Soo-Cheol Lim

Position tracking control of an optical pick-up device using piezoceramic actuator

Abstract This paper proposes a piezoactuator-driven optical pick-up for compact disc-read only memory (CD-ROM) drive in order to achieve fine motion control of objective lens. The dynamic model of the proposed optical pick-up consisting of piezoceramic bimorph, wire suspension and objective lens is derived from Hamilton’s principle. A state-space control model is subsequently formulated by considering hysteresis behavior of the piezoactuator and frequency variation of the device as uncertainties. A sliding-mode controller, which is known to be robust to system uncertainties is designed for fine motion tracking control of the objective lens in vertical direction (focusing). The controller is then experimentally realized and position-tracking responses of the optical pick-up are presented in time domain. In addition, control durability is demonstrated by showing favorable tracking performance of a sinusoidal trajectory up to 8000 cycles of operation.

Hysteresis identification of polymethylaniline-based ER fluid using Preisach model

This paper presents the identification of field-dependent hysteresis in an electrorheological (ER) fluid using the Preisach model. As a first step, polymethylaniline (PMA) particles are prepared and mixed with silicone oil to make an ER fluid. A Couette type electroviscometer is then employed to obtain the field-dependent shear stress. In order to show the suitability of the Preisach model to represent a physical hysteresis phenomenon of the ER fluid, two significant properties namely the minor loop property and the wiping-out property, are experimentally examined. Subsequently, the Preisach model for the PMA-based ER fluid is identified using experimental first order descending (FOD) curves. The effectiveness of the identified hysteresis model is verified in the time domain by comparing the predicted field-dependent shear stress with the measured one. In addition, the hysteresis model proposed in this work is compared to the Bingham model.

Vibration control of an HDD disk-spindle system utilizing piezoelectric bimorph shunt damping: I. Dynamic analysis and modeling of the shunted drive

This work proposes a new piezoelectric shunt damping methodology to control the vibration of a computer hard disk drive (HDD) disk-spindle system. The first part of this work (part I) deals with dynamic modeling of the piezoelectric shunted drive, while the second part of this work (part II) covers experimental implementation of the proposed shunt circuits. In the modeling, a target vibration mode which significantly restricts the recording density increment of the drive is determined by analyzing the dynamic characteristics of the conventional drive. This is achieved by undertaking both modal testing and finite element (FE) analysis. In order to effectively suppress the unwanted vibration of the target mode, a piezoelectric bimorph is then designed and integrated to the drive by considering the mode shapes of the target vibration mode. The mechanical impedance of the shunted bimorph is derived from lamination theory and piezoelectric constitutive equations. In this derivation, the electromechanical coupling coefficient of the shunted drive is analytically incorporated with the mechanical impedance. Using the coupling coefficient, the shunt damping performance for the target vibration mode is predicted and evaluated by presenting the displacement transmissibility.

Non-contact start/stop motion control of HDD suspension using shape memory alloy actuators

In hard disk drives (HDD), an important issue related to increased storage density is the tribological problem of the head/disk interface. The conventional head gimbal assembly (HGA) of the HDD is used in a contact start/stop mode which results in wear particles and debris. This may cause a serious problem for the read/write function. In this paper, we propose a new type of suspension featuring a shape memory alloy (SMA) actuator in order to prevent friction between the head (slider) and disk. As a first step, a finite element analysis is undertaken to investigate modal characteristics of the proposed HGA. Using the principal modal parameters, such as natural frequency, a control system model is established and a sliding mode control algorithm to achieve a non-contact start/stop (non-CSS) mode is formulated. The key control principle for accomplishing the non-CSS mode is that the control input is to be employed in the SMA actuator before the disk rotates, and is disconnected when the angular velocity of the disk is fully developed to achieve a certain flying height. In order to demonstrate the effectiveness of the proposed control system, a conventional HGA is modified to integrate the SMA actuator. The control algorithm is experimentally realized and controlled motions for the non-CSS mode are presented in the time domain.

Vibration control of an HDD disk-spindle system using piezoelectric bimorph shunt damping: II. Optimal design and shunt damping implementation

This paper presents the experimental implementation of piezoelectric shunt damping for an HDD disk-spindle system. Prior to evaluating the shunt damping performance of the drive, the piezoelectric bimorph designed in part I is optimally redesigned so as to satisfy desirable shunt damping performance. The electrical admittance of the bimorph is derived from the piezoelectric constitutive equation and stress–strain relationship. Subsequently, in order to maximize the electrical admittance two electrodes of the bimorph are formed on an annular piezoelectric disk by considering the target vibration mode. The sensitivity analysis method is then employed to determine the optimal design parameters. After manufacturing the piezoelectric bimorph with optimally obtained design parameters, the vibration control performance of the proposed shunt damping for the HDD disk-spindle system is empirically evaluated in the frequency domain by changing the impact and measuring points.

Vibration Control of a CD-ROM Feeding System Using Electro-Rheological Mounts

This paper presents vibration control of a CD-ROM (compact disc-read only memory) drive feeding system using an electro-rheological (ER) fluid mount. An appropriate size of the ER mount, which is adaptable to existing CD-ROM drive feeding system, is designed and manufactured on the basis of Bingham characteristics of an ER fluid. After verifying that damping force of the ER mount can be tuned by the intensity of electric field, the ER mount is installed to the drive feeding system. The governing equation of motion is then derived, and a skyhook controller is designed to effectively control unwanted vibration caused from external excitation. The controller is incorporated with the hardware-in-the-loop simulation (HILS) methodology, and vibration control performances are evaluated in both frequency and time domains.

Design of Capacitive Displacement Sensor and Gap Measurement with High Precision Using Surface Acoustic Wave Device

SAW device is widely used as band pass filters, chemical or physical sensors, and actuators. In this paper, we propose the capacitive gap measurement system with high precision using SAW device. The research process is mainly composed of theoretical and experimental part. In the theoretical part, equivalent circuit model was used to predict the SAW response by the change of load impedance. In the experimental part, commercialized capacitor was used to see the SAW response by the change of load capacitance to check the feasibility as a sensor unit. After that, experimental setup to measure and adjust the gap was made and the SAW response by the change of gap which caused the capacitance change was measured. Finally, resolution and stroke was decided compared with the signal change and basic measurement noise level.

Wireless Gap Sensor Based on Surface Acoustic Wave Device

In this paper, we report a high-precision wireless gap sensor based on a surface acoustic wave (SAW) device. The sensing element is a parallel-plate capacitor whose dimensions are , and is attached to the SAW device as an external load. The SAW device, equipped with an RF antenna, serves simultaneously as a signal conditioner and an RF transponder. The center frequency of the SAW device is 450 MHz. The wireless gap sensor prototype exhibits a resolution of 100 nm and a sensing range of . The proposed sensor system can be used for remote, high-precision gap measurement in hard-to-reach environments.

Vibration suppression of HDD spindle-disk system using piezoelectric shunt damping

This work presents the feasibility of the piezoelectric shunt damping for vibration suppression of the rotating HDD disk-spindle system. A target vibration mode which significantly restricts the recording density increment of the drive is determined through modal analysis and a piezoelectric bimorph is designed to suppress unwanted vibration. The shunt circuit is constructed by considering two-dimensional electromechanical coupling coefficient of the shunted drive. In addition, optimal design process using sensitivity analysis is undertaken in order to improve the shunt damping of the system. The effectiveness of the proposed methodology is verified through experimental implementation by observing the displacement transmissibility of the system in frequency domain.

Design and analysis programme of electrorheological devices for vehicle systems

In this work, a dynamic program for design and analysis of electrorheological (ER) devices for vehicle systems is developed in a graphic user-interface (GUI) environment. The initial window of the program shows four subprogram modules which are related to the design of ER shock absorber, ER seat damper, ER engine mount and ER anti-lock brake system, respectively. Each module consists of three structures: input design parameter, dynamic analysis, and output display. In order to demonstrate the effectiveness of the proposed program, the ER shock absorber and ER engine mount are designed and manufactured on the basis of the program. A comparison of damping force characteristics between analysed and measured results is undertaken.