Modeling and compensator designs for self-servowriting in disk drives

Abstract

This paper considers modeling and control design for self servowriting in disk drives. Self-servowriting is a process whereby the position and timing burst information are written on the disk surface by using the servo information from a previously written track as a reference (seed) for writing the burst information on the remaining tracks. An obstacle to this process is radial error propagation, whereby the written-in errors buildup due to amplification by the servo loop, causing distortion from circularity. In this paper, it is shown that the dynamics of the self servowriting process are inherently two-dimensional, the two dimensions being the time (track following direction) and track number (or radial offset in the propagation direction). A two dimensional track following compensator is designed to prevent radial error propagation in self servowriting. Simulation results illustrate the performance of the controller.