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Recently, the capacity of optical disk recording systems has been increasing. Optical disk drive systems must realize high-precision tracking control. For this purpose, we previously proposed a tracking control system that is composed of both a robust feedback controller and a zero-phase-error feedforward tracking controller. The proposed feedforward tracking control system effectively suppresses the tracking error caused by track eccentricity. However, it is sometimes difficult for conventional feedforward tracking control systems to realize higher precision in their tracking control. Hence, in this paper we propose a new perfect tracking control (PTC) system with a prediction state observer for next-generation optical disks. The experimental results confirm that the proposed system suppresses the tracking error at a disk rotation speed of 8000 rpm. Therefore, the proposed system realizes high-precision tracking control.

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We propose a high-speed and precise gap servo control system that is based on the feed-forward control method that can reduce the harmonic disturbance (RHD-FFC) on a near-field optical recording system with a solid immersion lens. An optical disk of 1.2 mm thickness rotates with about 30 µmp–p of axial run-out. The axial run-out prevents a gap servo from performing precisely at high rotational speed. The RHD-FFC method can suppress harmonic disturbances of gap error signal and can perform at high speed while keeping less than 25 nm of gap length between an optical head and a rotational disk surface. We confirmed that the gap servo applying the RHD-FFC method performed precisely and achieved at high disk rotational speed of 11000 rpm with a 1.2-mm-thick optical disk with a track pitch of 0.16 µm, corresponding to a data capacity of 100 Gbyte.