Biological Systems Engineering, Department of


First Advisor

Joe Luck

Date of this Version


Document Type



Rohrer, Rodney A, "Control System for Variable-Orifice Mechatronic Spray Nozzle for Regulation of Application Rate and Droplet Size Spectra" (2021). University of Nebraska-Lincoln.


A DISSERTATION Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Doctor of Philosophy, Major: Biological Engineering (Agricultural & Biological Systems Engineering), Under the Supervision of Professor Joe Luck. Lincoln, Nebraska: May, 2021

Copyright © 2021 Rodney A. Rohrer


Traditional fixed-orifice spray nozzles are selected for flow rate and droplet spectra required for a given pesticide application. Although limited variation in flow can be achieved by adjusting system pressure, this can adversely affect spray quality. Other nozzle configurations, such as Pulse Width Modulated (PWM) nozzles or passive variable-orifice designs, are intended to maintain consistent droplet size and spray pattern as flow rate is changed but those too have limitations.

A variable-orifice nozzle modified by Luck (2012) can span multiple droplet spectra and offers independent control of flow and droplet size; however, an advanced control system must be developed to make it practical for field use. 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 five sizes of variable-orifice nozzles were evaluated which showed that two nozzles, spanning fine to very coarse droplet spectra, could replace four of the five nozzles.

Validation tests confirmed the control method could independently vary flow rate and droplet size. Droplet volume mean diameter 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.

Although the control method was developed with a modified variable-orifice nozzle, literature implies there is potential for it to be applied to PWM nozzles. This adaptable control method provides a foundation for development of site-specific droplet size control, weather-based droplet size control, and it is well suited for robotic and autonomous spray systems.

Advisor: Joe Luck