Reaction forces, tool handle displacements and discomfort ratings during work with shut-off nutrunners

Reaction forces, hand-arm displacement and subjective ratings were studied during securing of threaded fasteners with nine right-angle nutrunners. The nutrunners had three different preset spindle torques and three different shut-off mechanisms. The tools were tested according to the international ISO method and with a method proposed by the authors in a previous study. Twelve male subjects participated in the study. A force platform measured the reaction forces between the subjects and the floor. Motions of the hand-arm system and shoulder were measured with an optoelectronic measuring system and a goniometer. Strong correlations between motions/ ground reaction forces and ratings were found. The ratings were also strongly correlated with the tool torque impulse, calculated according to ISO 6544, as well as with the time for which the torque exceeded 75% of the preset spindle torque multiplied by the preset spindle torque to produce a 'time-torque value'. The strongest correlation, though, was found with the time-torque value, but the difference was not large enough to propose a change of the ISO standard.