This paper presents a method to investigate the characteristics of a ball bearing and the dynamics of a HDD spindle system due to temperature variation. Finite element model is developed for the rotating and stationary parts of a HDD spindle system separately to determine their thermal deformations by using ANSYS, a finite element program. Then, the relative position of the rotating part with respect to the stationary part is determined by solving the equilibrium equation of the contact force between upper and lower ball bearings. The validity of the proposed method is verified by comparing the theoretical natural frequencies of a HDD spindle system with the experimental ones before and after temperature variation. The proposed method makes it possible to predict the characteristics of a ball bearing and the dynamics of a HDD spindle system due to temperature variation. It shows that the elevated temperature results in the increase of contact angle and the decrease of bearing deformation, contact force and bearing stiffness, which result in the decrease of the natural frequencies of a HDD spindle system. IntroductionNonrepeatable runout (NRRO) is one of the major obstacles to achieve high track density in a computer hard disk drive (HDD). One of its sources is the waviness of a ball bearing in a HDD spindle system, and it generates bearing frequencies and the excessive vibration especially when one of the bearing frequencies matches with one of the natural frequencies of HDD spindle system [1][2][3][4]. In HDD industry, this resonance has been avoided by designing the natural frequencies of a HDD spindle system not to coincide with bearing frequencies. However, the operating temperature inside a HDD has thermal cycles, starting from room temperature up to 80°C. This may result in looseness of a ball bearing, natural frequency shifts of a HDD spindle vibration, coincidence with bearing frequencies, and eventually read/write errors.Several researchers have investigated the sources of natural frequency shifts of a HDD spindle system due to temperature rise, i.e. disk media and ball bearing. Jr-Yi Shen et al. (2000) studied both experimentally and theoretically how temperature variations affect natural frequencies of disk media [5]. They pointed out that natural frequency shifts of aluminum and glass disks at elevated temperatures result primarily from residual stresses and thermal membrane stresses of the disks, respectively. Chaw-Wu Tseng et al. studied how temperature variation affects natural frequencies of rocking vibration of a rotating disk and spindle system through mathematical modeling and experimental measurement [6]. They pointed out that frequency shifts of rocking modes at elevated temperature primarily result from relaxation of bearing stiffness. In their mathematical thermal model, they only included the radial displacement of the outer race with respect to the inner race at the elevated temperature without taking account of the axial displacement. In addition to radial displacement, axial displacemen...

This research investigates hew the design variables of ball bearing change the beating stifthess 'and the natural frequencies of a HDD spindle system in elevated ternperature. It shovis that large contact angle reduces the variation of the bearing stiffhess and the natural frequencies in elevated terrrperature. It also proposes a robust design of the spindle motor, in which the wave spring maintains the constant preload even in elevated temperature. The theoretical investigation shews that the reduction ofnatural frequencies due to temperature rise is almos! negligible in the proposed HDD spindle system,