PWM Valve Flowrate Correction for Crop Sprayer Nozzle Control
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Solution Overview
Problem
Existing agricultural machines struggle to accurately measure and control the flowrate of chemicals such as fertilizers, pesticides, and herbicides, leading to potential overuse or underuse, which affects crop yields and uniform application patterns.
Innovation Solution
A method involving pulse width modulation valves to determine a duty cycle and apply a correction factor to measure and correct the flowrate, using sensors to monitor fluid properties and a control system to adjust application rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional flowrate measurement methods are used without correction, then the measurement process is simple, but the measurement precision is insufficient leading to inaccurate chemical application rates
Solution Approach 1:
The system uses feedback by measuring the duty cycle of the PWM valve and applying a correction factor based on this feedback signal. The control system continuously monitors the valve operation and adjusts the flowrate measurement accordingly, creating a closed-loop measurement system that improves accuracy without requiring complex hardware modifications.
Solution Approach 2:
The invention changes the measurement parameter from direct flowrate measurement to duty cycle measurement. By measuring the duty cycle (a electrical parameter) and applying a correction factor, the system transforms an difficult-to-measure physical quantity (flowrate through pulsing valve) into an easier-to-measure electrical parameter, thereby improving measurement precision while maintaining system simplicity.
2Adaptability or versatility
If PWM valves are used to control spray output, then the adaptability of the system is improved, but the difficulty of detecting and measuring the actual flowrate increases
Solution Approach 1:
The duty cycle measurement serves as an intermediary parameter between the PWM valve control and the actual flowrate. Instead of directly measuring the complex pulsing flow through the PWM valve, the system uses the duty cycle (an intermediate electrical parameter) as a mediator to infer and correct the flowrate measurement, thereby simplifying the detection process while maintaining adaptability.
3Reliability
If flowrate measurements are not corrected for duty cycle, then the ease of operation is maintained, but the loss of information occurs leading to inaccurate application rates
Solution Approach 1:
The system recovers lost information by implementing feedback through duty cycle measurement. The control system uses the duty cycle feedback to calculate and apply a correction factor, thereby recovering the accurate flowrate information that would otherwise be lost due to the pulsing nature of PWM valve operation. This ensures reliable chemical application rates without increasing operational complexity.
Data Source
AI summary
A method of operating a crop sprayer includes determining a duty cycle of a pulse width modulation valve, measuring a flowrate of a fluid through the pulse width modulation valve to determine a measured flowrate, and applying a correction factor to the measured flowrate to determine a corrected flowrate based on the duty cycle. A crop sprayer includes a chassis, a product tank containing a fluid, a boom comprising at least one boom arm configured to laterally extend from the chassis, and a nozzle assembly operably coupled to the at least one boom arm and in fluid communication with the product tank. The nozzle assembly includes a sensor housing, a flow meter, and a pulse width modulation valve. The crop sprayer includes a sensor monitoring system configured to determine a corrected flowrate through the nozzle assembly. Related control systems are also disclosed.