Dongho Oh

A Two-Dimensional Laser Scanning Mirror Using Motion-Decoupling Electromagnetic Actuators

This work proposes a two-dimensional (2-D) laser scanning mirror with a novel actuating structure composed of one magnet and two coils. The mirror-actuating device generates decoupled scanning motions about two orthogonal axes by combining two electromagnetic actuators of the conventional moving-coil and the moving-magnet types. We implement a finite element analysis to calculate magnetic flux in the electromagnetic system and experiments using a prototype with the overall size of 22 mm (W) × 20 mm (D) × 15 mm (H) for the mirror size of 8 mm × 8 mm. The upper moving-coil type actuator to rotate only the mirror part has the optical reflection angle of 15.7° at 10 Hz, 90°at the resonance frequency of 60 Hz at ±3V(±70mA) and the bandwidth of 91 Hz. The lowermoving-magnet type actuator has the optical reflection angle of 16.20°at 10 Hz and50°at the resonance frequency of 60 Hz at ±5V(±34mA) and the bandwidth of 88 Hz. The proposed compact and simple 2-D scanning mirror has advantages of large 2-D angular deflections, wide frequency bandwidth and low manufacturing cost.

Topology Optimization of a HDD Actuator Arm

A study on the topology optimization of Hard-Disk-Driver(HDD) actuator arm in free vibration is presented. The purpose of this research is to increasse the natural frequency of the first lateral mode of the HDD actuator arm under the constraint of total moment of inertia, so as to facilitate the position control of high speed actuator am. The first lateral mode is an important factor in the position control process. Thus the topology optimization for 2-D model of the HDD actuator arm is considered. A new objective function corresponding to multieigenvalue optimization is suggested to improve the solution of the eigenvalue optimization problem. The material density of the structure is treated as the design variable and the intermediate density is penalized. The effects of different element types and material property functions on the final topology are studied. When the problem is discretized using 8-node element of a uniform density, the smoothly-varying density field is obtained without checker-board patterns incurred. As a result of the study an improved design of the HDD actuator arm is suggested. Dynamic characteristics of the suggested design are compared computationally with those of the old design. With the same amount of the moment of inertia, the natural frequency of the first lateral mode or the suggested design is subsequently increased over the existing one.

Design of Rotating Moving-Magnet-Type VCM Actuator for Miniaturized Mobile Robot

A voice coil actuator with a rotating moving magnet has been developed for a miniaturized mobile robot. The actuator has simple structure comprising a magnet, a coil, and a yoke. Actuator performance is predicted using a linearized theoretical model, and dynamic performance based on the air-gap between the magnet and the coil is predicted using motor constant and restoring constant obtained through finite element simulations. The theoretical model was verified using a prototype with 60 Hz resonance and 80 Hz bandwidth. We found that an input of 1.5 V can make the actuator rotate by statically. The driving configuration of the proposed actuator can be simplified because of its implementation of open-loop control.

Optimization of wide-bandwidth hard disk drive actuator design using statistical methods

As track density of hard disk drives is intensified, actuator dynamics has emerged as one of the most important design factors not only for high-performance models but also desktop applications. In spite of many different complex physical considerations required for successful wide-bandwidth actuator designs, most current design processes that rely purely upon designers experience-based historical approaches do not effectively account all factors to determine optimum design. A development of design optimization procedure for a high-performance actuator is presented in this paper. A position error signal (PES) estimator employing both numerical model and experimental data is developed for effective and accurate optimization process. Statistically formulated optimization method presented here delivers not only wide-bandwidth actuator design for PES reduction but higher shockproof HDA design. Furthermore the presented method incorporates volume production parameters so that designers are able to predict design tolerance and cost relations.

Dynamic Analysis of Rotor Systems Considering Ball Bearing Contact Mechanism

We propose a finite element modeling method considering the ball bearing contact mechanism, and the developed method was verified through experimental and analytical results of inner and outer race-type rotor systems. A comparison of the proposed method with conventional method reveals that there is little difference in the results of the inner race-type rotor system, but there are considerable differences in the results of the outer race-type rotor system such that predictions of greater accuracy can be made. Therefore, the proposed method can be used for accurately predicting the dynamic characteristics of an outer race-type rotary machine.

Adaptive feedforward rejection of microactuator resonance in disk drive dual-stage actuator servo

This paper proposes a novel adaptive feedforward controller (AFC) design method for eliminating the effect of microactuator resonance on dual-stage actuator servo systems for hard disk drives. An adaptive resonance frequency tracking algorithm is also proposed to deal with uncertain resonance frequency, which is developed based on the orthogonality of AFC coefficients. The performance of the proposed AFC is tested by numerical simulations.

Identification of shock characteristics in hard disk drive by using time-frequency signal processing technique

A transient signal processing technique using Wigner distribution (WD) is applied to identify the dynamic characteristics when a disk drive system is subject to external shock vibration. It is shown that the smoothed WD technique essentially reveals the propagating characteristics of shock vibration on the specified position of disk drive system as well as head-slap and lift-off phenomena. A parametric investigation for the shock spectrum of suspension is also presented to provide a useful guideline for the shock-resistant disk drive design.

Active correction of mass imbalance for a precise rotor

An active mass imbalance correction method for a precision rotor that is formulated iteratively is introduced. Since mass imbalance of a precise rotor has been one of the critical volume production issues for a long time especially in the data storage industry, various imbalance correction methods are developed and successfully implemented. Nevertheless, volume manufacturing tolerance of the mass imbalance has ever been tightened up as the data storage density has been increased. Recognizing the limitation of the practicality of fine-tuned rotor balance for volume production, development of an adaptive dynamic rotor balance scheme is of great worth. In the present work an application of frequency based control method popularly used for repeatable runout compensation to the mass imbalance reduction enables reliable accurate balancing of precise rotor.