Dynamic analysis and control for accurate magnetic disk head positioning using a compact double-carriage rotary actuator is presented. Rolling mode vibration, due to a small dynamic imbalance in the head arm carriage, is one of the major factors in positioning servo instability. To avoid such vibration, structural symmetry should be maintained along the actuator pivot axis. Vibration interaction in the double-carriage rotary actuator is also clarified by mathematical modeling of a disk drive. The positioning error due to the interaction is reduced by one-third to the submicron order, even during very high-speed accessing, by a cross-feedforward decoupling control using a precompensator based on the model.

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