Integrated actuator for real time control of spray nozzle flow rate and droplet size spectrum

摘要

As sprayer working widths and ground speeds have increased, maintaining consistent application rate has required expanded dynamic range for spray nozzle flow rate. Concurrently, application buffer zones, for drift management, are often based on spraydroplet size spectra emitted by the nozzles. These requirements create the need for expanded, real time control of nozzle flow rate and spray droplet size. Pulse width modulation (PWM) of solenoid valves close-coupled to conventional nozzles has been developed and adopted for agricultural sprayers. Continuing to address these dynamic application needs, an advanced valve and system design was developed in which pressure throttling of a solenoid valve was integrated into PWM valve control. The throttlingallowed the fluid pressure into the nozzle, and correspondingly, the spray droplet size spectra, to be controlled during each 20-100 ms pulse of fluid from the nozzle. A dynamic model of pressure and flow characteristics of existing control valves for use with agricultural spray nozzles was developed. The dynamic model further simulated a pulse width modulation (PWM) condition in which average volumetric flow resulted from the duty cycle of 100-ms periods of instantaneous pressure. The mechanical and fluid modeling was accomplished using commercial solid modeling and computational fluid dynamics software. The dynamic mathematical modeling of valve performance was addressed using a commercial numerical solution package. A physical valve prototype was manufactured and performance was compared to model results. Both the model and physical performance indicated that variable pressure drop across the valve and duty cycle flow control for each fluid pulse during 10 Hz actuation is feasible.