Phase lead peak filter method to high TPI servo track writer with microactuators

A servo track writing (STW) platform with dual piezoelectric (PZT) microactuator is proposed for higher track density hard disk drives (HDDs). We mainly deal with the servo control issues to achieve high track density. Vibration and noise analysis based on the measured position error signal (PES) indicates that the PES is significantly disturbed by narrow-band vibrations. Hence, we propose a general second-order phase lead peak filter (PLPF) that is applicable to reject narrow-band disturbances at all frequency ranges. The filter zero is designed to minimally degrade the closed-loop system stability and obtain a smooth sensitivity curve around the disturbance frequency. A feedback controller is employed to stabilize the servo loop and then a PLPF is embedded to further suppress the specific vibrations. The readback position errors are evaluated and 6.4 nm 3a value of the true PES NRRO is achieved, corresponding to 395k track-per-inch (TPI) track density.