DYNAMIC PRESSURE PNEUMATIC BEARING STRUCTURE AND OPTICAL DEFLECTION SCANNER EMPLOYING THE STRUCTURE

摘要

Provided is a hydrodynamic gas bearing structure which can prevent occurrence of whirl not only in high-speed rotation but also in low-speed rotation, reduces such frequency that a floating rotational frequency in starting or stoppage of rotation increases, and is capable of shifting the floating rotational frequency to a low rotational frequency side. The hydrodynamic gas bearing structure comprises a shaft body (1) and a bearing body (2). A groove (11) is formed on the outer peripheral surface of the shaft body (1). The groove (11) consists of at least two concave parts, whose depths substantially differ from each other, which are formed serially in the circumferential direction, and has a circumferentially asymmetrical shape in a cross section perpendicular to the axis. The circumferential distance a between the intersection point (15) of a line (C) connecting the deepest point (14) of the groove (11) and the center (O) of the shaft body (1) and the outer peripheral line (Q) of the shaft body (1) and one edge (16) of the groove (11) positioned downward an air current (P) generated in rotation in relation to the intersection point (15) is larger than the circumferential distance b between the intersection point (15) and the other edge (17) of the groove (11) positioned upstream the air current (P) in relation to the intersection point (15). The ratio (d2/d1) of the mean depth d2 of a relatively shallow part of the groove (11) to the mean depth di of a relatively deep part of the groove (11) is less than 0.3. The hydrodynamic gas bearing structure is suitable for employment for a rotation driving part of a magnetic recording apparatus or a laser beam printer. IMAGE