Dynamic analysis and design guidelines of mechanical oscillators for cutting soil through vibrating tools

The reduction of the soil cutting force through vibrating tools was the object of many studies during the second half of the last century. These studies initially focused on soil movement by bulldozers and then on soil tillage in agriculture. Over the past years, the field of tree-nursery mechanization has been employing this knowledge due to the use of equipment with oscillating tools for root-balling plants. Transportation and planting must be performed with the roots contained in a hemispherical ball of the original soil. This hemispherical root-ball is obtained by using a vibrating semicircular blade that cuts the soil underneath the plant. The blade oscillator is complex because the blade must oscillate and advance in the frame to cut the root-ball. For this reason, we correlated the oscillation and cutting movements with the oscillator features through a dynamic analysis using the Hong’s formulae for Coulomb friction with a harmonic forcing torque. The resulting periodic motion has a substantial phase lag with respect to the forcing torque generated by the rotation of eccentric masses; instead, the amplitude predicted with the Coulomb friction is 15 % lower than the amplitude calculated without friction. Experiments were also conducted to verify the value of these amplitudes and to determine the correlations between the cutting torque of the blade in typical tree-nursery soil and the blade diameter. All the correlations proposed in this article, together with the performed literature survey, were useful for drafting new design guidelines for mechanical oscillators.