Cancellation and calibration procedures of harmonic disturbances in

Abstract

An adaptive feedforward method of canceling and calibrating harmonic disturbances in a magnetic disk drive storage system includes expressing harmonic disturbances to the system as d(t) and expressing an output of the system as y(t). A control signal u(t) is used to cancel the harmonic disturbance d(t), where u(t) is the estimated value of d(t) such that u(t) is an estimated value of d(t). Estimated coefficients a.sub.i and b.sub.i of u(t) are updated using the derivatives of the estimated coefficients and a constant adaptation gain g.sub.i for the ith frequency component of the disturbance. The values of estimated coefficients are implemented in real time. The control signal u(t) is combined with the system output signal y(t) to cancel u(t) from y(t). The functions representing d(t), y(t), and u(t) are included in drive code for the system. A sine function is implemented by a polynomial curve fitting method and the sine function is approximated as a polynomial function for a quarter cycle of the sine function using only four data points. Corrections for phase shift are obtained by modifying estimation equations for the coefficients of d(t) using a d-step delay in a position error signal (PES) measurement for the system. Calibration of the control signal u(t) is initiated in several ways. The coefficient function G.sub.p (s) for y(t) can be a simple plant transfer function or a plant transfer function with a feedback controller which stabilizes the open-loop plant and satisfies a desired specifications, including track-following.