Feedforward control for reducing disk-flutter-induced track misregistration

We show in this paper that the disk vertical vibration signal picked from the slider in a hard disk drive has a fairly good correlation to the track misregistration at the disk flutter frequencies. We propose to introduce a feedforward controller into the usual servo loop to reduce disk-flutter-induced track misregistration (TMR). The feedforward controller is an approximated differential element with the disk vertical direction velocity as input. In our experimental setup, we show that such a method can reduce the TMR induced by the first four disk flutter modes by an average of about 56%. The method can potentially be used in high-track-per-inch servo track writers to reduce the written-in repeatable runouts.