Fast servo signal acquisition in tape drives

Abstract

In a tape drive, the head assembly, which hosts servo readers and data writers/readers, must initially be moved to a target position, so that information can be written to or read from the desired tracks. The positioning of a servo reader over a servo band, from which the position-error signal for steady-state track-following operation is obtained, has to be fast, because of the moving-target nature of the problem. This is especially true in the presence of non-negligible lateral tape motion, as found in tape paths with flangeless rollers. In this paper, a method is proposed whereby not only the servo readers but also the data readers in a drive are used to detect the presence of a valid servo signal. If a servo reader is not positioned over a servo band, the distance between servo reader and servo band is continuously estimated by identifying the data reader detecting the presence of a servo signal. This information is then provided to a control element, which determines a trajectory for the actuator and outputs a control signal so that the servo reader rapidly lands over the servo band with optimum control effort. A realization of the proposed method is illustrated by simulation as well as experimental results. © 2010 IFAC.