Modelling the effect of passive vertical suspensions on the dynamic behaviour of sprayer booms

Chemical products for crop protection are usually distributed on the field as liquids by field sprayers. wanted horizontal and vertical sprayer boom movements create local under- and over-applications of spray liquid. A non-linear finite element model of a tractor and a mounted sprayer is developed to simulate these unwanted boom vibrations during field operations. Representative disturbance signals at the hitch point of the boom suspension are calculated for a tractor with a mounted sprayer driving over a standardized bumpy track. These disturbances are applied as input excitations to simulate boom movements for several types of suspensions (pendulum, single and double trapezium). Validation experiments with a simple 12 m boom on a hydraulic test rig indicate that this non-linear finite element modelling technique is a promising method for simulating boom movements of field sprayers. Further simulation results show that the modelled suspensions approximately halve the vertical motion of the boom compared with a rigidly mounted boom. Standard deviations of the vertical boom tip movements around the equilibrium position are, respectively, 0.44, 0.25 and 0.27 m for a fixed boom, a boom with pendulum suspension and a boom with trapezium suspension. This proves the effectiveness of existing vertical boom suspensions. (C) 1999 Silsoe Research Institute.