Anti-Shock Air Gap Control for SIL-Based Near-Field Recording System

• Published in: IEEE transactions on magnetics 2009-05, Vol.45 (5), p.2244-2247
• Main Authors: KIM, Jung-Gon, KIM, Wan-Chin, HWANG, Hyun-Woo, SHIN, Won-Ho, PARK, Kyoung-Su, PARK, No-Cheol, YANG, Hyunseok, PARK, Young-Pil
• Format: Article
• Language: English
• Subjects: Anti-shock control; Control systems; Controllers; Cross-disciplinary physics: materials science; rheology; dead-zone nonlinear controller; Disk recording; disturbance observer (DOB); Disturbances; Dynamical systems; Dynamics; Electric shock; Exact sciences and technology; gap error signal (GES); Lenses; Magnetism; Materials science; near-field recording (NFR); Nonlinear control systems; Nonlinearity; Optical control; Optical filters; Other topics in materials science; Physics; Recording; Robust control; Robustness; Rotating disks; Servomechanisms; Solids
• ISSN: 0018-9464; 1941-0069
• DOI: 10.1109/TMAG.2009.2016237

The aim of this research is to improve the robustness of the air gap controller for solid immersion lens (SIL)-based near-field recording (NFR) servo systems against dynamic disturbances such as external shocks. Stable control is essential in these systems because the air gap distance between the SIL and the rotating disk is less than 100 nm. To detect gap error and read-out signals for the SIL and the disk, the air gap control performance must be increased to avoid collisions due to external shocks. We propose an anti-shock air gap control system using a disturbance observer (DOB) and a dead-zone nonlinear controller. Experimental results demonstrate that a DOB with a Q filter bandwidth of 500 Hz reduced the minimum air gap distance due to an external 1 g@10 ms shock by 70.1%. A DOB and a dead-zone nonlinear controller maintained the optical head distance for a 2 g@10 ms shock. Thus the control performance in the presence of external shocks was improved.