Simultaneous control of a wide range of droplet sizes and application rates for agricultural sprayers has been elusive even when considering advanced pulse-width modulation valve technologies. The primary goal of this research was to develop such control logic by managing four system variables: flow rate, pressure, droplet size, and effective orifice size. A five-nozzle spray system was built as a testbed to develop and evaluate the control method which automatically targeted desired droplet spectra and flow rate. Performance characteristics of two electro-mechanically actuated variable-orifice nozzles were evaluated which showed that two nozzles, spanning fine to very coarse droplet spectra, could replace three to four fixed-orifice nozzles. Validation tests confirmed the control method could independently vary flow rate and droplet size. Droplet volume mean diameter (VMD) was within ±10% of desired size for all operating points. Actual flow rate was within ±10% of desired flow at nearly all operating points above 207 kPa. Optimization of the control method showed promise to reduce flow error to less than ±10% across the entire operating envelope but future work remains to fully implement and validate this in the control system. This adaptable control method provides a foundation for development of site-specific and/or weather-based droplet size control, and is well suited for robotic and autonomous spray systems.
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