Servo Control Design for a High TPI Servo Track Writer With Microactuators

This paper proposes modifications to enhance the original generalized Kalman-Yakubovic-Popov (G-KYP) lemma-based sensitivity function shaping technique that Q-parameterizes the controller and solves for the desired finite impulse response filter Q(z) using linear matrix inequalities (LMI) optimization. By representing Q(z) with an infinite impulse response filter and including an extra LMI that is derived based on the bounded real lemma into the original LMI optimization algorithm, our modifications avoid such problems as unnecessary increase and decrease in sensitivity gain at various frequency ranges, large sensitivity peak, degradation in noise rejection, and insufficient stability robustness against plant uncertainty. In other words, the proposed scheme achieves a better compromise between disturbance and noise rejection performance and stability robustness. The proposed control design was applied to a servo track writing platform. Experimental results show that the control design based on our proposed scheme further reduces the true PES NRRO 3sigma from 6 nm to 5.7 nm and improves the closed-loop stability robustness by 5.1%.