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Modeling Dynamic Response of an Actuator for Individual Nozzle Control of Agricultural Spray Flow Rate and 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): 371-377. (doi: 10.13031/2013.41375) @2012
Authors:   D. L. Needham, A. J. Holtz, D. K. Giles
Keywords:   Droplet size, Nozzle control, Precision agriculture, Pulse width modulation, Solenoid, State-space model, Throttling valve, Variable rate

A dynamic model of pressure and flow characteristics of solenoid-actuated control valves for use with agricultural spray nozzles was developed. The model analyzed a combined pulsing and throttling solenoid valve coupled to a spray nozzle. The valve's poppet position was varied to regulate the pressure drop across the valve and, subsequently, the inlet pressure to the downstream nozzle. The dynamic model further simulated a pulse width modulation (PWM) condition in which average volumetric flow resulted from a varied duty cycle of 100 ms periods of instantaneous pressure. The development of the actuator model was undertaken using two commercial software packages. The mechanical and fluid modeling was addressed using SolidWorks and SolidWorks Flow Simulation, a solid modeling and computational fluid dynamics (CFD) package. The dynamic mathematical modeling of valve performance was accomplished using MATLAB, a programming language based numerical solution package. Physical valve performance was measured in a novel experimental test apparatus and compared to model results. Both the model and physical performance indicated that the premise of variable pressure drop across the valve and duty cycle flow control for each 100 ms cycle is feasible. The implication of the results is that a single electronic actuator can be deployed to control spray flow rate and droplet size spectra from individual nozzles.

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