Method of centering a disk pack of a disk drive

A method of centering a disk pack of a disk drive, the disk drive including a base rotatably supporting the disk pack, the method comprising:

• rotating the disk pack;
• and
• while the disk pack is rotating:
• a) generating a reference timing signal;
• b) detecting a first imbalance in the rotating disk pack to produce a first imbalance signal;
• c) correlating the first imbalance signal with the reference timing signal to produce a first correlation value indicative of a location of the first imbalance relative to the reference timing signal;
• d) applying a first impact to the base to transfer sufficient momentum to the base causing the base to shift relative to the disk pack, the first impact applied based on the first correlation value;
• e) detecting a second imbalance in the rotating disk pack to produce a second imbalance signal, the second imbalance resulting from the first impact;
• f) correlating the second imbalance signal with the reference timing signal to produce a second correlation value indicative of a location of the second imbalance relative to the reference timing signal;
• g) determining a phase compensation value based on the first and second correlation values, the phase compensation value indicative of a phase difference between an actual location of the first imbalance and a desired location of the first imbalance when the first impact was applied;
• and
• h) applying a second impact to the base to transfer sufficient momentum to the base causing the base to shift relative to the disk pack, the second impact applied based on the phase compensation value.