Analyzing the Nozzle Spray Fan Pattern of an Agricultural Sprayer Using Pulse Width Modulation Technology to Generate an On-Ground Coverage Map

Abstract

Chemical application is an integral part of crop care. Today, advanced sprayers automatically control individual boom sections and nozzles to accommodate increased machine sizes and travel speeds, yet automatic control of flow-based systems raises concerns regarding coverage accuracy and uniformity during changes in travel speed and spray swath width. New commercial systems apply product at a constant pressure using varied duty cycles of pulse width modulated (PWM) solenoids to maintain a constant application rate. However, concerns exist regarding the dynamic effect of solenoid on/off latency on spray fan pattern and spray coverage. The objectives of this study were to investigate the on/off latency in PWM nozzles, determine if active nozzles affect spray fan pattern latency, and develop flow characteristics to simulate dynamic spray coverage. A PWM system and flow rate controller were installed on a 6.6 m three-section boom sprayer with 13 nozzles. A Raven Viper 4 controller regulated the product flow rate and pressure, while a Capstan Pinpoint controller was used to set the system pressure, nozzle on/off configuration, and duty cycle. The results indicated that the PWM spray system maintained the pressure within ±5% of the target value and applied an accurate amount of flow per pulse regardless of the number of nozzles activated. There was a 20 ms delay in nozzle pressure development during each cycle, and the delay was constant regardless of the number of nozzles activated. After de-energizing the solenoid, the nozzle continued spraying at system pressure for 10 ms. Static spray droplet distribution proved that the system applied the correct volume per pulse. In addition, PWM duty cycles of 100%, 80%, 60%, and 40% provided spray coverage within ±10% of the target rate for 100%, 94%, 77%, and 67% of the time, respectively. Greater signal overlap between odd and even nozzles increased the application coverage. Dynamic spray simulations showed that as-applied application error may vary beyond ±10% of the target rate. As such, while the PWM system provided the desired amount of product per pulse, the spray coverage results indicated that the on-ground coverage could result in areas with under- or over-application.