Abstract
This paper describes the robust optimum design which combines the geometrical optimization method proposed by Hashimoto and statistical method. Recently, 2.5″ hard disk drives (HDDs) are widely used for mobile devices such as laptops, video cameras and car navigation systems. In mobile applications, high durability towards external vibrations and shocks are essentials to the bearings of HDD spindle motor. In addition, the bearing characteristics are influenced by manufacturing error because of small size of the bearings of HDD. In this paper, the geometrical optimization is carried out to maximize the bearing stiffness using sequential quadratic programming to improve vibration characteristics. Additionally, the bearing stiffness is analyzed considering dimensional tolerance of the bearing using statistical method. The dimensional tolerance is assumed to distribute according to the Gaussian distribution, and then the bearing stiffness is estimated by combining the expectation and standard deviation. As a result, in the robust optimum design, new groove geometry of bearing can be obtained in which the bearing stiffness is four times higher than the stiffness of conventional spiral groove bearing. Moreover, the bearing has lower variability compared with the result of optimum design neglecting dimensional tolerance.
Highlights
Demand of hard disk drives (HDDs) has been continued to expand because of development of information technology in industries
This paper describes the robust optimum design which combines the geometrical optimization method proposed by Hashimoto and statistical method
In the robust optimum design, it is possible to determine the diameter of industrial tool under product design by providing the constraint condition for groove width and to reduce the Extent of angle change δ 1 Extent of angle change δ 2 Extent of angle change δ 3 Extent of angle change δ 4 Groove depth hg Number of grooves N Groove width ratio α Minimum film thickness hrmin Minimum groove width Lmin Bearing stiffness K (N/m)
Summary
Demand of hard disk drives (HDDs) has been continued to expand because of development of information technology in industries. There are several researchers [1,2,3,4,5,6,7] who attempted to investigate the research related to the improvement of vibration characteristics of the hydrodynamic bearings. Hashimoto and Ochiai [8] dealt with the geometrical optimization aimed at discovering the optimum groove geometry which have never found before and improving dramatically bearing stiffness of thrust air bearings. As far as the authors know, there is no research which had carried out the optimum design with the consideration of manufacturing errors for the hydrodynamic bearings of HDD spindle motors. The robust optimum design based on the geometrical optimization combined with the statistical method [15] is applied to thrust hydrodynamic bearings of 2.5′′ HDD spindle motor. The results obtained are compared with the result by the conventional optimum design neglecting tolerance to verify the effectiveness of the proposed method
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