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 m ovements create local under- and over-applications of spray liquid. A non-l inear finite element model of a tractor and a mounted sprayer is developed to simulate these unwanted boom vibrations during field operations. Represe ntative disturbance signals at the hitch point of the boom suspension are c alculated for a tractor with a mounted sprayer driving over a standardized bumpy track. These disturbances are applied as input excitations to simulat e boom movements for several types of suspensions (pendulum, single and dou ble trapezium). Validation experiments with a simple 12 m boom on a hydraul ic test rig indicate that this non-linear finite element modelling techniqu e is a promising method for simulating boom movements of field sprayers. Fu rther simulation results show that the modelled suspensions approximately h alve the vertical motion of the boom compared with a rigidly mounted boom. Standard deviations of the vertical boom tip movements around the equilibri um position are, respectively, 0.44, 0.25 and 0.27 m for a fixed boom, a bo om with pendulum suspension and a boom with trapezium suspension. This prov es the effectiveness of existing vertical boom suspensions. (C) 1999 Silsoe Research Institute.