Machine-cycling errors with foot switches in repetitive tasks: A workstation design simulation experiment

In this experiment a non-hazardous industrial machine simulator was used to evaluate errors made when using a foot switch to initiate dangerous, repetitive machine motions. Subjects were experienced employees who normally operated metalworking presses and similar hazardous machines on jobs matching the simulation. Four variables (force needed to push switch to closure, the switch's force feedback felt by the subject, subject working posture, and hand task involved in stamping a simulated workpiece) were evaluated for their main and interactive effects upon frequency of machine-cycling errors in a repetitive task. Equipment problems which required immediate correction were introduced at a rate of 4·9 events/h. Also, three covariables (the rate of repetitive use of the switch to make hits on simulated workpieces, subject age and subject experience at foot switch-controlled workstations) were examined for their contribution to cycling errors. Although hand task was a significant effect in error prediction models containing the four primary variables, it was found that a model containing the hit rate covariate (rate of repeated use of the foot switch) provided the best predictor of the frequency of inadvertent actuation errors. An error threshold was observed at about 17·5 hits/min with a high linear correlation between hit rate and machine-cycling errors at higher hit rates. Based on results of the experiment, this report presents design considerations for workstations which use foot controls to help minimise the chance of machine-cycling errors and injury.