Reducing the manufacturing costs associated with hard disk drives-a new disturbance rejection control scheme

A new disturbance rejection control scheme is developed for cost-effective hard disk drive manufacturing. The proposed disturbance rejection controller is capable of attenuating both repeatable disturbances and nonrepeatable disturbances, which are two of the major detractors to hard disk drive quality and performance. The control scheme overcomes the drawback of typical internal-model-based repetitive control schemes which cancel repeatable disturbances, but amplify disturbances at other frequencies. This is achieved by a systematic combination of the internal-model-based repetitive controller with a loop shaping filter. It is shown that the internal-model-based repetitive controller is a special case of the proposed controller. Robustness of the controller is also studied. Simulations using disturbances reconstructed from actual drive level position error signal (PES) measurements have been carried out to show the effectiveness of this control scheme.