Abstract: A free ball bearing includes: a main body that has a ball retainer where a ball-retaining recess having an inner surface of a semi-circular recessed surface is formed; a plurality of retainer balls that is disposed on the semi-circular recessed surface of the main body and a main ball that has a diameter larger than the retainer balls and is rotatably supported through the retainer balls; a cover portion that surrounds the ball retainer of the main body while ensuring a predetermined internal space; a retained ball-pressing ring that has a ring-shaped pressing member that is inserted in between the semi-circular recessed surface of the main body and the main ball and presses the retainer balls, and is disposed to be movable in the internal space in the depth direction of the ball-retaining recess, between a pressing position where the retainer balls are pressed and a releasing position where the retainer balls are released; and a releasing mechanism that moves the retained ball-pressing ring from the pressing

Abstract: A free ball bearing includes a retainer ball-pressing ring, the retainer ball-pressing ring including 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 being moved from a pressing position to a standby position along the unit center axis by the ring moving mechanism; the pressing member restricting or preventing rotation of the plurality of retainer balls by pressing the plurality of retainer balls when the retainer ball-pressing ring is at the pressing position; and the plurality of retainer balls of which the rotation is restrained or prevented by the pressing member being released when the retainer ball-pressing ring is at the standby position.

Abstract: A ball bearing includes a ball supporting member having a hemispherical concave surface, small balls freely disposed on the hemispherical concave surface, a large ball disposed on the small balls so as to be rotatable in all directions, and a casing that has an aperture through which an upper portion of the large ball projects, the casing accommodating the ball supporting member, the small balls, and the large ball; the small balls include primary small balls contacting the large ball so as to support the large ball, and auxiliary small balls, which are smaller than the primary small balls, for supporting the large ball and not contacting the large ball.

Abstract: A ball transfer unit comprising a body in a seat face recessed in a semispherical shape is formed, a plurality of small balls rollingly in contact with the seat face of the body, a large ball rollingly in contact with the plurality of small balls, and a cover fitted to the body to hold the large ball and hold the small balls between the large ball and the seat face of the body. At least the body and the large ball are formed of either of PAI, PBI, PCTFE, PEEK, PEI, PI, PPs, melamine resin, aromatic polyamide resin, aluminum oxide, zirconium oxide, and silicon nitride.