Showing papers by "Hyunseok Yang published in 2008"

Apparatus for acquiring 3-dimensional geomatical information of underground pipes and noncontact odometer using optical flow sensor and using the same

Abstract: An apparatus to acquire 3-dimensional geographical information of an underground pipe includes an in-pipe transfer unit which moves along the inside of the underground pipe, a sensing unit which senses 3-dimensional location information of the in-pipe transfer unit, and an information storage unit which stores a value measured by the sensing unit. Accordingly, the depth at which the underground pipe is located as well as 2-dimensional location information of the underground pipe is stored in the information storage unit so that maintenance and repair of the underground pipe can be carried out with greater efficiency.

Improved Gap Control System Using a Disturbance Observer for Near-Field Recording

Abstract: In a solid immersion lens (SIL) based near-field recoding (NFR) system which is one of the emerging technologies for next-generation optical data storage systems, it is essential that the air gap between the SIL and the rotating disk is maintained at less than 50 nm without collision in order to obtain the proper coupling efficiency of evanescent waves. To fabricate a reliable near-field air gap servo system, various disturbances such as disk vibration, external shock and overshoot have to be considered, and these possible disturbances have to be prevented effectively. We propose an improved gap servo system using a disturbance observer (DOB), which has a reduced overshoot and rejection performance for the previously mentioned disturbances. The effectiveness of the proposed controller is verified by experimentally. The experiment results, show that the overshoot was reduced using the proposed near-field air gap servo system with a DOB. In the case of the ramp approach mode with and without the hand-over mode in the mode-switching servo, the overshoots were decreased to 50.9% and collision was avoided, respectively. In addition, in the case of the modified approach mode with and without the hand-over mode in the mode-switching servo, the overshoot was decreased to 2.9 and 3.7%, respectively. Consequently, the access time was decreased in each approach case without the hand-over mode using the DOB-based controller. In addition, the disturbance rejection performance of the external shock was improved to 9.11%.

Discrete linear quadratic output feedback control with integrator for holographic data storage system

Abstract: In this paper, we focus on effects of radial deviation on the disk and propose a tracking error compensation method for the holographic data storage system (HDSS) that uses a disk type media. In our HDSS, when the tracking error is detected, the error compensation is achieved by a piezo actuator. A tracking servo controller is suggested, and the validity of the servo control is verified with simulation results.

Preisach modeling of dielectric elastomer EAP actuator

Abstract: DE EAP(Dielectric Elastomer ElectroActive Polymer) has advantages in its weight, ease of fabrication and low power consumption. There are many efforts applied to various field in recent ten years. But the present modeling is not enough to appear its characteristics because of its hysteresis. In this paper, we propose modeling of DE EAP with Preisach Model that is used in order to model the hysteretic response arising in PZT and SMA. The modeling of DE EAP with Presach model is verified by experiment with various DE EAP actuators.

A Study on Enhancing Data Storage Capacity and Mechanical Reliability of Solid Immersion Lens-Based Near-Field Recording System

Abstract: In this study, several technical issues on solid immersion lens (SIL)-based near-field recording (NFR) are explored, namely, to enhance storage capacity and to guarantee mechanical reliability of the device. For the purpose of enhancing the storage capacity of the NFR system, two optical configurations using radial polarization and dual recording layers are proposed. Through a feasibility analysis of the proposed optical configuration with radial polarization, it was determined that illumination of radial polarization is not a suitable solution to achieve higher areal density. To apply highly focusing characteristics of incidence of radial polarized light to cover-layer protected data storage, an annular pupil filtering method was introduced. Complete field analysis of the proposed dual layered NFR optics verified its feasibility, and the assembly of the SIL of the proposed model was successfully achieved. In addition, to improve mechanical reliability of the SIL-based NFR system, improved near-field (NF) air-gap servo methods and air flow analysis around the low part of the SIL have been evaluated. With improved NF gap servo methods using an error-based disturbance observer (EDOB) on a base air-gap controller, residual gap errors were markebly reduced by 26.26% while controlling the NF air-gap to 30 nm. Air flow near the head media interface was visualized and an undesirable effect of backward flow climbing from the bottom surface of the SIL was ovserved.

Gap servo control method and apparatus in near-field optical disc drive

Abstract: A gap servo control method and apparatus for increasing a disturbance cancellation capability and decreasing the occurrence of an overshoot in a near-field optical disc drive include: generating an actuator driving signal of a transient response process by using a signal obtained by removing a disturbance contained in the gap error signal using a first band when a level of a gap error signal reaches a first level; and generating the actuator driving signal of the transient response process by using a signal obtained by removing the disturbance contained in the gap error signal using a second band when the level of the gap error signal reaches a second level.

Preisach modeling of IPMC-EMIM actuator

Abstract: The IPMC-EMIM actuator is an improved IPMC actuator to replace the water by stable ionic liquids (1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([EtMeIM][TA])). Just as a general IPMC actuator which uses the solvent of water has hysteresis, so do the IPMC-EMIM actuator exhibits hysteresis like other smart materials such as piezoceramics (PZT), magnetostrictive materials, and shape memory alloys (SMA). Hysteresis can cause it to be unstable in closed loop control. The Preisach Model has been used to model the hysteretic response arising in PZT and SMA. Noting the similarity between IPMC-EMIM and other smart materials, we apply the Preisach model for the hysteresis in the IPMC-EMIN actuator. This paper reviews the basic properties of the Preisach model and confirms that the Preisach model of IPMC-EMIM actuator is possible.

Gap pull-in method for near-field optical disk driver and optical disk driving apparatus using the method

Abstract: A gap pull-in method that minimizes overshoot due to a moving speed of a light focusing element and disturbance of a disk when the light focusing element is converted from an open loop state to a closed loop state during a gap pull-in of a near-field optical disk driver, and an optical disk driving apparatus using the method, the gap pull-in method including: generating an inverse actuator driving signal having a pulse duration and a pulse amplitude according to a moving speed of a light focusing element when an open loop state is changed to a closed loop state in the gap pull-in; and driving an actuator using the inverse actuator driving signal.

Direction Assignment of Left Eigenvector in Linear MIMO System

Abstract: In this paper, we propose novel eigenstructure assignment method in full-state feedback for linear time-invariant MIMO system such that directions of some left eigenvectors are exactly assigned to the desired directions. It is required to consider the direction of left eigenvector in designing eigenstructure of closed-loop system, because the direction of left eigenvector has influence over excitation by associated input variables in time-domain response. Exact direction of a left eigenvector can be achieved by assigning proper right eigenvector set satisfying the conditions of the presented theorem based on Moore`s theorem and the orthogonality of left and right eigenvector. The right eigenvector should reside in the subspace given by the desired eigenvalue, which restrict a number of designable left eigenvector. For the two cases in which desired eigenvalues are all real and contain complex number, design freedom of designable left eigenvector are given.

Design of a digital image mask for intensity control of holographic data storage system using neural network

Abstract: Holographic data storage uses two dimensional page unit data. Because it uses a wide plane wave for large data area, the light can be distorted or affected by a noise. If intensity of the light for carrying a data in signal arm is controlled, we can store and reconstruct a better data page excluding some distortions and noises. A digital image mask is designed using back propagation algorithm of neural network to control the intensity distribution of the light for signal beam. In the simulation, the reconstructed data page with less error pixels are obtained in spite of an IPI noise.

Optical disc apparatus and method of driving the same

Abstract: An optical disc apparatus, and a method of driving the same, includes a light focusing element disposed to focus light emitted from a light source onto a disc; an actuator to move the light focusing element toward or away from the disc according to a voltage applied to the actuator; a light intensity detection unit to detect the intensity of light reflected from the disc; a servo unit to generate a gap error signal and a third voltage, the third voltage being the sum of a first voltage and a second voltage, and to apply the generated third voltage to the actuator; and a control unit to control the servo unit to perform a gap pull-in operation when the light focusing element is moved toward the disc according to the gap error signal and the third voltage.

Design and position control of AF lens actuator for mobile phone using IPMC-EMIM

Abstract: IPMC-EMIM (Ionic Polyer Metal Composites + 1-ethyl-3- methyl imidazolium trifluromethane sulfonate, EMIM-Tfo) is fabricated by substituting ionic liquid for water in Nafion film, which improves water sensitiveness of IPMC and guarantees uniform performance regardless of the surrounding environment. In this paper, we will briefly introduce the procedure of fabrication of IPMC-EMIM and proceed to introduce the Hook-type actuator using IPMC-EMIM and application to AF Lens actuator. Parameters of Hook-type actuator are estimated from experimental data. In the simulation, The proposed AF Lens Actuator is assumed to be a linear system and based on estimated parameters, PID controller will be designed and controlled motion of AF Lens actuator will be shown through simulation.