Patent ID: 8196673

Claim:
A method for determining when a threaded fastener has been tightened to a predetermined level of tightness by an impact wrench of the type comprising a microprocessor, a rotary anvil and a rotary hammer for impacting with the anvil and angularly advancing the anvil in response to each hammer impact, and a coupling means for coupling the anvil to the fastener for rotating the fastener as the anvil is being angularly advanced, the method comprising the steps of: receiving impacts and transmitting impact data to the microprocessor; determining one of the angle of rebound of the hammer resulting from each of at least some of the impacts of the hammer with the anvil, and the angle by which the anvil is advanced in response to each of at least some of the hammer impacts, the angular position of the anvil on each of the at least some of the hammer impacts with the anvil being determined from the angular position of the hammer at impact with the anvil, and determining that the fastener has been tightened to the predetermined tightness level when one of the angle through which the anvil is advanced by one of the hammer impacts falls below a predetermined angle, the number of hammer impacts to advance the anvil through a predetermined angle exceeds a predetermined number of hammer impacts, and the angle of rebound of the hammer exceeds a predetermined rebound angle.