Magnetic disk drive and method for efficiently determining and storing RRO compensation values using a secondary micro-actuator

1. A method for determining and writing repeatable runout (RRO) compensation value sets for data tracks on a magnetic disk in a disk drive, the disk drive having the disk, an actuator arm, a voice coil motor (VCM) for rotating the actuator arm about a pivot, a magnetoresistive (MR) head having a read element and a separate write element, and a secondary actuator coupled to a distal end of the actuator arm for adjusting a skew angle for the head, wherein each data track comprises a plurality of embedded servo sectors that define a circumferential path having repeatable runout error, the method comprising:

track following along a first data track;

setting the skew angle for the MR head using the secondary actuator such that the read element and the write element are substantially aligned along the first data track;

determining a position error signal for each servo sector over a predetermined number of disk revolutions;

calculating a repeatable runout compensation value set for the first data track based on the position error signals determined by track following along the first data track;

continuing the step of track following along the first data track while writing the repeatable runout compensation value set for the first data track; and

performing a seek operation to a second data track.

2. A method for determining and writing repeatable runout (RRO) compensation value sets as defined in claim 1 , wherein the secondary actuator comprises a piezo-microactuator.

3. A method for determining and writing repeatable runout (RRO) compensation value sets as defined in claim 1 , wherein the secondary actuator comprises an electro-magnetic microactuator.

4. A method for determining and writing repeatable runout (RRO) compensation value sets as defined in claim 1 , wherein the predetermined number of disk revolutions comprises about six disk revolutions.

5. A method for determining and writing repeatable runout (RRO) compensation value sets as defined in claim 1 , wherein the predetermined number of disk revolutions comprises about eight disk revolutions.

6. A method for determining and writing repeatable runout (RRO) compensation value sets as defined in claim 1 , wherein the skew angle is between about minus fifteen degrees and plus fifteen degrees.

7. A disk drive, comprising:

a magnetic disk having data tracks, each data track including a plurality of embedded servo sectors that define a circumferential path having repeatable runout (RRO) error;

an actuator arm;

a voice coil motor (VCM) for rotating the actuator arm about a pivot;

a magnetoresistive (MR) head having a read element and a separate write element;

a secondary actuator coupled to a distal end of the actuator arm for adjusting a skew angle for the head; and

a control system for setting the skew angle for the MR head using the secondary actuator such that, during a track following operation for determining and writing an RRO compensation value set for a followed track, the read element and the write element are substantially aligned along the followed track.

8. A disk drive as defined in claim 6 , wherein the secondary actuator comprises a piezo-microactuator.

9. A disk drive as defined in claim 6 , wherein the secondary actuator comprises an electro-magnetic microactuator.

10. A disk drive as defined in claim 6 , wherein the skew angle is between about minus fifteen degrees and plus fifteen degrees.