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This paper suggests a method for analyzing moving-magnet type actuators for optical pickups. To move the objective lens to the desired position, voice coil actuators use the electromagnetic force, which is the force exerted on a charge moving in a magnetic field. When an electric current passes through a coil, the coil becomes an electromagnet by the solenoid effect. This causes the force between a coil electromagnet and a permanent magnet. The force affects flexible modes of voice coil actuators because it is dynamic force with the frequency same as that of a driving current. Therefore, the analysis, which considers both the electromagnetic force and that between a coil electromagnet and a permanent magnet, is suggested. The moving-magnet-type actuator is fabricated and its dynamic behaviors are measured experimentally to demonstrate and validate the analysis method. As a result, it is verified that the analysis method offers more exact simulations than current methods. Finally, the dynamic behaviors of the moving-magnet-type actuator are improved using the analysis method. Index Terms--Actuator, electromagnet, moving magnet, solenoid, voice coil.

The aim of this research is to improve the robustness of the air gap controller for solid immersion lens (SIL)-based near-field recording (NFR) servo systems against dynamic disturbances such as external shocks. Stable control is essential in these systems because the air gap distance between the SIL and the rotating disk is less than 100 nm. To detect gap error and read-out signals for the SIL and the disk, the air gap control performance must be increased to avoid collisions due to external shocks. We propose an anti-shock air gap control system using a disturbance observer (DOB) and a dead-zone nonlinear controller. Experimental results demonstrate that a DOB with a Q filter bandwidth of 500 Hz reduced the minimum air gap distance due to an external 1 g@10 ms shock by 70.1%. A DOB and a dead-zone nonlinear controller maintained the optical head distance for a 2 g@ 10 ms shock. Thus the control performance in the presence of external shocks was improved. Index Terms--Anti-shock control, dead-zone nonlinear controller, disturbance observer (DOB), gap error signal (GES), near-field recording (NFR).

This paper explores the dynamic characteristics of slim optical disk drives and the modification of their structural dynamics to reduce vibration using a simplified finite-element (FE) model. The FE model was constructed using simplified geometry and valid element types that effectively reflect the dynamic characteristics. The FE model was verified by experimental modal analysis (EMA). Design parameters were extracted and selected to modify the structural dynamics using design of experiments, topology optimization, and modal strain energy distribution. A prototype of the modified model was constructed and its anti-vibration performance was estimated using EMA and comparison of frequency response function. Index Terms--Experimental modal analysis, finite-element method, slim optical disk drive, structural dynamics modification.

In this paper, a finite-element model of a slim optical disk drive is developed to investigate the transient response of the sled base and disk. The model is simplified by using beam, shell and lumped parameter elements, in order to decrease the computational time. After the dynamic characteristics of the finite-element model have been verified by modal test, the shock response is obtained and compared with the results of a drop test. Finally, dynamic characteristics are modified to improve the shock performance. Index Terms--Finite-element method, linear drop test, shock analysis, slim optical disk drive.

This research explores the design of a dynamic vibration absorber (DVA) using a cantilever beam with tip mass. Compared to a conventional DVA using a rubber bobbin, the proposed DVA isolates vibrations more effectively due to the low damping properties of its structure, which are the principal reason for its excellent anti-vibration performance near the anti-resonance frequency. This low damping decreases the harmonic response at the rotational frequency of the disk. To design the proposed DVA, the dynamic characteristics of the optical disk drive were represented with lumped parameter and finite element models. The dimensions of the beam were tuned to reduce the vibration in multiple axes based on this model. Tolerance analysis were performed so the drive would be robust against normal dimension variance due to the manufacturing process, and the variation in the dynamic characteristics with respect to the pickup position was investigated. The anti-vibration performance of the DVA was also measured experimentally. Index Terms--Dynamic vibration absorber, finite-element model, lumped parameter model, optical disk drive.

Most hard disk drives use ramp load/unload (L/UL) technology because of its many advantages. However, L/UL does have some unresolved drawbacks, such as slider-disk contact during fast unloading. The main objective of our research is to examine the use of a bump on the outer edge of the disk to prevent contact with the disk by the rebounding slider and to improve ramp unloading performance. In particular, this paper focuses on experimental verification of the design of the disk bump that resulted from our previous research. We formed the disk bump on the disk surface using mechanical pressing with tungsten tips and tested the effect of the bump in unloading experiments. An investigation of the acoustic emission burst signal and its power spectrum confirmed that the optimal disk bump prevented slider-disk contact. This improves the ramp unloading performance. Index Terms--Disk bump, load/unload, mechanical pressing method, slider-disk contact, unloading performance.

Most hard disk drives that apply the ramp load/unload technology unload the heads at the outer edge of the disk while the disk is rotating. During the unloading process, slider-disk contacts may occur by lift-off force and rebound of the slider. The main issue of this paper is to prevent the slider-disk contact by rebound, and we apply a disk bump to the unloading process. To do so, first, the ranges of bump dimension are determined. Second, the stability of each bump is checked by dynamic simulation. Finally, unload analyses are performed for stable bump designs. As a result of these analyses, we investigate proper bump design and position for the unloading process. Through this research, we propose the optimal bump design to improve the unloading performance. We can also identify to remove rebound contact by applying a bump on disk to the unloading process. Index Terms--Bump design, load/unload, rebound contact, unloading performance.

We propose a new load/unload (L/UL) suspension featuring shape memory alloy (SMA) thin film and demonstrate its effectiveness through the L/UL simulation. We estimated the mechanical properties of the SMA with respect to the material phases by experiment and designed the proposed suspension by considering the vibration modes related to the L/UL performance. In order to effectively verify the effectiveness of the proposed suspension, we designed the suspension to have similar L/UL performance to that obtained from the conventional suspension when the SMA film is not activated. After analyzing the L/UL design parameters of the proposed suspension when the SMA is activated, we examine the relative performance of the conventional and proposed suspensions by L/UL simulation by comparing the vibration motions of the slider and the minimum gap size between the disk and slider. Index Terms--Dynamic load/unload, phase transition, shape memory alloy, suspension design.

Current developments in the solid immersion lens (SIL) based near-field recording technology are briefly introduced and research results including design, analysis, and experiments in CISD are reported. Also, the concept and performance of the novel optics using SIL is described throughout this paper. To increase the center thickness tolerance of SIL and decrease chromatic aberration, we add the replicated lens on SIL and the diffractive optical element (DOE). As a result of this design, it is confirmed that the SIL thickness tolerance of the replicated SIL optics is from--15 up to 7 [micro]m at 0.035[lambda] rms, and wavefront aberration is less than 0.035[lambda] rms through variation of wavelength from 401 up to 412 nm. Index Terms--Gap-error signal, near-field recording (NFR), replicated lens, solid immersion lens (SIL).

Repetitive control is a widely used technique for the compensation of repeatable error in systems that contain rotating mechanisms or repeat a trajectory. Generally, it includes delay chains and a low-pass filter in the positive feedback loop, which generate a periodic signal. The controller has typically been implemented in a plug-in fashion and designed heuristically with the simplest form of the filter. However, this design approach is somewhat ambiguous in the selection of controller parameters because of its influence over nonharmonic frequencies. Also, it leaves the possibility for further improvement. This paper presents an improved design method for the repetitive controller that provides minimum track misregistration (TMR) in a hard disk drive (HDD). For TMR prediction, the method identifies disturbances acting on an HDD and estimates servo performance, using the identification result. We have confirmed the identification and estimation procedure through experiments. In our method, first the basic tracking controller is designed and later the repetitive controller is designed in conjunction with a Q filter. A cost function based on Parseval's theorem, reflecting the servo performance as TMR, is defined. Then the servo performance is estimated from the identified disturbance, and the plant and designed controller's frequency response are modified as necessary by changing the parameters of the controller, whose optimization is carried out with a commercial nonlinear optimization tool. The design strategy facilitates the controller design by providing an accurate estimation for the attainable servo performance and design criteria under the optimization framework. Index Terms--Disk drives, optimization methods, repetitive controller.

Disk runout consists of repeatable runout (RRO) and nonrepeatable runout (NRRO). NRRO is the main cause of track misregistration that prevents a high track density, whereas tracking servo control can compensate for most of RRO. An increase in the disk rotation speed increases the amplitude of disk flutter and, hence, causes head position error. Disk flutter is mainly caused by air disturbance due to disk rotation. Many previous researches, have intended to investigate the vibration characteristics of rotating disks and the head off-track mechanism. They have used the head position error signal in servo system and approximate solution of head and disk dynamics using finite element modeling for a stationary disk to investigate the head position error. In this paper, the displacement spectrum is obtained by integrating the velocity data and removing the low-frequency component associated with integration noise. The axial displacements are converted to radial track misregistration units by modal analysis, the reformed Barasch method, and experimental study of the disk. The interaction between head and disk is precisely solved, and it becomes possible to predict the track misregistration by analyzing the disk flutter and transfer ratio for various disks. Index Terms--Disk flutter, displacement metric, rotating disk, track misregistration.

We propose a gap servo method to reduce the overshoot in the near-field (NF) region. In general, we use a mode-switching servo which consists of approach, hand-over, and gap-control modes. However, there is a critical problem, such as an overshoot at the turning point from the approach mode to the hand-over mode, which may cause a collision between the SIL and the disk. In this paper, we propose an improved NF gap servo system using an exponential input in the approach mode which can reduce the overshoot and settling time of the mode-switching servo. Index Terms--Gap error signal (GES), mode-switching servo, near-field recording (NFR), overshoot.

As rotational speed and track density of disk media in optical disk drives increases, an optical pickup actuator must have a high servo bandwidth for its focusing and tracking control to follow disk fluctuations. In this paper, we propose an efficient method to improve control bandwidth of actuators through changing the shape of cross section of coils without redesigning structural parts. Index Terms--Actuators, coils, design, frequency response, optical recording, stability.

This paper analyzed the effect of lubricant contact on slider dynamics under the unsteady proximity condition, which is related to the intermolecular forces between the slider and disk. To investigate the slider dynamics, an experiment was conducted with a commercial drive, and the slider dynamics were analyzed during touch-down and takeoff (TO) considering the approach and withdrawal speeds of the slider. The instability of the slider dynamics increased under the rapid withdrawal condition during TO. [ABSTRACT FROM AUTHOR]

With an increased mobility, hard disk drives (HDDs) now use ramp load/unload technology, and multiple disks are used to increase the data capacity. This can result in contact between the ramp and the disks, which negatively affects the slider dynamics under operational shock conditions. There are several types of ramp–disk contact, such as simultaneous, successive, and single contact, and these depend on the distance between the ramp and each disk in a multi-disk HDD. This paper examines the effect of ramp–disk contact on the slider dynamics using a transient shock analysis. The ramp–disk contact affects the head stack assembly bending mode and slider dynamics. The effect of irregular gaps between the disks and adjacent ramp on the slider dynamics is analyzed with the ramp–disk contact force. The simulation shows that the gap irregularity between the ramp and each disk should be as small as possible to improve the stability of the slider dynamics. [ABSTRACT FROM AUTHOR]

Operational shock (op-shock) analysis has been developed to consider the dynamics of components of a hard disk drive (HDD). Op-shock simulation uses simplified models. However, the dynamics of the components affect the head–disk interface (HDI) response, especially the disk curvature and ramp–disk contact. This paper investigated the effect of the dynamics of HDD components on the HDI response. As the HDD is more sensitive to external shock and vibration, the effects of the dynamics of HDD components need to be considered for accurate op-shock analysis. The ramp–disk contact is an important factor in an op-shock simulation, because ramp–disk contact and disk deformation occur during the shock. Therefore, this op-shock simulation modeled the ramp–disk contact and considered the disk curvature. To obtain an accurate result, a two-way coupled method was used to investigate the HDD dynamic response during op-shock. Using the op-shock model, the fluid-structure coupling effect was investigated and compared with a decoupled model that used linear springs to replace the air bearing. Then, we investigated the effect of the ramp–disk contact and disk curvature on the HDI response during a shock. [ABSTRACT FROM AUTHOR]

Recent advancements in mobile devices have fueled a requirement for information storage systems with characteristics such as subminiature size, low cost, and minimum power consumption. Small optical disk drives could provide a good solution, be- cause their storage media is cheaper than those of hard disk drives or flash memories. In this paper, a small linear actuator that can be used to provide seeking and fine tracking for small optical disk drives was designed using structural and electromagnetic analyses. The designed actuator was optimized by applying design of experiments (DOE) and response surface method (RSM) techniques to verify the effectiveness of the initial design and further improve its performance characteristics, such as output power and compactness. The dynamic performance of the designed linear actuator was evaluated by experiments. [ABSTRACT FROM AUTHOR]