Hyun-Woo Hwang

Anti-Shock Air Gap Control for SIL-Based Near-Field Recording System

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.

Improved Antishock Air-Gap Control Algorithm with Acceleration Feedforward Control for High-Numerical Aperture Near-Field Storage System Using Solid Immersion Lens

A near-field storage system using a solid immersion lens (SIL) has been studied as a high-density optical disc drive system. The major goal of this research is to improve the robustness of the air-gap controller for a SIL-based near-field recording (NFR) system against dynamic disturbances, such as external shocks. The servo system is essential in near-field (NF) technology because the nanogap distance between the SIL and the disc is 50 nm or less. Also, the air-gap distance must be maintained without collision between the SIL and the disc to detect a stable gap error and read-out signals when an external shock is applied. Therefore, we propose an improved air-gap control algorithm using only an acceleration feedforward controller (AFC) to maintain the air-gap distance without contact for a 4.48 G at 10 ms shock. Thus, the antishock 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 antishock air-gap control, we use the AFC with a double disturbance observer and a dead-zone nonlinear controller. As a result, the air-gap distance is maintained without contact for a 6.56 G@10 ms shock.

High-Speed Gap Servo Control for Solid-Immersion-Lens-Based Near-Field Recording System with a Flexible Optical Disk

Higher data storage capacities and higher data transfer rates will be required in next-generation information storage devices. However, there is a limit to the rotational speeds of conventional disk structures. Hence, conventional disks will not be able to achieve high data transfer rates of over 250 Mbps that is required for next-generation storage devices. To increase the data transfer rate of a disk, flexible optical disks have been studied with the goal of stable rotation at a high speed, using a stabilizer to reduce disk oscillations. If a flexible optical disk is implemented in a near-field recording (NFR) system, simultaneous high data transfer rates and high-density recording should be possible. In an NFR system, it is very important to maintain the gap between the solid immersion lens (SIL) and the disk at distances below tens of nanometers. In this study, to simultaneously achieve high data storage capacity and high data transfer rate, we propose an improved gap servo control system for an SIL-based NFR system with a flexible optical disk. To enable robust control at a high rotational speed, a repetitive controller was designed and applied to the NFR servo algorithm. In both simulation and experiment, the newly designed gap servo controller stably maintained the gap distance in the SIL-based NFR system using a flexible optical disk.

Preisach modeling of dielectric elastomer EAP actuator

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.

Improved Air Gap Control With Acceleration Feedforward Controller Using Time Delay for Solid Immersion Lens-Based Near-Field Storage System

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.

Performance enhancement of IPMC by anisotropic plasma etching process

Ionic Polymer-Metal Composites (IPMCs) of EAP actuators is famous for its good property of response and durability. The performance of Ionic Polymer-Metal Composites (IPMCs) is an important issue which is affected by many factors. There are two factors for deciding the performance of IPMC. By treating anisotropic plasma etching process to 6 models of the IPMCs, enhanced experimental displacement and force results are obtained. Plasma patterning processes are executed by changing the groove and the land length of 6 patterns. The purpose of the present investigation is to find out the major factor which mainly affects the IPMC performance. Simulations using ANSYS have been executed to compare with the experimental results about the values and the tendency of data. Experimental and simulating data of the performances seem to have similar tendency. In the next part of the paper, we observed the other properties like capacitance, resistance and stiffness of 6 plasma patterned IPMCs. And we observed that the stiffness is the major factor which affects the performance of IPMCs. As we seen, our problem has been reduced to investigate about the property of stiffness. We suggest that the stiffness is largely changed mainly because of the different thickness of Platinum stacked of the groove and the land part which are produced by anisotropic plasma etching processes. And we understand that anisotropic plasma patterned IPMCs of better performance can be applied to various applications.

Enhanced Air-Gap Control for High-Speed Plasmonic Lithography Using Solid Immersion Lens With Sharp-Ridge Nanoaperture

Recently, plasmonic nanolithography is studied by many researchers (1, 2 and 3). This presented a low-cost and high-throughput approach to maskless nanolithography technique that uses a metallic sharp-ridge nanoaperture with a high strong nanometer-sized optical spot induced by surface plasmon resonance. However, these nanometer-scale spots generated by metallic nanoapertures are formed in only the near-field region, which makes it very difficult to pattern above the photoresist surface at high-speeds.© 2011 ASME

Performance improvement of IPMC using resonance frequency

Ionic polymer metal composites is the proposing material for applications, since it has many attractive qualities that are durability, aquatic, miniature and light-weighted. Especially, IPMC has extraordinary advantages that are large displacement at low driving voltage(~3V), low power consumption and simple structure. However, slow time response prevents IPMC from various applications. Since IPMC is generally used in simply-supported configuration, which has same characteristic with a cantilever beam, IPMC has natural frequency and it oscillates extremely at natural frequency. We propose new open loop control method based on frequency response, which is combined with conventional DC input. This method is experimentally tested and compared with result by conventional input.

Improvement of Protection Process Using Observer for Soild Imersion Lens-Based Near-Field Recording

In the near field recording (NFR) system, there always exists the possibility of collision between solid imersion lens (SIL) and media owing to dust, scratches on the media, and external shock because of the extremely small gap distance. The kinetic energy associated with damage from shock is directly proportional to the square of velocity, and the phase of velocity is faster than the phase of displacement with 90°. Thus, it is effective to prevent a collision on the basis of velocity information. The velocity of the actuator in the NFR system should be estimated by an observer without using a velocity sensor. In this paper, we propose an improved protection process with a mode switching servo method using a Luenberger observer. The gap distance state can be estimated earlier by detecting the velocity state yielded by external shock. Through simulations and experiments, we confirm that the protection process based on velocity and gap distance is more powerful than the protection process based only on the gap distance.