In this paper, the static and dynamic performance of herringbone, step-pocket, taper-pocket, and taper-flat thrust bearings were numerically analyzed. Optimal values for the design parameters of each type of bearing were analyzed in terms of both maximum axial stiffness (kzz) and maximum ratio of axial stiffness to friction torque (kzz/T) and bearing performance for both cases was calculated. The optimal performance characteristics of these bearings were compared in terms of application to hard disk spindles. Step-pocket and taper-pocket thrust bearings are superior to herringbone and taper-flat thrust bearings with respect to both the maximum kkk and the maximum kzz/T conditions. It was found that the dams of thrust bearings with pockets play an important part in improving the hearing performance. It was made clear that the taper-pocket and the taper-flat thrust bearings have a much larger load capacity than the other two types of thrust bearings in the proximity of zero clearance.

This paper aims at investigating the effects of variations in thrust hydrodynamic bearing (HDB) parameters such as axial stiffness and damping coefficients on the axial vibration of disk-spindle systems in hard disk drives. For a parametric study, a closed-form axial frequency response function (FRF) of HDB spindle systems is derived as a function of the axial stiffness and damping coefficients of thrust HDBs. It is known that the axial vibration of the disk-spindle system is composed of two main parts: the vibration of the rigid hub in the axial direction and the disk deflection in the transverse direction. The results from this research clearly show that the vibration amplitudes at low frequency range is dominated by the axial vibration of the hub, and the amplitude of the unbalanced (0,0) mode is dominated by the disk deflection. The parametric study reveals that at low frequency range an increase in the bearing stiffness significantly reduces the hub axial vibration, and hence the axial vibration of the disk-spindle system. Surprisingly, a too much increase in the damping results in a higher amplitude of the unbalanced (0,0) mode. This is because a heavy damping constrains the hub vibration to nearly no motion, resulting in a direct transmission of vibration from the base to disk. To confirm the parametric study, a vibration test was performed on two HDB spindle motors with identical design but different fluid viscosity. The higher viscosity represents the higher axial stiffness and damping in the thrust bearing. The test result indicates that the spindle motor with higher viscosity has a larger unbalanced (0,0) mode amplitude when subjected to an axial base excitation. IntroductionCurrently, hydrodynamic bearing (HDB) spindle motors are widely used in hard disk drives (HDDs) because of their capabilities for vibration suppression and acoustic noise reduction. Design criteria for the HDB spindles are reliability, low power consumption, and low vibration and shock responses (Asada et al. 2001; Matsuoka et al. 2001). As the spin speed and the density of HDD increase, the design of both radial and thrust bearings are a key to minimize the vibration of the HDB spindles. The radial HDBs are designed to suppress the rocking vibration which is the major contribution to track misregistration (Jintanawan 2002). The thrust HDBs have an impact not only on the rocking vibration but also on the axial vibration. The thrust HDBs provide rocking restoring and damping moments as well as axial restoring and damping forces. However only the axial forces have a great effect on the axial vibration. Suppression of this axial vibration through optimization of the thrust HDB parameters would be a practical and inexpensive solution. Experimental study on the effect of the thrust HDBs on the axial vibration of the disk-spindle systems for HDD was conducted by Ku (1997). In his study, the disk-spindle systems with four types of thrust HDBs, representing different compliance or stiffness, were tested. He has concluded that the complianc...

No abstract

No abstract

No abstract