Patent ID: 7155986
Filing Date: 2007-01-02
Classification: B25B,G05D

Abstract:
1. A power fastening tool comprising: a motor; a motor controller that controls the start and stop of the driving of the motor; a power transmitter that transmits a driving force of the motor to an output shaft to fasten or loosen a fastening member; a torque estimator that estimates a value of a torque that fastens the fastening member; and a fastening judger that judges whether the fastening member is fastened completely, or not; wherein the fastening judger calculates a torque variation quantity which is a ratio of variation of the estimated torque with respect to a rotation angle of a shaft of the motor or elapsed time, and a torque variation ratio which is a ratio of the torque variation quantity with respect to the rotation angle of the shaft of the motor or elapsed time, and judges that the fastening operation is completed when at least a condition that a value of the estimated torque becomes larger than a predetermined lower limit value of the torque and a value of the torque variation ratio varies from positive to negative is satisfied; and said power fastening tool further comprises a torque setter by which a user can optionally set the lower limit value.