This dissertation deals with the problem of implementing direct seek control for high-speed rotational ODDSs in the presence of uncertainty. In order to reduce the access time in ODDSs, it is indispensable to realize the direct seek control. As the rotational speed of a disk to achieve high data transfer rate is increased, the frequency and magnitude of a shaking disturbance generated by the eccentric rotation of the disk also increase. Such shaking disturbance has a harmful effect on the application of the direct seek control. In case of high-speed rotational ODDSs, thus it becomes almost impossible to apply the direct seek control with conventional seek control structures.
First, we analyze problems in application of the direct seek control to the high-speed rotational ODDSs and propose a new direct seek control structure which can solve such problems. The proposed direct seek control structure simultaneously two requirements―high data transfer rate and short access time, despite high-speed rotational ODDSs.
Secondly, we deal with a robust controller design problem. The optical disk drive mechanism is composed of many components. As a result, we can not avoid the variation of a system behavior according to the quality of components. The coarse and fine actuators of ODDS for reflecting such variation are described as a linear time-invariant system whose coefficients are unknown but lie in some known intervals, i.e., a linear time-invariant system with parametric uncertainties. In the frequency domain, we derive robust performance conditions for all admissible actuator uncertainties. Based on the derived conditions, we show that the direct seek control design problem in the presence of actuator uncertainties can be transformed to a robust control design problem. This implies that a direct seek controller can be systematically designed using well-established robust control design procedures such as $\mu$ synthesis.
Lastly, the proposed direct control structure and the robust controller design scheme are applied to the high-speed rotational ODDS. The feasibility of the proposed direct seek control structure and the design technique is shown by simulation and experimental results. We also compare performance(access time) between the conventional seek control structure and the proposed direct seek control structure.
