Seungho Lim

Optimal Design of Rubber Mounts Supporting Notebook HDD for Shock and Vibration Isolation

Notebook PCs, especially its hard disk, suffer impact-induced failure as well as vibration problems. Consequently shock and vibration performance plays a decisive role in the product design. To minimize the likelihood of failure in such cases, cushioning materials are often used. In this paper, we analyzed dynamic characteristics and shock response of the system supported by non-linear rubber mounts using modal parameters extracted from vibration test. In addition, optimal design of rubber mount was developed.

Cantilever Dynamic Vibration Absorber for Reducing Optical Disk Drive Vibration

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.

Structural Dynamics Modification of Slim Optical Disk Drive

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.

Finite-Element Shock Analysis of Slim Optical Disk Drives

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.

Modal Analysis of Optical Disk Rotating at 15,000 rpm Close to a Rigid Wall

The rotational speed of optical disks must be above 15,000 rpm owing to the required high data-transfer rates. At these speeds, the airflow between the rotating disk and a rigid wall is important when identifying the dynamic characteristics of the disk in a slim optical disk drive. This airflow is simulated using a numerical model and examined by a closed-form modal analysis. The calculated dynamic characteristics of the rotating disk can be used to predict the nonrepeatable runout for the servo controller design.

Opto-Mechatronics Issues in Solid Immersion Lens Based Near-Field Recording

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 mum at 0.035lambda rms, and wavefront aberration is less than 0.035lambda rms through variation of wavelength from 401 up to 412 nm

Vibration Source Identification and Finite Element Model Construction of Optical Disk Drive

Optical disk drives (ODDs) are subjected to vibrations caused by the high-speed rotation of the optical disk, and these vibrations can be excessive and reduce the read/write performance. Elastic rubber mounts with cushioning materials are often used to minimize these problems. In this paper, the source of vibrations was identified by experimental modal tests and high-speed photography. Structural modifications were made based on a lumped parameter model and a finite element model.

Shock Isolation of Optical Pickup in Optical Disk Drive

The optical disk drive is subjected to many different types of shock environments. Especially, the harsh shipping condition makes the mechanical failure of the optical components and damages to read/write performance. Thus it is necessary to improve the anti-shock performance of the shock isolator for optical pickup from external mechanical shock. In this paper, the shock analysis of the shock isolator is performed using the explicit finite element method and verified with the linear drop test. Based on the verified numerical model, the shape of the shock isolator is optimized via sensitivity analysis. As a result, the shock isolation performance under linear drop condition is considerably improved.

Modal Test of Scaled-Down Reactor Internals in SMART Considering the Fluid-Structure Interaction

The System-integrated Modular Advanced ReacTor (SMART) is a small modular integral-type reactor for the seawater desalination and small-scaled power generation under development in Korea. Although the SMART is innovative reactor with a sensible mixture of the proven technology and advanced design features aimed at enhanced safety, there is no valid prototype which can specify the structural dynamic characteristics of reactor internals. Thus, extensive research for the technology verification and standard design approval are in progress. One of them is to perform the dynamic characteristics identification of reactor internals. Especially, it is focused on the added mass effect caused by the fluid-structure interaction because the reactor internals is submerged in the reactor coolant. The extracted dynamic characteristics such as the natural frequencies and the vibratory mode shapes can be used as the basis on further dynamic analysis, for example, seismic analysis and a postulated pipe break analysis.Copyright

Hydroelastic Modal Analysis of the Perforated Cylindrical Shell in SMART

The System-integrated Modular Advanced ReacTor (SMART) developed by KAERI includes components like a core, steam generators, coolant pumps, and a pressurizer inside the reactor vessel. Though the integrated structure improves the safety of the reactor, it can be excited by an earthquake and pump pulsations. It is important to identify dynamic characteristics of the reactor internals considering fluid-structure interaction caused by inner coolant for preventing damage from the excitations. Thus, the finite element model is constructed to identify dynamic characteristics and natural frequencies and mode shapes are extracted from this finite element model.Copyright