Clamp force estimation via pulsed tightening

A method, for estimating a clamp force obtained at tightening of a screw joint via a torque pulse sequence, the method comprising:

• applying a primary torque pulse to rotate the screw joint in a tightening direction;
• measuring a torque level obtained by the primary torque pulse;
• applying a secondary torque pulse to move the screw joint in a loosening direction;
• measuring a torque level obtained by the secondary torque pulse;
• and
• calculating a difference between the torque level obtained by the primary torque pulse and the torque level obtained by the secondary torque pulse, wherein the obtained clamp force is estimated from the difference between the obtained torque levels,
• wherein a target clamp force is compared to the estimated clamp force, and when the estimated clamp force is lower than the target clamp force, the torque pulse sequence is repeated at successively higher torque rates, and
• wherein a screw joint tightening process comprises an initial stage including application of a number of subsequent primary torque pulses until a certain torque level is reached, whereupon a last of the primary torque pulses is followed by a secondary torque pulse to form a torque pulse sequence enabling estimation of an accomplished clamp force, and the target clamp force is reached by extrapolating the estimated clamp force obtained via at least one further pulse sequence.