Patent ID: 7467669

Claim:
A method for tightening a screw joint to a desired target torque level using an impulse wrench having an impulse unit with a motor driven inertia drive member, and a programmable control unit arranged to control a power supply to the impulse wrench, said method comprising: starting a screw joint tightening process at a reduced power supply to the impulse wrench, ascertaining an angular displacement and a retardation magnitude of the inertia drive member during each delivered impulse, calculating an instantaneous torque magnitude and a torque growth during a number of delivered impulses, increasing after a very first delivered impulse the power supply to the impulse wrench in response to the calculated torque growth, reducing the power supply to the impulse wrench in response to the instantaneous torque magnitude and to the calculated torque growth during each impulse as the instantaneous torque magnitude reaches a predetermined percentage of the desired target torque level, and interrupting the power supply to the impulse wrench as the target torque level is reached.