Predicting tool operator capacity to react against torque within acceptable handle deflection limits in automotive assembly

The proportion of tool operators capable of maintaining published psychophysically derived threaded fastener tool handle deflection limits were predicted using a biodynamic tool operator model, interacting with the tool, task and workstation. Tool parameters, including geometry, speed and torque were obtained from the specifications for 35 tools used in an auto assembly plant. Tool mass moments of inertia were measured for these tools using a novel device that engages the tool in a rotating system of known inertia. Task parameters, including fastener target torque and joint properties (soft, medium or hard), were ascertained from the vehicle design specifications. Workstation parameters, including vertical and horizontal distances from the operator were measured using a laser rangefinder for 69 tool installations in the plant. These parameters were entered into the model and tool handle deflection was predicted for each job. While handle deflection for most jobs did not exceed the capacity of 75% females and 99% males, six jobs exceeded the deflection criterion. Those tool installations were examined and modifications in tool speed and operator position improved those jobs within the deflection limits, as predicted by the model. We conclude that biodynamic tool operator models may be useful for identifying stressful tool installations and interventions that bring them within the capacity of most operators. •Tool, workstation, and task parameters were measured for 35 tools, representing 69 installations in an automotive assembly plant.•The dynamic forces acting against the human tool operator and resulting handle reaction deflections were predicted using a biodynamic tool operator model.•The proportion of threaded fastener tool operators capable of maintaining published psychophysically derived deflection limits were ascertained.•While handle deflection did not exceed the limit for most installations, changes in tool speed and operator position improved the six jobs that did.