Abstract: A power tool for tightening a fastener includes: an angle measurement unit for measuring a rotational angle (?) of the fastener; a torque measurement unit for measuring a torque (T) delivered to the fastener during tightening; a motor connected to rotatable parts of the power tool for driving the tightening of the fastener; a processor for calculating a tightening energy (Et) needed to complete tightening of the fastener from ? to a predetermined target angle (?t), wherein Et is calculated based on ?, ?t and a stiffness (k) of a joint; and a regulator to regulate a rotational speed (?) of the motor to provide rotational energy (Er) in the form of rotational inertia in the rotatable parts of the power tool to meet the needed Et, wherein the power tool interrupts the tightening of the fastener at ?t, ?t defined from snug, at a snug angle (?0).

Abstract: A power tool for tightening a fastener includes: an angle measurement unit for measuring a rotational angle (?) of the fastener; a torque measurement unit for measuring a torque (T) delivered to the fastener during tightening; a motor connected to rotatable parts of the power tool for driving the tightening of the fastener; a processor for calculating a tightening energy (Et) needed to complete tightening of the fastener from ? to a predetermined target angle (?t), wherein Et is calculated based on ?, ?t and a stiffness (k) of a joint; and a regulator to regulate a rotational speed (?) of the motor to provide rotational energy (Er) in the form of rotational inertia in the rotatable parts of the power tool to meet the needed Et, wherein the power tool interrupts the tightening of the fastener at ?tt, ?t defined from snug, at a snug angle (?0).