Measurement and modelling of disturbances in a servo track writer and advanced loop shaping to achieve higher track density

In this paper we present the idea of hybrid servo track writing and give a complete description of the developed hybrid servo track writer platform including its main functions and servo mechanism. The major disturbances and noise level in media-level servo track writing are identified based on the position error signal measured on the hybrid servo track writer platform. A dual-stage servo system, which is applicable in servo writing, is proposed and implemented on the experimental platform. With the disturbances and noise models, an advanced loop-shaping scheme based on Kalman-Yakubovic-Popov lemma is used to optimize the controller for the micro-actuator servo loop. The experimental results show that the tracking accuracy can reach 6 nm, which is able to support a track density of more than 400 000 tracks per inch.