| 摘要 |
PROBLEM TO BE SOLVED: To provide a fluid dynamic bearing with high precision and a longer life capable of maintaining an oil film in a bearing gap and a disk rotating device using the same bearing. SOLUTION: When an outer diameter, an inner diameter, and a diameter at a returning portion of herringbone patterns 3A and 3B of a third dynamic pressure generating groove provided on at least either of contact surfaces between a flange 3 and a thrust plate 4 are set to be D1o, D1i, and D1m respectively, these diameters satisfy numerical expressions of D1m=D<SB>sy</SB>-(D<SB>sy</SB>-D1i)×(0.05 to 1.0), and D<SB>sy</SB>=[(D1i<SP>2</SP>+D1o<SP>2</SP>)/2]<SP>1/2</SP>, and a coefficient of viscosity of oil or base oil of grease is 4 centistokes or more at 40°C. The highly accurate fluid dynamic bearing having no breakage of an oil film and a longer life is obtained so that one of outer peripheries of a sleeve 1 and a shaft 2 is fixed on a base 6, and the other outer periphery is fixed on a hub rotor 7. COPYRIGHT: (C)2004,JPO&NCIPI
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