Servo control techniques for track following on hard disk drive spin stand testers

This paper developed a real-time servo control system for high precision track following (head position control) on hard disk drive spin stand testers. The proposed servo control system includes a feedback linearization, a high-bandwidth feedback controller, an adaptive feedforward controller, and the Zero acceleration path technique. Experiments with a Seagate disk with track width of 77 nm showed that the servo control system could reduce the three-sigma (standard deviation) of the repeatable head position error to ~2.7 nm and the three-sigma of the non-repeatable error to ~2.2 nm. At the end it is demonstrated that with the track following ability, the head can coherently write and read data to and from the disk even with the presence of internal and external disturbances to the head.