel the RRO error.

14. The system of claim 13 , wherein the means for determining at least in part uses n+m=NS, 2NS, 3NS, . . . , wherein n is a wave number, m is a harmonic number, and NS is the number of fasteners.

15. The system of claim 13 , wherein the means for determining at least in part uses the magnitude of |n−m|=NS, 2NS, 3NS, . . . , wherein n is a wave number, m is a harmonic number, and NS is the number of fasteners.