Author ORCID Identifier

https://orcid.org/0009-0003-6486-1395

Date Available

7-22-2024

Year of Publication

2024

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Agriculture; Engineering

Department/School/Program

Biosystems and Agricultural Engineering

First Advisor

Michael P. Sama

Abstract

The overarching objective of this research was to enhance our understanding of pulse width modulation (PWM) based nozzle control system and develop an intelligent nozzle control system for agricultural spray applications. This dissertation focused on measuring and analyzing the transient nozzle pressure characteristics and performance under PWM control. Additionally, it explored the development of an innovative multi-degree-of-freedom (DOF) nozzle control system for precise chemical applications in specialty crop systems.

The pressure dynamics of a PWM system were studied by developing an instrumentation system capable of operating a solenoid valve and recording pressure signals. A nozzle body and two manifolds of different volumes were fitted with embedded pressure sensors. Time series pressure data were collected at a nominal pressure of 345 kPa, frequency of 10 Hz, and a 50% duty cycle for a series of flat fan nozzle tips. The pressure data were modeled with a second-order transfer function to extract the damping ratio (ζ). It was found that internal volume changes in the nozzle body affected pressure dynamics, suggesting that the predominant pressure measurement techniques might have affected the amplitude and duration of pressure fluctuations. Additional time-series pressure data were collected over a wide range of nominal pressures and PWM duty cycles to characterize the nozzle pressure dynamics. It was found that ζ depended on the orifice size, while the natural frequency (𝜔𝑛) depended on both the orifice size and the nominal pressure, influencing transient response characteristics such as maximum overshoot (Mp), rise time (tr), and settling time (ts). Therefore, the input parameters that result in a sufficiently fast and damped pressure response should be selected for optimal nozzle performance under PWM control.

Spray characteristics under PWM control were evaluated at a high spatial resolution using a sprayer test fixture and water-sensitive paper spray cards. Results indicated substantial variability in droplet size and spray coverage in both the off-path and along-path directions, influenced by the spray fan profile and transient nozzle pressure fluctuations due to high-frequency PWM actuation. ANOVA and Tukey HSD tests confirmed that nozzle orifice size significantly impacted spray coverage and droplet size, emphasizing the importance of selecting proper nozzle tips for higher spray efficacy. Additionally, spray card analysis at various resolutions revealed that higher resolutions increase droplet counts and decrease droplet sizes but have no effect on spray coverage. Welch’s ANOVA showed significant effects of scanning resolution on droplet size and count, but not on spray coverage, suggesting that the parameter of interest is an important factor in selecting an optimal resolution. Games-Howell post hoc analysis revealed that there was no statistical significance in droplet size and droplet count when scanning a spray card at 600 dpi and 4800 dpi. While this does not mean there was no effect of resolution on quantification, it indicates that there may not be a substantial advantage in scanning at excessively high resolutions.

A novel vision-based multi-DOF nozzle control system was developed for spraying within the desired spray boundary. It consisted of two servomotors for pitch and roll control of the nozzle mount and a PWM solenoid valve for spray control. An Intel RealSense D345i camera was used to detect simulated boundary conditions and extract the coordinates. A look-ahead feature was developed by positioning the camera ahead of the nozzle tip to ensure unobstructed detection and allow for latency due to image processing. Preliminary tests demonstrated that the nozzle can effectively track the boundaries based on the decision feedback from the vision system, indicating its potential to improve chemical use efficacy and reduce the environmental issues associated with off-target spray.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2024.267

Funding Information

This study was supported by the United States Department of Agriculture, National Institute of Food and Agriculture under grant number 2017-67021-26250.

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