DYNAMIC PRESSURE PNEUMATIC BEARING STRUCTURE AND METHOD OF ITS MANUFACTURE

摘要

A dynamic pressure pneumatic bearing structure by which a whirl can be avoided not only at the time of the high speed rotation but also at the time of the low speed rotation, the frequency of the increase of a floating revolution at the time of the start or stop of the rotation is reduced and, further, the floating revolution can be shifted to a low revolution side. This structure has a shaft (1) and a bearing (2). Trenches (11) are formed in the outer circumferential surface of the shaft (1). Each trench (11) is composed of two or more recesses which are formed continuously in a circumferential direction and have practically different depths. The cross section of the trench (11) which is perpendicular to an axial line is asymmetrical with respect to the circumferential direction. The circumferential distance (a) between the cross point (15) of a line (C) connecting the deepest point (14) of the trench (11) to the center (0) of the shaft (1) and the one side edge (16) of a trench (11) on the envelope line (Q) of the shaft (1) which is provided on the downstream side of an air flow (P) produced at the time of rotation with respect to the cross point (15) is larger than the circumferential distance (b) between the cross point (15) and the other side edge (17) of a trench (11) which is provided on the upstream side of the air flow (P) with respect to the cross point (15). The ratio (d2/d1) of the average depth (d2) of the relatively shallow parts of the trenches (11) to the average depth (d1) of the relatively deep parts of the trenches (11) is smaller than 0.3. The dynamic pressure pneumatic bearing structure can be applied to the rotation driving unit of a magnetic recorder, a laser beam printer, etc.