Analysis and control of rate and uniformity for granular fertilizer application systems

Variable rate application of fertilizers with traditional spinner-type spreaders is known to suffer from spread pattern uniformity variability as a function of the application rate. To demonstrate this variability, simulations using models from the literature were carried out. Simulations for the dual disc spreader showed that for higher application rates the pattern becomes "M" shaped, whereas for a single disc spreader the pattern becomes skewed, even though the pattern for low rates was near-Gaussian shaped in both cases.; The first research topic was the minimization of uniformity variability, by developing a feed gate control method based on an existing time-of-flight sensor. Simulations showed that the feed gate method produced high quality patterns for any given application rate, in both cases, the dual disc spreader with segment-type feed gates, as well as the single disc spreader with conical feed gates.; The second research topic focused on the study of dynamic fertilizer friction coefficient measurement. The governing differential equation for sliding particle motion with friction along a straight radial vane was reduced and a method of determining the friction coefficient based solely on the measured radial discharge velocity was derived.; To measure the dynamic friction coefficients of plastic spheres as well as Ammonium Nitrate and Potassium Chloride fertilizers more directly, a spinning tube device was developed. Photo interrupters were placed at strategic locations along the tube, which supplied timing information regarding particle passages from which the friction coefficients were computed using a reduced particle acceleration model. The measured friction coefficients were considered most reliable at the highest rotational speeds (800 RPM) leading to 0.25 for plastic spheres, 0.31 for Ammonium Nitrate and 0.44 for Potassium Chloride fertilizer.; A comparison was made between the spinning tube method discussed in this paper and a rheometer method. In the latter method, the particles are fixed in placeholders, and a spinning disc is kept in contact with them under a controlled normal force. The measured torque on the disc is then a measure for the friction coefficient. Data for the same fertilizer materials Ammonium Nitrate and Potassium Chloride indicated that the rheometer is not a good instrument to obtain friction coefficients with practical value, whereas the data from the spinning tube device is consistent with measured spread patterns. (Abstract shortened by UMI.)...