Linearity compensation for a position error signal based on repeatable and non-repeatable run out in a disk drive

Abstract

Linearity compensation is provided for a position error signal based on repeatable and non-repeatable run out in a data storage device. The run out is measured on a track of the data storage device at a plurality of points, such as a track center and one or more points offset from the track center. The run out is typically measured using either an unstitched primary position error signal or an unstitched quadrature position error signal. The offsets are usually stitch points for the position error signal. A component of the run out is extracted at the points, wherein the component generally comprises one or more characteristics of the run out, such as a frequency, a set of frequencies, a root mean square, or some other characteristic of the run out. The linearizing equation to be used for the position error signal is identified based on the measured run out and generally comprises a polynomial function. The coefficients of the linearizing equation are adjusted so that the run out and the component of the run out are substantially similar at the points. These steps are repeated until a satisfactory fit is achieved in the linearizing equation. Once a satisfactory fit is achieved, the coefficients for the linearizing equation are stored in the data storage device, so that they can be accessed by a servo controller during operation of the data storage device. The servo controller uses the linearizing equation to generate a linearized position error signal that is used to improve a track following capability of the data storage device.