Method and apparatus for feedforward repeatable runout compensation in a selected frequency range

Abstract

For runout compensation in a data handling system, a servo feedback loop is configured to control a head position relative to a corresponding disc surface. Operation of the feedback loop is complicated by a repeatable error in the head position having energy at harmonics of the spindle rotation frequency. Also, the feedback loop has a gain with a frequency sensitivity in a target frequency range. A feedforward controller generates an output injected into the feedback loop based on an error-indicative input. This defines a feedforward closed-loop transfer function, between the loop output and the feedforward controller input. The feedforward controller prevents the frequency sensitivity from substantially varying the feedforward closed-loop transfer function gain and phase within the target frequency range, thus reducing computational burden.