Predicting spread patterns of centrifugal fertiliser spreaders

Nowadays farmers recognize the importance of a correct and precise fertiliser application: non-uniform spread patterns cause extra pressure on the environment and might result in economic losses for the farmer. In Europe most spreading is done by centrifugal fertilizer spreaders but their spreading process is not easy to monitor and to control. To perform a precise fertilization farmers need proper tools to determine and evaluate the spread patterns at farm level. Therefore the Flemish Institute for Agricultural and Fisheries Research (ILVO)
and its partners are exploring and developing a fast and accurate technique for measuring the spread pattern of conventional centrifugal spreaders. This method aims to be low cost and applicable at the farm level. Also, the proposed solution has to be mobile to the extent that the device can be built up on-site to test several machines. The device should enable the adjustment of the spreader in such a way that a uniform spread pattern is obtained. At a later stage, an onboard sensor could be envisaged. Three main approaches for evaluating the spread pattern are currently available: the experimental collector tray method, the full modelling approach like the Discrete Element Method (DEM), and the hybrid approach that combines measurements and modelling. In this research the hybrid approach was applied: the spread pattern was predicted with a ballistic flight model based on the measurement of the horizontal outlet angle, the vertical outlet angle, the grain diameter, the grain density and
the initial velocity. In a first step, a 2-dimensional imaging technique was used with a small field of view (0.33m x 0.25m) to measure the horizontal outlet angle and the speed of the grains at different camera positions at the circumference of the disk. The vertical outlet angle and the mass distribution were measured with a cylindrical collector. The grains flying under
the measurement unit were imaged using two different techniques: the high speed technique and a newly developed multi-exposure imaging technique. For the high speed technique a camera, type MotionXtra HG 100K (Roper Scientific, New Jersey, USA), was used. The stroboscopic technique combined a specially designed LED stroboscope with a Nikon D 100
camera. Overall the stroboscopic technique and the high speed technique were capable of measuring the outlet angle and the outlet speed. Small differences between the measurements with both techniques existed, but ultimately in the aim is the determination of the resulting spread pattern in the field. When comparing the simulated and the measured spread pattern, relative errors amounted up to 30%. Therefore, in the next phase the twodimensional
imaging technique was adapted with a much larger field of view (1m x 1m),
improved lighting system and motion estimation algorithms, resulting in lower relative errors between the simulated and the measured cylindrical spread pattern. At the moment a 3D stereovision set-up (and related algorithms) to further improve the simulation of the spread pattern is being developed.