Experimental modeling and compensation of pivot nonlinearity in hard disk drives

This paper considers a new model-based friction compensator for servo control of hard disk drives (HDDs). Using measured and simulated responses in both time and frequency domains as a guide, an HDD designer can iteratively improve the friction model of the HDD system and verify the correctness of the HDD measurement through this new model. By feeding back the model-based estimated friction forces into the voice coil motor (VCM), the frequency response between the read/write head position and the VCM current can be linearized. This allows the cancellation scheme to be developed and implemented through model-based compensation. Experiments have confirmed that the cancellation scheme is indeed effective in the frequency range of 0-300 Hz. Furthermore, by using a sequence of square waves as references for track-to-track seeking, the overshooting in the time responses can be compared between servo controls with and without compensators for friction.