|Riassunto in Inglese:|
The European legislation 2002/44/CE indicates the minimum prescriptions, in safety and health matter, concerning workers’ exposition to the risk from vibrations. As ploughing is one of the most common and heavy agricultural operations, this paper deals with the aspect of the vibrations it transmits to the tractor driver. The tests consisted of the measurement of the vibration levels at the driver seat during in-furrow and out-of-furrow ploughing on a clay-loam soil conducted according to the ISO 2631-1:1997 standard. The data of the effective accelerations, awx, awy and awz, in the frequency interval 0.5 Hz up to 80 Hz, have been collected by a for-seat, tri-axial accelerometer oriented according to the above standard, a multi-channel system specific for real-time acquisition of noise and vibration and have been related to the inclination of the driver seat during the work, measured by a tri-axial gyroscope. The time of sampling was 120 s, sufficing to characterize the level of vibrations produced by the ploughing. Six replications have been made for each thesis. The tests have been performed using a three-furrow, reversible mouldboard plough coupled to a 205 kW, 4WD tractor. An hydraulic control system allows to vary the alignment between the tractor and the first body of the plough that can thus operate as a traditional in-furrow plough or as an out-of-furrow plough. Basing on the characteristics of the soil and of the plough, the working depth has been set at 0.40 m, as the working velocity was approximately 6.0 km h-1. The results show an average acceleration sum vector (Av) of 0.936 m s-2, during the in-furrow ploughing, with a standard deviation of 0.027 m s-2. As regards the axial accelerations (awx, awy, awz), the maximum solicitations occurred on the Y axis (transversal, solid to the cab’s floor) that, under these work conditions, had an average inclination of 4° on the horizontal plane. The acceleration sum vector (av) considerably decreased during the out-of-furrow ploughing. Its average value was 0.656 m s-2, with a standard deviation of 0.034 m s-2. The behaviours of the axial accelerations have been more homogeneous than in the previous case, showing higher values on the X axis. The gyroscopic measurements witnessed that the tractor-plough system operated without notable inclination.