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SUMMARYIn hard disk drives, it is important to enlarge the control bandwidth in order to shorten the track pitch for larger data capacity. However, it is difficult for the H ∞ control method to increase the control bandwidth if the mechanical resonance modes have uncertainty. This is because the robustness of the H ∞ control method 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 ∞ control method for high-bandwidth design by introducing a new uncertainty model with a feedforward and a feedback path in order to reduce the conservatism of robust design. The effectiveness is shown by numerical simulations.

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