US Patent 9038743 Electric tool

A hand-held power tool has a tool body, a motor housed in the tool body and a grip part designed to be held by a user, and performs a predetermined operation on a workpiece by a tool bit rotationally driven by the motor. The power tool includes a clutch that transmits torque and interrupts torque transmission between the motor and the tool bit, a non-contact torque sensor that detects torque acting on the tool bit in non-contact with a rotation axis rotating together with the tool bit, and a clutch control system that controls coupling and decoupling of the clutch according to a torque value detected by the non-contact torque sensor.