Patent ID: 6859341
Filing Date: 2005-02-22
Classification: G11B

Abstract:
1. An apparatus comprising: a servo feedback loop configured to control a loop output based on a loop input according to a predetermined feedback closed-loop transfer function having a gain with a frequency sensitivity, the loop output being a sensor position, the loop input being a reference signal; and a feedforward controller configured to generate a feedforward output based on a feedforward input, the feedforward input being indicative of a repeatable error in the sensor position, the feedforward output being injected into the servo loop so as to define a feedforward closed-loop transfer function between the loop output and the feedforward input, the feedforward controller including a module configured to counteract the frequency sensitivity enough so that the feedforward closed-loop transfer function has a gain that remains within a predetermined 6 decibel range and/or has a phase that remains within a predetermined 90 degree range throughout a substantial desired frequency range.