Kyoung Bog Jin

Robust H/sub /spl infin// control with multiple constraints for the track-following system of an optical disk drive

In this paper, the authors design a tracking controller which satisfies transient response specifications and maintains tracking error within a tolerable limit for the uncertain track-following system of an optical disk drive. To this end, a robust H/sub /spl infin// control problem, with regional stability constraints and sinusoidal disturbance rejection is considered. The internal model principle is used for rejecting the sinusoidal disturbance caused by eccentric rotation of the disk. The authors show that a condition satisfying the regional stability constraints can be expressed in terms of a linear matrix inequality (LMI) using the Lyapunov theory and S-procedure. Finally, a tracking controller is obtained by solving an LMI optimization problem involving two LMIs. The proposed controller design method is evaluated through an experiment.

Track-following control using a disturbance observer with asymptotic disturbance rejection in high-speed optical disk drives

To obtain the good tracking performance in an optical disk drive servo system, it is essential to attenuate periodic disturbances caused by eccentric rotation of the disk. As an effective control scheme for enhancing disturbance attenuation performance, disturbance observers (DOBs) have been successfully applied to the track-following servo system of optical disk drives. In disk drive systems, the improvement of data transfer rate has been achieved mainly by the increase of disk rotational speed, which leads to the increase of the disturbance frequency. Conventional DOBs are no longer effective in disk drive systems with a high-speed rotation mechanism because the performance of conventional DOBs is severely degraded as the disk rotational frequency increases. This paper proposes a new DOB structure for effective rejection of the disturbance in optical disk drives with a very high rotation speed. Asymptotic disturbance rejection is achieved by adopting a band-pass filter in the DOB structure, which is tuned based on the information on the disturbance frequency. In addition, performance sensitivity of the proposed DOB to changes in disk rotational frequency is analyzed. The effectiveness of the proposed DOB is verified through simulations and experiments using a DVD-ROM drive.

Robust direct seek control for high-speed rotational optical disk drives

This paper presents a new direct seek control scheme (SCS) that provides fast data access capability and robust performance for high-speed rotational optical disk drives (ODD). When a disk is rotated at a high speed to obtain fast data transfer in ODD, the magnitude and frequency of disturbances caused by eccentric rotation of the disk increase in proportion to the rotational speed of the disk. Such disturbances make it almost impossible for the conventional SCS to achieve stable and satisfactory seek performance. We analyze the problems that may arise when the conventional SCS are applied to high-speed rotational ODD and propose a new direct SCS that will solve such problems. In the proposed scheme, a seek control system is designed such that its performance is guaranteed for a set of plants with parameter perturbations. The performance of the proposed SCS are shown by experiments using a 24/spl times/CD-ROM drive.

Design of a robust track-following controller for optical disk drives

In this paper, we design a robust track-following controller that satisfies the transient response specifications and diminishes the influence of sinusoidal disturbance. To this end, a robust control problem with the multiple constraints is considered. We show that a sufficient condition satisfying the multiple constraints can be expressed by linear matrix inequalities. Finally, the robust track-following controller can be designed by solving an LMI optimization problem. The effectiveness of the proposed controller design method is verified though experiments.

A controller design method for constructing a robust track-following system

This paper provides a robust tracking controller design method for the track-following system of an optical disk drive. A tracking loop gain adjustment algorithm is introduced to accurately estimate the tracking vibration quantity in spite of the uncertainties of the actuator. A minimum tracking open-loop gain is calculated by the estimated tracking vibration quantity and a tolerable limit of tracking error. A weighting function is selected to have a slightly larger gain than the calculated minimum tracking open-loop gain. A robust tracking controller is designed by considering a robust Hinfin control problem with the reasonable weighting function. The proposed tracking controller design method is applied to the track-following system of a DVD rewritable drive and is evaluated through the experimental results .

New fine seek control for optical disk drives

An optical disk drive has an excellent advantage of random accessibility. However, increased rotational velocity of a disk and limitations of mechanical structure have hindered implementation of direct seek control despite its effectiveness in reducing access time. A two-stage seek operation is instead adopted in conventional optical disk drives. In this case, fine seek control is restricted in its applicable range by the risk of misalignment between objective lens and laser beam axis, which causes the access time to increase enormously. In the paper, a control algorithm for extending the applicable range of fine seek is proposed with an appropriate control structure. The conventional fine seek technique utilized only a fine actuator without any maneuvering of a coarse actuator. With assistance of the coarse actuator, however, the misalignment of objective lens is compensated and the range of fine seek is extended in result. The proposed algorithm is applied to an optical disk drive to show its feasibility and some results are presented.

An optimal tracking controller design based on the estimation of tracking vibration quantity

This paper provides a schematic method estimating the tracking vibration quantity occurring in the track-following system of an optical disk drive, A tracking loop gain adjustment algorithm is introduced to estimate accurately the tracking vibration quantity in spite of the uncertainties of the tracking actuator. Finally, the tracking vibration quantity can be estimated from the tracking error and the controller output measured when the drive operates and the compensated actuator model. An optimal tracking controller can be designed from a minimum tracking open-loop gain calculated by the estimated tracking vibration quantity. The proposed vibration quantity estimation and controller design method is applied to the track-following system of an optical recording device and is evaluated through the experimental results.

Design of a Robust Fine Seek Controller Using a Genetic Algorithm

This paper deals with a robust fine seek controller design problem with multiple constraints using a genetic algorithm. A robust H∞ constraint is introduced to attenuate effectively velocity disturbance caused by the eccentric rotation of the disk. A weighting function is optimally selected based on the estimation of velocity disturbance and the estimated minimum velocity loop gain. A robust velocity loop constraint is considered to minimize the variances of the velocity loop gain and bandwidth against the uncertainties of fine actuator. Finally, a robust fine seek controller is obtained by solving a genetic algorithm with an LMI condition and an appropriate objective function. The proposed controller design method is applied to the fine seek control system of a DVD recording device and is evaluated through the experimental results.

Design of a Tracking Gain-up Controller for the Vibration Suppression of Tracking Actuator

This paper presents a tracking gain-up controller design method to control effectively the vibration of tracking actuator caused by external shocks and remaining velocity after seek control. A pole placement constraint is considered to assure a desired transient response against the vibration of tracking actuator. A loop gain-up constraint is introduced to hold the tracking gain-up loop gain and control bandwidth within allowable bounds. The pole placement constraint is expressed by a matrix inequality and the loop gain-up constraint is considered as an objective function so that genetic algorithm can be applied. Finally, a tracking gain-up controller is obtained by integrating a genetic algorithm with LMI design approach. The proposed tracking gain-up controller design method is applied to the track-following system of a DVD recording device and its effectiveness is evaluated through the experimental results.