Improved Antishock Air-Gap Control Algorithm with Acceleration Feedforward Control for High-Numerical Aperture Near-Field Storage System Using Solid Immersion Lens

Abstract

A near-field storage system using a solid immersion lens (SIL) has been studied as a high-density optical disc drive system. The major goal of this research is to improve the robustness of the air-gap controller for a SIL-based near-field recording (NFR) system against dynamic disturbances, such as external shocks. The servo system is essential in near-field (NF) technology because the nanogap distance between the SIL and the disc is 50 nm or less. Also, the air-gap distance must be maintained without collision between the SIL and the disc to detect a stable gap error and read-out signals when an external shock is applied. Therefore, we propose an improved air-gap control algorithm using only an acceleration feedforward controller (AFC) to maintain the air-gap distance without contact for a 4.48 G at 10 ms shock. Thus, the antishock control performance for the SIL-based NF storage system in the presence of external shocks is markedly improved. Furthermore, to enhance the performance of the antishock air-gap control, we use the AFC with a double disturbance observer and a dead-zone nonlinear controller. As a result, the air-gap distance is maintained without contact for a 6.56 G@10 ms shock.

Application of phase-change materials in memory taxonomy

“…As the recording capacity of the optical disc based on the near-field technique strongly depends on the precise control of the gap distance between the SIL and disc, the ability to dynamically maintain the gap distance below 30 nm for a rotational, non-ideal plastic disc when encountering disturbances such as disc vibration and external physical shock becomes extremely critical [ 95–97 ]. As a result, a variety of advanced gap servo control technologies including feedforward control with zero phase error tracking method (ZPET-FF) [ 98 ], acceleration feedforward controller (AFC) method [ 97 ], and repetitive control method [ 99 ], have been assessed to improve the mechanical performance of the optical near-field system. Recently, an innovative near-field system with reducing harmonics of an axial run-out disturbance-feed-forward control (RHD-FFC) was proposed to show a precise gap servo for a 100 GB disc at 11,000 rpm [ 100 ].…”

High Precision Tracking Control based on Pseudo-Inverse Feedforward Control System for Next-Generation Optical Disks

“…Near field recording (NFR), which is a technology of large storage capacity, has been proposed. [1][2][3][4][5][6][7][8] To increase the recording density of optical disks, it is necessary to narrow the track pitch. Therefore, a high-precision tracking control system for optical disks is required.…”

High-Speed and Precise Gap Servo System for Near-Field Optical Recording

“…Other gap servo techniques for suppressing the disturbance of external shock have also been reported. 20,21) We have proposed a high-speed ZPET-FF control method 22) that is more precise and faster than repetitive control. Another research group also reported a compensation method of tracking error components.…”