Recipient Organization
CAPSTAN AG SYSTEMS, INC
101 N KANSAS AVE
TOPEKA,KS 66603
Performing Department
(N/A)
Non Technical Summary
Application of agrochemicals is essential to U.S. production of food, fiber, biofuels and ornamentals. However, it can also create environmental contamination if pesticides reach non-target areas through airborne displacement of spray, i.e., "spray drift". Drift is a concern for agriculture, especially for specialty crops grown in sensitive areas. Spray drift mitigation, through use of larger droplets, unsprayed buffer zones and slower ground speeds can conflict with efficient, economic crop production. Concurrently, precision pesticide application using GPS, sensors, etc., is growing; yet spray actuators can be the limiting factor in spatial resolution. This project will develop a single, at-nozzle actuator to control the application rate and spray droplet size at the spatial resolution of a single nozzle, allowing highly precise variable rate application and drift control. This will also allow buffer zones to be highly resolved and drift control to be electronically verified. The approach will be to develop a high-speed pulse width modulated (PWM) valve that can be partially opened during each pulse cycle. The duty cycle of pulses will control the flow rate while the modulated opening will control the pressure drop across the valve and correspondingly, the spray droplet size from the attached nozzle. This is a significant advance in spraying capability; yet, it will leverage the existing market acceptance of PWM spray rate control.
Animal Health Component
100%
Research Effort Categories
Basic
(N/A)
Applied
100%
Developmental
(N/A)
Goals / Objectives
The goal of the project is the development of a system for individual spray nozzle control providing a desired flow rate and spray droplet size spectrum. The system is defined as: a mechanical valve capable of utilizing high-frequency PWM control of the throttling mechanism (i.e., degree of openness) of the valve during each approximately 10 to 100 ms pulsed emission of spray, the necessary electronics for creating the required electronic actuation signal, and the means for interfacing each valve to a controlling network for a mobile spray system on an agricultural vehicle. The solenoid valve to be developed in this project will have the ability to manipulate droplet size and flow rate solely through electrical actuation signals. An additional goal of this project is to further the concept of single-actuator control of pressure and flow by developing an early design of a robust valve that could operate in the harsh environmental conditions of a typical agricultural application. The immediate objectives of the Phase I effort are: 1) develop candidate valve design performance goals and constraints; 2) develop a mathematical model and a mechanical prototype valve; 3) develop an electronic solenoid drive circuit for the valve; and 4) evaluate the performance of the test system valve and control circuit.
Project Methods
The following methods will be employed to achieve the immediate objectives of the project. A robust actuator valve will be conceptualized, designed, built, and the performance verified. Initially, the necessary performance characteristics of power consumption, proportionality in control, simplicity, reliability and cost will be quantified. Additional focus will be placed on selecting a design that can operate maintenance free for at least one thousand hours. Mechanical tolerances must allow adequate flow so as to resist plugging, sticking and corrosion from agricultural chemicals. Throttling mechanisms will be selected and mathematically modeled in order to establish a valve design capable of linearly controlling the pressure drop across the throttling mechanism. The mechanisms to be modeled will likely include a flat poppet with rubber face seals, a needle valve design with radial O-ring seals, a contour-profiled poppet with custom seals, and a spool-like design with sealed ports. Once a throttling mechanism, or multiple mechanisms have been adequately considered, the actuator driver apparatus will be selected. Throttling mechanism stroke distances may be measured with a laser distance-measuring device aimed through the orifice hole. Because this device is intended to operate on an agricultural sprayer, the necessary drive logic will all be designed for a 12 VDC power source. In order to achieve the exact waveform desired, a microcontroller will be used with custom firmware in order to generate the exact timing required for the project. The performance of this valve will be assessed for two characteristics. The first is the ability to control droplet size spectrum through proportional pressure control. The second is the ability to control time-averaged volumetric flow rate at constant and varied pressures. Within these two primary verification objectives, exist several performance parameters that affect the quality of the application. Among these are liquid pulse turn-on time, liquid pulse turn-off time, outlet pressure stability, and range of inlet pressure operation. Before any complex waveform tests are attempted, a basic test can be conducted to ensure that the valve mechanism can control outlet pressure. A simple high frequency square wave may be used with a FET amplifier circuit to drive the valve coil with varied duty cycle. Because the coil inductance prevents current from changing instantaneously, the 12-volt high-frequency waveform with varied duty cycle will essentially produce a direct current of varied amperage. This current is linearly related to the magnetic field produced and thus, to the force generated by the coil. Given a linear spring and little pressure effects on the actuator, the coil current should be linearly related to the displacement of the throttling mechanism, producing a controllable pressure drop across the valve. Validation of pressure throttling with pulsed flow control will be accomplished using two pressure transducers. Droplet size evaluation with pressure throttling and flow control will take measure flow rate volumetrically and droplet size with a laser diffraction droplet size analyzer.