Abstract: A spindle motor comprising a stator including a support shaft positioned on a base, a cap-shaped rotor rotatably and concentrically disposed around the support shaft, thrust and radial bearings disposed between the stator and the rotor, a stator coil secured to the stator, and a rotor magnet member secured to the rotor opposing the stator coil. The thrust and radial bearings are hydrodynamic bearings. A movable piece that constitutes a part of the thrust bearing is secured to the lower end of a cylindrical portion of the rotor and extended outwardly or inwardly from the cylindrical portion, or is disposed above the rotor. The stator coil is secured to the outer peripheral portion of the support shaft above or below the radial bearing. The rotor magnet member is securd to the inner peripheral surface or inner top surface of the rotor. Either a radial or axial gap is provided between the stator coil and the rotor magnet member.

Abstract: A rotation supporting device of a polygon mirror comprising a stationary shaft provided with a shaft sleeve around its circumference, a rotary assembly rotatably mounted around the circumference of the shaft sleeve and having a radial circumferential surface of a polygon made to serve as mirror surfaces and having a magnet member, thrust plates for suppressing the motion of a rotary assembly in the axial direction. The rotary assembly comprises a first rotor rotatably mounted at the outer circumference of the shaft sleeve, a second rotor having a circumferential surface of a polygon made to serve as mirror surfaces and being disposed at the outer circumference of the first rotor, and a yoke secured on the outer circumference of the first rotor. The first rotor is made of a ceramic material, the second rotor is made of aluminum and the yoke is made of steel. Radial dynamic pressure bearing is included between the outer circumference of the shaft sleeve and the rotary assembly.