Search

In this paper, a thermally assisted magnetic recording (TAMR) head gimbal assembly (HGA) with an optical fiber and prism is proposed. The stiffness of a TAMR HGA is increased by an optical fiber and prism. Therefore, in this paper, operating shock analysis of a TAMR HGA considering the thermal effects during writing to record the data is numerically performed. Flying height (FH) analysis considering the thermal deformation by laser source also is investigated. As a result, judging from shock point of view, the shock characteristic of a TAMR HGA is better than that of conventional HGA. However, when considering the thermal effects during writing to record the data, the risk of contact for a TAMR HGA between media and slider is larger than that of conventional HGA. Hence, to solve these problems of a TAMR HGA, we should consider selection for material of media and TAMR slider, and design for head parts of TAMR slider.

A mobile hard disk drive (HDD) is often faced with inevitable mechanical problems because of the portability of the drive. Then, almost HDD use much faster emergency parking system to protect the system from these problems. However, very fast emergency parking causes a large ramp contact, which could create dimple-flexure interactions such as a dimple-flexure slip, head-gimbal assembly vibration, unexpected slider motion. These dimple-flexure interactions largely affect the flyability of a slider. As such, dimple-flexure interactions are one of the most important factors in designing a mobile HDD. Therefore, in this study, we characterized the dimple-flexure slip among dimple-flexure interactions and analyzed it using a combination of experiments and finite element modeling. We evaluated the feasibility of dimple-flexure slip and verified the main cause of dimple-flexure slip. We also investigated the relationship between dimple-flexure slips and ramp contact during emergency parking. Finally, we designed the finite element ramp contact simulation, and analyzed dynamic characteristics for the dimple-flexure slip.

To increase the near-field coupling efficiency in a near-field recording (NFR) system, extremely small air gap (less than 100 nm) between the solid immersion lens (SIL) and media should be maintained. However, maintaining the air gap is very important and difficult. Despite various anti-shock control methods, there are physical limitations to controlling the air gap against external shock. A safety mode that moves the actuator to the initial position for large external shock is currently being used. The existing safety mode exhibits good performance for downward shocks of 6 G amplitude and 10 ms duration time, but some problems arise for upward shocks of 3 G amplitude and 10 ms duration time. To avoid collision for upward and downward shocks, we present an improved safety mode that considers the direction of the external shock for an SIL-based near-field recording system. We analyzed the upward and downward shock responses of the NFR system. The shape of the pulse input was designed to minimize the overshoot of the actuator. Through various experiments, the amplitude and duration time of the pulse input were optimized. Even with an upward shock with 8 G and 10 ms, no collision was observed between the actuator and the media by using the improved safety mode with the optimized pulse input.

Holographic data storage system is one of the next-generation data storage systems and is characterized by its high storage density and fast data transfer rate. However, holographic data storage systems are very sensitive to disturbances that affect the position of the media. Therefore, tracking servo control is needed to ensure a good performance of the system even if disturbances occur, such as eccentricity of the disk and external shock. In our previous researches on tracking servo methods, we used additional beams or recorded servo track images with data pages to record additional gratings with data pages. Therefore, the recording density may be reduced and the system may be complicated. In addition, the performance of the system may be compromised by cross-talk noise caused between the reference beams and additional beams. In this paper, we propose a tracking servo method using the residual beam, which is reflected by the reflective optical filter. This method does not require recording supplementary gratings or use additional beams, and only needs to record data pages. The residual beam is retrieved with desired retrieved beam by the reference beam and wasted during the retrieving process. We first constructed a holographic data storage system and designed a reflective optical filter to detect tracking error signals. After detecting the tracking error signals, a tracking servo controller using a lead-lag compensator was incorporated to reduce the tracking error signals. The performance of the designed controller was verified by simulated and experimental results. Finally, the performance of the tracking servo method was investigated by comparing the retrieved data images.

In microholographic data storage system (MDSS), compact recording is required to achieve high capacity.[1] When the data is recorded, neighbor monomer is also affected by reaction at the focal point.[2,3] This unintended process caused more monomer consumption and degradation of total capacity. To avoid this extra consumption of dynamic range, it is required to define the effective dynamic range for MDSS. In this paper, we experimentally investigate the relation between dynamic range consumption and micro grating formation. Dynamic range consumption was monitored by real time read-out system. Micrograting was recorded with different consumption ratio and compared by diffraction efficiency of track direction. Finally, we define suitable dynamic range for MDSS Key Words : Microhologram,, Photopolymer, Dynamic range 1. 서서 론론론 ! "# $% . & ' (!&)* + ,-. /012 34 +5 ,-. 6 7. 89 :; ? +5 ,-. /01 !@ ! A $6 BC% . (!&)* + ,-. /012 3D EF GF9 HI 3D J < = $%6 KL , MN , Shift, OPQR %'S T %'S 3UV WX , 34 +5 ,-. YZ [T HI V \W6 ] ^W% . _ (!&)* + ,-. /012 9 `

As a standard of optical disk drive (ODD) was determined to Blu-ray diks (BD), researches for securing slim drive thickness, high data transfer rate and high capacity have been progressed. The actuator for applying BD is also required to have high performances, such as compatibility, slim thickness and 3-axis motion. In this paper, an asymmetric dual lens actuator is proposed to satisfy abovementioned performances. To design the actuator in a limited space, stress analysis and design of experiment (DOE) are performed to reduce weight of moving part and increase driving force and flexible mode frequency. Consequently, the final model, which is satisfied with specifications, is secured.

Holographic Data Storage System (HDSS), one of the next generation data storage devices, is a 2-dimensional page oriented memory system using volume hologram. HDSS has many noise sources such as crosstalk, scattering and inter pixel interference, etc. The noise source is changing intensity of the light used for carrying the data signal in HDSS. The inter pixel interference results in decrease of Signal to Noise Ratio and increase of Bit Error Rate. In order to improve these problems, this paper proposes to compensate the inter pixel interference with simple interference mask.

A control method for the angle servo of reference beam during reading recoded data images of a holographic data storage system is presented. The recording scheme with angle offset is adopted in order to verify the proposed angle servo. Using this recording scheme, the angle error signal is generated and we can implement the angle servo. Experiments have been performed on recording and reading data images to compensate Bragg angle mismatch.

Holographic Data Storage System, one of the next generation data storage devices, is a 2-dimensional page oriented memory system using volume holograms in writing and retrieving process. Recently photopolymer with disc type substrate was selected as a media for the Holographic Data Storage System. The disc tilt occurs when the media rotates and the external disturbance applies. The disc tilt causes the change of the angle between the reference beam and the media, the data cannot be retrieved with the right angle or other data page is retrieved. The tilt is generated in a 2-axis direction (tangential, radial). The tangential tilt direction is the same with the multiplexing plane, while the radial tilt direction is a perpendicular to the multiplexing plane. In this research we propose 2-axis tilt angle servo system. The tilt errors are measured by using external photo detector and the additional red laser. Then the tangential direction tilt is compensated by using the galvano mirror. Also the radial direction tilt is compensated by the rotating prism between the relay lens in the reference field. Finally we confirm the compensation results through the Signal to Noise Ratio(SNR) and Bit Error Rate(BER).

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.

This paper presents the improvement of an asymmetric actuator for optical image stabilization in a mobile phone camera. The required specification was defined from typical hand vibrations. The actuator was designed to have an asymmetric shape to reduce its size, but this design caused several problems. These problems were analyzed, and a new electromagnetic component design that solved these problems was proposed. Detailed dimensions of proposed design were obtained through the design of experiments procedure. Simulation results show that the final model exhibited sufficient performance to satisfy the required specification.

With the progress of information technology (IT), we need more advanced storage devices to accommodate the unprecedented expansion of information and the rapidly changing IT environment. Magnetic and optical recording storage devices, such as hard disk drive (HDD) and optical disk drive (ODD), are the best candidates for satisfying these demands and requirements. For 10 Tb/in2 HDD magnetic recording, we need to develop several advanced and innovative technologies related to the head disk interface (HDI), head/media, servo, and signal processing in current perpendicular magnetic recording (PMR). And, several new read/write mechanisms, such as heat-assisted magnetic recording (HAMR) and bit-patterned media (BPM), are being investigated by many researchers at several institutes around the world. In optical data storage, the page-based holographic data storage system (HDSS) and micro-HDSS are expected to achieve a higher user capacity with beyond terabyte. The near field recording (NFR) system was developed to confirm the feasibility of achieving a multiple terabyte capacity, and currently, through the application of NF nanogap servo system using a flexible media, it is possible to enhance the recording density and data transfer rate together.

In this paper, we propose a thermally assisted magnetic recording (TAMR) system with an optical fiber and specially designed prism attachment. The TAMR system utilizes an optical fiber and prism to facilitate the delivery of light to the slider and media. However, problems such as increasing suspension stiffness were encountered. Using an optical fiber increases the TAMR suspension stiffness and affects the pitch torque of the system. The pitch torque affects the flying height (FH), which can lead to slider-disk contact. Therefore, we investigated the stiffness of the TAMR suspension and the relationship between FH and the pitch static attitude (PSA). The various factors affecting the FH loss and the environmental conditions were also investigated. Finally, to compensate the large pitch stiffness and prevent slider-disk contact, the air bearing surface (ABS) of the TAMR system was optimized for robust slider performance, and the tolerance of the TAMR system was analyzed for the PSA considering various parameters such as temperature, relative humidity, operating conditions and manufacturing errors. The final PSA tolerances of the conventional and TAMR suspension were calculated. These values were 1.58° and 0.37°, respectively. The sensitivity of the optimal PSA design was decreased by about 21.5%. The PSA tolerance using the optimal design was 0.47°. This indicates that the tolerance of the optimal model is larger than that of original model, which was about 21.3%.

This paper describes a design method of a leaf spring using a genetic algorithm. To avoid disconnected shape, a novel genetic representation which contains travel points and their order is proposed. A two-stage search is performed to improve the convergence and compared with the single stage search. To demonstrate the proposed method, it is applied to a leaf spring for an optical disc drive (ODD) actuator. The final result of the genetic algorithm has unnecessary parts, and thus manual mending process is needed. The obtained design of the leaf spring satisfies the required specification. The proposed design method is very simple, and hence it is expected that the proposed design method can be easily applied to other applications.

The recording of micro holographic storage is performed by the superposition of two tightly focused counter-propagating beams. The micrograting is affected by misalignment in the z -direction during the recording and read-out processes. Thus, the diffraction efficiency (DE) can be reduced by the defocusing of the micrograting. In this paper, we investigate the recording characteristics of a defocused micrograting. An optical system with a numerical aperture (NA) of 0.60 and a wavelength of 532 nm was designed for micro holographic recording. The recording tolerance was formulated by using vector diffraction theory. The recording tolerance was determined by using the Mahajan's Strehl ratio (SR) of the DE. The DE was dramatically reduced at the ±0.4λ defocusing position and we determined that the ±0.4λ was the recording tolerance in the defocusing direction. In addition, we propose a precise detection method to obtain a focus error signal (FES) within the recording tolerance range. Finally, the numerical results of a defocused micrograting were experimentally verified.

In recent years, there have been many research studies focusing on next generation optical data storage technologies, such as near-field recording and holographic data storage systems. Many studies from several disciplines have been perfoed and merged to realize of the next generation optical data storage. The technologies that have been developed for optical data storage are also essential for the other research areas. These technologies can be widely applied to various fields, such as near-field optics-based microscopy, small-sized imaging systems, plasmonic nanolithography using a solid immersion lens (SIL) and a nanoscale aperture, and bio-applications. In this paper, the applications and concepts of the next generation of optical storage technologies are discussed.

This paper aims to improve the robustness of the air-gap controller for a solid immersion lens (SIL)-based near-field (NF) storage system against dynamic disturbances, such as external shocks. The robust control system is essential in NF data storage technology because the nanoscale gap distance between the SIL and the disk is 50 nm or less. Also, the air-gap distance must be maintained without physical contact between the SIL and the disk to evaluate the efficient reading and recording signals when an external shock is applied. Therefore, we propose an improved air-gap control algorithm with an acceleration feedforward controller (AFC) using time delay to maintain the nanoscale air-gap distance without collision for a 5.76 G at 10 ms shock. Thus, the anti-shock control performance for the SIL-based NF storage system in the presence of external shocks is markedly improved. Furthermore, to enhance the performance of the anti-shock air-gap control with AFC using time delay, we use the AFC using time delay with a double disturbance observer (DOB). As a result, the air-gap distance is controlled without contact for a 6.85 G@10 ms shock.

Optical image stabilization is a device to compensate the camera movement in the exposure time. The compensation is implemented by movable lens or image sensor that adjusts the optical path to the camera movement. Generally, the camera is moved by a handshake, thus the handshake is considered as an external disturbance. However, there are many other vibrations such as car and train vibration. In this paper, the optical image stabilization system in high frequency region is presented. Notch filter and lead compensator are designed and applied to improve the stability without changing the actuator. To verify the performance of the optical image stabilization system in high frequency region, the experiment equipment with moving object is established. It is confirmed that the opticalimage stabilization system does not diverge at the resonance frequency.

In this paper, a novel hybrid optical image stabilization (OIS) actuator for digital camcorder is proposed. Image stabilization for this hybrid type consists of both radially and tangentially moving components to compensate for hand trembling. The proposed OIS actuator, which uses a voice coil motor method, is divided into two parts: a structure and a magnetic circuit. For the structural part, the driving mechanism consists of two systems: one system is based on a ball guide with a magnetic spring, and the other system is based on a pivot bearing. The former system is typically used as a driving mechanism in mobile devices, whereas the latter system has advantages such as mechanical stability and reduced friction. Overall, a magnetic spring between the magnet and yoke should be considered to select the best magnetic circuit part design and mechanism design. Regarding the electro-magnetic (EM) circuit, two types of EM circuits were designed to satisfy each direction: one circuit is a moving magnet circuit for the radial direction, and the other circuit is a moving coil for the tangential direction. In a digital camcorder, the space for the OIS actuator is limited, and thus, optimized actuator with adequate performances is required. To solve these problems, a sensitivity analysis was performed using the design of experiment procedure. Based on these results, an objective function was defined for the optimization procedure. Finally, the actuator was fabricated, and the dynamic characteristics and feasibility of adapting two types of mechanisms of the suggested OIS actuator were verified. The experimental results indicate that the proposed OIS actuator exhibits sufficient performance for the sensitivity.

This study investigates the design of a flexible auto balancer (FAB) for the compensation of disk eccentricity. The FAB has various advantages over a conventional auto ball balancer, such as low cost, ease of implementation, lack of noise and applicability to standing-type drives. For the FAB design, a finite element model is developed considering the prestress effect and spin-softening effect caused by rotation. The structure is optimized and fabricated based on finite element model verification via modal testing. In addition, the dynamic behavior of the FAB is recorded by high-speed photography, and the vibration transmission to the base deck is measured.

Nano-precision gap measurement in the sub-micron range presents its own unique engineering challenge. The popular capacitive sensor platform, for example, is susceptible to the erroneous effect of electrode tilting and high noise floor, both of which are exacerbated by the small form factor required of a nano-precision gap sensor. In this paper, a capacitive gap sensor with a hemispherical electrode, used in combination with a SAW filter is presented. The proposed system outperforms the existing ones on two fronts. First, the system is virtually immune to the effect of electrode tilting due to the improved capacitor geometry. Second, it benefits from the outstanding signal conditioning capability of the SAW filter. Construction and characterization of a SAW-based capacitive gap sensor having resolution as fine as 10 nm are described.

We propose dual-wavelength Fourier ptychography for topographic measurement. To extend the axial measurement range, a single light-emitting diode (LED) and two appropriate bandpass filters are employed. This provides a speckle-free phase image, and reduces the possibility of a systematic error, which yields a high-quality topographic image. The proposed system can measure the surface topography in the range of nano- to micro-structures. The performance of the system is experimentally verified.

In this paper, a voice-coil actuator for OIS integrated in mobile phone camera is developed. The actuator with compliant mechanism is free from friction, so open loop control becomes possible and the performance of optical image stabilization can be improved. The compliant mechanism that consist 4 wires is designed for the OIS actuator and the electromagnetic part is also design and improved by using design of experiments. After all, the final design is fabricated and verified experimentally. The experiment result shows that the developed actuator has sufficient performance and good linearity for open loop control.

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.

The precision positioning system for semiconductor lithography requires a robust structural design to obtain enough control bandwidth and an efficient actuator with fast access time. In this article, a three-axis stage is proposed as a fine stage of a dual stage for the precision positioning. Its actuators are voice coil motors (VCMs) whose coil windings are mounted on the coarse stage and its magnets are on the fine stage. Between the fine and coarse stages, there is no mechanical connection but only magnetic coupling. The eight pairs of magnets and four coil windings are arrayed symmetrically. The three-axis stage's dynamic characteristics are improved by enhancing the actuating force and modifying its own structure using finite-element analysis in order to meet its requirements of high bandwidth and large forces. The actuating force is strengthened by modifying each VCM's magnetic circuit. The structure is designed to be robust by using design of experiment (DOE) as well. The modified stage is verified to have enough dynamic characteristics through experiments.

This paper presents the analysis of pitch static attitude(PSA) in thermally assisted magnetic recording(TAMR) suspension. The TAMR suspension using an optical fiber has high stiffness such as vertical, pitch and roll. Therefore, P-torque is greatly increased by the optical fiber. Also, flying height(FH) of the slider with TAMR suspension can be largely changed by PSA. In this paper, we focus on the FH by PSA of TAMR suspension. The FH is investigated using various PSA and proper PSA is proposed.

A conventional unloading analysis was carried out in no consideration for fast lateral velocity and disk rpm drop during the emergency parking. However, current hard disk drive (HDD) systems need an improved performance in the portable aspect. Therefore, much faster emergency parking is absolutely necessary to protect the system from sudden power-off or an external shock. In case of fast emergency parking, the fast lateral velocity causes an effective skew, and then there is a flying height (FH) loss which does not occur in a normal unload. Also, the FH loss induced by a disk rpm drop occurs at an unloading point in case that a portable small form factor HDD like 1.8 in is suddenly parking from inner diameter to outer diameter. This means that the unloading performance considering the effective skew becomes lower than one of the conventional unloading analysis. In this paper, we propose the advanced unloading analysis that can be applied to the fast emergency parking velocity. To do so, we investigate the FH loss by the fast lateral velocity and the disk rpm drop, and introduce the result of the advanced unloading analysis.

It is important to accurately estimate the flying height (FH) of the ultralow flying slider in hard disk drive (HDD). Especially, during the track-seeking motion, the FH can change by the motion from inner diameter (ID) to outer diameter (OD) and vice versa. The FH variation induced by the track-seeking motion happens over discrete track media (DTM). Therefore, the FH variation during track-seeking is an important issue and it certainly should be considered for DTM. In this research, we performed the track-seeking simulation using quasi-static approximation to reduce the computation time. The effects on groove depth, width, and pitch with the effective skew angle taken into account were investigated with the simulation. As a result, we calculated the absolute change in FH as a function of the effective skew angle and groove depth. Finally, we proposed that the model that considers the effective skew angle over DTM should be adopted in the track-seeking motion-studies.

In this paper, a design method based on genetic algorithm is proposed. Proposed design method is useful for inexperienced engineers to select a concept design and it also offers optimized result. A voice-coil actuator for optical image stabilization system in mobile phone camera is designed by using this method. To reduce the size, the optical image stabilization system is integrated with auto-focusing module and the Hall Effect sensor shares a magnet with a voice-coil. Combined electromagnetic analysis is used to reduce computing time. The final design from genetic algorithm is fabricated and verified experimentally. Experiment result shows that combined electromagnetic analysis is reliable and the final design has good performance.

A mode-switching servo is widely used in solid immersion lens (SIL)-based near-field recording (NFR) systems to control the air gap between the bottom surface of the SIL and the top surface of the rotating media. In the mode-switching servo, it is very important to reduce the initial overshoot in the near field region, as this overshoot can cause collisions between the SIL and the media, and increase the settling time required for the SIL to be initially moved to the final air gap. In this paper, the mode-switching servo with a brake pulse is proposed to reduce the initial overshoot and settling time. The effectiveness of the proposed method is proved by experiments of which results show that the minimum air gap due to the initial overshoot is improved from 6.86 to 18.73 nm and the settling time is reduced from 30 to 4.5 ms.

Recently, the demand of the information storage devices with large storage capacity such as Blu-ray Disc and high-definition television is increased. In keeping with this trend, the optical storage devices are also required to have high data transfer rate and large storage capacity. To satisfy these requirements, the actuator for optical disc drive should have a high servo bandwidth to compensate the vibration of optical disc. The servo bandwidth is limited by some flexible modes of the actuator, thus it is essential to make these frequencies of flexible modes to high frequency region. The frequency of flexible mode depends on materials and shape. Stiff materials and simple shape is useful to increase the frequency of flexible mode. In this paper, we suggested a moving magnet type actuator having flexible modes which are happened at high frequency region. Generally, the moving magnet type actuator has an advantage to increase the frequency of flexible mode because the moving magnet type actuator has simple structure and the Young’s modulus of magnet is high. However, large moving mass and inefficiency of Electromagnetic (EM) circuit cut down driving sensitivities of actuator. To improve driving sensitivities, we designed the model with the closed EM circuit for tracking actuation. The design of experiments (DOE) procedure is applied to get proper design parameters and the variable metric method (VMM) which is a technique of optimization is used to improve driving sensitivity. The lens holder is also improved based on the optimization result of EM circuit. And to make up for the low efficiency of EM circuit, the thermal stability is checked on condition that the input current is very high. At last, the final design of moving magnet type actuator is suggested and it is verified that the driving performance and the structural stiffness of the final design is sufficient.

The hard disk drive (HDD) using load/unload (L/UL) technology includes the benefits which are increased areal density, reduced power consumption and improved shock resistance than those of contact-start-stop. Dynamic L/UL has been widely used in portable HDD and will become the key technology for developing the small form factor HDD. The main design objectives of the L/UL mechanisms are no slider-disk contact or no media damage even with contact during L/UL, and a smooth and short unloading process. In this paper, we focus on pitch static attitude (PSA), roll static attitude (RSA), force position and dimple point. PSA and RSA are very important parameters in L/UL system and stability of slider is mainly determined by PSA and RSA. Dimple point is also important indicator. Also, we should consider lift-off force. The lift-off force, defined as the minimum air bearing force, is another very important indicator of unloading performance. The large amplitude of lift-off force increases the ramp force, the unloading time, the slider oscillation and contact-possibility. Therefore, to minimize lift-off force, we find the robust dimple point in L/UL performance.

Recently, there has been a trend to have large capacity and high data transfer rate in optical disk drive. Pickup actuator also should have high performance for satisfying this trend. Since moving magnet type actuator has more simple and robust structure than moving coil type one, we designed moving magnet type to accomplish high flexible mode frequency. However, the driving sensitivity of moving magnet type actuator was low because of its characteristics as following. At first, moving parts including magnets are heavy and electromagnetic (EM) circuits are not closed-loop owing to yoke composed of paramagnetic materials. Therefore, in order to increase the driving sensitivity without the degradation of the other dynamic characteristics, EM circuits were redesigned by adding solenoid coils on existing mechanism. As a result, the hybrid type actuator composed of moving magnet type and moving coil type was suggested to obtain high sensitivities and high flexible mode frequency. Design variables of EM circuits and structure parts were decided through parametric study and design of experiments procedure. Optimization algorithm using variable metric method was used to improve performance. Based on these results, the final model was presented.

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.

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.

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.

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.

In this paper, the rotary VCM actuator for small form factor (SFF) optical disk drive (ODD) is designed. The rotary VCM actuator needs high driving sensitivity, sufficient structural stiffness and thermal stability. These three performances are closely connected, so the coupled-field analysis of three kinds of physics is established. In order to establish thermal analysis model, the heat generated from voice coils is analyzed and convection heat transfer coefficient of the rotary VCM actuator is defined by thermal experiment. Overall performance which consists of driving performance, structural stiffness and thermal stability is optimized through design of experiments (DOE) and optimization procedures. At last, optimized actuator is confirmed that it can satisfy all specifications: size, driving performance, structural stiffness and thermal stability.

Microactuators for micromirror system have found many applications in various areas including projection displays, optical switches, RF switches and so on. In this paper we demonstrated micromirror actuator using ionic polymer metal composites (IPMC) that is a suitable candidate, since it has many attractive qualities such as durability, aquatic, miniature and light-weighted. Specially, IPMC has extraordinary advantages which are simple bending motion for low driving voltage (1–2 V), low power consumption, and simple structure. The IPMC actuator is made of Nafion NE-1110 (Dupont Co, Ltd., 260 µm thick) layer and electrode (platinum) layers and driven by 1–4 V. The displacement measured vertically is 0.25 mm and tilting angle is 11.3°. The angular motion, which is more than 10°, is a good advantage in the field of display module. This paper shows that the IPMC actuator has enough possibility for other applications.

This paper aims to suggest a concept design of a small form factor actuator for focusing or zooming systems of the camera phone lens. A traditional voice coil motor (VCM) type is used because it is very small, simple and reliable solution for the lens system. The topology optimization method is applied to suggest a structural design to maximize the actuating force without changing the input power and coils. The VCM system is generally composed of a permanent magnet (PM), a stator and voice coils; therefore, a simultaneous design of a PM and a stator is demanded. So far, many researches for the topology optimization of a ferromagnetic material have been achieved; however, very little has been done for the simultaneous design of a PM and a ferromagnetic material part. This study proposes a new methodology for the concurrent structural optimization for both parts. The optimization process must be formulated to support the sufficient force over whole stroke of the voice coil since the coil has a going and returning motion. The sensitivity calculation is accomplished by the adjoint variable method. Through the design process, a final concept design is suggested and its performance is verified using a commercial finite element analysis (FEA) package.

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.

A dual-layer near-field recording (NFR) optical system with a high numerical aperture (NA) of 1.84 was designed by appropriate cover and spacing layer selection, using layers with refractive indices of 2.0. The designed aplanatic imaging optics exhibited additional aberrations in the multi-layered stack, mainly due to the air-gap and spacer layer. Given optics designed only to compensate for aberrations caused by a 2-μm-thick cover-layer, a 3-μm-thick spacer layer induces 96.2 mλ rms and 6.5 mλ rms of spherical aberration and defocus, respectively. A complete electric field calculation analysis for the inside of the multi-layer stack verified that diffraction-limited spot quality can be ensured on the recording layer with phase-only correction. As the aberration caused by the multi-layered stack cannot be corrected perfectly, due to the high oscillation of the aberration function along the radial direction in the exit pupil, three different types of liquid crystal (LC) electrodes were considered for practical implementation. Of the three phase-correction methods, the approximate linear phase-correction method was the most tolerant of axis decenter from the optical axis, providing acceptable diffraction-limited correction performance.

We propose a novel optical design method for small F/number (F/#) compact camera module using wavefront coding. Decreasing the F/# decreases the focus depth of the optical system, which can result in manufacturing tolerances so tight that fabrication is impossible. To obtain reasonable tolerances for easy fabrication and alignment of compact camera module, we designed the final imaging system to have a target wavefront with an extended focus depth. Because additional optical elements, such as phase plates, are not available for compact camera modules, target wavefront should be the combination of the wavefront errors of all lenses in the optical system. Wavefront-coded compact camera modules have higher tolerances and an extended focus depth, so that the images obtained from them have high resolution over a broad defocus range. Images simulated by a wavefront-coded optical system can be restored to much higher resolution using deconvolution of images and a point spread function given by the coded target wavefront.

In the assembly of the solid immersion lens (SIL) optical head for cover-layered incident near-field recordings (NFRs), disk contact with the bottom surface of the SIL has previously been regarded as essential. This is because SIL optical heads are designed to interface with a cover layer. However, SILs can be contaminated and damaged by this contact. We present a new SIL optical head assembly method for cover-layered incident NFRs without disk contact with the bottom surface of the SIL. To achieve this, we added zoom optics to a Twyman–Green interferometer in the measurement beam optical path. Our assembly method eliminates SIL contamination problems and the assembly procedure becomes simple because of removing the disk contact process. In addition, it is not necessary to consider the aberrations induced by disk tilt and cover-layer thickness variation. The SIL optical head assembled by the proposed method has good optical performance satisfying the optical tolerances and the measured wavefront aberration is good agreement with simulations.

We analyzed the effect of an annular aperture on solid immersion lens (SIL)-based near-field recording (NFR) to verify the feasibility of applying an aperture to SIL-based NFR. SIL-based NFR with an annular aperture, which blocks the propagating waves, shows good characteristics such as a beam profile on the recording layer and beam propagation inside a medium. By introducing the annular aperture, the focused beam spot size and its sensitivity to the gap between SIL and the surface of the medium can be decreased, and the axial confined beam distribution can be obtained inside the medium. We also show that the general gap control method can be applied to SIL-based NFR with an annular aperture through the calculated exit pupil intensity distribution of the reflected electric field.

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.

We introduce the design method of a hybrid lens composed a refractive lens and a diffractive optical element (DOE) considering the diffraction effect for a compact camera module. When imaging optical system is designed using the DOE, diffraction efficiency of the DOE and stray light due to the unintended diffraction light should be considered. Therefore, to analyze the effect of diffraction efficiency of the DOE on image characteristics, we evaluate the performances of two designed compact camera lenses, which have different construction wavelengths, using the modulation transfer function (MTF) considering diffraction efficiency. The stray light that is induced by the diffraction effect of the DOE is analyzed by calculating the focal position according to each diffraction order, and a method for the reduction of the stray light is proposed.

We have designed a novel solid immersion lens (SIL) optical head to increase SIL thickness tolerance for the fabrication and assembly of a SIL optical head. We have applied an aspherical replicated lens to a general SIL optical head to improve SIL thickness tolerance more than that of a hemispherical SIL and to maintain as high a numerical aperture as a super-hemispherical SIL. By using an aspherical replicated lens, we were able to reduce the sensitivity to spherical aberration with respect to variations in the SIL thickness, which are the main cause of narrow SIL thickness tolerance. This SIL optical head design shows that the SIL thickness tolerance is larger than 30 µm and the numerical aperture is 1.88, which is as high as that for a super-hemispherical SIL.

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%.

The near-field recording (NFR) system requires the clearance between a slider and disk surface in order to maintain the significant effect on the evanescent wave. The optical flying head (OFH) should also have a small pitch to control the contamination effect. The larger the gap between the leading edge of the slider and the disk, the more the particles come into solid immersion lens (SIL), thereby causing a negative influence on the NFR system. However, the flying stability turns out to be ineffective as the pitch angle reduces. Accordingly, it is necessary to consider dynamic characteristics of OFH in air-bearing surface (ABS) design. The objective of the ABS design is such that the flying height (FH) of the OFH should be as flat as possible over the inner diameter (ID) and outer diameter (OD) of the disk, and FH should be controlled at about 50 nm for both ID and OD in the static state. The better NFR system can also be obtained by a smaller modulation. The numerical optimization in the static state is first carried out, and the dynamic optimization is subsequently performed based on the static optimal model. The dynamic simulation and experiments are additionally performed to verify the proposed design optimization results.