| As a large agricultural country,the effective utilization rate of pesticides is only 40%.Although agricultural mechanization is widely promoted at present,most of them are still concentrated in small and medium-sized plant protection machinery and are not intelligent enough.When working,it is often not considered whether the severity of pests and weeds in different working areas of the working plot is consistent and whether the amount of pesticides applied is consistent with the severity of pests and weeds,the one size fits all operation mode of "uniform and balanced application of pesticides with different disease degree" has resulted in a large amount of waste of pesticides,and may even cause pesticide damage to crops.Therefore,a variable spraying operation method has been developed,which can spray different dosage for different diseases,pests and weeds.The current research mainly focuses on the variable flow operation mode,but this operation mode has a great influence on the uniformity of droplet distribution and higher cost.In order to reduce pesticide waste,environmental pollution and improve the spray effect of droplets,a variable spraying control system with concentration regulation is developed based on pulse width modulation(it is called PWM)technology in this paper,water and medicine are placed separately,and different concentrations of pesticides are prepared by precisely controlling the amount of water and medicine and mixing and accelerating the mixing of different concentrations of pesticides through the mixer,the system can be applied on demand according to the severity of diseases,pests and weeds in the operation area,the spray size and spray amplitude can be adjusted to effectively improve the operation effect and pesticide utilization rate,the research work and results are as follows:(1)Based on PWM technology,a method of concentration regulation is proposed.PWM technology is used to precisely regulate the rotation speed of peristaltic pump to control the dosage of water.During operation,the concentration of spraying liquid can be adjusted according to the severity of diseases,pests and weeds in the operation area.(2)A set of "variable concentration spraying system" test bed is developed.The single chip microcomputer,peristaltic pump,centrifugal nozzle and control unit are selected.The test proves that the system can realize the real-time dispensing of different concentrations of pesticides,and meet the requirements of precise variable spraying,at the same time,the spray amplitude and droplet size of the system can be adjusted according to different crops and different spraying chemicals,the weight of the whole test-bed is not more than 10 Kg,the pesticide spraying concentration can be controlled remotely,the response time of concentration change shall not exceed 1s,the whole system can work stably,and the error between the system flow and concentration and the preset value is not more than 2.00%.(3)The mathematical model between the concentration and the peristaltic pump comparison register is built.Through the model,only knowing the expected configuration concentration,a group of peristaltic pump comparison register values can be obtained,different values correspond to different rotating speeds of peristaltic pump,and different concentrations of pesticides can be configured by adjusting the corresponding comparison register values of water pump and chemical pump,the accuracy of the model is 96.00% through test verification.(4)The mixing performance of the system was tested and optimized,through the detection of the lemon-red concentration sprayed by the nozzle when the system was working,it is concluded that there is a gradual process of concentration change,the change time was between 0.5s and 2s when the control system issued the command,and the concentration gradually stabilized after 2s.In order to improve the system response and operation accuracy,the system was optimized,effectively shorten the concentration change time to 0.5s and 1s after the control system sends out the command,ensure that the concentration of the reagent sprayed by the nozzle has reached the preset concentration within 1.5s,and the mixing performance of the optimized system has been improved by about 25.13%.(5)The variable spray system was converted to 3WP-100 self propelled boom sprayer and field experiments were carried out,the corresponding relationship between the installation height and spray amplitude of the system nozzle is determined.according to the corresponding relationship,different nozzle heights are set for different crops,the relationship between the speed of the system and the droplet size of the droplet was tested,before the operation,adjust the rotation speed of the nozzle according to the appropriate droplet size during the reagent spraying operation.The size of droplet sprayed and the uniformity of droplet distribution were not changed when the system was running normally,and the concentration error was not more than 2.50%,at the same time,the best operation speed is 2.4km/h and the best spraying amount is 1400 ml/min through comprehensive analysis the four parameters of the deposition amount,the deposition density,the average particle size and the distribution uniformity of the droplets.The concentration regulation method and concentration regulation system based on PWM modulation provided technical support for the research and development of pesticide application reduction and efficiency enhancement and ground and aviation variable spraying plant protection machinery. |
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