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Actuator System for Individual Nozzle Control of Flow Rate and Spray Droplet Size

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  Transactions of the ASABE. 55(2): 379-386. (doi: 10.13031/2013.41376) @2012
Authors:   D. L. Needham, A. J. Holtz, D. K. Giles
Keywords:   Nozzle control, Pulse width modulation, Precision agriculture, Spray droplet size, State-space model, Throttling valve, Variable rate

A proportional solenoid valve control system was developed to control fluid pressure to individual agricultural spray nozzles in order to regulate the resulting spray droplet size spectrum. The actuation method utilized an electrical solenoid valve coupled to a spray nozzle such that the valve poppet position was varied to regulate pressure drop across the valve and subsequently the inlet pressure to the nozzle. The duty cycle of a high-frequency (10 kHz) pulse width modulation (PWM) signal was used to regulate the current in the valve's solenoid coil. The high-frequency modulation signal was incorporated into an arbitrary waveform that contained a low-frequency (10 Hz) PWM component, which regulated the average volumetric flow rate with a controlled duty cycle within the 100 ms periods of instantaneous pressure. The study included mathematical modeling of the system, fabrication of a spray actuator prototype and drive circuit, and development of the control algorithms. Actuator system performance was assessed for two characteristics: the ability to control the droplet size spectrum through proportional pressure control, and the ability to control time-averaged volumetric flow rate at constant and varied pressures.

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