Development of an integrated actuator for real time control of spray nozzle flow rate and droplet size spectrum

Typical agrochemical sprayers use nozzles to atomize a liquid stream into droplets; these droplets then travel to the target. Nozzles may be selected to provide a range of droplet sizes, spray distribution patterns, and flow rates for a desired liquid material application. Spray distribution, droplet size, and flow rate are important considerations in achieving a high quality agrochemical application. The size of the droplets and application conditions can influence the target coverage and the occurrence of spray drift, where droplets are displaced by ambient wind and subsequently land outside of the designated spray area. It has been shown that uniform deposition of small droplets can result in superior pest control efficacy. However, large droplets are less likely to drift than small droplets. Spray droplet size is the most important factor affecting the likelihood of spray drift and target coverage from conventional spray nozzles. The capability of pulse width modulated (PWM) flow control at individual nozzles can result in fewer application rate errors due to adjustment to the rate at the highest possible spatial resolution. However, the quality of an application is dependent on many other factors than only the quantity of material applied. Spray droplet size remains a critical ingredient in maximizing efficacy and minimizing drift. But, even with modern PWM flow control systems, droplet size on existing systems is controlled in per-machine width resolution, that is, every nozzle across the entire boom must produce the same droplet size spectrum. There are many situations where adjusting the droplet size on an individual nozzle is desirable, including use in narrow buffer zones where a larger droplet size is mandated for mitigating spray drift. With current technology, a spray machine with a 40 m boom would be required to maintain large droplets on a 40 m swath, even if the mandated buffer zone was only 3 m. This application would reduce the efficacy of the application in areas not at risk of drift. Modern global positioning systems with centimeter-scale accuracy and high-speed computers are capable of implementing very precise applications for diverse crops in close proximity. To gain full use of these sensor and processing technologies, the need for high treatable spatial resolution is increasing. However, one of the primary limitations to precision agricultural technology is the lack of good actuation systems to match the precision of today's advanced sensing systems. The basic premise of this project is a PWM-based valve in which the electromechanics of the valve and the driver electronics are designed to allow the valve to be partially opened, in a precisely and reliably controllable manner during each pulse of emitted spray. In this manner, the liquid pressure drop across the valve can be controlled, this controlling the inlet pressure to a spray nozzle and therefore, the spray droplet size. This control, when coupled with the existing PWM-based control of the flow rate of liquid, allows complete control, on a nozzle-by-nozzle basis, of spray application rate and droplet size of agricultural spray