H α disturbance observer design for high precision track following in hard disk drives

Contrary to the conventional method of disturbance observers (DOB) where Q-filter is designed to be a low-pass filter with unity DC gain, the optimal H_∞ method has been proposed to design the Q-filter and applied in the servo control system of hard disk drives in track following. Simulation and implementation results have shown that the resultant H _∞ DOB improves low-frequency disturbance attenuation without compromising the disturbances attenuation performance at higher frequency region achieved by the nominal feedback controller. In terms of track-following precision, the proposed method is approximately 5% more accurate than the conventional method.