The number of fatalities caused by tractor rollovers has decreased in recent years, but the number of fatal tractor rollover accidents with a folded-down rollover protective structure (ROPS) has increased. Operating a ROPS-equipped tractor in low overhead clearance zones is difficult and sometimes impossible. The foldable ROPS (FROPS) was designed to solve the rigid ROPS problem, but lowering and raising a conventional FROPS is a time-consuming and strenuous process. After operators fold down a FROPS to pass a low overhead clearance zone, some prefer to leave it in the folded or inoperative position, increasing the risk of a rollover fatality. The actuation forces for raising and lowering a FROPS are not well known and may be influenced by actuation speed. A completely randomized block design with two blocks, five levels of speed, and multiple replications was conducted to investigate the effect of speed on actuation torque. The blocks were two sizes of tractor FROPS. The test included five levels of speed, including two levels of static measurement and three levels of dynamic measurement. A variable-speed motor system was used to control the speed for raising and lowering the FROPS. The actuation torque is a function of the FROPS upper part shape, dimensions, material density, turning acceleration, and friction. A theoretical model was developed to predict the actuation torque based on the FROPS shape, dimensions, and material density. For one ROPS, due to friction, the dynamic actuation torque was greater for raising and less for lowering than the theoretical torque. Indicator variable regression was used to analyze the effect of speed on actuation torque. Results showed that speed had a significant (p > 0.05) effect on actuation torque. Although there were statistically significant differences between the dynamic actuation torques, these differences were relatively small and negligible compared to the differences between the static torques.
Keywords: Actuating force; Foldable rollover protective structure; Safety; Standards; Tractor.
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