Clamp Force Control (CFC)


Constant clamp force despite fluctuating tightening torques

Adaptive screwdriving procedure ensures a constant clamp force when drive-in torque values are fluctuating. The whole screw assembly consists of the head contact recognition and a screw assembly to differential torque or a specific angle.

A typical area of application is direct screwdriving into plastic and or metal. The patented screwdriving procedure for DEPRAG EC servo screwdrivers, combined with the AST40, is used for wildly varying tightening torques.

These fluctuations may result from alterations in the geometry of the screws and hole, the component’s material structure, variations in the screw thread's surface quality, the elasticity of elements or seating processes. The reliable recognition of head contact results in a constant clamp force.

Check out D-News

View the Newsletter



  • Improved constancy of the pre-load force
  • The calculation takes into account coincidental fluctuations in the torque during
  • the process, which is not caused by head contact
  • Minimal parameter adjustments

Method of calculation:

The main element is the head contact recognition: based on the torque flow, a mathematical valuation function is. Head contact generated is deemed to be recognized as soon as this function exceeds a fixed limit value. Torque and angle are calculated backward to the moment of head contact.

Torque procedure example – parameter head contact recognition screw template The upper torque limit serves as the shut-off criteria for the screwdriving step. The OK window for seating recognition can be monitored using the seating point torque upper/lower limit. The end values can either be saved as the torque and angle values at the point of seating or the end of the screwdriving step. The end values of the screwdriving template seating recognition provide the reference for the following program section. Screw assembly to differential torque relating to head contact recognition Screw assembly to the angle can follow instead of screw assembly to differential torque.