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Yield control
Using Yield control as tightening strategy gives higher clamp force
out of the same screw, than with Torque control. A problem joint could
benefi t from a change of strategy, or it can be redesigned into smal-
ler dimensions and lower weight, while meeting the same clamping
requirements.
Power Focus samples a fi ltered torque several times during the clamp
force build-up in the elastic zone of the screw. The increase (the dif-
ference) between the last and the third last mean torque is calculated.
If this increase is bigger than the previously biggest increase, it is
stored as the new shutoff reference (Tmax).
When the gradient decreases (approaching yield), the torque increase
will also get smaller, and fi nally go under the set percentage of Tmax
which is the criteria for tool shut-off.
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