New robust feedforward tracking control structure for optical disk recording system

Abstract

In optical recording system, the tracking servo system must follow the track of optical disk against the influence of the track eccentricity and the force disturbance. In tracking servo system, the influence of the track eccentricity becomes periodic disturbance. The influence of force disturbance caused by shaking is treated as sudden disturbance.The several control methods suppressing the periodic disturbance have been proposed. On the other hand, it is difficult to detect the sudden disturbance without force sensor. In the conventional tracking servo system, the influence of sudden disturbance has been suppressed by the feedback controller. This paper proposes a new structure of robust tracking servo system, which detects and suppresses the both periodic disturbance and the sudden disturbance without force sensor. The proposed system estimates the both periodic disturbance and sudden disturbance based on a new sudden disturbance observer and memory of tracking error. Moreover, in order to suppress the periodic disturbance quickly, this paper designs the ZPET feedforward servo system with prediction of tracking error.The experimental results point out that the proposed tracking servo system has a precise tracking response against both periodic disturbance and sudden disturbance.

Servo techniques for optical disk drives —high‐speed and precise optical beam‐positioning control—

“…is not possible to obtain a future value of the error signal, there is little change in the tracking error signal in one rotation at any point on the optical disk from that for an adjacent track in an optical disk drive, so the error signal can be regarded as a periodic function that is dependent on the rotation of the disk. Therefore, by recording the error signal proceeding from the d sample of the previous rotation and substituting that value as a predictive value, the introduction of a feed-forward control system becomes feasible [4][5][6].…”

High-Speed Tracking Servo Using Zero Phase Error Tracking-Feed-Forward Method for Professional-Use Optical Disks over 10000 rpm

“…For example, the employment of repetitive control techniques to the gap servo for near-field recording systems was reported. 4,5) We have proposed a high-speed tracking control system that combines a feedback (FB) control system with a feed-forward (FF) control system, which was based on the zero phase error tracking (ZPET) method [6][7][8][9][10] (referred to as the ZPET-FF control). This system has been shown to reduce residual tracking error far better than conventional FB control or repetitive control, 7) and has demonstrated the capability to reduce the residual tracking error on an optical disk rotated at a high speed with an optical system with an objective lens of a numerical aperture (NA) of 0.65.…”