Simon Cool

High Speed Stereovision Setup for Position and Motion Estimation of Fertilizer Particles Leaving a Centrifugal Spreader

A 3D imaging technique using a high speed binocular stereovision system was developed in combination with corresponding image processing algorithms for accurate determination of the parameters of particles leaving the spinning disks of centrifugal fertilizer spreaders. Validation of the stereo-matching algorithm using a virtual 3D stereovision simulator indicated an error of less than 2 pixels for 90% of the particles. The setup was validated using the cylindrical spread pattern of an experimental spreader. A 2D correlation coefficient of 90% and a Relative Error of 27% was found between the experimental results and the (simulated) spread pattern obtained with the developed setup. In combination with a ballistic flight model, the developed image acquisition and processing algorithms can enable fast determination and evaluation of the spread pattern which can be used as a tool for spreader design and precise machine calibration.

Development of a High Irradiance LED Configuration for Small Field of View Motion Estimation of Fertilizer Particles

Better characterization of the fertilizer spreading process, especially the fertilizer pattern distribution on the ground, requires an accurate measurement of individual particle properties and dynamics. Both 2D and 3D high speed imaging techniques have been developed for this purpose. To maximize the accuracy of the predictions, a specific illumination level is required. This paper describes the development of a high irradiance LED system for high speed motion estimation of fertilizer particles. A spectral sensitivity factor was used to select the optimal LED in relation to the used camera from a range of commercially available high power LEDs. A multiple objective genetic algorithm was used to find the optimal configuration of LEDs resulting in the most homogeneous irradiance in the target area. Simulations were carried out for different lenses and number of LEDs. The chosen configuration resulted in an average irradiance level of 452 W/m2 with coefficient of variation less than 2%. The algorithm proved superior and more flexible to other approaches reported in the literature and can be used for various other applications.

Development of a Stereovision-Based Technique to Measure the Spread Patterns of Granular Fertilizer Spreaders

Centrifugal fertilizer spreaders are by far the most commonly used granular fertilizer spreader type in Europe. Their spread pattern however is error-prone, potentially leading to an undesired distribution of particles in the field and losses out of the field, which is often caused by poor calibration of the spreader for the specific fertilizer used. Due to the large environmental impact of fertilizer use, it is important to optimize the spreading process and minimize these errors. Spreader calibrations can be performed by using collection trays to determine the (field) spread pattern, but this is very time-consuming and expensive for the farmer and hence not common practice. Therefore, we developed an innovative multi-camera system to predict the spread pattern in a fast and accurate way, independent of the spreader configuration. Using high-speed stereovision, ejection parameters of particles leaving the spreader vanes were determined relative to a coordinate system associated with the spreader. The landing positions and subsequent spread patterns were determined using a ballistic model incorporating the effect of tractor motion and wind. Experiments were conducted with a commercial spreader and showed a high repeatability. The results were transformed to one spatial dimension to enable comparison with transverse spread patterns determined in the field and showed similar results.

Measuring the dynamic mass flow from a centrifugal fertilizer spreader

Working widths of commercial centrifugal fertilizer spreaders are continuously increasing, increasing the sensitivity of the spread pattern to fertilizer and spreader properties. One very important parameter is the fertilizer mass flow rate from the hopper to the disks, since this determines the application rate on the field and has also an effect on the shape of the distribution pattern. In this study, the dynamic mass flow rate of a commercially available fertilizer spreader was evaluated for three types of fertilizer. Fluctuations of the flow rate were found and illustrate the need to consider the dynamic behavior of the mass flow rate when designing systems or procedures for measuring or simulating spread patterns of centrifugal fertilizer spreaders.

Comparison of different spread pattern determination techniques

Traditionally, the performance of fertilizer spreaders is assessed using a row of collection trays aligned perpendicular to the driving direction of the tractor. For precise calibration of the spreader this technique, however, does not provide adequate insight into the spreading process since particle distributions are measured in only one spatial dimension. In this paper, two different two dimensional spread pattern determination techniques (SPDT) were tested, each consisting of a sampling method and a matching interpolation algorithm. Tests were executed under similar conditions with three commonly used types of fertilizer (CAN, NPK, KCl) with different physical properties. Results were compared with the traditional technique. The differences found illustrate the importance of using an adequate SPDT to compare spread patterns.