| 摘要 |
PROBLEM TO BE SOLVED: To avoid a gall at the time of decrease of rigidity of a bearing due to decrease of viscosity of oil by forming herringbone shaped dynamic pressure generating grooves which consist of a pair of the inclining groove parts on either one of a spindle and a sleeve engaged freely to rotate with each other, and by providing a circumferential groove communicating to inclining groove parts on a central part of the dynamic pressure generating grooves. SOLUTION: A spindle 2 for integratedly rotating with a rotating polygon mirror is rotatively fitted into a sleeve 3, and the sleeve 3 is fitted into a boss part of an outer cylinder. A space of 3 to 10μm of a bearing is formed between the sleeve 3 and the spindle 2, and oil in the space flows by rotation of the spindle 2 to journal the spindle 2 in a non-contact state in a radial direction by the dynamic pressure. Two herringbone shaped dynamic pressure generating grooves 22b are formed on an outer circumferential surface (an outer diameter part) of the spindle 2. A circumferential groove 31 is formed on a central part of the dynamic pressure generating grooves 22b, and a pair of inclining groove parts arranged above and below which are composed of the herringbone shaped dynamic pressure generating grooves 22b is formed by communicating to the central part intersected with the grooves in a V-shape, and thereby producing a stably annular groove. When the spindle 2 is sopped or rotated at a low speed, and an exothermic action of bearing is generated, the spindle 2 inclines, and then abrasive powders generated by contact with the sleeve 3 are collected in the central part by pumping actions of the grooves. |
