Compensation of repeatable and nonrepeatable disturbances in high NA SIL-based near-field storage systems

This paper presents an effective control algorithm to avoid physical contact between the disk and the solid immersion lens (SIL) in near-field (NF) storage systems under dynamic operating conditions such as repeatable and nonrepeatable disturbances due to disk vibrations and external shocks. In particular, the air-gap distance between the disk and the SIL in the NFR system is less than 50 nm. Therefore, the disk and the SIL must be protected to detect the stable gap error signal (GES) during continuous control operation. In this manuscript, we propose an improved air-gap control system using a narrowband disturbance filter (NBDF), which is an effective control method for enhancing the performance of the system for the rejection of repeatable and nonrepeatable disturbances In addition, we demonstrate an improved air-gap controller using a double disturbance observer (DOB) to improve the anti-shock control performance under external shocks. The double DOB uses a binomial Q filter without additional sensors, which keeps the production cost low. Finally, to evaluate the robustness of the control system with the double DOB, we apply a design method that varies the bandwidth of the Q filter.