TIGHTENING METHOD AND CONTROL DEVICE FOR TIGHTENING MACHINE

PROBLEM TO BE SOLVED: To provide a tightening method which does not allow an actual torque to exceed set tightening torque and requires no expensive controller.SOLUTION: A tightening method includes a first tightening process which controls a motor drive current so that an electric motor 12 outputs a target torque Tt gradually incremented up to the first tightening process completion torque Tb that is lower than set tightening torque Ta after a screw member 30 has been seated, and a second tightening process which controls the drive current of the electric motor 12 so that the electric motor 12 outputs the target torque Tt continuously increased up to the set tightening torque Ta at a rate lower than an average increase rate at a gradual increment of the target torque Tt after the target torque Tt has reached the first tightening process completion torque Tb.