A Mechanical Experiment to Simulate the Nonlinear Hand-Arm Dynamics in Torque Tool Operation

Abstract

The purpose of this study is to design and test a mechanical DC torque tool testing rig that is capable of simulating dynamic response of the human arm under a torque impulse. The mechanical simulation of the human arm response is based on a nonlinear model derived from human subject testing. The testing rig, which uses both tension and compression springs to provide a bilinear stiffness rate to resist the motion of the torque tool handle, is used to analyze the tool handle angular displacement and reaction force, which has been strongly linked in previous studies to operator discomfort and injury. The mechanical simulation of the human arm response was tested under a number of different conditions, and compared to an analytical nonlinear model. The results showed that the mechanical simulation consistently underestimated the tool handle displacement by up to 16.2% when compared to the nonlinear model predictions. The discrepancy in handle displacement between the nonlinear model and mechanical simulation is likely due the coulomb friction not being included in the nonlinear model. Therefore, this study shows that by suing an offset to compensate for the coulomb friction, the tool testing rig can be used to accurately simulate the nonlinear dynamic response of the human arm under a torque impulse.