Timing Error Compensator Design for Spiral Based Self-Servowriting in Disk Drives

This paper considers the timing error compensation problem for spiral based Self-Servowriting (SSW) process in disk drives manufacturing, wherein the product servo patterns are written based on the prewritten spiral tracks. The disk eccentricity and position error in the spiral tracks cause Repeatable Timing Error (RTE) which deteriorates the product servo pattern format and, as a result, the servo sectors are not uniformly distributed along the circular tracks. The spindle speed variation and sensor noise induce Non-repeatable Timing Error (NRTE) which results in phase incoherency at the servo sectors between adjacent tracks. In this paper, a Recursive Least Square (RLS) based Parameter Adaptive Algorithm (PAA) is proposed to estimate and cancel the RTE. An error shaping filter is designed to improve the estimation performance of PAA and reduce the effect of NRTE in the system. Finally, simulation studies using industry supplied data show the effectiveness of the proposed control scheme. The RTE can be cancelled up to 90% and the quality of the written servo sectors is improved by 91%.