Tape transport control based on sensor fusion

Abstract

Reliable and precise tape transport is of fundamental importance to achieve larger volumetric recording densities in tape storage systems. The performance of the tape transport control system, which is affected by variations in the tape velocity and tension, impacts the write and read quality of the data tracks and eventually the achievable areal recording density. During operation in cruise velocity mode, disturbances in velocity and tension may be induced for example by tape reel eccentricities. This problem is particularly serious when the reel rotation frequencies are close to the resonance frequency determined by the tape path. Typically, the tape velocity is estimated at the tape head from a servo signal, which is obtained by reading pre-formatted servo information, and used for tape transport control during cruise mode. In such a scheme, velocity disturbances observed at the head cannot be attributed to an individual reel. Hence no targeted disturbance suppression can take place at the individual tape reels. However, Hall sensors are typically included in tape drives to obtain additional tape velocity information from the individual reels. This information is used to achieve proper tape transport operation in the absence of valid velocity estimates from the pre-formatted servo information, for example during tape acceleration. In this paper, we present a novel control scheme for tape transport that uses velocity measurements from three sources, the Hall sensors at the tape reels and the servo channel that yields velocity estimates at the head. Specifically, characterization of the multiple-input multiple-output (MIMO) tape transport system provides an accurate system model and enables an optimized two-sensor control design. Furthermore, H∞ filtering is employed to perform sensor fusion and the resulting state estimates are used in the feedback control of the two reels. Experimental results are presented to illustrate the behavior and performance of the proposed tape transport control system.