On investigation of vibro-acoustics of FDB spindle motors for hard disk drives

Abstract

The present work investigates vibro-acoustic behaviors of the fluid dynamic bearing (FDB) spindle motors for hard disk drives (HDD) through the sound spectra and the frequency response functions (FRF) of the motor structure. The quantitative evidence on the significance of the acoustic noise originated from the electromagnetic source is deduced from the sound spectra that were measured in two distinct cases of the spinning motor: in the normal operation and at the moment immediately after the power supply was disconnected. It is found that the effect of electromagnetic noise source is more dominant than the combined effect of the mechanical and aerodynamic sources. In addition, it is identified that, within the audible range of frequency, the frequency range of 13.4-20 kHz deems important to the noise problem as it is the main contributor to the acoustic noise for the FDB spindle motors. Moreover, the structural resonances that can be identified via the FRF are found to play an important role in the noise emitted by the motors. The concurrence of resonance and excitation frequencies clearly intensifies the sound spectrum, resulting in high discrete peaks, hence higher decibel level.

Exploration of vibro-acoustic characteristics of HDD spindle motors using electro-magnetic frequency-swept excitation

“…9 and 10, respectively. In each figure, the FRFs measured in various directions are compared to the sound power spectrum (SPW) that separately measured in an anechoic room when the motor spins at 7,200 rpm (Ajavakom et al 2006). The vibration modes of the motor and their natural frequencies can be identified at the peaks of the FRFs as seen in the bottom plots of Figs.…”

“…Propagation of the EM noise through these components is characterized by the natural vibration of the motor as can be revealed from the measured sound spectrum of a HDD motor in normal operation that shown in Fig. 1 (Ajavakom et al 2006). Firstly, it is observed from the sound spectrum that there exist the distinct harmonic peaks whose frequencies correspond to the EM-excitation frequencies.…”

“…Due to the small size of motor in HDD and the broad range of audible frequencies (from 0.1 to 20 kHz), the conventional vibration testing on the motor with mechanical excitation might not be appropriate. Specifically, the research work (Ajavakom et al 2006) reveals that the impulsive force applied by an impact hammer contains insufficient level of energy in exciting the high-frequency modes of the FDB motors for HDD. In addition the mechanical forces applied to the motor structure are significantly different in nature from the EM forces which are the major noise source in the motor operation.…”

“…In the conventional type of the HDD motors with fluid dynamic bearing (FDB), the mechanical noise sources due to metal-to-metal contact and unbalances are significantly reduced, and thus the electromagnetic (EM) forces become a major noise source of the motors (Bi et al 2003;Ajavakom et al 2006). The EM forces that induce vibrations and acoustic noises in the motor are caused by the reluctance effect of the motor machine and the switching harmonics produced by its electrical drive inverter.…”

A study of acoustic noise generating mechanisms of small form factor HDDs

“…Published work devoted to a systematic study of HDD acoustics, especially of the numerical models to predict the acoustic noise level has been limited. Studies made in the field towards understanding the dominant acoustic noise sources has been restricted to experimental measurements of acoustic noise from 3.5 00 HDDs (Gao et al 2003(Gao et al , 2005bAjavakom et al 2006;Jiang and MaCioce 2007;Tandon et al 2006). However, it is difficult to identify dominant sources relying solely upon the experimental data.…”