Jung Rae Ryoo

Robust disturbance observer for the track-following control system of an optical disk drive

For track-following control in an optical disk drive, a compensator should be designed to satisfy conflicting specifications. The compensator design procedure usually requires numerous trial and errors. Utilization of a disturbance observer (DOB) for enhancing track-following precision simplifies the compensator design procedure by removing the requirement for disturbance attenuation from the compensator design specifications. However, the absence of DOB design guideline considering plant modelling uncertainty has hindered practical application of the DOB. In this paper, a robust stability condition for the DOB-based track-following control system is presented. A graphical design guideline based on frequency response analysis is proposed, and a DOB is designed to preserve the overall stability. To show the validity, simulation and experimental results are presented.

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.

Repetitive controller design for track-following servo system of an optical disk drive

In the track-following servo system of an optical disk drive, external disturbances with significant periodic components cause tracking errors of a periodic nature. To effectively reject such disturbances, repetitive control has been employed. However, plant uncertainty makes it difficult to design a repetitive controller which both ensures system stability and improves tracking accuracy. In this paper, we examine the problem of repetitive controller design for an optical disk drive track-following servo system with norm bounded uncertainties. Using the Lyapunov functional for time-delay systems, a sufficient condition for robust stability of the repetitive control system is derived in terms of algebraic Ricatti inequality (ARI) or linear matrix inequality (LMI). Based on the derived condition, we show that the repetitive controller design problem can be reformulated as an optimization problem with an LMI constraint on the free parameter. Through an experiment, it is verified that the designed repetitive controller has a remarkable performance to attenuate the periodic disturbance while preserving the overall stability.

A Linear Matrix Inequality Approach to Initial Value Compensation for Mode Switching Control in Hard Disk Drive Servo Systems

In switching from the track-seeking or track-jumping control mode to the track-following control mode in hard disk drives, initial values of the feedback controller are tuned such that the transient response is improved. We present a simple initial value compensation (IVC) method using linear matrix inequalities (LMIs) instead of the conventional method that uses a Lyapunov equation. The LMIs include conditions for improving the transient response performance in the L 2-norm sense and minimizing the H infin norm of the closed-loop system in order to reduce the controlled outputs such as plant states, tracking error, and control efforts. We obtain optimal initial values of the controller by solving an optimization problem with constraints represented by only one LMI. We verified the feasibility of the method by using a series of simulations.

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.

Real-time implementation of an LUT-based image warping system

Image warping is a spatial transformation distorting an original image, and an elementary operation of image warping is moving pixel data to another position. Millions of iterations of the simple operation is adequate to be implemented using digital hardware better than software running on a CPU, and parallel architecture enables real-time processing. In this paper, a hardware architecture for real-time image warping using look-up table(LUT) is presented. An overall hardware architecture including buffer memories is explained. Finally, the hardware architecture is implemented using FPGA, and experimental results are presented.

A QFT design of disturbance observer for the track-following control system of an optical disk drive

For track-following control in an optical disk drive, a compensator should be designed to satisfy disturbance attenuation property, overall system stability, and so on. In order to ease the compensator design procedure by reducing trial and error, a disturbance observer is added on to a conventional single loop track-following control system, which may cause control input saturation due to excessive loop gain. Because the track-following control system is conditionally stable, control input saturation leads to actual reduction of loop gain whereby the system becomes unstable. To preserve the overall stability during transient response, where control input saturation possibly occurs, the circle criterion based on the pull-in condition is utilized to check the stability under control input saturation. The constraints from the circle criterion and robust stability condition are converted into frequency domain bounds, which are represented on a Nichols chart. Then a design method using quantitative feedback theory (QFT) is applied to satisfy the constraints shown on the Nichols chart. To show the feasibility, some experiments are conducted, and the results are presented.

Steering System in a Self-Balancing Electric Scooter

Abstract: In this paper, a new steering system for a self-balancing electric scooter is proposed with an intuitive steering command input method, where the steering command is generated from the rider’s motion of shifting body to move the center of gravity toward the rotational direction. For the purpose, weight distributions on the rider’s feet are measured using force sensors placed beneath the rider’s feet, and the difference is applied to a steering control system. Stability of the steering system and resultant radius of gyration is investigated by modeling the steering system in consideration of the rider’s motion and centrifugal force. The proposed steering system is applied to experiments, and the results are presented to prove the validity of the proposed method.

Real-time Gaze Control of an Active Head-EYe System without Calibration

This article describes real-time gaze control using position-based visual servoing. The main control objective of the system is to enable a gaze point to track the target so that the image feature of the target is located at each image center. The overall system consists of two parts: the vision process and the control system. The vision system extracts a predefined color feature from images. An adaptive look-up table method is proposed in order to get the 3-D position of the feature within the video frame rate under varying illumination. An uncalibrated camera raises the problem of the reconstructed 3-D positions not being correct. To solve the calibration problem in the position-based approach, we constructed an end-point closed-loop system using an active head-eye system. In the proposed control system, the reconstructed position error is used with a Jacobian matrix of the kinematic relation. The system stability is locally guaranteed, like image-based visual servoing, and the gaze position was shown to converge to the feature position. The proposed approach was successfully applied to a tracking task with a moving target in some simulations and some real experiments. The processing speed satisfies the property of real time.