Servo-Pattern Design and Track-Following Control for Nanometer Head Positioning on Flexible Tape Media

Achieving multi-Terabyte capacity in tape cartridges requires a substantially higher track density than that available in present systems, and hence a significantly higher positioning accuracy is required of the track-following servo in tape drives. In this paper, advanced concepts are considered for several elements of a tape system that enhance the track-following servo performance to reach nanometer positioning accuracy. We introduce a novel method for optimizing the geometry of servo patterns in a timing-based servo system. The design criterion aims to minimize the measurement error in the position-error signal (PES) yielded by a digital synchronous servo channel. A flangeless tape path is adopted to mitigate high-frequency components of the lateral tape motion. The track-following servo controller, which is designed based on the H_∞ approach, takes into account the measured plant transfer function, the disturbance characteristics of the tape path, and the properties of servo channel. These elements are combined to investigate the track-following performance achievable with a new high-SNR magnetic tape based on perpendicularly-oriented BaFe particles. With this setup, a record closed-loop track-following performance of less than 14 nm PES standard deviation is demonstrated.