A recently-validated formula may be able to predict the angular displacement or “kick” of a power tool handle at the end of threaded fastener task.
The formula is an equilibrium equation with the human operator represented as a dynamic system consisting of a linear spring, a mass and a viscous damper versus the estimated impulsive force from a power tool. Angular displacement occurs when the impulsive force from the power tool exceeds the operator force.
Formula predictions for handle displacement were compared to actual measured handle displacements. Nine operators used six power nutrunners to perform fastener tasks. The nutrunners had three common tool shapes (pistol grip, right angle, and in line) and the tasks were performed at various vertical/horizontal locations to a soft or hard joint. Tool handle displacement was measured as the nut was tightened down.
The predicted value strongly correlated with measured tool hand displacement with an error of three percent for all tools and task variables.
Lin J.H., Radwin R.G., and Richard T.G. “Handle Dynamics Predictions for Selected Power Hand Tool Applications.” The Journal of the Human Factors and Ergonomics Society 45: 645-656, 2003.
This article originally appeared in The Ergonomics Report™ on 2004-04-01.