Design and experiment of electronically controlled precision spray control system based on PWM

Aiming to address the problems of low precision of variable spray systems and low effective utilization rate of pesticides, this research designed an electronically controlled precision spray control system based on PWM. The system takes PIC18F258 single-chip microcomputer as the core, which is mainly composed of an upper computer, spray controller, electronic switch, and electronically controlled nozzle body. The system also has an HMI serial port screen that is used as the host computer to receive the spray amount set by the user and send it to the spray controller in real time through CAN bus communication. The spray controller then calculates the PWM duty cycle of the corresponding nozzle according to the received application amount, and adjusts the on-off time of each nozzle in real time to realize the independent control of the nozzle. In order to verify the accuracy of the system control, when the pulse frequency is 10 Hz and the system pressure is 0.3 MPa, 0.4 MPa, and 0.5 MPa, respectively, the spray time, system response time, and nozzle flow under different duty ratios of the spray system in a single cycle were measured. The test results showed that under the system pressure of 0.3 MPa, 0.4 MPa, and 0.5 MPa, the relationship between nozzle flow and PWM duty cycle was linear, and the linear fitting degree was greater than 0.95. The maximum errors of the on-off time of the electronically controlled nozzle body were 2.5 ms, 2.98 ms, and 2.9 ms, the maximum relative errors were 6.6%, 6.6%, and 6.8%, the RMS errors were 2.37 ms, 2.54 ms, and 2.27 ms, and the maximum response time of the spray system was 0.179 s, 0.176 s, and 0.167 s, respectively.