Impact wrench having torque controlling faculty

Abstract

An impact wrench with a torque controlling faculty including an air motor for generating a primary torque, an oil pressure pulse generating unit for converting the primary torque into a pulsatory secondary torque, a main spindle to which the pulsatory secondary torque is applied, a transducer for detecting the pulsatory secondary torque and a shut-off valve which is closed to stop a supply of a compressed air to the air motor when the secondary torque exceeds a predetermined threshold value. The main spindle is made of material having the magnetic strictive effect and the distortion of the main spindle is detected by a pair of coils arranged in opposition to the main spindle. The coils are connected into a bridge circuit together with resistors and an exciting current having a sinusoidal waveform is supplied to a first set of diagonal points of the bridge circuit. A voltage appearing across a second set of diagonal points is detected to produce a torque detection signal which represents the pulsatory secondary torque. Then the torque detection signal is sampled and held at a predetermined phase which is fixedly related to a phase of the exciting current to produce a torque measurement signal which represents a peak value of the pulsatory secondary torque applied to the main spindle.