Models to predict the force to operate front foldable rollover protective structures for narrow-track tractors

Narrow-track tractors are specifically designed to operate in narrow clearance areas, such as orchards and vineyards. A specific rollover protective structure (ROPS) was developed with a reduced clearance zone. Front mounted on the tractor it was designed to be lowered, if strictly required, to perform normal operations. However, this feature of the ROPS has been incorrectly used and this can be responsible for fatal injuries to the driver. The actuation force for raising and lowering the foldable ROPS is a function of design parameters, such as the mass, dimensions and hinge connection between the free upper and the fixed lower part of the structure. Nevertheless the accessible tractor zones and ROPS grasping area influence the operator's position in manual handling and affect the actuation force to be sustained during operation. Three theoretical models were developed to predict the actuation force using as reference ROPS shape, ROPS main dimensions and material density. The proposed models could help tractor and ROPS manufacturers to calculate the force required for operating the ROPS, planning the need for assisting devices when manual handling ROPS. Six new narrow-track tractors mounted with front foldable ROPS were evaluated in terms of their dimensions and the ROPS accessible zones for the operator. Results showed that the actuation force became higher, increasing the mass and dimensions of the tractors, not only because of the heavier ROPS but also for the uncomfortable zone during ROPS actuation. Near the articulation hinge of the ROPS the actuation torque is characterised by a higher force.