Bolt tightening.

摘要

The present invention provides an impact wrench and a bolt-tightening method wherein a spring force is applied, through the circumference of a spindle (6) coupled with the output shaft of an electric motor, in the forward direction to a hammer (8) which is capable of forward and rearward movement and of rotational motion following said spindle (6), with said hammer (8) and impact shaft (9) being brought in coaxial mesh alignment by leaving a gap between them in the direction of rotation so that when a bolt to be tightened is inserted into a socket fixed to an end of said impact shaft (9) to permit the bolt to be tightened, the mesh contact with said impact shaft (9) is released as a result of said hammer (8) being lifted up in the rearward direction against the reaction force due to the tightening of said bolt, and as said hammer (8) is again brought into mesh contact with the impact shaft (9) under the spring force applied in the forward direction so that an impact force is generated with respect to the direction of rotation of said impact shaft (9), an impact sensor (31) detecting the release of said hammer (8) from said impact shaft (9) and an angle sensor (32) measuring the angle of rotation of said impact shaft (9) are provided, so as to measure the torque of said impact shaft (9) by measuring the amount by which the angle of rotation of said impact shaft (9) advances each time said impact force is generated and to measure the amount by which the angle of rotation of said impact shaft (9) advances from the time at which said measured torque has reached the previously set snug torque value, so that the power supply to said electric motor is disconnected when the amount of advancement of the rotational angle has reached the pre-defined value of the preset angle of rotation to stop the rotation of said impact shaft (9) through the braking circuit.