The effects of vertical sprayer boom movements on the uniformity of spray distribution

Vertical sprayer boom movements are studied with experimental modal analysis. A distinction is made between rigid-body motions and flexible deformations of the sprayer boom. Pure vertical and rolling rigid-body motions of the boom are mainly caused by unwanted tractor movements which are caused primarily by soil undulations and tyre characteristics. Flexible boom vibrations are induced by vertical and rolling angular accelerations of the tractor body. The influence of the driving speed and tyre pressure is investigated on the distinct boom motions and the effect of speed seems to dominate. Increase of driving speed (4-12 km/h) results in a rise of the pure vertical translations (130%), the rolling motions (x 10) and the vertical flexible deformations (x 4). A change of tyre pressure from 60 to 180 kPa leads to fall of the pure vertical translations (-20%), while the rolling and vertical flexible deformations go up by 2%. These phenomena are due to frequency shifts and larger force intensities in the frequency band between 0.5 and 3.5 Hz. The spray deposit distribution is calculated and, from the simulated spray patterns, the effect of the boom motions on uniformity of the spray pattern is examined. Simulation outcomes reveal a minor effect of the vertical translations, while rolling of the boom and vertical flexible deformations have larger influences, especially at the extremities of the boom owing to their larger amplitudes. Maximum deposits reach 760% and minimum 0% in the case of the largest sprayer boom motions. From these calculated spray patterns, an optimal range of use is determined for the tested sprayer: a spraying height of 0.5 m or more in combination with a fixed nozzle spacing of 0.5 m, a limited tractor speed and low tyre pressure leads to a good spray distribution (correct overlap) with the flat fan nozzle with top angle of 110 degrees. (C) 1999 Silsoe Research Institute.