Ball screw nut, turning unit, and method for manufacturing ball screw nut
A ball screw nut includes a nut part and a pulley part integrally molded with the nut part on the outer peripheral side of the nut part and having external teeth. The pulley part has a cylindrical portion extending in an axial direction and facing the nut part in a radial direction, and an extended portion extending radially inward from the cylindrical portion and facing the nut part in the axial direction. A restriction part for restricting relative rotation of the nut part and the pulley part is provided between a facing surface of the extended portion facing the nut part and a facing surface of the nut part facing the extended portion.
1. A ball screw nut comprising:
a cylindrical nut part having, on an inner peripheral surface, a ball rolling groove in a helical shape; and
a cylindrical pulley part integrally molded with the cylindrical nut part on an outer peripheral side of the cylindrical nut part and having external teeth, wherein
the cylindrical pulley part includes a cylindrical portion extending in an axial direction and facing the cylindrical nut part in a radial direction, and an extended portion extending radially inward from the cylindrical portion and facing the cylindrical nut part in the axial direction,
a restriction part for restricting relative rotation of the cylindrical nut part and the cylindrical pulley part is provided between a facing surface of the extended portion facing the cylindrical nut part and a facing surface of the cylindrical nut part facing the extended portion,
an outer peripheral surface of the cylindrical nut part and an inner peripheral surface of the cylindrical portion have a circumferential surface over an entire axial range where the external teeth are formed,
the cylindrical pulley part is formed by insert molding on the an outer periphery of the cylindrical nut part using only a resin material as a molding material, and
external teeth are formed on an outer peripheral surface of the cylindrical portion excluding an axial range where the extended portion is formed.
2. The ball screw nut according to claim 1 , wherein
one of the facing surface of the cylindrical nut part and the facing surface of the cylindrical pulley part has a projection,
the other of the facing surface of the cylindrical nut part and the facing surface of the cylindrical pulley part has a recess into which the projection is fitted, and
the restriction part is configured to include the projection and the recess.
3. A turning unit comprising:
a motor; and
a transmission mechanism, wherein
the transmission mechanism includes the ball screw nut according to claim 1 , a ball screw shaft having a ball rolling groove helically formed on an outer peripheral surface, a plurality of balls provided between the ball rolling groove of the ball screw shaft and the ball rolling groove of the ball screw nut, a drive pulley connected to a rotary shaft of the motor and having external teeth on an outer peripheral surface, and a toothed belt having internal teeth that mesh with the external teeth of the drive pulley and the external teeth of the cylindrical pulley part, the toothed belt being stretched between the drive pulley and the cylindrical pulley part.
4. A method for manufacturing the ball screw nut according to claim 1 , wherein the cylindrical pulley part is integrally molded with the cylindrical nut part by insert molding using the cylindrical nut part as an insert.