Evaluation of a reaction load measurement system on Atlas Copco nutrunners

During operation, a nutrunner applies a torque to a joint. This causes a rotation of the handle, which an operator must resist to complete a fastening. In order to minimize the ergonomic effect this has, tightening tools must be designed with this reaction load in mind. Strain gauges are used to measure the bending stress in the tool handle as a result of reaction loads. The analog signal from the strain gauges was calibrated to evaluate these reaction loads during fastenings. The peak torque and impulse were estimated, and the accuracy of this measurement system was derived based on the performance of a current measurement method for a set of experimental conditions. The system was able to perform measurements with reasonable similarity to the current method for slower fastening sequences. The accuracy of the method was around 89,6%, the accuracy of the peak torque measurements was 84,7%, and the impulse was 90,4%. The effect of the inertia from the battery on the measurements was estimated numerically and compared with the behavior of the system for a set of dynamic measurements. As fastening times were reduced, the inertial effects of the battery had a significant impact on the signal. The lower limit on the fastening time was around 1 second.