High-Rate Skew Estimation for Tape Systems

In several recent magnetic tape drive designs, an actuator with two degrees of freedom has been adopted for joint skew- and track-following control. This enables the removal of flanges from guide rollers in the tape path, thus avoiding debris build-up, tape-edge damage, and high-frequency lateral tape motion. Skew compensation is needed to keep the head perpendicular to the direction of tape motion to enable read-while-write functionality in the presence of large lateral tape excursions originating from the removal of roller flanges. In this paper, we present a novel skew estimator that generates skew estimates at a high rate for an extended range of allowable tape-to-head skew values. A skew estimate is given by the sum of a fractional and an integer part, extracted from information provided by two parallel synchronous servo channels operating on timing-based servo patterns. The fractional part is obtained from the accurate measure of timing intervals between dibit correlation peaks, whereas the integer part is derived from longitudinal position information. The new method was implemented in an FPGA and verified experimentally using a commercial tape drive.