Distortion effects on servo position error transfer function

Two kinds of nonlinear distortion of hard-disk-drive position error signal (PES) transfer function are examined and modeled. The first distortion is the saturation of the PES due to narrow read width. The second distortion is the on-track dead band at the center of the transfer function due to wide erase band. Several formulas are developed to describe the relationships between the distortion effects and the design parameters: read width, track spacing, and erase width. These distortions are highly undesirable for the track following sectored servo system. However, they are predictable and avoidable if certain conditions are satisfied. The geometrical analysis of the distortion phenomenon is presented here