Vibration analysis and optimal control in self-servo track writer

In a typical HDD servo loop, there are major vibration sources: flex and windage disturbance, disk motion and that related to magnetic media and channel electronics. In this paper, the major vibration sources in self-servo track writing (SSTW) are identified and modeled. Experimental measurement of the position error signal (PES) is used to determine the spectrum of the PES. The identification of vibration sources is based primarily upon the spectral decomposition of the measured PES. Upon determining the vibration sources, an H₂ controller together with feedforward compensator is designed via LMI approach to achieve an optimal error propagation containment for the SSTW. Two methods, i.e., H_∞ and mixed H₂/H_∞ are employed in the design of the feedforward compensator and compared in the sense of error propagation containment effectiveness.