Patent ID: 8632249

Claim:
A bearing unit comprising: a ball retainer having a semispherical recessed surface; a plurality of retainer balls disposed on the semispherical recessed surface, the plurality of retainer balls having a first diameter; a main ball rotatably supported by the plurality of retainer balls and having a second diameter larger than the first diameter; a housing that has a shape surrounding the ball retainer, has a circular opening smaller than the second diameter, and is disposed such that a portion of the main ball protrudes toward a tip end from a base end through the opening; a retainer ball-pressing ring disposed in the housing; and a ring moving mechanism that is connected with the retainer ball-pressing ring, wherein: the retainer ball-pressing ring includes a substantially cylindrical pressing member inserted in an internal space between the semispherical recessed surface and the main ball toward the base end; the retainer ball-pressing ring is moved by the ring moving mechanism from a pressing position to a standby position along an unit center axis that extends along a protrusion direction of the main ball and passes through a center of the main ball; when the retainer ball-pressing ring is at the pressing position, the pressing member restricts or prevents rotation of the plurality of retainer balls by pressing the plurality of retainer balls; and when the retainer ball-pressing ring is at the standby position, the plurality of retainer balls of which the rotation is restrained or prevented by the pressing member is released.