Yun-Sik Han

The acoustic noise characteristics of HDD due to the structural excitation of spindle motor

HDD structure is excited by the dynamic motion of disk-spindle motor components. Those excitations which are generated from stator, magnet rotor, bearings and disks, are transmitted through motor spindle and flange to HDD cover and base. The operational deflection shape measurement can show the structural elicitation patterns at the most influential frequency of the acoustic noise level. One of those components is the axial excitation along spindle, and the other is the local orbital excitation at the contact area of motor flange and base. In order to make a reduction of those structural transmission excitations, the structure of spindle motor should be modified to the direction of reinforcement at transmission path. Some excitation of spindle motor component carrying out essential function is unavoidable. So it is the efficient may of HDD noise improvement to control the structural transmission of excitation.

Use of Directional Spectra for Detection of Engine Cylinder Power Fault

A diagnostic method, which uses the two-sided directional power spectra of complex-valued engine vibration signals, is presented and tested with four-cylinder compression and spark ignition engines for the diagnosis of cylinder power faults. As spectral estimators, the maximum likelihood and FFT methods are compared, and the multi-layer neural network is employed for pattern recognition. Experimental results show that the success rate for identifying the misfired cylinder is much higher with the use of two-sided directional power spectra than conventional one-sided power spectra.

Numerical Modeling for the Characterization of Flow Excitation for the HDD Disk Vibration Control

This article presents a modeling method for air flow analysis of a hard disk drive. Air flow excitation causes disk vibration that aggravates TMR budget of the design of modern high performance hard drives. And it is the most expensive budget consumer so that controlling of the flutter becomes the primary design issue of the data storage industry. In the presented work, air flow excitation forces are characterized by LES modeling and the results are verified with experiments. A squeeze-film-type disk damper is employed in the experiments and it is applied for a hardware design improvement for disk flutter reduction. LES and RANS are compared and alternately used in a calculation in order to minimize computational efforts.

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.

Noise source identification of hard disk drive using sound intensity and its control

Sound intensity technique and ODS (Operational Deflection Shape) technique are applied to identify the acoustic noise source of a hard disk drive system. The sound intensity is used to visualize the exact locations of noise sources, and the ODS to visualize the vibration pattern and to obtain the dynamic characteristics of the noise sources. Based on the visual information on the noise source location and its dynamic characteristic, the optimum structural modification and sound absorption are designed to modify the dynamics of the acoustic noise and to suppress the acoustic radiation power from the disk drive system.