DISTORTION EFFECTS ON SERVO POSITION ERROR TRANSFER-FUNCTION

Two kinds of nonlinear distortion of hard-disk-drive position error si gnal (PES) transfer function are examined and modeled. The first disto rtion is the saturation of the PES due to narrow read width. The secon d distortion is the on-track dead band at the center of the transfer f unction due to wide erase band. Several formulas are developed to desc ribe the relationships between the distortion effects and the design p arameters: read width, track spacing, and erase width. These distortio ns are highly undesirable for the track following sectored servo syste m. However, they are predictable and avoidable if certain conditions a re satisfied. The geometrical analysis of the distortion phenomenon is presented here.