Abstract:

 A variable rate system injection of soil pesticide was developed for control of soil pesticide amount by PWM. The paper analyzes the input and output conditions of control system, and designed hardware, algorithm and control of soil pesticide, mainly software flow and a feedback control way. In the paper, the variable-rate control system consisted of time delay, interface module, micro controller, speed sensor, PWM valve, and hydraulic motor. According to the amount of soil pesticide  information, controller can automatically control flow amount by adjusting solid solenoid valve and PWM valve based on working speed, which changes the pulse duty cycle to achieve the variable work. Experiments of injection of soil pesticide by pre-setting different dosage, the results shown that the errors of fertilizer amount are well in fact, and the errors are less than 5%, and it shown time delay is from 8s to 10.5s. It can meet the need of practical production. The system is well resolves to achieve variable rate injection of liquid pesticide into deep soil based on sensor. 

  The application system mainly includes four parts: crop positioning system based on Infrared sensor, interface module, variable controller and variable injection of soil pesticide applicator. Crop nutrition monitoring system installed in front of the tractor, for acquisition crop positioning the sensors were connected to interface module, and the collection data transmission to interface module. The interface module has serial and power connections.The paper is based on a variable input signals to output the electric signal to control PWM valve opening size. A infrared sensor was used which fixed with position of the injection point of soil. The flow rate of valve can be controlled by adjusting the opening position of PWM valve. Output signal is mainly PWM valve opening size which used to control flow rate, the pulse-width modulation (PWM) used to control the valve and the serial data which output to the LCD screen. In addition, the controller has a serial data interface to allow for the extended application.The core control unit used to carry out the data processing and exterior control which including serial ports, AD. Considering the measurement system upgrade, cost of general price, power consumption and compact, the system chosen STMF103VC as the whole system processing core. The core is Cortex™-M3 CPU used ARM 32-bit. It provides low cost of the platform, reduced pin number and reduced the system power consumption to achieve the needs of MCU. At the same time, the STM32 product embedded two 12 analog/digital converter (ADC), each ADC share up to 16 external channels, conversion rate can reach 1 μs.The chip can calculate the output PWM duty cycle according to the pre-set injection of soil pesticide amount after collected the speed of tractor.The feedback control is to regulate the PWM signal duty cycle according the real liquid flow  by the microcontroller chip collect the liquid sensor output signal which fixed on pesticide pipeline.