Recently, high-precision tracking control has been required for optical disks. For this purpose, we have previously proposed a tracking control system that is composed of an equivalent-perfect tracking control (E-PTC). However, the conventional control system is not able to operate the inverse system properly for the state equation. In this paper, we propose a new double E-PTC system. With this new system, the inverse system for the state equation operates properly. In addition, we propose a double E-PTC system with an error-based disturbance observer using a notch filter for non-periodic disturbance suppression. The proposed system achieves more precise control and experimental results demonstrate its effectiveness.

The crossover function for the specific heat of a disordered material is constructed to order E by solving the renormalisation group equations for the m n model (m + 0, n > 1).From this an effective exponent is obtained which provides a local measure of the degree of singularity of the specific heat in the critical region. It is seen that as the critical region is approached from above the critical temperature the effective exponent behaves initially as if no disorder were present. But as the critical temperature is more closely approached the effective exponent crosses over to the value predicted for the disordered material.

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Optical disk drive systems must realize high-precision tracking control for their proper operation. For this purpose, we previously proposed a tracking control system that is composed of a high-gain servo controller (HGSC) and a feedforward controller with an equivalent-perfect tracking control (E-PTC) system. However, it is difficult to design the control parameter for actual multi-harmonic disturbances. In this paper, we propose a precise disturbance model of an actual optical disk using the experimental spectrum data of a feedback controller and describe the design of a fine tracking control system. In addition, we propose a double feedforward control (DFFC) system for further high-precision control. The proposed DFFC system is constructed using two zero phase error tracking (ZPET) control systems based on error prediction and trajectory command prediction. Our experimental results confirm that the proposed system effectively suppresses the tracking error at 6000 rpm, which is the disk rotation speed of Digital Versatile Disk Recordable (DVD+R).

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