Control design of hard disk drive self-servo track writing via H2 and H∞ control synthesis

This paper considers two novel controller synthesis methodologies for performing self-servo track writing in hard disk drives using a feed forward control structure. In the first methodology, it is assumed that a conventional track-following causal controller has been designed and a non-causal feedforward controller, which utilizes the stored error signal from writing the previous track, is designed using standard H_∞, control synthesis techniques, in order to prevent the track errors from propagating and to achieve good disturbance attenuation. In the second methodology, both the track-following feedback controller and the feed forward controller are simultaneously designed via a mixed H₂H_∞, control scheme, which involves the solution of a set of linear matrix inequalities and achieves good disturbance attenuation while preventing the propagation of track errors from the previous tracks. Simulation results confirm that the two proposed control synthesis methodologies prevent error propagation from the previously written tracks and significantly improve self-servo track writing performance.