| 主权项 |
1. A motor, which moves a rod, which has a first screw groove of a spiral shape formed on its outer circumferential surface, in front and rear directions along a center axis of the rod, comprising:
a stationary unit; and a rotary unit which is rotatably supported relative to the stationary unit about the center axis, wherein the stationary unit comprises:
a stator comprising a plurality of coils arranged in a circumferential direction; anda housing which retains the stator, the rotary unit comprises:
a plurality of magnets disposed on a radially inner side of the stator, and arranged in the circumferential direction;a hollow shaft which has a tubular shape; anda ball nut disposed on a radially inner side of the hollow shaft, at least a portion of the magnets, at least a portion of the hollow shaft, and at least a portion of the ball nut overlap in a radial direction, the ball nut has a second screw groove of a spiral shape formed on its inner circumferential surface, a plurality of spheres are interposed between the first screw groove and the second screw groove in the radial direction, a radial thickness of the hollow shaft on a radially inner side of a circumferential center portion of the magnets is thinner than a radial thickness of the hollow shaft on a radially inner side of a boundary of neighboring magnets, or a radial thickness of the hollow shaft at a circumferential end portion of a part of the hollow shaft disposed on a radially inner side of the magnets, the hollow shaft and the ball nut are made of magnetic material, and an inner circumferential surface of the hollow shaft and an outer circumferential surface of the ball nut are in contact with each other. |
