A nut runner, an attachment unit, and a sliding member are provided in a second arm that is a leading arm of the robot and has a leading end shaft movable along the direction of an elevation axis. The nut runner includes a screw fastening driver, a drive shaft rotationally driven by the screw fastening driver, and an extension bar that is so connected to rotate together with the drive shaft in the circumferential direction and to move in the axial direction. The attachment unit fixedly connects the screw fastening driver to the second arm so that a screw fastening axis parallel to the elevation axis serves as a rotation axis of the screw fastening driver. The sliding member is connected to the leading end shaft and supports the extension bar so as to move together in the axial direction and are rotatable relatively in the circumferential direction.

A dual-arm robot system includes a controller configured or programmed to determine whether or not interference determination targets interfere with each other based on whether or not three-dimensional models generated with a plurality of portions including at least a hand among the hand, a horizontal link, and a body as the interference determination targets overlap each other.

The inventive concept provides a teaching method for teaching a transfer position of a transfer robot. The teaching method includes: searching for an object on which a target object to be transferred by the transfer robot is placed, based on a 3D position information acquired by a first sensor; and acquiring coordinates of a second direction and coordinates of a third direction of the object based on a data acquired from a second sensor which is a different type from the first sensor.