Digital servo control system for a data recording disk file

Abstract

A digital servo control system for a data recording disk file receives as input a digital head position error signal (PES) and a digital signal corresponding to the head actuator input signal, and outputs a digital control signal. The control signal is integrated and amplified to provide the input signal to the actuator. The control signal is calculated from estimated values of absolute head position, head velocity and the equivalent actuator input signal required to compensate for constant or very low frequency bias forces. The estimated values are functions of respective predicted values, which in turn are functions of, among other things, constants representing the digital sampling time and physical parameters of the actuator. The updating of the estimated values from the respective predicted values is made with the use of an error term, which is the error between the measured absolute head position and the predicted absolute head position. The predicted absolute head position is made sufficiently accurate that the error term is always less than a selected number of tracks. This permits the digital servo control system to operate during track seeking without counting track crossings so that the system is operable with servo information recorded either in sectors on a data disk or in continuous tracks on a dedicated servo disk.