Combined Feedforward/Feedback Control for Tape Head Track-Following Servo Systems

Abstract

AbstractIn order to remain competitive with other data storage technologies, the tape industry is planning to significantly increase track densities on tape. Higher track densities require narrower track pitch and more precise positioning of the read/write heads. Hence, improved track-following servo systems for the head assembly are needed. Longitudinal transport of the tape along the tape path is subject to lateral disturbances that cause displacement between the head and the desired track and hence increase position error. This paper proposes a combined feedforward/feedback control scheme to improve the track-following performance of the tape head positioning system in the presence of lateral tape motion (LTM). In this architecture, the feedback controller is designed to guarantee system stability and take into account the lower frequency components in the disturbances. The feedforward controller requires as its input a prediction of the lateral tape motion displacement (LTMD) at the head assembly. We propose a least squares based algorithm to predict the LTMD at the head from a history of upstream and downstream LTMD measurements. Compared to using feedback-only control, the combined feedforward/feedback controller enables the head assembly to be positioned more accurately over the desired track.