Patent ID: 6945337

Claim:
A power impact tool comprising: a hammer; a driving mechanism for rotating the hammer around a driving shaft; an output shaft to which a rotation force owing to an impact of the hammer is applied; an impact sensor for sensing occurrence of the impact of the hammer; a rotation speed sensor for sensing a rotation speed of the driving shaft with using a rotation angle of the driving shaft; a rotation angle sensor for sensing a rotation angle of the output shaft in a term from a time when the impact sensor senses an occurrence of the impact of the hammer to another time when the impact sensor senses a next occurrence of the impact of the hammer; a torque estimator for calculating an impact energy with using an average rotation speed of the driving shaft sensed by the rotation speed sensor, and for calculating a value of estimated torque for fastening a fastening member which is given as a division of the impact energy by the rotation angle of the output shaft; a torque setter for setting a reference value of torque to be compared; and a controller for stopping the rotation of the driving shaft when the value of the estimated torque becomes equal to or larger than a predetermined reference value set by the torque setter.