Rotation drive apparatus

A rotation drive apparatus comprising:

• a composite rotor supported by a base supported by a damper in such a manner that a recording member is rotatively supported through said support shaft and a disc table which is rotated together with said recording member by a rotational member;
• and
• an automatic aligning mechanism having a case that is rotated by a rotating means through a support shaft and having a movable space with a circular or annular cross-sectional shape perpendicular to the axial direction of the shaft, a plurality of balancing members movably disposed in said movable space in said case, and a magnetic field generating means joined to a portion of said case, said automatic aligning mechanism being capable of automatically positioning the center of gravity of said composite rotor to a position on said rotational member during rotations of said composite rotor,
• wherein each of said balancing members starts rotating to follow said composite rotor due to a starting torque transmitted from said composite rotor to each of said balancing members because said balancing members are attracted to said magnetic field generating means at the time said composite rotor starts rotating, and
• when the rotational frequency of said composite rotor is raised to a frequency not lower than the resonant frequency of said damper in a direction of a plane perpendicular to the support shaft of said composite rotor, said balancing members move away from the magnetic field generating means due to an adjustment torque to perform an automatic aligning operation.