Position error signal estimation at high sampling rates using data and servo sector measurements

Abstract

The sampling rate in most hard disk drives (HDDs) is limited by the number of servo burst sectors that have prewritten position error signal (PES) data and by the spinning speed of the HDD. The paper presents an algorithm that can generate estimates of the PES during read at high sampling rates by processing the dedicated servo burst measurements and the mean square error (MSE) path metric data used to choose the correct bit sequence using the Viterbi decoding process of the read signal. The MSE metric is a nonlinear function of the absolute value of the true position of the head relative to the center of the written data. The position estimation algorithm is nonlinear and is based on several logic statements together with the use of two state observers. The estimation algorithm is tested on an actual disk drive and demonstrated to provide values of the PES at a frequency four times higher than that generated by the servo burst measurements.