| This research investigates models of the position error signal (PES) generation process and control algorithms targeted towards increasing robustness and rejecting noise and disturbance in magnetic disk drives. We present a comparison of simple, yet inclusive techniques for predicting the position signal and noise profiles versus cross-track head position. The first method, proposed by the National Storage Industry Consortium, uses measurements of the track average amplitude (TAA) from direct measurements to cross-track PES profiles, signal-to-noise ratio, PES linearity, and stability. The second method uses measurements of the micro-track profile (MTP) to model read-back. Experimental data suggest that both methods have comparable accuracy for modeling the cross-track PES profile for different head and media combinations. For the predictions using MTP measurements, results show that the effect of magnetoresistive (MR) head amplitude asymmetry can be partially modeled by using the superposition of the data from the micro-track profile of positive and negative pulses. We also present a simple method for modeling the write head field; results show that combining this model with a zigzag transition model and a side-writing model improves the write process simulation. For controller design, we present windage spectrum data from two drives and illustrate using case studies optimal control problem setups for rejecting disturbance, noise, and modeling uncertainties. Simulations show that designing compensators to reject known disturbance spectra may benefit disturbance rejection in actual disk drives, depending on the specifics of the problem. We also suggest a systematic method of using the optimal control design framework to determine the best PES sampling rate under disk the best PES sampling rate under disk overhead constrains. |
