High bandwidth design of track-following control system of hard disk drive using H∞ control theory

In hard disk drives, it is important to increase the control bandwidth in order to shorten the track pitch for larger data capacity. However, it is difficult for H
_∞
control theory to increase the control bandwidth if the mechanical resonance modes have uncertainty. This is because that the robustness of the H
_∞
control theory is assured by the small-gain theorem for additive or multiplicative perturbation and the control bandwidth is limited by the uncertainty. In this study, we propose an H
_∞
design method for a high bandwidth design by introducing a new uncertainty model with feedforward and feedback path in order to reduce the conservatism of robust design. The effectiveness is shown by numerical simulations.