Fastening tool

1. A fastening tool, which uses a fastener including a bolt and a cylindrical hollow collar that is engageable with the bolt, the bolt having a head part integrally formed with a shaft part having a groove, to fasten a workpiece between the head part and the collar, the fastening tool comprising:

claws configured to grip an end region of the shaft part;

an anvil configured to engage the collar;

a ball screw assembly configured to drive the claws to move in a longitudinal-axis direction along a longitudinal axis of the fastening tool relative to the anvil;

a motor configured to drive the ball screw assembly; and

a housing that at least partially houses the ball screw assembly, wherein:

the fastening tool is configured such that:

when the claws grip the end region of the shaft part and move relative to the anvil in a first direction of the longitudinal-axis direction via the ball screw assembly, the anvil presses the collar fitted onto the shaft part in a second direction opposite to the first direction of the longitudinal-axis direction and inward in a radial direction of the collar, so that a hollow part of the collar is crimped to the groove while the workpiece is clamped between the collar and the head part, whereby swaging of the fastener is completed while the end region is integrated with the shaft part, and

when the claws grip the end region of the shaft part and move relative to the anvil in the second direction via the ball screw assembly, the collar swaged to the bolt is released from the anvil and the end region of the shaft part is allowed to be released from the claws;

the ball screw assembly includes:

ball nut supported by the housing such that movement of the ball nut in the longitudinal-axis direction relative to the housing is restricted, and configured to be rotationally driven by the motor; and

a ball screw shaft connected to the claws such that movement of the ball screw shaft in the longitudinal-axis direction is allowed and rotation of the ball screw shaft around the longitudinal axis is restricted;

the ball screw shaft is configured to be driven in the longitudinal-axis direction by the ball nut being rotationally driven, so that the claws are moved in the longitudinal-axis direction relative to the anvil; and

the fastening tool further includes:

thrust rolling bearings on a first direction side and a second direction side of the ball nut, each of the thrust bearings being configured to receive an axial force in the longitudinal-axis direction transmitted from the claws to the ball nut via the ball screw shaft while allowing the ball nut to rotate; and

radial rolling bearings that are (1) separate from the thrust rolling bearings and (2) radially between an outer periphery of the ball nut and an interior surface of the housing.

2. The fastening tool as defined in claim 1 , wherein the thrust rolling bearing on the first direction side is a needle bearing.

3. The fastening tool as defined in claim 1 , wherein the thrust rolling bearing on the first direction side abuts a rear end portion of the ball nut.

4. The fastening tool as defined in claim 1 , wherein:

a gear is formed on the ball nut and configured to rotationally drive the ball nut via the motor, and

an outer periphery of the gear is configured to lie within an outer shell of the housing in an upper portion of the housing.

5. The fastening tool as defined in claim 1 , wherein a planetary-gear assembly for speed reduction is in a power transmission path from the motor to the ball nut.

6. The fastening tool as defined in claim 1 , wherein at least one of the thrust rolling bearings on the first and second direction sides is configured to have a larger diameter than an outer diameter of the ball nut.

7. The fastening tool as defined in claim 1 , wherein thrust washers are between the housing and the thrust rolling bearing on the first direction side and between the housing and the thrust rolling bearing on the second direction side.