The traditional variable pesticide spraying adopts the method of pressure control flow, so the flow change needs a certain range to change the pressure, and the change of pressure will inevitably lead to the change of the spray particle size, which causes the spray to be unstable. To this end, the pesticide spraying method is adopted to realize the spraying of the pesticide, because it is realized under the condition of constant pressure, and the change of the flow rate is changed by changing the value while ensuring the same size of the spray particle. purpose.
2, PWM modulation principlePWM modulation is to convert a DC power supply into a PWM wave by pulse width modulation. The PWM wave is composed of a series of continuous rectangular waves with different duty cycles at a certain frequency, and it is widely used in many fields such as measurement, communication, and frequency conversion. Figure 1 shows the generation principle and waveform diagram. The system consists of a sawtooth generator and a comparator. If the signal is less than the output high level, otherwise the output is low. Therefore, as can be seen from Figure 1, the comparator outputs a series of waves.
Figure 1 modulation process
Therefore, the solenoid valve head can be driven by signal amplification of the output square wave. Change the opening time of the solenoid valve when the pressure and frequency are constant, so as to change the flow rate of the nozzle.
3. Overall structural design of the drone pesticide spraying systemThe overall structure of the drone pesticide spraying system includes electric centrifugal nozzle, folding boom, liquid tank, application control system, liquid pump, rack, etc. [3]. The pesticide spraying system is bolted to the connection point below the unmanned helicopter in a four-point manner. The application control system is fixed to the frame and is located on the side of the medicine box, and its signal input end is connected with the auxiliary control output end of the control host.
4 , uniform spray control system design 4.1, uniform spray central processing module (MCU) designThis design uses ST's STM32F407VGT6 as the main control chip and STM32F103CBT6 as the backup emergency chip. During the flight process, tasks such as remote control information capture, sensor data acquisition and filtering, real-time attitude calculation, and motor control require MCU processing, so the MCU needs very powerful processing capabilities. In addition, the multitasking feature of the flight control program itself requires the MCU to have enough Flash, RAM, and minimal interrupt time. Traditional 8-bit and 16-bit MCUs are difficult to meet the requirements.
Compared with other models of MCU, it has the following advantages: First, relatively high operating frequency, additional DSP instruction set, FPU floating-point arithmetic unit and CCM memory can provide sufficient computing power; second, rich peripherals make flying Control PCB design becomes simpler, reducing the number of external ICs and reducing the processing pressure of the MCU to a certain extent. Third, the Cortex-M core's unique interrupt processing has faster response speed than other cores. A richer priority configuration allows for faster switching.
4.2, power module designThis system uses a three-terminal fixed output voltage regulated power supply 7805, which can output 5V DC voltage. In order to increase the output current, it can be realized by using an additional power transistor. It has a collector current. When the current output is less, the regulator works and the transistor does not work. Once this value is exceeded, the transistor works and then sets. The current from the electrodes is passed into the load. The power circuit is capable of delivering excess load current.
4.3, relay module designThe relay of this module uses 12V relay module, the module size is 53mm & TImes; 18mm & TImes; 18.5mm; the control area and the load area have isolation slots; the module with optocoupler isolation, reliable and stable to the touch; double-sided FR-4 circuit board design , high-end patch production; using Songle-relay control; with power and relay action indication, attracting light, disconnecting is not bright; when the signal input has a low level signal, the common end and the normally open end will be turned on; It can directly control various equipments and loads; there are 1 normally open and 1 normally closed contact; the blue KF301 terminal is more convenient to connect the control line.
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