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A Minimum Parameter Adaptive Approach for Rejecting Multiple Narrow-Band Disturbances With Application to Hard Disk Drives

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Many servo systems are subjected to narrow-band disturbances that generate vibrations at multiple frequencies. One example is the track-following control in a hard disk drive (HDD) system, where the airflow-excited disk and actuator vibrations introduce strong and uncertain spectral peaks to the position error signal. Such narrow-band vibrations differ in each product and can appear at frequencies above the bandwidth of the control system. We present a feedback control scheme that adaptively enhances the servo performance at multiple unknown frequencies, while maintaining the baseline servo loop shape. A minimum parameter model of the disturbance is first introduced, followed by the construction of a novel adaptive multiple narrow-band disturbance observer for selective disturbance cancellation. Evaluation of the proposed algorithm is performed on a simulated HDD benchmark problem.
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... This situation is found in odd-harmonic current suppression of magnetically suspended rotor systems 4 power electronic systems 7,8 narrow-band disturbance rejection of active suspension systems 9 and single and multiple narrow-band disturbance rejections of hard-disk drive systems. 10,11 Considering this fact, applying the conventional RC is unnecessary if one only intends to suppress band-limited periodic disturbances. Furthermore, one is supposed to mind some issues of applying the conventional RC: it reduces system robustness, induces instability due to unmodeled dynamics, exhibits slow transient responses, and is incapable of rejecting aperiodic disturbances. ...
... The conventional RC (equation (9)) with an internal model (equation (11)) has N evenly spaced poles located on the unit circle. Thus, such an RC yields a perfect cancelation for any periodic disturbance signal composed of jf v frequencies, where j = 1, 2, . . . ...
... where m 2 N is the number of the disturbance's fundamental frequencies. We assert that it is unnecessary to target the fundamental frequencies and their harmonic components using the internal model (equations (11) and (12)) because actual disturbance signals may only be composed of band-limited frequencies. Therefore, it is reasonably sufficient to apply a low-order internal model expressed as 12 ...
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